c 2006 Wiley-VCH Verlag GmbH & Co. KGaA,
Weinheim10.1002/14356007.a06233.pub2Chlorinated Hydrocarbons
1Chlorinated HydrocarbonsManfred Rossberg, Hoechst
Aktiengesellschaft, Frankfurt/Main, Federal Republic of
GermanyWilhelm Lendle, Hoechst Aktiengesellschaft, Frankfurt/Main,
Federal Republic of GermanyGerhard Peiderer, Hoechst
Aktiengesellschaft, Frankfurt/Main, Federal Republic of
GermanyAdolf T ogel, Hoechst Aktiengesellschaft, Frankfurt/Main,
Federal Republic of GermanyEberhard-Ludwig Dreher, Dow Chemical
GmbH, Stade, Federal Republic of GermanyErnst Langer, BASF
Aktiengesellschaft, Ludwigshafen, Federal Republic of GermanyHeinz
Rassaerts, Chemische Werke H uls AG, Marl, Federal Republic of
GermanyPeter Kleinschmidt, Bayer AG, Dormagen, Federal Republic of
GermanyHeinz Strack, formerly Dynamit Nobel AG,Richard Cook, ICI
Chemicals and Polymers, Runcorn, United KingdomUwe Beck, Bayer AG,
Leverkusen, Federal Republic of GermanyKarl-August Lipper, Bayer
AG, Krefeld, Federal Republic of GermanyTheodore R. Torkelson, Dow
Chemical, Midland, Michigan, United StatesEckhard L oser, Bayer AG,
Wuppertal, Federal Republic of GermanyKlaus K. Beutel, Dow Chemical
Europe, Horgen, SwitzerlandTrevor Mann, INEOS Chlor Limited,
Runcorn, United Kingdom (Chap. 7)1. Chloromethanes ...........
31.1. Physical Properties.......... 41.2. Chemical Properties
......... 71.3. Production ............... 91.3.1. Theoretical
Bases ........... 91.3.2. Production of Monochloromethane 121.3.3.
Production of Dichloromethane andTrichloromethane ...........
131.3.4. Production of Tetrachloromethane . 181.4. Quality
Specications ........ 211.4.1. PurityoftheCommercialProductsand
Their Stabilization ........ 211.4.2. Analysis .................
221.5. Storage, Transport, and Handling 221.6. Behavior of
Chloromethanesin the Environment ......... 231.6.1. Presence in the
Atmosphere ..... 241.6.2. Presence in Water Sources ...... 241.7.
Applications of theChloromethanesand Economic Data ......... 252.
Chloroethanes ............. 262.1. Monochloroethane ..........
292.1.1. Physical Properties .......... 292.1.2. Chemical
Properties .......... 292.1.3. Production................ 302.1.4.
Uses and Economic Aspects..... 322.2. 1,1-Dichloroethane ..........
322.2.1. Physical Properties .......... 322.2.2. Chemical
Properties .......... 332.2.3. Production................ 332.2.4.
Uses and Economic Aspects..... 342.3. 1,2-Dichloroethane ..........
342.3.1. Physical Properties .......... 342.3.2. Chemical
Properties .......... 352.3.3. Production................ 352.3.4.
Uses and Economic Aspects..... 422.4. 1,1,1-Trichloroethane
........ 422.4.1. Physical Properties .......... 422.4.2. Chemical
Properties .......... 422.4.3. Production................ 432.4.4.
Uses and Economic Aspects..... 462.5. 1,1,2-Trichloroethane
........ 472.5.1. Physical Properties .......... 472.5.2. Chemical
Properties .......... 472.5.3. Production................ 472.5.4.
Uses and Economic Aspects. .... 492.6. 1,1,1,2-Tetrachloroethane
..... 492.6.1. Physical Properties .......... 492.6.2. Chemical
Properties .......... 492 Chlorinated Hydrocarbons2.6.3.
Production................ 492.7. 1,1,2,2-Tetrachloroethane .....
502.7.1. Physical Properties .......... 502.7.2. Chemical
Properties .......... 502.7.3. Production................ 512.7.4.
Uses and Economic Aspects..... 522.8. Pentachloroethane ..........
522.8.1. Physical Properties .......... 522.8.2. Chemical
Properties .......... 532.8.3. Production................ 532.8.4.
Uses and Economic Aspects..... 532.9. Hexachloroethane ..........
532.9.1. Physical Properties .......... 542.9.2. Chemical
Properties .......... 542.9.3. Production................ 542.9.4.
Uses and Economic Aspects..... 543. Chloroethylenes ............
543.1. Vinyl Chloride (VCM) ....... 553.1.1. Physical Properties
.......... 553.1.2. Chemical Properties .......... 563.1.3.
Production................ 563.1.3.1. Vinyl Chloride from Acetylene
... 573.1.3.2. Vinyl Chloridefrom 1,2-Dichloroethane .......
593.1.3.3. Vinyl Chloride from Ethyleneby Direct Routes
............ 633.1.3.4. Vinyl Chloride from Ethane ..... 643.1.3.5.
Vinyl Chloride by Other Routes .. 663.1.4. Uses and Economic
Aspects..... 663.2. 1,1-Dichloroethylene(Vinylidene Chloride, VDC)
.... 673.2.1. Physical Properties .......... 673.2.2. Chemical
Properties .......... 673.2.3. Production................ 673.2.4.
Uses and Economic Aspects..... 693.3. 1,2-Dichloroethylene.........
703.3.1. Physical Properties .......... 703.3.2. Chemical
Properties .......... 703.3.3. Production................ 713.3.4.
Uses and Economic Aspects..... 713.4. Trichloroethylene...........
713.4.1. Physical Properties .......... 713.4.2. Chemical
Properties .......... 723.4.3. Production................ 723.4.4.
Uses and Economic Aspects..... 743.5. Tetrachloroethylene .........
753.5.1. Physical Properties .......... 753.5.2. Chemical
Properties .......... 753.5.3. Production................ 753.5.4.
Uses and Economic Aspects..... 793.6. Analysis and Quality
Controlof Chloroethanesand Chloroethylenes ......... 803.7. Storage
and Transportationof Chloroethanes andChloroethylenes ............
803.8. Environmental Aspects in theProduction of Chloroethanes
andChloroethylenes ............ 814. Chloropropanes ............
824.1. 2-Chloropropane ........... 824.2.
1,2-Dichloropropane......... 834.3. 1,2,3-Trichloropropane .......
845. Chlorobutanes ............. 855.1. 1-Chlorobutane ............
855.2. tert-Butyl Chloride .......... 865.3.
1,4-Dichlorobutane.......... 866. Chlorobutenes .............
876.1. 1,4-Dichloro-2-butene ........ 876.2. 3,4-Dichloro-1-butene
........ 876.3. 2,3,4-Trichloro-1-butene ...... 886.4.
2-Chloro-1,3-butadiene ....... 886.4.1. Physical Properties
.......... 886.4.2. Chemical Properties .......... 896.4.3.
Production................ 896.4.3.1. Chloroprene from Butadiene
.... 896.4.3.2. Chloroprene from Acetylene .... 906.4.3.3. Other
Processes ............ 916.4.4. Economic Importance ........ 916.5.
Dichlorobutadiene .......... 916.5.1. 2,3-Dichloro-1,3-butadiene
..... 916.5.2. Other Dichlorobutadienes ...... 926.6.
3-Chloro-2-methyl-1-propene ... 926.6.1. Physical Properties
.......... 926.6.2. Chemical Properties .......... 926.6.3.
Production................ 936.6.4. Quality Specications and
ChemicalAnalysis ................. 946.6.5. Storage and Shipment
......... 956.6.6. Uses ................... 956.7.
Hexachlorobutadiene ........ 957. Chlorinated Parafns ........
967.1. Physical Properties.......... 977.2. Chemical Propertiesand
Structure ............. 977.3. Production ............... 997.4.
Analysis and Quality Control ... 1017.5. Storage and Transportation
.... 1017.6. Toxicology, EnvironmentalImpact and Regulation .......
1027.7. Uses ................... 1037.8. Summary ................
1048. Nucleus-ChlorinatedAromatic Hydrocarbons ...... 1048.1.
Chlorinated Benzenes ........ 1058.1.1. Physical Properties
.......... 1058.1.2. Chemical Properties .......... 105Chlorinated
Hydrocarbons 38.1.3. Production................ 1098.1.3.1.
Monochlorobenzene.......... 1128.1.3.2. Dichlorobenzenes
........... 1138.1.3.3. Trichlorobenzenes ........... 1148.1.3.4.
Tetrachlorobenzenes ......... 1148.1.3.5. Pentachlorobenzene
.......... 1158.1.3.6. Hexachlorobenzene .......... 1158.1.4.
Quality and Analysis ......... 1158.1.5. Storage and Transportation
..... 1158.1.6. Uses ................... 1168.2. Chlorinated
Toluenes ........ 1168.2.1. Physical Properties ..........
1168.2.2. Chemical Properties .......... 1178.2.3.
Production................ 1178.2.3.1. Monochlorotoluenes .........
1218.2.3.2. Dichlorotoluenes ............ 1218.2.3.3.
Trichlorotoluenes ........... 1228.2.3.4. Tetrachlorotoluenes
.......... 1228.2.3.5. Pentachlorotoluene .......... 1238.2.4.
Quality and Analysis ......... 1238.2.5. Storage and Transportation
..... 1238.2.6. Uses ................... 1248.3. Chlorinated
Biphenyls ....... 1248.3.1. Physical and Chemical Properties .
1258.3.2. Disposal ................. 1258.3.3. Analysis
................. 1268.3.4. Storage and Transportation .....
1268.3.5. Uses ................... 1278.4. Chlorinated Naphthalenes
..... 1278.4.1. Physical Properties .......... 1278.4.2. Chemical
Properties .......... 1288.4.3. Production................
1298.4.4. Quality and Analysis ......... 1298.4.5. Storage and
Transportation ..... 1298.4.6. Use .................... 1308.5.
Environmental Protection ..... 1308.6. Economic Facts ............
1319. Side-Chain Chlorinated AromaticHydrocarbons .............
1329.1. Benzyl Chloride ............ 1329.1.1. Physical Properties
.......... 1329.1.2. Chemical Properties .......... 1339.1.3.
Production................ 1349.1.4. Quality Specications and
Analysis 1369.1.5. Storage and Transportation ..... 1379.1.6. Uses
................... 1379.2. Benzal Chloride ............ 1379.2.1.
Physical Properties .......... 1379.2.2. Chemical Properties
.......... 1389.2.3. Production................ 1389.2.4. Quality
Specications and Analysis 1389.2.5. Storage and Transportation
..... 1389.2.6. Uses ................... 1399.3. Benzotrichloride
........... 1399.3.1. Physical Properties .......... 1399.3.2.
Chemical Properties .......... 1399.3.3. Production................
1409.3.4. Quality Specications and Analysis 1409.3.5. Storage and
Transportation ..... 1419.3.6. Uses ................... 1419.4.
Side-Chain Chlorinated Xylenes . 1419.4.1. Physical and Chemical
Properties . 1419.4.2. Production................ 1429.4.3. Storage
and Transportation ..... 1439.4.4. Uses ................... 1439.5.
Ring-Chlorinated Derivatives ... 1439.6. Economic Aspects
.......... 14510. Toxicology and OccupationalHealth
.................. 14510.1. Aliphatic ChlorinatedHydrocarbons
............. 14510.1.1. Chloromethanes ............ 14610.1.2.
Chlorinated C2 Hydrocarbons ... 14810.1.3. Chloropropanes
andChloropropenes ............ 15210.1.4. Chlorobutadienes
........... 15210.1.5. Ecotoxicology and EnvironmentalDegradation
............... 15210.2. Chlorinated AromaticHydrocarbons
............. 15410.2.1. Chlorinated Benzenes ......... 15410.2.2.
Chlorotoluenes ............. 15410.2.3. Polychlorinated Biphenyls
...... 15510.2.4. Chlorinated Naphthalenes ...... 15610.2.5. Benzyl
Chloride ............ 15610.2.6. Benzoyl Chloride ...........
15710.2.7. Benzotrichloride ............ 15710.2.8. Side-Chain
Chlorinated Xylenes .. 15711. References ............... 1571.
ChloromethanesAmong the halogenated hydrocarbons, thechlorine
derivatives of methane monochloro-methane (methyl chloride)
[74-87-3], dichloro-methane (methylene chloride) [75-09-2],
tri-chloromethane (chloroform) [67-66-3],
andtetrachloromethane(carbontetrachloride)[56-23-5] play an
important role fromboth industrialand economic standpoints. These
products ndbroad application not only as important chemi-cal
intermediates, but also as solvents.4 Chlorinated
HydrocarbonsHistorical Development. Monochloromethanewas produced
for the rst time in 1835 by J. Du-masandE.
Peligotbythereactionofsodiumchloride with methanol in the presence
of sulfu-ric acid. M. Berthelot isolated it in 1858 fromthe
chlorination of marsh gas (methane), as didC. Groves in 1874 from
the reaction of hydro-gen chloride with methanol in the presence
ofzinc chloride. For a time,
monochloromethanewasproducedcommerciallyfrombetainehy-drochloride
obtained in the course of beet sugarmanufacture.
Theearliestattemptstoproducemethyl chloride by the chlorination of
methaneoccurredbeforeWorldWar I, withtheintentof hydrolyzingit
tomethanol. Acommercialmethane chlorination facility was rst put
intooperation by the former Farbwerke Hoechst in1923. In the
meantime, however, a high-pressuremethanol synthesis based on
carbon monoxideand hydrogen had been developed, as a result ofwhich
the opposite process became practical synthesis of methyl chloride
from methanol.Dichloromethane waspreparedforthersttime in 1840 by
V. Regnault, who successfullychlorinatedmethylchloride.
Itwasforatimeproduced by the reduction of
trichloromethane(chloroform) with zinc and hydrochloric acid
inalcohol, but thecompoundrst acquiredsig-nicance as a solvent
after it was successfullyprepared commercially by chlorination of
meth-ane andmonochloromethane (Hoechst AG, DowChemical Co., and
Stauffer Chemical Co.).Trichloromethane was synthesized
indepen-dentlybytwogroupsin1831: J. vonLiebigsuccessfullycarriedout
thealkalinecleavageofchloral,whereasM.E.Soubeirainobtainedthe
compound by the action of chlorine bleachon both ethanol and
acetone. In 1835, J. Dumasshowedthat
trichloromethanecontainedonlyasinglehydrogenatomandpreparedthesub-stance
by the alkaline cleavage of trichloroaceticacid and other compounds
containing a termi-nal CCl3 group, such as
-trichloroacetoacrylicacid. In analogy to the synthetic method
ofM.E. Soubeirain, the use of hypochlorites was ex-tended to
include other compounds containingacetyl groups, particularly
acetaldehyde. V. Reg-naultpreparedtrichloromethanebychlorina-tion
of monochloromethane. Already by themiddle of the last century,
chloroform was be-ingproducedonacommercialbasisbyusingthe J. von
Liebig procedure, a method which re-tained its importance until ca.
the 1960s in placeswhere the preferred starting materials
methaneand monochloromethane were in short supply.Today,
trichloromethane along with
dichloro-methaneispreparedexclusivelyandonamassivescalebythechlorinationofmethaneand/ormonochloromethane.
Trichloromethanewas introduced into the eld of medicine in 1847by
J. Y. Simpson, who employed it as an inhaledanaesthetic. As a
result of its toxicologic proper-ties, however, it has since been
totally replacedby other compounds (e.g.,
Halothane).Tetrachloromethane was rst prepared in1839 by V.
Regnault by the chlorination of tri-chloromethane. Shortly
thereafter, J. Dumas suc-ceeded in synthesizing it by the
chlorination ofmarshgas. H.
Kolbeisolatedtetrachlorometh-anein1843whenhetreatedcarbondisuldewith
chlorine in the gas phase. The
correspond-ingliquidphasereactioninthepresenceofacatalyst, giving
CCl4 and S2Cl2, was developeda short time later. The key to
economical practi-cality of this approach was the discovery in
1893by M uller and Dubois of the reaction of S2Cl2with CS2 to give
sulfur and tetrachloromethane,thereby avoiding the production of
S2Cl2.Tetrachloromethane is produced on an indus-trial
scalebyoneoftwogeneral approaches.The rst is the methane
chlorination process, us-ing methane or mono-chloromethane as
startingmaterials. The other involves either perchlorina-tion or
chlorinolysis.Starting materials in
thiscaseincludeC1toC3hydrocarbonsandtheirchlorinated derivatives as
well as Cl-containingresidues obtainedinother
chlorinationprocesses(vinyl chloride, propylene oxide,
etc.).Originally, tetrachloromethane played a roleonly in the dry
cleaning industry and as a reextinguishingagent. Its
productionincreaseddramatically, however, with the introduction
ofchlorouoromethane compounds 50 years ago,these nding wide
application as non-toxic re-frigerants, as propellants for
aerosols, as foam-blowing agents, and as specialty solvents.1.1.
Physical PropertiesThemostimportantphysicalpropertiesofthefour
chloro derivatives of methane are presentedin Table 1; Figure 1
illustrates the vapor pressurecurves of the four chlorinated
methanes.Chlorinated Hydrocarbons 5Table 1. Physical properties of
chloromethanesUnit
Monochlorometh-aneDichloromethaneTrichloromethane
Tetrachloro-methaneFormula CH3Cl CH2Cl2CHCl3CCl4Mr50.49 84.94
119.39 153.84Melting pointC 97.7 96.7 63.8 22.8Boiling point at 0.1
MPaC 23.9 40.2 61.3 76.7Vapor pressure at 20 C kPa 489 47.3 21.27
11.94Density of liquid at 20 C kg/m3920 1328.3 1489 1594.7(0.5
MPa)Density of vapor at bp kg/m32.558 3.406 4.372 5.508Enthalpy of
formation H0298kJ/mol 86.0 124.7 132.0 138.1Specic heat capacity of
liquid at 20 C kJ kg1K11.595 1.156 0.980 0.867Enthalpy of
vaporization at bp kJ/mol 21.65 28.06 29.7 30.0Critical temperature
K 416.3 510.1 535.6 556.4Critical pressure MPa 6.68 6.17 5.45
4.55Cubic expansion coeff. of liquid (0 40 C) K10.0022 0.00137
0.001399 0.00116Thermal conductivity at 20 C W K1m10.1570 0.159
0.1454 0.1070Surface tension at 20 C N/m 16.2 10328.76 10327.14
10326.7 103Viscosity of liquid at 20 C Pa s 2.7 1044.37 1045.7
10413.5 104(0.5 MPa)Refractive index n20D1.4244 1.4467
1.4604Ignition temperatureC 618 605 Limits of ignition in air,
lower vol% 8.1 12 Limits of ignition in air, upper vol% 17.2 22
Partition coefcient air/water at 20 Cmg/L(air)mg/L(water)0.3 0.12
0.12 0.91Figure 1. Vapor pressure curves of chloromethanesThe
following sections summarize additionalimportant physical
properties of the
individualcompoundsmakingupthechloromethanese-ries.Monochloromethane
is a colorless, am-mable gas with a faintly sweet odor. Its
solubilityinwaterfollowsHenryslaw;thetemperaturedependence of the
solubility at 0.1 MPa (1 bar)is:t, C 15 30 45 60g of CH3Cl/kg of
H2O 9.0 6.52 4.36 2.64Monochloromethane at 20Cand 0.1 MPa (1bar) is
soluble to the extent of 4.723 cm3in 100cm3of benzene, 3.756 cm3in
100 cm3of tetra-chloromethane, 3.679 cm3in 100 cm3of aceticacid,
and 3.740 cm3in 100 cm3of ethanol. Itforms azeotropic mixtures with
dimethyl ether,2-methylpropane, and dichlorodiuoromethane(CFC
12).Dichloromethane is a colorless, highlyvolatile, neutral liquid
with a slightly sweetsmell, similar to that of trichloromethane.
Thesolubility of water in dichloromethane is:t, C 30 0 + 25g of
H2O/kg ofCH2Cl20.16 0.8
1.98Thesolubilityofdichloromethaneinwaterand in aqueous
hydrochloric acid is presented inTable 2.Dichloromethane forms
azeotropic mixtureswith a number of substances (Table 3).6
Chlorinated HydrocarbonsTable 2. Solubility of dichloromethane in
water and aqueous hydrochloric acid (in wt %)SolventTemperature,
C15 30 45 60Water 2.50 1.56 0.88 0.5310 % HCl 2.94 1.85 1.25 0.6020
% HCl 2.45 1.20 0.65Table 3. Azeotropic mixtures of
dichloromethanewt % Compound Azeotropic boilingpoint, in C, at101.3
kPa30.0 acetone 57.611.5 ethanol 54.694.8 1,3-butadiene 5.06.0
tert-butanol 57.130.0 cyclopentane 38.055.0 diethylamine 52.030.0
diethyl ether 40.808.0 2-propanol 56.67.3 methanol 37.851.0 pentane
35.523.0 propylene oxide 40.639.0 carbon disulde 37.01.5 water
38.1Dichloromethane is virtually nonammableinair, asshowninFigure2,
whichillustratesthe range of ammable mixtures with oxygen nitrogen
combinations [1, 2]. Dichloromethanethereby constitutes the only
nonammable com-mercialsolventwithalowboilingpoint. Thesubstance
possesses no ash point according tothedenitionsestablishedinDIN51
755andASTM5670 as well as DIN51 758 and ASTMD 9373. Thus, it is not
subject to the regula-tions governing ammable liquids. As a
resultof the existing limits of ammability (CH2Cl2vapor/air), it is
assigned to explosion category G1 (VDE 0165). The addition of small
amountsof dichloromethane to ammable liquids (e.g.,gasoline,
esters, benzene, etc.) raises their ashpoints; additionof10 30
%dichloromethanecan render such mixtures
nonammable.Trichloromethane is a colorless, highly vol-atile,
neutral liquid with a characteristic sweetodor. Trichloromethane
vapors form no explo-sive mixtures with air [2]. Trichloromethane
hasexcellent solvent propertiesfor manyorganicmaterials, including
alkaloids, fats, oils, resins,waxes, gums, rubber, parafns, etc. As
a resultof its toxicity, it is increasingly being replaced asa
solvent by dichloromethane, whose propertiesin this general context
are otherwise similar. Inaddition, trichloromethane is a good
solvent foriodine and sulfur, and it is completely
misciblewithmanyorganicsolvents. Thesolubilityoftrichloromethane in
water at 25 C is 3.81 g/kgof H2O, whereas 0.8 g of H2O is soluble
in 1 kgof CHCl3.Figure 2.RangeofammabilityofmixturesofCH2Cl2with O2
and N2 [1]Important azeotropic mixtures of chloroformwith other
compounds are listed in Table 4.Table 4. Azeotropic mixtures of
trichloromethanewt % Compound Azeotropic boilingpoint, in C,
at101.3 kPa15.0 formic acid 59.220.5 acetone 64.56.8 ethanol
59.313.0 ethyl formate 62.796.0 2-butanone 79.72.8 n-hexane 60.04.5
2-propanol 60.812.5 methanol 53.423.0 methyl acetate 64.82.8 water
56.1Chlorinated Hydrocarbons 7Ternaryazeotropes alsoexist
betweentri-chloromethane and ethanol water (boilingpoint 55.5C, 4
mol%ethanol + 3.5 mol%H2O), methanol acetone, and methanol
hex-ane.Tetrachloromethane isacolorlessneutralliquid with a high
refractive index and a strong,bitter odor. It possesses good
solubility proper-ties for many organic substances, but due to
itshigh toxicity it is no longer employed (e.g., as aspot remover
or in the dry cleaning of textiles).It should be noted that it does
continue to ndapplication as a solvent for chlorine in
certainindustrial processes.Tetrachloromethane is soluble in water
at 25C to the extent of 0.8 g of CCl4/kg of H2O, thesolubility of
water in tetrachloromethane being0.13 g of H2O/kg of
CCl4.Tetrachloromethaneforms constant-boilingazeotropic mixtures
with a variety of substances;corresponding data are given in Table
5.Table 5. Azeotropic mixtures of tetrachloromethanewt % Compound
Azeotropic boilingpoint, in C, at101.3 kPa88.5 acetone 56.417.0
acetonitrile 71.011.5 allyl alcohol 72.381.5 formic acid 66.6543.0
ethyl acetate 74.815.85 ethanol 61.171.0 2-butanone 73.82.5 butanol
76.621.0 1,2-dichloroethane 75.612.0 2-propanol 69.020.56 methanol
55.711.5 propanol 73.14.1 water 66.01.2. Chemical
PropertiesMonochloromethane as compared to otheraliphatic chlorine
compounds, is thermally quitestable. Thermal decomposition is
observed onlyat temperaturesinexcessof 400C, eveninthe presence of
metals (excluding the alkali andalkaline-earth metals). The
principal products ofphotooxidation of monochloromethane are
car-bon dioxide and phosgene.Monochloromethane forms with water or
wa-ter vapor a snowlike gas hydrate with the com-position CH3Cl 6
H2O, the latter decomposingintoitscomponentsat+7.5 Cand0.1MPa(1
bar). To the extent that monochloromethanestill nds application in
the refrigeration indus-try, its water content must be kept below50
ppm.This specication is necessary to prevent poten-tial failure of
refrigeration equipment pressurerelease valves caused by hydrate
formation.Monochloromethaneishydrolyzedbywa-teratanelevatedtemperature.
Thehydrolysis(tomethanol andthecorrespondingchloride)is greatly
accelerated by the presence of alkali.Mineral
acidsshownoinuenceonthecom-pounds hydrolytic
tendencies.Monochloromethane is converted in the pres-ence of
alkali or alkaline-earth metals, as wellas by zinc and aluminum,
into the correspond-ing organometallic compounds (e.g.,
CH3MgCl,Al(CH3)3 AlCl3). These have come to play arole both in
preparative organic chemistry andas catalysts in the production of
plastics.Reaction of monochloromethane witha sodium lead amalgam
leads to tetra-methyllead, an antiknocking additive to
gasolineintended for use in internal combustion engines.The use of
the compound is declining, however,as a result of ecological
considerations.Averysignicant reactionisthat
betweenmonochloromethane and silicon to producethe corresponding
methylchlorosilanes (the Ro-chow synthesis),
e.g.:2CH3Cl+SiSiCl2(CH3)2The latter, through their subsequent
conver-siontosiloxanes, serveas important startingpoints for the
production of silicones.Monochloromethane is employed as a
com-ponent inthe Wurtz-Fittigreaction; it is alsousedin
Friedel-Crafts reactions for the production
ofalkylbenzenes.Monochloromethane has acquiredparticu-larly great
signicance as a methylating agent:examples include its reaction
with hydroxylgroups to give the corresponding ethers
(methyl-cellulose from cellulose, various methyl ethersfrom
phenolates), and its use in the
preparationofmethyl-substitutedaminocompounds(qua-ternarymethylammoniumcompoundsforten-sides).
Allofthevariousmethylaminesresultfromitsreactionwithammonia.TreatmentofCH3Cl
withsodiumhydrogensulde under
pres-sureandatelevatedtemperaturegivesmethylmercaptan.8 Chlorinated
HydrocarbonsDichloromethane is thermally stable to tem-peratures
above 140 C and stable in the pres-enceofoxygento120 C.
Itsphotooxidationproduces carbon dioxide, hydrogen chloride,and a
small amount of phosgene [3]. Ther-mal
reactionwithnitrogendioxidegivescar-bon monoxide, nitrogen
monoxide, and hydro-genchloride[4]. Inrespecttomostindustrialmetals
(e.g., iron, copper, tin), dichloromethaneisstable,
exceptionsbeingaluminum, magne-sium, and their alloys; traces of
phosgene rstarise above 80 C.Dichloromethane forms a hydrate with
water,CH2Cl2 17 H2O, which decomposes at 1.6 Cand 21.3 kPa (213
mbar).Nodetectablehydrolysisoccursduringtheevaporation of
dichloromethane fromextracts orextraction residues. Only on
prolonged action ofsteam at 140 170 C under pressure are
form-aldehyde and hydrogen chloride produced.Dichloromethane can be
further chlorinatedeither thermallyor photochemically.
Halogenexchange leading to chlorobromomethane
ordibromomethanecanbecarriedout byusingbromine and aluminum or
aluminum bromide.In the presence of aluminum at 220 C and 90MPa
(900 bar), it reacts with carbon monoxidetogivechloroacetyl
chloride[5]. Warmingto125
Cwithalcoholicammoniasolutionpro-duceshexamethylenetetramine.
Reactionwithphenolates leads to the same products as are ob-tained
in the reaction of formaldehyde and phe-nols.Trichloromethane is
nonammable, al-thoughit does decompose ina ame or
incontactwithhotsurfacestoproducephosgene.Inthepresence of oxygen,
it is cleaved photochemical-ly by way of peroxides to phosgene and
hydro-gen chloride [6, 7]. The oxidation is catalyzed inthe dark by
iron [8]. The autoxidation and acidgeneration can be slowed or
prevented by sta-bilizers such as methanol, ethanol, or
amylene.Trichloromethaneformsahydrate,CHCl3 17H2O,
whosecriticaldecompositionpointis+1.6C and 8.0 kPa (80 mbar).Upon
heating with aqueous alkali, trichloro-methane is hydrolyzed to
formic acid, orthofor-mate esters being formed with alcoholates.
Withprimary amines in an alkaline mediumthe
isoni-trilereactionoccurs, aresultwhichalsondsuseinanalytical
determinations. Theinterac-tion of trichloromethane with phenolates
to givesalicylaldehydes is well-known as the Reimer-Thiemann
reaction. Treatment with benzeneunder Friedel-Crafts conditions
results intri-phenylmethane.The most important reaction of
tri-chloromethaneisthat withhydrogenuoridein the presence of
antimony pentahalides to givemonochlorodiuoromethane(CFC22),
apre-cursorintheproductionofpolytetrauoroeth-ylene (Teon, Hostaon,
PTFE).Whentreatedwithsalicylicanhydride,
tri-chloromethaneproducesacrystallineadditioncompoundcontaining2moloftrichlorometh-ane.
This result nds application in the prepa-ration of trichloromethane
of the highest purity.Under certain conditions, explosive and
shock-sensitive products can result from the combina-tion of
trichloromethane with alkali metals andcertain other light metals
[9].Tetrachloromethane is nonammableandrelatively stable even in
the presence of light andair at room temperature. When heated in
air inthe presence of metals (iron), phosgene is pro-duced in large
quantities, the reaction starting atca. 300 C [10]. Photochemical
oxidation alsoleads to phosgene. Hydrolysis to carbon dioxideand
hydrogen chloride is the principal result in amoist atmosphere
[11]. Liquid tetrachlorometh-ane has only a very minimal tendency
to hydro-lyze in water at room temperature (half-life ca.70 000
years) [12].Thermal decomposition of dry tetrachlor-omethaneoccurs
relativelyslowlyat 400Ceven in the presence of the common
industrialmetals (withtheexceptionof aluminumandother light
metals). Above 500 600Can equi-librium reaction sets in which is
shifted signi-cantly to the right above 700C and 0.1 MPa (1bar)
pressure. At 900Cand 0.1 MPa (1 bar), theequilibrium conversion of
CCl4is >70 % (seeChaps. 3.5, cf. Fig. 6).Tetrachloromethane
forms shock-sensitive,explosive mixtures with the alkali and
alkaline-earth metals. With water it forms a hydratelikeaddition
compound which decomposes at +1.45C.The telomerization of ethylene
and vinylderivatives with tetrachloromethane under pres-sure and in
the presence of peroxides hasChlorinated Hydrocarbons 9acquired a
certain preparative signicance[13 15]:CH2 =
CH2+CCl4CCl3CH2CH2ClThemost important industrial
reactionsoftetrachloromethane are its liquid-phase con-version with
anhydrous hydrogen uoridein the presence of antimony (III/V)
uo-rides or its gas-phase reaction over alu-minumor chromiumuoride
catalysts, bothofwhichgivethewidelyusedandimportantcompounds
trichloromonouoromethane (CFC11), dichlorodiuoromethane (CFC12),
andmonochlorotriuoromethane (CFC 13).1.3. Production1.3.1.
Theoretical BasesThe industrial preparation of
chloromethanederivativesisbasedalmost exclusivelyonthetreatment of
methane and/or monochlorometh-ane with chlorine, whereby the
chlorinationproducts are obtained as a mixture of the indi-vidual
stages of chlorination:Thermodynamic equilibrium lies entirely
onthe side of the chlorination products, so that thedistribution of
the individual products is essen-tially determined by kinetic
parameters.Monochloromethane can be used in place ofmethane as the
starting material, where this
inturncanbepreparedfrommethanolbyusinghydrogen chloride generated
in the previous pro-cesses. The corresponding reaction
is:Inthisway, theunavoidableaccumulationof
hydrogenchloride(hydrochloricacid) canbe substantially reduced and
the overall processcan be exibly tailored to favor the
productionofindividualchlorinationproducts.Moreover,given the ease
with which it can be transportedand stored, methanol is a better
starting mate-rialforthechloroderivativesthanmethane,
asubstancewhoseavailabilityistiedtonaturalgas resources or
appropriate petrochemical fa-cilities. There has been a distinct
trend in recentyears toward replacing methane as a carbon basewith
methanol.Methane Chlorination. The chlorination ofmethane and
monochloromethane is carried outindustrially by using thermal,
photochemical, orcatalytic methods [16]. The thermal
chlorinationmethodispreferred, anditisalsotheoneonwhich the most
theoretical and scientic inves-tigations have been carried
out.Thermal chlorinationof methane andits chlo-rine derivatives is
a radical chain reaction initi-ated by chlorine atoms. These result
from ther-mal dissociation at 300 350 C, and they leadto successive
substitution of the four hydrogenatoms of methane:The conversion to
the higher stages of chlori-nation follows the same scheme [17 21].
Thethermal reaction of methane and its
chlorinationproductshasbeendeterminedtobeasecond-order
process:dn(Cl2) /dt = kp (Cl2) p (CH4)It has further been shown
that traces of oxy-gen strongly inhibit the reaction. Controlling
thehigh heat of reaction in the gas phase (which av-erages ca. 4200
kJ per m3of converted chlorine)at STP is a decisive factor in
successfully carry-ing out the process. In industrial reactors,
chlo-rineconversionrst becomesapparent above250to270C, but it
increases
exponentiallywithincreasingtemperature[22],andintheregionof
commercial interest 350 to 550 C thereaction proceeds very rapidly.
As a result, it isnecessary to initiate the process at a
temperaturewhich permits the reaction to proceed by itself,but also
to maintain the reaction under adiabaticconditions at the requisite
temperature level of320 550Cdictatedbybothchemical andtech-nical
considerations. If a certain critical
temper-atureisexceededinthereactionmixture(ca.550 700 C, dependent
both on the residencetime in the hot zone and on the materials
makingup the reactor), decomposition of the
metastablemethanechlorinationproductsoccurs. Inthatevent, the
chlorination leads to formation of un-desirablebyproducts,
includinghighlychlori-nated or high molecular mass compounds
(tetra-chloroethene, hexachloroethane, etc.). Alterna-tively, the
reaction with chlorine can get com-10 Chlorinated
Hydrocarbonspletely out of control, leading to the
separationofsootandevolutionofHCl(thermodynami-callythemoststableendproduct).Oncesuchcarbon
formation begins it acts autocatalytically,resulting in a
progressively heavier buildup ofsoot,
whichcanonlybehaltedbyimmediateshutdown of the
reaction.Propertemperaturecontrolofthisvirtuallyadiabaticchlorinationisachievedbyworkingwith
a high methane : chlorine ratio in the rangeof 6 4 : 1. Thus, a
recyclingsystemis em-ployed in which a certain percentage of inert
gasis maintained (nitrogen, recycled HCl, or evenmaterials such as
monochloromethane or tetra-chloromethane derived from methane
chlorina-tion). Inthis way, the explosive limits of methaneand
chlorine are moved into a more favorable re-gion and it becomes
possible to prepare the
morehighlysubstitutedchloromethaneswithlowerCH4 : Cl2 ratios.Figure
3 shows the explosion range of meth-ane andchlorine andhowit canbe
limitedthroughtheuseof diluents, usingtheexam-ples of nitrogen,
hydrogen chloride, and tetra-chloromethane.Figure3. Explosive range
of CH4 Cl2mixtures con-taining N2, HCl, and CCl4Test conditions:
pressure 100kPa; temperature 50 C; ignition by 1-mm sparkThe
composition and distribution of the prod-ucts
resultingfromchlorinationis a denitefunction of the starting ratio
of chlorine to meth-ane, as can be seen from Figure 4 and Figure
5.Figure 4. Product distribution in methane chlorination,
plugstream reactora) Methane; b) Monochloromethane; c)
Dichloromethane;d) Trichloromethane; e) TetrachloromethaneFigure 5.
Product distributioninmethane chlorination, idealmixing reactora)
Methane; b) Monochloromethane; c) Dichloromethane;d)
Trichloromethane; e) TetrachloromethaneChlorinated Hydrocarbons
11Theserelationshipshavebeeninvestigatedfrequently [23, 24]. The
composition of the re-action product has been shown to be in
excel-lentagreementwiththatpredictedbycalcula-tions employing
experimental relative reactionrateconstants[25 28].
Theproductsarisingfrom thermal chlorination of monochlorometh-ane
and from the pyrolysis of primary productscan also be predicted
quantitatively [29]. The re-lationships among the rate constants
are nearlyindependent of temperature in the region of tech-nical
interest. If one designates as k1 through k4the successive rate
constants in the chlorinationprocess,
thenthefollowingvaluescanbeas-signed to the relative constants for
the individualstages:k1 =1 (methane)k2 =2.91 (monochloromethane)k3
=2.0 (dichloromethane)k4 =0.72 (trichloromethane)With this set of
values, the selectivity of thechlorination can be effectively
established withrespect to optimal product distribution for
reac-torsofvariousresidencetime(streamtypeormixing type, cf. Fig. 4
and Fig. 5).
Additionalrecyclingintothereactionofpartiallychlori-nated products
(e.g., monochloromethane) per-mits further control over the ratios
of the indi-vidual components [30, 31].It has been recognized that
the yield of par-tially chlorinated products (e.g.,
dichlorometh-ane and trichloromethane) is diminished by re-cycling.
This factor has to be taken into accountin the design of reactors
for those methane chlo-rinations which are intended to lead
exclusivelyto these products. If the emphasis is to lie moreon the
side of trichloro- and tetrachloromethane,then mixing within the
reactor plays virtually norole, particularly since less-chlorinated
materi-als can always be partially or wholly recycled.Details of
reactor construction will be discussedbelow in the context of each
of the various pro-cesses.Chlorinolysis. The technique for the
produc-tion of tetrachloromethane is based on what
isknownasperchlorination,
amethodinwhichanexcessofchlorineisusedandC1-toC3-hydrocarbonsandtheirchlorinatedderivativesare
employed as carbon sources. In this process,tetrachloroethene is
generated along with tetra-chloromethane, the relationship between
the twobeing consistent with Eq. 1 in page 13 and
de-pendentonpressureandtemperature(cf. alsoFig. 6).Figure 6.
Thermodynamic equilibrium 2 CCl4C2Cl4 +2 Cl2a) 0.1 MPa; b) 1 MPa;
c) 10 MPaIt will be noted that at low pressure (0.1 to 1MPa, 1 to
10 bar) and temperatures above
700C,conditionsunderwhichthereactiontakesplace at an acceptable
rate, a signicant amountoftetrachloroethenearises. Foradditional
de-tailsseeChap. 3.5.
Underconditionsofhighpressuregreaterthan10MPa(100bar)
thereactionoccursatatemperatureaslowas600 C. As a result of the
inuence of pressureandbytheuseofalargerexcessofchlorine,the
equilibrium can be shifted essentially 100 %to the side of
tetrachloromethane. These circum-stances are utilized in the
Hoechst high-pressurechlorinolysis procedure (see below) [32,
33].Methanol Hydrochlorination. Studieshavebeenconductedfor
purposes of reactordesign [34] on the kinetics of the gas-phase
re-actionofhydrogenchloridewithmethanol
inthepresenceofaluminumoxideascatalysttogive monochloromethane.
Aging of the catalysthas also been investigated. The reaction is
rstorder in respect to hydrogen chloride, but nearlyindependent of
the partial pressure of methanol.The rate constant is proportional
to the specicsurface of the catalyst, whereby at higher
tem-peratures(350 400C) aninhibitionduetopore diffusion becomes
apparent.12 Chlorinated Hydrocarbons1.3.2. Production of
MonochloromethaneMonochloromethane is produced commerciallyby two
methods: by the hydrochlorination (es-terication) of methanol using
hydrogen chlo-ride, and by chlorination of methane.
Methanolhydrochlorination has become increasingly im-portant in
recent years, whereas methane chlo-rination as the route to
monochloromethane asnal product has declined. The former
approachhastheadvantagethat it utilizes, rather thangenerating,
hydrogen chloride, a product whosedisposal
generallyashydrochloricacidhas become increasingly difcult for
chlorinatedhydrocarbon producers. Moreover, this
methodleadstoasingletarget product, monochloro-methane, in contrast
to methane chlorination (cf.Figs. 4 and 5). As a result of the
ready and low-cost availability of methanol (via the low pres-sure
methanol synthesis technique) and its faciletransport and storage,
the method also offers theadvantage of avoiding the need for
placing
pro-ductionfacilitiesinthevicinityofamethanesupply.Sinceinthechlorinationof
methaneeachsubstitution of a chlorine atom leads to gener-ation of
an equimolar amount of hydrogen chlo-ride cf. Eqs. 2 5 in page 7a
combinationof the two methods permits a mixture of chlori-nated
methanes to be produced without creatinglarge amounts of hydrogen
chloride at the sametime; cf. Eq. 6.Monochloromethane production
from
meth-anolandhydrogenchlorideiscarriedoutcat-alyticallyinthegasphaseat0.3
0.6MPa(3 6 bar) and temperatures of 280 350 C. Theusual catalyst is
activated aluminum oxide. Ex-cess hydrogen chloride is introduced
in order toprovide a more favorable equilibrium point (lo-cated 96
99 % on the side of products at 280 350C) and to reduce the
formation of dimethylether as a side product (0.2 to 1 %).The raw
materials must be of high purity inorder to prolong catalyst life
as much as possi-ble. Technically pure (99.9 %) methanol is
em-ployed, alongwithverycleanhydrogenchlo-ride. In the event that
the latter is obtained fromhydrochloric acid, it must be subjected
to spe-cial purication (stripping) in order to removeinterfering
chlorinated hydrocarbons.Process Description. In a typical
productionplant (Fig. 7), the two raw material streams, hy-drogen
chloride and methanol, are warmed
overheatexchangersandled,aftermixingandad-ditional preheating, into
the reactor, where con-version takes place at 280 350 C and ca.
0.5MPa (5 bar).The reactor itself consists of a large numberof
relatively thin nickel tubes bundled togetherand lled with
aluminumoxide. Removal of heatgenerated by the reaction (33 kJ/mol)
is accom-plishedbyusingaheatconductionsystem. Ahot spot forms in
the catalyst layer as a result ofthe exothermic nature of the
reaction, and thismigrates through the catalyst packing,
reachingthe end as the latters useful life expires.The reaction
products exiting the reactor arecooled with recycled hydrochloric
acid (>30 %)in a subsequent quench system, resulting in
sep-aration of byproduct water, removed as ca. 20 %hydrochloric
acid containing small amounts ofmethanol. Passage through a heat
exchanger ef-fects further cooling and condensation of morewater,
aswell asremoval of most of theex-cess HCl. The quenching uid is
recovered andsubsequentlyreturnedtothe
quenchcircula-tionsystem.Thegaseouscrudeproductisledfrom the
separator into a 96 % sulfuric acid
col-umn,wheredimethyletherandresidualwater(present in a quantity
reective of its partial va-por pressure) are removed, the
concentration ofthe acid diminishing to ca. 80 % during its
pas-sage through the column. In this step, dimethylether reacts
with sulfuric acid to form
oniumsaltsandmethylsulfate.Itcanbedrivenoutlater by further
dilution with water. It is advan-tageous to use the recovered
sulfuric acid in theproduction of fertilizers (superphosphates) or
todirect it to a sulfuric acid cleavage facility.Dry, crude
monochloromethane is subse-quentlycondensedandworkedupina
high-pres-sure (2 MPa, 20 bar) distillation column to
givepureliquidmonochloromethane. Thegaseousproduct emerging from
the head of this column(CH3Cl +HCl), along with the liquid
distillationresiduetogethermakingupca.5 15 %ofthe monochloromethane
product mixture canbe recovered for introduction into an
associatedmethane chlorination facility. The overall yieldof the
process, calculated on the basis of meth-anol, is ca. 99 %.The
commonly used catalyst for vapor-phasehydrochlorinationofmethanol
is-aluminumoxide with an active surface area of ca. 200
m2/g.Chlorinated Hydrocarbons 13Figure 7. Production of
monochloromethane by methanol hydrochlorinationa) Heat exchangers;
b) Heater; c) Multiple-tube reactor; d) Quench system; e) Quench
gas cooler; f) Quenching uid tank;g) Sulfuric acid column; h) CH3Cl
condensation; i) Intermediate tank; j) CH3Cl distillation
columnCatalystsbasedonsilicateshavenotachievedany technical
signicance. Catalyst aging can beascribed largely to carbon
deposition. Byprod-uct formation can be minimized and catalyst
lifeconsiderably prolonged by doping the catalystwith various
components and by introduction ofspecic gases (O2) into the
reaction components[35]. The life of the catalyst in a production
fa-cility ranges from about 1 to 2 years.Liquid-Phase
Hydrochlorination. Theonce commonliquid-phase hydrochlorinationof
methanol using 70 % zinc chloride solutionat 130 150Cand modest
pressure is currentlyof lesser signicance. Instead, new
productiontechniques involving treatment of methanol
withhydrogenchloride inthe liquidphase without theaddition of
catalysts are becoming preeminent.The advantage of these methods,
apart from cir-cumventing the need to handle the troublesomezinc
chloride solutions, is that they utilize aque-ous hydrochloric
acid, thus obviating the needfor an energy-intensive hydrochloric
acid distil-lation. The disadvantage of the process,
whichisconductedat 120 160C, isitsrelativelylowyieldonaspace
timebasis, resultinginthe need for large reaction volumes [36
38].Other Processes. Other techniques for
pro-ducingmonochloromethaneareof theoreticalsignicance, but are not
applied commercially.Monochloromethane is formed when a mix-ture of
methane and oxygen is passed into theelectrolytes of analkali
chloride electrolysis[39]. Treatment of dimethyl
sulfatewithalu-minumchloride[40]orsodiumchloride[41]results in the
formation of monochloromethane.Methane reacts with phosgene at 400C
to giveCH3Cl [42]. The methyl acetate methanol mix-ture that arises
during polyvinyl alcohol synthe-sis can be converted to
monochloromethane withHCl at 100Cin the presence of catalysts [43].
Ithas also been suggested that monochlorometh-ane could be made by
the reaction of methanolwith the ammonium chloride that arises
duringsodium carbonate production [44].The dimethyl ether which
results frommethylcellulose manufacture can be reactedwith
hydrochloric acid to give monochlorometh-ane [45]. The process is
carriedout at 80 240Cunder sufcient pressuresothat
wa-terremainsasaliquid. Similarly, cleavageofdimethyl
etherwithantimonytrichloridealsoleads to monochloromethane
[46].Inmethanolysisreactionsforthemanufac-tureofsilicones,
monochloromethaneisreco-vered and then reintroduced into the
process ofsilane formation [47]:Si+2CH3ClSiCl2(CH3)2(11)1.3.3.
Production of Dichloromethane andTrichloromethaneThe industrial
synthesis of dichloromethane alsoleads to trichloromethane and
small amounts of14 Chlorinated Hydrocarbonstetrachloromethane,
asshowninFigure4andFigure 5. Consequently, di- and
trichlorometh-ane are prepared commercially in the same
fa-cilities. In order to achieve an optimal yield ofthese products
and to ensure reliable tempera-ture control, it is necessary to
work with a largemethane and/or monochloromethane excess rel-ative
to chlorine. Conducting the process in thisway also enables the
residual concentration ofchlorinetobekept inthefullyreactedprod-uct
at an exceptionally low level ( 98 % based on chlo-rine.Other
Processes. Oxychlorination as a wayof producing tetrachloromethane
(as well as par-tiallychlorinatedcompounds) has repeatedlybeen the
subject of patent documents [80 82],particularlysinceit
leadstocompleteutiliza-tionof chlorinewithout anyHCl
byproduct.Pilot-plant studies using uidized-bed technol-ogy have
not succeeded in solving the problemof the high rate of combustion
of methane. Onthe other hand the Transcat process, a
two-stageapproach mentioned in page 13 and
embodyingfusedcoppersalts, canbeviewedmoreposi-tively.Direct
chlorination of carbon to tetrachloro-methane is thermodynamically
possible at atmo-spheric pressure below 1100 K, but the rate ofthe
reaction is very low because of the high acti-vation energy
(lattice energy of graphite). Sulfurcompounds have been introduced
as catalysts inthese experiments. Charcoal can be
chlorinatedChlorinated Hydrocarbons 21Figure 10. Production of
tetrachloromethane by stepwise chlorination of methane (Hoechst
process)a) Reactor; b) Cooling; c) First condensation (air); d)
Second condensation (brine); e) Crude product storage vessel;f)
Degassing/dewatering column; g) Intermediate tank; h) Light-end
column; i) Column for pure CCl4; j) Heavy-end column;k) HCl stream
for hydrochlorination; l) Adiabatic HCl absorption; m) Vapor
condensation; n) Cooling and phase separation;o) Off-gas coolerto
tetrachloromethane in the absence of catalystwith a yield of 17 %in
one pass at 900 to 1100 Kand 0.3 2.0 MPa (3 20 bar) pressure. None
ofthese suggested processes has been
successfullyintroducedonanindustrialscale.Areviewofdirect
chlorination of carbon is found in [83].In this context it is worth
mentioning the dis-mutation of phosgene2COCl2CCl4+CO2another
approach which avoids the formation ofhydrogen chloride. This
reaction has been stud-ied by Hoechst [84] and occurs in the
presenceof 10 mol%tungsten hexachloride and activatedcharcoal at
370 to 430 C and a pressure of 0.8MPa. The process has not acquired
commercialsignicance because the recovery of the WCl6is very
expensive.1.4. Quality Specications1.4.1. Purity of the Commercial
Productsand Their StabilizationThestandardcommercial gradesofall
ofthechloromethanes are distinguished by their highpurity (>99.9
wt %). Dichloromethane, the sol-vent with the broadest spectrum of
applications,is also distributed in an especially pure form
(>99.99 wt %) for such special applications as theextraction of
natural products.Monochloromethane and tetrachlorometh-ane do not
require the presence of any stabilizer.Dichloromethane and
trichloromethane, on theother hand, are normally protected
fromadverseinuencesofairandmoisturebytheadditionof small amountsof
efcient stabilizers. Thefollowing substances in the listed
concentrationranges are the preferred additives:Ethanol 0.1 0.2 wt
%Methanol 0.1 0.2 wt %Cyclohexane 0.01 0.03 wt %Amylene 0.001 0.01
wt %Othersubstanceshavealsobeendescribedas being effective
stabilizers, including phenols,amines, nitroalkanes, aliphatic and
cyclic ethers,epoxides, esters, and nitriles.Trichloromethane of a
quality correspondingtothat speciedintheDeutscheArzneibuch,8th
edition (D.A.B. 8), is stabilized with 0.6 1 wt % ethanol, the same
specications as ap-pear in the British Pharmacopoeia (B.P. 80).
Tri-22 Chlorinated Hydrocarbonschloromethane is no longer included
as a sub-stance in the U.S. Pharmacopoeia, it being listedonly in
the reagent index and there without anyspecications.1.4.2.
AnalysisTable6liststhoseclassical
methodsfortest-ingthepurityandidentityofthechlorometh-anes that are
most important to both producersand consumers. Since the majority
of these aremethods with universal applicability, the
corre-spondingDeutscheIndustrieNorm(DIN)andAmerican Society for the
Testing of Materials(ASTM) recommendations are also cited in
theTable.Table 6. Analytical testing methods for
chloromethanesParameter MethodDIN ASTMBoiling range 51 751 D
1078Density 51 757 D 2111Refraction index 53 491 D 1218Evaporation
residue 53 172 D 2109Color index (Hazen) 53 409 D 1209Water content
(K. Fischer) 51 777 D 1744pH value in aqueous extract D 2110Apart
fromthese test methods, gas
chro-matographyisalsoemployedforqualitycon-trol bothinthe
productionandshipment ofchloromethanes.
Gaschromatographyisespe-cially applicable to chloromethanes due to
theirlowboiling point. Even a relatively simple
chro-matographequippedonlywithathermalcon-ductivity (TC) detector
can be highly effectiveat detecting impurities, usually with a
sensitivitylimit of a few parts per million (mg/kg).1.5. Storage,
Transport, and HandlingDrymonochloromethaneisinert
withrespecttomostmetals,thuspermittingtheirpresenceduring its
handling. Exceptions to this general-ization, however, are
aluminum, zinc, and mag-nesium, as well as their alloys, rendering
theseunsuitablefor use. Thusmost vesselsfor thestorage and
transport of monochloromethane arepreferentially constructed of
iron and steel.Since it is normally handled as a com-pressedgas,
monochloromethanemust, intheFederal Republic of Germany, be stored
in ac-cord with Accident Prevention Regulation (Un-fallverh
utungsvorschrift, UVV) numbers 61
and62bearingthetitleGasesWhichAreCom-pressed, Liquied, or
DissolvedUnder Pres-sure (Verdichtete, ver ussigte, oder unterDruck
gel oste Gase) and issued by the
TradeFederationoftheChemicalIndustry(Verbandder
Berufsgenossenschaften der chemischen In-dustrie). Additional
guidelines are providedby general regulations governing
high-pressurestoragecontainers.Storedquantitiesinexcessof 500 t
also fall within the jurisdiction of theEmergency Regulations (St
orfallverordnung) ofthe GermanFederal
lawgoverningemissionpro-tection.Gas cylinders with a capacity of
40, 60,300, or 700kgaresuitablefor thetransportof smaller
quantities of monochloromethane.Shut-off valves on such cylinders
must be left-threaded. Larger quantities are shipped in
con-tainers, railroad tank cars, and tank trucks, thesegenerally
being licensed for a working pressureof 1.3 MPa (13 bar).The three
liquid chloromethanes are also
nor-mallystoredandtransportedinvessels con-structed of iron or
steel. The most suitable ma-terial for use with products of very
high purity isstainless steel (material no. 1.4 571). The use
instorage and transport vessels of aluminum andotherlight
metalsortheiralloysispreventedby virtue of their reactivity with
respect to thechloromethanes.Storage vessels must be protected
against theincursion of moisture. This can be
accomplishedbyincorporatingintheirpressurereleasesys-tems
containers lled with drying agents such assilica gel, aluminum
oxide, or calcium chloride.Alternatively, the liquids can be stored
under
adry,inertgas.Becauseofitsverylowboilingpoint,dichloromethaneissometimesstoredincontainersprovidedeitherwithexternalwatercooling
or with internal cooling units installedin their pressure release
systems.Strict specications withrespect
tosafetyconsiderationsareappliedtothestorageandtransfer of
chlorinated hydrocarbons in order toprevent spillage andoverlling.
Illustrative is thedocument entitled Rules Governing
FacilitiesfortheStorage, Transfer, andPreparationforChlorinated
Hydrocarbons 23Shipment of Materials Hazardous to Water
Sup-plies(Verordnungf urAnlagenzumLagern,Abf ullen und Umschlagen
wassergef ahrdenderStoffe, VAwS). Facilities for this purpose
mustbe equipped with the means for safely recover-ing and disposing
of any material which escapes[94].Shipment of solvents normally
entails the useof one-waycontainers (drums, barrels) madeof steel
andif necessarycoatedwithprotec-tive paint. Where product quality
standards areunusuallyhigh, especiallyasregardsminimalresidue on
evaporation, stainless steel is the ma-terial of
choice.Largerquantitiesareshippedincontainers,railroadtankcars,
tanktrucks, andtankersofboth the transoceanic and inland-waterway
va-riety. So that product specications may be metfor material long
in transit, it is important duringinitial transfer to ensure high
standards of purityand the absence of moisture.Rules for transport
by all of the various stan-dardmodes
havebeenestablishedonanin-ternational
basisintheformofthefollowingagreements: RID, ADR, GGVSee,
GGVBinSch,IATA-DGR. The appropriate identicationnum-bers and
warning symbols for labeling as haz-ardous substances are collected
in Table 7.Table 7. Identication number and hazard symbols
ofchloromethanesProduct Identication Hazard
symbolnumberMonochloromethane UN 1063 H (harmful)IG
(inammablegas)Dichloromethane UN 1593 H (harmful)Trichloromethane
UN 1888 H (harmful)Tetrachloromethane UN 1846 P (poison)The use and
handling of chloromethanes bothbyproducers andbyconsumers of
thesubstances and mixtures containing
themaregovernedintheFederalRepublicofGermanyby regulations
collected in the February 11, 1982version of the Rules Respecting
Working Mate-rials (Arbeitsstoff-Verordnung). To some ex-tent, at
least, these have their analogy in otherEuropean countries as well.
Included are
stipu-lationsregardingthelabelingofthepuresub-stancesthemselvesaswell
asofpreparationscontaining chloromethane solvents. The
centralauthorities of the various industrial trade organi-zations
issue informational and safety brochuresfor chlorinated
hydrocarbons, and these shouldbe studied with care.The standard
guidelines for handling mono-chloromethane as a compressed gas are
thePressure Vessel Regulation (Druckbeh alter-Verordnung) of
February 27, 1980, with the re-lated Technical Rules for Gases
(TechnischeRegeln Gase, TRG) and the Technical Rulesfor Containers
(Technische Regeln Beh alter,TRB), as well as Accident Prevention
Guide-line 29 Gases (Unfallverh utungsvorschrift[UVV] 29,
Gase).ForMAKvalues, TLVvalues,
andconsid-erationsconcerningthetoxicologyseeChap.10.
Theecologyandtheecotoxicologyofthechloromethanes are described in
Chapter 10.1.5.1.6. Behavior of Chloromethanes in
theEnvironmentChloromethanesareintroducedintotheenvi-ronment
frombothnatural andanthropogenicsources. Theyare foundinthe lower
atmosphere,and tetrachloromethane can even reach intothe
stratosphere. Trichloromethane
andtetra-chloromethanecanbedetectedinmanywatersupplies.The
chloromethanes, like other halogenatedhydrocarbons, are viewedas
water contami-nants. Thus, they are found in both national
andinternational guidelines related to water qualityprotection [85,
86].Therearefundamentalreasonsforneedingtorestrictchlorocarbonemissionstoanabso-lute
minimum. Proven methods for removal ofchloromethanesfromwastewater,
off-gas, andresidues areVapor stripping with
recyclingAdsorptiononactivatedcharcoal andrecy-clingRecovery by
distillationReintroduction into chlorination
processes[87]Combustion in facilities equipped with offgascleanup24
Chlorinated HydrocarbonsTable 8. Atmospheric concentration of
chloromethanes (in 1010vol.%) [90]Compound Continents Oceans Urban
areasCH3Cl 530 . . . 1040 1140 . . . 1260 834CH2Cl236 35 300C),
theyaresusceptibletothe eliminationof hydrogenchloride.
Inthepresence of light and oxygen, oxidation occursyielding
phosgene, carbon oxides, and acetyl orchloroacetyl chlorides. The
latter easily
hydro-lyzewithtracesofmoistureformingthecor-responding chloroacetic
acids, which are well-knownas stronglycorrosive agents. Topre-vent
this unwanted decomposition, most indus-trially used chlorinated
hydrocarbons are stabi-lized with acid acceptors such as amines,
unsat-uratedhydrocarbons, ethers, epoxidesorphe-nols, antioxidants,
and other compounds able toinhibit free radical chain reactions.
Longer stor-age periods and use without appreciable effecton tanks
and equipment is then possible.Of all chlorinated ethanes,
approxi-mately half are of industrial importance.Monochloroethane
(ethyl chloride) is an inter-mediate in the production of
tetraethyllead andiswidelyusedasanethylatingagent.
1,2-Di-chloroethane has by far the highest productionrates. It
isanintermediatefortheproductionof 1,1,1-trichloroethane and vinyl
chloride (seepage 43 and 3.1.3.2), but it is also used in
syn-Chlorinated Hydrocarbons 27Table 12. Demand and use pattern of
chloromethanes (1983)Western United JapanEurope
StatesMonochloromethane 230 000 t 250 000 t 50 000 tSilicone 52 %
60 % 83 %Tetramethyllead 12 % 15 % Methylcellulose 15 % 5 % 1
%Other methylation reactions, e.g., tensides,pharmaceuticals ca. 21
% ca. 20 % ca. 16 %Dichloromethane 210 000 t 270 000 t 35 000
tDegreasing and paint remover 46 % 47 % 54 %Aerosols 18 % 24 % 19
%Foam-blowing agent 9 % 4 % 11 %Extraction and other uses 27 % 25 %
16 %Trichloromethane 90 000 t 190 000 t 45 000 tCFC 22 production
78 % 90 % 90 %Other uses, e.g., pharmaceuticals, intermediate 22 %
10 % 10 %Tetrachloromethane 250 000 t 250 000 t 75 000 tCFC 11/12
production 94 % 92 % 90 %Special solvent for chemical reactions 6 %
8 % 10 %thetic applications (e.g., polyfunctional amines)and as a
fuel additive (lead scavenger).Table 13. Physical properties of
chlorinated ethanesCompound Boiling point Relative(at 101 kPa), C
density, d204Monochloroethane 12.3 0.92401,1-Dichloroethane 57.3
1.17601,2-Dichloroethane 83.7 1.23491,1,1-Trichloroethane 74.1
1.32901,1,2-Trichloroethane 113.5 1.44321,1,1,2-Tetrachloroethane
130.5 1.54681,1,2,2-Tetrachloroethane 146.5 1.5958Pentachloroethane
162.0 1.6780Hexachloroethane mp 186 187
2.09401,1,1-Trichloroethane,
trichloroethylene,(seeSection3.4)andtetrachloroethylene(seeSection
3.5) are important solvents widely usedin dry cleaning, degreasing,
and extraction
pro-cesses.Theotherchlorinatedethaneshavenoim-portant end uses.
They are produced as
interme-diates(e.g.,1,1-dichloroethane)orareformedas unwanted
byproducts. Their economical con-version into useful end products
is achieved ei-ther by cracking tetrachloroethanes yield
tri-chloroethylene or more commonly by chlori-nolysis, which
converts them into carbon tetra-chloride and tetrachloroethylene
(see page 76 ).Basic feedstocks for the production of chlo-rinated
ethanes and ethylenes (see Chap. 3) areFigure 11. Vapor pressure as
a function of temperature forchlorinated hydrocarbonsethane or
ethylene and chlorine (Fig. 12). Theavailability of ethylene
fromnaphtha feedstockshas shifted the production of chlorinated C2
hy-drocarbons during the past three decades in theWestern World
from the old carbide acetylene vinyl chloride route toward the
ethylene route.Withthedramaticincreaseof naphthapricesduring the
past decade, the old carbide route hasregained some of its
attractiveness [106]. Eventhough a change cannot be justied
presently in28 Chlorinated HydrocarbonsFigure 12. Chlorinated
hydrocarbons from ethane and ethylene (simplied)most countries, it
could offer an alternative forcountries where cheap coal is readily
available.Theuseofethanolderivedfrombiomassasastarting material
could likewise also be consid-ered [107, 108].Inafewcases, ethaneis
useddirectlyasahydrocarbonfeedstock. Thisdirectethaneroute could
offer an attractive alternative in somecases, because of the
substantial cost differencesbetweenethaneandethylene.
Itbecomesevi-dent whynumerous patents onethane-basedpro-cesses have
been led. However, the major costadvantage of such processes is the
reduced cap-ital investment for cracker capacity. The directethane
route must certainly be considered for fu-ture grass-root-plants,
but at present, the conver-sions and selectivities obtained seem
not to jus-tify the conversion of existing plants if
crackercapacity is available.Less is known about the situation in
Easternblock countries. The available information indi-cates,
however, that in some Eastern Europeancountries the acetylene route
is still used.Because chlorine is needed as a second feed-stock,
most plants producing chlorinated hydro-carbons are connected to a
chlor-alkali electrol-ysisunit.
Thehydrocarbonfeedstockiseithersuppliedfromanearbycracker, typical
forU.S. gulf coast, or via pipelines and bulk shiptransports. The
chlorine value of the hydrogenchloride produced as a byproduct in
most chlo-rination processes can be recovered by oxychlo-rination
techniques, hydrochlorination reactions(for synthesis of methyl and
ethyl chloride) or,lesseconomically byaqueousHCl
elec-trolysis.Aminorbuthighlyvaluableoutletisultrapure-grade
anhydrous HCl used for etchingin the electronic industry.Although
most unwanted byproducts can beused as feed for the chlorinolysis
process [109](see page 76 ), the byproducts of this process,mostly
hexachloroethane,
hexachlorobutadiene,andhexachlorobenzenetogetherwithresidualtars
from spent catalysts and vinyl chloride pro-duction, represent a
major disposal problem. Theoptimal ecological solution is the
incineration ofthese residues at a temperature above 1200 C,which
guarantees almost complete degradation.Presently,
incinerationisperformedat seaonspecial ships [110] without HCl
scrubbing or onsite with subsequent HCl or chlorine recovery.The
aqueous HCl recovered can then be used forChlorinated Hydrocarbons
29pHadjustment in biological efuent treatment orbrine
electrolysis.Due to their unique properties, the market
forchlorinated C2hydrocarbons has shown excel-lent growth over the
past 30 years and reached itsmaximum in the late 1970s. With
increasing en-vironmental consciousness, the production rateof some
chlorinated hydrocarbons such as ethylchloride,
trichloroethylene(seepage73), andtetrachloroethylene (see 3.5.4)
will in the longrun decrease due to the use of unleaded
gasoline,solvent recoverysystems, andpartial replace-ment by other
solvent and extraction chemicals.However,
newformulationsforgrowingmar-kets such as the electronic industry,
the availabil-ity of ecologically safe handling systems, know-how
in residue incineration, and the difculty innding superior
replacements causing fewerproblems
guaranteechlorinatedethanesandethylenes a long-term and at least
constant mar-ket share.2.1. MonochloroethaneMonochloroethane (ethyl
chloride) [75-00-3]
isthoughttobetherstsynthesizedchlorinatedhydrocarbon. It was
produced in 1440 by Valen-tine by reacting ethanol with
hydrochloric acid.Glauberobtaineditin1648byreactingetha-nol (spirit
of wine) with zinc chloride. Becauseof the growing automotive
industry in the early1920s, monochloroethane became an
importantbulk chemical. Its use as a starting material forthe
production of tetraethyl-lead (Lead Com-pounds) initiated a
signicant increase in
ethylchlorideproductionandisstillitsmajorcon-sumer.
Thetrendtowardunleadedgasolineinmost countries, however, will
inthelongrunlead to a signicant decrease in production.2.1.1.
Physical PropertiesMr64.52mp 138.3 Cbp at 101.3 kPa 12.3 C of the
liquid at 0 C 0.924 g/cm3 of the vapor at 20 C 2.76
kg/m3n20D1.3798Vapor pressure at50 C 4.480 kPa20 C 25.090 kPa10 C
40.350 kPa0 C 62.330 kPa+ 10 C 92.940 kPa+ 20 C 134.200 kPa+ 30 C
188.700 kPa+ 60 C 456.660 kPa+ 80 C 761.100 kPaHeat of formation
(liquid) H0298133.94kJ/molSpecic heat at 0 C 1.57 kJ kg1K1Heat of
evaporation at 298 K 24.7 kJ/molCritical temperature 456 KCritical
pressure 5270 kPaViscosity (liquid, 10 C) 2.79104PasViscosity
(vapor, bp) 9.3105PasThermal conductivity (vapor) 1.09
103Wm1K1Surface tension (air, 5 C) 21.18103N/mDielectric constant
(vapor, 23.5 C) 1.0129Flash point (open cup) 43 CIgnition
temperature 519 CExplosive limits in air 3.16 15
vol%monochloroethaneSolubility in water at 0 C 0.455 wt %Solubility
of water in monochloroethane at 0 C 0.07 wt
%Atambienttemperature,monochloroethaneis a gas with an etheral
odor.Monochloroethane burns with a green-edgedame.Combustion
products are hydrogen chloride,carbon dioxide, and water.Binary
azeotropic mixtures of monochloro-ethane have been reported [111].
The data, how-ever, have not been validated.2.1.2. Chemical
PropertiesMonochloroethane has considerable thermalstability.
Onlyat temperaturesabove400C,considerable amounts of ethylene and
hydrogenchloride are formed due to dehydrochlorination[111]a. This
decomposition can be catalyzed bya variety of transition metals
(e.g. Pt), transition-metal salts, and high-surface area oxides
such asalumina and silica. Catalyzed decomposition iscomplete at
temperatures slightly above 300Caccording to the thermodynamic
equilibrium.At ambient atmospheric conditions,
both,hydrolysis(toethanol)andoxidation(toacet-aldehyde) are
moderate.30 Chlorinated HydrocarbonsAt temperatures up to 100 C,
monochloro-ethane shows no detrimental effect on moststructural
materials if kept dry. Contact with alu-minum, however,
shouldbeavoidedunderallcircumstances for safety
reasons.Monochloroethane has the highest reactivityof all
chlorinated ethanes. It is mainly used asanethylatingagent
inGrignard- andFriedel-Crafts-typereactions, forether, thioether,
andamine synthesis. Halogene exchange [111]b anduorination is also
possible [111]c.2.1.3. ProductionMonochloroethane can be produced
by a varietyof reactions. Only two are of industrial impor-tance:
the hydrochlorination of ethylene and thethermal chlorination of
ethane.Hydrochlorination of Ethylene. Exother-mic hydrochlorination
of ethylene can be carriedout in either the liquid or gas
phase.C2H4+HClC2H5ClH = 98kJ/molThe liquid-phase reaction is
carried out mostlyat near ambient temperatures (10 50 C)
andmoderate pressure (0.1 0.5 MPa) in a boiling-bed type reactor.
The heat of reaction is used tovaporize part of the
monochloroethane formed,which in turn is then cooled down, puried,
orpartiallyrecycled. Thereactor temperatureiscontrolledbythe
recycle ratioandthe feedrate ofthe reactants. Unconverted ethylene
and hydro-gen chloride from reux condensers and over-head light end
columns are recycled back to thereactor.
Sufcientmixingandcatalystcontacttime is achieved through
recirculation of the re-actor sump phase. Aluminum chloride in a
0.5 5 wt % concentration is mostly used as a cat-alyst.
Apartofitiscontinuouslyorintermit-tentlyremovedviaarecirculationslipstream,together
with unwanted high boiling impuritiesconsisting mostly of low
molecular mass ethyl-ene oligomers formed in a Ziegler-type
reactionof the catalyst with the ethylene feed. New cat-alyst is
added to the system either by a hopperas a solid or preferably as a
solution after pre-mixing with monochloroethane or
monochloro-ethane/ethylene.
AgaseousfeedofvaporizedAlCl3hasalsobeensuggested[112]. Asim-plied
process diagram is shown in Figure 13;an optimized process has been
patented
[113].Inotherprocessvariations,theformedmono-chloroethane(sumpphase)iswashedwithdi-luted
NaOHto remove catalyst and acid and thendried and distilled. Excess
ethylene is recycled.Figure 13. Schematic diagram (simplied) of an
ethylenehydrochlorination processa) Reactor; b) Cooler; c)
Knock-out drum; d) Light-endcolumns; e) Reboiler; f) Stripper
column (heavy ends)Ethylene andHCl yields for
hydrochlori-nationarealmost quantitative; selectivitiesof98 99
%have beenreported. InadditiontoAlCl3, other Lewis-acid catalysts,
such as FeCl3[114], BiCl3 [116], and GaCl3 [117], have
beenpatented. Suggestions to perform the reaction inbenzene or
higher boiling hydrocarbons [118],in1,1,2-trichloroethane [119] or
tocomplexAlCl3 by nitrobenzene [120] have not found in-dustrial
acceptance.The troublesome handling of the catalyst
isminimizedwhenethyleneandhydrogenchlo-ride are reacted in the gas
phase. Although thereaction equilibrium becomes unfavorable at
atemperature above 200C, the process is carriedout at temperatures
of 250 450 C in order toachieve sufcient conversion. Ethylene and
HClarepreheated, mixed, andsentacrossthecat-alyst,
whichcanbeusedasxedoruidizedbed. The chloroethane formed is
separated andpuried. Unreacted ethylene and HCl are recy-cled.
Selectivities are comparable to those of theliquid-phase process,
conversion per pass, how-ever, may not exeed 50 %, so that
relatively highrecycle rates are necessary. Because high pres-sure
favors the formation of monochloroethane,the reaction is preferably
carried out at 0.5 1.5MPa.Chlorinated Hydrocarbons
31Thoriumoxychlorideonsilica[121], pla-tinium on alumina [122], and
rare-earth oxideson alumina and silica [123] have been patentedas
catalysts.Chlorination of Ethane. Thermal chlorina-tion of ethane
for the production of monochloro-ethane canbe usedindustriallyina
tandemprocessdevelopedbytheShell Oil Company(Fig. 14) [124]. This
process was especially de-signed for a plant in which sufcient
ethylenefeedstockcouldonlybesuppliedbyincreas-ingthecrackercapacity.
Ethaneandchlorinewere available, but not hydrogen chloride. Forthis
feedstock constellation, the tandem processseems
advantageous.Figure
14.ProductionofmonochloroethanebytheShellprocess [124]a) Preheater;
b) Ethane chlorinator; c) Cooler; d) Lightendtower; e) Crude
chloroethane storage; f) Hydrochlorinator;g) CompressorIn the rst
stage, ethane and chlorine are re-acted noncatalytically after
sufcient preheatingat 400 450 C in an adiabatic reactor. The
re-action gases are separated after cooling in a
rstmonochloroethane distillation tower. The
heavybottomsofthistowercontainingchloroethaneandmorehiglychlorinatedproducts
(mostly1,1-dichloroethane and 1,2-dichloroethane) aresent to the
purication stage. The overheads con-sistingmainlyof
unconvertedethane, hydro-gen chloride, and ethylene are sent to a
secondisothermal xed-bedreactor. Before enteringthis reactor, fresh
ethylene is added to achieve a1 : 1 ethylene to HCl feed ratio.
Even though thetypeofcatalystusedintheisothermalsectionis not
described, any of the catalysts mentionedfor gas-phase
hydrochlorination in the previoussectioncanbeused. Conversionat
thisstageis50 80 %. Theproductsarethenseparatedinasecondtower.
Unconvertedethane,ethyl-ene, and hydrogen chloride are recycled to
therst reactor. The monochloroethane formed byhydrochlorination is
drawn off and puried to-gether with the stream from the rst
tower.Even though the recycled ethylene from
thehydrochlorinationstepispresent duringther-mal chlorination, the
formation of 1,2-dichloro-ethane is insignicant. Because the rst
reactionis carried out at high temperatures, chlorine ad-dition to
the ethylene double bond is suppressed.The process is balanced by
the overall reac-tion equation:C2H6+Cl2C2H5Cl+HClHCl+C2H4C2H5ClA 90
% overall yield for ethane and ethyleneand a 95 % chlorine yield to
monochloroethaneare reported.Monochlorinationof
ethaneisfavoredbe-causeethanechlorinationisfour timesfasterthan the
consecutive chlorination of mono-chloroethane to
dichloroethanes.Major byproducts from the chlorination stepare
1,1-, 1,2-dichloroethane and vinyl
chloride.Toachieveahighselectivityformonochloro-ethane, a high
ethane surplus preferably a 3 5-fold excess over chlorine [125,
126]
andgoodmixingisrequired.Insufcientheatdis-sipationmayenhancecrackingandcoking.
Athermal chlorination reactor providing thoroughpremixing and
optimal heat transfer by meansof a uidized bed has been described
in [126].Other patents claimcontact of the reaction gaseswith metal
chlorides [127] or graphite [128].The photochemical chlorination of
ethane de-scribed in several patents [129] is less
important,because it is difcult to implement in large vol-ume
plants and offers no major advantages overthe thermal
process.Monochloroethane as a Byproduct of theOxy-EDCProcess.
Monochloroethane is a ma-jor byproduct in the Oxy-EDCprocess (see
page35), in which it is formed by direct hydrochlo-rinationof
ethylene. It canbecondensedorscrubbed fromthe light vent gases and
recoveredafter further purication.32 Chlorinated
HydrocarbonsMonochloroethane from Ethanol. The es-terication of
ethanol with HCl is possible in theliquid phase by using ZnCl2or
similar Lewis-acidcatalysts at 110 140C[130].
Similartotheproductionofmonochloromethane(see1.3.2),
thereactioncanalsobecarriedout inthe gas phase by using -alumina
[131], ZnCl2and rare earth chlorides on carbon [132] or
zeo-lites[133]ascatalysts.Atthepresentethanolprices,
theseproceduresareprohibitive. Withsome modication, however, they
can offer out-lets for surplus byproducts such as ethyl
acetatefromPVAproduction which can be converted tomonochloroethane
by HCl using a ZnCl2/silicacatalyst [134].OtherSyntheticRoutes
toMonochloro-ethane. Non-commercial routes to mono-chloroethane
consist of electrolytic chlorinationof ethane in melts [135],
reactions with diethylsulfates [136], metathesis of
1,2-dichloroethane[137], hydrogenationof vinyl chloride[138],and
conversion of diethyl ether [139]. The oxy-chlorination of ethane
is discussed later in thisChapter.Small amounts of monochloroethane
areformedduringthereactionof synthesisgas chlorine mixtures over
Pt/alumina [140] andmethane chlorine mixtures in the presence
ofcation-exchange resins complexedwithTaF5[141].2.1.4. Uses and
Economic AspectsMonochloroethanebecameindustriallysignif-icant as a
result of the developing automo-tive industry. It is the starting
material fortetraethyllead, the most commonly used octanebooster.
IntheUnitedStates, about 80 90 %and in Europe ca. 60 %of the
monochloroethaneproductionisusedfortheproductionoftetra-ethyl
lead.Production has already been cut signicantlydue to the
increased use of unleaded fuel for en-vironmentalreasons. U.S.
projectionsindicatean average annual decline of ca. 10 % per
year.With some delay, the same trend can also be pre-dicted for
Western Europe.Minor areas of use for monochloroethane arethe
production of ethyl cellulose, ethylating pro-cessesfor nechemical
production, useasablowingagent andsolvent forextractionpro-cesses
for the isolation of sensitive natural fra-grances.Production in
1984 in the Western World wasabout 300 000 t. Almost all processes
in use atpresent are ethylene based.2.2.
1,1-Dichloroethane1,1-Dichloroethane [75-34-3] is the less
impor-tant of the two dichloroethane isomers.It occurs oftenas
anunwantedbyprod-uct in many chlorination and
oxychlorinationprocesses of C2 hydrocarbons.The most important role
of 1,1-dichloro-ethaneisasanintermediateintheproductionof
1,1,1-trichloroethane.Other uses are negligible.2.2.1. Physical
PropertiesMr98.97mp 96.6 Cbp at 101.3 kPa 57.3 C at 20 C 1.176
g/cm3n20D1.4164Vapor pressure at0 C 9.340 kPa10 C 15.370 kPa20 C
24.270 kPa30 C 36.950 kPaHeat of formation (liquid)H0298160.0
kJ/molSpecic heat at 20 C 1.38 kJ kg1K1Heat of evaporation at
298K30.8 kJ/molCritical temperature 523 KCritical pressure 5070
kPaViscosity at 20 C 0.38103Pa sSurface tension at 20 C
23.5103N/mDielectric constant at 20C10.9Flash point (closed cup) 12
CIgnition temperature 458 CExplosive limits in air at 25C5.4 11.4
vol%1,1-dichloroethaneSolubility in water at 20 C0.55 wt
%Solubility of water in1,1-dichloroethane at 20C0.97 wt
%1,1-Dichloroethane is a colorless liquid. It isreadily soluble in
all liquid chlorinated hydro-carbons and in a large variety of
other organicsolvents (ethers, alcohols).Chlorinated Hydrocarbons
33Binary azeotropes are formed with water andethanol: with 1.9 %
water, bp 53.3 C (97 kPa)and with 11.5 % ethanol, bp 54.6C (101
kPa).2.2.2. Chemical PropertiesAt room temperature,
1,1-dichloroethane is ad-equately stable. Cracking to vinyl
chloride andhydrogen chloride takes place at elevated
tem-peratures.However,comparedtootherchlori-nated C2hydrocarbons,
the observed crackingratesaremoderate. Thisreactioncanbepro-moted
by traces of chlorine and iron [142]. 2,3-Dichlorobutane is often
found as a dimeric by-product of decomposition.1,1-Dichloroethane
was alsofoundtoen-hance 1,2-dichloroethane cracking when addedin
lower concentrations (10 wt %) [143].Corrosionrates for
dry1,1-dichloroethaneare marginal, increase however, with water
con-tent andtemperature. Aluminumiseasilyat-tacked.In the presence
of water or in alkaline solu-tion, acetaldehyde is formed by
hydrolysis.2.2.3. ProductionTheoretically 1,1-dichloroethane can be
pro-duced by three routes:1) Addition of HCl to acetylene:2)
Thermal or photochemical chlorination ofmonochloroethane:3)
Addition of HCl to vinyl chloride:For thesynthesis of
1,1-dichloroethaneasanintermediateintheproductionof1,1,1-tri-chloroethaneonlythelatterrouteisimportantand
industrially used.1,1-Dichloroethane via the 1,2-Di-chloroethane
Vinyl Chloride Route. Hydro-gen chloride and vinyl chloride
obtained from1,2-dichloroethane cracking see page 58) are re-acted
in a boiling-bed-type reactor [144] in thepresence of a
Friedel-Crafts catalyst, preferablyferricchloride(FeCl3).
1,1-Dichloroethaneisused as solvent and the temperature ranges
from30 to 70C.Depending on the process design, hydrogenchloride can
be used in excess to achieve com-plete conversion of the vinyl
chloride. The heatof reaction, which differs only slightly from
theheat requiredfor1,2-dichloroethanecracking,can be used to
distill the 1,1-dichloroethane andrecoverpartoftheenergyinput.
Downstreamhydrogen chloride and unconverted vinyl chlo-ride are
separated and recycled. If necessary, the1,1-dichloroethane can
then be further puriedbydistillation.
Duetotheformationofheavybyproducts (vinyl chloride polymers) and
deac-tivationofthecatalyst, aslipstreamfromthereactor bottom must
be withdrawn and new cat-alyst
added.Improvedprocessesusecolumn-typereac-torswithoptimizedheight
[145] (hydrostaticpressuretoavoidashingof vinyl chloride!)and
recycled 1,1-dichloroethane with intermit-tent cooling stages. In
this case, the stoichiomet-ric ratio of hydrogen chloride to vinyl
chloride,asobtainedfrom1,2-dichloroethanecracking,can often be
used. In such a process, the down-stream distillation equipment can
be less com-plexandexpensive, becausealmost
completeconversionisachievedandbecausenoexcesshydrogen chloride or
the entrained vinyl chlo-ride must be separated. However, the
energy re-quirements may be higher because most of theheat of
formation must be dissipated by cooling.Both process variations
yield between ca. 95and 98 %. Yield losses result through
polymer-ization of vinyl chloride. The concentration aswell as the
nature of the catalyst determine thissidereaction.
Zincchloride(ZnCl2) andalu-minumchloride (AlCl3), which also can be
usedas catalysts, promote the formation of high mo-lecular mass
byproducts more than ferric chlo-ride (FeCl3) [120, 146]. The
removed spent cat-alyst canbeburnedtogether
withtheheavybyproductsinanincinerator,iftheventgasesare
subsequently scrubbed and the wash liquorappropriately treated.
Environmental problems34 Chlorinated Hydrocarbonscaused by the
residues are thereby almost elim-inated.1,1-Dichloroethane via the
AcetyleneRoute. As with the synthesis of vinyl chlo-ride (see
3.1.3.1), 1,1-dichloroethane can beproduced fromacetylene by adding
2 mol of hy-drogen chloride. For the rst reaction
sequencetheformationof vinyl chloride mercurycatalyst is required
[147].Because ethylene has become the major feed-stock for
chlorinated C2 hydrocarbons, this pro-cess has lost its
importance.1,1-Dichloroethane fromEthane. 1,1-Di-chloroethane may
also be obtained by ethane orchloroethane chlorination. This
chlorination canbe carriedout as thermal chlorination[148],
pho-tochlorination, or oxychlorination [149].
Theseprocesses,however,areimpairedbyalackofselectivity and are not
used industrially.2.2.4. Uses and Economic AspectsAs mentioned
earlier, 1,1-dichloroethane is pri-marily used as a feedstock for
the production of1,1,1-trichloroethane.Although several other
applications havebeen patented [150], currently 1,1-dichloro-ethane
is rarely used for extraction purposes oras a
solvent.Basedonestimatedproductiongures of1,1,1-trichloroethane and
disregarding otheruses, the total
WesternWorldproductionof1,1-dichloroethane is estimated at 200 000
250000 t for 1985.2.3. 1,2-DichloroethaneThe rst synthesis of
1,2-dichloroethane (ethyl-ene dichloride, EDC) [107-06-2] was
achievedin 1795.Presently, 1,2-dichloroethane belongs tothose
chemicals with the highest productionrates. Averageannual
growthratesof >10 %were achieved during the past 20
years.Although these growth rates declined duringthepast several
years, inthelongrun1,2-di-chloroethane will maintain its leading
positionamong the chlorinated organic chemicals due toits use as
starting material for the production ofpoly(vinyl chloride)
(Poly(Vinyl Chloride)).2.3.1. Physical PropertiesMr98.97mp 35.3 Cbp
at 101.3 kPa 83.7 C at 20 C 1.253 g/cm3n20D1.4449Vapor pressure at0
C 3.330 kPa20 C 8.530 kPa30 C 13.300 kPa50 C 32.000 kPa70 C 66.650
kPa80 C 93.310 kPaHeat of formation (liquid)H298157.3 kJ/molSpecic
heat (liquid, at 20 C) 1.288 kJ kg1K1Heat of evaporation at 298 K
34.7 kJ/molCritical temperature 563 KCritical pressure 5360
kPaViscosity at 20 C 0.84103Pa sSurface tension at 20 C
31.4103N/mCoefcient of cubical expansion(0 30 C) 0.00116
K1Dielectric constant 10.5Flash point (closed cup) 17 CFlash point
(open cup) 21 CIgnition temperature (air) 413 CExplosive limits in
air at 25 C 6.2 15.6 vol%1,2-dichloroethaneSolubility in water at
20 C 0.86 wt %Solubility of water in1,2-dichloroethane at 20 C 0.16
wt %1,2-Dichloroethane is a clear liquid at ambi-ent temperature,
which is readily soluble in allchlorinated hydrocarbons and in most
commonorganic solvents.Binaryazeotropes with1,2-dichloroethaneare
listed in Table 14.Table 14. Binary azeotropes formed by
1,2-dichloroethanewt % Component Azeotropeboiling point(101.3
kPa),C18.0 2-propen-1-ol 79.938.0 formic acid 77.437.0 ethanol
70.319.5 1,1-dichloroethane 72.043.5 2-propanol 74.732.0 methanol
61.019.0 1-propanol 80.779.0 tetrachloromethane 75.618.0
trichloroethylene 82.98.2 water 70.5Chlorinated Hydrocarbons
352.3.2. Chemical PropertiesPure 1,2-dichloroethane is sufciently
stableevenatelevatedtemperaturesandinthepres-ence of iron. Above
340C, decomposition be-gins, yielding vinyl chloride, hydrogen
chloride,andtraceamountsofacetylene[111]a, [151].This
decompositionis catalyzedbyhalogens
andmorehighlysubstitutedchlorinatedhydrocar-bons
[152].Long-termdecompositionat ambient tem-perature caused by
humidity and UV light canbe suppressed by addition of stabilizers,
mostlyamine derivatives. Oxygen decient burning andpyrolytic and
photooxidative processes convert1,2-dichloroethane to hydrogen
chloride, carbonmonoxide, and phosgene.Bothchlorineatomsof
1,2-dichloroethanecan undergo nucleophilic substitution
reactions,which opens routes to a variety of bifunctionalcompounds
such as glycol (by hydrolysis or re-actionwithalkali),
succinicaciddinitrile(byreactionwithcyanide), orethyleneglycol
di-acetate (by reaction with sodium acetate). Thereaction with
ammonia to ethylenediamine anduse of 1,2-dichloroethane for the
production ofpolysuldes is of industrial importance.Iron and zinc
do not corrode when dry 1,2-di-chloroethane is used, whereas
aluminum showsstrong dissolution. Increased water content
leadstoincreasedcorrosionof ironandzinc; alu-minum, however,
corrodes less [153].2.3.3. Production1,2-Dichloroethane is
industrially produced bychlorination of
ethylene.Thischlorinationcaneitherbecarriedoutby using chlorine
(direct chlorination) or hydro-gen chloride (oxychlorination) as a
chlorinatingagent.In practice, both processes are carried out
to-gether and in parallel because most EDC
plantsareconnectedtovinyl chloride(VCM) unitsand the
oxychlorination process is used to bal-ance the hydrogenchloride
fromVCMpro-duction(seepage62andFig.24).Dependingon the EDC/VCM
production ratio of the inte-grated plants, additional surplus
hydrogen chlo-ride from other processes such as
chlorinolysis(perchloroethylene and tetrachloromethane pro-duction,
see page 18 and Section 3.5.3) or 1,1,1-trichloroethane (see page
43) can be fed to theoxychlorination stage for proper balancing
andchlorine recovery.The use of ethane as a starting material,
al-though the subject of numerous patent claims,is still in the
experimental stage. It could offereconomic advantages if the
problems related tocatalyst selectivity, turnover, and long-term
per-formance are solved.Direct Chlorinationinthe Ethylene
LiquidPhase.. In the direct chlorination process, ethyl-ene and
chlorine are most commonly reacted inthe liquid phase
(1,2-dichloroethane for temper-ature control) and in the presence
of a Lewisacidcatalyst, primarily iron(III)
chloride:Toavoidproblemsinproduct purication,the use of high-purity
ethylene is recommended.Especially its propane/propene content must
becontrolledinordertominimizetheformationofchloropropanesandchloropropenes,
whichare difcult to separate from
1,2-dichloroethanebydistillation.Puriedliquidchlorineisusedto avoid
brominated byproducts. Oxygen or airisoftenaddedtothereactants,
becauseoxy-gen was found to inhibit substitution chlorina-tion,
yielding particularly 1,1,2-trichloroethaneand its more highly
chlorinated derivatives [154,155]. Through this and an optimized
reactor de-sign, the use of excess ethylene is no longer re-quired
to control byproduct formation. In mostcases,
thereactantsareaddedinthestoichio-metricchlorine/ethyleneratioorwithaslightexcess
of chlorine. This simplies the
process-ingequipmentbecauseanexcessofethylene,which was often used
in the past [156], requirescomplicated condensor and post reactor
equip-ment to avoid the loss of expensive ethylene inthe off-gas
[155, 157].Although several other Lewis-acid catalystswith higher
selectivities such as antimony, cop-per, bismuth, tin, and
tellurium chlorides [158]have been patented, iron chloride is
widely used.Because the reaction selectivities are not depen-dent
on the catalyst concentration, it is used ina diluted concentration
between ca. 100 mg/kg36 Chlorinated Hydrocarbonsand0.5wt %.
Someprocessesuseironllerbodies in the reactor to improve mass and
heattransfer or use iron as a construction material.This equipment
generates sufcient FeCl3insitu[159].In the liquid-phase reaction,
ethylene absorp-tionwasfoundtobetherate-controllingstep[160].In
addition to the distinct process modica-tions with which each
producer of 1,2-dichloro-ethane has improved his process during the
pastyears,twofundamentalprocessvariationscanbe characterized:1)
low-temperature chlorination (LTC) and2) high-temperature
chlorination (HTC)In the LTC process, ethylene and chlorine re-act
in 1,2-dichloroethane as a solvent at temper-atures (ca. 20 70 C)
below the boiling pointof 1,2-dichloroethane.The heat of reaction
is transferred by exter-nal cooling either by means of heat
exchangersinside the reactor or by circulation through ex-terior
heat exchangers [161].Thisprocesshastheadvantagethatduetothe
lowtemperature, byproduct formation is low.The energyrequirements,
however, are consider-ably higher in comparison to the HTC
process,becausesteamisrequiredfortherecticationof
1,2-dichloroethane in the purication section.Conversions up to 100
% with chlorine and eth-ylene selectivities of 99 % are possible.In
the HTC process, the chlorination reactionis carried out at a
temperature between 85 and200 C, mostly, however, at about 100 C.
Theheat of reaction is used to distill the EDC. In ad-dition, EDC
from the Oxy-EDC process or un-converted EDC from the vinyl
chloride sectioncan be added, since the heat of formation equalsthe
heat required for vaporization by a factor ofca. 6.By sophisticated
reactor design and thoroughmixing conversion, and yields comparable
to theLTCprocess may be obtained with considerablylower energy
consumption for an integrated DC-Oxy-VCM process
[162].Descriptionof theHTCProcess (Fig. 15).Gaseous chlorine
andethylene are fedthor-oughly mixed into a reaction tower which is
alsosupplied with dry EDC from oxychlorination orrecycled EDC from
the VCM section.Figure 15. Simplied DC HTC processa)Reactor; b)
Cooler; c) Knock-out drum; d) Heavy-endtower; e) ReboilerThe light
ends are drawn off from the headsection, and ethylene is condensed
and recycled.In the following condensation section, vinylchloride
is separated and can then be processedwithvinyl
chloridefromEDCcracking(seepage 58). The remaining vent gas is
incinerated.Pure EDC is taken from an appropriate sectionand
condensed. In order to maintain a constantcomposition in the
reactor sump phase, a slip-stream is continuously withdrawn, from
whichthe heavy byproducts are separated by rectica-tion and sent to
a recovery stage or incinerated.In some designs, the reactor is
separated fromthe distillation tower [164]. In others, two tow-ers
are used for light ends/EDCseparation. Solidadsorption has been
patented for iron chlorideremoval [165].For optimal heat recovery,
crossexchangecan be used for chlorine feed evaporation [166].Due to
the relatively low temperatures and an-hydrous conditions, carbon
steel equipment canbe used
[167].Processdevelopmentsusingcrackinggasesinstead of highly puried
ethylene [168] and theuse of nitrosyl chloride [169] as a
chlorinatingagent have not found any industrial
importance.DirectChlorinationintheGasPhase. Acatalytic gasphase
process was patented by theSoci et e Belge de lAzote [170]. Because
of thehighly exothermic reaction, adequate dilution isChlorinated
Hydrocarbons 37necessary. Several catalysts have been
patented[171].Thenoncatalyticchlorineadditionreactionhas been
thoroughly studied [172], but is not in-dustriallyused,