{(Vex. - Veal)'}!- reac

TABLE 3 - VALUES OF THE PARAMETERS· Vi, OF EQ. (2)

Vo V. V, Va o(VE)(cm'molr")

(l-x)CHaCI.+xCH3COC.H.±0.0020.1397 --0.1247

(l-x)CHCI3 +xCH3COC.H.±0.008-1.0671 0.7941 0.2367 -0.4417

(l-x)CCI. +xCH3COC.H.+0.006--0.7857 -0.7718 0.1778

(l-x )C.C1. +xCH3COC.H.±0.0020.1810 --0.2887 0.1771 -0.1745

·We start with two parameters in EQ. (2) and keep onincreasing the number of parameters (K) tiII the standard devia-. VB {(Vexp - Veal)'}! h . . dtion o( ) ._- _ ..._- reac es a rrumrnum or oes

n-Knot change by including more parameter where n is thenumber of experimental points and K is the number of para-meters in Eq. (2).

pectively), whereas, for tetrachloromethane + MEKit is skewed towards the high mole fraction of MEK(maximum at x~0.6124). Thenature of the curvescannot be explained on the basis of different molarvolumes of the components. VE values of the titlemixtures at x = 0.5 increase in the followingorder : trichloromethane <tetrachloromethane <dichloromethane < tetrachloroethylene.

The positive values of VE forthe systems dichloro-methane + MEK and tetrachloroethylene + MEKindicate that interactions between unlike moleculesare weak and hence give rise to positive deviations.The results are indicative of weak interactions,involving dispersion forces between the molecules ofthese systems. The negative VE for tetrachloro-ethylene + MEK system are within experimentaluncertainty. On the other hand in the case oftrichloromethane + MEK the large negative VEvalues can be attributed to specific interactions,such as hydrogen bonding between oxygen (of MEK)and hydrogen (of CHCI3). The excess volumesfor tetrachloromethane + MEK are also negativein the mole fraction range x~O.I-I, indicating theexistence of specific interactions between the compo-nents, since the molar volumes of the two purecomponents are nearly equal. The specific inter-action could be of charge transfer type. Carbontetrachloride is known to act as an electron acceptorfor a number of donors. In this case the lone pairat carbonyl oxygen may act as the donor. Increasingexcess volume from trichloromethane to tetrachlo-roethylene has been assigned to the decrease inspecific interactions.

Financial assistance from Department of AtomicEnergy, Government of India to one of the authors(S. B. S.) is gratefully acknowledged.

References1. JAIN, D. V. S., WADI, R. K., SAINI, S. B. & SINGH J.,

Indian J. Chem., 16A (1978), 561.2. JAIN, D. V. S., SAINI, S. B. & CHAUDHRY, V., Indian J.

Chem., 18A (1979), 198.3. JAIN, D. V. S., WADI, R. K., SAINI, S. B. & PURl, K.,

J. chem. Thermodynamics, 10 (1978), 707.

NO·TES

4. RIDDICK, J. A. & BUNGER, W. B., Organic solvents :Physical properties and methods of purification (Wiley-Interscience, New York), 1970.

5. Handbook of chemistry and physics, edited by C. D.Hodgman (Chemical Rubber Publishing Co., Cleveland,Ohio), 1959, 3285.

6. DICKINSON, E., HUNT, D. C. & McLURE, I., J. chem.Thermodynamics, 7 (1975), 731.

7. GROLlER, JEAN-PIERER E., BENSON, G. C. & PICKER, P.,J. chem. Engng Data, 20(3) (1975), 243.

Kinetics of Thermal Desorption of Water & TrlcresylPhosphate from Synthetic Zeolites

SATI PRASAD BANERJEEDepartment of Chemistry, University of Saugar, Sagar 470003

Received 16 October 1979; revised 23 January 1980; rerevisedand accepted 15 March 1980

TG data have been used to evaluate the kinetic parameters ofthe joint desorption of water vapours and of tricresyl phosphatefrom zeolites 4A and 13X in O.S mm pellet form. Different rateconstant and desorption activation energy values distinguish thevarious first order reactions over different ranges of temperature.IR spectroscopic studies indicate chemisorption of the adsorbatthrough hydrogen bonding.

MOLECULAR sieves are found to be the mostversatile, selective and universally applicable

adsorbents available to industry. Adsorption pro-cesses utilizing zeolites as adsorbents are of greatsignificance in industry'. Kinetics of thermal de-sorption are important in determining the efficiencyof an adsorption process which is dependent on therecycling of the adsorbent. The present studydeals' with the evaluation of kinetic parameters ofthe joint desorption of water vapours and tricresyl-phosphate (TCP) from zeolites 4A and 13X, usingthermogravimetric techniquesv", Rate constants andactivation energies of the desorption processes havebeen calculated+, Differential thermal analysis andinfrared spectroscopic studies of TCP-adsorbedzeolite samples have also been carried out.

Materials used were synthetic zeolites of type 4Aand 13X supplied by the Associated Cement Com-pany, Bombay, marketed under the name 'Selecto-sorb' in 0.5 mm pellet form. The zeolites werekept in contact with excess of TCP [(CHa.CsH4)aPOj]having b.p. 537K for several days. The reactantswere heated over a water-bath (_373°K) from timeto time and later kept inside a refrigerator also forseveral days. After filtering off the excess liquidthe zeolite samples were kept on a filter paper anddried in air. The IR spectra of these samples wererecorded on a Perkin-Elmer instrument (model 577)between 4000 and 200 cm-l in cesium iodide. Ther-mogravimetric analysis was done on a thermo-balance supplied by the Fertilizer Corporation ofIndia, Sindri. Mass loss data were obtained at aheating rate of 10°C min ? upto 1073K. Differentialthermal analysis was carried out on a leeds and Nor-thurp unit using Robert Grimshaw type ceramicsample holder with Pt-Pt 10 % Rh Thermocoupleat a heating rate of 125°C min-! upto 1173°K TheTG curves and plots of [-loge(l-Cl)lIn] versus time

1009

INDIAN J. CHEM .• VOL. 19A, OCTOBER 1980

. [-lOg (l_~)l/n ] 1000and ~f2 vs Tfor n=2 are shown

in Figs. 1, 2 and 3 respectively. Values of II werecalculated from mass loss data using the expression,

Wt- Wr~=Wo- Wr

'where Wt is the indicated mass at time/temperature,t; Wo is the initial sample mass; and Wr is the re-sidual mass at the end of the process under study.

\>- The results of thermogravimetric analysis clearlydistinguish the various thermal reactions occurring

-13X-TCP--4A-TCP

en.€.::l 250"e

3

:I ""Cl ~ •••

,.'~.2\

\..._--=---- .10

TIME/MIN40

Fig. 2 - Plots of g (II) vs time for n=2; 1, 4A; 2, 13X.

over different ranges of temperature. Evolution ofwater begins around 353K, followed by desorptionof the adsorbate (TCP) just beyond its boiling point(537K). This is followed by high temperaturedehydration after 600K. Computation of massloss data has indicated that these are first orderreactions. These reactions occur at comparativelylower temperatures in the case of zeolite 13X.Earlier workers" have reported two types of waterevolution in NaA zeolite; a fast evolution at about373K and a slower evolution around 573K. Thelatter occurs for small concentration of water.Water molecules are adsorbed through cation inter-action as well as hydrogen bonding at the frame-work oxygens of zeolite. The heat of adsorption ofwater is mainly due to the energy of specific inter-actions of water with framework oxygens", Adsorp-tion capacity of molecular sieves is due to the elec-trostatic forces between the adsorbent and adsorbateand the mechanism of adsorption is influenced bythe structurally bound hydroxyl groups in the zeolite.

-11I;

,///

/I./

IIiii2IijJii

I,.

~O~ __ -J-=~~ L~~373 TEMP,K

Fig. 1 - TG Curves of TCP adsorbed zeolites; I, 4A;2,13X.

-15l- __ ..!....,- --J1 , 3

F· 3 I fIg (Cl) ,19. - Pots 0 og, ~ vs 10'fT for n=2; I, 4A;

2,13X.

TABLE 1- THERMALAND IR DATA ON THE DESORPTIONOF WATERAND TCP

Zeolite; total mass loss (%) at DTA Peaks Mass loss (%)at Rates of Activation IR bands (crn'<)temp. different time, reaction (mirr'") energy

Endo Exo temp. (klmol=')("K)

TCP-sorbed 4A; 36.S at 573-593K 390 610 . 12:.5 upto 9.0 X 10-- 28.3 3440, 1670, 1440,563K(29 min) 1400, 1310, 12S0,20.6 upto 3.9 X 10-1 171.4 1260, 1200, 10S0,613K(34 min) 1030, SOO,670,600,3.7 after 3.0 X 10-' 64.9 560, 470, 420, 380,618K(upto 56 250.min)

TCP-sorbed 13X; 37.2 at 533-553K 363 570 14.6 upto 1.1 x 10-1 33.1 3520, 1650, 1430,533K(26 min) 1320, 1280, 1200,18.4 upto 7.1 x 10-1 288.3 1090, 1040, 980,553K(2S rnin) SOO, 760, 6S0, 600,4.2 after 1.4 x 10-' 40.4 570, 460, 360, 230.553K(upto 48rnin)

1010

lattice. Both 4A and 13X exhibit high adsorptioncapacity for tricresyl phosphate. The chemisorptionof the adsorbate through hydrogen bonding is clearlyindicated by the broadening of the IR bands due tostretching and bending vibrations of water around3500 and 165Ocm-l respectively. Bands due tov (P=O) and v (P-O) appear between 1500 and120Ocm-l and 1200 and 900cml respectively in theIR spectra of the adsorbed samples. High valuesof desorption activation energy also indicate chemi-sorption. A strong exothermic peak is obtained inthe DTA curves for the oxidation of adsorbate justbeyond its boiling point. All the results have beentabulated in Table 1.

The author is thankful to the UGC, New Delhi,for financial support and the ACC, Bombay, for thezeolite samples.

References1. LEE, H., Applied aspects of zeolite adsorbents, molecular

sieves in Advances in chemistry series, Vol. 121(American Chemical Society, Washington, D.C.), 1973.

2. DHARWADKAR,S. R., CHANDRASEKHARAlAH,M. S. &KARKHANAVALA,M. D., Thermochim. Acta, 25 (1978),372.

3. REICH, LEO& STIVALA,S. S., Thermochim. Acta, 24 (1978),Y.

4. LATHAM,J. L., Elementary reaction kinetics, (Butterworths),1969, 145.

5. ASTAKHov, V. A., MEERSON,L. A. & KLYUSHKOVA,G. S.,Vestsi Akad Nauk BSSR. Ser. Khim. Nauk, (1978), 118;Chem. Abstr .• 89 (1978), 65907h.

6. DZHIGlT, O. M., KISELEV,A. V., MIKOS, K. N., MUTlK,G. G. & RAHMONOVA,T. A., Trans. Faraday Soc., 67(1971), 458.

Kinetics & Mechanism of Silver(I)-catalyscdCerium(IV) Oxidation of Glycine in Nitric Acid

Medium

V. K. SRIVASTAVA,K. K. SRIVASTAVA,M. N. SRIVASTAVA&B. B. L. SAXENA-

Department of Chemistry, University of Allahabad,Allahabad 211 002

Received 3 October 1978; revised and accepted 15 February 1980

The Ag(l) catalysed oxidation of glycine by Ce(IV) in nitricacid solution is first order each with respect to both the reactants,cerium(IV) and glycine. The reaction rate increases linearly with[Ag(l)]. The acid has an accelerating effect whereas neutralsalts retard the reaction rate. A suitable reaction mechanismbas been suggested.

A ERIAL oxidation! of glycine in the presenceof some transition metal ions as catalysts has

been shown to result in the formation of ammoniacarbon dioxide, and formaldehyde. Srivastava andChandra- studied the kinetics of silver(I)-catalysedoxidation of glycine by persulphate. The reactionwas first order each in peroxidisulphate and Ag(l)and almost independent of [glycine]. The rateconstants increased with increasing [peroxidisul-phate] and the addition of neutral salts produced aretarding effect. The present note reports resultsof a kinetic study of Ag(I)-catalysed oxidation of

NOTES

glycine by eerie ammonium nitrate (CAN) in nitricacid medium.

All the chemicals used were of AR grade and thesolutions were prepared in doubly distilled waterand standardized by appropriate methods. Glycinesolution was standardized by Sorenson's formaltitration method",

The reaction was initiated by mixing the requisitequantity of glycine solution with the solutions ofCAN, Ag(l), and nitric acid in dark-coloured bot-tles. All the solutions were equilibrated at thedesired temperatures before mixing. The progressof the reaction was followed by estimating theamount of unreacted cerium(IV) by an indirecttitration method via the titration of excess of Fe(II)with eerie sulphate using ferroin as an indicator.

In stoichiometric experiments approximately threeequivalents of [Ce(IV)] were consumed by one moleof glycine, whereas its oxidation to NHa, CO2, andformaldehyde, required only two equivalents; andfor complete conversion to formic acid it requiredfour equivalents. It thus appears that the reactionproceeds beyond the first stage and the productformaldehyde is also partially oxidized to formicacid.

Kinetic data at various initial [Ce(IV)], [glycine],[Ag(I)], and [HNOa] are graphically represented inFig. 1. The results show that the reaction is firstorder with respect to [Ce(IV)], and [glycine] andalso directly depends on [Ag(I)], and [acid]. Itis however interesting to note that the first order rateconstants decrease with increasing initial [Ce(IV)]probably due to the formation of less reactive poly-meric= Ce(IV) species at higher [Ce(IV)]. Salt

[A~.IO:M3 [HNo,],M

or.••...Q

2

7

6

5

3

2

2 4 6 8 10 12 [Glycin.]xlcf,M100 200 300 1/ C. OW

Fig. I - First order rate plots for cerium(Iv)-g1ycine reaction(Ce(IV)variation(l) : Glycine = O.IM. AgNO. = 5 x lo-eMHNO, = IN; glycine variation (2) : Ce(1V) = 5 x to-3M:AgNO. = 5 x lo-cM. HNO. = IN; Ag(l) variation (3) :Ce(IY) = s X lQ-3M. glycine = O.lM. HN03 "" IN andHNOa variation (4) : Ce(IV) = 5 x lo-3M, glycine = O.IM,

AgNOa = 5 x l()"""4M]

1011