Acknowledgement I wish to express my sincere thanks and gratitude to DR. Ratna Datta, Jadavpur University, for his continuous, encouragement and supervision over my entire project work on “Design a styrene plant of capacity 30 tonnes per day”. His most valuable advices and the paths he showed to me helped me in completion of my work. I also express my thanks to all faculty members and my fellow students of the Department of Chemical Engineering, Jadavpur University, for their help and moral supports. Thanking you, Yours faithfully, Bappa Saha [Class: B.Ch.E. – IV Sec: A-1 RollNo:000810301018] Date: 14 th Oct, 2012 Place: Jadavpur, Kolkata-32
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Acknowledgement
I wish to express my sincere thanks and gratitude to DR. Ratna Datta,
Jadavpur University, for his continuous, encouragement and supervision
over my entire project work on “Design a styrene plant of capacity 30
tonnes per day”. His most valuable advices and the paths he showed to me
helped me in completion of my work.
I also express my thanks to all faculty members and my
fellow students of the Department of Chemical Engineering,
Jadavpur University, for their help and moral supports.
Thanking you,
Yours faithfully,
Bappa Saha
[Class: B.Ch.E. – IV
Sec: A-1
RollNo:000810301018]
Date: 14th Oct, 2012
Place: Jadavpur, Kolkata-32
JADAVPUR UNIVERSITY
Faculty of Engineering and Technology
Department of Chemical Engineering
Certificate of Approval
This is to certify that the project entitled “Determination of fuel characteristics
of blended and pure biodiesel”, submitted by Bappa Saha, a fourth year student,
bearing Roll No. 000810301018, and accepted for partial fulfillment of the
degree of Bachelor of Chemical Engineering from The Department of Chemical
Engineering, Faculty of Engineering And Technology, Jadavpur University,
Kolkata, is prepared entirely by himself under my supervision and guidance.
Department of Chemical Engg. Department of Chemical Engg.
Jadavpur University, Jadavpur University,
Kolkata-32 Kolkata-32
INTRODUCTION:
The styrene process was developed in the 1930s by BASF
(Germany) and Dow Chemical (USA). Over 25×106 tons/year of
styrene monomer is produced worldwide.1 The annual
production of styrene in the U.S.A. exceeds 6×106 tons.2 The
major commercial process for the production of styrene is the
dehydrogenation of ethylbenzene, which accounts for 85% of
the commercial production.3 The potassium-promoted iron
oxide catalyst has been extensively used for styrene
production. 4 The average capacity of ethylbenzene
dehydrogenation plants is over 100,000 metric tons per year
and plants which have a capacity of 400,000 metric ton per year
is not uncommon.5 Obviously, a small improvement in the
plant operation will lead to a substantial increase of returns.
Nevertheless, the research towards the fundamental kinetic
modeling based upon the Hougen-Watson approach has not
been pursued by most styrene producers and researchers. They
rely on the empirical polynomial correlations for the unit
optimization.6-8 Furthermore, the reaction rates published in
the most of papers are not intrinsic but effective.9, 10 An
intrinsic kinetic model based upon the fundamental principles is
essentially required for the optimization of the various reactor
configurations with different operating conditions. The
objectives of this research are to develop the mathematical
kinetic model for the ethylbenzene dehydrogenation and to
investigate the effect of operating conditions on the fixed bed
industrial reactor formation of styrene, benzene, and toluene,
the understanding of the kinetic behavior of the minor by-
products, such as phenylacetylene, α-methylstyrene, β-
methylstyrene, cumene, n-propylbenzene, divinylbenzene, and
stilbene, is also important in terms of the styrene monomer
quality and separation cost of the final products. The formation
of these minor by-products is not taken into account for the
fundamental kinetic model. The general features of
ethylbenzene dehydrogenation are briefly discussed. The
theoretical and literature backgrounds are presented in each
chapter. Chapter III explains the experimental methods of
ethylbenzene dehydrogenation.
Problem statement :
It is proposed to design a styrene plant of capacity 30 tones par
day, by vapor phase catalytic dehydrogenation of
ethylbenzene, starting from ethylbenzene as raw material.
(1) Prepare an energy balance and mass balance of the
plant
(2) Design a catalytic fixed bed reactor involved in the
prosess with optimum conversion
Definition:
Styrene monomer is an aromatic hydrocarbon,under normal
condition it is clear,cocorless, flamableand toxic liquid.
Industrial alternate process for styrene production:
St is produced in industry mainly by two processes: I. dehydrogenation of ethyl benzene (EB) in presence of steam over iron oxide based catalysts. II. as a by-product in the oxidation of propene with ethyl benzene hydroperoxide and Mo complex-based catalysts. The former process (I), accounts for more than 90% of the worldwide capacity. The catalytic dehydrogenation route, in which the potassium promoted iron oxide catalyst is typically used since 1957, produces most of the Styrene .The process can be run industrially either adiabatically or isothermally over a fixed bed reactor in which the reactants are passed over the catalyst bed employing radial or axial flow [1,3]. Several catalysts, such as cobalt, copper, iron and zinc oxides, have been studied, both with and without promoters, but the potassium promoted iron oxide catalyst was found particularly efficient with respect to both selectivity and activity [2,3]
1.) C6H6+ C2H4↔C6 H5 C2 H5
2.) C6 H5 C2 H5↔C6 H5 C2 H3+ H2
However, styrene can be industrially produced by what is known as PO-SM Coproduction, where propylene oxide and styrene are made simultaneously. It proceeds as follows:
3.) C6H5CH2CH3 + O2↔C6H5CH(CH 3)OOH
4.)C6H5CH(CH 3)OOH + CH = CHCH3↔C 6H5 CH(CH3)OH +
H2COCHCH3
5.) C 6H5CH(CH3)OH ↔C 6H5 CH=CH2 +H2O
One downside to the PO-SM Coproduction is that the production capacity is dictated by the demand for propylene oxide. Since it is a more complex series of reactions makes it is less attractive to operate in industry.
Chemistry of Ethyl benzene Dehydrogenation
The main reaction produces styrene and hydrogen. Ethylbenzene ↔ styrene + H2, ΔHr (620oC) = 124.83 kJ/mol The dehydrogenation reaction is usually conducted at temperatures above 600oC with an excess of steam. The ethyl benzene dehydrogenation is an endothermic and reversible reaction with an increase in the number of mole due to
reaction. High equilibrium conversion can be achieved by a high temperature and a low ethyl benzene partial pressure. The main byproducts are benzene and toluene. Ethylbenzene ↔ benzene +C2H4, ΔHr (620oC) =101.50 kJ/mol Ethylbenzene + H2 ↔ toluene +CH4, ΔHr (620oC) = -65.06kJ/mol
Reaction thermodynamics
The dehydrogenation reaction of EB to Styrene is endothermic (DH=129.4kJ/mol) At room temperature, the reaction equilibrium is located far towards the educts side. It can be shifted towards the product side by increasing the temperature, which increases the equilibrium constant K due to the van´t Hoff relationship and by reducing the pressure, since two moles of product are formed from one mole of EB. Therefore the technical St synthesis is run at around 600°C with an excess of steam, the steam-EB mixtures has a molar ratios from 5:1 to 12:1. Styrene plants run their reactors under isothermal or adiabatic conditions with flow rates that ensure short contact times in order to prevent polymerization of Styrene. The equilibrium EB conversion at 600°C and 0.1 bar pressure is( ~ 83% ), and conversions between 50 and 60% are obtained in technical reactors. The
typical byproducts of the EB dehydrogenation are (~1%) benzene and (~2%) toluene formed by catalytic dealkylation and hydrodealkylation of Ethylebenzene,respectively, or they also can be formed by steam dealkylation.
Physical porperties of ethyl benzene Physical properties Styrene
Molar mass 104.15g/mol
Appearance Clear colorless to yellowish
Density at 20 oC 0.9059g/cm
3
Melting point -30.60 C
Boiling point 145.20 C
Solubility in water 280mg/L (150 C)
300mg/l (200 C)
400mg/L (400 C)
Solubility in organic solvent soluble in ethanol,ether,acetone
Air Solubility 0.73 mg/L 0.011 mg/L 1.36 mg/m3
Oder threshold 0.1 ppm
Specific gravity 0.906(water=1)(25 oC)
Conversion factor 1 ppm=4.33 mg/m3
Flash point 87 oF(closed cup)
Vapor pressure at 20 c 5 mmHg
Autoignition temperature 914 oF(490
oC)
Henry’s law constant 2.61x10-3 atm-m3/mol Odor If pure,sweet and pleasent
Physical porperties of styrene
Physical properties Ethylbenzene
Molar mass 106.17g/mol
Appearance Clear colorless
Density 0.8670g/cm3(20
oC)
o.8669 g/cm3(200
oC)
.86262 g/cm3(250
oC)
Melting point -94.9760 C
Boiling point 136.190 C
Solubility in water 140mg/L (150 C)
152mg/l (200 C)
160mg/L (250 C)
Solubility in organic solvent soluble in ethanol,ether,acetone
Oder threshold Water Air
0.029 mg/L o.140 mg/l 2.3 ppm
Conversion factor(25 oC,1atm) 1mg/m
3=0.230ppm
Specific gravity 0.867 at 20 oC (water = 1)
Flammability limits 0.8(lower)vol%-6.7(upper)vol%
Flash point 15oC
Vapor pressure at 20 c 7 mmHg
Autoignition temperature 810 oF(432
oC)
Henry’s law constant 6.6*10-3
atm-m3/mol
Physical state Liquid
Refractive Index(at 200 oC) 1.49320
Latent Heat(veporizatin) 335 j/kg
Heating value(gross) 42999 j/kg
Heating value(net) 40928 j/kg
Kinematic viscosity(at 98.90 oC) 0.390*10
-6 m
2/s
Surface tension 28.48 mN/m
Specific heat capacity(idea gas, 250
oC)
1169 -1 k-1
Physical porperties of ethyl benzene
Physical properties Methane(CH4)
Molar mass 16.04g/mol
Appearance Clear colorless to yellowish
Gas Density at 70 oF 0.0416lb/ft
3
Melting point -296.50 F
Boiling point -258.70 F
Solubility in water 280mg/L (150 C)
300mg/l (200 C)
400mg/L (400 C)
Solubility in organic solvent soluble in ethanol,ether,acetone
Specific heat 8.53 Btu/lbmol-oF
Specific gravity 0.466gm/cu.m (-164oC )
Conversion factor
Flash point 914 oF(490
oC)
Vapor pressure at 20 c
Autoignition temperature
Henry’s law constant
Odor
Physical porperties of toluene
Physical properties Toluene
Molar mass 92.14g/mol
Appearance Clear colorless to yellowish
Density at 25 oC 0.867g/cm
3
Melting point -93.990 C
Boiling point 110-1110 C
Solubility in water 0.052% at 25 0 C
Specific heat 1.72 kj/kg k
Flash point 4.40 C
Vapor pressure at 20 c 28.5 torr
Hazard class Flamable liquid
Styrene from Ethyl benzene
• Ethyl benzene is mainly used to produce styrene.
• Over 90% of the 12.7 billion pounds of EB produced in
the U.S. during 1998 was dehydrogenated to styrene.
• Styrene (vinyl benzene)
– A liquid (b.p. 145.2C)
– Polymerizes easily when initiated by a free radical or when
exposed to light.
• Dehydrogenation of ethyl benzene to styrene
– Catalysts:-
• Metal oxide catalysts. Oxides of Fe, Cr, Si, Co, Zn, or their
mixtures
– Reaction conditions:
• Temperature : 600-700o C
• Pressure : 1 atm or or lower
• 90% styrene yield
• 60-70% conversion:
Process Description
See Figure 1. The raw material is ethyl benzene, and steam is
fed as an inert. In the suggested process, ethyl benzene is
preheated in E-501 to a saturated vapor. This is then mixed with
steam produced from the fired heater H-501. The steam provides
the heat of reaction and serves as an inert diluent to help shift
the reaction to the right. Steam also tends to limit side reactions
and helps to extend catalyst life by reducing coke formation on
the catalyst. The ratio of steam to ethyl benzene entering reactor
R-501 in Stream 6 ranges between 6 and 12. The main reaction:
C6H5CH2CH3 → C6H5CHCH2 + H2 …………….. (1)
Ethyl benzene styrene
is endothermic, reversible, and limited by equilibrium. The
reaction occurs at high temperatures (600 – 700 0c) and low
pressures (0.4-1.4 bar) in order to shift the equilibrium to the
right to favor styrene production. In R-501, the process uses a
proprietary iron catalyst that minimizes (but does not eliminate)
side reactions at higher temperatures. For simplicity, assume that
the only side reaction that occurs in R-501 is the hydrogenation
of ethyl benzene to form toluene and methane:
C6H5CH2CH3 + H2 → C6H5CH3 + CH4 ……….(2)
Ethyl benzene toluene
The primary reaction is limited by equilibrium, and is assumed
to approach 80% of equilibrium. The selectivity of the toluene
side reaction is a function of reactor temperature.
The reactor effluent, Stream 7, is cooled in E-502 to produce
steam and then enters a three-phase separator (V-501). The
bottom phase of V-501 is waste water (Stream 11). This must be
decanted and sent for further processing before discharge. This
treatment is not shown in the PFD, but it is an expense which
must be included in the economic analysis. Stream 9 leaves the
top of the separator and contains all the light gases (methane and
hydrogen) and can be used as a fuel gas. Stream 10 contains
most of the toluene, ethyl benzene and styrene.
Stream 10 flows through a pressure-reducing valve and then
enters a distillation train (T-501 and T-502). The distillation
columns operate at (different) constant pressures, the values of
which are governed by the properties of the heating steam and
cooling water used, and the composition of the top and bottom
products, as described later. Most of the toluene is removed at
the top of first column (T-501) in Stream 16. The remaining
toluene, ethyl benzene and styrene leaving the bottom of this
column in Stream 15 enter the second column (T-502). From T-
502, Stream 24 (containing ethyl benzene, toluene and styrene)
is recycled and mixed with fresh ethyl benzene before the
reactor. The bottom product of T-502 leaving in Stream 28
constitutes the styrene (with small amounts of ethyl benzene
and toluene) leaving Unit 500.
Tolue
-ne
Purifi-
cation
Colu-
mn
Adiabatic Fixed Bed
Reactor Pre-Heater
Separator
Benzene
tolune column
Final
Purif
-ier
Colu
-mn
Pure Ethyl
Benzene
Hydrogen and
Methane Gas
Ethyl Benzene
Recycle
99% Styrene
Ethyl Benzene
Recycle
Process flow diagram
Styrene plant
MASS BALANCE AND ENERGY BALANCE:
C6H5CH2CH3 → C6H5CHCH2 + H2…………. (1)
Ethyl benzene styrene
C6H5CH2CH3 + H2 → C6H5CH3 + CH4 ….…(2)
Ethyl benzene toluene methane
Molecular weight of Ethyl benzene = 106
Molecular weight of Styrene = 104
Molecular weight of Benzene = 78
Molecular weight of Toluene= 80
The plant capacity for ethyl benzene plant =30 tones per day
For which we are suppose to produce the product as
follows: The product ethyl benzene which we will produce will contain:-