Bappa Saha (PROJECT)

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.

Head of the Department In-charge of Projet Work

(Prof. Chiranjib Bhattacharjee) (Prof. Ratna Datta)

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


Appearance Clear colorless

Density 0.8670g/cm3(20

oC)

o.8669 g/cm3(200

oC)

.86262 g/cm3(250

oC)


Boiling point 136.190 C


152mg/l (200 C)

160mg/L (250 C)


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)



Gas Density at 70 oF 0.0416lb/ft

3

Melting point -296.50 F

Boiling point -258.70 F


300mg/l (200 C)

400mg/L (400 C)


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



Density at 25 oC 0.867g/cm

3


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)


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:-

Styrene produced =

(30*1000) / 24 (kg/hr) *(104/106) (1/kg) *(1/104) (kmol)

=11.8 kmol/hr

Since we are using gas phase dehydrogenation process for styrene

production, for which yield and conversion are

as follows:

Yield=90%

Conversion=65% (w.r.t ethyl benzene)

Now consider FBR for Styrene plant

Styrene produced =11.8 kmol/hr

Now we know that:-

Yield = [{(moles of product produced)*(stochiomertric coefficient)}

/(moles of reactant converted)]/100

90/100=11.8/moles of reactant converted

Moles of reactant converted(ethyl benzene)= 13.4 kmol/hr

Now according to the reaction(1) and (2) in the reactor, we can say

that :-

For 1 mole of Styrene = 1 mole of ethyl benzene needed

Now after reactor 11.80 kmol of Styrene produced

So ethylene consume is = 11.8kmol

Thus rest ethyl benzene is = 13.4 – 11.8=1.6 kmol of ethyl benzene

Since conversion is 60%

It means that some of ethyl benzene had converted in to toluene and

methane(side reaction will occurred <10%) rest ethyl benzene are

unconverted and it is recycled.

Material balance of reactor

Input:

Ethylbenzene : 13.4 kmol/hr

Output

Ethyl benzene: 1.3 kmol/hr

Styrene : 11.8 kmol/hr

Hydrogen : 11.5 kmol/hr

Toluene : 0.27 kmol/hr

Methane : 0.27 kmol/hr

Material balance over Toluene column

Input

Ethyl benzene: 1.3 kmol/hr

Styrene :11.8 kmol/hr

Toluene :0.27 kmol/hr

Output

Toluene :0.27 kmol/hr

Output


Ethyl Benzene:1.3 kmol/hr

Material balance over final purification column

Input

Ethyl Benzene:1.3 kmol/hr


Output

Ethyl Benzene :1.3 kmol/hr

Output

Styrene:11.8 kmol/hr

ENERGY BALANCE

Estimated heat capacities at different temperature:

In the reactor the inlet feed temp is 6600C where the outlet

temp is 6000C. Hence for the energy balance about the reactor

it is assumed that the physical properties are constant, Ie

values at average temp (600+660)/2 = 6300C.

CP of steam at 6300C= 2.223 kJ/kg k

CP of EB at 6300C = 2.827 kJ/kg k

CP of styrene at 6300C = 2.610 kJ/kg k

Heat of raction = HR|25 =129.4 kJ/mol

Heat of formation (HR)= HR|25 + ∑( Ƴi* CPi)|PORDUCT -∑(Ƴi*CPi)|REACTANT

of styrene at 6300 = 86.99 kJ/mol

STEAM REQUIREMENT:

Let m is the mass of steam added to the feed per hour, in order

to supply the heat of reaction in the reactor .The steam and the

reactant feed entered the reactor at a temperature 6600C and

leave at 6000C temperature. Hence, it can be assumed that the

temperature drop solely due to the reaction the approx. energy

balance is made;

m*CPw*∆T +mST* CPST*∆T + mEB*CPEB *∆T + QR = 0

From the above balance the steam flow rate been calculated

as; m*2.223*(660-600) +122.97*2.613*(660-600)

+1422.68*2.827*(660-600)+86.99*11.8

m= 10948.07 kg/ hr

Henceforth the mol ratio of steam to hydrocarbon feed is

approximately calculated = 20:1

TEMPERATURE OF THE PREHEATED STREAM:

Let T be the temp of the preheated coming out of the

preheater. Assume the mixing of

the steam to hydrocarbon stream is adiabatic.

It is known that the temperature of the preheated steam is

8000C and after mixing with

the hydrocarbon stream, the temperature is dropped to 6600C.

Therefore, the heat balance

can be given as:

10948.07*2.293*(800-660)=(1450.5*2.133+4638.5*2.267)(660-

T)

i.e., T= 401.730 C

TEMPERATURE DETERMINATION OF THE REACTION

PRODUCT LEAVING THE PREHEATER:

Again, from mass balance about the reactor the wt fraction or

composition of the stream leaving the reactor can be given as:

Steam= 47.64%

EB = 13.95%

Styrene=36.63%

Toluene= 0.67%

Benzene= 0.38%

Hydrogen=0.73%

Therefore the average Cp value been determined=2.322 kJ/kg k

& the Cp value for the feed stream to the reactor= 2.235 kJ/kg k

The boiling point temp of the feed mixture at atmospheric

pressure is calculated by using

Roult’s law is=1380C

And the latent heat of vaporization of the mixture= 341.03

kJ/kg.

The Cp value for the liquid mixture = 1.939 kJ/kg k

Let the outlet temp of the product stream from the preheater=t

Therefore, the approx energy balance can be given as:

17036.97*2.322*(630-t)= 6088.9*(1.939*(138-

30)+341.03+2.235*(401-38))

i.e., t=472.90C

WASTE HEAT RECOVERY

The excess of superheat from the stream leaving the reactor

and through steam preheater,

is been utilized in generating steam in boiler, which further fed

back to the reactor

system.

The temp of the product stream leaving the preheater=472.90C

& Cp value of the stream is =2.322 kJ/kg k

Let the boiler operated at a temp of 1000C

The water feed to the condenser is at temp= 400C

The latent heat of vaporization of water at 1000C is= 2260 kJ/kg

Therefore the amt. of steam generated is:

17036.97*2.322*(472.9-100) = M*(4.184*(100-40)+2260)

ie, M=5874.72 kg/hr

hence the amount of steam been generated= 5874.72kg/hr

ENERGY REQUIRED FOR SUPER HEATING OF STEAM:

The steam is been heated to a temperature of 8000C in the

super heater.

The specific heat of steam at 4000C = 2.065 kJ/kg k

Therefore the heat requirement in the super heater=

Q= (10948.07/3600)*2.065*(800-100)

= 4395.95 KW

Fixed Bed Catalytic Reactor Process Design:

Feed composition component

lb mole/hr

Ethylbenzene 28.5

The catalytic dehydrogenation of ethyl benzene and found that

with a certain catalyst the rate could be represented by certain

catalyst.

C6H5CH2CH3↔C6H5CHCH2 + H2 (1)


The global rate was given as

rp= k(pe – 1/k*(psph))

where,

pe= partial pressure of ethylbenzene

ps= partial pressure of styrene

ph=partial pressure of hydrogen

the specific reaction rate and equilibrium constant

are

logk = - 4770/T + 4.10

where k is the pound mole of styrene produced per

hr/(atm)(lb catalyst) and T is degree kelvin

Temperature, T(°c) K

400 .0017

500 .0025

600 .0023

700 .0014

It is desired to estimate the volume of reactor necessary

to produce 30 tones of styrene par day, using vertical

tubes 4 ft in diameter, packed with catalyst pellets,

consider this problem by taking into account the side

reaction producing benzene and toluene. However to

simplify the calculation in this inductor example,

supposed that the sole reaction is the dehydrogenation

to styrene, and there is no heat exchange between the

reactor and the surrounding. Assumed that under normal

operation the exit conversion will be 65%. However also

prepare graphs conversion and temperature vs catalyst

bed depth, up to equilibrium conditions. The feed rate

per reactor tube is 13.5 lb moles/hr for ethylbenzene and

270lb moles/hr for stem. In addition

Temperature of mixed feed entering reactor =625 °c

Bulk density of catalyst as packed =90 lb/cu ft

Average pressure in rector tubes =1.2 atm

Heat of reaction = 60000 btu/lb mole

Surrounding temperature = 70 °F

The reaction is endothermic, so that heat must be

supplied to maintain the temperature. Energy must be

supplied by adding stream to the feed to provide a

reservoir of energy in its heat capacity.

In this problem the operation is adiabatic and the energy

balance is given by :

(F/M)(-∆H)dx =FtCpdT ……………………………….(01)

Since x refers to the conversion of ethylbenzene,

F/M =13.5 lb moles/hr. As there is large access of steam,

it will be satisfactory to take Cp=0.52 then the heat

capacity of the reaction mixture will be

FtCp=(270*18 + 13.5*106)(0.52) = 3270 Btu/°F

Substituting numerical value in equation (01), we obtain

13.5(-60000)dx=3270dT

-dT = 248x

T – 1616 = -248x ………………………………(02)

Where T is in degree and 625°c isthe entering

temperature of the feed.

The weight of catalyst expressed as :dW = pBAcdz

Ac= Cross sectional area

So we get, FdX= rppBAcdz …………………………(03)

dz = F/(rppBA) …………………………(04)

dz = 13.5dx/(90*0.78548*16)(rp) =(.0119/rp)dx

The partial pressure can be expressed in term of the

conversion as follows. At any conversion x the mole of

each component are

Steam= 20

Ethyl benzene =1-x

Hydrogen = x

Total moles = 21 + x

Then, pe= (1-x)*(1.2)/(21+x)

ps = ph= x*(1.2)/(21 +x)

then the total equation becomes

rp =1.2*k*[(1-x) – (1.2*x2)]/K*(21+x))/(21+x) ..…….(05)

or, with the expression for k determined by wanners and

Dybdal,

rp =1.2*(12600)*e-(19800/T)[(1-x) – (1.2*x2)/K*(21+x)]

……………………………………….(06)

Substituting this value of rpin equation (06) gives the

expression for the catalyst bed depth in terms of the

conversion and temperature,

dz=((21+x) *e(19800/T)/(1270000))*

[(1-x) – (1.2*x2)]/K*(21+x)]-1dx ………………………………(07)

Equation (02) and (07) can be solved numerically for the

bed depth for any conversion. If the coefficient of dx in

equation (07) is designated as α then we may wright eq.

(07) as: ∆z =α ∆x ………………………………..(07)’

At, z =0, x=0 and T=625°c

αo = (21/(1270000))*e12.25*(1/(1-0)) =3.30

If an increment ∆x of 0.1 is chosen, the temperature at

the end of the increment is, from equation (02),

T1 = 1616 – 248(0.1) =1591 °R =611°c

Then at the end of the first increment

α1 =((21+0.1) *e(12.43)/(1270000))*

[(1-0.1) – (1.2*0.12)]/0.28*(21+0.1)]-1=4.65

(Note: In the exponential term T has been converted to

degree Rankine.

The value of K is estimated to be 0.28 at 1591 °R from

the tabulation of data. )

The bed depth required for the first increment is given

by eq. (07)’ as

∆z = (3.30 + 4.65)*(0.1)/2 = 0.4 ft

Proceeding to the second increment, we find

T2 =1616 – 248*(0.2) = 1566 °R =597°c

α2 =((21+0.2) *e(12.66)/(1270000))*

[(1-0.2) – (1.2*0.22)]/0.22*(21+0.2)]-1= 6.60

z2-z1= α∆x = (α1 +α2)*(0.1)/2 =(4.65+6.60)*(0.1)/2 =0.56 ft

z2=0.4 +0.56= 0.96

The of further calculation are shown in table:

Conversion Temperature(°c) Catalyst bed depth(ft)

0 625 0

0.1 611 0.4

0.2 597 0.96

0.3 584 1.75

0.4 570 2.93

0.5 556 4.84

0.55 549 6.30

0.6 542 8.5

0.65 536 13.2

0.69 530 ∞

The rate of reaction becomes zero at conversion about

z=0.69 and a temperature of 530 °c, as determined from

equation (02) and (04) from the figure it is found that a

bed depth of 3.8 ft is required for a conversion of 65%.

The production of styrene from each reactor tube would

be,

Production/tube = 13.5*(104)(0.65)(24)=21,902 lb/day

Production/tube= 9.94 tons/day

Hence three 4 ft diameter reactor tubes packed with

catalyst to a depth of at least 3.8 ft would be required to

produced 30 tons/day of styrene.

CONCLUSION AND RECOMMENDATIONS

The catalytic dehydrogenation of ethylbenzene into styrene was

investigated in a tubular reactor over commercial potassium-

promoted iron oxide catalyst under atmospheric pressure. The

extensive kinetic experiments covered a wide range of operating

conditions and allowed the development of a fundamental kinetic

model. The kinetic study showed that the higher feed molar ratio of

H2O/EB give higher total ethylbenzene conversion and styrene

selectivity. The total ethylbenzene conversion and styrene selectivity

decreased as the addition of styrene or H2 to the feed mixture

increased. The addition of styrene or H2 leads to fast catalyst

deactivation. The intrinsic kinetics for the formation of styrene,

benzene, and toluene has been

modeled using the Hougen-Watson formula. The data analysis was

based on the integral method of kinetic analysis. The mathematical

model developed for the ethylbenzene dehydrogenation consists of

nonlinear simultaneous differential equations in multiple dependent

variables. The parameters were estimated from the minimization of

the multiresponse objective function which was performed by means

of the Marquardt algorithm. The significance of the individual model

parameters was tested by comparing the estimate bj with its standard

deviation. The estimate was significantly different from zero and

effectively contributes to the model. The kinetic model with set of

estimated198 parameters yielded an excellent fit of the experimental

data. The final estimated values of the adsorption enthalpies and

entropies was tested and validated using the physicochemical criteria

proposed by Boudart. The intrinsic kinetic parameters were used to

simulate 3-bed adiabatic industrial reactor with axial flow and radial

flow using the heterogeneous fixed bed reactor model.

Kinetic experiments for the formation of minor by-products, such

asphenylacetylene, α-methylstyrene, β-methylstyrene, cumene, n-

propylbenzene,divinylbenzene, and stilbene revealed that the

phenylacetylene selectivity did not depend on the total ethylbenzene

conversion. The selectivity of stilbene was highly increased with

increasing temperature. The selectivity of divinylbenzene was so low

(below0.01%) at all the reaction conditions that no correlation with

the ethylbenzene conversion was made. The selectivities of other

minor by-products decreased with increasing the total ethylbenzene

conversion. More research efforts can be contributed to the following

recommendations for

future work:

1. Experimental study for the coke formation and gasification using an

electrobalance to estimate the kinetic parameters for the coke

formation and

gasification, which leads to determine the dynamic equilibrium coke

content.

2. Process optimization of ethylbenzene dehydrogenation to

determine an optimal

reactor configuration and operating conditions, such as a molar ratio

of steam to

ethylbenzene, pressure, and temperature.

3. Empirical kinetic model for the production of minor by-products

which

correlates the selectivity with the total ethylbenzene conversion.

References: Chapter 22, Introduction to Multicomponent Distillation, Unit Operations of Chemical Engineering, by

McCabe-Smith-Harriott, 6th Edition, Published by McGraw . Hill International Edition, Chemical

Engineering Series.

Chapter 8, Process Design of distillation Column, Introduction to Process Engineering & Design,

Second

reprint 2009, Published by, Tata-McGraw-Hill Publishing Company limited, New Delhi.

Chapter 6, Costing & Project Evaluation, Coulson & Richardson’s volume 6, Third Edition, Chemical

Engineering Design, By R.K.Sinnot, Publisher by Butterworth- Heinemann Publications.

Chapter 11, Separation Columns, Coulson & Richardson’s volume 6, Third Edition, Chemical

Engineering

Design, By R.K.Sinnot, Publisher by Butterworth-Heinemann Publications.

Chapter 10, Process Design of Reactors, Introduction to Process Engineering & Design, Second reprint

2009, Published by, Tata-McGraw-Hill Publishing Company limited, New Delhi.

Process Equipment Design, By M.V. Joshi & V.V. Mahajani, Third edition, published by McMillan

India

Limited.

Kirk – Othmer Encyclopedia of chemical Technology 4th Edition.

Ullmann’s Encyclopedia, Industrial Organic Chemicals, Volume – 4

Chemical Weekly Buyer’s Guide 2005.

SAX’s Dangerous Properties of Industrial Materials.

Hydrocarbon Processing.

Basic Principals & Calculations in Chemical Engineering, David M. Himelblau, 6th Edition,

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