Modeling and Simulation a Catalytic Fixed Bed Reactor to Produce Ethyl Benzene from Ethanol

Transcription

1 Journal of Physical Chemistry and Electrochemistry Vol. No.3 (20) 55-6 Journal of Physical Chemistry and Electrochemistry Islamic Azad University Marvdasht ranch Journal homeage: htt://journals.miau.ac.ir/je Modeling and Simulation a Catalytic Fixed ed Reactor to Produce Ethyl enzene from Ethanol Masoomeh Emadi a,* and Asghar Emadi a a Deartment of Chemistry, Marvdasht ranch, Islamic Azad University, Marvdasht, Iran Abstract Ethyl benzene used increasingly each year is the raw material of roducing styrene monomer. his substance is roduced from benzene alkylation with ethylene or ethanol, deending on the availability and cost of raw materials. In this study benzene alkylation in the resence of ethanol in a catalytic fixed bed reactor in three states of isotherm, adiabatic and non-isotherm-non-adiabatic is mathematically modeled with onedimensional seudo- homogeneous model; and then has been rogrammed with math lab software. he reaction kinetics model is used in this study which comes from the exerimental equations found by Mr. U.S Ridevi et al. in a zeolite catalyst imregnated with AlCl 3 obtained in isotherm mode. he results of this simulation in isotherm state are comarable with exerimental data. he adiabatic and non-isotherm-nonadiabatic states also show accetable results. Furthermore, in this study the effect of various factors such as the feed flow rate, substrate temerature, substrate density, fixed and variable heat caacity and viscosity of fluid has been investigated. Keywords: Fixed ed Reactor, Ethyl enzene, Modeling, Simulation, Ethanol, Catalyst. Introduction In 985 the American Comany of UOP develoed a new rocess for benzene alkylation with ethylene gas in the resence of aluminum chloride whose main roduct was ethyl benzene which is the raw material of styrene monomer []. However, in countries which have no access to gas resources, benzene alkylation is used with ethanol. Ethylbenzene is a colorless liquid that has a gasoline-like odor and the air odor threshold concentration is 2.3 arts er million (m) arts of air. he amount of ethyl benzene in the crude oil is very low and it is used in other construction such as building stehen, diethyl * Corresonding author address: m_emadi90@yahoo.com benzene, cellulose acetate and etc in addition to the styrene roduction [2,3]. enzene alkylation rocess with ethylene on the catalyst by Friedel - Krafts is a commercial way for creating more than ninety ercents of ethyl benzene. However using this catalyst has many roblems including loading them inside the reactor, safety, waste and corrosion. A recently great effort was develoed for using environmentally friendly catalytic rocesses [4 and 5]. Zeolite-based catalyst tyes are used for this urose. Currently benzene alkylation in vaor hase with ethanol on ZSM-5 catalyst is carried out which is the well- known rocess of Mobil adger. his rocess is used in the commercial scale for roduction of ethyl benzene. here are many advantages of direct

2 56 M.Emadi & A. Emadi / Journal of Physical Chemistry and Electrochemistry Vol. No.3 (20) 55-6 use of ethanol instead of ethylene and benzene alkylation. One advantage is the catalyst long activity when alcohol was used instead of Olefin and the other one is that using ethanol instead of ethylene is more economical for countries in which ethanol is roduced through biological rocesses. Many surveys have been carried out to comare alkylation reactions of zeolite ZSM and zeolite X. Many researchers have erformed aromatic alkylation reactions based on the X tye of Zeolites. enzene alkylation reaction with -decen and trans alkylation of dialkyl benzene with AlCl 3 catalyst have been done, according to reorts the alkylation reaction with this method is twice faster than trans alkylation reaction. Catalyst activity has been increased in benzene alkylation reaction with roylene by using Cumen-AlCl 3 catalyst with alumina silicate [6]. enzene alkylation and ethanol with zeolite imregnated with AlCl 3 has been imlemented by U.S. Ridvai et al. Modeling was erformed to obtain a mathematical relationshi that can almost exactly redict the function of rocess in different conditions. In this study, kinetic model obtained from exeriments by U. S. Ridvi et al. for benzene alkylation with ethanol was used with the one-dimensional quasi-homogeneous model of a fixed bed reactor [7]. hen the equations obtained are solved with [0] numerical methods. 2. Reaction kinetics equation ethanol and Y E moles of ethyl benzene. Hence the amount of benzene converted by alkylation is Y E moles. Hence, the amount of benzene conversion by alkylation rocess is equal to: In examining any rate equation, internal and external resistance should be at least to develo an intrinsic rate equation. o estimate the imact of external influence two series of exeriments were erformed by different amounts of catalyst. For testing the effect of internal diffusion also two exeriments were done by two different catalyst sizes of.58 and.36 mm. he results of these exeriments have shown that the internal and external diffusion are ineffective. In the absence of internal diffusion resistance, mechanisms include chemical absortion and surface reactions and catalytic reaction controller. In the resent study the chemical absortion, in the stage of rate controlling, has not been alied and it has been only carried out in surface reaction controller cases. hen U.S. Ridvi et al. on the base of their exeriments roosed the following model for rate of this reaction: r kk EK E ( + K + K + K ) E E E E 2 (2) (3) he reaction of ethyl benzene alkylation with ethanol is erformed according to the following relationshi: C 6 H 6 + CH 3 CH 2 OH C 6 H 5 CH 3 +H 2 O () he catalytic reaction exeriment to obtain kinetics model has been carried out in a fixed bed reactor and a stainless steel cylinder with 2.5 cm of inner diameter and 33 cm in length. It was exerimentally observed that ethyl benzene is the only imortant roduct. Y E, Y and Y E are resectively ethanol, benzene and ethyl benzene. mol of the roduct will contain Y moles of benzene, Y E moles of artial ressures in the above equation are in relation with the conversion ercent and total ressures as they are illustrated in the following equations: (0.33 X ) P E X P 5.78 X E 5.78 X Putting artial ressures in the overall rate equation we will see the overall equation: 2 2 kk K E( X )(0.33 X ) P /(5.78 X ) r 2 [ + ( ) + (0.33 ) + /(5.78 ) ] { K X K X K X }{ P X } E E ( X ) P 5.78 X (4) (5)

3 M.Emadi & A. Emadi / Journal of Physical Chemistry and Electrochemistry Vol. No.3 (20) Four unknown arameters in the equation (5), obtained by exeriments in three different temeratures, are calculated by regression in the following way: Lnk ( ) LnK ( ) LnK E ( ) LnK E ( ) 3. Mass transfer equation (6) 4 G ( C ) + hw ( w ) rmρ ( H) z D Wall heat transfer term has been entered in this equation. Heat transfer coefficient which exists in this equation can be written as: hwd DG 3.6( ) K µε g Also this equation includes viscosity which is a function of temerature and is obtained from the following relationshi: (472.82( ) ) (686.64( ) ) µ 0.75* *0 (9) (0) () In all three modes isotherm, adiabatic and non-isotherm non adiabatic, mass transfer equation is as the following, the adiabatic mode non-isotherm non adiabatic mass transfer relationshi also find temerature deendence. 2 2 kk K E( X )(0.33 X ) P /(5.78 X ) r (7) 2 [ + ( ) + (0.33 ) + /(5.78 ) ] { K X K X K X }{ P X } E E 4. Isotherm Equations In this case there is no equation of temerature distribution in the reactor and all have the same temerature. 5. Adiabatic energy balance equation H rxn can be calculated as: rxn ( ) ( ) mix f 298 mix (2) H C feed d + H + C roduct 7. he results of mathematical modeling and equations 7.. Isotherm mode According to results of the study, the conversion ercentage of benzene into ethyl benzene decreases by increasing the amount of feed flow as they are illustrated in fig. and 2. In this case the energy balance equation are obtained as follows: 2 2 ρ( H ) kk K E( X )(0.33 X ) P /(5.78 X ) 2 z GC [ + K ( X ) + K (0.33 X ) + K X P /(5.78 X ) ] { }{ } mix E E (8) 6. Non-isotherm Non adiabatic energy balance equation In this case the energy balance equation is obtained by the following way : Fig.. fraction conversion in 0.28 feed flows

4 58 M.Emadi & A. Emadi / Journal of Physical Chemistry and Electrochemistry Vol. No.3 (20) 55-6 Fig.2. fraction conversion in 0.4 feed flows According to the results, the increase of the total bed ressure for each secific isotherm increases exchange ercentage ( see fig. 5 and 6). According to results of this study, for a secific isotherm, the bed density increase leads to an increase in the conversion ercentage of benzene to ethyl benzene. Isotherms are illustrated in fig. 3 and 4. Fig. 5. fraction conversion in 2 atm total ressure Fig. 3. fraction conversion in 0.3 Density of bed Fig. 6. fraction conversion in 22 atm total ressure Fig. 4. fraction conversion in 0.6 Density of bed 7.2. Adiabatic mode According to the results of this study, the bed density decrease and increase in the adiabatic mode and the constant heat caacity does not effect on the amount of conversion of benzene to ethyl benzene. However the conversion ercentage is higher than the isotherm mode. Furthermore, the bed density changes do not affect on the bed temerature rofile within the reactor. hese results are shown in fig. 7 and 8.

5 M.Emadi & A. Emadi / Journal of Physical Chemistry and Electrochemistry Vol. No.3 (20) Fig. 7. fraction conversion versus length of reactor in 0.6 bed density emerature Fig.0. conversion ercentage versus length of reactor in 700 Kelvin temerature feed flow Also, the results indicated in fig. and 2 show that the amount of conversion ercentage of ethyl benzene in the variable heat caacity mode increases by temerature raising that is less than constant heat caacity state. Fig. 8. emerature versus length of reactor in 0.6 bed density According to the results of this study, the feed temerature increase leads to a rise in the conversion ercentage. Also results of the search show that the ressure increase and decrease do not affect on the conversion ercentage and the temerature rofile in a constant and variable heat caacity state (see fig. 9 and 0). Fig : fraction conversion versus length of reactor in 673 Kelvin temerature Fig.. fraction conversion versus length of reactor in 673 Kelvin temerature Fig. 9. fraction conversion versus length of reactor in 673 Kelvin temerature feed flow Fig. 2. fraction conversion versus length of reactor in 700 Kelvin temerature

6 60 M.Emadi & A. Emadi / Journal of Physical Chemistry and Electrochemistry Vol. No.3 (20) 55-6 According to the results, the inut discharge changes do not have any effect on the conversion ercentage in both fixed and variable heat caacity, and temerature rofiles are the same with discharge changes. On the other hand the bed density affects on the conversion ercentage and temerature rofiles in variable heat caacity mode. Fig. 3. fraction conversion versus length of reactor in 700 Kelvin temerature Fig. 4. fraction conversion versus length of reactor in 700 Kelvin temerature 7.3. Non-isotherm - non-adiabatic According to this research, bed density changes in the fixed and variable heat caacities are similar and no changes have been observed in them (see fig 5, 6). Also changes in the amount of feed charge have no effect on ethyl benzene conversion ercentage but this amount is more in fixed heat caacity than the variable heat caacity. Fig. 5. fraction conversion versus length of reactor in variable fixed bed density and and fixed heat caacity Fig. 6. fraction conversion versus length of reactor in variable fixed bed density and and variable heat caacity Fig.7 and 8 demonstrate that the conversion ercentage of ethyl benzene in a fixed heat caacity and variable heat caacity increases by increasing feed temerature. Fig. 7. fraction conversion versus length of reactor in 600 Kelvin temerature

7 M.Emadi & A. Emadi / Journal of Physical Chemistry and Electrochemistry Vol. No.3 (20) References Fig. 8. fraction conversion versus length of reactor in 700 Kelvin temerature 8. Conclusion With the results obtained in this study it can be observed that in the isotherm mode, by increasing temerature of isotherm, conversion ercentage increases, and this result is similar to the exerimental results of [7] observed. Also by increasing bed density and ressure, the conversion ercentage of ethyl benzene increases in isotherm mode, and the conversion ercentage decrease by rising flow rate. In the adiabatic mode, for the same bed density in a constant heat caacity, the degree of increase of conversion ercentage is more than variable heat caacity. Also changes in temerature rofiles along the reactor in a state of constant heat caacity and adiabatic are much higher than variable heat caacity, the temerature rofiles increase in the constant heat caacity but they decrease in the variable heat caacity state along the reactor. Conversion ercent rofiles are alike in the non isotherm-non adiabatic mode for both fixed and variable heat caacities in the same flow rate. he temerature rofile changes are very small however their sloes of changes are oosite. [] Australian Petrochemical, Petroleum and Chemical Cororation, Internet (2000). [2] Agency for toxic substances and disease registry, toxic ecological. Profile for ethyl benzene, Atlanta, Internet (999). [3] K.L. Ring, j. surdik, Chemical Economic Handbook, (999). [4] Y. Zhuang, D. Wu, Huaxue Fang. Gong Cheng Yu Gongyi, 0 (994) 46. [5] C. Ercan, F.M. Dautzenberg, C.Y.Yeh, H.E.arner, Ind. Eng. Chem. Res., 37 (998) [6] I.M. Kolensinkov,.V Zaitesva, Chem. Abstr. 03 (985) 4529m. [7] U. Sridevi,.K. haskar Rao, Narayan C.Pradhan, Chemical Engineering Journal, 83 (200) [8] C. G. Hill, JR., An introduction to chemical engineering kinetics and reactor design book, Mc Graw Hill, New York (980). [9] J.M. Smith, Chemical engineering kinetics. 2 nd edition, McGraw Hill, NY (970). [0] S. C. Chara, R. P. Canel, Numerical method for engineering, 3 rd edition, McGraw Hill, Singaore (998). Signs and symbols with their units Particle diameter [cm] D Viscosity [centioises] µ Fluid thermal conductivity [w/mk] k g Adsortion constant of benzene [/atm] K Adsortion constant of Ethanol [/atm] K E Adsortion constant of ethyl benzene benzene [/atm] K E Adsortion constant of water [/atm] K w Adsortion constant of hydrogen [/atm] K H Kinetic constant [kgmole/ (kg catalyst.hr)] k Density of bed [gr/cubic centimeter] ρ Partial ressure [atm] otal ressure [atm] Rate of reaction of benzene [kgmole/ (kg cat.h)] r Porosity of bed ε Heat transfer coefficient [w/mk] hw Length of reactor [cm] z Fractional benzene conversion [dimensionless] X f Enthaly of formation [kcal/grmole] H 298 Enthaly of reaction [cal/grmole] H rxn Heat caacity [cal/grmole K] C Mass velocity [gr/s.cm^2] G Ambient temerature [K] w

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