- Email: [email protected]
Experimental and theoretical studies of the TAME synthesis by reactive distillation
European Symposium on Computer Aided Process Engineering - 13 A. Kraslawski and I. Turunen (Editors) © 2003 Elsevier Science B.V. All rights reserved.
713
Experimental and Theoretical Studies of the TAME Synthesis by Reactive Distillation Markus Kl6ker\ Eugeny Kenig\ Andrzej G6rak\ Kazimierz Fraczek^, Wieslaw Salacki^, Witold Orlikowski^, ^University of Dortmund, Chemical Engineering Department, Dortmund, Germany ^Research and Development Centre for the Refinery Industry, Plock, Poland Email: [email protected]. Fax: +49 231 755-3035
Abstract The heterogeneously catalysed synthesis of TAME (tert-amyl-methyl ether) via reactive distillation is investigated experimentally and theoretically. The structured catalytic packing Montz MULTIPAK®-2 is used in the catalytic section of a 200 mm diameter pilot scale column with a total packing height of 4 meters. Simulations with a developed rate-based model covering 11 components and 4 chemical reactions are in good agreement with experimental data. The simulations studies show the influence of the reflux ratio on conversion and selectivity.
1. Introduction Reactive separation is a novel technology that combines chemical reaction and product separation in a single apparatus. Depending on applied separation method, reactive distillation, reactive extraction, reactive absorption and other combined processes can be distinguished. The most popular in petrochemical industry are catalytic distillation processes (CD), e.g. selective hydrogenation of benzene, diolefins and acetylenes; desulfurization of fluid catalytic cracking (FCC) gasoline, jet and diesel fuels; aromatics alkylation; paraffine isomerisation and dimerisation. One of the most important CD processes is the production of tertiary ethers which are widely used as ecologically friendly additives for motor fuels. Currently, more than 100 units are in operation using CD to produce MTBE, TAME and ETBE. The major advantages for CD in ethers production are the capital cost reduction and lowering of energy costs due to the utilisation or reaction heat (more than 20%). Moreover, conversion is increased due to removal of products via distillation (25% for TAME), and the product selectivity is improved. The production of ethers via CD can also benefit from increased catalyst lifetime due to reduction of hot spots and removal of fouling substances from the catalyst. There are several possibilities of immobilising the solid catalyst in industrial CD columns on basis of trays, random and structured packings. A survey on available catalytic column internals is presented by Krishna and Taylor (2000). In this paper structured packing Montz MULTIPAK®-2 filled with catalyst Amberlyst 35 WET is applied for the TAME synthesis from light gasoline from the FCC process.
714
2. Chemical System The light gasoline of a FCC unit was used as the source of isoamylene fraction. Crude gasoline contains 12 wt% of active isoamylenes and about 1 wt% of dienes. Isoamylene fraction was obtained by distillation and diene hydrogenation of the light gasoline. The final content of isoamylenes in the feed was in the range 19-21 wt % and the concentration of dienes less then 0.01 wt %. The number of components identified by gas chromatography exceed 90 species. The methanol feed contains more then 99.9 wt% of pure methanol and water in the range 0.015 - 0.045 wt%. The reaction scheme for the production of TAME from these reagents is as follows: 2-Me-l-butene + MeOH <->TAME 2-Me-2-butene + MeOH o TAME 2-Me-1 -butene f-> 2-Me-2-butene 2-Me-1 -butene + 2-Me-2-butene -^ C10H20 2*2-Me-l-butene -> C10H20 2*2-Me-2-butene -^ C10H20 2*MeOH -^ CH3OCH3 + H2O 2-Me-l-butene+ H20<-^ rerr-amyl alcohol 2-Me-2-butene + H2O <-> ferr-amyl alcohol rerr-amyl alcohol + MeOH <^ TAME + H2O
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
The system (I)-(IO) is rather complicated for analysis and simulation. Several authors observed multiple steady states in CD columns (Sundmacher et al., 1999, Mohl et al., 1999). For some reactions, kinetic data are missing. Reactions 1, 2 and 3 are desired ones. Dimerisation of reactive isoamylenes (reactions 4, 5 and 6) is usually treated as unwanted in open literature, however, at commercial scale, there is no difficulty because of their high octane number and low volatility. Dimethyl ether (reaction 7) has also high octane number, but because of its large vapour pressure it is inapplicable as a gasoline component. The major problem is related to water which is introduced with methanol feed and formed during methanol dimerisation. Water adsorps on etherification catalyst more strongly then methanol and can inhibit desired reactions and for this reason the water content in reactants should not exceed 0.1 % (Piccoli and Lovisi, 1995). It was observed that even small amounts of water in distillate result in two liquid phases after cooling. Phase splitting is not problem at industrial scale but wanted if non-converted methanol is extracted with water and the afterwards distilled methanol is recycled,
3. Reactive Distillation Experiments A simplified sketch of the pilot plant installation is shown in Fig. 1. The basic equipment here are a pre-reactor and a catalytic distillation column equipped with skew situated total condenser and vertical evaporator. All units, packings, tanks and piping are made from stainless steel. The CD column (diameter 200 mm) has three sections: the rectifying section at the top of the column equipped with 1 meter of 12x12x0.4 mm Bialecki rings the catalytic section equipped with 1 meter of the structured catalytic packing MlJLTIPAK®-2 with 41 vol% of Amberlyst 35 WET in the catalyst bags the stripping section at the bottom of the column filled with two meters the same Bialecki rings as in the rectifying section
715 All parts of the column are isolated by 80 mm layer of mineral wool. Pressure on the top of column is adjusted by cooling water temperature in condenser. •C^d
<
^^—^tofsqe
stBsiii
Z
tank
1 ^
Figure 1: A sketch of pilot plant installation. Flow rates of isoamylene fraction, methanol and TAME fraction are measured using tensiometer balances, and reflux and distillate flow rates using a Coriolis-type flowmeter. The samples are analysed off line. Process data, such as temperatures, flows, levels and pressures are stored and visualised by a monitoring system based on microprocessor controller MSC68. This gives a way to identify steady states in the column. Several operational parameters have been varied and their influence on the process performance has been analysed. In particular, the feed rate has been changed in the range between 25 and 45 kg/h, the molar feed ratio of methanol/isoamylenes between 0.9 and 1.45 and the reflux ratio between 1 and 2.
4. Rate-based Modelling Traditional equilibrium stage models and efficiency approaches are often inadequate for reactive separation processes. In multicomponent mixtures, diffusion interactions can lead to unusual phenomena, and it is even possible to observe mass transport of the component in the direction opposite to its own driving force - the so-called reverse diffusion (Talyor and Krishna, 1993). For multicomponent systems, the stage efficiencies are different for different components and may range from -oo to +oo. To avoid possible qualitative errors in the parameter estimation, it is necessary to model
716 separations taking account of actual mass transfer rates (Taylor and Krishna, 1993, Noeres et al., 2002). Therefore, in this work a more physically consistent way is used by which a direct account of process kinetics is realised. This approach to the description of a column stage is known as the rate-based approach and implies that actual rates of multicomponent mass transport, heat transport and chemical reactions are considered immediately in the equations governing the stage phenomena. Mass transfer at the vapour-liquid interface is described via the well known two-film model. Multicomponent diffusion in the films is covered by the Maxwell-Stefan equations (Hirschfelder et al., 1964). In the rate-based approach, the influence of the process hydrodynamics is taken into account by applying correlations for mass transfer coefficients, specific contact area, liquid hold-up and pressure drop. Chemical reactions are accounted for in the bulk phases and, if relevant, in the film regions as well. The relevant models for the reactive distillation column and peripherals have been developed and implemented into the simulation environment ASPEN Custom Modeler™. Simulations of the heterogeneously catalysed synthesis of TAME have included 11 components. The species and the boiling points at the operating pressure of 4 bar are listed in Table 1. The key components of the inert fractions of the feed have been used to represent the hydrocarbon fractions (see Table 1). VLE is described by UNIQUAC model, with the Redlich-Kwong equation of state. In simulations, four reactions are considered: the main reactions (l)-(3) and the formation of dimethyl ether (7). Table 1: Selected components and boiling points (Ti,) at 4 bar. Component Dimethyl ether n-Butane i-Pentane 2-methyl-l-butene (2M1B) 2-methyl-2-butene (2M2B) Methanol 2-inethyl-pentane TAME Water 2,3 dimethyl-2-methoxy butane n-Decane
Representing inert C4 components inert C5 components
inert C6-C8 components
higher ethers inert C9+ components
TbPC] 12.0 41.9 74.6 77.3 85.7 104.1 110.8 140.2 143.7 156.1 237.2
The kinetics of reactions (l)-(3) have been determined for Amberlyst-35 as part of European research project INTINT (Intelligent Column Internals for Reactive Separations, see http://www.cpi.umist.ac.uk/intint/). Kinetics for reaction (7) have been measured by Kiviranta-Paakkonen et al. (1998) for Amberlyst-16. Since the properties of Amberlyst-16 and Amberlyst-35 are similar, the validity of these kinetics is assumed. According to Oost and Hoffmann (1995), the dimerisation of isoamlyenes is the main side reaction at low methanol concentrations. However, no kinetic data is available for the description of reactions (4) to (6) and therefore dimersiation is not considered in this work. Subawalla and Fair (1999) pointed out, that the hydration reactions of the isoamylene (reactions (8) and (9)) are strongly equilibrium limited and water must be present in large excess to form significant amounts of ^^r^-amyl alcohol. Thus, the reactions (8) to (10) are neglected.
717
5. Model Validation A series of simulations have been performed with the developed model for validation purposes. Figure 2 and 3 show the simulated temperature and concentration profiles (lines, solid symbols) of the main components for two experiments and the respective experimental values (empty symbols). A Experiment 13
>^
Experiment 13
1°=
^****v^A
f^p"^ K Y
^f"^^^ - • - TAME —•- C4 fraction -<^-2M2B+2M1B —*-C5 fraction —»— Methanol
' " *.
T
—j
'v
* yc ^ ^^cr*-^^**-—-u " T T I I I . • • T • • •!< . w r t - f - « - < - f - y i ^ T | ? t ~ t - r | ' ' t ' r ^ Packing height [m]
Pacldng height [m]
Figure 2: Temperature and concentration profiles (experiment 13). In experiment 13, reflux ratio is 2, the molar feed ratio methanol/isoamylenes is 0.9, with a total feed rate of 22.8 kg/h. Simulated profiles agree well with the corresponding experimental data. However, for this experiment, the TAME mass fraction in the bottom is slightly overpredicted, while the calculated bottom temperature is lower. This can be explained by the dimer and oligomer formation from isoamylene which is not considered in the model.
i \ ^
Experiment 15
A
-1
1
1
1
1
"^A***"""—^^
1
1
1
1.5 2 Pacldng height [m]
Figure 3: Temperature and concentration profiles (experiment 15). Iti experiment 15, the reflux ratio is 1, the molar feed ratio methanol/isoamylenes is 1.1, with a total feed rate of 22.5 kg/h. In this case, less high boiling by-products are formed and consequently the agreement between computed and experimental data is very good.
6. Simulation Studies The influence of the reflux ratio on conversion and on the formation of the by-product dimethyl ether has been studied (see Figure 4). All other operating parameters are chosen according to the conditions in experiment 15. For lower reflux ratios (<1.5), the selectivity for TAME with respect to methanol is lower due to the increased formation
718 of dimethyl ether. In addition, with increasing reflux ratios, the conversion is increased, since the recycle of non-converted methanol to the column is increased.
-*——"••
^
':'
"
^
^
^
J
I 0.3 I X
I
0.2 S
--o-S(TAMeMeOH) —tr-Y. (Isoamytene) - o- X (Methanol)
1I
Reflux ratio [kg/kg]
Figure 4: Influence of reflux ratio on conversion and selectivity. For the selected molar feed specifications and operating conditions, both conversion and selectivity remain almost constant for reflux ratios greater than 2.
7. Conclusions Both experimental and theoretical studies on the synthesis of TAME via reactive distillation have been performed. A rigorous model including 11 components and 4 reactions has been developed. The agreement between simulation and experiments is satisfactory. Simulations studies show a significant influence of the reflux ratio on conversion and selectivity for TAME related to methanol.
8. References Hirschfelder, J. O., Curtiss, C.F. and Bird, R.B., 1964, Molecular Theory of Gases and Liquids, Wiley, New York. Noeres, C , Kenig, E.Y. and Gorak, A., 2002, Chem. Eng. Process, in print. Kiviranta-Paakkonen, P., Struckmann (nee Rihko), L.K., Linnekoski, J.A., Krause, A.O.I., 1998, Ind. Eng. Chem. Res. 37, 18-24. Mohl, K., Kienle, A., Gilles, E., Rapmund, P., Sundmacher, K., and Hoffmann, U., 1999, Chem. Eng. Sci. 54 ,1029-1043. Oost, C , Hoffmann, U., 1995, Chem. Eng. Technol. 18, 203-209. Piccoli, R.L. and Lovisi, H.R., 1995, Ind. Eng. Res. 34, 510-515. Subawalla, H. and Fair, J.R., 1999, Ind. Eng. Chem. Res. 38, 3696-3709. Sundmacher, K., Uhde, G. and Hoffmann, U., 1999, Chem. Eng. Sci. 54, 2839-2847. Taylor, R. and Krishna, R., 1993, Multicomponent Mass Transfer, Wiley, New York. Taylor, R. and Krishna, R., 2000, Chem. Eng. Sci. 55, 5183-5229.
9. Acknowledgement The financial support of the European Commission (Contract No. GIRD CT1999 00048) and of the Swiss Federal Office for Education and Science (decree: 99.0724) is highly appreciated.
713
Experimental and Theoretical Studies of the TAME Synthesis by Reactive Distillation Markus Kl6ker\ Eugeny Kenig\ Andrzej G6rak\ Kazimierz Fraczek^, Wieslaw Salacki^, Witold Orlikowski^, ^University of Dortmund, Chemical Engineering Department, Dortmund, Germany ^Research and Development Centre for the Refinery Industry, Plock, Poland Email: [email protected]. Fax: +49 231 755-3035
Abstract The heterogeneously catalysed synthesis of TAME (tert-amyl-methyl ether) via reactive distillation is investigated experimentally and theoretically. The structured catalytic packing Montz MULTIPAK®-2 is used in the catalytic section of a 200 mm diameter pilot scale column with a total packing height of 4 meters. Simulations with a developed rate-based model covering 11 components and 4 chemical reactions are in good agreement with experimental data. The simulations studies show the influence of the reflux ratio on conversion and selectivity.
1. Introduction Reactive separation is a novel technology that combines chemical reaction and product separation in a single apparatus. Depending on applied separation method, reactive distillation, reactive extraction, reactive absorption and other combined processes can be distinguished. The most popular in petrochemical industry are catalytic distillation processes (CD), e.g. selective hydrogenation of benzene, diolefins and acetylenes; desulfurization of fluid catalytic cracking (FCC) gasoline, jet and diesel fuels; aromatics alkylation; paraffine isomerisation and dimerisation. One of the most important CD processes is the production of tertiary ethers which are widely used as ecologically friendly additives for motor fuels. Currently, more than 100 units are in operation using CD to produce MTBE, TAME and ETBE. The major advantages for CD in ethers production are the capital cost reduction and lowering of energy costs due to the utilisation or reaction heat (more than 20%). Moreover, conversion is increased due to removal of products via distillation (25% for TAME), and the product selectivity is improved. The production of ethers via CD can also benefit from increased catalyst lifetime due to reduction of hot spots and removal of fouling substances from the catalyst. There are several possibilities of immobilising the solid catalyst in industrial CD columns on basis of trays, random and structured packings. A survey on available catalytic column internals is presented by Krishna and Taylor (2000). In this paper structured packing Montz MULTIPAK®-2 filled with catalyst Amberlyst 35 WET is applied for the TAME synthesis from light gasoline from the FCC process.
714
2. Chemical System The light gasoline of a FCC unit was used as the source of isoamylene fraction. Crude gasoline contains 12 wt% of active isoamylenes and about 1 wt% of dienes. Isoamylene fraction was obtained by distillation and diene hydrogenation of the light gasoline. The final content of isoamylenes in the feed was in the range 19-21 wt % and the concentration of dienes less then 0.01 wt %. The number of components identified by gas chromatography exceed 90 species. The methanol feed contains more then 99.9 wt% of pure methanol and water in the range 0.015 - 0.045 wt%. The reaction scheme for the production of TAME from these reagents is as follows: 2-Me-l-butene + MeOH <->TAME 2-Me-2-butene + MeOH o TAME 2-Me-1 -butene f-> 2-Me-2-butene 2-Me-1 -butene + 2-Me-2-butene -^ C10H20 2*2-Me-l-butene -> C10H20 2*2-Me-2-butene -^ C10H20 2*MeOH -^ CH3OCH3 + H2O 2-Me-l-butene+ H20<-^ rerr-amyl alcohol 2-Me-2-butene + H2O <-> ferr-amyl alcohol rerr-amyl alcohol + MeOH <^ TAME + H2O
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
The system (I)-(IO) is rather complicated for analysis and simulation. Several authors observed multiple steady states in CD columns (Sundmacher et al., 1999, Mohl et al., 1999). For some reactions, kinetic data are missing. Reactions 1, 2 and 3 are desired ones. Dimerisation of reactive isoamylenes (reactions 4, 5 and 6) is usually treated as unwanted in open literature, however, at commercial scale, there is no difficulty because of their high octane number and low volatility. Dimethyl ether (reaction 7) has also high octane number, but because of its large vapour pressure it is inapplicable as a gasoline component. The major problem is related to water which is introduced with methanol feed and formed during methanol dimerisation. Water adsorps on etherification catalyst more strongly then methanol and can inhibit desired reactions and for this reason the water content in reactants should not exceed 0.1 % (Piccoli and Lovisi, 1995). It was observed that even small amounts of water in distillate result in two liquid phases after cooling. Phase splitting is not problem at industrial scale but wanted if non-converted methanol is extracted with water and the afterwards distilled methanol is recycled,
3. Reactive Distillation Experiments A simplified sketch of the pilot plant installation is shown in Fig. 1. The basic equipment here are a pre-reactor and a catalytic distillation column equipped with skew situated total condenser and vertical evaporator. All units, packings, tanks and piping are made from stainless steel. The CD column (diameter 200 mm) has three sections: the rectifying section at the top of the column equipped with 1 meter of 12x12x0.4 mm Bialecki rings the catalytic section equipped with 1 meter of the structured catalytic packing MlJLTIPAK®-2 with 41 vol% of Amberlyst 35 WET in the catalyst bags the stripping section at the bottom of the column filled with two meters the same Bialecki rings as in the rectifying section
715 All parts of the column are isolated by 80 mm layer of mineral wool. Pressure on the top of column is adjusted by cooling water temperature in condenser. •C^d
<
^^—^tofsqe
stBsiii
Z
tank
1 ^
Figure 1: A sketch of pilot plant installation. Flow rates of isoamylene fraction, methanol and TAME fraction are measured using tensiometer balances, and reflux and distillate flow rates using a Coriolis-type flowmeter. The samples are analysed off line. Process data, such as temperatures, flows, levels and pressures are stored and visualised by a monitoring system based on microprocessor controller MSC68. This gives a way to identify steady states in the column. Several operational parameters have been varied and their influence on the process performance has been analysed. In particular, the feed rate has been changed in the range between 25 and 45 kg/h, the molar feed ratio of methanol/isoamylenes between 0.9 and 1.45 and the reflux ratio between 1 and 2.
4. Rate-based Modelling Traditional equilibrium stage models and efficiency approaches are often inadequate for reactive separation processes. In multicomponent mixtures, diffusion interactions can lead to unusual phenomena, and it is even possible to observe mass transport of the component in the direction opposite to its own driving force - the so-called reverse diffusion (Talyor and Krishna, 1993). For multicomponent systems, the stage efficiencies are different for different components and may range from -oo to +oo. To avoid possible qualitative errors in the parameter estimation, it is necessary to model
716 separations taking account of actual mass transfer rates (Taylor and Krishna, 1993, Noeres et al., 2002). Therefore, in this work a more physically consistent way is used by which a direct account of process kinetics is realised. This approach to the description of a column stage is known as the rate-based approach and implies that actual rates of multicomponent mass transport, heat transport and chemical reactions are considered immediately in the equations governing the stage phenomena. Mass transfer at the vapour-liquid interface is described via the well known two-film model. Multicomponent diffusion in the films is covered by the Maxwell-Stefan equations (Hirschfelder et al., 1964). In the rate-based approach, the influence of the process hydrodynamics is taken into account by applying correlations for mass transfer coefficients, specific contact area, liquid hold-up and pressure drop. Chemical reactions are accounted for in the bulk phases and, if relevant, in the film regions as well. The relevant models for the reactive distillation column and peripherals have been developed and implemented into the simulation environment ASPEN Custom Modeler™. Simulations of the heterogeneously catalysed synthesis of TAME have included 11 components. The species and the boiling points at the operating pressure of 4 bar are listed in Table 1. The key components of the inert fractions of the feed have been used to represent the hydrocarbon fractions (see Table 1). VLE is described by UNIQUAC model, with the Redlich-Kwong equation of state. In simulations, four reactions are considered: the main reactions (l)-(3) and the formation of dimethyl ether (7). Table 1: Selected components and boiling points (Ti,) at 4 bar. Component Dimethyl ether n-Butane i-Pentane 2-methyl-l-butene (2M1B) 2-methyl-2-butene (2M2B) Methanol 2-inethyl-pentane TAME Water 2,3 dimethyl-2-methoxy butane n-Decane
Representing inert C4 components inert C5 components
inert C6-C8 components
higher ethers inert C9+ components
TbPC] 12.0 41.9 74.6 77.3 85.7 104.1 110.8 140.2 143.7 156.1 237.2
The kinetics of reactions (l)-(3) have been determined for Amberlyst-35 as part of European research project INTINT (Intelligent Column Internals for Reactive Separations, see http://www.cpi.umist.ac.uk/intint/). Kinetics for reaction (7) have been measured by Kiviranta-Paakkonen et al. (1998) for Amberlyst-16. Since the properties of Amberlyst-16 and Amberlyst-35 are similar, the validity of these kinetics is assumed. According to Oost and Hoffmann (1995), the dimerisation of isoamlyenes is the main side reaction at low methanol concentrations. However, no kinetic data is available for the description of reactions (4) to (6) and therefore dimersiation is not considered in this work. Subawalla and Fair (1999) pointed out, that the hydration reactions of the isoamylene (reactions (8) and (9)) are strongly equilibrium limited and water must be present in large excess to form significant amounts of ^^r^-amyl alcohol. Thus, the reactions (8) to (10) are neglected.
717
5. Model Validation A series of simulations have been performed with the developed model for validation purposes. Figure 2 and 3 show the simulated temperature and concentration profiles (lines, solid symbols) of the main components for two experiments and the respective experimental values (empty symbols). A Experiment 13
>^
Experiment 13
1°=
^****v^A
f^p"^ K Y
^f"^^^ - • - TAME —•- C4 fraction -<^-2M2B+2M1B —*-C5 fraction —»— Methanol
' " *.
T
—j
'v
* yc ^ ^^cr*-^^**-—-u " T T I I I . • • T • • •!< . w r t - f - « - < - f - y i ^ T | ? t ~ t - r | ' ' t ' r ^ Packing height [m]
Pacldng height [m]
Figure 2: Temperature and concentration profiles (experiment 13). In experiment 13, reflux ratio is 2, the molar feed ratio methanol/isoamylenes is 0.9, with a total feed rate of 22.8 kg/h. Simulated profiles agree well with the corresponding experimental data. However, for this experiment, the TAME mass fraction in the bottom is slightly overpredicted, while the calculated bottom temperature is lower. This can be explained by the dimer and oligomer formation from isoamylene which is not considered in the model.
i \ ^
Experiment 15
A
-1
1
1
1
1
"^A***"""—^^
1
1
1
1.5 2 Pacldng height [m]
Figure 3: Temperature and concentration profiles (experiment 15). Iti experiment 15, the reflux ratio is 1, the molar feed ratio methanol/isoamylenes is 1.1, with a total feed rate of 22.5 kg/h. In this case, less high boiling by-products are formed and consequently the agreement between computed and experimental data is very good.
6. Simulation Studies The influence of the reflux ratio on conversion and on the formation of the by-product dimethyl ether has been studied (see Figure 4). All other operating parameters are chosen according to the conditions in experiment 15. For lower reflux ratios (<1.5), the selectivity for TAME with respect to methanol is lower due to the increased formation
718 of dimethyl ether. In addition, with increasing reflux ratios, the conversion is increased, since the recycle of non-converted methanol to the column is increased.
-*——"••
^
':'
"
^
^
^
J
I 0.3 I X
I
0.2 S
--o-S(TAMeMeOH) —tr-Y. (Isoamytene) - o- X (Methanol)
1I
Reflux ratio [kg/kg]
Figure 4: Influence of reflux ratio on conversion and selectivity. For the selected molar feed specifications and operating conditions, both conversion and selectivity remain almost constant for reflux ratios greater than 2.
7. Conclusions Both experimental and theoretical studies on the synthesis of TAME via reactive distillation have been performed. A rigorous model including 11 components and 4 reactions has been developed. The agreement between simulation and experiments is satisfactory. Simulations studies show a significant influence of the reflux ratio on conversion and selectivity for TAME related to methanol.
8. References Hirschfelder, J. O., Curtiss, C.F. and Bird, R.B., 1964, Molecular Theory of Gases and Liquids, Wiley, New York. Noeres, C , Kenig, E.Y. and Gorak, A., 2002, Chem. Eng. Process, in print. Kiviranta-Paakkonen, P., Struckmann (nee Rihko), L.K., Linnekoski, J.A., Krause, A.O.I., 1998, Ind. Eng. Chem. Res. 37, 18-24. Mohl, K., Kienle, A., Gilles, E., Rapmund, P., Sundmacher, K., and Hoffmann, U., 1999, Chem. Eng. Sci. 54 ,1029-1043. Oost, C , Hoffmann, U., 1995, Chem. Eng. Technol. 18, 203-209. Piccoli, R.L. and Lovisi, H.R., 1995, Ind. Eng. Res. 34, 510-515. Subawalla, H. and Fair, J.R., 1999, Ind. Eng. Chem. Res. 38, 3696-3709. Sundmacher, K., Uhde, G. and Hoffmann, U., 1999, Chem. Eng. Sci. 54, 2839-2847. Taylor, R. and Krishna, R., 1993, Multicomponent Mass Transfer, Wiley, New York. Taylor, R. and Krishna, R., 2000, Chem. Eng. Sci. 55, 5183-5229.
9. Acknowledgement The financial support of the European Commission (Contract No. GIRD CT1999 00048) and of the Swiss Federal Office for Education and Science (decree: 99.0724) is highly appreciated.