Ind. Eng. Chem. Res. 2009, 48, 7065–7071
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Methanol Conversion to Dimethyl Ether over H-SAPO-34 Catalyst Grigore Pop,† Grigore Bozga,*,‡ Rodica Ganea,† and Natalia Natu† SC ZECASIN SA, Spl. Independentei, 202, Bucharest, Romania, Department of Chemical Engineering, UniVersity Politehnica, Spl. Independentei, 313, Bucharest, Romania
The process of methanol conversion to dimethyl ether over an H-SAPO-34 molecular sieve was studied, using the catalyst as synthesized or formulated in an alumina matrix. The experiments were performed on the temperature interval 100-250 °C, liquid space velocities of 1-5 h-1, and pressures between 1 and 10 bar. The results evidenced a high catalytic activity of the H-SAPO-34 molecular sieve, providing in these conditions a practically total methanol transformation to dimethyl ether. Also, a special run, performed at 180 °C, with an output composition close to chemical equilibrium, showed no significant change of catalyst activity during an on-stream time of 50 h, this proving a good stability and resistance to deactivation. A published rate expression for the methanol dehydration reaction was selected and adapted to describe the experimentally observed process kinetics. Introduction Dimethyl ether (DME) is receiving in the last years a growing attention from scientists and practitioners, as a chemical product having potential advantages in the diminution of global environmental pollution and clean energy supply. Presently, DME has a wide range of applications as LPG substitute, aerosol propellant, and refrigerant liquid to replace ozone destroying chlorofluorocarbons, as alternative diesel fuels for transportation, or in combustion cells. As a potential diesel fuel, DME exhibits a high cetane number (55-60) and some excellent burning characteristics: low level of soot products, low NOx emissions, and no release of sulfur compounds. DME is also a useful chemical intermediate for dimethyl sulfate and several highvalue oxygenated product syntheses. Since methanol can be produced from biomass derivatives, DME presents also the advantage of a product obtainable from renewable sources. Successful studies of the methanol dehydration to DME process were carried out over H-Mordenite,1 H-Mordenite dealuminated or modified with different metal oxides,1,2 Ferrierite, Y and Beta zeolites,1 H-ZSM-5,3 NaH-ZSM-5,4,5 SUZ4,6 modified natural clinoptilolite,7 H-SAPO-34,8,9 γ-alumina10-14 and silica modified γ-alumina,15 η-alumina,16 or ion exchange resins.17 MCM-22, H-MCM-41, modified MCM-41, and mesoporous alumina proved also to be interesting catalysts for methanol etherification.18 A number of published works are dedicated to the investigation of mechanism and kinetics of this process on different solid acidic catalysts. As underlined by Blaszkowski and van Santen,19 the intrinsic mechanism of the surface steps depends on the nature of catalyst. Thus, the catalytic activity of alumina is associated with the participation of the Lewis acid-Lewis base pair appearing during surface dehydration steps, while that of zeolites is related with the Brønsted acid-Lewis base pair. Bandiera and Naccache2 studied the mechanism and kinetics of methanol dehydration on a dealuminated H-mordenite. They proposed a scheme involving as first surface steps the adsorption of two methanol molecules, one on a Brønsted acid site and a second one at its adjacent base site, resulting two intermediate * To whom correspondence should be addressed. E-mail: g_bozga@ chim.upb.ro. † SC ZECASIN SA. ‡ University Politehnica.
species, [CH3 · OH2]+ and [CH3O]-, respectively. Further, these combine, giving dimethyl ether and water. Kubelkova et al.20 investigated the methanol dehydration process on HY and HZSM-5 catalysts modified with nonskeletal aluminum. On the basis of FTIR spectra analysis, the authors postulate that methanol is first protonated to methoxonium ion, [CH3 · OH2]+, which further eliminates a molecule of water, forming a methyl group bonded to the zeolitic center. This can react with a second nonadsorbed methanol molecule, to give DME. A similar reaction scheme was proposed by Qinwei and Jingfa21 for the methanol dehydration on tungstophosphosphoric acid catalyst (H3PW12O40). According to the mechanism proposed by Lu et al.,3 for the methanol dehydration on HZSM-5 zeolite, the first step is the protonation of a methanol molecule on a Brønsted acid site of the catalyst, forming a surface cation, CH3+. The second step is considered to be the reaction between the CH3+ cation and an adsorbed methanol molecule on a second Brønsted acid site, giving an adsorbed DME molecule. Our previous studies evidenced that H-SAPO-34 could be a very attractive methanol processing catalyst, as a result of its high catalytic activities both in etherification and in conversion to olefins (MTO), and consequently allowed for the possibility to perform both DME synthesis and MTO22 technologies in the same reactor, only by temperature adjustment. In this study we prepared the SAPO-34 molecular sieve by a method presenting original features, and we characterized it for crystallinity by X-ray diffraction (XRD), acidity by temperature programmed desorption (TPD) of ammonia, and specific surface area by BET method. The prepared molecular sieve was tested in the methanol dehydration reaction, by continuous reactor experiments. The data obtained in this way were used to study the process kinetics and to identify a kinetic model of the dehydration process on this catalyst. To the best of our knowledge, in the open literature there are no kinetic studies for methanol etherification on H-SAPO34 catalyst. Catalyst Synthesis and Characterization H-SAPO-34 was synthesized following an original route, by using tetraalkylammonium phosphate as the template. The amorphous phosphorus-alumina-silica gel was obtained by mixing an alumina-water suspension with silica sol, under
10.1021/ie900532y CCC: $40.75 2009 American Chemical Society Published on Web 06/19/2009
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continuous stirring, at room temperature and pressure and subsequent addition of tetraethylammonium phosphate (TEA+H2PO4-). The pH of the mixture was kept nearly constant by successive adding of phosphoric acid.8 The initial gel oxide composition is: P2O5: 1.67Al2O3: 0.34SiO2: 1.68TEAOH: 128H2O The molecular sieve SAPO-34 crystallization process is conducted for 72 h at 190-195 °C under continuous stirring. During the crystallization process, phosphorus atoms enter into the molecular sieve framework and release a corresponding free tetraalkylammonium hydroxide. Consequently, the reaction mixture pH value presents an increasing trend from an initial value in the interval 6.2-6.5, to a level between 8.0 and 8.5 where the crystallization is almost stopped. To avoid this phenomenon, the pH was kept close to the initial value, by adding orthophosphoric acid into the reaction mixture. Usually three pH adjustments followed by hydrothermal treatment has been applied. In this way, the following molar composition of the reaction mixture was obtained: P2O5: 1.44Al2O3: 0.29SiO2: 1.14TEAOH: 120H2O After crystallization, the product was separated from the mother liquor by centrifugation, washed twice with distilled water, and finally dried at 100-110 °C overnight. The powder X-ray diffraction patterns (XRD) of the synthesized SAPO-34 material, performed on a DRON-3 diffractometer and presented in Figure 1, confirm its structure and high crystallinity. The material synthesized in this way proved to have a good thermal stability, up to temperatures of 800 °C. In the structure obtained, about 25% of TEAOH is captured in spaces of pores, namely, the large cavities with narrow 0.38 × 0.38 nm channels, which is characteristic to a chabazite-CHA type structure. The thermogravimetric diagram of resulted product (DUPONT instrument), presented in Figure 2, indicates a practically complete template removal at 600-700 °C. Therefore, the hydrogen form of the molecular sieve (H-SAPO-34) was obtained by calcination in air at 600 °C for 4 h. The scanning electron microscopy picture of the H-SAPO34 molecular sieve that resulted after calcination, made on a Quanta Inspect F microscope, evidenced parallelepiped shape particles having dimensions lower than 3 µm (Figure 3). The concentration and the strength of the acid sites were evaluated by ammonia TPD technique. A micro reactor containing a sample of approximately 0.2 g of catalyst was coupled to a Hewlett-Packard GC-MS apparatus. After heating to 50 °C, the H-SAPO-34 sample was saturated with 30 pulses of 0.5 mL ammonia, physically sorbed ammonia being purged for 30 min. Then, the microreactor temperature was raised by 16°/min up to 490 °C, and the ammonia TPD curve presented in Figure 4 was recorded. Total concentration of the acid sites was determined by titration of the desorbed ammonia with sulfuric acid. The concentration of acid sites and strength distribution, obtained by processing the ammonia TPD curve, are presented in Table 1. It can be observed that the shape of the DTG curve presented in Figure 2 is very similar to the ammonia TPD curve given in Figure 4. This result suggests that the thermogravimetric analysis (TGA) could be used to evaluate the acidity of the SAPO-34 obtained by hydrothermal crystallization in the presence of tetraethylammonium ion as template. To be used in the methanol dehydration process, the SAPO34 dry powder was formulated by extrusion in an alumina
Figure 1. X-ray powder patterns for SAPO-34 samples.
matrix. A pseudoboehmite-type hydrated alumina (65% Al2O3) was used as γ-Al2O3 precursor in catalyst formulation. Further, the extruded catalyst pellets were activated by heating in air at 600 °C for 8 h. The H-SAPO-34/γ-Al2O3 weight ratio in the final calcined catalyst was roughly 1/4. Our tests evidenced that H-SAPO-34 concentrations in the formulated catalyst higher than 25% (by wt) do not improve significantly its activity in the process of methanol conversion to DME.8 BET surface area and porosity of the pure H-SAPO-34 molecular sieve and formulated catalyst were measured on a Quantachrome Instruments apparatus, by using nitrogen as analysis gas. The adsorption-desorption isotherms obtained for the active component (H-SAPO-34) and for the formulated catalyst are presented in Figure 5, and the main numerical data are in Table 2. A first activity test of the prepared H-SAPO-34 powder was carried out by the temperature programmed reaction (TPR) technique, comparatively with H-ZSM-5, a catalyst used for the methanol dehydration process in several works.3,19,20 The experiments were conducted in the same microreactor-GC-MS setup used in the TPD acidity study, by injection of methanol pulses. The TPR curves obtained in the range 100-490 °C are given in Figure 6, for H-SAPO-34 and H-ZSM-5. In the case of H-ZSM-5, the unreacted methanol desorption starts at 120 °C, that of dimethyl ether at 160 °C, and that of water at 280
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Figure 2. TGA curves of the SAPO-34 sample.
Figure 3. SEM images of H-SAPO-34.
°C, respectively. At temperatures higher than 300 °C there was evidence of olefin and aromatic desorption. H-SAPO-34 molecular sieve exhibits different TPR curves: unreacted methanol, dimethylether, and water desorb together in the temperature interval 200-300 °C, olefins desorb at 320 °C along with a smaller second water peak. No hydrocarbons were desorbed from H-SAPO-34 molecular sieve below 300 °C, the methanol etherification selectivity being practically 100%.
A more extensive experimental study of the methanol etherification on H-SAPO-34/γ-Al2O3 catalyst described above was carried out on a stainless steel laboratory fixed bed reactor. The reactor, having the internal diameter of 32 mm and the height of 500 mm, was provided with a coaxial thermowell permitting the temperature to be measured on the axial position along the bed. The catalytic reactor, loaded with diluted catalyst (50 vol % inert ceramic material), was continuously fed with methanol by a calibrated liquid pump. All the measurements
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Ind. Eng. Chem. Res., Vol. 48, No. 15, 2009 Table 2. Textural Data of H-SAPO-34 and Formulated H-SAPO-34/ γ-Al2O3 Catalyst surface area, m2/g pore volume, cm3/g
Figure 4. Ammonia TPD curve of H-SAPO-34 molecular sieve. Table 1. Number of Acid Sites and Acid Strength Distribution total number of acid sites, g acidic strength distribution: weak and physisorbed sites (W) maximum temperature, °C number of weak sites, g medium sites (M) maximum temperature, °C number of medium sites, g strong sites (S) maximum temperature, °C number of strong sites, g
11.1 × 1020 137 1.26 × 1020 198 6.05 × 1020 418 3.80 × 1020
were carried out on temperature and pressure domains corresponding to the vapor state of the reaction mixture. The reactor effluent was cooled and the main products liquefied. The uncondensed reaction products were analyzed by an online gas chromatograph and the liquid ones by off-line gas chromatography, both on a Chromosorb column. Essentially, only methanol, dimethylether, and water were detected in the reactor effluent mixture. A first set of experiments were aimed at elucidating the influence of mass transport steps on the overall process kinetics. The influence of the internal diffusion was investigated by performing experiments on catalyst pellets of different size in identical working conditions. The results, presented in Figure 7, show that the influence of internal diffusion on the global process kinetics is practically avoided for catalyst pellets having the diameter smaller than 1.5 mm. Consequently, all the kinetic experiments were performed with catalyst pellets having the average diameter around 1 mm. Several tests were carried out at different methanol feed flow rates, keeping constant the ratio
Figure 5. N2 adsorption-desorption isotherms.
sample
BET
micropore
total
micropore
H-SAPO-34 formulated catalyst
510 288
404
0.69 0.94
0.21
pore diameter, nm (BJH method) 1.23 5.07
of catalyst weight to methanol flow rate (or equivalently constant gas-solid contact time). The measured methanol conversions showed that, on the working domain, the influence of external mass transfer on process kinetics is not significant. Theoretical evaluations of internal and external temperature gradients, following the procedures described by Froment and Bischoff,23 have not evidenced significant internal and external heat transfer limitations. To assess the contribution of the alumina matrix on the catalyst activity, experiments were performed on pure alumina pellets. The results are presented as conversion-temperature curves in Figure 8. From this diagram it can be observed that a methanol conversion of 80% is obtained on the H-SAPO-34/ γ-Al2O3 catalyst at 200 °C and the chemical equilibrium is practically approached at 250 °C. The same diagram shows that, at reaction temperatures lower than 200 °C, the alumina catalytic activity is negligible as compared with that of H-SAPO-34. Consequently, the contribution of the alumina matrix on the formulated catalyst performance, in the working temperature range, is not significant. To test the stability of the H-SAPO-34/γ-Al2O3 catalyst, the catalytic activity of a sample was monitored during 50 h on stream time, without regeneration, at a constant temperature of 180 °C. The experimental results, presented in Figure 9, show that methanol conversion remains practically constant over this time interval, the catalyst exhibiting a good stability and deactivation resistance in the given operating conditions. Process Kinetics Modeling The intrinsic kinetics of methanol dehydration on the H-SAPO-34/alumina catalyst was investigated by performing experiments on the laboratory reactor described in the previous paragraphs, at temperatures on the interval 100 to 200 °C, pressures of 1-10 bar, and liquid methanol space velocity (LHSV) on the interval 2-5 h-1. These conditions correspond to the vapor state of the reaction mixture. The experiments were performed with fresh catalyst extruded pellets having the equivalent diameter approximately 1 mm and flow rates ensuring negligible influence of external diffusion on process kinetics. The intrinsic kinetics of the methanol dehydration was quantitatively investigated in a significant number of studies, many of them proposing rate expressions based on Langmuir-Hinshelwood (LH)3,10,11,13,14 or Eley-Rideal theories.24 To identify an appropriate kinetic expression for the methanol dehydration on the investigated H-SAPO-34/alumina catalyst, we tested the adequacy of the main published rate expressions, to our experimental data. To this aim, we used a nonlinear leastsquares regression procedure, based on the Levenberg-Marquardt algorithm existing in the scientific package MATLAB. The process taking place inside the catalyst bed was described by the pseudohomogeneous plug-flow model (Froment and Bischoff23). The contribution of axial mixing to the mass transport was neglected, considering that the ratio of catalyst
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Figure 6. Methanol TPR curves: a, H-ZSM-5; b, H-SAPO-34.
Figure 7. Methanol conversion versus the pellet dimension (p ) 1 bar; 9, T ) 200 °C, LHSV ) 1 h-1; 2, T ) 170 °C, LHSV ) 2 h-1).
Figure 10. Temperature dependence of the equilibrium constant and equilibrium methanol conversion. Table 3. Estimated Values of Kinetic Parameters
Figure 8. Temperature dependence of methanol conversion (p ) 1 bar; dp ) 1 mm; LHSV ) 1 h-1).
parameter
estimated value
A0 E/R AM0 AW0 (-∆HM)/R (-∆HW)/R
4.076 × 1010 mol/(gcat h bar) 9626.2 K 2.606 × 10-7 bar-1 1.023 × 10-4 bar-1 7683.3 K 5900 K
The temperature dependence of chemical equilibrium constant, Kp, was calculated from the usual thermodynamic equations and published data,25 assuming ideal behavior of the reaction mixture. The calculated temperature dependence of the equilibrium conversion, considering pure methanol reagent, is given in Figure 10. Among the published rate expressions we tested, the most adequate to our data proved to be the one published by Lu et al.,3 derived by LH theory and involving the participation of two Brønsted acid sites: rE )
Figure 9. Time stability of H-SAPO-34/γ-Al2O3 catalyst (T ) 180 °C; p ) 1 bar; dp ) 1 mm; LHSV ) 1 h-1).
bed height to particle diameter is relatively high (L/dp > 50) for all the experiments.
k[pM2/pW-pE/KP] (1 + KMpM + KWpW)2
(1)
This is in agreement with the observations of Marchi and Froment26 and Wu and Anthony,27 respectively, underlining the main role of Brønsted acid sites in the activity of SAPO catalysts. The temperature dependencies of the rate constant, k, and adsorption equilibrium constants KM, KE, and KW were expressed by the Arrhenius and Van’t Hoff equations:
( RTE );
k ) A0 exp -
(
KJ ) AJ0 exp -
)
∆HJ , RT
J ) M, W, E (2)
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synthesis and MTO technologies can be performed in the same catalytic reactor, the change of the reaction temperature being the only required adjustment. Acknowledgment We appreciate and thank to Dr. P. Tomi, Dr. R. Birjega, Dpl. Eng. S. Serban, and Dipl. Eng. A. M. Bobaru for their assistance in some of the presented instrumental analysis. Literature Cited
Figure 11. Calculated versus experimental values of the methanol conversion.
The estimated values of the parameters appearing in this expression are given in Table 3 and correspond to a correlation coefficient, r ) 0.967. The calculated value of activation energy (80.1 kJ/mol) is lower than the one estimated theoretically by Blaszkowski and Van Santen19 for methanol dehydration on the HZSM-5 zeolite (147 kJ/mol) but very close to the value obtained by Bandiera and Naccache2 for the same process conducted on a dealuminated H Mordenite (80 kJ/mol). The estimated heat of adsorption for the methanol molecule (63.89 kJ/mol) is also in agreement with the value for HZSM-5 zeolite published by Blaszkowski and Van Santen19 (65 kJ/mol). However, the estimated heat of adsorption for water molecules (49.06 kJ/mol) is lower than the adsorption energy reported by the same authors for the reaction product (74 kJ/mol). The calculated values of the methanol conversion are presented comparatively with the experimental ones in Figure 11. The distribution of the points in this diagram and the corresponding value of the correlation coefficient, r ) 0.967, are proving a reasonably good quality of the fit for our experimental data, by the kinetic expression eq 1. Conclusions This study evidenced a high catalytic activity and good selectivity of H-SAPO-34 materials in the dehydration of the methanol to dimethyl ether. Activity tests of the formulated catalyst containing 25 wt % H-SAPO-34 and 75% alumina evidenced a practically total selectivity, even for methanol conversions close to chemical equilibrium ones, at temperatures up to 300 °C. Our results demonstrate that at temperatures up to 200 °C, at space times corresponding to methanol conversion close to equilibrium, the alumina contribution to the catalyst activity is negligible as compared to the H-SAPO-34 one. Also, a stability test of the H-SAPO-34/alumina catalyst, for 50 h on stream time, indicated a good stability and deactivation resistance in these working conditions. Experimental data obtained on a fixed bed catalytic reactor were used to select a kinetic model of the catalytic process. By testing the main rate expressions proposed for the methanol dehydration process, the best fit of the data was obtained by using a rate expression corresponding to the LH surface mechanism, involving the participation of two Brønsted acid sites. This study and previously published ones prove that H-SAPO-34 is an interesting methanol processing catalyst, having high catalytic activities both in etherification and conversion to olefins (MTO). Consequently, both DME
(1) Khandan, N.; Kazemeini, M.; Aghaziarati, M. Determining an Optimum Catalyst for Liquid Phase Dehydration of Methanol to Dimethyl Ether. Appl. Catal. A 2008, 349, 6. (2) Bandiera, J.; Naccache, C. Kinetics of Methanol Dehydration in Dealuminated H-Mordenite:Model with Acid and Base Active Center. Appl. Catal. 1991, 69, 139. (3) Lu, W.; Teng, L.; Xiao, W. Simulation and Experiment Study of Dimethyl Ether Synthesis from Syngas in a Fluidized-Bed Reactor. Chem. Eng. Sci. 2004, 59, 5455. (4) Jiang, S.; Hwang, J.-S.; Jin, T.; Kai, T.; Cho, W.; Baek, Y. S.; Park, S.-E. Dehydration of Methanol to Dimethyl Ether over ZSM-5 Zeolite. Bull. Korean Chem. Soc. 2004, 25 (2), 185. (5) Kim, S. D.; Baek, S. C.; Lee, Y.; Jun, K.; Kim, M. J.; Yoo, I. S. Effect of γ-alumina on Catalytic Performance of Modified ZSM-5 for Dehydration of Crude Methanol to Dimethyl Ether. Appl. Catal. A 2006, 309, 139. (6) Hwang, J.-S.; Hwang, Y.-K.; Cai, T.; Chang, J.-S.; Park, S.-E. Methanol Dehydration toDME on Extremly Stable Catalyst. Presented at SUZ-4.13 ICC, July 11-17, 2004, Paris, France. (7) Royaee, S. J.; Sohrabi, M.; Falamaki, C. Methanol Dehydration fo Dimethyl Ether Using Modified Clinoptilolite. Mater. Sci. (Poland) 2007, 25 (4), 1149. (8) Pop, Gr.; Theodorescu, C. SAPO-34 Catalyst for Dimethyl Ether Production. Stud. Surf. Sci. Catal. 2000, 130 (1), 287. (9) Yoo, K. Y.; Kim, J.; Park, M.; Kim, S.; Joo, O.; Jung, K. Influence of Solid Acid Catalyst on DME Production Directly from Synthesis Gas over the Admixed Catalyst of Cu/ZnO/Al2O3 and various SAPO catalysts. Appl. Catal. A 2007, 330, 57. (10) Bercic, G.; Levec, J. Intrinsic and Global Reaction Rate of Methanol Dehydration over γ-Al2O3 pellets. Ind. Eng. Chem. Res. 1992, 31, 1035. (11) Bercic, G.; Levec, J. Catalytic Dehydration of Methanol to Dimethyl Ether. Kinetic Investigation and Reactor Simulation. Ind. Eng. Chem. Res. 1993, 31, 1035. (12) Lee, E.; Park, Y.; Joo, O.; Jung, K. Methanol Dehydration to Produce Dimethyl Ether over γ-Al2O3. React. Kinet. Catal. Lett. 2006, 89 (1), 115. (13) Mollavali, M.; Yaripour, F.; Atashi, H.; Sahebdelfar, S. Intrinsic Kinetics Study of Dimethyl Ether Synthesis from Methanol on γ-Al2O3 Catalyst. Ind. Eng. Chem. Res. 2008, 47, 3265. (14) Lee, E.; Park, Y.; Joo, O.; Jung, K. Methanol Dehydration to Produce Dimethyl Ether over γ-Al2O3. React. Kinet. Catal. Lett. 2006, 89 (1), 115. (15) Yaripour, F.; Baghaei, F.; Schmidt, I.; Perregaard, J. Catalytic Dehydration of Methanol to Dimethyl Ether (DME) over Solid-Acid Catalysts. Catal. Commun. 2005, 6, 147. (16) Seo, C. W.; Jung, K. D.; Lee, K. Y.; Yoo, K. S. Influence of Structure Type of Al2O3 on Dehydration of Methanol for Dimethyl Ether Synthesis. Ind. Eng. Chem. Res. 2008, 47, 6573. (17) An, W.; Chuang, K. T.; Sanger, A. Dehydration of Methanol to Dimethyl Ether by Catalytic Distilation. Can. J. Chem. Eng. 2004, 82, 948. (18) Pop, Gr.; Ganea, R.; Natu, N.; Bozga, G. New Catalysts for Methanol Conversion to Dimethyl Ether. Presented at 14th ICC, July 1318, 2008, Seoul; PII-12-04. (19) Blaszkowski, S. R.; Van Santen, R. A. Theoretical Study of the Mechanism of Surface Methoxy and Dimethyl Ether Formation from Methanol Catalyzed by Zeolitic Protons. J. Phys. Chem. B 1997, 101, 2292. (20) Kubelkova, L.; Novakova, J.; Nedomova, K. Reactivity of Surface Species on Zeolites in Methanol Conversion. J. Catal. 1990, 124, 441. (21) Qinwei, Z.; Jingfa, D. Studies on the Properties of Water in and Conversion of Methanol into Dimethyl Ether on H3PW12O40. J. Catal. 1989, 116, 298.
Ind. Eng. Chem. Res., Vol. 48, No. 15, 2009 (22) Pop, Gr.; Ganea, R.; Ivanescu, D.; Boeru, R.; Ignatescu, Gh.; Birjega, R. Catalytic Process for the preparation of Light Olefins from Methanol. U.S. Patent 6,710,218, 2004. (23) Froment, G. F.; Bischoff, K. Chemical Reactor Analysis and Design; John Wiley: New York, 1979. (24) Al Wahabi, S. M. Conversion of methanol to light olefins on Sapo34. Kinetic modeling and reactor design. Ph.D. Dissertation, Texas A&M University, 2003. (25) Reid, R. C.; Prausnitz J. M.; Poling B. E. The Properties of Gases and Liquids; McGraw-Hill: New York, 1987.
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(26) Marchi, A. J.; Froment, G. F. Catalytic Conversion of Methanol to Light Alkenes on SAPO Molecular Sieves. Appl. Catal. 1991, 71, 139. (27) Wu, X.; Anthony, R. G. Effect of Feed Composition on Methanol Conversion to Light Olefins over SAPO-34. Appl. Catal. A 2001, 218, 241.
ReceiVed for reView April 6, 2009 ReVised manuscript receiVed June 2, 2009 Accepted June 4, 2009 IE900532Y
