Chemical Engineering Science 62 (2007) 5349–5352www.elsevier.com/locate/ces

Ethylene and diethyl-ether production by dehydration reaction ofethanol over different heteropolyacid catalysts

Dilek Varislia, Timur Dogua,∗, Gulsen Dogub

aChemical Engineering Department, Middle East Technical University, Ankara, TurkeybChemical Engineering Department, Gazi University, Ankara, Turkey

Received 22 May 2006; received in revised form 25 December 2006; accepted 10 January 2007Available online 26 January 2007

Abstract

Dehydration reaction of ethanol was investigated in a temperature range of 140–250 ◦C with three different heteropolyacid catalysts, namelytungstophosphoricacid (TPA), silicotungsticacid (STA) and molybdophosphoricacid (MPA). Very high ethylene yields over 0.75 obtained at250 ◦C with TPA was highly promising. At temperatures lower than 180 ◦C the main product was diethyl-ether. Presence of water vapor wasshown to cause some decrease of catalyst activity. Results showing that product selectivities did not change much with the space time in thereactor indicated two parallel routes for the production of ethylene and DEE. Among the three HPA catalysts, the activity trend was obtainedas STA > TPA > MPA.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Heteropolyacid catalysts; Catalyst selectivity; Catalyst activation; Kinetics; Tungstophosphoricacid; Ethylene, diethylether, reaction engineering

1. Introduction

Diethyl-ether (DEE) is a valuable chemical and an attrac-tive motor vehicle fuel alternate (Kito-Borsa et al., 1998) andethylene is one of the major feedstock of petrochemical indus-try. Production of petrochemicals from a non-petroleum, envi-ronment friendly feedstock and development of new, efficientethylene production processes are considered as challengingresearch areas (Pereira, 1999; Gucbilmez et al., 2006). Bio-ethanol is an attractive alternative feedstock to be used for theproduction of these chemicals.

Different transition metal oxide catalysts (Golay et al., 1999;Zaki, 2005) were tested in the literature for the catalytic dehy-dration of ethanol. Solid catalysts with acidic character wereconsidered to have high activity for this reaction. Activitiesof some solid acid catalysts, such as H-Mordenites, H-ZSM5,H-beta-zeolite and silica-alumina on conversion of ethanol toDEE and ethylene were investigated by Takahara et al. (2005).Due to their higher activity than the conventional solid acid

∗ Corresponding author. Tel.: +90 312 210 26 31; fax: +90 312 210 26 00.E-mail address: tdogu@metu.edu.tr (T. Dogu).

0009-2509/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.ces.2007.01.017

catalysts, heteropolyacid catalysts (HPA) were also consideredin the dehydration reaction of alcohols (Vazquez et al., 2000;Haber et al., 2002). In these studies, activities of silica supportedtungstophosphoric acid (TPA), and salts of TPA were tested forthe dehydration of ethanol.

In the present study, activities of three different heteropoly-acid catalysts, namely silicotungstic acid (STA), molybdophos-phoric acid (MPA) and TPA in the dehydration reaction ofethanol were studied and effects of temperature and water con-tent of ethanol on product selectivities and ethanol conversionwere investigated.

2. Experimental

A differential tubular flow reactor, which was placed intoa tubular furnace, was used for the gas phase ethanol dehy-dration reaction. Temperature of the reactor was controlledby a temperature controller within ∓1%. Before each experi-ment, fresh catalyst was placed in the middle of the stainlesssteel tubular reactor of 1

4 inch in diameter, and supported byquartz wool from both ends. Liquid ethanol (99.8% Merck) orethanol–water mixture of known composition was pumped intoan evaporator (which was at 150 ◦C) by a syringe pump where

5350 D. Varisli et al. / Chemical Engineering Science 62 (2007) 5349–5352

it is mixed with helium gas to adjust the reactor feed composi-tion. The total flow rate of the vapor stream was kept constantat 44.2 ml/min. The composition of the reactor effluent streamwas analyzed using a gas chromatograph, which was equippedwith a (TCD) thermal conductive detector (Varian CP 3800GC). A Poropak T column was used in the analysis of the prod-uct stream. The chromatograph was connected online to thereactor outlet. Using a temperature program (hold the temper-ature at 75 ◦C for 2 min, increase the temperature upto 125 ◦Cwith a heating rate of 10 ◦C/min and then increase the temper-ature upto 175 ◦C with a heating rate of 5 ◦C/min) in GC anal-ysis, ethylene, ethanol and water peaks were observed at 0.49,9.77 and 5.08 min, respectively. All the connection lines wereheated to 150 ◦C to prevent condensation. Heteropoly acids,TPA, MPA (Acros Organics) and STA (Sigma-Aldrich) weredried at 100 ◦C overnight under vacuum before the experiments.

3. Results and discussions

Ethanol conversion and the selectivity values of DEE andethylene were evaluated basing on the chemical composi-tions of the reactor effluent stream. Each data point given inFigs. 1–6 is actually an average of the results obtained in atleast four successive measurements. In some cases, steadystate composition of the reactor effluent stream was determinedfrom the average of up to seven successive measurements.Fractional conversion of ethanol and selectivity values of DEEand ethylene, evaluated in these repeated runs were all within±3% error limits. Results obtained with diferent heteropoly-acid catalysts are discussed in the following sections.

3.1. Results obtained with TPA catalyst

Experimental results obtained with TPA catalyst (0.2 g)showed a significant increase in ethylene yield, and a cor-responding decrease in DEE yield, with an increase in tem-perature from 180 to 250 ◦C. For a feed stream containing5% ethanol in He, ethanol conversion and ethylene selectivityvalues increased from 0.58 to 0.88 and from 0.26 to 0.87,respectively, in this temperature range (Fig. 1). However, thecorresponding selectivity values of DEE decreased from 0.74to 0.13. An ethylene yield value of 0.77 obtained at 250 ◦Cindicated the possibility of a new avenue for ethylene produc-tion from a non-petroleum feedstock, namely ethanol, whichmight be produced by fermentation.

An increase in ethanol mole fraction in the feed stream from0.05 to 0.48 caused a decrease in ethanol conversion from0.88 to 0.53, a slight decrease in ethylene selectivity from0.87 to 0.74 and an increase in DEE selectivity from 0.13 to0.26, at 250 ◦C, with 0.2 g of TPA catalyst packed into the re-actor. Results obtained with a feed mixture containing 48%ethanol showed an increase in ethanol conversion with an in-crease in the amount of catalyst packed into the reactor (Fig. 2),as expected. However, ethylene and DEE selectivities did notdiffer much with this increase in space time (Fig. 3). These re-sults indicated that DEE and ethylene were probably producedmostly through parallel routes rather than following a con-

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Fig. 1. Conversion of ethanol and DEE and ethylene selectivities at differentreaction temperatures using 0.2 g TPA and a feed containing 5% ethanol inhelium.

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Fig. 2. Conversion of ethanol with different amounts of TPA catalyst (48%ethanol in helium).

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Fig. 3. Ethylene selectivity with different amounts of TPA catalyst (48%ethanol in helium).

secutive reaction scheme. These results supported the reactionmechanism proposed in the early work of Saito and Niiyama(1987), suggesting the formation of ethylene by the decom-position of chemisorbed ethanol molecules (C2H5OH+

2 ) andformation of DEE by the reaction between chemisorbed and

D. Varisli et al. / Chemical Engineering Science 62 (2007) 5349–5352 5351

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Fig. 4. Effect of water on ethanol conversion and DEE selectivity using 0.2 gTPA catalyst (feed composition: 48% ethanol, 4.8% water in He).

physisorbed ethanol molecules on the catalyst surface. Usinga catalyst amount of 0.8 g (space time of 1.08 s.g/cm3 mea-sured at 298 K), ethanol conversion and ethylene selectivityvalues of 0.94 and 0.73 were obtained at 250 ◦C, respectively(Figs. 2 and 3).

The economics of ethylene and DEE production by the dehy-dration reaction of ethanol strongly depends upon the possibleuse of bio-ethanol containing some water in the feed stream. Asshown in Fig. 4, the presence of water (H2O/Ethanol=0.1 v/v)

in the feed stream caused some reduction in ethanol conver-sion. Water is expected to adsorb more strongly than ethanol onthe catalyst surface, causing reduction in number of availableactive sites for the chemisorption of ethanol. Lower DEE selec-tivities and higher ethylene selectivities were observed in thepresence of water at temperatures lower than 230 ◦C (Fig. 4).This behavior was reversed at higher temperatures. Up to sevenrepeated experimental results proved that this observtion wasnot due to any experimental errors.

3.2. Comparison of activities of different heteropolyacidcatalysts

Activities of three different heteropolyacid catalysts, namelyTPA, MPA and STA in the ethanol dehydration reaction werecompared by experiments carried out in a temperature rangeof 140–250 ◦C and using a reactor feed stream containing 48%ethanol in helium. As it is clearly shown in Fig. 5, amongthese three solid acid catalysts STA showed the highest ac-tivity. The ratio of ethylene yield to W/F (W being the cat-alyst mass and F being molar flow rate of ethanol) obtainedwith STA, TPA and MPA at 250 ◦C were about 2.1, 1.8 and0.14, respectively. Corresponding values reported in the liter-ature (Takahara et al., 2005) using other solid acid catalysts,such as different zeolites and silica-alumina, are about one totwo orders of magnitude smaller than the results obtained inthis study with STA and TPA. Ethylene selectivity values ob-tained with STA and TPA were quite close to each other inthe temperature range studied (Fig. 6). The acid strengths ofthese three HPA catalysts were reported to follow the follow-ing trend TPA > STA > MPA (Wang et al., 2000). Considering

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Fig. 5. Ethanol conversion values obtained with different HPA catalysts(W = 0.2 g, feed: 48% ethanol in helium).

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Fig. 6. DEE and ethylene selectivities with different HPA catalysts (W =0.2 g,feed: 48% ethanol in helium).

this reported result, the higher ethanol dehydration activity ofSTA than TPA cannot be explained by the differences of acidstrengths only. Results reported by Verhoef et al. (1999) forthe esterification reactions carried out using supported TPA andSTA catalysts also showed higher activity of STA than TPA andthis was explained by the presence of higher number of Keg-gin protons of STA (four) as compared to TPA (three). Anotherdifference of these two heteropoly acids is their dehydrationbehavior and their thermal stability. At room temperature TPAis expected to have hexahydrate structure (H3PW12O40.6H2O).At higher temperatures anhydrous TPA was formed by the re-moval of water (Thomas et al., 2005) and at temperatures over180 ◦C TPA starts to decompose. As reported by Obali (2003),thermal analysis (TGA and DSC) of TPA showed decompos-tion of this heteropoly acid catalyst within the temperaturerange between 180 and 330 ◦C. However, STA (H4SiW12O40)is in completely dehydrated form, even at room temperature,and as reported by Thomas et al. (2005) it was much morestable than TPA at temperatures higher than 200 ◦C. Thesefindings supported our results that STA was more active thanTPA in the dehydration reaction of ethanol to produce ethyleneand DEE.

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4. Conclusions

Very high ethylene yield values, reaching to 0.77, obtained bydehydration of ethanol over heteropolyacid catalysts may opena new pathway for the production of a number of petrochemi-cals from a non-petroleum feedstock, namely bio-ethanol. Anincrease in reaction temperature from 140 to 250 ◦C caused asignificant increase in ethylene yield while at lower temper-atures the main product is DEE. Results obtained with TPAcatalyst showed a decrease of ethanol conversion with an in-crease in feed mole fraction of ethanol. Results also indicatedparallel routes for the production of ethylene and DEE, andsome decrease of catalyst activity in the presence of water va-por, with TPA catalyst. Among the three HPA catalysts (STA,TPA and MPA) STA showed the highest activity in ethanoldehydration. This was explained by the higher number of pro-tons and the higher stability of STA than TPA at temperaturesover 200 ◦C.

Acknowledgments

The financial supports of METU and DPT by BAP-03-04-DPT-2003(06K120920-17) and BAP-2006-03-04-02 projectsare gratefully acknowledged.

References

Golay, S., Kiwi-Minsker, L., Doepper, R., Renken, A., 1999. Influence of thecatalyst acid/base properties on the catalytic ethanol dehydration understeady state and dynamic conditions. In situ surface and gas phase analysis.Chemical Engineering Science 54, 3593–3598.

Gucbilmez, Y., Dogu, T., Balci, S., 2006. Ethylene and acetalehyde productionby selective oxidation of ethanol using mesoporous V-MCM-41 catalysts.Industrial and Engineering Chemistry Research 45, 3496–3502.

Haber, J., Pamin, K., Matachowski, L., Napruszewska, B., Poltowicz, J.,2002. Potassium and silver salts of tungstophosphoric acid as catalystsin dehydration of ethanol and hydration of ethylene. Journal of Catalysis207, 296–306.

Kito-Borsa, T., Pacas, D.A., Selim, S., Cowley, S.W., 1998. Properties of anethanol diethyl ether water fuel mixture for cold start assistance of anethanol-fueled vehicle. Industrial and Engineering Chemistry Research 37,3366–3374.

Obali, Z., 2003. Heteropolyacid catalysts for etherification of isoolefins. M.S.Thesis, Middle East Technical University, Ankara, Turkey.

Pereira, C.J., 1999. New avenues in ethylene synthesis. Science 285,670–671.

Saito, Y., Niiyama, H., 1987. Reaction mechanism of ethanol dehydrationon/in heteropoly compounds: analysis of transient behavior based onpseudo-liquid catalysis model. Journal of Catalysis 100, 329–336.

Takahara, I., Saito, M., Inaba, M., Murata, K., 2005. Dehydration of ethanolinto ethylene over solid acid catalysts. Catalysis Letters 105, 249–252.

Thomas, A., Dablemont, C., Basset, J.M., Lefebvre, F., 2005. Comparisonof H3PW12O40 and H4SiW12O40 heteropolyacids supported on silica by1H MAS NMR. C. E. Chimie 8, 1969–1974.

Vazquez, P., Pizzio, L., Caceres, C., Blanco, M., Thomas, H., Alesso, E.,Finkielsztein, L., Lantano, B., Moltrasio, G., Aguirre, J., 2000. Silica-supported heteropolyacids as catalysts in alcohol dehydration reactions.Journal of Molecular Catalysis 161, 223–232.

Verhoef, M.J., Kooyman, P.J., Peters, J.A., Bekkum, H., 1999. A study onthe stability of MCM-41 supported heteropoly acids under liquid and gasphase esterification conditions. Microporous Mesoporous Materials 27,365–371.

Wang, Y., Liu, J., Wenzhao, L., 2000. Synthesis of 2-butoxy ethanol withnarrow-range distribution catalyzed by supported heteropolyacids. Journalof Molecular Catalysis A-Chemical 159, 71–75.

Zaki, T., 2005. Catalytic dehydration of ethanol using transition metal oxidecatalysts. Journal of Colloid and Interface Science 284, 606–613.