Catalytic Dehydration of Methanol to Dimethyl Ether Catalyzed by Aluminum Phosphate Catalysts F. Yaripour,* ,† M. Mollavali,* ,‡ Sh. Mohammadi Jam, † and H. Atashi ‡ Catalyst Research Group, Petrochemical Research and Technology Company, National Petrochemical Company, 14358, Tehran, Iran, and Department of Chemical Engineering, Faculty of Engineering, UniVersity of Sistan & Baluchestan, P.O. Box 98164-161, Zahedan, Iran ReceiVed October 7, 2008. ReVised Manuscript ReceiVed February 7, 2009 A series of solid-acid catalysts with different content of components was prepared using the coprecipitation method. These samples comprised modified γ-Al 2 O 3 with phosphorus. The effects of various contents of phosphorus (Al/P ratio from 0.5 to 3) have been investigated to determine an optimum one. The samples were characterized using BET, TGA, XRD, and NH 3 -TPD techniques and were also tested in a fixed-bed flow reactor under the same operating conditions (T ) 573 K, P ) 16 barg, WHSV ) 26.07 h -1 ). According to the experimental results, phosphorus-modified catalysts have shown better performance compared to pure γ-alumina. It was found that surface areas increase with an increase in the molar ratio of aluminum-to-phosphorus. It was observed that aluminum phosphate samples with acidic sites whose acidity is very weak and/or moderate exhibit the best catalytic performance and stability. The sample with molar ratio of Al/P ) 1.5 have exhibited the best activity for methanol dehydration. 1. Introduction Production and application of dimethyl ether (DME) have attracted the attention of many researchers in the past years due both to environmental protection and to the increased price of crude oil. 1 DME has received global attention as a clean-burning alternative fuel for diesel engines due to increasingly stringent environmental regulations. DME can also be used as an aerosol propellant in the cosmetic industry to replace CFC and LPG. Then there would be a growing requirement for the large-scale production of DME to meet the future market. 3-5 Dimethyl ether can be produced by two methods. Tradition- ally, DME was produced via methanol dehydration (eq 1) over a solid-acid catalyst in the temperature range of 523-673 K and pressures up to 18 barg. Methanol dehydration to dimethyl ether is a potential process and more favorable in view of thermodynamics and economy. 2 Such reaction occurs by dif- ferent pathways on different types of solid-acid catalysts, such as γ-Al 2 O 3 , HZSM-5, HY zeolite, silica-alumina, phosphorus- alumina, and fluorinated alumina. γ-Al 2 O 3 is used as a common catalyst because of its fine particle size, high surface area, surface catalytic activity, excellent thermal stability, high mechanical resistance, and wide range of chemical, physical, and catalytic properties. However, this catalyst produces undesirable side products, such as hydrocarbons (and coke), due to the presence of strong acid sites and the high dehydration temperature. Thus, extensive research has been focused on finding better catalysts that have higher selectivity for DME formation and less tendency to generate hydrocarbons (and coke). 6-12 It has recent been found that DME formation is mainly related to these active sites with weak and medium acidity, and those catalysts with strong acid sites may be preferable for coke deposition. It has recently been found that, if the methanol dehydration takes place on the modified-alumina catalysts with silica, the amounts of coking and byproduct are reduced. 14 The one-step synthesis of DME from syngas has received growing attention due to its potential as an alternative clean fuel. This process consists of two steps, methanol synthesis followed by methanol dehydration. Typically, the hybrid catalysts used in the process are composed of a methanol catalyst (Cu/Zn, Zn/Al, Zn/Cr, Cu/Zn/Al, Cu/Zn/Cr, Cu/Zn/Co, etc.) and a methanol dehydration catalyst (γ-alumina or zeolites), which are made by mechanically mixing. Therefore, the active com- ponents in these hybrid catalysts were not finely dispersed. 13-17 In the present work, the catalytic dehydration of methanol to DME has been studied over pure γ-Al 2 O 3 , and modified alumina * Corresponding authors. Tel: +982188043037. Fax: +982188064161. E-mail: f.yaripour@npc-rt.ir (F.Y.), M.Mollavali@yahoo.com (M.M.). † National Petrochemical Company. ‡ University of Sistan & Baluchestan. (1) Zhiliang, W.; Fu, W. J.; Fei, R.; Minghan, H.; Yong, J. Tsinhua Sci. Technol. 2004, 9, 168–173. (2) Raoof, F.; Taghizadeh, M.; Eliassi, A.; Yaripour, F. Fuel 2008, 87, 2967–2971. (3) Xia, J.; Mao, D.; Zhang, B.; Chen, Q.; Zhang, Y.; Tang, Y. Catal. Commun. 2006, 7, 362–366. (4) Kim, J. H.; Park, M. J.; Kim, S. J.; Joo, O. 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Res. 2008, 47, 3265–3273. 2CH 3 OH T CH 3 OCH 3 + H 2 O (1) Energy & Fuels 2009, 23, 1896–1900 1896 10.1021/ef800856c CCC: $40.75  2009 American Chemical Society Published on Web 03/16/2009 Downloaded by BENEMERITA UNIV AUTONOMA DE PUEBLA on September 14, 2015 | http://pubs.acs.org Publication Date (Web): March 16, 2009 | doi: 10.1021/ef800856c