Gas phase dehydration of glycerol catalyzed by rutile TiO 2 -supported heteropolyacids Lingqin Shen, Yonghai Feng, Hengbo Yin *, Aili Wang *, Longbao Yu, Tingshun Jiang, Yutang Shen, Zhanao Wu Faculty of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, China 1. Introduction During the production of biodiesel, 1 ton of glycerol is produced as a byproduct with the formation of 10 tons of biodiesel. Conversion of glycerol is extensively attracting researcher’s attention because glycerol can be catalytically dehydrated or hydrogenated to high valued chemicals, such as acrolein, hydro- xyacetone, propanediols, and ethylene glycol. Among the glycerol derivatives, acrolein is an important chemical, which can be directly used as a microbicide in oil wells and as a slimicide in the manufacture of paper [1]. Furthermore, acrolein is largely used as a feedstock for production of acrylic acid and 1,3-propanediol, which are important monomers of industrial polyesters [1–4]. At present, acrolein is mainly produced by gas phase catalytic oxidation of propylene with a Bi/Mo-mixed oxide catalyst, causing a high cost [5–7]. Production of acrolein from surplus glycerol by catalytic dehydration leads to oil saving and cost lowering [5–7]. Catalytic dehydration of glycerol to acrolein by sulfuric acid is a conventionally industrial process, in which, the yield of acrolein is usually less than 28%. To increase the yield of acrolein and abandon the toxic and corrosive sulfuric acid catalyst, the catalytic activities of various solid catalysts in the gas phase dehydration of glycerol have been investigated recently. The solid catalysts can be categorized into five types: oxides, salts, zeolites, supported mineral acids, and supported heteropolyacids. Their catalytic activities were summarized as follows. When the oxides, such as Nb 2 O 5 , SiO 2 , Al 2 O 3 , MgO, La 2 O 3 , CeO 2 , and ZrO 2 , were used as catalysts in the gas phase dehydration of glycerol in a fixed bed continuous flow reactor, the most effective acid strength for the selective dehydration of glycerol to acrolein appeared between 8.2  H 0 3.0, with which acrolein was produced at a selectivity of 60–70% [8,9]. A series of rare earth pyrophosphates were used as catalysts in the gas phase dehydration of glycerol in a fixed bed reactor [7]. Among the rare earth pyrophosphate catalysts, Nd 4 (P 2 O 7 ) 3 and Gd 4 (P 2 O 7 ) 3 exhibited high acrolein selectivity of ca. 79% at 320 8C. The catalytic activity of rare earth pyrophosphates depended on the appropriate surface acidity. When zeolites were used as catalysts in a continuous fluidized- bed reactor, glycerol was converted into acrolein, olefins, and acetaldehyde. ZSM-5 catalyst exhibited the yields of acrolein of 55–61% at 350 8C and the weight hourly space velocities of 300– 1300 h 1 [3]. Small-sized HZSM-5 with high aluminum content showed high catalytic activity in the gas phase dehydration of glycerol to acrolein due to its high acidity [10]. Journal of Industrial and Engineering Chemistry 17 (2011) 484–492 ARTICLE INFO Article history: Received 16 October 2010 Accepted 8 December 2010 Available online 14 May 2011 Keywords: Glycerol dehydration Acrolein Rutile TiO 2 Heteropolyacids ABSTRACT Gas phase dehydration of glycerol catalyzed by the rutile TiO 2 -supported heteropolyacids was investigated. The TiO 2 -supported heteropolyacid catalysts were prepared by the incipient wetness impregnation method using silicotungstic, phosphotungstic, and phosphomolybdic acids as active compounds. The as-prepared catalysts were characterized by X-ray diffraction, infrared spectroscopy, temperature programmed desorption of ammonia, and surface area measurement. The heteropolyacids supported by rutile TiO 2 were crystallites. The catalytic activity of the catalysts in the gas phase dehydration of glycerol was significantly affected by the type and loading of heteropolyacids. TiO 2 - supported silicotungstic acid (20 wt.%) catalyst showed the highest catalytic activity with an acrolein selectivity of 80 mol% at a conversion of glycerol of 99% and a reaction temperature of 280 8C under ambient pressure. The possible reaction route in the gas phase dehydration of glycerol catalyzed by the TiO 2 -supported heteropolyacid catalysts was also discussed briefly. ß 2011 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. * Corresponding authors. Tel.: +86 511 88787591; fax: +86 0 511 88791800. E-mail addresses: yin@ujs.edu.cn (H. Yin), alwang@ujs.edu.cn (A. Wang). Contents lists available at ScienceDirect Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec 1226-086X/$ – see front matter ß 2011 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jiec.2011.05.038