Dehydration of Glycerol over High Surface Area Γ-alumina Supported Heteropoly Acid Catalysts

Dehydration of glycerol was performed over heteropoly acids (HPA), viz., silicotungstic acid (H-SiW), phosphotungstic acid (H-PW), and phosphomolybdic acid (H-PMo), supported high surface area γ-alumina (HSAI-S25) catalysts. Various physico-chemical studies of these supported catalysts indicate high dispersion of the active (HPA) species on the support surface. It was observed that the catalyst, HSiW/HSAI-S25 show high activity, i.e., high glycerol conversion and combined acrolein and hydroxylacetone selectivity. On the other hand, the catalysts such as HPW/HSAI-S25 and H-PMo/HSAI-S25 demonstrate low selectivity of the expected products owing to a very different acidity of the catalyst leading to side reactions like oligomerisation and carbonization of glycerol as well the formation of allyl alcohol. INTRODUCTION High surface area alumina, in particular γ-alumina (γ-Al2O3), is widely used as catalyst and catalyst support owing to their favorable textural properties and intrinsic acid-base characteristics (Pines et al., 1960). However, the preparation of alumina with high surface area and uniform pore size in a reproducible way is still a challenge. In this regard, recently, we have developed a facile route for preparation of high surface area γ-Al2O3 with desirable pore characteristics using aluminium salts and auxiliary chemicals such as ethylene glycol, n-butanol, etc. (Selvam et al. 2011). The textural properties could be tuned by substantially under varying experimental conditions, i.e., temperature, time, auxiliary chemical treatments, etc. In the context of increased biodiesel production, by transesterification of vegetable oils, the availability of a large volume of undesired glycerol requires valorization. Since glycerol is a highly functionalized molecule and forms one of the building blocks as a key feedstock for several value added products and intermediates such as acrolein, hydroxyacetone, glycericacid, epichlorohydrin, glyceraldehyde, lactic acid, tartronic acid, 1,2-propane diol and 1,3-propane diol, etc. Conversion of glycerol into such useful chemicals, in particular, acrolein, is one of the important reactions since it is an important intermediate in the preparation of polyester resin, polyurethane, propylene glycol, amino acid like DL-methionine and many other industrially important S. Mahendran, T. Nithya, K. P. Raju, B. Viswanathan and P. Selvam