Catalytic Gas-phase Dehydration Of Glycerol Over Heteroplyacid-pillared Layered Double Hydroxides(LDH) Catalysts

The valorization of glycerol obtained from biodiesel productionis a big challenging task in recent years. An effective usage or con-version of crude glycerol to specific products will further reducethe cost of biodiesel production. Acrolein is one of the most value-added products that can be converted form Catalytic dehydration of glycerol.Highly active catalyst as heteropoly acid pillared hydrotalcite was developed for glycerol dehydration in this work. Three different types of pillared hydrotalcites were prepared by the ion exchange method and their catalytic activities were evaluated. The order of catalyst activity of different metal hydrotalcites with heterpoly acid pillared was Ni2 Al > Zn2 Al > Mg2 Al. Then we used Ni2 Al hydrotalcite as optimized catalyst support, and tested the reactivities of different heterpoly acids pillaring on the support as HSiW > HPW. The better catalytic activity of the Ni2 Al catalysts could be related to the cooperative effect of atoms of Ni and Al, as the formation of a Ni-Al alloy, with smaller particle size and lower basicity. With a higher softness, HSiW is easier to form a more stable intermediate state as to have higher catalytic reactivity.Catalysts with different HSiW loadings and calcination temperatures were examined respectively. The results showed that Ni2 Al hydrotalcite catalyst with 40% HSiW pillared and calcinated at 550℃ had the best catalytic peformance with the acrolein selectivity of 49.4%.Correlating the catalytic performance with catalyst characterization evidenced that the activity of catalyst is mainly depended on the type and heteropoly acid loading on the hydrotalcite. Increasing HSiW loading led to steady decrease in the sample surface area for HSiW-Ni2 Al. The total acidity measurement of prepared catalysts carried out by NH3-TPD, was found to be 0.242 mmol/g at 550℃.The optimal reaction condition on 40%HSiW-Ni2 Al catalyst were as follows: the optimum reaction temperature is 290℃ and the best glycerol solution concentration is 5wt%. Under the optimum reaction conditions, the selectivity and the yield of acrolein over 40wt%-Ni2 Al reached 60.8% and 38%, respectively.