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BACKGROUND: The production of biodiesel has notably increased in recent years, with glycerol as the main by-product, an important raw material in the production of value-added products. Those obtained by dehydration are especially important. RESULTS: Gas phase dehydration of glycerol has been tested on mesoporous AlPO 4 and modified AlPO 4 , with a small amount (1 wt%) of a transition metal (Co, Cu, Cr, Fe), calcined at 450 ∘ C and 650 ∘ C, and compared with some commercial zeolites (HZSM and HY). All the catalysts were active in the reaction, the phosphates showing better catalytic behaviour than the zeolites. The main products of the reaction were acrolein and hydroxyacetone. CONCLUSIONS:The positive effect of metal on the catalytic behaviour of AlPO 4 in the dehydration has been verified, attaining the maximum yield to acrolein (54%) on AlCoPO650 with 50 mg of catalyst and 280 ∘ C of reaction temperature. Furthermore, the phosphates did not suffer deactivation after 22 h reaction, whereas the zeolites suffered a strong loss of activity (around 70%) due to blockage of the micropores by coke. Moreover, the yield to acrolein decreased with time, while the yield to hydroxyacetone increased. An E 2 mechanism for the acrolein formation and E 1 for the hydroxyacetone formation have been proposed.

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