Catalytic cracking of waste from biodiesel production using A1-SBA-15

Abstract

Hexagonal mesoporous silica SBA-15 was synthesized by hydrothermal method in acidic media (pH<1) in the presence of commercial nonionic triblock (poly(ethylene oxide)20–poly(propylene oxide)70–poly(ethylene oxide)20) or (PEO20PPO70PEO20; P123) copolymer as a structure directing agent with gel composition 1.00 TEOS : 1.65×10-2 P123 : 6.95 HCl : 140 H2O. The Al-SBA-15 catalysts with various Si/Al molar ratios were synthesized by stirring SBA-15 in sodium aluminate solution for 12 h. The Na+ of Al-SBA-15 was exchanged to H+ by reflux with 0.01 M NH4Cl for 24 h. The synthesized catalysts were characterized by X-ray powder diffraction, nitrogen sorption analysis, inductively coupled plasma-atomic emission, solid state 27Al-MAS-NMR and scanning electron microscopy. Catalytic cracking of waste from biodiesel production (WBP) over synthesized acidic and non-acidic SBA-15 at atmospheric pressure was investigated under different conditions. The average composition of the WBP was glycerol 37.18%, ash 6.49%, water 1.85% and matter organic non-glycerol 54.48% at pH 10.47 with the density of 1.03g/mL. The optimum condition on the WBP cracking in liquid-phase catalytic reaction is at the reaction temperature of 400oC with 10wt% catalyst amount to the WBP. When Al-SBA-15 was used as catalyst, the conversion of the WBP increases compared to that in the absence of catalyst. The conversion and yields of gas fraction and liquid fraction depend on the reaction temperature and the amount of catalyst. However, the product selectivity is not affected. The gas fraction obtained by WBP cracking mostly composes 1,3-butadiene and CO2, whereas the liquid fraction provides 2-cyclopenten-1- one as a major liquid product. However, catalyst in liquid-phase catalytic reaction cannot be regenerated because of the alkali-starting materials. Vapour-phase catalytic reaction was considered to solve this problem. The used Al-SBA-15 can be regenerated by simple calcination. The regenerated catalyst exhibits similar activity and performs the product composition closing to the fresh one.