Abstract:
Due to the thermal and oxidative instability of the biodiesel, the elimination of the oxygen content has been proposed to improve the stability of the fuel and its utilization potential. In this work, the cataltic conversion of methyl octanoate, a model biodiesel fuel, to hydrocarbon fuels and chemicals over the H-ZSM5, Zn/H-ZSM5 and CsNaX zeolite catalysts was investigated in a gas phase reaction. It was found that the deoxygenation of methyl octanoate over the H-ZSM5 yielded a variety of hydrocarbons (C₁-C₇), whti significant amounts of aromatics. Octanoic acid and 8-pentadecanone were primary products. Aromatics are formed through a series of reactions, cracking, oligomerization, cyclization, and direct dehydrocyclization. The addition of the Zn species does not provide any alternative route for aromatization, but only improve the dehydrogenation activity. Moreover, the deoxygenation of 10 wt% methyl octanoate in methanol over the CsNaX catalysts revealed that the decarbonylation/deacetylation activity can occur at high rate and stability. Heptenes and hexenes as main products are produced via primary decomposition of the methylester, forming octanoate-like species as an intermediate. Moreover, the methanol decomposition provides the hydrogen for hydrogenation/dehydration. The content of excess cesium on the CsNaX catalysts alters the basic strength, leading to the difference in the product distributions. The basicity and the highly polar character of the zeolite play an importang role in the decarbonylation.
