Deoxygenation of methylesters over CsNaX

The deoxygenation of methyl octanoate over a CsNaX zeolite catalyst has been investigated as a model reaction for the production of de-oxygenated liquid hydrocarbons from biodiesel. Several operating parameters were investigated, such as the type of basic catalyst used, the co-reactant incorporated in the reactor as a solvent of the liquid feed, and the reaction temperature. The CsNaX zeolite used in the study was prepared by ion exchange of NaX with CsNO3/CsOH solution. A significant role of the solvent (co-reactant) was found on the activity, selectivity, and stability of the catalyst. That is, when methanol was co-fed enhanced stability and decarbonylation activity were observed. By contrast, when nonane was used, the catalyst deactivated rapidly and the selectivity to coupling products was enhanced. Temperature programmed desorption (TPD) of methyl octanoate and methanol, as well as flow catalytic studies suggest that methyl octanoate first decomposes to an octanoate-like species. The decomposition of such species leads to the formation of heptenes and hexenes as major products. Octenes and other hydrogenated products are formed in lower amounts via hydrogenation by hydrogen produced on the surface by methanol decomposition, but not from gas phase H2, followed by dehydration. When the polarizable Cs cation is not present in the catalyst, reduced activity and formation of undesired products, such as aromatics and pentadecanone, occur. Similarly, non-zeolitic basic catalysts, such as MgO, exhibit low activity and low selectivity to de-oxygenated liquid hydrocarbons.