(73d) Conversion of Biodiesels into Normal Diesels

The objective of this research is to convert biodiesel into normal diesel in order to make biodiesel more fungible. The model compound representing biodiesel for this study is methyloctanoate (C9H18O2, MeOct). Reactions were carried at atmospheric pressure, at 603 K, and in the flow of hydrogen. Previously, it was found that Platinum and Palladium are active in decarboxylation of MeOct to n-heptane (C7H16). It is also known that metal oxides, such as TiO2, ZnO, ZrO2?, are capacable of deoxygenating carboxylic acids or esters to corresponding hydrocarbons via oxygen vacancy mechanism. Therefore, three catalysts (1%Pt/Al2O3, 1% Pt/TiO2 and pure TiO2) were tested. From the activity results, several main conclusions are drawn: - Although under the reaction conditions, pure TiO2 is partially reduced and oxygen vacancies are formed to some extent, the dominant products on TiO2 are heavy compounds: symmetrical ketone (C15H30O) and ester (C15H30O2), not alkanes. The catalyst deactivates fast due to strong adsorption of those heavy compounds on the catalyst surface. - When Pt is added on titania, the formation of heavy compounds is much suppressed. At the same time, both n-heptane and n-octane (C8H18) were observed. However, n-octane is the main deoxygenation product. This is due to the enhanced hydrogen spill-over effect from Pt to TiO2 support. More oxygen vacancies are formed compared with pure TiO2. In addition, sequential deoxygenation was seen. First, one oxygen is removed from MeOct to produce octanal (or octanol), and then these one-oxygen containing compounds deoxygenate to produce n-octane. - On alumina-supported Pt catalyst, n-heptane, not n-octane, appears as the main product. Here decarboxylation reaction on Pt is dominant compared to deoxygenation reaction via oxygen vacancy on oxide Al2O3. This can be explained by the fact that TiO2 is easier to be reduced than Al2O3 under the operating conditions. Therefore, not many oxygen vacancies are created on Al2O3 support. It is also found that octanoic acid is the intermediate product in decarboxylation reaction.