(335d) Conversion of Oxygenate Mixtures Obtained from the Catalytic Conversion of Syngas into Hydrocarbons

Syngas can be converted into hydrocarbons via non-Fisher Tropsch route by first converting it into alcohols on a copper-based catalyst and then convert the alcohols into gasoline range hydrocarbon using H+/ZSM-5. But this method has temperature limitation as copper and H+/ZSM-5 are not most effective at the same temperature. Also, there are some challenges yet to be overcome in making a single, bi-functional Cu/ZSM-5 catalyst that can work efficiently for this reaction system. Hence some other catalysts for syngas conversion have been explored. Rhodium- and molybdenum-based catalyst systems can convert the syngas into alcohols but yield some other oxygenates. Ketones, aldehydes, esters and carboxylic acids are found along with alcohols in rhodium-based system while carboxylic acids are found in molybdenum-based system. Oxygenates could also form when hydrogen-deficient syngas is used or product is recycled for increasing syngas conversion.

Ketones, aldehydes, alcohols can be converted into hydrocarbon on H+/ZSM-5 but esters and carboxylic acids are converted mainly to light gases and coke. Polycrystalline titania was found to convert acetic acid to mesitylene through a ketone intermediate. Experiments have shown that aldehydes can also be converted to useful hydrocarbons on a titania catalyst. Ketones, aldehydes, alcohols, esters and carboxylic acids were reacted separately on titania catalysts and the results will be discussed.

In real time application, all of these oxygenates will be present in the same reactant stream flowing over the catalyst. In order to understand the reactions in such a scenario, pairs of reactants was reacted over titania in 1:1 concentration. These batch reactor experiments were completed at 0 pisg and 350oC for 5 hours in order to give insight into the change in product distribution due to the presence of another oxygenate. The model compounds used for each of these class of oxygenates are acetone, acetaldehyde, ethanol, methyl ester and acetic acid.

The reactions of oxygenates mixtures performed on titania will help to understand the role played by each compound in either enhancement or inhibition of the reactions of other compounds in the stream. Also, the data will be discussed in contrast to the available literature of oxygenate mixtures reacted on H+/ZSM-5.