Catalytic synthesis of ketenes on silica monoliths at short contact times

Ketene and dimethylketene have been synthesized by dehydration of acetic acid and isobutyric acids, respectively, over silica functionalized monoliths at temperatures between 680 K and 850 K. Molar yields of ketene and dimethylketene of 79% and 87% per pass, respectively, were routine achieved. The catalytic dehydration of octanoic acid was demonstrated to produce hexylketene with carbon selectivities on the order of 90% at temperatures between 745 to 795 K over a functionalized silica monolith. It was found that vinlyacetic acid underwent dehydration over a functionalized silica monolith to produce vinylketene at 630–725 K at contact times on the order of 100 milliseconds. However lower values of carbon-basis selectivities for the vinylketene, of the order of 40%, were obtained. The main parallel reaction was the unselective decarboxylation to CO₂.; We have found that TiO₂-functionalized monoliths are selective catalysts for ketone synthesis at short contact times. However, changing contact times does not alter the selectivity to acetone formation from the ketonization of acetic acid.; Purification experiments of the ketene-water stream with cooling/condensation and adsorption with common desiccants gave unsatisfactory results for the selective removal of water. Therefore, it was decided to integrate the continuous ketene production with a continuous ketene derivatization without an intermediate purification step.; Cycloaddition of ketene with cyclopentene and styrene gave poor yields of the corresponding cyclobutenones. The main reaction for these olefins was polymerization. Ketene reacts easily with alcohols and phenols to produce the corresponding esters in high yields. Reaction of ketene with acetaldehyde, using acetic anhydride as a solvent and p-toluenesulfonic acid as a catalyst, produced vinyl acetate with a maximum yield of 32% based on the ketene fed. The hydration of ketene occurred to a measurable extent in all the derivatization reactions and was found to be more important at lower temperatures in the derivatization reactor.; The results of this research indicate that the control of contact time is a valid strategy for maximizing yield in catalytic ketene synthesis. Also, the ketene synthesis process can be integrated easily with ketene derivatization to prepare interesting ketene derivatives, especially esters, in high yields.