Pathways for the Deoxygenation of Triglycerides to Aliphatic Hydrocarbons over Activated Alumina

The functional group pathways for the high-yield conversion of triglycerides to aliphatic hydrocarbons (mainly monoalkenes) when passed over activated alumina at 450 °C (weight hourly space velocity (WHSV) 0.28-0.46 h^-1) were studied by using model compounds believed to be intermediates in the process. These compounds included methyl ketones, dodecyl aldehyde, and dodecanol. Previous results had been obtained on carboxylic acids and symmetrical ketones. It is concluded that the triglycerides can split out carboxylic acids by β-elimination or yield alkenes by a γ-hydrogen transfer mechanism. The carboxylic acids form symmetric ketones which preferably undergo a further γ-hydrogen transfer to produce monoalkenes and methyl ketones. An unknown reductive mechanism followed by dehydration produces monoalkenes from the methyl ketones. The latter can also undergo the γ-hydrogen rearrangement. It is proposed that the methyl ketone can also isomerize to aldehydes, which then undergo an oxidation producing carboxylic acids. This may involve a disproportionation and be coupled with the reduction mentioned previously. A cycling of the carboxylic acids through the ketone route is believed to be the source of monoalkenes having one more carbon atom than the methyl ketones. The relevance of this study to petroleum biogenesis is obvious.