Effect of Cu promotion on cracking and methanation during the Ni-catalyzed deoxygenation of waste lipids and hemp seed oil to fuel-like hydrocarbons

Deoxygenation of yellow grease and hemp seed oil was studied over 20% Ni/Al₂O₃ and 20% Ni-5% Cu/Al₂O₃ catalysts in the presence of H₂. In the deoxygenation of 25 wt% yellow grease (dissolved in dodecane) both catalysts afforded a liquid product consisting of mainly linear C10–C17 alkanes; however, the Cu-promoted catalyst showed improved selectivity to long chain (C15–C17) hydrocarbons as a result of its lower cracking activity. Analysis of the light hydrocarbon products (C10–C16) showed that cracking mainly occurred via the removal of terminal carbons (with methane formation), although a small amount of internal cracking also occurs based on the presence of C6–C11 in the product mixtures. Similar improvements were also observed in the deoxygenation of 25 wt% hemp seed oil, showing that Cu was able to curb cracking even when a highly unsaturated feed was employed. The Cu promotion effect was more pronounced in the deoxygenation of 75 wt% yellow grease in which the 20% Ni/Al₂O₃ catalyst did not yield any liquid products, whereas the 20% Ni-5% Cu/Al₂O₃ catalyst afforded liquid products consisting of >90% diesel-like hydrocarbons.