Catalytic hydroprocessing of camelina oil/AGO mixtures over NiMoP/γ-Al2O3 catalysts

Abstract

Inedible camelina oil (CSO) contains fatty acids with a high degree of unsaturation (1.8 double bonds per fatty acid on average). CSO was hydrotreated at temperatures 340–370 °C, pressures of 15–50 bar, and liquid hour space velocities (LHSVs) of 0.8–1.1 h-1 for the production of hydrocarbons that are usable as diesel components. First, hydrotreating pure CSO at 340–370 oC and low hydrogen pressures of 15–25 bar led to the formation of a mixture of n-/iso- alkanes, aromatics, and higher olefins. The presence of CC double bonds in the CSO molecule affected the progress of the side reactions and caused rapid deactivation and coking of the catalyst, especially at low hydrogen partial pressure. Hydrotreatment co-processing of polyunsaturated CSO and partially hydrogenated CSO was then done with two different gas oils or two paraffinic solvents in the range of concentration 5–20%. Co-hydrotreatment took place in a bench-scale trickle-bed reactor using commercial NiMoP/γ-Al2O3 catalysts (catalysts A and B) and a prepared catalyst, NiMoCuP/ZrO2-γ-Al2O3 (catalyst C). High triacylglyceride conversion to hydrocarbons was achieved when CSO was hydrogenated in a mixture with paraffinic solvents on NiMoP/γ-Al2O3 catalysts at hydrogen partial pressures above 30 bar and temperatures above 350 oC. CSO decarboxylation/decarbonylation reactions prevailed over hydrodeoxygenation. Hydrodeoxygenation (72%) was predominant for catalyst C with significant methanation of CO and CO2. There was a complete TAG conversion into hydrocarbons when co-processing a mixture of CSO and atmospheric gas oil at a temperature of 360 oC, LHSV of 0.8 h-1, a hydrogen pressure of 50 bar, and various ratios of hydrogen to raw material from 312 to 656 NL.L-1. The deoxygenation activity decreased in the order of catalysts C>B>A. Increasing the ratio of H2 to feed had a positive effect on the composition and properties of the liquid product. During experiments with catalyst C at 50 bar, 370 °C, and ratios of hydrogen to raw material of 293–656 NL.L-1, the cetane index increased from 46 to 58, and the polyaromatic content decreased from 12.5 to 4.4 wt%. The sulphur and nitrogen contents of the product (29.5 mg.kg-1 and 13.2 mg.kg-1) were higher than expected. In the case of catalyst C, the degree of desulphurization was lower than that of catalysts A and B.