Joint Transformations of Vegetable Oils with Vacuum Gas Oils under Catalytic Cracking Conditions
The paper studied joint transformations of vacuum gas oils characterised by the group composition with various vegetable oils under catalytic cracking conditions. It was determined that the distribution of target cracking products depended not only on the carbon component of mixed raw materials but also on the fatty acid composition of vegetable oils. The greater was the number of C=C double bonds in the composition of triglycerides of vegetable oil, the more pronounced promoting effect it has for vacuum cracking of gas oil, as established. This was related to the progression of hydrogen transfer reactions. Olefins that act as hydrogen acceptors were formed during cracking of initial glycerides, and paraffins and naphthenes in vacuum gas oils were donors. Herewith, an increase in the contents of mono- and polyaromatic hydrocarbons was noted in the composition of liquid products. Additionally, it was defined that the higher was the content of unsaturated fatty acids in the composition of glycerides of vegetable oils, the higher was the yield of target cracking products (light olefins, gasoline). It was demonstrated that a high content of aromatic hydrocarbons in the composition of vacuum gas oil during transformation of mixed raw materials resulted in a decrease in the yield of target cracking products with a simultaneous increase in the yield of liquid products of coke, too. This is related to the fact that aromatic hydrocarbons were poorly subjected to transformations and concentrated in highly-boiling fractions, with the result that an increase in the yields of light and heavy gas oils was observed. Additionally, heavy aromatic hydrocarbons actively took part in condensation reactions with the formation of polyaromatic compounds and coke, as evidenced by the increased formation of coke deposits on catalysts.