Influence of physicochemical properties of depressor additives on their performance in diesel fuels

The work investigates the influence of the physicochemical properties of depressor additives on their performance in diesel fuels of various chemical and fractional compositions. Heavy, summer and marine diesel fuels were used. The following physicochemical properties of fuels were determined: cloud point, freezing point, density, viscosity, fraction composition and hydrocarbon content that formed a complex with carbamide. The content and molar mass distribution of individual n-alkanes in diesel fuels were determined. The following foreign depressant-dispersing additives were used: Dodiflow with codes 4971, 5416, 5817 and 7118, Keroflux with codes 3501, 5696a and Ofi-8863. Their active agents were isolated from the commercial additives by dialysis using semi-permeable rubber membranes. The dropping point of the active agents, their intrinsic viscosity in kerosene and the refractive index at 100 °C were identified. The content of vinyl acetate components and the degree of branching of aliphatic radicals of depressor additives were determined using infrared spectroscopy of the active agents. The relationship between the physicochemical properties of depressor-dispersing additives and their performance in diesel fuels was established. Additives characterised by a relatively high melting point, an average intrinsic viscosity and low branching of aliphatic compounds in the polymer structure exhibit the best performance in fuels. The consumption of additives to achieve the maximum depression of freezing point decreases with the transition from summer to marine fuel and further to heavy diesel fuel. A complex tкп / СВА value, comprising the ratio of the dropping points tкп and the content of vinyl acetate components in the additives, was proposed as a means of predicting the efficiency of depressant additives СВА. In the range of tкп / СВА values of 3.02–4.00 the additives have universal depressant properties. A correlation was established between the refractive index nD100 of additives and the complex value tкп / СВА (R2 = 0.975).