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).
The possibility of improving the low-temperature properties of marine diesel fuel of the Antipinsky Refinery by dewaxing was studied. Paraffin was isolated from the fuel in a centrifuge in the presence of a depressant additive. The depressant additive is selected from a series of synthesized additives for depressant effectiveness. The influence of the centrifuge rotor speed, the additive content and the initial cooling temperature of the sample on the dewaxing parameters of the fuel was studied. The possibility of isolating the additive from the obtained paraffin concentrates is shown. The dewaxing products obtained under optimal conditions were studied. A paraffin concentrate product containing 40.03% solid paraffins was isolated from fuel. Paraffin was isolated from paraffin concentrate by dewaxing with a selective solvent. The cloud point and freezing point of paraffin were 30 and 29 ° C, respectively. When converted to the original fuel, the amount of released paraffins was 7.3% of the 21% by weight contained in the original fuel. The fuel obtained at optimal parameters for low temperature properties corresponds to grade D of diesel fuel according to EN 590: 2009.
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