## 1 Introduction
Such processes include urea and zeolite dewaxing processes, lowering the boiling point of the diesel fraction, blending the diesel fraction with the kerosene fraction, removing n-paraffins from diesel fuel by extractive crystallization, catalytic isomerization, catalytic dewaxing and the using of depressant additives [7; 8]. The method of lightening the fractional composition is ineffective in terms of re-sources, since a decrease in the end of boiling leads to a decrease in the volume of diesel fuel production [9; 10]. The use of catalytic, zeolite and urea dewaxing leads to the selective extraction of paraffinic hydrocarbons, making it possible to obtain fuel with improved low-temperature properties; however, the effectiveness of the process is highly dependent on the impurities contained in the purified fraction. One of the most economically profitable and promising ways to obtain low-freezing fuels is the involvement of depressants [11]. The principle of operation of the depressant additive is based on reducing the size of n-paraffin crystals in the composition of diesel fuel, changing the morphology of the n-paraffin crystal and providing more favorable crystal forms. The adding of copolymers of a PP depressant changes the lamellar shape of the n-paraffin crystal to a more granular one, forming a microcrystalline structure. The lighter structure of n-paraffin clogs fuel filters at a lower rate, which leads to an improvement in the CFPP, the main criteria for assessing the low-temperature properties of the fuel. Substances used as depressants to improve PP and CFPP can be divided into polymeric (copolymers of ethylene with polar monomers, polymers based on esters of acrylic and methacrylic acids, polyolefins, copolymers of maleic anhydride with alpha-olefins, alkylphenol-formaldehyde resins) and organic non-polymeric compounds (alkylnaphthalalenes, esters of polyhydric alcohols, esters of dibasic acids, nitrogen-containing compounds, nanohybrid additives and petroleum refining residues) [12; 13]. The most common additives are mixtures based on copolymers of vinyl acetate and ethylene. Thus, the authors of [14] conducted research on the addition of copolymers of vinyl acetate with ethylene and methacrylate with acrylamide. Additives based on ethylene vinyl acetate copolymer showed the best reduction in PP and CFPP of diesel fuel. The authors of [15] assessed the ability to improve the low-temperature properties of diesel fuels by adding additives from various manufacturers. It has been found that the most effective depressant additives are also copolymers of ethylene and vinyl acetate. The authors of [16] conducted research on the feasibility of adding various substances such as ethanol, toluene, n-heptane and xylene as additives to improve PP and CFPP. It was found that the addition of these substances to diesel fuel did not lead to a significant decrease in the CP of the fuel, but the addition of toluene had the best effect. Some researchers synthesize additives themselves and then introduce them into diesel fuel [17; 18; 19; 20]. For example, the authors of [21] synthesized depressant additives based on heterocyclic compounds of acrylic acid, such as benzoxazolone, benzoxazolethione, benzthiazolone, benzthiazolthene. The resulting polymers were used as depressant additives, the introduction of which in small quantities into diesel fuels led to a significant decrease in the PP and improved fluidity at low temperatures. Some authors are studying the effectiveness of simultaneous introduction of depressants and dispersants into diesel fuel. Thus, the authors of [22; 23] found that this experiment improves the low-temperature properties of diesel fuel, including sedimentation stability, and also leads to a synergistic action of the components of the complex depressant additive. In the work of [24] studied the results of the influence of sixteen different commercial depressants on PP and CFPP on commercial and straight-run diesel fuel.