Biodiesel and hydrotreated diesel fuels exhibit poor cold flow properties due to n-paraffin crystallization at low temperatures. In this work, environmentally friendly depressant additives based on chitosan from Apis mellifera exoskeletons and acrylic acid (AA)–styrene (St) copolymers were synthesized and evaluated for improving the cold flow properties of hydrotreated diesel fuel. Chitosan was obtained by alkaline deacetylation of chitin (DD = 85–90%), and AA–St copolymers were prepared by free-radical copolymerization with AIBN as the initiator. The effects of monomer molar ratio, reaction temperature, initiator concentration, reaction time, and solvent polarity on copolymer yield and molecular weight were systematically investigated. FTIR, ¹H NMR, and TGA were used for structural characterization. The copolymerization reactivity ratios, determined by the Mayo–Lewis method, were r₁ = 0.21 ± 0.04 (AA) and r₂ = 0.25 ± 0.05 (St), consistent with the known alternating copolymerization tendency of this system (r₁·r₂ ≈ 0.05). The activation energy ranged from 44 to 56 kJ/mol depending on solvent polarity. Optimal synthesis conditions were identified as: 75°C, AA:St = 50:50, 0.7% AIBN, 3 h in DMF, yielding a copolymer with Mw ≈ 8,700 g/mol. The chitosan–copolymer additive at 0.3 wt% reduced the cloud point by 3–5°C, the pour point by 6–10°C, and the cold filter plugging point by 4–7°C. These results suggest that renewable biopolymer-based depressants can moderately improve diesel cold flow properties, though further optimization of molecular weight and alkyl chain architecture is needed for industrially competitive performance.

chitosan; Apis mellifera; acrylic acid–styrene copolymer; depressant additive; biodiesel; cold flow properties; free radical copolymerization; pour point depressant

Dunn, R.O. Cold flow properties of biodiesel: A guide to getting an accurate analysis. Biofuels 2015, 6(1–2), 115–128. DOI: 10.1080/17597269.2015.1057791

Echim, C.; Maes, J.; De Greyt, W. Improvement of cold filter plugging point of biodiesel from alternative feedstocks. Fuel 2012, 93, 406–414. DOI: 10.1016/j.fuel.2011.11.036

Nifant'ev, I.E.; Tavtorkin, A.N.; Shlyakhtin, A.V.; Bagrov, V.V.; Chinova, M.S.; Tavtorkin, A.N.; Ivchenko, P.V. Polymer cold-flow improvers for biodiesel. Polymers 2021, 13(10), 1580. DOI: 10.3390/polym13101580

Yang, F.; Zhao, Y.; Sjoblom, J.; Li, C.; Paso, K.G. Polymeric wax inhibitors and pour point depressants for waxy crude oils: A critical review. J. Dispers. Sci. Technol. 2015, 36(2), 213–225. DOI: 10.1080/01932691.2014.901917

Rinaudo, M. Chitin and chitosan: Properties and applications. Prog. Polym. Sci. 2006, 31(7), 603–632. DOI: 10.1016/j.progpolymsci.2006.06.001

Kumar, M.N.V.R. A review of chitin and chitosan applications. React. Funct. Polym. 2000, 46(1), 1–27. DOI: 10.1016/S1381-5148(00)00038-9

Khor, E.; Lim, L.Y. Implantable applications of chitin and chitosan. Biomaterials 2003, 24(13), 2339–2349. DOI: 10.1016/S0142-9612(03)00026-7

Al-Sabagh, A.M.; Noor El-Din, M.R.; Morsi, R.E.; Elsabee, M.Z. Styrene–maleic anhydride copolymer esters as flow improvers of waxy crude oil. J. Pet. Sci. Eng. 2009, 65(3–4), 139–146. DOI: 10.1016/j.petrol.2008.12.022

Soni, H.P.; Kiranbala; Bharambe, D.P. Performance-based designing of wax crystal growth inhibitors. Energy Fuels 2008, 22(6), 3930–3938. DOI: 10.1021/ef800318a

Odian, G. Principles of Polymerization, 4th ed.; John Wiley & Sons: Hoboken, NJ, 2004. ISBN: 978-0-471-27400-1

Mayo, F.R.; Lewis, F.M. Copolymerization. I. A basis for comparing the behavior of monomers in copolymerization. J. Am. Chem. Soc. 1944, 66(9), 1594–1601. DOI: 10.1021/ja01237a052

Alfrey, T.; Price, C.C. Relative reactivities in vinyl copolymerization. J. Polym. Sci. 1947, 2(1), 101–106. DOI: 10.1002/pol.1947.120020112

Machado, A.L.C.; Lucas, E.F.; González, G. Poly(ethylene-co-vinyl acetate) (EVA) as wax inhibitor of a Brazilian crude oil. J. Pet. Sci. Eng. 2001, 32(2–4), 159–165. DOI: 10.1016/S0920-4105(01)00158-9

Xue, Y.; Yang, C.; Xu, G.; Zhao, B.; Lian, X.; Han, S. Effects of poly-alpha-olefin pour point depressant on cold flow properties of waste cooking oil biodiesel blends. Fuel 2016, 184, 110–117. DOI: 10.1016/j.fuel.2016.07.006

Huang, H.; Wang, Z.; Shi, X.; Li, J.; Chen, B. Review on cold flow properties of biodiesel and their improvement methods. Energies 2024, 17(18), 4543. DOI: 10.3390/en17184543

Du, T.; Wang, S.; Liu, H.; Song, C.; Nie, Y. The synthesis and characterization of methyl acrylate–styrene copolymer as a diesel cold flow improver. Pet. Sci. Technol. 2012, 30(2), 212–221. DOI: 10.1080/10916466.2010.499408

Madruga, E.L. From classical to living/controlled statistical free-radical copolymerization. Prog. Polym. Sci. 2002, 27(9), 1879–1924. DOI: 10.1016/S0079-6700(02)00023-0