Influence of poly (methacrylate-co-maleic anhydride) pour point depressant with various pendants on low-temperature flowability of diesel fuel

To investigate the influence of various pendants in comb-type copolymers on the low-temperature flowability of diesel fuel, a series of methacrylate-co-maleic anhydride copolymers R1MC-MA (R1 = C14, C16, C18) were synthesized. And C14MC-MA was aminated by R2NH2 (R2 = C14, C16, C18, phenyl, 1-naphthyl) to obtain a series of aminated copolymers C14MC-MA-a (C14MC-MA-14a, C14MC-MA-16a, C14MC-MA-18a, C14MC-MA-phenylamine, C14MC-MA-naphthylamine). They were characterized by Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). The influence of these pour point depressants (PPDs) on the cold flow properties of diesel fuel were investigated. The crystallization behavior and crystal morphology of diesel fuel were also studied by differential scanning calorimeter (DSC) and polarizing optical microscope (POM). When the dosage of PPDs was 1000 ppm, C14MC-MA-14a displayed an excellent depression on cold filter plugging point (CFPP) by 5 °C, C14MC-MA-phenylamine showed the best depression on solid point (SP) by 17 °C, and PPDC-1 (the mixture of C14MC-MA-14a with C14MC-MA-phenylamine) exhibited the best performance in depressing the CFPP and SP by 8 °C and 18 °C respectively. The results show that the effects of the PPDs on reducing SP and CFPP sometimes are inconsistent, because SP is closely related to the crystal/liquid interface, while CFPP is directly related to the wax crystal size. When pour point depressants are added, the wax crystals become smaller and regular (act as wax dispersants), thus inhibiting the formation of the porous network. So the CFPP decreased with decreasing the wax crystal size; and the SP first decreased with decreasing the wax crystal size, while when the wax crystals are too small, the large specific surface energy leads to the recovery of the SP. DSC and POM results showed that PPDs changed the crystallization behavior, size and shape of wax crystals, weakened the ability of wax crystals to form a three-dimensional network structure and made the wax crystals more uniform, compact, and dense. Therefore, the low temperature flowability of diesel fuel is improved by the synthesized pour point depressant.