Light crude oils are being progressively depleted as the dominant primary energy source, leading to increased attention on the extraction and utilization of highly waxy crude oils. To address the poor low-temperature fluidity of waxy crude oil, cashew nut shell liquid (CNSL), which is rich in anacardic acid, was extracted from low-cost and renewable cashew nut shells and subsequently modified with EVAL through esterification at different mass ratios (mEVAL:mCNSL = 1:1, 1:2, 1:3) to synthesize the EVAL-g-AAC pour point depressant. Chemical structure characterization confirmed the successful grafting of EVAL with anacardic acid. The experimental results demonstrated that EVAL-g-AAC 2 (mEVAL:mCNSL = 1:2) exhibited the best pour point-reducing performance at a dosage of 400 ppm, lowering the pour point of waxy model oils by 24 ℃. This reduction was 8 ℃ and 5 ℃ greater than that achieved by EVA and EVAL, respectively. In addition, its viscosity reduction rate increased by 28.5% relative to EVAL, while simultaneously decreasing the gelation temperature and viscoelastic properties of the model oils. Additionally, the low-temperature crystallization behavior of wax crystals was investigated using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). It proposed a possible mechanism of action for the new pour point depressant through the “alkyl long-chain promotes co-crystallization formation, polar groups promote dispersion, and rigid structure promotes nucleation” triple synergy to improve the crystallization behavior of wax molecules.

The effect of alcoholic polyethylene-vinyl acetate (EVA) product ethylene-vinyl alcohol copolymer (EVAL) on the low-temperature flow properties of model oil containing asphaltene (ASP) was investigated. The change of wax crystal microscopic morphology of model oil before and after modification were examined, and the influence of asphaltene mass fraction on the rheological improvement effect of EVAL was analyzed. The composite system of EVAL and asphaltene significantly reduced the pour point, gel point, apparent viscosity, storage modulus and loss modulus of waxy oil at low temperatures. When the EVAL concentration is 400 ppm and the asphaltene mass fraction is 0.5 wt%, the synergistic effect of the two is optimal, which can reduce the pour point by 17 °C and the modulus value by more than 98%. The introduction of EVAL strengthens the interaction between asphaltenes and wax crystals, forming EVAL-ASP aggregates, which promote the adsorption of wax crystals on asphaltenes to form composite particles, and the polar groups prevent the aggregation of wax crystals and reduce the size of wax crystals, thus greatly improving the fluidity of waxy oils.

Modified ethylene-vinyl acetate copolymer (EVAM) and amino-functionalized nano-silica (NSiO₂) particles were employed as the base materials for the synthesis of the nanocomposite pour point depressant designated as EVAM-g-NSiO₂. This synthesis involved a chemical grafting process within a solution system, followed by a structural characterization. Moreover, combining macro-rheological performance with microscopic structure observation, the influence of the nanocomposite pour point depressant on the rheological properties of the model waxy oil system was investigated. The results indicate that when the mass ratio of NSiO₂ to EVAM is 1:100, the prepared EVAM-g-NSiO₂ nanocomposite pour point depressant exhibits excellent pour point reduction and viscosity reduction properties. Moreover, the nanocomposite pour point depressant obtained through a chemical grafting reaction demonstrates structural stability (the bonding between the polymer and nanoparticles is stable). The pour points of model waxy oils doped with 500 mg/kg ethylene-vinyl acetate copolymer (EVA), EVAM, and EVAM/SiO₂ were reduced from 34 ℃ to 23, 20, and 21 ℃, respectively. After adding the same dosage of EVAM-g-NSiO₂ nanocomposite pour point depressant, the pour point of the model wax oil decreased to 12 ℃ and the viscosity at 32 ℃ decreased from 2399 to 2396.9 mPa ·s, achieving an impressive viscosity reduction rate of 99.9%. Its performance surpassed that of EVA, EVAM, and EVAM/SiO₂. The EVAM-g-NSiO₂ dispersed in the oil phase acts as the crystallization nucleus for wax crystals, resulting in a dense structure of wax crystals. The compact wax crystal blocks are difficult to overlap with each other, preventing the formation of a three-dimensional network structure, thereby improving the low-temperature flowability of the model waxy oil.

The nanocomposite EVAL-CNT was produced by chemical grafting in the solution system through the esterification of ethylene-vinyl alcohol copolymer (EVAL) and carboxylated multi-walled carbon nanotubes (O-MWCNT), and its structural properties were characterized. The improvement of the rheological properties of the waxy oil system by the novel pour point depressant was investigated using macroscopic rheological measurements and microscopic observations. The results showed that EVAL-CNT nanocomposite pour point depressant (PPD) could significantly reduce the pour point and improve the low temperature fluidity of crude oil and had better performance than EVAL-GO at the same addition level. The best effect was achieved at the dosing concentration of 400 ppm, which reduced the pour point by 13 °C and the low-temperature viscosity by 85.4%. The nanocomposites dispersed in the oil phase influenced the precipitation and crystallization of wax molecules through heterogeneous crystallization templates, which led to the increase of wax crystal size and compact structure and changed the wax crystal morphology, which had a better effect on the rheological properties of waxy oil.