To elucidate the mechanism by which pipeline shear increases the gel point of crude oil treated with a polymeric pour point depressant (PPD), pipeline⁃shear simulation experiments were conducted on T crude oil based on energy dissipation theory. Microscopic observations combined with ImageJ image analysis were used to characterize wax crystal morphology before and after shearing. The results showed that, after the addition of 25 mg/kg of PPD and heat treatment at 50 ℃, the gel point of T crude oil decreased from -8 ℃ to -14 ℃. Following simulated pipeline transportation, the gel point of the treated crude oil increased to -5 °C, representing greater deterioration than that observed for untreated crude oil. Each high⁃speed shearing event increased the gel point of the treated oil by 3-4 ℃. Microscopic analysis showed that the PPD promoted wax crystal aggregation and growth through co⁃crystallization and adsorption, reducing the crystal count from 605 to 272 and increasing the mean crystal area from 5.58 μm² to 7.33 μm². However, shear disrupted the aggregated wax crystal structures, causing the crystals to redisperse; wax crystal number increased to 771, while average wax crystal area decreased to 1.36 μm². This increased the dispersion and surface energy of the system, leading to a higher gel point. These findings clarify the microstructural mechanism by which shear weakens the effectiveness of polymeric PPD treatment and provide a theoretical basis for assessing shear⁃related safety during the pipeline transportation of waxy crude oil.

Silver?doped powders with n（Ag⁺）/n（Ti⁴⁺） of 0.001、0.003、0.005、0.010、0.030 and 0.050 and ceramic hollow microspheres loaded with titanium dioxide photocatalyst were prepared by sol?gel method. The prepared catalysts were characterized by SEM, XRD and Uv?Vis DRS, and their photocatalytic properties were tested under xenon lamp light source. The doping mechanism was analyzed using first?principles calculations.The results show that the degradation rate of 0.005Ag?TiO₂ powder after photocatalytic degradation of 10 mg/L methylene blue for 90 min is 76%. It is concluded that n（Ag⁺）/n（Ti⁴⁺）=0.005 is the best doping amount, and the degradation rate of ceramic hollow microsphere supported catalyst for 90 min is 97%. Ag doping can introduce impurity energy levels in the TiO₂ system, so that the valence band electrons can reach the conduction band by hierarchical transition. The calculation results are consistent with the experimental results.