Research On Comb-like Copolymers Pour Point Depressant And Modified Nano-SiO₂ Particles Synergistically Improving The Rheology Of Waxy Crude Oil

The combination of traditional polyacrylate pour point depressant and nanoparticle is a new hot spot in the field of pour point depressant.Meanwhile,the increasingly mature molecular simulation technology is applied to the development of pour point depressant more and more times.In this paper,law and mechanism of polyacrylate pour point depressant and modified nanometer SiO₂ particles synergistically improving the rheology of synthetic waxy oil were studied by means of experimental characterization and molecular dynamics simulation.Firstly,the effects of POA-VA,POA-St,POA-MA pour point depressant on the rheological properties of synthetic waxy oil were studied and found that polar groups improves the effect of the pour point depressant.With the increasing content of polar groups,the modification effect becomes better then worse and there is a moderate content of polar groups that can promote the effect of pour point depressant to achieve optimal.At the dose of 400ppm of POA-VA-4?OA:VA=3:1?,the condensation point of synthetic waxy oil can be reduce by 8?and the average viscosity reduction rate reaches 86.71%.At the same time,the yield value decreased by 84.87%.The wax precipitation temperature is reduced by 1-3?by adding PPDs and the wax crystal size of wax oil at low temperature is larger and the shape is more regular.Then,the paper studied the micromechanism of POA-VA PPDs improving the rheology of synthetic waxy oil by mesoscopic dynamics simulation by constructing a mesoscopic model that simulates a solvent oil system,an amorphous aggregate system of waxes,and a waxy crystal structure.It was found that the energy change of the pour point depressant molecules breaking away solvent oil system to amorphous aggregate system is negative.The addition of POA-VA-4 reduces the cohesive energy density?CED?of the wax molecules from the amorphous aggregate to the crystalline state by 10.81%,and is further reduced by 1.91%relative to the POA.It indicates that PPDs with better effects inhibit precipitation of wax crystal better,and promote the distribution of wax molecules more aggregated obtained by analysis of radial distribution function?RDF?.At the same time,it has also been found that the difference in the content of polar groups affects the configuration of the pour point depressant molecule,and thus affects the interaction with the wax molecule.Then,the paper composited of POA-VA-4 and nano-SiO₂ particles with different degrees of organic modification and the composite ratio of organically modified nano-SiO₂ particles to POA-VA-4 was screened by condensation point measurement.It is found that appropriate modification degree can optimize the traditional depressant.At the dose of 400ppm,PPD-3 and PPD-4 can further reduce the condensation point by 2?relative to the traditional depressant and PPD-3 can further make the viscosity reduction rate rised by 4.67%.The addition of the composite depressant also further optimized the wax crystal morphology of the waxy crude oil at low temperature.Finally,the paper established adsorption models and researched the mechanism of the effect of modification degree of nano-SiO₂ on of composite depressant using molecular dynamics method.The study found that the degree of organic modification of nanoparticles affects the adsorption and distribution of the components on the surface of the particles.On the surface of 50%modified particles,POA-VA depressant have the greatest adsorption energy distribution near the particle surface,and the concentration distribution of which is closer to the surface.At 293 K,the absolute value of the adsorption energy of POA-VA molecules on the surface of 50%organically modified particles is 50.97 kcal/mol.At the same time,the modification degree of 50%is also more conducive to the interaction between pour point depressant molecules and wax molecules.The analysis of radial distribution function?RDF?shows that the proper degree of modification makes wax molecules more compact.