Research On The Rheological Properties Of Waxy Crude Oil Of The Nanocomposite Pour Point Depressant With High-density Grafted

In recent years,nanocomposite PPDs have become a research hotspot in the field of PPDs for waxy crude oil.However,the stability of composite PPDs prepared by physical blending is not good and the polymer molecules adsorbed on the surface of nanoparticles are easy to desorb,which limits the effect of PPDs.Chemical grafting can solve the problem of poor stability of composite particles prepared by physical blending method,but due to the limitation of traditional solution free radical polymerization method,high density grafting is difficult to achieve.Based on the unique advantages of thiol-click reaction and good morphology and structural properties of organosilicate nanospheres,the high density graft of the octadecyl acrylate（OA）on the surface of organosilicate nanospheres was realized,the high density grafting nanometer PPDs was synthesized and the composite PPDs was prepared based on the grafting to explore the effect and mechanism of improving the low temperature rheological properties of waxy crude oil.Firstly this paper prepared polymercaptosilicon（PMPSQ）nanospheres by hydrolyzation-condensation reaction（sol-gel method）and characterized them.Then,OA monomer was grafted on the surface of PMPSQ by thiol-click reaction to obtain a grafted nano PPD（PMPSQ-OA）with high grafting density,the rheological improvement effect and mechanism of PMPSQ-OA on various oil systems were investigated.Finally,EVA/PMPSQ-OA nanocomposite PPD was obtained by PMPSQ-OA and EVA PPD with melt blending method,and its rheological improvement law and mechanism for waxy crude oil were investigated.The conclusions are as follows:（1）In the aspects of PMPSQ,the effects of reaction temperature and time,p H value of aqueous phase,stirring rate and mass fraction of silicon source（MPTMS）on the morphology and average particle size were investigated.It was found that in order to prepare nanospheres with regular morphology,the hydrolysis reaction time should be controlled at about 4 h,and the p H value of water phase should be less than 4,the polycondensation reaction time should not be less than 4 h,the p H of the aqueous phase should be greater than 11,and the mass fraction of MPTMS should not be higher than 5%.With the decrease of MPTMS mass fraction and the increase of the stirring rate,the average particle size of the nanosphere decreases continuously.For example,when the stirring speed increases from 100 r·min^-1 to900 r·min^-1,the average particle size of the nanosphere decreases from 923 nm to 601.7 nm.With the increase of reaction temperature,the average particle size of the prepared nanospheres decreases first and then increases.（2）The grafted nanometer PPD PMPSQ-OA was successfully prepared by thiol-click reaction and has been demonstrated by FT-IR,SEM,TGA,etc.The surface graft rate and properties of PMPSQ-OA were significantly affected by the concentration of BDK.When the molar ratio of OA to sulfhydryl group is 1:1,the surface graft rate,crystallization ability,pour point（PP）and viscosity reducing ability enhance with the increase of BDK concentration,and reached the maximum grafting rate（78.53%）when the BDK concentration was 4%.As the concentration of BDK increases further to 6%,the surface grafting rate of PMPSQ-OA decreased significantly（59.85%）,the crystallization properties ability to reduce PP and viscosity also decreased significantly.Control the concentration of BDK is 4%,with the increase of OA concentration,surface grafting rate of nanometer ball increases gradually,the crystallinity and dispersion of PMPSQ-OA-1～4 PPDs in oil phase are gradually enhanced.When the molar ratio of OA to sulfhydryl group is 1:1（PMPSQ-OA-4）,the grafted PPD can reduce the PP of Changqing crude oil by 14°C,the average viscosity reduction rate is 87.27%,and the rheological improvement effect is the best.With the increase of OA concentration（PMPSQ-OA-5）,the grafting rate and the rheological properties of the crude oil did not further improve.With the increase of dosage of PMPSQ-OA-4,the rheological improvement effect of Changqing crude oil becomes better.It also shows a good effect of reducing PP and viscosity when PMPSQ-OA-4 was added into Qinghai crude oil and artificial wax oil,and has good anti-reheating,anti-high-speed shear performance and time-efficiency.PMPSQ-OA can change the crystallization behavior of wax molecules through the action of wax crystallization template,and make the wax crystals change from the fine and long needle-like structure,at the same time,it can promote the agglomeration of wax crystals and reduce the crystal liquid area,thus improving the rheological properties of wax oils.（3）Ungrafted EVA/PMPSQ and grafted EVA/PMPSQ-OA-1～5 nanocomposite PPDs were successfully prepared by melt blending method with ungrafted PMPSQ-nanospheres and grafted PPDs PMPSQ-OA-1～5.For ungrafted nanocomposite PPD EVA/PMPSQ,its crystallization property and the improvement of rheological properties is not as good as EVA.For grafted nanocomposite PPDs EVA/PMPSQ-OA,with the increase of OA grafting amount on the surface of PMPSQ nano-spheres,the adsorption capacity of EVA on grafted nano-PPDs surface gradually weakened,and the pour point and viscosity reduction energy of composite pour point depressant also gradually deteriorated.At low grafting rate（EVA/PMPSQ-OA-1）,the best improvement effect on crude oil rheology was achieved,and the optimal dosage was 100ppm.Its resistance to high speed shear,resistance to reheating,timetableness and modification effect were better than EVA PPD.As a heterogeneous nucleation template for the precipitation of wax molecules,the grafted nanocomposite PPDs can promote the precipitation of wax molecules,increase the crystal volume of wax,make the structure of wax crystal flocculate more compact,and reduce the bondage to liquid oil.