Study On Configuration Design And Green Synthesis Of Ester Base Oil With High Viscosity

As one type of high-end synthetic base oils,ester base oil is increasingly favored for high its performance,multifunctionality,and environmental friendliness.However,due to the use of sulfur-containing catalyst and alkali washing refining process,the traditional production process of ester base oil usually causes many problems,such as high-sulfur content of product,excessive by-products,emulsification of oil,large amounts of sewage discharge,equipment corrosion and so on.In addition,up to now,systematic study on ester base oil with high viscosity has been rarely reported.In order to solve above-mentioned problems,studies on development of green catalyst,and configuration design,structure-function relationship,green synthesis,and refining of ester base oil with high viscosity were mainly focused in this dissertation.Sn/Zr mixed oxide catalysts were synthesized by hydrothermal method,and preformed catalysts were prepared by compression molding method.In the whole preparation process of catalyst,no template agent and surfactant were used,and the prepared catalysts did not contain sulfur,nitrogen,phosphorus,and halogen elements,which could realize harmlessness of catalyst preparation process and greenization of catalytic process,on the premise of maintaining high catalytic activity,low cost,and better separation of catalyst from oil.Characterization results of catalyst indicated that Sn/Zr mixed oxide catalysts were mixed valence metallic oxides with mesoporous structure.Although the number of active centers would be decreased by doping a small amount of Zr⁴⁺ions,catalytic activity was still enhanced by the improvement of surface hydrophobicity,specific surface area,pore volume,and pore diameter of catalyst,and dispersity of Sn²⁺ions.However,excessive doping of Zr could make catalysts from crystal structure change to amorphous structure,significantly decrease the number of active centers,and weaken surface hydrophobicity of catalyst,which would reduce catalytic activity markedly.Specific surface area,pore diameter distribution,acid amount,acid strength,and thermostability of catalyst were significantly improved by molding process of catalyst.By expanding the application range of the principle of equal reactivity of all functional groups and establishing simplified reaction kinetics models,kinetics of synthetic reaction for ester base oil with high viscosity was investigated without knowing the structure and composition of reaction intermediates.Results of kinetics study indicated that equal reactivity theory of functional groups could apply to oligomerization reaction and non-polymerization reactions involving polyhydric oligomers.Due to the high viscosity of reacting mixture and the strong adsorbability of catalyst to organic acids,esterification reaction mainly occurred on the outer surface of catalyst particle at first,and gradually on the inner surface of catalyst particle with molecular diffusion,therefore,the phenomenon on mutation of reaction order from 0 to 2 was found.Suitable synthetic temperature of polyhydric oligomer,enanthate,and 2-ethylhexoate with high viscosity were 160,170,and 180?,respectively.By programmed heating,the carboxyl conversion rate of synthetic reaction of mixed acid ester would be more than 97%.Bridging-type and diester-type neopentyl polyol esters were designed and synthesized,which belonged to high viscosity ester base oils with very high viscosity index(VHVI)and ultra high viscosity index(UHVI),respectively.To reduce environmental pollution and energy consumption,improve reaction conversion rate,and prevent oxidation of products,nitrogen gas was used as water-carrying agent instead of organic solvent in the synthesis process.Analysis results of basic physical properties for ester base oil showed that the kinematic viscosity,viscosity index,pour point,acid value,and chromaticity of crude bridging-type neopentyl polyol ester were 141.51 mm²/s(40?),17.49 mm²/s(100?),136,-38?,13.63 mg KOH/g,and 3,respectively.And the kinematic viscosity,viscosity index,pour point,acid value,and chromaticity of crude diester-type neopentyl polyol ester were 106.29 mm²/s(40?),16.74 mm²/s(100?),172,-45?,8.64 mg KOH/g,and 4,respectively.Diester-type neopentyl polyol ester has wider viscosity range,better viscosity-temperature performance and low-temperature fluidity,while bridging-type neopentyl polyol ester has higher stability,lower chromaticity and light component content,and more concentrated molecular weight distribution.Results of structure-function relationship study indicated that when synthetic raw materials remained unchanged,the viscosity of ester base oil with high viscosity mainly depended on molecular weight effect,and linearly increased with the increasing of molecular weight.However,when the synthetic raw materials were different,the basic physical properties of ester base oil with high viscosity were affected by molecular weight effect and configuration effect simultaneously.When the carbon chain of dicarboxylic acid was short,configuration effect mainly affected the basic physical properties of ester base oil with high viscosity.The steric hindrance of ester base oils synthesized by dicarboxylic acid with odd carbon or branched monohydric alcohol was relatively larger,which would go against the tight arrangement of ester molecules and reduce the attraction of ester groups to alkyl chains,so their viscosity and pour point were relatively lower.When the carbon chain of dicarboxylic acid was long,the influence of molecular weight of raw materials on basic physical properties of ester base oil was dominant,and the viscosity and pour point of ester base oil increased with the increasing of molecular weight of raw materials.To reduce sewage discharge and avoid emulsification of product,two-stage molecular distillation was used to refine crude bridging-type neopentyl polyol ester,and the nonideal components such as water,organic acid,semi-ester,and ester with low boiling point in the crude product were effectively removed.The kinematic viscosity,viscosity index,pour point,open cup flash point,acid value,chromaticity,density,and yield of refined bridging-type neopentyl polyol ester were 238.79 mm²/s(40?),25.77mm²/s(100?),138,-31?,268?,0.03 mg KOH/g,4,1.04 g/cm³(20?),and 82.31wt.%,respectively.And it could be used as a high-performance ester base oil with very high viscosity index and viscosity grade of 120BS.Results of elemental analysis demonstrated that the content of carbon,hydrogen and oxygen of the refined product were65.36,9.75,and 24.89 wt.%,respectively,the content of tin and zirconium of the refined product were 1.32 and 3.29?g/g,respectively,and the content of sulfur and nitrogen of the refined product were almost zero,which proved that the green synthesis of ester base oil with high viscosity could be realized by using Sn/Zr mixed oxides as catalyst,and greenization refinement of crude ester base oil with high viscosity could be achieved by two-stage molecular distillation.