Study On Mordenite-Catalyzed The Preparation Of Isostearic Acid From Oleic Acid Isomerization And Its Downstream Products

Isostearic Acid（IA）is a mixture of branched-chain saturated fatty acid isomers.Since it has alkyl branched-chain and the carbon chain does not contain carbon double bond structure,IA has the advantages of high temperature stability,low temperature fluidity,and biodegradation.It is applicable to lubrication,coatings,and cosmetics.Pentaerythritol isostearate,as an ester derivative of isostearic acid,not only has excellent oxidation resistance and thermal stability,but also has good viscosity-temperature properties and excellent lubricity.It can be used in industrial fields instead of traditional petroleum-based lubricating oil.In this paper,the reaction mechanism of acid zeolite-catalyzed oleic acid skeleton isomerization was taken as the starting point,and the preparation process and modification conditions of mordenite were investigated by using mordenite as the catalyst,and the effect of surface modification on the catalytic activity of filamentous zeolite was studied.In addition,the optimum synthesis process of pentaerythritol isostearate was optimized by single factor and orthogonal experiments using isostearic acid and pentaerythritol as raw materials.Mordenite was prepared by seed induction method under the conditions of crystallization time 12 h,crystallization temperature 180℃,seed addition of 6 wt%（based on the feeding quality of Si O₂）and feeding mole ratio of Si to Al of 20.Sodium mordenite was modified in 1mol/L NH₄Cl solution and calcined at 400℃to obtain acid mordenite.At this time,the acid mordenite has an ideal catalytic activity,oleic acid conversion rate of more than 93%,isostearic acid yield of nearly 67%.Acid mordenite was characterized by SEM,XRD,TGA,BET,FTIR and Py-IR,and the structural-activity relationship between the acid content of zeolite and the catalytic oleic acid isomerization was deeply understood.Since the acid site on the outer surface of zeolite does not have the performance of"shape selection catalysis",it will lead to oligomerization of part of oleic acid and reduce the yield of IA.Therefore,4-methylquinoline is used to modify the acid site on the outer surface of acid mordenite.The modified mordenite was characterized by SEM,XRD,TGA,NH₃-TPD,FTIR and Py-IR.The results showed that the modified mordenite Bronsted acid site content was reduced by 9.18%,the by-product dimeric acid content was reduced by 56%,and the yield of IA was more than 72%.The reuse performance of the mordenite was investigated.After washing the mordenite with n-hexane,calcination at high temperature,repeated modification of NH₄Cl and external surface modification of 4-methylquinoline and other steps,the catalytic activity of the mordenite could be restored.The yield of IA prepared from the catalytic isomerization of oleic acid was about 57%when the mordenite was reused for the 5th time.The characterization results of XRD,SEM,TGA,FTIR,UV-Vis showed that some of the alkenyl carbon cations would adsorb on the catalyst active center,resulting in the reduction of the zeolite catalyst activity.Pentaerythritol isostearate was synthesized by direct esterification using p-toluenesulfonic acid as catalyst.The process parameters of the esterification reaction were optimized by single-factor combined with orthogonal experiments,and the optimal process conditions were determined as 5 h reaction time,140℃reaction temperature,1 wt%catalyst dosage（based on the total reaction feed）,and 4.3 acid-to-alcohol ratio（molar ratio of isostearic acid to pentaerythritol）,at which the average esterification rate of isostearic acid was about 99%.The esterified products were purified by 5%Na₂CO₃ water solution.After refining,the 50%defocusing(T_50%)of esterified products was 460℃,which showed good thermal stability.The acid value was 3.227 mg KOH/g,the viscosity index was 132,the refractive index was n²⁰=1.4660,and the pour point was-31℃.The opening flash point is 292℃.The results showed that pentaerythritol isostearate had good viscosity-temperature properties,low temperature fluidity and safety.