Study On Surface Modification Of H~+-Mordenite And Zeolite-catalyzed Isomerization Of Oleic Acid

C₁₈-saturated branched-chain fatty acids?sbc-FAs?,also known as isostearic acid,are important intermediates for biodegradable surfactants,lubricants and hydraulic fluids.Compared to stearic acid,sbc-FAs and their simple alkyl esters have lower melting point and cloud point,and their antioxidant properties are superior to unsaturated fatty acids.They can be widely used in Cosmetics&Toiletries,Synthetic lubricating,Protective agent,Plastic additive,Food additives,Surface active agent,Drug additive and so on,has a good market and development prospects.Since the molecular dynamics size of tetraethoxysilane?10.3????and triphenylphosphine?11.4????is larger than that of one-dimensional 8-membered ring?MR??2.6???�5.7????and12-MR?6.5???�The 7.0????channel diameter of hydrogen mordenite,tetraethoxysilane and triphenylphosphine does not allow to diffuse into the pores of the hydrogen mordenite,but poison the acid sites on the external surface of the zeolite.After modification of the zeolite,the active sites in the pores are not affected and catalyze the isomerization of oleic acid,but most of the active sites on the outer surface are deactivated.In this paper,all samples were characterized by XRD,SEM,BET,TG,NH₃-TPD and ¹H MAS NMR.The infrared spectrum of 2,4,6-trimethylpyridine was used to characterize the acidic sites on the external surface of the zeolite.After hydrogen mordenite were modified with tetraethoxysilane?1 wt%?and triphenylphosphine?0.1 mol/L?,the Bronsted acid sites on the outer surface were reduced by92.7%,the dimer decreased from 16.19 wt%to 4.14 wt%,and the yield of sbc-FAs exceeds90%.Under certain conditions,ubc-FAs was prepared by the isomerization of oleic acid using hydrogen mordenite by surface-modification,and then obtained sbc-FAs by deep hydrogenation.The effects of the modifier addition and isomerization conditions on the yield of sbc-FAs were studied by single factor experiment.When TEOS added was 1 wt%and TPP was 0.1 mol/L,the yield of sbc-FAs was up to 88.1%.The outer surface active center without selective catalytic function is partially passivated.The catalyst has the advantages of high activity and high selectivity.Accoring to determine the relationship between the factors by the response surface analysis obtain the optimal process parameters for the production of sbc-FAs.The optimal reaction conditions for the isomerization reaction of oleic acid were determined by Design-Expert software:hydrogen mordenite?6.33%relative to OA?and oleic acid?90%?,the reactor was then heated to 272.03 ^? for 4.33 h,and the theoretical production of sbc-FAs is 92.232%.According to the actual conditions,the reaction conditions are as follows:the oleic acid purity was 90%,mass of the catalyst was 6.3 wt%,reaction time was 4.3 h at270 ^?,and the yield of sbc-FAs exceed 91%.Esterification of sbc-FAs crude product with isopropanol yields isopropyl isostearate and then separate dimer acid and excess isopropanol by vacuum distillation.Simulate the process of batch distillation column by Aspen Plus.The purity of the product is kept constant by adjusting the reflux ratio.isopropyl isostearate were obtained from the top of the tower.The results show that:when the reflux ratio is 3-20 and tower top temperature is 210-225 ^?,The purity of the product can reach 93%,the yield can be up to 82%.On the basis of the simulation results,separate isopropyl isostearate products by intermittent vacuum distillation,and finally sbc-FAs were prepared by hydrolysis.The purity of the product is 90.4%and the yield can be up to 74.6%.The purity of the product is 90.4%and the yield can be up to74.6%.The optimum conditions will be got through the process of continuous distillation for isopropyl isostearate crude product was simulated by Aspen Plus.Under this condition,we got the 90%isopropyl isostearate product,and provide theoretical guidance for industrial production.The process of oleic acid isomerization is simplified by establishing a reasonable model.The kinetic equation of the isomerization reaction was obtained by calculate the conversion rate of oleic acid at different times.The kinetic equation of isomerization at 260 ^o C,270 ^?,280 ^? was:-r?28?1.0042c_A⁰.⁸³⁹⁶,-r?28?1.1012c_A⁰.⁸⁵⁴²,-r?28?1.2063c_A⁰.⁸²⁶²respectively.The activation energy is 22.46 kJ/mol and frequency factor is 3.2�10³.