Study On The Isomerization Of Oleic Acid/Methyl Oleate Catalyzed By Modified Zeolites And The Mechanism Of Catalyst Deactivation And Regeneration

Saturated branched-chain fatty acids,which are commonly referred to as isostearic acids,are mixtures of isomers of stearic acids with alkyl branch chain on their carbon chain skeleton.Due to the branched chain structure and the absence of C=C,isostearic acids combine the advantages of straight-chain saturated fatty acids and straight-chain unsaturated fatty acids,such as lower melting point,stronger oxidation resistance,better low-temperature fluidity,etc.,making it easy for industrial processing.Therefore,isostearic acids have a wide range of industrial applications,and the market demand of isostearic acids continue to rise steadily,which have great development prospects.The production of isostearic acids with ferrierites catalyzed by oleic acid has the characteristics of high selectivity,but the reusability of the catalyst is poor and the regeneration of catalyst is complex.The ZSM-5 zeolite has good repeat stability,but the micropore size of ZSM-5 restricts its application in isomerization reactions.In this paper,the factors affecting the reusability of the catalyst in the process of preparing isostearic acids catalyzed by ferrierites were investigated,and the recycle capacity and regeneration catalytic performance of the ferrierites were investigated in detail.The ZSM-5zeolite has been modified to develop a more economical catalyst for isomerization of oleic acid and methyl oleate.The main research work is summarized as follows:Isostearic acids were prepared by isomerization of oleic acid and methyl oleate respectively with acidified ferrierites as catalysts,at the same time,the effects of raw materials on the conversion of isomerization reaction and yield of isostearic acids and the re-utilization performance of ferrierites were compared.The results showed that:（1）According to a series of analysis such as XRD,TG,NH₃-TPD,it was found that the accumulation of carbon deposition and the significant decrease of the acid amount are the main reasons for the loss of catalytic activity of ferrierites when used oleic acid as materials.But when selected methyl oleate as materials,ferrierites showed better catalytic properties and recyclability,the conversion and yield of the reaction could be maintained at about 90%and 70%after being reused five times.（2）In order to unblock the pores of the catalyst and increase the number of acid active sites to restore the catalytic activity of the ferrierites,the recovered ferrierites was washed with ethanol and separated by centrifugation,and then acidified with hydrochloric acid.After five times of reuse,the conversion and yield of the isomerization of methyl oleate could be maintained at the same high level,but when catalyzing the isomerization of oleic acid,the yield of isostearic acids decreased from 72%to 56%and the catalytic performance was still significantly attenuated.The ZSM-5 zeolite was subjected to alkali treatment,ion exchange and high-temperature calcination to adjust its silicon-to-aluminum ratio,pore structure,acidic sites and other characteristics,and then the modified ZSM-5 zeolite was used to catalyze the isomerization reaction of methyl oleate to prepare isostearic acids to test its catalytic activity.The results showed that:（1）According to the characterization analysis results,such as XRD,ICP,SEM,BET,NH₃-TPD,it was found that alkali treatment can reduce the Si/Al ratio of ZSM-5 zeolite and form a mesoporous structure.In addition,it also could increase the number of acid active centers.When the concentration of Na OH was 0.5 mol/L,the modified ZSM-5（0.5）zeolite could maintain a complete framework structure,while having high pore volume,good thermal stability and the highest content of acid active sites,making it shows the best catalytic activity in the isomerization reaction of methyl oleate,and the yield of isostearic acids reached the highest value of 68.41%.（2）The ZSM-5（0.5）zeolite with the best catalytic performance was selected to catalyze the isomerization reaction of methyl oleate,and the effects of catalyst addition,reaction temperature,reaction time on the yield of isostearic acids were investigated.When the additions of ZSM-5（0.5）is 6 wt%,the reaction temperature is 240℃,and the reaction time is 12 h,the conversion rate of methyl oleate is 89.50%,and the yield of isostearic acids is 69.80%.In addition,ZSM-5（0.5）zeolite can be reused at least five times after washing with ethanol and high-temperature calcination,and the conversion and yield of the methyl oleate isomerization reaction can reach 85.84%and 63.17%,indicating that the ZSM-5 has a simple regeneration process and excellent recycling performance.