Study On Synthesis、modification Of Ferrierite And Catalytic Isomerization Of Oleic Acid

C₁₈-saturated branched-chain fatty acids（sbc-FAs）,also known as isostearic acid,are a mixture of various isomers of stearic acid,in which the branched alkyl group（usually methyl）is located in a specific position of the straight fatty acid chain.Compared with stearic acid,it has better low-temperature fluidity,lower melting point and viscosity,and has better oxidation stability than linear unsaturated fatty acids with the same chain length.It is a fine chemical product with excellent performance,it is widely used in cosmetics,polymers,surfactants,penetration enhancers,lubricants and other fields.At present,most isostearic acid products at home and abroad are separated from the monoacid by-product in the production of dimer acid,and its physical and chemical properties are difficult to meet market requirements.In this paper,I am starting from the synthesis mechanism of isostearic acid,using ferrierite molecular sieves as catalysts,the synthesis and modification process of ferrierite molecular sieves are studied in detail,and the influence of the outer surface modification of ferrierite on the yield of isostearic acid is explored.At the same time,the synthetic process conditions of isostearic acid were optimized.Under the condition of not using organic templates,ferrierite molecular sieves were synthesized by the seed-directed method.Through single factor experiments,the crystallization time,crystallization temperature,silicon-to-aluminum ratio,and the amount of seed crystals added during the synthesis process were explored.The results show that under the conditions of silicon-to-aluminum ratio Si/Al=20,crystallization time 24 h,crystallization temperature170℃,and seed crystal addition amount 15 wt%（based on the total mass of Si O₂ and Al₂O₃）,ferrierite molecular sieves were successfully synthesized,and XRD,SEM analysis showed that the synthesized ferrierite had high crystallinity and regular crystal morphology.Ammonium chloride is selected as the modifying reagent to modify the synthesized ferrierite,and the modified ammonia ferrierite is converted into hydrogen ferrierite through high-temperature calcination.When the calcination temperature reaches 500℃and the calcination time is 3 h,the ammonia molecules in the ferrierite are almost completely removed.At this time,the catalyst activity reached the maximum,the conversion rate of oleic acid exceeded 98%,and the yield of isostearic acid was near 75%.Since the acid sites on the outer surface of ferrierite will catalyze the polymerization of oleic acid molecules to produce by-products,reduce the selectivity of the product and cause the pores to be blocked,the alkali neutralization method is used to passivate the acid sites on the outer surface of the zeolite.The molecular diameter of triphenylphosphine（7.2×11.0×11.4（?））is larger than the diameter of pores formed by ferrierite ten-membered ring（5.4×4.2（?））and eight-membered ring（4.8×3.5（?））,so triphenylphosphine cannot enter the internal pores of the molecular sieve and only combined with acid sites on the outer surface of the molecular sieve,thereby it inhibiting the polymerization reaction of oleic acid that occurs on the surface of the molecular sieve.XRD,SEM,TG,BET,NH₃-TPD,pyridine infrared and 2,4,6-trimethylpyridine infrared were used to characterize the surface-modified ferrierite.Studies have shown that after modification with triphenylphosphine,the number of acid sites on the outer surface of the zeolite was reduced by 66.21%,the dimer by-product content was reduced from 15.78 wt%to 4.58 wt%,at this time,the yield of isostearic acid reached more than 81%.The repeated use performance of ferrierite after surface modification was investigated.After each use,ferrierite was washed with ethanol and calcined at a high-temperature,and then surface modified by triphenylphosphine,the ferrierite catalyst activity can be restored.After repeated use for 3 times,the conversion rate of oleic acid and the yield of isostearic acid remained high.The effect of the amount of catalyst,reaction time,reaction temperature,and the amount of auxiliary water added on the isomerization reaction of oleic acid was studied through single factor experiments.The order of the influence of each factor is:reaction time>additive amount of water>reaction temperature>catalyst amount.The optimal process conditions were determined through response surface analysis,when the amount of catalyst added is 4.8 wt%,the reaction time is 6.8 h,the reaction temperature is 280℃,and the amount of auxiliary water added in 3.6 wt%,after three repeated experiments,the average yield of isostearic acid can reach 81.72%.A thermogravimetric analyzer was used to analyze the thermal stability of the isostearic acid product,and the acid value,iodine value,saponification value,and pour point of the sample were determined.The results show that isostearic acid has better thermal stability and does not undergo oxidative decomposition reaction before 200℃.The purified isostearic acid has an iodine value of 2.58 g I₂/100g,an acid value of 171.61 mg KOH/g,a saponification value of 189mg KOH/g,and a pour point of-15℃.