Study Of Acid Catalyst For Isoprene Synthesis By The Prins Condensation Of Methyl Tert-butyl Ether With Formaldehyde

The Prins condensation of methyl tert-butyl ether(MTBE)and formaldehyde to produce high value-added polymer monomer isoprene is a potential solution to the problem of the overcapacity of MTBE under the situation of energy quality upgrading.However,traditionally,there were some problems in this process,such as poor selectivity of isoprene,easy carbon deposition of solid acid catalyst,and serious corrosion of equipment by inorganic liquid acid catalyst.Therefore,it’s urgent to develop an efficient catalyst system to realize the green and economic development of the process.Based on this,we systematically studied two kinds of catalyst systems,sulfonic acid-functionalized ionic liquid(SFILs)and zeolites,and made some breakthroughs in catalytic performance and catalytic reaction mechanism.The achievements of this thesis were as followed.(1)High MTBE/FA feeding ratio and the addition of excess solvent were generally used to inhibit the excessive side reaction of isoprene and formaldehyde,which lead to the problem that the production intensity of isoprene was significantly limited.We evaluated different acid catalysts with the goal of improving selectivity and catalyst recyclability under the condition of high concentration solutions with stoichiometric ratio of MTBE/FA.Acidic sulfonic acidfunctionalized ionic liquid([HSO3-bmin]PTS)showed excellent performance.Reaction network studies have confirmed that 4,4-dimethyl-1,3-dioxane(DMD)was a key reaction intermediate in the synthesis of isoprene.The conversion of isoprene from intermediate products required ionic liquid catalysts with sufficient strong acid strength.In order to maximize the yield of isoprene,the effects of various reaction conditions were investigated in detail,including reaction time,reaction temperature,solvent,ionic liquid concentration,MTBE and formaldehyde amount.Under the optimal conditions,the production intensity of isoprene reached 55.0g/L,which was an order of magnitude higher than the previous literature.The[HSO3-bim]PTS ionic liquid showed excellent recycling and maintained its activity and selectivity after seven times reuses.(2)Zeolite with its rich pore structure,adjustable acid-base properties,excellent thermal stability,is a potential catalyst for the reaction.We investigated the catalytic properties of SSZ13,MOR,ZSM-5,BE A and USY zeolites with different pore sizes and found that BEA zeolite showed the best catalytic properties than other zeolites(formaldehyde conversion 99.1%,isoprene selectivity 24.4%).The acidity and catalytic performance of BEA zeolites with different silica-Al ratio were studied.It was found that with the decrease of the silica-alumina ratio,the acidity of the BEA zeolites was increased,the catalytic activity was enhanced and the yield of isoprene was improved.However,the acid content of BEA zeolites was significantly less than that of most small and medium pore zeolites,which meant the pore structure was the main factor affecting the catalytic performance.We put forward the hypothesis that although small and medium pore zeolite has more acidity,it was difficult for MTBE and intermediate DMD molecule to enter the pore due to the limitation of pore,and the number of acid sites available for effective contact with the substrate was small.The penetration curve experiment confirmed that the adsorption amount of MTBE and DMD was positively correlated with their conversion rate,and BEA had the highest adsorption capacity,which meant that BEA had the highest concentration of active site in the reaction process,making its catalytic performance significantly better than other small and medium pore zeolites.