| Mordenite(MOR)has high dimethyl ether carbonylation activity,mild process conditions,high target product selectivity,and few side reactions during the reaction process.It is an important step in the current industrial synthesis gas production ethanol route.Since the catalyst is very easy to deactivate carbon deposits during the process of the reaction,how to effectively suppress the carbon deposits and improve the stability of the catalyst has become the focus and hotspot of the MOR catalytic dimethyl ether carbonylation reaction.This thesis takes MOR as the research object,examines the effect of MOR synthesis conditions on the performance of carbonylation reaction,and optimizes it.The pore structure and acid center of MOR were controlled by in-situ boron doping modification and acid treatment.The main conclusions of the above studies are as follows:1.The crystallization time of MOR has an important influence on the structure,acid center distribution and carbonylation reaction performance of MOR.Characterization results show that the formation and growth of MOR crystal phases are divided into three stages:(1)the nucleation stage before 16 h;(2)the rapid growth stage of small grains between 16 h and 40 h;(3)40 h The latter is the stage of slow and stable growth of larger grains.In the stage of stable and slow growth of grains,large grain MOR grows slowly,and the defect sites with higher surface energy gradually decrease.The evaluation results show that the MOR sample with the initial crystallization time of 48 h in the stable growth stage has the highest dimethyl ether carbonylation reactivity.As the crystallization time of the MOR sample increases,the reactivity decreases,and the selectivity of methyl acetate and the selectivity of by-products increase.This shows that under steady state,the crystallization time increases in the stable growth phase,and the high energy defect sites corresponding to the high active sites on the MOR surface gradually decrease.The activity and by-products of dimethyl ether carbonylation on the MOR are mainly related to the surface high active defect sites.2.Introduced boron into the MOR system by in-situ doping,and investigated the effect of boron doping on the MOR structure,acid center and carbonylation performance.The evaluation and characterization results show that after boron doping,the unit cell volume of MOR decreases,the crystal particle size decreases and the state of aggregation appears,and the pore volume of mesopores and macropores increases.The evaluation results show that the single-pass life of the sample after boron modification is increased by 36.6%,which effectively improves the stability of the MOR carbonylation reaction.The TPO of the MOR after evaluation showed that the rate of carbon deposition of the MOR modified by boron during the carbonylation reaction was significantly slowed,and the total amount of carbon deposition decreased,indicating that the boron modification can inhibit the formation of carbon deposits to a certain extent.3.Modification of MOR by means of acid treatment.The evaluation results showed that the activity and stability of the catalyst after the MOR carrying the template agent was treated with citric acid(CA)were improved,and the stability was improved by 33.3%.The characterization results show that after treatment with citric acid,the twelvemembered ring pore acid center of MOR decreases and the mesoporous content increases.This indicates that the slowing of the carbon deposition rate of the reaction and the enhancement of the carbon holding capacity of the catalyst are the reasons for the improved catalytic stability of the catalyst after citric acid treatment. |
PDF Full Text Request