Study On Modification Of Mordenite And Carbonylation Performance Of Dimethyl Ether

Carbonylation reaction is an effective way to realize carbon chain growth and synthesis of oxygenated organic compounds at the same time.The route of dimethyl ether carbonylation reduction to ethanol has become a research hotspot in recent years due to the discovery of molecular sieve catalysts.The carbonylation of dimethyl ether to methyl acetate is an important step of the process route,and mordenite(MOR)is the key of the reaction.MOR has good activity of dimethyl ether carbonylation,but it has the problems of rapid deactivation,poor stability and short one-way life.The research shows that carbon deposition is the main cause of MOR inactivation.Aiming at the problem of carbon deposition,MOR molecular sieve was modified by the combination of metal doping and adjusting the silicon aluminum ratio.The carbonylation reaction of the modified molecular sieve was evaluated.A series of characterization techniques were used to investigate the structure,acid center and carbon deposition of the molecular sieve,and the following results were obtained:Firstly,a variety of metal doped MOR molecular sieves were used for carbonylation evaluation.It was found that the catalytic activity of MOR modified by Fe,Co,Ni,Ga and other metal decreased to varying degrees compared with unmodified MOR,and the catalytic activity of MOR Modified by Cu molecular sieves was improved to a certain extent,and the best carbonylation activity was obtained.The carbonylation activity of MOR molecular sieve can be further improved by doping Cu and adjusting silicon aluminum ratio.The characterization results show that after adding Cu and increasing the silicon aluminum ratio,MOR has preferred orientation growth on the [200] crystal surface,the specific surface area and mesoporous pore volume increase,the medium and strong acid centers decrease,the strong acid centers are not affected,and the total carbon deposition after the reaction is almost unchanged.Secondly,the side reaction of MOR molecular sieve before and after modification is evaluated.With the reaction,the amount of ethane in the by-product gradually decreases,the change of methane is small,and ethylene first increases and then decreases.The thermodynamic calculation of the side reaction shows that the thermodynamics of ethane and methane is favorable.In the metal modified molecular sieve,In modified MOR has more methane,Co modified MOR has more ethylene,and low silicon aluminum will produce more methane and ethylene than MOR.Finally,the MOR is pre carbonized,and the method of "carbon deposition passivation partial carbon elimination" is used to control the amount of pre carbonization.High temperature treatment will promote the transformation of carbon deposition into graphite like carbon.Proper pre carbon deposition can shield some active centers that are easy to deposit carbon,reduce the deactivation rate and delay the one-way life of MOR molecular sieve,but the maximum conversion of dimethyl ether decreases slightly.