Synthesis Optimization And Diffusion Performance Investigation Of Mor Catalyst For Dimethyl Ether Carbonylation

Based on our country’s energy structure,development of coal-to-ethanol routes,which achieves the efficient use of coal resources,could effectively ease our country’s dependence on petroleum-based fuels.The ethanol synthesis from syngas combining carbonylation of dimethyl ether（DME）to methyl acetate（MA）and MA hydrogenation is a high-atom-economy process for ethanol production with high industrial application prospect.At present,mordenite（MOR）catalyst is widely used in DME carbonylation.The superior shape-selectivity of its eight-membered ring leads to excellent selectivity of MA,which is also accompanied by several problems such as less accessibility of active sites and limited intracrystalline diffusion.The acid properties and pore structure of zeolite are the main factors affecting its catalytic performance in DME carbonylation.This paper aims to obtain a high-performance carbonylation catalyst by optimizing the MOR synthesis and post-treatment process,and further explore effects of diffusion properties on apparent catalytic properties.The effect of different seeds on the MOR synthesis was investigated.The optimized seed was beneficial to the synthesis of high crystallinity MOR and enrichment of Br（?）nsted acids in 8-MR,which was evidenced by XRD,NH₃-TPD,Pyridine-IR,and IR spectra in the hydroxyl region.Due to its high crystallinity and more active sites,MOR-2 exhibited the highest catalytic activity,and the space time yield of the product MA reached to 278 g·kg^-1·h^-1.The hierarchical MOR samples with different textural properties were obtained by etching with NH₄F solution at different temperatures.Characterizations such as Ar physical adsorption,TEM,XRD,ICP and acidity quantification showed that the mesopores were successfully introduced with maintained crystallinity,composition and acid properties.As the etching temperature increased,the mesopore surface area and volume of the samples gradually increased.The initial space time yield of MA increased first and then decreased,and the apparent TOF_MA monotonically increased.The deactivation rate constant（k）decreased first and then increased.Combined with the acid quantity and W-P criterion,changes of the above trends were attributed to co-contribution of acidity and diffusion performance.Diffusion coefficient of coke intermediates（taking toluene as an example）was determined by zero length column（ZLC）method.The result showed that the introduction of mesopores facilitated the diffusion of coke intermediates in the samples.The change of D_eff,DME/D_eff,toluenewas consistent with the trend of k value.Consequently,the change in deactivation rate for etched samples was dependent on the co-contribution of coke formation rate and molecule diffusion property.