Trace Benzene Separation from Vinyl Acetate: A Multiscale Simulation Study

Vinyl acetate (VAc) is a kind of widely used organic raw material which is mainly synthesized by the carbide acetylene method in China. However, trace amounts of benzene impurities in the VAc product has seriously limited its application in fine chemical industry. In this work, multiscale simulation method including molecular level and process simulation are used to screen an effective metal–organic frameworks (MOFs) which could be employed in the pressure swing adsorption (PSA) process. Grand canonical Monte Carlo (GCMC) and configure bias Monte Carlo (CBMC) are combined to investigate the adsorption behavior in different MOFs: Cu-BTC, Zn-BDC, IRMOFs, and M-DOBDC. Special interactions between exposed metal sites in Cu-BTC result in greater benzene adsorption capacity than VAc. Special square channels in Zn-BDC which is close to benzene molecule also favors the adsorption of benzene. The organic chain length and adding functional groups in IRMOFs have no influence on separation selectivity of benzene over VAc. M-DOBDC series MOFs show considerable adsorption capacity of benzene under low pressure. The selectivity of benzene over VAc in Mg-DOBDC at 170 kPa is as high as 12, showing the great ability to remove trace amount of benzene from VAc product. After the screening work, Mg-DOBDC is applied to the PSA process to remove trace benzene in an annual output of 250 000 tons of VAc plant by means of Aspen Adsorption software. Six steps are designed for the PSA process, duration of each step and parameters of fixed bed are optimized. After the optimization, benzene concentration in the VAc product, the VAc recovery, and the adsorbent productivity of VAc are less than 1 ppm (wt %), 83.67%, and 31.96 mol/(kg·h), respectively. These results indicate that Mg-DOBDC is an excellent adsorbent for removing trace benzene, and the purity is able to meet the requirement of high-quality VAc product. This work would provide some guidance for the removal of trace benzene.