A Novel Internal Coupling Process of a T-type Zeolite Membrane in a Distillation Column to Separate the PM/H₂O Mixture

Abstract

The recovery and purification of propylene glycol monomethyl ether (PM) could significantly enhance the economic benefits of the hydrogen peroxide to propylene oxide (HPPO) reaction to produce epichlorohydrin. However, the conventional distillation technique fails to achieve this aim due to the presence of an azeotropic mixture. To address this issue, we proposed a novel coupling process to recycle the PM component, where the membrane unit was internally embedded in the column vessel to remove water before the distillate. This concept was further verified by a designed packed column operated in batch mode. By introducing a hollow fiber T-type zeolite membrane, the PM purity in the distillate was promoted by 1.0 wt % compared with the result in the blank test, suggesting that the membrane unit improved the separation effect. To further explore the synergistic effect of the membrane unit in the internal coupling process, the process simulation was established to optimize the operation parameters of internal coupling, including membrane area, coupling position, z, and feeding stage. The results indicated that the internal coupling could efficiently achieve the defined separation target, by significantly changing the vapor–liquid equilibrium profiles. By comparing with the results in external coupling, it was found that the internal coupling method yielded a higher energy efficiency, resulting in a reduction of nearly 26% in heating energy consumption and almost 60% in condensing energy load; however, this approach required a relatively larger membrane area. The above results indicated that the internal coupling was equivalent to the external couplings, and both techniques could be used to break the azeotropic limit for separation of the PM/H2O mixture.