Vapor separation of methanol-dimethyl carbonate mixture on SAPO-34 zeolite membrane

The separation of methanol-dimethyl carbonate (DMC) is an important but challenging process. Polymer membranes suffered from poor separation performance and stability. High performance SAPO-34 zeolite membrane was prepared on porous α-alumina supports with oil-bath heating method. Vapor separation of methanol-DMC mixtures on SAPO-34 membranes was systematically studied, including pressure drop, feed composition, temperature, flow rate, membrane degradation etc. SAPO-34 membranes demonstrated outstanding vapor separation performance, with methanol flux ~ 15 kg/(m2 h) and methanol/DMC separation factor ~ 1000 at 403 K and 0.6 MPa pressure drop for 90methanol:10DMCwt% feed. SAPO-34 membranes exhibited great stability in ~ 20 d continuous test. Methanol flux decreased substantially with time but it can be recovered to 80% of original value by a simple methanol rinse. Methanol/DMC separation factor exhibited significant increase with time, which can be attributed to the defect blocking by the chemical bonding of DMC in the defects, as verified by XPS and FT-IR analysis. Too much DMC adsorption on crystal surface hindered the free permeation of methanol. The methanol adsorption induced expansion of SAPO-34 crystals also helped shrinking defects effectively, which contributed to high separation factor. The addition of 1% water in the feed had little impact on separation performance. Compared with polymer membranes and other inorganic membranes, SAPO-34 membranes exhibited significantly improved flux and separation factor for the vapor separation of methanol-DMC mixture.