Inorganic Membrane-based Reactive Separation and Reactant Recycle for Direct Synthesis of Dimethyl Carbonate

Dimethyl carbonate (DMC) is a promising green chemical due to its simplicity, versatility, low toxicity, high polarity, low corrosivity, and biodegradability. Further, “direct synthesis” of DMC using CO2 as a reactant offers a pathway forward to effective greenhouse gas reutilization. DMC is one of the most promising organic carbonates in terms of the range of applications.The US EPA has exempted DMC under its VOC classification rules making it a viable substitute for hydrocarbon solvents such as MEK, t-butyl acetate, etc. It has been proposed for use as a fuel additive (MTBE substitute), lithium ion battery electrolyte, an alternative methylating and carbonlylating agent to highly toxic chemicals such as phosgene and a platforming chemical for higher carbonates, polyurethanes, isocyanates, and polycarbonates. However, the commercial impact of DMC has been miniscule with worldwide production limited to <200MM lb/year or <1% of the potential 20,000MM lb/year demand from the fuel additives and polymer synthetics markets alone. Penetration of DMC into these markets is limited due to its currently high production cost, a result of the low reactor yields, and resultant high energy cost associated with product recovery and reactant recycle. To develop DMC as a commodity chemical, it is necessary to focus on solving the reactor yield and the downstream separation problems, simultaneously. In this project, MPT proposes to integrate its high-performance molecular sieving inorganic membranes into the DMC synthesis process. These membranes are ideally suited to this process, given their demonstrated high selectivity and excellent stability in high temperature aggressive chemical environments. In the first step, a membrane reactor will be deployed to simultaneously remove product water and substantially enhance the reactor conversion. In the second step, a membrane separator will be deployed to efficiently break the methanol/DMC azeotrope. Significant processing cost savings are achieved due to overlapping synergies that develop between these technologies. During the Phase I program we will be conducting bench scale testing of MPT membranes in the membrane reactor and membrane separator configurations. In the membrane reactor testing, the focus will be on determining DMC yield improvement under various reactor operating conditions. In the membrane separator testing, the focus will be on integration of the membrane reactor with the downstream distillation as a hybrid system to overcome the energy intensive azeotrope distillation. With this data, a membrane reactor and process model will be developed and technoeconomic analysis will be conducted/refined. This information will be used to establish the program technical approach in the Phase II pilot scale demonstration. Utilization of CO2 captured from power plant emissions remains a significant challenge. DMC represents a significant opportunity to tap this “no cost” reactant, with a market potential of over $3 billion/year. Further, renewable chemicals will improve US security and stability by reducing dependence upon depleting fossil oil supplies from politically volatile regions.