Optimal Production of Dimethyl Ether from Switchgrass-Based Syngas via Direct Synthesis

A conceptual optimal design for the production of dimethyl ether (DME) and/or power from switchgrass is proposed. A superstructure is formulated embedding two different gasification technologies, direct and indirect, two reforming modes, partial oxidation or steam reforming, gas cleaning, and composition adjustment. Next, DME is produced following direct synthesis, a novel one-step technology. The unreacted gas can be either recycled or used within a Brayton cycle for the simultaneous production of DME and power. The problem is formulated as a mixed integer nonlinear programming problem. The optimal topology involves indirect gasification followed by steam reforming. DME production is favored over power for current electricity prices. Thus, the investment cost for the production of 197 kt/yr of DME adds up to $133 million, at a price of $0.31/kg.