Techno-economic evaluation of the direct conversion of CO2 to dimethyl carbonate using catalytic membrane reactors

• Green production route for the production of dimethyl carbonate (DMC).
• Novel process for the direct synthesis of DMC from methanol and CO2.
• SPEEK membrane reactor playing a key role in enhancing the conversion.
• Energy demanding down-stream processing due to hindering azeotropes.
• Complete process design, equipment sizing and economic evaluation.

The production of dimethyl carbonate (DMC) caught more interest in the past decades due to its versatile use (e.g. as fuel additive), low toxicity and fast biodegradability. Different ‘green’ production routes are being developed to replace the conventional and rather toxic production of DMC via phosgene. The direct conversion of CO2 and methanol toward DMC is an environmental and economically interesting production route for the chemical industry.This work describes the process design of the direct conversion of CO2 to dimethyl carbonate, providing a valuable insight and a better understanding of the process limitations. In this design, membrane reactors are used for continuous removal of water by-product, in order to overcome the equilibrium limitations. The rigorous Aspen Plus simulations show that even when using an excess of methanol, the attainable conversion is low and the DMC concentration in the reactor effluent is less than 1.5 mol%. Purifying this diluted stream to the desired concentrations demands large size equipment and a substantial amount of energy (13.61 kWh/kg DMC) resulting in high investment and utility costs, thus making the process not profitable. The focus for new membrane reactors could be on the selective removal of DMC (instead of water) from the reaction area to allow for a more concentrated DMC stream.