Screening of CO2 utilization routes from process simulation: Design, optimization, environmental and techno-economic analysis

This work aims at evaluating potential direct CO2 conversion processes through systematic screening and process simulation. Fifteen direct routes converting CO2 to carbonates or carbamates, with in situ chemical dehydration using 2-cyanopyridine (2-CP) are focused. The work covers an extensive examination (and supplement) on the physical properties, selection of promising routes, process simulation, optimization, environmental, and techno-economic evaluation. Firstly, three promising routes were selected, producing dimethyl carbonate (DMC), dipropyl carbonate (DPC), and Isopropyl N-phenylcarbamate (IPPhCM), based on three criteria: azeotropic search, product selectivity and reacting conditions. Next, the corresponding processes were simulated, optimized, heat-integrated, and systematically compared with the previously-proposed diethyl carbonate (DEC) process through environmental and economic analysis. From environmental analysis, the CO2 emission rate (CO2-e, in kg/kg-product) was 0.067, 0.088, -0.040 and -0.154 for producing DMC, DPC, IPPhCM and DEC, respectively. By reducing the excess ratio used for reaction (i.e. 2-CP/alcohol or amine/alcohol), the CO2-e improved to -0.122, -0.086, and -0.117 for producing DMC, DPC and IPPhCM, respectively. Finally, the minimum required selling prices (MRSP) at 15 % internal rate of return (IRR) were determined, with the unit price of 2-CP, 2-picolinamide (2-PA), and the reactor residence time regarded as uncertainties. The MRSPs for DMC, DPC, IPPhCM and DEC are found in the range of 1.50-4.96, 2.29-4.24, 2.07-4.06 and 1.12-2.81 (all in USD/kg), respectively. Future studies exploring the commercial availability and the regeneration of 2-CP, and the feasibility of reducing the excess ratio and the reaction residence time are considered helpful.