Integrated direct dimethyl ether synthesis process based on internal cycle of CO2: Technical economy and multi-criteria evaluation for carbon capture, utilization, and storage

This study investigates a carbon-integrated direct dimethyl ether (DME) production system in which internal CO2 looping is implemented as a thermodynamic design variable rather than a separation burden. The integrated configuration comprises autothermal/dry reforming, acid gas removal (Rectisol or MDEA/PZ), direct DME synthesis, and heat recovery. Ten configurations at a fixed capacity of 5000 MTPD were evaluated under two target H2/CO ratios (1 and 2) with controlled internal CO2 recycling (λ_CO2), maintaining carbon balance deviations below 1%. System performance was assessed using carbon utilization, section-wise exergy destruction, and discounted cash-flow analysis. The carbon utilization index ranged from 0.1918 to 0.3058, while total exergy destruction varied between 953.5 and 1096.5 MW. A key finding is irreversibility relocation: at H2/CO = 1, reforming dominates exergy destruction (≈63%–67%), whereas at H2/CO = 2, synthesis becomes dominant (≈72%–78%). Techno-economic results indicate levelized costs of 480–761 USD t−1 and breakeven prices of 16.75–26.59 USD GJ−1. Under a reference gas price of 9.5 USD MMBTU−1, all cases yield negative net present values. The results demonstrate that internal CO2 looping reshapes carbon partitioning, exergy distribution, and economic performance, providing a multi-objective basis for rational process optimization.