Novel comprehensive life cycle assessment (LCA) of sustainable flue gas carbon capture and utilization (CCU) for surfactant and fuel via Fischer-Tropsch synthesis
Jhuma Sadhukhan, Oliver J. Fisher, Benjamin Cummings, Jin Xuan
Abstract
This novel study presents an effective comprehensive life cycle assessment (LCA) of a novel sustainable carbon dioxide capture and utilization (CCU) system to co-produce alcohol ethoxylate (AE7), a valuable surfactant (a high-value chemical component of liquid detergents), and low-medium distillate range liquid fuel. Conventionally, AE7 is produced by reacting fatty alcohols with ethylene oxide from mostly fossil and marginally bio-based resources. This research develops novel AE7 production using carbon sources from flue gas of paper and steel industries, addressing a critical gap in the literature. The core process is Fischer-Tropsch (FT) synthesis using syngas formed by the reverse-water-gas-shift reaction, where recycled CO 2 reacts with H 2 . FT produces C11-C13 alkanes and a light-to-medium fuel co-product. The alkanes are converted into C12-C14 fatty alcohols through dehydrogenation, hydroformylation, and hydrogenation. Fatty alcohols react with ethylene oxide to form AE7. The yields (w/w) of AE7 and the fuel co-products are 3.7 % and 3.4 % for paper industry flue gas, and 8.0 % and 9.5 % for steel industry flue gas, respectively. Renewable (wind) electricity meets the hydrogen demand and electricity needs for the reactions, a total of 13.4 and 33.3 kWh/kg flue gas, respectively. The life cycle impact assessment includes global warming potential (GWP) and other impacts using ReCiPe, Impact+ , and Product Environmental Footprint methods. Baseline scenarios show GWP ranging from 2.2 to 3.6 kg CO 2 e/kg surfactant for conventional cradle-to-gate AE production systems. The new systems have GWP ranging 0.4–1.3 kg CO 2 e/kg flue gas (cradle-to-gate) using mass allocation. Meanwhile, the paper industry’s flue gas system has biogenic CO 2 , while the steel industry’s CO 2 is fossil-based. Considering the GWP reductions due to biogenic CO 2 contents, their overall GWP is 2.56 kg CO 2 e and 10.33 kg CO 2 e per kg of product (AE7 +fuel) (cradle-to-grave) using economic allocation. Thus, biogenic CCU is critical for the sustainable co-production of high-value surfactants and fuel. • A novel methodology consists of LCA of industrial flue gas utilization systems. • Life cycle impact assessment of surfactant and fuel production from CO 2 . • GWP and ReCiPe, Impact Plus and Product Environmental Footprint estimated. • Biogenic CO 2 makes the CDU CCU viable for high-value productions. • Energy integration-renewable electricity including for heating, hydrogen essential.