Life cycle assessment of plasma-assisted ethylene production from rich-in-methane gas streams†
Herein, the sustainability of plasma-assisted processes for ethylene production from rich-in-methane gas streams namely, natural and shale gas, is investigated by performing life cycle assessment (LCA). Two plasma-assisted process alternatives, a direct gas conversion to ethylene (one-step) and a stepwise gas conversion to acetylene followed by acetylene-to-ethylene hydrogenation (two-step), both previously demonstrated in the lab and modeled on a large scale, are evaluated using the SimaPro® software and ecoinvent database. Different scenarios regarding purge stream utilization and electricity sources are considered for both process alternatives. On the basis of LCA results, it is highly probable (confidence interval 93.5%) that the two-step process results in a lower carbon footprint than the one-step process. The two-step process, powered by electricity generated by wind turbines and utilizing the purge stream as the byproduct (instead of flaring it), produces the lowest carbon footprint among all studied scenarios. When natural gas is utilized as the feedstock, the two-step plasma-assisted ethylene production process is more environmentally sustainable than other peer processes (i.e. thermally driven and bio-based). When shale gas is used, greenhouse gas emissions decrease compared to natural gas, resulting in a comparable carbon footprint to the conventional (naphtha cracking) process. Further, aside from ethylene production onshore, plasma reactors can also be employed for ethylene production offshore, thereby valorizing currently wasted rich-in-methane gas streams and thus reducing global greenhouse gas emissions.