Quantitative analysis of CO2 emissions reduction potential of alternative light olefins production processes

Abstract

Approximately 400 Mt CO₂ are emitted each year in the production of light olefins. Steam cracking of fossil feedstock is the predominant technology to produce ethylene and propylene, emitting around 1 t CO₂ per t light olefins. Most of these emissions result from the combustion of fuels to provide the required high-temperature reaction heat. Low-carbon technologies will need to be implemented to produce these light olefins. In this study, we compare the CO₂ emissions reduction potential (ERP) and electricity requirements of several of these alternative technologies. Steam crackers with electrical furnaces are limited to avoiding combustion-related CO₂ emissions and can achieve a maximum CO₂ emissions reduction of 92%. Replacement of fossil-based feedstock with CO₂ can achieve much larger CO₂ emissions reductions but requires five times more electricity. Four CO₂-to-olefins routes were evaluated: H₂O electrolysis coupled with (i) direct CO₂ hydrogenation to olefins (C²O), or with (ii) CO₂ hydrogenation to methanol coupled with methanol-to-olefins (C²M + MTO); and CO₂ and H₂O co-electrolysis to syngas coupled with (iii) CO hydrogenation to olefins (COhyd) or with (iv) Fischer–Tropsch synthesis (FTO). C²O and C²M + MTO show a similar CO₂ ERP of −2.98 t CO₂ per t olefins for an electricity requirement of 16 MW h t⁻¹ olefins. Both routes outperform the CO-based routes. C²O requires a multi-step separation to recover the light olefins, yet it requires less cooling water and exports more excess steam than C²M + MTO. The latter requires additional gas compression and an energy-intensive methanol–water distillation step. Heat integration between the hydrogenation reactions and Solid–Oxide (SO) electrolysis reduces electricity requirements by 20% compared to Proton Exchange Membrane (PEM) electrolysis.