Quantitative analysis of CO 2 emissions reduction potential of alternative light olefins production processes

• Published in: Green chemistry : an international journal and green chemistry resource : GC 2023-08, Vol.25 (16), p.6459-6471
• Main Authors: Flores-Granobles, Marian, Saeys, Mark
• Format: Article
• Language: English
• ISSN: 1463-9262; 1463-9270
• DOI: 10.1039/D3GC01237A

Approximately 400 Mt CO 2 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 CO 2 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 CO 2 emissions reduction potential (ERP) and electricity requirements of several of these alternative technologies. Steam crackers with electrical furnaces are limited to avoiding combustion-related CO 2 emissions and can achieve a maximum CO 2 emissions reduction of 92%. Replacement of fossil-based feedstock with CO 2 can achieve much larger CO 2 emissions reductions but requires five times more electricity. Four CO 2 -to-olefins routes were evaluated: H 2 O electrolysis coupled with (i) direct CO 2 hydrogenation to olefins (C 2 O), or with (ii) CO 2 hydrogenation to methanol coupled with methanol-to-olefins (C 2 M + MTO); and CO 2 and H 2 O co-electrolysis to syngas coupled with (iii) CO hydrogenation to olefins (COhyd) or with (iv) Fischer–Tropsch synthesis (FTO). C 2 O and C 2 M + MTO show a similar CO 2 ERP of −2.98 t CO 2 per t olefins for an electricity requirement of 16 MW h t −1 olefins. Both routes outperform the CO-based routes. C 2 O requires a multi-step separation to recover the light olefins, yet it requires less cooling water and exports more excess steam than C 2 M + 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.