Eric Johnson
Like many industries, chemicals aim to cut greenhouse-gases. Braskem, Dow and Petronas target carbon neutrality by 2050; many of the rest are tagging along. So, what better process to tackle than one that accounts for one-third of the sector’s energy and carbon count (Environ. Sci. Technol., 2015, 49, 14704)?
Steam cracking supplies the ethylene and propylene that mainly go into polyolefins plus so much else. Crackers have been improving steadily – less energy, which means lower carbon – since their invention in 1930s. But while technology vendors like Chiyoda, KBR and the rest are always announcing evolutions, these won’t meet the challenge of net-zero carbon.
Just as fuels can switch from fossil to bio feedstocks, so can olefins. Most advanced is dehydration of bioethanol to ethylene. This was the world’s main route to ethylene up to the 1940s, when steam-crackers made it obsolete. In the 1980s, it was revived in China and India, both short on fossil feedstocks; then in 2010-11 by Braskem and Solvay Indupa in Brazil, also in Taiwan by Greencol. Now, the path is heating up again: Braskem will at the end of 2022 boost its Brazilian output by 60kt to 260kt/yr. Around then, the Low Carbon Ventures subsidiary of Oxy Chemical will showcase its proprietary process at demo-scale near Houston, Texas, US. Both hope to avoid the fate of Dow and Mitsui, who in 2015 announced a sugar-cane-to-ethanol-to-ethylene JV in Brazil that never materialised.
Feedstocks from waste offer another avenue. Petchem powerhouses BASF, Ineos, Neste, ÖMV and SABIC are pursuing the industry’s albatross, waste plastic (C&I, 2020, 84(6), 37). Another waste of interest is food and agricultural residues – which can be fermented into biogas (50/50 methane and CO2). America’s Siluria Technologies and China’s Dalian Institute of Chemical Physics, have focused on catalytically converting the methane directly to ethylene. The economics ‘are kind of tough,’ opines Chris Dziedziak of The Catalyst Group consultancy. Despite licensing deals with Braskem and Saudi Aramco, in 2019 Silurian folded its tent and sold its intellectual property to McDermott International. Dalian has a joint-development deal with China National Petroleum and SABIC that has yet to go beyond the lab.
More promising seems to be converting the methane first to methanol and then onward to olefins. Some 20 methanol-to-olefins (MTO) plants already run in China, albeit based on methanol from coal, but cleaner feedstocks are on the march (Rev. Chem. Eng., 2020, 36, 21). A complex under construction in Uzbekistan promises in late 2023 to start making 720kt/year of olefins from ‘stranded’ natural gas – with MTO technology from Sinopec. Methanol-from-biogas is not yet commercial, but in early 2022, Topsoe fired up a demo plant in Denmark; Oberon Fuels is looking to do so in California; and Arbor Renewables says it will start up a commercial operation in Texas by late 2023.
Then there is the idea of making ethylene from atmospheric CO2 and water vapour. US companies EcoCatalytic and Twelve, plus Germany’s Siemens, are touting their lab-scale processes, which basically work like photosynthesis, yet end in ethylene rather than glucose. Siemens is also behind the world’s first full-size plant for ‘Power-to-X’: operations at a site in Chilean Patagonia, which will begin operations in mid-2022.
‘The [conventional] process of steam cracking is not fundamentally different if heated by electricity,’ says a BASF spokesman. The German giant is working with Linde and SABIC to develop an ‘eFurnace’, stoked to 850°C by low-carbon power, that could cut the olefins’ footprint by 90%. If seed funding from the European Commission and the German government is granted, BASF says it will build a demo at Ludwigshafen in 2023, with the aim of going full-scale by 2027. The aim is not to build new plants, but to retrofit existing, fossil-fuel-fired crackers.
A similar approach is being pursued by the ‘Cracker of the Future’, a consortium of Borealis, BP, ENI, Repsol and TotalEnergies. Indeed, BASF was part of the consortium, but withdrew in late 2021, citing conflicts with its existing Linde/SABIC deal. The Future group also aims to demonstrate in 2023 and go mainstream as early as 2026.
Finally, there are Dow’s plans to capitalise on carbon capture and storage (CCS). By 2030, the company promises to start up ‘the world’s first net-zero-carbon cracker’. This, at an existing site in Alberta, will run not on bio feedstocks, but on fossil gas liquids.
The trick is CO2 from the cracker exhaust – now discharged to the atmosphere – will instead be recovered and pumped underground into permanent sequestration. Another carbon saving will come from using the cracker’s product hydrogen to displace conventional fuels onsite. While declining to discuss costs and most technical details, Dow implies that zero-carbon ethylene and derivatives will draw premium prices – something Braskem has proven with low-carbon polyethylene from Brazil.
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