Editing IPCC:AR6/WGIII/Chapter-11 (section)

==== 11.4.1.3 Chemicals ====

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The chemical industry produces a broad range of products that are used in a wide variety of applications. The products range from plastics and rubbers to fertilisers, solvents, and specialty chemicals such as food additives and pharmaceuticals. The industry is the largest industrial energy user and its direct emissions were about 1.1–1.7 GtCO 2 -eq or about 10% of total global direct industrial emissions in 2019 (Olivier and Peters 2018; [[#IEA--2019f|IEA 2019f]] ; [[#Crippa--2021|Crippa et al. 2021]] ; [[#Lamb--2021|Lamb et al. 2021]] ; [[#Minx--2021|Minx et al. 2021]] ) (Figure 11.4 and [[#_idTextAnchor023|Table 11.1]] ). With regard to energy requirements and CO 2 emissions, ammonia, methanol, olefins, and chlorine production are of great importance (Boulamanti and Moya Rivera 2017). Ammonia is primarily used for nitrogen fertilisers, methanol for adhesives, resins, and fuels, whereas olefins and chlorine are mainly used for the production of polymers, which are the main components of plastics.

Technologies and process changes that enable the decarbonisation of chemicals production are specific to individual processes. Although energy efficiency in the sector has steadily improved over the past decades (Boulamanti and Moya Rivera 2017; [[#IEA--2018a|IEA 2018a]] ) (Figure 11.8), a significant share of the emissions is caused by the need for heat and steam in the production of primary chemicals ( [[#Bazzanella--2017|Bazzanella and Ausfelder 2017]] ) (Box 11.2). This energy is currently supplied almost exclusively through fossil fuels which could be substituted with bioenergy, hydrogen, or low or zero carbon electricity, for example, using electric boilers or high-temperature heat pumps ( [[#Bazzanella--2017|Bazzanella and Ausfelder 2017]] ; [[#Thunman--2019|Thunman et al. 2019]] ; [[#Saygin--2021|Saygin and Gielen 2021]] ). The chemical industry has among the largest potentials for industrial energy demand to be electrified with existing technologies, indicating the possibility for a rapid reduction of energy-related emissions ( [[#Madeddu--2020|Madeddu et al. 2020]] ).

The production of ammonia causes most CO 2 emissions in the chemical industry, about 30% according to the [[#IEA--2018a|IEA (2018a)]] and nearly one third according to [[#Crippa--2021|Crippa et al. (2021)]] , [[#Lamb--2021|Lamb et al. (2021)]] and [[#Minx--2021|Minx et al. (2021)]] . Ammonia is produced in a catalytic reaction between nitrogen and hydrogen – the latter most often produced through natural gas reforming ( [[#Stork--2018|Stork et al. 2018]] ; [[#Material%20Economics--2019|Material Economics 2019]] ) and in some regions through coal gasification, which has several times higher associated CO 2 emissions. Future low-carbon options include hydrogen from electrolysis using low- or zero-carbon energy sources ( [[#Philibert--2017a|Philibert 2017a]] ), natural gas reforming with CCS, or methane pyrolysis, a process in which methane is transformed into hydrogen and solid carbon ( [[#Bazzanella--2017|Bazzanella and Ausfelder 2017]] ; [[#Material%20Economics--2019|Material Economics 2019]] ; ( [[#11.3.5|Section 11.3.5]] and Box 11.1). Electrifying ammonia production would lead to a decrease in total primary energy demand compared to conventional production, but a significant efficiency improvement potential remains in novel synthesis processes ( [[#Wang--2018|Wang et al. 2018]] ; [[#Faria--2021|Faria 2021]] ). Combining renewable energy sources and flexibility measures in the production process could allow for low-carbon ammonia production on all continents ( [[#Fasihi--2021|Fasihi et al. 2021]] ). Steam cracking of naphtha and natural gas liquids for the production of olefins (i.e., ethylene, propylene and butylene), and other high-value chemicals is the second most CO 2 -emitting process in the chemical industry, accounting for another almost 20% of the emissions from the subsector ( [[#IEA--2018a|IEA 2018a]] ). Future lower-carbon options include electrifying the heat supply in the steam cracker as described above, although this will not remove the associated process emissions from the cracking reaction itself or from the combustion of the by-products. Further in the future, electrocatalysis of carbon monoxide, methanol, ethanol, ethylene and formic acid could allow direct electric recombination of waste chemical products into new intermediate products ( [[#De%20Luna--2019|De Luna et al. 2019]] ).

A ranking of key emerging technologies with likely deployment dates from the present to 2025 relevant for the chemical industry identified different carbon capture processes together with electrolytic hydrogen production as being of very high importance to reach net zero emissions ( [[#IEA--2020a|IEA 2020a]] ). Methane pyrolysis, electrified steam cracking, and the biomass-based routes for ethanol-to-ethylene and lignin-to-BTX were ranked as being of medium importance. While macro-level analyses show that large-scale use of carbon circulation through CCU is possible in the chemical industry as primary strategy, it would be very energy intensive and the climate impact depends significantly on the source of and process for capturing the CO 2 ( [[#Artz--2018|Artz et al. 2018]] ; [[#Kätelhön--2019|Kätelhön et al. 2019]] ; [[#Müller--2020|Müller et al. 2020]] ). Significant synergies can be found when combining circular CCU approaches with virgin carbon feedstocks from biomass ( [[#Bachmann--2021|Bachmann et al. 2021]] ; [[#Meys--2021|Meys et al. 2021]] ).

In a net zero world carbon will still be needed for many chemical products, but the sector must also address the lifecycle emissions of its products which arise in the use phase, for example, CO 2 released from urea fertilisers, or at the end of life, for example, the incineration of waste plastics which was estimated to emit 100 Mt globally in 2015 ( [[#Zheng--2019|Zheng and Suh 2019]] ). Reducing lifecycle emissions can partly be achieved by closing the material cycles starting with material and product design planning for reuse, remanufacturing, and recycling of products – ending up with chemical recycling which yields recycled feedstock that substitutes virgin feedstocks for various chemical processes (Rahimi and García 2017; Smet and Linder 2019).However, the chemical recycling processes which are most well-studied are pyrolytic processes which are energy intensive and have significant losses of carbon to off-gases and solid residues ( [[#Dogu--2021|Dogu et al. 2021]] ; [[#Davidson--2021|Davidson et al. 2021]] ). They are thus associated with significant CO 2 emissions, which can even be larger in systems with chemical recycling than energy recovery ( [[#Meys--2020|Meys et al. 2020]] ). Further, the products from many pyrolytic chemical recycling processes are primarily fuels, which then in their subsequent use will emit all contained carbon as CO 2 ( [[#Vollmer--2020|Vollmer et al. 2020]] ). Achieving carbon neutrality would thus require this CO 2 either to be recirculated through energy-consuming synthesis routes or to be captured and stored ( [[#Geyer--2017|Geyer et al. 2017]] ; [[#Lopez--2018|Lopez et al. 2018]] ; [[#Material%20Economics--2019|Material Economics 2019]] ; [[#Thunman--2019|Thunman et al. 2019]] ). As all chemical products are unlikely to fit into chemical recycling systems, CCS can be used to capture and store a large share of their end-of-life emissions when combined with waste combustion plants or heat-demanding facilities like cement kilns ( [[#Leeson--2017|Leeson et al. 2017]] ; [[#Tang--2018|Tang and You 2018]] ).

Reducing emissions involves demand-side measures, for example, efficient end use, materials efficiency and slowing demand growth, as well as recycling where possible to reduce the need for primary production. The following strategies for primary production of organic chemicals which will continue to need a carbon source are key in avoiding the GHG emissions of chemical products throughout their lifecycles:

'''Recycled feedstocks''' : ''Chemical recycling'' of plastics unsuitable for mechanical recycling was already mentioned. Through ''pyrolysis'' of old plastics, both gas and a naphtha-like pyrolysis oil can be generated, a share of which could replace fossil naphtha as a feedstock in the steam cracker ( [[#Honus--2018a|Honus et al. 2018a]] ,b). Alternatively, waste plastics could be ''gasified'' and combined with low-carbon hydrogen to a syngas, for example, the production and methanol and derivatives ( [[#Lopez--2018|Lopez et al. 2018]] ; [[#Stork--2018|Stork et al. 2018]] ). Other chemical recycling options include polymer selective chemolysis, catalytic cracking, and hydrocracking ( [[#Ragaert--2017|Ragaert et al. 2017]] ). Carbon losses and process emissions must be minimised and it may thus be necessary to combine chemical recycling with CCS to reach near-zero emissions ( [[#Thunman--2019|Thunman et al. 2019]] ; Smet and Linder 2019; [[#Meys--2021|Meys et al. 2021]] ).

'''Biomass feedstocks:''' Substituting fossil carbon at the inception of a product lifecycle for carbon from renewable sources processed in designated biotechnological processes ( [[#Lee--2019|Lee et al. 2019]] ; [[#Hatti-Kaul--2020|Hatti-Kaul et al. 2020]] ) using specific biomass resources ( [[#Isikgor--2015|Isikgor and Becer 2015]] ) or residual streams already available ( [[#Abdelaziz--2016|Abdelaziz et al. 2016]] ). Routes with thermochemical and catalytic processes, such as pyrolysis and subsequent catalytic upgrading, are also available ( [[#Jing--2019|Jing et al. 2019]] ).

'''Synthetic feedstocks:''' Carbon captured with direct air capture or from point sources (bioenergy, chemical recycling, or during a transition period from industrial-processes-emitting fossil CO 2 ) can be combined with low-GHG hydrogen into a syngas for further valorisation ( [[#Kätelhön--2019|Kätelhön et al. 2019]] ). Thus, low-carbon methanol can be produced and used in methanol-to-olefins/aromatics (MTO/MTA) processes, substituting the steam cracker ( [[#Gogate--2019|Gogate 2019]] ) or Fischer-Tropsch processes could produce synthetic hydrocarbons.

Reflecting the diversity of the sector, the listed options can only be illustrative. The above-listed strategies all rely on low-carbon energy to reach near-zero emissions. In considering mitigation strategies for the sector it will be key to focus on those for which there is a clear path towards (close to) zero emissions, with high (carbon) yields over the full product value chain and minimal fossil resource use for both energy and feedstocks ( [[#Saygin--2021|Saygin and Gielen 2021]] ), with CCU and CCS employed for all remnant carbon flows. The necessity of combining mitigation approaches in the chemicals industry with low-carbon energy was recently highlighted in an analysis ( [[#_idTextAnchor025|Figure 11.10]] ) which showed how the combined use of different recycling options, carbon capture, and biomass feedstocks was most effective at reducing global lifecycle emissions from plastics ( [[#Meys--2021|Meys et al. 2021]] ). While most of the chemical processes for doing all the above are well known and have been used commercially at least partly, they have not been used at large scale and in an integrated way. In the past, external conditions (e.g., availability and price of fossil feedstocks) have not set the necessary incentives to implement alternative routes and to avoid emitting combustion- and process-related CO 2 emissions to the atmosphere. Most of these processes will very likely be more costly than using fossil fuels and full-scale commercialisation would require significant policy support and the implementation of dedicated lead markets ( [[#Wesseling--2017|Wesseling et al. 2017]] ; [[#Bataille--2018a|Bataille et al. 2018a]] ; [[#Material%20Economics--2019|Material Economics 2019]] ; [[#Wyns--2019|Wyns et al. 2019]] ). As in other subsectors, abatement costs for the various strategies vary considerably across regions and products, making it difficult to establish a plausible cost range for each ( [[#Bazzanella--2017|Bazzanella and Ausfelder 2017]] ; [[#Philibert--2017a|Philibert 2017a]] ; [[#Philibert--2017b|Philibert 2017b]] ; [[#Axelson--2018|Axelson et al. 2018]] ; [[#IEA--2018a|IEA 2018a]] ; [[#De%20Luna--2019|De Luna et al. 2019]] ; [[#Saygin--2021|Saygin and Gielen 2021]] ).

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'''Figure 11.10 Feedstock supply and waste treatment in a scenario with a combination of mitigation measures in a pathway for low-c''' '''arbon plastics.''' Source: From Meys et al., “Achieving net-zero greenhouse gas emission plastics by a circular carbon economy”. Science , 374(6563), 71–76, DOI: 10.1126/science.abg9853. Reprinted with permission from AAAS.

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