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

=== 11.4.1 Sector-specific Mitigation Potential and Costs ===

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Based on the general discussion of strategies across industry in [[#11.3|Section 11.3]] , this subsection focuses on the sector perspective and provides insights into the sector-specific mitigation technologies and potentials. As industry is comprised of many different subsectors, the discussion here has its focus on the most important sources of GHG emissions, that is, steel, cement and concrete, as well as chemicals, before other sectors are discussed.

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==== 11.4.1.1 Steel ====

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For the period leading up to 2020, in terms of end-use allocation globally, approximately 40% of steel is used for structures, 20% for industrial equipment, 18% for consumer products, 13% for infrastructure, and 10% for vehicles ( [[#Bataille--2020b|Bataille 2020b]] ). The global production of crude steel increased by 41% between 2008 and 2020 ( [[#World%20Steel%20Association--2021|World Steel Association 2021]] ) and its GHG emissions, depending on the scope covered, is 3.7–4.1 GtCO 2 -eq. It represented 20% of total global direct industrial emissions in 2019 accounting for coke oven and blast furnace gases use ( [[#Crippa--2021|Crippa et al. 2021]] ; [[#Lamb--2021|Lamb et al. 2021]] ; [[#Minx--2021|Minx et al. 2021]] ; Olivier and Peters 2018; [[#World%20Steel%20Association--2021|World Steel Association 2021]] ; [[#IEA--2020a|IEA 2020a]] ) (Figure 11.4 and [[#_idTextAnchor023|Table 11.1]] ). Steel production can be divided into primary production based on iron ore and secondary production based on steel scrap. The blast furnace-basic oxygen furnace route (BF-BOF) is the main primary steel route globally, while the electric arc furnace (EAF) is the preferred process for the less energy and emissions-intensive melting and alloying of recycled steel scrap. The direct reduced iron (DRI) route is a lesser-used route that replaces BFs for reducing iron ore, usually followed by an EAF. In 2019, 73% of global crude steel production was produced in BF-BOFs, while 26% was produced in EAFs, a nominal 5.6% of which is DRI ( [[#World%20Steel%20Association--2021|World Steel Association 2021]] ).

An estimated 15% energy efficiency improvement is possible within the BF-BOF process (Figure 11.8). Several options exist for deep-GHG emissions reductions in steel-production processes ( [[#Fischedick--2014|Fischedick et al. 2014]] b; [[#Leeson--2017|Leeson et al. 2017]] ; [[#Axelson--2018|Axelson et al. 2018]] ; [[#Vogl--2018|Vogl et al. 2018]] ; [[#Bataille--2020a|Bataille 2020a]] ; [[#Holappa--2020|Holappa 2020]] ; [[#Rissman--2020|Rissman et al. 2020]] ; [[#Fan--2021|Fan and Friedmann 2021]] ; [[#Wang--2021|Wang et al. 2021]] ).Each could reduce specific CO 2 emissions of primary steel production by 80% or more relative to today’s dominant BF-BOF route if input streams are based on carbon-free energy and feedstock sources or if they deploy high-capture CCS:

• '''Increasing the share of the secondary route''' can bring down emissions quickly and potential emissions savings are significant, from a global average 2.3 tCO 2 –1 per tonne steel in BF-BOFs down to 0.3 (or less) tCO 2 –1 per tonne steel in EAFs ( [[#Pauliuk--2013a|Pauliuk et al. 2013a]] ; [[#Zhou--2019|Zhou et al. 2019]] ), the latter depending on scrap preheating and electricity GHG intensity. However, realising this potential is dependent on the availability of regional and global scrap supplies and requires careful sorting and scrap management, especially to eliminate copper contamination ( [[#Daehn--2017|Daehn et al. 2017]] ). There is significant uncertainty about how much new scrap will be available and usable ( [[#Xylia--2018|Xylia et al. 2018]] ; [[#IEA--2019b|IEA 2019b]] ; [[#Wang--2021|Wang et al. 2021]] ). Most steel is recycled already; the gains are mainly to be made in quality (i.e., separation from contaminants like copper). End-of-life scrap availability and its contribution to steel production will increase as in use stock saturates in many countries ( [[#Xylia--2016|Xylia et al. 2016]] ).

'''•''' '''BF-BOFs with CCU or CCS.''' [[#Abdul%20Quader--2016|Abdul Quader et al. (2016)]] and [[#Fan--2021|Fan and Friedmann (2021)]] indicate that it would be difficult to retrofit BF-BOFs beyond 50% capture, which is insufficient for long-term emission targets but may be useful in some cases for avoiding cumulative emissions where other options are not available. However, BF-BOFs need their furnaces relined every 15–25 years ( [[#IEA--2021a|IEA 2021a]] ; [[#Vogl--2021b|Vogl et al. 2021b]] ), at a cost of 80–100% of a new build, and this would be an opportunity to build a new facility designed for 90%+ capture (e.g., fewer CO 2 outlets). This would depend upon access to transport to geology appropriate for CCS.

'''•''' '''Methane-based syngas (hydrogen and carbon monoxide) direct reduced iron (DRI) with CCS''' . Most DRI facilities currently use a methane-based syngas of H 2 and CO as both reductant and fuel (some use coal). A syngas DRI-EAF steel-making facility has been operating in Abu Dhabi since 2016 that captures carbon emitted from the DRI furnace (where it is a co-reductant with hydrogen) and sends it to a nearby oil field for enhanced oil recovery.

'''•''' '''Hydrogen-based direct reduced iron (H-DRI)''' is based on the already commercialised DRI technology but using only hydrogen as the reductant; pure hydrogen has already been used commercially by Circored in Trinidad 1999–2008. The reduction process of iron ore is typically followed by an EAF for smelting. During a transitional period, DRI could start with methane or a mixture of methane and hydrogen as some of the methane (≤30% hydrogen can be substituted with green or blue hydrogen without the need to change the process). If the hydrogen is produced based on carbon-free sources, this steel-production process can be nearly CO 2 neutral ( [[#Vogl--2018|Vogl et al. 2018]] ).

'''•''' '''In the aqueous electrolysis route''' (small-scale piloted as Siderwin during the EU ULCOS programme), the iron ore is bathed in an electrolyte solution and an electric current is used to remove the oxygen, followed by an electric arc furnace for melting and alloying.

'''•''' In the ''molten'' '''oxide electrolysis''' route, an electric current is used to directly reduce and melt the iron ore using electrolysis in one step, followed by alloying. These processes both promise a significant increase in energy efficiency compared with the direct reduced iron (DRI) and blast furnace routes ( [[#Cavaliere--2019|Cavaliere 2019]] ). If the electricity used is based on carbon-free sources, this steel-production process can be nearly CO 2 neutral. Both processes would require supplemental carbon, but this is typically only up to 0.05% per tonne steel, with a maximum of 2.1%. Aqueous electrolysis is possible with today’s electrode technologies, while molten oxide electrolysis would require advances in high-temperature electrodes.

'''•''' '''The''' '''HIsarna® process''' is a new type of coal-based smelting reduction process, which allows certain agglomeration stages (coking plant, sintering/pelletising) to be dispensed with. The iron ore, with a certain amount of steel scrap, is directly reduced to pig iron in a single reactor. This process is suitable to be combined with CCS technology because of its relatively easy to capture and pure CO 2 exhaust gas flow. CO 2 emission reductions of 80% are believed to be realisable relative to the conventional blast furnace route ( [[#Abdul%20Quader--2016|Abdul Quader et al. 2016]] ). The total GHG balance also depends on further processing in a basic oxygen furnace or in an EAF. The HIsarna process was small-scale piloted under the EU ULCOS program.

• '''Hydrogen co-firing''' '''in BF-BOFs''' can potentially reduce emission by 30–40%, referring to experimental work by the Course50 projects and Thyssen Krupp, but coke is required to maintain stack integrity beyond that.

Reflecting the different conditions at existing and potential future plant sites, when choosing one of the above options a combination of different measures and structural changes (including electricity, hydrogen and CCU or CCS infrastructure needs) will likely be necessary in the future to achieve deep reductions in CO 2 emissions of steel production.

In addition, increases in material efficiency (e.g., more targeted steel use per vehicle, building or piece of infrastructure) and increases in the intensity of product use (e.g., sharing cars instead of owning them) can contribute significantly to reduce emissions by reducing the need for steel production. The [[#IEA--2019b|IEA (2019b)]] suggested that up to 24% of cement and 40% of steel demand could be plausibly reduced through strong material efficiency efforts by 2060. Potential material efficiency contribution for the EU is estimated to be much higher – 48% ( [[#Material%20Economics--2019|Material Economics 2019]] ). Recycling would cut the average CO 2 emissions per tonne of steel produced by 60% ( [[#Material%20Economics--2019|Material Economics 2019]] ), but globally by 2050 secondary steel production is limited to 40–56% in various scenarios ( [[#IEA--2019b|IEA 2019b]] ), with 46% in the [[#IEA--2021a|IEA (2021a)]] and up to 56% in 2050 in [[#Xylia--2016|Xylia et al. (2016)]] . It may scale up to 68% by 2070 ( [[#Xylia--2016|Xylia et al. 2016]] ). CCU and more directly CCS are other options to reduce GHG emissions but depend on the full lifecycle net GHGs that can be allocated to the process ( [[#11.3.6|Section 11.3.6]] ). Bio-based fuels can also substitute for some of the coal input, but due to other demands for biomass this strategy is likely to be limited to specific cases.

Abatement costs for these strategies vary considerably from case to case and for each a plausible cost range is difficult to establish; compare this with '''Table 11.3''' ( [[#Fischedick--2014|Fischedick et al. 2014]] b; [[#Leeson--2017|Leeson et al. 2017]] ; [[#Axelson--2018|Axelson et al. 2018]] ; [[#Vogl--2018|Vogl et al. 2018]] ; [[#Fan--2021|Fan and Friedmann 2021]] ; [[#Wang--2021|Wang et al. 2021]] ). A key point is that while cost of production increases are significant, the effect on final end uses is typically very small ( [[#Rootzén--2016|Rootzén and Johnsson 2016]] ), with significant policy consequences (see [[#11.6|Section 11.6]] on public and private lead markets for cleaner materials).

'''Table 11.3 | Technological potentials and costs for deep decarbonisation of basic industries.''' Percentages of maximum reduction are multiplicative, not additive.

{| class="wikitable"
|-
! Sector

! Current intensity (tCO 2 -eq t –1 )

! Potential GHG reduction

! NASA TRL

! Cost per tonne CO 2 -eq

(USD2019 tCO 2 -eq –1 for percentage of emissions)

? = unknown

! Year available, assuming policy drivers

|-
| colspan="6"| '''Iron and steel'''

|-
| Current intensity – all steel (worldsteel)

| 1.83

|
|-
| Current intensity – ~BF-BOF/Best BF-BOF and NG-DRI (with near-zero GHG electricity)

| 2.3/1.8 and 0.7

|
|-
| Current intensity – EAF (depends on electricity intensity &amp; pre-heating fuel)

| ≥0

| Up to 99%

|
|-
| Material efficiency (IEA 2019 ‘Material Efficiency…’)

|
| Up to 40%

| 9

| Subject to supply chain building codes and education

| Today

|-
| More recycling; depends on available stock, recycling network, quality of scrap, availability of DRI for dilution

|
| Highly regional, growing with time

| 9

| Subject to logistical, transport, sorting and recycling equipment costs

| Today

|-
| BF-BOF with top gas recirculation and CCU/S a

|
| 60%

| 6–7

| USD70–130 t –1

| 2025–2030

|-
| Syngas (H 2 &amp; CO) DRI EAF with concentrated flow CCU/S

|
| ≥ 90%

| 9

| ≥USD40 t –1

| Today

|-
| Hisarna with concentrated CO 2 capture b

|
| 80–90%

| 7

| USD40–70 t –1

| 2025

|-
| Hydrogen DRI EAF c – fossil hydrogen with CCS is in operation, electrolysis-based hydrogen scheduled for 2026

|
| Up to 99%

| 7

| USD39–79 t –1 and USD46 MWh –1 d

| 2025

|-
| Aqueous (e.g., SIDERWIN) or Molten Oxide (e.g., Boston Metals) Electrolysis (MOE) e

|
| Up to 99%

| 3–5

| ?

| 2035–2040

|-
| colspan="6"| '''Cement and concrete'''

|-
| Current intensity, about 60% is limestone calcination

| 0.55

|
|-
| Building design to minimise concrete ( [[#IEA--2019b|IEA 2019b]] , 2020a)

|
| Up to 24%

| 9

| Low, education, design and logistics related

| 2025

|-
| Alternative lower-GHG fuels, e.g., waste (biofuels and hydrogen, see above)

|
| 40%

| 9

| Cost of alt. fuels

| Today

|-
| CCUS for process heating &amp; CaCO 3 calcination CO 2 (e.g., LEILAC, possible retrofit) f

|
| 99% calc., ≤90% heat

| 5–7

| ≤USD40t –1 calc. ≤USD120t –1 heat

| 2025

|-
| Clinker substitution (e.g., limestone + calcined clays) g

|
| 40–50%

| 9

| Near zero, education, logistics, building code revisions

| Today

|-
| Use of multi-sized and well-dispersed aggregates d

|
| Up to 75%

| 9

| Near zero

| Today

|-
| Magnesium or ultramafic cements d

|
| Negative?

| 1–4

| ?

| 2040

|-
| colspan="6"| '''Aluminium and other non-ferrous metals'''

|-
| Current Al intensity, from hydro- to coal-based electricity production. 1.5 tCO 2 are produced by graphite electrode decay

| 1.5 t –1 + electricity required (i.e., 10 t –1 (NG) to 18 t –1 (coal))

|
|-
| Inert electrodes and green electricity h

|
| 100%

| 6–7

| Relatively low

| 2024

|-
| Hydro/electrolytic smelting (with CO 2 CCUS if necessary)

|
| Up to 99%

| 3–9

| Ore-specific

| &lt;2030

|-
| colspan="6"| '''Chemicals (see also cross-cutting feedstocks above)i'''

|-
| Catalysis of ammonia from low-/zero-GHG hydrogen H 2

| 1.6 (NG), 2.5 (naptha), 3.8 (coal)

| ≤99%

| 9

| Cost of H 2

| Today

|-
| Electrocatalysis: CH 4 , CH 3 OH, C 2 H 5 OH, CO, olefins j

|
| Up to 99%

| 3

| Cost: elec., H 2 , CO x

| 2030

|-
| Catalysis of olefins from: (m)ethanol, H 2 and CO x directly

|
| 9%

| 9, 3

| Cost: H 2 and CO x

| &lt;2030

|-
| End-use plastics, mainly CCUS and recycling

| 1.3–4.2, about 2.4

| 94%

| 5–6

| USD150–240 t –1

| 2030?

|-
| colspan="6"| '''Pulp and paper'''

|-
| Full biomass firing, including lime kilns

|
| 60–75%

| 9

| About USD50 t –1

| Today

|-
| colspan="6"| '''Other manufacturing'''

|-
| Electrification using current tech (boilers, 90 °C –140 ° C heat pumps

|
| 99%

| 9

| Cost: elec. vs NG

| 2025

|-
| Using new tech (induction, plasma heating)

|
| 99%

| 3–6

|
| 2025

|-
| colspan="6"| '''Cross-cutting (CCUS, H''' ''2'' ''', net zero C''' ''o'' '''O''' ''x'' '''H''' ''y'' '''fu''' '''els/feedstocks)'''

|-
| CCUS of post-combustion CO 2 diluted in nitrogen e

|
| Up to 90%

| 6–7

| ≤USD120 t –1

| 2025

|-
| CCUS of concentrated CO 2 e

|
| 99%

| 9

| ≤USD40 t –1

| Today

|-
| H 2 production: steam or auto-thermal CH 4 reforming with CCS e

|
| SMR ≤90% ATR &gt;90%

| 6*, 9**

| 56% @≤USD40 t –1 chem**, ≤USD120 heat*,+20%/kg

| ≤2025

|-
| H 2 production: coal with CCUS e

|
| ≤90%

| 6

| 25–50% per H 2 kg –1

| ≤2025

|-
| H 2 production: alkaline or PEM electrolysis k

|
| 99%

| 9

| About USD50 t –1 or &lt;USD20–30 MWh –1

| Today

|-
| H 2 production: reversible solid oxide fuel electrolysis j

|
| 99%

| 6–8

| About 40USD t –1 or &lt;USD40 MWh –1

| 2025

|-
| H 2 production: CH 4 pyrolysis or catalytic cracking l

|
| 99%

| 5

| ?

| 2030?

|-
| Hydrogen as CH 4 replacement

|
| ≤10%

| 9

| See above

| Today

|-
| Biogas or liquid replacement hydrocarbons

|
| 60–90%

| 9

| Biomass USD per GJ –1 ; ≥USD50 t –1 , uncertain

| Today

|-
| Anaerobic digestion/fermentation: CH 4 , CH 3 OH and C 2 H 5 OH m

|
| Up to –99%

| 9

| Biomass cost

| Today

|-
| Methane or methanol from H 2 and CO x (CCUS for excess). Maximum –50% reduction if C source is FF

|
| 50–99%

| 6–9

| Cost: H 2 and CO x

| Today

|-
| 850°C woody biomass gasification with CCS for excess carbon: CO, CO 2 , H 2 , H 2 O, CH 4 , C 2 H 4 and C 6 H 6 n

|
| Could be negative

| 7–8

| About USD50–75 t –1 , uncertain

| Today

|-
| Direct air capture for short- and long-chain C o O x H y o

|
| Up to 99%

| 3

| Cost: E, H 2, CO x about USD94–232 t –1

| ≤2030

|}

a Data for CCS costs for steel-making: [[#Birat--2012|Birat (2012)]] ; [[#Leeson--2017|Leeson et al. (2017)]] ; and [[#Axelson--2018|Axelson et al. (2018)]] .

b Data for Hisarna: [[#Axelson--2018|Axelson et al. (2018)]] .

c Data for hydrogen DRI electric arc furnaces: [[#Fischedick--2014b|Fischedick et al. (2014b)]] and [[#Vogl--2018|Vogl et al. (2018)]] .

d Converted from EUR2018 34–68 t –1 and EUR2018 40 MWh –1 .

e Data for Molten Oxide Electrolysis (also known as SIDERWIN): [[#Fischedick--2014|Fischedick et al. 2014]] b and [[#Axelson--2018|Axelson et al. 2018]] . The TRLs differ by source, the value provided is from [[#Axelson--2018|Axelson et al. (2018)]] , based on UCLOS SIDERWIN.

f Data for making hydrogen from SMR and ATR with CCUS: [[#Leeson--2017|Leeson et al. (2017)]] ; [[#Moore--2017|Moore (2017)]] ; and [[#IEA--2019f|IEA (2019f)]] . The cost of CCS disposal of concentrated sources of CO 2 at USD15–40 tCO 2 -eq –1 is well established as commercial for direct or EOR purposes and is based on the long-standing practice of disposing of hydrogen sulphide and oil brines underground: [[#Wilson--2003|Wilson et al. (2003)]] and [[#Leeson--2017|Leeson et al. (2017)]] . There is a wide variance, however, in estimated tCO 2 -eq –1 break-even prices for industrial post-combustion capture of CO 2 from sources highly diluted in nitrogen (e.g., [[#Leeson--2017|Leeson et al. (2017)]] at USD60–170 tCO 2 -eq –1 ), but most fall under USD120 tCO 2 -eq –1 .

g Data for clinker substitution and use of well-mixed and multi-sized aggregates: [[#Fechner--2012|Fechner and Kray 2012]] ; [[#Lehne--2018|Lehne and Preston 2018]] ; and [[#Habert--2020|Habert et al. 2020]] ).

h Rio Tinto, Alcoa and Apple have partnered with the governments of Québec and Canada to form a coalition to commercialise inert as opposed to sacrificial graphite electrodes by 2024, thereby making the standard Hall-Héroult process very low emissions if low-carbon electricity is used.

i Data and other information: [[#Bazzanella--2017|Bazzanella and Ausfelder (2017)]] ; [[#Axelson--2018|Axelson et al. (2018)]] ; [[#IEA--2018a|IEA (2018a)]] ; [[#De%20Luna--2019|De Luna et al. (2019)]] ; and Philibert (2017b,a).

j See [[#De%20Luna--2019|De Luna et al. (2019)]] for a state-of-the-art review of electrocatalysis, or direct recombination of organic molecules using electricity and catalysts.

k Data for hydrogen production from electrolysis: [[#Bazzanella--2017|Bazzanella and Ausfelder (2017)]] ; [[#Philibert--2017a|Philibert (2017a)]] ; [[#Philibert--2017b|Philibert (2017b)]] ; [[#IEA--2019f|IEA (2019f)]] ; and [[#Armijo--2020|Armijo and Philibert (2020)]] .

l Data for methane pyrolysis to make hydrogen: Abbas and Wan Daud (2010). Data for hydrogen production from methane catalytic cracking: [[#Amin--2011|Amin et al. (2011)]] and [[#Ashik--2015|Ashik et al. (2015)]] .

m Data for anaerobic digestion or fermentation for the production of methane, methanol and ethanol: [[#De%20Luna--2019|De Luna et al. (2019)]] .

n Data for woody biomass gasification: [[#Li--2019|Li et al. (2019)]] and [[#van%20der%20Meijden--2011|van der Meijden et al. (2011)]] .

o Data on direct air capture of CO 2 : [[#Keith--2018|Keith et al. (2018)]] and [[#Fasihi--2019|Fasihi et al. (2019)]] .

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==== 11.4.1.2 Cement and Concrete ====

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The cement sector is regarded as a sector where mitigation options are especially narrow ( [[#Energy%20Transitions%20Commission--2018|Energy Transitions Commission 2018]] ; [[#Habert--2020|Habert et al. 2020]] ). Cement is used as the glue to hold together sand, gravel and stone aggregates to make concrete, the most consumed manufactured substance globally. The production of cement has been increasing faster than the global population since the middle of the last century ( [[#Scrivener--2018|Scrivener et al. 2018]] ). Despite significant improvements in energy efficiency over the last couple of decades (e.g., a systematic move from wet to dry kilns with calciner preheaters feeding off the kilns), the direct emissions of cement production (the sum of energy and process emissions) are estimated to be 2.1–2.5 GtCO 2 -eq in 2019 or 14–17% of total global direct industrial GHG emissions ( [[#Lehne--2018|Lehne and Preston 2018]] ; [[#Bataille--2020a|Bataille 2020a]] ; [[#Sanjuán--2020|Sanjuán et al. 2020]] ; [[#Crippa--2021|Crippa et al. 2021]] ; [[#Hertwich--2021|Hertwich 2021]] ; [[#Lamb--2021|Lamb et al. 2021]] ) (Figure 11.4). Typically, about 40% of these direct emissions originate from process heating (e.g., for calcium carbonate (limestone) decomposition into calcium oxide at 850°C or higher, directly followed by combination with cementitious materials at about 1450°C to make clinker), while 60% are process CO 2 emissions from the calcium carbonate decomposition ( [[#Kajaste--2016|Kajaste and Hurme 2016]] ; [[#IEA%20and%20WBCSD--2018|IEA and WBCSD 2018]] ; [[#Andrew--2019|Andrew 2019]] ). Some of the CO 2 is reabsorbed into concrete products and can be seen as avoided during the decades-long life of the products; estimates of this flux vary between 15 and 30% of the direct emissions ( [[#Stripple--2018|Stripple et al. 2018]] ; [[#Andersson--2019|Andersson et al. 2019]] ; [[#Schneider--2019|Schneider 2019]] ; [[#Cao--2020|Cao et al. 2020]] ; [[#GCCA--2021a|GCCA 2021a]] ). Some companies are mixing CO 2 into hardening concrete, both to dispose of the CO 2 and more importantly reduce the need for binder ( [[#Lim--2019|Lim et al. 2019]] ).

One of the simplest and most effective ways to reduce cement and concrete emissions is to make stronger concrete through better mixing and aggregate sizing and dispersal; poorly and well-made concrete can vary in strength by a factor of four for a given volume ( [[#Fechner--2012|Fechner and Kray 2012]] ; [[#Habert--2020|Habert et al. 2020]] ). This argues for a refocus of the market away from ‘one size fits all’, often bagged cements to professionally mixed clinker, cementitious material and filler mixtures appropriate to the needs of the end use.

Architects, engineers and contractors also tend to overbuild with cement because it is cheap as well as corrosion- and water-resistant. Buildings and infrastructure can be purposefully designed to minimise cement use to its essential uses (e.g., compression strength and corrosion-resistance), and replace its use with other materials (e.g., wood, stone and other fibres) for non-essential uses. This could reduce cement use by 20–30% ( [[#Imbabi--2012|Imbabi et al. 2012]] ; Brinkerhoff and GLDNV 2015; [[#D’Alessandro--2016|D’Alessandro et al. 2016]] ; [[#Lehne--2018|Lehne and Preston 2018]] ; [[#IEA--2019b|IEA 2019b]] ; [[#Shanks--2019|Shanks et al. 2019]] ; [[#Habert--2020|Habert et al. 2020]] ).

Because so much of the emissions from concrete come from the limestone calcination to make clinker, anything that reduces use of clinker for a given amount of concrete reduces its GHG intensity. While 95% Portland cement is common in some markets, it is typically not necessary for all end-use applications, and many markets will add blast furnace slag, coal fly ash, or natural pozzolanic materials to replace cement as supplementary cementitious materials; 71% was the global average clinker content of cement in 2019 ( [[#IEA--2020a|IEA 2020a]] ). All these materials are limited in volume, but a combination of roughly two to three parts ground limestone and one part specially selected, calcined clays can also be used to replace clinker ( [[#Fechner--2012|Fechner and Kray 2012]] ; [[#Lehne--2018|Lehne and Preston 2018]] ; [[#Habert--2020|Habert et al. 2020]] ). Local building codes determine what mixes of cementitious materials are allowed for given uses and would need to be modified to allow these alternative mixtures where appropriate.

Ordinary Portland cement process CO 2 emissions cannot be avoided or reduced through the use of non-fossil energy sources. For this reason, CCS technology, which could capture just the process emissions (e.g., the EU LEILAC project, which concentrates the process emissions from the limestone calciner, see following paragraph) or both the energy and process-related CO 2 emissions, is often mentioned as a potentially important element of an ambitious mitigation strategy in the cement sector. Different types of CCS processes can be deployed, including post-combustion technologies such as amine scrubbing and membrane-assisted CO 2 -liquefation, oxycombustion in a low-to-zero nitrogen environment (full or partial) to produce a concentrated CO 2 stream for capture and disposal, or calcium-looping ( [[#Dean--2011|Dean et al. 2011]] ). The IEA puts cement CCS technologies at the technology readiness level (TRL) 6–8 ( [[#IEA--2020h|IEA 2020h]] ). These approaches have different strengths and weaknesses concerning emission abatement potential, primary energy consumption, costs and retrofittability ( [[#Hills--2016|Hills et al. 2016]] ; [[#Gardarsdottir--2019|Gardarsdottir et al. 2019]] ; [[#Voldsund--2019|Voldsund et al. 2019]] ). Use of biomass energy combined with CCS has the possibility of generating partial negative emissions, with the caveats introduced in Section ( [[#Hepburn--2019|Hepburn et al. 2019]] ).

The energy-related emissions of cement production can also be reduced by using bioenergy solids, liquids or gases (TRL 9) ( [[#IEA%20and%20WBCSD--2018|IEA and WBCSD 2018]] ), hydrogen or electricity (TRL 4 according to [[#IEA--2020h|IEA (2020h)]] ) for generating the high-temperature heat at the calciner – hydrogen and bioenergy co-burning could be complementary due to their respective fast-vs-slow combustion characteristics. In an approach pursued by the LEILAC research project, the calcination process step is carried out in a steel vessel that is heated indirectly using natural gas ( [[#Hills--2017|Hills et al. 2017]] ). The LEILAC approach makes it possible to capture the process-related emissions in a comparatively pure CO 2 stream, which reduces the energy required for CO 2 capture and purification. This technology (LEILAC in combination with CCS) could reduce total furnace emissions by up to 85% compared with an unabated, fossil fuelled cement plant, depending on the type of energy sources used for heating ( [[#Hills--2017|Hills et al. 2017]] ). In principle, the LEILAC approach allows the eventual potential electrification of the calciner by electrically heating the steel enclosure instead of using fossil burners.

In the long run, if some combination of material efficiency, better mixing and aggregate sizing, cementitious material substitution and 90%+ capture CCS with supplemental bioenergy are not feasible in some regions or at all to achieve near-zero emissions, alternatives to limestone-based ordinary Portland cement may be needed. There are several highly regional alternative chemistries in use that provide partial reductions ( [[#Fechner--2012|Fechner and Kray 2012]] ; [[#Lehne--2018|Lehne and Preston 2018]] ; [[#Habert--2020|Habert et al. 2020]] ), for example, carbonatable calcium silicate clinkers, and there have been pilot projects with magnesium-oxide-based cements, which could be negative emissions. Lower carbon cement chemistries are not nearly as widely available as limestone deposits ( [[#Material%20Economics--2019|Material Economics 2019]] ), and would require new materials testing protocols, codes, pilots and demonstrations.

Any substantial changes in cement and concrete material efficiency or production decarbonisation, however, will require comprehensive education and continuing re-education for cement producers, architects, engineers, contractors and small, non-professional users of cements. It will also require changes to building codes, standards, certification, labeling, procurement, incentives, and a range of polices to help create the market will be needed, as well as those for information disclosure, and certification for quality. Even an end-of-pipe solution like CCS will require infrastructure for transport and disposal. Abatement costs for these strategies vary considerably from case to case and for each a plausible cost range is difficult to establish, but they are summarised in Table 11.3 from the following literature and other sources ( [[#Wilson--2003|Wilson et al. 2003]] ; [[#Fechner--2012|Fechner and Kray 2012]] ; [[#Leeson--2017|Leeson et al. 2017]] ; [[#Moore--2017|Moore 2017]] ; [[#Lehne--2018|Lehne and Preston 2018]] ; [[#IEA--2019f|IEA 2019f]] ; [[#Habert--2020|Habert et al. 2020]] ).

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==== 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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[[File:9827bc5727729249f43222bb4197cf55 IPCC_AR6_WGIII_Figure_11_10.png]]

'''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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