産業の脱炭素化に向けた5つの道筋

According to the International Energy Agency (IEA), the industrial sector accounted for a quarter of direct global energy system emissions in 2022. Reducing these emissions is urgent if the world is to limit global warming and reach net zero goals. Most importantly, under the Paris agreement, countries agreed to limit greenhouse gas emissions so that the long-term average temperature increase is limited to 1.5 °C above the pre-industrial (1850-1900) average. The IEA notes that to get on track with 2050 emissions targets, industrial emissions must decrease by 43% by 2030, compared to 2019 emissions, and continue declining thereafter.

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As decarbonization technologies such as solar panels and batteries have matured, scientists are now turning their attention to industrial decarbonization. Since industrial facilities have an average lifespan of 20 years, it’s critical that facilities installed from 2030 onward must be non-emitting, and that means industries need technological solutions now. We analyzed the CAS Content Collection^TM, the largest human-curated repository of scientific information, and found a sharp uptick in publications relating to decarbonization since 2019 (see Figure 1).

Growth in journal publications has been notable, suggesting that research is flourishing while commercialization may still be a few years away. Decarbonizing heavy industries like steel and cement production has proven challenging since these processes use extreme heat generated by fossil fuels to drive various production processes and reactions. Replacing fossil-fuel-based processes has largely been technologically and economically infeasible.

However, there is no time to lose as the world continues to break temperature records, including surpassing 1.5 °C for the first time in 2024, and experiences worsening storms, droughts, and wildfires. To help sustainability efforts, we examine five major pathways to industrial decarbonization that are now benefiting from better technologies and wider applications.

5 pathways to successful industrial decarbonization

1. Electrification: Direct fuel combustion is responsible for 73% of global industrial energy usage, while only 27% is from electricity. There is ample opportunity to electrify more industrial processes, just as transportation and heating have increasingly electrified. To make meaningful progress on emissions reductions, however, electrical sources used for industrial processes must be renewable, like wind and solar.

2. Energy efficiency: Industrial energy efficiency is mostly focused on procuring more efficient equipment, but designing integrated systems based on energy efficiency could yield up to 90% energy savings. Major considerations include steam systems and heat recovery, since these account for extensive industrial energy usage. For example, the use of oxygen-enriched air to react with fuel can ensure complete combustion and higher concentrations of CO₂ in the exhaust gases, which can then be captured before being emitted into the atmosphere.

3. Carbon capture and storage: Industrial processes like cement production use high temperatures, which are achieved with fossil fuels easily and cheaply. It has been difficult to reach these temperatures and match current methods with decarbonized energy sources. In these situations where using fossil fuels is the only viable option, industries can use carbon capture and storage (CCS), where captured CO₂ is liquified and geologically sequestered deep underground. In certain cases, captured CO₂ can be used as feedstock in chemical production.  

The global capture rate is predicted to reach between 2-12 GtCO₂/year with most of this amount captured by industries. Interest in CCS has been growing recently with over 700 projects in various stages of development around the world, but this strategy will need to be accelerated and scaled up to meet net zero goals.

4. Green fuels: Shifting to emissions-free fuels will be crucial for industrial decarbonization. These can include hydrogen, which releases no emissions when burned as a fossil fuel replacement but can be challenging to produce in a sustainable manner .  

Currently, most hydrogen is produced by methane steam reforming, but this is an emissions-intensive process. To decarbonize it, industries can either use CCS or pursue green hydrogen. This is achieved by using electricity generated by renewable sources to split water molecules into oxygen and hydrogen. The hydrogen can then be stored for future use, either as a fuel or a feedstock for green ammonia.  

Biofuels can also be used in place of fossil fuels, for example, in aviation fuel, or as a feedstock for various chemicals. These often are derived from biomass, typically agricultural waste, wood, and other organic wastes.

5. Recycling: Recycling is expected to play a major role in decreasing the world’s demand for raw materials, particularly in the steel, aluminum, and plastics industries. Metal recycling rates generally reach over 50%, but it was estimated in 2022 that just 9% of global plastics were recycled. There is an urgent need for technological innovations to improve plastics recycling processes and expand both the collection and usage of recycled materials.

Decarbonizing the three highest-emitting industries

Not all industries produce the same amount of greenhouse gas (GHG) emissions. As seen in Figure 2, the three highest-emitting industries are steel/iron, chemicals/plastics, and cement. Each of these industries can benefit from the various paths to decarbonization, and as technologies become commercially available, they will also be more economically viable. Though emissions from aluminum are currently low, its use is poised to grow due to the need of lightweight materials to improve energy efficiency (ref).

1. Steel/Iron: Electrification, CCS, green fuels. The steel industry accounts for 7% of global GHG emissions. The most used method for steel production is a blast furnace (BF) or basic oxygen furnace (BOF). Iron ore is reduced by heating it with coke (purified coal) in a BF. Further modification of the carbon content and alloying of the steel take place in a BOF. Up to 30% of recycled scrap steel (secondary steel) is also added in the BOF to limit the need for raw iron ore.  The average emissions from the BF/BOF process ranges from 1.8-2.8 tons per ton of steel.  Coal combustion used in the BF/BOF, coke used for reduction, and carburization are the major sources of CO₂ emissions.

The IEA estimates that to achieve net zero emissions by 2050, CO₂ emissions from the steel industry must decrease to 600 kg per ton of steel. Strategies to meet this goal include decreasing the use of BF from the current 70% to 30%, doubling the use of electric arc furnaces (EAFs) for scrap steel recycling, carbon capture, and using hydrogen as clean fuel. Other processes are being explored to reduce emissions from the steel industry, such as EAFs in place of BOFs and the HIsarna process to eliminate high-emissions steps in the production process. Using biofuels or hydrogen — either CCS or green hydrogen— to power BFs/BOFs is also a workable strategy:

2. Chemicals/plastics: Electrification, energy efficiency, CCS, green fuels, and recycling. Petrochemicals account for 5% of global GHG emissions and 18% of industrial CO₂ emissions. More than 85% of emissions from chemical production are 排出される 多くの製造プロセスで高温が必要とされるため、熱や蒸気を供給するために燃料が燃焼される際に排出されます。その他の主な排出源としては、化学合成のための化石燃料からの水素生成、化石燃料からの化学原料の製造、および蒸留やろ過の工程で必要とされるエネルギーが挙げられます。

ネットゼロ目標を達成するためには、業界は現在のレベルから排出量を30〜45%削減しなければなりません。必要な排出削減量のうち、 削減 プロセス最適化や、より優れた分離方法や熱管理といったエネルギー効率の改善が、25%の貢献を果たすと見込まれています。石炭から天然ガスや電気への転換が、さらに25%の貢献を果たす可能性があります。プラスチックのリサイクルと炭素回収は、それぞれ15%と35%の排出削減に貢献すると期待されています。

3. セメント：エネルギー効率、CCS、およびグリーン燃料。 セメント業界は、 セメント業界 世界の温室効果ガス排出総量の8〜9%を排出し、世界のエネルギー需要の2〜3%を消費し、産業用水取水量の9%を占めています。普通ポルトランドセメント1kgの製造により、平均して約0.86kgのCO₂ が排出されます。セメントは世界で最も使用されている材料であるため、セメント1kgあたりの製造に伴うCO₂ 排出量は他の材料よりも低いものの、その高い生産量から、セメント業界は脱炭素化において極めて重要な産業となっています。  

セメント製造にはキルニング（焼成）と呼ばれるプロセスが含まれます。これには、水と反応してコンクリートを形成する「クリンカー」と呼ばれる基材を製造するために、高温（約1500℃）が必要です。セメント製造中のCO₂ 排出の主な原因は、キルニング工程で必要な高温に達するために燃料を燃焼させることによる排出と、クリンカーの主要成分であるCaCO₂ （石灰石）がCaO（生石灰）に分解される際に発生するCO₃ の排出です。プロセスに必要な加熱量を減らすことは排出削減にとって重要であるため、エネルギー効率の向上や、避けられないCOの回収が重要となります。₂ 排出量であり、グリーン燃料への転換が必要となります。  

脱炭素化のイノベーションを促進する新たな特許

CAS コンテンツのコレクションにおいて最も増加したのは学術論文ですが、商業利用に向けた重要なイノベーションをもたらす可能性のある特許技術も数多く存在します。私たちは、近年の活動をさらに分析するために、国際特許分類（IPC）コードを使用して特許のランドスケープを作成しました（図3を参照）。脱炭素化に関連する特許は、化学・冶金と作業・輸送という2つの主要なセクションに分類されます。作業セクションには、主に化学物質や吸着剤を使用した炭素回収に関連するプロセスが含まれています。化学・冶金セクションには、鉄鋼、セメント、水素、代替燃料の製造に関連する特許が含まれています。

研究者たちは、産業の脱炭素化に向けたタイムラインがどのようなものになるかについても調査しています（図4を参照）。国によっては指定された日付よりも早くこれらの目標を達成する可能性がありますが、このフレームワークは政策立案者、業界のリーダー、科学者にとっての一般的な指針となり得ます。

重工業の脱炭素化が遅々として進まなかった理由は多岐にわたりますが、最も大きな要因は、適切な技術が存在しなかったか、経済的に見合わなかったことにあります。しかし、ここ数年で研究が活発化したことで状況は変化しつつあります。例えば、 大規模な グリーン水素施設や、電化を推進するための再生可能エネルギー源の拡大などが挙げられます。課題は依然として大きいものの、勢いは増しており、産業プロセスは排出量を削減する準備が整いつつあります。