3

Potential Uses of CO₂ in Commercial Products

3.1 FRAMING, INTRODUCTION, AND SCOPE OF CHAPTER

Carbon is the central element of many manufactured products, notably plastics, fuels, and commodity chemicals; however, current production relies predominantly on fossil sources of carbon, carbon-emitting inputs such as fossil-fuel-powered heat, electricity, and transportation, and fossil-derived co-reagents such as hydrogen. These processes and, upon degradation, the embodied carbon in the products, result in greenhouse gas (GHG) emissions to the atmosphere. Emissions from chemicals and materials production and embodied carbon in products will need to be reduced to net zero for long-term sustainability. One route to net-zero emissions production of carbon-based chemicals and materials is to replace fossil sources of carbon with non-fossil-derived carbon dioxide (CO₂), and reduce to zero the emissions associated with all other inputs to the utilization process.

In the context of this report, it is useful to categorize products made from CO₂ into two tracks that are distinguished by the lifetime of the products: Track 1 with lifetime greater than 100 years and Track 2 with lifetime less than 100 years (Sick et al. 2022a). Although the exact lifetime to distinguish between the two tracks is debatable, 100 years is used here following a practice promoted by the United Nations Framework Convention on Climate Change (UNFCCC n.d.). The climate relevance of products in the tracks will be different. Track 1 products, especially concrete and aggregates, are considered durable storage options for CO₂. Likewise, most polymers have lifetimes of hundreds of years and therefore can hold carbon long enough to provide a removal-related climate benefit, if appropriately treated to prevent GHG emissions through degradation or incineration. Track 2 products, on the other hand, decompose back into CO₂ over a shorter timescale. Thus, their primary climate benefit is staked on avoiding the use of fossil carbon in their production (see Figure 3-1). CO₂ utilization can replace fossil carbon embedded in chemicals, fuels, and materials with renewable carbon from CO₂. The embedded carbon in chemicals and fuels will be released to the atmosphere upon degradation of chemicals and materials over short or long timescales, representing 450 million metric tons (MMT) carbon per year globally for chemicals and derived materials (Kahler et al. 2021), and 3,337 and 2,062 MMT carbon in oil and gas fuels, respectively, as of 2019 (Friedlingstein et al. 2022; Global Carbon Project 2021).¹ In addition to embodied carbon, emissions associated with chemical and fuel production, along with other aspects of the product life cycle, are significant. Net-zero carbon use for chemicals and fuels can be feasible, provided that all inputs sum to a zero-carbon budget on a life cycle basis.

___________________

¹ Embodied carbon in oil and gas fuels was estimated using the estimated emissions from combustion of such fuels in 2019.

The range of product categories accessible from CO₂ feedstock is very large. A 2019 National Academies study of CO₂ utilization status and research needs summarized the scope of technologies and products available for mineral, chemical, and biological processes (NASEM 2019). Mineralization processes were deemed the most highly developed potential growth areas for utilization, including carbonated precast and ready-mix concrete and aggregate materials. Chemical and biological processes are available to produce various chemicals and materials directly from CO₂, and prospects under development include one-carbon (C1), two-carbon (C2), and multi-carbon (C2+) hydrocarbons and oxygenates, monomers and polymers, and other materials. A 2016 study examined a similar scope of possible products and projected the potential annual use of CO₂ to make these products by 2030 to be between 2 and 8 gigatonnes (Gt), generating an annual revenue stream between $0.5 trillion and $2 trillion (Global CO₂ Initiative 2018). Subsequent studies reported similar magnitudes of CO₂ consumption and future market opportunity for CO₂ utilization (Biniek et al. 2020; CSIRO 2022; Hepburn et al. 2019; NASEM 2019; Sick et al. 2022b; some of which are summarized in Table 3-1). At this time, the future scope of this emerging industry is highly uncertain and thus estimates of potential will vary widely. Local needs, resource availability, and regulatory and incentive frameworks also will lead to significantly different outcomes for different regions. In general, the role of CO₂ utilization is to provide a sustainable source of carbon that can enable net-zero production of chemicals and materials, rather than contribute significantly to durable emissions mitigation (see, e.g., Mac Dowell et al. 2017).

CO₂ utilization enables net-zero or net-negative chemicals and materials production and provides opportunities to design new products and processes with preferred attributes. In some cases, especially for Track 2 chemicals, CO₂ substitutes for fossil carbon to produce the same product or products of similar function. Even in those cases, CO₂ offers opportunities to re-design products and processes, especially taking advantage of the

TABLE 3-1 Summary of Estimated and Projected Market Value and Volume of Products and CO₂ Amounts Utilized for Various Products

NOTES: This table represents a collection of available data for several broad product volume and market value studies. Absences of values indicate that the studies did not examine or make estimates for the categories. The volumes and values across different studies are independent estimates with different assumptions and are not directly comparable.

SOURCES: ^a Global CO₂ Initiative (2018); ^b Biniek et al. (2020); ^c Hepburn et al. (2019); ^d Sick et al. (2022b); ^e and Lux Research (2020).

oxygen content of CO₂ in the production of oxygenated products like polycarbonates (Zimmerman et al. 2020). For others, the introduction of carbon into these products is new, namely construction materials in Track 1 such as CO₂-cured concrete or carbonated aggregates. In addition to creating large-scale CO₂ removal opportunities, mineral carbonation to form building materials offers the chance to develop entirely new materials with new properties and performance, though these may trigger the need for extensive documentation and updated codes and standards.

Maximum growth rates of CO₂ utilization estimated in market studies have not been achieved to date, due to the high cost of CO₂ and zero-emission energy versus fossil inputs, a lack of supportive legislation and policy to incentivize production and use of net-zero carbon products, a lack of infrastructure for CO₂ and enabling inputs, and frequently a perception of immaturity of underlying technologies requiring a long duration to profitability.

Even with a supportive environment for producing net-zero carbon products, CO₂ utilization will compete with other means of reducing the lifecycle emissions of products and materials, including switching from hydrocarbon fuels to electricity and hydrogen and replacing fossil-carbon feedstocks with bio-based or recycled carbon inputs. Replacing hydrocarbon fuels with hydrogen or electricity rather than CO₂-based synthetic fuels, when feasible, requires less energy. The energy cost needed to convert CO₂ into a fuel can be two to four times the amount required to use electricity or clean hydrogen directly as an energy carrier (Bazzanella and Ausfelder 2017; Herzog 2018). Therefore, the production of hydrocarbon fuels may be motivated primarily by use cases where electricity or/and hydrogen are not (currently) a feasible option, for example, long-haul aviation. On the other hand, many carbon-based chemicals and materials cannot be substituted readily with noncarbon alternatives. Where carbon-based materials are required, fossil-free production from CO₂ (Kätelhön et al. 2019) will compete with alternative sources of carbon such as biomass and recycled products (Berg et al. 2020). Biomass feedstock, especially waste biomass as a lower-cost competitor to CO₂, is likely to be an important source of carbon in the future, but there is limited available land to derive carbon feedstocks from plants, particularly if waste biomass is being used. Recycled products are also an important carbon feedstock competing with CO₂, but even as challenges in chemical recycling are overcome, some processes will favor CO₂ as a starting material, and in some instances, it will be impractical to collect all product material for recycling. In addition, the demand for carbon-based products and associated export opportunities will continue to increase globally, as economies grow to meet the needs of billions of currently underserved people.

Development and deployment of CO₂-derived product technologies needs to be accompanied and guided by rigorous life cycle assessments (LCAs), coupled with techno-economic assessments (TEAs), to evaluate

benefits and risks to the environment as well as economic viability. LCAs and TEAs can be performed at different levels of detail appropriate to the project scope and stage, and the outcomes of such studies are inputs for decision making along the entire path from invention to full-scale commercialization. A recent international community effort developed CO₂-specific guidelines for LCAs and TEAs (Zimmermann et al. 2018), and a web resource initiated and supported by the U.S. Department of Energy (DOE) was made available in 2021 (Global CO₂ Initiative 2022a). The AssessCCUS resource includes databases of information as well as tools for conducting TEAs and LCAs. This effort begins to address 2022 guidance from the White House Council on Environmental Quality that called for consolidating and publishing a repository for LCA methodology, results, and information related to CO₂ capture and utilization (CCU) and carbon dioxide removal (CDR) (CEQ, 2022).

Choosing research directions, determining priority criteria for environmental risks, or directing policy support involves multifactor decision processes of potentially high complexity and ambiguity (Cremonese et al. 2022). For CO₂ utilization, comprehensive analyses and scenario studies are needed to identify technologies and processes that produce needed chemicals, offer environmental improvements, and have the best prospects of being cost competitive against other options for meeting the same goal (Fernández-Dacosta et al. 2017). Trade-offs need to be evaluated using a suitable unit of analysis that allows results to be compared. This applies both to comparing different CO₂ utilization production pathways and to comparing CO₂ utilization pathways with those that use other sustainable carbon feedstocks (Artz et al. 2018; Ravikumar et al. 2021b). Equally or more complex are comparisons between different products, such as concrete and chemicals, to identify the largest impact on CO₂ emissions (Ravikumar et al. 2021a), or different ways of meeting a greater goal, such as net-zero emissions to the atmosphere.

The remainder of this chapter describes in more detail the products and processes relevant for CO₂ utilization in a net-zero emissions future, in order to inform needs for infrastructure and policies described later in the report. The potential climate impact of net-zero CO₂ utilization processes and products is assessed, with a focus on either durable products that can offer long-term storage of CO₂ or nondurable products that will represent a large-scale displacement of fossil-based chemicals in a net-zero carbon economy. The chapter also enumerates needs for additional inputs such as energy, hydrogen, water, land, and facilities. As noted in Chapter 1, this report focuses on chemically transformative uses of CO₂ for a net-zero carbon future and does not include an analysis of CO₂ use for enhanced oil and gas recovery (EOR, EGR), as a process fluid (cooling, cutting, fire extinction), or for highly transient products (e.g., beverages, supercritical fluid extractions, low-temperature drying, insulation).

3.2 FUTURE SOURCES OF CO₂ FOR UTILIZATION

Chapter 1 describes the need to reduce atmospheric concentrations of GHGs; the most likely path to reduce emissions is to decarbonize the energy system via a shift from fossil-fuel combustion to zero-emissions energy conversion and storage. Decarbonization of the energy system means that most sources of CO₂ emissions today (see Section 2.1) are likely to be eliminated or significantly reduced by 2050. The sources that remain in the long term may be those that are most technically difficult or expensive to eliminate, including CO₂ emissions from the combustion of fuels for heavy-duty transportation such as aviation and shipping, and industrial process emissions such as those from steel or cement manufacturing, among others. Some of these emissions may be from combustion of fossil fuels, representing linear flows of carbon from the ground to the atmosphere, and some may represent circular flows of carbon into and out of the atmosphere. A 2021 National Academies report on accelerating deep decarbonization in the United States estimated that there would be a constant level of remaining CO₂ emissions at about 5 percent of 2005 levels, or about 300 MMT CO₂, in a net-zero emissions scenario for 2050 (NASEM 2021a). The same report also noted that two comprehensive modeling studies of pathways for decarbonization each included >500 MMT of carbon capture and storage (CCS) in the United States per year (DDP n.d.; Larson et al. 2021). A 2022 study of active carbon management summarized several modeling studies’ requirements for carbon removal, finding a range of ~500 MMT to ~8 Gt carbon removal required annually worldwide to reach net-zero goals (ITIF 2022). Another method to estimate the possible scale of remaining emissions in a decarbonized future is to consider the “hard to abate” sectors such as aluminum, plastic, steel, and cement, as addressed by the Mission Possible study. That study estimated that the remaining global emissions for those products in a circular carbon scenario would be 5.6 Gt CO₂ per year, 0.8 from aluminum, 0.9 from plastics, 1.9 from steel, and 2.0 from cement (Energy Transitions Commission 2018).

The remaining CO₂ produced in a net-zero system is likely to have multiple potential fates, including CO₂ utilization for durable storage (Track 1; see Figure 1-3-1) or circular processes (Track 2), but also CCS or non-utilization negative emissions processes such as land- or ocean-based enhanced weathering. Remaining fossil emissions can only be used sustainably for durable Track 1 products, while biogenic, direct air capture (DAC), and direct ocean capture (DOC) sources can be used sustainably for either Track 1 or Track 2 products. LCAs of complete CO₂ utilization systems will determine a particular product’s carbon footprint, which includes considering the emissions impact of the CO₂ source, as it relates to the product’s life cycle from sourcing of materials through manufacture, processing, use, and disposal. Such analyses require materials and processes to be accounted for and attributed, but that does not necessarily mean that different CO₂ sources must be segregated according to their emissions impact. As with other commodities, sources of CO₂ can be mixed, and the origin and fate of any particular molecule of CO₂ need not be specifically known, as long as reliable bookkeeping allows for appropriate attributions to be made and the balance known and accounted for.

For the circular processes generating Track 2 products, where carbon from CO₂ replaces fossil-origin carbon, CO₂ utilization will compete with other potential sustainable carbon feedstocks including biomass and recycled materials. The interplay between these carbon feedstocks is beginning to be explored, particularly with regard to their role in “de-fossilizing” the chemical industry (Bazzanella and Ausfelder 2017; Gabrielli et al. 2020; Lange 2021). Recycling used carbon products can be a first step toward a circular economy, but since it inherently cannot achieve 100 percent efficiency, meeting the demand for chemical products will require additional carbon inputs from biomass or CO₂ (Lange 2021). Among different routes to produce a carbon-neutral product, trade-offs exist between requirements for land, scarce materials and minerals, and water (Gabrielli et al. 2020). Efforts toward developing a circular economy are particularly strong in Europe, as evidenced by the European Commission’s Circular Economy Action Plan released in 2020 (EC 2020). A detailed analysis of the European chemical industry found that achieving carbon neutrality to meet the European Commission’s larger climate goals would require innovative research and development efforts, including through long-term public–private partnerships to facilitate deployment and de-risking of new technologies (Bazzanella and Ausfelder 2017). Other recommended policies to promote de-fossilizing the European chemical industry included establishing central, open-access databases for (1) LCA studies of low-carbon technologies and (2) carbon sources (biomass, CO₂, and other gases) and existing infrastructure (Bazzanella and Ausfelder 2017).

3.3 POTENTIAL UTILIZATION PRODUCTS AND PROCESSES

Going forward, transformations of CO₂ are likely to expand dramatically beyond the current limited set of chemically or biologically advantageous chemicals, described above, in order to synthesize many net-zero or net-negative carbon-containing products. Table 3-2 and the section that follows summarize classes of materials to consider for future CO₂ utilization, drawing from a comprehensive research status assessment published by the National Academies in 2019. When planning infrastructure for future CO₂ utilization, however, it is useful to consider not only what products can be made from CO₂, but also what products will be a high priority in a future net-zero economy, and what fraction of the product market will be made with carbon from biomass and recycling. Section 3.5 highlights priority technologies for a net-zero future.

TABLE 3-2 Summary of Major Potential CO₂ Utilization Opportunities Including Utilization Process and Infrastructure Aspects

3.3.1 Construction Materials

3.3.1.1 Concrete

Concrete materials offer a particularly attractive opportunity for CO₂ utilization. With an estimated annual global production of 20–40 Gt by 2030 (see Table 3-1) and resulting durable CO₂ use of up to 1.41 Gt per year by 2050, the potential CO₂ utilization could be at a climate-relevant scale. Furthermore, CO₂ use in concrete production results in durable conversion to solid Track 1 materials and thus constitutes a CDR process. CO₂ incorporation into concrete can occur via a variety of mechanisms, including curing via carbonation of the cement or supplemental cementitious material, as well as the use of fillers and aggregates that themselves have been manufactured from minerals or waste materials by carbonation with CO₂ (Hills et al. 2020; Woodall et al. 2019). An example of a mineral carbonation reaction is CO₂ interacting with portlandite, an alkaline mineral, to produce calcite, the mineral carbonate product, and water, Ca(OH)₂ + CO₂ à CaCO₃ + H₂O. This is a thermodynamically favored and exothermic reaction at ambient pressure and temperature.

The amount of CO₂ incorporated into the material during curing varies substantially between so-called precast concrete products (>1 percent by mass) and ready-mix concrete (<1 percent by mass). Although the methods differ in applications and performance, given suitable production conditions, both can yield concrete materials that exhibit higher compressive strength. In building applications where compressive strength is important, then the same structure could be built with less concrete (Monkman and MacDonald 2017; Ravikumar et al. 2021b). Note that cement curing with CO₂ reduces the pH of the resulting concrete compared to traditional concrete, which could be detrimental if steel reinforcements are used in the concrete, since corrosion of steel is suppressed only at higher pH levels. Solutions to this potential shortcoming could include use of alternative concrete materials that

seek to avoid the need for most, if not all, steel reinforcements via increased ductility and self-healing capability (Li 2019) or replacing steel rebar with sustainably sourced and produced carbon fiber bars. Concrete with modified properties often results in conflicts with existing codes, standards, and approved materials lists for procurement, making the introduction of these new concretes more difficult. Additionally, conventional and CO₂-cured concrete absorb CO₂ from the ambient air, so there has been some question of the impact of initial CO₂ curing on the total lifetime absorption of CO₂. Continued curing of concrete during its service life is slow and dependent on many factors, and quantitative understanding of the impact of CO₂-curing concrete during construction on future CO₂ uptake is not well understood (Zhang et al. 2020).

3.3.1.2 Aggregates

As with concrete materials, the carbonation of minerals and selected waste materials offers Track 1–type CO₂ utilization opportunities, that is, providing durable storage of CO₂. An inorganic material with sufficient alkalinity, typically from available Ca²⁺ or Mg²⁺ or their oxides, will react with CO₂ to form durable carbonates that could be considered for use as aggregates, such as in concrete production, as a substitute for gravel, or as fillers in paper or porcelain production, as illustrated in Figure 3-2 (La Plante et al. 2021; Woodall et al. 2019). Materials such as steel slag, cement kiln dust, and fly ash contain a significant amount of alkaline material readily available for direct reaction with CO₂, while some minerals require chemical processing to make the alkaline materials available. CO₂ dissolved in natural bodies of water can also be utilized to form inorganic carbonates. Such processes also have been designed as chemical looping processes with the purpose of capturing CO₂ (Adánez and Abad 2019).

3.3.2 Chemicals and Fuels

Using chemical or biological processes, CO₂ can be converted into various carbon-based chemicals and/or fuels. Present global efforts focus on converting CO₂ into C1 and C2 materials with single or multiple steps. The 2019 National Academies’ assessment of CO₂ utilization status and research needs identified major opportunities for chemical and fuel formation via CO₂ utilization. Figures 3-3 and 3-4 show the major products accessible via chemical and biological routes, respectively.

3.3.2.1 C1 Compounds

C1 compounds are important targets for CO₂ utilization because they are major commodity chemicals or intermediates and are more easily chemically synthesized from CO₂ than chemicals that require the formation of carbon-carbon bonds. CO₂ could be converted directly into partially or fully hydrogenated C1 compounds such as formic acid (HCOOH), methanol (CH₃OH), and methane (CH₄), as well as other important C1 products such as carbon monoxide (CO) and urea ((H₂N)₂CO). Many of these products are used on their own as is or for industrial processes, and some serve as feedstocks for other chemical syntheses.

Urea, an input to fertilizer production and other industrial processes, is currently the largest global chemical consumer of CO₂, and urea synthesis is expected to remain a major consumer. Carbon monoxide is also an important intermediate product of CO₂ utilization, because it may become an important intermediate to sustainable fuel production via Fischer-Tropsch pathways, or for other chemical processes, in a net-zero emissions future. Of the partially and fully hydrogenated products of CO₂, methane and methanol could serve as energy carriers; however, the toxicity of methanol may limit its distributed uses (chemeurope n.d.; IRENA and Methanol Institute 2021). Methanol and formic acid are commodity chemicals and could serve as intermediates for other sustainable chemical and fuel production, including methanol-to-gasoline via, for example, the Mobil zeolite catalysis process.

3.3.2.2 C2+ Compounds

C2+ compounds are important targets for CO₂ utilization because they constitute fuels, commodity chemicals, and chemical feedstocks. Key C2 compound targets are ethylene, ethanol, oxalate, and oxalic acid. Other C2+ compounds that could be synthesized from CO₂ include alcohols, carboxylic acids, fuels, pigments, and proteins. Both chemical and biological systems can produce C2+ chemicals, with biological systems being especially adept at forming multicarbon products. For example, a process using microbes to convert CO₂ to ethanol has been commercialized (Köpke et al. 2011; McCoy 2022). In addition to ethanol, C2+ products accessible via biological processes include various alcohols and hydrocarbons and their mixtures, diols, and carboxylic acids, particularly carboxylic acids that are also metabolic biomolecules. Both chemical and biological processes can produce individual chemicals and mixtures that may be used as fuels, such as C2–C8 hydrocarbons and alcohols. Processes to create synthetic fuels and biofuels from CO₂ can serve the potential markets for sustainable fuels for heavy-duty transportation, particularly aviation, and for storage of renewable energy in chemical bonds (so-called Power-to-X).

3.3.3 Polymers, Polymer Precursors, and Composites

Polymers and polymer precursors are high-demand commodities. The global market for polymers is expected to grow 5.1 percent annually and will reach more than $1 trillion by 2030 (Research and Markets 2020). The major driver of the rapid market growth has been the fast transfer from reusable packaging to one-time utilization of polymer-based plastics. While there are efforts to reduce single-use plastics, some single-use, disposable plastic requirements will remain, especially for medical applications. Other polymer uses include in fibers, rubbers, and fabrics, and for some durable plastic applications, such as materials in vehicles and appliances.

Chemical syntheses of polymers from CO₂ can occur via direct or indirect routes. CO₂ is directly incorporated into aliphatic polycarbonates as carbonate groups via copolymerization with epoxides, or indirectly incorporated via conversion to other monomers, such as methanol, carbon monoxide, ethylene, organic carbonates, or urea (NASEM 2019). CO₂ integration into polyols to produce polyurethanes has been demonstrated and scaled to pilot-size plants (Langanke et al. 2014). Benzene may be another polymer precursor of interest, as it is currently used to synthesize derivatives that are polymerized to form polystyrene and synthetic rubber, among others. Only a part of the carbon in polycarbonates is CO₂-derived when CO₂ is copolymerized with epoxides. Research is exploring renewable feedstocks such as cyclohexadiene oxide, limonene oxide, and α-pinene oxide. CO₂-derived polymers can be modified for more applications by blending with natural and synthetic compounds, integrating with fillers, and crosslinking (e.g., vulcanization).

In addition to chemical means of producing polymers from CO₂ utilization, biological systems can produce polymer precursors and biopolymers. Biologically derived polymer precursors can be used to synthesize polyesters, typically via an esterification reaction using a four-carbon dicarboxylic acid monomer and a diol monomer. Many dicarboxylic acids have been thoroughly investigated as valuable fermentation products that can be made efficiently in various microorganisms. Most of these dicarboxylic acids are found in the citric acid cycle and include succinate, fumarate, and malate. Other carboxylic acids of note include 2,5-furan dicarboxylic acids such as 2,5-dioxopentanoate. Research into the microbial production of the diol monomers is still in its infancy, including of 2,3-butanediol and 1,3-propanediol, but the promise of making industrially viable bioplastics has led to increased research investigating the production of various diols. Other biological polymer precursors include ethylene, for making polyethylene (NASEM 2019). Cyanobacteria can also produce biodegradable polymers, especially polyhydroxy alkanoates, and work is ongoing to produce this material from CO₂, rather than sugars (Troschl et al. 2017).

3.3.4 Elemental Carbon Materials

Conventional and advanced carbon materials with 0-3D structures, for example, carbon quantum dots, carbon nanotubes, graphene, graphite, amorphous carbon, carbon fiber, carbon black, and carbon-carbon composites, offer opportunities for advanced properties and new uses. The carbon materials are stable, although their stabilities are affected by the conditions in which they are utilized. The markets of carbon quantum dots, carbon nanotubes, graphene, graphite, amorphous carbon, carbon fiber, carbon black, and carbon-carbon composites in 2020 were $0.652B (Mordor Intelligence 2021), $0.877B (Emergen Research 2022), $0.286B (Fortune Business Insights 2022), $13.6B (Fortune Business Insights 2021), $0.226B (Research Reports World 2021a), $16.0B (Global Market Insights 2021), $2.523B (Research Reports World 2021b), respectively. Markets for carbon materials are expected to rapidly increase. A recent study of CO₂ utilization potential that examined carbon black estimated a market value of $14B–$66B in 2050 and a potential for CO₂ use of between 40 and 200 MMT (Sick et al. 2022b). Outside of carbon black production, technologies for the conversion of CO₂ to other carbon materials are less mature, and market projections are difficult. Carbon materials are rich in structure, texture, and properties. Zero-dimensional, or 0-D, carbon materials include graphene quantum dots, carbon quantum dots, nano-diamond, fullerenes (e.g., C60), carbon black, and carbon-coated metal nanoparticles. Representative 1D, 2D, and 3D carbon materials include carbon nanotubes and carbon nanofibers; graphene; and carbon foam and expanded graphite, respectively. Different dimensional materials have correspondingly different applications based on their structure and properties. For example, due to their tiny size, quantum confinement effects, desirable properties, and biocompatibility, 0D carbon materials have great potential in sensing applications (Uygun and Uygun 2020; Wang et al. 2020). 1D carbon nanotubes and 2D graphene are being explored for a plethora of advanced technologies. Three-dimensional hierarchical carbons are inexpensive, lightweight, have a high specific surface area and well-ordered channels, and have outstanding electronic and ionic conductivity, and thus are promising materials for energy conversion and storage for high-strength material applications. Carbon black applications range from filler materials, for example, for tires and toners, to additives for concrete. Using carbon black as a filler in durable materials offers opportunities for growing Track 1 type utilization of CO₂ with durable carbon storage. Finally, carbon-carbon composites, made from carbon fiber and graphite, are lightweight and very strong, enabling their use as structural materials in vehicles and buildings.

3.3.5 Niche Products: Diamonds, Perfumes, and Liquor

Consumer-facing products made with CO₂ might not have a large CO₂ utilization potential by volume but can serve as signaling products to increase consumer familiarity and comfort with CO₂-derived products (Arning et al. 2020; Lutzke and Árvai 2021). Examples of such products include diamonds, high-purity ethanol for the production of perfumes and vodka, personal care products, and food (Aether n.d.; Air Protein 2022; Gallon 2022; Kiverdi 2019; Köpke et al. 2011; Pace and Sheehan 2021). In some cases, these products also may provide a greater profit margin than the respective commodity chemicals or intermediates and may allow producers to successfully commercialize other higher-volume processes in tandem to bring down overall costs to compete in a larger market.

3.4 EMERGING, PILOT, AND COMMERCIAL FACILITIES UTILIZING CO₂

In 2016, less than 200 active entities were identified as working on CO₂ utilization (Global CO₂ Initiative 2018) and respective technology readiness levels were mostly below 5. Since then, more developers have entered the field, but the numbers are only now beginning to grow more rapidly. AirMiners and the Circular Carbon Network keep listings of carbon capture, utilization, and storage (CCUS) developers, which include 403 companies (as of May 13, 2022) that work on capture technologies or services, or utilization (AirMiners 2022; Circular Carbon Network 2022). A visual database that includes additional information, such as publications and policies, is also available (Global CO₂ Initiative 2022b). Figure 3-5 shows locations of startup CO₂ utilization companies in the United States.

3.5 PRIORITY NEEDS FOR CO₂-DERIVED PRODUCTS THAT COULD CONTRIBUTE TO A NET-ZERO CARBON FUTURE

3.5.1 CO₂-Derived Product Priorities

Products from CO₂ utilization that will be of highest importance and significance in a net-zero carbon future (IPCC 2022) include Track 1 materials that offer durable CO₂ storage and Track 2 materials for which the climate benefit comes from replacing fossil carbon with CO₂-based carbon in a circular fashion for carbon-containing products that continue to be necessary and desirable. These products are summarized in Table 3-2, above. Even-

tually, products in both tracks could conceivably displace the incumbent products completely. However, this outcome will depend on many factors related not only to manufacturability, cost, and other externalities, but also to the development of alternative processes and products that may replace incumbent fossil-carbon products. Examples of such alternative products include electricity and clean hydrogen as energy carriers for mobility applications.

3.5.2 Requirements for Other Inputs and Feedstocks

Success for CO₂ utilization depends not only on access to CO₂, but also on an array of other inputs and feedstocks, all of which must contribute to a net-zero or net-negative system. In particular, CO₂ utilization systems require scale-up of carbon-emission-free energy for both utilization processes and other parts of the CO₂ utilization system, including capturing and processing (separating and purifying) CO₂, generating other inputs, and transporting reactants and products. Additionally, some processes may require clean hydrogen, water, and land. Large-scale deployment of CO₂ conversion technology could be problematic if the technology relies on catalysts that require difficult-to-source and -secure access to raw materials (including some metals).

3.5.2.1 Electricity and Fuel Requirements for Carbon Capture

Figure 3-6 shows the electric and fuel energies, which, summed together, are required to capture CO₂ from various sources. For point sources, the amount of electric energy and/or fuel required for carbon dioxide capture and storage (CCS) is taken from the 2019 National Petroleum Council Carbon Capture study. For DAC, the energy requirements for liquid and solid capture come from IEA (2022).

Capital costs for carbon capture depend on CO₂ concentration and pressure of the waste gas stream and vary by more than 10-fold for the industrial processes shown. For all technologies other than DAC, the energy required

for CO₂ capture is less than 20 percent of the energy released via fossil-fuel combustion that generates the CO₂ (e.g., 18 GJ/ton of CO₂ released from methane combustion). Because of very low (~420 ppm) CO₂ concentrations in air, DAC requires a greater amount of energy than post-combustion carbon capture (IEA 2022). Current DAC research therefore is examining use of waste heat, or pressure or humidity swings, to improve the return on energy investment. Figure 3-6 shows that selecting a CO₂ source is important in assessing the electric power and fuel requirements for capture. CO₂ also must be captured from the fuel used in process heating and electricity generation. In the future, as electrical grids decarbonize, low- or zero-carbon electricity may replace the fuel portion of energy for capture (Müller et al. 2020).

3.5.2.2 Hydrogen Requirements for CO₂ Utilization Products

Once the CO₂ is captured, many different products can be made. Figure 3-7 depicts the inputs of hydrogen required for various classes of products formed based on reaction stoichiometries. Less hydrogen is required for materials that incorporate oxygen into the final product.

3.5.2.2.1 Electricity and Feedstock Requirements for Hydrogen Production

Figure 3-8 shows a tabulation of the amount of water, electricity, and natural gas to make clean hydrogen via water electrolysis, steam methane reforming (SMR), autothermal reforming (ATR), partial oxidation (POx) of methane, and methane pyrolysis (MP). Multiplying these inputs per unit of hydrogen by the hydrogen consumption per ton of product (see Figure 3-7) yields the inputs required per ton of final product. Note that hydrogen can be manufactured on-site or remotely and supplied by pipeline, truck, or rail. Chapter 4 discusses the infrastructure needs to deliver hydrogen and electricity to the utilization site.

The endothermic SMR process involves the following chemical reaction:

SMR: CH₄ + H₂O → CO + 3H₂.

The exothermic partial oxidation (POx) reaction is

POx: CH₄ + ½ O₂ → 2H₂ + CO.

Autothermal reforming seeks to balance exothermic and endothermic reactions to be energy neutral (Luque and Speight 2015):

ATR: CH₄ + ¼ O₂ + ½ H₂O → CO + ⁵/2 H₂.

CO produced in the above processes can be reacted with water to form more H₂ via the mildly exothermic water-gas shift (WGS) reaction:

WGS: CO + H₂O ⇌ CO₂ + H₂.

Though this section is about production of hydrogen as an input to CO₂ utilization, it should also be noted that the WGS reaction is a reversible equilibrium and can be used to convert captured CO₂ to CO via the reverse, or “backward,” reaction. CO in mixtures with H₂ constitutes “synthesis gas,” from which the entire fuels and petrochemical economy can be reproduced via Fischer-Tropsch synthesis (FTS) or methanol synthesis (plus subsequent conversion reactions). FTS and methanol synthesis are fully developed commercial processes that have been practiced for more than 100 years, at scales equivalent to full commercial petroleum refineries (e.g., gas-to-liquids production in Qatar). While catalysts are known and demonstration facilities have been operated, the reverse WGS reaction is the only step that is not fully optimized and practiced at commercial scale to enable CO₂ utilization, but technology readiness is already at a high level. Existing technology thus is proven and demonstrated for use of CO₂ as a full replacement for the fossil-based fuels-and-chemicals economy, if desired.

To avoid formation of gaseous CO₂ product, endothermic MP can be conducted to form solid carbon via

MP: CH₄ → C + 2H₂.

The process has been practiced for nearly a century to form carbon black or sometimes hydrogen. Current research and development (R&D) seeks to efficiently and continuously co-produce both, including formation of structured carbons for building materials and generation of hydrogen as an energy carrier for the clean energy input needed to drive the endothermic reaction. A portion (50 percent) of the hydrogen generated can be used for this purpose. Technology varies widely from thermal to thermo-catalytic, to plasmas.

The above stoichiometric reactions do not describe the full inputs required to generate hydrogen. Required water inputs can increase up to 10-fold above the stoichiometric need due to water purification (e.g., for electrolysis), treatment, and process cooling steps (Blanco 2021; Lampert et al. 2015, 2016), as well as the need to inject additional water (steam) to prevent coking of catalysts and equipment for natural gas–based synthesis. A similar problem holds for energy and hydrogen inputs above the thermodynamic or stoichiometric minimum. SMR requires energy inputs to run process equipment and heating steps for carbon capture, in addition to driving the endothermic reaction itself. ATR seeks to combust a portion of the natural gas feed to provide the endothermic reaction heat, but also requires electricity and heat (for capture solvent/sorbent regeneration) to run carbon capture, as well as water feed and final product purification steps. POx combusts additional natural gas feed to produce excess heat, which is used to generate electricity to power all process steps, such that all CO₂ is generated in one stream for capture, reducing capital costs (Liu 2021). If individual input materials and processes are net-emitting, then they can be paired with a separate, verifiable negative emissions process (e.g., DAC plus storage), which will allow the entire system to be net-zero or net-negative emissions.

3.5.2.3 Enabling Inputs Required for Mineral Products

Steel slag, cement kiln dust, fly ash, or some mined minerals (serpentines) can react exothermically with CO₂ to create valuable products (cements, aggregates). Crushing, grinding, and water exposure pretreatment of native minerals makes suitable cations available for reaction with CO₂ and requires relatively little energy. The reaction between CO₂, water, and the pretreated minerals is exothermic and also requires little energy input, so the total energy consumption needed for CO₂ mineralization is low (Dipple et al. 2021; Woodall et al. 2019). As discussed further in Section 4.4, concrete and aggregate production and use are highly distributed due to the difficulty in transporting both inputs and produced materials, which are large volume and heavy, and the inherent distribution of the final products, which are used in a wide variety of buildings and infrastructure, including roads and other major public works projects.

The primary enabling infrastructure requirement for carbon mineralization processes is the heavy-duty power for mining and comminution of minerals to a particle size that can react with CO₂ at acceptable rates. Hydrogen could be a zero-carbon fuel option for mining trucks and equipment, as battery-electric vehicles may lack the power density needed for the very heavy-duty cycles of equipment. Hydrogen can be supplied directly by pipeline to a refueling terminal, or can be generated on-site by supplying water and clean electricity from the grid. Running handling equipment and operations will require some additional electricity. For solids handling, these power requirements are generally higher per ton of product than from a facility producing a gas or liquid product.

3.5.3 Consumer Sentiment

Public awareness of the origin, production methods, and even the component ingredients in many everyday products is low. Acceptance or rejection of products and services therefore might be guided by perceptions and misconceptions. It is thus critical to include research on societal aspects in any planning for technology development and deployment (Buck 2016). Risk-benefit assessments point to CCU acceptance as being influenced by perceptions of CCS (Arning et al. 2020, 2021; Engelmann et al. 2020). Nature-based solutions for carbon removal might find preferential approval over technology (Wolske et al. 2019). A representative survey of adult U.S. citizens showed that a two-thirds majority would be inclined or comfortable with using CO₂-made products. Subtle differences with respect to product type, gender, and political preference of those surveyed had a mild impact on the responses (Lutzke and Arvai 2021).

3.5.4 Future Market Volumes and Current Price Points

Estimates for market penetration (rates) and price points for CO₂-derived products depend on supporting policy, competition from bio-based carbon sources, and alternative solutions, for example, electricity or hydrogen as an energy carrier instead of hydrocarbons. CO₂ utilization will compete with other sources of carbon (biomass, recycling) as well as other technologies to replace the current use of carbon-based products, for example, electricity or hydrogen for mobility applications. Table 3-1 describes various market projections for products of CO₂ utilization.

Projections for market volumes and CO₂ utilization potential vary widely between published studies, sensitively reacting to the assumptions made regarding technologies, cost, and other competing factors. A recent study projects CO₂ utilization for production of aggregates and precast concrete to grow substantially by 2050, reaching between 1 and nearly 11 gigatonnes per year (see Figures 3-9 and 3-10). While market shares for aggregates are projected to only reach 14–18 percent by 2050, CO₂-cured precast concrete could capture as much as 75–80 percent of the market in 2050. Figure 3-11 shows projections of market size through 2040 for various CO₂ utilization products, including building materials, fuels, polymers, chemicals, protein, and carbon additives.

3.6 NEAR-TERM OPPORTUNITIES, SYNERGIES, AND NEEDS

Significant opportunities exist to use CO₂ successfully at large scale to make products. While all of these products can have commercial value, the climate benefit from their production depends on their lifetime, as noted in Section 3.1. Categorizing products as Track 1 or Track 2 is a convenient way to identify what the climate benefits of a given product will be. Responsible launch of the CO₂ utilization industry requires that life cycle assessments in combination with societal impact and techno-economic assessments accompany and guide decision making from early stages of research to commercial deployments.

A CO₂ utilization industry as a whole does not yet exist, but components of it are emerging. Technology readiness for several product categories is at a level where commercial deployments are imminent. Supply and value chains are not established, and work is needed to ensure that infrastructure investments for CO₂ capture and transport strategically and synergistically enable CO₂ capture and utilization. Specifically, the government support enacted in the Infrastructure Investment and Jobs Act of 2021, calling for hubs for DAC and hydrogen, could be leveraged for synergies with CO₂ utilization. Developing such synergies may include, for instance, co-locating at least one DAC and hydrogen hub pair, or locating hubs in regions with an industrial focus to facilitate the adoption of CO₂ utilization and spur private investment. DOE’s Notice of Intent for the hydrogen hubs calls for such integration with industrial uses of hydrogen, which could include CO₂ utilization: “End-use diversity—at least one hub shall demonstrate the end-use of clean hydrogen in the electric power generation sector, one in the industrial sector, one in the residential and commercial heating sector, and one in the transportation sector” (DOE-OCED 2022). Such co-located hubs and other concentrations of CO₂ utilization could create nuclei where private investment may find a need for pipelines and other shared infrastructure. Centralized production and use of various fossil fuels and derived chemicals is the norm in the existing petrochemical industry and could be best for CO₂ and hydrogen production and use as well.

The largest amounts of CO₂ could be used to produce construction materials, polymers, fuels, and commodity chemicals. Track 1 CO₂ utilization may serve a need for consuming and storing large volumes of CO₂ that would otherwise be emitted to the atmosphere, such as in construction materials and some durable products. Track 2 CO₂ utilization will be a part of ensuring access to necessary chemicals in a circular carbon economy, including for large volumes of fuels, polymers, and commodity chemicals. The following sections detail opportunities, synergies, and needs for the important, large-volume products in Track 1 and Track 2.

3.6.1 Construction Materials

Opportunities for large-scale CO₂ utilization potential exist for the production of Track 1 construction materials that constitute a means of durable CO₂ storage, equivalent to CCS, yet with the potential for higher societal value and reduced cost.

CO₂ utilization that produces Track 1 construction materials can create synergies to address multiple pressing societal needs given the urgent need to rebuild a substantial portion of U.S. built environment infrastructure, addressing the acute housing shortage and the significant carbon footprint of the built environment. It is instructive to note how slowly durable products penetrate the market due to 10+-year use phases for legacy technology. Rapid launch of CO₂-based construction materials is therefore essential, since infrastructure investments are made for even longer-term use, and CO₂ removal opportunities would be lost with delayed deployments. Mineralization reactions such as by-product use of steel slag or fly ash to reduce energy requirements for concrete (IEA 2019; Mangan 2010) or mining of serpentine minerals for production of aggregates represent some of the most likely options for viable CO₂ utilization with very large potential for CO₂ removal.

To establish CO₂ utilization for concrete and aggregate production, distributed CO₂ sources will be needed, given the fragmented and very localized production requirements for this sector. Co-location with CO₂ point sources needs to be explored as much as possible to reduce transportation requirements. Properties of the new construction materials may differ from incumbents, triggering the need for testing and validation of the new materials, creation of new environmental product declarations, and adaptation of building codes and standards. The latter is nontrivial, given the conservative nature of building codes.

3.6.2 Synthetic Fuels

CO₂ utilization to produce synthetic fuels would provide energy-dense hydrocarbons derived from renewable, rather than fossil, carbon to power existing and future combustion processes. Synthetic fuels are a Track 2 chemical, and therefore their production must use DAC, DOC, or biogenic CO₂ sources because circular carbon flows are required for sustainability. Synthetic fuels may be particularly important for applications where hydrogen- or electric-powered vehicles will be challenging to produce or operate, such as in long-distance, heavy-freight applications in aviation and shipping. Synthetic fuels may also offer a daily, monthly, or seasonal energy storage opportunity. Additionally, local synthetic hydrocarbon fuel production may provide safe and secure access to fuels during overseas deployments, a potentially important application as continued use of existing defense-related vehicle fleets is a significant concern for national security. Such production methods could be cost-competitive relative to logistics costs of supplying today’s fuels (Poland 2021). Finally, developing CO₂ utilization for synthetic fuel production affords an opportunity not only to use existing infrastructure but also existing workers, many of whose skills will be translatable from the current fossil-fuel system to a synthetic fuel system.

Despite the opportunities and synergies in using aspects of the current energy system, synthetic fuels will be challenged to compete with alternative methods of de-fossilizing or de-carbonizing combustion applications in transportation, industry, and buildings. Synthetic fuels are expensive to produce, because of both the high capital costs of equipment needed for electrolysis and fuel synthesis and the high electricity consumption of the processes (Searle et al. 2021). Other potential sources of sustainable drop-in, energy-dense fuels include biomass- or waste-derived hydrocarbons. All drop-in fuels will compete with hydrogen and/or electricity to power equipment and processes, especially because combustion of hydrocarbon fuels is less efficient for powering transportation or other processes than use of hydrogen for combustion or in fuel cells, or direct electrification. A 2021 study of light-duty vehicle fuel economy examined the emissions and energy-use implications of various alternative fuels compared to conventional internal combustion engine vehicles powered with standard gasoline with 10 percent ethanol. Using the GREET model to estimate energy use of alternative-fueled vehicles, the study found that electric cars use 45 percent of the energy of conventional vehicles, fuel-cell vehicles powered with electrolytic hydrogen generated from renewable energy use 78 percent of the energy of conventional vehicles, and conventional vehicles powered by synthetic fuels synthesized from CO₂ and electrolytic hydrogen using renewable energy use 297 percent of the energy of conventional vehicles (NASEM 2021b).

In addition to the challenges associated with higher energy use, combustion of hydrocarbon fuels is a source of particulate matter, nitrogen oxides, and ozone (leading to smog in the presence of hydrocarbons), which adversely impact human health with disproportionate impact on disadvantaged communities, unlike zero-emission electrical power or hydrogen-powered fuel cells.² Because synthetic fuels may be designed to have lower criteria emissions than current fuels such as gasoline and diesel, they typically have fewer contaminants than fossil fuels and can be made as custom blends of chemicals. Aviation fuel or perhaps marine propulsion are possibly the best uses for synthetic hydrocarbon fuels, since local air quality impacts would be less severe and electrification is difficult due to the low energy and power densities afforded by batteries. Particularly for aviation, the ability to use existing aircraft and distribution infrastructure together with a decrease in manufacturing costs for synthetic aviation fuel may enable CO₂-derived synthetic fuels to be nearly cost-competitive with existing hydrocarbon fuels and other alternative hydrogen options by 2050, if there is a price on CO₂ emissions (Third Derivative n.d.).

3.6.3 Commodity Chemicals

CO₂ utilization can be one way to de-fossilize production and use of carbon-based commodity chemicals. Unlike the fuels described above, there are few options for replacing carbon-based commodity chemicals with carbon-free alternatives.

Commodity chemicals from CO₂, such as synthetic fuels, have synergy with the existing infrastructure for distribution and use of the final chemical or material product. The chemical industry is designed to make and use

___________________

² Hydrogen, when combusted rather than used in a fuel cell, can lead to criteria pollutant NOx, if not done judiciously.

several “building block” chemicals to synthesize a large number and volume of chemicals, and so if CO₂ utilization could be used to produce these central intermediates, then much of the same infrastructure and capital could be used for sustainable carbon-based chemical production. Similar to the fuels discussion above, the existing workforce will remain effective for the new circular carbon economy.

CO₂ utilization will compete with other sources of sustainable carbon, including biomass and waste-based resources. For hydrocarbon chemicals production, the same molecules can sometimes be made from bio-based feedstocks with lower specific energy needs, but higher land use (Haider 2022). Whether or not CO₂-derived hydrocarbon chemicals will be competitive with bio-based chemicals will depend on reduction in the cost of DAC and sufficient availability of low-cost, zero-carbon-emission energy. Hydrocarbon chemical products have sequestration lifetimes of less than 100 years (IEA 2019); thus, their chemical synthesis must not involve current fossil emission point sources.

3.6.4 Polymers

Polymers and polymer precursors are a major class of chemicals and materials, used for plastics, rubbers, fibers, and foams. CO₂ utilization has significant potential to displace existing polymer syntheses from fossil fuels and for CO₂ to be a feedstock for other, different polymers optimized for CO₂ utilization. Currently, there is some commercial-scale synthesis of polycarbonates from CO₂, though copolymerization methods and use of fossil-fuel–derived feedstocks result in only a portion of the carbon in the product being derived from CO₂. Biological and chemical systems can produce polymer precursors and polymers.

CO₂ utilization in the production of polymers can fill a need for materials in a circular economy, addressing huge existing markets and offering opportunities to improve polymer syntheses in some cases. However, challenges exist for converting CO₂ to polymers. The reaction conditions for producing polymer precursors, including ethylene and benzene, differ from those of conventional ethylene and benzene production technologies. Thus, the existing ethylene and benzene manufacturing infrastructures need to be modified. Also, the contaminants (trace gases, especially NOx/SOx, and particulates) in the captured CO₂ could lower the activities of the chemical catalysts used in CO₂-to-polymer synthesis. Contaminants in CO₂ feedstock streams are less of a problem for biological CO₂-to-polymer synthesis (Kondaveeti et al. 2020).

Production of polymers from CO₂ in a cost-effective and environmentally friendly manner will require synergistic efforts. First, CO₂ capture and purification will need to be available to provide high-purity CO₂, which not only will improve CO₂ utilization efficiency but also will increase the purity and productivity of polymers and thus the marketability of CO₂-derived polymers. Co-location of CO₂ and hydrogen sources could lower chemical polymer production costs. The choices for specific chemical and biological pathways need to be considered together with the capability of the existing polymer synthesis infrastructures. Polymers are a high-volume material class, accessible from CO₂, recycled material, and biomass feedstocks. CO₂ utilization will be favorable for certain polymer syntheses, including those of polycarbonates and polyurethanes, and will provide an opportunity to produce polymers that replace those lost in recycling processes, which are not 100 percent efficient. Biodegradability of polymers can be an asset for products that are frequently discarded and unlikely to be recycled, and CO₂ utilization can produce those polymers in a circular carbon economy. Some polymers are durable and can represent Track 1–type utilization if products are sufficiently long-lived (>100 years), such as some building materials.

3.6.5 Conclusion

Overall, it is clear that CO₂ utilization is not a silver bullet either to counter the effects of climate change or to meet the needs for carbon-based products. However, it is one of many tools that will be used to accomplish these goals, and in some cases, it is likely to be favorable over alternatives. For example, CO₂ utilization may offer opportunities for CDR at lower cost for Track 1 chemical products compared to CCS, access to Track 2 carbon products with lower land-use requirements than biomass-derived ones, and, for both product tracks, a new industry that may address environmental justice and other negative impacts related to the production of incumbent chemicals and materials. Forecasts for the magnitude of the emerging CCU industry necessarily cover a wide range, but even at

lower estimates, in 2050, nearly 2 Gt CO₂ could be utilized in products, generating $1.1 trillion in revenues. If conditions favor CO₂ utilization over other alternatives, a high estimate of 27 Gt CO₂ utilized and $4.4 trillion revenues has been projected. Policy guidance will be essential to ensure an expedited and just launch of the CCU industry.

3.7 FINDINGS AND RECOMMENDATIONS ON POTENTIAL USES OF CO₂ IN COMMERCIAL PRODUCTS

FINDING 3.1 Product Lifetime. Some CO₂-derived products, such as CO₂-cured concrete, carbonated aggregates, carbon fibers used in structural materials, and long-lived polymers, have lifetimes that will lead to durable CO₂ sequestration if handled appropriately. In contrast, short-lived products, for example, fuels, fertilizers, and many other chemicals, will decompose quickly and return the CO₂ to the atmosphere, presenting the opportunity to participate in a circular carbon economy.

FINDING 3.2 Sustainability of Products Based on Carbon Source. Long- and short-lived CO₂-derived products have fundamentally different relationships to carbon sources, resulting in different climate impacts. Long-lived products may be net-negative compatible if non-fossil CO₂ is used, or net-zero compatible if sourced from fossil CO₂. Short-lived products may be net-zero compatible if the CO₂ is sourced from non-fossil sources. If emissions cannot be reduced to be compatible with net-zero or net-negative pathways, such as use of fossil CO₂ for short-lived products, then the resulting product may be considered unsustainable relative to alternative options such as production from biomass or recycled material feedstocks, carbon sequestration, or use of non-carbon-based technologies, such as replacing hydrocarbon fuels with hydrogen or electricity. The long-term sustainability of different CO₂ utilization processes is an important consideration for infrastructure planning and policy.

FINDING 3.3 Carbon Accounting. Carbon accounting across the value chain will be important to assessing sustainability and climate impact of carbon management technologies, including CO₂ utilization.

RECOMMENDATION 3.1. The U.S. Department of Energy should fund research to quantify the dynamic impact of CO₂-derived products, for example, their specific lifetime, on the CO₂ balance in the atmosphere. The United States should incorporate knowledge acquired from European projects and regulatory activities in addressing circular carbon economies and net-negative emissions.

FINDING 3.4 Life Cycle, Techno-economic, and Societal Factors Assessment. For all assessments of net-zero or net-negative emissions status of CO₂ utilization products, it is important to estimate the full life cycle impact of the process, including upstream and downstream greenhouse gas emissions associated with the process, feedstock origin, energy use, product fate, co-product fate, and associated waste. To ensure simultaneous economic viability and environmental justice, techno-economic assessments and societal factors have to be fully integrated with life cycle assessments.

RECOMMENDATION 3.2. The U.S. Department of Energy (DOE) should build on ongoing efforts to harmonize and standardize life cycle assessment (LCA) for carbon capture, utilization, and storage projects. In addition to LCA, techno-economic assessment and analysis of societal impacts including environmental justice should be used by DOE to prioritize investments in project demonstrations and loan commitments.

FINDING 3.5 CO₂ Utilization Target Products. Targets for net-zero-emissions carbon products include concrete, aggregates, commodity carbon-containing chemicals, polymers, elemental carbon products, and high-value niche products. Many needs for carbon-based products will remain or grow in a net-zero-emissions economy, but a major class of materials, carbon-based fuels, is likely to decrease in use due to vehicle electrification. The use of zero-emission carbon fuels for heavy-duty transport, especially aviation, likely will remain substantial.

FINDING 3.6 Product Equivalence. Many CO₂-derived products (e.g., fuels, materials, chemicals) are chemically identical to their fossil-derived counterparts. These products can utilize existing infrastructure and systems and may displace incumbent fossil-derived products. Some CO₂-derived products, such as CO₂-cured concrete and carbonated aggregates, may have different composition, properties, and performance than the incumbent material, which could yield benefits or disadvantages.

FINDING 3.7 Displaced Emissions. Displacing fossil-derived products with CO₂ utilization-derived products may lead to avoidance of CO₂ emissions, if the CO₂ utilization processes are net-zero emissions. However, not all emissions may be displaced, particularly criteria emissions from combustion of fuels, such as nitrogen oxides and soot, which have local air quality and human health impacts.

FINDING 3.8 Net-Zero Emissions Enabling Inputs. For net-zero-emissions CO₂ utilization, all inputs—including but not limited to electricity, hydrogen, heat, and transportation—will need to have net-zero emissions on a life cycle basis. Electricity and hydrogen inputs can be substantially decarbonized by adding carbon capture and storage to existing infrastructure for generation from fossil fuels, or by building new infrastructure using zero-carbon-emissions options such as solar, wind, nuclear, or geothermal power.

FINDING 3.9 Energy and Hydrogen Requirements. Utilizing CO₂ as a starting material in chemical processes to produce fuels, commodity chemicals, and other hydrocarbon-based chemicals requires more external energy and often hydrogen inputs than generating the same products from fossil carbon sources. CO₂ utilization to produce hydrocarbon substitutes for fossil fuels will also require substantially more power and hydrogen than needed for direct use of electricity or hydrogen to power transportation and other energy services.

FINDING 3.10 Market Potential. The global utilization potential for CO₂ to make products is several gigatonnes per year. The volume of CO₂ utilized in a net-zero economy will be driven by the market value of carbon-based products and the competitiveness of CO₂ as a feedstock. These factors depend on (1) demand for services provided by carbon-based products; (2) their relative cost compared to fossil-based products, non-carbon-based alternatives such as electricity and hydrogen, and products derived from carbon sources other than CO₂, such as biomaterial carbon and recycled waste carbon products; (3) availability of inputs that enable net-zero product status, including clean hydrogen and energy; and (4) policy incentives and regulatory frameworks, including CO₂ abatement incentives. The potential for and cost of CO₂ removal will affect market demand directly in some cases—such as when the marketable product also provides carbon removal (e.g., concrete and aggregates or carbon fiber)—and indirectly in other cases, by changing the attractiveness of using CO₂ removal as an alternative to de-fossilization of chemical products.

3.8 REFERENCES