Globally, human activities release approximately 35,000 teragrams (Tg) (million metric tons [MMT]) of carbon dioxide and 320 Tg (MMT) of methane into the atmosphere each year. As researchers and policy makers search for strategies to mitigate the buildup of these greenhouse gases, increasing attention has turned to the capture of gaseous carbon waste. Once captured, the gaseous carbon waste can either be geologically sequestered or put to productive use. Both options have costs, but utilization offers the opportunity for benefits from the use of the material. Carbon utilization technologies, as referred to in this report, convert gaseous carbon waste feedstocks (carbon dioxide or methane) into valuable products such as fuels, construction materials, plastics, and other useful products. These technologies have the potential to transform waste streams into resources, reduce greenhouse gas emissions, and in some cases generate positive economic returns.
Only a small fraction of the carbon dioxide and methane emitted each year is currently being captured and used. Most carbon utilization technologies are in their infancy. The Committee on Developing a Research Agenda for Utilization of Gaseous Carbon Waste Streams was convened by the National Academies of Sciences, Engineering, and Medicine at the request of the U.S. Department of Energy and Shell to assess research and development needs relevant to understanding and improving the commercial viability of carbon utilization technologies (see Box S-1).
The report defines a research agenda to address the principal challenges associated with commercializing carbon utilization technologies. The report also identifies improvements needed in tools used for evaluating the economic and environmental attributes of carbon utilization technologies. Because an overarching goal of carbon utilization is to curb the accumulation of greenhouse gases in the atmosphere, the study focuses on technologies that have the potential to utilize gaseous carbon waste with a net reduction in greenhouse gas emissions. The report assumes that large volumes of gaseous carbon waste, especially carbon dioxide, will continue to be generated in the coming decades through continued use of fossil fuels. While the study considers utilization technologies for both carbon dioxide and methane, the larger
focus is on carbon dioxide.1 The report is intended to help inform decision making surrounding the development and deployment of carbon utilization technologies under a variety of
1 Methane is emitted in far lower quantities than carbon dioxide and is, without chemical transformation, useful as a fuel and as a chemical feedstock. Capture and reuse of methane waste gas as a fuel are relatively mature technologies, so the potential impact of development of methane utilization technologies, beyond direct capture and use as a fuel, is limited. Carbon dioxide, on the other hand, makes up a far larger share of overall greenhouse gas emissions and, once captured, generally requires chemical transformation for use. Most technologies for utilizing carbon dioxide are at a low level of maturity, suggesting carbon dioxide utilization technologies have both a larger potential for greenhouse gas mitigation and a greater need for research and development.
circumstances, whether motivated by a goal to improve processes for making carbon-based products, to generate revenue, or to achieve environmental goals.
Previous assessments have concluded that in excess of one billion tons of carbon per year (roughly 3.6 billion tons of carbon dioxide or greater than 10 percent of current global anthropogenic carbon dioxide emissions) could feasibly be utilized within the next several decades if certain technological advancements are achieved and if economic and policy drivers are put in place. While the eventual scale of carbon utilization will be determined by a variety of technical, economic, and policy drivers, over multiple decades, carbon utilization technologies could be instrumental in achieving a “circular carbon economy” in which waste is converted into resources, such as by capturing the products of hydrocarbon combustion and converting them back into hydrocarbon fuels. In the context of an envisioned economy based largely on solar and wind power inputs with no net carbon emissions, such technologies could enable hydrocarbon use while dramatically curbing greenhouse gas emissions.
Finding 1: Carbon utilization technologies have a role to play in future carbon management and the circular carbon economy.
Finding 2: To play a meaningful role in carbon management, carbon utilization needs to be done at scale. The scale of carbon waste utilization will depend on the pace of technology development and future energy, market, and regulatory landscapes.
Broadly, carbon dioxide utilization can be categorized into three main pathways: mineral carbonation to produce construction materials, chemical conversion to produce chemicals and fuels, and biological conversion to produce chemicals and fuels. Methane utilization pathways include chemical and biological conversion to produce chemicals and fuels, as well as the direct use of methane as a fuel.
Mineral carbonation processes transform carbon dioxide into mineral carbonates, which can be used to make concrete and cement. Because these building materials are used at enormous scale and have product lifetimes that span decades, mineral carbonation represents a significant opportunity for long-term carbon sequestration in addition to being an opportunity for carbon utilization. A variety of processes that use carbon dioxide in the production of concrete and cement are already operating at limited commercial scales.
Chemical and biological carbon utilization processes transform carbon dioxide and methane into carbon-containing materials such as fuels, polymers, commodity chemicals, and fine chemicals. Some processes that use waste carbon dioxide or methane to produce high-
value chemicals are already operating commercially (e.g., methanol, dimethyl ether, and polymers). In addition, some technologies that use waste carbon dioxide or methane to produce higher-volume, lower-margin chemicals have also begun to be operated commercially, though current operations are generally dependent on locally available, low-cost, nontransportable energy resources or feedstocks, so they are not currently scalable in every location.
Finding 3: Pathways for carbon dioxide utilization include mineral carbonation, chemical utilization, and biological utilization. Pathways for methane utilization include chemical utilization, biological utilization, and direct use as fuel. These pathways involve multiple scales of operation, are at various stages of maturity, and require different energy inputs, feedstocks, and infrastructures.
Gaseous waste streams can contain contaminants such as hydrogen sulfide, sulfur dioxide, nitrogen oxides, siloxanes, and other species. Often these contaminants pose barriers to the utilization of carbon dioxide or methane in these waste gases. As a result, cost-effective methods to separate contaminants from and clean gaseous waste will be important enabling technologies for carbon utilization. Additional enabling technologies, resources, and infrastructures may be particularly important for efficiently converting carbon dioxide into useful products. For example, low-cost, low-carbon sources of energy or energy-carrying components (hydrogen, heat, or electricity) are needed to utilize carbon dioxide at large scale with zero or net-negative greenhouse gas emissions. Finally, there is often a mismatch between the locations where such energy sources are available and the locations and magnitudes of emitted carbon streams, necessitating transportation or co-location infrastructures to bring energy and waste gases together for processing.
Finding 4: Enabling technologies, resources, and infrastructures to remove waste gas contaminants provide necessary inputs of energy or reactive gases, and transport resources may be required for operation of carbon utilization technologies at scale.
At all stages of development from fundamental research to commercialization, researchers, technology developers, and policy makers evaluate technologies to make investment decisions. To compare the potential commercial viability of carbon utilization technologies, it is necessary to identify the factors that are crucial for marketplace success.
Finding 5: Like all technologies, a comprehensive evaluation of carbon utilization technologies would include evaluation at various maturity levels based on economic, market, regulatory, and environmental factors. Because carbon utilization
technologies utilize waste streams and may involve social or regulatory barriers and incentives as well as disruptive change to energy and material manufacturers, there are unique facets to carbon utilization evaluation.
Table S-1 summarizes key factors to consider when evaluating carbon utilization technologies. Many of these factors, such as economic value, scale, and market penetration, are shared with any new technology. Other factors are specific to the context of gaseous carbon waste streams. While the criteria presented in Table S-1 provide a framework for evaluating technologies, they can be applied in different ways depending on the evaluator’s needs and the technology being assessed.
Evaluating the factors and criteria outlined in Table S-1 requires tools and methods such as life-cycle assessment and technoeconomic analysis. However, many existing life-cycle assessments and technoeconomic analyses for waste carbon utilization processes and products are not sufficiently transparent, consistent, or accessible to allow for easy comparison of the unique features of carbon utilization technologies.
Finding 6: Current reported technology assessments, such as life-cycle assessment and technoeconomic analysis, frequently do not provide the needed level of transparency, consistency, and accessibility. Advances in technology evaluation tools would need to take place in parallel with the development of carbon utilization technologies.
A RESEARCH AGENDA FOR CARBON UTILIZATION
A comprehensive research agenda is needed to advance a wide range of carbon utilization technologies suitable for utilizing various carbon waste streams, incorporating enabling technologies and resources, and producing a variety of carbon-based products. In order to generate economic value while reducing greenhouse gas emissions, research is needed to address knowledge gaps throughout the carbon utilization landscape (Figure S-1). While some research needs are specific to the particular utilization technologies, others are cross-cutting, including research needs related to carbon inputs, process system improvement, catalytic technologies, and tools for evaluating utilization technologies.
Finding 7: A robust carbon utilization technology portfolio includes high-volume and high-value products, as well as products or processes that utilize resources available at low cost regionally or temporally, infrastructure, and feedstocks. Development of such a portfolio will require a broad range of research and technology advances.
TABLE S-1 Factors to consider when comparing carbon utilization technologies, and associated criteria for evaluating those factors.
|Scale, market capacity, and market penetration||
|Control of external factors associated with the technology||
|Unintended outcomes and consequences||
|Availability and suitability of waste stream||
|Risks associated with the use of waste as a feedstock||
|Life-cycle greenhouse gas reductions||
Recommendation 1: In order to realize potential benefits including improved energy and resource efficiency, creation of valuable industrial products, and mitigation of greenhouse gas emissions, the U.S. government and the private sector should jointly implement a multifaceted, multiscale research agenda to create and improve technologies for waste gas utilization.
Specifically, the U.S. government and the private sector should support
- Research and development in carbon utilization technologies to develop pathways for making valuable products and to remove technical barriers to waste stream utilization;
- The development of new life-cycle assessment and technoeconomic tools and benchmark assessments that will enable consistent and transparent evaluation of carbon utilization technologies; and
- The development of enabling technologies and resources such as low- or zero-carbon hydrogen and electricity generation technologies to advance the development of carbon utilization technologies with a net life-cycle reduction of greenhouse gas emissions.
INTEGRATION WITH CURRENT RESEARCH ACTIVITIES
Research and development that is directly or indirectly relevant to carbon utilization is supported, directed, and performed in industry, academia, government, and the nonprofit sector. In the United States, research that impacts carbon utilization and enabling technologies is scattered throughout various federal research portfolios, including fundamental and applied research and development grant mechanisms administered by the Department of Energy, Department of Defense, and the National Science Foundation, as well as through private-sector research and development programs.
Finding 8: Numerous research efforts relevant to advancing carbon utilization are under way both in the United States and abroad, supported by both public and private funding. Coordination and communication among existing carbon utilization research programs can lead to more rapid technology advancements.
TABLE S-2 Key research needs to promote the development of a robust carbon utilization portfolio.
|Area of Focus||Key Needs||Relevant Research Goals|
|Research Needs Related to Carbon Inputs|
|Waste streams||Gaseous carbon waste mapping||Research is needed to map the detailed compositions and magnitudes of gaseous carbon waste streams, with particular attention to co-emitted species that could either hinder or enhance carbon utilization processes. This could increase opportunities for matching waste streams with appropriate utilization processes.|
|Research Needs Related to Utilization Processes|
|Mineral carbonation||Controlling carbonation reactions||Research is needed to understand the fundamental chemical features that control the relative rates of carbonation and hydration. This could lead to improved selection of alkaline solids and reaction conditions.|
|Process design||Research is needed to integrate mineral carbonation processes with existing carbon dioxide capture technologies. This could lead to improved process performance and ensure optimal carbon dioxide conversion rates and energy use efficiencies.|
|Accelerating carbonation and crystal growth||Research is needed to develop additives for enhanced carbon dioxide solubility or structure-directing agents that accelerate particle growth. This could accelerate carbonation reactions such as crystal growth rates in solution beyond what is achieved simply by increasing the pH.|
|Green synthesis routes for alkaline reactants||Research is needed to develop energy- and carbon dioxide–efficient pathways and processes for producing alkaline solids that can be readily carbonated and do not require high-temperature activation. This could lead to energy- and carbon dioxide–efficient pathways.|
|Structure-property relationships||Research is needed to develop physical and instrumental assessment methods, improved modeling, and performance-based criteria for product properties. This could improve predictions of structure-property relations and increase the durability, viability, and acceptance of carbonated solids.|
|Area of Focus||Key Needs||Relevant Research Goals|
|Mineral carbonation||Analytical and characterization tools||Research is needed to develop new analytical tools for studying carbonation reactions in dense and viscous suspensions, as well as the evolution of microstructure across length scales. This could lead to new scientific tools to characterize mineral carbonation technologies.|
|Construction methodologies||Research is needed to develop new material formulations with novel properties and to advance the use of additive manufacturing to construct components with superior strength-to-weight ratio, optimized topology, and more complex geometries compared to what can be made with existing construction methods. This could enable new categories of carbon utilization products.|
|Chemical carbon dioxide utilization||Chemical catalysis||Research is needed to improve existing catalysts or discover entirely new catalysts. In addition to the usual performance metrics (activity, selectivity, and durability), special attention should be given to designing catalysts that tolerate the impurities present in carbon dioxide–containing waste streams to avoid costly and energy-intensive carbon dioxide purifications.|
|Avoiding stoichiometric additives||Research is needed to find ways to avoid stoichiometric additives that are not integrated into products, or to identify additives that are easily regenerated. This could lead to processes that generate limited waste for commodity chemical or fuel production.|
|Integrating catalysis and reactor design||Research is needed to integrate catalysts with the most efficient reactor including the identification of factors that affect catalyst performance at synthetically relevant rates. This could accelerate the development of carbon dioxide conversion processes that are relevant at the commercial scale.|
|Pathways to new products||Research is needed to develop processes that produce nontraditional targets, especially those with carbon-carbon bonds. This could transform processes for producing a wide range of chemicals and could create new markets.|
|Coupling oxidation and reduction reactions||Research is needed to combine carbon dioxide reduction with the oxidation of substrates from other waste streams (e.g., agricultural or biomass waste). This could open new pathways to reduce the cost of carbon dioxide conversion and create multiple high-value products.|
|Area of Focus||Key Needs||Relevant Research Goals|
|Chemical carbon dioxide utilization||System engineering and reactor design||Research is needed to develop reactor technologies that are tailored to the demands of carbon dioxide conversion processes. For example, reactors that allow for very efficient removal of products that are formed at low conversion for thermodynamic reasons would be beneficial. For electrochemical conversions, reactors that optimize single-pass conversion would mitigate the costs of product separation. Systems that integrate carbon dioxide capture with conversion should also be explored to minimize the steps required for waste gas valorization.|
|Biological carbon dioxide utilization||Bioreactor and cultivation optimization||Research is needed to improve bioreactor system design for efficient carbon dioxide solvation, mass transfer, dewatering and harvesting, and management and recycling of water and nutrients. This may include development of better computational and modeling tools for optimizing cultivation processes. Advancement of nonphotosynthetic methods may require novel bioreactor design in order to incorporate new feedstocks or hybrid fermentative systems. This could improve culture-monitoring technologies and facilitate scale-up of utilization.|
|Analytical and monitoring tools||Research is needed to improve culture-monitoring technologies. This could facilitate scale-up.|
|Genome scale modeling and improvement of metabolic efficiency||Research is needed to develop and improve methods for in-depth computational modeling, genetic manipulation, biochemical validation, and fermentative demonstration. This could improve metabolic flux, including carbon dioxide uptake and incorporation, photosynthetic efficiency, metabolic streamlining, and product accumulation.|
|Bioprospecting||Research is needed to accelerate the identification and characterization of organisms or biological systems with unique attributes such as carbon dioxide uptake, various product profiles, photosynthetic efficiency, and environmental tolerance. This could enhance the ability to produce target products in diverse geographic locations.|
|Area of Focus||Key Needs||Relevant Research Goals|
|Biological carbon dioxide utilization||Valorization of coproducts||Research is needed to develop feed and food uses for co-products of biological conversion, including studies in product safety and acceptability. This could improve the efficiency of energy and materials use and increase the economic value of biological conversion technologies.|
|Genetic tools||Research is needed to enhance engineering of photosynthetic and nonphotosynthetic organisms, including expansion of tools for genetic incorporation, selectable markers, promoter elements, protein folding and stability, and posttranslational control. This could improve efficiency and rates of biomass production and selective product formation.|
|Pathways to new products||Research is needed to identify biological pathways to produce nontraditional products and new products for unmet needs in commodity and specialty chemicals. This could expand the portfolio of products made via carbon utilization.|
|Research Needs for Evaluating Utilization Technologies|
|Life-cycle assessment||Life-cycle assessment benchmarking||Research is needed to develop benchmark life-cycle assessments of waste gas generation, waste gas cleanup, waste gas transport, electricity inputs, hydrogen inputs, and other enabling technologies to facilitate consistent and transparent assessments of the net greenhouse gas emissions of carbon utilization technologies. These benchmark assessments would include multiple environmental attributes of carbon utilization life cycles, such as greenhouse gas emissions, water use, air emissions, and materials use. This could lead to more consistent assessments of technologies.|
|Life-cycle assessment of emerging waste carbon utilization technologies||Research is needed to learn from transparent life-cycle assessments (LCA) of emerging technologies, taking into account a system boundary that includes waste gas capture and cleanup, the conversion process, use phase, and end-of-life considerations. Although LCA results for emerging technologies will undoubtedly evolve, LCA at this early stage will help guide research toward activities that will heighten energy and environmental benefits.|
|Area of Focus||Key Needs||Relevant Research Goals|
|Life-cycle assessment||Assessment of disruptive change||Research is needed to develop life-cycle assessment tools that move beyond assessing marginal changes in existing, static systems and address disruptive changes resulting from large-scale carbon utilization. This will provide tools for assessing disruptive changes necessary for performing consequential LCAs of carbon capture and utilization systems.|
|Technoeconomic analysis||Technoeconomic assessment benchmarking||Research is needed to develop standardized, transparent inputs and assumptions for technoeconomic analysis implemented for carbon utilization. This could lead to more consistent assessments of technologies.|
|Entrepreneurial research hubs||Research is needed to elucidate issues such as social and behavioral acceptance and understanding of commercialization needs. Entrepreneurial research hubs could support links between fundamental research and market needs.|
|Pilot plant facilities||Research is needed at pilot plant facilities to reduce risks involved in the commercialization of new technologies. This could facilitate the development of technologies beyond the laboratory scale.|
|Advanced testing||Research is needed to develop predictive accelerated aging evaluation methodologies for mineral carbonation. Such models would help de-risk technologies and streamline their introduction into conservative market applications where extensive performance data are needed to establish codes for use.|
|Process system improvement: Examples include more efficient techniques for mass transport or solvation of gaseous waste, better process-monitoring techniques, process intensification and optimization, integration of carbon utilization processes with carbon capture technologies, integration of catalysis research with reactor design, and techniques for managing and recycling inputs or products to minimize waste.|
|Improved catalysis: Examples include catalysts for accelerating carbonation based on control and distributions of surface sites on catalysts (for mineral carbonation), catalysts that use sustainable raw materials (for chemical utilization), catalysts for hydrogenation of lipid extracts (for biological utilization), and catalytic technologies that reduce the cost and complexity of product recovery, as well as reduce toxicity to the host organism (for electrocatalysis).|
Recommendation 2: The U.S. federal science agencies should coordinate carbon utilization research and development efforts with private-sector activities in the United States and with international activities in the private and public sectors. Support for carbon utilization research and development should include technologies throughout different stages of maturity, from fundamental research through to commercialization, and evaluate them using a consistent framework of economic and environmental criteria.
This research agenda reflects the priority needs that would enable the advancement of a wide range of carbon utilization technologies suitable for utilizing various carbon waste streams to produce a variety of carbon-based products. Incorporating enabling technologies and resources and integrating better coordination among the current research efforts will advance the progress being made in carbon utilization, which may play a significant role in carbon management even if fossil fuels are largely replaced by low-emissions energy sources.