Nongovernmental valorization of carbon dioxide

https://doi.org/10.1016/j.scitotenv.2004.06.025Get rights and content

Abstract

Carbon dioxide (CO2) is considered the largest contributor to the greenhouse gas effect. Most attempts to manage the flow of CO2 or carbon into our environment involve reducing net emissions or sequestering the gas into long-lived sinks. Using CO2 as a chemical feedstock has a long history, but using it on scales that might impact the net emissions of CO2 into the atmosphere has not generally been considered seriously. There is also a growing interest in employing our natural biomes of carbon such as trees, vegetation, and soils as storage media. Some amelioration of the net carbon emissions into the atmosphere could be achieved by concomitant large withdrawals of carbon. This report surveys the potential and limitations in employing carbon as a resource for organic chemicals, fuels, inorganic materials, and in using the biome to manage carbon. The outlook for each of these opportunities is also described.

Introduction

Ascribing the rise in atmospheric CO2 concentrations as largely anthropogenic has elicited significant debate within both scientific and political communities. There are questions about whether we even need to manage carbon emissions or even can or choose to manage them. In discussions about carbon sequestration and management, a question that often arises involves whether the greenhouse gases carbon dioxide (CO2) and methane can be used and valued as sources of carbon rather than as waste emissions and molecules that need to be stored in long-term sinks. While methane is a low-carbon energy source, converting methane to higher value fuels yields CO2 as an end product. Attempts to couple methane to produce higher value fuels has been ongoing for many years (Srivastava et al., 1992, Villa and Rapagna, 1998, Iglesia, 2002). Reforming methane to hydrogen as a fuel is now being considered as well as its current use as a chemical feedstock (Choudhary et al., 2001). However, this report focuses on CO2 rather than methane.

Carbon dioxide has been branded as the primary culprit in discussions about carbon management and climate change. Some argue that this is not clear or that managing carbon will mitigate anything (Cunningham, 2001). This report focuses on the potential to value CO2 economically and technically as a resource in the context of carbon management as an alternative to relying on governmental valorization to dictate its fate and use. This is an economically driven carbon management model rather than one based on governmental responses to the Kyoto and Montreal protocols to valorize carbon in order to manage carbon emissions.

Ascribing the rise in atmospheric CO2 concentrations as largely anthropogenic has elicited significant debate within both scientific and political communities. Geologists have made public comment on this topic: “Because no tool is available to test the supposition of human-induced climate change and the range of natural variability is so great, there is no discernible human influence on global climate at this time” (Gerhard and Hanson, 2000). Others have looked at the issue more globally and politically and concluded that the relationship between carbon dioxide and climate change has not been demonstrated (Cunningham, 2001).

The cycles of carbon flows operating on Earth include geochemical and oceanic cycles involving physicochemical diffusion and chemical reactions; biotic cycles involving the biota, soil, and detritus in the soils; and the combustion of fossil fuel, concomitant production of CO2, and the interactions between these cycles. As the concentration of CO2 in the atmosphere continues to increase, the feasibility of instituting an alternative cycle wherein the atmosphere is considered a reservoir of carbon to be accessed and used like a bank merits examination. We are clearly making deposits into this atmospheric bank and, aside from the reported increases and changes in biomass growth due to a fertilization effect, we are not making many, if any withdrawals (Bazzaz and Sombroek, 1996, Berendse et al., 2001, Fang and Chen, 2001a). An alternative cycle, which uses CO2 as a resource, could provide for fundamental societal and infrastructure needs—roads, buildings, chemicals, and fuels. We address aspects of these that can serve as the basis for answering the following questions. Can such anthropogenic withdrawals, driven by economic need and technical capability, provide materials and resources needed to maintain societal growth using the carbon reservoir in the atmosphere? If so, what might be the impact on the carbon budget? Where might the greatest impacts occur and what are the uncertainties in current findings?

Specifically, this paper does not discuss climate change strategies, carbon flows, new approaches to CO2 capture, increasing energy efficiency to mitigate carbon emissions into the atmosphere, or replacing fossil fuels with renewables or carbon sequestration. Instead, we will discuss carbon uses that could be valued as materials and products. How such processes can be coupled to low-carbon energy sources such as renewable energy (solar, wind, biomass, hydropower, etc.) is briefly discussed. While there are no preset minima for the level of carbon fixed into these commodity products or the level of fossil fuels displaced that would justify this concept, this discussion deals with processes that have the potential to fix carbon into forms that are produced in Tg (one million metric tons) or more quantities and durable products that possess lifetimes for carbon storage of 50–200 years. This is a storage option rather than full-scale sequestration. Given the concerns over deep physical storage systems of carbon dioxide in oceans or mines that could leak or even “bump” to the surface with deleterious effects, storage may be a reasonable alternative to examine, particularly if the storage amounts could be large with 100–200 year lifetimes. Management of carbon in the marine environment is beyond the scope of this report, but some brief references to marine environments will be made in relation to specific opportunities.

The study of C1 chemistry and the use of CO2 as a reactant predates the debate over the potential impact of increased concentrations of CO2 on our climate. CO2 is a desirable carbon feedstock because of its abundance, nontoxicity, and low cost (Inui et al., 1993, Magrini, 1994, Carranza et al., 1999, Noh et al., 2000, Holm-Larsen, 2001, Zevenhoven et al., 2002). Industrially, if CO2 could be used to introduce Csingle bondC, Csingle bondO, or even Csingle bondX bonds, inexpensive organic syntheses could be facilitated. This rationale has also been successfully adopted by the green chemistry movement, which proposes using CO2 as a replacement for toxic reagents such as phosgene (McGhee et al., 1993, Anonymous, 1994), a solvent or reaction media in its supercritical state (Abraham and Moens, 2002), or even a mild oxidizing reagent (Noh et al., 2000, Park et al., 2000). In addition, the National Aeronautics and Space Administration (NASA) has a long history of developing bioregenerative life support systems in which the use of CO2 is an essential part of long-term space habitation scenarios (http://www.qadas.com/qadas/nasa/nasa-hm/0254.html, http://www.advlifesupport.jsc.nasa.gov/, http://www.bio.purdue.edu/nscort/homepage.html and http://www.elflore.org/celsslinks.html). In the NASA examples, integrated bioregenerative life support systems employed hybrid chemical/biological systems to convert CO2 to methanol and then to a single-celled food source (Stokes and Petersen, 1982, Petersen, 1983). In related work with military applications, reduction of CO2 to methanol was followed by conversion of the methanol to extracellular polysaccharides by yeasts (Petersen et al., 1989, Petersen et al., 1990). Also for the same applications, hydrogen-utilizing bacteria were used to reduce CO2 to polysaccharide (Kern, 1985).

The major challenge to using CO2 as a feedstock is that it lies at the bottom of a thermodynamic well. Nature elevates carbon to energy-rich molecules such as glucose using solar energy and biological catalysts in a low-temperature biological carbon cycle. In the oceans, the geochemistry of CO2 involves essentially three reactions in differing states of equilibrium involving CO2 gas, water, H2CO3 and the ions of carbonate (HCO3−1, CO3−2), calcium, H+, and other metal ions. This carbon buffer is immense—38,000–39,000 petagrams (Pg) (Baes, 1982, Butler, 1982)—and Butler estimates that the buffering capacity of rock weathering and the oceans far exceeds any reasonable estimate for the amount of CO2 that would be emitted over the next one or two centuries by fossil fuels (Butler, 1982). However, short-term impacts and changes that appear to be related to increased CO2 flux into the oceans, such as those observed on coral reefs, can and are occurring (Ver et al., 1999). Thus the geochemical cycles for carbon and its inorganic forms, CO2 and carbonates, generally exist in a steady state within the terrasphere and oceans, and essentially serve as large storage buffers for all carbon fluxes, albeit on millennial temporal scales. Unfortunately, the impacts of changes in carbon concentrations are also on millennial time scales and not quickly reversed.

Systems analysts have looked at individual systems for their contribution to carbon sequestration and consider them inadequate to meet the ability to manage carbon, citing that a systems approach is needed because there is not a natural “savior” to assimilate the anthropogenically derived carbon (Falkowski et al., 2000). There is also the issue of self-adjusting biomes and whether they can really do much to manage carbon flows.

Using CO2 as a reactant molecule (carbon source) to deal with overall carbon management must involve very large-scale production processes and more demanding process criteria, i.e., few steps, simple and very low cost. Finally, such an effort will require significant interdisciplinary efforts. There are three potential scenarios that could address the use of CO2 as a reactant for high-volume products and meet the constraints noted above:

  • 1.

    Use carbon and CO2 as a feedstock or precursor to produce long-lasting products such as plastics or as a fuel to displace fossil fuels;

  • 2.

    Enhance the levels of carbon stored in trees, vegetation, and soils;

  • 3.

    Use CO2 in novel inorganic applications.

The paper will discuss the current status of each approach (although not designed to be carbon sinks, they do in fact act as such in their current use), the potential impact on carbon budgets, opportunities to employ these approaches and any ancillary benefits, the limitations or barriers to using these approaches, and finally, the outlook for the future of such approaches. Halmann and Steinberg recently published a comprehensive science and technology analysis of carbon dioxide mitigation (Halmann, 1999). They employed a systematic and useful approach to analyze many of the concepts being proposed to mitigate CO2 and used common bases—energy and dollar values—to compare concepts. They also provided details on some of the options with some options discussed in more detail than others. This paper complements or expands on some of the information in their book. We take a more rigorous look at some items such as using CO2 for plastics. Our estimates of the potential for using CO2 in commodity goods such as plastics very closely match those estimated in Halmann and Steinberg using a systems approach. They also recognized the gap in data related to storing carbon in the biome and we provide some analysis of that option which was an area Halmann and Steinberg called out as a research need.

Many published studies relative to carbon budgets, cycling, and sequestration are based on modeling data. Most modeling uses some empirical data. In this report, we avoided basing any of our assumptions and conclusions on pure models as much as possible. We attempted to use actual data or theoretically sound projections based on known chemistries. We cited modeling when model databases contained substantial amounts of empirical data. McGuire et al. (2001) provides a good list of the steps needed to provide models with the kind of data that will allow for better analyses and potential predictive capability.

We did not differentiate between short and long tons in citing numbers, as many of the citations do not differentiate. Because the numbers are very large, the differences between short and long tons are likely to fall within error bars. Conventionally, we have employed the metric values, tera- and petagrams and where possible have converted cited numbers to such nomenclature. For reference, 1 petagram (Pg) or 1015 g is equivalent to 1 gigaton (Gt) or 109 metric tons; and 1 teragram (Tg) or 1012 g is equivalent to 1 megaton (Mt) or 106 metric tons.

Section snippets

Background and current use for production of chemicals

Carbon and CO2 are currently market commodities and tie up a small but significant fraction of carbon. Table 1 shows the carbon form, its annual consumption in the US, and representative uses (Greiner et al., 1999, Heydorn et al., 2000, Auchter et al., 2002).

The total US consumption of these commodities is approximately 50 Tg. Many of these uses do not embody carbon in long-lived forms. For example, CO2 used in enhanced oil recovery usually returns to the surface within 6 months to 2 years (

Background and current use

The simplicity of nature's storage mechanism for carbon in terrestrial ecological systems (exclusive of geologic formations) suggests that we might be able to leverage these natural mechanisms and employ them for the purpose of managing carbon. The carbon in these sinks possess lifetimes on a century time scale, although most soils may have forms of carbon that range from transient to persistent depending on the depth of the soil horizon and age. These storage media also meet the criteria

Background of current uses

Geochemical carbon cycles involve hundreds of Pgs of mass. Cycles generally occur on geologic time scales with occasional upset events such as volcanic eruptions. Carbon is generally present in the form of carbonate minerals such as limestone. Such geologic carbonates can be considered to be carbon buffers and are part of both terrestrial and oceanic carbon cycles. Carbonates for commercial applications contain both calcium and magnesium. The sets of reactions that yield lime and lime products

Potential

The largest potential for carbon storage lies in employing the terrasphere as a sink in the natural biota, replenishing soils and land with CO2-derived minerals, and in employing CO2 in the manufacture of inorganic commodity chemicals. The manufacture of organic chemicals from CO2 or use of carbon materials provides several orders of magnitude smaller impact. CO2-based fuels provide no long storage potential but a large mitigation effect. The range of impacts for all of these possibilities

Acknowledgement

This work was funded by an Interagency Agreement between the Environmental Protection Agency and the National Renewable Energy Laboratory (NREL). Some support by NREL was also provided to complete the study. Donn Viviani is a chemist in the National Center for Environmental Economics at the U.S. Environmental Protection Agency. The views expressed in this paper are entirely those of the author and do not necessarily represent the views of the U.S. Environmental Protection Agency. Editorial

References (135)

  • R. Lal

    Soil carbon dynamics in cropland and rangeland

    Environ. Pollut.

    (2002)
  • K. Magrini et al.

    Use of pyrolysis molecular beam mass spectrometry (py-MBMS) to characterize forest carbon soil: method and preliminary results

    Environ. Pollut.

    (2002)
  • G. Marland et al.

    Forests for carbon sequestration or fossil fuel substitution? A sensitivity analysis

    Biomass Bioenergy

    (1997)
  • G. McCarty et al.

    Impact of soil movement on carbon sequestration in agricultural ecosystems

    Environ. Pollut.

    (2002)
  • J. Micales et al.

    The decomposition of forest products in landfills

    Int. Biodeterior. Biodegrad.

    (1997)
  • N. Muradov

    Hydrogen via methane decomposition: an application for decarbonization of fossil fuels

    Int. J. Hydrogen Energy

    (2001)
  • D. Nowak et al.

    Carbon storage and sequestration by urban trees in the USA

    Environ. Pollut.

    (2002)
  • A. O'Connor et al.

    Catal. Today

    (1998)
  • G. Petersen

    The enhancement of carbohydrates in a methylotrophic yeast

    Enzyme Microb. Technol.

    (1983)
  • G. Petersen et al.

    Yeasts producing exopolysaccharides with drag reducing activity

    Enzyme Microb. Technol.

    (1990)
  • Clean Solvents: Alternative Media for Chemical Reactions and Processing

  • J.A. Andrews et al.

    Soil CO2 dynamics, acidification, and chemical weathering in a temperate forest with experimental CO2 enrichment

    Glob. Biogeochem. Cycles

    (2001)
  • Anonymous

    Plastics without phosgene. Chemistry in Britain (December, 1994)

    (1994)
  • H. Arakawa et al.

    Catalysis research of relevance to carbon management: progress, challenges and opportunities

    Chem. Rev.

    (2001)
  • J. Auchter et al.

    CEH marketing research report: carbon black. Chemical economics handbook. Palo Alto, CA, Stanford Research Institute International

    Carbon

    (2002)
  • C.F. Baes

    Effects of ocean chemistry and biology on atmospheric carbon dioxide

  • D. Baldocchi et al.

    FLUXNET: a new tool to study the temporal and spatial variability of ecosystem-scale carbon dioxide, water vapor and energy flux densities

    Bull. Am. Meteorol. Soc.

    (2001)
  • A. Barr et al.

    Comparing the carbon budgets of boreal and temperate deciduous forest stands

    Can. J. For. Res.

    (2002)
  • A. Barr et al.

    Comparing the carbon budgets of boreal and temperate deciduous forest stands

    Can. J. For. Res.

    (2002)
  • Bazzaz F, Sombroek W. Global climate change and agricultural production. Direct and indirect effects of changing...
  • F. Berendse et al.

    Raised atmospheric CO2 levels and increased N deposition cause shifts in plant species composition and production in Sphagum moss

    Glob. Chang. Biol.

    (2001)
  • C. Bondavalli et al.

    Insights into the processing of carbon in the South Florida Cypress Wetlands: a whole-ecosystem approach using network analysis

    J. Biogeogr.

    (2000)
  • P. Bousquet et al.

    Regional changes in carbon dioxide fluxes of land and oceans since 1980

    Science

    (2000)
  • D. Breshears et al.

    The importance of rapid, disturbance-induced losses in carbon management and sequestration

    Glob. Ecol. Biogeogr.

    (2002)
  • J. Butler

    Effect of increased atmospheric CO2 on the oceans

  • E. Carey et al.

    Are old forests underestimated as global carbon sinks?

    Glob. Chang. Biol.

    (2001)
  • S. Carranza et al.

    An experimental investigation of thermochemical processes for in-situ production of propellants on Mars

    Proc. Heat Transfer Fluid Mech. Inst.

    (1999)
  • C & EN

    Facts and figures for the chemical industry: production

    Chem. Eng. News

    (2002)
  • J. Chambers et al.

    Decomposition and carbon cycling of dead trees in tropical forests of the central Amazon

    Oecologia

    (2000)
  • F.S. Chapin et al.

    Arctic and boreal ecosystems of western North America as components of the climate system

    Glob. Chang. Biol.

    (2000)
  • J. Chen et al.

    Annual carbon balance of Canada's forests during 1895–1996

    Glob. Biogeochem. Cycles

    (2000)
  • P. Ciais et al.

    Regional biospheric carbon fluxes as inferred from atmospheric CO2 measurements

    Ecol. Appl.

    (2000)
  • T.A. Clair et al.

    Changes in freshwater carbon exports from Canadian terrestrial basins to lakes and estuaries under a 2xCO(2) atmospheric scenario

    Glob. Biogeochem. Cycles

    (1999)
  • R. Connor et al.

    Carbon Accumulation in Bay of Fundy salt marshes: implications for restoration of reclaimed marshes

    Glob. Biogeochem. Cycles

    (2001)
  • W. Cunningham

    A sensible response to global warming hysteria

    World Energy

    (2001)
  • J. Dahl et al.

    Solar-thermal processing of methane to produce hydrogen and syngas

    Energy Fuels

    (2001)
  • R. Davenport

    CEH Marketing Research Report: Methanol. Chemical Economics Handbook. Palo Alto, CA, Stanford Research Institute International

    Methyl Alcohol

    (2002)
  • R. Dickson et al.

    Forest Atmosphere Carbon Transfer and Storage (FACTS-II) The Aspen Free-air CO2 and O3 Enrichment (FACE) Project: An Overview. St. Paul, MN, North Central Research Station

    (2000)
  • P. Dijkstra et al.

    Elevated atmospheric CO2 stimulates aboveground biomass in a fire-regenerated scrub–oak ecosystem

    Glob. Chang. Biol.

    (2002)
  • P. Falkowski et al.

    The global carbon cycle: a test of our knowledge of earth as a system

    Science

    (2000)
  • Cited by (0)

    View full text