Carbon dioxide (CO2) utilization efforts focus on pathways and novel approaches for reducing CO2 emissions by developing beneficial uses for the CO2 that will mitigate CO2 emissions in areas where geologic storage may not be an optimal solution. CO2 can be used in applications that could generate significant benefits. It is possible to develop alternatives that can use captured CO2 or convert it to useful products such chemicals, cements, or plastics. Revenue generated from the utilized CO2 could also offset a portion of the CO2Processes or concepts must take into account the life cycle of the process to ensure that additional CO2 is not produced beyond what is already being removed from or going into the atmosphere. Furthermore, while the utilization of CO2 has some potential to reduce greenhouse gas emissions to the atmosphere, CO2 has certain disadvantages as a chemical reactant. Carbon dioxide is rather inert and non-reactive. This inertness is the reason why CO2 has broad industrial and technical applications. Each potential use of CO2 has an energy requirement that needs to be determined; and the CO2 produced to create the energy for the specific utilization process must not exceed the CO2 utilized.
The figure below illustrates most of the current and potential uses of CO2. However, many of these uses are small scale and typically emit the CO2 to the atmosphere after use, resulting in no reduction in overall CO2 emissions. Some of the more significant current and potential uses of CO2 are highlighted in the research underway in this focus area.
Schematic Illustrating the Uses of CO2 (click to enlarge)
CO2 Utilization Goals
CO2 Utilization covers a broad area of research with different technical challenges. The goals of the Carbon Storage Program are set to achieve successful implementation of various applications at different time horizons.
In general, the area of CO2 utilization for carbon storage is relatively new and less well-known compared to other storage approaches, such as geologic storage. Thus, more exploratory technological investigations are needed to discover new applications and new reactions. Many challenges exist for achieving successful CO2 utilization, including the development of technologies capable of economically fixing CO2 in stable products for indirect storage.
CO2 Utilization Technologies
Four main CO2 utilization research focus areas the Carbon Storage Program supports include:
- Instead of the traditional energy intensive steam curing technology, develop a concrete curing process that consumes substantial amounts of waste CO2 from onsite flue gases and local combustion sources. The produced concrete products should exhibit material performance equal to that of the traditional curing process, while using less energy. This use of CO2 should sequester the carbon for many years. The transition between demonstration and commercial scale should be rapid, since the new process and technology is anticipated to require limited modification to the existing curing process.
- Improve curing rates and CO2 yield to increase efficiency of CO2 use.
- Develop curing processes based on carbonation chemistry rather than hydration chemistry to reduce energy requirements and CO2 emissions.
- Develop cement to meet American Standard Test Method (ASTM) standards.
- Polycarbonate Plastics
- Traditional monomers, such as ethylene and propylene, can be combined with CO2 to produce polycarbonates, such as polyethylene carbonate and polypropylene carbonate. The advantage of this process is that it copolymerizes CO2 directly with other monomers without having to first convert the CO2 to carbon monoxide (CO) or some other reactive species. This significantly reduces energy requirements. There are many potential uses for polycarbonate plastics, including coatings, plastic bags, and laminates. Depending on the final fate of the plastic, such as a landfill, this use could represent semi-permanent storage of carbon. This promising CO2 utilization technology needs to be proven at pilot scale.
- Utilize waste energy or alternative energy sources to convert CO2.
- Develop catalysts to reduce energy requirements.
- Develop stabilizers to inhibit degradation of plastics.
- Carbonate mineralization refers to the conversion of CO2 to solid inorganic carbonates. Naturally occurring alkaline and alkaline-earth oxides react chemically with CO2 to produce minerals, such as calcium carbonate (CaCO3) and magnesium carbonate (MgCO3). These minerals are highly stable and can be used in construction or disposed of without concern that the CO2 they contain will release into the atmosphere. One problem is that these reactions tend to be slow, and unless the reactions are carried out in situ, there is a large volume of rock to move. Carbonates can also be used as filler materials in paper and plastic products.
- Reduce energy requirements for grinding feedstock materials needed for the mineralization process.
- Utilize waste streams to obtain oxides from existing mining operations.
- Develop chemicals or catalysts to speed reaction rates and reduce thermal and pressure requirements.
- Meet industrial standards for building materials.
- Enhanced Hydrocarbon Recovery
- Enhanced Recovery (ER) involves the injection of CO2 into a depleted oil or gas bearing field to increase production. This could involve injecting CO2 into clastic, carbonate, coal, or organic shale formations.
- Maximize the amount of CO2 that could be stored as well as maximize hydrocarbon production as part of these ER operations.
Each technology approach has a specific application, advantages over others, and challenges that are the focus of the existing and future research. Information on active CO2 utilization projects receiving DOE funds that aim to obtain these goals for the Carbon Storage Program is provided in the following table.