Carbon capture and utilization

CO₂ electroreduction to a variety of value-added products has been under development for many years. Some major targets are formate, oxalate, and methanol, as electrochemical formation of these products from CO₂ would constitute a very environmentally sustainable practice.[11] For example, CO₂ can be captured and converted to carbon-neutral fuels in an aqueous catalysis process.[12][13][14] It is possible to convert CO₂ in this way directly to ethanol, which can then be upgraded to gasoline and jet fuel-[15]

A carbon-neutral fuel can be synthesized by using the captured CO₂ from the atmosphere as the main hydrocarbon source. The fuel is then combusted and CO₂, as the byproduct of the combustion process, is released back into the air. In this process, there is no net carbon dioxide released or removed from the atmosphere, hence the name carbon-neutral fuel. An example of the technology include biofuel from microalgae as discussed below.

A proven process to produce a hydrocarbon is to make methanol. Methanol is easily synthesized from CO
2 and H₂. Based on this fact the idea of a methanol economy was born.

Methanol, or methyl alcohol, is the simplest member of the family of alcohol organic compound with a chemical formula of CH₃OH. Methanol fuel can be manufactured using the captured carbon dioxide while performing the production with renewable energy. Consequently, methanol fuel has been considered as an alternative to fossil fuels in power generation for achieving a carbon-neutral sustainability.[16][17] Carbon Recycling International, a company with production facility in Grindavik, Iceland, markets such Emission-to-Liquid renewable high octane methanol fuel with current 4,000 metric ton/year production capacity.[18]

As a highly desirable C₁ (one-carbon) chemical feedstock, CO₂ captured previously can be converted to a diverse range of products. Some of these products include: polycarbonates (via Zinc based catalyst) or other organic products such as acetic acid,[19] urea,[19] and PVC.[20] Currently 75% (112 million tons) of urea production, 2% (2 million tons) of methanol production, 43% (30 thousand tons) of salicylic acid production, and 50% (40 thousand tons) of cyclic carbonates production utilize CO₂ as a feedstock.[21] Chemical synthesis is not a permanent storage/utilization of CO₂, as aliphatic (straight chain) compounds may degrade and release CO₂ back to the atmosphere as early as 6 months.[20]

Novomer is a chemicals company working on a zinc-based catalyst for production of polyethylene carbonate (PEC) and polypropylene carbonate (PPC) feedstock. A March 2011 report by Global CCS Institute foresaw annual production potential of 22.5 MtCO₂/yr. They have received funding from multiple sources such as the Department of Energy (DOE) ($2.6 million) and NSF ($400,000) to achieve commercialization as well as converting their production process from a batch process to a continuous process.[20]

In EOR, the captured CO₂ is injected into depleted oil fields with the goal to increase the amount of oil to be extracted by the wells. This method is proven to increase oil output by 5-40%.[20] The scale of CO₂ utilization through this technologies ranges from 30-300 MtCO₂/yr. It is a permanent and mature technology in CCU. The biggest market driver for EOR is the heavy reliance on oil. In United States, some of the additional market drivers include: tax revenue for foreign oil as well as the presence of carbon tax credits.

Carbon dioxide from sources such as flue gas are reacted with minerals such as magnesium oxide and calcium oxide to form stable solid carbonates. Sources of minerals include brine and waste industrial minerals. The carbonates can then be used for construction, consumer products, and as an alternative for carbon capture and sequestration (CCS). The scale of this technology may reach more than 300 Mt of CO₂ removed per year. 0.5 tonnes of CO₂ is removed from the air for every tonne of mineral carbonate produced. However, it needs 1–5 years to commercialization as the technology is not mature yet.

The company Calera proposed a way to mineralize CO₂ through the CMAP process. This process involves precipitating a carbonate slurry from a mixture of water, solid minerals, and flue gas. The products are concentrated pumpable carbonate suspension, fresh water, and CO₂-free flue gas.

Benefits of this process includes the production of fresh water and that the CO₂ used does not require separation or compression. A barrier of this technology is, however, the competition with existing cement industries.

Fuels can be produced from algae

A study has suggested that microalgae can be used as an alternative source of energy.[22] A pond of microalgae is fed with a source of carbon dioxide such as flue gas and the microalgae is then let to proliferate. The algae is then harvested and the biomass obtained is then converted to biofuel. 1.8 tonnes of CO₂ is removed from the air per 1 metric tonne of dry algal biomass produced. This number actually varies depending on the species. The scale of this technology may reach more than 300Mt of CO₂ removed per year. The CO₂ captured will be stored non-permanently as the biofuel produced will then be combusted and the CO₂ will be released back into the air. However, the CO₂ released was first captured from the atmosphere and releasing it back into the air makes the fuel a carbon-neutral fuel. This technology is not mature yet.[23]

Dead algae can sink to the bottom of the lake and result in permanent storage. However, the algae needs a large area of pond and sunlight all year round to remove CO₂ all year round. Furthermore, the pond environment needs to be controlled since the algae needs to live in a specific condition. There are concerns about how the algae-filled pond might affect the environment and ecosystem around it.

An approach that is also proposed as a climate change mitigation effort is to perform plant-based carbon capture.[24] The resulting biomass can then be used for fuel, while the biochar byproduct is then utilized for applications in agriculture as soil-enhancer. Cool Planet is a private company with an R&D plant in Camarillo, California, performed development of biochar for agricultural applications and claimed that their product can increase crops yield by 12.3% and three-fold return of investment via improvement of soil health and nutrient retention.[25] However, the claims on the efficacy of plant-based carbon capture for climate change mitigation has received a fair amount of skepticism.[26]