With the global effort underway to reduce greenhouse gas emissions, particularly carbon dioxide, most activities focus on carbon capture and storage (CCS). These technologies involve scrubbing CO2 from the flue gasses of facilities using fossil fuels such as power plants and cement plants, concentrating the CO2 and then pumping it deep underground into storage caverns. However, rather than store the CO2 underground, other companies are working on technologies to convert the CO2 intosome useful product. Following is a description of three such CO2 utilization technologies.
Located in Dartmouth, Nova Scotia, CarbonCure technology involves injecting CO2 into cement during mixing, where it reacts with calcium to form calcium carbonate. The actual chemistry is a bit complicated involving nanomaterials. Extremely small and fine particles of CO2 are injected into the cement as it is mixed with water to make concrete form carbonate ions. The carbonate ions then react with calcium ions in the cement mixture to form calcium carbonate imparting strength to the resultant concrete.
CarbonCure has been piloting its technology for a number of years, and according to its website, it has been tested by a number of cement makers. Over the last several months, Thomas Concrete of Atlanta, Georgia has utilized CarbonCure technology in about half of the concrete made at its plan and has verified that this technology improves the strength of the concrete.
One drawback inhibiting large scale use of this technology is that the CO2 source is required at the site where the cement is mixed with water to form concrete. This operation is typically performed where the resultant concrete is used, not necessarily at major CO2 emitters such as power plants or cement plants. There is, thus, still the economic penalty involved in capturing the CO2 from emitters, storing it, and then transporting it to wherever the cement mixing occurs.
Since October 2014, Skyonics’ SkyMine technology has been used at the Capitol Aggregates cement plant in San Antonio, Texas. The project consists of contacting a portion of the cement plant’s flue gas with an aqueous solution of sodium hydroxide (caustic soda) where it reacts with the CO2 to produce sodium bicarbonate, more commonly known as baking soda. The plant is designed to capture 75,000 tons per year of CO2 which is converted into 143,000 tons per year of baking soda.
The caustic soda scrubbing solution is produced onsite via electrolysis of salt (sodium chloride) delivered to the plant. In addition to the caustic soda, the electrolysis plant also produces hydrochloric acid and a small quantity of bleach (sodium hypochlorite). Large scale implementation of this technology will depend upon the successful marketing of its primary products; baking soda and hydrochloric acid. This could be a formidable obstacle since the global market for sodium bicarbonate is only around 4 million metric tons per year.
Merchant Marketing of hydrochloric acid poses additional challenges. The majority of hydrochloric acid is produced as a by-product in the production of organic compounds and essentially all such acid is used in the production of other chemicals, mostly for ethylene dichloride, a raw material for polyvinyl chloride, PVC. There is a relatively small merchant market which includes steel pickling and oil well acid treatments. When U.S. shale oil activities were booming just a few years ago, the merchant market for HCI saw significant increases. However, with the slump in crude oil prices and the drop in shale oil development, this market for HCI has been significantly curtailed.
Recognizing the programs with large scale implementation of its SkyMine technology, Skyonics is piloting an alternative process called SkyCycle, which will produce calcium carbonate instead of sodium bicarbonate. The markets for calcium carbonate are on the order of 25 times greater than baking soda, so marketing should not be a constraint. However, the market issue for merchant hydrochloric acid sales remain.
Carbon Recycling International
Since 2012, Carbon Recycling International (CRI) has been operating a very small methanol plant in Svartsengi, near Grindavik, Iceland, which converts CO2 removed from the flue gas of an adjacent geothermal power plant into methanol. The hydrogen for the reaction is produced via electrolysis of water using energy from Iceland’s electric grid, all of which is produced from renewable sources; hydro or geothermal energy.
CRI has branded methanol made from all renewable sources as Vulcanol™. The methanol is sold for blending into gasoline or in the production of biodiesel, domestically or abroad. It is currently being tested in Europe for use in Chinese-made Geely cars that use pure methanol. It is well known that CO2 can be converted into methanol. However, when the product is used for transportation fuels, CO2 is released from the vehicle’s tail pipe after combustion in the gasoline or diesel driven vehicles. Thus, there is no net removal of CO2 from the atmosphere, just a transfer from one location to another. If the methanol were to be used in any of its many other applications, such as building products, adhesives or paints, the CO2 would be effectively captured and emissions reduced.
The above three technologies are just a sampling of what organizations around the globe are doing to capture and utilize carbon emissions, to reduce the presence of greenhouse gasses, and to protect the world from the potentially devastating effects of climate change.