University of Nottingham Establishes Carbon Capture and Storage Center; One Focus To Be on Serpentinization
The University of Nottingham (UK) is establishing a Centre for Innovation in Carbon Capture and Storage (CICCS) with £1.1 million (US$2.23 million) in funding from the Engineering and Physical Sciences Research Council (EPSRC).
The center, which is due to open in October 2007, will develop novel technologies to trap and store greenhouse gases permanently and safely. One of the processes the center will work on will use “serpentinization”—the acceleration of the natural geologic process of the carbonation of a magnesium silicate material such as serpentine (Mg3Si2O5(OH)4) to magnesite (MgCO3).
The natural process can be accelerated by increasing the surface area, increasing the activity of carbon dioxide in the solution, introducing imperfections into the crystal lattice by high-energy attrition grinding, and by thermally activating the mineral by removing the chemically bound water.
The US Department of Energy Office of Fossil Fuel’s Albany Research Center has run a series of tests on similar ex-situ mineral carbonation in an aqueous system. The process developed at ARC utilizes a slurry of water mixed with a magnesium silicate mineral, olivine [forsterite end member (Mg2SiO4)], or serpentine. This slurry is reacted with supercritical carbon dioxide (CO2) to produce magnesite.
The CO2 is dissolved in water to form carbonic acid (H2CO3), which dissociates to H+ and HCO3. The H+ reacts with the mineral, liberating Mg2+ cations which react with the bicarbonate to form the solid carbonate. The process is designed to simulate the natural serpentinization reaction of ultramafic minerals.
In a review of baseline test results, the Albany researchers noted:
Tests conducted at ambient temperature (22°C) and subcritical CO2 pressures (below 73 atm) resulted in very slow conversion to the carbonate. However, when elevated temperatures and pressures are utilized, coupled with continuous stirring of the slurry and gas dispersion within the water column, significant reaction occurs within much shorter reaction times.
Extent of reaction, as measured by the stoichiometric conversion of the silicate mineral (olivine) to the carbonate, is roughly 90% within 24 hours, using distilled water, and a reaction temperature of 185°C and a partial pressure of CO2 (PCO2) of 115 atm. Recent tests using a bicarbonate solution, under identical reaction conditions, have achieved roughly 83% conversion of heat treated serpentine and 84% conversion of olivine to the carbonate in 6 hours. The results from the current studies suggest that reaction kinetics can be improved by pretreatment of the mineral, catalysis of the reaction, or some combination of the two. Future tests are intended to examine a broader pressure/temperature regime, various pretreatment options, as well as other mineral groups.
The University of Nottingham estimates that once its serpentinization process is fully developed, the mineral carbonation of CO2 will take place within minutes.
The end product magnesite can be used as aggregates for road-building or shaped into bricks for construction. Carbon dioxide makes up 40% of its weight.
Compared to other proposed processes for carbon storage, such as geosequestration, once the CO2 is locked inside the rock, it cannot revert to its previous state. Moreover, the end result is a commercial product. Fossil fuel power plants could utilize the new process by adding a reactor to their emissions treatment system, allowing CO2 to be turned into a useful building material. The Centre’s ultimate goal will be to sign collaborative agreements with power and construction companies to move forward with commercialization of the technology.
Carbon Dioxide Sequestration by Aqueous Mineral Carbonation of Magnesium Silicate Minerals (Albany Research Center, Office of Fossil Energy, US DOE)
Carbon Dioxide Sequestration by Direct Mineral Carbonation with Carbonic Acid (Albany Research Center)