The Tec-Reactor Hydroxide / Carbonate Slurry Process

The Tec-Reactor hydroxide/carbonate slurry carbon capture technology involves the solution of carbon dioxide into water forming carbonic acid, the precipitation of carbonates and the recharging the water with the carbon dioixde again.

Depending on temperature and the partial pressure, carbon dioxide is more or less taken up by water and more so by a solution of a metal hydroxides and in relation to Eco-Cement concretes this can include magnesium hydroxide. The extent to which the system could be used are still being worked out but it looks very promising especially in combination with other Gaia Engineering technologies.

CO2 could be introduced into the mix water thereby forming carbonic acid or as bubbles in a foam into Eco-Cement concretes and will accelerate the formation of carbonates.

CO2 is absorbed into water to make carbonic acid according to the reaction

H2O + CO2 <=> H2CO3
H2CO3 <=> H+ + HCO3
HCO3 <=> H+ + CO32-

In an alkaline solution such as in a concrete containing MgO, the precipitation of carbonates will occur as below

M2+ + CO32- = MCO3, where M is a divalent cation like Mg2+ or Ca2+

In the case of our Eco-Cement concretes - more rapid carbonation can be achieved however making carbonic acid or indroducing CO2 into our Eco-Cement concretes involves unnecessary extra energy and processing and is therefore less economic.

The science behind the process is well known and we believe cannot be validly patented [1] so we did not cover the introduction of CO2 directly in our magnesium concretes.

The take up of CO2 in water and precipitation of carbonates is potentially useful as part of Gaia Engineering and is further described below in relation to a recipe for making a magnesium health drink used by the Arabs who sell us most of the oil causing the problem serves to indicate the feasibility of this process.

It is well known that the colder water is (as long as it is not frozen) the more CO2 is will absorb. At say 4 degrees C the following reaction is encouraged

Mg(OH)2 + 2CO2 <=> Mg(HCO3)2 (with precipitation making the water cloudy)

At higher temperatures and with a lower partial pressure of CO2 the above reaction is easily reversed.

The Tec-Reactor hydroxide/carbonate slurry carbon capture process results in the uptake of CO2 and release of carbonate and is potentially an important part of the Gaia Engineering tececology. Inputs include fresh magnesium oxide from the Tec-Kiln and low-concentration CO2 from for example a power station.  Outputs include high-concentration CO2 as carbonate and magnesium hydroxide.

Magnesium oxide from the TecEco Tec-Kiln is dissolved in water to produce magnesium hydroxide slurry.  Gas containing CO2 is bubbled through the slurry, wherein carbonation occurs, creating magnesium carbonate hydrates in solution. The slurry is then heated to cause de-carbonation whereby the CO2 previously absorbed is driven off and captured, resulting in the reformation of magnesium hydroxide that recycles through the process.

There is a limit to how many cycles can occur before contamination of the magnesium carbonate hydrate needs to be addressed.  The rate of contamination by elements like, for example, iron will depend on a number of factors including what is in the flue gasses from for example a power station. It is hoped that processing through the Tec-Kiln will remove most of this form of contamination and at least enable the reprocessed magnesium oxide to be used as inputs to make TecEco magnesium cements. Further research needs to be undertaken prior to finalising the design of the process plant to establish the number of cycles that can be run prior to decontamination via the Tec-Kiln.

Several research groups are involved in further developing it including the university of Cincinnati, Ohio (Keener 2001 [2]), Los Alamos National University (Butt, Lackner et al. 1996[3]), the university of Barcelonia (Fernandez, Segarra et al. 1999[4]) and Arizona State University (Bearat, McKelvy et al. 2002[5]).

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[1] See for example EP 0 650 940 A1, inventor Kobori, Shigeji.

[2] Keener, T. (2001). Annual Project Report - CO2 Separation and Sequestration Utilizing FGD
Scrubber By-Products, University of Cincinatti.

[3] Butt, D. P., K. S. Lackner, et al. (1996). "Kinetics of Thermal Dehydroxylation and Carbonation of Magnesium Hydroxide." Journal of the American Ceramic Society 79(7): 1892-1898.

[4] Fernandez, A. I. C., J M, M. A. Segarra, et al. (1999). "Kinetic study of carbonation of MgO slurries." Hydrometallurgy 53: 155-167.

[5] Bearat, H., M. J. McKelvy, et al. (2002). "Magnesium Hydroxide Dehydroxylation/Carbonation Reaction Processes: Implications for Carbon Dioxide Mineral Sequestration." Journal of the American Ceramic Society 85(4): 742-748.