Method of Sequestering Carbon Dioxide

Abstract

A method of sequestering carbon dioxide comprises reacting the carbon dioxide with aqueous magnesium ions at elevated pH to form magnesium carbonate-containing salts. The carbon dioxide is preferably reacted with alkali to form carbonate and/or bicarbonate anions at elevated pH, and the carbonate and/or bicarbonate anions are subsequently reacted with aqueous magnesium cations to form the magnesium carbonate-containing salts. A preferred alkaline material for use in elevating the pH of the aqueous solution in the present invention is Cement Kiln Dust (CKD), and a preferred source of aqueous magnesium ions is reject water from a desalination plant.

Claims

1-13. (canceled)

14. A method of sequestering carbon dioxide produced by a cement plant which comprises reacting the carbon dioxide with aqueous magnesium ions at an elevated pH, defined as a pH of 8 to 12, to form magnesium carbonate-containing salts, wherein the carbon dioxide is reacted with alkali to form carbonate and/or bicarbonate anions at the elevated pH, and the carbonate and/or bicarbonate anions are subsequently reacted with aqueous magnesium cations to form the magnesium carbonate-containing salts, and wherein the cement plant is coupled with a desalination plant in that effluent from the desalination plant is provided to the cement plant.

15. The method according to claim 14, wherein the source of aqueous magnesium ions is reject water from the desalination plant.

16. The method according to claim 14, wherein the magnesium ions are present in the aqueous solution in an amount of 2-5 g/L.

17. The method according to claim 14, wherein the elevated pH is defined as a pH of 10 to 12.

18. The method according to claim 14, wherein the elevated pH is defined as a pH of 9 to 11.

19. The method according to claim 14, wherein the carbon dioxide is reacted with the alkali at 1 to 3 equivalent moles of alkali per litre.

20. The method according to claim 14, wherein the equivalent moles of alkali per mole of sequestered carbon dioxide is between 1 and 2.

21. The method according to claim 14, wherein the carbonate and/or bicarbonate containing aqueous solution resulting from the reaction of the carbon dioxide with alkali reacts with the magnesium ions precipitating magnesium carbonate-containing salts at a temperature of 10 to 80 C.

22. The method according to claim 21, wherein the carbonate and/or bicarbonate containing aqueous solution resulting from the reaction of the carbon dioxide with alkali reacts with the magnesium ions precipitating magnesium carbonate-containing salts at a temperature of 20 to 70 C.

23. The method according to claim 14, wherein the alkaline material used to elevate the pH of the aqueous solution comprises Cement Kiln Dust (CKD).

24. The method according to claim 23, wherein a condensate salt is added to the CKD from the kiln gas phase.

25. The method according to claim 24, wherein the condensate salt comprises potassium chloride.

26. The method according to claim 14, wherein the magnesium carbonate-containing salts formed by the method include salts of the nesquehonite-lansfordite family, Mg(CO.sub.3).nH.sub.2O, the hydromagnesite-dypingite family, Mg.sub.5(CO.sub.3).sub.4(OH).sub.2.nH.sub.2O, and/or the artinite family, Mg.sub.2(CO.sub.3)(OH).sub.2.3H.sub.2O.

Description

EXAMPLE

Synthesis Study

[0025] Experiments were performed to study the effect of varying the temperature and reaction time on the phase of product formed from the reactions of the method of the present invention, including the yields of magnesium and consequently carbon dioxide in the product.

[0026] Thus, 100 ml of a 1M MgCl.sub.2 solution was added to 1 L of a 0.1M Na.sub.2CO.sub.3 solution brought to the target temperature. After filtration, the solid was dried over silica gel, ground, and scanned by XRD and SEM.

[0027] The yield of the reaction for Mg was calculated from the relation: Mg yield [mass %]=100*(mass of Mg in initial solutionmass of Mg in filtrate)/mass of Mg in initial solution. The mass of Mg in the filtrate was calculated from AAS measurements: the lower the Mg concentration in the filtrate, the higher the yield and so the higher the amount of Mg being precipitated. The uncertainty of the yield values is +/5% due to uncertainties in amounts recovered and in analyses. For example, variations in the total volume as well as the amount of water incorporated in the solid products have been neglected: for 0.1 mol of NQ precipitated, the volume of water incorporated is the order of 5 mL, whereas for 0.02 mol of HM precipitated, the volume of water incorporated is the order of 2 mL (results for an initial total volume of approximately 1.1L).

[0028] The yield of the reaction for CO.sub.2 can be calculated from the Mg yield as such: CO.sub.2 yield [mass %]=Mg yield*R where R is the CO.sub.2/Mg molar ratio in the product formed (R=1 for NQ and R=0.8 for HM/DG/DG*), see Table 1 above. (N.B. DG* is short-hand notation for a dypingite-like phase, i.e. a phase similar to hydromagnesite but with more than 4 moles of crystallisation water per formula unit, DG being the specific case where there are 5 moles of crystallisation water). As HM, DG and DG* have the same R value, there is no need to define the relative amounts of each phase in the case of a mixture. However, in the case of a mixture of NQ and HM/DG/DG*, the two R values are different and so the relative proportions of the phases need to be estimated from the XRD patterns. Because of the approximation made, a range of values instead of a single value is given in Table 2. The uncertainty of each value is +/5%.

TABLE-US-00002 TABLE 2 Main phase in Mg yield CO.sub.2 yield T ( C.) t (h) product (mass %) (mass %) 25 1 NQ 59 59 2 NQ 82 82 4 NQ 91 91 24 NQ 86 86 35 1 NQ 68 68 2 NQ 77 77 4 NQ + DG* 77 76-77 24 DG* (2 phases) 73 58 45 1 NQ + DG* 77 76-77 2 NQ + DG* 82 81-82 4 NQ + DG* 82 75-78 24 DG* 86 69 55 1 NQ + DG* 77 76-77 2 DG* 73 58 4 DG* 82 66 24 HM + DG* 82 66 65 1 HM + DG 86 69 2 HM + DG 86 69 4 HM + DG* 86 69 24 HM 95 76