METHOD OF MINERALIZATION OF CO2 IN INORGANIC POLYMERS (GEOPOLYMERS)

Abstract

A process of sequestering CO.sub.2 is generally described. The process involves the use of geopolymeric precursors to which the CO.sub.2 is added. The process for a solid, cementitious material comprising geopolymer(s) and CO.sub.2.

Claims

1. A method of capturing CO.sub.2 in a geopolymer-based material wherein the method comprises the following steps: mixing of at least one geopolymeric precursor with a liquid hardener to form a slurry; adding CO.sub.2 into the slurry to initiate a reaction between the CO.sub.2 and the slurry; and allowing the slurry comprising the at least one geopolymeric precursor and CO.sub.2 to solidify, wherein the ration of SiO.sub.2/M.sub.2O in the geopolymer-based material is 2.1-2.4.

2. The method according to claim 1 wherein the CO.sub.2 is in gaseous state.

3. The method according to claim 1 wherein the CO.sub.2 is in liquid state.

4. The method according to claim 1 wherein the liquid hardener comprises potassium.

5. The method according to claim 1 wherein all the steps are conducted at a temperature of 10-150 ° C.

6. The method according to claim 1 wherein all the steps are conducted at a pressure of 0.1-20 MPa.

7. The method according to claim 1 wherein the pH is 12-14 at the start of the reaction.

8. The method according to claim 1 wherein the geopolymeric precursors are selected from rock-based, fly ash-based and slag-based geopolymeric precursors.

9. The method according to claim 1 wherein the geopolymeric precursors are rock-based.

10. The method according to claim 1 wherein the average particle size of the geopolymeric precursor is ≤100 μm.

11. A method of forming a solidified cementitious geopolymer-based material having a permeability of <100 μD, wherein the method comprises the steps according to claim 1.

12. Use of CO.sub.2 as setting accelerator for a cementitious precursor composition, wherein the cementitious material comprises at least one geopolymeric precursor material.

13. A solidified cementitious geopolymer-based material having a permeability <100 μD.

14. The method according to claim 1 wherein all the steps are conducted at temperature of 20-50° C.

15. The method according to claim 1 wherein all the steps are conducted at a pressure of 0.1-10 MPa.

16. The method according to claim 1 wherein the average particle size of the geopolymeric precursor is ≤63 μm.

17. The method according to claim 1 wherein the average particle size of the geopolymeric precursor is ≤20 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a flow-chart according to a method of the invention;

[0018] FIG. 2 a) shows a picture of a sample according to the process of the invention, b) shows a picture from a comparative example; and

[0019] FIG. 3 a) shows a picture of a sample according to the process of the invention, b) shows a picture from a comparative example.

DEFINITIONS

[0020] The following terms are defined: [0021] ‘cementitious’: a material that has the functional performance of a cement; [0022] ‘geopolymer’: inorganic polymers comprising aluminosilicate; [0023] ‘geopolymeric precursor’: solid particles in tetrahedral form which are reactive to participate in geopolymerization; [0024] ‘rock-based’: natural rocks which have reactive aluminosilicate components or can be activated through mechanical grinding, calcination or a combination of both; [0025] ‘fly-ash based’: amorphous aluminosilicate materials produced when coal is burned; [0026] ‘slag-based’: amorphous aluminosilicate materials with CaO and MgO content; [0027] ‘D’: darcy, unit for permeability, 1 darcy≈10.sup.−12 m.sup.2; and [0028] ‘Portland cement’: a calcium alumina silicate compound that is manufactured from limestone and clay (or shale) with minor amounts of iron oxide, silica sand and alumina as additives where required to balance the mineral composition.

DETAILED DESCRIPTION

[0029] Geopolymers are a class of inorganic materials, often aluminosilicate materials, that can be used as an alternative to conventional Portland cement. Generally, geopolymers has high mechanical strength, high thermal stability and other properties that are advantageous for a cementitious material. Geopolymers can come from different sources such as fly-ash, rocks and slag etc.

[0030] The present invention stores and utilizes CO.sub.2 in a geopolymeric structure by a method wherein CO.sub.2 is mixed with a slurry comprising geopolymeric precursors. In the reaction a solid geopolymeric material that comprises CO.sub.2 is formed. The formed geopolymeric material is similar to a cement. Herein, being similar to a cement implies that the material can be used in load-bearing applications. That is due to high strength and low permeability.

[0031] Herein, CO.sub.2 capture and CO.sub.2 sequestration all refer to a process of capturing waste CO.sub.2, and hence preventing it from entering the atmosphere. The CO.sub.2 can for example by captured by geopolymers by a chemical reaction, i.e. a mineralization reaction. In case of a mineralization reaction another material, for example a carbonate such as kalicinite KHCO.sub.3 may be formed. An advantage with mineralization is that the CO.sub.2 is captured in the material via a chemical reaction and hence will not escape during for example destruction of the material.

[0032] In a first aspect of the invention there is a method comprising the following sequential steps, FIG. 1: [0033] 10: mixing of at least one geopolymeric precursor with a liquid hardener to form a slurry; [0034] 11: adding CO.sub.2 to the slurry comprising at least one geopolymeric precursor to initiate a reaction between the CO.sub.2 and the slurry; and [0035] 12: allowing blend of the geopolymeric slurry and CO.sub.2 to react and solidify.

[0036] The geopolymeric precursor material advantageously have a modular ratio, i.e. the ratio of SiO.sub.2/M.sub.2O, that is 2.1-2.4. M stands for metal and can be sodium, potassium, rubidium, or cesium. In the present method if the ratio is too low ratio, such as 1.8 for example the mixture formed in step 10 will set/hardened too fast. On the other hand, in case of a too high ratio, such as 2.5 or above the time for setting will be too long to be of interest for any commercial use. In the method of the present invention the geopolymeric precursor sets after been in contact with the CO.sub.2.

[0037] Adding can be performed by injecting the CO.sub.2 into the slurry or any other suitable way.

[0038] A geopolymeric precursor is non-cured, in order to form a (cured) geopolymer a hardener must be added to the precursor mixture, e.g. a liquid hardener or a curing agent. Upon the addition of such a component, a reaction is initiated during which the geopolymeric precursors react and form an inorganic polymeric network, hence a geopolymer. In order words, the liquid hardener is used to initiate the reaction between the geopolymeric precursors and CO.sub.2 and participates in the reaction. Examples of liquid hardeners are sodium silicate solution, potassium silicate solution or a combination of both. It is advantageous that the liquid hardener comprises potassium. Potassium will make the system more stable and increase the temperature resistance of the material.

[0039] In one example of the first aspect, the mixing in step 10 can be performed using different equipment such as planetary mixers, screw blenders, high shear mixers, etc.

[0040] In one example of the first aspect the CO.sub.2 in step 11 is added in a liquid state, in another example of the first aspect, the CO.sub.2 in step 11 is added in gaseous state preferably by injection. The CO.sub.2 can also be in a mixture of both liquid and gaseous state. Once the CO.sub.2 has been added to the geopolymeric slurry, the CO.sub.2 reacts with the slurry comprising geopolymeric precursors and hardener forming a solidified and stable geopolymer-based material. The reaction is rapid, in one example of the method the reaction between CO.sub.2 and the slurry is finished within a few minutes, such as within 2 minutes. In one embodiment the geopolymeric material sets/solidifies immediately, i.e. a flash setting, when CO.sub.2 comes in contact with the geopolymeric precursor and hardener mixture.

[0041] Different geopolymeric precursors may be used. In one example of the first aspect, the geopolymeric precursors are fly ash-, slag- or rock-based. It may also be a mixture of different geopolymeric precursors. In one example of the first aspect, the geopolymeric precursors are rock-based. In another example of the first aspect, the geopolymeric precursors are a mixture of rock-based geopolymeric precursors and at least one other geopolymeric precursor.

[0042] The geopolymeric precursors in step 10 may have different particle sizes. If the particle size is too large, the geopolymeric precursors may not be reactive and hence there may be no reaction. In one example of the first aspect the average particle size of the geopolymeric precursors is ≤100 μm, preferably ≤63 μm, or more preferably ≤20 μm in average particle size. The geopolymeric precursors are sieved to control the particle sizes. The average particle size can be determined by a particle size distribution of the geopolymeric precursors determined e.g. using a Particle Size Analyzer. Such methods are known to persons skilled in the art.

[0043] The different steps of the reaction may be performed at different temperatures. In one example of the first aspect, steps 10-13 are conducted at 0-150° C., preferably 4-100° C., more preferably 4-60° C. In one example of the first aspect, steps 10-13 are conducted at 10-150° C., or 20-50° C. The temperature may be varied between the different steps, i.e. steps 10-13, so that step 11 is performed at one temperature, and step 12 at another temperature, and step 13 at a third temperature. That the reaction can be performed at low or moderate temperature as described above means that the geopolymeric material solidifies, or sets, at such low/moderate temperature. This is advantageous in terms of working temperature, when the geopolymeric material sets at a low or moderate temperature it is easier to handle and to use in different applications.

[0044] The different steps of the reaction, i.e. step 10-13, may be performed at different pressures. In one example of the first aspect, steps 10-13 are conducted at 0.1-20 MPa. In another example of the first aspect, steps 10-13 are conducted at 0.1-10 MPa.

[0045] The starting pH of the reaction may vary. In one example of the first aspect, the pH may be 12-14. The pH may drop after the reaction has finished, for example to 10-13.

[0046] After the reaction, the slurry solidifies to a solid cementitious material of CO.sub.2 and geopolymers. In one example of the first aspect the solid material may comprise or have captured up to 10 wt %, or 2-7 wt %, or 3-5 wt % CO.sub.2, as determined by weight. The CO.sub.2 may be comprised in the material in the form of a carbonate formed by mineralization.

[0047] All examples and variations of the first aspect can be combined with the second, third and the fourth aspect.

[0048] In a second aspect of the invention, there is a method comprising the steps 10-13 wherein the method is used to form a solid geopolymeric material having a permeability <100 μD. The permeability is a measure of the ability of a material to allow fluids to pass through it, which is related to the connected pores (number of pores, shape of pores, connectivity of the pores) of the material. A high permeability will allow fluids to move more rapidly through the material. It is an advantage with a low permeability, such in the μD range, since such a material will be more resistant to chemicals and minimize internal deterioration when exposed to different fluids. Said material may also act as a barrier material.

[0049] All examples and variations of the second aspect can be combined with the first, third and the fourth aspect.

[0050] In a third aspect of the invention, CO.sub.2 is used as a setting accelerator for a cementitious precursor composition where the cementitious precursor comprises at least one geopolymer. In such aspect, the CO.sub.2 is injected into a mixture of cementitious precursors to accelerate the setting reaction. It is an advantage with such a use that the cementitious material formed from the reaction comprises and stores CO.sub.2 in the material.

[0051] All examples and variations of the third aspect can be combined with the first, second and the fourth aspect.

[0052] In a fourth aspect of the invention there is provided a solidified cementitious geopolymer-based material having a permeability <100 μD from a reaction comprising steps 10-13. Such a product can be used in all applications where Portland cement is used today, e.g. as a construction material, or a load bearing element, or a replacement material, or in a mixture with Portland cement.

[0053] All examples and variations of the fourth aspect can be combined with the first, second and the third aspect.

EXPERIMENTS

Experiment 1

[0054] Four different types of geopolymeric slurries were produced to evaluate their reaction with CO.sub.2. Fly ash class F and aplite rock were used as geopolymeric precursors. The hardener was potassium silicate solution. The liquid to solid weight ratio was selected to be 0.52. The different ratios etc. can be seen in table 1.

[0055] The hardener was poured into a commercial blender and then the geopolymeric precursor was added to and mixed with the hardener for 15 seconds at 4000 rpm speed, after which the geopolymeric slurry was stirred at 12000 rpm for 35 seconds to obtain a homogenous slurry. After mixing, the slurry was poured into an atmospheric consistometer cup to be conditioned for 20 minutes. The conditioning produces a homogeneous geopolymeric slurry. After conditioning, the geopolymeric slurry was poured into a test cell, with a known weight, and CO.sub.2 was injected into the slurry. The slurry was left until the reaction with CO.sub.2 was complete, the reaction between the geopolymeric slurry and CO.sub.2 was almost immediate. When the setting was completed, the cell was disconnected from the CO.sub.2 source and the pressure lowered to atmospheric condition to remove the non-reacted CO.sub.2, trapped as gas inside the geopolymer matrix. The cell, with the reacted geopolymer, was weighed again to calculate the wt % of captured/reacted CO.sub.2.

TABLE-US-00001 TABLE 1 Compositions and corresponding weight of adsorbed CO.sub.2. The temperature was the same during each method. Geo- Type of pH Weight of polymeric geopoly- value absorbed wt. % of Hardener precursor Type of meric Modular (start Temp. CO.sub.2 absorbed (g) (g) hardener precursor ratio* value) (° C.) (g) CO.sub.2 66.4 127.7 K-Silicate Rock- 2.35 13.5 50 4.52 2.3 solution based 73.8 142 K-Silicate Rock- 2.35 13.5 22 4.59 2.1 solution based 26.4 50.8 K-Silicate Fly ash- 2.3 13.5 22 3.35 4.3 solution based 30 57.2 K-Silicate Slag- 2.4 13.5 22 6 6.9 solution based *Modular ratio means the ratio of SiO.sub.2/M.sub.2O where M can be sodium, potassium, rubidium, or cesium.

Experiment 2

[0056] Two different geopolymer recipes GP1 and GP2 were prepared and exposed for CO.sub.2. The different compositions etc. can be seen in Table 2. As comparison one sample of each recipe (GP1 and GP2) was kept in an isolated cell without exposure to CO.sub.2.

[0057] The GP1 samples were cured for 7 days, after which it was exposed to CO.sub.2 in gaseous form. After the CO.sub.2 exposure the sample area exposed to CO.sub.2 solidified/set immediately. The GP1 sample that was not exposed to CO.sub.2 did not solidify/set at all.

[0058] In the next step both GP1 samples, the sample exposed to CO.sub.2 and the one not exposed, were placed in an oven and cured at 70° C. for 4 days. Both samples solidified after the oven treatment. The GP1 sample not exposed to CO.sub.2 shrunk, while the GP1 sample exposed to CO.sub.2 maintained its dimension. The GP1 sample exposed to CO.sub.2 formed kalicinite (KHCO.sub.3) on top and 0.5 cm below the exposure area, as determined by XRD analysis. Pictures of the different GP1 samples can be seen in FIG. 2a and b. FIG. 2a shows a GP1 sample that was exposed to CO.sub.2 and cured as described above, and FIG. 2b shows a GP sample that was not exposed to CO.sub.2 but cured. The kalicinite formed on top of the sample is visible in FIG. 2a.

[0059] The GP2 samples were manufactured to solidify at room temperature. Both GP2 samples, the one exposed to CO.sub.2 and the one not exposed to CO.sub.2 solidified at room temperature. However, the GP2 sample exposed for CO.sub.2 was harder at the surface (the CO.sub.2 exposure area) than the non-CO.sub.2 exposed sample.

[0060] The GP2 sample exposed for CO.sub.2 formed kalicinite at the surface, as determined by XRD analysis. FIG. 3a and b shows the GP2 samples. FIG. 2a shows the GP2 sample that was not exposed to CO.sub.2 while FIG. 2b shows the sample that was exposed to CO.sub.2. In FIG. 2b the kalicinite formed on top of the sample is visible

[0061] The GP1 samples exposed for CO.sub.2 had taken up 2.2 wt % CO.sub.2, and the GP2 sample exposed for CO.sub.2 had taken up ˜0.8 wt % CO.sub.2 as determined by weight analysis, before and after exposure.

TABLE-US-00002 TABLE 2 Compositions and corresponding weight of adsorbed CO.sub.2. The temperature was the same during each method. Geo- Type of pH Weight of polymeric geopoly- value absorbed wt. % of Hardener precursor Type of meric Modular (start Temp. CO.sub.2 absorbed (g) (g) hardener precursor ratio* value) (° C.) (g) CO.sub.2 GP1 71 128 K-silicate Rock- 2.4 13.5 22 4.22 2.1 solution based GP2 73 132 K-silicate Rock- 2.3 13.5 22 1.59 0.8 solution based *Modular ratio means the ratio of SiO.sub.2/M.sub.2O where M can be sodium, potassium, rubidium, or cesium.