SODIUM-CALCIUM-ALUMINOSILICATE COLUMN FOR ADSORBING CO2

Abstract

A new adsorbent CO.sub.2-ONE for removal of acidic gases such as carbon dioxide and hydrogen sulfide was developed from hydrothermal reaction of natural limestone with natural kaolin via sodium hydroxide. Several synthesis conditions were employed such as initial concentration of NaOH, weight ratio of limestone to kaolin, reaction temperature and pressure. The produced CaNaSiO.sub.2Al.sub.2O.sub.3 samples were characterized using XRD and EDS and showed that a mixture of Gehlenite Ca.sub.2Al(A.sub.1.22Si.sub.0.78O.sub.6.78)OH.sub.0.22 and Stilbite Na.sub.5.76Ca.sub.4.96(Al.sub.15.68Si.sub.56.32O.sub.144) with percentage of 43 and 57 was successfully produced, respectively. Another produced sample showed the presence of Gehlenite Ca.sub.2Al(Al.sub.1.22Si.sub.0.78O.sub.6.78)OH.sub.0.22, Stilbite Na.sub.5.76Ca.sub.4.96(Al.sub.15.68Si.sub.56.32O.sub.144) and Lawsonite CaAl.sub.2Si.sub.2O.sub.7OH.sub.2(H.sub.2O) with percentage of 4.1 and 7.4 and 88, respectively.

Claims

1-9. (canceled)

10: A CO.sub.2 adsorption column, comprising: an gas adsorption column having: a CO.sub.2 inlet, a gas outlet, and a fixed bed column disposed inside the column between the CO.sub.2 inlet and the gas outlet, wherein the fixed bed column comprises a CaNaSiO.sub.2Al.sub.2O.sub.3/Sodium-Calcium-Aluminosilicate composition comprising 3-6% gehlenite, 5-9% stilbite, and 86-92% lawsonite.

11: The CO.sub.2 adsorption column of claim 10, wherein the CaNaSiO.sub.2Al.sub.2O.sub.3/Sodium-Calcium-Aluminosilicate composition comprises 4-5% gehlenite, 6-8% stilbite, and 87-91% lawsonite.

12: The CO.sub.2 adsorption column composition of claim 10, wherein the CaNaSiO.sub.2Al.sub.2O.sub.3/Sodium-Calcium-Aluminosilicate composition comprises 4.1% gehlenite, 7.4% stilbite, and 88% lawsonite.

13-15. (canceled)

16: The CO.sub.2 adsorption column of claim 10, wherein the fixed bed column has an acidic gas adsorption capacity of 0.10 mol/g to 0.2 mol/g after a 1.sup.st regeneration cycle.

17: The CO.sub.2 adsorption column of claim 10, wherein the fixed bed column has an acidic gas adsorption capacity of 2.0 mol/g to 2.5 mol/g after a 5.sup.th regeneration cycle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

[0035] FIG. 1 is an X-Ray diffraction diagram for the CO.sub.2-ONE adsorbent;

[0036] FIG. 2 is an X-Ray diffraction diagram of natural limestone, calcite, and quartz;

[0037] FIG. 3 is an X-Ray diffraction diagram of natural kaolin, kaolinite, and anatase;

[0038] FIG. 4 is a diagram of a breakeven curve for adsorption/desorption of CO.sub.2 by CO.sub.2-ONE adsorbent;

[0039] FIG. 5 is a diagram of a breakeven curve for adsorption/desorption of CO.sub.2 by limestone;

[0040] FIG. 6 is a diagram of a breakeven curve for adsorption/desorption of CO.sub.2 by kaolin;

[0041] FIG. 7 is a diagram of the effect of temperature on the adsorption of the CO.sub.2-ONE adsorbent; and

[0042] FIG. 8 is a diagram of the effect of the regeneration cycles on the amount of CO.sub.2 adsorbed, desorbed and reacted onto the CO.sub.2-ONE adsorbent.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views.

[0044] A new mixture of aluminosilicates linked with calcium and sodium oxides in their crystalline structure is disclosed. The produced materials were tested for adsorption of acidic gases such as CO.sub.2 from a gas stream.

[0045] The present disclosure relates to a CaNaSiO.sub.2Al.sub.2O.sub.3/Sodium-Calcium-Aluminosilicate composition (e.g., a CO.sub.2-ONE adsorbent) and a method for making the CO.sub.2-ONE adsorbent. The CO.sub.2-ONE composition is a CaNaSiO.sub.2Al.sub.2O.sub.3/sodium-calcium-aluminosilicate composition. In embodiments of the disclosure the CO.sub.2-ONE composition may comprise a mixture of materials such as Gehlenite (e.g., Ca.sub.2Al(Al.sub.1.22Si.sub.0.78O.sub.6.78)OH.sub.0.22) and Stilbite (e.g., Na.sub.5.76Ca.sub.4.96(Al.sub.15.68Si.sub.56.32O.sub.144)). The CO.sub.2-ONE composition may contain different amounts of Gehlenite and Stilbite. For example, the Gehlenite may be present in an amount of from 40 to 60% by mass and the Stilbite may be present in an amount of 40-60% by mass based on the total weight of the Gehlenite and Stilbite. Preferably the Gehlenite is present in an amount of 41-55, 42-50, 43-48 or 44-46% by mass. Preferably the Stilbite is present in an amount of 45-59, 50-58, 48-57 or 50-53% by mass. The CO.sub.2-ONE preferably contains at least 50% by mass, more preferably 60%, 70%, 80%, 90%, 95% or 99% by mass of a total amount of Gehlenite and Stilbite, wherein % by mass is based on the total weight of the CO.sub.2-ONE composition.

[0046] In another embodiment the CO.sub.2-ONE composition comprises a mixture of Gehlenite, Stilbite and Lawsonite (e.g., CaAl.sub.2Si.sub.2O.sub.7OH.sub.2(H.sub.2O)). The Gehlenite is preferably present in an amount of 1-10% by mass, more preferably 2-8, 3-6 or 4-5% by mass based on the total mass of Gehlenite, Stilbite and Lawsonite. The Stilbite is preferably present in an amount of 5-15% by mass, more preferably 6-14, 7-13, 8-12 or 9-11% by mass. The Lawsonite is preferably present in an amount of 80-95% by mass, more preferably 81-94%, 82-93%, 83-92%, 84-91%, 85-90%, 86-89% or 87-88% by mass. As is the case for the CO.sub.2-ONE composition that comprises Gehlenite and Stilbite without Lawsonite, the Lawsonite-containing CO.sub.2-ONE composition preferably contains Gehlenite, Stilbite and Lawsonite in an amount of at least 50% by mass, more preferably 60%, 70%, 80%, 90%, 95% or 99% by mass based on the total mass of the CO.sub.2-ONE composition. The CO.sub.2-ONE composition may contain other tectosilicate minerals and/or zeolites. Stilbite-Na is preferred over Stilbite-Ca. Because silicon and aluminum ions in Stilbite occupy equivalent positions it is possible for the Si/Al ratio to vary. Variance in the Si/AI ratio must be compensated by adjusting the corresponding sodium/calcium ratio. The Stilbite is ordinarily present in the monoclinic 2/m phase although orthorhombic or triclinic phases may also be present in minor amounts.

[0047] Sorosilicates other than Gehlenite may also be present in the CO.sub.2-ONE composition. In some embodiments the Gehlenite may be present in an aluminum-rich phase. The Gehlenite has a tetragonal crystal system and may be interlinked with a crystal system of the aluminosilicate framework structure.

[0048] Lawsonite, like Gehlenite, is a sorosilicate mineral but is present in its hydrous calcium aluminum form in the present disclosure. Lawsonite is preferably present in a major amount in its orthorhombic phase but may also be present in a minor amount in one or more other phases.

[0049] Lawsonite may have an idealized composition of formula of CaAl.sub.2Si.sub.2O.sub.7(OH).sub.2. Gehlenite has an idealized formula of Ca.sub.2Al(AlSiO.sub.7). Stilbite has an idealized formula of NaCa.sub.4(Si.sub.27Al.sub.9)O.sub.72.28(H.sub.2O).

[0050] The CO.sub.2-ONE composition may be obtained by treating mixtures of minerals by heating and/or calcination. Kaolin is a convenient clay mineral that may be used as one precursor to the CO.sub.2-ONE composition. Kaolin has an idealized chemical composition of Al.sub.2Si.sub.2O.sub.5(OH).sub.4 although variations in chemical composition are included. Heating kaolin leads to dehydroxylation and formation of materials having a generalized formula of Al.sub.2Si.sub.2O.sub.7 which may be further heated to separate portions of SiO.sub.2 and form spinels such as Si.sub.3Al.sub.4O.sub.12. Calcination of kaolin or a spinel or metakaolin derived from kaolin can further drive out SiO.sub.2 to form compounds of general formula Si.sub.2Al.sub.6O.sub.15.

[0051] The kaolin may be treated in combination with limestone (CaCO.sub.3). Heating mixtures of kaolin and limestone provides a method of forming the CO.sub.2-ONE composition of the present disclosure. Treating limestone and kaolin with a base such as NaOH under certain temperature and environmental conditions forms the CO.sub.2-ONE composition of the present disclosure.

[0052] First, rocks of limestone and kaolin are crushed. Once the rocks are crushed, they are sieved into different particle sizes. The particle sizes of the rocks are in the range of 4 mm-650 m, 3 mm-550 m, or 2 mm-450 m. Preferably, the particle sizes of the rocks are in the range of 2 mm-450 m. The rocks are then placed in a closed-capped container for further use. Limestone and kaolin are mixed using different amounts of a base containing a single OH functional group. The base can include but is not limited to sodium hydroxide (NaOH), lithium hydroxide (LiOH), or potassium hydroxide (KOH). Preferably the base is NaOH. The amount of base that is mixed with the sample of limestone and kaolin includes different concentrations in the range of including but not limited to 2 g/100 mL-40 g/100 mL, 3 g/100 mL-38 g/100 mL, or 4 g/100 mL-36 g/100 mL. for a time period in the range of 30 minutes-2 hours, 45 minutes-2.5 hours, or 55 minutes-1.5 hours. Preferably, the amount of base mixed with the sample of limestone and kaolin includes a concentration in the range of 4 g/100 mL-36 g/100 mL over a time period of 1 hour.

[0053] The mixed sample of limestone, kaolin, and base is then placed in a hydrothermal reactor operating at different reaction temperatures in the range of 30 C.-300 C., 40 C.-250 C., or 50 C.-200 C. and a pressure in the range of 2 bar-20 bar, 3 bar-18 bar, or 4 bar-15 bar. Preferably, the reaction temperature in the reactor is in the range of 50 C.-200 C. and the reaction pressure in the reactor is in the range of 4 bar-15 bar. Nitrogen is then introduced to the reactor to maintain the desired temperature and pressure ranges.

[0054] Once the reaction occurs, the produced samples are cooled to room temperature. Cooling occurs through a natural process in which the samples settle and over time the temperature reaches equilibrium with the air surrounding it. Cooling occurs over a time period in the range of 1 hour-3 hours, 1.5 hours-2.5 hours, or 1.75 hours-2.25 hours. Preferably, cooling occurs over a time period of 2 hours.

[0055] Following cooling, the dried residue is subject to calcination treatment. Calcination can be carried out in shaft furnaces, rotary kilns, multiple hearth furnaces, and/or fluidized bed reactors. Calcination is conducted over a time period of 1-4 hours, 1.25-3.5 hours, or 1.5-3.25 hours at a temperature ranging from 400-700 C., 500-650 C., or 525-575 C. Preferably calcination is conducted for about 2 hours at a temperature of 550 C. Following calcination, the sample is washed with deionized water, dried and stored to be used in a sorption-desorption method. The CO.sub.2-ONE composition is preferably used as a sorbent for CO.sub.2. By contacting the CO.sub.2-ONE composition with CO.sub.2-containing gaseous phase the CO.sub.2 is absorbed by the CO.sub.2-ONE composition and its concentration in the surrounding gaseous environment is reduced. The CO.sub.2-ONE composition may be used to reduce the amount of CO.sub.2 in a gaseous environment by an amount of 50-99.5% by mass based on the total mass of CO.sub.2 present in the gaseous environment. Preferably the CO.sub.2 concentration in the gaseous environment is reduced by an amount of 60%, 70%, 80%, 90%, 95% by mass based on the total amount of CO.sub.2 present in the gaseous atmosphere.

[0056] A method of sorption of a sample of CO.sub.2 is carried out by placing a fixed amount of different ranges of sample sizes in an isothermal column. CO.sub.2 is introduced to the bed from the bottom of the column using a fixed flow rate. The initial concentration of CO.sub.2 is in the range of 1.6%-2.2%, 1.7%-12.0%, or 1.8%-1.9% and the flow rate of the CO.sub.2 is in the range of 2 L/min-6 L/min, 3 L/min-5 L/min, or 3.5 L/min-4.5 L/min. Preferably, the initial concentration of CO.sub.2 is 1.87% and the flow rate is 4 L/min. The concentration of CO.sub.2 at the exit stream is measured at different periods of time at one minute intervals ranging from 0 minutes-12 minutes. The difference in concentration between the inlet and outlet streams is calculated. A similar procedure is carried out to detect the sorption capacity of the sample against CO.sub.2-free gas to use as a comparison.

[0057] After having absorbed CO.sub.2 the CO.sub.2-ONE composition may be regenerated and/or recycled by desorbing the previously-absorbed CO.sub.2. Desorption may be carried out by heating the CO.sub.2-containing CO.sub.2-ONE composition and passing one or more inert gases over the CO.sub.2-ONE composition. At sufficient temperature CO.sub.2 will desorb from the CO.sub.2-ONE composition. Desorption may remove more than 50%, preferably more than 60%, 70%, 80%, 90%, 95% of the CO.sub.2 adsorbed thereon from a gaseous environment.

[0058] A method of desorption of a sample of N.sub.2 is carried out by placing a fixed amount of different ranges of sample sizes in an isothermal column. N.sub.2 is introduced to the bed from the bottom of the column using a fixed flow rate. The initial concentration of N.sub.2 is in the range of 1.6%-2.2%, 1.7%-12.0%, or 1.8%-1.9% and the flow rate of the N.sub.2 is in the range of 2 L/min-6 L/min, 3 L/min-5 L/min, or 3.5 L/min-4.5 L/min. Preferably, the initial concentration of N.sub.2 is 1.87% and the flow rate is 4 L/min. The concentration of N.sub.2 at the exit stream is measured at different periods of time at one minute intervals ranging from 0 minutes-12 minutes. The difference in concentration between the inlet and outlet streams is calculated.

Example

Preparation of Adsorbent

[0059] Rocks of limestone and kaolin were crushed and sieved to different particles sizes ranging from 2 mm-450 m, then placed in a closed-capped container for further use. A representative sample of each of limestone and kaolin was mixed with different concentrations of sodium hydroxide for 1 h then placed in a hydrothermal reactor operated at different reaction temperature and pressure (Table 1). Nitrogen was introduced to the reactor to maintain the desired pressure. Upon completion of the reaction, the produced samples were cooled to room temperature and exposed to air for 2 h, then calcinated at 550 C. for 2 h. Then the sample was washed with deionized water, dried and stored in closed-container for application. Table 1 is presented below.

TABLE-US-00001 TABLE 1 Full factorial design for proposed experiments Carbonate [NaOH] Pressure DESIGN EXP RUN (g) (g/100 ml) Temperature (bar) ORDER ORDER A B C D 1 1 2 4 50 15 2 2 6 4 50 4 3 3 6 4 50 15 4 4 2 4 50 4 5 5 2 36 50 4 6 6 6 36 50 4 7 7 2 36 50 15 8 8 6 36 50 15 9 9 2 4 200 4 10 10 6 4 200 4 11 11 2 4 200 15 12 12 6 4 200 15 13 13 6 36 200 15 14 14 2 36 200 4 15 15 6 36 200 4 16 16 2 36 200 15

Example

Sorption-Desorption Procedure

[0060] Sorption-desorption procedure was carried out by placing fixed amount of different particle sizes of the produced sample in an isothermal column. Gas stream containing a fixed concentration of CO.sub.2 were introduced to the bed from the bottom of the column at fixed flow rate. Then the concentration of CO.sub.2 at the exit stream was measured at different periods of time and the difference in concentration between the inlet and outlet streams were calculated. Similar procedure was used to detect the sorption capacity of the sample against CO.sub.2-free gas for comparison. Desorption procedure was similar to the above procedure except that nitrogen gas was introduced instead of CO2. All the experiments were repeated at different conditions such as bed temperature and gas flow rate.

[0061] A new adsorbent CO.sub.2-ONE for removal of acidic gases such as carbon dioxide and hydrogen sulfide was developed from hydrothermal reaction of natural limestone with natural kaolin and sodium hydroxide. Several synthesis conditions were employed such as initial concentration of NaOH, weight ratio of limestone to kaolin, reaction temperature and pressure. The produced CaNaSiO.sub.2Al.sub.2O.sub.3 samples were characterized using XRD and EDS and showed that a mixture of Gehlenite Ca.sub.2Al(Al.sub.1.22Si.sub.0.78O.sub.6.78)OH.sub.0.22 and Stilbite Na.sub.5.76Ca.sub.4.96(Al.sub.15.68Si.sub.56.32O.sub.144) with percentage of 43 and 57 was successfully produced, respectively. Another produced sample showed the presence of Gehlenite Ca.sub.2Al(Al.sub.1.22Si.sub.0.78O.sub.6.78)OH.sub.0.22 Stilbite Na.sub.5.76Ca.sub.4.96(Al.sub.15.68Si.sub.56.32O.sub.144) and Lawsonite CaAl.sub.2Si.sub.2O.sub.7OH.sub.2(H.sub.2O) with percentage of 4.1 and 7.4 and 88, respectively.

[0062] Both produced samples were tested for adsorption/desorption of CO.sub.2 at 22 C. and 1 atm, and compared with raw materials and found that for a given mass of sample of 13.5 g, initial flow rate and concentration of CO.sub.2 of 4 L/min and 1200 mg/L, respectively, the breakeven adsorption curves as follows: for the produced sample it took 59 min to get saturated with CO.sub.2 while limestone and kaolin took 0.27 and 0.23 min, respectively to reach the same saturating value.

[0063] The adsorptions of CO.sub.2 by the treated samples follow chemisorptions process where a chemical reaction between the CO.sub.2 and the surface took place. This sorption is enhanced with increasing bed temperature which concludes endothermic process at the surface of the produced samples.

[0064] The new adsorbent was tested after several regeneration cycles with 14 M NaOH and found that its capacity increases with increasing the regeneration cycles as a result of more Na oxide linked aluminosilicate structure with the treatment of NaOH. When the initial gas concentration is 1.87% and the flow rate is 4 L/min, the maximum adsorption capacity initially is 0.143 mol/g, followed by 0.513 mol/g after 1.sup.st regeneration, by 0.435 mol/g after 2.sup.nd regeneration, by 0.526 mol/g after 3.sup.rd regeneration, by 1.272 mol/g after 4.sup.th regeneration and by 2.223 mol/g after 5.sup.th regeneration. FIG. 1 is an XRD for the produced CO2-ONE adsorbent. FIG. 2 is an XRD of natural limestone, Calcite 34%, and Quartz 66%. FIG. 3 is an XRD of natural kaolin, Kaolinite 83.5% and Anatase 16.5%. FIG. 4 is a graph depicting a breakeven curve for adsorption/desorption of CO2 by CO2-ONE adsorbent. FIG. 5 is a graph depicting a breakeven curve for adsorption/desorption of CO2 by Limestone. FIG. 6 is a graph depicting a breakeven curve for adsorption/desorption of CO2 by Kaolin. FIG. 7 is a graph depicting the effect of temperature (5, 15, 25, 35, 50, 60, and 70 C.) on the adsorption of the CO2-ONE adsorbent. The initial CO.sub.2 concentration was 18700 mg/L (1.87%). FIG. 8 is a graph depicting the effect of regeneration cycles on amount of CO2 adsorbed, desorbed and reacted onto CO2-ONE adsorbent. The initial CO2 concentration was 18700 mg/L (1.87%).

[0065] Thus, the foregoing discussion discloses and describes merely exemplary embodiments of the present invention. As will be understood by those skilled in the art, the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting of the scope of the invention, as well as other claims. The disclosure, including any readily discernible variants of the teachings herein, define, in part, the scope of the foregoing claim terminology such that no inventive subject matter is dedicated to the public.