Process for producing a highly porous CaO-based material modified with carbon nanotubes for capturing vehicle CO.SUB.2 .product and use

Abstract

The invention refers to the process of obtaining porous spheres based on CaO modified with carbon nanotubes for the capture of CO.sub.2. The invention also refers to the spheres obtained and their use to capture CO.sub.2 generated by a vehicular internal combustion engine, aiming to reduce the amount of CO.sub.2 released into the atmosphere.

Claims

1. A process for obtaining a CaO-based material or a MgO-based material comprising the following steps: a) Solubilizing between 0.005 and 0.05 g of a carbon material with 20.0 mL to 200.0 mL of distilled water; b) Stirring for 15 to 20 minutes; c) Adding to the solution obtained in step b, 10.00 to 50.00 g of calcium oxide or magnesium oxide; d) Shaking for 10 to 15 minutes; e) Transferring the compound obtained in step d to an ultrasound bath for 25 to 30 minutes; f) Transferring the compound obtained in step e to silicone molds containing hemispherical cavities from 6 to 8 mm in diameter; g) Transferring the material obtained in f to an oven at a temperature of 60 to 80 C. for a time of 9 to 12 h to dry the material and to obtain hemispherical granules; h) Demolding the hemispherical granules obtained in step g and heating in an air atmosphere in a temperature range of 400 to 500 C. for a period of time of 20 to 30 minutes then heating up to 700 to 800 C. for 20 to 30 minutes, thus removing the carbon material; i) Cooling the material obtained in step h to room temperature.

2. The process of claim 1, wherein the carbon material is carbon nanotubes, carbon, activated carbon, or graphene.

3. The process of claim 2, wherein the carbon material is carbon nanotubes.

4. The process of claim 3, wherein the CaO-based material or the MgO-based material contains 0.05 to 0.1% carbon nanotubes by mass.

5. The process of claim 4, wherein the CaO-based material or the MgO-based material contains 0.05% carbon nanotubes by mass.

6. The process of claim 1, wherein the addition of step c occurs by physical mixture or chemical incorporation.

7. The process of claim 1, wherein: in step a, the amount of the carbon material used is 0.005 g and the amount of distilled water used is 20.0 mL; in step b, the stirring occurs for 20 minutes; in step d, the shaking occurs for 15 minutes; in step e, the compound is transferred to the ultrasound bath for 30 minutes; in step f, the diameter of the hemispherical cavities is 8 mm; in step g, the temperature of the oven is 80 C. and the material is transferred to the oven for 12 hours; in step h, the temperature of the air atmosphere is initially 500 C. and the hemispherical granules are heated for 30 minutes; and in step h, the air atmosphere is raised to 800 C. and the hemispherical granules are heated for an additional 30 minutes.

8. The process of claim 1, wherein calcium oxide is added in step c.

9. The process of claim 1, wherein magnesium oxide is added in step c.

10. A method of capturing CO.sub.2, comprising the step of providing the CaO-based material or the MgO-based material obtained from the process of claim 1 to capture the CO.sub.2.

11. The method of claim 10, wherein the CO.sub.2 captured is vehicular CO.sub.2 and wherein the CaO-based material or the MgO-based material is coupled to car exhausts to capture the vehicular CO.sub.2.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 graphically shows the ability of materials capturing CO.sub.2 before and after modification with carbon nanotube.

(2) FIGS. 2A-2B graphically show CO.sub.2 adsorption isotherm under CO.sub.2/N.sub.2 atmosphere at 350 C. for 12 h (FIG. 2A). Carbonation at 350 C. and regeneration at 900 C. of the CaO-NanCal adsorbent in five performance cycles (FIG. 2B).

(3) FIG. 3 graphically shows adsorption/desorption isotherms of N.sub.2 at 196 C. and pore size distribution of the materials.

DETAILED DESCRIPTION OF THE TECHNOLOGY

(4) The invention refers to the process of obtaining CaO-based material, modified with carbon nanotubes for the capture of CO.sub.2. The invention also refers to the product obtained, which consists of the CaO-material, preferably in the form of porous spheres, which capture CO.sub.2 and, therefore, can be used to capture the CO.sub.2 generated by a vehicular internal combustion engine, aiming to reduce the amount of CO.sub.2 released into the atmosphere.

(5) The process for obtaining porous spheres based on CaO modified with carbon nanotubes of the present invention comprises the following steps: a. Solubilizing between 0.005 and 0.05 g, preferably 0.005 g of carbon nanotubes with 20.0 to 200.0 mL of distilled water, preferably 20.0 mL; b. Stirring for 15 to 20 minutes, preferably 20 minutes; c. Adding to the solution obtained in step b, 10.00 to 50.00 g of calcium oxide; d. Shaking for 10 to 15 minutes, preferably 15 minutes; e. Transferring the compound obtained in step d to the ultrasound bath for 25 to 30 minutes, preferably 30 minutes; f. Transferring the compound obtained in step e to silicone molds containing hemispherical cavities from 6 to 8 mm in diameter, preferably 8 mm in diameter; g. Transferring the material obtained in f to an oven at a temperature of 60 to 80 C., preferably 80 C., for a time of 9 to 12, preferably 12 hours to dry the material; h. Demolding the hemispherical granules obtained in step g and heating in an air atmosphere in a temperature range of 400 to 500, preferably 500 C., for a period of time of 20 to 30 minutes, preferably 30 minutes, then heating up to 700 to 800 C., preferably 800 C., for 20 to 30 minutes, preferably 30 minutes, thus removing the carbon nanotubes; i. Cooling the material obtained in step h to room temperature.

(6) The CaO-based material obtained contains carbon nanotubes in small amounts, from 0.05 to 0.1%, preferably 0.05% by mass.

(7) The CaO-based carbon nanotube material of the present invention can employ CaO or MgO formulations through physical mixing or chemical incorporation with carbon materials such as carbon nanotube, carbon, activated carbon or graphene. The material based on CaO with carbon nanotubes, can also be presented in the form of spheres or semi-spheres.

(8) The material defined above captures CO.sub.2. Thus, it can be used coupled to car exhausts to capture vehicle CO.sub.2.

(9) The present invention is best understood in accordance with the examples described below.

Example 1Preparation of Modified Cao with Carbon Nanotube

(10) To prepare the adsorbent, 0.005 g of carbon nanotubes (Sigma-Aldrich), 10.00 g of calcium oxide (Neon) and 20.0 mL of distilled water were used. The carbon nanotubes were quantitatively dispersed in distilled water in an ultrasound bath for 20 min, then the solution containing carbon nanotubes was poured over the 10.00 g of calcium oxide. The addition of distilled water over the solid resulted in the formation of a pasty material. The pasty material was manually mixed with the aid of a glass rod for 15 min and then transferred to an ultrasound bath and left under stirring for 30 min. The pasty material was transferred to silicone molds containing 8 mm hemispherical cavities. The mold containing pasty material was left in an oven at 80 C. for 12 hours for drying.

(11) Then the material was demolded and hemispherical granules of approximately 8 mm in diameter were obtained. The removal of carbon nanotubes was done by thermal treatment in an air atmosphere with two heating ramps: both with a heating rate of 20 C./min, the first at a temperature of 500 C. for 30 min; in the second heating step the temperature was increased to 800 C. and remained for another 30 min, after which the material was cooled to room temperature, the material was named CaO-NanCal. This procedure was necessary to completely remove the carbon nanotube and release the pores where the CO.sub.2 will be chemically adsorbed.

(12) Two other materials were tested, a commercial calcium oxide (Neon) named CaO, and calcium oxide with carbon nanotubes in the structure, named CaO-Nan. The form of preparation of CaO-Nan was identical to the CaO-Nan Cal adsorbent, except for the heat treatment step so that the material remained with the nanotube in its structure.

(13) The CO.sub.2 capture process by the developed adsorbents occurs physically and/or chemically through the surface of the adsorbent at a pressure of 1 atm. Calcium oxide-based adsorbents have capture activity at temperature in the range between 300-1000 C., which allows greater possibility of study with relative efficiency as a function of temperature.

Example 2Capture Tests of Co.SUB.2

(14) Thermogravimetric analyzes of materials before and after carbon nanotube modification (CaO, CaO-Nan and CaO-NanCal) were performed on a Netzsch STA 449 F3 Jupiter TGA analyzer to perform CO.sub.2 capture performance studies.

(15) The thermal analyzes were carried out in a CO.sub.2 atmosphere, and the experiments carried out under this atmosphere elucidate the ability of these substances to capture CO.sub.2 as a function of temperature. About 10 mg of sample was added to a standard alumina crucible and subjected to a temperature variation between 25 and 1,000 C. at a heating rate of 20 C. min.sup.1.

(16) The results analyzed by TG (FIG. 2) showed that the material without modification with carbon nanotube (CaO) had a capture capacity of CO.sub.2 of 32%, with saturation of that capacity after 600 C. After modification with nanotube, but without calcination of the material (CaO-Nan), there is a slight decrease in CO.sub.2 capture capacity. The presence of nanotube seems to hinder the formation of carbonate, formed from the interaction of CO.sub.2 with calcium in the adsorbent material. However, with the calcination of the material, such as to remove the carbon nanotube, a material with a CO.sub.2 capture capacity of 53% is obtained. This material probably shows a more suitable porous structure for the reaction with CO.sub.2 once the thermal removal of the nanotube promotes the formation of larger channels in the structure of adsorbent material.

(17) This differential in porosity due to generation of channels in the structure not only improved the CO.sub.2 capture capacity, but also allowed the process to occur continuously, without saturating this capacity up to the maximum temperature studied. This result makes the material produced in the present invention with good capacity for use on a commercial scale, since the ability to capture CO.sub.2 can be maintained for longer in case of use in a vehicular system. FIG. 2 also presents a schematic drawing of this channel generation process in the CaO-NanCal structure.

Example 3Capture of Co.SUB.2.Isothermal Studies at 350 C. and Reuse of Adsorbent Material

(18) Aiming at application in automobiles, an isothermal study was carried out at a temperature of 350 C. This temperature was chosen since it is the starting temperature of the material's reaction with CO.sub.2, as shown in FIG. 2. Furthermore, this temperature can be obtained in automobile exhausts, which would allow the generation of a kit of balls to be coupled to an automobile.

(19) Initially, samples were heated from room temperature to 350 C. at a rate of 20 C. min.sup.1 in a pure flow of N.sub.2 of 70 mL min.sup.1 and kept at 350 C. for 60 minutes to remove impurities. The flow of N.sub.2 was then changed to a mixture of flow of CO.sub.2/N.sub.2, while the sample weight change was instantly monitored for 12 hours (FIG. 3a).

(20) The results again indicate that the material that was modified with carbon nanotube and after calcination to generate the porous channels had a greater capacity to capture CO.sub.2. The capture capacity was 27.3% at the temperature studied. Another point to consider is that the capture curve continues to ascend afterwards, indicating that the material has not lost its ability to react with CO.sub.2. These results indicate that the material produced in this invention is very promising for use as a component of a kit to be adapted to car exhausts to reduce the emission of carbon dioxide into the atmosphere. For the most efficient material, a reuse study was carried out in order to study its limit recovery capacity.

(21) A series of experiments were carried out, using the material CaO-NanCal in carbonation/decarbonation cycles. Initially, the sample was heated to 350 C. under flow of N.sub.2 and then the gas flow was changed to a mixture of CO.sub.2/N.sub.2. The sample remained under the saturated atmosphere of CO.sub.2 for 2 hours, after this step the flow of CO.sub.2 was changed and the sample was heated to 900 C. under flow of N.sub.2 for sample regeneration. The steps took place in five carbonation/decarbonation cycles (FIG. 3B). The results indicate that the material has a regenerative capacity, maintaining, after reaction cycles, a removal of 5.6%. These results indicate that the material can be reused, so that after its saturation it can be recovered after heat treatment.

Example 4Characterization of Porosity of Materials

(22) The materials were characterized by nitrogen adsorption at 196 C. in an AUTOSORB IQ2-Quantachrome system (FIG. 4). Surface area was calculated using the BET model; The total pore volume was estimated from the amount of nitrogen adsorbed at P/Po=0.95; The pore size distribution was determined based on the density functional theory (DFT). The N.sub.2 adsorption/desorption isotherms show that the materials show similar N.sub.2 adsorption capacity indicating that the materials show similar specific areas. However, the pore distribution shows that the most promising material, the one treated with carbon nanotube and calcined, has greater adsorption in larger pore diameters, above 100 A. This corroborates previous discussions that indicated that this material had its porous structure developed with the modification with the carbon nanotube.