Ceramic materials for absorption of acidic gases

Abstract

The present invention describes the process of preparing ceramics for the absorption of ACIDIC gases, which worsen the greenhouse effect, that are released in combustion systems, or that are present in closed environments. In relation to carbon dioxide, principal target of the present invention, the process of absorption, transport, processing and transformation of the gas into other products is described. The process uses ceramic materials prepared through the solid mixture of one or more metallic oxides, with one or more binding agents and an expanding agent. The product generated can be processed and the absorbent system regenerated. The carbon dioxide obtained in the processing can be used as analytic or commercial carbonic gas, various carbamates and ammonium carbonate.

Claims

1. A ceramic material for absorption, storage, and recovery of CO.sub.2, SO.sub.3, SO.sub.2, NO, and NO.sub.2 at 25° C. to 700° C., comprising a solid mixture of one or more metal oxides 80-95% (p/p), one or more binding agents 5-10% (w/w), and an expanding agent 0-2% (w/w).

2. The ceramic material according to claim 1, wherein said solid mixture comprises alkaline earth metal oxides, metal alkaline hydroxides, and/or transitional metal oxides.

3. The ceramic material according to claim 1, wherein the binding agent is selected from the group consisting of magnesium oxide, bentonite, kaolin, and Plaster of Paris.

4. The ceramic material according to claim 1, wherein the expanding agent is selected from the group consisting of metallic aluminum and calcium oxalate.

5. The ceramic material according to claim 1, wherein said solid mixture comprises CaO and La.sub.2O.sub.3, CaO and KOH, CaO and MgO, or MgO and KOH.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present invention describes a method for reducing the emission of ACIDIC gases and contributors to the greenhouse effect that are released by combustion systems and industrial plants such as in the steel, cement, and thermoelectric industries, or systems of gas purification. The absorbent material, after its saturation by ACIDIC gases, is then processed thermally or chemically, generating a flow of purified gas which is then used in processes of the synthesis of various useful products such as analytical or commercial compressed gas; useful products for the chemical industry for the synthesis of carbonates and related ACIDICs; and useful products for the agricultural industry with the manufacture of carbonates, nitrates, sulfates and sulfites. The thermal or chemical processing has the capacity to regenerate the absorbent material, thus creating a cycle of atmospheric cleansing with the generation of useful products relevant to the various industrial sectors, at a low cost.

(2) The present invention proposes absorbent mixtures containing oxides of alkaline earth metals, alkaline metals or transition metals that show a kinetic reaction favorable to the absorption of carbon dioxide and other ACIDIC gases such as, but not limited to, SO.sub.2, SO.sub.3, NO and NO.sub.2. The proposed absorbent mixtures also contain a binding (hardener) agent and an expanding agent. The different compositions represented have the property of absorbing ACIDIC gases at different temperatures, which can vary from 25° C. to 700° C., as shown below.

(3) Some forms of absorbent mixtures described in the present patent request have the capacity to absorb ACIDIC gases in different environments and under various thermodynamic conditions. Therefore, they are effective in diverse situations such as when rapid or moderate absorption is necessary, as well as those in which an extremely slow absorption is necessary. Therefore, the method proposed in the present invention shows control that is as much thermodynamic as kinetic. In this way, the proposed technology can be applied to the decontamination of closed environments in ambient temperatures (˜25° C.); purification of flowing gases; the absorption of industrially rejected gases (exhaust systems) at temperatures between 50° C. and 600° C., such as in the production of coke, sintering of materials, lamination; the absorption of ACIDIC gases released during the burning of fuels in internal combustion engines, in addition to the intake airflow of internal combustion engines; and energy production through thermoelectrics, all aiming at improving the efficiency of the process of burning fuels.

(4) The operating cycle of absorbent materials is illustrated in FIG. 1. This illustration makes it possible to observe the ideal coupling between the absorption process of polluting gases of ACIDIC nature with methods of reusing the absorbent material having the capacity to reduce and even extinguish the emission of ACIDIC gases in combustion systems such as furnaces that burn fuel, internal combustion engines, and industrial plants. The method proposes a cycle of reusing the absorbent material which, after its saturation, is collected, exchanged, and analyzed in order to determine the composition of the absorbed gases. Next, aside from its composition, the saturated material is brought to an industrial plant outfitted for the recovery of the absorbed gas, transforming it into industrial useful material, totally or partially regenerating the absorbent material.

(5) The present invention describes the use of a solid mixture composed of one or more oxides of alkaline earth metals, one or more hydroxides of alkaline metals, and oxides of transition metals, enhanced with a binding agent and an expanding agent. The mixture of these components must be done in an aqueous medium so that the final solid acquires its consistency, and is expanded uniformly, through the action of the binding and the expanding agent. After the complete homogenization of the components, the mixture is left to settle for a period of 1 to 5 hours so that the expanding agent, such as pulverized metallic aluminum or calcium oxalate, can act to generate bubbles uniformly throughout the entire mass. The reaction of the expanding agent occurs slightly before that of the binding agent, thus permitting the formation of bubbles that will be structurally maintained through the gradual, subsequent activation of the hardening/binding agent, such as: magnesium oxide, bentonite, kaolin, or Plaster of Paris. After a partial hardening of the mixture, it is submitted to a process of moderate heating (100° C.-200° C.) for a period from 3 to 72 hours, although not limited to it to eliminate the excess water. It is subjected thereafter to intense heating (between 500° C. and 800° C., although not limited to it) for a period of 1 hour, although not limited to it, that guarantees the hardening of the mixture. This heating must be done in the presence of nitrogen or in the absence of airflow; or, in a closed chamber or in the absence of ACIDIC gases that could be absorbed during the synthesis of the material.

(6) In the stage following the homogenization, the material can be shaped into specific forms, for example, compact blocks, cast blocks (bricks), or pellets of varying sizes (5 a 20 mm), among others. For the shaping of blocks (compact or cast) the mixture can have a more fluid consistency by the addition of excess water, facilitating its homogenization. In this case, you can also use a larger amount of expanding agent in order to increase the area and the efficiency of the absorption process. For the shaping of the pellets, the initial mixture must have a more pasty consistency that makes the manufacture of the pellets possible, which next should be submitted to heating to stop the recombining of the material.

(7) The intense heating stage can be done in an autoclave at a lower temperature, approximately 200° C. The process guarantees greater rigidity of the formed solid, giving it greater mechanical resistance.

(8) The absorbent material described in this patent request shows a basic (Translater's Note: opposite of ACIDIC) character, allowing its use in processes of the absorption of ACIDIC gases such as carbon dioxide (CO.sub.2), sulfur dioxide (SO.sub.2), sulfur trioxide (SO.sub.3), among others. Although all the gases mentioned worsen the greenhouse effect and ACIDIC rains, it is carbon dioxide that appears to be the main pollutant, owing mostly to the increased quantity produced in industries that use combustion processes. Thus. CO.sub.2 will be used in examples showing the reactions and illustrating the efficiency of the process of absorption to reduce the emissions of gases which worsen the greenhouse effect. It will show the subsequent use of the material formed from the regeneration of the absorbent ceramic, and the creation of important products of high aggregate value, for various industrial sectors.

(9) The potential for the absorption of materials is determined by the kinetic reaction of the gas with the existing oxides. Hence, every mixture has a range of ideal temperatures for absorption, and the speed of absorption depends on the composition, the temperature, and the flow of gas over the material. The ranges of absorbent temperatures and the conditions of regeneration of materials are discussed below, individually, for each type of composition. As previously described, the main focus of this current invention is the absorption of carbon dioxide, among others; therefore, the equations below show the chemical reactions that occur during the process of absorption of the CO2, aside from the absorbent mixture containing calcium oxide and potassium hydroxide, among others.
CO.sub.2(g)+CaO.sub.(s).fwdarw.CaCO.sub.3(s)
CO.sub.2(g)+2KOH.sub.(s).fwdarw.K.sub.2CO.sub.3(s)+H.sub.2O.sub.(g)

(10) The absorbent material makes the transport and the concentration of the absorbed gases for industrial installations which are suitable for its processing. The recovery of carbon dioxide can be done through the thermal decomposition of the material, or from chemical treatment with nitric ACIDIC, among others, and subsequent regeneration of absorbent material through the addition of sodium hydroxide, among others, in the presence of 1-2% of aluminum, among others. The mixture that is formed is filtered and heated to 100° C. in order to eliminate water, thus regenerating the absorbent material.

(11) The carbon dioxide that is formed from the saturated absorbent ceramic shows an elevated concentration, making possible various industrial methods. Initially, that same carbon dioxide can be compressed and bottled for its subsequent commercialization as an analytic reagent, or in distinct processes that use CO.sub.2 gas. In addition to this direct application of the CO.sub.2 that was absorbed from polluting industrial plants, two more methods, among others, are proposed in this patent request for the chemical transformation of carbon dioxide into various carbonates and carbamates, among others.

(12) The carbon dioxide gas can be injected into a basic solution of sodium hydroxide or ammonium hydroxide, among others. The chemical reactions for those processes are shown in equations 1 and 2 (Eq. 1 and Eq. 2). After the formation of the carbonate, the solution of sodium carbonate is heated until the water is completely evaporated (approximately 100° C.), and the ammonium carbonate (when the basic solution that is used is ammonium hydroxide) is left to evaporate at 40° C. to avoid the sublimation of the desired material, leaving only the carbonate corresponding to the base utilized.

(13) ##STR00001##

(14) The synthesis of ammonium carbamate can be done at room temperature by passing a stream of CO.sub.2 through a container with liquid ammonia. The reaction is kinetically favorable, as the immediate formation of a white solid is observable. Following this, the system is kept still and the carbamate can be separated through filtering or decantation, among others. The corresponding reaction for this process is shown in the following chemical equation (Eq. 3).
CO.sub.2(g)+2NH.sub.3(l).fwdarw.NH.sub.4[H.sub.2NCO.sub.2].sub.(s)  Eq. 3

(15) In case the CO.sub.2 is collected in a container with a basic aqueous solution or a suspension of secondary amines, HNR2, the carbamate of alkaline metals or of corresponding ammonia can finally be obtained, according to the following equation (Eq. 4).

(16) ##STR00002##

Example 1: Preparation of Class 1 Absorbent Material: Test of the Speed of Absorption and Saturation Time to 90%

(17) The Class 1 absorbent ceramics use MgO as the binding agent, with a concentration of up to 10% (p/p) and aluminum powder as the expanding agent, with a concentration up to 1%. The rest of the mixture, which corresponds to the absorbent components, is composed of mixtures of CaO and La.sub.2O.sub.3 (FIG. 3), CaO and KOH (FIG. 4), CaO and MgO (FIG. 5), MgO and KOH (FIG. 6) with the proportions in defined amounts for every range of temperature in which the absorption process is more intense than the thermal decomposition process of the saturated material. The mixtures containing magnesium absorb more effectively between 50 and 400° C. while the mixtures CaO+La.sub.2O.sub.3 and CaO+KOH can be used in the absorption process between 100 and 700° C. The use of MgO as binding agent gives the material superior mechanical resistance in relation to the binders bentonite and kaolin as, for example, a sphere of approximately 5 mm diameter, containing CaO 75% and MgO 25%, resists up to 55N.

(18) For the Class 1 compositions, the potential for absorption is maximized because the binding material (MgO) also has the capacity to absorb CO.sub.2.

(19) Based on the kinetic study of the Class 1 materials it was possible to estimate the storage time (t.sub.90) of the absorbent materials, i.e., the time for the consumption of 10% of the stored material in ambient conditions for the composites with CaO content greater than or equal to 80%, to be approximately 15 days. This makes possible the storage and transportation of the ceramic material for industrial installation where it will be used for the absorption of CO.sub.2.

Example 2: Preparation of Class 2 Absorbent Material: Bentonite

(20) The Class 2 absorbent ceramics use bentonite as the binding agent with concentration of up to 10% (p/p), and aluminum powder as the expanding agent with concentration of up to 1%. The rest of the mixture, which corresponds to the absorbent components, is composed of binary mixtures of CaO and La.sub.2O.sub.3 (FIG. 7), CaO and KOH (FIG. 8), CaO the MgO (FIG. 9).

(21) Bentonite is made of 66.9% SiO.sub.2, 16.3% Al.sub.2O.sub.3 and 6% H.sub.2O; with the most common impurities being Fe.sub.2O.sub.3 (˜3.3%), NaOH (2.6%), Ca(OH).sub.2 (1.8%) and Mg(OH).sub.2 (1.5%). As mentioned previously, the mechanical resistance of the material using bentonite (Table 1) is poorer compared to MgO as a binding agent, but that does not prevent its use as a structuring agent for absorbent mixtures of CO.sub.2, In the same way, the compositions containing CaO+KOH or CaO+La.sub.2O.sub.3 absorb in a range of higher temperature (100 to 700° C.), while the mixture CaO+MgO can absorb between 50 and 400° C.

(22) TABLE-US-00001 TABLE 1 Content of bentonite and mechanical resistance for mixtures containing 80% or more of CaO Content of Diameter of bentonite Resistance the sphere (% p/p) (N) (mm) 10 31 5.8 8 44 6.0 6 41 7.4 4 35 6.9 2 28 6.5

Example 3: Preparation of Class 3 Absorbent Material: Kaolin

(23) Class 3 ceramic absorbents use kaolin as the binding agent with a concentration of up to 10% (p/p) and aluminum powder as expanding agent with a concentration of up to 1%. The rest of the mixture, which corresponds to absorbent components, is composed of binary mixtures of CaO and La.sub.2O.sub.3 (FIG. 10), CaO and KOH (FIG. 11), CaO and MgO (FIG. 12). This class of materials shows physical and kinetic properties similar to Class 2. Kaolin corresponds to a mixture of aluminosilicates with the empirical formula Al.sub.2O.sub.3.mSiO.sub.2.nH.sub.2O, in which m can assume values from 1 to 3 and n can vary between 2 and 4.

(24) To exemplify the efficiency and the speed of the absorption of the Class 2 materials, a composition containing 88.5% CaO, 1% KOH, 10% kaolin and 1% aluminum was used. The absorption experiment was performed with a flow of CO.sub.2 proportional to the mass of the absorbent, including 26 grams of CO.sub.2 per minute per gram of ceramic material (26 g.Math.min.sup.−1g.sup.−1). The average speeds of CO.sub.2 absorption, at different temperatures for the analyzed mixtures, are found in Table 4, along with the time for saturation of 90% of the material. In composites containing higher KOH content, the speed of absorption increases considerably, up to 10% faster, however, due to the stoichiometric proportions of the material, efficiency is impaired.

(25) TABLE-US-00002 TABLE 2 Speed of absorption and time to saturation for 90% of the ceramic material composed of 88.5% CaO, 0.5% KOH, 10% kaolin and 1% aluminum with exposure to a flow of CO.sub.2 from 26 g .Math. min.sup.−1kg.sup.−1 per gram of absorbent material. Temperature Speed (g .Math. Time ~90% (° C.) min.sup.−1kg.sup.−1) (min) 200 1.2 576 300 12.2 57 400 38.6 18 500 49.7 14 600 189.0 4

Example 4: Preparation of Class 4 Absorbent Material: Plaster

(26) Class 4 absorbent ceramics use Plaster of Paris as binding agent with a concentration of up to 10% (p/p) and aluminum powder as expanding agent with a concentration of up to 1%. The rest of the mixture, which corresponds to the absorbent components, is composed of binary mixtures of CaO and La.sub.2O.sub.3 (FIG. 13), CaO and KOH (FIG. 14), CaO and MgO (FIG. 15).

(27) Mixtures with a quantity of less than 5% of plaster lose their rigidity, damaging the handling of the material. An inverse relation between the aluminum content and rigidity can be observed, because the excessive increase in the quantity of bubbles in the structure of the material demands a greater amount of binding agent (plaster). For the process of absorbing the carbon dioxide, the temperature of decomposition of calcium carbonate in the mixture must be higher than 750° C. The process of regenerating the material demands the addition of an expanding agent (aluminum), reducing thus the concentration of the binding agent and absorbent in approximately 1 to 2% for every cycle. Therefore, considering the minimum concentration of calcium oxide and Plaster of Paris, every mixture makes it possible to perform approximately 5 cycles of absorption/regeneration with no considerable loss of efficiency and mechanical resistance of the material. Calcium oxalate can be used as the expanding agent although it is necessary to treat it thermally so that, through the decomposition of oxalate to calcium oxide, the carbon dioxide generated causes the aeration of the material. In this process, the carbon dioxide needs to be transformed into useful products in the initial process of the preparation of the ceramic.

Example 5: CO2 Absorption Test

(28) To verify the absorption process, a chainsaw two-stroke engine, which uses a composite fuel containing 96% gasoline and 4% oil, was used. A Class 2 ceramic, composed of 88% CaO, 1% KOH, 10% kaolin and 2% aluminum was placed in a tubular furnace at 500° C., in a hood with an exhaust system. Then, the motor was started and the discharged gases were directed to the entrance of the furnace to allow contact of those gases and the ceramic at the temperature of the furnace. After about 1 hour, the furnace and the engine were shut off. The material obtained was weighed comparing the difference in mass in relation to the original mass of the ceramic. A gain in mass showing a 40% absorption was verified. An elemental analysis of carbon and nitrogen showed an additional mass related to these elements of about 45% carbon coming from the CO.sub.2, and less than 1% nitrogen coming from the nitrogen oxides.

DETAILED DESCRIPTION OF THE FIGURES

(29) FIG. 1 describes the absorption cycle, the production of useful products and the recovery of absorbent materials. FIG. 1 outlines the cyclical process proposed in the patent request for the absorption of ACIDIC gases and the reuse of them for the synthesis of useful products, regenerating the absorbent material. The process begins with the preparation of the absorbent material (101), which is made of two or more oxides of alkaline earth metals or earth alkaline with alkaline oxide, binding agents and expanding agents. The absorbent ceramic is then exposed to a flow of gas, at a temperature between 50 and 600° C. (110), the saturated material is exchanged (112) and analyzed (113) in order to determine the type of process that was used in its processing (120), yielding for each composition one or more types of useful products (121). During the processing of the saturated material, the absorbent ceramic can be regenerated (130) by recomposition and shaped again (140) being, therefore, ready to be reused in the absorption of ACIDIC gases.

(30) FIG. 2 describes processes of regenerating absorbed carbon dioxide and the regeneration of absorbent material. FIG. 2 highlights the process of recovering the ceramic materials described in the present patent request after saturation with carbon dioxide, which does not limit the use of the absorbent materials, which can be used for any gas of an ACIDIC nature. Initially, the absorbent ceramic (200) is exposed to a flow of CO.sub.2 at a temperature between 100 and 600° C. The saturated material (210) can be processed in two distinct ways. The first way corresponds to the thermal decomposition of the carbonates produced at a temperature of approximately 500° C. (260). In this way, the released CO.sub.2 (250) is brought to the processing systems of industrial interest. The carbon dioxide can be stored (251) or transformed into other products such as carbonate (252) and carbamate (253). The flow of CO.sub.2, which has an elevated percentage of concentration, can be used in the production of ammonium carbamate or various other carbonates such as ammonium carbonate or sodium carbonate. The carbon dioxide (250) can also be regenerated through the reaction of the saturated material (210) with an ACIDIC (220) such as nitric ACIDIC, among others. The remaining mixture produced is alkalinized by the addition of NaOH (230), turning the alkaline earth metal hydroxides and other insoluble hydroxides into precipitates, enabling the separation by filtering or decantation. Then, pulverized aluminum is added to complete the process of expanding the mass. Finally, the material is heated to remove excess water (240) and for the hardening of the ceramic material, which is available to restart the cycle of absorption and the use of carbon dioxide.

(31) FIGS. 3, 4, 5 and 6 correspond to the compositions of the mixtures that are best suited to each temperature, and which use MgO as binding agent forming CaO and La.sub.2O.sub.3. CaO and KOH, CaO and MgO or MgO and KOH, respectively.

(32) FIGS. 7, 8, and 9 correspond to the compositions of the mixtures of the absorbents comprising CaO and La.sub.2O.sub.3. CaO and KOH, CaO and MgO, and which are enriched through the addition of bentonite in temperature ranges at which they can absorb CO.sub.2, respectively.

(33) FIGS. 10, 11, and 12 show the composition of materials containing kaolin, used for enrichment, comprising Cao and La203, Cao and KOH or Cao and MgO, 30 respectively.

(34) FIGS. 13, 14 and 15 correlate the composition of the absorbent material with mixtures containing up to 10% Plaster of Paris, for all ranges of temperature at which it is possible to use these materials.