The present invention addresses to cyclic sorption/desorption processes for the capture or purification of gaseous streams containing acidic gases using solutions of organic salts, herein called zwitterionic bases, with application in the energy, chemical and oil and gas fields in order to minimize the main intrinsic drawbacks in large-scale CO2 and H2S capture processes.
The processes for capturing acidic gases, such as carbon dioxide (CO2) and hydrogen sulfide (H2S) are used in various industrial segments both for environmental reasons and for economic reasons, as they are used, for example, to obtain products with a higher added value or to purify the gaseous feed streams of catalytic reactors. These processes are especially important in the oil and gas industry, where they are used to remove CO2 and H2S from natural gaseous streams from oil extraction plants.
One of the widely disseminated technologies for the separation of CO2 and H2S from natural gas is based on the reversible absorption of these gases using aqueous solutions of ethanolamines such as, for example, methyldiethanolamine (MDEA). The use of amines, although effective, presents some intrinsic problems, the main ones being related to the volatility of these compounds, which causes mass loss of the absorbent agent during the process, the relative high enthalpy of absorption and their gradual thermal and chemical decomposition for the formation, for example, of carbamates. These drawbacks motivated the search for new compounds to replace amines both in new plants and in existing plants for capturing CO2 and H2S.
The main strategy studied to increase chemical and thermal stability, eliminate the mass loss by evaporation and reduce the enthalpy of absorption of the acidic gas capture processes has been the use of ionic compounds and their solutions. There is a growing number of publications reporting the use of ionic liquids (ILs), ionic liquid solutions or organic salt solutions in CO2 absorption processes.
In one of the first studies that demonstrated the solubility of CO2 in ionic liquids, BLANCHARD, L. A. et al. “Processing using ionic liquids and CO2”, Nature, v. 399, p. 28-29, 1999 reported molar fractions of up to 0.72 moles of CO2 for each mole of 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIm·PF6) under pressures of 83 bar (8.3 MPa). Since then, numerous publications have demonstrated that CO2 is remarkably soluble in ILs based on imidazolium cations, as described in the references of ANTHONY, J. L.; MAGINN, E. J.; BRENNECKE, J. F. “Gas solubilities in 1-n-butyl-3-methylimidazolium hexafluorophosphate”, Ionic liquids, p. 260-269, 2002; Cadena, C., et al. “Why is CO2 so soluble in imidazolium-based ionic liquids?”, Journal of the American Chemical Society, v. 126, p. 5300-5308, 2004; BARA, J. E. et al. “Room-temperature ionic liquids and composite materials: platform technologies for CO2 capture”, Accounts of Chemical Research, v. 43, p. 152-159, 2010; HASIB-UR-RAHMAN, M. et al. “Ionic liquids for CO2 capture—Development and progress”, Chemical Engineering and Processing: Process Intensification, v. 49, p. 313-322, 2010; BRENNECKE, J. F.; GURKAN, B. E. “Ionic Liquids for CO2 Capture and Emission Reduction”, The Journal of Physical Chemistry Letters, v. 1, p. 3459-3464, 2010; SHARMA, P. et al. “Effects of anions on absorption capacity of carbon dioxide in acid functionalized ionic liquids”, Fuel Processing Technology, v. 100, p. 55-62, 2012; ZHANG, X. et al. “Carbon capture with ionic liquids: overview and progress”, Energy & Environmental Science, v. 5, p. 6668-6681, 2012. The absorption of CO2 in ionic liquids can occur either by physisorption or by chemisorption, or by a combination thereof. The physical absorption, or gas solubility, is influenced by a number of factors such as free volume, counterion size, strength of cation-anion interactions, pressure, temperature, and structural changes in the ionic pair. The chemisorption is normally influenced by the basicity of the salt and leads to the capture of CO2 by the formation of species such as bicarbonate and carbamate. Therefore, when using ionic liquids or functionalized organic salts with basic groups, it is expected to combine the effects of physical and chemical absorption.
In a recent literature review, CUI, G. et al., “Active chemisorption sites in functionalized ionic liquids for carbon capture”, Chemical Society Reviews, v. 45, p. 4307-4339, 2016 report the existence of at least 77 different amino-functionalized ionic liquids, 102 ionic liquids free of the amine group (including those that use the phenolate anion) and 55 ionic liquids with multiple active sites that were used to capture CO2. Although these ionic liquids have interesting properties, so far there is no proof of the industrial viability of these compounds, due to several factors such as, for example, high viscosity, complexity of synthesis processes, incompatibility with water.
In the specific case of amino-functionalized ionic liquids, the advantage over alkanolamines is related only to the low volatility of these compounds. This advantage is not enough to compensate the disadvantages related to its high viscosity and cost, mainly because, as they have the same functional group, they do not represent gains in thermal and chemical stability.
Ionic liquids with alternative functional groups, specifically the phenolate anion, draw attention because they eliminate decomposition via the formation of carbamates; however, in the presence of water or another source of protons, the phenolate is converted to phenol, a volatile and toxic compound, making its industrial use unfeasible.
The alternative to the use of phenolate groups without the formation of volatile products is the use of inner salts. In the study by Sakai, T. et al. “Bifunctional organocatalyst for Activation of carbon dioxide and epoxy to produce cyclic carbonate: betaine as a new catalytic Motif”, Organic Letters, v. 12, p. 5728-5731, inner salts containing the phenolate anion covalently associated with quaternary ammonium-type cations have been reported. Such a study is focused on the nucleophilicity of these compounds for the formation of adducts with CO2 that are intermediates in coupling reactions of carbon dioxide with epoxides for the formation of cyclic carbonates, without investigating absorption of CO2 under industrial conditions with such compounds.
A method for removing CO2 from exhaust gases using ionic liquids associated with anions containing carboxylate groups was disclosed by U.S. Pat. No. 7,527,775B2. More recently, U.S. Pat. No. 8,721,770 describes the use of functionalized ionic liquids in CO2 capture. Although promising, the use of ionic liquids for CO2 absorption has the inconvenience of the high viscosity of these compounds, which, in practice, would make pumping and flow of these compounds difficult in industrial pipes and would impair mass transfer in the liquid.
An evolution of these methodologies is the use of solutions, including aqueous solutions, of ionic liquids and other organic salts that have lower viscosity than pure ionic liquids and similar or even greater capture capacity. One of the most important methods in the field of the present discovery was disclosed in the U.S. Pat. No. 8,536,371B2, which refers to the use of aqueous solutions of amino-functionalized organic salts for the capture of CO2.
Furthermore, in 2017, SIMON, N. M. et al. “Carbon dioxide capture by aqueous ionic liquid solutions”, ChemSusChem, v. 10, p. 4927-4933, 2017 reported, for example, the capture of CO2 through aqueous solutions of ionic liquids containing imidazolium cations associated with acetate and imidazolate anions. Some other examples of CO2 absorption methods by ionic compounds are reported in references US2005/0129598A1, U.S. Pat. No. 10,086,331B2, US2012/0063977A1, US2015/0314235A1, US2018/0179157A1 and WO2014/144523A3.
Document BR122012033196A2 refers to a method for absorbing CO2 from a gaseous mixture, preferably a combustion exhaust gas containing from 1 to 60% by volume of CO2, and also to the absorption medium and a device to perform the method, where absorption of CO2 is carried out by contacting a gaseous mixture with an absorption medium comprising water and at least one amine. The method uses zwitterionic surfactants for CO2 absorption, such as betaines, alkylglycines, sultaines, amphopropionates, amphoacetates, tertiary amine oxides and silicobetaines.
U.S. Pat. No. 8,741,246B2 discloses methods for preparing compositions in order to capture volatile compounds in industrial power generation and commercial natural gas production facilities. More specifically, systems for the reduction of volatile compounds, where the system comprises an N-functionalized imidazole and may optionally include an amine. The method uses the non-ionic N-functionalized imidazole under neutral conditions and about 20% to 80% by weight of the solvent system. In addition, this document discloses a process of absorption of CO2 and other volatile compounds, such as H2S, with the regeneration of N-functionalized imidazole through heating. However, the use of ethanolamine compounds, although effective, presents some intrinsic problems, the main ones being related to the volatility of these compounds, which causes mass loss of the absorbent agent during the process, the relative high enthalpy of absorption and its gradual thermal and chemistry decomposition for the formation.
Document U.S. Pat. No. 9,586,175B2 discloses a process for separating at least a portion of an acidic gas from a gaseous mixture, comprising contacting the gaseous mixture with an absorption medium and/or adsorption medium, being carried out in the presence of an acidic catalyst. The described absorption and regeneration method uses zwitterionic substances providing compositions, devices and apparatus for capturing acidic gases, such as carbon dioxide (CO2), from flue gas flows, reform gas flows, natural gas flows or other industrial gas flows.
The study by YEBEDRI, S. et al. “Characterizations of crystalline structure and catalytic activity of zwitterionic imidazole derivatives”, Journal of Molecular Structure, v. 1193, p. 45-52, 2019 discloses the synthesis of a zwitterionic imidazole derivative and studies of catecholase activity by copper complexes in situ. Such a study focuses on the characterization of the crystalline structure and its catalytic activity, not being used on an industrial scale in the absorption of CO2.
Thus, no document of the state of the art discloses a process for capturing CO2 through solutions of zwitterionic bases such as that of the present invention.
In order to solve such problems, the present invention was developed, by obtaining a very specific family of organic salts, whose aqueous solutions have low viscosity and molar absorption capacity similar to conventional absorbents, such as MDEA, with the advantage of not being volatile, being less susceptible to chemical and thermal decomposition, as well as having a lower enthalpy of absorption. Such unique characteristics make them different from the aforementioned examples or from any other compound already used for the capture of acidic gases, especially carbon dioxide and hydrogen sulfide.
The present invention results in economic advantages when compared to traditional processes that use MDEA, such as, elimination of costs corresponding to the evaporation of the absorbent species, since the zwitterionic bases, as well as their conjugated acids, are not volatile; the reduction of about 20% of energy required for the desorption processes with zwitterionic solutions and the functional groups of the zwittwerions are extremely robust.
In addition, the invention has environmental and safety advantages that are related to the non-volatility of the inner salts, thus eliminating risks of possible human and environmental contaminations.
The present invention addresses to the discovery of a family of inner salts with a basic character, whose solutions are used in cyclic processes of gas capture on a large scale, through the contact of a gaseous stream containing one or more acidic gases with such solutions in order to minimize the main intrinsic inconveniences in large-scale CO2 and H2S capture processes.
These inner salts, or zwitterionic bases, can be combined with different solvents, including water, to obtain low viscosity solutions that have molar absorption capacity similar to conventional absorbents, such as MDEA, with the advantage of not being volatile, being less susceptible to chemical and thermal decomposition, in addition to having a lower enthalpy of absorption.
The present invention can be applied in several industrial segments, such as in the energy sector for capturing CO2 from exhaust gases, in the chemical sector for removing CO2 from gaseous streams of catalytic processes in which CO2 can poison the catalysts and, especially, in the oil and gas sector for the purification of natural gas.
The present invention will be described in more detail below, with reference to the attached figures which, in a schematic way and not limiting the inventive scope, represent examples of its embodiment. In the drawings there are:
The process of synthesizing zwitterionic salts according to the present invention is characterized by comprising three very simple steps that occur successively promoting reactions between its components in the liquid phase, in the presence of solvent, under mechanical stifling, under pressure atmospheric and at temperatures between −10° C. and 100° C., typically between 0° C. to 70° C.
The first step is characterized by promoting the reaction between a compound of the hydroxy-benzaldehyde type with a primary amine of general formula R1-NH2 for the formation of the corresponding imine, followed by the cyclization reaction of this imine, in the presence of a salt of ammonium and a vicinal dialdehyde, to obtain a compound of the 2-(hydroxy-phenyl)-imidazole type, according to Step 1—
The first step is characterized by occurring at temperatures that can vary between −10° C. and 80° C., typically 0° C. to 40° C. and reaction times between 10 minutes and 24 hours, typically 24 hours.
The first step is characterized by the reaction product of the 2-(hydroxy-phenyl)-imidazole type being purified by simple techniques of precipitation, crystallization and/or filtration followed, or not, by washing and/or evaporation of the solvent.
The compound of the hydroxy-benzaldehyde type is characterized by containing, in its aromatic ring, at least one hydroxyl group and the other substituents of the benzene ring being hydrogen, alkoxy groups containing between 1 and 10 carbons, halides, phenyl or alkyl group or containing between 1 and 10 carbons, with 3-hydroxy-benzaldehyde and 4-hydroxy-benzaldehyde being typically used.
The primary amine of general formula R1-NH2 is characterized in that the radical R1 comprises an alkyl, aryl, alkylether or alkylalcohol group containing between 1 and 10 carbons, typically methylamine, and in that being used in the proportion of 0.5 to 2 equivalents to benzaldehyde, typically 1.05 equivalents.
The ammonium salt is characterized by having the general formula (NH4)nY, where Y comprises the bromide, chloride, sulfate, acetate, carbonate and bicarbonate anions; n has a value of 1 or 2 and, because this salt is used in a proportion of 0.3 to 2 equivalents relative to the benzaldehyde, typically 0.75 equivalents.
Dialdehyde is characterized by being typically glyoxal and can also be analogues of glyoxal with alkyl, aryl, alkylether or alkylalcohol substituents containing 1 to 10 carbons and for being used in the proportion of 0.5 to 2 equivalents in relation to benzaldehyde, typically 1 equivalent.
The solvent used in the first step comprises water, acetonitrile, ethyl acetate, aliphatic alcohols containing from 1 to 10 carbons in the alkyl chain or a mixture of these in any proportion in the amount of 1 time to 100 times the mass of benzaldehyde, typically 10 times.
The purification of the reaction products of the first step is characterized by using water, acetonitrile, ethyl acetate, aliphatic alcohols containing from 1 to 10 carbons in the alkyl chain or a mixture of these in proportions suitable for, under temperatures of −10° C. to 30° C., typically 0° C., the precipitation or crystallization of compounds of the 2-(hydroxy-phenyl)-imidazole type is carried out followed by removal of the solvent by filtration or simple decantation, being recommended to wash the product with the same solvent and evaporating the residual solvent under reduced pressure.
The second step is characterized by promoting the N-alkylation reaction between the compound of the 2-(hydroxy-phenyl)-imidazole type obtained in the previous step and an alkylating agent of general formula R9-X to form a salt of 2-(hydroxy-phenyl)-imidazolium, in the presence of solvent, according to Step 2—
The second step is characterized by occurring at temperatures that can vary between 40° C. and 100° C., typically 70° C., and reaction times between 10 minutes and 24 hours, typically 1 hour.
The second step is characterized in that the reaction product of the 2-(hydroxy-phenyl)-imidazolium salt type precipitates as it is formed and is removed from the reaction mixture by filtration or decantation followed by washing and evaporation of the residual solvent under reduced pressure.
The alkylating agent of general formula R9-X is characterized in that R9 comprises an alkyl, arylalkyl, alkylether or alkylalcohol group containing between 1 and 10 carbons, and the X group comprises the halide, alkylsulfonate and alkylsulfate group, in which the alkyl group has between 1 and 5 carbons, typically iodomethane or methanesulfonyl chloride.
The solvent used in the second step comprises water, acetonitrile, ethyl acetate, aliphatic alcohols containing from 1 to 10 carbons in the alkyl chain or the mixture of these in appropriate proportions in the amount of 1 time to 20 times the mass of the compound of 2-(hydroxy-phenyl)-imidazole type, typically 5 times.
The third step is characterized by promoting the deprotonation of the phenolic OH group of the 2-(hydroxy-phenyl)-imidazolium salt, obtained in the previous step, through the reaction of an aqueous solution of this component with a strongly basic ion exchange resin, which results in the formation of the inner or zwitterionic salt of the 2-(oxy-phenyl)-imidazolium type, as shown in Step 3—
The third step is also characterized in that the reaction between the 2-(hydroxy-phenyl)-imidazolium salt and the ion exchange resin occurs by simply mixing and stifling these components for periods of up to 60 minutes, typically 10 minutes, or by passing a solution of the 2-(hydroxy-phenyl)-imidazolium salt through a fixed or fluidized bed column of resin at temperatures between 10° C. and 80° C., typically 30° C.
Furthermore, the third step is characterized in that the aqueous solution containing the product is separated from the ionic resin by filtration or simple decantation and the reaction product, inner salt of the 2-(oxy-phenyl)-imidazolium type, is isolated by simple evaporation of the solvent under reduced pressure and temperatures between 10° C. and 80° C., typically 40° C.
The zwitterionic bases obtained in the synthesis process disclosed herein have as their main structural characteristic the presence of an imidazolium cation covalently linked, through carbon C-2, to an oxy-phenyl group, having as possible substituents of the imidazolium ring, R7 and R8, hydrogen or alkyl, aryl, alkylether or alkylalcohol groups containing 1 to 10 carbons; and as substituents on the benzene ring, necessarily an O− group, the others being hydrogen, hydroxyl, alkoxy groups containing between 1 and 10 carbons, halide, phenyl or alkyl group containing between 1 and 10 carbons, as shown in
The zwitterionic bases obtained in the synthesis processes are neutral compounds that have opposite charges in different regions of their structure and can also be called inner salts or hybrid salts.
The zwitterionic bases obtained in the synthesis processes are solids soluble in water and polar organic solvents, such as alcohols, polyalcohols, acetonitrile and acetone.
Unlike most traditional zwitterions, which are amphoteric amino acids, the main property of zwitterionic bases is precisely the fact that they are basic inner salts, and have relatively high basicity, typical of the phenolate group, and may vary depending on the substituents of the benzene ring.
The zwitterionic bases have a unique characteristic for the process of capturing acidic gases, the fact that both they and their acid-conjugates are organic salts, therefore, non-volatile.
The key aspect of the zwitterionic bases disclosed herein is the presence of a phenolate group covalently linked to an imidazolium cation to form a basic salt with good solubility in water and polar solvents.
The process for capturing acidic gases through zwitterionic base solutions comprises contacting, under sorption conditions, a gaseous stream containing one or more acidic gases with a zwitterionic base sorbent solution for the removal of at least part of the acidic gases, and obtaining a purified gaseous stream and a solution with sorbed acidic gases; and the regeneration of the sorbent solution, under desorption conditions, to obtain a zwitterionic base solution and a stream of acidic gases.
Conventional equipment can be used for the various functions necessary for the process of capturing acidic gases by solutions of zwitterionic bases, such as, for example, to control the gaseous flow, to promote contact between the gas and the sorbent solutions, for pumping the solutions between the sorption and desorption units, to promote heat exchanges between the process streams in such a way as to obtain an efficient cyclic process of capturing acidic gases.
The absorption step of the process promotes the direct or indirect contact, by means of contact membranes, of the gaseous feed stream, with zwitterionic solutions without concentration between 0.5 M and 7 M, temperatures (T1) between 0° C. to 60° C. and pressures (P1) between 1 and 150 bar absolute (100 kPa and 15 MPa), typically 40° C. and 1.3 bar to 3 bar absolute (130 kPa to 300 kPa).
The desorption step of the process promotes the regeneration of zwitterionic solutions by heating the solution rich in acidic gases at temperatures (T2) greater than the absorption temperature (T1) and/or through the use of pressures (P2) lower than the absorption pressure (P1), the desorption temperatures (T2) being between 60° C. and 150° C. and the desorption pressures between 0 and 10 bar absolute (1 MPa), typically 100° C. and 1 bar absolute (100 kPa).
The process feed gaseous stream can be composed of any gaseous stream or gaseous mixture containing one or more acidic gases, such as carbon dioxide and hydrogen sulfide, in concentrations of 5% to 90%, typically streams of natural gas containing from 1% to 20% CO2.
The zwitterionic solutions used in the capture process are any of those in which the zwitterionic base is dissolved in water, methanol, ethanol, isopropanol or other hydrocarbon, aliphatic alcohol having from 1 to 18 carbons in the alkyl chain, diols having from 2 to 5 carbon atoms or polyols having from 3 to 6 carbon atoms, ethylene glycol monoalkylethers of the formula H(OCH2CH2)nOR2, where n varies from 1 to 4 and R2 consists of an alkyl group containing from 1 to 12 carbons or ionic liquids functionalized with the hydroxyl group as well as mixing these solvents in appropriate proportions, typically water, ethylene glycol, glycerol and ionic liquids functionalized with the hydroxyl group.
Ionic liquids functionalized with the hydroxyl group are compounds with the general formula A+Z−, wherein A+ represents a quaternary ammonium cation, an imidazolium cation, a pyridinium cation, a pyrrolidinium cation or a phosphonium cation, and Z− represents susceptible anions to form a liquid salt with these cations at the absorption temperature.
The cations of ionic liquids include derivatives of the imidazolium cation, the pyridinium cation, the pyrrolidinium cation, the quaternary phosphonium cation or the quaternary ammonium in which, as shown in
The anions of ionic liquids include chloride, bromide, iodide, perchlorate, nitrate, tetrafluoroborate, tetrachloroborate, hexafluorophosphate, trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)imidate, typically NTf2− and PF6−.
From the mere direct extrapolation of the results disclosed herein, in particular, the results of example 3, example 4, example 5 and example 6 and example 7, it can be concluded that the zwitterionic bases have a predictable effect for capturing acidic gases and that have in their structure an organic cation covalently linked to a phenolate anion; therefore, the process of capturing acidic gases described herein is characterized by the zwitterionic base being an organic compound formed by the covalent association of quaternary ammonium, quaternary phosphonium, and pyridinium cations, pyrrolidinium or imidazolium with substituents, independent of each other, comprising hydrogen and alkyl, aryl, alkylether or alkylalcohol groups containing between 1 and 10 carbons, with the phenolate anion with substituents, independent of each other, comprising hydrogen, halides, phenyl, alkoxy containing between 1 and 10 carbons or alkyl containing between 1 and 10 carbons, according to
The use of solutions, especially aqueous solutions, of the inner salts called herein zwitterionic bases, object of the present invention, minimizes the main intrinsic inconveniences of large-scale CO2 capture processes based on aqueous solutions of ethanolamines, as follows:
The zwitterion solutions containing the phenolate group, especially aqueous solutions, can be used in gas washing or scrubbing equipment, that is, in conventional equipment intended for the absorption of acidic gases by liquids.
Therefore, in addition to the various technical advantages, this technology is easy to implement, as it allows already-existing CO2 absorption plants that use aqueous alkanolamine solutions, in particular, in CO2 and H2S removal plants from natural gas, are converted into absorption plants by zwitterionic base solutions without all the equipment having to be replaced, requiring only small adaptations, for example, to adjust the energy demand of the process.
For this work, the following tests were carried out, which represent examples of embodiment of the present invention.
The synthesis of 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt is carried out in three steps. In the first step, 1-methyl-2(3-hydroxy-phenyl)-imidazole is obtained, as shown in
In a reaction flask, methylamine (40% aqueous solution, 3.3 g; 42 mmol) was added over a solution of 3-hydroxy-benzaldehyde (4.88 g; 40 mmol) in 20 mL of methanol at room temperature. The exothermic reaction causes a slight heating of the reaction mixture and, then, the precipitation of the corresponding imine is observed. The suspension was stirred for another 10 minutes and then ammonium carbonate (2.88 g, 30 mmol) was added. The resulting mixture was cooled to 0° C. using an external ice-water bath. Glyoxal (40% aqueous solution, 5.8 g; 40 mmol) dissolved in 15 mL of CH3OH was added slowly and under stirring. The reaction mixture was stirred for another 30 minutes at 0° C., generating a gradual dissolution of the solids. The ice bath was removed and the reaction was stirred for another 24 hours at room temperature, observing the precipitation of the desired reaction product. At the end, 15 mL of water were added to the suspension, the solid was filtered in a Büchner funnel, icy washed with CH3OH/H2O 1:1 and dried under reduced pressure. 2.69 g of a slightly yellowish solid were obtained (38.6% yield).
In the second step of the synthesis, 1,3-dimethyl-2(3-hydroxy-phenyl)-imidazolium iodide is obtained, as shown in
In the third step of the synthesis, the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt is obtained, as shown in
The synthesis of 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salt is carried out in three steps. In the first step, 1-methyl-2-(4-hydroxy-phenyl)-imidazole is obtained, as shown in
Into a reaction flask, there was added at room temperature methylamine (40% aqueous solution, 3.30 g; 42 mmol) over a solution of 4-hydroxy-benzaldehyde (4.88 g; 40 mmol) in 30 mL of methanol. The reaction mixture warms up a little and is stirred for another 10 minutes. After that time, ammonium carbonate (2.88 g; 30 mmol) was added and to the resulting suspension there was added glyoxal (40% aqueous solution, 5.80 g; 40 mmol) dissolved in 15 mL of CH3OH, slowly and under stirring. After the addition, the reaction mixture was stirred for another 2 hours at room temperature and then 60 mL of water were added, observing the precipitation of the desired reaction product. The solid was filtered on a Büchner funnel, cold washed with CH3OH/H2O 1:1 and dried under reduced pressure. 1.57 g of a slightly yellowish solid were obtained (22.5% yield).
In the second step of the synthesis, 1,3-dimethyl-2-(4-hydroxy-phenyl)-imidazolium iodide was obtained, as shown in
In the third step of the synthesis, the 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salt was obtained, as shown in
The laboratory tests of absorption and desorption of CO2 of the solutions of the inner salts were carried out in an experimental apparatus that allows the temperature and pressure of the sorption vessel to be kept constant while the pressure drop in a CO2 reservoir is monitored for determining the amount of gas absorbed, as shown in
To carry out the test, the reservoir with calibrated volume 402 is previously filled with CO2 contained in the cylinder 401. The pressure control valve 403 is adjusted to maintain the pressure of the sorption vessel at 1.3 bar absolute (130 kPa) during the absorption test. The temperature of the sorption vessel 404 is adjusted by circulating, in its jacketed wall, thermal fluid from the thermostatic bath 407 to the absorption temperature (T1), typically 40° C. Then, 5 mL of 1 M aqueous solution of 1,3-dimethyl-2-(3-oxyphenyl)-imidazolium or 1,3-dimethyl-2-(4-oxy-phenyl)-imidazolium inner salt is added to the reaction vessel. The system was purged with CO2 for 5 seconds by opening purge valve 406, and the reservoir 402 was refilled with CO2 at 4 bar absolute (400 kPa). The absorption process begins when the magnetic stirrer 408 is activated and, from then on, the pressure drop in the CO2 reservoir is monitored to determine the number of moles of CO2 consumed. The pressure is monitored through a transducer installed in the CO2 reservoir coupled to a recorder 409 and a computer 410 for data processing. For the calculations, the ideal gas equation of state and the previously calibrated volume of the reservoir were considered. The end of absorption was considered when the reservoir pressure as a function of time remained at an unchanged level for at least 10 minutes.
At the end of the absorption step, the sorption vessel 404 was opened and the temperature of the thermostatic bath 407 adjusted to the desorption temperature (T2), typically 100° C. The system was kept under stifling for 30 minutes to regenerate the zwitterionic solution. With the aim of validating the method and obtaining a parameter for comparison, the absorption test was carried out with the commercial mixture MDEA/piperazine/water normally used in industrial CO2 absorption processes (Input 1, Table 1). It is important to point out that the tested salts present absorption at wavelengths in the UV-VIS region typical of phenolic decompositions. The wavelengths before and after absorption differ, as shown in
a Reaction conditions: 5 mL of solution with a concentration of 1 mol/L, temperature of 40° C. and pressure. Mean of at least two analyses ± standard deviation.
b Absorption values expressed in moles CO2 per moles of absorbent obtained by pressure measurements of 1.3 bar (130 kPa).
c Absorption values expressed in moles CO2 per moles of absorbent obtained by quantitative 13C NMR.
d Desorption percentage = (1-(HCO3− equivalents after desorption at 100° C. for 30 minutes / 13C NMR absorption))*100.
e CO2 absorption in relation to the number of moles of MDEA + moles of piperazine.
The recyclability of aqueous solutions of the new developed absorbents was tested in cyclic tests of absorption followed by desorption. These tests were carried out in the same experimental apparatus used in Example 1 and shown in
a Reaction conditions: 5 mL of solution with a concentration of 1 mol/L, absorption temperature 40° C., and pressure of 1.3 bar (130 kPa), desorption temperature 100° C., atmospheric pressure (30 min.).
b Absorption values determined through the pressure drop in reservoir and expressed in moles CO2 per moles of absorbent. Mean represents mean absorption value of the cycles ± standard deviation.
c moles of CO2 per total moles of amines (MDEA + piperazine) MDEA/piperazine/water 40%:10%:50% solution.
The capture of CO2 by zwitterionic solutions of the 1,3-dimethyl-2-(3-oxy-phenyl)-imidazolium inner salt was also studied through quantitative analyses of 13C. This analysis methodology was described by SIMON, N. M. et al. “Carbon dioxide capture by aqueous ionic liquid solutions”, ChemSusChem, v. 10, p. 4927-4933, 2017 and allows to directly quantify both the chemisorption and the physisorption of CO2 in the solutions.
To carry out this experiment, a syringe pump coupled to a zirconia NMR tube installed in an NMR spectrometer was used. The syringe pump allows CO2 pressure control during experiments. The results were analyzed considering the proportion between the integrals of the signals corresponding to the dissolved CO2 and the bicarbonate formed in relation to the integral of the methyl carbons of the zwitterion. The results are presented in Table 3.
a Reaction conditions: 0.5 mL of solution with a concentration of 2.2 mol/L (1.1 mmol of the inner salt, dissolved in 0.5 mL of D20), absorption temperature 40° C. The NMR spectra were obtained in a Bruker-400-Avance-IIIHD NMR equipment operating at a frequency of 100 MHz for 13C equipped with a 5 mm probe with direct detection, with field gradient in z and thermostated via BCU-xtreme with constant temperature and spectral window from −15 ppm to 235 ppm. Used syringe pump: Xtreme-10 syringpump - deadalus innovation.
One of the main advantages of the CO2 capture process using zwitterionic solutions is that the zwitterionic bases are not volatile. On the other hand, a fraction of the solvent (usually water) can be lost by evaporation and during the desorption step, which represents energy losses in the process and the need of replacing this solvent. The cyclic CO2 capture processes with the inner salts disclosed in the present discovery can also be carried out using non-aqueous solvents to minimize, or even eliminate, such mass losses in the desorption step. Alcohols, diols, polyols and ionic liquids functionalized with a hydroxyl group are solvents that, when combined with zwitterionic bases, are capable of reversibly absorbing CO2 through the formation of the respective alkyl carbonates. In Table 4, some examples of absorption in non-aqueous systems are presented. n-propanol, n-butanol, ethylene glycol or glycerol are alternative solvents with boiling points of 97.0° C., 117.7° C., 197.6° C. and 290° C., respectively. On the other hand, the 1,2-dimethyl-3-(3-hydroxypropyl)-imidazolium bistrifluoromethylsulphonylimidate ionic liquid is a solvent with negligible vapor pressure and represents a totally ionic system for CO2 capture in which there is certainly no loss of mass by evaporation.
13C NMR
a Reaction conditions: 5 mL of solution with a concentration of 1 mol/L, temperature of 40° C. and pressure. Mean of at least two analyses ± standard deviation.
b Absorption values expressed in moles CO2 per moles of absorbent obtained by pressure measurements of 1.3 bar (130 kPa).
c Absorption values expressed in moles CO2 per moles of absorbent obtained by quantitative 13C NMR.
d Desorption percentage = (1-(HCO3− equivalents after desorption at 100° C. for 30 minutes /13C NMR absorption))*100.
The experimental apparatus shown in
a Reaction conditions: 0.5 mL of solution with a concentration of 1 Mol/L, absorption temperature between 10° C. and 60° C. Equilibrium pressure between 0.9 bar and 1.4 bar absolute (90 a 140 kPa).
It should be noted that, although the present invention has been described in relation to the attached drawings, it may undergo modifications and adaptations by technicians skilled on the subject, depending on the specific situation, but provided that within the inventive scope defined herein.
Number | Date | Country | Kind |
---|---|---|---|
10 2020 027071-0 | Dec 2020 | BR | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/BR2021/050557 | 12/17/2021 | WO |