KR20220067591A - Ion-exchanged regenerative catalyst for carbon dioxide capture - Google Patents

Abstract

The present invention provides an ion-exchanged montmorillonite catalyst for capturing carbon dioxide, a method for producing the same, and a method for regenerating a solvent for capturing carbon dioxide using the same. The ion-exchanged montmorillonite catalyst of the present invention exhibits material properties including an excellent BET specific surface area, an intermediate porosity, and a surface acidity, and thus CO_2 desorption rate can be efficiently optimized at a low temperature in a carbon dioxide capture and amine solvent regeneration process, thereby minimizing an energy demand for amine solvent regeneration. In addition, the catalyst activity is constantly maintained even when the catalyst is repeatedly used, and the catalyst can be obtained from naturally-existing raw materials as a clay mineral, and thus a final catalyst material can be prepared at a low cost. Thus, the method can be advantageously used as a technology capable of energy-effectively designing a CO_2 capture process in the carbon capture and storage fields.

Description

Ion-EXCHANGED REGENERATIVE CATALYST FOR CARBON DIOXIDE CAPTURE

The present invention relates to a catalyst for capturing carbon dioxide, and more particularly, to a technology using ion-exchanged montmorillonite as a catalyst for capturing carbon dioxide as a regeneration catalyst.

Significant increases in anthropogenic carbon dioxide emissions are considered a major cause of global warming and climate change. CO ₂ capture and storage (CCS) is widely recognized as an important short- and medium-term measure to reduce CO ₂ emissions. The main techniques currently used to separate CO ₂ from flue gas streams include chemical absorption, adsorption, membrane separation and cryogenic distillation. However, low CO ₂ concentrations in the flue gases (7-15 %) make physical separation techniques (adsorption, membrane filtration and cryogenics) unsuitable for large-scale CO ₂ capture. Chemical absorption of CO ₂ into aqueous alkanolamine solutions is the most advanced commercial technology capable of processing large volumes of gases even at low CO ₂ partial pressures. However, this technology has several major drawbacks such as energy-intensive regeneration, solvent decomposition, and corrosion of equipment, making it difficult to apply it on a wide scale.

In the thermal amine scrubbing process, CO ₂ is selectively absorbed by an aqueous amine solution at a low temperature (~ 50°C), and then this CO ₂ -rich solution is thermally regenerated in a stripper column at a high temperature (~ 120°C) to obtain pure CO ₂ collect stream. The regeneration solvent, ie the CO ₂ -lean solvent, is pumped back to the absorber column for cycle use. In particular, not all absorbed CO ₂ is desorbed in the stripper column, instead, the goal is to regenerate the amine solvent at a temperature where the reboiler thermal duty is not large, the thermal decomposition of the solvent is limited, and most importantly, the absorbed CO ₂ is sufficiently discharged to induce sufficient absorption of fresh CO ₂ into the absorber column. Therefore, a certain amount of CO ₂ is released from the amine solution to ensure an economically efficient process. For example, when using the benchmark 30 wt.% monoethanolamine (MEA) solvent, typically about 50% _of the absorbed CO2 is released from the stripper column and CO2 _- lean at about 0.20-0.30 mol CO2/mol MEA The load is maintained downstream of the stripper. Unfortunately, an enormous amount of thermal energy is still consumed to release _half of the captured CO2, mainly due to _the low CO2 desorption power. More precisely, the energy required to perform solvent regeneration accounts for about 70% of the total process cost. Insights into regenerative heat duty show that only half of the total heat duty is actually spent breaking chemical bonds and releasing CO ₂ , and the other half is wasted heating and evaporating water (Qsen and Qvap).

The two primary challenges in this scenario are (i) performing amine solvent regeneration at a temperature below 100 °C, to avoid the loss of thermal energy to evaporate water, and ( _ii ) to rapidly generate higher amounts of CO2 per unit of energy consumption. Optimize the CO ₂ desorption kinetics at low temperatures to release, which in turn leads to a lower regeneration heat duty (GJ/ton CO ₂ ).

Several advanced (advanced) solvent formulations such as mixed absorbents, two-phase absorbents, non-aqueous absorbents, etc. and advanced solvent regeneration methods including microwave irradiation, electrochemical mediated regeneration, additive introduction, etc. Several innovative approaches have been reported. For example, Chowdhury et al. and colleagues have developed a series of non-aqueous absorbents that have excellent CO2 capture performance and can be regenerated at moderate temperatures of ~80–90 °C. Pri et al. developed a soy-based solvent (SBB, a mixture of amino acids) and thoroughly tested its CO ₂ capture performance and thermal regeneration compared to a benchmark MEA solution. SBB was very effective and improved the CO ₂ desorption rate by 195% and reduced non-renewable energy by 37%.

A relatively new innovation to overcome the energy penalty problem is to improve the CO ₂ desorption rate at low temperature by adding a catalyst to the amine solvent regeneration step. It has been reported that the addition of a metal-based catalyst can aid in carbamate decomposition and release CO ₂ at low temperatures, thereby reducing the regenerative thermal duty. Idem et al. investigated MEA solvent regeneration using HZSM-5 and γ-Al ₂ O ₃ catalysts and demonstrated that catalyst-mediated regeneration can reduce the amine regeneration thermal duty by 24%. Liang et al. synthesize excellent catalysts such as Fe-promoted SO ₄ ^2- /ZrO ₂ /MCM-41, SO ₄ ^2- /ZrO ₂ /SBA-15 and Al ₂ O ₃ /HZSM-5 and further reduce the energy penalty This technique was extended by optimizing key catalytic properties (mesoporosity, surface acidity, BET specific surface area) for this purpose. Li et al. synthesized and investigated the catalytic performance of a SO ₄ ^2- /TiO ₂ solid acid catalyst in a CO ₂ rich MEA solution at 95 °C and reported that the CO ₂ desorption rate could be improved by ~29%. Solid metal oxides, TiO(OH) ₂ and metals have been shown to promote carbamate decomposition at moderate temperatures. However, this approach is in its infancy and only a limited number of catalysts have been reported in the literature. Also, since most of the reported catalysts are expensive, the benefit obtained in terms of reduced thermal duty may be offset by the cost of the catalyst. Therefore, there is an urgent need to develop an inexpensive and abundant catalyst that can substantially optimize CO ₂ desorption at low temperatures.

The technical problem to be achieved by the present invention is to improve the CO 2 desorption rate by minimizing the energy requirement by lowering the amine regeneration temperature in the carbon capture and solvent regeneration process, while improving the CO ₂ desorption rate, based on the raw materials abundantly in nature, at a low cost, as a final catalyst material It is to provide a technology that can reduce the process cost by manufacturing

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by those of ordinary skill in the art to which the present invention belongs from the description below. There will be.

In order to achieve the above technical object, according to an aspect of the present invention, an ion-exchanged montmorillonite catalyst for capturing carbon dioxide is provided.

In one embodiment, the ion-exchange may be characterized in that the ions contained in the montmorillonite are replaced with the cations of the acid aqueous solution or the metal aqueous solution.

In one embodiment, the ion-exchange may be characterized in that Si, Al, O, Fe, Mg, Na, Ca or K ions contained in the montmorillonite are replaced with cations of H ⁺ or Zr.

In one embodiment, the ion-exchanged montmorillonite catalyst may have a fraction of one element selected from 0 to 7% Al, 0 to 1.2% Fe, 0 to 1% Mg, and combinations thereof.

In one embodiment, the ion-exchanged montmorillonite catalyst may have a surface area of 50 to 500 m ² /g.

In one embodiment, the ion-exchanged montmorillonite catalyst may have a pore volume of 0.15 to 0.50 cm ³ /g.

In one embodiment, the ion-exchanged montmorillonite catalyst may have an average pore diameter of 1 ~ 15 nm.

In one embodiment, the ion-exchanged montmorillonite catalyst may have a surface acidity of 2 mmol/g or more.

In one embodiment, the ion-exchanged montmorillonite catalyst may have a total acid site of 0.3 mmol/g or more.

According to another aspect of the present invention, there is provided a method comprising the steps of: (a) reacting montmorillonite with an aqueous acid solution to obtain a product; And (b) filtering the product of step (a) and washing until the pH of the filtrate becomes 5 to 9. There is provided a method for preparing an ion-exchanged montmorillonite catalyst.

In one embodiment, the reaction of step (a) may be characterized in that it proceeds with stirring.

In one embodiment, the acid of step (a) is hydrochloric acid, nitric acid, sulfuric acid, benzoic acid, oxalic acid, acetic acid, propionic acid, pyridinium ion, chloric acid, oxonium ion, iodic acid, oxylic acid, sulfurous acid, chlorous acid, phosphoric acid, Arsenic acid, chloroacetic acid, hydrogen fluoride, nitrous acid, formic acid, carbonic acid, hydrogen sulfide, hypochlorous acid, hydrogen iodide, hydrogen bromide, perchloric acid, and combinations thereof can be characterized as one selected from the group consisting of .

In one embodiment, the metal aqueous solution of step (a) may include at least one selected from SnCl ₄ , TiCl ₄ , TiOCl ₂ , TiOSO ₄ , ZrOCl ₂ , ZrCl ₄ , ZrOSO ₄ , MnCl ₂ , and CoCl ₂ . have.

In one embodiment, the aqueous acid solution of step (a) may have a concentration of 0.5 to 10 mol/L.

In one embodiment, the montmorillonite and the acid aqueous solution of step (a) may be reacted in a ratio of 1:1 to 1:100 (weight:volume).

에서 수행될 수 있다.In one embodiment, the reaction of step (a) is 70 to 110

can be performed in

In one embodiment, the reaction of step (a) may be performed for 1 to 20 hours.

In one embodiment, the filtration of step (b) may be performed after cooling to room temperature.

According to another aspect of the present invention, there is provided a method for regenerating a solvent for capturing carbon dioxide, using the ion-exchanged montmorillonite catalyst.

By the ion-exchanged montmorillonite catalyst of the present invention, the CO ₂ desorption rate is improved by lowering the amine regeneration temperature in the carbon capture and solvent regeneration process to minimize the energy requirement, while the low cost based on the raw material abundant in nature It is possible to provide a technology that can reduce the process cost by manufacturing the final catalyst material.

The effects of the present invention are not limited to the above-described effects, and it should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

1 is a schematic diagram of a Mont structure;
2 is a raw material and ion-exchanged Mont catalyst characteristics evaluation results, (a) XRD pattern, (b) N ₂ adsorption-desorption isotherm, (c) NH ₃ -TPD curve, (d) Py-FTIR spectrum to be.
3 is a schematic diagram of the experimental setup used to perform the solvent regeneration experiment.
4 is a raw material and an ion-exchanged Mont catalyst MEA solvent regeneration characteristics evaluation results according to the presence or absence, (a) CO ₂ desorption rate curve, (b) the total amount of CO ₂ desorbed during the ramp section and the entire experiment, (c) Relative thermal duty of the amine solution.
5 shows a possible reaction mechanism of an ion-exchanged Mont catalyst to promote carbamate decomposition and release CO _{2 from CO 2 -enriched} MEA.
6 shows (A) the recyclability of the ion-exchanged Mont catalyst and (B) the effect of the ion-exchanged Mont catalyst on CO ₂ absorption in MEA solution.

As used herein, "acid activation" refers to a process of inducing generation of an acid site by treating a material with an acidic material.

The present invention provides an ion-exchanged montmorillonite catalyst for carbon dioxide capture.

Montmorillonite (Montmorillonite, Mont) is a kind of clay mineral, it is a monoclinic crystal, chemical composition (AI,Mg) ₂ Si ₄ O ₁₀ (OH) ₂ 4H ₂ O, bulk (塊狀) earth (土狀) make up It absorbs water between layers and swells 7 to 10 times its original volume, and has high ion exchange properties. It is a clay with special properties such as low internal frictional resistance as the main component mineral of bentonite, which is altered from volcanic ash or tuff. It has a hardness of 1-1.5, a specific gravity of 2-2.5, and a refractive index of 1.48-1.6. It is white, yellow, light yellow, light green, green, or blue in color and has no luster.

Currently, clay minerals are considered promising catalysts because they are environmentally friendly and inexpensive. Montmorillonite is an inexpensive, abundant and naturally occurring clay composed of an aluminosilicate layer and exchangeable cations ( FIG. 1 ). In the present invention, it is provided by easily improving the surface acidity of montmorillonite through a simple ion-exchange process.

The ion-exchanged montmorillonite catalyst of the present invention may have a fraction of one element selected from 0 to 25% Si, 0 to 7% Al, 0 to 1.2% Fe, 0 to 1% Mg, and combinations thereof. The raw material of montmorillonite has Na, Ca, Fe, Mg and K cations in the intermediate layer, and SiO ₂ and Al ₂ O ₃ are the main components, but the ion-exchanged montmorillonite catalyst is mainly octahedral by ion-exchange. Metals such as silicon (Si), aluminum (Al), iron (Fe), magnesium (Mg), sodium (Na), calcium (Ca) and potassium (Ka) are leached from the cation intermediate layer, changing the elemental composition ratio . In particular, Na, Ca and K are not detected in the ion-exchanged montmorillonite catalyst. This process promotes the collapse of the layer structure, removes impurities, and changes the structure and chemical composition of montmorillonite. Accordingly, the major structural properties of the montmorillonite catalyst such as surface area, pore volume, mesoporosity and surface acidity are substantially improved.

In one embodiment, the ion-exchanged montmorillonite catalyst has a surface area of 50 to 500 m ² /g, preferably 60 to 400 m ² /g, more preferably 70 to 300 m ² /g, most preferably 80 ~ 200 m ² /g.

In one embodiment, the ion-exchanged montmorillonite catalyst has a pore volume of 0.15 to 0.50 cm ³ /g, preferably 0.16 to 0.45 cm ³ /g, more preferably 0.17 to 0.40 cm ³ /g, most preferably 0.18 to 0.35 cm ³ /g.

In one embodiment, the ion-exchanged montmorillonite catalyst may have an average pore diameter of 1 to 15 nm, preferably 2 to 14 nm, more preferably 3 to 13 nm, and most preferably 4 to 13 nm.

In one embodiment, the ion-exchanged montmorillonite catalyst may have a surface acidity of 2 mmol/g or more, preferably 3 mmol/g or more, more preferably 3.5 mmol/g or more, and most preferably 3.56 mmol/g or more. have.

In one embodiment, the ion-exchanged montmorillonite catalyst may have a total acid site of 0.2 mmol/g or more, preferably 0.25 mmol/g or more, more preferably 0.3 mmol/g or more.

The ion-exchanged montmorillonite catalyst of the present invention can significantly increase the BET specific surface area, mesoporosity and surface acidity of the raw material montmorillonite without noticeably destroying the clay structure in the ion-exchange process. Through a solvent regeneration experiment at an intermediate temperature of 86 ° C, the catalyst is effective at low temperatures, and the CO ₂ desorption rate and the amount of desorbed CO ₂ can be significantly increased. In addition, the prepared catalyst can be easily separated by simple filtration and stable This can be secured.

The ion-exchanged montmorillonite catalyst of the present invention comprises the steps of (a) reacting montmorillonite with an aqueous acid solution or an aqueous metal solution to obtain a product; And (b) filtering the product of step (a) and washing until the pH of the filtrate becomes 5 to 9. It is prepared by a method for preparing an ion-exchanged montmorillonite catalyst.

The manufacturing method is a process of inducing generation of an acid site by treating montmorillonite with an acidic material. This process promotes the collapse of the layer structure, removes impurities, and changes the structure and chemical composition of montmorillonite.

The preparation method of the present invention includes a step (ie, step (a)) of reacting montmorillonite with an aqueous acid solution or an aqueous metal solution to obtain a product. Step (a) is a step of inducing leaching of cations and generation of acid sites by treating montmorillonite with an acidic material. The acid used in step (a) is silicon (Si), aluminum (Al), iron (Fe), magnesium (Mg), sodium (Na), calcium (Ca) and potassium (Ka) in the octahedral region and cation intermediate layer of montmorillonite. Any acid aqueous solution or metal aqueous solution capable of leaching metals such as hydrogen ions or metal ions and exchangeable with hydrogen ions or metal ions may be used without limitation, and preferably, the acid aqueous solution is hydrochloric acid, nitric acid, sulfuric acid, benzoic acid, oxalic acid, acetic acid, propionic acid, Pyridinium ion, chloric acid, oxonium ion, iodic acid, oxylic acid, sulfurous acid, chlorous acid, phosphoric acid, arsenic acid, chloroacetic acid, hydrogen fluoride, nitrous acid, formic acid, carbonic acid, hydrogen sulfide, hypochlorous acid, iodide It may be one selected from the group consisting of hydrogen, hydrogen bromide, perchloric acid, and combinations thereof, and the aqueous metal solution is SnCl ₄ , TiCl ₄ , TiOCl ₂ , TiOSO ₄ , ZrOCl ₂ , ZrCl ₄ , ZrOSO ₄ , MnCl ₂ , and CoCl It may be characterized in that it is an aqueous solution of an inorganic metal salt comprising at least one selected from among ₂ . The aqueous acid solution in which the acid is dissolved or the aqueous metal solution in which the inorganic metal salt is dissolved may be used at a concentration that can induce cation leaching, generation of acid sites, or substitution with metal ions, preferably at a concentration of 0.3 to 12 mol/ L, more preferably 0.5 to 10 mol/L, but is not limited thereto.

The reaction of step (a) may be performed at 90 to 110 ° C. so that cation leaching and generation of acid sites can be induced, and for an appropriate time for the reaction to proceed, for example, 1 to 20 hours. can be In addition, it may be characterized in that it proceeds while stirring, and in some cases, it may be reacted with strong stirring.

The production method of the present invention includes the step of filtering the product of step (a) and washing until the pH of the filtrate becomes 5 to 9 (ie, step (b)). Step (b) is a step of neutralization by washing the surface of the ion-exchanged montmorillonite catalyst from which the cations are leached and the acid sites are increased. The filtration of step (b) may be performed after cooling to room temperature. In addition, the washing may be performed with a material (eg, water, etc.) capable of neutralizing by washing the acidic material remaining on the surface of the ion-exchanged montmorillonite catalyst. The washed ion-exchanged montmorillonite catalyst can be dried and pulverized as needed.

The present invention also provides a method for regenerating a solvent for capturing carbon dioxide, using the ion-exchanged montmorillonite catalyst. The use of the ion-exchanged montmorillonite catalyst of the present invention can efficiently optimize the CO ₂ desorption rate at low temperature in the carbon dioxide capture process and the amine solvent regeneration process, thereby minimizing the energy requirement of the amine solvent regeneration. In addition, it has been shown that the catalytic activity remains constant even with repeated catalyst use, which is useful for commercial applications of carbon capture processes.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited thereto.

<Example>

This study advances this approach by preparing an abundant and inexpensive Montmorillonite (Mont) clay-based catalyst using a simple ion-exchange process and evaluating its catalytic performance for CO2 desorption from MEA solutions. Montmorillonite is a very abundant, inexpensive, naturally occurring clay that has a wide range of applications in adsorption and catalytic processes. It has a three-sheet lattice structure consisting of a central layer of alumina octahedron sandwiched between two layers of silica tetrahedron (Fig. 1). Interlayer cations are exchangeable and their acidic properties can be altered by simple ion-exchange with acids or metals. The prepared catalyst was thoroughly characterized using XRD, BET, NH3-TPD, Pyridine-FTIR and EDS to confirm the physicochemical transformation and efficiency induced by the ion-exchange process. Catalytic CO ₂ desorption performance was evaluated at 86° C. for CO ₂ desorption rate, total amount of desorbed CO ₂ and relative thermal duty compared to non-catalytic reference MEA solution.

1. Preparation of catalyst

(1) Purchasing materials and preparing catalysts

Montmorillonite (Cas No. 1302-78-9), monoethanolamine (>99 %), H ₂ SO ₄ (96 %), and ZrOCl ₂ .8H ₂ O (reagent grade, 98%) were obtained from Sigma-Aldrich (Sigma -Aldrich) and used without further purification.

The ion-exchanged Mont catalyst was prepared using a slightly modified method. In a typical preparation, Mont (5 g) was slowly added to 80 mL of ZrOCl ₂ .8H ₂ O solution (0.5 mol/L) at 80 °C with vigorous stirring. After 12 h, the process was repeated for 4 h with fresh ZrOCl ₂ .8H ₂ O solution (0.5 mol/L, 80 mL). For H ₂ SO ₄ -mont, 5 g Mont was slowly added to the H ₂ SO ₄ solution (4 mol/L) in a ratio of 1: 5 (weight per volume). The reaction was carried out at 100 °C for 4 h under reflux conditions. After the ion-exchange process was completed, both samples were cooled to room temperature and washed repeatedly with deionized water until the pH of the filtrate was about 7. The obtained clay was dried in an oven at 110° C. for 12 hours, and then pulverized with a mortar-peel. The prepared catalysts were named SO ₄ -Mont and Zr-Mont depending on the solution used for ion-exchange.

(2) Physical property evaluation

X-ray diffraction (XRD) patterns were scanned at 0.5° min ^-1 in the range of 5 to 80° using a Rigaku D/max 2200PC diffractometer equipped with a Cu sealed tube (λ=1.54178 Å). speed was recorded.

The BET (Brunauer-Emmett-Teller) specific surface area and porosity of the catalyst were measured using a nitrogen adsorption method at -200 °C using a constant volume adsorption apparatus (Micromeritics, ASAP-2420).

Surface density and acid site strength were measured with a temperature programmed ammonia desorption apparatus (Micromeritics, Autochem II). About 0.1 g of the sample was pretreated at 200° C. in a helium flow for 2 hours to clean the surface. The sample was then cooled to room temperature and ammonia was introduced into the reactor at 100° C. for 1 hour.

For Py-FTIR spectroscopy, free-standing wafers (11 ton cm ⁻² , 30 mg and 1 cm ² ) were pretreated in a stainless steel IR cell under vacuum (10 ⁻³ mbar) at 300° C. for 2 h. Thereafter, high-temperature pyridine vapor at 100° C. was introduced into the IR cell for 2 hours until the pressure inside the IR cell reached 5 bar. The IR cell was then connected to an infrared spectrometer, and the IR spectrum of the material was recorded in the range of wavelengths from 600 to 4000 cm ^-1 with an optical resolution of 8 cm ^-1 and a co-addition of 32 scans.

Quantitative values of Bronsted and Lewis acid sites were calculated using equations 1 and 2.

(식 1)

(Equation 1)

(식 2)

(Equation 2)

where C is the concentration of acid sites (mmol g-1 catalyst), IA (B, L) is the integrated absorbance of the B or L band (cm-1), R is the radius of the catalyst disk (cm), W = disk weight ( mg).

(3) Regeneration evaluation

A 250 mL glass reactor was connected to an oil circulator to heat the amine solution. A K-type thermocouple was inserted into the reactor to record the temperature of the amine solution. A glass condenser was fitted to the reactor to condense and reflux water and amine vapors. A magnetic stirrer was used at 300 rpm to stir the solution during the regeneration experiment. MEA solution regeneration was measured by heating 100 g of a CO ₂ -enriched MEA solution from room temperature to about 86°C. Thereafter, the temperature was kept constant at 86° C. until the emitted CO ₂ was less than 0.1%. In the catalyst experiments, 5% by weight of each catalyst was added to 100 g of a MEA solution at room temperature. The released CO ₂ gas was mixed with N ₂ carrier gas (50 mL/min) through a check valve before quantitative analysis in gas chromatography. The amount of desorbed CO ₂ was calculated by integrating the CO ₂ desorption profile.

2. Material properties

(1) XRD analysis

The XRD patterns of raw material and ion-exchanged Mont catalyst are shown in Fig. 2a. For the raw material Mont, the d001 basis spacing diffraction was observed at 2θ at 7.41 ^o . For both catalysts, the d001 diffraction peak was broadened and the intensity was lowered, indicating laminar torsion induced by the ion-exchange process that disturbed the laminar stacking. Different characteristic reflections assigned to the crystal lattice planes of 020, 110, 005, 200, 130 and 060 at 2θ 19.7, 26.6, 28.5, 35.3, 36.1 and 61.9 ^o , respectively, can be clearly identified in both ion-exchange catalysts. Overall, the persistence of all diffraction peaks of the ion-exchanged Mont clearly confirms that the crystal structure of the raw material Mont was not damaged and that the ion-exchange process did not noticeably change the layer structure of Mont.

(2) N ₂ adsorption-desorption

The nitrogen adsorption-desorption isotherms of the raw material and the ion-exchanged Mont catalyst are summarized in Figure 1b, and the calculated tissue properties are summarized in Table 1. As can be seen from the table, the ion-exchange process significantly increased the surface area of the raw material Mont. The raw material Mont had a BET surface area of 24.4 m ² /g, which increased to 118.02 and 223.35 m ² /g after ion-exchange with H ₂ SO ₄ acid and Zr metal solution, respectively. The significant increase in surface area was mainly caused by the removal of cations from the clay to promote porosity. Also, a higher amount of adsorption-desorbed N ₂ was observed for the ion-exchanged Mont catalyst compared to the raw material Mont. In general, the N ₂ isotherm belongs to the type II profile and the hysteresis loop is of the H4 type, indicating that N ₂ adsorption and desorption occurred on the smooth surface.

[Table 1]

(3) temperature-programmed NH ₃ Desorption

The density and intensity of acid sites were determined using temperature-programmed NH ₃ desorption and the obtained spectra are shown in Fig. 2c. The strength of the acid sites was designated as weak, moderate, or strong depending on the temperature range of NH ₃ desorption. The raw material Mont exhibited two peaks, a small peak at ~124 ^o C due to physically adsorbed NH ₃ and another peak in the strong temperature region of 679 ^o C due to the structural Al sites of Mont. The NH ₃ -TPD profile of the ion-exchanged Mont catalyst showed the appearance of an additional peak in the middle region, clearly indicating that the ion-exchange process improved the acidity of Mont. In addition, it can be seen that the peak in the high-temperature region is widened, so that a strong acid site is formed during the ion-exchange process.

[Table 2]

^{a NH} ₃ ^{-obtained from TPD}

^{b Lewis acid sites (LAS), Bronsted acid sites (BAS) and total acid sites calculated by Py-FTIR}

(4) pyridine-infrared spectroscopy

The properties of the acidic sites were determined by FTIR analysis of the pyridine-adsorbed species. A pyridine molecule reacts with a hydroxyl group present on the catalyst surface (Brönsted acid site) to form a pyridinium ion (HPy species), and exhibits a characteristic peak at about 1540 cm ^-1 . In addition, pyridine can interact with the coordinating unsaturated metal sites of the catalyst to form LPy species (Lewis acid sites). The obtained FTIR spectra are presented in Figure 2d and the quantitative values for Lewis and Brønsted acid sites are provided in Table 2. In the case of the raw material Mont, three prominent peaks appear at 1447, 1490, and 1592 cm ^-1 , and it can be seen that only the Lewis acid site exists. For the ion-exchange catalyst, well resolved peaks were recorded at 1440 and 1590 cm ⁻¹ for pyridine adsorbed on the Lewis acid site and at about 1540 ⁻¹ for the pyridine adsorbed on the Bronsted acid site. The peak appearing at about ˜1490 cm ⁻¹ indicates the presence of both Lewis and Brønsted acid sites.

(5) elemental analysis

EDS (Energy Dispersive X-ray spectroscopy) was used to determine the quantitative elemental composition of the raw material catalyst and the ion-exchanged Mont catalyst, and the results obtained are summarized in Table 3. The raw material Mont was mainly composed of SiO ₂ and Al ₂ O ₃ octahedral sheets, with Fe ⁺³ , Mg ⁺² , Na ⁺ , Ca ⁺² and K ⁺ cations in the middle layer. In the case of the ion-exchange catalyst, Si and Al are leached from the octahedral sheet, and Na ⁺ , Ca ⁺² , K ⁺ are completely extracted from the cation interlayer to confirm the effect of the ion-exchange process. This also indicates that the concentrations of the acid and metal solutions were optimal, resulting in a strong attack on the Mont structure in which the exchangeable cations were replaced by H ⁺ and Zr metals. Nevertheless, significant amounts of Fe ⁺³ and Mg ⁺² remained in the ion-exchanged Mont catalyst. This may be due to the presence of insoluble quartz impurities.

[Table 3]

3. How data is calculated

CO ₂ Desorption rate:

The CO ₂ desorption rate (mmol/min) during the regeneration experiment was calculated using Equation 1.

(1)

(One)

where Q _CO2 is the CO ₂ desorption rate (mmol/min), r _CO2 is the volume concentration of CO ₂ , and the volume flow rate of V _N2 N ₂ (mL/min).

adsorbed CO ₂ Quantity of:

The total amount of CO ₂ adsorbed during regeneration experiments was calculated by integrating the recorded CO ₂ adsorption profiles.

(2)

(2)

Here, Q _CO2 is the CO ₂ desorption rate (mmol/min), and N _CO2 is the total amount of CO ₂ desorbed during the solvent regeneration experiment (mmol).

Thermal Duty of Solvent Regeneration:

The thermal duty (KJ/mol CO ₂ ) of MEA solvent regeneration was calculated using Equation 3. Power consumption was measured using a power meter, and the amount of CO ₂ emitted was calculated using Equation 2. Thermal duty was determined by dividing power consumption by the total amount of CO ₂ emitted during the regeneration experiment.

(3)

(3)

For better comparison of catalytic and non-catalytic systems, we used relative thermal duty as previously suggested by Liang et al. The relative thermal duty of solvent regeneration is defined as Equation 4.

(4)

(4)

where RHD is the relative thermal duty (%) and HD _baseline and HD _cat are the thermal duties for uncatalyzed and catalytic MEA solutions, respectively.

4. Experimental Apparatus and Methods

The experimental setup used to perform the CO ₂ desorption experiment is shown in FIG. 3 . A 250 mL volume flat bottom glass reactor was connected to an oil circulator to heat the amine solution. A condenser was fitted to the reactor to minimize vapor loss during regeneration experiments. A K-type thermocouple and pressure gauge were installed to monitor the temperature of the amine solution and the pressure inside the reactor. The CO ₂ released during solvent regeneration passed through a check valve and then mixed with a nitrogen carrier gas (50 mL/min) before analysis using a gas chromatograph (Agilent Technologies 7890A). The amine solution was continuously stirred at 300 rpm using a magnetic stirrer. The thermal duty of solvent regeneration was recorded using a wattmeter (Wattman HPM-100A) connected to a heating oil circulator. All pipelines were purged with nitrogen gas before and after each experiment to remove residual CO ₂ .

CO ₂ was absorbed into a 30 wt. % MEA solution using 15 vol. % CO ₂ balanced N ₂ gas at 40 °C. The CO ₂ loading of the MEA solution was measured with a TOC analyzer (Analytik Jena multi N / C 3100) and found to be 0.517. For the solvent regeneration experiment, 100 g of CO ₂ rich MEA solution with and without 5 wt % catalyst was poured into the reactor at room temperature and heated continuously until the desired temperature point, i.e., 86° C., was reached. 86 ℃ was kept constant so that CO ₂ could be released.

5. Experimental Results and Interpretation

(1) CO ₂ Desorption performance

The CO ₂ desorption rate profile of the MEA solution without the 5 wt.% raw catalyst and the ion-exchange catalyst is shown in FIG. 4A . The baseline non-catalytic MEA solution was unable to desorb significant amounts of CO ₂ until reaching ~75° C., after which the CO ₂ desorption rate increased significantly. This shows that the MEA solvent regeneration process is highly temperature dependent. A maximum CO ₂ desorption rate of 0.65 mmol/min at 87° C. and 24 min was recorded for the uncatalyzed MEA solution. Raw material Mont slightly improved the CO ₂ desorption rate and reached the highest CO ₂ desorption value of 0.72 mmol/min at 87°C. This is ~11% higher than the non-catalytic MEA solution. This slight improvement in CO ₂ desorption rate is mainly due to the presence of a small number of Lewis acid sites. Both ion-exchange catalysts promoted the CO ₂ desorption rate and started to desorb a significant amount of CO ₂ after ~66°C. The SO ₄ -Mont catalyst solution achieved the highest CO ₂ desorption rate value of 1.18 mmol/min at 22 min and 85° C., which is 100% higher than the non-catalytic solution at the same point. The Zr-Mont catalyst solution also showed similar performance, improving the CO ₂ desorption rate in the temperature rising step, and at 85° C., the highest CO ₂ desorption rate of 1.04 mmol/min was about ~76° C. higher than the reference solution at the same point.

In addition to optimizing the CO ₂ desorption rate, the catalyst solution desorbed a higher amount of CO ₂ compared to the non-catalytic MEA solution ( FIG. 4b ). The raw material Mont released 13.56 % of CO ₂ while SO ₄ -Mont and Zr-Mont catalysts desorbed 44.9 and 48.6 % higher amounts during regeneration experiments. The increase in the total amount of CO ₂ desorbed from the catalyst solution is actually due to the limited time allowed for regeneration (1 hour), not a change in the thermodynamic equilibrium. The addition of a catalyst to the amine regeneration system improves the CO ₂ desorption rate, resulting in a higher CO ₂ release per unit of heat energy provided per unit time, resulting in lower thermal duty. The relative thermal duty of the catalyst solution is shown in Figure 4c. As can be seen, the raw material Mont reduced the thermal duty by about 12% compared to the non-catalytic solution, and the SO ₄ -Mont and Zr-Mont catalysts reduced the thermal duty by 31.1 and 32.7%.

The catalyst not only accelerated the CO ₂ desorption rate and desorbed higher amounts of CO ₂ but also shifted the CO ₂ desorption significantly to the lower temperature region (ie, <86° C.). Uncatalyst and raw material Mont solution desorbed ˜37.4% of the total desorbed CO ₂ during the temperature rising step (≤86° C.). On the other hand, SO ₄ -Mont and Zr-Mont catalyst solutions desorbed 51.6% and 44.3% of the total desorbed CO ₂ respectively during the temperature rise (ramp) step. The increased CO ₂ desorption rate, especially at low temperatures, allows the solvent to be regenerated in a smaller column, thus minimizing the dimensions of reboilers, stripper columns and lean-rich heat exchangers.

It is interesting to note that the SO ₄ -Mont catalyst desorbed a higher amount of CO ₂ in the ramp stage, whereas the Zr-Mont catalyst desorbed a higher amount of CO ₂ in the isothermal step and overall experiment. The main reason for this trend is that the SO ₄ -Mont catalyst has a higher number of Brønsted acid sites, which is important for optimizing the CO ₂ desorption rate at lower temperatures. The Zr-Mont catalyst had slightly fewer Brønsted acid sites, but was more effective throughout the entire experiment because of a higher total acid sites (LAS + BAS) than the SO ₄ -Mont catalyst.

(2) catalytic mechanism

In the MEA solution, CO ₂ desorption occurs by carbamate decomposition through zwitterion formation as shown in Equation 5. Carbamate degradation mainly depends on the availability of protons, which can be provided as water in the proton transfer reaction of protonated amines (Eq. 6). However, in basic conditions, proton transfer is difficult, so a huge amount of thermal energy is required. The amine solvent regeneration operation is energy intensive due to the unviability of protons and the endothermic nature of both reactions (Eqs. 5 and 6).

(5)

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(6)

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(9)

A reasonable reaction mechanism for ion-exchanged Mont-facilitated carbamate decomposition and subsequent CO ₂ release is shown in FIG. 5 . When the ion-exchanged Mont catalyst is added to the MEA solution, it provides free protons to the system that attack the N atom of the carbamate. Zr metal can help to attack the O and N atoms of the carbamate and increase the NC bond. Involvement of acid sites converts sp2 hybridization of NC bonds to sp3, followed by lengthening of NC bonds and degradation at low temperature. This novel catalytic pathway of lower activation energy leads to CO ₂ desorption at low temperatures and minimizes the thermal energy requirements of the CO ₂ desorption reaction.

In addition, as reported in previous studies, bicarbonate and carbonate are also present in the CO ₂ rich MEA solution at a CO ₂ loading of 0.42 mol CO ₂ /mol MEA or more. Carbonate and bicarbonate can also accept protons from the ion-exchanged Mont catalyst to form carbonic acid and release CO ₂ directly (Equations 8 and 9). Regeneration of the catalyst is probably accomplished by a proton restoration reaction provided by an amine deprotonation reaction.

(3) catalyst stability test

The stability of the prepared catalyst was investigated by recycling all of the ion-exchanged catalyst and reusing it in 5 cycle solvent regeneration experiments. A fresh catalyst was added to the CO ₂ rich MEA solution and the solution was heated to ˜86° C. to obtain a CO ₂ desorption profile. When the experiment was completed, the catalyst was filtered to prevent amine vapor from adhering to the catalyst surface, washed repeatedly with water, and dried in an oven at 200° C. for 2 hours. The average catalyst recovery was >95%, so the recovered catalyst was replenished with a fresh dose to keep the catalyst amount at 5% by weight. Then, the recovered catalyst was reused with fresh CO ₂ rich MEA solution (100 mL) and solvent regeneration was studied under the same conditions. In this way, the catalyst was used in five periodic experiments, and the catalyst regeneration performance with respect to the total amount of desorbed CO ₂ is shown in FIG. 6A . It can be clearly seen that the catalyst efficiency decreased by ~4% and ~7% for SO ₄ -Mont and Zr-Mont catalysts, respectively, after 5 cycles. The slight decrease in catalytic activity may be due to particle agglomeration and/or regression induced by the stir bar, which is consistent with the contents of published literature. Overall, it can be seen that the catalyst is stable and remains active during regeneration tests, demonstrating its potential for use in continuous stripper columns.

(4) CO ₂ Effect of catalyst on adsorption performance:

Since thermal amine scrubbing is a continuous absorption/stripper process, it is equally important to ensure that these catalysts affect the CO ₂ absorption performance of the solution when using catalyst regeneration techniques. To find the answer, we tested the CO ₂ uptake with and without 5 wt.% of each catalyst in 5M MEA. Feed gas (CO ₂ 15 vol.% balanced N ₂ , 40° C.) was bubbled through the solution and the reactor exhaust gas was analyzed by GC. The experiment was conducted until the CO ₂ composition of the exhaust gas was the same as the inlet CO ₂ composition. The concentration of outgassed CO ₂ as a function of time was recorded experimentally. Once the amine solvent was saturated, the CO ₂ loading of the solvent was also calculated using a TOC analyzer. The curve of CO ₂ emissions over time is shown in FIG. 6B . The results show that the presence of the catalyst had no effect on the CO ₂ uptake rate or the uptake capacity. The same CO ₂ rich loading was achieved in all solvents regardless of catalyst addition. These results are further justified by the fact that the catalyst's role in assisting the CO ₂ desorption is clear, but the catalyst regeneration pathway also requires a certain amount of thermal energy. The thermal energy provided at 40°C is much less than the energy level required to activate the catalytic role. Therefore, under absorbent conditions, these catalysts do not exhibit any adverse effect on the CO ₂ absorption process.

In conclusion, an inexpensive montmorillonite clay catalyst was readily prepared by simple ion-exchange with H ₂ SO ₄ acid and Zr metal, and the catalytic activity to optimize the CO ₂ desorption rate of amine solutions at low temperature was experimentally evaluated. The ion-exchange process leached Si and Al atoms from the octahedral sheet of raw material Mont and replaced most of the cations in the interlayer, which significantly improved the BET specific surface area, surface acidity and total acidity sites. Both catalysts are effective in optimizing CO ₂ desorption in the MEA solution, improving the CO ₂ desorption rate by up to 196%, improving the total amount of desorbed CO ₂ by 48.6%, and reducing the relative thermal duty by 32.7% compared to the non-catalytic solution. reduced Detailed characterization and experimental results showed that the increased BET specific surface area and the role of total acid sites are important for improving the CO ₂ desorption efficiency. The catalyst's stability was then tested by recycling and reusing the catalyst in five catalyst solvent regeneration experiments. This shows that the catalyst is completely stable and remains active during periodic use, demonstrating its ability to scale-up. This study reports a new class of practical and abundant catalysts for optimizing the CO ₂ desorption rate and highlights the catalyst and its facilitated CO ₂ desorption role for an efficient CO ₂ capture process.

The scope of the present invention is indicated by the following claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention.

Claims (19)

Ion-exchanged montmorillonite catalyst for carbon dioxide capture. The ion-exchanged montmorillonite catalyst according to claim 1, wherein the ion-exchange is characterized in that ions contained in the montmorillonite are replaced with cations of an aqueous acid solution or a metal aqueous solution. According to claim 1, wherein the ion-exchange is characterized in that Si, Al, O, Fe, Mg, Na, Ca or K ions contained in the montmorillonite are replaced with cations of H ⁺ or Zr, ion- Exchanged montmorillonite catalyst. The ion of claim 1 , wherein the ion-exchanged montmorillonite catalyst has a fraction of one element selected from 0 to 7% Al, 0 to 1.2% Fe, 0 to 1% Mg and combinations thereof. -Exchanged montmorillonite catalyst. The ion-exchanged montmorillonite catalyst according to claim 1, wherein the ion-exchanged montmorillonite catalyst has a surface area of 50 to 500 m ² /g. The ion-exchanged montmorillonite catalyst according to claim 1, wherein the ion-exchanged montmorillonite catalyst has a pore volume of 0.15 to 0.50 cm ³ /g. The ion-exchanged montmorillonite catalyst according to claim 1, wherein the ion-exchanged montmorillonite catalyst has an average pore diameter of 1 to 15 nm. The ion-exchanged montmorillonite catalyst according to claim 1, characterized in that the ion-exchanged montmorillonite catalyst has a surface acidity of at least 2 mmol/g. The ion-exchanged montmorillonite catalyst according to claim 1, characterized in that the ion-exchanged montmorillonite catalyst has at least 0.3 mmol/g of total acid sites. (a) reacting montmorillonite with an aqueous acid solution or an aqueous metal solution to obtain a product; and
(b) filtering the product of step (a) and washing until the pH of the filtrate becomes 5 to 9
A method for producing an ion-exchanged montmorillonite catalyst comprising a. 11. The method of claim 10,
The reaction of step (a) is characterized in that it proceeds with stirring, ion-exchanged method for producing a montmorillonite catalyst. 11. The method of claim 10, wherein the acid in step (a) is hydrochloric acid, nitric acid, sulfuric acid, benzoic acid, oxalic acid, acetic acid, propionic acid, pyridinium ion, chloric acid, oxonium ion, iodic acid, oxylic acid, sulfurous acid, chlorous acid, phosphoric acid , Arsenic acid, chloroacetic acid, hydrogen fluoride, nitrous acid, formic acid, carbonic acid, hydrogen sulfide, hypochlorous acid, hydrogen iodide, hydrogen bromide, perchloric acid, and combinations thereof, characterized in that one selected from the group consisting of Way. 11. The method of claim 10, wherein the metal aqueous solution of step (a) SnCl ₄ , TiCl ₄ , TiOCl ₂ , TiOSO ₄ , ZrOCl ₂ , ZrCl ₄ , ZrOSO ₄ , MnCl ₂ , CoCl ₂ and at least one selected from FeCl3 It contains A manufacturing method, characterized in that it is an aqueous solution of an inorganic metal salt. The method according to claim 10, wherein the aqueous acid solution or the aqueous metal solution in step (a) has a concentration of 0.5 to 10 mol/L. The method according to claim 10, wherein the montmorillonite and the acid aqueous solution or the metal aqueous solution in step (a) are reacted in a 1:1 to 1:100 ratio (weight:volume). The method according to claim 10, wherein the reaction of step (a) is carried out at 70 to 110 °C. The method according to claim 10, wherein the reaction of step (a) is performed for 1 to 20 hours. 11. The method according to claim 10, wherein the filtration in step (b) is performed after cooling to room temperature. [10] The method for regenerating a solvent for capturing carbon dioxide using the ion-exchanged montmorillonite catalyst of any one of claims 1 to 9.

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