A preparation method of a supported ferric oxide-sepiolite catalyst for CO2 amine solution desorption

Abstract

The application discloses a preparation method of a ferroferric oxide-sepiolite (Fe2O3-SEP) catalyst for CO2 amine solution desorption, wherein the catalyst is obtained by loading metal oxides on sepiolite through an impregnation method. The method comprises the following steps: firstly, magnetically stirring and impregnating a metal nitrate solution and sepiolite in a water bath, then performing suction filtration, drying, grinding and calcination to obtain the supported Fe2O3-SEP catalyst. The obtained catalyst is used for desorption of saturated amine-rich solution, the amine-lean solution after desorption is cooled, the CO2 loading amount of the amine-lean solution is titrated, CO2 is introduced again for absorption, and the amine-lean solution is recycled for 4-5 times. Compared with existing catalysts, the catalyst has the advantages of wide raw material distribution, low price, simple preparation process, no other by-products, stable catalytic performance and no influence on CO2 absorption performance of the amine solution.

Description

Technical Field

[0001] This invention belongs to the field of industrial carbon dioxide emission reduction and control technology, specifically relating to a method for preparing a supported ferric oxide-sepiolite (Fe2O3-SEP) catalyst for CO2 amine solution desorption. Background Technology

[0002] With the industrial revolution, the burning of large quantities of fuels such as coal, oil, and natural gas has led to a surge in CO2 emissions. The use of fossil fuels accounts for over 80% of all CO2 emissions from human activities. Excessive CO2 emissions have exacerbated environmental problems such as global warming and sea-level rise, making effective reductions in CO2 emissions a major concern.

[0003] Carbon dioxide capture and storage (CCS) technology refers to the process of separating CO2 produced by industry and related energy sectors through carbon capture technology, and then storing it in locations isolated from the atmosphere, such as the seabed or underground, using carbon storage methods. CO2 capture and storage is a powerful weapon for reducing CO2 emissions and combating global warming.

[0004] Current CO2 capture technologies mainly include three methods: pre-combustion capture, oxy-fuel combustion capture, and post-combustion capture. Pre-combustion capture, based on integrated gasification cycle (IGCC) technology, first gasifies coal into clean gaseous energy, thus separating CO2 before combustion and preventing it from entering the combustion process. Oxy-fuel combustion capture directly replaces air with a mixture of high-concentration O2 and some extracted flue gas. The flue gas produced by oxy-fuel combustion mainly consists of water and CO2. After cooling and steam condensation for dehydration, the CO2 content in the flue gas is between 80% and 90%. This high-concentration CO2 is then compressed, dried, and further purified before storage. Post-combustion capture separates and recovers CO2 from the flue gas. Methods include chemical absorption, physical adsorption, membrane separation, and chemical chain separation, among others. Currently, the organic amine solvent chemical method for CO2 absorption is considered the most economical and feasible method due to the fast absorption rate, good reactivity, relatively mature process route, and relatively stable operation of organic amine solvents. However, it also has disadvantages such as high energy consumption for solvent heating and easy corrosion of equipment by flue gas components such as sulfur and nitrogen oxides.

[0005] The organic amine absorption method comprises two parts: absorption and desorption. First, fresh amine solution selectively absorbs CO2 from the flue gas in an absorption tower, transforming the fresh amine solution into a CO2-rich amine solution. This rich amine solution then enters a desorption tower, where it undergoes thermal desorption by heating, converting it into a CO2-poor amine solution, which then re-enters the absorption tower for the next CO2 absorption cycle. The CO2 released during desorption is collected, compressed, and stored at the top of the desorption tower after cooling, and can be used for chemical production, oilfield enhanced oil recovery, refrigeration, and other applications.

[0006] In traditional CO2 desorption and regeneration processes using amine-rich solutions, a significant amount of energy is consumed. This includes the sensible heat required to raise the amine solution to the regeneration temperature, the heat of reaction required for desorption, and the heat carried away by the regeneration gas discharged from the top of the regeneration tower. Furthermore, organic amine absorption methods suffer from drawbacks such as the easy degradation of amine solvents and the susceptibility of equipment to corrosion by sulfur, nitrogen oxides, and other flue gas components. Therefore, reducing the energy consumption of amine-rich solution regeneration and developing stable amine solvents are of paramount importance for the development of CO2 capture technology. Currently, two main methods are used to achieve efficient and low-energy CO2 capture and separation using amine solvents. One method focuses on the composition of the amine solvent. Given that each individual organic amine has its own advantages and disadvantages, different amine solutions are mixed to maximize the advantages of each individual amine solvent while addressing its shortcomings, thus finding an efficient amine reagent to replace traditional monoethanolamine. The other method involves adding a catalyst to catalyze the removal of CO2 from the CO2-rich amine solution, promoting the regeneration of the amine solution and reducing the energy consumption of CO2 desorption.

[0007] Bhatti et al. reported that adding metal oxide catalysts such as V₂O₅, MoO₃, WO₃, ZrO₂, TiO₂, MnO₂, and ZnO can reduce the regeneration heat load by approximately 20-48% (Bhatti et al. Chem. Eng. 2018, 6, 12079-12087). Liang Zhiwu et al. studied that adding γ-Al₂O₃, HZSM-5, MCM-41, and SAPO-34 catalysts to MEA (monoethanolamine) solvent regeneration can reduce the heat load by 30% (Liang et al. AIChE Journal. 2016, 62, 753-765; Zhang et al. Appl. Energy 2018, 229, 562-576). Zhang Xiaowen et al. found that adding SO₄²⁻ during MEA solvent regeneration promoted the CO₂ desorption process by adding various solid acid catalysts to the MEA solvent. 2-TiO2 and SAPO-34 can reduce the heat load by 24% (Zhang et al. Applied Energy 202(2017)673-684). Cheng Chin-hung et al. found that introducing copper ions into MEA-rich solvents reduced the heat load by 13-24% compared with the blank experiment (Cheng CH et al. Appl Energy 2018,211:1030-1038).

[0008] Table 1 Comparison of CO2 desorption energy consumption of commonly used catalysts

[0009]

[0010] Sepiolite (SEP) is a magnesium silicate clay mineral with a layered chain structure. It is inexpensive, widely distributed, and is one of the important mineral resources in my country and the world. Sepiolite belongs to the orthorhombic or monoclinic crystal system, and its chemical formula is Mg8Si. 12 O 30 Sepiolite contains (OH)₄(H₂O)₄·8H₂O, with SiO₂ content generally between 54% and 60%, and MgO content mostly between 21% and 25%. Sepiolite contains a large number of external silicon-hydroxyl groups, exhibiting a strong affinity for organic matter. It can directly react with gaseous or liquid organic reactants to form organic mineral derivatives while preserving the mineral's framework. Furthermore, sepiolite possesses high chemical inertness; its suspension is rarely affected by electrolytes, and its structure is not eroded by acids.

[0011] Currently, widely used catalyst supports include Al2O3, zeolite molecular sieves, and SiO2, but these suffer from problems such as poor stability and short service life. Sepiolite, with its large specific surface area, numerous adsorption centers, and good mechanical and thermal stability, can support Ni, Fe, Zn, Cu and Mo, W, Ni, Co group metals, as well as other copper group metals, in desulfurization, denitrification, and demetallization processes, thus serving as both a catalyst and a catalyst support.

[0012] To address the high energy consumption during CO2 capture of organic amines, Baek et al. pointed out that metal oxides, due to their acidic surface sites, also exhibit certain catalytic CO2 desorption performance, and their catalytic regeneration process can be carried out at desorption temperatures below 90℃. Studies by Idem, Liang Zhiwu et al. have shown that catalysts such as molecular sieves, superacids, and metal oxides can all promote the regeneration process of rich amine solutions (Liang et al. AIChE Journal. 2016, 62, 753-765; Zhang et al. Applied Energy 202(2017) 673-684; Bhatti et al. ACS Sustainable Chem. Eng, 2017, 5, 5862-5868; Zhang et al. Applied. Energy 218(2018) 417-429). Sepiolite can be used as a support to load metal oxides, which can then be used as a catalyst to promote CO2 desorption, thereby reducing the energy consumption of rich amine solution regeneration. Adding a catalyst to overcome the shortcomings of existing solvents and reduce CO2 capture costs is of great significance for industrial applications.

[0013] MEA solvents are considered fundamental solvents for CO2 capture by organic amines due to their low cost, high adsorption activity, and strong CO2 mass transfer capacity. 5 mol / L MEA is already used industrially to capture carbon dioxide from flue gas. This invention, based on MEA solvents, proposes a novel method for CO2 amine solvent desorption using a highly efficient Fe2O3-SEP catalyst, aiming to reduce desorption energy consumption during the CO2 desorption process. Summary of the Invention

[0014] The technical problem solved by this invention is to design and synthesize a novel Fe2O3-SEP catalyst to improve the desorption rate of amine solution in the CO2 desorption process and reduce desorption energy consumption, in order to address the problem of high energy consumption in the regeneration of rich amine solutions.

[0015] The technical solution of this invention is to provide a method for preparing a Fe2O3-SEP catalyst for CO2 amine solvent desorption, and for use in CO2 amine solvent desorption. The main steps of catalyst preparation are as follows: sepiolite and 0.1-1 mol / L ferric nitrate solution are added to a beaker at a solid-liquid ratio of 1:10-20. The mixture is magnetically stirred and impregnated in a water bath at 40°C for 12 hours. The temperature is then raised to 80°C for evaporation for 3 hours, and the mixture is transferred to an oven and dried at 80-110°C for 8 hours. After grinding, the mixture is calcined at 300-500°C for 3-6 hours to obtain the Fe2O3-SEP catalyst. The catalyst of this invention can be represented as X-SEP-T, where X represents one of Fe2O3 and CuO, and T represents the calcination temperature.

[0016] The catalytic desorption method is as follows: A 5 mol / L monoethanolamine solution is used to absorb CO2. 100% CO2 is bubbled through the solution at 200 ml / min at 40°C until saturation, resulting in a rich amine solution. The CO2 loading of the MEA solution is then measured by titration with 1M HCl solution. Fe2O3-SEP catalyst is added to the rich amine solution, and the solution is then transferred to an oil bath at 100°C for desorption. Pure nitrogen gas is bubbled through the solution at 500 ml / min to entrain the CO2 produced during desorption. The desorption time is 2 hours. After the desorbed, lean amine solution is cooled, its CO2 loading is analyzed by titration, and CO2 is bubbled through the solution again for absorption. This absorption and desorption cycle is repeated 4–5 times.

[0017] This invention synthesizes a supported Fe2O3-SEP catalyst via an impregnation method. The main process involves impregnating sepiolite with a ferric nitrate solution, filtering, drying, and then grinding and calcining to obtain the supported Fe2O3-SEP catalyst. Sepiolite is a chain-layered magnesium silicate, soluble in hydrochloric acid, with good plasticity and low shrinkage. In the sepiolite structure, silicon-oxygen tetrahedra and magnesium-oxygen octahedra are linked together by common vertices, and their alternating arrangement forms a three-dimensional framework structure. Sepiolite exhibits both layered and chain-like transitional characteristics. Pores and voids exist throughout the structure, making the internal structure of sepiolite very open, similar to the structure of zeolite molecular sieves, making it a porous material. Sepiolite also has a fibrous structure with directional channels inside and numerous surface grooves, resulting in a specific surface area as high as 800–900 m². 2 / g, of which the pore surface area is 500m² 2 / g, channel surface area is 400m² 2 Sepiolite has a high density of 1 g / g, a large pore capacity, and abundant active sites. Its unique internal structure contributes to its excellent catalytic performance.

[0018] Sepiolite's unique structure endows it with excellent physicochemical properties, strong adsorption capacity, good rheological properties, and good catalytic performance. The abundance of basic and acidic centers in sepiolite increases its polarity, which is beneficial for reactions. Furthermore, its microporous structure and surface characteristics enable it to exhibit acid-base synergistic catalysis and shape-selective catalytic cracking. Therefore, metals from the Ni, Fe, Zn, Cu group and the Mo, W, Ni, Co group, as well as other copper group metals, can be loaded onto sepiolite to leverage their properties, effectively promoting the decomposition of carbamates, improving CO2 removal at low temperatures, and thus reducing reaction temperature and energy consumption.

[0019] Compared with existing technologies, the present invention has the following advantages:

[0020] (1) Catalyst raw materials are widely distributed and inexpensive.

[0021] (2) The preparation process is simple and there are no other by-products.

[0022] (3) It has stable catalytic performance, good circulation effect, and no effect on the CO2 absorption performance of amine solution. Detailed Implementation

[0023] The present invention will be further described below with reference to the embodiments.

[0024] Example 1: Fe2O3-SEP-500

[0025] Sepiolite powder and 1 mol / L ferric nitrate solution were added to a beaker at a solid-liquid ratio of 1:10 and stirred evenly. After soaking in a 40℃ water bath for 12 hours, the solution was filtered to remove moisture and then dried in an oven at 100℃ for 10 hours. Finally, it was calcined at 500℃ for 5 hours to obtain a supported sepiolite catalyst, which can be abbreviated as Fe2O3-SEP-500.

[0026] Comparative Example 1: SEP

[0027] Comparative Example 2: Fe2O3-SEP-300

[0028] In comparison, the synthesis of Fe2O3-SEP-300 was carried out in the same manner as in Example 1 above, except that the calcination temperature was 300°C.

[0029] Example 2: CuO-SEP-500

[0030] Same as Example 1, except that the nitrate solution added during catalyst preparation is copper nitrate solution, which can be abbreviated as CuO-SEP-500.

[0031] Example 3: CuO-SEP-300

[0032] Same as Example 1, except that the nitrate solution added during catalyst preparation is copper nitrate solution, and the calcination temperature is 300℃, which can be abbreviated as CuO-SEP-300.

[0033] Application example:

[0034] Catalytic desorption of CO2-rich monoethanolamine solvent

[0035] First, a lean amine solution and an olive-shaped magnetic ball are placed in a three-necked flask and immersed in a water bath for stirring. The water bath temperature is maintained at 40°C using a temperature controller. A fixed flow rate of gas is introduced into the fresh MEA solution for a period of time by adjusting the mass flow meter to obtain a rich amine solution. The CO2 loading of the MEA solution is then measured by titration with 1M HCl solution.

[0036] The specific procedure for CO2 loading determination is as follows: Clean the rotor and place it in an Erlenmeyer flask. Add 10 ml of distilled water and 1-2 drops of 1 wt% methyl orange solution, and transfer 1 mL of the sample to be tested using a pipette. Then, slowly move the Erlenmeyer flask from the edge to the center of the magnetic stirrer, ensuring good airtightness of the apparatus. With the three-way valve open, place the open glass bottle (containing red indicator liquid) at a certain height so that the indicator liquid inside the bottle is at the same level as the indicator liquid in the glass tube, and record this as the 0 mark. Next, perform the acid-base titration experiment. Close the three-way valve and slowly place the open glass bottle on the table. After 8 minutes, titrate with HCl, recording the equivalence point (V0), excess value (V1), and the volume of HCl consumed (V). HCl (mL), wait until the liquid level of the indicator in the glass tube remains unchanged, place the liquid level of the indicator in the glass bottle and the liquid level in the glass tube parallel, and read the reading of the glass tube (V2)mL.

[0037] The volume of CO2 released (mL) is calculated using the following formula (1):

[0038] V CO2 =V2-V1 (1)

[0039] The CO2 loading α (mol CO2 / mol amine) is calculated using formula (2):

[0040]

[0041] Where C HCl It is a standard HCl solution with a concentration of 1.0M, V m The value is the molar volume of the gas, 22.4 L / mol, and T is the room temperature (°C).

[0042] In the desorption and regeneration process of the rich amine solution, an oil bath is used to provide the heat required for the desorption reaction, and the desorption temperature is measured by a thermometer. Unlike the absorption device, the gas introduced is pure N2, with a mass flow rate adjusted to 500 ml / min. The three-necked flask is placed in a 100°C oil bath containing an absorption-saturated rich amine solution and 2.5 g of catalyst. Before desorption begins, a new three-necked flask is used to replace the air in the device until the CO2 detector reading is in single digits, indicating that the air in the device has been completely replaced by N2. During desorption, magnetic stirring ensures more thorough contact between the amine solvent and the catalyst. A condenser is connected to the right neck of the three-necked flask to prevent the amine solution from evaporating due to excessively high desorption temperatures. The outlet pipe of the condenser is connected to the N2 pipe via a Y-connector to a mixer, and after passing through a drying tube, the N2 flows into a carbon dioxide detector to record the signal value.

[0043] During the experiment, the oil bath and an electricity meter were connected in series to record the electricity consumption, thereby calculating the relative desorption energy consumption of the CO2 desorption process. The concentration of the MEA solution used for desorption was 5 mol / L, and the catalysts used were the Fe2O3-SEP-500 catalyst, Fe2O3-SEP-300 catalyst, CuO-SEP-500 catalyst, and CuO-SEP-300 catalyst prepared in the above examples and comparative examples. The three-necked flask containing the rich amine solution was placed in the oil bath while the carbon dioxide detector began recording data. After the desorbed lean amine solution cooled, its CO2 loading was titrated, and CO2 was reintroduced for absorption. This process was repeated 4-5 times.

[0044] The catalytic performance evaluation parameters are calculated as follows:

[0045] Substitute the obtained data into formula (3) to calculate the CO2 desorption rate mol CO2 / (mol amine·min):

[0046]

[0047] Where 0.5 represents the flow rate of N2 (500 mL / min); C represents the concentration in the mixed gas; V m The value is the gas molar volume, 22.4 L / mol, T is the room temperature (°C), 5 is the amine solution concentration, and 0.2 is the amine solution volume.

[0048] To better compare the desorption performance of the catalysts, a relative desorption rate was used for evaluation. The desorption rate of the regenerated blank MEA solution was taken as the baseline R, where R = 100%. Therefore, R for the catalytic CO2 desorption process is the desorption rate R0 of the catalytic CO2 desorption process. i The ratio of R to R is calculated using formula (4):

[0049]

[0050] The desorption energy consumption per mole of CO2 is denoted as H (kJ / mol), defined as the ratio of the energy input rate to the CO2 desorption rate, and calculated using formula (5):

[0051]

[0052] Here, E refers to the amount of electricity consumed by CO2 desorption within a certain time period, as recorded by the electricity meter, in kW.h. It needs to be converted to kJ for use. Since the desorption reaction is relatively rapid in the first 20 minutes, the energy consumption calculation here uses the ratio of the energy input rate to the CO2 desorption rate in the first 20 minutes.

[0053] The energy consumption for CO2 desorption is only a relative value. To better evaluate the catalytic performance of a catalyst in CO2 desorption, the relative desorption energy consumption RH (%) is used to evaluate catalyst performance. Using the desorption energy consumption of the blank MEA solution regeneration as a baseline (H, kJ / mol), with RH equal to 100%, the RH of the catalytic CO2 desorption process is the desorption energy consumption H of the catalytic CO2 desorption process. i The ratio of (kJ / mol) to H is calculated using formula (6):

[0054]

[0055] The experimental results are shown in the table below.

[0056] Table 2 Comparison of relative desorption energy consumption of catalysts in the examples and comparative examples.

[0057]

[0058] Table 3 Comparison of the cycle stability of the catalysts in Example 1

[0059]

[0060] As shown in the table above, compared with the blank MEA, the addition of catalysts significantly reduced the desorption energy consumption of amine solvents, and the catalytic performance of the catalysts prepared in the examples was far superior to that of sepiolite powder alone.

Claims

1. An application of a supported ferric oxide-sepiolite catalyst for the desorption of CO2 amine solutions, characterized in that... Ferric oxide was loaded onto sepiolite via impregnation and used for the desorption of CO2 amine solution. The catalyst preparation method is as follows: In a beaker, sepiolite and 0.1-1 mol / L ferric nitrate solution were added at a solid-liquid ratio of 1:10-20. The mixture was magnetically stirred and impregnated in a water bath at 40°C for 12 hours. The temperature was then raised to 80°C for 3 hours of evaporation. The mixture was then transferred to an oven and dried at 80-110°C for 8 hours. After grinding, the mixture was calcined at 300-500°C for 3-6 hours to obtain the ferric oxide-sepiolite Fe2O3-SEP catalyst. In application, a 5 mol / L monoethanolamine solution was used to absorb CO2 at 40℃ for 10 hours. The amount of CO2 absorbed was titrated and analyzed. After the CO2 absorption reached saturation and the solution became rich in amine, Fe2O3-SEP catalyst was added to the rich amine solution. Nitrogen gas was then introduced at 100℃ to desorb the adsorbed CO2 for 2 hours. After the desorbed lean amine solution was cooled to room temperature, the amount of CO2 absorbed was titrated and CO2 was introduced again for absorption. This cycle of CO2 absorption and desorption was repeated 6 times, and the desorption energy consumption increased by only 7.21%, indicating that the Fe2O3-SEP catalyst still maintained good catalytic desorption effect.

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