Preparation method of porous carbon loaded magnesium oxide adsorbent

Abstract

The invention provides a preparation method of a porous carbon-loaded magnesium oxide adsorbent, and relates to the technical field of gas purification material preparation, and the preparation method comprises the following steps: S1, taking magnesium nitrate, dichromate, concentrated sulfuric acid, glucose and fuel as raw materials, forming a homogeneous solution, heating the solution at a certain temperature to form gel, and further carrying out a combustion reaction to obtain a porous carbon-loaded magnesium oxide adsorbent; fluffy precursor powder is obtained; s2, performing high-temperature calcination on the precursor powder in air to obtain a carbon-loaded intermediate product; and S3, placing the carbon-loaded intermediate product in a sodium hydroxide solution, carrying out a heating reaction, separating the solid obtained after the reaction, and drying to obtain the porous carbon-loaded magnesium oxide adsorbent. The invention provides a simple and extensible synthesis method for developing a CO2 adsorbent with large working capacity and high selectivity, the production process is environment-friendly and pollution-free, the operation cost is low, the economic benefit is high, and the method has a better industrial application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of gas purification material preparation, in particular to a method for preparing a porous carbon-loaded magnesium oxide adsorbent. Background Art

[0002] Currently, adsorption has attracted wide attention due to its efficient operation and low energy cost, but the success of adsorption technology depends on the development of efficient adsorption materials. However, the adsorption performance of widely studied CO2 adsorption materials, such as activated carbon (AC), zeolite, molecular sieve, metal oxide and metal organic framework is not ideal. Therefore, it is still very challenging to develop materials with high CO2 adsorption capacity and high stability.

[0003] Physical adsorption is the process of using solid adsorbent materials to adsorb CO2 onto the surface of the adsorbent through physical forces under high pressure conditions, and then releasing it under low pressure conditions. This method has the advantages of low energy consumption and renewability, but its disadvantage is that the adsorption capacity is low and cannot meet the adsorption needs in practical applications. Chemical adsorption is a strong adsorption process in which a chemical reaction occurs between the adsorbent and the adsorbate due to the action of chemical bonds. The adsorption capacity of chemical adsorption is much higher than that of physical adsorption. Therefore, the introduction of chemical adsorption into the adsorbent can further enhance the CO2 adsorption performance of the adsorbent material. It is reported that the alkaline oxide MgO can absorb CO2, and Mg(Ⅱ) is low in price, environmentally friendly, and has stable performance. It is a good metal ion for the preparation of CO2 adsorbents. Carbon carriers are widely used as gas adsorbents due to their remarkable properties such as stability, durability, and catalytic activity over a wide temperature range. Therefore, introducing MgO active adsorption sites on porous carbon is a promising CO2 adsorption material. Summary of the invention

[0004] The present invention provides a method for preparing a porous carbon-loaded magnesium oxide adsorbent. The simple solution combustion synthesis assisted Cr2O3 alkaline washing method of the present invention prepares a composite adsorbent with improved pore structure and high specific surface area, and MgO is in situ loaded on the carbon carrier. Compared with the traditional method, using our strategy, the yield of the material is significantly improved, and the pore structure of the porous carbon, the degree of MgO dispersion and the amount of MgO loading can be accurately adjusted according to the actual application needs to improve the CO2 adsorption amount and regeneration. Its application is cost-effective, widely used and easy to scale up. Specifically, the evaluation method described in the present invention is as follows:

[0005] A method for preparing a porous carbon-supported magnesium oxide adsorbent comprises:

[0006] Step S1, using magnesium nitrate, dichromate, concentrated sulfuric acid, glucose, and fuel as raw materials, and stirring them evenly according to a certain molar ratio to form a homogeneous solution, heating the solution at a certain temperature to form a gel, and then further increasing the temperature to cause the gel to undergo a combustion reaction to obtain a fluffy precursor powder;

[0007] Step S2, calcining the precursor powder at a high temperature in air to obtain a carbon-loaded intermediate product loaded with magnesium oxide and chromium trioxide;

[0008] Step S3, placing the carbon-loaded intermediate product in a sodium hydroxide solution for heating reaction, separating and drying the solid obtained after the reaction, and obtaining a porous carbon-loaded magnesium oxide adsorbent.

[0009] Furthermore, in step S1, the concentration of concentrated sulfuric acid (the formation of CrO3 must rely on concentrated sulfuric acid to react, and further rely on CrO3 to complete subsequent pore formation) is 70-80wt%; the molar ratio of magnesium nitrate, dichromate, concentrated sulfuric acid (calculated as H2SO4 in concentrated sulfuric acid), glucose, and fuel is 1: (2.3~11.7): (4.6~23.4): (0.08~0.14): (0.9~1.49).

[0010] Furthermore, in step S1, the dichromate is at least one of sodium dichromate and potassium dichromate.

[0011] Furthermore, in step S1, the fuel is a combination of glycine and at least one of citric acid, urea, and oxalic acid, and the mixture of different fuels has multiple advantages for the reaction. Glycine is preferably used as a fuel to prevent reaction deposition, but excessive amounts will weaken combustion, and the proportion of glycine in the total fuel is about 30%-70%. Citric acid is high in carbon and suitable for low-temperature combustion, and urea and oxalic acid are relatively cheap, reducing costs. A variety of fuels can make different types of biomass complement each other and obtain higher energy utilization; they can also affect the growth and accumulation of carbon carriers, thereby forming a more regular pore structure, avoiding excessive growth or collapse of the pores, and improving the quality and performance stability of porous carbon materials.

[0012] Furthermore, in step S1, the heating temperature is 100° C. or above to form a gel, and the temperature is continuously raised to 120-200° C. to cause a combustion reaction.

[0013] Furthermore, in step S2, the high temperature calcination heating rate is 3-6°C / min, the calcination temperature is 300-600°C, and the calcination holding time is 2-6 h.

[0014] Furthermore, in step S3, the molar ratio of the carbon-loaded intermediate product to sodium hydroxide (calculated as NaOH in the sodium hydroxide solution) is 1:(0.8-1.5); and the reaction temperature is 200-300°C.

[0015] The porous carbon-supported magnesium oxide composite material obtained by the present invention has a thickness of more than 1800 m 2 / g total specific surface area, with >3.6 cm 3 Total pore volume of g, >2.9 cm 3 / g of mesopore volume.

[0016] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0017] The present invention provides a method for preparing a high-performance CO2 adsorbent. Micropores are formed on the surface of a carbon carrier by utilizing the gas released during the combustion process, and the reaction thermodynamics are affected by adjusting the raw material content and ratio, calcination temperature and other conditions to obtain a porous carbon material with a high specific surface area, a large pore volume, regular order, and uniform pore size, thereby providing a prerequisite for obtaining a high-capacity adsorbent.

[0018] The adsorbent of the present invention introduces CrO3 into porous carbon by solution combustion method, decomposes into Cr2O3 by heating, and Cr2O3 further reacts with hot sodium hydroxide solution to become sodium salt (sodium chromite), leaving mesopores in the original position in the carbon carrier. In addition, since various reactions are carried out at a relatively low temperature, alkali washing does not react with the composite adsorbent material, and the porous carbon structure loaded with magnesium oxide is well preserved, so the adsorbent of the present invention is an adsorbent material with a well-structured structure and has good adsorption performance for CO2.

[0019] The present invention adopts in-situ reaction to synthesize magnesium oxide in a porous carbon body, thereby improving the bonding stability between the two. MgO is not easy to fall off in the carbon carrier, and the carbon carrier itself has stable physical and chemical properties. Therefore, the obtained composite adsorbent material has a stable structure and thus has good cycle stability.

[0020] The present invention optimizes the distribution and loading of MgO in the pores generated by alkali washing of Cr2O3 by controlling the molar ratio of magnesium nitrate to 1:(2.3-11.7), thereby improving the adsorption and separation capacity of the adsorbent for CO2. When the molar ratio of Cr2O3 is less than 2.3, the pores are too small, the adsorption performance is low, and the rate is low; when the molar ratio is greater than 11.7, the dispersion effect of MgO particles is poor, the loading capacity is small, and the adsorption rate is low.

[0021] The porous carbon-loaded MgO adsorbent prepared by the present invention has a strong hydrophobic surface, which can reduce the competitive adsorption of water vapor and CO2 gas and improve the adsorption efficiency; on the other hand, it can effectively solve the problem that MgO is easy to deteriorate in humid air and improve the stability of adsorption performance.

[0022] The present invention adopts a solution combustion synthesis method to prepare the precursor powder, and the raw materials undergo redox reaction to achieve uniform mixing at the molecular level, which is beneficial to the uniform loading and high dispersion of MgO.

[0023] The porous carbon-loaded MgO adsorbent prepared by the present invention has high overall stability, and the preparation method is simple in process, has low requirements on the environment and equipment, and has good industrial application prospects. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is described below.

[0025] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0026] In the embodiments of the present invention, "image" and "picture" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same. "of", "corresponding" and "corresponding" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same.

[0027] In the embodiments of the present invention, sometimes a subscript such as W1 may be mistakenly written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are consistent.

[0028] In order to make the technical problems to be solved, technical solutions and advantages of the present invention more clear, they are described in detail below in conjunction with specific embodiments.

[0029] Example 1

[0030] 14.832 g of magnesium nitrate, 104.32 g of sodium dichromate, 1.796 g of glucose, 3.118 g of urea, and 13.514 g of glycine were weighed and dissolved in 380 mL of 80% concentrated sulfuric acid, and a uniform solution was formed under magnetic stirring at 200 rpm. Next, the solution was placed on a resistance furnace for heating, and stirred and evaporated at 100 °C to form a gel. Subsequently, it was heated at 130 °C for combustion reaction. During this process, the gel volume expanded rapidly, releasing a large amount of gas, accompanied by a violent combustion reaction, and a large amount of heat was released at the same time to obtain a precursor. The precursor was heated to 350 °C at a heating rate of 3 °C / min in an air atmosphere for high-temperature calcination, and kept warm for 3 h to obtain a carbon carrier loaded with magnesium oxide and chromium trioxide. The intermediate product was then mixed with 45 mL of sodium hydroxide solution, stirred under magnetic stirring at 600 rpm for 1 day, and then left to stand for 2 days. Then, the centrifugation was performed 4 times, each time for 3 mins, at a speed of 7000 r / min. After completion, the sample was placed in a drying oven for drying, and the total specific surface area was 1863.59 m 2 / g, and a total pore volume of 3.91 cm 3 / g of adsorbent. The adsorbent has good CO2 adsorption performance, and the saturated adsorption capacity at 293 K is 4.57 mmol / g.

[0031] Example 2

[0032] 15.446 g of magnesium nitrate, 98.752 g of potassium dichromate, 1.976 g of glucose, 4.289 g of glycine, and 10.924 g of citric acid were weighed and dissolved in 450 mL of 80% concentrated sulfuric acid. A uniform solution was formed under magnetic stirring at 200 rpm. Next, the solution was placed on a resistance furnace for heating and stirred and evaporated at 100 °C to form a gel. Subsequently, it was heated at 160 °C for combustion reaction. During this process, the gel volume expanded rapidly, releasing a large amount of gas, accompanied by a violent combustion reaction, and a large amount of heat was released at the same time to obtain a precursor. The precursor was heated to 400 °C at a heating rate of 4 °C / min in an air atmosphere for high-temperature calcination, and kept warm for 4 h to obtain a carbon carrier loaded with magnesium oxide and chromium trioxide. The intermediate product was then mixed with 60 mL of sodium hydroxide solution, stirred under magnetic stirring at 700 rpm for 1 day, and allowed to stand for 2 days. Then, the centrifugation was performed 4 times, each time for 3 mins, at a speed of 6800 r / min. After completion, the sample was placed in a drying oven for drying, and the total specific surface area was 1882.65 m 2 / g, and a total pore volume of 3.81 cm 3 / g of adsorbent. The adsorbent has good CO2 adsorption performance, and the saturated adsorption capacity at 293K is 4.67 mmol / g.

[0033] Example 3

[0034] 16.519 g of magnesium nitrate, 200.572 g of sodium dichromate, 1.932 g of glucose, 2.568 g of urea, 4.283 g of glycine, and 9.843 g of citric acid were weighed and dissolved in 480 mL of 80% concentrated sulfuric acid. A uniform solution was formed under magnetic stirring at 200 rpm. Next, the solution was placed on a resistance furnace for heating and stirred and evaporated at 100 °C to form a gel. Subsequently, it was heated at 160 °C for combustion reaction. During this process, the gel volume expanded rapidly, releasing a large amount of gas, accompanied by a violent combustion reaction, and a large amount of heat was released at the same time to obtain a precursor. The precursor was heated to 450 °C in an air atmosphere at a heating rate of 5 °C / min for high temperature calcination, and kept warm for 4 h to obtain a carbon carrier loaded with magnesium oxide and chromium trioxide. The intermediate product was then mixed with 70 mL of sodium hydroxide solution, stirred under magnetic stirring at 700 rpm for 1 day, and allowed to stand for 2 days. Then, the centrifugal operation was performed five times, each time for 3 mins, at a speed of 6500 r / min. After completion, it was placed in a drying oven for drying, and the total specific surface area was 1887.71 m 2 / g, and a total pore volume of 3.84 cm 3 / g of adsorbent. The adsorbent has good CO2 adsorption performance, and the saturated adsorption capacity at 293 K is 4.72 mmol / g.

[0035] Example 4

[0036] 18.296 g of magnesium nitrate, 283.127 g of sodium dichromate, 2.364 g of glucose, 4.682 g of glycine, and 6.327 g of oxalic acid were weighed and dissolved in 520 mL of 80% concentrated sulfuric acid. A uniform solution was formed under magnetic stirring at 200 rpm. Next, the solution was placed on a resistance furnace for heating and stirred and evaporated at 100 °C to form a gel. Subsequently, it was heated at 160 °C for combustion reaction. During this process, the gel volume expanded rapidly, releasing a large amount of gas, accompanied by a violent combustion reaction, and a large amount of heat was released at the same time to obtain a precursor. The precursor was heated to 550 °C at a heating rate of 3 °C / min in an air atmosphere for high-temperature calcination, and kept warm for 3 h to obtain a carbon carrier loaded with magnesium oxide and chromium trioxide. The intermediate product was then mixed with 120 mL of sodium hydroxide solution, stirred under magnetic stirring at 800 rpm for 1 day, and allowed to stand for 2 days. Then, the centrifugal operation was performed five times, each time for 3 mins, at a speed of 6500 r / min. After completion, it was placed in a drying oven for drying, and the total specific surface area was 1873.84 m 2 / g, and a total pore volume of 3.73 cm3 / g of adsorbent. The adsorbent has good CO2 adsorption performance, and the saturated adsorption capacity at 293 K is 4.44 mmol / g.

[0037] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing a porous carbon-supported magnesium oxide adsorbent, characterized in that: include: Step S1, using magnesium nitrate, dichromate, concentrated sulfuric acid, glucose, and fuel as raw materials, and stirring them evenly according to a certain molar ratio to form a homogeneous solution, heating the solution at a certain temperature to form a gel, and then further increasing the temperature to cause the gel to undergo a combustion reaction to obtain a fluffy precursor powder; Step S2, calcining the precursor powder at a high temperature in air to obtain a carbon-loaded intermediate product loaded with magnesium oxide and chromium trioxide; Step S3, placing the carbon-loaded intermediate product in a sodium hydroxide solution for heating and reaction, separating and drying the solid obtained after the reaction, and obtaining a porous carbon-loaded magnesium oxide adsorbent; In step S1, the concentration of concentrated sulfuric acid is 70-80wt%; the molar ratio of magnesium nitrate, dichromate, concentrated sulfuric acid, glucose, and fuel is 1: (2.3-11.7): (4.6-23.4): (0.08-0.14): (0.9-1.49); In step S1, the fuel is a combination of glycine and at least one of citric acid, urea and oxalic acid.

2. The method according to claim 1, characterized in that In step S1, the dichromate is at least one of sodium dichromate and potassium dichromate.

3. The method according to claim 1, characterized in that In step S1, the heating temperature is 100° C. or above to form a gel, and the temperature is continuously raised to 120-200° C. to cause a combustion reaction.

4. The method according to claim 1, characterized in that: In step S2, the high temperature calcination heating rate is 3-6°C / min, the calcination temperature is 300-600°C, and the calcination holding time is 2-6 h.

5. The method according to claim 1, characterized in that In step S3, the molar ratio of the carbon-loaded intermediate product to sodium hydroxide is 1:(0.8-1.5); the reaction temperature is 200-300°C.

6. The porous carbon-supported magnesium oxide composite material obtained by the method according to any one of claims 1 to 5, characterized in that: Composite materials have >1800 m 2 / g total specific surface area, with >3.6 cm 3 Total pore volume of g, >2.9 cm 3 / g of mesopore volume.

7. Use of the porous carbon-supported magnesium oxide composite material according to claim 6 in CO2 adsorption.