A method for preparing rare earth element modified resin for dichloromethane adsorption

Abstract

This invention pertains to the application of rare earth element-modified resins in the adsorption of dichloromethane. Specifically, it relates to a method for preparing a rare earth element-modified resin for dichloromethane adsorption. The main steps include: mixing and stirring divinylbenzene, acrolein, tetrahydrofuran, benzoyl peroxide, and deionized water; subjecting the mixture to a hydrothermal reaction; and drying to obtain aldehyde-modified PDVB. The aldehyde-modified PDVB, aniline, sodium hydroxide, and ethanol are then mixed and reacted with a Schiff base to obtain imine-modified PDVB. The imine-modified PDVB is placed in a cerium or lanthanum salt solution, and cerium or lanthanum cations are loaded using a swelling impregnation method to obtain a rare earth metal-modified resin. This invention utilizes the benzene ring structure in PDVB and aniline to exhibit ultra-high hydrophobicity and lipophilicity. The imine structure and rare earth metal cations form a strong interaction with dichloromethane, promoting its adsorption capacity. After dichloromethane adsorption saturation, the resin can be regenerated through steam thermal desorption or vacuum desorption, enabling recycling.

Description

Technical Field

[0001] This invention belongs to the fields of air pollution control technology and organic polymer synthesis, and specifically relates to a method for preparing a rare earth element modified resin for dichloromethane adsorption. Background Technology

[0002] With industrial development, volatile organic compounds (VOCs) emitted from paints, coatings, artificial leather, household brighteners, and cleaning agents are among the main contributors to air pollution. VOCs include alkanes, aromatic compounds, and halogenated hydrocarbons, among which chlorinated volatile organic compounds (CVOCs) such as dichloromethane, chlorobenzene, and vinyl chloride are a key focus of current air pollution control efforts due to their persistent and difficult-to-degrade nature. Current major CVOCs treatment technologies include catalytic combustion, adsorption, biological methods, absorption, and chemical scrubbing. However, due to the presence of chlorine, combustion technologies can easily produce secondary highly toxic pollutants, such as dioxins. Therefore, adsorption has become the mainstream CVOCs purification technology. Adsorption methods primarily use activated carbon, silica gel, molecular sieves, and macroporous adsorption resins as adsorbents.

[0003] In recent years, porous resins have received widespread attention for their gas adsorption properties due to their advantages such as large specific surface area, fast adsorption rate, and modifiability. Currently, the adsorption capacity of porous resins for dichloromethane is generally low, and related research results are limited. Patent CN113145084A reports a method for carboxyl modification of traditional polyvinylbenzene (PDVB) to improve the adsorption performance of low-concentration benzene gases. However, due to the high saturated vapor pressure of dichloromethane, the waste gas concentration is usually high, and the resin cannot completely adsorb medium to high concentrations of dichloromethane. Furthermore, literature (Fuel, 2023, 337, 127130) reports a method of loading ferrous ions onto commercial porous resins via swelling impregnation to improve the adsorption capacity for toluene. Subsequently, advanced oxidation technology is used to decompose the adsorbed toluene, regenerating the resin's adsorption capacity. However, dichloromethane is highly polar and easily ionizes to release protons, classifying it as an acidic gas. Ferrous ions, due to their weak acidity, cannot effectively improve the adsorption capacity for dichloromethane. In summary, there is an urgent need for a modified porous resin material with high adsorption capacity and good adsorption performance for dichloromethane. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a method for preparing a rare earth element-modified resin for dichloromethane adsorption. This modified resin incorporates a basic imine structure, which enhances the adsorption of acidic dichloromethane gas. The pore structure of the imine-modified material is predominantly mesoporous, possessing a high pore volume and excellent gas diffusion channels, thereby improving the adsorption performance and capacity for dichloromethane. Furthermore, rare earth elements cerium or lanthanum ions are loaded using a swelling impregnation method. These two metals are basic metals, which increase the adsorption active sites on the resin surface and enhance the affinity for dichloromethane, thus improving the adsorption capacity for dichloromethane gas. Additionally, PDVB has a benzene ring structure, thus exhibiting good hydrophobicity and reducing the competitive adsorption of dichloromethane by water vapor in the environment.

[0005] The technical solution of the present invention is as follows:

[0006] Divinylbenzene, acrolein, tetrahydrofuran, benzoyl peroxide, and deionized water are mixed and stirred, and after hydrothermal reaction, dried to obtain aldehyde-modified PDVB. The aldehyde-modified PDVB, aniline, sodium hydroxide, and ethanol are mixed and reacted with a Schiff base to obtain imine-modified PDVB. The imine-modified PDVB is placed in a cerium or lanthanum salt solution, and cerium or lanthanum cations are loaded using a swelling impregnation method to obtain a rare earth metal-modified resin. A method for preparing a rare earth element-modified resin for dichloromethane adsorption is carried out according to the following steps:

[0007] Step 1: Mix divinylbenzene, acrolein, benzoyl peroxide, and deionized water in a certain mass ratio, then add an appropriate amount of tetrahydrofuran, stir at room temperature for a period of time, and obtain aldehyde-modified PDVB after hydrothermal reaction.

[0008] Step 2: The aldehyde-modified PDVB obtained in Step 1 is placed in ethanol until completely dissolved. An appropriate amount of aniline and sodium hydroxide are added as a catalyst. After stirring in a water bath at a certain temperature for a period of time, the mixed solution is transferred to a hydrothermal reactor. A Schiff base reaction is carried out at a certain temperature to form an imine structure. After the ethanol evaporates, the solution is filtered and dried to obtain the imine-modified PDVB, whose structural formula is:

[0009]

[0010] Step 3: Soak the obtained imine-modified PDVB in an appropriate amount of ethanol to make it swell, then add a certain amount and concentration of cerium or lanthanum salt solution, and then place it in a shaking incubator to shake for a certain time so that the cerium or lanthanum cations are loaded on the surface and internal channels of the porous resin. Then dry it overnight at a certain temperature, and then wash it with deionized water and ethanol. After drying, the rare earth element modified resin is obtained.

[0011] Preferably, the mass ratio of divinylbenzene, acrolein, benzoyl peroxide, and deionized water in step 1 is 1.5–3:0.5–1.5:0.05:1–3; the volume ratio of tetrahydrofuran to the former is 8–15:1; the stirring time is 6–9 h; and the hydrothermal reaction time is 24–72 h.

[0012] Preferably, the amount of aniline used in step 2 is in a molar ratio of 1 to 1.6:1 with that of acrolein in step 1; the amount of sodium hydroxide is 0.2 to 0.6 g; the water bath stirring temperature is 40 to 80°C and the stirring time is 12 to 36 h; the Schiff base reaction temperature is 60 to 120°C and the reaction time is 24 to 72 h.

[0013] Preferably, in step 3, the amount of ethanol used is such that the ethanol level is 10-20 mm above the resin; the cerium or lanthanum salt solution is a nitrate, sulfate, or chloride solution, the amount of which is 5-20 ml and the concentration is 1-4 M; the oscillation speed is 50-150 r / min and the oscillation time is 12-18 h; and the drying temperature is 60-120 °C.

[0014] Preferably, the mass ratio of divinylbenzene, acrolein, benzoyl peroxide, and deionized water in step 1 is 2:1:0.05:2; the amount of tetrahydrofuran used is 30 ml; the stirring time is 8 h; and the hydrothermal reaction time is 48 h.

[0015] Preferably, the amount of sodium hydroxide in step 2 is 0.5g; the water bath stirring temperature is 60℃ and the stirring time is 24h; the Schiff base reaction temperature is 120℃ and the reaction time is 48h.

[0016] Preferably, in step 3, the amount of ethanol used is such that the ethanol level is 10 mm above the resin; the cerium or lanthanum salt solution is nitrate, and the amount of the salt solution is 10 ml; the oscillation speed is 80 r / min, and the oscillation time is 12 h; the drying temperature is 80 °C.

[0017] The purification method for using the obtained resin for the adsorption / desorption of dichloromethane organic waste gas includes the following steps:

[0018] (1) First, the resin is assembled into the adsorption device. The waste gas mixed with dichloromethane passes through the above device and is adsorbed into the resin pores after contacting the resin.

[0019] (2) After the dichloromethane adsorption reaches saturation, water vapor is introduced for desorption and regeneration. The enriched high-concentration gaseous dichloromethane is desorbed and then condensed at low temperature by a condenser to form a mixed solution of liquid dichloromethane and water. This solution is then introduced into a stratification tank for stratification and finally the liquid phase dichloromethane is recovered.

[0020] (3) After the resin is desorbed by water vapor, it is purged by air at room temperature. After cooling to room temperature, it can adsorb dichloromethane again, thereby realizing the adsorption / desorption cycle purification of dichloromethane.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0022] (1) The present invention provides a rare earth element modified resin. The composite material uses aldehyde-modified PDVB as the backbone and forms an imine structure by Schiff base condensation reaction on the polymer, so that the material has a high volume and good pore structure. At the same time, the proportion of micropores is increased in the original mesoporous pore structure, which further enhances the adsorption performance of the material.

[0023] (2) The present invention loads rare earth elements cerium or lanthanum onto imine-modified PDVB, which forms active sites in the pores, improves the affinity with dichloromethane, and enhances its adsorption effect and adsorption capacity for dichloromethane.

[0024] (3) The present invention has ultra-high hydrophobicity and oleophilicity due to the benzene ring structure in PDVB and aniline. The addition of aniline to form an imine structure and the loading of rare earth elements cerium and lanthanum give the resin a high specific surface area, rich pore structure and good thermal stability. In addition, after dichloromethane adsorption saturation, the composite material can be regenerated by steam thermal desorption or vacuum desorption, thereby realizing the multiple recycling of the modified resin. Specific Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and examples. These descriptions are for illustrative purposes only and should not be construed as limiting the invention. Examples 1 to 3 are preferred embodiments based on the technical solutions of the present invention, but are not limited thereto.

[0026] Example 1:

[0027] At room temperature, 3.0 g of divinylbenzene, 1.5 g of acrolein, 0.075 g of benzoyl peroxide, 3 ml of deionized water, and 30 ml of tetrahydrofuran were mixed and stirred for 8 h. The mixture was then placed in a polytetrafluoroethylene-lined reactor and reacted at 120 °C for 48 h. The mixture was then removed from the oven and allowed to cool on its own until the solvent evaporated. After that, the mixture was placed in a vacuum drying oven and dried overnight at 80 °C. Finally, the mixture was removed and ground to obtain aldehyde-modified PDVB.

[0028] Example 2:

[0029] Step 1 is the same as in Example 1;

[0030] Step 2: Pour the obtained aldehyde-modified PDVB into ethanol until completely dissolved, add 2.5g aniline, and then add 0.5g sodium hydroxide as a catalyst. Stir at 60℃ for 24h, then place in a polytetrafluoroethylene-lined reactor and react at 120℃ for 48h to carry out Schiff base condensation reaction. Then remove from the oven and let cool on its own. After the solvent evaporates, remove, filter, and place in a vacuum drying oven to dry overnight at 80℃. Remove and grind to obtain PDVB with an imine structure.

[0031] Example 3:

[0032] The rest is the same as in Example 2, except that the amount of aniline used is 3g.

[0033] Example 4:

[0034] The rest is the same as in Example 2, except that the amount of aniline used is 3.5g.

[0035] Example 5:

[0036] The rest is the same as in Example 2, except that the amount of aniline used is 4g.

[0037] The adsorption performance of the above embodiments was evaluated.

[0038] The evaluation was conducted using the following method: 1g of imine-modified PDVB was placed into the adsorption performance evaluation device. The adsorption device temperature was set at 20, 30, 40, and 50℃, the dichloromethane concentration was controlled at 600ppm, and the space velocity was 8500h⁻¹. ～1 The total gas flow rate was 200 ml / min. The tail gas was connected to a gas chromatograph, and the concentration of dichloromethane before and after adsorption was detected to obtain the adsorption curve. Additionally, the mass change of the adsorbent before and after adsorption was measured to obtain the adsorption capacity of the adsorbent for dichloromethane. The adsorption capacity of the adsorbent for dichloromethane is shown in Table 1.

[0039] Table 1 Effect of aniline dosage on adsorption capacity

[0040]

[0041]

[0042] The data above shows that Example 4 has the highest adsorption capacity for dichloromethane, indicating that the optimal amount of aniline used in this invention is 10 ml.

[0043] To further investigate the effect of cerium or lanthanum salt solution concentration on the adsorption capacity of dichloromethane, Examples 6-9 with different salt solution concentrations were prepared by keeping the amount of aniline used in Example 4 constant. The preparation methods are as follows:

[0044] Example 6:

[0045] Step 1 is the same as in Example 4;

[0046] Step 2 is the same as in Example 4;

[0047] Step 3: Pour ethanol into the obtained imine-based porous resin until it is 10 mm above the resin and allow it to swell. Then add 10 ml of 1M cerium nitrate solution and place it in a shaking incubator at 80 r / min for 12 h. After filtration, place it in an oven at 80 °C and dry overnight. Then wash it with deionized water and ethanol and dry it to obtain the rare earth element modified resin.

[0048] Example 7:

[0049] The rest is the same as in Example 6, except that the concentration of the cerium nitrate solution is 2M.

[0050] Example 8:

[0051] The rest is the same as in Example 6, except that the concentration of the cerium nitrate solution is 3M.

[0052] Example 9:

[0053] The rest is the same as in Example 6, except that the concentration of the cerium nitrate solution is 4M.

[0054] The adsorption performance of the above embodiments was evaluated.

[0055] The evaluation was conducted using the following method: 1g of rare earth element modified resin was placed into the adsorption performance evaluation device. The adsorption device temperature was set at 20, 30, 40, and 50℃, the concentration of dichloromethane was controlled at 600ppm, and the space velocity was 8500h⁻¹. ～1 The total gas flow rate was 200 ml / min. The tail gas was connected to a gas chromatograph, and the concentration of dichloromethane before and after adsorption was detected to obtain the adsorption curve. Additionally, the mass change of the adsorbent before and after adsorption was measured to obtain the adsorption capacity of the adsorbent for dichloromethane. The adsorption capacity of the adsorbent for dichloromethane is shown in Table 2.

[0056] Table 2 Effect of cerium nitrate solution concentration on adsorption capacity

[0057]

[0058] Based on the above data, it can be seen that Example 8 has the highest adsorption capacity for dichloromethane, indicating that a cerium or lanthanum salt solution concentration of 3M is the optimal value in this invention.

[0059] Table 3. Effects of imine structure and loading of rare earth elements cerium or lanthanum on adsorption capacity.

[0060]

[0061] Based on the above data, it can be seen that the adsorption capacity of dichloromethane in Example 4 is higher than that in Example 1, and the adsorption capacity of Example 8 is much higher than that in Examples 1 and 4. This indicates that the addition of an imine structure and the loading of rare earth elements can greatly improve the adsorption capacity of dichloromethane.

[0062] To further investigate the effects of space velocity and dichloromethane concentration on the adsorption capacity and breakthrough time of the adsorbent, the adsorption performance of Example 8 was tested at different space velocities or different initial concentrations of dichloromethane.

[0063] The effect of airspeed, except for airspeeds of 6000, 10000, and 12000 h. ～1 .

[0064] Adsorption performance test of Example 8

[0065] The evaluation was conducted using the following method: 0.71, 1.00, 1.18, and 1.41 g of rare earth element-modified resin were taken and placed into an adsorption performance evaluation device. The adsorption device temperatures were set at 20, 30, 40, and 50 °C, respectively; the concentration of dichloromethane was controlled at 600 ppm; and the space velocities were set at 6000, 8500, 10000, and 12000 h⁻¹, respectively. ～1 The total gas flow rate was 200 ml / min. The tail gas was connected to a gas chromatograph, and the concentration of dichloromethane before and after adsorption was detected to obtain the adsorption curve. In addition, the mass change of the adsorbent before and after adsorption was weighed to obtain the adsorption capacity of the adsorbent for dichloromethane. The adsorption capacity of the adsorbent at different space velocities is shown in Table 4.

[0066] Table 4 Effect of space velocity on adsorption capacity

[0067]

[0068] Based on the above data, it can be seen that the adsorption capacity of the modified resin first increases and then decreases with increasing space velocity. Example 8 exhibits the highest adsorption capacity, indicating that the present invention works at a space velocity of 8500 h⁻¹. ～1 The left and right sides have the highest adsorption capacity.

[0069] Adsorption performance test of Example 8

[0070] The evaluation was conducted using the following method: 1g of rare earth element modified resin was placed into the adsorption performance evaluation device. The adsorption device temperature was set at 20, 30, 40, and 50℃, the initial concentration of dichloromethane was 400, 500, 600, and 700 ppm, and the space velocity was 8493 h⁻¹. ～1The total gas flow rate was 200 ml / min. The tail gas was connected to a gas chromatograph, and the concentration of dichloromethane before and after adsorption was detected to obtain the adsorption curve. Additionally, the mass change of the adsorbent before and after adsorption was measured to obtain the adsorption capacity of the adsorbent for dichloromethane. The breakthrough time of the adsorbent at different initial concentrations of dichloromethane is shown in Table 5.

[0071] Table 5 Effect of initial dichloromethane concentration on adsorption breakthrough

[0072]

[0073] The data above show that the adsorption breakthrough time is negatively correlated with the initial concentration of dichloromethane. Even at 700 ppm, the adsorption breakthrough time is still relatively long at 190 min, indicating that the present invention still has a high adsorption effect on high concentrations of dichloromethane gas.

[0074] The applicant declares that this invention illustrates the detailed composition of the rare earth element modified resin described above through the above embodiments, but this invention is not limited to the above detailed composition, that is, it does not mean that this invention must rely on the above detailed composition to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of the raw materials of this invention, addition of auxiliary components, and selection of specific methods, etc., are all within the protection scope and disclosure scope of this invention.

Claims

1. A method for preparing a rare earth element modified resin for dichloromethane adsorption, characterized in that: First, the resin is assembled into the adsorption equipment. The waste gas mixed with dichloromethane passes through the equipment and is adsorbed into the resin pores after contacting the resin. After the dichloromethane adsorption reaches saturation, water vapor is introduced for desorption and regeneration. The enriched high-concentration gaseous dichloromethane is desorbed and then condensed at low temperature by the condenser to form a mixed solution of liquid dichloromethane and water. This solution enters the stratification tank for stratification and finally recovers the liquid phase dichloromethane. The resin after water vapor desorption is purged with room temperature air and cooled to room temperature, so that it can adsorb dichloromethane again, thereby realizing the adsorption / desorption cycle purification of dichloromethane. The resin has the following characteristics: Divinylbenzene, acrolein, tetrahydrofuran, benzoyl peroxide, and deionized water were mixed and stirred, and after hydrothermal reaction, dried to obtain aldehyde-modified PDVB; aldehyde-modified PDVB, aniline, sodium hydroxide, and ethanol were mixed and subjected to Schiff base reaction to obtain imine-modified PDVB; imine-modified PDVB was placed in a cerium or lanthanum salt solution, and cerium or lanthanum cations were loaded by swelling impregnation method to obtain rare earth metal-modified resin; The resin is prepared as follows: Step 1: Mix divinylbenzene, acrolein, benzoyl peroxide, and deionized water in a certain mass ratio, then add an appropriate amount of tetrahydrofuran. Stir at room temperature for a period of time, and obtain aldehyde-modified PDVB after hydrothermal reaction. Step 2: Dissolve the aldehyde-modified PDVB in ethanol until completely dissolved, add an appropriate amount of aniline, and add an appropriate amount of sodium hydroxide as a catalyst. Stir in a water bath at a certain temperature for a period of time, then transfer the mixed solution to a hydrothermal reactor. Perform a Schiff base reaction at a certain temperature to form an imine structure. After the ethanol evaporates, filter and dry to obtain imine-modified PDVB. Step 3: Soak the obtained imine-modified PDVB in an appropriate amount of ethanol to make it swell, then add a certain amount and concentration of cerium or lanthanum salt solution, and then place it in a shaking incubator to shake for a certain time, so that the cerium or lanthanum cations are loaded on the surface and internal channels of the porous resin. Then dry at a certain temperature overnight, then wash with deionized water and ethanol, and dry to obtain rare earth element modified resin.

2. The resin preparation method according to claim 1, wherein the precursor of the rare earth element modified resin used for dichloromethane adsorption is imine-modified PDVB, and its structural formula is: .

3. The resin preparation method according to claim 1, wherein in step one, the mass ratio of divinylbenzene, acrolein, benzoyl peroxide, and deionized water is 1.5~3 : 0.5~1.5 : 0.05 : 1~3; the volume ratio of tetrahydrofuran to the mixed solution of divinylbenzene, acrolein, benzoyl peroxide, and deionized water is 8~15 : 1; the stirring time is 6~9 h; and the hydrothermal reaction time is 24~72 h.

4. The resin preparation method according to claim 1, wherein the amount of aniline in step two is in the range of 1~1.6:1 molar ratio with acrolein in step one; the amount of sodium hydroxide is 0.2~0.6g; the water bath stirring temperature is 40~80℃, and the stirring time is 12~36h; the Schiff base reaction temperature is 60~120℃, and the reaction time is 24~72h.

5. In the resin preparation method according to claim 1, the amount of ethanol used in step three is such that the ethanol level is 10-20 mm above the resin; the cerium or lanthanum salt solution is an aqueous solution of nitrate, sulfate and chloride, the amount of salt solution is 5-20 ml, and the concentration is 1-4 M; the oscillation speed is 50-150 r / min, and the oscillation time is 12-18 h; the drying temperature is 60-120 °C.

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