A method for preparing a set-acid pretreated solvent-free cation exchange resin

Abstract

The application provides a preparation method of a no-solvent cation exchange resin with acid pretreatment, and a multi-gradient sulfuric acid concentration step-by-step increasing acid pretreatment process is used before a sulfonation reaction, so as to avoid the use of an organic solvent, strengthen a swelling process, overcome the defect of excessive local heat release caused by directly using high-concentration sulfuric acid, and thus prepare a strong acid cation exchange resin with high mechanical strength, the full exchange capacity of the resin is greater than 4.5 mmol / g, the water content is 45-58%, the round ball rate after grinding is greater than 99%, and the permeable grinding round ball rate is greater than 98%.

Description

Technical Field

[0001] This invention belongs to the field of ion exchange resin preparation technology, specifically relating to a method for preparing a solvent-free cation exchange resin with acid pretreatment. Background Technology

[0002] Cation exchange resins are granular polymer materials with cation exchange capabilities. Because they can remove cations through ion exchange, they are widely used for the separation of cations in fluids, such as the removal of calcium and magnesium ions, heavy metal cations, and ammonia nitrogen from water. Hydrogen-form cation exchange resins, as solid acids, can also be used as catalysts for many chemical reactions or as carriers for nanomaterials.

[0003] The existing preparation process of cation exchange resins generally involves swelling with organic solvents followed by sulfonation. For example, the method disclosed in patent CN 112062888 A involves swelling the resin white spheres with dichloroethane and then sulfonating them with concentrated sulfuric acid under heating conditions. In fact, the method of preparing strongly acidic cation exchange resins by swelling with organic solvents is quite mature, but the cation exchange resins prepared by this method will eventually have organic solvent residues. The article "Study on Organic Leakage of Ion Exchange Resins for Condensate Treatment" (Ion Exchange and Adsorption, 1999, (03): 272-278) points out that the organic matter leached from the cation exchange resin may not only affect the water treatment effect, but also pollute the anion exchange resin in the mixed bed. Moreover, some leached organic matter is toxic or carcinogenic, which will harm the environment and human health when used in water treatment. Therefore, there is an urgent need for a solvent-free method for preparing cation exchange resins.

[0004] Chinese patent CN108102032 A discloses a method for preparing a solvent-free, green styrene-based cation exchange resin. Instead of using dichloroethane as a swelling agent for sulfonation, it employs a combination of processes including crosslinking agents to increase skeleton elasticity, secondary polymerization to increase strength, high-concentration sulfuric acid sulfonation, and multi-gradient concentration stepwise acid layering. This method yields a resin with performance and properties consistent with ion exchange resins prepared without dichloroethane as a swelling agent. Furthermore, the multiple layering of the aqueous phase reduces water phase pollution to the environment. However, not using a swelling agent increases the risk of reduced resin strength. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a solvent-free cation exchange resin with acid pretreatment based on existing technology. Before the sulfonation reaction, an acid pretreatment process with gradually increasing sulfuric acid concentration is adopted. This aims to avoid the use of organic solvents while strengthening the swelling process and overcoming the defect of excessive local exothermic reaction caused by directly using high-concentration sulfuric acid. This results in the preparation of a strong acid cation exchange resin with high mechanical strength, a total exchange capacity > 4.5 mmol / g, a water content of 45-58%, a sphericity after grinding > 99%, and a sphericity after infiltration grinding > 98%.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a solvent-free cation exchange resin pretreated with tannic acid includes the following steps:

[0008] (1) Acid pretreatment: Polystyrene-divinylbenzene white balls were pretreated with sulfuric acid. The concentration of sulfuric acid was increased in a gradient distribution during the acid pretreatment process, with each stage lasting 10 to 120 minutes, to obtain the pretreated resin.

[0009] (2) Sulfonation reaction: The resin obtained in step (1) is mixed with concentrated sulfuric acid and heated to 95-155℃ for sulfonation reaction for 1-10 hours.

[0010] (3) Acid coating: The resin obtained in step (2) is coated with sulfuric acid. During the acid coating process, the concentration of sulfuric acid is gradually reduced according to the gradient distribution, with each stage lasting 0.5 to 2 hours.

[0011] (4) Washing: The resin obtained in step (3) is transformed with sodium hydroxide solution and then washed until neutral to obtain the solvent-free cation exchange resin with acid pretreatment.

[0012] In this invention, in step (1), sulfuric acid is pretreated with an acid gradient of 1 to 8 progressively increasing concentrations, with the sulfuric acid concentration ranging from 3% to 89%. Preferably, the sulfuric acid is pretreated with an acid gradient of 3 to 6 progressively increasing concentrations, and more preferably, it is pretreated with an acid gradient of 6 progressively increasing concentrations.

[0013] For example, sulfuric acid is used for pretreatment in three progressively increasing concentration gradients: 20-30%, 40-60%, and 75-85%; preferably, the concentration gradients are 25%, 50%, and 80%.

[0014] For example, sulfuric acid is used for pretreatment in four progressively increasing concentration gradients: 5-25%, 35-50%, 65-75%, and 83-88%; preferably, the concentration gradients are 10-20%, 40-45%, 70%, and 85-87%.

[0015] For example, sulfuric acid is used for pretreatment in six progressively increasing concentration gradients: 3–18%, 19–32%, 33–47%, 48–57%, 58–77%, and 78–87%; preferably, the sulfuric acid concentration gradients are 5–15%, 20–30%, 35–45%, 50–55%, 60–75%, and 80–85%.

[0016] In this invention, in step (1), the moisture content of the polystyrene-divinylbenzene white spheres is 1-10%, specifically 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0017] For the purposes of this invention, in step (2), the concentration of concentrated sulfuric acid is 90-98%, preferably 90-95%.

[0018] In step (3) of this invention, during the acid treatment, the sulfuric acid concentration gradient is successively reduced, with the sulfuric acid concentration ranging from 87% to 3%. The sulfuric acid can be divided into 5 to 12 successively decreasing concentration gradients for the acid treatment. Preferably, it can be divided into 5 to 10 successively decreasing concentration gradients, and more preferably, it can be divided into 8 successively decreasing concentration gradients.

[0019] Specifically, when sulfuric acid is divided into eight progressively decreasing concentration gradients, the concentration gradients are 87–79%, 77–69%, 67–59%, 57–49%, 47–39%, 37–29%, 27–19%, and 17–3%; more preferably, the concentration gradients are 85–80%, 75–70%, 65–60%, 55–50%, 45–40%, 35–30%, 25–20%, and 10–5%.

[0020] The advantages of using the technical solution of this invention are as follows:

[0021] This invention provides a method for preparing a solvent-free cation exchange resin pretreated with tandem acid. Before the sulfonation reaction, a tandem acid pretreatment process with progressively increasing sulfuric acid concentration is adopted. This aims to avoid the use of organic solvents while enhancing the swelling process and overcoming the defect of excessive local exothermic reaction caused by directly using high-concentration sulfuric acid. As a result, a strong acid cation exchange resin with high mechanical strength is prepared, with a total exchange capacity > 4.5 mmol / g, a water content of 45-58%, a sphericity after grinding > 99%, and a sphericity after infiltration grinding > 98%. Detailed Implementation

[0022] The present invention can be better understood from the following embodiments. However, those skilled in the art will readily understand that the descriptions in the embodiments are for illustrative purposes only and should not, and will not, limit the invention as detailed in the claims.

[0023] Example 1

[0024] A method for preparing a solvent-free cation exchange resin pretreated with tannic acid includes the following steps:

[0025] (1) Acid pretreatment: Polystyrene-divinylbenzene white balls with a moisture content of 1% were pretreated with sulfuric acid. The sulfuric acid was divided into 6 concentration gradients that increased sequentially: 5%, 20%, 35%, 50%, 60%, and 80%.

[0026] The specific acid pretreatment process is as follows: Polystyrene-divinylbenzene white balls with a moisture content of 1% are mixed with 5% sulfuric acid for 90 minutes, and then centrifuged to separate solid material I; solid material I is mixed with 20% sulfuric acid for 80 minutes, and then centrifuged to separate solid material II; solid material II is mixed with 35% sulfuric acid for 80 minutes, and then centrifuged to separate solid material III; solid material III is mixed with 50% sulfuric acid for 80 minutes, and then centrifuged to separate solid material IV; solid material IV is mixed with 60% sulfuric acid for 80 minutes, and then centrifuged to separate solid material V; solid material V is mixed with 80% sulfuric acid for 80 minutes, and then centrifuged to separate solid material VI.

[0027] (2) Sulfonation reaction: The resin obtained in step (1) (i.e. solid material VI) is mixed with 90% concentrated sulfuric acid and heated to 120°C for sulfonation reaction. The reaction time is 9 hours, and solid material VII is separated.

[0028] (3) Acid coating: The resin (i.e. solid material VII) obtained in step (2) is coated with sulfuric acid. During the acid coating process, the concentration of sulfuric acid is gradually reduced according to the gradient distribution. The sulfuric acid concentrations are 85%, 70%, 60%, 54%, 43%, 30%, 21%, and 6% respectively, with each stage lasting 1 hour.

[0029] (4) Washing: The resin obtained in step (3) is washed with deionized water, then transformed with 5% sodium hydroxide solution, and then washed until neutral to obtain solvent-free cation exchange resin with acid pretreatment.

[0030] Example 2

[0031] A method for preparing a solvent-free cation exchange resin pretreated with tannic acid includes the following steps:

[0032] (1) Acid pretreatment: Polystyrene-divinylbenzene white balls with a moisture content of 5% were pretreated with sulfuric acid. The sulfuric acid was divided into 4 concentration gradients that increased sequentially: 10%, 40%, 70%, and 85%.

[0033] The specific acid pretreatment process is as follows: Polystyrene-divinylbenzene white balls with a moisture content of 5% are mixed with 10% sulfuric acid for 60 minutes, and then solid material I is separated by centrifugation; solid material I is mixed with 40% sulfuric acid for 60 minutes, and then solid material II is separated by centrifugation; solid material II is mixed with 70% sulfuric acid for 60 minutes, and then solid material III is separated by centrifugation; solid material III is mixed with 85% sulfuric acid for 60 minutes, and then solid material IV is separated by centrifugation.

[0034] (2) Sulfonation reaction: The resin obtained in step (1) (i.e. solid material IV) is mixed with 95% concentrated sulfuric acid, heated to 95°C for sulfonation reaction, and the reaction time is 1 hour. Then the temperature is raised to 100°C to continue the sulfonation reaction, and the reaction time is 2 hours. Solid material V is separated.

[0035] (3) Acid coating: The resin (i.e. solid material V) obtained in step (2) is coated with sulfuric acid. During the acid coating process, the concentration of sulfuric acid is gradually reduced according to the gradient distribution. The sulfuric acid concentrations are 85%, 70%, 60%, 54%, 43%, 30%, 21%, and 6%, respectively, with each stage lasting 1 hour.

[0036] (4) Washing: The resin obtained in step (3) is washed with deionized water, then transformed with 5% sodium hydroxide solution, and then washed until neutral to obtain solvent-free cation exchange resin with acid pretreatment.

[0037] Example 3

[0038] A method for preparing a solvent-free cation exchange resin pretreated with tannic acid includes the following steps:

[0039] (1) Acid pretreatment: Polystyrene-divinylbenzene white balls with a moisture content of 10% were pretreated with sulfuric acid. The sulfuric acid was divided into four concentration gradients that increased sequentially: 20%, 45%, 70%, and 87%.

[0040] The specific acid pretreatment process is as follows: Polystyrene-divinylbenzene white balls with a moisture content of 10% are mixed with 20% sulfuric acid for 30 minutes, and then solid material I is separated by centrifugation; solid material I is mixed with 45% sulfuric acid for 45 minutes, and then solid material II is separated by centrifugation; solid material II is mixed with 70% sulfuric acid for 30 minutes, and then solid material III is separated by centrifugation; solid material III is mixed with 87% sulfuric acid for 30 minutes, and then solid material IV is separated by centrifugation.

[0041] (2) Sulfonation reaction: The resin obtained in step (1) (i.e. solid material IV) is mixed with 93% concentrated sulfuric acid, heated to 100°C for sulfonation reaction for 2 hours, and then heated to 120°C for sulfonation reaction for 6 hours to separate solid material V.

[0042] (3) Acid coating: The resin (i.e. solid material V) obtained in step (2) is coated with sulfuric acid. During the acid coating process, the concentration of sulfuric acid is gradually reduced according to the gradient distribution. The sulfuric acid concentrations are 85%, 70%, 60%, 54%, 43%, 30%, 21%, and 6%, respectively, with each stage lasting 1 hour.

[0043] (4) Washing: The resin obtained in step (3) is washed with deionized water, then transformed with 5% sodium hydroxide solution, and then washed until neutral to obtain solvent-free cation exchange resin with acid pretreatment.

[0044] Example 4

[0045] A method for preparing a solvent-free cation exchange resin pretreated with tannic acid includes the following steps:

[0046] (1) Acid pretreatment: Polystyrene-divinylbenzene white balls with a moisture content of 10% were pretreated with sulfuric acid. The sulfuric acid was divided into 6 concentration gradients that increased sequentially: 15%, 30%, 45%, 55%, 75%, and 85%.

[0047] The specific acid pretreatment process is as follows: Polystyrene-divinylbenzene white balls with a moisture content of 10% are mixed with 15% sulfuric acid for 20 minutes, and then centrifuged to separate solid material I; solid material I is mixed with 30% sulfuric acid for 30 minutes, and then centrifuged to separate solid material II; solid material II is mixed with 45% sulfuric acid for 30 minutes, and then centrifuged to separate solid material III; solid material III is mixed with 55% sulfuric acid for 30 minutes, and then centrifuged to separate solid material IV; solid material IV is mixed with 75% sulfuric acid for 30 minutes, and then centrifuged to separate solid material V; solid material V is mixed with 85% sulfuric acid for 20 minutes, and then centrifuged to separate solid material VI.

[0048] (2) Sulfonation reaction: The resin obtained in step (1) (i.e. solid material VI) is mixed with 93% concentrated sulfuric acid, heated to 110°C for sulfonation reaction, and the reaction time is 2 hours. Then the temperature is raised to 130°C to continue the sulfonation reaction, and the reaction time is 6 hours. Solid material VII is then separated.

[0049] (3) Acid coating: The resin (i.e. solid material VII) obtained in step (2) is coated with sulfuric acid. During the acid coating process, the concentration of sulfuric acid is gradually reduced according to the gradient distribution. The sulfuric acid concentrations are 85%, 70%, 60%, 54%, 43%, 30%, 21%, and 6% respectively, with each stage lasting 1 hour.

[0050] (4) Washing: The resin obtained in step (3) is washed with deionized water, then transformed with 5% sodium hydroxide solution, and then washed until neutral to obtain solvent-free cation exchange resin with acid pretreatment.

[0051] Example 5

[0052] A method for preparing a solvent-free cation exchange resin pretreated with tannic acid includes the following steps:

[0053] (1) Acid pretreatment: Polystyrene-divinylbenzene white balls with a moisture content of 8% were subjected to acid pretreatment with sulfuric acid. The sulfuric acid was divided into three concentration gradients that increased sequentially: 25%, 50%, and 80%.

[0054] The specific acid pretreatment process is as follows: Polystyrene-divinylbenzene white balls with a moisture content of 8% are mixed with 25% sulfuric acid for 45 minutes, and then solid material I is separated by centrifugation; solid material I is mixed with 50% sulfuric acid for 45 minutes, and then solid material II is separated by centrifugation; solid material II is mixed with 80% sulfuric acid for 45 minutes, and then solid material III is separated by centrifugation.

[0055] (2) Sulfonation reaction: The resin obtained in step (1) (i.e. solid material III) is mixed with 94% concentrated sulfuric acid, heated to 100°C for sulfonation reaction, and the reaction time is 1 hour. Then the temperature is raised to 155°C to continue the sulfonation reaction, and the reaction time is 3 hours. Solid material IV is then separated.

[0056] (3) Acid coating: The resin (i.e. solid material IV) obtained in step (2) is coated with sulfuric acid. During the acid coating process, the concentration of sulfuric acid is gradually reduced according to the gradient distribution. The sulfuric acid concentrations are 85%, 70%, 60%, 54%, 43%, 30%, 21%, and 6%, respectively, with each stage lasting 1 hour.

[0057] (4) Washing: The resin obtained in step (3) is washed with deionized water, then transformed with 5% sodium hydroxide solution, and then washed until neutral to obtain solvent-free cation exchange resin with acid pretreatment.

[0058] Comparative Example 1

[0059] (1) Sulfonation reaction: Polystyrene-divinylbenzene white balls with a moisture content of 1% are mixed with 93% concentrated sulfuric acid and heated to 120°C for sulfonation reaction. The reaction time is 9 hours, and solid material I is separated out.

[0060] (2) Acid coating: The resin (i.e. solid material I) obtained in step (1) is coated with sulfuric acid. During the acid coating process, the concentration of sulfuric acid is gradually reduced according to the gradient distribution. The sulfuric acid concentrations are 85%, 70%, 60%, 54%, 43%, 30%, 21%, and 6% respectively, with each stage lasting 1 hour.

[0061] (3) Washing: The resin obtained in step (2) is washed with deionized water, then transformed with 5% sodium hydroxide solution, and then washed until neutral to obtain solvent-free cation exchange resin with acid pretreatment.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications may still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions may be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an acid-pretreated solvent-free cation exchange resin, characterized in that, Includes the following steps: (1) Acid pretreatment: Polystyrene-divinylbenzene white balls were pretreated with sulfuric acid. The concentration of sulfuric acid was increased in a gradient distribution during the acid pretreatment process, with each stage lasting 10 to 120 minutes, to obtain the pretreated resin. The moisture content of the polystyrene-divinylbenzene white balls is 1-10%. Sulfuric acid was used for pretreatment in three progressively increasing concentration gradients: 20-30%, 40-60%, and 75-85%; or, Sulfuric acid was used for pretreatment in four progressively increasing concentration gradients: 5-25%, 35-50%, 65-75%, and 83-88%; or, Sulfuric acid was used for pretreatment in six progressively increasing concentration gradients: 3–18%, 19–32%, 33–47%, 48–57%, 58–77%, and 78–87%. (2) Sulfonation reaction: The resin obtained in step (1) is mixed with concentrated sulfuric acid and heated to 95~155℃ for sulfonation reaction, and the reaction time is 1~10 hours; the concentration of concentrated sulfuric acid is 90~98%; (3) Acid Coating: The resin obtained in step (2) is acid coated with sulfuric acid. During the acid coating process, the concentration of sulfuric acid is gradually reduced according to the gradient distribution, with each stage lasting 0.5 to 2 hours. The sulfuric acid is divided into 8 successively decreasing concentration gradients for acid coating treatment. The concentration gradients of sulfuric acid are 87~79%, 77~69%, 67~59%, 57~49%, 47~39%, 37~29%, 27~19%, and 17~3%. (4) Washing: The resin obtained in step (3) is transformed with sodium hydroxide solution and then washed until neutral to obtain solvent-free cation exchange resin with acid pretreatment.

2. The preparation method according to claim 1, characterized in that, In step (1), sulfuric acid is pretreated with three progressively increasing concentration gradients: 25%, 50%, and 80%.

3. The preparation method according to claim 1, characterized in that, In step (1), sulfuric acid is divided into four progressively increasing concentration gradients for acid pretreatment, with the sulfuric acid concentration gradients being 10~20%, 40~45%, 70%, and 85~87%.

4. The preparation method according to claim 1, characterized in that, In step (1), sulfuric acid is divided into 6 concentration gradients that increase sequentially for acid pretreatment. The concentration gradients of sulfuric acid are 5~15%, 20~30%, 35~45%, 50~55%, 60~75%, and 80~85%.

5. The preparation method according to claim 1, characterized in that, In step (2), the concentration of concentrated sulfuric acid is 90-95%.

6. The preparation method according to claim 1, characterized in that, In step (3), the concentration gradient of sulfuric acid is 85~80%, 75~70%, 65~60%, 55~50%, 45~40%, 35~30%, 25~20%, and 10~5%.