RU2791811C1 - Method for producing composite sorbent based on chitosan - Google Patents

Abstract

FIELD: chemical industry.

SUBSTANCE: invention relates to methods for producing composite sorbents containing chitosan, designed to extract heavy metal ions. The method of obtaining a sorbent is mixing a solution of chitosan in 5% by volume of acetic acid with a suspension of a filler in a ratio of 1:10–1:2, the resulting mixture is added dropwise to a 1–2 M sodium hydroxide solution, and sorbent granules are formed, which are then washed to neutral pH with water, after which the granules are kept in a 1–2% (by weight) solution of a cross-linking agent and washed with water and a water-alcohol mixture. In addition, dopamine is additionally added to the initial mixture at a ratio of dopamine:chitosan=1:10–1:3, and silicon dioxide is used as an additional filler.

EFFECT: invention makes it possible to increase the sorption capacity of the sorbent with respect to heavy metal ions and to simplify the processing of composite microspheres based on chitosan in an aqueous alkaline solution.

1 cl, 1 tbl, 3 ex

Description

The invention relates to the chemical industry, and in particular to methods for producing composite sorbents containing chitosan, designed to extract heavy metal ions by sorption from solutions of various compositions resulting from various technological processes, and can be used to improve membrane and sorption technologies, in water treatment , in the development of technologies for the utilization of heavy metal ions from aqueous solutions and wastewater of various nature.

A known method for producing granules of cross-linked chitosan, including the stage of formation of granules and cross-linking of the polymer with glutaraldehyde in an acidic solution, in which the polymer is first cross-linked using a hydrochloric acid solution containing glutaraldehyde, at a molar ratio of chitosan : hydrochloric acid : glutaraldehyde 1 :( 0.5-1.0):(0.1-1.0), and then the gel is extruded in the form of threads, they are mechanically cut into granules and dried at a temperature of 40-70°C for 1-2 hours [Patent 2590982 Russian Federation, IPC A61K 47/36 B01J 20/24 C08B 37/08. The method of obtaining granules of cross-linked chitosan / Pestov A.V., Bratskaya S.Yu.; applicant and patentee Federal State Budgetary Institution of Science Institute of Organic Synthesis. AND I. Postovsky Ural Branch of the Russian Academy of Sciences (RU), Federal State Budgetary Institution of Science Institute of Chemistry of the Far Eastern Branch of the Russian Academy of Sciences (RU). - No. 2015125829/15; dec. 06/29/2015; publ. 07/10/2016, Bull. No. 19.].

A known method of obtaining a sorbent for water purification based on natural aluminosilicate modified with chitosan by treating aluminosilicate with a solution of chitosan in dilute acetic acid, in which the treatment is carried out at a mass ratio of aluminosilicate to a solution of chitosan in dilute acetic acid, equal to 1:1, and the final pH value of the solution above the precipitate equal to 8-9, then the formed mass is granulated by forcing through the spinneret, the obtained granules are dried, after which they are treated with a solution of humic acids taken in an amount that ensures complete binding of the amino groups of chitosan, the sorbent granules are separated from the solution and the resulting polymer layer is cured on the surface of the granules , wherein: - zeolite, expanded vermiculite or their mixture is used as natural aluminosilicate; - processing of aluminosilicate is carried out with a 2-4% solution of chitosan in 3% acetic acid; - treatment of sorbent granules with humic acids is carried out with a 10% solution of humic acids containing 3.1 mg-eq/g COOH-groups and 6.0 mg-eq/g COOH-groups at room temperature for 3-4 hours; - curing of the polymer layer on the surface of the granules is carried out by keeping the granules at room temperature until dry or heat treatment at 120-150°C for 2-3 hours [Patent 2277013 Russian Federation, IPC B 01 J 20/16, B 01 J 20/26 , B 01 J 20/32. The method of obtaining a sorbent for water purification / Shapkin NP, Postoykin VV, Zavyalov BB, Nguyen Tinh Ngia; applicant and patentee Shapkin N.P., Postoykin V.V., Zavyalov B.B., Nguyen Tinh Ngia - No. 2004135113/15; dec. 12/01/2004; publ. May 27, 2006, Bull. No. 15.].

A known method for producing composites based on chitosan and clinoptilolite in the form of microspheres with increased sorption capacity for copper ions by embedding (dispersing) clinoptilolite microparticles into a matrix of cross-linked chitosan at a mass ratio of clinoptilolite and chitosan 1:10 - 1:2, while in the composite is achieved at the same time, ionic/covalent bonding is “in tandem”: ionic (ionotropic) interaction (gelation) of chitosan is carried out with sodium tripolyphosphate, and epichlorohydrin acts as a covalent crosslinking agent with respect to chitosan.

The maximum sorption capacity of the composite with respect to copper ions is 9.04 mmol/g at pH 5.

The preparation of composite microspheres is carried out as follows: a solution of chitosan with a concentration of 3 g/l is obtained by dissolving chitosan powder in 1 vol% acetic acid with vigorous stirring for at least 48 hours. The required amount of clinoptilolite powder is mixed with distilled water, and the volume of water is ½ volume of the chitosan solution, and kept under vigorous stirring on a magnetic stirrer for 1 hour.

Then, 20 g of a solution of chitosan in 1% acetic acid is mixed with 10 ml of a dispersion of clinoptilolite in distilled water, and after vigorous stirring, epichlorohydrin is gradually added as a crosslinking agent. Stirring is continued until the epichlorohydrin is completely incorporated into the reaction mixture. Then the prepared mixture is injected with a syringe into an aqueous solution of sodium tripolyphosphate with a concentration of 0.05 M with stirring.

Composite microspheres are kept under stirring for 5 h at 37°С, separated from the dispersion medium and thoroughly washed with distilled water from unreacted sodium tripolyphosphate and dried for 24 h at room temperature and 48 h under vacuum at 40°С. The average dry microsphere size is 800 µm [Dragan ES, Dinu MV, Timpu D. Preparation and characterization of novel composites based on chitosan and clinoptilolite with enhanced adsorption properties for Cu ²⁺ // Bioresource Technology (2010) V. 101, P. 812-817].

The extraction of metal ions by the chitosan/clinoptilolite composite from aqueous solutions is carried out as follows. 0.25 g of dry microspheres of the composite is placed in a flask, 25 ml of an aqueous solution of CuSO ₄ is added, with a concentration of 0.07 mol/l, and contact is carried out for 24 hours.

The sorption capacity of the sorbent is calculated by the formula

where C ₀ is the initial concentration of metal ions in solution, mg/l;

C - equilibrium concentration of metal ions in solution, mg/l;

m is the weight of the sample of the sorbent (composite), g;

V is the volume of the solution, ml;

63.5 is the atomic mass of copper.

However, the disadvantages of this method are: long processing time of the sorbent (5 h) in a solution of sodium tripolyphosphate; - long drying time (24 hours at room temperature and 48 hours under vacuum at 40°C); insufficiently high degree of extraction of heavy metal ions from aqueous solutions (no data for metals other than copper).

The closest in technical essence and the achieved result, that is, the prototype, is a method for producing a composite sorbent for extracting heavy metal ions from aqueous solutions, which consists in mixing a solution of chitosan in 1% acetic acid with a dispersion of reinforcing material in distilled water at a mass ratio of reinforcing dispersed material and chitosan 1:10 - 1:2, intensive stirring, gradual addition of epichlorohydrin as a crosslinking agent and stirring until it is completely included in the reaction mixture, subsequent dropwise introduction of the prepared mixture into an aqueous solution of sodium tripolyphosphate with a concentration of 0.05 M with stirring, keeping microspheres formed in it, followed by their separation from the dispersion medium and thorough washing with distilled water from unreacted sodium tripolyphosphate, in which as reinforcing particulate material using polymethylsiloxane polyhydrate, and keeping the composite microspheres in an aqueous solution of sodium tripolyphosphate is carried out under microwave irradiation with a power of 300 W at a frequency of 2.45 GHz and a temperature of 25-40°C for 15-25 min [US Pat. 2691050 RF, IPC C 1 51, B 01 J 20/30, B 01 J 20/24. B 01 J 20/26, B 01 J 20/103. The method of obtaining a composite sorbent for the extraction of heavy metal ions from aqueous solutions [Text] / Nikiforova T.E., Kozlov V.A., Lipatova I.M., Natareev S.V., Kuzmina M.V.; applicant and patent holder Ivan. state chemical tech. un-t. - No. 2018116841; dec. 05/04/2018; publ. 06/07/2019, Bull. No. 16.].

The disadvantages of the prototype are:

- insufficiently high sorption capacity of the sorbent in the extraction of heavy metal ions;

- the need to use microwave equipment for processing sorbents.

The technical result of the invention is to increase the sorption capacity of the sorbent in relation to heavy metal ions; simplification of the processing of composite microspheres based on chitosan in an aqueous alkaline solution in the preparation of sorbents by eliminating the use of microwave processing.

This result is achieved by the fact that in the method of obtaining a composite sorbent based on chitosan, which consists in mixing a solution of chitosan in acetic acid with a suspension of the filler in distilled water at a mass ratio of the filler and chitosan 1:10-1:2, intensive mixing, followed by dropwise introduction of the prepared mixture into an aqueous alkaline solution with stirring, keeping the formed granules of the composite sorbent in it, followed by their separation from the liquid phase and thorough washing with distilled water to neutral pH, according to the invention, an aqueous solution of dopamine is additionally added to the initial mixture of reagents in a mass ratio of dopamine : chitosan 1 :10-1:3, acetic acid for the preparation of a solution of chitosan is used with a concentration of 3-5 vol. %, silicon dioxide is additionally used as a filler, and aqueous solution of sodium hydroxide with a concentration of 1-2 M, in which the formed granules are kept for 20-50 minutes, followed by washing with distilled water, and the granules washed from an alkaline solution are placed in a 1-2 wt.% aqueous solution of a cross-linking agent selected from glutaraldehyde and epichlorohydrin and kept under stirring at room temperature for 1.5-2 hours, after which they are washed with distilled water, then 50 vol. . % ethanol solution and again with distilled water and stored in distilled water until use.

To implement the claimed invention, the following materials and reagents are used:

- Chitosan. TU 9289-067-00472124-03 "Food chitosan". Food grade chitosan (acid-soluble) is obtained in the form of a powder from the shell of crustaceans (manufactured by CJSC Bioprogress) with a molecular weight of 200 kDa and a deacetylation degree of 88%;

- Polymethylsiloxane polyhydrate (methylsilicic acid hydrogel) Polymethylsiloxane polyhydrate has a porous structure of an organosilicon matrix (molecular sponge) of a hydrophobic nature; It is a mass of white color, consisting of jelly-like lumps of different sizes, odorless and tasteless. Practically insoluble in water.

- Silica. GOST 9428-73. Silicon (IV) oxide. Specifications;

- Dopamine. CAS code 51-61-6

Structural formula:

- Glutaraldehyde CAS #: 111-30-8 Clear and colorless liquid, easily soluble in water. Structural formula:

;

;

- Epichlorohydrin. GOST 12844-74 Technical epichlorohydrin. Specifications;

- Sodium hydroxide. GOST R 55064-2012. Technical caustic soda. Specifications;

- Acetic acid CH ₃ COOH. GOST R 55982-2014. Acetic acid for the food industry. Specifications;

- Ethanol. GOST 5962-2013 Rectified ethyl alcohol from food raw materials. Specifications.

- Distilled water. GOST R 58144-2018. Distilled water. Specifications.

The sorption capacity of the sorbent is calculated by the formula

where C ₀ is the initial concentration of metal ions in solution, mg/l;

C - equilibrium concentration of metal ions in solution, mg/l;

m is the weight of the sample of the sorbent (composite), g;

V is the volume of the solution, ml;

63.5 is the atomic mass of copper.

The invention is carried out as follows.

Example 1

To prepare 20 g of a 3 wt.% solution of chitosan, weigh a portion of chitosan weighing 0.6 g, dissolve in 12.4 ml of 5 vol. % acetic acid and intensively stirred for 2 hours until a thick homogeneous gel is formed, 5 ml of an aqueous solution containing 0.2 g of dopamine (mass ratio of dopamine : chitosan 1:3) is added, mixed with 2 ml of an aqueous suspension containing 0. 06 g of polymethylsiloxane polyhydrate (mass ratio filler/chitosan 1:10), stirred for 0.5 h, then the prepared mixture is introduced dropwise into 180 ml of sodium hydroxide solution with a concentration of 1.5 M with constant stirring until granules are formed and kept at room temperature for 35 minutes, followed by their separation by filtration from the liquid phase and thoroughly and washed with distilled water until neutral pH, then the granules washed from an alkaline solution are placed in a beaker containing 50 ml of 1 wt.% aqueous solution of glutaraldehyde and kept under stirring at room temperature for 2 hours, then washed with distilled water, then 50 vol. % ethanol solution and again with distilled water and stored in distilled water until use.

Extraction of metal ions by a composite of chitosan/dopamine/polymethylsiloxane polyhydrate from aqueous solutions. 0.25 g of a composite sorbent based on chitosan in terms of dry matter is placed in a flask, 25 ml of an aqueous solution of CuSO ₄ (module solution / sorbent 100) is added with a concentration of 0.7 mol/l at pH 5 and contact is carried out. After 24 hours, the solution is filtered off and the content of Cu(II) ions in the filtrate is determined by atomic absorption spectroscopy.

The concentration of copper ions in the solution after contact with the sorbent was 0.601 mol/l. The sorption capacity determined by formula (1) was 9.90 mmol/g.

Example 2

To prepare 20 g of a 3 wt.% solution of chitosan, weigh a sample of chitosan weighing 0.6 g, dissolve in 12.4 ml of 4 vol. % acetic acid and intensively stirred for 2 hours until a thick homogeneous gel is formed, 5 ml of an aqueous solution containing 0.12 g of dopamine (mass ratio of dopamine : chitosan 1:5) is added, mixed with 2 ml of an aqueous suspension containing 0. 30 g of silicon dioxide (mass ratio filler/chitosan 1:2), stirred for 0.5 h, then the prepared mixture is introduced dropwise into 180 ml of sodium hydroxide solution with a concentration of 1 M with constant stirring until granules are formed and kept at room temperature temperature for 50 min, followed by their separation by filtration from the liquid phase and thoroughly and washed with distilled water to neutral pH, then the granules washed from an alkaline solution are placed in a beaker containing 50 ml of a 1.5 wt.% aqueous solution of glutaraldehyde and kept under stirring at room temperature for 1.5 h, then washed with distilled water, then 50 vol. % ethanol solution and again with distilled water and stored in distilled water until use.

Extraction of metal ions by a chitosan/dopamine/silicon dioxide composite from aqueous solutions. 0.25 g of a composite sorbent based on chitosan in terms of dry matter is placed in a flask, 12.5 ml of an aqueous solution of NiSO ₄ (module solution / sorbent 50) is added with a concentration of 0.7 mol/l at pH 5 and contact is carried out. After 20 hours, the solution is filtered off, and the content of Ni(II) ions in the filtrate is determined by atomic absorption spectroscopy.

The concentration of nickel ions in the solution after contact with the sorbent was 0.507 mol/l. The sorption capacity determined by formula (1) was 9.65 mmol/g:

Example 3

To prepare 20 g of a 3 wt.% solution of chitosan, weigh a portion of chitosan weighing 0.6 g, dissolve in 12.4 ml of 3 vol. % acetic acid and intensively stirred for 2 hours until a thick homogeneous gel is formed, 5 ml of an aqueous solution containing 0.06 g of dopamine (mass ratio of dopamine : chitosan 1:10) is added, mixed with 2 ml of an aqueous suspension containing 0. 10 g of polymethylsiloxane polyhydrate (mass ratio filler/chitosan 1:6), stirred for 0.5 h, then the prepared mixture is introduced dropwise into 180 ml of sodium hydroxide solution with a concentration of 2 M with constant stirring until granules are formed and kept at room temperature temperature for 20 min, followed by their separation by filtration from the liquid phase and thoroughly and washed with distilled water until neutral pH, then the granules washed from an alkaline solution are placed in a beaker containing 50 ml of a 2 wt.% aqueous solution of epichlorhydgin and kept under stirring at room temperature for 1 h, then washed with distilled water, then 50 vol. % ethanol solution and again with distilled water and stored in distilled water until use.

Extraction of metal ions by a composite of chitosan/dopamine/polymethylsiloxane polyhydrate from aqueous solutions. 0.25 g of a composite sorbent based on chitosan in terms of dry matter is placed in a flask, 50 ml of an aqueous solution of ZnSO ₄ (module solution / sorbent 200) with a concentration of 0.7 mol/l is added, and contact is carried out for 22 hours.

The concentration of zinc ions in the solution after contact with the sorbent was 0.6524 mol/l. The sorption capacity determined by formula (1) was 9.52 mmol/g:

The results of studies on the extraction of heavy metal ions from solutions with a concentration of 0.7 mol/l according to the prototype and according to the claimed invention are presented in the table.

Table

examples Sorption capacity, mmol/g Use of microwave equipment Cu2 ⁺ Ni2 ⁺ Zn2 ⁺ 1. 9.90 - - - 2. - 9.65 - - 3. - - 9.52 - Prototype 1 9.3 used 2 9.1 used 3 9.2 used

Thus, it follows from the data in the table that the proposed method allows us to solve the problem, namely, to increase the sorption capacity of the sorbent when extracting heavy metal ions from solutions (by about 3-5%), to simplify the processing of composite granules based on chitosan in aqueous solution of sodium hydroxide in the preparation of sorbents due to the exclusion of the use of microwave treatment.

The study was carried out using the resources of the Center for the Collective Use of Scientific Equipment of the ISUCT (with the support of the Ministry of Education and Science of Russia, agreement No. 075-15-2021-671 dated July 28, 2021).

Claims (1)

A method for producing a composite sorbent based on chitosan, which consists in mixing a solution of chitosan in acetic acid with a suspension of a filler in distilled water at a mass ratio of filler and chitosan of 1:10–1:2, intensive mixing, followed by dropwise introduction of the prepared mixture into an aqueous alkaline solution with stirring , keeping the formed granules of the composite sorbent in it, followed by their separation from the liquid phase and thorough washing with distilled water to neutral pH, characterized in that an aqueous solution of dopamine is additionally introduced into the initial mixture of reagents in a dopamine:chitosan mass ratio of 1:10-1:3 , acetic acid for the preparation of a solution of chitosan is used with a concentration of 3-5 vol.%, silicon dioxide is additionally used as a filler, and alkaline solution is used aqueous solution of sodium hydroxide with a concentration of 1-2 M, in which the formed granules are kept for 20-50 minutes, followed by washing with distilled water, and the granules washed from the alkaline solution are placed in a 1-2 wt.% aqueous solution of a cross-linking agent selected from glutaraldehyde and epichlorohydrin, and kept under stirring at room temperature for 1.5-2 hours, after which they are washed with distilled water, then 50 vol.% ethanol solution and again with distilled water and stored in distilled water until use.