A method for preparing a hydrophobically modified alginate

Abstract

This invention discloses a method for preparing hydrophobically modified alginate, belonging to the field of aerogel adsorption technology. The hydrophobically modified alginate of this invention can directionally adsorb chromium-containing wastewater, solving the problems of low capacity, poor water solubility, and slow adsorption rate of traditional biomass adsorbents. It also utilizes the synergistic effect of multiple functional groups to achieve full-coverage adsorption of chromium, exhibiting good adsorption capacity and stability in the deep treatment of industrial chromium-containing wastewater. This invention utilizes the oxygen-containing groups abundant in sodium lignosulfonate and sodium alginate, which can strongly complex and electrostatically adsorb chromium ions, and provide sites for subsequent chromium ion reduction. Furthermore, after modification with γ-aminopropyltriethoxysilane, potassium hexatitanate whiskers have amino groups on their surface, which can electrostatically attract chromium ions in water, achieving targeted capture of anionic chromium.

Description

Technical Field

[0001] This invention belongs to the field of aerogel adsorption technology, specifically a method for preparing hydrophobically modified alginate. Background Technology

[0002] Chromium and its compounds are widely used in industrial production such as electroplating, metallurgy, chemicals, and leather. The resulting chromium-containing wastewater has become a significant source of water pollution. Chromium in wastewater mainly exists in two forms: Cr(VI) and Cr(III). Cr(VI) has strong oxidizing properties, high toxicity, and high mobility, posing serious threats to human health and the ecological environment. Long-term exposure or ingestion can lead to skin damage, respiratory diseases, and even cancer. Although Cr(III) has lower toxicity, excessive accumulation can also adversely affect aquatic organisms and the soil environment. Therefore, the efficient treatment of chromium-containing wastewater has become an urgent need in the field of industrial environmental protection.

[0003] Currently, the main methods for treating chromium-containing wastewater include chemical reduction, precipitation, adsorption, and membrane separation. Among these, adsorption has become one of the mainstream technologies for the deep treatment of industrial chromium-containing wastewater due to its advantages such as simple operation, low cost, and no secondary pollution. In the selection of adsorbents, biomass adsorbents have received widespread attention due to their wide availability, environmental friendliness, and renewability. Biomass materials such as alginate and sodium lignosulfonate, rich in oxygen-containing functional groups, possess a certain chromium ion adsorption capacity and are widely used in adsorbent preparation.

[0004] However, existing biomass adsorbents still have many shortcomings in practical applications: traditional biomass adsorbents have low adsorption capacity, which is difficult to meet the needs of deep treatment of industrial chromium-containing wastewater; some biomass adsorbents have poor water solubility and are easily lost in aqueous solutions, resulting in low adsorbent utilization; the adsorption rate is slow and cannot achieve rapid removal of chromium ions; at the same time, most adsorbents can only achieve simple enrichment of chromium ions, and it is difficult to convert highly toxic Cr(VI) into low-toxic Cr(III) and fix it stably, which poses a risk of secondary pollution. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing hydrophobically modified alginate. The hydrophobically modified alginate of this invention can directionally adsorb chromium-containing wastewater, which not only solves the problems of low capacity, poor water solubility and slow rate of traditional biomass adsorbents, but also achieves full coverage adsorption of chromium by utilizing the synergistic effect of multiple groups. It has good adsorption capacity and stability in the deep treatment of industrial chromium-containing wastewater.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing hydrophobically modified alginate includes the following steps: Step 1: Sodium lignosulfonate and sodium alginate are activated and solubilized using lithium chloride and N,N-dimethylformamide. Triethylamine is used as the acid-binding catalyst, and pyromellitic dianhydride is used as the esterification grafting agent to induce an esterification grafting reaction between sodium lignosulfonate and sodium alginate molecules. At the same time, a benzene ring hydrophobic group is introduced to obtain a sodium lignosulfonate-g-alginate graft copolymer.

[0007] Step 2: Modified potassium hexatitanate whiskers are obtained by dehydration condensation of γ-aminopropyltriethoxysilane with hydroxyl groups on the surface of potassium hexatitanate whiskers after hydrolysis.

[0008] Step 3: Using sodium dodecylbenzenesulfonate as a foaming agent, a stable foam system is formed in the solution of sodium lignosulfonate-g-alginate graft copolymer. Modified potassium hexatitanate whiskers are used as nano-pore-forming agents. By utilizing the physical occupancy and support of rigid whiskers, a multi-level porous structure is formed in the gel network. Then, under the action of calcium chloride, they are chelated and cross-linked to obtain hydrophobic modified alginate.

[0009] Furthermore, the specific preparation steps of the sodium lignosulfonate-g-alginate graft copolymer are as follows: Lithium chloride and N,N-dimethylformamide were stirred and mixed to obtain an active liquid with a mass fraction of 12%. Sodium lignosulfonate and the active liquid were added to a reaction vessel and stirred for 40-50 min under a nitrogen atmosphere, at 95-100℃ and 500-600 r / min. The mixture was then cooled to room temperature, and pyromellitic dianhydride, sodium alginate and triethylamine were added. The mixture was then heated to 70-80℃ and stirred for 24-26 h. The mixture was centrifuged at 9000-10000 r / min for 6-8 min, filtered, and the supernatant was retained. Isopropanol was added to the supernatant, and the mixture was centrifuged at 9000-10000 r / min for 6-8 min, filtered, and the filter cake was washed 2-4 times with deionized water and anhydrous ethanol, respectively. The mixture was then vacuum dried at 60-70℃ for 1-2 h to obtain sodium lignosulfonate-g-alginate graft copolymer.

[0010] Furthermore, the ratio of sodium lignosulfonate, active liquid, pyromellitic dianhydride, sodium alginate, triethylamine, and isopropanol is 30-40g: 350-500mL: 20-30g: 70-90g: 12-15g: 7-8L.

[0011] Furthermore, the specific preparation steps for modified potassium hexatitanate whiskers are as follows: Ethanol and deionized water were added to a reaction vessel and stirred for 30-40 min at 60-70℃ and 400-500 r / min. The pH was then adjusted to 5-7 with acetic acid, followed by the addition of γ-aminopropyltriethoxysilane. Stirring was continued for 2-4 h. Potassium hexatitanate whiskers with an average diameter of 0.5 μm and an average length of 6 μm were added and ultrasonically dispersed for 40-60 min. The mixture was allowed to stand naturally for 40-50 min, filtered, and the product was washed 2-4 times with deionized water and vacuum dried at 120-130℃ for 1-2 h to obtain modified potassium hexatitanate whiskers.

[0012] Furthermore, the ratio of ethanol, deionized water, γ-aminopropyltriethoxysilane and potassium hexatitanate whiskers is 1000-1200mL: 120-130mL: 40-50g: 120-130g.

[0013] Furthermore, the specific preparation steps for hydrophobically modified alginate are as follows: Sodium dodecylbenzenesulfonate, sodium lignosulfonate-g-alginate graft copolymer, and N,N-dimethylformamide were added to a reactor and stirred for 30-40 min at 60-70℃ and 400-500 r / min. Then, modified potassium hexatitanate whiskers were added as nanopore-forming agents, and sodium carbonate was added to adjust the pH to 6-8. Stirring was continued for 60-70 min, and then 5-6% (w / w) calcium chloride solution was added. Stirring was continued for 24-26 h. The product was washed with deionized water until neutral to obtain hydrophobic modified alginate.

[0014] Furthermore, the ratio of sodium dodecylbenzenesulfonate, sodium lignosulfonate-g-alginate graft copolymer, N,N-dimethylformamide, modified potassium hexatitanate whiskers, and calcium chloride solution is 0.3-0.5g: 100-120g: 800-900mL: 0.2-0.4g: 20-30mL.

[0015] The beneficial effects of this invention are: 1. The hydrophobically modified alginate of the present invention can directionally adsorb chromium-containing wastewater, which not only solves the problems of low capacity, poor water solubility and slow rate of traditional biomass adsorbents, but also achieves full coverage adsorption of chromium by utilizing the synergistic effect of multiple groups. It has good adsorption capacity and stability in the deep treatment of industrial chromium-containing wastewater.

[0016] 2. This invention utilizes the oxygen-containing groups abundant in sodium lignosulfonate and sodium alginate, which can both strongly complex and electrostatically adsorb chromium ions, and provide sites for subsequent chromium ion reduction. Furthermore, after modification with γ-aminopropyltriethoxysilane, potassium hexatitanate whiskers have amino groups on their surface, which can electrostatically attract chromium ions in water, achieving targeted capture of anionic chromium. Sodium lignosulfonate has natural reducing properties, which can reduce highly toxic and easily migrating Cr(VI) in situ to less toxic and easily fixed Cr(III). The reduced Cr(III) is immediately and firmly complexed and fixed by carboxyl and sulfonic acid groups, preventing re-oxidation or release back into the water, thus truly achieving harmlessness, rather than simply enrichment.

[0017] 3. This invention uses modified potassium hexatitanate whiskers as a nanoporous agent, which can construct abundant pores in the alginate system, increase the specific surface area, promote smooth mass transfer channels, and enable chromium ions to diffuse rapidly into the interior of the material, significantly improving the adsorption rate. The three-dimensional hydrogel network formed by calcium ion crosslinking solves the problem of pure sodium alginate being easily soluble in water and easily lost. It is structurally stable in chromium-containing wastewater, does not collapse or dissolve, and the whiskers themselves are rigid enough to support the gel skeleton and prevent swelling and collapse. The pore structure can also be maintained for a long time. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: A method for preparing hydrophobically modified alginate, comprising the following steps: S1: Lithium chloride and N,N-dimethylformamide were stirred and mixed to obtain an active solution with a mass fraction of 12%; 30g of sodium lignosulfonate and 350mL of the active solution were added to a reaction vessel and stirred for 40min under a nitrogen atmosphere, at 95℃ and 500r / min. The mixture was then cooled to room temperature, and 20g of pyromellitic dianhydride, 70g of sodium alginate and 12g of triethylamine were added. The mixture was then heated to 70℃ and stirred for 24h. The mixture was centrifuged at 9000r / min for 6min, filtered, and the supernatant was retained. 7L of isopropanol was added to the supernatant, and the mixture was centrifuged at 9000r / min for 6min, filtered, and the filter cake was washed twice with deionized water and anhydrous ethanol, respectively. The mixture was then vacuum dried at 60℃ for 1h to obtain the sodium lignosulfonate-g-alginate graft copolymer.

[0020] S2: Add 1000 mL of ethanol and 120 mL of deionized water to the reaction vessel, stir for 30 min at 60 °C and 400 r / min, then adjust the pH to 5 with acetic acid, add 40 g of γ-aminopropyltriethoxysilane, continue stirring for 2 h, add 120 g of potassium hexatate whiskers with an average diameter of 0.5 μm and an average length of 6 μm, disperse by ultrasonication for 40 min, let stand naturally for 40 min, filter, wash the product twice with deionized water, and vacuum dry at 120 °C for 1 h to obtain modified potassium hexatate whiskers.

[0021] S3: 0.3g sodium dodecylbenzenesulfonate, 100g sodium lignosulfonate-g-alginate graft copolymer and 800mL N,N dimethylformamide were added to a reaction vessel and stirred at 60℃ and 400r / min for 30min. Then, 0.2g modified potassium hexatitanate whiskers were added as nanopore-forming agents, sodium carbonate was added to adjust the pH to 6, and stirring was continued for 60min. Then, 20mL of 5% calcium chloride solution was added and stirring was continued for 24h. The product was washed with deionized water until neutral to obtain hydrophobic modified alginate.

[0022] Example 2: A method for preparing hydrophobically modified alginate, comprising the following steps: S1: Lithium chloride and N,N-dimethylformamide were stirred and mixed to obtain an active solution with a mass fraction of 12%. 35g of sodium lignosulfonate and 425mL of the active solution were added to a reaction vessel and stirred for 45min under a nitrogen atmosphere, at 97.5℃ and 550r / min. The mixture was then cooled to room temperature, and 25g of pyromellitic dianhydride, 80g of sodium alginate and 13.5g of triethylamine were added. The mixture was then heated to 75℃ and stirred for 25h. The mixture was centrifuged at 9500r / min for 7min, filtered, and the supernatant was retained. 7.5L of isopropanol was added to the supernatant, and the mixture was centrifuged at 9500r / min for 7min. The mixture was filtered, and the filter cake was washed three times with deionized water and three times with anhydrous ethanol. The mixture was then vacuum dried at 65℃ for 1.5h to obtain the sodium lignosulfonate-g-alginate graft copolymer.

[0023] S2: Add 1100 mL of ethanol and 125 mL of deionized water to the reaction vessel, stir for 35 min at 65 °C and 450 r / min, then adjust the pH to 6 with acetic acid, then add 45 g of γ-aminopropyltriethoxysilane, continue stirring for 3 h, add 125 g of potassium hexatite whiskers with an average diameter of 0.5 μm and an average length of 6 μm, ultrasonically disperse for 50 min, let stand naturally for 45 min, filter, wash the product three times with deionized water, and vacuum dry at 125 °C for 1.5 h to obtain modified potassium hexatite whiskers.

[0024] S3: 0.4 g sodium dodecylbenzene sulfonate, 110 g sodium lignosulfonate-g-alginate graft copolymer and 850 mL N,N dimethylformamide were added to a reaction vessel and stirred at 65 °C and 450 r / min for 35 min. Then, 0.3 g modified potassium hexatitanate whiskers were added as nanopore-forming agents, sodium carbonate was added to adjust the pH to 7, and stirring was continued for 65 min. Then, 25 mL of 5.5% calcium chloride solution was added and stirring was continued for 25 h. The product was washed with deionized water until neutral to obtain hydrophobic modified alginate.

[0025] Example 3: A method for preparing hydrophobically modified alginate, comprising the following steps: S1: Lithium chloride and N,N-dimethylformamide were stirred and mixed to obtain an active solution with a mass fraction of 12%; 40g of sodium lignosulfonate and 500mL of the active solution were added to a reaction vessel and stirred for 50min under a nitrogen atmosphere, 100℃ and 600r / min. The mixture was then cooled to room temperature, and 30g of pyromellitic dianhydride, 90g of sodium alginate and 15g of triethylamine were added. The mixture was then heated to 80℃ and stirred for 26h. The mixture was centrifuged at 10000r / min for 8min, filtered, and the supernatant was retained. 8L of isopropanol was added to the supernatant, and the mixture was centrifuged at 10000r / min for 8min. The mixture was then filtered, and the filter cake was washed 4 times with deionized water and anhydrous ethanol, respectively. The mixture was then vacuum dried at 70℃ for 2h to obtain the sodium lignosulfonate-g-alginate graft copolymer.

[0026] S2: Add 1200 mL of ethanol and 130 mL of deionized water to the reaction vessel, stir for 40 min at 70 °C and 500 r / min, then adjust the pH to 7 with acetic acid, add 50 g of γ-aminopropyltriethoxysilane, continue stirring for 4 h, add 130 g of potassium hexatate whiskers with an average diameter of 0.5 μm and an average length of 6 μm, ultrasonically disperse for 60 min, let stand naturally for 50 min, filter, wash the product 4 times with deionized water, and vacuum dry at 130 °C for 2 h to obtain modified potassium hexatate whiskers.

[0027] S3: 0.5g sodium dodecylbenzenesulfonate, 120g sodium lignosulfonate-g-alginate graft copolymer and 900mL N,N dimethylformamide were added to a reaction vessel and stirred at 70℃ and 500r / min for 40min. Then, 0.4g modified potassium hexatitanate whiskers were added as nanopore-forming agents, sodium carbonate was added to adjust the pH to 8, and stirring was continued for 70min. Then, 30mL of 6% calcium chloride solution was added and stirring was continued for 26h. The product was washed with deionized water until neutral to obtain hydrophobic modified alginate.

[0028] Comparative Example 1: Based on Example 3, the sodium lignosulfonate-g-alginate graft copolymer in step S3 was replaced with sodium alginate.

[0029] Comparative Example 2: Based on Example 3, the modified potassium hexatitanate whiskers in step S3 were discarded.

[0030] Performance tests were conducted on Examples 1-3 and Comparative Examples 1-2, and the results are shown in Table 1. For the adsorption performance test, the prepared aerogel was used for the adsorption experiment of chromium (III) ions. The pH value of the 0.1M chromium (III) ion solution was adjusted to 5.0, and the contact time was set to 2h to evaluate its adsorption efficiency.

[0031] Table 1 , As shown in Table 1, the pure sodium alginate in Comparative Example 1 only contains carboxyl coordination sites and lacks multiple chelating groups such as sulfonic acid groups and phenolic hydroxyl groups brought by sodium lignin sulfonate. The complexation and electrostatic adsorption capacity of chromium ions is greatly weakened. Therefore, the adsorption capacity and efficiency are far lower than those of the examples. The system lacks the natural reduction sites of sodium lignin sulfonate and cannot reduce the highly toxic Cr(VI) to the less toxic Cr(III). The chromium ions are simply adsorbed and enriched, and are easily re-desorbed and migrated, failing to achieve a truly harmless treatment effect. Without the hydrophobic grafting modification of pyromellitic dianhydride, the surface of the material is too hydrophilic, and a dense hydrated film is formed at the interface, which hinders the diffusion of chromium ions to the adsorption sites, further reducing the adsorption rate and utilization rate. Without the molecular support and hydrophobic regulation of sodium lignin sulfonate, the pure calcium alginate gel is prone to excessive swelling and partial dissolution and loss in wastewater. The skeleton is easily deformed after adsorption, resulting in poor recyclability.

[0032] In Comparative Example 2, the lack of nanoporous structure and framework support resulted in collapsed and blocked pores. The absence of the physical pore-forming and supporting effect of rigid potassium hexatitanate whiskers led to fewer internal pores and a lower specific surface area in the alginate gel. Furthermore, the gel was prone to swelling, collapse, and pore blockage during adsorption, making it difficult for chromium ions to diffuse rapidly into the material. Consequently, the adsorption kinetics were poor. The amino groups on the surface of the silane-modified whiskers could target and capture chromium ions. Removing this component resulted in a lack of synergistic adsorption sites in the system, significantly reducing the total adsorption capacity and adsorption efficiency. The rigidity-enhancing effect of the inorganic whiskers disappeared, and the alginate hydrogel framework was soft and easily deformed. Its structure was easily damaged during water disturbance and long-term adsorption, making it impossible to maintain continuous and stable adsorption performance.

[0033] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing hydrophobically modified alginate, characterized in that, Includes the following steps: Step 1: Sodium lignosulfonate and sodium alginate were activated and solubilized using lithium chloride and N,N-dimethylformamide. Triethylamine was used as the acid-binding catalyst, and pyromellitic dianhydride was used as the esterification grafting agent to induce an esterification grafting reaction between sodium lignosulfonate and sodium alginate molecules. At the same time, a hydrophobic group of benzene ring was introduced to obtain sodium lignosulfonate-g-alginate graft copolymer. Step 2: Modified potassium hexatitanate whiskers are obtained by dehydration condensation of γ-aminopropyltriethoxysilane with hydroxyl groups on the surface of potassium hexatitanate whiskers after hydrolysis. Step 3: Using sodium dodecylbenzenesulfonate as a foaming agent, a stable foam system is formed in the solution of sodium lignosulfonate-g-alginate graft copolymer. Modified potassium hexatitanate whiskers are used as nano-pore-forming agents. By utilizing the physical occupancy and support of rigid whiskers, a multi-level porous structure is formed in the gel network. Then, under the action of calcium chloride, they are chelated and cross-linked to obtain hydrophobic modified alginate.

2. The method for preparing hydrophobically modified alginate according to claim 1, characterized in that, The specific preparation steps of the sodium lignosulfonate-g-alginate graft copolymer are as follows: Lithium chloride and N,N-dimethylformamide were stirred and mixed to obtain an active liquid with a mass fraction of 12%. Sodium lignosulfonate and the active liquid were added to a reaction vessel and stirred for 40-50 min under a nitrogen atmosphere, at 95-100℃ and 500-600 r / min. The mixture was then cooled to room temperature, and pyromellitic dianhydride, sodium alginate and triethylamine were added. The mixture was then heated to 70-80℃ and stirred for 24-26 h. The mixture was centrifuged at 9000-10000 r / min for 6-8 min, filtered, and the supernatant was retained. Isopropanol was added to the supernatant, and the mixture was centrifuged at 9000-10000 r / min for 6-8 min, filtered, and the filter cake was washed 2-4 times with deionized water and anhydrous ethanol, respectively. The mixture was then vacuum dried at 60-70℃ for 1-2 h to obtain sodium lignosulfonate-g-alginate graft copolymer.

3. The method for preparing hydrophobically modified alginate according to claim 2, characterized in that, The ratio of sodium lignosulfonate, active liquid, pyromellitic dianhydride, sodium alginate, triethylamine and isopropanol is 30-40g: 350-500mL: 20-30g: 70-90g: 12-15g: 7-8L.

4. The method for preparing hydrophobically modified alginate according to claim 1, characterized in that, The specific preparation steps for the modified potassium hexatitanate whiskers are as follows: Ethanol and deionized water were added to a reaction vessel and stirred for 30-40 min at 60-70℃ and 400-500 r / min. The pH was then adjusted to 5-7 with acetic acid, followed by the addition of γ-aminopropyltriethoxysilane. Stirring was continued for 2-4 h. Potassium hexatitanate whiskers with an average diameter of 0.5 μm and an average length of 6 μm were added and ultrasonically dispersed for 40-60 min. The mixture was allowed to stand naturally for 40-50 min, filtered, and the product was washed 2-4 times with deionized water and vacuum dried at 120-130℃ for 1-2 h to obtain modified potassium hexatitanate whiskers.

5. The method for preparing hydrophobically modified alginate according to claim 4, characterized in that, The ratio of ethanol, deionized water, γ-aminopropyltriethoxysilane and potassium hexatitanate whiskers is 1000-1200mL: 120-130mL: 40-50g: 120-130g.

6. The method for preparing hydrophobically modified alginate according to claim 1, characterized in that, The specific preparation steps of the hydrophobically modified alginate are as follows: Sodium dodecylbenzenesulfonate, sodium lignosulfonate-g-alginate graft copolymer, and N,N-dimethylformamide were added to a reactor and stirred for 30-40 min at 60-70℃ and 400-500 r / min. Then, modified potassium hexatitanate whiskers were added as nanopore-forming agents, and sodium carbonate was added to adjust the pH to 6-8. Stirring was continued for 60-70 min, and then 5-6% (w / w) calcium chloride solution was added. Stirring was continued for 24-26 h. The product was washed with deionized water until neutral to obtain hydrophobic modified alginate.

7. The method for preparing hydrophobically modified alginate according to claim 6, characterized in that, The ratio of sodium dodecylbenzenesulfonate, sodium lignosulfonate-g-alginate graft copolymer, N,N-dimethylformamide, modified potassium hexatitanate whiskers, and calcium chloride solution is 0.3-0.5g: 100-120g: 800-900mL: 0.2-0.4g: 20-30mL.