JP2004358292A - Purifying agent using chitin and chitosan derivative hydrogel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem: natural materials such as starch, chitin, and chitosan, although there is a method for synthesizing a water absorbent by chemical crosslinkage by using a reagent, these chemical substances are strongly poisonous, cause the environmental pollution of a working site, and remain in the water absorbent. <P>SOLUTION: Water is added to CM (carboxymethyl)-chitin and/or CM-chitosan, and the mixture is kneaded sufficiently into paste. Water absorbent hydrogel obtained by irradiating the paste with ionizing radiation adsorbs harmful metals which are desorbed by pH adjustment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２３】
（実施例２）
ＣＭ−キチン３０％／水７０％の割合で混合したペースト状試料をシート状に加工し、電子線の７５ｋＧｙ照射によりＣＭ−キチンハイドロゲルを合成した。ゲル分率６５％の得られたハイドロゲルシートは実施例１と同じ方法により金属の吸着を行った。
【００２４】
【表２】

【００２５】
以上の結果から、放射線照射により得たＣＭ−キトサン及びＣＭ−キチンハイドロゲルは、親水性が大きいため金属イオンを容易に吸着した。これらは０．１モルの塩酸で洗うことにより銅イオンを脱離することができるため、繰り返して使用することができる。
【００２６】
【発明の効果】
ＣＭ−キチン及びＣＭ−キトサンハイドロゲルは、金属で汚染された工場廃水や湖水の有害金属及び腐敗臭の浄化に応用できる。また、海水や水溶液中に溶解している希少金属の捕集もこの技術は応用できる。これらの捕集材は、生分解性の天然由来であるため、使用後の処理が容易であるという利点があり、発展が期待できる吸着剤である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a chitin derivative, a chitosan derivative, and a hydrogel that remove harmful metals and putrefaction odor in swamps, industrial wastewater, hot spring water, and mine wastewater. The material is a crosslinked hydrogel obtained by irradiation of high-concentration paste-like water-soluble CM-chitin (carboxymethylated chitin) and CM-chitosan (carboxylated chitosan). The hydrogel of the present invention is a polymer water-absorbing gel which is made of a hydrophilic polymer and is easily compatible with water, so that it is easy to remove contaminants in water and is useful for environmental protection.
[0002]
[Prior art]
The water-absorbing gel is made of sodium acrylate, starch obtained by graft polymerization of acrylic acid, polyethylene oxide, polyvinyl alcohol, acrylamide, or polyvinyl pyrrolide aqueous solution, which is irradiated with ionizing radiation and polymer absorption obtained by a crosslinking reaction. There is a gel. There is also a water-absorbing gel obtained by crosslinking a water-soluble polymer by a chemical treatment with formalin, glutaraldehyde, or the like. Water-absorbing gels are used in large quantities in the fields of agriculture, medical care and hygiene products. It is expected that production will increase in the future. It is known that CM-chitin and CM-chitosan, when irradiated with water in a paste state having a concentration of 10% or more, undergo a crosslinking reaction and become a biodegradable water-absorbing gel (for example, Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Application No. 2001-362131 [0004]
[Problems to be solved by the invention]
BACKGROUND ART A water-absorbing gel obtained by crosslinking a water-soluble polymer such as sodium acrylate is widely used in sanitary articles such as disposable diapers. However, infants and disposable diapers used in hospitals are mainly disposed of by incineration. Placing wet diapers etc. in an incinerator lowers the combustion temperature and leads to the generation of dioxins. When buried in soil, it does not decompose and stays for a long time.
[0005]
For natural materials such as starch, chitin and chitosan, there is a method of synthesizing a water absorbing agent by chemical crosslinking using a reagent such as formalin, glutaraldehyde, epichlorohydrin and the like. However, these chemicals are highly toxic and have problems such as environmental pollution at work sites and residual in water absorbing agents. For this reason, there is a demand for a water-absorbing agent made of a material that does not burden the environment. Biodegradable polymers that are decomposed and digested by microorganisms in soil and are easy to treat after use have attracted attention as environmentally friendly materials. Since the hydrogel is made of a hydrophilic polymer and is easily compatible with water, introduction of a functional group that easily binds to a metal is considered to be applicable to removal of harmful substances in water.
[0006]
[Means for Solving the Problems]
In the present invention, water is added to CM-chitin and / or CM-chitosan to form a well-kneaded paste (paste), and the superabsorbent hydrogele obtained by irradiating with ionizing radiation adsorbs harmful metals. Adsorbed harmful metals are desorbed by pH adjustment.
[0007]
As described above, it is known that when irradiated with CM-chitin and CM-chitosan in a paste state having a concentration of 10% or more with water, a cross-linking reaction occurs to form a biodegradable water-absorbing gel. In order to promote the practical use of this gel, intensive studies were conducted to clarify the adsorption characteristics of CM-chitin and CM-chitosan hydrogel for metal ions and putrefactive substances.
[0008]
In the present invention, CM-chitin, CM-chitosan and a mixture thereof, which have been radiation-crosslinked in a paste form, collect and remove harmful metals and putrefactive odor substances, thereby solving the problem of the present invention.
[0009]
The crosslinking reaction of the CM-chitin derivative, the CM-chitosan derivative and a mixture thereof occurs in a paste form having a high concentration of 10 to 60%. At a concentration of 60% or more, water is not uniformly dispersed, so that radiation crosslinking hardly occurs.
[0010]
The hydrogel obtained by the paste-like crosslinking captures metal ions in water, and has developed a technology capable of desorbing the collected metal by adjusting the pH to an acidic side, thereby completing the present invention.
[0011]
The metals that can be collected are as follows.
Alkali metals such as sodium and potassium, alkaline earth metals such as magnesium and calcium, water such as copper, manganese, zinc, nickel, lead, cadmium, iron, uranium, vanadium, mercury, chromium, titanium, selenium, arsenic, and boron Metal ions or metal compound ions soluble in water.
[0012]
The hydrogel obtained by cross-linking high-concentration pastes of CM-chitin and CM-chitosan with ionizing radiation is preferably γ-rays from cobalt-60, electron beams and X-rays by an accelerator for industrial production. The electron accelerator is most preferably a medium energy to high energy electron accelerator capable of irradiating a thick object with an acceleration voltage of 1 MeV or more. If pressure is applied to the sample before irradiation and the sample is processed into a film shape, the electron beam passes through even a low energy electron accelerator of 1 MeV or less, so that a hydrogel can be obtained by crosslinking with radiation. Oxygen during irradiation has little effect on cross-linking, but it is desirable to irradiate by covering the top surface with a plastic film such as polyester to prevent evaporation of water during irradiation and to suppress a decrease in cross-linking density. .
[0013]
The ionizing radiation of the present invention is a gamma ray, an electron beam, or an X-ray, and the irradiation dose is 0.1 to 1,000 kGy.
[0014]
The materials used in the present invention are CM-chitin and CM-chitosan which dissolve in water at room temperature to form a paste (paste).
[0015]
CM-chitin is carboxymethylated chitin obtained from crab and shrimp shells, and CM-chitosan is deacetylated and carboxymethylated chitin. Compounds having a degree of substitution by carboxymethylation of from 0.05 to 1.0 can be synthesized and dissolved in water.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
The gel fraction indicating the cross-linking ratio of CM-chitosan and CM-chitin gel obtained by irradiation in the paste state and the method of metal adsorption and desorption are shown in the following (1) and (2).
[0017]
(1) The hydrogel obtained after irradiation with the gel fraction is freeze-dried and dried in a vacuum dryer at 50 ° C. until a constant weight is obtained. The dried sample is placed in a 200 mesh stainless steel net and immersed in a large amount of water for 48 hours. Since the non-crosslinked dissolved components move to the water side, only the gel components remain in the wire mesh. The stainless steel mesh containing the gel is immersed in methanol for 1 hour, and then dried at 50 ° C. for 24 hours. The gel fraction is calculated by the following equation.
[0018]
Gel fraction (%) = (Gel weight excluding dissolved components / Initial dry weight) × 100
(2) Measurement of metal adsorption and desorption The gel obtained by irradiation in paste form was dried, immersed in an aqueous solution containing a known concentration of metal ions for a certain period of time, and the UV absorption of the aqueous solution reduced by adsorption was measured per gram of gel. The amount of metal adsorbed on the sample was determined.
[0019]
The metal adsorbed on the crosslinked CM-chitin and CM-chitosan was eliminated by washing with 0.1 M hydrochloric acid.
[0020]
Example (Comparative Example)
(Comparative Example 1)
A 0.005 molar (320 ppm copper ion) aqueous solution of copper sulfate was prepared (pH 5.5), and 2 g of unirradiated CM-chitosan powder was added thereto. CM-chitosan adsorbed copper ions, and the blue color of the aqueous solution decreased over time. However, it takes time and effort to collect the precipitate, and it is difficult to remove the metal.
[0021]
(Example 1)
A paste-like sample mixed at a ratio of 30% CM-chitosan / 70% water was processed into a sheet, and a CM-chitosan hydrogel was synthesized by irradiating 100 kGy with an electron beam. The obtained sheet having a gel fraction of 45% was cut into about 5 mm square, and 2 g of the sheet was immersed in the same copper ion aqueous solution as in Comparative Example 1 for 180 minutes. The blue color due to copper ions in the aqueous solution gradually decreased due to the adsorption of the CM-chitosan gel. The adsorption of copper ions on the CM-chitosan hydrogel is as shown in Table 1.
[0022]
[Table 1]

[0023]
(Example 2)
A paste-like sample mixed at a ratio of 30% CM-chitin / 70% water was processed into a sheet, and a CM-chitin hydrogel was synthesized by irradiating 75 kGy with an electron beam. The obtained hydrogel sheet having a gel fraction of 65% was subjected to metal adsorption by the same method as in Example 1.
[0024]
[Table 2]

[0025]
From the above results, CM-chitosan and CM-chitin hydrogel obtained by irradiation with radiation were large in hydrophilicity and easily adsorbed metal ions. These can be used repeatedly because copper ions can be eliminated by washing with 0.1 mol of hydrochloric acid.
[0026]
【The invention's effect】
CM-chitin and CM-chitosan hydrogel can be applied to purification of toxic metals and putrefactive odors in industrial wastewater and lake water contaminated with metals. This technique can also be applied to the collection of rare metals dissolved in seawater or an aqueous solution. Since these trapping materials are biodegradable natural sources, they have the advantage of easy treatment after use, and are adsorbents that can be expected to develop.

Claims (11)

A purifying agent comprising a hydrogel of a chitosan derivative, a chitin derivative or a mixture thereof obtained by radiation crosslinking and capable of desorbing a metal or a putrefactive substance after adsorption. A chitin derivative and a chitosan derivative, (a) a derivative in which a part of the hydroxyl group is substituted by alkylation with a methyl, ethyl, carboxymethyl, hydroxypropyl group or at least two groups thereof, (b) one of the hydroxyl groups Part of which is substituted by allylation with acetyl, hexanoyl, decanoyl, formyl, propionyl, bityryl, benzoyl group or at least two groups thereof, (c) part of the amino group is methyl, ethyl, carboxymethyl, A hydroxypropyl group or a derivative substituted by alkylation with at least two groups thereof, (d) converting part of an amino group to acetyl, hexanoyl, decanoyl, formyl, propionyl, bityryl, benzoyl, or at least two groups thereof; By (E) a derivative in which a part of the amino group is substituted by sulfation, nitration, or formation of a ship base having a sulfone group, or (f) both a hydroxyl group and an amino group. 2. The purifying agent according to claim 1, wherein the purifying agent is a derivative partially substituted with the functional group. The purifying agent according to claim 1, wherein the chitin and the chitosan derivative used are carboxymethyl chitin (CM-chitin) and carboxymethyl chitosan (CM-chitosan), and the degree of substitution is 0.1 to 1.0. The purifying agent according to any one of claims 1 to 3, wherein the ionizing radiation used for crosslinking is a γ-ray, an electron beam, or an X-ray, and the dose is 0.1 to 1,000 kGy. The purifying agent according to any one of claims 1 to 4, wherein the radiation crosslinking condition is a hydrogel obtained by kneading chitin and a chitosan derivative well with water and irradiating with ionizing radiation in a paste form of 5% or more. The purifying agent according to any one of claims 1 to 5, wherein the chitin derivative or the chitosan derivative may be mixed in any ratio. The purifying agent according to claim 1, wherein the metal to be collected is dissolved in water and an organic solvent. The purifying agent according to claim 8, wherein the metal collection is soil and liquid in which the metal is dissolved, such as soil, water, seawater, industrial wastewater, hot spring water, and mine wastewater. 2. The purifying agent according to claim 1, which adsorbs humic acid which is present in water and emits putrefactive odor. The purifying agent according to any one of claims 7 to 9, wherein the metal and the putrefaction odor are removed by contacting a sheet or particles of a hydrogel of the chitin derivative, the chitosan derivative and a mixture thereof. The purifying agent according to any one of claims 1 to 10, wherein the metal adsorbed on the CM-chitosan and CM-chitin hydrogel is desorbed and recovered by soaking the pH in an acidic range, and the hydrogel is used repeatedly.