KR20000052018A - The Manufacturing Method for a High Molecular Coagulant of Chitosan Group - Google Patents

Abstract

PURPOSE: A preparation method of chitosan-based coagulant for wastewater treatment is provided, which minimizes the rate of acid hydrolysis and the decrease of viscosity by controlling ion strength, concentration and pH of the chitosan-based coagulant, thereby consequently activating microorganisms in an aeration tank. CONSTITUTION: A process comprises the steps of: (A) adding (i) 0.2-0.45 wt.% of a salt for controlling ion strength selected from the group consisting of water soluble chloride, nitrate, sulfides, acetate (ii) 0.8-1.5 wt.% of chitosan having degree of polymerization of 4000-10000 and degree of deacetylation of 80-85% to a solvent. (B) adjusting pH of the solvent to be 4.5-5, followed by agitating.

Description

Manufacturing method for chitosan-based polymer coagulant {The Manufacturing Method for a High Molecular Coagulant of Chitosan Group}

The present invention relates to a method for producing a chitosan-based polymer coagulant, and more particularly, by adjusting the ionic strength pH, the degree of deacetylation of chitosan, the molecular weight, and the like to improve the viscosity reduction rate due to acid hydrolysis, thereby providing physical stability. It relates to a method for producing a chitosan-based polymer flocculant.

In today's wastewater treatment process, solids separation by flocculation is one of the widely used methods to secure more improved discharge water quality.

Conventional organic / inorganic polymer coagulant used as a coagulant for wastewater treatment is widely used in wastewater treatment process because of its high cohesiveness and economical efficiency, but it is contained in sludge or final dewatering sludge after use, so it is not rapidly reduced to nature when disposed. It has a disadvantage.

In particular, the organic synthetic polymer flocculant is accumulated in the return sludge in the wastewater treatment process, which causes a deterioration of the activity of the microorganisms in the aeration tank and the deterioration of the wastewater treatment efficiency.

As environmental pollution has recently emerged as a social problem, the development of more environmentally friendly polymer flocculant is required.

Chitosan is a biomass estimated to produce more than 100 billion tons annually on earth. Chitosan, which is already commercially available, has undergone alkaline saponification of N-acetyl group based on N-acetyl amino glucose composed of amino glucose units. Chitin is the starting material.

When the acetyl group is removed from the chitin by chemical or biological treatment, the acetyl group is converted into a free amino group (-NH ₂ ), and the pyranose unit of the glucosamine thus formed is a natural polymer connected by a myriad of β-1,4 bonds. Commercially used chitosan mainly has a degree of deacetylation of 60 to 90% and a mean degree of polymerization in the range of 500 to 10,000.

Already, chitosan ((1-4) -2-amino-deoxy-β-D-glucan) is a functional polymer containing many amine groups, and it is a bioabsorbable suture, artificial skin (Korean Journal of polymer, vol. 14, No.5, p527 ~ 533 (1990), Korean Journal of polymer, vol.14, No.4, p385 ~ 391 (1990)), immunostimulating agents, anti-cholesterol agents, tumor metastasis inhibitors, drug delivery media (Journal of the Korean Institute of Chemical Engineering, Vol. 36, No. 2, p24-256 (1998), Journal of the Korean Institute of Chemical Engineering, Vol. 36, No. 3, p484-490 (1998), Carbohydrate polymer, Vol.31, p141 ~ 148 (1996)), moisturizers, film-forming agents (Korean Journal of Food Science and Technology, Vol.24, No.6, p574 ~ 580 (1992)), texture modifiers, etc. Cosmetic field, key agent, functional additives (Food & Development, Vol. 33, No. 3, p36 (1998)), antimicrobial / antifungal agent (Polymers' Paper, Vol. 53, No. 1, p70 ~) 76 (1996), The Chemical Society of Japan, p48 ~ 53 (1996), Polymer Bulletin, 38, p387 ~ 3 93 (1997)), flocculants (water treatment technology (Japan), Vol. 38, No. 11 (1997), Bioindusty (1996)) and natural biodegradable materials have been studied a lot.

In particular, it has been used as a polymer flocculant for wastewater / wastewater treatment by applying the adsorption property of chitosan for a long time by utilizing the property as a cationic polymer electrolyte of high molecular weight band, and occupies the largest part of the application field of all chitosan.

However, chitosan is a polymer electrolyte having a free primary amino group, but it is not soluble in pure water, but soluble in diluted inorganic and organic acids, that is, dissolved in the dilute acid solvent by the solvation between amino and acid molecules of chitosan. It has

For this reason, a gradual molecular weight decrease occurs due to hydrolysis by dilute acid and water component (Macromol. Chem. Phys, Vol. 198, p471 ~ 484 (1997)) in the production of environmental flocculant, resulting in a decrease in coagulation activity and It has the disadvantage of shortening the shelf life.

Introduction of hydrophobic groups or other alkyl groups to chitosan polymer chains to impart physical stability of existing chitosan coagulants (International Journal of Biological Macromolecules, Vol. 19, p21-28 (1996), Polymer Science, Ser.B, Vol. 39, p259-263 (1997), Langmuir, Vol. 13, p4948-4952 (1997)), or by blending with other synthetic polymers, or by using high concentrations of chitosan Although there is a method of preventing or minimizing the rate of degradation, the introduction of other functional groups of the chitosan polymer chain may have an undesirable effect on microorganisms in biological treatment wastewater treatment plants, and may cause delays and inhibition of biodegradability.

In the case of blending with synthetic polymers, the accumulation of synthetic polymers by the return sludge into the aeration tank may occur, which may cause the deactivation of microorganisms by the synthetic polymers in the long term.

In addition, when chitosan is used in high concentrations, cohesion may occur due to aggregation of chitosan molecules in an acid atmosphere and above a certain concentration, and degradability due to intermolecular agglutination may cause a change in solid content and accumulation of microorganisms in the aeration tank. There may be an impact on.

In the present invention, in order to improve the viscosity decrease phenomenon due to the hydrolysis of chitosan, by changing the morphology of chitosan by adjusting the appropriate ionic strength, concentration, pH, etc. of the chitosan flocculant, imparting resistance to acid hydrolysis Accordingly, an object of the present invention is to provide a chitosan coagulant having physical property stability in terms of securing product safety through lowering acid hydrolysis rate and extending shelf life of chitosan.

In the present invention, the content of chitosan having a degree of polymerization of 4,000 to 10,000 deacetylation of 80 to 95% is 0.8 to 1.5% by weight, and the solvent pH is adjusted to 4.5 to 5.0 with 0.2 to 0.45% by weight of an ionic strength adjusting salt. It consists of stirring, dissolving and aging.

Hereinafter, the present invention will be described in detail.

Generally, in order to prepare a chitosan flocculant, it is dissolved in an acid solution of an appropriate concentration. At this time, the pH of the acid solution, the concentration of the chitosan, the molecular weight of the chitosan, etc. are important factors for the dissolution rate and the physical properties of the prepared solution. It becomes an important factor of molecular weight fall.

Chitosan is dissolved in the dilute acid solvent by the solvation between free amino groups and acid molecules of chitosan, and due to the linear structure of the chitosan molecule, a sharp increase in viscosity occurs due to the dissolution viscosity.

However, unlike the initial dissolution increase in viscosity, the molecular weight decreases due to acid hydrolysis over time after dissolution, which leads to a decrease in viscosity and loss of function as a flocculant.

Already, chitosan-related data show that the effect of hydrogen ion concentration and ionic strength in solution on the intrinsic viscosity of chitosan during the dissolution of chitosan (Carbohydrate Polymer, Vol. 34, p141 ~ 148 (1996)), especially the deacetylation of chitosan. Depending on the degree of saturation, concentration, and molecular weight, the behavior of the solution is accompanied (Biological Macromolecules, Vol. 19, p21 ~ 28 (1996)), and concentration-dependent self-aggregation tendency (Carbohydrate Polymer, Vol.31, p253 ~ 261 (1996)). And agglomeration of chitosan molecules (Carbohydrate Polymer, Vol. 32, p23 ~ 26 (1997)) due to the decrease in solvent power of the solvent with increasing temperature.

Therefore, in the present invention, by adjusting the appropriate pH and ionic strength in the preparation of the chitosan flocculant, the acid hydrolysis rate and solution by giving the minimum solubility of chitosan through the uniform dispersion of chitosan molecules rather than the complete solubilization of chitosan polymer in the solution The viscosity decrease of was minimized.

The degree of deacetylation of the chitosan used is preferably 80 to 95%, more preferably 85 to 90%. When the deacetylation degree is less than this range, the charge density may be lowered, thereby lowering the coagulation efficiency. When the deacetylation degree is exceeded, manufacturing difficulties, as well as molecular weight, may lower the coagulation efficiency.

The degree of polymerization of chitosan to be used is preferably 4,000 to 10,000, more preferably 5,000 to 7,000. If the degree of polymerization is less than this range, the sedimentation rate after flocculation is low during flocculation, and if it exceeds this range, the degree of deacetylation is lowered, thereby lowering the economic efficiency of wastewater treatment.

PH of the solvent used at the time of melt | dissolution is 4.5-5.0, Preferably it is 4.7-4.9.

If the pH is less than 4.5, the linearity of the chitosan polymer chain is increased, and the rate of acid hydrolysis is increased. If the pH is more than 5.0, the pre-aggregation precipitation may occur when the chitosan coagulant is introduced into the wastewater treatment process.

The salt added to adjust the ionic strength is 0.20 to 0.45% by weight, and salts used here include chlorides, nitrates, sulfides or acetates having excellent solubility in water, and alkali metal salts or ammonium metal salts. Etc.

As the metal salt, sodium chloride, sodium sulfate, ammonium chloride, potassium chloride, ammonium sulfate, or sodium acetate is used.

The amount of chitosan added is preferably 0.8 to 1.5% by weight, preferably 1.0 to 1.3% by weight relative to the total solution. If the amount of chitosan coagulant is less than 0.8% by weight, the use of chitosan coagulant increases, and if it exceeds 1.5% by weight, a network may be formed by aggregation between chitosan polymers. When applied, it takes a long time to dissolve but is uneconomical

The particle size of the chitosan used is less than 1 mm, more preferably 0.04 to 0.3 mm.

If the particle size is 1mm or more, the dissolution rate may be low, and the efficiency may be lowered.

An embodiment of the present invention is as follows.

<Example 1>

0.5% acetic acid was added to 2.0 g of chitosan to make 200 ml, and the mixture was dissolved at a stirring speed of 200 rpm for 4 hours, and then aged at room temperature for 12 hours. Since the viscosity decrease for 2 weeks at 37 ℃ was measured. The chitosan used at this time was 1,100,000 in molecular weight and 90.1% of deacetylation degree.

At this time, the initial viscosity of the prepared chitosan flocculant was 4,790 cps, pH was 4.36, and after 2 weeks, the final viscosity was 803 cps, and the viscosity drop rate was 83.2%.

<Example 2>

To 2.0 g of chitosan, pH 4.8% acetate was added to make 200 ml, and the mixture was dissolved at a stirring speed of 200 rpm for 4 hours and then aged at room temperature for 12 hours. Since the viscosity decrease for 2 weeks at 37 ℃ was measured. The chitosan used at this time was 1,100,000 in molecular weight and 90.1% of deacetylation degree. At this time, the initial viscosity of the prepared chitosan coagulant was 4,483cps, pH was 5.18, and after 2 weeks, the final viscosity was 1,387cps and the viscosity decrease rate was 69.1%.

<Example 3>

Chitosan 2.0g, sodium chloride 0.88g, pH 4.8 acetate acetate was added to 200ml, dissolved for 4 hours at a stirring speed of 200rpm and aged for 12 hours at room temperature.

Since the viscosity decrease for 2 weeks at 37 ℃ was measured. The chitosan used at this time was 1,100,000 in molecular weight and 90.1% of deacetylation degree. At this time, the initial viscosity of the prepared chitosan coagulant was 3,703 cps, pH was 5.16, and after 2 weeks, the final viscosity was 1,407 cps and the viscosity decrease rate was 62.0%.

Comparative Example 1

A chitosan coagulant was prepared in the same manner as in Example 1 except that 2.4 g of chitosan was added thereto. At this time, the initial viscosity of the prepared chitosan flocculant was 5,310 cps, pH was 4.36, and after 2 weeks, the final viscosity was 1,407 cps and the viscosity decrease rate was 74.0%.

Comparative Example 2

A chitosan flocculant was prepared in the same manner as in Example 3 except that 0.59 g of sodium chloride was added in Example 3. The initial viscosity of the prepared chitosan coagulant was 3510 cps, pH was 5.14, and after 2 weeks, the final viscosity was 963 cps, and the viscosity drop rate was 72.6%.

The chitosan polymer flocculant according to the present invention may replace the use of the inorganic / organic polymer flocculant currently used, and furthermore, the effect of preventing environmental pollution and increasing the activity of the microorganisms in the aeration tank during the introduction of the actual biological wastewater treatment process. It is expected to be able.

In addition to the above-mentioned use, it will be possible to apply the method to increase the physical stability rather than chemical modification of the natural polymer material in the future.

Claims (4)

The content of chitosan having a degree of polymerization of 4,000 to 10,000 and a degree of deacetylation of 80 to 95% is 0.8 to 1.5% by weight, and the solvent pH is adjusted to 4.5 to 5.0 with 0.2 to 0.45% by weight of an ionic strength adjusting salt. Method for producing a chitosan-based polymer coagulant, characterized in that the aging after dissolution. The method for preparing chitosan-based polymer coagulant according to claim 1, wherein the salt for adjusting the ionic strength is one selected from chloric acid, nitrate, sulfide, and acetate having excellent solubility in water. The method of producing a chitosan-based polymer coagulant according to claim 1, wherein the particle size of chitosan used is less than 1 mm. The method of producing a chitosan-based polymer coagulant according to claim 1, wherein the particle size of chitosan used is less than 1 mm.