JPH0459335B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing chitosan powder, and particularly to a method for producing chitosan powder with uniform particle size.

[Conventional technology]

Chitosan is a cationic polymer substance used as a flocculant. In this case, chitosan is in the form of a powder and is used after being dissolved in water, but if the particle sizes are not uniform, there will be differences in the amount of chitosan supplied and the rate of dissolution, making it impossible to obtain quantitative results. Chitosan is usually produced by deproteinizing and decalcifying the shells of crabs and shrimps to obtain chitin, and then deacetylating this chitin. It is necessary to grind the chitosan, or to grind it at the chitin stage, or to grind it after converting it to chitosan. However, in any of these methods, it is extremely difficult to make the powder particles uniform in size and shape.

Generally, even if each reaction to obtain chitosan is carried out carefully, the obtained chitosan still contains insoluble matter that does not dissolve in acid. This insoluble matter does not necessarily need to be removed, but may be required depending on the application. In order to remove the insoluble matter in chitosan, the insoluble matter is removed by dissolving the chitosan with an acid and purifying this solution by filtration or the like. Therefore, a method can be considered in which chitosan is recovered from a liquid from which insoluble matter has been removed by filtration or the like and powdered.

The following method can be considered as a method for recovering chitosan from an acid solution of chitosan from which insoluble matter has been removed.

An organic solvent such as acetone is added to an acid solution of chitosan to precipitate the acid salt of chitosan, which is dried by vacuum drying or the like and then pulverized.

Freeze-dry the chitosan acid solution as it is.

Chitosan is precipitated by adding an alkali to an acid solution of chitosan, and washed with deionized water to remove salts generated by the reaction between acid and alkali and excess alkali. After washing and dehydrating with an organic solvent,
Dry by vacuum drying or hot air drying,
Grind into powder.

[Problem that the invention seeks to solve]

However, in the above method, a large amount of organic solvent such as acetone is used, so there is a problem in terms of economic efficiency. Furthermore, since the excess amount of acid used to dissolve chitosan cannot be completely removed by organic solvents such as acetone, there is a problem of corrosion of equipment during vacuum drying.

In the method, when the molecular weight of chitosan is high,
Since it cannot be dissolved at a high concentration, it is necessary to freeze-dry a large amount of solution, which poses an economical problem. There is also the problem of corrosion of equipment due to acid.

In this method, since the precipitated chitosan is a fine and soft precipitate, it is difficult to wash it with deionized water. Further, it takes a long time to dry the precipitated chitosan under reduced pressure or with hot air. Furthermore, chitosan forms extremely hard lumps when dried;
There are problems such as difficulty in grinding and coloring of the powder yellow or brown.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an object of the present invention is to propose a method for producing chitosan powder with a uniform particle size through simple operations.

[Means for solving problems]

The present invention involves dissolving chitosan with an acid, adding an alkali to form a chitosan suspension, freezing and thawing this suspension to form chitosan into particles, and then desalting using deionized water and drying. This is a method for producing chitosan powder characterized by the following.

The raw material chitosan is deacetylated chitin obtained by deproteinizing and decalcifying the shells, shells, etc. of arthropods such as crabs and shrimps, and chitosan of any purity and molecular weight can be used. Particularly in the case of low-molecular-weight chitosan, the suspension of low-molecular-weight chitosan precipitated with an alkali has extremely fine chitosan particles and is difficult to desalt or dry powder. Particularly excellent effects can be obtained when powdering low molecular weight chitosan. Low molecular weight chitosan is obtained by adding hydrogen peroxide, nitrite ions, alkali, acid, etc. to naturally obtained chitosan to cleave glucoside bonds.

As the acid used to dissolve chitosan, any acid such as acetic acid that can dissolve chitosan can be used, and the acid is used as an aqueous solution. The concentration of acid in the acid solution in which chitosan is dissolved is 0.05 to 20% by weight, preferably 0.5 to 10% by weight, and the concentration of chitosan dissolved in this is 0.05 to 20% by weight, preferably
It is about 0.5 to 10% by weight.

It is preferable to remove insoluble matter from the acid solution in which chitosan is dissolved by filtration or the like before adding an alkali. There are no particular restrictions on the method for removing insoluble matter, but since the viscosity of the solution is high, filtration using a stainless steel wire mesh or the like is suitable.

An alkali is added to the acid solution of chitosan from which insoluble matter has been removed to precipitate the chitosan to form a suspension. The alkali used to precipitate chitosan is not particularly limited either, and sodium hydroxide, potassium hydroxide, etc. can be used. In this case, the pH should be 8 or higher, and is usually about PH8 to 11. By adding alkali, chitosan becomes a gel-like substance and precipitates, forming a highly viscous gel-like suspension. Sufficient stirring at the time of addition of the alkali is preferable because the gel-like material becomes particulate and becomes dispersed.

When the chitosan suspension thus produced is frozen, the development of ice crystals compresses the chitosan into uniform particles, and the water contained therein migrates toward the crystals and becomes concentrated. By melting this, non-adhesive and non-disintegrating chitosan particles are dispersed, and a low viscosity suspension consisting of particles of uniform particle size is obtained.

There is no particular limit to the freezing temperature, and it is usually between -10 and -
The temperature is around 40℃. In order to increase the size of chitosan particles, it is best to freeze them as slowly as possible, and the freezing time is about 20 to 50 hours.

Melting may be carried out by leaving it to stand naturally, or by heating it with hot water or the like.

The suspension after freezing and thawing is then desalted using deionized water. The method of solid-liquid separation and desalting is not particularly limited, such as a method of desalting by immersing in deionized water,
Possible methods include placing particulate chitosan in a column and continuously passing deionized water through it to desalt it. In this case, since the chitosan particles are granulated in a non-adhesive and non-disintegratable state, washing operations are easy and desalting is also easily performed. By this operation, impurities such as salts, excessive alkali, and extremely low molecular weight water-soluble chitosan contained in the chitosan particles are removed, and highly pure chitosan particles are obtained.

The desalted suspension is separated into solid and liquid and then dried to obtain chitosan powder. Any method can be used for solid-liquid separation, but the separation property is good.
The drying method is not particularly limited either, but freeze drying, or a method in which the solvent is replaced with an organic solvent and then dried under reduced pressure, etc. are preferable.

The chitosan powder produced in this way has a uniform particle size and a low content of impurities.

〔Effect of the invention〕

As described above, according to the present invention, since the chitosan suspension is desalted after freezing and thawing, it is possible to produce chitosan powder with low impurity content and uniform particle size through simple operations.

〔Example〕

Examples of the present invention will be described below. In addition, % is weight %.

The particle size distribution of the raw material chitosan was measured using a sieve. The range was from 9 meshes passed to 200 meshes remaining, and the average particle size was between 16 and 24 meshes. The physical properties of this chitosan are shown below.

Evaporation residue *1/product = 90.4% Ash content *2/evaporation residue = 2.1% Intrinsic viscosity *4 = 13.8 (dl/g chitosan *3) Colloid equivalent value = 5.1meq/g chitosan*3 *1 105℃ *2 600℃ *3 Chitosan = evaporation residue - ash content.

*4 30℃, 0.2N acetic acid + 0.1N sodium acetate The measurement method is to dissolve chitosan in water using the same amount of acetic acid, use 0.2N acetic acid + 0.1N sodium acetate as a solvent, and measure using an Ubbelohde viscometer. do.

An acid aqueous solution of chitosan (1) was prepared using 10 g of raw chitosan, 10 g of glacial acetic acid, and water. This solution was filtered using a 200 mesh stainless steel wire gauze to remove undissolved substances, and the pH of this solution was adjusted to 11 using a sodium hydroxide solution to precipitate chitosan. The amount of liquid at the time when chitosan precipitates is 1.2.

Divide this liquid into two parts (600 ml each), put one in a container with a lid and a shape that will not break even if the volume increases due to freezing, and place in a -20℃ freezer for 24 hours to freeze. I let it happen. Thereafter, when it was melted at room temperature, the chitosan became particles of about 1 to 2 mm. Add this particle twice/day to 3 ml of deionized water.
By washing the column by passing water through the column for 30 minutes, sodium acetate and sodium hydroxide are removed, and the electrical conductivity of the renewed deionized water is increased.
Six replacements were required to reduce the value to below 20 μS/cm. Thereafter, it was freeze-dried for one day to obtain white powdered chitosan (particle size 0.1 to 0.4 mm). It was confirmed that the intrinsic viscosity and colloidal equivalent value of the obtained chitosan were unchanged from those of the raw material chitosan.

As a comparative example, the other 600 ml of the liquid was washed using a polypropylene filter cloth twice a day and deionized water 3 times, and the electrical conductivity of the deionized water was 20μS. It took 12 replacements to reduce the diameter to less than /cm. Before freeze-drying, chitosan had poor drainage, and its volume was about five times that of the frozen and thawed one, so it took three days to freeze-dry it. The obtained chitosan was a fine powder (particle size 0.04 to 0.2 mm) and was difficult to handle.

Claims (1)

[Claims] 1. After dissolving chitosan in an acid, adding an alkali to make a chitosan suspension, freezing and thawing this suspension to form chitosan into particles, and then desalting using deionized water. A method for producing chitosan powder, which is characterized by drying. 2. The method according to claim 1, wherein the alkali is added after removing insoluble matter in the acid solution. 3. The method according to claim 1 or 2, wherein the drying is freeze drying or drying under reduced pressure after substitution with an organic solvent.