FI83426B - FOERFARANDE FOER KONTINUERLIG FRAMSTAELLNING AV MICROCRYSTALLINE KITOSAN. - Google Patents

Description

83426

This invention relates to the continuous production of microcrystalline chitosan. Prior to this, a process for the preparation of chitosan by a batch system is known, in which case the chitosan obtained has a developed internal surface and in particular a degree of deacetylation of more than 30%. The process is based on the periodic precipitation of chitosan-10, in which the chitosan is dissolved in an aqueous solution of an organic or inorganic acid, and is precipitated with aqueous solutions of alkali metal hydroxides using vigorous stirring. The precipitated chitosan in the form of a gel or dispersion is subjected to a purification process by washing it several times with water. A process for preparing precipitated chitosan in the form of a gel or dispersion is also known, which is preceded by a thermal decomposition process carried out by treatment with an organic or inorganic acid at a temperature of at least 50 ° and for more than one hour. Chitosan can be obtained in 70-90% yield by known methods. The known methods are carried out in reactors with stirrers or homogenizers. Known methods are described in Polish Patent 125,995 and in the Journal of Applied Polymer Science, Vol. 33, pp. 177, 1987.

The batch process of microcrystalline chitosan causes the production cycle to take a lot of time, at least 12-24 hours. It also causes high energy and wash water consumption. The resulting microcrystalline chitosan is characterized by heterogeneous properties in different batches. By the known method, microcrystalline chitosan with uniform properties cannot be obtained.

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The object of the invention is the continuous preparation of microcrystalline chitosan by continuous precipitation of microcrystalline chitosan from standard dicitosan dissolved in an aqueous solution of an organic or inorganic acid or their salts with an aqueous solution of alkali metal hydroxides.

According to a preferred embodiment of the process according to the invention, the continuous preparation of microcrystalline chitosan by precipitating chitosan from its aqueous solution in organic or inorganic acids with an aqueous solution of alkali metal hydroxides or their alkaline salts is carried out with an aqueous solution of chitosan, especially acetic acid. %, is continuously fed to the reactor together with an aqueous solution of alkali metal hydroxides, in particular sodium hydroxide, or their alkaline salts at a concentration of 0.1 to 20% by weight, and at the same time the chitosan solution is fed to 20 reactors at a rate of 0.1 to 20 parts by volume per hour. while the alkaline solution is passed at a rate of 0.1 to 10 parts by volume per hour per part by volume of the reactor working volume. The reagent introduced into the reactor at the above rate ensures that the pH of the reaction mixture remains at pH> 7. At the same time, a microcrystalline chitosan dispersion with a pH> 7 is continuously withdrawn from the reactor at a rate suitable to ensure a constant volume of the reaction mixture. Next, the microcrystalline chitosan dispersion is stored in a tank, and then it is purified by continuous water washing or ultrafiltration, and the purification is continued until the conductivity of the effluent is the same as that of the water used. The polymer content of the purified microcrystalline chitosan dispersion is finally concentrated to 0.5-10.0% by weight and the dispersion is dried by known methods.

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According to a preferred embodiment of the invention, the continuous production of microcrystalline chitosan also comprises continuously introducing the chitosan solution in aqueous acid solutions and the aqueous solution of alkali metal hydroxides or their salts at the rate described above into a reactor equipped with a continuous recycle system and the product recycled in a closed reactor system. ti the flow of microcrystalline chitosan is continuously taken out and divided into two parts. The first part is returned to the reactor and the second part is led to a surge tank and is then cleaned. The microcrystalline chitosan dispersion is removed from the reactor at a rate suitable to maintain a constant volume of the reaction mixture in the reactor. The use of additional recycling makes it possible to obtain microcrystalline chitosan with good uniformity properties. To increase the content and to improve the uniformity of the properties of the microcrystalline chitosan, an aqueous solution of alkali metal hydroxide is fed directly to the reactor recycle system.

With the process according to the invention, it is possible to obtain microcrystalline chitosan in a dispersion form which is characterized by properties suitable for colloids and which is characterized by a water retention value WRV of up to 5000%, a particle size between 0.1 and 50 μm and stability of the dispersion form. The dried product 30 is characterized by a powder form with a particle size between 1 and 100 μm and a WRV of 200-600%, a crystallinity index of Krl up to 95% and minimal dispersion of the chitosan parameters. The process according to the invention makes it possible to obtain a good yield of products at a level of 95-99% compared to the amount of standard chitosan used, while at the same time ensuring a reduction in raw material and energy consumption and eliminating the process compared to a batch process and 4 83426. An important object of the process according to the invention is to reduce the time for the preparation of microcrystalline chitosan compared to the batch process. Studies have shown that the microcrystalline chitosan obtained by the process of the invention in 1 to 5 hours is proportional to the amount of product produced by the batch process in 12 to 24 hours. Another important object of the process according to the invention is to ensure the continuous precipitation of microcrystalline chitosan, thereby obtaining the required particle sizes and properties, by controlling the concentration, the feed rate of the reagents and also finally the recirculation rate of the dispersion in the reactor. The process according to the invention makes it possible to produce homogeneous products with reproducible parameters without external interruption during production, which has taken place in a batch process.

The microcrystalline chitosan obtained by the process of the invention is used for the formation of polymer films in the chemical, medical, pharmaceutical and cosmetic industries and in agriculture.

The process for the continuous production of microcrystalline chitosan according to the invention is carried out with the apparatus exemplified in the schematic diagram.

The apparatus for producing microcrystalline chitosan comprises a reactor 1 containing a stirrer 2. At the top there is a tube 3 for conducting the chitosan solution and a tube 4 for conducting the hydroxide solution. The pipes 5 for the dispersion of microcrystalline chitosan 35 to be removed from the reactor 1 are provided with a pump 6, the outlet of which is connected to a recirculation system 7 for continuous return of a dispersion part to the reactor 1, and secondly the outlet is connected to a pipe 8 for a dispersion 5. Pipes 5 are located in the lower part of the reactor 1. The expansion tank 9 is connected to an apparatus 10 for the continuous purification of a microcrystalline chitosan dispersion, the apparatus being provided with pipes 11 for supplying and discharging purification water, and a pipe 12 for discharging the purified product. The apparatus 10 may also be in the form of an ultrafiltration system. In addition, the recirculation system 7 of the reactor 1 is provided at its top with a pipe 13 for supplying a hydroxide solution. The operation of the apparatus is as follows: The start of the precipitation process after the feed to the reactor 1 while the mixer 2 is running is carried out by continuously feeding the feed to reactor 1. The hydroxide solution is fed to reactor 1 via pipe 4 or pipe 13 to recycle system 7. Neutralization of the reaction mixture to pH> 7 takes place in reactor 1 with constant stirring and possibly by circulating the dispersion. The resulting 20 microcrystalline chitosan dispersion is removed from the reactor 1 in a continuous system via a pipe 5 and is completely conveyed to the surge tank 9 or divided into two parts, the first being conveyed to the surge tank 9 and the second to the recycle system 7 and returned to reactor 1.

The microcrystalline chitosan introduced into the expansion tank 9 is next delivered to the purification plant 10. After purification, the microcrystalline chitosan is delivered to the storage plant or dryer.

30

The invention is further described in the following examples, which do not limit the scope of the claims.

Example 1 35,500 parts by volume of a 1% solution of chitosan in 4% aqueous solution of acetic acid and a 2.5% aqueous solution of sodium hydroxide are introduced into the reactor shown in the figure, which has a working volume of 6,838,426 parts by volume. The chitosan used in the reaction was characterized by an average molecular weight of 6.07 x 105, a degree of deacetylation of 71.8% and a WRV of 129%. The dispersion of microcrystalline chitosan was precipitated with the stirrer in operation to reach pH 8.0, and then a 1% solution of chitosan in a 4% solution of acetic acid was continuously fed at a feed rate of 2400 volumes per hour, and a 4% aqueous solution of hydroxide was fed at a feed rate of 1728 vol. parts per hour to reach a pH of 8.0 ± 0.3. At the same time, the microcrystalline chitosan dispersion was taken out of the reactor at a rate suitable for maintaining a constant volume of the mixture in the reactor. The dispersion was then delivered to 15 expansion tanks and subsequently delivered continuously to a purification plant where it was continuously washed with water to obtain a product with EMP = 28 mV (electromotive force), while the initial product was characterized by an EMP of 95 mV.

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The product was obtained in the form of a stable gel, white in color, characterized by 2.45% by weight of microcrystalline chitosan, calculated as the weight of dry polymer, WRV 906% and an average molecular weight of 3.59 x 10 5. The product yield was 30.9 parts by weight of microcrystalline polymer per 1000 parts of reactor volume and per hour.

Example 2 30,400 volumes of a 1.0% solution of chitosan, the properties of which are shown in Example 1, in a 4% aqueous solution of acetic acid were fed to the reactor as in Example 1. A microcrystalline chitosan dispersion was precipitated with 2.5% aqueous sodium hydroxide solution with constant stirring to pH 7.5. and a 1.0% solution of chitosan in a 4% aqueous solution of acetic acid at a feed rate of 2940 parts by volume per hour, and

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7 83426 A 2.5% aqueous solution of sodium hydroxide at a feed rate of 3060 parts by volume per hour was continuously fed to the reactor to achieve a pH of 7.5 ± 0.2 of the mixture.

5 The process for the formation of microcrystalline chitosan was carried out with an integrated recycling system characterized by a recycling rate of 2940 parts by volume per hour. The co-precipitated microcrystalline chitosan dispersion was taken out for the expansion tank 10 at a rate suitable for maintaining a constant volume in the reactor. Next, a dispersion of microcrystalline chitosan with an EMP value = 112 mV was supplied to a purification apparatus to obtain an eluate with an EMP value of 34 mV.

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The product was obtained in the form of a stable gel with a white color and a yield of 30.9 parts by weight of microcrystalline chitosan per 1 hour and per 1000 parts of reactor volume. The product was characterized by 4.8% by weight of 20 microcrystalline chitosan, calculated as the dry weight of the polymer, and a WRV of 3,993%.

Example 3 A microcrystalline chitosan dispersion was made in a reactor as in Example 1 using a 1% chitosan solution in 4% aqueous acetic acid at a feed rate of 3780 volumes per hour and a suitable 4% aqueous sodium hydroxide solution in 3960 volumes per hour under other conditions as in Example 1.

The product was obtained in the form of a stable gel, white in color, characterized by a microcrystalline chitosan content of 7.44% by weight based on the weight of polymer 35 and a WRV of 1459%.

The product yield was 36 parts by weight of polymer per 1000 parts by volume of reactor and per hour.

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Example 4 400 volumes of a 0.5% solution of chitosan in a 4% aqueous solution of acetic acid, which was characterized by the properties of Example 1, were introduced into the reactor as in Example 1.

With continuous stirring, a microcrystalline chitosan dispersion was precipitated with 2.5% aqueous sodium hydroxide solution to obtain a pH of 7.8. A 0.5% solution of chitosan in a 4% aqueous solution of acetic acid was fed at a constant feed rate of 5280 parts by volume per hour and a 2.5% aqueous solution of sodium hydroxide at a feed rate of 5900 parts by volume per hour was fed continuously to reach a pH of 7.7 ± 0.3. The production and purification process was the same as in Example 1.

The product was obtained in the form of a stable gel, white in color, characterized by a microcrystalline chitosan content of 6.5% by weight, based on the weight of the dry polymer, and a WRV of 1994%. The reaction yield was 26.4 parts by weight of microcrystalline chitosan per 1000 parts of reactor volume and per hour.

Example 5 400 volumes of a 0.5% solution of chitosan in a 2% aqueous solution of acetic acid characterized by the properties of Example 1 were fed to a reactor as in Example 30 1. A microcrystalline chitosan dispersion was precipitated with continuous stirring using a 2.5% aqueous solution of sodium hydroxide to reach a pH of 7.4. and a 0.5% solution of chitosan in a 2% aqueous solution of acetic acid was continuously fed at a constant rate of 5280 35 parts by volume per hour and a 2.5% aqueous solution of sodium hydroxide at a rate as in Example 4 to reach a pH of 7.4 ± 0.1.

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The production and purification processes were the same as in Example 1. The initial microcrystalline chitosan dispersion was characterized by an EMP value of 85 mV and after the purification process it had an EMP value of 15 mV.

5

The product was obtained in the form of a stable white gel characterized by a microcrystalline chitosan content of 9.25% by weight based on the dry weight of the polymer and a WRV of 850%. The product yield was 15.7 parts by weight of micro-10 crystalline chitosan per 1000 parts of reactor volume and per hour.

Example 6 A dispersion of microcrystalline chitosan was obtained in the reactor of Example 1 using a 1% solution of chitosan in a 4% aqueous solution of acetic acid and a 7.5% aqueous solution of sodium hydroxide introduced into a functioning recycling system. Thereafter, a 1% solution of chitosan in 4% aqueous acetic acid was continuously fed at a constant feed rate of 5280 volumes per hour and a 7.5% aqueous solution of sodium hydroxide at a feed rate of 1944 volumes per hour to a reaction mixture initially having a pH of 7.8, a pH of 7.7 ± 0 , 2 25 to achieve. The production and purification process was analogous to Example 1. The initial dispersion produced was characterized by an EMP value of 99 mV and after purification the appropriate EMP was 29 mV.

The product was obtained in the form of a stable white gel characterized by a microcrystalline chitosan content of 9.05 wt%, calculated as dry polymer weight, WRV 587% and an average molecular weight of 3.62 x 105. The product yield was 36 parts by weight of microcrystalline 35 chitosan per 1000 reactors. per volume and per 1 hour.

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Example 7 500 parts by volume of a 0.5% solution of chitosan in 4% aqueous acetic acid were fed to the reactor as in Example 5 1. The chitosan used was characterized by an average molecular weight of 7.7 x 10 5, a degree of deacetylation of 67.5% and a WRV of 230%.

The microcrystalline chitosan dispersion was precipitated by stirring a 0.5% chitosan solution in 4% aqueous acetic acid to pH 7.9, and then using a continuous recirculation system of Example 2, a 0.5% chitosan solution in 4% aqueous acetic acid was fed to the reactor at a constant feed rate of 5280 vol. and a 0.5% aqueous solution of sodium hydroxide at a constant feed rate of 2880 parts by volume per hour and the pH of the mixture was 7.7 ± 0.3.

The production process was carried out as in Example 2, 20 while the purification process was carried out in an ultrafiltration apparatus to obtain an EMP value of 9 mV.

The product was obtained in the form of a stable white gel characterized by a microcrystalline chitosan content of 9.05% by weight based on the weight of the dry polymer, WRV

830% and an average molecular weight of 4.9 x 105.

The product yield was 36 parts by weight of microcrystalline polymer per 1000 reactor volumes and 1 hour per 30 hours.

Example 8 500 volumes of a 0.75 wt% solution of chitosan in a 1.5% aqueous solution of acetic acid 35 were introduced into the reactor as in Example 1. The chitosan had the same properties as in Example 7. The microcrystalline chitosan dispersion was precipitated by continuous stirring using 5.5 wt% aqueous sodium carbonate solution. 7.6% by weight of a chitosan solution in 1.5% by weight aqueous acetic acid was continuously introduced into the reactor at a constant rate of 6250 parts by volume in 5 hours, and 5.5% by weight of aqueous sodium carbonate solution was introduced into the reactor at a rate of 9500 parts by volume per hour. to reach a pH of 7.6 ± 0.1 of the mixture. The production and purification steps were the same as in Example 7. The initial dispersion of microcrystalline chitosan 10 was characterized by an EMP value of 70 mV and after purification the EMP value was 8 mV.

The product was obtained in the form of a stable white gel characterized by a microcrystalline chitosan content of 4.5% by weight based on the weight of the dry polymer and a WRV of 1450%. The product yield was 19.5 parts by weight of microcrystalline chitosan per 1000 parts of reactor volume and per hour.

Example 9 600 volumes of a 0.5% solution of chitosan in 0.58% aqueous hydrochloric acid containing 0.15% sodium chloride were introduced into the reactor as in Example 1. The chitosan used had the same properties as in Example 1. The microcrystalline chitosan dispersion was mixed by stirring continuously with sodium hydroxide 3 With a 0% aqueous solution to achieve a pH of 7.6. A 0.5% solution of chitosan in a 0.58% aqueous solution of hydrochloric acid containing 0.15% sodium chloride at a feed rate of 3,200 volumes per hour was then continuously fed to the reactor, and a 3.0% aqueous solution of sodium hydroxide was continuously introduced into the reactor. at a feed rate of 35,300 parts by volume per hour, giving a pH of 7.9 ± 0.3.

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The microcrystalline chitosan formation process was carried out in a recycling system with a recycling rate of 3150 parts by volume per hour. At the same time, the precipitated microcrystalline chitosan dispersion was taken out for 5 expansion vessels at a rate suitable for maintaining a constant volume in the reactor. The microcrystalline chitosan dispersion with an EMP value of 120 mV was then subjected to purification to give an eluate with an EMP value of 20 mV.

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The product was obtained in the form of a stable gel with a white color and a yield of 30.8 parts by weight of microcrystalline chitosan per 1 hour and per 1000 parts of reactor volume. The product was characterized by a polymer content of 3.9% to 15% by weight, a WRV of 4050% and an average molecular weight of 1.5 x 10 5.

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Claims (4)

13 83426 Claims; A process for the continuous preparation of microcrystalline chitosan by precipitation of chitosan from its aqueous solutions in organic or inorganic acids, using aqueous solutions of alkali hydroxides or their alkaline salts, characterized in that the chitosan solution in an aqueous solution of an acid, especially acetic acid, has a chitosan content of at least 10 0.01 wt%, preferably 0.1-2.0% by weight, is continuously fed to the reactor together with an aqueous solution of alkali hydroxides, in particular sodium hydroxide, or their alkaline salts at a concentration of 0.1-20.0% by weight, while the chitosan solution is fed to the reactor 15 at a rate of 0.1 to 20 parts by volume for 1 hour and 1 part by volume of the reactor, and a solution of the alkali hydroxide or its alkaline salt is fed to the reactor at a rate of 0, Ι to ΙΟ.0 parts by volume for 1 hour and the volume of the reactor 1 by volume. per pH of the mixture to reach> 7, and at the same time microcrystalline yield a slurry dispersion having a pH> 7 is withdrawn from the reactor continuously at a rate suitable to maintain a constant volume of the reaction mixture in the reactor, and the microcrystalline chitosan dispersion is collected in a surge tank and continuously purified, especially by continuous water washing or ultrafiltration, followed by purified microcrystalline chitosan , 5-10.0% by weight and dried by a known method. Process according to Claim 1, characterized in that the microcrystalline chitosan dispersion prepared in the reactor is continuously recycled in a closed reactor system, and at the same time the microcrystalline chitosan dispersion is continuously removed from the reactor at a rate suitable to maintain a constant volume of reaction mixture and microcrystalline chitosan. the cleaning process. Process according to Claim 2, characterized in that the alkaline solution is fed directly to a recirculation system containing a dispersion of crystalline chitosan. Process according to Claim 1 or 2, characterized in that the purification of the microcrystalline chitosan is carried out in such a way as to obtain a conductivity of the effluent which is equal to the conductivity of the water used. li is 8 3 426