DE3227267A1 - Process for the preparation of cellulose carboxylates - Google Patents

Abstract

A process is described for the preparation of cellulose carboxylates by adding activated cellulose to an amide selected from the group comprising dimethyl acetamide, 1-methyl-2-pyrrolidone and a mixture of these, an addition of 3-12% by weight of lithium chloride to bring about a solution, followed by treatment of the resulting homogeneous solution which contains cellulose, lithium chloride and the amide, with an acylating agent in the presence of a catalyst which is effective for acylating the cellulose.

Description

description

The invention relates to a process for the production of cellulose carboxylates, in particular cellulose acetate, with a uniform distribution of ester groups Dissolving cellulose in a mixture of a special amide compound and lithium chloride and acylating the cellulose in the homogeneous solution system.

Cellulose acetate is useful for various purposes such as manufacturing of fabrics, fibers, cigarette filter tips, plastics, foils or films and Paints. Among the cellulose derivatives, cellulose acetate is the largest Quantity produced and is industrially important.

A common industrial process for producing cellulose acetate comprises the following stages: a cellulosic material, such as wood pulp or wood pulp or Cotton fibers (cotton linters) are pretreated with a suitable amount of acetic acid and then the pretreated material is placed in a previously cooled acetylation mixture poured containing acetic acid, acetic anhydride and a catalyst. In the In the latter stage, acetic anhydride is used in an amount which is greater as the stoichiometric amount based on that in the cellulosic material and that Reaction system and the water contained in the cellulose itself, and a catalyst, which is often used for industrial purposes is sulfuric acid.

As a result, primary cellulose acetate (fully esterified cellulose or cellulose triacetate). Then an aqueous solution of a neutralizing agent, such as an aqueous solution of carbonate, hydroxide, oxide or acetate of calcium, magnesium, Iron, aluminum or zinc, added to the reaction system to remove excess acetic anhydride, that after the completion of the acetylation reaction still there is to hydrolyze and also to partially neutralize the esterification catalyst. The primary cellulose acetate is then saponified and held at 50-90 OC in the presence of a small amount of the remaining acetylation catalyst, like sulfuric acid, matured, causing it to be converted into secondary cellulose acetate with the desired degree of acetylation and polymerization. If the secondary Cellulose acetate obtained with the desired degree of acetylation and polymerization is, the catalyst remaining in the system becomes complete with the above mentioned neutralizing agent neutralized, or alternatively not neutralized, and then the ripened reaction mixture is diluted to water or a Acetic acid solution added, whereby the secondary cellulose acetate is deposited, and then the separated secondary cellulose acetate is washed and subjected to a stabilization treatment to obtain the desired product.

This common process for the production of cellulose acetate in industrial The benchmark is the so-called secondary cellulose acetate process1 ,. However it was not possible for this process, cellulose acetate in a solvent, like acetone, is very soluble on an industrial scale at low cost to obtain.

It is believed that in the first stage of the acetylation reaction of cellulose a so-called heterogeneous reaction takes place, namely becomes fibrous Cellulose dispersed in a diluent such as acetic acid or methylene chloride to form a dispersion, and the acetylation reaction occurs predominantly in an amorphous area of cellulose. In one stage of the acetylation reaction the resulting product is a mixture of almost entirely esterified cellulose and essentially unreacted cellulose. This product is therefore in one Insufficiently soluble solvent. Therefore, according to the prior art, the cellulose once completely esterified by esterification conditions chosen in such a way that the reaction even in the crystalline region with a relatively low reactivity can be done.

Since the almost completely esterified cellulose in acetic acid or Methylene chloride is soluble, a homogeneous solution system is obtained in this way. Water is introduced into the homogeneous solution system to make the hydrolysis reaction in This system effect and acetyl groups evenly ton each part of the primary Remove cellulose triacetate molecule, thereby producing cellulose acetate with a uniform Acetyl group distribution, which is essentially homogeneously soluble in an industrial Solvent such as acetone is achieved.

The above usual procedure is complicated and takes a long time Response times. In these circumstances, there is an urgent need for the Providing an advantageous process for the production of cellulose acetate with excellent solubility in a solvent by a one-step esterification. Various methods have been proposed, but all of them have proven to be unsatisfactory. proven. The main reason for this is that the cellulose has both amorphous and crystalline areas and the difference in the The reactivity of these areas is great in the heterogeneous reaction system. Accordingly it will in principle, if possible, the reaction using a solution of cellulose to perform in a solvent, considered possible that to overcome morphological defects of cellulose.

As is known, notable solvents have been used recently developed for cellulose. Organic solvents that can be mentioned are, for example will Dimethyl sulfoxide / formaldehyde, dimethylformamide / N204 and N-ethylpyridinium salt. Various methods have been recommended in which cellulose in such a Solvent is dissolved and the solution is esterified.

However, these methods are not always successful. As part of the The present invention has been found to have the following problems include: (1) The process of dissolving cellulose in the solvent is complicated.

(2) Side reactions in addition to the intended esterification reaction occur and cellulose acetate cannot have the desired physical properties be achieved.

(3) The esterification operation itself is troublesome.

(4) The recovery of the reaction solvent and reagents is difficult.

Only a recommendation from W. B. Russo and G. A. Serad, the esterification The effect of cellulose nitrate via the sulfate gave relatively good results (W. B. Russo, G.A. Serad: Amer. Chem. Soc. Symposium vol. 58, p. 115).

Recently, a process has been developed in which cellulose activated by a suitable procedure and then in dimethylacetamide or 1-methyl-2-pyrrolidone is dissolved in the presence of lithium chloride (cf. JA-OS No. 32501/1981). In the context of the invention it has been shown that in this Process cellulose is dissolved in the solvent without forming any Cellulose adducts. Extensive investigations have shown that those mentioned above Compounds also useful as esterification reaction solvents can be used. The present invention is based on this.

The inventive method accordingly comprises the steps of (1) the Addition of activated cellulose to an amide selected from the group of dimethylacetamide, 1-methyl-2-pyrrolidone and mixtures thereof, as an esterification reaction solvent; (2) the addition of 3 to 12 weight percent based on the combined weights of activated cellulose and the amide, of lithium chloride, creating a homogeneous cellulose is achieved; and (3) treating the resulting homogeneous solution with a Acylating agent in the presence of an acylation catalyst to form the Cellulose carboxylic acid ester. Organic anhydrides are used as acylating agents and are used with a catalyst that is a basic compound when a carboxylic acid is generated by the reaction with. The catalyst can also be a Lewis acid or protic acid. When the catalyst is a protic acid the preferred acetylating agent is isopropenyl acetate.

In the production of a cellulose solution according to the method described in JA-OS No. 32501/1981 process described cellulose before dissolving in the solvent to be activated.

The activation methods recommended there are as follows Listed: (1) A method in which cellulose is refluxed in dimethylacetamide or 1 -Methyl-2 -pyrro lidon is heated to the cellulose with the steam of a or activate both of these amides.

(2) A method in which cellulose pulp or cellulose pulp in water is activated and then water extracted and through one this amide is replaced.

(3) A method in which cellulose pulp or cellulose pulp with steam is activated and the remaining water using an amide a solvent substitute is subjected.

(4) A process in which cellulose pulp is converted into liquid ammonia the activation of which is immersed and then ammonia is gradually evaporated will.

(5) A method in which a slurry of cellulose in water and dimethyl sulfoxide is treated with a homogenizer to achieve finer Pulp fibers.

The cellulose activated in this way is used in one of the aforementioned Amides dissolved in the presence of lithium chloride, thereby forming a homogeneous solution will.

In the context of the invention it has been shown that this esterification reaction solvent are very compatible with a basic catalyst such as pyridine, and that cellulose can be kept in the form of a solution in these solvents, even in Presence of a small amount of a Lewis acid such as zinc chloride or boron trifluoride, or a protic acid such as sulfuric acid or p-toluenesulfonic acid. The cellulose solutions according to the invention are with some acylating agents such as acetic anhydride and isopropenyl acetate are compatible, but are incompatible with acetic acid. if Acetic acid to a solution of cellulose in one of these esterification reaction solvents is joined, the cellulose is regenerated. It cannot therefore be assumed that all commonly used combinations of acylating agents and catalysts in this solvent can be used. For example in the acetylation of cellulose with acetic anhydride in the presence from a proton catalyst or a Lewis acid catalyst, the system gels or becomes gel-like a few minutes or a few tens of minutes after the introduction of the Acetic anhydride and a homogeneous reaction system could be found in almost all Cases are not achieved. It is therefore believed that a reason for this is therein is that the acetic acid, which is essentially associated with the esterification reaction solvent is incompatible, is formed as a by-product during the acetylation reaction. Therefore, in order to achieve acetylation in the homogeneous system according to the invention the following conditions are essential: (1) If acetic acid is produced as a by-product, it must be removed or neutralized, or (2) an acylating agent must be used that does not produce acetic acid as a by-product.

In order to carry out the condition (1), it is recommended that when using of acetic anhydride as acylating agent, a basic substance as a reaction catalyst is used to neutralize the acid formed.

The reaction has been found to proceed smoothly when using a pyridine / acetic anhydride system is used. However, cellulose acetate has been formed by this process is, in general, an extremely high degree of polymerization in such a way that even Cellulose diacetate that is produced with high degree of substitution of about 2.4 in common solvents for cellulose diacetate is poorly soluble. To achieve of cellulose acetate with the desired solubility in a common solvent it is therefore necessary to use a starting cellulose with a degree of polymerization use, which is lower than the usual cellulose, or the degree of polymerization after the end of the esterification to decrease.

Isopropenyl acetate can be used as an acylating agent to carry out the condition (2). It is believed that isopropenyl acetate reacts with cellulose to form acetone as a by-product, as shown below: Water contained in the starting cellulose and other starting materials decomposes isopropenyl acetate into acetic acid and acetone. However, in general, the water content of these materials can be controlled so as to reduce the amount of by-produced acetic acid to an extent insufficient to disturb the solution state of the system.

As described above, the invention provides a method to achieve a cellulose ester with a degree of substitution of about 2-2.6, which is very soluble in a solvent, after a one-step acylation reaction provided. It is also possible to temporarily use a triester with a degree of substitution of about 3.0 using the esterification reaction solvent of the present invention to form according to a conventional method and then the triester one verse to undergo an elution reaction by introducing water into the reaction system with Formation of the Secondary Cellulose Ester The following examples illustrate embodiments of the invention without representing a restriction. The designation "parts" and "Percent" means parts by weight or percent by weight.

Example 1 A dissolvable pulp (slurry) (containing 96.5% alpha-cellulose) is obtained after the sulphite process, was finely disintegrated in a household electric mixer. The finely disintegrated pulp had a water content of 7.4%. 5.9 parts of the finely disintegrated pulp was added to 85.5 parts of dimethylacetamide. The mixture was refluxed with external heating to about 1650C for about 30 minutes touched. The mixture was then gradually cooled to 100 ° C. and 8.6 parts anhydrous lithium chloride gradually added to the mixture with vigorous stirring joined. The resulting mixture was left at room temperature with stirring overnight allowed to stand to form a cellulose solution. The solution was viewed through a microscope observed and only very fine undissolved cellulose was found. The solution was diluted with 60 parts of dimethylacetamide and the mixture was stirred under Achieving a homogeneous solution. A mixture of 20 parts and dimethylacetamide 35.8 parts of pyridine was added dropwise to the solution. The mixture was on Heated to 70 ° C. and a mixture of 38.6 parts of acetic anhydride and 20 parts of dimethylacetamide was added over a period of about 10 minutes. There was a build-up of heat found corresponding to a temperature increase of about 5 OC, but remained the Cellulose solution homogeneous.

About 4 hours after the addition of acetic anhydride is complete the reaction solution was dissolved in about 1,000 parts of methanol with vigorous stirring cast to coagulate a translucent product. The product changed gradually to a white opaque substance. This substance was made with methanol washed several times to remove the solvent and lithium chloride. After this Drying gave a white product with a degree of acetylation determined by Acid-base titration method of 56.0% (the number of acetyl substituents was 2.49 per anhydroglucose unit).

The product obtained was in a mixture of methylene chloride and Methanol (weight ratio 9: 1) completely soluble. A film or a slide, obtained by pouring the solution, showed an infrared absorption spectrum that was completely matched that of commercial cellulose diacetate, and a sUxzfenPeak due to the ester carbonyl group at 1750 cm 1. The product was also gel permeation chromatography (Column used: CPG-10) using a methylene chloride / methanol mixture chs as a solvent, at room temperature. It was found that the peak had shifted and a higher degree of polymerization in comparison with cellulose acetate showed that using the same starting pulp a conventional method using acetic acid as a solvent became.

The cellulose acetate thus obtained was entirely in nitromethane as well as in Methylene chloride / methanol mixture soluble but swelled or was essentially insoluble in acetone, tetrahydrofuran and dioxane.

Example 2 A cellulose solution was prepared from 5.9 parts of pulp to be dissolved, containing 96.5% alpha-cellulose, obtained by the sulphite process, in the same way as described in Example 7. The solution was 60 parts Dimethylacetamide and the whole mixture was stirred to form a homogeneous solution. 19.2 parts of DBU-SA-1 (trade name for the phenol salt of 1,8-diazabicyclo / 5. 4.0 / -undecen-7, commercial product of Sun-Abbott Ltd.) and 20 parts of dimethylacetamide were added to the solution, which remained homogeneous. The mixed solution was increased to 70 OC heated and a mixture of 38.6 parts of acetic anhydride and 20 parts of dimethylacetamide was added dropwise over about 10 minutes. An increase in temperature was observed of about 6 OC, but the solution remained homogeneous. The mixture was longer than 3 hours kept at 70 OC and then in about 1000 parts of methanol under vigorous Stir poured. The precipitates thus obtained were washed several times with methanol and dried to give a white product. The product had a degree of acetylation of 51.4%. The number of acetyl substituents was 2.17 per anhydroglucose unit. The product was completely in methylene chloride / methanol (weight ratio 9: 1) soluble. A sheet obtained by pouring the solution showed a Infrared spectrum completely identical to that of commercial cellulose diacetate. The product was also soluble in nitromethane or dioxane, but swelled in acetone. According to the gel permeation chromatography, which is carried out in the same way as in Example 1, the cellulose diacetate product had a higher level Degree of polymerization than that of a product obtained by the usual method was obtained.

Example 3 The same pulp as used in Example 1 was used with dilute hydrochloric acid to remove the amorphous portion of the Cellulose hydrolyzed. The pulp was then ground, washed and dried to obtain microcrystalline cellulose. 6.3 parts of this cellulose (water content 4.8%) was poured into 85.5 parts of dimethylacetamide and the mixture was made of refluxed outside and stirred for about 30 minutes. Then the Mixture gradually cooled to 100 "C and finally 8.6 parts became anhydrous Lithium chloride added slowly with vigorous stirring. The resulting mixture was allowed to stand with stirring at room temperature overnight to achieve a cellulose solution with a relatively low viscosity. This solution was diluted with 60 parts of dimethylacetamide and then the entire mixture stirred to obtain a homogeneous solution. A mixture of 20 parts of dimethylacetamide and 19.2 parts of DBU-SA-1 (trade name of the phenolic salt of 1,8-diazabicyclo [5.4.0 / -undecen-7, Commercial product of Sun Abbott Ltd.) was added to the solution. The mixture was heated to 70 0C and its mixture of 49.8 parts of propionic anhydride and 20 parts Dimethylacetamide was added dropwise over about 10 minutes. It was a temperature increase of about 4 ° C was noted, but the cellulose solution remained homogeneous. About 5 hours after all of the propionic anhydride has been added the reaction solution was poured into about 1000 parts of methanol with vigorous stirring Poured formation of a white product. The product was treated with methanol several times washed and dried to give a product. This product had 2.0 Propionyl substituents per anhydroglucose unit and was completely soluble in methylene chloride / methanol (Weight ratio 9: 1).

Example 4 5.9 parts of finely disintegrated pulp (containing 96.5% alpha-CelluloseX, obtained by the sulfite method, were in a mixture of dimethylacetamide and dissolved anhydrous lithium chloride. The solution was made with 60 parts of dimethylacetamide diluted to give a homogeneous solution. A solution of 5.6 parts of p-toluenesulfonic acid monohydrate in 20 parts of dimethylacetamide was added dropwise and the solution remained homogeneous. The solution was heated to 75 ° C. and a solution of 46.6 parts of isopropenyl acetate in 20 parts of dimethylacetamide was added for about 10 minutes. Subsequently was the reaction continued for about 7 hours at 75 "C and then the reaction solution became in about 1000 parts of methanol with vigorous stirring to give a white powdered product poured.

The product obtained had a degree of acetylation of 40.2%. The number of acetyl substituents was 1.51 per anhydroglucose unit. The product was soluble in heated 60% aqueous acetone solution.

Example 5 5.9 parts of microcrystalline cellulose as in Example 3 used, with a water content of 3.4%, were in 85.5 parts of 1-methyl-2-pyrrolidone introduced. The mixture was refluxed for about 30 minutes during which time from outside heated and stirred. The mixture then slowly increased to 100 OC cooled. When the mixture was cooled to 100 ° C: it became anhydrous with 8.6 parts Lithium chloride mixed with vigorous stirring.

It was then left to stand with stirring overnight at room temperature to form a cellulose solution having a relatively low viscosity. the Solution was diluted with 60 parts of 1-methyl-2-pyrrolidone and stirred forming a uniform solution. A mixture of 35.6 Parts of pyridine and 20 parts of 1-methyl-2-pyrrolidone were added. When the resulting The mixture was heated to 70 ° C, became a mixture of 38.5 parts of acetic anhydride and 20 parts of 1-methyl-2-pyrrolidone were added dropwise over about 7 minutes. At this point it was found that enough heat was generated to raise the reaction temperature by about 5 ° C, but the solution remained homogeneous. After 6 hours after the Adding the acetic anhydride was the reaction solution in about 1000 parts of methanol poured with stirring and a white precipitate formed. The precipitation was washed several times with methanol and dried to obtain a product, whose number of acetyl substituents was 2.4 per anhydroglucose unit.

Example 6 A cellulose solution was prepared in the same manner as in Example 3, using 5.9 parts of the microcrystalline Cellulose, as used in Example 3, with a water content of 5.1 %, 85.5 parts of dimethylacetamide and 8.6 parts of anhydrous lithium chloride. the Solution was diluted with 80 parts of dimethylacetamide and stirred to achieve an even solution. If it was heated up to 90 OC from the outside, it was a mixture of 39.8 parts of acetic anhydride and 20 parts of dimethylacetamide during Added for 10 minutes while vigorously stirring the cellulose solution. After this 2 hours had passed since acetic anhydride addition was started the reaction solution was poured into 500 parts of methanol to form a precipitate of cellulose acetate. The precipitate was washed with methanol and reduced under reduced pressure Pressure dried to achieve a product for the number of Acetyl substituents Was 1.7 per anhydroglucose.

Separately, the same procedure as in Example 5 was followed carried out using pyridine as a basic catalyst, and was obtained a product for which the number of acetyl substituents is 2.0 per anhydroglucose fraud.

Claims (8)

Process for the production of cellulose carboxylic acid esters Patent claims 1. A process for the production of cellulose carboxylic acid esters, characterized in that activated cellulose to form an amide selected from the group of dimethylacetamide, 1-methyl-2-pyrrolidone and mixtures thereof, add and add 3-12% by weight lithium chloride, under conditions effective to obtain a homogeneous solution of cellulose, whereupon this homogeneous solution, which contains the cellulose, the lithium chloride and the Contains amide, with an acylating agent in the presence of an acylation catalyst treated ators, whereby the cellulose to form the cellulose carboxylic acid ester is acylated. 2. The method according to claim 1, characterized in that as The catalyst is a basic compound and the acylating agent is an organic acid anhydride used. 3. The method according to claim 1, characterized in that as Catalyst a protic acid and isopropenyl acetate used as acylating agent. 4. The method according to claim 1, 2 or 3, characterized in that an amount of acylating agent is used that is effective to form one Cellulose carboxylic acid esters with a degree of substitution of about 2.0 to 2.6. 5. The method according to claim 1, 2 or 4, characterized in that an acylating agent is used which forms acetic acid as a by-product, and that the acetic acid is removed from the solution or neutralized therein. 6. The method according to claim 5, characterized in that as Catalyst uses a basic compound and neutralizes the acetic acid. 7. The method according to claim 2, characterized in that as The catalyst is pyridine and the acylating agent used is acetic anhydride or isopropenyl acetate used. 8. The method according to claim 1, 4 or 5, characterized in that a Lewis acid is used as the catalyst.