TWI404844B - Method of preparing cellulose acetate - Google Patents

Abstract

The present invention provides a method of preparing cellulose acetate, comprising the step of (a) activating treatment of the cellulose raw material to obtain the activated cellulose; and (b) esterifying the activated cellulose by acetic anhydride in the presence of a catalyst in order to obtain the cellulose acetate. The method of the present invention prepares cellulose acetate in the absence of solvent, so as to effectively decrease the cost of manufacturing.

Description

Method for producing cellulose acetate

The present invention relates to a process for producing cellulose acetate, and more particularly to a process for producing cellulose acetate in an environment where no additional solvent is added.

Cellulose acetate is obtained by esterification of cellulose. It is divided into cellulose triacetate, cellulose diacetate and cellulose acetate according to the degree of substitution. It is applied to different products according to the degree of substitution, such as: movie Film, textiles, cigarette filters, plastic products, films and other materials. At present, cellulose triacetate is widely used, and it is widely used in liquid crystal displays because of its excellent optical properties and structural strength.

Cellulose is abundant in nature, mainly from plants, such as cotton, pulp, bagasse, ramie, corn stalk, wheat straw, etc., which contain high amounts of cellulose. The advantages include natural source, low price, abundant quantity and regenerability. It is easy to biodegrade and is an excellent raw material for the preparation of cellulose acetate.

There are many synthetic methods for cellulose acetate. At present, the commercial production methods include acetic acid method, dichloromethane method and heterogeneous method. Among them, the dichloromethane method and the heterogeneous method cannot be combined with acetic acid due to factors such as cost and quality. The competition gradually fades out, and the acetic acid method has become the main production method of commercialization. However, in the case of the acetic acid method, since a large amount of acetic acid is required as a solvent, it is not possible to meet environmental protection requirements and needs to be further improved.

It can be seen from the above that in addition to the natural cellulose raw materials, in order to meet the large demand for cellulose acetate and reduce the environmental burden, it is still necessary to propose an improved method for the process, so that the cellulose acetate manufacturing method is more environmentally friendly and lower. Production costs and competitiveness.

Accordingly, it is an object of the present invention to provide a more simplified and environmentally friendly method of making cellulose acetate.

Thus, the method for producing cellulose acetate of the present invention comprises (a) activating a cellulose raw material to obtain an activated cellulose; and (b) treating the activated material in the presence of a catalyst. The cellulose acetate is obtained by esterification of cellulose with acetic anhydride.

The invention does not need to add additional solvent to manufacture cellulose acetate, saves the cost of using and recovering the solvent, and the reaction time is further reduced, which can effectively reduce the manufacturing cost and reduce the amount of waste liquid.

The method for producing cellulose acetate of the present invention comprises: (a) activating a cellulose raw material to obtain an activated cellulose; and (b) activating the treated fiber in the presence of a catalyst The cellulose acetate is obtained by esterification reaction with acetic anhydride.

The purpose of this step (a) activation treatment is to increase the reactivity of the cellulose. By weakening the hydroxyl binding force between the cellulose macromolecules, the reaction ability of the reaction reagent with cellulose is increased, and the rate of subsequent reaction is increased.

Preferably, the step (a) activation treatment is to soak the cellulose raw material in an activation treatment solution. Still preferably, the activation treatment solution is water or a glacial acetic acid solution. More preferably, the activation treatment of the step (a) is to soak the cellulose raw material in the activation treatment solution for 10 to 34 hours.

More preferably, the present invention further comprises a step (a1) after the step (a), wherein the step (a1) is to separate the activation treatment liquid from the activated cellulose, and the separation is not limited to press-off or Filter and so on.

Preferably, the cellulosic material is selected from the group consisting of cotton, pulp, bagasse, ramie, corn stover, straw or a combination thereof. The invention selects natural material as the raw material of cellulose, and has the advantages of cost saving and environmental protection. The raw materials are abundant in source, easy to obtain, low in price, and can be recycled.

Among them, cotton has the highest cellulose content and cellulose content of about 90%, which is the most suitable cellulose raw material of the present invention; other cellulose sources have a slightly lower cellulose content, but the price is relatively lower.

This step (b) does not require the addition of glacial acetic acid as a solvent. Since acetic anhydride reacts with cellulose to form water, water reacts with acetic anhydride to form acetic acid. Acetic acid can be used as a reaction dispersant, and under good agitation, for example, but not limited to, an anchor stirrer can be used to achieve a good dispersion effect; therefore, the esterification reaction step of the present invention does not require additional solvent, and the solvent is omitted. The cost of use and recovery, and because no solvent is added, the concentration of the reactants is high, resulting in an increase in the reaction rate and a decrease in the reaction time.

Preferably, in the presence of the catalyst, the activated cellulose and acetic anhydride are stirred in a reactor to carry out an esterification reaction to obtain the cellulose acetate.

Preferably, the weight ratio of the activated cellulose to acetic anhydride ranges from 1:0.5 to 1:20. When the weight ratio of the activated cellulose to the acetic anhydride is less than 1:0.5, the number of substituents for replacing the hydroxyl group of the cellulose is insufficient; when the weight ratio is higher than 1:20, the excess portion corresponds to the solvent. Increase manufacturing costs and cause environmental pollution. Still preferably, the weight ratio of the activated cellulose to acetic anhydride ranges from 1:2 to 1:10. More preferably, the weight ratio of the activated cellulose to acetic anhydride ranges from 1:5 to 1:7.

Preferably, the catalyst is selected from the group consisting of sulfuric acid, perchloric acid, sulfonic acid, zinc chloride or phosphoric acid. To produce a high quality cellulose acetate, preferably, the weight ratio of the activated cellulose to the catalyst ranges from 1:0.033 to 1:0.4. When the amount of the catalyst is too high, the cellulose backbone will be degraded, resulting in a decrease in molecular weight. However, if the amount of the catalyst is too small, the degradation of a small amount of hemicellulose in the cellulose may be incomplete, which may affect the quality of the final product.

Preferably, the reaction temperature in the step (b) ranges from 13 to 85 °C. When the reaction temperature is lower than 13 ° C, the reaction rate is too slow, which is unfavorable commercialization; when the reaction temperature is higher than 85 ° C, the rate at which the catalyst cuts the cellulose main chain increases, causing the cellulose acetate to have a too low molecular weight.

Preferably, the reaction time of the step (b) is between 10 and 20 minutes. When the reaction time is too short, the reaction is not yet complete; the longer the reaction time, the higher the degree of substitution, but the molecular weight decreases. The degree of substitution is caused by the esterification reaction of acetic anhydride with three hydroxyl groups on cellulose over time; however, the effect of the catalyst is not stopped by the substitution of the hydroxyl group of the cellulose by the ethyl thiol group. The cellulose backbone causes the molecular weight to decrease over time. When the reaction time is too long, the degree to which the catalyst cuts the cellulose main chain increases, and the molecular weight of the cellulose acetate is too low.

Preferably, the method for producing cellulose acetate of the present invention further comprises a step (c) of subjecting the cellulose acetate to a hydrolysis reaction and a neutralization treatment. The cellulose acetate obtained in the steps (a) and (b) is cellulose triacetate, and the cellulose triacetate is subjected to the hydrolysis reaction of the step (c) to form cellulose diacetate and cellulose acetate monoacetate. The purpose of the neutralization process in step (c) is to neutralize the catalyst.

Still preferably, the neutralization treatment neutralizes the cellulose acetate in a mixed solution containing magnesium acetate. More preferably, the mixed solution contains magnesium acetate and glacial acetic acid.

The present invention will be further illustrated by the following examples, but it should be understood that this embodiment is intended to be illustrative only and not to be construed as limiting.

<Chemicals and equipment>

1. Glacial acetic acid: purity 95%, purchased from Changchun Petrochemical Co., Ltd.

2. Acetic anhydride: 95% purity, purchased from Acros.

3. Sulfuric acid: 1N, purchased from Panreac.

4. Anhydrous magnesium acetate: the reagent grade, purchased from Shimajiu Pharmaceutical Co., Ltd.

5. Sodium hydroxide: 1N, purchased from Panreac.

6. Chloroform: HPLC grade, purchased from TEDIA.

7. Nuclear Magnetic Resonance Spectrometer (NMR): purchased from BRUKER, model "400 Ultra ShieldTM" for molecular structure analysis of compounds.

8. Colloidal Osmograph (GPC): purchased from HITACHI, model "pump L-2130" for molecular weight identification of compounds.

9. Fourier Transform Infrared Spectroscopy (FT-IR): purchased from Perkin Elmer, model "spectrum one", used to detect the functional groups of organic compounds to determine their molecular structure.

<Example> [Preparation of cellulose acetate]

First, 15.02 g of cotton was completely immersed in 500 mL of glacial acetic acid. After 24 hours, the glacial acetic acid was filtered off to obtain activated treated cellulose.

The activated cellulose and 1 g of sulfuric acid were placed in a reactor, stirred well, and then 75 g of acetic anhydride was slowly dropped at a rate of 1 ml/sec. The reaction temperature was set to 55 ° C, the reaction time was 15 minutes, and the activated cellulose was subjected to esterification reaction with continuous stirring to obtain a crude cellulose acetate.

20.03g of water was added to the reactor, and the crude cellulose acetate was subjected to hydrolysis reaction for 2 minutes with continuous stirring; 2.06 g of magnesium acetate and 20.02 g of glacial acetic acid aqueous solution were further added to the reactor, stirring was continued, and neutralization reaction was carried out for 3 minutes. .

The crude cellulose acetate obtained by the above hydrolysis and neutralization treatment is taken out from the reactor, poured into water, and then washed with a magnesium acetate solution until neutral, and then washed with water for 1 to 2 times, and then baked at 60 ° C. The cellulose acetate of the examples was prepared.

[Property test] 1. Structure identification: (1) Nuclear magnetic resonance spectroscopy:

The cellulose acetate of the example was ground and pulverized by a grinder to obtain a sample of the examples. A small sample of the sample was weighed and placed in an NMR standard test tube, and chloroform was added to dissolve the sample.

The ¹ H-NMR spectrum of the cellulose acetate of the examples was measured by a nuclear magnetic resonance spectrometer (as shown in Fig. 1). Among them, the two peaks of 3.66 ppm and 3.47 ppm are hydrogen on the cellulose main bodies C ⁴ and C ⁵ respectively, and the two peaks of 4.42 ppm and 4.06 ppm are hydrogen on the cellulose main bodies C ¹ and C ⁶ respectively, 4.79 ppm and 5.07. The two peaks of ppm are hydrogen on the C ² and C ³ cellulose bodies, and three peaks appearing between 1.8 and 2.2 ppm, respectively, which are the hydrogen of the methyl group on the ethyl group. From the above signals, it was judged that the obtained product was indeed cellulose acetate.

(2) Fourier infrared spectroscopy:

Potassium bromide (KBr) powder and the above-mentioned sample were ground and uniformly mixed at a weight ratio of 99:1, and the aforementioned mixed powder was pressed into a sheet with a carrier.

The measured IR pattern is compared to the IR image of the starting cellulose (as shown in Figure 2), wherein (a) is the map of the examples, (b) is the map of the comparative example, and (c) is cellulose. Map of raw materials. Among them, the characteristic absorption peak located near 3400 cm ^-1 is caused by the OH group, and the absorption peak of the OH group of cellulose acetate is caused by the substitution of three OH groups on the cellulose by the acetamino group to form cellulose acetate. Significantly weaker than cellulose. In addition, the IR diagram of cellulose acetate shows the characteristic absorption peaks of cellulose acetate at 1750 cm ^-1 and 1300 cm ^-1 , and the C=O and CH ₃ functional groups are different from the raw material cellulose, which can confirm the obtained product. It is cellulose acetate.

2. Determination of degree of substitution:

The degree of substitution (i.e., the degree of esterification) is determined in accordance with ASTM D-817-91 test standard. 0.5 g of the sample of the example was placed in an Erlenmeyer flask, and then 20 ml of a mixed solvent of acetone/DMSO (4/1 ratio) was added to completely dissolve the sample.

Next, an excess of 1.0 N sodium hydroxide standard solution was added to the Erlenmeyer flask for saponification for 2 hours. After the reaction was completed, a phenolphthalein indicator was added dropwise, and unreacted sodium hydroxide in the Erlenmeyer flask was back-titrated to a titration end point with a 1.0 N sulfuric acid standard solution.

The degree of acetylation of cellulose acetate (abbreviated as Dac) was determined according to the following formula:

Dac (%) = 6.005 × (B-A) ÷ W

Where A = the amount of 1N sulfuric acid standard solution required for sample titration

B = amount of 1N sulfuric acid standard solution required for blank test titration

W = sample weight (g)

3. Determination of molecular weight

A sample of the example of 0.005 g was weighed and placed in a test tube, 20 ml of chloroform was added, and after the sample was dissolved, the molecular weight was measured by a GPC apparatus.

<Comparative example> [ Preparation of cellulose acetate]

First, 15.02 g of cotton was completely immersed in 500 mL of glacial acetic acid. After 24 hours, the activated cellulose was obtained by filtration and deicing glacial acetic acid.

The activated cellulose, 195.2 g of glacial acetic acid and 1 g of sulfuric acid were placed in the reactor, and after stirring for 30 minutes, 75 g of acetic anhydride was slowly added dropwise at a rate of 1 ml/sec, and the reaction temperature was set to 35 ° C, and the reaction time was 80. In a minute, the agitated reaction was carried out by subjecting the activated cellulose to an esterification reaction to obtain a crude cellulose acetate.

20.03g of water was added to the reactor, and the crude cellulose acetate was subjected to hydrolysis reaction for 2 minutes by continuous stirring; 2.06 g of magnesium acetate and 20.03 g of glacial acetic acid aqueous solution were further added to the reactor, stirring was continued, and neutralization reaction was carried out for 3 minutes. .

The crude cellulose acetate which has been hydrolyzed and neutralized is taken out from the reactor, poured into water and precipitated, and then washed with a magnesium acetate solution until neutral, and then washed with water for 1 to 2 times, and then dried at 60 ° C. That is, the cellulose acetate of the comparative example was obtained.

[Property test]

The cellulose acetate of the comparative example was tested in accordance with the degree of substitution and molecular weight test methods of the above examples, and the results obtained are shown in Table 1 below.

In summary, the method for producing cellulose acetate according to the present invention, wherein acetic anhydride reacts with cellulose to form water, water reacts with acetic anhydride to form acetic acid, and acetic acid can be used as a reaction dispersant, and can be uniformly obtained under conditions of sufficient agitation. The effect of dispersion. Therefore, the method for producing cellulose acetate of the present invention does not require additional glacial acetic acid solvent, reduces the cost of solvent use and recovery, and because the reactant is not diluted by the solvent, the concentration is relatively increased, the reaction rate is increased, and the reaction time is shortened and reduced. The manufacturing cost of cellulose acetate.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

Figure 1 is a ¹ H-NMR spectrum of an example.

2 is an FT-IR spectrum diagram, wherein (a) is an example, (b) is a comparative example, and (c) is a cellulose raw material.

Claims (7)

A method for producing cellulose acetate, comprising: (a) activating a cellulose raw material to obtain an activated cellulose; and (b) in the presence of a catalyst without adding a solvent, The cellulose acetate is obtained by esterification of the activated cellulose with acetic anhydride. The method for producing cellulose acetate according to claim 1, wherein the cellulose raw material is selected from the group consisting of cotton, pulp, bagasse, ramie, corn stalk, wheat straw, or the like. The method for producing cellulose acetate according to the first aspect of the invention, wherein the reaction temperature in the step (b) is in the range of 13 to 85 °C. The method for producing cellulose acetate according to claim 1, wherein the weight ratio of the activated cellulose to acetic anhydride ranges from 1:0.5 to 1:20. The method for producing cellulose acetate according to claim 1, wherein the catalyst is selected from the group consisting of sulfuric acid, perchloric acid, sulfonic acid, zinc chloride or phosphoric acid. The method for producing cellulose acetate according to claim 1, further comprising a step (c) of subjecting the cellulose acetate to a hydrolysis reaction and a neutralization treatment. The method for producing cellulose acetate according to claim 6, wherein the neutralization treatment neutralizes the cellulose acetate in a mixed solution containing magnesium acetate.