JP5193591B2 - Method for producing methylcellulose - Google Patents

Description

  The present invention relates to a method for producing methylcellulose. More specifically, emulsion stabilizers for cosmetics, dispersants and suspension stabilizers for building materials, thickeners, adhesives, dispersants and stabilizers in pharmaceuticals, binders, protective colloids, foods The present invention relates to a method for producing methylcellulose having extremely various uses such as an emulsion stabilizer.

As with other cellulose ether production methods such as carboxymethylcellulose, a common method for producing methylcellulose is to first impregnate cellulose raw materials such as pulp with a large amount of water and a large excess of alkali metal hydroxide such as sodium hydroxide. After the cellulose activation process called so-called acerylation or mercerization, which is mixed into alkali cellulose, is reacted with methyl chloride, which is an etherifying agent, in a slurry state, and as a by-product neutralized salt, etc. It is manufactured through steps such as washing and removal, drying, and pulverization.
In this arselle formation process, in order to remove excess alkali and water from the alkali cellulose prepared by the arselle treatment, complicated operations such as filtration and washing are performed. Alkali cellulose is considered to have an alcoholate in most of the hydroxyl groups in the cellulose molecule, and is usually equivalent to about 1 to 3 mol amount, at least 1 mol amount or more per glucose unit in the cellulose molecule. In addition, an amount of water equal to or greater than that of cellulose remains. Therefore, when reacting with an etherifying agent, this water may also react with the etherifying agent, so that not only a large amount of neutralized salt is produced as a by-product during the reaction, but also these hydrates. By-products derived from this will also be produced.

In addition, since the reaction needs to efficiently bring the cellulose that is solid and the etherifying agent into contact with each other, the alkali cellulose is usually made into a slurry state having good dispersibility using various polar solvents. As the polar solvent, various secondary solvents such as lower secondary or tertiary alcoholic solvents having relatively low reactivity such as isopropanol, ethers, and ketones may be added. Is a method of adding a polar solvent that is not readily compatible with water, such as tert-butanol or methyl isobutyl ketone, during the reaction with the acerylation and etherification agent, and separating and recovering the solvent from the aqueous phase after the reaction. It is disclosed.
However, unless the amount of alkali and water can be greatly reduced, it is practically difficult to significantly reduce by-products such as neutralized salts.

On the other hand, the method of obtaining methyl ether by reacting alcohol with methanol in the presence of a strong acid catalyst such as sulfuric acid is a very classic method that has been known for a long time, and includes 1,2-diols such as ethylene glycol. Methyl etherification is also disclosed in Patent Document 3, for example.
However, these methods easily cause side reactions in the case of having an acid-sensitive functional group such as an aldehyde. For example, in a polysaccharide such as cellulose, the 1,4-glycosyl bond of the main chain is easily cleaved, There is a problem that the molecular weight is significantly reduced.
Patent Document 4 discloses a method of using kaolin clay mineral as a catalyst, filling the reaction tube with the catalyst, and reacting ethylene glycol and methanol in a liquid phase at a reaction temperature of 200 to 300 ° C. ing.
In Patent Document 5, a solid acid-base catalyst such as an alkali metal-phosphorus-silicon composite oxide is used, and the reaction temperature is 0.9 to 1.5 times the critical temperature of methanol; Tc = 239 ° C. (512 K). In addition, a method is disclosed in which a methanol solution of ethylene glycol is allowed to flow through a tubular catalyst tank under a pressure condition of 0.5 to 4.5 times that of Pc = 8.1 MPa. However, even when trying to apply to this method, since cellulose is hardly dissolved in methanol, it is difficult to circulate in the liquid phase described above, and even when it is reacted in batch mode, it is solid as well as a solid catalyst. It is very difficult to separate the cellulose or methyl cellulose.
Therefore, it is a very useful problem from an industrial viewpoint to develop a simple, efficient, low waste, and catalytic methylcellulose production method.

JP-A-8-245701 JP-A-6-1999021 JP-A-61-186336 JP-A-55-104221 Japanese Patent Laid-Open No. 2004-196783

  An object of this invention is to provide the manufacturing method of methylcellulose which is industrially simple and efficient.

  We have made cellulose, preferably powdered cellulose with reduced crystallinity, in a subcritical state of methanol in the presence of a catalytic amount of catalyst, preferably with a neutral salt that is industrially available. It has been found that if a certain alkali metal salt is used as a catalyst, methyl etherification of cellulose with methanol proceeds very well and selectively.

  That is, the present invention relates to methylcellulose in which cellulose, preferably low-crystalline powdery cellulose, is reacted with methanol in a subcritical state in the presence of a catalytic amount of a catalyst, preferably a catalyst such as an alkali metal salt of a specific inorganic acid. It is a manufacturing method.

  According to the present invention, an industrially simple and efficient method for producing methyl cellulose can be provided.

〔cellulose〕
The cellulose used in the present invention is not particularly limited, but it is preferable to use low crystalline powdery cellulose. Among these, cellulose having a crystallinity of low-crystalline powdery cellulose of 50% or less is more preferable.
In general, cellulose has several known crystal structures, and is defined as the crystallinity from the ratio of the amorphous part and the crystal part present in a part. The “crystallinity” in the present invention is natural. The degree of crystallinity of type I derived from the crystal structure of cellulose is shown, and is defined by the degree of crystallinity represented by the following formula (1) obtained from the powder X-ray crystal diffraction spectrum.
Crystallinity (%) = [(I _22.6 −I _18.5 ) / I _22.6 ] × 100 Formula (1)
[I _22.6 is the diffraction intensity of the lattice plane (002 plane) (diffraction angle 2θ = 22.6 °) in X-ray diffraction, and I _18.5 is the diffraction intensity of the amorphous portion (diffraction angle 2θ = 18.5 °). Show

Further, the “low crystallinity” of the low crystalline powdery cellulose in the present invention indicates a state in which the ratio of the amorphous part is large in the crystal structure of the above cellulose, and preferably the crystallization obtained from the above formula (1). The degree is desirably 50% or less.
Since there is a very small amount of amorphous part in generally known powdered cellulose, the crystallinity thereof is so-called in the range of approximately 60 to 80% according to the calculation formula (1). It is crystalline cellulose and has very low reactivity in cellulose ether synthesis.

The low crystalline powdery cellulose used in the present invention can be prepared very easily from a sheet-like or roll-like pulp having a high cellulose purity obtained as a general-purpose raw material. The method for preparing the low-crystalline powdery cellulose is not particularly limited. For example, JP-A-62-236801, JP-A-2003-64184, JP-A-2004-331918, etc. Mention may be made of the preparation methods described.
Further, for example, a method of preparing a chip-like pulp obtained by roughly pulverizing a sheet-like pulp by an extruder and further by a ball mill can be mentioned.
As the extruder used in this method, a single-screw or twin-screw extruder can be used, and from the viewpoint of applying a strong compressive shear force, a so-called kneading disk portion is provided in any part of the screw. There may be. Although there is no restriction | limiting in particular as a processing method using an extruder, The method of throwing a chip-form pulp into an extruder and processing continuously is preferable.
As the ball mill, a known vibration ball mill, medium stirring mill, rolling ball mill, planetary ball mill, or the like can be used. There is no restriction | limiting in particular in the material of the ball | bowl used as a medium, For example, iron, stainless steel, an alumina, a zirconia etc. are mentioned. The outer diameter of the ball is preferably 0.1 to 100 mm from the viewpoint of efficiently amorphizing the cellulose. In addition to the ball, a medium such as a rod or tube can be used as the medium.
The ball mill treatment time is preferably 5 minutes to 72 hours from the viewpoint of reducing the crystallinity. Further, in this treatment, it is preferable to carry out the treatment within a temperature range of 250 ° C. or less, preferably 5 to 200 ° C., and further necessary, in order to minimize denaturation and deterioration due to the generated heat. Accordingly, the reaction can be performed in an inert gas atmosphere such as nitrogen.

By using the method as described above, it is possible to control the molecular weight, and it is possible to easily prepare powdered cellulose having a high degree of polymerization and low crystallinity, which is generally difficult to obtain. As, it is 100-2000, More preferably, it is 100-1000.
The crystallinity of the low-crystalline powdery cellulose used in the present invention is preferably 50% or less as determined from the calculation formula (1). When the crystallinity is 50% or less, the reaction with various etherifying agents proceeds extremely well. In this respect, 40% or less is more preferable, and 30% or less is still more preferable. In particular, in the present invention, it is most preferable to use amorphous cellulose that has been completely amorphized, that is, the degree of crystallinity obtained from the above formula is approximately 0%.
The average particle size of the low crystalline powdery cellulose is not particularly limited as long as it can be dispersed well in methanol, but is preferably 300 μm or less, more preferably 20 to 150 μm, and even more preferably 25 to 50 μm.

[Production of methylcellulose]
The method for producing methylcellulose of the present invention is characterized by reacting cellulose, preferably low crystalline powdered cellulose, in the presence of a catalytic amount of catalyst using subcritical methanol. In the present invention, the subcritical state means that the reaction temperature and the reaction pressure are the subcritical and supercritical condition regions of methanol defined in paragraph [0041] of the aforementioned Patent Document 5 [that is, critical temperature; Tc = 512K ( The reaction temperature is 0.9 to 1.5 times that of 239 ° C. and the critical pressure; the reaction pressure region is 0.5 to 4.5 times that of Pc = 8.1 MPa]. Indicates a low area. Specifically, the reaction temperature is a critical temperature; a reaction temperature region (180 to 239 ° C.) in the range of 0.75 to 1.0 times Tc = 512 K (239 ° C.), and the reaction pressure is a critical pressure; Pc = 8 A reaction pressure region (0.8 MPa or more and less than 4.0 MPa) of 0.1 MPa or more and less than 0.5 times of 0.1 MPa is shown. Among these, the reaction temperature region in the present invention is more preferably in the range of 180 to 230 ° C. from the viewpoint of suppressing decomposition and coloring of the raw material cellulose and generated methyl cellulose.
Within this reaction temperature region and reaction pressure region, methyl etherification of cellulose, preferably low crystalline powdered cellulose in the present invention proceeds very well.

The catalyst used in the present invention is not particularly limited, but a metal salt is preferable. For example, an alkali metal salt, an alkaline earth metal salt, or aluminum of an inorganic acid selected from sulfuric acid, phosphoric acid, and boric acid. More specifically, a water-soluble neutralized salt is preferable. By utilizing this water-soluble feature, after the reaction is completed, unreacted methanol is distilled off and collected, and the product can be easily washed with water or with water-containing isopropanol used in general cellulose ether production. It is possible to remove the solid product from the catalyst, which is difficult with a general solid catalyst such as methylcellulose synthesis. Examples of these catalysts include sodium phosphate, cesium phosphate, cesium sulfate, magnesium phosphate, aluminum phosphate, and aluminum borate.
With respect to the amount of these catalysts used, a catalytic amount relative to cellulose is sufficient, and specifically, it is preferably about 1 to 30% by weight, more preferably 10 to 25% by weight based on cellulose. These catalysts can be used alone or in combination of two or more.

In the present invention, the cellulose and the catalyst are reacted in a sufficiently dispersed state in methanol. For this purpose, it is preferable to effectively stir the reaction system with a stirring blade or the like. From this viewpoint, the amount of methanol used is preferably 5 times by weight or more, more preferably 10 to 50 times by weight the amount of cellulose.
The reaction of cellulose and subcritical methanol in the present invention is usually carried out using a pressure vessel such as an autoclave as a reaction vessel, but in a heated pressure-resistant tube reaction vessel, cellulose and catalyst It is also possible to react the methanol dispersion in a slurry state.
Furthermore, a mixer such as a so-called kneader used for kneading resins as disclosed in JP-A-2002-114801 is used as a reaction vessel, and the amount of methanol used is reduced to a pressure pressure or lower during the reaction. It is also possible to adjust so that it is heated and to react with a hot medium such as hot oil.

In addition, the present invention is preferably performed by adding cellulose, catalyst, and methanol to the reaction vessel and then heating to the temperature range to be used with stirring, but it is also necessary to avoid coloring during the reaction. Accordingly, it is more preferable that the reaction is sufficiently performed after sufficiently substituting with an inert gas such as nitrogen in advance.
In the present invention, the methyl group may be bonded to the hydroxyl group at any position in the glucose unit in the cellulose molecule, but the glucose unit can be adjusted by adjusting the reaction conditions such as reaction time, temperature, amount of methanol, and amount of catalyst used. It can be prepared to have any substitution degree, and can be used very widely as a blending component for various compositions.

(1) Calculation of cellulose crystallinity, degree of polymerization, and average particle diameter Calculation of the crystallinity of cellulose used in the present invention was performed under the following conditions using "Rigaku RINT 2500VC X-RAY diffractometer" manufactured by Rigaku Corporation. It was carried out according to the above calculation formula from the peak intensity of the diffraction spectrum measured in (1).
X-ray source: Cu / Kα-radiation, tube voltage: 40 kv, tube current: 120 mA, measurement range: 2θ = 5 to 45 °, measurement sample: produced by compressing pellets with an area of 320 mm ² × thickness of 1 mm, X-ray Scan speed: 10 ° / min
The degree of polymerization was measured by the copper ammonia method described in ISO-4312 method. The average particle size was measured using a laser diffraction / scattering particle size distribution analyzer “LA-920” manufactured by Horiba, Ltd.

(2) Calculation of substitution degree of methylation The degree of substitution indicates the average number of moles of methyl group added per glucose unit in cellulose. As the calculation method, first, methoxyacetylation of a hydroxyl group which is not methyletherified in a product is performed using methoxyacetyl chloride in a pyridine solvent, and a ¹ H NMR spectrum of the methoxyacetylated product is measured, and 3. From the integral ratio of methyl proton and methylene proton signals in the methoxyacetyl group and methyl proton signals in the methyl etherified methyl group observed at 3 to 4.3 ppm (in deuterated chloroform solvent, based on trimethoxysilane) Calculated.

Production Example 1 (Production of Amorphized Powdered Cellulose)
First, a wood pulp sheet (a pulp sheet manufactured by Boleguard, crystallinity 74%) was cut into a chip by using a shredder (“MSX2000-IVP440F” manufactured by Meiko Shokai Co., Ltd.).
Next, the obtained chip-like pulp was charged into a twin screw extruder (“EA-20” manufactured by Suehiro EPM Co., Ltd.) at 2 kg / hr, and the outside was cooled with a shear rate of 660 sec ⁻¹ and a screw rotation speed of 300 rpm. The powder was formed by a one-pass treatment while being cooled.
Next, the obtained powdered cellulose was put into a batch-type medium stirring mill (“Sand grinder” manufactured by Igarashi Machine Co., Ltd .: container volume 800 mL, filled with 720 g of 5 mmφ zirconia beads, filling rate 25%, stirring blade diameter 70 mm). While cooling the outside of the container with cooling water, the mixture was treated for 2.5 hours at a stirring speed of 2000 rpm and a temperature of 30 to 70 ° C. to obtain amorphous powdered cellulose (0% crystallinity, 600 polymerization degree, average particle size) 40 μm in diameter) was obtained. For the reaction of the powdered cellulose, an unsieved product (90% of the input amount) with a sieve having an opening of 32 μm was used.
In addition, the powder cellulose from which each crystallinity differs was prepared by changing the processing time in a ball mill process.

Example 1
In a small autoclave (container capacity: 30 ml), 0.50 g of the non-crystalline powdery cellulose (crystallinity 0%, polymerization degree 600) obtained in Production Example 1 was added, 0.1 g of sodium phosphate, 10 ml of methanol. Was added and purged with nitrogen, followed by deaeration. While stirring, the temperature was raised to 220 ° C. in a high-temperature oil bath. The pressure in the container initially showed 2 MPa. The mixture was stirred for 16 hours and then cooled to room temperature. Unreacted methanol was distilled off, washed with hydrous isopropanol (water content 15%) and acetone, and then dried under reduced pressure to obtain methylcellulose as a light brown solid. From ¹ HNMR analysis after methoxyacetylation, the substitution degree of methylcellulose as a methyl group was 2.8 per glucose unit, and the reaction proceeded very well. Moreover, the same reactivity was shown with respect to all the hydroxyl groups in a cellulose.

Example 2
The reaction was conducted in the same manner as in Example 1 except that 0.1 g of cesium phosphate was used as a catalyst. As a result, methylcellulose was obtained as a light brown solid. The degree of substitution as methyl groups in the produced methylcellulose was 2.0 per glucose unit in the cellulose molecule, and the reaction proceeded very well.

Example 3
A reaction was carried out in the same manner as in Example 1 except that 0.1 g of cesium sulfate was used as a catalyst. As a result, methylcellulose was obtained as a light brown solid. The degree of substitution as methyl groups in the produced methylcellulose was 2.0 per glucose unit in the cellulose molecule, and the reaction proceeded very well.

Example 4
A reaction was carried out in the same manner as in Example 1 except that 0.1 g of magnesium phosphate was used as a catalyst. As a result, methylcellulose was obtained as a light brown solid. The degree of substitution as methyl groups in the produced methylcellulose was 2.5 per glucose unit in the cellulose molecule, and the reaction proceeded very well.

  In the present invention, methylcellulose can be produced by an industrially simple and efficient production method, and the obtained methylcellulose is used as an emulsion stabilizer for cosmetics and foods, as a dispersant or suspension for building materials. It can be suitably used for various applications such as turbid stabilizers, thickeners, adhesives, pharmaceuticals, dispersants and stabilizers, binders, protective colloids, and the like.

Claims (5)

  A method for producing methylcellulose, comprising reacting cellulose with methanol in a subcritical state in the presence of a catalytic amount of a catalyst.   The method for producing methylcellulose according to claim 1, wherein the cellulose is low crystalline powdery cellulose.   The method for producing methylcellulose according to claim 2, wherein the crystallinity of the low-crystalline powdery cellulose is 50% or less.   The method for producing methylcellulose according to any one of claims 1 to 3, wherein the catalyst is an alkali metal salt, alkaline earth metal salt or aluminum salt of an inorganic acid selected from sulfuric acid, phosphoric acid and boric acid.   The method for producing methylcellulose according to claim 4, wherein the catalyst is a water-soluble salt.