JP2001002701A - Production of alkali cellulose and cellulose ether - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an alkali cellulose, improved in the yield when washed, and to provide a method for producing a cellulose ether, giving improved transparency to an aqueous solution of the cellulose ether. SOLUTION: This method for producing an alkali cellulose comprises decreasing oxygen content in a reactor before adding an alkali to such an amount that oxygen content is not more than 1 g per kg of cellulose, then feeding the reactor with oxygen in such an amount as necessary for attaining an aimed viscosity. The cellulose ether is produced by adding an etherifying agent to the resulting alkali cellulose.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing cellulose ether used in the fields of chemistry, medicine and the like.

[0002]

2. Description of the Related Art As a method for lowering the viscosity of cellulose ether, a method using hydrogen peroxide (JP-B-48-192).
432), a method using a volatile acid such as hydrogen halide (Japanese Patent Publication No. 48-26385), a method using ozone (Japanese Patent Application Laid-Open No. 55-145701), a method using gamma rays or an electron beam ( JP-B-47-3964 and JP-B-47-3965 have been proposed. However, these methods are not satisfactory on an industrial level because the reagents used for lowering the viscosity are expensive, the reagents remain in the product, and special equipment is required. Was. Therefore, as a method that does not cause these inconveniences, JP-A-61-264001 proposes to adjust the amount of oxygen in a reactor in an alkali cellulose production process. In the presence of alkali, the degree of polymerization of cellulose is reduced by the reaction between oxygen and cellulose (depolymerization reaction). Therefore, as the amount of oxygen increases, cellulose ether having a lower viscosity can be obtained. Oxygen is inexpensive because it can be used in air, does not require special equipment, and does not remain in the product.

[0003] On the other hand, in Japanese Patent Application Laid-Open No. 59-56401, after powder pulp is charged into a reactor having a stirring structure inside, first, the amount of oxygen in the reactor is changed to the amount of oxygen necessary for a desired viscosity. After that, the inside and outside of the reactor are prevented from entering and exiting oxygen to produce alkali cellulose. As the pulp comes into contact with the alkali, it reacts with oxygen in the reactor and is depolymerized. However, especially when the viscosity at 20 ° C. of a 2% by weight aqueous solution of cellulose ether to be obtained is not more than 100 mm ² / s, especially not more than 20 mm ² / s, the low-viscosity cellulose ether produced by this method will be There is a problem that the so-called washing loss amount is large, that is, the washing product is melted and leaks out of the filter in the washing step with hot water, and that the transparency of the aqueous solution of the obtained product is poor. That is, since the pulp and oxygen come into contact with each other in a state where the distribution of alkali on the pulp is uneven at the initial stage of spraying, the portion where the alkali adheres is depolymerized for the longest time, resulting in a portion having a very low degree of polymerization. However, this part melts out during washing and causes loss. In addition, it is considered that the chemical structure of the cellulose molecules is altered due to the non-uniform depolymerization, which causes a decrease in transparency.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to improve the washing yield in a method for producing cellulose ether and to improve the transparency in an aqueous solution of cellulose ether.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, in the method for producing cellulose ether, the amount of oxygen in the reactor before the production of alkali cellulose was reduced per kg of cellulose. 1g
After reducing to below, by using the alkali cellulose obtained by supplying the required amount of oxygen into the reactor to obtain the desired viscosity, it is possible to improve the washing yield and the transparency in the aqueous solution. The inventors have found that the present invention can be performed, and have accomplished the present invention.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. Cellulose ether is usually added to the pulp as a raw material alkali to make an alkali cellulose,
Although it is produced by adding an etherifying agent, in the present invention, after reducing the amount of oxygen in the reactor before the production of alkali cellulose as compared with the conventional method, the amount of oxygen necessary to obtain the desired viscosity is reduced. By feeding into the reactor,
Manufactured.

The pulp used in the present invention is wood pulp,
What usually becomes a raw material of cellulose ether, such as linter pulp, can be used, and it is preferable that it has good fluidity and an average particle diameter of 500 μm or less. The degree of polymerization of the pulp can be appropriately selected according to the target viscosity of the cellulose ether.

Before the production of alkali cellulose, the smaller the amount of oxygen in the reactor in the reactor, the better, but less than 1 g per kg of cellulose, preferably 0.1 g.
1 g or less. The amount of oxygen is 1 g per kg of cellulose
If the ratio exceeds, the effect of the present invention cannot be obtained. In addition, 1 kg of cellulose means 1 kg of a cellulose component in pulp. 1kg of cellulose before production of alkali cellulose
The amount of oxygen to be reduced to 1 g or less per unit can be adjusted before, during, or after the pulp is charged into the reactor. The method for adjusting the amount of oxygen is not particularly limited.For example, after exhausting the gas in the reactor, a method of refilling a gas containing no oxygen such as nitrogen gas, helium gas, or the like, replacing the gas by passing the gas containing no oxygen is used. Can be carried out by a method or the like. The amount of oxygen can be easily calculated based on the gas law if the type of gas in the reactor before preparation, the space volume in the reactor, the atmospheric pressure, the gas temperature, and the like are known. The oxygen amount in the reactor calculated in this way is set to 1 g or less per 1 kg of cellulose.

Regarding the reactor in the present invention, regardless of the reaction vessel for the etherification reaction, any vessel having a stirring structure inside the vessel and capable of containing alkali cellulose can be applied.

The next supply of oxygen is performed during the addition of the alkali or after the addition of the alkali is completed.
If the supply of oxygen is performed before the addition of the alkali, the effect of the present invention cannot be obtained. The supply of oxygen is performed continuously or intermittently during the addition of the alkali or after the completion of the addition of the alkali. After the addition of the alkali proceeds, for example, one third or more of the alkali addition amount, particularly the total amount Preferably after addition. By supplying oxygen after the addition of the alkali proceeds in this manner, the more the alkali is added, the more uniform the alkali distribution on the pulp, and the more uniform the depolymerization reaction. Oxygen can be supplied several minutes to several tens of minutes after the total addition of the alkali. For the supply of oxygen, oxygen gas or a gas containing oxygen such as air can be used. When air is used, it is preferable because it is inexpensive and has high safety.

The method of supplying oxygen includes a method of injecting an oxygen gas or a gas containing oxygen into a reactor, a method of once exhausting a gas in the reactor and then filling the same with an oxygen-containing gas, and a method of supplying a valve having a different position to the reactor. Is provided, and a gas containing oxygen is supplied from one valve and exhausted from the other valve. Means for moving the oxygen gas or the gas containing oxygen in the method of providing a valve at a different position includes a supply by a compressed gas, a discharge or supply of a gas by an exhaust fan, and a discharge of a gas by a vacuum pump.

The supply amount of oxygen depends on the degree of polymerization of the pulp used,
The target viscosity of the cellulose ether, the depolymerization temperature of oxygen and cellulose, the time of the depolymerization reaction, and the amount of oxygen already present in the reactor before the supply of oxygen vary depending on the amount of the cellulose ether. Is supplied in an amount of 0.5 g or more. If the supply amount of oxygen is 0.1 g or less per 1 kg of cellulose, the desired viscosity cannot be obtained. Here, the target viscosity of the cellulose ether of the present invention is lower than the viscosity of the cellulose ether obtained by a method without supplying oxygen.

Examples of the added alkali include sodium hydroxide, potassium hydroxide and the like. The alkali concentration is 10 to 60% by weight, preferably 20 to 55%.
% By weight. When the alkali concentration is less than 10% by weight, the water content in the alkali cellulose increases, and the reaction efficiency of the etherification reaction in the subsequent step decreases. On the other hand, when the alkali concentration exceeds 60% by weight, the alkali distribution of the alkali cellulose becomes uneven. In addition, the transparency of the cellulose ether solution is reduced. The weight ratio of alkali to cellulose in the alkali cellulose can be appropriately changed depending on the desired degree of substitution of the ether group, but is usually 0.01 to 2.0, preferably 0.5 to 1.5. The weight ratio of alkali is 0.1.
If it is less than 01, the degree of substitution of the ether group is reduced, so that the transparency of the cellulose ether solution is reduced. If it exceeds 2.0, the reaction efficiency of the etherification reaction, which is a subsequent step, is reduced due to excess alkali.

The production and depolymerization of the alkali cellulose are preferably carried out with sufficient stirring. This makes it possible to uniformly distribute alkali, oxygen gas or a gas containing oxygen, and heat in the pulp, and the effects of the present invention can be obtained.

In the present invention, a depolymerization catalyst can be added as required. Examples of the depolymerization catalyst include cobalt chloride, benzenediazonium hydroxide and the like. The addition amount thereof is preferably 3 mg or less per 1 kg of cellulose, and the effect of the depolymerization catalyst does not change even if it is added more.

The depolymerization reaction is usually carried out at 60 to 100 ° C., preferably 70 to 90 ° C. Reaction temperature is 60 ° C
When the temperature is less than 100 ° C., the progress of the depolymerization reaction becomes slow, so that a long time is required for the reaction.

After the production and the depolymerization reaction of the alkali cellulose are completed, an etherification reaction is carried out by a usual method,
Through a purification step, a cellulose ether is obtained. Examples of the cellulose ether in the present invention include methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl cellulose and the like. The etherifying agent for the alkali cellulose in the present invention is not particularly limited, and examples thereof include chloromethyl, propylene oxide, and ethylene oxide.

[0018]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Example 1 In a reactor having an internal stirring structure having a volume of 144 liters,
8 kg of powdery pulp having a degree of polymerization Dpw = 860 was charged. At this time, the amount of oxygen per 1 kg of cellulose in the reactor was 4.8 g. Reduce the gauge pressure in the reactor to minus 0.0
After reducing the pressure to 96 MPa, the operation of returning to 0 MPa with nitrogen gas was repeated twice. This operation reduced the amount of oxygen in the reactor to 0.02 g per kg of cellulose. Next, an aqueous solution containing 16.3 kg of a 49% by weight aqueous sodium hydroxide solution and 8 mg of cobalt chloride was added under stirring for 20 minutes. Thereafter, while maintaining the internal temperature of the reactor at 80 ° C., air was passed through the reactor at a rate of 10 NL / min for about 24 minutes, and after the completion of the ventilation, mixing was performed until 25 minutes had elapsed from the start of the ventilation. The cumulative amount of oxygen that had passed was 8.98 g per kg of cellulose. Aeration was performed by connecting compressed air to a valve at one end of the reactor and venting gas in the reactor from a valve at another end.

After the completion of the aeration, the gauge pressure in the reactor was reduced to minus 0.096 MPa, and 2.8 kg of dimethyl ether and 13.6 kg of chloromethyl were added thereto.
The reaction was performed at 0 ° C. for 110 minutes. The unpurified product after the reaction was dispersed in hot water to prepare a slurry containing 15 g of methylcellulose. The slurry was filtered with a pressure filter, and the obtained cake was dried. As a result, 14.1 g of methylcellulose was recovered. The recovery was 94.1% by weight. The viscosity of the obtained 2% by weight aqueous solution of methylcellulose was measured according to the capillary viscometer method of the Japanese Pharmacopoeia, and was 9.8 mm ² /
s. The light transmittance of the obtained 2% by weight aqueous solution of methylcellulose was measured using a photoelectric colorimeter PC-50, a cell length of 20 m.
m was 97.5% as measured using visible light.

Examples 2 to 6 and Comparative Examples 1 to 4 Table 1 shows the results obtained by changing the amount of oxygen before the addition of sodium hydroxide and the amount of oxygen supplied by the aeration operation in the same manner. The amount of oxygen before the addition of sodium hydroxide was adjusted by changing the degree of pressure reduction.

[0021]

According to the present invention, pulp and oxygen are contacted for the first time after the alkali is added in a state of low oxygen and the distribution of the alkali becomes uniform. Is improved, and a product having good transparency in an aqueous solution can be obtained.

[0022]

[Table 1]

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Atsushi Hatayama 28, Nishifukushima, Nishigusuku-mura, Nakakubijo-gun, Niigata Prefecture Shin-Etsu Chemical Co., Ltd. Synthetic Technology Laboratory F-term (reference) 4C090 AA03 AA06 BA24 BA28 BA30 BB92 CA07 CA27 CA33 CA36 DA22 DA31

Claims (2)

[Claims] 1. A method for producing alkali cellulose, comprising the steps of reducing the amount of oxygen in a reactor before adding alkali to 1 g or less per kg of cellulose, and obtaining a desired viscosity during or after addition of alkali. Supplying a necessary amount of oxygen into the reactor. 2. A method for producing cellulose ether, comprising adding an etherifying agent to the alkali cellulose obtained by the method according to claim 1.