JP2010174261A - Apparatus for the industrial production of methyl hydroxyalkyl cellulose - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a large amount of MHAC extremely economically, while certainly and simultaneously performing actions of removing generated heat to avoid local temperature peaks; controlling pressure rise safely; nearly preventing accumulation of products at the product changeover; suppressing side reaction products; and obtaining products with uniform substitution patterns. <P>SOLUTION: The apparatus for industrially producing methyl hydroxyalkyl celluloses (MHACs) by the reaction of cellulose with an alkali metal hydroxide and subsequent reaction with an alkyl halide and a hydroxy alkylating agent includes a reactor which has an L/D ratio of less than 2.5. The reaction is carried out batchwise in a reactor in which the unmixed regions are minimized and the batch reactor is preceded at the inlet by a continuously operated cellulose milling facility and is followed at the outlet by a continuously running plant for milling and drying the products. The product is transported by the action of gravity. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an apparatus for industrial production of methylhydroxyalkylcellulose (hereinafter referred to as MHAC), preferably methylhydroxylethylcellulose (MHEC) and methylhydroxypropylcellulose (MHPC).

  It is known that MHAC and these specific mixed ethers can be produced in a multistage process. In the first stage, the cellulose used is gently milled to the desired particle size spectrum. In the second stage, the milled cellulose is intimately mixed and activated in a mixer with a concentrated aqueous solution of alkali metal hydroxide, especially sodium hydroxide, to form a cellulose alkali metal salt. This pretreatment is critical to the nature of the resulting cellulose ether. A known method is spray alkalization in a suitable mixing device, in which milled cellulose is sprayed with an alkaline solution. In the slurry step, the milled cellulose is slurried with a non-solvent and then alkali is added. The more uniform the alkalinization in the slurry, the more uniformly substituted product is obtained. In the grinding and alkalizing step, cellulose is slurried in an aqueous sodium hydroxide solution and then passed through a screw press or a sieve drum press.

  In the third stage, a heterogeneous reaction of an alkyl group halide added as an etherifying agent, for example, methyl chloride with a hydroxyalkylating agent such as ethylene oxide and / or propylene oxide occurs. This reaction is exothermic and proceeds under pressure. The reaction sequence in this method can be partially alkalized, then partially etherified, and repeated partially alkalized or etherified.

  The difficulty is that this alkalinization and etherification is accompanied by considerable heat generation and simultaneous pressure increase as an exothermic reaction step. Furthermore, there is a risk that uncontrolled temperature peaks lead to a decrease in the molecular weight of cellulose.

  Furthermore, in order to achieve good economic efficiency in an industrial production process, this reaction proceeds with a high space-time yield and, for methyl and hydroxyalkyl substitution, respectively, the average degree of substitution DS of methyl There is a need to provide high throughput combined with a uniform substitution pattern characterized by the average molar substitution MS (HAC) of (M) and hydroxyalkyl.

  Various properties of this product, such as thermal aggregation point, solubility, viscosity, film-forming ability and adhesive strength, are set by the degree of etherification and the type of substituent.

  This further process step comprises the purification, milling and drying of the cellulose ether.

  The production of cellulose ethers, their properties and applications are described in general form in Non-Patent Document 1 and Non-Patent Document 2.

Cellulose ethers are produced without the use of a separate reaction vessel for the production of cellulose alkali metal salts or heterogeneous etherification in a single stage process by reacting cellulose to cellulose ether in a mechanical mixer It is known from Patent Document 1 that this can be done. Containing a ladle mixer with chopper in a closed vessel with suitable internal pressure and cooling of the inner wall of the vessel, which can adjust the mixing element moving at high speed, the heat of reaction generated in alkalinization is substantially due to vaporization of the alkyl halide And the evaporated alkyl halide is condensed on the cooling wall of the vessel. The mixing vessel having a total volume of 20 m ³ described in Patent Document 1 is charged with the milled cellulose into the reactor and then to the end point of discharging methylcellulose having DS = 1.3 at 75% conversion. Having a batch time of 4 hours calculated by This document describes, for ethylcellulose, a reactor with a total volume of 25 m ³ that makes it possible to produce ethylcellulose with DS = 2.45 with a conversion of 75% in 4.5 hours. Yes. The maximum capacity that can be reached is 6000 tons per year with a usage time of 8400 hours / year.

It is impossible to further increase the capacity and improve the economy using the 20 or 25 m ³ reactor described in Patent Document 1.

  Depending on the method described, some of the described methods are exothermic reactions because sufficiently rapid mixing, high mixing efficiency and sufficiently high cooling capacity cannot be obtained industrially for relatively large reactors. The pressure and temperature rise caused by can not be controlled. Thus, the reactor size claimed by the prior art represents the upper limit of safe control for the reaction.

  U.S. Patent No. 6,057,031 describes a process for producing polysaccharide ethers using a multi-stage agitator and a reactor having baffles. A universal mixer for different ingredients comprises a multistage stirrer and a stirring vessel with a central vertical mixer shaft with baffles. This design is limited to a shaft attached at one end, and as a result, the torque for mixing the starting material and reaction product is limited, which limits the capacity.

  Patent Document 3 also describes a stirring vessel having an axial flow pump type stirrer and at least one baffle and a method of mixing liquids with the help of this stirring vessel. A vertically mounted central stirrer with baffles configured as a hydrofoil profile allows quick mixing of liquids of different densities in the axial direction. This arrangement is also constrained by the notion of a shaft attached at one end, limiting capacity.

  U.S. Patent No. 6,057,032 describes an upright container having a central agitator and baffle for rapid and uniform mixing of highly viscous media. The difficulty is the constrained torque that can be introduced from a shaft attached at one end, which limits the volume of the reaction product that undergoes mixing and homogenization. An apparatus as described in US Pat. No. 6,057,056 for mixing a solid / liquid or liquid / liquid substance to produce a suspension, transverse to the flow direction operable at different rotational speeds. This is also true for devices with built-in split tools.

  Patent Document 6 describes an apparatus that disperses a solid that is sensitive to shearing in a liquid by a horizontally installed shaft or an obliquely mounted shaft. Compared to a vertical mixer, heavier particles are lifted, resulting in better mixing of the suspension. The difficulty with this arrangement is the limited torque and throughput limits that can be introduced from a shaft attached at one end.

  In industrial manufacturing processes, it is known that increased throughput can be achieved by increasing the volume of the reactor. However, as described in Patent Document 1, for example, in the production of MHAC, it is necessary to remove heat from the reactor wall for the exothermic reaction of alkalinization and etherification. As a result, prior art reactors have a length / cross-sectional area ratio of> 2.5.

In Patent Document 7, a finely pulverized polysaccharide slurry, an aqueous alkali metal hydroxide solution, and an etherifying agent are introduced almost continuously into a tube reactor (with a serpentine tube) that does not obstruct the flow of the slurry. And describes a continuous process for the production of polysaccharide ether in which the slurry is conveyed in the reactor during the reaction. The length / cross-sectional area ratio (L / D) of the tube reactor is from 5 to 2000, preferably from about 100 to 800. Although it was possible to achieve capacities of over 6000 tonnes per year with this reactor, the large L / D ratio is due to product residues in the reactor when changing products frequently to different substitution patterns. It is disadvantageous for such a tube reactor.

DE-A-2 635 403 EP-A-023692 EP-A-0347653 EP-A-0470493 SE940 1144A US-A-4 199 266 US-A-4015067

Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, 1986, A5, 461-488, VCH Verlagsgesellschaft, Weinheim Encyclopedia of Polymer Science and Engineering, 2nd edition, 1985, 3, pp. 226-269

  Therefore, the generated heat of reaction is removed to avoid local temperature peaks, the pressure rise is safely controlled, product build-up during product changes is largely avoided, and by-products are suppressed and uniform. It is an object of the present invention to produce MHAC in a very economically large quantity while simultaneously ensuring that a replacement pattern product is obtained.

  Surprisingly, the desired MHAC product can be produced in high quality and economically by stepwise alkalinization and etherification using a reactor of the present invention having an L / D ratio of less than 2.5. It turns out that you can.

  Accordingly, the present invention provides an apparatus for industrially producing methyl hydroxyalkyl cellulose (MHAC) by reacting cellulose with an alkali metal hydroxide and subsequently reacting an alkyl halide with a hydroxyalkylating agent. An apparatus comprising a reactor having an L / D ratio of less than 2.5. The reaction is carried out in batches in the reactor, in which the unmixed zone is minimized, and the batch reactor is pre-positioned with a continuous cellulosic mill facility at the inlet and the product at the outlet. A continuous operation plant for milling and drying is followed, and this product is transported by the action of gravity.

Surprisingly, the combination of a continuous cell milling plant, a batch reactor with an L / D ratio of less than 2.5, and a continuous plant for milling and drying the product is the first to empty. It has been found that the volume fraction is minimized, allowing the economical production of large quantities of MHAC. This method is advantageous for producing MHAC with a capacity of over 6000 tons per year.

  This reactor preferably comprises a mixing device and a mechanical mixer with a horizontal shaft attached at least one end, and particularly preferably driven at both ends to enable obtaining high torque, thereby starting Mix the materials quickly and vigorously, shorten the diffusion path and homogenize the contact of the anhydroglucose units with etherification and alkylation reactions. Advantageously, the heat of reaction is reliably removed, the empty volume fraction is minimized, and product build-up during product changes is avoided.

  The reactor can be equipped with a shaft for mixing drive so that mutual cleaning of the shaft is possible.

  In a special embodiment, the shaft can also be split and the product can be backmixed in different directions and rotational speeds.

  For rapid ejection, both the rotational speed and direction of rotation can be individually tailored to the product being manufactured. Furthermore, complete discharge is ensured by the addition of a liquid, preferably water. This also achieves the purpose of flushing the reactor in order to ensure that no product residue remains in the apparatus. Selection and arrangement of suitable spray nozzles ensures uniform wetting and cleaning of all areas including the mixing tool.

  The reactor preferably delivers the heat of reaction by vigorous cooling of the inner wall and by one or more steam domes distributed symmetrically over the length of the reactor for reflux cooling by condensation of the vapor phase. Configured to remove.

  This reaction is usually carried out in the absence of solvents at temperatures up to 150 ° C., preferably at temperatures from 90 to 110 ° C. and pressures up to 40 bar, preferably 20 to 30 bar.

Furthermore, the reactor is preferably configured to minimize the area where mixing does not occur for technical reasons. For the purposes of the present invention, the empty volume fraction is the ratio of the unmixed region volume V _{U to} the total volume V _T. The minimum possible empty volume fraction for each desired reactor size can be determined by calculation. This calculation requires the mixing tool to be the appropriate minimum distance from the wall, and in addition, there is a requirement that there is no area in the area of the installed chopper where no mechanical movement occurs and mixing cannot occur. Based on.

Surprisingly, the smallest possible empty volume fraction can be obtained with a length / diameter ratio (L / D) of less than 2.5 in a volume greater than 25 m ³ , and as a result is proportional to this reduction. It was found that the proportion of unmixed finished products was reduced and product quality was improved. It has been found that at L / D less than 2.5, the V _U / V _T ratio should be less than 0.007, for example in the range of 0.007 to 0.004.

  In a particularly preferred embodiment having an L / D of 2.35, the empty volume fraction is minimized, and the reactor comprises a chopper disposed on the inner wall and has a cylindrical shape, the inlet And the outlet valves are arranged for complete filling and discharging, and the shape of the shaft is such that the caked product is scraped off at the end face of the reactor, resulting in a high quality MHAC product. It is done.

As an alternative to the procedure described above, the downstream of the reactor is advantageously characterized in that the vessel is alternately filled and likewise discharged alternately to ensure a continuous product flow. It has been found that two buffer vessels can maintain continuous operation of the milling and drying plant.

  Furthermore, in the case of a plant with a capacity of more than 6000 tons per year, the installation of two reactors that are operated alternately enables a continuous product flow to be fed to the milling and drying units. Turned out to be. This eliminates the need for a separate buffer container.

  The present invention further provides the use of an apparatus for carrying out the reaction described above.

In particular, according to the present invention, a fiber-free product that dissolves to produce a clear solution is obtained in increased yield. Thus, the present invention further provides a MHAC that can be obtained by use of the device of the present invention and that dissolves to give a clear solution having a relative turbidity of less than 10 NTU. Turbidity is measured by a laboratory nephelometer model 2100AN (Hach Company, Loveland, Colorado, USA). The object of the present invention, NTU (nephelometric turbidity units (N ephelometric T urbidity U nits) ) is a relative scattering signal. The greater the value of this relative scattering signal NTU, the higher the turbidity of this solution and the worse the transparency of the product concerned.

Example 1 (L / D <2.5)
A reaction mixer having a ratio of L / D = 1.5 and equipped with a spatula as mixing element is charged with 67.92 kg of milled cellulose (Ethenier F). The reactor is subsequently evacuated and then returned to atmospheric pressure with nitrogen. Then 150.4 kg of 50% strength aqueous sodium hydroxide solution are added. After this alkalinization, 41.76 kg of propylene oxide are added, followed by the introduction of 218.9 kg of chloromethane / dimethyl ether mixture having a chloromethane content of 52.6%.

  After the reaction is complete and the reaction product is purified, methyl hydroxypropyl cellulose having an average methyl substitution degree of DS methyl = 1.88 and a molar substitution degree of MS = 0.21 is obtained. A value of 6.14 NTU is obtained by turbidity measurement on a 2% strength solution using a laboratory nephelometer model 2100AN (Hach Company, Loveland, Colorado, USA). This value is significantly lower and better than that for methylhydroxypropylcellulose produced in Example 2 using a reactor having an L / D greater than 2.5.

Example 2 (L / D> 2.5) Comparative Example L / D = 2.6 A reaction mixer equipped with a spatula as a mixing element was 990 kg of milled cellulose (Ethenier F) Load it. The reactor is subsequently evacuated and then returned to atmospheric pressure with nitrogen. Next, 1505 kg of 50% strength aqueous sodium hydroxide solution is added. After this alkalization, 300 kg of propylene oxide are added, followed by introduction of 1861 kg of chloromethane / dimethyl ether mixture having a chloromethane content of 47%. After the reaction is complete and the reaction product is purified, methyl hydroxypropylcellulose having an average methyl substitution degree of DS _methyl = 1.98 and a molar substitution degree of MS _propoxy = 0.28 is obtained. A value of 15.3 NTU is obtained by turbidity measurement on a 2% strength solution using a relative turbidity measuring device. This value is significantly worse than in the case of methylhydroxypropylcellulose produced in Example 1 in a reactor having an L / D of 1.5. The product of this example has a higher fiber content than that of Example 1 described in the present invention, and the solution is less transparent.

  The features and aspects of the present invention are as follows.

  1. A process for industrially producing methyl hydroxyalkyl cellulose (MHAC) by reacting cellulose with an alkali metal hydroxide and subsequently reacting an alkyl halide with a hydroxyalkylating agent, wherein In batches in a reactor having an L / D ratio of less than 5 and in which the unmixed zone is minimized, and the batch reactor is pre-installed with a continuously operating cellulose mill facility at the inlet. And the outlet is followed by a continuous plant for milling and drying the product, and the product is transported by the action of gravity.

  2. A process according to claim 1, characterized in that the reactor comprises a mechanical mixer with a mixing tool having at least one horizontal axis attached at both ends.

  3. 3. The method according to 1 or 2 above, wherein the shaft is driven at both ends.

  4). 4. A process according to any one of the above 1 to 3, characterized in that the reactor is located directly opposite each other and has two separate axes that can be operated independently at different rotational speeds, directions and shapes. .

5). The reactor has a cylindrical shape, and the inlet and outlet valves are arranged for complete filling and discharging,
And the shape of this shaft is like scraping off the caked product at the end face of this reactor, and the number and arrangement of this chopper matches the shape of the mixer with shaft The method according to any one of 1 to 4 above.

6). 6. The method according to any one of 1 to 5 above, wherein the minimum empty volume fraction V _U / V _T is <0.007.

  7). An apparatus for industrially producing methylhydroxyalkylcellulose (MHAC) by reacting cellulose with an alkali metal hydroxide and subsequently reacting an alkyl halide with a hydroxyalkylating agent, comprising 2.5. An apparatus comprising a reactor having an L / D ratio of less than

  8). 8. A device according to claim 7, characterized in that the reactor comprises a mechanical mixer with a mixing tool having at least one horizontal axis attached at both ends.

  9. 9. A device according to claim 8, wherein the shaft is driven at both ends.

  10. 10. An apparatus according to any one of the above 7 to 9, characterized in that the reactor is located directly opposite each other and has two separate axes that can be operated independently at different rotational speeds, directions and shapes. .

11. The reactor has a cylindrical shape, and the inlet and outlet valves are arranged for complete filling and discharging,
And the shape of this shaft is like scraping off the caked product at the end face of this reactor, and the number and arrangement of this chopper matches the shape of the mixer with shaft The apparatus according to any one of 7 to 10 above.

12 12. Apparatus according to any one of the above 7 to 11, characterized in that the reactor has an empty volume fraction V _U / V _T of less than 0.007.

  13. 12. The apparatus according to any one of 7 to 11 above for producing methylhydroxyalkylcellulose, wherein the methylhydroxyalkylcellulose can be dissolved to obtain a transparent solution having a relative turbidity of less than 10 NTU. use.

  14 The methyl hydroxyalkyl cellulose obtainable by the method according to any one of 1 to 6 above, wherein the methyl hydroxyalkyl cellulose can be dissolved to obtain a transparent solution having a relative turbidity of less than 10 NTU. .

Claims (1)

An apparatus for industrially producing methylhydroxyalkylcellulose (MHAC) by reacting cellulose with an alkali metal hydroxide and subsequently reacting an alkyl halide with a hydroxyalkylating agent, comprising 2.5. An apparatus comprising a reactor having an L / D ratio less than 25 and a volume greater than 25 m ³ .