Continuous process for producing depolymerized cellulose ether

Abstract

To provide a continuous production method of depolymerized cellulose ether, capable of saving a space, having high productivity, reducing adhesion of powder of cellulose ester to a reactor, and capable of acquiring depolymerized cellulose ester in which occurrence amounts of yellowness and debris can be suppressed.SOLUTION: There is provided a production method of depolymerized cellulose ether comprising: a) a humidification step for bringing raw material cellulose ether A which is continuously supplied from a raw material tank 1 to a humidification tank 2, and whose temperature is 3°C or more and less than 40°C, into contact with steam B, for acquiring humidified cellulose ether; b) a temperature rise step for heating the humidified cellulose ether, for acquiring temperature rise cellulose ether; c) a depolymerization step for continuously bringing gas hydrochloric acid C with the temperature rise cellulose ether, for acquiring the depolymerized cellulose ether product; d) and a neutralizing step for acquiring the depolymerized cellulose ether F, by mixing the depolymerized cellulose ether product and the basic compound E.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a continuous process for producing depolymerized cellulose ethers. [Background technology]

[0002] Low-polymerization cellulose ethers are used for film coating of solid preparations such as tablets. Such film coatings are intended to mask the unpleasant taste of drugs, prevent denaturation of the contained drugs, and control the dissolution behavior in the digestive tract after ingestion. In addition, films obtained by drying solutions of low-polymerization cellulose ethers are widely used as bases for film preparations and hard capsules.

[0003] Generally, low-polymerization cellulose ethers are obtained by depolymerizing high-polymerization cellulose ethers. A widely used depolymerization method involves contacting a powdered high-polymerization cellulose ether with an acid such as hydrogen chloride and heating it. As described in Patent Documents 1 and 2, the apparatus used for depolymerizing high-polymerization cellulose ethers is generally a batch-type reactor in which the reactor itself rotates, such as a conical blender. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 08-301901 [Patent Document 2] Special Publication No. 2020-531599 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the methods described in Patent Documents 1 and 2 have the drawback of requiring a large batch reactor when industrially mass-producing a low-polymerization degree cellulose ether, resulting in large installation space for the reactor and high investment costs.

[0006] Furthermore, when low-polymerization cellulose ether is produced on an industrial scale using a batch reactor, there is a problem that the adhesion of cellulose ether powder to the inside of the reactor increases over time as the number of production runs increases. When the adhesion of cellulose ether powder increases inside the reactor, the heat transfer characteristics from the reactor jacket to the cellulose ether powder deteriorate, resulting in problems such as variations in the viscosity of the obtained low-polymerization cellulose ether from batch to batch and poor discharge of the low-polymerization cellulose ether from the reactor. Furthermore, when the adhered cellulose ether powder peels off from the inside of the reactor, it becomes black foreign matter and gets mixed into products, thereby reducing the commercial value of the low-polymerization cellulose ether. In order to remove this cellulose ether powder adhesion, when a low-polymerization degree cellulose ether is industrially produced in a batch-type reactor, it has often become necessary to carry out cleaning of the reactor between batches.

[0007] If a continuous reactor is used instead of a batch reactor, the reactor can be made smaller, and it is thought that a low polymerization degree cellulose ether can be efficiently produced industrially while reducing the reactor installation space and investment costs. However, in a continuous reactor, unlike a batch reactor, it is not possible to perform a reactor cleaning operation between batches, so it is difficult to remove cellulose ether powder that has adhered once. In addition, it is difficult to prevent adhesion, so continuous production of a low polymerization degree cellulose ether has not been realized. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a continuous method for producing depolymerized cellulose ether, which is space-saving, highly productive, can reduce adhesion of cellulose ether powder to a reactor, and can produce depolymerized cellulose ether with reduced yellowness and reduced amounts of foreign matter. [Means for solving the problem]

[0008] As a result of intensive research aimed at solving the above-mentioned problems, the present inventors have found that by adjusting the temperature of the raw cellulose ether supplied from a raw material tank to a humidity control tank to less than 40°C and by providing a humidity control step in which the supplied raw cellulose ether is brought into contact with water vapor, it is possible to reduce adhesion of cellulose ether powder to a reactor and continuously produce depolymerized cellulose ether with reduced yellowness and reduced amounts of foreign matter, which led to the completion of the present invention. That is, the present invention provides the following method for continuously producing depolymerized cellulose ether. [1] 1. A continuous process for producing depolymerized cellulose ethers, comprising: a) a humidity control step of contacting a raw cellulose ether continuously supplied from a raw material tank to a humidity control tank with water vapor to obtain a humidity-controlled cellulose ether; b) a temperature-raising step of heating the humidity-controlled cellulose ether continuously supplied in the humidity-controlling step to obtain a temperature-controlled cellulose ether; c) a depolymerization step of continuously contacting the heated cellulose ether with gaseous hydrogen chloride to depolymerize the cellulose ether, thereby obtaining a depolymerized cellulose ether product; d) a neutralization step of mixing the depolymerized cellulose ether product with a basic compound to obtain a depolymerized cellulose ether; At least and the temperature of the raw cellulose ether continuously supplied from the raw material tank to the humidity control tank is 3°C or higher and lower than 40°C. [2] The method for continuously producing depolymerized cellulose ether according to [1], further comprising, between the depolymerization step and the neutralization step, a washing step of removing hydrogen chloride and water from the depolymerized cellulose ether product continuously supplied by the depolymerization step to obtain a washed depolymerized cellulose ether product. [3] The method for continuously producing depolymerized cellulose ether according to [1] or [2], wherein the ratio of the supply rate of the humidity-conditioned cellulose ether from the humidity conditioning step to the temperature-raising step to the discharge rate of the depolymerized cellulose ether product discharged from the depolymerization step is in the range of 0.9 to 1.1. [4] The method for continuously producing a depolymerized cellulose ether according to any one of [1] to [3], further comprising, after the neutralization step, a cooling step of cooling the depolymerized cellulose ether. [5] The method for continuously producing depolymerized cellulose ether according to any one of [1] to [4], wherein the temperature of the humidity-conditioned cellulose ether continuously supplied from the humidity-conditioning step to the temperature-raising step is 50°C to 90°C. [6] The method for continuously producing a depolymerized cellulose ether according to any one of [1] to [5], wherein in the humidity adjustment step, the jacket temperature of the humidity adjustment tank is 20°C to 120°C. [7] The method for continuously producing a depolymerized cellulose ether according to any one of [1] to [6], wherein the raw material cellulose ether is at least one selected from the group consisting of alkyl cellulose, hydroxyalkyl cellulose, and hydroxyalkyl alkyl cellulose. Depolymerized cellulose ether has a lower degree of polymerization than the cellulose ether before depolymerization, and includes cellulose ethers with a low degree of polymerization that are used for film coating of solid preparations such as tablets. [Effects of the Invention]

[0009] According to the present invention, a cellulose ether with a low degree of polymerization, which has reduced yellowness and reduced amounts of foreign matter, can be produced by a continuous production method that requires less space and is highly productive. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an example of a manufacturing system used in the manufacturing method of the present invention. [Figure 2] FIG. 1 is a diagram showing an example of a manufacturing system used in the manufacturing method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Depolymerized cellulose ether can be produced by a space-saving, highly productive continuous production method that includes at least a humidity control step in which steam is brought into contact with raw cellulose ether, which is continuously supplied from a raw material tank to a humidity control tank, to obtain a humidity-controlled cellulose ether; a temperature increase step in which the humidity-controlled cellulose ether, which is continuously supplied from the humidity control step, is heated to obtain a temperature-controlled cellulose ether; a depolymerization step in which gaseous hydrogen chloride is continuously brought into contact with the temperature-controlled cellulose ether to depolymerize it, to obtain a depolymerized cellulose ether product; and a neutralization step in which the depolymerized cellulose ether product is mixed with a basic compound to neutralize it, to obtain a depolymerized cellulose ether, wherein the temperature of the raw cellulose ether continuously supplied from the raw material tank to the humidity control tank is 3°C or higher and lower than 40°C.

[0012] A continuous method for producing depolymerized cellulose ether will be described. In the following description, the term "continuous method" refers to a method in which, during production, powder is continuously supplied from a previous process to each process and discharged to a subsequent process, and is distinguished from a batch method in which the supply and discharge of raw material (powder) to each process are discontinuous. The devices used in each step are connected by piping. It is preferable to provide rotary valves at the powder supply and discharge ports of the devices used in each step to quantitatively supply and discharge the powder.

[0013] First, the raw material cellulose ether will be described. Examples of the raw material cellulose ether include cellulose ethers with a high degree of polymerization, such as hydroxyalkyl alkyl cellulose, alkyl cellulose, and hydroxyalkyl cellulose.

[0014] Examples of hydroxyalkyl alkyl cellulose include hydroxypropyl methylcellulose (hereinafter also referred to as "HPMC") having preferably 4.0 to 13.0% by mass of hydroxypropoxy groups and preferably 19.0 to 32.0% by mass of methoxy groups, hydroxyethyl methylcellulose having preferably 4.0 to 15.0% by mass of hydroxyethoxy groups and preferably 20.0 to 26.0% by mass of methoxy groups, and hydroxyethyl ethylcellulose having preferably 8.0 to 20.0% by mass of hydroxyethoxy groups and preferably 20.0 to 38.0% by mass of ethoxy groups.

[0015] Examples of alkyl cellulose include methyl cellulose (hereinafter also referred to as "MC") in which methoxy groups preferably account for 18.0 to 36.0% by mass, and ethyl cellulose in which ethoxy groups preferably account for 40.0 to 50.0% by mass.

[0016] Examples of hydroxyalkyl cellulose include hydroxyethyl cellulose in which the hydroxyethoxy group content is preferably 2.0 to 70.0% by mass, and hydroxypropyl cellulose in which the hydroxypropoxy group content is preferably 2.0 to 70.0% by mass.

[0017] The content of alkoxy groups and hydroxyalkoxy groups in alkyl cellulose, hydroxyalkyl cellulose, and hydroxyalkyl alkyl cellulose can be measured in accordance with the analytical method for hypromellose in the 18th edition of the Japanese Pharmacopoeia.

[0018] The viscosity of a 2% by mass aqueous solution of the raw cellulose ether at 20° C. is preferably 400 to 200,000 mPa·s, more preferably 400 to 150,000 mPa·s, and even more preferably 400 to 100,000 mPa·s, from the viewpoint of the washability of the raw cellulose ether. The viscosity of a 2% by mass aqueous solution of the starting cellulose ether at 20°C can be measured using a single-cylinder rotational viscometer in accordance with the rotational viscometer method in the viscosity measurement method of the general test methods described in the Japanese Pharmacopoeia, 18th Edition, if the viscosity is 600 mPa s or more. On the other hand, if the viscosity is less than 600 mPa s, it can be measured using an Ubbelohde viscometer in accordance with the capillary viscometer method in the viscosity measurement method of the general test methods described in the Japanese Pharmacopoeia, 18th Edition.

[0019] The starting cellulose ether can be produced by a known method. For example, it can be obtained by a production method including at least a step of contacting pulp with an alkali metal hydroxide solution to obtain alkali cellulose, a step of reacting the alkali cellulose with an etherifying agent to obtain a cellulose ether product, a step of washing and drying the cellulose ether product, and an optional grinding step. The alkali metal hydroxide solution is not particularly limited, but from an economical point of view, an aqueous alkali metal hydroxide solution is preferred. The aqueous alkali metal hydroxide solution is not particularly limited, but from an economical point of view, an aqueous sodium hydroxide solution is preferred. The etherifying agent is not particularly limited, but examples thereof include alkyl halides such as methyl chloride and ethyl chloride, and alkylene oxides such as ethylene oxide and propylene oxide. Thereafter, the cellulose ether product can be washed, dried and pulverized as necessary to produce the raw cellulose ether. The water content of the raw cellulose ether is preferably more than 0 and 2.00% by mass, more preferably 0.1 to 1.50% by mass, from the viewpoint of preventing aggregation of the raw cellulose ether. The moisture content is defined as {(total mass of cellulose ether−bone dry mass of cellulose ether) / (total mass of cellulose ether)}×100%. Here, "total mass of cellulose ether" refers to the mass of the raw cellulose ether before drying, which is precisely weighed according to the "Loss on Drying Test" in the Japanese Pharmacopoeia, 18th Edition. Also, "bone-dry mass of cellulose ether" refers to the mass of the raw cellulose ether after drying according to the "Loss on Drying Test" in the Japanese Pharmacopoeia, 18th Edition.

[0020] The temperature (product temperature) of the raw cellulose ether is 3°C or higher and lower than 40°C, preferably 5°C to 38°C, more preferably 7°C to 35°C, and even more preferably 10°C to 30°C. If the temperature (product temperature) of the raw cellulose ether is 40°C or higher, cellulose ether powder will adhere to the equipment during the humidity adjustment step and the temperature increase step. Furthermore, if the temperature (product temperature) of the raw cellulose ether is, for example, lower than 3°C, the temperature increase during the temperature increase step will be large, which may result in an increase in the size of the equipment or a large amount of energy consumption.

[0021] The method for adjusting the temperature of the raw cellulose ether is not particularly limited, and examples thereof include a method in which the cellulose ether is placed in a jacketed container, a fluid such as water is passed through the jacket, and the temperature of the raw cellulose ether is adjusted by adjusting the jacket temperature; a method in which the cellulose ether is placed in a jacketed screw conveyor, the jacket temperature is adjusted, and the temperature of the raw cellulose ether is continuously adjusted while transporting the raw cellulose ether; and a method in which air, nitrogen, or the like at a predetermined temperature is passed through the cellulose ether to adjust the temperature of the raw cellulose ether.

[0022] The temperature of the raw cellulose ether can be measured by a thermometer provided in the raw material tank or in the piping that transports the raw cellulose ether from the raw material tank to the humidity adjustment step.

[0023] a) Humidity control process Next, the humidity control step will be described. In the humidity control step, the raw cellulose ether is brought into contact with water vapor in a humidity control tank to obtain a humidity-controlled cellulose ether. The humidity control tank is a continuous type, and is equipped with at least one supply port and at least one discharge port. The supply port of the humidity control tank is connected by piping to the discharge port of a raw material tank containing the raw cellulose ether, and the discharge port of the humidity control tank is connected by piping to the supply port of a temperature-raising device described below. The humidity control tank also has a water vapor supply port. Examples of continuous humidity control tanks include vertical high-speed agitation mixers, horizontal mixers, and continuous mixing mixers. Examples of vertical high-speed agitation mixers include the Axial Mixer (manufactured by Sugiyama Heavy Industries). Examples of horizontal mixers include the Pamapec Mixer WA type ( large Examples of continuous mixers include Flexomix (manufactured by Hosokawa Micron) and Turbulizer (manufactured by Hosokawa Micron).

[0024] In a humidity control tank, the raw cellulose ether is brought into contact with water vapor while being stirred. Here, water vapor refers to saturated water vapor and superheated water vapor. Saturated water vapor refers to gaseous water that exists in equilibrium with liquid water, and superheated water vapor refers to gaseous water that exists at a temperature higher than the boiling point of water at a given pressure. From the viewpoint of efficiently adjusting the humidity of the raw material cellulose ether, it is preferable to use saturated steam. The temperature of the water vapor is preferably 100°C to 150°C from the viewpoint of efficiently controlling the humidity of the raw material cellulose ether and from the viewpoint of the quality of the depolymerized cellulose ether obtained. The ratio of the amount of water vapor supplied to the humidity control tank in the humidity control step to the amount of raw cellulose ether supplied ([amount of water vapor supplied] / [amount of raw cellulose ether supplied]) is preferably 0.02 to 0.1 by weight, more preferably 0.025 to 0.08, and most preferably 0.027 to 0.05, from the viewpoint of preventing adhesion of cellulose ether powder to the equipment and from the viewpoint of the quality of the depolymerized cellulose ether obtained.

[0025] From the viewpoint of preventing an increase in the internal pressure of the humidity-conditioning tank and condensation, it is preferable to provide a bag filter in the humidity-conditioning tank and discharge excess water vapor not absorbed by the raw cellulose ether to the outside of the humidity-conditioning tank. For the purpose of discharging excess water vapor to the outside of the humidity-conditioning tank, an inert gas such as nitrogen may be blown into the humidity-conditioning tank. An inert gas such as nitrogen may be mixed with water vapor in advance and supplied to the humidity control chamber as a mixture of water vapor and inert gas, or may be supplied into the humidity control chamber from a supply port separate from that for water vapor.

[0026] From the viewpoint of preventing adhesion of the cellulose ether powder to the humidity control tank and the temperature raising device described below, the jacket temperature of the humidity control tank is preferably 20° C. to 120° C., more preferably 30° C. to 100° C., and even more preferably 35° C. to 85° C. The jacket temperature of the humidity control tank can be controlled by adjusting the temperature of the fluid flowing through the jacket of the humidity control tank.

[0027] The humidity control tank may be equipped with either a main shaft or a chopper, or both, to mix the raw cellulose ether and water vapor. The rotation speed of the main shaft is preferably 10 rpm to 1000 rpm from the viewpoint of thoroughly mixing the raw cellulose ether and water vapor, and the rotation speed of the chopper is preferably 10 rpm to 5000 rpm from the viewpoint of thoroughly mixing the raw cellulose ether and water vapor.

[0028] The temperature of the humidity-conditioned cellulose ether at the outlet of the humidity-conditioning tank is preferably 30 to 100° C., more preferably 50 to 90° C., from the viewpoint of preventing adhesion of cellulose ether powder to the apparatus after the temperature-raising step and from the viewpoint of the quality of the obtained depolymerized cellulose ether. In this specification, the "temperature of the humidity-conditioned cellulose ether" refers to the temperature of the humidity-conditioned cellulose ether at the outlet of the humidity-conditioning tank.

[0029] The moisture content of the humidity-conditioned cellulose ether at the outlet of the humidity-conditioning tank is preferably 1.5 to 6 mass%, more preferably 2.0 to 4.0 mass%, from the viewpoint of preventing adhesion of cellulose ether powder to the equipment after the temperature-raising step and from the viewpoint of the quality of the obtained depolymerized cellulose ether. In this specification, the "moisture content of the humidity-conditioned cellulose ether" refers to the moisture content of the humidity-conditioned cellulose ether at the outlet of the humidity-conditioning tank.

[0030] b) Temperature rising process Next, the temperature increasing step will be described. In the temperature-raising step, the humidity-conditioned cellulose ether is heated in a temperature-raising device to obtain a temperature-raised cellulose ether. The temperature-raising step is carried out using a continuous temperature-raising apparatus having at least one supply port and at least one discharge port. The supply port of the temperature-raising apparatus is connected to the discharge port of the humidity control tank via a pipe, and the discharge port of the temperature-raising apparatus is connected to the supply port of the depolymerization apparatus described below via a pipe. Examples of the continuous temperature raising device include a jacketed screw conveyor and a jacketed continuous mixer.

[0031] From the viewpoint of preventing adhesion of the cellulose ether powder to the temperature-elevating device, the jacket temperature of the temperature-elevating device is preferably 20° C. to 120° C. The jacket temperature of the temperature-elevating device can be controlled by adjusting the temperature of the fluid flowing through the jacket of the temperature-elevating device.

[0032] The temperature of the heated cellulose ether at the outlet of the heating device is preferably 55 to 90°C, more preferably 60 to 88°C, and even more preferably 63 to 85°C, from the viewpoint of controlling the viscosity of the resulting depolymerized cellulose ether and preventing adhesion of cellulose ether powder to the device. In this specification, the "temperature of the heated cellulose ether" refers to the temperature of the heated cellulose ether at the outlet of the heating device.

[0033] The moisture content of the heated cellulose ether at the outlet of the heating device is preferably 1.5 to 6 mass%, more preferably 2.0 to 4.0 mass%, from the viewpoint of preventing adhesion of cellulose ether powder to the device in the depolymerization step and thereafter and from the viewpoint of the quality of the obtained depolymerized cellulose ether. In this specification, the "moisture content of the heated cellulose ether" refers to the moisture content of the heated cellulose ether at the outlet of the heating device.

[0034] c) Depolymerization process Next, the depolymerization step will be described. In the depolymerization step, the heated cellulose ether is continuously contacted with gaseous hydrogen chloride (hydrogen chloride gas) in a continuous depolymerization apparatus to depolymerize it, thereby obtaining a depolymerized cellulose ether product. The depolymerization apparatus has at least one supply inlet and at least one outlet. The supply inlet of the depolymerization apparatus is connected to the outlet of the heating apparatus by a pipe, and the outlet of the depolymerization apparatus is connected to the supply inlet of the neutralization tank or the washing apparatus described below by a pipe. Examples of continuous depolymerization equipment include vertical high-speed agitation mixers, horizontal mixers, continuous mixing mixers, and jacketed screw conveyors. Examples of vertical high-speed agitation mixers include the Axial Mixer (manufactured by Sugiyama Heavy Industries). Examples of horizontal mixers include the Pamapec Mixer WA type ( large Examples of continuous mixers include Flexomix (manufactured by Hosokawa Micron) and Turbulizer (manufactured by Hosokawa Micron). In the depolymerization step, from the viewpoint of uniformly carrying out depolymerization, it is preferable to use a combination of two or more continuous depolymerization apparatuses selected from the above-mentioned continuous depolymerization apparatuses. For example, when two continuous depolymerization apparatuses are used in combination, the depolymerization apparatus connected to the temperature-raising apparatus is designated as the first depolymerization apparatus, and the depolymerization apparatus connected to the first depolymerization apparatus is designated as the second depolymerization apparatus. The supply port of the first depolymerization apparatus is connected to the discharge port of the temperature-raising apparatus via a pipe, the discharge port of the first depolymerization apparatus is connected to the supply port of the second depolymerization apparatus via a pipe, and the discharge port of the second depolymerization apparatus is connected to the supply port of a neutralization tank or a cleaning apparatus, which will be described later, via a pipe. Furthermore, the supply port for gaseous hydrogen chloride (hydrogen chloride gas) is preferably provided in the first depolymerization apparatus, but is not limited to this. The same applies when the number of depolymerization apparatuses is increased to three or more. More preferably, one selected from a vertical high-speed agitating mixer, a horizontal mixer, and a continuous mixer is used as the first depolymerization apparatus, and a jacketed screw conveyor is used as the second depolymerization apparatus, in this order.

[0035] From the viewpoint of controlling the viscosity of the obtained depolymerized cellulose ether, the jacket temperature of the depolymerizer is preferably 20° C. to 120° C., more preferably 30° C. to 90° C., and even more preferably 50° C. to 85° C. The jacket temperature of the depolymerizer can be controlled by adjusting the temperature of the fluid flowing through the jacket of the depolymerizer. The internal pressure of the depolymerization apparatus is preferably −40 to 0 kPaG from the viewpoint of preventing leakage of hydrogen chloride gas to the outside of the depolymerization apparatus.

[0036] The depolymerization apparatus may be equipped with either or both of a main shaft and a chopper to thoroughly mix the temperature-elevated cellulose ether and hydrogen chloride gas. The rotation speed of the main shaft is preferably 10 rpm to 1,000 rpm to thoroughly mix the temperature-elevated cellulose ether and hydrogen chloride gas. The rotation speed of the chopper is preferably 10 rpm to 5,000 rpm to thoroughly mix the temperature-elevated cellulose ether and hydrogen chloride gas.

[0037] The acid to be brought into contact with the heated cellulose ether is preferably gaseous hydrogen chloride, from the viewpoints of enabling continuous production while preventing adhesion to equipment and suppressing the generation of black foreign matter in the product.

[0038] The ratio of the amount of gaseous hydrogen chloride supplied to the amount of heated cellulose ether supplied ([amount of gaseous hydrogen chloride supplied] / [amount of heated cellulose ether supplied]) is preferably 0.0001 to 0.01, more preferably 0.001 to 0.008, in terms of controlling the viscosity of the resulting depolymerized cellulose ether.

[0039] The product temperature of the depolymerized cellulose ether product in the depolymerization step is preferably 55°C to 90°C, more preferably 60°C to 88°C, and even more preferably 63°C to 85°C, from the viewpoint of controlling the viscosity of the resulting depolymerized cellulose ether.

[0040] The depolymerization time in the depolymerization step is not particularly limited as long as the depolymerized cellulose ether has the desired viscosity. However, from the viewpoint of obtaining a depolymerized cellulose ether with low yellowness, it is preferably 0.1 to 4.0 hours, more preferably 0.2 to 2.0 hours. Here, the depolymerization time refers to the time from when the heated cellulose ether is supplied to the depolymerizer until it is discharged from the depolymerizer as a depolymerized cellulose ether product. When two or more depolymerizers are used in combination in the depolymerization step, the depolymerization time in the depolymerization step is the sum of the depolymerization times in each depolymerizer. The depolymerization time can be calculated by dividing the amount of cellulose ether powder retained in the depolymerizer (kg) in terms of anhydrous cellulose ether by the discharge rate (kg / hr) of the depolymerized cellulose ether product at the outlet of the depolymerizer (converted to anhydrous cellulose ether). The ratio of the supply rate of the humidity-conditioned cellulose ether from the humidity adjustment step to the temperature-raising step to the discharge rate of the depolymerized cellulose ether product discharged from the depolymerization step ([supply rate of the humidity-conditioned cellulose ether from the humidity adjustment step to the temperature-raising step] / [discharge rate of the depolymerized cellulose ether product discharged from the depolymerization step]) is 0.9 to 1.1, preferably 0.95 to 1.05, and more preferably 0.98 to 1.02, from the viewpoint of continuously producing depolymerized cellulose ether in a stable state.

[0041] After the depolymerization step is completed, in order to reduce the amount of hydrogen chloride remaining in the depolymerized cellulose ether product, a washing step may be further included in which hydrogen chloride and the like are removed from the depolymerized cellulose ether product under reduced pressure to obtain a washed depolymerized cellulose ether product. In the washing step, hydrogen chloride (hydrogen chloride gas or hydrochloric acid aqueous solution) and water (water vapor or liquid water) can be removed from the depolymerized cellulose ether product. The washing step can be carried out in a washing device. The washing device is preferably of a continuous type because the steps before and after (the depolymerization step and the neutralization step) are continuous. A continuous washing device has at least one supply inlet and at least one discharge outlet. The supply inlet of the washing device is connected to the discharge outlet of the depolymerization device by piping, and the discharge outlet of the washing device is connected to the supply inlet of the neutralization tank described below by piping. The washing device also has discharge outlets for hydrogen chloride and water that can be discharged outside the system during the washing step. The continuous cleaning equipment includes a jacketed screw conveyor, a jacketed continuous mixer, a continuous vibration vacuum dryer (manufactured by Chuo Kakoki), and a belt vacuum dryer ( day Examples of jacketed continuous mixers include those similar to humidity control tanks. The internal pressure of the washing device in the washing step is preferably −99 to −60 kPaG from the viewpoint of efficiently removing hydrogen chloride and the like from the depolymerized cellulose ether product. The jacket temperature of the washing device in the washing step is preferably 20 to 120°C from the viewpoint of efficiently removing hydrogen chloride from the depolymerized cellulose ether product.

[0042] d) Neutralization process Next, the neutralization step will be described. In the neutralization step, the depolymerized cellulose ether product is mixed with a basic compound in a neutralization tank to obtain the depolymerized cellulose ether. The neutralization tank can be a continuous mixer similar to the humidity control tank, and is equipped with at least one supply inlet and at least one discharge outlet. The supply inlet of the neutralization tank is connected by piping to the discharge outlet of the depolymerization apparatus or the washing apparatus, and the discharge outlet of the neutralization tank is connected by piping to the supply inlet of the product tank or the cooling apparatus described below. The neutralization tank also has a supply inlet for a basic compound.

[0043] The neutralization tank may be equipped with either or both of a main shaft and a chopper to mix the depolymerized cellulose ether product and the basic compound. The rotation speed of the main shaft is preferably 10 rpm to 1,000 rpm to thoroughly mix the depolymerized cellulose ether product and the basic compound. The rotation speed of the chopper is preferably 10 rpm to 5,000 rpm to thoroughly mix the depolymerized cellulose ether product and the basic compound. The jacket temperature of the neutralization tank is preferably 30°C to 120°C from the viewpoint of efficient neutralization.

[0044] Examples of basic compounds include weakly alkaline compounds such as sodium bicarbonate and sodium carbonate. The amount of the basic compound added is not particularly limited as long as it neutralizes the acid, but the ratio of the amount of the basic compound supplied to the amount of the depolymerized cellulose ether product supplied ([amount of basic compound supplied] / [amount of depolymerized cellulose ether product supplied]) is preferably 0.001 to 0.01 by weight.

[0045] The temperature of the depolymerized cellulose ether at the outlet of the neutralization tank is preferably 30°C to 100°C, more preferably 40°C to 90°C, and even more preferably 50°C to 85°C, from the viewpoint of efficient neutralization.

[0046] The method may further include a cooling step of cooling the depolymerized cellulose ether after the neutralization step, which reduces the temperature of the depolymerized cellulose ether supplied to the product tank, thereby preventing condensation in the product tank, contamination of the product with foreign matter due to condensation, and corrosion of the product tank. The cooling step can be carried out in a continuous cooling device. The cooling device can be the same as the heating device and the depolymerization device, and the depolymerized cellulose ether can be cooled by lowering the jacket temperature of the cooling device below that of the depolymerized cellulose ether. The cooling device has at least one supply inlet and at least one discharge outlet. The supply inlet of the cooling device is connected to the discharge outlet of the neutralization tank by piping, and the discharge outlet of the cooling device is connected to the supply inlet of the product tank (described below) by piping. The jacket temperature of the cooling device is preferably 5°C to 60°C from the viewpoint of efficiently cooling the depolymerized cellulose ether. The product temperature of the depolymerized cellulose ether at the outlet of the cooling device is preferably 20°C to 70°C, from the viewpoint of preventing condensation in the product tank, the inclusion of foreign matter in the product (depolymerized cellulose ether) due to condensation, and corrosion of the product tank.

[0047] The depolymerized cellulose ether may be dried, crushed, and sieved through a sieve of any mesh size, if necessary. The apparatus for carrying out the drying, crushing, and sieving is not particularly limited, but a continuous apparatus is preferred.

[0048] The viscosity reduction rate of the depolymerized cellulose ether relative to the starting cellulose ether is preferably 40.0 to 99.99%, more preferably 50.0 to 99.99%, and even more preferably 60.0 to 99.99%, from the viewpoint of obtaining a depolymerized cellulose ether with low yellowness. Here, the viscosity reduction rate is the ratio of the difference between the viscosity (before depolymerization) and the viscosity (after depolymerization) of a 2% by mass aqueous solution of the depolymerized cellulose ether at 20°C to the viscosity (before depolymerization) of a 2% by mass aqueous solution of the starting cellulose ether, and is defined as {(viscosity before depolymerization - viscosity after depolymerization) / viscosity before depolymerization} × 100. The viscosity of a 2 mass% aqueous solution of the depolymerized cellulose ether at 20°C is preferably 1.0 to 20.0 mPa·s, more preferably 2.0 to 20.0 mPa·s, and even more preferably 3.0 to 15.0 mPa·s, from the viewpoint of maintaining a low solution viscosity during film coating. The viscosity of a 2 mass% aqueous solution of the depolymerized cellulose ether at 20°C is a value measured in the same manner as the viscosity of the 2 mass% aqueous solution of the raw material cellulose ether at 20°C. [Example]

[0049] EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way. The measurement of yellowness, evaluation of the amount of black foreign matter, and evaluation of the #100 pass rate were carried out by the methods described below. <Yellowness measurement> A 2% by mass aqueous solution of the depolymerized cellulose ether was prepared at 20° C., and the yellowness index was measured using an SM color computer (product name "SM-4", manufactured by Suga Test Instruments Co., Ltd.). <Evaluation of the amount of black foreign matter generated> 18 mesh sieve (effective sieve area 0.0314 m 2200 g of depolymerized cellulose ether was fed into a low-tap sieve shaker (Takeda Rika Kogyo Co., Ltd.) equipped with one stage of sieves (0.85 mm mesh, Kansai Wire Mesh Co., Ltd.), and sieved for 10 minutes at a rotation speed of 250 rpm, a shaking width of 50 mm, and 67 hammer blows per minute. 2.5 g of the depolymerized cellulose ether that passed through the sieve was sampled, spread evenly on a 10 cm diameter Petri dish, and visually observed. The number of black particles measuring 0.1 mm or larger was counted. The above sampling of depolymerized cellulose ether and counting of the number of black particles were repeated 20 times, and the total value was doubled, i.e., the number of black particles per 100 g, was determined as the amount of black particles. <#100 pass rate evaluation> 100 mesh sieve (effective sieve area 0.0314 m 2 200 g of depolymerized cellulose ether was fed into a low-tap sieve shaker (manufactured by Takeda Rika Kogyo Co., Ltd.) equipped with one stage of sieves (0.15 mm mesh, manufactured by Kansai Wire Mesh Co., Ltd.), and then sieved for 10 minutes at a rotation speed of 250 rpm, a shaking width of 50 mm, and 67 hammer blows per minute. The weight of the depolymerized cellulose ether that passed through the sieve was measured, and the #100 pass rate was calculated as (weight of depolymerized cellulose ether that passed through the sieve / weight of depolymerized cellulose ether fed to the sieve) x 100. This evaluation was performed to confirm the presence or absence of aggregates.

[0050] A schematic diagram of a production system 10 used in the continuous production method of depolymerized cellulose ether of the present invention is shown in Fig. 1. In the production system 10 shown in Fig. 1, the discharge outlet of raw material tank 1 is connected by piping to the supply inlet of humidity control tank 2, the discharge outlet of humidity control tank 2 is connected by piping to the supply inlet of temperature raising device 3, the discharge outlet of temperature raising device 3 is connected by piping to the supply inlet of depolymerization device 4, the discharge outlet of depolymerization device 4 is connected by piping to the supply inlet of neutralization tank 6, and the discharge outlet of neutralization tank 6 is connected by piping to the supply inlet of product tank 8. Furthermore, the raw material tank 1 is provided with a supply port for raw material cellulose ether A, the humidity control tank 2 is provided with a supply port for water vapor B, the depolymerization device 4 is provided with a supply port for gaseous hydrogen chloride (hydrogen chloride gas) C, and the neutralization tank 6 is provided with a supply port for basic compound E. Example 1 FIG. 2 shows a schematic diagram of a production system 20 used in the continuous production method of depolymerized cellulose ether of the present invention, which is different from the embodiment shown in FIG. In the following examples, a production system shown in Fig. 2 was used. In production system 20 shown in Fig. 2, the discharge outlet of raw material tank 1 is connected by piping to the supply inlet of humidity control tank 2, the discharge outlet of humidity control tank 2 is connected by piping to the supply inlet of temperature raising device 3, the discharge outlet of temperature raising device 3 is connected by piping to the supply inlet of depolymerization device (1) 41, the discharge outlet of depolymerization device (1) 41 is connected by piping to the supply inlet of depolymerization device (2) 42, the discharge outlet of depolymerization device (2) 42 is connected by piping to the supply inlet of washing device 5, the discharge outlet of washing device 5 is connected by piping to the supply inlet of neutralization tank 6, the discharge outlet of neutralization tank 6 is connected by piping to the supply inlet of cooling device 7, and the discharge outlet of cooling device 7 is connected by piping to the supply inlet of product tank 8. Furthermore, the raw material tank 1 is equipped with a supply port for raw material cellulose ether A, the humidity control tank 2 is equipped with a supply port for water vapor B, the depolymerization device (1) 41 is equipped with a supply port for gaseous hydrogen chloride (hydrogen chloride gas) C, the washing device 5 is equipped with an outlet for hydrogen chloride and water D, and the neutralization tank 6 is equipped with a supply port for basic compound E. Each device will be explained below. (1) Humidity control tank The humidity-conditioning tank used had an effective volume of 50 L and was equipped with a jacketed, vertical, high-speed agitating mixer equipped with a main shaft and a chopper. A supply port with a rotary valve was installed on the top plate of the humidity-conditioning tank, allowing the raw cellulose ether to be continuously supplied at a constant rate. A discharge port with a rotary valve was installed on the wall of the humidity-conditioning tank, allowing the humidity-conditioned cellulose ether in the tank to be continuously discharged at a constant rate. A bag filter was also installed on the top plate. (2) Heating device The heating device used was equipped with a jacketed screw conveyor with a screw diameter of 120 mm, a shaft diameter of 80 mm, a screw length of 5 m, and a screw pitch of 100 mm. (3) Depolymerization equipment (1) The depolymerization apparatus (1) used had an effective volume of 50 L and was equipped with a jacketed, vertical, high-speed agitating mixer equipped with a main shaft and a chopper. A supply port with a rotary valve was installed on the top plate of the depolymerization apparatus (1), allowing the heated cellulose ether to be continuously supplied at a constant rate. A discharge port with a rotary valve was installed on the wall of the depolymerization apparatus (1), allowing the depolymerized cellulose ether in the tank to be continuously discharged at a constant rate. (4) Depolymerization equipment (2) The depolymerization apparatus (2) used was equipped with a screw conveyor having a screw diameter of 120 mm, a shaft diameter of 80 mm, a screw length of 100 m, and a screw pitch of 100 mm. (5) Cleaning equipment The cleaning device used was equipped with a jacketed screw conveyor with a screw diameter of 120 mm, a shaft diameter of 80 mm, a screw length of 40 m, and a screw pitch of 100 mm. (6) Neutralization tank The neutralization tank had an effective volume of 50 L and was equipped with a jacketed, vertical, high-speed agitating mixer equipped with a main shaft and a chopper. A supply port with a rotary valve was installed on the top plate of the neutralization tank, allowing the depolymerized cellulose ether product to be continuously supplied at a constant rate. A discharge port with a rotary valve was installed on the wall of the neutralization tank, allowing the depolymerized cellulose ether in the tank to be continuously discharged at a constant rate. (7) Cooling device The cooling device used was equipped with a jacketed screw conveyor with a screw diameter of 120 mm, a shaft diameter of 80 mm, a screw length of 5 m, and a screw pitch of 100 mm. A low polymerization degree cellulose ether was continuously produced under the following operating conditions. (i) Humidity control process The raw material cellulose ether (HPMC with 29.0% methoxy group, 9.1% hydroxypropoxy group, 2% viscosity of 1000 mPa·s, and water content of 0.5% by mass) at 20°C was continuously fed from the raw material tank to the humidity control chamber at a rate of 180 kg / hr in terms of anhydrous cellulose ether. The humidity control chamber was operated under the following conditions: spindle rotation speed 250 rpm, chopper rotation speed 1000 rpm, and jacket temperature 80°C. Nitrogen was also supplied to the humidity control chamber. Steam at 110°C was continuously supplied to the powder layer of raw cellulose ether through the steam inlet of the humidity-conditioning tank at a feed rate of 0.040 by weight relative to the feed rate of the raw cellulose ether, and contacted with the raw cellulose ether to obtain a humidity-conditioned cellulose ether. While continuing to supply the raw cellulose ether, the humidity-conditioned cellulose ether was continuously discharged from the outlet of the humidity-conditioning tank at a rate of 180 kg / hr in terms of anhydrous cellulose ether. The temperature of the humidity-conditioned cellulose ether discharged from the humidity-conditioning tank was 70°C, and the moisture content was 2.9% by mass. The equipment used as the humidity control tank, the jacket temperature of the humidity control tank, the form of water, the amount of water supplied relative to the amount of raw cellulose ether supplied (water supply amount / raw cellulose ether supply amount), the temperature of the raw cellulose ether, the temperature of the humidity-controlled cellulose ether, and the moisture content of the humidity-controlled cellulose ether are shown in a) Humidity Control Step in Table 1. (ii) Temperature increase process The humidity-controlled cellulose ether was continuously supplied to the temperature-raising device at a rate of 180 kg / hr in terms of anhydrous cellulose ether. Hot water at 90°C was circulated through the jacket of the temperature-raising device. The screw of the temperature-raising device was rotated at a speed of 20 rpm. The heated cellulose ether was discharged from the outlet of the temperature-raising device at a rate of 180 kg / hr in terms of anhydrous cellulose ether. The product temperature of the heated cellulose ether when discharged from the temperature-raising device was 80°C, and the moisture content was 2.8% by mass. The temperature raising device, the jacket temperature of the temperature raising device, the temperature of the moisture-conditioned cellulose ether, the temperature of the heated cellulose ether, and the moisture content of the heated cellulose ether are shown in Table 1 for b) the heating step. (iii) Depolymerization step The temperature-elevated cellulose ether was continuously fed to the depolymerizer (1) at a rate of 180 kg / hr, calculated as anhydrous cellulose ether. The depolymerizer (1) was operated under the following conditions: a main shaft rotation speed of 250 rpm, a chopper rotation speed of 1000 rpm, a jacket temperature of 80°C, and an internal pressure of -30 kPaG. Hydrogen chloride gas was continuously fed from the gaseous hydrogen chloride feed port of the depolymerizer (1) to the powder layer of the temperature-elevated cellulose ether at a feed rate of 0.0040 by weight relative to the feed rate of the temperature-elevated cellulose ether, and contacted with the temperature-elevated cellulose ether. While continuing to feed the temperature-elevated cellulose ether, the depolymerized cellulose ether product was continuously fed to the depolymerizer (2) from the outlet of the depolymerizer (1). The jacket temperature of the depolymerizer (2) was 80° C., and the internal pressure was −5 kPaG. The screw of the depolymerizer (2) was rotated at 20 rpm. The depolymerization time of the depolymerized cellulose ether product in depolymerizer (1) was 0.1 hours, and the depolymerization time of the depolymerized cellulose ether product in depolymerizer (2) was 1 hour, for a total depolymerization time of 1.1 hours. The depolymerized cellulose ether product was continuously discharged from the outlet of depolymerizer (2) at a flow rate of 180 kg / hr in terms of anhydrous cellulose ether. The temperature of the depolymerized cellulose ether product was 80°C. (iv) Cleaning process The depolymerized cellulose ether product was continuously fed into the washer at a rate of 180 kg / hr in terms of anhydrous cellulose ether. The jacket temperature of the washer was 80°C. The screw of the washer was rotated at 20 rpm. The pressure inside the washer was maintained at -98 kPaG using a vacuum pump, and hydrogen chloride gas, water vapor, and a portion of the hydrochloric acid aqueous solution were removed from the hydrogen chloride and water outlet of the washer. The washed depolymerized cellulose ether product was continuously discharged from the outlet of the washer at a flow rate of 180 kg / hr in terms of anhydrous cellulose ether. (v) Neutralization process The washed depolymerized cellulose ether product was continuously fed into the neutralization tank at a rate of 180 kg / hr, calculated as anhydrous cellulose ether. The neutralization tank was operated under the following conditions: a main shaft rotation speed of 250 rpm, a chopper rotation speed of 1000 rpm, and a jacket temperature of 80°C. Sodium bicarbonate powder was continuously fed into the neutralization tank through the basic compound feed port at a feed rate of 0.0040 by weight relative to the feed rate of the depolymerized cellulose ether product, and mixed with the cellulose ether product to obtain depolymerized cellulose ether. While continuing to feed the depolymerized cellulose ether product, the depolymerized cellulose ether was continuously discharged from the outlet of the neutralization device at a flow rate of 180 kg / hr, calculated as anhydrous cellulose ether. The temperature of the depolymerized cellulose ether when discharged from the neutralization tank was 80°C. (vi) Cooling process The depolymerized cellulose ether was continuously fed into the cooling device at a rate of 180 kg / hr in terms of anhydrous cellulose ether. Water at 10°C was circulated through the cooling device jacket. The cooling device screw was rotated at 20 rpm. The depolymerized cellulose ether was continuously discharged from the outlet of the cooling device into a product tank at a flow rate of 180 kg / hr in terms of anhydrous cellulose ether. The temperature of the depolymerized cellulose ether when discharged from the cooling device was 30°C. Under the above conditions, depolymerized cellulose ether was produced continuously for 24 hours, and a total of 4,320 kg of depolymerized cellulose ether was produced in terms of anhydrous cellulose ether. The depolymerized cellulose ether was sampled from the product tank and analyzed. After 24 hours of continuous production, the humidity control chamber and the temperature raising device were visually inspected to check for adhesion. Furthermore, the viscosity of a 2% by mass aqueous solution of each of the obtained depolymerized cellulose ethers at 20°C was measured by the above-mentioned method, and the viscosity reduction rate was calculated from the viscosity value of the raw material cellulose ether. Furthermore, the yellowness of the obtained depolymerized cellulose ether was measured, the amount of black foreign matter was evaluated, and the #100 pass rate was calculated by the above-mentioned methods. The results are shown in Tables 2 and 3.

[0051] Example 2 Depolymerized cellulose ether was produced in the same manner as in Example 1, except that the jacket temperature of the humidity control tank was set to 25° C. and the jacket temperature of the temperature-raising device in the temperature-raising step was set to 100° C. The results are shown in Tables 2 and 3.

[0052] Comparative Example 1 Depolymerized cellulose ether was produced in the same manner as in Example 1, except that the jacket temperature of the raw material tank was set to 100°C to control the temperature of the raw material cellulose ether in the raw material tank, the temperature of the raw material cellulose ether supplied to the humidity adjustment step was set to 80°C, and the jacket temperature of the temperature-raising device was set to 75°C in the temperature-raising step to make the temperature of the heated cellulose ether 80°C, the same as in Examples 1 and 2. The results are shown in Tables 2 and 3.

[0053] Comparative Example 2 An attempt was made to produce depolymerized cellulose ether in the same manner as in Example 1, except that the jacket temperature of the raw material tank was set to 100°C to regulate the temperature of the raw material cellulose ether in the raw material tank, the temperature of the raw material cellulose ether supplied to the humidity adjustment step was set to 80°C, and 110°C steam was supplied to the raw material cellulose ether at a feed rate of 0.150 by weight relative to the feed rate of the raw material cellulose ether. However, a large amount of adhesion occurred at the outlet of the humidity adjustment tank, causing clogging, making continuous operation impossible and making it impossible to carry out the steps after the temperature increase step. The results are shown in Tables 2 and 3.

[0054] Comparative Example 3 Depolymerized cellulose ether was produced in the same manner as in Example 1, except that the jacket temperature of the humidity control tank was set to 25°C, liquid water at 20°C was brought into contact with the raw cellulose ether in the humidity control step instead of steam, and the jacket temperature of the heating device in the heating step was set to 130°C in order to bring the temperature of the heated cellulose ether to 80°C, the same as in Examples 1 and 2. The results are shown in Tables 2 and 3.

[0055] [Table 1]

[0056] [Table 2]

[0057] [Table 3]

[0058] In Examples 1 and 2, in which the temperature of the raw cellulose ether supplied to the humidity-conditioning tank was 20°C, adhesion of cellulose ether powder to the equipment during the humidity-conditioning step and the temperature-raising step was not significant, and depolymerized cellulose ether could be produced continuously. Furthermore, the obtained depolymerized cellulose ether had a low yellowness and no black foreign matter was generated. In particular, in Example 1, in which the jacket temperature of the humidity-conditioning tank was 80°C, adhesion of cellulose ether powder to the equipment during both the humidity-conditioning step and the temperature-raising step was not observed. In Comparative Example 1, in which the temperature of the raw material cellulose ether supplied to the humidity-conditioning tank was 80°C, the moisture content of the humidity-conditioned cellulose ether was low, and as a result, the yellowness of the resulting depolymerized cellulose ether was high, even though the same amount of steam was supplied as in Example 1. In Comparative Example 2, in which the amount of steam supplied in the humidity-conditioning step was increased, the moisture content of the humidity-conditioned cellulose ether was high, but adhesion of cellulose ether powder in the humidity-conditioning tank was significant, and clogging occurred at the discharge port of the humidity-conditioning tank, making the discharge amount of humidity-conditioned cellulose ether unstable, and it was not possible to continuously produce depolymerized cellulose ether. In Comparative Example 3, in which liquid water at 20°C was used in the humidity adjustment step, adhesion occurred to the humidity adjustment tank and the temperature raising device. In addition, the amount of black foreign matter in the obtained depolymerized cellulose ether increased, impairing the product value, and the number of aggregates increased, decreasing the #100 pass rate and the yield. [Explanation of symbols]

[0059] 10, 20 Manufacturing System 1 Raw material tank 2 Humidity control tank 3 Heating device 4 Depolymerization equipment 41 Depolymerization equipment (1) 42 Depolymerization equipment (2) 5. Cleaning equipment 6 Neutralization tank 7 Cooling device 8 Product Tank A Raw material cellulose ether B. Water vapor C Hydrogen chloride gas D Hydrogen chloride and water E Basic compounds F Depolymerized cellulose ether

Claims

1. 1. A continuous process for producing depolymerized cellulose ethers, comprising: a) a humidity control step of contacting a raw cellulose ether continuously supplied from a raw material tank to a humidity control tank with water vapor to obtain a humidity-controlled cellulose ether; b) a temperature-raising step of heating the humidity-conditioned cellulose ether continuously supplied in the humidity-conditioning step to obtain a temperature-raised cellulose ether; c) a depolymerization step of continuously contacting the heated cellulose ether with gaseous hydrogen chloride to depolymerize the cellulose ether, thereby obtaining a depolymerized cellulose ether product; d) a neutralization step of mixing the depolymerized cellulose ether product with a basic compound to obtain a depolymerized cellulose ether; At least and wherein the temperature of the raw cellulose ether continuously supplied from the raw material tank to the humidity-conditioning tank is 3°C or higher and lower than 40°C, and the moisture content of the humidity-conditioned cellulose ether at the outlet of the humidity-conditioning tank is 1.5 to 4.0% by mass.

2. 2. The method for continuously producing depolymerized cellulose ether according to claim 1, further comprising, between the depolymerization step and the neutralization step, a washing step of removing hydrogen chloride and water from the depolymerized cellulose ether product continuously supplied by the depolymerization step to obtain a washed depolymerized cellulose ether product.

3. 2. The method for continuously producing depolymerized cellulose ether according to claim 1, wherein a ratio of a supply rate of the humidity-conditioned cellulose ether from the humidity conditioning step to the temperature-raising step to a discharge rate of the depolymerized cellulose ether product discharged from the depolymerization step is in the range of 0.9 to 1.

1.

4. 2. The method for continuously producing depolymerized cellulose ether according to claim 1, further comprising a cooling step of cooling the depolymerized cellulose ether after the neutralization step.

5. 2. The method for continuously producing depolymerized cellulose ether according to claim 1, wherein the temperature of the humidity-conditioned cellulose ether continuously supplied from the humidity-conditioning step to the temperature-raising step is 50°C to 90°C.

6. 2. The method for continuously producing a depolymerized cellulose ether according to claim 1, wherein the jacket temperature of the humidity control tank is 20°C to 120°C in the humidity control step.

7. 7. The method for continuously producing a depolymerized cellulose ether according to claim 1, wherein the starting cellulose ether is at least one selected from the group consisting of alkyl cellulose, hydroxyalkyl cellulose, and hydroxyalkyl alkyl cellulose.

Images