JP2017001918A - Apparatus and method for continuous carbonization of cellulose acetate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a useful method for producing a high-quality carbonized material useful as a production raw material of activated carbon by heat-firing a block-shaped material or powder of cellulose acetate using a continuous heating furnace in an inert gas atmosphere.SOLUTION: An apparatus for continuously carbonizing cellulose acetate comprises: a tunnel type carbonization furnace for, while moving in an inert gas atmosphere a block-shaped material or powder of cellulose acetate stored in a container having an opening in its top surface, continuously heat-firing the cellulose acetate to produce a carbonized material thereof; and a condenser for condensing a gas mixture containing gaseous acetic acid generated by the heat-firing of the cellulose acetate and discharged outside the carbonization furnace. A scrubber is provided downstream of the condenser through a blower capable of accelerating discharge of the gas mixture from the carbonization furnace, and the blower is installed with piping for returning a part of the gas mixture, condensed, and discharged from the condenser, into the carbonization furnace. A method for continuously carbonizing cellulose acetate uses the continuous carbonization apparatus.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a continuous carbonization apparatus and continuous carbonization method for bulk or powdery cellulose acetate. More specifically, the present invention relates to a continuous carbonization apparatus and continuous carbonization method for cellulose acetate suitable for continuously producing a carbide useful as a raw material for the production of activated carbon having high purity and excellent properties using cellulose acetate as a raw material. About.

  Activated carbon is used in various applications such as air purification, radioactive substance adsorption, iodine trap, methane occlusion, hydrogen occlusion, solvent recovery, decolorization, and water treatment. In recent years, it is also used as an electrode active material for capacitors such as electric double layer capacitors and lithium ion capacitors.

  Activated carbon is usually produced by heating and firing a carbonaceous raw material to obtain a carbide, and activating the carbide. Conventionally, materials derived from plants such as wood and coconut shells, pitches of petroleum and coal, and synthetic resin materials such as phenolic resins and polyacrylonitrile resins have been generally used as carbonaceous raw materials. Among these carbonaceous raw materials, plant-derived materials and petroleum and coal pitches are cheap and easy to obtain, so they have generally been used before. Therefore, there is a problem in use as an electrode active material such as an electric double layer capacitor, and there is a disadvantage that the generated carbide needs to be repeatedly washed. On the other hand, synthetic resin materials such as phenol resin and polyacrylonitrile have a problem of relatively high cost.

  On the other hand, recently, cellulose acetate has attracted attention as a carbonaceous raw material for producing a carbide as an activated carbon raw material. That is, cellulose acetate is produced by acetylating cellulose of plant origin, but since most of impurities such as alkali metals contained in plant raw materials are removed in the process of producing cellulose, high purity is obtained. It becomes a carbonaceous material. In addition, cellulose acetate is used as a raw material for the production of various molded products such as silver salt photographic film substrates, optical filters, optical protective films, cigarette filters, eyeglass frames, acetate fibers, etc. Since there is no useful use for the milling material generated in a large amount during the manufacturing process, it can be said to be a carbonaceous material that is easily available, highly pure and inexpensive.

  Various techniques have been developed for a method of obtaining activated carbon by heating and baking cellulose acetate and converting the activated carbon into activated carbon, and many techniques have been disclosed in published patent publications. However, among activated carbons, especially activated carbon used as an electrode active material for electric double layer capacitors, etc. needs to be excellent not only in high purity but also in various properties such as BET specific surface area. Research into the production of carbides as activated carbon raw materials has also been conducted.

  Patent Document 1 discloses a method for continuously producing a carbide suitable for producing activated carbon having a large BET specific surface area using a cellulose acetate lump or powder as a raw material. In this Patent Document 1, a cellulose acetate lump or powder is stored in a container having an open top, and the cellulose acetate lump or powder is heated and fired while the container is conveyed in a horizontal direction in a continuous heating furnace. A method for producing a cellulose acetate carbide comprising the steps of: heating and melting a cellulose acetate lump or powder contained in a container to form a viscous liquid, and then subjecting the viscous liquid to thermal decomposition of the viscous liquid. Activated carbon having a large BET specific surface area is obtained by using a method of heating and firing while preventing droplets composed of acetic acid vapor generated by the liquid and a viscous liquid accompanying the acetic acid vapor from scattering to the outside of the container. There is a disclosure that a carbide useful as a raw material for stable production can be obtained.

  Patent Document 1 discloses a tunnel furnace typified by a roller hearth kiln as an example of a continuous heating furnace used for heating and baking cellulose acetate lump or powder. That is, in the carbonization step by heating and baking cellulose acetate lump or powder described in Patent Document 1, the cellulose acetate lump or powder is accommodated in a container having an open top surface, and the container is continuously placed in a tunnel furnace. It is carried out with high efficiency by feeding and baking from the container while the viscous liquid which is a lump of cellulose acetate or a melt of powder is not scattered outside. In addition, the continuous heating furnace disclosed in Patent Document 1 is provided with a condenser (acetic acid recovery device) for condensing and recovering acetic acid generated by thermal decomposition of cellulose acetate.

  The method for producing a carbide by heating and baking cellulose acetate lump or powder disclosed in Patent Document 1 is an invention by a researcher belonging to the applicant of the present application. Furthermore, as a result of continuing examination of the production method, it has been found that the method for producing carbide from cellulose acetate disclosed in Patent Document 1 has several points to be improved.

  As described above, the continuous heating furnace disclosed in Patent Document 1 is provided with a condenser (acetic acid recovery device) for condensing and recovering acetic acid generated by thermal decomposition of cellulose acetate. However, when a carbide is actually produced by heating and firing cellulose lump or powder using the roller hearth kiln type continuous heating furnace disclosed in Patent Document 1 (particularly, FIG. 4), the heating furnace is particularly used. Acetic acid vapor generated by the thermal decomposition of cellulose acetate is intense in the area near the entrance of the acetic acid, and the acetic acid condensation recovery by the condenser attached to the heating furnace makes it difficult to recover sufficient acetic acid. It turned out that there is a tendency to contaminate the inner wall of the kiln with acetic acid as well as the carbides.

  On the other hand, when recovering a liquefied gas using a condenser, in order to increase the condensation efficiency, an exhaust means such as a blower is attached to the condenser, and the condensed gas exhausted by the exhaust means is then scrubbed. In general, a treatment that is released into the atmosphere after performing a washing treatment by a washing device such as the above is used. For this reason, the inventor of the present invention adds such an exhaust means and a scrubber to the acetic acid recovery device of the continuous heating furnace disclosed in FIG. 4 of Patent Document 1 to heat the cellulose acetate lump or powder. A study was made to improve the method for producing carbides by firing. As a result, it was confirmed that the efficiency of exhausting and collecting acetic acid vapor from the continuous heating furnace was improved by the improvement of such an apparatus. However, this time, the internal pressure of the continuous heating furnace is greatly reduced. For this reason, the inlet / outlet of the continuous heating furnace (the container containing the cellulose acetate lump or powder provided at both ends of the continuous heating furnace is used. Air flows in through an opening (inlet) for feeding and an opening (outlet) for removal (usually closed by a shutter) under an inert gas atmosphere of cellulose acetate lump or powder It has been found that the heating and firing conditions of this lead to a decrease in the physical properties of the resulting carbide.

JP 2014-91653 A

  The present invention provides a useful method for producing a carbide useful as a raw material for producing activated carbon by heating and baking a cellulose acetate lump or powder in an inert gas atmosphere using a continuous heating furnace. Objective. In particular, when producing a carbide useful as a raw material for producing a roller hearth kiln type continuous heating furnace activated carbon using a continuous heating furnace, the generated carbide is contaminated with acetic acid and the inner wall of the heating furnace is contaminated with acetic acid. It aims at providing the method which can suppress effectively.

  The inventor of the present invention installs exhaust means such as a blower and an exhaust gas cleaning device such as a scrubber in a condenser for acetic acid recovery of a tunnel-type continuous heating furnace disclosed in Patent Document 1, and further exhausts the exhaust. A switch is installed in the means, and a pipe for returning a part of the gas subjected to the acetic acid recovery treatment in the condenser to the continuous heating furnace is provided in the switch, and the cellulose acetate lump or powder The internal pressure of the heating furnace does not fluctuate greatly from the external pressure (that is, atmospheric pressure) by returning a part of the acetic acid recovered gas to the heating furnace during the heating and baking treatment in an inert gas atmosphere. By adjusting the internal pressure of the heating furnace, the acetic acid produced by the thermal decomposition of cellulose acetate can be efficiently recovered by the condenser while stably maintaining the inert gas atmosphere in the heating furnace. Removal Rukoto becomes possible, it found that contamination of the inner wall of the carbide and the heating furnace with acetic acid can be significantly suppressed. The present invention has been completed based on this novel finding by the present inventors.

  Accordingly, the present invention provides a tunnel type for making a carbide by continuously heating and baking a cellulose acetate lump or powder contained in a container having an opening on the upper surface while moving in an inert gas atmosphere. A carbonization furnace and a condenser for condensing a gaseous mixture containing gaseous acetic acid produced by heating and baking cellulose acetate and discharged out of the carbonization furnace, on the downstream side of the condenser The exhaust gas cleaning device is provided via an exhaust means capable of accelerating the discharge of the gas mixture from the carbonization furnace, and the exhaust means includes one of the condensed gas mixture discharged from the condenser. A continuous carbonization apparatus for cellulose acetate, characterized in that a pipe for returning the part into the carbonization furnace is provided.

A preferred embodiment of the continuous carbonization apparatus for cellulose acetate of the present invention will be described below.
(1) A plurality of inert gas supply ports are formed at the bottom of the carbonization furnace.
(2) A plurality of condensers are connected to a gas mixture discharge port formed on the upstream side of the carbonization furnace via a pipe.

  In the present invention, when the cellulose acetate lump or powder is continuously heated and fired while moving in an inert gas atmosphere using the above-mentioned continuous carbonization apparatus for cellulose acetate, The carbonization furnace for the condensed gas mixture discharged from the condenser by adjusting the operating conditions of the exhaust means so that the atmospheric pressure in the carbonization furnace is maintained within ± 10 Pa (preferably within ± 2 Pa) of the atmospheric pressure. There is also a continuous carbonization method of cellulose acetate, characterized by adjusting the amount of return to the water.

  The cellulose acetate lump or powder is heated and fired in an inert gas atmosphere using the continuous carbonization apparatus and continuous carbonization method of the present invention, so that high-quality contamination with less acetic acid produced during heating and baking is reduced. Stable production of carbides becomes possible, and contamination by acetic acid on the inner wall of the continuous carbonization apparatus is significantly reduced. Furthermore, the recovery of acetic acid produced by the thermal decomposition of cellulose acetate is also highly efficient.

It is a conceptual diagram of the roller hearth type continuous carbonization apparatus which is a typical example of the continuous carbonization apparatus of the cellulose acetate of this invention. It is a figure which shows the example of the container which accommodates the lump of the cellulose acetate used in the case of implementation of the continuous carbonization method of the cellulose acetate of this invention.

  Next, the continuous carbonization apparatus and continuous carbonization method for cellulose acetate of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a conceptual diagram of a roller hearth type continuous carbonization apparatus which is a typical example of a continuous carbonization apparatus for cellulose acetate according to the present invention. Since the roller hearth type continuous carbonization apparatus of FIG. 1 has a configuration improved from the roller hearth type continuous carbonization apparatus shown in FIG. 4 of Patent Document 1, the basic configuration is shown in FIG. It is the same as the roller charskin type continuous carbonization equipment shown.

  That is, the roller hearth type continuous carbonization apparatus (heating furnace) 1 includes a tunnel furnace 10 in which a plurality of heaters 11 are provided on the inner surface of a wall body made of a heat-resistant material. An inlet-side inert gas purge region 12 is provided at one end of the tunnel furnace 10 (left side in FIG. 1), and an outlet-side inert gas purge region 13 is provided on the other side (right side in FIG. 1). Each region is filled with an inert gas. Although the left side surface of the inlet-side inert gas purge region 12 is open, a shutter 12a for preventing gas flow between the inner region and the outside air is provided. Further, the right side surface of the outlet-side inert gas purge region 13 is also open, but this is also provided with a shutter 13a for preventing gas flow between the inner region and the outside air. Inside the heating furnace 1, a conveying means 14 composed of a number of rollers penetrating the inlet side inert gas purge region 12, the tunnel furnace 10, and the outlet side inert gas purge region 13 is disposed.

  The bottom of the tunnel furnace 10 is provided with an inert gas supply hole penetrating the bottom wall. The inert gas supply hole is provided with an inert gas such as nitrogen gas through an inert gas supply pipe 15 from the outside. Gas is supplied, and as a result, the inside of the tunnel furnace 10 also becomes an inert gas atmosphere. A plurality of acetic acid vapor discharge holes 16 are provided in the upper wall near the entrance of the tunnel furnace 10, and the acetic acid vapor discharge holes 16 communicate with a condenser (acetic acid recovery device) 18 via an acetic acid vapor discharge pipe 17. ing. An exhaust unit 19 typified by a blower is connected to the downstream side of the condenser 18, and an exhaust gas cleaning device 20 typified by a scrubber is connected to the exhaust unit 19 via a pipe. An exhaust gas return pipe (gas mixture return pipe) 21 communicating with the inside of the tunnel furnace 10 is also connected to the exhaust means 19. The amount of gas discharged from the exhaust means 19 to the exhaust gas cleaning device 20 and the amount of gas discharged to the tunnel furnace 10 (gas return amount) are provided inside the exhaust means 19 or downstream of the exhaust means 19. The discharged amount adjusting tool 22 is adjusted. The adjustment of the gas discharge amount to the exhaust gas cleaning device 20 and the gas discharge amount to the tunnel furnace 10 by the discharge amount adjusting tool 22 is performed by adjusting the atmospheric pressure (atmospheric pressure) outside the tunnel furnace 10 and the tunnel furnace 10. In consideration of the difference from the internal pressure measured by the pressure gauge 23 provided inside, the control is performed by computer control or manually. According to the study of the present inventors, the difference between the atmospheric pressure outside the tunnel furnace 10 (atmospheric pressure) and the internal pressure of the tunnel furnace 10 is maintained within ± 10 Pa (particularly within ± 2 Pa). It has been found preferable for effective exhaust of acetic acid vapor and maintenance of an inert gas atmosphere in the tunnel furnace 10.

  The heating and firing of the cellulose acetate lump (or powder) using the roller hearth kiln type continuous carbonization apparatus (heating furnace) 1 of FIG. A plurality of containers 24 are prepared, and a lump (or powder) 25 of cellulose acetate is accommodated in the containers 24 and sequentially conveyed into the heating furnace 1.

  The cellulose acetate lump (or powder) 25 accommodated in the container 24 is transferred to the heating furnace 1, then sequentially passes through the inlet-side inert gas purge region 12 and into the tunnel furnace provided with the heating means 11. Is done. The cellulose acetate lump (or powder) 25 is heated by the heating means 11 and melted in the container 24 to change into a viscous liquid, and then further heated and fired to become a carbide. The internal temperature of the heating region 10a of the tunnel furnace 10 (corresponding to the heating and firing temperature of the cellulose acetate lump (or powder)) is generally in the range of 300 to 700 ° C, preferably 310 to 500 ° C, particularly preferably 330 to 450 ° C. Maintained in the range. The conveyance residence time in the heating region 10a of the tunnel furnace 10 of the container 24 containing the cellulose acetate lump (or powder) 25 is generally 30 minutes or longer, preferably 2 to 20 hours. The container 24 that has passed through the heating region 10a is then sent to the slow cooling region 10b, gradually cooled to a temperature in the range of room temperature to 100 ° C., and then taken out through the outlet side inert gas purge region 13. By the heat treatment in such a process, the cellulose acetate lump (or powder) 25 becomes a viscous liquid inside the container 24, and then baked to lump carbide. This massive carbide is usually recovered as a carbide having a size of 10 mm or more, particularly 20 to 200 mm.

  In order to produce activated carbon from the carbide obtained in the above process, normally used gas activation (by water vapor, carbon dioxide gas, oxygen gas, hydrogen chloride gas, etc.) chemical activation (alkali metal, alkaline earth metal, phosphorus Any of acid, phosphate, etc. can be used. This activation process has already been described in detail in many prior art documents including the above-mentioned Patent Document 1.

  Next, carbonization by heating and baking of a cellulose acetate lump (or powder) using the continuous carbonization apparatus of the present invention will be described more specifically with reference to examples.

[Example]
A powdery cellulose acetate is accommodated in a container (alumina container) 24 having the shape shown in FIG. 2, and this container 24 is placed on the roller hearth kiln (internal temperature: 350 ° C.) shown in FIG. While feeding and conveying, cellulose acetate was heated and melted, and then heated and fired. The blower 19 was operated, the acetic acid vapor generated by the decomposition of cellulose acetate was taken out from the tunnel furnace 10 and guided to the condenser 18, and then the gas discharged from the condenser 18 was sent into the scrubber 20. At the same time, a part of the gas discharged from the condenser 18 was returned to the tunnel furnace 10 by operating the switching tool 22. In this operation, the amount of gas discharged from the condenser 18 to the scrubber 20 and the amount returned to the inside of the tunnel furnace 10 were about 1: 5 in volume ratio. As a result, the difference between the pressure (atmospheric pressure) inside the tunnel furnace 10 and the atmospheric pressure was maintained within ± 2 Pa.

[Comparative example]
Except that the operation of returning a part of the gas discharged from the condenser 18 to the inside of the tunnel furnace 10 was not performed, a carbide production work was performed by heating and baking powdered cellulose acetate in the same manner as in the above example. However, the pressure (atmospheric pressure) inside the tunnel furnace 10 is 199 Pa or more (note: measurement shakeout) lower than the atmospheric pressure. It was confirmed that a phenomenon of flowing into the tunnel furnace 10 occurred. Further, the amount of acetic acid recovered by the condenser 18 was about ½ of the amount of acetic acid recovered in the example.

  As described above, since the continuous carbonization apparatus and continuous carbonization method for cellulose acetate of the present invention are the continuous carbonization apparatus for cellulose acetate and the improvement apparatus and improvement method for continuous carbonization described in Patent Document 1, As long as the description of 1 is a description that does not contradict the present invention, it is an accompanying description of the present invention.

1 Heating furnace (roller hearth kiln type continuous carbonization equipment)
10 Tunnel furnace 11 Heating means (heater)
12 Inlet side inert gas purge region 12a Shutter 13 Outlet side inert gas purge region 13a Shutter 14 Conveying means (roller)
15 Inert gas supply pipe 18 Acetic acid recovery device (condenser)
19 Exhaust means (blower)
20 Exhaust gas cleaning device (scrubber)
21 Exhaust gas return pipe 22 Switching tool (Discharge amount adjusting tool)
23 Pressure gauge 24 Container 25 Cellulose acetate lump

Claims (4)

  A tunnel-type carbonization furnace for converting a lump or powder of cellulose acetate contained in a container having an opening on the upper surface into a carbide by continuously heating and firing while moving in an inert gas atmosphere, and acetic acid A carbonization apparatus including a condenser for condensing a gas mixture containing gaseous acetic acid produced by heating and baking cellulose and discharged out of the carbonization furnace, the carbonization of the gas mixture is downstream of the condenser An exhaust gas cleaning device is provided through an exhaust means that can accelerate the exhaust from the furnace, and the exhaust means contains a portion of the condensed gas mixture discharged from the condenser into the carbonization furnace. A continuous carbonization apparatus for cellulose acetate, characterized in that a return pipe is provided.   The continuous carbonization apparatus for cellulose acetate according to claim 1, wherein a plurality of inert gas supply ports are formed at the bottom of the carbonization furnace.   The continuous carbonization apparatus for cellulose acetate according to claim 1 or 2, wherein the condenser is connected to a gas mixture discharge port formed in a plurality on the upstream side of the carbonization furnace via a pipe.   When using the continuous carbonization apparatus for cellulose acetate according to claim 1, carbonization is carried out when the cellulose acetate lump or powder is continuously heated and fired while being moved in an inert gas atmosphere. Adjust the operating conditions of the exhaust means so that the pressure inside the furnace is maintained within ± 10 Pa of atmospheric pressure, and adjust the return amount of the condensed gas mixture discharged from the condenser to the carbonization furnace. A continuous carbonization method for cellulose acetate.

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