WO2022054784A1 - Acetic-acid collection method - Google Patents

Acetic-acid collection method Download PDF

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WO2022054784A1
WO2022054784A1 PCT/JP2021/032798 JP2021032798W WO2022054784A1 WO 2022054784 A1 WO2022054784 A1 WO 2022054784A1 JP 2021032798 W JP2021032798 W JP 2021032798W WO 2022054784 A1 WO2022054784 A1 WO 2022054784A1
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Prior art keywords
acetic acid
cellulose acetate
organic solvent
membrane
liquid
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PCT/JP2021/032798
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French (fr)
Japanese (ja)
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秀人 松山
直之 福井
重典 松井
秀隆 早水
一隆 三好
充宏 河野
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国立大学法人神戸大学
株式会社ダイセル
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Publication of WO2022054784A1 publication Critical patent/WO2022054784A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/42—Separation; Purification; Stabilisation; Use of additives
    • C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
    • C07C51/44—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C53/00—Saturated compounds having only one carboxyl group bound to an acyclic carbon atom or hydrogen
    • C07C53/08—Acetic acid
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B3/00—Preparation of cellulose esters of organic acids
    • C08B3/06—Cellulose acetate, e.g. mono-acetate, di-acetate or tri-acetate

Definitions

  • the invention according to the present disclosure relates to a method for recovering acetic acid.
  • This disclosure claims the priority of Japanese Patent Application No. 2020-150253 filed in Japan on September 8, 2020, the contents of which are incorporated herein by reference.
  • Cellulose acetate is used for various purposes such as cigarette filter tow, fiber, photographic film, and artificial kidney.
  • a method for producing cellulose acetate a method of reacting cellulose with an acetylating agent in an aqueous acetic acid solution is known. Further, acetic acid is contained in the residual liquid after obtaining cellulose acetate, and the acetic acid contained in the residual liquid is recovered and reused through an extraction step and a distillation step.
  • the residual liquid contains cellulose acetate in a dissolved state, and when the dissolved cellulose acetate is introduced into the distillation column, the cellulose acetate precipitates at the bottom of the column, resulting in poor liquid transfer and heat transfer. The problem was that it became difficult to maintain the safe power transfer of the distillation column.
  • the residual liquid is subjected to an extraction treatment using an organic solvent to remove water, and then the obtained extract (including acetic acid, an organic solvent and cellulose acetate) is vaporized to be free of cellulose acetate.
  • a gas (including acetic acid and an organic solvent) was obtained, and the obtained gas was introduced into a distillation column to distill an organic solvent having a boiling point lower than that of acetic acid, whereby acetic acid was recovered as a canned liquid.
  • an object of the present invention is to provide a method for recovering acetic acid, which is excellent in steam saving effect or production efficiency improving effect.
  • Another object of the invention according to the present disclosure is to provide a method for producing cellulose acetate by recovering high-purity acetic acid and reusing it by a method excellent in steam saving effect or production efficiency improving effect. be.
  • the invention according to the present disclosure is a method for recovering acetic acid from an acetic acid aqueous solution in which acetic acid cellulose is dissolved, and the acetic acid aqueous solution in which the acetic acid cellulose is dissolved is subjected to a back-penetration film treatment to permeate the film containing acetic acid and water.
  • B) a step of evaporating the extract phase to separate it into a vapor containing acetic acid and an organic solvent and an evaporation residual liquid containing cellulose acetate (2-2-B), and a step of charging the vapor into a distillation column (3-B).
  • a method for recovering acetic acid which comprises a step (4) of recovering acetic acid as a canned liquid from a distillation column.
  • the invention according to the present disclosure is a method for producing cellulose acetate by acetylating cellulose in an acetic acid aqueous solution to obtain cellulose acetate, wherein the cellulose acetate is recovered from the reaction solution after the acetylation, and the residual liquid is used as described above.
  • a method for producing cellulose acetate in which acetic acid is recovered by a method and reused as a raw material for the acetic acid aqueous solution.
  • separation is performed as compared with the conventional method (that is, a method of gasifying to remove cellulose acetate before charging to the distillation column and charging to the distillation column in the gas phase).
  • the efficiency can be improved, and acetic acid having the same purity as the conventional one can be recovered even if the reflux ratio is lowered accordingly. Therefore, it is possible to reduce the enormous energy cost required for vaporizing the refluxed portion (steam saving effect). Further, by lowering the reflux ratio, the amount charged into the distillation column can be increased as compared with the case of the conventional method, so that the production can be increased (improvement of production efficiency). Further, if the acetic acid recovered by the method of the present disclosure is reused, the production cost of cellulose acetate can be reduced.
  • the method for recovering acetic acid of the present disclosure is a method for recovering acetic acid from an acetic acid aqueous solution in which cellulose acetate is dissolved, and the acetic acid aqueous solution in which the cellulose acetate is dissolved is subjected to a back-penetration membrane treatment to permeate the film containing acetic acid and water.
  • Step (1) Membrane separation step
  • the step (1) is a step of separating the acetic acid aqueous solution in which cellulose acetate is dissolved into a membrane permeation liquid (A) and a membrane concentrate (B) using a reverse osmosis membrane.
  • the acetic acid aqueous solution may contain other components other than soluble cellulose acetate as a non-volatile component.
  • cellulose acetate that is insoluble in the acetic acid aqueous solution (hereinafter, may be referred to as "insoluble cellulose acetate"). May be contained.
  • insoluble cellulose acetate cellulose acetate that is insoluble in the acetic acid aqueous solution
  • a microfiltration membrane or the like should be applied before subjecting to membrane separation by a reverse osmosis membrane. It is preferable to remove them by utilizing them in that clogging of the reverse osmosis membrane can be prevented.
  • the reverse osmosis membrane treatment can be performed, for example, by using a filtration device equipped with at least one reverse osmosis membrane module.
  • the reverse osmosis membrane module is not particularly limited as long as it has a configuration for separating the membrane permeable liquid that has permeated the reverse osmosis membrane and the membrane concentrate that does not permeate the reverse osmosis membrane.
  • Examples of the reverse osmosis membrane module include a so-called spiral reverse osmosis membrane module in which a columnar reverse osmosis membrane element in which a reverse osmosis membrane is wound around a water collecting pipe is housed in a cylindrical casing.
  • Examples of the material of the reverse osmosis membrane include polyamide, polysulfone, cellulose acetate and the like, and among these, polyamide such as aromatic polyamide and crosslinked aromatic polyamide is preferable.
  • the water to be treated is flowed parallel to the surface of the filtration membrane, and a part of the water to be treated is filtered on the side of the flow of the water to be treated while preventing the filtration membrane from being contaminated due to the deposition of the filter slag. It is a method.
  • Membrane separation using a reverse osmosis membrane can be performed at, for example, 30 to 50 ° C, and more preferably 35 to 45 ° C.
  • the filtration pressure for membrane separation using a reverse osmosis membrane is, for example, about 0.001 to 6.0 MPaG, preferably 0.01 to 5.0 MPaG, and particularly preferably 0.1 to 4.0 MPaG.
  • the circulation flow rate is, for example, 10 to 40 L / min, preferably 15 to 30 L / min, and particularly preferably 20 to 25 L / min.
  • the circulation flow rate is, for example, 5 to 22 L / min, preferably 6 to 17 L / min, and particularly preferably 8 to 12 L / min.
  • the membrane separation operation using the reverse osmosis membrane is preferably repeated until the cellulose acetate content in the membrane permeate (A) becomes 1000 ppm or less (preferably 500 ppm or less) by using a circulating membrane filtration method or the like.
  • a membrane permeation solution (A) and a membrane concentrate (B) can be obtained by subjecting an acetic acid aqueous solution in which cellulose acetate is dissolved to a membrane separation step using a reverse osmosis membrane.
  • the membrane permeation liquid (A) is a liquid that has passed through the reverse osmosis membrane and contains acetic acid and water.
  • the membrane concentrate (B) is a liquid that has not passed through the reverse osmosis membrane and contains acetic acid, water, and soluble cellulose acetate.
  • the membrane permeate (A) obtained through the step (1) is brought into contact with an organic solvent to form an extract phase containing mainly acetic acid and an organic solvent, and an extraction residue mainly containing water. It is a process of separating into a phase.
  • organic solvent it is preferable to use a solvent having high solubility of acetic acid and low solubility in water, for example, aromatic hydrocarbons such as benzene, toluene and xylene; n-hexane, cyclohexane, etc.
  • Aromatic hydrocarbons such as heptane, octane and nonane; esters such as ethyl acetate, n-amyl acetate, cyclohexyl acetate, isoamyl propionate and methyl benzoate; halogenated hydrocarbons such as chloroform and chlorbenzene tetrachloride; 1 , 2-Dimethoxyethane, ethers such as dimethyl ether and the like are preferable. These can be used alone or in combination of two or more.
  • a mixed solvent of an ester such as ethyl acetate (particularly preferably an acetate) and an aromatic hydrocarbon such as benzene is preferable, and the mixing ratio of the ester and the aromatic hydrocarbon (the former / the latter).
  • the weight ratio is, for example, 5/95 to 95/5, preferably 20/80 to 90/10, particularly preferably 40/60 to 85/15, and most preferably 55/45 to 85/15.
  • the amount of the organic solvent used is, for example, about 1.0 to 5.0 times (volume ratio) the amount of the membrane permeate (A) used.
  • the extraction operation can be performed intermittently or continuously. If the extraction effect is insufficient, the extraction operation can be repeated.
  • an apparatus is not particularly limited, and examples thereof include a known method using an extraction apparatus such as an extraction tower.
  • extraction tower extraction of commonly used types such as mixer setra type extraction tower, perforated plate type, packed tower type, baffle tower type, vibrating perforated plate type, stirring and mixing type, pulsating filling type, centrifugal extraction type and the like. Equipment etc. can be used.
  • the membrane permeation liquid (A) and the organic solvent come into countercurrent contact inside the extraction device.
  • the contact temperature between the membrane permeate (A) and the organic solvent is preferably in the range of, for example, 20 to 60 ° C, preferably 30 to 50 ° C.
  • the contact time is, for example, about 0.1 to 10 hours.
  • the contact between the membrane permeate (A) and the organic solvent can be performed under normal pressure, pressure, or reduced pressure, and the gauge pressure is, for example, about -30 to 30 kPa.
  • the extraction rate of acetic acid into the extract phase can be increased, and the water separation / removal efficiency can be improved.
  • the extract phase obtained in this step mainly contains acetic acid and an organic solvent, and the water content is, for example, 15% by weight or less, preferably 10% by weight or less.
  • the cellulose acetate content is 200 ppm or less (preferably 150 ppm or less).
  • the extraction residual phase mainly contains water, and the content of acetic acid is, for example, 0.5% by weight or less, preferably 0.1% by weight or less.
  • Step (3-A) to Step (4) Distillation Step A
  • the extract phase obtained through step (2-A) is charged into a distillation column in a liquid phase state, and acetic acid and an organic solvent are used by utilizing the difference in boiling point.
  • This is a step of separating and distilling off an organic solvent to obtain high-purity acetic acid as a canned liquid.
  • the distillation step A can be performed in parallel with the distillation step B described later.
  • distillation column examples include a shelf column, a packed column, and the like.
  • the tower top temperature is, for example, 20 to 120 ° C, preferably 30 to 100 ° C, and more preferably 40 to 80 ° C.
  • the pressure in the distillation column can be appropriately adjusted in the range of, for example, 0 to 60 kPa.
  • the distillation step may be composed of a single step or a combination of a plurality of steps.
  • the actual number of stages of the distillation column is, for example, 1 to 100 stages, preferably 10 to 100 stages, particularly preferably 30 to 80 stages, and most preferably 40 to 60 stages in terms of excellent separation efficiency.
  • the reflux ratio in the distillation column can be set low, and the reflux ratio is, for example, in the range of 0.5 to 1.0, preferably 0.6 to 0.9. It is a range.
  • high-purity acetic acid can be obtained as canned liquid.
  • the acetic acid concentration in the canned liquid is, for example, 90% by weight or more, preferably 98% by weight or more, and more preferably 99.9% by weight or more.
  • the content of water in the canned liquid is, for example, 0.1% by weight or less, preferably 0.01% by weight or less, more preferably 0.001% by weight or less, still more preferably 0.0001% by weight or less. be.
  • the acetic acid concentration in the distillate is, for example, 0.02% by weight or less, preferably 0.01% by weight or less, and more preferably 0.005% by weight or less.
  • the acetic acid concentration in the distillate can be controlled by adjusting the reflux ratio.
  • the membrane concentrate (B) is brought into contact with an organic solvent to extract an extract phase mainly containing acetic acid, an organic solvent and soluble cellulose acetate, and an extraction mainly containing water and soluble cellulose acetate.
  • This step can be performed in the same manner as the above extraction step A except that the membrane concentrate (B) is used instead of the membrane permeate (A).
  • the extract phase obtained in this step mainly contains acetic acid, an organic solvent and soluble cellulose acetate.
  • the extraction residual phase mainly contains water and soluble cellulose acetate.
  • the extract phase obtained through the step (2-1-B) is evaporated and separated into a vapor containing acetic acid and an organic solvent and an evaporation residue containing soluble cellulose acetate. It is a process. In this step, cellulose acetate dissolved in the extract phase can be separated and removed.
  • the extract phase can be carried out by subjecting the extract phase to heat treatment.
  • the heat treatment temperature is, for example, 80 to 100 ° C.
  • the heat treatment can be performed under normal pressure, pressure, or reduced pressure, and the gauge pressure is, for example, about -50 to 50 kPa. It may be configured by a single process, or may be configured by combining a plurality of processes. Further, a distillation column type evaporation tank may be used.
  • the steam obtained in this step mainly contains acetic acid and an organic solvent, and the content of water is, for example, 15% by weight or less, preferably 10% by weight or less.
  • the soluble cellulose acetate content is 50 ppm or less (preferably 20 ppm or less), and the insoluble cellulose acetate content is 25 ppm or less (preferably 10 ppm or less).
  • Step (3-B) to Step (4) Distillation Step B
  • step (3-B) to step (4) the steam obtained through step (2-2-B) is charged into a distillation column, acetic acid and an organic solvent are separated by utilizing the difference in boiling point, and the organic solvent is used.
  • acetic acid and an organic solvent are separated by utilizing the difference in boiling point, and the organic solvent is used.
  • This step can be performed in the same manner as the above-mentioned distillation step A except that the vapor obtained through the step (2-2-B) is used instead of the extract phase obtained through the step (2-A). can.
  • the distillation step B is performed in parallel with the distillation step A described above.
  • the total amount charged to the distillation column is 10% by weight or more, preferably 20% by weight or more, particularly preferably 30% by weight or more), and the effect of improving the separation efficiency can be obtained.
  • the upper limit of the liquid phase charging ratio is, for example, 90% by weight.
  • the ratio (weight ratio) of the liquid phase charge to the total amount charged to the distillation column is 23% by weight, the energy cost can be reduced by about 10% as the reflux ratio is lowered. Therefore, the invention according to the present disclosure is extremely useful as a method for industrially recovering and reusing acetic acid (particularly, a method for recycling residual liquid discharged by the production of cellulose acetate).
  • an acetic acid aqueous solution in which cellulose acetate is dissolved (or a residual liquid after the production of cellulose acetate) is supplied to the membrane separation device A by line 1 and subjected to reverse osmosis membrane treatment.
  • the membrane permeation liquid (A) that has permeated the reverse osmosis membrane is introduced from line 2 to the top of the extraction tower B-1.
  • the organic solvent is introduced from the line 3 to the bottom of the extraction tower B-1, and is in countercurrent contact with the membrane permeate (A) in the extraction tower B-1, mainly with the extract phase containing acetic acid and the organic solvent.
  • the extract phase is charged into the distillation column C from line 4 as a liquid phase.
  • the extracted residual phase is discharged from the line 13 to the outside of the system.
  • the extract phase is charged into the distillation column C, most of the organic solvent contained in the extract phase is cooled by the cooler D from the top of the column via the line 8 and introduced into the tank E from the line 9.
  • the upper layer liquid mainly contains an organic solvent and is discharged from the line 10 to the outside of the system. This can be reused as an organic solvent to be introduced into the extraction tower B-1 or B-2 again.
  • the lower layer liquid of the tank E mainly contains water and is discharged from the line 11 to the outside of the system.
  • a part of the upper layer liquid of the tank E may be recycled to the distillation column C as it is in the liquid phase.
  • a part of the upper layer liquid of the tank E is recycled to the distillation column C through the line 12.
  • high-purity acetic acid is recovered as canned out liquid from the bottom of the distillation column C via the line 5.
  • the membrane concentrate (B) that did not permeate the reverse osmosis membrane in the membrane separation device A is introduced from the line 14 to the top of the extraction tower B-2.
  • the organic solvent is introduced from the line 15 to the bottom of the extraction tower B-2, and is in countercurrent contact with the membrane concentrate (B) in the extraction tower B-2, and extracts mainly containing acetic acid, an organic solvent and soluble cellulose acetate. It is separated into a liquid phase and an extraction residual phase mainly containing water and soluble cellulose acetate.
  • the extract phase is introduced into the evaporator G from the line 16.
  • the extracted residual phase is discharged from the line 17 to the outside of the system.
  • the extract phase is evaporated in the evaporator G and separated into a vapor containing acetic acid and an organic solvent and an evaporation residual liquid containing soluble cellulose acetate, and the vapor containing acetic acid and an organic solvent is vaporized from line 18 into the distillation column C. It is prepared in.
  • the subsequent flow is the same as the extract phase charged in the distillation column C as a liquid phase.
  • the evaporation residue containing soluble cellulose acetate is discharged from the line 19 to the outside of the system.
  • the method for producing cellulose acetate of the present disclosure is a method for producing cellulose acetate by acetylating cellulose in an acetic acid aqueous solution to obtain cellulose acetate, in which cellulose acetate is recovered from the reaction solution after acetylation and the residual liquid thereof is recovered. Therefore, acetic acid is recovered by the above-mentioned acetic acid recovery method and reused as a raw material for the acetic acid aqueous solution.
  • the production of cellulose acetate includes, for example, the following steps 1 to 3.
  • Step 1 The cellulose raw material is dissociated and crushed, and then acetic acid or acetic acid containing a small amount of an acidic catalyst is sprayed to activate the cellulose.
  • Step 2 Activated cellulose , Acetic acid aqueous solution to obtain cellulose acetate by acetylation
  • Step 3 Purification step
  • the reaction solution after acetylation contains insoluble cellulose acetate, soluble cellulose acetate, and acetic acid aqueous solution obtained by acetylation.
  • the acetic acid aqueous solution may contain other components other than acetic acid and water, such as an acetylating agent (for example, acetic anhydride) and an acidic catalyst (for example, sulfuric acid).
  • an acetylating agent for example, acetic anhydride
  • an acidic catalyst for example, sulfuric acid
  • the primary cellulose acetate obtained through the acetylation step can be hydrolyzed to obtain the secondary cellulose acetate having a desired degree of acetic acidation.
  • acetic acid is recovered from the reaction solution after the acetylation step and reused, so that the production cost of cellulose acetate can be reduced.
  • each configuration of the invention according to the present disclosure and combinations thereof are examples, and the configurations can be added, omitted, replaced, and changed as appropriate within the range not deviating from the gist of the invention according to the present disclosure. .. Further, the invention according to the present disclosure is not limited to the embodiments, but is limited only by the description of the scope of claims.
  • Example 1 A 30% aqueous acetate solution (cellulose acetate content: 1%) in which cellulose acetate is dissolved is applied to a reverse osmosis membrane (ES15, 2-inch membrane module manufactured by Nitto Denko Co., Ltd., liquid circulation volume: 8 L / min, material: polyamide).
  • the membrane permeation liquid (a) and the membrane concentrate (b) were obtained by performing cross-flow filtration using the above.
  • the membrane permeate (a) was extracted with an organic solvent (ethyl acetate: 75%, benzene: 25%) to obtain an extract phase (a).
  • the membrane concentrate (b) was extracted with an organic solvent (ethyl acetate: 75%, benzene: 25%) to obtain an extract phase (b) containing cellulose acetate, and the obtained extract phase (b) was obtained.
  • b) was subjected to an evaporator (distillation rate: 99%) to remove cellulose acetate to obtain gas (b).
  • the extract phase (a) and the gas (b) were simultaneously charged into a distillation column (60 stages of older show) at a weight ratio of 3:10.
  • the extract phase (a) is the 24th stage from the top
  • the gas (b) is the 34th stage from the top
  • the amount of the liquid charged in the extract phase (a) is 233 g / h
  • the gas (b) is charged.
  • the liquid volume was 776 g / h.
  • the tower top pressure is normal pressure
  • the thermometer is the tower top (1st step from the top), 4th step, 8th step, 14th step, 18th step, 24th step, 28th step, 38th step from the top.
  • a method for recovering acetic acid from an acetic acid aqueous solution in which cellulose acetate is dissolved A step of subjecting the acetic acid aqueous solution in which cellulose acetate is dissolved to a back-penetration membrane treatment to separate the membrane permeate (A) containing acetic acid and water and the membrane concentrate (B) containing acetic acid, water and cellulose acetate (B).
  • Step (2-A) in which the membrane permeate (A) is brought into contact with an organic solvent and separated into an extract phase mainly containing acetic acid and an organic solvent and an extraction residual phase mainly containing water (2-A).
  • Step of charging the extract phase into the distillation column (3-A) A step of contacting the membrane concentrate (B) with an organic solvent to separate it into an extract phase containing mainly acetic acid, an organic solvent and cellulose acetate, and an extraction residual phase mainly containing water and cellulose acetate (2-1-).
  • B) Step of evaporating the extract phase to separate it into vapor containing acetic acid and an organic solvent and an evaporation residue containing cellulose acetate (2-2-B), Step of charging the steam into the distillation column (3-B),
  • a method for recovering acetic acid which comprises a step (4) of recovering acetic acid as a canned liquid from a distillation column.
  • step (2-A) The organic solvent used in step (2-A) is at least one solvent selected from aromatic hydrocarbons, aliphatic hydrocarbons, esters, halogenated hydrocarbons, and ethers, [1]. ] To [3]. The method for recovering acetic acid according to any one of [3].
  • the organic solvent used in the step (2-A) is a mixed solvent of an ester and an aromatic hydrocarbon, and the weight ratio of the ester to the aromatic hydrocarbon (the former / the latter) is 5/95 to 95.
  • the method for recovering acetic acid according to any one of [1] to [3], which is / 5.
  • the organic solvent used in the step (2-1-B) is at least one solvent selected from aromatic hydrocarbons, aliphatic hydrocarbons, esters, halogenated hydrocarbons, and ethers.
  • the organic solvent used in the step (2-1-B) is a mixed solvent of an ester and an aromatic hydrocarbon, and the weight ratio of the ester to the aromatic hydrocarbon (the former / the latter) is 5/95.
  • [11] The method for recovering acetic acid according to any one of [1] to [10], wherein the acetic acid concentration in the canned liquid obtained in the step (4) is 90% by weight or more.
  • [12] A method for producing cellulose acetate by acetylating cellulose in an acetic acid aqueous solution to obtain cellulose acetate. From the reaction solution after acetylation, cellulose acetate is recovered, and from the residual liquid, [1] to [1] to [ 11] A method for producing cellulose acetate, which recovers acetic acid by the method for recovering acetic acid according to any one of the above methods and reuses it as a raw material for the acetic acid aqueous solution.
  • acetic acid having the same purity as the conventional method can be recovered even if the reflux ratio is lowered as compared with the conventional method. Therefore, it is possible to reduce the enormous energy cost required for vaporizing the refluxed portion. Further, by lowering the reflux ratio, the amount charged into the distillation column can be increased as compared with the case of the conventional method, so that the production can be increased.

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Abstract

Provided is an acetic-acid collection method that has an excellent vapor saving effect or a production efficiency improving effect.　The acetic-acid collection method includes: a step (1) in which an aqueous acetic acid solution in which cellulose acetate has been dissolved is separated by a reverse osmosis membrane treatment into a membrane-permeated liquid (A) that includes acetic acid and water and a membrane-concentrated liquid (B) that includes acetic acid, water, and cellulose acetate; a step (2-A) in which the membrane-permeated liquid (A) is brought into contact with an organic solvent and is separated into an extracted liquid phase that primarily includes the acetic acid and the organic solvent and an extraction residue phase that primarily includes the water; a step (3-A) in which the extracted liquid phase is loaded into a distillation tower; a step (2-1-B) in which the membrane-concentrated liquid (B) is brought into contact with an organic solvent and is separated into an extracted liquid phase that primarily includes the acetic acid, the organic solvent and the cellulose acetate and an extraction residue phase that primarily includes the water and the cellulose acetate; a step (2-2-B) in which the extracted liquid phase is vaporized and separated into a vapor that includes the acetic acid and the organic solvent and a vaporization residue liquid that includes the cellulose acetate; a step (3-B) in which the vapor is loaded into a distillation tower; and a step (4) in which the acetic acid is collected from the distillation tower as a bottom product liquid.

Description

酢酸の回収方法Acetic acid recovery method
　本開示に係る発明は酢酸の回収方法に関する。本開示は、２０２０年９月８日に日本に出願した、特願２０２０－１５０２５３号の優先権を主張し、その内容をここに援用する。 The invention according to the present disclosure relates to a method for recovering acetic acid. This disclosure claims the priority of Japanese Patent Application No. 2020-150253 filed in Japan on September 8, 2020, the contents of which are incorporated herein by reference.
　酢酸セルロースは、たばこ用のフィルタートウ、繊維、写真用フィルム、人工腎臓等の種々の用途に用いられている。酢酸セルロースの製造方法としては、酢酸水溶液中において、セルロースにアセチル化剤を反応させる方法が知られている。また、酢酸セルロースを得た後の残液には酢酸が含まれるが、残液に含まれる酢酸は抽出工程及び蒸留工程を経て回収され、再利用される。 Cellulose acetate is used for various purposes such as cigarette filter tow, fiber, photographic film, and artificial kidney. As a method for producing cellulose acetate, a method of reacting cellulose with an acetylating agent in an aqueous acetic acid solution is known. Further, acetic acid is contained in the residual liquid after obtaining cellulose acetate, and the acetic acid contained in the residual liquid is recovered and reused through an extraction step and a distillation step.
　しかし、残液中には、酢酸セルロースが溶解した状態で含まれており、溶解した状態の酢酸セルロースが蒸留塔に導入すると、酢酸セルロースが塔底部において析出するため、送液不良や伝熱不良を引き起こし、蒸留塔の安全運電を維持することが困難となることが問題であった。 However, the residual liquid contains cellulose acetate in a dissolved state, and when the dissolved cellulose acetate is introduced into the distillation column, the cellulose acetate precipitates at the bottom of the column, resulting in poor liquid transfer and heat transfer. The problem was that it became difficult to maintain the safe power transfer of the distillation column.
　そこで、残液を、有機溶媒を用いた抽出処理に付して水を除去し、その後、得られた抽出液（酢酸と有機溶媒と酢酸セルロースを含む）を気化させることにより酢酸セルロースを含まないガス（酢酸と有機溶媒を含む）を得、更に、得られたガスを蒸留塔に導入して、酢酸より低沸点の有機溶媒を留出させることで、酢酸を缶出液として回収していた（例えば、特許文献１）。 Therefore, the residual liquid is subjected to an extraction treatment using an organic solvent to remove water, and then the obtained extract (including acetic acid, an organic solvent and cellulose acetate) is vaporized to be free of cellulose acetate. A gas (including acetic acid and an organic solvent) was obtained, and the obtained gas was introduced into a distillation column to distill an organic solvent having a boiling point lower than that of acetic acid, whereby acetic acid was recovered as a canned liquid. (For example, Patent Document 1).
特表２０１４－５２００８０号公報Special Table 2014-52080 Gazette
　しかし、抽出液をガス化させるには膨大なエネルギーが必要である。さらに、ガス化した状態で蒸留塔に仕込むと分離効率が悪化すること、分離効率の悪化は、還流比を高めることで対応可能だが、それにより酢酸の回収コストが嵩むことがわかった。 However, enormous energy is required to gasify the extract. Furthermore, it was found that the separation efficiency deteriorates when the gasified state is charged into the distillation column, and the deterioration of the separation efficiency can be dealt with by increasing the reflux ratio, but this increases the recovery cost of acetic acid.
　従って、本開示に係る発明の目的は、省蒸気効果若しくは生産効率向上効果に優れる酢酸の回収方法を提供することにある。
　本開示に係る発明の他の目的は、省蒸気効果若しくは生産効率向上効果に優れる方法で、高純度の酢酸を回収し、これを再利用して、酢酸セルロースを製造する方法を提供することにある。 Therefore, an object of the present invention is to provide a method for recovering acetic acid, which is excellent in steam saving effect or production efficiency improving effect.
Another object of the invention according to the present disclosure is to provide a method for producing cellulose acetate by recovering high-purity acetic acid and reusing it by a method excellent in steam saving effect or production efficiency improving effect. be.
　本発明者等は上記課題を解決するため鋭意検討した結果、以下の事項を見いだした。すなわち、
１．蒸留塔の仕込みの少なくとも一部を気相から液相に変更すれば、分離効率が向上し、それに伴い還流比を低下させることができるため、省蒸気効果が得られること
２．酢酸セルロースが溶解した酢酸水溶液を、逆浸透膜を利用した膜処理に付せば、酢酸セルロース濃度が蒸留塔の塔底部に析出する問題を生じない程度にまで低減された膜透過液を得ることができ、当該膜透過液はガス化して酢酸セルロースを除去する操作を行う必要がなく、そのまま液相にて蒸留塔に仕込むことが可能であること
　本開示に係る発明はこれらの知見に基づいて完成させたものである。 As a result of diligent studies to solve the above problems, the present inventors have found the following matters. That is,
1. 1. If at least a part of the preparation in the distillation column is changed from the gas phase to the liquid phase, the separation efficiency can be improved and the reflux ratio can be lowered accordingly, so that a steam saving effect can be obtained. By subjecting an acetate aqueous solution in which cellulose acetate is dissolved to a membrane treatment using a reverse osmosis membrane, a membrane permeate can be obtained in which the concentration of cellulose acetate is reduced to the extent that the problem of precipitation at the bottom of the distillation column does not occur. The membrane permeate can be gasified to remove cellulose acetate, and can be charged into the distillation column as it is in the liquid phase. The invention according to the present disclosure is based on these findings. It was completed.
　すなわち、本開示に係る発明は、酢酸セルロースが溶解した酢酸水溶液から酢酸を回収する方法であって、前記酢酸セルロースが溶解した酢酸水溶液を逆浸透膜処理に付して酢酸と水を含む膜透過液（Ａ）と酢酸と水と酢酸セルロースとを含む膜濃縮液（Ｂ）とに分離する工程（１）、
膜透過液（Ａ）を有機溶媒と接触させて主に酢酸と有機溶媒を含む抽出液相と主に水を含む抽出残相とに分離する工程（2-A）、抽出液相を蒸留塔に仕込む工程（3-A）、
膜濃縮液（Ｂ）を有機溶媒と接触させて主に酢酸と有機溶媒と酢酸セルロースを含む抽出液相と、主に水と酢酸セルロースを含む抽出残相とに分離する工程（2-1-B）、抽出液相を蒸発させて酢酸と有機溶媒とを含む蒸気と酢酸セルロースを含む蒸発残液に分離する工程（2-2-B）、前記蒸気を蒸留塔に仕込む工程（3-B）、
蒸留塔から缶出液として酢酸を回収する工程（４）を含む、酢酸の回収方法を提供する。 That is, the invention according to the present disclosure is a method for recovering acetic acid from an acetic acid aqueous solution in which acetic acid cellulose is dissolved, and the acetic acid aqueous solution in which the acetic acid cellulose is dissolved is subjected to a back-penetration film treatment to permeate the film containing acetic acid and water. Step (1) of separating into a membrane concentrate (B) containing the liquid (A), acetic acid, water and cellulose acetate.
Step (2-A) of contacting the membrane permeate (A) with an organic solvent to separate the extract phase mainly containing acetic acid and the organic solvent into the extraction residual phase mainly containing water, the extraction phase is separated into a distillation column. (3-A),
A step of contacting the membrane concentrate (B) with an organic solvent to separate it into an extract phase mainly containing acetic acid, an organic solvent and cellulose acetate, and an extraction residual phase mainly containing water and cellulose acetate (2-1-). B), a step of evaporating the extract phase to separate it into a vapor containing acetic acid and an organic solvent and an evaporation residual liquid containing cellulose acetate (2-2-B), and a step of charging the vapor into a distillation column (3-B). ),
Provided is a method for recovering acetic acid, which comprises a step (4) of recovering acetic acid as a canned liquid from a distillation column.
　本開示に係る発明は、セルロースを酢酸水溶液中にてアセチル化して酢酸セルロースを得る酢酸セルロースの製造方法であって、前記アセチル化後の反応液から酢酸セルロースを回収し、その残液から、前記方法により酢酸を回収して、前記酢酸水溶液の原料として再利用する酢酸セルロースの製造方法を提供する。 The invention according to the present disclosure is a method for producing cellulose acetate by acetylating cellulose in an acetic acid aqueous solution to obtain cellulose acetate, wherein the cellulose acetate is recovered from the reaction solution after the acetylation, and the residual liquid is used as described above. Provided is a method for producing cellulose acetate, in which acetic acid is recovered by a method and reused as a raw material for the acetic acid aqueous solution.
　本開示の方法によれば、従来の方法（すなわち、蒸留塔への仕込み前に、酢酸セルロースを除去するためガス化を行い、蒸留塔への仕込みを全量気相で行う方法）に比べて分離効率を向上することができ、それに伴い還流比を下げても、従来と同じ純度の酢酸を回収することができる。そのため、還流分の気化に要していた膨大なエネルギーコストを削減することができる（省蒸気効果）。
　また、還流比を低下させることにより、蒸留塔への仕込み量を従来の方法の場合より上昇させることができるので、増産が可能となる（生産効率の向上）。
　更に、本開示の方法で回収された酢酸を再利用すれば、酢酸セルロースの製造コストの削減が可能となる。 According to the method of the present disclosure, separation is performed as compared with the conventional method (that is, a method of gasifying to remove cellulose acetate before charging to the distillation column and charging to the distillation column in the gas phase). The efficiency can be improved, and acetic acid having the same purity as the conventional one can be recovered even if the reflux ratio is lowered accordingly. Therefore, it is possible to reduce the enormous energy cost required for vaporizing the refluxed portion (steam saving effect).
Further, by lowering the reflux ratio, the amount charged into the distillation column can be increased as compared with the case of the conventional method, so that the production can be increased (improvement of production efficiency).
Further, if the acetic acid recovered by the method of the present disclosure is reused, the production cost of cellulose acetate can be reduced.
本開示の酢酸の回収方法の一例を示す概略フロー図である。示す。It is a schematic flow chart which shows an example of the acetic acid recovery method of this disclosure. show. 本開示の酢酸の回収方法における、蒸留塔への液相仕込み比率と省蒸気率の相関図である。It is a correlation diagram of the liquid phase charge ratio to the distillation column and the steam saving rate in the acetic acid recovery method of this disclosure.
　［酢酸の回収方法］
　本開示の酢酸の回収方法は、酢酸セルロースが溶解した酢酸水溶液から酢酸を回収する方法であって、前記酢酸セルロースが溶解した酢酸水溶液を逆浸透膜処理に付して酢酸と水を含む膜透過液（Ａ）と、酢酸と水と酢酸セルロースとを含む膜濃縮液（Ｂ）とに分離する工程（１）、
膜透過液（Ａ）を有機溶媒と接触させて主に酢酸と有機溶媒を含む抽出液相と主に水を含む抽出残相とに分離する工程（2-A）、前記抽出液相を蒸留塔に仕込む工程（3-A）、
膜濃縮液（Ｂ）を有機溶媒と接触させて主に酢酸と有機溶媒と酢酸セルロースを含む抽出液相と、主に水と酢酸セルロースを含む抽出残相とに分離する工程（2-1-B）、前記抽出液相を蒸発させて酢酸と有機溶媒とを含む蒸気と酢酸セルロースを含む蒸発残液に分離する工程（2-2-B）、前記蒸気を蒸留塔に仕込む工程（3-B）、
蒸留塔から缶出液として酢酸を回収する工程（４）を含む。 [Acetic acid recovery method]
The method for recovering acetic acid of the present disclosure is a method for recovering acetic acid from an acetic acid aqueous solution in which cellulose acetate is dissolved, and the acetic acid aqueous solution in which the cellulose acetate is dissolved is subjected to a back-penetration membrane treatment to permeate the film containing acetic acid and water. Step (1) of separating the liquid (A) into a membrane concentrate (B) containing acetic acid, water and cellulose acetate.
The step (2-A) of contacting the membrane permeate (A) with an organic solvent to separate the extract phase mainly containing acetic acid and the organic solvent into the extraction residual phase mainly containing water, distilling the extract phase. The process of filling the tower (3-A),
A step of contacting the membrane concentrate (B) with an organic solvent to separate it into an extract phase mainly containing acetic acid, an organic solvent and cellulose acetate, and an extraction residual phase mainly containing water and cellulose acetate (2-1-). B), a step of evaporating the extract phase to separate it into a vapor containing acetic acid and an organic solvent and an evaporation residual liquid containing cellulose acetate (2-2-B), and a step of charging the vapor into a distillation column (3-3). B),
The step (4) of recovering acetic acid as a can drain from the distillation column is included.
　（工程（１）：膜分離工程）
　工程（１）は、酢酸セルロースが溶解した酢酸水溶液を、逆浸透膜を使用して膜透過液（Ａ）と膜濃縮液（Ｂ）とに分離する工程である。 (Step (1): Membrane separation step)
The step (1) is a step of separating the acetic acid aqueous solution in which cellulose acetate is dissolved into a membrane permeation liquid (A) and a membrane concentrate (B) using a reverse osmosis membrane.
　前記酢酸水溶液には、不揮発分として、可溶性酢酸セルロース以外にも他の成分を含有していても良く、例えば、酢酸水溶液に溶解しない酢酸セルロース（以後、「不溶性酢酸セルロース」と称する場合がある）を含有していてもよい。酢酸水溶液に不溶性酢酸セルロースが含まれる場合、すなわち、酢酸水溶液中に溶けずに懸濁若しくは沈殿した状態の酢酸セルロースが含まれる場合、逆浸透膜による膜分離に付す前に、精密ろ過膜等を利用してこれらを除去することが、逆浸透膜の目詰まりを防止することができる点で好ましい。 The acetic acid aqueous solution may contain other components other than soluble cellulose acetate as a non-volatile component. For example, cellulose acetate that is insoluble in the acetic acid aqueous solution (hereinafter, may be referred to as "insoluble cellulose acetate"). May be contained. If the aqueous acetate solution contains insoluble cellulose acetate, that is, if the aqueous acetate solution contains cellulose acetate that is suspended or precipitated without being dissolved, a microfiltration membrane or the like should be applied before subjecting to membrane separation by a reverse osmosis membrane. It is preferable to remove them by utilizing them in that clogging of the reverse osmosis membrane can be prevented.
　逆浸透膜処理は、例えば、少なくとも１つの逆浸透膜モジュールを具備する濾過装置を利用して行うことができる。逆浸透膜モジュールは、逆浸透膜を透過した膜透過液と逆浸透膜を透過しない膜濃縮液とを分離する構成を有している限りにおいて、特に制限されない。 The reverse osmosis membrane treatment can be performed, for example, by using a filtration device equipped with at least one reverse osmosis membrane module. The reverse osmosis membrane module is not particularly limited as long as it has a configuration for separating the membrane permeable liquid that has permeated the reverse osmosis membrane and the membrane concentrate that does not permeate the reverse osmosis membrane.
　逆浸透膜モジュールとしては、例えば、集水管のまわりに逆浸透膜を巻き回した円柱状の逆浸透膜エレメントを円筒状のケーシングに収納した、いわゆるスパイラル型逆浸透膜モジュール等が挙げられる。逆浸透膜の材質としては、ポリアミド、ポリスルフォン、セルロースアセテート等が挙げられ、これらの中でも芳香族ポリアミドや架橋芳香族ポリアミド等のポリアミドが好ましい。 Examples of the reverse osmosis membrane module include a so-called spiral reverse osmosis membrane module in which a columnar reverse osmosis membrane element in which a reverse osmosis membrane is wound around a water collecting pipe is housed in a cylindrical casing. Examples of the material of the reverse osmosis membrane include polyamide, polysulfone, cellulose acetate and the like, and among these, polyamide such as aromatic polyamide and crosslinked aromatic polyamide is preferable.
　本開示に係る発明においては、クロスフロー濾過方式による膜処理を施すことが、ろ過速度低下を防止できる点で好ましい。尚、クロスフロー濾過方式とは濾過膜面に平行に被処理水を流し、濾滓の沈着による濾過膜汚染を防ぎながら被処理水の一部を、被処理水の流れの側方で濾過する方式である。 In the invention according to the present disclosure, it is preferable to perform membrane treatment by a cross-flow filtration method in that a decrease in filtration rate can be prevented. In the cross-flow filtration method, the water to be treated is flowed parallel to the surface of the filtration membrane, and a part of the water to be treated is filtered on the side of the flow of the water to be treated while preventing the filtration membrane from being contaminated due to the deposition of the filter slag. It is a method.
　逆浸透膜を使用した膜分離は、例えば３０～５０℃で行うことができ、なかでも３５～４５℃で行うことが好ましい。 Membrane separation using a reverse osmosis membrane can be performed at, for example, 30 to 50 ° C, and more preferably 35 to 45 ° C.
　逆浸透膜を使用した膜分離の濾過圧力は、例えば０．００１～６．０ＭＰａＧ程度であり、好ましくは０．０１～５．０ＭＰａＧ、特に好ましくは０．１～４．０ＭＰａＧである。 The filtration pressure for membrane separation using a reverse osmosis membrane is, for example, about 0.001 to 6.0 MPaG, preferably 0.01 to 5.0 MPaG, and particularly preferably 0.1 to 4.0 MPaG.
　逆浸透膜を使用した膜分離の膜面を流れる液の循環量（＝循環流量）は、使用する膜モジュールのサイズに準じて変更することができる。例えば、４インチ膜モジュールを使用する場合、循環流量は、例えば１０～４０Ｌ／ｍｉｎ、好ましくは１５～３０Ｌ／ｍｉｎ、特に好ましくは２０～２５Ｌ／ｍｉｎである。２インチ膜モジュールを使用する場合、循環流量は、例えば５～２２Ｌ／ｍｉｎ、好ましくは６～１７Ｌ／ｍｉｎ、特に好ましくは８～１２Ｌ／ｍｉｎである。 The circulation amount (= circulation flow rate) of the liquid flowing on the membrane surface of the membrane separation using the reverse osmosis membrane can be changed according to the size of the membrane module used. For example, when a 4-inch membrane module is used, the circulation flow rate is, for example, 10 to 40 L / min, preferably 15 to 30 L / min, and particularly preferably 20 to 25 L / min. When a 2-inch membrane module is used, the circulation flow rate is, for example, 5 to 22 L / min, preferably 6 to 17 L / min, and particularly preferably 8 to 12 L / min.
　逆浸透膜を使用した膜分離操作は、循環膜濾過方式等を利用して、膜透過液（Ａ）中の酢酸セルロース含有量が１０００ｐｐｍ以下（好ましくは５００ｐｐｍ以下）となるまで繰り返すことが好ましい。 The membrane separation operation using the reverse osmosis membrane is preferably repeated until the cellulose acetate content in the membrane permeate (A) becomes 1000 ppm or less (preferably 500 ppm or less) by using a circulating membrane filtration method or the like.
　酢酸セルロースが溶解した酢酸水溶液を、逆浸透膜を使用した膜分離工程に付すことで、膜透過液（Ａ）と膜濃縮液（Ｂ）が得られる。膜透過液（Ａ）は逆浸透膜を通過した液であり、酢酸及び水が含まれる。一方、膜濃縮液（Ｂ）は逆浸透膜を通過しなかった液であり、酢酸、水、及び可溶性酢酸セルロースが含まれる。 A membrane permeation solution (A) and a membrane concentrate (B) can be obtained by subjecting an acetic acid aqueous solution in which cellulose acetate is dissolved to a membrane separation step using a reverse osmosis membrane. The membrane permeation liquid (A) is a liquid that has passed through the reverse osmosis membrane and contains acetic acid and water. On the other hand, the membrane concentrate (B) is a liquid that has not passed through the reverse osmosis membrane and contains acetic acid, water, and soluble cellulose acetate.
　（工程（2-A）：抽出工程Ａ）
　工程（2-A）は、工程（１）を経て得られた膜透過液（Ａ）を有機溶媒と接触させて主に酢酸と有機溶媒を含む抽出液相と、主に水を含む抽出残相とに分離する工程である。 (Step (2-A): Extraction step A)
In the step (2-A), the membrane permeate (A) obtained through the step (1) is brought into contact with an organic solvent to form an extract phase containing mainly acetic acid and an organic solvent, and an extraction residue mainly containing water. It is a process of separating into a phase.
　前記有機溶媒としては、酢酸の溶解性が高く、且つ水への溶解性が低い溶媒を使用することが好ましく、例えば、ベンゼン、トルエン、キシレンなどの芳香族炭化水素類；ｎ－ヘキサン、シクロヘキサン、ヘプタン、オクタン、ノナンなどの脂肪族炭化水素類；酢酸エチル、酢酸ｎ－アミル、酢酸シクロヘキシル、プロピオン酸イソアミル、安息香酸メチル等のエステル；クロロホルム、四塩化炭素クロルベンゼン等のハロゲン化炭化水素；１，２－ジメトキシエタン、ジメチルエーテル等のエーテル等が好ましい。これらは１種を単独で、又は２種以上を組み合わせて使用することができる。 As the organic solvent, it is preferable to use a solvent having high solubility of acetic acid and low solubility in water, for example, aromatic hydrocarbons such as benzene, toluene and xylene; n-hexane, cyclohexane, etc. Aromatic hydrocarbons such as heptane, octane and nonane; esters such as ethyl acetate, n-amyl acetate, cyclohexyl acetate, isoamyl propionate and methyl benzoate; halogenated hydrocarbons such as chloroform and chlorbenzene tetrachloride; 1 , 2-Dimethoxyethane, ethers such as dimethyl ether and the like are preferable. These can be used alone or in combination of two or more.
　前記有機溶媒としては、なかでも、酢酸エチル等のエステル（特に好ましくは、酢酸エステル）とベンゼンなどの芳香族炭化水素との混合溶媒が好ましく、エステルと芳香族炭化水素の混合比（前者／後者；重量比）は、例えば５／９５～９５／５、好ましくは２０／８０～９０／１０、特に好ましくは４０／６０～８５／１５、最も好ましくは５５／４５～８５／１５である。 As the organic solvent, a mixed solvent of an ester such as ethyl acetate (particularly preferably an acetate) and an aromatic hydrocarbon such as benzene is preferable, and the mixing ratio of the ester and the aromatic hydrocarbon (the former / the latter). The weight ratio) is, for example, 5/95 to 95/5, preferably 20/80 to 90/10, particularly preferably 40/60 to 85/15, and most preferably 55/45 to 85/15.
　前記有機溶媒の使用量としては、膜透過液（Ａ）の使用量の例えば１．０～５．０倍（体積比）程度である。 The amount of the organic solvent used is, for example, about 1.0 to 5.0 times (volume ratio) the amount of the membrane permeate (A) used.
　前記抽出操作は、間欠的又は連続的に行うことができる。また、抽出効果が不十分である場合は、繰り返し抽出操作を行うこともできる。 The extraction operation can be performed intermittently or continuously. If the extraction effect is insufficient, the extraction operation can be repeated.
　前記抽出操作は、膜透過液（Ａ）と有機溶媒を、抽出液相（＝有機相）と抽出残相（＝水相）に分離できる装置を用いることが好ましい。このような装置としては、特に制限されないが、例えば、抽出塔等の抽出装置を用いた公知の方法等が挙げられる。前記抽出塔としては、通常用いられる形式、例えば、ミキサーセトラ型抽出塔、多孔板型、充填塔型、バッフル塔型、振動多孔板型、撹拌混合型、脈動充填型、遠心抽出型等の抽出装置等が使用できる。このような抽出装置を用いた場合、膜透過液（Ａ）と有機溶媒は、前記抽出装置内部で向流接触する。 For the extraction operation, it is preferable to use an apparatus capable of separating the membrane permeate (A) and the organic solvent into an extract liquid phase (= organic phase) and an extraction residual phase (= aqueous phase). Such an apparatus is not particularly limited, and examples thereof include a known method using an extraction apparatus such as an extraction tower. As the extraction tower, extraction of commonly used types such as mixer setra type extraction tower, perforated plate type, packed tower type, baffle tower type, vibrating perforated plate type, stirring and mixing type, pulsating filling type, centrifugal extraction type and the like. Equipment etc. can be used. When such an extraction device is used, the membrane permeation liquid (A) and the organic solvent come into countercurrent contact inside the extraction device.
　膜透過液（Ａ）と有機溶媒の接触温度は、例えば２０～６０℃、好ましくは３０～５０℃の範囲で行うことが好ましい。接触時間は、例えば０．１～１０時間程度である。 The contact temperature between the membrane permeate (A) and the organic solvent is preferably in the range of, for example, 20 to 60 ° C, preferably 30 to 50 ° C. The contact time is, for example, about 0.1 to 10 hours.
　膜透過液（Ａ）と有機溶媒の接触は、常圧下、加圧下、又は減圧下で行うことができ、ゲージ圧力は、例えば、約－３０～３０ｋＰａ程度である。 The contact between the membrane permeate (A) and the organic solvent can be performed under normal pressure, pressure, or reduced pressure, and the gauge pressure is, for example, about -30 to 30 kPa.
　前記条件下で抽出操作を行うことにより、酢酸の抽出液相への抽出率を高めることができ、水の分離・除去効率を向上することができる。 By performing the extraction operation under the above conditions, the extraction rate of acetic acid into the extract phase can be increased, and the water separation / removal efficiency can be improved.
　本工程で得られる抽出液相は主に酢酸と有機溶媒を含み、水の含有量は例えば１５重量％以下、好ましくは１０重量％以下である。また、酢酸セルロース含有量は２００ｐｐｍ以下（好ましくは１５０ｐｐｍ以下）である。一方、抽出残相は主に水を含み、酢酸の含有量は例えば０．５重量％以下、好ましくは０．１重量％以下である。 The extract phase obtained in this step mainly contains acetic acid and an organic solvent, and the water content is, for example, 15% by weight or less, preferably 10% by weight or less. The cellulose acetate content is 200 ppm or less (preferably 150 ppm or less). On the other hand, the extraction residual phase mainly contains water, and the content of acetic acid is, for example, 0.5% by weight or less, preferably 0.1% by weight or less.
　（工程（3-A）～工程（４）：蒸留工程Ａ）
　工程（3-A）から工程（４）は、工程（2-A）を経て得られた抽出液相を、液相状態で蒸留塔に仕込み、沸点の差異を利用して酢酸と有機溶媒を分離し、有機溶媒を留去して、高純度の酢酸を缶出液として得る工程である。蒸留工程Ａは、後述の蒸留工程Ｂと並行して行うことができる。 (Step (3-A) to Step (4): Distillation Step A)
From step (3-A) to step (4), the extract phase obtained through step (2-A) is charged into a distillation column in a liquid phase state, and acetic acid and an organic solvent are used by utilizing the difference in boiling point. This is a step of separating and distilling off an organic solvent to obtain high-purity acetic acid as a canned liquid. The distillation step A can be performed in parallel with the distillation step B described later.
　前記蒸留塔としては、例えば、棚段塔、充填塔等が挙げられる。塔頂温度は、例えば２０～１２０℃、好ましくは３０～１００℃、より好ましくは４０～８０℃である。また、蒸留塔内の圧力は、例えば０～６０ｋＰａの範囲で適宜調整することができる。蒸留工程は、単一の工程で構成してもよく、複数の工程を組み合わせて構成してもよい。 Examples of the distillation column include a shelf column, a packed column, and the like. The tower top temperature is, for example, 20 to 120 ° C, preferably 30 to 100 ° C, and more preferably 40 to 80 ° C. Further, the pressure in the distillation column can be appropriately adjusted in the range of, for example, 0 to 60 kPa. The distillation step may be composed of a single step or a combination of a plurality of steps.
　前記蒸留塔の実段数は、例えば１～１００段であり、分離効率に優れる点で、好ましくは１０～１００段、特に好ましくは３０～８０段、最も好ましくは４０～６０段である。 The actual number of stages of the distillation column is, for example, 1 to 100 stages, preferably 10 to 100 stages, particularly preferably 30 to 80 stages, and most preferably 40 to 60 stages in terms of excellent separation efficiency.
　そして、本開示に係る発明においては、蒸留塔への仕込みの一部を液相にて行うため、蒸留塔への仕込みの全てを気相にて行う場合に比べて分離効率が向上する。従って、本開示に係る発明においては蒸留塔での還流比を低く設定することができ、還流比は、例えば０．５～１．０の範囲であり、好ましくは０．６～０．９の範囲である。 Further, in the invention according to the present disclosure, since a part of the charging to the distillation column is performed in the liquid phase, the separation efficiency is improved as compared with the case where all the charging to the distillation column is performed in the gas phase. Therefore, in the invention according to the present disclosure, the reflux ratio in the distillation column can be set low, and the reflux ratio is, for example, in the range of 0.5 to 1.0, preferably 0.6 to 0.9. It is a range.
　上記工程を経て、缶出液として高純度の酢酸が得られる。缶出液中の酢酸濃度は、例えば９０重量％以上、好ましくは９８重量％以上、より好ましくは９９．９重量％以上である。また、缶出液中の水の含有量は、例えば０．１重量％以下、好ましくは０．０１重量％以下、より好ましくは０．００１重量％以下、更に好ましくは０．０００１重量％以下である。 Through the above steps, high-purity acetic acid can be obtained as canned liquid. The acetic acid concentration in the canned liquid is, for example, 90% by weight or more, preferably 98% by weight or more, and more preferably 99.9% by weight or more. The content of water in the canned liquid is, for example, 0.1% by weight or less, preferably 0.01% by weight or less, more preferably 0.001% by weight or less, still more preferably 0.0001% by weight or less. be.
　また、留出液中の酢酸濃度は、例えば０．０２重量％以下であり、好ましくは０．０１重量％以下、より好ましくは０．００５重量％以下である。留出液中の酢酸濃度は、還流比を調整することによりコントロールできる。 The acetic acid concentration in the distillate is, for example, 0.02% by weight or less, preferably 0.01% by weight or less, and more preferably 0.005% by weight or less. The acetic acid concentration in the distillate can be controlled by adjusting the reflux ratio.
　（工程（2-1-B）：抽出工程Ｂ）
　工程（2-1-B）は、膜濃縮液（Ｂ）を有機溶媒と接触させて主に酢酸と有機溶媒と可溶性酢酸セルロースを含む抽出液相と、主に水と可溶性酢酸セルロースを含む抽出残相とに分離する工程である。本工程は、膜透過液（Ａ）に代えて膜濃縮液（Ｂ）を使用する以外は上記抽出工程Ａと同様に行うことができる。本開示に係る発明においては、なかでも、上記抽出工程Ａと抽出工程Ｂにおいて同じ有機溶媒を使用することが好ましい。 (Step (2-1-B): Extraction step B)
In the step (2-1-B), the membrane concentrate (B) is brought into contact with an organic solvent to extract an extract phase mainly containing acetic acid, an organic solvent and soluble cellulose acetate, and an extraction mainly containing water and soluble cellulose acetate. This is the process of separating into the residual phase. This step can be performed in the same manner as the above extraction step A except that the membrane concentrate (B) is used instead of the membrane permeate (A). In the invention according to the present disclosure, it is preferable to use the same organic solvent in the extraction step A and the extraction step B.
　本工程で得られる抽出液相は主に酢酸と有機溶媒と可溶性酢酸セルロースを含む。 The extract phase obtained in this step mainly contains acetic acid, an organic solvent and soluble cellulose acetate.
　また、抽出残相は主に水と可溶性酢酸セルロースを含む。 In addition, the extraction residual phase mainly contains water and soluble cellulose acetate.
　（工程（2-2-B）：蒸発工程）
　工程（2-2-B）は、工程（2-1-B）を経て得られた抽出液相を蒸発させて酢酸と有機溶媒とを含む蒸気と可溶性酢酸セルロースを含む蒸発残液に分離する工程である。本工程において、抽出液相中に溶解した酢酸セルロースを分離し、除去することができる。 (Step (2-2-B): Evaporation step)
In the step (2-2-B), the extract phase obtained through the step (2-1-B) is evaporated and separated into a vapor containing acetic acid and an organic solvent and an evaporation residue containing soluble cellulose acetate. It is a process. In this step, cellulose acetate dissolved in the extract phase can be separated and removed.
　本工程では、酢酸と有機溶媒とを含む蒸気と可溶性酢酸セルロースを含む蒸発残液に分離することができれば良く、例えば、前記抽出液相を加熱処理及に付すことにより行うことができる。加熱処理温度は、例えば８０～１００℃である。また、加熱処理は、常圧下、加圧下、又は減圧下で行うことができ、ゲージ圧力は、例えば、約－５０～５０ｋＰａ程度である。単一の工程で構成してもよく、複数の工程を組み合わせて構成してもよい。また、蒸留塔形式の蒸発槽を用いてもよい。 In this step, it suffices if it can be separated into a vapor containing acetic acid and an organic solvent and an evaporation residual liquid containing soluble cellulose acetate. For example, it can be carried out by subjecting the extract phase to heat treatment. The heat treatment temperature is, for example, 80 to 100 ° C. Further, the heat treatment can be performed under normal pressure, pressure, or reduced pressure, and the gauge pressure is, for example, about -50 to 50 kPa. It may be configured by a single process, or may be configured by combining a plurality of processes. Further, a distillation column type evaporation tank may be used.
　本工程で得られる蒸気は主に酢酸と有機溶媒を含み、水の含有量は例えば１５重量％以下、好ましくは１０重量％以下である。また、可溶性酢酸セルロース含有量は５０ｐｐｍ以下（好ましくは２０ｐｐｍ以下）、不溶性酢酸セルロース含有量は２５ｐｐｍ以下（好ましくは１０ｐｐｍ以下）である。 The steam obtained in this step mainly contains acetic acid and an organic solvent, and the content of water is, for example, 15% by weight or less, preferably 10% by weight or less. The soluble cellulose acetate content is 50 ppm or less (preferably 20 ppm or less), and the insoluble cellulose acetate content is 25 ppm or less (preferably 10 ppm or less).
　（工程（3-B）～工程（４）：蒸留工程Ｂ）
　工程（3-B）から工程（４）は、工程（2-2-B）を経て得られた蒸気を蒸留塔に仕込み、沸点の差異を利用して酢酸と有機溶媒を分離し、有機溶媒は留去して、高純度の酢酸を缶出液として得る工程である。本工程は、工程（2-A）を経て得られた抽出液相に代えて工程（2-2-B）を経て得られた蒸気を使用する以外は上記蒸留工程Ａと同様に行うことができる。蒸留工程Ｂは、前述の蒸留工程Ａと並行して行われる。 (Step (3-B) to Step (4): Distillation Step B)
In step (3-B) to step (4), the steam obtained through step (2-2-B) is charged into a distillation column, acetic acid and an organic solvent are separated by utilizing the difference in boiling point, and the organic solvent is used. Is a step of distilling off to obtain high-purity acetic acid as a canned liquid. This step can be performed in the same manner as the above-mentioned distillation step A except that the vapor obtained through the step (2-2-B) is used instead of the extract phase obtained through the step (2-A). can. The distillation step B is performed in parallel with the distillation step A described above.
　本開示に係る発明においては、蒸留塔への仕込みの一部を、上記蒸留工程Ａで記載の通り液相にて行い、その他の仕込みを蒸気（＝気相）にて行うため、蒸留塔への仕込みの全てを蒸気（＝気相）にて行う場合に比べて分離効率が優れる。そのため、還流比を引き下げても従来と同様に優れた純度の酢酸を得ることができ、還流比の引き下げに伴い、エネルギーコストを削減することができる（省蒸気効果）。また、還流比を引き下げる場合は、蒸留塔への仕込み量を増量することができ、それによって酢酸の回収量が増加する効果が得られる（生産効率向上効果）。 In the invention according to the present disclosure, a part of the charging to the distillation column is performed in the liquid phase as described in the above distillation step A, and the other charging is performed in the steam (= vapor phase), so that the distillation column is charged. The separation efficiency is superior to the case where all of the preparation is performed by steam (= vapor phase). Therefore, acetic acid having excellent purity can be obtained even if the reflux ratio is lowered, and the energy cost can be reduced as the reflux ratio is lowered (steam saving effect). Further, when the reflux ratio is lowered, the amount charged into the distillation column can be increased, which has the effect of increasing the amount of acetic acid recovered (effect of improving production efficiency).
　本開示に係る発明においては、蒸留塔への仕込み量の少なくとも一部が液相にて行われておればよいが、液相仕込み量の割合が多ければ多いほど（例えば、液相仕込み割合が蒸留塔への仕込み量全量の１０重量％以上、好ましくは２０重量％以上、特に好ましくは３０重量％以上であることが）、分離効率を向上する効果が得られる点で好ましい。尚、液相仕込み割合の上限は、例えば９０重量％である。例えば蒸留塔への仕込み量全量における液相仕込み量の割合（重量比）が２３重量％である場合、還流比の引き下げに伴いエネルギーコストを１０％程度削減することが可能となる。従って、本開示に係る発明は工業的に酢酸を回収して再利用する方法（特に、酢酸セルロースの製造により排出される残液のリサイクル方法）として極めて有用である。 In the invention according to the present disclosure, it is sufficient that at least a part of the amount charged into the distillation column is carried out in the liquid phase, but the larger the ratio of the liquid phase charged amount (for example, the liquid phase charged ratio). It is preferable that the total amount charged to the distillation column is 10% by weight or more, preferably 20% by weight or more, particularly preferably 30% by weight or more), and the effect of improving the separation efficiency can be obtained. The upper limit of the liquid phase charging ratio is, for example, 90% by weight. For example, when the ratio (weight ratio) of the liquid phase charge to the total amount charged to the distillation column is 23% by weight, the energy cost can be reduced by about 10% as the reflux ratio is lowered. Therefore, the invention according to the present disclosure is extremely useful as a method for industrially recovering and reusing acetic acid (particularly, a method for recycling residual liquid discharged by the production of cellulose acetate).
　以下、本開示の酢酸の回収方法の一例を図１により詳細に説明する。
　図１では、酢酸セルロースが溶解した酢酸水溶液（若しくは、酢酸セルロース製造後の残液）がライン１により膜分離装置Ａに供給され逆浸透膜処理に付される。そして、逆浸透膜を透過した膜透過液（Ａ）は、ライン２より抽出塔B-1の塔頂に導入される。有機溶媒はライン３より抽出塔B-1の塔底に導入され、抽出塔B-1内において膜透過液（Ａ）と向流接触し、主に酢酸と有機溶媒を含む抽出液相と主に水を含む抽出残相に分離される。前記抽出液相はライン４より蒸留塔Ｃに液相で仕込まれる。前記抽出残相はライン１３より系外へ排出される。
　抽出液相を蒸留塔Ｃに仕込むと、前記抽出液相に含まれていた有機溶媒の大部分が塔頂からライン８を経て冷却器Ｄで冷却され、ライン９よりタンクＥに導入される。タンクＥに導入された液のうち上層液は主に有機溶媒を含有し、ライン１０より系外へ排出される。これは再び抽出塔B-1若しくはB-2へ導入する有機溶媒として再利用することができる。タンクＥの下層液は主に水を含有し、ライン１１より系外へ排出される。タンクＥの上層液の一部は液相のまま蒸留塔Ｃにリサイクルしてもよい。図１の例では、タンクＥの上層液の一部を、ライン１２を通じて蒸留塔Ｃにリサイクルしている。一方、蒸留塔Ｃの塔底からは、ライン５を経て高純度の酢酸が缶出液として回収される。 Hereinafter, an example of the acetic acid recovery method of the present disclosure will be described in detail with reference to FIG.
In FIG. 1, an acetic acid aqueous solution in which cellulose acetate is dissolved (or a residual liquid after the production of cellulose acetate) is supplied to the membrane separation device A by line 1 and subjected to reverse osmosis membrane treatment. Then, the membrane permeation liquid (A) that has permeated the reverse osmosis membrane is introduced from line 2 to the top of the extraction tower B-1. The organic solvent is introduced from the line 3 to the bottom of the extraction tower B-1, and is in countercurrent contact with the membrane permeate (A) in the extraction tower B-1, mainly with the extract phase containing acetic acid and the organic solvent. Is separated into an extraction residual phase containing water. The extract phase is charged into the distillation column C from line 4 as a liquid phase. The extracted residual phase is discharged from the line 13 to the outside of the system.
When the extract phase is charged into the distillation column C, most of the organic solvent contained in the extract phase is cooled by the cooler D from the top of the column via the line 8 and introduced into the tank E from the line 9. Of the liquids introduced into the tank E, the upper layer liquid mainly contains an organic solvent and is discharged from the line 10 to the outside of the system. This can be reused as an organic solvent to be introduced into the extraction tower B-1 or B-2 again. The lower layer liquid of the tank E mainly contains water and is discharged from the line 11 to the outside of the system. A part of the upper layer liquid of the tank E may be recycled to the distillation column C as it is in the liquid phase. In the example of FIG. 1, a part of the upper layer liquid of the tank E is recycled to the distillation column C through the line 12. On the other hand, high-purity acetic acid is recovered as canned out liquid from the bottom of the distillation column C via the line 5.
　また、膜分離装置Ａにおいて逆浸透膜を透過しなかった膜濃縮液（Ｂ）はライン１４より抽出塔B-2の塔頂に導入される。有機溶媒はライン１５より抽出塔B-2の塔底に導入され、抽出塔B-2内において膜濃縮液（Ｂ）と向流接触し、主に酢酸と有機溶媒と可溶性酢酸セルロースを含む抽出液相と、主に水と可溶性酢酸セルロースを含む抽出残相に分離される。前記抽出液相はライン１６より蒸発器Ｇに導入される。前記抽出残相はライン１７より系外へ排出される。
　抽出液相は蒸発器Ｇにおいて蒸発させて酢酸と有機溶媒とを含む蒸気と可溶性酢酸セルロースを含む蒸発残液に分離され、酢酸と有機溶媒とを含む蒸気はライン１８より蒸留塔Ｃに気相で仕込まれる。以後のフローは蒸留塔Ｃに液相で仕込まれた抽出液相と同じである。可溶性酢酸セルロースを含む蒸発残液はライン１９より系外へ排出される。 Further, the membrane concentrate (B) that did not permeate the reverse osmosis membrane in the membrane separation device A is introduced from the line 14 to the top of the extraction tower B-2. The organic solvent is introduced from the line 15 to the bottom of the extraction tower B-2, and is in countercurrent contact with the membrane concentrate (B) in the extraction tower B-2, and extracts mainly containing acetic acid, an organic solvent and soluble cellulose acetate. It is separated into a liquid phase and an extraction residual phase mainly containing water and soluble cellulose acetate. The extract phase is introduced into the evaporator G from the line 16. The extracted residual phase is discharged from the line 17 to the outside of the system.
The extract phase is evaporated in the evaporator G and separated into a vapor containing acetic acid and an organic solvent and an evaporation residual liquid containing soluble cellulose acetate, and the vapor containing acetic acid and an organic solvent is vaporized from line 18 into the distillation column C. It is prepared in. The subsequent flow is the same as the extract phase charged in the distillation column C as a liquid phase. The evaporation residue containing soluble cellulose acetate is discharged from the line 19 to the outside of the system.
　［酢酸セルロースの製造方法］
　本開示の酢酸セルロースの製造方法は、セルロースを酢酸水溶液中にてアセチル化して酢酸セルロースを得る酢酸セルロースの製造方法であって、前記アセチル化後の反応液から酢酸セルロースを回収し、その残液から、上述の酢酸の回収方法により酢酸を回収して前記酢酸水溶液の原料として再利用するものである。 [Method for producing cellulose acetate]
The method for producing cellulose acetate of the present disclosure is a method for producing cellulose acetate by acetylating cellulose in an acetic acid aqueous solution to obtain cellulose acetate, in which cellulose acetate is recovered from the reaction solution after acetylation and the residual liquid thereof is recovered. Therefore, acetic acid is recovered by the above-mentioned acetic acid recovery method and reused as a raw material for the acetic acid aqueous solution.
　酢酸セルロースの製造は、例えば下記工程１～３を含む。
工程１：セルロース原料を、離解・解砕し、その後、酢酸又は少量の酸性触媒を含んだ酢酸を散布して、セルロースを活性化する、活性化処理工程
工程２：活性化処理後のセルロースを、酢酸水溶液中にてアセチル化して、酢酸セルロースを得るアセチル化工程
工程３：精製工程 The production of cellulose acetate includes, for example, the following steps 1 to 3.
Step 1: The cellulose raw material is dissociated and crushed, and then acetic acid or acetic acid containing a small amount of an acidic catalyst is sprayed to activate the cellulose. Step 2: Activated cellulose , Acetic acid aqueous solution to obtain cellulose acetate by acetylation Step 3: Purification step
　前記アセチル化後の反応液には、アセチル化により得られた、不溶性酢酸セルロース、可溶性酢酸セルロース、及び酢酸水溶液が含まれる。 The reaction solution after acetylation contains insoluble cellulose acetate, soluble cellulose acetate, and acetic acid aqueous solution obtained by acetylation.
　前記酢酸水溶液には、酢酸と水以外にも他の成分、例えば、アセチル化剤（例えば、無水酢酸）や酸性触媒（例えば、硫酸）を含んでいてもよい。 The acetic acid aqueous solution may contain other components other than acetic acid and water, such as an acetylating agent (for example, acetic anhydride) and an acidic catalyst (for example, sulfuric acid).
　アセチル化工程を経て得られる１次酢酸セルロースは、加水分解することにより所望の酢酸化度の２次酢酸セルロースを得ることができる。 The primary cellulose acetate obtained through the acetylation step can be hydrolyzed to obtain the secondary cellulose acetate having a desired degree of acetic acidation.
　本開示の酢酸セルロースの製造方法では、アセチル化工程後の反応液から、酢酸を回収して再利用するため、酢酸セルロースの製造コストを削減することができる。 In the method for producing cellulose acetate of the present disclosure, acetic acid is recovered from the reaction solution after the acetylation step and reused, so that the production cost of cellulose acetate can be reduced.
　以上、本開示に係る発明の各構成及びそれらの組み合わせ等は一例であって、本開示に係る発明の主旨から逸脱しない範囲において、適宜、構成の付加、省略、置換、及び変更が可能である。また、本開示に係る発明は、実施形態によって限定されることはなく、特許請求の範囲の記載によってのみ限定される。 As described above, each configuration of the invention according to the present disclosure and combinations thereof are examples, and the configurations can be added, omitted, replaced, and changed as appropriate within the range not deviating from the gist of the invention according to the present disclosure. .. Further, the invention according to the present disclosure is not limited to the embodiments, but is limited only by the description of the scope of claims.
　以下、実施例により本開示に係る発明をより具体的に説明するが、本開示に係る発明はこれらの実施例により限定されるものではない。 Hereinafter, the invention according to the present disclosure will be described more specifically by way of examples, but the invention according to the present disclosure is not limited to these examples.
　実施例１
　酢酸セルロースが溶解した３０％酢酸水溶液（酢酸セルロース含有量：１％）を、逆浸透膜（日東電工（株）製ＥＳ１５、２インチ膜モジュール、液の循環量：８Ｌ／ｍｉｎ、材質：ポリアミド）を用いたクロスフロー濾過を行って、膜透過液（ａ）と膜濃縮液（ｂ）とを得た。
　前記膜透過液（ａ）を有機溶剤（酢酸エチル：７５％、ベンゼン：２５％）にて抽出して、抽出液相（ａ）を得た。
　また、前記膜濃縮液（ｂ）を有機溶剤（酢酸エチル：７５％、ベンゼン：２５％）にて抽出して、酢酸セルロースを含む抽出液相（ｂ）を得、得られた抽出液相（ｂ）を蒸発器（留出率：９９％）に付して酢酸セルロースを除去して、ガス（ｂ）を得た。
　抽出液相（ａ）とガス（ｂ）を３：１０の重量比で同時に蒸留塔（オールダーショウ６０段）に仕込んだ。仕込段は、抽出液相（ａ）を上から２４段目、ガス（ｂ）を上から３４段目とし、抽出液相（ａ）の仕込液量を２３３ｇ／ｈ、ガス（ｂ）の仕込液量を７７６ｇ／ｈとした。
　塔頂圧は常圧であり、温度計は塔頂（上から１段目）、上から４段目、８段目、１４段目、１８段目、２４段目、２８段目、３８段目、４４段目、４８段目、５４段目、５８段目、リボイラー液（ＢＴＭ液）に設置し、抽出液相（ａ）／ガス（ｂ）の各温度もそれぞれ計測した。
　還流比（還流量／（上層液量＋下層水量））は０．６で連続運転を行い、缶出液（製品酢酸）を１７２ｇ／ｈを得た。
　この結果より、シミュレーションソフトを用いてフィッティングした結果、段効率（理論段／実段）＝０．３５を得た。 Example 1
A 30% aqueous acetate solution (cellulose acetate content: 1%) in which cellulose acetate is dissolved is applied to a reverse osmosis membrane (ES15, 2-inch membrane module manufactured by Nitto Denko Co., Ltd., liquid circulation volume: 8 L / min, material: polyamide). The membrane permeation liquid (a) and the membrane concentrate (b) were obtained by performing cross-flow filtration using the above.
The membrane permeate (a) was extracted with an organic solvent (ethyl acetate: 75%, benzene: 25%) to obtain an extract phase (a).
Further, the membrane concentrate (b) was extracted with an organic solvent (ethyl acetate: 75%, benzene: 25%) to obtain an extract phase (b) containing cellulose acetate, and the obtained extract phase (b) was obtained. b) was subjected to an evaporator (distillation rate: 99%) to remove cellulose acetate to obtain gas (b).
The extract phase (a) and the gas (b) were simultaneously charged into a distillation column (60 stages of older show) at a weight ratio of 3:10. In the charging stage, the extract phase (a) is the 24th stage from the top, the gas (b) is the 34th stage from the top, the amount of the liquid charged in the extract phase (a) is 233 g / h, and the gas (b) is charged. The liquid volume was 776 g / h.
The tower top pressure is normal pressure, and the thermometer is the tower top (1st step from the top), 4th step, 8th step, 14th step, 18th step, 24th step, 28th step, 38th step from the top. It was placed in the eyes, the 44th stage, the 48th stage, the 54th stage, the 58th stage, and the reboiler liquid (BTM liquid), and the temperatures of the extract phase (a) / gas (b) were also measured.
The continuous operation was performed at a reflux ratio (reflux amount / (upper layer liquid amount + lower layer water amount)) to obtain 172 g / h of canned out liquid (product acetic acid).
From this result, as a result of fitting using simulation software, stage efficiency (theoretical stage / actual stage) = 0.35 was obtained.
　実施例２
　抽出液相（ａ）とガス（ｂ）の蒸留塔への仕込み段、及び還流比を以下の通り変更した以外は実施例１と同様にして、缶出液（製品酢酸）を得た。この結果より、シミュレーションソフトを用いてフィッティングした結果、段効率（理論段／実段）＝０．３５を得た。
仕込段：抽出液相（ａ）を上から１４段目、ガス（ｂ）を上から３４段目
還流比（還流量／（上層液量＋下層水量））：０．６４ Example 2
A canned out liquid (product acetic acid) was obtained in the same manner as in Example 1 except that the stage of charging the extract phase (a) and the gas (b) into the distillation column and the reflux ratio were changed as follows. From this result, as a result of fitting using simulation software, stage efficiency (theoretical stage / actual stage) = 0.35 was obtained.
Preparation stage: Extract phase (a) is in the 14th stage from the top, gas (b) is in the 34th stage from the top.
　実施例３
　抽出液相（ａ）とガス（ｂ）の蒸留塔への仕込み段、及び還流比を以下の通り変更した以外は実施例１と同様にして、缶出液（製品酢酸）を得た。この結果より、シミュレーションソフトを用いてフィッティングした結果、段効率（理論段／実段）＝０．３５を得た。
仕込段：抽出液相（ａ）を上から１４段目、ガス（ｂ）を上から３４段目
還流比（還流量／（上層液量＋下層水量））：０．４２ Example 3
A canned out liquid (product acetic acid) was obtained in the same manner as in Example 1 except that the stage of charging the extract phase (a) and the gas (b) into the distillation column and the reflux ratio were changed as follows. From this result, as a result of fitting using simulation software, stage efficiency (theoretical stage / actual stage) = 0.35 was obtained.
Preparation stage: Extract phase (a) is in the 14th stage from the top, gas (b) is in the 34th stage from the top.
　以上の結果を図２に示す。図２より、蒸留塔への仕込み量全量における液相仕込み量の割合が増加するに従い省蒸気率が向上し、液相仕込み量を０％から２３％に増やすことで約１０％の省蒸気効果が得られることが分かった。 The above results are shown in Fig. 2. From FIG. 2, the steam saving rate improves as the ratio of the liquid phase charging amount to the total amount charged to the distillation column increases, and increasing the liquid phase charging amount from 0% to 23% has a steam saving effect of about 10%. Was found to be obtained.
　以上のまとめとして、本開示の構成及びそのバリエーションを以下に付記する。
［１］　酢酸セルロースが溶解した酢酸水溶液から酢酸を回収する方法であって、
前記酢酸セルロースが溶解した酢酸水溶液を逆浸透膜処理に付して酢酸と水を含む膜透過液（Ａ）と酢酸と水と酢酸セルロースとを含む膜濃縮液（Ｂ）とに分離する工程（１）、
膜透過液（Ａ）を有機溶媒と接触させて主に酢酸と有機溶媒を含む抽出液相と主に水を含む抽出残相とに分離する工程（2-A）、
抽出液相を蒸留塔に仕込む工程（3-A）、
膜濃縮液（Ｂ）を有機溶媒と接触させて主に酢酸と有機溶媒と酢酸セルロースを含む抽出液相と、主に水と酢酸セルロースを含む抽出残相とに分離する工程（2-1-B）、
抽出液相を蒸発させて酢酸と有機溶媒とを含む蒸気と酢酸セルロースを含む蒸発残液に分離する工程（2-2-B）、
前記蒸気を蒸留塔に仕込む工程（3-B）、
蒸留塔から缶出液として酢酸を回収する工程（４）を含む、酢酸の回収方法。
［２］　逆浸透膜処理が、クロスフロー濾過方式による膜処理である、［１］に記載の酢酸の回収方法。
［３］　工程（１）において、膜透過液（Ａ）中の酢酸セルロース含有量が１０００ｐｐｍ以下となるまで逆浸透膜処理を繰り返す、［１］又は［２］に記載の酢酸の回収方法。
［４］　工程（2-A）において使用する有機溶媒が、芳香族炭化水素、脂肪族炭化水素類、エステル、ハロゲン化炭化水素、及びエーテルから選択される少なくとも１種の溶媒である、［１］～［３］の何れか１つに記載の酢酸の回収方法。
［５］　工程（2-A）において使用する有機溶媒が、エステルと芳香族炭化水素との混合溶媒であり、前記エステルと芳香族炭化水素の重量比（前者／後者）が５／９５～９５／５である、［１］～［３］の何れか１つに記載の酢酸の回収方法。
［６］　工程（2-A）における有機溶媒の使用量が膜透過液（Ａ）の使用量の１．０～５．０体積倍である、［１］～［５］の何れか１つに記載の酢酸の回収方法。
［７］　工程（2-1-B）において使用する有機溶媒が、芳香族炭化水素、脂肪族炭化水素類、エステル、ハロゲン化炭化水素、及びエーテルから選択される少なくとも１種の溶媒である、［１］～［６］の何れか１つに記載の酢酸の回収方法。
［８］　工程（2-1-B）において使用する有機溶媒が、エステルと芳香族炭化水素との混合溶媒であり、前記エステルと芳香族炭化水素の重量比（前者／後者）が５／９５～９５／５である、［１］～［６］の何れか１つに記載の酢酸の回収方法。
［９］　工程（2-1-B）における有機溶媒の使用量が膜濃縮液（Ｂ）の使用量の１．０～５．０体積倍である、［１］～［８］の何れか１つに記載の酢酸の回収方法。
［１０］　工程（3-A）において蒸留塔に仕込む抽出液相の重量と、工程（3-B）において蒸留塔に仕込む蒸気の重量の合計に対する、工程（3-A）において蒸留塔に仕込む抽出液相の重量が１０重量％以上である、［１］～［９］の何れか１つに記載の酢酸の回収方法。
［１１］　工程（４）で得られる缶出液中の酢酸濃度が９０重量％以上である、［１］～［１０］の何れか１つに記載の酢酸の回収方法。
［１２］　セルロースを酢酸水溶液中にてアセチル化して酢酸セルロースを得る酢酸セルロースの製造方法であって、前記アセチル化後の反応液から酢酸セルロースを回収し、その残液から、［１］～［１１］の何れか１つに記載の酢酸の回収方法により酢酸を回収して前記酢酸水溶液の原料として再利用する酢酸セルロースの製造方法。 As a summary of the above, the configuration of the present disclosure and its variations are described below.
[1] A method for recovering acetic acid from an acetic acid aqueous solution in which cellulose acetate is dissolved.
A step of subjecting the acetic acid aqueous solution in which cellulose acetate is dissolved to a back-penetration membrane treatment to separate the membrane permeate (A) containing acetic acid and water and the membrane concentrate (B) containing acetic acid, water and cellulose acetate (B). 1),
Step (2-A), in which the membrane permeate (A) is brought into contact with an organic solvent and separated into an extract phase mainly containing acetic acid and an organic solvent and an extraction residual phase mainly containing water (2-A).
Step of charging the extract phase into the distillation column (3-A),
A step of contacting the membrane concentrate (B) with an organic solvent to separate it into an extract phase containing mainly acetic acid, an organic solvent and cellulose acetate, and an extraction residual phase mainly containing water and cellulose acetate (2-1-). B),
Step of evaporating the extract phase to separate it into vapor containing acetic acid and an organic solvent and an evaporation residue containing cellulose acetate (2-2-B),
Step of charging the steam into the distillation column (3-B),
A method for recovering acetic acid, which comprises a step (4) of recovering acetic acid as a canned liquid from a distillation column.
[2] The method for recovering acetic acid according to [1], wherein the reverse osmosis membrane treatment is a membrane treatment by a cross-flow filtration method.
[3] The method for recovering acetic acid according to [1] or [2], wherein the reverse osmosis membrane treatment is repeated until the cellulose acetate content in the membrane permeate (A) becomes 1000 ppm or less in the step (1).
[4] The organic solvent used in step (2-A) is at least one solvent selected from aromatic hydrocarbons, aliphatic hydrocarbons, esters, halogenated hydrocarbons, and ethers, [1]. ] To [3]. The method for recovering acetic acid according to any one of [3].
[5] The organic solvent used in the step (2-A) is a mixed solvent of an ester and an aromatic hydrocarbon, and the weight ratio of the ester to the aromatic hydrocarbon (the former / the latter) is 5/95 to 95. The method for recovering acetic acid according to any one of [1] to [3], which is / 5.
[6] Any one of [1] to [5], wherein the amount of the organic solvent used in the step (2-A) is 1.0 to 5.0 times by volume the amount of the membrane permeate (A) used. The method for recovering acetic acid described in 1.
[7] The organic solvent used in the step (2-1-B) is at least one solvent selected from aromatic hydrocarbons, aliphatic hydrocarbons, esters, halogenated hydrocarbons, and ethers. The method for recovering acetic acid according to any one of [1] to [6].
[8] The organic solvent used in the step (2-1-B) is a mixed solvent of an ester and an aromatic hydrocarbon, and the weight ratio of the ester to the aromatic hydrocarbon (the former / the latter) is 5/95. The method for recovering acetic acid according to any one of [1] to [6], which is ~ 95/5.
[9] Any of [1] to [8], wherein the amount of the organic solvent used in the step (2-1-B) is 1.0 to 5.0 times by volume the amount of the membrane concentrate (B) used. The method for recovering acetic acid according to one.
[10] Charged into the distillation column in step (3-A) with respect to the total weight of the extract phase charged in the distillation column in step (3-A) and the weight of steam charged in the distillation column in step (3-B). The method for recovering acetic acid according to any one of [1] to [9], wherein the weight of the extract phase is 10% by weight or more.
[11] The method for recovering acetic acid according to any one of [1] to [10], wherein the acetic acid concentration in the canned liquid obtained in the step (4) is 90% by weight or more.
[12] A method for producing cellulose acetate by acetylating cellulose in an acetic acid aqueous solution to obtain cellulose acetate. From the reaction solution after acetylation, cellulose acetate is recovered, and from the residual liquid, [1] to [1] to [ 11] A method for producing cellulose acetate, which recovers acetic acid by the method for recovering acetic acid according to any one of the above methods and reuses it as a raw material for the acetic acid aqueous solution.
　本開示の方法によれば、従来の方法に比べて還流比を下げても、従来と同じ純度の酢酸を回収することができる。そのため、還流分の気化に要していた膨大なエネルギーコストを削減することができる。また、還流比を低下させることにより、蒸留塔への仕込み量を従来の方法の場合より上昇させることができるので、増産が可能となる。 According to the method of the present disclosure, acetic acid having the same purity as the conventional method can be recovered even if the reflux ratio is lowered as compared with the conventional method. Therefore, it is possible to reduce the enormous energy cost required for vaporizing the refluxed portion. Further, by lowering the reflux ratio, the amount charged into the distillation column can be increased as compared with the case of the conventional method, so that the production can be increased.
Ａ　　　　膜分離装置
B-1、B-2　抽出塔
Ｃ　　　　蒸留塔
Ｄ　　　　冷却器
Ｅ　　　　タンク
Ｆ　　　　リボイラー
Ｇ　　　　蒸発器 A Membrane separation device
B-1, B-2 Extraction column C Distillation column D Cooler E Tank F Reboiler G Evaporator

Claims (2)

  1. 　酢酸セルロースが溶解した酢酸水溶液から酢酸を回収する方法であって、
    前記酢酸セルロースが溶解した酢酸水溶液を逆浸透膜処理に付して酢酸と水を含む膜透過液（Ａ）と酢酸と水と酢酸セルロースとを含む膜濃縮液（Ｂ）とに分離する工程（１）、
    膜透過液（Ａ）を有機溶媒と接触させて主に酢酸と有機溶媒を含む抽出液相と主に水を含む抽出残相とに分離する工程（2-A）、
    抽出液相を蒸留塔に仕込む工程（3-A）、
    膜濃縮液（Ｂ）を有機溶媒と接触させて主に酢酸と有機溶媒と酢酸セルロースを含む抽出液相と、主に水と酢酸セルロースを含む抽出残相とに分離する工程（2-1-B）、
    抽出液相を蒸発させて酢酸と有機溶媒とを含む蒸気と酢酸セルロースを含む蒸発残液に分離する工程（2-2-B）、
    前記蒸気を蒸留塔に仕込む工程（3-B）、
    蒸留塔から缶出液として酢酸を回収する工程（４）を含む、酢酸の回収方法。     A method of recovering acetic acid from an acetic acid aqueous solution in which cellulose acetate is dissolved.
    A step of subjecting the acetic acid aqueous solution in which cellulose acetate is dissolved to a back-penetration membrane treatment to separate the membrane permeate (A) containing acetic acid and water and the membrane concentrate (B) containing acetic acid, water and cellulose acetate (B). 1),
    Step (2-A), in which the membrane permeate (A) is brought into contact with an organic solvent and separated into an extract phase mainly containing acetic acid and an organic solvent and an extraction residual phase mainly containing water (2-A).
    Step of charging the extract phase into the distillation column (3-A),
    A step of contacting the membrane concentrate (B) with an organic solvent to separate it into an extract phase containing mainly acetic acid, an organic solvent and cellulose acetate, and an extraction residual phase mainly containing water and cellulose acetate (2-1-). B),
    Step of evaporating the extract phase to separate it into vapor containing acetic acid and an organic solvent and an evaporation residue containing cellulose acetate (2-2-B),
    Step of charging the steam into the distillation column (3-B),
    A method for recovering acetic acid, which comprises a step (4) of recovering acetic acid as a canned liquid from a distillation column.
  2. 　セルロースを酢酸水溶液中にてアセチル化して酢酸セルロースを得る酢酸セルロースの製造方法であって、前記アセチル化後の反応液から酢酸セルロースを回収し、その残液から、請求項１に記載の方法により酢酸を回収して前記酢酸水溶液の原料として再利用する酢酸セルロースの製造方法。 A method for producing cellulose acetate by acetylating cellulose in an acetic acid aqueous solution to obtain cellulose acetate, wherein the cellulose acetate is recovered from the reaction solution after the acetylation, and the residual solution is used by the method according to claim 1. A method for producing cellulose acetate, which recovers acetic acid and reuses it as a raw material for the acetic acid aqueous solution.
PCT/JP2021/032798 2020-09-08 2021-09-07 Acetic-acid collection method WO2022054784A1 (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5610131A (en) * 1979-07-06 1981-02-02 Daicel Chem Ind Ltd Recovery of acetic acid
JPS61123601A (en) * 1984-11-19 1986-06-11 Daicel Chem Ind Ltd Separation of cellulose acetate by filtration
JP2014520080A (en) * 2011-05-17 2014-08-21 ソルベイ アセトウ ゲーエムベーハー Acetic acid recovery method
JP2016534167A (en) * 2013-10-10 2016-11-04 ソルベイ アセトウ ゲーエムベーハー Acylation method
JP2017159220A (en) * 2016-03-08 2017-09-14 株式会社ダイセル Separation method of liquid mixture

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5610131A (en) * 1979-07-06 1981-02-02 Daicel Chem Ind Ltd Recovery of acetic acid
JPS61123601A (en) * 1984-11-19 1986-06-11 Daicel Chem Ind Ltd Separation of cellulose acetate by filtration
JP2014520080A (en) * 2011-05-17 2014-08-21 ソルベイ アセトウ ゲーエムベーハー Acetic acid recovery method
JP2016534167A (en) * 2013-10-10 2016-11-04 ソルベイ アセトウ ゲーエムベーハー Acylation method
JP2017159220A (en) * 2016-03-08 2017-09-14 株式会社ダイセル Separation method of liquid mixture

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