JPH0416213A - Separation of lower alcohol - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for industrially separating lower alcohols from an organic mixed vapor containing lower alcohols such as methanol by a membrane separation method using a gas separation membrane. .

In the method of the present invention, for example, lower alcohols such as methanol can be effectively membrane-separated from a mixed vapor of organic substances such as methanol-ester compounds, methanol-ether compounds, methanol-aliphatic or aromatic hydrocarbon compounds, etc. It is possible.

[Description of Prior Art] Conventionally, a distillation method has generally been adopted as a method for separating methanol from an organic solution containing methanol.

However, the conventional distillation method has a problem in that an extremely large amount of thermal energy is required to evaporate the solution and separate it in a distillation column.

In addition, normal distillation methods can produce azeotropic mixtures that cannot be separated or mixtures of organic substances with similar boiling points/8'f! In cases such as i, it is necessary to use an azeotropic distillation method that involves a large number of extremely complicated steps, a special distillation separation method that adds an entrainer for separation or purification, or extraction steaming. there were.

Furthermore, in the case of organic mixtures with close boiling points, there are almost the same problems as in separation using an azeotrope.

Recently, as a separation method for organic mixed solutions, which is different from the conventional distillation separation method, the organic mixed solution is brought into direct contact with the supply side of the separation membrane to selectively permeate and permeate specific organic substances. pervaporation, which separates specific organic substances by vaporizing them on the side (reduced pressure) and condensing the vapor;
Alternatively, a membrane separation method in which organic matter is separated by evaporating an organic matter mixed solution, supplying the vapor to the supply side of a gas separation membrane, and selectively passing a specific organic matter through the permeation side of the gas separation membrane. is proposed.

For example, as a method for separating alcohol aqueous solutions, JP-A-6
0-99314 describes a method of using polyamide membranes, cellulose membranes, and silicone membranes as gas separation membranes, and JP-A-60-202705 describes a method of using ceramic membranes as gas separation membranes. Furthermore, in JP-A No. 63-267415,
A method of using polyimide membranes as gas separation membranes is described.

Furthermore, a document describing the permeability of organic substances regarding polyimide hollow fiber membranes (AIST=AFME, 19
89.5.23. ), suggesting the possibility of membrane separation of organic mixed vapors, but even if the polyimide hollow fiber membrane used in those documents is used, the vapor permeation rate of organic substances is low, making practical separation difficult. It did not become law.

[Problems to be solved]

This invention provides a method for separating lower alcohols from a mixed vapor of organic matter containing lower alcohols such as methanol and ethanol by a gas separation method using a gas separation membrane, in which lower alcohols permeate at a high permeation rate and with high selectivity. An object of the present invention is to provide an industrial gas separation method for efficiently separating lower alcohols using a specific separation membrane.

(Means for Solving the Problems) That is, the present invention solves the problem by improving the degree of separation at 25°C [the permeation rate of helium gas (PHe) and the permeation rate of sulfur hexafluoride gas (
Ratio to PSF, ) (P Hel P SF6 ) )
is 2 to 400, and the permeation rate of methanol at 80°C (PcHioH) is 1. OX 10-'cm/c+f
A gas separation membrane made of a heat-resistant aromatic polymer with a temperature of t -seccmHg or more is used, and an organic mixed vapor containing a lower alcohol having 1 to 2 carbon atoms is supplied to one side (supply side) of the gas separation membrane. , relates to a method for separating lower alcohols, characterized in that the lower alcohols are selectively permeated to the other side (permeation side) of the gas separation membrane through contact at a temperature of 60° C. or higher.

Each requirement of the present invention will be explained in more detail below.

The gas separation membrane used in the separation method of the present invention has a separation degree at 25° C. (ratio of helium gas permeation rate to sulfur hexafluoride gas permeation rate (PHel P SFb )) of 2.
0-400, preferably 2. 0 to about 300, more preferably about 2.2 to 280, and the permeation rate of methanol at 80°C (PCI3OH) is 1, OX 10
”'CTI/c+fl-sec-cmt1g or more, preferably 1.5 X 10-' to 5 X 10-
3cj/ai-sec -cmHg, more preferably 2.0X10-' to 3X10-3cj/aA-se
This is a gas separation membrane made of a heat-resistant aromatic polymer with a temperature of approximately c-cttrHg.

The gas separation membrane described above has a helium gas permeation rate (PHe
) is 0.8 X 10-'ctA/ci-sec
・More than cmHg, especially 1. OX 10-'~25X
10-'ctA/c+fl·sec·cmHg and preferably has the above-mentioned gas separation performance.

The gas separation membrane described above is made of a heat-resistant aromatic polymer such as aromatic polyamide, aromatic polyimide, polyphenylene sulfone, polyphenylene ether, or polyacrylonitrile, and has the above-mentioned specific gas separation performance. A heat-resistant aromatic polymer having an extremely thin dense layer (thickness of about 0.001 to 1.0 μm) formed in a part of the separation membrane in the thickness direction (for example, the surface layer). Any asymmetric gas separation membrane consisting of the following may be used.

In the present invention, an asymmetric gas separation membrane made of aromatic polyimide having the above-mentioned gas separation performance is suitable in terms of heat resistance and solvent resistance.

The above-mentioned aromatic polyimide is preferably an aromatic polyimide soluble in a phenolic solvent obtained by polymerizing and imidizing an aromatic tetracarboxylic acid component and an aromatic diamine component in approximately equimolar amounts.

Examples of the aromatic tetracarboxylic acid component include Eva,
Biphenyltetracarboxylic acid, pyromellitic acid, diphenylethertetracarboxylic acid, diphenylsulfonetetracarboxylic acid, hensiphenonetetracarboxylic acid, diphenylpropanetetracarboxylic acid, diphenylhexafluoropropanetetracarboxylic acid, or their acid dianhydrides , or esterified products of these acids (in a proportion of at least 80 mol %, particularly 90 mol % or more).

Examples of the aromatic diamine component include (a) diaminodiphenyl ethers, diaminodiphenylthioethers, diaminodiphenylsulfones, diaminodiphenylmethanes, diaminodiphenylpropanes,
Aromatic diamine compounds with two Hensen rings, such as diaminodibenzothiophenes, diaminothioxanthines, and diaminobenzophenones; (C) di(aminophenoxy)-diphenylsulfones, di(aminophenoxy)-diphenylmethanes, di(aminophenoxy)-diphenylmethanes,
Aromatic diamine compounds 1 having four r-Hensen rings, such as aminophenoxy)-diphenylpropanes, di(aminophenoxy)-diphenyl ethers, and di(aminophenoxy)-biphenyls (at least 60 mol%, especially 70 It is preferable that the content is mol % or more.

The aromatic diamine components include phenylenediamines such as 0-, t-, or p-phenylenediamine, 4-methyl-I-phenylenecyamine, 3,5-diaminobenzoic acid, and 2,6-diaminobenzoic acid. Aromatic diamine compounds having one Hensen ring of
may be contained in a proportion of mol % or less.

The gas separation membrane made of aromatic polyimide can be produced by, for example, using a solution of aromatic polyimide in a phenolic solvent and forming a thin film (flat film or hollow fiber) of the solution by a solution casting method, an extrusion method, or the like. The thin film is then brought into contact with a specific coagulating liquid at a relatively low temperature to coagulate the thin film to form an asymmetric gas separation membrane in the form of a flat or hollow fiber. can do.

In the separation method of the present invention, a gas separation membrane made of the above-mentioned heat-resistant aromatic polymer is used, and a lower alcohol having 1 to 2 carbon atoms (
Mixed organic matter vapor containing methanol, etc.) at 60℃ or higher,
Preferably 60-200℃1 Particularly preferably 65-16
Lower alcohols such as methanol are separated by contacting them at a temperature of about 0"C and selectively permeating the lower alcohols to the other side (permeation side) of the gas separation membrane.

The separation method of the present invention includes, for example:) Injecting the vapor of an organic mixture containing lower alcohols such as methanol and ethanol into a gas separation membrane module incorporating the above-mentioned flat or hollow gas separation membrane. 11) directly contacting the vapor of the organic mixture with the feed side of the gas separation membrane in a gas separation membrane module; The gas separation membrane is separated from the vapor of the organic mixture by flowing a sweep gas (sweep gas) or by connecting it to a decompression pump (or vacuum pump) installed outside the gas separation membrane module. ii) Finally, the lower alcohol vapor is selectively permeated and separated through the gas separation membrane, and ii) finally, the vapor of the organic mixture with a reduced lower alcohol concentration is transferred from the supply side of the gas separation membrane to the outside of the gas component MIA module. Similarly, from the permeation side of the gas separation membrane, the "vapor with improved lower alcohol concentration" that has permeated the gas separation membrane is transferred to the outside of the gas separation membrane module. )" and, if necessary, the retentate and permeate vapors are cooled, condensed, and recovered.

In this invention, the organic mixed vapor containing lower alcohol supplied to the gas separation membrane module is a mixture of lower alcohol and an organic compound that is in a liquid state at normal pressure (atmospheric pressure) and 50°C (including an organic mixed solution). ) steam is sufficient.

In this invention, the organic substance mixed vapor is methanol,
The composition ratio of the lower alcohol such as ethanol and the organic compound is not particularly limited, and may be any composition ratio (lower alcohol content).

Examples of the organic compounds include (a) aliphatic hydrocarbons such as n-pentane, n-hexane, n-hebutane, n-octane, and isooctane; (2) dichloroethane, trichloroethane, tetrachloroethane, dichloroethane, and chloroform; Halogenated aliphatic hydrocarbons such as carbon tetrachloride, methylene chloride, and ethyl bromide; (C) Alicyclic hydrocarbons such as cyclopentane, cyclohexane, and methylcyclohexane; (d) Aromatics such as Hensen, toluene, and xylene. (e) Halogenated aromatic hydrocarbons such as fluorohenzene, (f) Nitriles such as acetonitrile, acrylonitrile, (chains methyl-tert-butyl ether, tetrahydrofuran, methylpropyl ether, ethylpropyl ether, butyl) Ethers such as ethyl ether and butyl vinyl ether, (5) esters such as formate, methyl acetate, ethyl acetate, vinyl acetate, isobutyl formate, isopropyl acetate, methyl propionate, and (i) acetone, methyl ethyl ketone, bukunon, Examples include ketones such as cyclohexanone, (j) carbon disulfide, etc.

In this invention, as the organic substance mixed vapor, methanol and
Particularly preferred are organic mixed vapors with ethers, esters, aliphatic hydrocarbons, or aromatic hydrocarbons, and the use of mixtures of lower alcohols and the above-mentioned plurality of organic compounds. It is also possible to use a vapor of an azeotropic mixture of a lower alcohol and the organic compound.

In this invention, the organic mixed vapor supplied to the gas separation membrane has a supply temperature of 60'C or more, particularly 60 to 200C.
The supply pressure is preferably about atmospheric pressure to 50 kg/cd, particularly about atmospheric pressure to 30 kg/cd, particularly about atmospheric pressure to 20 kg/ctll.

In the separation method of this invention, when the organic mixed vapor is supplied to the gas separation membrane module for separation, the pressure on the permeation side of the gas separation membrane must be lower to some extent than the pressure on the supply side of the gas separation membrane. However, especially 500 torr (torr)
) or less, more preferably 200 torr or less, which is a reduced pressure state.

The structure and type of the gas separation membrane module are not particularly limited, but suitable examples include a plate mantle frame type module, a spiral type module, and a hollow fiber type module.

[Examples] Hereinafter, examples relating to the separation method of the present invention will be shown to explain the present invention in more detail.

The abbreviations for "each compound" used in the aromatic tetracarboxylic acid component and the aromatic diamine component used in the production of the aromatic polyimides of Reference Examples 1 to 7 are shown below.

[Tetracarboxylic acid component] 5-BPDA; 3,3', 4,4'-biphenyltetracarboxylic anhydride a-BPDA; 2,3,3°, 4'-biphenyltetracarboxylic dianhydride DSDA, 3.3',4.4"-Diphenylsulfonetetracarboxylic dianhydride 6FD8; 2,2-bis(3,4-dicarboxyphenylhexafluoropropane dianhydride [aromatic diamine component] TSN; 2 , s-dimethyl-3,7-diamitudiphenylene sulfone, 2,6-dimethyl-3,7-diamitudiphenylene sulfone, 4,6-dimethyl 3,7-diamitudiphenylene sulfone isomers mixture DADE; 4,4'-diaminodiphenyl ether DADM; 4,4'-diaminodiphenylmethane DAB; 3,5-diaminobenzoic acid TPEQ i L4-bis(4-aminophenoxy)henzene AD8; 4-aminophenyl)anthraceneHFIP; 2,2-bis(4-aminophenyl)
Hexafluoropropane HFMIP; 2,2-bis(3-amino-4-methylphenyl)hexafluoropropane Reference Examples 1 to 7 [Manufacture of gas separation hollow fiber membrane made of polyimide] Charge ratio (composition) shown in Table 1 , mol%) and an aromatic diamine component (diamine component).
A polyimide solution was produced by polymerization and imidization using approximately equimolar amounts of 1 and 2 in an organic polar solvent of parachlorophenol at a polymerization temperature of 180° C. for the polymerization time shown in Table 1.

Table 1 shows the polymer concentration and solution viscosity (rotational viscosity at 100° C.; voids) of each polyimide solution produced as described above.

Using the polyimide solution obtained as described above,
After performing a semi-dry wet film forming method in which hollow fibers are formed by extruding hollow fibers into a coagulation solution (alcohol aqueous solution, O''C) and drawing the hollow fibers at a take-up speed of 10 m/min, alcohol and Washed with aliphatic hydrocarbon, dried and treated at the heat treatment temperature shown in Table 1 for 60 minutes to obtain
Asymmetric hollow fiber separation membranes made of aromatic polyimide having the shapes shown in the table (inner diameter of hollow fibers and membrane thickness) were manufactured.

[Manufacture of gas separation membrane module] Length 7. manufactured as described above. Four 5 cm hollow fiber separation membranes are bundled together to form a fiber bundle, one end of the fiber bundle is sealed with epoxy resin to create a hollow bundle element, and an organic substance mixed vapor is supplied. Gas separation membrane modules were manufactured by placing the hollow bundle element inside a container having a port, an outlet for unpermeated matter, and an outlet for permeated matter.

Reference Example 8 [Manufacture of gas separation hollow fiber membrane made of polysulfone] Using a polysulfone solution in which 12 parts by weight of polysulfone (P-3500, manufactured by Sumima Kagaku Kogyo ■) was dissolved in 88 parts by weight of N,N-dimethylacetamide. , from the hollow fiber spinning nozzle [orifice-in-tube, using pure water (25°C) as the core liquid] into the coagulation liquid (pure water, 0°C) through the atmosphere (approx. IC11 interval). A semi-dry wet membrane forming method was performed in which hollow fibers were formed by extruding the hollow fibers and taking them off at a take-up speed of 10 m/min, followed by washing with pure water.

After drying the wet hollow fiber membrane obtained as described above at 25°C, it was heat-treated at 130°C for 1 hour to obtain an outer diameter of 600 μm.
A hollow fiber membrane made of polysulfone and having an inner diameter of 300 μm was manufactured.

[Manufacture of gas separation membrane modules]

A gas separation membrane module was manufactured in the same manner as in Reference Example 1, except that four hollow fiber separation liquids having a length of 7.5 am manufactured as described above were bundled to form a fiber bundle.

Reference Example 9 [Production method of polyamide gas separation membrane (flat membrane)] A polyamide solution in which 18 parts by weight of polyamide having the repeating unit and 5 parts by weight of lithium chloride were dissolved in 100 parts by weight of N,N-dimethylacetamide. was prepared.

The above polyamide solution was cast onto a glass plate, a liquid thin film with a uniform thickness of 0.2 nm was formed using a doctor knife, and the film was immersed in a coagulation solution (pure water, 5°C). , a wet polyamide membrane was produced.

After drying the wet polyamide membrane at 25°C,
A flat gas separation membrane made of polyamide F was produced by heat treatment at 50° C. for 1 hour.

A flat gas separation membrane made of polyamide produced as described above is installed inside a container having an inlet for an organic mixed vapor, an outlet for unpermeated matter, and an outlet for permeated matter. A separation membrane module was manufactured.

[Measurement test of vapor permeation performance of gas separation membrane] Reference examples 1 to 9
For the gas separation membrane obtained in , the helium gas permeation rate (PHe), hexafluorine sulfur permeation rate (PSF&), and nitrogen gas permeation rate (PN
z) was measured at a measurement temperature of 25° C. and a feed pressure of 0.5 to 3 kg1 cdG.

For each gas separation membrane, the helium permeation rate (
PHe) and permselectivity (separation degree) (P He/
P SF and P He/P Nz ) are shown in Table 2.

Table 2 8 Polysulfone 22.0 2.39 Polyamide 3.4 5.5 Examples 1 to 9 and Comparative Example 1 A mixed solution of methanol and methyl tert-butyl ether was vaporized in an evaporator under atmospheric pressure. A "mixed vapor of methanol vapor and methyl tert-butyl ether vapor" having the composition shown in Table 3 was produced, and the mixed vapor was heated to the temperature shown in Table 3 by heating with a heater. The supply side (outside of the hollow fiber membrane) of the hollow fiber membrane (made of polyimide or polysulfone) that is supplied to each gas separation membrane module manufactured in Examples 1 to 9 and constitutes the fiber bundle element built into the module. ), and the permeate side of the hollow fiber membrane (inner side of the hollow fiber membrane) was maintained at a reduced pressure of 3 m+Hg to separate the mixed vapor into gases.

In gas separation as described above, "permeated vapor with a high concentration of methanol vapor" obtained from the permeated material outlet of the gas separation container is condensed in a dry ice ethanol trap to collect the condensate, while , the unpermeated side of the hollow fiber membrane (
The unpermeated vapor obtained from the feed side) was returned to the evaporator and used for circulation, while gas separation of the mixed vapor was performed.

The weight of the condensate collected in the trap described above was measured, an internal standard solution was added to the condensate, and the permeation rate of methanol vapor (P
CIIOH), and separation coefficient [methanol vapor permeation rate (PCH,O)I)/methyl-tert-
The permeation rate of butyl ether vapor (PMTBE) was calculated and the results are shown in Table 3.

Table 3 [Mixed vapor of methanol and methyl tert-butyl ether (WrBE)]
Example 1 Example 2 Example 3 Example 4 Reference Example 1 (11 Reference Example 2 Reference Example 3 Reference Example 4 22.2 22.6 19.2 19.8 92.70 97.20 98.00 99.95 Example 7 Comparative Example 1 Example 8 Example 9 Reference Example 7 Reference Example 1 (3) Reference Example 8 Reference Example 9 ■9.8 19.8 22.6 23.0 99.95 99.95 8 +, 40 89.29 5.5 0.57 2.2 12.6 Examples 10 to 11 Using the gas separation membrane module manufactured in Reference Example 1 (1), r methanol and acetic acid at the temperature and concentration shown in Table 4 were used. A test was conducted to measure the vapor permeation performance of the mixed vapor in the same manner as in Example 1, except that "mixed vapor with vinyl" was used, and the results are shown in Table 4.

Example 12 and Comparative Example 3 Using the gas separation membrane module manufactured in Reference Example 1 (1) or Reference Example 1 (3), a mixed vapor of methanol and toluene was produced at the temperature and concentration shown in Table 5. A test was conducted to measure the vapor permeation performance of the mixed vapor in the same manner as in Example 1, except that the following was used, and the results are shown in Table 5.

Example 13 Using the gas separation membrane module manufactured in Reference Example 7,
A test was conducted to measure the vapor permeation performance of the mixed vapor in the same manner as in Example 1, except that mixed vapor J of methanol and n-hexane was used at the temperature and concentration shown in Table 6. It is shown in Table 5.

Example n Reference example 2 115 35.0 Comparative example 2 Reference example H3+ 115 35.2 Comparative example 3 Reference example 1 (3) 66.4 91.5 86.0 98.0 0.68 0.025 20.1 11.3 24.2 [Operations and Effects of the Present Invention] The lower alcohol separation method of the present invention uses a gas separation membrane (normal hydrogen, helium, nitrogen, oxygen, - Mixed vapors of lower alcohols such as ethanol and organic compounds are produced using a porous membrane (which has virtually no separation performance for mixed gases of low atomic weight such as carbon oxide and carbon dioxide). From 1, lower alcohols can be selectively permeated and separated, and it is also possible to separate lower alcohols from r-lower alcohol and azeotropic mixed vapor 1, etc., which was previously thought to be extremely difficult by distillation. It can be done easily.

Patent applicant: Ube Industries Co., Ltd.

Claims (1)

[Claims] Degree of separation at 25°C (ratio of helium gas permeation rate (PHe) to sulfur hexafluoride gas permeation rate (PSF_6) (P
He/PSF_6)] is 2 to 400, and the permeation rate of methanol at 80°C (PCH_3OH) is 1.0×1.
A gas separation membrane made of a heat-resistant aromatic polymer with a resistance of 0^-^4cm^3/cm^2・sec・cmHg or more is used, and one side of the gas separation membrane has a carbon number of 1 to 2. A method for separating lower alcohols, which comprises contacting an organic mixed vapor containing lower alcohols at a temperature of 60° C. or higher to selectively permeate the lower alcohols to the other side of the gas separation membrane.