JPH07227517A - Separation of liquid mixture - Google Patents

Abstract

PURPOSE:To provide a separation method in which used equipment is compact and which excels in energy efficiency. CONSTITUTION:A liquid mixture as a raw liquid is fed to the top part of a distillation column 1. The overhead mixed vapor generated is introduced into a membrane separator 2 equipped with a gas separation membrane to separate it into a membrane impermeable vapor which is a low boiling point component vapor, and a membrane permeable vapor which is a mixed vapor contg. a high boiling point component in higher concentration. In this method, the membrane permeable vapor is introduced into the intermediate part of the distillation column 1 to circulate the low boiling point component mixed in the membrane permeable vapor as an overhead vapor in the membrane separator 2. The membrane impermeable vapor exchanges heat with the bottom liquid of the distillation column 1 to condense it. The condensate is taken out as the low boiling point component liquid, and on the other hand, the high boiling point component liquid is taken out as a bottom product from the bottom part of the distillation column 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating a liquid mixture by combining distillation technology and membrane separation technology.

[0002]

2. Description of the Related Art As a membrane separation technique, a pervaporation method or a vapor permeation method has attracted attention and various studies have been conducted, but a membrane for completely separating components has not been developed. There is the problem of how to treat a poorly separated membrane permeation mixture. Further, these membrane separation methods require supply of evaporation latent heat for evaporating a feed material or a membrane permeation component, which is also an energy problem. On the other hand, distillation, which is a general-purpose liquid separation technique, has the drawbacks that it is difficult to separate an azeotropic substance, and the amount of energy consumed is large because a reflux operation is performed.

In recent years, a liquid separation technique combining both techniques has been developed as a method for improving the above-mentioned problems of the membrane separation technique and the distillation technique and for developing a separation method utilizing the respective advantages. (JP-A-63-59308,
JP-A-63-258601, JP-A-2-253802
Etc.).

[0004]

However, in the known separation method in which the above-mentioned distillation and membrane separation are combined, the energy saving effect is not yet sufficiently achieved as described below, and this is accompanied by an increase in equipment size and cost. It is a factor of increase. That is, the separation method of Japanese Patent Laid-Open No. 63-59308 is a combination of membrane separation using a pervaporation membrane and distillation for recovering the membrane-impermeable component mixed in the membrane permeation vapor. It is necessary to condense and liquefy when the distillate vapor from is circulated to the membrane separation device. Further, in order to carry out reflux in the distillation column, it is necessary to condense and liquefy the distillate vapor, which is still unsatisfactory in terms of energy saving.

On the other hand, the separation methods of JP-A-63-258601 and JP-A-2-253802 have a combination of membrane separation using a gas separation membrane and distillation.
In the former, it is necessary to evaporate all the raw materials and supply them to the membrane separation device, which consumes a large amount of energy and is uneconomical. In particular, when the raw material is a mixture containing a large amount of high-boiling substance (water) that is a membrane-permeable component such as low-concentration ethanol, the drawback becomes remarkable. The latter is a method performed by the flow shown in FIG. 2, and the distillate vapor from the distillation column is supplied to the membrane separation device as it is. Is condensed and liquefied and circulated at the top of the distillation column, resulting in energy loss.

An object of the present invention is to improve the above-mentioned drawbacks in a method for separating a liquid mixture by combining distillation and membrane separation, use a compact facility, and have a higher energy efficiency. To provide. Other purposes will be clarified together with the following configuration description.

[0007]

In order to achieve the above object, the method for separating a liquid mixture according to the present invention is such that a liquid mixture as a stock solution is supplied to the top of a distillation column, and the top mixed vapor generated here is supplied. Is introduced into a membrane separation device equipped with a gas separation membrane, and is separated into a membrane non-permeation vapor that is a low boiling point component vapor and a membrane permeation vapor that is a mixed vapor with a high content of a high boiling point component. Is introduced into the middle part of the distillation column,
The low boiling point component liquid, which is mixed with the membrane permeated vapor, is circulated to the membrane separation device as a column top vapor, and the membrane non-permeated vapor is condensed by exchanging heat with the column bottom liquid of the distillation column. Meanwhile, the high boiling point component liquid was taken out as a bottom liquid from the bottom of the distillation column. In the above-mentioned structure, it is more preferable that the vapor mixture at the top of the distillation column is introduced into the membrane separation device after being pressurized by the vapor compressor.

[0008]

The above-mentioned method of the present invention can be applied to the separation of various liquid mixtures, and is not limited to the kind, but dehydration from a mixture of water and an organic solvent having a boiling point lower than that of water. Is particularly suitable for. As the organic solvent, for example,
Examples thereof include alcohols such as methanol and ethanol propanol, ketones, esters, ethers and the like.

As the gas separation membrane used in the present invention,
There is no particular limitation as long as it is a membrane that preferentially permeates high-boiling components of the liquid mixture from which the components are to be separated. Examples thereof include a polyvinyl alcohol film, a silicon rubber film, a polyimide film, and a porous ceramics film, and a known gas separation film such as a polysaccharide film such as a chitosan derivative and an alginic acid derivative can be used. The form of the gas separation membrane is not limited to a flat membrane, and may be a hollow fiber membrane or the like. Further, in the membrane separation device incorporating the same, the specific form, the number of stages, and the like can be arbitrarily set according to the components of the liquid mixture, the performance of the separation membrane, the purity of the designed separation component, and the like.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The essential parts of the present invention will be described in more detail below with reference to FIG. 1 showing a schematic flow of an apparatus for carrying out the present invention. The apparatus of FIG. 1 is mainly composed of a distillation column 1 and a membrane separation device 2, and a liquid mixture as a stock solution is supplied to the top of the distillation column 1 through a pipe line 3. Here, the distillation column 1 is a packed column,
A normal one such as a tray tower is used. The membrane separation device 2 is
It is composed of a gas separation membrane module that preferentially permeates high boiling point components of the liquid mixture to be separated.
At this predetermined location, a pipe line 4 for introducing the overhead vapor mixture
A pipe 5 for guiding the non-membrane permeation vapor, which is a low boiling point component vapor, to the outside of the device, and one end of a pipe line 6 for guiding the high boiling point component, which is the membrane preferential permeability component, to the outside of the device are connected.

Further, the vapor mixture at the top of the column has a higher content of low boiling point components than the stock solution,
From the top of the distillation column 1 through the pipe line 4, it is pressurized by a vapor compressor 7 provided in the middle of the pipe line 4 and supplied to the primary side 2a of the membrane separation device 2. In this membrane separation device 2,
The high boiling point component, which is the membrane-preferred permeable component in the supplied mixed vapor, permeates the gas separation membrane together with a small amount of the low boiling point component,
It is separated into a non-membrane permeation vapor which is a low boiling point component vapor and a membrane permeation vapor which is a high boiling point component high content mixed vapor.

The non-membrane permeation vapor is introduced into the reboiler 8 of the distillation column 1 by the line 5. In this reboiler 8, the membrane-impermeable vapor is heat-exchanged with the bottom liquid of the distillation column 1 to heat the bottom liquid. The non-membrane permeation vapor is condensed by this heat exchange and taken out as a low boiling point component liquid. In addition, the secondary side 2 of the gas separation membrane
The membrane-permeated vapor that has permeated through b collects the low-boiling point component mixed with the high-boiling point component, so that the distillation column 1 is connected through the pipe 6.
Is supplied to the middle part of. That is, the low-boiling point component is circulated in the distillation column 1 together with the column top mixed vapor through the vapor compressor 7 to the membrane separation device 2.

In the above-mentioned structure of the present invention, it is necessary to set the pressure on the secondary side 2b of the gas separation membrane to be lower than the pressure on the primary side 2a. Therefore, as shown in FIG. It is preferable to install the machine 7. In this way, by introducing the overhead vapor into the membrane separation device 2 after pressurizing it with the vapor compressor 7, the vapor temperature rises due to this compression, and the membrane separation device 2 can be operated efficiently.
In short, the action of the vapor compressor 7 ensures a partial pressure difference between the membrane permeable components on the primary side 2a and the secondary side 2b of the gas separation membrane, and at the same time, allows the circulation of the membrane permeable vapor to the distillation column 1. To do.

As another structure for obtaining the same operation,
The vapor compressor 7 can be installed in the pipe 6 that guides the membrane permeated vapor to the intermediate portion of the distillation column 1, and may be installed in both the pipe 4 and the pipe 6. When the vapor compressor 7 is installed only in the pipe line 6, in order to use the membrane permeated vapor as a heating source for the distillation column 1, a vapor compressor is additionally installed in the pipe line 5 to allow the membrane permeation. The steam is compressed and heated, and then introduced into the reboiler 8.

From the bottom of the distillation column 1, the high-boiling components from which the low-boiling components have been removed are discharged as bottoms, a part of which is heated and circulated by the reboiler 8 and the rest is taken out of the system by a pipe 9. Is discharged. If the high boiling point component discharged from the pipe 9 is heat-exchanged with the stock solution supplied from the pipe 3, the thermal efficiency can be further improved.

Next, examples of embodiments of the present invention will be given.
The present invention is not limited to this.

Example 1 Based on the flow of FIG. 1, dehydration of an ethanol aqueous solution was performed under the following conditions. 8 heated to 78.5 ° C
8 wt% of 0.0 wt% ethanol aqueous solution by pump 10
It was supplied to the top of the distillation column 1 at a rate of 34 kg / h, and the distilled top vapor was pressurized to 1.9 kg / cm ² · G by the vapor compressor 7 and introduced into the membrane separation device 2. Due to the pressurization of the vapor compressor 7, the temperature of the vapor introduced into the membrane separation device 2 is 14
It rose to 1 ° C. In the membrane separator 2, the membrane-permeated vapor was circulated from the secondary side 2b to the middle part of the distillation column 1 as vapor. Then, the distillation action of the distillation column 1 separates the low-boiling component high-ethanol content vapor circulated in the permeable membrane vapor and the high-boiling component water, and the latter is removed from the bottom of the distillation column 1. It was discharged as a liquid. On the other hand, the non-membrane permeation vapor is heat-exchanged in the reboiler 8 of the distillation column 1 at 107 ° C.
After cooling to 40 ° C. and condensing, the product was further cooled to 40 ° C. by a condenser (not shown) to obtain purified ethanol. The top vapor distilled from the distillation column 1 contains 85.9 wt% of ethanol (8
66 kg / h), and the circulated membrane permeated vapor is 4% ethanol.
The amount of purified ethanol was 1.6 wt% (184 kg / h) and 97.8 wt% (682 kg / h). The amount of utility used was as shown in Table 1.

[0017]

Comparative Example The aqueous ethanol solution was dehydrated on the basis of the flow shown in FIG. 2 (in FIG. 2, an apparatus corresponding to FIG. 1 is shown with the same reference numerals and attached with “′”). The distillation column 1 ′ and the membrane separation device 2 ′ are the same as those in Example 1, and the pump 1 is used to supply the 80.0 wt% ethanol aqueous solution heated to 78.5 ° C.
0'at 834 kg / h at distillation column 1 '(1.9 kg / h
cm ² · G) was supplied to the top of the column, and the top vapor distilled off was introduced into the membrane separator 2 ′. Membrane permeation vapor is the membrane separation device 2 '
Was introduced into the condenser 13 from the secondary side thereof and cooled, and the liquefied mixed solution at 70 ° C. was circulated by the pump 11 to the top of the distillation column 1 ′. The water from which the ethanol was removed was discharged as bottoms from the bottom of the distillation column 1'through the pipe line 9 '. In the distillation column 1 ', pressurized steam was blown into the bottom liquid of the distillation column 1'from the steam supply pipe 14 to heat it. The membrane-impermeable vapor was cooled to 40 ° C. by the condenser 12 to obtain purified ethanol. The overhead vapor distilled from the distillation column 1 ′ was 80.9 wt% (927 kg / h) of ethanol, and the circulated membrane permeated vapor was 33.7 wt% of ethanol (245 k
g / h), the obtained purified ethanol is 97.8 wt%
(682 kg / h). The utility usage was as shown in Table 1.

In this comparative example, the membrane separation apparatus 2'is arranged so that the concentration and amount of purified ethanol are the same as in Example 1.
The gas separation membrane area at was set. This membrane area was 1.13 times that of Example 1.

[0019]

[Table 1]

In Example 1, as shown in Table 1, since the steam compressor is operated, the power cost is higher than that of the comparative example, but the steam for heating is not required except at the time of starting, and the cooling water is not required. Since the load is extremely low, the equipment can be simplified, and the total utility cost is extremely advantageous over the comparative example.

[0021]

As described above, in the method for separating a liquid mixture according to the present invention, the distillation column is composed of only the recovery section,
It does not require a reflux operation and does not condense the vapor distilled from the distillation column, and circulates the membrane separation device and then the membrane-permeated vapor to the middle part of the distillation column. Will be extremely high. Further, since the non-membrane permeation vapor is used as a heat source in the distillation column to condense the non-permeation vapor and heat the bottom liquid of the distillation column, there is almost no heat loss, which is extremely superior industrially.

[Brief description of drawings]

FIG. 1 is a flowchart showing an outline of a main part of an apparatus for carrying out the present invention.

FIG. 2 is a flowchart showing an outline of a main part of an apparatus for carrying out the method of the comparative example.

[Explanation of symbols]

 1 Distillation tower 2 Membrane separation device 7 Vapor compressor 8 Reboiler 10 Pump

Claims (2)

[Claims] 1. A liquid mixture, which is a stock solution, is supplied to the top of a distillation column, and the overhead mixed vapor generated here is introduced into a membrane separation device equipped with a gas separation membrane to obtain a non-membrane component vapor that is a low boiling point component vapor. In the method of separating the permeated vapor and the membrane permeated vapor, which is a mixed vapor having a high content of high boiling point components, the membrane permeated vapor is introduced into the middle part of the distillation column, and the low permeation vapor mixed in the membrane permeated vapor is introduced. The boiling point component is circulated as a top vapor in the membrane separator, and the non-membrane permeation vapor is condensed by heat exchange with the bottom liquid of the distillation column to be taken out as a low boiling point component liquid, while it is extracted from the bottom of the distillation column. A method for separating a liquid mixture, characterized in that a high boiling point component liquid is taken out as a bottom product. 2. The apparatus for separating a liquid mixture according to claim 1, wherein the mixed vapor at the top of the distillation column is pressurized by a vapor compressor and then introduced into the membrane separation apparatus.