WO2009123223A1

WO2009123223A1 - Purification treatment method for fermented alcohol

Info

Publication number: WO2009123223A1
Application number: PCT/JP2009/056727
Authority: WO
Inventors: 政夫菊地; 俊介中西
Original assignee: 宇部興産株式会社
Priority date: 2008-03-31
Filing date: 2009-03-31
Publication date: 2009-10-08
Also published as: JP2009263356A

Abstract

Disclosed is a purification treatment method for producing an absolute alcohol from an aqueous fermented alcohol solution. The method is characterized by reducing the pressure of a mixed steam containing an alcohol and water distilled in a distillation column and supplying the mixed steam to a membrane separation unit. The method can achieve a purification treatment through a more convenient process as a whole and with extremely high energy efficiency.

Description

Method for purifying fermentation alcohol

The present invention relates to a fermentation alcohol purification process, particularly a fermentation alcohol purification process that combines a mash tower, a distillation tower (and an evaporator), and a membrane separation device. The present invention relates to a method for purifying alcohol.

As a method for purifying the fermentation alcohol solution taken out from the fermentation tank, conventionally, the alcohol-water mixture solution is separated and concentrated from the fermentation alcohol solution (moromi) by the moromi tower, and then the alcohol-water mixture solution by the concentration tower (distillation tower). Was concentrated to near the azeotropic composition, and then a high-purity anhydrous alcohol was obtained by an azeotropic distillation column.

Patent Document 1 describes a method in which an azeotropic mixture is distilled in a distillation tower, vapor of the azeotropic mixture is supplied to a membrane separation device, and separated by a separation membrane.

In Patent Document 2, a membrane separation device is used instead of an azeotropic distillation column, and an alcohol-water mixture concentrated to near the azeotropic composition in the distillation column is evaporated by an evaporator and introduced into the membrane separation device for purification. A method of processing is disclosed. Further, it is described that the mixed vapor supplied to the membrane separation apparatus is superheated.

Patent Document 3 also discloses the same system as Patent Document 2. In this document, in the same system, when a distillation column fraction is introduced into an evaporator and heated, a mixed vapor of alcohol and water having a pressure higher than the operation pressure of the distillation column is generated, and this high pressure vapor is converted into a membrane separator. It is described that the membrane separation apparatus can be operated with high efficiency.

JP 2003-93827 A Japanese Unexamined Patent Publication No. 63-258602 WO2004 / 073841

If a membrane separator is used instead of the azeotropic distillation tower, the equipment can be simplified and the energy efficiency can be improved. However, in the method for purifying fermentation alcohol by combining the moromi tower, distillation tower (and evaporator) and membrane separator, the fermentation alcohol is simpler and more energy efficient as a whole process. Sufficient studies have not been conducted on whether or not the product can be purified.

That is, the object of the present invention is (Step 1) supplying a fermentation alcohol aqueous solution to a mash tower, heating the fermentation alcohol aqueous solution in the mash tower to distill a distillate containing a mixed vapor of alcohol and water, A distillate or a first condensate obtained by condensing the distillate is supplied to a distillation column. (Step 2) a) The distillate or the first condensate is heated by a distillation column to produce alcohol, water, Or b) a second condensate in which the distillate or the first condensate is heated by a distillation column to distill a mixed vapor of alcohol and water, and the mixed vapor is condensed. The liquid is supplied to the evaporator, the second condensate in the evaporator is heated to generate a mixed steam of alcohol and water, and (step 3) the mixed steam distilled from the distillation column in a) or The mixed vapor generated from the evaporator in b) is converted into a film. (Step 4) In the purification method for obtaining anhydrous alcohol that selectively removes water vapor from the mixed vapor of alcohol and water in the membrane separator, the process is simpler and extremely energy efficient as a whole process. It is to provide a well-purified process.

The present invention relates to the following matters.
1. (Step 1) A fermentation alcohol aqueous solution is supplied to the mash tower, the fermentation alcohol aqueous solution in the mash tower is heated to distill a distillate containing a mixed vapor of alcohol and water, and this distillate or this distillate. Supplying a first condensate condensed with a product to a distillation column;
(Step 2) a) a step of heating the distillate or the first condensate by a distillation column to distill a mixed vapor of alcohol and water, or b) the distillate or the first by a distillation column. The condensate is heated to distill the mixed vapor of alcohol and water, the second condensate condensed with the mixed vapor is supplied to the evaporator, and the second condensate in the evaporator is heated. Generating a mixed steam of alcohol and water;
(Step 3) a step of supplying the mixed vapor distilled from the distillation column in the a) or the mixed vapor generated from the evaporator in the b) to the membrane separator after reducing the pressure;
(Step 4) A purification method for obtaining anhydrous alcohol from a fermented alcohol aqueous solution, comprising a step of selectively removing water vapor from a mixed steam of alcohol and water by a membrane separator.
2. Item 2. The method according to Item 1, wherein the pressure of the mixed steam distilled from the distillation column in Step 2a) or the mixed steam generated from the evaporator in Step 2b) is 150 kPa (absolute pressure) or more.
3. Item 3. The method according to Item 1 or 2, wherein in Step 3, the pressure is reduced so that the condensation temperature of the mixed vapor of alcohol and water is lower than the temperature of the mixed vapor.
4). Item 4. The method according to any one of Items 1 to 3, wherein in step 3, the pressure is reduced by 5 kPa or more.
5). Item 5. The method according to any one of Items 1 to 4, wherein the alcohol concentration of the distillate or the first condensate supplied from the mash column to the distillation column in Step 1 is less than 50% by mass.
6). Item 6. The method according to any one of Items 1 to 5, wherein the alcohol concentration of the mixed vapor of alcohol and water supplied to the membrane separator in Step 4 is 55 to 90% by mass.

According to the present invention, (1) a fermentation alcohol aqueous solution is supplied to a mash tower, the fermentation alcohol aqueous solution in the mash tower is heated to distill a distillate containing a mixed vapor of alcohol and water. The first condensate obtained by condensing the distillate is supplied to the distillation column, and (2) a) the distillate or the first condensate is heated by the distillation column to distill the mixed vapor of alcohol and water. Or b) heating the distillate or the first condensate with a distillation column to distill the mixed vapor of alcohol and water, and supplying the second condensate condensed with the mixed vapor to the evaporator Then, the second condensate in the evaporator is heated to generate a mixed vapor of alcohol and water. (3) The mixed vapor distilled from the distillation column in a) or the evaporator in b) The generated mixed vapor is supplied to the membrane separator, and (4 In a purification process for obtaining anhydrous alcohol from an aqueous fermentation alcohol solution that selectively removes water vapor from the mixed steam of alcohol and water by a membrane separator, a simpler and extremely energy efficient purification process as a whole process. Can be provided.

It is the schematic (block diagram) of an example of the embodiment which concerns on the refinement | purification processing method for obtaining anhydrous alcohol from the fermentation alcohol aqueous solution of this invention. It is the schematic (block diagram) of another example of the embodiment which concerns on the refinement | purification processing method for obtaining anhydrous alcohol from the fermentation alcohol aqueous solution of this invention. It is the schematic (block diagram) of another example of the embodiment which concerns on the refinement | purification processing method for obtaining anhydrous alcohol from the fermentation alcohol aqueous solution of this invention.

In the drawing, the solid line indicates the flow of liquid or gas (vapor), and the broken line indicates the connection of the control system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Moromi tower 11 Condenser 12 Condensate tank 20 Distillation tower 21 Reboiler 22 Condenser 23 Condensate tank 24 Decompression means 30 Evaporator 40 Membrane separator 41 Heat exchanger (condenser)
42 Vacuum pump 43 Condensate tank FIC: Flow controller LIC: Liquid level controller TIC: Temperature controller PIC: Pressure controller

Description will be made based on FIG. 1 showing an outline of an example of an embodiment according to the present invention.

In the present invention, anhydrous alcohol has a purity of 99.0% by mass or more, preferably 99.5% by mass or more, more preferably 99.7% by mass or more, and particularly preferably 99.8% by mass or more. Means alcohol.

In the present invention, the alcohol includes lower alkyl alcohols such as methyl alcohol, propyl alcohol, and butyl alcohol, and is preferably ethanol.

In the present invention, the fermented alcohol aqueous solution is not limited. For example, it is a fermented alcohol aqueous solution obtained by fermenting raw materials such as saccharides, starches, and celluloses. These materials are fermented in a fermenter to form a fermented alcohol aqueous solution. The alcohol concentration of the aqueous fermentation alcohol solution is usually about 5 to 12% by mass. In addition to the main components water and alcohol, this fermented alcohol aqueous solution includes alcohols such as yeast, fungus, methanol, fatty acids such as formic acid, acetic acid, succinic acid, lactic acid, butyric acid, aldehydes such as acetaldehyde, formaldehyde, Esters such as ethyl acetate and butyl acetate, acetals such as diethyl acetal, ketones such as acetone and methyl ethyl ketone, amines such as pyridine, picoline, 3-methylamine and 4-methylpyridine, and higher alcohols and fatty acid esters It contains various by-produced compounds such as so-called fusel oil which is a mixture. Moreover, normally, unfermented raw material components and the like remain as insoluble components to form a slurry.

This aqueous fermented alcohol solution is directly supplied from the fermenter or temporarily stored in a tank and then indirectly supplied to the mash tower 10. It is preferable that a large insoluble component is removed from the fermentation alcohol aqueous solution by rough filtration before being supplied to the mash tower. In addition, the fermented alcohol aqueous solution after fermenting in the fermenter may have a pH of about 3 to 5 depending on by-product fatty acids. For this reason, it is preferable to neutralize the acid component contained in the fermentation alcohol aqueous solution by adding an alkali component or the like. By performing this neutralization treatment, it is possible to reliably prevent the acid from being mixed into the purified anhydrous alcohol. Suitable examples of the alkali component to be added include water-soluble alkali compounds such as sodium hydroxide, potassium hydroxide, and potassium permanganate.

In the moromi tower 10, the aqueous fermentation alcohol solution is heated to distill a distillate containing a mixture of alcohol and water, and a condensate obtained by condensing the distillate is supplied to the distillation tower 20. The distillate containing a mixture of alcohol and water is preferably a mixed vapor of alcohol and water (in a gaseous state), but a mixture containing droplets of a fermented alcohol aqueous solution in a mixed vapor of alcohol and water ( It may be a gas-liquid mixed state).
In the present invention, the main role of the moromi tower 10 is to suppress the discharge (loss) of alcohol outside the system as much as possible from the aqueous solution of fermentation alcohol, insoluble components such as unfermented raw material components, and high-boiling components such as fusel oil. Is preferably separated and removed together with low-boiling by-product components and water. As long as this object can be achieved, the moromi tower is not particularly limited, and a conventionally known type can be suitably used. Simple distillation or continuous distillation may be used. The number of distillation stages is preferably about several stages. For example, a tray-type tray such as a mountain-cap tray or a baffle tray with little scale adhesion can be suitably used. Furthermore, it may be a single distillation type such as flash distillation or a combination of a plurality of them. The operating pressure of the moromi tower is preferably reduced pressure or atmospheric pressure.

As shown in FIG. 1, the raw fermentation alcohol aqueous solution is introduced into the tower from a feed port relatively close to the top of the moromi tower 10. On the other hand, steam (steam) is blown from the inlet near the tower bottom. This water vapor rises in the tower while exchanging heat and materials with the liquid flowing down the tower. For this reason, the steam component at the bottom of the tower is almost water, and the alcohol concentration in the steam increases near the top of the tower. As a result, water containing almost no alcohol is discharged from the bottom of the tower together with insoluble components as a bottom liquid. It is also possible to use a method in which a part of the column bottom liquid discharged from the column bottom is vaporized by a reboiler and introduced into the column instead of or in combination with the introduction of water vapor from the column bottom.

The distillate containing a mixture of alcohol and water taken from the top of the moromi tower 10 or the concentration stage is sent to the condenser 11 and condensed. A part of this condensate is refluxed to the mash column, and the remaining condensate is supplied to the distillation column 20. The alcohol concentration of the alcohol aqueous solution of the condensate supplied from the mash tower 10 to the distillation tower 20 can be controlled by changing the ratio of the condensate refluxed to the mash tower 10 and the number of stages of the distillation tower 20. Although not the embodiment described in FIG. 1, the distillate containing a mixed vapor of alcohol and water taken out from the top of the mash tower 10 or the concentration stage is not condensed and is in a gaseous state or a gas-liquid mixture. It can also be supplied to the distillation column 20 in a state. In this embodiment, although not limited, a part of the distillate containing a mixed vapor of alcohol and water was supplied to the distillation column 20 and the remaining distillate was condensed by a condenser. The entire amount of the condensate can be refluxed to the mash tower. At that time, the alcohol concentration of the distillate supplied from the mash column 10 to the distillation column 20 can be controlled by the ratio of the distillate supplied to the condenser.

In addition, when the mixed vapor of alcohol and water contains many low boiling components such as aldehyde compounds that adversely affect the separation membrane of the membrane separation device 40, the top of the mash column 10 is used to protect the separation membrane. The steam mixed with alcohol and water extracted from the water is partially condensed (some low-boiling components remain as steam, and the other steam-water mixture is condensed), and low-boiling components such as aldehydes are mixed with alcohol. It is preferable to separate from the mixed vapor with water and remove it out of the system.

In the present invention, the alcohol concentration of the alcohol aqueous solution of the condensate supplied from the mash tower 10 to the distillation tower 20 is (of course fermented alcohol aqueous solution) in order to improve the energy efficiency in the entire process from the mash tower to the membrane separator. The concentration is less than 50% by mass, preferably 12% by mass or more and less than 50% by mass, more preferably 20% by mass or more and less than 50% by mass, and further preferably 30% by mass or more and less than 50% by mass. Be controlled. By concentrating the alcohol to some extent in the mash tower, the energy consumption required for heating and vaporizing in the distillation tower 20 can be suppressed. However, at 50% by mass or more, the above-mentioned role of the mash tower (insoluble components such as unfermented raw material components and high-boiling components such as fusel oil are preferably added to the low-boiling side while suppressing the discharge of alcohol as much as possible. In addition to being separated and removed together with biological components and water, the role of concentrating the alcohol is excessively added, so that it is necessary to further increase the concentration stage above the supply port of the fermentation alcohol aqueous solution of the mash tower 10 Therefore, the size and complexity of the device cannot be avoided. When an aqueous solution of fermentation alcohol containing insoluble components (not completely removed by rough filtration) or high boiling components is supplied to such a large and complicated mash tower, the insoluble components and high boiling components are accompanied by steam. Then, since it is brought into the concentration stage, problems such as accumulation as a scale are likely to occur, and it becomes extremely difficult to operate the mash tower stably and energy-efficiently.

The alcohol concentration of the distillate supplied to the distillation column 20 or the condensate of this distillate is less than 50% by mass, preferably 12% by mass or more and less than 50% by mass, more preferably 20% by mass or more and less than 50% by mass, Preferably, 30% by mass or more and less than 50% by mass can be easily achieved by a simple apparatus having about several distillation stages or less, and a part of the mixed steam of alcohol and water distilled from the distillation column. This is because, even when the water is condensed or refluxed to the mash tower, the rate of reflux can be made extremely low, so that rapid processing becomes possible and energy consumption can be suppressed.

When the mixed steam of alcohol and water is condensed and refluxed to the mash tower, if the reflux rate increases, the amount of mash processed per unit operation decreases, and conversely, the energy consumption per unit alcohol decreases. This increases the energy efficiency of the entire process.

The ratio of the condensate refluxed in the moromi tower is preferably 20% or less, more preferably 10% or less.

The role of the distillation column 20 is that the distillate from the mash column is 150 kPa (absolute pressure) or more, preferably 150 to 700 kPa (absolute pressure), more preferably 200 to 600 kPa (absolute pressure), and even more preferably 200 to 500 kPa. Distilling at an operating pressure of (absolute pressure) is to concentrate the alcohol concentration to 55% by mass or more, preferably 60% by mass or more, more preferably 65% by mass or more. Although it may concentrate to near azeotropic composition here, it is preferred to concentrate to 90 mass% or less, more preferably 80 mass% or less.

If the alcohol concentration in the distillation tower 20 is less than 55% by mass, the burden on the membrane separator increases, so the membrane separator becomes large and the fermentation alcohol is more convenient and extremely energy efficient as a whole process. This is not preferable because it cannot be purified to obtain anhydrous alcohol. On the other hand, it is not limited to make the alcohol concentration too high, but it is not preferable because the fermentation alcohol cannot be purified and processed in an extremely energy efficient manner as the whole process, so that anhydrous alcohol cannot be obtained.

A part of the mixed vapor of alcohol and water distilled in the distillation column 20 is condensed and refluxed as a condensate to the distillation column. The remaining mixed vapor is reduced in pressure by a pressure reducing means while maintaining the vapor temperature. Then, it is supplied to the membrane separator 40. The pressure reducing means is not particularly limited, but a pressure regulating valve having a throttle valve is preferably used. In addition, it is important that this depressurization results in the condensation temperature of the mixed steam of alcohol and water being lower than the temperature of the mixed steam. Usually, the pressure is reduced to about 5 kPa or more, preferably 10 kPa or more, more preferably 10 to 500 kPa, and still more preferably about 10 to 300 kPa.

One of the features of the present invention is that after a mixed vapor of alcohol and water is generated by a distillation tower, the pressure is reduced by a pressure reducing means while maintaining the vapor temperature, and then supplied to the membrane separator. The purpose of reducing the pressure is to sufficiently reduce the condensation temperature of the mixed vapor to be lower than the temperature of the mixed vapor so that the saturated mixed vapor does not condense in the membrane separator. It is suitable that the condensation temperature of the mixed steam is 3 ° C. or more, preferably 5 ° C. or less lower than the temperature of the mixed steam. In addition, it is 10 degrees C or less normally. In addition, reducing the pressure of the mixed steam once heated to a high pressure is poor in energy efficiency only in the process, but it is possible to improve the energy efficiency in the whole process.

The operating pressure of the distillation column 20 is set to 150 kPa (absolute pressure) or more, preferably 150 to 700 kPa (absolute pressure), because the pressure of the mixed vapor of alcohol and water supplied to the membrane separator is increased to increase the separation efficiency ( This is to improve the purification efficiency. A pressure of less than 150 kPa (absolute pressure) is not preferable because the pressure of the mixed vapor supplied to the membrane separation device 40 becomes too low and the separation efficiency is lowered. On the other hand, when the pressure exceeds 700 kPa (absolute pressure), the separation efficiency in the membrane separation apparatus is improved, but the pressure resistance performance of the distillation apparatus and the membrane separation apparatus is excessively required, and there is a problem that the apparatus is enlarged. Since it occurs, it is not necessarily preferable.

The distillation column 20 is not particularly limited as long as it is suitable for a normal high-pressure distillation operation, such as a plate type or a packed column. A supply unit for supplying an aqueous alcohol solution is disposed in the middle stage of the distillation column. A part of the column bottom liquid is heated by the reboiler 21 to become vapor, and rises in the column while exchanging heat and materials with the liquid flowing down in the column. And the mixed vapor | steam of alcohol and water with which the alcohol concentration was concentrated distills from a tower top or a concentration stage.

A part of the mixed vapor of alcohol and water distilled by the distillation column 20 is cooled by the condenser 22 to become a condensate, and passes through the condensate tank 23 by, for example, a condensate pump. Alternatively, it is refluxed to the concentration stage. The remainder of the mixed steam of alcohol and water distilled by the distillation tower 20 is decompressed by the decompression means 24 and then supplied to the membrane separation device 40.

The reboiler 21 that heats the bottom liquid of the distillation column 20 can also use the condensation heat of steam supplied from the outside.

The operating pressure of the distillation column 20 is suitably controlled by adjusting (limiting) the flow rate of steam for heating the bottom liquid of the distillation column.

In the distillation column 20, by adjusting the ratio of the mixed vapor of alcohol and water distilled from the top of the column or the concentration stage to the distillation column 20 as a condensate and the number of stages of the distillation column, The alcohol concentration of the mixed steam of alcohol and water to be distilled can be suitably controlled.

If the ratio of reflux increases, the throughput in the distillation column 20 decreases, the processing speed decreases, and the efficiency is reduced, for example, the energy consumption increases. Therefore, the ratio of the condensed liquid to be refluxed is relatively low. Is preferred. Preferably it is less than 50% of the condensate, more preferably less than 40%, even more preferably less than 20%, particularly preferably less than 10%.

In the present invention, the alcohol concentration of the mixed vapor of alcohol and water distilled from the top of the column or from the concentrating stage is not particularly limited. For example, any alcohol concentration from 50% by mass to azeotropic composition (or 96% by mass) can be used. In terms of controlling the energy consumption, it is more preferably 55% to 90% by weight, further preferably 60% to 90% by weight, and particularly preferably 65% to 85% by weight. is there.

The condensation heat of the condenser 22 is preferably recovered by using the preheating of the aqueous alcohol solution supplied to the distillation column 20 or the reboiler heating of the mash column 10 and the necessary amount of reflux liquid cannot be condensed. It is preferable to add an auxiliary condenser and condense with cooling water. The aqueous alcohol solution supplied to the distillation column 20 is preferably preheated to near its boiling point. At that time, it is preferable to effectively use the heat of the anhydrous alcohol purified by the reflux liquid of the distillation column 20 or the membrane separation device 40.

The mixed vapor of alcohol and water supplied to the membrane separation device 40 flows while in contact with the selectively permeable separation membrane. At that time, since the water vapor selectively permeates the separation membrane, the mixed vapor having a reduced alcohol concentration mainly composed of water vapor is recovered on the permeation side of the separation membrane. The alcohol concentration of the mixed steam is about several to several mass% (for example, 20 mass% of alcohol), and is preferably circulated and supplied to the distillation column 20 in order to increase the alcohol recovery rate. On the other hand, since water vapor is removed on the non-permeating side of the separation membrane, high-purity anhydrous alcohol can be recovered.

Generally, the permeation amount of water vapor that permeates the separation membrane is proportional to the partial pressure difference between the water vapors on both sides of the membrane. For this reason, separation efficiency (purification efficiency) can be increased by increasing the partial pressure difference between the water vapors on both sides of the membrane. In the present invention, a high-pressure mixed vapor of alcohol and water of 150 kPa (absolute pressure) or higher, preferably 150 to 700 kPa (absolute pressure) is supplied to the membrane separator. At the same time, it is also preferable to reduce the pressure on the permeate side of the separation membrane. Specifically, the space on the permeate side of the separation membrane is connected to a vacuum pump 42 via a heat exchanger (condenser) 41 to reduce the pressure, and the permeated vapor that has permeated the separation membrane is condensed in the condenser to be condensed. And This condensate is preferably stored in the condensate tank 43 and then circulated and supplied to the distillation column 20.

The membrane separation device 40 is not limited as long as it can separate water vapor from the mixed vapor of water vapor and ethanol vapor with a separation membrane. The separation membrane is not particularly limited as long as it selectively permeates water vapor with respect to alcohol vapor. It may be made of a polymer such as polyimide, polyetherimide, polycarbonate, polysulfone or high molecular weight polyvinyl alcohol, or may be made of an inorganic material such as zeolite or zirconia. And the form of the membrane separation device is also a hollow fiber separation membrane module made of, for example, an asymmetric polyimide hollow fiber membrane, a shell-and-tube module comprising a tubular separation membrane element in which a zeolite is formed on a porous tubular support, etc. The conventionally known ones can be suitably used. Examples of these include, but are not limited to, Japanese Unexamined Patent Application Publication Nos. 2000-262828 and 2001-62257 using polyimide hollow fiber membranes, and Japanese Unexamined Patent Application Publication No. 2003-93844 using zeolite membranes. Preferred examples include those described in JP-A-2006-263574, JP-A-2007-203210 and the like.

As the permeation performance of the separation membrane, the water vapor transmission rate (P ′ _{H 2 O 2} ) is preferably 0.5 × 10 ⁻³ cm ³ (STP) / cm ² · sec · cm Hg or more, more preferably 1.0 in use. × 10 ⁻³ cm ³ (STP) / cm ² · sec · cmHg or more, ratio of water vapor transmission rate (P ′ _{H 2 O} ) to alcohol transmission rate (P ′ _alcohol ) (P ′ _{H 2 O} / P ′ _alcohol ) Is preferably 50 or more, more preferably 100 or more.

Next, a description will be given based on FIG. 2 showing an outline of an example of another embodiment according to the present invention.

The role of the distillation column in FIG. 1 is that an aqueous alcohol solution having an alcohol concentration of less than 50% by mass from the mash column is distilled under pressure to concentrate the alcohol, and at the same time, the high-pressure alcohol of 150 kPa (absolute pressure) or higher and water It was to produce mixed steam. On the other hand, the embodiment shown in FIG. 2 is characterized in that the distillation column is operated at a low pressure of about 50 to 150 kPa, preferably at atmospheric pressure, and the condensate obtained by condensing the mixed vapor of alcohol and water obtained here is evaporated. To generate a mixed vapor of alcohol and water having a high pressure of 150 kPa (absolute pressure) or higher. Hereinafter, the distillation tower and the evaporator which are the features of FIG. 2 will be described. The other points are as described with reference to FIG.

In FIG. 2, the operating pressure of the distillation column 20 is preferably in the range of 50 to 150 kPa, and is usually atmospheric pressure.

The reboiler 21 that heats the bottom liquid of the distillation column 20 can use the condensation heat of steam supplied from the outside, but the condensation heat of the non-permeated vapor of the membrane separation device 40 can be suitably used as preheating, for example. it can.

The condenser 22 cools the mixed vapor of alcohol and water distilled from the top of the distillation column 20 or the concentration stage to form a condensate. The condensate may be temporarily stored in the condensate tank 23. A part of this condensate is refluxed to the top of the column or the concentration stage by, for example, a condensate pump, and the remainder is sent to the evaporator 30. The alcohol concentration of the mixed vapor of alcohol and water obtained at the top of the distillation column or at the concentration stage can be suitably controlled by the ratio of the condensate refluxed to the distillation column 20 and the number of stages of the distillation column. In the present invention, by adjusting the ratio of the condensate refluxed to the distillation column 20 and the number of stages of the distillation column, the alcohol concentration of the mixed steam of alcohol and water obtained at the top of the distillation column 20 or at the concentration stage. Is controlled to be 55% by mass or more.

If the ratio of reflux increases, the throughput in the distillation column 20 decreases, the processing speed decreases, and the efficiency is reduced, for example, the energy consumption increases. Therefore, the ratio of the condensed liquid to be refluxed is relatively low. Is preferred. Preferably it is less than 50% of the condensate, more preferably less than 35%, even more preferably less than 20%, particularly preferably less than 10%.

The condensation heat of the condenser 22 may be used for preheating the aqueous alcohol solution supplied to the distillation column. The supplied aqueous alcohol solution is preferably preheated to near its boiling point. At that time, it is preferable that the steam that cannot be condensed by the condenser 22 is condensed by cooling water by the auxiliary condenser.

In the present invention, an aqueous alcohol solution having an alcohol concentration of 55% by mass or more is supplied from the distillation column 20 through the condenser 22 to the evaporator 30. The role of the evaporator 30 is to heat the alcohol aqueous solution to evaporate the whole amount and supply it to the membrane separation device 40 as a mixed vapor of alcohol and water. The evaporator 30 is provided with a sufficient heating function, and can be operated at a relatively high pressure of 150 kPa (absolute pressure) or higher, preferably 200 kPa (absolute pressure) or higher, in the pressure of the mixed alcohol and water vapor obtained. . The upper limit of the pressure is usually about 700 kPa (absolute pressure) or less.

The operating pressure of the evaporator 30 is controlled by the amount of heat (steam amount) applied to the evaporator, but at that time, the flow rate of the mixed vapor distilled from the evaporator may be controlled. Further, the pressure of the mixed vapor can be suitably adjusted by adjusting (restricting) the flow rate of the vapor flowing through the pressure reducing means between the evaporator and the membrane separator and the non-permeate side of the membrane separator 40. And it is preferable to adjust the pressure in an evaporator so that the evaporation temperature in the evaporator 30 may become about 5 degreeC or more higher than the temperature of the tower bottom of the distillation column 20. FIG. This makes it possible to use the non-permeate vapor of the membrane separator 40 as a heat source for the reboiler of the distillation column 20.

The total amount of the mixed vapor of alcohol and water obtained in the evaporator 30 is reduced in pressure by the decompression means, and then supplied to the membrane separation device 40 for purification. The pressure reducing means is not particularly limited, but a pressure regulating valve having a throttle valve is preferably used. In addition, it is important that this depressurization results in that the condensation point of the mixed steam of alcohol and water is lower than the temperature of the mixed steam after depressurization. Usually, the pressure is reduced to about 5 kPa or more, preferably 10 kPa or more, more preferably 10 to 500 kPa, and still more preferably about 10 to 300 kPa.

As described with reference to FIG. 1 below, one of the features of the present invention is that after the high-pressure alcohol / water mixed vapor is generated by the evaporator, the pressure of the mixed vapor is maintained while maintaining the temperature of the mixed vapor. It is to supply to the membrane separator after decompressing. The purpose of reducing the pressure is to sufficiently reduce the condensation temperature of the mixed vapor to be lower than the temperature of the mixed vapor so that the saturated mixed vapor does not condense in the membrane separator. It is suitable that the condensation temperature of the mixed steam is 3 ° C. or more, preferably 5 ° C. or more lower than the temperature of the mixed steam. In addition, it is 10 degrees C or less normally. In addition, reducing the pressure of the mixed steam once heated to a high pressure is poor in energy efficiency only in the process, but it is possible to improve the energy efficiency in the whole process.

FIG. 3 shows an outline of another example of the embodiment according to the present invention which is basically the same as FIG.

That is, the bottom liquid discharged from the mash tower 10 is used for preheating the aqueous fermentation alcohol solution supplied to the mash tower 10, and the reflux steam of the distillation tower 20 is obtained by condensing the permeate condensate of the membrane separation apparatus 40. The non-permeated vapor (anhydrous alcohol vapor) of the membrane separation device 40 is preheated when the condensed liquid of the permeated vapor of the membrane separation device 40 is circulated and supplied to the distillation column 20. , And a portion of the bottom liquid of the moromi tower 10 is used for heating the bottom liquid when it is circulated to the mash tower, and each is suitably heat-recovered.

In the present invention, the thermal energy of the mixed steam generated in the mash column, distillation column (and evaporator) and membrane separation apparatus is preferably recovered in another process in the system as described above. It may be recovered in a completely different heating process.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

[Example 1]
The fermented ethanol aqueous solution with the ethanol concentration of 7.3 mass% obtained in the fermenter was refined using 72.7 tons per hour using the apparatus schematically shown in Fig. 3, and 99.8 mass% absolute ethanol was purified. An attempt was made to obtain 5 tons per hour.
(Process 1)
A fermented ethanol aqueous solution having an ethanol concentration of 7.3% by mass is preheated with a preheater, and is fed at a flow rate of 72.7 t / hour to a mash tower having a theoretical plate number equivalent to 5 with a liquid feed pump. Water vapor (steam 1) necessary for carrying out a distillation process by evaporating the supplied aqueous solution of fermentation ethanol is directly blown into the bottom of the mash column. The distillate containing the mixed vapor of ethanol and water produced in the moromi tower and sent from the top of the tower is condensed by the condenser. A part of the condensate is refluxed to the mash column, and the remaining condensate is supplied to the distillation column. The reflux amount is adjusted so that the ethanol concentration at the top of the mash column is 39% by mass.
(Process 2)
An ethanol aqueous solution having an ethanol concentration of 13.3 t per hour and an ethanol concentration of 39% by mass is supplied to a distillation column corresponding to 6 theoretical plates by a liquid feed pump. A reboiler is provided at the bottom of the distillation column, and the bottom liquid extracted from the bottom is converted to a mixed vapor by the reboiler supplied with steam 2 and circulated and supplied to the distillation column. At the same time, the column bottom liquid extracted from the column bottom is circulated and supplied to the mash column at a flow rate of 8.3 t per hour. The column bottom liquid is kept at an ethanol concentration of about 2.5% by mass or less.

The temperature of the mixed vapor of ethanol and water distilled from the distillation tower and sent from the top of the tower is adjusted to 135 ° C. by adjusting the heating amount of the distillation tower. A part of the mixed vapor is condensed by a condenser and refluxed to the distillation column. By adjusting the reflux amount, the ethanol concentration of the mixed vapor of ethanol and water at the top of the distillation column is adjusted to 75% by mass.
(Process 3)
The remaining mixed vapor of ethanol and water that has not been condensed is reduced from 551 kPa to 300 kPa (gauge pressure) by a pressure adjusting valve (throttle valve) while maintaining the vapor temperature, and supplied to the membrane separation device.

The mixed vapor of ethanol and water supplied to the membrane separator is 10.4 t per hour.
(Process 4)
The membrane separation device is a module as described in Japanese Patent Application Laid-Open No. 2000-262838, and has a water vapor transmission rate (P ′ _H2O ) at 135 ° C. of 1.2 × 10 ⁻³ cm ³ (STP) / cm. ² · sec · cmHg, the ratio of the water vapor transmission rate 'as _(H2O ethanol permeation rate (P P)' and _{_{EtOH) (P 'H2O / P}} ' EtOH) 143, an outer diameter of 500 [mu] m, inner diameter of 310μm polyimide asymmetric A module containing 26 modules each having an effective membrane area of 125 m ^{2 made} of a hollow fiber separation membrane is used.

On the permeate side of the membrane separator, a vacuum pump is provided via a condenser, and the pressure is reduced to 12 kPa (absolute pressure). The vapor that has permeated the separation membrane is completely condensed by a condenser so that the degree of vacuum on the permeate side of the separation membrane is maintained. In addition, a part of the non-permeated vapor discharged from the membrane separation device is configured to be supplied to the permeation side of the membrane separation device as a purge gas for increasing the separation efficiency of the membrane separation device.

Vapor recovered from the permeation side of the separation membrane of the membrane separation apparatus (permeated vapor and vapor supplied as purge gas) is condensed, preheated with non-permeated vapor, and circulated and supplied to the distillation column. Further, the non-permeate vapor recovered from the non-permeate side of the separation membrane of the membrane separator is used for heating the bottom liquid when circulating the low column liquid of the mash tower to the mash tower in addition to the preliminary heating. After being recovered by heat, it is cooled and recovered as absolute ethanol having an ethanol concentration of 99.8% by mass in a product tank at 5 tons per hour.

When 99.8% by mass of absolute ethanol was obtained by such a method, the amount of heat necessary to obtain 1kg of 99.8% by mass of absolute ethanol was determined as the total amount of steam used in all steps (steam 1 to Converted from 2). The results are shown in Table 1.

[Reference Example 1]
Table 1 shows the results when the same operation as in the example was performed except that the operation in the step 2 was changed as follows in the example 1.
(Process 2)
An ethanol aqueous solution having an ethanol concentration of 13.3 t per hour and an ethanol concentration of 39% by mass is supplied to a distillation column corresponding to 6 theoretical plates by a liquid feed pump. A reboiler is provided at the bottom of the distillation column, and the bottom liquid extracted from the bottom is converted to a mixed vapor by the reboiler supplied with steam 2 and circulated and supplied to the distillation column. At the same time, the column bottom liquid extracted from the column bottom is circulated and supplied to the mash column at a flow rate of 8.3 t per hour. The column bottom liquid is kept at an ethanol concentration of about 2.5% by mass or less.

The mixed vapor of ethanol and water sent from the top of the distillation column in the distillation column is adjusted by adjusting the flow rate at which the non-permeate side vapor of the membrane separation device 40 is discharged from the outlet of the membrane separation membrane device. Is adjusted to 300 kPa (gauge pressure). A part of the mixed vapor is condensed by a condenser and refluxed to the distillation column. By adjusting the reflux amount, the ethanol concentration of the mixed vapor of ethanol and water at the top of the distillation column is adjusted to 75% by mass. The remaining mixed vapor of ethanol and water that has not been condensed is heated to 135 ° C. by a superheater (steam 3) and supplied to the membrane separation apparatus.

The mixed steam of ethanol and water supplied to the membrane separator is 10.4 t per hour.

[Examples 2 to 7]
Except that the conditions shown in Table 1 were adopted, an attempt was made to obtain 9 tons of absolute ethanol at 5 t / hour by the same operation as in Example 1.

The results are shown in Table 1.

[Reference Examples 2 and 3]
Table 1 shows the results when operating in the same manner as in Reference Example 1 except that the conditions shown in Table 1 were adopted.

As is apparent from Table 1, the examples are extremely energy efficient when viewed as a whole process.

According to the present invention, (1) a fermentation alcohol aqueous solution is supplied to a mash tower, the fermentation alcohol aqueous solution in the mash tower is heated to distill a distillate containing a mixed vapor of alcohol and water. The first condensate obtained by condensing the distillate is supplied to the distillation column, and (2) a) the distillate or the first condensate is heated by the distillation column to distill the mixed vapor of alcohol and water. Or b) the distillate or the first condensate is heated by a distillation column to distill a mixed vapor of alcohol and water, and the second condensate obtained by condensing the mixed vapor is supplied to an evaporator. And the second condensate in the evaporator is heated to generate a mixed vapor of alcohol and water and supplied to the membrane separator. (3) Mixed vapor distilled from the distillation column in a) Or the mixed vapor generated from the evaporator in b) (4) In a purification method for obtaining anhydrous alcohol from a fermented alcohol aqueous solution in which water vapor is selectively removed from the mixed steam of alcohol and water with a membrane separator, the purification process method for obtaining anhydrous alcohol is simpler and extremely A method for energy efficient purification can be provided.

Claims

(Step 1) A fermentation alcohol aqueous solution is supplied to the mash tower, the fermentation alcohol aqueous solution in the mash tower is heated to distill a distillate containing a mixed vapor of alcohol and water, and this distillate or this distillate. Supplying a first condensate condensed with a distillation column;
(Step 2) a) a step of heating the distillate or the first condensate by a distillation column to distill a mixed vapor of alcohol and water, or b) the distillate or the first by a distillation column. The condensate is heated to distill the mixed vapor of alcohol and water, the second condensate condensed with the mixed vapor is supplied to the evaporator, and the second condensate in the evaporator is heated. Generating a mixed steam of alcohol and water;
(Step 3) a step of supplying the mixed vapor distilled from the distillation column in the a) or the mixed vapor generated from the evaporator in the b) to the membrane separator after reducing the pressure;
(Step 4) A purification treatment method for obtaining anhydrous alcohol from a fermented alcohol aqueous solution, comprising a step of selectively removing water vapor from a mixed steam of alcohol and water by a membrane separator.
The method according to claim 1, wherein the pressure of the mixed steam distilled from the distillation column in step 2a) or the mixed steam generated from the evaporator in step 2b) is 150 kPa (absolute pressure) or more.
3. The method according to claim 1, wherein in step 3, the pressure is reduced so that the condensation temperature of the mixed steam of alcohol and water is lower than the temperature of the mixed steam.
The method according to any one of claims 1 to 3, wherein in step 3, the pressure is reduced to 5 kPa or more.
The method according to any one of claims 1 to 4, wherein the alcohol concentration of the distillate or the first condensate supplied from the mash column to the distillation column in step 1 is less than 50% by mass.
The method according to any one of claims 1 to 5, wherein the alcohol concentration of the mixed steam of alcohol and water supplied to the membrane separator in step 4 is 55 to 90 mass%.