JPH0389922A - Separation of dissolving volatile substance from volatile substance dissolving solution by distillation - Google Patents

Abstract

PURPOSE:To separate a dissolving volatile substance efficiently by bringing a raw solution in which the volatile substance dissolves into contact with one side of a hydrophobic porous membrane having continuous fine pores and bringing an aqoueous solution for recovery at lower temperature than the raw material into contact with the other side of the membrane. CONSTITUTION:In the case where an ethanol-containing aqueous solution as a raw material and distilled water are respectively brought into contact with one side of a hydrophobic porous membrane and with the other side, gaseous layers 4, 6 are formed on the surface of the hydrophobic porous membrane and gas-liquid interfaces 3, 7 exist outer side of the layers. When the raw material 1 flows, a liquid boundary membrane exists in the liquid side and ethanol molecules move in the boundary membrane due to diffusion. When a gas and a liquid are not in the equilibrium state in the gas-liquid interface 3, ethanol and water are evaporated according to the gas- liquid equilibrium theory and move in the gas on the surface of the membrane and in the membrane owing to gas diffusion. As an apparatus, one by which the raw material solution and an absorption liquid are respectively brought into contact with one side and the other of a hydrophobic flat membrane is preferable.

Description

[Detailed Description of the Invention] (Industrial Application Field) The method of the present invention recovers a distillate with a higher alcohol concentration from an alcohol-containing aqueous solution at room temperature and pressure without causing any thermal change in the raw material. Therefore, in the liquor manufacturing process, alcohol is continuously recovered from the fermenting moromi and, for example, in sake manufacturing, it is returned to the moromi just before the upper tank to produce a new type of sake without using raw alcohol. If alcohol is continuously recovered using this method while continuously supplying the substrate to the fermenting moromi, it is possible to produce an alcohol aqueous solution that does not contain a large amount of extract from a fixed amount of the moromi, so it is possible to produce aqueous alcohol solution that does not contain a large amount of extract. The burden of wastewater treatment in production is reduced.

Moreover, if the distillation of alcohol is repeated three times using this method, 1
Since it is possible to concentrate a 5 VO 1% alcohol aqueous solution to approximately 48 VO 1%, it is used in the production of fuel alcohol.
It can be in the raw material liquid.

According to the method of the present invention, alcohol can be easily removed from an alcohol-containing aqueous liquid, and therefore alcohol can be removed from distilled spirits such as wine, beer, or sake to produce low-alcohol alcoholic beverages or non-alcoholic beverages. It can be used in the raw material liquid.

When the purpose is to culture baker's yeast and produce yeast cells, alcohol increases as the yeast grows, which has a negative physiological effect on the yeast, slows down the cell growth rate, and increases the alcohol concentration. It can kill yeast and increase the culture density of yeast.

Therefore, the method of the present invention can be used for beverage/alcohol production, microbial cell production, and industrial alcohol production.

The method of the present invention can be used to concentrate or remove not only alcohol but also various hydric and volatile substances such as low-molecular esters, ketones, and aldehydes in the raw material liquid.

(Prior art and problems) In alcoholic fermentation, the alcohol produced by yeast has an adverse effect on the physiology of yeast, and alcohol
Since the fermentation ability of yeast decreases when the concentration of alcohol reaches 1%, various attempts have been made to recover alcohol from the fermenting moromi. Methods for recovering alcohol from moromi are broadly divided into distillation methods and membrane separation methods. Distillation methods include blowing gas into the moromi to evaporate the alcohol, and extracting the acid solution and pouring it in, which do not allow for a high gas flow rate and are not practical. There is a Japanese Patent Publication No. 63=8753 that uses flash evaporation to remove the raw material liquid, but the equipment is large and it is difficult to separate solid and liquid in the moromi when sending the acid solution to the distillation equipment. Therefore, it is difficult to prevent bacterial contamination of the entire device. Although the vacuum distillation method is an effective method, it requires the entire equipment to be of pressure-resistant structure, it is necessary to constantly exhaust the carbon dioxide gas associated with fermentation, and the thermal efficiency of cooling is poor in a vacuum state, causing the temperature of the cooler to drop to - There are drawbacks such as the need for a temperature of 20 to -30°C.

Recently, separation technology using membranes has progressed, and separation methods in raw material liquids, such as microfiltration, ultrafiltration, and reverse osmosis, in which membranes with large and small pore sizes are brought into contact, are widely used for food separation. These physical methods cannot separate only volatile substances from fermentation liquor, etc., and cannot concentrate alcohol.

On the other hand, membrane separation methods involving phase change include pervaporasin method and membrane distillation method. It permeates through the liquid held in the pervapor array by diffusion, and is expressed by a model of dissolution-diffusion-evaporation-condensation. Membrane distillation is a special case of the pervaporation method, in which a hydrophobic porous membrane is used, and volatile components pass through the membrane in the form of vapor, and is expressed by the evaporation-diffusion-condensation model. Membrane distillation, which uses gas to diffuse, provides a higher permeation rate than the pervaporation method, which uses gas to diffuse. However, the method currently called membrane distillation has a composition of raw material liquid - membrane - gas, and the recovery side is depressurized or inert gas such as nitrogen is circulated to cool the gas containing vapor. The cooling efficiency is poor because volatile substances are recovered by distillation, and in order to efficiently recover the distillate, the temperature of the condenser must be kept very low, such as keeping the temperature of the condenser below -30℃. There is.

Methods using raw material liquid - hydrophobic porous membrane - absorption liquid type equipment include collecting dissolved iodine from volatile dissolved aqueous solutions, natural gas brine, removing dissolved ammonia from sewage and wastewater, and removing dissolved ammonia from industrial water. removing dissolved oxygen, etc.
The purpose is simply to separate volatile substances dissolved in water, and as a volatile substance absorption liquid (1)
Reacts well with the target volatile substance, changing the chemical species of the volatile substance and at the same time being able to dissolve the product well;
(2) Considering that it is advantageous to take out the target volatile substance that has been dissolved and collected, for example, in the iodine recovery process, an alkaline aqueous solution such as an aqueous sodium hydroxide solution is used, and ammonia recovery (or removal) Since it is recommended to use an acidic aqueous solution such as a phosphoric acid aqueous solution in the process, Japanese Patent Publication No. 54-39833 proposed a liquid that chemically reacts with volatile substances dissolved in water through a porous membrane based on gas absorption theory. This is a method of absorbing different chemical species using water, and is not a method of concentrating volatile substances based on distillation theory using low-temperature water.

There is no simple and effective method to concentrate and recover or remove alcohol.

(Means for Solving the Problem) The present inventors focused on membrane distillation as an alcohol distillation method that can be used at room temperature while yeast remains alive without heating an alcohol-containing aqueous liquid such as moromi during fermentation. As a result of intensive research, we discovered that the structure of raw material liquid, hydrophobic porous membrane, and absorbing liquid was used instead of the conventional structure of raw material liquid, hydrophobic porous membrane, and gas, which is used in conventional membrane distillation. He learned that alcohol could be concentrated using a simple device even at room temperature by lowering the temperature of the raw material liquid.

When a hydrophobic porous membrane is brought into contact with an ethanol-containing aqueous solution as a raw material and distilled water on the other side, a model as shown in Figure 1 can be considered if the double layer theory is adopted. A gas layer 4.6 is formed on the surface of the hydrophobic porous membrane, and a gas-liquid interface 3.7 exists outside of the gas layer 4.6. When raw material 1 is the driving force,
Move the podium to the liquid side. When the gas and liquid are not in equilibrium at the gas-liquid interface 3, ethanol and water evaporate according to the theory of gas-liquid equilibrium and move through the membrane surface and the gas within the membrane material by gas diffusion. At the gas-liquid interface 7 on the absorption liquid side, if equilibrium is not established with respect to ethanol, the ethanol is dissolved until equilibrium is reached, and the ethanol molecules move through the liquid film 8 toward the absorption liquid main body 9 by diffusion.

Therefore, if the vapor pressure of the ethanol in the gas held on both surfaces of the membrane is different, the overall evaporation -
A phenomenon called absorption (condensation) occurred, and distillation took place.

The membrane permeation rate of ethanol is considered to be proportional to the difference in concentration of ethanol in the gas on both sides of the membrane, and inversely proportional to the thickness of the membrane. The membrane permeation rate of ethanol is Q (mol ・cm'
-5ee-'), the membrane thickness L (cm), and the vapor pressure in the gas on the membrane surface on the raw material and absorption liquid side, Pl and P2, respectively.
(Pa), the temperature is TI, T2 (K), the gas constant is R (cnLPa-1·mol'), and the proportionality constant is KCcrl/5ec), then Q can be expressed by the first equation.

When water is brought into contact with one side for a long time, when T1 and T2 are equal, P, P2 are equal, and the right side of the first equation becomes zero, and from then on, ethanol does not move and is absorbed. The ethanol concentration in the liquid cannot be higher than that of the raw material.

However, when the salinity of the absorption liquid is lowered below the temperature of the raw material skin, the rate at which P2 decreases is greater than the rate at which T2 decreases, so P2/T2 becomes smaller than PI/Tl, and the ethanol concentration in the absorption liquid decreases. Equilibrium occurs at a higher level in the raw material. In other words, ethanol can be concentrated.

In addition, the apparatus used for the removal of the present invention includes a method in which the raw material liquid and the absorption liquid are brought into contact with each other through a hydrophobic porous flat membrane, a method in which a hydrophobic porous body formed in a tube shape is provided in a stirring tank,
As can be deduced from the model in Figure 1, it is possible to determine whether a method of flowing the raw material liquid into a stirring tank and an aqueous liquid for alcohol recovery into tubes, or whether a shell-and-tube heat exchanger type device can be used. Since there are membranes on both sides of the membrane, it is desirable to flow the liquid on both sides of the membrane, for example in a fermentation tank. Although the pore size of the membrane has little effect on the permeation rate of alcohol, it is important that there is no leakage, and special attention must be paid to pinholes. In the method of the present invention, since there is a temperature difference on both sides of the membrane, it is desirable that the membrane has excellent heat insulation properties. Hydrophobic porous membranes retain gas within the membrane and have excellent insulation properties, but a certain degree of thickness is required, 0.5 to 2 mm.
It is desirable that it has a certain thickness. As a material for the membrane, polytetrafluoroethylene (PTFE) resin is excellent because it has strong hydrophobicity, is non-adhesive to substrates such as rice, and is hard to clog.

Next, an experimental example of the present invention will be shown.

Experimental Example 1 Figure 2 shows an outline of the experimental apparatus. Porous polytetrafluoroethylene (PTFE) tube (outer diameter 9 mm,
The raw material 11 was placed in a stirring tank with an inner diameter of 7 mm, a length of 93 cm, and a pore diameter of 1 μm, and the valve 15 was closed. The temperature of the stirring tank was 30°C, the temperature at the inlet of the PTFE tube was 4.5 and 17.0°C, and the rotation speed of the stirrer was 110°C.
At 0 rpm, the raw material liquid and the absorption liquid were sampled over time, and the increase in the absorption liquid was measured.

The experimental results are shown in Figure 3. In Figure 3, the horizontal axis is the absorption liquid circulation time (h''), and the vertical axis is the ethanol concentration (vo
1%). Approximately 7 to 8 hours after circulating distilled water as the absorption liquid, the ethanol concentration in the absorption liquid reached its maximum, and thereafter, the concentration of the absorption liquid also decreased as the ethanol concentration in the raw material liquid decreased.

The temperature difference between the raw material liquid and the absorption liquid has a large effect on the ethanol concentration rate (ethanol concentration in the absorption liquid/ethanol concentration in the raw material liquid), and when the temperature difference is 25.5 degrees, the ethanol concentration in the raw material liquid is The concentration of the absorption liquid was 17.3 vol. 1%, which was about 1.6 times concentrated. However, if the temperature difference is 13 degrees, ]], 5vo1% to 1
It was only concentrated about 1.3 times to 5.4 vol. The absorption l when the ethanol concentration in the absorption liquid reaches the maximum value when the temperature difference is 25.5 and 13 degrees. This experimental result shows that the lower the temperature of the absorption liquid is compared to the temperature of the raw material liquid, the more advantageous it is to concentrating ethanol and increasing the amount of recovered liquid.

Experimental Example 2 The relationship between the ethanol concentration in the raw material and the concentration in the absorption liquid was investigated. In the experiment, the valve 15 is opened in FIG.
The increased amount of the absorption liquid is returned to the stirring tank by the pump 11, the amounts of the raw material liquid and the absorption liquid are kept constant, and the mixture is kept at a constant temperature for about 20 hours until the ethanol concentration in the absorption liquid reaches equilibrium with the raw material liquid. After continued circulation, sampling was performed and the reflux amount was measured. P with outer diameter 4mm, inner diameter 3mm, length 1m
The flow rate of the absorption liquid is 30ml using a TFE porous tube.
/min. The concentration of the raw material liquid is 8 to 43 vol%,
The temperature of the absorption liquid was 5°C.

The experimental results are shown in Figure 4. The horizontal axis of FIG. 4 is the ethanol concentration in the raw material, and the vertical axis is the ethanol concentration in the absorption liquid and the amount of absorption liquid reflux. The concentration ratio by the method of the present invention was much lower than distillation at the boiling point, and the effect of ethanol concentration on the reflux rate was small.

When the ethanol concentration of the absorption liquid exceeded 50 vol%, the PTFE membrane surface became wet with the liquid, and the raw material passed through the membrane in liquid form, making it impossible to distill it.

The dotted line in Figure 4 shows that when 15 vol of the raw material is concentrated three times by the method of the present invention, with the temperature of the raw material liquid being 30°C and the temperature of the absorption liquid being 5°C, the concentration is 24 vol 1% in the first time and 3 vol in the second time.
This shows that it is possible to concentrate from 5.5 vol 1% to 47.5 vol 1% in the third time.

Experimental Example 3 Three porous PTFE tubes with different diameters were stacked in order of diameter to form a triple tube, and separate absorption liquid was circulated in each tube, and the increase in absorption liquid was equal to the total amount as in Experimental Example 2. It was refluxed to the previous stage. The flow direction of the absorbent liquid was set to be opposite to each other. According to this method, the raw material in the stirred tank is distilled three times at once. In other words, compared to normal distillation, this is equivalent to three stages of a distillation column. Use ita chi
The tube was 113.5 cm.

Ethanol concentration in raw material liquid and each absorption liquid, absorption liquid flow rate,
The flow rate of the reflux liquid is shown in Table 1. When the temperature at the inlet of the innermost tube was 6.7°C and the concentration in the stirred tank was 30°C, the temperature at the entrance and exit of each tube was as shown in Table 2. The concentration rate for each tube was small because the temperature difference between each tube was small, and the overall concentration was 9.4vo1%.
It is concentrated about 1.9 times from 18.3vo1%, and membrane 1
The concentration rate was higher than that of Experimental Example 1, which was a single sheet.

Table 1 Ethanol concentration in absorption liquid, etc.

[Brief explanation of drawings]

Figure 1 is a diagram explaining the principle of the separation method of the present invention, Figure 2 is a schematic diagram of a liquid-membrane one-component membrane distillation experimental apparatus, and Figure 3 is an explanation of changes over time in the ethanol concentration in the raw material liquid and absorption liquid by membrane distillation. Figure, 4th
The figure is an explanatory diagram of the relationship between the ethanol concentration in the raw material, the ethanol concentration in the absorption liquid, and the reflux amount of the absorption liquid in membrane distillation.

Claims (2)

[Claims] (1) One side of the membrane formed of a continuous microporous hydrophobic material is contacted with an aqueous liquid containing a volatile substance as a raw material, and the other side is contacted with an aqueous recovery liquid whose temperature is lower than that of the raw material liquid. The volatile substances in the raw material liquid evaporate at the interface with the gas held on the surface of the hydrophobic porous material, and the gas layer held on the membrane surface and in the pores is driven by the vapor pressure difference of the substance. It moves by gas diffusion as a force and is absorbed by the aqueous liquid for recovery at the other gas-liquid interface of the membrane, making the liquid on the recovery side an aqueous solution with a higher concentration than the raw material liquid in terms of volatile substances. Distillation method. (2) One side of the membrane formed of a continuous microporous hydrophobic material is contacted with an aqueous liquid containing a volatile substance as a raw material, and the other side is contacted with an aqueous recovery liquid whose temperature is lower than that of the raw material liquid. The volatile substances in the raw material liquid evaporate at the interface with the gas held on the surface of the hydrophobic porous material, and the gas layer held on the membrane surface and in the pores is heated by the vapor pressure difference of the substance. A method for removing dissolved volatile substances from an aqueous liquid in which the volatile substances are moved by gas diffusion as a driving force and absorbed by the aqueous liquid for recovery at the other gas-liquid interface of the membrane.