JPH0536418B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for purifying and concentrating alcohol, and more particularly, to a method suitable for concentrating and purifying high-purity alcohol from synthetic alcohol, used alcohol aqueous solution, fermented alcohol, etc. in an energy-saving manner. [Prior art] Fermented alcohol made from carbohydrates such as amashiyo, sweet potato, and corn is an important starting material for beverages and industrial use, but the alcohol concentration of the alcohol aqueous solution obtained by the fermentation method is 10 to 10.
Since it is low at 20wt%, it is necessary to concentrate it to about 95-100wt%. Conventionally, distillation has been used as a concentration method, but water, which makes up most of the water, must be heated to 80 to 100°C, which is economically disadvantageous.Therefore, an alternative energy-saving concentration method has been developed. is desired. On the other hand, as an energy-saving concentration method, a method has been proposed in which alcohol is extracted and separated from water using carbon dioxide gas in a supercritical or quasi-critical state and then concentrated. (JP-A-56-56201 and JP-A No. 59-141528) However, when carbon dioxide gas is used as a solvent, there is a limit to the selective extraction of alcohol, and the maximum concentration is limited to approximately 91 wt%. It has recently been reported that it is impossible to concentrate In addition, since the solubility of alcohol in carbon dioxide gas is not large enough, a large amount of carbon dioxide gas (10
There is a problem that 15 parts by weight or more is required per 1 part by weight of aqueous alcohol solution, and an improvement is desired. For this reason, there is currently a need for a method that can improve alcohol concentration and increase alcohol solubility. [Problems to be Solved by the Invention] The present invention aims to provide an economical method for concentrating alcohol that can increase alcohol concentration to 91 wt% or more, increase alcohol solubility, and concentrate and recover alcohol with a small amount of solvent. It is something to do. [Means for Solving the Problems] That is, the present invention supplies a raw material mainly consisting of alcohol and water from the upper part of a countercurrent extraction column to a material selected from the group consisting of propane, propylene, n-butane, and i-butane from the lower part. One solvent is supplied, and the two are brought into contact with each other in countercurrent so as to maintain the inside of the countercurrent extraction column in a supercritical or quasi-critical state of the solvent, and the solvent phase containing concentrated alcohol is added from the top of the countercurrent extraction column. In the primary dehydration step, the solvent phase is cooled and separated by gravity sedimentation into a water-rich heavy liquid phase and a light liquid phase containing concentrated alcohol, and the heavy liquid phase is refluxed to the upper part of the countercurrent extraction column. In the next dehydration step, after reducing the pressure of the light liquid phase to below the upper critical pressure of the solvent, it is introduced into a solvent extraction distillation column, and the bottom mixed liquid of alcohol and solvent that does not contain substantially water is produced from the bottom of the column. An alcohol characterized by comprising a tertiary dehydration step in which a mixed vapor of water and solvent that does not substantially contain alcohol is extracted from the top of the column, and a desolvation step in which the mixed liquid at the bottom of the column is separated into solvent and alcohol by a distillation operation. This is a dehydration method. The present invention can be applied to the concentration and purification of all alcohol aqueous solutions, but as an example, in the case of fermented alcohol, the alcohol concentration is approximately
It is around 10wt% and the rest is water. Furthermore, in synthetic alcohol, the alcohol concentration is around 20wt%, with the remainder being water. On the other hand, the solvent referred to in the present invention refers to the following. Solvent name Chemical formula Critical temperature Critical pressure TC Pc (℃) (atm) Propylene C ₃ ll ₆ 92 45.6 Propane C ₃ ll ₈ 96.8 41.9 n-Butane n-C ₄ ll ₁₀ 152.2 37.5 i-Butane i-C ₄ ll ₁₀ 135.1 36.0 In addition, the supercritical state of a solvent as referred to in the present invention is a state in which the solvent is maintained at a temperature and pressure above its critical temperature Tc and critical pressure Pc, and the quasi-critical state is a state below its critical temperature Tc, but 80 The temperature is above ℃,
Pressure refers to the state maintained above the saturated vapor pressure of the solvent at that temperature. An embodiment of the present invention will be described in detail below with reference to FIG. In Fig. 1, 1 is a countercurrent extraction column (preferably a packed column, tray column, or multistage extraction column), 2 is a raw material supply line for an aqueous solution containing alcohol as a raw material, and 3 is an extraction residual liquid (water is 4 is a solvent phase (solvent and primary concentrated alcohol mixed phase) extraction line, 5 is a cooler, 6 is a gravity settling tank, 7 is a heavy liquid phase (main component is water with a small amount of alcohol, 8 is a light liquid phase (solvent and secondary concentrated alcohol mixture) takeoff line;
9 is a liquid level adjustment valve for the heavy liquid in the gravity settling tank 6, 10 is a pressure adjustment valve for the gravity settling tank 6, 11 is a heavy liquid reflux line, 12 is a solvent extraction column raw material supply line, 13 is a solvent extraction column, and 14 is a 15 is a bottom liquid level adjustment valve, 16 is a top steam (composed of solvent and water) takeout line, 17 is a compressor, 18 is a boiler (heat exchange 19 is a water separation tank, 20 is a water extraction line, 21 is a solvent extraction line, 22 and 23 are solvent reflux lines, 24 is a solvent heater, and 25 is a solvent supply line. 1 part by weight of the raw alcohol aqueous solution is supplied from the raw material supply line 2 and 3 to 6 parts by weight of the solvent is supplied from the solvent supply line 25 to the countercurrent extraction column 1, and the solvent is converted into an alcohol aqueous solution in a supercritical or pseudocritical state. Through countercurrent contact, the low-density solvent phase rises and selectively extracts alcohol from the alcohol aqueous solution, and is taken out as a light liquid through the solvent phase removal line 4. At this time, as the temperature increases, the solubility of alcohol in the solvent increases, but conversely the selectivity of alcohol decreases.The method of the present invention takes this point into account and adjusts the solubility of alcohol according to the type of solvent used. A range of preferred operating conditions for the countercurrent extraction column 1 should be established. In the countercurrent extraction column 1, alcohol is almost completely extracted, and the extracted alcohol concentration only needs to be primarily concentrated to about 50 to 90 wt%.
The temperature should be 80°C or higher, and the pressure should be higher than the saturated vapor pressure or critical pressure of the solvent used. Next, by cooling the solvent phase taken out from the solvent phase take-out line 4 in the cooler 5, the heavy liquid phase from the heavy liquid phase take-out line 7 and the light liquid phase from the light liquid phase take-out line 8 are separated in the gravity separation tank 6. The liquid phase separates into a heavy liquid phase containing water as the main component and a small amount of alcohol and solvent, and a light liquid phase containing solvent as the main component and secondary concentrated alcohol. The lower the cooling temperature, the higher the alcohol concentration in the light liquid phase, but the maximum alcohol concentration is approximately 95wt%.
Therefore, it was not possible to concentrate it any further. The preferred pressure of the gravity settling tank 6 is the same as that of the countercurrent extraction column 1, and the preferred temperature must be lower than that of the primary dehydration step, but the temperature varies depending on the type of solvent, and the temperature in the light liquid phase Alcohol concentration is approx.
It should be set to 95wt%, but it is preferable to optimize it based on the overall thermal energy balance. Further, the heavy liquid phase is preferably refluxed to the vicinity of the upper part of the countercurrent extraction column 1 via the liquid level adjustment valve 9 and the heavy liquid reflux line 11 in order to recover a small amount of alcohol and solvent. Next, the light liquid phase is reduced in pressure to below the critical pressure of the solvent by a pressure regulating valve 10 and is supplied to a solvent extractive distillation column 13 . The solvent sent from the process described below is supplied from the solvent reflux line 22 at the top of the solvent extraction distillation column 13 to the solvent extraction distillation column 13 as an extraction material for alcohol, and extractive distillation is performed. A liquid mixture of anhydrous alcohol and a solvent that does not substantially contain water is taken out from the top vapor extraction line 16 as a mixed gas of water and a solvent that does not substantially contain alcohol. The mixed liquid from the bottom mixed liquid take-out line 14 is a two-component system (alcohol and solvent) with significantly different boiling points, and can be easily separated into anhydrous alcohol and solvent by ordinary distillation, substantially eliminating water and solvent. Anhydrous alcohol free is obtained. In the solvent extraction tower 13, the solvent is maintained in a state where the solvent vapor and liquid coexist, and when it is brought into contact with an alcohol aqueous solution under the conditions where the solvent vapor and liquid coexist, the alcohol is selectively extracted due to the difference in affinity. Under conditions where water is extracted with a solvent and a large amount of solvent is present in the liquid phase relative to the alcohol, water is hardly dissolved in the liquid phase and the water concentration in the solvent vapor phase falls below the saturation concentration of water. If you set conditions such that
Moisture can be selectively transferred to the solvent vapor phase. In this way, alcohol and water can be separated using a solvent, and anhydrous alcohol can be obtained. In order to create a condition where the solvent vapor and liquid coexist in the extractive distillation column 13, the temperature must be set to the critical temperature Tc of the solvent.
In the following, pressure is the equilibrium vapor pressure corresponding to the liquid phase composition at this temperature (the maximum value is the critical pressure of the solvent Pc)
should be. Note that the amount of solvent from the solvent reflux line 22 should be changed depending on the alcohol concentration in the raw material from the solvent extraction column raw material supply line 12 and the product alcohol concentration. The number of stages should be determined to be an economical amount using chemical engineering techniques in the same way as in general distillation. The overhead vapor (consisting of solvent and water and substantially free of alcohol) from the overhead vapor take-off line 16 of the extractive distillation column 13 is recompressed in the compressor 17, and then its heat of adiabatic compression is transferred to the After being used as a heat source for the reboiler 18 of the extractive distillation column 13, the water separation tank 19
After separation into water and solvent through a water extraction line 20 and a solvent extraction line 21, the solvent is circulated and used through solvent reflux lines 22 and 23. The temperature difference between the top and bottom of the extractive distillation column 13 is 4 to 10
℃ and the small compression ratio of the compressor 17 allows heat exchange in the reboiler 18, resulting in significant energy savings compared to existing distillation methods. The solvent in the solvent reflux line 23 is given heat by the cooler 5, and after its temperature is adjusted by the heater 24, it is supplied from the lower part of the countercurrent extraction column 1 through the solvent supply line 25. Hereinafter, the present invention will be explained in detail by giving examples of the present invention. Example 1 As shown in Figure 2, alcohol 10wt%, water
Raw material consisting of 90wt% is transferred from raw material supply line 2 to 1
Countercurrent extraction tower (inner diameter 50 mm, height 4
m) 5 kg/h of propane solvent from the top of 1.
is supplied from the lower solvent supply line 25 at a flow rate of
A countercurrent extraction operation was carried out at a temperature of 130° C. and a pressure of 100 Kg/cm ² G. Next, the solvent phase taken out from the solvent phase take-off line 4 at the top of the countercurrent extraction tower 1 is cooled to 60°C in a heat exchanger 5, separated into a light liquid and a heavy liquid in a gravity settling tank 6,
The entire amount of the heavy liquid was refluxed to the upper part of the countercurrent extraction column through the heavy liquid reflux line 11. After reducing the pressure of the light liquid from 100 Kg/cm ² G to 19 Kg/cm ² G by the pressure regulating valve 10, it is introduced into the middle of the extractive distillation column 13, and 2.5 Kg/h of propane solvent is supplied from the solvent line 22 at the top of the column. Extractive distillation with propane was carried out. As a result, the material balance is as shown in Figure 2, and the raw material 10wt% alcohol is 80wt after primary concentration.
%, 95wt% in the second concentration, and 95wt% in the final tertiary concentration.
It was concentrated to 99.9 wt%, and a mixture of absolute alcohol and propane was obtained from the bottom mixed liquid take-off line 14. Anhydrous alcohol and propane have no azeotropic point and have a large difference in boiling point, so they can be completely separated by normal distillation. On the other hand, no alcohol loss was observed throughout the entire process. In addition, the top and bottom temperatures of the extractive distillation column 13 are respectively
They are small at 57℃ and 61℃, which is very advantageous for heat pump systems that utilize the heat of recompression of tower gas, and the process simulation shows that the heat source of the reboiler can be completely supplemented with a small compression ratio of the compressor. It was confirmed by Shion that the energy required for the entire process is approximately 800 kcal/kg of ethanol, which is approximately 1/3 to 1/5 the energy saving of existing distillation methods. Example 2 In Example 1, propylene, n-butane and i-butane were used in addition to propane as the solvent,
Tests were conducted by varying the temperature and pressure of the countercurrent extraction tower, gravity settling tank, and extractive distillation tower, and the preferred temperature and pressure ranges were determined.

【table】

[Table] Comparative example In Example 1, CO ₂ , ethane,
Tests using n-hexane and benzene were conducted, but as shown in Table 2, no absolute alcohol was obtained.

〔Effect of the invention〕

As detailed above, the present invention has an alcohol concentration of 10
When producing anhydrous alcohol by separating water from ~20wt% aqueous solution, specific solvents (propylene, propane, n-butane, i-butane) are used, and the specific properties of the solvent are controlled by changing temperature and pressure. By skillful use, primary, secondary,
and tertiary concentration to easily obtain anhydrous alcohol with an alcohol concentration (99.2wt% or more) that meets the proprietary law and JIS standards.Compared to existing distillation methods, the heat of compression of the solvent is used as a reboiler heat source. The heat pump system has the effect of significantly saving energy.

[Brief explanation of the drawing]

FIG. 1 is a process flow for implementing the present invention, and FIG. 2 is a diagram showing a process flow and material balance showing the results of Example 1.

Claims (1)

[Claims] 1. A raw material mainly consisting of alcohol and water is supplied from the upper part of the countercurrent extraction tower, and one solvent from the group consisting of propane, propylene, n-butane, and i-butane is supplied from the lower part, and the inside of the countercurrent extraction tower is A primary dehydration step in which the solvent is kept in a supercritical or quasi-critical state by contacting them in countercurrent flow, and a solvent phase containing concentrated alcohol is extracted from the upper part of the countercurrent extraction column; the solvent phase is cooled; Gravitational sedimentation separation into a heavy liquid phase rich in water and a light liquid phase containing concentrated alcohol.
The heavy liquid phase is refluxed to the upper part of the countercurrent extraction column in a secondary dehydration step, and after the pressure of the light liquid phase is reduced to below the upper critical pressure of the solvent, it is introduced into the solvent extractive distillation column, and substantially removed from the bottom of the column. A tertiary dehydration step is carried out in which the bottom mixed liquid of alcohol and solvent that does not contain water is extracted from the top of the tower, and the mixed vapor of water and solvent that does not substantially contain alcohol is extracted from the top of the tower, and the mixed liquid at the bottom of the tower is removed as a solvent by distillation. A method for dehydrating alcohol, characterized by comprising a desolvent step of separating it into alcohol.