JPH0811161B2 - Method for separating impurities in high-concentration ethanol - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for separating impurities derived from a gas solvent contained in high-concentration ethanol obtained by extracting water-containing ethanol with a gas solvent in the vicinity of a critical point.

[0002]

Fermented alcohols made from carbohydrates such as sweet potatoes, sweet potatoes and corns are important starting materials for beverages and industrial purposes, but the alcohol concentration of the aqueous alcohol solution obtained by the fermentation method is 10 to 20% by weight. Therefore, it is necessary to concentrate to about 95 to 100 wt%. Conventionally, a distillation method has been used as the concentration method, but water, which occupies most of the concentration method, has to be heated to 80 to 100 ° C., which is economically disadvantageous, and an alternative energy-saving type concentration method is used. Development is desired.

On the other hand, as an energy-saving type concentration method, a method has been proposed in which carbon dioxide in a supercritical state or a pseudocritical state is used to extract and separate alcohol from water to concentrate it.
(JP-A-56-56201 and JP-A-59-141528) However, when carbon dioxide is used as a solvent, there is a limit to the selective extraction of alcohol, and the maximum concentration is about 91 wt%. It has recently been reported that it is impossible to further concentrate. Further, since the solubility of alcohol in carbon dioxide gas is not sufficiently large, there is a problem that a large amount of carbon dioxide gas (15 parts by weight or more per 1 part by weight of 10% alcohol aqueous solution) is required. Is desired.

Therefore, at present, there is a demand for a method capable of improving the alcohol concentration and increasing the alcohol solubility. In response to this demand, the present inventors have previously made an improvement using a carbon dioxide gas solvent near the critical point. Method for Dehydrating Ethanol (Japanese Patent Application No. 1-160697) and Energy-saving Method for Dehydrating Ethanol Using Propane, Butane, and Propylene Solvents Near the Critical Point (Japanese Patent Application No. 1-160696,
Japanese Patent Application No. 1-294032).

However, in these proposed methods, in order to substantially eliminate gases such as propane, butane, propylene and CO ₂ dissolved in dehydrated ethanol,
Pressure distillation has to be carried out, the lower temperature of the distillation column being the boiling point of ethanol at its operating pressure (10-35 atm.), Which is in the range 100-210 ° C. However, when the distillation operation was carried out in a stainless steel distillation column or a carbon steel distillation column under these temperature conditions, impurities such as acetaldehyde and ethyl ether were produced in the range of several tens of ppm, failing to meet the alcohol proprietary standard for industrial alcohol. There was found.

[0006]

DISCLOSURE OF THE INVENTION The present invention separates gases such as propane, butane, propylene and carbon dioxide, which are present in high-concentration ethanol obtained by the method proposed by the present inventors, by pressure distillation. An object of the present invention is to provide a method capable of preventing the production of trace impurities such as acetaldehyde and ethyl ether due to the thermal decomposition reaction of ethanol upon removal, and obtaining ethanol that can pass the proprietary alcohol standard (industrial alcohol). Is.

[0007]

The present invention SUMMARY OF] is a a method of separating impurities from the gas solvent high concentrations of ethanol obtained by extracting the water-containing ethanol gas solvent in the vicinity of the critical point in the pressure distillation tower And the pressure distillation at which the number of stages from the high-concentration ethanol raw material inlet to the bottom reboiler of the pressure distillation column is sufficient to eliminate dissolved oxygen in the high-concentration ethanol raw material and the temperature is 100 ° C. or higher. The method for separating impurities in high-concentration ethanol is characterized in that the material of the tower is copper or copper-plated material.

[0008]

The operation of the present invention will be described in detail below with reference to FIG. In FIG. 1, 1 is a raw material supply line (propane, butane, propylene or CO
Ethanol in which light gas such as ₂ is dissolved) 2 is a pressure distillation column, 3 is a tray (or packed bed), 4 is a heater,
5 is a bottom liquid part, 6 is a bottom liquid extraction line (ethanol substantially containing no light gas), 7 is a bottom liquid level control valve,
8 is a top gas extraction line (light gas that does not substantially contain ethanol), 9 is a compressor, 10 is a cooler,
11 is a separation tank, 12 is a water (liquid) extraction line, 13
Is an O ₂ or N ₂ purge line, 14 is a reflux line (liquid light gas), 15 is an overhead reflux line, 16 is a light gas extraction line, and 17 and 18 are flow control valves.

Propane, butane, propylene or CO
Ethanol in which a light gas such as ₂ is dissolved is supplied from the raw material supply line 1 to the middle part of the pressure distillation column 2. These light gases and ethanol can be easily separated by a distillation operation without forming an azeotropic composition. Ethanol containing substantially no light gas is extracted from the bottom liquid extraction line 6 and substantially separated from the top gas extraction line 8. It is possible to extract light gas that does not contain ethanol.

The light gas in the overhead gas extraction line 8 is recompressed by the compressor 9, cooled and liquefied by the cooler 10 and sent to the separation tank 11, where water is taken out from the water take-out line 12, and O ₂ , N ₂ purge line 1
No. 3, O ₂ , N ₂ and C which may be dissolved in the raw material
Purge gases such as H ₄ .

The liquefied light gas is taken out from the reflux line 14, is refluxed from the overhead reflux line 15 to the top of the pressure distillation column 2 through the flow control valve 17, and is dissolved in the raw material from the light gas removal line 16. The entire amount of the light gas that has been discharged is taken out through the flow rate control valve 18.

The light gas in the light gas extraction line 16 needs to be circulated for reuse as an extraction solvent. Therefore, in order to reduce the circulating power, the pressure distillation column 2 is used.
It is necessary to increase the operating pressure of 10 to 40 kg / cm ² G. Under this pressure, the bottom liquid of the bottom liquid portion 5 has a boiling point of 100% ethanol at that pressure,
Since the temperature became as high as 0 ° C., a phenomenon in which trace amounts of impurities such as acetaldehyde and ethyl ether were generated due to the reaction of ethanol was observed, and the alcohol monopoly standard (industrial alcohol) was not passed.

The inventors of the present invention have made extensive studies as to a method for preventing trace impurities from being produced. As a result, copper is used as a material for the distillation column to prevent the formation of ethyl ether, and dissolved oxygen in the raw material is used in advance to prevent the formation of acetaldehyde. The present invention has been completed by discovering that the problem can be solved by setting the number to zero or providing a sufficient number of stages for stripping oxygen in the portion below the raw material supply position.

[0014]

EXAMPLES The effects of the present invention will be proved by the following test examples of the present invention. Reagent grade ethanol was charged into a container made of stainless steel (SUS304), carbon steel (STS38), copper, and glass, and the temperature was 2 under N ₂ pressure and air pressure.
It was kept at 10 ° C. for 10 minutes, and the presence or absence of trace impurities in ethanol was analyzed by gas chromatography.

From the above, in the case of the glass container, no impurities were generated at all, but it is difficult and expensive to coat the inner surface of the pressure container with glass, which is not practical.
On the other hand, in the case of stainless steel and carbon steel, acetaldehyde,
Several 10 ppm of ethyl ether and isoamyl alcohol were produced. In the case of copper, about 200 ppm of acetaldehyde was produced under the pressure of air, but no trace impurities were detected under the pressure of N ₂ , which was a preferable result.

[0016]

According to the present invention, the previously proposed method (for example, Japanese Patent Application Nos. 1-160696 and 1-294032).
No. 1 to 160697), it is possible to produce industrial alcohol that can pass the alcohol monopoly standard with significantly less energy than the conventional distillation method.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Goo Yamamoto 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory Koichi Nakano (56) Reference JP-A-2-196739 (JP, A) JP-A-3-157340 (JP, A) JP-A-3-27336 (JP, A) JP-A-3-27337 (JP, A)

Claims (1)

[Claims] 1. A impurities from the water-containing ethanol to the gas solvent high concentrations of ethanol obtained by extraction with a gas solvent in the vicinity of the critical point to a process for separating at pressure distillation column, pressurizing the distillation column The number of stages from the inlet of the high-concentration ethanol raw material to the bottom reboiler is sufficient to eliminate the dissolved oxygen in the high-concentration ethanol raw material, and the temperature is 100.
A method for separating impurities in high-concentration ethanol, characterized in that the material of the pressure distillation column having a temperature of ℃ or higher is copper or copper-plated material.