JPH05132302A - Method for purifying hydrogen chloride gas - Google Patents

Abstract

PURPOSE:To lower organic acid concentration in a hydrogen chloride gas by bringing a crude hydrogen chloride gas containing an organic acid into contact with sulfuric acid solution. CONSTITUTION:A crude hydrogen chloride gas containing 500-1000ppm organic acid is introduced from an inlet pipe 2 into the bottom of an adsorbing gas. A sulfuric acid solution containing <=30wt.% organic acid and kept at -10 to 30 deg.C is introduced into the top of an adsorbing tower 4 and brought into countercurrent contact with the organic acid and the liquid is passed through a pump 5 and a heat exchanger 6 to control the temperature and fed to the tower top of the absorbing tower 4. The purified hydrogen chloride gas is taken out through an inlet pipe 7 and a sulfuric acid mist separator 8 from an inlet pipe 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to purification of hydrogen chloride gas. More specifically, it relates to a method of separating an organic acid by treating hydrogen chloride gas containing the organic acid with sulfuric acid.

[0002]

2. Description of the Related Art Conventionally, various methods for purifying hydrogen chloride gas containing an organic acid have been proposed. For example, compression liquefaction distillation method (Japanese Patent Publication No. 42-174), extraction method (Japanese Patent Publication No. 49-42796), thermal decomposition method (Japanese Patent Publication No. 56-116).
43) etc., but these require complicated steps,
In addition, it consumes a large amount of auxiliary agents, energy, etc., and is not industrially sufficiently satisfactory.

Of these, the thermal decomposition method is a relatively easy and reliable refining method, but a facility for reacting chlorine gas and hydrogen gas to produce synthetic hydrochloric acid is required, and synthetic hydrochloric acid is not required. Not usable by the way. There is a limit to the amount of crude hydrogen chloride gas that can be treated with respect to the production amount of synthetic hydrochloric acid.

On the other hand, it is known that some organic compounds dissolve in concentrated sulfuric acid, and if hydrogen chloride gas containing an organic compound soluble in concentrated sulfuric acid is brought into contact with sulfuric acid, hydrogen chloride gas Is hardly dissolved in sulfuric acid, the organic compound in hydrogen chloride gas is selectively dissolved in sulfuric acid, and purification of hydrogen chloride gas can be expected to some extent. However, there are few examples in which hydrogen chloride gas is actually highly purified by contact with sulfuric acid.

The reason for this is that it is difficult in terms of vapor-liquid equilibrium to reduce the concentration of organic compounds in hydrogen chloride gas to a concentration that can actually be called purified hydrogen chloride gas, and sulfuric acid-organic compounds-
This is probably because the vapor-liquid equilibrium relationship of the hydrogen chloride ternary system was not known in detail, or even if high-level purification was possible, the amount of sulfuric acid used was large and could not be economically established as a purification technique. As a slight refining method of this kind, a refining method in which hydrogen chloride gas containing acetyl chloride is contacted with a washing liquid composed of water, acetic acid and sulfuric acid to remove acetyl chloride from the hydrogen chloride gas (Japanese Patent Laid-Open No. 51-143596). Has been reported. However, in such a purification method, acetic acid content of about 200 ppm (volume basis, the same applies hereinafter) remains as an impurity in hydrogen chloride gas, and therefore cannot be directly used in other manufacturing steps except for some applications.

[0006]

SUMMARY OF THE INVENTION The present invention has the above-mentioned drawbacks,
That is, the present invention provides a method for purifying crude hydrogen chloride gas containing an organic acid extremely economically without problems such as the use of complicated equipment and restrictions on use.

[0007]

The present inventors have studied in detail the gas-liquid equilibrium relationship between an organic acid and sulfuric acid and hydrogen chloride, which have not been known in detail in the past, and as a result, It was found that it can be easily and economically refined by bringing it into contact with sulfuric acid.

That is, the first invention of the present invention is characterized in that in the method for removing the organic acid from the hydrogen chloride gas containing the organic acid, the crude hydrogen chloride gas is brought into contact with a sulfuric acid solution. A second aspect of the present invention is a method for purifying hydrogen chloride gas, wherein a sulfuric acid solution containing a maximum of 30% by weight of an organic acid is added.
The method for purifying hydrogen chloride gas according to claim 1, wherein the crude hydrogen chloride gas is contacted at a temperature of 10 to 30 ° C.

Typical organic acids applicable to the present invention include formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, pivalic acid, lauric acid, myristic acid, palmitic acid, stearic acid, acrylic acid, Monocarboxylic acids such as propiolic acid, methacrylic acid, crotonic acid, oleic acid, benzoic acid, and oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, maleic acid And dicarboxylic acids such as fumaric acid, itaconic acid, phthalic acid, isophthalic acid, and terephthalic acid.

As an impurity, 500 of the above organic acids is used.
The crude hydrogen chloride gas containing 1000 ppm to 1000 ppm was added to a sulfuric acid solution containing these organic acids in an amount of 0 to 30% by weight.
Using a known absorption tower such as a packed tower at a temperature of up to 30 ° C. to efficiently bring them into contact with each other to selectively dissolve an organic acid in hydrogen chloride gas in sulfuric acid to purify hydrogen chloride gas. You can

The reason why the sulfuric acid solution containing 0 to 30% by weight of acetic acid is selected is mainly due to economic reasons and restrictions due to the gas-liquid equilibrium relationship. Therefore, in order to be industrially advantageous, while keeping the organic acid concentration in the purified hydrogen chloride gas below an allowable constant concentration, the organic acid in the crude hydrogen chloride gas should be added as much as possible to the sulfuric acid solution that is the absorbing liquid. It is preferable to dissolve it.

According to the research conducted by the present inventors, the dissolution of an organic acid contained in hydrogen chloride gas in a sulfuric acid solution depends on the concentration of the organic acid in the sulfuric acid solution in contact with the hydrogen chloride gas. A certain gas-liquid equilibrium relationship is established between the organic acid concentration in the solution and the organic acid concentration in sulfuric acid. Therefore, in order to keep the concentration of the organic acid in the purified hydrogen chloride gas below a certain concentration, it is important to control the concentration and temperature of the organic acid in the sulfuric acid solution which is the absorbing liquid.

The organic acid concentration in the sulfuric acid solution is 30
It is preferable to set the content to not more than 30% by weight, and if it exceeds 30% by weight, it becomes difficult to keep the concentration of the organic acid in the purified hydrogen chloride gas below 10 ppm.

The temperature of the sulfuric acid solution is -10 to 30.
It is necessary to keep at ℃. The reason for this is that the temperature of the absorbing liquid is
Lowering the temperature below 10 ° C causes problems such as freezing of the absorption liquid, increase in viscosity, and the need for a large refrigerator.
With the above, the concentration of organic acid in the purified hydrogen chloride gas is 10 ppm.
It is very difficult to keep below. Since the freezing point of the sulfuric acid solution changes depending on the concentration of the contained organic acid, the optimum operating temperature is in the temperature range of -10 to 30 ° C, the type of organic acid and the allowable organic acid concentration in the purified hydrogen chloride gas. Also, it is determined by comprehensively considering the utility usage cost, etc.

The method for contacting the crude hydrogen chloride gas with the absorbing solution may be any method as long as it can sufficiently contact the gas-liquid, but an absorption tower is usually used. As the absorption tower, a known tower such as a packed tower or a tray tower can be used as long as it has a theoretical plate number of 10 or more. Further, in this case, it is important to select the tower diameter such that the superficial velocity of hydrogen chloride gas is about 0.4 m / sec.

Next, the method of the present invention can be carried out by either a batch method or a continuous method. In the case of the continuous method, while the sulfuric acid solution, which is the absorbing solution, has a concentration of the organic acid not exceeding 30% by weight, preferably 20% by weight, while extracting a part of the absorbing solution from the absorption tower, concentrated sulfuric acid is used. Need to be supplied to the absorption tower.

The present invention is particularly applicable as an impurity of 1000 pp.
10 p of organic acid in hydrogen chloride gas containing organic acid of m or less
It is useful as a method for purification to pm or less. 1 organic acid
The method of the present invention can be applied even when it contains 000 ppm or more, but in this case, the absorption tower becomes large and the amount of sulfuric acid used also increases. In fact, 1 in hydrogen chloride gas
When the organic acid is contained in an amount of 000 ppm or more, it can be easily reduced to 500 to 1000 ppm by another method such as cooling. Therefore, it is possible to apply the purification method of the present invention after performing these pretreatments. It is advantageous.

[0018]

The present invention will be specifically described with reference to the following examples.

Example 1 Hydrogen chloride gas containing about 800 ppm of acetic acid as an impurity was blown into 1 liter of concentrated sulfuric acid at a rate of 1 Nm ³ / H at 20 ° C. to make gas-liquid contact. Blowing about 10
After 0 hour, the hydrogen chloride gas after gas-liquid contact was analyzed by gas chromatography to find that the acetic acid content was 5 ppm.
At this time, acetic acid in hydrogen chloride gas was absorbed by sulfuric acid over time, and the concentration of acetic acid in sulfuric acid increased to 10% by weight. This operation was further continued, and after 200 hours, the acetic acid concentration in sulfuric acid became 20% by weight, but the acetic acid concentration in hydrogen chloride gas after the gas-liquid contact was kept at 8 ppm. Below 400
The results of continuing this operation until time are shown in Table 1.

Embodiment 2 Next, a case where the flow is shown in FIG. 1 will be described. As an impurity, 500-1000 pp of acetic acid, which is a by-product when producing monochloroacetic acid from acetic acid and chlorine
Hydrogen chloride gas containing 50 m ³ / h containing m was introduced into the bottom of the absorption tower 4 (height 3000 mm, tower diameter 200 mm packed tower) from the introduction pipe 2, and the sulfuric acid solution 300 containing 20% by weight of acetic acid introduced from the tower top. Continuous countercurrent contact with liter / h at 20 ° C was carried out. The liquid flowing out from the bottom of the absorption tower 4 is pump 5
The temperature is adjusted through the heat exchanger 6 using the absorption tower 4
Was supplied to the top of the tower. The washed hydrogen chloride gas was made into purified hydrogen chloride through the conduit 7 to the sulfuric acid mist separator 8 and taken out from the conduit 9. As a result, the acetic acid concentration in the hydrogen chloride gas after the gas-liquid contact was 10 ppm or less over 960 hours when gas chromatographic analysis was performed every 6 hours. In order to keep the concentration of acetic acid in the sulfuric acid solution below a certain concentration, fresh sulfuric acid was replenished from conduit 1 and a part of the sulfuric acid solution in which acetic acid was dissolved was extracted from conduit 3.

Example 3 Hydrogen chloride gas containing 500 ppm of acetic acid as an impurity was brought into contact with a sulfuric acid solution containing 10% by weight of acetic acid at a temperature of −7 ° C. in the same manner as in Example 2. As a result, the concentration of acetic acid in hydrogen chloride gas was 1 ppm or less.

Example 4 Crude hydrogen chloride gas containing 100 to 1000 ppm of chloroacetic acid as an impurity was purified by the same method as in Example 2. Purified hydrogen chloride gas at regular intervals,
As a result of gas chromatographic analysis, chloroacetic acid was not detected. (Detection limit of chloroacetic acid: 1 pp
m)

[0023]

[Table 1]

[0024]

According to the present invention, an organic acid, especially 100-
Treating crude hydrogen chloride gas containing 1000 ppm of carboxylic acid with concentrated sulfuric acid solution facilitates and economically
It can be refined to below ppm. Therefore, the hydrogen chloride gas purified by the present invention can be used for other purposes as it is.

[Brief description of drawings]

FIG. 1 is a process explanatory view showing an embodiment of the present invention.

[Explanation of symbols] 1 concentrated sulfuric acid inlet 2 crude hydrogen chloride gas inlet 3 discharge outlet of sulfuric acid solution in which organic acid is dissolved 4 absorption tower 5 sulfuric acid circulation pump 6 water cooler 7 wash hydrogen chloride gas outlet 8 sulfuric acid mist separator 9 Purified hydrogen chloride gas outlet

Claims (2)

[Claims] 1. From hydrogen chloride gas containing an organic acid,
A method for purifying hydrogen chloride gas, which comprises contacting the crude hydrogen chloride gas with a sulfuric acid solution in the method for removing the organic acid. 2. A sulfuric acid solution containing up to 30% by weight of an organic acid,
The method for purifying hydrogen chloride gas according to claim 1, wherein the crude hydrogen chloride gas is contacted at a temperature of -10 to 30 ° C.