JP2779387B2 - Production method of hydrogen chloride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hydrogen chloride gas from an aqueous hydrogen chloride solution.

[0002]

2. Description of the Related Art As a method for producing hydrogen chloride gas from an aqueous solution of hydrogen chloride, an aqueous solution of hydrogen chloride is heated to gasify the dissolved hydrogen chloride, most of the water is removed by a condenser, and then, if necessary, a hydrochloric acid is removed by a dehydrating agent. Hydrogen gas is dehydrated and used for the intended use. However, in the system of water and hydrogen chloride, an azeotropic composition is formed.
The hydrogen phase can be obtained by heating and concentrating the liquid phase up to the weight%, but the hydrogen chloride concentration of the liquid phase cannot be reduced to 20.2% by weight or less. Therefore, the production of hydrogen chloride gas reaches a plateau at this azeotropic composition.

As a method for avoiding this azeotrope, there is a method of adding sulfuric acid to an aqueous solution of hydrogen chloride. However, this method requires a large amount of sulfuric acid or concentrates the aqueous solution of sulfuric acid remaining after the production of hydrogen chloride. The problem is that it cannot be easily executed due to the necessity of equipment for reuse.

[0004]

Among the methods described in the prior art, the method of producing a hydrogen chloride gas by heating an aqueous hydrogen chloride solution is simpler than the method using sulfuric acid.
It is more efficient to lower the concentration on the hydrogen chloride side as much as possible in the azeotropic composition of water and hydrogen chloride. An object of the present invention is to provide a method for simply reducing the concentration of hydrogen chloride on the liquid phase side.

[0005]

Means for Solving the Problems The present inventors have found that the concentration of hydrogen chloride in the liquid phase at the time of azeotropic reduction is reduced by pressurizing the aqueous solution of hydrogen chloride when heating the solution. That is, in the present invention, in a process for continuously producing hydrogen chloride gas by heating an aqueous solution of hydrogen chloride, a continuous distillation column having a reboiler and a condenser and having two or more stages is used, and the pressure is 3 to 7 atm. And an aqueous solution containing 20% by weight or more of hydrogen chloride is heated to a temperature of 70 ° C. or more.
It is heated and continuously supplied to the top or middle of the continuous distillation column, the bottom temperature of the continuous distillation column is set to 130 ° C. or more, and the gas temperature is cooled to 60 ° C. or less by a condenser, and the temperature is slightly increased. This is a method for producing hydrogen chloride in which a hydrogen chloride gas containing water is obtained and an aqueous solution of hydrogen chloride of 18.5 % by weight or less is obtained from the column bottom.

Hereinafter, the present invention will be described in detail. The equipment to be used is a continuous distillation column equipped with a reboiler and a condenser and having two or more stages, and in consideration of the corrosiveness of hydrogen chloride, glass lining, Hastelloy, Inconel,
It must be made of a corrosion-resistant material such as tantalum, resin-impregnated carbon, Teflon, and ceramic. A larger number of columns is advantageous because the concentration of hydrogen chloride in the liquid phase at the bottom of the column is as close as possible to the azeotropic composition at the operating pressure. In practice, two or more columns are required. The reboiler must be capable of boiling the bottom aqueous hydrogen chloride solution at operating pressure. In addition, the condenser must be capable of lowering the gas temperature below a certain level.
Practically, it is desirable that it can be cooled to 60 ° C. or less.

In the present invention, setting of the operating pressure is important.
Under normal pressure, the azeotrope of water-hydrogen chloride has a boiling point of 108.6.
At 20 ° C., the concentration of hydrogen chloride in the liquid phase is 20.2% by weight. The present inventors investigated the vapor-liquid equilibrium of the water-hydrogen chloride system before embarking on the present invention, and found that the hydrogen chloride concentration in the liquid phase was slightly reduced at a pressure of 1.58 atm. However, even at higher operating pressures, no data could be found after investigation. Therefore, when a continuous distillation operation was performed under pressure, the hydrogen chloride concentration in the liquid phase was reduced to 16% by weight at 6.5 atm, and the hydrogen chloride concentration in the liquid phase was reduced as the operating pressure was increased. Therefore, the operating pressure is preferably at least 3 atm, more preferably at least 4 atm. At this time, the bottom of the continuous distillation column becomes the boiling point of the aqueous hydrogen chloride solution at the operating pressure, and the bottom temperature becomes 130 ° C. or higher.

[0008] The hydrogen chloride concentration of the aqueous hydrogen chloride solution supplied to the continuous distillation column needs to be higher than the hydrogen chloride concentration of the liquid phase in the azeotropic state determined by the operating pressure. The concentration of hydrogen chloride is preferably as high as possible. The supply temperature of the aqueous hydrogen chloride solution is desirably about the temperature in the distillation column, and at least 70 ° C. or higher is required. When an aqueous solution of hydrogen chloride at a temperature significantly lower than the temperature in the column is supplied, the aqueous solution of hydrogen chloride at a low temperature causes absorption of hydrogen chloride gas in the column, and the pressure in the column rapidly decreases.
In particular, when the supply flow rate of the aqueous hydrogen chloride solution is changed, the pressure fluctuates greatly, which makes it difficult to stably operate the continuous distillation column, and causes troubles such as flooding. However, if the temperature of the hydrogen chloride aqueous solution to be supplied is about the temperature in the column, at least 70 ° C. or more, even if the aqueous hydrogen chloride solution is supplied into the column, the amount of hydrogen chloride gas absorbed in the hydrogen chloride aqueous solution in the column is It will not hinder the driving.

The feed position to the continuous distillation column should be at the top or the middle of the column, and the bottom should be supplied without effectively using the column. Is far from the azeotropic composition, and the production efficiency of hydrogen chloride gas decreases.

The hydrogen chloride gas thus obtained from the top of the continuous distillation column can be obtained in gaseous form, although it contains saturated moisture corresponding to the temperature cooled by the condenser. In addition, since the distillation operation is performed under pressure, if the pressure of the hydrogen chloride gas consuming equipment is lower than the distillation column operating pressure, the hydrogen chloride gas can be sent to the consuming equipment without any hydrogen chloride transport equipment. Further, the obtained hydrogen chloride gas can be converted to anhydrous hydrogen chloride by performing a dehydration operation using a dehydrating agent known in the art.

The aqueous hydrogen chloride solution obtained from the bottom of the column can be used as it is. For example, it is used as an absorbing solution for crude hydrogen chloride gas mixed with nitrogen, oxygen and the like generated in a chemical plant. If the absorption liquid is treated in a continuous distillation column, the purification of crude hydrogen chloride gas can be performed without waste.

[0012]

The present invention will be further described below with reference to examples. Example 1 An experiment was performed using the continuous distillation apparatus shown in FIG. # 1
Is a supply pump for the aqueous hydrogen chloride solution, # 2 is a continuous distillation column, # 3 is a reboiler, # 4 is a condenser, # 5 is a cooler, # 6 is a pressure regulator in the column, and # 7 is the bottom of the continuous distillation column. A liquid level controller, # 8 indicates a raw material heater.

The # 2 distillation column has a column diameter of 150 mm and a height of 72 mm.
In a 00 mm glass lining tower, Cascade Mini Ring 0X type was packed in two stages to a height of 1500 mm, and the total filling height was 3000 mm. The # 3 reboiler was made of resin-impregnated carbon and had a heat transfer area of 1.7 m ² , and the # 4 condenser was also made of resin-impregnated carbon and had a heat transfer area of 1.7 m ² . All piping connecting each device is made of glass lining.

[0014] The pump 8 through the # 1 pump and the heater # 8
39.4 kg / h of a 36.2% by weight aqueous hydrogen chloride solution at 0 ° C.
H was fed to the top of the distillation column, heated by passing a heat medium through a reboiler, and adjusted to an operation pressure of 5 atm with a column pressure controller. Gas was generated from the top of the column, partly condensed in the condenser, and the condensate was returned to the top of the column, and the uncondensed gas was extracted out of the system as hydrogen chloride gas. After operating for 3 hours until the inside of the system became steady, the hydrogen chloride gas and the concentration of hydrogen chloride in the bottom liquid were analyzed. Table 1 shows the results.

Examples 2 to 5 Experiments were carried out in the same manner as in Example 1 except that the flow rate and operating pressure of the raw material hydrogen chloride were changed. Table 1 shows the results.

[0016]

[Table 1]

Example 6 After the same operation as in Example 1 was performed to reach a steady operation, the supply flow rate of the raw hydrogen chloride aqueous solution was changed to 44.0 kg / H. The pressure in the column hardly changed, and the operation could be continued smoothly.

Comparative Example 1 The feed temperature of the aqueous hydrogen chloride solution to the distillation column was set at a steady operation.
When the same operation as in Example 1 was performed except that the temperature was changed to 20 ° C. in the middle , the pressure in the system rapidly decreased from 5 atm to 4.3 atm, and the top temperature rapidly increased to near the bottom temperature. The operation was stopped on the assumption that the bottom liquid was flushed due to the pressure drop and the flooding phenomenon in the tower.

[0019]

As is apparent from the above description, it is possible to reduce the concentration of hydrogen chloride in the liquid phase at the azeotropic point of the water-hydrogen chloride system by distilling the aqueous solution of hydrogen chloride under pressure. And the production efficiency of hydrogen chloride from the aqueous hydrogen chloride solution is increased. This means that the manufacturing equipment becomes smaller as the manufacturing efficiency increases, the construction cost becomes lower, and its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of equipment using a continuous distillation column for carrying out the present invention.

[Explanation of symbols]

 # 1: Feed pump of raw hydrogen chloride aqueous solution # 2: Continuous distillation column # 3: Reboiler # 4: Condenser # 5: Cooler # 6: Internal pressure regulator # 7: Tower bottom level controller of continuous distillation column # 8: Raw material heater

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-B-33-6964 (JP, B1) JP-B-38-14903 (JP, B1) Chemical Industry Association, Japan, Scientific Equipment Handbook 1977 Maruzen 878 −893 (58) Fields investigated (Int.Cl. ⁶ , DB name) C01B 7/01

Claims (1)

(57) [Claims] In a process for continuously producing hydrogen chloride gas by heating an aqueous solution of hydrogen chloride, a continuous distillation column having a reboiler and a condenser and having two or more stages is used, and the pressure is 3 to 7 atm. And an aqueous solution containing 20% by weight or more of hydrogen chloride is heated to a temperature of 70 ° C. or more and continuously supplied to the top or middle of the continuous distillation column, and the bottom temperature of the continuous distillation column To 130 ° C. or higher, and cool the gas temperature to 60 ° C. or lower with a condenser to obtain a hydrogen chloride gas containing a small amount of water from the top of the tower, and obtain a 18.5 % by weight or less aqueous hydrogen chloride solution from the bottom of the tower. Manufacturing method.