JPS5953204B2 - Method for removing sulfur dioxide contained in hydrogen chloride gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing sulfur dioxide from impure hydrogen chloride gas containing sulfur dioxide.

Impure hydrogen chloride gas containing sulfur dioxide is generated, for example, when common salt is decomposed with sulfuric acid or when cycloalkanone oxime hydrochloride obtained by photonitrosation of cycloalkane is subjected to Beckmann rearrangement using sulfuric acid or fuming sulfuric acid.

As a method for removing sulfur dioxide from such hydrogen chloride gas containing sulfur dioxide, the hydrogen chloride gas is absorbed into dilute hydrochloric acid, the sulfur dioxide in the absorption liquid is oxidized to non-volatile sulfuric acid using an oxidizing agent, and then the absorption liquid is A method of generating and recovering hydrogen chloride by heating, for example (A) Japanese Patent Publication No. 43-2345
9, (B) Japanese Patent Publication No. 42-3376 and (C) Japanese Patent Publication No. 46-32567 are known.

(A) uses nitrite or nitrite as an oxidizing agent; (B)
uses nitrosyl chloride, and (C) uses chlorine.

In these known methods, hydrogen chloride gas containing sulfur dioxide is first absorbed into dilute hydrochloric acid, and after oxidation, the hydrogen chloride gas is recovered by heating, so not only do they require two towers, an absorption tower and a stripping tower, as processing equipment. This is a very unreasonable method from a thermal energy perspective.

Needless to say, it would be industrially advantageous if it were possible to efficiently and selectively remove sulfur dioxide contained as an impurity without substantially absorbing hydrogen chloride gas.

The conventional method for this purpose is (D)
No. 6-31535 and (E) Special Publication No. 16930/1973
It is stated in the No.

In (D), hydrogen chloride gas containing sulfur dioxide is brought into contact with saturated concentrated hydrochloric acid while using nitrosyl chloride as an oxidizing agent, and in (E), hydrogen chloride is brought into contact with nitrosyl sulfuric acid to convert hydrogen chloride into nitrosyl chloride gas and sulfur dioxide is converted into sulfuric acid. It oxidizes and separates into.

The reaction formula for this is as follows.

In these conventional methods, purified hydrogen chloride gas can be obtained by removing the sulfur dioxide contained therein. However, as can be seen from the above reaction formula, hydrogen chloride gas contains nitrogen oxide gas, so hydrogen chloride It is impossible to avoid the restrictions on usage.

Therefore, the present inventors have conducted intensive studies to establish a method that removes only sulfur dioxide while leaving hydrogen chloride in a gaseous state, and does not contain nitrogen oxide gas in purified hydrogen chloride gas, and has developed the present invention. I arrived at the eggplant.

Therefore, it is an object of the present invention to remove sulfur dioxide from hydrogen chloride gas containing sulfur dioxide without consuming more thermal energy than necessary, and to remove hydrogen chloride from hydrogen chloride gas without converting it into hydrochloric acid, leaving it as a gas and containing nitrogen oxide gas. In addition, the sulfur dioxide-containing hydrogen chloride gas generated in the series of steps of photonitrosation and Beckmann rearrangement of cycloalkanes is treated to remove sulfur dioxide and is suitable for reuse. The purpose is to provide a method.

The above object is achieved by using a substantially saturated hydrochloric acid solution containing nitric acid as the hydrochloric acid in a method for removing sulfur dioxide contained in the hydrogen chloride gas by contacting hydrogen chloride gas containing sulfur dioxide with hydrochloric acid. be done.

Specifically, the method of the present invention will be explained in detail with reference to the drawings.

The drawing is a flow sheet of one step in which the method of the present invention is applied.

When the cycloalkanone oxime hydrochloride 2 produced in the cycloalkane photonitronation reaction apparatus 1 is subjected to Beckmann rearrangement with sulfuric acid or oleum 4 in the Beckmann rearrangement apparatus 3, hydrogen chloride is converted as the main component at the same time as the corresponding lactam sulfate 5. Dislocation exhaust gas 6 containing a small amount of sulfur dioxide and the like is generated.

This rearranged exhaust gas is introduced into the oxidation reactor 7 and brought into contact with a substantially saturated hydrochloric acid solution 13 supplemented with nitric acid 12 from the storage tank 8 via the pump 9 and the pipe 11.

Although the hydrochloric acid solution is recycled, the sulfuric acid produced by the following formula accumulates in the circulation system.

SO2+HNO3+HC1→H2SO4+NOCI When the sulfuric acid concentration in the hydrochloric acid solution increases, the absorption of sulfur dioxide is inhibited and the removal efficiency of sulfur dioxide decreases.

Therefore, the sulfuric acid concentration in the hydrochloric acid solution is controlled so as not to reduce the removal efficiency of sulfur dioxide, and for this control, the hydrochloric acid solution is appropriately discharged from the circulation system outlet 10 to the outside of the system.

Hydrogen chloride gas 14 from which sulfur dioxide has been removed and which contains a small amount of nitrosyl chloride is brought into contact with nitrosyl sulfuric acid 16 in a nitrosyl chloride production device 15, and is recycled for photonitrosation reaction as a hydrogen chloride mixed gas 17 containing a considerable amount of nitrosyl chloride. be done.

Next, preferred operating conditions when implementing the present invention in the above steps will be described.

As the sulfur dioxide-containing hydrogen chloride gas that is the object of the present invention, sulfur dioxide may be 30 mol% or less, and further 10 mol% or less.
Those containing the following are preferred.

When sulfur dioxide is contained in an amount exceeding 30%, the amount of nitric acid used increases, and the amount of water that nitric acid brings into the oxidation reaction system increases accordingly, making it difficult to oxidize and remove sulfur dioxide sufficiently.

In the above, a substantially saturated hydrochloric acid solution containing nitric acid refers to an amount of nitric acid sufficient to oxidize sulfur dioxide in hydrogen chloride gas, preferably 1.0 to 1 nitric acid per mole of sulfur dioxide. A solution containing hydrogen chloride gas at a ratio of .5 mol and having an absorption amount of hydrogen chloride gas of 30% or less is preferable.

Here, the absorption amount refers to the amount of hydrogen chloride gas absorbed based on the hydrogen chloride gas supplied into the oxidation reaction system.

The nitric acid used in the present invention includes up to 61% normal nitric acid, fuming nitric acid, or a mixture of both, as well as industrially produced nitric acid, and may also contain other inorganic acids or strong acids such as hydrochloric acid. You may use one that does.

Extremely low concentration of nitric acid increases the amount of water brought in by adding nitric acid, which increases the amount of hydrogen chloride gas absorbed, and the absorbed hydrogen chloride must be recovered by separate treatment such as heating. This is not desirable as it reduces the advantage.

Nitric acid may be added by any method; for example, as shown in the drawing, it may be added to a hydrochloric acid solution circulating outside the apparatus, or it may be added directly into the apparatus.

Further, the addition method may be continuous or intermittent.

The reaction conditions in the oxidation reactor are selected to be a temperature of 10 to 50°C, preferably 20 to 40°C, and a pressure of normal pressure or slightly increased pressure.

Temperatures outside the above range are not good because the sulfur dioxide removal efficiency decreases.

Also, it is not a good idea from a thermal energy perspective.

The method of contacting the hydrogen chloride gas containing sulfur dioxide with the hydrochloric acid solution containing nitric acid is to blow the hydrogen chloride into a reaction tank containing the hydrochloric acid solution, or to use a general gas-liquid contact method such as a perforated plate column or a packed column. It will be held in

In the above oxidation reactor, sulfur dioxide is converted to sulfuric acid, and an equimolar amount of nitrosyl chloride is generated. For example, hydrogen chloride containing sulfur dioxide generated when cycloalkanone oxime hydrochloride is subjected to Beckmann rearrangement with sulfuric acid or fuming sulfuric acid. The generation of nitrosyl chloride is advantageous when the gas treatment is carried out according to the invention and the treated hydrogen chloride gas is sent to the nitrosyl chloride production process.

In the method of the present invention, it is presumed that the nascent chlorine produced by adding nitric acid to the hydrochloric acid solution effectively acts on the oxidation of sulfur dioxide.

This is derived from the fact that as a result of comparing the case where nitric acid is added to the oxidation reaction system as an oxidizing agent and the case where chlorine gas is added as an oxidizing agent, the nitric acid addition method of the present invention has a high sulfur dioxide removal efficiency.

As described above, the feature of the present invention is that impure hydrogen chloride gas containing sulfur dioxide is brought into contact with a substantially saturated hydrochloric acid solution containing nitric acid, whereby the impurity sulfur dioxide is oxidized to sulfuric acid and the hydrochloric acid solution is This method can be recovered and reused without substantially absorbing and removing hydrogen chloride gas and containing no nitrogen oxide gas, and - compared to conventionally known methods, the processing equipment is simpler. Furthermore, since it is compatible with recent energy saving measures, it can be effectively used not only in the above-mentioned Beckmann rearrangement process but also in a wide range of industrial applications.

Next, the effects of the method of the present invention will be described using examples.

Example 1 Concentrated hydrochloric acid 11 was placed in a glass reaction tube with a diameter of 55 mm and a length of 500 mm, and hydrogen chloride gas containing 1.20 vol.
Introduced at a rate of 1/min, while 30 min.
While continuously adding wt% of nitric acid to concentrated hydrochloric acid in an amount equivalent to the sulfur dioxide, the temperature of the concentrated hydrochloric acid was lowered to 3% by external cooling.
It was kept at 0°C.

As a result of the 2-hour treatment, the sulfur dioxide content in the hydrogen chloride gas for the reaction tube that passed through the concentrated hydrochloric acid in the form of bubbles was 0.04 vol%, and the sulfur dioxide removal rate was equivalent to 97%.

Furthermore, the concentration of nitrosyl chloride in the reaction tube gas was measured to be 1.20 vol%.

Example 2 The same procedure as in Example 1 was conducted except that a saturated hydrochloric acid solution containing 16 vol. % of sulfuric acid was used instead of concentrated hydrochloric acid.

The sulfur dioxide concentration in the reaction tube gas was 0.06 vO1%, and the sulfur dioxide removal rate was 95%.

Example 3 5X5X3 in a glass tube with a diameter of 30mm and a length of 1200mm
Hydrogen chloride gas containing 1.10 vol.
00ml/min, while 20wt of sulfuric acid
% of saturated hydrochloric acid solution at 20°C.
The hydrochloric acid solution was supplied from the top of the column at a rate of 1/min, and 20 wt % nitric acid was continuously added to the hydrochloric acid solution at a molar ratio of 1.1 times that of sulfur dioxide.

The sulfur dioxide concentration in the bath gas was 0.04 vol%, and the sulfur dioxide removal rate was 96%.

Example 4 0.90 vol of sulfur dioxide generated by rearranging cyclohexanone oxime hydrochloride obtained by photonitrosation reaction with sulfuric acid
The same procedure as in Example 3 was carried out except that a dislocation exhaust gas containing 1% was used.

The sulfur dioxide concentration in the bath gas was 0.04 vol%, and the sulfur dioxide removal rate was 96%.

Comparative Example A process was carried out in the same manner as in Example 1, except that instead of 30 wt % nitric acid in Example 1, chlorine gas of equimolar amount to nitric acid was introduced into the sulfur dioxide-containing hydrogen chloride as an oxidizing agent.

The sulfur dioxide concentration in the reaction tube gas was 0.60%, and the sulfur dioxide removal rate was 50%.

[Brief explanation of drawings]

The drawing is a flow sheet showing one step in which the method of the present invention is applied. 1...Photonitrosation reaction device, 3...
Beckmann rearrangement device, 6... Hydrogen chloride gas containing sulfur dioxide, 7... Oxidation reaction device, 8...
...Storage tank, 12...Nitric acid, 13...
Hydrochloric acid solution, 14...Hydrogen chloride gas containing nitrosyl chloride, 15...Nitrosyl chloride production equipment.

Claims (1)

[Claims] 1. A method for removing sulfur dioxide contained in hydrogen chloride gas by contacting hydrogen chloride gas containing sulfur dioxide with hydrochloric acid, characterized in that a substantially saturated hydrochloric acid solution containing nitric acid is used as the hydrochloric acid. A method for removing sulfur dioxide contained in hydrogen gas.