JPH0369841B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing chlorine by photochemically oxidizing hydrogen chloride.

Currently, the mainstream method for producing chlorine industrially is by electrolysis of common salt, but the mercury method, diaphragm method, and ion exchange membrane method all require huge capital investment, and the co-production method with caustic soda is not recommended. Therefore, the balance between the demand for chlorine and the demand for caustic soda is always an issue. A more important problem is that when producing chlorine-based derivatives in the petrochemical industry, it is common to produce by-products of more than the same mole of hydrogen chloride.

For example, production of allyl chloride, production of vinyl chloride monomer, production of monochlorobenzene, dichlorobenzene, monochloroacetic acid, chloroprene, propylene chlorohydrin, epichlorohydrin, methane chloride, trichlorethylene, tetrachlorethylene, methylchloroethylene, vinylidene chloride, etc. A large amount of hydrogen chloride is generated.

Among these processes, a process to produce dichloroethane and water by oxychlorination of ethylene and hydrogen chloride with oxygen or air, such as dichloroethane, has been established, but in many cases, by-products are produced. Hydrogen chloride is neutralized with an expensive alkaline source,
It is discarded as industrial waste.

Generally, the method of converting hydrogen chloride into chlorine has been known for a long time.

For example, there is the Weldon method, which produces chlorine from hydrochloric acid and manganese dioxide, but in this method, half of the hydrochloric acid used becomes manganese chloride, so the amount of chlorine generated is theoretically only half of the amount of hydrochloric acid used. Moreover, industrially, the yield is only 30 to 40% of the amount used. Also known is the Deacon method, which produces chlorine by direct air oxidation at high temperatures of 450 to 600°C in the presence of a catalyst such as cupric chloride. hand
It is a highly exothermic reaction of 5.2 Kcal/mole, and many catalysts are being studied as applications for this reaction.

Furthermore, there is a hydrochloric acid electrolysis method that electrochemically electrolyzes hydrochloric acid to generate chlorine, but with this method it is necessary to maintain the conductivity of the electrolyte, so it is difficult to completely convert hydrochloric acid into chlorine and hydrogen. Only a portion of the hydrochloric acid is electrolyzed.

As mentioned above, in producing chlorine from hydrogen chloride or hydrochloric acid, the generation of by-products is unavoidable.
Extremely high temperature conditions are unavoidable, and huge capital investment is required.

The present invention provides an excellent method for producing chlorine that drastically improves the drawbacks of the conventional production methods.

That is, in the present invention, when producing chlorine by oxidizing hydrogen chloride by photochemical reaction in the presence of oxygen and/or air, gaseous hydrogen chloride is heated at a pressure and temperature of 10 ^-5 to ¹⁰ cm in a reaction chamber. This method of producing chlorine is characterized by irradiation with pulsed coherent light controlled to have an absorption cross section of ² /mole.

According to the present invention, gaseous hydrogen chloride is irradiated with pulsed coherent light in a reaction chamber, and an absorption cross section of 10 ^-5 -10 ¹⁰ cm ² /mol can be obtained under pressure and temperature conditions in the reaction chamber. This can be achieved by selecting: However, the absorption cross section referred to in the present invention is defined by Lambert-Beer's law I=I ₀ exp (-αl)
is the value of α expressed as Note that here, I is the intensity of transmitted light, I ₀ is the intensity of incident light, and l is the optical path length (absorption step). In the case of a solution, the coefficient α is proportional to the concentration of the solute, and in the case of a gas as in the present invention, it is expressed as α∝PV/T, and is proportional to the pressure P,
It is inversely proportional to temperature T.

This method allows monochromatic light with extremely high photon densities and powers and extremely sensitive wavelengths, and this coherent laser beam enables photoreactions that were previously impossible with conventional light sources. enable.

Known laser light sources are light sources with an ultraviolet, visible and infrared spectrum, but particularly advantageous are excimer lasers with an ultraviolet spectrum. There is essentially no problem even if the hydrogen chloride gas used in the present invention contains moisture and/or some impurities.
Particularly when using hydrogen chloride, a by-product of the chlorination reaction, an advantageous process can be constructed.

The pressure inside the reaction chamber during light irradiation is 0.5 to 20
It is preferable to carry out the reaction under atmospheric pressure, preferably in the range of 1 to 10 atmospheres. Furthermore, the temperature condition is 0~400℃, preferably 100~
It is appropriate to carry out the test in the range of 300℃. When the temperature condition is below the dew point of water, the quantum yield of this reaction is 1 or more, so it is considered that a chain reaction also contributes to this reaction. In that case, the reaction format can be considered as follows.

_{HClhυ ―― → H. ＋ Cl . _} Free chlorine atoms are present.

Laser light can advantageously be used with an impulse time of at least 10 ^-15 seconds and a luminous flux with an energy of 0.01 to 100 Joules.

The laser used in the present invention is not particularly limited, but for example, Nd:YAG (λ = 265nm), KrF
(λ=249nm), KrCl (λ=225nm) or ArF
(λ=193nm). Other suitable lasers are dye lasers or gas lasers in the infrared range. Furthermore, in addition to such coherent light, known incoherent light can also be used in combination. It is presumed that the role of the incoherent light at this time is to promote the dissociation of the generated chlorine, and the generated chlorine radicals act as chain linkers for this reaction. Therefore, the reaction is further promoted by irradiating coherent light into the reaction chamber illuminated with a low-pressure mercury lamp and/or a medium-high pressure mercury lamp.

Furthermore, hydrogen chloride, which is a raw material used in the present invention,
The respective proportions of oxygen can be set arbitrarily. However, considering the complexity of the post-treatment process, it is more appropriate for the hydrogen chloride/oxygen molar ratio to be closer to 4/1. Of course, there is no problem in using air as the oxygen source.
After the oxidation reaction, nitrogen can be removed by purification by liquefaction or alternative purification.

Further, this reaction can be achieved using either a batch system or a continuous system. It is preferable to carry out the process in a continuous manner.

According to the method of the present invention, there is no generation of by-products and the reaction proceeds under relatively low temperature conditions, so that equipment investment is small and it is therefore economically advantageous.

This will be further explained below using examples.

Example 1 A quartz reactor was charged with a krypton fluoride laser beam (λ=
249 nm, power 10 W) was irradiated with a 20 cm absorption step. The absorption cross section α was 1.78×10 ² cm ² /mol. The reaction product contained 2.9 mol/min of chlorine. Chlorine was produced at a conversion rate of 93% and a selectivity of 100%.

Example 2 Using the apparatus of Example 1, under conditions of 3 atm and 200°C, hydrogen chloride was 6.24 mol per minute and oxygen was 1.6 mol per minute.
While charging it, it was irradiated with krypton fluoride laser light (λ = 249 nm, output 10W), and at the same time, it was irradiated with a 100W mercury high-pressure lamp perpendicular to the laser light. In addition, the absorption cross section α is 1.78×10 ²
cm ² /mol. per minute in the reaction products.
It contained 3.12 mol of chlorine. This shows that the reaction is quantitative.

Example 3 Using the apparatus of Example 1, under conditions of 3 atm and 200°C, hydrogen chloride was 6.24 mol per minute and oxygen was 1.6 mol per minute.
Argon fluoride laser light (λ
= 193 nm, output 10 W). The absorption cross section α was 3.25×10 ² cm ² /mol. The reaction product contained 2.8 mol of chlorine per minute. The conversion rate was 90% and the selectivity was 100%.

Reference Example Using the apparatus of Example 1, light was irradiated with a 100W low-pressure mercury lamp under the conditions of 3 atmospheres and 200° C. while charging 6.24 mol of hydrogen chloride and 1.6 mol of oxygen per minute.

Analysis of the reaction product revealed that it contained 0.09 mol of chlorine. This indicates a conversion rate of 3%.

[Brief explanation of drawings]

FIG. 1 shows an example of a reaction apparatus suitable for carrying out the present invention. In the figure, 1...Hydrogen chloride inlet, 2...Oxygen-containing gas inlet, 3...Gas preheater, 4...Reactor, 5
...Laser light irradiation direction, 6...Mercury lamp irradiation direction, 7...
Product outlet.

Claims (1)

[Claims] 1. In producing chlorine by oxidizing hydrogen chloride by photochemical reaction in the presence of oxygen and/or air, gaseous hydrogen chloride is heated at a pressure and temperature of 10 ^-5 to ¹⁰ cm in a reaction chamber. A method for producing chlorine, characterized by irradiation with pulsed coherent light in a controlled state so as to have an absorption cross section of ² /mole. 2 Impulse time of at least 10 ^-15 seconds and 0.01~
2. The method of claim 1, wherein an energy flux of 100 Joules is used. 3. The method according to claim 1 or 2, wherein the light is irradiated under a pressure of 0.5 to 20 atmospheres. 4. The method according to any one of claims 1 to 3, wherein the light is irradiated at a temperature in the range of 0 to 400°C. 5. The method according to any one of claims 1 to 4, in which coherent light and incoherent light are used alternately, or coherent light is irradiated in pulses during irradiation with incoherent light.