JPH0149131B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing vinyl chloride by thermally decomposing 1,2-dichloroethane. The method of producing vinyl chloride by thermally decomposing 1,2-dichloroethane is well known and is commonly used industrially.
Reaction conditions of 400-550℃ and 4-30 atm were adopted.
The plant is operated at a decomposition rate of 50-60% for 1,2-dichloroethane. If the decomposition rate is increased to more than 60%, coke will accumulate in the reaction tube and the operation will have to be stopped, and by-products such as chloroprene, acetylene, other chlorinated hydrocarbons, tar, and carbon will increase, causing chlorination. Vinyl yield decreases. but,
Even if the decomposition rate is maintained at 50-60% as is generally adopted, by-products mainly consisting of chloroprene and acetylene are usually produced at 1000-3000 ppm each. Industrially, after the thermal decomposition products are rapidly cooled, hydrogen chloride is separated in a first distillation column, and then in a second distillation column.
Usually, vinyl chloride and unreacted 1,2-dichloroethane are separated in a distillation column. Here, by-product acetylene is not separated from hydrogen chloride, and hydrogen chloride containing acetylene is directly supplied to the next oxychlorination step, where it is reacted with ethylene and oxygen (or air) to produce 1,2-dichloroethane. It will be collected. At this time, acetylene is oxychlorinated together with ethylene and converted into dichloroethylene, trichlorethylene, tetrachlorethylene, and other chlorinated hydrocarbons, resulting in wasteful consumption of hydrogen chloride. Furthermore, since trichlorethylene produced in the oxychlorination step is difficult to separate from 1,2-dichloroethane, it is supplied as is to the thermal decomposition step, but it exhibits the effect of suppressing the rate of thermal decomposition. for that,
A method for removing trichlorethylene by chlorination has been studied and is being implemented industrially, but it wastes chlorine and is uneconomical. A method is also known in which hydrogen chloride containing acetylene is selectively converted to ethylene in the presence of a palladium catalyst by adding hydrogen before it is fed to the oxychlorination process, thereby preventing the formation of trichlorethylene in the oxychlorination process. has been developed and is being implemented industrially. However, in general, the selectivity to ethylene is not sufficiently high, and there are problems with the life of the catalyst, so it is estimated that it is not very advantageous economically. On the other hand, chloroprene is extracted as a bottom liquid from the second distillation column along with unreacted 1,2-dichloroethane, but since the chloroprene is concentrated in the distillation column, it polymerizes and blocks the distillation column, causing the operation to be interrupted. There are often cases where it is necessary. 1,2-dichloroethane containing chloroprene is purified by chlorinating chloroprene to convert it into a high-boiling substance and then separating it by distillation, or by removing chloroprene by distillation separation, and then supplied to the thermal decomposition process again. . In this case, it is uneconomical because chlorine is consumed and the distillation separation method requires dilution to a concentration below which chloroprene starts polymerization. As mentioned above, in the conventional method, it is not possible to avoid the by-product of acetylene and chloroprene during the thermal decomposition of 1,2-dichloroethane, which causes problems such as deterioration of the yield of vinyl chloride and the inability to continue stable operation for a long period of time. It has caused drawbacks. In research on catalytic cracking of 1,2-dichloroethane using catalysts, for example, a method for catalytic cracking of 1,2-dichloroethane at 350 to 400°C using a fluorine-treated platinum-alumina catalyst [Khim.
Prom. 48 (10) 741 ('72)], it is known that when 1/2.1 mol of hydrogen is added per 1 mol of 1,2-dichloroethane, by-produced acetylene and coke decrease and ethylene increases. This method gives one suggestion for the production of acetylene, but does not mention chloroprene. Also, a method without using a catalyst like the method of the present invention,
It is not clear whether a similar phenomenon occurs in thermal decomposition reactions at reaction temperatures of 400 to 550°C. As a result of intensive research to overcome the drawbacks of conventional methods, the present inventors discovered a method for suppressing the by-products of chloroprene and acetylene without inhibiting the thermal decomposition reaction of 1,2-dichloroethane, and accomplished the present invention. I've reached it. The present invention enables 1,2-dichloroethane to be produced without a catalyst.
In producing vinyl chloride by thermal decomposition at 400 to 550°C, 1,2-dichloroethane is thermally decomposed by adding 0.05 to 3.0 moles of hydrogen per 100 moles of 1,2-dichloroethane. The gist is the manufacturing method. In the method of the present invention, the amount of hydrogen added is 0.05 to 3.0 mol, preferably 0.2 to 1.0 mol, per 100 mol of raw material 1,2-dichloroethane. If the amount of hydrogen added is small, the effect of suppressing chloroprene and acetylene will be small, and if the amount of hydrogen added is large, 1.
Suppress the thermal decomposition rate of 2-dichloroethane. Further, since unreacted hydrogen is supplied to the oxychlorination step together with hydrogen chloride, it is not preferable to add a large amount of hydrogen from the viewpoint of safety in the oxychlorination step. Practically 1.0 hydrogen per 100 moles of 1,2-dichloroethane
Even if more than one mole is added, the inhibitory effects of chloroprene and acetylene remain unchanged. Therefore, it is preferable to add 0.2 to 1.0 moles of hydrogen per 100 moles of 1,2-dichloroethane. Hydrogen is obtained by electrolysis of sodium chloride and can be used as it is, but hydrogen obtained from other sources may also be used, and there is no particular restriction for the purposes of the present invention. Furthermore, the method of the present invention can also be applied as is when a small amount of carbon tetrachloride, trichlorethylene, or other impurities in industrially used 1,2-dichloroethane are present in 1,2-dichloroethane. , no particular influence of these impurities was observed. If the amount of hydrogen added is maintained within the above range, 1.2
-Since the decomposition rate of dichloroethane is not particularly affected by the addition of hydrogen, the thermal decomposition conditions for 1,2-dichloroethane can be the same as in the conventional method, and the reaction temperature can be 400 to 550°C. .
Industrially, it is possible to maintain the decomposition rate of 1,2-dichloroethane at 50 to 60% by operating under 4 to 30 atmospheres as with the conventional method, and requires no new equipment except for the addition of hydrogen addition equipment. There's no need to make money.
A known method is to add carbon tetrachloride as a thermal decomposition accelerator in order to increase the decomposition rate of 1,2-dichloroethane to a level higher than that of conventional methods or to lower the thermal decomposition temperature. In this case, there is no problem even if the method of the present invention is applied as is, and by adding hydrogen, the amount of by-products of chloroprene and acetylene can be suppressed. As shown in the examples, the method of the present invention, for example, produces more acetylene than the conventional method in a reaction at normal pressure when the decomposition rate of 1,2-dichloroethane is 58%.
It can reduce 100-200ppm, chloroprene by 500-1200ppm. In particular, the effect of suppressing the amount of chloroprene by-product is 25% to 45% compared to conventional methods.
can be reduced. These effects can also be obtained under industrial operating conditions. Furthermore, even in the method of the present invention, the effect of suppressing by-product acetylene is not sufficient, and the formation of trichlorethylene in the oxychlorination step due to acetylene cannot be avoided. However, after carrying out the method of the present invention, a selective hydrogenation method of acetylene in hydrogen chloride using a palladium catalyst is applied to selectively convert acetylene to ethylene, thereby preventing the by-product and accumulation of trichlorethylene. be able to. In this case, there is no need to newly supply hydrogen to the selective hydrogenation equipment from outside,
Since most of the hydrogen used in the method of the present invention remains, hydrogen and acetylene-containing hydrogen chloride may be supplied as they are to the hydrogenation equipment. The present invention will be explained below by way of examples. Example 1 Inner diameter with a thermometer protection tube with an outer diameter of 6 mm inside
A 16.7 mm stainless steel tube was used as a reaction tube, and the reaction was carried out by heating from the outside with a tubular electric furnace having a length of 60 cm and maintaining it at a predetermined temperature. 1 mole of purified 1,2-dichloroethane, 0.25 mole of nitrogen and a predetermined amount of hydrogen were fed into the reaction tube through a 1,2-dichloroethane vaporizer per hour. After the reaction tube outlet gas was cooled and washed with water, the produced gas and produced liquid were analyzed by gas chromatography. Table 1 shows the results of reactions with varying amounts of hydrogen added to 1,2-dichloroethane. Since a temperature distribution occurred in the axial direction of the reaction tube, Table 1 shows the effective average temperature (tav) as the reaction temperature. The effective average temperature was determined by the method of Nobuo Otake, "Reactor Design" (1956, Science and Technology Publishing), with an activation energy of 28 Kcal/mol. 1,2-dichloroethane (hereinafter referred to as EDC)
The decomposition rate and selectivity of by-products were determined using the following formula. Decomposition rate (%) = (1 - number of moles of unreacted EDC / number of moles of supplied EDC) × 100 Selectivity (%) = (number of moles of by-product / number of moles of reacted EDC) × 100 RUN N 101~ 104 is a control example in which no hydrogen is added.

[Table] Example 2 The same procedure as in Example 1 was carried out except that 1,2-dichloroethane containing 2400 ppm of carbon tetrachloride was used. The results are shown in Table-2.

[Table] Example 3 Trichlorethylene 400ppm, carbon tetrachloride
The same procedure as in Example 1 was carried out except that 1,2-dichloroethane (industrial product) containing 900 ppm was used. The results are shown in Table-3.

【table】

[Table] In all of Examples 1 to 3, it is clear from the diagram of the decomposition rate of 1,2-dichloroethane with respect to the effective average temperature that if the amount of hydrogen added is appropriately adjusted as described above, 1,2-dichloroethane can be reduced. It can be seen that the decomposition rate of is not suppressed (Figure 1). Also,
If the selectivity of by-products is plotted against the decomposition rate of 1,2-dichloroethane, it can be seen that chloroprene and acetylene are reduced by adding hydrogen. An example is shown in Figures 2 and 3.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the decomposition rate of 1,2-dichloroethane and the effective average temperature.
Figures 2 and 3 are graphs showing the relationship between 1,2-dichloroethane decomposition rate and chloroprene and acetylene selectivity.

Claims (1)

[Claims] 1 1,2-dichloroethane under non-catalytic conditions 400 to 550
In producing vinyl chloride by thermal decomposition at °C,
0.05 hydrogen per 100 moles of 1,2-dichloroethane
A method for producing vinyl chloride, which comprises adding up to 3.0 mol of 1,2-dichloroethane and thermally decomposing it. 2 Hydrogen per 100 moles of 1,2-dichloroethane
The method according to claim 1, wherein 0.2 to 1.0 mol is added. 3. The method according to claim 1, wherein 1,2-dichloroethane containing carbon tetrachloride is used.