JP2003212802A - Method for recovering 1,2-dichloroethane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering 1,2-dichloroethane from discharged water containing a hypochlorous acid compound and 1,2-dichloroethane by which chloroform produced as a by-product is reduced and the chloroform concentration in the treated discharged water after recovering 1,2-dichloroethane is reduced and after-treatment of the treated discharged water is readily carried out. <P>SOLUTION: This method for recovering 1,2-dichloroethane comprises reacting a discharged water containing a hypochlorous acid compound and 1,2- dichloroethane with a reducing agent to reduce an oxidation-reduction potential in the discharged water to ≤400 mV and recovering 1,2-dichloroethane by distillation. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to 1,2-dichloroethane from a wastewater containing hypochlorous acid.
-A new method for recovering dichloroethane. More specifically, the present invention provides a method for recovering 1,2-dichloroethane for the purpose of reducing chloroform produced as a by-product when 1,2-dichloroethane is recovered from the waste water by a distillation operation.

[0002]

2. Description of the Related Art As a method for producing 1,2-dichloroethane, a method of reacting chlorine and ethylene in the presence of an iron catalyst is used. Since the gas component discharged from the above reaction system contains unreacted chlorine, it is treated by contacting it with an alkaline aqueous solution such as caustic soda in a detoxification tower.
The wastewater generated at that time (hereinafter referred to as “harmful wastewater”) contains several thousand ppmw of sodium hypochlorite, and a small amount of 1,2-dichloroethane present in the gas in the reaction system. contains.

On the other hand, 1,2-dichloroethane obtained by the reaction contains by-products such as 1,1,2-trichloroethane and ferric chloride as an iron-based catalyst, and it is necessary to remove them. The above-mentioned purification employs a method in which the iron-based catalyst is extracted and removed from crude 1,2-dichloroethane by using water as an extractant, and then by-products are separated by distillation.
Wastewater generated at this time (hereinafter referred to as "extracted wastewater")
Together with the extracted iron-based catalyst have a saturation solubility of 1 or 2.
-Contains dichloroethane and small amounts of chlorine, hypochlorous acid.

Wastewater containing hypochlorous acid such as hypochlorite and hypochlorous acid together with 1,2-dichloroethane, such as the above-mentioned detoxifying wastewater and extraction wastewater, is stored in a pit and then , 2-dichloroethane is recovered.

However, when trying to recover 1,2-dichloroethane by distillation from wastewater containing the above hypochlorous acid, if the concentration of 1,2-dichloroethane present in the wastewater is reduced to 40 ppbw or less, the wastewater The chloroform concentration in the solution rose to several thousand ppbw, and it was confirmed that chloroform was produced in the above recovery.

Further, the waste water containing the chloroform needs to be subjected to a separate adsorption treatment or the like to reduce the chloroform and then discarded, which causes a problem of complicating the treatment of the waste water.

A method of treating the wastewater containing chloroform of about several thousand ppbw as a chloroform treatment method other than the adsorption, and using the wastewater containing hypochlorous acid as process water in the process of producing propylene oxide by the chlorhydrin method. Can be considered. In this case, the wastewater can be used in the process without any problem, but when the manufacturing process does not exist nearby or when the manufacturing process is stopped, the wastewater needs to be treated.

[0008]

Therefore, an object of the present invention is to provide a method for recovering 1,2-dichloroethane from wastewater containing 1,2-dichloroethane and hypochlorous acid by a distillation operation. Another object of the present invention is to provide a method for recovering 1,2-dichloroethane in which chloroform produced as a by-product is reduced.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above object. As a result, 1,2-
By controlling the redox potential of the wastewater containing dichloroethane and hypochlorite by a reducing agent to adjust the oxidation-reduction potential in the wastewater to a specific value, the formation of chloroform during the distillation of the wastewater is extremely highly suppressed. While discovering that 1,2-dichloroethane can be recovered, the present invention has been completed.

That is, the present invention relates to hypochlorous acid and 1,2-
After the reducing agent is caused to act on the wastewater containing dichloroethane so that the redox potential in the wastewater is 400 mV or less,
A method for recovering 1,2-dichloroethane is characterized in that 1,2-dichloroethane is separated by distillation.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the waste water targeted for the recovery of 1,2-dichloroethane is not particularly limited as long as it contains 1,2-dichloroethane and hypochlorous acid. 2-dichloroethane 100pp
Waste water that is dissolved at a concentration of mw or higher is preferable. Also,
The concentration of hypochlorous acid is 100 to 1000 in terms of OCl.
The effect of the present invention is particularly remarkable with respect to the waste water of 00 ppmw.

The above hypochlorous acid is a general term for hypochlorous acid and hypochlorite. Further, the type of the salt is determined by the alkaline species used in the exclusion treatment and the like. For example, when caustic soda is used, it becomes sodium hypochlorite, and when lime milk is used, it becomes calcium hypochlorite. In the present invention, any form of salt can be applied.

The most important feature of the present invention is that, when 1,2-dichloroethane is recovered from the wastewater by distillation, a reducing agent acts on the wastewater so that the redox potential of the wastewater is 400 mV or less, preferably 300 mV or less. , And more preferably 200 mV or less. That is, when the wastewater having a redox potential of more than 400 mV is distilled,
The formation of chloroform in the distillation was not suppressed,
-A large amount of chloroform remains in the waste water after recovery of dichloroethane.

In the present invention, the reducing agent is not particularly limited as long as it can act on waste water to reduce its redox potential. For example, reducing agents such as sodium hydrogen sulfite, sodium sulfite and sodium thiosulfate are generally used. Further, Group 8A metal oxides, particularly nickel oxides, cobalt oxides and their inclusions, and Group 8A metal powders, particularly nickel and cobalt metal powders, as disclosed in JP-A-2-303538, Reduction catalysts such as Group 8A metal salts such as Group 8A metal chlorides and mixtures thereof can also be used as reducing agents in the present invention.

Further, regarding the above-mentioned reducing agent, an example of the case of addition will be described. The adding amount of the reducing agent may be determined so that the redox potential of the waste water can be reduced to 400 mV or less. The amount of the reducing agent used is preferably a control method in which, after introducing the reducing agent, the redox potential is measured at an appropriate position before being subjected to distillation, and the redox potential is adjusted to the above range based on the measured value. . Further, when the composition of the wastewater is stable, the amount of the reducing agent to be used may be determined in advance, and such an amount of the reducing agent may be continuously added to the wastewater.

The mixing method of the reducing agent and the waste water is not particularly limited and is appropriately determined according to the type of the reducing agent. For example, a method of adding a reducing agent in a pit and mixing and stirring,
A general method is to provide a static mixer such as a static mixer in the middle of a line for supplying waste water to a distillation column and add a reducing agent in front of the mixer.

In the present invention, the distillation column used for recovering 1,2-dichloroethane from the waste water is not particularly limited, and a known type distillation column such as a plate column or a packed column can be generally used. Further, in the distillation of waste water using the above distillation tower, waste water is supplied from above the distillation tower, steam is supplied from below the distillation tower, and steam is distilled as a gas together with 1,2-dichloroethane from the top of the tower. , 1,2-dichloroethane is condensed with a condenser installed at the top of the column to recover 1,2-dichloroethane together with water.

Regarding the operating conditions of the distillation column, the pressure inside the column is not particularly limited, and any pressure may be selected. The column internal temperature is substantially determined by the selected column internal pressure, and the column bottom temperature is preferably in the range of boiling temperature to boiling temperature + 5 ° C.

On the other hand, from the bottom of the distillation column, treated wastewater containing almost no 1,2-dichloroethane can be obtained.
Chloroform hardly exists in the treated wastewater obtained by distilling the wastewater adjusted to the redox potential, and thus the treated wastewater which does not require the removal of the chloroform is obtained.

A more specific description will be given with reference to FIG. 1 showing an embodiment of the method of the present invention, but the present invention is not limited to the embodiment shown in FIG.

As shown in FIG. 1, hypochlorite, 1,2
-A reducing agent input pipe 2 is connected to the flow path of the drainage introduction pipe 1 for supplying the waste water containing dichloroethane to the distillation column, and the reducing agent is injected from this, and the static electricity is provided downstream from the injection position. Mixing is performed in the mixer 3. A redox potential measuring device 4 for measuring a redox potential is installed further downstream of the mixer, and the redox potential of waste water supplied to the distillation column is measured to compare the measured value with a set value. Control the supply of reducing agent.

The wastewater whose redox potential is adjusted in this way is introduced into the distillation column 5, and the vapor is introduced from the bottom of the distillation column 5 through the vapor injection pipe 6 to add 1,2-dichloroethane together with the vapor. It is taken out from the top of the tower, further cooled by the top condenser 7, and 1,2-dichloroethane recovery pipe 8
1,2-dichloroethane is recovered as a liquid and reused. Further, the uncondensed gas is generally discharged from the exhaust gas pipe 9 and incinerated. Further, the bottom liquid is cooled by the condenser 10 and recovered.

[0023]

As will be understood from the above description, according to the present invention, when 1,2-dichloroethane is recovered by distillation from wastewater containing 1,2-dichloroethane together with hypochlorite, By causing a reducing agent to act on the wastewater so that its redox potential is 400 mV or less,
Chloroform production during the distillation of the waste water is suppressed. As a result, the concentration of chloroform in the treated effluent obtained by distilling this can be suppressed to a low level, and 1,2-dichloroethane can be recovered without spending a great deal of effort on the effluent treatment, and its industrial value. Is extremely high.

[0024]

EXAMPLES In order to describe the present invention more specifically,
Examples are shown, but the present invention is not limited to these examples.

Example 1 Obtained from a 1,2-dichloroethane production plant,
1,2-dichloroethane 6000ppmw, chloroform 50ppmw, hypochlorous acid (OCl conversion) 20
2000 kg / h of wastewater containing 00 ppmw and pH 11
To the above, 21.94 kg / h of 35 wt% sodium bisulfite solution and 9.84 kg / h of 30 wt% sodium hydroxide solution were added as a reducing agent, mixed with a collision type static mixer, and supplied from above the distillation column.

The redox potential of the waste water supplied to the distillation column is 350 mV, and the hypochlorous acid (OCl conversion) is 90 ppmw.
Met.

Incidentally, the above distillation is carried out with a tower diameter of 450 mmφ, 2B.
A distillation column filled with Raschig rings of 6000 mm was supplied with 270 kg / h of vapor from a vapor port below the column, the internal pressure was atmospheric pressure, the top temperature was 98 ° C., and the bottom temperature was 101.
It was ℃.

The gas distilled from the top of the column was cooled to 10 ° C. by a condenser and the composition was analyzed as a distillate component. The liquid discharged from the bottom of the distillation column was cooled to 30 ° C. from a condenser and the composition was analyzed as the bottom drain.

As a result, the amount of distillate was 53 kg / h, the components were 22.5 wt% 1,2-dichloroethane, 2250 ppmw chloroform, and the other components were almost water.

The bottom drainage rate was 2245 kg / h, and its components were 1,2-dichloroethane of 2 ppbw, chloroform of 15 ppbw, and hypochlorous acid (OCl conversion) of 80 p.
pmw, the others were almost water.

Comparative Example 1 The procedure of Example 1 was repeated except that the sodium bisulfite solution and the sodium hydroxide solution were not added to the supplied wastewater.

The redox potential of the liquid supplied to the distillation column is 6
00 mV, and hypochlorous acid (OCl conversion) is 2000
It was ppmw.

As a result, the amount of distillate was 53 kg / h, the components were 22.5 wt% of 1,2-dichloroethane, 2250 ppmw of chloroform, and other components were almost water.

The amount of waste water discharged from the bottom of the column was 2,213 kg / h, and its components were 2 ppbw of 1,2-dichloroethane, 2000 ppbw of chloroform and 1 part of hypochlorous acid (OCl conversion).
At 800 ppmw, the others were almost water.

Example 2 The same procedure as in Example 1 was carried out except that the reducing agent added to the supplied waste water was 35 wt% sodium bisulfite solution 22.86 kg / h and 30 wt% sodium hydroxide solution 10.25 kg / h.

The redox potential of the liquid supplied to the distillation column is 2
10 mV, 20 pp of hypochlorous acid (OCl conversion)
It was mw.

As a result, the amount of distillate was 53 kg / h, and the components were 22.5 wt% 1,2-dichloroethane, 2250 ppmw chloroform, and the other components were almost water.

The bottom drainage rate was 2246 kg / h, and its components were 1,2-dichloroethane of 2 ppbw, chloroform of 10 ppbw, and hypochlorous acid (OCl conversion) of 18 p.
pmw, the others were almost water.

Example 3 The same procedure as in Example 1 was carried out except that the reducing agents added to the supplied waste water were 35 wt% sodium bisulfite solution 23.09 kg / h and 30 wt% sodium hydroxide solution 10.36 kg / h.

The redox potential of the liquid supplied to the distillation column is 1
It was 50 mV, and hypochlorous acid (OCl conversion) was not detected.

As a result, the amount of distillate was 53 kg / h, the components were 22.5 wt% 1,2-dichloroethane, 2250 ppmw chloroform, and the other components were almost water.

The amount of waste water discharged from the tower was 2247 kg / h, and its components were 1,2-dichloroethane of 2 ppbw, chloroform of 8 ppbw, hypochlorous acid (OCl conversion) was not detected, and the other components were almost water.

Example 4 Example 4 was repeated except that 81.81 kg / h of 30 wt% sodium thiosulfate was used as the reducing agent added to the waste water and sodium hydroxide was not used.

The redox potential of the liquid supplied to the distillation column is 1
It was 60 mV, and hypochlorous acid (OCl conversion) was not detected.

As a result, the amount of distillate was 53 kg / h, the components were 22.5 wt% 1,2-dichloroethane, 2250 ppmw chloroform, and the other components were almost water.

The amount of waste water discharged from the bottom was 2295 kg / h, and its components were 1,2-dichloroethane of 2 ppbw, chloroform of 8 ppbw, hypochlorous acid (OCl conversion) was not detected, and the other components were almost water.

[Brief description of drawings]

FIG. 1 is a process chart showing a preferred embodiment of the method of the present invention.

[Explanation of symbols]

1 Drainage introduction pipe 2 Reductant introduction tube 3 mixer 4 Redox potential measuring device 5 distillation tower 6 Steam introduction pipe 7 condenser (top of tower) 8 1,2-Dichloroethane recovery pipe 9 Exhaust gas piping 10 condenser (bottom of tower)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomoaki Fujii             Toku Co., Ltd. 1-1 Mikagecho, Tokuyama City, Yamaguchi Prefecture             In Yama F-term (reference) 4D034 AA26 BA01 CA12 CA21                 4D050 AA13 AB19 AB46 BA07 CA02                 4D076 AA05 AA12 AA22 BB01 EA19Z                       EA32 FA12 GA10 HA06 HA11                       JA01                 4H006 AA02 AD11 AD40 BB31 BE10                       BE63 EA02 EB02

Claims (2)

[Claims] 1. A reducing agent is caused to act on wastewater containing hypochlorous acid and 1,2-dichloroethane to adjust the oxidation-reduction potential in the wastewater to 400 mV, and then 1,2-dichloroethane is separated by distillation. A method for recovering 1,2-dichloroethane, which comprises: 2. The concentration of hypochlorous acid after addition of the reducing agent is 1
The recovery method according to claim 1, which is not more than 00 ppmw.