JP2609194B2 - Desorption method of organic chlorine solvent - 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 desorbing an organochlorine solvent contained in soil.

[0002]

2. Description of the Related Art As a conventional method for analyzing the desorption of an organic chlorine-based solvent, one method uses an organic solvent such as ethyl alcohol or acetone, mixes it with soil, and shakes to remove a small amount of the organic chlorine-based solvent. There is a method of elution in these organic solvent layers. There are many methods for elution with this organic solvent, but the one proposed as the best method is
Using ethyl alcohol as an organic solvent, shaking for a long time, adding water, further dissolving in hexane, an organic solvent that is insoluble in water, removing the interfering substances, and quantifying by gas chromatography. It is. However, in this method, it takes a long time to elute the organochlorine solvent from the soil, the operation is somewhat complicated, and attention must be paid to the scattering of the target substance into the air during the test operation and the entry of interfering substances from the outside. I had to. Also, it was difficult to determine whether or not all the target substances had eluted from the soil.

Another conventional method for desorption analysis of an organic chlorine-based solvent is a method in which nitrogen gas or the like is passed through the soil at room temperature or with heating to remove the organic chlorine-based solvent from the soil. This is a simpler desorption analysis method than the elution method using a solvent.

[0004]

However, in the conventional method of purging the organic chlorinated solvent from the soil with nitrogen gas or the like, when the method is carried out at room temperature, the target substance is not removed so much from the soil. Had issues. On the other hand, the method of passing nitrogen gas or the like while heating the soil has a problem in that the target substance is decomposed by the heating and correct measurement cannot be performed. In any case, since the organic chlorine-based solvent has a low boiling point and is easily scattered in the atmosphere, even if the soil is collected at the site and sealed, the target substance passes through the gap between the stoppers while returning to the laboratory. There was a problem that the risk of scattering inside was very high.

Accordingly, the present invention provides a method for desorbing an organic chlorine-based solvent through nitrogen gas, which is a simpler desorption analysis method than an elution method using an organic solvent, in which desorption can be carried out for accurate analysis of an organic chlorine-based solvent. The aim is to provide a method. Specifically, an object of the present invention is to prevent a target substance from scattering into the atmosphere before desorption is performed. Also,
The purpose is to prevent the target substance from being decomposed at the time of desorption.

[0006]

In order to achieve the above object, the method for desorbing an organochlorine solvent according to the present invention comprises the steps of: The method for desorbing a chlorine-based solvent is characterized in that distilled water is added to the sampled soil and the soil is directly heated. The soil to which the distilled water has been added is preferably subjected to ultrasonic treatment using distilled water contained before heating. In addition, the method for desorbing the organic chlorine-based solvent, the heating conditions are selected according to the decomposability of the target component in the soil by heating, and it is preferable that the heating is performed in a plurality of times under different heating conditions and the desorption is performed. . The method for desorbing an organic chlorine-based solvent is as follows: when the target components in the soil are 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene, heating is performed at 120 ° C. for 80 minutes for 1,1,1. -To remove trichloroethane, trichloroethylene and tetrachloroethylene,
It is preferable to remove tetrachloroethylene under heating conditions of 00 ° C. for 60 minutes.

[0007]

According to the method for desorbing an organic chlorine-based solvent of the present invention,
By adding distilled water after collecting the soil, the target substance can be prevented from scattering into the atmosphere. Further, by adding distilled water, the decomposition of the target substance which has been conventionally decomposed by heating can be prevented. In addition, if ultrasonic treatment is performed before heating using distilled water added to the soil, the recovery rate of the target substance from the soil can be further increased. Further, by selecting a heating temperature and a heating time and desorbing under a plurality of heating conditions, the recovery rate can be further increased while preventing decomposition of the target substance.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an exploded perspective view of the sampling container of the present invention, and FIG.
FIG. 3 is an exploded perspective view showing a dehydration pipe section connected to the sampling vessel, and FIG. 3 is an overall configuration diagram of an organic chlorine-based solvent desorbing apparatus using the sampling vessel.

As shown in FIG. 1, the sampling vessel includes a vessel body 1 made of a stainless steel tube for containing soil, and the vessel body 1 is provided with screw portions 1a and 1b at both ends. Reference numerals 2a and 2b denote stainless steel joints, each having a thread groove at one end corresponding to the threaded portions 1a and 1b of the container body 1, and attached to both ends of the container body 1. The other end of the joint 2a is threaded so that the nitrogen gas introduction pipe 3 can be connected. The nitrogen gas introduction pipe 3 is made of stainless steel and is bent in an L-shape. The upper end is a nitrogen gas introduction part 3a, and the lower end is a connection part 3b with the joint 2a. The nitrogen gas inlet 3a is a blind plug (not shown) at the time of sampling.
However, at the time of thermal desorption, the nitrogen gas inlet 3c can be connected as shown in FIG. Joint 2b
Is threaded so that the joint 4 can be connected. The joint 4 is made of stainless steel and has a configuration to which a stop valve 5 can be connected. The stop valve 5 is also made of stainless steel and has an outlet 5a on the side.
And an operating rod 5b at the upper end. Between the container body 1 and the joint 2a, there is provided a stainless steel plate 6 having pores, and a filter 7 made of glass fiber on the stainless steel plate 6. A glass wool 8 is provided between the stainless steel tube 1 and the joint 2b so that the soil is not scattered during heating desorption. In the above embodiment, the nitrogen gas introduction part 3a is provided in the nitrogen gas introduction pipe 3, but may be provided directly on the bottom of the container body 1.

A dehydrating pipe 9 connected to the sampling vessel
Is a stainless steel tube with a bottom, and has a screw portion 9a on the upper open end side. The stainless steel cap 10 is provided with a screw groove corresponding to the screw portion 9 a on the inner periphery, and seals the opening end of the dehydrating tube 9. The stainless steel cap 10 has two holes, into which a connection pipe 11 on the gas inflow side and a connection pipe 12 on the gas outflow side are respectively inserted. In order to prevent water from flowing out of the dehydrating tube 9,
The lower end of the connection pipe 12 is located above the lower end of the connection pipe 11. The upper ends of the connection pipes 11 and 12 are connected to connection sections 11a and 12a connectable to stainless steel pipes 13 and 14, respectively.
It has become. Also, in order to make the sealing of the screw portion for connecting the respective components more complete, a Teflon seal is wound around each screw.

Next, a method of using an organic chlorine-based solvent desorption apparatus will be described. First, a method of collecting soil on site will be described. In the sampling container shown in FIG. 1, the container body 1, the joint 2a, and the nitrogen gas introducing pipe 3 are connected in advance. At this time, the stainless steel plate 6
The filter 7 is attached when connecting the container body 1 and the joint 2a. In addition, the nitrogen gas introduction pipe 3
The nitrogen gas inlet 3a is plugged in blind. On the other hand, the joint 2b, the joint 4, and the stop valve 5 are also connected in advance. Then, the total weight of these is measured. The soil collected at the site is immediately put into the container body 1, 10 ml of distilled water prepared in advance is added, and the joint 2b is connected to the container body 1. At this time, it is confirmed that the stop valve 5 is always closed.

Next, the sampling container is taken back to the laboratory as it is, and the weight is measured. Based on the difference between the previously measured empty weight of the entire sampling container and the weight of 10 ml of distilled water, the weight of the collected soil is determined. Ask. Then, this sampling container is subjected to ultrasonic treatment for a predetermined time in the state as it is, and then put into a temperature control device. In addition,
In this embodiment, a gas chromatograph oven was used as a temperature control device.

Next, as shown in FIG. 3, the sampling vessel is placed in an oven 16 and an outlet 5 of the stop valve 5 is provided.
The stainless steel tube 13 is connected to a. The nitrogen gas inlet 3a of the nitrogen gas inlet tube 3 is connected to the inlet 3c of the gas chromatograph by removing the blind plug. Stainless steel tube 1
3 has one end connected to the outlet part 5a of the stop valve 5 and the other end connected to the connecting part 11a of the connection pipe 11, but is connected so that the dewatering pipe 9 side is at least at the part coming out of the oven 16. This is because the stainless steel tube 13 is at room temperature when it comes out of the oven 16, so that the water does not flow backward. The stainless steel thin tube 14 has one end connected to the connecting portion 12a of the connecting tube 12 and the other end connected to the tedlar bag 15 for collecting gas, and the connecting portion 12a is connected below the connecting portion with the tedlar bag 15. . The dewatering tube 9 is immersed in a cooling container 17 containing, for example, ice water or the like in order to completely remove water. After assembling the entire apparatus as described above, the stop valve 5 is opened, and nitrogen gas flows from the nitrogen gas inlet 3c, and the nitrogen gas is collected in the Tedlar bag 15.

Next, the method for desorbing an organic chlorine-based solvent according to the present invention will be described. FIG. 4 shows a process diagram of the desorption method. First, distilled water is added to the collected soil, and ultrasonic treatment is performed for a predetermined time. Thereafter, the sample is subjected to thermal desorption and collected in a Tedlar bag, and the thermal desorption is performed a plurality of times under different heating conditions. The nitrogen gas is passed at a rate of 30 to 50 ml / min.

Next, specific experimental results regarding the analysis method will be shown. First, the results of studies on the soil used will be described.
As standard gas, 1,1,1-trichloroethane, trichloroethylene, tetrachloroethylene 2500 pp each
m was prepared in a vacuum bottle. As target soils, two types of soil were examined: a plant C soil where contamination of tetrachloroethylene was remarkable, and a soil of plant D where contamination of trichlorethylene was remarkable. It was found that when 5 ml of the standard gas was injected into these soils, almost all of them were not adsorbed on the soil but were desorbed at room temperature. Therefore, the soil was placed in a sampling tube at 240 ° C for about half a day with nitrogen gas. The soil was desorbed to completely remove the water content and the target substance from the soil. When a standard gas is injected into this soil at room temperature,
Even after desorption for 20 minutes, none of the three substances were detected in the Tedlar bag, suggesting that they were completely adsorbed in the soil. Therefore, in order to perform accurate evaluation, a decomposition experiment was performed using this soil.

Next, the examination results of the decomposition experiment by heating are shown. After injecting a standard gas at a constant temperature, desorb with nitrogen gas for 20 minutes, collect in a Tedlar bag, and inject 0.2 ml in the Tedlar bag into a gas chromatograph-mass spectrometer (GC-MS) to obtain a TIC. The comparison was made based on the peak height on the chromatogram. Table 1 shows the decomposition products of the three substances and the production ratio when the soil temperature was changed.

[0017]

[Table 1]

The measurement of 1,1,1-trichloroethane was carried out from 40 ° C. to 200 ° C. At 40 ° C., trace amounts of 1,1,1-trichloroethane were confirmed, but in all other cases, only dichloroethylene was formed. In this case, in the desorption at 40 ° C., the amount of 1,1,1-trichloroethane adsorbed on the soil is large, so
Around 0% was collected in the Tedlar bag as dichloroethylene. 100% in Table 1 refers to a state where only dichloroethylene is found on the TIC chromatogram.

The measurement of trichlorethylene was carried out from 120 ° C. to 240 ° C. At 200 ° C., trace amounts of dichloroethylene were observed, and at 240 ° C., 5 to 6% of dichloroethylene, but at lower temperatures, no decomposition products were observed.

200 ° C. for tetrachloroethylene
6 to 8%, and at 13 ° C., 11 to 13% was decomposed to trichlorethylene. At this temperature, a trace amount of dichloroethylene was also observed. However, no decomposition products were observed at other temperatures.

Next, the results of studies on the effect of the amount of water on the decomposition of 1,1,1-trichloroethane will be described. As described above, most of 1,1,1-trichloroethane collected via the soil was converted to dichloroethylene even at 40 ° C. Then, the influence of the amount of water was investigated in order to suppress the decomposition.

At room temperature, 1,1,
Five milliliters of 2500 ppm of 1-trichloroethane standard gas was injected, and distilled water was further injected from the injection port in different amounts of 1 ml, 3 ml, 5 ml, 8 ml and 10 ml. These wet soils were heated to 120 ° C., desorbed with nitrogen gas for 20 minutes, and collected in a Tedlar bag. 0.2 ml of gas in the Tedlar bag is injected into GC-MS, and TIC
The peak was confirmed on the chromatogram. as a result,
Only when 1 ml of distilled water was added, the presence of a trace amount of dichloroethylene was confirmed, but when the water content was other than that, all the injected 1,1,1-trichloroethane was collected in the Tedlar bag.

After the soil was desorbed at 120 ° C. for further 60 minutes, neither 1,1,1-trichloroethane nor dichloroethylene was detected in the Tedlar bag collected at 200 ° C. From these results, 1,1,1-
To remove trichloroethane from the soil, add 10 ml of distilled water to the soil to obtain as much water content as possible.
It was found that when desorption was performed at 120 ° C. together with the desorption of 1,1-trichloroethane, the desorption was performed from the soil without decomposition.

Next, the results of a study of the change in the amount of desorption due to the difference in the pretreatment method will be described. For the soil of Factory C, tetrachloroethylene, which is contained very much in this soil and is considered to be difficult to desorb, was examined. As an experimental method, a change in the amount of desorption was observed when 10 ml of distilled water was added to the soil and no ultrasonic wave was applied, and when the sample was applied for 5 minutes, 10 minutes, and 30 minutes. The test was also performed without adding distilled water.

With respect to the desorption temperature, high conditions were set in order to find out where the desorption of tetrachloroethylene from the soil was almost completed. Heating temperature 1 for the first 20 minutes
After desorption at 20 ° C., the temperature was raised to 240 ° C., desorption was performed for 20 minutes each for 100 minutes, and then desorption was performed at 270 ° C. for 20 minutes. However, even if the heating temperature is set to 240 ° C., it is considered that the soil temperature is maintained at approximately 100 ° C. for about 60 minutes until the moisture in the stainless steel tube disappears. The results obtained are shown in FIG.

The amount of tetrachloroethylene desorbed was lowest when no distilled water was added. In addition, when distilled water was added, the value was slightly lower when no ultrasonic wave was applied, but showed almost the same value when the ultrasonic wave was applied. However, if the time for applying the ultrasonic wave is long, the inside of the sample collection tube is heated, and particularly in the case of a substance having a low boiling point, loss may occur. Further, in the present experimental method, even when the temperature was raised from 240 ° C. to 270 ° C., the amount of tetrachlorethylene desorbed did not increase, and it was considered that the desorption from soil was almost completed at a temperature lower than 240 ° C.

Finally, the results of experiments on the change in the amount of desorption due to the difference in desorption time and desorption temperature are shown. As soil, those of the D factory and the C factory were used. The soil of Factory D has a very high content of trichlorethylene and a low content of tetrachloroethylene. Therefore, as described above, the generation of trichlorethylene by the thermal decomposition of tetrachlorethylene when the desorption temperature was increased was almost negligible, and it was thought that the end point of the soil content of trichlorethylene could be almost known.

As for the soil of the plant C, the content of tetrachloroethylene is very large, and the production of trichloroethylene by the thermal decomposition of tetrachloroethylene when the desorption temperature is increased cannot be ignored. Was studied only with tetrachloroethylene because of its small content. Ten grams of soil was placed in a sample collection tube and treated with 10 ml of distilled water for 10 minutes with ultrasound. The sample was collected at 120 ° C. for 20 minutes for 80 minutes, and then heated to 200 ° C. for 2 minutes.
The temperature was raised to 240 ° C. for 60 minutes each for 0 minute, then collected for 20 minutes for 40 minutes, and finally collected at 270 ° C. for 20 minutes. The obtained results are shown in FIGS.

FIG. 6 shows that almost all of 1,1,1-trichloroethane was desorbed from the soil at 120 ° C. in the presence of moisture. FIG. 7 shows that trichloroethylene was desorbed at 120 ° C. for 80 minutes to collect 88 to 90% of the soil content. At this temperature, there is no influence from the thermal decomposition of tetrachlorethylene as described above,
It was performed at 20 ° C. for 80 minutes. When the temperature of the sample collection tube was increased from 120 ° C. to 200 ° C., the amount of trichlorethylene desorbed slightly increased, but the amount of trichloroethylene desorbed did not increase at 240 ° C., and almost no desorbed at 270 ° C. Therefore, it was considered that almost all of the trichlorethylene in the soil was desorbed at this stage.

As can be seen from FIGS. 8 and 9, tetrachloroethylene desorbed at 120 ° C. for 80 minutes has a sufficient desorption rate of 76 to 77% in the soil of Plant D and 65 to 66% in the soil of Plant C. I couldn't do it. Therefore, at 200 ° C, 6
When desorption was performed for 0 minutes, 93% was obtained in the soil of Plant D, and C
In the factory soil, 90% or more was collected even when considering the loss due to decomposition after the desorption temperature was set to 200 ° C. Therefore,
Tetrachloroethylene was determined by the sum of the amount desorbed at 120 ° C. for 80 minutes and the amount desorbed at 200 ° C. for 60 minutes. Further, even if the temperature of the sampling tube was increased from 200 ° C. to 240 ° C., the amount of tetrachloroethylene to be desorbed did not increase, and the desorption amount was greatly reduced at a temperature rise to 270 ° C. Therefore, it was considered that almost all the tetrachloroethylene in the soil was completely desorbed at this stage.

[0031]

As is apparent from the above description, according to the method for desorbing an organic chlorine-based solvent of the present invention, the target substance is scattered into the atmosphere by adding distilled water after collecting the soil, and the conventional method is achieved by heating. Decomposition of the decomposed target substance can be prevented. If the ultrasonic treatment is performed before the heating, the recovery rate of the target substance from the soil can be further increased. Furthermore, by performing desorption under a plurality of heating conditions, the recovery rate can be further increased while preventing decomposition of the target substance.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a sampling container of a desorption device used in the present invention.

FIG. 2 is an exploded perspective view showing a dehydrating tube section of the apparatus.

FIG. 3 is an overall configuration diagram of the apparatus.

FIG. 4 is a process diagram of the desorption method according to the present invention.

FIG. 5 is a characteristic diagram showing a change in the amount of desorbed tetrachloroethylene due to a difference in pretreatment conditions.

FIG. 6 is a characteristic diagram showing a change in the amount of desorbed 1,1,1-trichloroethane in soil at the site of the D factory.

FIG. 7 is a characteristic diagram showing a change in the amount of desorbed trichlorethylene in the soil at the factory D.

FIG. 8 is a characteristic diagram showing a change in the amount of desorbed tetrachlorethylene in soil at the site of the D factory.

FIG. 9 is a characteristic diagram showing a change in the amount of desorbed tetrachloroethylene in soil on the premises of plant C.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Container main body 3 Nitrogen gas introduction pipe 3a Nitrogen gas introduction part 5 Stop valve 9 Dehydration pipe 15 Tedlar bag 16 Oven 17 Cooling vessel

Claims (4)

(57) [Claims] 1. A method for desorbing an organic chlorine-based solvent by passing nitrogen gas through the soil while heating the soil, wherein distilled water is added to the sampled soil,
A method for desorbing an organic chlorine-based solvent, wherein the soil is heated as it is. 2. The method according to claim 1, wherein the soil to which the distilled water is added is subjected to ultrasonic treatment before heating. 3. The method according to claim 1, wherein a heating condition is selected according to the decomposability of the target component in the soil by heating, and heating and desorption are carried out a plurality of times under different heating conditions. 5. The method for desorbing an organic chlorine-based solvent according to the above. 4. The target components in the soil are 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene, which are heated at 120 ° C. for 80 minutes.
1,1-trichloroethane, trichloroethylene,
While removing tetrachloroethylene, another 200
The method for desorbing an organic chlorine-based solvent according to any one of claims 1 to 3, wherein tetrachloroethylene is desorbed under heating conditions of 60 ° C for 60 minutes.