Chloromethane is an important chemical raw material for the production of silicone polymer in our factory. With the development of polymer synthesis industry, its demand is increasing day by day.
Most of the methyl chloride we use comes from the by-product of the pesticide trichlorfon. Therefore, methyl chloride often contains many low-boiling and high-boiling impurities. The unstable impurity content directly affects the quality of the silicone monomer. In order to stabilize the production and ensure the quality of the products produced. It is necessary to clarify the impurities and their contents in methyl chloride. Therefore, it is required to establish a fast and accurate analysis method to check the content of impurities in methyl chloride.
About the analytical test method of methyl chloride. Since it is a by-product in the pesticide plant, there is no much requirement for the content of the components. The analysis is extremely rough. The Jilin Institute once reported. They are only testing for recovery of methyl chloride. The composition is very different from that in the raw material methyl chloride. Other units are said to have different test methods. But no reports have been seen.
We use gas chromatography to directly determine methyl chloride and its impurities. Two kinds of fixatives were selected and qualitative and quantitative analysis were performed on FID and TCD detectors respectively.
Tests show that gas chromatography is a feasible method for methyl chloride and its impurities. Simple, fast and accurate.
1. Experimental part
1. Domestic 102G gas chromatograph. XWC-100 type, 0 ~ 5mv recorder, use FID detector for qualitative analysis, TCD detector for quantitative analysis.
2. Chromatographic separation conditions
(1) Chromatography column:
a. Stainless steel with an inner diameter of 4mm and a column length of 4m, containing 30% diisooctyl sebacate, glazed 6201 (60 ~ 80 mesh), coated with 1% triethanolamine as a tailing agent (referred to as decyl column)
b. Stainless steel with an inner diameter of 4mm and a column length of 3.2m, with GDX-01 inside.
(2) Separation conditions:
a. FID detector: the carrier gas is nitrogen decyl:
Nitrogen: 32ml / min Column temperature: 79 ℃
Air: 420 ml / min Vaporization temperature: 86 ℃ (see Figure 1)
Hydrogen: 32 ml / min Hydrogen flame temperature: 100 ° C
GDX-01:
Nitrogen: 55ml / min Column temperature: 79 ℃
Air: 440 ml / min Vaporization temperature: 86 ℃ (see Figure 2)
Hydrogen: 30 ml / min Hydrogen flame temperature: 100 degrees decyl column:
Column temperature: 78 ° C Air hydrogen: 60 ml / min
Vaporization temperature: 100 ℃ Thermal conductivity current: 220mA
Injection volume: 2ml (see Figure 3)
3. Qualitative analysis:
a. Column selection:
Methyl chloride and its impurities are mostly gaseous substances at normal temperature. Chloromethane has a boiling point of -24 ° C, a molecular weight of 50.5, and is of medium polarity. We have selected SE-30 fluorine oil, 2-2 dipropionitrile, 2-2 imine dipropionitrile, triethanolamine, trimethyl phosphate, diethyl phthalate, and GDX-01 sebacic acid diiso Octyl ester, etc., among which diisooctyl sebacate and GDX-01 have better separation effect. That is, these two columns are selected for qualitative double columns.
Chloromethane and its impurities are separated on the dipolar octyl sebacate in the order of boiling point. Except for hydrogen-bonded compounds on the GDX-01 column. Basically, they are separated in order of boiling point. The tailing of the alcohol peak on the decyl column appears, so first apply 1% triethanolamine as a tailing agent, and then apply a fixing solution. In this way, the tailing of the alcohol peak is improved, and the methanol can be advanced to facilitate the separation.
b. Qualitative:
â… . Qualitative on the deciduous column: (See Figure 1 for separation)
Qualitative peaks on the chromatogram. We use the injection reaction method (1). Compare the changes in the chromatogram before and after the reaction. Preliminary judgment of the functional group of each impurity. Combining chemical synthesis and the characteristic reaction of organic compounds, a comprehensive verification was made. Basically solved the qualitative problem of each peak.
Figure 1. 30% diisooctyl sebacate measured by FID detector
1. methyl ether 2. methyl chloride 3. methyl ethyl ether 4. ethyl chloride 5. methanol 6. ethyl ether 7. ethanol
Figure 2. Determination of GDX-01 column with FID detector Figure 1. Chloromethane 2, formaldehyde 3, methanol 4, bromomethane 5, ethyl chloride 6, methyl ethyl ether 7, ethanol 8, ethyl ether Determination of isooctyl ester column with TCD detector Figure 1, methyl ether 2, methyl chloride 3, ethyl chloride 4, methanol 5, ethyl ether 6, ethanol
We first did (1) mercury salt deolefination (2) hydroxylamine hydrochloride to remove aldehyde and ketone (3) fuchsin sulfurous acid reagent to remove aldehyde. The comparison of chromatographic results shows that there may be no olefins, aldehydes, or ketones in methyl chloride.
(1) Peak 1:
It is estimated that the samples contain ethers based on the workshop reaction and the source of the raw materials. In order to confirm the existence of ethers, we did the following experiment.
a. Ether can be dissolved in concentrated hydrochloric acid and concentrated sulfuric acid to form zinc salt (1). We put concentrated hydrochloric acid in the absorption tube and slowly passed methyl chloride for chromatographic comparison. As a result, peak 1 became significantly smaller, peak 3 disappeared, and peak 6 also changed. It is inferred that all 1.3.6 may be ethers.
b. Peak 1 is close to methyl chloride, indicating that the boiling point of peak 1 is similar to that of methyl chloride. The boiling point of methyl ether in ethers is -23.6 ° C, which is similar to that of methyl chloride.
Since we do not have pure methyl ether. To verify peak 1, we used methanol and dehydrating agent sulfuric acid to synthesize methyl ether (2) at room temperature. The product was analyzed by chromatographic control. The retention times of the synthesized methyl ether and peak 1 are the same. Therefore, peak 1 is judged to be dimethyl ether.
(2) Peak 3:
Proved by the above hydrochloric acid dissolution experiment. Peak 3 may also be an ether. Peak 3 is behind methyl chloride, but it is also relatively close, so its boiling point is not expected to be high. The ethers with a higher boiling point than methyl ether are methyl ethyl ether (boiling point 7.6 ℃). To confirm peak 3, methanol, ethanol and dehydrating agent sulfuric acid are boiled and dehydrated to produce methyl ether (2).
The product was subjected to chromatographic control analysis, and the synthesis of methyl ether and peak 3 was used as a control for determination. The retention time was the same, so peak 3 was determined to be methyl ether.
(3) Peak 4:
The experiment confirmed that peak 4 was a stable component. It is inferred that it may be chloroalkane, and the chloroethane with a boiling point inferior to methyl chloride is ethyl chloride (boiling point is 12.2 degrees).
Still using chemical synthesis of ethyl chloride. Ethanol and hydrochloric acid are heated in the presence of a strong dehydrating agent (anhydrous zinc chloride) to produce ethyl chloride. The resulting product was subjected to a chromatographic control reaction, and the resulting ethyl chloride coincided with the retention time of peak 4. Therefore, peak 4 was judged as ethyl chloride.
(4) Peak 5, 7:
Peaks 5 and 7 trailed on the decyl column without triethanolamine, that is, there may be hydroxyl groups. In addition, methanol is present in the raw materials of trichlorfon, so it is estimated that peaks 5 and 7 are methanol and ethanol. We used pure methanol and ethanol as a qualitative control. The results showed that peak 5 was methanol and peak 7 was ethanol.
(5) Peak 6:
The hydrochloric acid dissolution test showed that peak 6 may be ethers, but it still has two characteristic inversions of olefins (Br addition reaction, KmnO4 oxidation reaction). Therefore, we used the 102G chromatograph to prepare and collect the peak pure components and sent them to Chenguang Chemical Research for mass spectrometry analysis.
Mass spectrometry analysis indicates that the mass-to-charge ratio of 74 is a molecular peak. According to the formation of fragments and referring to the mass spectrum data of ether, it is concluded that peak 6 is ether.
â…¡. GDX-01 column is used as a double column qualitative one (see Figure 2 for separation)
Use FID detector to do double-column characterization, the test method is the same as above.
It was further confirmed on the GDX-01 column that the impurities in methyl chloride were methyl ether, ether, methyl ethyl ether, methanol, ethanol, and ethyl chloride. There is also an unknown peak. That is, peak 4 in FIG. 2. A large number of qualitative tests have confirmed that Peak 4 is also relatively stable. It may also be an alkane. Peak 4 appears before ethyl chloride, and its boiling point is the lower component.
Another raw material for trichlorfon is chlorine gas. There may be bromine in the chlorine gas. After the reaction, methyl bromide (boiling point 3.5 degrees) is generated as the confirmed peak 4. The results of the chromatographic comparison of our synthetic bromomethane (total heating with concentrated sulfuric acid and methanol in KBr) showed that peak 4 was methyl bromide.
â…¢. The peaks X0, X1 and X2 have appeared in the raw material methyl chloride since 1979 (see Figure 4)
X0 peak is the same as a small group of natural gas, about lower alkanes
The X1 peak content is very low, and the probability of occurrence is very small, so it is not given.
There are many opportunities for X2 peak to appear, and sometimes the content is also higher. We characterize one according to the retention time.
Figure 4 30% diisooctyl sebacate column / glazed 6201 (60 ~ 80 mesh) coated with 1% triethanolamine
1. X0 2. X1 3. Methyl ether 4. Chloromethane 5. Chloroethane 6. Methanol
7. Ether 8, ethanol 9, X 10, chloroform results confirmed that X2 peak is chloroform
4. Quantitative analysis The quantitative analysis of methyl chloride and its impurities is carried out on the decyl column using the TCD detector (see Figure 3).
The weight correction factor for methyl chloride and its impurities is calculated according to the empirical formula (listed in Table 1). The peak area is multiplied by the weight correction factor and quantified by the normalization method.
Table 1. Composition of weight correction factors for methyl chloride and its impurities
CH3Cl 0.64 1
C2H5Cl 0.72 1.12
CH3OCH3 0.54 0.84
C2H5OC2H5 0.68 1.06
CH3OH 0.58 0.91
C2H5OH 0.63 0.98
CH3Br 1.10 1.72
CH3OC2H5 0.62 0.97
In order to investigate the accuracy of this method, different batches of methyl chloride samples were taken for chromatographic determination. The quantitative results are listed in Table 2.
(1) Quantitative data show that the minimum detection amount of this method is 200ppm.
(2) The relative deviation of the main components in methyl chloride is 0.03%, the low-content components (<0.05%), the relative deviation is less than 10%, and the accuracy is good.
(3) Due to the lack of pure samples and incomplete empirical data, the correction factor is calculated using empirical formulas (among which, the empirical data cannot be calculated for the methanol correction factor), which seems to be a certain error in quantification.
Table 2 Red Star Chemical Factory Zhangdian Pesticide Factory Determination of Chloromethane Content Raw Material Origin Batch Number% Composition 1 # 2 # 3 # 4 # 5 #
1 2 3 phase% 1 2 3 phase% 1 2 3 phase% 1 2 3 phase% 1 2 3 phase%
Red Star Chemical Factory methyl ether 0.12 0.12 0.12 0 0.07 0.07 0.06 4.3 0.12 0.12 0.12 0 0.04 0.04 0 0.15 0.15 0.15 0
Methyl chloride
Ethyl chloride 0.06 0.06 0.07 5 0.06 0.05 0.05 6 0.04 0.04 0.04 0 0.04 0.04 0 0.04 0.03 0.03 10
Methanol 0.05 0.05 0.05 0 0.11 0.10 0.09 7 0.03 0.03 0.03 0 0.02 0.02 0
Ether
Zhangdian Pesticide Factory Ether 0.89 0.87 0.91 1.50 0.84 0.82 0.82 0.84 0.59 0.58 0.61 1.69 6.67 0.68 0.68 0.4 0.64 0.65 0.63 1
Methyl chloride
Ethyl chloride 0.27 0.25 0.23 3.70 0.43 0.43 0.44 0.007 0.11 0.11 0.12 2.73 0.21 0.25 0.22 3.18 0.18 0.19 0.19
Methanol 0.62 0.64 0.58 3.77 0.70 0.67 0.69 1.45 0.21 0.19 0.20 3.50 0.24 0.26 0.24 4.00 0.36 0.35 0.36
Ether 0.34 0.34 0.38 4.86 0.84 0.82 0.85 1.19 0.15 0.15 0.15 2.00 0.35 0.36 0.36 0.86 0.36 0.35 0.35
Phase% refers to relative deviation%
5. The representative test of the sampling method We used the direct sampling method of the syringe to take the gasified methyl chloride sample discharged from the liquid pipe of the chloromethane steel bottle of the factory. This method is simple and fast to operate, but the sampling volume is small. This sampling method lacks representativeness of the sample. Therefore, we take different batches of raw steel cylinders to take their full cylinders and empty cylinder samples after the completion of the samples for measurement and comparison. The results are shown in Table 3.
A peak X1 appeared in the empty bottle sample, which was estimated to be a lower alkane or alkene (see dotted peak in Figure 4). Peak X0 will increase, sometimes increase significantly.
From the table, it can be seen that the measurement results of the second sampling have a relatively close (but irregular) methane content in the empty bottle. In addition to the increase of X0 and X1 peaks, the content of other components in the empty bottle sample changes irregularly. Therefore, we believe that the direct sampling method is basically representative, and this method is feasible.
2. Experimental results and discussion
1. Analysis by gas chromatography with diisooctyl sebacate and GDX-01 column FID detector. Under the foregoing operating conditions, methyl chloride and its impurities methyl ether, ether, methyl ethyl ether, methanol, ethanol, ethyl chloride and Components such as methyl bromide can be separated.
2. Calculate the weight correction factor of methyl chloride and its impurities on the TCD detector using an empirical formula. The peak area normalization method can be used for quantification. Analysis of impurities in different batches of methyl chloride, the detection limit is 200ppm, the relative deviation of impurity content is 10%, which shows that gas chromatography analysis of methyl chloride and its impurities is completely feasible, the method is simple, fast, and the error is small.
3. Apply 1% triethanolamine as a tailing agent to the diisooctyl sebacate column, and then fix the liquid, which not only improves the tailing phenomenon of the alcohol peak, but also selects methanol as the chlorine after selecting the appropriate column temperature. Between methane and ethanol, this is beneficial for separation, and finally we selected this column for qualitative and quantitative analysis.
4. The total separation effect of the GDX-01 column is not as good as that of the decyl column, and the ether peak is dragged so far that the peak shape is not good, but the more valuable thing is the application of the TCD detector, the water peak can be out of methyl chloride, we have tested in GDX -01 is coated with a fixing solution, etc., and it is expected to improve the separation, but the effect is not satisfactory. It needs to be discussed in these aspects in the future.
5. We use the FID detector for qualitative one. Because the FID detector lacks a quantitative correction factor, the TCD detector is used for quantitative analysis. The weight correction factor of methyl chloride and its impurities in the TCD detector can be calculated according to the empirical formula. Due to its low sensitivity, two impurity peaks do not appear, and the calculation result will be high.
6. Sampling method: At present, direct sampling is performed by using a syringe. This method is simple and quick to operate, and can basically represent the content of raw material components. However, in winter and outdoor temperatures are low, which makes sampling difficult.
reference book:
(1) "Filled Gas Chromatography" of Lanzhou Institute of Chemistry
Table 3 Measurement results of samples of full and empty methyl chloride bottles (2), trial textbook "Organic Chemistry" in colleges and universities
Component Date X0 X1 (CH3) 2O CH3Cl C2H5Cl CH3OH (C2H5) 2O C2H5OH X CHCl3
4.15 Full 0.04 0.51 99.36 0.05 0.05
Empty 0.64 0.17 99.11 0.11 0.02 0.03 0.12
4.17 Full 0.09 0.18 99.23 0.16 0.06 0.06 0.22
Empty 0.23 0.02 0.20 99.28 0.26 0.03 0.02 0.03 0.93
4.19 Full 0.06 0.26 98.64 0.33 0.09 0.03 0.05 0.54
Empty 0.21 0.05 0.25 98.36 0.27 0.06 0.03 0.03 0.74
4.23 Full 0.05 0.14 99.37 0.13 0.03 0.07 0.01 0.14
Empty 0.37 0.04 0.18 98.97 0.12 0.01 0.08 0.23
4.28 Full 0.04 0.18 99.25 0.14 0.09 0.02 0.28
Empty 0.19 0.01 0.18 98.89 0.11 0.09 0.01 0.52
5.28 Full 0.07 0.31 99.26 0.10 0.14 0.02 0.02 0.12
Empty 0.12 0.12 0.32 98.78 0.06 0.15 0.01 0.03 0.10
5.30 full 0.02 0.26 98.45 0.17 0.14 0.03 0.93
Empty 0.11 0.01 0.35 98.16 0.07 0.06 0.34
6.5 Full 0.02 0.75 98.33 0.26 0.23 0.13 0.04 0.05 0.19
Empty 0.10 0.71 98.39 0.17 0.18 0.07 0.03 0.35
6.6 Full 0.02 0.24 99.11 0.16 0.12 0.03 0.32
Empty 0.15 0.21 99.03 0.10 0.10 0.41
6.7 Full 0.02 0.71 98.39 0.15 0.27 0.06 0.05 0.35
Empty 0.17 0.18 0.51 98.59 0.11 0.13 0.03 0.28
6.11 Full 0.04 0.34 99.16 0.15 0.06 0.25
Empty 0.24 0.32 99.02 0.10 0.04 0.28
6.13 Full 0.02 0.38 98.57 0.14 0.12 0.05 0.71
Chloromethane is an important chemical raw material for the production of silicone polymer in our factory. With the development of polymer synthesis industry, its demand is increasing day by day.
Most of the methyl chloride we use comes from the by-product of the pesticide trichlorfon. Therefore, methyl chloride often contains many low-boiling and high-boiling impurities. The unstable impurity content directly affects the quality of the silicone monomer. In order to stabilize the production and ensure the quality of the products produced. It is necessary to clarify the impurities and their contents in methyl chloride. Therefore, it is required to establish a fast and accurate analysis method to check the content of impurities in methyl chloride.
About the analytical test method of methyl chloride. Since it is a by-product in the pesticide plant, there is no much requirement for the content of the components. The analysis is extremely rough. The Jilin Institute once reported. They are only testing for recovery of methyl chloride. The composition is very different from that in the raw material methyl chloride. Other units are said to have different test methods. But no reports have been seen.
We use gas chromatography to directly determine methyl chloride and its impurities. Two kinds of fixatives were selected and qualitative and quantitative analysis were performed on FID and TCD detectors respectively.
Tests show that gas chromatography is a feasible method for methyl chloride and its impurities. Simple, fast and accurate.
1. Experimental part
1. Domestic 102G gas chromatograph. XWC-100 type, 0 ~ 5mv recorder, use FID detector for qualitative analysis, TCD detector for quantitative analysis.
2. Chromatographic separation conditions
(1) Chromatography column:
a. Stainless steel with an inner diameter of 4mm and a column length of 4m, containing 30% diisooctyl sebacate, glazed 6201 (60 ~ 80 mesh), coated with 1% triethanolamine as a tailing agent (referred to as decyl column)
b. Stainless steel with an inner diameter of 4mm and a column length of 3.2m, with GDX-01 inside.
(2) Separation conditions:
a. FID detector: the carrier gas is nitrogen decyl:
Nitrogen: 32ml / min Column temperature: 79 ℃
Air: 420 ml / min Vaporization temperature: 86 ℃ (see Figure 1)
Hydrogen: 32 ml / min Hydrogen flame temperature: 100 ° C
GDX-01:
Nitrogen: 55ml / min Column temperature: 79 ℃
Air: 440 ml / min Vaporization temperature: 86 ℃ (see Figure 2)
Hydrogen: 30 ml / min Hydrogen flame temperature: 100 degrees decyl column:
Column temperature: 78 ° C Air hydrogen: 60 ml / min
Vaporization temperature: 100 ℃ Thermal conductivity current: 220mA
Injection volume: 2ml (see Figure 3)
3. Qualitative analysis:
a. Column selection:
Methyl chloride and its impurities are mostly gaseous substances at normal temperature. Chloromethane has a boiling point of -24 ° C, a molecular weight of 50.5, and is of medium polarity. We have selected SE-30 fluorine oil, 2-2 dipropionitrile, 2-2 imine dipropionitrile, triethanolamine, trimethyl phosphate, diethyl phthalate, and GDX-01 sebacic acid diiso Octyl ester, etc., among which diisooctyl sebacate and GDX-01 have better separation effect. That is, these two columns are selected for qualitative double columns.
Chloromethane and its impurities are separated on the dipolar octyl sebacate in the order of boiling point. Except for hydrogen-bonded compounds on the GDX-01 column. Basically, they are separated in order of boiling point. The tailing of the alcohol peak on the decyl column appears, so first apply 1% triethanolamine as a tailing agent, and then apply a fixing solution. In this way, the tailing of the alcohol peak is improved, and the methanol can be advanced to facilitate the separation.
b. Qualitative:
â… . Qualitative on the deciduous column: (See Figure 1 for separation)
Qualitative peaks on the chromatogram. We use the injection reaction method (1). Compare the changes in the chromatogram before and after the reaction. Preliminary judgment of the functional group of each impurity. Combining chemical synthesis and the characteristic reaction of organic compounds, a comprehensive verification was made. Basically solved the qualitative problem of each peak.
Figure 1. 30% diisooctyl sebacate measured by FID detector
1. methyl ether 2. methyl chloride 3. methyl ethyl ether 4. ethyl chloride 5. methanol 6. ethyl ether 7. ethanol
Figure 2. Determination of GDX-01 column with FID detector Figure 1. Chloromethane 2, formaldehyde 3, methanol 4, bromomethane 5, ethyl chloride 6, methyl ethyl ether 7, ethanol 8, ethyl ether Figure 3. 30% sebacic acid dichloride Determination of isooctyl ester column with TCD detector Figure 1, methyl ether 2, methyl chloride 3, ethyl chloride 4, methanol 5, ethyl ether 6, ethanol
We first did (1) mercury salt deolefination (2) hydroxylamine hydrochloride to remove aldehyde and ketone (3) fuchsin sulfurous acid reagent to remove aldehyde. The comparison of chromatographic results shows that there may be no olefins, aldehydes, or ketones in methyl chloride.
(1) Peak 1:
It is estimated that the samples contain ethers based on the workshop reaction and the source of the raw materials. In order to confirm the existence of ethers, we did the following experiment.
a. Ether can be dissolved in concentrated hydrochloric acid and concentrated sulfuric acid to form zinc salt (1). We put concentrated hydrochloric acid in the absorption tube and slowly passed methyl chloride for chromatographic comparison. As a result, peak 1 became significantly smaller, peak 3 disappeared, and peak 6 also changed. It is inferred that all 1.3.6 may be ethers.
b. Peak 1 is close to methyl chloride, indicating that the boiling point of peak 1 is similar to that of methyl chloride. The boiling point of methyl ether in ethers is -23.6 ° C, which is similar to that of methyl chloride.
Since we do not have pure methyl ether. To verify peak 1, we used methanol and dehydrating agent sulfuric acid to synthesize methyl ether (2) at room temperature. The product was analyzed by chromatographic control. The retention times of the synthesized methyl ether and peak 1 are the same. Therefore, peak 1 is judged to be dimethyl ether.
(2) Peak 3:
Proved by the above hydrochloric acid dissolution experiment. Peak 3 may also be an ether. Peak 3 is behind methyl chloride, but it is also relatively close, so its boiling point is not expected to be high. The ethers with a higher boiling point than methyl ether are methyl ethyl ether (boiling point 7.6 ℃). To confirm peak 3, methanol, ethanol and dehydrating agent sulfuric acid are boiled and dehydrated to produce methyl ethyl ether (2).
The product was subjected to chromatographic control analysis, and the synthesis of methyl ether and peak 3 was used as a control for determination. The retention time was the same, so peak 3 was determined to be methyl ether.
(3) Peak 4:
The experiment confirmed that peak 4 was a stable component. It is inferred that it may be chloroalkane, and the chloroethane with a boiling point inferior to methyl chloride is ethyl chloride (boiling point is 12.2 degrees).
Still using chemical synthesis of ethyl chloride. Ethanol and hydrochloric acid are heated in the presence of a strong dehydrating agent (anhydrous zinc chloride) to produce ethyl chloride. The resulting product was subjected to a chromatographic control reaction, and the resulting ethyl chloride coincided with the retention time of peak 4. Therefore, peak 4 was judged as ethyl chloride.
(4) Peak 5, 7:
Peaks 5 and 7 trailed on the decyl column without triethanolamine, that is, there may be hydroxyl groups. In addition, methanol is present in the raw materials of trichlorfon, so it is estimated that peaks 5 and 7 are methanol and ethanol. We used pure methanol and ethanol as a qualitative control. The results showed that peak 5 was methanol and peak 7 was ethanol.
(5) Peak 6:
The hydrochloric acid dissolution test showed that peak 6 may be an ether, but it still has two characteristics of olefins (Br addition reaction, KmnO4 oxidation reaction). Therefore, we used the 102G chromatograph to prepare and collect the peak pure components and sent them to Chenguang Chemical Research for mass spectrometry analysis.
Mass spectrometry analysis indicates that the mass-to-charge ratio of 74 is a molecular peak. According to the formation of fragments and referring to the mass spectrum data of ether, it is concluded that peak 6 is ether.
â…¡. GDX-01 column is used as a double column qualitative one (see Figure 2 for separation)
Use FID detector to do double-column characterization, the test method is the same as above.
It was further confirmed on the GDX-01 column that the impurities in methyl chloride were methyl ether, ether, methyl ethyl ether, methanol, ethanol, and ethyl chloride. There is also an unknown peak. That is, peak 4 in FIG. 2. A large number of qualitative tests have confirmed that Peak 4 is also relatively stable. It may also be an alkane. Peak 4 appears before ethyl chloride, and its boiling point is the lower component.
Another raw material for trichlorfon is chlorine gas. There may be bromine in the chlorine gas. After the reaction, methyl bromide (boiling point 3.5 degrees) is generated as the confirmed peak 4. The results of the chromatographic comparison of our synthetic bromomethane (total heating with concentrated sulfuric acid and methanol in KBr) showed that peak 4 was methyl bromide.
â…¢. The peaks X0, X1 and X2 have appeared in the raw material methyl chloride since 1979 (see Figure 4)
X0 peak is the same as a small group of natural gas, about lower alkanes
The X1 peak content is very low, and the probability of occurrence is very small, so it is not given.
There are many opportunities for X2 peak to appear, and sometimes the content is also higher. We characterize one according to the retention time.
Figure 4 30% diisooctyl sebacate column / glazed 6201 (60 ~ 80 mesh) coated with 1% triethanolamine
1. X0 2. X1 3. Methyl ether 4. Chloromethane 5. Chloroethane 6. Methanol
7. Ether 8, ethanol 9, X 10, chloroform results confirmed that X2 peak is chloroform
4. Quantitative analysis The quantitative analysis of methyl chloride and its impurities is carried out on the decyl column using the TCD detector (see Figure 3).
The weight correction factor for methyl chloride and its impurities is calculated according to the empirical formula (listed in Table 1). The peak area is multiplied by the weight correction factor and quantified by the normalization method.
Table 1. Composition of weight correction factors for methyl chloride and its impurities
CH3Cl 0.64 1
C2H5Cl 0.72 1.12
CH3OCH3 0.54 0.84
C2H5OC2H5 0.68 1.06
CH3OH 0.58 0.91
C2H5OH 0.63 0.98
CH3Br 1.10 1.72
CH3OC2H5 0.62 0.97
In order to investigate the accuracy of this method, different batches of methyl chloride samples were taken for chromatographic determination. The quantitative results are listed in Table 2.
(1) Quantitative data show that the minimum detection amount of this method is 200ppm.
(2) The relative deviation of the main components in methyl chloride is 0.03%, the low-content components (<0.05%), the relative deviation is less than 10%, and the accuracy is good.
(3) Due to the lack of pure samples and incomplete empirical data, the correction factor is calculated using empirical formulas (among which, the empirical data cannot be calculated for the methanol correction factor), which seems to be a certain error in quantification.
Table 2 Red Star Chemical Factory Zhangdian Pesticide Factory Determination of Chloromethane Content Raw Material Origin Batch Number% Composition 1 # 2 # 3 # 4 # 5 #
1 2 3 phase% 1 2 3 phase% 1 2 3 phase% 1 2 3 phase% 1 2 3 phase%
Red Star Chemical Factory methyl ether 0.12 0.12 0.12 0 0.07 0.07 0.06 4.3 0.12 0.12 0.12 0 0.04 0.04 0 0.15 0.15 0.15 0
Methyl chloride
Ethyl chloride 0.06 0.06 0.07 5 0.06 0.05 0.05 6 0.04 0.04 0.04 0 0.04 0.04 0 0.04 0.03 0.03 10
Methanol 0.05 0.05 0.05 0 0.11 0.10 0.09 7 0.03 0.03 0.03 0 0.02 0.02 0
Ether
Zhangdian Pesticide Factory Ether 0.89 0.87 0.91 1.50 0.84 0.82 0.82 0.84 0.59 0.58 0.61 1.69 6.67 0.68 0.68 0.4 0.64 0.65 0.63 1
Methyl chloride
Ethyl chloride 0.27 0.25 0.23 3.70 0.43 0.43 0.44 0.007 0.11 0.11 0.12 2.73 0.21 0.25 0.22 3.18 0.18 0.19 0.19
Methanol 0.62 0.64 0.58 3.77 0.70 0.67 0.69 1.45 0.21 0.19 0.20 3.50 0.24 0.26 0.24 4.00 0.36 0.35 0.36
Ether 0.34 0.34 0.38 4.86 0.84 0.82 0.85 1.19 0.15 0.15 0.15 2.00 0.35 0.36 0.36 0.86 0.36 0.35 0.35
Phase% refers to relative deviation%
5. The representative test of the sampling method We used the direct sampling method of the syringe to take the gasified methyl chloride sample discharged from the liquid pipe of the chloromethane steel bottle of the factory. This method is simple and fast to operate, but the sampling volume is small. This sampling method lacks representativeness of the sample. Therefore, we take different batches of raw steel cylinders to take their full cylinders and empty cylinder samples after the completion of the samples for measurement and comparison. The results are shown in Table 3.
A peak X1 appeared in the empty bottle sample, which was estimated to be a lower alkane or alkene (see dotted peak in Figure 4). Peak X0 will increase, sometimes increase significantly.
From the table, it can be seen that the measurement results of the second sampling have a relatively close (but irregular) methane content in the empty bottle. In addition to the increase of X0 and X1 peaks, the content of other components in the empty bottle sample changes irregularly. Therefore, we believe that the direct sampling method is basically representative, and this method is feasible.
2. Experimental results and discussion
1. Analysis by gas chromatography with diisooctyl sebacate and GDX-01 column FID detector. Under the foregoing operating conditions, methyl chloride and its impurities methyl ether, ether, methyl ethyl ether, methanol, ethanol, ethyl chloride and Components such as methyl bromide can be separated.
2. Calculate the weight correction factor of methyl chloride and its impurities on the TCD detector using an empirical formula. The peak area normalization method can be used for quantification. Analysis of impurities in different batches of methyl chloride, the detection limit is 200ppm, the relative deviation of impurity content is 10%, which shows that gas chromatography analysis of methyl chloride and its impurities is completely feasible, the method is simple, fast, and the error is small.
3. Apply 1% triethanolamine as a tailing agent to the diisooctyl sebacate column, and then fix the liquid, which not only improves the tailing phenomenon of the alcohol peak, but also selects methanol as the chlorine after selecting the appropriate column temperature. Between methane and ethanol, this is beneficial for separation, and finally we selected this column for qualitative and quantitative analysis.
4. The total separation effect of the GDX-01 column is not as good as that of the decyl column, and the ether peak is dragged so far that the peak shape is not good, but the more valuable thing is the application of the TCD detector, the water peak can be out of methyl chloride, we have tested in GDX -01 is coated with a fixing solution, etc., and it is expected to improve the separation, but the effect is not satisfactory. It needs to be discussed in these aspects in the future.
5. We use the FID detector for qualitative one. Because the FID detector lacks a quantitative correction factor, the TCD detector is used for quantitative analysis. The weight correction factor of methyl chloride and its impurities in the TCD detector can be calculated according to the empirical formula. Due to its low sensitivity, two impurity peaks do not appear, and the calculation result will be high.
6. Sampling method: At present, direct sampling is performed by using a syringe. This method is simple and quick to operate, and can basically represent the content of raw material components. However, in winter and outdoor temperatures are low, which makes sampling difficult.
reference book:
(1) "Filled Gas Chromatography" of Lanzhou Institute of Chemistry
Table 3 Measurement results of samples of full and empty methyl chloride bottles (2), trial textbook "Organic Chemistry" in colleges and universities
Component Date X0 X1 (CH3) 2O CH3Cl C2H5Cl CH3OH (C2H5) 2O C2H5OH X CHCl3
4.15 Full 0.04 0.51 99.36 0.05 0.05
Empty 0.64 0.17 99.11 0.11 0.02 0.03 0.12
4.17 Full 0.09 0.18 99.23 0.16 0.06 0.06 0.22
Empty 0.23 0.02 0.20 99.28 0.26 0.03 0.02 0.03 0.93
4.19 Full 0.06 0.26 98.64 0.33 0.09 0.03 0.05 0.54
Empty 0.21 0.05 0.25 98.36 0.27 0.06 0.03 0.03 0.74
4.23 Full 0.05 0.14 99.37 0.13 0.03 0.07 0.01 0.14
Empty 0.37 0.04 0.18 98.97 0.12 0.01 0.08 0.23
4.28 Full 0.04 0.18 99.25 0.14 0.09 0.02 0.28
Empty 0.19 0.01 0.18 98.89 0.11 0.09 0.01 0.52
5.28 Full 0.07 0.31 99.26 0.10 0.14 0.02 0.02 0.12
Empty 0.12 0.12 0.32 98.78 0.06 0.15 0.01 0.03 0.10
5.30 full 0.02 0.26 98.45 0.17 0.14 0.03 0.93
Empty 0.11 0.01 0.35 98.16 0.07 0.06 0.34
6.5 Full 0.02 0.75 98.33 0.26 0.23 0.13 0.04 0.05 0.19
Empty 0.10 0.71 98.39 0.17 0.18 0.07 0.03 0.35
6.6 Full 0.02 0.24 99.11 0.16 0.12 0.03 0.32
Empty 0.15 0.21 99.03 0.10 0.10 0.41
6.7 Full 0.02 0.71 98.39 0.15 0.27 0.06 0.05 0.35
Empty 0.17 0.18 0.51 98.59 0.11 0.13 0.03 0.28
6.11 Full 0.04 0.34 99.16 0.15 0.06 0.25
Empty 0.24 0.32 99.02 0.10 0.04 0.28
6.13 Full 0.02 0.38 98.57 0.14 0.12 0.05 0.71
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