N-Methyldiethanolamine is called MDEA for short. It has high selectivity to H2S and low energy consumption. Today’s low-energy decarbonization method. It is one of the incoming raw materials of our factory. It is mainly used for the deacidification treatment in the decarbonization unit of the methanol blowing and degassing artificial extraction coal-to-natural gas device in our factory. It can be used repeatedly after process treatment. In order to timely and accurately analyze the content of the raw material deacidification agent N-methyldiethanolamine, it is necessary to find an analysis method with high accuracy and fast analysis rate, so as to provide the required raw material data for the process in a timely and accurate manner. The detection method provided by the manufacturer of N-methyldiethanolamine is the hydrochloric acid-alcohol standard titration solution titration method. Because the reagents used in this method are toxic, the analysis time is long, and the calculation is troublesome. Because capillary gas chromatography has high separation efficiency and fast analysis speed, etc. characteristics, so its content was analyzed by chromatography. This method is simple, fast, and the result is satisfactory.
1 The detection method of N-methyldiethanolamine provided by the manufacturer is briefly described as follows: the method is hydrochloric acid-alcohol standard titration solution titration method
1.1 Reagents
Acetic anhydride (analytical grade)
Ethylene glycol + isopropanol (1:1)
Hydrochloric acid-alcohol standard solution (0.5mol/L)
Methyl Yellow-Methylene Blue Indicator
1.2 Inspection steps
Weigh 1.0-1.5g sample (accurate to 0.001g) into a 150ml Erlenmeyer flask, add 10ml acetic anhydride, 30ml ethylene glycol + isopropanol (1:1) and add 3-4 drops of methyl yellow-methine Base blue indicator, titrated with hydrochloric acid-alcohol standard solution (0.5mol/L) to reddish brown as the end point.
2 Improved detection method for N-methyldiethanolamine
2.1 Method principle
This method is a gas chromatography method, using a DB-WAX capillary column, under specified working conditions, using a hydrogen flame ion detector to detect, determine its correction factor, and quantitatively analyze the content of N-methyldiethanolamine according to the external standard method.
2.2 Instruments (instruments with the same accuracy can be selected)
2.2.1 Gas chromatograph: a gas chromatograph equipped with a high-precision hydrogen flame detector
2.2.2 Recording system
Workstation compatible with Agilent Model 7890A instrument
2.2.3 Columns
DB-WAX capillary column: column length: 30m, column inner diameter: 0.45mm, liquid film thickness: 0.85μm
2.2.4 Sampling equipment
Injector: 10μL, with automatic sampler (manual injection available)
2.3 Materials and reagents
(1) Hydrogen: the volume fraction is not less than 99%, dried and purified through silica gel and molecular sieves.
(2) Nitrogen: The volume fraction is not less than 99.99%, dried and purified through silica gel and molecular sieves.
(3) Air: dried and purified by silica gel and molecular sieve.
(4) N-methyldiethanolamine: analytically pure
(5) distilled water
2.4 Chromatographic conditions
Hydrogen flow: 30ml/min; air flow: 400ml/min; make-up flow (nitrogen): 25ml/
min;
Oven temperature: 190°C, keep for 20 minutes;
Inlet temperature: 350°C;
Hydrogen flame detector temperature: 350°C;
Injection volume: 0.2μL; split ratio: 10:1
2.5 Operation steps
(1) Drawing of standard curve
Pipette analytically pure MDEA to prepare 35%, 38%, 41%, 45%, 47%, 49% concentration of N-methyldiethanolamine aqueous solution, respectively injected into 6 automatic sampling vials, start the gas chromatograph, Turn on the workstation, set the instrument according to the chromatographic conditions in 2.3, inject 0.2?L standard sample with the autosampler, start the instrument, and stop after the peak with the solution is taken out. Use the hydrogen flame ion method to measure the chromatographic peak area of MDEA. The standard method calculates the correction factor, and then draws the standard working curve. Due to the chromatographic workstation, the curve is in. The correction factor is calculated as follows:
fi=Ei/Ai
Where: fi-correction factor
Ei-concentration of MDEA in the ith standard solution
Ai-the peak area of the i-th standard solution MDEA
(2) Determination of samples
Put the N-methyldiethanolamine sample directly into the auto-sampler vial, start the gas chromatograph, turn on the workstation, use the same chromatographic conditions as above to measure its corresponding value, and check the exact concentration of MDEA from the standard curve. The spectrogram is as follows:
2.5 Result presentation
The sample is injected and analyzed under the chromatographic working conditions. After the analysis is completed, the integrator directly gives the quantitative result.
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2.6 Precision test The standard solution with a concentration of 45% was injected 3 times in parallel, and measured under the chromatographic conditions in 2.3. The measurement results are listed in the following table:
3 Discussion
Through the comparison of these two methods, the detection method provided by the manufacturer is the hydrochloric acid-alcohol standard titration solution titration method, but because the reagent acetic anhydride used is a precursor-2 drug, methyl yellow is a suspected human carcinogen, cancer research The center has listed it as the third class of carcinogens; the preparation and calibration of the hydrochloric acid-alcohol standard titration solution is cumbersome and time-consuming; many reagents are used in the titration, and the results cannot be reported in time to provide data for the process. Therefore, it is necessary to find an analysis method with high accuracy and fast analysis rate. After many tests, it is decided to use gas chromatography external standard method to quantitatively analyze the content of N-methyldiethanolamine.
4 Epilogue
After the application of the method, no toxic and harmful reagents are used; the sample solution is directly injected, and the analysis speed is fast; the capillary column is used for detection, the injection volume is small, the separation degree is high, and the accuracy of the analysis result is high. After many tests, this method can accurately analyze the content of N-methyldiethanolamine, and can guide N-methyldiethanolamine deacidification agent to deal with our company’s natural gas process in a timely and effective manner, making outstanding contributions to improving the quality of gas supply.
