In order to monitor the yield of N-methylmorpholine produced by morpholine methylation, a set of methods for determining the mass fraction of N-methylmorpholine by temperature programmed with N-methylpyrrolidone as internal standard was established by gas chromatography. The method mainly relies on HP6890A gas chromatography, and its detector is hydrogen flame ion detector, the carrier gas is nitrogen, and the chromatographic column is SE-54 capillary column (specification 50rex 0.53mmx1.00txm). Through the determination of recovery rate and repeatability, it is verified that the method has high accuracy and precision, and can accurately determine the content of N-methylmorpholine in the mixed solution.
N- M ethylm orpholine (4-methyl morpholine, N-methyl morpholine), also known as 4-methyl morpholine, is an important chemical product. It is often used as catalyst, solvent and extractant in industry, and is mostly used in polyurethane industry, dye industry and pharmaceutical industry. N-methylmorpholine oxide, the downstream product of N-methylmorpholine, can be used as spinning solvent for man-made fiber filament and also as solvent for producing vegetable casing. There are several methods to synthesize N-methylmorpholine: methylation of morpholine; Methylamine cyclization of diethylene glycol: Methyl cyclization of diethylene glycol amine: Methylamine cyclization of dichloroethyl ether. In the following, aiming at the reaction process of synthesizing N-methylmorpholine by methylating morpholine with dimethyl carbonate, chemical manufacturers established a method for determining the mass fraction of N-methylmorpholine in this reaction system, which has high separation and high sensitivity.
1, reagents and instruments
The reagents morpholine, methanol, dimethyl carbonate, N-methyl morpholine and N-methyl pyrrolidone used in the experiment are all analytically pure reagents, which are produced by Chengdu Kelong Chemical Reagent Factory. Gas chromatography with HP6890A (FID detector) (agilent technologies); Chromatographic data processing workstation ZB-2020; 1/10000 electronic balance, sai Dolis scientific instrument co., ltd.
2. Chromatographic conditions
|色谱柱||sE一54，规格50 m ×0．53 m m ~ 1．O0 m ；|
|汽化室温度||250 ℃ ；|
初始温度50 qC ，保持 9 min，温度梯度 70 ~C／min，最终温度250 ℃，保持9 m in
|柱前压||5 —10 kPa|
|进样针||微量进样器厂，规格 0．5 IxL|
3. Experimental methods
Qualitative analysis: Determine the retention time of each substance under chromatographic conditions.
Quantitative analysis: after selecting the internal standard substance, measuring the response factor and drawing the corresponding response curve, adding the quantitative internal standard substance into the reaction stock solution, through the response curve, the suitable response factor can be selected and the N-methylmorpholine content in the reaction solution can be accurately determined.
Finally, the reliability of this method is verified by repeated determination and calculation of recovery rate.
Second, the results and discussion
1. Qualitative analysis
The analytically pure methanol, N-methylmorpholine, dimethyl carbonate and N-methylpyrrolidone reagents were injected with 0．1 }xL under experimental conditions, and the retention time of each reagent was obtained. The results are shown in Table 1.
It can be seen from Table 1 that the resolution of each component is good under the chromatographic condition of 1.2, which can meet the analysis requirements of this paper.
2. Quantitative analysis
(1) determination of standard curve
The response values of different substances on the same detector are different, and the data measured by the area normalization method are deviated from the real data, so an internal standard can be selected for comparative determination. In this paper, the internal standard N-methyl pyrrolidone was added to calibrate the measured N-methyl morpholine, and the standard curve of relative correction factor was drawn. The points with mass concentrations of N-methylmorpholine of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90% were selected as standard points. Relative correction factor. The calculation formula of professional methyl morpholine manufacturer is:
See table 2 for specific data of relative correction factor determination of n-methyl morpholine obtained by using n-methyl pyrrolidone as internal standard.
According to the data in table 2, the standard curve of relative correction factor is made. the abscissa is the mass fraction of n-methyl morpholine (NM M), and the ordinate is the relative correction factor I, as shown in figure 1.
It can be seen from the data in Figure 1 and Table 2 that the relative correction factor of N-methylmorpholine basically keeps a linear relationship with its concentration at various concentrations, and the correction factor increases when the concentration is higher. The solid line in the figure is the added trend line. It can be seen from Figure L that the trend line equation is y = 0. 112x+0.586. R = 0. 982
It shows that the linear fitting degree is high and can be used as a relative correction factor curve.
(2) Examples of quantitative analysis
Measure the reaction solution sample N M M 20 160219, take 1．0 132 g of reaction solution, add 0．5295 g of internal standard, sample 0．1 tzL with injection needle, and get the gas chromatogram as shown in fig. 2.
Select an appropriate correction factor by trial and error method, and bring the data in Table 3 into equation (2) to calculate the concentration of N-methylmorpholine in the reaction stock solution = 14.35%. At this time, the relative correction factor is 0.6021. From the above calculation, it can be seen that the internal standard method for determining the concentration of a certain substance in the reaction solution is simple and can eliminate the interference of other reaction products, and can be used for reactions with many reaction products but only need to determine the concentration of single or few reaction products.
(3) Determination of the accuracy and reproducibility of the method
① Prepare 10%, 25%, 35%, 50%, 65%, 75%, 90% standard solutions for concentration determination, and calculate the recovery rate of gas chromatography, so as to test the accuracy of this method. The calculation formula of recovery rate R is: collect 6 surface water samples respectively, measure the recovery rate of the 6 actual samples, and the recovery rate of the 6 samples is 83.1% 108.
Automatic purge and trap-gas chromatography-mass spectrometry was used to determine chloral in water, and chloral was alkalized into chloroform by sodium hydroxide. The content of chloral in water was indirectly calculated by measuring the content of chloroform. Experiments show that the method is simple, rapid, low detection limit, high sensitivity and good reproducibility, and can fully meet the daily monitoring requirements of environmental monitoring departments for chloral in surface water.
②为验证方法的重现性 ，同一反应液(N M M 20 160219 )按2．2．2 中的方法测定5 次，结果见表 5
From the calculation results in Table 4, it can be seen that the recovery rate of the analysis method established in this paper is 97% ~ 102%, and the deviation is within 3%, so the accuracy of the response factor in the previous paper is higher. It can be seen from the data obtained in Table 5 that the samples were measured five times repeatedly
The relative standard deviation (R SD) of five n-methylmorpholine concentrations obtained by N M M 20160219 is 0.3487%, which indicates that the data determined by this method has good reproducibility. Therefore, the analytical method established in this paper can be used to determine the concentration of methyl morpholine in the methylation of dimethyl carbonate to produce methyl morpholine with high accuracy and repeatability.
In this paper, n-methyl pyrrolidone was selected as the internal standard, and the reaction solution of morpholine methylation to n-methyl morpholine was analyzed by using H P5890A (SE -54 capillary column) with temperature programmed. the obtained spectrum has good peak shape and high separation degree. after verification, this method has high accuracy and reproducibility, and can meet the requirements of scientific research and production.