Determination of amine solution concentration
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The required mass volume concentration (w/w%) of the amine solution used for natural gas desulfurization (methyl diethanolamine) is 35%, but the values obtained from several batches sent to the laboratory on the same day varied significantly (76–48). According to the laboratory, they use a weighing method; we analyzed the issue and concluded that the amine solution is mixed with deionized water, and since the specific gravity of the amine solution is 1.0418, which is very close to that of deionized water, this may be the reason for the variations in the analysis results Can other methods be used for measurement? For example, using distillation? Please discuss and offer your advice. . .
Methyldiethanolamine is miscible with water and alcohols, and slightly soluble in ethers. Boiling point 247°C; distillation is not advisable.
Reply 1# sinopecdxx: After digesting the sample with concentrated sulfuric acid and hydrogen peroxide, analyze it using the method described in http://bbs.hcbbs.com/thread-939038-1-2.html. Please refer to the volumetric analysis method for the pesticide ‘acetamiprid’ by the original poster.
Reply to 3# djycjx: Are you sure this method works? The standards you mentioned are completely different from what the landlord is asking about
Reply to 4# *ngguanglueguo: The poster mainly needs the content of “methyl diethanolamine”. The purpose of the first step, which involves adding concentrated sulfuric acid and 30% hydrogen peroxide for digestion (performed in a fume hood), is to convert amino groups into ammonium ions (present here in the form of sulfate amine). Afterwards, under alkaline conditions, the \"nitrogen\" is detected using the nitrogen distillation method. I used this method 30 years ago, so I can’t remember the exact amounts of the reagents. However, the principle is sound.
I think this issue is the same as that with N-methyldiethanolamine used in liquefied petroleum gas; in this case, acid-base titration can be used directly, with the mass fraction generally kept between 25-35%, and hydrochloric acid is used for the titration. A 0.2M hydrochloric acid solution is used, with the indicator being a mixture of 0.2% methyl red in ethanol and 0.1% methylene blue in ethanol in a volume ratio of 1:1. The sample volume is determined by the sample concentration; at the titration endpoint, the solution changes from bright green to light purple. After the sample is retrieved, a 250-milliliter Erlenmeyer flask is placed on an electronic analytical balance to determine its mass. The sample is then added to the flask using a dropper, and the mass is read from the balance. After that, 30 to 50 milliliters of distilled water are added, along with three to four drops of indicator, followed by titration with hydrochloric acid. If your burette has a capacity of 50.00 milliliters, the concentration of hydrochloric acid is 0.5000 moles per liter, and the concentration of the sample is estimated to be 40%, then your sample mass can be approximated as 25 divided by 1000 multiplied by 0.5 multiplied by 119 divided by 0.4
The answer provided above is correct; it is also necessary to analyze the heat-stable salt content. Since the result of the titration is the concentration of free amine, the content of heat-stable salts must be added to obtain the total amine concentration. If you have any questions, you can send a private message.