Problems with finished product methanol test indicators.
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At present, our company is a 10W tons/year coke oven gas-to-methanol enterprise. It has been more than three months since we started operating~. Some time ago, due to export, some trace substances in the finished product were controlled and adjusted. Recently, a new indicator of trimethylamine was released to test the content of our refined methanol. The content of trimethylamine is 700PPb. I checked some information. Trimethylamine is mainly produced by the precipitation of copper in the synthesis catalyst and then participates in the reaction. However, the boiling point of trimethylamine is very low. How to bring it into the product is puzzling. The expert has also seen this situation. Please help analyze it.
My analysis may be that the N gas component in your raw gas exceeds the standard. When a trace amount of ammonia containing 20×10-6 (equivalent to 0.015g/m3 ammonia in coal gas) exists in the raw material, under the conditions of methanol synthesis, the chemical reaction will be accompanied by the formation of monomethylamine, dimethylamine and trimethylamine. The reaction formula is as follows: CH3OH+NH3=NH2CH3+H2O+20.75kJ/mol 2CH3OH+NH3= NH(CH3)2+2H2O+60.88kJ/mol 3CH3OH+NH3= N(CH3)3+3H2O+407.55kJ/mol Due to the above mixed amine reaction, the crude methanol produced contains fishy odor and methylamine (especially dimethylamine and trimethylamine) ； On the other hand, the increase in mixed amines has high base value and low ammonia value, which is conducive to the formation of fusel alcohol side reactions and increases the difficulty of the crude methanol distillation process. It not only affects the product quality of refined methanol, but also increases the consumption of various materials. The fundamental measure of prevention is: ① Strengthen the purification management of synthetic raw gas, strictly prevent ammonia from entering the methanol synthesis system, and avoid the generation of methylamine ； ②Master the operation of the pre-distillation tower. The boiling points of dimethylamine and trimethylamine are 7.4°C and 3.5°C respectively. It can generally be removed by mastering the extractive distillation of the pre-distillation tower and controlling the condensation temperature at the top of the pre-distillation tower.
What are the things that need to be paid attention to in the operation of the distillation pre-column mentioned by the brother upstairs? Because the boiling points of these three amines are relatively low. The temperature controlled by our pre-column is also 84 to 85 for the tower kettle and about 75 degrees for the top of the tower. It should be possible to remove it. I wonder if these amines The class will form an azeotrope with some high-boiling components. Now what kind of reflux flow should be controlled in the pre-tower? Will the concentration of crude methanol when entering the pre-tower also have a certain impact on these? If more extraction water is added to the crude methanol, will it improve the distillation effect of these substances: hug:
Sir, please tell me how to detect trimethylamine in methanol.
Amine substances exist in crude methanol in the form of salts such as CH3-NH2.H2CO3 or ammonia aqueous solutions such as (CH3-NH3).OH. They are removed by: 1. Add alkali to decompose the compound state into the free state CH3-NH2.H2CO3+2NaoH=2CH3-NH2+Na2CO3+2H2O 2. Remove free amines and control the pre-tower venting temperature above 38°C to remove amines when removing ethers.
I also want to ask about the monitoring method of trimethylamine in methanol. It is best to use gas chromatography. Can you clarify the column, detector, method, etc.