Weekly Topic 2.28, Issue 16: The role of adding alkali in methanol distillation and the location where alkali is added
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This post was last edited by wawjia on 2011-3-1 07:33. Let’s discuss what the role of adding alkali in methanol distillation actually is What is the amount to add? Where is the base added? What are their advantages and disadvantages?
Its effect is to break down certain substances within it, thereby reducing acidity! The purpose is to prevent equipment corrosion; in addition, adding alkali serves to promote the hydrolysis of amine substances. The location where alkali is added is usually at the inlet of the heat exchanger, while in older processes it seemed to be added before the material entered the pre-tower. Changing it to the heat exchanger inlet can help reduce corrosion to some extent. The amount of alkali added is determined based on the pH value of the rough pre-treatment tower, which is generally between 7 and 9
The purpose of adding alkali is to convert the insoluble organic substances in the crude alcohol into a solution, thereby facilitating extraction and distillation in subsequent processes. The standard amount of alkaline solution is used to maintain the pH of the pre-column between 7 and 9. In our company, the alkali is added separately at the middle part of the column, and the rationale behind this approach was explained rather vaguely by the design team. I wonder where the alkali solution from other units is added?
The last edit to this post was made by wu0406 on 2011-3-23 at 08:34. The purpose of adding alkali in the distillation process is to break down certain amine compounds and prevent acid from corroding the equipment; the amount of alkali added is generally controlled at 2 to 4 liters per hour, although this amount also needs to be determined based on actual conditions. We add the alkali before the crude methanol preheater (on the pipeline carrying crude methanol from the synthesis and storage areas)
The purpose of adding alkali is to convert the insoluble organic substances in the crude alcohol into a soluble form, to adjust the pH of methanol, and to meet the requirements for product quality. The standard amount of alkali added is intended to keep the pH in the pre-tower between 7 and 9, and the location where the alkali is added is at the inlet of the feed pump.
Actually, this proposition is a bit broad; for different processes, it may serve different functions. Bases can act as reactants to remove impurities, they can be used to adjust the pH, or they may participate in certain reactions to facilitate separation, or they can provide OH-. Several people upstairs mentioned several different functions. In the process of producing phenol from isopropylbenzene, distillation and the addition of alkali serve two purposes: one is to neutralize phenol and prevent its presence in other products, and the other is for OH- to act as a catalyst that promotes the condensation of aldehydes.
Adding alkali is intended to neutralize any acidic substances that may be produced as by-products in the synthesis reaction, thereby protecting equipment such as towers or heat exchangers from corrosion; it should be added at the inlet of the preheater
Ethyl acetate is distilled; little amount is added to adjust the pH, about one beaker, roughly 2 KG
I haven’t had much exposure to it; I learned about it today.
I suggest everyone discuss the advantages and disadvantages of the location for adding alkali! Some are added in the middle of the tower, some at the bottom of the tower, some on the feed pipeline, and some near the top of the tower – what are the advantages of each?
The purpose of adding alkali during distillation is to decompose organic amine compounds; these compounds, along with dimethyl ether, aldehydes, and very small amounts of alkanes, are removed from the tower. The amount of alkali added is typically such that the pH value inside the distillation tower remains around 8. In the two-tank process designed by our company, it is added to the pre-condenser reflux tank, while in the three-tank and four-tank processes it is added to the pre-distillation tower. According to the book on ligroin production written by Professor Feng Yuanqi, it should be added before the crude methanol preheater. In reality, it seems to work properly in all cases!