Add alkali to the distillation pre-column
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On adding alkali to the distillation pre-column and corrosion. Our facility is under construction, and from what I can see in the design, the location for adding the dilute alkali solution is: 1. Add it directly at the bottom of the pre-tower. 2. Add it to the crude methanol before the crude methanol preheater. In actual production, which location is used most often for adding alkali, and under what circumstances is it used elsewhere?
Add it to the feed pipe first; if the acid value of your finished product is within the acceptable range, then continue using it in this way. If adding it causes the acid value to exceed the specified limits, it is recommended that you use the one located below the tower.
Reply to 2# Shouhou: Will adding alkali during system import affect product quality? What is the difference from adding alkali in the pre-tower reactor? I think the entire system, including the import of alkali, is protected.
It’s better to add alkali to the crude alcohol pipeline!
Reply to 3# Qingfeng Liushui: There are still some differences. Check the relevant properties of the equipment and pipes; first and foremost, consider the issue of alkali corrosion! There are some other reasons as well; I can’t remember them right now! sorry!
Thank you all! It turns out that their actual unit value is directly added to the pre-tower, but it seems no problems have arisen
This is mainly because, before entering the tower, the alkali solution reacts with some light components, and the resulting substances are not easy to be removed in the pre-tower; they end up in the product tower. I’ve only heard others say that, and personally I think the sodium carbonate produced contains some unknown components that undergo thermal decomposition in the pressure tower.
Reply to 3# Qingfeng Liushui: The main reason is that when it is added before entering the tower, the alkali solution reacts with some light components; the resulting substances are difficult to remove in the pre-tower and end up in the product tower. I’ve only heard others say that, and personally I think the sodium carbonate produced contains some unknown components that undergo thermal decomposition in the pressure tower. As for protection, since it is acidic from the synthesis process and as it comes in through the crude methanol pipes, no protection is needed.
I’ve seen it stated in some places that the effect of adding alkali and the impact of the amount of alkaline solution on the equipment are as follows: A neutralizes the small amounts of organic acids present in crude methanol, thereby preventing corrosion of the equipment and pipelines； B promotes the decomposition of amines and carbonyl compounds. Too high: Firstly, it is a waste, and it also tends to cause the alkaline solution to crystallize within the equipment pipes. Too low: Trace amounts of acid can cause corrosion in pipeline equipment. So, the high alkalinity mentioned here can lead to crystallization within the equipment’s pipelines; is the substance that forms these crystals sodium methoxide?
If too much alkali is added, the acidity of the product increases – it might seem strange, but if you search online, you’ll find detailed explanations on this. As for where to add the alkali, it’s better to do it in the feed pipeline, as that’s exactly what we did during one of our technical upgrades; previously, it was added in the middle of the tower
Reply to 2# Shouhou senior, why? Could you explain in more detail?