Discussion on the color of caustic soda in the falling film process using molten salt as a heat source
Thread Content
Dear sea friends, regarding caustic soda production: what colors can appear in the caustic soda, and what are the reasons for this? 1. White: The normal color of the product. 2. Yellowish: An excessive amount of sugar causes sucrose to hydrolyze into monosaccharides in a sodium hydroxide solution; these monosaccharides then form polyaldehydes, giving the solution a yellowish color (the sucrose solution itself also turns yellow). 3. Green to dark green: Too little sugar was used, and the alkali contains nickel oxide. I’m not sure if the descriptions of these colors and their causes are correct Also, why does caustic soda have red or gray colors as well?
Is this post just going to stay like this? May I ask, if too much sugar is added, will the caustic soda turn black?
Excessive sugar addition leads to a dark color; this is likely due to carbonization caused by high temperatures acting on the sugar solution. We have not encountered this issue here, and we are not sure whether there is any black substance in your system – it was brought in along with the 32% alkaline solution.
Redness occurs as a result of cooking in a pot. Generally, there is a small amount of black scale at the beginning of vehicle use due to nickel corrosion. Too much sugar is used, which affects heat transfer, and the concentration of caustic soda does not reach the required level. I think the green and dark green you’re referring to are that dark, alkaline substance that appears before driving; it’s nickel oxide that has been washed away by the alkali, resulting in a high nickel content.
Sometimes, at the beginning of driving, the alkali takes on a slight red color; I think it’s due to rust on the drum of the caustic soda production machine (after all, drums made of nickel are too expensive). I’m not sure if this is correct
Blackening or graying, usually due to excessive nickel impurities
Redness is caused by an excessive level of iron oxide in the alkaline raw material; in the case of carbon steel drums, it could also be rust that forms at the time when the alkali is applied. Grayish discoloration occurs rarely – could it be something inside the pipeline equipment? I’ve never encountered it. Blackening may be caused by a high sugar content leading to carbonization, but this blackness should appear as spots. Additionally, the 32% alkaline solution contains many impurities, and during evaporation nickel oxide or nickel hydride may also be introduced, which can be detected during cleaning.