Interesting chemical engineering exam question – 1: A question that not even the CEO of a distillation company has been able to answer correctly – Standard answer available
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This post was last edited by yjqin1 on 2015-8-20 at 17:44. I created a test question of my own; I asked several chemical industry professionals at the level of chief engineer or above from well-known distillation companies, and none of them answered it correctly. The only one who answered correctly was my cousin, a third-year student majoring in chemical engineering machinery; he got it right by chance. There are N variations of these exam questions; today I have formulated the question as follows: There are 6 types of wastewater, each containing one type of low-carbon alcohol – specifically 1% methanol, ethanol, isopropanol, n-propanol, isobutanol, and n-butanol. The goal is to remove 99% of these alcohols through distillation, reducing their concentration in the wastewater to 0.01%. Roughly speaking: which one is easier to handle? A more professional question: If the tower hardware, top temperature, and bottom temperature are all identical, for wastewater containing which alcohol is the reflux ratio required for treatment the highest, and which one is the lowest? Another way to ask it: If the column and operating conditions are exactly the same, which alcohol will have the highest concentration and which will have the lowest concentration in the wastewater flowing out of the reactor? Or you can arrange a sequence.
Personal thought: Among these six alcohols, the one that is easiest to distill is likely the one that is most soluble in water. Is this related to the solubility of alcohols in water? @Deserved punishment @ylb913
This post was last edited by ylb913 on 2015-8-2 21:36. How can one know so much about dry equipment production? Butanol and isobutanol have boiling points higher than that of water, while the others have boiling points lower than that of water. Compared to water, the molecular structure of alcohols features a hydroxyl group replacing one of the hydrogen atoms in water. I guess the smaller the molecular weight, or the greater the polarity, the more similar such compounds are to water, and therefore the harder it is to separate them.
It’s probably harder to separate those with similar boiling points, as one also has to take into account the case of azeotropes, such as ethanol-water
This is somewhat idealized; it mainly depends on the ease with which hydrogen bonds can be formed – methanol, ethanol, n-propanol, n-butanol, isopropanol, isobutanol
From a qualitative analysis perspective, your analysis is extremely thorough. But chemical engineering is not chemistry; quantitative considerations are still important. This involves mathematics or formulas.
In dilute aqueous solutions, there are not many substances that form an azeotrope with water; I know phenol is one of them. Low-carbon alcohols are not the case.
Background of this problem: Several professors from the TD College of Chemical Engineering were assigned a research and development project by YANKUANG Technology Company, aimed at dealing with the wastewater generated in the coal-to-oil process. After a series of treatments, the wastewater contains small amounts of alcohols with carbon numbers below 4; distillation is used to bring it up to standard before the pure water can be reused. But this brilliant professor TD just can’t make the wastewater meet the standards through simulation. Ask me where the problem lies?
Use the following keywords as reminders: Raoult’s law, Henry’s law, and their areas of application. Activity coefficient, infinite dilution activity coefficient. Boiling point, vapor pressure.
This post was last edited by Zaihui Kangqiao on 2015-8-4 at 11:44. I work in distillation sales; the technical team has deep expertise in this area. If it’s convenient for you, please get in touch with our technical staff!