Actual situation on site: Why is the light component at the bottom of the tower? Please provide an explanation
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Raw materials: two components along with a small amount of impurities; one light component has a boiling point of 114°C, while the other heavy component has a boiling point of 118°C. The purity of the light component in the raw materials is 98%. Design purpose: To separate the components using a distillation tower in order to obtain a light-component product with a purity of 99.9% (the impurities are relatively heavy and exit the plant as part of the bottom product, while the light components at the top of the tower represent the qualified product). Actual operation conditions: The bottom product consists of light components with a purity of 99.99%, whereas the top product contains heavy components with a purity of 97%. Since the impurities are also present in the bottom product, the target product does not meet the required standards. An explanation and a solution are requested
The difference between the two boiling points is too small. Also, could impurities form an azeotrope with one of the components?
It can be separated to 4 degrees; it has been done before. It could be due to an azeotrope; we are also suspecting that now.
I know they can be separated, but the difference is very small, and there are impurities present; therefore, it’s likely that the volatility of the light and heavy components gets reversed
First, determine what the impurities in the components are, and then analyze whether the heavy components and light components are miscible with each other; in other words, whether the light components have a strong affinity for the impurities, which results in a higher boiling point for the mixture of light components and impurities, causing it to remain at the bottom of the tower； After analysis, other solvents are added to inhibit the miscibility of impurities and light components.
I agree with the view on azeotropy; for such a system, I think it’s better to find other methods – distillation isn’t necessarily the right approach either
1. The components at the top and bottom of the tower are reversed, but what about the temperatures at those positions? Has inversion occurred as well? ? 2. It’s very likely that it is azeotroping with certain impurities, but the purity of the light components at the bottom of the tower reaches 99.99% – is it okay to discharge the product directly from there?
The original poster first said that a three-nine ratio for the light component content was required; now the output has reached a four-nine ratio. So why does the poster still claim it’s not up to standard?
If azeotropy is excluded, check whether there is any change in the pressure during the distillation process – is it the same as the pressure you observed in previous experiments? With only a 4-degree difference in temperature, the effect of pressure is still quite significant, right?
Let’s clarify all the conditions: what are the components and impurities, the height of the distillation tower, its design, the feed location, and the requirements for the qualified product. With so many conditions unclear, it’s pointless to guess the reasons.