Distillation Techniques: Identifying the Wrong Statement
This question requires identifying the incorrect statement regarding steam distillation and vacuum distillation.
Analyzing the Statements
- Statement 1: Steam distillation is used for mixtures that are immiscible with water.
Correct. Steam distillation is effective for temperature-sensitive compounds that are immiscible or sparingly soluble in water. Steam lowers the boiling point.
- Statement 2: Vacuum distillation is used for mixtures that are miscible with water.
Correct. Vacuum distillation reduces the boiling point of liquids, making it suitable for compounds that decompose at their atmospheric boiling point. It can be applied to miscible mixtures.
- Statement 3: Steam distillation is used for mixtures that are miscible with water.
Incorrect. The principle of steam distillation relies on the low solubility or immiscibility of the substance in water. If a mixture is miscible, steam distillation is generally not the appropriate technique.
- Statement 4: Vacuum distillation columns have larger diameters as compared to atmospheric columns for the same throughput.
Correct. Reduced pressure in vacuum distillation leads to lower vapor density and higher vapor velocity. A larger column diameter is needed to maintain the same throughput and prevent flooding.
Conclusion
Statement 3 incorrectly claims that steam distillation is used for miscible mixtures. Therefore, this is the WRONG statement.
Important Questions from Distillation
A binary mixture of butane and butadiene is to be separated in an extractive distillation using furfural. Furfural lowers the activity of butadiene more than it does for butane. Consider the distillation sequence shown in the figure.
Match the component labels in Group I with chemical species in Group II.
Group I Group II P. Component X 1. Butane Q. Component Y 2. Butadiene R. Component Z 3. Furfural A continuous distillation column is used to separate an equimolar mixture of diethylamine (DEA) and methanol. The feed enters the column as saturated liquid at a flow rate of $30 \text{ mol s}^{-1}$. It is desired to obtain $92 \text{ mol}\%$ DEA as distillate. The rate of withdrawal of the distillate from the column is $10 \text{ mol s}^{-1}$. The equilibrium curve for the conditions in the column is given below. The latent heat of vaporization of the reboiler contents is $35 \text{ kJ mol}^{-1}$. Neglect heat loss to the surroundings and assume constant molal overflow. Which one of the following is the minimum reboiler heat duty (in kW)?
- A binary AB liquid mixture containing 30 mol% A is subjected to differential (Rayleigh) distillation at atmospheric pressure in order to recover 60 mol% A in the distillate. Assuming a constant relative volatility $ \alpha_{AB} = 2.2 $, the average composition of the collected distillate is _______ mol% A (rounded off to nearest integer).
A binary feed consisting of $25$ mol% liquid and $75$ mol% vapour is separated in a staged distillation column. The mole fraction of the more volatile component in the distillate product is $0.95$. The molar flow rate of distillate is $50$% of the feed flow rate and the McCabe-Thiele method can be used to analyze the column. The q-line intersects the operating line of the enriching section at $(0.35, 0.5)$ on the x-y diagram. The slope of the stripping section operating line (up to one decimal place) is ____________
- A binary distillation column is to be designed using McCabe Thiele method. The distillate contains 90 mol% of the more volatile component. The point of intersection of the q-line with the equilibrium curve is (0.5, 0.7). The minimum reflux ratio (rounded off to the first decimal place) for this operation is
