Q1: An aqueous solution of methanol is to be distilled in a tray column. High pressure steam is available as a source of heat. For a given reflux ratio and overhead composition, two options are being explored; (i) a reboiler is used and (ii) no reboiler is used but steam is fed directly to the bottom of the column. As compared to option (i), in option (ii)

ANS:A - less number of trays are required.

Option (ii), where steam is fed directly to the bottom of the column without a reboiler, would typically require more number of trays compared to option (i) where a reboiler is used. When steam is directly fed to the bottom of the column in option (ii), it acts as a stripping agent, helping to remove lighter components from the liquid phase. However, this method may not efficiently transfer heat to the liquid mixture compared to a dedicated reboiler. As a result, more trays may be required in the column to achieve the desired separation efficiency and product purity. Additionally, without a reboiler, the heating may not be as precise, leading to potentially less control over the temperature profile within the column. This can result in a less efficient separation process, requiring more trays to achieve the same separation performance as with a reboiler. Regarding the composition of the residue:

• Without a reboiler, the composition of the residue (bottom product) may indeed be more dilute in methanol. This is because direct steam injection can cause greater stripping of methanol from the liquid phase, leading to a lower concentration of methanol in the bottom product.