Q1: __________ column is preferred to be used, when a high liquid hold up is required in a reactor for gas-liquid reaction.

ANS:C - Spray

A spray column is a type of equipment used in chemical engineering for gas-liquid contact and mass transfer processes. It is commonly employed in applications where intimate mixing and large interfacial area between a gas phase and a liquid phase are required, such as absorption, scrubbing, and humidification processes. Here's an explanation of the key features and operation of a spray column:

1. Design: A spray column typically consists of a vertical cylindrical vessel equipped with a spray nozzle or multiple nozzles located at the top of the column. The liquid phase, usually a solvent or absorbent, is pumped to the top of the column and sprayed into the column as fine droplets.
2. Gas-Liquid Contact: The gas phase, containing the component to be absorbed or scrubbed, enters the column from the bottom and flows upward countercurrent to the liquid phase. As the gas rises through the column, it comes into contact with the descending liquid droplets. This interaction creates a large interfacial area between the gas and liquid phases, facilitating mass transfer between them.
3. Mass Transfer: Mass transfer occurs through mechanisms such as absorption, adsorption, or chemical reaction, depending on the specific process being carried out. For example, in gas absorption processes, the gas phase components are transferred into the liquid phase through dissolution or chemical reaction with the solvent.
4. Enhanced Mixing: The fine droplets produced by the spray nozzles enhance mixing and promote turbulence within the column. This promotes efficient contact between the gas and liquid phases, maximizing mass transfer rates.
5. Separation: As the gas and liquid phases move through the column, they undergo separation. The absorbed or scrubbed components are transferred from the gas phase to the liquid phase, resulting in a purified gas stream exiting the top of the column, while the enriched liquid phase exits the bottom.
6. Applications: Spray columns are used in various industrial applications, including gas absorption processes for removal of pollutants from exhaust gases, scrubbing of acid gases from industrial flue gases, humidification of air streams, and liquid-liquid extraction processes.