ANS:D - gas absorption with chemical reaction.

Gas absorption with chemical reaction refers to a process where a gas, typically a pollutant or a desired component, is absorbed into a liquid solvent accompanied by a chemical reaction between the gas and the solvent. This process is widely used in various industries, including environmental engineering, chemical processing, and gas purification. Here's an overview of gas absorption with chemical reaction:

1. Process Description: Gas absorption with chemical reaction involves bringing a gas stream into contact with a liquid solvent. As the gas passes through the solvent, it undergoes a chemical reaction with one or more components of the solvent. This reaction results in the transfer of the gas component from the gas phase to the liquid phase.
2. Chemical Reactions: The chemical reactions occurring during gas absorption can vary depending on the specific system and the desired outcome. In environmental applications, for example, gas absorption may involve the removal of pollutants such as sulfur dioxide (SO2) from industrial flue gases by reacting it with an alkaline solution to form sulfite or sulfate compounds.
3. Mass Transfer: Gas absorption with chemical reaction involves both physical mass transfer and chemical reaction. Physical mass transfer refers to the transport of gas molecules across the gas-liquid interface, driven by concentration gradients. Chemical reaction occurs between the gas molecules and the solvent molecules, leading to the formation of reaction products.
4. Rate Controlling Steps: The overall rate of gas absorption with chemical reaction is often controlled by both the rate of mass transfer and the rate of chemical reaction. The slower of the two processes typically determines the overall efficiency of the absorption process. Therefore, optimizing both mass transfer and reaction kinetics is essential for maximizing absorption efficiency.
5. Design Considerations: Designing a gas absorption system with chemical reaction involves considerations such as selecting an appropriate solvent, optimizing operating conditions (temperature, pressure, flow rates), and designing efficient contacting equipment (such as packed towers or bubble columns). The choice of solvent and operating conditions can significantly affect both the rate of chemical reaction and the rate of mass transfer.

Overall, gas absorption with chemical reaction is a versatile and widely used process for removing or recovering gas components from a gas stream while simultaneously converting them into more desirable forms. It plays a crucial role in environmental protection, gas purification, and various chemical processes.