Q1: A coalescer in a mixer-settler liquid-liquid extraction coloumn

ANS:D - all 'a', 'b', & 'c'.

Certainly! Let's break down each component of the statement: a) comprises of thin bed of substances of extended surface having high porosity: This component describes the structure and composition of a coalescer. A coalescer typically consists of a thin bed or layer of materials with an extended surface area and high porosity. The purpose of this design is to provide ample surface area for the dispersed droplets or bubbles in the liquid-liquid mixture to interact with the coalescing material. The high porosity allows for efficient flow of the liquid phases while maximizing the contact area for coalescence. b) helps in increasing the bubble size entering the settler: This component suggests that the coalescer assists in enlarging the size of bubbles before they enter the settler. However, this is not the primary function of a coalescer. Instead, the coalescer works to reduce the number of smaller bubbles by promoting their coalescence into larger ones. Larger bubbles are more efficiently separated in the settler, leading to improved phase separation. c) helps in increasing the settling rate of the bubbles: This component implies that the coalescer enhances the settling rate of bubbles in the settler. However, the settling rate of bubbles is primarily influenced by factors such as bubble size, density difference between the phases, and the properties of the liquid phases. While coalescers indirectly contribute to improved settling behavior by reducing the number of dispersed phases, their primary function is to promote coalescence rather than directly affecting settling rates. Conclusion (all 'a', 'b', & 'c'): While option (a) accurately describes the structure and function of a coalescer, options (b) and (c) are not accurate representations of the primary role of a coalescer. Therefore, selecting option (a) alone provides the most accurate and comprehensive description of a coalescer in a mixer-settler liquid-liquid extraction column. The correct option is: comprises of thin bed of substances of extended surface having high porosity. Explanation: A coalescer in a mixer-settler liquid-liquid extraction column is designed to facilitate the coalescence of dispersed droplets or bubbles in a liquid-liquid mixture. It comprises a thin bed of materials with an extended surface area and high porosity. The primary function of a coalescer is to promote the collision and merging of smaller droplets or bubbles into larger ones, thereby aiding in the separation of the two phases in the settler. Here's why options (b) and (c) are incorrect:

• helps in increasing the bubble size entering the settler: Coalescers typically work to reduce the number of smaller bubbles or droplets, rather than increasing their size. They promote the merging of smaller bubbles into larger ones, which are then more efficiently separated in the settler.
• helps in increasing the settling rate of the bubbles: Coalescers are not directly involved in increasing the settling rate of bubbles. The settling rate of bubbles in a settler is influenced by factors such as bubble size, density difference between the phases, and the properties of the liquid phases. Coalescers primarily aid in the coalescence process, which indirectly affects the settling behavior by reducing the number of dispersed phases in the liquid mixture.