## Q1. Attempt any five questions **[5 x 5 = 25]** Below are step-by-step solutions and explanations for each sub-question. Answer any five as required. --- ### (a) Define and explain relative of binary mixture and multicomponent mixture. **Relative Volatility (α):** - It is a measure of the ease of separation by distillation. - For a binary mixture of components A (more volatile) and B (less volatile): \[ \alpha_{AB} = \frac{(y_A/x_A)}{(y_B/x_B)} \] Where: - \(y_A, y_B\): Mole fractions in vapor phase - \(x_A, x_B\): Mole fractions in liquid phase **Explanation:** - If α > 1, A is more volatile and easier to separate from B. - As α increases, separation becomes easier. - For multicomponent mixtures, relative volatility is determined for each component with respect to a reference component. --- ### (b) Explain minimum reflux ratio and optimum reflux ratio in distillation. **Minimum Reflux Ratio (\(R_{min}\)):** - The lowest possible reflux ratio at which the desired separation can still be achieved. - At \(R_{min}\), the number of stages required becomes infinite. **Optimum Reflux Ratio:** - Lies between the minimum and total reflux. - At total reflux, all condensed vapor is returned as liquid (maximum stages, minimum energy). - The optimum is chosen as a trade-off between capital cost (number of trays) and operating cost (reflux ratio). --- ### (c) Discuss the effect of quality of feed on minimum reflux ratio. **Feed Quality (q):** - Defined as the fraction of liquid in the feed. - If q = 1: saturated liquid; if q = : saturated vapor. **Effect:** - The position of the feed line on the McCabe-Thiele diagram changes with q. - As feed becomes more vapor (q decreases), the minimum reflux ratio decreases. - If feed is subcooled liquid (q > 1) or superheated vapor (q < ), minimum reflux ratio increases. --- ### (d) Discuss about the basic principles of design of a trayed distillation tower. **Basic Principles:** 1. **Stage-wise Contact:** Liquid and vapor phases contact on each tray. 2. **Mass Transfer:** Component transfer occurs between phases. 3. **Number of Stages:** Determined by desired separation (McCabe-Thiele or Ponchon-Savarit methods). 4. **Tray Types:** Sieve, valve, and bubble-cap trays. 5. **Tray Spacing:** To allow vapor-liquid disengagement. 6. **Column Diameter:** Based on vapor and liquid flow rates. 7. **Feed and Withdrawal Points:** Located for efficient separation. --- ### (e) "Selection of appropriate solvent is the key for successful separation by solvent extraction" – Explain. **Explanation:** - An effective solvent must: 1. Have high selectivity for the solute. 2. Be immiscible with feed phase. 3. Have high solubility for solute. 4. Be chemically stable and non-reactive. 5. Be easily recoverable and low in toxicity. - Proper solvent selection ensures high separation efficiency and cost-effectiveness. --- ### (f) Discuss criteria for selection of adsorbent in adsorption. **Criteria:** 1. **High Surface Area:** For maximum adsorption. 2. **Pore Size and Distribution:** Suitability for target molecules. 3. **Selectivity:** Preferential adsorption for desired component. 4. **Regenerability:** Can be reused after desorption. 5. **Mechanical Strength:** Withstands operating conditions. 6. **Cost and Availability:** Economically feasible. 7. **Thermal and Chemical Stability:** Withstands process conditions. --- ### (g) Explain basic principles of leaching with applications. Obtain the rate expression of leaching when dissolving a solid. **Principles:** - Involves extraction of soluble component from solid by solvent. - Used in metallurgy (gold, copper), food (sugar, oil extraction). **Rate Expression:** - Assume solid particles are spheres, leaching is diffusion-controlled: \[ \text{Rate} = kA(C_s - C) \] Where: - \(k\): Mass transfer coefficient - \(A\): Surface area - \(C_s\): Saturation concentration - \(C\): Bulk concentration --- ### (h) Explain various membrane separation process in terms of separation mechanism, pore size, operating pressure, and type of solute to be separated. **Membrane Processes:** 1. **Microfiltration (MF):** - Pore Size: .1–10 μm - Pressure: Low (1–3 bar) - Solutes: Suspended solids, bacteria 2. **Ultrafiltration (UF):** - Pore Size: .01–.1 μm - Pressure: Moderate (3–10 bar) - Solutes: Proteins, polymers 3. **Nanofiltration (NF):** - Pore Size: 1–10 nm - Pressure: Higher (5–20 bar) - Solutes: Small organics, divalent ions 4. **Reverse Osmosis (RO):** - Pore Size: <2 nm (non-porous) - Pressure: High (10–100 bar) - Solutes: Salts, small molecules **Mechanisms:** - Size exclusion, charge repulsion, and solution-diffusion. --- ## **Final Note** **Any five of the above can be chosen as answers. Each is explained with definitions, key points, and examples where required.**