Introduction to Separation Processes

Introduction to Separation Processes

• Separation processes are crucial in chemical plants, often used alongside chemical reactors to achieve desired outcomes.
• A separation process converts an initial mixture into two or more distinct product mixtures.
• Separation processes are needed for pre-purifying raw materials, separating unreacted feed from products for recycling, and purifying products.

Chemical Process Plant Operations

• Most chemical processing involves at least one reactor and one or more separation operations.
• There is a feed mixture that is sent into a separation process, which yields multiple products.

Separation Processes

• A separation process is a method to separate a mixture into its constituents.

When are Separation Processes Needed?

• Pre-purification of raw materials.
• Separation of unreacted feed from products for recycling.
• Purification of by-products.

Case: Hydration of Ethylene

• Reaction: C2H4 + H2O → C2H5OH
• Case 1: Single-pass reactor yields 5% overall conversion.
• Case 2: Unreacted C2H4 recovery via partial condensation and recycling, giving ~100% overall conversion.
• This case also includes a block flow diagram.

Classification of Separation Processes

• Phase creation.
• Phase addition.
• Separation by barrier.
• Separation by an external force field.

Phase Creation

• The most common technique in the industry.
• Involves using energy to separate components via transfer among distinct phases.
• Energy is applied by heat, shaft work via compression, or pressure reduction via a nozzle.

Phase Creation Processes

• Partial condensation/vaporization or flash vaporization; heat transfer (ESA) and changes in pressure are used.
• Distillation employs heat transfer to separate components based on differing volatilities.
• Components like benzene and toluene are amenable to this technique.
• Distillation involves rigorous mixing to separate vapor and liquid.

Phase Addition Techniques

• Absorption: a component from vapor is transferred to an MSA (mass separating agent--liquid)
• Stripping: a component from liquid is transferred to a gaseous MSA.
• Liquid-liquid extraction: a solute from a feed mixture is transferred to another solvent that's immiscible or partially with the feed solvent.
• Adsorption: a component from a gaseous or liquid feed binds to a solid MSA.

Barrier Separation

• Uses microporous and nonporous membranes as barriers to separate vapor and liquid mixtures depending on particle size differences or solubility/diffusivity differences.
• Common methods involving this technique include dialysis, reverse osmosis, gas permeation, and pervaporation.

Separation by an External Force Field

• Separates species with preferential attraction to an external force field.
• Techniques include centrifugation (separates based on size, shape, density, viscosity and rotor speed).
• Electrophoresis (separates charged colloidal or suspended particles based on migration velocity differences in an electric field).
• Other techniques include thermal diffusion, electrolysis, and electrodialysis.

What Method of Separation to Use?

• Factors affecting method selection include fixed/operating cost, technological maturity, ease of providing multiple stages, ease of scale-up from lab experiments, and need for parallel units to handle large capacities.

Equilibrium and Stagewise Operations

• Equilibrium means thermal equilibrium, mechanical equilibrium, and phase equilibrium.
• An equilibrium stage represents sufficient time for two phases to reach equilibrium.
• Stagewise operations involve multiple equilibrium stages to achieve better levels of separation, often using countercurrent, co-current, or cross-current contact modes.
• Processes like distillation, absorption, stripping, and liquid-liquid extraction often utilize stagewise operations.

Explore the fundamental concepts of separation processes used in chemical processing. This quiz covers the importance of these processes in purifying raw materials, recycling unreacted feed, and achieving desired product outputs. Get ready to delve into the intricacies of separating mixtures in chemical plants.