A Review of Separation Topics Group 6: Ben, Brendan, Sonia, Loyan, Eyuel

Overview of Topics: Different Types of Separation techniques Brief Review of Thermodynamics Overview of Mass Transfer Principles Absorption/Stripping Binary and Multicomponent Distillation Liquid-Liquid Extraction/Membrane Separation Conclusion

Different Types of Separation 1. Phase Creation (most common) Examples: - Distillation - Crystallization 2. Phase Addition Examples: - Liquid-Liquid Extraction - Absorption 3. Barrier Examples: - Reverse Osmosis - Gas Permeation 4. External Field Examples: - Electrophoresis (sep. by charge) - Centrifugation (centrifugal force) Phase 1 Phase 1 Phase Creation Barrier Feed Feed Phase 2 Phase 2 Feed Phase Addition Phase 1 Phase 1 Feed Force Field Input-output control volume for phase separation Input-output control volume for phase addition Input-output control volume for barrier separation Input-output control volume for external field separation Mass Separating Agent Phase 2 Phase 2

Review of Thermodynamics T-x,y and P-x,y diagrams for a binary system.

Overview of Mass Transfer Principles Fick’s Laws of Diffusion High Concentration → Low Concentration https://biologydictionary.net/diffusion/ Mass transfers from areas of high concentration to low concentration.

Overview of Mass Transfer Principles http://mathbench.umd.edu/modules/cell-processes_diffusion/page08.htm Steady state diffusion Transient diffusion Quasi-steady state Chemical reactions Convective mass transfer Graphical representation of concentration changes with distance at steady state.

Overview of Mass Transfer Principles https://www.quora.com/What-is-the-meaning-of-%E2%80%9Cquasi-steady-state-assumption%E2%80%9D Steady state diffusion Transient diffusion Quasi-steady state Chemical reactions Convective mass transfer Concentration profiles of a change in concentration at transient conditions and quasi-steady state conditions.

Overview of Mass Transfer Principles Steady state diffusion Transient diffusion Quasi-steady state Chemical reactions Convective mass transfer A first-order chemical reaction with respect to species A.

Overview of Mass Transfer Principles http://slideplayer.com/slide/8248957/ Steady state diffusion Transient diffusion Quasi-steady state Chemical reactions Convective mass transfer Graphs and dimensionless quantities for determining the convective mass transfer coefficient.

Absorption/Stripping Absorption (gas scrubbing): The process by which one or more species is transferred from the gas phase to a liquid solvent Absorption is used to separate gas mixtures, remove impurities, or recover valuable chemicals. The solvent is the separating agent. Stripping: The operation of removing the absorbed solute from the solvent is called stripping. Absorbers are normally used with strippers to permit regeneration (or recovery) and recycling of the absorbent. In this case, the insoluble gas is the separating agent.

Absorption/Stripping: Physical Principles Absorption and stripping units operate using equilibrium stages, where liquid and vapor are in contact with each other (assumed to be at equilibrium). The Kremser Method is employed to estimating the minimum absorbent or stripping agent flow rate.

Absorption/Stripping: Physical Principles Columns can either be packed or trayed, where the minimum number of stages is determined through either an algebraic or graphical method. Murphree Stage Efficiency For a packed column a rate based approach is used to determine the specifications of the column. Packed-Height Equivalent to Theoretical Stages (HETP) HOG (overall height of a gas transfer unit) NOG (overall number of gas transfer units)

Absorption/Stripping: Industrial Example In the pretreatment of natural gas in the processes to produce LNG, an amine solution is typically used to scrub acid gas (H2S, CO2). The rich amine is then sent downstream to a stripping unit where the lean amine is regenerated. Make-up water is often used to dilute the the rich amine, to a desirable weight percentage.

Distillation: Binary Systems McCabe-Thiele Graphical method (trayed columns) Most useful to find Nmin and Rmin Equilibrium data is needed. Xd, Xb and Zf are usually known or specified. Then you have to calculate D and B through a mass balance. You can determine Nmin by stepping off stages from xd to xb in between the equilibrium line and the 45 degree line. To determine Rmin: Find the slope of the line that intersects the point where the q-line intersects the equilibrium curve. That is equal to R/(R+1) (Shown above). Then, given a multiple of Rmin to operate at, you can re-step off stages and find the actual number of stages required. Seader, Separation Process Principles

Multicomponent Systems FUG method (for multicomponent systems) Fenske Equation for Min stages Underwood Equation for min reflux Gilliland Correlation for actual reflux ratio and number of stages For Multicomponent Systems: Use the FUG method. The flowsheet gives a good idea of how the process works, but realistically this method is used for finding Nmin and Rmin and then plugging that into a process simulator such as aspen. Alpha m is the geometric mean of the relative volatilities of the heavy key and light key on the top and bottom stages. Seader, Separation Process Principles

Multicomponent Systems To Find Rmin: Gilliland Correlation isn’t all that practical to use, you just select an appropriate multiple of Rmin and plug into Aspen Seader, Separation Process Principles

Liquid-Liquid Extraction The separation of a liquid feed with two or more components using a solvent. Solvent dissolves one or more of the components to facilitate separation. Example: Acetic acid/Water and Ethyl acetate Equipment for extraction Mixer-Settlers Spray Columns Packed Columns Plate Columns Seader, Separation Process Principles

Liquid-Liquid Extraction Graphical methods Hunter-Nash Graphical Equilibrium Stage Number of Equilibrium Stages Minimum Solvent to Feed ratio Maximum Solvent to Feed ratio Maloney-Schubert Graphical Equilibrium Stage Seader, Separation Process Principles

Membrane Separation Mass Transfer Through Porous Membranes Permeance Retentate Permeate Fick’s Law of Diffusion Seader, Separation Process Principles (top right) Input-output of control volume for a membrane separation process. (bottom right) Tubular air membrane separator of oxygen and nitrogen. (bottom left) Illustrations of varying porous media through which species diffuse through. https://en.wikipedia.org/wiki/Membrane_gas_separation

Work Cited Separation Process Principles, 3e, Seader et al http://jollythermodynamics.weebly.com/phase-diagrams-pxy-txy.html https://biologydictionary.net/diffusion/ https://www.quora.com/What-is-the-meaning-of-%E2%80%9Cquasi-steady-state-assumption%E2%80%9D http://slideplayer.com/slide/8248957/