SEPARATION METHODS

Objectives Explain the role of separations operations in industrial chemical process Explain what constitutes the separation of a chemical mixture and enumerates general separation techniques Explain the use of external fields to separate chemical mixtures

Introduction Early civilization techniques: –- Extracts metal from ores –- Perfume from flower –- Dyes from plant –- Evaporation of sea water to obtain salt –- Distill liquor

Introduction Chemist – use chromatography to separate complex mixtures quantitatively Chemical engineers – concerned with the manufacture of chemicals using large scale separation methods

Chemical Processes Conducted: –Batchwise –Continuous –Semi-continuous Key operations in chemical process involved: - Reaction Processes - Separation Processes

Mechanism of Separation Mixture of homogenous phase Mixture of two or more immiscible phases Feed PERMEATE RESIDUE Caustic Scrubber FURNAC E MEMBRANE HYDROGEN LIQUIDS COOLING Sieve Dryer Light Hydrocarbons Heavier Hydrocarbons EXAMPLE: SEPARATION PROCESS

Mechanism of Separation Mixing of chemical is spontaneous, increase entropy and randomness. Separation of chemicals requires the uses of energy. Separation includes: –- Separation of component A from mixture in homogenous phase –- Separation of component A from mixture in different phases

Mechanism of Separation If two or more immiscible phases exist mechanical separation is preferable E.g: Centrifuge, pressure reduction, electric/magnetic field

Basic of separation

Types of Separation Process 1)Separation by phase addition or creation 2)Separation of barrier 3)Separation by solid agent 4)Separation by external field or gradient  - Centrifugation  - Thermal diffusion  - Electrophoresis  - Electrodialysis

Phase creation process Involve the creation of a second phase that is immiscible with the feed. Accomplished by energy or pressure reduction. Suitable for mixture that have tendency to vaporize. E.g: Evaporation, sublimation, crystallization, distillation.

Phase addition processes For separation of homogenous, single phase mixture, a second immiscible phase must be developed. This is achieved by: –- Creation of energy separating agent (ESA) –- Mass separating agent (MSA) When 2 immiscible fluid phases are contacted, intimate mixing of the 2 phases is important in enhancing mass transfer rates. After phase contact, employing gravity and/or enhanced techniques completed the separation process.

Cont’ Disadvantages of MSA: -Need additional separator to recover MSA -Need for MSA make up -Possible contamination of the product -More difficult design procedure Eg: Extractive distillation, liquid-liquid extraction, leaching

Separation by Barrier Includes the use of microporous and nonporous membrane as semipermeable barriers Membrane are fabricated from polymer, natural fiber, ceramic, metal etc. Microporous membrane – separation occur at different diffusion rate Nonporous – separation based on the solubility

Cont’ Hydrogen removal in refineries, ammonia plants, and olefin units.

Separation by Solid Agent Process that use solid mass-separating agents. Solid normally in the form of a granular material or packing. E.g: activated carbon, aliminium oxide, silica gel, or calcium aluminosilicate zeolite. Example of process: Adsorption, Chromatography, & Ion Exchange.

Generalized downstream processing

Bioseparation Techniques Liquid-solids separations (dewatering, concentration, particle Recovery Solute-solute separations (Isolation, Purification) Solute-liquid separations (Polishing) RIPP Scheme

Bioseparation Techniques StageObjective(s)Typical Unit Operations Recovery (separation of insolubles) Remove or collect cells, cell debris Reduce volume Filtration, sedimentation, extraction, adsorption, centrifugation IsolationRemove materials having properties widely different from those of target product Reduce volume Extraction, adsorption, ultrafiltration, precipitation PurificationRemove remaining impurities, which typically are similar to those of target product Chromatography, affinity methods, precipitation PolishingRemove liquids Convert product to crystalline form (not always possible) Drying, crystallization

Example of bioseparation fermentation Cell removal and concentration Cell disruption Removal of cell debris Protein precipitation or aqueous two- phase extraction lyophilization dialysis Solvent precipitation Chromatographic purification ultrafiltration Separation and purification of intracellular enzymes

Rules of thumb Remove the most plentiful impurities first Remove the easiest-to-remove impurities first Make the most difficult and expensive separations last Select processes that make use of the greatest differences in the properties of the product and its impurities Select and sequence processes that exploit different separation driving forces

Cyclodextrin Remove the most plentiful impurities first: CD-agent complex Remove the easiest-to-remove impurities first: unused starch, linear dextrins, glucose, maltose, etc Make the most difficult and expensive separations last: CD crystals Select processes that make use of the greatest differences in the properties of the product and its impurities: decanol and CD Select and sequence processes that exploit different separation driving forces

Example 1 You have been given a task to purify the erythromycin antibiotic from fermentation broth. The information on erythromycin is given below. What do you think the most likely unit operations that should be used for the isolation and purification of erythromycin? Justify the reasons for the selection of the unit operations. Information on erythromycin Formula: C 37 H 67 NO 13, Molecular weight : Form : Salts with acids, Melting point : 56 °C UV max: 280 nm, pKa: pH 8.8 Freely soluble in alcohols, acetone, chloroform, acetonitrile, ethyl acetate. Moderately soluble in ether, ethylene dichloride, amyl acetate. Hydrated crystals from water, melting point °C. Resolidifies with second melting point °C

Solution Erthromycin has limited solubility in water but is soluble in several solvents, including amyl acetate. Since the solubility of amyl acetate is low, isolation could be performed by a liquid-liquid extraction of erythromycin using water-amyl acetate system. For the extraction, it would be desirable to raise the pH of the aqueous phase above the pKa of erythromycin of 8.8, so that the secondary amino group is converted from the positively charged from the neutral free base form. For the purification step, crystallization is a good choice, since hydrated crystals have been obtained from water.

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