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DESCRIPTIONSeparation methods for Mass Transfer
ObjectivesExplain the role of separations operations in industrial chemical processExplain what constitutes the separation of a chemical mixture and enumerates general separation techniquesExplain the use of external fields to separate chemical mixtures
IntroductionEarly civilization techniques:- Extracts metal from ores- Perfume from flower- Dyes from plant- Evaporation of sea water to obtain salt- Distill liquor
IntroductionChemist use chromatography to separate complex mixtures quantitativelyChemical engineers concerned with the manufacture of chemicals using large scale separation methods
Key operations in chemical process involved: - Reaction Processes- Separation Processes
Mechanism of SeparationMixture of homogenous phaseMixture of two or more immiscible phases
EXAMPLE: SEPARATION PROCESS
Mechanism of SeparationMixing 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 preferableE.g: Centrifuge, pressure reduction, electric/magnetic field
Basic of separation
Types of Separation ProcessSeparation by phase addition or creationSeparation of barrierSeparation by solid agentSeparation by external field or gradient- Centrifugation- Thermal diffusion- Electrophoresis- Electrodialysis
Phase creation processInvolve 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 processesFor 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.
ContDisadvantages of MSA:Need additional separator to recover MSANeed for MSA make upPossible contamination of the productMore difficult design procedure Eg: Extractive distillation, liquid-liquid extraction, leaching
Separation by BarrierIncludes the use of microporous and nonporous membrane as semipermeable barriersMembrane are fabricated from polymer, natural fiber, ceramic, metal etc.Microporous membrane separation occur at different diffusion rateNonporous separation based on the solubility
ContHydrogen removal in refineries, ammonia plants, and olefin units.
Separation by Solid AgentProcess 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 TechniquesLiquid-solids separations (dewatering, concentration, particle removing) @ RecoverySolute-solute separations (Isolation, Purification)Solute-liquid separations (Polishing)RIPP Scheme
StageObjective(s)Typical Unit OperationsRecovery (separation of insolubles)Remove or collect cells, cell debrisReduce volumeFiltration, sedimentation, extraction, adsorption, centrifugationIsolationRemove materials having properties widely different from those of target productReduce volumeExtraction, adsorption, ultrafiltration, precipitationPurificationRemove remaining impurities, which typically are similar to those of target productChromatography, affinity methods, precipitationPolishingRemove liquidsConvert product to crystalline form (not always possible)Drying, crystallization
Example of bioseparationfermentationCell removal and concentrationCell disruptionRemoval of cell debrisProtein precipitation or aqueous two-phase extractionlyophilizationdialysisSolvent precipitationChromatographic purificationultrafiltrationSeparation and purification of intracellular enzymes
Rules of thumbRemove the most plentiful impurities firstRemove the easiest-to-remove impurities firstMake the most difficult and expensive separations lastSelect processes that make use of the greatest differences in the properties of the product and its impuritiesSelect and sequence processes that exploit different separation driving forces
CyclodextrinRemove the most plentiful impurities first: CD-agent complexRemove 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 CDSelect and sequence processes that exploit different separation driving forces
Example 1You 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 erythromycinFormula: C37H67NO13, Molecular weight : 733.94Form : Salts with acids, Melting point : 56 CUV max: 280 nm, pKa: pH 8.8Freely soluble in alcohols, acetone, chloroform, acetonitrile, ethyl acetate. Moderately soluble in ether, ethylene dichloride, amyl acetate. Hydrated crystals from water, melting point 135-140 C. Resolidifies with second melting point 190-193 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.