Separation Methods

S E P A R A T IO IO N M E T H O D S

Objectives •

Explain the role of separations operations in industrial chemical process

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Explain what constitutes the separation of a chemical mixture and enumerates general separation techniques

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Explain the use of external fields to separate chemical mixtures

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

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- Perfume from flower

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- Dyes from plant

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- Evaporation of sea water to obtain salt

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- Distill liquor

Introduction •

Chemist  – use chromatography to separate complex mixtures quantitatively

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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

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Mixture of two or more immiscible phases MEMBRANE

PERMEATE

HYDROGEN

Light Hydrocarbons RESIDUE

Sieve Dryer Feed

FURNAC  E

COOLING

Caustic Scrubber

LIQUIDS

EXAMPLE: SEPARATION PROCESS

Heavier

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

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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

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- Thermal diffusion

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- Electrophoresis

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- 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 •

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For separation of homogenous, single phase mixture, a second immiscible phase must be developed. This is achieved by:  –  –

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- 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

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Eg: Extractive distillation, liquid-liquid extraction, leaching

Separation by Barrier •

Includes the use of microporous and nonporous membrane as semipermeable barriers

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Membrane are fabricated from polymer, natural fiber, ceramic, metal etc.

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Microporous membrane  – separation occur at different diffusion rate

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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.

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Solid normally in the form of a granular material or packing. E.g: activated carbon, aliminium oxide, silica gel, or calcium aluminosilicate zeolite.

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Example of process: Adsorption, Chromatography, & Ion Exchange.

Generalized downstream processing

Bioseparation Techniques RIPP Scheme •

Liquid-solids separations (dewatering, concentration, particle removing) @ Recovery

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Solute-solute separations (Isolation, Purification)

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Solute-liquid separations (Polishing)

Bioseparation Techniques Stage

Objective(s)

Typical Unit Operations Filtration, sedimentation, extraction, adsorption, centrifugation

Recovery (separation of insolubles)

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Remove or collect cells, cell debris

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Reduce volume

Isolation

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Remove materials having Extraction, adsorption, properties widely different ultrafiltration, from those of target precipitation product

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Reduce volume

Purification

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Remove remaining impurities, which typically are similar to those of target product

Chromatography, affinity methods, precipitation

Polishing

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Remove liquids

Drying, crystallization

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Convert product to crystalline form (not

Example of bioseparation Separation and purification of intracellular enzymes fermentation

lyophilization Cell removal and concentration

Cell disruption Removal of cell debris Protein precipitation or aqueous twophase extraction

dialysis Solvent precipitation Chromatographic purification

ultrafiltration

Rules of thumb • • • •

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

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 : C37H67NO13, Molecular weight : 733.94 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 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.