Liquid-liquid extraction, Aqueous Two Phase Extraction,Supercritical Fluid Extration

Dr. N. Banu,Associate Professor,

Vels University.

Liquid – liquid extraction• Definition:

separation of a component from a liquid mixture by treatment with a solvent in which the desired component is soluble is known as liquid-liquid extraction.

Requirement:high percentage of product.conc. In a smaller volume of solvent.solubility characteristics like:polar liquid mix with each other and dissolves salts and other polar solids and for non-polar compounds nil polarity or low polarity solvents are used.dieletric constant: is a measure of molar polarization of a compound. (polar/non-polar). High value indicates high polarity.D = C/Co where C is electrostatic capacity of a condenser containing susbstances between the plates,

Co is the vlaue of the same condenser when completely evaculated.

Types of liquid-liquid extraction

• Co-current system• Counter – current systemCo-current system:Feed mixer raffinate mixer raffinate mixer raffinate

separator separator separtorSolvent 1 2 n

extract

solvent solvent extract

extract

Counter-current system

Feed mixer raffinate mixer raffinate mixer depleted raff.

separator separator separator solvent

Solvent enriched with product

Podbielniak centrifugal extractor

• Horizontal cylindrical drum• 5000 rpm• Penicillin G extraction• Steps:• Extraction of pen. G from broth into organic solvent

(amyl or butyl acetate or methyl iso-butyl ketone)• Extraction from organic solvent into aqueous buffer.• Extraction from aqueous buffer into organic solvent• Extraction of the solvent to obtain the penicillin salt.

Aqueous two phase extraction (ABS)

• Used for chemical processing and biochemical processing• Limited application for sensitive biologicals.Aqueous two phase:

high water contentlow interfacial surface tensionbiocompatible

Materials: Natural and synthetic hydrophilic polymers.Phase separation occurs when hydrophilic polymers are added to an

aqueous solution, when the conc. Exceeds the value, two immiscible aqueous phases are formed.

Settling time for the two phases can be prolonged depending on the components used and vessel geometry.

Phase separation improved by centrifugal separators or magnetic separators.

systems

• Non-ionic polymer/non-ionic polymer/watere.g. polyethylene glycol/dextran

• Polyelectrolyte/non-ionic polymer/water.e.g. sodium carboxymethyl cellulose/PEG

• Polyelectrolyte/polyeletrolyte/watere.g. sodium dextran sulphate/sodium carboxy methyl cellulose.

• Polymer/low mol. Wt. component/watere.g. dextran/propyl alcohol.

Factors affecting distribution of solute

• Partition coefficient• Temperature• Polymer type and mol. Wt.• Salt conc.• Ionic strength• pH• Mole. Wt of the solute.

Affinity technique

• To selectively recover and conc. the solute.e.g. PEG – NADH derivatives in the extraction of

dehydrogenases.p-aminobenzamidine – trypsincibacron blue – phosphofructokinase.

Use of ligands to incrase the selectivity and recovery.

Applications

• Proteins, enzymes, cells, subcellular particles, extractive bioconversion.

• For large scale sepration: PEG – upper phase polymer with dextran.

• Conc. Slat solution or hydroxypropyl starch – lower phase.

• Fumarase and penicillin acylase.

Supercritical fluid extraction (SCFs)It utilizes the dissolution power of supercritical fluids. i.e.

fluids above their critical temp. and pressure.Advantages:• Use of moderate temp.• Use of cheap and non-toxic fluids.• Used in the extraction of hop oils, caffeine, vanilla, veg.

oils and β-carotene, steroids, chemotherapeutic drugs.• Other uses: removal of undesirable substances such as

pesticide residues, removal of bacteriostatic agents from fermentation broths, the recovery of organic solvents from aqueous solutions, cell disintegration, destruction and treatment of industrial wastes and liposome preparation.

Disadvantages

• Phase equilibria of the solvent/solute is complex, so design of extraction condition is difficult.

• CO2 is non-polar and useful in extraction of non-polar solutes. Use of co-solvents for extraction of polar compounds complicates further downstreaming.

• Use of high pressure leads to capital cost for plant and operating costs high.

Membrane processes

• Ultra filtration• Reverse osmosis.• Ultra filtration:Definition: solutes of high molecular wt. are

retained and low mol. Wt solutes are forced under hydralic pressure (around 7 atm.) through a membrane of a very fine pore size.

Use: product conc. And purification.

Membranes

• Membranes with mole. Wt. cut-offs between 500 – 300,000.

• Types: microporous and diffusive.• Microporous membrane:• Rigid with small pores with 500 – 5000 A dia.• Very small mole. Will pass through the membrane

and large ones will be retained at the filter surface. • Intermediate sized mole. Will be retained within the

structure of the membrane and block the pores.

Types of membranes• Diffusive ultrafilters:• Made up of homogenous hydrogel membranes through

which solvents and solutes are transported, under the influence of a conc. Or activity gradient, by molecular diffusion.

• It requires kinetic energy and high temp. • Readily permeable membrane – readily hydrated and

composed of polymer with a strong affinity for its solvent. • Anisotropic diffusive membranes with very thin (0.1 -

5µ)active skin supported by substructure (20-1mm).

Membrane polarization• Mole. Wt of solute affect the passage of mole through the

membranes.• Accumulation of solute at the membrane surface which

can be reduced by shear forces at the membrane surface by conventional agitation or cross-flow system.

• Slurry of protein may accumulate on the membrane surface forming a gel layer which is not easily removed by agitation. It is controlled by pH.

• Polarization layers can be minimized at small scale by stirring and at large scale by high fluid flow rates over the membrane surface.

Advantages• Gentle and non-destructive• No chemical reagents • No phase change• Operated at low hydrostatic pressures• Low temp. operation • Constant pH and ionic strength • Simultaneous conc. And purification • Economical

Applications • Dialysis and other blood treatments• Conc. Of milk before making cheese• Fractionation of proteins• Clarification of fruit juices• Recovery of vaccines and antibiotics from

fermentation broth• Lab. Grade water purification• Wastewater treatment• Drinking water disinfection• Removal of endocrines and pesticides combined with

suspended activated carbon pretreatment.

Precipitation

• Is the formation of a solid in a solution during a chemical reaction.

• The solid formed is precipitate, and liquid is supernatant.

• Use: product isolation and purification.• Operated at industrial scale.• Effected by addition of inorganic salts, organic

solvents or high mole. Polymer.

Precipitation • Agents causing precipitation:• Acids and bases to change the pH of a solution until the

isoelectric point of the compound is reached.• Salts of ammonium and sodium sulphate –proteins. Salts

removes water from the surface of the protein revealing the hydrophobic patches which come together causing the proteins to precipitate.

• Organic solvents. E.g. dextran – methanol. Proteins – chilled ethanol and acetone.

• Non-ionic polymers – PEG – proteins• Polyelectrolytes.• Protein binding dyes (triazine dyes) – proteins• Affinity precipitants for selective compounds.

Drying

It involves the final removal of water from a heat-sensitive material with min. loss in viability, activity or nutritional value.

Drying is necessary because:The cost of transport can be reduced.The material is easier to handle and package.Easy storage.

Drying • Initial water removal by centrifugation and filtration to reduce

heating cost.• Driers classified based on heat transfer to the product and the

degree of agitation of the product.• Types:• Drum dryer• Spray dryer• Freeze dryer• Fluidized bed dryer.• Rotary vacuum dryer• Vacuum drum dryer

Types of driers

• Drum dryer: contact dryer – product is contacted with a heated surface. Heat stable bioproducts are used.

• Rotary vacuum dryer:Rotating steam heated drum, evaporation takes

place and the dry product is removed by a scraper blade.solids contacts with heating surface for 6 – 15 min.

Vacuum drum dryer: uses low temperature.

Spray dryer• Suitable for biological material.• Starting materials – liquid or paste• Materials does not contact with heating surface but atomized

into small droptlets through a nozzle or rotating disc.• The droplets falls into a spiral stream of hot gat at 150 to

250°.• The high surface area : volume ratio of the droplet results

evaporation and drying.• Suitable for biologically active products.• Jet spray dryer: heat sensitive materials. Operates at 350°,

residence times 0.01 seconds because very fine droplets produced by atomizing nozzle.

• Spray dryer: economical , large volume handling, feed rate below 6 kg/min.

Freeze drying

• Lyophilization• Biologicals and pharmaceuticals• Materials first frozen and then dried by

sublimation in a high vacuum.• Does not harm heat sensitive materials.

Fluidized bed driers

• Pharmaceutical industry.• Heated air is fed into a chamber of fluidized

solids, to which wet material is continuously added and dry material continuously removed.

• High mass transfer rate gives rapid evaporation.

• Whole bed to be maintained in dry condition.