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Liquid extraction

Mass transfer Oeration Liquid extraction notes

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Liquid extraction

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  1. Separation processes - general • Mechanical separations e.g. filtration of a solid from a suspension in a liquid, centrifugation, screening etc • Mass transfer operations e.g. distillation, extraction etc

  2. Mass transfer operations – nature of interface between phases • Gas-liquid contact e.g. absorption, evaporation, distillation etc • Liquid-liquid contact e.g. extraction • Liquid-solid contact e.g. crystallisation, adsorption • Gas-solid contact e.g. adsorption, drying etc

  3. Mass transfer operations – controlling transport phenomenon • Mass transfer controlling e.g.distillation, absorption, extraction, adsorption etc • Mass transfer and heat transfer controlling e.g. drying, crystallisation • Heat transfer controlling e.g. evaporation

  4. Choice of separation process Factors to be considered: • Feasibility • Product value • Cost • Product quality • selectivity

  5. Extraction can be • Liquid-Liquid Extraction ( Solvent Extraction) • Solid – Liquid Extraction ( Leaching ) • Super Critical fluid Extraction

  6. Liquid-liquid extraction principles Feed phase contains a component, i, which is to be removed. Addition of a second phase (solvent phase) which is immiscible with feed phase but component i is soluble in both phases. Some of component i (solute) is transferred from the feed phase to the solvent phase. After extraction the feed and solvent phases are called the raffinate (R) and extract (E) phases respectively.

  7. Normally one of the two phases is an organic phase while the other is an aqueous phase. Under equilibrium conditions the distribution of solute i over the two phases is determined by the distribution law. After the extraction the two phases can be separated because of their immiscibility. Component i is then separated from the extract phase by a technique such as distillation and the solvent is regenerated. Further extractions may be carried out to remove more component i. Liquid liquid extraction can also be used to remove a component from an organic phase by adding an aqueous phase.

  8. Example - Penicillin G 6-aminopenicillanic acid (6-APA) is manufactured by GSK in Irvine. It is used to manufacture amoxicillin and ‘Augmentin’. Fermentation products (penicillin G broth) are filtered (microfiltration) and extracted at low pH with amyl acetate or methyl isobutyl ketone. The penicillin G is then extracted further at a higher pH into an aqueous phosphate buffer.

  9. Extractants The efficiency of a liquid liquid extraction can be enhanced by adding one or more extractants to the solvent phase. The extractant interacts with component i increasing the capacity of the solvent for i. To recover the solute from the extract phase the extractant -solute complex has to be degraded.

  10. Distribution coefficient K = mass fraction solute in E phase mass fraction solute in R phase

  11. Immiscible liquids e.g. water – chloroform Consider a feed of water/acetone(solute). K = mass fraction acetone in chloroform phase mass fraction acetone in water phase K = kg acetone/kg chloroform = y/x kg acetone/kg water K = 1.72 i.e. acetone is preferentially soluble in the chloroform phase

  12. Partially miscible liquids E.g. water – MIBK (Methyl isobutyl ketone) Consider a solute acetone. Need to use a triangular phase diagram to show equilibrium compositions of MIBK-acetone-water mixtures. Characteristics are single phase and two phase regions, tie lines connecting equilibrium phase compositions in two phase region.

  13. Triangular phase diagrams Each apex of triangle represents 100% pure component B %S %A P %B A S

  14. A mixture of overall composition M will split into two phases – E & R. R phase is in equilibrium with E phase R/E = line ME/line MR B E M R S A

  15. Distribution curve Plot of y (kgsoluteB/kgsolventS) in E phase vs x (kgsoluteB /kg A) in R phase

  16. Choice of solvent Factors to be considered: • Selectivity • Distribution coefficient • Insolubility of solvent • Recoverability of solute from solvent • Density difference between liquid phases • Interfacial tension • Chemical reactivity • Cost • Viscosity, vapour pressure • Flammability, toxicity

  17. Distribution coefficient K = y/x Large values are desirable since less solvent is required for a given degree of extraction

  18. Recoverability of solvent and solute • No azeotrope formed between solvent and solute • Mixtures should have a high relative volatility • Solvent should have a small latent heat of vapourisation

  19. Density A density difference is required between the two phases.

  20. Interfacial tension The larger the interfacial tension between the two phases the more readily coalescence of emulsions will occur to give two distinct liquid phases but the more difficult will be the dispersion of one liquid in the other to give efficient solute extraction.

  21. Chemical reactivity Solvent should be stable and inert.

  22. Physical properties For material handling: • Low viscosity • Low vapour pressure • Non-flammable (high flash point) • Non-toxic

  23. Mass balances For counter-current contact with immiscible solvents a simple mass balance for solute B at steady state gives the operating line: yn+1 = a/s(xn – xF) + y1 ,where yn+1 = kgB/kgS in solvent feed a = mass component A s = mass solvent xn = kgB/kgA after n stages xF = kgB/kgA in feed y1 = kgB/kgS in extract after first stage

  24. A graphical procedure may be used to analyse these systems. The number of theoretical stages (n) required to pass from xF to xn is found by drawing in ‘steps’ between the operating line and the equilibrium curve (yn, xn). In practice equilibrium conditions may not be attained and extraction efficiency will be less than 100% thus requiring more stages in practice than the above analysis would suggest. Also partial miscibility of the solvents has to be considered in the separation process.

  25. continued y y1,xF yn+1,xn x

  26. Operation • Batch • Continuous • Single/multi stage contact

  27. When both phases are flowing: Co-current contact Cross flow Counter-current flow Stage 1 Stage 2 etc 1 2 1 2

  28. Equipment • Mixer-settler units • Columns • Centrifugal contactors

  29. Paul Ashall 2007

  30. Spray Tower

  31. Packed Extraction column

  32. Perforated plate extractor

  33. CM Contactor

  34. Rotating disk contactor

  35. Pulse Column

  36. Super Critical Extraction

  37. What is SCE : The supercritical fluid state occurs when a fluid is above its critical temperature (Tc) and critical pressure (Pc), when it is between the typical gas and liquid state. Manipulating the temperature and pressure of the fluid can solubilize the material of interest and selectively extract it. The sample is placed in an extraction vessel and pressurized with CO2 to dissolve the sample. Transferred to a fraction collector, the contents are depressurized and the CO2 loses its solvating power causing the desired material to precipitate. The condensed CO2 can be recycled.

  38. Supercritical Fluids • A supercritical fluid (SCF) is characterized by physical and thermal properties that are between those of the pure liquid and gas. The fluid density is a strong function of the temperature and pressure. The diffusivity of SF is much higher than for a liquid and SCF readily penetrates porous and fibrous solids. Consequently, SCF can offer good catalytic activity.

  39. Properties of Supercritical Fluids • There are drastic changes in some important properties of a pure liquid as its temperature and pressure are increased approaching the thermodynamic critical point. For example, under thermodynamic equilibrium conditions, the visual distinction between liquid and gas phases, as well as the difference between the liquid and gas densities, disappear at and above the critical point. Similar drastic changes exist in properties of a liquid mixture as it approaches the thermodynamic critical loci of the mixture. • Other properties of a liquid fuel that change widely near the critical region are thermal conductivity, surface tension, constant-pressure heat capacity and viscosity. In comparing a liquid sample with a supercritical fluid (SCF) sample of the same fuel both possessing the same density, thermal conductivity and diffusivity of a SF are higher than the liquid , its viscosity is much lower, while its surface tension and heat of vaporization have completely disappeared. These drastic changes make a supercritical fuel

  40. Supercritical Fluid Extraction (SFE) • Supercritical Fluid Extraction (SFE) is based on the fact that, near the critical point of the solvent, its properties change rapidly with only slight variations of pressure. • Supercritical fluids can be used to extract analytes from samples. The main advantages of using supercritical fluids for extractions is that they are inexpensive, extract the analytes faster and more environmentally friendly than organic solvents. For these reasons supercritical fluid CO2 is the reagent widely used as the supercritical solvent.

  41. SCE Methodology

  42. SFE applications in the food, pharmaceutical, and fine chemicalindustries: • Decaffeinating of coffee and tea • Extraction of essential oils (vegetable and fish oils) • Extraction of flavors from natural resources (nutraceuticals) • Extraction of ingredients from spices and red peppers • Extraction of fat from food products • Fractionation of polymeric materials • Extraction from natural products • Photo–resist cleaning • Precision part cleaning

  43. Super critical extraction Equipment

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