Chapter 14 Membrane separation

Chapter 17 Crystallization

Feed: consisting of mixture of two or more componentsRetentate: The part of the feed that does not pass through the membranePermeate: The part that does pass through the membraneSweep: Is a liquid or gas used to facilitate removal of the permeate

Bulk Flow: Bulk Flow is pressure driven through semi permeable barrier

Pore Resistance to flowIdeal straight cylindrical: Poiseuille flow

Real porous

Liquid diffusion through porous membrane

Liquid Diffusion through Nonporous membrane

Gas Diffusion through porous membrane

Gas Diffusion through nonporous membrane

Solution-Diffusion for Liquid MixturesPorous membrane

Nonporous Membrane

Note the same could be derived for Gas Mixture Reverse Osmosis

(c) If we apply a pressure P1 that is higher than the sum of the osmotic pressure and P2. Thisallows us to push the seawater through the membrane in the reverse direction of normal osmosis.

Dialysis: Sweep is fed

Liquid diffusate (permeate) contains solvent, solutes of type A, and little or none of type B solutes. Liquid dialysate (Retentate) contains solvent, type B solutes, remaining type A solutes, and colloidal matter

Gas Permeation The membrane, often dense but sometimes micro porous, is permselective for the low-molecular-weight species A. But if the membrane is dense, these species are absorbed at the surface and then transported through the membrane by one or more mechanisms

Pervaporation: Phase on one side of the revaporation membrane is different from that on the other. Feed to the membrane module is a liuid mixture at P1. The retentate is enriched in species B. Other side of the membrane P2 is held below the dew point of the permeate, making it vapor. The vapor permeate is enriched in species A. Overall permeabilities of species A and B

depend on solubilities and diffusion rates.

Membrane Requirements for Biotechnology:(1)Preserve biological activity:Denaturation, proteolytic cleavage, or mishorming of protein projects must be avoided.(2) Satisfy cGmp requiremments:may include biocompatibility, sterilizability, and flushout of extractables.(3) Accommodate modes scales of operation. (4) Include batch operation. Filtration Challenges:(1)Integrated process: The process may define the product. Filtration cannot be implemented or optimized in isolation, but must be approached as an integral part of the entire series of fermentation, purification, and formulation steps.(2)Compressed development: Pressing market need for biotechnology products to prevent or treat public health problems drives accelerate timelines for development.(3)Limited raw materials: Only mL to L of fermentation or cell culture broth may be initially available for filter selection, characterization, and optimization.(4)Variable fermentation or cell culture:Membrane filter operation must accommodate wide variations in sell culture and fermentation composition and productivity while providing consistent yield and purity.(5) Operability:Filter operations that maximize the robustness of process operations must be selected to provide consistent purity and yield, resulting in an economical, vaildatable process.(6)Virus removal: Must reduce the virus to a level of less than on virus particle per 10^6 doses. Fouling:(1)Macromolecular sorption:Dissolved macromolecules introduced in the feed adsorb rapidly to membrane surfaces, decreasing permeate rate in proportion to coverage.(2)Particle deposition:The first sublayer builds as colloids, slowly deposit, decreasing permeate flux as monolayer coverage is approached.(3)Sublayer rearrangement: Additional sublayer build, reducing the cross section for axial flow, which increases the wall shear rate and axial pressure gradient. More shear increases Brownian and shear-induced back-diffusion of solids and inertial lift while higher TMP grows and compresses the sublayer, reducing the flux.(4)Non-Newtonian viscos effects

Bioprocessing:Membrane Selection Criteria:(1)Selectivity: The membrane must retain active species and pass contaminants at targeted specifications.(2)Biocompatibility: The membrane should resist inactivation, pluging, and fouling by biological species or solution components.(3)Chemical inertness: Must tolerate use and validatable cleaning and sterilization cycles.(4)mechanical Stability: Must be able to withstand pressures and temperatuires ranges employed during use and validatable cleaning.(5)Econmics: Reasonable operating conditions, consumable costs

Crystallization is a solid-fluid separation in which crystalline particles are formed from a homogeneous fluid phase. Crystals are pure chemicals, are obtained in a high yield with a desirable shape.

Industry.(1)Solution crystallization: inorganic salt is the solute crystallized, and water is the solvent remaining as a liquid.(2)Precipitation: Fast crystallization( not good) Organic solutions.(3)Evaporation: Used in Organic

solutions..(4)Cooling: Used in Organic solutions.(5)Melt: Used when both components of a homogeneous, binary solution have melting( freezing) points not far removed from each other.

Crystal Geometry: In a solid, motion of molecules, atoms, or ions is restricted largely to oscillations about fixed positions. In amorphous solid, these positions are not arranged in a regular or lattice pattern, where as in crystalline solids, they are. Amorphous solids are isotropic, i.e., physical properties are independent of the direction of measurement; crystalline solids are anisotropic, unless the crystals are cubic in structure. Bravais showed that only the 14 space lattices are possible. The 14 lattices can be classified into the seven crystal systems. Cubic, Tetragonal, Orthorhombic, Monoclinic, Rhombohedral, Hexagonal, Triclinic. Crystals of a given substance and a given system exhibit markedly different appearances when the faces grow at different rates. Crystal-size Distributions: Crystallizer magmas contain a distbution of crystal

sizes and shapes. It is highly desiable to cahraterize a batch of crystals by an average crystal size and a crystal-size distribution. Relate the irregular-shaped particle to a shere by the spericity.

Size techniques:(1)Electron microscope.(2)Optical.(3)Laser Light.(4) Wire mash. Distribution. (1)Differential.(2)Cumulative

Different Mean Particle Sizes: Surface-Mean Diameter

Arithmetic-Mean Mass-Mean D Volume-Mean Diameter

Solubility: For systems of water and soluble inorganic and organic chemicals, presents extensive tables of solubility as a function of temperature, and heat of solution at infinite dilution and room temperature. Solubility is expressed as a solubility product, Kc in terms of ion concentration.

Effect of Temperature: Solubility of most inorganic compounds increase with temperature, but a few common compounds exhibit a negative or inverted solubility in certain ranges of temperature where solubility decreases with increasing temperature. When solubility increases with temp. best method for crystallization would be cooling. When solubility remains constant along with increase in temp. the best method for crystallization would be evaporation. Solid compound with low solubility can be produced by reacting two soluble compounds.

Kinetics and Mass: Steps-(1) Nucleation, (2) Mass transfer: Solute to surface, (3) Solute addition. Driving force for all three steps is supersaturation. Supersaturation: As crystals size decreases, solubility noticeably increases, making it possible to supersaturate a solution if it is cooled slowly with agitation

Ion Exchange: one sorbate is exchanged for a solute ion, gonverned by a reversible, stoichiometic, rXn.

Kelvin equation

Relative Supersaturation Nucleation: Primary nucleation requires high supersaturation and is the principal mechanism in precipitation-RequiressS>>1-No forging matter (dust). Secondary nucleation is the key in commercial crystallizers, where crystalline surfaces are present and large crystals are desired.

Primary nucleation : Can be homogeneous or heterogeneous. Molecules in the solution first associate to form a cluster. If a cluster gets larger enough to take on the appearance of a lattice structure, it becomes an embryo. Further growth can result in a stable crystalline nucleus. The rate of homogeneous nucleation:

Secondary Nucleation: Nucleation in industrial crystallizers occurs mainly by secondary nucleation caused by existing crystals in the supersaturated solution. It is initiated by: (1) Fluid shear past crystal surfaces that sweep away nuclei. (2) Collisions of crystals with each other. (3) Collisions of crystals with metal surfaces such as the crystallizer vessel wall or agitator blades. The rate of secondary nucleation:

Crystal growth: Mass

Adsorption process: molecules or atoms or ions, in a gas or liquid, diffuse to the surface of a solid, where they bond with the solid surface or are held by weak intermolecular forces. Ion-Exchange process: ions of positive charge or negative in a liquid solution usually aqueous, replace dissimilar and displaceable ions, called counterion, of the same charge contained in a solid ion exchanger. Chromatography: the sorbent may be a solid absorbent: an insoluble, nonvolatile liquid adsorbent contained in the pores of a granular sold support: or an ion exchanger.

Precipitation: In solution crystallization, a liquid containing a solute is cooled or partially evaporated; causing the solute to exceeds its solubility sufficiently to partially crystallize. Precipitation is the opposite of solution crystallization. Precipitation involves solutes that are only sparingly soluble. Fast crystallization, formed by changing pH, solvent, temperature, adding reagent.

Chapter 15 Adsorption, Ion Exchange, ChromatographyAdsorption, ion exchange and chromatography are sorption operation in which components of a fluid phase are selectively transferred to insoluble, rigid particles suspended in a vessel or packed in a column. Ex Adsorption of gas species into a liquid and penetration of fluid species into a nonporous membrane are sorption operations. In sorption process, the sorbed solutes are referred to as sorbate, and the sorbing agent is the sorbent.

Adsorbents: Most adsorb species from gases and liquids, but few have a sufficient selectivity and capacity to qualify as serious candidates for commercial adsorbents.

Surface Area/Volume (solid sphere)

Specific surface area, in area per unit mass of adsorbent

Activated carbon(small pore): Surface Area, Sg, m2/g=>400-1200. Molecular-Sieve Zeolites: Pore Diameter, dp, =>3-10….Two types of Adsorption: (1) Physical adsorption(Physisorption): physical adsorption from gas occurs when intermolecular attractive forces between solid and gas molecules attractive forces between solid and gas molecules are greater than those between gas molecules. (2) Chemical adsorption (Chemisorption): Involves formation of chemical bonds between adsorbent and adsorbate in a monolayer, oftern with a release of heat larger that the heat of vaporization. Commercial adsorbents rely on physical adsorption to achieve separation: solid catalysts rely on chemisorptions to catalyze chemical reaction.

Specific surface area of an adsorbent is measured by adsorbing gaseous nitrogen, using the BET method (Brenauer, Emmett, and Teller). N2 adsorption is oftern called “BET”, Operate in a vacuum (5 to 250 mmHg), Measures the equilibrium volume of pure N2 physically adsorbed on solid adsorbents

BET equation

Measuring Pore Volume and Pore Distribution

For N2 adsorption, filling of pores depends on the size of the pore. Kelvin Equation:

Physical meaning: Change in vapor pressure due to the curved liquid-vapor interface.

Pure-Gas Adsorption:

Linear Isotherms: When the amount of adsorbed molecule is low, isotherms are approximately linear (form of Henry’s law

Adsorption is an exothermic process: What are the effects of temperature ?

Monolayer Isotherms: (1) Freundlish Isotherm: (2) Langmuir Isotherm

(3) Binary Mixture(Langmuir Modification

Ion exchange material: (1)Natural resins:Polysaccharides, (2) Organic Polymer resins, (3) Inorganic Materials(zeolites)

General Equation: