Mass Transfer Notes.pdf

Dr Rao Irfan Associate Professor (IPS) PUMHS Industrial Pharmacy [Theory] Industrial Pharmacy  Industrial pharmacy is a discipline which includes manufacturing, development, Marketing and distribution of drug products including quality...

Dr Rao Irfan Associate Professor (IPS) PUMHS Industrial Pharmacy [Theory] Industrial Pharmacy  Industrial pharmacy is a discipline which includes manufacturing, development, Marketing and distribution of drug products including quality assurance of these activities.  The reasons for increasing the large scale manufacturing. Economic – As the scale of manufacturing batches increases so, proportionally, does the cost of production decreases Accuracy – The larger the quantities of materials involved so, proportionally, is the accuracy of measurement increased. Mass Transfer Mass transfer is the net movement of mass from one location to another.  Some common examples of mass transfer processes are the evaporation of water from a pond to the atmosphere  The purification of blood in the kidneys and liver  The distillation of alcohol  Mass transfer in industrial process In industrial processes, mass transfer operations include  Separation of chemical components in distillation columns,  Absorbers such as scrubbers, adsorbers such as activated carbon beds  Liquid-liquid extraction. Mass Transfer  Mass Transfer involves the movement of material from one phase to another  Eg. in drying a wet solid, the liquid is converted to vapor and carried away  when a drug is extracted with a solvent, soluble material passes from the solid phase into solution and is taken away in the liquid phase Solid fluid Mass Transfer  Consider a crystal of a soluble material immersed in a solvent in which it is dissolving  The crystal in this scenario is going to be surrounded by a stationary boundary layer of the solute, with the bulk of the fluid able to move.  transport of the molecules of the dissolving solid will take place in two stages  First the molecules move through the boundary layer by molecular diffusion, with no mechanical mixing  Once material has passed through the boundary layer, mass transfer takes place by bulk movement of the solution, known as eddy diffusion,  the controlling factor in the rate of solution of the crystal will be the molecular diffusion through the boundary layer.  Equation for mass transfer by molecular diffusion Diffusion coefficient is a proportionality constant. The higher the value of diffusion coefficient, the faster they diffuse into each other. E.g. Carbon dioxide in air has a diffusion coefficient of 16 mm2/s, and in water its diffusion coefficient is 0.0016 mm2/s Fluid/Fluid Mass transfer  The transfer of mass between two immiscible fluids,  Which maybe two liquids or a liquid and a gas (or vapour).  In this case there will be boundary layers of both fluids on each side of the interface  The slope of the concentration gradients depends on the diffusion coefficients in the two materials. Mass transfer Influence on Unit Operations  Mass transfer theory can be applied to any operation  In which material changes phase, whether it is solid/liquid, solid/vapour (or gas), liquid/liquid, or liquid/vapour (or gas).  The effect can be seen in simple operations  such as the making of a solution of a solid in liquid, where the rate of solution can be increased by:  – Agitation, which reduces the thickness of the boundary layers and disperses any local concentrations of solution, so increasing the concentration gradient  – Elevated temperatures (which increases the solubility of most materials) which increase the diffusion coefficient and decrease the viscosity of the liquid, so reducing boundary layer thickness.  – Size reduction of the solid, which increases the area over which diffusion can occur.