Mass transfer Introduction P.M. Dr Mahmad Nor Jaafar Room # 3 Bioprocess Tel: Or Agrotechnology Unit Tel

Mass transfer Define, Discuss, Calculate and Apply the mechanism and principles of mass transfer Introduction to Fick’s law. Diffusion in gases Diffusion in liquids Diffusion in solids Molecular diffusion in biological solution and gels

1.Understand the Principles of Mass Transfer 2.Unit use ( ISU) and the relative magnitude or values use 3.General formula and Application of mass transfer coefficient. 4.Tables of References 5.Differentiate Diffusion between gas, liquid and Solid> Biological materials. 6.Application of terminology use in diffusion Molecular, Convective Diffusion Diffusivity Permeability Porosity Tortousity 7. Solve problems related to Gas, liquid, Solid and Biological materials. Students are expected to be able to understand and apply the principles of the 7 points below:

Mass transfer Introduction Mass transfer occurs: Distillation Adsorption Drying Liquid-liquid extraction Adsorption Ion exchange Crystallization Membrane process

Molecular diffusion in liquids Separation operation as liquids-liquid extraction or solvent extraction,gas absorption and distillation Oxygenation of rivers & lakes by air Diffusions of salt in blood Rate of molecular diffusion is slower than gas ( 10 5 <Gas), Flux only 100 less. Gas 10 -4, liquid 10 -9, Solid m 2 /s.

Principles of Mass Transfer the mass transfer coefficient is a diffusion rate constant that relates the mass transfer rate, mass transfer area, and concentration gradient as driving force diffusionrate constant mass transfer

Diffusion is the macroscopic result of random thermal motion on a microscopic scale. The flux is proportional to the gradient in concentration (molecular or molar): ("Fick's Law)

driving force rate of a transfer process = –––––––––––– resistance

dc A J* Az = -D AB –––– dz

Principles of Mass Transfer Fick's first law is used in steady-state diffusion, i.e., when the concentration within the diffusion volume does not change with respect to time. In one (spatial) dimension, this isdiffusion where J is the diffusion flux in dimensions of [(amount of substance) length −2 time -1 ], exampleamount of substance is the diffusion coefficient or diffusivity in dimensions of [length 2 time−1], examplediffusivity

Principles of Mass Transfer is proportional to the velocity of the diffusing particles, which depends on the temperature, viscosity of the fluid and the size of the particles according to the Stokes-Einstein relation. In dilute aqueous solutions the diffusion coefficients of most ions are similar and have values that at room temperature are in the range of 0.6x10 -9 to 2x10 -9 m 2 /s. For biological molecules the diffusion coefficients normally range from to m 2 /s. viscosityStokes-Einstein relation

Gas: Diffusion of CO2-Butanol Diffusivity m2/s about Liquid: Diffusion of Ethanol through water ……………… Solid: Diffusion of dilute Biological Solutes…………… to

Diffusion in Porous Solids That depends on Structure Homogeneous-like materials.. Diffusivity D AB Porous solid >> pores >> interconnected. N A = E D AB ( Ca 1 - Ca 2 ) / T ( z 2 -z 1 ) E = Porosity ; void fraction T = Tortuosity, 1.5 to 5 x

Permeability Pm is a measure of the ability of a material (solids) to transmit fluids of gas/liquid in m3 of solute gas/liquid at STP ( 0 and 1 atm pressure) diffusing per second per m2 cossectional area through a solid 1 m thick under a preassure of difference of 1 atm pressure. Realate to Fick’s Law = D AB ( CA1 –CA2) NA = Z2 –Z1 Porosity is a measure of the void spaces in a material, and is measured as a fraction, between 0–1, or as a percentage between 0–100%.percentage Tortousity is a factor that describe the diffusion of fluid /solution in the void volume in winding path, thus increasing the path length, usually measure 1.5 to 5 time that of straight line for inert-type solids.

PROBLEMS Chapter 6. Transport Processes and Separation Process Principles 4 th Edition. CHRISTIE JOHN GEANKOPLIS 2003 Tutorial 1: 6.4-1, 6.4-2; 6.4-3; Tutorial 2: 6.1-2; 6.2-2; ; 6.5-6