FLUID-SOLID SEPARATION PROCESSES (ADSORPTION PROCESSES) ENGR. DR. MOHD IRFAN HATIM MOHAMED DZAHIR

What is adsorption? Adsorption is a process in which one or more components of a gas or liquid stream are adsorbed on the surface on the solid adsorbent and a separation is accomplished. Operation of adsorption process:- -The adsorbent is usually in the form of small particles in a fixed bed. -The fluid is passed through the bed and the solid particles adsorb components from the fluid. -When the bed is almost saturated, the flow through the bed is stopped and the bed regenerated thermally or by other method that can promotes desorption. -The adsorbed component (adsorbate) is thereby recovered and the solid adsorbent is ready for another cycle of adsorption.

Liquid-phase adsorption Removal of organic compound from:- 1)water or organic solution, 2)colored impurities from organics, 3)and various fermentation products from fermentor effluents Example of separation:- -Paraffin from aromatics -fructose from glucose using zeolite adsorbent. Gas-phase adsorption 1)Removal of water from hydrocarbon gases 2)Sulphur compounds from natural gas 3)Solvent from air and other gases 4)Odor from air

Physical properties of adsorbent -In the form of small pellets, beads, or granules ranging 0.1 mm to 12 mm in size. -Adsorbent particle has a very porous structure, with many fine pores and pore volumes up to 50% of total particle volume. -Adsorption occurs as a monolayer although several layers sometimes occur. -Physical adsorption (van der Waals) is the type of force presence between the adsorbed molecules and the solid internal pore surface and readily reversible.

Commercial adsorbent, 1.Activated carbon (SA of 300 – 1200 m 2 /g) 2.Silica gel (SA of 600 to 800 m 2 /g) 3.Activated alumina (SA of 200 – 500 m 2 /g) 4.Molecular sieve zeolites 5.Synthetic polymer or resins

BATCH ADSORPTION Commonly used to adsorb solute from liquid solution when the quantities treated are small in amount. q F M + c F S = qM + cS Material balance on the adsorbate is, q F = Initial concentration of solute adsorbed q = final concentration of solute adsorbed c F = Initial feed concentration c = final equilibrium concentration

DESIGN OF FIXED-BED ADSORPTION COLUMNS Cb – break-point concentration Cb/Co of 0.01 to 0.05

Time equivalent to total or stoichiometric capacity of packed-bed tower t t (represented by total shaded area) T u time equivalent to the usable capacity or the time at which the effluent concentration reaches its maximum permissible level, t u is very close to t b Numerical integration of both equations can be solved using a spreadsheet!

t u /t t is a fraction of total bed capacity H B is the length of bed used up to the break point, The length of unused bed H UNB, Total bed length,

Adsorption Problems

Assignment (To be submitted before 12 noon, 19 March 2012)