PTT 350 SEPARATION ENGINEERING ADSORPTION Zulkarnain Mohamed Idris

  • Slides: 29
Download presentation
PTT 350 -SEPARATION ENGINEERING ADSORPTION Zulkarnain Mohamed Idris zulkarnainidris@unimap. edu. my

PTT 350 -SEPARATION ENGINEERING ADSORPTION Zulkarnain Mohamed Idris zulkarnainidris@unimap. edu. my

Adsorption ü Adsorption- A physical process that involves the transfer of solute from fluids

Adsorption ü Adsorption- A physical process that involves the transfer of solute from fluids to the surface of a solid matrix. Example of Adsorption Process: CO 2 Capture ü Adsorbent- The solid material onto which a solute is adsorbed. ü Adsorbate- A substance (solute) that becomes adsorbed surface of adsorbent. at the ü The existence of an affinity between molecules of adsorbate and the surface of adsorbent, resulting in a higher concentration of adsorbate in the adsorbed phase than in the fluid after equilibrium is reached. CO 2 (solute) Zeolite (adsorbent)

Adsorption üAdsorption is suitable separation technique for: o The components of mixtures present similar

Adsorption üAdsorption is suitable separation technique for: o The components of mixtures present similar physical properties (volatility, solubility etc. ) o Very low concentration mixtures. üEfficiency of adsorption is depends on: o Adsorbent capacity o Selectivity

Type of Adsorption üPhysisorption- A physical adsorption in which the adsorbate adheres to the

Type of Adsorption üPhysisorption- A physical adsorption in which the adsorbate adheres to the surface only through Van der Waals (weak intermolecular) interactions. üChemisorption- A chemical nature adsorption whereby a molecule adheres to a surface through the formation of a chemical bonds.

Adsorption Isotherm üAdsorption is usually described through isotherm, that is, functions which connect the

Adsorption Isotherm üAdsorption is usually described through isotherm, that is, functions which connect the amount of adsorbate on the adsorbent with its pressure (if gas) or concentration (if liquid) üAdsorption isotherm, shows the equilibrium relationship of solute concentration between the liquid solvent phase and the solid adsorbent phase at a given temperature, pressure, p. H and total solute concentration. üThe isotherm equilibrium relationship is shown as a q versus y plot, where q is the concentration of solute in the solid adsorbent phase and y is the concentration of solute in the liquid phase.

Common Adsorption Isotherm o Freundlich Isotherm o Langmuir Isotherm o Linear Isotherm

Common Adsorption Isotherm o Freundlich Isotherm o Langmuir Isotherm o Linear Isotherm

ü Freundlich Isotherm o It is an empirical equation. o Used widely for antibiotics,

ü Freundlich Isotherm o It is an empirical equation. o Used widely for antibiotics, steroids and hormones. ü Langmuir Isotherm o Has a strong theoretical basis. o Shows good correlation for protein adsorption systems. ü Linear Isotherm o In a limited range gives an estimation for other isotherms. o It is not common

Example 1

Example 1

q vs y 16 14 12 10 R 2 = 0. 9708 8 6

q vs y 16 14 12 10 R 2 = 0. 9708 8 6 log q vs log y 4 1. 4 2 1. 2 0 0 0. 02 0. 04 0. 06 0. 08 0. 12 1 0. 8 R 2 = 0. 9999 1/q vs 1/y 0. 6 0. 4 0. 25 0. 2 0 0. 15 -2. 5 0. 1 R 2 = 0. 9662 0. 05 0 0 20 40 60 80 100 120 -2 -1. 5 -1 -0. 5 0

The data is linear on a log q Vs Log y plot. So the

The data is linear on a log q Vs Log y plot. So the equilibrium isotherm fit the Freundlich Isotherm (since R 2 = 0. 999 which closer to 1) with the following equation: log q vs log y 1. 4 1. 2 log q 1 0. 8 R 2 = 0. 9999 0. 6 0. 4 0. 2 0 -2. 5 -2 -1. 5 -1 log y -0. 5 0

Solid Adsorbent üTypically, adsorbent are in the form of pellets, granules, beads, flakes or

Solid Adsorbent üTypically, adsorbent are in the form of pellets, granules, beads, flakes or powder whose size ranges from 50μm to 1. 2 cm. üThe particle of adsorbent has very porous structure (approximately 85%). üThe pore size distribution may determine the selectivity of the adsorption because it allows the discrimination among the adsorbates as a function of its molecular size.

Characteristics of Adsorbent üHigh surface area per unit weight to maximize the adsorption. üHigh

Characteristics of Adsorbent üHigh surface area per unit weight to maximize the adsorption. üHigh selectivity and capacity to improve the efficiency of the separation. üSlow aging for maximum profit. üHigh resistance against abrasion because agitation unit and transportation may cause solid rupture. üEasy to recover and clean to save energy in the regeneration stage.

Commercial Types of Adsorbents Particulate solid adsorbents used to adsorb solutes, are made from

Commercial Types of Adsorbents Particulate solid adsorbents used to adsorb solutes, are made from different natural and synthetic organic or inorganic materials. ü Activated carbon- Made by thermal decomposition of wood, vegetable shells, coal etc. Generally adsorbed the organic materials. ü Silica gel- Made by acid treatment of sodium silicate solution and the drying. Used to dehydrate gases an liquids/fractionate hydrocarbon. ü Activated alumina- Made by heating the hydrated alumina oxide. Used to dry gases and liquid. ü Zeolites- A porous crystal of aluminosilicate. Used for separation of hydrocarbon and many other applications. ü Synthetic resins- A synthetic polymers made by polymerizing the monomers. Resins made from aromatics, such as styrene and divinylbenzene are used to adsorb nonpolar organics from aqueous solution.

ü In separation processes the following adsorbents materials are generally used: o Cellulose o

ü In separation processes the following adsorbents materials are generally used: o Cellulose o Modified cellulose o Silica gel o Synthetic resins Silica gel Activated carbon Synthetic resin Zeolite

Adsorbent Regeneration/Desorption üAs adsorption is going on, the pores of the adsorbent are filling

Adsorbent Regeneration/Desorption üAs adsorption is going on, the pores of the adsorbent are filling with adsorbate molecules until the capacity of the adsorbent is exceeded. üThe adsorbent is usually expensive, and for environmental concern, the regeneration of the solid is currently necessary. üTherefore, the adsorption operation really includes two stages which are the adsorption and the regeneration process (desorption). üIn many cases, the economy of the whole operation depends on this regeneration process.

Possibilities for Adsorbent Regeneration üThermal reactivation o Desorption occurred by an increase in temperature

Possibilities for Adsorbent Regeneration üThermal reactivation o Desorption occurred by an increase in temperature which leads to a decrease in the concentration of the adsorbed phase. üRegeneration by a decrease in pressure o Only applicable for gases o Pressure is decrease so the concentration in the adsorbed phase at equilibrium is less.

üRegeneration by purge o It is achieved by feeding an inert, non-adsorbing purge that

üRegeneration by purge o It is achieved by feeding an inert, non-adsorbing purge that reduces the adsorbate concentration and thus its degree of adsorption. üRegeneration by displacement with desorbent o Desorbent is an adsorbate of higher affinity. o This type of operation is adequate when the adsorbate has a strong interaction with the adsorbent and no thermal regeneration is possible.

Design of Fixed-Bed Adsorption Column MTZ = Mass Transfer Zone ü Prior tb, the

Design of Fixed-Bed Adsorption Column MTZ = Mass Transfer Zone ü Prior tb, the outlet solute concentration is < than permissible value of 0. 05 ü At tb, this value is reached, adsorption step discontinued & regeneration of adsorbent initiated. ü t>tb, the outlet solute concentration would rise rapidly, approaching the inlet concentration as the outlet end become saturated. ü Steepness of breakthrough curve capacity of adsorbent bed that can be utilized. ü Thus, shape of the curve is IMPORTANT to determine the length of the bed.

Determination of capacity column from breakthrough curve •

Determination of capacity column from breakthrough curve •

Determination of capacity column from breakthrough curve •

Determination of capacity column from breakthrough curve •

Example 2 A waste stream of n-butanol vapor in air from a process was

Example 2 A waste stream of n-butanol vapor in air from a process was adsorbed by activated carbon particles in a packed bed having a diameter of 4 cm and length of 14 cm containing 79. 2 g of carbon. The inlet gas stream having a concentration, C 0 of 600 ppm entered the bed at the solute feed rate, FA of 0. 063 g/cm 2. s. Data in Table 2 give the concentrations of the fluid in the bed, C. The break point concentration is set at C/Co = 0. 05. Determine the breakthrough point, the fraction of total capacity used up to the break point, and the length of the unused bed. Table 2 Breakthrough concentration Time (h) 0. 0 3. 5 4. 0 4. 5 5. 0 c/co 0 0 0. 002 0. 030 0. 155 0. 396 Time (h) 5. 5 6. 0 6. 2 6. 5 6. 8 c/co 0. 658 0. 903 0. 933 0. 975 0. 993

Example 2 Solution: 1. Plot the breakthrough curve based on the data in Table

Example 2 Solution: 1. Plot the breakthrough curve based on the data in Table 2: 1 0. 8 c/co 0. 6 0. 4 At c/co = 0. 05, the breakthrough point (tb) is at 4. 1 h 0. 2 0 0 1 2 3 4 Time (h) 5 6 7 8

 • Simpson’s Rule of integration, use n =4; n should be even no.

• Simpson’s Rule of integration, use n =4; n should be even no. t (h) C/C 0 f(x) = (1 C/C 0) 0. 00 0 1 1. 75 0 1 3. 50 0. 002 Refer breakthrough curve 0. 998 5. 25 0. 5 7. 00 1 0

 • Trapezoidal Rule of integration, use n =1 Refer breakthrough curve t (h)

• Trapezoidal Rule of integration, use n =1 Refer breakthrough curve t (h) C/C 0 f(x) = (1 C/C 0) 0. 00 0 1 4. 1 0. 05 0. 95

Thank You

Thank You