ION EXCHANGE Presentation Outline n Ion Exchange Reactions

  • Slides: 57
Download presentation
ION EXCHANGE

ION EXCHANGE

Presentation Outline n Ion Exchange Reactions n Unit Operations of Ion Exchange n Sodium,

Presentation Outline n Ion Exchange Reactions n Unit Operations of Ion Exchange n Sodium, Hydrogen Cycle and Regeneration n Production of Pure Water n Active or Exchange Zone n Design of Ion Exchangers n Quantity of Regenerant n Wastewater Production

Ion Exchange Reactions n Ion Exchange is the displacement of ion by another n

Ion Exchange Reactions n Ion Exchange is the displacement of ion by another n Ion Exchange is a reversible chemical reactions wherein an ion from solution is exchanged for a similarly charged ion attached to an immobile solid particles n The displaced ion moves into solution and the displacing ion becomes a part of the insoluble materials (Resin) Resin

Ion Exchange n Two types of ion exchange materials are used n The cation

Ion Exchange n Two types of ion exchange materials are used n The cation exchange material n The anion exchange material

Ion Exchange

Ion Exchange

Ion Exchange

Ion Exchange

Ion Exchange n The insoluble part of the exchange materials is called the host

Ion Exchange n The insoluble part of the exchange materials is called the host n The cation exchange materials may be represented by r : the number of active sites in the insoluble material n r n/m: n/m the number of charged exchangeable particles attached to the host materials n -n: -n is the charge of the host n +m: +m is the charge of the exchangeable cation n

Ion Exchange Reactions n cation exchange reaction as well as the anion exchange reaction

Ion Exchange Reactions n cation exchange reaction as well as the anion exchange reaction are as follows n Ion exchange reaction are governed by Equilibrium. For this reason, effluents from ion exchange processes never yield pure water

Ion Exchange Reactions Displacement Series for Ion Exchange • Displacement series for ion exchange

Ion Exchange Reactions Displacement Series for Ion Exchange • Displacement series for ion exchange materials is shown in left side table • when an ion species high in table is in solution, it can displace ion species in the insoluble material below it in the table. • to remove any cation in solution, the displaceable cation must be the proton, and to remove any anion, the displaceable anion must be the hudroxyl ion.

ION Exchange Reactions n Examples of exchange materials n n Zeolites (Natural Material) Synthetic

ION Exchange Reactions n Examples of exchange materials n n Zeolites (Natural Material) Synthetic resins n Synthetic resins are insoluble polymers n These polymers are either acidic or basic group, and they are called functional group

Ion Exchange Reactions n These groups are capable of performing reversible exchange reactions with

Ion Exchange Reactions n These groups are capable of performing reversible exchange reactions with ions in solution n The total number of these groups determine the exchange capacity of the exchange material n The type of selectivity functional group determines ion n The exchanger may be regenerated by the reverse reactions (upon exhaustion)

Unit Operation of Ion Exchange

Unit Operation of Ion Exchange

Unit Operation of Ion Exchange n In both units, the influent is introduced at

Unit Operation of Ion Exchange n In both units, the influent is introduced at the top of the vessel n the bed of ion exchanger materials would be inside the vessels n As the to be treated passes through, exchange of ions takes place n This exchange of ions is the chemical reaction of the unit process of ion exchange

Sodium, Hydrogen cycle, And Regeneration n Sodium and Hydrogen are the logical choices for

Sodium, Hydrogen cycle, And Regeneration n Sodium and Hydrogen are the logical choices for the exchangeable ions. n The cation exchange resin using sodium to remove the Ca+2 may be represented by the following reactions

Sodium, Hydrogen Cycle, And Regeneration n As soon as the resin is exhausted, it

Sodium, Hydrogen Cycle, And Regeneration n As soon as the resin is exhausted, it may be regenerated n The resin is regenerated by using a concentration of Na. Cl of a bout 5 to 10%, thus, driving the reaction to the left n Operations where regeneration is done using Na. Cl, the cycle is called the Sodium Cycle n Operations where regeneration is done using acids (H 2 SO 4), the cycle is called the Hydrogen Cycle

Sodium, Hydrogen Cycle, And Regeneration n The following table shows approximate exchange capacities and

Sodium, Hydrogen Cycle, And Regeneration n The following table shows approximate exchange capacities and regeneration requirements for ion exchangers

Sodium, Hydrogen Cycle, And Regeneration Exchanger, cycle Exchange Capacity (geq/m 3) Regenerant Requirement (geq/m

Sodium, Hydrogen Cycle, And Regeneration Exchanger, cycle Exchange Capacity (geq/m 3) Regenerant Requirement (geq/m 3) Cation exchangers: Natural zeolite, Na 175 -350 Na. Cl 3 -6 Synthetic zeolite, Na 350 -700 Na. Cl 2 -3 Resin, Na 350 -1760 Na. Cl 1. 8 -3. 6 Resin, H 350 -1760 H 2 SO 4 2 -4 700 -1050 Na. OH 5 -8 Anion exchanger: Resin, OH

Sodium, Hydrogen Cycle, And Regeneration n In order to determine the exchange capacities and

Sodium, Hydrogen Cycle, And Regeneration n In order to determine the exchange capacities and regeneration requirements we have to do the following: n Perform an actual experiment n Obtain data form the manufacturer

Sodium, Hydrogen Cycle, And Regeneration Table below shows some additional properties of exchangers

Sodium, Hydrogen Cycle, And Regeneration Table below shows some additional properties of exchangers

Sodium, Hydrogen Cycle, And Regeneration n The strongly acidic (cation) exchangers readily remove cations

Sodium, Hydrogen Cycle, And Regeneration n The strongly acidic (cation) exchangers readily remove cations from solutions n The weakly acidic exchangers have limited ability to remove certain cations n The strongly basic (anion) exchangers can readily remove all the anions n The weakly basic one remove mainly the anions of strong acid such as SO 4 -2 and Cl

Production of “PURE WATER’’ n Theoretically, It would seem possible to produce pure water

Production of “PURE WATER’’ n Theoretically, It would seem possible to produce pure water by combining the cation exchanger and the anion exchanger n The following equation for the hydrogen cycle is

Production of “PURE WATER’’ n Letting the molar concentration of be n The corresponding

Production of “PURE WATER’’ n Letting the molar concentration of be n The corresponding concentration in geq / L is

Production of “PURE WATER’’ n Therefore, the total concentration in gram equivalents per liter

Production of “PURE WATER’’ n Therefore, the total concentration in gram equivalents per liter of removable cations in solutions is the sum of all the cations. Thus, n As, [Cat. T]eq of cations is removed form solution, a corresponding number of equivalent concentrations of anions pair with the H+ ions displaced from the cation bed

Production of “PURE WATER’’ n The total anions and the hydrogen ions displaced is

Production of “PURE WATER’’ n The total anions and the hydrogen ions displaced is expressed as follows n Practically, we may say that “ pure water” is produced and expressed as follows The units of ti are equivalents per mole

Production of “PURE WATER’’ n Example: A wastewater contains the following ions: Calculate the

Production of “PURE WATER’’ n Example: A wastewater contains the following ions: Calculate the total equivalents of cations and anions, assuming the volume of the wastewater is 450 m 3.

Production of “PURE WATER’’ n Solution: Ions (mg/L) a Equiv. mass Equiv. Mass Cations

Production of “PURE WATER’’ n Solution: Ions (mg/L) a Equiv. mass Equiv. Mass Cations (meq/L) Anions (meq/L) 58 a __ 2. 069 b 31. 75 0. 945 __ 32. 7 0. 469 __ 29. 35 0. 681 __ b 120/58 = 2. 069

Production of “PURE WATER’’ n Solution (Cont’d) n Total equivalents of cations = 2.

Production of “PURE WATER’’ n Solution (Cont’d) n Total equivalents of cations = 2. 395(450) = 1077. 75 Ans n Total equivalents of cations = 2. 069(450) = 931. 05 Ans

Active or Exchange Zone n Active zone is a segment of exchanger bed engaged

Active or Exchange Zone n Active zone is a segment of exchanger bed engaged in exchanging ions

Active or Exchange Zone Where: = length of active zone = total volume of

Active or Exchange Zone Where: = length of active zone = total volume of water or wastewater treated at complete exhaustion of bed = volume treated at breakthrough = influent concentration to = total volume treated at time

Active or Exchange Zone (Cont’d) = total volume treated at time = concentration of

Active or Exchange Zone (Cont’d) = total volume treated at time = concentration of solute at effluent of = surficial area of exchanger bed at time

Active or Exchange Zone n Active zone at various times during adsorption and the

Active or Exchange Zone n Active zone at various times during adsorption and the breakthrough curve

Active or Exchange Zone n Example 2: A breakthrough experiment is conducted for a

Active or Exchange Zone n Example 2: A breakthrough experiment is conducted for a wastewater producing the results below. Determine the length of the active zone. The diameter of the column used is 2. 5 cm. and the packed density of the bed is 750 kg/m 3. is equal to 2. 2 meq/L. And n The experiments results are tabulated on the next slide

Active or Exchange Zone C, meq/L 0. 06 1 0. 08 1. 2 0.

Active or Exchange Zone C, meq/L 0. 06 1 0. 08 1. 2 0. 09 1. 3 0. 1 1. 4 0. 2 1. 48 0. 46 1. 58 1. 3 1. 7 1. 85 2. 1 2

Active or Exchange Zone Solution:

Active or Exchange Zone Solution:

Active or Exchange Zone 0. 06 1. 0 0. 20 0. 07 0. 014

Active or Exchange Zone 0. 06 1. 0 0. 20 0. 07 0. 014 0. 08 1. 20 0. 10 0. 085 0. 09 1. 30 0. 10 0. 095 0. 0095 0. 10 1. 40 0. 08 0. 15 0. 012 0. 20 1. 48 0. 10 0. 33 0. 033 0. 46 1. 58 0. 12 0. 88 0. 1056 1. 30 1. 70 0. 15 1. 55 0. 2325 1. 80 1. 85 0. 15 1. 95 0. 2925 2. 10 2. 00

Active or Exchange Zone Therefore, = 1. 2 mm

Active or Exchange Zone Therefore, = 1. 2 mm

Design of Ion Exchangers n Designs of ion exchangers should include the following: n

Design of Ion Exchangers n Designs of ion exchangers should include the following: n Quantity of exchange materials n Quantity of regenerant

Quantity of Exchange Materials n The amount of exchange bed materials required can be

Quantity of Exchange Materials n The amount of exchange bed materials required can be determined by the calculating the amount of displacing ions in solution to be removed n The equivalents of ion displaced from the bed is equal to the equivalents of displacing ion in solution n The mass of bed materials Cat. TBed. Mass in kilograms is

Quantity of Exchange Materials Q is the m 3/d of flow and tint is

Quantity of Exchange Materials Q is the m 3/d of flow and tint is the interval of regeneration in hours

Quantity of Exchange Materials n By analogy, the mass bed materials for the anion

Quantity of Exchange Materials n By analogy, the mass bed materials for the anion exchanger in Kiograms is:

Quantity of Exchange Materials n The volume in m 3 for Cat. Bed. Vol

Quantity of Exchange Materials n The volume in m 3 for Cat. Bed. Vol

Quantity of Exchange Materials n the volume in m 3 For Anion. TBed. Vol

Quantity of Exchange Materials n the volume in m 3 For Anion. TBed. Vol q The percentage of swell of the exchanger bed is a very important property q It determines the final size of the tank into which the material is to be put q This value can be obtained through q Experiments q from the manufacturer

Quantity of Exchange Materials n Example: Using a bed exchanger, 75 m 3 of

Quantity of Exchange Materials n Example: Using a bed exchanger, 75 m 3 of water per day is to be treated for hardness removal between regenerations having intervals of 8 h. the raw water contains 400 mg/L of hardness as Ca. CO 3. The exchanger is a resin of exchange capacity of 1412. 8 geq/m 3. Assume that the packed density of the resin is 720 kg/m 3. Calculate the mass of exchanger material to be used and the resulting volume when the exchanger is put into operation.

Quantity of Exchange Materials n Solution: Assume cation exchanger: Also, assume that all of

Quantity of Exchange Materials n Solution: Assume cation exchanger: Also, assume that all of the cations are removed

Quantity of Exchange Materials Therefore, Assume swell= 0. 8

Quantity of Exchange Materials Therefore, Assume swell= 0. 8

Quantity of Regenerant q The Kilogram equivalents of regenerant, Cat. Regenerant, used to regenerate

Quantity of Regenerant q The Kilogram equivalents of regenerant, Cat. Regenerant, used to regenerate cation exchangers is q The Kilograme equivalents of regenerant, Anion Regenerant, used to regenerate anion exchange is

Quantity of Regenerant n Example: Using a bed exchanger, 75 m 3 of water

Quantity of Regenerant n Example: Using a bed exchanger, 75 m 3 of water per day is to be treated for hardness removal between regeneration having intervals of 8 hours. The raw water contains 80 mg/L of Ca+2 and 15 mg/L of Mg 2+. The exchanger is a resin of exchange capacity of 1412. 8 geq/m 3. Assume that the packed density of the resin is 720 kg/m 3. Calculate the kilograms of sodium chloride regenerant required assuming R = 2 and that all of the cations were removed

Quantity of Regenerant n Solution: Therefore,

Quantity of Regenerant n Solution: Therefore,

Wastewater Production n In the operation of ion exchangers, wastewater are produced. These come

Wastewater Production n In the operation of ion exchangers, wastewater are produced. These come form: n Solvent water (used to dissolve the regenerant) n Backwash and rinse requirements

Wastewater production n In the sodium cycle, the concentration of Na. Cl is about

Wastewater production n In the sodium cycle, the concentration of Na. Cl is about 5 to 10% for an average of 7. 5% n If the quantity of regenerant required is 0. 26 Kg n The volume of wastewater produced from regeneration can be calculated as follows n The total mass of regenerant solution is 0. 26 / 0. 075 = 3. 47 Kg

Wastewater Production The corresponding volume is 3. 47/ 1000 = 0. 0035 m 3

Wastewater Production The corresponding volume is 3. 47/ 1000 = 0. 0035 m 3 n For an interval of regeneration of 8 h and assuming a rate of flow for the water treated of 75 m 3 / d n The volume of water treated is 75/24(8) = 25 m 3 n Thus, the wastewater produced is 0. 0035/25 * 100 = 0. 014 % by volume n

Wastewater Production n The quantity of backwash and rinse water requirements should be determined

Wastewater Production n The quantity of backwash and rinse water requirements should be determined by experiment on the actual exchanger bed to be used in the design and is expressed as a function of bed volume n For the cation exchanger the volume of bed was previously derived as

Wastewater Production With the swelling not being considered. Thus, For the anion exchangers

Wastewater Production With the swelling not being considered. Thus, For the anion exchangers

Wastewater Production n Example: using a bed exchangers, 75 m 3 of water per

Wastewater Production n Example: using a bed exchangers, 75 m 3 of water per day is to be treated for hardness removal between regeneration having 8 hours. The raw water contains 80 mg/l of Ca and 15 mg/l of Mg. the exchanger is a resin of exchange capacity of 1412. 8 geq/m 3. Assume that the packed density of the resin is 720 kg/m 3. calculate the total volume of rinse and backwash requirement if the backwash and rinse per unit volume of bed is 18 m 3/m 3

Wastewater Production n Solution:

Wastewater Production n Solution: