CHEMICAL EQUILIBRIA BETWEEN THE ION EXCHANGER AND GAS PHASE. Vladimir Soldatov and Eugeny Kosandrovich

Transcription

1 CHEMICAL EQUILIBRIA BETWEEN THE ION EXCHANGER AND GAS PHASE Vladmr Soldatov ad Eugey Kosadrovch Isttute of Physcal Orgac Chemstry Natoal Academy of Sceces of Belarus, 13, Surgaov St, Msk 2272, Rep. of Belarus. 1

2 Io exchage techologes for ar purfcato (fbrous o exchagers form of fabrcs) Purfcato of dustral ad agrcultural exhaust gases from ozable or catalytcally covertble mpurtes (. g. NH 3, HCl, SO 2, H 2 S, Cl 2, ) Removal malodorous substaces from breathg ar (orgac acds, ames, mercaptaes, ) Idvdual protecto meas for humas lugs ad sk Deep ar purfcato clea rooms producto of mcrochps, precse mechacs, optcs, pharmaceutcals 2

3 Examples of the sorpto processes systems GAS-ION EXCHANGER Sorpto of ammoa ad ames: R - H + + NH 3 R - NH 4 + Sorpto of acds: R + OH - + HCl R + Cl - +H 2 O R + Cl - + HCl R + Cl -. HCl Sorpto of ahydrdes: R + OH - +SO 2 R + 2SO H 2 O R + 2SO SO 2 +H 2 O 2R + HSO 3-2R 2+ SO O 2 2R 2+ SO 4 2-2R + OH - + CO 2 R 2+ CO H 2 O Sorpto of eutral substaces : R + OH - + Cl 2 2RCl + H 2 +O 3

4 Features of practcally mportat gaseous processes wth o exchagers Extremely short cotact tme of the o exchager ad ar reurg applcato of the sorbets form of fbers (fractos of secod) Low cocetrato of the sorbate the ar ( 2 mg/m 3 ) Pletful sde processes (oxdato the sorbate by atmospherc O 2, sorpto competto wth CO 2, ) Extremely strog effect of the ar relatve humdty o the sorpto ad catalyss 4

5 The am of theory To calculate sorpto of a oc sorbate, exemplfed by NH 3, by the o exchager from ts cocetrato ad relatve water humdty the gas phase o the bass of the followg formato: 1. Exchage capacty of the o exchager. 2. The acdty parameters of fuctoal groups pk ad Δpk (obtaable from the ttrato curves) 3. Parameters of sopestc curve W=W(P/P ) (obtaable from the sopestc data) 4. Costat of o exchage eulbrum K + -NH 4 + (obtaable from the expermet o the o dstrbuto) 5

6 Assumptos: 1. The water o exchager presets two forms free water ad hydrate water. 2. Molecular NH 3 s dssolved oly the free water. 3. Dstrbuto of NH 3 betwee gas phase ad the free water s cotrolled by the Hery s law wth the same dstrbuto costat as that for the lud water. 4. Dstrbuto of NH 4+ betwee the teral soluto ad the sorpto ceters of o exchager s cotrolled by o exchage reacto RH + NH 4+ RNH 4 +H + descrbed by the eulbrum coeffcet k = [RNH 4 ][H + ]/([RH] [NH 4+ ]) k = k(x) 6

7 Scheme of theoretcal calculato of ammoa sorpto Ar cotag NH 3 ad H 2 O + o exchager H + - form sorpto of water, formato of hydrates dssoluto of ammoa the free water, ammoa dssocato teracto of ammoa wth the fuctoal group 7

8 8 Evaluato of the amout of hydrato water the o exchager R h K α =,, + = = h h K K α α 1, - umber of water molecules hydrate α relatve humdty P/P h ad R - umber of moles of the hydrate ad o-hydrated groups RH + H 2 O RH H 2 O

9 Evaluato of the amout of the free water We assume the frst approxmato the o exchager s a deal mxture of hydrates ad free water molecules ad the system obeys the Rault s law the followg form: α = X W f W /(X W f W ) where X W, X W ad f W, f W are respectvely mole fractos ad the ratoal actvty coeffcets of free water a partally ad completely swolle o exchager (α = 1): X W = W / ( W +1), X W = W / ( W +1) W s a umber of free water moles per mole of the fuctoal groups 9

10 1 Evaluato of the amout of the free water Choosg the referece state as f W = 1 at X W = X W we obta for the amout of free water the o exchager: f W = α m m s emprcal costat, usually eual to. ) ( - 1 ) (,,, + = h h W h W W W f W α α

11 11 A ew euato for the sopestc curve W(α) = + W h, ) ( - 1 ) ( 1,,, = h h W h W W f W K K W α α α α

12 Comparso of expermetal data for Dowex-5x8 from Boyd ad Soldao wth theoretcal calculato (les) mol H2O/e H L + 12,,2,4,6,8 1, 12,,2,4,6,8 1, 8 Na + 8 K + 4 4,,2,4,6,8 1,,,2,4,6,8 1, 12

13 1-sopestc curve of sulfoc o exchagers FIBAN K- 1, H form. The les are calculated from the ew euato wth the followg parameters: = 2; K= 5; m =. -hydrato water; 3 free water 18 mol H2O/e a 4 2 α,,2,4,6,8 1, 13

14 1-sopestc curve of carboxylc o exchagers FIBAN K-4. The les are calculated from the ew euato wth the followg parameters: = ½; K=5; m= hydrato water; 3 free water 4 mol H2O/e b 1 α,,2,4,6,8 1, 14

15 Molecular ammoa dstrbuto betwee the o exchager ad gas phase We assume that ammoa gas ca dssolve oly free water the phase of o exchager. I ths assumpto Hery s law s formulated as: [NH 3 ] R = K H [NH 3 ] G X W where [NH 3 ] R s cocetrato of NH 3 the teral soluto, the mole fracto of free water X W s calculated from sopestc data. Costat K H s assumed to be the same as that for eulbrum of aueous soluto of ammoa wth water soluto. It was calculated from the lterature data ad eualed x 1-5 (mol/kg)/ (mg/m 3 ). 15

16 Determato of amout of RNH 4 + as a fucto of x I order to compute amout of NH 3 boud to the fuctoal groups we apply euato of hydrolyss: RNH 4 + H 2 O RH + NH 4+ + OH - k hyd (x) = (1-X) [NH 4+ ] [OH - ]/(X [H 2 O]), X = [RNH 4 ]/E, (1-X) = [RH]/E E exchage capacty k hyd (x) depeds o degree of hydrolyss (1-X). It ca be determed va the acdty parameters of o exchager obtaable from the ttrato curve 16

17 The acdty parameters Ttrato of the H form of o exchager wth alkal KtOH s descrbed as eulbra RH + Kt + RKt + H + H + + OH - H 2 O Depedece of the eulbrum coeffcet of o exchage Kt + -H + k(x) = X [H +] / ((1 X)[Kt + ]) wth suffcet accuracy ca be descrbed as pk = pk + Δpk (X-1/2) K s the thermodyamc costat of o exchage depedet of the degree of o exchage, Δpk s a costat eual to pk x=1 pk x=. I our works we use K + as a stadard cato for determato of the acdty parameters, Kt + = K +. 17

18 Coecto betwee the acdty parameters ad RNH 4 hydrolyss eulbrum coeffcet Value pk for the case Kt + = NH 4+ s obtaable from drect expermet or from combg costats of o exchage eulbra H + -K + ad K + -NH 4 + Combe euatos of eulbrum coeffcets of hydrolyss ad o exchage wth those for water ad ammoa dssocato, K D : pk hyd = 14 - pk - Δpk (X RNH4+ -1/2) X RNH4+ = [NH 3 ] R K D / (k hyd + K D [NH 3 ] R ) Apply the modfed Hery s euato: X RNH4+ = K H X W [NH 3 ] G K D / (k hyd + K D K H X W [NH 3 ] G ) 18

19 The formato eeded for aprorstc calculato of the ozable sorbate sorpto by the o exchager 1. Dssocato costat of the sorbate 2. The acdty parameters of o exchager (obtaable from the ttrato curves) 3. Isopestc curve of the o exchager the acd form 4. The costat of Hery s law. 19

20 The pathway for a aprorstc calculato of ammoa sorpto by the o exchager 1. Fttg the sopestc data for the o exchage H form to the theoretcal euato ad fdg parameters, K ad m. 2. Fdg the mole fracto of free water the o exchager, X W,at a gve relatve humdty α. 3. Calculato of the relatve mole fracto of ammoa the o exchager usg the fal euato. 2

21 Breakthrough ad sorpto curves of NH 3 (18 mg/m 3 ) for carboxylc acd fbrous o exchager FIBAN K-4 at dfferet relatve humdty of the ar passg through the layer of o exchage fabrc 6 mm thck wth lear flow rate.8 m/s 1 35%; 2 42%; 3 47%; 4 52%; 5 56%; 6 68%; 7 8%; 8 94%. 21

22 Breakthrough ad sorpto curves of NH 3 (18 mg/m 3 ) for sulfoc acd fbrous o exchager FIBAN K-1 at dfferet relatve humdty of the ar passg through the layer of o exchage fabrc 3 mm thck wth lear flow rate.8 m/s α = 7,5%, 15,5%; 51%, 85%. 22

23 4 4 b Е, m-e/g K-4 K C (NH 3 ), mg/m 3 Ammoa sorpto o o exchagers FIBAN K-1 ad K- 4 depedece cocetrato of ammoa at α =.48 for K-1 ad α =.55 for K-4. Symbols expermetal data, the curves are computed 23

24 Е, m-e/g a 1 K-4 1 K-1,,2,4,6,8 1, α Ammoa sorpto o o exchagers FIBAN K-1 ad K- 4 depedece of relatve ar humdty at [NH3] G =18 mg/m 3. Symbols expermetal data, the curves are computed. 24