Hongyun Yang 2, Donald R. Cahela 1 and Bruce J. Tatarchuk 1

Transcription

1 A Study of Kinetic Effects Using Microfibrous ous Entrapped ZnO Sorbents for H 2 S Removal Hongyun Yang 2, Donald R. ahela and Bruce J. Tatarchuk. enter for Microfibrous Materials Manufacturing Department of hemical Engineering Auburn University, AL, IntraMicron Inc., 368 Industry Dr., Auburn, AL, November 7, 27 AIhE 27 Annual Meeting, Salt Lake ity, Utah

2 Objectives To establish a mathematic model for adsorption/reaction processes using both packed beds and microfibrous entrapped sorbents. To investigate the effects due to using microfibrous media. AIhE 27 Annual Meeting, Salt Lake ity, Utah 2

3 Outline Microfibrous Entrapped Sorbents/atalysts Model Evaluation Particle size effects The relationship between lumped shape factor (K) and apparent reaction rate constant (k a ) The relationship between K and challenge concentration ( A ) The relationship between K and sorebent bed capacity density ( c ) Effects of microfibrous media and void omposite Bed (Packed Bed+Polisher) onclusions Acknowledgements AIhE 27 Annual Meeting, Salt Lake ity, Utah 3

4 Microfibrous Entrapped Sorbents/atalysts t t oncept: Properties: Unique form factors and thermal integration High contacting efficiency High intrabed thermal conductivity Enhanced mass and heat transfer Ease of regeneration High voidage (i.e., 75% for glass fiber entrapped sorbents) Microfibrous Entrapped Micro-catalyst/sorbent particles AIhE 27 Annual Meeting, Salt Lake ity, Utah 4

5 Glass Fiber Entrapped Sorbents SiO 2 particle glass fiber 2m Properties of Glass Fiber Entrapped Sorbent (GFE) omponent Wt.% Vol.% ZnO 2 N.A. SiO Fiber 22 3 Void N.A. 75 Glass fiber entrapped SiO 2 particles AIhE 27 Annual Meeting, Salt Lake ity, Utah 5

6 Bed Service Time Models General Equation t=a +B Term Yoon s Model Wheeler Model Mecklenburg Model A W e F W W s F c W s AZn' F c B W e kf W k s c v An' dg ( ) a c.4 ( ) D a.67 W s F Yoon s model b b ln ln A b A ln b A A ln A K t K=? Yoon, Y.H., Nelson, J.H., (984). Application of Gas Adsorption Kinetics: I. A Theoretical Model for Respirator artridge Service Life. American Industrial Hygiene Association Journal, 45, AIhE 27 Annual Meeting, Salt Lake ity, Utah 6

7 Modified Amundson Model For a second order heterogeneous reaction Amundson model A A k 2c zt exp k t exp 2 A U Modified Amundson model A ln k A 2 A A ln K t A t k 2 k a c c defined as capacity density, is actually an effective ZnO molar density. Apparent reaction rate Gas reactant A K k a c Solid reactant Amundson, N.R., (948). A note on the mathematics of adsorption in beds. Journal of Physical olloid hemistry, 52, AIhE 27 Annual Meeting, Salt Lake ity, Utah 7

8 Mass Transfer orrelation for Apparent Reaction Rate k k a c 6( ) d p D AB kc Sh 3 d Sh J d Re Sc p J d.24 Re.39 Re" Re ( ) k a d p U.6 Sc 3 D d AB 2 p K.6.39 d pu DAB 3 A Sc 2 d p c 7.44 a f a p External surface area based average For Packed Bed d d d s f f p p d su DAB 3 k a Sc d s d p K d U D d sd p c For Microfibrous Media.39 s 3 AB A Sc AIhE 27 Annual Meeting, Salt Lake ity, Utah 8

9 Model Evaluation Breakthrough curve Ln( /-)~t 6 4 H2S / Ln(/-) = -.257t R 2 = ln(/- -) Time (min) A commercial ZnO sorbent (6-8 mesh, g) was tested t with challenge gas concentration ti of 2 vol. % H 2 S in H 2 and flow rate of ml/min STP, at 4 º. AIhE 27 Annual Meeting, Salt Lake ity, Utah 9

10 Particle Size Effects H2S / ZnO.5 mm ZnO 4-6 mesh ZnO 6-8 mesh ZnO 8- mesh ZnO -4 mesh ZnO/SiO2 GFES Time (min) Breakthrough curves of the commercial ZnO sorbent particles (.2 g,.8 g ZnO) with different sizes, and these of ZnO/SiO2 sorbent and glass fiber entrapped ZnO/SiO2 sorbent (GFES). Tested with challenge gas of 2 vol. % H 2 S in H 2 at a face velocity of.2 cm/s at 4 º. AIhE 27 Annual Meeting, Salt Lake ity, Utah

11 Lumped K vs. k a H2S / m:v..6 2m:2v m:4v.4.4 8m:8v GFES.2.. K (s - ) K K =.7-4 k a R 2 =.996 A ka c A Apparent rate constant k a (s - ) Time (min) Breakthrough curves of ZnO/SiO 2 sorbent at different face velocities (m=.g, v=.24 cm/s). Tested with challenge gas of 2 vol. % H 2 S in H 2 at 4 º. AIhE 27 Annual Meeting, Salt Lake ity, Utah c 4

12 Lumped K vs. / H2S K =2.6 K 2 =.2 K 3 =.67 =2ppmv =98 ppmv =495 ppmv K (s - ) K = 8843 A 2 R 2 =.9985.E+.E-7 2.E-7 3.E-7 4.E-7 H 2S initial concentration (mol/cm 3 ) K k a Time (min) c k A a c In each experiment,.8 g ZnO/SiO 2 was tested at face velocity of 5. cm/s at 4º. AIhE 27 Annual Meeting, Salt Lake ity, Utah 2

13 Lumped K vs. c H2S / ZnO wt% 7% 3% 9% 5% Time (min) Breakthrough curves of ZnO/SiO 2 sorbents at various ZnO loadings and the same amount of ZnO of.34 g. Sorbents tested with challenge gas of 2 vol. % H 2 S in H 2 at a face velocity of.2 cm/s at 4 º. AIhE 27 Annual Meeting, Salt Lake ity, Utah 3

14 Lumped K vs. c ont d c / H2S sorbent only M sorbent mixed with part inert M2 sorbent mixed with 2 part inert M3 sorbent mixed with 2 part inert M4 sorbent mixed with 2 part inert Time (min) Breakthrough curves of ZnO/SiO 2 sorbents (.2g ZnO/SiO 2 with ZnO loading at 7 wt.%) diluted by various amount of SiO 2 particles. Tested with challenge gas of 2 vol. % H 2 S in H 2 at a face velocity of.2 cm/s at 4 º. AIhE 27 Annual Meeting, Salt Lake ity, Utah 4

15 Lumped K vs. c -ont d c K= /c R 2 =.999 ka A =.95-5 A K k A a c K (s - ) K= /c R 2 = B / c (cm 3 /mol) Tested at a face velocity of.2 cm/s at 4 with 2 vol. % H 2 S -H 2. (A) packed kdbd beds of fzo/sio ZnO/SiO 2 sorbents (-2 m) ) with various ZnO Oloadings (B) diluted packed beds of ZnO/SiO 2 sorbents (-2 m). AIhE 27 Annual Meeting, Salt Lake ity, Utah 5

16 Effects of Void and Microfibrous Media Packed bed Packed bed Microfibrous (void iddiluted) d) entrapped sorbents* c (mol/cm ) d p (m) d s (m) k c /k cp k a /k ap.6.22 K/K p.67.3 K/K p (experimental) -.32 *ontains 3 vol.% 8um glass fiber AIhE 27 Annual Meeting, Salt Lake ity, Utah 6

17 Kinetics in omposite Bed H2S /.9 A-Polisher -2 m ZnO/SiO 2 in microfibrous media SiO 2 24 vol.% and 53 w t. % ZnO 2 w t.% of composite Thickness: 4.4mm B+A Packed Bed +Polisher B+A B-Packed Bed Performance of Polishing Sorbent and Packed Bed + Polishing ppm H 2S in H 2 2, 4 o, 8.5 cm/s..3.2 Area=Area2 G72-E, 3/6" extraduate.7 9 w t.% ZnO Bed thickness: 2.2 cm BedID:24cm ID:2.4. Packed Bed 56 % omposite Bed 35 % BT ppm BT 94 vs. 29 min. Time (min.) AIhE 27 Annual Meeting, Salt Lake ity, Utah 7

18 Kinetics in omposite Bed K (s - ) τ (min.) z c (cm) Test initial final initial final ( ppmv) (. ppmv)* Polishing layer Packed bed omposite bed AIhE 27 Annual Meeting, Salt Lake ity, Utah 8

19 onclusions A modified damundson model successfully characterized dthe adsorption process taking place in fixed bed reactors; Lumped K is introduced to describe the breakthrough curves. K is a function of apparent reaction rate, challenge gas concentration, and sorbent capacity density; High voidage decreased the apparent reaction rate; the micronsized fibers reduce the characteristic dimension. The low capacity density increase the lumped K; Microfibrous entrapped sorbents have low capacity but high sorbent utilization. omposite bed (a packed bed followed by microfibrous entrapped sorbent polisher) synergistically combines the high volume loading of packed beds and the overall contacting efficiency of small particulates. AIhE 27 Annual Meeting, Salt Lake ity, Utah 9

20 Acknowledgements This work was supported by the US Army under a U.S. Army contract at Auburn University (ARMY-W56HZV ) administered i d through h the US Army Tank- Automotive Research, Development and Engineering enter (TARDE). AIhE 27 Annual Meeting, Salt Lake ity, Utah 2

21 Thank you for your attention AIhE 27 Annual Meeting, Salt Lake ity, Utah 2