Introduction to Flow Reactors

Transcription

1 Introduction to Flow Reactors Advanced Atmospheric chemistry CHEM 5152 Spring 2015 Prof. J.L. Jimenez 1 Types of Reactors Which ones can be simulated w KinSim? A. Batch B. Batch and Plug C. All D. Batch & CSTR E. I don t know engineering/10 37 chemical and biological reaction engineering spring 2007/lecture notes/lec05_ _g.pdf 2 1

2 Flow inreactors: Laminar vs Plug Flow Laminar flow has a distribution of speeds and residence times Plug Flow is a simplification for analysis purposes Turbulent flow is closer to plug, but more wall contact astr.gsu.edu/hbase/pfric.html & 3 Residence Time Distribution Laminar Flow Reactor

3 Finlayson Pitss Nucleation Flow Reactor I 78 cm x 6.5 cm Volume = 5.9 L S/V = 53 m 2 m LPM (Re ~200) v ~ 5 cm s 1 t ~ 30 s 5 NO NO 2 in Flow Reactor 6 3

4 Finlayson Pitts Large Flow Reactor I Ezell et al., AS&T Finlayson Pitts Large Flow Reactor II 850 cm x 46 cm Volume = 1200 L S/V = 10 m 2 m 3 20 LPM (Re ~61) v ~ 0.2 cm s 1 t ~ 60 min Very large volume to reduce wall effects Very long length to allow long reaction times Controlled flow to keep laminar profile 8 4

5 Potential Aerosol Mass (PAM) Oxidation Flow Reactor (OFR) Ambient Air OFR185: OFR185 & OFR254: H 2 O + hv(185nm) OH + H O 2 + hv(185nm) O 3 O 3 + hv(254nm) + H 2 O 2 OH Studies using OFRs: Kang et al., ACP 2007, 2011; Lambe et al., AMT 2011 Our work: Ortega et al. ACP 2013, Li et al. ES&T 2013; Li et al. JPCA 2015; Hu et al. ACPD in press; Peng et al. AMTD in press; Palm et al. and Ortega et al. in prep. 9 Residence Time distribution in PAM OFR With Inlet Plate Vs. Laminar Flow Reactor Li et al., JPCA 2015 In the field we use it w/o an inlet plate, distribution will be narrower 10 5

6 Why we use the PAM OFR in the Field Ortega et al. in prep. 11 OFR x O x x O 3 OH x x HO 2 H 2 O % water mixing ratio; medium lamp setting; no external OH reactivity x H 2 O Peng et al., AMTD, in press 10 6

7 Time Evolution of Species in OFR185 Li et al., JPCA OFR254 70: using 254 nm photons only, with 70 ppm O 3 injected 1.1x OH x O x x HO 2 H 2 O % water mixing ratio; medium lamp setting; no external OH reactivity H 2 O 2.1x Peng et al., AMTD, in press 11 7

8 Clicker Questions The OH exposure in OFR185 will change with water vapor A. Increase strongly B. Increase a little C. No change D. Decrease E. I don t know The OH exposure in OFR185 will change with external OH reactivity (OHR ext ) A. Increase strongly B. Increase a little C. No change D. Decrease E. I don t know 15 OH exposure OFR185 External OH reactivity = 0 1 mo 1 d 1 h OH+SO 2 HSO 3 Δ[HSO 3 ] = k*[so 2 ] * [OH]*t OH reactivity OH exposure Peng et al., AMTD, in press 16 8

9 OH exposure 1 mo 1 d 1 h OFR185 1 mo 1 d 1 h OFR External OH reactivity = 0 External OH reactivity = 10 s 1 (Remote or clean urban air) External OH reactivity = 100 s 1 (Polluted urban air) Peng et al., AMTD, in press 17 OH suppression OH suppression = 1 [OH] 0 /[OH] s [OH] 0 : OH conc. without external OH reactivity [OH] s : OH conc. with external OH reactivity OFR Peng et al., AMTD, in press 18 9

10 OH suppression vs. OH reactivity OHR O3 = k(oh+o 3 ) * [O 3 ] OHR ext = k(oh+so 2 ) * [SO 2 ] Peng et al., AMTD, in press 19 Fate of NOx / RO 2 NOx destroyed quickly NO + O 3 NO 2 + O 2 NO 2 + OH + M HNO 3 (HNO 3 + hv is slow) HO 2 is very high RO 2 + HO 2 dominates No way to study high NO chemistry in this type of reactor has been reported Li et al., JPCA

11 Uncertainty on OH exposure due to k and σ The uncertainties on rate constants and photolysis rates propagate to the species you predict Easy to do a Montecarlo simulation to study the impact Change the rate constant by a random amount within its uncertainty distribution Further details in Z. Peng et al. in AMTD Case labels: water mixing ratio/ lamp setting / external OH reactivity 0=no; L=low; M=medium; H=high e.g., LH0=low water mixing ratio, high lamp setting, no external OH reactivity Peng et al., AMTD, in press 21 Introduction to Flow Reactors II Advanced Atmospheric chemistry CHEM 5152 Spring 2015 Prof. J.L. Jimenez 22 11

12 Advantages & Limitations of PAM OFRs Advantages Fast (~3 5 min), can do lots of experiments quickly Wide range of OH exp (~ days) Easily portable to sources & field sites Can do the same exp. in field & lab Non tropospheric chemistry not enhanced relative to OH if careful Limitations Can only do low NO chemistry Can t study processes that don t scale w/ [OH] E.g. reactive uptake of IEPOX (next slide) Autooxidation? Crounse et al. (2013): Experiments that use very high radical abundances and therefore very short RO 2 lifetimes may not be fully characterizing the in situ chemistry. But Ehn et al. (Nature 2014) quotes 0.5 s 1, would still compete at lower OH/HO 2 Non tropospheric chemistry can dominate if not careful 23 Details on OFR Limitations Reminder of autooxidation reactions: Fate of IEPOX in OFR during SOAS: Crounse et al., 2013 Hu et al., in prep

13 Dimensionless Axial Distance z* D g,x : gas=phase diffusion coeff of X. Sherwood Number X : thermal molecular velocity X X : wall uptake coefficient

14 Penetration of Aerosol Particles What fraction of 50 nm particles will penetrate 25 m of tubing at 0.1 lpm? A. ~100% B. ~30% C. ~10% D. ~1% E. I don t know = D gp l tube /Q 27 14