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Introduction to Flow Reactors
Advanced Atmospheric chemistry
CHEM‐5152
Spring 2015
Prof. J.L. Jimenez
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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 know2http://ocw.mit.edu/courses/chemical‐engineering/10‐37‐chemical‐and‐biological‐reaction‐engineering‐spring‐2007/lecture‐notes/lec05_02212007_g.pdf
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Flow inReactors: Laminar vs Plug Flow
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• 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
http://hyperphysics.phy‐astr.gsu.edu/hbase/pfric.html & http://en.wikipedia.org/wiki/Chemical_reactor#PFR_.28Plug_Flow_Reactor.29
Residence Time Distribution
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Laminar Flow Reactor
http://www.comsol.com/paper/download/200363/junior_paper.pdfhttp://authors.library.caltech.edu/25070/9/FundChemReaxEngCh8.pdf
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Finlayson‐Pitss Nucleation Flow Reactor I
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78 cm x 6.5 cmVolume = 5.9 LS/V = 53 m2 m‐3
6‐17 LPM (Re ~200)v ~ 5 cm s‐1
t ~ 30 s
NO NO2in Flow Reactor
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Finlayson‐Pitts Large Flow Reactor I
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Ezell et al., AS&T 2010
Finlayson‐Pitts Large Flow Reactor II
• Very large volume to reduce wall effects
• Very long length to allow long reaction times
• Controlled flow to keep laminar profile8
850 cm x 46 cm Volume = 1200 LS/V = 10 m2 m‐3 20 LPM (Re ~61)v ~ 0.2 cm s‐1 t ~ 60 min
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Potential Aerosol Mass (PAM) Oxidation Flow Reactor (OFR)
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.
OFR185: H2O + hv(185nm) OH + HO2 + hv(185nm) O3
OFR185 & OFR254: O3 + hv(254nm) + H2O 2 OH
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Am
bien
t Air
Residence Time distribution in PAM OFR
• In the field we use it w/o an inlet plate, distribution will be narrower
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With Inlet Plate Vs. Laminar Flow Reactor
Li et al., JPCA 2015
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Why we use the PAM OFR in the Field
11Ortega et al. in prep.
1.7
0.6
0.6
1.7
2.2
1.7
1.7
OFR185
O3
O2
4.2x 1018
128.21.6x 10104.9x 1013
OH
6.1x 10116.3x 1010
H2O2
2.1x 1017
H2O
HO2
8.3
5.1
5.1
9.1
10.9
10.9
8.3
9.1
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1% water mixing ratio; medium lamp setting; no external OH reactivity
Peng et al., AMTD, in press
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Time Evolution of Species in OFR185
13Li et al., JPCA 2015
55.6
28.9
55.6
28.9
28.9
28.9
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O3
1.8x 10101.1x 1015
OH
9.0x 1012
2.5x 1011
H2O2
2.1x 1017
H2O
HO2
171.2
146.4146.4
51.5
51.5
171.2
OFR254‐70: using 254 nm photons only, with 70 ppm O3 injected
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1% water mixing ratio; medium lamp setting; no external OH reactivity
Peng et al., AMTD, in press
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Clicker Questions
• The OH exposure in OFR185 will change with water vaporA. 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 (OHRext)A. Increase strongly
B. Increase a little
C. No change
D. Decrease
E. I don’t know
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OFR185External OH reactivity = 0
OH exposure
1 h
1 mo
1 d
OH+SO2→HSO3
Δ[HSO3] = k*[SO2] * [OH]*t
OH reactivity OH exposure
http://tinyurl.com/ac-cheat
Peng et al., AMTD, in press
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OFR185 OFR254‐70
External OH reactivity = 0
External OH reactivity = 10 s‐1
External OH reactivity = 100 s‐1
(Remote or clean urban
air)
(Polluted urban air)
1 h
1 mo
1 d
1 h
1 mo
1 d
OH exposure
Peng et al., AMTD, in press
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OH suppression
OFR254‐70
OH suppression = 1 – [OH]0/[OH]s
[OH]0: OH conc. without external OH reactivity[OH]s: OH conc. with external OH reactivity
Peng et al., AMTD, in press
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OHRO3 = k(OH+O3) * [O3]OHRext = k(OH+SO2) * [SO2]
OH suppression vs. OH reactivity
Peng et al., AMTD, in press
Fate of NOx / RO2
• NOx destroyed quickly
NO + O3 NO2 + O 2NO2 + OH + M HNO3
(HNO3+ hv is slow)
• HO2is very high
• RO2 + HO2 dominates
• No way to study high‐NO chemistry in this type of reactor has been reported
20Li et al., JPCA 2015
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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
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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
Introduction to Flow Reactors II
Advanced Atmospheric chemistry
CHEM‐5152
Spring 2015
Prof. J.L. Jimenez
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Advantages & Limitations of PAM OFRsAdvantages
• Fast (~3‐5 min), can do lots of experiments quickly
• Wide range of OHexp (~0.5‐40 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 RO2lifetimes 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/HO2
• “Non‐tropospheric” chemistry can dominate if not careful
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Details on OFR Limitations
• Reminder of autooxidation reactions:
• Fate of IEPOX in OFR during SOAS:
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Crounse et al., 2013
Hu et al., in prep.
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•
25http://pubs.acs.org/doi/pdf/10.1021/ac5042395
Dg,X: gas=phase diffusion coeff of X.
Sherwood Number
Dimensionless Axial Distance z*
X: thermal molecular velocity XX: wall uptake coefficient
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Penetration of Aerosol Particles
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= Dgp ltube/Q
• 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