THE OXIDATION OF FUEL RADICALS the treatment of chemical

Physical and Chemical Properties Division

THE OXIDATION OF FUEL RADICALS(the treatment of chemical activation processes)

Wing TsangNational Institute of Standards and Technology

Gaithersburg, MD 20899

Multi Agency Coordination Committee for Combustion Research [MACCCR]

Fuel Research ReviewArgonne National Laboratory

September 21, 2011


MOTIVATION

Contribute to the development of a fundamentally based combustion kinetics database for the simulation of combustion phenomena

Serve as a basis for the development of correlationsProvide a test of theory

Development of mixing rules for mixtures

Experimental studies on larger molecules and structuresreal fuels

Pay particular attention to oxygen attack to larger radicals

Develop methodology for treating chemical activation reactions


Mechanism For Fuel Breakdown During Combustion

FuelRadical attack

Fuel Radical 1-olefin + smaller alkyl radical

Radical O2 attack

1-olefinyl H, methylEthylenePropene

Fuel –O2 allyl dienes

Olefin + HO2

QOOH β-bond scission

Cyclic Ether + OH O2

O2QOOH

Ketohydroperoxide +OH

Fuel => Fuel Radical => Smaller Radical + 1-olefin => 1-olefinyl radical =>olefins, diene and cyclic radicals.

Chemical activation process

Thermal activation processes


Kinetics Modules in Databases

GRIMECH - methane (light hydrocarbon) combustion

Pyrolysis of fuels

Oxidation of larger fuels

Soot formation

Recent NIST experimental and data

evaluation programTarget of most models Focus of current

NIST work

Widely used Problems with rich

mixtures

Many models, begin with unsaturates

7


Thermodynamic PropertiesEnthalpiesEntropies

As a function of temperature

Rate ExpressionsAs a function of temperature and

pressure

CONTENTS OF DATABASE


CHEMICAL ACTIVATED REACTIONS

Consequence of the unimolecular reactions of molecules with non-thermal energy distribution function

Usually occurs through the formation of excited molecule from combination of two reactive species

Important in combustion environments

Neglected in all combustion kinetics databases


Special Features of Chemical Activation Processes

Non-thermal (Boltzmann) energy distribution

Collisions will lead to thermal distributiom: measure of energy transfer(a) stabilization

(b) Thermal decomposition

Consequences: time dependent distribution function

Direct pertinence to combustion

How does one describe processes in terms of rate constants


RELEVANT RELATIONS

k (T, P) = Σ k(E) ρ (E) dE

Macroscopic rate constant

RRKM expression for specific rate

Experimental data from chemical activation

Physical and Chemical Properties DivisionP h ys ic a l a n d C h e m ic a l P ro p e rtie s D iv i s io n

TYPICAL WINDOW FOR MASTER EQUATION SOLVER (CHEMRATE)


PAST WORK

Extensive experimental work by Rabinovitch and coworkersEmphasis of H+olefin reactions

Most studies at room temperature and low pressuresClean systems very reliable experiments

Structure for treating results in terms of stabilizatiom to decompositiom ratiosRRKM theory and energy transfer model

Leading to prohibitively large step-size down paramter

Knyazev and Tsang demonstrated that actual values for step sizes down were really much smaller for s-butyl

Due to errors in thermochemistry and high pressure rate expressions


Log [P, torr]0.0 0.2 0.4 0.6 0.8 1.0

Log

[Sta

biliz

atio

/Dec

ompo

sitio

n]

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

120 cm-1

150 cm-1

180 cm-1

H2-exponential down

400 cm-1-step ladder[Tardy and Rabinovitch]

Log [P, torr]0.0 0.2 0.4 0.6 0.8

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Log

[Sta

iliatio

n/D

ecom

posi

tion]

CH4-exponenial down

300 cm-1360 cm-1

400 cm-1

1500 cm-1 step ladder(Tardy and Rabinovitch}

Log [ P,torr]0.0 0.2 0.4 0.6 0.8 1.0

Log

[Sta

biliz

atio

n/D

ecom

posi

tion]

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

210 cm-1

240 cm-1

270 cm-1

N2-exponential down

800cm-1step ladder [Tardy and Rabinovitch]

Log P[torr]0.0 0.2 0.4 0.6 0.8 1.0

Log

[Sta

biliz

atio

n/D

ecom

posi

tion]

0.8

1.0

1.2

1.4

1.6

1.8

2.0

360

420

480

CF4-exponential down

>3000cm-1 step ladder(Tardy and Rabinovitch}

COMPARISON BETWEEN EXPERIMENTSL AND CALCULATED RESULTS ON THE CHEMICALLY ACTIVATED DECOMPOSITION OF HEXYL-2


STRATEGY FOR STUDYING RADICAL OXIDATION

Generate radicals as in pyrolysis experiments

Dilute concentrations of radicals

Vast excess of chemical inhibitor

Add sufficient amount of oxygen molecules to change reaction direction from pyrolysis to oxidation

Determine cracking patterns as function of oxygen concentration

Reproduce oxidative cracking pattern through solution of the master equation for chemical activation process


RADICALS STUDIED

C H3CH2CH2CH2CH2*

CH3CH2CH2CH2CH2CH2*

CH3CH2CH2CH2CH2CH2CH2*

CH3CH2CH2CH2CH2CH2CH2CH2*

CH2=CHCH2CH2CH2*

CH2=CHCHCH2CH2CH2*

CYCLOHEXYL

CYCLOPENTYL

CH3CH(CH3)CH2CH2CH2*

CH3CH(CH3)CH2CH2CH2CH2*


CH3CH2CH2CH2 + O2 CH3CH2CH2CH2OO CH3CH2CH=CH2+HO2

CH2CH2CH2CH2OOH CH3CHCH2CH2OOH

oHO + C2H4 + CH2CH2OOH C2H4 + HO2

C3H6+ CH2OOH

CH2O + OH

Oxidative Decomposition of n-Butyl Radical

CH3CH2CH2CH2ICH3CH2CH=CH2 +HI CH3CH2CH2CH2

CH3CH2 + C2H4

C2H4 + H

Pyrolytic Decomposition of n-Butyl Radical (through n-Butyl Iodide)


Molecular Properties Necessary for the Analysis of Chemical Activation Results

Properties of reactants and productsVery little experimental data on peroxy compounds nnd radicals

How good are ab initio calculations?.

Properties of transition statesLeading to rate expressions for unimolecular reactions

No experimental data on oxygenatesDependent on ab initio calculations

Energy transferred on collisions for bath moleculeStep size down


SOURCES OF ALKYL RADICAL

RCH2CH22CH2--I = RCH2CH2=* + I source of radicalI = RCH2CH2=* + I source of radicalRCH=CH2 + HI parallel processRCH=CH2 + HI parallel process

Interference for 1Interference for 1--butene production from oxidation of radicalbutene production from oxidation of radicalR = CH3 CH2R = CH3 CH2

RCH2CH2CH2CH2ONO = NO + RCH2CH2CH2CH2O*=RCH2CH2CH2*+ CH2ORadical source

RCH=CH2 + CH2=CH2 + OHInterference for propene formation from oxidation of radical

R = CH3


E xpan sion fan

In ciden t sh ock

R eflec ted shock

D istan ce

Tim

e

In terface

L ow pressureH igh pressure

D iaphragm

Tim

e

P ressu re T em p eratu re

E xpan sion fan

P artic le pa th

S am pling port

D um p tank

2

1

3

4

5

SINGLE PULSE SHOCK TUBE AND ASSOCIATED WAVE PROCESSES


800 850 900 950 1000 1050 1100

LOG

[MO

L-FR

AC

TIO

N]

-1.0

-0.5

0.0

0.5

1.0

800 850 900 950 1000 1050 1100

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

800 850 900 950 1000 1050 1100

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

150 torr O % O2150 torr 1.54% O2 150 torr 4.07% O2150 torr 9.21% O2300 torr 10.35% O2600 torr 10.15% O2

800 850 900 950 1000 1050 1100

-3.0

-2.5

-2.0

-1.5

-1.0

800 850 900 950 1000 1050 1100-3.5

-3.0

-2.5

-2.0

-1.5

-1.0-0.5

LOG

[MO

L-FR

AC

TIO

N]

LOG

[MO

L-FR

AC

TIO

N]

LOG

[MO

L-FR

AC

TIO

N]

LOG

[MO

L-FR

AC

TIO

N]

Ethylene

Propene

1-Butene

Butanal

THF

Temp [K} Temp [K}

Temp [K} Temp [K}

Temp [K}

PRODUCT YIELDS FROM THE OXIDATIVE DECOMPOSITIOM OF BUTYL RADICALS FROM BUTYL

IODIDE


850 900 950 1000 1050

Log

[mol

e-fr

actio

n]

-1.0

-0.5

0.0

0.5

1.0

850 900 950 1000 1050

-2.0

-1.5

-1.0

-0.5

0.0

850 900 950 1000 1050-2.5

-2.0

-1.5

-1.0

-0.5

850 900 950 1000 1050

-2.5

-2.0

-1.5

-1.0

850 900 950 1000 1050

-3.0

-2.5

-2.0

-1.5

-1.0

150 torr 0% O2150 torr 1.25% O2150 torr 3.13% O2150 torr 6.05% O2150 torr 10.1% O2150 torr 22.6% O2

Ethylene

Log

[mol

e-fr

actio

n]Lo

g [m

ole-

fract

ion]

Log

[mol

e-fr

actio

n]Lo

g [m

ole-

frac

tion]

Propene

1-Butene

Butanal

THF

PRODUCT YIELDS FROM THE OXIDATIVE DECOMPOSITIOM OF BUTYL RADICALS FROM

PENTYL NITRITE


1000 /T0 .90 0 .95 1 .00 1 .05 1 .10 1 .15 1 .20

Log[

C3H

6/TH

F]

0 .0

0 .5

1 .0

1 .5

2 .0

150 , 1 .54%

150 .4 .04%

150 , 9 .15%300 ,10 .35% 600 .10 .15%

PROPENE/THF RATIOS AS A FUNCTION OF TEMPERATURE AND OXYGEN CONCENTRATION

Log [C3H6/THF] = 2.92 -2120/T= .64 (930K)

Physical and Chemical Properties Divisionlog[time,s]

-10 -8 -6 -4

log[

bran

chin

g ra

tio]

-4

-3

-2

-1

0

C4H9OO

C4H9 +O2

1-C4H9OO 3-C4H9OO2-C4H9OOH

1-butanal

THF

1-butene

ethylene

propene

BRANCHING RATIOS FROM THE CHEMICALLY ACTIVATED DECOMPOSITION 0F BUTYLPEROXYL

RADICAL FROM OXYGEN ADDITION TO BUTYL


1000/T[K]0.8 1.0 1.2 1.4 1.6 1.8 2.0

LOG

[k,c

c/m

ol-s

]

11.0

11.5

12.0

12.5

13.0

13.5

HEXYL-2

CIS-BUTENE-2

RATE CONSTANTS FOR ADDITION AND ABSTRACTION TO OLEFINS (LABELS ARE

FOR PRODUCTS)


Log [time,s]-10 -8 -6 -4 -2 0

Log

[bra

nchi

ng ra

tio]

-3

-2

-1

0

s-butyl =propene+methyl

s-butyl =cis-butene-2 + H

s-butyl600 K, 0.1 bar

-10 -8 -6 -4 -2 0-3

-2

-1

0

Log [time,s]

s-butyl

s-butyl =propene+methyl

s-butyl =cis-butene-2 + H

Log

[bra

nchi

ng ra

tio]

1400 K, 10 bar

TEMPORAL BEHAVIOR OF S-BUTYL RADICALS AND PRODUCTS FORM FROM H + CIS-BUTENE-

2


Energy(kcal/mol]0 20 40 60 80 100

Log

[con

cent

ratio

n]

-20

-18

-16

-14

-12

-10

-8

-6

-4

--12-11

-10

-9

-8

-7-6-5-4

-3

-2 - 0

Distribution function for s-butyl radicalat 600 K and 1 bar

S-BUTYL RADICAL DISTRIBUTION FUNCTION FROM H + CIS-BUTENENE-2


0.8 1.0 1.2 1.4 1.6

Log

[cc/

mol

-s]

10

11

12

13

1000/T[K]

s-C4H9

10

0.1

CH3 + C3H6

10

1.0

0.11.0

H + c-C4H8-2

0.1

1.0

10

RATE CONSTANTS FOR THE CHEMICALLY ACTIVATED REACTIONS OF S-BUTYL RADICAL FROM H + CIS-BUTENE-2


1000/T0.96 0.98 1.00 1.02 1.04 1.06 1.08 1.10

log(

olef

ini/ Σ

olef

ini)

-2.0

-1.8

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

C2H4

C3H6

1-C4H8

1-C5H10

EXPERIMENTAL OLEFINIC BRANCHING RATIOS FROM 1-HEXYL RADICAL DECOMPOSITION

1-hexyl

2-hexyl 3-hexyl

C2H4 + 1-C4H9

C3H6 + 1-C3H7 1-C4H8 + C2H5

1-C5H10 + CH3


TEMPORAL BEHAVIOR OF HEXYL-2 RADICAL AND PRODUCTS FORMED FROM H+HEXENE-1 AT 800 K AND 1 BAR PRESSURE

Log [time, s]

-10 -8 -6 -4

Log

[bra

nchi

ng ra

tio]

-4

-3

-2

-1

0

-10 -8 -6 -4-4

-3

-2

-1

0

-10 -8 -6 -4-4

-3

-2

-1

02-hexyl

1-hexyl

3-hexyl

2-hexyl = propene+ propyl

2-hexyl = hexene-2 +H

1-hexyl = ethylene +butyl

3-hexyl = 1-butene + ethyl

3-hexyl = 1-pentene + methyl

Log [time, s]Log [time, s]Lo

g [b

ranc

hing

ratio

]

Log

[bra

nchi

ng ra

tio]


SUMMARY and CONCLUSIONS

Chemical activation reactions are very important components of combustion processes .

Can be treated in the context of unimolecular rate theory

Added complication in converting results to rate constants for combustion conditions is the necessity of considering three distinct processes:

stabilization, reaction from excited species and thermal processing

Theory must be considered in the interpretation of experimental data

Need for fundamental information on molecular properties of non-hydrocarbon (OXYGENATES} compounds and

transition states

Documents

THE OXIDATION OF FUEL RADICALS the treatment of chemical