Influence of micromixing on parallel reactions - ETH E

Diss ETH No. 10257
Influence of
micromixing
parallel reactions
on
A dissertation submitted to the
SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH
for the
degree
of
Doctor of Technical Sciences
presented by
Louis Alfred De Boni
Serge
dipl. Chem.-Ing.
born
May 17,
citizen of Bonfol
accepted
on
ETH
1963
(JU)
the recommendation of
Prof. Dr. J.R. Bourne, examiner
Prof. Dr. S. Hartland, co-examiner
Zurich 1993
V
Abstract
When the characteristic time of
of the
order of
same
magnitude
chemical reaction is much shorter
a
as
that of
micromixing,
the
or
transport of
fresh reagents to the reaction site controls the conversion rate. In the
of
case
a
complex
reaction the
product
The rules of chemical kinetics alone
evolution
time
Baldyga
of the
and Bourne
take
of the
concentrations
developed
model), which shows how
turbulent flow,
distribution
are no more
building fluid
in
also be affected.
Involved substances.
1989 the E-model (
completely
two
can
able to describe the
misclble
Engulfment-
liquids
mix In
a
laminae in which the chemical reactions
place.
After
having
reactions in
applied
been
previous work,
reaction schemes.
Systems
to
a
system of consecutive, competitive
the E-model had to be evaluated for other
of
parallel, competitive
of fast and Instantaneous reactions,
A+B
A+C
reactions, made up
studied in this work.
are
P
k2
Q
Consider, for example, the system of parallel, competitive reactions,
sketched above, where the ratio of the rate constants ki/k2 is about
1010. The
reactions
containing
the
A is
slowly
expected
are
reagents
semi-batch reactor
already
these
and 1/2
Xq,
is
10"10, according
to the laws of chemical kinetics.
actually
measured. The E-model could
Values of about 30 %
k2/ki
a
added. The portion of A-molecules reacting with C,
to be about
reproduce
carried out in
B and C at the same concentrations, into which
were
experimental
depending
results and
predicts
upon the intensity of mixing.
values between
vi
Two different reaction
two reactions: of
a
systems
ions and of the alcaline
one
were
tested. The first
neutralisation between
hydrolysis
of
one
hydroxide
methyl
is
composed
and
chloroacetate. The second
is made up of three reactions: of the same neutralisation
and
of the
alcaline
hydrolyses
pyruvate. The experiments
This
was
operated
into the reactor
The
were
a
better
ethyl
chloroacetate
carried out in
a
of the E-model
was
were
good
experimentally,
knowledge
an
before
methyl
hydroxide
was
fed
acidic solution of esters.
compared
with the
in the sense that the
while
of the
as
and
baffled stirred tank.
in the semi-batch mode. Sodium
agreement
confirmed
needed
were
already containing
predictions
results. The
of
of
hydronium
a more
experimental
predicted trends
quantitative agreement
hydrodynamic parameters
turbulent flow, where the reactions took
place.
of the
vii
Resume
Lorsque
plus
temps caracteristique d'une
le
court
l'apport
ou
du
de reactifs frais
conversion et
reactions
chimique
est
beaucoup
que celui du
melange,
reaction
grandeur
le site de reaction limlte le taux de
sur
peut modifier la distribution des produits
Les lois de la
chimiques complexes.
parviennent alors plus
la
ordre de
meme
concentration
a
des
reproduire
de
ne
dans le
seules revolution dans le
substances
(Engulfment-model) developpe
facon dont deux
cas
cinetique chimique
impliquees.
Le
Baldyga
par Bourne et
liquides parfaitement
misclbles
se
en
temps de
modele
«E»
1989 decrit la
melangent
en
milieu
turbulent, formant des lamelles de fluides dans lesquelles les reactions
chimiques
Apres
ont lieu.
avoir ete
systeme de
confronte
applique
reactions
dans
ce
avec succes,
competitives,
consecutives,
travail
a
lors de travaux
systeme de
un
precedents,
a un
le modele «E»
reactions
est
paralleles,
competitives.
ki
A
+
B
P
k2
A+C
Considerons,
par
constantes de vitesses
un
meme
ki/k2
est
reacteur semi-continu
concentration, et
molecules de A reagissant
on
avec
valeur de 10"10 selon la cinetique
l'ordre de 30 % ont pu etre
egal
qui
auquel
de
systeme
ci-dessus,
competitives, represents
dans
le
exemple,
Q
-
C
pour
a
lequel
environ
contient
ajoute
reactions
deja
le
1010. On laisse reagir
les reactifs B et C
a
la
lentement A. La fraction de
plutot qu'avec B, Xg,
chimique. Cependant,
mesurees
paralleles,
rapport des
dans la
admet
une
des valeurs de
partie experimentale de
ce
vlii
travail. Le modele «E» est
experimentaux
predits
et
1/2 selon l'intensite de
Deux
hydronium
deuxieme,
et
quant
chloracetate et de
deja
predictions
experimentaux.
tendances
du milieu
une
du
La
Xg
methyle
trois
de pyruvate. Une
partie experimentale
generates
quantitative plus
alcaline de
l'hydroxide
de
k2/ki
a
de sodium
hydroxide
et
la
ete
meme
ethyle
de
et chicanee
agitee
travail. On
a
compose
de chloracetate. Le
alcaline d'
cuve
ce
se
reactions:
precedemment, l'hydrolyse
mode semi-continu. De
contenait
resultats
ces
variant de
reactions ont ete testes. L'un
comprend
lui,
a
methyle
ete utilisee pour la
compte de
neutralisation entre des ions
hydrolyse
une
de rendre
des valeurs de
l'agitation.
une
neutralisation que
Les
meme
systemes differents de
de deux reactions:
qui
en mesure
a
ajoute
travaille
au
a
en
reacteur
solution acide d'esters.
modele
«E»
concordance
ont ete
exacte
ont
est
ou
comparees
ce
aux
resultats
sens
que
les
confirmees, tandis qu'une description
requiert des
hydrodynamlque
ete
bonne dans
connaissances
les reactions
se
plus approfondies
deroulent.