industrial _ engineering chemistry process design and development volume 11 issue 3 1972 [doi...
TRANSCRIPT
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Homogeneous Kinetics
Chloride Chlorination
Bruce
of
Methyl
E.
Kur tz
Syracuse Technical Center, Allied Chemical Corp., P.O. Box 6, Solvay,
N Y
13909
The commercially important homogeneous thermal chlorination of methyl chloride yields major amounts
of
higher chloromethanes (methylene chloride, chloroform, arid carbon tetrachloride) as pr imary products,
minor amounts of chloroethanes as secondary products, and still more minor amounts of chloroethylenes
as tertiary products. Using the rigorous reaction mechanism and a priori values for individual reaction rate
constants, the products of reaction were calculated as a function of chlorine-methyl chloride ratio, number
of reaction stages, and temperature. Over 200 simultaneous reactions were involved, and a computer pro-
gram was developed to obtain the results. Experiments were carried out in a multistage tubular flow reactor,
and the calculated and observed results compared. For primary and secondary products the agreement
obtained was well within the accuracy of the rate constant data. Calculated amounts of tertiary products
were about cne fourth of the observed amounts. The primary ptoducts depend largely on chlorine-
methyl chloride ratio. The relative amounts
of
secondary products depend only on chlorine-methyl chlo-
ride ratio, while absolute amounts depend on temperature and amount of free chlorine.
T h e mechanisms by which homogeneous chlorination of
aliphatic hydrocarbons proceeds are relat ively well
understood, and a substant ial number of data on the rate
cons tants for individual reactions are available. Because of
this, and because of th e commercial importance of the prod-
ucts derived by chlorination of al iphatic hydrocarbons, the
development of a com puter model of th e reaction system
comprising chlorine, metha ne, ethan e, ethylene, and all of the
chlorinat 'ed derivatives was undertaken. This computer
model has been used to sim ulate chlorinations of m ethan e,
me thyl chloride, various m ixture s of chloroet,hanes, etha ne,
and 1,2-dichloroethane. Some of these results as well as t h e
deta ils of th e development of th e computer m odel have been
presented earl ier (Kurtz, 1967).
In this art icle, results from the computer model are com-
pared with experimental data obtained for the chlorination
of methyl chloride (CHsC1). The primary products are, of
course, methylene chloride (CH2C12), hloroform (CHCL) , and
carb on tetrachloride (CC lJ. T he relat ive amoun ts of t 'hese
products are readily calculable from
a
knowledge of relative
reaction rate s (Fuoss, 1943; Pot ter an d Ylacdonald, 1947;
n 'at ta and l la nt i ca , 1952; Johnson et al . , 1959; Scipioni and
Rapisardi , 1961) without ' recourse to the computer model
employed here.
However , in addi t ion to the amo unts of pr imary products ,
we wish to calculate the amounts of by-products (chloro-
ethanes and chloroethylenes) result ing from interactions
among the f ree radical react ion in term ediates and compare
them wi th the observed amounts .
A
detailed stu dy of by-
product form ation in the production of chlorome thanes has
not previously been published, al though there is
a
large
amo unt of exper imental da ta on the pr imary products (McBee
et al . , 1942; Johnson et al . , 1959; Werezak and Hodgins,
1968; Belenko e t al . , 1969).
Mechanism
of
Reactions
Hom ogeneous chlorinat'ion of aliphatic hyd rocar bons
proceeds by a free radical mechanism involving chlorine
atom s and organic free radicals as alternate chain carriers.
A
chlor ine atom abst racts a hydrogen atom from a saturated
molecule or adds to the double bond of an unsa t u ra t ed
molecule, forming a n organic free radical . The free radical
reacts with a chlorine molecule or splits
off a
chlorine atom
(forming a double bond), thus regenerating a chlorine atom.
The introduction of a single chlorine atom or organic free
radical normally results in ma ny c hain-propagating reactions;
that is, the reaction chain is very long. The overall reaction
rate depends on the competibion between chain init iat ion
reactions which form atoms or free radicals, and chain ter-
mina tion reactions which dest 'roy them .
Th e reac tion scheme for chlorination of me thyl chloride is
shown by Figure 1. Primary products (chloromethanes)
result from chain-propagating reactions involving t,he chloro-
methane molecules and free radicals. Secondary products
(chloroethanes ) result from free radical-free radica l chain-
terminating reactions. Tert iary products (chloroethylenes)
may result from chlorination and dehydrochlorination of the
secondary products.
Derivation
o f
Rate Equations
Fo r ease of c om putat ion, the four chain-propagating reac-
t ions (and the usually unimportant organic molecule dis-
sociation) involving each free radical are grouped together
as shown below. The reactions are designated by n where
n = 1, 6, 11,
.
. . For subst i tu t ion of methane and chloro-
met hanes
:
Reactants Products
React ion
No.
i i k I
n R H + C1
-
R
+
HC1
n f l . . .
n + 2 R R . . . R + R
n + 3 Clz + R C1 + RC1
n + 4
. . . , . .
. . .
, . .
For subs ti tution or addit ion of ethane, chloroethanes, ethylene,
or chloroethylenes:
. . .
. . . . . .
33
Ind. Eng. Chem. Process Des. Develop.,
Vol.
11,
No. 3, 1972
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Table 1 Numbers Ass igned to Componen ts in the
Co mp u te r Mo d e l
01
CH , 22 CH3
02 CH3Cl 23 CHzCl
03 CH2C12 24 CHC12
04 CHC13 25 CC13
05 CCl4 26 CHaCHz
06 C H ~ C H B 2 7 C H3 CH C1
07 CHIC HzCl 28 CH2CH2Cl
08 CH3CHC12 29 CHZCHC lz
09 CHiC lCHz Cl 30 CH3CC12
10 CH3CC13 31 CH zClC HC l
11
CH2ClCHC12 32 CH2CC13
12 CH2ClCC13 33 CHClCHC12
13 CHC12CHC12 34 CH2CICC12
14 CHC12CC13 35 CHClCC13
15 CC13CCl3 36 CHC12CC12
16 CI12=CH2 37 CC12CC13
17 CH ,=CH Cl 44 C3's
18
CH2=CC12 45
C4 s
19 CHCl =CHCl 46
c1,
2 0 C H C k C C 1 2 47 C1
21 CC12=CC12 48 H Cl
~~ ~~
Table 11 React ion Rate Data for Abstract ion of
Hydrogen by a Ch lo r ine Atom
Reactants Products to g A
E
R H + C1-R + HC1
H R R C l + C1+ RRCl + H C l
01 47 22 48 10 7
3 9
02 47
23 48 10 5
3 1
03 47
24 48 10 4
3 1
04 47
25 48 10 2
3 3
06 47 26 48
11
0
1 0
07 47
27 48 10
3 1 4
07 47 28 48 9 9
1 5
08 47
29 48 10 0
3 3
08 47 30 48
9 8 1 4
09 47
31 48 10
8
2 9
10 47 32 48 9 4 3 4
11 47
3 3 48 10 2 3 2
11 47 34 48 10 1 2 7
12 47
35 48 10 4
3 3
13 47 36 48
9 8 3 3
14 47
37 48 9 8
3 3
Table 111 React ion Rate Data for Addi t ion t o an
Unsa tu ra te by a Ch lo r ine Ato m
Reactants Products l og A E
R = R
+
C1+ RRCl
16 47 28 10 2 0 0
17 47 29 9 8 0 0
17 47 31 10 0 0 0
18
47 32 8 9
0 0
18 47 34 9 7 0 0
19 47 33 10 0 0 0
20 47 35 9 1 0 0
20 47 36 9 7 0 0
21 47 37 9 4 0 0
so that accurate dat ,a o n chlorine atom recombination
is
no t
needed to calculate the ra te of chlorine dissociation.
Tab l e I shows the numbers assigned to components in
the computer model of the reaction system comprising chlo-
r ine, methan e, ethane , ethylene, and thei r chlor inat ,ed der iva-
tives. Tab les 11-V lis t, respectively, th e values of frequ ency
factor an d act ,ivation energy used for abstra ction of hydrogen
Table IV. React ion Rate Data for React ion of a Chlor ine
Mo lecu le wi th an Organ ic Free Rad ica l
Reactants Products to g A EA
Cln
+
R 1
+
RCl
C1z
+
RRCl 1
+
Cl RRCl
46 22 47 02 9 9 2 3
46 2 3 47 0 3 9 6
3 0
46 24 47
04
9 0 4 0
46 25 47 05
8 7 6 0
46 26 47 07
10 1 1 0
46 27
47 08
9 4 1 0
46 28
47 09
9 4 1 0
46 30
47 10
8 8 1 0
46 29 47
11
8 8 1 0
46 31
47 11
8 8 1 0
46 32 47 12
8 7 2 5
46 34
47 12
8 7 2 5
46 33 47 13 8 7 2 5
46 36 47 14 8 8
5 2
46 35 47 14 8 8 5 2
46 37 47 15 8 3 5 4
Table V. React ion Rate Data for L o s s o f a Ch lo rine Atom
by an Organic Free Radica l
R R C l 1 + R = R
Reactants Products log A EA
28
29
31
32
34
33
3 5
36
37
47
47
47
47
47
47
47
47
47
16
17
17
18
18
19
20
20
21
1 3 . 9
13.8
13.8
1 3 . 7
1 3 . 7
1 3 . 7
1 3 . 7
1 3 . 7
1 2 . 8
2 3 . 6
2 1 . 2
2 3 . 8
2 0 . 1
2 3 . 0
2 0 . 9
1 9 . 2
1 8 . 2
1 6 . 8
b y
a
chlor ine atom , addi t ion to an unsaturat ,e by a chlorine
at'oni, reac tion of a chlorine molecule with a n organic free
radical , and loss of a chlorine atom by a n organic free radical .
Ma ny of the values are taken di rec t ly from the com pi lation
b y Chiltz et al . (1963) and from work by Martens (1964,
1966); others have been derived from these results by K urtz
(1967) . More recent dat a o n the hydrogen abst ract ion reac-
t ions are available fro m Cillien et a l . (1967), but are no t much
different from the earl ier values. Tables VI and VI1 l i s t ,
respect ' ively, the values for free radical-free radical an d free
radical-chlorine ato m combiiiat ion reactions. The act ' ivation
energies for such reactions are essential ly zero. The frequen cy
factors for combination reactions of like free radicals have
been compiled by Chil tz et a l . (1963). Wi th th e exception
of m ethy l and et hyl (H eller, 1958) there are no da ta on fre-
quency factors for combiiiation reactions of unlike free radi-
cals. Frequency factors have been estimated by Kurtz (1967)
using a collision frequency averaging method. The source of
the equil ibrium constant ' values used by the computer m odel
to calculate chlorine dissociation from the tabulated data for
combination reactions was Ev an s et al . (1955).
Induction Periods
A char acter istic of ch ain reactions is th e induction period-
th at t im e during which the conc entrations of the intermedi-
ates a re building 1111 from the init ial zero values. An eq uatio n
334
Ind. Eng. Chern. Process Des. Develop.,
Vol.
11, No.
3,
1972
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Table
VI.
Reaction Rate Data for Free Radical-Free Radic al Com bin ation
Reactants
22
22
22
22
22
22
22
22
22
22
22
22
22
22
22
22
23
23
2 3
23
23
23
23
23
23
23
23
23
23
23
23
24
24
24
24
24
24
24
24
24
24
24
24
24
24
22
2 3
24
25
26
27
28
29
30
31
32
33
34
35
36
37
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
24
25
26
27
28
29
30
31
32
33
34
35
36
37
Products
06
07
08
10
44
44
44
44
44
44
44
44
44
44
44
44
9
11
12
44
44
44
44
44
44
44
44
44
44
44
44
13
14
44
44
44
44
44
44
44
44
44
44
44
44
l o g A
10 5
10 1
10 1
10 0
10 5
10 4
10
4
10
3
10 3
10 3
10 1
10 1
10
1
10 1
10 1
10
0
9 6
9 5
9 3
10
1
9 9
9 9
9 7
9 7
9 7
9 6
9 6
9 6
9 5
9 5
9 3
9 4
9 1
10
1
9 8
9 8
9 6
9 6
9 6
9 5
9 5
9 5
9 4
9 4
9 1
Reactants Products
R + R + R R
25
25
25
25
25
25
25
25
25
25
25
25
25
26
26
26
26
26
26
26
26
26
26
26
26
2;
27
27
27
27
27
27
27
27
27
27
28
28
28
28
28
28
28
28
28
2 ?
26
27
28
29
30
31
32
33
34
35
36
37
26
27
28
29
30
31
32
33
34
35
36
37
27
2 s
29
30
31
32
33
34
35
36
37
28
29
30
31
32
33
34
3 5
36
15
44
44
44
44
44
44
44
44
‘14
44
44
44
45
4
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
Log A
8 8
10
0
9 7
9 7
9 4
9 4
9 4
9 2
9 2
9 2
9 1
9 1
8 8
10 5
10 3
IO 3
10 2
10 2
10 2
10 1
10 1
10 1
10 1
10 1
9 9
10 1
10 1
10 0
10 0
I0 0
9 9
9 9
9 9
9 8
9 8
9 6
10
1
10
0
10 0
10
0
9 9
9 9
9 9
9 8
9 F
Reactants
2s
29
29
29
29
29
29
29
29
29
30
3
0
30
3
0
30
30
30
30
31
31
31
31
31
31
31
32
32
32
32
32
32
33
33
33
33
33
34
34
34
34
35
3 5
3 5
36
36
37
37
29
30
3 I
32
33
34
35
3
6
37
30
31
32
3:j
34
:? 5
36
37
3 1
32
33
34
35
36
37
32
33
34
35
36
37
33
34
35
36
37
34
35
36
37
35
36
37
36
37
37
Products
45
45
45
45
45
4 f5
45
45
45
45
43
45
4
t5
45
4
5
45
45
45
45
4 5
45
45
45
45
45
45
45
45
4
5
4 5
45
4 5
45
45
45
45
49
45
45
45
45
45
43
45
45
45
Log
A
9 6
9 8
9 8
9 8
9 7
9 7
9 7
9 6
9 0
9 4
9 8
9 8
9 7
9 7
9 7
9 6
9 6
9 4
9 8
9 7
9 7
9 7
9 6
9 6
9 4
9 5
9 5
9 5
9 4
9 4
9 2
9 5
9 5
9 4
9 4
9 2
9 5
9 4
9 4
9 2
0 3
9 3
9 1
9 3
9 1
8 7
for the length of the induct ion per iod can be der ived as
follows:
Subs t i t u t i ng (R,)
=
Bn(C1) n Equat i on 3 we have
(Cl)’
=
a
+
b(Cl)* + c(C1)
5 )
where
a = [kd (C l ?) (*~t )+ n
kn+n(JIn)
c
=
C B ‘ n / ( l +
B n )
I t h a s b e en s t a t e d t h a t k r
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~
~ _ _ _ _ _ _
Table VII . React ion Rate Data f o r Free Radical-Chlor ine
A to m Co mb in at i o n
R
+
C1 --f RC1
22
47
2
11 6
23 47
3 11 4
24 47 4
11
4
25 47 5 11 4
26 47 7 11 3
27 47
8
11
3
28
47
9 11 3
29 47
11
11 3
30 47
10 11 3
31
47
11 11 3
32 47
12 11 3
33 47
13 11 3
34
47
12 11
3
35 47 14 10 9
36 47 14 1 0
9
37 47
15
11
0
Reactants Products
Log
A
S 10 72
2 l I '
-
Figure 3. Design of laboratory tubular thermal chlorination
reactor
+
LL
-
I
400'C
-
6
7
-
-
-
z
- -
U
350 .
-
-
0-0-
-
-
-
-
-
G
-
-
I
-
-
-
-
-
-
2x10 3
I I I I I
On i n t eg ra t i on , Equat i on 7 yields
Figure 2. Induction
period in the ther-
mal chlorination of
methyl chloride for
ch lor ine - methy l
chloride m o l ratio
= 0.1
(curve I
numerical solution;
curve 2, analytic
solution)
t =
where
(C1)max = [K(Clz)
Th e relevant rate constants for calculation of th e inductio n
period in the thermal chlorination of methyl chloride are
t aken f rom Tab l es
I1
and Is leading to
LL
_ 0.8
I
Figure 4.
Ob-
served and calcu-
lated primary
g 0 4 prodlicts
of
meth-
yl chloride chlo-
2
0.2
rination
0.6
t
+
a
I 2 3
0
MOLS
GI e REACTED
/
MOL
CH3CI
FED
so
that the organic free radical concentration greatly exceeds
the chlorine atom c oncentration und er usual circumstances,
Figure 2 shows how the chlor ine atom concent rat ion
changes with t ime in the chlorinat ' ion
of
methyl chlor ide at
350
and 400°C wi th a chlorine-methyl chloride rat'io of
0.1. Curve
1
was produced by the co mputer model (num erical
solution of the re action ra te expressions) while curve 2 is from
Equat i on
8.
It
is interesting to note that with homogeneous
init iat io n the calculated induction period is negligibly small ,
which is consistent with observations. Based on a n analysis
by Benson (1952) , i t has been suggested by Benson and B uss
(1958) that only heterogeneous init iat ' ion could explain this
small induct ' ion period, bu t the ir calculated homogeneous
induc tion period was based on t 'he incorrect assumption th at
the chlorine atom-chlorine atom reco mbination was the
dominant chain-terminat ing s tep .
Experimental Procedure
Data on pr imary products and by-products formed in
the chlorination of me thyl chloride were obtained in a reactor
designed according to Figure
3.
Th e reac tor consist's of 10
loops of 1/4-in, i.p.s. nickel pipe par tially immerse d i n a salt,
bat h. T he effluent from each loop is cooled in th e integral
heat exchangers , and addi t ional chlor ine can be in jected a t
these points. Without interstage cooling, the high local
conce ntrations of chlorine near the injec tion point will cause
rapid react ' ion, excessive temperatures, and pyrolysis of the
organics. Th e feed stream s to th e reactor were individually
metered. The m ethyl chloride was obtained f rom the Mathe-
son Co. and showed less than 100 ppm organic impurit ies.
The chlorine was obtained from a Solvay (Industrial Chemi-
cals Div., Allied C hemical Cor p.) 1-ton cylinder throug h a stan-
dar d st 'eam-heated vaporizer.
Th e gaseous reactor effluent mas sam pled periodically wit h
a
gas-t ight heated syringe and analyzed by gas chromatog-
raph y. T he effluent
was
passed thro ugh a condenser a t
-8OoC,
and the condensate sampled with a chil led microli t 'er
syringe and analyzed in the same way. T he inst rument used
was an F M Model 500 with a 1 4 in .
X
10 ft S ilicone Oil 200
on Chromosorb P column. Peak areas and retention t imes
from a Days t rom
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Figure 5.Observed and
calculated total second-
ary products of methyl
chloride chlorination
MOLS
c i P REACTED/MOL
CH,CI
FED
t wo runs by use of the apparatus
described. Chlorine was
injected a t every othe r loop at a to tal ra te of 5.7 grams/ mi n .
Th e me thyl chloride rate was decreased f rom 3.6 to less than
0.5 gram s/min over the course of the run s. The sal t bath was
held at 46OOC. The individual effluent analyses are plotted
on Figure 4 against the m olar rat io of chlor ine reacted to
meth yl chlor ide fed. Curves generated by th e com puter
model using th e values of the ra te constants g iven by Tables
11-VI1 are superimposed on the observed results.
Curves relating am ounts of p r imary products of methy l
chloride chlorinations are readily derived from the hydrogen
abst ract ion rate constants alone. The t im e der ivat ives of the
chloromethanes concentrations c an be expressed as :
(JP2)’
=
-k*SP*(Cl) (9)
(10)
(1 1)
M6)’ k4M4(Cl) (12)
L1f3)’
= (k z
-
k3*113)(C1)
ilr4)’
= (k 113- kzL1f2)(C1)
Dividing Equat ions 10-12 by Equation 9 yields differential
equations which can be solved in
a
st raight forward manner
(Fuoss, 1943; Ka t ta and Man t ica, 1952). Th e solut ions give
the product composit ion as a function of methyl chloride
conversion or, by trans form ation , of th e rat io of chlorine
reacted to methyl chloride fed. This simple dependency
leads one to expect tha t the num ber of stages of chlorine
injection will have no effect on the relat ive amounts of
primary products, which is confirmed by the results of
RIcBee e t al . (1942) as wel l as in th is labo ratory . The act iva-
t ion energies for the three hydrogen abstractions involved
here are near ly the sa me, hence tempera ture has l i t t l e ef fect
on product d is t r ibut ion.
Fro m t he di f ferent ial equat ions we have:
k3,‘kz
=
-112/.113
a t
J13 )m8x
k4/kz
= (k3 /kz )
-U3/-U4)
a t JI4)max
(13)
(14)
Hence f ro m a s ingle hydrogen abst ract ion rate constant and a
set of product d is t r ibut ion curves, the o ther rate constants
can be determined.
Secondary and Tertiary Products. Et hane and e t hy l ene
deriv ative s occur as by-products from chlorination
of
met hane
or chloromethanes (Johnson e t al . , 1959) . The y resul t f rom
free radical-free rad ical chain termina tions and normally
occur to the extent of a t most a few tenths of a percent.
The amounts of secondary products of methyl chlor ide
chlorination were obtaine d from four runs. T he to tal chlorine
rate var ied f rom 2.5 to 8 .5 grams/min and th e methyl chlor ide
3
5
I I
Figure 6. Observed
culated secondary
of methyl chloride
tion, CHzCICHzCI
Figure 7. Observed
culated secondary
of methyl chloride
tion, CH2CICHCl2
Figure 8. Observed
culated secondary
of
methyl chloride
tion, CH2CICCl3
Figure
9.
Observed
culated secondary
of methyl chloride
tion, CHCIzCHC12
and cal-
products
chlorina-
and
cal-
products
chlorina-
and cal-
products
chlorina-
and cal-
products
chlorina-
Figure 10. Observed and cal-
culated secondary products
of methyl chloride chlorina-
tion, CHCIzCCIZ
Figure 1 1. Observed and ccl-
culated secondary products
of methyl chloride chlorina-
tion, CCl CI3
rate f rom 2.9 to
3.7
grams/ mi n . The sa l t ba t h was he l d a t
400” C . Th e condensate was analyzed an d coverted to a basis
of mols/mol of tota l chloromethanes. The results for tota l
secondary products are p lot ted on Figure 5 The curveq
generated by numerical in tegrat ion are superposed. Over 200
simultaneous reactions were take n into account in the calcula-
t ions. S o t al l of these react ions are equal ly importa nt fo r the
case of m ethy l chloride chlorina tion, bu t the c omp uter model
is
designed to h andle a l l reactions ink olving chlori i ie, metha ne,
ethane, ethylene , and thei r chlor inated der ivat ives, and the
full compleme nt of rea ctions was used for th e sake of com-
pleteness and to al low the m odel to be used ni tho ut al tera-
t ion for o ther react ion systems
The react ion temperature has a profound effect on the
absolute (but not relat ive) amo unts of iec onda ry prod ucts.
The ac t ua l tempera t u res i n t he r eact o r were no t kno nn , bk t
were wel l below the sal t bath temperature at the points of
chlorine injection and well above a t the points of m axim um
temperature. Hence the temperature used in the calculat ion
of the total amounts of secondary products nas adju- ted
unti l reasonable agreement with the ob.er\ ed results nas
obtained.
The observed results for individual secondary products
(1,2-dicliloroethane; 1,1,2-trichloroetha11e; 1 ,1,1,2-tetra chloro -
e t hane; 1,1,2,2-tetrachloroethane; entachloroethane; and
hexachloroethane) a re plotted as a furict ion of th e molar
ratio of chlorine reacted to m eth yl chloride fed on Figures
6-11 with the calculated curves superposed. The 95% con-
Ind.
Eng.
Chem. Process
Des.
Develop.,
Vol. 1 1,
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1972
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Figure
12.
Observed and
calculated tertiary products
--
2 of methyl chloride chlorina-
- 0 tion,
CHCI=CCIz
r:
F
-
> Figure 13. Observed and
calculated tertiary products
of
methyl chloride chlorina-
tion,
CC12=CC12
-
MOLS
C 1 2 R E A C T E D I t 4 I L
CH CI FED
fidence interval is shown for each observation. Relative
amo unt s of secondary produ cts depend only on the relative
amou nts of primar y products , hence depend only on the ra t io
of chlorine reacted to m eth yl chloride fed. However, absolu te
am oun ts depend on absolute con centrations of free radicals,
hence are affected b y th e amo un t of free chlorine and r eactor
temperatures. Therefore, while the relative amounts of
secondary products shown by Figures 6-11 are general ly
applicable, the absolute amoun ts apply only to the part icular
reactor configurat ion (number of s tages) and bath tempera-
ture employed here .
The observed resul ts for individual ter t iary products
(trichloroethylene and tetrachloroethylene), assumed to
result from dehydro chlorination of secondary products, are
plot ted on Figures 12 and 13 with th e calculated curves
superposed. The re la t ively poor agreement may be a t t r ibu ted
to heterogeneous catalysis of dehydrochlorination reactions,
as the reactor w alls were coated with a layer of finely divided
carbon known to cata lyze dehydrochlorinat ions (Ghosh and
R a m a Das Guha, 1951). An al ternat ive explanat ion is that
unsaturated by-products resul t not predominantly from
dehydrochlorinat ion of sa turated by-products but from
disproportionation in which chloroethylenes and hydrogen
chloride are directly formed by reactions between free radicals
(Hassler and Setser, 1966).
Conc lus ions
Observed and calculated resul ts for the amou nts of primary
products (chloromethanes) of methyl chloride chlorination
agree to within the accuracy of the ra te constant data . The
primary product dis tr ibut ion is a function of the ratio of
chlorine reacted to methy l chloride fed ; i t is unaffected by
stagewise addition
of
chlorine and little affected by tempera-
ture .
Observed and calculated results for the a mo unt s of secon-
dary products (chloroethanes) of methyl chloride chlorina-
t ion agree to within the accuracy of t he ra te co nstant data .
Relat ive amounts of secondary products depend only on
the r a t io of chlorine reacted to methy l chloride fed; absolute
am oun ts depend
on
tempe rature and amo unt of free chlorine.
Observed amou nts of tert iar y produc ts (chloroethylenes)
exceed the calculated amounts by a factor
of
about 4 . Th i s
may be a t t r ibuted to heterogeneous cata lys is by carbon
deposited on the nickel reactor wall or to disproportionation
between free radicals.
The reac t ion m echan ism as sum ed in s e t t ing up the ra te
express ions and the a pr iori values of the ra te constan ts used
(Tables
11-VII)
are supported by the good agreement be-
tween observed and calculated results. This is especially
remarkable considering that the ra te constants used were
based on photochlorinat ion experiments a t tempera tures
below
300”C,
while the results reported here were obtained
from thermal chlorinat ion experiments a t temperatures over
400°C.
Perhap s the most imp orta nt implication of this work resul ts
from th e fact th at a very complex sys tem of react ions could be
s imulated
so
accurate ly. This e l iminates the need for a gre at
deal of ex perimen tation in th e investigation of propo sed
aliphatic hydrocarbon chlorination processes and should
result in a significant reduction in develo pment costs.
Acknowledgment
The au thor i s indeb ted to
A . J.
Ba rdu hn of Syracuse
University for helpful discussions and
to
many persons
a t the Syracuse Technical Cente r (All ied Chemical Corp. )
for assistance in obtainin g th e experimen tal results.
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1972