industrial _ engineering chemistry process design and development volume 11 issue 3 1972 [doi...

8/18/2019 Industrial _ Engineering Chemistry Process Design and Development Volume 11 Issue 3 1972 [Doi 10.1021_i26004…

1/7

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


2/7


3/7

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


4/7

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


5/7

~

~ _ _ _ _ _ _

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


6/7

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,

No. 3 ,

1972

337


7/7

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.

Literature Cited

Bader ,

L. W.,

gryzlo, E.

A.,

Nature, 201,491-2 (1964).

Bar ton ,

D

H. R., Howlet t , K .

E.,J . Chem. Soc.,

1949, 155-

Bar ton . D .

H.

R., Onvon, P.

F., J

dmer. Chem. Soc., 72,

64 (1949).

“

988-95 (1950).

Belenko. Yu. G. . Berl in.

E.

R. . F l id . R . M.. na l in . 4.

L . ,

-

Russ. J . Phys.’Chem.,

43, 1063-5 (1969).

Benson,

S.

W. ,

J

Chem.

Phys.,

20, 1605-12 (1952).

Benson,

S. IT.,

“Th e Foundat io ns of Chemical Kinetics ,”

pp 49-54, McGraw-Hil l , Se w York, YY, 1960.

Benson,

S. IT.,

Buss,

J.

H., J . Chem. Phys.,

28,301-9 (1958).

Chiltz, G., Goldfinger, P., Huybrech t s , G . , Mar tens , G . ,

Verbeke, G.,

Chem. Rev.,

63,355-72 (1963).

Chil tz , G. , Eckl ing, R., Goldfinger,

P.,

Huybrechts , G. ,

Mar tens ,

G.,

Simoens, G.,

Bull. SOC.

him

elg.,

71,747-58

(1962).

Christie. M . I.,R o y ,

R . S.,

Thrush , B . A. ,

Trans. Faraday S OC .,

55,

1139-48 (1959).

Christie,

If

., R o y , R .

S. ,

hru sh, B. A. ,

ib id . ,

1149-52 (1959).

Cillien. C ., Goldfinger.

P.,

Huybrech t s ,

G.,

M a r t e n s , G . ,

bid.,

63, 1631-5 (19677.

’

E v a n s .

W. ..

Munson.

T. R..

W a a m a n .

0.

0..

J .

Res. Nut.

,

.

Bur.’ Stand.; 55 ,

147-64 (1955).

F uoss ,

R .

h l . ,

J.Amer.

Chem.

Soc.,

65,2406-8 (1943).

Gava las , G . R . ,

Chem. Eng. Sci.,

21, 133-41 (1966).

Ghosh,

J .

C . , R a m a

Das

G u h a , S., Petroleum, October 1951,

Hassler, J.

C.,

Setser , D.

W., J

Chem. Phys.,

45, 3237-45

pp 261-4.

(1966).

Heller,

C.

A. ,

ibid. , 28,

1255-6 (1958).

Hi raoka ,

H.,

Hardwick, R. ,

ibid. ,

36, 1715-20 (1962).

H u t t o n ,

E., Nature,

203, 835-6 (1964).

H u t t o n ,

E.,

Wright ,

hf., Trans. Faraday SOC . ,

1, 78-89

(1965). ’

Johnson.

P. R..

P arsons ,

J. L.,

Rober t s , J. B. ,

Ind .

Ens.

Chem.:

51, 499-506 (1959).

1967 (Universitv Microfilms 68-5470).

Kur tz , B .

E.,

Ph D disserta t ion, Syracuse Un ivers i ty, ,4pril

Lloyd,

.4

C. ,

Int .“J. Chem. Kinetics, 3,

39-68 (1971).

Mar tens , G .

J., Discuss. Faraday Soc.,

33, 297 (1963).

Mar tens . G .

J..

DA-91-591-EUC-3200 Sci. Note

No.

1,

~

June 15, 1964.’

N a r t e n s , G. J., personal communications, 1966.

McBee.

E. T..

Hass .

H. B..

Keher . C . AI.,Strickland,

H., Ind .

~

Eng.’Chem.j

34,296-300 (1942).’

n ‘a t t a , G . , Mant ica ,

E., J . A m er .

Chem.

SOC.,

4, 3152-6

(19 52).

P o t te r , C. l acdona ld ,

IT. C.,

Can.

J Res.,

25, 415-19

(1947).

(1961).

Scipioni,

A , ,

Rapisardi, E,,

Chim. Ind.

(Milan), 43, 1286-93

S n o F , R .

H., J . Phys. Chem.,

70,2780-6 (1966).

Werezak, G.

X.,

Hodgins , J.

W., Can. J . Chem. Eng.,

46,

R E C E I V E Dor review August 21, 1970

ACCEP TEDpril 7, 1972

41-8 (1968).

338

Ind. Eng.

Chem. Process Des. Develop., Vol. 1 1 ,

No.

3 ,

1972

industrial _ engineering chemistry process design and development volume 11 issue 3 1972 [doi...

Documents