The slow combustion of ethane at high pressuresrspa.royalsocietypublishing.org/.../140/841/426.full.pdfIn 1904 tbe slow combustion of etbane at atmospheric pressure was shown by Bone

426

The Slow Combustion of Ethane at High Pressures.

By D. M. N ew itt , D .S c., and A. M. B loch, B .Sc.

(Communicated by W. A. Bone, F.R.S.—Received November 30, 1932.)

In 1904 tbe slow combustion of etbane at atmospheric pressure was shown by Bone and Stockings* to proceed smoothly without any separation of carbon or liberation of hydrogen, via acetaldehyde, formaldehyde, formic and carbonic acids to the ultimate production of oxides of carbon and steam, as though the process really involved a series of successive hydroxylations. A more recent study of the same reaction by Bone and Hillf shows it to be preceded by an “ induction period ” during which practically no oxidation occurs. Moreover, although ethyl alcohol was not identified among the products of oxidation, there was strong indirect evidence that C2H 60 (or possibly even some less oxygenated-ethane) had been initially formed.

At the temperature at which ethane and oxygen interact with measurable velocity at atmospheric pressure ethyl alcohol oxidizes so very rapidly that the chances of its surviving in the products are remote. For this reason upholders of the hydroxylation theory have always postulated a “ non-stop ” run through the mono-hydroxy to the di-hydroxy stage, the first identifiable intermediate product being acetaldehyde, thus :

CHo CHo CH3 CH3| — > | — > | — > | + H 20, etc.CH3 CH2OH CH(OH)2 CHO

On employing ozonized oxygen, however, the temperature of interaction is considerably lowered, and Drugman showed that at 100° C. ethyl alcohol, acetaldehyde and acetic acid are successively formed.

High pressure is particularly favourable to the survival of intermediate products in such reactions, because not only does it allow of comparatively low temperatures being used, but also where the change involves a diminution in the number of molecules in the system it assists by increasing the thermal stability of the products. Thus in previous work from these laboratories on the oxidation of methane at pressures between 50 and 100 atmospheres and temperatures between 330° and 400° C. all the intermediate products

* ‘ J. Chem. Soc.,’ vol. 85, p. 693 (1904). f ‘ Proc. Roy. Soc.,’ A, vol. 129, p. 434 (1930).

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Sloiv Combustion o f Ethane at High Pressures. 427

methyl alcohol, formaldehyde, formic acid, etc.) arising from successive “ hydroxylations ” were identified and isolated.*

In the present paper experiments upon the slow oxidation of ethane in a static system at pressures up to 100 atmospheres are described, and it is shown that in favourable circumstances upwards of 60 per cent, of the ethane burnt may appear in the products as alcohols, aldehydes and acids.

Experimental.

Apparatus and Method.—The apparatus used consisted of an electrically heated steel reaction vessel of 500 c.c. capacity connected through an inlet valve with (a) a storage cylinder containing the initial ethane-oxygen mixture previously compressed to the requisite high pressure, (b) a standard Bourdon tube pressure gauge, and (c) a train of cooling coils surrounded by an ice-salt mixture, followed by scrubbers containing distilled water, for the removal at atmospheric pressure of condensable and water-soluble reaction products. The general lay-out of the apparatus has been described in a previous com- munication.f

The experimental method consisted in bringing the reaction vessel to the required temperature, evacuating and then rapidly filling it to the desired pressure with the compressed ethane-oxygen mixture the composition of which was varied in different experiments between the limits 85 to 90 C2H6/15 to 10 0 2. The inlet valve was closed and the progress of the reaction followed by observing the change in temperature of the gaseous media as indicated by a platinum-rhodium couple situated in a tube traversing axially the reaction chamber.

On completion of the reaction, the products were released through the outlet valve and passed successively through the cooling coils and scrubbers, the contents of which were subsequently mixed, diluted with distilled water and aliquot parts used for the quantitative estimation of the various constituents so removed. The remaining gaseous products were analysed.

Preparation of Gases.—Ethane not being available commercially in sufficiently large quantities for the experiments, a method was developed for its preparation by (i) the catalytic hydrogenation of ethylene, over a reduced nickel catalyst at 80° C. and 50 atmospheres pressure, followed by (ii) liquefaction of the product (after removal therefrom of any unchanged ethylene by means of bromine), and subsequent fractionation of the liquid. This finally resulted in

* * Proc. Roy. Soc.,’ A, vol. 134, p. 591 (1932). t L og. oit., p. 593.



428 D. M. Newitt and A. M. Bloch.

a product containing 97*3 per cent, of ethane (C/A on explosion analysis = 1*250) and 2*7 per cent, of nitrogen.

The oxygen employed was purchased in cylinders from the British Oxygen Company, and after its composition had been checked by analysis, was used without further purification.

Ethane-oxygen mixtures of the desired composition were made up in 10 cubic foot gas holders and were compressed into cylinders to 150 atmospheres by means of a 2-stage water-lubricated compressor. I t was found necessary to keep the cylinder in a thermostat at 40° C. as otherwise there was a tendency for the constituents to separate. As a precaution, samples were taken and their compositions checked by analysis immediately before each experiment.

Identification and Estimation of the Products.—A qualitative analysis of the condensed products from a few preliminary experiments with a 90 C2H6/10 0 2 medium at 270° C. and 100 atmospheres pressure revealed the presence of ethyl and methyl alcohols, aldehydes and acids in considerable quantities. The identification and quantitative estimation of all the components of such a complex mixture proved a matter of considerable difficulty and numerous comparative tests had to be made before reliable methods could be evolved. Finally the following methods were adopted.

Ethyl Alcohol.—After removal of any acetaldehyde and acetic acid present, this was identified by oxidizing it to acetic acid and preparing the corresponding anilide, which was identified by its melting point (112° C.). The quantitative estimation was similarly based on its conversion to acetic acid. The condensate was first refluxed for 2 hours with aniline and phosphoric acid and was then distilled, the distillate so obtained being entirely free from aldehyde. Whereupon the alcohol was oxidized by refluxing with acid dichromate, the resultant acetic acid separated by steam distillation, and estimated by titration with N/10 caustic potash. From the total so obtained, the amount of free acetic acid originally present in the condensate, if any, was deducted.

Methyl Alcohol was identified by means of its j?-nitrobenzoyl derivative, and by conversion into methyl salicylate. I t was estimated (together with any formaldehyde present) by a modification of the Deniges method.* Measured quantities of the condensate were oxidized with potassium permanganate under standard conditions, excess of the oxidizing agent being removed by oxalic acid. Sufficient concentrated sulphuric acid was then added to prevent the development of any colour caused by acetaldehyde produced from ethyl alcohol, and finally the total formaldehyde was estimated colorimetrically

* ‘ C. R. Acad. Sci. Paris,’ vol. 150, p. 832 (1910).



with Schiff’s reagent against standard solutions of methyl alcohol oxidized in the same way.

Aldehydes were detected by Schiff’s reagent, and acetaldehyde by the instant precipitation of amorphous iodoform when treated in the cold with a solution of iodine followed by caustic potash. The total aldehydes present were estimated by Ripper’s bisulphite method, and formaldehyde by Romijn’s potassium cyanide method, the difference between the two results giving the acetaldehyde present.

Acids.—The total acidity was determined by N/10 alkali. Formic acid was estimated separately by neutralizing the condensate, evaporating to dryness twice and oxidizing the residue by permanganate, according to a method of Fauchet.*

Peroxides and Glyoxal were always tested for but never found.Gases.—The gaseous products after removal of aldehyde vapour by exposure

to solid zinc chloride were analyzed in the usual way. Finally, after the foregoing estimation and analyses, “ balances ” were drawn up showing how the carbon of the ethane actually burnt was distributed among the various products.

Isolation of Alcohols, Aldehydes and Acids from the Products of Combustion of a90 C2H6/10 0 2 Mixture.

In this preliminary series of experiments an initial mixture containing a large excess (90 C2H6/10 0 2) of the combustible gas was employed at an initial pressure of 100 atmospheres, the reaction being carried out in a copper-lined vessel, the temperature of which was varied from one experiment to another so as to include both slow and rapid rates of combustion.

The general character of the oxidation was found to be similar to that previously found by one of us and A. E. Haffner for corresponding methane- oxygen mixtures. For example, at the lowest initial temperature employed (260° C.) there was an induction period of 81*5 minutes, during which neither heat evolution nor any appreciable oxidation occurred; this was followed by a reaction period of 14 minutes, during which the temperature rose 3° C., and the whole of the free oxygen was used up. With increase of the initial temperature, both the “ induction ” and the “ reaction ” periods were shortened, until at 278° C. the induction period became inappreciable and the reaction was completed in 1 minute, the temperature rise being 21° C.

Slow Combustion o f Ethane at High Pressures. 429

* ‘ Chem. Soc. Abs.,’ vol. 2, p. 499 (1912).




A complete quantitative analysis of the condensable intermediate products was made with results as summarized in Table I.

I t will be seen that ethyl alcohol was always the predominant condensable product, the maximum yield of it being at 272*5° C., when it represented no less than 36 • 5 per cent, of the ethane burnt. Also, methyl alcohol, acetaldehyde and acetic acid were all present in comparatively large quantities, together with smaller amounts of formaldehyde and formic acid ; indeed the total carbon appearing in the combined alcohols, aldehydes, and acids varied between 43*6 and 71*7 per cent, of the ethane burnt in the different experiments, but peroxides were never found at all. Steam was always found in these and all subsequent experiments.

The isolation, for the first time, of ethyl alcohol from the products of the interaction of ethane and oxygen is of special interest in that it substantiates much previous indirect evidence all pointing to its initial formation. Moreover, the formations of methyl alcohol and acetic acid, in addition to the previously observed acetaldehyde and formaldehyde, have also an important bearing on the mechanism of the combustion, which will be discussed later on.

Second Series.—A Comparison between the Reaction Products of an 88*2 C2H6/ 11*8 0 2 Medium at Pressures of 50 and 100 Atmospheres and Temperatures

between circa 270° and 310° C.

Owing to the presence of acetic acid among the oxidation products it was decided to replace the copper-lined reaction vessel used hitherto by one of the same design and dimensions made of a highly resistant alloy steel.

In comparing the results of oxidation experiments at two different pressures regard must be had to both the maximum reaction temperature and the reaction velocity; for the most favourable condition for the isolation of condensable intermediate products are those in which the reaction takes place comparatvely slowly and with only a small temperature rise.

Two groups of experiments were therefore carried out with a mixture of initial composition 88*2 C2H6/11 *8 0 2 at 50 and 100 atmospheres, respectively, in which the initial temperature was varied over a wide range so as to obtain both slow and rapid reaction.

From the results, which (with the exception of the steam formation) are detailed in Table II, it will be seen that (i) at each reaction pressure there was always a well-defined “ induction ” and “ reaction ” period, the duration of which so rapidly diminished with rising temperature that at 310° both had



Tabl

e I.

—R

eact

ion

Prod

ucts

of

a 9

0 C2

H6/1

0 0

2 M

ediu

m

at

100

Atm

osph

eres

an

d Te

mpe

ratu

res

betw

een

260°

C. a

nd 2

78°

C.

Dur

atio

n of

Perc

enta

ge o

f the

car

bon

of th

e et

hane

bur

nt su

rviv

ing

asR

atio

Initi

alCO

/CO

2te

mpe

ratu

re.

Tota

l in

inIn

duct

ion.

Rea

ctio

n.c

2h5o

h.

CH3O

H.

CH

3CH

O.

H. C

HO

.c

h3 c

oo

h.

H. C

OO

H.

cond

ensa

ble

gase

ous

prod

ucts

.pr

oduc

ts.

°C.

min

s.m

ins.

260-

081

-514

-029

-59-

34-

50-

0619

-50-

461

-26

0-54

268-

510

-25

7-0

27-5

9-5

5-0

0-06

13-5

0-3

55-8

60-

5327

2-0

5-5

3-25

36-5

20-0

8-0

0-30

6-5

0-4

71-7

01-

0827

2-2

1-5

5-0

33-5

19-1

7-0

0-20

6-5

0-4

66-7

00-

6927

8-0

Nil

1022

-311

-47-

72-

20N

ilN

il43

-60

5-19

%

Slow Combustion of Ethane at High 431

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Tabl

e II

.—R

eact

ion

Prod

ucts

of

an 8

8-2

C2H

6/11

-8 0

2 M

ediu

m a

t Pr

essu

res

of 5

0 an

d 10

0 A

tmos

pher

es a

nd T

empe

ratu

res

betw

een

262 •

2° a

nd 2

94 • 0

° C.

Initi

alte

mpe

ra

ture

.°C

.

Dur

atio

n of

Max

imum

reac

tion

tem

pera

tu

re.

°C.

Perc

enta

ge o

f the

car

bon

of th

e et

hane

bur

nt su

rviv

ing

as—

Tota

l ca

rbon

so

acco

unte

d fo

rpe

r ce

nt.

Rat

ioco

/co2

inga

seou

spr

oduc

ts.In

duct

ion,

min

s.R

eact

ion,

min

s.a o lO a O*

W O CO a o

o a a o

H. CHO.

a o o a o

H. COOH.

o ovt o o

* M o

Totalliquidproducts.Totalgaseousproducts.

50 A

tmos

pher

es.

279-

218

-010

0-0

281-

214

-810

-84-

70-

215

-20-

319

-332

-5N

il46

-051

-897

-80-

5928

6-0

7-0

3-75

295-

524

-414

-18-

32-

01:

70-

934

-810

-0N

il51

-444

-896

-23-

4828

8-0

6-5

3-75

296-

020

-511

*37-

31-

22-

30-

731

-67-

113

-743

-252

-495

-74-

4528

9-0

4-25

2-75

295-

016

-014

-44-

92-

02-

40-

436

-04-

620

-740

-161

-310

1-4

7-80

294-

02-

03-

2530

7-5

17-2

14-1

5-2

1-9

Nil

0-7

40-8

7-8

8-1

39-1

56-1

95-2

5-22

262-

225

-015

-026

5-0

21-0

13-0

266-

523

-511

-027

0-5

12-0

4-5

275-

05-

752-

7527

8-0

4-0

1-25

100

Atm

osph

eres

.

271-

222

-610

-56-

20-

0427

-20-

88-

919

-22-

067

-34

30-1

97-4

40-

4627

7-0

21-8

12-5

6-6

0-08

22-4

0-7

18-8

15-9

1*1

64-0

835

-899

-88

1-18

277-

523

-711

*26-

00-

0523

-80-

69-

314

-28-

665

-35

32-1

97-4

50-

6528

3-5

23-6

14-0

9-7

0-05

12-5

0-5

22-4

8-7

8-6

60-3

539

-710

0-05

2-58

305-

016

-513

-16-

80*

104-

90-

337

-25-

116

-141

-70

58-4

100-

107-

3031

2-0

14-6

15-4

11*1

0-60

2-2

0-3

37-6

2-8

14-3

44-2

054

-798

-90

13-4

0


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Slow Combustion of Ethane at High Pressures. 433

become exceedingly sh o rt; and (ii) increasing the “ reaction pressure ” so favoured the survival of alcohols, aldehydes, and acids that in several of the experiments at 100 atmospheres as much as about two-thirds of the carbon of the ethane burnt so survived, as compared with between about 40 and 50 per cent, only at 50 atmospheres.

At both pressures ethyl alcohol and/or acetic acid always predominated among the surviving condensable products, there being apparent in each case a fairly low “ optimum ” temperature for their separate or joint survival. The proportion of ethane burnt surviving as methyl alcohol was not nearly so much affected by variations in temperature and pressure. Moreover, in most of the experiments there was a fairly constant ratio between the survival of ethyl alcohol and acetaldehyde, namely, about 3-0 at 50 atmospheres and between 3-3 and 4-0 at 100 atmospheres. Formaldehyde and formic acid were found in relatively small quantities only and “ peroxides ” not at all.

As regards the gaseous products with slow' reaction speeds they consisted entirely, or almost so, of oxides of carbon, but as reaction quickened both methane and traces of hydrogen appeared, doubtless as the result of secondary thermal decomposition of acetaldehyde and formaldehyde, respectively, thus

CH3 . CHO = CH4 + CO H . CHO = H 2 + CO.

It will be seen that in each experiment the whole of the carbon of the ethane burnt was substantially accounted for among the foregoing products showing how complete had been the analyses involved.

Third Series.—Influence of Pressure upon the Survival of Products from EqualReaction Rates.

In this series of experiments, while the reaction-pressure was raised in steps from 15 up to 100 atmospheres care was taken simultaneously to lower the temperature so as to maintain an approximately equal reaction speed and temperature rise throughout, thus enabling data to be obtained for what seems a true comparison of the yield of condensable products obtained at the different pressures.

The results, which are detailed in Table III, showed that whereas an increase in pressure favoured the survival of ethyl alcohol, acetaldehyde, and acetic acid (i.e., of products not involving any rupture of the ethane molecule) it seemed to have an opposite effect upon the survival of methyl alcohol and formaldehyde.

2 FVOL. CXL.— A.



Tabl

e II

I.—

The

Effe

ct

of

Initi

al

Pres

sure

on

th

e Su

rviv

al

of

Inte

rmed

iate

Pr

oduc

ts

from

th

e re

actio

n of

an

88-4

C2H

6/11*

6 0

2 M

ediu

m.

Initi

alpr

essu

re.

Initi

alte

mpe

ratu

re.

Dur

atio

n of

re

actio

n.

Perc

enta

ge o

f the

car

bon

of th

e et

hane

bur

nt s

urvi

ving

as—

c2h

5oh

.C

H3O

H.

CH

3CH

O.

H .

CHO

.c

h3 c

oo

h.

H.C

OO

H.

Tota

l in

cond

ensa

ble

prod

ucts

.

atm

os.

°c.

• min

s.15

315

3-0

16-0

19-4

1-9

4-5

Nil

Nil

41-8

5029

43-

2517

-214

15-

21-

9N

il0-

739

-175

279

2-5

18-0

16-6

6-8

0-4

3-6

0-6

46-0

100

270-

54-

523

-614

-09-

70-

112

-50-

550

-4

434 D. M. N ew itt and A. M. Bloch.

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Sloiv Combustion o f Ethane at High Pressures. 435

Fourth Series.—The Influence of Oxygen Concentration upon the Survival ofIntermediate Products.

So far we had not worked with C2H6- 0 2 mixtures containing more than 11 *8 per cent, of oxygen, because of the difficulty of controlling the temperature in the reaction chamber with higher oxygen content. Later on, however, we succeeded in carrying out two comparative experiments, the results of which are detailed in Table IV, with mixtures of composition 89 C2H6/11 0 2 and 84*5 C2H6/15*5 0 2, respectively, each at a pressure of 100 atmospheres and the same initial temperature of about 270° C.

In comparing the results it should be remembered that whereas with the first mixture the reaction temperature rose to 283 • 5° only, with the second it rose to 315*8° owing to the greater oxygen content. I t was therefore not surprising in the latter experiment that there was a much smaller survival of condensable products, and especially of ethyl alcohol, acetaldehyde, and acetic acid, although that of methyl alcohol was not so much affected. In the second experiment there was much more methane formed than in the first, a circumstance also associated with a slight carbon deposition and some liberation of hydrogen, neither of which had been observed in the firs t; these features are attributable to more secondary decomposition of acetaldehyde and formaldehyde at the higher reaction temperature reached in the second experiment.

Fifth Series.—Progressive Pressure Oxidation.

In the following series of three experiments starting with an 88 C2H6/12 0 2 mixture, so as to avoid any large rise in reaction temperature, a progressive oxidation was effected in the following manner : (1) In the first instance as soon as all the original oxygen had disappeared, the resulting products were withdrawn and analysed, but (2) on repeating the experiment, a second charge of oxygen was introduced into the reaction chamber as soon as the first had disappeared, and the products were not withdrawn for analysis until this additional oxygen had disappeared, whilst (3) in the third experiment two such additional charges of oxygen were successively introduced and were allowed to be used up before the products were finally withdrawn.

We were thus enabled to follow the course of oxidation much further than before, while keeping the oxygen concentration low and preventing any undue rise in reaction temperature. The results, which are detailed in Table V (where the various products therein are expressed as cubic centimetres of gas or vapour per litre of the original mixture taken) showed that, as the oxidation

2 f 2



Tabl

e IV

.—Th

e Ef

fect

of

Oxy

gen

Con

cent

ratio

n on

the

rel

ativ

e pr

opor

tions

of

In

term

edia

te

Prod

ucts

Su

rviv

ing

at10

0 A

tmos

pher

es.

Com

posit

ion

ofin

itial

gas

es

per

cent

.In

itial

tem

pera

ture

.°C

.

Max

imum

reac

tion

tem

pera

ture

.°C

.

Perc

enta

ge o

f the

Car

bon

of th

e et

hane

bur

nt su

rviv

ing

as—

Tota

l ca

rbon

so

acco

unte

d fo

rpe

r ce

nt.

a °. aw a Q

6 a a o

O a o a

a o o a o

H . COOH.

o oA. 8

a o

Total incondensableproducts.Total in gaseous products.

c2h

6.o2

.

89-0

84-5

11-0

15-5

270-

5

271-

8

283-

531

5-8

23-6 7-4

14-0

10-0

9-7

4-8

0-05

0-90

12-5 2-4

0-5

0-15

22-4

31-2

8-7

3-7

8-6

33-4

60-3

525

-65

39-7

68-3

100-

0593

-95*

* Th

ere

was

som

e ca

rbon

dep

osite

d in

this

expe

rim

ent.

436 D. M. N ew itt and A. M. Bloch.

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§ oTa

ble

V.—

The

Effe

ct o

f Pr

ogre

ssiv

e O

xida

tion

on

the

Rel

ativ

e Pr

opor

tions

of

th

e Pr

oduc

ts

at

289°

C.

an

d i

50 A

tmos

pher

es.

§T

Rea

ctin

g m

ediu

m.

Prod

ucts

from

rea

ctin

g m

edia

(1),

(2),

and

(3) a

s cu

bic

cent

imet

res

of v

apou

r or

gas

per

litr

e of

initi

al m

ixtu

re (

1) a

t N.T

.P.

Rat

ioco

/co

2.C2

H5O

H.

CH

30H

.C

H3C

HO

.H

. CH

O.

CH

3CO

OH

.H

. CO

OH

.CO

.co

2.c

h4.

(1)

88 C

2H6/1

2 0

2 ...

......

......

......

......

...14

-425

-94-

53-

621

0-7

70-0

13-4

39-3

5-2

(2)

Prod

ucts

from

(1) -

f an

add

ition

al

12 0

2 ...

......

......

......

......

......

..13

-538

-94-

73-

22-

30-

715

8-8

30-7

37-1

5-2

(3)

Prod

ucts

from

(2) -

f- an

add

ition

al

12 0

2 ...

......

......

......

......

.....

131

42-9

5-7

311-

910

206-

435

-137

-25-

9

of Ethane at High Pr. 437

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proceeded, while there was a small progressive falling off in the concentrations of the ethane, ethyl alcohol and formaldehyde, those of methyl alcohol, acetaldehyde and both oxides of carbon materially increased ; the C0/C02 ratio remaining fairly constant throughout. The concentration of acetic and formic acids (always relatively small) were, however, not much affected. Also the products contained about 5 per cent, of methane and less than 2 per cent, of hydrogen. Obviously, the further the oxidation proceeded, the more of the hydrocarbon was burnt to oxides of carbon and steam.

Discussion.

The prominence, and in some experiments the predominance, of ethyl alcohol among the surviving condensable and water-soluble intermediate oxidation products—which taken together accounted in many experiments for upwards of 60 (and in one case for more than 70) per cent, of the carbon in the ethane burnt—without any trace of peroxide ever being detected, adds greatly to the already overwhelming weight of evidence in favour of the “ hydroxylation ” as against the “ peroxidation ” theory of hydrocarbon combustion.

In one experiment no less than 36-5 per cent, of the total carbon of the ethane burnt was found in the products as ethyl alcohol, another 20 per cent, as methyl alcohol, 8 per cent, more as acetaldehyde, 6-5 per cent, as acetic acid, besides smaller proportions as formaldehyde and formic acid, together substantiating almost quantitatively the following “ hydroxylation ” scheme. In this (be it noted) each one of the six possible “ hydroxylation ” steps is represented by one or more of the products actually isolated, thus making the proof complete.

Stage 1 2CH3 c h 3 c h 3

CH2o r t c h (o h )2OH OH

H20 + CH3 . CHO

CH3. COOH CO + c h 3oh

OH OH

H ,: C - C : O = CO + H20 +

CH2(OH)2 = H20 +

>H»: C : 0

HOv>C :0->

H/f-----A ' fh 2o + co i

There was neither any liberation of carbon nor hydrogen except when the reaction temperature had risen so rapidly as to cause an inflammation of the reacting medium ; usually, though not invariably, some methane appeared in the products as the result of the thermal decomposition of some of the acetaldehyde vapour. Otherwise the only thermal decompositions accompanying the



Slow Combustion o f Ethane at High Pressures. 439

main course of the oxidation were those of the less stable of the successively formed hydroxylated molecules, as shown in the scheme.

The general influence of an increase in the reaction pressure was favourable to the survival of those products ( i.e., ethyl alcohol, acetaldehyde and acetic acid) whose formation did not involve any disruption of the bond between the two carbon atoms of the ethane burnt ; conversely a lowering of the pressure tended to promote such disruption and to favour the formation, or survival, of methyl alcohol, formaldehyde, and formic acid.

Carbon monoxide was, or might be, formed as the result of thermal decomposition (i) simultaneously with methyl alcohol at the third hydroxylation stage, (ii) simultaneously with steam and formaldehyde at the fourth stage, and (iii) simultaneously with steam at the fifth stage ; while in all experiments carbon dioxide was certainly formed by the thermal decomposition of carbonic acid at the sixth stage and possibly also to a small extent in some experiments by the independent oxidation of the monoxide.

In conclusion we desire to thank Professor Bone for his interest in the work and Radiation Limited for their Research Fellowship which has enabled one of us (A.M.B.) to devote his whole time to it.

In the slow combustion of ethane-oxygen mixtures of composition 85 to 90 C2H 6/15 to 10 0 2, at high pressures, intermediate products, representing the six possible “ hydroxylation ” steps whereby the ethane molecule is oxidized, have been isolated.

At 100 atmospheres pressure upwards of 60 (and in one case more than 70) per cent, of the carbon of the ethane burnt survived as condensable and water soluble intermediate products. Ethyl alcohol and/or acetic acid predominated among the surviving intermediate products but, in addition, considerable quantities of methyl alcohol, acetaldehyde and steam were always present together with smaller amounts of formaldehyde and formic acid.

The effect of increasing the initial pressure of the reacting medium was in general to favour the survival of ethyl alcohol, acetaldehyde and acetic acid {i.e., of products formed without any rupture of the ethane molecule).



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The slow combustion of ethane at high pressuresrspa.royalsocietypublishing.org/.../140/841/426.full.pdfIn 1904 tbe slow combustion of etbane at atmospheric pressure was shown by Bone