578 W. A. Bone and R. E. Allum. - Proceedings of the …rspa.royalsocietypublishing.org/content/royprsa/134/825/...578 W. A. Bone and R. E. Allum. Summary. Measurements of the relative

578 W. A. Bone and R. E. Allum.

Summary.

Measurements of the relative abundance of isotopes by means of the photometric of their mass-spectra have been extended to six more elements. Improvements in technique and new application of anode rays are described.

The results for the ratio of Li 7 to Li 6 support the values obtained by other direct physical methods as against those calculated from observations on band spectra.

New isotopes have been discovered in strontium and barium and the constitution of thallium determined.

Scandium is shown to be simple.The packing fractions of caesium, barium and thallium have been measured.The calculated atomic weights are in good agreement with the accepted

chemical values with the exception of those of caesium and scandium.

The Slow Combustion of Methane.

By W illiam A. B o n e , D.Sc., F.R.S., and R. E. A llu m , B.Sc., A.R.C.S., D.I.C.

(Received September 15, 1931.)

The slow combustion of methane was studied nearly thirty years ago by W. A. Bone and R. V. Wheeler, who showed* (i) that 2CH4 + 0 2 mixtures react at temperatures between 300 and 400° C. and pressures of 2 to 2*3 atmospheres in borosilicate glass tubes with enormously greater velocities than do 2Ha -j- 0 2 or moist 2CO + 0 2 mixtures under similar conditions, and yield C02, CO and H 20 without any liberation of either carbon or hydrogen, and (ii) that when CH4 + 0 2 mixtures were continuously circulated at between 600 and 350 mm. pressure in a closed system comprising a “ reaction tube ” packed with fragments of porous porcelain and maintained at temperatures between 450° and 500° C., large quantities of formaldehyde (equivalent to between 13 and 20 per cent, of the methane burnt) could be isolated from the products.

Such results, together with others on the slow combustion of ethane, ethylene

* ‘ J. Chem. Soc.,’ vol. 81, pp. 535-549 (1902), and vol. 83, pp. 1074-1087 (1903).

on May 30, 2018http://rspa.royalsocietypublishing.org/Downloaded from

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Slow Combustion of Methane. 579

and acetylene, led to the process being formulated as essentially one of successive stages of hydroxylation, thus :—

CH4 -* CH3OH -> CH2 (0H )2 HO H 0 X>C : 0 -> >C : 0

H 20 + H 2 : C : 0 ^ H H 0 /_____ A

CO + h 2o co2 + h 2o

The mechanism of hydrocarbon combustion was further discussed about a year ago in a paper on the “ Slow Combustion of Ethane,” by W. A. Bone and S. G. Hill,* with special reference to suggestions put forward in recent years that the initial stage is one of peroxidation rather than of hydroxylation; and it was proved (inter alia) that, at 300° C. and atmospheric pressure(i) after well-marked induction periods, 2C2H6 -j- 0 2 are much more reactive than C2H6 -f- 0 2 mixtures, (ii) the initial product is either C2H60 or some less oxygenated ethane, but not C2H60 2, (iii) its further oxidation proceeds, consistently with the hydroxylation view, via the successive intermediate formations of acetaldehyde, formaldehyde, formic acid and carbonic acid, to the ultimate production of steam and oxides of carbon, without any liberation of either carbon or hydrogen, although (iv) inconsiderable amounts of a “ peroxide ” are, or may be, formed as a concomitant of the acetaldehyde, but not earlier.

About the same time also, in a paper on the “ Kinetics of Gaseous Oxidation Reactions,” R. Fort and C. N. Hinshelwood described experiments on the slow oxidations of methane, methyl alcohol and formaldehyde,f which had shown in each case (i) an initial ' ‘induction period,” most pronounced with methane,(ii) a dependence of the rate of reaction on the concentration of the combustible gas, and the relatively small influence of oxygen concentration, and(iii) a marked decrease in the rate of reaction in vessels of small dimensions. I t was considered by the authors in question that probably “ chain reactions ” are much more easily propagated when the intermediate active molecules encounter more hydrocarbon than oxygen, and that “ some intermediate peroxidised substance (which was neither specified nor apparently even detected) is responsible for the propagation of the chains,” although it was conceded (p. 287) that the hydroxylation scheme “ undoubtedly expresses the general behaviour correctly.”

* ‘ Proc. Roy. Soc.,’ A, vol. 129, pp. 434-487 (1930).t ‘ Proc. Roy. Soc.,’ A, vol. 129, p. 284 (1930).




The only satisfactory evidence as to the initial oxidation product (whether alcohol or peroxide) would be either its unimpeachable isolation and detection, or (failing that) at least such a combination of simultaneous pressure and analytical data as would enable its nature being deduced from complete carbon-hydrogen-oxygen balances. And, in the case of ethane, such balances pointed unmistakably to the initial stage being one of “ hydroxylation ” rather than “ peroxidation.” The point is of such importance to the general theory of hydrocarbon combustion, that it was decided to re-investigate the case of methane which, as the simplest of all, would be freest from complications and most likely to afford decisive evidence. Accordingly it was arranged that while Dr. D. M. Newitt and Mr. A. E. Haffner were investigating the slow oxidation of methane at high pressures, we would study the process at atmos- spheric pressure and some suitable temperature range (423-447°) in such a manner as would enable us to determine (i) which is the most reactive methane- oxygen mixture, (ii) what influence (if any) have small amounts of moisture, methyl alcohol, etc., upon its “ induction ” and “ reaction ” periods, respectively, (iii) the influence of both temperature and pressure, respectively, thereon, (iv) whether or not any signs of “ peroxidation ” are manifested, and (v) complete carbon-hydrogen-oxygen balances throughout the whole reaction period. The principal results of our investigation, which should be read in conjunction with those recorded by Dr. Newitt and Mr. Haffner in the next paper of this issue, are embodied herein.

E x pe r im e n t a l .

I .—General Arrangements.

Apparatus and Method.—The experimental mixtures—3CH4 + 0 2, 2CH4 -j- 0 2, CH4 + 0 2, and CH4 -f- 1 • 86 0 2—having been made up at room temperature {circa 18° C.) over mercury from their highly purified constituents, and then analysed,* each of them was separately introduced into the vacuous reaction vessel A (fig. 1)—a cylindrical bulb (27-5 cm. long, 5 cm. internal diameter and 586 c.c. capacity) of transparent silica—which previously had been heated up to the desired constant experimental temperature (usually 447° C.) in the electric resistance furnace B. The vessel had suitable external connection with (i) the manometer, C, (ii) a “ hyvac ” pump, and (iii) the gas-holder containing the experimental mixture. For further details the previous paper on

* The amount of adventitious nitrogen present was usually well below 1 per cent.



581

the “ Slow Combustion of Ethane ” should be consulted.* Arrangements were made whereby, as and when desired, the vessel and its contents could be suddenly cooled at any moment by plunging it into a mixture of ice and water, so as to stop the reaction and enable the chemical composition of the medium thereat being exactly ascertained.

Slow Combustion of Methane.

F ig . 1.—Diagram of Apparatus.

I I .— The Induction Period and General Characteristics of the Reaction.

(a) As previously observed by Fort and Hinshelwood, and in keeping with former experiments in our laboratories with ethane-oxygen mixtures, the slow interaction of methane and oxygen throughout the temperature-range (423- 447°) of our experiments is always homogeneous and preceded by a well- marked “ induction period ” during which little or no perceptible pressure or other change occurs in the system. Certainly no sign whatever of any “ peroxidation ” could he detected, either during the “ induction period ” or at any subsequent stage of the oxidation, although the most delicate means for its detection were employed. And in conformity with this, the 2CH4 -f- 0 2 {not the CH4 + 0 2) was found to be by far the most reactive of all methane-oxygen mixtures.

* Loc. cit., pp. 438-440.

2 QVOL. CXXXIV.— A.




(b) The subsequent “ reaction period ” is marked by a steady pressure-rise in the system (condensation of steam being prevented) continuing until reaction has ceased, and by the production of steam and oxides of carbon, but neither free hydrogen nor carbon. The intermediate formation of formaldehyde could always be detected.

(c) Although both the “ induction ” and “ reaction ” periods for a given mixture at a given temperature were considerably retarded by packing the reaction vessel with fragments of silica, both were accelerated by introducing a small percentage of water vapour into the dry system ; while at 447° the “ induction period ” was entirely obliterated, and the reaction speeded up, by the introduction of 2 per cent, of either methyl alcohol, formaldehyde, iodine or nitrogen peroxide vapour.

I I I .— Comparison oj Reactivities of various Moist Methane-Oxygen Mixtures at447° C. and 760 to 770 mm.

On making careful comparative observations upon the duration of the “ induction ” and “ reaction ” periods, respectively, when various methane- oxygen mixtures (saturated with moisture at 20° C.) were introduced into the reaction vessel at 447° C. and pressure between 760 and 770 mm., the following highly significant results, which are also set forth graphically in fig. 2 were obtained :—

Original mixture.

Durations of observed periods of Percentage of initial

oxygen remaining at end of observed reaction period.“ Induction.” “ Reaction.”

3CH4 + 0 2 ...............................minutes

/ 101 10

minutes113153

4-8Nil

2CH4 + 0 2 ...............................{ i

3635

NilNil

r 8 153* 29-28 165* 22-5

c h 4 + 0 2 ............................... 8 187* 24-110 470 2-612 1507 2-3

CM, + 1 -86 0 2 ....................... / 2 1

\ i o1

364*311*

531531

* It will be seen that in these cases the oxidation had by no means finished when the experiment was broken off.




I t is thus apparent that, judged whether by its “ induction ” or reaction ” period, the 2CH4 -j- 0 2 was by far the most reactive of all the mixtures tried, requiring no more than 30 minutes for the complete disappearance of oxygen after reaction had begun. In the corresponding 3CH4 -f- 0 2 and CH4 -f- 0 2 experiments the “ induction periods ” were always two to three times, and the

Time (minutes)

F ig. 2.—Curves showing Influence of Mixture-Composition on Rate of Reaction at447° C. (moist).

“ reaction periods ” four or five times, longer, respectively, than with 2CH4 -f 0 2. Indeed, the “ retarding ” influence of oxygen over and above the last- named properties is a very remarkable feature of our results.

While such facts are just what would be predicted by the “ hydroxylation ” theory, they seem inconsistent with that of an initial “ peroxidation,” which presumably would require the equimolecular (and not the 2CH4 + 0 2) to be the most reactive of all methane-oxygen mixtures. And, together with Dr. Newitt’s and Mr. HafEner’s recent isolation of methyl alcohol as the primary product of the direct pressure-oxidation of methane ( .), they constitute asstrong a proof of a primary hydroxylation as could well be desired.

2 q 2




IV.—Further Experiments with the 2CH4 + 0 2 Mixtures.

Our remaining experiments with the most reactive 2CH4 -f- 0 2 mixture will be briefly described with the aid of a series of pressure-time curves, and some analytical data.

(a) Showing the Influences of Temperature and Pressure, respectively, upon the Induction and Reaction Periods.—The results set forth diagrammatically in figs. 3 and 4, as well as in the following tabulated data, show how potent are both temperature and pressure in shortening the “ induction ” and “ reaction ” periods.

Time (minutes)F ig. 3.—Curves showing effect of Temperature on Rate of Reaction of moist 2CH4 + 0 2

at Normal Pressure.

(i) Influence of Temperature at Atmospheric Pressure (768-770 mm.).

Temperature.

Observed durations of

“ Induction.” “ Reaction.”

°C. minutes minutes447 4 36 ̂ Reaction 98 per442 5 65 y cent, or more435 11 150 J complete.423 50 .




(ii) Influence of Pressure at 447° C.

Pressure.

Observed durations of


mm. minutes minutes770 4 38 1 Reaction 98 per706 10 160 > cent, or more575 12 270 J complete.

Time (minutes)

F ig. 4.—Curves showing Influence of Pressure on Moist 2CH4 + 0 2 Mixture at 447° C.

(b) Showing the Influences of Moisture other Foreign Vapours upon the Duration of Induction and Reaction Periods, respectively, at 447° C. and Atmospheric Pressure.—At the outset of each experiment the reaction vessel was thoroughly dried out by prolonged evacuation at 447° C. ; the experimental 2CH4 + 0 2 mixture, after being well dried by slow passage through a metre- long column of pure redistilled phosphoric anhydride, was then admitted into it at atmospheric pressure either in such condition (i.e., in a “ dry ” control- experiment) or with the addition of 2 per cent, by volume of either moisture, methyl alcohol, or some other vapour. Observations of the subsequent “ induction ” and “ reaction ” periods were then taken, with results as shown graphically in fig. 5 and by the following data :—




Moist

Time (minutes)Fig. 5.—Curves showing Influence of Third Bodies on Rate of Reaction of Dry 2CH4 + 0 2

at 447° C.

2CH4 + 0 2 mixture.Total durations of


Plus--- minutes minutesNil, dry ................................................................ 6 to 7 91 to 982 per cent. H 20 .................................................... 3 to 4 35 to 36

„ CH3OH ............................................ 0 60„ H : C : 0 ............................................ 0 40„ NO, .................................................... 0 30,, Iodine vapour................................... 0 40

From these results it will be seen that (i) the addition of 2 per cent, of moisture to the well-dried mixture materially shortened both its “ induction ” and “ reaction ” periods at this temperature, and (ii) similar additions of other foreign vapours completely obliterated the “ induction ” and shortened the “ reaction ” period. I t is interesting to note that, whereas methyl alcohol, like formaldehyde, caused the “ induction period ” to vanish, it quickened the “ reaction period ” much less than did the aldehyde.

(c) Analytical Data showing Full Course of the 2CH4 + 0 2 Interaction at 447° and Atmospheric Pressure.—A complete series of experiments was made in




each of which a P 20 5-dried 2CH4-|- 0 2 mixture was introduced at atmospheric pressure into the reaction vessel at 447°. At the end of predetermined time intervals—varying from 6 minutes ( i.e., the end of the “ induction period ”) to 97 minutes (or nearly the end of the “ reaction period ”)—thereafter the vessel and its contents were suddenly plunged into a mixture of ice and water whereby reaction was stopped. Such procedure, supplemented by appropriate pressure readings, gas analyses, and tests for formaldehyde, and other possible intermediate bodies, enabled complete series of carbon-hydrogen-oxygen balances being drawn up for the system at each predetermined point during the experiment.

The full data for the whole series are given in Table I, from which the pressuretime curves shown in fig. 6 have been deduced.

Time (minutes)Fig. 6.—Dry 2CH4 -f 0 2 Mixture at 446*8° C.

During the “ induction period ” (6 minutes) no trace whatever of any “ peroxide ” could be detected in the system, which at the end thereof contained only methane and oxygen plus about 0*17 per cent, of formaldehyde



Tabl

e I.

—Ex

perim

ents

with

Dry

2C

H4

+ 0

2 Mix

ture

at

T =

447

° C.

Tim

e in

min

utes

from

sta

rt

(indu

ctio

n pe

riod

= 6

min

s.)

(i) 6

(ii)

21

(iii)

28

(iv)

44

(v)

57

(vi)

97

mm

.m

m.

mm

.m

m.

mm

.m

m.

Initi

al p

ress

ure

of d

ry m

ixtu

re a

t T° C

.76

1-4

769-

675

8-1

760-

575

9-6

762-

2Fi

nal

pres

sure

of

prod

uct

(incl

udin

gH

20)

at T

° C .

......

......

......

......

......

.76

1-4

779-

677

5-4

793-

179

9-4

822-

3

Part

ial p

ress

ure

of o

rigi

nal m

ixtu

re a

t0°

C.—

mm

.m

m.

mm

.m

m.

mm

.m

m.

CH

,.....

......

......

......

......

......

......

.....

196-

519

9-5

197-

019

7-5

197-

419

6-8

o2

......

......

......

......

......

......

......

.....

97-9

99-2

98-0

98-3

98-2

98-0

Part

ial

pres

sure

of

gase

ous

prod

ucts

(mm

.) at

0°

C.—

mm

.m

m.

mm

.m

m.

mm

.m

m.

C02

......

......

......

......

......

......

......

.....

Nil

0-6

1-6

3-7

5-2

14-4

CO

......

......

.....

Nil

18-1

17-7

32-7

35-8

40-6

ch

4 ....

......

......

......

......

...19

6-0

179-

017

6-7

161-

015

5-8

141-

302

...

......

......

......

......

......

......

......

..97

-571

-766

-543

-035

-84-

6

Rat

io 0

2/CH

4 use

d u

p...

......

—1-

341-

531-

521-

511-

68

C.h

2.o

2.C.

h2.

02.

C.h

2.o

2.C.

h2.

o2.

C.h

2.o

2.C.

h2.

o2.

C . H

2.0

2 Bal

ance

s—U

nits

in o

rigi

nal m

ixtu

re

.19

6-5

393-

097

-919

9-5

399

99-2

197-

039

4-0

98-0

197-

539

598

-319

7-4

394-

398

-219

6-8

393-

698

-0U

nits

in a

bove

pro

duct

s ..

196-

039

2-0

97-5

197-

735

881

-319

635

3-4

77-0

197-

432

263

196-

831

1-6

58-9

196-

328

2-6

39-3

Diff

eren

ce a

s H20

(and

trac

es o

f CH

20)

0-5

1-0

0-4

1-8

4117

-91-

040

-621

-00-

173

35-3

0-6

82-7

39-3

0-5

111-

058

-7

588 W. A. Bone and B. E. Allum.

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May

30,

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8ht

tp://

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ciet

ypub

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from


vapour and a similar amount of steam ( . , CH20 + H 20) without any oxidesof carbon.

As the oxidation proceeded, however, oxides of carbon plus further steam rapidly appeared, without much (if any) further accumulation of formaldehyde vapour in the system ; the ratio of the 0 2/CH4 disappearing kept between 1*34 and 1-68 (and nearly constant at 1*5 during the middle part of the process), the ratio of the C0/C02 formed always keeping high and nearly constant at 10 • 0 during the middle part of the process. Neither carbon nor hydrogen were ever liberated ; and the volumetric formation of steam always equalled that of the formaldehyde plus twice the combined oxides of carbon.

Moreover, analyses of the time-pressure curves reproduced in fig. 6 reveal that whereas the relative rate of CH4-disappearance decreased, that of the 0 2-disappearance increased as time progressed, a circumstance indicative of a very rapid further oxidation of intermediate products.

From first to last no trace of any “ peroxide ” could ever be detected, all the carbon of the methane oxidised (save the small amount always present as formaldehyde) being accounted for as CO -f C02 in the gaseous products. Finally, the ratio of the H 2/0 2 unaccounted for in the cold dry gaseous products was always nearly that required for H 20 plus the small proportion of CH20 referred to.

Considered from the hydroxylation point of view, the results showed a nonstop oxidation-run, through the mono-hydroxy and di-hydroxy stages, to steam and formaldehyde, the latter being very rapidly further oxidised to formic acid, most (about nine-tenths) of which was instantly resolved into CO + H 20, the remainder being further oxidised through carbonic acid to C02 -j- H 20, neither carbon nor hydrogen being liberated. The end of the “ induction period ” apparently synchronised with a certain very small accumulation in the system of formaldehyde, which remained fairly constant throughout the subsequent “ reaction period.”

Y.—Experiments with CH4 + 0 2 and CH4 + 202 Mixtures at 448° C.

To complete the story, particulars are appended (Table II) of typical experiments at 448° and atmospheric pressure with CH4 + 0 2 and CH4 + 2 0 2 mixtures, respectively, These reacted so slowly, however, as to prevent our following the oxidation to completion ; indeed, their chief interest lies in the evidence thus afforded of the very remarkable retardation of the whole process by oxygen. In each case the end products contained small amounts of




Tabl

e II

.—Ty

pica

l Ex

perim

ents

with

. CH

4 +

02

and

CH

4 -f-

1-8

6 0

2 M

ixtu

re a

t 44

8° C

.

Dur

atio

n of

Initi

alFi

nal

pres

sure

(in

clud

ing

H20

) at

448

° C.

Perc

enta

ge c

ompo

sitio

n of

col

d dr

y N

«-fr

eeR

atio

Rat

ioC

0/C

02fo

rmed

.

Perc

enta

geO

rigi

nal

mix

ture

.In

duct

ion

peri

od.

Obs

erve

dre

actio

n.

pres

sure

aten

d pr

oduc

ts.

o2/

ch

4us

edof

ori

gina

lo2

448°

C.

co2.

CO.

ch

4.o2

.up

.us

ed u

p.

ch

4 + 0

2...

......

......

......

..m

ins. 8

min

s.18

7m

m.

768-

6m

m.

811-

913

-522

-045

-319

-21-

701-

6375

-9

CH4 +

1-8

6 0

2 ....

......

.....

1631

176

1-2

793-

19-

915

-923

-650

-61-

691-

6047

0

590 Slow Combustion of .

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Methyl Alcohol and Formaldehyde.591

formaldehyde. The ratio of the 0 2/CH4 used up was practically the same (1*7), and of the C0/C02 formed (1*6) was almost the same in each case.

The results as a whole, together with those recently obtained by Dr. Newitt and Mr. Haffner for the pressure-oxidation of methane ( cit.), have demonstrated a case of direct hydrocarbon oxidation, entirely uncomplicated by any sign of “ peroxidation,” in which (i) the most reactive mixture is that corresponding with the alcohol-forming proportion, (ii) substantial quantities of the alcohol have actually been isolated in circumstances (chiefly high pressure) favouring its stability and survival, and (iii) all other happenings fulfilled the predictions of the hydroxylation theory.

In conclusion, we desire to thank the firm of Radiation, Ltd., of London, for their Research Fellowship, which has enabled one of us (R.E.A.) to devote his whole time to the investigation and out of which its expenses have been defrayed.

The Formation of Methyl Alcohol and Formaldehyde in the Combustion of Methane at High Pressures.

By D. M. N e w it t and A. B. H a f f n e r .

(Communicated by W. A. Bone, F.R.S.—Received July 24, 1931.)

The isolation and identification of the primary oxidation product of a hydrocarbon are so important from the point of view of the theory of hydrocarbon combustion that chemists have spared no effort to overcome the difficulties involved, but so far with incomplete success.

The mechanism of the oxidation process was elucidated many years ago by the researches of Professor W. A. Bone and his collaborators as one essentially of hydroxylation, in the case of methane as involving the following stages :—

Summary.

CH4 -> CH3OH -* CH2(OH)2 OH OH

H 20 + H 2: C : 0 ^ H . C : 0 - * H 0 . C : 0

CO + H20 C02 + H20



Documents

578 W. A. Bone and R. E. Allum. - Proceedings of the …rspa.royalsocietypublishing.org/content/royprsa/134/825/...578 W. A. Bone and R. E. Allum. Summary. Measurements of the relative