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State Bridge and Tunnel Commission with reference to the physiological effects of motor exhaust gas, it was of first importance to find a method for d...
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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol.

12,

No.

IO

ORIGINAL PAPERS THE DETERMINATION OF CARBON MONOXIDE IN AIR CONTAMINATED WITH MOTOR EXHAUST GAS1 By M. C. Teague TUNNEL GAS INVESTIGATIONS, u.

s. BUREAUOF

MINES,

PITTSBURGH,

PA.

Received August 12, 1920

I n connection with t h e joint investigation of t h e Bureau of Mines and t h e New York-New Jersey S t a t e Bridge and Tunnel Commission with reference t o t h e physiological effects of motor exhaust gas, i t was of first importance t o find a method for determining carbon monoxide in low concentrations and in t h e presence of other oxidizable gases. T h e analytical determination of this gas in t h e concentrations here encountered (0.01t o 0.I O per cent) offers a much more difficult problem t h a n t h e usual determination. The Orsat method, using ammoniacal cuprous chloride solution as t h e solvent for carbon monoxide, does not remove t h e last traces of the gas; 0 . 2 or more may not be absorbed.2 The Haldane analyzer as modified by Burrell and Seibeljt,s when operated by an expert, does not exceed a precision of 0.01 per cent. The Haldane blood m e t h ~ d although ,~ applicable t o small concentrations, is subject t o many variations, which do not always give concordant results. The method which offered t h e greatest possibilities for t h e present work was t h a t of iodine pentoxide, which consists in oxidizing t h e gas with iodine pentoxide and determining t h e amount either of carbon dioxide formed or of iodine liberated. Considerable study of this method has been made since its first use in 1888.~ A portable apparatus described by Graham6 makes use of bromine in potassium bromide solution t o remove any unsaturated hydrocarbons, and dries t h e gas with calcium chloride and phosphorus pentoxide before i t enters the iodine pentoxide tube, which is held at temperatures between g o o and 150' C., there being no observed difference i n results over this range, except in t h e presence of relatively large amounts of hydrogen. Under carefully controlled conditions, a n accuracy t o within 0.005 per cent carbon monoxide i s claimed. Lt. Col. A. B. Lamb' and his coworkers made use of t h e iodine pentoxide method in connection with their work on carbon monoxide absorbents for gas masks. At t h a t time there was developed by A. T. 1 Published by permission of the Director of the Bureau of Mines and the Chief Engineer of the New York-New Jersey State Bridge and Tunnel Commission. 2 G. A. Burrell and F. M. Seibert, "The Sampling and Examination of Mine Gases and Natural Gas," Bureau of Mines, Bulletin 42, 48 8 L O C .cit., p. 17. 4 Forthcoming Bureau of Mines Bulletin on "Physiological Effects of Motor Exhaust Gases." 6 C. de la Harfe and F. Reverdin, Chem. Z t g , 12 (1888), 1726; Maurice Nicloux, Compt. rend., 126 (1898), 746; Armabd Gautier, I b i d . , 126 (1898), 1299; 128 (1899), 487; L. R . Kinnicutt and G. R. Sanford, J . A m . Chem. SOC.,22 (1900), 14; E. H. Weiskoff, ,J.Chem. Met. SOC.S . Africa, 9 (1909), 258, G. A. Burrell and F. M. Seibert, Bureau of Mines, Bulletzn 48 (1913), 60. 8 J. Ivon Graham, J . SOG. Chem. Ind., 38 (1919), 10. 7 I n charge of the Defense Research Section, C. W. S., U. S. A.

Larson and E. C. Whitel a 6-unit multiple apparatus. This was designed for use with carbon monoxide-air mixtures only, although they experimented and found an interference b y hydrogen. The purifying train included a tower of sodium hydroxide solution, another containing hot concentrated sulfuric acid, and finally a tube of dry alkali. The attempted accuracy- was 0.01 per cent carbon monoxide. There has been a difference of opinion among earlier investigators as t o t h e advantages of determining t h e amount of carbon dioxide formed or t h a t of the iodine liberated. Upon first inspection of t h e equation 1206

f

5co + scot

f 21

it would seem preferable t o determine t h e carbon dioxide, since a relatively large amount of i t is formed. At these very low concentrations, however, t h e complete absorption of carbon dioxide is an exceedingly difficult operation. For most types of absorption tubes there would be t h e inconvenience of psing several such tubes or of passing t h e gas through t h e apparatus at a slower rate. Furthermore, i t has been found undesirable t o work with baryta solution much weaker t h a n 0 . 0 2 N , whereas in determining t h e iodine liberated by t h e reaction 0.001 N sodium thiosulfate can be used, a difference which offsets t h e advantage of t h e greater amount of carbon dioxide formed. APPARATUS-TYPE

I

An apparatus practically t h e same as t h a t of Larson and White was constructed with t h e view of adapting i t for carbon monoxide determinations in dilute exhaust gases. The iodine pentoxide tubes were made of about three-quarter inch pyrex tubing, with t h e U about I O in. long. They were filled with alternate layers of glass wool and iodine pentoxide (each tube containing 30 t o 40 g. of t h e latter). The a r m on t h e exit side of t h e U-tube was somewhat longer t h a n t h e other and tapered t o make an interlock glass joint with t h e guard tube. A similar joint was made with t h e absorption bulb, thus removing t h e possibility of error due t o rubber connections. PREPARATION O F PENTOXIDE

After t h e apparatus was assembled i t was necessary t h a t t h e iodine pentoxide be conditioned before making any determinations. This was accomplished by raising t h e temperature t o 220' t o 2 3 0 ° C. for several hours, while air was drawn through. (Iodic acid begins t o decompose at 170' C. t o form water and iodine pentoxide.) With t h e water, considerable iodine was at first driven off. Two varieties of iodine pentoxide were tried: one, t h e ordinary commercial variety, prepared b y t h e oxidation of iodine with fuming nitric acid, required about 2 5 hrs. heating; while t h e other variety, prepared by t h e chloric acid method,z required only about 1 5 hrs. heating, The tubes con1 Appreciation is here expressed for the use of unpublished data relative t o Larson and White's iodine pentoxide apparatus. 2 This method will be described later by A. B. Lamb and W. C. Bray.

a

Qct.,

T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

1920

taining t h e latter variety gave lower blanks and seemed more active a n d therefore less sensitive t o temperature changes t h a n did t h e other tubes. I n making t h e determinations, t h e iodine pentoxide t u b e was usually maintained a t a temperature of 150' C. One-liter samples were drawn through t h e apparatus a n d then displaced with outside air. T h e r a t e of flow was about I liter i n I j min. T h e liberated iodine was absorbed in one Bowen's absorption t u b e containing a I O per ce.zt potassium iodide solution, a n d titrated with sodium thiosulfate ( 0 . 0 0 2 3 8 7 N ) ( I cc. thio == 0.1j cc. carbon monoxide a t 25' C. a n d 760 mm. pressure, or I. j parts i n IO,OOO for a I-liter sample). E X P ERIMEK'CS U P O N C A R B O N IMONOXIDE-AIR MIXTURES

T h e determinations made on carbon monoxide-air mixtures are summarized i n Tables I a n d 11. I t is apparent t h a t t h e temperature of t h e iodine pentoxide is not a sensitive factor when working with carbon monoxide-air mixtures. Table I1 shows t h e increased precision obtained by sweeping out t h e train more thoroughly.

--

TABLEI-EFFECT

O F Izos TEMPERATURE Parts CO in 10,000----1000 c. 1500 c. 175' C. 6.1 0 .0 5.7 5.7 5.7 5 .6 5.7 5.5 3: 4 5.9 5.7 5.8 6.0 5.7 5.8 6.2 (1.2 6.1 r M ~5.8 ~ ~ , 5.9 5.7

.

TABLE IT-VARIATIONS OF PRECISION WITH TIMEOF SWEEPING THE TRAIN No. of Parts CO Series Determina(Mean No. Procedure tions Value) 1 Total time, 30 min. (15 min. for 6 8.8 sample, and 15 min. for sweeping the train) 2 Total time, 45 min. (15 min. for 6 4.1 sample, and 30 min for sweeping the train) 3 Total time, 60 min. (15 min. for 6 4.9 sample, and 45 rnin. for sweeping the train) 4 Total time, 60 min. (30 min. for 6 5.5 the (1 liter) sample, and 30 min. (2 liter) for sweeoinc the train) 5 Total time, 75 min. (15 min. for 6 4.0 sample, anti 60 min. for sweeping the train) .

Maximum Variation from Mean (Parts C O ) 10.4

i0.z f0.2 k0.3

I

i o .I

EXPERIMENTS UPON EXHAUST GAS

Attention was next turned t o t h e use of exhaust gases. Analysis showed t h e following constituents: carbon dioxide, carbon monoxide, oxygen, hydrogen, methane a n d perhaps other low saturated hydrocarbons, traces of unsaturated hydrocarbons, a n d some unburned gaso1ine.l Obviously, there were also water a n d varying amounts of oil-smoke particles. T h e carbon dioxide was sufficiently removed b y t h e sodium hydroxide. T h e concentrated sulfuric acid was heated t o 160' C. t h a t i t might absorb any traces of unsaturated hydrocarbons, i n addition t o drying t h e gas.2 As noted above, several investigators h a d found hydrogen t o be partly oxidized b y t h e hot iodine pentoxide. I n each case, however, t h e amount of hydrogen was relatively large, while in exhaust gases t h e hydrogen content varies u p t o about one-half t h a t of carbon 1

2

Analyses made by G W. Jones, Pittsburgh Station, Bureau of Mines E H. Weiskoff, J. Chem. M e t . SOC.S Afrzca, 9 (19091, 258

96 5

T h e effect of such low concentrations h a d monoxide. therefore t o be determined. While methane a n d ethane do not interfere with t h e iodine pentoxide reaction, Graham observed t h a t normal pentane when present i n large concentrations was slightly affected a t t h e temperatures used (90" t o 150' C.). If t h a t was true, it was t o be expected t h a t gasoline (hexane and heptane) would undergo oxidation even more readily. There were, therefore, three possible sources of difficulty in applying this apparatus t o t h e determination of carbon monoxide i n these mixtures, namely, t h e presence of hydrogen, smoke particles, a n d gasoline vapor. T h e following determinations were made t o compare t h e iodine pentoxide method with t h e Orsat and similar methods. TABLE111-COMPARISONOF METHODS Method of co Concentration Expt. Determining CO Method Concentration (Calculated) No. 1 CO from formic acid In gassing chamber 1.82 (not analyzed) 1.98 parts 2 95 per cent CO, Hend- I n gassing chamber 3.86 3.9 erson analyzer 3 Exhaust gas, Orsat In gassing chamber 3.90 3.0 method 6.7 Der cent CO 4 Exhaust gas, Orsat In gassing chamber, 3 . 5 0 method approximately 2.8 6.5 per cent CO 5 Exhaust gas, Orsat In gassing chamber 1.34 method 1 .o 8.4 per cent CO 6 Exhaust gas, Orsat In gassing chamber 17.8 method 13.5 7 Exhaust gas, Orsat Orsat buret to sam- 13.77 method pling tube, then diluted t o 1 liter 6.3 per cent CO 10.29 8 Exhaust gas, 6.3 per Orsat buret t o sam- 13.62 pling tube, then dicent CO luted t o 1 liter 9.59-

Cty%$d

In06 Value (Calc. Value) 0.92 1.00 1.30 1.25 1.34 1.32 1.34

1.42

I n Expts. I a n d 2 t h e pure carbon monoxide was measured in a graduated cylinder a n d displaced by water. I n others, using t h e gassing chamber, t h e exhaust gas was displaced from a large graduated gasometer. I n t h e last two experiments t h e exhaust gas was measured out of t h e Orsat buret directly into t h e sampling tube, a n d then diluted t o about one liter. T h e methods of diluting in t h e chamber were probably accurate t o * I O per cent. Nevertheless, when exhaust gas was used, consistently higher results were obtained by t h e iodine pentoxide method. This increase varied with gas from different cars; on t h e car used for t h e above tests i t was 3 0 t o 40 per cent, while for another car i t was 60 t o 8 0 per cent. It was t r u e t h a t t h e cuprous chloride solution of t h e Orsat apparatus did not absorb t h e last traces of carbon monoxide, yet t h a t unabsorbed could not account for t h e observed high results. I t was evident t h a t some one or more of t h e other constituents of t h e exhaust gas were also being oxidized b y t h e iodine pentoxide. EFFECT O F HYDROGEN-A mixture of carbon monoxide a n d air was prepared a n d analyzed. A known volume of hydrogen was then added t o t h e remaining gas a n d t h e carbon monoxide again determined. These experiments justify t h e conclusion t h a t such quantities of hydrogen as occur i n exhaust gases (about one-half t h e carbon monoxide concentration) are not sufficient a t these low concentrations t o influence t h e

T H E J O U R N A L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol.

966

carbon monoxide determinations as obtained b y t h e iodine pentoxide method. It was not until hydrogen was present in about twice t h e volume of carbon monoxide t h a t any effect was observed in t h e above determinations, and even then t h e results were not conclusive. Exm. A :

PARTS CO IN MIXTURE With Hydrogen = With Hydrogen = 0.5 Volume of CO 1 Volume of CO 1000 1500 1500 4.9 4.8 4.9 4.9 4.9 4.9 4.9 4.9

Without Hydrogen 1500 4.7 4.8 MEAN, 4 . 8

c.

EXPT.B:

1.3 1.2

1.3 1.2 1.1

...

MEAN, 1.2

c.

...

METHOD(Temperature 150' C.) SERIESI11 1.2 Parts CO and Approximately 2.2 Parts proximately 4.5 Parts Hydrogen Hydrogen 1.5 1.9 1 ..5 1.5 ~.~ 1.6 1.5 1.7 1.8 1.6 1.9 1.9 1.6 1.8

PARTSCO

SERIESI Without Hydrogen

c.

c.

BY Is06

SERIES I1 1.2 Parts CO and Ap-

...

EFFECT OP S M O K E PARTICLES F R O M T H E oIL-~41though a pad of glass wool was used i n t h e sodium hydroxide t u b e just before t h e iodine pentoxide, it was possible for small smoke particles to pass through this and perhaps increase t h e iodine liberated. To determine whether or not this caused t h e observed high results from exhaust gas, a paper filter was inserted into t h e train. T h e filter was made by clamping two I I-cm. "quantitative filter papers" of good quality between two ground-edge funnels, permitting a filtering area of about 90 sq. cm. T h e use of this filter made no difference i n t h e determinations on exhaust gas, i. e . , t h e carbon monoxide determinations were t h e same as those when t h e filter was n o t used (60 t o 80 per cent higher t h a n t h e value calculated from t h e Orsat analysis). EFFECT OF GASOLINE-Three determinations were made upon a mixture of carbon monoxide and air containing about 4 parts of carbon monoxide. Motor gasoline was placed i n a n Erlenmeyer flask, and t h e flask stoppered. After standing for several hours, a small portion of t h e flask atmosphere (equal t o about I p a r t gasoline in 10,000)was withdrawn b y a Luer syringe and inserted into t h e above carbon monoxide-air mixture. T h e carbon monoxide equivalent in two samples of this mixture was determined on t h e same apparatus as used above. PARTSCO BXPT

OR

EQUIVALENT

Air 4- CO Mixtures 1. . . . . . . . . . . . . . . . . . . 4.1 2................... 4.3 3................... 4.0 MSAN, 4 . 1

No

Air

+ Mixtures CO + Gasoline ...

I t is evident from t h e above experiments t h a t whereas t h e concentrations of hydrogen and smoke particles encountered i n exhaust gases do not interfere in t h e 1 2 0 6 method of determining carbon monoxide, t h e unburned gasoline vapor does interfere t o a considerable extent. Several absorbents were tried for t h e removal of t h e gasoline vapor without affecting t h e carbon monoxide concentration. ( I ) Cold concentrated sulfuric acid inserted in the train before the heated acid had no effect upon the results.

No.

IO

( 2 ) Dry, activated coconut charcoal was known to be a good absorbent for gasoline vapor and at the same time useless for absorbing carbon monoxide. A tube of this absorbent was, therefore, inserted before the IzOr tube in the place of the solid sodium hydroxide. With this arrangement the high results on exhaust gas were reduced to very nearly the calculated value. When determinations were made upon carbon monoxide-air mixtures, however, the carbon monoxide was appreciably absorbed by the charcoal. ( 3 ) Many heavy mineral oils are also good absorbents of gasoline vapor at higher concentrations. A bead tower containing such an oil (Albolene) was therefore inserted in the train in front of the sulfuric acid tower. It was found that the vapor pressure of this oil was sufficiently high to cause an undesirable and somewhat variable blank due to its reaction with the IzOs. This was true at both room and freezing temperatures, and therefore prevented its use, even though it completely removed the gasoline vapor €rom exhaust gases. (4)Shaved paraffin had no effect upon the results with exhaust gas or carbon monoxide-air mixtures. The average of three determinations on exhaust gas using the usual train showed an increase of 74 per cent over the calculated carbon monoxide value, whereas with the paraffin in the train an average of the same number of determinations showed an increase of 70 per cent. On the two procedures with carbon monoxide-air mixtures, the determinations checked. ( 5 ) It was thought possible that by chilling the dried entering gases to -80" C., the gasoline would be condensed to droplets capable of being filtered out. The gas was led through a small U-tube containing glass wool and about which was packed carbon dioxide snow. With the failure of this to give the desired result, the tube containing the glass wool was replaced by one containing an alundum cylinder (Norton, medium porosity). The chilled gas was thus drawn through this porouc; cup The results on exhaust gas were still unaffected. ( 6 ) The next lower convenient temperature was that of liquid air. A similar U-tube containing glass wool was employed While liquid gasoline cooled to this temperature (-190" C.) becomes a glass-like solid, it was realized that its vapor at such exceedingly low partial pressures might still prove difficult to completely remove.

A twenty-liter carbon monoxide-air mixture was prepared; three samples were withdrawn; and air containing gasoline vapor was injected into t h e remainder, and six samples taken. T h e carbon monoxide values of three of t h e latter samples were determined on t h e apparatus previously used (Type I) and three on t h e train with t h e liquid-air cooled t u b e .

+

CO Air Mixtures Old Apparatus Parts CO

7.0 7.2 7.1

12,

BAN,

8.3 8.0 7.5 7.9

+

+

4-Gasoline f Air C O Gasoline Air Old Apparatus "Liquid Air Tube" in Trrriir Parts CO Equivalent Parts CO Equivalent 48.0 7.8 46.7 7.6 46.0 7.8 46.9 i.7

CO

Thus, a t this temperature,< t h e gasoline vapor was completely removed even under greatly exaggerated conditions. The liquid air temperature also condensed t h e water, carbon dioxide, and probably all of t h e unsaturated hytirocarbons. APPARATUS-

TY PE II

All of t h e members of t h e former purifying train were therefore removed, leaving only the liquid-air cooled t u b e (Type I1 apparatus, see Fig. I ) . Repeated determinations showed t h e same results.

O c t . , 1920

T H E J O C R N A L OF I N D G S l R I i l L A N D ENGINEERING C H E M I S T R Y

967

nation of liquid seals also facilitates t h e manipulation, Blank determinations on Type I1 were constantly at zero. About 300 cc. of liquid air were used per train per day. PORTABLE APPARATUS

CARBONMONOXIDE-AIR MIXTURES Type I Apparatus Type I1 Apparatus Parts CO Parts CO 5.8 5.2 5.9 5.7 5.i 5.4 4.9 5.0 5 .3 MEAN, 5 . 6 16.1 16.4 16.3 16.2 16.4 MEAN, 1 6 . 2

Zn t h e following tables are found t h e results of numerous determinations on exhaust gases. From t h e results i t is noted t h a t a t liquid air temperature all of t h e gases in dilute exhaust gas which interfere with the accurate carbon monoxide determination by t h e T206 met hod are removed.

A convenient method for accurately determining carbon monoxide in such mixtures as dilute exhaust gas having been developed, i t was further modified into a portable apparatus for use in exploring vehicular tunnels, garages, and other enclosed places where i t is desired t o determine low carbon monoxide concentrations, in t h e absence of relatively large amounts of hydrogen. The apparatus is shown in Fig. 2 . The gas sample, which has been reduced t o j o o cc., is drawn into t u b e j by use of t h e leveling bulb e, and through 3-way cock g. b and a are stoppered vacuum cylinders (8 t o I O in. tall) containing U-tubes immersed in liquid air and hot Crisco oil, respectively. I n t h e cold U-tube are condensed t h e water vapor, carbon dioxide, gasoline vapor, and traces of other saturated a n d unsaturated hydrocarbons. The hydrogen, methane, a n d carbon monoxide pass on into t h e iodine pentoxide U-tube immersed in t h e oil bath a heated t o 100’ t o 1 7 5 O C. Only t h e carbon monoxide is oxidized b y t h e iodine pentoxide (the concentration of hydrogen in dilute exhaust gas being too low t o be affected). The liberated iodine is absorbed in potassium iodide solution in test tube c, using t h e bubbler as shown in t h e sketch, and titrated with sodium thiosulfate from buret vz Buret m is used for t h e starch solution.

c l;l

~- - 6-4

-~

EXHAUSTGAS CONTAINING 3 8 PER CENT CO FROM MACHINE IN APPARENTLY GOODCONDITIOK Measured from -Type I Apparatus-Type I1 ApparatusPer cent Gas Buret Per cent cc. c c . co of co c c . co of Taken Found Calculated Found Calculated 1.16 .. 1.12 97 ... I .08 103 1.05 0.80 0 : 87 111 .. ...

co

co

...

EXHAUSTGAS CONTAINING 4.0 PER CENT CO PROM ARMYTRUCKWITH ONE CYLINDER NOT FUNCTIONING -Type I Apparatus-Type I1 ApparatusPer cent Per cent c c . co of co c c . co of CO Found Calculated Found Calculated

Measured from Gas Buret c c . co Taken

MEAN,166

100

EXHAUST G!AS CONTAINING 9.6 PER CENT co FROM ARMYTRUCK(ENGINE RACING) Measured from -Type 11 ApparatusGas Buret Per cent cc.co of cc. Taken Found Calculated 0.78 0.79 101 1.04 101 1.03 1.16 1.19 103 MEAN, 102

co

co

I n Type I1 t h e Dewar vacuum tube has replaced four members of t h e Type I purifying train. This simplified apparatus will probably reduce t h e time per determination b y jo per cent, owing t o t h e shorter time necessary t o clear t h e train completely. The elimi-

u/

FIG. 2

By filling t h e Dewar tubes before starting t o work. they will be found quite sufficient for a day’s work, which will be much too long for t h e operator t o remain in most atmospheres containing carbon monoxi de. In making a determination, a sample is drawn into f b y means of e (filled with water), and slowly passed through t h e apparatus. The r a t e of flow is regulated b y placing t u b e e on rack j a n d adjusting t h e pinchcock 1. From 6 t o 7 min. is t h e best rate for a joo-cc.

968

T H E J O U R N A L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 1701.

sample. During this procedure, stopcock i is turned t o permit t h e evaporating liquid air t o escape into t h e atmosphere. Since t h e apparatus must be cleared with fresh air and t h e determination is being made in t h e gas t o be tested, stopcocks i and h are now turned t o place t h e liquid air chamber in communication with f and t h e tube t h u s filled with “pure air’’ for sweeping t h e train. The apparatus is contained in a cabinet 24 in. X 2 0 in. X 7 in. A determination should take about I j min. a n d should be accurate t o from 0.003 t o 0.005 per cent carbon monoxide (0.3 t o 0.5 part in 10,000). SUMMARY

The iodine pentoxide method for determining low concentrations of carbon monoxide has been investigated with reference t o its use with dilute motor exhaust gas. The type of apparatus heretofore used was found t o give appreciably high results owing t o t h e presence of small amounts of unburned gasoline. A new iodine pentoxide apparatus (Type 11) has therefore been developed. All of t h e interfering gases are first removed a t t h e temperature of liquid air. This method has been found quite satisfactory for determining carbon monoxide in small quantities in t h e presence of gasoline vapor. A portable iodine pentoxide apparatus has been designed which should permit a determination t o be made in I 5 min. with an accuracy of from 0.003 t o 0.00 j per cent carbon monoxide (0.3 t o 0.5 part in 10,000). ACKKO WLEDGMENT

Appreciation is expressed t o Dr. A. C. Fieldner, supervising chemist in charge of tunnel gases investigation, and Dr. Yandell Henderson, in charge of physiological investigations, for valuable suggestions and advice, and t o Mr. W. B. Fulton for making many of t h e determinations herein reported. THE USE OF CATALYSTS IN T H E SULFONATION OF AROMATIC COMPOUNDS By Joseph A. Ambler and William J. Cotton COLORLABORATORY, U. S. BUR$AUOF

CHEMISTRY, WASHINGTON,

D.

c.

Received May 12, 1920

During t h e course of experimentation on t h e vaporphase sulfonation of compounds, i t was found t h a t b y using t h e continuous method of Ambler and Gibbs,l with a given set-up of apparatus and given temperature range, t h e amount of material sulfonated per minute was practically constant; t h a t is, t h e apparatus had a certain “capacity” for sulfonation, since so long as t h e baffies in t h e apparatus were not disturbed, t h e free space for vapors and t h e absorbing or sulfonating surface were constant. The method, therefore, provided a good means of studying t h e effect of various substances introduced with t h e reacting materials, and of ascertaining which were catalyzers of t h e sulfonation reaction. This work is intended as introductory t o a much more complete study of sulfonation catalysts. Inasmuch as t h e study will be unavoidably 1 U. S. Patents 1,292,950; 1,300,227; 1,300,228. this process will be published in subsequent papers.

A description of

12,

NO. T O

delayed for some time, i t seems best t o publish t h e work thus far accomplished, although it is incomplete. Various workers have reported t h a t t h e sulfonation of aromatic compounds m+y be accelerated by adding different catalysts. T h e addition of sodium sulfate] or various acid sodium sulfates2 has long been common practice, and a similar use of potassium sulfate3 has also been reported. It is also well known t h a t various sulfonic acids can easily be further sulfonated in t h e form of their sodium or potassium salts; whereas, if t h e free acid is used, t h e introduction of more sulfonic acid groups becomes extremely difficult, as, for example, in t h e production of b e n z e n e - ~ , gj-trisulfonic , acid4 from t h e salts of benzene disulfonic acid. I n all of these cases, t h e large amount of t h e alkali salts used makes it almost impossible t o decide whether t h e action is catalytic, or caused by t h e greatly increased boiling point of t h e sulfuric acid-alkali sulfate mixture used. Other substances recommended as accelerating catalysts are vanadium6 in t h e sulfonation of anthraquinone, and iodine6 in t h e sulfonation of benzene. Compounds of mercury, aluminium, iron, lead, arsenic, bismuth, cadmium, and manganese7 have also been studied from t h e standpoint of their effect upon t h e position in t h e molecule taken b y the entering sulfonic acid group. EXPERIMENTAL DETAILS

I n t h e present work some of t h e compounds mentioned above have been studied t o ascertain whether they exert any accelerating (catalytic) effect on t h e sulfonation of benzene, and all so far examined have shown some catalytic action. These substances are copper sulfate, mercuric sulfate, vanadium pentoxide, sodium sulfate, chromic acid, potassium sulfate, lithium sulfate, and mixtures of sodium sulfate an& vanadium pentoxide. I n every case t h e substance was dissolved in 7 0 per cent sulfuric acid, thus insuring a constant concentration of t h e catalyst in t h e reaction tower. The concentration of catalyst is expressed as t h e percentage of t h e characteristic element, although in making t h e solutions t h e above-mentioned compounds were actually added t o t h e sulfuric acid. For example, 0.1 per cent copper means t h a t t h e amount of copper sulfate used was chemically equivalent t o t h a t weight of copper which was 0.1 per cent of t h e weight of t h e sulfuric acid. I n each case t h e experiment was carried on for from a n hour t o an hour and a half, after which time t h e products of t h e reaction were discarded, a t t h e same time “cutting in” with weighed quantities of acid and benzene. The experiment was considered as starting 1 Girard, Bull. soc. chim., 26 (1876), 333; Miihlhauser, Dinglev’s polytech. 1,.263 (1887), 154. 2 Lambert, D. R. P. 113,784 (1899); Kendall, U. S. Patent 1,217,462

(191 7). 8 Jackson and Wing, Am. Chem. J., 9 (1887), 325. 4 Jackson and Wing, LOC. cit.; Behrend and Murtelsmann, Ann., 378 (1911), 352. 6 Thummber, D. R. P. 214,156 (1909). 5 Hinemann, Brit, Patent 12,260 (1915). 7 Iljinsky, Ber., 36 (1903), 4194; Schmidt, Ibid., 37 (1904), 66; Dunschmann, Ibid., 37 (1904), 331; Holdermann, Ibid., 39 (1906), 1250; Dimrotb and Schmaedel, Ibid., 40 (1907), 2411; Behrend and Mertelsmann, LOG. c i t . ; Mohrmann, Ann., 410 (1915), 373.