used i n t,hese tests. The first solution in 0.3 N KCI buffer gave S = 7.92 with a typical sharp boundary. Another aliquot in 0.05 Af MgClZ buffer was characterized , b y S = 9.48 with a broader and lower boundary, A third solution made up in 0.05 M MgClz buffer, which stood for the same length of time required to mR.ke the previoiis run, was then adjusted t o 0.05 AT ATgClz 0.16 N KCI 0.01 A4 huffer and found to have S = 8.51 with an intermediate sharpness. Finally the solution in 0.05 M MgClz h f f e r was dinlyzcd against 0.3 N KC1 buffer overnight and the following day gave an S value of 7.98 which is similar to the original value in 0.3 N MCl ( 8 = 7.92) and the boundary was of similar sharp appearance. The results on the mouse lymphoma preparation thus show the same qualitative effects as the calf thymus preparation. Discussion According to the Tolman-Tiselius theory4 of the charge effects, the primary charge effect,is eliminated on using salts of sufficient,conductivity such as 0.3 N KC1 or 0.05 M MgC12. The secondary charge effect is caused by differences in sedimentation velocity of the salt cation and anion. For salts, with lighter cations than anions such as MgC12, the sedimentation rate of a colloid ion would be slightly diminished. Since tjhere is actually an increase in the nucleatJevelocity in MgC12, this must be attributable to causes other than these charge effects. The decrease in sharpness of the DNA boundaries in MgCla solutions as compared tlo ICC1 is a re-
+
+
+
+
+
+
+
(41 T. Svedberg and K. 0. Peterson, in “The Ultraocntrifiige.” Oxford University Press. 1940.
siilt of R stndler change i n t)he dependence of sediincntat,ion on concentrat,ion (see Introduckn). The similarity in sedimentation values a t infinite dilution for DNA in MgC12 and KCI indicates that the free particles of DNA have the same diameter in both solvents but no conclusions can be drawn concerning small differences in length or hetiding of the flexible rods. If t8heultimate explanat.ion of differencns in salt effect is on a morphologic rat,her than nn an electrical basis, these results would be coiisistent, wit8ha short,ening of t,he DNA part,icle in MgCI, solutions. Limited observatJionss on light sc,attering at, higher salt strengths than those used here indicated that the length of infinitely dilute DNA is the same in magnesium and IW1 solutions. On the other hand, Kat26 found a shortening of the length in HgClz solutions. The reversal of the magnesium effect by the addition of KC1 to DNA solutions at finite concentrat’ionfi indicates that Mg++ ion and K + ion are in competition for sites on t,he DNA, probably a t the P-0 positions. from experiments on the relative The binding of Mg++ and Na+ indicates that a t low salt concentrations Mg++ binds t o DNA more strongly than does Na+, but there is no direct evidence as yet indicating that the DNA particle has a smaller charge in the presence of hrge amounts of Mg++ than in Na+ or K+. (5) ,J. W. Rowon, Biochim. Eiophya. Acln, 10, 301 (1952). Kats. J . Am. CAern. h e . , 94, 2238 (1952). (7) J. Shack, R. .T. Jenkins Rnd J. 111. Thompaett, J. E M . CAsm., aoa, 373 (1952);198, a~ (1952). (81 J. M . Crecth and D. 0. Jordan, J . Cham. Soc., 1400 (1040). (0) L. F. Cavalieri, J. Am. Chcm. Soc., 72, 1242 (19.92). (6)
THE WATER-CATALYZED OXIDATION OF CARBON MONOXIDE BY OXYGEN AT HIGH TEMPERATURE BY C. P. FENIMORE AND G. W. JONES Reaearch Laboratory, General Electric Co., Schenecladv, N . Y . Recrived December 19. 1966
By sampling burnt gases from leiin flat hydrocarbon flame8 at one :ctmog here pressure the oxidation rate in the presence of ample water tbt 1700-2000’K.is determined to be - l/(02)(dln(C0)/cf) = 1.2 x i o 0 ~ - ~ ‘ , O ” ‘ R T ( ~ O ’ ~ . ” . ) - -sec.-l. I In the burnt, gas from carbon monoxide flames, containing very lit,tle wat8er, -dln(CO)/di is independent of oxygen and roughly proportional to water. The slower ratc of comparatively dry carbon monoxide flames is raised toward the vnliie appropriate to hydrocarbon flames by adding hydrogen t o the cwhon monoxide. A partial mechanism is suggested which is consifltcnt with these resrilt,s.
Introduction In principlc, wnt,er-cooled poroiw burners’ offer n. simple method of st,udying ccrtain fast, rcsct,ions at, high t,rmpcrskirrs. The brirncrs produre st!eady flnnics which are flal. unless t,hc normnl hiirning veloait,.v is excwded. The t,emperatturc of t,he burnt gafi caai bo varied sevcra.1hrundrerl rlegrecs by varying the supply of reactants to the hurncr. If the burnt gas, downstream of the flat Iiiminous zone, maintains a reasonably consta,nt, tcmperst,ure for a distance of 1 cm. or more, and if some re(1) J. P. Botha and D;B. spatding, Proc. Roy. Soc. (London), A226, 71 (1954).
action is stJill occurring in this region, one might follow it, by prohe sampling. Thk rnport will discuss rnrssureine~it~ of the clean iip of osrhon monoxide in burnt gases from lean flames. Thc rcaction st’udied is tlhe wstercatalyzed oxidst.ioii of carbon monoxide hy oxygen. A succeeding papor reports the application of the same mct’hod t,o the decomposition of nitric oxide. Experimental Two different hurncrs were used in this work. One thick possessed a porous burner surface, made of */32-in~h sintered bronze, of 11.09 cm.* area. The surface was cooled by a water coil pushed against the upstream side.
C.P. FENJMORE A N D G.W.,JONES
652
A cmtrnl tube, also pushed against thr ripstrcam side, covered 1.9% of the entire area of the burnar surface. This ceiitral tube was fed separatcly from the rcmnindcr of the burner with 1.9% of tho t o l d reactant flow. Sodium chloride dust could be supplied to the central tube when desired., and burnt gas temperatures determined by the sodium line reversal method. For acetylene flames, cooling was insufficient in the burner 'ust described, and we used a burner obtained from W. E. kaskan, of this Laboratory. The burner had a surface area of 22.3 cm.a. It was made of a half-inch thick layer of sintered copper shot with a cooling coil immersed in the layer. Burnt gas tein erlttures for thiH burner for acctylene f l m e s were suppliecf by Kaskan's rncasurement,s mnde with quartz roated thermocouples.* The burnt gas was sampled through small rincoolrd quartz probes. The distance bctwcen probc tip and burner surface was varied by racking the burner, niouiited on a micro-manipulator, up or down. The uestioii must be considered, does the presence of the proto invdiclate our measuremonts of the reaction rute? A t the higher tempcrntures, the probe slowly closed up and it was sonietimcs necessary to renew the tip. But this did not change the slopos of our curves within experimental error, though it might slightly displace the entire curve of logarithm of carbon monoxide RS. distance. The dis lacement of the curves was presumably due to some cooing of the gas upstream of the probe tip, different for different size robes. Sinoe different probes gave the same slope of In(80) us. distance, we concluded that the reaction within this cooler region was a negligible contribution to the total reaction measured. That is, when the probe was moved out a distance, AX, the burnt gas flowing to it enjoyed a greater time, VAX, to react at the tempcraturo maasured in the absence of the probe ( V streaming velocity of the burnt gas). A second question arises-is the hot burnt gas unaffected by ita mode of preparation? Or, for example, might an inordinate concentration of radicals from the flame reaction zone carry over into the burnt gas? Since our results are inde endent of the kind of fuel burnt, we believe the answer to t i s question is no. Finally, different sampling positions were converted to different reaction times by assuming that the gas flow did not diverge and that the velocity of the burnt grLs was given by multiplyin the approach velocity of the reart:tnta by the product ofvolume change due to reaction and the tempersture ratio. Some support for this is offered by the fact hat two different size burners were used and gave conclistent results. The gas samples drawn through the quart8 probes were collected at a pressure low enough (cO.2 atm.) to ensure critical flow throiigh the probe. In this way the sample spent the minimum timo possible in the probe tip. Water in the sample was absorbed on magnesium perchlorate, carbon dioxide on Ascarite. The residue wan passed through a liquid nitrogen trap, compressed to one atmosphere in a Toepler pump, pmsed over hot copper oxide, and the water and carbon dioxide so formed subsequently absorbed. Sampling times were up to one hour for burnt gases containing very little carbon monoxide. The absence of hydrocarbons in the sample was proven mass s ectroscopically Mass spectromopic measurements also ctecked the relative flow measurements by determining oxy en. Air and gas flows were measured with calibratef critical flow orifice meters. The gases were Matheson C.P. methane, ethane, ethylene and Prest-o-lite acetylene. Acetone was removed from acetylene with charcoltl traps.
VOl. 61
with Friedman and C y p h e r ~ 'rcsult ~ on a 2.1t5% uncooled propane flame burning at 46 mm. pressure. The amount of hydrogen is generally considerably less than carbon monoxide and does not change much with distance. For all flames examined, the hydrogen found in the burnt gas corresatm. ponded to PH,= 4 to 6 X Figure 1 shows the residual carbon monoxide,for a number of acetylene flames. If the probe is placed too close to the luminous zone of the flame, carbon monoxide increases to a value greater than an extrapolation of the curves. This may result from disturbing the zone of vigorous oxidation. Curves similar to those of Fig. 1 were obtained for other fuels. From the experimental data, we derive - d In(CO)/dz. Since the disappearance of carbon monoxide by reaction is opposed by its accumulation through diffusion down the concentration gradient thus formed, the measured slopes must be converted to - d ln(CO)/df by use of the expression given by Friedman and Cyphers.
- d l ndt( C 0 ) _ ~40[ ( - ~ dV l n ( dxC O )+ 1)' - 11 where V = linear velocity of the burnt gas, D = diffusion coefficient of carbon monoxide in the burnt gas. We took D = 3.5, 4.3, 5.1, 0.0 cm.a/ sec. a t 1600, 1800, 2000 and 2200"K.,respeotively . When the resulting values of - d ln(CO)/df are examined, it is obvious that they vary with oxygen concentration in the burnt gas unless the concentration of water is very small. 8ince the conmmption of oxygen is small over the region sampled, we consider it constant and equal to the ox gen in excess over that required to burn the fue to carbon dioxide and water. I n Fig. 2 we plot both -d In(CO)/dt and - [l/(Oa)] (d ln(CO)/dt) against
P
0.10
r
.
Results The carbon monoxide in burnt gases from lean flames (containing 1.1 times the stoichiometric amount of air or more) may amount to several per cent. of the total carbon fed in the fuel, far more than the equilibrium quantity. As one samples further downstream, the logarithm of the carbon monoxide content is found to decrease linearly with distance. This first-order decrease agrees (2)
\6.54%,
0.001
Iem.
DISTANCE OF PROBE FROM BURNER SURFACE.
Fig. 1.-Clean u of CO in burnt a s s from various GH,, air flames. % CI& in reactante an! burnt gas temperature noted on each curve.
the reciprocal of absolute temperature. We conclude that unless t.he concentrtltion of water is very small
W. E. Ksstan, Sixth Symposium on Combustion, New Haven,
Augurt, 1958.
0.5
1076.
(3)
B. Friedman and J. A. Cyphee, J . Chrm. Phyr., P1, 1875 (1965).
?
WATElt-(,!ATAI~YZlCD OXIDATION OF
hlay, 1057
If the concentration of wat,cr is vcry sinall, the rate does not depend on oxygcri, 1,ut rather appears to depend on the water concentration in the burnt RRS. Roughly, at leest when the water concentration is vcry small in tho burnt gas. The data are collected in Table I. 1)ATA ON
TABLE I co CLEAN UP IN BURNTFLAMEGASES
co IIY OXYGEN
SXld
653
I
Id 1 -
dt
T
Fuel
CaHp
CtI4 CZH4
CJia
CO (0.747,
%
Fiiol
5.88 6.18 (3.54 6.90 7.20 7.30 8.01
8.67 5.41 5.80 3.00 3.24 3.24 3.63 3.63 26.6 27.0
burnt Ran.
OK.
1885 1870 1675 1700 1800 1728 1005 1943 1063 2006 1800 1780 1848 1830 2020 2061 1903
In(C0) - 1 d In(C0) - d In(C0) - d___ dr dl dl 01
2.70 2.48 3.00 1.45 1.16 0.91 3.75 1.82 2.31 0.99 3.86 3.96 4.20 2.00 1.40 0.26 0.24
700 500 270 186 140 79 540 240 600 229 533 386 640 188 314 24 20
2 . 1 x 108 1.8 1.1 1.2 1.4 1.0 2.0 2.3 2.7 1.5 1.2 2.1 1.4 2.5 0.17 0.16
(1)
is generally accepted as an important step for the oxidation of carbon monoxide in systems containing hydrogen or water. According to Avromenko and Lorentso,4 its activation energy is El = 7 kcal. The hydrogen atoms from eq. 1 would certainly react, in part at least, with oxygen
+0
100
f
Discussion Figure 3 shows that -d in(CO)/dl varies dircctly with oxygen concentration when ample water is present. But when very little water is prcsent, as in the CO mixture^, -d ln(CO)/dt varies roughly with the concentration of water and does not depend on oxygen. These observations strongly suggest that the oxidation is catalyzed by water. A ossible mechanism will now be offered. $he reaction
OH
-9
XIO'.
Fig. 2.-Temperatrire dependence of CO oxidation. Bame data plotted in two ways.
0.43 30 0.65 28.6 1009 0.40 60 0.24 2003 (1.670/, 2 5 . 2 0.38 53 0.36 2170 Hz) 2 6 . 3 1 .so 240 1.4 CO" 25.5 1763 (46% I I z ) 0To tho mixture of 25.5% fuel in air, N1 WRR d d c d = 1.9 X CO 80 a8 to ive burnt gaN Aimilar to that obtairied from hydrocarbon kels.
+ Oz+
IYOROCARBONS, w1 CO WITH lUCH He
IO
CO
H
500
2.9
Hz)
OH+CO+COs+H
IO
(2)
and Lewis and Von Elbe6 have proposed the value, E2 = 17 kcal. (4) L. Avromenko and Lorontso, Zhur. F i r . K h i m . , Z4, 207 (IU50);
C.A . , 44, 6245 (1950).. ( 5 ) B. Lewia and 0.von Elbe. "Combustion, Flames and Explosions i n Umes," Acadernio Press, New York. N. Y.,1851.
If eq. 2 is a brmching reaction in our system, that is, if the 0 atom continue8 the reaction chain, and if the radicals reach a stehdy Concentration, then eq. 2 must be opposed by Home chain terminabing reaction. We postulate as the terminatH + OH + M HrO + M (3) ing step, whence the steady hydroxyl concentration can bo obtained by equating the rate of branching to terminating reactions, and
I n this expression, M is any inert molcculo which absorbs part, of the energy released in reaction 3. The experted activation energy is 24 kcal. E,. Since ES should be very small, our experimental value (24 f 5 ) is consistent with the suggest,ed mechqnism. The mechanism requires that IC vary inversely with pressure, The ratio of Friedman and Cyphers' single determination a t 46 mm. P , 1605'K., t o our extrapolated result a t 1 atmosphere is about 8, while the inverse ratio of the pressures is 17. Thus, the variation of k with pressure is qualitatively correct, and one can imaginc factors which would surely decrease the expected ratio of rates in a more complete reaction mechanism; for example, the loss of radicals by diffusion would be expected to be more serious a t low pressures. I n mixtures poor in hvdrogen or water, reactions 1-3 should still occur, but the assumptiorl that rcaction 2 is nlwnys a branching reaction may be false, the 0 atom may not always regenerate OH in the absence of ample water. In that case, the steady hydroxyl concentration might very well
C.P. PENIMORE A N D G. W. JONES
654
Vol. 61
become independent of oxygen and proportiorid nitrogen is added to give a burnt gas with the same to water, as is suggested by our results for carbon nitrogen concentration as was obtained from hydromonoxide flames containing 0.74 or 1.67% hydro- carbon flames. Then the rate for the carbon gen. On adding 20 or 4001, hydrogim t o carbon monoxide flame becomes the same as the rate obmonoxide, the rate of clean up of carbon monoxide tained from hydrocarbon flames. The requirement in the buriit gas is raised toward the value ap- that nitro en be added may mean that carbon propriate to hydrocarbon flames. The rat,e is still dioxide a n /or water are more efficient third bodies low, however, (by about 40%) rinlesR enough than is nitrogen.
d
NITRIC OXIDE DECOMPOSITION AT 2"20-2400 OK. BY C. P. FENIMORE AND G. W. JONES Reaearch Laboratory, Ueneral Electric Co., Scheneciadu, N. Y. Received December 13, 1068
Flat premixed flames of nitrous oxide and fuel are burnt at controlled temperatures on B water-cooled porous burner. The nitrous oxide decom oms entirely in the flame, pertly to nitric oxide, end the subsequent decay of nitric oxide in the burnt gas downstream o?the flame is observed b robe sampling. The deca is second order in nitric oxide, impeded by The range of variablee oxygen and ade uetely described by [(Og]'hd(l/J8)/dt] 2 X 1019c-e8~~~R~~olell.)-'he/i.)-1/~ sec,-l. covered is Os= 70-8 10-7 molee/l. (NO)/@%) 13 0.6 2,000. We agree fairly well with Zeldovich's experimental results obtained by B different technlque. gowever, hie proposed mechanism must be modified in part at least.
--
-
Introduction
Second, (02)'/' d (l/NO)/dt should decrease with increasing values of the ratio, (YO)/(Od. Zeldovich never found this to happen u to (NO)/ (Oa) ratios of about one. Consequent y, his data give no real indication that the nitrogen etom concentration is maintained by reaction 1 and its re1 verse. It is obvious that, granting his mechaniam, 0 NO p N Oa he measured only reaction 2, and that the concen-1 tration of nitrogen stoms was determined by the 2 equilibrium with nitric oxide and oxygen. N NO,'Nz 0'8 At far lower temperatures, 1400-1600"K., Kauf-a man and Kelso' showed that the decomposition of and supposing that oxygen atoms were in equilib- nitric oxide is strictly second order and independent rium with oxygen molecules, he derived an ex- of oxygen with an activation energy of 63.8 kcal. pression eauivalent to I. Thcy gave reasons for believing this low temperature reaction to be the direct decomposition 2x0 -t N, 02, involving no intermediates, and showed that many previously published data agree with their determination, so the low temperature where (NO,,,) is the equilibrium concentration of gas phase mechanism scems well estsblished. Because of its smaller temperature de endence, nitric oxide and K = kl(0)/k-l(Oa)'/t = the equilibthe low tymperature decomposition coul not conrium constant for the reaction tribute appreciably to the reaction in Zeldovich's NO N $- 1/20~,AH 91 kcal. temperature range. But Vetters found a composite Zeldovich set the denominator of I equal to one reaction at, 1500-1900°K. since (NO)/(Oa) was generally small, and obtained - dt = k, (NO)' + k a ( N O ) ( O ~ ) lapproximately /~ 2Kk2 6 x 101le-@J~~+IOJ")O'RT (rnole)/l.)-% sec.-1 Zeldovichl carried out an ingenious, non-isothermal study of the nitrogen oxygen reactioii a t 2000-2900°K. Assuming that the high temperature reactions were
+
+
+
+
f
+
-
J
-
D.
Two comments can be made about this work. First,, the higher dissociation energy of nitrogen, 325 kcaI./mole, accepted since Zeldovich published, requireA that K contribute 91 kcal. to the activation energy of Kk2. This is not a major matter perhaps, for he recognized that his technique would give too low an activation energy. He allowed 4 kcal. correction, but there is room for R larger correction within the assigned error, and one can read his result as indicating an activation energy of 91-96 kcol. if the mechanism is retained. (1) J . Zeldovioh, A& Phyricoahim. U R M ,P1, 577 (1848). (la) Zeldovioh called his sohems e obaln resotion, and 80 it is aa written. But hisaubaequent assumption that oxygen is in equilibrlurn with respect to dirrnoattion destroys the chain oharaoter. Reaotion 2 no longer creates an aotive oe&r to carry on tlm deoomporition. ainan the iiumber or oxygw utoitis tn
iilwltatigrtl
wlwthrr 2 owura or uat
and Ihufman and Kelson rccomputcd his data, assuming t h a t the term in ks was due to I. Then kz (NO)/k-,(Oa) >> 1 necessarily, and they obtaincd 2Kk-1 = 4.6 x 1012 e-loltm'RT (mole/l.)%" eec.-'
A comparison of Vetter s recomputed remit with Zeldovich shows that kslk-1 must assume a value of order unity R t 1800"K.,but this is inconsistmt with the magnitude assigned to Ica/k-I in recomputirig Vetter's work. Without further measurements it is uncertain in a given situation how the high temperatii w tletwmposition will be affected by oxygen. (2) F. ICntlftiinu and 7. 1MRo. J . Clem. Pbfin., 93, 1709 (1954). (.I) I< V r L h c, %. Ilekbwbem., 68, :+ob9 (1949).
C
