September 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
1719
all batches of the liquors studied; further information Sugar Solvents Production is needed on the factors affeck Fermented Yield on Distribution, 70 Rate of ing fermentation and on methInoculation, G./100 % of Total, sugar ferButyl Ethyl ods t o guarantee consistently % ml. total g./liter mented, % alcohol Acetone alcohol Iron Added good fermentation of the hyReduced iron 5 4.48 89.1 13.8 30.8 61.4 32.5 6.1 5 4.57 80.9 13.2 30.9 62.5 31.7 5.8 drolysis liquors. Because of 10 4.45 88.5 13.8 30.9 61.0 30.8 8.2 10 4.54 90.3 14.2 31.3 61.0 32.3 6.6 frequent difficulties in fermenCommercial powder 5 4.38 87.1 13.7 31.2 61.1 31.6 7.3 tation, the 10% inoculum 5 4.49 89.3 13.8 30.7 60.3 31.6 8.1 10 4.49 89.3 13.3 30.4 63.6 31.4 5.0 series was included, but use 10 4.58 91.1 13.9 30.4 63.0 32.1 4.9 of a 10% inoculum offered Original sugar Concentration 5.03%; concentration of iron powder, 0.5%. little advantage over use of the regular inoculation level of 5%. On the average, the solvent yield was 30.6% of the sugar ferBecause reduced iron was found t o be effective in supporting mented; this compares favorably with yields obtained in the good butyl fermentation, a number of other iron powders were fermentation of glucose and molasses media. The distribution of investigated. Of the commercial iron powders studied, one, a solvents, which averaged 61.7% butyl alcohol, 31.8% acetone, by-product in the production of chemical iron from cast iron and 6.5% ethyl alcohol, also is comparable t o distributions obborings, was found to be almost as good as the more expensive tained when glucose and molasses media are fermented. reduced iron. It was found that iron powders produced by grinding iron filings in a ball mill t o pass the 325-mesh screen LITERATURE CITED also were effective substitutes for reduced iron. (1) Christensen, L. M., and Fulmer, E. I., IND. ENG.CHEM.,ANAL. ED.,7, 180-1 (1935). PRODUCTS FROM B U T Y L FERiMENTATION OF X Y L O S E SACCHARIFICATION LIQUOR (2) Dunning, J. W., and Lathrop, E. C., IND. ENG.CHEM.,37, 24-9 (1945). An experiment in which fermentations of xylose saccharifica(3) Goodwin, L. I?., J.Am. Chem. Soc., 4 2 , 3 9 4 5 (1920). (4) Hall, I. C., J. Bact., 17, 255-301 (1929). tion liquor were conducted in the presence of two different iron (5) Sjolander, N. O., Langlykke, A. F., and Peterson, W. H., IND. samples is shown in Table VII. The standard medium was preEN@. CHEM..30.1251-5 (1938). pared in a series of flasks and t o each flask was added 0.5% of Somogyi,M., J . Bid. Chem, 160; 61-8 (1945). Speakman, H. B., Ibid., 70, 135-50 (1926). iron powder. One set contained reduced iron and the other the Underkofler,L. A., Fulmer, E.I., and Rayman, M. M., IXD. ENG. commercial iron powder. I n one series of flasks the rate of inCHEM.,29, 1290-2 (1937). oculation was 5%, whereas in the other a 10% inoculum was used. Wiley, A. J., Johnson, M. J., McCoy, E., and Peterson, W. H., After fermentation the flasks were analyzed for residual sugars Ibid., 33, 606-10 (1941). and for solvents. REOEIVED June 19, 1947. Presented before the Division of Agricultural end The fermentation of the xylose saccharification liquors proFood Chemistrv a t the 111th Meetine: of the AMIERICAN CEEMICAL SocImTT. ceeded well. However, uniform success TV&S not obtained with Atlantic City, N. J.
PRODUCTION IN FERMENTATION OF XYLOSBHYDROLYZATES~ TABLE VII. SOLVENTS
Q
'
Fixation of Atmospheric Nitrogen in a Gas Heated Furnace NATHAN GILBERT1 AND FARRINGTON DANIELS University of Wisconsin, Madison, Wis.
and fertilizers. Now, however, pilot plant experiments have I T R I C oxide is produced by heating air above 2000' C. shown t h a t it is possible t o produce nitric oxide from air in P, and chilling it very quickly. In practice these operations simple furnace constructed of magnesia refractories and heated can be effected by blowing air through a n electric arc; but the old with gas under conditions that suggest interesting practical aparc process for the fixation of nitrogen was rendered obsolete plications. The present research program was started in 1939 at Over 30 years ago by the Haber process for ammonia. I n spite the University of Wisconsin a t the suggestion of Frederick G. of the high-pressure equipment and the elaborate methods required for the production of purified nitrogen and hydrogen, no other procIt has been found possible to raise the temperature of ordinary air to above 2100' C. with ess up t o the present time gas, heating. The apparatus used for attaining these high temperatures consists of two has been able to compete beds of magnesium oxide pebbles in which there is excellent heat exchange with the gases successfully with the passing through them. Air is preheated by passing through the first pebble bed, mixed Haber process for the with fuel gas, and then passed through the second pebble bed, which removes most of production of fixed nithe heat. The flow of air is then reversed and the second bed becomes the preheating bed trogen in the form of and the first bed is used to conserve the heat from the exit gases. Calculations and experinitric acid, explosives, ments show that it is possible to obtain nitric oxide from air in a furnace of this type. There is adequate time for the formation of nitric oxide and the exit gases are cooled in 1 Present address, Chemithe pebble bed so rapidly that the nitric oxide is chilled before extensive decomposition can cal Engineering Department, occur. Nitric oxide concentrations greater than 1% have been obtained. TVA, Wilson Dam, Ala.
INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
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CONCENTRATIONS OF NITRIC OXIDE IN TABLEI. EQUILIBRIUM AIR^ Temperature,
K.
KP I Atmos. x 104
02
10%02
8%
02
0.22 0.31 0.31 0.43 0.40 0.57 0.53 6.86 0.74 0.94 0.67 11 .oo 1.16 16.90 0.82 1.42 25.10 1.00 2.00 2.40 1.20 1.70 36.00 1.42 2.84 2.01 50.30 3.32 2.34 1.66 68.70 Nitrogen concentration assumed t o remain constant and equal t o SO'%. 1.21 2.31 4.08
Q
Volume Per Cent NO 20%
0.44 0.61 0.81 1.05 1.33 1.64
Cottrell who, together with his associate, Pcrcy €3. Royster, had developed an efficient and economical method for the regenerative heating and cooling of gases (1, 9) which utilizes a pair of pebble beds of refractory materials. The present article recording the work through August 1942, was delayed for reasons of security. [Some details regarding part of this work are given in ( 4 ) ] . It will be follo\T-edby others describing operations on a larger scale together with additional material on different types of furnaces, refractories, and methods for recovering the nitrogen oxides. Although approximately 1700' C. is the maximum temperature that can be realized from burning gas in a stream of ordinary air, the higher temperatures required for the practical fixation of nitrogen can be readily achieved by burning the fuel with preheated air. Thc pebble-bed furnace with its rapid heat exchange between gases and refractory pebbles accomplishes three objectives in a very simple manner: By passing the air through the preheating bed bcforc it mixes with the fuel gas it is easily possible t o obtain temperatures of 2100' C. and higher. The second pebble bed cools the nitric oxide with extreme rapidity t o temperatures of thermal "stability" below 1800O C. before appreciable dissociation takes place. The second pebble bed stores the heat for heating the incoming air when the flow of gases through the furnace is reversed. .Ilthough all the air is heated above 2000 ' C. in the combustion zone of the furnace, it emerges from the furnace at temperatures of only 100" t o 300" C. and thus the cost of heating is greatly reduced. THEORETICAL CALCULATIONS
For the reaction
Nz
+ 02 S 2x0
the equilibrium constant
has been calculated accurately from spectroscopic data ( 3 ) . The calculated values are more rcliable than the experimental measurements of Kernst and his associates, with which they are in fair agreement. The concentration of nitric oxide in equilibrium with nitrogen and oxygen increases with the temperature and with the oxygen concentration as shown in Table I. Accurate data are not available on the rates of formation and decomposition of nitric oxide. T h e specific reaction rates for the decomposition of nitric oxide, 2 N 0 + Kz 0 2 , were estimated with the help of Equation 3
Vol. 40, No. 9
w.,
tances of the normal molecules, 1.096 A,, 1.208 and 1.1508. for t h e nitrogen, oxygen, and nitric oxide molecules, respectively, were assumed to be stretched by 207, in the activated complex. Vibration frequencies for the five vibrational degrees of freedom of the activated complex were guessed to be 100, 450, 450, 1200, and 1200 cm-l.) If the concentrations of reacting molecules are expressed in moles per liter, this estimated frequency becomes approximately 2 X 109, which is in qualitative agreement with the frequency factors t h a t obtain in many bimolecular ga9 reactions. The activation energy of 50,000 calories was obtained by using the frequency factor of 107, and giving 12 the values reported experimentally by Nernst (8) and Jellinelr (6) in the neighbor hood of 2000' C. and solving for thc activation energy. An estimate of the activation energy was made also by the Hirschfelder rule (5)that in a bimolecular reaction the activation energy is equal t o 28% of the bonds broken. The bond strength of nitric oxide is probably about 123,000 calories, and 0.28 X 2 X 123,000 gives approximately 70,000 calories. By using this value for the activation energy and again using the Jellinek experimental values for k in the neighborhood of 2000" C., a value of 109 is obtained for the frequency factor and the ovei-all equation is: kdecomposlt,on = LO9 e - 7 0 , 0 0 0 ~ E T atmoS.-' see.-' i4 These two equations are entirely different with respect t o activation energy and frequency factor, and yet they give values of k over the temperature range of interest which are near11 the same, as shown in columns 3 and 4 in Table 11. The calculated columns in the latter half of Table I1 were obtained with the help of Equation 3, but, until further experimental data can be obtained no satisfactory choice can be made between Equations 3 and 4. The first seems better as far as the frequency factor is concerned; the second better as far as the activation energy is concerned. Both, however, are estimates subject to seiious error and the experimentally determined rate also may be very inaccurate. It is not satisfactory to obtain the activation energy from a graph of log k plotted against I/l'obtained from Jellinclr's data because the slope appears t o change greatly with the temperature. It is very necessary to obtain new exact experimental data on the kinetics of the decomposition and formation of nitric oxide a t thcsc high temperatures. Attempts to obtain such information with the furnace described here have thus far been unsatisfactory, but i t can be said t h a t the furnace data as far as they can be regarded as significant are not inconsistent with either of these formulas. On three occasions the nitric oxide obtained was considerably greater than the theoretical equilibrium value; this indicated that there were serious experimental difficulties. The most likely explanation is t h a t in these cases the actual temperature at the time of taking the nitric oxide sample was considerably greater than that read at a later time on the optical pyrometer. Another, but less plausible, explanation is that the oxygen concentration happened t o increase considerably (owing t o a gas shut-off) when the nitric oxide sample v a s taken. The data prove that nitric oxide is formed in considerable quantity, but because the different measurements could not a h ays be made simultaneously in these early furnaces, the data cannot be used for quantitative calculations. Better data will be presented in a subsequent contribution. The specific rate of formation
+
dpxo kdeoomposition = - - -P 2 N 0 dt
1
= 1x 1 0 7
xe
- 50,000 RT at,mos.-I sec.-1
The frequency factor, 1 X 107, represents a rough estimate based on the theory of absolute reaction ratcs ( 2 ) . (A symmetrical activation complex was assumed. Interatomic dis-
ca.n be calculated from the familiar relation that
(3)
= kiormation kdeoomposition
The time required t o form or decompose a given quantity of nitric oxide in air can be calculated from the specific rate constants, but the situation is complicated by the fact t h a t under
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
September 1948
1721
-
able for its recovery by quick chilling. At the lower temperatures the rate of formaTime for tion of nitric oxide is the Time to Form 90% Decompositlon kform, kdeoompos, ~ ~ d e e o m D a a . Time to Form 50% limiting factor, whereas a t the of Equlllbrlum of Equilibrium 2% NO 3% N O Atmos. -1 Atmos. -1 Atmos. -1 T ~ ~ ~see. . -I, sea. - I see,- 1 -Concentration, See. Concentration. See. t o I % , to 2,75%, higher temperatures the rate 20% Oz 10% Oz see. seo. (Eq. 4) 20% 0 3 10% 02 Iionof nitric oxide. Moreover, cracks developed in the lining which forced shutdowns of this furnace. Figure 2 ehows in cross section one of the two ident,ical furnaces that comprised a larger and a better insulated furnace pair. The assembly operated during the, summer of 1942 is also illustra~tedin Figure 3. Each furnace contained a bed, 18 inches in diameter and approximately 18 inches deep, of -6- +10-mesh periclase pebbles having approximately 40% voids and an over-all densit,y of 110 pounds per cubic foot. A Crowell blower passed up to 150 cubic feet of air per minute through the furnace a t a total niaxiniuin pressure drop of 3 to 4 pounds per square inch. The gas vas forced in under the same pressure a t a rate of up to 30 cubic feet per minute. Experiments mere continued up t o 48 hours, but again refractory failures occurred a t the interface betrveen the magnesia insulation and the insulating brick, usually where t,he horizontal crossover joined the dome. This structural weakness was eliminat,ed in furnaces of a different design t o be described in a later communication. The temperatures were measured through right-angled periscopes with a calibrated optical pyrometer sighted on the top of the pebble beds, as can be seen in Figure 3. The flon. of air and gas, the pressure drop through the furnace, and the temperature of the exit gases were measured with conventional apparatus and recorded as a function of the time. The exit gas wa6 analyzcd for the oxygen content and the concentrations of nitrogen dioxide were measured by titration and with a calibrated photocell. Some of the results are summarized in Table ?ST. The total flow of air and combustion products ranged from about 68 to 93 cubic feet (S.T.P.) per minute per square foot of bed. The temperature varied during any given cycIe and only t'he niaxinium temperahres are recorded here. DISCUSSION
The experimental data prove that temperatures of 2100" C. and above can be obtained by burning gas with preheated air in Royster pebble bed furnace? of the t,ype described here, and that it is possible to fix atmospheric nitrogen by this means.
INDUSTRIAL AND ENGINEERING CHEMISTRY
September 1948
TABLE IV. YIELDSOF NITRICOXIDE Maximum Cycle Temperature. C.
Air Flow, Cu. ,Feet/ Min. at S.T.P.
1900 1960 1980 2020
100 145 145 145 100 140
2060
2050
148 148 148 148 148 148 148 148 148 147 148 148 148 148 148 1980 2020
148 148
2020
120 120 120
2020 2030 2030 2060 2100
120
120 120
Gas Flow, 3'% Oxygen Cu., Feet/ in Exit Min. a t N.T.P. Gas Experiment 1
6.7 6.7 6.0 6.0 5.0 3.0 20 Experiment 2 16 1.6 10 6.9 10 6.9 10 6.9 6.9 10 5.6 16 6.7 13 7.1 13 6.9 16 5.0 15 10 7 0 13 2.6 13 3.4 13 6.0 1.9 15 Experiment 3 20 3.8 20 1.8 Experiment 4 12 5.6 12 7.1 12 5.0 10 6.5 15 2.6 16 3.4 20
20 20 20 20
To, Calculated Nitric % Nitric Oxide a t Oxide in Exit Gas Equilibrium 0.21 0.55
0.44 0.34 0.42 0.55
0.76 0.87 0.86 1 .oo 0.99 0.70
0.24 0.39 0.36 0.46 0.34 0.55 0.45 0.61 1.36 0.34 0.43 0.55 0.82 1.36 0.39
0.45 0.93 0.98 0.98 0.99 0.90
0.40 0.36
0.69 0.50
0.55 0.61 0.46 1.35 0.55 0.86
0.90 1.02 0.87 0.99 0.67 0.83
1 .oo
1.03 1.01 1.00 1.07 0.72 0.84 1.12 0.66
T h e fact t h a t nitric oxide is produced shows t h a t the conditions are such as t o give the air sufficient time at the high temperatures t o approach equilibrium and t o provide sufficiently rapid cooling t o permit recovery of the nitric oxide formed. An experiment was performed t o prove t h a t the pebble bed chilling is effective. A water-cooled copper capillary tube was introduced into t h e combustion zone and samples were withdrawn simultaneously with the withdrawal of the exit gases after they had passed through the second pebble bed. Analyses showed t h a t the nitric oxide content was practically the same and t h a t the chilling by t h e pebble bed t o a temperature of thermal stability (1500" C.) was as effective as the chilling in a small water-cooled pipe. When the furnace is operating at 2100" C. and the exit temperature of the gases is 300" C. there is a temperature difference of 1800" between t h e top and bottom of t h e cooling bed, which are 18 inches apart. If the temperature gradient were linear there would be a temperature drop of 100O per inch.
For the case when the gas is passing through the furnace at the rate of 90 cubic feet per minute per square foot of bed (measured at 0' and atmospheric pressure) at 2400 OK. (2127" C.) the volume 2400 of the gas is - X 90 or 800 cubic feet per minute or 13.3 cubic 273 feet per second per square foot of bed. The voids are 40%, so t h a t the volume of the free space under 1 square foot of bed is 0.4 cubic foot per foot of bed depth, or 0.033 cubic foot per linear inch per square foot. The 13.3 cubic feet of gas must pass through this inch of distance in a period of or 0.0025 second. If the tem13.3 perature drop over this 1-inch distance was 100 ', the gases were being cooled at the rate of 40,000 C. per second.
0.033
As shown above, chilling a t this rate is adequate t o recover most of the nitric oxide. It is known t h a t the temperature gradient produced by passing a hot gas through a cold pebble bed is not linear, but the calculation given above is probably of the right order of magnitude. Detailed calculations of the temperature pattern were made subsequent t o the work described here and experimental observations ,of the temperature gradient in a packed bed have been made
1723
with thermocouples a t temperatures below 1000O C. These measurements were extended t o higher temperatures and will be described in a later publication. The time at which the gases are at 2400' K. can be estimated from the dimensions of the furnace shown in Figure 2. The reaction space consisting of t h e two open domes and the crossover was about 4 cubic feet. Inasmuch as the gases are passing through this hot part of the furnace at the rate of 20 cubic feet per second, the gases must be at 2400" K. during
4 a or
0.2
second. For the oxygen concentration of about 6% which obtained in a large number of experiments, this time should be sufficient to form over 50% of the equilibrium concentration of nitric oxide if t h e empirical Equation 3 is correct. I n most of the determinations reported in Table I V the nitric oxide conceno t h a t which can be predicted trations are between 50 and 1 0 0 ~ of on the basis of this equation. The chemical kinetics uf the formation and decomposition of nitric oxide at the high temperatures discussed here are in a very unsatisfactory state and accurate experimental measurements in this temperature range are greatly needed. The best estimate of the frequency factor is lo7 atmospheres-1 seconds-1 and the best estimate of the activation energy for the bimolecular reaction, 70,000 calories per mole, is not consistent with the existing experimental measurement of Jellinek in t h e temperature range between 1800 ' and 2200' C. Several different hypotheses may be offered t o explain the apparent discrepancy. The method of calculating the frequency factor is uncertain; the method of estimating the activation energy is very uncertain; the reaction at high temperature may not be bimolecular; the experimental data of Jellinek may be inaccurate; and, finally, the reaction may be complex, involving one or more steps in a sequence of reactions t h a t may include the production of atoms of oxygen or of nitrogen. Future research should be directed along these lines. The research described in this paper has been continued with the objectives of developing more adequate refractories for service in the extremely high range of temperatures required in this process, developing different designs of pebblepaclred furnaces which will be suitable for large scale continuous operation, and developing economically feasible methods for the recovery of oxides of nitrogen, a t the low concentrations resulting from the fixation reaction. ACKNOWLEDGMENT
The authors wish t o acknowledge the financial support given for this work by the Research Committee of the University of Wisconsin and the Wisconsin Alumni Research Foundation, and to acknowledge the inspiration and suggestions offered by Frederick G. Cottrell and Percy H. Royster. The authors are indebted t o the Department of Mining and Metallurgy of the University of W'isconsin for laboratory space and facilities for part of the work. They wish t o acknowledge also the assistance of Frank M. Wolf, who developed a n efficient reversing valve used in later experiments. LITERATURE C I T E D
Cottrell, F. G., U. S. Palent 2,121,733 (June 21, 1938). Eyring, H., J. Chem. Phys., 3,107 (1935). Giauque, W. F., and Clayton, J . O., J. Am. Chem. SOC.,54, 1731 (1932).
Gilbert, Nathan, Ph.D. thesis, University of Wisconsin, June 1942.
Hirschfelder, J. O., J. Chem. Phys., 9, 645 (1941). Jellinek, K., 2. anorg. Chem., 49,229 (1906). Laird, J. S., and Simpson, T. C., J . Am. Chem. Soc., 41, 524 (1919). Nernst, W., Z.anorg. Chem., 49, 213 (1906). Royster, P. E., U. S. Patent 1,940,371(Dec. 19, 1933). RECEIVED J u l y 14, 1947.
