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T H E JOURNAL OF INDUSTRIAL A N D ENGINRERING CHEMISTRY
Jan., 1922
are engaged in the study of nutrition on the fresh and extended lines that, unless we who work elsewhere work very hard, the new science which is developing will. come into the same category.
Presentation of Chandler Medal By George B. Pegram COLUMBIA UNIVZRSITY, NEW YORI, N. Y.
There are certain names that stand for whole periods in the existence of institutions, epitomize epochs of development and accomplishment. No such name a t Columbia stands for more than Chandler. Reaching from the foundation of the School of Mines in 1864 to the present and covering nearly half a century of labor and responsibility in active connection with the development and progress of scientific work a t Columbia, his great personality has built itself into the structure of this University in so intimate a fashion that the keenest analysis could not separate it out. It was, therefore, a most appropriate action for a group of his friends to present to the Trustees of Columbia
University a sum of money constituting the Charles Frederick Chandler Foundation, the income from which is to be used to provide each year a lecture by a n eminent chemist and t o provide a medal t o be presented to the lecturer in public recognition of his achievements in science. The previous lecturers on this Foundation have been I,. H. Baekeland, Sc.D., W F. Hillebrand, Ph.D., and W. R. Whitney, Ph.D. On the recommendation of a University committee, the Trustees of Columbia University have awarded the Chandler Medal for this year to Frederick Gowland Hopkins, F.R.C.P., F.R.S., F.I.C., F.C.S., Fellow of Trinity College, Honorary Fellow of Ernantiel College, Cambridge, Member of the Medical Research Council, and of the Consultative Council to the Minister of Health, Professor of Biological Chemistry, Cambridge University. Professor Hopkins, this medal is presented to you in public recognition of your pioneer and valuable researches in biochemistry, particularly in connection with food accessories, such as vitamines, and your public service on the Medical Research Council and the Consultative Council to the Minister of Health.
ADDRESSES AND CONTRIBUTED ARTICLES Contribution to the Theory of the Water-Gas Process' By S. Kohn ROHM& HAASCo., INC., 40 N. FRONTST., PEILADELPHIA, PENNSYLVANIA
The usual explanation of the interaction between steam and carbon is that at about 600" C. carbon dioxide and hydrogen are the chief products formed, according to the equation
C
+ 2H20 = COz + 2H2
(A)
and that, as the temperature rises, more and more carbon monoxide appears in the resulting gases. Finally, at about 1000°C. and above, carbon monoxide and hydrogen are practically the sole constituents of the gases, which may conceivably be formed according to the equation C
+ HzO = CO + Hz.
c + cog c,2C0," and he uses this third equation for further elucidating the peculiar relations between the volume concentrations of the resulting gases in the water-gas process. Rideala thinks that the following combination of three equations represents the chemistry, of the water-gas process: C Hz0 = CO Hz CO HzO COz HZ c f'COa % 2 c o
+
+
These instances will suffice t o prove that our present conception of the chemistry of the Brocess is open for discussion, and that 1 2
Received August 3, 1921. "Thermodynamik technischer Gasreaktionen," 293. J . SOG.Chcm. Ind., 40 ( I W l ) , 13t.
POSSIBLE REACTIONS OF STBAM AND CARBON
(B)
At temperatures between 600" and 1000" C., both reactions may be considered as taking place simultaneously. The standing of Equations A and B, as an explanation of the chemistry of the water-gas process, is that of a fairly useful hypothesis. We have no proof that the reactions actually proceed in the manner indicated. Furthermore, while these equations do explain satisfactorily some of the phenomena, they are not sufficient to explain all. Haber,2 after introducing and discussing Equations A and B, adds: "Now one can consider that A and B are also connected by the equation
+ +
each investigator is wont to call upon such a set of two or three equations as may seem to him necessary and sufficient t o depict the reactions and explain the results obtained. As will be shown below, ten sets of equations are theoretically possible. This number will be reduced to three by making a certain assumption, and it will also be demonstrated that the analysis of the resulting gases, in the cases under observation, not only supports the assumption made but also contains a definite clue as to which of the three sets of equations represents the actual procedure of the reactions. When steam reacts on carbon,'carbon dioxide, carbon monoxide, and hydrogen are formed (we shall ignore here the formation of small amounts of methane and other hydrocarbons), and all possible interactions between the steam and carbon and the resulting three gases are represented by four reversible equations:
+ 2Hz0 = COz + 2Hz + HzO = CO +Hz COS+ Hz = CO + HzO coz + c = 2 c o C C
(A)
(B) (C) ID)
It may happen that reactions according to all four equations occur simultaneously (A, B, C, and D) or that under certain conditions only the four possible combinations of three will assert themselves, and finally we can think of the possibility of either one of five possible pairs of equations representing the actual procedure, that is, A and B, A and C, A and D, €3 and C, and B and D. If we consider, however, that there are indications that carbon monoxide is not formed by the direct oxidation of carbon' but that carbon dioxide is formed primarily and the occurrence of carbon monoxide in the gases is to be ascribed to a secondary reduction of COZ to CO by means of hydrogen or carbon, the ten combinations enumerated above dwindle to three, namely, A and C, A and D, or A, C, and D. That is to say, the chemistry of the water-gas process most probably consists of two consecu4
Haber, LOC.cit., 238.
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tive steps: first, carbon dioxide and hydrogen are formed from steam and carbon, and, second, the dioxide is reduced to monoxide either by hydrogen or by carbon or by both hydrogen and carbon simultaneously. The main object of this paper is to answer the following questions: Do the differencesin the manner of working of Schemes A and C , A and D, and A, C , and D make themselves felt in the composition of the resulting gases? If so, how can we use these differences t o determine whether a gas of given composition has been the result of the first, second, or third combination?
RELATIONS BETWEEN VOLUMES OF GASES Before going into this matter, the relationship between the volumes of Ha,CO, and COZ will be shown by utilizing one of the pairs of equations which have been dropped as practically improbable but which remain, of course, theoretically correct and useful. The pair chiefly used in textbooks is A and B. It probably does not represent actual working conditions for several reasons, but its merit lies in its clearness and in the fact that the two reactions proceed parallel and not in series, However the water:gas process actually proceeds, it is theoretically correct to say that the resulting gases could have been formed according to these two reactions. Certain general characteristics of the process can be deduced from them more easily than from any other. One of these characteristics of which we shall make repeated use in the following calculations lies in the fact that the volume of hydrogen is always equal to the sum of the volume of carbon monoxide plus double the volume of carbon dioxide. If we call X, Y, and Z the respective concentrations by volume in the end gases of C02, CO, and HZwe can say that
z = Y + 2x.
detect the law of interdependence. Considering the fact that the first step produces C02 which the second uses for the production of CO, it is to the point to endeavor to find the relationship between the rate of production of COz by the first step and the rate of destruction of COn by thesecond step; or, what amounts to the same thing, between the rate of decomposition of water by the first step and the rate oE decomposition of COZ by the second step. Further, if the combination A and C works differently from A and D, these differences will show themselves in the end gases and permit answering the problem. EQUATIONS A AND D-I& us consider first pair A and D, as the simpler one, taking as a basis one volume of steam before it is decomposed. Assuming that under given conditions of temperature, etc., fraction p of the steam used has been actually decomposed by interaction with carbon according to A, and that fraction q of the formed COShas been reduced to CO according to D, the volumes of the four resulting gases will be proportionate to the following values: Undecomposed steam =' 1-9 Hydrogen Carbonmonoxide = P = =P (1-n)
Carbon dioxide
2
z
While it is evident enough that p is equal to u we Y call p equal to x+u'because, as Equation D shows, the volume
+
of the COa doubles by the change to CO. As the rate of reaction will depend on the volume concentration of the COt during the reaction and not after the reaction, we must make V
(E)
Equation E also indicates that, for a given value of any one of the three gases after removal of the excess of steam, only one set of values for the other two gases is possible. For instance, if X i s given or determined, Y and Z can be calculated as follows:
Vol. 14, No. 1
q=-u
-2
P
X+?
Or=
-
2X+Y
EQUATIONS A AND c-Conditions are slightly more complicated with pair A and C. This combination differs in two respects from A and D:
(1) One volume of Con produces only one volume of CO and we can therefore put q
RELATIONS-Returning now to the problem Of determining the direction which the reaction has taken by the analysis of the resulting gases, the first advance in attacking this problem has been made by recognizing the apparent impossibility of utilizing the law of reaction equilibrium for this purpose. The equilibrium of the resulting gases with each other and with the carbon, that is, the equilibrium represented by the two following equations, is in the first instance only exceptionally obtainable; in the second, as a rule, not even approximately reached. EQUILIBRIUM
u y =K X Z A
X, IT, and Z are again the volume concentrations of Cot, CO, and Hz,and U is the volume concentration of the unconsumed steam. The explanation of the failure of these equilibria to establish themselves under ordinary working conditions lies in the fact, proved by experiment, that even if the observations are started with definite amounts of, say, COSand Hz, which are not changed from the outside, it takes a longer or shorter time, depending on conditions, for the equilibrium to assert itself. If then, as is the case in the water-gas process, one of the gases is continually introduced in new quantities, we can hardly be surprised that the equilibrium can never be reached. Evidently if the two reactions under observation are not working in parallel, and if the second is dependent upon the reaction products of the first, we must took for other means to
-
X+Y'
(2) Equation C reproduces one volume of steam for each volume of
CO;
used up.
In order to finish our observations again with p volumes of water decomposed and 1- p undecomposed, we must start our observations with a large volume of steam initially decomposed by Reaction A, which we shall call P. P can be determined by the following equations:
P
=zp
2-P 2P If then =P water is decomposed according to Equation A,
2-¶
==
@ water is reproduced according to Equation C. This 2-q is the same as if only p water had been decomposed and 1-9 had been left undecomposed, and the four gases after the reaction are again represented in the following proportions: 2
Undecomposed steam = 1- p Hydrogen =P Carbon monoxide Carbon dioxide
P4 -- ;(
