Relationship Between the Production and Consumption of Hydrogen in the Process of Synthesis from Carbon Monoxide and Water Vapor
Abstract Generated abstract
The paper addresses the contested role of hydrogen in the synthesis of organic compounds from carbon monoxide and water vapor. It compares possible routes of hydrogen formation, including carbon monoxide conversion with steam and steam conversion of hydrocarbons, and proposes a simplified reaction scheme linking hydrogen production and consumption with the overall synthesis process. Using this scheme, the authors interpret observed maxima in the dependence of carbon monoxide conversion to hydrogen on linear gas velocity, temperature, and contact time as arising from the superposition of parallel and consecutive reactions with differing kinetic behavior.
Full Text
INTERRELATION BETWEEN THE PRODUCTION AND CONSUMPTION OF HYDROGEN IN THE PROCESS OF SYNTHESIS FROM CARBON MONOXIDE AND WATER VAPOR
V. M. Mironov, S. I. Smolyaninov
(Presented by the scientific-methodological seminar of the CTF)
The question of the role of hydrogen in the process of synthesis of organic compounds from carbon monoxide and water vapor is rather controversial. Thus, for example, H. Kölbel and co-workers [1] and I. F. Bogdanov [2] believe that the indicated synthesis proceeds only through the intermediate formation of hydrogen due to the conversion of CO with water vapor according to the equation
\[ \mathrm{CO}+\mathrm{H_2O}=\mathrm{CO_2}+\mathrm{H_2}. \tag{1} \]
In an earlier work by the authors [3] it was assumed that hydrogen in the synthesis process is formed predominantly due to complete and incomplete conversion of hydrocarbons with water vapor according to the equations
\[ \mathrm{C}_n\mathrm{H}_m+2n\mathrm{H_2O}=n\mathrm{CO_2}+(^{m}/_{2}+2n)\mathrm{H_2}, \tag{2} \]
\[ \mathrm{C}_n\mathrm{H}_m+2\mathrm{H_2O}=\mathrm{CO_2}+3\mathrm{H_2}+\mathrm{C}_{n-1}\mathrm{H}_{m-2}. \tag{3} \]
Further, a more complete study of the appearance of hydrogen in the reaction volume depending on the conditions of conducting the process (contact time, temperature, linear velocity of the synthesis gas), as well as a study of the possibility of reactions (2) and (3) proceeding under synthesis conditions [4], makes it possible to adopt a certain compromise solution regarding the role of hydrogen in synthesis from carbon monoxide and water vapor.
It is necessary to determine the pathways of hydrogen supply and consumption in the complex synthesis process. Estimating these pathways, one can propose a simplified scheme of the interrelation of synthesis according to the equation
\[ 3\mathrm{CO}+\mathrm{H_2O}=(-\mathrm{CH_2}-)+2\mathrm{CO_2} \tag{4} \]
and of the above-listed reactions in the form proposed in Fig. 1.
Relying on this scheme, one can explain the dependence of the degree of conversion of carbon monoxide to hydrogen on the linear velocity of the synthesis gas, characterized by the presence of a maximum [5]. According to the data of diffusion kinetics, improvement of the conditions of external diffusion for consecutive reactions leads to a relative increase in the yield of the intermediate product, while for parallel reactions we have shown [6] that an increase in linear velocity will lead to a relative increase in the rate of the reaction whose kinetic order is higher.
Assuming that the kinetic order of the conversion reaction according to (1) is higher than that of the reaction according to (4), it can be concluded that the initial increase in the relative yield of hydrogen with increasing linear velocity is caused by a decrease in the share of hydrogen-consuming reactions, i.e., all processes in which hydrogen is an intermediate product. Further increas-
Fig. 1. Simplified scheme of the interrelation of reactions in the synthesis process from carbon monoxide and water vapor.
a decrease in the linear flow velocity leads to a sharp decrease in its production both due to dehydrogenation of hydrocarbons and due to reactions (1–3), especially the reaction of conversion of carbon monoxide with water vapor, which is a parallel reaction to the synthesis according to (4). Such superposition of processes is characterized by an extremum point.
Similarly, one can explain the presence of maximum values in the study of the dependence of the degree of conversion of carbon monoxide to hydrogen on temperature and contact time.
Conclusion
A simplified scheme has been proposed for the interrelation of reactions of hydrogen formation and consumption in the synthesis process from carbon monoxide and water vapor, with the aid of which some regularities in the appearance of hydrogen in the reaction volume have been explained.
REFERENCES
- N. Kölbel, Fr. Engelhardt. Z. Elektrochem. Ber. Bunsenges. phys. Chem., 64, 224–234, 1960.
- I. F. Bogdanov. Tr. IGI AN SSSR, 18, 34–39, 1962.
- S. I. Smolyaninov, V. M. Mironov. Izv. TPI, 136, 58–60, 1965.
- S. I. Smolyaninov, A. V. Kravtsov, V. M. Mironov. Izv. TPI, 162.
- S. I. Smolyaninov, V. M. Mironov. Izv. TPI (in press).