Investigation of the kinetics of synthesis from carbon monoxide and water vapor by the flow-circulation method
Abstract Generated abstract
This paper addresses the need for kinetic data on the catalytic interaction of carbon monoxide with water vapor, a reaction related to Fischer Tropsch synthesis for which satisfactory rate equations and mechanistic consensus were lacking. It describes a flow circulation, gradientless experimental apparatus designed for kinetic measurements, including gas purification, water vapor dosing, thermostated circulation, a glass reactor, and chromatographic analysis of reactants and products. Experiments were performed on an iron copper catalyst supported on kieselguhr at 210°C after reduction, carburization, and pretreatment with carbon monoxide and a carbon monoxide water mixture. Under the reported conditions, with a catalyst bed volume of 0.8 cm³ and a reduced contact time of about 0.9 s, the process rate was found to be 1.28 × 10⁻⁷ cm³/cm²·s.
Full Text
STUDY OF THE KINETICS OF SYNTHESIS FROM CARBON MONOXIDE AND WATER VAPOR BY THE FLOW-CIRCULATION METHOD
N. V. USHEVA
(Presented by the scientific-methodological seminar of the organic departments of the Faculty of Chemical Technology)
The study of the mechanism of reactions in the Fischer–Tropsch synthesis process and the study of the role of water vapor in the course of the complex of reactions in this process gave impetus to the development of the synthesis of hydrocarbons and oxygen-containing compounds from carbon monoxide and water vapor.
To date, no kinetic equation has been obtained that satisfactorily describes the available experimental data. Nor is there a single point of view regarding the mechanism by which this process proceeds [1, 2].
In this connection, there arises the need for a detailed study of the kinetics and mechanism of the reaction of interaction of carbon monoxide and hydrogen or water vapor.
At present, the most convenient and universal methods for detailed studies of the kinetics of various catalytic reactions are gradientless methods [3].
For carrying out kinetic experiments, a flow-circulation apparatus was assembled (figure).
Circulation of the vapor–gas mixture is effected by means of a glass electromagnetic pump 3 with a capacity of 700 l/h. The circulation pump and valve box 2 are placed in an air thermostat 4 at a temperature of 100°C. The connecting tubes through which the vapor–gas mixture arrives from the saturation system are heated by a nichrome coil.
Carbon monoxide, obtained by decomposition of formic acid, was purified of impurities (oxygen, carbonyls, carbon dioxide, and water) by passing it successively through columns with a chromonickel catalyst (temperature 110°C), activated carbon, ascarite, and zeolites.
Nitrogen was purified of impurities by passing it through columns with a chromonickel catalyst and zeolites.
The gas flow rate was measured with rheometers. In the study of kinetics, the ratio of water to carbon monoxide in the initial mixture is varied. Measurement of the concentration of one of the reaction components while the concentrations of the other components are practically constant is achieved by adding various amounts of nitrogen to the gas mixture.
Water is dosed by saturating the initial gas mixture with water vapor in a special system 5. The temperature
saturation is maintained with an accuracy of ±0.1°C by means of ultrathermostat 6.
Reactor 7 is a glass tube with a sealed-in coarse-pore filter on which the catalyst is placed. The reactor is equipped with a coil for preliminary heating of the reaction mixture and a pocket for the thermocouple.
The temperature in the catalyst zone was measured with a calibrated thermocouple (copper–constantan) and maintained by means of an automatic potentiometer EPR-09 M3 with an accuracy of ±2°C.
Fig. 1. Diagram of the flow-circulation installation. 1 — rheometer, 2 — valve box, 3 — circulation pump, 4 — air thermostat, 5 — saturator, 6 — thermostat, 7 — reactor, 8 — furnace, 9 — refrigerator
From the circulation loop the steam–gas mixture enters refrigerator 9 for condensation of water vapor.
Analysis of the initial gases and reaction products is carried out by gas chromatography. Experiments were conducted on an iron–copper catalyst deposited on kieselguhr with a specific surface area of 42.4 m²/g. The specific surface area was determined by low-temperature nitrogen adsorption.
Before the start of the experiment, the catalyst was reduced in a stream of hydrogen at a temperature of 300°C, and then carburized with carbon monoxide at a temperature of 200°C.
After being loaded into the reactor, the catalyst was treated with carbon monoxide at a temperature of 200°C for 3 hours, and then with a CO + H₂O mixture in a volume ratio of 3:1.
Kinetic measurements were carried out at a temperature of 210°C on a catalyst bed with a volume of 0.8 cm³.
The reduced contact time, calculated by the formula
\[ \tau_0 = \frac{W}{U_0}, \]
where \(W\) is the volume of the catalyst bed,
$U_0$ is the volume of the vapor–gas mixture, reduced to 0°C at 760 mm Hg, leaving the cycle in 1 sec; at a temperature of 210°C it amounted to about 0.9 sec. The rate of the process under these conditions proved to be $1.28 \cdot 10^{-7}\ \mathrm{cm^3}/\mathrm{cm^2}\cdot\mathrm{sec}$.
References
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- M. A. Kostomarov, I. F. Bogdanov. Chemistry and Technology of Fuels and Oils, 1961, No. 1, pp. 19–25.
- S. L. Kiperman. Kinetics and Catalysis, 1972, vol. 3, pp. 625–639.