The Reaction of Carbon with Carbon Dioxide at High Pressure

1960 ◽  
Vol 13 (2) ◽  
pp. 194 ◽  
Author(s):  
JD Blackwood ◽  
AJ Ingeme
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Active Sites ◽  
High Pressures ◽  
Carbon Dioxide Molecule ◽  
Partial Pressures ◽  
Different Temperatures ◽  
Adsorbed Carbon ◽  
Forward Process ◽  
High Carbon Dioxide

A study has been made of the reactions of purified carbon with carbon dioxide at pressures up to 40 atm and in the temperature range 790-870 �C. The effect of carbon monoxide has been examined by adding varying proportions of this gas to the carbon dioxide supplied to the reactor bed. At high carbon dioxide and carbon monoxide partial pressures, the rate of formation of carbon monoxide is greater than would be expected from the mechanism proposed by Gadsby et al. (1948). A mechanism has been proposed whereby the increased rate may be explained by additional steps involving the interaction of a carbon dioxide molecule with an adsorbed carbon monoxide to produce adsorbed oxygen, thus : ������������������ CO2 + (CO) → 2CO +(O) A general rate equation has been derived which includes this step and satisfies the experimental results. The reverse mechanism by which carbon monoxide can disappear is not the simple reverse of the forward process and at high pressures equilibrium cannot be expressed by the usual expression derived for the simple single-stage reversible process. The possible nature of active sites has been examined by studying the reactivity of a series of chars prepared at different temperatures. The reactivity appears to be related to the oxygen content of the chars and the type of active centres involved may be different from those which control the carbon-steam mechanism.

Reactions of carbon with atomic gases

1959 ◽  
Vol 12 (4) ◽  
pp. 533 ◽  
Author(s):  
JD Blackwood ◽  
FK McTaggart
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Water Vapour ◽  
Active Sites ◽  
Atmospheric Temperature ◽  
Carbon Surface ◽  
Hydrogen Atoms ◽  
Different Temperatures ◽  
Atomic Species ◽  
Oxygen Groups

Wood chars were reacted at atmospheric temperature with hydrogen atoms, oxygen atoms and carbon monoxide, hydrogen atoms and hydroxyl radicals, produced by the action of a radio frequency field on hydrogen, carbon dioxide, and water vapour respectively. The chars were prepared at different temperatures and contained different amounts of oxygen. The experimental results showed that the gases must be present in the atomic form before reaction with the carbon can take place and that such species react on the carbon-surface independently of active sites. In normal gasification processes the atomic species appear to be produced at active centres, which for the chars used could be correlated with specific oxygen groups remaining in the carbon. It is suggested that these groupings may have a pyran structure. An explanation has been put forward for the retardation of the carbon-water vapour reaction by hydrogen, and of the carbon-carbon dioxide reaction by carbon monoxide. These are considered as due to reverse mechanisms which decrease the concentration of the atomic species and not to the blocking of active sites by adsorption of the retardant.

scholarly journals The mechanism of the carbon dioxide-carbon reaction

1948 ◽  
Vol 193 (1034) ◽  
pp. 357-376 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Carbon Surface ◽  
General Nature ◽  
Exponential Factor ◽  
Carbon Dioxide Molecule ◽  
Partial Pressures ◽  
Rate Of Reaction ◽  
Order Of Magnitude ◽  
The Individual

The detailed mechanism of the reaction between carbon dioxide and coconut shell charcoal has been studied by both flow and static methods. The temperature has been varied in the range 700 to 830° C and the pressures of the gases from 10 to 760 mm. The static method has been used to investigate the adsorption of the gases on the carbon surface during the course of the reaction, and thus to illustrate in a very direct way the general nature of the mechanism. Accurate measurements of the rate of reaction have been made by the flow method. At a given temperature the rate of reaction can be represented in terms of the partial pressures of the gases by an expression of the form rate = k 1 pco 2 / 1+k 2 pco + k 3 pco 2 . The three separate constants have been evaluated and each has been found to vary exponentially with temperature. From these results the rates of the individual stages of the mechanism have been calculated. The first stage is the decomposition of the carbon dioxide molecule into an atom of oxygen which is adsorbed by the carbon and a molecule of carbon monoxide which passes into the gas phase. Only certain sites on the charcoal surface take part in the reaction; they represent about 0-5 % of the total area and probably consist of some of the less firmly bound carbon atoms situated at lattice discontinuities. The rate of the first stage can be accounted for by assuming that reaction occurs in those collisions in which the combined energy of the active carbon atom and the incident carbon dioxide molecule exceeds 68 kcal. The second stage is the evaporation of the adsorbed oxygen atom, together with an atom of carbon from the solid, to form gaseous carbon monoxide; the activation energy is thought to be 38 kcal., and the low value of 107 sec. -1 obtained for the non-exponential factor is discussed. The retarding effect of carbon monoxide is due to the adsorption of the gas on the reaction sites, the heat given out in the change being 46 kcal. On the basis of this value, which implies that the molecule is adsorbed chemically, it is possible to calculate theoretically the order of magnitude of the retardation constant, k 2 .

scholarly journals The structure of the high pressure carbon bands and the swan system

1929 ◽  
Vol 124 (795) ◽  
pp. 668-688 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
High Pressure ◽  
High Pressures ◽  
Carbon Electrodes ◽  
High Dispersion ◽  
Pressure System ◽  
True Nature ◽  
Discharge Tubes ◽  
Condensed Discharge

The so-called high pressure “ CO ” bands—or high pressure carbon bands, as they are better called—were first found by Fowler* in 1910 in tubes containing carbon monoxide at relatively high pressures. The system was described as consisting of some six apparently double-headed bands degraded to the violet, their wave-lengths being approximately at— 6441 6420 } 5897 5878 } 5431 5413 } 5030 5015 } 4679 4663 } 4365 4353 } Å. U. In 1923 the conditions of production of this spectrum were further investigated by Merton and Johnson who obtained the bands with considerable strength by condensed discharges in capillary tubes fitted with carbon electrodes, and containing CO at pressures of 5 mm. and more. It was found that while the high pressure bands and the Swan bands were mingled in the light from the capillary of the tube, the former bands were isolated in bluish jets where the two ends of the capillary merged into the wider parts of the tube. Further observations indicated that the introduction of a little C0 2 destroyed the bands, but that the system re-apppeared after a few minutes, in which time presumably the carbon dioxide had been reduced to monoxide by the carbon electrodes. A reproduction of these bands photographed under low dispersion is given in the above-mentioned paper. No further experimental work appears to have been done on this system, and it has not been correlated with any other band system or assigned any place in the system of electronic levels of the CO molecule. We have therefore made an attempt to photograph the system under high dispersion with a view to fine structure analysis and identification of the molecular emitter. For this purpose large discharge tubes having a bore of about 15 to 20 mm. and a length of 60 or 70 cm. were used. These had at least one of the electrodes made of carbon and were fitted with side bulbs containing caustic potash and phosphorus pentoxide and a palladium regulator. The tubes were filled with carbon monoxide to such a pressure (probably 20-40 mm.) that a condensed discharge could just be forced through by the ¼ kilowatt 15,000 volt transformer used. Some of the tubes had large side flasks attached to them, increasing thereby the volume of gas in the tube, and giving the tubes a life of 4 to 6 hours during which the high pressure bands were emitted strongly. After some such period the pressure fell below the optimum value, and deposits of carbon had accumulated on the walls of the tube. Impurities such as hydrogen, carbon dioxide, and water-vapour were found to inhibit formation of the high pressure bands, and the tube always attained its best condition after running for about an hour (removing meanwhile any little hydrogen present through the regulator). Under these conditions the wide bore is practically filled with light, and presents a remarkable appearance, as of dense pale blue puffs of smoke (showing the high pressure system), threaded by a narrow green ribbon (showing the Swan system). If side tubes having a fair capacity ( e . g ., flasks) are attached to the discharge tube the high pressure glow is capable of diffusion into these. The appearance is suggestive of an afterglow emitter, but if this is its true nature it is of very short duration. Photographs of the H. P. bands were taken in times varying from 4 to 10 hours in the first order of a 21-foot grating. The green band in the neighbourhood of λ 5000 is exceedingly faint and was not attempted. Before considering the results -obtained it will be an advantage to summarise our present knowledge of the Swan spectrum and its emitter, with which it will subsequently be shown that the high pressure carbon system is intimately related.

scholarly journals Survival and Behaviour of Ammocoetes at Low Oxygen Tensions

1970 ◽  
Vol 53 (1) ◽  
pp. 59-73 ◽  
Author(s):  
I. C. POTTER ◽  
B. J. HILL ◽  
SUSAN GENTLEMAN
Keyword(s):  
Carbon Dioxide ◽  
Haemoglobin Concentration ◽  
Low Oxygen ◽  
Lethal Level ◽  
Partial Pressures ◽  
Oxygen Conditions ◽  
Oxygen Tensions ◽  
High Concentrations ◽  
Ph Range ◽  
High Carbon Dioxide

1. Survival and behaviour studies were made on ammocoetes subjected to water of various tensions of oxygen and carbon dioxide. 2. Ammocoetes can tolerate, for at least 4 days, oxygen tensions as low as 7-10 mmHg at 5 °C, 12-16 mmHg at 15.5 °C and between 13-16 and 19-21 mmHg at 22.5 °C. A limited ability to acclimate to low oxygen tensions was found in some animals. 3. A characteristic emergence behaviour is evoked by low partial pressures of oxygen that approach the lethal level and by high concentrations of carbon dioxide. 4. Ammocoetes respond to low oxygen and high carbon dioxide by an increase in the rate and amplitude of beating of the branchial basket. This increase is maintained in animals able to survive at low oxygen tensions. 5. A high affinity of the blood for oxygen is evident from oxygen equilibrium curves determined on erythrocytes suspension. There was an insignificant Bohr effect at 15.5 °C in the pH range 7.68-6.70, although a change occurred in the n value. 6. Haemoglobin concentration, haematocrit and oxygen equilibria suggest that the characteristics of the blood contribute significantly to the ability of ammocoetes to survive in low oxygen conditions.

scholarly journals Co-pyrolysis of rubberwood sawdust (RWS) and polypropylene (PP) in a fixed bed pyrolyzer

2019 ◽  
Vol 13 (1) ◽  
pp. 4636-4647 ◽  
Author(s):  
N. I. Izzatie ◽  
M. H. Basha ◽  
Y. Uemura ◽  
M. S. M. Hashim ◽  
M. Afendi ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Water Content ◽  
Fixed Bed ◽  
Oil Yield ◽  
Pyrolysis Oil ◽  
Pyrolysis Process ◽  
Increasing Trend ◽  
Different Temperatures

Co-pyrolysis of rubberwood sawdust (RWS) waste and polypropylene (PP) was carried out at different temperatures (450,500,550, and 600°C) with biomass to plastics ratio 1:1 by using fixed bed drop-type pyrolyzer. The yield of pyrolysis oil has an increasing trend as the temperature increased from 450°C to 550°C. However, the pyrolysis oil yield dropped at a temperature of 600°C. Co-pyrolysis of RWS and PP generated maximum pyrolysis oil with 36.47 wt.% at 550°C. The result is compared with the pyrolysis of RWS only without plastics, with the same feedstock, and the maximum pyrolysis oil yield obtained was 33.3 wt.%. The water content in pyrolysis oil of co-pyrolysis RWS with PP is lower than RWS only with 54.2 wt.% and 62 wt.% respectively. Hydrocarbons, acyclic olefin, alkyl, and aromatic groups are the major compound in the pyrolysis oil from the co-pyrolysis process. Carbon monoxide (52.2 vol.%) and carbon dioxide (38.2 vol.%) are the major gas components.

scholarly journals The mechanism of the steam-carbon reaction

1948 ◽  
Vol 193 (1034) ◽  
pp. 377-399 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Hydrogen Atom ◽  
Active Carbon ◽  
Active Sites ◽  
Adsorbed Oxygen ◽  
Adsorbed Hydrogen ◽  
Hydrogen Atoms ◽  
Exponential Factor ◽  
Gaseous Carbon Monoxide

The detailed mechanism of the reaction between steam and coconut shell charcoal has been studied by the method described in the preceding paper. The temperature has been varied in the range 680 to 800° C and the pressures of the gases from 10 to 760 mm. Steam first reacts with the carbon to give oxygen and hydrogen atoms separately adsorbed on neighbouring sites. An initial dissociation into an adsorbed hydrogen atom and an adsorbed hydroxyl radical is probably followed by the more rapid transfer of the second hydrogen atom to the carbon. Only about 2% of the total surface takes part in the reaction; these sites are distinct from the smaller group which reacts with carbon dioxide, but they are also thought to be atoms at the edges of lattice planes. The rate of the first stage can be accounted for by assuming that reaction occurs in those collisions in which the combined energy of the incident steam molecule and the two active carbon atoms exceeds 75 kcal. Adsorbed hydrogen evaporates rapidly, but in the steady state much remains on the surface. A close correlation has been observed between the fraction of the active sites occupied by hydrogen and the extent to which the reaction is retarded by that gas. Adsorbed oxygen reacts much more slowly to form gaseous carbon monoxide; the latter, which has no retarding effect, is not appreciably adsorbed by the sites accessible to steam. The activation energy for the conversion of an adsorbed oxygen atom into gaseous carbon monoxide is found to be 55 kcal., and the non- exponential factor to be 10 11±1.7 sec. -1 which may be compared with the value of 10 13 sec. -1 predicted by simple theory. As the active carbon atoms are thought to be exerting less than their maximum valency, it is suggested that the two types differ in the number of extra bonds which they can form. Energetic considerations show that whereas those which can form a single bond should react with steam, only the relatively few capable of forming a double bond should react with carbon dioxide. This theory also explains why hydrogen is strongly adsorbed by both the steam and the carbon dioxide sites, but carbon monoxide only by the latter type. The relation of these views to outstanding problems of the oxygen-carbon and nitrous oxide-carbon reactions is discussed, and an explanation of the main kinetic features of those processes is given.

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