Chemistry of inorganic compounds – Sulfur or compound thereof – Elemental sulfur
Reexamination Certificate
2000-05-24
2002-04-16
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Elemental sulfur
C423S576800, C502S305000, C502S325000, C502S345000, C502S514000
Reexamination Certificate
active
06372193
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for oxidizing H
2
S contained at low concentration in a gas directly to sulphur by catalytic means in the vapour phase.
BACKGROUND
In order to recover H
2
S contained at low concentration, namely a concentration of less than 25% by volume and, more particularly, between 0.001% and 20% and most especially ranging from 0.005% to 10% by volume in gases from various sources, use may especially be made of processes involving a direct catalytic oxidation of H
2
S to sulphur according to the reaction:
H
2
S+1/2O
2
→S+H
2
O.
In such processes, the H
2
S-containing gas to be treated, mixed with a suitable amount of gas containing free oxygen, for example, air, oxygen or oxygen-enriched air, is brought into contact with a catalyst for oxidizing H
2
S to sulphur by carrying out this contact at temperatures either above the dew point of the sulphur formed, in which case the sulphur formed is present in the vapour state in the reaction medium coming from the reaction, or at temperatures below the dew point of the sulphur formed, in which case the sulphur is deposited on the catalyst, thereby requiring the sulphur-laden catalyst to be periodically regenerated by vaporizing the sulphur by flushing with a non-oxidizing gas having a temperature of between 200° C. and 500°
0
C.
In particular, the oxidation of H
2
S to sulphur at temperatures above the dew point of sulphur, that is to say, at temperatures greater than approximately 180° C., may be carried out in contact with a catalyst consisting of titanium oxide (EP-A-0,078,690), titanium oxide containing an alkaline-earth metal sulphate (WO-A-8302068), titanium oxide containing nickel oxide and optionally aluminium oxide (EP-A-0,140,045), an oxide of the titanium oxide or zirconium oxide or silica type, combined with one or more compounds of transition metals chosen from Fe, Cu, Zn, Cd, Cr, Mo, W, Co and Ni, preferably Fe, and optionally with one or more compounds of precious metals chosen from Pd, Pt, Ir and Rh, preferably Pd (FR-A-2,511,663) or else a thermally stabilized alumina combined with one or more compounds of transition metals, such as those mentioned above, especially Fe, and, optionally, with one or more compounds of precious metals chosen from Pd, Pt, Ir and Rh (FR-A-2,540,092).
The catalysts as mentioned above, consisting of a catalytic phase based on at least one oxide, salt or sulphide of a transition metal and combined with a support consisting of at least one material chosen from alumina, titanium oxide, zirconium oxide, silica, zeolites, silica/alumina mixtures, silica/titanium oxide mixtures and active carbon, which are used for the catalytic oxidation of H
2
S to sulphur, still have certain inadequacies in prolonged use. In particular, the catalysts which have an alumina-based support are susceptible to changing over time by sulphurization. With regard to the catalysts whose support consists of active carbon, precautions must be taken during their use to prevent oxidation of the support, which is accompanied by a loss of the support. In addition, for these various catalysts, the catalytic phase impregnating the support has a tendency to migrate into the interstices of the support and, thereby, makes it difficult, or indeed often impossible, to recover the metal from the catalytic phase in the spent catalyst. Finally, the abovementioned catalysts have a mediocre thermal conductivity, which means that the temperature within the catalytic beds containing them cannot be effectively controlled by heat exchange with a coolant.
To remedy the drawbacks of the catalysts of the above mentioned type, which are used in processes for the direct catalytic oxidation of H
2
S to sulphur, carried out in the vapour phase, that is to say at temperatures above the dew point of the sulphur formed and, thus, to obtain a process resulting in an improved sulphur selectivity that continues lastingly over time, the Applicant in FR-A-2,727,101 and WO-A-97/19019 has proposed to carry out the oxidation in contact with a catalyst formed from a silicon carbide support combined with a catalytically active phase containing at least one transition metal, especially Ni, Co, Fe, Cu, Ag, Mn, Mo, Cr, Ti, W and V, in the oxide or salt form and/or in the elemental state.
SUMMARY OF THE INVENTION
A process for catalytically oxidizing H
2
S contained in a gas directly to sulphur containing the following steps:
combining the H
2
S-containing gas with a gas containing free oxygen in an amount to produce an oxygen-enriched H
2
S-containing gas having O
2
/H
2
S molar ratio ranging from about 0.05 to about 15; and
contacting the oxygen-enriched H
2
S-containing gas with a catalyst for selective oxidation of H
2
S to sulphur, wherein the catalyst includes a catalytically active phase combined with a silicon carbide-based support and wherein the active phase of the catalyst consists of at least one oxysulphide of at least one metal selected from the group consisting of iron, copper, nickel, cobalt, chromium, molybdenum and tungsten, at a temperature above the dew point of sulphur formed during H
2
S oxidation.
DETAILED DESCRIPTION OF THE INVENTION
The Applicants have found that the desulphurizing activity and sulphur selectivity of the catalyst with a silicon carbide support in the process for direct oxidation of H
2
S to sulphur, carried out at temperatures above the dew point of the sulphur formed, can further be improved by carrying out the oxidation using an active phase of the catalyst, which consists of one or more oxysulphides of selected transition metals.
The subject of the invention includes, therefore, a process for oxidizing H
2
S contained at low concentration in a gas directly to sulphur by catalytic means, which process is of the type in which the H
2
S-containing gas with a gas containing free oxygen, in a suitable amount to give an O
2
/H
2
S molar ratio ranging from about 0.05 to about 15, is brought into contact with a catalyst for the selective oxidation of H
2
S to sulphur, which includes a catalytically active phase combined with a silicon carbide-based support and formed from at least one compound of at least one transition metal, the process being carried out at temperatures above the dew point of the sulphur formed during the H
2
S oxidation, and it is characterized in that the active phase of the catalyst consists of at least one oxysulphide of at least one metal chosen from iron, copper, nickel, cobalt, chromium, molybdenum and tungsten.
Advantageously, the metal constituting, in the oxysulphide form, the active phase of the oxidation catalyst is iron or a mixture of iron and of at least one of the metals copper, nickel, cobalt, chromium, molybdenum and tungsten. The mixture preferably is mostly iron.
As indicated above, the H
2
S-to-sulphur oxidation reaction is carried out at temperatures above the dew point of the sulphur produced and, more particularly, at temperatures above about 180° C. and possibly going up to about 500° C. Preferably, the H
2
S-to-sulphur oxidation reaction is carried out at temperatures of between about 190° C. and about 300° C. and more especially between about 200° C. and about 260° C.
The active phase of the oxidation catalyst, measured by weight of metal, usually represents from about 0.1 to about 20%, more particularly from 0.2% to 15% and more especially from about 0.2% to about 7% of the weight of the catalyst.
The silicon carbide support advantageously forms at least about 40% and, more particularly, at least about 50% of the weight of the oxidation catalyst.
The specific surface area of the H
2
S-to-sulphur oxidation catalyst may vary quite widely depending on the conditions under which the oxidation process is carried out. Advantageously, the specific surface area, determined by the BET nitrogen absorption method at the temperature of liquid nitrogen (NF X 11-621 standard), may range from about 0.05 m
2
/g to about 600 m
2
/g and more particularly from about 0.1 m
2
/g to about 400 m
2
/g.
The oxidation catalyst with a silicon carb
Crouzet Claude
Keller Nicolas
Ledoux Marc
Nougayrede Jean
Pham-Huu Cuong
Elf Exploration Production
Griffin Steven P.
Schnader Harrison Segal & Lewis LLP
Vanoy Timothy C
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