Chemistry of inorganic compounds – Sulfur or compound thereof – Elemental sulfur
Reexamination Certificate
1999-11-22
2001-08-28
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Elemental sulfur
C423S575000, C423S576200
Reexamination Certificate
active
06280698
ABSTRACT:
FIELD OF THE INVENTION
The object of the present invention is a method for processing, by means of an organic solvent containing at least one catalyst, a gaseous effluent containing at least hydrogen sulfide and sulfur dioxide, during which most of the by-products formed during said treating process is removed.
The by-product removal stage, or processing stage, is notably carried out at a temperature allowing formation and growth of the crystals of these by-products, i.e. crystallization of these by-products.
The method according to the invention is for example applied in Clauspol processing units used after the Claus process.
BACKGROUND OF THE INVENTION
The Claus process is widely used, notably in refineries (after hydrodesulfurization or catalytic cracking units) and for processing of natural gas, to recover elemental sulfur from gaseous feeds containing hydrogen sulfide. However, the fumes produced by Claus plants contain, even after several catalytic stages, appreciable amounts of acid gases. It is then necessary to process these Claus plant effluents (tail gas) to remove most of the toxic compounds so as to abide by antipollution standards.
It is for example well-known to recover about 95% by weight of the sulfur present from a Claus plant.
Processing this Claus plant effluent with a Clauspol plant allows for example to each 99.8% by weight of solvent recovered, from the exothermic Claus reaction:
2H
2
S+SO
2
&rlarr2;←→3S+2H
2
O (reaction 1)
Such processing requires a reaction medium consisting of an organic solvent and at least one catalyst comprising an alkaline or alkaline-earth salt of an organic acid. Contacting the gas to be processed and the organic solvant containing the catalyst is carried out in a gas-liquid contactor reactor whose temperature is controlled by passage of the solvent, that has been extracted from the contactor reactor by a circulation pump, into a heat exchanger so as to favour the highest sulfur conversion coefficient while preventing formation of solid sulfur. It is well-known that, in this type of plant, the solvent that has a limited capacity for dissolving elemental sulfur becomes loaded with free liquid elemental sulfur that can be separated from the solvent by simple decantation. This liquid sulfur-solvent decantation is carried out in a liquid-liquid decantation zone that can be situated at the bottom of the contactor reactor. The sulfur is thus recovered in liquid form.
Operation of such a plant is for example described in one of the following reference books:
Y. BARTHEL, H. GRUHIER, The IFP Clauspol 1500 process: eight years of industrial experience, Chem. Eng. Monogr., 10 (Large Chem. Plants), 1979, pp.69-86;
HENNICO A., BARTHEL Y., BENAYOUN D., DEZAEL C., Clauspol 300: the new IFP TGT process, For presentation at AIChE Summer National Meeting, Denver (Colo.), Aug. 14-17, 1994.
It is furthermore well-known that the desulfurization rate of a plant of this type can be improved by desaturating the solvent in sulfur in a desaturation loop according to a process described in patent FR-2,735,460 filed by the applicant. In this case, part of the single-phase solvent and sulfur solution extracted at the end of the contactor reactor is cooled in order to crystallize the sulfur. This crystallized sulfur is then separated from the solvent by various known solid-liquid separation means such as filtration, decantation or centrifugation. A sulfur-depleted solvent that can be recycled to the contactor reactor is obtained on the one hand, and a suspension enriched in solid sulfur that can be reheated to melt the sulfur, then sent to a solvent-sulfur liquid-liquid decantation zone where the liquid sulfur is recovered is obtained on the other hand.
Although such a method proves to be effective, it can however be limited.
For example, side reactions occur in the contactor reactor, leading to formation of by-products, mainly salts such as alkaline or alkaline-earth sulfates or thiosulfates, due for example to the slow degradation of the catalyst. These by-products tend to accumulate in the decantation zone at the interface between the organic solvent and the liquid sulfur, which makes decantation of the liquid sulfur difficult.
One way allowing to overcome this problem is described in patent FR-2,735,460, which discloses the possibility of passing a solvent containing such salts through a filter. The salts settle on the filter, and the sulfur-containing solvent is sent to a sulfur-desaturation stage. On the one hand, such processing of the circulating solvent is not sufficient to entirely remove any accumulation of these salts at the liquid sulfur-solvent interface, including the liquid sulfur-solvent decantation zone situated downstream from the zone intended for sulfur desaturation of the solvent. On the other hand, if the solvent is not desaturated in sulfur by means of a desaturation loop, sulfur might be co-eliminated with the solid salts, so that processing of the fluid resulting from regeneration of the filter will be delicate.
SUMMARY OF THE INVENTION
The object of the present invention is a method and its associated device, wherein a solution extracted from the contactor reactor and containing at least solvent, catalyst, sulfur and by-products is subjected to at least one heating stage and to at least one separation stage so as to remove most of the by-products it contains and to obtain a solvent practically free of said by-products.
These by-products are for example the result of the slow degradation of the catalyst.
It has been observed that heating the fluid extracted from the contactor reactor and containing at least solvent, catalyst, sulfur and by-products to a suitable temperature:
favours crystallization of the by-products in solution in the solvent, which facilitates removal of said by-products,
causes solubilization of the free sulfur droplets possibly present in the solvent, which prevents co-elimination of sulfur with the by-products and facilitates the possible processing of the fluid resulting from regeneration of elements in the processing zone.
The solvent practically free of by-products can be advantageously recycled, partly or totally, to the contactor reactor where the gas is processed.
The invention relates to a method for processing a gas containing at least hydrogen sulfide (H
2
S) and at least sulfur dioxide (SO
2
), wherein said gas is contacted, at a suitable temperature, with an organic solvent containing at least one catalyst, a gaseous effluent substantially containing no hydrogen sulfide and no sulfur dioxide any more is recovered, as well as liquid sulfur separated from the solvent by liquid-liquid decantation.
It is characterized in that:
a fluid F containing at least solvent, catalyst, sulfur and by-products is extracted after the contacting stage,
said fluid F is sent to a processing stage comprising at least one heating stage during which said fluid F is brought to a determined temperature favouring crystallization of the by-products, and to a stage of separation of the by-products from the solvent,
after the processing stage, at least a stream F
1
comprising mainly solvent, catalyst and sulfur and nearly free of by-products and a stream F
2
comprising most of the by-products are recovered.
Fluid F is for example a liquid single-phase solution.
The by-products contained in fluid F can be dissolved and/or crystallized.
The temperature to which said fluid F is brought ranges for example between 120 and 180° C., preferably between 120 and 150° C.
The processing stage is for example carried out by implementing at least one of the following procedures:
a) carrying out at least one filtering stage so as to recover said fluid F
1
mainly consisting of solvent depleted in solid by-products and said fluid F
2
resulting from regeneration of the filtering support and containing most of the by-products, and/or
b) carrying out at least one stage of capture, on a solid support, of the by-products so as to recover at least said fluid F
1
mainly consisting of solvent depleted in by-products an
Barrere-Tricca Cecile
Lecomte Fabrice
Streicher Christian
Antonelli Terry Stout & Kraus LLP
Griffin Steven P.
Institut Francais du Pe'trole
Vanoy Timothy C.
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