Mineral oils: processes and products – Refining – Metal contaminant removal
Reexamination Certificate
1999-10-26
2001-04-24
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Metal contaminant removal
C208S299000, C208S301000, C208S302000, C208S303000, C208S246000, C208S247000, C208S248000, C208S296000, C208S297000, C208S253000, C208S20800M, C095S133000, C095S134000, C095S135000, C095S136000, C095S137000, C585S820000, C585S822000
Reexamination Certificate
active
06221241
ABSTRACT:
This invention relates to a purification process and in particular to the removal of sulphur compounds together with other contaminants from fluid streams by absorption using particulate absorbent materials.
As a fluid stream containing a contaminant is passed through a bed of an absorbent for that contaminant, the contaminant is absorbed, initially at the inlet region of the bed, and the effluent from that bed contains little or none of the contaminant. Gradually the inlet region of the absorbent becomes saturated with the contaminant and the region where the absorption occurs moves gradually towards the outlet of the bed. Often the absorption front is relatively sharp: i.e. there is a clear distinction between the region of the bed where absorption has occurred (where the bed is partially or fully saturated with the contaminant) and downstream regions where the bed is essentially free of contaminant. When the adsorption front reaches the outlet of the bed, break-through is said to have occurred since the contaminant can then be detected in significant quantities in the effluent from the bed. Continued passage of the contaminated fluid through the bed will result in little or no further absorption of the contaminant.
Fluid streams, such as hydrocarbon liquids and gases, for example natural gas, are often contaminated with sulphur compounds and other contaminants such as elemental mercury, phosphine, stibine, arsine and/or organo-arsenic compounds such as mono-, di-, or tri-alkyl arsines. Various references, for example GB 1 533 059 and EP 0 465 854, disclose that mercury and such arsenic compounds can be removed by passing the fluid through a bed of a copper sulphide absorbent. U.S. Pat. No. 4,593,148 discloses that arsines and hydrogen sulphide can be removed together by the use of a bed of copper oxide and zinc oxide. EP 0 480 603 discloses that sulphur compounds and mercury may be removed together by passing the fluid stream through a bed of an absorbent containing copper compounds: the sulphur compounds are absorbed, forming copper sulphide, which then serves to remove the mercury.
The fluid stream generally contains a far greater amount of sulphur compounds, particularly hydrogen sulphide, than other contaminants. It is generally necessary to remove essentially all the mercury and arsine compounds, but often it is permissible for the product to contain a small amount of hydrogen sulphide. For example a typical natural gas may contain about 50 &mgr;g/m
3
of mercury and about 10 ppm by volume of hydrogen sulphide and it is desired that this gas is purified to a mercury content of less than 0.01 &mgr;g/m
3
and to a hydrogen sulphide content of 1-3 ppm by volume.
We have devised a simple process whereby essentially all of the mercury and/or arsenic compounds can be removed and the sulphur compounds content decreased to a specified level.
Accordingly the present invention provides a process for the purification of a fluid stream containing at least one sulphur contaminant selected from hydrogen sulphide, carbonyl sulphide, mercaptans and hydrocarbon sulphides and at least one second contaminant selected from mercury, phosphine, stibine, and arsenic compounds comprising passing said fluid stream through a bed of a particulate absorbent containing a sulphide of a variable valency metal that is more electropositive than mercury whereby said second contaminant is removed from said fluid stream but little or none of said sulphur contaminant is absorbed and then passing at least part of the effluent from said bed containing the variable valency metal sulphide through a bed of a particulate sulphur absorbent comprising at least one compound selected from oxides, hydroxides, carbonates and basic carbonates of said variable valency metal, whereby said sulphur contaminant is absorbed from that part of the effluent passing through said sulphur absorbent and converting said sulphur absorbent to a sulphide of said variable valency metal, characterised in that said bed of the variable valency metal sulphide has been produced by absorbing sulphur contaminants from a previous portion of said fluid stream from which said second contaminant has been removed.
In a preferred form, the present invention provides a process for the purification of a fluid stream containing at least one sulphur contaminant selected from hydrogen sulphide, carbonyl sulphide, mercaptans and hydrocarbon sulphides and at least one second contaminant selected from mercury, phosphine, stibine, and arsenic compounds comprising passing said fluid stream through a primary bed of a particulate absorbent containing a sulphide of a variable valency metal that is more electropositive than mercury, and having essentially no capacity for absorption of said sulphur contaminant under the prevailing conditions, whereby essentially all of said at least one second contaminant is removed from said fluid stream, passing part of the effluent from said primary bed through at least one secondary bed of a particulate sulphur absorbent comprising at least one compound selected from oxides, hydroxides, carbonates and basic carbonates of said variable valency metal, whereby at least part of said sulphur contaminant is absorbed from said part of the effluent from the primary bed by said variable valency metal compound by conversion thereof to a sulphide of said variable valency metal giving a first product stream that has a decreased sulphur contaminant content, mixing said first product stream with the remainder of the effluent from said primary bed to give a final product stream, the proportion of said effluent stream that is passed through said at least one secondary bed being such that the final product stream has the desired sulphur contaminant content, and, after at least one secondary bed is saturated so that it can no longer absorb said sulphur contaminant under the prevailing conditions, switching the flow of said fluid stream so that a saturated secondary bed is used as the primary bed of absorbent, replacing the absorbent in the previous primary bed with a fresh charge of particulate absorbent comprising said variable valency metal compound and then using said previous primary bed as a secondary bed.
It is seen that the absorption of the sulphur contaminant, e.g. hydrogen sulphide, by the secondary bed converts the aforesaid sulphur absorbent, i.e. oxide, hydroxide, carbonate or basic carbonate of the variable valency metal, in that bed to a sulphide of said variable valency metal which is then used as the bed, i.e. primary bed, of a sulphide of the variable valency metal required for removal of the second contaminant. When the process is first started up it is necessary that the absorbent in the primary bed comprises a sulphide of the variable valency metal. A pre-sulphided variable valency metal absorbent may be charged to the vessel as the primary bed. Alternatively the absorbent may be the product of sulphiding an absorbent comprising an oxide, hydroxide, carbonate or basic carbonate of the variable valency metal in situ, for example as described in aforesaid EP 0 480 603. Thus an unsulphided absorbent may be charged to the vessel and then a fluid containing a sulphur compound that reacts with the variable valency metal compounds to give the variable valency metal sulphide may be passed through the bed until the variable valency metal compounds have been converted to the sulphide. At that stage, flow of the fluid containing the second contaminant may be commenced.
As will be described hereinafter, it is preferred to employ a series of three secondary beds, and the fluid stream flow is switched after the second of the secondary beds has become saturated with sulphur, with the second of the secondary beds being used as the new primary bed and the replenished previous primary bed being used as the second of the secondary beds. In this case, the first of the secondary beds will also be saturated with sulphur when the second secondary bed is saturated and this saturated first secondary bed is also replenished and is then used as the
Carnell Peter John Herbert
Willis Edwin Stephen
Griffin Walter D.
Imperial Chemical Industries plc
Pillsbury & Winthrop LLP
Preisch Nadine
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