Chemistry of hydrocarbon compounds – Plural serial diverse syntheses – To produce unsaturate
Reexamination Certificate
1999-12-06
2001-02-27
Yildirim, Bekir L. (Department: 1764)
Chemistry of hydrocarbon compounds
Plural serial diverse syntheses
To produce unsaturate
C585S264000, C585S311000, C585S314000, C585S315000, C585S613000, C585S615000, C208S050000
Reexamination Certificate
active
06194626
ABSTRACT:
BACKGROUND OF THE INVENTION
The field of art to which this invention pertains is the purification of a diolefin hydrocarbon stream produced in a naphtha steam cracker and containing trace quantities of undesirable acetylene compounds. The production of diolefins by means of naphtha cracking processes is well known and widely practiced to produce a wide variety of products and precursor products. Most of these diolefin production processes produce undesirable trace quantities of acetylene. One technique which is used to purify diolefin streams selectively hydrogenates the acetylene compounds while minimizing the destruction or hydrogenation of the diolefin compounds.
The selective hydrogenation of the acetylene compounds is generally conducted in the presence of a selective hydrogenation catalyst and hydrogen and conducted at an elevated pressure and temperature. Such selective hydrogenation catalysts are well known in the art and include, for example, a catalyst containing copper metal associated with one or more activator metals impregnated on an alumina support. During the acetylene hydrogenation polymers are formed and deposited on the catalyst thereby reducing the activity of the catalyst. One known method of regenerating spent or partially spent catalyst is to perform a controlled carbon bum and subsequent metal reduction to remove catalyst contaminants which are formed as an undesirable by-product of the acetylene hydrogenation. The carbon burn regeneration techniques necessarily require that the reaction zone containing the spent catalyst be taken off-line and that ancillary regeneration equipment be provided.
INFORMATION DISCLOSURE
U.S. Pat. No. 3,634,536 (Frevel et al) discloses a process for selectively hydrogenating acetylenic impurities in an isopropene- or butadiene-containing stream whereby carbon monoxide is utilized during hydrogenation over a copper-based catalyst.
U.S. Pat. No. 4,440,956 (Couvillion) discloses a catalyst for the removal of acetylenes from liquid hydrocarbon streams with a minimum loss of diolefinic unsaturation present in the liquid composition.
Although a wide variety of process flow schemes, operating conditions and catalysts have been used in commercial activities, there is always a demand for new selective hydrotreating processes which provide lower costs, higher selectivity and longer on-stream operation.
The present invention is able to maintain the high activity of the selective hydrogenation catalyst by discontinuing the flow of diolefinic hydrocarbon feedstock to at least one off-line hydrogenation reaction zone and contacting the at least partially spent catalyst with hydrogen and a stream containing naphtha in order to recover at least a portion of the lost activity.
BRIEF SUMMARY OF THE INVENTION
The present invention is a process for the purification of a diolefin hydrocarbon stream produced in a naphtha steam cracker to produce a high quality diolefin hydrocarbon stream having extremely low levels of acetylene over an extended period because of the ability to readily regenerate catalyst contained in an off-line selective hydrogenation reaction zone while continuing to operate an on-line selective hydrogenation reaction zone. The spent or partially spent catalyst is contacted with hydrogen and a stream containing naphtha in order to restore at least a portion of the fresh catalyst activity. The naphtha in combination with hydrogen is unexpectedly able to remove deactivating polymers and a dragstream of naphtha containing polymers is able to be admixed with the naphtha feedstock to the steam cracker in order to satisfactorily dispose of the polymers while simultaneously reclaiming useful hydrocarbons.
In accordance with one embodiment, the present invention relates to a process for the purification of a diolefin hydrocarbon stream from a naphtha steam cracker and containing trace quantities of acetylene compounds and the cyclic regeneration of an at least partially spent selective hydrogenation catalyst which process comprises: (a) introducing a naphtha feedstock and a recycle stream comprising naphtha and polymer compounds into a naphtha steam cracker to produce a diolefin hydrocarbon stream containing trace quantities of acetylene compounds; (b) passing the diolefin hydrocarbon stream containing trace quantities of acetylene compounds and elemental hydrogen into a selective hydrogenation zone to selectively hydrogenate at least a portion of the acetylene compounds and to produce an at least partially spent selective hydrogenation catalyst; (c) passing the resulting effluent from the selective hydrogenation zone in step (b) to a fractionation zone to produce a diolefin hydrocarbon stream having a reduced concentration of acetylene compounds; (d) contacting the at least partially spent selective hydrogenation catalyst in the selective hydrogenation zone with a stream comprising naphtha and hydrogen to reduce the polymer content of the selective hydrogenation catalyst to thereby increase hydrogenation activity; (e) passing the resulting effluent from the selective hydrogenation zone in step (d) to the fractionation zone to produce a stream comprising naphtha and polymer compounds; (f) recycling at least a portion of the stream comprising naphtha and polymer compounds to provide at least a portion of the stream comprising naphtha and hydrogen in step (d); (g) recycling at least another portion of the stream comprising naphtha and polymer compounds to step (a); (h) recovering the diolefinic hydrocarbon stream having a reduced concentration of acetylene compounds produced in step (c); and (i) reintroducing the diolefin hydrocarbon stream containing trace quantities of acetylene compounds and elemental hydrogen into the selective hydrogenation zone after contact and extraction with the stream comprising naphtha and hydrogen.
REFERENCES:
patent: 3634536 (1972-01-01), Frevel et al.
patent: 4440956 (1984-04-01), Couvillion
patent: 5981818 (1999-11-01), Purvis et al.
Cottrell Paul R.
Vora Bipin V.
Cutts, Jr. John C.
Spears, Jr. John E.
Tolomei John G.
UOP LLC
Yildirim Bekir L.
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