Chemistry of hydrocarbon compounds – Adding hydrogen to unsaturated bond of hydrocarbon – i.e.,... – Hydrocarbon is contaminant in desired hydrocarbon
Reexamination Certificate
1999-07-22
2001-08-07
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Adding hydrogen to unsaturated bond of hydrocarbon, i.e.,...
Hydrocarbon is contaminant in desired hydrocarbon
C585S258000, C585S810000, C208S296000
Reexamination Certificate
active
06271428
ABSTRACT:
BACKGROUND OF THE INVENTION
The field of art to which this invention pertains is the purification of a diolefin hydrocarbon stream containing trace quantities of acetylene compounds. The production of diolefins is well known and widely practiced to produce a wide variety of products and precursor products utilizing a variety of diolefin production processes including naphtha cracking processes and by-products from fluid catalytic cracking processes. 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 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 burn 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 continuously maintains the high activity of the selective hydrogenation catalyst during an extended run length without shutdown for catalyst regeneration. Higher average product quality when integrated over time on-stream improves the process economics and demonstrates the unexpected advantages.
BRIEF SUMMARY OF THE INVENTION
The present invention is a selective acetylene hydrogenation process which is able to produce a high quality diolefin having extremely low levels of acetylene over an extended period of time compared with the prior art. The process of the present invention provides a selective hydrogenation reaction zone wherein the catalyst activity is maintained at a high level while the process unit remains on stream by contacting the selective hydrogenation catalyst with a polymer solvent, diolefin feed and hydrogen.
In accordance with one embodiment, the present invention relates to a process for the purification of a diolefin hydrocarbon stream containing trace quantities of acetylene compounds which process comprises: (a) contacting the diolefin hydrocarbon stream containing trace quantities of acetylene compounds with a polymer solvent and introducing the resulting admixture together with elemental hydrogen into a selective hydrogenation zone to selectively hydrogenate at least a portion of the acetylene compounds; (b) passing the resulting effluent from the selective hydrogenation zone in step (a) to a fractionation zone to produce a diolefin hydrocarbon stream having a reduced concentration of acetylene compounds and a stream containing polymer solvent and polymer compounds; (c) recycling at least a portion of the stream containing polymer solvent and polymer compounds to provide at least a portion of the polymer solvent in step (a); (d) recovering at least another portion of the stream containing polymer solvent and polymer compounds; and (e) recovering the diolefin hydrocarbon stream having a reduced concentration of acetylene compounds produced in step (b).
In accordance with another embodiment, the present invention relates to a process for the purification of a butadiene hydrocarbon stream containing trace quantities of acetylene compounds which process comprises: (a) contacting the butadiene hydrocarbon stream containing trace quantities of acetylene compounds with a hexane solvent and introducing the resulting admixture together with elemental hydrogen into a selective hydrogenation zone containing a copper catalyst to selectively hydrogenate at least a portion of the acetylene compounds; (b) passing the resulting effluent from the selective hydrogenation zone in step (a) to a fractionation zone to produce a butadiene hydrocarbon stream having a reduced concentration of acetylene compounds and a stream containing hexane solvent and polymer compounds; (c) recycling at least a portion of the stream containing hexane and polymer compounds to provide at least a portion of the hexane solvent in step (a); (d) recovering at least another portion of the stream containing hexane solvent and polymer compounds; and (e) recovering the butadiene hydrocarbon stream having a reduced concentration of acetylene compounds produced in step (b).
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a simplified process flow diagram of a preferred embodiment of the present invention. The drawing is intended to be schematically illustrative of the present invention and not be a limitation thereof.
DETAILED DESCRIPTION OF THE INVENTION
It has been discovered that a selective hydrogenation zone for the hydrogenation of trace quantities of acetylene contained in a stream of diolefins may achieve continued start-of-run activity, yields and product quality by contacting the selective catalyst with a polymer solvent, diolefin feed and hydrogen. These advantages enable superior performance and economic results.
The process of the present invention is particularly useful for the production of high quality diolefin streams in a process having an extended on-stream capability. The diolefin feed stream may be any convenient hydrocarbon stream containing diolefin compounds and having undesirable trace quantities of acetylene compounds. It is contemplated that the diolefin feedstream contains diolefins containing from 3 to about 5 carbon atoms. A preferred diolefin feedstream contains butadiene.
In accordance with the present invention, the selected diolefin feedstock is introduced along with a polymer solvent and hydrogen into a selective hydrogenation reaction zone operating at selective hydrogenation conditions and containing a selective hydrogenation catalyst to produce an improved diolefin stream having a reduced concentration of acetylene compounds.
The polymer solvent may be selected from any compound or mixtures of compounds and which polymer solvent is capable of acting as a solvent for polymers which are produced during the selective hydrogenation reaction. Suitable solvents may be selected from alkane compounds having from about 4 to about 8 or more carbon atoms. In the case where the fresh feedstock is a stream of butadiene, a particularly preferred polymer solvent is hexane. The polymer solvent may be present in an amount of about 5 to about 100 weight percent based on the weight of diolefin. It is preferred that the polymer solvent has a boiling point greater than the diolefin feedstream. The selective hydrogenation conditions will depend upon the selected diolefinic feed and may be selected from a pressure from about 200 psig to about 500 psig and a temperature from about 90° F. to about 180° F.
The resulting effluent from the selective hydrogenation reaction zone is passe
Cutts, Jr. John G.
Griffin Walter D.
Preisch Nadine
Tolomei John G.
UOP LLC
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