Mineral oils: processes and products – Chemical conversion of hydrocarbons – Plural parallel stages of chemical conversion
Reexamination Certificate
1999-07-26
2001-12-11
Myers, Helane E. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Plural parallel stages of chemical conversion
C208S058000, C208S061000, C208S080000
Reexamination Certificate
active
06328879
ABSTRACT:
BACKGROUND OF THE INVENTION
The field of art to which this invention pertains is the simultaneous hydroprocessing of two hydrocarbonaceous feedstocks. Petroleum refiners often produce desirable products such as turbine fuel, diesel fuel and other products known as middle distillates as well as lower boiling hydrocarbonaceous liquids such as naphtha and gasoline by hydrocracking a hydrocarbon feedstock derived from crude oil, for example. Feedstocks most often subjected to hydrocracking are gas oils and heavy gas oils recovered from crude oil by distillation. A typical heavy gas oil comprises a substantial portion of hydrocarbon components boiling above about 700° F., usually at least about 50 percent by weight boiling above 700° F. A typical vacuum gas oil normally has a boiling point range between about 600° F. and about 1050° F.
Hydrocracking is generally accomplished by contacting in a hydrocracking reaction vessel or zone the gas oil or other feedstock to be treated with a suitable hydrocracking catalyst under conditions of elevated temperature and pressure in the presence of hydrogen so as to yield a product containing a distribution of hydrocarbon products desired by the refiner. The operating conditions and the hydrocracking catalysts within a hydrocracking reactor influence the yield of the hydrocracked products.
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 hydrocracking methods which provide lower costs and higher liquid product yields and quality. It is generally known that enhanced product selectivity can be achieved at lower conversion per pass (60% to 90% conversion of fresh feed) through the catalytic hydrocracking zone. However, it was previously believed that any advantage of operating at below about 60% conversion per pass was negligible or would only see diminishing returns. Low conversion per pass is generally more expensive, however, the present invention greatly improves the economic benefits of a low conversion per pass process and demonstrates the unexpected advantages.
INFORMATION DISCLOSURE
U.S. Pat. No. 5,720,872 discloses a process for hydroprocessing liquid feedstocks in two or more hydroprocessing stages, which are in separate reaction vessels and wherein each reaction stage contains a bed of hydroprocessing catalyst. The liquid product from the first reaction stage is sent to a low pressure stripping stage and stripped of hydrogen sulfide, ammonia and other dissolved gases. The stripped product stream is then sent to the next downstream reaction stage, the product from which is also stripped of dissolved gases and sent to the next downstream reaction stage until the last reaction stage, the liquid product of which is stripped of dissolved gases and collected or passed on for further processing. The flow of treat gas is in a direction opposite the direction in which the reaction stages are staged for the flow of liquid. Each stripping stage is a separate stage, but all stages are contained in the same stripper vessel.
International Publication No. WO 97/38066 (PCT/US 97/04270) discloses a process for reverse staging in hydroprocessing reactor systems.
U.S. Pat. No. 3,328,290 (Hengstebech) discloses a two-stage process for the hydrocracking of hydrocarbons in which the feed is pretreated in the first stage.
U.S. Pat. No. 5,114,562 (Haun et al) discloses a process wherein a middle distillate petroleum stream is hydrotreated to produce a low sulfur and low aromatic product employing two reaction zones in series. The effluent from the first reaction zone (desulfurization) is cooled and introduced into a hydrogen stripping zone wherein hydrogen sulfide is removed overhead along with a small amount of hydrocarbons which were in the vapor at conditions present at the top of the stripping zone. The bottom stream from the stripping zone is reheated and introduced into the second reaction zone (aromatic saturation) containing sulfur-sensitive noble metal hydrogenation catalyst. The operating pressure increases and the temperature decreases from the first to the second reaction zones. The desulfurization conditions employed are relatively moderate as only a very limited amount of cracking is desired. It is totally undesired to perform any significant cracking within the second reaction zone. It is specifically desired to minimize the content of heavy product distillate hydrocarbons such as diesel fuel in the vapor phase of the stripping zone.
BRIEF SUMMARY OF THE INVENTION
The present invention is a catalytic hydrocracking process which simultaneously hydroprocesses two feedstocks to provide higher liquid product yields and increase the quality of the liquid products. The process of the present invention provides the yield advantages associated with a low conversion per pass operation without compromising unit economics. In addition, lower capital costs will be realized with the use of the present invention.
In the present invention, a first hydrocarbonaceous feedstock and hydrogen are passed to a hydrocracking reaction zone to produce a stream containing lower boiling hydrocarbonaceous compounds which stream is in turn passed to a hot, high pressure stripper utilizing a hot, hydrogen-rich stripping gas to produce a vapor stream containing hydrogen and hydrocarbonaceous compounds boiling at a temperature below the first feedstock and a liquid stream containing hydrocarbonaceous compounds boiling in the range of the first feedstock. A second hydrocarbonaceous feedstock having a boiling temperature range lower than the first hydrocarbonaceous feedstock is passed into an upper end of the stripper to serve as reflux. The vapor stream containing hydrogen and hydrocarbonaceous compounds boiling at a temperature below the first feedstock is introduced into a post-treat hydrogenation reaction zone to saturate at least a portion of the aromatic compounds contained therein. At least a portion of the second feedstock is vaporized in the stripper and passes into the post-treat hydrogenation reaction zone to saturate aromatic compounds and thereby improve the quality of the hydrocarbonaceous effluent from the post-treat zone. At least a portion of the effluent from the post-treat hydrogenation reaction zone is condensed to produce a second liquid stream containing hydrocarbonaceous compounds boiling at a temperature below the first feedstock and a second vapor stream containing hydrogen and hydrogen sulfide. In a preferred embodiment, at least a portion of the hydrogen sulfide is removed from the second vapor stream before it is recycled to the hydrocracking zone.
In accordance with one embodiment the present invention relates to a process for the simultaneous hydroprocessing of two feedstocks having different boiling ranges which process comprises: (a) passing a first hydrocarbonaceous feedstock and hydrogen to a hydrocracking zone containing a hydrocracking catalyst and operating at a temperature of about 400° F. to about 900° F., a pressure from about 500 psig to about 2500 psig, a liquid hourly space velocity from about 0.1 hr
−1
to about 15 hr
−1
and recovering a hydrocracking zone effluent therefrom; (b) passing the hydrocracking zone effluent directly to a hot, high pressure stripper utilizing a hot, hydrogen-rich stripping gas to produce a first vapor stream comprising hydrogen, hydrogen sulfide and hydrocarbonaceous compounds boiling at a temperature below the first hydrocarbonaceous feedstock, and a first liquid stream comprising hydrocarbonaceous compounds boiling in the range of the first hydrocarbonaceous feedstock; (c) passing a second hydrocarbonaceous feedstock having a boiling temperature range lower than that of the first hydrocarbonaceous feedstock into an upper end of the stripper to serve as reflux; (d) passing at least a portion of the first vapor stream recovered in step (b) to a post-treat hydrogenation reaction zone to saturate aromatic compounds; (e) condensing at least a portion of the resulting effluent from the post-t
Cutts, Jr. John G.
Myers Helane E.
Tolomei John G.
UOP LLC
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