Hydrocracking process with interstage steam stripping

Abstract

In a hydrocracking process, the product from the first stage reactor passes through a steam stripper to remove hydrogen, H.sub.2S, NH.sub.3, light gases (C.sub.1-C.sub.4), naphtha and diesel products. The stripper bottoms are separated from hydrogen, H.sub.2S, NH.sub.3, light gases (C.sub.1-C.sub.4), naphtha, and diesel products and treated in a second stage reactor. The effluent stream from the second stage reactor, along with the stream of separated hydrogen, H.sub.2S, NH.sub.3, light gases (C.sub.1-C.sub.4), naphtha, and diesel products, are passed to a separation stage for separating petroleum fractions. Preferably, the effluent stream from the first stage reactor is passed through a steam generator prior to the steam stripping step. In an alternate embodiment, the effluent stream from the first stage reactor is passed through a vapor/liquid separator stripper vessel prior to the steam stripping step.

Claims

1. A process for hydrocracking a hydrocarbon feedstock comprising the steps of: supplying the feedstock and hydrogen to an input of a first stage reactor containing a first stage hydrocracking catalyst for removal of heteroatoms and cracking of high molecular weight molecules into lower molecular weight hydrocarbons to produce a first-stage reactor effluent; thereafter passing the first stage effluent to a steam stripper vessel to separate hydrogen, H.sub.2S, NH.sub.3, light gases (C.sub.1-C.sub.4), naphtha, and diesel products; passing the stripper bottoms from the stripper vessel, and hydrogen, to a second stage reactor containing a second stage hydrocracking catalyst; combining a hydrocracked effluent stream of the second stage reactor with the hydrogen, H.sub.2S, NH.sub.3, light gases (C.sub.1-C.sub.4), naphtha, and diesel products separated in the steam stripper vessel to form a combined product stream; and passing the combined product stream to a separation stage for separation of the components into predetermined product streams.

2. The process of claim 1, wherein the effluent stream from the first stage reactor is passed through a heat exchange steam generator prior to being passed to the steam stripper vessel.

3. The process of claim 1, wherein the effluent stream from the first stage reactor is passed through vapor/liquid separator stripper vessel to produce tops and bottoms, the bottoms being passed to the steam stripper vessel.

4. The process of claim 1, wherein the first stage hydrocracking catalyst is selected from the group consisting of amorphous alumina catalysts, amorphous silica alumina catalysts, zeolite-based catalysts, and a combination comprising at least one of amorphous alumina catalysts, amorphous silica alumina catalysts, and zeolite-based catalyst.

5. The process of claim 1, wherein the first stage hydrocracking catalyst further comprises an active phase of Ni, W, Mo, Co, or a combination comprising at least one of Ni, W, Mo, and Co.

6. The process of claim 1, wherein 10% to 80% by volume of hydrocarbons boiling above 370° C. at a hydrogen partial pressure in the range of 100200 kg/cm.sup.2 are converted in the first reactor to one or more light gases selected from the group consisting of methane, ethane, propane, n-butane, isobutene, hydrogen sulfide, ammonia, naphtha fractions boiling in the range of 180° C. to 375° C., diesel fractions boiling in the range of 180° C. to 375° C., and combinations comprising at least one of the foregoing light gases.

7. The process of claim 1, wherein the first reactor is at a hydrogen partial pressure is in the range of 100-150 kg/cm.sup.2.

8. The process of claim 1, wherein the flow of feedstock oil to the first reactor is in the range of 300-2000 m.sup.3 over 1000 m.sup.3 of hydrotreating catalyst per hour.

9. The process of claim 1, wherein the first or second reactor is a fixed-bed, an ebullated-bed, a slurry-bed, or a combination thereof.

10. The process of claim 1, wherein a portion of the effluent stream of hydrogen, H.sub.2S, NH.sub.3, light gases (C.sub.1-C.sub.4), naphtha, and diesel products removed from the steam stripper vessel are directed through a separator vessel to separate water, gas, and liquids; a sour diesel stream is also supplied to the separator vessel to mix with the effluent stream; and wherein the combined effluent stream/sour diesel stream is directed through a diesel hydrotreater unit to produce ultra-low sulfur diesel fuel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be described in further detail below and with reference to the attached drawings in which the same and similar elements will be referred to by the same number, and where:

(2) FIG. 1 is a schematic diagram of a conventional two-stage hydrocracking unit of the prior art;

(3) FIG. 2 is a schematic diagram of an embodiment of the present invention;

(4) FIG. 3 is a schematic diagram of another embodiment of the present invention; and

(5) FIG. 4 is a schematic diagram of a further embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) Referring to FIG. 2, the hydrocarbon feedstock stream 11 and a hydrogen stream 12 are fed to the first stage reactor vessel 10 for removal of heteroatoms containing sulfur, nitrogen and trace amounts of such metals as Ni, V, Fe, and also to crack high molecular weight, high boiling molecules into lower molecular weight, lower boiling hydrocarbons in the range 5-60 W %.

(7) The effluent stream 13 is sent to a steam generating heat exchanger 20 to cool the reaction products and to generate a steam 22 from water 21. The cooled products 23 from the steam generator are sent to a steam stripper vessel 30 to remove hydrogen, H.sub.2S, NH.sub.3, light gases (C.sub.1-C.sub.4), naphtha and diesel products boiling in the nominal range of 36-370° C. The steam stripper is supplied with the steam 22 from the steam generator 20.

(8) The stripper bottoms 32, free of light gases, H.sub.2S, NH.sub.3 and light fractions stream 31, are combined with a hydrogen stream 33 and sent to the second stage of the hydrocracking unit vessel 40. The second stage effluent stream 41 are combined with the light stripper products 31, and the combined stream 42 is sent to several separation and cleaning vessels including a fractionator vessel 50 to obtain final hydrocracking gas and liquid products.

(9) Hydrocracker products include stream 51 containing H.sub.2S, NH.sub.3, light gases (C.sub.1-C.sub.4), naphtha stream 52 boiling in the range C5-180° C., kerosene stream 53 boiling in the range of 180-240° C., diesel stream 54 boiling in the range 240-370° C., and unconverted hydrocarbon fractions stream 55 boiling above 370° C.

(10) Referring now to the embodiment of FIG. 3, the hydrocarbon feedstock stream 11 and hydrogen stream 12 are fed to the first stage reactor vessel 10 for removal of heteroatoms containing sulfur, nitrogen and trace amounts of such metals as Ni, V and Fe, and also for the cracking of high molecular weight, high boiling molecules into lower molecular weight, lower boiling hydrocarbons in the range of from 5-60 W %. The effluent stream 13 is sent to a heat exchanger steam generator 20 to cool the reaction products and generate steam 22 from feed water 21. The cooled products 23 from the steam generator are sent to a vapor/liquid separator stripper 30 to remove the light gases including hydrogen, H.sub.2S, NH.sub.3 and C.sub.1-C.sub.4 hydrocarbons which exit as the effluent stream 31

(11) The vapor/liquid separator bottoms stream 32 is sent to a steam stripper vessel 40 to remove naphtha and diesel products nominally boiling in the range of from 36-370° C. The steam stripper is fed by the steam 22 generated by the steam generator 20. The stripper bottoms 42, free of light gases, H.sub.2S, NH.sub.3 and light fractions, are combined with hydrogen stream 43 and sent to a second stage hydrocracking unit vessel 50.

(12) The second stage effluent stream 51 is then combined with the light stripper products 41, and the combined stream 52 is sent to several separation and cleaning vessels including a fractionator vessel 60 to obtain final hydrocracking gas and liquid products. Hydrocracker products include H.sub.2S, NH.sub.3, light gases (C.sub.1-C.sub.4) stream 61, naphtha boiling in the range 36-180° C. stream 62, kerosene stream 63, diesel boiling in the range 180-370 C stream 64 and unconverted hydrocarbon fractions boiling above 370° C. stream 65.

(13) The embodiment shown in FIG. 4 includes unit operations performing processes similar to the embodiment of FIG. 2. In addition, however, the FIG. 4 embodiment includes a diesel hydrotreater for hydrotreating a diesel stream and a water recycle stream. As shown in FIG. 4, part of the stripper top stream 31 is passed through a steam generator to a separator vessel 60 to separate water, gas, and liquids. A portion of the water is extracted and sent back to the steam generator 20 and thereafter to stripper unit 30.

(14) A sour diesel stream from the refinery is supplied to the vessel 60, combined with the top stream, and sent to the diesel hydrotreater 70 for ultra-low sulfur diesel production. The remaining water from the hydrotreater unit 70 is recycled to the stripper unit 30, while ultra-low sulfur, or sweet, diesel (“ULSD”) from the hydrotreater is recovered for the market.

EXAMPLE

(15) A feedstock blend containing 15 V % demetalized oil (DMO) and 85 V % vacuum gas oil (VGO) of which 64% is heavy VGO and 21% is light VGO, the properties of which are shown in Table 1, was subjected to hydrocracking over a catalytic system consisting of amorphous and zeolite supports promoted with Ni, W, Mo metals at 115 kg/cm.sup.2 hydrogen partial pressure, 800 m.sup.3 of feedstock over 1000 m.sup.3 of catalyst per hour, 1,265 liters of hydrogen to oil ratio and at a temperature ranging from 370-385° C.

(16) TABLE-US-00001 TABLE 1 Property Unit Method Blend Specific Gravity 0.918 API Gravity ° ASTM D4052 22.6 Sulfur W % ASTM D5453 2.2 Nitrogen ppmw ASTM D5762 751 Bromine Number g/100 g 3.0 Hydrogen W % ASTM D4808 12.02 Simulated Distillation ASTM D7213 IBP ° C. 210 10/30 ° C. 344/411 50/70 ° C. 451/498 90/95 ° C. 590/655 98 ° C. 719

(17) The product yields are shown in Table 2. The steam stripping of the first stage effluent improved the mid-distillate yields by about 5 W % and lowered the naphtha and light gas produced by about 5 W % and 0.5 W %, respectively.

(18) TABLE-US-00002 TABLE 2 Once-Through with Once-Through Interstage Stripping H.sub.2S, W % 2.58 2.58 C.sub.1-C.sub.4, W % 3.21 2.85 Naphtha, W % 25.16 19.77 Mid-distillates, W % 42.11 47.86 Bottoms, W % 29.60 29.60 Total, W % 102.65 102.65

(19) The current invention utilizes a steam stripper to simulate a two-stage hydrocracking unit configuration by removing the H2S, NH3, light gases (C1-C4), naphtha and diesel products nominally boiling in the range 36-370° C. from the first stage effluents. The steam-stripped products will be free of H2S and NH3 and NH3 and will contain unconverted hydrocarbons, resulting in higher activity for the catalysts because there is no poisonous H2S and NH3, and higher mid distillate selectivity because the light products will not be subjected to further cracking.

(20) Although the invention had been described in detail in several embodiments and illustrated in the figures, other modifications will be opponent to those of ordinary skill in the art from the description and the scope of the invention is to be determined by the claims that follow.