Note: Descriptions are shown in the official language in which they were submitted.
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1 MULTI-STAGE HYDROCRACKER WITH KEROSENE RECYCLE
2
3 FIELD OF THE INVENTION
4
This invention relates to a multi-stage hydrocracking process in which light
6 products from the first stage, such as naphtha, kerosene and diesel, are
7 joined with naphtha, kerosene and diesel from other sources and recycled
8 from fractionation to a second stage (or subsequent stage) hydrocracker in
9 order to produce lighter products, such as gas and naphtha.
11 BACKGROUND OF THE INVENTION
12
13 Historically, there has been little interest in cracking kerosene or other
light
14 products to even lighter products. In the United States, there is little
demand
for gas or other very light volatile products. Bottoms materials are usually
the
16 material recycled in two-stage hydrocracking as practiced in the United
17 States. There is, however, a demand for products such as LPG and LNG in
18 Asia.
19
Although there has been demand for very light products in some parts of the
21 world, there was a belief by many experts that light products would not
crack
22 in most reactors (using conventional hydrocracking catalysts as opposed to
23 FCC catalysts) because they are in the vapor phase as opposed to the liquid
24 phase. This belief apparently originated due to the fact that the
environment
in a single-stage hydrocracker, in the preserice of H2S and NH3, is not
26 conducive to cracking of light products.
27
28 The concept of recycling bottoms material back to an initial hydrocracking
29 stage (rather than a second hydrocracking stage) is well known. U.S. Pat.
No. 6,261,441 (Gentry et al.) discloses recycling of bottoms material which
31 has been hydrocracked and dewaxed back to a hydrocracker.
32
1
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1 U.S. Pat. No. 5,447,621 (Hunter) discloses a middle distillate upgrading
2 process. A middle distillate side stream of a conventional single-stage
3 hydrocracking process is circulated to a hydrotreating stage, such as an
4 aromatics saturation reactor and/or a catalytic dewaxing reactor in order to
effect middle distillate upgrade. The upgraded product is then finished in a
6 fractionation stage side-stripper column. This invention discloses passing
7 middle distillate to a hydrotreating stage. The middle distillates are being
8 upgraded, not cracked, as in the instant invention.
9
U.S. Pat. No. 4,789,457 (Fischer et al.) discloses a process in which a highly
11 aromatic substantially dealkylated feedstock is processed directly to high
12 octane gasoline by hydrocracking over a catalyst preferably comprising a
13 large pore zeolite such as zeolite Y, in addition to a hydrogenation-
14 dehydrogenation component. The feedstock is preferably a light cycle oil.
Light cycle oil is heavier than the kerosene and naphtha cracked in the
instant
16 invention, and only one hydrocracking stage is employed in Fischer et al.
17
1g SUMMARY OF THE INVENTION
19
The Applicants have found that in the environment of a clean second-stage
21 hydrocracker, with heteroatoms removed, light products will crack. The
22 examples demonstrate that the net yield of kerosene decreased when
23 recycled to the second stage on a raw feed blend basis, while the qualities
of
24 the middle distillates remained the same. Recycling the kerosene to the
second stage increased the yield of 170-350°F reformer naphtha, the
product
26 most highly valued by the customer.
27
28 The invention disclosed herein is a process for the production of light
29 products, such as gas and naphtha, by processing kerosene in a second
stage (or a subsequent stage) of a multi-stage hydrocracker. Kerosene,
31 diesel and naphtha from other sources are included in the recycle, and
32 subsequent hydroprocessing stages are maintained at lower pressures than
33 the initial hydroprocessing stage. This results in cost savings.
2
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1 The instant invention is summarized as follows:
2
3 A method for hydroprocessing a hydrocarbon feedstock, the method
4 employing multiple hydroprocessing zones within a single reaction loop and
comprising the following steps:
6
7 (a) passing a hydrocarbonaceous feedstock to a first hydroprocessing zone
8 having one or more beds containing hydroprocessing catalyst, the
9 hydroprocessing zone being maintained at hydroprocessing conditions,
wherein the feedstock is contacted with catalyst and hydrogen to
11 produce a vapor stream and a liquid stream as effluent;
12
13 (b) removing the vapor stream of step (a), which comprises hydrogen,
14 hydrogen sulfide and light hydrocarbonaceous gases overhead;
16 (c) combining the liquid stream of step (b) with the liquid effluent from
other
17 hydroprocessing zones;
18
19 (d) passing the liquid stream of step (c), which comprises
hydrocarbonaceous compounds boiling in approximately the same range
21 of the hydrocarbonaceous feedstock, to fractionation;
22
23 (e) separating the liquid stream of step (d), in fractionation, into gas,
24 naphtha, kerosene and diesel fractions, in addition to the bottoms
fraction;
26
27 (f) passing the bottoms fraction of step (e) to further processing or
recycling
28 to one or more of the other hydroprocessing zones of step (c);
29
(g) passing one or more of the naphtha, kerosene and diesel fractions to
31 further processing as products or recycling one or more of the fractions
32 to one or more of the other hydroprocessing zones of step (c) the
33 kerosene, naphtha, and diesel fractions being in combination with
3
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1 kerosene, naphtha and diesel fractions from other sources, said
2 hydroprocessing zones or zones being maintained at hydroprocessing
3 conditions and at lower pressure than the first hydroprocessing zone,
4 and possessing an environment substantially free of H2S, NH3, or other
heteroatom contaminants;
6
7 (h) passing the effluent of step (g) to fractionation; and
8
9 (i) recovering in fractionation an increased amount of gas and naphtha, in
the fractionation stage of step (h) than in the fractionation step of
11 step (e).
12
13 BRIEF DESCRIPTION OF THE DRAWING
14
The Figure illustrates a two-stage hydrocracking process having the capability
16 for recycle of bottoms fractions, diesel fractions, kerosene fraction or
naphtha
17 fractions to the second reactor stage.
18
19 DETAILED DESCRIPTION OF THE INVENTION
21 Preheated oil feed in stream 1 is mixed with hydrogen in stream 2 prior to
its
22 entrance into first stage or primary hydroprocessing zone 10. This
23 hydroprocessing zone is preferably a downflow, fixed bed reactor. This
24 reactor contains multiple beds of hydroprocessing catalysts. At least one
bed
contains hydrocracking catalyst.
26
27 The effluent 3 of the first stage reactor, which has been hydrotreated and
28 partially hydrocracked, comprises a liquid stream and a vapor stream. The
29 vapor stream 3(a) is removed overhead. It comprises hydrogen, hydrogen
sulfide and light hydrocarbonaceous gases. The liquid stream 3(b) is
31 combined with the liquid effluent from other process zones, represented by
32 stream 4. Stream 3(b) and stream 4 are combined to create stream 5.
33 Stream 5 is passed to the fractionation unit 30, where it is separated into
gas
4
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1 stream 6, naphtha stream 7, kerosene stream 8, diesel stream 9, and bottoms
2 stream 14. The naphtha product may alternately be recycled, in whole or in
3 part, through stream 11 to stream 15, and ultimately to second stage reactor
4 20. Kerosene product may alternately be recycled, in whole or in part,
through stream 12 to stream 15, and ultimately to second stage reactor 20.
6 Diesel product may be alternately recycled, in whole or in part, through
stream
7 13 to stream 15, and ultimately to second stage reactor 20. Bottoms material
8 in stream 14 may be passed to further processing (in stream 14a) or,
9 alternately, may be recycled in stream 14(b) to second reactor 20. Second
reactor 20 represents hydroprocessing zones subsequent to the first
11 hydroprocessing zone. Each of these zones possesses an environment
12 substantially free of H2S, NH3 or other heteroatom components.
13
14 Feeds
16 A wide variety of hydrocarbon feeds may be used in the instant invention.
17 Typical feedstocks include any heavy or synthetic oil fraction or process
18 stream having a boiling point above 392°F (200°C). Such
feedstocks include
19 vacuum gas oils, heavy atmospheric gas oil, delayed coker gas oil,
visbreaker
gas oil demetallized oils, vacuum residua, atmospheric residua, deasphalted
21 oil, Fischer-Tropsch streams, and FCC streams.
22
23 Products
24
Although emphasis is placed on the increased production of gas and naphtha,
26 the process of this invention is also useful in the production of middle
distillate
27 fractions boiling in the range of about 250-700°F (121-
371°C). A middle
28 distillate fraction is defined as having an approximate boiling range from
about
29 250°F to 700°F. At least 75 vol %, preferably 85 vol %, of
the components of
the middle distillate have a normal boiling point of greater than
250°F. At
31 least about 75 vol %, preferably 85 vol %, of the components of the middle
32 distillate have a normal boiling point of less than 700°F. The term
"middle
33 distillate" includes the diesel, jet fuel and kerosene boiling range
fractions.
5
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1 The kerosene or jet fuel boiling point range refers to the range between
280°F
2 and 525°F (38-274°C). The term "diesel boiling range" refers
to hydrocarbons
3 boiling in the range from 250°F to 700°F (121-371°C).
4
Gasoline and naphtha production is emphasized in the process of this
6 invention. Gasoline or naphtha normally boils in the range below
400°F
7 (204°C), or Coo-. Boiling ranges of various product fractions
recovered in any
8 particular refinery will vary with such factors as the characteristics of
the crude
9 oil source, local refinery markets, and product prices.
11 Heavy hydrotreated gas oil, another product of this invention, usually
boils in
12 the range from 550°F to 700°F.
13
14 Conditions
16 Hydroprocessing conditions is a general term which refers primarily in this
17 application to hydrocracking or hydrotreating, preferably hydrocracking.
The
18 first stage reactor, as depicted in Figure 1, is a ,partial conversion
19 hydrocracker.
21 Typical hydrocracking conditions include a reaction temperature of from
22 400°F-950°F (204°C-510°C), preferably
650°F-850°F (343°C-454°C).
23 Reaction pressure ranges from 500 to 5000 psig (3.5-4.5 MPa), preferably
24 1500-3500 psig (10.4-24.2 MPa). LHSV ranges from 0.1 to 15 hr ~ (v/v),
preferably 0.25-2.5 hr'. Hydrogen consumption ranges from 500 to
26 2500 SCF per barrel of liquid hydrocarbon feed (89.1-445m3 H2/m3 feed).
27 Reactors subsequent to the first hydroprocessing reactor are operated at a
28 pressure at least 100 psig lower than that of the first reactor, and
preferably
29 from 500 to 1000 psig lower than the first reactor.
6
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1 Catalyst
2
3 Each hydroprocessing zone may contain only one catalyst, or several
4 catalysts in combination.
6 The hydrocracking catalyst generally comprises a cracking component, a
7 hydrogenation component, and a binder. Such catalysts are well known in the
8 art. The cracking component may include an amorphous silica/alumina phase
9 and/or a zeolite, such as a Y-type or USY zeolite. Catalysts having high
cracking activity often employ REX, REY and USY zeolites. The binder is
11 generally silica or alumina. The hydrogenation component will be a Group
VI,
12 Group VII, or Group VIII metal or oxides'or sulfides thereof, preferably
one or
13 more of iron, chromium, molybdenum, tungsten, cobalt, or nickel, or the
14 sulfides or oxides thereof. If present in the catalyst, these hydrogenation
-
components generally make up from about 5% to about 40% by weight of the
16 catalyst. Alternatively, noble metals, especially platinum and/or
palladium,
17 may be present as the hydrogenation component, either alone or in
18 combination with the base metal hydrogenation components iron, chromium
19 molybdenum, tungsten, cobalt, or nickel. If present, the platinum group
metals will generally make up from about 0.1 % to about 2% by weight of the
21 catalyst.
22
23 Hydrotreating catalyst usually is designed to remove sulfur and nitrogen
and
24 provide a degree of aromatic saturation. It will typically be a composite
of a
Group VI metal or compound thereof, and a Group VIII metal or compound
26 thereof supported on a porous refractory base such as alumina. Examples of
27 hydrotreating catalysts are alumina supported cobalt-molybdenum, nickel
28 sulfide, nickel-tungsten, cobalt-tungsten and nickel-molybdenum. Typically,
29 such hydrotreating catalysts are presulfided.
31 Catalyst selection is dictated by process needs and product specifications.
In
32 particular, a noble catalyst may be used in the second stage when there is
a
33 low amount of H2S present.
7
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1 The Examples below demonstrate the relative effectiveness of recycling
2 kerosene to produce lighter products of high quality, as opposed to not
3 recycling kerosene.
4
EXAMPLE
6
7 The "recycle" of kerosene was simulated by passing kerosene from the first
8 hydrocracking stage over the catalyst in the second hydrocracking stage. The
9 first stage kerosene possessed a smoke point of 14 mm and 25 LV%
aromatics. Net yields from the runs where kerosene was "recycled" have
11 been calculated by deducting the supplemental kerosene feed from the gross,
12 measured kerosene yield (gross weight of kerosene product-weight of
13 kerosene "recycled" = net yield of kerosene product).
14
In kerosene recycle mode, a base metal zeolite hydrocracking catalyst
16 cracked a substantial fraction of the kerosene to naphtha and gas (see
17 Tables 1 and 2). The net yield of kerosene decreased on a raw feed blend
18 basis and the qualities of the middle distillates remained the same.
Recycling
19 the kerosene to the second stage did increase the yield of 170-350°F
reformer
naphtha, a product in most demand by the customer.
8
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1 TABLE 1
2
3 Two-Stage Hydrocracking of
4 Vacuum Gas Oil / Hydrocracking Gas Oil /
Liaht Cycle Oil Feed Blend Usina Hydrocracking Catalyst
6
7 Run Hours 600-624
8 Reactor 1 Temp, °F 725
9 Reactor 2 Temp, °F 669
Overall LHSV, h~' 1.00
11 Per Pass Conversion 58
12 Total Pressure, PSIG 2297
13No Loss Prod. Yields Wt. % Vol.
14C~ 0.13
15C2 0.18
16C3 0.56
17iC4 0.94 1.62
18nC4 0.63 1.06
19C5-170F 3.43 5.04
20170-350F 13.04 16.48
21350-550F 29.99 33.44
22550-RCP 15.57 16.92
23Recycle Bleed 34.84 38.17
24Recycle Cut Point, F 656
25Total C4- 2.44
26Total C5+ 96.87 110.04
27Closure 99.6 //
28
29Fractionator Bottoms Nitrogen,24.5
ppm
9
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1 TABLE 2
2
3 Two-Stage H ydrocracking
of
4 Vacuum Gas Oil / Hydrocracked
Gas Oil / Light Cycle Oil
Feed Blend Using HydrocrackingCatalyst, Kerosene Recycle"
with "
6
7 Hours 816-840
8 Reactor 1 Temperature, F 725
9 Reactor 2 Temperature, F 691
LHSV, 1/Hr 1.00
11 Per Pass Conversion, % 60
12 Total Pressure, psig 2294
13
14 No Loss Product Yields Wt. % Vol
C~ 0.13
16 C2 0.20
17 C3 0.80
18 i C4 1.80
19 nC4 0.99
C5-170F 6.4 9.5
21 170-350F 18.0 22.8
22 350-550F 24.0 26.8
23 550-650F 15.3 16.6
24 650F+ ' 32.4 35.3
Recycle cut point 650F
26 Total C5+ 96.1 111.0
27 Total C4- 3.72
28 Chemical HZ Consumption, 2080
SCF/B
29 Closure, % 99.7
31 Fractionator Bottoms Nitrogen,28
ppm
