Process for the production of light olefins and aromatics from a hydrocarbon feedstock

Abstract

The present invention relates to a process for the production of light olefins and aromatics from a hydrocarbon feedstock, comprising the following steps of: (a) feeding a hydrocarbon feedstock into a FCC unit (b) separating reaction products, which are generated from the FCC reaction, into a bottom stream, and middle stream and a top stream; (c) feeding the middle stream from (b) to a gasoline hydrocracker (GHC) unit, (d) separating reaction products of said GHC of step (c) into an overhead gas stream comprising hydrogen, methane and C2-C4 paraffins, and a bottom stream comprising aromatic hydrocarbon compounds, (e) feeding the overhead stream from the gasoline hydrocracker (GHC) unit into a steam cracker unit.

Claims

1. A process for the production of light olefins and aromatics from a hydrocarbon feedstock, the process consisting of (a) feeding a hydrocarbon feedstock into a fluid catalytic cracker (FCC) unit (b) separating reaction products, which are generated from the FCC reaction, into a bottom stream, and middle stream and a top stream; (c) feeding the middle stream from (b) to a gasoline hydrocracker (GHC) unit, (d) separating reaction products of said GHC of step (c) into an overhead gas stream comprising hydrogen, methane and C2-C4 paraffins, a stream rich in BTX and a heavy cycle oil stream, (e) separating C2-C4 paraffins from said overhead gas stream coming from the gasoline hydrocracker (GHC) unit, and feeding only said C2-C4 paraffins from said overhead gas stream from the gasoline hydrocracker (GHC) unit directly to the furnace section of a steam cracker unit; (f) combining the heavy cycle oil stream from (d) and the bottom stream from (b); (g) separating reaction products of said steam cracking unit in a separation section into an overhead stream, which contains C2-C6 alkanes, a middle stream, which contains C2-olefins, C3-olefins and C4-olefins, a first bottom stream comprising C9+ hydrocarbons, and a second bottom stream comprising aromatic hydrocarbon compounds and non-aromatic hydrocarbon compounds; and (h) sending the top stream from (b) to the separation section from (g), wherein the temperature in the FCC is 700 C.

Description

(1) The sole FIGURE provides a schematic flow sheet of an embodiment of the present invention.

EXAMPLE

(2) The process scheme can be found in the sole FIGURE. A typical feedstock 20, for example gas condensates, is sent directly to FCC unit 4. In FCC unit 4 the long-chain molecules of the gas condensates are broken into much shorter molecules by contacting the feedstock, at high temperature and moderate pressure, with a fluidized powdered catalyst. The reaction products, which are generated from the FCC reaction, are separated into a bottom stream 16, a middle stream 13 and a top stream 9. The middle stream 13 from FCC unit 4 is sent to a gasoline hydrocracker (GHC) unit 5. The reaction products of said GHC unit 5 are separated into an overhead gas stream 25 comprising hydrogen, methane and C2-C4 paraffins, and a stream 15 comprising aromatic hydrocarbon compounds, predominantly a so-called BTX fraction and a heavy fraction 24. The overhead stream 25 from the gasoline hydrocracker (GHC) unit 5 is sent to a steam cracker unit 1. As shown in the FIGURE feedstock 20 can be fractionated in a distillation tower 3 to obtain a top stream 19. Top stream 19 can be sent to steam cracker unit 1. A bottom stream 21 from distillation tower can be sent directly to FCC unit 4 as the sole feedstock. However, it is also possible to mix bottom stream 21 with feedstock 29 and to feed the mixture thus obtained as a feedstock 30 to FCC unit 4. In a specific embodiment feedstock 20 can be divided in a stream 12 and a stream 7, wherein only stream 12 is fractionated in distillation tower 3. Such a stream 7 is sent directly to FCC unit 4. Feedstock 29 is a feed type that will not be fractionated in distillation tower 3 but will be sent directly to FCC unit 4.

(3) Although not shown in the sole FIGURE it is possible to separate the C2-C4 paraffins from said overhead gas stream 25 coming from the gasoline hydrocracker (GHC) unit 5 and to feed said C2-C4 paraffins thus separated from the overhead gas stream 25 to the furnace section of a steam cracker unit 1. Moreover, it is also possible to separate the C2-C4 paraffins in individual streams, each stream predominantly comprising C2 paraffins, C3 paraffins and C4 paraffins, respectively, and feeding each individual stream to a specific furnace section of said steam cracker unit 1. The reaction products 18 of said steam cracking unit 1 are separated in separation section 2 into an overhead stream 17, which contains C2-C6 alkanes, a middle stream 14, which contains C2-olefins, C3-olefins and C4-olefins, and a first bottom stream 26 comprising C9+ hydrocarbons, and a second bottom stream 10 comprising aromatic hydrocarbon compounds and non-aromatic hydrocarbon compounds. The overhead stream 17 is returned to steam cracking unit 1. The second bottom stream 10 is sent to the gasoline hydrocracker (GHC) unit 5. The second bottom stream 10 comprises pygas, C5-C8. From separator 2 also hydrogen and methane can be recovered as separate streams and re-used elsewhere. The first bottom stream 26 is sent to the FCC unit 4, preferably by first combining first bottom stream 26 with a hydrogen donor type feedstock and then feeding the thus combined materials to said FCC unit 4. Examples of the hydrogen donor type feedstock is hydrogen 28 or a light feedstock 7, 20, such as naphtha, or a combination thereof. After mixing the recycled hydrogen 28 from the separation section 2 with the first bottom stream 26 the mixed stream 22 is sent to the FCC unit 4. The mixed stream 22 can be further mixed with other types of feedstock, such as streams 20, 29 and 21. In another embodiment (not shown) a part of first bottom stream 26 can be sent to the gasoline hydrocracker (GHC) unit 5.

(4) The overhead stream 25 from the gasoline hydrocracker (GHC) unit 5 can be divided into two streams 8 and 11, wherein stream 11 is sent to a dehydrogenation unit 23. Stream 11 preferably comprises C3-C4 alkanes and low amounts of hydrogen and methane. The top stream 9 from said FCC unit 4 can be combined with stream 18 of reaction products coming from the steam cracking unit 1 and sent to the separation section 2.

(5) The first bottom stream 26 can be divided in a stream 22 and a stream 27, wherein stream 27 is combined with bottom stream 16 of the FCC unit 4. Stream 16 can be further combined with stream 24 of gasoline hydrocracker (GHC) unit 5. In another embodiment (not shown) stream 16 can be recycled to FCC unit 4, in combination with a purge.

(6) The Example disclosed herein makes a distinction between several cases. The experimental data as provided herein were obtained by flowsheet modelling in Aspen Plus. The steam cracking kinetics were taken into account rigorously (software for steam cracker product slate calculations).

(7) Applied steam cracker furnace conditions:

(8) ethane and propane furnaces: COT (Coil Outlet temperature)=845 C. and steam-to-oil-ratio=0.37, C4-furnaces and liquid furnaces: Coil Outlet temperature=820 C. and Steam-to-oil-ratio=0.37. For the gasoline hydrocracking unit, a reaction scheme has been used that is based on experimental data. A fluid catalytic cracking unit was modeled based on data from literature.

(9) According to case 1 naphtha is only processed through a steam cracker unit.

(10) According to case 2 naphtha is sent to a cascade of a FCC unit and a gasoline hydrocracker (GHC) unit, wherein the gaseous stream formed in the GHC unit is sent to a steam cracker unit and the reaction products from the steam cracker unit are separated. The top stream from the FCC unit is sent to the separation section of the steam cracker unit, and the middle stream of the FCC unit is sent to the GHC unit. the C2-C4 paraffins is separated and fed to the furnace section of a steam cracker unit.

(11) The process flow scheme in case 3 is similar to case 2 but the feedstock in this case is hydrotreated VGO.

(12) The process flow scheme in case 4 is similar to case 2 but the feedstock is sent to a splitter, i.e. a distillation tower, and its bottom stream is used as a feedstock for the FCC unit and its top stream is sent to the steam cracker unit.

(13) Case 1 is a comparative example and case 2, case 3 and case 4 are examples according to the present invention.

(14) Table 1 shows the feedstock for case 1, case 2 and case 4, respectively.

(15) TABLE-US-00001 TABLE 1 Feedstock Cases 1 & 2 Case 4 Naphtha Splitter Feed n-Paraffins wt-% 36.3 19.3 i-Paraffins wt-% 27.4 14.6 Naphthenes wt-% 24.1 37.6 Aromatics wt-% 12.3 28.5 Density 60 F. kg/L 0.728 0.867 IBP C. 7.9 228.5 BP10 C. 274.1 BP30 C. 294.9 BP50 C. 120.4 315.3 BP70 C. 352.1 BP90 C. 411.2 FBP C. 178.3 472.8
Table 2 shows the feedstock for case 3.

(16) TABLE-US-00002 TABLE 2 Feedstock Case 3 SARA Analysis VGO Saturates wt-% 55.5 Aromatics wt-% 28 Resins wt-% 15.7 Asphaltenes wt-% 0.8 Density 60 F. kg/L 0.9012 CCR wt-% 4.7 Hydrogen wt-% 12.84 Sulfur wt-% 0.16 Nitrogen wt-% 0.25 Nickel ppm 6.3
Table 3 shows the characteristics of the top steam and bottom stream resulting from fractionating the feedstock sent to the splitter.

(17) TABLE-US-00003 TABLE 3 characteristics of top stream and bottom stream from splitter Top stream from splitter Bottom stream Steam from splitter Cracker feed FCC Feed Split factor wt-% 65.2 34.8 n-Paraffins wt-% 19.9 18.3 i-Paraffins wt-% 15.0 13.8 Naphthenes wt-% 39.2 34.8 Aromatics wt-% 26.0 33.1 Density 60 F. kg/L 0.857 0.92 IBP C. 217.6 339.3 BP10 C. 263 366.3 BP30 C. 279.1 379.1 BP50 C. 291.6 393 BP70 C. 305.5 410.6 BP90 C. 325.3 445.6 FBP C. 350.2 495.6
The battery limit product slate (wt. % of feed) for each of the cases 1, 2, 3, and 4 can be found in Table 4.

(18) TABLE-US-00004 TABLE 4 battery limit product slate (wt. % of feed) Feed: naphtha Feed: HT-VGO Diesel + CASE 2 CASE 3 LVGO2 BATTERY LIMIT CASE 1 HS-FCC + HS-FCC + CASE 4 PRODUCT SLATE SC GHC + SC GHC + SC Splitter H2 1% 1% 1% 1% CO/CO2 1% 1% 0% 0% COKE 0% 3% 8% 3% CH4 16% 16% 9% 12% ETHYLENE 33% 27% 22% 27% PROPYLENE 18% 35% 29% 20% BUTADIENE 6% 0% 1% 4% ISO-BUTENE 3% 0% 4% 3% BENZENE 8% 2% 4% 6% TX CUT 6% 14% 9% 6% STYRENE 1% 0% 0% 1% OTHER C7-C8 1% 0% 0% 0% C9 RESIN FEED 1% 0% 0% 2% CD 2% 0% 0% 2% CBO 3% 0% 0% 9% LCO 0% 0% 12% 4% % HIGH VALUE 76% 79% 69% 67% CHEMICALS

(19) From the modeling results one can see that for cases 2, 3 and 4 long normal and iso-paraffins are cracked into LPG. The present inventors further found that C7 naphthenes, C8 naphthenes and C9 naphthenes are upgraded by the gasoline hydrocracker (GHC) unit to toluene and xylenes.

(20) In addition, the present inventors found real benefits when processing naphtha through a cascade of an FCC unit followed by a gasoline hydrocracker (GHC) unit. The present inventors assume that, because of the dehydrogenation of naphthenes into aromatics (toluene and xylene), the BTX amount can be increased to 65% with respect to the BTX already present in FCC naphtha, which could be recovered by a pygas treatment unit. An additional potential advantage of the present method is that top stream 19 from distillation tower 3 does not need to be full condensed, if not required for reflux, therefore resulting in potential energy benefits.