METHOD FOR CRACKING A HYDROCARBON FEEDSTOCK IN A STEAM CRACKER UNIT

Abstract

The present invention relates to process for cracking a hydrocarbon feedstock in a steam cracker unit, comprising the following steps of: feeding a hydrocarbon feedstock to a first hydrocracking unit, feeding the hydrocarbon feedstock thus cracked to a separation unit for obtaining a stream high in paraffins and naphtenes, a stream high in heavy aromatics and a stream high in mono-aromatics feeding the stream high in paraffins and naphtenes to a second hydrocracking unit, wherein the process conditions in the first hydrocracking unit differ from the process conditions in the second hydrocracking unit, separating the stream thus hydrocracked in the second hydrocracking unit in a high content aromatics stream and gaseous stream comprising C2-C4 paraffins, hydrogen and methane, feeding the gaseous stream to a steam cracker unit.

Claims

1-17. (canceled)

18. A process comprising the steps of: feeding a feed comprising a hydrocarbon feedstock to a first hydrocracking unit, feeding the hydrocarbon feedstock thus cracked to a separation unit for obtaining a stream high in paraffins and naphthenes, a stream high in heavy aromatics and a stream high in mono-aromatics, feeding the stream high in paraffins and naphthenes to a second hydrocracking unit, wherein the process conditions in the first hydrocracking unit differ from the process conditions in the second hydrocracking unit, separating the stream thus hydrocracked in the second hydrocracking unit into a high content aromatics stream and a gaseous stream comprising C2-C4 paraffins, hydrogen and methane, separating the gaseous stream into a stream comprising the C2-C4 paraffins and a stream predominantly comprising the hydrogen and the methane; feeding the stream comprising the C2-C4 paraffins to a steam cracker unit, and returning said stream high in heavy aromatics to the first hydrocracking unit.

19. The process according to claim 17, consisting of said steps.

20. A process for cracking a hydrocarbon feedstock in a steam cracker unit, comprising the steps of: feeding a hydrocarbon feedstock to a first hydrocracking unit, feeding the hydrocarbon feedstock thus cracked to a separation unit for obtaining a stream high in paraffins and naphthenes, a stream high in heavy aromatics and a stream high in mono-aromatics feeding the stream high in paraffins and naphthenes to a second hydrocracking unit, wherein the process conditions in the first hydrocracking unit differ from the process conditions in the second hydrocracking unit, separating the stream thus hydrocracked in the second hydrocracking unit into a high content aromatics stream and a gaseous stream consisting of C2-C4 paraffins, hydrogen and methane, separating via solvent extraction a stream comprising C3-C4 paraffins and a stream comprising C2 paraffins from said gaseous stream consisting of C2-C4 paraffins; feeding said stream comprising C3-C4 paraffins to a dehydrogenation unit for obtaining hydrogen, C3-olefins and C4-olefins; and feeding said stream comprising C2 paraffins to the furnace section of a steam cracker unit wherein the second hydrocracker unit conditions are optimized for the production of ethane, propane and butane.

21. The process according to claim 17, wherein separating said C2-C4 paraffins from said gaseous stream is carried out by solvent extraction.

22. The process according to claim 17, further comprising recovering from said gaseous stream a stream predominantly comprising hydrogen and methane and recycling said stream to the first and/or second hydrocracking unit.

23. The process according to claim 17, further comprising recovering mono-aromatics from said stream high in heavy aromatics before returning said stream high in heavy aromatics to the first hydrocracking unit.

24. The process according to claim 17, wherein the separation unit comprises an extraction unit, wherein the top stream from the distillation unit is sent to the inlet of said extraction unit.

25. The process according to claim 17, further comprising returning said high content aromatics stream to said separation unit.

26. The process according to claim 17, wherein the temperature in the first hydrocracking unit is lower than the temperature in the second hydrocracking unit.

27. The process according to claim 17, wherein the hydrogen partial pressure in the first hydrocracking unit is higher than the hydrogen partial pressure in the second hydrocracking unit.

28. The process according to claim 17, wherein the second hydrocracker unit conditions are also optimized for the production of BTX aromatics.

29. The process according to claim 17, wherein the hydrocarbon feedstock to said first hydrocracking unit is a gas condensate.

30. The process according to claim 17, wherein said stream comprising the C2-C4 paraffins consists thereof.

31. The process according to claim 17, wherein said second hydrocracking unit is operated at a temperature of 300-550 C., a pressure of 300-5000 kPa gauge and a Weight Hourly Space Velocity of 0.1-10 h.sup.1.

32. The process according to claim 31, wherein the temperature is 300-450 C., the pressure is 300-5000 kPa gauge, and the Weight Hourly Space Velocity is 0.1-10 h.sup.1.

33. The process according to claim 31, wherein the temperature is 300-400 C., the pressure is 600-3000 kPa gauge, and the Weight Hourly Space Velocity is 0.2-2 h.sup.1.

34. A process for cracking a hydrocarbon feedstock in a steam cracker unit, comprising the steps of: feeding a hydrocarbon feedstock to a first hydrocracking unit, wherein said first hydrocracking unit is operated as a ring opening hydrocracker unit at a temperature of 200-600 C. and a pressure of 3-35 MPa, feeding the hydrocarbon feedstock thus cracked to a separation unit for obtaining a stream high in paraffins and naphthenes, a stream high in heavy aromatics and a stream high in mono-aromatics feeding the stream high in paraffins and naphthenes to a second hydrocracking unit, wherein said second hydrocracking unit is operated at a temperature of 300-550 C., a pressure of 300-5000 kPa gauge and a Weight Hourly Space Velocity of 0.1-10 h1, the temperature in the first hydrocracking unit being lower than the temperature in the second hydrocracking unit, separating the stream thus hydrocracked in the second hydrocracking unit in a high content aromatics stream and gaseous stream consisting of C2-C4 paraffins, hydrogen and methane, feeding the gaseous stream to a steam cracker unit; and cracking said gaseous stream in said steam cracker unit.

35. The process according to claim 17, wherein the hydrocarbon feedstock consists of the hydrocarbon feedstock.

36. The process according to claim 18, wherein the hydrocarbon feedstock consists of the hydrocarbon feedstock.

37. The process according to claim 19, wherein the hydrocarbon feedstock consists of the hydrocarbon feedstock.

Description

EXAMPLE

[0061] The process scheme can be found in the sole FIGURE. Feedstock 48, which can include different types of feedstock, for example naphtha 35, kerosene 36, diesel 37, atmospheric gas oil (AGO) 38 originating from tanks 2,3,4,5 respectively, is sent to a first hydrocracker unit 16. In hydrocracking unit 16 a feedstock 48 is hydrocracked in the presence of hydrogen. The hydrocracking process results in the formation of a stream 61 of reaction products, which stream 61 is sent to a distillation unit 60, resulting in a top stream 50 of light components, i.e. a stream high in paraffins and naphtenes, and a bottom stream 62 of more heavy components, i.e. a stream high in heavy aromatics. Top stream 50 can also be indicated as a stream comprising light paraffins and naphtenes. Stream 50 is further treated in an extraction or dearomatization unit 21, and in extraction unit 21 a stream 47 high in paraffins and naphtenes and a stream 43 high in mono-aromatics is obtained. The stream 47 high in paraffins and naphtenes is sent to a second hydrocracking unit 17, wherein the process conditions in the first hydrocracking unit 16 differ from the process conditions in the second hydrocracking unit 17. The operating pressure for the first hydrocracker unit 16 is preferably in the range 3-35 MPa, more preferably 5 to 20 MPa, whereas the operating pressure range for the second hydrocracker unit 17, is preferably in the range of 300-5000 kPa. Gaseous stream 41 coming from second hydrocracking unit 17 and comprising C2-C4 paraffins, hydrogen and methane is sent to a separator 12, e.g. cryogenic distillation or solvent extraction, and separated into different streams, i.e. a stream 55 comprising C2-C4 paraffins, a stream 52 comprising hydrogen and methane and a purge stream 33. Stream 52 can be recycled to hydrocracking unit 17 or hydrocracking unit 16, possibly after separation/purification integrated with/in steam cracker separation section 6. Stream 62 high in heavy aromatics is returned to the first hydrocracking unit 16, but it is preferred to recover a stream high in mono-aromatics (not shown) from stream 62 before returning said stream 62 to the first hydrocracking unit 16.

[0062] The present inventors found that it is preferred to separate stream 61 and send the heavier material 62 back to unit 16 to produce a stream 50 which is low in di-ring and tri-ring aromatic material. The benefit of this action is to operate the two hydrocracking units 16, 17 under differently optimized conditions, i.e. for the first hydrocracker unit 16 conditions suited open aromatic rings (i.e. trickle bed operation at high pressure and moderate temperature) and for the second hydrocracker unit 17 conditions optimized for the production of ethane, propane and butane plus some BTX aromatics (i.e. vapor phase operation at relatively low operating pressure and high temperature).

[0063] Stream 55 can be sent directly (not shown) to a steam cracker unit 11. However, before sending stream 55 to steam cracker unit 11 it is preferred to carry out a separation on stream 55 first. In separator 56 the C2-C4 paraffins are separated into individual streams 30, 31 and 32. This means that stream 30 predominantly comprises C2, stream 31 predominantly comprises C3 and stream 32 predominantly comprises C4. If necessary, further separation of unwanted components or temperature adjustments can made. The individual streams 30, 31 and 32 will be sent to specific furnace sections of steam cracker unit 11. In a preferred embodiment stream 31 will be divided in a stream 54 and stream 32 in a stream 63, respectively. Stream 54 predominantly comprising C3 and stream 63 predominantly comprising C4 will be sent to dehydrogenation unit 57. This means that only stream 30 which predominantly comprises C2 will be sent to steam cracker unit 11.

[0064] Although steam cracker unit 11 is shown as one single unit, in the present method is to be understood that in a preferred embodiment steam cracker unit 11 comprises different furnace sections each dedicated for a specific chemical composition, that is a furnace section for C2, a furnace section for C3 and a furnace section for C4.

[0065] In steam cracker unit 11 streams 30, 31 and 32 and a feedstock 27, for example gases coming from a unit 1 are processed and its reaction products 14 are separated in a separation section 6. A gas stream 7 containing C2-6 alkanes is recycled to the steam cracker unit 11. Hydrogen 15 and pygas 34 can be sent to second hydrocracking unit 17, or even to first hydrocracking unit 16. This latter embodiment has not been shown. According to a preferred embodiment (not shown) pygas 34 is sent to the inlet of extraction unit 21.

[0066] The valuable product stream 8 like unsaturated hydrocarbons such as lighter alkenes including ethylene, propylene and butadienes is sent to further petrochemical processes. In case heavy hydrocarbons such as carbon black oil (CBO), cracked distillates (CD) and C9+ hydrocarbons are produced in steam cracker unit 11 these products can be recovered in separator 6 and optionally be recycled to hydrocracking unit 16 (not shown) and/or hydrocracking unit 17 as well. However, it is preferred to recycle these types of material (CBO and CD) to the first hydrocracking unit 16 because these materials are more suitable for the first hydrocracker unit than the second hydrocracker unit.

[0067] The process further comprises returning the high content aromatics stream 40 to the extraction unit 21. This means that feedstock 18 can be seen as a combination of stream 50 coming as a top stream from distillation unit 60 and a stream 40 coming from hydrocracking unit 17. High content mono aromatics stream 43 can be separated into a stream 42 for further processing in unit 23 and converted in unit 24 into a benzene rich fraction 53 and a methane rich fraction 44.

[0068] The Example disclosed herein makes a distinction between several situations, i.e. a process (case 1) in which diesel as a feedstock is first processed through liquid hydrocracking unit and its reaction products are processed through a steam cracker unit and a process (case 2) in which the feedstock for the hydrocracking unit is pretreated in a sequence of another hydrocracking (first unit) unit and an extraction unit, wherein the aromatics fraction obtained is directly sent to the steam cracker separation section, and the remainder fraction of the extraction unit is used as a feedstock for the second hydrocracking unit. Case 1 is a comparative example and case 2 is an example according to the present invention.

[0069] In table the results of case 1 and case 2 are shown.

TABLE-US-00001 TABLE Battery limit product slate (wt. % of feed) CASE 1 CASE 2 BATTERY LIMIT PRODUCT SLATE Feed: diesel SC MHC + Dearom + FHC + SC H2 1% 2% CO/CO2 1% 0% CH4 13% 19% ETHYLENE 30% 39% PROPYLENE 14% 10% BUTADIENE 5% 2% ISO-BUTENE 1% 0% BENZENE 8% 2% TX CUT 5% 17% STYRENE 1% 0% OTHER C7-C8 0% 1% C9 RESIN FEED 3% 6% CD 3% 0% CBO 14% 0% % HIGH VALUE 65% 72% CHEMICALS

[0070] Comparative case 1 shows high yields of heavy products (C9 Resin Feed, CD and CBO). In contrast case 2, which illustrates processing diesel according to the present invention, shows a much lower yield of heavy products, with essentially no CD and CBO production. For case 1 one can see in the product slate more ethylene but less propylene and heavier products. The BTX production is kept high because due to the existing mono-aromatics in the feed and an upgrade of a part of the heavy material (reduction of C9 resin feed, CD & CBO production). An aspect of the present method is that methane production is increased because of a shift from liquid steam cracking to gas steam cracking. When applying PDH/BDH there will actually be a decrease in methane production due to the higher efficiency of the dehydrogenation in this respect. In overall terms, the amount of high value chemicals (components starting from ethylene and ending with other C7-C8 as defined in Table 1), increases incrementally from 65 to 72% from case 1 to case 2.

[0071] The present inventors further found that when using a hydrocracking unit the benzene-toluene-xylene ratios are changed from a benzene-rich stream (steam cracker without any hydrocracking unit, case 1) to a toluene-rich stream (steam cracker with hydrocracking unit, case 2).