REMOVING IMPURITIES IN A PROCESS FOR PRODUCING HYDROCARBON PRODUCTS

Abstract

Process for producing a hydrocarbon product, said process comprising: i) passing a feedstock originating from a renewable source and/or from a fossil source through a hydroprocessing step for producing a main hydrotreated stream; said hydroprocessing step comprising: passing the feedstock through one or more catalytic hydrotreating units under the addition of hydrogen for producing a first hydrotreated stream; passing the first hydrotreated stream to a first separation step comprising the use of a separation unit for particularly removing the impurities H.sub.2S, CO, CO.sub.2 and H.sub.2O; withdrawing from said first separation step an overhead stream and separating an overhead hydrocarbon liquid stream thereof which is passed as a reflux stream to said first separation unit; withdrawing from said first separation step a bottom stream and passing at least a portion of said bottom stream to a dewaxing step comprising the use of one or more catalytic hydrotreating units under the addition of hydrogen for producing said main hydrotreated stream; and ii) passing the main hydrotreated stream to a second separation step for producing said hydrocarbon product.

Claims

1. A process for producing a hydrocarbon product, said process comprising: i) passing a feedstock originating from a renewable source and/or from a fossil source through a hydroprocessing step for producing a main hydrotreated stream; said hydroprocessing step comprising: passing the feedstock through one or more catalytic hydrotreating units under the addition of hydrogen for producing a first hydrotreated stream, said hydrotreated stream comprising the impurities: H.sub.2S, NH.sub.3, CO, CO.sub.2 and H.sub.2O; passing the first hydrotreated stream to a first separation step comprising the use of a separation unit, for removing the impurities; withdrawing from said first separation step an overhead stream and separating an overhead hydrocarbon liquid stream thereof of which at least a portion is passed as a reflux stream to said first separation unit; withdrawing from said first separation step a bottom stream; passing at least a portion of said bottom stream to a dewaxing step comprising the use of one or more catalytic hydrotreating units under the addition of hydrogen for producing said main hydrotreated stream; ii) passing the main hydrotreated stream to a second separation step for producing said hydrocarbon product; wherein the one or more catalytic hydrotreating units for producing said first hydrotreated stream comprises hydrodeoxygenation (HDO) wherein the one or more catalytic hydrotreating units in the dewaxing step for producing said main hydrotreated stream comprises hydrodewaxing (HDW) under the presence of a noble metal catalyst; and wherein the entire overhead hydrocarbon liquid stream is passed as reflux stream to the separation unit.

2. The process according to claim 1, wherein step ii) comprises passing said main hydrotreated stream to a separator, for producing an aqueous stream (sour water stream), a hydrogen-rich stream, and a hydrocarbon stream which is further separated into said hydrocarbon product in a subsequent stripping section; and wherein said hydrogen-rich stream is supplied as a single recycle loop in the process by adding it to the one or more catalytic hydrotreating units for producing said first hydrotreated stream.

3. The process according to claim 2, further comprising: not adding the hydrogen-rich stream to the dewaxing step; adding a make-up hydrogen gas to the dewaxing step, and after passing it through the dewaxing step, mixing it with the hydrogen-rich stream thus generating a mixed hydrogen stream, which is then supplied as said single recycle loop.

4. The process according to claim 2, further comprising: separating an overhead gaseous stream comprising the impurities from said overhead stream from the first separation step, and passing said overhead gaseous stream, suitably after mixing it with said main hydrotreated stream and suitably also by subsequently cooling, to said separator in step ii).

5. The process according to claim 1, wherein said hydrocarbon product boils at above 30° C. and comprises one or more of: jet fuel, diesel, and naphtha.

6. The process according to claim 1, wherein in the first separation step, the separation unit is a high-pressure stripper, suitably in the form of a stripping column using make-up hydrogen gas as stripping medium and operating in the pressure range 40-70 barg and temperature range 150-250° C.

7. The process according to claim 1, wherein the first separation step further comprises using a hot separator upstream the separation unit, suitably in the form of a two-phase or three-phase vertical or horizontal-separator, whereby water is removed as vapor in said gas stream.

8. The process according to claim 1, wherein in step i) a recycle oil stream is divided from said bottom stream and passed to the one or more catalytic hydrotreating units upstream.

9. The process according to claim 1, wherein the feedstock originating from a renewable source is obtained from a raw material of renewable origin.

10. The process according to claim 1, wherein the feedstock originating from a fossil fuel source is selected from diesel, kerosene, naphtha, and vacuum gas oil (VGO).

11. The process according to claim 1, wherein the feedstock originates from a renewable source and from a fossil source, and wherein the fossil source represents a minor portion thereof amounting to up to 30 wt % or less of the feedstock, such as up to 10 wt %.

12. The process according to claim 1, wherein the one or more catalytic hydrotreating units for producing said first hydrotreated stream further comprises hydrodenitrification (HDN).

13. The process according to claim 1, wherein the one or more catalytic hydrotreating units in the dewaxing step for producing said main hydrotreated stream further comprises hydrocracking (HCR).

14. The process according to claim 1, wherein the separator in step ii) comprises a cold separator.

15. The process according to claim 2, wherein the make-up hydrogen gas is from outside sources.

16. The process according to claim 2, wherein the subsequently cooling is provided by an air cooler.

17. The process according to claim 1, wherein the hydrocarbon product further comprises lube base stock.

18. The process according to claim 1, wherein the two-phase or three-phase vertical or horizontal separator is two-phase, with a gas stream from the top and a liquid stream from the bottom, running at a temperature above 100° C.

19. The process according to claim 1, wherein the feedstock originating from a renewable source is obtained from the raw material of renewable origin originating from plants, algae, animals, fish, vegetable oil refining, domestic waste, waste rich in plastic, industrial organic waste like tall oil or black liquor.

20. The process according to claim 1, wherein the feedstock originating from a renewable source is obtained from a feedstock derived from one or more oxygenates taken from the group consisting of triglycerides, fatty acids, resin acids, ketones, aldehydes or alcohols where said oxygenates originate from one or more of a biological source, a gasification process, a pyrolysis process, Fischer-Tropsch synthesis, or methanol based synthesis.

Description

[0065] FIG. 1 shows a schematic process and plant layout for producing naphtha, jet and diesel from a feedstock, according to the prior art. The figure includes an expanded view of the separation unit used in the first separation step.

[0066] FIG. 2 shows a schematic process and plant layout for producing naphtha, jet and diesel from a feedstock, according to an embodiment of the invention. The figure includes an expanded view of the separation unit used in the first separation step.

[0067] With specific reference to FIG. 1, a block flow diagram of the overall process/plant 10 is shown. A feedstock 12, such as a feedstock originating from a renewable source, is fed to the hydroprocessing step or hydroprocessing section 110. This step or hydroprocessing section comprises an optional feed step or feed section 112 and a reactor section including a catalytic hydrotreating unit 114 such as HDO, dewaxing step or dewaxing section 118, as well as a first separation step 116, here illustrated by the use of a separation unit 116 in the form a HP stripper. From the hydroprocessing step 110, in particular from the dewaxing step 118, a main hydrotreated stream 14 is produced, which is then passed to a second separation step 120, which produces: aqueous (water) stream 16; off-gas stream 20 comprising hydrocarbons such as light hydrocarbon stream, also comprising NH.sub.3, CO, CO.sub.2 and H.sub.2S; and hydrocarbon products in the form of diesel 22, jet fuel 24 and naphtha 26.

[0068] After optionally passing the feedstock 12 through the optional feed step 112, the feedstock 12′ passes through a catalytic hydrotreating unit 114 such as HDO wherefrom a first hydrotreated stream 12″ is withdrawn. This stream is then passed to the HP stripper 116 under the production of a vapor stream 46 i.e. an overhead gaseous stream comprising a major portion of the impurities, a bottom stream 44 from which recycle oil stream 44′ is divided as well as a stream 44″ which is combined with overhead liquid stream from HP stripper 116 thereby forming a purified first hydrotreated stream 12′″. The latter enters a dewaxing step 118 comprising the use of a catalytic hydrotreating unit, HDW unit 118, for producing the main hydrotreated stream 14. An additional catalytic hydrotreating unit in the form of a hydrocracking unit (HCR unit) may also be provided for instance downstream or upstream the HDO or HDW unit for respectively producing the first hydrotreated stream 12″ or main hydrotreated stream 14.

[0069] The second separation step 120 includes the use of a separator 122, preferably a cold separator, and a stripping section 124 including a product stripper and a fractionator e.g. distillation column (not shown). Overhead gaseous stream 46 generated in the previous HP stripper 116 may be used e.g. mixed with the main hydrotreated stream 14 for the operation of separator 122. From the separator 122, hydrogen-rich stream 18 is withdrawn which may be used as hydrogen gas recycle, for instance by mixing with streams 12′ and 44′ entering catalytic hydrotreating unit 114, as well as the separator 122 also generating the above-mentioned water stream 16. The impurities are thus carried over into said water stream 16 (sour water stream). From the separator 122, a hydrocarbon stream 14′ is produced which is then fed to the stripping section 124 under the production of off-gas stream 20 comprising hydrocarbons, as well as the hydrocarbon products diesel 22, jet fuel 24 and naphtha 26. Make-up hydrogen gas 40 e.g. from outside battery limits, is added to the HP stripper 116, and optionally also to the catalytic units 114, 118 of the hydroprocessing step 110.

[0070] An expanded schematic view of the HP stripper 116 is also provided in FIG. 1. Stream 12″ is for instance fed to the first tray of HP stripper 116. The HP stripper overhead stream, as shown in the figure, is withdrawn and partly condensed in e.g. an air cooler 116′ and sent to a separator 116″ for withdrawing a condensed hydrocarbon liquid stream, i.e. an overhead hydrocarbon liquid stream 28, as well as sour water stream 30 and vapor stream 46. The overhead hydrocarbon liquid stream 28 is sent as feed to the dewaxing step 118 optionally after combining with the bottom stream 44″ withdrawn from the HP stripper 116. Make-up hydrogen gas 40 is used in the stripping and recycle oil stream 44′ is divided from the bottom stream 44 of the HP stripper 116 and passed to the one or more catalytic hydrotreating units 114 upstream.

[0071] Now with reference to FIG. 2, which shows an embodiment according to the invention, the block flow diagram of the overall process/plant 10 is identical to that of FIG. 1, except that stream 44″ divided from the bottom stream 44 from the HP stripper 116 is the only hydrocarbon feed to the dewaxing step 118.

[0072] The expanded schematic view of the HP stripper 116 shows now the use of the overhead liquid stream 28 as reflux to the HP stripper instead. As illustrated herein, the entire overhead hydrocarbon liquid stream 28 is passed as reflux, thereby surprisingly obtaining a significant improvement in the overall impurity removal and consequently better protecting the catalytic hydrotreating unit(s) in the dewaxing step 118.

[0073] From the separator 122, preferably a cold separator, a hydrogen-rich stream 18 is withdrawn which may be used as hydrogen gas recycle, and which is suitably supplied as a single recycle loop in the process, i.e. the hydrogen-rich stream 18 is added to the one or more catalytic hydrotreating units 114 for producing the first hydrotreated stream 12″.

EXAMPLE

[0074] Prior Art:

[0075] In accordance with FIG. 1, the level of impurities in the liquid phase to the dewaxing step or dewaxing section 18 before any heating, is as follows:

[0076] H.sub.2O: 1589 wppb, NH.sub.3: 14 wppb, H.sub.2S: 1528 wppb, CO+CO.sub.2: 3798 wppb.

[0077] Invention:

[0078] In accordance with FIG. 2, the entire overhead hydrocarbon liquid stream 28 is passed as reflux to the HP stripper 116, i.e. full reflux. The same operating conditions in the HP stripper (pressure, temperature, stripping gas flow) as for FIG. 1 are used. The level of impurities in the liquid phase to the dewaxing step or dewaxing section 18 before any heating, is now as follows:

[0079] H.sub.2O: 136 wppb, NH.sub.3: 9 wppb, H.sub.2S: 124 wppb, CO+CO.sub.2: 1197 wppb

[0080] A surprisingly high reduction in the level of the impurities, particularly H.sub.2S, H.sub.2O and/or CO+CO.sub.2 is thereby achieved. A reduction of about one order of magnitude is obtained for H.sub.2S and H.sub.2O.