WO2025093819A1

WO2025093819A1 - A method for producing a fuel product

Info

Publication number: WO2025093819A1
Application number: PCT/FI2024/050584
Authority: WO
Inventors: Fredrik NYHOLM; Jaana KANERVO; Sonja KOUVA; Pekka Nurmi; Sami Toppinen
Original assignee: Neste Oyj
Current assignee: Neste Oyj
Priority date: 2023-11-02
Filing date: 2024-10-31
Publication date: 2025-05-08
Anticipated expiration: 2026-05-02
Also published as: FI20236222A1; FI131462B1

Abstract

The present invention relates to a method for processing a low-temperature Fischer-Tropsch reaction effluent (1) into a fuel product, the method comprising fractionating the Fischer-Tropsch effluent; processing the C5 and higher hydrocarbons by a catalytic isomerising hydrocracking (7) to produce an isomerised product (8); fractionating the isomerised product to obtain hydrogen (11), a mixture of gases (12) at least mainly other than hydrogen, water (15), at least one fuel product (16, 16') and a fraction consisting mainly of C17 and higher hydrocarbons (17). The method also comprises directing at least part of the gases to a reverse water gas shift reaction (18); and recycling the fraction consisting mainly of C17 and higher hydrocarbons from the third fractionation to the catalytic isomerising hydrocracking.

Description

A METHOD FOR PRODUCING A FUEL PRODUCT

FIELD

The present invention relates to a method for processing a low-temperature Fischer- Tropsch reaction effluent into a fuel product. The invention further relates to a system for carrying out the method.

BACKGROUND AND OBJECTS

In view of climate change and reducing the use of natural resources, for example fossil oil, there exists a need to find alternatives for the production of fuel products and fuel components. Various biomasses are currently either used as feedstock for fuel production, or studied for such use. Alternatives for sustainable biomass are thus desired, in the search of alternative energy sources.

Production of synthetic fuels from renewable hydrogen and carbon dioxide by power-to-liquids (PtL) processes is one option. However, PtL production consumes considerable amounts of electricity, and thus it would be best to use these processes for the manufacturing of liquid fuels that are difficult to replace by other sources of energy, such as electricity. One such fuel product is aviation fuel. While electricity or hydrogen may be usable in aviation, for the time being the use of electricity is limited by the weight of the batteries, while hydrogen suffers from challenges with storage.

For the moment, two PtL technologies, namely the Fischer-Tropsch (FT) and Alcohol-to-Jet (AtJ) pathways are currently accepted by the ASTM D7566-22 jet fuel standard and allowed for production of kerosene, i.e. aviation fuel. The FT synthesis, however, produces a wide range of hydrocarbons and thus exhibits a poor selectivity for the kerosene product. There is therefore a need for a good upgrading process to maximise the efficiency of the overall process as well as the yield of the desired product(s).

It is therefore an aim to provide a viable large scale (i.e. industrial size) process solution taking into account carbon efficiency and reuse of side streams, to have an overall process that is efficient in all aspects. Another aim is to provide a system for carrying out the method.

SUMMARY

The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims. According to one aspect, there is provided a method for processing a low-temperature Fischer-Tropsch reaction effluent into a fuel product, the method comprising

- fractionating the Fischer-Tropsch effluent in a first fractionation into at least a first mixture of gases, a mixture of water and oxygenates, a fraction consisting mainly of C17 and higher hydrocarbons, and a fraction consisting mainly of C5-C16 hydrocarbons;

- processing the fraction consisting mainly of C17 and higher hydrocarbons, and the fraction consisting mainly of C5-C16 hydrocarbons by a catalytic isomerising hydrocracking to produce an isomerised product;

- fractionating the isomerised product in a second fractionation, in the presence of water, to obtain hydrogen, a second mixture of gases at least mainly other than hydrogen, and a fractionated isomerised product,

- fractionating the fractionated isomerised product in a third fractionation, to obtain water, at least one fuel product and a fraction consisting mainly of C17 and higher hydrocarbons;

- directing at least the first mixture of gases to a reverse water gas shift reaction; and

- recycling the fraction consisting mainly of C17 and higher hydrocarbons from the third fractionation to the catalytic isomerising hydrocracking.

According to another aspect, there is provided a system for processing a low- temperature Fischer-Tropsch reaction effluent into a fuel product, comprising

- first means for fractionating the Fischer-Tropsch into at least a first mixture of gases, a mixture of water and oxygenates, a fraction consisting mainly of C17 and higher hydrocarbons, and a fraction consisting mainly of C5-C16 hydrocarbons; - a catalytic isomerising hydrocracking reactor for processing the fraction consisting mainly of C17 and higher hydrocarbons, and the fraction consisting mainly of C5- C16 hydrocarbons to produce an isomerised product;

- second means for fractionating the isomerised product, in the presence of water, to obtain hydrogen, a second mixture of gases at least mainly other than hydrogen, and a fractionated isomerised product,

- third means for fractionating the fractionated isomerised product, to obtain water, at least one fuel product and a fraction consisting mainly of C17 and higher hydrocarbons;

- means for directing at least the first mixture of gases to a reverse water gas shift reactor; and

- means for recycling the fraction consisting mainly of C17 and higher hydrocarbons from the third means for fractionating to the catalytic isomerising hydrocracking reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a system and process according to an embodiment.

Figure 2 shows a system and process according to another embodiment.

Figure 3 shows part of a system and method according to an embodiment.

Figure 4 shows part of a system and method according to another embodiment.

Figure 5 shows another part of a system and method according to an embodiment.

Figure 6 shows part of a system and method according to an embodiment. Figure 7 shows part of a system and method according to an embodiment.

DETAILED DESCRIPTION

In the present description, weight percentages (wt-%) are calculated on the total weight of the material in question (typically a blend or a mixture). Any amounts defined as ppm (parts per million), are based on weight. The following abbreviations may also be used: FT for Fischer-Tropsch; HTHP for high temperature-high pressure flash; MTHP for medium temperature-high pressure flash; and LTHP for low temperature-high pressure flash. The term “renewable” in the context of a renewable fuel component refers to one or more organic compounds derived from any renewable source (i.e., not from any fossil-based source). Thus, the renewable fuel component is based on renewable sources and consequently does not originate from or is derived from any fossilbased material.

The 14C-isotope content can be used as evidence of the renewable or biological origin of a feedstock or product. Carbon atoms of renewable material comprise a higher number of unstable radiocarbon (14C) atoms compared to carbon atoms of fossil origin. Therefore, it is possible to distinguish between carbon compounds derived from biological sources, and carbon compounds derived from fossil sources by analysing the ratio of 12C and 14C isotopes. Thus, a particular ratio of said isotopes can be used to identify and quantify renewable carbon compounds and differentiate those from non-renewable i.e. fossil carbon compounds. The isotope ratio does not change in the course of chemical reactions. Example of a suitable method for analysing the content of carbon from biological sources is ASTM D6866- 20 (2020). An example of how to apply ASTM D6866-20 to determine the renewable content in fuels is provided in the article of Dijs et al., Radiocarbon, 48(3), 2006, pp 315-323. For the purpose of the present invention, a carbon-containing material, such as a feedstock or product is considered to be of renewable origin if it contains 90 % or more modern carbon (pMC), such as about 100 % modern carbon, as measured using ASTM D6866-20.

In the present case, the feedstock fed to the Fischer-Tropsch reaction may also comprise components of fossil origin and/or recycled components. The recycled components may be of fossil or renewable origin.

According to one aspect, there is provided a method for processing a low- temperature Fischer-Tropsch reaction effluent into a fuel product, the method comprising

- fractionating the Fischer-Tropsch effluent in a first fractionation into at least a first mixture of gases, a mixture of water and oxygenates, a fraction consisting mainly of C17 and higher hydrocarbons, and a fraction consisting mainly of C5-C16 hydrocarbons; - processing the fraction consisting mainly of C17 and higher hydrocarbons, and the fraction consisting mainly of C5-C16 hydrocarbons by a catalytic isomerising hydrocracking to produce an isomerised product;

In the FT synthesis H2, CO2 and, if needed, O2 are first heated and fed to a reverse water gas shift (RWGS) reactor. Water is separated from the outlet stream and syngas from the RWGS is fed to the FT reactor. The effluent, i.e. product, obtained from FT is also called “syncrude”, and the present method thus upgrades the “syncrude” produced with the low-temperature Fischer-Tropsch synthesis into synthetic paraffinic kerosene, which can be used as a blend stock for jet fuel, and a small naphtha fraction as a by-product.

Typically, the reaction effluent from the FT synthesis includes, in addition to the paraffins, some further compounds in small amounts, such as H2, CO, CO2, O2, H2O, N2, C1 , C2, C3 and C4 (straight chain and branched) hydrocarbons; mainly C2 to C30 olefins with a carbon-carbon double bond and optionally some C30+ olefins; C2-C22 alcohols, such as CH3OH, C2H6O, Ci 2^H26O> C22H46O; and C1- C22 acids, such as HCOOH, C2H4O2, C12H24O2, 622^402-

The method thus allows for refining of FT syncrude into liquid fuels, with a jet fuel component, such as e-kerosene as the main product, and a small fraction of e- naphtha as by-product. Indeed, with the present method, a major part of the FT syncrude is treated to produce liquid fuels, thus leading to a high yield of e-kerosene. By “major part of the FT syncrude” is meant all of the FT syncrude except gases, water and oxygenates dissolved in the water.

The method concentrates on maximising the carbon efficiency as well as minimising waste, as both the feedstock and the products of the process are of high value. This is mainly achieved through the presently disclosed processing scheme with suitable re-circulations and suitable process conditions, as explained in more detail below. The present method thus maximises the production of synthetic paraffinic kerosene from Fischer-Tropsch syncrude with two reactors. The configuration of the process and system is simple, relatively economical and can also be used on a small scale. For example, no naphtha splitter distillation column may be needed. Further, light gases are recycled back to FT synthesis to enhance the kerosene yield of the process.

Reverse water gas shift

The feedstock and various recycle streams are first converted into syngas in a reverse water gas shift (RWGS) process. Wastewater from the RWGS is separated and typically sent to wastewater treatment.

The pressure of the synthesis section is propagated forward from the feed streams through the reactors and heat exchangers. The RWGS reactor converts the feed streams (such as H2 and CO2) into syngas (mainly CO and H2, with H2O as a byproduct). Shorter hydrocarbons (C1 -C4) can also be recycled back into the reactor, which then acts as a reformer to convert them to syngas. Alternatively, the shorter hydrocarbons can be processed by partial oxidation to carbon monoxide and carbon dioxide, which are then fed to the RWGS. All or part of the recycled gas stream may also pass through a purge, in case there are any inert impurities in the feed that would otherwise accumulate.

A feed preheater heats up the gas feeds to the RWGS reactor temperature. Maximum outlet temperature of preheater is typically 800-1100 °C, such as 1000 °C. The RWGS reactor can be for example an electrically heated RWGS reactor. It may also be an isothermal equilibrium reactor. Low-temperature Fischer Tropsch process

The FT process is known per se, thus it is discussed here only generally. A description of the FT process can be found for example in the PhD (chemical engineering) thesis by Arno de Klerk, University of Pretoria, South-Africa, February 2008, titled Fischer-Tropsch Refining, the contents of which are herein incorporated by reference.

The FT process is affected by reactor size, temperature, pressure, feed H2/CO-ratio and water content. In the FT process, the syngas from RWGS is synthesised into hydrocarbons, to produce syncrude. The produced syncrude is sent downstream to the present method.

Either the FT process or the RWGS process typically comprises a syngas cooler to cool the syngas to condense and separate the water generated by the RWGS reaction. Thereafter the syngas can be re-heated by an FT feed preheater, which thus sets the FT reactor temperature. The FT reactor generates hydrocarbon chains through the Fischer-Tropsch synthesis, using for example a cobalt catalyst.

H2 and CO are consumed in the reactor, while any other components in the feed are typically inert. Water has an effect on the reaction rate. The FT process typically generates a continuous paraffin distribution, preferably mostly in the C1 -C30 range, while the effluent may comprise up to C100 paraffins. The paraffin distribution follows the Anderson-Schulz-Flory distribution, with a rate correction for methane. The chain growth probability is influenced by the reactor temperature and partial pressures of CO and H2O. Olefin distribution is determined in a similar manner as the paraffins, with a rate correction for ethylene. The cobalt-catalysed FT also produces small amounts of alcohols and carboxylic compounds. Additionally, aldehydes, ketones and esters may be formed.

According to an embodiment, the FT effluent comprises 20-50 wt-% of hydrocarbons, 20-40 wt-% of water and 20-40 wt-% of other gases (as water is in gaseous form at the outlet of the FT reactor). According to an embodiment, the low temperature Fischer-Tropsch process takes place at 170-270 °C, preferably 210-230 °C. The pressure in the FT reactor is typically in the range of 1 -5 MPa, preferably 1 -3 MPa, more preferably 1 .9-2.8 MPa, such as 2.0-2.2 MPa. The H2 feed is adjusted to keep the molar H2/CO ratio in the feed at 2. The length of the reactor is typically such that 75 % of the carbon monoxide fed to the reactor is converted.

Operation of the low temperature FT aims to maximise the yield of longer chain hydrocarbons, which are easier to upgrade into liquid fuel products. A high once- through conversion of CO2 is beneficial for reducing the size of the recirculated stream.

As examples, it can be mentioned that the CO2 feed can have a temperature of 30 °C and a pressure of 2.2 MPa, while the recycled gases from the FT itself are typically mixed with the CO2 feed prior to feeding it to the RWGS and, consequently, the FT reactor. Additional gases from the syncrude section, reformed to syngas in a separate reformer, can be mixed with the feed to the FT reactor. The H2 feed may be at a temperature of 60 °C, and a pressure of 2.2 MPa.

First fractionation

The product from the low-temperature FT reaction, i.e. its effluent, the syncrude is then fractionated in a first fractionation. The first fractionation may, and preferably does, comprise several steps. In this first fractionation, the effluent is split into at least four fractions, namely a first mixture of gases, a mixture of water and oxygenates, a fraction consisting mainly of C17 and higher hydrocarbons (i.e. a wax fraction), and a fraction consisting mainly of C5-C16 hydrocarbons.

The first mixture of gases consists mainly of unreacted or inert gases, but also contains some lighter hydrocarbons. This fraction is directed back upstream to the reverse water-gas shift reactor (RWGS), where it is reformed to syngas, and preferably synthesised in the low-temperature FT reactor again into syncrude. The mixture of water (generated in the FT reaction) and oxygenates may consist of over with traces of olefins and some paraffins. The remaining fractions, namely the fraction consisting mainly of C17 and higher hydrocarbons, and the fraction consisting mainly of C5-C16 hydrocarbons, are directed to the next step of the process.

The first fractionation may be for example a sequence of flashes. According to an embodiment, the first fractionation comprises

- separating C17 and higher hydrocarbons from a first remaining part of the effluent in a first high temperature flash;

- lowering the temperature of the first remaining part of the effluent in a heat exchanger;

- separating the first mixture of gases from a second remaining part of the effluent in a second low temperature flash; and

- separating the mixture of water and oxygenates from the fraction consisting mainly of C5-C16 hydrocarbons in a decanter.

The advantage of first separating the fraction consisting mainly of C17 and higher hydrocarbons is that heat of the stream is thus conserved, and practical issues with solidifying wax at low temperatures are avoided.

The temperature in the high temperature flash is typically 170-270 °C, preferably 210-230 °C. The temperature is thus preferably identical or very close to the temperature at the FT reactor. A small pressure drop, for example of about 30 kPa, typically occurs due to the flash, but the pressure is otherwise preferably not lowered between the FT reactor and the first flash, similarly between the first and eventual second flash.

A heat exchanger to lower the temperature of the first remaining part of the effluent is then preferably used to cool down the temperature of the remaining hot gas stream to 35 °C.

In one embodiment, the cooled stream is flashed again in a second low temperature flash, with again a small pressure drop, for example of 30 kPa. According to an embodiment, the temperature in the low temperature flash is 20-70 °C. This separates the water and distillate range hydrocarbons (C5-C16 hydrocarbons) from the lighter gases. The second low temperature flash does a separation to split out a liquid stream, consisting of water and hydrocarbons. The liquid stream is then fed to the decanter to separate the mixture of water and oxygenates from the fraction consisting mainly of C5-C16 hydrocarbons. The resulting aqueous phase is sent to wastewater treatment, while the liquid hydrocarbon stream is mixed with the previously separated heavy fraction and sent to the next step of the process.

The gases from the second low temperature flash are preferably pressurised by a recycle gas compressor and returned to the RWGS reactor for reforming back into syngas.

According to another embodiment, the first fractionation comprises

- lowering the temperature of the first remaining part of the effluent in a heat exchanger; and

- separating the first mixture of gases, the mixture of water and oxygenates, and the fraction consisting mainly of C5-C16 hydrocarbons in a three phase separation.

In this embodiment, the first steps are identical to the embodiment discussed above, but instead of a second low temperature flash and a decanter, the remaining part of the effluent (i.e. without the C17 and higher hydrocarbons) is directed to a three phase separation. This reduces the number of equipment needed.

Isomerising hydrocracking

The fraction consisting mainly of C17 and higher hydrocarbons, and the fraction consisting mainly of C5-C16 hydrocarbons are then led to a catalytic isomerising hydrocracking to produce an isomerised product. By the term “isomerising hydrocracking” is meant that a hydrocracker capable of both isomerisation and cracking is used. Typically, a paraffinic hydrocarbon is first isomerised, i.e. branched, and subsequently, part of the branched hydrocarbons are split at the branch, i.e. cracked. The amount of cracking depends on e.g. the processing temperature. This method step takes place in a single reactor, preferably using sulphur free catalyst(s), such as noble metal catalyst(s), on a support. The single reactor may have only one catalyst bed or several catalyst beds (such as two, three, four, five or more catalyst beds), with the same or different catalysts. The catalyst in the isomerising hydrocracking is selected from a group consisting of noble metals on a support. Preferably, the noble metals are selected from Pt, Rh, Pd, more preferably Pt. The support may be selected from zeolite, such as beta-zeolite, alumina, silica or mixtures thereof. A noble metal catalyst is preferred for easier recycling of the gaseous effluents.

This step thus upgrades the hydrocarbons from the syncrude fractionation by cracking and branching the hydrocarbon chains in an isomerising hydrocracker to produce an isomerised product. The hydrocarbons are thus treated to improve the cold flow properties.

The reactions crack paraffinic and isomer compounds to shorter chain lengths and generate 1 -, 2- or 3-methylated isomers. Cracking of tribranched isomers is by far the fastest reaction compared to cracking of lower isomers, which means higher degrees of branching would be very rare as the tribranched species do not get to build up in meaningful quantities before rapidly undergoing cracking. Methyl branches are most abundant, typically the ratio of methyl/ethyl/propyl branches is of the order of 100/10/1 , as has been described e.g. in Calemma et al., Middle distillates from hydrocracking of FT waxes: Composition, characteristics and emission properties, Catalysis Today 149 (2010) 40-46.

The fraction consisting mainly of C17 and higher hydrocarbons, and the fraction consisting mainly of C5-C16 hydrocarbons are preferably combined before feeding them to the next reactor.

According to an embodiment, a pre-hydrotreating with an excess H2 may be used to convert the olefins and any remaining oxygenates to paraffins, before the actual isomerising hydrocracking. By excess hydrogen it is here meant for example from five- to twenty-fold excess compared to the chemical consumption. Prehydrotreating the feed is beneficial for the operation of the isomerising hydrocracking, as the oxygenate compounds may have an adverse effect on its performance.

The fraction consisting mainly of C17 and higher hydrocarbons, and the fraction consisting mainly of C5-C16 hydrocarbons, optionally pre-hydrotreated, is fed to an isomerising hydrocracker, which cracks the hydrocarbon chains and produces 1 -, 2- and 3-methylated isomers, i.e. an isomerised product.

The feed to the isomerising hydrocracked is preferably pressurised to the required pressure, by a feed pump. The system may also comprise a hydrogen compressor to pressurise the recycle and make-up H2 to required pressure before being preferably mixed with the liquid feed.

According to an embodiment, the isomerising hydrocracker works at two phases, and thus the temperature of the combined stream can then be increased, for example by a feed heat exchanger, which sets the feed temperature at an appropriate level so that its outlet stream remains two-phase. The isomerising hydrocracker then adiabatically converts olefins and oxygenates in the feed to their corresponding paraffins.

According to an embodiment, the isomerising hydrocracking is carried out at a temperature of 240-400 °C, such as 300-370 °C, or 320-350 °C. The pressure in the reactor is typically 3-10 MPa, preferably 4-8 MPa, more preferably 5-7 MPa. The pressure is preferably at a slightly raised level in an attempt to prevent excessive vaporisation of the feed and to allow raising of the temperature. Preferably, the isomerising hydrocracking is carried out at a temperature of 320-350 °C and at a pressure of 5-7 MPa. The weight hourly space velocity (WHSV) may be 0.15-5 /h. The make-up H2 feed is adjusted to keep the H2 feed to the reactor at a desired level, for example at 110 kg H2/ton feed oil, while the temperature of the H2 feed can be for example 60 °C, and its pressure 2.2 MPa.

Achieving a high once-through conversion of the feed, while avoiding over-cracking it, is beneficial for reducing the recycle streams and maintaining a high selectivity to the kerosene product. Second and third fractionation

The isomerised product is then directed to a second fractionation, followed by a third fractionation, to obtain at least one fuel product.

The second fractionation of the isomerised product is carried out in the presence of water, to obtain hydrogen, a second mixture of gases at least mainly other than hydrogen, and a fractionated isomerised product. In the third fractionation, the fractionated isomerised product is fractionated again, to obtain water, at least one fuel product and a fraction consisting mainly of C17 and higher hydrocarbons. Often two fuel products are obtained, a small portion of naphtha and a main portion of kerosene.

According to an embodiment, the second fractionation comprises

- lowering the temperature of the isomerised product in a heat exchanger;

- separating a gas stream from the isomerised product in a flash;

- separating hydrogen from the gas stream with a membrane; and

- stripping the isomerised product with steam.

This type of second fractionation thus allows separating unreacted H2 from the gas stream. Preferably, the H2 is returned to the isomerising hydrocracking.

The lowering of the temperature of the isomerised product aims at lowering the temperature to a suitable level for the H2 membrane. This also helps to prevent unwanted flashing of valuable product range components, in particular in case a high pressure flash vessel is used, which adiabatically flashes the stream. The membrane permeate pressure may be set to drop from 3 MPa to 2.2 MPa, matching the pressure needed in the make-up H2 feed. Temperature of the isomerised product entering the flash may be for example around 60-90 °C.

The liquid stream from the flash then goes to a steam stripper, in which steam is adjusted to remove the remaining light end components in the liquid stream from the flash, such as 90-95 % of C4 from the stream, resulting in the fractionated isomerised product. In this second fractionation, non-condensable gases are thus flashed and the lightest hydrocarbons are steam stripped away, while unreacted hydrogen is recovered. The remaining fraction from the second fractionation consists mainly of hydrocarbons and possibly some condensed steam from the stripper. This stream is sent to third fractionation where it is preferably split to a naphtha and a kerosene stream.

The steam stripper may be a column without a condenser or reboiler. It preferably uses a separate steam feed stream to separate the remaining light components from the hydrocarbon stream. The steam feed and the conditions of the steam stripper can be used to adjust the light end of the product distribution and the amount of naphtha produced.

Conditions in the steam stripper may be, for example, temperature at the top around 92 °C, temperature at the bottom around 100 °C, pressure about 1 MPa. The used steam may have a temperature of 250 °C and a pressure of 1 MPa.

The fractionated isomerised product is thus fractionated again in a third fractionation. According to an embodiment, the third fractionation comprises distillation in at least one distillation column. Using only one column can save on the number of equipment, but the column design and operation may be more complex. According to another embodiment, the third fractionation comprises distillation in two distillation columns, in which case the first column separates a naphtha fraction and the second one produces a kerosene and a heavy bottoms fraction, consisting mainly of C17 and higher hydrocarbons. This heavy bottom fraction from the kerosene distillation column is recycled to the isomerising hydrocracking. An important function of this third fractionation is to do the final adjustment of the properties of the kerosene product so that they are on-spec, which is mainly achieved through controlling the distillation column(s), or other fractionation methods as used.

The liquid stream from the steam stripper of the second fractionation may thus be sent to a first distillation column, called naphtha splitter. It separates a naphtha fraction from the fractionated isomerised product. The flash point of the kerosene product is typically set by adjusting the distillate rate of the naphtha splitter. The reflux ratio of the column is preferably adjusted to give a sharp cut point and minimise the loss of kerosene range material to the naphtha stream. All material up to and including C8 is considered as product for the naphtha splitter and the purity target is typically set to 99 %.

In one embodiment, the liquid feed enters at the middle of the column. The column has a total condenser at the top which also does a separation to split out any condensed water from the steam stripper. In order to avoid thermal cracking, the column pressure is preferably set so that the bottom temperature is kept below 300 °C.

In this embodiment of two distillation columns, the bottom stream from the naphtha splitter enters the kerosene column. This column typically separates the kerosene product from the heavy fraction. The distillate rate of the kerosene column determines how much of the column feed stream is ready product and how much is to be recycled to the isomerising hydrocracking for further treatment. It is preferably adjusted so that the mass purity of the kerosene column distillate stream is at least 90 %, more preferably at least 96 %. All material up to and including C16 is considered as kerosene product. The column may also have a total condenser at the top and its pressure can be set on the same basis as for the naphtha splitter. The heavy bottom fraction is preferably pressurised and recycled to the isomerising hydrocracking by a recycle pump.

The distillation column(s) typically operate at pressures 5-1000 kPa, such as 55-586 kPa, and top/bottom temperatures 20/100 - 200/360 °C, such as 43/271 -152/314 °C. As an example, the temperature at the top of the first column, the naphtha splitter, may be about 83 °C, temperature at its bottom about 218 °C, and pressure 200 kPa. In the second, kerosene column, the temperature at the top of the column may be about 130 °C, temperature at its bottom about 272 °C, and pressure 30 kPa.

In an embodiment, the product slate is for example 85 % kerosene and 15 % naphtha and the kerosene product is expected to fulfil the requirements for FT-SPK defined in ASTM D7566-22. Any remaining water may be split from the naphtha stream in a decanter. Recycling

As explained also above, recycling of various side products from the different steps is performed, to increase carbon efficiency and overall efficiency of the present method. In addition to the recycling mentioned above, some further embodiments increase the recycling within the present method.

According to an embodiment, the method further comprises directing the second mixture of gases and water to reforming or to the reverse water gas shift reaction. Optionally, when directing the second mixture of gases and water to reforming, at least syngas and carbon dioxide are obtained, and these are then recycled to the Fischer-Tropsch reaction. By recycling the gases, loss of feedstock material to a gaseous product can be avoided.

Further, in this embodiment, the reforming of the second mixture of gases and water is carried out by a method selected from steam reforming, dry reforming, electric reforming, autothermal reforming, partial oxidation, and catalytic partial oxidation.

Gases from the flash and stripper of the second fractionation may thus be sent via a steam reformer to the FT reactor. A stream of steam is fed to the reformer, which mainly produces syngas, CO2 and methane.

The separated H2 from the second fractionation is preferably fed back to the isomerising hydrocracking, while the remaining gas stream, i.e. the retentate from the hydrogen membrane can be mixed with the gases from the steam stripper for further processing. The gases may be pressurised to the required level by a recycle gas compressor. The hydrogen may also be fed to the pre-hydrotreatment with an excess H2 before the isomerising hydrocracking, if used.

The steam reformer may be an isothermal equilibrium reactor, similar to the RWGS reactor. It converts the recycle stream mainly into syngas, CO2 and methane with the help of an additional steam stream. The reformed stream is sent to the FT reactor. The reformer temperature is in the range 800-1100+ °C, such as 950 °C. The pressure may be 2200 kPa. The various wastewater streams generated for example by the RWGS, FT and naphtha splitter condenser are preferably gathered in a flash, which adiabatically flashes these at low temperature and atmospheric pressure. This causes a small stream of dissolved hydrocarbons and oxygenates to vaporise from the water. The water stream can then be sent on to a wastewater treatment facility. The gas stream may be flared or recycled. For a large scale facility, or for a process generating more dissolved oxygenates, the wastewater and flash gas can be sent to a work-up section to recover and valorise the dissolved compounds. Such wastewater flash may work for example at a temperature of about 87 °C and a pressure of about 101 kPa.

System

The present method can be carried out in a system for processing a low-temperature Fischer-Tropsch reaction effluent into a fuel product, the system comprising

- first means for fractionating the Fischer-Tropsch into at least a first mixture of gases, a mixture of water and oxygenates, a fraction consisting mainly of C17 and higher hydrocarbons, and a fraction consisting mainly of C5-C16 hydrocarbons;

- a catalytic isomerising hydrocracking reactor for processing the fraction consisting mainly of C17 and higher hydrocarbons, and the fraction consisting mainly of C5- C16 hydrocarbons to produce an isomerised product;

- means for recycling the fraction consisting mainly of C17 and higher hydrocarbons from the third means for fractionating to the catalytic isomerising hydrocracking reactor. The various embodiments and options described above in connection with the process apply mutatis mutandis to the system.

The first means for fractionating may comprise

- a first high temperature flash;

- a heat exchanger arranged downstream of the first high temperature flash;

- a second low temperature flash arranged downstream of the heat exchanger; and

- a decanter arranged downstream of the second low temperature flash.

According to an alternative, the first means for fractionating comprises

- a first high temperature flash;

- a heat exchanger arranged downstream of the first high temperature flash; and

- a three phase separation means arranged downstream of the heat exchanger.

Still further, the system may comprise a pre-hydrotreatment reactor upstream of the isomerising hydrocracking reactor.

According to an embodiment, the second means for fractionating comprises

- a heat exchanger;

- a flash arranged downstream of the heat exchanger;

- a hydrogen separator with membrane arranged downstream the flash; and

- a steam stripper arranged downstream of the hydrogen separator with membrane.

The third means for fractionating may comprise at least one distillation column. The number of distillation columns is selected according to the aimed purity of the final product, and is preferably one, two, three or four.

The different flashes, heat exchanger, decanters and phase separation means, as well as strippers and distillation columns are known perse to a person skilled in the art. Typically, when a flash is mentioned, be it a high temperature, medium temperature or low temperature, it is operated at high pressure. When heat exchangers are mentioned, it is naturally also possible to use any other kind of device for either lowering or raising the temperature of the stream. Most preferably recovered heat is re-used in the method. The system may still further comprise means for directing the second mixture of gases and water to a reformer or to the reverse water gas shift reactor. These means may comprise pipes, heat exchangers and pumps, as need be. The reformer is typically selected from steam reformer, dry reformer, electric reformer, partial oxidation reactor, and catalytic partial oxidation reactor.

Obtained product

The product obtained by the present method and system fulfils the requirements of the standard ASTM D7566-22 for hydroprocessed synthetic blendstock for aviation fuels.

It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the description, numerous specific details are provided to provide a thorough understanding of embodiments of the invention.

The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 shows a process according to an embodiment. In this process, a Fischer- Tropsch effluent 1 is directed to a first fractionation 2a, 2b, wherein it is fractionated into a first mixture 3 of gases, a mixture 4 of water and oxygenates, a fraction 5 consisting mainly of C17 and higher hydrocarbons, and a fraction 6 consisting mainly of C5-C16 hydrocarbons.

The fraction 5 consisting mainly of C17 and higher hydrocarbons, and the fraction 6 consisting mainly of C5-C16 hydrocarbons are combined and processed by a catalytic isomerising hydrocracker 7 to produce an isomerised product 8.

The isomerised product 8 is fractionated in a second fractionation 9, in the presence of water 10, to obtain hydrogen 11 , a second mixture 12 of gases at least mainly other than hydrogen, and a fractionated isomerised product 13.

The fractionated isomerised product 13 is fractionated in a third fractionation 14, to obtain water 15, at least one fuel product 16, 16’ and a fraction 17 consisting mainly of C17 and higher hydrocarbons. The fraction 17 consisting mainly of C17 and higher hydrocarbons from the third fractionation 14 is recycled to the catalytic isomerising hydrocracking 7.

The first mixture 3 of gases is recycled to a reverse water gas shift reaction 18.

Figure 2 shows a process according to another embodiment. In this embodiment, the second mixture 12 of gases and water is directed to reforming 19 to obtain a mixture 20 of at least syngas and carbon dioxide, which are recycled to the Fischer- Tropsch reactor 22. The reforming may take place in the presence of water 21 .

Figure 3 shows part of a system and method according to an embodiment. In this part, one embodiment of the first fractionation is illustrated. It comprises a first high temperature flash 23 to separate C17 and higher hydrocarbons 5 from a first remaining part of the effluent 24 and a heat exchanger 25 to lower the temperature of the first remaining part of the effluent. Further, the first fractionation comprises a second low temperature flash 26 to separate the first mixture of gases 3 from a second remaining part of the effluent 27; and a decanter 28 to separate the mixture of water and oxygenates 4 from the fraction consisting mainly of C5-C16 hydrocarbons 6.

Figure 4 shows part of a system and method according to another embodiment, namely another embodiment of the first fractionation comprising a first high temperature flash 23 to separate C17 and higher hydrocarbons 5 from a first remaining part of the effluent 24; a heat exchanger 25 to lower the temperature of the first remaining part of the effluent; and a three phase separation 29 to separate the first mixture of gases 3, the mixture of water and oxygenates 4, and the fraction consisting mainly of C5-C16 hydrocarbons 6.

Figure 5 shows another part of a system and method according to an embodiment, the second fractionation and one embodiment of the third fractionation. The second fractionation comprises a heat exchanger 30 to lower the temperature of the isomerised product 8; a flash 37 to separate a gas stream 38 from the isomerised product; a membrane 31 to separate hydrogen 11 from the gas stream 38; and a steam stripper 32 for stripping the isomerised product. In this embodiment, the third fractionation comprises one distillation column 33.

Figure 6 shows part of a system and method according to an embodiment of the third fractionation. In this embodiment, the third fractionation comprises two distillation columns 33 and 35.

Figure 7 shows part of a system and method according to an embodiment, wherein a pre-hydrotreatment reactor 36 is arranged before the isomerising hydrocracking 7.

EXAMPLES

The following describes hot to carry out the method.

Syncrude is produced by first feeding CO2 and H2 to an eRWGS reactor (pressure 2.2 MPa), which iss an isothermal equilibrium reactor, after having been heated to the reactor temperature, namely 1000 °C. The feed stream is converted into syngas and cooled in a syngas cooler/condenser to condense and separate the water generated by eRWGS. Temperature in the cooler/condenser is set to 35 °C. The obtained syngas is then preheated by an FT feed preheater to set it to the FT reactor temperature, i.e. 220 °C. Pressure in the FT reactor is 2.2 MPa, and the residence time 0.07 h. The obtained syncrude is then fractionated in a first fractionation, namely in a first high temperature flash (temperature 220 °C, pressure 2.17 MPa), whereafter the heavy distillate (C17 and higher) is directed to the hydrocracking isomerisation, while the rest is directed to a heat exchanger and a second low temperature flash (temperature 35 °C, pressure 2.14 MPa). From the second flash, gases are directed to FT gas recycle via a recycle gas compressor, and the rest to a decanter, which is operated at the same conditions as the low temperature flash. The aqueous phase (water and oxygenates) are directed to wastewater treatment, and the rest to the hydrocracking isomerisation.

The feed to the isomerising hydrocracker is first heated to a temperature of 300 °C and pre-hydrotreated at this temperature and pressure of 5 MPa. The prehydrotreated effluent is then directed to an isomerising hydrocracker, temperature 320 °C, pressure 5 MPa and WHSV 0.9 /h. The catalyst used is Pt on an alumina- silica support.

After the isomerising hydrocracker, the isomerised product is fractionated in a second and third fractionation as follows.

First, the isomerised product is cooled down and thereafter sent to a high pressure flash (60 °C, pressure 5 MPa) to make a first separation of the light gases from the rest of the isomerised product. These gaseous compounds are passed through a membrane that separates the hydrogen to be fed back into the reactor from the rest of the gas stream. This is followed by a steam stripper, operated at a temperature of 65 °C at the top and 84 °C at the bottom, pressure 1 MPa (stripper steam at 250 °C, pressure 1 MPa). The separated gases are combined with the retentate light gases from the hydrogen membrane. The combined gas stream continues to a steam reformer, operated at 950 °C and a pressure of 2.2 MPa. The obtained syngas is recirculated back to the FT reactor.

The fractionated isomerised product is then directed to a naphtha splitter (condenser temperature 83 °C, reboiler temperature 218 °C, pressure 0.2 MPa). Naphtha is retrieved, water directed to wastewater treatment and the rest to a kerosene column (condenser temperature 130 °C, reboiler temperature 272 °C, pressure 0.03 MPa). From the kerosene column, the C17 and higher hydrocarbons are recirculated to the isomerising hydrocracker, and the kerosene retrieved.

The wastewater treatment comprises also a wastewater flash, operated at 35 °C and a pressure of 0.101 MPa. The yield of kerosene was 3345 kg/h while the yield of naphtha was 644 kg/h, i.e. a very large amount of kerosene was obtained. The obtained kerosene fulfills the requirements of the ASTM D7566-22 for jet fuel. The overall yield of the process is about 83 % of kerosene, on a carbon efficiency basis. The product slate consists of 84 wt-% of kerosene and 16 wt-% of naphta.

Claims

1 . A method for processing a low-temperature Fischer-Tropsch reaction effluent (1 ) into a fuel product, the method comprising

- fractionating the Fischer-Tropsch effluent in a first fractionation (2a, 2b) into at least a first mixture of gases (3), a mixture of water and oxygenates (4), a fraction consisting mainly of C17 and higher hydrocarbons (5), and a fraction consisting mainly of C5-C16 hydrocarbons (6);

- processing the fraction consisting mainly of C17 and higher hydrocarbons, and the fraction consisting mainly of C5-C16 hydrocarbons by a catalytic isomerising hydrocracking (7) to produce an isomerised product (8);

- fractionating the isomerised product in a second fractionation (9), in the presence of water (10), to obtain hydrogen (11 ), a second mixture of gases (12) at least mainly other than hydrogen, and a fractionated isomerised product (13),

- fractionating the fractionated isomerised product in a third fractionation (14), to obtain water (15), at least one fuel product (16, 16’) and a fraction consisting mainly of C17 and higher hydrocarbons (17); wherein

- at least the first mixture of gases (3) is directed to a reverse water gas shift reaction (18); and

- the fraction consisting mainly of C17 and higher hydrocarbons (5) from the third fractionation is recycled to the catalytic isomerising hydrocracking (7).

2. The method according to claim 1 , wherein the low temperature Fischer-Tropsch reaction has taken place at 170-270 °C.

3. The method according to any of the preceding claims, wherein the first fractionation comprises

- separating C17 and higher hydrocarbons (5) from a first remaining part of the effluent (24) in a first high temperature flash (23);

- lowering the temperature of the first remaining part of the effluent in a heat exchanger (25);

- separating the first mixture of gases (3) from a second remaining part of the effluent (27) in a second low temperature flash (26); and - separating the mixture of water and oxygenates (4) from the fraction consisting mainly of C5-C16 hydrocarbons (6) in a decanter (28).

4. The method according to claim 1 or 2, wherein the first fractionation comprises

- lowering the temperature of the first remaining part of the effluent in a heat exchanger (25); and

- separating the first mixture of gases (3), the mixture of water and oxygenates (4), and the fraction consisting mainly of C5-C16 hydrocarbons (6) in a three phase separation (29).

5. The method according to claim 3 or 4, wherein the temperature in the high temperature flash is 170-270 °C, preferably 210-230 °C.

6. The method according to claim 3, wherein the temperature in the low temperature flash is 20-70 °C.

7. The method according to any of the preceding claims, wherein the isomerising hydrocracking is carried out at a temperature of 240-400 °C, preferably 300-370 °C or 320-350 °C.

8. The method according to any of the preceding claims, wherein the isomerising hydrocracking is carried out at a pressure of 3-10 MPa, preferably 4-8 MPa, more preferably 5-7 MPa.

9. The method according to any of the preceding claims, wherein the isomerising hydrocracking is carried out at a weight hourly space velocity of 0.15-5 /h.

10. The method according to any of the preceding claims, wherein the catalyst in the isomerising hydrocracking is selected from a group consisting of a noble metal on a support.

11. The method according to any of the preceding claims, further comprising prehydrotreating (36) the fraction consisting mainly of C17 and higher hydrocarbons, and the fraction consisting mainly of C5-C16 hydrocarbons with an excess hydrogen before the isomerising hydrocracking (7).

12. The method according to any of the preceding claims, wherein the second fractionation comprises

- lowering the temperature of the isomerised product (8) in a heat exchanger (30);

- separating a gas stream (38) from the isomerised product in a flash (37);

- separating hydrogen (11 ) from the gas stream with a membrane (31 ); and

- stripping the isomerised product with in a steam stripper (32).

13. The method according to any of the preceding claims, wherein the third fractionation comprises distillation in at least one distillation column (33).

14. The method according to any of the preceding claims, further comprising directing the second mixture of gases and water (12) to reforming (19) or to a reverse water gas shift reaction.

15. The method according to claim 13, further comprising directing the second mixture of gases and water (12) to reforming (19) to obtain a mixture of at least syngas and carbon dioxide (20); and recycling the syngas and carbon dioxide to the Fischer-Tropsch reaction.

16. The method according to claim 14, wherein the reforming of the second mixture of gases and water (12) is carried out by a method selected from steam reforming, dry reforming, electric reforming, autothermal reforming, partial oxidation, and catalytic partial oxidation.

17. A system for processing a low-temperature Fischer-Tropsch reaction effluent into a fuel product, comprising

- first means for fractionating (2a, 2b) the Fischer-Tropsch reaction effluent (1 ) into at least a first mixture of gases (3), a mixture of water and oxygenates (4), a fraction consisting mainly of C17 and higher hydrocarbons (5), and a fraction consisting mainly of C5-C16 hydrocarbons (6); - a catalytic isomerising hydrocracking reactor (7) for processing the fraction consisting mainly of C17 and higher hydrocarbons, and the fraction consisting mainly of C5-C16 hydrocarbons to produce an isomerised product (8);

- second means for fractionating (9) the isomerised product, in the presence of water (10), to obtain hydrogen (11 ), a second mixture of gases (12) at least mainly other than hydrogen, and a fractionated isomerised product (13),

- third means for fractionating (14) the fractionated isomerised product, to obtain water (15), at least one fuel product (16, 16’) and a fraction consisting mainly of C17 and higher hydrocarbons (17);

- means for directing at least the first mixture of gases to a reverse water gas shift reactor (18); and

18. The system according to claim 17, wherein the first means for fractionating comprises

- a first high temperature flash (23);

- a heat exchanger (25) arranged downstream of the first high temperature flash;

- a second low temperature flash (26) arranged downstream of the heat exchanger; and

- a decanter (28) arranged downstream of the second low temperature flash.

19. The system according to claim 17, wherein the first means for fractionating comprises

- a first high temperature flash (23);

- a heat exchanger (25) arranged downstream of the first high temperature flash; and

- a three phase separation means (29) arranged downstream of the heat exchanger.

20. The system according to any one of the claims 17-19, further comprising a prehydrotreatment reactor (36) arranged upstream the isomerising hydrocracking reactor (7).

21. The system according to any one of the claims 17-19, wherein the second means for fractionating comprises

- a heat exchanger (30);

- a flash (37) arranged downstream of the heat exchanger; - a hydrogen separator (31 ) with membrane arranged downstream the flash; and

- a steam stripper (32) arranged downstream of the hydrogen separator with membrane.

22. The system according to any one of the claims 17-19, wherein the third means for fractionating comprises at least one distillation column (33, 35).

23. The system according to any one of the claims 17-19, further comprising means for directing the second mixture of gases and water to a reformer (19) or to the reverse water gas shift reactor (18).

24. The system according to claim 23, wherein the reformer is selected from steam reformer, dry reformer, electric reformer, partial oxidation reactor, and catalytic partial oxidation reactor.