EP4615627A1

EP4615627A1 - Reactor and reaction method

Info

Publication number: EP4615627A1
Application number: EP22814331.9A
Authority: EP
Inventors: Zbigniew Boguslaw URBAN
Original assignee: Siemens Industry Software Ltd; Siemens Industry Software Ltd Great Britain
Current assignee: Siemens Industry Software Ltd; Siemens Industry Software Ltd Great Britain
Priority date: 2022-11-07
Filing date: 2022-11-07
Publication date: 2025-09-17
Also published as: CN120500380A; WO2024099536A1

Abstract

A Fischer-Tropsch reactor (100) comprising: a) a pressure vessel (130) adapted to contact an enriched carrier fluid (F) with a catalyst to form a hydrocarbon product, wherein the carrier fluid (F) is enriched with carbon monoxide and hydrogen by contact with a synthesis gas (G); b) a carrier fluid (F) recirculation pump (104) in fluid connection with the base (B) of the pressure vessel (130) and adapted to pump (104) carrier fluid (F) from the pressure vessel (130) to be recycled and reintroduced to the top T of the pressure vessel (130); and c) a heat exchanger (105) in fluid connection with the top (T) of, and external to, the pressure vessel (130) and the carrier fluid (F) recirculation pump (104) and adapted to cool the carrier fluid (F) before reintroduction to the top (T) of the pressure vessel (130); wherein the pressure vessel (130) is provided with a vertical alternating arrangement of gas enrichment zones (106) and catalyst-containing reaction zones (116) through which the carrier fluid (F) flows before being pumped from the pressure vessel (130) to be recycled.

Description

REACTOR AND REACTION METHOD

The present disclosure relates to a reactor and a reaction method.

In particular the disclosure is concerned with a Fischer-Tropsch (FT) reactor and a FT synthesis method.

Background

Conventional Fischer-Tropsch (FT) reactors in commercial operations or under development to date achieve relatively low conversions at single pass operation and hence are not able to achieve relatively high conversions at single pass operation. This relatively low conversion at single pass operation limitation is common to different conventional FT reactor types, for example: i. Multitubular fixed bed reactors typically can be operated at single pass conversion up to 40%; ii. Slurry bubble column reactors typically can be operated at single pass conversion up to 55%; and iii. Microchannel reactors typically can be operated at single pass conversion up to 70% but only if charged with a proprietary catalyst.

An attempt to operate at conversions exceeding the above limits results in water- induced oxidation of the cobalt in the catalyst, leading to a total loss of catalyst activity over a short period of time. Thus, conventional FT reactors have to be operated with limited conversion of the raw material, which results in large recycles of the off-gas. This, in turn, makes it uneconomic to employ these conventional FT reactors in conjunction with gasification for converting waste materials to energy sources like synthetic liquid fuels and high-purity hydrogen. This is because gasifiers cannot accommodate large off-gas recycles, and the latter would have to be processed in expensive reformers.

Additionally and/or alternatively, conventional FT reactors in commercial operations or under development to date require relatively high pressure drops for driving the gas flow through 3 phase system composed of gas, liquid and catalyst. This relatively high pressure drop limitation is common to different conventional FT reactor types, for example: i. Multitubular fixed bed reactors are typically operated with a pressure drop of 6 bar; ii. Slurry bubble column reactors are typically operated with a pressure drop of 2 bar; and iii. Microchannel reactors are typically operated with a pressure drop of about 6 bar.

The relatively high pressure drop increases the cost of gas compression and/or reduces the effectiveness of energy recovery in the expander. This increases the electric power consumption, which goes against the concept of renewable energy plants that are expected to be self-sufficient for energy (no electric power supply from external sources).

Hence, achieving a relatively high conversion (for example, greater than 55% or at greater than 70%) at single pass operation is highly desirable. Additionally and/or alternatively, operating at a relatively low pressure drop (for example, less than 2 bar) is highly desirable.

Summary

According to the present disclosure there is provided a reactor and a reaction method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

A first aspect provides a Fischer-Tropsch reactor comprising: a) a pressure vessel adapted to contact an enriched carrier fluid with a catalyst to form a hydrocarbon product, wherein the carrier fluid is enriched with carbon monoxide and hydrogen by contact with a synthesis gas; b) a carrier fluid recirculation pump in fluid connection with the base of the pressure vessel and adapted to pump carrier fluid from the pressure vessel to be recycled and reintroduced to the top of the pressure vessel; and c) a heat exchanger in fluid connection with the top of, and external to, the pressure vessel and the carrier fluid recirculation pump and adapted to cool the carrier fluid before reintroduction to the top of the pressure vessel; wherein the pressure vessel is provided with a vertical alternating arrangement of gas enrichment zones and catalyst-containing reaction zones through which the carrier fluid flows before being pumped from the pressure vessel to be recycled.

Additionally and/or alternatively, the first aspect provides a Fischer-Tropsch reactor comprising: a) a pressure vessel provided with a vertical alternating arrangement of gas enrichment zones and catalyst-containing reaction zones through which an enriched carrier fluid flows downwards before being pumped from the pressure vessel to be recycled, whereby the pressure vessel is adapted to contact the enriched carrier fluid with a catalyst to form a hydrocarbon product, wherein the carrier fluid is enriched with carbon monoxide and hydrogen by countercurrent contact with a synthesis gas flowing upwards; b) a carrier fluid recirculation pump in fluid connection with the base of the pressure vessel and adapted to pump the carrier fluid from the pressure vessel to be recycled and reintroduced to the top of the pressure vessel; and c) a heat exchanger in fluid connection with the top of, and external to, the pressure vessel and the carrier fluid recirculation pump and adapted to cool the carrier fluid before reintroduction to the top of the pressure vessel.

That is, the carrier fluid and the synthesis gas (also known as syngas) flow in countercurrent, having different or counter paths in the pressure vessel. The syngas flows (more generally, moves) upwards through the gas enrichment zones, for example through only the gas enrichment zones. It should be understood that the syngas does not flow (more generally, does not move) upwards through and/or enter the catalyst-containing reaction zones, at least as gas. In contrast, the carrier fluid flows (more generally, moves) downwards (for example, under gravity) through the pressure vessel, through the vertical alternating arrangement of gas enrichment zones and catalyst-containing reaction zones and the carrier fluid recirculation pump, external to the pressure vessel, pumps the carrier fluid to be recycled from the base of the pressure vessel, via the heat exchanger wherein the carrier fluid is cooled, to the top of the pressure vessel, where the carrier fluid is reintroduced.

In contrast to conventional FT reactors, the FT reactor according to the first aspect may achieve relatively high conversions of 80% to 90% with no premature deactivation of the catalyst. This significantly reduces the amount of remaining reactants in the off-gas, to the extent that it is no longer necessary to recycle the offgas in order to achieve economic operation.

In contrast to conventional FT reactors, the FT reactor according to the first aspect may be operated at a relatively lower pressure drop of about only 50 mbar, thereby decreasing the cost of gas compression and/or increasing the effectiveness of energy recovery in the expander. This decreases the electric power consumption.

In more detail, the heat exchanger (also known as a reboiler, for example a standard reboiler) is external to the pressure vessel. In contrast, the heat exchanger of a conventional FT reactor is typically internal to the pressure vessel. The inventors have found that an increase in temperature of the carrier fluid, for example wax, between the vertical alternating arrangement of gas enrichment zones and catalyst-containing reaction zones (also known as stages) may be less than about 5°C, less than about 2°C or less than about 1°C, for example 1°C to 2°C, depending on the activity of the catalyst. Accordingly, the need for cooling apparatus inside the pressure vessel, for example cooling tubes, may be reduced or eliminated, since the heat of reaction is removed via the external heat exchanger, for example of a standard design. The external heat exchanger may be operated in a manner resulting in very high heat transfer coefficient on the carrier fluid, for example wax, side, which in turn allows a significant reduction in the heat exchange surface area. The reactor according to the first aspect may be used with a range of coolants in the external heat exchanger, including ambient air or a water cooling tower if the heat generated by the reaction is not intended to be utilised for generating steam for electricity production. The temperature difference between the coolant and the carrier fluid, for example wax, circulated between the pressure vessel and external heat exchanger can be at least 50°C or at least 100°C and may be up to about 180 to 190 °C, which may allow about 40 to 50-fold reduction in the heat exchange area as compared to slurry reactors. Additionally and/or alternatively, the temperature difference between the coolant and the carrier fluid (e.g. circulated wax) can be no less than 20°C resulting in 5-6 fold reduction of heat exchange area as compared to slurry reactors, but not higher than 100°C to assure the carrier fluid (e.g. circulated wax) does not solidify in tubes of external heat exchanger.

Optionally, a pressurised water loop may be used, as in other FT reactor designs, except that the heat exchange area is outside the pressure vessel and the pressure in the water loop may be lower as there are no constraints on the coolant temperature relating to reactor operability considerations. In particular, a temperature difference of about 50°C may be employed between the carrier fluid, for example wax, and the boiling water, which allows about 10 to 15-fold reduction in the heat exchange area over conventional designs while still being able to generate steam that is suitable for electricity production. Additionally and/or alternatively, the temperature difference between the coolant and the carrier fluid (e.g. circulated wax) can be no less than 20°C resulting in 5-6 fold reduction of heat exchange area, but not higher than 30°C to assure high pressure and temperature of generated water steam.

Typically, the catalyst (for example, in the form of 100-350 pm particles) is contained in cylindrical cartridges of annular form in the catalyst-containing reaction zones.

The FT reactor according to the first aspect may be considered as an adiabatic reactor with typically three to four sections (floors or plates) from which catalyst cartridges are suspended. The typically three to four sections process the syngas feed in parallel. Each section of cartridges typically has a block of structured packing above it. The typically three to four sections of cartridges are fed with the same recycled stream of wax. A final, optional section acting as a finishing water stripper may be located at the bottom of the reactor.

The FT reactor according to the first aspect effectively reduces the three-phase system (comprising gas, liquid wax, and solid catalyst) to a two-phase reaction system (wax plus catalyst). In particular, the gas phase containing the reactants (hydrogen and carbon monoxide) never needs to come in direct contact with the catalyst. Instead, the reactants may be pre-loaded into the carrier fluid, for example wax, via countercurrent flow in the structured packing. The carrier fluid, for example wax, is then contacted with the solid catalyst held in the cartridges. Overall, this results in a much simpler and more stable operation.

A key characteristic of the reactor according to the first aspect is that the gas and carrier fluid, for example wax, follow different paths therethrough.

The path followed by the carrier fluid, for example wax, within the reactor is as follows: 1. The carrier fluid, for example wax, enters the reactor on the sieve tray located at the reactor top. 2. The sieve tray distributes the carrier fluid, for example wax, over the top of the structured packing material; the carrier fluid, for example wax, flows down across the packing under gravity.

3. Within the structured packing material, the carrier fluid, for example wax, is in countercurrent contact with the first part of the syngas feed, which passes upwards through the packing; as a result, the carrier fluid, for example wax, becomes saturated with hydrogen and carbon monoxide.

4. The carrier fluid, for example wax, runs off the packing to form a liquid pool of about 300 mm in height on the first plate.

5. The hydrostatic pressure of the pool drives the carrier fluid, for example wax, flow across the walls of the catalyst cartridges.

6. While passing through the layer of catalyst in the cartridges, up to 45 % of the hydrogen and carbon monoxide dissolved in the carrier fluid, for example wax, are converted to hydrocarbons and water. At the same time, the temperature of the carrier fluid, for example wax, increases by 1°C to 2°C, effectively removing the heat of reaction from the catalyst.

7. The carrier fluid, for example wax, leaving below the cartridges is distributed over the second layer of packing.

8. Within the second block of packing, the carrier fluid, for example wax, comes in countercurrent contact with the second part of the syngas feed, which passes upwards through the packing. As a result, the carrier fluid, for example wax, again becomes saturated with hydrogen and carbon monoxide while also being stripped of the dissolved water that was produced by the reaction in the cartridges above. The water and most of the light hydrocarbon products are transferred from the carrier fluid, for example wax, to the passing gas, and exit the pressure vessel.

9. Below the second block of packing the carrier fluid, for example wax, forms a liquid pool and flows through the catalyst cartridges

10. The same sequence of enriching the carrier fluid, for example wax, with hydrogen and carbon monoxide, stripping water and light hydrocarbons from it in packing and passing the carrier fluid, for example wax, through the catalyst cartridges can be repeated three to four times in the pressure vessel.

11. The carrier fluid, for example wax, leaving the cartridges in the last, lowest section is distributed over the bottom block of packing.

12. In the bottom block of packing, water is removed from the carrier fluid, for example wax, by the combined outlet gas from all the sections, which is dried, heated back to the pressure vessel temperature, and returned to the pressure vessel as stripping gas. This achieves a final dewatering of the carrier fluid, for example wax, which avoid cavitation in the carrier fluid recirculation pump and/or heat exchanger (also known as reboiler) and provides additional control of catalyst deactivation.

13. The carrier fluid, for example wax, from the final packing is collected in the reactor sump to be directed to the carrier fluid recirculation pump, for example an axial pump, in fluid communication with the base of the pressure vessel.

14. The carrier fluid, for example wax, is cooled down by 6°C to 8°C in the heat exchanger, which operates with a temperature difference of about 20°C and with high heat transfer coefficients on both carrier fluid, for example wax, and vaporizing water sides.

15. The cooled carrier fluid, for example wax, now free of water and light hydrocarbons, is recycled back and reintroduced to the top of the pressure vessel.

The path of the gas within the reactor is as follows:

1. The syngas feed is equally distributed between the three to four sections by the annular tube via openings to each section.

2. After passing through the structured packing in each section, the gas is directed to a manifold and driven out of the pressure vessel.

3. The water from the collected outlet gas is condensed out.

4. The gas is then heated back to the reactor temperature and returned to the pressure vessel as stripping gas. The gas collected from the stripping section constitutes the off-gas from the FT reactor.

The carrier fluid, for example wax, circulation within the FT reactor effectively provides an internal recycle stream that allows the FT reactor to reach very high conversions of the order of 80% to 90% as has already been confirmed experimentally. It is worth noting, however, that the conversion incurred within any single catalyst cartridge can be maintained below 45% by manipulating the carrier fluid, for example wax, circulation flowrate. This protects the catalyst from oxidation, thereby addressing one of the key deficiencies of conventional FT reactor designs.

Another remarkable characteristic of the design is the very low pressure drop incurred by the gas. This is a consequence of the fact that the only significant resistance to gas flow is that induced by the structured packing; the latter is designed to produce very low pressure drop for gas flows in countercurrent arrangement to liquid flow. In contrast, conventional FT reactors in commercial operation or under development to date force the gas (either alone or in the presence of liquid) to get in contact with the catalyst in the form of fixed bed or suspension, resulting in very high pressure drops.

In one example, each gas enrichment zone contains a structured packing material material that the synthesis gas and the carrier fluid, for example wax, can pass through and that provides a large surface area for contact between the synthesis gas and the carrier fluid, for example wax. The structured packing material may be a randomly arranged material or a structured packing material. In one example, the structured packing material comprises corrugated metal plates or gauzes that are arranged together to form a fluid flow path. In one example, the structured packing material has an open honeycomb structure. Exemplary structured packing material includes MellapackPlus® or Intalox®. In one example, the carrier fluid, for example wax, is driven through the structured packing material under and/or by gravity.

The porous cartridges containing a catalyst may be retained in some or all of the apertures of plate. In other embodiments, the plate may have a single aperture 120 in which a porous cartridge is retained. Apertures may be of any shape. Apertures may have an area of about 35 to 40% of the total surface of the substrate. Each substrate may have about 1500 to 2500 apertures.

In one example, the cartridges are dimensioned to removably fit in the apertures and I or may be removably fixed to the plate.

The H2 and CO enriched carrier fluid, for example wax, passes through the porous cartridges, where the H2 and CO contact the catalyst particles contained in the cartridges, and react to form hydrocarbons and water. The carrier fluid, for example wax, transport mechanism across the wall of cartridge may be dominated by hydrostatic pressure-driven convection. The reaction environment is a 2-phase system of H2 and CO enriched carrier fluid, for example wax, and catalyst. The dominating mass transport mechanism across the wall of the cartridge is convection driven by pressure differences. If the dimension of catalyst particles does not exceed a maximum size, optionally about 100 microns, then there may be no diffusive limitations within the catalyst material, thereby reducing selectivity to methane as compared to processes in which the mass transport of reactants and products is limited by molecular diffusion.

By providing separate gas enrichment zones and catalyst-containing reaction zones and by ensuring that the catalyst-containing reaction zones remain covered by carrier fluid, for example wax, layers, little or no free (unabsorbed) hydrogen and carbon monoxide delivered to a gas enrichment zone may reach catalyst in cartridges 222 within a catalyst-containing reaction zone; substantially all hydrogen and carbon monoxide reaching the catalyst may be hydrogen and carbon monoxide absorbed in the carrier fluid, for example wax, such that the reaction is effectively a two-phase reaction between the enriched carrier fluid, for example wax, and the catalyst. Water comprises a significant part of the total product of the reaction, as illustrated by formation of pentane from hydrogen and carbon monoxide:

11 H₂+ 5 CO C5H12 + 5 H₂O

For every mole (72 g) of pentane formed, 5 moles (90 g) of water are also formed. Water may form about 60 weight % of the combined product from all reactions.

When a homogeneous mixture containing water by-product and carrier fluid, for example wax, passes through a gas enrichment zone, the water by-product may be desorbed into a stream of components of the syngas and low-boiling hydrocarbon products that are not absorbed by the carrier fluid, for example wax. Under the envisaged operating conditions, practically all of this water may be removed from the reactor, along with unabsorbed components of the syngas (including unreacted hydrogen and carbon monoxide, as well as other species such as nitrogen) and low- boiling hydrocarbon products, for example C1 to C5 hydrocarbons, through a gas outlet. It will be appreciated that the flow of carrier fluid, for example wax, in the pressure vessel of the reactor according to the first aspect may allow for efficient separation of water from the wax, thereby avoiding the dilution of the reactants in the gas phase, and consequently in the liquid phase, that is an undesirable characteristic of conventional FT reactors. It is preferred that most or all of the hydrogen and carbon monoxide of the syngas, optionally at least 80 % or at least 90 % is absorbed by the wax in the gas enrichment zones. Water and low-boiling hydrocarbon products are desorbed in the gas enrichment zones, thereby selectively removing water from both gas and liquid phases over the entire inventory of the catalyst without the need for inter-stage condensation. Low-boiling hydrocarbon products in the gas exiting via gas outlet may be recovered or may be combusted.

By removal of water in the gas enrichment zones, and/or by providing that substantially all hydrogen and carbon monoxide coming into contact with the catalyst is absorbed in the carrier fluid, for example wax, rather than free gas, the water formed within cartridges may amount to no more than about 1 weight % of the carrier fluid, for example wax, which may not have a significant effect on the reaction rate. After passing through a first reaction zone, the carrier fluid, for example wax, may pass through one, two, three or more further gas enrichment and catalyst-containing reaction zones before being pumped by the carrier fluid recirculation pump from the base of the pressure vessel, for example a sump thereof, to the top of the pressure vessel via the heat exchanger, for example above the uppermost or first gas enrichment zone. An excess of carrier fluid, for example wax, such as above a controlled level in the sump, is removed from the pressure vessel as the hydrocarbon product.

In one example, each catalyst-containing reaction zone is provided with a gas outlet. For example, after passing through the structured packing material in each catalystcontaining reaction zone (also known as a section), the gas is directed to a manifold and driven out of the pressure vessel.

In one example, the base of the pressure vessel comprises a dewatering region where the gas from each gas outlet is used to dewater the carrier fluid prior to being pumped from the pressure vessel to be recycled. For example, in the bottom block of structured packing material, water is removed from the carrier fluid, for example wax, by the combined outlet gas from all the sections, which is dried, heated back to the pressure vessel temperature, and returned to the pressure vessel as stripping gas. This achieves a final dewatering of the carrier fluid, for example wax, which avoid cavitation in the carrier fluid recirculation pump and/or heat exchanger (also known as reboiler) and provides additional control of catalyst deactivation.

In one example, the pressure vessel further comprises a central stripping gas column. In one example, the gas used to dewater the carrier fluid is recirculated into the pressure vessel via the stripping gas column. For example, the gas is then heated back to the reactor temperature and returned to the pressure vessel as stripping gas. The gas collected from the stripping section constitutes the off-gas from the FT reactor.

In one example, the pressure vessel further comprises at least one inlet for synthesis gas (also known as syngas) and/or at least one outlet for the hydrocarbon product (i.e. a product of the FT reaction).

In one example, the syngas is introduced to the pressure vessel, for example to the top of the pressure vessel i.e. downwardly, via the at least one inlet for synthesis gas and is optionally directed by one or more gas-directing plates towards a gas channel. More than one gas channel may be provided. In one example, the gas channel and the stripping gas channel are concentric tubes, although in other examples, the gas channel and the stripping gas channel are separate tubes. In one example, the gas channel comprises one or more openings for distribution of the syngas into the gas enrichment zones, whereby the syngas flows (more generally, moves) upwards through the gas enrichment zones, for example through only the gas enrichment zones. It should be understood that the syngas does not flow (more generally, does not move) upwards through and/or enter the catalyst-containing reaction zones, at least as gas. In one example, the gas channel comprises one or more openings for distribution of the syngas into the respective gas enrichment zones, whereby the syngas flows (more generally, moves) upwards through the respective gas enrichment zones, for example through only the respective gas enrichment zone. In other words, the gas channel may comprise one or more openings for each gas enrichment zone and the syngas flows upwards through only one gas enrichment zone.

The syngas may consist solely of carbon monoxide and hydrogen or it may contain one or more further components. Exemplary further components may be residual gases from the feedstock used to form the syngas or may be by-products from formation of the syngas and include, without limitation, carbon dioxide, nitrogen, methane and water. In one example, the syngas contains about 30 vol. % to 50 vol. % of hydrogen. Preferably, the syngas contains about 35 vol. % to 40 vol. % of hydrogen. More preferably, the syngas contains 36 vol. % to 37 vol. % of hydrogen.

In one example, the syngas contains at least 15 vol.% of carbon monoxide. Preferably, the syngas contains about 15 vol. % to 25 vol. % of carbon monoxide. More preferably, the syngas contains about 17 vol. % to 20 vol. % of carbon monoxide. Most preferably, the syngas optionally contains about 17 vol. % to 18 vol. % of carbon monoxide.

In one example, the syngas contains about 30 vol. % to 50 vol. % of hydrogen and about 15 vol % to 25 vol. % of carbon monoxide. Preferably, the syngas contains about 36 vol. % to 37 vol% of hydrogen and about 17 vol % to 18 vol. % of carbon monoxide. In one example, the syngas has a H2:CO molar ratio of about 2.10 : 1 to 2.20 : 1. More preferably, the syngas has a H2:CO molar ratio of about 2.15 : 1.

In one example, the gas enrichment zones comprise a structured packing material that is permeable to the carrier fluid, carbon monoxide and hydrogen. For example, within the structured packing material, the carrier fluid, for example wax, is in countercurrent contact with the first part of the syngas feed, which passes upwards through the structured packing material; as a result, the carrier fluid, for example wax, becomes saturated with hydrogen and carbon monoxide.

In one example, the catalyst-containing zones comprise a Fischer-Tropsch catalyst supported by a substrate.

In one example, the carrier fluid is a wax. It should be understood that the carrier fluid comprises and/or is a carrier material that is in liquid form at the operating temperature of the FT reactor and that is capable of absorbing carbon monoxide and hydrogen. Exemplary carrier fluids include hydrocarbons, optionally heavy hydrocarbons. The carrier fluid may be hydrocarbons formed by the Fischer-Tropsch process. Exemplary hydrocarbons, including hydrocarbons formed by the Fischer- Tropsch process, may include naphtha (about C6 to C9); Kerosene (about C10 to 15); Diesel (about C16 to C21); and a heavy fraction (about C22 to C100). The liquid carrier is referred to hereinafter as a "wax" and the wax may include, without limitation, C5 to C100 hydrocarbons, including one or more of the hydrocarbon fractions described above. In a preferred example, the wax is the material produced by the reactor.

In one example, the FT reactor is operated at a pressure in a range from about 20 to about 35 barg, for example from 20 to 25 barg. In the absence of heat-exchange structures inside the reactor tank, only the external tank body needs to withstand the operating pressure. The highly exothermic nature of the FT process can lead to "runaway" temperature increase during the process, particularly if "hot-spots" develop within a reactor. This temperature increase can be dangerous as well as damaging to the catalyst. However, in the reactor according to the first aspect, the reaction may be stopped simply by closing the gas inlet or inlets to allow the concentration of hydrogen and carbon monoxide in wax to deplete. Additionally and/or alternatively, the pump may be stopped such that only the gas carried by carrier fluid, for example wax, that is already in contact with the catalyst will react. Furthermore, the concentration of hydrogen and carbon monoxide that is absorbed by the carrier fluid, for example wax, is typically lower at higher temperatures, and so without any access of the gas phase to the catalyst cartridges the overall rate of reaction will not increase significantly if the temperature of the carrier fluid, for example wax, exceeds an optimum operating temperature for a given catalyst.

In one example, the reactor is operated at a temperature that is selected according to the catalyst being used. For example, for cobalt-based catalysts, the temperature may be in a range from about 200°C to about 240°C, for example in a range from 200°C to 240°C.

A second aspect provides a Fischer-Tropsch synthesis method comprising: a) enriching a carrier fluid with carbon monoxide and hydrogen by contact with a synthesis gas within a gas enrichment zone provided in a pressure vessel; b) contacting the enriched carrier fluid with a catalyst to form a hydrocarbon product; c) pumping carrier fluid from the pressure vessel to be recycled and reintroduced to the top of the pressure vessel using a carrier fluid recirculation pump in fluid connection with the base of the pressure vessel; and d) cooling the carrier fluid before reintroduction to the top of the pressure vessel using a heat exchanger in fluid connection with the top of, and external to, the pressure vessel and the carrier fluid recirculation pump.

In one example, the method comprises the step of: e) using the gas from a gas outlet provided in each catalyst-containing reaction zone to dewater the carrier fluid in a dewatering region in the base of the pressure vessel prior to being pumped from the pressure vessel to be recycled.

In one example, the method comprises the step of: f) recirculating the gas used to dewater the carrier fluid into the pressure vessel via a central stripping gas column provided in the pressure vessel.

In one example, the method comprises the steps of: introducing a synthesis gas to the pressure vessel and recovering the hydrocarbon product from the pressure vessel.

In one example, the method comprises enriching a carrier fluid with carbon monoxide and hydrogen by contact with a synthesis gas within at least a second gas enrichment zone provided in the pressure vessel and contacting the enriched carrier fluid with a catalyst to form the hydrocarbon product, wherein the pressure vessel is provided with a vertical alternating arrangement of gas enrichment zones and catalyst-containing reaction zones through which the carrier fluid flows before being pumped from the pressure vessel to be recycled.

The method may provide for controlled and cost effective formation of hydrocarbons. The rate of reaction, and heat generated per unit time, may be controlled by a number of factors including, without limitation, one or more of gas pressure applied by a gas compressor (not shown); flow-rate delivered by the carrier fluid recirculation pump; the temperature set point in the controller of the external heat exchanger; the quantity of catalyst in each cartridge; cartridge thickness; the number of cartridges per reaction zone; and the total number of reaction zones.

The method does not require that catalyst be dispersed in the carrier fluid. By using a carrier fluid that is substantially free of catalyst, the risk of catalyst clogging within the pressure vessel is reduced or eliminated. Brief Description of the Drawings

Examples of the present disclosure will now be described with reference to the accompanying drawings, in which:

Figure 1 schematically shows a Fischer-Tropsch reactor according to an exemplary embodiment;

Figure 2 schematically shows a Fischer-Tropsch reactor according to an exemplary embodiment;

Figure 3 schematically shows results for the Fischer-Tropsch reactor of Figure 2; and

Figure 4 is a photograph of a Fischer-Tropsch reactor according to an exemplary embodiment.

Detailed Description

Figure 1 schematically shows a Fischer-Tropsch reactor 100 according to an exemplary embodiment.

The Fischer-Tropsch reactor 100 comprises: a) a pressure vessel 130 adapted to contact an enriched carrier fluid F with a catalyst to form a hydrocarbon product, wherein the carrier fluid F is enriched with carbon monoxide and hydrogen by contact with a synthesis gas G; b) a carrier fluid F recirculation pump 104 in fluid connection with the base B of the pressure vessel 130 and adapted to pump 104 carrier fluid F from the pressure vessel 130 to be recycled and reintroduced to the top T of the pressure vessel 130; and c) a heat exchanger 105 in fluid connection with the top T of, and external to, the pressure vessel 130 and the carrier fluid F recirculation pump 104 and adapted to cool the carrier fluid F before reintroduction to the top T of the pressure vessel 130; wherein the pressure vessel 130 is provided with a vertical alternating arrangement of gas enrichment zones 106 and catalyst-containing reaction zones 116 through which the carrier fluid F flows before being pumped from the pressure vessel 130 to be recycled. In contrast to conventional FT reactors, the FT reactor 100 according to the first aspect may achieve relatively high conversions of 80% to 90% with no premature deactivation of the catalyst. This significantly reduces the amount of remaining reactants in the off-gas, to the extent that it is no longer necessary to recycle the offgas in order to achieve economic operation.

In contrast to conventional FT reactors, the FT reactor 100 may be operated at a relatively lower pressure drop of about only 50 mbar, thereby decreasing the cost of gas compression and/or increasing the effectiveness of energy recovery in the expander. This decreases the electric power consumption.

In more detail, the heat exchanger 105 (also known as a reboiler, for example a standard reboiler) is external to the pressure vessel 130. In contrast, the heat exchanger 105 of a conventional FT reactor 100 is typically internal to the pressure vessel 130. The inventors have found that an increase in temperature of the carrier fluid F, for example wax, between the vertical alternating arrangement of gas enrichment zones 106 and catalyst-containing reaction zones 116 (also known as stages) may be less than about 5°C, less than about 2°C or less than about 1°C, for example 1°C to 2°C, depending on the activity of the catalyst. Accordingly, the need for cooling apparatus inside the pressure vessel 130, for example cooling tubes, may be reduced or eliminated, since the heat of reaction is removed via the external heat exchanger 105, for example of a standard design. The external heat exchanger 105 may be operated in a manner resulting in very high heat transfer coefficient on the carrier fluid F, for example wax, side, which in turn allows a significant reduction in the heat exchange surface area. The reactor 100 according to the first aspect may be used with a range of coolants in the external heat exchanger 105, including ambient air or a water cooling tower if the heat generated by the reaction is not intended to be utilised for generating steam for electricity production. The temperature difference between the coolant and the carrier fluid F, for example wax, circulated between the pressure vessel 130 and external heat exchanger 105 can be at least 50°C or at least 100°C and may be up to about 180 to 190 °C, which may allow about 40 to 50-fold reduction in the heat exchange area as compared to slurry reactors. Additionally and/or alternatively, the temperature difference between the coolant and the carrier fluid (e.g. circulated wax) can be no less than 20°C resulting in 5-6 fold reduction of heat exchange area as compared to slurry reactors, but not higher than 100°C to assure the carrier fluid (e.g. circulated wax) does not solidify in tubes of external heat exchanger.

Optionally, a pressurised water loop may be used, as in other FT reactor 100 designs, except that the heat exchange area is outside the pressure vessel 130 and the pressure in the water loop may be lower as there are no constraints on the coolant temperature relating to reactor 100 operability considerations. In particular, a temperature difference of about 50°C may be employed between the carrier fluid F, for example wax, and the boiling water, which allows about 10 to 15-fold reduction in the heat exchange area over conventional designs while still being able to generate steam that is suitable for electricity production. Additionally and/or alternatively, the temperature difference between the coolant and the carrier fluid (e.g. circulated wax) can be no less than 20°C resulting in 5-6 fold reduction of heat exchange area, but not higher than 30°C to assure high pressure and temperature of generated water steam.

Typically, the catalyst (for example, in the form of 100-350 pm particles) is contained in cylindrical cartridges 122 of annular form in the catalyst-containing reaction zones 116.

The FT reactor 100 according to the first aspect may be considered as an adiabatic reactor 100 with typically three to four sections (floors or plates 118) from which catalyst cartridges 122 are suspended. The typically three to four sections process the syngas G feed in parallel. Each section of cartridges 122 typically has a block of structured packing above it. The typically three to four sections of cartridges 122 are fed with the same recycled stream of wax. A final, optional section acting as a finishing water stripper may be located at the bottom of the reactor 100.

The FT reactor 100 effectively reduces the three-phase system (comprising gas, liquid wax, and solid catalyst) to a two-phase reaction system (wax plus catalyst). In particular, the gas phase containing the reactants (hydrogen and carbon monoxide) never needs to come in direct contact with the catalyst. Instead, the reactants may be pre-loaded into the carrier fluid F, for example wax, via countercurrent flow in the structured packing. The carrier fluid F, for example wax, is then contacted with the solid catalyst held in the cartridges 122. Overall, this results in a much simpler and more stable operation. A key characteristic of the reactor 100 is that the gas and carrier fluid F, for example wax, follow different paths therethrough.

The path followed by the carrier fluid F, for example wax, within the reactor 100 is as follows:

1. The carrier fluid F, for example wax, enters the reactor 100 on the sieve tray 141 located at the reactor 100 top T.

2. The sieve tray 141 distributes the carrier fluid F, for example wax, over the top T of the structured packing material; the carrier fluid F, for example wax, flows down across the packing under gravity.

3. Within the structured packing material 114, the carrier fluid F, for example wax, is in countercurrent contact with the first part of the syngas G feed, which passes upwards through the packing; as a result, the carrier fluid F, for example wax, becomes saturated with hydrogen and carbon monoxide.

4. The carrier fluid F, for example wax, runs off the packing to form a liquid layer or pool 140 of about 300 mm in height on the first plate 118 or sieve tray 141 .

5. The hydrostatic pressure of the pool 142 drives the carrier fluid F, for example wax, flow across the walls of the catalyst cartridges 122.

6. While passing through the layer of catalyst in the cartridges 122, up to 45 % of the hydrogen and carbon monoxide dissolved in the carrier fluid F, for example wax, are converted to hydrocarbons and water. At the same time, the temperature of the carrier fluid F, for example wax, increases by 1°C to 2°C, effectively removing the heat of reaction from the catalyst.

7. The carrier fluid F, for example wax, leaving below the cartridges 122 is distributed over the second layer of packing as a layer 142.

8. Within the second block of packing, the carrier fluid F, for example wax, comes in countercurrent contact with the second part of the syngas G feed, which passes upwards through the packing. As a result, the carrier fluid F, for example wax, again becomes saturated with hydrogen and carbon monoxide while also being stripped of the dissolved water that was produced by the reaction in the cartridges 122 above. The water and most of the light hydrocarbon products are transferred from the carrier fluid F, for example wax, to the passing gas, and exit the pressure vessel 130.

9. Below the second block of packing the carrier fluid F, for example wax, forms a liquid pool and flows through the catalyst cartridges 122

10. The same sequence of enriching the carrier fluid F, for example wax, with hydrogen and carbon monoxide, stripping water and light hydrocarbons from it in packing and passing the carrier fluid F, for example wax, through the catalyst cartridges 122 can be repeated three to four times in the pressure vessel 130.

11. The carrier fluid F, for example wax, leaving the cartridges 122 in the last, lowest section is distributed over the bottom block of packing.

12. In the bottom block of packing, water is removed from the carrier fluid F, for example wax, by the combined outlet gas from all the sections, which is dried, heated back to the pressure vessel 130 temperature, and returned to the pressure vessel 130 as stripping gas SG. This achieves a final dewatering of the carrier fluid F, for example wax, which avoid cavitation in the carrier fluid F recirculation pump 104 and/or heat exchanger 105 (also known as reboiler) and provides additional control of catalyst deactivation.

13. The carrier fluid F, for example wax, from the final packing is collected in the reactor 100 sump 134 to be directed to the carrier fluid F recirculation pump 104, for example an axial pump 104, in fluid communication with the base B of the pressure vessel 130 via an outlet pipe 126.

14. The carrier fluid F, for example wax, is cooled down by 6°C to 8°C in the heat exchanger 105, which operates with a temperature difference of about 20°C and with high heat transfer coefficients on both carrier fluid F, for example wax, and vaporizing water sides.

15. The cooled carrier fluid F, for example wax, now free of water and light hydrocarbons, is recycled back and reintroduced to the top T of the pressure vessel 130 via an inlet pipe 102.

The path 132 of the gas within the reactor 100 is as follows:

1. The syngas G feed 110 is equally distributed between the three to four sections by the annular tube of the gas channel 112 via openings 128 to each section.

2. After passing through the structured packing in each section, the gas is directed to a manifold and driven out of the pressure vessel 130.

3. The water from the collected outlet gas is condensed out.

4. The gas is then heated back to the reactor 100 temperature and returned to the pressure vessel 130 as stripping gas SG. The gas collected from the stripping section constitutes the off-gas from the FT reactor 100.

The carrier fluid F, for example wax, circulation within the FT reactor 100 effectively provides an internal recycle stream that allows the FT reactor 100 to reach very high conversions of the order of 80% to 90% as has already been confirmed experimentally. It is worth noting, however, that the conversion incurred within any single catalyst cartridge 122 can be maintained below 45% by manipulating the carrier fluid F, for example wax, circulation flowrate. This protects the catalyst from oxidation, thereby addressing one of the key deficiencies of conventional FT reactor 100 designs.

In this example, each gas enrichment zone 106 contains a structured packing material 114 material that the synthesis gas G and the carrier fluid F, for example wax, can pass through and that provides a large surface area for contact between the synthesis gas G and the carrier fluid F, for example wax. The structured packing material 114 may be a randomly arranged material or a structured packing material 114. In this example, the structured packing material 114 comprises corrugated metal plates or gauzes that are arranged together to form a fluid flow path. In this example, the structured packing material 114 has an open honeycomb structure. Exemplary structured packing material 114 includes MellapackPlus® or Intalox®. In this example, the carrier fluid F, for example wax, is driven through the structured packing material 114 under and/or by gravity.

The porous cartridges 122 containing a catalyst are retained in some or all of the apertures 120 of plate 118. In other embodiments, the plate 118 may have a single aperture 120 in which a porous cartridge 122 is retained. Apertures 120 may be of any shape. Apertures 120 may have an area of about 35 to 40% of the total surface of the substrate. Each substrate may have about 1500 to 2500 apertures 120.

In this example, the cartridges 122 are dimensioned to removably fit in the apertures 120 and / or may be removably fixed to the plate 118. The H2 and CO enriched carrier fluid F, for example wax, passes through the porous cartridges 122, where the H2 and CO contact the catalyst particles contained in the cartridges 122, and react to form hydrocarbons and water. The carrier fluid F, for example wax, transport mechanism across the wall of cartridge 122 may be dominated by hydrostatic pressure-driven convection. The reaction environment is a 2-phase system of H2 and CO enriched carrier fluid F, for example wax, and catalyst. The dominating mass transport mechanism across the wall of the cartridge 122 is convection driven by pressure differences. If the dimension of catalyst particles does not exceed a maximum size, optionally about 100 microns, then there may be no diffusive limitations within the catalyst material, thereby reducing selectivity to methane as compared to processes in which the mass transport of reactants and products relies entirely on molecular diffusion.

By providing separate gas enrichment zones 106 and catalyst-containing reaction zones 116 and by ensuring that the catalyst-containing reaction zones 116 remain covered by carrier fluid F, for example wax, layers, little or no free (unabsorbed) hydrogen and carbon monoxide delivered to a gas enrichment zone 106 may reach catalyst in cartridges 122 within a catalyst-containing reaction zone 116; substantially all hydrogen and carbon monoxide reaching the catalyst may be hydrogen and carbon monoxide absorbed in the carrier fluid F, for example wax, such that the reaction is effectively a two-phase reaction between the enriched carrier fluid F, for example wax, and the catalyst. Water comprises a significant part of the total product of the reaction, as illustrated by formation of pentane from hydrogen and carbon monoxide:

11 H₂+ 5 CO C5H12 + 5 H₂O

When a homogeneous mixture containing water by-product and carrier fluid F, for example wax, passes through a gas enrichment zone, the water by-product may be desorbed into a stream of components of the syngas G and low-boiling hydrocarbon products that are not absorbed by the carrier fluid F, for example wax. Under the envisaged operating conditions, practically all of this water may be removed from the reactor 100, along with unabsorbed components of the syngas G (including unreacted hydrogen and carbon monoxide, as well as other species such as nitrogen) and low- boiling hydrocarbon products, for example C1 to C5 hydrocarbons, through a gas outlet 124. It will be appreciated that the flow of carrier fluid F, for example wax, in the pressure vessel 130 of the reactor 100 according to the first aspect may allow for efficient separation of water from the wax, thereby avoiding the dilution of the reactants in the gas phase, and consequently in the liquid phase, that is an undesirable characteristic of conventional FT reactors. It is preferred that most or all of the hydrogen and carbon monoxide of the syngas G, optionally at least 80 % or at least 90 % is absorbed by the wax in the gas enrichment zones 106. Water and low- boiling hydrocarbon products are desorbed in the gas enrichment zones 106, thereby selectively removing water from both gas and liquid phases over the entire inventory of the catalyst without the need for inter-stage condensation. Low-boiling hydrocarbon products in the gas exiting via gas outlet 124 may be recovered or may be combusted.

By removal of water in the gas enrichment zones 106, and/or by providing that substantially all hydrogen and carbon monoxide coming into contact with the catalyst is absorbed in the carrier fluid F, for example wax, rather than free gas, the water formed within cartridges 122 may amount to no more than about 1 weight % of the carrier fluid F, for example wax, which may not have a significant effect on the reaction rate. After passing through a first reaction zone 116, the carrier fluid F, for example wax, may pass through one, two, three or more further gas enrichment and catalyst-containing reaction zones 116 before being pumped by the carrier fluid F recirculation pump 104 from the base B of the pressure vessel 130, for example a sump 134 thereof, to the top T of the pressure vessel 130 via the heat exchanger 105, for example above the uppermost or first gas enrichment zone. An excess of carrier fluid F, for example wax, such as above a controlled level in the sump 134, is removed from the pressure vessel 130 as the hydrocarbon product.

In this example, each catalyst-containing reaction zone 116 is provided with a gas outlet 124. For example, after passing through the structured packing material 114 in each catalyst-containing reaction zone 116 (also known as a section), the gas is directed to a manifold and driven out of the pressure vessel 130.

In this example, the base B of the pressure vessel 130 comprises a dewatering region where the gas from each gas outlet 124 is used to dewater the carrier fluid F prior to being pumped from the pressure vessel 130 to be recycled. For example, in the bottom block of structured packing material 114, water is removed from the carrier fluid F, for example wax, by the combined outlet gas from all the sections, which is dried, heated back to the pressure vessel 130 temperature, and returned to the pressure vessel 130 as stripping gas SG. This achieves a final dewatering of the carrier fluid F, for example wax, which avoid cavitation in the carrier fluid F recirculation pump 104 and/or heat exchanger 105 (also known as reboiler) and provides additional control of catalyst deactivation.

In this example, the pressure vessel 130 further comprises a central stripping gas SG column. In this example, the gas used to dewater the carrier fluid F is recirculated into the pressure vessel 130 via the stripping gas SG column. For example, the gas is then heated back to the reactor 100 temperature and returned to the pressure vessel 130 as stripping gas SG. The gas collected from the stripping section constitutes the off-gas from the FT reactor 100.

In this example, the pressure vessel 130 further comprises at least one inlet for synthesis gas G (also known as syngas G) and/or at least one outlet for a hydrocarbon product (i.e. a product of the FT reaction).

In this example, the syngas G is introduced to the pressure via the at least one inlet for synthesis gas G and is optionally directed by one or more gas-directing plates towards a gas channel 112. More than one gas channel 112 may be provided. In this example, the gas channel 112 and the stripping gas SG channel are concentric tubes, although in other examples, the gas channel 112 and the stripping gas SG channel are separate tubes.

The syngas G may consist solely of carbon monoxide and hydrogen or it may contain one or more further components. Exemplary further components may be residual gases from the feedstock used to form the syngas G or may be by-products from formation of the syngas G and include, without limitation, carbon dioxide, nitrogen, methane and water. In this example, the syngas G contains about 30 vol. % to 50 vol. % of hydrogen. Preferably, the syngas G contains about 35 vol. % to 40 vol. % of hydrogen. More preferably, the syngas G contains 36 vol. % to 37 vol. % of hydrogen.

In this example, the syngas G contains at least 15 vol.% of carbon monoxide.

Preferably, the syngas G contains about 15 vol. % to 25 vol. % of carbon monoxide. More preferably, the syngas G contains about 17 vol. % to 20 vol. % of carbon monoxide. Most preferably, the syngas G optionally contains about 17 vol. % to 18 vol. % of carbon monoxide.

In this example, the syngas G contains about 30 vol. % to 50 vol. % of hydrogen and about 15 vol % to 25 vol. % of carbon monoxide. Preferably, the syngas G contains about 36 vol. % to 37 vol% of hydrogen and about 17 vol % to 18 vol. % of carbon monoxide. In this example, the syngas G has a H2:CO molar ratio of about 2.10 : 1 to 2.20 : 1. More preferably, the syngas G has a H2:CO molar ratio of about 2.15 : 1.

In this example, the gas enrichment zones 106 comprise a structured packing material 114 that is permeable to the carrier fluid F, carbon monoxide and hydrogen. For example, within the structured packing material 114, the carrier fluid F, for example wax, is in countercurrent contact with the first part of the syngas G feed, which passes upwards through the structured packing material 114; as a result, the carrier fluid F, for example wax, becomes saturated with hydrogen and carbon monoxide.

In this example, the catalyst-containing zones comprise a Fischer-Tropsch catalyst supported by a substrate.

In this example, the carrier fluid F is a wax. It should be understood that the carrier fluid F comprises and/or is a carrier material that is in liquid form at the operating temperature of the FT reactor 100 and that is capable of absorbing carbon monoxide and hydrogen. Exemplary carrier fluid Fs include hydrocarbons, optionally heavy hydrocarbons. The carrier fluid F may be hydrocarbons formed by the Fischer- Tropsch process. Exemplary hydrocarbons, including hydrocarbons formed by the Fischer-Tropsch process, may include naphtha (about C6 to C9); Kerosene (about C10 to 15); Diesel (about C16 to C21); and a heavy fraction (about C22 to C100). The liquid carrier is referred to hereinafter as a "wax" and the wax may include, without limitation, C5 to C100 hydrocarbons, including one or more of the hydrocarbon fractions described above. In a preferred example, the wax is the material produced by the reactor 100.

In this example, the FT reactor 100 is operated at a pressure in a range from about 20 to about 35 barg, for example from 20 to 25 barg. In the absence of heat-exchange structures inside the reactor 100 tank, only the external tank body needs to withstand the operating pressure. The highly exothermic nature of the FT process can lead to "runaway" temperature increase during the process, particularly if "hot-spots" develop within a reactor 100. This temperature increase can be dangerous as well as damaging to the catalyst. However, in the reactor 100 according to the first aspect, the reaction may be stopped simply by closing the gas inlet 108 or inlets to allow the concentration of hydrogen and carbon monoxide in wax to deplete. Additionally or alternatively, the pump 104 may be stopped such that only the gas carried by carrier fluid F, for example wax, that is already in contact with the catalyst will react. Furthermore, the concentration of hydrogen and carbon monoxide that is absorbed by the carrier fluid F, for example wax, is typically lower at higher temperatures, and so without any access of the gas phase to the catalyst cartridges 122 the overall rate of reaction will not increase significantly if the temperature of the carrier fluid F, for example wax, exceeds an optimum operating temperature for a given catalyst.

In this example, the reactor 100 is operated at a temperature that is selected according to the catalyst being used. For example, for cobalt-base Bd catalysts, the temperature may be in a range from about 200°C to about 240°C, for example in a range from 200°C to 240°C.

Figure 2 schematically shows a Fischer-Tropsch reactor 200 according to an exemplary embodiment. The FT reactor 200 is generally as described with respect to the FT reactor 100. Table 1 summarises conversion results for the FT reactor 200.

Table 1: Conversions

The experimental results summarised in Table 1 indicate that the reactor is capable of achieving gas balance-based conversions of 80% and after increasing conversion to 90% the reactor can be operated back with 80% at the same operation parameters, meaning that the catalyst has not been deactivated by an extreme as for FT reactor conversion of 90%. This is because the conversion the catalyst in cartridges is subjected to in these experiments is below 45%.

Figure 3 schematically shows results for the Fischer-Tropsch reactor 200 of Figure 2. In more detail, Figure 3 shows time trajectories of temperature over cycle of experiments and indicates very stable operation of the reactor. The temperature difference between circulated wax at the inlet to the catalyst cartridge and at the outlet from the catalyst cartridge is 2°C as predicted by the energy balance in mathematical model of the reactor.

Figure 4 is a photograph of the Fischer-Tropsch reactor 200. Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A Fischer-Tropsch reactor comprising: a) a pressure vessel adapted to contact an enriched carrier fluid with a catalyst to form a hydrocarbon product, wherein the carrier fluid is enriched with carbon monoxide and hydrogen by contact with a synthesis gas; b) a carrier fluid recirculation pump in fluid connection with the base of the pressure vessel and adapted to pump carrier fluid from the pressure vessel to be recycled and reintroduced to the top of the pressure vessel; and c) a heat exchanger in fluid connection with the top of, and external to, the pressure vessel and the carrier fluid recirculation pump and adapted to cool the carrier fluid before reintroduction to the top of the pressure vessel; wherein the pressure vessel is provided with a vertical alternating arrangement of gas enrichment zones and catalyst-containing reaction zones through which the carrier fluid flows before being pumped from the pressure vessel to be recycled.

2. The reactor of claim 1 , wherein each catalyst-containing reaction zone is provided with a gas outlet, and wherein the base of the pressure vessel comprises a dewatering region where the gas from each gas outlet is used to dewater the carrier fluid prior to being pumped from the pressure vessel to be recycled.

3. The reactor of claim 2, wherein the pressure vessel further comprises a central stripping gas column, and wherein the gas used to dewater the carrier fluid is recirculated into the pressure vessel via the stripping gas column.

4. The reactor of claim 1 , 2 or 3, wherein the pressure vessel further comprises at least one inlet for synthesis gas and at least one outlet for the hydrocarbon product.

5. The reactor of any preceding claim, wherein the gas enrichment zones comprise a structured packing material 114 that is permeable to the carrier fluid, carbon monoxide and hydrogen.

6. The reactor of any preceding claim, wherein the catalyst-containing zones comprise a Fischer-Tropsch catalyst supported by a substrate.

7. The reactor of any preceding claim, wherein the carrier fluid is a wax.

8. A Fischer-Tropsch synthesis method comprising: a) enriching a carrier fluid with carbon monoxide and hydrogen by contact with a synthesis gas within a gas enrichment zone provided in a pressure vessel; b) contacting the enriched carrier fluid with a catalyst to form a hydrocarbon product; c) pumping carrier fluid from the pressure vessel to be recycled and reintroduced to the top of the pressure vessel using a carrier fluid recirculation pump in fluid connection with the base of the pressure vessel; and d) cooling the carrier fluid before reintroduction to the top of the pressure vessel using a heat exchanger in fluid connection with the top of, and external to, the pressure vessel and the carrier fluid recirculation pump.

9. The method of claim 8, further comprising the step of: e) using the gas from a gas outlet provided in each catalyst-containing reaction zone to dewater the carrier fluid in a dewatering region in the base of the pressure vessel prior to being pumped from the pressure vessel to be recycled.

10. The method of claim 9, further comprising the step of: f) recirculating the gas used to dewater the carrier fluid into the pressure vessel via a central stripping gas column provided in the pressure vessel.

11. The method of any of claims 8 to 10, further comprising the steps of: introducing a synthesis gas to the pressure vessel and recovering the hydrocarbon product from the pressure vessel.

12. The method of any of claims 8 to 11 , further comprising enriching a carrier fluid with carbon monoxide and hydrogen by contact with a synthesis gas within at least a second gas enrichment zone provided in the pressure vessel and contacting the enriched carrier fluid with a catalyst to form the hydrocarbon product, wherein the pressure vessel is provided with a vertical alternating arrangement of gas enrichment zones and catalyst-containing reaction zones through which the carrier fluid flows before being pumped from the pressure vessel to be recycled.