WO2021044125A1

WO2021044125A1 - Process for producing one or more hydrocarbon products

Info

Publication number: WO2021044125A1
Application number: PCT/GB2020/052061
Authority: WO
Inventors: Michael English
Original assignee: Michael English
Priority date: 2019-09-06
Filing date: 2020-08-28
Publication date: 2021-03-11
Also published as: GB201912886D0; GB2586867A

Abstract

The World needs carbon-neutral fuel to avoid further increases in atmospheric carbon dioxide concentration leading to increased levels of global warming that result in detrimental side effects. Currently mooted processes for producing carbon-neutral fuel are neither truly carbon neutral because they use fossil fuel such as coal as a feedstock, nor commercial at the scale required to replace world oil production, or are impractical. A process for producing one or more hydrocarbon products is provided. The process is preferably carbon-neutral in that fossil fuels are neither used as a feedstock in the process nor used to generate electricity for the process. The process is based on the Fischer-Tropsch process but wherein the feedstock is vegetal, preferably based on lignin, cellulose or hemicellulose, for example agricultural waste such as straw or corn husks, and electricity for raising steam as a reactant and for heating purposes is provided by a source of renewable energy, which can be intermittent. An apparatus for producing one or more hydrocarbon products is also provided.

Description

PROCESS FOR PRODUCING ONE OR MORE HYDROCARBON PRODUCTS

A process for producing one or more hydrocarbon products is provided. The process is preferably carbon-neutral in that fossil fuels are neither used as a feedstock in the process nor used to generate electricity for the process. The process is based on the Fischer-Tropsch process but wherein the feedstock is vegetal, preferably based on lignin, cellulose or hemicellulose, for example agricultural waste such as straw or corn husks, and electricity for raising steam as a reactant and for heating purposes is provided by a source of renewable energy, which can be intermittent. An apparatus for producing one or more hydrocarbon products is also provided.

Background

The World needs carbon-neutral fuel to avoid further increases in atmospheric carbon dioxide concentration which leads to increased levels of global warming and detrimental side effects. Currently mooted processes for producing carbon-neutral fuel are neither truly carbon neutral because they use fossil fuel such as coal as a feedstock, nor commercial at the scale required to replace world oil production, or are impractical.

The present invention is a process for producing one or more hydrocarbon products which is not only carbon-neutral in that it uses no fossil fuel in the process whatsoever, but can be used commercially to produce fuels at rates of millions of barrels per day.

Summary of the invention

In a first aspect of the invention a process for producing one or more hydrocarbon products is provided, the process comprising the steps of:

(a) Producing charcoal from a vegetal feedstock in the absence of oxygen;

(b) Producing a mixture of carbon monoxide and hydrogen from the charcoal of step (a) in the presence of steam; and

(c) Producing one or more hydrocarbon products from the mixture of step (b) using the Fischer-Tropsch process; wherein steam is raised as a reactant for step (b) and as a source of heat for step (c) by electrically heating water using a renewable energy source; wherein a portion of the one or more hydrocarbon products is burnt to produce heat and an oxygen free environment for step (a); and wherein waste heat remaining from step (a) is used to raise steam to maintain operating temperatures for steps (b) and (c) when the source of renewable energy is unavailable or unable to raise steam to at least maintain operating temperatures for steps (b) and (c).

The inventive process is based on the Fischer-Tropsch process, which was used historically to produce hydrocarbon fuels from coal in South Africa and Germany. The inventive process replaces the traditional coal feedstock with charcoal, with the latter produced by pyrolising, preferably, cellulose and/or lignin and/or hemicellulose materials in an oxygen free atmosphere.

Using waste heat remaining from step (a) to raise steam to maintain operating temperatures for steps (b) and (c) when the source of renewable energy is unavailable or unable to raise steam to at least maintain operating temperatures for steps (b) and (c) thereby avoids the detrimental effects of thermal cycling of process equipment.

Using dodecane as a representative example of a hydrocarbon product, the key chemical reactions in the claimed process are:

(1) (Ci₂H₂₂0ii)_n + Heat -> 12nC + llnH₂0 (Pyrolisation)

(2) C + H₂0 + Heat -> CO + H₂ (Reforming)

(3) 12CO + 25H₂ + Heat -> C_I2H₂₆ +12H₂0 (Fischer-Tropsch process)

In principle any hydrocarbon can be manufactured using the Fischer-Tropsch process by varying the pressure and temperature in the reactor and use of specific catalysts. Dodecane is merely considered representative of the typical hydrocarbons desired to manufacture high value petroleum products such as petrol, diesel, and jet fuel. In a second aspect of the invention an apparatus for producing one or more hydrocarbon products is provided, the apparatus comprising:

(a) a pyrolizer for producing charcoal from a vegetal feedstock in the absence of oxygen;

(b) a gasifier for producing a mixture of carbon monoxide and hydrogen from the charcoal in the presence of steam;

(c) a Fischer-Tropsch reactor for producing one or more hydrocarbon products from the mixture of carbon monoxide and hydrogen;

(d) a renewable energy source for raising steam as a reactant for use in the gasifier and as a source of heat for the Fischer-Tropsch reactor by electrically heating water;

(e) a means for transporting a portion of the one or more hydrocarbon products to the pyrolizer to be burnt to produce heat and an oxygen free environment for producing charcoal from a vegetal feedstock; and

(f) a waste heat recovery unit for recovering waste heat from the pyrolizer for raising steam to maintain operating temperatures in the gasifier and the Fischer-Tropsch reactor when the source of renewable energy is unavailable or unable to raise steam to at least maintain operating temperatures in the gasifier and the Fisher-Tropsch reactor.

Summary of the figures

The invention is exemplified with reference to Figure 1 which illustrates one embodiment of the inventive process.

Detailed description

(a) Producing charcoal from a vegetal feedstock in the absence of oxygen;

(c) Producing one or more hydrocarbon products from the mixture of step (b) using the Fischer-Tropsch process; wherein steam is raised as a reactant for step (b) and as a source of heat for step (c) by electrically heating water using a renewable energy source; wherein a portion of the one or more hydrocarbon products is burnt to produce heat and an oxygen free environment for step (a); and wherein waste heat remaining from step (a) is used to raise steam to maintain operating temperatures for steps (b) and (c) when the source of renewable energy is unavailable or unable to at least raise steam to maintain operating temperatures for steps (b) and (c).

Preferably at least one of the one or more hydrocarbon products is an alkane.

Step (a) is preferably carried out at a temperature of 350-500, preferably 375-500, most preferably 375-500 degrees centigrade at atmospheric pressure.

The precise process conditions for each of steps (b) and (c) are well-known to the skilled person in the art, for example the skilled person would know which catalyst and the most suitable operating temperature and pressure to use to obtain a high yield of a particular hydrocarbon product or mixture thereof. Steps (b) and (c) are, nevertheless, carried out in the absence of oxygen.

The source of renewable energy may be selected from solar, wind, wave, tidal, and a mixture thereof.

In the absence of any one or more hydrocarbon products in storage, in order to start the process, a small amount of hydrocarbon fuel is required, although this too can be produced in a carbon-neutral way, for example in the form of bio-diesel.

Steam raised for step (c) is purely for heating purposes as the step does not require water as a reactant. Preferably water from waste steam produced from step (a) is used to raise steam as a reactant for step (b) and/or as a source of heat for step (c), thereby reducing the amount of external feed water required for step (b)

Preferably waste heat produced from step (a) is used to produce steam as a reactant in step (b) and/or as a source of heat for step (c).

In a further embodiment, excess steam is provided for step (b) to provide energy thereby improving the yield of step (b).

Preferably, an external source of water is provided to raise steam as a reactant for step (b) and as a source of heat for step (c) for, at least, starting the process because initially recovered water (i.e., water recovered from the process as a by-product) is not available for either step even though the process as a whole is a net producer of water. Excess recovered water can, following clean up, be used for agricultural or industrial use.

Preferably step (a) is performed in a furnace or in the presence of exhaust gases produced by an electricity generating turbine, wherein the portion of the one or more hydrocarbon products is burnt in the furnace or to power the electricity generating turbine. Preferably the portion of the one or more hydrocarbon products is burnt to power an electricity generating turbine, and electricity generated by the turbine is used to raise steam to maintain operating temperatures for steps (b) and (c) when the source of renewable energy is unavailable or unable to raise steam to at least maintain operating temperatures for steps (b) and (c). The electricity generated may also power ancillary plant needs such as pumping or lighting,

Preferably an external supplementary supply of hydrogen is provided for step (c), preferably wherein the external supplementary supply of hydrogen is carbon-neutral. At present, carbon-neutral hydrogen is produced by electrolysis of water using renewable electricity, for example from wind, solar, wave or tidal power. Alternatively landfill gas can be steam reformed to produce hydrogen. An external supplementary supply of hydrogen provides the correct molar ratio of carbon monoxide and hydrogen for the Fischer-Tropsch process in step (c). Alternatively, the excess carbon monoxide produced in step (b) is used as a fuel or vented to atmosphere.

Preferably the vegetal feedstock is based on lignin, cellulose, hemicelluloses or mixtures thereof. A suitable source for lignin, cellulose, or hemicellulose is agricultural waste such as straw or corn husks.

Preferably a portion of the one or more hydrocarbon products is stored permanently to provide a net reduction in atmospheric carbon dioxide concentration. The portion may be as large as desired. One example of permanent storage is by injecting the one or more hydrocarbon products into a disused oil or gas reservoir. In addition, 5-15, preferably 10-15 % w/w of the one or more hydrocarbon products is burnt to produce heat and an oxygen free environment for step (a).

In a second aspect of the invention, an apparatus for producing one or more hydrocarbon products is provided, the apparatus comprising:

(d) a renewable energy source for raising steam as a reactant for use in the gasifier and as a source of heat for the Fischer-Tropsh reactor by electrically heating water;

Preferably the apparatus further comprises means to recover water from waste steam produced in the pyrolizer for use in raising steam as a reactant for use in the gasifier and as a source of heat for the Fischer-Tropsh reactor.

The apparatus preferably comprises an external source of water for raising steam as a reactant for use in the gasifier and as a source of heat for the Fischer-Tropsh reactor for, at least, starting the process.

Preferably the pyrolizer is a furnace or is heated by exhaust gases from an electricity generating turbine. Preferably, the electricity generated by the electricity generating turbine is used to raise steam to maintain operating temperatures in the gasifier and Fischer- Tropsch reactor when the source of renewable energy is unavailable or unable to raise steam as a reactant for use in the gasifier and as a source of heat for the Fisher-Tropsch reactor.

Preferably an external supplementary supply of hydrogen is provided for use in the Fischer- Tropsch reactor to provide the correct molar ratio of carbon monoxide and hydrogen, preferably wherein the external supply of hydrogen is carbon-neutral.

The apparatus optionally additionally comprises permanent storage for permanently storing a portion of the one or more hydrocarbon products to provide a net reduction in atmospheric carbon dioxide concentration.

All three key chemical reactions set forth above are strongly endothermic, so energy is required to drive them. Traditionally this has come from the thermal energy of steam, which is introduced in the reforming step. In order to produce carbon-neutral hydrocarbons, the steam is produced by a renewable electricity source such as solar, wind, wave or tidal. Such energy sources can be intermittent and a degree of waste heat recovery is necessary to keep the temperature of the process equipment constant during periods of low steam generation to avoid the detrimental effects of thermal cycling. This is accomplished in the inventive process by burning a portion of the one or more hydrocarbon products to produce heat and an oxygen free environment for step (a) and recovering the waste heat remaining from step (a) to raise steam to maintain operating temperatures for steps (b) and (c) when the source of renewable energy is unavailable or unable to at least raise steam to maintain operating temperatures for steps (b) and (c).

Figure 1 is a schematic of a process plant according to the invention operating one embodiment of the inventive process.

The process has two operating modes. In a first mode, steam for steps (b) and (c) is produced by electrically heating water, the source of electricity being renewable such as solar, wind, wave or tidal. In a second mode when little or no renewable energy is available, steam for steps (b) and (c) is raised solely by recovering the waste heat remaining from step (a) to raise steam to maintain operating temperatures for steps (b) and (c) when the source of renewable energy is unavailable or unable to at least raise steam to maintain operating temperatures for steps (b) and (c) thereby avoiding the detrimental effects of thermal cycling of process equipment.

With reference to Figure 1, a feed pre-processor (A) treats vegetal feedstock to optimise the conversion of the feedstock into charcoal, for example, by shredding or chopping the feedstock to increase the surface area. For some feedstocks, removal of contaminants that might poison the catalyst used during subsequent reforming and Fischer-Tropsch processing, such as sulphur or chlorine based contaminants, may be appropriate at this stage using techniques well-known to the skilled person in the art.

A portion of the one or more hydrocarbon products (around 11 % w/w of net production) is used to power a power turbine (B), whose exhaust gases are used to provide heat and an appropriate oxygen free atmosphere for the pyrolizer. Whilst a furnace can be used instead of a power turbine, the advantage of using a turbine is that power can be generated to supply a steam raising plant (F) and for other requirements. The power turbine runs continuously in both first and second modes with the second mode producing lower volumes of one or more hydrocarbon products and, indeed, principally used to maintain the process equipment at operating temperature thereby avoiding the detrimental effects of thermal cycling.

Vegetal feedstock, whether pre-processed or not, is exposed to the exhaust gases in a pyrolizer (C) and pyrolised to charcoal, in the absence of oxygen, into carbon and water vapour (steam) at a temperature of 350-500, preferably 375-500, most preferably 375-500 degrees centigrade at atmospheric pressure.

A renewable energy array (D) produces electric power, principally for steam generation by the steam raising plant. In principle any renewable source of electric power can be used, such as solar, wind, wave or tidal. The steam produced by the steam raising plant is used as a feedstock for a reformer (G) and as a source of heating a Fischer-Tropsch reactor (J).

Waste heat in the exhaust gases leaving the pyrolizer is recovered by a waste heat recovery unit (E) and used to preheat boiler feed water feeding the steam raising plant. The exhaust gases also contain a considerable amount of water, in the form of steam, which can optionally also be recovered downstream of the waste heat recovery unit and be used, for example, as boiler feed water feeding the steam raising plant. An external source of boiler feed water is provided for at least initial process plant start-up, regardless of arrangements for using recovered water within the process plant.

In the reformer, the charcoal is reacted with steam to produce synthesis gas (a mixture of carbon monoxide and hydrogen). As reforming produces carbon monoxide and hydrogen in equimolar quantities, whereas the subsequent Fischer-Tropsch process requires an excess of hydrogen, additional hydrogen, preferably from a carbon-neutral source, is optionally provided. Reforming takes place in the absence of oxygen at a temperature and pressure and utilising a catalyst well-known to the skilled person in the art. Impurities such as H₂S, HCI and COS, amongst others, are removed from the synthesis gas in a syngas treatment plant (I) prior to reaction in the Fischer-Tropsch reactor in order to avoid poisoning the catalyst used in the Fischer-Tropsch reactor. The purification technology is well-known to the skilled person in the art and typically includes a combination of counter current absorption with a regenerative solvent, washing with water and adsorption onto a solid carrier bed.

The Fischer-Tropsch reactor converts the (purified) synthesis gas to one or more hydrocarbon products at elevated temperature with heat being supplied from steam provide by the steam raising plant. The choice of catalyst, temperature and pressure determines the composition of the product, which can range from ethane to heavy hydrocarbons, but will typically be medium length alkanes suitable for use in high value products such as petrol, diesel or jet fuel, or ethane or other hydrocarbons suitable for use as a petrochemical feedstock. The precise process conditions within the Fischer-Tropsch reactor are well-known to the skilled person in the art, for example the skilled person would know which catalysts and the most suitable operating temperature and pressure to use in order to maximise the yield of the desired hydrocarbon product. Nevertheless, the Fischer- Tropsch reactor is operated in the absence of oxygen.

As well as the one or more hydrocarbon products, the output of the Fischer-Tropsch reactor typically also includes water vapour, carbon monoxide, and small quantities of hydrogen. If the Fischer Tropsch reactor conditions are set up to produce lighter hydrocarbons such as ethane, then a conventional separation column well-known to the skilled person in the art is used to separate the hydrocarbon products. If the Fischer Tropsch reactor produces mostly heavier hydrocarbon products that are liquid at room temperature, then the output of the Fischer-Tropsch reactor is cooled in a liquid-gas separator (K). The gas that is left (mostly carbon monoxide) can either be recycled or it can be burnt to provide supplementary energy to preheat boiler feed water in the steam raising plant. The heat recovered from the condensation can optionally be used to preheat boiler feed water in the steam raising plant. The liquid component resulting from liquid-gas separation, which is mostly the one or more hydrocarbon products and water, is then treated in a liquid-liquid separator (L) thereby to separate water from the one or more hydrocarbon products using, for example, gravity separation or treatment with a centrifuge.

The one or more hydrocarbon products are then sent to storage (M) for onward transfer to market and to provide a reliable source of fuel for the power turbines. For initial process plant start-up, an external supply of fuel is required, although this too can be produced in a carbon-neutral way, for example in the form of bio-diesel. However afterwards, a portion of the one or more hydrocarbon products is retained for future process plant start-ups.

Water separated in the liquid-liquid separator is treated in a waste water treatment plant (N) using conventional processes known to the skilled person in the art, such as a centrifuge. The resulting treated water provides a source of water for the steam raising plant and any excess can be used for agricultural or other industrial uses.

Claims

1. A process for producing one or more hydrocarbon products comprising the steps of:

(a) Producing charcoal from a vegetal feedstock in the absence of oxygen;

2. A process according to claim 1, wherein water from waste steam produced from step (a) is used to raise steam as a reactant for step (b) and/or as a source of heat for step (c).

3. A process according to claim 1 or claim 2, wherein an external source of water is provided to raise steam as a reactant for step (b) and as a source of heat for step (c) for, at least, starting the process.

4. A process according to any one of the preceding claims, wherein step (a) is performed in a furnace or in the presence of exhaust gases produced by an electricity generating turbine, wherein the portion of the one or more hydrocarbon products is burnt in the furnace or to power the electricity generating turbine.

5. A process according to claim 4, wherein the portion of the one or more hydrocarbon products is burnt to power an electricity generating turbine, and electricity generated by the turbine is used to raise steam to maintain operating temperatures for steps (b) and (c) when the source of renewable energy is unavailable or unable to raise steam to at least maintain operating temperatures for steps (b) and (c).

6. A process according to any one of the preceding claims, wherein an external supplementary supply of hydrogen is provided for step (c), preferably wherein the external supply of hydrogen is carbon-neutral.

7. A process according to any one of the preceding claims, wherein the vegetal feedstock is based on lignin, cellulose, hemicellulose or mixtures thereof.

8. A process according to any one of the preceding claims, wherein a portion of the one or more hydrocarbon products is stored permanently.

9. A process according to any one of the preceding claims, wherein at least one of the one or more hydrocarbon products is an alkane.

10. An apparatus for producing one or more hydrocarbon products, the apparatus comprising:

(d) a renewable energy source for raising steam as a reactant for use in the gasifier and as a source of heat for the Fischer-Tropsch reactor by electrically heating water; (e) a means for transporting a portion of the one or more hydrocarbon products to the pyrolizer to be burnt to produce heat and an oxygen free environment for producing charcoal from a vegetal feedstock; and

11. An apparatus according to claim 10 further comprising means to recover water from waste steam produced in the pyrolizer for use in raising steam as a reactant for use in the gasifier and as a source of heat for the Fischer-Tropsch reactor.

12. An apparatus according to claim 10 or claim 11 comprising an external source of water for raising steam as a reactant for use in the gasifier and as a source of heat for the Fischer-Tropsch reactor for, at least, starting the process.

13. An apparatus according to any one of claims 10 to 12, wherein the pyrolizer is a furnace or is heated by exhaust gases from an electricity generating turbine.

14. An apparatus according to claim 13, wherein electricity generated by the electricity generating turbine is used to raise steam to maintain operating temperatures in the gasifier and Fischer-Tropsch reactor when the source of renewable energy is unavailable or unable to raise steam as a reactant for use in the gasifier and as a source of heat for the Fisher-Tropsch reactor.

15. An apparatus according to any one of claims 10 to 14, wherein an external supplementary supply of hydrogen is provided for use in the Fischer-Tropsch reactor, preferably wherein the external supply of hydrogen is carbon-neutral.

16. An apparatus according to any one of claims 10 to 15 additionally comprising permanent storage for permanently storing a portion of the one or more hydrocarbon products.