Production method of biofuel

Abstract

The invention relates to a method for producing a biofuel, and to a plant for carrying out the method. In particular, the present invention relates to a method and an apparatus for producing sustainable aviation fuels (SAF).

Description

[0001] Invention Field

[0002] This invention relates to a method for producing biofuels, and apparatus for carrying out the method. In particular, this invention relates to a method and apparatus for producing sustainable aviation fuel (SAF). Background Technology

[0003] There is a growing need to develop sustainable pathways for commonly used fuels, such as aviation fuel. For example, the UK government has set a target that by 2030, 10% of all aviation fuel should be sustainable. However, current methods for producing sustainable aviation fuel are insufficient to achieve this goal.

[0004] Sustainable fuels can be produced through various methods. For example, it is known to convert waste vegetable oils and fats (such as cooking oil) into aviation fuel. However, waste oils have a limited volume, meaning there aren't enough quantities to rely on as the sole solution, and their high monetary value suggests they are unlikely to be cost-effective. Biomass gasification also offers a pathway for fuel production, but gasification can be a highly energy-intensive process and requires dry feedstock, which limits overall sustainability.

[0005] WO2018 / 076093 A1 describes a method based on hydrothermal liquefaction (HTL) for co-processing high-moisture-content wastewater sludge and other lignocellulosic biomass to co-produce biogas and biocrude oil.

[0006] US2021 / 0214633 A1 describes a hydrothermal liquefaction system and method for converting organic matter or biomass into biocrude oil and gas.

[0007] CN116554912A describes a method for producing biomass oil from sludge through hydrothermal liquefaction in the presence of steel slag catalysis.

[0008] CN115180790A describes a method for preparing bio-oil from sludge, including regulation and continuous hydrothermal liquefaction.

[0009] EE202100001 A describes methods and systems for the hydrothermal liquefaction and gasification of biomass using cavitation. This enables the conversion of biomass into chemical feedstocks suitable for the production of fuels and organic chemicals. In cavitation, rapid changes in liquid pressure cause the liquid to form small, steam-filled bubbles (“cavities”) in areas of relatively low pressure. Pressures up to 15 bar are described.

[0010] The aforementioned literature does not disclose the processing of bio-oil to provide hydrocarbon fuels.

[0011] CN116179232A describes a system combining the liquefaction of municipal sludge with the modification and preparation of liquid fuels. The system is characterized by comprising a hydrothermal liquefaction reaction unit and a separation unit, a hydrotreating and re-separation unit, and a washing unit. The sludge is hydrothermally liquefied at pressures lower than those described herein to obtain a mixed oil phase of biocrude dichloromethane.

[0012] In seeking more environmentally friendly and sustainable solutions, there is a need to transition to waste-to-fuel conversion schemes that use widely available, low-cost raw materials and relatively low-energy-consumption processes.

[0013] The purpose of this invention is to eliminate or mitigate one or more of the aforementioned disadvantages. This invention provides an alternative or more efficient method for converting waste into fuel. Invention Overview

[0015] Hydrothermal treatment of carbonaceous feedstocks, such as waste plastics or wood pulp, is another pathway to generating sustainable fuels. Various conditions and feedstocks have been developed for hydrothermal treatment technologies; one example of such work is EP2718404B2. However, research on producing economically viable fuels using very low-value feedstocks, such as sewage sludge, is extremely limited. Sewage sludge is a particularly challenging feedstock due to its high moisture, ash, and other components.

[0016] Therefore, in a first aspect of the invention, a method for producing hydrocarbon fuels is provided. The method may include subjecting a slurry of waste to a hydrothermal liquefaction reaction to obtain a hydrothermal liquefaction product. The waste may include one or more of sewage sludge, animal slurry, microalgae culture paste, effluents from paper mills and palm oil mills, and slaughterhouse waste. The method may include separating bio-oil from the hydrothermal liquefaction product. The method may include treating the modified bio-oil to provide hydrocarbon fuels.

[0017] The term "slurry" is well known in the art, but to avoid ambiguity, it is used herein to refer to a mixture in which solid particles are dispersed in a liquid (e.g., the solid particles may be derived from sewage sludge). For example, a slurry may be an aqueous slurry. Aqueous slurries are advantageous because they offer a more environmentally friendly and cost-effective solution, avoiding the use of potentially harmful industrial solvents and chemicals.

[0018] Specifically, it has been found that bio-oils can be produced from waste materials—synthetic liquid hydrocarbons derived from biomass—and then modified to produce high-value hydrocarbon fuels. Advantageously, the method described herein allows for the production of high-value hydrocarbon fuels (e.g., sustainable aviation fuels) from very low-value feedstocks in reasonable yields. This method also eliminates the need for expensive and energy-intensive pretreatment steps, such as drying the feedstock, which typically offsets the environmental benefits of existing methods (e.g., gasification). Furthermore, in some embodiments, the method can produce initial bio-oils without the need to add catalysts or organic solvents to the hydrothermal liquefaction reaction. Advantageously, this provides a more environmentally friendly and cost-effective solution than existing methods and avoids the need to separate catalysts from the reaction products.

[0019] The hydrocarbon fuel can be one or more of the following: sustainable aviation fuel, marine fuel, road fuel, heating fuel, or generator fuel. Preferably, the hydrocarbon fuel comprises sustainable aviation fuel. In some embodiments, the method can be adjustable, allowing the operator to select the hydrocarbon fuel yield. For example, hydrothermal liquefaction operating parameters can be selected to facilitate the formation of a specific hydrocarbon fuel.

[0020] The inventors have discovered that under specific conditions, particularly a residence time of 5-25 minutes, a temperature of 280-373°C, and a pressure of 18 MPa to 22 MPa, a surprisingly large bio-oil to biochar ratio is obtained, wherein the bio-oil has properties particularly advantageous for use as a sustainable aviation fuel (SAF).

[0021] This method may include preparing a slurry of waste, for example, prior to hydrothermal liquefaction. The preparation of the slurry may include adding a diluent to the waste. The diluent may contain water. The method may include mixing or homogenizing the slurry.

[0022] In a range of embodiments, the waste comprises sewage sludge. Sewage sludge may comprise treated sewage sludge, such as wastewater treated by anaerobic digestion (e.g., conventional or advanced anaerobic digestion) and / or thermal hydrolysis. In some embodiments, the sewage sludge comprises anaerobic digested sewage sludge (also known as digester cake). Alternatively or alternatively, the sewage sludge may be removed from alternative points within the wastewater treatment system. Thus, the method of the present invention uses material considered landfill waste as a raw material, but also produces highly desirable products.

[0023] Furthermore, this method can produce other useful byproducts, such as biochar. Biochar is a useful soil conditioner that can improve agricultural yields and carbon sequestration through soil application or direct burial. Overall, the method of this invention provides an efficient and “green” approach for producing hydrocarbon fuels, particularly for aviation fuels.

[0024] The term "digestive cake" is well known in the art, but to avoid ambiguity, it is used herein to refer to the final material obtained after anaerobic digestion in the treatment of domestic sewage, industrial, and commercial wastewater. Digestive cake may also be referred to as treated sludge, biological solids, or digested sludge. Digestive cake differs from primary sludge or activated sludge, which are generated early in the water treatment process. Typically, digestive cake has a solids content (e.g., dry solids content) of 15% to 40% by weight, for example, 20% to 30% by weight. Preferably, digestive cake has a solids content (e.g., dry solids content) of 23% to 28% by weight, for example, 26% by weight. In some embodiments, sewage sludge is generated entirely from digestive cake and a diluent, such as water. In other words, sewage sludge consists of or is composed of digestive cake.

[0025] The direct use of digester cake feedstock with high water content allows for the production of hydrocarbon fuels (such as sustainable aviation fuels) without the need for energy-intensive pretreatment steps that typically require drying the feedstock, a process often required in other cyclical processes.

[0026] The term "hydrothermal liquefaction" is well known in the art, but to avoid ambiguity, it is used herein to refer to the process of hydrolyzing or degrading carbonaceous feedstocks with water at certain temperatures and pressures. This process typically involves placing the feedstock at temperatures of 200°C to 400°C and pressures of 10 MPa to 40 MPa (100 to 400 bar) for a period of time.

[0027] In a range of embodiments, the waste slurry has a dry solids content of 20% by weight or less. The waste slurry may have a dry solids content of 1-20% by weight, 2-20% by weight, 5-20% by weight, 10-20% by weight, 12-18% by weight, 14-16% by weight, or about 15% by weight. It should be understood that the endpoints of the ranges described in this specification can be combined in any way.

[0028] Using low-concentration slurries has proven to yield surprisingly high bio-oil yields, contrary to intuition. This is an improvement over existing techniques where low-concentration feedstocks typically result in lower yields and less economical processes. Therefore, prior art methods such as EP2718404B2 opted to incorporate organic solvents to aid homogenization and allow them to operate at higher concentrations. For example, the inventors of EP2718404B2 used a 25% slurry of dry-distilled particles in their embodiments. Not wanting to be bound by any theory that the high bio-oil yield is due to slurry stability, the inventors surprisingly found that using reduced solids content did not limit biomass hydrolysis, nor did altering the relative proportions of hydrothermal liquefaction to provide higher bio-oil yields and impair biochar production.

[0029] In some embodiments, the hydrothermal liquefaction reaction involves subjecting the waste slurry to a temperature of 280-373°C. This temperature can be 290-370°C, 295-360°C, 300-350°C, 310-340°C, 320-330°C, or 325°C.

[0030] In some embodiments, the hydrothermal liquefaction reaction involves subjecting the waste slurry to a pressure of 18-22 MPa (180-220 bar). The pressure can be 19-21 MPa, or 20 MPa. In some embodiments, the temperature can be below the critical temperature of water.

[0031] The waste slurry can have a residence time of 5-60 minutes under hydrothermal liquefaction conditions. The residence time can be at least 10 minutes, 12 minutes, 14 minutes, 15 minutes, 16 minutes, 18 minutes, or 20 minutes. The residence time can be less than 50 minutes, 40 minutes, 30 minutes, or 25 minutes.

[0032] In some embodiments, the residence time is less than 25 minutes and / or at least 10, 12, 14, 15, 16, 18, or 20 minutes. In a particular embodiment, the residence time is 15-25 minutes. The inventors have found that the residence time unexpectedly provides a large bio-oil to biochar ratio, giving the bio-oil properties that are particularly advantageous for use as a sustainable aviation fuel (SAF).

[0033] In a series of examples, the hydrothermal liquefaction temperature was 325°C, the pressure was 20 MPa, and the residence time was 20 minutes. It was found that the aforementioned range of temperature, pressure, and residence time unexpectedly maximized the yield of the bio-oil.

[0034] In some implementations, the method is an intermittent method. In alternative implementations, the method is a continuous method.

[0035] Separation operations may include using, for example, organic solvents to separate bio-oil from hydrothermal liquefaction products. In some embodiments, the organic solvent is one or more of hexane, cyclohexane, acetone, dichloromethane, and ethyl acetate. The organic solvent can be separated by evaporation (e.g., from bio-oil). The organic solvent can be recovered and recycled. Solvent separation can provide a method for separating bio-oil in high yields and / or consume less energy than other separation methods.

[0036] Alternatively, the separation of bio-oil from hydrothermal liquefaction products can be carried out without the use of solvents, for example by filtration or centrifugation (where centrifugal force is used to accelerate the settling rate of particles and to separate particles according to size, shape, and specific gravity), such as using a centrifuge, like an oil centrifuge, or a cyclone separator, like a hydrocyclone separator. In some embodiments, a centrifuge is used to separate bio-oil from hydrothermal liquefaction products.

[0037] The method may also include separating biochar from the hydrothermal liquefaction products. The biochar itself may be an ideal product of the process. The method may include processing the biochar to obtain refined biochar. Refining may include extracting further bio-oil from the biochar. In a particular embodiment, the biochar is separated from the hydrothermal liquefaction products under elevated pressure. The inventors have found that separating the biochar from other hydrothermal liquefaction products when carried out under elevated pressure is particularly effective in increasing bio-oil yield.

[0038] In certain embodiments, a hydrocyclone separator is used to remove biochar from the hydrothermal liquefaction product, and then a centrifuge is used to separate the bio-oil from the remaining aqueous components. These embodiments are particularly advantageous when separating bio-oil from hydrothermal liquefaction products on a large scale, such as when separating bio-oil from at least one tonne of hydrothermal liquefaction product per day.

[0039] In some embodiments, the operation of processing bio-oil to provide hydrocarbon fuel includes hydrotreating the bio-oil. Hydrotreating of bio-oil may include hydrodeoxygenation, hydrodesulfurization, and hydronitrogenation. In some embodiments, the operation of hydrotreating bio-oil includes hydrodeoxygenation. In some embodiments, the operation of hydrotreating bio-oil includes hydrodeoxygenation, hydrodesulfurization, and hydronitrogenation. This reaction, for example, hydrodeoxygenation, can be carried out at a temperature of 360-400°C. This temperature may be 365-395°C, 370-390°C, 375-385°C, or 380°C. This reaction, for example, hydrodeoxygenation, can be carried out at a pressure of 10 MPa to 13 MPa (100-130 bar), for example, 10-12 MPa, 10.5-11.5 MPa, or 11 MPa. This reaction, for example, hydrodeoxygenation, can be carried out in the presence of a catalyst, such as a transition metal-based sulfidation catalyst, such as NiMo and NiW-based catalysts. Hydrotreating can be designed to maximize the yield of desired hydrocarbon fuels, such as sustainable aviation fuels.

[0040] Operations for processing bio-oil to provide hydrocarbon fuels may include fractionation and / or hydrocracking of the bio-oil. Fractionation and / or hydrocracking of the bio-oil can be designed to maximize the yield of the desired hydrocarbon fuel, such as sustainable aviation fuel. In some embodiments, fractionation and / or hydrocracking can produce a first hydrocarbon fuel and a heavy fuel. The first hydrocarbon fuel may include aviation fuel. The method may also include recycling the heavy fuel to the fractionation and / or hydrocracking reaction, thereby increasing the yield of the first hydrocarbon fuel. Recycling the heavy fraction can increase the yield of the desired product and reduce the energy cost per unit of desired product. In some embodiments, fractionation and / or hydrocracking of the bio-oil can also produce bionaphtha. Bionaphtha is a further desired product and can be further processed and / or separated, or used as a chemical feedstock or fuel.

[0041] In some embodiments, the hydrothermal liquefaction reaction and / or the separation of hydrothermal liquefaction reaction products generate waste gas. The method may include oxidizing or combusting (e.g., burning off) the waste gas or components thereof in a heat recovery unit. For example, the waste gas can be used to generate heat and / or energy. The method may also include supplying the heat and / or energy generated from combusting the waste gas in the heat recovery unit to the hydrothermal liquefaction reaction. This improves the overall efficiency of the method while minimizing potentially harmful emissions. Alternatively, or as another option, the waste gas or components thereof can be used as feedstock (e.g., C1 feedstock) for the production of syngas and / or fine chemicals. The waste gas is typically rich in CO2 and short-chain hydrocarbons (e.g., C1-C6 hydrocarbons) and can be separated or further processed and used.

[0042] According to a second aspect of the invention, a hydrocarbon fuel produced according to the method described herein is provided. The hydrocarbon fuel may be a sustainable aviation fuel.

[0043] The inventors have discovered that aviation fuel produced according to the above method can contain high levels of aromatic compounds, cycloalkanes, and straight-chain and branched (e.g., isoalkanes) alkanes. These compositions can be advantageous for alternative synthetic pathways to produce sustainable aviation fuels, for example, allowing the use of lower proportions of fossil aviation fuels in sustainable aviation fuel blends. The hydrocarbon fuel can have a n-alkane content greater than 10% by weight, for example, greater than 12%, 14%, 15%, 16%, 18%, or 19% by weight. In some embodiments, the hydrocarbon fuel has a n-alkane content greater than 16% by weight, for example, greater than 17%, 18%, or 19% by weight. The hydrocarbon fuel can have a n-alkane content less than 30% by weight, for example, less than 28%, 26%, 25%, 24%, 22%, or 20% by weight. The hydrocarbon fuel can have an isoalkane content greater than 5% by weight, for example, greater than 6%, 7%, 8%, 9%, 10%, 12%, 14%, or 15% by weight. In some embodiments, the hydrocarbon fuel has an isoalkane content of greater than 8% by weight, for example, greater than 9%, 10%, 11%, 12%, 13%, 14%, or 15% by weight. The hydrocarbon fuel may have an isoalkane content of less than 25% by weight, for example, less than 24%, 22%, 20%, 18%, 16%, 15%, 14%, 12%, or 10% by weight. In some embodiments, the hydrocarbon fuel has an isoalkane content of less than 20% by weight, for example, less than 19%, 18%, 17%, 16%, or 15% by weight. The hydrocarbon fuel may have a monocycloalkane content of greater than 10% by weight, for example, greater than 12%, 14%, 15%, 16%, 18%, or 20% by weight. In some embodiments, the hydrocarbon fuel has a monocycloalkane content of greater than 15% by weight, for example, greater than 16%, 17%, 18%, 19%, or 20% by weight. The hydrocarbon fuel may have a monocycloalkane content of less than 40% by weight, for example, less than 38%, 36%, 35%, 34%, 32%, or 30% by weight. In some embodiments, the hydrocarbon fuel has a monocycloalkane content of less than 38% by weight, for example, less than 37%, 36%, 35%, 34%, 32%, 30%, 29%, 28%, 27%, 26%, 25%, 24%, 23%, 22%, or 20% by weight. The hydrocarbon fuel may have a polycycloalkane content of more than 5% by weight, for example, more than 6%, 7%, 8%, 9%, or 10% by weight.In some embodiments, the hydrocarbon fuel has a polycyclic aromatic hydrocarbon (PAH) content greater than 7% by weight, for example, greater than 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15% by weight. The hydrocarbon fuel may have a PAH content less than 35% by weight, for example, less than 34%, 32%, 30%, 28%, 26%, or 25% by weight. The hydrocarbon fuel may have an aromatic compound content greater than 10% by weight, for example, greater than 12%, 14%, 15%, 16%, 80%, or 20% by weight. The hydrocarbon fuel may have an aromatic compound content less than 30% by weight, for example, less than 28%, 26%, 25%, 24%, 22%, or 20% by weight. In some embodiments, the hydrocarbon fuel has an aromatic compound content less than 25% by weight, for example, less than 20% by weight or 10% by weight. The inventors have discovered that certain conditions can provide hydrocarbon fuels with lower aromatic compound contents, for example, less than 20% by weight. This has the advantage of reducing fuel soot when fuel is burned, for example in a jet engine.

[0044] According to a third aspect of the invention, apparatus for producing sustainable aviation fuel is provided. The apparatus may include a hydrothermal liquefaction reactor. The reactor may be configured to receive a slurry of waste and subject the slurry to a hydrothermal liquefaction reaction to obtain a hydrothermal liquefaction product. The apparatus may include a separation unit, for example, configured to receive the hydrothermal liquefaction product and separate bio-oil from it. The apparatus may include a processing unit configured to receive and process the bio-oil to obtain hydrocarbon fuel. The hydrocarbon fuel may be a sustainable aviation fuel.

[0045] The apparatus may include a mixer configured to prepare a slurry of waste. The mixer may include a diluent inlet for mixing the diluent with the waste. The diluent may contain water. The mixer may be configured to homogenize the slurry.

[0046] Alternatively, or as an alternative, hydrocarbon fuels can be sustainable gasoline fuels.

[0047] The processing unit may include a hydrotreating unit configured for hydrotreating bio-oil.

[0048] The processing unit may include a fractionation unit configured to separate bio-oil to provide sustainable aviation fuel and other fuel byproducts. Alternatively, the processing unit may include a hydrocracking unit configured to crack the bio-oil. For example, the hydrocracking unit may be configured to provide sustainable aviation fuel and other fuel byproducts.

[0049] The processing unit may include a circulation pipeline configured to recycle at least some other fuel products to a fractionation unit, a hydrocracking unit, and / or a hydroprocessing unit.

[0050] The treatment unit may include a heat recovery unit configured to combust waste gases generated from the hydrothermal liquefaction reaction. The heat recovery unit may be configured to supply energy to the hydrothermal liquefaction reactor and / or the treatment unit.

[0051] To avoid ambiguity, it should also be understood that, where appropriate, any embodiments described herein relating to one aspect of the invention will also apply to other aspects of the invention. Brief description of the attached diagram

[0053] The invention will now be described with reference to the following figures, in which: Figure 1 This is a process flow diagram showing an embodiment of the present invention; Figure 2 It is a graph showing the temperature and pressure distribution in a hydrothermal liquefaction (HTL) experiment; Figure 3 It is a graph showing the effect of reaction temperature on the yield of bio-oil and biochar; Figure 4 It is a chart showing the effect of residence time on bio-oil yield and biochar yield; Figure 5 It is a chart showing the effect of the dry solids content of the slurry on the yield of bio-oil and biochar. Figure 6 It is a graph showing a comparison of bio-oil yield and biochar yield obtained at 20 MPa (200 bar) and 18 MPa (180 bar); Figure 7 It is a chart showing the effect of feedstock on bio-oil yield and biochar yield; and Figure 8 It is a simulated distillation curve for a hydrotreated bio-oil sample.

[0054] Detailed Explanation

[0055] Various aspects of the invention will now be further described by way of various non-limiting examples and with reference to the accompanying drawings.

[0056] Overview of methods and systems

[0057] Figure 1This diagram shows a process flow diagram for the production of biofuels. A sample of the raw material (in this case, digester cake 101) is mixed with water 102 in mixer 110 to prepare slurry 111. This slurry is fed into a hydrothermal liquefaction reactor 120 and hydrolyzed under elevated temperature and pressure (e.g., at 325°C and 20 MPa (200 bar)) to obtain hydrothermal liquefaction products 121 and waste gas 122. Hydrothermal liquefaction product 121 is fed into a separation unit 130 and separated into bio-oil 131, biochar 132, wastewater stream 133, and any other waste gas 134. Waste gases 122 and 134 are sent to a heat recovery unit 200, where they are burned, and the resulting heat energy is used to provide a portion of the energy for the hydrothermal liquefaction reaction.

[0058] Bio-oil 131 is pretreated 140 with hydrogen 181 from hydrogen storage 180, and then subjected to hydrotreating 150 (e.g., exposure to a reaction, such as hydrodeoxygenation, at a temperature of 360-400°C and a pressure of 10-13 MPa using a transition metal-based sulfidation catalyst, such as a NiMo or NiW-based catalyst), thereby providing modified bio-oil 151 with a lower oxygen content than bio-oil 131. Modified bio-oil 151 may also contain lower nitrogen and / or sulfur content compared to bio-oil 131. A further wastewater stream 152 is also obtained. The modified bio-oil 151 is then sent to a fractionation and stabilization unit 160, where it is separated according to boiling point into a sustainable aviation fuel fraction 161, a bio-naphtha fraction 162, a heavy fuel fraction 163, and a residual fraction 164. Sustainable aviation fuel fractions, bionaphtha fractions, and heavy fuel fractions are sent to storage for later use. The remaining fractions can enter a hydrocracking unit 170, configured to decompose very heavy hydrocarbons in the presence of hydrogen 183, thereby increasing the yield of light fuel products. The hydrocracking product 171 is separated and mixed with the sustainable aviation fuel stream 161, the bionaphtha stream 162, and the heavy fuel stream 163. Any unusable product 174 can be recycled to the hydrotreatment unit 150 for further processing.

[0059] Biochar 132 separated from hydrothermal liquefaction product 121 can be further processed 190 to provide refined biochar 191. Any bio-oil 192 obtained from the biochar refining operation is mixed with bio-oil 131 in a pretreatment step 140. Wastewater 193 from the biochar refining operation is combined with other wastewater streams 133, 152, 165 and sent to wastewater treatment 210.

[0060] raw material

[0061] Wastewater sludge was collected in the summer of 2021 from a wastewater treatment facility in Avonmouth. Table 1 below shows samples of wastewater sludge collected from different points in the wastewater treatment process: Table 1 – Example of wastewater sludge raw materials:

[0062] Table 2a – Characterization of average digestive cake samples:

[0063] Both activated sludge and thickened undigested sludge were obtained after primary sedimentation and before anaerobic digestion. The thickened digested sludge contained a thickener added thereto. The ash content of digested cake sample 1 was analyzed and characterized using elemental analysis (CHNSO) and ICP-OES. The oxygen content was calculated by the difference (100% - ∑(CHNSO + ash)). The characterization results are shown in Table 2b.

[0064] Table 2b – Characterization of digestive biscuit sample 1:

[0065] The reproducibility of the wastewater source was investigated by analyzing digest cake samples collected from the wastewater treatment facility over a continuous 54-week period from June 2022 to June 2023 and comparing the composition of these samples. The results are shown in Table 2c.

[0066] Table 2c – Characterization of digest cake samples collected from wastewater treatment facilities during a continuous 54-week period from June 2022 to June 2023:

[0067] As is well known, anaerobic digestion of sewage sludge (i.e., digestive cake, also known as biosolids) is a final product of wastewater treatment processes. It has a high water content, and its uses are highly limited. Currently, digestive cake is mainly used as fertilizer, but recent regulatory changes will restrict the use of this type of sewage sludge in agricultural applications; some countries have already banned disposal through this route.

[0068] Slurry preparation

[0069] Prior to the hydrothermal liquefaction reaction, digested cake samples 1 and 2 were diluted with water to prepare slurries with specific solid contents, as shown in Table 3. In contrast, activated sludge and thickened undigested sludge were used as received materials as control materials, since they already had low solid contents.

[0070] Table 3 – Samples used in the example hydrothermal liquefaction reaction:

[0071] hydrothermal liquefaction

[0072] Hydrothermal liquefaction reactions are carried out using a benchtop high-pressure stirred reactor system, such as the 300 mL Parr series 4560. A pressure regulator is installed to control the reactor pressure and ensure isobaric operation. The maximum operating conditions for a batch reactor are 200 bar at 350°C. Typically, the maximum operating conditions for a batch reactor are 180–220 bar at 300–350°C. These conditions are within the subcritical range of water and are easier and less expensive to achieve than supercritical conditions (>373°C, 220 bar).

[0073] In a typical experiment, approximately 200g of sewage sludge slurry was loaded into the reactor. The reactor was purged three times with nitrogen and pressurized at 100 bar with nitrogen at room temperature. The temperature was then raised to the target temperature using the programmable settings of the Palkia reactor controller. After the residence time was reached, the reactor was cooled to 200°C and then quenched to room temperature with cold water. The reactor was then depressurized.

[0074] Figure 2 The display shows the temperature and pressure distribution during HTL experiments with sample E3 at a reaction temperature of 325°C, a pressure of 180 bar, and a residence time of 20 minutes. Red dots represent pressure changes over time, and black dots represent temperature changes over time.

[0075] Separation of hydrothermal liquefaction products

[0076] To separate the products of the hydrothermal liquefaction reaction, dichloromethane is added to the product mixture, and the resulting liquid phase is separated from the solid phase by filtration. The solid (corresponding to biochar) is dried overnight at 85°C and its weight is measured. The liquid is then separated into an aqueous phase and an oil phase, which are then separated by decanting. Dichloromethane is removed from the oil phase using a rotary evaporator, thereby obtaining bio-oil. The bio-oil is dried overnight at 85°C and its weight is measured. Alternatively, phase separation can be performed by centrifugation, for example, using a horizontal solid bowl centrifuge for three-phase separation.

[0077] Calculate the yield of bio-oil obtained from hydrothermal liquefaction reaction.

[0078] The yield of HTL bio-oil is defined as the ratio between the weight of the bio-oil produced and the weight of the wastewater sludge, calculated using Formula 1 on a dry solids basis.

[0079] The biochar yield is defined as the ratio between the weight of biochar produced and the weight of sewage sludge, calculated using Formula 2 on a dry solids basis.

[0080] Hydrogenation of bio-oil

[0081] The bio-oil received from separation unit 130 is hydrotreated as described in subsequent subsections (see Table 5 for a detailed description of the initial bio-oil characteristics). Hydrotreatment includes hydrodeoxygenation (the main process) and accompanying hydrodesulfurization and hydrodenitrogenation reactions. Hydrodeoxygenation is performed using a transition metal-based sulfidation catalyst (e.g., a tetralobed extruded Ni / Mo catalyst supported on alumina (NiMoOx / γ-Al₂O₃)) at temperatures ranging from 360 to 450 °C and pressures ranging from 10 to 20 MPa. Hydrogen consumption is in the range of 40 to 60 g / kg of bio-oil.

[0082] Fractionation and hydrocracking

[0083] Hydrocracking provides the cracking of long-chain alkanes into shorter-chain compounds in the presence of transition metal-based catalysts (e.g., cylindrical extruder dewaxing catalysts, Ni / W supported on acidic silica-alumina), at temperatures typically 360–450 °C and pressures of 10–20 MPa, in the presence of hydrogen. Operators can adjust the conditions used for hydroprocessing and hydrocracking to optimize fuel yield, composition, and performance.

[0084] Fractionation involves separating a mixture of alkane compounds—namely, straight-chain alkanes, isoalkanes, cycloalkanes, and aromatic compounds—into several fuel fractions based on their boiling point range, such as bionaphtha fractions (boiling point <150°C), jet fuel fractions (boiling point between 140°C and 270°C), and diesel fractions (boiling point >270°C).

[0085] The modified bio-oil after hydrotreating and hydrocracking was analyzed by GC-MS / FID. The results are summarized in Table 4 below.

[0086] Table 4 – Summary of GC-MS / FID for modified bio-oils:

[0087] The modified bio-oils in Table 4 have a significantly lower proportion of long-chain hydrocarbons and a lower proportion of oxygenated compounds.

[0088] Refining of biochar

[0089] After separating the liquid phase consisting of bio-oil and HTL wastewater, the recovered biochar can be washed with an organic solvent to extract the remaining bio-oil. The organic solvent may be, for example, hexane, cyclohexane, acetone, or dichloromethane. The organic solvent is then evaporated to recover the bio-oil, and the organic solvent is recycled back into the process.

[0090] Effect of hydrothermal liquefaction reaction temperature

[0091] The effect of hydrothermal liquefaction reaction temperature on the conversion of wastewater sludge into bio-oil was investigated. Sample E3 was tested at reaction temperatures of 300℃, 325℃, and 345℃. Residence time and target pressure were set to 20 minutes and 18 MPa (180 bar), respectively.

[0092] Figure 3 This study shows the effect of reaction temperature on the yield of bio-oil and biochar obtained from hydrothermal liquefaction. Data shows that the highest bio-oil yield was achieved at 325°C, with a yield of 29.1% by weight for bio-oil and 41.2% by weight for biochar.

[0093] Effect of residence time in hydrothermal liquefaction

[0094] The effect of residence time in hydrothermal liquefaction reactions on the conversion of wastewater sludge into bio-oil was investigated. Sample E3 was tested with residence times of 10 min, 20 min, and 30 min. The reaction temperature was set at 325 °C, and the target pressure was set at 18 MPa (180 bar).

[0095] Figure 4 This study demonstrates the effect of residence time on the yields of bio-oil and biochar. The results show that a maximum bio-oil yield is achieved at a residence time of 20 minutes. The inventors have discovered that an optimal residence time for the maximum bio-oil yield relative to biochar can be determined—surprisingly, both shorter and longer residence times increase biochar yield, thereby impairing bio-oil yield. It is not intended to limit the study to any theory that residence times shorter than 20 minutes do not achieve maximum conversion of wastewater sludge to bio-oil, while residence times longer than 20 minutes lead to further degradation of bio-oil into char, possibly due to secondary or tertiary reactions.

[0096] Effect of dry solids content of slurry on hydrothermal liquefaction reaction

[0097] The effect of dry solids content in the slurry on the conversion of wastewater sludge to bio-oil was investigated. Hydrothermal liquefaction reactions were performed on samples E1-E4 (i.e., these samples had dry solids contents of 4.5 wt%, 10 wt%, 15 wt%, and 20 wt%). The hydrothermal liquefaction reaction parameters were set to a residence time of 20 min, a reaction temperature of 325 °C, and a target pressure of 180 bar. HTL experiments were also conducted using the same stirring rate. The viscosity / consistency of the slurry increased with increasing dry solids content.

[0098] Figure 5This study shows the effect of dry solids content on the yields of bio-oil and biochar. The maximum bio-oil yield was achieved when the dry solids content was 15% by weight. Surprisingly, both lower and higher dry solids contents led to lower bio-oil yields. It is not intended to be limited by any theory that using slurry with a dry solids content higher than 15% by weight might restrict biomass hydrolysis, increase biochar yield, and impair bio-oil yield. Similarly, slurry with a dry solids content lower than 15% by weight had lower yields, indicating that hydrolysis was not fully achieved. Therefore, it appears that careful optimization of the dry solids content (i.e., the water-to-biomass ratio) in the slurry is necessary, as it is one of the most important parameters in HTL reactions.

[0099] Using low water content (i.e., high dry solids content) is generally considered a way to improve reaction yield, but it can compromise mechanical processing performance. Surprisingly, however, it has been found that high solids content can promote the hydrolysis of biomass, leading to lower bio-oil yields and higher biochar yields. Therefore, this method may achieve high bio-oil yields without being challenged by mechanical processing.

[0100] Effect of hydrothermal liquefaction reaction pressure

[0101] The effect of hydrothermal liquefaction reaction pressure on the conversion of wastewater sludge to bio-oil was investigated. Target pressures of 18 MPa (180 bar) and 20 MPa (200 bar) were used for sample E5. Residence time and temperature were set at 20 minutes and 325 °C, respectively.

[0102] Figure 6 The changes in bio-oil and biochar yields obtained at 20 MPa (200 bar) are shown and compared with those obtained at 18 MPa (180 bar). For comparison, the bio-oil yield at 18 MPa (180 bar) was 18.7 wt%, and the biochar yield was 44.5 wt%. The results indicate that increasing pressure has a positive effect on bio-oil production and an adverse effect on biochar production.

[0103] Raw material selection

[0104] Wastewater sludge samples collected from different sites in the wastewater treatment process were studied for hydrothermal liquefaction. The tested samples were E3, E5, C1, and C2. Samples C1 and C2 were comparative examples based on the use of activated sludge and thickened undigested sludge. Samples E3 and E5 comprised digested cake slurry (i.e., anaerobically digested wastewater sludge) formed by diluting the digested cake with deionized water. The hydrothermal liquefaction parameters were set to a residence time of 20 minutes, a reaction temperature of 325°C, and a target pressure of 180 bar.

[0105] Figure 7The yields of bio-oil and biochar obtained from the HTL reactions of various wastewater sludge samples analyzed are shown. The data indicate that using E3 obtained from digest cake 1 resulted in a higher bio-oil yield and a lower biochar yield compared to the HTL reaction using E5. It is not intended to be limited to any particular theory, and this is considered to be due to natural variations in the composition of the digest cake samples.

[0106] The HTL reaction using control samples C1 and C2 (activated sludge and thickened undigested sludge, respectively) showed lower yields than when using E3. A key factor in this result is likely the lower dry solids content of C1 and C2. However, while drying the activated sludge and thickened undigested sludge samples to provide a more concentrated feedstock could potentially lead to higher bio-oil yields, drying the feedstock to increase the dry solids content of the sludge would be energy-intensive and expensive. The drying process significantly reduces the cost-efficiency of this invention due to the energy-intensive pretreatment. Therefore, the results indicate that digestive cake is a highly desirable whole feedstock that provides the highest yields with only a simple dilution process, while minimizing costly pretreatment.

[0107] Characterization of hydrothermal liquefaction products

[0108] After separation by hydrothermal reaction using sample E3 at a residence time of 20 minutes, a reaction temperature of 325°C, and a target pressure of 180 bar, the resulting bio-oil and biochar were further analyzed as described below.

[0109] bio-oil

[0110] We found that the resulting bio-oils typically contain a range of chemicals (see Table 4 below). The complexity of the bio-oils is expected to contribute to the range of hydrocarbons in the resulting aviation fuel fractions, which may contain higher levels of aromatics or isoalkanes and cycloalkanes compared to sustainable aviation fuels from some other pathways.

[0111] Table 5 shows the weight percentages of a range of hydrocarbons and various types of compounds, such as hydrocarbons, fatty acid methyl esters (FAME), aromatic compounds, and other compounds, based on the percentage of chromatographic peak area. The results regarding the composition of bio-oils indicate that they are primarily composed of oxygen- and nitrogen-containing compounds. Significant proportions of FAME (19.1 wt%) and vegetable cholesterol (34.6 wt%) are present.

[0112] Table 5. Estimated weight percentage of different types of hydrocarbons in bio-oil obtained by HTL reaction of sample E3 at 325°C, 20 min residence time, and 18 MPa (180 bar) pressure:

[0113] The ash content (according to the method specified in BS EN 15403), CH4NSO4, and inorganic contaminants of the bio-oil samples were also analyzed. Oxygen content was calculated by the difference (100% - ∑(CH4NSO4 + ash)). Inorganic contaminants were determined based on ICP-OES. Moisture content and TAN values ​​were also estimated using a Karl Fischer V20S and an automated titrator T5 manufactured by Mettler Toledo, respectively. The results of these analyses are shown in Table 6.

[0114] The high calorific value (HHV) of bio-oils was also estimated using the Boie formula (Formula 3): HHV (MJ / Kg) = 0.3419C + 1.11783H + 0.1005O – 0.1034N (3) Table 6. Characterization of bio-oil obtained from HTL reaction using sample E3 at 325°C, 20 min residence time, and 18 MPa (180 bar) pressure:

[0115] The reproducibility of bio-oil from anaerobic wastewater sludge produced under optimized conditions was investigated by analyzing bio-oil collected over a continuous 54-week period from June 2022 to June 2023 and comparing the composition of the bio-oil. The results are shown in Table 6a. Since the submission of the original samples in the summer of 2021 (data shown in Table 6), the separation scheme has been improved, resulting in a significant reduction in ash content in the bio-oil (Table 6a).

[0116] Table 6a. Compositional analysis of 54 bio-oil samples produced by hydrothermal liquefaction:

[0117] The digestive biscuits used as raw materials for these experiments were collected weekly for 54 consecutive weeks from June 2022 to June 2023. The high calorific value (HHV) of the bio-crude oil was estimated using the Boie formula, and the low calorific value (LHV) was estimated using the formula LHV (MJ / Kg) = HHV – 2.44 (W + 8.9H).

[0118] Hydrogenated bio-oil

[0119] Bio-oil was hydrotreated and then analyzed to determine the various useful fuel fractions contained therein. Analysis of the samples showed that specific samples of hydrotreated bio-oil contained 9% hydrocarbons suitable for bio-naphtha, 22.3% hydrocarbons suitable for jet fuel (140°C to 235°C), and 68.7% hydrocarbons suitable for heavy fuels. Figure 8The simulated distillation curves of the hydrotreated bio-oil are shown in Table 7, which provides detailed information on various fuel fractions.

[0120] Table 7 – Hydrocarbon fractions of hydrotreated bio-oil based on boiling point, from Figure 8 The simulated distillation curve shown yielded the following data:

[0121] Sustainable Aviation Fuel (SAF) fraction

[0122] Table 8 compares the types of hydrocarbons found in four samples A through D of sustainable aviation fuel (SAF) derived from HTL wastewater.

[0123] Table 8 – Hydrocarbon types found in four samples A through D of sustainable aviation fuel (SAF) derived from HTL wastewater, in weight %:

[0124] Effect of manipulated variables on hydrocarbon composition

[0125] The effects of manipulated variables, such as the ratio of bio-oil to catalyst and residence time, on hydrocarbon composition were investigated. By adjusting the catalytic reforming conditions, the distribution of hydrocarbons (i.e., n-alkanes, isoalkanes, monocyclic alkanes, polycyclic alkanes, and aromatics) could be controlled without significantly affecting the average carbon number, which was generally similar to that of fossil aviation fuels (11.5).

[0126] Different hydrocarbon types impart different fuel properties, thus affecting fuel quality and suitability for a given application. For example, specific energy can be increased by the compositional fraction of n-alkanes and isoalkanes, energy density can be improved by the compositional fraction of cycloalkanes and aromatic compounds, and freezing point can be increased by the presence of isoalkanes, cycloalkanes, and aromatic compounds. For traditional reasons, aircraft may require a certain level of aromatic compounds for sealing expansion to prevent fuel line leaks. Soot is a major drawback of high aromatic compound content, therefore, the aromatic compound content should be kept at the minimum necessary to avoid soot formation.

[0127] The range of fuel characteristics for representative SAF samples has been tested and is shown in Table 8a.

[0128] Table 8a. Fuel characteristics and trace contaminant (metallic and non-hydrocarbon composition) detected in representative net SAF samples:

[0129] The SAF produced according to the present invention is similar in many respects to fossil-derived Jet A / A1 aviation fuel. However, the SAF produced according to the method of the present invention has a higher aromatic compound content compared to most other SAF pathways, but a lower aromatic compound content than that found in fossil-derived aviation fuels. This is ideal because existing aircraft engines are designed to consume fuels containing 8-25% by weight of aromatic compounds, and therefore the SAF produced according to the present invention can be used in a higher proportion in any blended aviation fuel. Another advantage is that a higher aromatic compound content is known to produce a greater amount of soot; therefore, the SAF of the present invention will advantageously reduce soot generation compared to existing fossil aviation fuels.

[0130] Bio-naphtha fraction

[0131] Bio-naphtha is a sustainable alternative to petroleum-derived naphtha and can be used in many of the same applications. Therefore, the bio-naphtha fraction obtained from the method of this invention is of great value. One of the main applications of naphtha is as a precursor to gasoline and other liquid fuels. The Motor Octane Number (MON) and Research Octane Number (RON) of naphtha are used to assess its feasibility in such applications, as they provide information on its performance as a fuel at high and low speeds and temperatures, respectively.

[0132] The data on naphtha fractions shown in Table 9 indicate that hydrotreating conditions affect MON, but have limited impact on RON, C / H molar ratio, and estimated net and total heat.

[0133] Table 9. Composition information and fuel properties of two different bio-naphtha fractions:

[0134] Biochar

[0135] The ash content, CH4NSO4, and inorganic contaminants of the biochar obtained from the hydrothermal liquefaction reaction were also analyzed. Oxygen content was calculated by the difference (100% - ∑(CH4NSO4 + ash)). Inorganic contaminants were determined based on ICP-OES. Table 10 shows the results of these analyses and compares them with standard quality requirements for biochar. These data indicate that the biochar is suitable for further use. Many inorganic contaminants are within the limits required for high-quality biochar.

[0136] Table 10. Characterization of biochar obtained from sample E3 by HTL reaction at 325 °C, 20 min residence time, and 18 MPa (180 bar) pressure (experimental column), compared with the requirements for conventional biochar:

[0137] By analyzing biochar produced from digested cake collected over a continuous 54-week period from June 2022 to June 2023 and comparing the composition of the biochar, the reproducibility of the corresponding biochar produced and recovered from anaerobic wastewater sludge under optimized conditions via the hydrothermal liquefaction reaction was investigated. The results are shown in Table 10a.

[0138] Table 10a. Compositional analysis of 54 samples of biochar produced from hydrothermal liquefaction processes:

[0139] Digestive biscuits were collected weekly for 54 consecutive weeks from June 2022 to June 2023 and used as raw materials for these experiments. The high calorific value (HHV) was estimated using the Boie formula, and the low calorific value (LHV) was estimated using the formula LHV (MJ / Kg) = HHV – 2.44 (W + 8.9H).

[0140] While the invention has been described in detail, it should be understood that various changes, substitutions, and modifications may be contemplated without departing from the principles and scope of the invention. Therefore, the scope of the invention as defined herein and, in particular, by the appended claims, should be interpreted in consideration of suitable equivalents. The terms “a,” “an,” and “the” do not exclude the existence of multiple referents unless the context clearly specifies otherwise. The terms “optional” or “optionally” mean that the feature or activity may or may not be present. Both are contemplated. In an embodiment, one or more optional features may be present. Alternatively, one or more optional features may not be present. A scope may be expressed herein as “from” a particular value and / or “to” another particular value, intended to include the endpoints of the scope.

Claims

1. A method for producing hydrocarbon fuels, the method comprising: (i) subjecting a slurry of waste to a hydrothermal liquefaction reaction to obtain a hydrothermal liquefaction product, said waste comprising one or more of sewage sludge, animal slurry, microalgae culture paste, effluent from paper mills and palm oil mills, and slaughterhouse waste, wherein the hydrothermal liquefaction reaction is carried out at a residence time of 15-25 minutes, a temperature of 280-373°C, and a pressure of 18 MPa to 22 MPa; (ii) Separating bio-oil from the hydrothermal liquefaction product; and (iii) Processing bio-oil to provide hydrocarbon fuels.

2. The method of claim 1, wherein the hydrocarbon fuel is one or more of the following: sustainable aviation fuel, marine fuel, road fuel, heating fuel, or generator fuel.

3. The method of any one of the preceding claims, further comprising preparing a slurry of the waste prior to hydrothermal liquefaction, which includes adding a diluent to the waste and optionally mixing or homogenizing the slurry.

4. The method of any of the preceding claims, wherein the waste comprises sewage sludge, and wherein the sewage sludge comprises anaerobic digested sewage sludge.

5. The method of claim 4, wherein the sewage sludge has a solid content of 20% to 30% by weight before being used to prepare the slurry.

6. The method according to any one of the preceding claims, wherein the slurry of said waste has a dry solids content of 20% by weight or less, preferably wherein the slurry of said waste has a dry solids content of 10-20% by weight.

7. The method according to any one of the preceding claims, wherein the hydrothermal liquefaction reaction comprises subjecting the slurry of the waste material to a temperature of 300-350°C.

8. The method according to any one of the preceding claims, wherein the hydrothermal liquefaction reaction comprises subjecting the slurry of the waste material to a pressure of 19-21 MPa (190-210 bar) or 20 MPa (200 bar).

9. The method according to any one of the preceding claims, wherein the slurry of said waste has a residence time of at least 16, 18 or 20 minutes under hydrothermal liquefaction conditions.

10. The method according to any one of the preceding claims, wherein the separation operation includes using an organic solvent, and wherein the organic solvent is separated, recovered, and recycled by evaporation.

11. The method according to any one of the preceding claims, further comprising separating biochar from the hydrothermal liquefaction product, and optionally processing the biochar to obtain refined biochar.

12. The method according to any one of the preceding claims, wherein the operation of processing bio-oil to provide hydrocarbon fuel includes hydrogenation of the bio-oil.

13. The method of claim 12, wherein the hydrotreating of bio-oil comprises hydrodeoxygenating the bio-oil at a temperature of 360-400°C and a pressure of 100-130 bar in the presence of a transition metal-based sulfidation catalyst.

14. The method according to any one of the preceding claims, wherein the operation of processing bio-oil to provide hydrocarbon fuel includes fractionation and / or hydrocracking of the bio-oil.

15. The method of claim 14, wherein the fractionation and / or hydrocracking produces aviation fuel and heavy fuel, and wherein the method further comprises recycling the heavy fuel to the fractionation and / or hydrocracking reaction to increase the yield of aviation fuel.

16. The method of claim 15, wherein fractionation and / or hydrocracking of the bio-oil further produce bio-naphtha.

17. The method according to any one of the preceding claims, wherein the hydrothermal liquefaction reaction and / or the separation of the hydrothermal liquefaction reaction products generate waste gas, and wherein the method includes using the waste gas or components thereof as raw materials for generating syngas, for producing e-fuel, and / or for burning the waste gas or components thereof in a heat recovery unit and supplying energy to the hydrothermal liquefaction reaction.

18. A hydrocarbon fuel produced according to any one of claims 1-17, wherein the hydrocarbon fuel is a sustainable aviation fuel.

19. The hydrocarbon fuel according to claim 18, wherein the content of monocyclic alkanes is greater than 10% by weight, and / or the content of polycyclic alkanes is greater than 5% by weight, and / or the content of aromatic compounds is greater than 10% by weight.

20. An apparatus for producing sustainable aviation fuel, the apparatus comprising: A hydrothermal liquefaction reactor is configured to receive a slurry of waste material and subject the slurry to a hydrothermal liquefaction reaction to obtain hydrothermal liquefaction products. A separation unit is configured to receive hydrothermal liquefaction products and separate bio-oil from the hydrothermal liquefaction products; The processing unit is configured to receive bio-oil and process it to obtain hydrocarbon fuel.

21. The apparatus of claim 20, further comprising a mixer configured for preparing a slurry of waste.

22. The apparatus of claim 20 or 21, wherein the processing unit comprises a hydrotreating unit configured for hydrotreating bio-oil.

23. The apparatus according to any one of claims 20-22, wherein the processing unit comprises a fractionation unit configured to separate bio-oil to provide sustainable aviation fuel and other fuel products; and / or wherein the processing unit comprises a hydrocracking unit configured to crack the bio-oil to provide sustainable aviation fuel and other fuel products.

24. The apparatus of claim 23, wherein the processing unit comprises a circulation pipeline configured to recycle at least some other fuel products to the fractionation unit, the hydrocracking unit, and / or the hydrotreatment unit.

25. The apparatus according to any one of claims 20-24, wherein the processing unit comprises a heat recovery unit configured to burn waste gas generated from the hydrothermal liquefaction reaction and supply energy to the hydrothermal liquefaction reactor and / or the processing unit.

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