Process for production of HTL oils with improved thermal stability and low inorganic content

Abstract

A simple chemical treatment method for low oxygen content HTL biological crude oil has been developed. The process reduces the organic acid content by reacting HTL bio-crude oil with alcohols without the need for a hydrotreating catalyst or hydrogen source, thereby improving the stability of the bio-crude oil and compatibility with petroleum fuels or petroleum fractions, such as marine fuels or co-processing feedstocks in commercial refineries.

Description

Technical Field

[0001] This invention relates to a method for producing low-oxygen HTL oil with improved thermal stability and low inorganic content, making it directly usable as a blendable marine fuel. The invention also relates to HTL oil with improved thermal stability and low inorganic content, and its use as marine fuel, a co-processing feedstock in commercial refineries or independent upgrading units. Background Technology

[0002] Biofuels refer to any fuel derived from biological mass. Unlike fossil fuels such as oil, which undergo very slow natural processes during formation, biofuels can be produced in a short time. Biofuels can be produced from plants or from agricultural, domestic, or industrial biological waste. Biofuels are primarily used for transportation, but can also be used for heating and power generation.

[0003] First-generation biofuels, also known as "traditional biofuels," are produced from food crops grown on arable land. They are typically produced by converting the carbonaceous materials of crops (i.e., sugars, starches, and oils) into biodiesel or ethanol through transesterification or yeast fermentation.

[0004] Second-generation biofuels, also known as "advanced biofuels" or "sustainable biofuels," are derived from waste, thus avoiding the conflict between food and fuel. The feedstocks for second-generation fuels originate from agricultural and forestry activities. The feedstocks used to produce fuels are either byproducts of main crops grown on arable land or grown on marginal land. Second-generation fuels are typically produced through biochemical or thermochemical pathways (such as pyrolysis and hydrothermal liquefaction).

[0005] Hydrothermal liquefaction (HTL) is one of the known methods for producing second-generation fuels. HTL biocrude oil can be produced from a variety of organic wastes and residues, such as biomass remaining in forests after forestry operations (forestry residues). Steeper Energy has developed a promising application of this HTL pathway and described it in WO 2020 / 228990A1. This HTL process produces a high-density biocrude oil rich in diesel-boiling-range hydrocarbons, with a high calorific value (HHV) of approximately 38 MJ / kg, high quality, and high carbon yield. Up to 45 wt% of the feed biomass is captured into the HTL biocrude oil. Compared to other biocrude oils, this biocrude oil has a low oxygen content of approximately 10 wt%, low levels of heteroatoms, approximately 0.25 wt% nitrogen, approximately 150 ppm sulfur, and a lower water content (<1 wt%).

[0006] HTL biocrude oil is a promising ready-to-use fuel that can be blended with marine fuels. While biocrude oil shares many properties with its fossil fuel counterparts, it exhibits different physicochemical characteristics compared to conventional marine fuels. Its miscibility is limited due to the presence of heteroatoms and polar compounds in HTL biocrude oil. Furthermore, due to the presence of reactive residual oxygen compounds, HTL biocrude oil is generally not completely thermally stable, especially at temperatures above 80°C. This implies the need for improvements to ensure the suitability of biocrude oil during storage, processing, and blending.

[0007] It is known that as HTL bio-crude oil ages, dehydration, polymerization, aldol condensation, oligomerization, and acid formation reactions occur. These reactions increase the viscosity, water content, and corrosiveness of the bio-crude oil, thus affecting its processing, including atomization, pumping, and injection in engines. The effect of temperature is critical in the aging process, as the aging reactions are exacerbated by increasing temperature.

[0008] Bio-crude oil must meet six properties to be accepted for use as marine fuel. These properties include ash content, metal content (especially sodium, vanadium, aluminum + silicon), acidity, flash point, and thermal stability at the temperature required to reach a specified viscosity of approximately 10 cSt for fuel atomization, while ensuring that the temperature required to reach this viscosity does not exceed the engine's permissible upper limit (≤130°C). Furthermore, because the bio-crude oil must be miscible with petroleum fuels, it needs to be compatible with petroleum fuels.

[0009] HTL biocrude oil typically requires upgrading to make it acceptable for use as marine fuel. Mild hydrotreating is a common method for upgrading HTL biocrude oil to produce marine fuel. Mildly hydrotreated HTL oil has lower oxygen content, total acid number (TAN), viscosity, and density compared to HTL biocrude oil, which improves its compatibility with petroleum-derived marine fuels. However, this hydrotreating method requires a hydrogen source and a commercial catalyst, as well as a hydrotreating reactor and gas processing equipment to recover unreacted hydrogen and remove gaseous impurities such as ammonia and hydrogen sulfide.

[0010] Other methods to improve the quality of HTL bio-crude oil and slow down the aging process include emulsification, solvent extraction, and vacuum distillation. However, these methods do not improve the oil's thermal stability under the higher temperatures required for combustion, and they only make a very small amount of HTL bio-crude oil usable for marine applications, leaving approximately 40% by weight of bio-crude oil unmarketable. Furthermore, they require high concentrations of solvents and emulsifying agents, making HTL bio-crude oil more expensive.

[0011] Adding solvents is another option for enhancing the stability of biocrude oil and its compatibility with petroleum fuels. Several solvents have been evaluated, including ethyl acetate, methyl ethyl ketone, acetone, ethanol, and methanol. The most promising solvent additive is methanol at concentrations of 5 to 20% by weight. Adding methanol will significantly reduce the viscosity of biocrude oil and inhibit polymerization reactions, thereby reducing the oil's aging rate; however, it will negatively impact key properties used in marine fuel infrastructure, such as flash point, lowering it to a minimum of below 60°C. This will worsen handling and storage operations and reduce the fuel's calorific value, potentially causing ignition delays.

[0012] Azeotropic distillation with at least one alcohol followed by alcoholysis is another known method for converting crude bio-oil into upgraded bio-oil for use as marine fuel. Such methods are disclosed in, for example, US 2014 / 0256965 A1. Another method is disclosed in WO2024 / 051909 A1. In this method, HTL bio-oil is mixed with at least one alcohol and the mixture is then subjected to a processing temperature to form a viscosity-reduced bio-oil and to separate the evaporated water fraction. However, these methods do not focus on reducing the mineral content of the final upgraded bio-oil.

[0013] The inventors of this invention have developed a new method to improve the thermal stability and acidity of HTL bio-crude oil (especially HTL bio-crude oil), so that the obtained HTL oil can be used as marine fuel, a co-processing feedstock for refineries or independent upgrading units. Summary of the Invention

[0014] The inventors of this invention have discovered that heat-stable HTL oil can be produced by heating HTL bio-crude oil at 80°C to 200°C for 1 to 200 hours in the presence of additives. This heat-stable HTL bio-crude oil can undergo an additional washing stage to obtain heat-stable HTL oil with a lower inorganic content, which can be used directly as a co-processing feedstock in, for example, marine fuel, commercial refineries, or independent upgrading units where high inorganic content significantly shortens the lifespan of hydrotreating catalysts. Furthermore, the lower total acid value of the stabilized HTL oil reduces corrosive effects on existing marine engines or refinery metallurgy. Attached Figure Description

[0015] Figure 1 A schematic diagram of the continuous high-pressure method for converting carbonaceous materials into HTL biocrude oil, as described in Example 1, is shown.

[0016] Figure 2 A schematic diagram of a continuous process for producing HTL oil with improved thermal stability is shown.

[0017] Figure 3A schematic diagram of a continuous process for producing HTL oils with improved thermal stability and low inorganic content is shown.

[0018] Figure 4 A schematic diagram of a two-stage continuous process for producing HTL oil with improved thermal stability is shown.

[0019] Figure 5 The corrosion effects on carbon steel sheets are shown: A) before accelerated aging test; B) after accelerated aging test using fresh HTL bio-crude oil; C) after accelerated aging at 160°C for 140 hours using chemically treated HTL bio-crude oil.

[0020] Figure 6 The chemical group distribution of fresh HTL bio-crude oil and chemically treated HTL oil, as determined by FTIR, is shown compared to petroleum-derived marine fuels.

[0021] Figure 7 The spot test described in Example 4 for evaluating the compatibility between chemically treated HTL oil and commercial marine fuel is shown. Detailed Implementation

[0022] The results of the experimental work presented in this patent application provide valuable insights into the scale-up of the chemical treatment method and its potential for commercial application. Furthermore, the chemical treatment according to the invention offers a sustainable and efficient solution to address the strong energy demands of the maritime sector, a key component of global transportation infrastructure. Utilizing chemically treated HTL oil as a fuel source promises to significantly reduce the shipping industry's carbon footprint and facilitate the transition to a more sustainable energy system.

[0023] In a first aspect, the present invention relates to a method for producing hydrothermal liquefaction (HTL) oils with improved thermal stability and low inorganic content. The method is as follows: Figures 2-4 As shown. The method includes the following steps: a. Provides low-oxygen HTL bio-crude oil, which has the following characteristics: - Oxygen content in the range of 3.0 to 15% by weight. - Less than 1.5% by weight of water content, - Total acid value in the range of 20 to 80 mg KOH / g - Less than 70% by weight of oil fractions with a boiling point below 350°C - At least 10% by weight of the residual distillate with a boiling point above 450°C; and - Ash content less than 0.1% by weight; b. Heat the low-oxygen HTL bio-crude oil from step a to a temperature in the range of 25°C to 80°C; c. Add an additive containing at least one alcohol to the heated low-oxygen HTL bio-crude oil from step b and mix. d. Further heat the mixture from step c in the reaction zone to a temperature in the range of 80°C to 200°C; e. The heated mixture from step d is kept in the reaction zone for a conversion time of 1 to 200 hours; f. Cool the converted mixture from step e to a temperature ranging from 20°C to 180°C; and g. Separate the cooled, converted feed mixture from step f into chemically treated HTL oil, light boiling point fraction, water, and unconsumed additives.

[0024] As used herein, the term "HTL bio-crude oil" refers to bio-crude oil produced through hydrothermal liquefaction. For example, the HTL bio-crude oil is produced using a method developed by Steeper Energy and described in WO 2020 / 228990A1. This method is as follows... Figure 1 As shown. Preferably, the HTL bio-crude oil is produced by hydrothermal liquefaction of carbonaceous materials, wherein the hydrothermal liquefaction is carried out under supercritical water conditions of 390℃-420℃ and 300 bar-350 bar.

[0025] As used herein, the term "low inorganic content" means a content of less than 400 ppm, preferably less than 200 ppm. As used herein, the term "inorganic matter" refers to the metal content determined by ICP digestion analysis and ash determination according to ASTM D482. Some metals determined by ICP are aluminum (Al), arsenic (As), calcium (Ca), chromium (Cr), copper (Cu), iron (Fe), nickel (Ni), phosphorus (P), potassium (K), silicon (Si), sodium (Na), tin (Sn), titanium (Ti), vanadium (V), and zinc (Zn).

[0026] In step a, HTL bio-crude oil is provided. The HTL bio-crude oil has an oxygen content ranging from 3.0 to 15% by weight, a water content of less than 1.5% by weight, a total acid value ranging from 20 to 80 mg KOH / g, an oil fraction with a boiling point below 350°C of less than 70% by weight, a residual fraction with a boiling point above 450°C of at least 10% by weight, and an ash content of less than 0.1% by weight.

[0027] In step b, the low-oxygen HTL bio-crude oil from step a is heated to a temperature in the range of 25°C to 80°C to reduce viscosity and improve miscibility with additives.

[0028] In step c, an additive is added to and mixed with the heated, low-oxygen HTL bio-crude oil from step b. The additive contains at least one alcohol. In this step, esterification and acetalization reactions occur, accelerating the conversion of reactive molecules (such as organic acids and aldehydes) in the HTL bio-crude oil into esters, acetals, and water. Concurrently with this process, polymerization and agglomeration reactions also occur, affecting the homogeneity and viscosity of the blend, i.e., an increase in viscosity. This increase in viscosity is an unavoidable negative consequence of the method according to the invention and is only acceptable if the viscosity of the final chemically treated HTL oil meets the requirements of ISO 8217 for conventional marine fuels. On the positive side, as carboxylic acids are consumed in this process, a decrease in TAN is observed, which is beneficial for improving the thermal stability of the HTL bio-crude oil.

[0029] The additive comprises at least one alcohol. The at least one alcohol includes short-chain alcohols and / or long-chain alcohols. The at least one alcohol is added at a ratio of up to 50% by weight of the additive mixture. Preferably, the concentration of the alcohol in the additive is 1 to 70% by weight based on the total weight of the additive mixture, more preferably in the range of 3 to 50% by weight, and most preferably in the range of 5 to 40% by weight. Examples of suitable alcohols include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol, isoamyl alcohol, hexanol, isohexanol, octanol, nonanol, decanol, undecyl alcohol, dodecanol, tridecanol, tetradecanol, pentadecyl alcohol, hexadecyl alcohol, and heptadecanol. Preferred examples of alcohols include methanol, ethanol, isopropanol, n-butanol, isobutanol, and n-pentanol, and particularly preferred examples of alcohols include methanol, ethanol, and isopropanol. Preferred alcohols are those produced from renewable sources (such as organic waste).

[0030] In step d, the mixture of the low-oxygen HTL bio-crude oil and additives is further heated in the reaction zone to a temperature in the range of 80°C to 200°C. More preferably, the mixture is heated to a temperature in the range of 110°C to 180°C, and even more preferably to a temperature in the range of 130°C to 170°C.

[0031] In step e, the heated mixture from step d is held in the reaction zone at a specified temperature for a period of time to allow conversion to occur. More specifically, the further heated mixture is held at this temperature for a conversion time of 1 to 200 hours, more preferably 3 to 180 hours, and particularly more preferably 10 to 160 hours.

[0032] In a preferred embodiment, the heated mixture in step d reaches a pressure of 3 to 200 bar in the reaction zone, more preferably 5 to 150 bar, and even more preferably 7 to 110 bar.

[0033] In a preferred embodiment, the mixture is stirred during the conversion time to increase the reaction rate. With the mixture stirred, the conversion time can be reduced to 1 to 70 hours.

[0034] It is important to note that during the heat treatment step bf, water or other compounds are essentially not removed. This is a significant difference compared to other methods (such as the azeotropic distillation methods mentioned in US 2014 / 0256965 and WO 2024 / 052909), in which water and alcohol evaporate and are thus removed during the heat treatment step, resulting in reaction products that differ from those of the method of this invention. This is evidenced by the fact that viscosity increases during the heat treatment according to the method of this invention, while a decrease in viscosity is observed during the azeotropic distillation method.

[0035] In step f, the converted mixture from step e is cooled to a temperature in the range of 20°C to 180°C, more preferably 40°C to 150°C, and even more preferably 50°C to 130°C.

[0036] In step g, the cooled, converted mixture from step f is separated into chemically treated HTL oil, light-boiling fraction, water, and unconsumed additives. Preferably, the unconsumed additives are recovered to step c.

[0037] The specific preferred implementation scheme is as follows: Figure 3 As shown. In this embodiment, the method further includes reducing the inorganic content level to below 200 ppm, preferably below 100 ppm, by mixing the cooled, converted mixture from step f with a liquid containing at least 70% by weight of demineralized water before separating the mixture into the fractions mentioned in step g. In a preferred embodiment, this mixing step with water is carried out at 5 to 80°C and a pressure below 20 bar. When the mixture is mixed with water, at least a portion of the inorganic content is transferred to the aqueous phase, providing a chemically treated HTL oil with reduced inorganic content. Excess water is removed by gravity. Subsequently, by removing the formed water and reducing the concentration of light hydrocarbons, a heat-stable HTL oil with a flash point and viscosity within the permissible range for marine fuels is produced.

[0038] Another specific preferred embodiment is as follows: Figure 4As shown, in this embodiment, the method focuses on reducing the Total Acid Number (TAN). In this embodiment, step e is carried out in two stages: the first stage (first sub-reaction zone) aims to reduce the TAN by at least 50% compared to the low-oxygen HTL bio-crude oil, while the second stage (second sub-reaction zone) is a polishing step to further reduce the TAN by at least 20%. In the first sub-reaction zone, the mixture of the heated low-oxygen HTL bio-crude oil and the additive from step c is maintained at a temperature of 80°C to 200°C for 10 to 170 hours. In the second sub-reaction zone, the reaction mixture from the first sub-reaction zone is mixed with additional additives to achieve an additive concentration in the range of 5 to 30% by weight, and the temperature of the second sub-reaction zone is maintained at 100°C to 170°C for 10 to 170 hours, preferably 15 to 140 hours.

[0039] Preferably, compared to the low-oxygen HTL bio-crude oil, the total TAN of the low-oxygen HTL oil is reduced by at least 70%, more preferably at least 75%, and even more preferably at least 80%. Therefore, the total acid value of the chemically treated HTL oil in step g is at most 24 mg KOH / g, more preferably at most 6 mg KOH / g, and even more preferably at most 5 mg KOH / g.

[0040] As mentioned above, the viscosity of chemically treated HTL oil is generally higher than that of the low-oxygen HTL bio-crude oil. In one embodiment, the low-oxygen HTL bio-crude oil in step a has a kinematic viscosity of 150-200 cSt at 50°C, while the chemically treated HTL oil in step g has a kinematic viscosity of 230-280 cSt at 50°C.

[0041] In a preferred embodiment, the low-oxygen HTL biocrude oil in step a is provided by a method comprising the following steps: - Provide carbon-containing materials in biomass form contained in one or more raw materials; - By slurring the carbonaceous material in one or more fluids to provide a feed mixture, wherein at least one of the fluids contains water; - Pressurize the feed mixture to a pressure in the range of 150 to 400 bar; - The pressurized feed mixture is heated to a temperature in the range of 300°C to about 450°C; - The pressurized and heated feed mixture is maintained in the reaction zone for a conversion time ranging from 3 to 30 minutes, thereby causing the carbonaceous material to be converted; - Cool the converted feed mixture to a temperature ranging from 25°C to 200°C; and - The converted feed mixture is expanded to a pressure in the range of 1 to 120 bar and separated into at least low oxygen HTL biocrude oil, a gas phase and an aqueous phase containing water-soluble organic matter and dissolved salts; The low-oxygen HTL bio-crude oil thus provides an oxygen content ranging from 3.0% to 15% by weight, a water content of less than 1.5% by weight, a total acid value ranging from 20 to 80 mg KOH / g, an oil fraction with a boiling point below 350°C of less than 70% by weight, a residue fraction with a boiling point above 450°C of at least 10% by weight, and an ash content of less than 0.1% by weight.

[0042] In a second aspect, the present invention relates to chemically treated HTL oils with improved thermal stability and low inorganic content, preferably obtained using the method according to the invention. The HTL oil is characterized by: an oxygen content of up to 10% by weight, a water content of less than 0.1% by weight, a total acid value of up to 6 mg KOH / g, an ash content of less than 400 ppm, a flash point of at least 60°C, an oil fraction with a boiling point below 150°C of up to 0.1% by weight, an oil fraction with a boiling point below 350°C of 30% to 40% by weight, and a residual fraction with a boiling point of at least 550°C of at least 20% by weight.

[0043] In a specific preferred embodiment, the ash content of the HTL oil is less than 100 ppm.

[0044] In a third aspect, the present invention relates to the use of the chemically treated HTL oil, which has improved thermal stability and low inorganic content, as a marine fuel, a co-processing feedstock in commercial refineries or independent upgrading units. Those skilled in the art will understand that the above list of suitable uses is not limited to those mentioned in the list.

[0045] Example Example 1: Preparation and characterization of HTL bio-crude oil produced by hydrothermal liquefaction use Figure 1 The method described above produces low-oxygen HTL bio-crude oil from a 50 / 50 mixture of spruce and pine. This mixture is then subjected to hydrothermal liquefaction at supercritical water conditions of 390-420°C and 300-350 bar. The analysis of the resulting wood chips is shown in Table 1 below.

[0046] Table 1. Composition of carbon-containing materials on a dry, ash-free basis.

[0047]

[0048] Feed preparation Wood chips are reduced to wood flour using a hammer mill system and then mixed with recycled / circulated water (containing dissolved salts and water-soluble organic matter), recycled / circulated oil, and catalyst to produce a homogeneous and pumpable feed mixture. Potassium carbonate is used as the catalyst, and sodium hydroxide is used to adjust the pH. During operation, a constant potassium concentration is maintained by measuring the potassium concentration in the aqueous phase and determining the required replenishment catalyst concentration accordingly. Sufficient sodium hydroxide is added to maintain the outlet pH of the separated aqueous phase within the range of 8.0–8.5. Additionally, 0.8% by weight CMC (carboxymethyl cellulose, Mw = 30000) is added to the feed slurry as a texturing agent to prevent sedimentation in the feed tank and improve pumpability.

[0049] Since no water or oil phase was available in the initial cycle (batch), crude tall oil was used as the start-up oil, and 5.0% by weight ethanol and pure water (reverse osmosis water, RO water) were used to simulate the aqueous phase in the initial cycle. Multiple cycles (batches) were required before the method reached steady state and produced representative oil and aqueous phases. Approximately six cycles were needed to produce oil with a concentration 10% lower than that of the start-up oil. Therefore, six cycles were performed, in which the oil and aqueous phase produced in the previous cycle were added to the feed mixture for subsequent cycles. The feed composition used for the sixth cycle is shown in Table 2 below: Table 2. Composition of the feed mixture used for the 6th cycle

[0050] The feed mixtures in Table 2 were processed at a pressure of approximately 320 bar and a temperature of approximately 400°C. The degassed products were collected as independent mass balance samples (MBs) from the beginning of each test and numbered MB1, MB2, MB3, etc. The collected products were weighed, and the oil and aqueous phases were separated by gravity and weighed. Data for each batch were recorded both electronically and manually.

[0051] Total mass balance Total Mass Balance (MBTot) is the ratio between the total mass leaving a cell and the total mass entering a cell during a specific time period. MBTot can also be considered a quality parameter of the generated data, with an average MBTot closure rate of 100.8%.

[0052] HTL biocrude oil yield from biomass Oil yield from biomass represents the proportion of dry biomass entering the cell that is converted into dry ash-free oil. It is defined as the mass of dry ash-free oil produced from dry biomass within a specific time period divided by the mass of dry biomass entering the cell during the same period. Recycled oil is not included in the balance and is deducted from the total amount of oil recovered when calculating oil yield from biomass. The average oil yield is 45.3% by weight, with a standard deviation of 4.1% by weight, meaning that 45.3% of the mass of dry biomass (wood + CMC) in the feed is converted into dry ash-free oil.

[0053] Detailed analysis of HTL bio-crude oil The measured HTL biocrude oil data are presented in Table 3.

[0054] Table 3. Physicochemical properties of low oxygen content HTL bio-crude oil

[0055] DAF: Dry and ash-free Energy recovery rate in the produced HTL bio-crude oil Energy recovery rate (ERoil) indicates how much of the chemical energy in the feed wood is recovered into the oil. It does not consider the energy required for heating or the electrical energy supplied to the unit. For the recovery rate calculation, the higher heating value (HHV) of the oil is used as 38.6 MJ / kg, combined with the HHV of the wood mixtures listed in Table 1. The resulting ERoil energy recovery rate for the 6th cycle was 85.6%, with a standard deviation of 7.7, meaning that 85.6% of the (chemical) energy in the wood fed into the equipment was recovered into the produced oil.

[0056] Gas production and gas analysis Gases are generated during the biomass-to-oil conversion process. The gas yield from the dried wood feedstock was 41.2% by weight. The gases consisted primarily of CO2, CH4 and other short-chain hydrocarbons (C2-C4), H2, and some lower carbon number alcohols. The gases were sampled and analyzed by the Swedish Institute of Technology (Sveriges Tekniska Forskningsinstitut) (SP). The analysis of the sixth cycle gas and the estimated calorific value from the gas composition are shown in Table 4. Since the HTL process operates under reducing conditions, it was assumed that the gas was oxygen-free (O2), and any oxygen detected in the gas originated from air leaking into the sampling bag during gas sample filling. The gas composition was corrected for oxygen (and nitrogen). The calculated elemental composition of the gases is shown in Table 4.

[0057] Table 4. Composition of gases produced during the process

[0058] * The oxygen (O2) in the resulting gas (ar) is assumed to originate from air pollution in the gas sample during filling. The composition of the generated gas is assumed to be free of air (oxygen).

[0059] Table 5. Elemental Gas Composition

[0060] Example 2: Suitability test of HTL bio-crude oil for direct use as marine fuel The potential use of HTL bio-crude oil as a marine fuel is being evaluated according to various standards, including bio-crude oil characterization, stability in bench testing (where the bio-crude oil is heated and sprayed through a pressure nozzle, followed by combustion and engine testing). While the shipping industry is flexible on some ISO 8217 characteristics, certain characteristics must be met to ensure safe operation, engine life, and reduced emissions. Metallic properties (especially sodium, vanadium, and silicon + aluminum) and characteristics such as flash point, thermal stability, compatibility with conventional marine fuels, ash content, and heteroatom (S and N) composition are all important considerations. The characteristics of HTL bio-crude oil, marine fuels, and ISO 8217 are listed in Table 6.

[0061] Table 6 shows that the oxygen content (9-10 wt%) of HTL bio-crude oil is higher than that of marine fuel (0.03 wt%), but the sulfur content (146 ppm) and nitrogen content (0.25 wt%) of HTL bio-crude oil are lower than those of marine fuel (S: 4591 ppm and N: 0.28 wt%). SAP hydrocarbon analysis indicates that 51.9 wt% of the marine fuel composition consists of aromatics, 36.9 wt% of saturated hydrocarbons, and 11.2 wt% of polar substances. In contrast, HTL bio-crude oil has a significantly higher concentration of polar substances (65.4 wt%), a slightly lower concentration of aromatics (26.37 wt%), and a much lower concentration of saturated hydrocarbons (8.23 wt%). These differences in functional group distribution limit compatibility, resulting in a maximum blending ratio of 2 wt%. In terms of distillation, HTL bio-crude oil covers the entire boiling range of crude oil (i.e., from naphtha to vacuum residue), while marine fuel mainly consists of heavy gas oil fractions and does not contain components with boiling points in the naphtha boiling range.

[0062] The ash content in HTL bio-crude oil is at the upper limit specified in ISO 8217 (<0.1 wt%); however, in-depth analysis of the metal types revealed high potassium (237 ppm) and sodium (297 ppm) content, almost three times the recommended values ​​in ISO 8217. Vanadium, silicon, and aluminum levels are within permissible levels (V < 450 ppm and Si+Al < 60 ppm). The flash point is also above the minimum critical value of 60°C.

[0063] Table 6. Comparison of the properties of HTL bio-crude oil with conventional marine fuels and ISO 8217.

[0064] DAF: Dry and ash-free While HTL bio-crude oil appears suitable for marine fuel, thermal stability and aging tests suggest otherwise. According to thermogravimetric analysis (TGA), HTL bio-crude oil becomes thermally unstable above 80°C. Therefore, prolonged heating or storage of HTL bio-crude oil above 80°C significantly affects its properties such as water content, TAN, and viscosity. Furthermore, for some engines, preheating HTL bio-crude oil to 103°C is necessary to achieve the viscosity (10 cSt) required for adequate fuel atomization at the engine nozzles. This can negatively impact engine metals, as demonstrated in accelerated aging tests conducted at 160°C for 140 hours using two pieces of carbon steel for qualitative corrosion analysis. Figure 5 Visible corrosion was observed in the carbon steel sheet after accelerated aging tests.

[0065] The results in Table 7 show that higher temperatures accelerate the aging reaction, leading to increased water production and a decrease in TAN. Dehydration, polymerization, aldol condensation, oligomerization, and acid formation are all reactions that occur with the aging of HTL bio-crude oil. These reactions are inherently related to water content and acidity. Notably, when the oil was stored at atmospheric conditions (25°C and atmospheric pressure) for more than 8 months, the water content, TAN, and viscosity remained almost unchanged, confirming that HTL bio-crude oil stored at room temperature degrades more slowly than HTL bio-crude oil stored at 80°C–160°C.

[0066] Table 7. Results of accelerated aging studies

[0067] HTL bio-crude oil contains a wide variety of chemical compounds. FTIR analysis enabled the overall determination of the compound families throughout the bio-crude oil, GC-MS analysis determined the distribution of light fractions (boiling point below 350°C), and SAP analysis analyzed heavy fractions (boiling point above 300°C). FTIR analysis of HTL bio-crude oil revealed the distribution of major component families, including alkanes, aromatics, ketones, esters, ethers, free and bound phenols, as well as carbonyl components (free and bound).

[0068] GC-MS analysis revealed that 34% of the light fraction (IBP - 350°C) of HTL bio-crude oil contained predominantly oxygen-containing compounds with polar heteroatoms, along with smaller amounts of nitrogen- and sulfur-containing compounds. The oxygen-containing components were primarily carboxylic acids, ketones, and phenols, with smaller amounts of esters and aldehydes. These oxygen-containing compounds in HTL bio-crude oil likely originated primarily from the hydrothermal liquefaction conversion products of the lignocellulosic component. Additionally, 58% consisted of aromatic hydrocarbons and polycyclic aromatic hydrocarbons, including phenanthrene, alkylbenzenes, and naphthalene. The remaining 8% were saturated compounds. A similar distribution was observed in the heavy fraction (boiling point above 300°C), where SAP tests indicated a predominantly polar composition > aromatic hydrocarbons > saturated hydrocarbons. Furthermore, a significant increase in viscosity (70%) was observed.

[0069] Example 3: Quality Improvement of Chemically Treated HTL Oil The HTL bio-crude oil produced from a 50 / 50 mixture of spruce and pine described in Example 1 was subjected to the following process: Figure 2 and Figure 3 The chemical treatment is illustrated below. First, the low-oxygen HTL bio-crude oil is preheated to 35°C, followed by the addition of 5 to 10% by weight of an alcohol additive (as shown in Table 8). The mixture of the low-oxygen HTL bio-crude oil and the additive is then heated to 160°C and maintained in a closed system for 140 hours. After the residence time, the product is distilled at atmospheric pressure to separate unreacted additives, water, and light fractions from the chemically treated HTL oil (IBP-180°C).

[0070] Various chemical treatment experiments were conducted using different types of alcohols, different concentrations, and different temperatures (see Table 8).

[0071] The results in Table 8 indicate that both heating and alcohol concentration accelerate esterification and acetalization reactions. When aging tests were conducted using a blend of HTL bio-crude oil and IPA (90:10), a significant reduction in TAN (70%) was observed at 160°C compared to 130°C (a 46% reduction). This suggests that higher temperatures favor the chemical processing. However, temperatures above 200°C were observed to be detrimental to this process; instead, agglomeration and coke formation were observed at these temperatures.

[0072] Consistent with temperature observations, higher alcohol concentrations resulted in a faster reduction in TAN, and this also varied depending on the specific type of alcohol used. For example, the results in Table 8 show a significantly higher TAN reduction (89%) achieved when using 10% wt% methanol, compared to an 84% reduction using 10% ethanol and a 77% reduction using 10% IPA. This is primarily related to the amount of OH- ions available in the mixture, specifically 3.1% more OH- ions per 100 g of methanol compared to 2.2% using ethanol and 1.7% using IPA.

[0073] Table 8. Changes in water content and TAN in chemical treatment tests of HTL bio-crude oil at 160°C for 140 hours using various additives.

[0074] At 160°C and with varying concentrations of the tested alcohol, a residence time of 140 hours is required to reach steady state. When using 10% methanol by weight, stirring can halve the residence time to reach process stability (70 hours).

[0075] The thermal stability of the chemically treated HTL bio-crude oil was demonstrated through an accelerated aging test at 160°C for 140 hours. Carbon steel sheets were added during the test for visual corrosion assessment. The results are shown in Table 9. Figure 5 As shown.

[0076] The results shown in Table 9 indicate that the changes in water content and TAN are minimal, and as... Figure 5 As shown, no signs of corrosion were observed in the carbon steel sheet. It is noteworthy that the test temperature was higher than the temperature required to achieve the 10 cSt viscosity (128°C) needed for proper nozzle spraying in marine engines. Therefore, the thermal stability of the HTL oil under the test conditions was verified.

[0077] Table 9. Changes in water content and TAN in chemically treated HTL oil during accelerated aging tests (accelerated aging tests were conducted at 160°C for 140 hours).

[0078] Compared to HTL bio-crude oil, the chemically treated HTL oil showed an 86% reduction in TAN and a slight decrease in oxygen content. Furthermore, SAP analysis (Tables 6 and 10) confirmed a slight change in the distribution of saturated hydrocarbons, aromatic hydrocarbons, and polar substances, with an increase in saturated hydrocarbons and aromatic hydrocarbons. FTIR analysis (…) Figure 6 In the region, aromatic hydrocarbons were observed (100-1500 cm⁻¹). -1 The changes are slight, while the combined carboxylic acid group (1705 cm) -1 ) clearly leans towards free carbonyl groups (1742 cm) -1 The movement of carbonyl groups in HTL oil after chemical treatment results in a 47% reduction in bound carbonyl groups and a 98% increase in free carbonyl groups.

[0079] Table 10. Characteristics of low-oxygen HTL bio-crude oil and chemically treated HTL oil

[0080] By Figure 3In step f, the cooled, converted mixture is combined with demineralized water in a 1:1 ratio to further reduce the sodium content in the chemically treated HTL oil (from 158 ppm to 90 ppm). The water and the cooled, converted mixture are then separated by gravity, and the separated product is distilled at atmospheric pressure to separate unreacted additives, residual water, and light fractions (IBP-180°C) from the chemically treated HTL oil.

[0081] Example 4: Compatibility of chemically treated HTL oil with conventional marine fuels The compatibility of the chemically treated HTL oil produced according to Example 3 with conventional marine fuels was tested.

[0082] All the property improvements shown in Example 3 slightly increased HHV and improved the compatibility of the chemically treated HTL oil with petroleum-derived marine fuels, achieving a 50% blend, such as Figure 7 This is confirmed by the dot test and microscopy shown.

[0083] The chemical treatment method according to the present invention has shown significant potential for the thermal stabilization of HTL bio-crude oil. This method effectively improves thermal stability while reducing the acidity of the bio-crude oil without requiring hydrogenation treatment.

[0084] A comparative analysis of the chemical properties of chemically treated HTL oils and marine fuels provides evidence that the former has the potential to become a viable option for marine fuel applications. Chemically treated HTL oils exhibit superior properties compared to conventional marine fuels, such as lower sulfur content, a key factor in reducing GHG emissions from shipping.

Claims

1. A method for producing low-oxygen hydrothermal liquefaction (HTL) oils with improved thermal stability and low inorganic content, comprising the following steps: a. Provides low-oxygen HTL bio-crude oil, which has the following characteristics: - Oxygen content in the range of 3.0 to 15% by weight. - Less than 1.5% by weight of water content, - Total acid value in the range of 20 to 80 mg KOH / g - Less than 70% by weight of oil fractions with a boiling point below 350°C - At least 10% by weight of the residue fraction with a boiling point above 450°C; and - Ash content less than 0.1% by weight; b. Heat the low-oxygen HTL bio-crude oil from step a to a temperature in the range of 25°C to 80°C; c. Add an additive containing at least one alcohol to the heated low-oxygen HTL bio-crude oil from step b and mix. d. Further heat the mixture from step c in the reaction zone to a temperature in the range of 80°C to 200°C; e. The heated mixture from step d is kept in the reaction zone for a conversion time of 1 to 200 hours; f. Cool the converted mixture from step e to a temperature ranging from 20°C to 180°C; and g. Separate the cooled, converted feed mixture from step f into chemically treated HTL oil, light boiling point fraction, water, and unconsumed additives.

2. The method according to claim 1, wherein the additive in step c comprises at least one alcohol at a concentration of 1 to 70% by weight, preferably 3 to 50% by weight, more preferably 5 to 40% by weight.

3. The method according to claim 1 or 2, wherein in step d, the mixture of low oxygen HTL bio-crude oil and additives is heated to a temperature in the range of 100°C to 180°C, preferably 130°C to 170°C.

4. The method according to any one of claims 1-3, wherein in step e, the mixture of heated low-oxygen HTL bio-oil and additives is maintained in the reaction zone for a conversion time of 3 to 180 hours, preferably 10 to 160 hours.

5. The method according to any one of claims 1-4, wherein the pressure reached in the reaction zone by the heated mixture in step e is 3 to 200 bar, more preferably 5 to 150 bar, and particularly more preferably 7 to 110 bar.

6. The method according to any one of claims 1-5, wherein the total acid value of the chemically treated HTL oil obtained in step g is at least 6 to 24 mg KOH / g.

7. The method according to any one of claims 1-6, wherein the method further comprises reducing the inorganic content level to less than 200 ppm, preferably less than 100 ppm, by mixing the cooled converted mixture in step f with a liquid containing at least 70% by weight of demineralized water.

8. The method of claim 1, wherein in step e, the heated mixture of low-oxygen HTL bio-crude oil and additives is maintained in the reaction zone under continuous stirring, thereby reducing the conversion time to 1 to 70 hours.

9. The method according to any one of claims 1-8, wherein the reaction zone in step d comprises a first sub-reaction zone and a second sub-reaction zone, and wherein the mixture of low-oxygen HTL bio-oil and additives in step c is maintained in the first sub-reaction zone for 10 to 170 hours to reduce TAN by at least 50%, and subsequently the reaction mixture product in the first sub-reaction zone is further mixed with the additives to obtain an additive concentration ranging from 5 to 30% by weight, and the mixture is maintained in the second sub-reaction zone for 10 to 110 hours to further reduce TAN by at least 20%.

10. The method of claim 9, wherein after mixing the reaction mixture product in the first sub-reaction zone with the additive, the temperature is adjusted to 100 to 170°C.

11. The method according to any one of claims 1-10, wherein the low-oxygen HTL bio-crude oil provided in step a has a kinematic viscosity range of 150-200 cSt at 50°C, and the chemically treated HTL oil obtained in step g has a kinematic viscosity range of 230-280 cSt at 50°C.

12. The method according to any one of claims 1-11, wherein the low-oxygen HTL bio-oil in step a is provided by a method comprising the following steps: - Provide carbon-containing materials in biomass form contained in one or more feedstocks; - By slurrying the carbonaceous material in one or more fluids to provide a feed mixture, wherein at least one of the one or more fluids contains water; - Pressurize the feed mixture to a pressure in the range of 150 to 400 bar; - The pressurized feed mixture is heated to a temperature in the range of 300°C to about 450°C; - The pressurized and heated feed mixture is maintained for a conversion time ranging from 3 to 30 minutes, thereby causing the carbonaceous material to be converted; - Cool the converted feed mixture to a temperature ranging from 25°C to 200°C; and - The converted feed mixture is expanded to a pressure in the range of 1 to 120 bar and the converted feed mixture is separated into at least low oxygen HTL biocrude oil, a gas phase and an aqueous phase containing water-soluble organic matter and dissolved salts; The low-oxygen HTL bio-crude oil thus provides an oxygen content ranging from 3.0% to 15% by weight, a water content of less than 1.5% by weight, a total acid value ranging from 20 to 80 mg KOH / g, an oil fraction with a boiling point below 350°C of less than 70% by weight, a residue fraction with a boiling point above 450°C of at least 10% by weight, and an ash content of less than 0.1% by weight.

13. An HTL oil having improved thermal stability and low inorganic content, preferably obtained by the method according to any one of claims 1-12, wherein the HTL oil comprises: - At most 10% by weight of oxygen content, - Less than 0.1% by weight of water content, - A total acid value of up to 6 mg KOH / g, - Ash content less than 400 ppm, - Flash point of at least 60°C - Up to 0.1% by weight of oil fractions with a boiling point below 150°C, - 30% to 40% by weight of oil fractions with boiling points below 350°C, and - At least 20% by weight of the residue fraction with a boiling point of at least 550°C.

14. The HTL oil according to claim 13, wherein the ash content is less than 100 ppm.

15. The use of the chemically treated HTL oil with improved thermal stability and low inorganic content as described in any one of claims 13 and 14, preferably the chemically treated HTL oil obtained by the method according to any one of claims 1-11, as marine fuel, co-processing feedstock in commercial refineries or independent upgrading units.

Images