WO2024132816A1 - A method for the production of a bark oil - Google Patents

Abstract

The present invention relates to a method for the preparation of a bark oil derived from a biomass comprising at least 50 wt% bark, wherein the method comprises the steps of: - adding a biomass comprising at least 50 wt% bark, calculated as dry bark on the total dry weight of the biomass, wherein the biomass contains from 0.1 to 65 wt% water; - adding a base comprising potassium hydroxide, potassium alkoxide or potassium hydride, and a non-aqueous fluid comprising methanol, ethanol, propanol, or a bio-oil; - obtaining a mixture and subjecting said mixture to thermal treatment at a temperature of from 100 to 350 °C to obtain a bark oil; - adding an acid to the bark oil to precipitate salt; and - removing inorganic compounds from the bark oil. The invention further relates to a bark oil obtainable by the method.

Description

A METHOD FOR THE PRODUCTION OF A BARK OIL

FIELD OF THE INVENTION

The present invention relates to a bark oil, a method for the production thereof, and use of the bark oil.

TECHNICAL BACKGROUND

The current and expected demand for biofuels greatly exceeds the available supply. Advanced biofuels derived from lignocellulosic materials are of particular interest, as this class of biofuels does not compete with food crops for feedstock biomass. There is great potential for bioenergy from residues and wastes from wood logging and wood processing - this global potential has been estimated to be 2.4 Gm³ per year (28 EJ per year), and the economic-ecological potential for Europe's existing disturbed forests was estimated to be 405 Mm³ (Smeets & Faaij, Bioenergy potentials from forestry in 2050, Climatic Change, 2007). Bark is currently a waste product commonly burned as fuel and, like sawdust, is considered a secondary forest residue. It is an available feedstock that can be utilized without a negative environmental impact. However, bark is a complex and highly variable material that is more complex and difficult to process than are sugars and vegetable oils, and thus, cannot be economically converted into bio-oils and, subsequently, into biofuels and biochemicals by the currently available technologies. Methods described in the prior art are primarily focused on extracting certain compounds from bark, rather than liquefying all of the solids in the production of a biooil.

A major barrier to the efficient conversion of lignocellulosic materials to biofuels is liquefaction of the raw materials, due to the low solubility of lignin in water and other common solvents. The most prominent methods currently in use for the production of bio-oils from lignocellulosic materials are hydrothermal liquefaction and pyrolysis.

Hydrothermal liquefaction (HTL) processes typically operate at high temperatures (300-

400 °C) and pressures (100-350 bar), requiring expensive equipment. Yields of HTL processes are limited by repolymerization and condensation reactions that lead to the formation of char and other solids.

Pyrolysis of biomass into bio-oil is most commonly done via flash pyrolysis at temperatures of 400 to 700 °C, requiring expensive equipment. Pyrolysis yields are also limited by the formation of char. Pyrolysis of lignocellulosic materials with higher lignin content has been reported to result in higher amounts of char. Pyrolysis oils are highly corrosive and unstable due to the high levels of acids, water, and aldehydes. The challenging properties of pyrolysis oils currently limit large-scale processes to corefining, where the pyrolysis oils are blended into crude oil-derived streams, for example, with vacuum gas oil when fed to a fluidized bed catalytic cracking unit.

Recent studies have explored the liquefaction of bark and bark-containing biomass, but a bark oil wherein there are neither bark solids remaining, nor char from the production process, has not yet been demonstrated. Complete liquefaction of bark to bark oil without formation of char, nor presence of solid residue is desired. It is also desirable to minimize the yield loss to CO2 during the liquefaction process.

Another challenge for the production of fuels and chemicals from lignocellulosic materials is the presence of metals that can inhibit or deactivate catalysts used in refining processes, such as hydroprocessing. Certain methods for the demetallization of bio-oils disclose low product phosphorus levels but have not effectively reduced the levels of other metals. For example, the method described in WO 2015/095453 Al was effective for reducing phosphorus but not potassium.

In traditional crude oil refineries, hydroprocessing catalyst beds are protected by guard beds that comprise an inert trapping material, hydrodemetallization catalysts, or a combination of both. The higher the metal content in the hydroprocessing feed and/or the longer the time period between catalyst changeouts or catalyst skims, the larger the guard bed needed. Bark constitutes the outermost layer of woody plants, and is defined as all plant tissues outside the vascular cambium. Bark differs in composition from wood and there is greater variation in composition between species in bark than in wood. Further, the water content of bark is more variable than in wood, being as high as 65% water in the winter. In addition, the de-barking processes used in the forest products industry results in some amounts of wood (e.g., pulp) to remain in the removed bark. Other forestry wastes, such as needles, leaves, and cones, also sometimes end up in the bark supplies. A variety of feedstocks with seasonal availability, requires a flexible biorefinery for the process to tolerate a wide range of feed compositions.

Bark can contain up to 6 wt% of metals. Phosphorus is of particular concern, as it is present in bio-oils in the form of phospholipids and, thus, is more difficult to remove than water-soluble metals. Both phospholipids and phosphorus are known to deactivate hydroprocessing catalysts. Other metals, such as calcium and magnesium, have been reported to be bound to phospholipids. In order to remove phosphorus from bio-oils, the phospholipids must be decomposed. Decomposition of the phospholipids facilitates removal of phosphorus either from the aqueous phase or at the interface between the two phases.

There is a need for methods providing reduction of both the content of phosphorus and metals such as aluminium, calcium, magnesium, manganese, phosphorus, potassium, and sodium of the bio-oil via demetallization prior to hydroprocessing to maximize the time period between catalyst changeouts or catalyst skims and to minimize the volume of guard bed required. Moreover, it is also desirable to reduce the content of phosphorus and metals by a means that allows for hydroprocessing of the entire bio-oil, as opposed to, for example, removal of fractions of the bio-oil containing high levels of metals prior to hydroprocessing.

As is apparent from the above, there is still a need for an improved method for efficient production of bark oil with a low water and metal content. SUMMARY OF THE INVENTION

An object of the present invention is to provide a bark oil derived from biomass comprising a greater part of bark. A further object is to provide a method for the production of bark oil. Yet an object is to provide a bark oil with a low water content. This bark oil is flowable and is a suitable feedstock for hydroprocessing into fuel or chemicals.

The bark oil and the method for its preparation according to the present invention are defined in the appended claims.

LIST OF DEFINITIONS

Some expressions used herein are defined in the list below:

Hydroprocessing: a number of catalytic processes in the presence of hydrogen gas for removal of sulphur, oxygen, nitrogen and metals, or saturation of olefins and aromatics. Hydroprocessing encompasses hydrocracking, hydrotreating, hydrodewaxing, and hydrodemetallization.

Hydrocracking: a catalytic process for breaking down large organic molecules into smaller molecules by the breaking of carbon-carbon bonds in the presence of hydrogen gas.

Hydrotreating: a catalytic process for the removal of heteroatoms from chemicals, biogas, bio-oils, oils or fuels in the presence of hydrogen. Hydrotreating also includes saturation of olefins and aromatics. Hydrotreating encompasses hydrodearomatization (HDA), hydrodenitrogenation (HDN), hydrodesulfurization (HDS), hydrodeoxygenation (HDO), hydrofinishing, and olefin saturation.

Hydrodesulfurization (HDS): a catalytic process for removing sulphur (S) from chemicals, bio-gas, oils, bio-oils or fuels in the presence of hydrogen gas. HDS reactions release sulphur as hydrogen sulphide (H2S). Hydrodenitrogenation (HDN): a catalytic process for removing nitrogen (N) from chemicals, bio-gas, oils, bio-oils or fuels in the presence of hydrogen gas. HDN reactions release nitrogen as ammonia (NH3). Also known as hydrodenitrification.

Hydrodeoxygenation (HDO): a catalytic process for removing oxygen (O) from chemicals, bio-gas, oils, bio-oils or fuels in the presence of hydrogen gas. HDO reactions release oxygen as water.

Hydrodemetallization (HDM): a catalytic process for the removal of metals from chemicals, bio-gas, oils, bio-oils or fuels in the presence of hydrogen gas.

Hydrofinishing: a final hydrotreating step after hydrocracking and/or hydrotreating that improves the colour and oxidation stability of the product.

Hydrodewaxing: the reduction of the wax content, such as paraffin wax (C18-C36 hydrocarbons), during oil refining in the presence of hydrogen gas. Hydrodewaxing includes dewaxing by shape-selective hydrocracking, isomerization, and combinations of shape-selective hydrocracking and isomerization.

Shape-selective hydrocracking: hydrocracking using shape-selective catalysts.

Shape-selective catalysts: catalysts whose shape, such as pore structure, affects a chemical reaction. Hydrodewaxing via shape-selective hydrocracking uses the pore structure to selectively crack normal paraffins.

Simulated Distillation: a method for determination of the boiling point distribution in an oil or fractions thereof by gas chromatography according to EN 15199-1, or by ASTM 2887 extended, where the percentage distilled is calculated as a function of temperature.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows simulated distillation of bark oil by gas chromatography. The cumulative weight percentage recovered is presented as a function of the boiling point of the components of the sample (x-axis: effective temperature; y-axis: cumulative weight percent recovered).

Figure 2 shows simulated distillation of bark oil by gas chromatography. The analysis area percentage of the gas chromatogram is presented as a function of the effective temperature. DETAILED DESCRIPTION OF THE INVENTION

In a first aspect, the present invention relates to a method for providing a bark oil, wherein the method comprises the steps of a) adding a biomass comprising at least 50 wt% bark, as calculated on the total dry weight of the biomass, wherein the biomass contains of from 0.1 to 65 wt% water, preferably from 1 to 45 wt%, more preferably from 1 to 40 wt%, as calculated on the total weight of the biomass; b) adding a base comprising potassium ions, preferably a base selected from potassium hydroxide, potassium alkoxide and/or potassium hydride, and a non-aqueous fluid comprising methanol, ethanol, propanol, or a bio-oil, e.g. a bark oil, preferably ethanol, to the biomass; c) obtaining a mixture comprising the biomass, the base, and the nonaqueous fluid, and subjecting said mixture to thermal treatment at a temperature of from 100 to 350 °C, preferably of from 120 to 300 °C, more preferably of from 150 to 250 °C, to obtain a bark oil; d) adding a first acid to the bark oil to precipitate salt; e) removing inorganic compounds from the bark oil; and f) optionally recycling the bark oil obtained in step c) or e) to step b).

In one embodiment, the obtained bark oil is subjected to subsequent demetallization after step d) or step e), wherein the demetallization comprises: g) adding one or more of water, a second acid, a bio-oil, and a solvent to the bark oil to obtain a mixture thereof; h) subjecting the bark oil mixture obtained in the previous step to a temperature of from 10 °C to 320 °C, preferably of from 80 °C to 250 °C, more preferably of from 120 °C to 200 °C, to obtain a liquid fraction comprising an aqueous phase and a bark oil; i) removing the aqueous phase from the liquid fraction comprising the bark oil to obtain a demetallized bark oil; j) optionally repeating steps g)- i); and k) optionally subjecting the demetallized bark oil to hydroprocessing; whereby the demetallized bark oil obtained has a total metal content of less than 200 ppm, preferably of from 0 to 50 ppm, more preferably of from 0 to 20 ppm.

The steps a) to j) may be performed in consecutive order. Alternatively, steps a) and b) could be performed in any order. When demetallization according to steps g) to j) is performed, step g) may, as an alternative, be performed before step e). Step c) has to be performed after steps a) and b). Steps h) and i) have to be performed in said order after the last of steps e) and g).

Steps g)-i) may be repeated at least once. Repeating steps g)-i) enables reduction of the total metal content and facilitates efficient phosphorus removal. In one embodiment, an acid is added when step g) is performed for the first time, and when repeated, water without acid is added.

All aspects and embodiments disclosed herein can be combined with any other aspect and/or embodiment disclosed herein.

The term "fluid" is used herein for gases as well as liquids.

The biomass used for the preparation of bark oil herein comprises at least 50 wt% bark, preferably at least 70 wt% bark, as calculated on the total weight of the biomass. The biomass can comprise up to and including 100 wt% bark. The biomass may comprise up to 50 wt% of plant material other than bark. Said biomass can comprise biomass originating or being selected from other remains from de-barking processes, cones, needles, leaves, softwood, hardwood, pieces of trunk, branches, roots, other types of forest biomass, straw, bagasse, grass, algae, seagrass, seaweed, nutshell, fruit kernel, husk, corn stover, agriculture residues, food industry residues, wood pulp, and other biomass types. As used herein, the expression "agriculture residues" include the parts of the plants with agricultural origin not used for food, including stalks, stems, haulm, leaves, straw, corn stover, bagasse, peel, nutshell, fruit kernel, husks. As used herein, the expression "other types of forest biomass" encompasses plants and trees from plantations of any age, including short rotation coppice, and includes all parts of the tree, such as the trunk, including pieces thereof, bark, branches, needles or leaves, cones and roots.

The bark may have a water content of from 0.1 to 65 wt%, preferably from 0.5 to 45 wt%, more preferably from 1 to 40 wt%, as calculated on the total weight of the bark. The biomass may have a total water content of from 0.1 to 65 wt%, preferably of from 0.1 to 45 wt%, more preferably from 0.1 to 30 wt%, even more preferably 0.1 to 10 wt%, not including 10 wt%, as calculated on the total weight of the biomass.

In one embodiment, the biomass comprises from 0.1 to 40 wt% lignin, as calculated on the total dry weight of the biomass. The amount of lignin refers to Klason lignin, which is the residue obtained after removal of the carbohydrate portion of wood or plant tissue by total acid hydrolysis. The content of Klason lignin is determined by a gravimetric method, for example TAPPI Standard T 222.

Bark is defined herein as the outermost layer of woody plants, defined as all plant tissues outside the vascular cambium. The bark may contain up to 65 wt% water. The bark biomass used as feedstock is preferably selected from biomass comprising softwood bark or hardwood bark, or combinations thereof. Examples of hardwood are the Betulaceae family: such as alder, birch, hazel, hornbeam; Fabaceae family: such as acacia (subfamily mimosoideae); Fagaceae family: such as beech, chestnut, oak; Juglandaceae family: such as hickory, pecan, walnut; Myrtaceae family: such as gum, eucalyptus, angophora; Rosaceae family: such as Prunus genus: cherry; Salicaceae family: such as aspen, cottonwood, poplar, willow; Sapindaceae family: such as maple, buckeye, horse chestnut, and Ulmaceae family: such as elm, zelkova. Examples of softwood are Ginkgoaceae family: ginkgo biloba; and conifers, comprising Araucariaceae family: such as kauri; Cupressaceae family: such as cypress, juniper, redwood; Pinaceae family: such as cedar, Douglas-fir, fir, hemlock, larch, pine, spruce, tamarack; Podocarpaceae family: such as yellowwood; Taxaceae family: such as yew.

Bark differs in composition from wood and there is greater variation in composition between species in bark than in wood. Bark contains lignin and suberin polymers, which are highly crosslinked, as well as hemicellulose and cellulose. Lignin is a phenolic biopolymer, while suberin is an aromatic-aliphatic polyester. Bark further contains lipophilic extractives that include triglycerides, fatty acids, resin acids, sterols, and steryl esters. Bark also contains terpenes, triterpenoids, phenolic glycosides, and polyphenols, such as, lignans, stilbenes, monomeric flavonoids, and tannins (water-soluble polyphenols). Bark has higher ash content and water content than wood.

In a preferred embodiment, the non-aqueous fluid comprises methanol, ethanol, n- propanol or iso-propanol, or a combination of one or more thereof.

In one embodiment, the non-aqueous fluid further comprises an additional Cuo alcohol; a Ci-30 hydrocarbon; an ether; an alkyl acetate; a ketone; sulfolane; a fluid stream recycled from a hydroprocessing step; or any combination thereof. The ketone is preferably acetone. The use of a recycled fluid stream, such as bark oil or a fluid stream from a hydroprocessing step, reduces the requirement for fresh non-aqueous fluid.

In one embodiment the additional Cuo alcohol comprises methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, glycerol, propylene glycol, cresol, resorcinol, hydroquinone, guaiacol, catechol, phenol, or benzyl alcohol, or any combination thereof. Preferably the additional Cuo alcohol has a boiling point of from 50 to 250 °C. More preferably the additional Cuo alcohol is selected from guaiacol, catechol, phenol, or benzyl alcohol. Preferably, the alcohol is derived from renewable sources. The alcohol functions not only as a solvent but also as a capping agent of lignin derivatives and suberin derivatives via alkylation, thereby suppressing repolymerization reactions between reactive phenolic compounds that lead to char formation. Selection of the alcohol impacts the solubility and solvation characteristics of the resulting bark oil, whereby selection of an alcohol with more hydrophobic character results in more hydrophobic lignin derivatives.

The recovery of methanol or ethanol is relatively energy-efficient in comparison with other solvents, and distillation may be performed at relatively low temperatures. The use of ethanol facilitates precipitation of potassium sulphate and other sulphate salts when a sulfuric acid is added in step d). Consequently, the use of ethanol is preferred when precipitating salts, while other alcohols may be used earlier in the process, i.e., during liquefaction of the bark (i.e. steps a) - c) as disclosed herein). Ethanol may also dissolve both hydrophobic and hydrophilic molecules. In addition, ethanol is an excellent solvent for purifying the precipitated salt, as it washes away the bio-oil and organic compounds remaining in the precipitated salt without dissolving the salt. Thus, in a more preferred embodiment, the non-aqueous fluid comprises ethanol.

In one embodiment the non-aqueous fluid added in step b) further comprises a C1-30 hydrocarbon or a mixture of C1-30 hydrocarbons. Preferably, the C1-30 hydrocarbon is a saturated hydrocarbon, more preferably a C1-30 alkane, which may be branched, linear, or cyclic. The C1-30 hydrocarbon is preferably selected from propane, butane, hexane, heptane, octane, nonane, decane, undecane and dodecane, which may be branched or linear, or from cyclic (naphthenic) hydrocarbons, such as those produced from the saturation of lignin and lignin derivatives.

In one embodiment the non-aqueous fluid added in step b) comprises a bio-oil. The biooil added as a non-aqueous fluid in step b) or the bio-oil added in step g) is each independently preferably selected from bark oil, such as bark oil recycled from a process comprising the method according to the invention; or a bio-oil selected from tall oil pitch, crude tall oil, pyrolysis oil, lignin oil, hydrothermal liquefaction oil, turpentine, a liquid stream recycled from a hydroprocessing step of biomass, vegetable oil, oil obtained from any one of lignocellulosic material, softwood, hardwood, bagasse, bark, sawdust, other types of forest biomass, algae, seagrass, seaweed, cones, needles, leaves, bark, nutshell, fruit kernel, husk, corn stover, agriculture raw materials, or agriculture residues, aquaculture residues, animal residues, food industry residues; or any combination thereof.

In one embodiment, vegetable oils are excluded as non-aqueous fluid. A reason for this is not to compete with resources from food industry. Examples of vegetable oils excluded are a$ai palm oil, avocado oil, Brazil nut oil, buriti oil, canola oil, carapa oil, coconut oil, corn oil, cottonseed oil, grape seed oil, graviola oil, hazelnut oil, hemp seed oil, jambu oil, linseed oil, olive oil, palm oil, palm kernel oil, passion fruit oil, peanut oil, pracaxi oil, rapeseed oil, rice bran oil, safflower oil, sesame oil, Solarium oil, soybean oil, sunflower oil, tucuma oil, and walnut oil. More preferably, the bio-oil added as a nonaqueous fluid in step b) or the bio-oil added in step g) is each independently preferably selected from a bark oil recycled from a process comprising the method presented herein; tall oil pitch; crude tall oil; pyrolysis oil; lignin oil; hydrothermal liquefaction oil; turpentine; oil obtained from any one of lignocellulosic material, softwood, hardwood, bagasse, bark, sawdust, other types of forest biomass, algae, seagrass, seaweed, cones, needles, leaves, bark, nutshell, fruit kernel, husk, corn stover, agriculture raw materials, agriculture residues, food industry residues; or any combination thereof.

In one embodiment, the non-aqueous fluid comprises a Cuo alcohol and bark oil recycled from a process comprising the method presented herein.

In one embodiment, the non-aqueous fluid comprises a bio-oil or a liquid stream recycled from a hydroprocessing step.

Liquefaction of bark can be carried out in the presence of a catalyst to aid in the depolymerization of the lignin and suberin, as well as decomposition of cellulose and hemicellulose. Base-catalyzed depolymerization of lignin and suberin suppresses repolymerization and char formation during liquefaction and thus is favoured over acid- catalyzed depolymerization. Complete dissolution of the biomass without char formation is desirable in order to maximize the yield of the process.

In one embodiment, the base comprising potassium ions that is added in step b) is selected from potassium hydroxide, potassium methoxide, potassium ethoxide, potassium isopropoxide, potassium tert-butoxide or potassium hydride. More preferably the base is selected from potassium hydroxide, potassium ethoxide and potassium hydride. Even more preferably the base is potassium hydroxide.

Addition of a metal hydroxide, such as sodium hydroxide or potassium hydroxide, to a mixture comprising biomass, and an alcohol, such as methanol, ethanol, or propanol, provides for the formation of potassium alkoxide, e.g., potassium methoxide, potassium ethoxide, or potassium isopropoxide, upon heating, which is a stronger base than potassium hydroxide, thus improving the process economy in the conversion of the biomass to bark oil. Alternatively, a metal alkoxide in an alcohol solution, such as potassium ethoxide in ethanol solution, can be added to the biomass.

An advantage with using potassium-containing bases is that potassium is more reactive than sodium. This may be due to the valence electrons being situated further away from the nucleus in potassium than in sodium, thus providing for a quicker dissociation. Using a base comprising potassium ions in the method according to the present invention, provides for 100 % liquefaction of the biomass, i.e. no solid residue from the biomass remains.

Too small amounts of potassium in relation to the amount of bark will not give 100 % liquefaction. In one embodiment the amount of potassium ions to Moisture and Ash Free (MAF) biomass is at least 0.35:1 part by weight, preferably at least 0.4:1. For biomasses that are easier to liquefy than bark, such as straw or seaweed, the content of potassium can be lower. The upper limit of the amount of potassium ions is irrelevant for effecting the method, although from an economic perspective the upper limit of the amount of potassium ions to Moisture and Ash Free (MAF) biomass may be 100:1, preferably 10:1. The person skilled in the art knows how to calculate the amount of potassium ions and that the moisture content of the base used must be taken into account.

The base added in step b) may further comprise a weak base, a strong base or a superbase. Use of a homogeneous base, i.e., without a support, rather than a heterogeneous supported base, as catalyst, avoids operational difficulties involved with the separation and recovery of the catalyst from the resulting bark oil, as well as deactivation of the heterogeneous catalyst.

The weak base can be selected from organic bases, such as pyridines, anilines, tertiary aliphatic amines; or from inorganic bases, such as sodium bicarbonate. A weak organic base may also function as a solvent or co-solvent for the liquefaction mixture.

In one embodiment the strong base further added in step b) is selected from sodium sulphide, sodium hydroxide, barium hydroxide, calcium hydroxide, caesium hydroxide, lithium hydroxide, rubidium hydroxide, or strontium hydroxide, or any combination thereof. The strong base further added in step b) is preferably selected from sodium sulphide, or sodium hydroxide, or any combination thereof.

A superbase is defined in IUPAC as a compound that has a very high basicity. In this specification the same definition is used. Examples of superbases are organometallic or inorganic compounds, such as a Grignard reagent; hydrides of alkali metals, such as lithium hydride, potassium hydride, or sodium hydride; combinations of organolithium compounds with alkali metal alkoxides, such as n-butyllithium and potassium tert- butoxide; or from organic compounds, such as phosphazenes, e.g. Schwesinger phosphazenes, proazaphosphatranes , such as Verkade proazaphosphatranes; phosphines; amidines; such as Schwesinger vinamidines; guanidines; or metal amides, such as lithium diisopropylamide; or any combination thereof. Specific examples of alkali metal alkoxides are alkali-metal Ci-6 alkoxides, such as sodium methoxide, sodium ethoxide, potassium methoxide, potassium ethoxide, or potassium tert-butoxide. In one embodiment of the method, the mixture subjected to thermal treatment in step c) comprises 5-50 wt% biomass, 1-35 wt% base, and 30-94 wt% of a non-aqueous fluid up to a maximum or a total of 100 %, as calculated on the total weight of the mixture. Preferably, the mixture comprises 8-40 wt% biomass, 5-25 wt% base, and 40-87 wt% of a non-aqueous fluid, up to a maximum or a total of 100 %, as calculated on the total weight of the mixture. More preferably, the mixture comprises 10-35 wt% biomass, 10- 20 wt% base, and 50-80% of a non-aqueous fluid, up to a maximum or a total of 100 %, as calculated on the total weight of the mixture.

In one embodiment the biomass, or the mixture comprising biomass obtained when the biomass in step a) of the method disclosed herein is mixed with the base and nonaqueous fluid in step b), has a water content of from 0.1 - 65 wt%, preferably from 0.1- 45 wt%, more preferably from 0.1 to 30 wt%, most preferably 0.1 to 10 wt%, not including 10 wt%, as calculated on the total weight of the biomass, or the mixture comprising biomass.

By dispersing the biomass in a non-aqueous fluid , the base (e.g., KOH) can form alkoxide ions instead of hydroxide ions, increasing the strength of the base and thereby improving the rate and extent of depolymerization of lignin and suberin. Use of a stronger base, such as an alkoxide instead of the corresponding hydroxide, can also reduce the amount of base required for liquefaction. Consequently, it is advantageous to minimize water during liquefaction, e.g., by limiting the initial water content of the mixture. Preferably, no free water is added in steps a) to b). The term "free water" is used herein for water that is, or was, not contained in the biomass.

Water can be formed via dehydration reactions during the liquefaction process. Said water can be removed by evaporation, distillation, or liquid-liquid extraction once the bark material has been liquefied. By using a non-aqueous fluid, such as an alcohol, a biooil, or a Ci-30 hydrocarbon, with a boiling point above 100 °C, water can be selectively removed by evaporation or distillation. The skilled person in the field is well equipped to select said alcohol bio-oil or C1-30 hydrocarbon.

By subjecting the mixture comprising biomass, a base, and non-aqueous fluid to a temperature of from 100 °C to 350 °C, preferably of from 120 °C to 300 °C, more preferably of from 150 °C to 250 °C; during a time period of from 1 to 360 min, preferably of from 5 to 300 min in step c), a liquid comprising bark oil is provided, without any extraction of solid materials being carried out.

In one embodiment the time period is from 5 to 360 min, preferably from 16 to 300 min, more preferably from 30 to 120 min, even more preferably from 35 to 90 min.

Liquefaction of the biomass to a bark oil preferably proceeds as depolymerization of lignin and suberin, as well as decomposition of cellulose and hemicellulose, occurs, catalyzed by the base. The rate of depolymerization depends on the temperature of the mixture. Achieving a certain extent of depolymerization requires shorter time periods when using higher temperatures. The time for the thermal treatment in step c) is preferably long enough to provide heat uniformity.

The temperature during the thermal treatment in step c) may be changed gradually, continuously, or in several heating stages over a period of time. Preferably, the thermal treatment is performed with two heating stages. The desired temperature may be reached by using pre-heated biomass, or pre-heated non-aqueous fluid, or pre-heated base, from any of the previous steps a) and b); and/or by heating of the mixture in step c).

When performing several heating stages, the biomass may be liquefied during any or all of the first heating stage(s), with biomass conversion being performed to the desired extent during the final heating stage(s). The temperature could be kept constant, or essentially constant, during any one heating stage. Essentially constant is in this context defined as a temperature variation of less than 10% of the desired temperature. Removing water prior to the final heating stage ensures that the base is in the alkoxide form rather than the hydroxide form, thereby improving the effectiveness of the base during the depolymerization reactions. Water, when present, may be removed by distillation, evaporation or by liquid-liquid extraction.

The quality and yield of the resulting bark oil also depend on the temperature applied, wherein excessively high temperatures (> 380 °C) result in significant yield losses due to decarboxylation and gas formation, as well as char formation. Using excessively high temperatures also requires a greater energy input than that needed to liquefy the biomass into a bark oil. The required time period also depends on the temperature that the components, i.e. the biomass, base, and non-aqueous fluid, have when they are added the mixture.

As used herein, time period is equal to residence time. Whereas time period is usually used for a batch process and residence time is usually used for a continuous process, the terms may be used interchangeably herein.

The thermal treatment in step c) may be performed at conditions where the nonaqueous fluid is in a near-supercritical or supercritical state. As used herein, the near- supercritical state denotes the state where the fluid is in the vicinity of its critical point, such as 20 °C below its critical temperature, for example at temperatures of 220-240 °C when using ethanol at a pressure of 63 bar.

In one embodiment, wherein during the thermal treatment in step d), the mixture is subjected to at least one temperature in the range from 130 °C to 190 °C in a first heating stage, whereupon the mixture is subjected to at least one temperature in the range from 180 °C to 350 °C in a second heating stage. The temperature of the second heating stage is preferably higher than the temperature of the first heating stage, more preferably by at least 20 °C. In one embodiment, the first heating stage lasts for a time period of from 30 to 180 minutes, and the second heating stage lasts for a time period of from 30 to 120 minutes. The liquefaction process of steps a)-c) may be done batch-wise, semi-batch-wise or in continuous operation, in a single vessel or in multiple vessels. Different types of equipment may be used, such as a stirred tank reactor, plug flow reactor, or vessels in series. Digesters used in the pulp industry in various configurations, such as batch, continuous, horizontal, and multitube reactors, are examples of suitable equipment. Heat exchange can be attained in various configurations, such as by using a heated vessel, multitube heat exchangers, or combinations thereof. Heating the mixture in stages to different temperatures can be accomplished with different types of vessels in series using various residence times and different configurations. For example, the first stage of liquefaction may take place in a stirred tank at a first temperature with a long residence time, followed by a second liquefaction stage at a higher temperature with a shorter residence time than that of the first stage. Pre-heated, base, and/or nonaqueous fluid(s), or combinations thereof may be added between stages of liquefaction.

Addition of the non-aqueous fluid can be performed at any point or at multiple points throughout the liquefaction process. In one embodiment, methanol and/or ethanol are added in the vapor phase, preferably above the boiling point of water. Water is condensed and removed from the process, while methanol and/or ethanol vapours are recycled to the reactor. This distillation process can be performed under vacuum or under pressure. The advantage with this procedure is the continuous removal of water. If the liquefaction is performed in two stages, the second stage could then be performed at a higher pressure than the first, so that the alcohol is in the liquid phase in the second stage and in the gas phase in the first stage. An advantage of using relatively low pressure in the first stage is simplified feeding of biomass to the reactor.

In one embodiment any solids remaining from the biomass are removed from the bark oil obtained in step c). Preferably, such biomass solids are removed from the bark oil obtained before the second heating stage in step c). The removed solids may be used for sugar production or as a pulp material. An acid, preferably a strong acid, is added in step d), and neutralizes or acidifies the liquid comprising the bark oil. The addition of the acid may also precipitate salts. In one embodiment, the method further comprises a step of removing salts from the liquid comprising bark oil obtained in step d). The precipitated salts are preferably removed by filtration. Removal of salts produces a higher quality bio-oil, while at the same time allowing the salts to be used for other purposes, e.g. as fertilizer.

In one embodiment, the precipitated salt is purified with a washing liquid essentially not dissolving the salt or acting as an anti-solvent to the salt. Preferably, the washing liquid is selected from Cuo alcohol, C2-7 ester or C3-7 ketone, or any combination thereof. More preferably, the washing liquid comprises ethanol, ethyl acetate or acetone. Even more preferably the washing liquid is ethanol.

In one embodiment, the potassium salt precipitated in step b) is further purified to obtain a salt having an organic content of less than 1000 ppm, preferably less than 500 ppm, more preferably less than 100 ppm.

Washing the precipitated salt to a suitable purity allows it to be used as fertilizer, since fertilizers should preferably have a maximum organic content of 100 ppm. Yet another reason to wash the salt is to remove organics, including bio-oil, from the salt. The biooil washed away from the salt may be pooled with the bark oil obtained in the liquefaction step, thereby providing a higher overall bio-oil yield.

Acids and bases used in the method according to the present invention can be selected so as to obtain precipitates that can be used as fertilizers or other useful products. The skilled person is well equipped to choose suitable acids and bases to this end. For example, addition of sulfuric acid or nitric acid causes potassium ions occurring in the lignin oil to precipitate as potassium sulphate and potassium nitrate, respectively. Thus, in a preferred embodiment the acid for salt precipitation, i.e., the first acid, is selected from sulfuric acid or nitric acid. In one embodiment, the bark oil obtained in step e) after the removal of inorganic compounds, is subjected to demetallization, preferably by acid treatment. Demetallization provides the removal of metals from the bark oil. Demetallization of the bark oil, i.e., steps g) -j) of the present invention, may comprise addition of one or more of water, a second acid, the bio-oil, or a solvent, to the bark oil to obtain a mixture. The obtained bark oil, or the mixture comprising the obtained bark oil, is subjected to a temperature of from 10 °C to 320 °C, preferably of from 80 °C to 250 °C, more preferably of from 120 °C to 200 °C, to obtain a second mixture comprising an aqueous phase and a bark oil, followed by removal of the aqueous phase to obtain a demetallized bark oil. The entire process of liquefaction and demetallization may be performed continuously or batchwise. The latter would minimize the required equipment.

In one embodiment, the bio-oil added in step g) is dispersed in a solvent. The dissolution of the added bio-oil may be performed either before or after the any addition of water. Addition of a water-insoluble solvent in step g) can be advantageous for the subsequent removal of the aqueous phase. The solvent aids in the separation of the aqueous phase from the bio-oil. The need for a solvent depends on the miscibility of the bio-oil with water, which can vary widely depending on the composition of the bio-oil. For example, tall oil pitch and crude tall oil are not readily miscible with water, thus, addition of a solvent to such bio-oils is not necessary from a phase separation standpoint. However, a solvent may be desirable for reducing the viscosity of a bio-oil to facilitate transport or mixing. The mixture of bio-oil and solvent is preferably in a liquid form at a temperature above 120°C, or above 150 °C.

In one embodiment the solvent added in step g) is selected from a water-insoluble C4-6 alcohol, preferably butanol; ethers, such as methyl tetrahydrofuran; alkyl acetates, such as butyl acetate or ethyl acetate; a liquid stream recycled from a hydroprocessing step, or mixtures thereof. The hydroprocessing step from which a liquid stream can be recycled may be the hydroprocessing in step k) according to the invention. Using a recycled stream lowers the requirement for fresh solvent. Solvents of bio-renewable origin are preferred in the production of fuels and chemicals. In one embodiment of step g), one or more acids are added, preferably selected from mineral acids, e.g., hydrochloric acid, sulfuric acid, or nitric acid; or from organic acids, such as citric acid, formic acid, lactic acid, oxalic acid or acetic acid. More preferably sulfuric acid or nitric acid is added in step g). The addition of the one or more acids preferably adjusts the pH of the aqueous phase in the mixture to a pH of 0-6, preferably a pH of 0-4, more preferably a pH of 0-2, even more preferably the pH is less than 1. In an alternative embodiment, the addition of the one or more acids adjusts the pH of the aqueous phase in the mixture to a pH of 1-4, preferably a pH of 1-2.

The addition of an acid neutralizes or acidifies the liquid comprising the bark oil. If sufficient acid is added in step d), any acid addition in step g) may be omitted. The acid added in step d) and the acid added in step g) could be the same or different.

The mixtures of step c) and g) may be obtained by any suitable mixing method.

The present method allows for a large amount of water to be present in the mixture when it is heated during demetallization. The mixture may have a water content of from 10 to 90 wt%, based on the total weight of the mixture, preferably 15-75 wt%, and more preferably 20-60 wt%. Increasing the water content improves removal of metals. Alternatively, repeating the steps without increasing the water content can also improve the removal of metals.

The desired temperature in step h), may be reached by pre-heating the bark oil or the liquids added in step g); or by direct heating of the mixture obtained in step g). When the contents of step g) are pre-heated prior to obtaining the mixture in step g), said mixture is obtained at a time point when said contents are still warm or hot. Preferably, when step h) is carried out for the first time, the temperature is from 120 °C to 200 °C, more preferably from 130 °C to 200 °C and not including 200 °C, and most preferably from 130 °C to 190 °C. This temperature is required for effective decomposition of the phospholipids and subsequent phosphorus removal. However, when step g) is repeated, the phospholipids have already been decomposed and lower temperatures may be used, such as from 10 °C to 200 °C, preferably from 10 °C to 190 °C. The temperature used, depends on the composition of the bio-oil, whereby the temperature used shall be sufficient for phase separation. When the biomass does not contain phospholipids, lower temperatures, such as from 10 °C to 200 °C, preferably from 10 °C to 190 °C. may also be used the first time step h) is carried out.

A higher temperature facilitates a lower content of phosphorus in the obtained demetallized bio-oil. However, if the temperature is too high, e.g., above 200 °C, the separation of the organic and aqueous phases becomes more difficult due to increasing emulsification. Additionally, temperatures below 200 °C are preferred to avoid excess energy usage in the form of heat input beyond that required for an efficient phase separation.

When steps are repeated, lower temperatures may be used in subsequent repetitions than originally used. Heavy bio-oils with high viscosities require higher temperatures than lighter bio-oils to achieve effective mixing and, subsequently, an efficient phase separation. The use of a solvent can be advantageous to decrease the viscosity of the lignin oil without increasing the temperature.

The mixture of step g) may be subjected to the desired temperature gradually, continuously, or in several stages over a period of time. The time required for heating depends on the rate of heating and the thoroughness of mixing. The mixture is subjected to the desired temperature for a period of from 0.01 to 10 minutes.

After heat treatment in step h) a liquid fraction comprising an aqueous phase and a bark oil is obtained. The aqueous phase may have formed through dehydration reactions or derive from the water content of the biomass, an aqueous solution of the base added in step e), and/or addition of water in the optional step f). In one embodiment, the phases of the mixture in step h) are allowed to separate before water is removed. The time required for phase separation depends on the temperature of the mixture, the composition of the mixture, the optional addition of an emulsion breaker, and the process equipment used. Phase separation can be carried out in a batch process or a continuous process. In a continuous process using a decanter, for example, the mixture is continuously fed to the decanter, while an aqueous stream and an organic stream are continuously removed from the decanter.

Removal of the aqueous phase from the bark oil is critical for the removal of metals from the bark oil, as the metals are partitioned into the aqueous phase. Poor phase separation thereby results in poor demetallization performance. Removal of the aqueous phase by evaporation does not facilitate demetallization, as the metals are then not removed with the water. Removal of the aqueous phase can be facilitated by the use of mechanical means, such as a centrifuge, decanter, decanter centrifuge, coalescer, electrostatic coalescer, oil desalter, API (American Petroleum Institute) separator, rotating separator, or by any combination of these; electrical means, such as electrostatic desalting units; chemical means, such as addition of an emulsion breaker; or by any combination of these. Suitable emulsion breakers, also known as demulsifiers, are selected from amines, such as octylamine or dioctylamine; alcohols, such as ethanol or long-chain alcohols; polyhydric alcohols, such as propylene glycol or polyethylene glycol; fatty acid alkoxylates; oxyalkylated alkyl phenols; oxyalkylated alkyl resins; sulfonates; other nonionic surfactants comprising both hydrophilic and hydrophobic groups; or any combination thereof. The removal of the aqueous phase in the method disclosed herein does not involve the use of enzymes.

When removal of the aqueous phase in step i) is facilitated by the use of mechanical means, the need for repeating the washing steps may be eliminated due to the effectiveness of the phase separation resulting in efficient removal of metals.

In one embodiment, removal of the aqueous phase in step i) is carried out by decanting. After decanting, residual water containing metals may be removed from the liquid fraction comprising the bark oil by mechanical means, electrical means, or chemical means, or any combination of these. In embodiments, the residual water is removed by any one of distillation, evaporation, membrane separation, or by liquid-liquid extraction.

In one embodiment, after removal of the aqueous phase in step i) using a decanter, the bark oil is subjected to centrifugation to remove any remaining water.

While optional, repeating steps g)-i) enables further reduction of the total metal content, including further phosphorus removal. In one embodiment, an acid is added the first time step g) is carried out, and when repeated, water without acid is added. Using water without acid in the final repetition of step b) reduces the corrosivity of the demetallized bark oil in downstream processing, thus without needing a base for neutralization. Addition of a base to the demetallized bark oil is not desirable, as this would result in the addition of metals, nitrogen compounds, or other species that are hydroprocessing catalyst inhibitors or catalyst poisons.

The aqueous phase in step i) may be demineralized and/or extracted with an organic solvent to separate organic compounds from the aqueous phase. The water added in step g) may be demineralized water, including distilled water; or the aqueous phase recycled from step i). Recycling of the aqueous phase may be performed to reduce the need for demineralized water, whereby recycled water is used the first time or times step g) is carried out, and fresh water is used when step g) is repeated, at least once. Using demineralized water in the final execution of step g) ensures that no metals are introduced to the bark oil from the wash water.

Residual water, when present in the demetallized bark oil, may be removed by distillation, evaporation, membrane separation, liquid-liquid extraction or any other suitable method. The obtained demetallized bark oil preferably has a water content of less than 10 wt%, more preferably of from 0.01 to 5 wt%, most preferably 0.01 to 1 wt%. In one embodiment the bark oil obtained in i) is subjected to further treatment, such as hydroprocessing, Fluid Catalytic Cracking (FCC), steam cracking, or gasification, to obtain fuel or chemicals; preferably hydroprocessing.

Hydroprocessing of the bark oil may comprise passing the bark oil through a guard bed, followed by hydrotreating and optionally, mild hydrocracking and/or hydrodewaxing, and lastly, optionally hydrofinishing the bio-oil with various catalysts. Fractionation is performed to obtain the product fuels and/or chemicals. Hydroprocessing, hydrotreatment, hydrocracking, hydrodewaxing, hydrofinishing and fractionation are concepts well known to the skilled person.

In one embodiment, the method further comprises extraction or fractionation of the obtained bark oil. The extraction or fractionation is preferably performed at a pressure of from 0.1 mbar to 1 bar, and a temperature of from 50 °C to 400 °C.

Removal of low-boiling components, such as water, methanol, ethanol, formic acid, acetic acid, or ethyl acetate, from the bark oil would shift the lower boiling points to higher temperatures.

In one embodiment, the demetallized bark oil obtained by the method according to the invention has a total metal content of less than 200 ppm, preferably of from 0 to 50 ppm, more preferably of from 0 to 20 ppm, even more preferably of from 0 to 10 ppm, and a total phosphorus content of less than 10 ppm, preferably of from 0 to 5 ppm.

In a second aspect, the present invention relates to a bark oil obtainable by the method according to the present invention, wherein the total content of char and/or solid residue in the bark oil is from 0 to 5 wt%. Preferably, the total content of char and/or solid residue in the bark oil is from 0 to 2 wt%, more preferably of from 0 to 1 wt%, most preferably 0 wt%. In one embodiment, the water content of the bark oil is from 0 to 10 wt%, preferably from 0 to 5 wt%.

In one embodiment, the bark oil is characterized by: i. a boiling point distribution of up to 700 °C, preferably from 70 °C to 700 °C, more preferably of from 100 to 675 °C, with at most 20 wt% boiling above 440 °C, and at most 10 wt% boiling above 500 °C, ii. a water content of from 0 to 5 wt%, iii. a caloric value of from 10 to 45 MJ/kg, and iv. an oxygen content of from 5 to 35 wt%, preferably of from 5 to 25 wt%.

The boiling point distribution of the bark oil depends on the kind or kinds of bark used for the preparation of the bark oil. Addition of a solvent to the bark oil underlies the presence of the lower boiling points. The boiling point distribution may be attained through simulated distillation. In one embodiment, the bio-oil obtainable with the method according to the present invention, has a Final Boiling Point (FBP) below 700 °C, preferably below 650 °C, more preferably below 640 °C.

In one embodiment, the bark oil additionally comprises a non-aqueous solvent. Preferably, the non-aqueous solvent comprises one or more alcohols. The alcohols may remain from the preparation of the bark oil or may have been added afterwards. The amount of non-aqueous solvent in the bark oil affects its caloric value and oxygen content.

In one embodiment, the bark oil has a total metal content of less than 200 ppm, preferably of from 0 to 50 ppm, more preferably of from 0 to 20 ppm, even more preferably of from 0 to 10 ppm. As used herein the total metal content preferably refers to the content of metal selected from aluminium, calcium, magnesium, manganese, phosphorus, potassium, and sodium. Preferably, the bark oil has a total phosphorus content of less than 10 ppm, preferably of from 0.2 to 5 ppm, more preferably of from 0 to 2 ppm.

In a further aspect the present invention relates to the use of a bark oil according to the present invention in extraction or fractionation.

Different components can be recovered from the bark oil according to the present invention via fractionation, extraction, or other separation methods. Among these components are long-chain suberin acid monomers and their alkyl esters, fatty acids and esters thereof, fatty alcohols, a,<n-diacids, oj-hydroxyacids, hydroxycinnamic acids, partially hydrolyzed suberin, monoacylglycerols, tannins, polyphenols (lignans, stilbenes, monomeric flavonoids), lignin phenolic monomers and oligomers, glycerol, terpenes (turpentine), triterpenoids, phenolic acids and their esters, acetophenones, sterols, steryl esters, resins, or resin acids and their esters.

Fractions of the bark oil can be further refined into products that are typically made from crude oil feedstocks, such as gas and liquid fuels, olefins, aromatics, alcohols, glycols, ethers, glycol ethers, ethylene oxide, propylene oxide, alkyl acetates, polyols, aldehydes, ketones, isoparaffins, paraffins, naphthenics, waxes, acetone, phenols, styrene, ethoxylates, nonenes, and other chemicals.

Components of bark oil can be utilized as feedstocks for other processes, such as polyester synthesis via transesterification of fatty acid esters. Other potential uses include use as base oils, process oils, lubricants, transformer oils, white oils, medical white oils, tire oils, rubber oils, greases, adhesives, plasticizers, polyethylene battery separators, wood treatments, anti-caking oils, printing inks, silicone sealants, ammonium nitrate/fuel oil and emulsion-based industrial explosives, metalworking fluids, hydraulic fluids, heat transfer fluids, compressor oils, solvents, mineral spirits, paints, defoamers, aerosols, detergents, engine oils, gear oils, de-icing fluids, polycarbonates, polyolefins, polystyrenes and other styrene polymers, alpha olefins, internal olefins, polyurethanes, resole phenolic resins and other resins, pour point depressants, packaging, cosmetics, coatings.

Organic compounds recovered from the aqueous phase in the method for the preparation of bark oil according to the present invention, such as sugars and sugar derivatives, glucuronic acids, furfural and derivatives; volatile alcohols, aldehydes, ketones, acetic acid and other acids; amino acid derivatives, such as amines, amides, indoles, quinolines, may be recovered and used in other processes, such as fermentation of sugars, as nutrients for biological processes, or for methane production via anaerobic digestion.

The present invention will now be further illustrated by the below examples. The presented examples should not be seen as limiting the scope of the invention, and the skilled person would realize that there are obvious alternatives and modifications that could be carried out. Experimental methods presented without specific conditions in the following examples generally follow the conventional conditions known to the person skilled in the art. Unless otherwise stated, parts and percentages are parts by weight and weight percent.

EXAMPLES

EXAMPLES 1-6

Liquefaction of biomass:

60 g biomass (a dried, ground mixture of pine and spruce bark), 60 g of a base, and 280 g of a non-aqueous fluid were added to an autoclave. The mixture was heated to a first temperature, Tl, and held at this temperature with stirring for a time, tl. Subsequently, the temperature was increased to a second temperature, T2, and kept at this level for a time, t2, while stirring. A liquid comprising an oil-phase was obtained. The results are presented in Table 1. Table 1

*) Not determined

For each one of the Examples 1-4 of Table 1, 100% liquefaction was achieved and no char formation was observed in the obtained bio-oil. Examples 5-6, catalyzed by NaOH, still contained unreacted material with visible particles remaining in the obtained biooil.

Acidification and salt separation

For each one of the Examples 1-4 of Table 1, where 100% liquefaction was achieved, acidification and salt separation were performed according to the below procedure. The contents in the autoclave were cooled to 60 °C and transferred into a beaker. Concentrated sulfuric acid (23 mL) was slowly added to the mixture. A salt precipitation was formed. The liquid containing the precipitation was filtrated over a 22 pm retention filter paper in a Buchner funnel. The precipitated salt formed a filter cake on the filter paper. The precipitated salt was rinsed with ethanol. The ethanol was removed from the filtrate comprising the bio-oil using a rotary evaporator.

EXAMPLE 7

Demetallization

100 mL of bio-oil from Example 1 was added to an autoclave. Sulfuric acid in water (100 mL, pH 1) was added to the bio-oil. The mixture was stirred while heated to about 170 °C. After the target temperature was reached, the stirring was turned off, and the two phases were given 30 minutes to separate. After the contents in the autoclave had cooled to 90 °C, for ease of handling, the contents were transferred to a separation funnel. 50 mL of butanol and 50 mL of 2-methyl tetrahydrofuran were added to the biooil sample. An aqueous phase and an oil phase were collected. The water and butanol were boiled off using a rotary evaporator, leaving the isolated bio-oil.

RESULTS

Liquefaction of the biomass into a bark oil was achieved, whereby no char formation was observed. The simulated distillation of the demetallized bio-oil was done by gas chromatography (EN 15199-1), whereby the entire sample was vaporized and exited the column, showing that no solids were present. The simulated distillation curve is shown in Figure 1, presenting the cumulative weight percentage recovered as a function of the boiling point of the components of the sample, and IN Figure 2, presenting the area percentage as a function of the boiling point of the components of the sample. The final boiling point of the bio-oil obtained in Example 1 was determined to be 654 °C.

Elemental analysis of the resulting bark oil was made by a LECO CHN elemental analyzer using a combustion method and the results are shown in Table 2.

Table 2: Bark and bark oil properties

The metal contents of the bark oil and the demetallized bark oil were analyzed using inductively coupled plasma mass spectroscopy (ICP SCAN CM-38) and the results are shown in Table 3.

Table 3: Demetallization results: Metal analyses of bark oil and treated products

Claims

1. A method for the preparation of a bark oil, comprising the steps of: a) adding a biomass comprising at least 50 wt% bark, calculated as dry bark on the total dry weight of the biomass, wherein the biomass contains of from 0.1 to 65 wt% water, preferably from 1 to 45 wt%, more preferably from 1 to 40 wt% water, as calculated on the total weight of the biomass; b) adding a base comprising potassium ions, preferably a base selected from potassium hydroxide, potassium alkoxide and/or potassium hydride; and a non-aqueous fluid comprising methanol, ethanol, propanol, or a bio-oil, e.g. a bark oil, preferably ethanol, to the biomass; c) obtaining a mixture comprising the biomass, the base, and the non-aqueous fluid, and subjecting said mixture to thermal treatment at a temperature of from 100 °C to 350 °C, preferably of from 120 °C to 300 °C, more preferably of from 150 °C to 250 °C, to obtain a bark oil; d) adding a first acid to the bark oil to precipitate salt; e) removing inorganic compounds from the bark oil; and f) optionally recycling the bark oil obtained in step c) or e), to step b).

2. The method according to claim 1, wherein the bark oil is subjected to subsequent demetallization after step d) or step e), wherein the demetallization comprises: g) adding one or more of water, a second acid, a bio-oil and a solvent to the bark oil to obtain a mixture thereof; h) subjecting the bark oil mixture obtained in the previous step to a temperature of from 10 °C to 320 °C, preferably of from 80 °C to 250 °C, more preferably of from 120 °C to 200 °C, to obtain a liquid fraction comprising an aqueous phase and a bark oil; i) removing the aqueous phase from the liquid fraction comprising the bark oil to obtain a demetallized bark oil; j) optionally repeating steps g)- i); and k) optionally subjecting the demetallized bark oil to hydroprocessing; whereby the demetallized bark oil obtained has a total metal content of less than 200 ppm, preferably of from 0 to 50 ppm, more preferably of from 0 to 20 ppm.

3. The method according to claim 1 or 2, wherein the biomass, or the combination of biomass and the non-aqueous fluid in c), has a water content of from 0.1- 65 wt%, preferably from 0.1-45 wt%, more preferably from 0.1 to 30 wt%, most preferably from 0.1 to 10 wt%, and not including 10 wt%.

4. The method according to any one of claims 1-3 wherein the non-aqueous fluid comprises a bio-oil, or a liquid stream recycled from a hydroprocessing step.

5. The method according to claim 4, wherein the bio-oil or liquid stream comprises a Ci-io alcohol selected from methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, glycerol, propylene glycol, cresol, resorcinol, hydroquinone, guaiacol, catechol, phenol or benzyl alcohol.

6. The method according to any one of one of claims 1-5 wherein the mixture of step c), comprises 5-50 wt% biomass, 1-35 wt% base, and 30-94 wt% of a non-aqueous fluid up to a maximum or a total of 100 %, as calculated on the total weight of the mixture.

7. The method according to any one of claims 1-6, wherein the demetallized bark oil undergoes hydroprocessing into fuel and/or chemicals.

8. The method according to any one of claims 1-7, wherein a bio-oil is added in step g) and/or is added as a non-aqueous fluid in step b), the bio-oil being independently selected from tall oil pitch, crude tall oil, pyrolysis oil, lignin oil, bark oil, e.g. bark oil recycled according to step f), hydrothermal liquefaction oil, turpentine, vegetable oil, oran oil obtained from any one of softwood, hardwood, bagasse, sawdust, other types of forest biomass, grass, algae, aquaculture residues, animal residues, agriculture raw materials, or agriculture residues; or combinations thereof.

9. The method according to any one of claims 1-8, wherein the solvent added in step g) is selected from a water-insoluble C4-6 alcohol, preferably butanol; ethers, such as methyl tetrahydrofuran; alkyl acetates, such as butyl acetate or ethyl acetate; a liquid stream recycled from a hydroprocessing step, or mixtures thereof.

10. The method according to any of claims 1-9, wherein the mixture in step c) is subjected to the desired temperature gradually, continuously, or in several stages over a period of time, whereupon any water present is removed.

11. The method according to claim 10, wherein during the thermal treatment the mixture in step c) is subjected at least one temperature in the range from 130 °C to 190 °C in a first heating stage, whereupon the mixture is subjected to at least one temperature in the range from 180 °C to 350 °C in a second heating stage.

12. The method according to claim 11, wherein the temperature of the second heating stage is higher than the temperature of the first heating stage, preferably by at least 20 °C.

13. The method according to claim 11 or 12, wherein the first heating stage lasts for a time period of 30 to 180 minutes, and the second heating stage lasts for a time period of from 30 to 120 minutes.

14. The method according to any of claims 1-13, wherein any of the first acid and second acid is independently a strong acid, preferably independently selected from sulfuric acid, hydrochloric acid, or nitric acid.

15. The method according to any of claims 2-14, wherein steps g)-i) are repeated at least once.

16. The method according to any of claims 2-15, wherein when the temperature in step h) is from 120 °C to 200 °C, and the total phosphorus content of the obtained demetallized bark oil in step i) is less than 10 ppm, preferably from 0.2 to 5 ppm, more preferably from 0 to 2 ppm.

17. The method according to any of claims 2-16, wherein the demetallized bark oil has a total metal content of less than 200 ppm, preferably of from 0 to 50 ppm, more preferably of from 0 to 20 ppm, even more preferably of from 0 to 10 ppm, and a total phosphorus content of less than 10 ppm, preferably of from 0 to 5 ppm.

18. The method according to any one of claims 1-17, further comprising extraction and/or fractionation of the obtained bark oil.

19. The method according to claim 18, wherein the extraction or fractionation is performed at a pressure of from 0.1 mbar to 1 bar, and a temperature of from 50 °C to 400 °C.

20. A bark oil obtainable by the method according to any one of claims 1-19, wherein the total content of char and/or solid residue in the bark oil is from 0 to 5 wt%.

21. The bark oil according to claim 20, wherein the water content is from 0 to 10 wt%, preferably from 0 to 5 wt%

22. The bark oil , according to claim 20 or 21, wherein the bark oil is characterized by: i. a boiling point distribution of up to 700 °C, preferably from 70 °C to 700 °C, more preferably of from 100 °C to 675 °C, with at most 20 wt% boiling above 440 °C, and at most 10 wt% boiling above 500 °C, ii. a water content of from 0 to 5 wt%, iii. a caloric value of from 10 to 45 MJ/kg, and iv. an oxygen content of from 5 to 35 wt%, preferably of from 5 to 25 wt%.

23. The bark oil according to any one of claims 20 to 22, wherein the bark oil have a total content of char and/or solid residue in the bark oil of from 0 to 2 wt%, preferably of from 0 to 1 wt%, more preferably 0 wt%.

24. The bark oil according to any one of claims 20 to 23, wherein the bark oil has a total metal content of less than 200 ppm, preferably of from 0 to 50 ppm, more preferably of from 0 to 20 ppm, more preferably of from 0 to 10 ppm.

25. The bark oil according to any one of claims 20 to 24, wherein the bark oil has a phosphorus content of less than 10 ppm, preferably from 0.2 to 5 ppm, more preferably of from 0 to 2 ppm.