Process for producing BIO-oil from lignin

Abstract

Process for producing bio-oil from lignin comprising the following steps: (a) subjecting the lignin to extraction of the oligomers in the presence of at least one alcohol having from 1 to 5 carbon atoms, preferably from 1 to 2 carbon atoms, operating at the boiling temperature of said alcohol or, in the case of a mixture of alcohols at the temperature of the higher-boiling alcohol, for a time comprised between 30 minutes and 90 minutes, preferably comprised between 40 minutes and 70 minutes, obtaining a liquid phase comprising oligomers and at least one alcohol and a solid phase comprising lignin essentially free of said oligomers; (b) subjecting the solid phase comprising lignin essentially free of said oligomers obtained in step (a) to depolymerization in the presence of at least one alcohol having from 1 to 5 carbon atoms, preferably from 1 to 2 carbon atoms, in supercritical conditions, operating at a temperature comprised between 200°C and 300°C, preferably comprised between 220°C and 295°C, at a pressure comprised between 40 bar and 170 bar, preferably comprised between 50 bar and 150 bar, for a time comprised between 5 minutes and 150 minutes, preferably comprised between 10 minutes and 130 minutes, obtaining: - (i) a gas phase; - (ii) a mixture comprising an oily phase consisting of bio-oil, a liquid phase comprising at least one alcohol and a solid phase comprising carbon residues ("char"), an oily phase consisting of bio-oil and, optionally, unconverted lignin; (c) recovering the oily phase consisting of bio-oil from the mixture (ii) obtained in step (b). The bio-oil obtained from the aforesaid process can be advantageously used, for example, as an antioxidant agent or anti-UV agent, in particular as an antioxidant agent or anti-UV agent in biofuels which can be used as such, or mixed with other fuels in diesel engines for automotive or aviation. Furthermore, the bio- 25 oil obtained from the aforesaid process can be advantageously used, for example, as an antioxidant agent in bio-feedstocks such as vegetable oils and animal or vegetable fats, in order to slow down their rancidity during transport and storage.

Description

[0001] PROCESS FOR PRODUCING BIO-OIL FROM LIGNIN

[0002] DESCRIPTION

[0003] The present invention relates to a process for producing bio-oil from lignin.

[0004] More in particular, the present invention relates to a process for producing bio-oil from lignin, comprising the following steps: (a) subjecting the lignin to extraction of the oligomers in the presence of at least one alcohol operating at specified conditions of temperature and time; (b) subjecting the lignin essentially free of said oligomers obtained in step (a) to depolymerization in the presence of at least one alcohol operating in supercritical conditions, at specified conditions of temperature, pressure and time; (c) recovering the oily phase consisting of bio-oil from the mixture obtained in step (b).

[0005] The bio-oil obtained from the aforesaid process can be advantageously used, for example, as an antioxidant agent or anti-UV agent, in particular as an antioxidant agent or anti-UV agent in biofuels which can be used as such, or mixed with other fuels in diesel engines for automotive or aviation. Furthermore, the biooil obtained from the aforesaid process can be advantageously used, for example, as an antioxidant agent in bio-feedstocks such as, for example, vegetable oils and animal or vegetable fats, in order to slow down their rancidity during transport and storage.

[0006] The present invention also relates to a bio-oil from lignin having the specific characteristics set out below.

[0007] Furthermore, the present invention also relates to the use of said bio-oil from lignin as an antioxidant agent or anti-UV agent, in particular as an antioxidant agent or anti-UV agent in biofuels which can be used as such, or mixed with other fuels in diesel engines for automotive or aviation.

[0008] In addition, the present invention also relates to the use of said bio-oil from lignin as an antioxidant agent in bio-feedstocks such as, for example, vegetable oils and animal or vegetable fats.

[0009] Lignin is one of the most industrially accumulated waste materials. The main source of lignin waste (the second most common natural polymer on the planet, after cellulose) comes from the paper industry. However, its disposal is very complicated and is presently carried out by means of incinerators, which are able to drastically reduce the volume thereof, while recovering energy. However, this process involves the production of contaminants in both gaseous and solid form, with consequent emissions of carbon dioxide (CO2) and carbon monoxide (CO). The remaining amount of lignin produced comes mainly from biorefineries, viz., biological processes such as treating lignocellulosic biomass in order to obtain biofuels. In said processes, cellulose is extracted with the aim of obtaining glucose, which is then used in the fermentation process from which bio-alcohol, in particular bio-ethanol, is obtained, with the consequent high added value. However, lignin remains a by-product and is disposed of, again, by incineration. The extraction of lignin from lignocellulosic biomass, which can be carried out by means of various technologies, for example, by chemical, physical, biological or mechanical means, is in fact necessary before subjecting said lignocellulosic biomass to the enzymatic hydrolysis process to obtain glucose, in order to avoid the inhibition of the enzymes usually used in said process.

[0010] Although processes for obtaining bio-oil from lignin for producing bio-fuels, especially diesel and naphtha cutting, are known, the not yet high yields and the complicated scalability of said processes sometimes make these technologies difficult to use industrially.

[0011] In patent literature, there are several patents and patent applications that aim to obtain bio-oil from partially depolymerized lignin with values, with respect to the starting lignin, lower than the O / C and O / H ratios and higher than the H / C ratio: in fact, these parameters, together with those characteristic of combustion (in particular, the High Heating Value (HHV) parameter), make the bio-oil obtained a good fuel for naphtha or diesel cutting, but not yet satisfactory for cutting such as petrol.

[0012] For example, US patent application US 2020 / 0231879 describes a process for producing a distilled fuel from lignin comprising: preparing a biomass-derived lignin solvent; dissolving the lignin in the solvent from biomass-derived lignin; and separating the undissolved lignin from the mineral matter to produce synthetic crude oil ("syncrude").

[0013] International patent application WO 2019 / 053287 describes a process for producing crude oil from lignin ("Crude Lignin Oil" - CLO), said process comprising the steps of providing a feedstock rich in lignin and subjecting it to a treatment in a polar organic solvent (for example, alcohols, ketones, esters or mixtures thereof) in the absence of an effective amount of a reaction promoter, such as a heterogeneous and / or homogeneous catalyst and / or hydrogen, and providing a lignin-based composition, said treatment comprising the step of contacting said lignin-rich feedstock with a polar organic solvent under the following operating conditions: temperature up to 210°C, pressure less than 50 bar and residence time up to 240 minutes, wherein the weight / volume (w / v) ratio between the lignin (in the lignin-rich feedstock) and the organic solvent is comprised between 1 : 1.5 and 1 : 15, or between 1 :2 and 1: 10, or between 1 :2 and 1 :5. The crude oil from lignin ("Crude Lignin Oil" - CLO), obtained from the aforesaid process is said to be particularly useful as a fuel or chemical component.

[0014] International patent application WO 2016 / 113280 describes a process for producing a liquid fuel from lignin, comprising the steps of: (i) providing a ligninrich solid residual from lignocellulosic biomass which has been hydrothermally pre-treated and subsequently subjected to enzymatic hydrolysis; (ii) subjecting the lignin-rich solid residual to a treatment in ethanol, propanol or butanol in supercritical conditions in the absence of an effective amount of a reaction promoter and (iii) recovering the liquid product from the reaction mixture comprising alcohol as a mixture of a heavy liquid fraction having a boiling point above 120°C and one or more light fractions having a boiling point below 120°C; wherein the water content, solid / solvent weight / weight (w / w) ratio, temperature and reaction time are selected so as to produce a heavy liquid fraction having an O:C ratio less than or equal to 0.20. Step (ii) of the aforesaid process can be carried out at a temperature comprised between 325°C and 450°C, for a time comprised between 0 and 8 hours, at a solid / solvent weight / weight (w / w) ratio comprised between 0.02 and 0.43.

[0015] International patent application WO 2010 / 037178 describes a process for producing bio-oil from lignocellulosic biomass, comprising the steps of: (a) extracting hemicellulose from the lignocellulosic biomass with a solvent; (b) recovering hemicellulose from step (a); and (c) solvating lignin and cellulose present in the lignocellulosic biomass after extraction of hemicellulose with a solvent, wherein the solvating step produces bio-oil. The bio-oil obtained from the aforesaid process is said to be advantageously used as bio-fuel or as a fuel additive.

[0016] The use of both lignin as such or its derivatives and depolymerized lignin as an antioxidant agent is also known.

[0017] For example, European patent EP 2435454 describes lignin derivatives recovered from a "pulping" treatment of lignocellulosic biomass wherein said lignin derivatives have an aliphatic hydroxyl content comprised between 1.5 mmol / g and 3.5 mmol / g, a Radical Scavenging Index (RSI) comprised between 35 and 60, and a weight-average molecular weight (Mw) comprised between 500 g / mol and 5000 g / mol. The aforesaid lignin derivatives are said to be usable as antioxidant agents in thermoplastic and thermosetting polymers.

[0018] International patent application WO 2009 / 028969 describes lignin polymers obtained from plant material by means of a process comprising:

[0019] (a) contacting a continuous flow of the plant material with a co-current or counter-current continuous flow of an aqueous ethanol solution at an elevated temperature and an elevated pressure, for a retention time sufficient to produce a solvent mixture comprising ethanol, ethanol-soluble lignin and water and a plant pulp material; and

[0020] (b) separating the plant pulp material from the liquid mixture and recovering the lignin polymers from the liquid mixture.

[0021] The aforesaid lignin polymers are said to be usable in various applications for the purpose of providing antioxidant, immunopotentiation, anti-mutagenic, antiviral and / or anti-bacterial activity and improving the general health of animals and humans.

[0022] Umar Y. et al, in “Renewable Energy” (2022), Vol. 182, p. 867-878, describe a process for depolymerizing lignin in the presence of glycerol as a co-solvent to give a bio-oil that can be used as an additive from renewable sources to biodiesel in order to improve its oxygen stability. However, the above-mentioned lignin depolymerization processes can have some drawbacks. For example, a low bio-oil yield (for example, less than 40% by weight with respect to the total weight of the lignin subjected to depolymerization), use of low solid (i.e., lignin) / solvent (for example, less than 0.50) weight / weight (w / w) ratios, use of high depolymerization temperatures (for example, greater than 300°C), obtaining high weight-average molecular weight (Mw) bio-oil (for example, greater than 1000 Daltons), high gas production [mainly carbon monoxide (CO) and carbon dioxide (CO2)], in particular when operating at high temperatures, solvent losses with negative effects on the process costs.

[0023] The Applicant has posed the problem of finding a process for producing biooil from lignin which is able to overcome the aforesaid drawbacks.

[0024] The Applicant has now found that the production of bio-oil from lignin can be advantageously carried out by means of a process comprising subjecting the lignin to an oligomer extraction step before subjecting it to a depolymerization step. In particular, the Applicant has now found a process for producing bio-oil from lignin comprising the following steps: (a) subjecting the lignin to extraction of the oligomers in the presence of at least one alcohol, operating at specified temperature and time conditions; (b) subjecting the lignin essentially free of said oligomers obtained in step (a) to depolymerization in the presence of at least one alcohol operating in supercritical conditions at specified conditions of temperature, pressure and time; (c) recovering the oily phase consisting of bio-oil from the mixture obtained in step (b), capable of overcoming the aforesaid drawbacks.

[0025] There are numerous advantages to be gained from the aforesaid process. For example, the aforesaid process allows to: obtain high bio-oil yields (i.e., yields comprised between 40% and 60% by weight with respect to the total weight of the lignin subjected to depolymerization); conduct the depolymerization, operating at high solid (i.e., lignin) / alcohol weight (w / w) ratios (i.e., weight ratios greater than 0.40); conduct the depolymerization at temperatures not exceeding 300°C; obtain a lower gas yield (mainly consisting of a mixture of hydrocarbons having from 1 to 4 carbon atoms and, at a lesser percentage, other gases, for example, carbon monoxide(CO)) (gas yield less than or equal to 5% by weight with respect to the total weight of the lignin subjected to depolymerization); recycle the solvent, i.e., the alcohol used, at the extraction and / or depolymerization step, reducing solvent losses; obtain low molecular weight bio-oils (i.e., weight-average molecular weight (Mw) less than or equal to 1100 Daltons and number-average molecular weight (Mn) less than or equal to 400 Daltons).

[0026] Furthermore, the aforesaid process, due to the lower gas yield, the possibility of operating at high solid (i.e., lignin) / alcohol weight / weight (w / w) ratios, the recycling of alcohol, and the specific temperature and time conditions, is easily scalable industrially.

[0027] In addition, the bio-oil obtained from the aforesaid process can be advantageously used, for example, as an antioxidant agent or anti-UV agent, in particular as an antioxidant agent or anti-UV agent in biofuels which can be used as such, or mixed with other fuels in diesel engines for automotive or aviation. Furthermore, the bio-oil obtained from the aforesaid process can be advantageously used, for example, as an antioxidant agent in bio-feedstocks such as, for example, vegetable oils and animal or vegetable fats, in order to slow down their rancidity during transport and storage.

[0028] Therefore, an aim of the present invention is a process for producing bio-oil from lignin, comprising the following steps:

[0029] (a) subjecting the lignin to extraction of the oligomers in the presence of at least one alcohol having from 1 to 5 carbon atoms, preferably from 1 to 2 carbon atoms, operating at the boiling temperature of said alcohol or, in the case of a mixture of alcohols at the temperature of the higher-boiling alcohol, for a time comprised between 30 minutes and 90 minutes, preferably comprised between 40 minutes and 70 minutes, obtaining a liquid phase comprising oligomers and at least one alcohol and a solid phase comprising lignin essentially free of said oligomers; (b) subjecting the solid phase comprising lignin essentially free of said oligomers obtained in step (a) to depolymerization in the presence of at least one alcohol having from 1 to 5 carbon atoms, preferably from 1 to 2 carbon atoms, in supercritical conditions, operating at a temperature comprised between 200°C and 300°C, preferably comprised between 220°C and 295°C, at a pressure comprised between 40 bar and 170 bar, preferably comprised between 50 bar and 150 bar, for a time comprised between 5 minutes and 150 minutes, preferably comprised between 10 minutes and 130 minutes, obtaining:

[0030] (i) a gas phase;

[0031] (ii) a mixture comprising an oily phase consisting of bio-oil, a liquid phase comprising at least one alcohol and a solid phase comprising carbon residues ("char"), an oily phase consisting of bio-oil and, optionally, unconverted lignin;

[0032] (c) recovering the oily phase consisting of bio-oil from the mixture (ii) obtained in step (b).

[0033] For the purpose of the present description and the following claims, the definitions of the numerical intervals always comprise the extreme values unless otherwise specified.

[0034] For the purpose of the present description and the following claims, the term "comprising" also includes the terms "which essentially consists of' or "which consists of'.

[0035] For the purpose of the present description and the following claims, the phrase "lignin essentially free of said oligomers" means that if present, said oligomers are present in an amount less than or equal to 1% by weight, preferably less than or equal to 0.5% by weight, with respect to the total weight of the lignin.

[0036] Any type of lignin, i.e., lignin deriving from the paper industry or from biorefineries, or from lignocellulosic materials of various kinds (e.g., grass clippings, pruning residuals, straw, grain processing waste, etc.) can be used for the purpose of the process object of the present invention.

[0037] In accordance with a preferred embodiment of the present invention, in said step (a), said lignin can be selected, for example, from: pre-treated lignin from biorefineries, i.e., deriving from a process wherein the starting lignocellulosic biomass is subjected to a "steam explosion" process to separate the cellulosic matrix from the lignin, which is then subjected to a purification step, obtaining dried and purified lignin; non-pretreated lignin, from biorefinery, i.e. deriving from a process wherein the starting lignocellulosic biomass is subjected to a "steam explosion" process to separate the cellulosic matrix from the lignin which is used as is without being subjected to a purification step.

[0038] Preferably, said lignocellulosic biomass can be selected, for example, from:

[0039] - plants specifically cultivated for energy use such as, for example, miscanthus, panicum (Panicum virgatuni), common reed (Arundo donctx

[0040] - plants not specifically cultivated for energy use such as, for example, sorghum

[0041] (for example, sorghum fibre);

[0042] - scraps, residues and waste products from agriculture such as, for example, guayule, maize (for example, maize stalks, maize cobs), soybean, cotton, flax, rapeseed, wheat (for example, wheat straw), rice (for example, rice straw, rice hulls, rice husk), sugar cane (for example, sugar cane straw, sugar cane bagasse), palm (for example, palm leaves, palm trunks, palm mibrids, palm empty fruit bunches);

[0043] - scraps, residues and waste products from forestry, silviculture, or wood processing such as, for example, poplar, alder, birch;

[0044] - scraps from agri-food products intended for human consumption or animal husbandry;

[0045] - residues, not chemically treated, from the paper industry;

[0046] - waste from separate collection of municipal solid waste (for example, municipal vegetable waste, paper);

[0047] - algae such as, for example, microalgae or macroalgae, in particular macroalgae.

[0048] In accordance with a preferred embodiment of the present invention, before being subjected to said step (a) of extraction, said lignin can be subjected to a preliminary grinding process. Preferably, said lignin can be ground up to obtaining particles having a diameter comprised between 0.05 mm and 0.5 mm, more preferably comprised between 0.08 mm and 0.15 mm. Particles having a diameter less than 0.15 mm are particularly preferred.

[0049] In accordance with a preferred embodiment of the present invention, in said step (a) said at least one alcohol can be selected, for example, from methanol, ethanol, propanol, butanol, pentanol, or mixtures thereof; preferably from methanol, ethanol, or mixtures thereof.

[0050] In accordance with a preferred embodiment of the present invention, in said step (a) said lignin and said at least one alcohol can be used in a weight / weight (w / w) ratio comprised between 0.05 and 1.1, preferably comprised between 0.1 and 1.

[0051] In accordance with a preferred embodiment of the present invention, before being subjected to depolymerization, the solid phase comprising lignin essentially free of oligomers obtained in said step (a) can be subjected to washing with at least one alcohol having from 1 to 5 carbon atoms, preferably from 1 to 2 carbon atoms, even more preferably with the alcohol used in said step (a) of extraction, in an amount such as to maintain the weight / weight (w / w) ratio used in said step (a), and subsequently to filtration and drying.

[0052] In accordance with a preferred embodiment of the present invention, the liquid phase comprising oligomers and at least one alcohol obtained in said step (a) can be subjected to evaporation, for example under vacuum or by means of rotation, obtaining alcohol and a solid residue comprising lignin. The alcohol obtained can be recycled to the extraction step (a) and / or the following depolymerization step (b). The solid residue comprising lignin can be dried and used as fuel, or sent as such to depolymerization step (b). Preferably, said solid residue comprising lignin is sent as such to depolymerization step (b).

[0053] In accordance with a preferred embodiment of the present invention, in said step (b) said at least one alcohol can be selected, for example, from methanol, ethanol, propanol, butanol, pentanol, or mixtures thereof; preferably from methanol, ethanol, or mixtures thereof.

[0054] It should be noted that, for the purpose of the process object of the present invention, said at least one alcohol used in extraction step (a) and in depolymerization step (b) can be either of synthetic origin or of bio-origin (bioalcohol).

[0055] In accordance with a preferred embodiment of the present invention, in said step (b) said lignin and said at least one alcohol can be used in a weight / weight (w / w) ratio comprised between 0.45 and 1.1, preferably comprised between 0.48 and 1.

[0056] The gas phase (i) obtained in step (b) of the aforesaid process is generally less than or equal to 5% by weight with respect to the weight (dry weight) of the starting lignin. Said gas phase consists mainly of a mixture of hydrocarbons having from 1 to 4 carbon atoms or other gases [for example, carbon monoxide (CO)]. Such a gaseous phase, after separation, a separation which can be carried out for example by depressurization of the pressure vessel in which said step (b) is carried out, before the mixture (ii) obtained in said step (b) is sent for separation, is generally sent for further treatments in order to enhance its combustible organic component.

[0057] In accordance with a preferred embodiment of the present invention, step (c) of recovery of the oily phase consisting of bio-oil comprises the following steps: (ci) subject the mixture (ii) obtained in step (b) to separation, obtaining:

[0058] (iii) a solid phase comprising carbon residues (“char”), an oily phase consisting of bio-oil and, optionally, unconverted lignin;

[0059] (iv) a liquid phase comprising an oily phase consisting of bio-oil and at least one alcohol;

[0060] (c2) subjecting the solid phase (iii) obtained in step (cl) to purification and separation obtaining:

[0061] (v) an oily phase consisting of bio-oil;

[0062] (vi) a solid phase comprising carbon residues (“char”) and, optionally, unconverted lignin;

[0063] (c3) combining the oily phase consisting of bio-oil (v) obtained in step (c2) to the liquid phase comprising an oily phase consisting of bio-oil and at least one alcohol (iv) obtained in step (cl) and subjecting the whole to evaporation obtaining:

[0064] (vii) an oily phase consisting of bio-oil; (viii) a liquid phase comprising at least one alcohol.

[0065] In accordance with a preferred embodiment of the present invention, said separation step (ci) can be carried out, for example, by means of filtration, decantation, centrifugation, preferably by means of filtration.

[0066] In accordance with a preferred embodiment of the present invention, said purification step (ci) can be carried out, for example, by means of washing with at least one alcohol, preferably with at least one alcohol used in depolymerization step (b), more preferably methanol, ethanol, or mixtures thereof.

[0067] In accordance with a preferred embodiment of the present invention, in said step (C2) the separation can be carried out, for example, by means of filtration, decantation, centrifugation, preferably by means of filtration.

[0068] At the end of the purification and separation step (C2): the solid phase comprising carbon residues ("char") and optionally unconverted lignin (vi) can be dried, for example, in an oven, so as to remove the residual alcohol and fed to the depolymerization step (b); the oily phase consisting of bio-oil (v) is combined with the liquid phase (iv) obtained in the separation step (ci) and the whole is subjected to the evaporation step (C3), for example, under vacuum or by means of rotation.

[0069] The liquid phase comprising at least one alcohol (viii) can be purified in order to recover pure (i.e., regenerated) alcohol by means of distillation under vacuum, which can be fed to the extraction step (a) and / or to the depolymerization step (b), while the oily phase (vii) comprising bio-oil can be used as such.

[0070] As mentioned above, the present invention also relates to bio-oil from lignin obtained by the aforesaid process.

[0071] Accordingly, a further aim of the present invention is a bio-oil from lignin having the following characteristics: weight-average molecular weight (Mw) less than or equal to 1100 Daltons, preferably comprised between 560 Daltons and 1000 Daltons; number average molecular weight (Mn) less than or equal to 400 Daltons, preferably comprised between 250 Daltons and 390 Daltons; percentage variation between the H / C ratio of the bio-oil from lignin and the H / C ratio of the starting lignin equal to at least 3% more, preferably comprised between 5% more and 50% more, compared to the H / C ratio of the starting lignin; percentage variation between the H / O ratio of the bio-oil from lignin and the H / O ratio of the starting lignin equal to at least 25% more, preferably comprised between 28% more and 120% more, compared to the H / C ratio of the starting lignin.

[0072] As mentioned above, the present invention relates to the use of bio-oil from lignin as an antioxidant agent or anti-UV agent.

[0073] Accordingly, it is a further aim of the present invention to use bio-oil from lignin as an antioxidant agent or anti-UV agent, preferably as an antioxidant agent or anti-UV agent in bio-fuels which can be used as such, or in mixtures with other fuels in diesel engines for automotive or aviation.

[0074] It is also a further aim of the present invention the use of bio-oil from lignin as an antioxidant agent in bio-feedstocks such as vegetable oils and animal or vegetable fats.

[0075] The present invention will now be illustrated in greater detail through an embodiment with reference to Figure 1 reported below.

[0076] Figure 1 schematically illustrates an embodiment of the process object of the present invention. For this purpose, lignin (1) (for example, lignin from a biorefinery) is subjected to an oligomers extraction step (2) in the presence of at least one alcohol (for example, methanol, ethanol), obtaining a liquid phase (3) comprising oligomers and at least one alcohol, and a solid phase (4) comprising lignin essentially free of oligomers. Said solid phase (4), after optional washing with alcohol (for example, methanol, ethanol), filtration and drying, is subjected to a depolymerization step (5) in the presence of at least one alcohol (for example, methanol, ethanol), obtaining a gas phase (6) and a mixture (7) comprising an oily phase consisting of bio-oil, a liquid phase comprising at least one alcohol and a solid phase comprising carbon residues ("char"), an oily phase consisting of bio-oil and, optionally, unconverted lignin. Said mixture (7) is sent to separation (8) (for example, by filtration), obtaining a solid phase (10) comprising carbon residues ("char"), an oily phase consisting of bio-oil and, optionally, unconverted lignin, and a liquid phase (9) comprising an oily phase consisting of bio-oil and at least one alcohol. The solid phase (10) is subjected to purification and separation (11), obtaining an oily phase (13) consisting of bio-oil which is combined with the liquid phase (9) comprising an oily phase consisting of bio-oil and at least one alcohol and a solid phase (12) comprising carbon residue ("char") and optionally unconverted lignin which can be dried in order to remove the alcohol completely and subsequently recycled to the depolymerization step (not shown in Figure 1). The liquid phase (9) to which the oily phase (13) consisting of bio-oil has also been added is sent to evaporation (14), obtaining a liquid phase (15) comprising at least one alcohol which is recycled to the extraction step (2) and / or to the depolymerization step (5) and an oily phase (16) comprising bio-oil.

[0077] In order to better understand the present invention and to put it into practice, some illustrative and non-limiting examples thereof are reported below.

[0078] Analysis and characterization methods

[0079] The analysis and the characterization methods reported below were used. Determination of the molecular weight

[0080] The bio-oil obtained in the following examples was subjected to molecular weight determination by Gel Permeation Chromatography (GPC) on an Agilent 1100 GPC using two PFG M (PSS) columns connected in series with an Agilent 1100 VWD / UV detector operating at wavelengths comprised between 200 nm and 300 nm, connected in turn to an RI detector with hexafluoro-2-propanol (HFIP) eluent. The samples of bio-oil from lignin obtained in the examples provided below were diluted in hexafluoro-2-propanol (HFIP) at a concentration of approximately 5 mg / mL. The samples were then filtered on 0.2 nm polytetrafluroethylene (PTFE) filters before being inserted for analysis. The analysis was carried out at a flow rate of 1 mL / min, at 40°C, for approximately 40 minutes.

[0081] The weight-average molecular weight (Mw), number-average molecular weight (Mn) and poly dispersity index (i.e., the Mw / Mnratio) were assessed by means of polyethylene terephthalate (PET) standards. Determination of H / C and H / O ratios

[0082] For this purpose, the elemental analysis CHNS(O) was performed using an ICP-OES analyser (ICAP 6500 DV Thermo Fisher Scientific, Waltham, MA, USA). This analysis allows the amounts of carbon (C), hydrogen (H), nitrogen (N), sulphur (S) and oxygen (O) present in a sample to be determined.

[0083] After thoroughly washing with ethanol and drying all the instruments, the following steps were taken.

[0084] The sample to be analysed (2 mg) was placed in a tin crucible which was then closed to ensure that the sample was well sealed inside. The crucible was then placed in the aforesaid elemental analyser and, using the software connected to it, the percentages of C, H, N and S were obtained. From these values, the H / C and H / O ratios were obtained.

[0085] EXAMPLE 1

[0086] Production of bio-oil from lignin

[0087] In a 250 ml reactor, 64.52 g of pre-treated lignin from biorefineries, i.e., deriving from a process wherein the starting lignocellulosic biomass was subjected to a "steam explosion" process to separate the cellulosic matrix from the lignin, which was subsequently subjected to a purification step, obtaining dried and purified lignin, comprising oligomers in an amount equal to approximately 7% by weight with respect to the total weight of the dry lignin, and 387.1 g of methanol (Aldrich) [lignin / methanol (w / w) ratio of 0.17], were placed: the whole was kept, under stirring, at 65°C, for 60 minutes, obtaining a liquid phase comprising oligomers and methanol equal to 391.61 g and a solid phase comprising lignin essentially free of oligomers in an amount equal to 60 g.

[0088] The liquid phase was subjected to evaporation by means of Rotavapor operating at 650 mbar and 85°C, for 30 minutes, in order to recover the methanol (387.1 g) which can be recycled to the oligomer extraction step and / or to the depolymerization step and the oligomers (4.52 g). The solid residue comprising lignin can be sent as such to depolymerization.

[0089] The solid phase (60 g) was fed to a 500 ml reactor to which 120 g of methanol was added [lignin / methanol (w / w) ratio equal to 0.5]: the whole was kept, under stirring, at 250°C, at 130 bar, for 120 minutes, obtaining a gas phase (about 3.5 g) which was removed by depressurization and a mixture comprising an oily phase consisting of bio-oil, a liquid phase comprising methanol and a solid phase comprising carbon residues ("char"), an oily phase consisting of bio-oil and unconverted lignin.

[0090] The aforesaid mixture was subjected to separation by means of filtration, obtaining a solid phase comprising carbon residues ("char"), an oily phase consisting of bio-oil and unconverted lignin (40 g), and a liquid phase comprising an oily phase consisting of bio-oil and methanol (136.5 g).

[0091] Subsequently, the aforesaid solid phase was subjected to purification and separation. For this purpose, said solid phase was placed in a 250 ml beaker, equipped with a magnetic stirrer, and 100 g of pure methanol was added: the whole was kept, under stirring, at room temperature (25°C), for 15 minutes. At the end, the resulting mixture was subjected to separation by means of filtration twice, obtaining an oily phase consisting of bio-oil (105 g), which was then combined with the aforesaid liquid phase comprising an oily phase consisting of bio-oil and methanol, and a solid phase comprising carbon residues ("char") and unconverted lignin, which was dried in an oven, at 85°C and 10 mbar, for 10 hours so as to completely remove the residual methanol: the amount of final dried solid corresponds to approximately 30 g.

[0092] The liquid phase obtained by combining the liquid phase comprising an oily phase consisting of bio-oil and methanol (136.5 g) with the oily phase consisting of bio-oil (105 g), was subjected to evaporation by means of Rotavapor operating at 650 mbar and 85°C, for 30 minutes, obtaining an oily phase consisting of bio-oil (approximately 26.9 g - yield 45%) and a liquid phase comprising methanol (214.6 g) which can be recycled to the oligomer extraction step and / or to the depolymerization step.

[0093] The oily phase consisting of bio-oil was subjected to molecular weight and H / C and H / O ratio determination, operating as described above.

[0094] The results obtained were as follows: weight-average molecular weight (Mw) 641.5 Daltons; number-average molecular weight (Mn) 221 Dalton;

[0095] H / C ratio equal to 0.16 (starting lignin H / C ratio equal to 0.12);

[0096] H / O ratio equal to 0.30 (starting lignin H / O ratio equal to 0.14).

[0097] EXAMPLE 2

[0098] Production of bio-oil from lignin

[0099] In a 250 ml reactor 64.52 g of pre-treated lignin from biorefineries, i.e., deriving from a process wherein the starting lignocellulosic biomass was subjected to a "steam explosion" process to separate the cellulosic matrix from the lignin, which was subsequently subjected to a purification step, obtaining dried and purified lignin, comprising oligomers in an amount equal to approximately 7% by weight with respect to the total weight of the dry lignin, and 516.2 g of ethanol (Aldrich) [lignin / ethanol (w / w) ratio of 0.125], were placed: the whole was kept, under stirring, at 78°C, for 60 minutes, obtaining a liquid phase comprising oligomers and ethanol equal to 520.72 g and a solid phase comprising lignin essentially free of oligomers in an amount equal to 60 g.

[0100] The liquid phase was subjected to evaporation by means of Rotavapor operating at 650 mbar and 85°C, for 30 minutes, in order to recover the ethanol (516.2 g) which can be recycled to the oligomer extraction step and / or to the depolymerization step and the oligomers (4.5 g). The solid residue comprising lignin can be sent as such for depolymerization.

[0101] The solid phase (60 g) was fed to a 500 ml reactor to which 120 g of ethanol was added [lignin / ethanol (w / w) ratio equal to 0.5]: the whole was kept, under stirring, at 250°C, at 130 bar, for 120 minutes, obtaining a gas phase (about 3.4 g) which was removed by depressurization and a mixture comprising an oily phase consisting of bio-oil, a liquid phase comprising ethanol and a solid phase comprising carbon residues ("char"), an oily phase consisting of bio-oil and unconverted lignin.

[0102] The aforesaid mixture was subjected to separation by means of filtration, obtaining a solid phase comprising carbon residues ("char"), an oily phase consisting of bio-oil and unconverted lignin (40 g), and a liquid phase comprising an oily phase consisting of bio-oil and ethanol (136.6 g). Subsequently, the aforesaid solid phase was subjected to purification and separation. For this purpose, said solid phase was placed in a 250 ml beaker, equipped with a magnetic stirrer, and 100 ml of pure ethanol was added: the whole was kept, under stirring, at room temperature (25°C), for 15 minutes. At the end, the resulting mixture was subjected to separation by means of filtration twice, obtaining an oily phase consisting of bio-oil (102.6 g), which was then combined with the aforesaid liquid phase comprising an oily phase consisting of bio-oil and ethanol, and a solid phase comprising carbon residues ("char") and unconverted lignin, which was dried in an oven, at 85°C and 10 mbar, for 10 hours so as to completely remove the residual ethanol: the amount of final dried solid corresponds to approximately 32.4 g.

[0103] The liquid phase obtained by combining the liquid phase comprising an oily phase consisting of bio-oil and ethanol (136.6 g) with the oily phase consisting of bio-oil (136.6 g), was subjected to evaporation by means of Rotavapor operating at 650 mbar and 85°C, for 30 minutes, obtaining an oily phase consisting of bio-oil (approximately 29 g - yield 48.3%) and a liquid phase comprising ethanol (210.2 g) which can be recycled to the oligomer extraction step and / or to the depolymerization step.

[0104] The oily phase consisting of bio-oil was subjected to molecular weight and H / C and H / O ratio determination, operating as described above.

[0105] The results obtained were as follows: weight-average molecular weight (Mw) 585.72 Daltons; number-average molecular weight (Mn) 324.23 Dalton; H / C ratio equal to 0.14 (starting lignin H / C ratio equal to 0.12); H / O ratio equal to 0.23 (starting lignin H / O ratio equal to 0.14). EXAMPLE 3

[0106] Determination of antioxidant power

[0107] The bio-oil obtained in Example 2 was compared with a commercial antioxidant [butylated hydroxytoluene (BHT - Merck)] using the Rancimat Test in accordance with standard EN 15751-2014: said test allowed to determine the oxidation stability of the bio-oil by measuring the induction period up to a maximum of 48 hours.

[0108] For this purpose, a sample was prepared by mixing commercial, antioxidant- free, food-grade sunflower oil with the bio-oil obtained in Example 2 so as to have a bio-oil concentration equal to 1% by weight with respect to the total weight of the sunflower oil (Sample A). The sample thus prepared was inserted into the Rancimat apparatus (Metrohm Herisau Switzerland).

[0109] Subsequently, a stream of purified air was passed through the sample previously heated to 110°C. During the oxidation process, the volatile compounds formed pass, together with the air, into a flask containing demineralised water and a conductivity electrode: said conductivity electrode allows to measure the end of the induction period, which is marked by a rapid increase in conductivity due to the dissociation of the volatile carboxylic acids absorbed in the water.

[0110] For comparison purposes, the following samples were prepared by mixing commercial, antioxidant-free, food-grade sunflower oil with: commercial antioxidant butylated hydroxytoluene (BHT - Merck) so that the concentration of butylated hydroxytoluene (BHT) is equal to 0.3% by weight with respect to the total weight of the sunflower oil (Sample B); pre-treated lignin from biorefineries as used in Example 2 as such so as to have a concentration of lignin as such equal to 1% by weight with respect to the total weight of the sunflower oil (Sample C); oligomers obtained as shown in Example 2 so as to have a concentration of oligomers equal to 1% by weight with respect to the total weight of the sunflower oil (Sample D).

[0111] For comparison purposes, Sample E consisting of commercial, antioxidant- free, food-grade sunflower oil as such, is also shown in Figure E

[0112] The samples prepared as described above were inserted into the Rancimat apparatus (Metrohm Herisau Switzerland) and the antioxidant power was determined by operating as described above: the results obtained are shown in Figure 2.

[0113] From the data shown in Figure 2 [the abscissa shows the samples; the ordinate shows the average induction time expressed in hours (h)], it can be deduced that the bio-oil obtained in Example 2 at 1% by weight in sunflower oil has similar antioxidant activity to the commercial antioxidant butylated hydroxytoluene (BHT - Merck) at 0.3% by weight in sunflower oil.

[0114] EXAMPLE 4

[0115] Determination

[0116] For this purpose, a commercial, antioxidant free, food-grade sunflower oil was used and comparative tests were carried out, operating out as follows.

[0117] In a 10 ml flask, under magnetic stirring, at a temperature of 35°C, the following was added to the sunflower oil: commercial antioxidant butylated hydroxytoluene (BHT - Merck) at 0.3% by weight with respect to the total weight of the sunflower oil (Sample B); bio-oil obtained in Example 2 at a concentration equal to 1% by weight with respect to the total weight of the sunflower oil (Sample A); pre-treated lignin from biorefineries as used in Example 2 as such so as to have a concentration of lignin as such equal to 1% by weight with respect to the total weight of the sunflower oil (Sample C); oligomers obtained as shown in Example 2 so as to have a concentration of oligomers equal to 1% by weight with respect to the total weight of the sunflower oil (Sample D).

[0118] For comparison purposes, Sample E consisting of commercial, antioxidant- free, food-grade sunflower oil as such, is also shown in Figure 3.

[0119] Subsequently, after placing the flask in a silicon bath and topping it with a condenser, a (previously calibrated) oxygen-sensitive probe was inserted: the whole was kept under magnetic stirring, the temperature was brought to 130°C, and the consumption of oxygen due to the auto-oxidation of the sunflower oil was then measured by means of said oxygen-sensitive probe.

[0120] In Figure 3 [the abscissa shows the time in seconds (s); the ordinate shows the percentage (%) of oxygen (O2) present in the test atmosphere], it can be seen how the addition of the bio-oil obtained in Example 2 increases the oxidation time of the sunflower oil.

Claims

CLAIMS1. Process for producing bio-oil from lignin comprising the following steps:(a) subjecting the lignin to extraction of the oligomers in the presence of at least one alcohol having from 1 to 5 carbon atoms, preferably from 1 to 2 carbon atoms, operating at the boiling temperature of said alcohol or, in the case of a mixture of alcohols at the temperature of the higher-boiling alcohol, for a time comprised between 30 minutes and 90 minutes, preferably comprised between 40 minutes and 70 minutes, obtaining a liquid phase comprising oligomers and at least one alcohol and a solid phase comprising lignin essentially free of said oligomers;(b) subjecting the solid phase comprising lignin essentially free of said oligomers obtained in step (a) to depolymerization in the presence of at least one alcohol having from 1 to 5 carbon atoms, preferably from 1 to 2 carbon atoms, in supercritical conditions, operating at a temperature comprised between 200°C and 300°C, preferably comprised between 220°C and 295°C, at a pressure comprised between 40 bar and 170 bar, preferably comprised between 50 bar and 150 bar, for a time comprised between 5 minutes and 150 minutes, preferably comprised between 10 minutes and 130 minutes, obtaining:(i) a gas phase;(ii) a mixture comprising an oily phase consisting of bio-oil, a liquid phase comprising at least one alcohol and a solid phase comprising carbon residues ("char"), an oily phase consisting of bio-oil and, optionally, unconverted lignin;(c) recovering the oily phase consisting of bio-oil from the mixture (ii) obtained in step (b).

2. Process for producing bio-oil from lignin according to claim 1, wherein in said step (a), said lignin is selected from: pre-treated lignin from biorefinery, i.e. deriving from a process wherein the starting lignocellulosic biomass is subjected to a "steam explosion" process to separate the cellulosic matrix from the lignin which is subsequently subjected to a purification step obtaining dried and purified lignin;non-pretreated lignin, from biorefinery, i.e. deriving from a process wherein the starting lignocellulosic biomass is subjected to a "steam explosion" process to separate the cellulosic matrix from the lignin which is used as is without being subjected to a purification step.

3. Process for producing bio-oil from lignin according to any one of the preceding claims, wherein before being subjected to said extraction step (a), said lignin is subjected to a preliminary grinding process.

4. Process for producing bio-oil from lignin according to any one of the preceding claims, wherein in said step (a) said at least one alcohol is selected from methanol, ethanol, propanol, butanol, pentanol, or mixtures thereof; preferably from methanol, ethanol, or mixtures thereof.

5. Process for producing bio-oil from lignin according to any one of the preceding claims, wherein in said step (a) said lignin and said at least one alcohol are used in a weight / weight (w / w) ratio comprised between 0.05 and 1.1, preferably comprised between 0.1 and 1.

6. Process for producing bio-oil from lignin according to any one of the preceding claims, wherein before being subjected to depolymerization, the solid phase comprising lignin essentially free of oligomers obtained in said step (a) is subjected to washing with at least one alcohol having from 1 to 5 carbon atoms, preferably from 1 to 2 carbon atoms, even more preferably with the alcohol used in said extraction step (a), in a quantity such as to maintain the weight / weight ratio (w / w) used in said step (a) and, subsequently to filtration and drying.

7. Process for producing bio-oil from lignin according to any one of the preceding claims, wherein the liquid phase comprising oligomers and at least one alcohol obtained in said step (a) is subjected to evaporation obtaining alcohol and a solid residue comprising lignin.

8. Process for producing bio-oil from lignin according to any one of the preceding claims, wherein in said step (b): said at least one alcohol is selected from methanol, ethanol, propanol, butanol, pentanol, or mixtures thereof; preferably from methanol, ethanol, or mixtures thereof; and / orsaid lignin and said at least one alcohol are used in a weight / weight (w / w) ratio comprised between 0.45 and 1.1, preferably between 0.5 and 1.

9. Process for producing bio-oil from lignin according to any one of the preceding claims, wherein the step (c) of recovery of the oily phase consisting of bio-oil comprises the following steps:(cl) subjecting the mixture (ii) obtained in step (b) to separation obtaining:(iii) a solid phase comprising carbon residues (“char”), an oily phase consisting of bio-oil and, optionally, unconverted lignin;(iv) a liquid phase comprising an oily phase consisting of bio-oil and at least one alcohol;(c2) subjecting the solid phase (iii) obtained in step (cl) to purification and separation obtaining:(v) an oily phase consisting of bio-oil;(vi) a solid phase comprising carbon residues (“char”) and, optionally, unconverted lignin;(c3) combining the oily phase consisting of bio-oil (v) obtained in step (c2) to the liquid phase comprising an oily phase consisting of bio-oil and at least one alcohol (iv) obtained in step (cl) and subjecting the whole to evaporation obtaining:(vii) an oily phase consisting of bio-oil;(viii) a liquid phase comprising at least one alcohol.

10. Process for producing bio-oil from lignin according to claim 9, wherein said separation step (cl) is carried out by filtration, decantation, centrifugation, preferably by filtration.

11. Process for producing bio-oil from lignin according to claim 9, wherein said purification step (c2) is carried out by washing with at least one alcohol, preferably with at least one alcohol used in the depolymerization step (b), more preferably methanol, ethanol, or mixtures thereof.

12. Process for producing bio-oil from lignin according to claim 9, wherein in said step (c2) the separation is carried out by filtration, decantation, centrifugation, preferably by filtration.

13. Bio-oil from lignin having the following characteristics: weight average molecular weight (Mw) less than or equal to 1100 Daltons, preferably comprised between 560 Daltons and 1000 Daltons; number average molecular weight (Mn) less than or equal to 400 Daltons, preferably comprised between 250 Daltons and 390 Daltons; percentage variation between the H / C ratio of the bio-oil from lignin and the H / C ratio of the starting lignin equal to at least 3% more, preferably between 5% more and 50% more, compared to the H / C ratio of the starting lignin; percentage variation between the H / O ratio of the bio-oil from lignin and the H / O ratio of the starting lignin equal to at least 25% more, preferably between 28% more and 120% more, compared to the H / C ratio of the starting lignin.

14. Use of bio-oil from lignin according to claim 13, as an antioxidant agent or anti-UV agent, preferably as an antioxidant agent or anti-UV agent in biofuels used as such, or in mixtures with other fuels in diesel engines for automotive or aviation.

15. Use of bio-oil from lignin according to claim 13, as an antioxidant agent in bio-feedstocks such as vegetable oils and animal or vegetable fats.

Images