Efficient catalytic conversion technology for lignins to hydrocarbon fuels

Abstract

The invention relates to a process for converting lignin, the process comprising: liquefaction of lignin by hydrotreatment of the lignin in a solvent with a Zn-salt as catalyst resulting in a liquefied lignin mixture; optional removal of the salt from the liquified lignin mixture; hydrotreatment of the liquefied lignin mixture with a further catalyst resulting in a hydrotreated liquefied lignin mixture; separation of the product of step c) resulting in at least two different liquid fractions, wherein at least a part of a liquid fraction from step d) is recycled to step a). Using the process, hydrocarbon fuels can efficiently be produced.

Description

[0001] Efficient catalytic conversion technology for lignins to hydrocarbon fuels

[0002] The present invention relates to a process for converting lignin and to an apparatus for performing the process.

[0003] Background Art

[0004] The development of sustainable aviation fuel (SAF) is crucial in reducing the aviation industry's carbon footprint. However, few viable approaches have been demonstrated to supply SAF at the necessary scale from bio-based feedstocks.

[0005] Lignin is the largest natural source of renewable aromatic compounds; however, significant challenges related to deoxygenation have hindered its use as a feedstock for SAFs. Lignin constitutes a significant portion of lignocellulosic biomass, typically ranging from 15% to 30% by weight and accounting for up to about 40% of its energy content. It stands as one of the most abundant renewable sources of carbon on our planet. Currently, global commercial lignin production is mainly associated with papermaking. Unfortunately however, the majority of lignin is currently incinerated.

[0006] Some methods have been assessed for converting lignin into more valuable materials. However, these processes are not as advanced as those for carbohydrate conversion. Only a few processes are reported that demonstrate the production of liquid hydrocarbon fuels from lignin. Typical yields of lignin pyrolysis are low due to losses in the form of char. Piskorz et al. (Energy and Fuels 1989, 3, 723) demonstrated a liquid yield of around 60 - 64 wt% of hydrotreated fuel of which 50 wt% was in the gasoline range. Stone et al. (Joule, 2022, 6, 2324) demonstrated a continuous process to convert native poplar wood lignin to hydrotreated fuels using a reductive catalytic fractionization step coupled with catalytic hydrotreatment. A net mass yield of about 32 - 40 wt% of hydrotreated liquids was reported based on the mass of lignin in the poplar wood used as feedstock.

[0007] The relatively low yields have resulted in any fuel products resulting from prior art processes being relatively expensive. Furthermore, one of the main issues with existing processes is the cost of the catalysts, which are often formulated materials containing precious or rare metals. Thus, the use of such expensive catalysts further increases the costs of the resulting products. Finally, char formation in prior art processes has resulted in machine blockage and down time, which is also unfavorable from an economic perspective. Invention

[0008] It is an objective of the present invention to provide a solution for one or more of the abovementioned drawbacks, or at least to provide a useful alternative. It is therefore an objective of the present invention to provide a process for converting lignin, preferably to fuelrange hydrocarbons, which is economically viable. It is a further objective of the present invention to provide a process for converting lignin, preferably to fuel-range hydrocarbons, with a high carbon yield. It is a further objective of the present invention to provide a process for converting lignin, preferably to fuel-range hydrocarbons, which uses cheap and / or abundant materials. It is a further objective of the present invention to provide a process for converting lignin, preferably to fuel-range hydrocarbons, which is versatile.

[0009] Thereto, the present invention provides a process for converting lignin, the process comprising a) liquefaction of lignin by depolymerization, preferably by hydrotreatment, of the lignin in a solvent with an inorganic salt as catalyst resulting in a liquefied lignin mixture, b) optional removal of the inorganic salt from the liquified lignin mixture, c) hydrotreatment of the liquefied lignin mixture with a further catalyst resulting in a hydrotreated liquefied lignin mixture, d) separation of the product of step c) resulting in at least two different liquid fractions, wherein at least a part of a liquid fraction from step d) is recycled to step a).

[0010] The at least two different liquid fractions of step d) for example have a different composition and / or different boiling point (at identical pressure). The process of the invention results in minimal losses of carbon as char, which is positive from an economic point of view but also from a technical perspective as continuous operation without any clogging or blockage related problems by char is made possible. Preferably, the process is a continuous process.

[0011] Furthermore, the process of the invention uses a cheap catalyst for liquefaction without the need for precious or noble metals. Again this has a positive effect on the manufacturing costs.

[0012] The lignin used in the invention may be any type of lignin. Lignins are materials derived from biomass by techniques such as chemical pumping (soda, sulfite, acid and kraft), biomass delignification and fractionization, or pyrolysis. Lignins typically have a carbon content from 45 - 80 mol%, a hydrogen content of 5 - 10 mol% and an oxygen content of 10 - 50 mol%. For example, lignins may have a C / H / O ratio ranging between 45 / 5 / 50 to 80 / 10 / 10. Specific examples of lignins are technical lignins such as kraft lignin, soda lignin, organosolv lignin, lignins derived from pyrolysis of biomass, and lignin obtained from the reductive fractionization and delignification of biomass. Depolymerization of lignin is preferably achieved by hydrotreatment, more preferably by hydropyrolysis.

[0013] Hydrotreatment is a reaction that involves contacting a carbonaceous feed with hydrogen (either molecular hydrogen or a hydrogen donor) and a catalyst, optionally in combination with a suitable solvent. Typical hydrotreating reactions include hydropyrolysis, hydrogenolysis, hydrocracking, hydrogenation, hydrodeoxygenation and more.

[0014] Pyrolysis is the cracking of biomass at elevated temperature, typically at temperatures above 200 °C. Hydropyrolysis is pyrolysis under hydrotreatment conditions.

[0015] Hydrodeoxygenation is the reaction of organic compounds in the presence of a hydrodeoxygenation catalyst and high pressure hydrogen, such as a hydrogen partial pressure of at least 10 bar, such as at least 18 bar, with the objective to reduce or remove oxygen (deoxygenation) along with other heteroatoms (nitrogen, sulfur, and chlorine).

[0016] Preferably step a) is performed in the presence of molecular hydrogen. More preferably, step a) is performed under a hydrogen partial pressure ranging from 1 - 200 bar, more preferably 20 - 150 bar, most preferably 75 to 150 bar.

[0017] Preferably, step a) is performed at a temperature below 400 °C, more preferably below 375 °C, most preferably below 350 °C. Preferably, step a) is performed at an elevated temperature with respect to ambient temperature, more preferably step a) is performed at a temperature above 150 °C. A suitable temperature range for step a) is from 200 - 400 °C, such as from 225 - 375 °C, preferably from 250 - 350 °C.

[0018] Step a) results in a liquefied lignin mixture. This mixture is preferably depolymerized lignin with a molecular weight (Mw) in the range of 300 - 1300 Da. The molecular weight of depolymerized lignin may suitably be determined by gel permeation chromatography, preferably in tetra hydrofuran (THF) using polystyrene (PS) as a calibration standard, for example such as disclosed in the experimental section.

[0019] The inorganic salt is a catalyst. The inorganic salt may be an alkali salt, preferably a salt chosen from the group consisting of Zn, Ni, Co, Na, K, Li, and Mg-salts and mixtures thereof, more preferably a Zn-salt (i.e. a salt containing Zn, for example ZnCh, ZnO, ZnS, Zn(OH)2, ZnSCL, etc.) and mixtures thereof, even more preferably ZnCI2, ZnO or ZnS and mixtures thereof, most preferably ZnCI2. Preferably, the ZnCI2 is comprised in a mixture of ZnCI2, KCI and NaCI, comprising at least 20, such as at least 30 or 40 mol% of ZnCI2.

[0020] In an embodiment, the salt is or comprises is a mixture of ZnCI2, KCI and NaCI, comprising at least 20, such as at least 30 or 40 mol% of ZnCI2.

[0021] In some cases, the salt may act as a poison for a catalyst used in further reactions, such as the hydrotreatment of step c). Therefore, the salt may be removed in step b).

[0022] Preferably, when the salt is removed in step b), removal is performed by combining the liquefaction mixture with water, thereby dissolving the salt in a water phase, and subsequent separation and removal of the water phase, preferably at temperatures < 250 °C, such as from 50 °C - 250 °C, preferably from 100 - 250 °C. Preferably, the salt is removed at a pressure of between 1 - 200 bar, more preferably 75 - 150 bar. If salt removal is performed at increased temperatures along with increased pressure (i.e. increased from ambient conditions), heavy cooling of the liquefied lignin mixture is not necessary and the process can be performed more efficiently.

[0023] In alternative embodiments, the salt is not removed for efficiency reasons. This is particularly the case for Ni and Co salts, which do not act as a poison for most commercial hydrodeoxygenation catalysts.

[0024] Preferably, the inorganic salt in step a) is present in an amount below 50 wt.%, more preferably below 20 wt.%, yet more preferably below 10 wt.%, and most preferably below 5 wt.% based on the weight of the unconverted lignin. Preferably, the inorganic salt in step a) is present in an amount of at least 0.01 wt.%, more preferably at least 0.1 wt.%, more preferably at least 1 wt.%. As the salt serves as catalyst, it is only required to be present in catalytic amounts. Higher amounts may aid in dissolution of the lignin in the solvent, but are less preferred from a cost and efficiency perspective.

[0025] Preferably, step a) is performed in the liquid phase. Step a) may be performed in any type of reactor, i.e. in any vessel which can contain liquids and be operated at elevated temperature and pressure. Examples of which are: stirred tank reactors, pressured autoclaves, slurry reactors, heated screw extruders, and plug flow reactors. Preferably, step a) is performed under continuous agitation of the lignin mixture. More preferably, step a) is performed in a stirred reactor, such as a continuously stirred tank reactor (CSTR).

[0026] Lignin, solvent, and salt may be added to the reactor in any fashion. For example, the reactor may comprise a lignin inlet, a solvent inlet, and a salt inlet and mixing is performed in the reactor. Alternatively, pre-mixing is performed. For example, lignin and at least part of the solvent may be pre-mixed, optionally including the salt. Thus, step a) may comprise a first step a1) of pre-mixing lignin, at least part of the solvent and optionally the salt, and a step a2) of adding the pre-mixed lignin, solvent and optionally salt to the reactor after which liquefaction is performed. Recycling of at least a part of a liquid fraction from step d) to step a) may then be to step a1) and / or to step a2). Thus, the at least part of the liquid fraction may serve as the, or part of the, solvent for pre-mixing lignin, and / or it may be added to the premixed lignin for further dissolution.

[0027] Preferably, the residence time in step a) is from 1 - 120 min, preferably from 1 - 60 min, more preferably from 1 - 30 min, based on the unconverted lignin.

[0028] The hydrotreatment of step c) can hydrogenate and stabilize the reactive lignin oil (liquefied lignin) at relatively mild process conditions and results in a mixture from which a solvent for step a) can easily be separated. Preferably, the hydrotreatment of step c) is a hydrodeoxygenation. The hydrodeoxygenation may be a mild hydrodeoxygenation, i.e. a hydrodeoxygenation in which up 50 to 98% of the oxygen in the liquefied lignin mixture is removed.

[0029] The process allows for the use of a (further) hydrodeoxygenation step (step e)), in which fuel range hydrocarbons can efficiently be produced, making the overall process very efficient. Step e) preferably removes from 50 up to 100 % and preferably 95 - 100 % of the oxygen calculated on the basis of the amount of oxygen present in the fraction that is to be hydrodeoxygenated in step e).

[0030] Preferably, the hydrotreatment in step c) is performed at a hydrogen partial pressure of between 100 - 300 bar, such as between 125 - 250 bar, most preferably between 150 - 225 bar.

[0031] Preferably, the hydrotreatment in step c) is performed at a temperature below 350 °C, preferably below 325 °C, more preferably below 300 °C. Preferably, step c) is performed at an elevated temperature with respect to ambient temperature, more preferably step c) is performed at a temperature above 150 °C. It has been found that these relatively low temperatures result in a stable mixture which can efficiently be separated into at least two fractions. More preferably, the hydrotreatment in step c) is performed at a temperature of between 175 and 350 °C, such as between 200 and 325 °C, most preferably between 225 and 300 °C. Too low temperatures result in a lower efficiency due to increased reaction times. The further catalyst of step c) is different from the inorganic salt catalyst of step a). Preferably, the further catalyst is a hydrodeoxygenation catalyst. Any commercial hydrodeoxygenation catalyst may be used. Preferably, the hydrodeoxygenation catalyst is a heterogeneous hydrodeoxygenation catalyst. Preferably the hydrodeoxygenation catalyst is sulfided nickel- molybdenum or cobalt-molybdenum on gamma alumina. Most preferably, the hydrodeoxygenation catalyst is sulfided nickel-molybdenum on gamma alumina. Preferably, the WHSV (feed rate in g / h divided by amount of catalyst in the reactor in g) in step c) is in the range of 0.5 - 1.

[0032] Preferably, the at least two liquid fractions of step d) comprise a light fraction and a heavy fraction, and at least a part of the light fraction from step d) is recycled to step a). Preferably the light fraction comprises phenolics, more preferably at least 50 wt.%, such as at least 70 wt.% of phenolics. Phenolics are compounds comprising a phenol group. The phenolics preferably are phenolic compounds derived from lignin, such as cresols, guaiacols, and catechols. The light fraction may further comprise aromatic hydrocarbons other than phenolics and / or naphthalenes. Preferably, the light fraction is a fraction that boils at a temperature that is lower than the boiling point of the heavy fraction at the same pressure. The light fraction for example is a fraction boiling at a temperature below 145 °C under a pressure of 50 mbar. The heavy fraction for example is a fraction boiling at a temperature above 145 °C under a pressure of 50 mbar.

[0033] The amount of light fraction that is recycled to step a), is preferably such that the light fraction can serve as the solvent in step a). Thus, preferably such that the ratio of lignin to light fraction is in the range of 1 :1 - 1 :20, preferably 1 :1 - 1 :10, more preferably 1 :1 - 1 :5.

[0034] Separation in step d) may be performed by any suitable physical separation method, such as filtration, distillation, centrifugation, or evaporation. Preferably, separation in step d) is performed by distillation. Distillation provides the best results as a light fraction from the liquefied lignin mixture obtained by distillation provides for the best solubility of lignin in step a).

[0035] Preferably, the solvent in step a) is a phenolic solvent. Preferably, the phenolic solvent comprises at least 50 wt.%, such as at least 70 wt.% of phenolics. In an embodiment, the phenolic solvent comprises cresol, guaiacol, and / or catechol. The use of a phenolic solvent is preferred due to the high solubility of lignin in such a solvent.

[0036] Preferably, the ratio of lignin to solvent in step a) is in the range of 1 :1 - 1 :20, more preferably 1 :1 - 1:10, most preferably 1 :1 - 1 :5, based on the unconverted lignin. High amounts of solvent provide for easier handling of the lignin, but provide for a less efficient process. If less solvent then lignin is used, the mixture is not only difficult to handle, but also depolymerization becomes less efficient. Preferably, the process further comprises e) a hydrodeoxygenation of at least one of the fractions, preferably of the heavy fraction, resulting in fuel-range hydrocarbons. The process of the invention comprising step e) allows the production of hydrocarbon fuels from a waste product from the pulp and paper industry (lignin) at an unprecedented high yield (> 87% carbon), thus having a very positive impact on the manufacturing costs of the hydrocarbon fuels.

[0037] The hydrodeoxygenation of step e) may be performed under relatively harsher reaction conditions than those of step c), to result in deoxygenation and the production of fuel range hydrocarbons.

[0038] Preferably, the hydrotreatment in step e) is performed at a hydrogen partial pressure of between 100 - 300 bar, such as between 150 - 250 bar, most preferably between 175 - 225 bar. Preferably, the hydrogen partial pressure in step e) is higher than the hydrogen partial pressure in step c).

[0039] To result in adequate deoxygenation, preferably, the hydrodeoxygenation in step e) is performed at a temperature above 250 °C, preferably above 275 °C, more preferably above 300 °C. More preferably, the hydrodeoxygenation in step e) is performed at a temperature of between 250 and 500 °C, such as between 275 and 475 °C, most preferably between 300 and 450 °C. Too low temperatures result in a lower efficiency due to increased reaction times. Preferably, the hydrodeoxygenation in step e) is performed with a hydrodeoxygenation catalyst. Any commercial hydrodeoxygenation catalyst may be used. Preferably the hydrodeoxygenation catalyst is a heterogeneous catalyst. Preferably the hydrodeoxygenation catalyst is sulfided nickel-molybdenum or cobalt-molybdenum on gamma alumina. Most preferably, the hydrodeoxygenation catalyst is sulfided nickel-molybdenum on gamma alumina.

[0040] The hydrodeoxygenation catalyst used in step e) may be the same as or different from the further catalyst in step c).

[0041] Preferably, step e) is performed at a higher temperature than the temperature in step c). Preferably, the temperature in step e) is at least 50 °C higher than the temperature in step c). Preferably, the lowest temperature in step e) is higher than the highest temperature in step c). Preferably, the lowest temperature in step e) is at least 50 °C higher than the highest temperature in step c).

[0042] Preferably, the WHSV in step e) is in the range of 0.25 - 0.75.

[0043] Performing step e) preferably results in fuel range hydrocarbons. These are deoxygenated lignin oil products, i.e. lignin-derived oils with an oxygen level of 0 - 5 wt.%.The oxygen level may suitably be determined by elemental analysis. Steps c) and e) may be performed in a hydrogenation reactor. Examples of hydrogenation reactors are packed bed reactors and slurry type continuously stirred tank reactors.

[0044] The invention further relates to an apparatus, preferably an apparatus for performing the process of the invention and / or its preferred embodiments. The apparatus comprises, in the following order and each in fluid communication with the previous: a hydrotreatment reactor for liquefaction of lignin in a solvent with an inorganic salt, a collection vessel for collecting the liquified lignin mixture, optionally, a mixing vessel for mixing the liquified lignin mixture with water, optionally, a separator for separating salt and water from the liquified lignin mixture, a first hydrodeoxygenation reactor for hydrotreatment of the liquefied lignin mixture, a further separator for separating the hydrotreated liquified lignin mixture into a light fraction and a heavy fraction and a second hydrodeoxygenation reactor for hydrodeoxygenation of the heavy fraction, wherein the further separator is in fluid connection with the hydrotreatment reactor for adding the light fraction to the hydrotreatment reactor.

[0045] Brief Description of Figures

[0046] Fig. 1 is a schematic picture of an embodiment of a process according to the invention.

[0047] Fig. 2 shows the hydropyrolysis reactor pressure over experimental time when using a salt mixture of ZnCI2, KCI and NaCI as catalyst.

[0048] Fig. 3 shows the product yields of the hydropyrolysis step.

[0049] Fig. 4 shows the molecular weight distribution of the hydropyrolysis oil obtained after four consecutive passes with recycled cresol.

[0050] Fig. 5 shows individual product yields of hydrodeoxygenation of oil from hydropyrolysis of lignin.

[0051] Fig. 6 is a van Krevelen plot of the conversion of biomass to hydrocarbons, modified to show only the lignin fraction of the individual process streams

[0052] Figure description

[0053] Figure 1. In a laboratory scale continuous unit 1, a feed 2 of lignin, a phenolic solvent (e.g. cresol and / or the light fraction of the first hydrodeoxygenation step) and salt is fed into a hydrotreatment reactor 4 via feeding unit 3 (e.g. a pump). A feed 5 of hydrogen also enters the hydrotreatment reactor 4. Liquified lignin mixture 7 is removed from the reactor, e.g. via a dip-tube 8, and fed to collection vessel 6. Gaseous products 9 are removed from collection vessel 6, and separated into gas 10 and light organics 11 by condenser 12. The gas 10 leaves the condenser 12 via a back-pressure valve 13. Liquid products 15 are removed from collection vessel 6 via back-pressure valve(s) 14 and added to mixing vessel 16. Water 17 is also fed to mixing vessel 16. Light organics 11 from condenser 12 may be added to mixing vessel 16 as well (not shown). Water, liquid products and optional light organics are mixed in mixing vessel 16 and the mixture 18 is fed to a phase separator 19. Salt water 20 is removed from phase separator 19 and the organic phase 21 enters the hydrodeoxygenation reactor 22. Hydrotreated products 23 are fed to a further separator 24, such as a distillation device. The further separator 24 separates the hydrotreated products into a light fraction 25 and a heavy fraction 26 which is fed to a second hydrodeoxygenation reactor 27. Fuel-range hydrocarbons 28 are produced by the second hydrodeoxygenation reactor 27. Light fraction 25 is combined with feed 2.

[0054] Example

[0055] Chemicals

[0056] LignoBoost lignin samples were supplied by the RISE Innventia, Sweden and used as received. Elemental composition of the LignoBoost used is shown in Table 1.

[0057] Hydrogen gas was obtained from Linde (> 99.99% purity).

[0058] Tetrahydrofuran (THF, anhydrous, > 99.9%, with 250 ppm BHT as inhibitor), and di-n-butyl ether (DBE) were purchased from Sigma-Aldrich.

[0059] Cresol used as diluent was of technical grade (mix of isomers, >90 % purity) and was sourced from Sigma-Aldrich.

[0060] Salts used (ZnCh, NaCI, KCI, ZnS, analytical purity, 99%) were purchased from VWR Chemicals (Belgium). The salts were stored in an oven at 150 °C and mixed into the desired ratios prior to an experiment.

[0061] Catalytic hydrotreatment / hydrodeoxygenation catalyst, presulfided NiMo / AhCh was supplied by Biomass Technology Group B.V. (BTG, Enschede, The Netherlands) and used as received without prior pretreatment / activation.

[0062] Table 1. Elemental composition of the LignoBoost a data from the provider’s specification sheet,bobtained by difference (100 - CH NS)

[0063] Experimental Setup

[0064] Hydropyrolysis

[0065] LignoBoost and cresol, in the mass ratio 1:3, along with 2.5 wt.% (based on the weight of the lignoboost) of a salt mixture of ZnCh, KCI and NaCI, in the molar ratio of 44.3 : 41.9 : 13.8 mol%, were stirred using an overhead stirrer for at least 3 hours at 40 °C to ensure complete dissolution. Due to the viscosity of the feed mixture, the salts used were suspended in the feed.

[0066] A 100mL parr autoclave was used for the hydropyrolysis experiments. The reactor was initially filled with 30 mL of cresol, pressurized using hydrogen and tested for leaks. The reactor was then heated to the predetermined hydropyrolysis temperature. Upon reaching the desired temperature, the pump was switched on and the feed was added to the heated reactor continuously.

[0067] The feed solution (cresol, lignin and molten salts) was injected into the pressured stirred autoclave reactor using an air driven piston pump. The rate of feed added to the reactor was continuously monitored by an electronic scale. Hydrogen was added to the reactor and its flow rate was modulated using a mass flow controller. The delivery line was extended into the reactor using a dip tube with a 100 pm filter fitted at its end, reducing the effective reactor volume to about 30 mL. The liquid products produced after hydropyrolysis (PO) were removed continuously through this dip tube while the solids (char) remained in the reactor due to the use of a filter in the dip tube.

[0068] After leaving the reactor, the liquid products in the delivery line were cooled to room temperature and were depressurized by passing a series of valves that acted like locks. By continuously switching the valves, the liquid products were brought stepwise to atmospheric pressure. At atmospheric pressure, the reactants passed a gas-liquid separator. The liquid product was collected, and the gas was vented. The rate of liquid production was monitored by an electronic scale and the gas flow rate exiting the system was monitored by a gas flow meter. The yield of total liquid, organic liquid and char from the hydropyrolysis experiments were calculated using equations 1 - 3. Process conditions used in the hydropyrolysis experiments are shown in Table 2.

[0069] Table 2. Process conditions for the continuous hydropyrolysis of lignin

[0070] Desalting

[0071] The liquid products from the continuous hydropyrolysis of lignin contained a measurable fraction of the dissolved salts (500 ppm), particularly ZnCh. The concentration of the salts dissolved was measured using XRF analysis, calibrated for ZnCh. Since the salts used are detrimental to the catalytic activity of the NiMo used in the catalytic hydrotreatment, the hydropyrolysis liquids were washed in an intermediate desalting step. Hydropyrolysis oil and water (pH 4), in a mass ratio of 2:1 , was stirred vigorously using an ultra turrax vortex stirrer for 10 - 15 minutes. The mixture was then decanted to obtain a salt rich aqueous phase (top) and an organic phase (bottom). The organic phase was centrifuged to remove any water or salt precipitates and the cleaned oil was used for the catalytic hydrotreatment steps. The concentration of the zinc chloride in the organic phase was ensured to be below 40 ppm using XRF analysis. Due to the weak solubility of cresol and other phenolic monomers in water, a small fraction of cresol (around 3-4 wt%) was lost in the saltwater phase after separation. Catalytic Hydrotreatment

[0072] The hydrodeoxygenation unit used for catalytic hydrotreatment (step c) consisted of 4 packed bed reactors in series. Each reactor was 50 cm long with an internal diameter of 10 mm and was filled with NiMo catalyst. Each reactor was equipped with a separately controlled heating coil. This enabled the operation of the different sections at different temperatures. The reactors were operated in top-down mode where reactants enter at the top and leave at the bottom.

[0073] Lignin oil from the continuous hydropyrolysis experiments was fed with an air-driven piston pump at a rate of 50 g / hour. In the present experiments, the feed vessel, pump and the feed line were heated up to 80 °C using electrical tracing, to allow a smoother feeding of viscous feed materials into the reactor. The feed rate was monitored by an electronic scale. Hydrogen was fed to the reactor at a rate of 250-1000 NmL / min. The gas feed rate was controlled by a mass-flow controller. After leaving the reactor, the reactants were cooled to room temperature and were depressurized by passing a series of valves that act like locks. By continuously switching the valves, the products were brought stepwise to atmospheric pressure. At atmospheric pressure, the products passed a gas-liquid separator. The liquid product was collected and the gas was vented. The rate of liquid production was monitored by an electronic scale and the gas flow rate exiting the system was monitored by a gas flow meter.

[0074] Hydrotreatment was performed in two steps: a milder stabilization HDO (HDO 1) at temperatures between 250 - 275 °C and a harsher deep hydrodeoxygenation (HDO 2) at temperatures between 350 - 425 °C. Typical process conditions used in these steps are shown in Table 3.

[0075] The oil (SPO) obtained after the first HDO step (HDO 1) was distilled at 145 °C under a vacuum pressure of 50 mBar to remove cresol and other light phenolics. The heavier residue, free of cresol, was treated further at higher temperatures in HDO 2.

[0076] Table 3. Process conditions used

[0077] Analytical Procedures

[0078] The water content was determined by Karl Fischer titration using a Metrohm 702 SM Titrino titration device. About 0.01 g of sample was injected in an isolated glass chamber containing Hydranal (Karl Fischer solvent, Riedel de Haen). The titrations were carried out using the Karl Fischer titrant - Titrant 5. All analyses were per- formed at least 3 times and the average value is reported

[0079] Gas chromatography-mass spectroscopy (GC-MS) analyses were performed on a Hewlett- Packard (HP 5890 series GC system) gas chromatograph equipped with an RTX-1701 capillary column (30 m x 0.25 mm i.d. and 0.25 pm film thickness) and a Quadrupole Hewlett- Packard 6890 mass selective detector 5973 attached. Helium was used as a carrier gas at a flow rate of 2 mL min-1. The injector was set at 280 °C. The oven temperature was kept at 40 °C for 5 min and then increased to 250 °C at a rate of 3 °C min-1and held at 250 °C for 15 min.

[0080] Two-Dimensional Gas Chromatography with a Time of Flight Mass Spectrometer (GC*GC- ToF-MS). GCxGC / TOF-MS analysis was performed on an Agilent 7890B system equipped with a JEOL AccuTOF GCv 4 G detector and two capillary columns, i.e. a RTX-1701 capillary column (30 m x 0.25 mm i.d. and 0.25 pm film thickness) connected by a solid state modulator (Da Vinci DVLS GC2) to a Rxi-5Sil MS column (120 cm x 0.10 mm i.d. and 0.10 pm film thickness).

[0081] Heteronuclear single quantum correlation (HSQC) spectra were acquired on a Bruker NMR spectrometer (600 MHz) with the following parameters: 11 ppm sweep width in the F2 domain (1H), 220 ppm sweep width in the F1 domain (13C), 8 scans, 512 increments, and a total acquisition time of approximately 1 h. Sample preparation involved the dissolution of a sample in DMSO-de.

[0082] 13C-NMR spectra were recorded on a Bruker NMR spectrometer (600 MHz) using a 90° pulse and an inverse-gated decoupling sequence with a relaxation delay of 10 s, sweep width of 225 ppm, and 1024 scans. Samples were prepared by dissolving about 100 mg of product in deuterated chloroform (CDCh-di, Sigma-Aldrich, 99.5 atom % D).

[0083] Gas-phase analysis was performed on a gas chromatograph equipped with a thermal conductivity detector (GC-TCD, Hewlett-Packard 5890 Series II GC equipped with a Poraplot Q AhO3 / Na2SO4 column and a molecular sieve (5A) column). The injector temperature was set at 150 °C and the detector temperature at 90 °C. The oven temperature was kept at 40 °C for 2 min, then heated up to 90 °C at 20 °C min-1, and kept at this temperature for 2 min. A reference gas containing H2 (55.19%), CH4 (19.70%), CO2 (18.01%), CO (3.00%), propane (1.50%), ethane (1.49%), ethylene (0.51%), and propylene (0.51%) was used for quantitative analysis.

[0084] Elemental analyses (C, H, N, S) were performed using a EuroVector EA3000 Series CHNS-0 analyzer with acetanilide as the reference. The oxygen content was determined indirectly by difference. All analyses were conducted in duplicate, and the average value is reported.

[0085] X-ray fluorescence (XRF) measurements on an Epsilon 3XLE spectrometer from PANalytical. The liquid sample to be measured was placed in a plastic cup with 6 pm mylar film. Quantification was done using the fundamental parameters method. XRF analysis was calibrated to quantitatively measure the concentration of ZnCh.

[0086] Gel Permeation Chromatography (GPC) analyses were performed using an Agilent HPLC 1100 system equipped with a refractive index detector. Three columns in series of Agilent MIXED type E (length 300 mm, i.d. 7.5 mm) were used, with polystyrene as the calibration standard. 0.05 g of the sample was dissolved in 4 mL of tetrahydrofuran (THF) together with 2 drops of toluene as the marker and filtered (filter pore size of 0.2 pm) before analysis.

[0087] Results

[0088] Continuous conversion of lignin to hydrocarbon rich liquid fuels was demonstrated over an extended period of about 100 hours using an integrated hydropyrolysis and catalytic hydrotreatment with hydrodeoxygenation approach.

[0089] Hydropyrolysis

[0090] Continuous hydropyrolysis of lignin, diluted in cresol and with molten salts as catalysts, was demonstrated in a pressured autoclave reactor. Using the autoclave as a continuously stirred slurry reactor, feed of lignin, cresol and suspended solid molten salts were continuously pumped into a heated reactor under pressure. Depolymerized products (and spent salts) were continuously removed from the reactor using a system of valves operating in sequence. Using 2.5 wt% of zinc chloride (ZnCI2:KCI:NaCI 44.3: 41.9: 13.8 mol%,) based molten salt mixture, continuous hydropyrolysis was demonstrated over an extended period of approximately 100 hours. The pressure measured inside the feed line, inside the reactor and in the outlet line were stable over the course of the reaction (time on stream, TOS), as shown in Figure 4, indicating no clogging in the filter inside the reactor due to char formation.

[0091] A comparative experiment was performed where the hydropyrolysis reaction was repeated at identical process conditions but without using any molten salts. The pressure in the feed line, reactor and (product) delivery line was continuously logged and were plotted over experimental time. In the absence of any salt catalysts, just lignin and cresol, the filter inside the reactor was clogged due to char formation after approximately 6 hours of operation, evidenced by an increase in reactor pressure. The experiment had to be interrupted after 16 hours due to a fully clogged filter. The zinc chloride based molten salts used thus are crucial in reducing the char formed, enabling continuous uninterrupted operation of the hydropyrolysis unit.

[0092] In a further comparative experiment, when NaCI only was used as catalyst, pressures over TOS showed a stable trend until around 20 hours of operation. Subsequently, pressure built up inside the reactor due to char formation, although to a lesser extent than the experiment without any salts

[0093] Zinc sulfide and zinc oxide were used at similar process conditions, with similar results but obtaining slightly higher molecular weights of the final products. Results when using only ZnS as the salt demonstrated a smooth experiment without any pressure increase over 24 hours of operation. Also use of zinc oxide did not lead to clogging.

[0094] The catalytic activity of the salts on lignin depolymerization was hypothesized to be an effect of the anion (zinc) used rather than the cation (chloride).

[0095] The overall mass balance of the hydropyrolysis reaction using the 2.5 wt% of zinc chloride (ZnCI2:KCI:NaCI 44.3: 41.9: 13.8 mol%,) based molten salt mixture was close to 100%, demonstrating little or no accumulation as char inside the reactor during the continuous steady state operation of the unit. Based on the measured weight of the liquid products collected and the measured water content in the liquid, individual product balances were calculated, as shown in Figure 3. An overall organic yield of around 85 wt% was obtained, with a corresponding char and gas yield of about 3 and 2 wt% respectively. Elemental analysis results of the oil obtained after hydropyrolysis showed a lower oxygen content than that of the input feed and lignin. Overall carbon yield of the hydropyrolysis step was high: 96 C% based on input lignin.

[0096] The molecular weight distribution of the liquid products obtained after molten salt hydropyrolysis was determined using GPC analysis. A noticeable decrease in the molecular weight distribution of the oil was observed. The averaged molecular weight decreased significantly from -1600 Da of the lignoboost to -600 Da of the oil obtained after hydropyrolysis, demonstrating strong depolymerization. No peaks heavier than that of the lignin were measured, signifying the absence of any repolymerization or condensation products.

[0097] The molecular weight distribution of hydropyrolysis oil using different zinc salts (ZnCh, ZnS and ZnO) was compared. Oil obtained with ZnCh showed a lower molecular weight than oil obtained with either ZnO or ZnS. ZnCh shows a relatively higher solubility in cresol while ZnS and ZnO are completely insoluble. The increased solubility of ZnCh could explain its better catalytic activity to depolymerize lignin than other insoluble Zinc salts.

[0098] Recyclability of Cresol

[0099] The diluent used, cresol, was removed from the product oil by rotary evaporation under vacuum and its recyclability evaluated by comparing the molecular weight distribution of the oil products obtained. The cresol used was recycled four times and the molecular weight distribution of the oils obtained from hydropyrolysis experiments involving the same process conditions (340 °C, 125 bar, 2.5wt% salt loading and a cresol-lignin ratio of 3:1) was measured by GPC analysis. After each pass, the ‘cresol’ removed contains a small fraction of other lignin derived light phenolic monomers. The measured molecular weight distribution of the heavier fraction of the oils from four passes, shown in Figure 4, were compared to the molecular weight distribution of the input lignoboost used. The molecular weight distribution of the oils from the four successive passes closely resembled each other, validating the effective recyclability of the cresol used.

[0100] Catalytic Hydrotreatment

[0101] The hydropyrolysis oil used as feed could be hydrotreated easily over the two step approach. In appearance, the oil collected after the first HDO step resembled the feed used. However, the fraction of cresol in the oil after HDO1 increased measurably from 71 to 75 wt%. Alternatively, the oil collected after the second hydrotreatment step was completely transparent and slightly yellowish in colour. Individual product yields of the two steps of HDO are shown in Figure 5 and in Table 4.

[0102] Overall mass yields of the oil after HDO 1 (SPO) and HDO 2 (HPO) were high, with little mass lost to the gas phase and no measurable char produced. The liquid product collected after the HDO steps were biphasic, with an organic and an aqueous phase. Mass of aqueous phase measured in the liquid after HDO 1 was much smaller in comparison to HDO 2, as the mild process conditions employed enabled the considerable hydrogenation of the hydropyrolysis oil without significant deoxygenation, evidenced by a hydrogen uptake of about 3.3 wt% (based on the dry lignin oil in HDO 1 feed). The liquid after HDO 2 on the other hand was composed of almost 14-15 wt% of water due to the deoxygenation reaction.

[0103] Table 4. Process results of the two HDO steps employed

[0104] The composition of the final hydrotreated product was analyzed using 2DGC-Tof analytical methods. Only three major product classes were identified: straight chain / branched alkanes, saturated cycloalkanes and aromatic hydrocarbons.

[0105] NMR (2D - HSQC and13C) analysis methods were used to obtain information on the molecular structure of the obtained hydrotreated product. The final hydrotreated product contained a significant fraction of saturated aliphatic hydrocarbons and relatively smaller concentration of aromatic hydrocarbons, evidenced by signals measured only in the aliphatic and aromatic regions. No signals in the region corresponding to the oxygenated aliphatics were measured, which agrees with the results of the 2DGC-Tof analysis.

[0106] Hence, the final product is rich in hydrocarbons, with minimal oxygenated compounds identified, making it suitable for the use in biofuels.

[0107] Elemental composition of the oil obtained after the two HDO steps are compared with that of the lignin used as feed in Table 5. Table 5. Elemental composition of the products from catalytic hydrotreatment experiments aElemental composition calculated based on computed values.

[0108] Based on the elemental compositions measured and listed in Table 5, a van Krevelen plot was constructed for the entire process (Figure 6). From the original H / C and O / C ratio of the lignin used (lignoboost and cresol), 1.11 and 0.3 respectively, the hydropyrolysis oil obtained showed a strong decrease in the O / C ratio (0.19) while the H / C ratio (1.14) remained similar. In the next step, mild hydrotreatment, increase in the H / C from 1.11 to 2 demonstrated the significant hydrogenation of the hydropyrolysis oil. The hydrogenated product after HDO 1 was deoxygenated further in the second HDO step, with dehydration reactions being the most observed pathway, evidenced by the decrease in both the H / C (2 to 1.83) and O / C ratios (0.08 to 0).

[0109] Carbon losses in each of the three steps of the process as char were limited: an overall carbon yield from lignin to final hydrotreated product of around 87 C% was calculated. The most significant carbon loss (11 C%) was from the loss of cresol in the water phase after the desalting step (dilute acid wash).

[0110] The loss of carbon is further minimized by a separate liquid / liquid extraction using apolar solvents (e.g. dichloromethane, MIBK) to remove residual organics from the water phase.

Claims

CLAIMS1. Process for converting lignin, the process comprising a) liquefaction of lignin by hydrotreatment of the lignin in a solvent with an inorganic salt as catalyst resulting in a liquefied lignin mixture, b) optional removal of the inorganic salt from the liquified lignin mixture, c) hydrotreatment of the liquefied lignin mixture with a further catalyst resulting in a hydrotreated liquefied lignin mixture, d) separation of the product of step c) resulting in at least two different liquid fractions, wherein at least a part of a liquid fraction from step d) is recycled to step a), wherein the inorganic salt is a Zn-salt.

2. Process according to claim 1 , wherein the at least two liquid fractions of step d) comprise a light fraction and a heavy fraction, and at least a part of the light fraction from step d) is recycled to step a).

3. Process according to claim 2, wherein the light fraction is a fraction boiling at a temperature below 145 °C under a pressure of 50 mbar.

4. Process according to any one of the preceding claims, wherein the process further comprises e) hydrodeoxygenation of at least one of the fractions, preferably of the heavy fraction of claim 2, resulting in fuel-range hydrocarbons.

5. Process according to any one of the preceding claims, wherein the solvent in step a) is a phenolic solvent.

6. Process according to any one of the preceding claims, wherein the Zn-salt is chosen from ZnCI2, ZnO or ZnS and mixtures thereof, most preferably wherein the Zn-salt is ZnCI2.

7. Process according to any one of the preceding claims, wherein step c) is performed at a temperature below 350 °C, preferably below 325 °C, more preferably below 300 °C.

8. Process according to any one of the preceding claims, wherein the inorganic salt in step a) is present in an amount below 50 wt.%, preferably below 20 wt.%, more preferably below 10 wt.%, and most preferably below 5 wt.% based on the weight of the unconverted lignin.

9. Process according to any one of the preceding claims, wherein step a) is performed in the liquid phase in a continuously stirred tank reactor.

10. Process according to any one of the preceding claims, wherein step a) is performed under a hydrogen partial pressure ranging from 1 - 200 bar, more preferably 50 - 150 bar, most preferably 75 to 150 bar.

11. Process according to any one of the preceding claims, wherein step a) is performed at a temperature below 400 °C, preferably below 375 °C, more preferably below 350 °C.

12. Process according to any one of the preceding claims, wherein a residence time in step a) is from 1 - 120 min, preferably from 1 - 60 min, more preferably from 1 - 30 min, based on the unconverted lignin.

13. Process according to any one of the preceding claims, wherein the salt is removed in step b), and removal is performed by combining the liquefied lignin mixture with water, thereby dissolving the salt in a water phase, and subsequent separation and removal of the water phase, preferably at temperatures < 250 °C.

14. Process according to any one of the preceding claims, wherein separation in step d) is performed by distillation.

15. Process according to any one of the preceding claims, wherein the ratio of lignin to solvent in step a) is in the range of 1 :1 - 1 :20, preferably 1 :1 - 1 :10, more preferably 1 :1 - 1 :5, based on the unconverted lignin.

16. Process according to any one of the preceding claims, wherein step c) and / or step e) are performed with a hydrodeoxygenation catalyst, preferably wherein the hydrodeoxygenation catalyst is sulfided nickel-molybdenum or cobalt-molybdenum on gamma alumina, more preferably wherein the hydrodeoxygenation catalyst is sulfided nickelmolybdenum on gamma alumina.

17. Process according to any one of the preceding claims, wherein step e) is performed at a higher temperature than the temperature in step c), preferably, wherein the temperature in step e) is at least 50 °C higher than the temperature in step c).

18. Apparatus for performing the process of any one of claims 1 - 17, the apparatus comprising, in the following order and each in fluid communication with the previous: a hydrotreatment reactor for liquefaction of lignin in a solvent with an inorganic salt, a collection vessel for collecting the liquified lignin mixture, - optionally, a mixing vessel for mixing the liquified lignin mixture with water, optionally, a separator for separating salt and water from the liquified lignin mixture, a first hydrodeoxygenation reactor for hydrotreatment of the liquefied lignin mixture, a further separator for separating the hydrotreated liquified lignin mixture into a light fraction and a heavy fraction and - a second hydrodeoxygenation reactor for hydrodeoxygenation of the heavy fraction, wherein the further separator is in fluid connection with the hydrotreatment reactor for adding the light fraction to the hydrotreatment reactor.

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