Methods for rapid heating of biomass slurries for solvent liquefaction using recirculated product oil

Abstract

A method for rapid heating of a biomass slurry for solvent liquefaction comprising the sequential steps of: providing a biomass feedstock slurry, mixing the feedstock slurry with a sufficient quantity of carrier oil having temperature within the range 250 - 400 o C so as to produce a combined slurry that can be pumped through heat exchanger tubing with pipe velocity at least 1 m s -1 and pressure drop less than 30 bar, and heating the combined slurry to temperature within the range 300 to 400 o C using a heat exchange system operated with pipe velocity at least 1 m s -1 and pressure drop less than 30 bar.

Description

[0001] Methods for rapid heating of biomass slurries for solvent liquefaction using recirculated product oil.

[0002] Field: The invention relates generally to systems and methods for solvent liquefaction of lignocellulosic biomass to produce bio-crude oil and specifically to systems and methods in which recirculated product oil is used as solvent.

[0003] Solvent liquefaction is a thermochemical method widely known in the art for producing biocrude oil from lignocellulosic biomass. While the composition and stability of bio-oils varies widely between different feedstocks and methods of production, these can typically be directly used as a crude liquid fuel or, with some additional treatment, co-processed along with petroleum-crude to refined commercial transport fuels.

[0004] The term “hydrothermal liquefaction” (HTL) is applied to solvent liquefaction processes in which the solvent is water. These processes are typically applied to feedstocks which comprise a substantial water content. For comparatively dry biomass feedstocks, however, recirculated product oil or some fraction thereof can itself be advantageously used as solvent. For review see (Behrendt 2008, Lange 2018, Kim 2019). Relative to HTL, solvent liquefaction using recirculated product oil improves oil yields and reduces undesirable char formation and oxygen content of the product oil (Kumar 2014, Van Rossum 2014, Kumar 2015, Kumar 2016, Castvelli-Barnes 2017, Haverly 2018). Further addition of ethanol and / or methanol in these processes produces synergistic effects whereby the inherent advantages of using recirculated product oil as solvent are amplified and an overall reduction is obtained in undesirable product oil acidity. (WO2021 / 209555).

[0005] The underlying chemical reactions in solvent liquefaction involve depolymerization of the biomass as well as partial deoxygenation of the resulting intermediates through dehydration, decarboxylation and decarbonylation reactions. Concurrent undesirable char formation is an inevitable consequence of competing re-condensation and repolymerisation reactions involving these same intermediates. The tendency for char formation is reduced where recirculated product oil is used as solvent because the solvent has a small “Hansen radius of interaction” with the depolymerization products and thereby dissolves them, favoring dehydration rather than re-condensation to char (WO2012 / 005784, Castvelli 2017). The tendency for char formation can be further reduced by controlling the rate at which the process stream is heated to reaction temperature. In general, rapid heating favors reactions with high activation energy. At temperatures beneath 240° C, undesirable char formation reactions dominate compared with desirable thermal decomposition (Chornet 1985, Elliot 2015, Mathanker 2021 ). Thus it is, in theory, advantageous to bring the process stream to temperatures above 240° C as quickly as possible. Residence time is particularly undesirable within the temperature range 120 to 180° C wherein hemicellulose depolymerizes (Behrendt 2008) since this produces intermediates that are particularly notorious for condensation and re-polymerization. For review see (Shinde 2018).

[0006] The effect of rapid heating to reduce char formation with associated increased oil yield has been demonstrated experimentally both in “fast pyrolysis” processes which are typically conducted at temperatures considerably above 400° C as well as with HTL systems where heating rate is on the order of 70-140° C / minute. For review see (Ni 2022).

[0007] Fast pyrolysis systems typically achieve rapid heating using a circulating fluidized bed or other system where heat is introduced via some gas or via solid heat carrier particles.

[0008] For fast HTL systems, a variety of rapid heating schemes have been proposed. One demonstrated, commercially available technology includes the FLASH-HTL system Flashing for Low-fouling, Steam-based Heat recovery in Hydrothermal Liquefaction (FLASH-HTL) which is described in W02024 / 076806. This provides direct flashing of the aqueous output fraction into a mixer processing the incoming biomass feedstock. Other reported experimental technologies include use of inert solid heat carriers

[0009] (WO2013 / 015888, ON 106010616) including specialized silicon carbide material which can be heated by microwave radiation (CN115651694), and use of specialized “nozzle reactors” which achieve rapid heating by mixing heated aqueous phase with incoming cold biomass slurry (Curakovs 2022, Tran 2017).

[0010] Here we report an alternative advantageous approach to rapid heating of biomass slurries in solvent liquefaction systems that use recirculated product oil as solvent and that, accordingly, lack significant aqueous output fraction. A comparatively “cold” biomass slurry is rapidly heated by mixing with a quantity of hot carrier oil (in some embodiments recirculated product oil) sufficient to reduce viscosity to the point where the combined slurry can then be pumped through small diameter heat exchanger tubing with high pipe velocities > 1 m s-1and pressure drop less than 30 bar. A traditional heat exchanger can then be applied with very fast pipe velocity to rapidly bring the process stream to reaction temperature. Prior art systems applying traditional heat exchangers to solvent liquefaction process streams have typically relied on inherently gradual counter-current heat exchange whereby the outgoing process stream heats the incoming stream with pipe velocities within the range of 10-20 cm s'1. (Ghadge 2022). Much faster pipe velocities > 1 m s-1applied using methods of the invention impart the further advantage of reducing the tendency for heat exchanger tubing to become fouled over time. Once the process stream reaches reaction temperature, excess hot carrier oil can be separated and used to rapidly heat the incoming comparatively “cold” process stream as described. The remaining process stream after separation of excess hot carrier oil can be further processed at reaction temperature. In the particular case where ethanol and / or methanol are added to the process, the added alcohol contributes to viscosity reduction of the biomass slurry that permits very fast pipe velocities for rapid heating and also further reduces the tendency for heat-exchanger fouling.

[0011] Brief description of the figures.

[0012] Fig. 1 . Measured viscosity at different temperatures of product oil, a fraction thereof and a biomass slurry using product oil as carrier liquid.

[0013] Fig. 2. Calculated viscosity as a function of temperature for slurry of biomass feedstock and product oil.

[0014] Fig. 3. Process diagram for one embodiment of methods and systems of the invention.

[0015] Description of embodiments.

[0016] With bio-oils in general, and in particular, with product oil from solvent liquefaction processes in which product oil is itself used as solvent, viscosity is very high such that the material is not even flowing at room temperature. But viscosity can be readily reduced by increasing temperature. As a consequence, the viscosity of an incoming, comparatively “cold” biomass slurry can be reduced by mixing with hot carrier oil which also provides very rapid initial heating. With sufficiently low viscosity, the combined slurry can then be pumped with very high velocity through a heat exchanger so as to achieve very rapid heating to reaction temperature.

[0017] In some embodiments, the invention provides a method for rapid heating of a biomass slurry for solvent liquefaction comprising the sequential steps of:

[0018] - providing a biomass feedstock slurry,

[0019] - mixing the feedstock slurry with a sufficient quantity of carrier oil having temperature within the range 250 - 400° C so as to produce a combined slurry that can be pumped through heat exchanger tubing with pipe velocity at least 1 m s-1and pressure drop less than 30 bar, and

[0020] - heating the combined slurry to temperature within the range 300 to 400° C using a heat exchange system operated with pipe velocity at least 1 m s-1and pressure drop less than 30 bar.

[0021] In some embodiments, ethanol or methanol is added to the initial biomass slurry or to the combined slurry.

[0022] In some embodiments, the method comprises the further steps of

[0023] - separating a stream of carrier oil having temperature within the range 300 to 400° C from the heated combined slurry to form a reactor feed stream that is subject to further processing, and

[0024] - using the separated stream of carrier oil in the method to mix with biomass slurry so as to produce a combined slurry that can be pumped through heat exchanger tubing with pipe velocity at least 1 m s-1and pressure drop less than 30 bar.

[0025] As used herein, the following terms have the following meanings:

[0026] “Carrier liquid” refers to the liquid which is add to a biomass feedstock to produce a biomass slurry. The “carrier liquid” may or may not be the same as the “carrier oil.”

[0027] “Carrier oil” refers to oil that is introduced at high temperature to an incoming biomass slurry so as to concurrently lower viscosity and raise the temperature of the product stream and may include any combination of exogenous oil, product oil obtained from a solvent liquefaction process, or one or more fractions thereof. Median particle size” refers to the diameter at which the cumulative weight % is 50 in a particle size distribution determined by sieve analysis.

[0028] “Pipe velocity” refers to the linear speed in meters per second traveled by a biomass slurry though process tubing.

[0029] “Pumpable” refers to a slurry in which the slump measured in slump test ASTM C143 / C143M-12 is more than 100 mm 4 minutes after cone lifting, where the cone is filled with larger diameter upwards and then the cone is quickly flipped once full, where a tamping rod is used to tap the side of the cone, and where any liquid which separates from the slurry cone during the slump test comprises no more than 3 wt% of the initial weight of the slurry cone 4 minutes after cone lifting.

[0030] “Solvent liquefaction process” refers to a thermochemical conversion of solid lignocellulosic biomass to liquid by processing as a slurry formed with some other liquid termed a “solvent.”

[0031] Any suitable biomass may be used to form a biomass feedstock slurry including wood chips, sawdust, paper or lumber production wastes, straw feedstocks such as wheat, barley, oat, rye, canola, rape, rice and corn straw (including stover), energy grasses, biorefinery or other biomass-processing residuals.

[0032] One skilled in the art will readily understand that the rheology and viscosity of such a slurry depends on the average particle size to which the feedstock has been reduced. In some embodiments, average particle size is reduced to beneath 1 cm, or between 0.2 and 0.6 cm, or between 0.014 and 0.2 cm. In some embodiments, the slurry is formed by combining biomass feedstocks with a sufficient quantity of comparatively “cold” carrier liquid so as to render the slurry “pumpable.” In some embodiments the carrier liquid is product oil or one or more fractions thereof obtained from a solvent liquefaction process in which product oil is used as solvent. Alternatively the carrier liquid can be an “exogenous” oil such as light cycle oil obtained from a petroleum refinery, or tall oil obtained from a pulp mill. In some embodiments the carrier liquid can be aqueous, for example where a slurry of sewage sludge is used as feedstock for the solvent liquefaction process. One skilled in the art will readily determine an appropriate dry matter content of a biomass slurry which is advantageously kept as high as practicable while remaining “pumpable.” The “pumpability” of course depends on the carrier liquid and the properties of the biomass feedstock itself. In some embodiments, the biomass slurry has a feedstock dry matter content within the range 10 and 30 wt. % In some embodiments, the carrier liquid itself comprises some suspended solids, for example where recirculated product oil or some fraction thereof is used.

[0033] Where product oil obtained from a solvent liquefaction process or one or more fractions thereof is used as carrier liquid for a biomass slurry, its temperature should advantageously typically be increased to the point where its viscosity is within the manageable range less than 6000 cP. Figure 1 shows viscosity as a function of temperature determined as described in Example 2 for product oil obtained as described in Example 1 from a solvent liquefaction process in which product oil was used as solvent, for the THF soluble fraction thereof, and for a slurry of the product oil further comprising 8 wt. % dry matter biomass feedstock. As shown, using whole product oil as carrier liquid, it is typically advantageous to increase temperature to at least 78° C prior to mixing with biomass feedstock to form a slurry whereas using only the THF soluble fraction, lower temperatures on the order of at least 50° C are manageable. In some embodiments, the biomass feedstock slurry has initial temperature within the range 30 - 100° C, or 20 to 150° C, or 50 to 110° C at the time of mixing with carrier oil having temperature within the range 250 - 400° C.

[0034] In order for the biomass slurry to be pumped with high velocity through heat exchanger tubing to permit its very rapid heating to reaction temperature, its viscosity is further reduced by mixing with carrier oil at temperature within the range 250 - 400° C to produce a combined slurry. One skilled in the art can readily determine the relative quantity of hot carrier oil or fraction thereof that must be added to any given biomass slurry. The aim is to reduce viscosity of the combined slurry to the point where it can be pumped through a heat exchanger with pipe velocity at least 1 m s-1while experiencing a pressure drop across the heat exchanger of less than 30 bar. The maximum target viscosity can be readily calculated using methods well known in the art as the viscosity associated with the desired maximum pressure drop with the desired pipe velocity using the intended pipe dimensions. In some embodiments, maximum target viscosity can be calculated using Aspen HTFS Technology Version V12.2 (39.1.0.323) as described in “Aspen Exchanger design & rating - Applying Aspen HTFS Technology Version V12.2 (39.1 .0.323).” This calculation is typically an overestimate in that only the initial flow through the heat exchanger system will be laminar while heating introduces turbulence as viscosity is further reduced. In determining how much hot carrier oil to add to achieve the target viscosity, one skilled in the art can calculate the viscosity as a function of temperature for the initial biomass slurry, which will always be greater than the viscosity of carrier oil at the same temperature. The appropriate amount of hot carrier oil to be added is then determined as the amount required at the intended temperature to bring the combined slurry to the temperature corresponding to the target viscosity. For example, Figure 2 shows viscosity values as a function of temperature calculated as explained in Example 3 for biomass feedstock slurry comprising 8 wt. % dry matter biomass (ground pine wood having average particle size 0.15 cm) in product oil obtained as described in Example 1 (itself comprising 12 wt. % suspended char particles). As shown, a sufficient quantity of hot carrier oil to be added to this biomass feedstock slurry in order to reach a target viscosity of 50 cP is the amount at the intended temperature required to bring the combined slurry to temperature 168° C after mixing.

[0035] In some embodiments, the feedstock slurry is mixed with a sufficient quantity of carrier oil having temperature within the range 250 - 400° C so as to produce a combined slurry having viscosity within the range 10 to 130 cP, or 20 to 80 cP. One skilled in the art can readily determine without undue experimentation an appropriate quantity of carrier oil to add at intended temperature to achieve viscosity within this range.

[0036] In some embodiments, ethanol and / or methanol is added during mixing of carrier oil with biomass feedstock slurry with ratio of added alcohol mass to total mass of biomass and oil within the range 0.01 to 0.20, which serves to further reduce viscosity.

[0037] In some embodiments, the carrier oil having temperature within the range 250 - 400° C comprises dissolved gases, which serves to further reduce viscosity, which gases may include any of ethanol and / or methanol, CO2 and CO produced during heating of combined slurry and re-circulation of carrier oil, and oil fractions with boiling points lower than carrier oil temperature.

[0038] In some embodiments, carrier oil having temperature within the range 250 - 400° C is mixed with mass ratio to the initial biomass feedstock slurry within the range 0.2 to 0.8, or within the range 0.4 to 1 .0 to form a combined slurry having temperature within the range 150 to 300° C.

[0039] One skilled in the art will readily understand that, while it is, at some level, advantageous to achieve the most rapid possible pipe velocity so as to avoid sedimentation of suspended particles within the heat exchanger, at the upper extemes of velocity, pipe erosion caused about by abrasive components of the combined slurry such as silicate content within the biomass feedstock or suspended solids in general, can be limiting. Accordingly, in some embodiments, the combined slurry is heated to temperature within the range 300 to 400° C using a heat exchange system operated with pipe velocity greater than 1 m s-1but within the range 2 to 5 m s-1.

[0040] The initial biomass feedstock slurry can be mixed with carrier oil using any of a variety of methods well known in the art. In some embodiments, a simple static mixer can be used where the “in line” input of carrier oil introduces turbulent mixing with the biomass feedstock slurry. In some embodiments, a more elaborate “in line” system can be used comprising multiple carrier oil injection ports. In some embodiments, any suitable mechanical mixing system can be used including but not limited to free-fall mixers or impeller mixers such as helical ribbon mixers. While time of mixing to achieve homogeneous temperature distribution may vary between different mixing systems, this approach to increasing temperature of the biomass feedstock slurry will typically be at least 7 to 12 times faster than systems using heat exchangers operated with pipe velocities on the order of 10-20 cm s'1.

[0041] In some embodiments, product oil from a solvent liquefaction process is subject to a separation process to remove char or other solid particles prior to its use to practice methods of the invention. In some embodiments product oil from a solvent liquefaction process is fractionated using methods known in the art including temperature swing extraction, solvent extraction, or distillation. One or more fractions rather than whole product oil can then be used as carrier oil to practice methods of the invention. In some embodiments, an aqueous product fraction of a solvent liquefaction process that includes water produced chemically during the process, is separated from product oil and not included in the recirculation solvent used in the process. The combined slurry with viscosity reduced below the maximum target velocity is pumped through a tubing with velocity at least 1 m s-1and pressure drop less than 30 bar through a heat exchange system configured to rapidly bring the process stream to temperature within the range 300 to 400° C. In some embodiments, the inner diameter of heat exchanger tubing through which the combined slurry is pumped is within the range 3 / 8 to 2 inches. Any suitable heat exchange system known in the art may be used including but not limited to mono-tube exhangers and heating block exchangers where the block is heated by direct fire. In some embodiments, the combined slurry is brought to temperature within the range 300 to 400° C in between 0.1 and 2 minutes, or between 1 and 5 minutes, or less than 10 minutes.

[0042] In some embodiments, an excess of carrier oil is added to the initial biomass slurry for purposes of providing rapid heating and viscosity reduction above and beyond the amount desired to be included within the actual liquefaction reaction as conducted within a reactor that provides residence time at temperature within the range 300 to 400° C. In this case, after heating to temperature, the combined slurry can be directed through a separator that removes a stream of carrier oil prior to downstream processing at reaction temperature. Any convenient separator system known in the art can be used, including a simple vertical density separator, from which combined slurry is removed from the bottom, while a stream of product oil, with reduced suspended solids content, is concurrently removed from a point situated higher up on the separator. In some embodiments, where ethanol or methanol have been added, a stream of supercritical or gaseous ethanol or methanol mixed with water can be removed by the same separator. In some embodiments, between 20 and 50 wt. % of the carrier oil within the combined slurry is removed after it reaches reaction temperature but prior to its subsequent processing and used to provide rapid heating and viscosity reduction of an incoming biomass slurry.

[0043] In some embodiments, methods of the invention are practiced using a continuous processing of between 0.1 and 30 metric tons dry biomass feedstock per hour.

[0044] Figure 3 shows a diagram for a process whereby methods of the invention are practiced using a continuous system for solvent liquefaction of the invention. As shown, biomass slurry, in some embodiments between 10 to 95 metric tons per hour, drawn from a slurry mixer (1) which slurry comprises, in some embodiments, 10 to 28 wt. % pine sawdust with average particle size 75 to 400 pm in carrier oil (in some embodiments recirculated product oil) at 80° C is pumped through a first inlet into a mixer system (2). While an impeller mixer is shown, a static mixer or other system can alternatiely be used. Recirculated product oil at 350° C (in some embodiments between 10 to 51 tons per hour) is recovered from a downstream vertical density separator (5) and pumped through a second inlet into the mixer concurrently with addition of ethanol or methanol (in some embodiments between 1 and 8 tons per hour) drawn from an alcohol dosing system (3). The resulting combined slurry is pumped through a reduction in process tubing diameter so as to achieve a pipe velocity at least 1 m s_1through a heating system (4) configured to heat the stream to reaction temperature within the range 300 to 400° C. The combined slurry at reaction temperature is directed through a vertical density separator (5) that separates a stream of carrier oil with temperature within the range 300 to 400° C through a first outlet in fluid communication with the mixer (2), a stream of biomass and carrier oil slurry through a second outlet in fluid communication with a liquefaction reactor (6) and a stream of supercritical alcohol through a third outlet in fluid communication with the liquefaction reactor (6).

[0045] EXAMPLES

[0046] 1. Preparation of product oil and a fraction thereof from a solvent liquefaction process in which recirculated product oil was used as solvent and preparation of a biomass slurry using product oil as carrier liquid.

[0047] Product oil from a solvent liquefaction process in which recirculated product oil was used as solvent was prepared using the hydrothermal liquefaction mini-pilot unit at Aalborg University.

[0048] The feed was prepared in a barrel by mixing biomass feedstock, oil, and ethanol with a handheld mixer. The feed was then poured into a mixer tank, where it was continuously stirred by an agitator, and pumped into a recycle loop by a progressive cavity pump (Rotopump RJCA142R6CF1Q) at 50 kg / h. The section of the feed loop between the progressive cavity pump, the high pressure pump, and the feed tank was pressurised to 5- 10 bar - controlled by an air-actuated pinch valve (AKO VM020.07X.80.80). This pressure ensured filling of the high-pressure syringe pumps that follow. A pair of Teledyne ISCO D-series (500HPx) syringe pumps were used to feed and pressurise the slurry to the heated section of the system.

[0049] A heat-traced horizontal tube (3 / 8”) of 800 mm in length, sleeved with a solid aluminum cylinder, was used as a preheater. The temperature of the preheater was controlled automatically through a skin measurement on its outlet.

[0050] The reactor was a vertical pipe (5 / 8”) of 850 mm in length, enclosed in a Carbolite gero tbs 1200 tube furnace for heating. The temperature was set to achieve a predefined outlet temperature measured in the reactor effluent. The thermocouple measuring the outlet flow temperature was removed, because this could affect the stability of the system by providing a choke point where solid material accumulated and created clogging. However, due to thin wall-thickness of the tubing it was verified that the internal temperature was approximately the same as the skin temperature. Thus, the reactor outlet skin measurement was used. The cooler was a double pipe exchanger with an inner tube diameter of 3 / 8”. The length of the cooler was 500 mm, and it was cooled by cooling water at approximately 5° C temperature. There was no control on the cooling water flow, which was over-dimensioned to ensure adequate cooling.

[0051] The pressure was relieved by two Enerpac AHB66 plunger pumps, which have been reconfigured with sleeves to make it act more like a piston pump. The two pumps were in parallel (one emptying chamber, while the other is in operation). The pumps control the pressure of the system by adjusting the back pressure with compressed air.

[0052] The product was collected in a blue cap sample bottle, which were connected to a vent or gas flow unit for outgassing. The gas flow unit is based on the water displacement principle, where the liquid level of a beaker displays the volume of gas during cycles of the pressure let down pumps. The volume of the gas flow unit was 2 L of gas.

[0053] An initial biomass slurry was formed from pine wood flour, mesh 100 (i.e., 149 pm particle size) Traemel Bog Mesh 100 from Dansk Traemel A / S mixed with Kiln fired pine tar, CAS: 8011-48-1 from Linolie 1-2-3. Ethanol was added to this mixture for a final mass ratio of wood biomass 19 wt. %, oil 70 wt. %, ethanol 11 wt. %. The initial slurry was fed with flow rate 500 ml / hour at 80 bar pressure, 350° C outlet temperature.

[0054] The bulk product was collected, subjected to evaporation, to remove water and ethanol, then used as feed solvent for a subsequent cycle. In subsequent cycles, the mass ratio was wood biomass 17.5 wt. %, oil 75 wt. %, ethanol 7.5 wt. %.

[0055] Bulk product after 11 cycles was used to prepare a biomass feedstock slurry comprising 8 wt.% added wood flour, 80% product oil, and 12 wt. % char (A - Soborg mix).

[0056] In similar experiments, bulk product obtained after 7 cycles was prepared (B - AAU 260 ) comprising 93 wt% product oil, 7 wt. % char.

[0057] In similar experiments, bulk product obtained after 5 cycles was dissolved in tetrahydrofuran (THF), filtered to remove THF-insoluble material, after which THF was removed by distillation (C - AAU 388 ), comprising 100 wt. % product oil THF soluble fraction.

[0058] 2. Measurement of viscosity as a function of temperature for product oil solvent, a fraction thereof and a biomass slurry prepared using product oil as carrier liquid.

[0059] Viscosity of sample A (Soborg mix) described in example 1 was measured using an IKA ROTAVISC me-vi with SP-10 spindle at various temperatures.

[0060] Viscosity of samples B (AAU 260) and C (AAU 388) were measured using a Brookfeld RV- DV ll-Pro rotational viscometer with a cylindrical spindle SC4-21 at various temperatures.

[0061] Results are shown in Figure 1 with A (Soborg mix) shown in green (upper trace), B (AAU 260) shown in red (middle trace) and C (AAU 388) shown in blue (lower trace).

[0062] As shown, and as expected, the viscosity of all samples drops with heating. In order to achieve a manageable viscosity lower than 6000 cP, the biomass slurry should advantageously be heated to at least about 78° C while product oil alone is manageable at 58° C and THF-extracted product oil is manageable at 32° C. 3. Calculation of viscosity as a function of temperature for a biomass feedstock slurry prepared using product oil as carrier liquid.

[0063] Viscosity of the biomass slurry sample A (Soborg mix) referred to in example 2 was calculated as a function of temperature based on extrapolations from the measured values using Aspen HTFS Technology Version V12.2 (39.1 .0.323) as described in “Aspen Exchanger design & rating - Applying Aspen HTFS Technology Version V12.2

[0064] (39.1 .0.323).” The extrapolation was informed by estimates at 90° C for density, specific heat, thermal conductivity, surface tension, “molecular weight,” and specific enthalpy.

[0065] Results are shown in Figure 2 with A (Soborg mix) shown in green.

[0066] As shown, in order to achieve a viscosity about 50 cP, the biomass slurry should advantageously be heated to at least about 168° C.

[0067] The embodiments and examples presented are representative only and not intended to limit the scope of the invention as defined by the claims.

[0068] PATENT REFERENCES CITED

[0069] WO20 12 / 005784

[0070] WO2013 / 015888

[0071] WO202 1 / 209555

[0072] CN106010616

[0073] CN 115651694

[0074] NON-PATENT REFERENCES CITED

[0075] Behrendt, F. et al. “Direct liquefaction of biomass,” Chem. Eng. Technol. (2008) 31 (5):667.

[0076] Castvelli-Barnes 2017 Castvelli-Barnes, M. et al. “Wood liquefaction: role of solvent,” Ind. Eng. Chem. Res. (2017) 56:635.

[0077] Chornet, E. and Overend, R. “Biomass liquefaction: an overview,” Chapter 54, Fundmentals of Thermochemical Biomass Conversion, Elsevier 1985.

[0078] Curakovs, A. and Trans, K. “On The Development of a Counter-Flow Mixing Reactor for Fast Hydrothermal Liquefaction,” Chem. Eng. Trans. (2022) 92:163. Elliot, D. et al. “Hydrothermal liquefaction of biomass: Developments from batch to continuous process,” Bioresource Technology (2015) 178:147.

[0079] Ghadge, R. et al. “Design and scale-up challenges in hydrothermal liquefaction process for biocrude production and its upgradation,” Energy Conservation and Management (2022) 14: 100223

[0080] Haverly, M. et al. “Continuous solvent liquefaction of biomass in a hydrocarbon solvent,” Fuel (2018) 211 :291.

[0081] Kim, J. et al. “Overview of the recent advances in lignocellulose liquefaction for producing biofuels, bio-based materials and chemicals,” Bioresource Technology (2019) 279:373. Kumar, S. et al. “Liquefaction of Lignocellulose: Process Parameter Study To Minimize Heavy Ends,” Ind. Eng. Chem. Res. (2014) 53:11668.

[0082] Kumar, S. et al. “Liquefaction of Lignocellulose in Fractionated Light Bio-Oil: Proof of Concept and Techno-Economic Assessment,” ACS Sustainable Chem. Eng. (2015) 3:2271.

[0083] Kumar, S. et al. “Liquefaction of Lignocellulose in Light Cycle Oil: A Process Concept Study,” ACS Sustainable Chem. Eng. (2016) 4:3087.

[0084] Lange, J-P. “Lignocellulose Liquefaction to Biocrude: A Tutorial Review,” ChemSusChem (2018) 11 :997.

[0085] Mathanker, A. et al. “A Review of Hydrothermal Liquefaction of Biomass for Biofuels Production with a Special Focus on the Effect of Process Parameters, Co-Solvents, and Extraction Solvents,” Energies (2012) 14:4916.

[0086] Ni, J. et al. “A review on fast hydrothermal liquefaction of biomass,” Fuel (2022) 327:1.

[0087] Shinde, S. et al. “Recent advances in understanding the pseudo-lignin formation in a lignocellulosic biorefinery,” Green Chem. (2018) 20:2192.

[0088] Tran, K. et al. “CFD pre-study of Nozzle reactor for fast hydrothermal liquefaction,” Energy Procedia (2017) 142:861.

[0089] Van Rossum, G. et al. “Liquefaction of Lignocellulosic Biomass: Solvent, Process Parameter, and Recycle Oil Screening,” ChemSusChem (2014) 7:253.

Claims

CLAIMS1 . A method for rapid heating of a biomass slurry for solvent liquefaction comprising the sequential steps of:- providing a biomass feedstock slurry,- mixing the feedstock slurry with a sufficient quantity of carrier oil having temperature within the range 250 - 400° C so as to produce a combined slurry that can be pumped through heat exchanger tubing with pipe velocity at least 1 m s-1and pressure drop less than 30 bar, and- heating the combined slurry to temperature within the range 300 to 400° C using a heat exchange system operated with pipe velocity at least 1 m s-1and pressure drop less than 30 bar.

2. The method of claim 1 comprising the further steps of:- separating a stream of carrier oil having temperature within the range 300 to 400° C from the heated combined slurry to form a reactor feed stream that is subject to further processing, and- using the separated stream of carrier oil in the method to mix with biomass slurry so as to produce a combined slurry that can be pumped through heat exchanger tubing with pipe velocity at least 1 m s-1and pressure drop less than 30 bar.

3. The method of claim 1 wherein ethanol and / or methanol is added during mixing with ratio of added alcohol mass to total mass of biomass and oil within the range 0.01 to 0.20.

4. The method of claim 2 wherein ethanol and / or methanol is added during mixing with ratio of added alcohol mass to total mass of biomass and oil within the range 0.01 to 0.20.

5. The method of claim 4 wherein the combined slurry at reaction temperature is separated by a vertical density separator that separates a stream of biomass and solvent oil slurry and a stream of supercritical alcohol that are introduced to a liquefaction reactor for further processing.

6. The method of claim 2 or 4 wherein between 20 and 50 wt. % of the product oil or fraction thereof within the combined slurry is removed after it reaches reaction temperature but prior to its subsequent processing and used to provide rapid heating and viscosity reduction of an incoming biomass slurry.

7. The method of any of claims 1-4 wherein the biomass feedstock slurry is between 10 and 30 wt. % feedstock dry matter in oil solvent.

8. The method of claim 7 wherein the feedstock is wood particles having average particle size less than 0.2 cm.

9. The method of any of claims 1-4 wherein carrier oil at temperature within the range 250 - 400° C is mixed with mass ratio to the initial biomass slurry within the range 0.2 to 0.8 to form a combined slurry having temperature within the range 150 to 300° C.

10. The method of any of claims 1 -4 wherein viscosity of the combined slurry after addition of hot product oil or fraction thereof is lower than 130 cP.11 . The method of any of claims 1-4 wherein viscosity of the combined slurry after addition of hot product oil or fraction thereof is lower than 60 cP.

12. The method of any of claims 1 -4 wherein viscosity of the combined slurry after addition of hot product oil or fraction thereof is lower than 50 Cp.

13. The method of any of claims 1 -4 wherein diameter of heat exchanger tubing through which the combined slurry is pumped is within the range 3 / 8 to 2 inches.

Images