Process for producing furfural and catalysts for use in the process

Abstract

Provided herein is a method for producing furfural from lignocellulosic biomass or an extract thereof, such as a sugar-rich extract, using a solid zinc sulfate-rich catalyst to catalyze the conversion to furfural. Also provided herein are zinc sulfate-rich catalysts, and methods for producing zinc sulfate and zinc sulfate-rich catalysts from tire carbon black.

Description

Technical Field

[0001] This disclosure relates to a method for producing furfural from lignocellulosic biomass or its extracts using a catalyst rich in solid zinc sulfate. This disclosure also relates to zinc sulfate-rich catalysts that can be used in such methods, and further to a method for producing zinc sulfate and a zinc sulfate-rich catalyst from tire black. Background Technology

[0002] The generation of value-added renewable chemicals from lignocellulosic biomass is crucial for a smooth transition of the current economy to a carbon-neutral future. Furfural, a useful precursor and platform material for the synthesis of a wide range of end products, including pharmaceuticals, herbicides, stabilizers, and polymers, has been listed as one of the top 12 biomass-derived products recognized by the United States Department of Energy (DOE) [1,2]. Traditionally, furfural has been generated from C5 hemicellulose via hydrolysis. The conversion of C6 sugars to furfural remains unsuccessful compared to the generation from C5 hydrocarbons, due to the extremely low furfural yield of C6 resulting from differences in composition and structure between C6 and C5 [1,3].

[0003] Solvothermal reactions, i.e., solvent decomposition or hydrolysis, have to date proven to be one of the most effective methods for improving the selectivity of chemicals derived from biomass [1,4]. Industrially, furfural is currently produced from hemicellulose using concentrated or diluted mineral acids (such as H2SO4, HCl, and H3PO4) as catalysts, achieving furfural yields of 50%–75% in water over a typical temperature range of 160–240 °C [1,5,6].

[0004] One such example is described in US2011 / 0144359[7], which provides a method for producing furfural from lignocellulosic biomass in a plug flow reactor. Under optimal conditions, at 230°C, with 0.5 wt% H2SO4 as a catalyst, 5 wt% xylose in water is converted to 67.6 mol% furfural in 5.87 min. The overall conversion of xylose is 98.78%. As another example, US2013 / 0109869[8] introduces a metal halide in an aqueous miscible solution for a similar furfural production method from lignocellulosic biomass. Under optimal conditions including the use of 25% corn cob in a mixed solvent of water (7.3 g), tetrahydrofuran (THF, 42.0 g), and sodium chloride (0.7 g), 0.15 M H2SO4, and 1% NaCl, at 160°C for 30 min, the yield of furfural is reported to reach 87%.

[0005] Recently, US2014 / 0171664[9] describes a method for producing furfural from xylan-containing lignocellulose feedstock. A mixture of corn cob (16 g) and aqueous sulfuric acid (6.4 g) at different pH values ​​was loaded into an autoclave and subjected to a series of six temperature / pressure cycles. Under optimal conditions, 68% furfural yield and complete xylan conversion were achieved using aqueous sulfuric acid at pH 0.50. Another study reported that the highest yield of furfural from glucose was up to 0.69 mol / mol glucose after 33 min at 180 °C in a γ-valerol (GVL) solvent with modified Sn-β zeolite as a catalyst[1].

[0006] Regardless of whether solvent decomposition is a mature method, it has many drawbacks that need to be overcome, including the difficulty and high cost of separating and recovering furfural, the corrosiveness of mineral acids, and the large amount of wastewater generated by the use of mineral acids

[10] .

[0007] Due to the potential environmental and processing issues in furfural production, there remains a need to reduce the large amounts of acid currently used during the solvent decomposition process.

[0008] Around the world, an estimated 1.5 billion vehicle tires are replaced each year.

[11] While some tires can be retreaded, a significant proportion end up in landfills, and waste vehicle tires pose a major environmental problem. For example, hazardous tire components can leach into the surrounding environment, and tire stockpiles pose a fire risk.

[0009] Vehicle tires typically contain a complex mixture of materials, including natural and synthetic rubber compounds, reinforcing compounds (such as steel wires and polymer fibers), plasticizers, fillers (including carbon black and silica), and chemicals used for vulcanization (such as sulfur and zinc oxide compounds). This complex mixture increases the difficulty of recycling and reusing tire components.

[0010] One method already used to generate useful products from waste tires is the pyrolysis of waste tires

[12] . Typically, this involves heating tires at high temperatures in a reactor to produce components such as tire oil, carbon black, and gaseous products. However, there is still a need to determine further uses for waste tire products and methods for recovering useful components from waste tires.

[0011] It is desirable to provide an additional method for producing furfural that addresses at least one of the aforementioned problems. It is also desirable to provide a method for producing furfural that allows for high conversion rates of biomass components and / or high selectivity for furfural.

[0012] They also expect to find ways to efficiently recover valuable materials from waste such as tire black. Summary of the Invention

[0013] The inventors have determined that catalysts rich in solid zinc sulfate exhibit strong catalytic activity for the production of furfural from various biomass components via rapid pyrolysis. Both purified zinc sulfate and transition metal-doped zinc sulfate catalysts have been found to be effective in the methods described. The inventors have also discovered a novel method for obtaining zinc sulfate and transition metal-doped zinc sulfate from waste tire carbon black, for example, to provide catalysts that can be used to produce furfural.

[0014] Therefore, in a first aspect, a method for producing furfural is provided, comprising the steps of pyrolyzing lignocellulosic material or fractions thereof and producing furfural, wherein the production of furfural is catalyzed by a catalyst rich in solid zinc sulfate.

[0015] In some embodiments, the catalyst contains at least 50 wt% zinc sulfate.

[0016] In some embodiments, the catalyst rich in solid zinc sulfate contains an additional transition metal. In some embodiments, the additional transition metal is palladium, iron, copper, cobalt, or nickel. In some embodiments, the additional transition metal is palladium.

[0017] In some implementations, the catalyst rich in solid zinc sulfate contains palladium metal and / or palladium oxide.

[0018] In another embodiment, the catalyst rich in solid zinc sulfate contains 0.2 wt% to 5 wt% of an additional transition metal.

[0019] In some embodiments, the catalyst rich in solid zinc sulfate contains 1 wt% to 5 wt% of an additional transition metal.

[0020] In some implementations, the catalyst is essentially composed of zinc sulfate.

[0021] In some embodiments, the lignocellulosic material or its fractionation is free from the group consisting of: wood chips, sawdust, sugarcane, corn cobs, bagasse, oat hulls, cottonseed hulls, rice hulls, and wheat bran.

[0022] In another embodiment, the lignocellulose material or its fractions are selected from the group consisting of free cellulose fractions and hemicellulose fractions.

[0023] In another embodiment, the lignocellulosic material or its fractionation is free from the group consisting of monosaccharides, disaccharides and oligosaccharides.

[0024] In some embodiments, the lignocellulosic material or its fractions are free from the group consisting of allose, glucose and xylan.

[0025] In some embodiments, prior to pyrolysis, the lignocellulosic material or its fractions are subjected to one or more preprocessing steps to remove lignin fractions and / or hydrolyze sugar bonds.

[0026] In some implementations, furfural is generated in the absence of steam.

[0027] In some implementations, furfural is generated in the presence of vapor.

[0028] In a preferred embodiment, the weight ratio of steam to lignocellulose material or its fraction is in the range of about 0.1:1 to about 20:1, optionally from about 8:1 to about 20:1.

[0029] In some implementations, the pyrolysis and / or generation of furfural is carried out at temperatures ranging from about 300 to about 500°C.

[0030] In some implementations, the method according to the invention is performed as a batch method.

[0031] In some embodiments, the method according to the invention is performed as a continuous or semi-continuous method.

[0032] In some embodiments, the method according to the invention includes separating furfural from other reaction products.

[0033] In another implementation, furfural is separated by distillation.

[0034] In another embodiment, furfural is separated by selectively condensing the product vapor stream containing furfural.

[0035] On the other hand, furfural produced by methods as defined herein is also provided.

[0036] In another aspect, a method is provided for producing one or more of furfuryl alcohol, furoic acid, furan, tetrahydrofuran, levulinic acid, butadiene, hexamethylenediamine, tetrahydrofurfuryl alcohol, methyltetrahydrofuran, and furfural-phenolic resin, comprising producing furfural according to the method of the invention; and converting furfural into furfuryl alcohol, furoic acid, furan, tetrahydrofuran, levulinic acid, butadiene, hexamethylenediamine, tetrahydrofurfuryl alcohol, methyltetrahydrofuran, and furfural-phenolic resin.

[0037] In another aspect, a method for producing solid zinc sulfate is provided, comprising the steps of: contacting tire black with aqueous sulfuric acid to produce a mixture of aqueous zinc sulfate and solid tire black residue; separating the solid tire black residue from the aqueous zinc sulfate; and recovering the solid zinc sulfate from the aqueous zinc sulfate.

[0038] In a preferred embodiment, the step of contacting tire carbon black with aqueous sulfuric acid is carried out at a temperature in the range of about 25 to about 90°C.

[0039] In some embodiments, the aqueous sulfuric acid has a sulfuric acid concentration in the range of about 1 mol / L to about 5 mol / L, and is used at a mass ratio of aqueous sulfuric acid to tire carbon black in the range of 1.5:1 to 10:1.

[0040] In some implementations, aqueous zinc sulfate is separated from solid tire carbon black residue by filtration.

[0041] In some implementations, solid zinc sulfate is recovered through one or more of evaporation, crystallization, and precipitation.

[0042] In some implementations, solid zinc sulfate is recovered by evaporating water from the aqueous sulfate at a temperature in the range of 50 to 100°C to reduce the water content, and then precipitating the solid zinc sulfate.

[0043] In some implementations, the reduction in water content during evaporation is controlled so that subsequent precipitation produces solid zinc sulfate heptahydrate.

[0044] In some embodiments, the method includes the step of calcining solid zinc sulfate.

[0045] In some implementations, the calcination step is carried out at a temperature in the range of about 400 to about 800°C.

[0046] In another aspect, a method for producing transition metal-doped zinc sulfate is provided, comprising contacting tire black with aqueous sulfuric acid to produce a mixture of aqueous zinc sulfate and solid tire black residue; separating the aqueous zinc sulfate from the solid tire black residue; recovering solid zinc sulfate from the aqueous zinc sulfate; contacting the zinc sulfate with a salt of another transition metal; and producing transition metal-doped solid zinc sulfate.

[0047] In some implementations, the additional transition metal is palladium, iron, cobalt, or nickel.

[0048] In some implementations, solid zinc sulfate is recovered from aqueous zinc sulfate before contact with other transition metal salts.

[0049] In some embodiments, solid zinc sulfate is mixed with a salt of another transition metal in the presence of an organic solvent. In some embodiments, the organic solvent is ethanol.

[0050] In some implementations, ultrasonic treatment is used to mix solid zinc sulfate with salts of other transition metals.

[0051] In some embodiments, solid zinc sulfate is mixed with a salt of another transition metal in a solvent-soluble form so as to impregnate the zinc sulfate with the other transition metal.

[0052] In some implementations, organic solvents are removed by heating and / or vacuum drying.

[0053] In some implementations, a salt of another transition metal is vaporized and then condensed onto the surface of solid zinc sulfate.

[0054] In some embodiments, a salt of another transition metal is mixed with aqueous zinc sulfate, and transition metal-doped solid zinc sulfate is produced by co-precipitation and / or co-crystallization.

[0055] In some implementations, stabilizing metal salts and / or acidity-adjusting metal salts are added.

[0056] In some embodiments, a stabilizing metal salt and / or an acidity-adjusting metal salt are mixed with aqueous zinc sulfate and salts of other transition metals, and transition metal-doped solid zinc sulfate is produced by co-precipitation and / or co-crystallization.

[0057] In some embodiments, the method according to the invention further includes the step of calcining transition metal-doped solid zinc sulfate. In some embodiments, the calcination step is carried out at a temperature in the range of about 400 to about 800°C.

[0058] In some embodiments, after calcination, the transition metal-doped solid zinc sulfate undergoes a reduction step by being exposed to hydrogen at a temperature in the range of about 400 to about 800°C.

[0059] Also provided is the use of zinc sulfate produced according to the methods defined herein or transition metal-doped zinc sulfate produced according to the methods defined herein as a catalyst for the production of furfural from lignocellulosic materials or their fractions.

[0060] On the other hand, a method is provided for regenerating an active transition metal-doped zinc sulfate catalyst that has been used to produce furfural from lignocellulosic materials or fractions thereof, the method comprising subjecting the transition metal-doped zinc sulfate to a reduction step by exposing it to hydrogen at a temperature in the range of about 400 to about 800°C.

[0061] On the other hand, solid zinc sulfate is provided when produced according to the methods defined herein.

[0062] On the other hand, a transition metal-doped solid zinc sulfate is provided, wherein the transition metal is selected from the group consisting of palladium, iron, nickel and cobalt.

[0063] In some embodiments, the transition metal-doped solid zinc sulfate contains at least 50 wt% zinc sulfate.

[0064] In some embodiments, the transition metal in the transition metal-doped solid is palladium. In other embodiments, the transition metal-doped solid contains palladium metal and palladium oxide.

[0065] In some embodiments, the transition metal-doped solid zinc sulfate contains 1 wt% to 5 wt% of transition metal.

[0066] In some embodiments, the transition metal-doped solid zinc sulfate contains additional metals that act as stabilizers and / or additional metals that regulate acidity.

[0067] On the other hand, transition metal-doped zinc sulfate produced according to methods as defined herein is provided. Attached Figure Description

[0068] Figure 1 The selectivity (a) of different products obtained from the pyrolysis of D-allose and the conversion of D-allose are shown at 400 °C with different catalysts.

[0069] Figure 2 The selectivity of different products obtained from the pyrolysis of D-allose and the conversion rate of D-allose are shown at different temperatures with and without a ZnSO4 / PdO catalyst (a) and (b).

[0070] Figure 3 The selectivity (a) and conversion of D-allose of different products obtained from the pyrolysis of D-allose are shown at 400 °C under different catalyst-allose mass ratios.

[0071] Figure 4 The selectivity (a) and conversion of D-allose are shown in the pyrolysis of D-allose at different water-to-allose mass ratios, with ZnSO4 / PdO as a catalyst at 400 °C and eight times the mass of allose.

[0072] Figure 5 The results show the selectivity of different products obtained from the pyrolysis of D-glucose and the conversion rate of D-glucose at 400℃ with different catalysts (a) and different catalyst-to-glucose mass ratios (b).

[0073] Figure 6 DTG analysis of D-glucose (a) and D-aloose (b) is shown with a catalyst-to-glucose or-aloose mass ratio of 2 and without a catalyst.

[0074] Figure 7 The results show the selectivity of different products obtained from the pyrolysis of xylan and the conversion rate of xylan at 400℃ with different catalysts (catalyst to xylan mass ratio: 4). Detailed Implementation

[0075] Throughout the specification and claims, the word “comprise” and other forms of the word (such as “comprising” and “comprises”) mean, but are not intended to exclude, for example, other additives, components, integers or steps.

[0076] Unless the context clearly specifies otherwise, the singular forms “a (a, an)” and “described” as used in this specification and the appended claims include a plural of indicators. Thus, for example, reference to “composition” includes a mixture of two or more such compositions, reference to “compound” includes a mixture of two or more such compounds, reference to “metal” includes a mixture of two or more such metals, etc.

[0077] This disclosure references, in whole or in part, certain documents which are incorporated herein by quotation. In the event of any inconsistency between the teachings of this disclosure and those documents, the teachings of this disclosure shall prevail.

[0078] Methods for producing furfural

[0079] In a first aspect, this disclosure relates to a method for producing furfural, comprising the steps of pyrolyzing lignocellulosic material or fractions thereof and producing furfural, wherein the production of furfural is catalyzed by a catalyst rich in solid zinc sulfate.

[0080] The inventors have discovered that increased selectivity and / or yield of furfural is observed when using a zinc sulfate-rich catalyst. The method according to the invention can be carried out with a short residence time, thus enabling high throughput. Furthermore, the method according to the invention using a zinc sulfate-rich catalyst generates low levels of wastewater and results in low levels of corrosion to process equipment.

[0081] Furfural is an important industrial chemical derived from biomass, and it can be used as a bio-based starting material for the production of various high-value-added chemicals. Furfural has a chemical structure... It is also known by the names furan-2-carboxaldehyde, furan-2-carboxaldehyde, furfural, and 2-furancarboxaldehyde. Besides being an important chemical in itself, furfural can be converted, for example, into liquid hydrocarbon fuels, into derivative monomers for plastics, or into food additives and pharmaceuticals. Specific examples of downstream chemicals that can be produced from furfural include furfuryl alcohol, furoic acid, furans, tetrahydrofuran, levulinic acid, butadiene, hexamethylenediamine, tetrahydrofurfural alcohol, methyltetrahydrofuran, and furfural-phenolic resins.

[0082] The method involves using lignocellulosic materials or fractions thereof as raw materials. The lignocellulosic materials contain cellulose, hemicellulose, and / or lignin. In some embodiments, the lignocellulosic material used in the method is selected from the group consisting of: sawdust, sawdust, sugarcane, corn cob, bagasse, oat hulls, cottonseed hulls, rice hulls, and wheat bran. In some embodiments, the lignocellulosic material used in the method is sugarcane. In some embodiments, the lignocellulosic material used in the method is bagasse. In some embodiments, the lignocellulosic material used in the method is corn cob.

[0083] If desired, fractions of lignocellulose material can be used instead of coarse lignocellulose. In some embodiments, cellulose fractions (e.g., fractions containing at least 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, or at least 95 wt% cellulose material) are used, for example, cellulose can be used. In some embodiments, hemicellulose fractions (e.g., fractions containing at least 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, or at least 95 wt% hemicellulose material) are used, for example, hemicellulose can be used. In some embodiments, fractions with low levels of lignin (e.g., fractions containing less than 10 wt%, less than 5 wt%, or less than 2 wt% lignin material) or fractions without lignin material are used.

[0084] Raw materials used in furfural production methods include monosaccharides, disaccharides, oligosaccharides, polysaccharides, and mixtures thereof. In some embodiments, lignocellulose fractions selected from the group consisting of monosaccharides, disaccharides, oligosaccharides, and polysaccharides are used.

[0085] In some embodiments, monosaccharides or mixtures of monosaccharides are used. In some embodiments, disaccharides, or mixtures of disaccharides, or mixtures of monosaccharides and disaccharides are used. In some embodiments, oligosaccharides, or mixtures of oligosaccharides, or mixtures of oligosaccharides and monosaccharides, or mixtures of oligosaccharides and disaccharides, or mixtures of oligosaccharides, monosaccharides, and disaccharides are used. In some embodiments, polysaccharides, or mixtures of polysaccharides, or mixtures of polysaccharides and monosaccharides, or mixtures of polysaccharides and disaccharides, or mixtures of polysaccharides and oligosaccharides, or mixtures of polysaccharides, oligosaccharides, monosaccharides, and / or disaccharides are used.

[0086] In some embodiments, fractions rich in monosaccharides (e.g., fractions containing at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, or at least 95 wt% monosaccharides) or fractions rich in disaccharides (e.g., fractions containing at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, or at least 95 wt% disaccharides) or fractions rich in oligosaccharides (e.g., fractions containing at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, or at least 95 wt% oligosaccharides) may be used.

[0087] Specific examples of monosaccharides suitable for use in the methods according to the invention include allose, glucose, xylose, arabinose, mannose, fructose, and galactose. In some embodiments, the raw material used in the method is a monosaccharide or a monosaccharide-rich fraction, wherein the monosaccharide is selected from the group consisting of allose, glucose, xylose, arabinose, mannose, fructose, and galactose. In some embodiments, the raw material is allose or an allose-rich fraction (e.g., containing at least 50 wt% allose). In some embodiments, the raw material is glucose or a glucose-rich fraction (e.g., containing at least 50 wt% glucose).

[0088] Specific examples of disaccharides suitable for use in the methods according to the invention include sucrose, lactose, and maltose. In some embodiments, the raw materials used in the method are disaccharides or disaccharide-rich fractions, wherein the disaccharides are selected from the group consisting of sucrose, lactose, and maltose.

[0089] In some embodiments, oligosaccharides are used. In some embodiments, polysaccharides are used. Specific examples of oligosaccharides and / or polysaccharides include xylan, mannan, arabinogalactan, fructan, and cellulose. In some embodiments, the fraction of the lignocellulosic material used is xylan. In some embodiments, the fraction of the lignocellulosic material used is cellulose.

[0090] When using lignocellulose fractions, they can be obtained from lignocellulose materials through any suitable method or process steps. Such method steps or process steps can be performed as part of this method if desired. Alternatively, pretreatment or preprocessing can be carried out separately from this method, for example using lignocellulose fractions already obtained from a supplier.

[0091] When the method includes one or more preprocessing steps, the steps may include, for example, one or more of the following: separating cellulose, hemicellulose and / or lignin fractions from one or more other fractions of the lignocellulosic material; hydrolyzing sugar bonds (e.g., present in polysaccharides and / or oligosaccharides); and separating monosaccharide fractions and / or disaccharide fractions and / or oligosaccharide fractions and / or polysaccharide fractions.

[0092] For example, lignocellulose materials can be exposed to increased temperature and / or pressure, and / or can undergo enzymatic hydrolysis and / or acidic and / or alkaline conditions to produce monosaccharides, disaccharides and / or oligosaccharides.

[0093] In some embodiments, one or more preprocessing steps may be performed to remove lignin fractions and / or hydrolyze sugar bonds. This can be achieved, for example, by physical pretreatment (such as by grinding and crushing), chemical pretreatment (such as with acidic or alkaline solutions and solvents), or biological pretreatment (such as with microorganisms including bacteria and / or by enzymatic saccharification). For example, if sawdust is used as a raw material, one or more preprocessing steps may be performed to improve the recovery of cellulose material, thereby improving the yield of furfural.

[0094] If desired, the fraction of interest can be separated from other components to provide a feedstock rich in the material of interest. Examples of suitable techniques include aqueous / organic extraction, precipitation / crystallization of the material from solution, and separation of solid / liquid fractions (e.g., filtration, decantation).

[0095] In cases where it is desirable to remove lignin fractions from solid lignocellulosic materials prior to their use in the method, in some embodiments, preprocessing includes treating the lignocellulosic material with an aqueous alkali at elevated temperatures to dissolve lignin, and separating the solid and liquid components.

[0096] Methods for producing furfural include the pyrolysis of lignocellulosic materials or fractions thereof. Pyrolysis involves thermally decomposing the material at elevated temperatures, typically in the presence of nitrogen or argon.

[0097] The pyrolysis of lignocellulosic materials or their fractions can be carried out at any suitable temperature, for example, in the range of about 200 to about 600°C. In some embodiments, the pyrolysis step is carried out in the temperature range of about 300 to about 500°C, or about 300 to about 400°C, or about 350 to about 450°C, or about 400 to about 500°C. In some embodiments, the pyrolysis step is carried out at a temperature of about 300°C, about 350°C, about 400°C, about 450°C, or about 500°C.

[0098] The pyrolysis step is performed for an appropriate period of time to effectively pyrolyze the lignocellulosic material or its fractions. For example, the duration of the pyrolysis step (e.g., the hold or residence time of the pyrolysis reaction) is in the range of about 5 seconds to about 2 minutes, or about 10 seconds to about 60 seconds, or about 20 seconds to about 50 seconds. In some embodiments, the duration of the pyrolysis step (hold time) is in the range of about 25 seconds to 45 seconds. In some embodiments, the duration of the pyrolysis step is about 10 seconds, about 15 seconds, about 20 seconds, about 25 seconds, about 30 seconds, about 35 seconds, about 40 seconds, about 45 seconds, about 50 seconds, about 55 seconds, or about 60 seconds.

[0099] The pyrolysis step can be performed using any suitable pyrolysis reactor, such as a fluidized bed reactor. In some implementations, a fluidized bed reactor is used.

[0100] The inventors have discovered that catalysts rich in solid zinc sulfate exhibit high catalytic activity, providing high conversion and selectivity for furfural production when used in the catalytic pyrolysis of lignocellulosic materials.

[0101] As defined herein, the term "zinc sulfate-rich" refers to a material containing at least 20 wt% zinc sulfate. In some embodiments, the zinc sulfate-rich material (e.g., a zinc sulfate-rich catalyst) comprises at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt% zinc sulfate, or at least 95 wt% zinc sulfate, or at least 98 wt% zinc sulfate, or at least 99 wt% zinc sulfate. In some embodiments, the catalyst is substantially composed of zinc sulfate, or is composed of zinc sulfate.

[0102] In some embodiments, zinc sulfate may be present in anhydrous or hydrated form. For example, in some embodiments, zinc sulfate may be zinc sulfate heptahydrate. In some other embodiments, zinc sulfate may be anhydrous zinc sulfate. References to zinc sulfate in this disclosure as wt% refer to wt% of the form of zinc sulfate used. For example, in the case of using zinc sulfate heptahydrate, the term wt% zinc sulfate refers to the wt% of zinc sulfate heptahydrate present in the material (e.g., in a zinc sulfate-rich catalyst).

[0103] In the method, any suitable amount of a catalyst rich in solid zinc sulfate can be used. In some embodiments, the weight ratio of catalyst to lignocellulosic material is in the range of 1:1 to 20:1, for example, in the range of 2:1 to 15:1 or about 6:1 to 10:1. In some embodiments, the weight ratio of catalyst to feedstock is about 1:1, about 2:1, about 3:1, about 4:1, about 5:1, about 6:1, about 7:1, about 8:1, about 9:1, about 10:1, about 11:1, about 12:1, about 13:1, about 14:1, or about 15:1.

[0104] Different forms of solid zinc sulfate-rich catalysts can be used in the methods described. For example, depending on the lignocellulosic material used as the feedstock, catalysts in transition metal-doped or undoped forms can provide particularly advantageous results. While in some embodiments pure or substantially pure zinc sulfate may be used, in some other embodiments the solid zinc sulfate-rich catalyst contains additional transition metals. The reference to additional transition metals should be understood as transition metals other than zinc.

[0105] As demonstrated by the examples, doping zinc sulfate with a transition metal such as palladium can provide the desired properties when used in the methods according to this disclosure. In some embodiments, the additional transition metal is selected from the group consisting of palladium, iron, copper, cobalt, and nickel. In some embodiments, the additional transition metal is palladium or iron. In some embodiments, the additional transition metal is palladium.

[0106] Unbound by any particular theory, it is believed that incorporating transition metals such as palladium helps to cleave the C-C bonds present in C6 sugars, thereby improving the conversion of furfural from feedstock and subsequent yield.

[0107] Therefore, in some embodiments, a catalyst rich in solid zinc sulfate that has been doped with another transition metal (e.g., palladium) is used, and the lignocellulosic material or fraction used in the method is a lignocellulosic material or fraction rich in C6 sugars (e.g., C6 monosaccharides, C6 disaccharides, C6 oligosaccharides, and / or C6 polysaccharides). The C6 sugar-rich lignocellulosic material or fraction is a lignocellulosic material or fraction containing at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, or at least 95 wt% of C6 sugars.

[0108] It was also found that solid zinc sulfate catalysts without additional transition metals performed particularly well in the method for feedstocks rich in C5 sugars (such as xylan). Therefore, in some embodiments, due to the use of solid zinc sulfate catalysts without additional transition metals, and because the lignocellulosic material or fraction used in the method is a lignocellulosic material or fraction rich in C5 sugars (e.g., C5 monosaccharides, C5 disaccharides, C5 oligosaccharides, and / or C5 polysaccharides), the lignocellulosic material or fraction is a lignocellulosic material or fraction containing at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, or at least 95 wt% of C5 sugars.

[0109] When a catalyst rich in solid zinc sulfate is doped with an additional transition metal, the additional transition metal is typically present in an amount up to 20 wt%. In some embodiments, the transition metal is present in an amount from about 0.1 wt% to about 10 wt% or from about 1 wt% to about 5 wt% based on the total weight of the catalyst. In some embodiments, the transition metal is present in an amount of about 0.5 wt%, about 1 wt%, about 1.5 wt%, about 2 wt%, about 2.5 wt%, about 3 wt%, about 3.5 wt%, about 4 wt%, about 4.5 wt%, or about 5 wt%.

[0110] In some embodiments, the catalyst rich in solid zinc sulfate contains about 0.1 wt% to about 5 wt% of an additional transition metal, such as 0.2 wt% to 5 wt%, or 0.5 wt% to 3 wt%, or about 0.2 wt%, about 0.5 wt%, about 1 wt%, about 2 wt%, about 3 wt%, about 4 wt%, or about 5 wt% of an additional transition metal.

[0111] When a catalyst rich in solid zinc sulfate is doped with another transition metal, the other transition metal may, for example, be mixed with or co-precipitated with the catalyst rich in solid zinc sulfate. Alternatively, the surface (or at least a portion of the surface) of the catalyst rich in solid zinc sulfate may be coated with another transition metal.

[0112] Any other suitable form of transition metal may be used with the catalyst rich in solid zinc sulfate. For example, the salt form of the other transition metal may be used. The other transition metal may also be present, or alternatively, as an oxide. The other transition metal may also be present, or alternatively, as the metal itself. In some embodiments, the other transition metal may be present in a mixture of multiple forms, such as as an oxide and as the metal itself. For example, in some embodiments, the other transition metal present on the surface of the catalyst rich in solid zinc sulfate may be present primarily as an oxide, and the other transition metal present inside the catalyst rich in zinc sulfate may be present primarily as the metal. In the case of palladium, for example, in some embodiments, palladium may be present in the catalyst rich in solid zinc sulfate as palladium metal and / or palladium oxide.

[0113] When another transition metal is added in the form of a salt of another transition metal, exemplary salts include nitrates, sulfates, acetates, chlorides, bromides, and iodides. In some embodiments, the other transition metal is added using a nitrate of a transition metal. In some embodiments, the other transition metal is palladium, and palladium nitrate is added to solid zinc sulfate.

[0114] In some embodiments, the transition metal-doped solid zinc sulfate-rich catalyst contains additional metals for stabilization and / or additional metals for adjusting acidity.

[0115] If desired, the catalyst may undergo additional processing steps before use. For example, the catalyst may be granulated to produce catalyst particles.

[0116] The method can be carried out using any suitable apparatus or reactor equipment. In some embodiments, the method is carried out as a batch process. In some other embodiments, the method is carried out as a continuous or semi-continuous process.

[0117] In some embodiments, the pyrolysis of lignocellulosic material or its fractions and the production of furfural catalyzed by a zinc sulfate-rich catalyst can be carried out as a single step in a single reactor. However, in other embodiments, the pyrolysis of lignocellulosic material or its fractions and the production of furfural catalyzed by a zinc sulfate-rich catalyst can be carried out as separate steps. For example, pyrolysis can be performed to generate a lignocellulosic vapor stream (e.g., in a first reactor), and then the lignocellulosic vapor stream can be contacted with a zinc sulfate-rich catalyst to produce furfural (e.g., in a second reactor). For example, the lignocellulosic vapor stream can pass over and / or through a zinc sulfate-rich catalyst bed. In some embodiments, the furfural production step is carried out using a moving bed reactor or a packed bed reactor. For example, a reactor containing a granular catalyst (e.g., a moving bed reactor or a packed bed reactor) can be used.

[0118] In some embodiments, pyrolysis and contact with the catalyst are carried out as separate steps, wherein the lignocellulosic material or its fractions are pyrolyzed in a first step (e.g., in a fluidized bed reactor) to produce a lignocellulosic vapor stream, which is carried by a stream containing argon and / or nitrogen to a second reactor (e.g., a packed bed reactor or a moving bed reactor) containing a particulate catalyst. If desired, water vapor is introduced, and then the lignocellulosic vapor stream is contacted with the catalyst to produce furfural, resulting in a product vapor stream containing furfural.

[0119] Furfural production can be carried out at any suitable temperature, for example, in the range of about 200 to about 600°C. In some embodiments, furfural production is carried out in the temperature range of about 300 to about 500°C, or about 300 to about 400°C, or about 350 to about 450°C, or about 400 to about 500°C. In some embodiments, furfural production is carried out at temperatures of about 300°C, about 350°C, about 400°C, about 450°C, or about 500°C.

[0120] The production of furfural is achieved by contacting a catalyst rich in solid zinc sulfate for a suitable period of time to provide a high conversion rate to furfural. For example, the contact with the catalyst may be for a period ranging from about 5 seconds to about 2 minutes, or from about 10 seconds to about 60 seconds, or from about 20 seconds to about 50 seconds. In some embodiments, the contact with the catalyst rich in solid zinc sulfate is for a period ranging from about 25 seconds to 45 seconds. In some embodiments, the duration is about 10 seconds, about 15 seconds, about 20 seconds, about 25 seconds, about 30 seconds, about 35 seconds, about 40 seconds, about 45 seconds, about 50 seconds, about 55 seconds, or about 60 seconds.

[0121] When the pyrolysis and production of furfural are carried out as part of a single step, the temperatures and time periods listed above may be applied, for example, to that single step.

[0122] The inventors have discovered that the presence or absence of water vapor / steam can affect the final yield of furfural. In some embodiments, the method for producing furfural is carried out in the absence of steam, for example, where furfural production is carried out in a nitrogen or argon atmosphere. In some other embodiments, furfural production is carried out in the presence of steam, for example, where steam / water vapor is added to a nitrogen and / or argon atmosphere. In some embodiments, the weight ratio of the steam used to the lignocellulosic material or its fraction is in the range of about 0.1:1 to about 30:1, or about 5:1 to about 30:1, or about 0.1:1 to about 20:1, or about 1:1 to about 20:1, or about 8:1 to about 20:1. In some embodiments, the weight ratio of steam to lignocellulosic material is about 0.1:1, about 0.5:1, about 1:1, about 2:1, about 3:1, about 4:1, 5:1, about 6:1, about 7:1, about 8:1, about 9:1, about 10:1, about 11:1, about 12:1, about 13:1, about 14:1, about 15:1, about 16:1, about 17:1, about 18:1, about 19:1, or about 20:1.

[0123] Typically, after the reaction, a product vapor stream containing furfural is obtained, which can be easily separated from the catalyst rich in solid zinc sulfate.

[0124] If desired, the furfural-containing product mixture can be separated from other organic components. For example, numerous byproducts may be generated, such as light compounds (LC, e.g., acetic acid and furan), levulinic acid (LA), 5-hydroxymethylfurfural (5-HMF), and L-glucanone (LGO), and it may be desirable to separate furfural from those components or reduce the levels of those byproducts. Any suitable processing technique can be used to separate and / or purify furfural.

[0125] In some implementations, furfural is separated from other components by distillation. For example, fractional distillation can be used, such as with a series of columns and appropriate temperature conditions, to separate furfural from the high and / or low boiling point components of the product mixture as needed.

[0126] In some other embodiments, furfural is separated by selectively condensing a product vapor stream containing furfural. The furfural-containing product vapor stream exists at an elevated temperature. By appropriately adjusting (i.e., lowering) the temperature of the product stream, byproducts with boiling points higher than furfural can be separated first from the furfural remaining in the gas phase. After separating the high-boiling-point materials, the furfural-containing vapor stream can then be subjected to a lower temperature (e.g., below the boiling point of furfural), resulting in the condensation of furfural, which can then be separated from the byproducts with lower boiling points.

[0127] As discussed above, this method produces furfural. Therefore, furfural produced by a method as defined herein is also provided.

[0128] The method for producing furfural also provides pathways for downstream chemicals that can be generated from furfural. Therefore, in another aspect, a method is provided for producing one or more of furfuryl alcohol, furoic acid, furan, tetrahydrofuran, levulinic acid, butadiene, hexamethylenediamine, tetrahydrofurfuryl alcohol, methyltetrahydrofuran, and furfural-phenolic resin, comprising producing furfural according to the method of the invention; and converting said furfural into furfuryl alcohol, furoic acid, furan, tetrahydrofuran, levulinic acid, butadiene, hexamethylenediamine, tetrahydrofurfuryl alcohol, methyltetrahydrofuran, and furfural-phenolic resin.

[0129] Methods for producing the above-mentioned compounds from furfural are known in the art. For example, furfuryl alcohol can be produced, for instance, by reduction with a suitable catalyst (such as nickel, palladium, platinum, or zinc-copper based catalyst), electrocatalytic reduction, enzymatic reduction, or by biotransformation using suitable bacteria or yeast (see, for example, US2077409; Gutierrez et al., Appl. Biochem. Biotechnol., 2002, 98-100, 327-40; Brosnahan et al., Nanoscale, 2021, 13, 2312-2316, the entire contents of which are incorporated herein by reference).

[0130] Furosic acid can be produced, for example, by the oxidation of furfural or furfuryl alcohol (e.g., with permanganate or dichromate). As another example, an aqueous Cannizaro reaction (e.g., treatment of furfural with an aqueous alkali metal, such as sodium hydroxide) can be used to produce a mixture of furrosic acid (following the acidification product mixture) and furfuryl alcohol.

[0131] Furans can be produced, for example, by decarbonylation of furfural (e.g., over palladium, zeolite, or nickel-magnesium oxide catalysts) or by decarboxylation of furoic acid (which itself can be generated from furfural). See, for example, Jiminez-Gomez et al., ACS SustainableChem.Eng., 2019, 7, 8, 7676-7685; WO2015 / 020845; EP3126342 and US 7044480, the entire contents of which are incorporated herein by reference.

[0132] Tetrahydrofuran can be produced, for example, by hydrogenation of furan (which itself can be produced from furfural), for example using a palladium catalyst such as palladium oxide, or directly from furfural without separating intermediates (e.g., by reduction using hydrogen and a palladium catalyst). See, for example, WO2014 / 118806 and Org. Synth. 1936, 16, 77, the entire contents of which are incorporated herein by reference.

[0133] Levulopyric acid can be produced, for example, by treatment with an alcohol (e.g., methanol) and a dialkoxymethane (e.g., dimethoxymethane) to produce an alkyl ester of levulopyric acid, which can then be hydrolyzed (e.g., under acidic aqueous conditions) to produce levulopyric acid (see, for example, Shao et al., Green Energy and Environment, 2019, 4, 4, 400-413, the entire contents of which are incorporated herein by reference).

[0134] Butadiene can be produced, for example, by converting furfural to tetrahydrofuran (as described above) and tetrahydrofuran to butadiene (for example, by dehydration-ring opening) (for example, using zeolite catalysts, such as silica-phosphorus zeolite (see, for example, Abdelrahman et al., ACS Sustainable Chem. Eng., 2017, 5, 5, 3732-3736, the entire contents of which are incorporated herein by reference).

[0135] Hexamethylenediamine can be produced, for example, by converting furfural to 1,6-hexanediol and then amination to produce hexamethylenediamine (see, for example, US9518005, the entire contents of which are incorporated herein by reference).

[0136] Tetrahydrofurfuryl alcohol can be produced, for example, from furfuryl alcohol (which itself can be produced from furfural), or directly from furfural, for example, by hydrogenation in the presence of a suitable catalyst, such as a palladium catalyst supported on hydroxyapatite (see, for example, Li et al., Ind. Eng. Chem. Res., 2017, 56, 31, 8843-8849, the entire contents of which are incorporated herein by reference).

[0137] 2-Methyltetrahydrofuran can be produced, for example, by reducing furfural, such as by hydrogenation in the presence of a suitable catalyst (e.g., reduction in the presence of a Co-based catalyst to produce 2-methylfuran, followed by reduction in the presence of a Ni-based catalyst to produce 2-methyltetrahydrofuran). See, for example, Liu et al., Molecular Catalysis, 2020, 490, 110951, the entire contents of which are incorporated herein by reference.

[0138] Furfural-phenolic resins can be produced, for example, by reacting furfural with phenol, for example, in the presence of an alkali such as sodium hydroxide.

[0139] Methods for producing solid zinc sulfate

[0140] The disposal of rubber tires at the end of their life cycle presents waste management challenges for many developing and developed countries. Improper disposal of waste tires can lead to numerous health, safety, and environmental hazards. Waste tire pyrolysis is a commonly used method for processing waste tires, involving exposure to high temperatures in an oxygen-deficient atmosphere. Typically, waste tire pyrolysis produces an equivalent amount of solid tire carbon black, but the demand for post-pyrolysis carbon black is limited because it usually contains many contaminants. One use of post-pyrolysis carbon black is to convert it into activated carbon; however, such methods often result in the leaching of metal ions into water, causing environmental hazards.

[0141] The inventors have discovered a method for producing zinc sulfate from waste sources such as tire black, for example, by promoting the production of a catalyst rich in solid zinc sulfate as described above. Therefore, in another aspect, a method for producing solid zinc sulfate is provided, comprising the steps of: contacting tire black with aqueous sulfuric acid to produce a mixture of aqueous zinc sulfate and solid tire black residue; separating the aqueous zinc sulfate from the solid tire black residue; and recovering solid zinc sulfate from the aqueous zinc sulfate.

[0142] This method enables waste zinc to be captured and separated in a solid state and used in materials or downstream processes, such as for the pyrolysis and conversion of lignocellulosic materials into furfural.

[0143] The method involves contacting tire black with aqueous sulfuric acid. Typically, the aqueous sulfuric acid and tire black are mixed (e.g., the tire black can be added to the aqueous sulfuric acid, or vice versa), and then mixed for a suitable time period to allow leaching of zinc from tire residues and produce aqueous zinc sulfate. A mixer can be used, for example, to agitate or mix the mixture to promote the reaction. In some embodiments, the mixing of tire black and sulfuric acid is carried out under controlled stirring at a specific rate. When stirring the mixture, the stirring rate can be, for example, within the following ranges: about 100 rpm to about 600 rpm, or about 200 rpm to about 400 rpm, or about 100 rpm, about 200 rpm, about 300 rpm, about 400 rpm, about 500 rpm, or about 600 rpm.

[0144] The step of contacting tire black with aqueous sulfuric acid is carried out at a temperature suitable for leaching zinc from the tire black and producing aqueous zinc sulfate. For example, the step can be carried out at temperatures in the following ranges: about 25 to about 90°C, or about 40 to about 80°C, or about 30°C, about 40°C, about 50°C, about 60°C, about 70°C, about 75°C, about 80°C, about 85°C, or about 90°C.

[0145] The concentration of sulfuric acid in aqueous sulfuric acid is typically in the range of about 0.5 to about 15 mol / L, for example, in some embodiments, it is in the range of about 1 to about 10 mol / L or about 1 to about 5 mol / L. In some embodiments, the concentration of aqueous sulfuric acid is about 1, about 2, about 3, about 4, or about 5 mol / L.

[0146] A certain amount of aqueous sulfuric acid is used to facilitate the extraction of zinc from tire black. The volume-to-mass ratio of aqueous sulfuric acid to tire black is typically in the range of about 1:1 to 20:1, or about 1:1 to 10:1, or about 1.5:1 to 10:1, or about 1:1 to 6:1, or about 1.5:1 to 6:1, or about 1:1, or about 2:1, or about 3:1, or about 4:1, or about 5:1, or about 6:1.

[0147] In some embodiments, the aqueous sulfuric acid has a sulfuric acid concentration in the range of about 1 mol / L to about 5 mol / L, and is used at a volume:mass ratio of aqueous sulfuric acid to tire carbon black in the range of 1.5:1 to 10:1.

[0148] The contacting step between tire carbon black and aqueous sulfuric acid is carried out for an appropriate period of time to promote the extraction of zinc as zinc sulfate. In some embodiments, the contacting step is carried out for a period ranging from 5 minutes to 24 hours, for example, within the following ranges: 5 minutes to 12 hours, or 5 minutes to 6 hours, or 10 minutes to 2 hours, or about 10 minutes, about 20 minutes, about 30 minutes, about 40 minutes, about 50 minutes, about 1 hour, about 1.5 hours, or about 2 hours.

[0149] Contact between tire carbon black and aqueous sulfuric acid can be carried out using any suitable equipment. For example, a continuous stirred tank reactor (CSTR) can be used.

[0150] If desired, tire black may undergo one or more preprocessing steps before contact with aqueous sulfuric acid. For example, after the pyrolysis of waste tires, if desired, the resulting tire black may be ground and sieved to reduce particle size, for example, to produce tire black with an average particle size in the range of 100 μm to 500 μm, or about 200 μm to 400 μm, or about 250 μm to 300 μm. Reducing particle size is understood to facilitate zinc extraction. Steel and / or wire components may be removed from the tire black, for example, before contact with aqueous sulfuric acid. Before contact with aqueous sulfuric acid, the tire black may be washed, for example, with water or an aqueous solvent.

[0151] Therefore, in some embodiments, tire carbon black is subjected to one or more of the following process steps before contact with aqueous sulfuric acid:

[0152] Reduce particle size (e.g., by grinding tire carbon black and / or sieving);

[0153] Removal of steel and / or wire from tire carbon black; and

[0154] Wash with water or an aqueous solvent.

[0155] Following the step of contacting tire black with aqueous sulfuric acid, the aqueous zinc sulfate is separated from the solid tire black residue. Many methods can be used to separate the aqueous zinc sulfate from the solid tire black residue, such as by filtration, or by allowing the solid portion to settle and decanting, siphoning, or otherwise collecting the liquid component. In some embodiments, the aqueous zinc sulfate is separated from the solid tire black residue by filtration. If desired, the solid tire black residue can be washed, for example, with water or an aqueous solvent to recover additional zinc sulfate.

[0156] Solid zinc sulfate is recovered from aqueous zinc sulfate after separation from tire carbon black residue. Suitable processing techniques include recovery of solid zinc sulfate by one or more of evaporation, crystallization, and precipitation.

[0157] In some embodiments, water is removed by one or more of evaporation and / or distillation. The hydrated zinc sulfate can be heated, for example, to a temperature in the range of 50 to 100°C, such as about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 95°C, or about 100°C. Vacuum distillation can be used, for example, so that water can be removed at temperatures lower than atmospheric pressure.

[0158] For example, in some embodiments, water is evaporated from aqueous zinc sulfate by boiling the mixture (e.g., heating to about 100°C). In some other embodiments, water can be evaporated by reducing pressure and heating at a temperature in the range of 50 to 60°C.

[0159] Evaporation and / or distillation serve to concentrate aqueous zinc sulfate mixtures. Typically, reducing the water content results in a saturated solution of zinc sulfate, and solid zinc sulfate crystallizes and / or precipitates from the solution.

[0160] Therefore, in some embodiments, solid zinc sulfate is recovered by evaporating water from the aqueous sulfate at a temperature in the range of 50 to 100°C to reduce the water content, and then allowing the solid zinc sulfate to precipitate and / or crystallize.

[0161] In some other embodiments, solid zinc sulfate can be obtained by adding an antisolvent (e.g., a water-miscible organic solvent) to cause solid zinc sulfate to precipitate and / or crystallize.

[0162] Evaporation, distillation, precipitation, and / or crystallization steps can be performed using any suitable equipment. For example, a crystallizer can be used to obtain solid zinc sulfate, such as, for example, the Swenson DTE crystallizer.

[0163] The obtained solid zinc sulfate can be separated from water or aqueous solvent by any suitable method, such as by filtration, or by allowing the solid component to settle and removing the liquid fraction, such as by siphoning or decantation.

[0164] In some embodiments, the residual liquid component may be subjected to further processing to recover additional zinc sulfate from the solution. For example, in some embodiments, the resulting solution may be subjected to one or more evaporation-precipitation cycles.

[0165] In some implementations, zinc sulfate is recovered from hydrated zinc sulfate in the form of zinc sulfate heptahydrate.

[0166] Therefore, in some embodiments, an evaporation or distillation step is performed to remove water and concentrate the zinc sulfate in the solution to a concentration such that subsequent crystallization and / or precipitation produces zinc sulfate heptahydrate. In some embodiments, the reduction in water content during evaporation is controlled so that subsequent precipitation produces solid zinc sulfate heptahydrate. In some embodiments, when recovering solid zinc sulfate by crystallization from water or an aqueous solvent, the amount of water used is controlled so that crystallization produces solid zinc sulfate heptahydrate.

[0167] The evaporation step can be controlled, for example, under specific conditions, so that the subsequent precipitation step produces solid zinc sulfate heptahydrate. For example, the aqueous zinc sulfate mixture can first be heated to about 100°C and the water removed to produce a saturated solution of zinc sulfate, which can then be heated at a lower temperature (e.g., in the range of 50 to 60°C) while being subjected to reduced pressure to remove additional water to produce zinc sulfate heptahydrate.

[0168] Depending on the intended use of the recovered solid zinc sulfate, it may then be exposed to a calcination step, for example, to remove impurities. Therefore, in some embodiments, the method includes the step of calcining the solid zinc sulfate.

[0169] Calcination is the process of heating a solid to a high temperature in the absence of air or oxygen. Any suitable equipment that allows for controlled calcination conditions can be used, such as a reactor like a packed bed reactor.

[0170] The calcination step is carried out at elevated temperatures, for example, in the range of about 300 to about 1000°C. In some embodiments, the calcination step is carried out at temperatures in the range of about 400 to about 800°C (e.g., about 400°C, about 500°C, about 600°C, about 700°C, or about 800°C).

[0171] The calcination step can be carried out, for example, in the presence of an inert atmosphere such as argon or nitrogen.

[0172] After zinc is recovered from waste tire carbon black, the resulting tire carbon black can then be used as a clean fuel in power plants or further upgraded using conventional methods to become an advanced adsorbent, such as carbon black. Therefore, in some embodiments, the method includes recovering solid tire carbon black residue. In some embodiments, the method includes recovering solid tire carbon black residue and converting the solid tire carbon black residue into carbon black.

[0173] Methods for producing transition metal-doped zinc sulfate

[0174] This article also provides methods for producing transition metal-doped zinc sulfate (i.e., zinc sulfate doped with another transition metal that is not zinc). Such materials can be used as catalysts, for example, for producing furfural as discussed herein.

[0175] The method includes contacting tire black with aqueous sulfuric acid to produce a mixture of aqueous zinc sulfate and solid tire black residue; separating the aqueous zinc sulfate from the solid tire black residue; recovering solid zinc sulfate from the aqueous zinc sulfate; contacting the zinc sulfate with a salt of another transition metal; and producing transition metal-doped solid zinc sulfate.

[0176] The steps of contacting tire black with aqueous sulfuric acid, separating aqueous zinc sulfate from solid tire black residue, and recovering solid zinc sulfate from aqueous zinc sulfate can be performed as described above in the context of discussing methods for producing solid zinc sulfate, and the embodiments discussed with respect to those methods are also applicable to methods for producing transition metal-doped zinc sulfate.

[0177] The transition metal used to dope zinc sulfate can be any desired transition metal other than zinc. When the transition metal-doped zinc sulfate is intended to be used as a catalyst for the production of furfural, the transition metal can be, for example, a transition metal that improves catalytic activity, and can be selected from the group consisting of palladium, iron, cobalt, and nickel. In some embodiments, the transition metal is palladium or iron. In some embodiments, the transition metal is palladium.

[0178] Transition metal-doped solid zinc sulfate can be produced in a variety of ways.

[0179] In some implementations, solid zinc sulfate is recovered from aqueous zinc sulfate before contact with transition metal salts.

[0180] When a transition metal is added in the form of a salt, exemplary salts include nitrates, sulfates, acetates, chlorides, bromides, and iodides. In some embodiments, a transition metal nitrate is used to add the transition metal. In some embodiments, the transition metal is palladium, and palladium nitrate is added to solid zinc sulfate.

[0181] In embodiments where the transition metal salt is contacted with solid zinc sulfate, this can be accomplished, for example, by mixing the solid zinc sulfate with the transition metal salt in the presence of an organic solvent. Any organic solvent that dissolves the transition metal salt can be used, such as an alcohol solvent. In some embodiments, the organic solvent is ethanol.

[0182] Typically, solid zinc sulfate and a transition metal salt solution are mixed together in appropriate amounts. In some embodiments, the liquid-to-solid ratio is 10 mL / g.

[0183] Typically, a solution containing a transition metal salt and solid zinc sulfate is mixed together for a suitable period of time to ensure good mixing of the components and the formation of a homogeneous mixture. Mixing can be accomplished using any suitable means, such as a top-mounted stirrer. In some embodiments, ultrasonic treatment is used to mix the solid zinc sulfate with the salt of another transition metal. Ultrasonic treatment uses acoustic energy at ultrasonic frequencies to agitate and mix particles in the solution. The ultrasonic treatment step can be performed for a suitable period of time. In some embodiments, the solution containing the solid zinc sulfate catalyst and the salt of another transition metal is subjected to ultrasonic treatment for a period ranging from about 5 minutes to 1 hour, or from about 10 minutes to about 30 minutes.

[0184] In some embodiments, solid zinc sulfate is mixed with a salt of another transition metal salt that is present in a solvent-soluble form, so as to impregnate the zinc sulfate with the other transition metal.

[0185] The mixing of solid zinc sulfate with other transition metal salts can be carried out using any suitable equipment. For example, a continuous stirred tank reactor (CSTR) can be used.

[0186] When a transition metal is introduced using an organic solvent solution, the organic solvent is typically removed after mixing. This can be achieved, for example, by heating and / or vacuum drying steps. The mixture can be heated, for example, in an oven or autoclave, at temperatures ranging from about 50°C to about 250°C, or about 150°C to about 250°C, or about 160°C to about 200°C, or about 150°C, or about 160°C, or about 170°C, or about 180°C, or about 190°C, or about 200°C, or about 210°C, or about 220°C, or about 230°C, or about 240°C, or about 250°C. Suitable time periods for removing the organic solvent at high temperatures can be, for example, within the range of: 3 to 24 hours, or 6 to 24 hours, or 12 to 16 hours, or about 6 hours, about 8 hours, about 10 hours, about 12 hours, about 14 hours, or about 16 hours. In some implementations, organic solvents are removed by hydrothermal treatment in an autoclave at a temperature ranging from 150°C to about 250°C for a period ranging from 12 hours to about 16 hours.

[0187] In some embodiments, when recovering solid zinc sulfate from aqueous zinc sulfate before contact with a transition metal salt, transition metal-doped solid zinc sulfate is produced by condensing transition metal vapor onto the surface of the solid zinc sulfate. For example, a salt of another transition metal can be vaporized and then condensed onto the surface of the solid zinc sulfate. This allows the transition metal to be directly loaded onto the surface of the solid zinc sulfate catalyst.

[0188] As an alternative method, transition metal-doped solid zinc sulfate can be produced, for example, by mixing a transition metal salt with aqueous zinc sulfate, and by co-precipitation and / or co-crystallization.

[0189] For example, a solution of a transition metal salt in an organic solvent (such as an alcohol like ethanol) can be added to aqueous zinc sulfate to produce a solution, and then the mixture can be subjected to one or more evaporation, distillation, precipitation and / or crystallization steps.

[0190] Evaporation, distillation, precipitation, and / or crystallization steps can be performed using any suitable equipment. For example, a crystallizer can be used to obtain transition metal-doped solid zinc sulfate, such as, for example, the Swenson DTE crystallizer.

[0191] Any suitable form of transition metal can be used with solid zinc sulfate. For example, a salt of the transition metal can be used. The transition metal can also or alternatively exist as an oxide. The transition metal can also or alternatively exist in its own metal form. In some embodiments, the transition metal can exist in a mixture of multiple forms, such as as an oxide and as its own metal. For example, in some embodiments, the transition metal present on the surface of solid zinc sulfate can be present as an oxide (or primarily as an oxide), and the transition metal present inside the zinc sulfate can be present as a metal (or primarily as a metal). In the case of palladium, for example, in some embodiments, palladium can exist as palladium metal and / or palladium oxide within and / or on solid zinc sulfate.

[0192] In some implementations, in addition to doping with a transition metal such as palladium, iron, cobalt, or nickel, a stabilizing metal salt and / or an acidity-tuning metal salt are added. Such steps can be performed to improve the efficiency of the doping process, for example, by stabilizing the transition metal by forming a stable spinel or alloy that is not prone to agglomeration after heat treatment. Examples of stabilizing metals and / or acidity-tuning metals that can be used include lanthanum and cesium.

[0193] In some embodiments, a stable metal salt and / or an acidity-modifying metal salt are introduced by impregnation on a solid zinc sulfate support or by co-precipitation with zinc sulfate and transition metals.

[0194] In some implementations, solid zinc sulfate is recovered from aqueous zinc sulfate before being mixed with transition metal salts, as well as stabilizing metal salts and / or acidity-adjusting metal salts.

[0195] In some embodiments, a stabilizing metal salt and / or an acidity-adjusting metal salt are mixed with aqueous zinc sulfate and a salt of a transition metal, and transition metal-doped solid zinc sulfate is produced by co-precipitation and / or co-crystallization.

[0196] In some embodiments, a calcination step is performed after the production of transition metal-doped solid zinc sulfate, for example, to remove impurities. Therefore, in some embodiments, the method includes the step of calcining transition metal-doped solid zinc sulfate.

[0197] The calcination step can be used to provide any one or more of the following benefits: mechanically and thermodynamically stabilizing the microstructure of transition metal-doped zinc sulfate, removing other impurities or volatile substances, providing a more uniform and homogeneous distribution of transition metal-doped zinc sulfate, and / or improving catalytic activity.

[0198] Any suitable equipment that allows for controlled calcination conditions can be used, such as a reactor such as a packed bed reactor.

[0199] The calcination step is carried out at elevated temperatures, for example, in the range of about 300 to about 1000°C. In some embodiments, the calcination step is carried out at temperatures in the range of about 400 to about 800°C (e.g., about 400°C, about 500°C, about 600°C, about 700°C, or about 800°C).

[0200] The calcination step can be carried out, for example, in the presence of an inert atmosphere such as argon or nitrogen.

[0201] In some embodiments, after calcination, the transition metal-doped solid zinc sulfate undergoes a reduction step by exposure to hydrogen at a temperature in the range of about 400 to about 800°C, for example, in the range of about 500 to 700°C, or at about 400°C, or about 500°C, or about 600°C, or about 700°C, or about 800°C. It is believed that carrying out the reduction step can help produce a particularly active catalyst. Typically, the reduction step is carried out in the presence of an inert gas such as hydrogen.

[0202] The reduction step can be carried out using any suitable equipment. For example, a packed bed reactor can be used.

[0203] Zinc sulfate produced by the above methods and transition metal-doped solid zinc sulfate can be used as catalysts, for example, for the production of furfural. Therefore, the use of zinc sulfate produced by the methods defined herein or transition metal-doped solid zinc sulfate produced by the methods defined herein as catalysts for the production of furfural from lignocellulosic materials or their fractions is also provided.

[0204] In some embodiments, when transition metal-doped solid zinc sulfate is used as a catalyst for the production of furfural, it may be used only once or for a small amount of reaction. However, in other embodiments, the catalyst may be used to produce many batches of furfural, or for extended periods of time in a continuous process. In some cases, it may be desirable to treat the catalyst after it has been used multiple times or for a sufficient period of time to regenerate and / or improve its activity, for example by subjecting it to the reduction conditions described above.

[0205] Therefore, a method is provided for regenerating an active transition metal-doped zinc sulfate catalyst that has been used to produce furfural from lignocellulosic materials or fractions thereof, the method comprising, for example, subjecting the transition metal-doped zinc sulfate to a reduction step by exposing it to hydrogen at a temperature in the range of about 400 to about 800°C.

[0206] As discussed above regarding methods for producing solid zinc sulfate, tire carbon black residue can then be used as fuel in power plants or converted into adsorbents such as carbon black using conventional methods. Therefore, in some embodiments, the method includes recovering the solid tire carbon black residue. In some embodiments, the method includes recovering the solid tire carbon black residue and converting the solid tire carbon black residue into carbon black.

[0207] Materials rich in zinc sulfate and zinc sulfate doped with transition metals

[0208] This disclosure also relates to zinc sulfate-rich materials and catalysts themselves, which can be used as catalysts in furfural production.

[0209] Therefore, in another respect, solid zinc sulfate produced by methods as defined herein is provided.

[0210] Transition metal-doped solid zinc sulfate is also provided, wherein the transition metal is selected from the group consisting of palladium, iron, nickel, and cobalt. In some embodiments, the transition metal is palladium.

[0211] In some embodiments, the transition metal-doped solid zinc sulfate contains at least 20 wt% zinc sulfate. In some embodiments, the transition metal-doped solid zinc sulfate contains at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt% zinc sulfate, or at least 95 wt% zinc sulfate, or at least 98 wt% zinc sulfate, or at least 99 wt% zinc sulfate.

[0212] In some embodiments, zinc sulfate may be present in anhydrous or hydrated form. For example, in some embodiments, zinc sulfate may be zinc sulfate heptahydrate. In some other embodiments, zinc sulfate may be anhydrous zinc sulfate. References to zinc sulfate in this disclosure as wt% refer to wt% of the form of zinc sulfate used. For example, in the case of using zinc sulfate heptahydrate, the term wt% zinc sulfate refers to the wt% of zinc sulfate heptahydrate present in the material (e.g., in a zinc sulfate-rich catalyst).

[0213] In some embodiments, the transition metal is selected from the group consisting of palladium, iron, copper, cobalt, and nickel. In some embodiments, the transition metal is palladium or iron. In some embodiments, the transition metal is palladium.

[0214] Transition metals are typically present in amounts up to 20 wt%. In some embodiments, transition metals are present in amounts from about 0.1 wt% to about 10 wt% or from about 1 wt% to about 5 wt% based on the total weight of the catalyst. In some embodiments, transition metals are present in amounts of about 0.5 wt%, about 1 wt%, about 1.5 wt%, about 2 wt%, about 2.5 wt%, about 3 wt%, about 3.5 wt%, about 4 wt%, about 4.5 wt%, or about 5 wt%.

[0215] Transition metals may be mixed with, for example, solid zinc sulfate, or co-precipitated. Alternatively, the surface (or at least a portion of the surface) of solid zinc sulfate may be coated with a transition metal.

[0216] Any suitable form of transition metal can be used with solid zinc sulfate. For example, a salt of the transition metal can be used. The transition metal can also or alternatively exist as an oxide. The transition metal can also or alternatively exist in its own metal form. In some embodiments, the transition metal can exist in a mixture of multiple forms, such as as an oxide and as its own metal. For example, in some embodiments, the transition metal present on the surface of solid zinc sulfate can be present as an oxide (or primarily as an oxide), and the transition metal present inside a zinc sulfate-rich catalyst can be present as a metal (or primarily as a metal). In the case of palladium, for example, in some embodiments, palladium can exist as palladium metal and / or palladium oxide within and / or on solid zinc sulfate.

[0217] When a transition metal is added in the form of a salt, exemplary salts include nitrates, sulfates, acetates, chlorides, bromides, and iodides. In some embodiments, a transition metal nitrate is used to add the transition metal. In some embodiments, the transition metal is palladium, and palladium nitrate is added to solid zinc sulfate.

[0218] In some embodiments, the transition metal-doped solid zinc sulfate contains additional metals that act as stabilizers and / or adjust acidity. The role of these additional stabilizing and / or acidity-adjusting metals can be, for example, to improve catalytic performance, or to stabilize the transition metal dopant present on the catalyst by forming spinels or alloys, which can prevent the catalyst from agglomerating after heat treatment.

[0219] This article also provides transition metal-doped solid zinc sulfate produced according to methods as defined herein.

[0220] Example

[0221] This disclosure is further illustrated by the following non-limiting examples.

[0222] experiment

[0223] 1. Preparation of zinc sulfate from waste tire carbon black

[0224] Waste tire carbon black was derived from the pyrolysis of waste tires (mixture) in a pilot-scale moving bed reactor at 800 °C. The tire carbon black sample was ground and sieved to a size of 250–300 μm and dried at 105 °C for 15 h. For tire carbon black, steel and wire were removed before washing. The elemental analysis of waste tire carbon black was presented in our previous study

[17] (see Table 1). The ash content was 13.3 wt%, with Zn being the most abundant element, followed by silicon (Si). Their compositions in the ash were 30 wt% and 12 wt%, respectively. Other major metals were calcium (Ca, 4.7 wt%, based on ash), aluminum (Al, 1.2 wt%, based on ash) and iron (Fe, 1.0 wt%, based on ash).

[0225] To recover zinc from tire black, sulfuric acid of varying concentrations (1-5 mol / L) was mixed with water-washed tire black, with an L / S ratio of 1 ml / g-6 ml / g. All leaching experiments were conducted in 250 mL Erlenmeyer flasks in a controlled temperature bath at 25°C-80°C, with stirring for 10-120 min periods. For all cases studied, the stirring rate was controlled at 300 rpm. Subsequently, the slurry was separated by filtration using filter paper with a 450 μm cutoff size. (S4) The Zn-rich leachate was then evaporated at approximately 100°C until saturated. The resulting saturated solution was transferred to a water bath to precipitate zinc sulfate. The resulting solution was further subjected to evaporation-precipitation cycles three times. Alternatively, the saturated solution was slowly evaporated at 50-60°C under low pressure, and the resulting crystalline precipitate was separated as ZnSO4·7H2O.

[0226] Table 1. Elemental composition of waste tire carbon black

[0227]

[0228] 2. Preparation of Zinc Sulfate Catalyst

[0229] Pure ZnS, ZnO, and ZnSO4 were purchased from Merck Ltd. A certain amount of Pd(NO3)2·2H2O (Merck) was mixed with ZnSO4·7H2O (Merck) and 30 mL of ethanol at a liquid-to-solid (L / S) ratio of 10 mL / g in a beaker and ultrasonicated for 15 min. The mixture was then transferred to an autoclave for hydrothermal treatment at 180 °C for 12 h, followed by vacuum drying at 80 °C. Subsequently, the powder was calcined at 550 °C for 2 h for future use. The prepared catalyst was labeled ZnSO4 / PdO with a PdO content of approximately 0.8 wt% (1.1 mol%).

[0230] 3. Formation of furfural

[0231] 3.1 Materials

[0232] D-allose (C6H) was used as a raw material for testing in this study. 12 O6), D-glucose (C6H) 12 O6) and xylan ((C5H) 10 O5) n It is reagent grade, with a purity >99%, and was purchased from Merck Ltd.

[0233] 3.2 Pyrolysis Experiment

[0234] The pyrolysis experiments were conducted in a Pyro-GC system with a fixed-bed quartz tube reactor (2 mm in diameter and 30 mm in length), as previously described

[13] . In short, the biomass component and the catalyst (with and without H2O) were located in the first and second stages, respectively. Temperatures varied in the range of 300–500 °C, and the carrier gas was helium (He, 26 mL / min). The holding time was set to 25 s for each terminal temperature. The effluent from the reactor was fed to an FID detector (Agilent, 7890B) coupled to a capillary column for the liquid product. The oven was ramped up from 50 °C (held for 2 min) to 250 °C (held for 2 min) at a rate of 25 °C / min. The split ratio was set to 25:1. Each condition was repeated at least twice.

[0235] 3.3 Results

[0236] 3.3.1 D-Allose as a raw material

[0237] The catalytic pyrolysis of D-allose (C6) at 400 °C was tested with different catalysts at a catalyst-to-biomass mass ratio of 4. The results showed... Figure 1 The conditions are as follows: pyrolysis in a Pyro-GC system; feedstock: D-allose; pyrolysis temperature: 400℃; heating rate: 20℃ / ms; holding time: 25s; mass ratio of catalyst to D-allose: 0 or 4; mass ratio of water to D-allose: 0.

[0238] Regarding the conversion of allosugar, it increased from 70 wt% with allosugar alone to 94 wt% with the use of a ZnSO4 / PdO catalyst (0.8 wt% (1.1 mol%) PdO). Following the blank case (i.e., allosugar alone), ZnS, ZnSO4, and ZnSO4 / PdO, the selectivity for furfural increased from 22% with allosugar alone to 30%, 34%, and 48%, respectively. In contrast, the use of ZnO or PdO promoted the production of furans other than furfural.

[0239] Considering the strong influence of temperature on catalytic activity, different temperatures ranging from 300 to 500 °C were tested with and without ZnSO4 / PdO as a catalyst. Figure 2 As observed, compared to D-allose alone, the use of this catalyst simultaneously improved both the conversion of D-allose and the selectivity for furfural at all test temperatures. In particular, 400°C was further confirmed as the optimal temperature for both the overall conversion of allose and the selectivity for furfural.

[0240] The conditions are as follows: pyrolysis in a Pyro-GC system; raw material: D-allose; pyrolysis temperature: 300-500℃, temperature difference of 50℃; heating rate: 20℃ / ms; holding time: 25s; mass ratio of ZnSO4 / PdO to D-allose: 0 or 4; mass ratio of water to D-allose: 0.

[0241] In addition, such as Figure 3 As shown, different catalyst / allose ratios were tested at 400 °C. The conditions were as follows: pyrolysis in a Pyro-GC system; feedstock: D-allose; pyrolysis temperature: 400 °C; heating rate: 20 °C / ms; holding time: 25 s; mass ratio of ZnSO4 / PdO to D-allose: 0-8; mass ratio of water to D-allose: 0.

[0242] When using 2x and 4x ZnSO4 / PdO catalysts, the selectivity for furfural increased linearly, and then gradually increased to about 52% when using 8x catalyst. Similarly, with a catalyst-to-allose mass ratio of 8, the allose conversion increased from 69 wt% to 96 wt%.

[0243] The effect of water vapor was investigated by injecting different ratios of H₂O into a reactor with a ZnSO₄ / PdO to allosugar mass ratio of 8. The results showed... Figure 4 The conditions are as follows: pyrolysis in a Pyro-GC system; raw material: D-allose; pyrolysis temperature: 400℃; heating rate: 20℃ / ms; holding time: 25s; mass ratio of ZnSO4 / PdO to D-allose: 8; mass ratio of water to D-allose: 0-20.

[0244] Steam was found to promote the formation of levulinic acid (LA). Steam inhibited the formation of light compounds (LC), while furfural selectivity showed an interesting increasing trend as the steam-to-allose ratio increased to 10:1. At a steam-to-allose ratio of 10, the selectivity for furfural was approximately 56%, and the allose conversion was 92 wt%.

[0245] 3.3.2 D-glucose as a raw material

[0246] The ability of zinc sulfate catalysts to convert glucose to furfural was also evaluated. Similar to its catalytic performance for D-allose, ZnSO4 / PdO was found to be the optimal catalyst for selectively converting glucose to furfural. Figure 5 This was confirmed in section a. The conditions used were as follows: pyrolysis in a Pyro-GC system; feedstock: D-glucose; pyrolysis temperature: 400℃; heating rate: 20℃ / ms; holding time: 25s; mass ratio of catalyst to D-glucose: 0-8; mass ratio of water to D-glucose: 0.

[0247] By increasing the ratio of catalyst to glucose, such as Figure 5 As shown in b, the furfural selectivity increased from 23% in the case of glucose alone to 43% in the case of a ZnSO4 / PdO catalyst to glucose mass ratio of 8:1. The furfural selectivity for glucose and allose without the catalyst was similar, at 23% and 22%, respectively.

[0248] Thermogravimetric analysis (TGA, see below) Figure 6 The results showed that when using the ZnSO4 / PdO catalyst, the decomposition temperature of glucose decreased by 30°C, compared to a 127°C decrease for allose. This supports the view that ZnSO4 / PdO is a particularly good catalyst for allose as a feedstock.

[0249] 3.3.4 Xylan as a raw material

[0250] The use of zinc sulfate catalyst in the catalytic conversion of allose to furfural was also investigated. Unlike the cases using D-glucose (C6) and D-allose (C6) as feedstocks (where ZnSO4 / PdO exhibited the highest catalytic activity for furfural production), pure ZnSO4 was found to be the optimal catalyst when xylan (C5) was used as the feedstock (see [link to relevant documentation]). Figure 7 The conditions for use are as follows: pyrolysis in a Pyro-GC system; raw material: xylan; pyrolysis temperature: 400℃; heating rate: 20℃ / ms; holding time: 25s; mass ratio of catalyst to xylan: 4; mass ratio of water to xylan: 0 or 10.

[0251] When using ZnSO4 or ZnSO4 / PdO catalysts, the conversion rate of xylan was found to be close to 100%. Furthermore, after using a ZnSO4 catalyst, the selectivity for furfural increased from 36% for xylan alone to 72% with a ZnSO4 catalyst and a catalyst:xylan mass ratio of 4:1. When steam was added at a catalyst:xylan mass ratio of 10:1, the selectivity for furfural further increased to 87%.

[0252] 3.3.5 Real biomass as raw materials - sugarcane bagasse and corn cobs

[0253] ZnSO4 and Pd-supported ZnSO4 catalysts were also tested using real biomass, including bagasse (see Table 2) and corn cobs (see Table 3).

[0254] For bagasse, the highest amount of furfural was produced by ZnSO4 / PdO(0.4) at 400 °C and a water-to-bagasse mass ratio of 10, with a selectivity of 44 wt%. This furfural yield is about twice that reported by WestPro / Huaxia Technology as 8-11 wt%

[14] . Acetic acid of 14.6 wt% was also produced.

[0255] For corn cobs, furfural was obtained at a mass ratio of 32.2–32.9 wt% using a catalyst containing 0.4–1.1 mol% PdO (ZnSO4 / PdO) and water at a mass ratio of 10 to corn cobs. This furfural yield is about three times that of Westpro / Huaxia Technology's 10–12 wt%

[14] . The overall liquid yield ranged from 65.0–69.1 wt%, and the selectivity for furfural varied between 58.8–61.2 area %. The main byproduct was 12.5–13.7 wt% acetic acid.

[0256] The conditions for use are as follows: pyrolysis in a Pyro-GC system; raw material: bagasse or corn cob; pyrolysis temperature: 400℃; heating rate: 20℃ / ms; holding time: 25s; mass ratio of catalyst to biomass: 8; mass ratio of water to biomass: 0 or 10.

[0257] Table 2 shows the yields of different products obtained from the pyrolysis of bagasse at 400°C using different catalysts with a catalyst-to-bagasse mass ratio of 8:1.

[0258]

[0259] Table 3 shows the yields of different products obtained from the pyrolysis of corn cobs at 400℃ under different catalyst conditions and with a catalyst-to-corn cob mass ratio of 8:1.

[0260]

[0261] 4. Conclusion

[0262] This study reports a novel method for producing zinc sulfate from waste materials via a convenient process involving the treatment of waste tire carbon black with sulfuric acid and the separation of solid zinc sulfate from the leachate.

[0263] This study also reports a series of novel ZnSO4 catalysts, both loaded and unloaded with PdO, their production methods, and their applications in the production of furfural from various biomass components via rapid pyrolysis at 300–500 °C. For C6 sugars, ZnSO4 / PdO was found to be the optimal catalyst compared to other catalysts in this study. At 400 °C, with ZnSO4 / PdO as the catalyst and steam (steam to allose mass ratio = 10:1), the selectivity for furfural was approximately 56%, and the D-allose conversion was 83.3 wt%.

[0264] When D-glucose is used as a raw material and ZnSO4 / PdO is used as a catalyst, the selectivity for furfural is 43%, the selectivity for light compounds (LC) is 28.3%, and the conversion rate of D-glucose is 90%.

[0265] For C5 xylan, ZnSO4 was found to be the optimal catalyst, increasing the selectivity of furfural from 36% with xylan alone to 72% with ZnSO4 catalyst, and further to 87% with steam (steam to xylan mass ratio = 10:1). When using ZnSO4 or ZnSO4 / PdO as catalyst, the xylan conversion approached 100%.

[0266] For real biomass feedstocks such as bagasse and corn cobs, in the presence of a ZnSO4 / PdO catalyst, furfural was obtained at a mass ratio of steam to biomass of 10, yielding 22.8 wt% and 32.9 wt% respectively.

[0267] References

[0268] [1] Zhang L, Xi G, Chen Z, Jiang D, Yu H, Wang X. Highly selective conversion of glucose into furfural overmodified zeolites. Chemical Engineering Journal 2017; 307: 868-76.

[0269] [2] Gurbuz EI, Wettstein SG, Dumesic JA. Conversion of hemicellulose to furfural and levulinic acid using biphasic reactors with alkylphenol solvents. ChemSusChem2012;5(2):383-7.

[0270] [3] Agirrezabal-Telleria I, Gandarias I, Arias PL. Heterogeneous acid-catalysts for the production of furan-derived compounds (furfural and hydroxymethylfurfural) from renewable carbohydrates: A review. Catalysis Today 2014; 234:42-58.

[0271] [4] Alonso DM, Wettstein SG, Melmer MA, Gurbuz EI, Dumesic JA. Integrated conversion of hemicellulose and cellulose from lignocellulosic biomass. Energy & Environmental Science 2013; 6(1):76-80.

[0272] [5] Mehdi Dashtban AG, Pedram Fatehi. Production of furfural: overview and challenges. Journal of Science & Technology for Forest Products and Processes 2012; 2:44-53.

[0273] [6] Gravitis J, Vedernikov N, Zandersons J, Kokorevics A, Mochidzuki K, Sakoda A, et al. Chemicals and biofuels from hardwoods, fuel crops and agricultural wastes. 2000: https: / / www.esf.edu / outreach / pd / 2000 / cellulose / gravitis.pdf.

[0274] [7] Heide EVD, Zhang T. Method for producing furfural from lignocellulosic biomass material. US 2011 / 0144359A1.

[0275] [8] Sabesan SS, Christina Jacy. Production of furfural from biomass. US2013 / 0109869 A1.

[0276] [9] Burket C, Hutchenson KW. Furfural production from biomass. US2014 / 0171664 A1.

[0277]

[10] Luo Y, Li Z, Li X, Liu X, Fan J, Clark JH, et al. The production of furfural directly from hemicellulose in lignocellulosic biomass: A review. Catalysis Today 2019; 319:14-24.

[0278]

[11] Earthbound Report. What can the world do with 1.5 billion waste tires?, 2017

[0279]

[12] Paul T. Williams. Pyrolysis of Waste tyres: A review. Waste Management, 2013, Vol. 33(8), 1714-1728.

[0280]

[13] Zhou Q, Yang S, Wang H, Liu Z, Zhang L. Selective deoxygenation of biomass volatiles into light oxygenates catalyzed by S-doped, nanosized zinc-rich scrap tyre char with in-situ formed multiple acidic sites. Applied Catalysis B: Environmental 2021; 282.

[0281]

[14] Win, DT, Furfural – gold from garbage. AUJ.T., 2005.8(4): pp. 185-190.

[0282] All content from each of the above references is incorporated herein by reference in its entirety.

Claims

1. A method for producing furfural, comprising the following steps: Pyrolysis of lignocellulose materials or their fractions and the production of furfural; The production of furfural is catalyzed by a catalyst containing solid zinc sulfate having at least 20% zinc sulfate; wherein the catalyst containing solid zinc sulfate contains palladium.

2. The method of claim 1, wherein the catalyst comprises at least 50 wt% zinc sulfate.

3. The method according to claim 1, wherein the catalyst containing solid zinc sulfate contains palladium metal and / or palladium oxide.

4. The method according to claim 1, wherein the catalyst containing solid zinc sulfate contains 0.2 wt% to 5 wt% of the palladium.

5. The method according to claim 1, wherein the lignocellulosic material or its fractionation is free from the group consisting of: wood chips, sawdust, sugarcane, corn cobs, bagasse, oat hulls, cottonseed hulls, rice hulls, and wheat bran.

6. The method according to claim 1, wherein the lignocellulose material or its fractions are selected from the group consisting of cellulose fractions and hemicellulose fractions.

7. The method according to claim 1, wherein the lignocellulose material or its fractionation is free from the group consisting of monosaccharides and oligosaccharides.

8. The method of claim 7, wherein the lignocellulose material or its fractionation is free from the group consisting of allosugar, glucose and xylan.

9. The method of claim 1, wherein prior to pyrolysis, the lignocellulosic material or its fractions are subjected to one or more pre-processing steps to: -Removal of lignin fractions and / or - Hydrolyzed sugar bonds.

10. The method of claim 1, wherein the generation of furfural is carried out in the absence of steam.

11. The method of claim 1, wherein the generation of furfural is carried out in the presence of vapor.

12. The method of claim 11, wherein the weight ratio of steam to the lignocellulose material or its fraction is in the range of 0.1:1 to 20:

1.

13. The method of claim 12, wherein the weight ratio of steam to the lignocellulose material or its fraction is in the range of 8:1 to 20:

1.

14. The method of claim 1, wherein the pyrolysis and / or production of furfural is carried out at a temperature in the range of 300 to 500°C.

15. The method according to claim 1, wherein the method is performed as a batch method.

16. The method of claim 1, wherein the method is performed as a continuous or semi-continuous method.

17. The method of claim 1, wherein the method comprises separating furfural from other reaction products.

18. The method of claim 17, wherein furfural is separated by distillation.

19. The method of claim 17, wherein furfural is separated by selectively condensing a product vapor stream containing furfural.

20. A method for producing one or more of furfuryl alcohol, furfural acid, furan, tetrahydrofuran, levulinic acid, butadiene, hexamethylenediamine, tetrahydrofurfuryl alcohol, methyltetrahydrofuran, and furfural-phenolic resin, comprising: Furfural is produced according to claim 1; as well as The furfural is converted into furfuryl alcohol, furoic acid, furan, tetrahydrofuran, levulinic acid, butadiene, hexamethylenediamine, tetrahydrofurfural alcohol, methyltetrahydrofuran and furfural-phenolic resin.

21. Use of palladium-doped zinc sulfate as a catalyst for the production of furfural from lignocellulosic materials or their fractions. The palladium-doped zinc sulfate described herein has at least 20% zinc sulfate, and The palladium-doped zinc sulfate is produced by a method comprising the following steps: The process involves contacting tire black with aqueous sulfuric acid to produce a mixture of aqueous zinc sulfate and solid tire black residue. Separate aqueous zinc sulfate from solid tire carbon black residue; Recover solid zinc sulfate from the aqueous zinc sulfate; Contact zinc sulfate with palladium salt; and Palladium-doped solid zinc sulfate is produced.

22. A method for regenerating an active palladium-doped zinc sulfate catalyst, said palladium-doped zinc sulfate catalyst having been used to produce furfural from lignocellulosic materials or fractions thereof, said method comprising subjecting the palladium-doped zinc sulfate to a reduction step by exposing it to hydrogen at a temperature in the range of 400 to 600°C.

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