Method for producing and utilizing oxidized lignin derived from organic, plant-based, synthetic, or other lignin sources through nitric acid oxidation (NOP) for industrial, agricultural, environmental, and technological applications

Abstract

A method for producing oxidized lignin includes providing a material including lignin; oxidizing the lignin in the material to form oxidized lignin, the oxidized lignin includes a reactive group; and collecting the oxidized lignin. The reactive group can include a carboxyl (-COOH) functional group, a hydroxyl (-OH) functional group, an aldehyde (-CHO) functional group, or a nitrate ester (-ONO2). The material can include organic waste, agricultural residues, plant-based materials, synthetic or genetically modified lignin, or industrial byproducts. The oxidized lignin can include molecular fragments, oligomers, or monomers.

Description

Attorney Docket No. 201291.8. PCTMETHOD FOR PRODUCING AND UTILIZING OXIDIZED LIGNIN DERIVED FROM ORGANIC, PLANT-BASED, SYNTHETIC, OR OTHER LIGNIN SOURCES THROUGH NITRIC ACID OXIDATION (NOP) FOR INDUSTRIAL, AGRICULTURAL, ENVIRONMENTAL, AND TECHNOLOGICAL APPLICATIONSCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Patent Application No. 63 / 695,548 filed on September 17, 2024. The entire contents of this application are hereby incorporated by reference.BACKGROUND OF THE INVENTION1. Field of the Invention

[0002] The present invention relates to oxidation methods of lignin from a variety of sources, including but not limited to organic waste, plant-based materials, synthetic or genetically modified lignin, renewable or non-renewable sources, and other lignin-containing materials, using Nitro-Oxidation Processes (NOPs) or other NOP derivative processes.2. Description of the Related Art

[0003] The growing demand for sustainable, bio-based materials has led to increasing interest in lignin, a natural biopolymer found in plant biomass. Traditionally underutilized, lignin's potential as a feedstock for industrial applications has been limited by its complex structure and poor reactivity.SUMMARY OF THE INVENTION

[0004] To overcome the problems described above, example embodiments of the present invention provide versatile and robust methods for producing oxidized lignin using NitroOxidation Processes (NOPs) or other suitable processes. The lignin can be sourced from any organic waste, plant-based, synthetic, genetically modified, or other lignin-containing materials, can be oxidized into various functionalized forms, ranging from molecular fragments and nanoscale particles to larger particles, and can retain the carbon inherent to the lignin, making it suitable for industrial applications such as adhesives, coatings, bio-composites, renewable energy products.

[0005] Example embodiments of the present invention apply to lignin sourced from any organic waste, including but not limited to agricultural residues, industrial biomass byproducts, forestry waste, plant-based materials, synthetic lignin, genetically modified lignin, and other lignin sources. The oxidized lignin produced by the processes of example embodiments retain their inherent carbon content and provide carbon containment and sequestration, which can be applied in both industrial products and environmental remediation efforts. The processes of the example embodiments can be tailored to produce oxidized lignin in various particle sizes and functional forms, making it adaptable to a wide range of industrial, agricultural, environmental, and technological uses. The oxidation process results in lignin in various forms— ranging from molecular fragments, nanoscale, microscale, and larger particle sizes— depending on process parameters such as temperature, pressure, acid concentration, stirring rate, co-oxidizing agents, and reaction time.

[0006] In addition to its use in industrial applications such as adhesives, coatings, dispersants, bio composites, and renewable energy products, the oxidized lignin retains its inherent carbon, making it a useful medium for carbon containment in agricultural and industrial systems. The flexibility of the processes allows for customization of lignin properties, providing versatile applications for both material development and environmental remediation.

[0007] According to an example embodiment of the present invention, a method for producing oxidized lignin includes providing a material including lignin; oxidizing the lignin in the material to form oxidized lignin, the oxidized lignin includes a reactive group; and collecting the oxidized lignin.

[0008] The reactive group can include a carboxyl (-COOH) functional group, a hydroxyl (-OH) functional group, an aldehyde (-CHO) functional group, or a nitrate ester (-ONO2). The content of the carboxylate group (-COO ) in the oxidized lignin can be above about 1 mmol / g. The material can include organic waste, agricultural residues, plant-based materials, synthetic or genetically modified lignin, or industrial byproducts. The oxidized lignin can include molecular fragments, oligomers, or monomers.

[0009] The oxidized lignin can have a size less than about 1 nm, in a range between about 1 nm and 100 nm, in a range between about 100 nm and about 4 pm, or has size greater than about 4 pm.

[0010] Oxidizing the lignin in the material can include applying a nitric-acid oxidation process (NOP) by contacting the material with nitric acid. The NOP can be performed at a temperature in a range from about 25°C to about 100°C. The NOP can be performed at a pressure in a range from about 10 psi to about 750 psi. The NOP can be performed at a nitric- acid concentration in a range from about 30% to about 70%. The nitric acid can be mixed with an additional acid. The additional acid can include phosphoric acid, hydrochloric acid, sulfuric acid, acetic acid, hydrobromic acid, hydrofluoric acid, or a combination thereof. The minimum nitric acid weight percentage can be about 25%. The NOP can include stirring or agitating the material and the nitric acid. The NOP can be performed for a time period in a range of about 0.1 hours to about 72 hours. The NOP can include a co-oxidizing agent that includes a nitrites-based salt, a metal element, an oxygen-containing oxidizing agent, or a combination thereof. The NOP can include a co-oxidizing agent that includes sodium nitrite (NaNO2), potassium nitrite (KNO2), ammonium nitrite (NH4NO2), calcium nitrite (Ca(NO2)2), magnesium nitrite (Mg(NO2)2), barium nitrite (Ba(NO2)2), lithium nitrite (LiNO2), zinc nitrite (Zn(NO2)2), copper(ll) nitrite (Cu(NO2)2), silver nitrite (AgNO2), magnesium (Mg), manganese (Mn), zinc (Zn), copper (Cu), iron (Fe), aluminum (Al), calcium (Ca), strontium (Sr), oxygen (O2), ozone (O3), nitrogen dioxide (NO2), nitrous oxide (N2O), sulfur dioxide (SO2), hydrogen peroxide (H2O2), or a combination thereof.

[0011] According to an example embodiment of the present invention, an oxidized lignin material including the oxidized lignin produced by one of the methods of one of the various example embodiments of the present invention, wherein the oxidized lignin retains inherent carbon derived from the oxidizing.

[0012] The material can be included in a sprayable, liquid, or granular form designed to reintroduce lignin-derived carbon into soil.

[0013] According to an example embodiment of the present invention, an oxidized lignin is soluble in acid and / or has a content of a carboxylate group (-COO ) above about 1 mmol / g.

[0014] The above and other features, elements, characteristics, steps, and advantages of the present invention will become more apparent from the following detailed description of example embodiments of the present invention with reference to the attached drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The patent or application file contains at least one drawing executed in color. The patent or application file also contains a corresponding black and white line drawing for each of the at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0016] Fig. 1 are a1H NMR spectrum of NOP effluent containing small molecule carbohydrate / lignin fragments (solvent CDCh, 400 MHz).

[0017] Fig. 2 are a1H NMR spectrum of NOP effluent containing lignin (D2O, 400 MHz).

[0018] Fig. 3 are a13C NMR spectrum of NOP effluent containing lignin (DMSO-de,400 MHz).

[0019] Fig. 4 are1H NMR spectra comparing NOP effluent extracted lignin and commercial alkaline lignin (D2O, 400 MHz).

[0020] Fig. 5 shows a1H NMR spectrum of NOP lignin precipitated after neutralization with NaOH (D2O, 400 MHz).

[0021] Figs. 6A and 6B are photographs of extracted low-molecular weight carbohydrates and lignin mixture from hardwood feedstocks. Fig. 6A is in black and white. Fig. 6B is in color.

[0022] Figs. 7A and 7B are photographs of NOP extracted lignin, prior to the removal of salts / sugars. Fig. 7A is in black and white. Fig. 7B is in color.

[0023] Figs. 8A and 8B are photographs of lignin precipitated after neutralization with NaOH. Fig. 8A is in black and white. Fig. 8B is in color.

[0024] Fig. 9A is an XPS spectrum of Kraft Lignin.

[0025] Fig. 9B is an XPS spectrum of commercial microcrystalline cellulose.

[0026] Fig. 9C is an XPS spectrum of raw jute (containing ~20% lignin).

[0027] Fig. 9D is an XPS spectrum of NOP-treated jute.DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS1. Nitro-Oxidation Processes (NOPs) for Lignin

[0028] Nitro-Oxidation Processes (NOPs) or other suitable processes can be applied to lignin derived from a wide variety of feedstocks, including but not limited to organic waste (such as agricultural residues, industrial biomass, forestry byproducts), plant-based materials, synthetic lignin, genetically modified lignin, and other lignin-containing sources. The oxidation processes can involve treating lignin with nitric acid under controlled conditions to introduce functional groups such as carboxyl (-COOH), hydroxyl (-OH), aldehyde (-CHO), nitrate esters (-ONO2), or other reactive moieties, enhancing its solubility, reactivity, and performance in industrial applications.

[0029] Through NOPs or other suitable processes, lignin can be functionalized to introduce reactive groups such as carboxyl groups (-COOH), hydroxyl groups (-OH), aldehyde groups (-CHO), nitrate esters (-ONO2), and other functional moieties that improve its solubility, reactivity, and industrial compatibility. The lignin can be oxidized using any of the NOPs disclosed in U.S. Patent No. 10,894,838, PCT Application No. PCT / US2024 / 055838, and PCT Application No. PCT / US2015 / 060261. The entire contents of U.S. Patent No. 10,894,838, PCT Application No. PCT / US2024 / 055838, and PCT Application No. PCT / US2015 / 060261 are hereby incorporated by reference. Alternatively, the lignin can be oxidized using any other suitable process.

[0030] Different from the NOP treatment disclosed in U.S. 10,894,838, which produces carboxylated cellulose fibers and carboxylated lignin-containing cellulosic fibers, the example embodiments of the present invention are directed to the extraction and isolation of oxidized lignin using an NOP treatment. Oxidized lignin produced by NOP treatment in the example embodiments of the present invention have different properties and chemical compositions from the carboxylated cellulose fibers and carboxylated lignin-containing cellulosic fibers disclosed in U.S. 10,894,838. The processes of the example embodiments of the present invention extract and isolate oxidized lignin after NOP treatment, separating the oxidized ligninfrom the cell u lose-ligni n complex, and recovering the oxidized lignin as an independent product that can be characterized and utilized in downstream applications

[0031] To produce oxidized lignin, a material including lignin can be oxidized, e.g., by an NOP or other process, such that the oxidized lignin includes a reactive group, and then the oxidized lignin can be collected from effluent created during the oxidization of the material including lignin.

[0032] The oxidized lignin produced through NOPs or other suitable processes may take various particle forms, ranging from molecular fragments to nanoscale and larger particle sizes, and is suitable for use in a wide array of applications, including industrial adhesives, coatings, dispersants, bio-composites, agricultural products, carbon sequestration, renewable energy, medical technologies, and other environmental applications. Example embodiments of the present invention enable lignin to be transformed into a functional material, while retaining its inherent carbon, supporting both industrial and environmental sustainability.1.1 Reaction Conditions

[0033] The oxidation process is controlled by key variables, including temperature, pressure, acid concentration, acid mixtures, stirring rate, reaction time, and co-oxidizing agents.

[0034] NOP reaction temperature can be in a range from about 25°C to about 100°C, within manufacturing and / or measurement tolerances. Higher temperatures promote increased oxidation rates and produce smaller, more reactive lignin particles.

[0035] NOP reaction pressures can be in the range from about 10 psi to about 750 psi, within manufacturing and / or measurement tolerances. Adjusting pressure within the NOP reactor affects both particle size distribution and the degree of oxidation.

[0036] Nitric acid concentration in NOPs can be in the range from about 30% to about 70%, within manufacturing and / or measurement tolerances. Careful control over nitric acid concentration is used to balance oxidation without over-degrading the lignin structure.

[0037] Nitric acid can be mixed with other acids, including, for example, phosphoric acid, hydrochloric acid, sulfuric acid, acetic acid, hydrobromic acid, hydrofluoric acid, or a combination thereof at different ratios, where the minimum nitric acid weight percentage is about 25%, within manufacturing and / or measurement tolerances.

[0038] The stirring or agitation rate ensures uniform oxidation and influences the particle size distribution. Higher agitation rates may result in smaller and more uniform particle sizes.

[0039] NOP reaction time can be in the range of about 0.1 hours to about 72 hours, within manufacturing and / or measurement tolerances. The duration of the oxidation process determines the degree of functionalization and the size of the resulting particles, which may vary from molecular fragments, nanoscale particles, to larger particle sizes.

[0040] The co-oxidizing agents that can assist the NOP reaction can include (i) nitrites-based salt, including sodium nitrite (NaNO2), potassium nitrite (KNO2), ammonium nitrite (NH4NO2), calcium nitrite (Ca(NO2)2), magnesium nitrite (Mg(NO2)2), barium nitrite (Ba(NO2)2), lithium nitrite (LiNO2), zinc nitrite (Zn(NO2)2), copper(ll) nitrite (Cu(NO2)2), silver nitrite (AgNO2), or a combination thereof; (ii) metal element, including magnesium (Mg), manganese (Mn), zinc (Zn), copper (Cu), iron (Fe), aluminum (Al), calcium (Ca), strontium (Sr), or a combination thereof, (iv) oxygen containing oxidizing agents, including oxygen (O2), ozone (O3), nitrogen dioxide (NO2), nitrous oxide (N2O), sulfur dioxide (SO2), hydrogen peroxide (H2O2), or a combination thereof. Co-oxidizing agents can be introduced to increase the efficiency of the oxidation process, promoting specific functional group formation and enhancing the overall process yield.1.2 Functionalization

[0041] The oxidation processes introduce reactive groups such as carboxyl (-COOH), hydroxyl (-OH), aldehyde (-CHO), nitrate esters (-ONO2), or other functional groups. Example embodiments are not limited to these groups, allowing for the generation of additional functional groups, such as sulfates, phosphates, and epoxides, which may arise from advanced oxidation methods or subsequent chemical reactions. These functional groups improve lignin's solubility, reactivity, and compatibility with various industrial processes.2. Forms of Oxidized Lignin

[0042] Depending on the oxidation-process conditions, oxidized lignin produced through an NOP can take various forms, as discussed below.2.1 Molecular Fragments or Oligomers

[0043] In cases where lignin undergoes extensive oxidative degradation, the lignin structure can be broken down into very small molecular fragments, oligomers, or even monomers. These fragments may be smaller than about 1 nanometer (nm), within manufacturing and / ormeasurement tolerances, approaching the atomic or sub nanoscale range. At this size, lignin exists as molecular clusters or individual molecules, retaining certain functional characteristics but no longer behaving as traditional particles. These molecular fragments exhibit unique chemical reactivity and solubility, which may be advantageous for applications that require high dispersibility, enhanced solubility, or increased chemical reactivity.2.2 Nanoscale Oxidized Lignin

[0044] Under shorter or milder oxidation periods and / or lower temperatures, lignin can be reduced to particles smaller than about 100 nm, within manufacturing and / or measurement tolerances. This form of lignin maintains high dispersibility and reactivity, making it suitable for applications such as coatings, adhesives, dispersants, and emulsifiers. The small particle size allows for fine distribution in formulations, improving surface interactions and overall product performance.2.3 Microscale Oxidized Lignin

[0045] With particle sizes ranging from about 100 nm to several microns (e.g. about 3 or 4 microns), within manufacturing and / or measurement tolerances, microscale oxidized lignin offers a balance between structural integrity and reactivity. This form is particularly well suited for applications requiring mechanical strength, such as bio-composites, industrial coatings, and renewable energy products. Microscale lignin retains its ability to chemically interact with other components while providing greater physical robustness, making it useful for industrial products where both durability and functionality are important.2.4 Larger Particle Oxidized Lignin

[0046] In applications where larger lignin particles are desired (e.g., greater than several microns (e.g., greater than about 3 or about 4 microns)), such as in bulk fillers or certain industrial additives, the oxidation process can be controlled to preserve higher molecular weight lignin structures. These larger particles provide enhanced mechanical strength and are useful in applications where lignin's structural properties are critical. The preserved molecular weight makes them suitable for bulk materials and industrial products that require rigidity or support.3. Carbon Containment and Sequestration Mechanism

[0047] The carbon contained in oxidized lignin is derived from the lignin itself-a biopolymer naturally rich in carbon. During the oxidation process, the lignin structure is degraded, but much of the inherent carbon remains intact and is retained within the oxidized product. This offers a method for carbon containment without requiring external carbon capture.3.1 Carbon from Lignin Degradation

[0048] Oxidation processes can preserve lignin's inherent carbon, which is contained within the oxidized material. This carbon may be used in applications requiring carbon retention, such as environmental remediation, carbon management, and long-term carbon storage.3.2 Carbon Sequestration in Fertilizers

[0049] Oxidized lignin can be incorporated into liquid or granular fertilizers that reintroduce carbon into the soil. This method enhances soil health and promotes carbon sequestration, contributing to the reduction of carbon emissions. Example embodiments of the present invention include the use of carbon-containing oxidized lignin for soil enrichment, nutrient cycling, and carbon management in agricultural systems, whether marketed as carbon sequestration or otherwise.3.3 Carbon Retention in Industrial Materials

[0050] In industrial applications, oxidized lignin can serve as an additive in bio-composites, plastics, coatings, renewable energy products, or any material designed to retain carbon and improve environmental sustainability. The retained carbon in these materials helps reduce the overall carbon footprint of the final product, providing a sustainable solution for carbon containment across various industries.4. Applications of Oxidized Lignin

[0051] Oxidized lignin produced via NOPs or other suitable processes can be used in a wide range of applications, with flexibility in particle size and functional properties.4.1 Adhesives and Coatings

[0052] Oxidized lignin can be used as a bio-based component in adhesives and coatings to enhance adhesion, durability, and environmental sustainability. The reactive functional groups allow the oxidized lignin to bond with various substrates, making it a valuable addition to industrial formulations.4.2 Dispersants and Emulsifiers

[0053] Oxidized lignin acts as a dispersant or emulsifier, stabilizing emulsions or suspensions in products such as paints, inks, and cosmetics.4.3 Bio-composites

[0054] Oxidized lignin in larger particle sizes is useful as a reinforcing agent in biocomposites, improving mechanical strength and biodegradability. Oxidized lignin can serve as a renewable alternative to petroleum-based additives.4.4 Renewable Energy Products

[0055] The inherent properties of oxidized lignin make it suitable for use in renewable energy applications, including energy storage systems, batteries, and fuel cells. Its carbon- containing structure offers both mechanical and chemical benefits for these high performance applications.4.5 Sprayable Fertilizers for Carbon Sequestration

[0056] The inherent carbon in oxidized lignin makes it an excellent candidate for use in fertilizers that sequester carbon in the soil. This method promotes soil health, carbon sequestration, and enhanced nutrient cycling, while contributing to the reduction of carbon emissions.4.6 Emerging Technologies

[0057] Oxidized lignin can be further processed or derivatized for use in emerging fields, such as biodegradable electronics, smart materials, nanotechnology, and advanced materials for biotechnology applications.5. Tailoring Oxidized Lignin Forms Based on Process Variables5.1 Feedstock Flexibility

[0058] NOPs or other suitable processes can be applied to lignin sourced from any organic waste, plant-based materials, synthetic lignin, genetically modified lignin, and other lignincontaining materials. Lignin from renewable or non-renewable sources can also be processed, providing versatility in the selection of raw materials for oxidized lignin production.5.2 Process Variables

[0059] The oxidation conditions, including, for example, temperature, pressure, acid concentration, acid mixtures, stirring rate, reaction time, and co-oxidizing agents, can beadjusted to produce oxidized lignin in a range of particle sizes and functionalization levels. This flexibility ensures that the lignin can be customized for specific industrial, agricultural, environmental, or technological applications.5.3 Scalability

[0060] NOPs can be adaptable and scalable, suitable for both small-scale laboratory production and large-scale industrial manufacturing. Example embodiments can be modified to achieve desired lignin oxidation at any production scale, ensuring widespread applicability across industries such as agriculture, renewable energy, construction, and biotechnology, environmental remediation, while also contributing to carbon sequestration in agricultural and technological applications. By providing multiple oxidation pathways and conditions, example embodiments of the present invention ensure that oxidized lignin can be tailored for specific industrial needs, protecting both material performance and environmental sustainability. Example embodiments of the present invention support the development of renewable, carbon-containing materials and position oxidized lignin as a valuable tool in efforts to mitigate carbon emissions, to enhance sustainability, and to drive innovation across a wide range of industries.6. Example Examples6.1 Extraction and Characterization of Hardwood Lignin and Other Carbohydrates by NOP

[0061] Harwood samples in the form of granular powder were used, where the samples were treated by nitric acid (HNO3, 65%) and potassium nitrite (KNO2, 97%) according to the NOP procedures discloses in U.S. Patent No. 10,894,838. After the NOP treatment, the majority of the lignin component was degraded, oxidized, and soluble in the acidic NOP effluent. The residual oxidized cellulose fibers were filtered from the nitric acid effluent. The recovered effluent was then neutralized to pH - about 2, within manufacturing and / or measurement tolerances, with NaOH to characterize the oxidized lignin fragments. Subsequently, the NOP effluent was mixed with diethyl ether for liquid-liquid extraction. The organic layer, containing small molecule carbohydrates and degraded lignin fragments, was collected, where the solvent was removed under reduced pressure. Proton nuclear magnetic resonance (1H NMR) andcarbon-13 nuclear magnetic resonance (13C NMR) spectroscopy were performed using a Bruker 400 MHz spectrometer.

[0062] The1H NMR spectrum of NOP hardwood effluent, containing small molecule carbohydrates and degraded lignin fragments extracted from the organic layer (diethyl ether) is shown in Fig. 1 (sample dissolved in CDCI3, 400 MHz NMR). The results showed multiple functional groups are present in the carbohydrates and degraded lignin fragments of the NOP effluents.6.2 Extraction and Characterization of Hardwood Lignin by NOP

[0063] After the NOP treatment of hardwood biomass, the cellulose fibers were filtered from the nitric acid effluent. The effluent was then neutralized to pH of about 1-about 2, within manufacturing and / or measurement tolerances, with NaOH. Next, the effluent was mixed with 50 / 50 methanol / tetrahydrofuran and an excess of sodium chloride, for liquid-liquid extraction. The organic layer was collected, where the solvent was removed subsequently under reduced pressure. Furthermore, sodium chloride and carbohydrates were removed by dissolution in cold water, leaving behind a brown color solid of lignin fragments. The lignin compositions were confirmed by the1H NMR spectrum (sample dissolved in D2O, using 400 MHz NMR) as seen in Fig. 2, and the13C NMR spectrum (sample dissolved in DMSO-de using 400 MHz NMR) as seen in Fig. 3.

[0064] Fig. 4 shows the comparison of1H NMR spectra for NOP effluent extracted lignin and commercial alkaline lignin (all samples were dissolved in D2O using the 400 MHz NMR). Fig. 4 shows that the main characteristic features of NOP effluent extracted lignin and commercial alkaline lignin are similar. However, the degree of oxidation in NOP-produced lignin is significantly higher than known commercial alkaline lignin. For example, the content of the carboxylate group (-COO ) in the oxidize lignin can be above about 1 mmol / g, within manufacturing and / or measurement tolerances. In addition, known commercial alkaline lignin might have a higher molecular weight, depending on the type of lignin, and the oxidized lignin produced by an NOP treatment might have more carboxylic acids groups. And known alkaline lignin is not soluble in acid, while the oxidized lignin produced by an NOP treatment can be soluble in acid, implying smaller molecular weight and more polar functional groups.6.3 Solubility and Color Appearance of NOP Extracted Lignin from Hardwood

[0065] The NOP extracted lignin component was soluble under aqueous acidic conditions (pH < 2) at approximately 0.25g / mL, within manufacturing and / or measurement tolerances. At the neutral pH, the solubility decreased to ~0.02g / mL, within manufacturing and / or measurement tolerances. After addition of NaOH to the NOP effluent, precipitation of lignin can occur. Fig. 5 shows the1H NMR spectrum of NOP extracted lignin precipitated after neutralization using NaOH (the sample was dissolved in D2O using 400 MHz NMR).

[0066] Fig. 6 is a photograph of NOP extracted low-molecular weight carbohydrates and lignin mixtures from hardwood feedstocks. Fig. 7 is a photograph of NOP extracted lignin, prior to the removal of salts / sugars. Fig. 8 is a photograph of NOP extracted lignin, after the removal of salts / sugars, and subsequently precipitated after neutralization with NaOH. The brown color seen in Figs. 6-8 is typically seen in lignin components.6.4 XPS Characterizations of NOP Prepared Lignin Containing Cellulose Fibers from Raw Jute

[0067] X-Ray Photoelectron Spectroscopy (XPS) was used to determine quantitative atomic composition of the lignin content on the NOP prepared nanocellulose. The raw jute (containing about 20% lignin) was used as the feedstock, where the lignin-containing oxidized cellulose fibers were analyzed instead of the NOP effluents. The NOP conditions were chosen based on the NOP procedures disclosed in U.S. Patent No. 10,894,838. The lignin-containing cellulose fibers were prepared by drop casting a 0.04 wt% solution onto a gold coated silicon wafer. The water was allowed to evaporate, leaving an inhomogeneous sample film. The samples were loaded into an ambient pressure X-ray photoelectron spectrometer. The instrument has a SPECS PHIOBOS 150 NAP hemispherical analyzer and a 2D-delay line detector. The X-ray source was a monochromatic Al Ka source focused to ~300 pm diameter spot size. The small spot size was used to find a sufficiently thin area of the film with minimal charge accumulation and shifting of the binding energy scale. The core level spectra were collected in ultra-high vacuum conditions with a base pressure better than 5 x IO-9mbar. A pass energy of 20 eV was used. The step size was 0.1 eV, and the dwell time was 0.2 s for each data point. The C Is spectra were calibrated by shifting the adventitious carbon peak to 285 eV. Voight functions with aLorentzian width constrained to 0.25 was used to fit the C Is data. All peaks were constrained to have the same peak width.

[0068] Fig. 9A shows the deconvoluted XPS data of commercial kraft lignin. Fig. 9B shows the deconvoluted XPS data of commercial microcrystalline cellulose. Fig. 9C shows the deconvoluted XPS data of raw jute. Fig. 9D shows the deconvoluted XPS data of jute fibers after NOP treatment. The XPS analysis of commercial kraft lignin (Fig. 9A) found peaks around 285 eV (C-C / C=C), 286.6 eV (C-O-C / C-O-H), and 289.2 eV (O-C-O / C=O / O-C=O). The XPS analysis of commercial microcrystalline cellulose (Fig. 9B) found three peaks at 285 eV, 286.6 eV, and 288.7 eV, correlating to C-C / C=C, C-O-C / C-O-H, and O-C-O / C=O / O-C=O bond energies, respectively. The XPS analysis of raw jute (Fig. 9C) found four prominent peaks at approximately 285 eV, 286.6 eV, 288.7 eV, and 289.9 eV, corresponding to the bonding energies of C-C / C=C, C- O-C / C-O-H, O-C-O / C=O, and O-C=O, respectively. The XPS analysis of NOP-treated jute fibers (Fig. 9D) found a diminished peak area at 288.7 eV and an enhanced peak at 286.6 eV, indicating the removal of lignin and hemicellulose, which contain aldehyde and ester functionalities. Additionally, the NOP-treated jute fibers showed an increased intensity for the peak at 286.6 eV (C-O-C / C-O-H), suggesting more exposure of cellulose. However, it is clear that the NOP treatment does not completely remove the lignin content, where some lignin components were oxidized.6.5 Zeta Potential and Degree of Oxidation of NOP Prepared Lignin Containing Cellulose Fibers from Sugarcane Bagasse

[0069] Carboxylated lignin containing cellulose fibers were prepared by NOP treatment of raw sugarcane bagasse (SCB) sample according to the procedures demonstrated in U.S. Patent No. 10,894,838. Following the NOP reaction, the effluent was separated, where the treated fibrous residues (termed lignin containing cellulose nanofibers, LCNF) were thoroughly rinsed with deionized water until a pH of ~3 was achieved. The yield percentage of LCNFs was measured based on the initial weight of untreated SCB as follows:100 (1) where Wf is the weight of the obtained LCNFs (g), and Wo is the initial weight of untreated SCB used (g).

[0070] The lignin content was measured using a UV-Vis spectrophotometer (GENESYS 10S, Thermo Fisher Scientific, NY, USA) at the wavelength of 280 nm. The lignin content was calculated as follows:100 (2) where C is the lignin content (%) of the biomass sample; Abs is the UV absorbance; V is the total volume of the solution (L); n is the dilution factor; E (L g-1cm-1) is the absorptivity of lignin at appropriate wavelength; m (g) is the dry mass of the sample; and L is the light path length (=1 cm).

[0071] Potentiometric titration was carried out using a potentiometric titrator (HI 902, HANNA Instrument, Rl, USA) to quantitatively determine the carboxylate group (COO ) content of the carboxylated LCNF sample. The degree of oxidation (DO) of LCNF was calculated using Equation (3)where AV represents the volume of NaOH solution consumed by the oxidized cellulose fibers (L), CNOOH is the NaOH concentration (M), and m is the mass of the cellulose fibers used in the titration (g). The colloidal stability of the oxidized LCNFs was measured at 25 °C using a zeta potential analyzer (Zetasizer Nano ZS, Malvern Panalytical, UK). In this measurement, a 0.05 wt% LCNF suspension was vortexed for 10 min before the analysis. All measurements were conducted in triplicate at pH of ~7.Table 1: The chosen NOP reaction conditions for the preparation of carboxylated LCNFs from SCB.Table 2: The yield (based on untreated SCB feedstock), lignin content, carboxylate content, zeta potential, and crystallinity index (Crl) of carboxylated LCNFs produced under different NOP reaction conditions.

[0072] Table 1 summarizes the chosen NOP reaction conditions for the preparation of carboxylated LCNFs from raw SCB. The reaction times in the NOP procedures are varied under the same reaction conditions. Table 2 summarizes the yield, lignin content, carboxylate content, zeta potential, and crystallinity index (Crl) of the carboxylated LCNFs produced under the different reaction conditions. The zeta potential analysis was conducted to examine the dispersibility and colloidal stability of the LCNF suspensions in reactions nos. R1-R4. All samples exhibited negative zeta potential values (< about -30 mV) across the different reaction times, indicating the high colloidal stability of the suspensions and a reduced tendency for nanofiber aggregation. This stability can be attributed to strong electrostatic repulsion generated by negatively charged carboxylate groups on both lignin and cellulose surfaces. This study indicates that the lignin component was also effectively oxidized under varying NOP reaction conditions.

[0073] It should be understood that the foregoing description is only illustrative of the present invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the present invention. Accordingly, the present invention isintended to embrace all such alternatives, modifications, and variances that fall within the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method for producing oxidized lignin comprising: providing a material including lignin; oxidizing the lignin in the material to form oxidized lignin, the oxidized lignin includes a reactive group; and collecting the oxidized lignin.

2. The method of claim 1, wherein the reactive group includes a carboxyl (-COOH) functional group, a hydroxyl (-OH) functional group, an aldehyde (-CHO) functional group, or a nitrate ester (-ONO2).

3. The method of claim 1, wherein a content of a carboxylate group (-COO ) in the oxidized lignin is above about 1 mmol / g.

4. The method of one of claims 1-3, wherein the material includes organic waste, agricultural residues, plant-based materials, synthetic or genetically modified lignin, or industrial byproducts.

5. The method of one of claims 1-4, wherein the oxidized lignin includes molecular fragments, oligomers, or monomers.

6. The method of one of claims 1-4, wherein the oxidized lignin has a size less than about 1 nm.

7. The method of one of claims 1-4, wherein the oxidized lignin has a size in a range between about 1 nm and 100 nm.

8. The method of one of claims 1-4, wherein the oxidized lignin has a size in a range between about 100 nm and about 4 pm.

9. The method of one of claims 1-4, wherein the oxidized lignin has a size greater than about 4 pm.

10. The method of one of claims 1-9, wherein oxidizing the lignin in the material includes applying a nitric-acid oxidation process (NOP) by contacting the material with nitric acid.

11. The method of claim 10, wherein the NOP is performed at a temperature in a range from about 25°C to about 100°C.

12. The method of claim 10 or 11, wherein the NOP is performed at a pressure in a range from about 10 psi to about 750 psi.

13. The method of one of claims 10-12, wherein the NOP is performed at a nitric-acid concentration in a range from about 30% to about 70%.

14. The method of one of claims 10-13, wherein the nitric acid is mixed with an additional acid.

15. The method of claim 14, wherein the additional acid includes phosphoric acid, hydrochloric acid, sulfuric acid, acetic acid, hydrobromic acid, hydrofluoric acid, or a combination thereof.

16. The method of claim 14 or 15, wherein a minimum nitric acid weight percentage is about 25%.

17. The method of one of claims 10-16, wherein the NOP include stirring or agitating the material and the nitric acid.

18. The method of one of claims 10-17, wherein the NOP is performed for a time period in a range of about 0.1 hours to about 72 hours.

19. The method of one of claims 10-18, wherein the NOP includes a co-oxidizing agent that includes a nitrites-based salt, a metal element, an oxygen-containing oxidizing agent, or a combination thereof.

20. The method of one of claims 10-18, wherein the NOP includes a co-oxidizing agent that includes sodium nitrite (NaNO2), potassium nitrite (KNO2), ammonium nitrite (NH4NO2), calcium nitrite (Ca(NO2)2), magnesium nitrite (Mg(NO2)2), barium nitrite (Ba(NO2)2), lithium nitrite (LiNO2), zinc nitrite (Zn(NO2)2), copper(ll) nitrite (Cu(NO2)2), silver nitrite (AgNO2), magnesium (Mg), manganese (Mn), zinc (Zn), copper (Cu), iron (Fe), aluminum (Al), calcium (Ca), strontium (Sr), oxygen (O2), ozone (O3), nitrogen dioxide (NO2), nitrous oxide (N2O), sulfur dioxide (SO2), hydrogen peroxide (H2O2), or a combination thereof.

21. An oxidized lignin material including the oxidized lignin produced by the method of one of claims 1-20, wherein the oxidized lignin retains inherent carbon derived from the oxidizing.

22. The oxidized lignin material of claim 21, wherein the material is included in a sprayable, liquid, or granular form designed to reintroduce lignin-derived carbon into soil.

23. An oxidized lignin that is soluble in acid and / or that has a content of a carboxylate group (-COO ) above about 1 mmol / g.

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