Cellulose pretreatment agent and application thereof in cellulose biomass enzyme hydrolysis

Abstract

The invention provides a cellulose pretreating agent, a method for pretreating cellulose by using the pretreating agent and a method for preparing reducing sugar. The cellulose pretreatment agent is an organic acid containing a sulfonic acid group, a carbon-based material derived from the organic acid containing the sulfonic acid group, or a g-C3N4 / FeOCl Fenton-like composite material. The pretreatment step is mild in condition, and the cellulose-containing biomass energy obtained through treatment of the pretreatment agent can be subjected to enzyme hydrolysis under milder reaction conditions while the use of dangerous chemicals is reduced.

Description

Technical Field

[0001] The invention relates to the field of catalysis / material science, and in particular to a cellulose pretreatment agent and application thereof in enzymatic hydrolysis of cellulose biomass. Background Art

[0002] In recent years, the concept of "carbon neutrality" has gained increasing attention within the chemical and biochemical processing industries as part of a broader commitment to decarbonization and climate action. Biomass conversion has become an important method for a variety of applications, including energy and chemical production. The feedstock for biomass conversion is usually waste materials containing cellulose, which are initially converted through pretreatment and enzymatic hydrolysis to form intermediates such as reducing sugars and amorphous biomixtures, followed by additional chemical or biological processing to obtain the final potential products.

[0003] The conversion of cellulose-containing biomass involves a pretreatment step that is often considered the most difficult to tame. In general, biomass consists of 40%-50% cellulose, 25%-30% hemicellulose, and 15%-20% lignin, with these proportions varying depending on the source. The presence of hemicellulose and lignin hinders the availability of cellulose during enzymatic hydrolysis, and the crystalline structure of cellulose further complicates the process. The goal of pretreatment is to remove these obstacles by disrupting the hydrogen bonding network and van der Waals forces associated with lignin and hemicellulose. Once pretreatment is complete, enzymatic hydrolysis can be performed under mild conditions, significantly increasing the conversion rate of the intermediates formed.

[0004] Conventional textile recycling processes face several challenges beyond the initial pretreatment stage. Issues related to sorting, decolorization, and quality of intermediate products have hindered the widespread adoption of textile recycling. Today, most textiles are made from blended fabrics, which requires sorting the shredded materials into different recycling streams. This separation process is complex, resulting in inefficiencies in subsequent recycling stages. In addition, after the enzymatic hydrolysis stage, residual textile dyes remain, making decolorization through activated carbon columns a critical step. Ultimately, the fibers produced by these recycling efforts are mainly short fibers, which limits their application to low-value products.

[0005] Therefore, there is still a need in the art for a method for pretreating cellulose biomass, so that the cellulose biomass obtained thereby can be enzymatically hydrolyzed under milder reaction conditions while reducing the use of hazardous chemicals. Summary of the invention

[0006] The present invention aims to provide a cellulose biomass conversion method with mild reaction conditions and environmental friendliness. The inventors have developed a cellulose pretreatment agent, and the cellulose-containing biomass obtained by treatment with the cellulose pretreatment agent of the present invention can be enzymatically hydrolyzed under milder reaction conditions while reducing the use of hazardous chemicals, thereby achieving the present invention.

[0007] In a first aspect of the present invention, a cellulose pretreatment agent is provided. The pretreatment agent is an organic acid containing a sulfonic acid group or a carbon-based material derived from the organic acid containing a sulfonic acid group.

[0008] In a second aspect of the present invention, a cellulose pretreatment method is provided, the method comprising: (1) pretreating cellulose-containing biomass using a cellulose pretreatment agent, wherein the pretreatment agent is an organic acid containing a sulfonic acid group, a carbon-based material derived from the organic acid containing a sulfonic acid group, or a g-C3N4 / FeOCl-type Fenton composite material.

[0009] In a third aspect of the present invention, there is provided a method for producing reducing sugars, the method comprising the following steps:

[0010] (1) pretreating cellulose-containing biomass using a cellulose pretreatment agent, wherein the pretreatment agent is an organic acid containing a sulfonic acid group, a carbon-based material derived from the organic acid containing a sulfonic acid group, or a g-C3N4 / FeOCl-type Fenton composite material;

[0011] (2) separating the cellulose-containing biomass and the cellulose pretreatment agent; and

[0012] (3) Enzymatic hydrolysis of the separated pretreated cellulose-containing biomass.

[0013] In a fourth aspect, there is provided use of the cellulose pretreatment agent of the first aspect of the present invention for pretreating cellulose-containing biomass.

[0014] In a fifth aspect, a g-C3N4 / FeOCl-type Fenton composite material is provided for use in pretreating cellulose-containing biomass.

[0015] Cellulose-containing biomass pretreated with the cellulose pretreatment agent of the present invention, such as textiles (such as cotton fabrics or polyester / cotton blended textiles), can be enzymatically hydrolyzed under milder reaction conditions while reducing the use of hazardous chemicals, and the milder reaction conditions include, for example, lower temperatures such as 40-60° C., without the need to use any acid, alkali, inducer or ionic liquid, and using a more neutral reaction system. Cellulose-containing biomass pretreated with the cellulose pretreatment agent of the present invention exhibits higher enzymatic hydrolysis efficiency, and the same amount of enzyme can be used to increase the reducing sugar yield of the fabric, or a similar sugar yield can be achieved with less enzyme. The yield of reducing sugars formed by enzymatic hydrolysis of cellulose-containing biomass treated with the cellulose pretreatment agent of the present invention can be higher than 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings are included to provide a further understanding of the present invention, and are incorporated into and constitute a part of this specification. The drawings described herein are for illustration purposes only and are not intended to limit the scope of the disclosure in any way.

[0017] Figure 1 The infrared spectra of tannic acid, sulfomethyl tannic acid of the present invention, carbon quantum dots and carbon black are shown.

[0018] Figure 2 A transmission electron microscope image of the carbon quantum dots of the present invention is shown.

[0019] Figure 3 The ultraviolet-visible absorption spectrum and photoluminescence fluorescence spectrum of the carbon quantum dots prepared from citric acid and sulfomethyltannic acid of the present invention are shown.

[0020] Figure 4 The photographs show the carbon quantum dots prepared from citric acid and sulfomethyltannic acid under sunlight (left picture) and after excitation with 365 nm light (right picture).

[0021] Figure 5 Photographs showing carbon quantum dots prepared from citric acid and m-aminobenzenesulfonic acid according to the present invention under sunlight (left) and after excitation with 365 nm light (right).

[0022] Figure 6 Photographs of the pretreatment mixture comprising blue fabric before and after pretreatment are shown.

[0023] Figure 7 A photograph of a fabric obtained by washing the fabric with deionized water and drying it at 70°C is shown.

[0024] Figure 8 A schematic diagram showing the cellulose pretreatment agent of the present invention. DETAILED DESCRIPTION

[0025] The following detailed description is merely exemplary and is in no way intended to limit the invention or its application or uses.

[0026] Although the numerical ranges and parameters given for the broad scope of the present invention are approximate, the numerical values ​​in the specific examples should be as precise as possible. However, any numerical value itself contains certain errors, such as within ± 5%, which are inevitably caused by the standard variation in the respective test measurements.

[0027] In addition, it should be understood that any numerical range described herein is intended to include the given end value and all sub-ranges and values ​​contained in the range. For example, a numerical range of "1 to 10" is intended to include a minimum value of 1 and a maximum value of 10 and all sub-ranges therebetween, i.e., the minimum value may be equal to or greater than 1, and the maximum value may be equal to or less than 10.

[0028] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting.

[0029] As used herein, the articles "a," "an," and "the," and the expressions "at least one" and "one or more" are used interchangeably to indicate that there is at least one of a specified element, material, component, or method step, unless the context clearly indicates otherwise.

[0030] The terms "about", "mainly" and "substantially" as used herein refer to measurable values ​​and ranges due to expected variations known to those skilled in the art (such as measurement limitations and variability). The term "about" also means that the numerical value allows for some slight imprecision (the numerical value has some approach to precision; approximately or reasonably close to the numerical value; close). If the imprecision provided by the term "about" is not understood in the art as this ordinary meaning, then the term "about" as used herein at least represents the variation that may occur due to ordinary methods of measuring and using such parameters. In addition, the disclosed range includes the disclosure of all values ​​and further ranges within the entire range.

[0031] The terms "include", "comprising" and similar terms, together with their grammatical variations, used herein are synonymous with the term "comprises" and its grammatical variations. They are open-ended and should be understood in the context of the present invention to include not only the specified elements, materials, components or method steps, but also other unspecified elements, materials, components or method steps, provided that the other unspecified elements, materials, components or method steps do not have contradictory or conflicting meanings with the specified elements, materials, components or method steps.

[0032] When describing the specific aspects of the present invention in detail, those skilled in the art will appreciate that various modifications and substitutions can be made to these details according to the overall teaching of the present invention. Therefore, the disclosed specific embodiments are only for illustration, rather than limiting the scope of disclosure, and the scope of disclosure should include the full scope of the attached claims and any and all equivalents thereof.

[0033] As mentioned above, the present invention aims to provide a method for converting cellulose-containing biomass with mild reaction conditions and environmental friendliness.

[0034] In a first aspect, a cellulose pretreatment agent is provided, wherein the cellulose pretreatment agent is an organic acid containing a sulfonic acid group or a carbon-based material derived from the organic acid containing a sulfonic acid group.

[0035] As used herein, the term "pretreatment" refers to a thermal and / or chemical treatment of a cellulose-containing biomass material prior to enzymatic hydrolysis of the cellulose-containing biomass material using cellulase.

[0036] In the present invention, the term "organic acid containing sulfonic acid group" may refer to an organic acid that originally contains sulfonic acid group, or may refer to an organic acid that does not contain sulfonic acid group but is modified by sulfonic acid group to contain sulfonic acid group. The organic acid modified by sulfonic acid group mainly introduces sulfonic acid group through one or more, preferably multiple hydroxyl groups or other active groups that can undergo substitution reaction with sulfonic acid group on the organic acid. It is understood that the sulfonic acid group may completely replace the hydroxyl group or active group on the organic acid, or may partially replace the hydroxyl group or active group on the organic acid, and the present invention has no particular limitation on this, as long as the obtained product can effectively pretreat cellulose-containing biomass.

[0037] In a specific embodiment, the organic acid containing a sulfonic acid group may be sulfonate tannic acid and / or m-aminobenzenesulfonic acid, but is not limited thereto.

[0038] In the present invention, the term "carbon-based material" refers to a carrier mainly formed of carbon that can support active ingredients including substituents, catalysts, etc. The inventors have found that the carbon-based material prepared from the organic acid containing sulfonic acid groups of the present invention still retains the sulfonic acid groups, thereby forming a structure in which the carbon-based material is the central particle, and the sulfonic acid groups and hydroxyl groups or other active groups (if present) are located on the surface of these central particles, such as Figure 8 shown.

[0039] Due to the presence of sulfonic acid groups and hydroxyl groups or active groups (in some cases) on the cellulose pretreatment agent of the present invention, the cellulose pretreatment agent of the present invention can fully react chemically with the cellulose-containing biomass under mild conditions, promote the loosening of the cellulose structure, reduce the crystallinity and polymerization degree of cellulose, and further promote the subsequent cellulase hydrolysis to proceed smoothly under relatively mild conditions.

[0040] In another specific embodiment, the carbon-based material derived from an organic acid containing a sulfonic acid group may be carbon black or carbon quantum dots, but is not limited thereto. For example, the carbon-based material may be carbon black or carbon quantum dots prepared from an organic acid containing a sulfonic acid group, such as sulfonic tannic acid and / or m-aminobenzenesulfonic acid, and citric acid.

[0041] In the present invention, the term "carbon quantum dot" (Carbon Quantum Dot, CQD) is also referred to as carbon dots or carbon nanodots, which are quantum structures composed of ultrafine, dispersed, quasi-spherical, nanoscale carbon nanoparticles with a size below 10 nm. In the present invention, the carbon quantum dot may have a particle size of less than 10 nm, for example, a particle size in the range of 2-5 nm.

[0042] The cellulose pretreatment agent of the present invention is soluble in water when in the form of an organic acid containing a sulfonic acid group, but is insoluble in water when in the form of a carbon-based material. Therefore, the cellulose pretreatment agent can be selected accordingly according to subsequent use requirements, such as whether the cellulose pretreatment agent is to be recycled.

[0043] In another specific embodiment, the cellulose pretreatment agent can be a sulfonate tannic acid having a sulfonate content of 1mmol / g-4mmol / g. For example, the sulfonate content in the sulfonate tannic acid can be 1mmol / g, 1.25mmol / g, 1.5mmol / g, 1.75mmol / g, 2mmol / g, 2.25mmol / g, 2.5mmol / g, 2.75mmol / g, 3mmol / g, 3.25mmol / g, 3.5mmol / g, 3.75mmol / g or 4mmol / g, or a range consisting of any two of the values. In a preferred embodiment, the cellulose pretreatment agent can be a sulfonate tannic acid having a sulfonate content of 1.5mmol / g-2mmol / g.

[0044] In yet another specific embodiment, the sulfonyl tannic acid is sulfomethyl tannic acid.

[0045] In a second aspect of the present invention, a cellulose pretreatment method is provided, the method comprising (1) pretreating cellulose-containing biomass using a cellulose pretreatment agent, wherein the cellulose pretreatment agent is an organic acid containing a sulfonic acid group, a carbon-based material derived from the organic acid containing a sulfonic acid group, or a g-C3N4 / FeOCl-type Fenton composite material.

[0046] In a specific embodiment, the organic acid containing a sulfonic acid group may be sulfonate tannic acid and / or m-aminobenzenesulfonic acid, but is not limited thereto.

[0047] In a specific embodiment, the carbon-based material derived from an organic acid containing a sulfonic acid group can be carbon black or carbon quantum dots, but is not limited thereto. For example, the carbon-based material can be carbon black or carbon quantum dots prepared from an organic acid containing a sulfonic acid group, such as sulfonic tannic acid and / or m-aminobenzenesulfonic acid, together with citric acid.

[0048] In another specific embodiment, the cellulose pretreatment agent may be a sulfonate tannic acid having a sulfonate content of 1 mmol / g to 4 mmol / g. For example, the sulfonate content in the sulfonate tannic acid may be 1 mmol / g, 1.25 mmol / g, 1.5 mmol / g, 1.75 mmol / g, 2 mmol / g, 2.25 mmol / g, 2.5 mmol / g, 2.75 mmol / g, 3 mmol / g, 3.25 mmol / g, 3.5 mmol / g, 3.75 mmol / g or 4 mmol / g, or a range consisting of any two of these values.

[0049] In a preferred embodiment, the cellulose pretreatment agent may be sulfonate tannic acid having a sulfonate content of 1.5 mmol / g to 2 mmol / g.

[0050] In yet another specific embodiment, the sulfonyl tannic acid is sulfomethyl tannic acid.

[0051] It is understood that the above description of the cellulose pretreatment agent of the first aspect of the present invention is also applicable to the cellulose pretreatment agent used in the cellulose pretreatment method of the second aspect of the present invention. For the sake of brevity, it will not be repeated here.

[0052] In another specific embodiment, the cellulose pretreatment agent is a g-C3N4 / FeOCl-type Fenton composite material. The g-C3N4 / FeOCl-type Fenton composite material can be used to pretreat colored cellulose-containing biomass to effectively remove the color of the cellulose-containing biomass.

[0053] In the present invention, the term "Fenton-like composite material" refers to a material containing a polyvalent metal such as Fe, Cu, Co, Mn, Ce, Ag, Cr, Ru, W, Mo, V, Ti, etc. The polyvalent metal in the material can activate peroxides such as H2O2, potassium peroxymonosulfate, etc., through the metal low valence state (M n+ ) and oxidizing metal high valence states (M (n+z)+ ) produces reactive oxygen species (ROS). Taking metal Fe as an example, its low valence state is Fe 2+ , the high valence state is Fe 3+ , then n is 2 and z is 1.

[0054] As used herein, the term "cellulose-containing biomass" refers to biomass made from plant materials such as wood, straw, corn stalks, and hemp.

[0055] In a specific embodiment, the cellulose-containing biomass is a textile, such as a cotton textile, a polyester / cotton blended textile, and the like.

[0056] In a specific embodiment, step (1) comprises heating the mixture of the cellulose pretreatment agent and the cellulose-containing biomass to a certain temperature, such as 40-60° C., and maintaining the mixture at the temperature for a period of time. Preferably, the heating is carried out under shaking or stirring conditions to promote more complete mixing of the cellulose pretreatment agent and the biomass and to promote the uniformity of the temperature of the entire reaction system.

[0057] The pretreatment in the prior art is usually carried out at a relatively high temperature, such as 90-120° C. In contrast, the pretreatment of the present invention can be carried out at a relatively mild temperature.

[0058] In a preferred embodiment, step (1) comprises heating the mixture of the pretreatment agent and the cellulose-containing biomass to 45°C to 55°C.

[0059] In a more preferred embodiment, step (1) comprises heating the mixture of the pretreatment agent and the cellulose-containing biomass to 50°C.

[0060] In a specific embodiment, the mixture can be kept at the above temperature for 12 h to 48 h, for example, for 24 h.

[0061] In addition, in the prior art cellulose pretreatment method, an acid solution, an alkaline solution, or an ionic liquid is usually used as a solvent. However, in the cellulose pretreatment of the present invention, water can be used as a solvent without using these solutions or liquids. Therefore, the cost problem associated with acid and alkali recovery and waste disposal no longer exists, and there is no need to use a corrosion-resistant container.

[0062] Therefore, in a specific embodiment, step (1) comprises adding the cellulose pretreatment agent and the cellulose-containing biomass into water to form a mixture of the cellulose pretreatment agent and the cellulose raw material, and then heating the mixture.

[0063] In another specific embodiment, in step (1), the concentration of the cellulose pretreatment agent ranges from 0.5 g / L to 20 g / L. For example, the concentration of the cellulose pretreatment agent can be 0.5 g / L, 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L, 5 g / L, 5.5 g / L, 6 g / L, 6.5 g / L, 7 g / L, 7.5 g / L, 8 g / L, 8.5 g / L, 9 g / L, 9.5 g / L, 10 g / L, 10.5 g / L, 11g / L, 11.5g / L, 12g / L, 12.5g / L, 13g / L, 13.5g / L, 14g / L, 14.5g / L, 15g / L, 15.5g / L, 16g / L, 16.5g / L, 17g / L, 17.5g / L, 18g / L, 18.5g / L, 19g / L, 19.5g / L or 20g / L, or a range consisting of any two of them.

[0064] In a specific embodiment, in step (1), the concentration of the g-C3N4 / FeOCl-type Fenton composite material ranges from 1 g / L to 3 g / L. For example, the concentration of the g-C3N4 / FeOCl-type Fenton composite material can be 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L or 3 g / L, or a range consisting of any two of these values.

[0065] It is understood that before using the cellulose pretreatment agent to pretreat the cellulose-containing biomass, the cellulose-containing biomass can be ground into fine powder to increase the contact area between the cellulose pretreatment agent and the cellulose-containing biomass and promote the pretreatment effect of the cellulose pretreatment agent on the cellulose-containing biomass. However, from the perspective of subsequent separation of the cellulose pretreatment agent and the cellulose-containing biomass, it is preferred not to grind the cellulose-containing biomass into fine powder.

[0066] In a third aspect, there is provided a method for producing reducing sugars, comprising the following steps:

[0067] (1) pretreating cellulose-containing biomass using a cellulose pretreatment agent, wherein the pretreatment agent is an organic acid containing a sulfonic acid group, a carbon-based material derived from the organic acid containing a sulfonic acid group, or a g-C3N4 / FeOCl-type Fenton composite material;

[0068] (2) separating the cellulose-containing biomass and the cellulose pretreatment agent; and

[0069] (3) Enzymatic hydrolysis of the separated pretreated cellulose-containing biomass.

[0070] In a specific embodiment, the organic acid containing a sulfonic acid group may be sulfonate tannic acid and / or m-aminobenzenesulfonic acid, but is not limited thereto.

[0071] In a specific embodiment, the carbon-based material derived from an organic acid containing a sulfonic acid group can be carbon black or carbon quantum dots, but is not limited thereto. For example, the carbon-based material can be carbon black or carbon quantum dots prepared from an organic acid containing a sulfonic acid group, such as sulfonic tannic acid and / or m-aminobenzenesulfonic acid, together with citric acid.

[0072] In another specific embodiment, the cellulose pretreatment agent may be a sulfonate tannic acid having a sulfonate content of 1 mmol / g to 4 mmol / g. For example, the sulfonate content in the sulfonate tannic acid may be 1 mmol / g, 1.25 mmol / g, 1.5 mmol / g, 1.75 mmol / g, 2 mmol / g, 2.25 mmol / g, 2.5 mmol / g, 2.75 mmol / g, 3 mmol / g, 3.25 mmol / g, 3.5 mmol / g, 3.75 mmol / g or 4 mmol / g, or a range consisting of any two of these values.

[0073] In a preferred embodiment, the cellulose pretreatment agent may be sulfonate tannic acid having a sulfonate content of 1.5 mmol / g to 2 mmol / g.

[0074] In yet another specific embodiment, the sulfonyl tannic acid is sulfomethyl tannic acid.

[0075] It is understood that the description given above for the cellulose pretreatment agent of the first aspect of the present invention is also applicable to the cellulose pretreatment agent used in the cellulose pretreatment step of the method for producing reducing sugars in the third aspect of the present invention, and the description given above for the cellulose pretreatment method of the second aspect of the present invention is also applicable to the cellulose pretreatment step (1) in the method for producing reducing sugars in the third aspect of the present invention. For the sake of brevity, it will not be repeated here.

[0076] In one embodiment, step (1) comprises heating the mixture of the cellulose pretreatment agent and the cellulose-containing biomass to a certain temperature, such as 40-60° C., and maintaining the mixture at the temperature for a period of time. Preferably, the heating is carried out under shaking or stirring conditions to promote more thorough mixing of the cellulose pretreatment agent and the biomass and to promote uniformity of the temperature of the entire reaction system.

[0077] The pretreatment in the prior art is usually carried out at a relatively high temperature, such as 90-120° C. In contrast, the pretreatment of the present invention can be carried out at a relatively mild temperature.

[0078] In a preferred embodiment, step (1) comprises heating the mixture of the pretreatment agent and the cellulose-containing biomass to 45°C to 55°C.

[0079] In a more preferred embodiment, step (1) comprises heating the mixture of the pretreatment agent and the cellulose-containing biomass to 50°C.

[0080] In a specific embodiment, the mixture can be kept at the above temperature for 12 h to 48 h, for example, for 24 h.

[0081] In another specific embodiment, the concentration of the pretreatment agent in the pretreatment step ranges from 0.5 g / L to 20 g / L. For example, the concentration of the cellulose pretreatment agent can be 0.5 g / L, 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L, 5 g / L, 5.5 g / L, 6 g / L, 6.5 g / L, 7 g / L, 7.5 g / L, 8 g / L, 8.5 g / L, 9 g / L, 9.5 g / L, 10 g / L, 10.5 g / L, 11g / L, 11.5g / L, 12g / L, 12.5g / L, 13g / L, 13.5g / L, 14g / L, 14.5g / L, 15g / L, 15.5g / L, 16g / L, 16.5g / L, 17g / L, 17.5g / L, 18g / L, 18.5g / L, 19g / L, 19.5g / L or 20g / L, or a range consisting of any two of them.

[0082] In a specific embodiment, in step (1), the concentration of the g-C3N4 / FeOCl-type Fenton composite material ranges from 1 g / L to 3 g / L. For example, the concentration of the g-C3N4 / FeOCl-type Fenton composite material can be 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L or 3 g / L, or a range consisting of any two of these values.

[0083] In addition, in the prior art cellulose pretreatment method, an acid solution, an alkaline solution, or an ionic liquid is usually used as a solvent. However, in the cellulose pretreatment of the present invention, water can be used as a solvent without using these solutions or liquids. Therefore, the cost problem associated with acid and alkali recovery and waste disposal no longer exists, and there is no need to use a corrosion-resistant container.

[0084] Therefore, in a specific embodiment, step (1) comprises adding the cellulose pretreatment agent and the cellulose-containing biomass into water to form a mixture of the cellulose pretreatment agent and the cellulose-containing biomass, and then heating the mixture.

[0085] After the cellulose-containing biomass is pretreated with the cellulose pretreatment agent, step (2) is performed: separating the cellulose-containing biomass and the cellulose pretreatment agent. In the method for producing reducing sugars of the present invention, since the cellulose pretreatment agent has been separated before the enzymatic hydrolysis step, it can be understood that the cellulose pretreatment agent of the present invention does not participate in the subsequent enzymatic hydrolysis step of the cellulose-containing biomass, and therefore does not interact with the enzyme used in the enzymatic hydrolysis step.

[0086] The separation of the cellulose-containing biomass and the cellulose pretreatment agent can be performed simply by filtering, but other methods can also be used as long as the two can be separated. Through this separation step, the cellulose pretreatment agent can be recovered for reuse.

[0087] In addition, the cellulose-containing biomass can be ground into fine powder before the cellulose-containing biomass is pretreated with the cellulose pretreatment agent to increase the contact area between the cellulose pretreatment agent and the cellulose-containing biomass and promote the pretreatment effect of the cellulose pretreatment agent on the cellulose-containing biomass. However, from the perspective of subsequent separation of the cellulose pretreatment agent and the cellulose-containing biomass, it is preferred not to grind the cellulose-containing biomass into fine powder before pretreatment.

[0088] After the separation in step (2), step (3) is performed: enzymatic hydrolysis of the separated pretreated cellulose-containing biomass. The cellulase used in step (3) may include CTec3, Enzyme Blend, CTec2, but is not limited thereto.

[0089] In addition, in the prior art, enzymatic hydrolysis usually needs to be carried out at a relatively high temperature (eg, above 100° C.). However, due to the pretreatment method of the present invention, the subsequent enzymatic hydrolysis step can be carried out at room temperature or a temperature slightly higher than room temperature.

[0090] Therefore, in one embodiment, the enzymatic hydrolysis step, i.e., step (3), is carried out at a temperature of 40° C. to 60° C. Specifically, step (3) can be carried out at a temperature of 40° C., 45° C., 50° C., 55° C., or 60° C., or a range consisting of any two of these values.

[0091] In a preferred embodiment, step (3) can be performed at a temperature of 50°C.

[0092] In addition, in the prior art enzymatic hydrolysis, ionic liquids are sometimes required as solvents. In contrast, in the enzymatic hydrolysis of the present invention, conventional buffers such as sodium citrate buffer solutions can be used as solvents, thereby greatly reducing costs and effectively maintaining the activity of cellulase.

[0093] Thus, in one embodiment, step (3) may comprise mixing together the pretreated cellulose-containing biomass, cellulase and buffer.

[0094] In a preferred embodiment, step (3) is carried out at a pH of 4-10. Specifically, step (3) can be carried out at pH 4, pH 4.5, pH 5, pH 5.5, pH 6, pH 6.5, pH 7, pH 7.5, pH 8, pH 8.5, pH 9, pH 9.5 or pH 10, or a pH range consisting of any two of these values.

[0095] In a further preferred embodiment, step (3) is carried out at pH 5-7.

[0096] In a further preferred embodiment, step (3) is performed at pH 5.5.

[0097] In addition, it should be noted that before enzymatic hydrolysis of the pretreated cellulose-containing biomass by cellulase, the pretreated cellulose-containing biomass can be ground into fine powder to increase the surface area of ​​the cellulose-containing biomass and promote the enzymatic hydrolysis of the cellulose-containing biomass by cellulase.

[0098] The cellulose pretreatment agent of the present invention is used to pretreat cellulose-containing biomass, so that the cellulose structure can be loosened under mild conditions, thereby making the subsequent cellulase hydrolysis more efficient and the reducing sugar yield higher.

[0099] Compared with the prior art, the pretreatment of the present invention enables cellulose pretreatment and enzymatic hydrolysis to be performed under relatively mild conditions. In the method of the present invention, no alkali, acid, inducer or ionic liquid is used, and the reaction system is simpler.

[0100] In a fourth aspect, there is provided use of the cellulose pretreatment agent of the first aspect of the present invention for pretreating cellulose-containing biomass.

[0101] As mentioned above, by using the organic acid containing sulfonic acid groups of the present invention, or carbon-based materials such as carbon black or carbon quantum dots derived from the organic acid containing sulfonic acid groups, the sulfonic acid groups and active groups such as hydroxyl groups on the cellulose pretreatment agent (in some cases) can fully react with cellulose under mild conditions, promote the cellulose structure to become loose, reduce the crystallinity and polymerization degree of cellulose, and then promote subsequent cellulase hydrolysis. The inventors have found that the yield of reducing sugars formed by enzymatic hydrolysis of cellulose-containing biomass treated with the pretreatment agent of the present invention can be higher than 80%.

[0102] In a fifth aspect, a g-C3N4 / FeOCl-type Fenton composite material is provided for use in pretreating cellulose-containing biomass.

[0103] The inventors have found that by using the composite material to pretreat colored cellulose-containing biomass, not only can the color of the cellulose-containing biomass be effectively removed, but also the yield of reducing sugars formed by the cellulose-containing biomass in the subsequent enzymatic hydrolysis step can be increased to a certain extent.

[0104] Example

[0105] In the following examples, the preparation method of the cellulose pretreatment catalyst of the present invention and the characterization of its related properties are shown. Unless otherwise specified, the test methods used are conventional methods, and the test materials used in the following examples are purchased from conventional reagent stores. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by technicians in the technical field of the present invention.

[0106] Example 1: pH Optimization of Enzymatic Hydrolysis

[0107] Enzymatic hydrolysis: 0.3 g of blue fabric (about 1 cm x 1 cm) and 120 FPU / g of raw material cellulase CTec2 were added to 0.05 M sodium citrate buffer solution (solid-to-liquid ratio of 3%). The pH value of the sodium citrate buffer solution was adjusted to 4-10 with 5% H2SO4 solution, 1 M NaOH solution or water. The resulting mixture was incubated at 50°C for 96 hours with shaking for enzymatic hydrolysis. After enzymatic hydrolysis, the mixture was filtered to obtain a reducing sugar solution, and the yield of reducing sugar was measured by a DNS test. The results are shown in Table 1 below. The results in Table 1 show that the yield of reducing sugar is the highest when enzymatic hydrolysis is performed at a pH of 5.5-7. Since a reaction system of pH 5.5 can be obtained by diluting a commercially available citrate buffer, pH 5.5 is used in subsequent enzymatic hydrolysis.

[0108] Table 1: Reducing sugar yields at different enzymatic hydrolysis pH

[0109] pH Reducing sugar yield (%) 10 50 7 51 5.5 62 5 48 4 49

[0110] Example 2: Synthesis and characterization of sulfomethyl tannic acid

[0111] 5g of tannic acid, 45mL of 0.8M NaOH and 37% by weight of formaldehyde are added to a reaction vessel in sequence, wherein the molar ratio of the amount of formaldehyde to the amount of sodium sulfite to be added in the next step is controlled to be 0.8, the reaction time is 1.5 hours, and the temperature is 70°C. Then sodium sulfite is added, and the amount ratio of sodium sulfite (mmol) to tannic acid (g) is controlled to be 1mmol / g, 1.5mmol / g, 1.75mmol / g, 2mmol / g and 4mmol / g, respectively, the temperature is adjusted to 95°C, and the reaction time is 3 hours. After the reaction is completed, the powder obtained by freeze drying or drying is sulfomethyl tannic acid with sulfonic acid groups of 1mmol / g, 1.5mmol / g, 1.75mmol / g, 2mmol / g and 4mmol / g, respectively.

[0112] The infrared spectra of tannic acid and sulfomethyl tannic acid were tested respectively, and the results are as follows Figure 1 As shown. Figure 1 It can be seen that compared with tannic acid, tannic acid containing sulfomethyl group has a higher peak at 1030 cm -1 Up to 1050cm -1 There is an O=S=O vibration peak at .

[0113] Example 3: Pretreatment temperature optimization

[0114] Pretreatment: 50 mg of freeze-dried sulfomethyltannic acid with a sulfonic acid content of 1.75 mmol / g was added to 50 mL of deionized water. 1 g of blue fabric was added to the resulting solution. The resulting mixture was incubated at 40°C, 50°C and 60°C for 24 hours. The pretreated fabric was then filtered, rinsed with water and dried at 70°C overnight. The dried fabric was ground into a fine powder and used as a raw material for enzymatic hydrolysis.

[0115] Enzymatic hydrolysis: 0.3 g of ground blue fabric and 120 FPU / g of raw material cellulase CTec2 were added to 0.05 M sodium citrate buffer solution (solid-to-liquid ratio of 3%, pH 5.5). The resulting mixture was incubated at 50°C with shaking for 96 hours for enzymatic hydrolysis. After enzymatic hydrolysis, the mixture was filtered to obtain a reducing sugar solution, and the yield of reducing sugar was measured by DNS test, as shown in Table 2 below. The results in Table 2 show that although the pretreatment was carried out at a relatively low temperature of 40°C-60°C, the yield of reducing sugar was very high.

[0116] Table 2: Reducing sugar yields at different pretreatment temperatures

[0117] Temperature(℃) Reducing sugar yield (%) 40 73 50 79 60 67

[0118] Example 4: Enzymatic hydrolysis of pretreated blue fabric

[0119] Pretreatment: 25 mg, 50 mg, 100 mg, 150 mg, 250 mg, 500 mg, 750 mg, 1000 mg of sulfomethyl tannic acid (lyophilized and dried) with sulfonic acid content of 1 mmol / g, 1.75 mmol / g and 4 mmol / g, respectively, were added to 50 mL of deionized water to make the concentrations 0.5 g / L, 1 g / L, 2 g / L, 3 g / L, 5 g / L, 10 g / L, 15 g / L and 20 g / L, respectively. 1 g of blue fabric was added to the resulting solution. The resulting mixture was incubated at 50°C for 24 hours. The pretreated fabric was then filtered, rinsed with water and dried at 70°C overnight. The dried fabric was ground into fine powder and used as a raw material for enzymatic hydrolysis.

[0120] Enzymatic hydrolysis: 0.3 g of ground blue fabric and 120 FPU / g of raw material cellulase CTec2 were added to 0.05 M sodium citrate buffer solution (solid-to-liquid ratio of 3%, pH 5.5). The resulting mixture was shaken and incubated at 50°C for 96 hours for enzymatic hydrolysis. After enzymatic hydrolysis, the mixture was filtered to obtain a reducing sugar solution, and the yield of reducing sugar was measured by DNS test, as shown in Table 3 below.

[0121] Table 3: Reducing sugar yields of blue fabrics pretreated with different concentrations of sulfomethyltannic acid after enzymatic hydrolysis

[0122]

[0123] * indicates a control, which was subjected to the same enzymatic hydrolysis steps but without pretreatment.

[0124] The results show that, compared with the control, the fabric pretreated with the cellulose pretreatment agent of the present invention can obtain a higher reducing sugar yield after enzymatic hydrolysis.

[0125] Example 5: Synthesis of Carbon Black Containing SO3H Groups and Related Pretreatment and Enzymatic Hydrolysis

[0126] Synthesis: 1 g of sulfomethyltannic acid having a sulfonic acid group content of 1.75 mmol / g and 4 mmol / g was placed in a crucible and heated at 300° C. for 6 hours in a muffle furnace and then naturally cooled to room temperature, thereby obtaining carbon black.

[0127] Characterization: The infrared spectrum of the carbon black prepared in this way was tested and the results are also shown in Figure 1 .Depend on Figure 1 It can be seen that the carbon black prepared in this way also has a peak at 1030 cm -1 Up to 1050cm -1 There is an O=S=O vibration peak at the cation, indicating that it still carries a sulfonic acid group.

[0128] Pretreatment: 50 mg (final concentration of 1 g / L) and 250 mg (final concentration of 5 g / L) of carbon black with sulfonic acid content of 1.0 mmol / g, 1.5 mmol / g, 1.75 mmol / g, 2.0 mmol / g and 4 mmol / g were added to 50 mL of deionized water. 1 g of blue fabric was added to the resulting solution. The resulting mixture was incubated at 50°C for 24 hours. The pretreated fabric was then filtered, rinsed with water and dried at 70°C overnight. The dried fabric was ground into a fine powder and used as a raw material for enzymatic hydrolysis.

[0129] Enzymatic hydrolysis: 0.3 g of ground blue fabric and 120 FPU / g of raw material cellulase CTec2 were added to 0.05 M sodium citrate buffer solution (solid-to-liquid ratio of 3%, pH 5.5). The resulting mixture was incubated at 50°C with shaking for 96 hours for enzymatic hydrolysis. After enzymatic hydrolysis, the mixture was filtered to obtain a reducing sugar solution, and the yield of reducing sugar was measured by DNS test, and the results are shown in Table 4 below.

[0130] Table 4: Reducing sugar yield of blue fabrics pretreated with different carbon blacks

[0131]

[0132] * indicates a control, which was subjected to the same enzymatic hydrolysis steps but without pretreatment.

[0133] The results in Table 4 show that, compared with the control, the carbon black of the present invention can effectively pretreat cellulose-containing biomass, and the pretreated cellulose-containing biomass can also obtain a higher reducing sugar yield by enzymatic hydrolysis under milder conditions.

[0134] Example 6: Preparation of carbon quantum dots from citric acid and sulfomethyltannic acid and related pretreatment and enzymatic hydrolysis

[0135] Synthesis: 10 mmol of citric acid and 0.01 mmol of sulfomethyl tannic acid (sulfonic acid content of 4.0 mmol / g) were dissolved in 20 mL of ethanol. The solution was filtered into a 50 mL Teflon-lined container. The container was placed in a stainless steel autoclave and treated in an oven at 160°C for 5 hours. After the reaction was completed, the autoclave was cooled at room temperature. The resulting solution was dried to obtain carbon quantum dots.

[0136] Characterization: The infrared spectrum of the carbon quantum dots prepared in this way was tested, and the results were as follows Figure 1 As shown. Figure 1 It can be seen that, similar to sulfomethyl tannic acid and carbon black, carbon quantum dots also have a -1 Up to 1050cm -1The O=S=O vibration at the position indicates that it carries a sulfonic acid group.

[0137] In addition, a transmission electron microscopy (TEM) image of the carbon quantum dots prepared in this way is provided, such as Figure 2 As shown, the size of the carbon quantum dots obtained by the above steps is in the range of 2-5 nm.

[0138] The photoluminescence properties of the carbon quantum dots prepared in this way were further tested, and the results were as follows Figure 3 and Figure 4 shown.

[0139] Pretreatment: 50 mg (final concentration of 1 g / L) and 500 mg (final concentration of 10 g / L) of carbon quantum dots containing SO3H groups (sulfonic acid content of 4.0 mmol / g) prepared in the above step were added to 50 mL of deionized water. 1 g of blue fabric was added to the resulting solution. The resulting mixture was incubated at 50°C for 24 hours. The pretreated fabric was then filtered, rinsed with water and dried at 70°C overnight. The dried fabric was ground into a fine powder and used as a raw material for enzymatic hydrolysis.

[0140] Enzymatic hydrolysis: 0.3 g of ground blue fabric and 120 FPU / g of raw material cellulase CTec2 were added to 0.05 M sodium citrate buffer solution (solid-to-liquid ratio of 3%, pH 5.5). The resulting mixture was shaken and incubated at 50°C for 96 hours for enzymatic hydrolysis. After enzymatic hydrolysis, the mixture was filtered to obtain a reducing sugar solution, and the yield of reducing sugar was measured by DNS test. The results are shown in Table 5 below.

[0141] Table 5: Reducing sugar yields of blue fabrics pretreated with carbon quantum dots at different concentrations

[0142]

[0143] * indicates a control, which was subjected to the same enzymatic hydrolysis steps but without pretreatment.

[0144] The results in Table 5 show that, compared with the control, the carbon quantum dots of the present invention can effectively pretreat cellulose-containing biomass, and the pretreated cellulose-containing biomass can also obtain a relatively higher reducing sugar yield by enzymatic hydrolysis under milder conditions.

[0145] Example 7: Preparation of carbon quantum dots from citric acid and m-aminobenzenesulfonic acid and related pretreatment and enzymatic hydrolysis

[0146] Synthesis: 1.728 g of citric acid, 0.7 g of metanilic acid and 600 μL of ethylenediamine were dissolved in 20 mL of dimethylformamide (DMF). The solution was filtered into a 50 mL Teflon-lined container, which was then placed in a stainless steel autoclave and treated in an oven at 160°C for 5 hours. After the reaction was completed, the autoclave was cooled at room temperature. The resulting solution was dried to obtain carbon quantum dots with a sulfonic acid group content of 5.6 mmol / g.

[0147] Characterization: The photoluminescence properties of the carbon quantum dots prepared in this way were tested, and the results were as follows Figure 5 As shown in the figure, it can be seen that the solution appears brown under sunlight and emits blue fluorescence under 365nm excitation, which indicates that carbon quantum dots have been successfully prepared.

[0148] Pretreatment: 50 mg (final concentration of 1 g / L), 250 mg (final concentration of 5 g / L) and 500 mg (final concentration of 10 g / L) of the carbon quantum dots prepared in the above step were added to 50 mL of deionized water. 1 g of blue fabric was added to the resulting solution. The resulting mixture was incubated at 50 ° C for 24 hours. The pretreated fabric was then filtered, rinsed with water and dried at 70 ° C overnight. The dried fabric was ground into a fine powder and used as a raw material for enzymatic hydrolysis.

[0149] Enzymatic hydrolysis: 0.3 g of ground blue fabric and 120 FPU / g of raw material cellulase CTec2 were added to 0.05 M sodium citrate buffer solution (solid-to-liquid ratio of 3%, pH 5.5). The resulting mixture was incubated at 50°C for 96 hours with shaking for enzymatic hydrolysis. After enzymatic hydrolysis, the mixture was filtered to obtain a reducing sugar solution, and the yield of reducing sugar was measured by DNS test, and the results are shown in Table 6 below.

[0150] Table 6: Reducing sugar yields of blue fabrics pretreated with carbon quantum dots at different concentrations

[0151]

[0152] * indicates a control, which was subjected to the same enzymatic hydrolysis steps but without pretreatment.

[0153] The results in Table 6 show that, compared with the control, the carbon quantum dots of the present invention can effectively pretreat cellulose-containing biomass, and the pretreated cellulose-containing biomass can also obtain a significantly higher reducing sugar yield by enzymatic hydrolysis under milder conditions.

[0154] Example 8: Pretreatment using a Fenton-like catalyst

[0155] Synthesis: Melamine (10.002 g) was calcined at 500°C for 2 hours at a heating rate of Δ10°C / min, and then calcined at 520°C for 2 hours at a heating rate of Δ10°C / min. The blocky C3N4 was ground into a fine powder and then calcined at 520°C for 2 hours at a heating rate of Δ10°C / min to finally obtain a C3N4 nanosheet product. 0.45 g of C3N4 nanosheets were ultrasonically treated in 100 mL of H2O. 20 mL of an aqueous solution containing 0.13 g of FeCl3·6H2O was added dropwise to the suspension. The resulting mixture was stirred for 4 hours and then completely dried in an oven at 70°C. The resulting powder was calcined at 250°C for 2 hours at a heating rate of Δ10°C / min. Thus, a g-C3N4 / FeOCl Fenton-like composite material was obtained.

[0156] Pretreatment: 50 mg, 100 mg or 150 mg of g-C3N4 / FeOCl Fenton-like composite and 384 mg of potassium persulfate (oxone) were added to 50 mL of deionized water. 1 g of blue fabric was added to the mixture. The resulting mixture was incubated at 50 ° C for 24 hours. The pretreated fabric was then washed with deionized water and dried at 70 ° C overnight.

[0157] The conditions before and after incubation with the pretreatment agent are as follows Figure 6 As shown, the left picture is before pretreatment, the right picture is after pretreatment, and the fabric after drying is as shown in Figure 7 As shown in these two figures, it can be seen that the blue pigment on the fabric pretreated with g-C3N4 / FeOCl-like Fenton composite material was successfully removed.

[0158] Enzymatic hydrolysis: 0.3 g of fabric and 40 FPU / g of raw material cellulase CTec2 were added to 0.05 M sodium citrate buffer solution (solid-to-liquid ratio of 3%). The resulting mixture was incubated at 50°C with shaking for 96 hours. After enzymatic hydrolysis, the mixture was filtered to obtain a reducing sugar solution, and the yield of reducing sugar was measured by DNS test, and the results are shown in Table 6 below.

[0159] Table 6: Reducing sugar yield of blue fabric pretreated with different concentrations of g-C3N4 / FeOCl-based Fenton composites

[0160] <![CDATA[g-C3N4 / FeOCl(g / L)]]> Reducing sugar yield (%) 1 48 2 47 3 51 * 40

[0161] * indicates a control, which was subjected to the same enzymatic hydrolysis steps but without pretreatment.

[0162] It can be seen from Table 6 that the use of the Fenton-like catalyst of the present invention significantly increases the yield of reducing sugars.

Claims

1. A cellulose pretreatment agent, which is an organic acid containing a sulfonic acid group or a carbon-based material derived from the organic acid containing a sulfonic acid group, wherein the organic acid containing a sulfonic acid group is, for example, sulfonyl tannic acid and / or m-aminobenzenesulfonic acid.

2. The cellulose pretreatment agent according to claim 1, wherein The cellulose pretreatment agent is sulfonic acid tannic acid with a sulfonic acid content of 1 mmol / g-4 mmol / g.

3. The cellulose pretreatment agent according to claim 1 or 2, wherein The carbon-based material derived from an organic acid containing a sulfonic acid group is carbon black or carbon quantum dots.

4. A cellulose pretreatment method, the method comprising: (1) Pretreating cellulose-containing biomass using a cellulose pretreatment agent, wherein the cellulose pretreatment agent is an organic acid containing a sulfonic acid group, a carbon-based material derived from the organic acid containing a sulfonic acid group, or a g-C3N4 / FeOCl-type Fenton composite material; the organic acid containing a sulfonic acid group is, for example, sulfonic tannic acid and / or m-aminobenzenesulfonic acid.

5. A method for producing reducing sugar, the method comprising the following steps: (1) pretreating cellulose-containing biomass using a cellulose pretreatment agent, wherein the pretreatment agent is an organic acid containing a sulfonic acid group, a carbon-based material derived from the organic acid containing a sulfonic acid group, or a g-C3N4 / FeOCl-type Fenton composite material; the organic acid containing a sulfonic acid group is, for example, sulfonic tannic acid and / or m-aminobenzenesulfonic acid; (2) separating the cellulose-containing biomass and the cellulose pretreatment agent; and (3) enzymatically hydrolyzing the separated pretreated cellulose-containing biomass.

6. The method according to claim 4 or 5, wherein: The cellulose pretreatment agent is sulfonate tannic acid having a sulfonate content of 1 mmol / g to 4 mmol / g.

7. The method according to claim 4 or 5, wherein: The carbon-based material derived from an organic acid containing a sulfonic acid group is carbon black or carbon quantum dots.

8. The method according to claim 4 or 5, wherein: Step (1) comprises heating the mixture of the pretreatment agent and the cellulose-containing biomass to a temperature of, for example, 40°C to 60°C, preferably 45°C to 55°C, more preferably 50°C, and maintaining it at this temperature for a period of time, for example 12h to 48h, preferably 24h.

9. The method according to claim 4 or 5, wherein: In step (1), the concentration of the cellulose pretreatment agent ranges from 0.5 g / L to 20 g / L.

10. The method according to claim 4 or 5, wherein: In step (1), the concentration range of the g-C3N4 / FeOCl Fenton-type composite material is 1 g / L to 3 g / L.

11. The method according to any one of claims 5 to 10, wherein: Step (3) is carried out at a temperature of 40°C-60°C, preferably 50°C.

12. The method according to any one of claims 5 to 11, wherein: Step (3) is carried out at pH 4-10, preferably pH 5-7.

13. Use of the cellulose pretreatment agent according to any one of claims 1 to 3 for pretreating cellulose-containing biomass.

14. Use of g-C3N4 / FeOCl Fenton-type composite materials for pretreatment of cellulose-containing biomass.

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