阅读说明：本技术 一锅法合成的功能性碳基磁性固体酸催化剂及其在催化甘蔗渣水解产糖中的应用 (Functional carbon-based magnetic solid acid catalyst synthesized by one-pot method and application thereof in catalyzing bagasse hydrolysis to produce sugar ) 是由 苏同超 冯宜鹏 周海旭 曾洁 高海燕 李光磊 于 2019-09-27 设计创作，主要内容包括：本发明涉及一种一锅法合成功能性碳基磁性固体酸催化剂的方法,其以纳米四氧化三铁、葡萄糖、柠檬酸、香草醛和羟乙基磺酸为原料,通过新型的一步水热沉淀-磺化的方法合成碳基磁性固体酸催化剂C-SO3H@Fe3O4/C。研究发现：合成的催化剂具有高达1.23 mmol g-1的酸度和15.65 Am2/kg的磁强度。使用该催化剂对经碱-冷冻预处理过的甘蔗渣在180℃进行水解,能够得到高达62.59%的葡萄糖和73.01%的总还原糖。此外,通过外接磁场的作用可以对使用后的催化剂进行分离和回收,能够得到93.18%的回收率。催化剂循环使用5次后,仍能催化甘蔗渣水解得到54.47%的葡萄糖和60.65%的总还原糖。本发明C-SO<Sub>3</Sub>H@Fe<Sub>3</Sub>O<Sub>4</Sub>/C催化剂能够高效的催化甘蔗渣转化为可发酵糖,并且该催化剂表现出良好的催化活性和稳定性。(The invention relates to a method for synthesizing a functional carbon-based magnetic solid acid catalyst by a one-pot method, which takes nano ferroferric oxide, glucose, citric acid, vanillin and isethionic acid as raw materials and synthesizes the carbon-based magnetic solid acid catalyst C-SO3H @ Fe3O4/C by a novel one-step hydrothermal precipitation-sulfonation method. The research finds that: the synthesized catalyst had an acidity of up to 1.23 mmol g-1 and a magnetic strength of 15.65 Am 2/kg. Hydrolysis of alkali-frozen pretreated bagasse at 180 ℃ using this catalyst can yield up to 62.59% glucose and 73.01% total reducing sugars. In addition, the catalyst after use can be separated and recovered by the action of an external magnetic field, and a recovery rate of 93.18% can be obtained. After the catalyst is recycled for 5 times, the sugarcane can still be catalyzedHydrolysis of the residue yielded 54.47% glucose and 60.65% total reducing sugars. C-SO of the invention 3 H@Fe 3 O 4 the/C catalyst can efficiently catalyze the bagasse to be converted into fermentable sugar, and the catalyst shows good catalytic activity and stability.)

1. A method for synthesizing a functional carbon-based magnetic solid acid catalyst by a one-pot method is characterized by comprising the following steps:

1) Mixing nano Fe₃O₄Mixing glucose and water, and pyrolyzing and carbonizing the mixed solution after water evaporation at 650-750 ℃ for 0.5-1.5 hours to obtain carbon-based magnetic core MCC;

2) Mixing carbon-based magnetic core MCC, distilled water, glucose, citric acid, vanillin and isethionic acid, and adding into the mixture₂Keeping the temperature at 160-180 ℃ for 2-6 hours in the atmosphere to obtain a solid acid catalyst which is carbonized and sulfonated simultaneously;

3) Washing the catalyst obtained in the step 2) with hot water at 160-180 ℃ until the pH value is 7, naturally cooling to room temperature, collecting the washed catalyst, and freeze-drying to obtain the catalyst C-SO₃H/Fe₃O₄@C。

2. The method for synthesizing the functional carbon-based magnetic solid acid catalyst according to claim 1, wherein in the step 1), 2g of nano Fe is added₃O₄Mixing 12-18 g glucose and 60-100 mL water.

3. The method for synthesizing a functional carbon-based magnetic solid acid catalyst according to claim 1, wherein in the step 2), 0.5g of carbon-based magnetic core MCC, 40-80 mL of distilled water, 7.5-10.5g of glucose, 45-135 mg of citric acid, 45-135 mg of vanillin, and 6-8 g of isethionic acid are mixed.

4. The method for synthesizing the functional carbon-based magnetic solid acid catalyst according to claim 1, wherein in the step 2), N is₂The purity is more than or equal to 99.99 percent; the freeze-drying condition in the step 3) is drying for 48 hours at the temperature of minus 47 ℃.

5. The functional carbon-based magnetic solid acid catalyst prepared by the one-pot synthesis method of any one of claims 1 to 4.

6. The use of the functional carbon-based magnetic solid acid catalyst as claimed in claim 5 for catalyzing the sugar production from the hydrolysis of bagasse.

7. the use of a functional carbon-based magnetic solid acid catalyst according to claim 6 for catalyzing the sugar production from the hydrolysis of bagasse, wherein bagasse is previously treated with: 2g of bagasse powder and 200ml of sodium hydroxide solution with the mass concentration not more than 5 percent are stirred for 24 hours at normal temperature, and the mixture is placed for 24 to 48 hours at the temperature of minus 18 ℃; taking out, thawing, filtering, washing with water to neutrality, and freeze drying.

8. The use of a functional carbon-based magnetic solid acid catalyst as claimed in claim 7 for catalyzing the hydrolysis of bagasse to produce sugar, wherein 0.027 g of pretreated bagasse, 0.06-0.27 g of catalyst C-SO, are mixed together₃H/Fe₃O₄@ C and 15 mL of water are mixed and reacted at a temperature of 160-200 ℃ for 2-4 hours.

9. The application of the functional carbon-based magnetic solid acid catalyst in catalyzing sugar production by hydrolyzing bagasse, as claimed in claim 8, wherein after the reaction is finished, the used catalyst is recovered by a permanent magnet, washed with distilled water until the pH is 7, and then freeze-dried at-47 ℃ for reuse.

Technical Field

The invention belongs to the technical field of catalysts, and particularly relates to a functional carbon-based magnetic solid acid catalyst synthesized by a one-pot method and application thereof in catalyzing bagasse hydrolysis to produce sugar.

Background

With increasing demand for energy, increasing consumption of traditional petroleum and serious environmental pollution problems, renewable biomass can be considered as the most potential alternative to synthetic fuels and related chemicals. Carbohydrates in biomass exist mainly in the form of cellulose and hemicellulose, and both can be hydrolyzed to produce fermentable sugars such as glucose and xylose, which are the most important bio-based platform compounds that can be used for producing fuels. Cellulose is mainly a straight-chain polymer molecule formed by connecting glucose units through beta-1, 4-glycosidic bonds, and the cellulose molecular structure has a large number of intramolecular and intermolecular hydrogen bonds to form a firm structure of cellulose, so that the cellulose molecules are difficult to hydrolyze and utilize. Therefore, in order to promote the hydrolysis of cellulose and increase the yield of hydrolyzed sugars, catalysts are often added to the reaction system to disrupt the structure of cellulose molecules and reduce the crystallinity of cellulose.

It is well known that the most common method of cellulose hydrolysis is enzymatic hydrolysis. The cellulase can hydrolyze cellulose with high selectivity and high efficiency at lower temperature (50 ℃). However, hydrolysis of cellulose with cellulase is a relatively slow reaction, and there are still some limitations in cellulase systems, such as taking several days to obtain a satisfactory sugar yield, the cost of the enzyme is high, and it is difficult to reuse the enzyme many times. Thus, subsequently, a plurality of homogeneous acids (HCl, H)₂SO₄, H₃PO₄) For the hydrolysis of cellulose, in which H₂SO₄Most commonly. However, excessive use of these acid catalysts also has many disadvantages, such as easy corrosion of reaction equipment, difficulty in regeneration of homogeneous acid catalysts, andRecovering and generating a large amount of acid wastewater, acid residues and the like.

The problems of cost, efficiency, convenience, environment and the like are comprehensively considered, the heterogeneous catalyst is widely applied to cellulose hydrolysis reaction, and the limitation of the defects can be overcome by using the solid acid catalyst. So far, in order to improve the yield of glucose, some solid acid catalysts are often used in the hydrolysis reaction of cellulose, such as metal oxides, heteropolyacids, zeolites, activated carbon, etc., wherein sulfonated carbon shows better catalytic activity in the hydrolysis of cellulose. For example, sulfonated carbons formed by pyrolysis or hydrothermal carbonization of carbohydrates have substantial amounts of-SO₃H. The acid groups of-OH and-COOH have good catalytic activity and stability, and the catalyst is used for catalyzing the hydrolysis of corn starch to obtain total reducing sugar with the concentration of 19.91 mg/mL. In addition, sulfonated carbons having sulfonic acid groups have high acidity and activity in many conventional acid catalyst reactions.

Although sulfonated activated carbon can be easily recycled for reuse by external precipitation or filtration, it also results in a lot of time and energy consumption. Many researchers have begun to combine sulfonated carbon with magnetic fields to synthesize magnetic solid acid catalysts, and many people prefer magnetic solid acid catalysts over homogeneous acids due to their non-toxicity, recyclability, and reusability.

A novel carbon-based magnetic solid acid catalyst (preparation of the carbon-based magnetic solid acid catalyst and a hydrolysis sugar production method for plant wastes, university of Chinese science and technology, doctor paper of 2017) researched recently mainly comprises the steps of preparing carbon-based magnetic cores by incompletely carbonizing carbohydrates and iron-containing compounds at a temperature of more than 400 ℃, and then sulfonating the carbon-based magnetic cores under the condition of certain concentrated sulfuric acid at a higher temperature. By mixing Fe₃O₄The magnetic core is embedded in sulfonated active carbon to prepare Fe with a core-shell structure₃O₄@C-SO₃H nanoparticles, the resulting Fe may then be₃O₄@C-SO₃H is used in the hydrolysis reaction of the cellulose,The cellulose conversion and glucose selectivity were 48.6% and 52.1% at 140 ℃ hydrolysis temperature and 12 hours, respectively. In addition, a carbon-based magnetic solid acid catalyst can be obtained by the impregnation-carbonization-sulfonation process, and then the catalyst is used for hydrolyzing the corncobs, so that the xylose yield of 74.9 percent can be obtained. A porous carbon-based magnetic solid acid catalyst can be prepared from wood chips and has a weight of up to 2.57 mmol g^-1The total acidity, the activity of the catalyst did not significantly decrease after 5 repeated uses of the catalyst, and the results are sufficient to demonstrate that the catalyst has a stable porous carbon-sulfonic acid group structure. However, the carbon-based magnetic solid acid catalyst is mostly synthesized by a two-step method: carbonization and sulfonation at a higher temperature are carried out, and finally the prepared catalyst product is separated from concentrated sulfuric acid, but the separation of the magnetic catalyst is still a very complicated work.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a functional carbon-based magnetic solid acid catalyst synthesized by a one-pot method and prepared from nano Fe₃O₄Glucose and isethionic acid are taken as raw materials and are synthesized by a one-pot method through a pyrolysis-hydrothermal process, and the method does not need a concentrated sulfuric acid sulfonation process; the prepared carbon-based magnetic solid acid catalyst has high acidity and magnetic strength, and can be used for catalyzing bagasse hydrolysis to produce sugar.

The invention also provides application of the functional carbon-based magnetic solid acid catalyst in catalyzing hydrolysis of NaOH-freezing pretreated bagasse to produce sugar.

In order to achieve the purpose, the invention adopts the following technical scheme:

A method for synthesizing a functional carbon-based magnetic solid acid catalyst by a one-pot method comprises the following steps:

1) Mixing nano Fe₃O₄Mixing glucose and water, and pyrolyzing and carbonizing the mixed solution after water evaporation at 650-750 ℃ for 0.5-1.5 hours to obtain carbon-based magnetic core MCC;

2) Mixing carbon-based magnetic core MCC, distilled water, glucose, and fructus Citri LimoniaeAfter mixing the acid, vanillin and isethionic acid, in N₂Keeping the temperature at 160-180 ℃ for 2-6 hours in the atmosphere to obtain a solid acid catalyst which is carbonized and sulfonated simultaneously;

3) washing the catalyst obtained in the step 2) with hot water at 160-180 ℃ until the pH value is 7, naturally cooling to room temperature, collecting the washed catalyst, and freeze-drying to obtain the catalyst C-SO₃H/Fe₃O₄@C。

Specifically, in step 1), 2g of nano Fe is preferably added₃O₄Mixing 12-18 g glucose and 60-100 mL water. The pyrolysis carbonization aims to prepare the carbon-based magnetic core carrier, and the subsequent hydrothermal carbonization-sulfonation is completed in one step, which is the innovation and core of the application.

Specifically, in step 2), preferably, 0.5g of carbon-based magnetic core MCC, 40-80 mL of distilled water, 7.5-10.5g of glucose, 45-135 mg of citric acid, 45-135 mg of vanillin, and 6-8 g of isethionic acid are mixed.

Specifically, in step 2), N is preferred₂The purity is more than or equal to 99.99 percent; the freeze-drying condition in the step 3) is drying for 48 hours at the temperature of minus 47 ℃.

The invention provides a functional carbon-based magnetic solid acid catalyst prepared by the one-pot synthesis method.

The invention also provides application of the functional carbon-based magnetic solid acid catalyst in catalyzing bagasse hydrolysis to produce sugar.

The functional carbon-based magnetic solid acid catalyst is applied to catalyzing bagasse hydrolysis to produce sugar, and specifically, the bagasse is preferably subjected to the following treatment in advance: 2g of bagasse powder and 200ml of sodium hydroxide solution with the mass concentration not more than 5 percent are stirred for 24 hours at normal temperature, and the mixture is placed for 24 to 48 hours at the temperature of minus 18 ℃; taking out, thawing, filtering, washing with water to neutrality, and freeze drying.

The application of the functional carbon-based magnetic solid acid catalyst in catalyzing bagasse hydrolysis to produce sugar specifically comprises the following steps: 0.027 g of pretreated bagasse, 0.06-0.27 g of catalyst C-SO₃H/Fe₃O₄@ C and 15 mL of water are mixed and reacted at a temperature of 160-200 ℃ for 2-4 hours.

The functional carbon-based magnetic solid acid catalyst is applied to catalyzing bagasse hydrolysis to produce sugar, and further, after the reaction is finished, the used catalyst is recovered through a permanent magnet, washed by distilled water until the pH value is 7, and then freeze-dried at the temperature of 47 ℃ below zero, so that the catalyst can be repeatedly used.

Compared with the prior art, the invention has the following beneficial effects:

1) The invention takes glucose as a carbon source and nano Fe₃O₄Production of Fe for magnetic nuclei₃O₄The @ C carbon-based magnetic core, and the carbon nano-microsphere can be connected to the surface of the activated carbon to form a novel composite carbon material. Therefore, in this work, nano-Fe is used₃O₄Glucose and isethionic acid are used as raw materials, and a functional carbon-based magnetic solid acid catalyst is synthesized by a one-pot method through a pyrolysis-hydrothermal process without a concentrated sulfuric acid sulfonation process. The prepared carbon-based magnetic solid acid catalyst has high acidity and magnetic strength, and can be used for catalyzing the sugar production process by hydrolyzing bagasse;

2) In the prior art, in order to further improve the bagasse hydrolysis efficiency, a magnetic catalyst is used, and meanwhile, a plurality of pretreatment means such as ball milling, acid, alkali, freezing-dissolving, ionic liquid, microwave and the like are combined to treat hydrolysis raw materials; the invention adopts NaOH-freezing pretreatment, so that the bagasse hydrolysis efficiency can be better improved.

3) C-SO of the invention₃H/Fe₃O₄The @ C catalyst is synthesized in one step through a pyrolysis-hydrothermal process, the sulfonation of concentrated sulfuric acid is not needed in the process, and the catalyst has high magnetic strength (15.65 Am)² kg^-1) And acidity (1.23 mmol g)^-1). Compared with the traditional synthesis method of the carbon-based magnetic solid acid catalyst, the catalyst has various functional groups, and the hydrothermal carbonization and sulfonation processes of the catalyst are completed in one step. Then, the catalyst is utilized to hydrolyze bagasse subjected to 3 percent NaOH-freezing pretreatment, a hydrolysis reaction system is subjected to single-factor optimization, and yields of glucose and total reducing sugar obtained by hydrolysis under optimal conditions respectively reach 62.59 percent and 73.0 percent1 percent. The catalyst is recovered by using the permanent magnet, the catalyst can be recovered and used for at least 5 times, no obvious deactivation phenomenon exists, and the yields of glucose and total reducing sugar obtained by hydrolyzing bagasse after 5 times of recycling are 54.47% and 60.65% respectively; and the catalyst recovery was 93.18%. The research provides a novel synthetic method of a carbon-based magnetic solid acid catalyst capable of effectively promoting biomass hydrolysis.

Drawings

FIG. 1 shows C-SO synthesized under different conditions₃H/Fe₃O₄The VSM curves for the @ C catalyst (A) different amounts of glucose added (a: 7.5 g; B: 9 g; C: 10.5 g), (B) different amounts of citric acid added (a: 45 mg; B: 90mg; C:135 mg), (C) different amounts of vanillin added (a: 45 mg; B: 90mg; C:135 mg), (D) different amounts of isethionic acid added (a: 6 g; B: 7.5 g; C: 8 g);

FIG. 2 shows C-SO synthesized under different conditions₃H/Fe₃O₄XRD patterns of the @ C catalyst (A) different amounts of glucose added (a: 7.5 g; B: 9 g; C: 10.5 g), (B) different amounts of citric acid added (a: 45 mg; B: 90mg; C:135 mg), (C) different amounts of vanillin added (a: 45 mg; B: 90mg; C:135 mg), (D) different amounts of isethionic acid added (a: 6 g; B: 7.5 g; C: 8 g);

FIG. 3 shows C-SO synthesized under different conditions₃H/Fe₃O₄FT-IR diagram for catalyst @ C (A) different amounts of glucose added (a: 7.5 g; B: 9 g; C: 10.5 g), (B) different amounts of citric acid added (a: 45 mg; B: 90mg; C:135 mg), (C) different amounts of vanillin added (a: 45 mg; B: 90mg; C:135 mg), (D) different amounts of isethionic acid added (a: 6 g; B: 7.5 g; C: 8 g);

FIG. 4 shows C-SO synthesized under different conditions₃H/Fe₃O₄SEM picture of @ C catalyst (A) different amounts of glucose added (a: 7.5 g; B: 9 g; C: 10.5 g), (B) different amounts of citric acid added (a: 45 mg; B: 90mg; C:135 mg), (C) different amounts of vanillin added (a: 45 mg; B: 90mg; C:135 mg), (D) different amounts of isethionic acid added (a: 6 g; B: 7.5 g; C: 8 g);

FIG. 5For C-SO synthesized under different conditions₃H/Fe₃O₄TG and DTG curves for the @ C catalyst (A) different amounts of glucose added (a: 7.5 g; B: 9 g; C: 10.5 g), (B) different amounts of citric acid added (a: 45 mg; B: 90mg; C:135 mg), (C) different amounts of vanillin added (a: 45 mg; B: 90mg; C:135 mg), (D) different amounts of isethionic acid added (a: 6 g; B: 7.5 g; C: 8 g);

FIG. 6 is a graph of hydrolysis of 3wt% NaOH-frozen pretreated bagasse (A) temperature, (B) time, (C) FPB/catalyst mass ratio, and (D) water/catalyst mass ratio;

FIG. 7 shows C-SO₃H/Fe₃O₄Repeated use of the @ C catalyst.

Detailed Description

The technical solution of the present invention is further described in detail with reference to the following examples, but the scope of the present invention is not limited thereto.

1. Experiment of

1.1 materials

Alkali-freezing pretreatment of bagasse: taking 2g of bagasse powder sample sieved by a 200-mesh sieve and 200ml of 3wt% sodium hydroxide solution, stirring at normal temperature for 24h, and standing at refrigerator-18 ℃ for 24-48 h. Taking out, thawing, filtering, washing with water to neutrality, and freeze drying at (-47 deg.C for 48 hr) to obtain alkali-frozen pretreated bagasse, which is recorded as FPB. The composition of FPB was then analyzed according to the methods of united states department of energy composition analysis, with the results for cellulose, hemicellulose, lignin, ash components being 61.7%, 20.5%, 12.8%, 2.4%, respectively.

NaOH (more than or equal to 96.0 percent), isethionic acid, citric acid, vanillin and standard samples (glucose, xylose, 5-hydroxymethylfurfural and furfural) are all common commercial products; nano Fe₃O₄(particles less than 20 nm) was purchased from Shanghai Allantin Biotechnology Ltd.

1.2 preparation of the catalyst

1) Mixing nano Fe₃O₄(2 g) Glucose (12 g) and water (100 mL) were mixed in a round bottom flask, and the mixture after evaporation of water was transferred to a muffle furnace and heated to 700 ℃ at 70 ℃Pyrolyzing and carbonizing at 0 ℃ for 1 hour to obtain carbon-based magnetic cores MCC;

2) Mixing carbon-based magnetic core MCC (0.5 g), distilled water (40 mL), glucose (7.5-10.5 g), citric acid (45-135 mg), vanillin (45-135 mg) and isethionic acid (6-8 g) in a high-temperature high-pressure reaction kettle, and adding N₂(the purity is more than or equal to 99.99 percent) for 4 hours at 180 ℃ to obtain a solid acid catalyst which is carbonized and sulfonated simultaneously;

3) Subsequently, the catalyst obtained in step 2) was washed with hot water at a temperature of 200 ℃ to a pH of 7 (about 3 hours, in this case by passing CaCl)₂No SO4 was detected^2-Existing) is naturally cooled to room temperature, the washed catalyst is collected and is frozen and dried in a freeze dryer for 48 hours at the temperature of minus 47 ℃, and the catalyst C-SO is obtained₃H/Fe₃O₄@ C. Catalyst C-SO₃H/Fe₃O₄@ C is used for the hydrolysis of bagasse.

1.3 characterization of the catalyst

Analyzing the C, N, H and S elements of the catalyst by using an Element Analyzer (EA), and calculating the acidity of the catalyst according to the S elements. The surface structure of the catalyst was observed by a Scanning Electron Microscope (SEM). And the crystal structure of the catalyst was examined by X-ray diffraction (XRD). The magnetic saturation (Ms) of the catalyst was measured by a Vibrating Sample Magnetometer (VSM). The functional groups of the catalyst were then characterized using a Fourier transform Infrared Spectroscopy (FT-IR). Finally, the stability of the catalyst was analyzed by thermogravimetric analysis (TGA).

1.4 hydrolysis of bagasse to sugar and recovery of catalyst

the FPB hydrolysis sugar-producing reaction is carried out in a microwave reactor under the following reaction conditions: FPB (0.027 g), catalyst C-SO₃H/Fe₃O₄@ C (0.09-0.45 g) and water (15 mL), at a temperature of 160-200 deg.C (heated to the set temperature within 3 minutes), for a period of 2-4 hours. The rotational speed was 600 rpm throughout the reaction.

After the reaction is finished, the used catalyst is recovered through a permanent magnet, then the recovered catalyst is washed with distilled water for multiple times until the pH value is 7, and finally the washed catalyst is collected and freeze-dried at the temperature of 47 ℃ below zero for later use. After the catalyst is repeatedly used for 5 times, the catalyst is collected, repeatedly washed with water and water until the pH value is 7, and finally the catalyst after being repeatedly used for 5 times is dried and weighed, so that the recovery rate of the catalyst is calculated:

。

1.5 hydrolysis analysis

After the reaction is finished, the solid residue and the hydrolysate are separated by a permanent magnet, then the hydrolysate is filtered by a filter membrane with the diameter of 0.22 μm, and the components in the hydrolysate can be detected and analyzed by an H column, a differential detector and an ultraviolet detector in High Performance Liquid Chromatography (HPLC). During the detection, the concentration of the reagent is measured at 0.01 mmol L^-1dilute sulfuric acid is used as mobile phase, and the flow rate and column temperature are set to 0.6 mL min^-1And 60 degrees. A standard curve was prepared using 5 glucose concentrations (0.2, 0.4, 0.6, 0.8 and 1.0 mg/mL) as standard points, and R of the prepared standard curve was determined²Is 0.9999. Further, the Total Reducing Sugar (TRS) in the hydrolysate was calculated by the DNS (3, 5-dinitrosalicylic acid) method, and the TRS content in the hydrolysate was calculated using a standard curve prepared using 5 glucose concentrations (0.2, 0.4, 0.6, 0.8 and 1.0 mg/mL) as standard points, and the R of the prepared standard curve was used as the standard curve²Is 0.9985. The calculation formula of glucose and total reducing sugar is as follows:

。

Results and discussion

2.1 Synthesis of a carbon-based magnetic catalyst

2.1.1 addition of glucose

Adding glucose (7.5-10.5 g), carbonizing and sulfonating at 180 deg.C for 4h, and optimally screening according to acidity and magnetic strength of the prepared catalyst, wherein Table 1 is acidity of the catalyst, and FIG. 1A is differentgraph of relationship between glucose addition amount and catalyst magnetism (table 1, fig. 1A). C-SO with increasing glucose addition from 7.5g to 9g₃H/Fe₃O₄The magnetic strength and acidity of the @ C catalyst are respectively from 11.86 Am² kg^-1、0.51 mmol g^-1Increased to 15.65 Am² kg^-1And 0.67 mmol g^-1(ii) a C-SO when the amount of glucose added was increased from 9g to 10.5g₃H/Fe₃O₄The magnetic strength and acidity of the @ C catalyst are respectively from 15.65 Am² kg^-1And 0.67 mmol g^-1Reduced to 5.16 Am² kg^-1And 0.46 mmol g^-1。

FIGS. 2A-b show that C-SO increases with increasing amounts of glucose added₃H/Fe₃O₄The @ C catalyst has good Fe₃O₄A crystal structure. The results show that C-SO increases with increasing glucose addition₃H/Fe₃O₄In the @ C catalyst-SO₃The content of H groups increased and then decreased, mainly due to the excessive glucose addition amount resulting in agglomeration of the carbon nanospheres, and this phenomenon was also confirmed by SEM scanning electron micrographs in fig. 4A.

In addition, C-SO in FIG. 5A₃H/Fe₃O₄Thermogravimetric analysis of the @ C catalyst also confirmed this phenomenon. However, FIGS. 5A-C and the results in Table 1 show that excessive addition of glucose results in a large amount of carbon coating the Fe₃O₄@ C carbon based magnetic core surface, resulting in a reduction in catalyst magnetic strength and acidity. Therefore, the optimum amount of glucose added was 9 g.

TABLE 1C-SO prepared under different conditions₃Elemental analysis (N, C, H and S) of H/[email protected] C catalyst and catalyst after 5 reuses

2.1.2 addition amount of citric acid

Adding citric acid 45-135 mg, carbonizing and sulfonating at 180 deg.C for 4 hr, and preparing the catalyst according to the acidAnd (3) optimally screening the catalyst according to the degree and the magnetic strength, wherein the table 1 is the acidity of the catalyst, and the figure 1B is a relational graph of different citric acid addition amounts and the magnetism of the catalyst (table 1 and figure 1A). When the addition amount of the citric acid is 45mg, the prepared catalyst has lower magnetic strength and acidity which are respectively 7.76 Am² kg^-1And 0.57 mmol g^-1(ii) a However, when the amount of citric acid added was increased to 90mg, the magnetic strength and acidity of the catalyst reached the highest values, respectively, 15.65 Am² kg^-1And 0.67 mmol g^-1(ii) a However, as the amount of citric acid added continues to increase, the magnetic strength and acidity of the catalyst begin to decrease (table 1, fig. 1B).

The FT-IR results for the catalyst in FIG. 3B show that: the catalyst OH and O = S = O intensities in fig. 3B-B are higher than those in 3B-a and 3B-c, which is consistent with the acidity results for the catalysts in table 1. In addition, the SEM results of FIGS. 4B-c show that: when the addition amount of citric acid reached the maximum, the carbon spheres formed from glucose formed agglomerated carbon, thereby reducing the specific surface area of the catalyst, reducing the acidity of the catalyst, and the results were consistent with the acidity results of the catalyst in table 1. In addition, the crystal structure and the thermal stability of the catalyst are also influenced by the addition amount of citric acid, and the catalyst has good Fe along with the increase of the addition amount of the citric acid₃O₄the crystal structure (fig. 2B-B), and the fig. 5B results show that the thermal stability of the catalyst is also gradually enhanced. Therefore, the optimum amount of citric acid to be added was selected to be 90mg in consideration of the magnetic strength and acidity of the catalyst.

Vanillin adding amount

Adding vanillin 45-135 mg, carbonizing at 180 deg.C, sulfonating for 4 hr, and optimally screening according to acidity and magnetic strength of the catalyst. When the adding amount of vanillin is increased from 45mg to 90mg, the magnetic strength and acidity of the prepared catalyst are respectively 10.75 Am² kg^-1And 0.65 mmol g^-1Increasing to a maximum value of 15.65 Am² kg^-1And 0.67 mmol g^-1(ii) a But as the added amount of vanillin is continuously increased, the magnetic strength and acidity of the catalyst are reduced to 5.58 Am² kg^-1And 0.45 mmol g^-1(Table 1, FIG. 1C).

the FT-IR results for the catalyst in fig. 3C show that: the catalyst OH and O = S = O intensities in fig. 3C-b are higher than those in 3C-a and 3C-C, which is consistent with the acidity results for the catalysts in table 1. In addition, SEM FIGS. 4C-C, XRD FIGS. 2C-C, and TGA FIGS. 5C-C demonstrate: as the vanillin content increases, the activity and structural stability of the catalyst are adversely affected. Therefore, the optimum addition amount of vanillin of 90mg is selected by taking the magnetic strength and acidity of the catalyst into consideration.

the addition amount of the hydroxyethyl sulfonic acid

The amount of 6-8 g of different isethionic acid added was optimized. When the addition amount of the isethionic acid was increased from 6 g, 7.5g to 8g, the acidity of the catalyst was from 0.67 mmol g^-1Increasing to 1.23 mmol g^-1Then reduced again to 1.07 mmol g^-1. However, as the amount of isethionic acid added increased from 6 g, 7.5g to 8g, the magnetic strength of the catalyst rapidly increased from 15.65 Am² kg^-1Down to 10.64 Am² kg^-1(Table 1, FIG. 1D), mainly due to Fe during sulfonation₃O₄Is caused by the falling off of (b).

The FT-IR results for the catalyst in fig. 3D show that: the catalyst OH and O = S = O intensities in fig. 3D-b are higher than those in 3D-a and 3D-c, which results are consistent with the acidity results for the catalysts in table 1. In addition, as the amount of the isethionic acid added was increased, the catalyst surface had a large amount of pore generation (FIG. 4D-c), and XRD results showed that the catalyst represented by FIG. 2D-a had better Fe than the interior of the catalysts represented by 2D-b and 2D-c₃O₄A crystal structure. In addition, thermogravimetric FIG. 5Da-c results show that: the stability of the catalyst was affected by the amount of isethionic acid added, and as the amount added increased to 8g, the stability of the catalyst decreased (fig. 5D-c). In conclusion, the magnetic strength and acidity of the catalyst are comprehensively considered, and 8g is selected as the optimal addition amount of the hydroxyethyl sulfonic acid. Under the condition, the magnetic strength and the acidity of the prepared catalyst are respectively 12.85 Am² kg^-1And 1.23 mmol g^-1。

Characterization of carbon-based magnetic acid catalysts

2.2.1 VSM and XRD

According to the JCPDS card of the powder diffraction standard combination Commission No. 19-629 to Fe in the catalyst₃O₄The crystal structures of Fe and amorphous carbon were analyzed. The following chemical reactions, which occur during the preparation of the catalyst, result in small amounts of Fe and Fe₃Presence of C:. In addition, from C-SO₃H/Fe₃O₄the XRD pattern of the @ C catalyst can show that a strong absorption peak exists between 20 and 30 beta angles of 2 beta, and the result can confirm that Fe in the catalyst₃O₄the peripheral amorphous carbon is in ordered arrangement. FIG. 1 shows that: preparation of the resulting C-SO under different conditions₃H/Fe₃O₄the magnetic strength of the @ C catalyst is obviously influenced by amorphous carbon and Fe₃O₄And the influence of the Fe content. FIGS. 1A-D and FIGS. 2A-D show the relationship between the magnetic strength and crystal structure of the catalyst and the amounts of glucose, citric acid, vanillin, and isethionic acid added, respectively. Along with the increase of the addition amount of glucose, the carbon-based magnetic core Fe₃O₄The carbon sheet layer of the @ C outer layer becomes thick, resulting in the magnetic strength of the catalyst from 15.65 Am²kg^-1Reduced to 5.16 Am² kg^-1(FIG. 1A-a); and this result is consistent with the result in XRD pattern 2A-a, which has a strong absorption peak of amorphous carbon. FIGS. 1B a-c and 1C a-c show the magnetic strength of the resulting catalysts prepared with varying amounts of citric acid and vanillin added. As the addition amount of the two is increased, both the graph of FIG. 1B a-c and the graph of FIG. 1C a-c show similar curve characteristics, and the curve characteristics are increased and then decreased, mainly because a large amount of citric acid and vanillin can cause agglomeration of carbon microspheres; and this phenomenon was also confirmed by SEM pictures. In addition, FIGS. 2B-C and 2C-C have stronger amorphous carbon absorption peaks than FIGS. 2B-B and 2C-B. FIG. 1 Da-C shows C-SO prepared by different addition amounts of isethionic acid₃H/Fe₃O₄Magnetic Strength of the @ C catalyst, excessive hydroxyethylsulfonic acid being destroyed during sulfonationFe₃O₄Outer carbon layer structure to reduce Fe in catalyst₃O₄Resulting in a catalyst magnetic strength of from 15.65 Am² kg^-1(FIG. 1D-a) to 10.64 Am² kg^-1(FIGS. 1D-c); the results were also confirmed by XRD, amorphous carbon and Fe in FIG. 2D-b₃O₄The peaks are clearly comparable to the absorption peaks in FIG. 2D-c.

And elemental analysis

FIGS. 3A-D show the C-SO values obtained from the preparation of different amounts of glucose, citric acid, vanillin and isethionic acid₃H/Fe₃O₄Infrared absorption spectrum of @ C catalyst. All catalysts had a wavelength of 3463 cm^-1And 1615 cm^-1There are distinct absorption peaks on both the left and right, mainly due to OH and C = O oscillations, which demonstrate the attachment of-OH and-COOH functional groups to the catalyst surface. In addition, it is about 1360 cm^-1And 1645 cm^-1Around the wavelength, absorption peaks of O = S = O and C = C, respectively, were found mainly due to-SO connected to the carbon layer on the surface of the catalyst₃H group (fig. 3). At a wavelength of 560 cm^-1The absorption peak of Fe-O is shown on the left and the right, and the result proves that the magnetic core Fe in the catalyst₃O₄Presence of (a); furthermore, the results were consistent with XRD analysis results (fig. 2). In addition, the acidity of the catalyst was calculated from the results of elemental analysis (table 1).

FIG. 3A a-c is an infrared image of catalysts prepared with varying amounts of glucose added, with increasing amounts of glucose added, -SO₃The absorption intensity of the H group gradually decreased (FIGS. 3A-c and 3A-b), and the acidity was 0.67 mmol g in this phenomenon and the result of the elemental analysis, respectively^-1And 0.46 mmol g^-1Consistent (Table 1), mainly due to excessive glucose leading to aggregation and agglomeration of carbon spheres, leading to-SO in the catalyst₃Reduction of H loading. Similar results as above were obtained when the amounts of citric acid and vanillin were gradually increased (fig. 3B and 3C), as further confirmed by SEM images (fig. 4). FIG. 3D shows the amount of isethionic acid added and the-SO of the catalyst₃The relationship between H and acidityincreasing the amount of isethionic acid added and the-SO of the catalyst₃The H absorption peak and the acidity are both enhanced, and the acidity is from 0.67 mmol g^-1 Increased to 1.23 mmol g^-1(ii) a But the magnetic strength of the catalyst is from 15.65 Am² kg^-1Down to 10.64 Am² kg^-1The magnetism of the catalyst is reduced mainly due to corrosion inside the catalyst caused by excessive amount of isethionic acid.

2.2.3 scanning Electron microscopy and thermogravimetric analysis

FIGS. 4A-D are scanning electron micrographs of catalysts prepared under different conditions. As the addition amount of glucose, citric acid and vanillin increased, the carbon spheres on the surface of the catalyst had the phenomena of aggregation and agglomeration (FIGS. 4A-C, 4B-C and 4C-C). However, as the amount of the isethionic acid added was increased, the catalyst particle surface had a much larger pore structure, mainly due to the penetration of the isethionic acid (fig. 4D-c). FIGS. 5A-D are graphs of TG and DTG of the catalyst. FIGS. 5Aa-c show the temperatures at which the maximum absorption peaks of the catalyst correspond to 449.7 deg.C, 453.7 deg.C and 486.1 deg.C, 458.4 and 527 deg.C, respectively; meanwhile, as the addition amount of glucose is increased, the weight loss rates of the catalyst below 200 ℃ are respectively 7.09%, 4.77% and 4.22%. The aggregation and agglomeration of the carbon spheres improved the thermal stability of the catalyst, as also confirmed by the SEM images (FIGS. 4 Aa-c).

FIGS. 5 Ba-c and 5 Ca-c are graphs of TG and DTG of the catalyst prepared under different addition levels of citric acid and vanillin, respectively, and the temperatures corresponding to the maximum absorption peaks of the catalyst are respectively increased from 458.9 ℃ to 486.1 ℃, from 480.7 ℃ to 486.1 ℃, and then are respectively decreased to 454.3 ℃ and 456.7 ℃; meanwhile, with the increase of the addition amount of citric acid and vanillin, the weight loss rates of the catalyst below 200 ℃ are respectively 4.22%, 4.77%, 2.88%, 4.14%, 4.77% and 2.33%, and the thermal stability of the catalyst is improved mainly due to a large amount of formed aggregated carbon. FIG. 5Da-c are graphs of TG and DTG of the catalyst prepared under different addition amounts of isethionic acid, the temperatures corresponding to the maximum absorption peaks of the catalyst are 486.1 deg.C, 465.4 deg.C and 463.5 deg.C, respectively, and the weight loss rates of the catalyst below 200 deg.C are 4.77%, 6.35% and 15.60%, respectively. An excessive amount of isethionic acid causes corrosion and less oxygen-containing functional groups (COOH, OH) on the catalyst surface, thereby reducing the thermal stability of the catalyst.

In conclusion, the magnetic strength and the acidity of the catalyst are comprehensively considered to prepare the C-SO₃H/Fe₃O₄The optimum conditions for the @ C catalyst are: 9g of glucose, 90mg of citric acid, 90mg of vanillin and 7.5g of isethionic acid, and the catalyst synthesized under these conditions was then used to catalyze the hydrolysis sugar-production reaction of alkali-frozen pretreated bagasse.

Hydrolysis of alkali-Freeze Pretreated Bagasse (FPB)

Single-factor optimization: the reaction conditions of FPB hydrolysis for producing sugar are as follows, the reaction time is 2-4 h, the reaction temperature is 160-200 ℃, the FPB/catalyst mass ratio is 3/50-15/50, and the water/catalyst mass ratio is 25/1-125/1.

Reaction temperature

The temperature was studied in five parts from 160 to 200 ℃ under conditions of reaction time, FPB/catalyst mass, water/catalyst mass ratio of 3h, 9/50 and 100/1, respectively (FIG. 6A). The cellulose in the bagasse can be rapidly hydrolyzed into glucose, and at the same time, the glucose is degraded along with the increase of the reaction temperature. When the reaction temperature is 160 ℃, the yields of glucose and total reducing sugar are very low, and are respectively 10.12 percent and 18.36 percent; when the temperature was increased to 180 ℃, the yields of glucose and total reducing sugars reached the highest values of 46.48% and 57.94%, respectively. However, as the reaction temperature continues to increase, the yields of glucose and total reducing sugars decrease to f 18.34% and 26.15%, while resulting in increased yields of hydroxymethylfurfural, levulinic acid, primarily due to depolymerization of glucose at 200 ℃. Thus, select 180The temperature is the optimum temperature for the hydrolysis reaction.

Reaction time

At a reaction temperature, FPB/catalyst mass, water/catalyst mass ratio of 180The reaction times were studied at five temperatures, from 2h to 4h, at C, 9/50 and 100/1 (FIG. 6B). As the reaction time increased to 3h, the cellulose was hydrolyzed to a glucose yield of 46.48% with a maximum total reducing sugar yieldA maximum value of 57.94% is reached. However, as the reaction time was extended to 4 hours, the glucose and total reducing sugar yields rapidly decreased to 31.45% and 39.68%, but some small molecule compounds were produced as a by-product, mainly due to degradation of glucose over a longer reaction time, and adverse to the catalyst-SO under such conditions₃Stability of the H group. Therefore, to increase the glucose yield, 3h was chosen as the optimal reaction time.

Mass ratio of catalyst

The FPB/catalyst mass ratio was studied at five points from 3/50 to 15/50 min under the conditions of a reaction temperature, a reaction time, a water/catalyst mass ratio of 180 deg.C, 3 hours and 100/1, respectively (FIG. 6C). As the FPB/catalyst mass ratio was increased from 3/50 to 6/50, the glucose and total reducing sugar yields increased from 43.05%, 49.63% to 53.37%, 61.54%, respectively. However, as the FPB/catalyst mass ratio continued to increase from 6/50 to 15/50, the glucose and total reducing sugar yields decreased to 30.46%, 41.97%, respectively. The sugar yields tend to increase and decrease with increasing FPB/catalyst mass ratio, primarily due to the fact that at higher FPB/catalyst mass ratios, cellulose is less soluble, making it difficult for the beta-1, 4-glycosidic linkages in the cellulose chain to contact the acidic sites of the catalyst. Thus, 6/50 was chosen as the optimum FPB/catalyst mass ratio.

Water/catalyst mass ratio

To investigate the effect of water/catalyst mass ratio on sugar yield from bagasse hydrolysis, five points were investigated at water/catalyst mass ratios from 25/1 to 125/1 (FIG. 6D). When the mass ratio of water/catalyst is increased from 25/1 to 75/1, the yields of glucose and total reducing sugar are respectively increased from 32.58%, 41.17% to 62.59%, 73.01%; mainly due to the fact that the catalyst-SO can be enhanced by a suitable water/catalyst mass ratio₃The activity of the catalyst is improved by the interaction between H groups and beta-1, 4-glycosidic bond hydrogen bonds and oxygen atoms in the cellulose, and then the cellulose can be connected to the surface of the catalyst through the hydrogen bonds, thereby promoting the hydrolysis reaction. As the water/catalyst mass ratio was increased from 75/1 to 125/1, the glucose and total reducing sugar yields decreased to 44.36%, 51.87%, primarily due to excess water resulting in-SO₃H is removed, thereby deactivating the active sites of the catalyst. Therefore, 75/1 was chosen as the optimum water/catalyst mass ratio.

In conclusion, the optimal conditions for producing sugar by hydrolyzing bagasse after catalytic pretreatment by using the catalyst are as follows: the reaction temperature was 180 ℃, the time was 3h, the FPB/catalyst mass ratio was 6/50, the water/catalyst mass ratio was 75/1, and the glucose yield under these conditions was 62.59%.

Catalyst repeatability

In order to examine the stability of the catalyst, the catalyst after use was recovered under the above optimum conditions, and the relationship between the number of times the catalyst was used and the amount of produced sugar was as shown in FIG. 7. As can be seen from fig. 7, the yields of glucose and total reducing sugars obtained from catalytic hydrolysis with the catalyst were 62.59%, 60.78%, 61.04%, 57.32%, 54.47% and 73.01%, 73.23%, 71.98%, 66.39%, 60.65% from 1 to 5 times, respectively, and the recovery rate of the catalyst after 5 times of repeated use was 93.18%, which is a good evidence of the catalyst's stability and activity. The glucose and total reducing sugar yields at catalyst 5 use were 54.47% and 60.65%, respectively, slightly lower than the initial use of the catalyst (62.59% and 73.01%), with the decrease in glucose and total reducing sugar yields being primarily due to catalyst-SO₃A small amount of H groups were detached, which was likewise determined by the S element (2.48% by weight) and the acidity (0.78 mmol g) of the catalyst^-1) Confirmation (table 1). The results show that the catalyst can be used stably at least 5 times. Compared with other carbon-based magnetic solid acid catalysts, the C-SO₃H/Fe₃O₄@ C has high magnetic strength and acidity in the process of producing sugar by cellulose hydrolysis.

Conclusion

C-SO₃H/Fe₃O₄The @ C catalyst is synthesized in one step through a pyrolysis-hydrothermal process, the sulfonation of concentrated sulfuric acid is not needed in the process, and the catalyst has high magnetic strength (15.65 Am)² kg^-1) And acidity (1.23 mmol g)^-1). Compared with the traditional synthesis method of the carbon-based magnetic solid acid catalyst, the catalyst has various functional groups, and the hydrothermal carbonization and sulfonation processes of the catalyst are completed in one step. Then, by using the catalyst, the catalyst is used,Hydrolyzing the bagasse subjected to 3% NaOH-freezing pretreatment, and performing single-factor optimization on a hydrolysis reaction system, wherein the yields of glucose and total reducing sugar obtained by hydrolysis under the optimal conditions respectively reach 62.59% and 73.01%. The catalyst is recovered by using the permanent magnet, the catalyst can be recovered and used for at least 5 times, no obvious deactivation phenomenon exists, and the yields of glucose and total reducing sugar obtained by hydrolyzing bagasse after 5 times of recycling are 54.47% and 60.65% respectively; and the catalyst recovery was 93.18%. The research provides a novel synthetic method of a carbon-based magnetic solid acid catalyst capable of effectively promoting biomass hydrolysis.