TWI704955B - Modified carbonaceous material, carbon dioxide adsorbent and method for cellulose hydrolysis using the same - Google Patents

Abstract

Disclosed is a modified carbonaceous material, which includes hexagonal carbon networks in a layered stacking structure and acidic functional groups bonded to the hexagonal carbon networks and mainly existing at edges of the layered carbonaceous structure. Accordingly, the close proximity of acid moiety at the edges can resemble the center of hydrolysis enzymes, resulting in enhancement of hydrolytic efficiency. Additionally, the acid-functionalized carbonaceous material can also be applied in the capture and storage of carbon dioxide due to its unexpectedly higher capacity for CO ₂molecular.

Description

Modified carbon material, carbon dioxide adsorbent and cellulose hydrolysis method using it

The present invention relates to a carbon material modified with functional groups, in particular to a modified carbon material with functional groups at the edge of a layered carbon structure, a carbon dioxide adsorbent using the carbon material and a cellulose hydrolysis method.

Carbon materials have been used in various research fields of traditional and new technologies. For example, porous carbon materials have been extensively studied in the field of CO ₂ capture. Among various solid adsorbents, porous carbon materials have attracted attention because of their ideal physical and chemical properties, such as low cost, multiple morphologies, easy processing, controllable porosity, and customized surface properties.

In addition, some researchers have explored the possibility of carbon materials as catalysts for various reactions. Carbon-based catalysts are not harmful to the environment and can provide cost competitive advantages. In particular, the adjustable surface properties and excellent physical properties of carbon materials are compatible with various catalytic reactions. For example, the modification of acidic functional groups on the carbon surface has been studied in the cellulose hydrolysis reaction, such as mesoporous carbon (CMK-3) with acid site density of 0.41 mmol g ^-1 and containing 0.88 mmol g ^-1 acid site density of oxygen-containing alkali activated carbon (K26). However, the hydrolysis efficiency of these acid-functional carbon-based materials still needs to be improved.

Due to the above reasons and other reasons described below, there is an urgent need to develop a new surface-modified carbon material that can solve the problem of hydrolysis efficiency and/or has great potential in various other applications.

The object of the present invention is to provide a carbon material with acidic functional groups with high surface coverage, which can be used for cellulose hydrolysis or/and other applications. These acidic functional groups mainly exist on the edges of the layered carbon structure, so the acid groups closely adjacent to the layered structure can imitate the center of a hydrolase (such as glucosidase), thereby improving the hydrolysis efficiency. In addition, the acid-functionalized carbon material has an unpredictable high adsorption capacity for CO ₂ molecules, so it can also be used for carbon dioxide capture and storage.

According to the above and other objectives, the present invention provides a modified carbon material, which includes a layered stacked structure of hexagonal carbon nets and acidic functional groups bonded to the hexagonal carbon nets, most of the acidic functional groups are Covalently linked to the in-plane sp ² carbons at the edges of the hexagonal carbon meshes. Specifically, in the present invention, all or plural of the acidic functional groups are covalently linked to the sp ² carbons at the edges of the hexagonal carbon network, wherein the acidic functional groups located at the sp ² carbons of the hexagonal carbon network These plurals are more in number than the others connected to the sp ³ carbons of the hexagonal carbon network among the acidic functional groups.

Based on ¹³ C DP / MAS solid-state nuclear magnetic resonance (ssNMR), Raman spectroscopy and X-ray photoelectron spectroscopy to study the relationship between acidic functional groups and the hexagonal carbon network, it can be found that the acidic functional groups mainly exist at the edge of the hexagonal carbon network: ( i) ¹³ C solid state NMR substantially no or only weak sp ³ carbon peak (δ 22ppm); (ii) a Raman spectrum measured by the I _D / I _G ratio of not more than 1 band (even not greater than 0.9) (Iii) The C1s/O1s ratio measured by X-ray photoelectron spectroscopy is not less than 3 (or even not less than 4).

In the present invention, the modified carbon material can be prepared by acid modification of pitch materials, such as mesophase pitch (MP), so that acidic functional groups are mainly formed on the aromatic ring plane in the layered stacked structure On the edge. Accordingly, a series of non-porous carbon materials with high density of acidic functional groups can be synthesized, which can exhibit improved catalytic efficiency in cellulose hydrolysis. Specifically, according to a preferred embodiment, the modified carbon material has a specific surface area of less than 56 m ² /g and about 1.5 mmol/g (for example, 1.5~4.0 mmol/g) through nitrogen adsorption. Or higher total acid site density, which is greater than mesoporous carbon (CMK-3) and oxygen-containing alkali activated carbon (K26).

In the present invention, the modified carbon material has an interlayer distance in the range of about 0.34 nm to about 0.37 nm as measured by X-ray diffraction. According to this, the acidic functional groups close to the edge can imitate the center of the hydrolase, thereby resulting in better hydrolysis efficiency.

In the present invention, the pitch material containing the hexagonal carbon mesh can be treated with sulfuric acid, nitric acid or hypochlorite, and then optionally subjected to hydrothermal treatment. Accordingly, the asphalt-based materials can be modified into acidic functional groups with high surface coverage, such as sulfonic, carboxyl, lactone and phenolic hydroxyl, which are mainly located in On the edge of the layered structure.

In the state of sulfuric acid treatment, almost all acidic functional groups are covalently connected to the in-plane sp ² carbons at the edges of the hexagonal carbon network substantially composed of aromatic carbons. Therefore, the carbon material treated with sulfuric acid has no sp ³ carbon peak observed in the ¹³ C CP/MAS NMR spectrum. This means that the sulfuric acid-treated carbon material does not substantially contain aliphatic carbons. After acid-modified with sulfuric acid, the modified carbon material may have a total acid site density of about 2.0 mmol/g or higher (such as 2.0-3.5 mmol/g). The density of sulfonic groups, phenolic hydroxyl groups, carboxyl groups and lactone groups contained in the sulfuric acid-treated carbon material can be about 0.8 mmol/g or more, respectively. High (such as 0.8～1.5 mmol/g), about 0.5 mmol/g or higher (such as 0.5～0.8 mmol/g), about 0.1 mmol/g or higher (such as 0.1 ～0.3 mmol/g), about 0.4 mmol /g or higher (such as 0.4～0.9 mmol/g). One embodiment of the present invention, in the particular embodiment, it has been confirmed that treatment of the carbon material having a sulfation of from about 0.7 to about 0.9 I _D / I _G ratio and C1s of about 4.0 to about 6.0 / O1s ratio.

In another aspect of nitric acid or hypochlorite treatment, the acidic functional groups are not only modified at the edges of the material, but also partially modified on the benzene ring. Therefore, carbon materials treated with nitric acid and hypochlorous acid have a weak sp ³ carbon peak in the ¹³ C CP/MAS NMR spectrum. After acid-modified with nitric acid or hypochlorite, the modified carbon material may have a total acid site density of about 1.5 mmol/g or higher (such as 1.5-2.5 mmol/g). The density of phenolic hydroxyl group, carboxyl group and lactone group contained in the carbon material treated with nitric acid or hypochlorous acid may be about 0.3 mmol/g or higher (such as 0.3-0.8 mmol/g), about 0.2 mmol/g or Higher (such as 0.2 to 1.5 mmol/g), about 0.3 mmol/g or higher (such as 0.3 to 0.9 mmol/g). In one embodiment of the present invention, it has been confirmed that the carbonaceous material with nitric acid or hypochlorous acid treatment of about 0.9 to about 1.0 of the I _D / I _G ratio of from about 3.0 to about 4.0 and of C1s / O1s ratio.

In view of the good catalytic efficiency of the modified carbon material in cellulose hydrolysis, the present invention further provides a cellulose hydrolysis method, including: mixing the modified carbon material and cellulose in an aqueous solution; and applying the modified carbon The cellulose is hydrolyzed at a predetermined temperature in the presence of the material as a catalyst. The predetermined temperature may range from 130°C to 210°C. In a specific embodiment of the present invention, it has been proved that the modified carbon material can degrade cellulose (such as crystalline phase cellulose, amorphous phase cellulose and pre-hydrolyzed fiber) at a catalytic ratio of 4.8 mol% (acid base/cellulose) Vegetarian). In addition, it can be observed that only less than 3 mol% of the glucose yield is caused by the sulfonic acid group leaching and hydrolysis reaction. According to this, it can be known that the modified carbon material of the present invention has hydrolytic stability, so that the entire catalytic process is more efficient and environmentally friendly.

In the present invention, it has been proved that the basic functional group can be modified by neutralizing the acidic functional group. This basic functionalized surface can isomerize glucose to fructose with a selectivity of up to 90%, which means conjugation Alkali can be used for base-catalyzed isomerization of glucose.

Furthermore, based on CO ₂ adsorption analysis, it can be known that the acid functionalized material of the present invention has the potential for CO ₂ storage. Accordingly, the present invention further provides an acid-functionalized adsorbent for capturing CO ₂ which includes hexagonal carbon nets in a layered stacked structure and acidic functional groups bonded to the hexagonal carbon nets, wherein the hexagonal carbon nets It is substantially composed of aromatic carbons, and substantially all of the acidic functional groups are covalently connected to the in-plane sp ² carbons at the edges of the hexagonal carbon meshes. In one specific embodiment of the present invention, it has been confirmed that the modified carbon material of the present invention exhibits a high carbon dioxide adsorption capacity of up to about 11 wt% (weight percentage).

The term "most of the acidic functional groups" used in this specification and the accompanying patent application is defined by the percentage of acidic functional groups in the material. That is, more than 50% of the total acidic functional groups of the material are modified at the edges of the material. For example, at least 60% of the total acidic functional groups of the material are modified at the edges of the material. For example, at least 70% of the total acidic functional groups of the material are modified at the edges of the material. For example, at least 80% of the total acidic functional groups of the material are modified at the edges of the material. For example, at least 90% of the total acidic functional groups of the material are modified at the edges of the material.

The above and other objectives, advantages and new features of the present invention can be more clearly understood by the following detailed description with reference to the accompanying drawings.

Example- Preparation of functionalized mesophase pitch

Before further processing and reaction, the mesophase pitch (softening point: 275-295℃, Mitsubishi Gas Chemical Co., Ltd., Japan) is ground and sieved on a 230-mesh screen to a particle size of 63 microns.

[MP-SO ₃ H]

Use concentrated H ₂ SO ₄ (95-97% SO ₃ ) solution as oxidant to synthesize functionalized mesophase pitch (SO ₃ H-MP). In a dry nitrogen environment, heat at 80°C for 20 hours in concentrated sulfuric acid, and then heat at 150°C to 7 hours to sulfonate the mesophase pitch (1.2 g). After the reaction, the functionalized MPs were collected by filtration and washed with a large amount of water. Then the material was subjected to Soxhlet extraction with 500 mL of water for 8 hours, and this extraction procedure was repeated twice. Finally, the modified material is placed in a freeze dryer for drying.

[MP-SO ₃ H-HT]

The hydrothermal treatment of MP-SO ₃ H was repeated three times to prepare MP-SO ₃ H-HT. Place MP-SO ₃ H (0.5 g) in an autoclave with 30 mL of water at 200 °C for 8 hours. After the hydrothermal treatment, the material was collected by filtration and cleaned by Soxhlet extraction procedure. Repeat the same step twice to synthesize MP-SO ₃ H-HT.

[MP-COOH]

Put 500 mg of MPs in a 100 mL round bottom bottle, and synthesize MP-COOH with 50 mL of nitric acid with different concentrations (7.9 M, 7 M, 6 M, 5 M, 4 M, or 1 M). Reflux the solution at 105 °C for 1.5 to 3 hours. After the reaction, the functional MPs were collected by filtration and washed with a large amount of water. The obtained material was subjected to Soxhlet extraction with 500 mL of water for 8 hours and repeated twice. Finally, the modified material is placed in a freeze dryer for drying. Among the different reaction conditions, the concentration of 6M and the reaction for 1.5 hours are considered to be the best conditions for the carboxylic acid group. Therefore, the MP-COOH synthesized under the conditions of a concentration of 6M and a reaction time of 1.5 hours will be subjected to subsequent analysis.

In addition, the pretreated material can also be modified to produce MP-COOH: under different gases (nitrogen and air), sintering MPs (300mg) at 250°C or 280°C for 2 hours, 4 hours or 6 hours, then add 30 mL of nitric acid (7.9 M, 7 M, 6 M, 5 M, 4 M, or 1 M) and react at 105 °C for 1.5 hours or 3 hours.

[MP-Oxy]

Put 500 mg of MPs in a 500 mL round-bottomed bottle with 5% sodium hypochlorite (250 mL), adjust the pH to about 4 to 5 with 37% hypochlorous acid, and react at 30 °C for 12 hours, 18 Hours or 24 hours to synthesize MP-Oxy. After the reaction, the functional MPs were collected by filtration and washed with a large amount of water. The obtained material was subjected to Soxhlet extraction with 500 mL of water for 8 hours and repeated twice. Among the MP-Oxy materials synthesized under different reaction times, the materials that have been processed for 24 hours will be selected for subsequent analysis. After acid reformation, a hydrothermal treatment can be selected to repair the structure of MP-Oxy material and obtain MP-Oxy-HT.

Comparative Example- Preparation of MCN-HSO ₃

Using fuming H ₂ SO ₄ (20% SO ₃ ) solution as oxidant and mesoporous carbon nanoparticles (MCN for short) mesoporous carbon nanoparticles, functionalized mesoporous carbon nanoparticle materials (HSO ₃ -MCN) were synthesized. The MCN material (1.2 g) was treated with fuming sulfuric acid solution (80 mL) in a round bottom flask (50 mL), and the mixture was heated at 80 °C under nitrogen for 24 hours. After the reaction, the synthesized functional MCN was collected by filtration, and washed with a large amount of water. The synthesized MCN material (1.2 g) was subjected to Soxhlet extraction with 250 mL of water for 3 hours, and this extraction procedure was repeated four consecutive times.

Nitrogen and carbon dioxide gas isotherm adsorption

Under a vacuum of 1×10 ^-6 mmHg, a Micromeritics 3Flex analyzer was used to perform the adsorption isotherm analysis of nitrogen (N ₂ ) and carbon dioxide (CO ₂ ) of the sample. Under the temperature of liquid nitrogen (77 K), analyze the N ₂ adsorption isotherm curve with the relative pressure (P/P ₀ ) between 0.05 and 0.995, and the relative pressure (P/P ₀ ) between 0.05 and 0.3 The Brunauer-Emmett-Teller (BET) specific surface area is obtained under the range of time. At 273 K (P ₀ = 26,142 mmHg) and 298 K (P ₀ = 48,273 mmHg), the relative analysis pressure (P/P ₀ ) is between 0.0003 and 0.03 CO ₂ adsorption isotherm curve. Use Micromeritics ISO controller (within 0.1°C) to reach CO ₂ analysis temperature. Initially, the Micromeritics Smart VacPrep degassing device was used to degas the sample (50 mg) at 393K and a vacuum of 1×10 ^-3 mmHg for 12 hours. Use helium (He) with a purity of 99.996% to measure the free space in the sample tube. The nitrogen (N ₂ ) adsorption isotherm of the sample is shown in Figures 1 and 2, and the carbon dioxide (CO ₂ ) adsorption isotherm of the sample is shown in Figure 3.

The results show that the surface area of all materials (MP-HSO ₃ surface area is 55.2 m ² /g, MP-HSO ₃ -HT surface area is 25.2 m ² /g, MP-COOH surface area is 2.18 m ² /g, MP-Oxy surface area is 1.56 m ² /g) is relatively lower than other porous materials. This means that functional MPs are non-porous materials. In the study of physical adsorption of linear gas molecules (CO ₂ ) (273K), it is surprising that MP-SO ₃ H and MP-SO ₃ H-HT exhibit high CO ₂ adsorption capacity (MP-SO ₃ H is 2.46 mmol/g, MP-SO ₃ H-HT is 2.23 mmol/g), which shows a type II isotherm. In MP-SO ₃ H and MP-SO ₃ H-HT, it is an unexpected phenomenon to observe a considerable amount of CO ₂ physical adsorption, because it is different from the conventional concept of CO ₂ storage using high surface area or basic functional group materials. Conflicting.

Acid site density determination

The acid site determination is performed based on the trans titration method (Boehm's method), and elemental analysis is used to analyze sulfur, which is expressed as a sulfonic group. Use different alkali solutions to perform Boehm selective neutralization of each functional group to determine functional groups such as carboxyl, lactone and phenolic hydroxyl: sodium hydroxide (NaOH) is used to determine three functional groups; sodium carbonate (Na ₂ CO ₃ ) Used for the determination of carboxyl and lactone; sodium bicarbonate (NaHCO ₃ ) is only used for the determination of carboxylic acid. All acid and alkali solutions (HCl, NaOH, Na ₂ CO ₃ , NaHCO ₃ , KHP) are formulated to a concentration of 0.01 M. Since the concentration of NaOH is easily changed by exposure to CO ₂ in the air, Potassium Hydrogen Phthalate (KHP) is used to determine the concentration of sodium hydroxide. The concentration value obtained is the sodium hydroxide concentration. Subsequently, HCl was titrated with NaOH to measure the HCl concentration. Finally, use HCl to determine the concentration of Na ₂ CO ₃ and NaHCO ₃ . Phenolphthalein was used as an indicator for NaOH solutions, and bromocresol green was used as an indicator for Na ₂ CO ₃ and NaHCO ₃ solutions.

。 Carry out Boehm titration as follows: add 50 mg of material (MP series material) to 20 mL of each alkali solution (NaOH, Na ₂ CO ₃ and NaHCO ₃ ) in a 50 mL tube. After vortexing all three samples for 2 hours, the solution was recovered by filtration. Subsequently, each alkali recovery solution was titrated with HCl. The acid site is measured from the alkali solution corresponding to the titration of HCl. Using NaHCO ₃ , Na ₂ CO ₃ and NaOH, respectively, calculate the addition of carboxylic acid, carboxyl group and lactone, and total acid sites. The density of phenol is calculated from the density difference measured by NaOH and Na ₂ CO ₃ . Use the following equation to calculate the acid site of each group:

.

The research results show that the total acid sites of MP-HSO ₃ -HT (2.25 mmol/g) are lower than that of MP-HSO ₃ (3.12 mmol/g). This is because the hydrothermal treatment will remove the functionalities of MP-HSO ₃ -HT. base. In addition, the total acid sites of MP-COOH (2.00 mmol/g) are lower than MP-HSO ₃ or MP-HSO ₃ -HT, which means that the oxidation of nitric acid is not as good as that of sulfuric acid, and the total acidity of MP-Oxy (1.96 mmol/g) /g) is the lowest of all materials.

The acid site distribution of untreated MPs and functionalized MPs is shown in Table 1 below.

[Table 1]

Powder X- ray diffraction ( PXRD )

In this experiment, a Bruker D8 Advance spectrometer was used to record powder XRD spectra, which was operated at a voltage of 40 kW and CuKα radiation (λ = 1.5418 Å) was used to generate a current of 40 mA. The scanning angle is 10° to 90°, and the scanning rate is 6°/min.

The XRD pattern of MP series materials shows a signal peak at a 2θ angle of 24°-25°, which can be interpreted as the (002) plane of the amorphous carbon structure. Compared with the high-intensity peak phase of the unmodified MP, the modified material shows a broad and weak signal peak at the same angle, which means that the oxidation treatment makes the crystal phase weaker and the layered structure is randomly stacked.

Further, by Bragg's law (Bragg's Law) 2d (hkl ) sinθ = nλ calculate all material d-spacing (distance between its layer structure) as _{follows: 0.366 nm (MP-HSO 3} ), 0.366nm (MP-HSO 3 -HT ), 0.343 nm (MP-COOH) and 0.345 nm (MP-Oxy).

Fourier transform infrared spectroscopy (FTIR )

The FTIR spectrum of the functionalized MP material is shown in Figure 4. The bands at 1027 cm ^-1 and 1151 cm ^-1 on MP-SO ₃ H and MP-SO ₃ H-HT refer to the asymmetric and symmetrical stretching of SO and S=0 of the sulfonic acid group (SO ₃ H). The band at 1326cm ^-1 refers to CO stretching. The band at 1521～1596 cm ^-1 is attributed to the C = C stretching mode of the graphite structure. The band at 1712 cm ^-1 refers to the C=O stretching mode of the carboxylic acid group. In addition, the band between 2850 and 3045 cm ^-1 is due to the CH stretching mode, and the band between 3300 and 3400 cm ^-1 is due to the carboxylic acid group and the OH functional group on the phenolic acid.

¹³ C solid state nuclear magnetic resonance ( SSNMR )

^{The 13} C solid-state nuclear magnetic resonance spectrum ( ¹³ C DP-mass rotation, ¹³ C DP-MAS) is shown in Figure 5. The MP spectrum has two main peaks, and the center chemical shifts are 22 ppm and 125 ppm, which means that there are two main chemical compositions, which are aliphatic carbon and aromatic carbon. In the spectra of MP-SO ₃ H and MP-SO ₃ H-HT, the aliphatic carbon peak is not clearly observed, while the aromatic carbon peak is slightly shifted to the lower field, and the new peak center is at the chemical shift 180 ppm , This can represent an oxidizing group, such as a carboxylic acid. The chemical shift of the aromatic carbon adjacent to the sulfonic acid may have merged at about 130 ppm, making it difficult to distinguish it from other aromatic carbons. In addition to the above results, it is also found that MP-COOH and MP-Oxy still have aliphatic carbon peaks, and MP-Oxy has a new peak at a chemical shift of 57 ppm. According to the literature, this is an O-alkyl-C group. The above results confirm that the modification of acidic functional groups mainly occurs at the edge of the material, while MP-COOH and MP-Oxy have a little modification of acidic functional groups on the benzene ring.

X -ray photoelectron spectroscopy ( XPS )

The XPS analysis is shown in Figure 6. The C/O ratio is calculated from the following formula: [(C1S integrated area)/(C1S sensitive factor)/(O1S integrated area)/(O1S sensitive factor)]. The analysis results show that the C/O ratio of the unfunctionalized material MP is 4.89, while the C/O ratios of the functional materials MP-SO ₃ H, MP-SO ₃ H-HT, MP-COOH and MP-Oxy are 5.85. , 4.75, 3.72 and 3.32. MP-SO ₃ H has a higher ratio because most of the functional groups are modified at the edges. As for MP-SO ₃ H-HT, the C/O ratio of MP-SO ₃ H-HT will decrease because the hydroxyl group will replace the sulfonated group after hydrothermal treatment. The functional groups of MP-COOH and MP-Oxy are not only modified at the edges of the material, but also partially modified on the benzene ring, resulting in a lower C/O ratio.

Raman spectroscopy

In the Raman spectroscopy analysis, the D band and G band were observed at 1360 cm ^-1 and 1585 cm ^-1 respectively, as shown in Figure 7. The D band at 1360 cm ^-1 represents out-of-plane vibration caused by structural defects (sp ³ ), while the G band at 1585 cm ^-1 refers to the in-plane vibration of sp ² bonded carbon atoms. Analysis showed that non-functional material MP, I _D / I _G ratio of 0.83, and the MP-SO ₃ H (0.74) and _{MP-SO 3 H-HT (} 0.88) of the I _D / I _G ratio is below MP- I _D / I _G ratio of COOH (0.96) and MP-Oxy (0.97). Therefore, it can be confirmed that MP-SO ₃ H and MP-SO ₃ H-HT have more functional groups on the edge than MP-COOH and MP-Oxy.

Preparation of amorphous cellulose and pre-hydrolyzed cellulose

First wetting 5g of commercially available microcrystalline cellulose (Avicel® PH-101) in 40mL concentrated HCl, and then adding 160mL cold HCl (pre-cooled in a dry ice bath for 1.5 hours) to dissolve the cellulose to synthesize amorphous fiber Vegetarian. Pour the β-glucan/HCl solution into 1L cold acetone to directly re-precipitate into a fluffy white solid, or dissolve it at room temperature for 2 hours and then re-precipitate (pre-hydrolyzed cellulose). Next, the separation was performed by ultracentrifugation at 15,000 rpm at 4°C for 15 minutes, and repeated three times. During the centrifugation process, the solid was washed with cold acetone and stored at a low temperature to reduce the possibility of unusable short β-glucan chains produced by cellulose hydrolysis. First, disperse the separated solid in 1.5L cold deionized (DI) water, then filter the white powder with PTFE filter paper, and wash it with cold DI water to a neutral pH. In addition, the synthesized amorphous cellulose was subjected to Soxhlet extraction with DI water for 24 hours, and then freeze-dried for 3 days.

Cellulose hydrolysis

Cellulose hydrolysis: choose commercially available microcrystalline cellulose (Avicel ^® PH-101), amorphous cellulose or pre-hydrolyzed cellulose (50 mg) for hydrolytic degradation, using (i) heterogeneous catalyst: MP or functional Reactive MP (5 mg), MCN-HSO ₃ (5 mg), commercially available strong acid resin Amberlyst 15 (5 mg) or Nafion 50 (about 40 mg pellets) in deionized aqueous solution (2 mL); or (ii) homogeneous aqueous sulfuric acid (7.5mN, 2mL). The resulting suspension solution was placed in a special high-pressure glass tube (outer diameter: 1.9 cm, length: 6.0 cm), which contained a magnet. Place the tube in a preheated heating plate, stir at 400 rpm, and treat at 130, 150 or 180°C for 2, 3, 4, 12, 24 or 48 hours under autogenous pressure. After the reaction, the high-pressure glass tube was removed from the heating plate for cooling. Use the SPE filter set (200mg / 3mL SPE column, silica) to collect the mixture and filtrate, and then wash the filtered mixture with 75℃ water (8mL) to completely wash the residual sugars or derivatives to the pre-weighed 15 ml polypropylene tube. The volume of the filtrate (Vfiltrate) is the difference in tube mass before and after filtration divided by the water density (1g / cm ³ ) (Vfiltrate = (Mfull-Mempty)/(1 g / cm ³ ); empty: empty tube mass; Mfull: The mass of the filtered tube) is calculated. The concentration of the filtrate was characterized by HPLC to estimate the product produced by the reaction and the weight percentage of the converted cellulose. The reaction conditions of the control group experiment were the same as the above except that no catalyst was added.

Three different types of cellulose (50 mg of crystalline phase cellulose, amorphous phase cellulose and pre-hydrolyzed cellulose) and functionalized MP (5 mg of MP-SO ₃ H, MP-SO ₃ H-HT, MP- The hydrolytic degradation results of COOH and MP-Oxy) are shown in Figure 8 to Figure 13. These materials and three celluloses were reacted at 180°C for 2, 3, and 4 hours in 2 mL of aqueous solution. The results showed that three products were obtained after hydrolysis: cellobiose, glucose and Hydroxymethyl Furfural (HMF). Glucose is the main product after hydrolysis. Therefore, it is found that MP-COOH has a lower glucose yield due to its relatively low density of acid sites, while MP-SO ₃ H and MP-SO ₃ H-HT have more acid sites and their strong acidic functions The base is concentrated on the edge of the material, thus promoting the cleavage of glycosidic bonds. In particular, MP-SO ₃ H reacted with pre-hydrolyzed cellulose at 180°C for 3 hours to obtain the highest glucose yield of 44%. As the reaction time increases, only MP-Oxy has a higher glucose yield.

Leaching (leaching) test

First, add 3 mL of deionized water to the 7.5 mg MP series catalyst in the reaction tube, and heat the reaction tube at 180°C for 3 hours. After the reaction, filter the solution with a 0.22 μm PTFE Syringe filter, and add 2 mL of the clear filtrate to the 50 mg cellulose in the other reaction tube at the same temperature and time as the first reaction tube Dispose of the second reaction tube.

The amorphous phase cellulose and different catalysts were subjected to a 3-hour leaching test at 180°C. The results are shown in FIG. 14. It can be seen that the glucose yields caused by MP-SO ₃ H, MP-SO ₃ H-HT and MP-COOH leaching are 2.3%, 0.5% and 0.3%, respectively. The glucose yield caused by acid leaching of these materials is very low, which means that the hydrolysis of cellulose is mainly caused by the acidic functional groups on the edges of functional MP series materials, while the glucose yield caused by acid leaching of MP-Oxy materials is as high as 39%.

Compare cellulose hydrolysis efficiency with other catalysts

Compare MP series catalysts with other materials (such as Amberlyst ^® 15 hydrogen type (5 mg) or Nafion ^® NR50 (beads about 40 mg) commercially available strong acid resins, sulfonated mesoporous carbon nanoparticles (MCN-SO ₃ H) And the cellulose hydrolysis efficiency of homogeneous sulfuric acid aqueous solution (7.5 mN, 2 mL)) is shown in Figure 15. The results showed that the amorphous cellulose hydrolysis reaction with Amberlyst 15 as the catalyst at 180°C for 3 hours can obtain a glucose yield of about 9.5%, while the yield of Nafion 50 as a catalyst is only about 5.9%. Although these commercially available heterogeneous catalysts have strong acid groups on the surface which can cause high hydrolysis efficiency of cellulose, the acid groups on the surface may be located very far away. Therefore, although the leaching tests of Amberlyst 15 and Nafion 50 yield glucose yields of 2.5% and 0.4%, respectively, the glucose yield of functional MP can be 3 times higher. On the other hand, the heterogeneous catalyst MCN-SO ₃ H as a catalyst can obtain a glucose yield of 6.9%. This low glucose yield can be attributed to the lower acid surface coverage in the porous channel, and even a 0.6% glucose yield is caused by material leaching. As for the homogeneous sulfuric acid aqueous solution with the same amount of acid as MP-SO ₃ H, the hydrolysis efficiency of the homogeneous reaction is half lower than that of MP-SO ₃ H. It is speculated that in the same aqueous solution, MP-SO ₃ H has a high acid surface coverage, which can more effectively destroy the glycosidic bonds in cellulose.

In the above embodiments, a series of mesophase pitch (MP) materials with acidic functional groups and high surface coverage were synthesized through chemical oxidation methods, including MP-SO ₃ H (treated with sulfuric acid), MP-SO ₃ H-HT ( Hydrothermal treatment of MP-SO ₃ H), MP-COOH (treated with nitric acid) and MP-Oxy (treated with sodium hypochlorite). Acid-base trans titration results show that MP-SO ₃ H has the highest acid site density (3.1 mmol/g), and it contains 1.5 mmol/g of main sulfonic acid and 0.84 mmol/g of lactone. After the hydrothermal treatment, the sulfonic acid groups of MP-SO ₃ H-HT are reduced and more phenol is produced. Nitrogen adsorption analysis showed that the specific surface area of the functional MP is less than 56 m ² /g, which indicates that these materials have a non-porous structure. The weak acid molecules close to MP can imitate cellulose hydrolase (its active center has close carboxyl groups) and can be used as an alternative catalyst for cellulose hydrolysis. Surprisingly, MP-SO ₃ H can observe the highest CO ₂ adsorption capacity (2.46 mmol/g). It has a very large CO ₂ storage potential, so it can be used as a non-porous acid function for capturing carbon dioxide. Base adsorbent.

The above-mentioned embodiments are intended to illustrate the specific implementation and technical features of the present invention, rather than to limit the protection scope of the present invention. Many other possible modifications and changes can be made without departing from the spirit and scope of the invention requested in the scope of the attached patent application. The scope of the rights claimed in the present invention should be subject to the scope of the patent application.

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Figures 1 and 2 are the nitrogen isotherm adsorption curves of MP series materials; Figure 3 is the carbon dioxide gas adsorption isotherm curves of MP series materials; Figure 4 is the FTIR spectrum of MP series materials; Figure 5 is the solid state of MP series materials NMR analysis chart; Fig. 6 is the XPS analysis chart of MP series materials; Fig. 7 is the Raman analysis chart of MP series materials; Fig. 8 is the total yield of functional MP series materials used in crystalline phase cellulose hydrolysis for 2 hours; Fig. 9 Is the total output of functional MP series materials used in crystalline phase cellulose hydrolysis for 3 hours; Figure 10 is the total output of functional MP series materials used in crystalline phase cellulose hydrolysis for 4 hours; Figure 11 is the total output of functional MP series materials used in crystalline phase cellulose hydrolysis The total yield of amorphous cellulose hydrolysis for 3 hours; Figure 12 shows the total yield of functional MP series materials used in amorphous cellulose hydrolysis for 4 hours; Figure 13 shows the functional MP series materials used for pre-hydrolyzed cellulose hydrolysis 3 Hours of total output; Figure 14 shows the leaching test of amorphous cellulose with functional MP series materials at 180°C for 3 hours; and Figure 15 shows functional MP series materials, H ₂ SO ₄ , Amberlyst 15, Nafion 50 And MCN-HSO ₃ cellulose hydrolysis efficiency.

Claims (23)

A modified carbon material comprising hexagonal carbon nets in a layered stacked structure and acidic functional groups bonded to the hexagonal carbon nets, wherein all or plural of the acidic functional groups are covalently linked to the hexagonal carbon nets The sp ² carbons in the plane at the edge of the carbon net, wherein the plural ones of the sp ² carbons of the hexagonal carbon nets in the acidic functional groups are more in number than the acidic functional groups are connected to The other sp ³ carbons of these hexagonal carbon nets. The modified carbon material as described in item 1 of the patent application, wherein the acidic functional groups include at least one of a sulfonic acid group, a carboxyl group, a lactone, and a phenolic hydroxyl group. The modified carbon material described in item 1 of the scope of patent application, wherein the modified carbon material is a non-porous material. The modified carbon material as described in item 1 of the scope of patent application, wherein the modified carbon material has a total acid site density of 1.5 mmol/g or higher. The modified carbon material described in item 2 of the scope of the patent application, wherein the modified carbon material includes the sulfonic acid group with a density of 0.8 mmol/g or higher, and the density of 0.5 mmol/g or higher A phenolic hydroxyl group, the carboxyl group having a density of 0.1 mmol/g or higher, and the lactone group having a density of 0.4 mmol/g or higher. The modified carbon material described in item 2 of the scope of patent application, wherein the modified carbon material includes the phenolic hydroxyl group with a density of 0.3 mmol/g or higher, and the carboxyl group with a density of 0.2 mmol/g or higher And the lactone group with a density of 0.3 mmol/g or higher. The modified carbon material according to any one of items 1 to 6 in the scope of the patent application, wherein the modified carbon material is prepared by using the acidic functional groups to modify asphalt materials. The modified carbon material according to any one of items 1 to 6 in the scope of the patent application, wherein the modified carbon material is prepared by treating asphalt materials with sulfuric acid, nitric acid or hypochlorite. According to the modified carbon material described in item 8 of the scope of patent application, the pitch material is further subjected to hydrothermal treatment after the sulfuric acid treatment. For the modified carbon material described in any one of items 1 to 5 in the scope of the patent application, the ¹³ C CP/MAS NMR spectrum of the modified carbon material does not substantially have sp ³ carbon peaks. The scope of the patent as one of the modified carbon material according to any of items 1 to item 6, wherein the modified carbon material to Raman spectrum of I _D / I _G ratio is not greater than 1. The modified carbon material described in any one of items 1 to 6 of the scope of patent application, wherein the C1s/O1s ratio of the modified carbon material measured by X-ray photoelectron spectroscopy is not less than 3. The modified carbon material according to any one of items 1 to 6 of the scope of patent application, wherein the interlayer distance of the modified carbon material measured by X-ray diffraction is in the range of 0.34 nm to 0.37 nm. An acid-functional adsorbent for capturing CO ₂ comprising hexagonal carbon nets in a layered stacked structure and acidic functional groups bonded to the hexagonal carbon nets, wherein the hexagonal carbon nets are essentially made of aromatic carbon The composition and substantially all of the acidic functional groups are covalently connected to the in-plane sp ² carbons at the edges of the hexagonal carbon meshes. The acid functionalized adsorbent for capturing CO ₂ as described in item 14 of the scope of the patent application, wherein the acid functionalized adsorbent for capturing CO ₂ is a non-porous material. The acid functionalized adsorbent for capturing CO ₂ as described in item 14 of the patent application, wherein the acidic functional groups include sulfonic acid groups, carboxyl groups, lactones and phenolic hydroxyl groups. The acid functionalized adsorbent for capturing CO ₂ as described in item 14 of the scope of patent application, wherein the acid functionalized adsorbent for capturing CO ₂ has a total acid site density of 1.5 mmol/g or higher. The acid functionalized adsorbent for capturing CO ₂ as described in item 16 of the scope of patent application, wherein the acid functionalized adsorbent for capturing CO ₂ includes the sulfonic acid group with a density of 0.8 mmol/g or higher , The phenolic hydroxyl group with a density of 0.5 mmol/g or higher, the carboxyl group with a density of 0.1 mmol/g or higher, and the lactone group with a density of 0.4 mmol/g or higher. The acid functionalized adsorbent for capturing CO ₂ as described in any one of items 14 to 18 of the scope of patent application, wherein the acid functionalized adsorbent for capturing CO ₂ utilizes the acidic functional groups It is made by modifying asphalt materials. The acid functionalized adsorbent for capturing CO ₂ as described in any one of items 14 to 18 in the scope of the patent application, wherein the acid functionalized adsorbent for capturing CO ₂ is measured by Raman spectroscopy I _D / I _G ratio is not greater than 1. The acid functionalized adsorbent for capturing CO ₂ as described in any one of items 14 to 18 of the scope of the patent application, wherein the acid functionalized adsorbent for capturing CO ₂ is measured by X-ray photoelectron spectroscopy The ratio of C1s/O1s is not less than 3. The acid functionalized adsorbent for capturing CO ₂ as described in any one of items 14 to 18 of the scope of patent application, wherein the acid functionalized adsorbent for capturing CO ₂ is measured by X-ray diffraction The distance between layers is in the range of 0.34 nm to 0.37 nm. A method of cellulose hydrolysis, including: Mixing the modified carbon material and cellulose as described in any one of items 1 to 13 of the scope of patent application in an aqueous solution; and The hydrolysis of the cellulose is carried out at a predetermined temperature in the presence of the modified carbon material as a catalyst.

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