CN113426408B - A kind of hydrophobically modified biochar using natural organic acid and its preparation method and application - Google Patents

Abstract

The invention discloses a hydrophobically modified biochar using natural organic acid and a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing biochar and hydrogen peroxide solution, softening, stirring and filtering to obtain hydroxylated biochar; (2) mixing the hydroxylated biochar, sodium borohydride, anhydrous Mixing with ethanol, stirring, filtering, and drying in an inert gas atmosphere at 50-100° C. to obtain dry biochar; (3) adding the dry biochar to a solution in which natural macromolecular organic acid, anhydrous ethanol, and dehydrating agent are dissolved (4) filter the mixed solution, then rinse with ethanol and deionized water, and dry in an inert gas atmosphere at 50-100° C. to obtain the modified biochar. The invention has the advantages of simple operation, low price, green environmental protection, little influence on the pore size structure of the carbon material, and good adsorption performance for volatile organic compounds in a high humidity environment.

Description

A kind of hydrophobically modified biochar using natural organic acid and its preparation method and application

technical field

The invention belongs to the field of porous carbon materials, and in particular relates to a hydrophobically modified biochar using natural organic acid and a preparation method and application thereof.

Background technique

At present, adsorption technology and adsorption-catalytic combustion technology are the main technologies for effective treatment of medium and low concentration organic waste gas. Among them, adsorbents have become one of the key materials, and carbon-based hierarchical porous materials are widely used as adsorbents for VOCs due to their wide range of sources, such as activated carbon, biochar, and biochar fibers, low price and excellent performance. However, engineering practical experience shows that common carbon-based adsorbents face the problem of competing with water vapor in engineering applications. For example, in the painting process of automobile manufacturing, wet spraying is often used to remove excess paint, thereby increasing its VOCs exhaust gas humidity. In addition, with the gradual promotion of water-based raw and auxiliary materials to replace solvent-based raw and auxiliary materials, the contradiction between carbon-based adsorbents in the selective adsorption of VOCs and water vapor has become more and more prominent. However, the adsorption capacity of carbon-based adsorbent VOCs will be greatly reduced under high humidity conditions, and it is easy to reach a saturated state, which is not conducive to the purification of organic waste gas.

Regarding the hydrophobicity of materials, it has been reported in the literature that the use of functional coatings can effectively achieve stable superhydrophobicity, which can be applied to building environment control, hydrodynamic drag reduction, etc. In addition, some coatings such as organosilanes and perfluorinated compounds tend to be toxic, flammable, corrosive, difficult to handle and damage the environment. However, the application of natural macromolecular organic acid-modified hydrophobic carbon materials for VOCs adsorption in high-humidity environments is rarely reported. Therefore, the development of hierarchical porous carbon materials with high hydrophobic properties as high-efficiency VOCs adsorbents is expected to overcome the shortcomings of existing carbon materials such as low adsorption capacity and poor adsorption performance when competing with water vapor, and has good application prospects.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention provides a hydrophobically modified biochar using natural organic acid and a preparation method and application thereof.

The purpose of the present invention is to achieve at least one of the following solutions.

A preparation method of hydrophobically modified biochar utilizing natural organic acid, comprising the following steps:

(1) mixing biochar and hydrogen peroxide solution, stirring and filtering to obtain hydroxylated biochar;

(2) mixing the hydroxylated biochar in step (1), sodium borohydride, and dehydrated alcohol, stirring, filtering, and drying in an inert gas atmosphere at 50-100° C. to obtain dry biochar;

(3) adding the dry biochar described in step (2) into the solution in which natural macromolecular organic acid, dehydrated alcohol, and dehydrating agent are dissolved, and heating and stirring to obtain a mixed solution;

(4) Filter the mixed solution described in step (3), rinse the precipitate with ethanol and deionized water, and dry in an inert gas atmosphere at 50-100° C. to obtain the modified biochar.

Further, in step (1), the biochar is one or more of coconut shell biochar, bagasse biochar and walnut shell biochar; the mass fraction of the hydrogen peroxide solution is 5-30% .

Further, in step (1), the stirring time is 1-6h.

Further, in step (2), the mass ratio of the hydroxylated biochar to sodium borohydride is 10:1 to 0.1:1; the ratio of the volume of the anhydrous ethanol to the mass of the hydroxylated biochar is 1:1-1:50L/g; the stirring time is 1-6h.

Further, in step (3), the natural macromolecular organic acid is one or more of cinnamic acid, caffeic acid, myristic acid or lauric acid.

Further, in step (3), the quality of the natural macromolecular organic acid and the volume ratio of dehydrated ethanol are (1-20:1) g/L; the consumption of the dehydrating agent is the consumption of the natural macromolecular organic acid 10-50wt%.

Further, in step (3), the stirring time is 6-24h.

The natural organic acid hydrophobically modified biochar is prepared by the above preparation method.

The application of the above-mentioned hydrophobically modified biochar using natural organic acids in the adsorption of VOCs.

Further, the relative humidity of the environment for adsorbing VOCs is greater than 70%.

The basic principle of the present invention is: the natural macromolecular organic acid has a large number of carboxyl groups, and the ethanol chemical deposition method is used to carry out an esterification reaction between the organic acid and the hydroxyl functional group on the surface of the biochar to form a chemical bond, wherein the dehydrating agent in the reaction process can promote the carboxyl group and the hydroxyl group. Covalent bonds are formed between them without being adsorbed on the surface, so that the biochar forms a stable hydrophobic structure.

Compared with the prior art, the present invention has the following advantages:

(1) The preparation method of the present invention is simple in operation, low in price, environmentally friendly, hydrophobic, and has little influence on the pore size structure of the carbon material;

(2) The hydrophobically modified biochar using natural organic acid prepared by the present invention has good adsorption performance for volatile organic VOCs in a high humidity environment.

Description of drawings

Fig. 1 is the flow chart of the preparation method of utilizing natural organic acid hydrophobically modified biochar provided by the present invention;

Fig. 2 is the infrared spectrogram before and after biochar modification in the embodiment;

Fig. 3 is the penetration curve of adsorbing VOCs in dry environment before and after biochar modification in the embodiment;

Figure 4 is the breakthrough curve of the adsorption of VOCs under the environment of relative humidity of 70% before and after biochar modification in the example.

Detailed ways

The specific implementation of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

In the following examples, the method for preparing the hydrophobically modified biochar using natural organic acid refers to the preparation steps shown in FIG. 1 .

Application: The biochar before and after modification prepared in Example 1 was applied to the adsorption of volatile organic compounds in a dry environment and a relative humidity of 70%, respectively, and the VOCs adsorption performance test experiment was carried out;

(1) Adsorption of volatile organic compounds in a dry environment: first measure the VOCs concentration of VOCs and air mixed gas by GC, let it stabilize at 100ppm, put 0.05g of adsorption material (biochar) in the adsorption evaluation device, mix VOCs and air The mixed gas was passed into the adsorption material, and finally, the concentration of VOCs at the outlet was determined by gas chromatography (GC). The analysis time of each chromatogram was 8.5 minutes, and the adsorption capacity of the material to VOCs was determined.

(2) Adsorption of volatile organic compounds in an environment with a relative humidity of 70%: first use GC and a hygrometer to measure the VOCs concentration and humidity of VOCs, water vapor and air mixed gas, let it stabilize at 100ppm and 70% relative humidity, and finally use gas chromatography (GC) to measure the concentration of VOCs at the outlet, the analysis time of each chromatogram is 8.5min, and the adsorption capacity of the material to VOCs is measured.

Example 1

(1) Take 1.5 g of biochar (marked as BC) into a beaker, then add 50 mL of 10% hydrogen peroxide solution for mixing and softening, stir for 2 h, and filter to obtain hydroxylated biochar.

(2) Mix the hydroxylated biochar with sodium borohydride in a mass ratio of 1:1 and 50 mL of absolute ethanol, stir for 2 hours, filter, and dry in a nitrogen atmosphere at 80°C for 60 minutes to obtain dry biochar.

(3) 0.5 g of biochar dried in step (2), 1 g of myristic acid, 0.4 g of dehydrating agent and 100 mL of absolute ethanol were added to a round-bottomed flask, heated and stirred at 75° C. for 24 h to obtain a mixed solution.

(4) Finally, the filtered precipitate of the mixed solution in step (3) was rinsed with ethanol and deionized water, and dried in a nitrogen atmosphere at 80° C. for 60 min to obtain modified biochar (marked as BC-E).

The functional group changes after hydrophobic modification obtained in the above examples and the evaluation results of VOCs adsorption performance under dry and wet conditions are as follows:

Figure 2 uses infrared spectroscopy (FTIR) to study the difference in the surface functional groups of biochars BC and BC-E before and after modification, and to explore the chemical reaction on the surface of hydrophobically modified activated carbon. The results show that the signals of aliphatic compounds such as _-CH3 in organic acids only appear in the modified material BC-E, which preliminarily proves that natural hydrophobic substances can be effectively modified to carbon materials to change their surface groups.

VOCs adsorption performance of BC and BC-E biochar materials under different relative humidity:

Table 1 shows the adsorption performance of VOCs under the conditions of drying and relative humidity of 70% before and after biochar modification;

Table 1

Fig. 3 is the penetration curve of adsorbing VOCs in dry environment before and after biochar modification in the embodiment;

Fig. 4 is the penetration curve of adsorbing VOCs under the environment of relative humidity of 70% before and after biochar modification in the embodiment;

Combined with Figure 3, Figure 4 breakthrough curves and Table 1, it can be found that in a dry VOCs environment (RH=0%), the adsorption capacity of BC on VOCs is greater than that of BC-E. When the relative humidity increased from 0% to 70%, the adsorption capacity of unmodified biochar BC decreased by 44% from 380 to 212 mg/g, and the adsorption performance of VOCs in humid environment was greatly reduced. However, the adsorption capacity of biochar BC-E modified by organic acid decreased by only 20% from 308 to 245 mg/g. Compared with BC, the presence of moisture has less effect on the adsorption of VOCs by BC-E, and the selectivity of hydrophobically modified biochar to VOCs is enhanced. It can be seen from the above results that the hydrophobically modified activated carbon obtained in the present invention has good adsorption performance for VOCs in a high-humidity environment, and greatly reduces the treatment cost of VOCs in a high-humidity environment.

The above descriptions are merely preferred embodiments of the present invention, and do not limit the present invention in any form. Any equivalent changes, modifications or evolutions made by those skilled in the art to the above embodiments by utilizing the technical solutions of the present invention still fall within the scope of the technical solutions of the present invention.

Claims (1)

1. The application of the hydrophobically modified biochar utilizing natural organic acid in the aspect of adsorbing VOCs is characterized in that the relative humidity of the environment for adsorbing VOCs is more than 70%;

the preparation method of the biochar hydrophobically modified by utilizing the natural organic acid comprises the following steps:

(1) mixing the biochar with a hydrogen peroxide solution, stirring and filtering to obtain hydroxylated biochar; the biochar is one or more of coconut shell biochar, bagasse biochar and walnut shell biochar; the mass fraction of the hydrogen peroxide solution is 5-30%; the stirring time is 1-6 h;

(2) mixing the hydroxylated biochar in the step (1), sodium borohydride and absolute ethyl alcohol, stirring, filtering, and drying at 50-100 ℃ in an inert gas atmosphere to obtain dried biochar; the mass ratio of the hydroxylated biochar to the sodium borohydride is (10: 1) - (0.1: 1); the ratio of the volume of the absolute ethyl alcohol to the mass of the hydroxylated biochar is (1: 1) - (1: 50) L/g; the stirring time is 1-6 h;

(3) adding the dried biochar in the step (2) into a solution in which natural organic acid, absolute ethyl alcohol and a dehydrating agent are dissolved, heating and stirring to obtain a mixed solution; the natural organic acid is one or more of myristic acid or lauric acid; the volume ratio of the mass of the natural organic acid to the absolute ethyl alcohol is (1-20): 1 g/L; the dosage of the dehydrating agent is 10-50wt% of the dosage of the natural organic acid; the stirring time is 6-24 h;

(4) and (4) filtering the mixed solution obtained in the step (3), washing the precipitate with ethanol and deionized water, and drying at 50-100 ℃ in an inert gas atmosphere to obtain modified biochar.

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