阅读说明：本技术 酸水热预处理强化木质纤维素类废物水热腐殖化的方法 (Method for strengthening hydrothermal humification of lignocellulose waste by acid hydrothermal pretreatment ) 是由 陆文静 邵宇超 鲍梦港 霍巍中 叶蓉 刘彦情 付心迪 于 2021-07-05 设计创作，主要内容包括：本发明公开了酸水热预处理强化木质纤维素类废物水热腐殖化的方法。该方法包括：(1)将木质纤维素类废物进行破碎、烘干,得到干燥碎料；(2)将所述干燥碎料与水混合,将混合体系调节为酸性环境,并进行第一水热反应；(3)将步骤(2)所得混合体系调节为碱性环境,并进行第二水热反应,得到水热产物；(4)对所述水热产物进行固液分离,得到含腐植酸的液相产物和含水热炭的固相产物；(5)将所述液相产物调节为酸性环境,得到腐植酸。该方法结合酸性水热处理和碱性腐殖化的特点对有机废弃物进行有效利用,可以在相对较低的处理处置成本下提高腐植酸产率,同时制备水热炭,进一步提高有机废弃物的资源化利用程度。(The invention discloses a method for strengthening hydrothermal humification of lignocellulose waste by acid hydrothermal pretreatment. The method comprises the following steps: (1) crushing and drying the lignocellulose waste to obtain dry crushed materials; (2) mixing the dried crushed materials with water, adjusting a mixed system to be in an acid environment, and carrying out a first hydrothermal reaction; (3) adjusting the mixed system obtained in the step (2) to be in an alkaline environment, and carrying out a second hydrothermal reaction to obtain a hydrothermal product; (4) carrying out solid-liquid separation on the hydrothermal product to obtain a liquid-phase product containing humic acid and a solid-phase product containing hydrothermal carbon; (5) and regulating the liquid-phase product to be in an acidic environment to obtain humic acid. The method combines the characteristics of acidic hydrothermal treatment and alkaline humification to effectively utilize the organic waste, can improve the humic acid yield at relatively low treatment and disposal cost, and simultaneously prepares the hydrothermal carbon to further improve the resource utilization degree of the organic waste.)

1. A method for strengthening hydrothermal humification of lignocellulose waste by acid hydrothermal pretreatment is characterized by comprising the following steps:

(1) crushing and drying the lignocellulose waste to obtain dry crushed materials;

(2) mixing the dried crushed materials with water, adjusting a mixed system to be in an acid environment, and carrying out a first hydrothermal reaction;

(3) adjusting the mixed system obtained in the step (2) to be in an alkaline environment, and carrying out a second hydrothermal reaction to obtain a hydrothermal product;

(4) carrying out solid-liquid separation on the hydrothermal product to obtain a liquid-phase product containing humic acid and a solid-phase product containing hydrothermal carbon;

(5) and regulating the liquid-phase product to be in an acidic environment to obtain humic acid.

2. The method for enhancing hydrothermal humification of lignocellulosic waste by hydrothermal pretreatment of acid water as claimed in claim 1, wherein the lignocellulosic waste comprises at least one of straw, fallen leaves, waste wood.

3. The method for enhancing hydrothermal humification of lignocellulosic waste by hydrothermal pretreatment of acidic water as claimed in claim 1, wherein in the step (2), the dry crushed material is mixed with water at a solid-to-liquid ratio of (0.1-1) g/10 mL.

4. The method for enhancing hydrothermal humification of lignocellulosic waste by acid hydrothermal pretreatment according to claim 1, wherein in the step (2), the pH of the acidic environment is 1 to 3.

5. The method for enhancing hydrothermal humification of lignocellulosic waste by hydrothermal pretreatment of acid water as claimed in claim 1, wherein in step (3), the alkaline environment has a pH of 11-13.

6. The method for enhancing hydrothermal humification of lignocellulosic waste by acid hydrothermal pretreatment according to claim 1, wherein the temperatures used for the first hydrothermal reaction and the second hydrothermal reaction are respectively and independently 170-190 ℃.

7. The method for enhancing hydrothermal humification of lignocellulosic waste by acid hydrothermal pretreatment according to claim 1, wherein the first hydrothermal reaction and the second hydrothermal reaction are performed for 2 to 6 hours, respectively and independently.

8. The method for enhancing hydrothermal humification of lignocellulosic waste by hydrothermal pretreatment of acidic water as claimed in claim 1, wherein in step (5), the pH of the acidic environment is 1-3.

9. The method for enhancing hydrothermal humification of lignocellulosic waste by acidic hydrothermal pretreatment of water according to claim 1, wherein step (5) further comprises: and adjusting the liquid phase product to be in an acidic environment to precipitate humic acid, and then carrying out solid-liquid separation to obtain humic acid precipitate and waste liquid.

10. The method for enhancing hydrothermal humification of lignocellulosic waste by acidic hydrothermal pretreatment of water according to claim 9, wherein step (5) further comprises: and (3) returning the waste liquid to the step (2) for the first hydrothermal reaction.

Technical Field

The invention relates to the field of waste recycling, in particular to a method for strengthening hydrothermal humification of lignocellulose waste by acid hydrothermal pretreatment.

Background

Lignocellulosic wastes are very slowly degraded in nature due to their high cellulose and lignin contents, and the carbon in such wastes can be finally fixed in the soil in the form of humus through a series of physical, chemical and biological actions. The content of humus in the total organic matters of soil is reported to be up to 75%, the humus can promote the growth and metabolism of plants, and the importance of the humus is reflected. In addition, a great deal of research currently shows that humus is widely used due to the fact that the humus is rich in oxygen-containing functional groups and can be used as an anion affinity agent, an adsorbent, a modified catalyst and the like.

With the accelerated intensive development process of the planting industry and the improvement of the urban greening level, a large amount of lignocellulose waste (such as straws, branches, fallen leaves and the like) is generated. The current mainstream treatment technologies such as landfill and incineration not only waste resources, but also pollute the environment to a certain extent. Therefore, it is of great value to find a clean and efficient method for converting lignocellulosic waste into humus.

The hydrothermal technology can efficiently and directionally convert the biomass wastes into solid carbon materials, liquid products rich in high value-added compounds and gaseous products such as hydrogen, methane and the like under certain operating conditions. Researchers have proposed to convert biomass wastes into humic acid by using a hydrothermal technology under an alkaline condition in 2019, however, the yield obtained by the research corresponding to hydrothermal humification of several raw materials is less than 2%, and the existing method for obtaining humic acid by treating biomass by using a hydrothermal method still needs to be improved.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. To this end, an object of the present invention is to propose a method for enhancing hydrothermal humification of lignocellulosic waste by acid hydrothermal pretreatment. The method combines the characteristics of acidic hydrothermal treatment and alkaline humification to effectively utilize the organic waste, can improve the humic acid yield at relatively low treatment and disposal cost, and simultaneously prepares the hydrothermal carbon to further improve the resource utilization degree of the organic waste.

In one aspect of the invention, the invention provides a method for strengthening hydrothermal humification of lignocellulose waste by acid hydrothermal pretreatment. According to an embodiment of the invention, the method comprises: (1) crushing and drying the lignocellulose waste to obtain dry crushed materials; (2) mixing the dried crushed materials with water, adjusting a mixed system to be in an acid environment, and carrying out a first hydrothermal reaction; (3) adjusting the mixed system obtained in the step (2) to be in an alkaline environment, and carrying out a second hydrothermal reaction to obtain a hydrothermal product; (4) carrying out solid-liquid separation on the hydrothermal product to obtain a liquid-phase product containing humic acid and a solid-phase product containing hydrothermal carbon; (5) and regulating the liquid-phase product to be in an acidic environment to obtain humic acid.

According to the method for enhancing hydrothermal humification of lignocellulosic waste by acid hydrothermal pretreatment of the above embodiment of the present invention, the first hydrothermal reaction is performed on the dried crushed lignocellulosic waste in an acidic environment, and the humification process of the material by the second hydrothermal reaction in a subsequent alkaline environment can be enhanced by performing the first hydrothermal reaction in an acidic environment. After the first hydrothermal reaction, the solid phase part in the material is obviously reduced, and the yield of the precursor (soluble carbohydrate, micromolecular acid, furan compounds, phenolic substances and the like) for synthesizing the humic acid is obviously increased. Subsequently, the reaction system is adjusted to be in an alkaline environment, the materials are humified through a second hydrothermal reaction, and the precursor for synthesizing humic acid is easy to generate polymerization and aromatization reactions under the alkaline hydrothermal condition to form humic acid substances, so that the humic acid can be obtained with high yield. And then carrying out solid-liquid separation on the hydrothermal product to obtain a liquid-phase product containing humic acid and a solid-phase product containing hydrothermal carbon. Wherein, the humic acid can be obtained by adjusting the liquid phase product to be an acid environment for precipitation, and the extraction process is convenient; the byproduct hydrothermal carbon can be used as clean fuel, adsorbent, carbon-based soil remediation agent, etc. Therefore, when the method is used for treating the lignocellulose waste, the obtained liquid-phase product and the obtained solid-phase product can be effectively utilized, and the method has the advantages of short time consumption, high yield, clean and environment-friendly production process and the like.

In addition, the method for enhancing hydrothermal humification of lignocellulosic waste by acid hydrothermal pretreatment according to the above embodiment of the present invention may further have the following additional technical features:

in some embodiments of the invention, the lignocellulosic waste comprises at least one of straw, fallen leaves, waste wood.

In some embodiments of the invention, in the step (2), the dry crushed material is mixed with water according to a solid-to-liquid ratio of (0.1-1) g/10 mL.

In some embodiments of the present invention, in the step (2), the pH of the acidic environment is 1-3.

In some embodiments of the present invention, in the step (3), the pH of the alkaline environment is 11 to 13.

In some embodiments of the present invention, the first hydrothermal reaction and the second hydrothermal reaction are performed at temperatures of 170 to 190 ℃ respectively.

In some embodiments of the present invention, the first hydrothermal reaction and the second hydrothermal reaction are performed for 2 to 6 hours, respectively and independently.

In some embodiments of the present invention, in the step (5), the pH of the acidic environment is 1-3.

In some embodiments of the invention, step (5) further comprises: and adjusting the liquid phase product to be in an acidic environment to precipitate humic acid, and then carrying out solid-liquid separation to obtain humic acid precipitate and waste liquid.

In some embodiments of the invention, step (5) further comprises: and (3) returning the waste liquid to the step (2) for the first hydrothermal reaction.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a schematic flow diagram of the method for enhancing hydrothermal humification of lignocellulosic waste by acid hydrothermal pretreatment in example 1;

FIG. 2 shows hydrothermal carbon yield results of solid phase products obtained after hydrothermal three tests of pH 1, pH 13 and M in example 1, comparative example 1a and comparative example 1 b;

FIG. 3 is the total organic carbon results of the liquid phase products obtained after hydrothermal three sets of test pH 1, pH 13 and M in example 1, comparative example 1a and comparative example 1 b;

FIG. 4 shows the results of humic acid yields in liquid phase products obtained after hydrothermal treatment in three sets of test pH 1, pH 13 and M in example 1, comparative example 1a and comparative example 1 b.

Detailed Description

The following describes embodiments of the present invention in detail. The following examples are illustrative only and are not to be construed as limiting the invention. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

The invention provides a method for strengthening hydrothermal humification of lignocellulose waste by acid water thermal pretreatment. The method for enhancing hydrothermal humification of lignocellulosic waste by acid hydrothermal pretreatment according to an embodiment of the present invention is further described in detail below.

First, according to an embodiment of the present invention, lignocellulosic waste is crushed and dried to obtain dry crushed material. The specific operating conditions of crushing and drying are not particularly limited, and for example, the material may be crushed to a particle size of 0.1mm and dried at 80 ℃ for subsequent processing.

According to some embodiments of the present invention, the above-mentioned lignocellulosic waste may include at least one of straw, fallen leaves, and waste wood.

Further, according to an embodiment of the present invention, the above-described dried pulverized material is mixed with water, the mixed system is adjusted to an acidic environment, and the first hydrothermal reaction is performed. By carrying out the first hydrothermal reaction in an acidic environment, the humification process of the second hydrothermal reaction on the material in a subsequent alkaline environment can be enhanced. After the first hydrothermal reaction, the solid phase part in the material is obviously reduced, and the yield of the precursor (soluble carbohydrate, micromolecular acid, furan compounds, phenolic substances and the like) for synthesizing the humic acid is obviously increased. Subsequently, the reaction system is adjusted to be in an alkaline environment, the materials are humified through a second hydrothermal reaction, and the precursor for synthesizing humic acid is easy to generate polymerization and aromatization reactions under the alkaline hydrothermal condition to form humic acid substances, so that the humic acid can be obtained with high yield.

According to some embodiments of the invention, the dry grind may be mixed with water at a solid to liquid ratio of (0.1-1) g/10mL (on a dry basis of the dry grind). Specifically, the solid-to-liquid ratio may be 0.1g/10mL, 0.2g/10mL, 0.3g/10mL, 0.4g/10mL, 0.5g/10mL, 0.6g/10mL, 0.7g/10mL, 0.8g/10mL, 0.9g/10mL, 1g/10mL, or the like, and preferably 0.5g/10 mL. If the solid-liquid ratio is too low, the hydrothermal efficiency is low, so that water resources are wasted, and engineering application is not facilitated; if the solid-to-liquid ratio is too high, hydrolysis may be insufficient and the direct carbonization of the raw material may result in a limitation of the humification effect.

According to some embodiments of the present invention, the mixed system of the dried crushed aggregates and water is adjusted to an acidic environment with a pH of 1 to 3 (preferably, a pH of 1) to perform the first hydrothermal reaction. If the system pH is too low, more carbon loss may be caused to result in low final humification efficiency; if the pH value of the system is too high, the biomass raw material is insufficiently hydrolyzed, resulting in low humification efficiency. In addition, it is to be noted that the pH of the mixed system may be adjusted to the above range by using an acid commonly used in the art, for example, hydrochloric acid, sulfuric acid, or the like.

According to some embodiments of the present invention, the temperature used for the first hydrothermal reaction may be 170 to 190 ℃, preferably 180 ℃; the first hydrothermal reaction may be performed for 2 to 6 hours, preferably for 4 hours. If the temperature adopted in the first hydrothermal reaction is too low, the lignocellulose waste is insufficiently hydrolyzed, the solid residues are too much, and the yield of the target product humic acid is reduced. If the temperature adopted by the first hydrothermal reaction is too high, although the hydrolysis of the lignocellulose waste is facilitated, the too high temperature can lead soluble low-molecular organic matters obtained by hydrolysis to re-polymerize insoluble matters, so that the yield of solid residues is improved, and the yield of the target product humic acid is reduced; in addition, too high temperature can also cause a large amount of carbon-containing gas to be generated, so that carbon loss is caused, and the yield of the target product humic acid is reduced.

Further, according to the embodiment of the present invention, the mixed system obtained after the first hydrothermal reaction is completed is adjusted to an alkaline environment, and a second hydrothermal reaction is performed to obtain a hydrothermal product.

According to some embodiments of the present invention, the mixed system obtained after the first hydrothermal reaction is completed is adjusted to an alkaline environment with a pH of 11 to 13 (preferably pH 13). If the pH value of the system is too low, the humification efficiency is low due to insufficient polymerization and aromatization reactions of the humic acid precursor; if the pH value of the system is too high, the alkali agent is wasted, the cost for extracting humic acid by subsequent acidification is increased, and the industrial production is not facilitated. In addition, the pH of the mixed system may be adjusted to the above range by using a base commonly used in the art, for example, potassium hydroxide, sodium hydroxide, etc.

According to some embodiments of the present invention, the temperature used for the second hydrothermal reaction may be 170 to 190 ℃, preferably 180 ℃; the second hydrothermal reaction can be carried out for 2-6 h, preferably 4 h. If the temperature adopted by the second hydrothermal reaction is too low, the humification efficiency may be low due to insufficient polymerization and aromatization reactions of the humic acid precursor; if the temperature used for the second hydrothermal reaction is too high, more carbon loss and an increase in the yield of solid phase residue may result, reducing the humification efficiency.

Further, according to the embodiment of the invention, the hydrothermal product is subjected to solid-liquid separation to obtain a liquid phase product containing humic acid and a solid phase product containing hot charcoal. For the liquid phase product, humic acid can be obtained by adjusting the liquid phase product to be in an acidic environment.

According to some embodiments of the invention, humic acid precipitate and waste liquid can be obtained by subjecting the liquid phase product to an acidic environment with a pH of 1-3 (preferably a pH of 1) to precipitate humic acid, and then performing solid-liquid separation. If the pH value of the system is too high, the precipitation of humic acid is incomplete, so that the yield is low; if the system pH is too low, acid consumption will increase. In addition, it is to be noted that the pH of the mixed system may be adjusted to the above range by using an acid commonly used in the art, for example, hydrochloric acid, sulfuric acid, or the like.

Additionally, according to some embodiments of the present invention, the waste liquor resulting from precipitation of humic acid may be further returned for mixing with a dried crushed material of lignocellulosic waste and subjected to the first hydrothermal reaction. Therefore, a large amount of water resources can be saved.

The invention will now be described with reference to specific examples, which are intended to be illustrative only and not to be limiting in any way.

Example 1

Referring to fig. 1, after drying and crushing a typical lignocellulosic waste material using straw, 1g of the dried crushed material was put into a hydrothermal reaction vessel, 20mL of water having a pH of 1 was added, hydrothermal reaction was carried out at 180 ℃ for 4 hours, and then the test was repeated three times by adjusting the pH of the product to 13 with sodium hydroxide and hydrothermal reaction was carried out at 180 ℃ for 4 hours, and the set of test was labeled as "M".

Comparative example 1a

Straw is taken as a typical lignocellulose waste raw material, after the raw material is dried and crushed, 1g of the dried crushed material is taken to be put into a hydrothermal reaction kettle, 20mL of water with the pH value of 1 is added, the hydrothermal reaction is carried out for 4h at the temperature of 180 ℃, the test is repeated for three times, and the test is marked as 'pH 1'.

Comparative example 1b

Straw is taken as a typical lignocellulose waste raw material, after the raw material is dried and crushed, 1g of the dried crushed material is taken into a hydrothermal reaction kettle, 20mL of water with the pH value of 13 is added, the hydrothermal reaction is carried out for 4h at 180 ℃, the test is repeated for three times, and the test is marked as 'pH 13'.

The experimental results of example 1, comparative example 1a and comparative example 1b are shown in FIGS. 2 to 4.

As can be seen from FIG. 2, the highest yield of hydrothermal charcoal was obtained in the pH 13 test, which was 50.09 + -1.97 wt% (based on dry straw basis, the same applies hereinafter), indicating that the liquefaction effect of straw during hydrothermal process was low. The hydrothermal carbon yield obtained in the pH 1 test was 30.26. + -. 0.45 wt%, which is significantly lower than that in the pH 13 test. This is because the acidic aqueous acid heat treatment can hydrolyze the originally insoluble macromolecular components such as cellulose and hemicellulose in the straw to a large extent. This phenomenon can also be found by comparing the results of TOC (total organic carbon content) tests at pH 1 and pH 13 of FIG. 3. However, according to the results of fig. 4, the liquid phase product of the pH 1 test group did not obtain the target product humic acid, whereas the pH 13 test group could obtain the yield of humic acid of 7.97 ± 0.48 wt%. Therefore, the hydrothermal humification process needs to be carried out in an alkaline environment.

With the method according to the embodiment of the invention, the hydrothermal humification test is carried out under alkaline conditions after the acid water thermal pretreatment, so as to strengthen the humification process. From the M test groups in FIG. 2 and FIG. 3, the hydrothermal charcoal yield is only 5.15. + -. 0.38 wt%, while the liquid phase product TOC is as high as 16723. + -. 1050mg/L, which shows that the hydrothermal liquefaction effect is very good. Further according to the results of the M experimental group in FIG. 4, the humic acid yield is as high as 28.74 + -0.98 wt%, which is more than 3 times of the corresponding results of the pH 13 experimental group. In order to eliminate the influence of the reaction time, a verification example is supplemented, namely the reaction time of the pH 13 test group is adjusted to 8 hours, and the yield of humic acid in the finally obtained liquid phase product is only 5.76 +/-0.40 wt%. In conclusion, the method for strengthening hydrothermal humification of lignocellulose waste by acid hydrothermal pretreatment has obvious innovativeness and huge practical application potential.

Example 2

Humification tests were performed at different hydrothermal temperatures using straw as a typical lignocellulosic waste material, and the results are shown in table 1 below. As can be seen from table 1, the yield of solid residue obtained from straw in the acidic hydrothermal environment of 160 ℃ is high, because the hydrolysis is insufficient due to the low temperature, and thus the yield of humic acid, which is a target product obtained from further alkaline hydrothermal humification, is low, and is 18.94%. The yield of solid residue obtained by straw in the acidic hydrothermal environment of 200 ℃ is slightly higher than 180 ℃, which is caused by the fact that soluble low-molecular organic matters are polymerized into insoluble matters again at high temperature. In addition, the yield of humic acid obtained by straw hydrothermal humification at the temperature is lower than that at 180 ℃, and is 23.59%, probably because a large amount of carbon-containing gas is generated due to high temperature, and carbon loss is caused. Therefore, the hydrothermal temperature of 180 ℃ is beneficial to the hydrothermal humification of the straws.

TABLE 1 influence of hydrothermal temperature on hydrothermal humification after strengthening

Note: in table 1, a indicates that the hydrothermal reaction is performed at pH 1; b means that the hydrothermal reaction is carried out under the environment of pH 1, and then the product is further subjected to the hydrothermal reaction under the environment of pH 13.

Example 3

The wastewater after the target product humic acid is extracted under the optimal hydrothermal humification conditions (180 ℃, 4h) is recycled, so that the precious water resource is saved, the efficient humification operation process of wastes is maintained, and the results are shown in the following table 2. In the first cycle test, the yield of solid residue obtained by straw in the acidic hydrothermal environment is 34.32%, which is higher than the case of pure water as solvent. The reason for this may be that a large amount of organic matter contained in the waste liquid is polymerized into insoluble matter in the solid phase in the system. Likewise, the yield of solid residue obtained under alkaline hydrothermal conditions (case b) is higher. From the perspective of the yield of the target humic acid, the yield of the humic acid obtained in the first waste liquid circulation test is 25.04 percent, and the yield is not obviously reduced. The invention further carries out a second cycle test, the result is similar to the first cycle test, and the yield of the target product humic acid is 27.13 percent and is not obviously reduced. Therefore, the wastewater reuse scheme not only ensures the yield of the target object, but also can save a large amount of water resources.

TABLE 2 influence of wastewater recycling after humic acid extraction on hydrothermal humification of straw

Note: in table 1, a indicates that the hydrothermal reaction is performed at pH 1; b means that the hydrothermal reaction is carried out under the environment of pH 1, and then the product is further subjected to the hydrothermal reaction under the environment of pH 13.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.