Method for preparing humic acid through ultrasonic-enhanced ozone oxidation depolymerization of lignite

Abstract

The invention discloses a method for preparing humic acid through ultrasonic-enhanced ozone oxidation depolymerization of lignite. An ultrasonic enhanced ozone oxidation depolymerization experiment is carried out on three types of lignite, including Shengli lignite (SL), Xiaolong Tan coal (XLT) and Mongdong lignite (MD), under mild conditions, so that the oxidation efficiency of the lignite can be effectively improved, and coal macromolecular structures are promoted to be cracked and converted into humic acid. Methanol is used as a solvent, the organic matter conversion rates of the three kinds of lignite SL, MD and XLT subjected to ultrasonic enhanced ozonation are 82.5%, 84.9% and 92.3% respectively, and the humic acid yields are 51.1%, 36.0% and 46.2% respectively; compared with single ultrasonic treatment and single ozone treatment, the organic matter conversion rate and the humic acid product yield of the ultrasonic enhanced ozone oxidation depolymerization SL are respectively increased by 69.0 / 42.9% and 44.7 / 36.4%. The method for preparing the humic acid through ultrasonic-enhanced ozone oxidation depolymerization of Shengli lignite provides a new thought for clean and efficient utilization of coal.

Description

Technical Field

[0001] The invention relates to the technical field of comprehensive utilization of lignite, and in particular to a method for preparing humic acid by ultrasonically enhanced ozone oxidation depolymerization of lignite. Background Art

[0002] my country has abundant lignite reserves. As a typical low-rank coal, it has the characteristics of high moisture, high ash content and low calorific value. How to use lignite efficiently and cleanly has become an urgent problem to be solved. Oxidative depolymerization is one of the main means of deep processing and utilization of lignite, which can produce many high-value-added oxygen-containing organic chemicals (such as lignite wax, humic acid, etc.), which can meet various needs of the national economy.

[0003] At present, the main methods to improve the humic acid yield of lignite include thermal oxidation, chemical oxidant oxidation, catalytic oxidation, microbial oxidation, etc. Chemical oxidation has a high impurity content, and the organic matter conversion rate of lignite is not high. The reaction cycle of the microbial dissolution method is long, which is not conducive to large-scale production. Due to its advantages such as strong oxidizing properties, mild and controllable oxidation conditions, fast reaction speed and mature production technology, ozone is expected to achieve precise regulation of the depth of oxidative depolymerization of lignite macromolecules under mild conditions, and promote the effective conversion of lignite macromolecules into soluble humic acid under mild conditions. In addition, ozone can react with C=C, attack the carbon atoms on the aromatic ring, destroy the aromatic ring structure or aliphatic bonds, generate hydroxyl or carbonyl groups, and thus produce a large number of oxygen-containing aromatic compounds. Oxidative cracking pre-treats the coal sample with oxidation to break the weak covalent bonds in the coal structure and achieve partial cracking of the coal macromolecular structure, which can effectively improve the humic acid yield. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing humic acid by depolymerizing lignite by ultrasonic enhanced ozone oxidation, which method has high conversion rate and yield of organic matter in the oxidized lignite.

[0005] To achieve the above object, the present invention provides a method for preparing humic acid by ultrasonically enhanced ozone oxidation depolymerization of Shengli lignite, comprising the following steps:

[0006] S1: grind lignite to less than 40 mesh to obtain coal powder; weigh the coal powder and add it to the solvent, the mass volume ratio of coal powder to solvent is 1g:10-50mL;

[0007] S2: Open the oxygen cylinder and adjust the oxygen input to the ozone generator to 0.5L / min and the ozone input to 0-60m 3 / h, the mixed gas of ozone and oxygen is directly introduced into the three-necked flask after passing through the ozone concentration detector; at the same time, the ultrasonic crusher is turned on, and the ultrasonic probe is directly inserted into the three-necked flask, and stirred at room temperature for 1 to 4 hours, and the lignite undergoes oxidation reaction under the conditions of ultrasonic-coupled ozone oxidation;

[0008] S3: After the oxidation reaction is completed, the mixture is centrifuged and filtered, the color of the liquid sample is photographed and recorded, the solid residue is washed twice with a solvent, all the filtered liquid samples are dried at 105°C overnight, and the evaporated solid samples are collected and weighed.

[0009] Preferably, the lignite used in S1 includes Shengli lignite (SL), Xiaolongtan lignite (XLT) and Mengdong lignite (MD).

[0010] Preferably, the solvent described in S2 is one of methanol, acetic acid or deionized water.

[0011] Preferably, the solvent used in S2 is methanol.

[0012] Preferably, the ozone input in S2 is 40m 3 / h.

[0013] Preferably, the oxidation reaction time in S2 is 3 h.

[0014] Preferably, the ultrasonic frequency in S3 is 20 kHz and the pulse is 3s, and the ultrasonic power is adjusted to 320-640W.

[0015] Preferably, the ultrasonic power is adjusted to 480W in S3.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. Ultrasonic-assisted oxidation allows the generation of hydroxyl radicals to attack lignite molecules, thereby allowing more oxygen to be incorporated into the macromolecular structure of lignite. This oxygen enrichment method helps to increase -OH and -COOH functional groups. In addition, the changes in the free radical concentration in the medium under the three conditions of ultrasonic physical field coupled to ozone chemical field system, ozone and ultrasound show that ultrasonic physical field coupled to ozone chemical field can effectively enhance the oxidation capacity within the reaction system.

[0018] 2. Ultrasound-enhanced ozone oxidation depolymerization experiments were conducted on three types of lignite, including Shengli lignite (SL), Xiaolongtan coal (XLT) and Mengdong lignite (MD). The organic combination of ultrasound-coupled ozone can effectively improve the oxidation efficiency of lignite and promote the cracking of coal macromolecular structure into humic acid. Using methanol as solvent, the organic matter conversion rates of SL, MD and XLT by ultrasound-enhanced ozone oxidation were 82.5, 84.9 and 92.3%, respectively, and the humic acid yields were 51.1, 36.0 and 46.2%, respectively; compared with ultrasound alone and ozone alone, the organic matter conversion rate / humic acid product yield of SL by ultrasound-enhanced ozone oxidation depolymerization increased by 69.0 / 42.9% and 44.7 / 36.4%, respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1Diagram of the ultrasonic enhanced ozone oxidation experimental device, in which: 1-oxygen cylinder, 2-ozone generator, 3-thermal collector constant temperature magnetic stirrer, 4-three-necked flask, 5-ultrasonic crusher, 6-ultrasonic probe, 7-potassium iodide solution.

[0020] Figure 2 Soluble components of SL oxidized by ultrasound-enhanced ozone in different solvents.

[0021] Figure 3 SL transformation diagram of ultrasound-enhanced ozone oxidation in different solvents.

[0022] Figure 4 Diagram of soluble components of SL oxidized by ultrasound-enhanced ozone at different ultrasonic powers.

[0023] Figure 5 Ultrasonic power gradient diagram of ultrasound-enhanced ozone oxidation of SL.

[0024] Figure 6 Soluble components of SL oxidized by ultrasound-enhanced ozone at different times.

[0025] Figure 7 Time gradient diagram of ultrasound-enhanced ozone oxidation of SL.

[0026] Figure 8 Diagram of soluble components of SL oxidized by ultrasound-enhanced ozone at different ozone input levels.

[0027] Fig. 9 Plot of the ozone input gradient for ozone oxidation of SL.

[0028] Fig.10 Figure 3 Soluble components of three types of lignite subjected to ultrasound-enhanced ozone oxidation.

[0029] Fig.11 Conversion diagram of three types of lignite after ultrasound-enhanced ozone oxidation.

[0030] Fig.12 XRD patterns of lignite and solid residues depolymerized by ultrasound-enhanced ozone oxidation.

[0031] Fig.13 Three-dimensional fluorescence image of humic acid in SL oxidized by ultrasound-enhanced ozone.

[0032] Fig.14 GPC chart of humic acid from SL oxidized by ultrasound-enhanced ozone.

[0033] Fig.15 FTIR spectrum of soluble components of SL oxidative depolymerization by ultrasound-enhanced ozone.

[0034] Fig.16 SEM image of lignite oxidative depolymerization by ultrasound-enhanced ozone.

[0035] Fig.17EPR diagram of ultrasound-enhanced ozone oxidation depolymerization of lignite. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] The following examples all adopt Figure 1 The ultrasonic enhanced ozone oxidation experimental device shown in the figure comprises an oxygen cylinder 1, an ozone generator 2, a heat collecting constant temperature magnetic stirrer 3, a three-necked flask 4 and an ultrasonic disruptor 5, wherein the air inlet end of the ozone generator 2 is connected to the oxygen cylinder 1, the air outlet end of the ozone generator 2 is connected to one flask port of the three-necked flask 4, the ultrasonic probe 6 of the ultrasonic disruptor 5 is inserted into another flask port of the three-necked flask 4, one flask port of the three-necked flask 4 is used as an exhaust gas outlet, and the exhaust gas interface is inserted into a 2% potassium iodide solution 7 for absorbing and decomposing ozone.

[0038] The abbreviations involved in the following embodiments are explained as follows:

[0039] ORA: Oxidized residue acetic acid, ORW: Oxidized residue water, ORM: Oxidized residue methanol; OLA: Oxidized liquid acetic acid, OLW: Oxidized liquid water, OLM: Oxidized liquid methanol; D: Dry.

[0040] Example 1

[0041] S1: Preparation of coal powder: grind lignite to a size of less than 40 meshes to obtain coal powder, wherein the lignite is selected from Shengli lignite (SL);

[0042] S2: Weigh 1.00 g of lignite into a three-necked flask 4, and add 30 mL of solvent (acetic acid, deionized water, methanol);

[0043] S3: Open the oxygen cylinder 1, adjust the oxygen input into the ozone generator 2 to 0.5L / min, control the ozone input, and pass the mixed gas of ozone and oxygen directly into the three-necked flask 4 after passing through the ozone concentration detector; at the same time, turn on the ultrasonic crusher 5, fix the ultrasonic frequency to 20kHZ and the pulse to 3s, adjust the ultrasonic power, and insert the ultrasonic probe 6 directly into the three-necked flask 4. At room temperature, due to the additional heat generated by the ultrasonic wave, the temperature is accurate to ±5°C, and the heat collecting constant temperature magnetic stirrer 3 is used for stirring. Keep at room temperature for 4h, and the lignite undergoes oxidation reaction under the conditions of ultrasonic coupled ozone oxidation;

[0044] S4: After the reaction is completed, the mixture is centrifuged and filtered to obtain a soluble liquid component. The color of the liquid sample is photographed and recorded. The solid residue is washed twice with a solvent and dried at 105°C overnight for weighing. All the liquid samples after filtration are dried at 105°C overnight to obtain soluble macromolecules, namely humic acid. The solid samples after evaporation are collected and weighed.

[0045] Oxidation experiments were conducted under the conditions of no ultrasound and no ozone (blank experiment), ultrasound alone, ozone alone, and ultrasound and ozone. The reaction conditions and related product numbers are shown in Table 1.

[0046] Table 1 Reaction conditions and related product numbers of ultrasonic enhanced ozone oxidation of lignite

[0047]

[0048]

[0049] Reaction conditions: 0.5 L / min oxygen feed, room temperature, ultrasonic frequency 20 kHz, pulse 3 s, 30 mL solvent.

[0050] like Figure 2 As shown in the figure, the soluble components of SL were depolymerized by ultrasound-enhanced ozone oxidation under different conditions. From left to right, the oxidation conditions are blank experiment, ultrasound alone, ozone alone, and ultrasound-ozone. Figure 4 It can be seen from a that when deionized water is used as the solvent, the color of the liquid product gradually deepens from colorless to dark brown. Figure 4 b It can be seen that when methanol is used as the solvent, the color of the liquid product gradually deepens from light yellow to brown. Figure 4 c It can be seen that when acetic acid is used as the solvent, the color of the liquid product gradually deepens from light yellow to brown. The results show that under the same conditions, the effect of ultrasound-coupled ozone oxidation depolymerization of lignite is better, and the color of the obtained liquid product is darker.

[0051] Depend on Figure 3It can be seen that the conversion rate of lignite organic matter gradually increased when comparing the oxidation experiments under four oxidation conditions: blank experiment, ultrasound alone, ozone alone, and ultrasound-ozone. Under the conditions of no ultrasound and no ozone, the oxidation effect was the worst, followed by ultrasound alone, and then ozone alone, which had a certain improvement. Finally, under ultrasound-coupled ozone, the oxidation effect was greatly improved. The results show that under the same conditions, ultrasound-coupled ozone oxidation depolymerization of lignite is more effective, and the lignite organic matter conversion rate and humic acid yield are higher. The three solvents of deionized water, methanol and acetic acid were compared. From left to right, there are four oxidation conditions: blank experiment, ultrasound alone, ozone alone and ultrasound ozone. The organic matter conversion rate and soluble matter yield of lignite showed a gradually increasing trend. When deionized water was used as the solvent, the oxidation conditions from left to right, the organic matter conversion rate and soluble matter yield of lignite gradually increased from 2.5% / 3.5% in the blank experiment to 63.8% / 37.5% in ultrasound ozone; when methanol was used as the solvent, the oxidation conditions from left to right, the organic matter conversion rate and soluble matter yield of lignite increased from 2.5% / 3.5% in the blank experiment to 63.8% / 37.5% in ultrasound ozone. The conversion rate of organic matter and the yield of soluble matter in lignite increased gradually from 7.1% / 1.3% in the blank experiment to 82.5% / 51.1% in ultrasonic ozone. When acetic acid was used as the solvent, the oxidation conditions from left to right, the conversion rate of organic matter and the yield of soluble matter in lignite increased gradually, from 7.7% / 6.8% in the blank experiment to 84.7% / 52.2% in ultrasonic ozone. The results showed that compared with deionized water and acetic acid, the effect of ultrasonic ozone oxidation depolymerization of lignite increased most rapidly when methanol was used as the solvent under the same conditions, and the obtained lignite organic matter conversion rate and soluble matter yield were higher.

[0052] Example 2

[0053] The preparation method is basically the same as that in Example 1, except that the experiments on the conversion rate of organic matter in Shengli lignite and the yield of humic acid obtained by varying the ultrasonic power (320W, 400W, 480W, 560W, 640W) in methanol solvent are different.

[0054] like Figure 4 As shown, it can be observed that the color of the liquid products is dark brown, and with the increase of ultrasonic power, there is no obvious change in the color of the liquid before and after.

[0055] Depend on Figure 5It can be seen that with the increase of ultrasonic power, the organic matter conversion rate and humic acid yield of lignite gradually increase. When methanol is used as solvent, the organic matter conversion rate of lignite is very high when the ultrasonic power is 320W. With the increase of ultrasonic power, the organic matter conversion rate of lignite also shows a gradual increasing trend, from 73.5% at 320W to 91.7% at 640W. The humic acid yield of lignite is low at 320W, which is 33.1%. With the increase of ultrasonic power, the humic acid yield of lignite also shows a gradual increasing trend, which increases to 51.1% at 480W. When the ultrasonic power is further increased, the humic acid yield does not change significantly. The results show that the organic matter conversion rate and humic acid yield of lignite with ultrasonic ozone oxidation depolymerization are higher when the ultrasonic power is 480W, and the oxidation depolymerization effect of lignite is better.

[0056] Example 3

[0057] The preparation method is basically the same as that in Example 1, except that the experiments in which the lignite organic matter conversion rate and humic acid yield are different as the oxidation time (1h, 2h, 3h, 4h) of Shengli lignite in methanol solvent is changed.

[0058] like Figure 6 As shown, with the increase of oxidation time, the color of the liquid product first deepened from reddish brown to dark brown, and then there was no obvious change in color.

[0059] Depend on Figure 7 It can be seen that with the increase of oxidation time, the conversion rate of organic matter in lignite gradually increases. When methanol is used as the solvent, with the increase of oxidation time, the conversion rate of organic matter in lignite increases from 35.3% at 1h to 82.5% at 3h. With the increase of oxidation time, the humic acid yield of lignite also shows a gradual increasing trend, from 18.4% at 1h to 51.1% at 3h. Further extending the oxidation time, the organic matter conversion rate and humic acid yield remain almost unchanged. The results show that the optimal oxidation time for ultrasonic ozone oxidation depolymerization of lignite is 3h, at which time the organic matter conversion rate and humic acid yield are higher, and the oxidation depolymerization effect is better.

[0060] Example 4

[0061] The preparation method is basically the same as that in Example 1, except that the Shengli lignite in methanol solvent changes with the ozone input (0, 20m 3 / h、40m 3 / h、60m 3 / h) to obtain different lignite organic matter conversion rates and humic acid yields.

[0062] like Figure 8 As shown, with the increase of ozone input, the color of the liquid product first deepened from light yellow to yellow-brown, and then there was no obvious color change.

[0063] Depend on Fig. 9 It can be seen that with the increase of ozone input, the conversion rate of organic matter and the yield of humic acid in lignite increased rapidly. When methanol was used as the solvent, when the ozone input was 0, the conversion rate of organic matter and the yield of humic acid were 13.5% and 8.2% respectively. 3 / h, the organic matter conversion rate and humic acid yield reached 58.3% and 39.3% respectively, while at an ozone input of 40m 3 / h, the organic matter conversion rate and humic acid yield increased rapidly, reaching 82.5% and 51.1% respectively. The organic matter conversion rate remained almost unchanged when the ozone input was further increased. The results showed that in the absence of ozone, the degree of oxidative depolymerization of lignite was very low. With the increase of ozone input, the oxidative depolymerization effect of lignite gradually improved. The optimal ozone input for ultrasonic ozone oxidative depolymerization of lignite was 40m 3 / h, at this time, the organic matter conversion rate and humic acid yield are higher, and the oxidative depolymerization effect is better.

[0064] Example 5

[0065] The preparation method is basically the same as that in Example 1, except that the lignite is selected from Mengdong lignite (MD)

[0066] Oxidation experiments were conducted under the conditions of no ultrasound and no ozone (blank experiment), ultrasound alone, ozone alone, and ultrasound and ozone. The reaction conditions and related product numbers are shown in Table 2.

[0067] Table 2 Reaction conditions and related product numbers of ultrasonic enhanced ozone oxidation of lignite

[0068]

[0069] Reaction conditions: 0.5 L / min oxygen feed, room temperature, ultrasonic frequency 20 kHz, pulse 3 s, 30 mL solvent.

[0070] Example 6

[0071] The preparation method is basically the same as that of Example 1, except that the lignite is selected from Xiaolongtan coal (XLT).

[0072] Oxidation experiments were conducted under the conditions of no ultrasound and no ozone (blank experiment), ultrasound alone, ozone alone, and ultrasound and ozone. The reaction conditions and related product numbers are shown in Table 3.

[0073] Table 3 Reaction conditions and related product numbers of ultrasonic enhanced ozone oxidation of lignite

[0074]

[0075]

[0076] Reaction conditions: 0.5 L / min oxygen feed, room temperature, ultrasonic frequency 20 kHz, pulse 3 s, 30 mL solvent.

[0077] The calculation process of organic matter conversion rate, soluble matter yield and solvent recovery rate is as follows:

[0078]

[0079] Where: m a ——initial mass of raw coal, g;

[0080] m b ——mass of oxidation solid residue, g;

[0081] m c ——Soluble macromolecular mass, g;

[0082] m d ——Mass of solvent recovered after reaction, g;

[0083] m e ——Mass of feed before reaction, g.

[0084] M ad and A ad ——are respectively the moisture content and ash content of the raw coal on an air-dried basis, %;

[0085] M′ ad and A′ ad ——are respectively the air-dried basis moisture and ash content of the oxidized solid residue, %;

[0086] M″ ad and A″ ad ——Water content and ash content on air-dried basis of soluble macromolecules, %;

[0087] The moisture and ash content of each sample are based on air-dried basis and obtained by industrial analysis. Through industrial analysis of oxidation products, it is found that the ash content in soluble macromolecules accounts for about 1-2%, indicating that the ash mainly remains in the solid residue; all samples are dried at 105°C overnight, and the industrial analysis results show that there is almost no moisture in the oxidation products, so in order to simplify the calculation, the solid residue and soluble macromolecules are not tested one by one.

[0088] The ultrasonic enhanced ozone oxidation depolymerization experiments of three kinds of lignite including Shengli lignite (SL), Xiaolongtan coal (XLT) and Mengdong lignite (MD) were investigated. Fig.10 As shown in the figure, the color of the liquid products of the three types of lignite ozonation gradually deepens from colorless to light yellow and finally turns to yellow-brown. Compared with XLT and MD, the color of the liquid product after SL ultrasonic enhanced ozone oxidation is obviously darker.

[0089] like Fig.11 As shown in the figure, the three types of lignite were compared under blank experiment, ultrasound alone, ozone alone, and ultrasound-ozone oxidation. It can be observed that the liquid color gradually deepened and the organic matter conversion rate gradually increased. In particular, the organic matter conversion rate and humic acid yield were significantly improved after ultrasound-ozone oxidation. Fig.11 As shown in the results, the organic matter conversion rate of SL under ultrasonic ozone conditions was 82.5%, and the humic acid yield after oxidative depolymerization was 51.1%; the organic matter conversion rate of MD under ultrasonic ozone conditions was 84.9%, and the humic acid yield after oxidative depolymerization was 36.0%. The organic matter conversion rate of XLT under ultrasonic ozone conditions was 92.3%, and the humic acid yield after oxidative depolymerization was 46.2%; the results show that ultrasound-coupled ozone oxidation can further improve the conversion of organic matter in lignite into humic acid. The corresponding results show that lignite can be effectively converted into humic acid by ultrasound-enhanced ozone oxidation, and the obtained humic acid can be dissolved in solvents such as methanol, ethanol, tetrahydrofuran, acetic acid, alkali solution and water. The ultrasonic-enhanced ozone oxidation depolymerization experiment was carried out at room temperature. For the methanol solvent used, the solvent recovery rate can be guaranteed to be above 98.5%.

[0090] The oxidized solid residues of various lignites and SL were characterized and analyzed.

[0091] 1. Elemental analysis of the oxidized solid residues and corresponding humic acid products of three types of lignite and SL was carried out.

[0092] As shown in Table 4, compared with MD and XLT, the carbon content, hydrogen content and sulfur content in SL raw coal are lower, the oxygen content is higher, and the O / C ratio is higher; compared with SL raw coal, the carbon content, oxygen content and O / C ratio in the solid residues of ultrasound alone, ozone alone and ultrasonic ozone after oxidative depolymerization decrease in turn, while the hydrogen content and H / C ratio increase. The carbon content, oxygen content, hydrogen content, O / C ratio and H / C ratio in the oxidation products of ultrasound alone, ozone alone and ultrasonic ozone after oxidative depolymerization increase in turn. Compared with ultrasound alone and ozone alone, the carbon content, hydrogen content, oxygen content, H / C ratio and O / C ratio in the humic acid oxidation products of SL depolymerized by ultrasound-coupled ozone are higher. The results show that the process of SL oxidative depolymerization by ultrasound-coupled ozone causes oxygen atoms to gradually enter the oxidation products, and the oxidation products contain relatively more oxygen-containing functional groups.

[0093] Table 4 Elemental analysis results of different samples

[0094]

[0095] a : Subtraction method

[0096] 2. Industrial analysis of three types of lignite and SL ultrasonic coupled ozone oxidation solid residues.

[0097] As shown in Table 5, compared with MD and XLT, the moisture and ash content in SL raw coal are higher, and the volatile matter is lower; compared with SL raw coal, the moisture content in the solid residue after oxidative depolymerization is reduced, and the ash and volatile matter are increased. Compared with ultrasound alone and ozone alone, there is more ash, less volatile matter and fixed carbon in the solid residue of SL depolymerization by ultrasound-coupled ozone. The results show that the ultrasound-coupled ozone oxidation process mainly decomposes and decomposes the organic matter in the lignite, and the ash remains in the solid residue. Compared with ultrasound alone and ozone alone, the gradual increase in the ash content of ultrasonic ozone further illustrates the enrichment of ash in the solid oxidized slag.

[0098] Table 5 Industrial analysis results of different samples

[0099]

[0100] 3. XRD analysis of ultrasonic enhanced ozone oxidation depolymerization of lignite and solid residue.

[0101] like Fig.12 As shown in the figure, from the XRD spectrum, it can be seen that SL lignite and oxidized solid residue show different characteristic peaks. An obvious characteristic diffraction peak can be observed at a 2θ value of about 27°, which belongs to SiO2, the main component of ash in the coal sample; the intensity of the SiO2 diffraction peak gradually increases (ultrasound alone < ozone alone < ultrasound ozone), indicating that ash accumulates in the solid oxidized slag. Since the SiO2 diffraction peaks of different raw coal samples and oxidized slag are almost the same, it means that the ash composition has not changed during the oxidation process and still exists in the oxidized slag, which is consistent with the above industrial analysis and characterization results.

[0102] 4. Three-dimensional fluorescence spectroscopy (3D-EEM) analysis of ultrasonic enhanced ozone oxidation depolymerization of humic acid in SL.

[0103] Depend on Fig.13It can be seen that the maximum excitation wavelength of ultrasound alone (a), ozone alone (b) and ultrasonic ozone (c) is around 350nm, and the fluorescence intensity is ultrasound alone>ozone alone>ultrasonic ozone, among which ultrasonic ozone has the smallest fluorescence intensity at the maximum emission wavelength. Ultrasonic ozone contains a lower level of conjugated fluorophores and a simpler aromatic structure, indicating that ultrasound-coupled ozone oxidative cracking of lignite macromolecular structure, which is consistent with several other characterization results. The maximum emission wavelength range of humic acid for ultrasound alone, ozone alone and ultrasonic ozone is 400-450nm, and Ex / Em is in the range of 250-400nm / 380-500nm. The maximum values ​​of the excitation / emission wavelengths of these three substances appear almost the same, indicating that they have similar structures and components. This is quite consistent with the fluorescence characteristics of humic acid, and the fluorescence emission spectrum of humic acid has at least one peak. When the degree of aromatization of humic acid increases, the wave number of its peak increases.

[0104] 5. GPC analysis of humic acid from SL oxidized by ultrasonic enhanced ozone.

[0105] Depend on Fig.14 It can be seen that the molecular weight of the humic acid product of ultrasonic enhanced ozone oxidation depolymerization of SL was determined by gel chromatography (GPC). The molecular weight of the humic acid products of ultrasound alone, ozone alone and ultrasound ozone are mainly concentrated in the range of 250-1500Da, and the molecular weight (Mw) of ultrasound, ozone, and ultrasound-ozone treatment is 579, 545, and 650, respectively. Compared with ultrasound alone oxidation, the molecular weight of HA is significantly reduced when ozone is oxidized alone, indicating that ozone destroys the structure of lignite and increases its solubility in the solvent. According to the molecular weight distribution results, it can be seen that the obtained product is mainly humic acid.

[0106] 6. FTIR analysis of soluble components of SL oxidative depolymerization by ultrasonic enhanced ozone.

[0107] Depend on Fig.15 It can be seen that the infrared characteristic peaks of the soluble components are similar, both at about 3425 cm -1 There is an obvious broad peak at 1800-1500 cm -1 There is an obvious double peak at about 1714 cm -1 The peak at about 1629 cm -1The characteristic peak at 2925cm-1 is attributed to the stretching vibration of the C=C bond in the aromatic group and the C=CO vibration conjugated with the carbonyl group. As the ultrasonic power increases, the relative content of the carboxyl functional group gradually increases; compared with ultrasound alone and ozone alone, the relative content of the carboxyl functional group of ultrasound-enhanced ozone is higher, indicating that ultrasound-coupled ozone oxidation can significantly improve the oxidation efficiency, and the ability to enrich oxygen increases with the increase of ultrasonic power. At about 2925cm-1 -1 and 2855cm -1 A small characteristic peak appears at 1401 cm -1 The characteristic peak at 1270 cm-1 is attributed to the asymmetric stretching of the COO- group and the deformation vibration of the methyl and methylene groups in the ring structure and the CH bond in the tert-butyl group. -1 The characteristic peaks at are caused by the stretching vibration of the CO bond (ester, ether and phenol, etc.), the stretching vibration of the CO bond in the carboxyl group and the deformation vibration of the OH.

[0108] 7. SEM analysis of ultrasonic enhanced ozone oxidation depolymerization of lignite.

[0109] SEM characterization was used to observe the morphological characteristics of the solid residue of SL after ultrasonic enhanced ozone oxidation. Fig.16 As shown in the figure, compared with the blank experiment, ultrasound alone and ozone alone, after ultrasound-enhanced ozone oxidation, the lignite sample was oxidized more fully, more organic matter was precipitated, the surface became very rough, and more pore structures were formed on the surface; the untreated solid residue had a rough microscopic surface, the surface treated with ultrasound alone formed more pore structures, and the surface treated with ozone alone began to have a laminar structure. A large number of closely parallel layers or flaky structures appeared in the microstructure of the solid residue after ultrasound-coupled ozone oxidation.

[0110] 8. EPR analysis of ultrasonic enhanced ozone oxidation depolymerization of lignite.

[0111] EPR characterization is used to determine hydroxyl radicals under different processes. Fig.17 As shown in the figure, the changes in the free radical concentration in the medium under the three conditions of ultrasonic physical field coupled ozone chemical field system, ozone and ultrasound show that the peak intensity of hydroxyl radicals is low when ozone and ultrasound are used alone, and the quantitative data are 0.696×e 4 and 1.660×e 4 The combined effect of ultrasound coupled with ozone significantly increased the peak intensity of hydroxyl radicals, with a quantified value of 2.468×e 4. Hydroxyl radicals are strong oxidizing substances that can quickly and effectively achieve oxidative depolymerization of macromolecular organic matter. The total amount of hydroxyl radicals produced by the ultrasonic ozone process is significantly higher than that of the other two systems. The results show that the ultrasonic-coupled ozone system greatly promotes the formation of hydroxyl radicals and effectively enhances the oxidation efficiency of the reaction system, confirming the synergistic effect of the ultrasonic-coupled ozone advanced oxidation system. Therefore, ultrasound-enhanced ozone oxidation is a promising method for the efficient extraction of humic acid from coal.

Claims

1. A method for preparing humic acid by depolymerizing lignite by ultrasonic enhanced ozone oxidation, characterized in that: The specific steps include: S1: grind lignite to less than 40 mesh to obtain coal powder; weigh the coal powder and add it to the solvent, the mass volume ratio of coal powder to solvent is 1g:10-50mL; S2: Open the oxygen cylinder and adjust the oxygen input to the ozone generator to 0.5L / min and the ozone input to 0-60m 3 / h, the mixed gas of ozone and oxygen is directly introduced into the three-necked flask after passing through the ozone concentration detector; at the same time, the ultrasonic crusher is turned on, and the ultrasonic probe is directly inserted into the three-necked flask, and stirred at room temperature for 1 to 4 hours, and the lignite undergoes oxidation reaction under the conditions of ultrasonic-coupled ozone oxidation; S3: After the oxidation reaction is completed, the mixture is centrifuged and filtered, the color of the liquid sample is photographed and recorded, the solid residue is washed twice with a solvent, all the filtered liquid samples are dried at 105°C overnight, and the evaporated solid samples are collected and weighed.

2. The method for preparing humic acid by ultrasonically enhanced ozone oxidation depolymerization of lignite according to claim 1, characterized in that: The lignite used in the S1 includes Shengli lignite, Xiaolongtan coal and Mengdong lignite.

3. The method for preparing humic acid by ultrasonically enhanced ozone oxidation depolymerization of lignite according to claim 1, characterized in that: The solvent used in S2 is one of methanol, acetic acid or deionized water.

4. The method for preparing humic acid by ultrasonically enhanced ozone oxidation depolymerization of lignite according to claim 3, characterized in that: The solvent used in S2 is methanol.

5. The method for preparing humic acid by ultrasonically enhanced ozone oxidation depolymerization of lignite according to claim 1, characterized in that: The ozone input in S2 is 40m 3 / h.

6. The method for preparing humic acid by ultrasonically enhanced ozone oxidation depolymerization of lignite according to claim 1, characterized in that: The oxidation reaction time in S2 is 3h.

7. The method for preparing humic acid by ultrasonically enhanced ozone oxidation depolymerization of lignite according to claim 1, characterized in that: The ultrasonic frequency in S3 is 20 kHz and the pulse is 3s, and the ultrasonic power is adjusted to 320-640W.

8. The method for preparing humic acid by ultrasonically enhanced ozone oxidation depolymerization of lignite according to claim 5, characterized in that: In the S3, the ultrasonic power is adjusted to 480W.

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