Method for producing nitro-humic acid by nitric acid-ozone combined oxidation of lignite

Abstract

This invention discloses a method for producing nitrohumic acid from lignite through a combined nitric acid-ozone oxidation process. Dilute nitric acid is added to ground coal powder, followed by water bath treatment and two ozone oxidation experiments to obtain nitrohumic acid. Nitric acid attacks the aromatic rings and aliphatic side chains in the coal macromolecular structure, leading to the initial degradation of the coal's macromolecular network structure. Then, oxygen free radicals generated by ozone attack the stronger bridging bonds in the coal, further breaking them down and resulting in deep depolymerization of the coal macromolecular structure. Acetic acid is used as the solvent in the ozone oxidation experiment. Through two ozone oxidation processes to modify nitric acid-modified Shengli lignite (NASL), oxidized solid residue and oxidation products are obtained. The organic matter conversion rate of ozone oxidation depolymerization of NASL is 81.55%, and the solvent-soluble yield is 82.38%. The combined nitric acid and ozone oxidation method for the stepwise degradation of Shengli lignite demonstrates that this combined nitric acid and ozone oxidation depolymerization method is a promising approach for the efficient extraction of nitrohumic acid from coal.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization technology of lignite, specifically to a method for producing nitrohumic acid from lignite by combined nitric acid-ozone oxidation, and particularly to a method for preparing humic acid from lignite by ozone oxidation and depolymerization modification. Background Technology

[0002] Oxidative depolymerization is one of the most important methods for the deep processing and utilization of lignite, yielding numerous high-value-added oxygen-containing organic chemicals (such as lignite wax and humic acid), which can meet various needs of the national economy. Currently, methods to improve the yield of humic acid extracted from lignite mainly include thermal oxidation, chemical oxidant oxidation, catalytic oxidation, and microbial oxidation. Microbial dissolution has a long reaction cycle, which is not conducive to large-scale production; thermal oxidation is energy-intensive and its oxidation effect is not significant; while in catalytic oxidation, coal and catalyst are difficult to separate, leading to difficulties in recycling. Chemical pretreatment has advantages such as rapid activation, low cost of chemical reagents, mild reaction conditions, and environmental friendliness, and is therefore widely used in coal pretreatment. However, in practical industrial applications, chemical treatment has problems of over-oxidation and environmental risks. In pure chemical pretreatment, controlling the degree of oxidation is not easy; over-oxidation leading to chemical degradation may alter the structure of the extracted humic acid and reduce its biological activity. Given the limitations of the above oxidation methods, developing an efficient strategy is imperative. Combining chemical pretreatment with other oxidation methods (such as alkaline oxidation, hydrogen peroxide oxidation, sodium hypochlorite oxidation, or ozone oxidation) is a common approach to obtaining high-quality humic acid and controlling the degree of oxidation. Recently, ozone has been applied to the oxidative depolymerization of coal due to its advantages, including high oxidative activity, mild and controllable oxidation conditions, fast reaction rate, and mature production technology. Therefore, seeking an efficient oxidation method to improve the organic matter conversion rate and nitrohumic acid yield of lignite is of great significance. Summary of the Invention

[0003] The purpose of this invention is to provide a method for producing nitrohumic acid from lignite through the combined oxidation of nitric acid and ozone. This method can improve the organic matter conversion rate of lignite and the yield of humic acid, while reducing the impurity content in the humic acid.

[0004] To achieve the above objectives, the present invention provides a method for producing nitrohumic acid from lignite through nitric acid-ozone combined oxidation, comprising the following steps:

[0005] S1. Grind the lignite raw material to below 40 mesh to obtain lignite powder;

[0006] S2. Take the lignite powder treated in step S1, add it to 1-4 mol / L dilute nitric acid, treat it in a water bath at 30-90℃, filter and wash it until neutral, and then vacuum dry it to obtain lignite modified by nitric acid, named NASL.

[0007] S3. The NASL obtained in step S2 is subjected to the first ozone oxidation treatment using a mixture of ozone and oxygen. After the oxidation reaction is completed, the mixture is centrifuged and filtered. The solid residue after filtration is washed with solvent and then filtered again. The solid sample obtained after filtration is the first solid residue of nitric acid modified lignite oxidation. All the filtrates in this step are combined and dried. The solid sample obtained after drying is the first oxidation product of nitric acid modified lignite, which is humic acid.

[0008] S4. Repeat the S3 operation on the solid residue obtained in S3 to obtain the solid residue of nitric acid modified lignite after the second oxidation.

[0009] Preferably, in step S2, the water bath treatment time is 1-10 hours.

[0010] Preferably, in step S2, the mass-to-volume ratio of lignite powder to dilute nitric acid is 1:10 g / mL.

[0011] Preferably, in step S2, the concentration of the dilute nitric acid is 2 mol / L, the water bath treatment temperature is 70°C, and the treatment time is 2 h.

[0012] Further, the ozone oxidation process in step S3 is as follows: Weigh NASL and place it in a three-necked flask, add solvent, and connect the device; then, open the oxygen cylinder, and introduce ozone generated by the ozone generator into the reactor. Adjust the oxygen inflow rate to 0.5 L / min and the ozone output rate to 0-0.375 L / min. Directly introduce the ozone and oxygen mixture into the three-necked flask. The ozone amount is detected by an ozone concentration detector. Heat and stir at 30°C for 1-4 hours to allow the oxidation reaction to occur.

[0013] Preferably, the solvent in the ozone oxidation process of step S3 is methanol or acetic acid, the ozone output is 0.250 L / min, and the oxidation reaction takes place for 3 hours.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] (1) In this invention, nitric acid releases HNO3, HNO2, N2O and active oxygen atoms with strong electrophilicity to attack the aromatic rings and aliphatic side chains in the macromolecular structure of coal, resulting in the initial degradation of the macromolecular network structure in coal. Then, the oxygen free radicals generated by ozone attack the strong bridging bonds in coal to further crack them, resulting in the deep depolymerization of the coal macromolecular structure. Under mild conditions, the depth of oxidative depolymerization of lignite macromolecules is precisely controlled, which promotes the effective conversion of lignite macromolecules into nitrohumic acid under mild conditions.

[0016] (2) This invention uses a combination of nitric acid and ozone oxidation to degrade Shengli lignite stepwise. The strong oxidizing properties of nitric acid are used to destroy the condensed aromatic rings and aliphatic side chain structures in the macromolecular structure of coal. Then, ozone oxidation is used to achieve further deep transformation of the solid residue, gradually destroying the polycyclic aromatic hydrocarbon structure in the coal and realizing the staged oxidation and depolymerization of organic matter in the coal. The organic matter conversion rate and solvent soluble yield of ozone oxidation and depolymerization of nitric acid-modified Shengli lignite (NASL) are 82.48% and 72.75%, respectively. In the cycle experiment, after the second cycle of oxidation, the total conversion rate of NASL reached 81.55%, and the total macromolecular product yield was 82.38%. Attached Figure Description

[0017] Figure 1 Diagram of ozone oxidation experimental setup: 1-Oxygen cylinder, 2-Ozone generator, 3-Ozone concentration detector, 4-Heat-collecting constant-temperature magnetic stirrer, 5-Three-necked flask, 6-Potassium iodide solution.

[0018] Figure 2 Oxidation products (a) and solid products (b) of ozone oxidation of nitric acid-modified lignite.

[0019] Figure 3 Time gradient diagram of ozone oxidation of nitric acid to modify Shengli lignite.

[0020] Figure 4 Ozone gradient diagram of ozone oxidation of nitric acid in Shengli lignite.

[0021] Figure 5 The oxidation products (a) and solid products (b) of the ozone oxidation cycle experiment of nitric acid-modified Shengli lignite.

[0022] Figure 6 XRD patterns of ozone-oxidized nitric acid-modified lignite and solid residue.

[0023] Figure 7 FTIR images of ozone oxidation of polynitrate-modified lignite, oxidation products and solid residues; (a) raw coal and solid oxidation residues, (b) oxidation products.

[0024] Figure 8 GPC diagrams of oxidation products of ozone-oxidized nitric acid-modified Shengli lignite, where (a) is NASL-HA, (b) is NASL-C1-HA, and (c) is NASL-C2-HA.

[0025] Figure 9 XPS image of the oxidation products of ozone-oxidized nitric acid-modified lignite.

[0026] Figure 10 SEM image of ozone-oxidized nitric acid-modified Shengli lignite. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] The lignite used in the following implementation is Shengli lignite.

[0029] The following embodiments all adopt the following... Figure 1 The diagram shows an experimental setup for the combined oxidation of nitric acid and ozone in Shengli lignite. This setup includes an oxygen cylinder 1, an ozone generator 2, an ozone concentration detector 3, a heat-collecting constant-temperature magnetic stirrer 4, a three-necked flask 5, and an ultrasonic disruptor. The inlet of the ozone generator 2 is connected to the oxygen cylinder 1, and the outlet of the ozone generator 2 passes through the ozone concentration detector 3 and connects to one flask opening of the three-necked flask 5. The ultrasonic probe of the ultrasonic disruptor is inserted into the other flask opening of the three-necked flask 5. One flask opening of the three-necked flask 5 serves as the exhaust outlet, and the exhaust outlet is inserted into a 2% potassium iodide (KI) solution 6 containing ozone absorber and decomposer.

[0030] Example 1

[0031] A method for producing nitrohumic acid from lignite through nitric acid-ozone combined oxidation includes the following steps:

[0032] S1. Grind Shengli lignite to below 40 mesh to obtain coal powder;

[0033] S2. Take 10g of Shengli lignite treated in step S1, stir it with 100mL of 2mol / L dilute nitric acid solution at 70℃ for 2h, filter it and vacuum dry it overnight to obtain lignite modified with nitric acid, named NASL.

[0034] S3. In a typical oxidation experiment, 1.00 g of NASL was weighed and placed in a three-necked flask, 30 mL of acetic acid was added, and the apparatus was connected. Then, the oxygen cylinder was opened, and ozone generated by the ozone generator was introduced into the reactor. The oxygen inflow rate was adjusted to 0.5 L / min, and the ozone output rate was 0.250 L / min. The ozone and oxygen mixture was passed through an ozone concentration detector and then directly introduced into the three-necked flask. The ozone concentration was detected by the ozone concentration detector. At room temperature (30°C), a heat-collecting constant-temperature magnetic stirrer was used for heating and stirring. The oxidation reaction was carried out for 3 hours. After the reaction was completed, the mixture was centrifuged and filtered. The color of the liquid sample was photographed and recorded. The solid oxidation residue was washed twice with solvent and dried overnight at 105°C. All the filtered liquid samples were dried overnight at 105°C. The solid samples after evaporation were collected and weighed. The obtained solid sample is the nitric acid-modified lignite oxidation product, named NASL-HA. The solid sample obtained after washing is the nitric acid-modified lignite oxidation solid residue, named NASL-OR.

[0035] S4. For cyclic oxidative depolymerization, a mixture of ozone and oxygen was used to oxidize 4.00 g of NASL in 50 mL of acetic acid. The specific oxidation process was repeated in step S3, yielding nitric acid-modified lignite primary solid residue (NASL-C1-OR) and nitric acid-modified primary oxidation product (NASL-C1-HA). A second cyclic ozone oxidation experiment was then conducted on the nitric acid-modified lignite primary solid residue under the same conditions as in step S3. After the oxidation reaction was completed, the mixture was centrifuged and filtered. The filtered solid residue was washed with solvent and then filtered again. All filtrates from this step were combined and dried. The solid sample obtained after drying was the nitric acid-modified lignite secondary oxidation product (NASL-C2-HA), and the solid sample obtained after washing was the nitric acid-modified lignite secondary oxidation solid residue (NASL-C2-OR).

[0036] The calculation process for organic matter conversion rate, soluble matter yield, and solvent recovery rate is as follows:

[0037]

[0038] Where: m a —Initial mass of nitric acid-modified Shengli lignite, g;

[0039] m b —Mass of oxidized solid residue, g;

[0040] m c —Soluble macromolecular mass, g;

[0041] m d —Mass of solvent recovered after reaction, in g;

[0042] m e —Mass of feed material before reaction, in grams.

[0043] M ad and A ad —These are the air-dried moisture and ash content of raw coal, respectively, in %;

[0044] M′ ad and A′ ad —representing air-dried moisture and ash content of the oxidized solid residue, %;

[0045] A″ d — Ash content of soluble macromolecules on a dry basis, %;

[0046] Moisture and ash content of each sample were determined by industrial analysis. Industrial analysis of the oxidation products revealed that ash content was approximately 1%, indicating that ash mainly remained in the solid residue. All samples were dried overnight at 105°C, and industrial analysis results showed that the oxidation products contained almost no moisture.

[0047] Comparative Example 1

[0048] The difference from Example 1 is that step S2 in Example 1 is omitted, and the oxidation experiment is carried out directly with the Shengli lignite (SL) obtained in step S1.

[0049] Example 2

[0050] The difference from Example 1 is that "30 mL acetic acid" in step S3 is replaced with "30 mL methanol", while the other steps remain the same as in Example 1.

[0051] Comparative Example 2

[0052] The difference from Example 2 is that step S2 in Example 2 is omitted, and the oxidation experiment is carried out directly with the Shengli lignite (SL) obtained in step S1.

[0053] Table 1. Experimental results of ozone oxidation of different types of lignite.

[0054]

[0055] As shown in Table 1, the conversion rate and nitrohumic acid yield of untreated Shengli lignite were relatively low. The oxidation effect was significantly improved after nitric acid modification, resulting in a substantial increase in both organic matter conversion and nitrohumic acid yield. Using acetic acid as a solvent, nitric acid-modified Shengli lignite was oxidized to obtain oxidized solid residue and nitrohumic acid via ozone oxidation, with significantly improved conversion and yield. The conversion rate / nitrohumic acid yield of ozone oxidation depolymerization of NASL was 82.48% and 72.75%, respectively. In contrast, using methanol as a solvent, the conversion rate / nitrohumic acid yield of ozone oxidation depolymerization of NASL was 75.41% and 63.42%, respectively.

[0056] Table 2. Results of ozone oxidation experiments on lignite pretreated with nitric acid under different conditions.

[0057]

[0058] Comparative Example 3

[0059] The difference from Example 1 is that in step S2, the concentration of dilute nitric acid is set to 1-4 mol / L and the pretreatment temperature is set to 30°C, while the other steps remain the same as in Example 1.

[0060] The effects of different nitric acid concentrations (1-4 mol / L) on the conversion rate of NASL oxidized by ozone and the yield of nitrohumic acid were studied. With the gradual increase of nitric acid concentration, the organic matter conversion rate and the yield of nitrohumic acid showed a trend of first increasing and then decreasing. The conversion rate and product yield were the highest when the nitric acid concentration was 2 mol / L, which were 78.65% and 63.52%, respectively.

[0061] Comparative Example 4

[0062] The difference from Example 1 is that in step S2, the pretreatment temperature of dilute nitric acid is set to 30-90℃, while the other steps remain the same as in Example 1.

[0063] The effects of different nitric acid pretreatment temperatures (30-90℃) on the conversion rate and nitrohumic acid yield of ozone oxidation of NASL were studied. As the treatment temperature gradually increased, the organic matter conversion rate increased slowly, while the nitrohumic acid yield showed a trend of first increasing and then decreasing. The highest conversion rate and product yield were achieved at a treatment temperature of 70℃, which were 82.48% and 72.75%, respectively.

[0064] Example 3

[0065] The difference from Example 1 is that "oxidation reaction for 3 hours" in step S3 is replaced with "oxidation reaction for 1 hour", while the other steps remain the same as in Example 1.

[0066] Example 4

[0067] The difference from Example 1 is that "oxidation reaction for 3 hours" in step S3 is replaced with "oxidation reaction for 2 hours", while the other steps remain the same as in Example 1.

[0068] Example 5

[0069] The difference from Example 1 is that "oxidation reaction for 3 hours" in step S3 is replaced with "oxidation reaction for 4 hours", while the other steps remain the same as in Example 1.

[0070] like Figure 2 As shown in (a), with increasing oxidation time, the liquid product first darkens in color, changing from reddish-brown to dark brown, and then turns completely yellow. Figure 3 It can be seen that with the increase of oxidation time, the organic matter conversion rate of nitric acid-modified Shengli lignite gradually increases, while the nitrohumic acid yield of nitric acid-modified Shengli lignite first increases and then decreases. When acetic acid is used as a solvent, with the increase of oxidation time, the organic matter conversion rate / nitrohumic acid yield of lignite increases from 25.55 / 21.71% at 1 h to 82.48 / 72.75% at 3 h. Further extending the oxidation time to 4 h, the increase in organic matter conversion rate is not significant (86.14%), and the nitrohumic acid yield decreases slightly (55.90%) due to over-oxidation of the product caused by the longer oxidation time. The results indicate that the optimal oxidation time for ozone oxidation and depolymerization of nitric acid-modified Shengli lignite is 3 h, at which time the organic matter conversion rate and humic acid yield are higher, and the oxidation and depolymerization effect is better.

[0071] Example 6

[0072] The difference from Example 1 is that "ozone output is 0.25L / min" in step S3 is replaced with "ozone output is 0.125L / min", while the other steps remain the same as in Example 1.

[0073] Example 7

[0074] The difference from Example 1 is that "ozone output is 0.25L / min" in step S3 is replaced with "ozone output is 0.375L / min", while the other steps remain the same as in Example 1.

[0075] Comparative Example 3

[0076] The difference from Example 1 is that "ozone output is 0.25L / min" in step S3 is replaced with "ozone output is 0L / min", while the other steps remain the same as in Example 1.

[0077] like Figure 2 As shown in (a), with the increase of ozone concentration, the color of the liquid product first deepens, changing from reddish-brown to dark brown, and then the color lightens slightly. Figure 2 (b) is the solid product of ozone oxidation of successfully modified lignite with nitric acid. Figure 4 It can be seen that with the increase of ozone concentration, the organic matter conversion rate of nitric acid-modified lignite gradually increases, while the nitrohumic acid yield of nitric acid-modified lignite first increases and then decreases. When acetic acid is used as a solvent, with the increase of ozone concentration, the ratio of organic matter conversion rate / nitrohumic acid yield of lignite decreases from 0% to 0%. 3 The organic matter conversion rate increased from 16.24% / 13.32% at an ozone input rate of 0.25 L / min to 82.48% / 72.75%. Further increasing the ozone input rate increased the organic matter conversion rate to 84.06%, while the nitrohumic acid yield decreased significantly to 66.21% due to excessive oxidation of the product caused by the high ozone concentration. The results indicate that the degree of oxidative depolymerization of lignite is very low in the absence of ozone. With increasing ozone input, the oxidative depolymerization effect of lignite gradually improves. The optimal ozone input rate for successful ozone oxidative depolymerization of nitric acid-modified lignite is 0.25 L / min, at which point the organic matter conversion rate and humic acid yield are higher, and the oxidative depolymerization effect is better.

[0078] Example 8

[0079] A method for producing nitrohumic acid from lignite through nitric acid-ozone combined oxidation includes the following steps:

[0080] S1. Grind Shengli lignite to below 40 mesh to obtain coal powder;

[0081] S2. Take 10g of Shengli lignite treated in step S1, stir it with 100mL of 2mol / L dilute nitric acid solution at 70℃ for 2h, filter it and vacuum dry it overnight to obtain lignite modified with nitric acid, named NASL.

[0082] S3. The first ozone oxidation experiment was conducted on the NASL obtained in step S2 using a mixture of ozone and oxygen. The specific procedure was as follows: In a typical oxidation experiment, 4.00g of... NASL was placed in a three-necked flask, 50 mL of acetic acid was added, and the apparatus was connected. Then, the oxygen cylinder was turned on, and ozone generated by the ozone generator was introduced into the reactor. The oxygen inflow rate was adjusted to 0.5 L / min, and the ozone output rate was 0.25 L / min. The ozone and oxygen mixture was directly introduced into the three-necked flask after passing through an ozone concentration detector. The ozone concentration was detected by the ozone concentration detector. At room temperature (30℃), the mixture was heated and stirred using a heat-collecting constant-temperature magnetic stirrer for 3 hours to carry out the oxidation reaction. After the reaction was completed, the mixture was centrifuged and filtered. The color of the liquid sample was photographed and recorded. The solid oxidation residue was washed twice with solvent and dried overnight at 105℃ and weighed. All the filtered liquid samples were dried overnight at 105℃, and the solid samples after evaporation were collected and weighed. The obtained solid sample is the first oxidation product of nitric acid modified Shengli lignite, named NASL-C1-HA. The solid sample obtained after washing is the solid residue of the first oxidation of nitric acid modified Shengli lignite, named NASL-C1-OR.

[0083] S4. A second ozone oxidation experiment was conducted on NASL-C1-OR obtained in step S3 using a mixture of ozone and oxygen. The specific process was the same as in step S3. The solid residue of the secondary oxidation of nitric acid-modified Shengli lignite was named NASL-C2-OR, and the secondary oxidation product of nitric acid-modified Shengli lignite was named NASL-C2-HA.

[0084] Depend on Figure 5 (a) It can be seen that after two cycles of the experiment, the color of the liquid in SL deepened, changing from yellow to dark brown. Figure 5(b) shows the solid products from the ozone oxidation cycle experiment of nitric acid-modified Shengli lignite. Table 3 shows that, in the ozone oxidation depolymerization experiment conducted at room temperature (30℃), the total organic matter conversion rate of NASL gradually increased with the increase in the number of cycles. In the first cycle, the total amount of humic acid obtained exceeded the amount of converted organic matter. The increase in product weight was due to the addition of nitrogen and oxygen elements to the reaction product molecules. After the second oxidation cycle, the total conversion rate of NASL reached 81.55%, and the total mass of evaporated liquid was 2.6405 g, with a total macromolecular product yield of 82.38%. Since the low-boiling-point small-molecule solvent-soluble components are evaporated during the liquid evaporation process, the solvent-soluble yield obtained for NASL in the ozone oxidation depolymerization experiment at room temperature (30℃) is greater than 98.10%.

[0085] Table 3 Results of the cyclic experiment on ozone oxidation of nitric acid-modified Shengli lignite

[0086]

[0087] Characterization analysis was performed on nitric acid-modified Shengli lignite, oxidation products, and oxidation solid residues.

[0088] 1. Elemental analysis was performed on SL, NASL, their oxidized solid residues, and corresponding oxidation products.

[0089] Table 4 shows that, compared to raw SL coal, NASL treated with nitric acid exhibits decreased carbon, hydrogen, sulfur, and H / C ratios, while significantly increased nitrogen, oxygen, and O / C ratios. In particular, the nitrogen content increased from 1.12% to 3.90%, indicating a nitration reaction during the oxidative depolymerization process, resulting in a certain amount of nitro groups in the macromolecular structure of the lignite organic matter. After ozone oxidation and depolymerization, compared to NASL, the oxygen, nitrogen, hydrogen, and O / C ratios in the oxidation solid residue significantly decreased, while the carbon and hydrogen contents increased. However, the carbon and nitrogen contents in the oxidation products decreased, while the oxygen, hydrogen, and O / C ratios significantly increased. This indicates that ozone oxidation can extract a large amount of organic matter from NASL, and the oxidation products contain a large number of nitro functional groups. In the cyclic oxidation process, with the increase of the number of NASL oxidation-depolymerization cycles, the oxygen content, nitrogen content, and O / C ratio in the oxidized solid residue decreased, while the carbon content, hydrogen content, and H / C ratio increased. In the oxidation products, the carbon content, hydrogen content, and nitrogen content decreased, while the oxygen content, H / C ratio, and O / C ratio increased sequentially. The results indicate that the nitric acid oxidation-depolymerization process allows nitrogen and oxygen atoms to enter NASL, and the successful nitration reaction introduces -NO2 and -NO into the aromatic ring structure of lignite.

[0090] Table 4 Elemental analysis results of different samples

[0091]

[0092]

[0093] a Subtraction method

[0094] 2. Industrial analysis of SL, NASL, their oxidized solid residues, and corresponding oxidation products.

[0095] Table 5 shows that, compared to raw SL coal, the ash content of NASL treated with nitric acid decreased slightly, indicating that dilute nitric acid treatment has a certain deashing effect. After oxidative depolymerization of NASL, the ash accumulated in the oxidized solid residue, and there was almost no ash in the oxidation products (accounting for only 1.32%). In the cyclic oxidative depolymerization experiment, after oxidative depolymerization of NASL, the ash content in the solid residue increased significantly, and there was almost no ash in the oxidation products, accounting for only about 1%. The results indicate that the ozone oxidation process mainly decomposes and releases the organic matter in NASL, while the ash remains in the solid residue.

[0096] Table 5. Industrial analysis results of different samples

[0097]

[0098] 3. XRD analysis of ozone-oxidized nitric acid-modified Shengli lignite and solid residue.

[0099] like Figure 6 As shown in the XRD patterns, NASL and the oxidized residue exhibit the same characteristic peaks. A distinct characteristic diffraction peak can be observed at approximately 27°, which belongs to SiO2, the main component of ash in coal. The SiO2 diffraction peak intensity of NASL and its oxidized residue gradually increases, indicating that the ash composition is mainly present in the oxidized residue and remains unchanged during the oxidation process. For the cyclic experiment, the SiO2 diffraction peak intensity of NASL and its oxidized residue gradually increases, indicating that ash gradually accumulates in the solid oxidized residue, which is consistent with the above industrial analysis and characterization results.

[0100] 4. FTIR analysis of ozone oxidation of polynitrate-modified lignite, oxidation products and solid residues.

[0101] Depend on Figure 7 It can be seen that the infrared characteristic peaks of nitric acid-modified lignite, oxidation products, and solid residues are similar, with a peak at 1538 cm⁻¹. -1 and 1392cm -1Two peaks appeared nearby, which can be attributed to the absorption of the -NO2 symmetric extension vibration and the asymmetric vibration. This indicates that nitro groups directly linked to the aromatic nuclei of lignite do exist in the structure of lignite pretreated with nitric acid. Comparing the infrared peaks of typical nitrohumic acids in the literature, it is inferred that the oxidation product is nitrohumic acid. Furthermore, the change in the intensity of the nitro peak is consistent with the increase in nitrogen content observed in elemental analysis, reaching 3440 cm⁻¹. -1 OH was detected nearby at 1722 and 1735 cm⁻¹. -1 C=O(COOH) was detected nearby at 1612 cm⁻¹. -1 Aromatic C=C was detected nearby at 2948 and 2848 cm⁻¹. -1 Variable C was detected nearby al The intensity of the -H peak increased in NSL after nitric acid oxidation pretreatment, while the absorption peak of COOH in the solid residue remained very low. For all oxidation products, the absorption band of COOH was stronger than that of NSL, indicating that the oxidation process led to the oxidation of functional groups in coal to COOH. The 900-700 cm⁻¹ peak intensity was also observed in all spectra. -1 The region contains bands generated by the out-of-plane bending vibrations of aromatic CH groups. Nitrification and oxidation reactions lead to an increase in nitro and carboxyl groups in lignite treated with nitric acid, while ozone oxidation can break weaker bridging bonds and longer side chains in lignite.

[0102] 5. GPC analysis of oxidation products of ozone oxidation of nitric acid-modified Shengli lignite.

[0103] Depend on Figure 8 The molecular weights of the oxidation products of ozone oxidation and depolymerization of NASL were determined using gel permeation chromatography (GPC). The molecular weights of the oxidation products were mainly concentrated in the range of 250-1000 Da. The molecular weights (Mw) of NASL-HA, NASL-C1-HA, and NASL-C2-HA were 449, 521, and 456, respectively. The molecular weights decreased significantly after ozone oxidation, indicating that ozone disrupted the structure of lignite and increased its solubility in solvents. This is because nitric acid has strong oxidizing properties, enabling the gradual degradation of large organic molecules into smaller molecules.

[0104] 6. XPS analysis of oxidation products of ozone-oxidized nitric acid-modified lignite.

[0105] XPS analysis was performed on the oxidation products from the NASL ozone oxidation cycle experiment to observe the different chemical valence states of C and O in the samples. For example... Figure 9 (a)- Figure 9 As shown in (c), for the oxidation products in the NASL cycle experiment, as the number of cycles increases, as... Figure 9 (d)- Figure 9As shown in (f), the C1s plot of XPS clearly shows that the content of CC / CH bonds gradually decreases, while the content of COO- functional groups gradually increases. At the same time, the O1s plot of XPS clearly shows that the content of COO- functional groups gradually increases with the increase of the number of cycles. The corresponding results indicate that ozone oxidation depolymerization of NASL can effectively cleave CO and CC bonds in lignite, and the product has a relatively large number of carboxyl functional groups.

[0106] 7. SEM analysis of ozone-oxidized nitric acid-modified Shengli lignite.

[0107] like Figure 10 As shown, compared to NASL, the surface of the oxidation residue becomes loose and porous, forming more pore structures. This indicates that the organic macromolecular structure of lignite is severely damaged after ozone oxidation. In the cyclic experiment, as the number of cycles increases, the dense structure of the coal sample gradually collapses, and a richer pore structure is formed on the surface. The solid residue after ozone oxidation has a rich pore structure and a rough surface, indicating that ozone oxidation significantly changes the surface morphology of lignite.

[0108] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for producing nitrohumic acid from lignite through nitric acid-ozone combined oxidation, characterized in that, Includes the following steps: S1. Grind the lignite raw material to below 40 mesh to obtain lignite powder; S2. Take the lignite powder treated in step S1 and add it to 1-4 mol / L dilute nitric acid. Heat to 30-90 ml. o After C-bath treatment, the lignite was filtered, washed until neutral, and vacuum dried to obtain nitric acid-modified lignite, named NASL; S3. The NASL obtained in step S2 is subjected to the first ozone oxidation treatment using a mixture of ozone and oxygen. After the oxidation reaction is completed, the mixture is centrifuged and filtered. The solid residue after filtration is washed with solvent and then filtered again. The solid sample obtained after filtration is the first solid residue of nitric acid modified lignite oxidation. All the filtrates in this step are combined and dried. The solid sample obtained after drying is the first oxidation product of nitric acid modified lignite, which is humic acid. S4. Repeat the S3 operation on the solid residue obtained in S3 to obtain the solid residue of nitric acid modified lignite after the second oxidation. The ozone oxidation process in step S3 is as follows: NaSL is weighed and placed in a three-necked flask, solvent is added, and the apparatus is connected. Then, the oxygen cylinder is opened, and ozone generated by the ozone generator is introduced into the reactor. The oxygen inflow rate is adjusted to 0.5 L / min, and the ozone output rate is 0.125-0.375 L / min. The ozone and oxygen mixture is directly introduced into the three-necked flask. The ozone concentration is detected by an ozone concentration detector. The concentration is maintained at 30... o Heating and stirring at C for 2-4 hours to induce oxidation.

2. The method for producing nitrohumic acid from lignite by combined nitric acid-ozone oxidation according to claim 1, characterized in that, In step S2, the water bath treatment time is 1-10 hours.

3. The method for producing nitrohumic acid from lignite through nitric acid-ozone combined oxidation according to claim 1, characterized in that, In step S2, the mass-to-volume ratio of lignite powder to dilute nitric acid is 1:10 g / mL.

4. The method for producing nitrohumic acid from lignite by combined nitric acid-ozone oxidation according to claim 1, characterized in that, In step S2, the concentration of the dilute nitric acid is 2 mol / L, and the water bath treatment temperature is 70°C. o C, the processing time is 2 hours.

5. The method for producing nitrohumic acid from lignite through nitric acid-ozone combined oxidation according to claim 1, characterized in that, In step S3, the solvent used in the ozone oxidation process is methanol or acetic acid, the ozone output is 0.250 L / min, and the oxidation reaction takes place for 3 hours.

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