Method and system for preparing humic acid compound fertilizer based on caprolactam byproduct APU oil

Abstract

The invention relates to the technical field of chemical preparation, and provides a method and system for preparing a humic acid compound fertilizer based on caprolactam byproduct APU oil, and the method comprises the following steps: carrying out a catalytic oxidation reaction on the caprolactam byproduct APU oil and an immobilized FeOCl catalyst under an aerobic condition to generate an active intermediate; carrying out condensation reaction on the active intermediate under an anoxic condition to generate a humic acid-like substance; and carrying out post-treatment on the humic acid-like substance to obtain the humic acid compound fertilizer. According to the scheme, the caprolactam byproduct APU oil is converted into the humic acid compound fertilizer which is high in organic matter content and good in soil improvement effect through catalytic oxidation and condensation reaction, resource utilization of industrial byproducts is achieved, and the production cost of the fertilizer is reduced. Moreover, the immobilized FeOCl catalyst is selected as the catalyst, on one hand, secondary pollution of a liquid-phase catalyst is avoided, and on the other hand, carbon and nitrogen elements in the caprolactam byproduct APU oil can be efficiently converted into humus and nutrients, so that the environmental protection property of the whole process is ensured from the source.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical preparation, in particular to a method and system for preparing humic acid compound fertilizer based on caprolactam by-product APU oil. BACKGROUND

[0002] Caprolactam is an important monomer for producing nylon-6, and a large amount of by-product APU oil with complex components is generated in the production process. The APU oil mainly contains caprolactam oligomers (35-45 wt%), ammonium sulfate (14-18 wt%), water (25-35 wt%), other organic matters such as benzoic acid and cyclohexanone (5-10 wt%), and a small amount of impurities. The APU oil has the characteristics of high chemical oxygen demand (COD > 100,000 mg / L), high salinity, and difficult biodegradation. At present, the treatment methods of APU oil in enterprises are mainly paid outsourcing or incineration disposal, which not only has high cost (about 3000 yuan / ton), but also has great environmental risk and resource waste.

[0003] Humic acid is the core component of soil humus, and has the functions of improving soil, increasing fertilizer efficiency, and stimulating crop growth. The market demand for humic acid fertilizer is increasing, and the traditional humic acid is derived from non-renewable resources such as coal (such as weathered coal and lignite), which has high energy consumption in the extraction process and is easy to cause acid and alkali pollution.

[0004] Although there are studies on preparing humic acid fertilizer from organic waste in the prior art, this technology has poor adaptability to APU oil and other difficult-to-degrade industrial waste liquids, cannot realize efficient catalytic conversion, is difficult to direct regulation and control of the product to be a humic acid-like macromolecule that meets the fertilizer standard, and lacks a low-cost continuous production scheme, which makes it difficult to meet the demand for resource utilization of APU oil and sustainable supply of humic acid fertilizer.

[0005] Therefore, how to provide a method for efficiently converting APU oil into humic acid compound fertilizer is a technical problem that needs to be solved by those skilled in the art. SUMMARY

[0006] The present application provides a method and system for preparing humic acid compound fertilizer based on caprolactam by-product APU oil, which realizes efficient and green conversion of caprolactam by-product APU oil to humic acid compound fertilizer.

[0007] The technical solution adopted by the present application is as follows: In a first aspect, a method for preparing humic acid compound fertilizer based on caprolactam by-product APU oil is provided, comprising: catalyzing and oxidizing the caprolactam by-product APU oil and the solid-state FeOCl catalyst under aerobic conditions to generate an active intermediate; carrying out condensation reaction on the active intermediate under anoxic condition to generate humic acid-like substance; carrying out post-treatment on the humic acid-like substance to obtain humic acid compound fertilizer.

[0008] Preferably, the carrier of the supported FeOCl catalyst is selected from activated carbon, alumina or ceramic honeycomb.

[0009] Preferably, the catalytic oxidation reaction is carried out in a fixed bed reactor, the reaction temperature is 50-60℃, and the hydraulic retention time is 12-24 hours.

[0010] Preferably, the condensation reaction is carried out under the condition of inert gas being introduced and oxygen content being not more than 0.5%, the reaction temperature is 50-60℃, and the reaction time is 24-72 hours.

[0011] Preferably, before carrying out the catalytic oxidation reaction, the method further comprises pretreating the caprolactam by-product APU oil, and the pretreatment comprises: mixing and diluting the caprolactam by-product APU oil with dilution water and then adjusting the pH.

[0012] Preferably, the dilution is diluting the APU oil by 3-5 times, and the pH adjustment is adjusting the pH value to the acidic range of 3-5 by using acid liquid.

[0013] Preferably, the post-treatment comprises the steps of membrane separation, dehydration, compounding with nutrient elements, drying and granulation, which are carried out in sequence.

[0014] Preferably, the membrane separation step is performed by using ultrafiltration membrane or nanofiltration membrane, the dehydration step is performed by using plate and frame filter press, and the drying step is performed by using dehumidification heat pump.

[0015] Preferably, the molecular weight cut-off of the ultrafiltration membrane or the nanofiltration membrane is 1000-5000 Da, and the temperature of the drying is 50-60℃.

[0016] In the second aspect, a system for implementing the method in the first aspect is provided, and the system comprises, which are connected in sequence by pipelines: a catalytic oxidation reaction device, which is filled with a supported FeOCl catalyst; a condensation reaction device, which is configured to maintain anoxic environment; a post-treatment device, which is used for post-treating the product from the condensation reaction device.

[0017] According to the specific embodiments provided in the present application, the following technical effects are disclosed: In the technical solutions of the present application, a method and system for preparing humic acid compound fertilizer based on caprolactam by-product APU oil are provided, wherein the method comprises: performing catalytic oxidation reaction on the caprolactam by-product APU oil and a solid-supported FeOCl catalyst under aerobic conditions to generate an active intermediate; performing condensation reaction on the active intermediate under anoxic conditions to generate humic acid-like substances; and performing post-treatment on the humic acid-like substances to obtain humic acid compound fertilizer. The scheme converts the caprolactam by-product APU oil into humic acid compound fertilizer with high organic matter content and good soil improvement effect through catalytic oxidation reaction and condensation reaction, realizes resource utilization of industrial by-products, and reduces the production cost of fertilizer. In addition, the catalyst is a solid-supported FeOCl catalyst, which can avoid secondary pollution of liquid catalysts and efficiently convert carbon and nitrogen elements in the caprolactam by-product APU oil into humus and nutrients, thereby ensuring the environmental friendliness of the entire process from the source. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Figure 1 is a method flowchart for preparing humic acid compound fertilizer based on caprolactam by-product APU oil provided by the embodiments of the present application; Figure 2 is a UV spectrum comparison chart of humification effects of different iron mineral catalysts on caprolactam by-product APU oil provided by the embodiments of the present application; Figure 3 is a Fourier transform infrared spectrum of a humic acid compound fertilizer product provided by the embodiments of the present application, wherein (a) is a Fourier transform infrared spectrum of a filtered solid; Figure 4 is a Fourier transform infrared spectrum of a humic acid compound fertilizer product provided by the embodiments of the present application, wherein (b) is a Fourier transform infrared spectrum of a freeze-dried solid; Figure 5 is an architecture diagram of an industrial production system provided by the embodiments of the present application; Figure 6 is a schematic diagram of a system for preparing humic acid compound fertilizer based on caprolactam by-product APU oil provided by the embodiments of the present application.

[0020] Reference signs: 1, caprolactam by-product APU oil barrel; 2, fixed bed reaction tower; 3, secondary reaction tower; 4, membrane separation device; 5, dewatering device; 6, low-temperature dryer; 7, granulator. Detailed Implementation

[0021] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art are within the scope of protection of this application.

[0022] As described in the background section, although there are existing studies on the preparation of humic acid fertilizers from organic waste, this technology is poorly adapted to recalcitrant industrial waste liquids such as APU oil. It cannot achieve efficient catalytic conversion, nor can it directionally control the product to be a humic acid-like macromolecule that meets fertilizer standards. Furthermore, it lacks a low-cost continuous production solution, making it difficult to meet the demand for APU oil resource utilization and sustainable supply of humic acid fertilizers.

[0023] Based on this, this application provides a method and system for preparing humic acid compound fertilizer based on caprolactam by-product APU oil, aiming to solve the technical problems of inefficient conversion of caprolactam by-product APU oil into humic acid compound fertilizer and imperfect conversion scheme in the prior art.

[0024] The embodiments of this application will be analyzed in detail below with reference to the accompanying drawings.

[0025] Example 1 This embodiment provides a method for preparing humic acid compound fertilizer based on caprolactam byproduct APU oil, referencing... Figure 1 The methods include: S1: Caprolactam byproduct APU oil is reacted with a supported FeOCl catalyst under aerobic conditions to generate an active intermediate; S2: Causes the active intermediate to undergo a condensation reaction under anaerobic conditions to generate humic acid-like substances. S3: Post-process the humic acid-like substances to obtain humic acid compound fertilizer.

[0026] In step S1, the caprolactam byproduct APU oil mainly contains caprolactam oligomers, ammonium sulfate, water, other organic compounds such as benzoic acid and cyclohexanone, and a small amount of impurities. The caprolactam byproduct APU oil is pumped into a catalytic oxidation reactor equipped with a supported FeOCl catalyst to undergo a reaction. FeOCl catalyzes the ring-opening and oxidation reactions of the organic compounds in the caprolactam byproduct APU oil, generating small molecule active intermediates such as aldehydes, ketones, and carboxylic acids.

[0027] FeOCl has a unique layered structure and strong Lewis acidity, which makes its surface have a very high affinity and activation capacity for the C-N bond and amide bond in the caprolactam by-product APU oil, which is rich in electrons. It can preferentially adsorb and polarize these chemical bonds, making them unstable, thus creating conditions for subsequent oxidation reactions. FeOCl can efficiently activate oxygen to produce high-activity oxygen species dominated by hydroxyl radicals, which preferentially attack the heterocyclic structure and C-N bond activated by FeOCl, triggering a series of radical chain reactions, leading to selective ring opening to trim large molecular oligomers into smaller, more reactive molecular fragments. The molecular fragments after ring opening will be further oxidized, and under the catalytic regulation of FeOCl, the reaction path is directed to generate a large number of oxygen atom-rich oxygen-containing functional groups. Finally, the organic matter in the APU oil is directionally converted into small molecule active intermediates dominated by aldehydes, ketones, and especially carboxylic acid compounds.

[0028] In step S2, the small molecule active intermediates generated in step S1 are transferred to a condensation reaction device. In an anaerobic environment, small molecule aldehydes, ketones, carboxylic acids, and amino compounds undergo dehydration condensation and free radical polymerization through Aldol condensation, Michael addition, Schiff base reaction, etc. to generate high molecular weight humic acid-like substances.

[0029] Among them, Aldol condensation is initiated by aldehyde or ketone intermediates, and the carbon chain is extended and the skeleton is constructed through intermolecular addition-dehydration reaction. Michael addition is a chain growth reaction that can occur between unsaturated carbonyl compounds and other reagents, increasing the molecular complexity and branching degree of the product. Schiff base reaction is the reaction of aldehyde intermediates with amino compounds from caprolactam by-product APU oil to form imine structures containing C=N bonds, which efficiently and stably fix nitrogen elements in the raw materials into the final humic acid-like macromolecules, realizing the resource utilization of waste nitrogen. Free radical polymerization is a free radical that remains in the reaction or is initiated by intermediates, which is more prone to coupling reactions than oxidation termination under anaerobic conditions, thus further promoting the growth of molecular weight.

[0030] It should be noted that the aforementioned multiple reaction pathways are not isolated, but are interwoven to form a complex reaction network.

[0031] In step S3, the macromolecular humic acid substance generated in step S2 is transferred to a post-treatment device, and the post-treatment operation includes the steps of membrane separation, dehydration, compounding with nutrient elements, drying and granulation in sequence. First, the condensed slurry is subjected to membrane separation pre-concentration treatment, and the concentrated liquid containing macromolecular humic acid substances is obtained; then, the concentrated liquid is dehydrated to obtain a wet cake with a water content of 40 to 60%; then, the wet cake is crushed and compounded with other nutrient elements; finally, the compounded product is subjected to low-temperature drying, fine grinding, granulation and screening to obtain a granular humic acid compound fertilizer product.

[0032] In summary, the scheme converts the caprolactam by-product APU oil into humic acid compound fertilizer with high organic matter content and good soil improvement effect through catalytic oxidation and condensation reactions, realizes the resource utilization of industrial by-products, and reduces the production cost of fertilizers. Moreover, the catalyst used is a solid-supported FeOCl catalyst, which on the one hand avoids secondary pollution of liquid catalysts, and on the other hand can efficiently convert carbon and nitrogen elements in the caprolactam by-product APU oil into humus and nutrients, thereby ensuring the environmental friendliness of the entire process from the source.

[0033] As a preferred embodiment, the carrier of the solid-supported FeOCl catalyst is selected from activated carbon, alumina or ceramic honeycomb.

[0034] Among them, activated carbon has a high specific surface area, which can increase the active sites; alumina can provide mechanical strength and stability; ceramic honeycomb is suitable for continuous flow reaction, which can reduce the pressure drop. The arrangement of these carriers increases the active site exposure area of FeOCl and the efficiency of contact with reactants, thereby improving the rate of catalytic oxidation ring-opening.

[0035] As an example of an activated carbon carrier, the preparation method of the solid-supported FeOCl catalyst includes: using the impregnation-calcination method, impregnating FeCl3 solution on the activated carbon carrier, calcining in an air atmosphere at 200 to 250°C for 2 to 4 hours, and obtaining the solid-supported FeOCl after natural cooling, with an iron loading of 5 to 10wt%.

[0036] As an example of regeneration of FeOCl catalyst, the method for regenerating FeOCl catalyst includes: soaking and cleaning the deactivated FeOCl catalyst with dilute acid with a pH of 2 to 3, and calcining and activating in an air atmosphere at 180 to 220°C for 1 to 3 hours to obtain the regenerated FeOCl catalyst.

[0037] As a preferred embodiment, the catalytic oxidation reaction is carried out in a fixed bed reactor, the reaction temperature is 50 to 60°C, and the hydraulic retention time is 12 to 24 hours.

[0038] The fixed bed reactor is configured to ensure stable and continuous contact between the supported FeOCl catalyst and the caprolactam by-product APU oil. The reaction temperature of 50-60°C is selected to activate the FeOCl catalyst to generate sufficient free radicals to drive the ring-opening oxidation, while inhibiting excessive oxidation of organic matter, thereby precisely guiding the reaction path to generate active intermediates. The hydraulic retention time of 12-24 hours is selected to ensure the diffusion, adsorption and reaction of the reactants on the active sites of the catalyst, and to ensure that the components such as caprolactam oligomers in the caprolactam by-product APU oil can be fully converted.

[0039] As a preferred embodiment, the condensation reaction is carried out under the condition of passing in inert gas, oxygen content not more than 0.5%, reaction temperature 50-60°C, reaction time 24-72 hours.

[0040] Among them, the inert gas, oxygen content not more than 0.5% is the prerequisite for the condensation reaction. The same 50-60°C as the oxidation step is selected, on the one hand, to provide the necessary activation energy for Aldol condensation, Schiff base reaction and other condensation paths, and on the other hand, to effectively prevent the possible coking or generation of inert polymers at high temperature, ensuring the activity of the final product. The reaction time of 24-72 hours is selected to ensure that the active intermediates can fully react to generate humic acid-like substances through various paths.

[0041] As a preferred embodiment, before the catalytic oxidation reaction is carried out, the method further comprises pretreating the caprolactam by-product APU oil, and the pretreatment comprises: The caprolactam by-product APU oil is diluted by mixing with dilution water and then pH adjusted.

[0042] Among them, the pretreatment step creates the optimal initial conditions for the subsequent catalytic oxidation reaction through dilution and acidity adjustment.

[0043] As a preferred embodiment, the dilution is to dilute the APU oil by 3-5 times, and the pH adjustment is to adjust the pH value to the acidic range of 3-5 by using acid solution.

[0044] The APU oil by-product of caprolactam is usually thick, and direct treatment can cause difficulty in transportation. If the dilution is less than 3 times, the viscosity is not reduced enough, which is still not conducive to the reaction. If the dilution is more than 5 times, the fluidity is improved, but the solvent of the reactor is unnecessarily increased, which causes the energy consumption of the equipment to rise. Therefore, dilution of 3 to 5 times can improve the fluidity and balance the treatment efficiency and economy. The FeOCl catalyst can exist stably and activate oxygen efficiently in an acidic environment. If the pH is too high, the FeOCl catalyst will be deactivated or even decomposed. If the pH is too low, the corrosion of the equipment will be aggravated. Therefore, the selection of a pH of 3 to 5 can maximize the activity of the catalyst and minimize the corrosion risk.

[0045] As a preferred embodiment, the membrane separation step is performed using an ultrafiltration membrane or a nanofiltration membrane, the dehydration step is performed using a plate-and-frame filter press, and the drying step is performed using a dehumidification heat pump.

[0046] The ultrafiltration membrane or the nanofiltration membrane achieves molecular-level screening and purification. The plate-and-frame filter press provides reliable solid-liquid separation. The dehumidification heat pump can efficiently remove water while retaining the activity of the humic acid compound fertilizer.

[0047] As a preferred embodiment, the molecular weight cut-off of the ultrafiltration membrane or the nanofiltration membrane is 1000 to 5000 Da, and the drying temperature is 50 to 60°C.

[0048] The selection of a molecular weight cut-off of 1000 to 5000 Da ensures that the active humic acid components with ideal molecular sizes are effectively retained and concentrated. The lower limit of the molecular weight avoids the loss of target components, and the upper limit ensures sufficient flux and separation efficiency. Controlling the drying temperature at 50 to 60°C, which is consistent with the reaction temperature, can take advantage of the dehumidification heat pump to efficiently remove water while avoiding thermal damage and ensuring the product quality and agricultural efficacy of the final humic acid compound fertilizer.

[0049] Example Two This Example Two will further illustrate the beneficial effects of the present application in combination with Examples and Comparative Examples.

[0050] Example One This Example One process was carried out in the laboratory. A caprolactam by-product APU oil was taken as the raw material, which contained 40wt% caprolactam and its oligomers, 16wt% ammonium sulfate, and 30wt% water. The APU oil was mixed and diluted 5 times with deionized water at a volume ratio of 1:4, and then the pH was adjusted to 4.0 with dilute sulfuric acid to obtain a pretreated feed solution.

[0051] Take 100 mL of the above solution into a 250 mL conical flask with a stopper, add 0.5 g of FeOCl powder catalyst (catalyst concentration is 5 g / L). Put the conical flask in a constant temperature water bath oscillator, control the temperature at 25°C, oscillate at a speed of 180 rpm for 48 hours, complete the catalytic oxidation reaction.

[0052] After the reaction is completed, the reaction solution is transferred into a dialysis bag with a molecular weight cut-off of 1000 Da, and dialyzed in ultrapure water for 48 hours to remove salts and unreacted small molecules. The dialyzed solution is freeze-dried to obtain a brown-black solid product. Referring to Figure 2 , the effect of different iron minerals on (a) single component, (b) salt-containing composite model component and (c) actual waste liquid component; wherein the horizontal coordinate Wavelength represents wavelength, unit: nm, the vertical coordinate Absorbance represents absorbance. As shown in the figure, whether the substrate is a single component, a salt-containing composite system or an actual waste liquid, FeOCl can significantly promote the humification process within 0-48h, generating more small molecule intermediates containing active functional groups. In figure (a), for the system of pure caprolactam, FeOCl mainly catalyzes the oxidative ring-opening reaction to provide high-activity monomers for subsequent condensation. In figure (b), after adding ammonium sulfate to the substrate, a new peak appears in the ultraviolet spectrum and the absorbance increases significantly, indicating that ammonium sulfate and caprolactam cooperatively participate in the construction of intermediates; the reaction path is thus complicated, generating more active intermediates with aromaticity and conjugated structure. In figure (c), the real APU oil, under the catalytic oxidation of FeOCl, the absorbance at 400 nm is significantly improved due to the accumulation of substrates in the early stage of the reaction, indicating that the humification process is obvious. This shows that in this system, the FeOCl catalyst exhibits better catalytic performance than other iron minerals, ensuring the process efficiency.

[0053] The obtained solid product was characterized: the TOC analyzer was used to determine that the organic carbon content was 12.38%; the gel permeation chromatography (GPC) was used to determine that the weight average molecular weight (Mw) was 12.6 kDa; referring to Figure 3 (a) the Fourier transform infrared spectrum (FTIR) of the filtered solid and Figure 4 (b) the Fourier transform infrared spectrum (FTIR) of the freeze-dried solid, wherein the horizontal coordinate Wavenumber represents wave number, unit: cm -1 , the vertical coordinate Absorbance represents absorbance. (FT-IR) analysis results show that the product has peaks at 3400 cm -1 , 2920 cm -1 , 1650 cm -1 , 1540 cm -1 and 1400 cm -1The functional group composition of the product is similar to that of natural humic acid. Figure 3 (a) The organic matter separated by filtration has aliphatic long chain structure, contains a large number of amide groups and contains more oxygen-containing functional groups, which indicates that FeOCl successfully catalyzed the conversion of APU oil to form organic active intermediates with active functional groups similar to the characteristic functional groups of humus. A part of the precipitate was separated by dialysis and freeze-drying, and the freeze-dried solid showed obvious brown-black color. Figure 4 (b) The aliphatic long chain and active functional group signals of the product are weakened, and more conjugated structures are formed, forming aromatic macromolecules with C-O and C-N as the core skeleton, which is highly similar to humus. It is confirmed that FeOCl successfully catalyzed the formation of high-molecular-weight nitrogen-containing end products, which is beneficial to plant nutrient absorption.

[0054] This example demonstrates that under the above conditions, FeOCl can effectively catalyze the conversion of caprolactam by-product APU oil.

[0055] Example 2 This example 2 process is carried out in an industrial production system. For example, referring to Figure 5 , the system includes APU storage tank, pre-treater, fixed bed reaction tower, secondary reaction tower, first ultrafiltration system, stirring tank, second ultrafiltration system, plate and frame filter press, low-temperature drying machine, shear crusher, fine grinder, screening machine, granulator, low-temperature drying machine and packaging machine connected in sequence by pipelines. The system is also equipped with a dehumidification heat pump to provide heat source for the low-temperature drying machine and the low-temperature drying machine, and a bag-type dust collector is provided at each dust point.

[0056] As an example of a specific process step: (1) Pretreatment: The caprolactam by-product APU oil is pumped from the APU storage tank into the pre-treater, mixed with part of the permeate returned from the first and second ultrafiltration systems, and diluted 4 times, while adding sulfuric acid to adjust the pH to 4.5.

[0057] (2) Catalytic oxidation: The pretreated feed liquid is delivered by the feed pump to the bottom of the fixed bed reaction tower. The reaction tower is filled with a solid FeOCl catalyst supported on activated carbon. The reaction temperature is controlled at 55°C, the liquid space velocity is 0.8h -1 , and the reaction is carried out for 15 hours under these conditions to fully oxidize the organic matter to form active small molecule intermediates.

[0058] (3) Anaerobic condensation: The oxidized reaction liquid is self-flowed into the secondary reaction tower by pressure difference. Nitrogen gas is continuously introduced into the reaction tower to maintain an anaerobic environment (oxygen content <0.5%), and the reaction temperature is controlled at 55°C, and the residence time is 50 hours, so that the small molecule intermediates can fully condense and polymerize to form humus-like macromolecules.

[0059] (4) Membrane separation and dehydration: The condensed slurry is first treated by the first and second ultrafiltration systems, and the concentrated liquid is sent to a plate-and-frame filter press to obtain a wet filter cake with a water content of about 55%. The ultrafiltration permeate is partially returned to the pretreatment section.

[0060] (5) Crushing and compounding: The wet filter cake is crushed by a shear crusher and then sent to a stirring tank, where inorganic nutrients are added for mixing and compounding according to a specific formula.

[0061] (6) Drying and granulation: The mixed material is sent to a low-temperature drying machine equipped with a dehumidification heat pump for drying, and then processed into granules by a fine grinder and a granulator.

[0062] (7) Screening and packaging: The qualified products are selected by a screening machine after granulation, and finally metered and packaged by a packaging machine to obtain the humic acid compound fertilizer product.

[0063] The system runs stably, and the conversion rate of organic components in caprolactam byproduct APU oil to humic acid-like substances is 35-45%, of which macromolecular humic acid (Mw>10 kDa) accounts for about 12 to 15%. The obtained black-brown granular product has an organic matter content of ≥12%, a total nutrient (N+P2O5+K2O) content of ≥30%, a humic acid content of ≥8%, a moisture content of ≤12%, and a heavy metal content meeting the limit requirements of NY 884-2012, meeting the first-grade product standard of GB / T 18877-2020 “Organic and Inorganic Compound Fertilizer”.

[0064] Comparative Example 1 An equal amount of caprolactam byproduct APU oil raw material is directly taken without catalytic oxidation and condensation reaction, only simple acid treatment is performed, and then mixed and granulated with the same proportion of chemical fertilizer. The obtained product granules are loose and fragile, and when applied to soil, not only cannot promote plant growth, but also inhibit seed germination due to the presence of unconverted organic toxicants.

[0065] Comparative Example 2 In this comparative example, β-FeOOH catalyst is used instead of solid-supported FeOCl catalyst, and other process conditions are the same as in Example 1.

[0066] The caprolactam byproduct APU oil raw material is diluted 5 times and adjusted to pH 4.0, and then 0.5 g of β-FeOOH catalyst (catalyst concentration of 5 g / L) is added. The reaction is carried out at 25°C and 180 rpm for 48 hours. After the reaction is completed, the product is obtained by dialysis and freeze-drying. The characterization results show that the organic carbon content is 8.52%, the weight average molecular weight (Mw) is 8.1 kDa, and the ultraviolet spectrum analysis shows that E 300 nm is 0.112 (reference Figure 2 (a)), E 600The nm value was 0.680, significantly lower than the effect of the FeOCl catalyst used in Example 1 (E 300 nm is 0.272, E 600 nm is 1.180).

[0067] This comparative example shows that although β-FeOOH also has a certain catalytic oxidation ability, its catalytic efficiency is significantly lower than that of FeOCl. The humic acid-like substances generated are inferior to the FeOCl catalytic products in terms of molecular weight and degree of humification, which verifies the superiority of FeOCl catalyst.

[0068] Based on the above embodiments and comparative examples, this scheme converts caprolactam byproduct APU oil into a humic acid compound fertilizer with high organic matter content and excellent soil improvement effect through catalytic oxidation and condensation reactions, realizing the resource utilization of industrial byproducts and reducing fertilizer production costs. Furthermore, the catalyst used is a supported FeOCl catalyst, which avoids secondary pollution from liquid-phase catalysts and efficiently converts carbon and nitrogen elements in the caprolactam byproduct APU oil into humic substances and nutrients, thus ensuring the environmental friendliness of the entire process from the source.

[0069] Example 3 This third embodiment provides a system for implementing the method of embodiment one.

[0070] A system for preparing humic acid compound fertilizer based on caprolactam byproduct APU oil includes: (The system is described in the original text, but the translation is incomplete.) A catalytic oxidation reactor, which is filled with a supported FeOCl catalyst; The condensation reaction apparatus is configured to maintain an oxygen-deficient environment. A post-processing apparatus is configured to post-process the products from the condensation reaction apparatus.

[0071] In one specific implementation, the system also includes a storage device connected to the catalytic oxidation reactor, which stores caprolactam byproduct APU oil.

[0072] For an example of the overall operation process, refer to Figure 6, the storage device adopts a caprolactam by-product APU oil barrel 1, the catalytic oxidation reaction device adopts a fixed bed reaction tower 2, the condensation reaction device adopts a two-stage reaction tower 3, and the post-processing device includes a membrane separation device 4, a dehydration device 5, a low-temperature dryer 6, and a granulator 7. The caprolactam by-product APU oil is pumped out from the caprolactam by-product APU oil barrel 1, pretreated by dilution and acidity adjustment, and then enters the fixed bed reaction tower 2. In the fixed bed reaction tower 2, the caprolactam by-product APU oil contacts with the solid-supported FeOCl catalyst, and catalytic oxidation reaction occurs under aerobic conditions, and the caprolactam by-product APU oil is converted into an active intermediate. The active intermediate enters the two-stage reaction tower 2, and the active intermediate undergoes condensation reaction under anoxic conditions to generate humic acid-like substances. The humic acid-like substances are concentrated and purified by the membrane separation device 4 to intercept target humic acid-like substances. After the target humic acid-like substances are mechanically dehydrated by the dehydration device 5, wet solids are obtained. The wet solids are dried by the low-temperature dryer 6 to obtain powdered humic acid-like substances. The powdered humic acid-like substances are mixed with nutrient elements by the granulator 7 and granulated to finally obtain humic acid compound fertilizer products.

[0073] The method and system for preparing humic acid compound fertilizer based on caprolactam by-product APU oil provided by the present application are described in detail above, and specific examples are applied to explain the principles and implementation modes of the present application. The above examples are only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed. In summary, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A method for preparing humic acid compound fertilizer based on caprolactam by-product APU oil, characterized by, The method comprises: carrying out catalytic oxidation reaction of caprolactam by-product APU oil and solid-supported FeOCl catalyst under aerobic conditions to generate active intermediates; carrying out condensation reaction of the active intermediates under anoxic conditions to generate humic acid-like substances; carrying out post-treatment of the humic acid-like substances to obtain humic acid compound fertilizer.

2. The method for preparing humic acid compound fertilizer based on caprolactam by-product APU oil according to claim 1, characterized in that, The carrier of the solid-supported FeOCl catalyst is selected from activated carbon, alumina or ceramic honeycomb.

3. The method for preparing humic acid compound fertilizer based on caprolactam by-product APU oil according to claim 1, characterized in that, The catalytic oxidation reaction is carried out in a fixed bed reactor, the reaction temperature is 50-60℃, and the hydraulic retention time is 12-24 hours.

4. The method for preparing humic acid compound fertilizer based on caprolactam by-product APU oil according to claim 1, characterized in that, The condensation reaction is carried out under the condition of inert gas being passed in and the oxygen content being not more than 0.5%, the reaction temperature is 50-60℃, and the reaction time is 24-72 hours.

5. The method for preparing humic acid compound fertilizer based on caprolactam by-product APU oil according to claim 1, characterized in that, Before the catalytic oxidation reaction is carried out, the method further comprises pretreatment of the caprolactam by-product APU oil, and the pretreatment comprises: mixing and diluting the caprolactam by-product APU oil with dilution water and then adjusting the pH.

6. The method for preparing humic acid compound fertilizer based on caprolactam by-product APU oil according to claim 5, characterized in that, The dilution is dilution of the APU oil by 3-5 times, and the pH adjustment is adjustment of the pH value to the acidic range of 3-5 by using acid liquid.

7. The method for preparing humic acid compound fertilizer based on caprolactam by-product APU oil according to claim 1, characterized in that, The post-treatment comprises the steps of membrane separation, dehydration, compounding with nutrient elements, drying and granulation which are carried out in sequence.

8. The method for preparing humic acid compound fertilizer based on caprolactam by-product APU oil according to claim 7, characterized in that, The membrane separation step is carried out by using ultrafiltration membrane or nanofiltration membrane, the dehydration step is carried out by using plate and frame filter press, and the drying step is carried out by using dehumidification heat pump.

9. The method for preparing humic acid compound fertilizer based on caprolactam by-product APU oil according to claim 8, characterized in that, The molecular weight cut-off of the ultrafiltration membrane or the nanofiltration membrane is 1000-5000 Da, and the temperature of the drying is 50-60℃.

10. A system for implementing the method of any one of claims 1 to 9, characterized in that, The system comprises, which are connected in sequence by pipelines: a catalytic oxidation reaction device, which is filled with solid-supported FeOCl catalyst; a condensation reaction device, which is configured to maintain anoxic environment; a post-treatment device, which is configured to carry out post-treatment of the product from the condensation reaction device.

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