Reactors for in-situ chemical oxidation remediation of soil, their preparation methods and applications

Abstract

This invention discloses a reactor for in-situ chemical oxidation remediation of soil, its preparation method, and its application. The reactor includes a support body; the support body is a tubular hollow structure; one end of the tubular hollow structure is open, and the opposite end is closed; the outer wall of the support body is covered with a membrane layer; both the support body and the membrane layer have a plurality of micropores distributed on them. This reactor has adjustable micropores, allowing for the controlled release of various oxidative remediation agents according to soil mass transfer characteristics, and can simultaneously achieve heating activation. When used for in-situ chemical oxidation remediation of polluted environments such as soil and groundwater, this reactor features precise dosing of oxidative agents and efficient activation.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation, specifically relating to a reactor for in-situ chemical oxidation remediation of soil, its preparation method, and its application. Background Technology

[0002] Soil is a vital environmental medium, but many human industrial activities cause soil pollution, resulting in the presence of various organic pollutants. Petroleum hydrocarbons are a significant type of soil pollutant. Petroleum hydrocarbons are primarily mixtures of hydrocarbons composed of carbon and hydrogen, mainly including alkanes, cycloalkanes, alkenes, and polycyclic aromatic hydrocarbons. The production processes of petroleum extraction, storage, refining, processing, use, and transportation all result in the emission of petroleum hydrocarbons, which enter the atmosphere, water bodies, and soil environment. Petroleum hydrocarbons are typical hydrophobic organic pollutants; they have a high viscosity coefficient and a density less than water. When they combine with soil, they cause a series of changes in the soil's physicochemical properties. Petroleum hydrocarbons entering the soil cause a series of important ecological impacts on soil plants, animals, and microorganisms, and can also pose serious health hazards to humans through various exposure routes such as respiration, skin contact, and oral ingestion.

[0003] Highly polluted petroleum hydrocarbons in soil are generally difficult to remove naturally, requiring remediation to reduce their ecological impact. Chemical oxidation is one of the commonly used remediation technologies. Petroleum hydrocarbons contaminate soil through various means, including exploration, production, transportation, storage, tank leaks, accidental spills during loading and unloading, and bursts of aging underground pipelines. The diversity of pollution sources leads to significant differences in the distribution of petroleum hydrocarbons between different soil layers. Soils of different depths and textures also exhibit varying water conductivity and aeration characteristics. This results in significant differences in the distribution and migration patterns of petroleum pollution in soils of different textures. The concentration, composition, distribution, and aging degree of pollutants vary considerably between soil layers. Therefore, the challenge in remediating petroleum hydrocarbon-contaminated soil lies in accurately injecting and dispersing oxidants into the polluted area without strong mechanical disturbance, ensuring thorough and effective mixing with the pollutants. Mass transfer of the oxidant in the soil is a crucial factor affecting its oxidative effect. Both excessively rapid and slow mass transfer in the contaminated soil layer will not achieve optimal results; excessively rapid mass transfer wastes the agent, while excessively slow mass transfer limits the oxidation rate and remediation effectiveness. Therefore, based on the characteristics of soil mass transfer and the distribution characteristics of petroleum hydrocarbon pollution, regulating the release and mass transfer capacity of oxidants is very important for improving the efficiency of oxidative remediation.

[0004] Persulfate is currently one of the most commonly used oxidants, promoting pollutant degradation by generating sulfate and hydroxyl radicals. Its application is increasing due to its good stability in soil, resistance to decomposition at room temperature, high solubility in water, wide applicable pH range, and diverse activation methods. Effective activation of the oxidant is also crucial for ensuring oxidation efficiency. Persulfate activation methods mainly include thermal activation, alkaline activation, and transition metal ion activation. Among these, alkaline activation is particularly damaging to soil ecology. 2+ While activation has a good remediation effect on persulfate in water, it is often adsorbed and fixed in soil, making it difficult to exert a good catalytic activation effect. Although thermal activation consumes some energy, it can efficiently activate persulfate to produce sulfate free radicals, which can rapidly degrade pollutants and thus achieve efficient remediation of contaminated soil. According to a novelty search, there is currently a lack of integrated reactors and corresponding remediation methods for the controlled release of oxidants such as persulfate in soil and thermal activation. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to provide a reactor for in-situ chemical oxidation remediation of soil, its preparation method, and its applications. This reactor features adjustable micropores, allowing for the controlled release of various oxidative remediation agents based on soil mass transfer characteristics, and simultaneously enables heating and activation. When used for in-situ chemical oxidation remediation of polluted environments such as soil and groundwater, this reactor offers precise agent dosing and efficient activation.

[0006] The first aspect of the present invention is to provide a reactor for in-situ chemical oxidation remediation of soil, wherein the reactor includes a support body; the support body is a tubular hollow structure; one end of the tubular hollow structure is an open end, and the opposite end is a closed end; the outer wall of the support body is covered with a membrane layer; and both the support body and the membrane layer have a plurality of micropores distributed on them.

[0007] According to the present invention, the area of ​​the outer wall of the support body covered with a membrane layer accounts for about 70% to 100% of the total area of ​​the outer wall of the support body.

[0008] According to the present invention, there is a section without a membrane layer on the outer wall of the support body near the opening end. Further, this section is made of a PVC tubular material of a size matching the support body, nested outside the support body, and the two are tightly bonded together with silicone sealant, so that this section of the support body does not have the ability to release oxidants, and is called the non-release zone.

[0009] According to the present invention, the micropores distributed on the membrane layer have a pore size of 0.5 μm to 20 μm, and the size of the micropores can be adjusted. The porosity of the membrane layer is 30% to 50%.

[0010] According to the present invention, the membrane layer is divided into several zones according to the distribution of surface micropores; the membrane pore size of each zone can be designed and combined according to the mass transfer capacity of different soil layers.

[0011] According to the present invention, the membrane layer partitions include one or more of the following: a rapid release zone, a medium-speed release zone, and a slow release zone, or any combination thereof. The size, arrangement order, pore size, and porosity of the membrane layer partitions are not particularly limited and can be freely combined according to the mass transfer capacity and depth of the soil layer to achieve precise addition and release of the oxidant.

[0012] According to the present invention, preferably, the pore size of the membrane layer in the rapid release zone is 10.1 to 20.0 μm; the pore size of the membrane layer in the medium-speed release zone is 5.1 to 10.0 μm; and the pore size of the membrane layer in the slow release zone is 0.5 to 5.0 μm.

[0013] According to the present invention, preferably, the membrane porosity of the rapid release zone is 35% to 45%; the membrane porosity of the medium-speed release zone is 32% to 40%; and the membrane porosity of the slow release zone is 30% to 36%.

[0014] According to the present invention, the thickness of the film layer is 28–60 μm.

[0015] According to the present invention, the porosity of the micropores distributed on the support is 30% to 50%, and the micropore diameter is 22 to 40 μm. The thickness of the support is 200 to 800 μm.

[0016] According to the present invention, the support comprises: metal oxide and clay mineral; preferably, the weight ratio of metal oxide to clay mineral is 60-80:5-8; more preferably, the metal oxide is alumina and the clay mineral is montmorillonite.

[0017] According to the present invention, the film material is a metal oxide, and its specific composition includes at least one of ZrO2, SiO2, TiO2, and Al2O3, preferably ZrO2.

[0018] According to the present invention, an oxidant may be placed in the reactor; the oxidant is preferably persulfate and hydrogen peroxide. The persulfate is preferably sodium persulfate or disodium persulfate. The oxidant may also be mixed with a release retarder and placed together in the reactor.

[0019] According to the present invention, a thermal resistor can be installed inside the reactor; the heating requirements of the oxidant inside the reactor can be met by adjusting the size and power of the thermal resistor. The temperature range adjustable by the thermal resistor is 20–100°C, preferably 40–90°C. Preferably, the heating power of the thermal resistor is 500–5000W.

[0020] A second aspect of the present invention is to provide a method for preparing the above-mentioned in-situ chemical oxidation remediation soil reactor. The preparation method includes the following steps: applying a suspension of the composition onto a support using a dip-coating method, followed by curing, to obtain the in-situ chemical oxidation remediation soil reactor;

[0021] The composition suspension comprises: 2 wt% to 4 wt% dispersant, 2 wt% to 4 wt% binder, 15 wt% to 22 wt% film precursor and 5 wt% to 20 wt% pore-forming agent.

[0022] According to the present invention, the film precursor is a metal oxide. The metal oxide includes at least one selected from ZrO2, SiO2, TiO2, and Al2O3, preferably ZrO2. The metal oxide is preferably a powder. The powder particle size is 0.5–18 μm. The particle size is the average particle size.

[0023] According to the present invention, the curing can be at least one of drying and calcination. Preferably, the drying conditions are: temperature 40-60°C, time 8-16 hours. The calcination conditions are: temperature 900-1100°C, time 0.5-3 minutes. The calcination atmosphere is an oxygen-containing atmosphere, such as air. After calcination, the mixture is allowed to cool naturally to room temperature. The natural cooling rate can be 3-5°C / min.

[0024] According to the present invention, the dispersant is polyacrylic acid; the binder is polyvinyl alcohol; and the pore-forming agent is ammonium bicarbonate.

[0025] According to the present invention, the composition suspension further includes a pH adjuster; the pH adjuster is preferably ammonia; the amount of ammonia added is sufficient to make the pH value of the composition suspension 9 to 10.

[0026] According to the present invention, the composition suspension can be prepared by conventional methods. Preferably, the prepared suspension is subjected to ball milling homogenization. The ball milling homogenization time is 20-30 hours.

[0027] According to the present invention, the specific steps of the dip-coating method are as follows: the support is dipped into the composition suspension and then pulled out. Preferably, the dip-coating time is 25-35 seconds; the pulling speed is 4-7 mm / min; the number of dip-coatings is 1-3 times; and the next dip-coating is performed after the support has dried. The drying conditions can be conventional conditions, such as a temperature of 40-60°C and a time of 8-16 hours.

[0028] According to the present invention, depending on the requirements of membrane layer partitioning, several support segments can be selected for dip coating and then combined to obtain a reactor.

[0029] According to the present invention, the combination can be achieved through adhesive bonding and / or mechanical fixation. Silicone glass adhesive is preferred. The mechanical fixation can be further secured using stainless steel clamps.

[0030] According to the present invention, the preparation method of the support can be an extrusion method. Specifically, it includes: mixing metal oxide, binder, and pore-forming agent evenly, kneading, aging, and extruding into shape.

[0031] According to the present invention, the metal oxide is alumina; the average particle size of the alumina is 16-48 μm; the binder is a clay mineral, preferably montmorillonite; the average particle size of the montmorillonite is 68-75 μm. The pore-forming agent is corn starch; the average particle size of the corn starch is 40-50 μm.

[0032] According to the present invention, the raw materials in the support preparation method include, by weight, 60-80 parts of metal oxide, 5-8 parts of binder, and 4-6 parts of pore-forming agent. An appropriate amount of water may be added according to the kneading requirements.

[0033] According to the present invention, the aging conditions are to stand in a sealed container for 20 to 40 hours at a temperature of 10 to 25°C.

[0034] According to the present invention, the extrusion molding equipment is a twin-screw extruder.

[0035] According to the present invention, preferably, the extruded material can be placed into a mold to obtain a tubular hollow structure support. The forward speed of the extruded material is controlled in the range of 0.6 to 0.8 cm / s.

[0036] According to the present invention, the obtained extruded material is further cured in a humid environment, air-dried, and then sintered. The humidity of the humid environment is 60% to 90%. The air-drying temperature is 10 to 25°C, and the air-drying time is 10 to 12 hours. The sintering temperature is 600 to 1200°C, and the time is 9 to 15 hours. Preferably, segmented sintering can be used. The sintering heating step can be programmed, with a heating rate of 1 to 5°C / min.

[0037] A third aspect of the present invention is to provide the application of the reactor or the reactor prepared by the preparation method in soil oxidative remediation.

[0038] According to the present invention, the method of application is as follows: placing a reactor containing an oxidant into the soil to be remediated, so that the oxidant penetrates into the soil.

[0039] According to the present invention, the oxidant is preferably persulfate and hydrogen peroxide. The persulfate is preferably sodium persulfate or disodium persulfate.

[0040] According to the present invention, the reactor can be used in conjunction with existing soil pollution monitoring devices.

[0041] According to the present invention, in the aforementioned application, the oxidant may be mixed with a release retarder before being injected into the reactor; the release retarder includes at least one of attapulgite, montmorillonite, and bentonite powder. The mixing ratio of the oxidant to the release retarder, by weight, is 1:1 to 5.

[0042] According to the present invention, the oxidant can be heated during application. The heating temperature is 20–100°C, preferably 40–90°C.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] 1. The prepared microporous reactor has the following characteristics:

[0045] (1) It has good chemical stability, is resistant to acid and alkali corrosion, and will not be corroded by microorganisms;

[0046] (2) It has high mechanical strength and good thermal stability, and is stable below 800℃;

[0047] (3) Easy to clean and regenerate, can be used for a long time, and is not prone to aging;

[0048] (4) The size of the reactor (inner and outer diameters, length, etc.) can be adjusted according to the soil depth of the soil to be repaired and the needs of the repair project;

[0049] (5) The size of the voids on the outer wall of the reactor can be adjusted by controlling the coating material according to the oxidant release rate.

[0050] 2. The reactor of the present invention has mechanical, chemical and biological stability. After achieving the remediation function in a specific soil, it can be removed from the soil and transferred to other soils that need remediation for recycling. The oxidant decomposition products released by the reactor of the present invention and the reactor itself are both pollution-free environmentally friendly materials and products.

[0051] 3. The reactor of this invention includes a support body; the support body is a tubular hollow structure; one end of the tubular hollow structure is an open end, and the opposite end is a closed end; the outer wall of the support body is covered with a membrane layer; both the support body and the membrane layer have a plurality of micropores distributed on them. This invention allows for the addition of an oxidant (e.g., sodium persulfate, disodium persulfate, H2O2, etc.) in the form of a solution of a specific concentration into the hollow pipe of the reactor, which is closed at one end. The reactor has high mechanical strength and can be buried in the corresponding petroleum hydrocarbon contaminated soil area through soil drilling based on soil pollution monitoring information, ensuring the oxidant is in the core pollution area. Due to the specific micropore distribution on the reactor support body and membrane layer of this invention, the oxidant can be diffused and released at the required release rate, achieving precise addition to the contaminated soil area.

[0052] 4. This invention can adjust the pore size of the reactor at different depths in stages according to the pollution status and mass transfer characteristics of different soil layers. It can set up non-release layer, slow release layer, medium-speed release layer and fast release layer to achieve precise control of release.

[0053] 5. According to the needs of release regulation, if a particularly long release cycle is required in soil and groundwater, the oxidant can be mixed with clay minerals in an appropriate ratio before being added to the reactor, which can further extend the oxidant release cycle.

[0054] 6. The reactor of this invention has adjustable micropores, which can regulate the release of various oxidative remediation agents according to the soil mass transfer characteristics, and can also achieve heating activation simultaneously. When used for in-situ chemical oxidative remediation of polluted environments such as soil and groundwater, this reactor features precise dosing of oxidants and efficient activation. Attached Figure Description

[0055] Figure 1 These are schematic diagrams of the microporous reactor structures and their operation in Examples 1-3;

[0056] Figure 2 The figures show the cumulative release curves of sodium persulfate in aqueous solution tested by the microporous reactors of Examples 1-3; in the figures, 12.4 μM is the test curve of reactor F3 of Example 3, 5.6 μM is the test curve of reactor F2 of Example 2, and 1.8 μM is the test curve of reactor F1 of Example 1.

[0057] Figure 3 The cumulative release curves of sodium persulfate in soil tested by the microporous reactors in Examples 1-3 are shown.

[0058] In the figure, 12.4 μM sandy loam is the test curve of reactor F3 in Example 3 in sandy loam, 5.6 μM sandy loam is the test curve of reactor F2 in Example 2 in sandy loam, and 1.8 μM sandy loam is the test curve of reactor F1 in Example 1 in sandy loam.

[0059] The test curve for reactor F3 in Example 3 is 12.4 μM clay loam; the test curve for reactor F2 in Example 2 is 5.6 μM clay loam; and the test curve for reactor F1 in Example 1 is 1.8 μM clay loam.

[0060] Figure 4 This is a graph showing the cumulative release of oxidant mixed with clay minerals tested in the microporous reactor F1 of Example 1.

[0061] Figure 5 This is a comparison diagram of the oxidant release from the reactor and the PVC pipe in Example 4;

[0062] Figure 6 The test curve for the oxidative removal of petroleum hydrocarbons in soil by in-reactor heating activation of the present invention, as tested in Example 5;

[0063] Figure 7 The test curves for the removal of petroleum hydrocarbons by the oxidant released from the reactor and PVC pipe in Example 6 are shown.

[0064] Figure 8 The test curves for the removal of petroleum hydrocarbons by the reactor simultaneously releasing persulfate and hydrogen peroxide in Example 7 are shown.

[0065] Figure 9 The release curve of the oxidant during the three cycles of reactor utilization in Example 8;

[0066] Figure 10 The release curve of the reactor oxidant in composite soil in Example 9 is shown. Detailed Implementation

[0067] The present invention will be further described below with reference to specific embodiments, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0068] In this invention, the concentration of the oxidant was analyzed using the iodometric method proposed by Liang et al. (Chemosphere, 2008, 73: 1540-1543), and was measured at 352 nm using a UV spectrophotometer.

[0069] In this invention, referring to the "Determination of Petroleum in Soil by Infrared Spectrophotometry" (HJ 1051-2019), an infrared oil analyzer is used to determine the concentration of petroleum hydrocarbons in the purified extract.

[0070] In this invention, the aperture is the average aperture.

[0071] In this invention, the water mass transfer coefficient of sandy loam soil is 0.014 cm·s. -1 The mass transfer coefficient of the loam is 0.006 cm·s. -1 The mass transfer coefficient of clay loam is 0.002 cm·s. -1 .

[0072] In this invention, the petroleum hydrocarbon content in the contaminated soil is 2400 mg / kg.

[0073] Example 1

[0074] This example uses an extrusion method to prepare the tubular reactor support, as detailed below:

[0075] The materials used are (1) alumina (Al2O3) with an average particle size of 36 μm; (2) montmorillonite with an average particle size of 70 μm; and (3) corn starch, food grade, with an average particle size of 45 μm. The formula is: 68 wt% alumina + 7 wt% montmorillonite + 5 wt% corn starch + 20 wt% H2O.

[0076] Alumina, montmorillonite, corn starch, and deionized water are mixed, kneaded, and aged at 20°C for 24 hours before being fed into a twin-screw extruder. The mixture is then extruded using the twin-screw extruder. During extrusion, the screw continuously forces the feed material through the die, producing a tubular extrudate. The extrudate's forward speed is controlled at 0.7 cm / s.

[0077] The resulting extruded material was further cured in a humid environment with 80% humidity for 48 hours, air-dried at 20°C for 12 hours, and then sintered. The sintering temperature was increased from room temperature by 1°C / min to 600°C, and then by 1.8°C / min to 1200°C, with each sintering temperature held at 600°C, 900°C, and 1200°C for 3 hours. The support Z1 was tested and found to have a porosity of 42%, an average pore size of 28 μm, and a thickness of 600 μm.

[0078] Method for preparing modified membranes for tubular reactors:

[0079] The composition suspension was prepared using 3 wt% dispersant polyacrylic acid, 2 wt% binder polyvinyl alcohol, 20 wt% ZrO2 powder with an average particle size of 3 μm, and 8 wt% ammonium bicarbonate. The pH of the suspension was adjusted to 10 using a 30 wt% ammonia solution under continuous mechanical stirring.

[0080] The composition suspension was poured into a polyethylene bottle and ball-milled for 24 hours using a 9 mm alumina ball mill to ensure homogeneity.

[0081] The prepared alumina support was immersed in the suspension for 30 seconds. Then, the membrane reactor was pulled out of the suspension at a speed of 5 mm / min. The membrane was then dried in a drying oven at 40°C for 12 h.

[0082] After drying, the membrane is dip-coated again. A total of three dip-coatings are performed. After drying, the membrane is sintered in air. After holding at 1000℃ for 1 minute, it is cooled to room temperature and dried to obtain the tubular reactor F1 with the membrane layer. The cooling rate is 4℃ / min. The membrane layer area of ​​reactor F1 accounts for 100% of the total outer wall area. The membrane porosity of the reactor is 36%, and the average pore size of the micropores on the membrane layer is 1.8 μm. The membrane layer thickness of the reactor is 54 μm. A schematic diagram of the reactor is shown below. Figure 1 As shown.

[0083] A slow-release test of the oxidant in water was conducted on the reactor. The specific steps were as follows: A 5 wt% sodium persulfate solution was added to the test device. The device was then placed in a glass beaker containing 1 L of distilled water. The release of sodium persulfate from the device was measured at time points of 1, 2, 4, 8, 16, 24, 32, and 48 hours. The cumulative release curve of sodium persulfate in the aqueous solution is shown below. Figure 2 As shown.

[0084] A slow-release test of the oxidant in soil was conducted on the reactor. The specific steps were as follows: A 5wt% sodium persulfate solution was added to the test device. The device was then placed in a 30cm deep soil column containing 5kg of soil. Sandy loam and clay loam were selected as test soils, and the soil moisture content was pre-adjusted to 50% of maximum water holding capacity. With the reactor opening above the soil layer, a 5wt% sodium persulfate solution was continuously replenished from the storage tank using a low-speed water pump, based on the solution diffusion loss. The release of sodium persulfate from the soil at a distance of 5cm from the reactor wall was tested at hourly intervals of 1, 4, 8, 12, 24, 48, 72, and 96 hours. For each test, 10g of soil sample was taken, 30ml of ultrapure water was added, and the mixture was shaken for 1 hour. The mixture was then centrifuged at 3000 rpm for 20 minutes. The supernatant was collected, and the concentration of sodium persulfate was tested. The accumulation of sodium persulfate was recorded as follows. Figure 3 As shown.

[0085] A cumulative release test experiment was conducted on the reactor using a mixture of oxidant and clay minerals. Considering the need for an exceptionally long oxidant release period in a specific project, to further extend the release period, the oxidant was mixed with attapulgite, montmorillonite, and bentonite powders, and then added to the controlled-release reactor. This reduced the transport and diffusion of the oxidant within the reactor tubes, thereby slowing the release rate and extending the release period. The specific steps were as follows: sodium persulfate and attapulgite powder (average particle size 15 μm) were mixed at mass ratios of 1:1, 1:2, and 1:3, respectively, to obtain three different mixed solutions. The concentration of sodium persulfate in the sodium persulfate mixtures was kept consistent at 5 wt%. Additionally, a 5 wt% sodium persulfate solution without attapulgite powder was used as a parallel test experiment. Using the above mixed solutions, cumulative release tests of the oxidant mixed with clay minerals were conducted in the reactor and support structure in soil. The test procedures were the same as the controlled-release test experiment of the reactor in soil described above. The test results are as follows: Figure 4 As shown.

[0086] from Figure 4It can be seen that, compared with a 5% sodium persulfate solution, when clay mineral powder is mixed with the oxidant in a certain proportion and added to the controlled-release reactor, the release rate of the oxidant sodium persulfate can be further slowed down, and the release cycle of the oxidant can be extended. The higher the proportion of clay minerals, the slower the release rate, which provides more solutions for long-term remediation scenarios.

[0087] Example 2

[0088] Method for preparing the support:

[0089] The support Z2 was prepared using the same method as in Example 1.

[0090] Method for preparing modified membranes for tubular reactors:

[0091] The composition suspension was prepared using 3 wt% dispersant polyacrylic acid, 3 wt% binder polyvinyl alcohol, 20 wt% ZrO2 powder with an average particle size of 7 μm, and 10 wt% ammonium bicarbonate. The pH of the suspension was adjusted to 10 using a 30% ammonia solution under continuous mechanical stirring.

[0092] The composition suspension was poured into a polyethylene bottle and ball-milled for 24 hours using a 9 mm alumina ball mill to ensure homogeneity.

[0093] The prepared alumina support was immersed in the suspension for 30 seconds. Then, the membrane reactor was pulled out of the suspension at a speed of 5 mm / min. The membrane was then dried in a drying oven at 40°C for 12 h.

[0094] After drying, the membrane is dip-coated again. A total of three dip-coatings are performed. After drying, the membrane is sintered in air. After holding at 1000℃ for 1 minute, it is cooled to room temperature and dried to obtain the tubular reactor F2 with the membrane layer. The cooling rate is 4℃ / min. The membrane layer area of ​​reactor F2 accounts for 100% of the total outer wall area. The membrane porosity of the reactor is 38%, and the average pore size of the micropores on the membrane layer is 5.6 μm. The membrane layer thickness of the reactor is 56 μm. A schematic diagram of the reactor is shown below. Figure 1 As shown.

[0095] A slow-release test of the oxidant in water was conducted on the reactor. The test method was the same as in Example 1, and the test results are as follows. Figure 2 As shown.

[0096] A slow-release test of the oxidant in the soil was conducted on the reactor. The test method was the same as in Example 1, and the test results are as follows. Figure 3 As shown.

[0097] Example 3

[0098] Method for preparing the support:

[0099] The support Z3 was prepared using the same method as in Example 1.

[0100] Method for preparing modified membranes for tubular reactors:

[0101] The composition suspension was prepared using 3 wt% dispersant polyacrylic acid, 3 wt% binder polyvinyl alcohol, 20 wt% ZrO2 powder with an average particle size of 16 μm, and 12 wt% ammonium bicarbonate. The pH of the suspension was adjusted to 10 using a 30 wt% ammonia solution under continuous mechanical stirring.

[0102] The composition suspension was poured into a polyethylene bottle and ball-milled for 24 hours using a 9 mm alumina ball mill to ensure homogeneity.

[0103] The prepared alumina support was immersed in the suspension for 30 seconds. Then, the membrane reactor was pulled out of the suspension at a speed of 5 mm / min. The membrane was then dried in a drying oven at 40°C for 12 h.

[0104] After drying, the membrane is dip-coated again. A total of three dip-coatings are performed. After drying, the membrane is sintered in air. After holding at 1000℃ for 1 minute, it is cooled to room temperature and dried to obtain the tubular reactor F3 with the membrane layer. The cooling rate is 4℃ / min. The membrane layer area of ​​reactor F3 accounts for 100% of the total outer wall area. The membrane porosity is 40%, and the average pore size of the micropores on the membrane layer is 12.4 μm. The membrane layer thickness is 58 μm. A schematic diagram of the reactor is shown below. Figure 1 As shown.

[0105] A slow-release test of the oxidant in water was conducted on the reactor. The test method was the same as in Example 1, and the test results are as follows. Figure 2 As shown.

[0106] A slow-release test of the oxidant in the soil was conducted on the reactor. The test method was the same as in Example 1, and the test results are as follows. Figure 3 As shown.

[0107] from Figure 2 It can be seen that reactors F1 (with an average pore size of 1.8 μm after coating modification), F2 (with an average pore size of 5.6 μm after coating modification), and F3 (with an average pore size of 12.4 μm) can all release the oxidant persulfate into the water at a relatively stable rate. The controlled-release reactors with pore sizes of 1.8 μm (F1) and 5.6 μm (F2) showed significantly slower release rates than the reactor with 12.4 μm pore size (F3), indicating that the release rate of the oxidant can be controlled to some extent by adjusting the reactor membrane pore size. This characteristic can be used to regulate the release of oxidants from polluted groundwater to optimize remediation parameters.

[0108] from Figure 3It can be seen that both reactor F3 (with an average pore size of 12.4 μm) and reactor F1 (with an average pore size of 1.8 μm after coating modification) can release the oxidant persulfate into the soil at a relatively stable rate. The release rate of reactor F3 (12.4 μm) is significantly faster than that of reactor F1 (1.8 μm), indicating that the release rate of the oxidant in the soil can be controlled to some extent by adjusting the reactor membrane pore size. In the two soil types, the three reactors with different pore sizes also exhibited different release rates. For sandy loam, the release rate of the oxidant was: reactor F3 (12.4 μm) > reactor F2 (5.6 μm) > reactor F1 (1.8 μm); for clay loam, the release rates of all three reactors with different pore sizes were significantly slower. Furthermore, the release efficiency of the three reactors in loam soil showed some differences, but these differences were not significant and did not fully reflect the differences between the reactors. All three were similar to reactor F1 (1.8 μm), indicating that the 1.8 μm reactor is more suitable for clay soils with weak mass transfer. By regulating the release of oxidants, we can better design the parameters for oxidative remediation, improve the utilization rate of oxidants, increase the removal efficiency of pollutants, and save remediation costs.

[0109] Example 4

[0110] Reactor F1 was prepared according to the method in Example 1. A 5% sodium persulfate solution was added to F1, which was then placed in a 30cm deep soil column containing 5kg of soil. The soil moisture content was pre-adjusted to 50% of its maximum water holding capacity. Sodium persulfate solution was replenished in real-time at the reactor opening based on solution diffusion loss, hourly. At 48-hour intervals, one soil sample was collected from each of the four directions (left, right, front, and back) at a horizontal distance of 5cm and a vertical distance of 10cm outside the controlled-release reactor. Each time, 10g of soil sample was taken, 30ml of water was added, and the mixture was shaken for 1 hour. The sample was then centrifuged at 3000 rpm for 20 minutes, and the supernatant was collected. The concentration of sodium persulfate in the soil was determined as follows: Figure 5 As shown.

[0111] Using a PVC pipe of the same size as F1 specification with open ends as a comparative experiment, the concentration of sodium persulfate in the soil was tested according to the above method. Figure 5 As shown.

[0112] from Figure 5 It can be seen that reactor F1 can effectively release oxidant from different directions, and the oxidant concentration measured around the reactor is very similar. This has important practical significance for the precise injection and effective diffusion of oxidants, as well as for subsequent oxidation reactions.

[0113] from Figure 5It can be seen that using a polyvinyl chloride (PVC) pipe with open ends as the oxidant injection tool, and measuring the persulfate concentration of the oxidant at four different locations, revealed that the oxidant distribution was highly uneven, with significant concentration differences in the four directions. This method failed to achieve precise injection and effective diffusion of the oxidant, creating considerable uncertainty in the control of the subsequent oxidation reaction, affecting the effective utilization of the oxidant, and resulting in an inability to effectively control the remediation efficiency. The reactor of this invention can effectively release the oxidant from different directions, offering significant advantages.

[0114] Example 5

[0115] Reactor F1 was prepared according to Example 1. A 5% sodium persulfate solution was added, and the reactor was placed in a 30cm deep soil column containing 5kg of contaminated soil. After 48 hours of oxidant release and diffusion, a 500W resistance heater was placed at the open end, and the temperature was controlled at 20℃±2℃, 40℃±2℃, 60℃±2℃, and 80℃±2℃ using thermocouples. The reaction was continued for 96 hours. Soil samples were collected at a horizontal distance of 5cm and a vertical distance of 10cm to analyze the oxidation and removal of petroleum hydrocarbons in the soil at different temperatures. The petroleum hydrocarbon removal results are as follows: Figure 6 As shown.

[0116] like Figure 6 As shown, the 1.8μm controlled-release reactor of reactor F1 diffuses the oxidant evenly for 48 hours, and then heats it with a resistance of a specific power to control the temperature at 20℃±2℃. After continuous heating for 96 hours, the removal efficiency of petroleum hydrocarbons in the soil can reach 18%.

[0117] like Figure 6 As shown, in the reactor F1 of this invention, after the oxidant is released for 48 hours and uniformly diffused, it is then heated by a resistance heater with specific power and temperature control. After continuous heating for 96 hours, petroleum hydrocarbon pollutants in the soil can achieve a removal efficiency of 78% at 60℃±2℃ and 81% at 80℃±2℃. This demonstrates that the reactor F1 of this invention can simultaneously achieve the dual functions of controlled-release oxidant and heating-activated oxidant through electric heating and water heat transfer, enabling effective oxidative remediation of pollutants in the soil.

[0118] Reactor F2 was prepared according to the method described in Example 2. The oxidation and removal of petroleum hydrocarbons in the soil at different temperatures were tested using the method described above. Figure 6 As shown, petroleum hydrocarbon pollutants in soil can be removed at an efficiency of 76% at 60℃±2℃ and at 80℃±2℃, the removal efficiency can reach 82%.

[0119] Reactor F3 was prepared according to the method described in Example 3, and the oxidation and removal of petroleum hydrocarbons in soil at different temperatures were tested according to the above method. The removal efficiency of petroleum hydrocarbon pollutants in soil reached 75% at 60℃±2℃ and 80% at 80℃±2℃.

[0120] Example 6

[0121] Reactor F1 was prepared according to Example 1. The oxidation and removal of petroleum hydrocarbons using F1 and a polyvinyl chloride (PVC) pipe with open ends was tested. A 5 wt% sodium persulfate solution was added to the test device, which was then placed in a 30 cm deep soil column containing 5 kg of petroleum hydrocarbon-contaminated soil. After 48 hours of oxidant release and diffusion, a 500 W resistance heater was placed at the open end, and the heating temperature was controlled at 60 ± 2 °C. The reaction was continued for 96 hours. One sample was collected at a horizontal distance of 5 cm and a vertical depth of 10 cm around the test device. The oxidation and removal of petroleum hydrocarbons in the soil were analyzed. The petroleum hydrocarbon removal results are as follows: Figure 7 As shown. Additionally, after 48 hours of oxidant release and diffusion, a petroleum hydrocarbon oxidation and removal test was conducted without heating, i.e., at a temperature of 20±2℃. The results are shown below. Figure 7 .

[0122] from Figure 7 It can be seen that polyvinyl chloride (PVC) pipes with openings at both ends not only fail to effectively and uniformly release the oxidant, but also cannot be combined with other activation methods. Therefore, the removal of petroleum hydrocarbons from soil is not only low but also highly variable, making it difficult to effectively control remediation efficiency. The reactor of this invention, with its controllable release and coupled thermal activation, has significant advantages in oxidant release and activation. It can simultaneously achieve controlled release and activated oxidation of the oxidant in a single unit, showing great promise for engineering applications.

[0123] from Figure 7 As can be seen, the F1 1.8μm controlled-release reactor of this invention can not only accurately and controllably disperse the oxidant into the contaminated soil, but also effectively activate the oxidant through electric heating and water heat transfer to remove petroleum hydrocarbons from the soil. Moreover, since the oxidant is evenly dispersed around the reactor and the heating and activation are also effective, the removal rate of petroleum hydrocarbons around the reactor is relatively stable, reaching 80%, thus achieving a good remediation purpose.

[0124] like Figure 7As shown, the reactor of this invention can effectively disperse the oxidant persulfate into the contaminated soil. However, without an effective activation method, the rate at which persulfate decomposes and releases free radicals in the soil is very slow, and the removal rate of petroleum hydrocarbon pollutants is only 10% after 96 hours. Only by adopting an effective activation method (such as thermal activation) can pollutants be removed rapidly within a shorter period of time, achieving the goal of efficient remediation.

[0125] Example 7

[0126] Reactor F1 was prepared according to the method described in Example 1. The oxidation of petroleum hydrocarbons was tested under three conditions: sodium persulfate, hydrogen peroxide, and a combination of sodium persulfate and hydrogen peroxide (weight ratio 1:1). In all three conditions, the concentration of the oxidant was 5 wt%.

[0127] The above solutions were added to the test apparatus, which was then placed in a soil column containing 5 kg of petroleum hydrocarbon-contaminated soil at a depth of 30 cm. After 48 hours of oxidant release and diffusion, a 500 W resistance heater was placed at the open end, with the maximum heating temperature controlled at 60 ± 2 °C. The reaction was continued for 96 hours. One sample was collected at a depth of 10 cm and approximately 5 cm around the perimeter of the controlled-release reactor. The oxidation and removal of petroleum hydrocarbons in the soil were analyzed. The petroleum hydrocarbon removal results are as follows: Figure 8 As shown.

[0128] like Figure 8 As shown, the controlled-release reactor of this invention can simultaneously release two oxidants, persulfate and H2O2. Furthermore, by activating the oxidants through electric heating and water heat transfer, the oxidants can be effectively activated, removing petroleum hydrocarbon pollutants from the soil. The simultaneous addition and activation of persulfate and H2O2 can further improve the removal of petroleum hydrocarbons from the soil, achieving a removal rate of >85%. This is likely because the free radicals released by persulfate and H2O2 are sulfate radicals and hydroxyl radicals, respectively. These two free radicals have different oxidizing properties and reactivity with the pollutants, exhibiting a certain degree of complementarity, which can further improve the pollutant removal efficiency. This embodiment demonstrates that the reactor designed in this invention is applicable to water-soluble oxidants and can be used simultaneously for the controlled release and oxidative remediation of different oxidants to achieve excellent soil remediation goals.

[0129] Example 8

[0130] Reactor F1 was prepared according to the method described in Example 1. A 5 wt% sodium persulfate solution was added and placed in a 30 cm deep soil column containing 5 kg of petroleum hydrocarbon-contaminated soil. After 48 hours of oxidant release and diffusion, and once the oxidant diffusion was relatively uniform, a 500 W resistance heater was placed at the open end, and the heating temperature was controlled at 60 ± 2 °C. The reaction was continued for 96 hours. After the test, the reactor was removed and first cleaned with tap water, then with ultrasonically distilled water twice each. The reactor was then reburied in the soil following the above procedure, and a persulfate release test was conducted. The release of sodium persulfate from the soil at a distance of 5 cm from the outer wall of the reactor was tested at time points of 1, 4, 8, 12, 24, 48, 72, and 96 hours. After completing this test, the reactor was removed and cleaned with tap water, then with ultrasonically distilled water twice each. The reactor was then reburied in the soil following the above procedure, and three tests were conducted on persulfate oxidation, post-oxidation reactor cleaning, and sodium persulfate release. The results of the three tests were compared. Figure 9 As shown.

[0131] from Figure 9 It can be seen that after the controlled-release reactor of the present invention is buried in the soil three times to release and activate the oxidant, and after simple tap water washing and ultrasonic distilled water washing, the release rate of sodium persulfate in the reactor does not change significantly, which shows that it has good recyclability. This indicates that the mechanical and chemical properties of the reactor are very stable and can be recycled multiple times, which can effectively save repair costs and improve the value of engineering applications.

[0132] Example 9

[0133] Reactor F4 was prepared according to the method in Example 1. F4 was identical to F1. F4 was a tubular structure with one end open and the other end closed.

[0134] Reactor F5 was prepared according to the method in Example 2. The difference between F5 and F2 is that F5 is a tubular structure open at both ends. Everything else is the same.

[0135] Reactor F6 was prepared according to the method in Example 1. The difference between F6 and F3 is that F6 is a tubular structure open at both ends. Everything else is the same.

[0136] F4, F5, and Z6 are all 20 cm in length. F4 (1.8 μm), F5 (5.6 μm), and F6 (12.4 μm) are fixed in pairs in the following order: The open end of F4 is fixed to either open end of F5, and the other open end of F5 is fixed to either open end of F6. Stainless steel hoops are used for mechanical fixation, resulting in the oxidative remediation soil reactor ZF.

[0137] The reactor ZF was then placed in a soil column containing, from bottom to top, clay loam, loam, and sandy loam, each layer 20 cm deep. The soil moisture content was pre-adjusted to 50% of its maximum water holding capacity. The open end of the reactor ZF faced upwards, and the closed end faced downwards. The open end was flush with the soil surface. Using hourly intervals, with 48 hours as the time node, soil samples were taken from 5 cm away from the outer wall of the reactor, at depths of 10 cm, 30 cm, and 50 cm from four directions (left, right, front, and back) to measure the release of sodium persulfate from the soil. For each sample, 10 g of soil was taken, 30 ml of water was added, and the mixture was shaken for 1 hour. The mixture was then centrifuged at 3000 rpm for 20 minutes. The supernatant was collected, and the concentration of sodium persulfate was measured. The accumulation of sodium persulfate was recorded as follows: Figure 10 As shown.

[0138] from Figure 10 It can be seen that the controlled-release reactor of the present invention can adopt flexible segmented combinations according to the soil texture and mass transfer capacity at different soil depths. The release concentration of oxidant is relatively similar in the four directions of left, right, front, and back in three different soil textures, indicating that the reactor has the function of precise stratified release of oxidant and has good application prospects in chemical oxidation remediation.

[0139] The above embodiments are merely a few of the many embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. The scope of protection of the present invention is determined by the scope of the claims. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention are covered within the scope of protection of the present invention.

Claims

1. Application of a reactor in the oxidative remediation of petroleum hydrocarbon contaminated soil, wherein the application employs in-situ chemical oxidative remediation, and the reactor includes a support body; the support body is a tubular hollow structure; one end of the tubular hollow structure is an open end, and the opposite end is a closed end; the outer wall of the support body is covered with a membrane layer; and both the support body and the membrane layer have a number of micropores distributed on them. The support is composed of metal oxides and clay minerals, wherein the weight ratio of metal oxides to clay minerals is 60-80:5-8; the micropores distributed on the support have a porosity of 30-50% and a pore size of 22-40 μm. The film material is at least one of ZrO2, SiO2, TiO2, and Al2O3; An oxidant is placed inside the reactor; The reactor is equipped with a thermal resistor; The micropores distributed on the membrane have a pore size of 0.5 μm to 20 μm, and the membrane porosity is 30% to 50%. The area of ​​the outer wall of the support structure covered by the membrane layer accounts for 70% to 100% of the total area of ​​the outer wall of the support structure; The membrane layer partitions include one or more of the following: a fast release zone, a medium-speed release zone, and a slow release zone; The membrane pore size in the rapid release zone is 10.1~20.0 μm; the membrane pore size in the medium-speed release zone is 5.1~10.0 μm; and the membrane pore size in the slow release zone is 0.5~5.0 μm. The membrane porosity in the rapid release zone is 35%~45%; the membrane porosity in the medium-speed release zone is 32%~40%; and the membrane porosity in the slow release zone is 30%~36%.

2. The application according to claim 1, characterized in that, The thickness of the film is 28~60μm.

3. The application according to claim 1, characterized in that, The thickness of the support is 200~800μm.

4. The application according to any one of claims 1 to 3, characterized in that, The method for preparing the reactor includes the following steps: applying a composition suspension onto a support using a dip-coating method, and then solidifying it to obtain a reactor for in-situ chemical oxidation remediation of soil; The composition suspension comprises: 2wt%~4wt% dispersant, 2wt%~4wt% binder, 15wt%~22wt% film precursor and 5wt%~20wt% pore-forming agent.

5. The application according to claim 4, characterized in that, In the composition suspension, the dispersant is polyacrylic acid; the binder is polyvinyl alcohol; and the pore-forming agent is ammonium bicarbonate.

6. The application according to claim 4, characterized in that, The pH of the composition suspension is 9-10.

7. The application according to claim 4, characterized in that, The support is prepared by extrusion, in which the extrudate is placed into a mold to obtain the support.

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