Oily sludge restoration method based on photocatalyst catalytic oxidation

Abstract

The invention discloses an oily sludge remediation method based on photocatalyst catalytic oxidation, and belongs to the technical field of soil pollution control and treatment. The method comprises the following steps: recycling petroleum hydrocarbon which can be recycled in the oily sludge to form oily sludge with low oil content; the method comprises the following steps: adding an inorganic oily sludge repairing agent, a photocatalyst and water into oily sludge with low oil content under an illumination condition, and uniformly stirring; wherein the inorganic oily sludge repairing agent comprises calcium oxide and magnesium oxide. The photocatalyst and the traditional inorganic soil remediation agent are mixed for use, the added photocatalyst can treat components which are difficult to treat by the traditional inorganic soil remediation agent, and meanwhile, the activity of the photocatalyst can be accelerated by an alkaline environment formed by the traditional inorganic soil remediation agent and heat released by the traditional inorganic soil remediation agent; and finally, high-efficiency treatment of the oily sludge is realized under the condition that a large amount of oily sewage is not generated, and the oil content of the oily sludge is reduced.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, as well as soil pollution control and treatment technology, and water pollution and natural pollution control and treatment technology, specifically a method for remediating oily sludge based on photocatalytic oxidation. Background Technology

[0002] Oil extraction, refining, and other industrial activities generate oily sludge, which poses significant environmental risks and is difficult to manage. Typically, oily sludge with high oil content is extracted to recover the crude oil, resulting in low-oil-content sludge (2%–5% oil content). However, this oil content still falls short of landfill requirements, necessitating further treatment to reduce the oil content.

[0003] Currently, bioremediation and chemical treatment are the main methods used to treat this type of low-oil-content oily sludge. Bioremediation utilizes microorganisms to degrade the organic components in oily sludge, offering environmental advantages, but it has a long remediation cycle and requires stringent environmental conditions. Chemical treatment is more widely used, employing chemical agents to treat the oily sludge and achieve oil removal. However, this method requires careful consideration of the selection of chemical agents and their environmental impact, and it is also costly. For example, CN106746401A discloses a method for treating oily sludge, which involves mixing inorganic minerals (calcium oxide, magnesium oxide, volcanic ash, etc.) with oily sludge and water. The alkaline environment created by the dissolution of alkaline oxides such as calcium oxide and magnesium oxide in water promotes the decomposition / degradation of large-molecule ethers into smaller-molecule products, and utilizes the heat released during dissolution to promote the volatilization of light hydrocarbons, thereby reducing the oil content. However, polycyclic aromatic hydrocarbons are often difficult to degrade and have high boiling points, thus remaining in the sludge and making it difficult to further reduce the oil content. In addition, photocatalysts have been widely used in oily wastewater. Under light conditions, photocatalysts can generate hydroxyl radicals, which can degrade almost all petroleum hydrocarbon molecules. The final products are water and carbon dioxide, achieving deep degradation while also being environmentally friendly. However, sludge has poor light transmittance and significantly blocks light, resulting in a slow overall reaction rate. Currently, some experiments add water to oily sludge to form a suspension to improve the system's light transmittance, thereby increasing the reaction rate. However, this leads to the generation of a large amount of oily wastewater, bringing new problems. Summary of the Invention

[0004] To address the aforementioned problems, one objective of this invention is to provide a method for the remediation of oily sludge based on photocatalytic oxidation. This invention combines a photocatalyst catalyst with a traditional inorganic soil remediation agent. In the traditional inorganic soil remediation agent, calcium oxide and magnesium oxide react with water to form magnesium hydroxide and calcium hydroxide. This process raises the system temperature and adjusts the pH to alkaline, both of which enhance the catalytic activity of the photocatalyst catalyst. This invention combines the advantages of both traditional inorganic soil remediation agents and photocatalyst catalysts. Simultaneously, the inorganic soil remediation agent synergistically enhances the efficiency of the photocatalyst catalyst, ultimately achieving efficient treatment of oily sludge without generating large amounts of oily wastewater and reducing the oil content of the sludge.

[0005] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows: A method for remediating oily sludge based on photocatalytic oxidation includes the following steps: S1. Recover recoverable petroleum hydrocarbons from oily sludge to form oily sludge with low oil content; S2. Under light conditions, add inorganic oily sludge remediation agent, photocatalyst catalyst and water to oily sludge with low oil content and stir evenly; wherein, the inorganic oily sludge remediation agent includes calcium oxide and magnesium oxide.

[0006] In this invention, recyclable resources in oily sludge are first recovered to conserve resources. Many existing recovery technologies exist, such as extraction, which can reduce the oil content of oily sludge to below 5%. The inorganic oily sludge remediation agent, when mixed with water, adjusts the pH of the oily sludge system to alkaline. Under water and light conditions, the photocatalyst generates free radicals to decompose petroleum hydrocarbons. Simultaneously, the alkaline environment created by the inorganic oily sludge remediation agent and the heat released when dissolved in water enhance the activity of the photocatalyst, accelerating the degradation of petroleum components, especially aromatic hydrocarbons that the inorganic oily sludge remediation agent cannot handle, thereby further reducing the oil content of the oily sludge. The amounts of inorganic oily sludge remediation agent, photocatalyst, and water can be adjusted as needed. For example, the amount of water added is based on the required amount for the reaction, maintaining the water content in the oily sludge mixture at 20%–80% throughout the reaction process to avoid generating oily wastewater. The amount of photocatalyst added is 0.1%–2% of the mass of the oily sludge.

[0007] In this invention, the photocatalyst can be titanium dioxide (TiO2) or rutile, anatase, or other ores containing titanium dioxide.

[0008] In this invention, the alkaline environment and heat released by the inorganic oily sludge remediation agent accelerate the activity of the photocatalyst catalyst. However, the photocatalyst catalyst requires light to react. For example, TiO2 requires ultraviolet light with a wavelength less than 400 nm, and light has poor penetration into oily sludge. Therefore, it mainly improves the photodegradation rate of petroleum hydrocarbons on the surface of the oily sludge exposed to light, while the petroleum hydrocarbons inside the oily sludge are not actually photocatalytically degraded. This results in a large amount of photocatalyst catalyst being wasted. Therefore, as a specific embodiment of this invention, a luminescent material, such as a thermoluminescent material, is added to the oily sludge. This material absorbs the heat released when magnesium oxide or calcium oxide dissolves in water or sunlight as energy and emits light, thereby increasing the light inside the sludge and promoting the photodegradation inside the sludge.

[0009] Furthermore, rare earth phosphorescent powder is used as the luminescent material, which is a typical phosphorescent material.

[0010] In this invention, the activity of naturally occurring photocatalysts is lower than that of existing synthetic photocatalysts. To further accelerate the degradation rate, synthetic photocatalysts can be used. However, synthetic photocatalysts are expensive. Therefore, as a specific embodiment of this invention, a magnetic photocatalyst is used, such as the catalyst disclosed in "Preparation and characterization of the magnetic FeSO@TiO, nanocomposite with the in-situ synthesis coating method," to facilitate the subsequent recovery of the photocatalyst through magnetic attraction. Similarly, the luminescent material can be a naturally occurring thermoluminescent material or a magnetic thermoluminescent material, which facilitates its recovery.

[0011] In one specific embodiment of the present invention, the photocatalyst is lanthanum hexaboride. Unlike other photocatalysts, this catalyst catalyzes over a longer wavelength range, meaning it can directly achieve catalysis using temperature or light, thus enabling catalysis even at night. This is a rather special photocatalyst, and can even be considered a thermal catalyst, emitting light using the heat from magnesium oxide and calcium oxide.

[0012] The lighting conditions of this invention can be sunlight, but at night or on cloudy or rainy days when there is a lack of sunlight, or can be provided by artificial light, such as ultraviolet lamps. However, the former is more energy-efficient. As a specific embodiment of this invention, the lighting conditions are sunlight, and the oily sludge is turned over at intervals during the daytime lighting period so that the oily sludge in all places can participate in the photocatalytic reaction evenly.

[0013] Furthermore, the inorganic oily sludge remediation agent is added to the oily sludge in multiple intervals, and after each addition, water is sprayed and the oily sludge, inorganic oily sludge remediation agent and water are mixed evenly and then spread evenly on the ground again.

[0014] Furthermore, the inorganic oily sludge remediation agent should be added at least once during nighttime when there is little or no light.

[0015] Beneficial effects: This invention combines a photocatalyst catalyst with a traditional inorganic soil remediation agent. While traditional inorganic soil remediation agents can treat oily sludge, they are ineffective at removing components such as aromatic hydrocarbons from the sludge. The photocatalyst catalyst added in this invention can treat these components that traditional inorganic soil remediation agents struggle with. Simultaneously, the alkaline environment and heat released by traditional inorganic soil remediation agents accelerate the activity of the photocatalyst catalyst, ultimately achieving efficient treatment of oily sludge without generating large amounts of oily wastewater, thus reducing the oil content of the sludge. Furthermore, this invention also improves the overall degradation rate by adding luminescent materials or specific types of photocatalysts to the oily sludge. Detailed Implementation

[0016] To more clearly illustrate the present invention, specific embodiments are described below. Those skilled in the art should understand that the following description is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0017] The oily sludge used in the following examples all came from a historical oily sludge contaminated site in a petrochemical plant area. It was a mixture of oily sludge and oily soil, and was solid with no flowability. The main pollutants were crude oil hydrocarbons (C10~C40), a small amount of heavy metals (such as lead and cadmium), and organic halides. The oil content was 2.09 wt% and the water content was 27 wt%. Therefore, it was a low-oil-content oily sludge, and no petroleum hydrocarbon recovery operation was performed on it in the following examples. In addition, the oily sludge in the following examples was in a lumpy state. In order to facilitate its mixing with other components, it was crushed and passed through a 4-mesh soil sieve for use in the following examples and comparative examples.

[0018] Example 1 A method for remediating oily sludge based on photocatalytic oxidation includes the following steps: Take 50 kg of oily sludge, add 5 kg of inorganic oily sludge remediation agent (calcium oxide and magnesium oxide in a mass ratio of 2:3) and 1 kg of photocatalytic catalyst (TiO2) to it and stir evenly. Then, spread the mixture evenly on a 3 m... 2In the field, the oily sludge was turned over every 2 hours under daylight conditions, but not at night. Starting the next day, 5 kg of water was sprayed into the oily sludge mixture at 10:00 am every day. After 5 days (i.e., 9:00 am on the sixth day), the final oil content of the oily sludge was measured to be 1.76 wt%.

[0019] Comparative Example 1 The procedure was the same as in Example 1, but without the addition of 1 kg of photocatalyst. After 5 days, the final oil content was measured to be 1.98 wt%.

[0020] Example 2 The difference from Example 1 is that 1 kg of rare earth phosphorescent powder was added to the oily sludge on the first day, and the final oil content was measured to be 1.62 wt% after 5 days.

[0021] Example 3 The difference from Example 1 is that the added photocatalyst is lanthanum hexaboride (LaB6), and the final oil content measured after 5 days is 0.85 wt%.

[0022] Example 4 The difference from Example 1 is that the photocatalyst added is lanthanum hexaboride (LaB6). At the same time, 5 kg of inorganic oily sludge remediation agent (calcium oxide and magnesium oxide in a mass ratio of 2:3) is added in 4 portions (once a day for the first four days). The first addition is 2 kg, and the subsequent additions are 1.0 kg each time. Starting from the second day, each addition is made before spraying water and mixed evenly with the original material before being spread out again. The final oil content measured after 5 days is 0.78 wt%.

[0023] Example 5 The difference from Example 4 lies in the timing of adding the inorganic oily sludge remediation agent and spraying water. The second addition of the inorganic oily sludge remediation agent was at 12:00 AM on the first day, and subsequent additions were also made at 12:00 AM every night. After adding the oily sludge remediation agent, water was sprayed, and the mixture was thoroughly mixed with the existing material before being redistributed (no water was sprayed or the material was redistributed at 10:00 AM). The final oil content measured after 5 days was 0.61 wt%.

[0024] As shown in Comparative Example 1 and Example 1, the oil content decreased significantly after the addition of the photocatalyst, indicating a significant photocatalytic effect. This is mainly because the alkaline environment formed by the calcium oxide and magnesium oxide in the inorganic soil remediation agent after contact with water enhances the reactivity of the photocatalyst. As shown in Examples 1 and 2, the final oil content decreased significantly after the addition of rare earth luminescent powder. This is because rare earth luminescent powder is a light-storing and light-emitting material; it can store energy under light conditions and emit light under dark conditions. Thus, when the oily sludge is turned over during the day, the catalyst in the shaded area (i.e., the catalyst in the non-surface oily sludge) can continue to react using the light emitted by the rare earth luminescent powder, resulting in more catalysts simultaneously undergoing the photocatalytic reaction and a longer reaction time, thus significantly reducing the oil content. As shown in Examples 1 and 3, lanthanum hexaboride exhibits stronger activity than titanium dioxide. As shown in Examples 4 and 3, adding 5 kg of inorganic oily sludge remediation agent in multiple stages is beneficial to improving its photocatalytic rate. This is likely because each addition releases heat, resulting in a longer overall time that the mixture of oily sludge and photocatalyst catalyst remains at a high temperature. This also indicates that the higher the temperature, the faster the photocatalytic reaction. As shown in Examples 4 and 5, adding the inorganic oily sludge remediation agent at night is more advantageous. This is because lanthanum hexaboride reacts slowly under weak light at night, but the reaction releases heat after adding the inorganic oily sludge remediation agent, and lanthanum hexaboride can utilize this heat to emit light, thereby increasing the reaction rate.

[0025] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for remediating oily sludge based on photocatalytic oxidation, characterized in that, Includes the following steps: S1. Recover recoverable petroleum hydrocarbons from oily sludge to form oily sludge with low oil content; S2. Under light conditions, add inorganic oily sludge remediation agent, photocatalyst catalyst and water to oily sludge with low oil content and stir evenly; wherein, the inorganic oily sludge remediation agent includes calcium oxide and magnesium oxide.

2. The method for remediating oily sludge based on photocatalytic oxidation according to claim 1, characterized in that, The photocatalyst is titanium dioxide. In step S2, a luminescent material is also added to the oily sludge.

3. The method for remediating oily sludge based on photocatalytic oxidation according to claim 2, characterized in that, The luminescent material is rare earth phosphorescent powder.

4. The method for remediating oily sludge based on photocatalytic oxidation according to claim 1, characterized in that, The photocatalyst is a magnetic photocatalyst.

5. The method for remediating oily sludge based on photocatalytic oxidation according to claim 1, characterized in that, The illumination conditions are sunlight. During the daytime illumination period, the oily sludge is turned over at intervals so that the oily sludge in all places can participate in the photocatalytic reaction evenly.

6. The method for remediating oily sludge based on photocatalytic oxidation according to claim 1, characterized in that, The photocatalyst is lanthanum hexaboride.

7. The method for remediating oily sludge based on photocatalytic oxidation according to claim 6, characterized in that, The illumination conditions are sunlight. During the daytime illumination period, the oily sludge is turned over at intervals so that the oily sludge in all places can participate in the photocatalytic reaction evenly.

8. The method for remediating oily sludge based on photocatalytic oxidation according to claim 7, characterized in that, The inorganic oily sludge remediation agent is added to the oily sludge in multiple intervals. After each addition, water is sprayed and the oily sludge, inorganic oily sludge remediation agent, and water are mixed evenly before being spread back on the ground.

9. The method for remediating oily sludge based on photocatalytic oxidation according to claim 8, characterized in that, The inorganic oily sludge remediation agent should be added at least once during nighttime when there is little or no light.