A method for simultaneous recovery of high-value oil and gas and carbon control in the treatment of oily sludge using molten salt thermo-electrochemical coupling

Abstract

This invention discloses a method for the simultaneous recovery of high-value oil and gas and carbon control in the treatment of oily sludge using molten salt thermo-electrochemical coupling. It relates to the field of hazardous waste treatment and resource utilization technology. The method provided by this invention addresses the industry pain points commonly found in existing oily sludge treatment technologies, such as incomplete treatment of recalcitrant organic matter, low resource utilization, insufficient carbon emission control, high risk of secondary pollution, and low energy efficiency. It achieves synergistic effects of harmless treatment of oily sludge, high-value resource recovery, and low-carbon management, and has significant technical advantages and engineering application value.

Description

Technical Field

[0001] This invention relates to the field of hazardous waste treatment and resource utilization technology, specifically to a method for simultaneous recovery of high-value oil and gas and carbon control in the treatment of oily sludge by molten salt thermo-electrochemical coupling. Background Technology

[0002] Oily sludge is a typical semi-solid hazardous waste generated during petroleum extraction, refining, and deep processing, and has been listed in the "National Hazardous Waste List." Global annual production of oily sludge exceeds 60 million tons, while my country's annual production will surpass 8 million tons, with petroleum hydrocarbons accounting for 15% to 50%. Oily sludge has a complex composition, containing large amounts of toxic and harmful substances such as benzene compounds, phenols, and pyrene, and even heavy metals. Improper treatment can pose a serious threat to the ecological environment and human health. Currently, the main technologies for treating oily sludge include: ① separation technologies, such as centrifugal separation, solvent extraction, and thermal treatment; ② degradation technologies, such as biological methods, incineration, and supercritical water oxidation.

[0003] However, existing technologies all have limitations to varying degrees. Centrifugation is only suitable for oily sludge with high water content, and the recovery rate of PHCs is limited; solvent extraction requires large amounts of organic solvents, which may cause secondary pollution; pyrolysis can recover oil, but it usually needs to be carried out at high temperatures (600-800℃), and it is energy-intensive and prone to coking. Biological treatment has a long cycle and is difficult to completely decompose large molecules such as asphalt; incineration can completely decompose organic matter, but it is energy-intensive and may produce harmful gases such as dioxins. More importantly, most existing technologies ignore the resource attributes of oily sludge, mainly aiming at harmlessness, failing to fully realize resource utilization, and lacking effective carbon emission control measures. In terms of carbon emission control, existing technologies mostly focus on end-of-pipe treatment, failing to organically combine carbon capture with resource recovery processes. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, this invention provides a method for the simultaneous recovery of high-value oil and gas and carbon control in the treatment of oily sludge using molten salt thermo-electrochemical coupling. This method achieves complete harmlessness of the oily sludge while recovering high-value oil and gas products, and controls carbon emissions through in-situ molten salt capture and electrochemical reduction.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for simultaneous recovery of high-value oil and gas and carbon control in the treatment of oily sludge via molten salt thermo-electrochemical coupling is provided, which adopts the following specific steps: S1: Dry the oily sludge to a moisture content of less than 5%, and press the dried oily sludge into oily sludge sheets. S2: An anode plate is obtained by embedding a foamed metal sheet inside an oil sludge sheet; S3: A closed molten salt electrolysis cell is constructed using an inert electrode as the cathode and a mixed molten salt as the electrolyte; the mixed molten salt also contains additives, which are one or more of Li2O, CaCO3, Na2B4O7 and Li3BO3. S4: Heat the electrolyte to 400~800℃, with an anodic current density of 50~1000mA / cm². 2 Under a cell voltage of 2.0~5V, constant cell voltage electrolysis is performed. The gaseous products of the electrolysis process are collected and condensed to obtain combustible gas and high-quality oil. The cathode products are collected to obtain solid carbon products.

[0006] Furthermore, the molten salt electrolyte is one or more of carbonates, chlorides, nitrates, and sulfates that remain chemically stable and do not decompose at 400~800℃.

[0007] Furthermore, the carbonate is one or a mixture of Li2CO3, Na2CO3, K2CO3 or CaCO3.

[0008] Furthermore, the chloride salt is one or a mixture of LiCl, NaCl, KCl, CaCl2, ZnCl2, MnCl2 or MgCl2.

[0009] Furthermore, the nitrate is one or a mixture of LiNO3, NaNO3, KNO3 or Ca(NO3)2.

[0010] Furthermore, the sulfate is a mixture of at least two of Li2SO4, Na2SO4, K2SO4, or CaSO4.

[0011] Furthermore, the mass ratio of the additive to the mixed molten salt is 3:100.

[0012] Furthermore, the foamed metal is foamed nickel, foamed copper, or foamed steel.

[0013] Furthermore, oily sludge is a by-product sludge from petroleum extraction, refining, or deep processing, with an oil content of 15% to 50% and a water content of 5% to 40%.

[0014] Furthermore, the high-quality oil consists of light olefins and alkanes, the combustible gas is methane, and the solid carbon products are carbon nanotubes or nanoporous carbon.

[0015] The beneficial effects of this invention are as follows: The method provided by this invention addresses the industry pain points commonly found in existing oily sludge treatment technologies, such as incomplete treatment of recalcitrant organic matter, low resource utilization, insufficient carbon emission control, high risk of secondary pollution, and low energy efficiency. It achieves synergistic effects of harmless treatment of oily sludge, high-value resource recovery, and low-carbon management, and has significant technical advantages and engineering application value.

[0016] This method utilizes the dual effects of molten salt catalysis and electrochemical oxidation to efficiently break down large molecular organic components in oily sludge, such as asphalt and gums, which are difficult to degrade using traditional technologies. After treatment, the oil content of the residue can be reduced to below 0.3%, far below the national standard limit of 2%, achieving thorough harmless treatment. Simultaneously, through thermo-electrochemical coupling, the organic components in the oily sludge can be directionally and efficiently converted into high-value oil products and combustible gases, resulting in a significantly higher degree of resource utilization than traditional treatment technologies, achieving efficient conversion of pollutants into high-value resources.

[0017] In terms of energy utilization, this method achieves efficient utilization of system energy through the synergistic coupling of thermal, electrical, and chemical energy. At the same time, the combustible gas produced by the reaction can be used as a supplementary energy source for system operation, effectively reducing external energy input and further improving overall energy utilization efficiency.

[0018] In terms of carbon emission control, this method combines in-situ molten salt capture with cathodic electrochemical reduction to efficiently convert carbon dioxide generated during the treatment process into solid carbon, achieving precise control of carbon emissions at the source and avoiding direct greenhouse gas emissions. The entire treatment process is completed within a closed system, with no harmful gases escaping. The core molten salt medium can be recycled, significantly reducing the risk of secondary pollution and demonstrating excellent environmental friendliness. Attached Figure Description

[0019] Figure 1 The curves showing the changes in CO and CH4 concentrations during the treatment process in Example 1 and Comparative Example 1 are compared. Figure 2 The curves showing the change in CO2 concentration during the treatment process of Example 1 and Comparative Example 1 are compared. Figure 3 This is a comparison diagram of the three-phase distribution in the products of Example 1 and Comparative Example 1; Figure 4 This is a scanning electron microscope image of solid carbon from Example 1; Figure 5 This is a pore size distribution diagram of solid carbon in Example 3. Detailed Implementation

[0020] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0021] In this embodiment of the invention, oily sludge from Daqing Petrochemical Company was used, with a measured oil content of 25% and a water content of 30%, containing heavy metals and asphaltenes. Other raw materials, unless otherwise specified, were commercially available industrial-grade pure materials.

[0022] Example 1 S1: Dry the oily sludge at 105℃ until the moisture content is <5%, and then press it into oily sludge sheets with a diameter of 5cm and a thickness of 1cm; S2: Cut a foamed copper sheet with dimensions of 3cm*3cm*2mm, sandwich the foamed copper sheet between two clay sheets to obtain the anode sheet; in specific implementation, foamed nickel sheet or foamed steel sheet can also be used. S3: Using inert electrodes as cathode plates, a mixed molten salt of Li2CO3, Na2CO3 and K2CO3 with a molar ratio of 43.5:31.5:25 is used as the electrolyte, and 3% Li2O is added to the electrolyte to construct a closed molten salt electrolysis cell. In specific implementation, the electrolyte can also be one or more of Li₂CO₃, Na₂CO₃, K₂CO₃, CaCO₃, LiCl, NaCl, KCl, CaCl₂, ZnCl₂, MnCl₂, MgCl₂, LiNO₃, NaNO₃, KNO₃, or Ca(NO₃)₂, Li₂SO₄, Na₂SO₄, K₂SO₄, or CaSO₄. The prepared mixed molten salt should remain chemically stable and not decompose at 400–800℃. The additive can also be any one of Na₂CO₃, K₂CO₃, or CaCO₃, or a mixture of any number of Li₂CO₃, Na₂CO₃, K₂CO₃, or CaCO₃. The mass ratio of the additive to the mixed molten salt can be 3:100. The addition of additives enhances the CO₂ capture capacity of the molten salt electrolyte.

[0023] S4: Heat the electrolyte to 600℃, with an anodic current density of 50mA / cm². 2 Under a cell voltage of 3.2V, constant cell voltage electrolysis was performed for 2 hours. The gaseous products of the electrolysis process were collected and condensed to obtain combustible gas and high-quality oil. The cathode products were collected to obtain solid carbon products.

[0024] Example 2 The difference between this embodiment and Embodiment 1 is that the additive used is Na2B4O7, and in step S4, the electrolyte is heated to 700°C and the cell voltage is 2.8V.

[0025] Example 3 The difference between this embodiment and Embodiment 1 is that a mixed molten salt of LiCl, NaCl and KCl with a molar ratio of 47.5:15:37.5 is used as the electrolyte, and 3% Li2O is added to the electrolyte to construct a closed molten salt electrolysis cell. Comparative Example 1 The difference between this comparative example and Example 1 is that in step S4, no electricity is applied to the anode and cathode, and the oily sludge is treated using the existing pyrolysis method.

[0026] Comparative Example 2 The difference between this comparative example and Example 1 is that no additives are added.

[0027] CO and CH4 were measured in the confined space during the treatment of oily sludge in Example 1 and Comparative Example 1, respectively. The results are as follows: Figure 1 As shown, by Figure 1 It can be seen that the CH4 and CO concentrations in both groups showed a trend of first rapidly increasing, reaching a peak concentration, and then gradually decreasing to zero with reaction time, with the gas production cycle being basically the same. However, throughout the entire reaction process, the CH4 and CO gas concentrations in Example 1 were consistently significantly higher than those in Comparative Example 1. Simultaneously, the combustible gas concentration in Example 1 increased at a faster rate and reached the peak gas production earlier, indicating that the method of the present invention can significantly accelerate the kinetic process of organic matter conversion reaction.

[0028] The CO2 levels in the confined space during the treatment processes of Example 1 and Comparative Example 1 were measured, and the results are as follows: Figure 2 As shown, by Figure 2 It can be seen that the conventional pyrolysis technology used in Comparative Example 1 generated a large amount of CO2 gas during the treatment process, and there was significant CO2 emission throughout the entire reaction cycle; in Comparative Example 2, without additives to enhance carbon capture, the CO2 release intensity was significantly reduced. In Further Example 1, during the treatment process using the method of the present invention, the CO2 concentration in the exhaust gas remained consistently near the detection limit, with no significant CO2 gas emission. These results fully demonstrate that the present invention, through molten salt in-situ capture coupled with cathode electrochemical reduction technology, can efficiently capture and completely convert and fix the CO2 generated during the treatment of oily sludge, achieving precise control of carbon emissions from the source and completely avoiding direct greenhouse gas emissions. Compared with conventional pyrolysis technology, it has superior low-carbon emission reduction advantages.

[0029] Statistical analysis was performed on the gas, liquid, and solid phases of the products from Example 1 and Comparative Example 1. The three-phase yield distribution results are as follows: Figure 3 As shown, by Figure 3It can be seen that, compared with Comparative Example 1, the yield of solid residue in Example 1 is lower; at the same time, the yield of liquid product (high-value oil) and the yield of gaseous product (combustible gas) are increased. The above results indicate that, through the dual action of molten salt catalysis and electrochemical oxidation, the present invention can efficiently convert more organic components in oily sludge, including macromolecular organic matter such as asphalt and gum that are difficult to degrade by conventional pyrolysis, into high-value liquid oil and gaseous combustible gas, significantly reducing the yield of solid residue.

[0030] The solid carbon product of Example 1 was characterized by scanning electron microscopy, and the results are as follows: Figure 4 As shown, by Figure 4 It can be seen that the obtained solid carbon product exhibits a large number of one-dimensional, interwoven tubular nanostructures with excellent aspect ratios. The tube diameters are uniform and at the nanoscale, which is typical of multi-walled carbon nanotube morphology, and there are no obvious amorphous carbon impurities. The pore size distribution of the solid carbon product is shown in the figure below. Figure 5 As shown, by Figure 5 It can be seen that the pore volume of the product exhibits a significant segmented distribution characteristic as the pore size changes. The pore size distribution characteristic is highly consistent with the morphology of the carbon nanotube interwoven network obtained by the aforementioned SEM characterization, further confirming that the obtained product is a carbon nanotube material with good crystallinity and uniform structure and nanoporous carbon.

[0031] In summary, this series of comparative experiments comprehensively verifies the integrated technical advantages and application value of the molten salt thermo-electrochemical coupling method for the simultaneous recovery of high-value oil and gas and carbon control of oily sludge.

Claims

1. A method for simultaneous recovery of high-value oil and gas and carbon control in the treatment of oily sludge using molten salt thermo-electrochemical coupling, characterized in that, The specific steps are as follows: S1: Dry the oily sludge to a moisture content of less than 5%, and press the dried oily sludge into oily sludge sheets. S2: An anode plate is obtained by embedding a foamed metal sheet inside an oil sludge sheet; S3: A closed molten salt electrolysis cell is constructed using an inert electrode as the cathode and a mixed molten salt as the electrolyte; the mixed molten salt also contains additives, which are one or more of Li2O, CaCO3, Na2B4O7 and Li3BO3. S4: Heat the electrolyte to 400~800℃, with an anodic current density of 50~1000mA / cm². 2 Under a cell voltage of 2.0~5V, constant cell voltage electrolysis is performed. The gas and liquid products of the electrolysis process are collected and condensed to separate them, yielding combustible gas and high-quality oil. The cathode deposits were collected to obtain solid carbon products.

2. The method for simultaneous recovery of high-value oil and gas and carbon control in the treatment of oily sludge by molten salt thermo-electrochemical coupling according to claim 1, characterized in that, The molten salt electrolyte is one or more of carbonates, chlorides, nitrates, and sulfates that remain chemically stable and do not decompose at 400-800℃.

3. The method for simultaneous recovery of high-value oil and gas and carbon control in the treatment of oily sludge by molten salt thermo-electrochemical coupling according to claim 2, characterized in that, The carbonate is one or a mixture of Li2CO3, Na2CO3, K2CO3 or CaCO3.

4. The method for simultaneous recovery of high-value oil and gas and carbon control in the treatment of oily sludge by molten salt thermo-electrochemical coupling according to claim 2, characterized in that, The chloride salt is one or a mixture of LiCl, NaCl, KCl, CaCl2, ZnCl2, MnCl2 or MgCl2.

5. The method for simultaneous high-value oil and gas recovery and carbon control in the molten salt thermo-electrochemical coupling treatment of oily sludge according to claim 2, characterized in that, The nitrate is one or a mixture of LiNO3, NaNO3, KNO3 or Ca(NO3)2.

6. The method for simultaneous recovery of high-value oil and gas and carbon control in the treatment of oily sludge by molten salt thermo-electrochemical coupling according to claim 2, characterized in that, The sulfate is a mixture of at least two of Li2SO4, Na2SO4, K2SO4 or CaSO4.

7. The method for simultaneous recovery of high-value oil and gas and carbon control in the treatment of oily sludge by molten salt thermo-electrochemical coupling according to claim 1, characterized in that, The mass ratio of the additive to the mixed molten salt is 3:

100.

8. The method for simultaneous recovery of high-value oil and gas and carbon control in the treatment of oily sludge by molten salt thermo-electrochemical coupling according to claim 1, characterized in that, The foam metal is foamed nickel, foamed copper, or foamed steel.

9. The method for simultaneous recovery of high-value oil and gas and carbon control in the treatment of oily sludge by molten salt thermo-electrochemical coupling according to claim 1, characterized in that, The oily sludge is a by-product sludge from petroleum extraction, refining, or deep processing, with an oil content of 15% to 50% and a water content of 5% to 40%.

10. The method for simultaneous high-value oil and gas recovery and carbon control in the molten salt thermo-electrochemical coupling treatment of oily sludge according to claim 1, characterized in that, The high-quality oil is composed of light olefins and alkanes, the combustible gas is methane, and the solid carbon product is carbon nanotubes or nanoporous carbon.

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