A method for dephosphorization of waste oil

Abstract

This invention relates to a method for dephosphorizing waste oils. First, the raw material is pretreated using a low-pressure pyrolysis process, causing thermal degradation and polymerization of the non-hydrated phospholipids that are difficult to remove. Then, an ultrasonic-assisted acid washing process is coupled in, utilizing the ultrasonic cavitation effect to effectively disrupt the chelate structure between metal ions and phospholipid groups in the non-hydrated phospholipids. Simultaneously, the displacement effect of the ultrasound promotes relative movement and accelerated coagulation of the colloidal particles loosened by pyrolysis and acid washing in the oil phase, achieving ultrasonic-assisted demulsification and enhancing the subsequent separation efficiency between the aqueous and oil phases. Based on this, an organic acid solution is used as a complexing extractant to in-situ complex the released metal ions into water-soluble complexes, which are then transferred to the aqueous phase for separation. Through the synergistic effect of pyrolysis activating the structure, ultrasonic breaking of chelates, and organic acid complexation and transfer, this invention achieves deep dephosphorization of waste oils, significantly reducing their phosphorus content while preserving the original quality of the oils to the greatest extent possible.

Description

Technical Field

[0001] This invention relates to the field of waste oil resource utilization technology, specifically to a method for dephosphorizing waste oil. Background Technology

[0002] With the continued growth in global demand for renewable energy and the increasing urgency of carbon emission reduction targets, the production of biodiesel, aviation biofuel, and green fine chemicals from waste oils has become an important way to achieve the recycling of oil resources and replace fossil fuels. Waste oils mainly include waste cooking oil, waste frying oil, and acidified oil, a byproduct of oil refining. They are widely available, produced in huge quantities, and have significant resource potential.

[0003] However, unlike crude vegetable oils, waste oils undergo complex thermal oxidation, hydrolysis, and polymerization reactions during high-temperature cooking, storage, and collection and transportation, resulting in an extremely complex composition. In addition to containing large amounts of free fatty acids, water, colloids, and pigments, waste oils are also enriched with various forms of phosphides. Specifically, these phosphides include not only the non-hydrated phospholipids inherent in the oil itself (such as phosphatidylethanolamine and phosphatidylinositol), but also small-molecule phosphorus-containing compounds generated during the thermal degradation of phospholipids during cooking, residues of phosphorus-containing food additives (such as phosphates and pyrophosphates), and phospholipid-metal ion complexes and metal phosphate precipitates formed during contact with various metal containers and pipes. The mixture of these various forms of phosphides constitutes the complex occurrence of "total phosphorus" in waste oils.

[0004] The presence of these phosphides severely restricts the subsequent deep processing of waste oils. In the process of producing biodiesel from waste oils (especially second-generation biodiesel or aviation biofuels via hydrogenation), residual phosphides in the feedstock directly poison and deactivate the hydrogenation catalyst, significantly shortening its lifespan and substantially increasing operating costs. Simultaneously, phosphides can also trigger polymerization and coking of the oils at high temperatures, leading to a darker product color and increased acid value, severely impacting the quality and yield of the final product. Therefore, before catalytic conversion of waste oils, deep dephosphorization pretreatment is essential to reduce the phosphorus content to an acceptable level.

[0005] Currently, existing technologies for dephosphorization of oils and fats mainly include the following categories: (I) Chemical dephosphorization method: This method involves adding acids (such as citric acid, phosphoric acid, etc.) to the oil, causing the metal ions in the non-hydrated phospholipids to be chelated or replaced by the acid, converting the non-hydrated phospholipids into hydrated phospholipids. Subsequently, water and alkaline solutions (such as sodium hydroxide solution) are added, causing the phospholipids to absorb water and flocculate. The phospholipids are then removed by centrifugation or sedimentation. This method is widely used in conventional vegetable oil refining. However, for waste oils with extremely complex compositions, due to the large amount of heat-denatured phospholipids and inorganic phosphides present, conventional acid-base conversion reactions cannot effectively flocculate them, resulting in a significantly low dephosphorization efficiency.

[0006] (II) Physical Adsorption Dephosphorization Method: This method utilizes the adsorption properties of porous materials such as activated clay, silica gel, or activated carbon to adsorb phospholipids and polar impurities in oils onto the material surface, followed by separation through filtration. While relatively simple to operate, this method suffers from limited adsorption capacity, difficulty in regeneration after a single use, and a lack of selectivity in the adsorption process. It adsorbs large amounts of neutral glycerides and free fatty acids from the oils along with phosphides, resulting in a significant loss of effective components and generating substantial amounts of waste adsorbent solids, increasing treatment costs.

[0007] (III) Enzymatic Dephosphorylation: This method utilizes specific phospholipases (such as phospholipases A1 and A2) to catalyze the hydrolysis of non-hydrated phospholipids, converting them into phospholipids that are easily removed by hydration. This method is mild and highly specific, but it requires a high degree of cleanliness in the raw materials. The large amounts of metal ions, free fatty acids, and thermal polymerization products present in waste oils can significantly inhibit and inactivate enzyme activity. Furthermore, the enzyme catalytic reaction time is long, and the enzyme preparation cost is high, making it difficult to meet the economic requirements of industrial waste oil treatment.

[0008] (iv) Membrane separation dephosphorization technology: This technology utilizes ultrafiltration or nanofiltration membranes with specific molecular weight cutoffs to retain larger phospholipid molecules on one side of the membrane under pressure, thereby achieving separation from triglycerides. Although this technology has the advantage of no chemical additives, the high content of free fatty acids, colloids, and solid impurities in waste oils easily causes membrane fouling, leading to rapid decline in membrane flux, high frequency of membrane cleaning and replacement, and significantly higher equipment investment and operation and maintenance costs.

[0009] In summary, existing methods for removing multi-form, thermally denatured, and metal-complexed phosphides from the complex raw material system of waste oil generally suffer from prominent problems such as poor dephosphorization effect, poor process adaptability, large loss of effective components, and high equipment requirements.

[0010] The above background information is provided only to aid in understanding the concept and technical solution of this application. It does not necessarily belong to the prior art of this application, nor does it necessarily provide technical guidance. In the absence of clear evidence that the above information was disclosed before the filing date of this application, the above background information should not be used to evaluate the novelty and inventiveness of this application. Summary of the Invention

[0011] The purpose of this invention is to provide a novel method for dephosphorizing waste oils, which can significantly reduce the phosphorus content in waste oils and has strong process adaptability and is easy to operate.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for dephosphorizing waste oil, comprising the following steps: (1) The waste oil is placed in a negative pressure environment and heat-treated at 230℃~300℃, wherein the relative pressure of the negative pressure environment is -0.06MPa~-0.1MPa; (2) The waste oil after heat treatment is mixed with an organic acid solution with a mass concentration of 2% to 5%, and then pickled under ultrasonic irradiation. (3) After pickling, the resulting mixture is centrifuged to separate the aqueous phase, and the remaining oil phase is dehydrated to obtain the dephosphorized waste oil.

[0013] In some embodiments, the organic acid in the organic acid solution is citric acid and oxalic acid.

[0014] Further, the mass ratio of citric acid to oxalic acid is 1:(0.8~1.2), preferably 1:(0.9~1.1).

[0015] Furthermore, the organic acid solution is an aqueous solution of an organic acid.

[0016] In some embodiments, the weight ratio of the waste oil after heat treatment to the organic acid solution is 1:(0.05~0.2), preferably 1:(0.05~0.15), and more preferably 1:(0.08~0.12).

[0017] In some embodiments, the ultrasonic irradiation has an ultrasonic frequency of 20kHz to 40kHz, a power density of 0.2W / mL to 0.5W / mL, and an ultrasonic duration of 20min to 40min.

[0018] In some embodiments, the pickling temperature is 40°C to 60°C, preferably 45°C to 55°C.

[0019] In some embodiments, the heat treatment time is 2h to 4h, preferably 2h to 3h.

[0020] In some embodiments, the waste oil is an oil containing non-hydrated phospholipids, and the phosphorus content of the waste oil is 20 mg / kg to 500 mg / kg.

[0021] Furthermore, the waste oil also contains one or more of the following: phosphates, pyrophosphates, phospholipid-metal ion complexes, and metal phosphates.

[0022] In some embodiments, the waste oil includes one or more of the following: kitchen waste oil, frying waste oil, and acidified oil, a byproduct of oil refining.

[0023] In some embodiments, in step (3), a centrifuge is used for centrifugal separation, with the centrifuge speed being 2000 r / min to 4000 r / min and the time being 20 min to 40 min.

[0024] Due to the application of the above-mentioned technical solution, the present invention has the following advantages compared with the prior art: This invention pretreats raw materials using a low-pressure pyrolysis process, causing the thermal degradation and polymerization of difficult-to-remove non-hydrated phospholipids, transforming them into an intermediate transition state. Subsequently, an ultrasonic-assisted acid washing process is coupled, utilizing the ultrasonic cavitation effect to effectively disrupt the chelate structure between metal ions and phospholipid groups in the non-hydrated phospholipids. Simultaneously, the displacement effect of ultrasound promotes relative movement and accelerated coagulation of colloidal particles loosened by pyrolysis and acid washing in the oil phase, achieving ultrasonic-assisted demulsification and further enhancing the subsequent separation efficiency between the aqueous and oil phases. Based on this, an organic acid solution is used as a complexing extractant to in-situ complex the released metal ions into water-soluble complexes, which are then transferred to the aqueous phase for separation. Through the synergistic effect of pyrolysis activation, ultrasonic dechelation and demulsification, and organic acid complexation and transfer, this invention achieves deep dephosphorization of waste oils, significantly reducing their phosphorus content while preserving the original quality of the oils to the greatest extent possible. Detailed Implementation

[0025] In the existing process of waste oil resource utilization, the deep removal of phosphorus content has always been a key technical bottleneck restricting its high-value transformation. Phosphorus in waste oil mainly exists in the form of non-hydrated phospholipids, especially chelated complex salts formed by phosphatidic acid and phosphatidylethanolamine with metal ions such as calcium and magnesium. These substances have stable molecular structures, are extremely hydrophobic, and are insoluble in water. Traditional hydration degumming processes are almost ineffective against them, and simply increasing the acid content or extending the reaction time not only results in low dephosphorization efficiency (usually only reducing total phosphorus to 50ppm~100ppm), but also causes a surge in the acid value of the oil due to the generation of a large amount of free fatty acids, severely degrading the quality of the oil.

[0026] To address the difficulty in separating non-hydrated phospholipids, existing technicians have attempted various process routes, including chemical dephosphating, physical adsorption dephosphating, and enzymatic dephosphating (see the background technology section above for details). However, these methods are not ideal for waste oils with complex compositions.

[0027] Building upon this, the inventors attempted to introduce a high-temperature pyrolysis process to disrupt the chelate bonds between phospholipid groups and metal ions through thermochemical action. However, research revealed that high-temperature pyrolysis inevitably induces intermolecular thermal polymerization reactions between unsaturated fatty acids and phospholipid molecules in the oil, leading to deep condensation into charred, high-molecular-weight carbon compounds. This results in a rapid deterioration of the product's color, turning it dark brown and rendering it unusable. In other words, the high-temperature pyrolysis pathway presents an irreconcilable contradiction between "dephosphorylation" and "preservation of the core components of the oil." More critically, the metal ions and phosphate groups form a strong coordination chelate ring. This structure endows non-hydrated phospholipids with additional thermal stability, requiring even higher temperatures for effective destruction. This heating process, in turn, exacerbates the carbonization and deterioration of the oil, creating a vicious cycle.

[0028] To address the aforementioned technical challenges, the inventors have broken with conventional thinking and creatively adopted low-pressure pyrolysis technology. This technology can induce pyrolysis and preliminary thermal polymerization of non-hydrated phospholipids at temperatures below the pyrolysis temperature, thereby effectively avoiding side reactions of the oil matrix at high temperatures while initiating the dephosphorization process.

[0029] However, further research revealed that low-pressure pyrolysis alone is insufficient to completely dismantle the chelate core composed of metal ions such as calcium and magnesium in non-hydrated phospholipids. Therefore, the inventors introduced ultrasound into the acid washing process. Utilizing the instantaneous (microsecond-level) high-temperature, high-pressure cavitation bubbles generated by ultrasound in the liquid phase, the released physical shock waves can precisely act on the metal-phosphate coordination bonds of non-hydrated phospholipids. This purely physical cavitation effect selectively disrupts the coordination microenvironment of the chelate structure, without triggering large-scale thermal polymerization and carbonization of the oil as high temperatures would. Simultaneously, the displacement effect of ultrasound causes relative movement and accelerated coagulation of the colloidal particles loosened by pyrolysis and acid washing in the oil phase, achieving ultrasound-assisted demulsification and further enhancing the subsequent separation efficiency between the aqueous and oil phases.

[0030] After the chelated structure is "pried open" by ultrasonic cavitation, a solution of organic acid with a specific composition is further introduced. Here, the organic acid acts not only as a conventional acid refining agent but also as a highly efficient complexing extractant. It rapidly complexes the released calcium, magnesium, and other metal ions in situ into polar, water-soluble complexes, which are then extracted into the aqueous phase. Through the synergistic effect of three interconnected steps—pyrolysis activation of the structure, ultrasonic disruption of the chelation, and organic acid complexation and transfer—this invention achieves deep stripping of stubborn non-hydrated phospholipids from waste oils.

[0031] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other. Unless otherwise specified, the reagents and instruments used in the following embodiments and comparative examples are commercially available products or can be prepared with reference to existing technology.

[0032] In this invention, unless the context explicitly requires otherwise, the numerical range referred to as "numerical value A to numerical value B" refers to the range including the endpoints A and B. The numerical range referred to as "above" or "below" refers to the numerical range including the stated number. "Optional" or "optional" indicates that certain substances, components, execution steps, application conditions, etc., may or may not be used, and there is no limitation on the manner of use.

[0033] In this invention, unless the context explicitly requires otherwise, all numerical parameters modified by terms such as "about" (including but not limited to time, temperature, pressure, concentration, weight percentage, pH value, and size) should be understood to cover a reasonable range centered on the stated value, based on the fluctuation range of conventional experimental or production equipment. Specifically, this range typically includes ±10% of the stated value, and may be extended to ±20% of the stated value in certain embodiments or where conventional precision in the art allows. Such deviations should be understood as inherent fluctuations caused by differences in measuring instruments, operating methods, environmental conditions, or batch variations of materials, and the technical solutions within this range of fluctuations can achieve the core objectives and beneficial effects of this invention.

[0034] In this invention, unless the context explicitly requires otherwise, all pressures refer to relative pressure (gauge pressure).

[0035] In this invention, unless the context clearly requires otherwise, the raw materials involved in the following examples and comparative examples are all commercially available products or can be prepared according to existing technology.

[0036] Experimental Example 1: This embodiment provides a method for dephosphorizing waste oil, which includes: Waste cooking oil (source: Chongqing Kerun Environmental Protection Renewable Resources Development Co., Ltd., whose main components are fatty acids and triglycerides, phosphorus content: 80mg / kg) was pumped into the reactor and heated to 230~245℃, and kept under pressure conditions of -0.06MPa to -0.07MPa for 2 hours.

[0037] Afterwards, the waste oil treated under high temperature and negative pressure conditions was cooled to 80°C, the pressure was released to atmospheric pressure, and it was transferred to an ultrasonic reactor by a pump. A mixture of citric acid and oxalic acid, accounting for 10% of the weight of the waste oil, was added (the mixture was an aqueous solution, in which the total mass concentration of citric acid and oxalic acid was 2%, and the mass ratio of citric acid to oxalic acid was 1:1). The ultrasonic reactor was set with an ultrasonic frequency of 25kHz, a power density of 0.3W / mL, a temperature of 50°C, and an ultrasonic time of 30min.

[0038] The oil-water mixture obtained after ultrasonic treatment is pumped into a centrifuge for centrifugation (centrifuge speed is 3000 r / min, time is 30 min) to separate the aqueous phase. Then, the oil phase is dehydrated using negative pressure or normal pressure to obtain dehydrated oil.

[0039] After dehydration, the oil was clear and the phosphorus content of the dehydrated oil was measured to be 3.30 ppm using inductively coupled plasma atomic emission spectrometry.

[0040] The dephosphorization rate was calculated to be 95.88%. The dephosphorization rate was calculated using the following formula: Dephosphorization rate (%) = [(C0 – C1) / C0] × 100%; C0 represents the phosphorus content in the waste oil, and C1 represents the phosphorus content in the treated product.

[0041] Experimental Example 2: This embodiment provides a method for dephosphorizing waste oil, which includes: Waste oil (same as in Example 1) was pumped into the reactor and heated to 240~260℃, and kept under a pressure of -0.07MPa to -0.08MPa for 2 hours.

[0042] Afterwards, the waste oil treated under high temperature and negative pressure conditions was cooled to 80°C, the pressure was released to atmospheric pressure, and it was transferred to an ultrasonic reactor by a pump. A mixture of citric acid and oxalic acid (same as in Example 1) accounting for 10% of the weight of the waste oil was added. The ultrasonic reactor was set with an ultrasonic frequency of 25 kHz, a power density of 0.3 W / mL, a temperature of 50°C, and an ultrasonic time of 30 min.

[0043] The oil-water mixture obtained after ultrasonic treatment is pumped into a centrifuge for centrifugation (process parameters are the same as in Example 1) to separate the aqueous phase. Then, the oil phase is dehydrated using negative pressure or normal pressure to obtain dehydrated oil.

[0044] After dehydration, the oil was clear, and the phosphorus content was measured to be 3.0 ppm using inductively coupled plasma atomic emission spectrometry. The dephosphorization rate was calculated to be 96.25%.

[0045] Experimental Example 3: This embodiment provides a method for dephosphorizing waste oil, which includes: Waste oil (same as in Example 1) was pumped into the reactor and heated to 260~280℃, and kept under a pressure of -0.08MPa to -0.09MPa for 2 hours.

[0046] Afterwards, the waste oil treated under high temperature and negative pressure conditions was cooled to 80°C, the pressure was released to atmospheric pressure, and it was transferred to an ultrasonic reactor by a pump. A mixture of citric acid and oxalic acid (same as in Example 1) accounting for 10% of the weight of the waste oil was added. The ultrasonic reactor was set with an ultrasonic frequency of 25 kHz, a power density of 0.3 W / mL, a temperature of 50°C, and an ultrasonic time of 30 min.

[0047] The oil-water mixture obtained after ultrasonic treatment is pumped into a centrifuge for centrifugation (process parameters are the same as in Example 1) to separate the aqueous phase. Then, the oil phase is dehydrated using negative pressure or normal pressure to obtain dehydrated oil.

[0048] After dehydration, the oil was clear. Inductively coupled plasma atomic emission spectrometry (ICP-AES) showed that the phosphorus content of the dehydrated oil was 2.80 ppm. The dephosphorization rate was calculated to be 96.50%.

[0049] Experiment Example 4: This embodiment provides a method for dephosphorizing waste oil, which includes: Waste oil (same as in Example 1) was pumped into the reactor and heated to 280~300℃, and kept under a pressure of -0.09MPa to -0.1MPa for 2 hours.

[0050] Afterwards, the waste oil treated under high temperature and negative pressure conditions was cooled to 80°C, the pressure was released to atmospheric pressure, and it was transferred to an ultrasonic reactor by a pump. A mixture of citric acid and oxalic acid (same as in Example 1) accounting for 10% of the weight of the waste oil was added. The ultrasonic reactor was set with an ultrasonic frequency of 25 kHz, a power density of 0.3 W / mL, a temperature of 50°C, and an ultrasonic time of 30 min.

[0051] The oil-water mixture obtained after ultrasonic treatment is pumped into a centrifuge for centrifugation (process parameters are the same as in Example 1) to separate the aqueous phase. Then, the oil phase is dehydrated using negative pressure or normal pressure to obtain dehydrated oil.

[0052] After dehydration, the oil was clear and transparent. Inductively coupled plasma atomic emission spectrometry (ICP-AES) showed that the phosphorus content of the dehydrated oil was 3.00 ppm. The dephosphorization rate was calculated to be 96.25%.

[0053] Experimental Example 5: This embodiment provides a method for dephosphorizing waste oil, which is basically the same as that in Embodiment 1, except that the concentration of the citric acid and oxalic acid mixture used is different. In this embodiment, the total mass concentration of the citric acid and oxalic acid mixture is 4%.

[0054] After dehydration, the oil was clear. Inductively coupled plasma atomic emission spectrometry (ICP-AES) showed that the phosphorus content of the dehydrated oil was 2.30 ppm. The dephosphorization rate was calculated to be 97.12%.

[0055] Example 6: This embodiment provides a method for dephosphorizing waste oil, which is basically the same as that in Embodiment 1, except that the concentration of the citric acid and oxalic acid mixture used is different. In this embodiment, the total mass concentration of the citric acid and oxalic acid mixture is 5%.

[0056] After dehydration, the oil was clear and bright. Inductively coupled plasma atomic emission spectrometry (ICP-AES) showed that the phosphorus content of the dehydrated oil was 2.50 ppm. The dephosphorization rate was calculated to be 96.87%.

[0057] Experiment Example 7: This embodiment provides a method for dephosphorizing waste oil, which is basically the same as that in Embodiment 1, except that the waste oil is kitchen waste oil with a phosphorus content of 20.83 ppm (source: Chongqing Kerun Environmental Protection Renewable Resources Development Co., Ltd., the main component is triglycerides).

[0058] After dehydration, the oil was clear. Inductively coupled plasma atomic emission spectrometry (ICP-AES) showed that the phosphorus content of the dehydrated oil was 0.72 ppm. The dephosphorization rate was calculated to be 96.54%.

[0059] Experimental Example 8: This embodiment provides a method for dephosphorizing waste oil, which is basically the same as that in Embodiment 1, except that the waste oil is acidified oil with a phosphorus content of 230 ppm (source: Chongqing Kerun Environmental Protection Renewable Resources Development Co., Ltd., whose main component is free fatty acids).

[0060] After dehydration, the oil was clear. Inductively coupled plasma atomic emission spectrometry (ICP-AES) showed that the phosphorus content of the dehydrated oil was 4.70 ppm. The dephosphorization rate was calculated to be 97.96%.

[0061] Comparative Example 1: This comparative example provides a method for dephosphorizing waste oil, which adopts a traditional acid washing dephosphorization process. Specifically, 1% phosphoric acid (or citric acid or oxalic acid) and 10% water are added to the waste oil (same as in Example 1) according to the total weight of the waste oil, stirred at 80°C for 1 hour, and then centrifuged to dehydrate.

[0062] After dehydration, the oil was clear and the phosphorus content of the dehydrated oil was measured to be 55 ppm using inductively coupled plasma atomic emission spectrometry.

[0063] The dephosphorization rate was calculated to be 31.25%.

[0064] Comparative Example 2: This comparative example provides a method for dephosphorizing waste oil, which adopts a traditional physical adsorption process. Specifically, 5% of the total weight of the waste oil is added to the waste oil (same as in Example 1), and the mixture is stirred for 1 hour at 60°C and 3000 rpm. After adsorption, the mixture is filtered under reduced pressure.

[0065] The obtained oil was clear, and the phosphorus content of the filtered oil was measured to be 35.8 ppm using inductively coupled plasma atomic emission spectrometry.

[0066] The dephosphorization rate was calculated to be 55.25%.

[0067] Comparative Example 3: This comparative example provides a method for dephosphorizing waste oil, which includes: Waste oil (same as in Example 1) was pumped into the reactor and heated to 230~245℃, and kept under pressure conditions of -0.06MPa to -0.07MPa for 2 hours.

[0068] Afterwards, the mixture was pumped into a centrifuge for centrifugation (process parameters are the same as in Example 1) to separate the aqueous phase. Then, the oil phase was dehydrated using negative pressure or normal pressure. The phosphorus content of the dehydrated oil was measured to be 50 ppm using an inductively coupled plasma atomic emission spectrometer.

[0069] After dehydration, the oil became dark, and the dephosphorization rate was calculated to be 37.50%.

[0070] Comparative Example 4: This comparative example provides a method for dephosphorizing waste oil, which includes: Waste oil (same as in Example 1) was pumped into the reactor and heated to 230~245℃, and kept under pressure conditions of -0.06MPa to -0.07MPa for 2 hours.

[0071] Afterwards, the waste oil treated under high temperature and negative pressure conditions was cooled to 80°C, the pressure was released to atmospheric pressure, and it was transferred to the reactor by a pump. A mixture of citric acid and oxalic acid (same as in Example 1) accounting for 10% of the weight of the waste oil was added, and the mixture was stirred at 50°C for 1 hour.

[0072] The oil-water mixture obtained after pickling is pumped into a centrifuge for centrifugation (process parameters are the same as in Example 1) to separate the aqueous phase. Then, the oil phase is dehydrated using negative pressure or normal pressure to obtain dehydrated grease.

[0073] After dehydration, the oil was clear, and the phosphorus content was measured to be 15 ppm using inductively coupled plasma atomic emission spectrometry. The dephosphorization rate was calculated to be 81.25%.

[0074] Comparative Example 5: This comparative example provides a method for dephosphorizing waste oil, which includes: Waste oil (same as in Example 1) was used as raw material and pumped into an ultrasonic reactor. A mixture of citric acid and oxalic acid (same as in Example 1) accounting for 10% of the weight of the waste oil was added. The ultrasonic reactor was set with an ultrasonic frequency of 25 kHz, a power density of 0.3 W / mL, a temperature of 50 °C, and an ultrasonic time of 30 min.

[0075] The oil-water mixture obtained after ultrasonic treatment is pumped into a centrifuge for centrifugation (process parameters are the same as in Example 1) to separate the aqueous phase, and then the oil phase is dehydrated using negative pressure or normal pressure.

[0076] The dehydrated oil is pumped into the reactor and heated to 230~245℃, and maintained at a pressure of -0.06MPa to -0.07MPa for 2 hours.

[0077] The obtained oil was dark in color, and after cooling, the phosphorus content was measured to be 37.78 ppm using inductively coupled plasma atomic emission spectrometry. The dephosphorization rate was calculated to be 52.77%.

[0078] Comparative Example 6: This comparative example provides a method for dephosphorizing waste oil, which is basically the same as that in Example 1, except that the pyrolysis is carried out under normal pressure. Specifically, waste oil (same as in Example 1) is used as raw material, pumped into a reactor, and heated to 230~245°C under normal pressure and maintained for 2 hours. Then, the subsequent steps of the example are followed.

[0079] After dehydration, the oil became dark. Inductively coupled plasma atomic emission spectrometry (ICP-AES) showed that the phosphorus content of the dehydrated oil was 19.7 ppm. The dephosphorization rate was calculated to be 75.37%.

[0080] Comparative Example 7: This comparative example provides a method for dephosphorizing waste oil, which is basically the same as that in Example 1, except that the pyrolysis temperature is different. Specifically, waste oil (same as in Example 1) is used as raw material, pumped into a reactor, heated to 190~210℃, and maintained at a pressure of -0.06MPa to -0.07MPa for 2 hours. Then, the subsequent steps of the example are followed.

[0081] After dehydration, the oil was clear. Inductively coupled plasma atomic emission spectrometry (ICP-AES) showed that the phosphorus content of the dehydrated oil was 24.5 ppm. The dephosphorization rate was calculated to be 69.37%.

[0082] Comparative Example 8: This comparative example provides a method for dephosphorizing waste oil, which is basically the same as that in Example 1, except that the pyrolysis temperature is different. Specifically, waste oil (same as in Example 1) is used as raw material, pumped into a reactor, heated to 310~320℃, and maintained at a pressure of -0.06MPa to -0.07MPa for 2 hours. Then, the subsequent steps of the example are followed.

[0083] After high-temperature treatment, the oil developed into black solid coke with a distinct burnt odor. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis showed that the phosphorus content of the dehydrated oil was 4.0 ppm. The dephosphorization rate was calculated to be 95%.

[0084] The present invention has been described in detail above, with the aim of enabling those skilled in the art to understand and implement the invention. However, this description should not be construed as limiting the scope of protection of the invention. All equivalent changes or modifications made in accordance with the spirit and essence of the invention should be included within the scope of protection of the invention.

Claims

1. A method for dephosphorizing waste oil, characterized in that, Includes the following steps: (1) The waste oil is placed in a negative pressure environment and heat-treated at 230℃~300℃, wherein the relative pressure of the negative pressure environment is -0.06MPa~-0.1MPa; (2) The waste oil after heat treatment is mixed with an organic acid solution with a mass concentration of 2% to 5%, and then pickled under ultrasonic irradiation. (3) After pickling, the resulting mixture is centrifuged to separate the aqueous phase, and the remaining oil phase is dehydrated to obtain the dephosphorized waste oil.

2. The method for dephosphorizing waste oil according to claim 1, characterized in that, The organic acids in the organic acid solution are citric acid and oxalic acid.

3. The method for dephosphorizing waste oil according to claim 2, characterized in that, The mass ratio of citric acid to oxalic acid is 1:(0.8~1.2).

4. The method for dephosphorizing waste oil according to any one of claims 1 to 3, characterized in that, The weight ratio of the waste oil after heat treatment to the organic acid solution is 1:(0.05~0.2).

5. The method for dephosphorizing waste oil according to claim 1, characterized in that, The ultrasonic irradiation has an ultrasonic frequency of 20kHz to 40kHz, a power density of 0.2W / mL to 0.5W / mL, and an ultrasonic time of 20min to 40min.

6. The method for dephosphorizing waste oil according to claim 1, characterized in that, The pickling temperature is 40℃~60℃.

7. The method for dephosphorizing waste oil according to claim 1, characterized in that, The heat treatment time is 2h to 4h.

8. The method for dephosphorizing waste oil according to claim 1, characterized in that, The waste oil is an oil containing non-hydrated phospholipids, and the phosphorus content of the waste oil is 20 mg / kg to 500 mg / kg.

9. The method for dephosphorizing waste oil according to claim 1, characterized in that, The waste oil includes one or more of the following: kitchen waste oil, frying waste oil, and acidified oil, a byproduct of oil refining.

10. The method for dephosphorizing waste oil according to claim 1, characterized in that, In step (3), a centrifuge is used for centrifugal separation. The centrifuge speed is 2000 r / min to 4000 r / min and the time is 20 min to 40 min.