A production process of soapstock demulsification decomposition and recovery of acidified oil and coproduction of struvite

Abstract

The application discloses a production process of soapstock demulsification, acidified oil decomposition and recovery and struvite co-production, which comprises the following steps: adding reaction aids composed of antioxidants, phosphorus fixatives and stabilizers into soapstock, carrying out phospholipid hydrolysis and demulsification under nitrogen protection, and obtaining oil-water two-phase; then adding acetic acid for acid decomposition, and obtaining acidified oil and weak acid water phase by layering; then adjusting the pH of the water phase to synthesize struvite, and realizing phosphorus recovery; and finally, concentrating the filtrate to obtain sodium acetate carbon source and reused steam water. The process effectively inhibits the oxidation side reaction, improves the quality of the acidified oil, realizes the recovery of phosphorus resources and the full utilization of the water phase, and has the advantages of green, high efficiency and near zero emission.

Description

Technical Field

[0001] This invention relates to the field of oleochemical process technology, and in particular to a production process for demulsifying and recovering acidified oil from soap residue and co-producing struvite. Background Technology

[0002] Soapstock is mainly derived from the alkali refining and deacidification process in vegetable oil refining and is an important byproduct of the oleochemical industry. Its main component is sodium fatty acid, and it also contains impurities such as neutral oil, phospholipids, pigments, and unreacted alkali. As a key raw material for the production of acidified oils, industrial oleic acid, and biodiesel, the efficient resource utilization of soapstock is of great significance in the oleochemical field.

[0003] Currently, the mainstream process for recovering acidified oil from soap residue uses sulfuric acid acidification. This involves adding concentrated sulfuric acid to convert sodium fatty acids into fatty acids, followed by acidification, demulsification, settling and separation, washing, and drying to obtain the acidified oil. However, this traditional process suffers from the following significant technical bottlenecks:

[0004] (1) Soap residue has a complex composition, and the phospholipids and other substances contained therein can form a stable emulsion, which makes it difficult to break the emulsion through acidification and the oil-water separation is incomplete, thus affecting the yield and quality of the acidified oil.

[0005] (2) Traditional process acidifies soap foot by adding concentrated sulfuric acid. As a strong oxidant, concentrated sulfuric acid not only promotes the hydrolysis of glycerides into fatty acids and glycerol in the reaction, but also causes glycerol to dehydrate and generate acrolein. At the same time, it causes unsaturated fatty acids to undergo complex side reactions such as sulfonation and oxidation, forming a large amount of tar compounds known as "plant asphalt".

[0006] (3) Acidification reaction is generally carried out at high temperature. The unsaturated fatty acids and unsaturated glycerides in soapstock are easily affected by oxygen in the air, which causes chain breakage and polymerization into large molecular fat compounds, further increasing the generation of plant asphalt and leading to a significant decrease in the quality of acidified oil.

[0007] (4) Traditional processes focus only on recovering acidified oil. The large amount of acidic aqueous phase with high concentration, high salinity and rich in inorganic and organic phosphorus produced after acidification is usually treated as wastewater with costly end-of-pipe treatment, which fails to realize resource utilization. This not only wastes phosphorus resources, but also greatly increases the environmental burden of enterprises.

[0008] Existing technologies attempt to improve traditional processes, but the fundamental problems remain unresolved. For example, patent document CN118909690A discloses a method using sodium benzenesulfonate solution for demulsification and concentrated sulfuric acid for acidification. However, this method introduces sodium benzenesulfonate, causing secondary pollution to the aqueous phase, and cannot overcome the carbonization and coking problems caused by concentrated sulfuric acid. Furthermore, it fails to decompose phospholipids in soapstock, affecting the quality of the acidified oil, and the phosphorus component in the aqueous phase is not utilized as a resource. Another patent document, CN117551509A, uses enzymatic hydrolysis for demulsification and acidification under mild reaction conditions, but it also introduces enzymatic hydrolysate pollution into the aqueous phase and does not recover the phosphorus element from the aqueous phase.

[0009] Existing soap residue treatment technologies generally suffer from three major bottlenecks: the introduction of new pollutants during the process, the deterioration of product quality due to oxidation side reactions, and the high cost of wastewater treatment due to the failure to recover phosphorus resources. Therefore, there is an urgent need in this field to develop an innovative process route that can simultaneously achieve efficient demulsification, inhibit oxidation, improve the quality of acidified oil, and efficiently recover and utilize phosphorus components in the aqueous phase. Summary of the Invention

[0010] This invention aims to solve problems in existing technologies such as the difficulty in breaking down emulsions, incomplete phospholipid decomposition, the formation of plant asphalt due to oxidation side reactions, and the lack of recovery of acidic aqueous phase resources. By adding reaction aids to soapstock under nitrogen protection, efficient emulsion breaking down and simultaneous phospholipid decomposition are achieved. Acetic acid is then used instead of concentrated sulfuric acid for acidification to obtain high-quality acidified oil. The resulting weakly acidic aqueous phase is pH-adjusted to synthesize struvite for phosphorus recovery. Finally, the remaining filtrate is concentrated to obtain sodium acetate as a carbon source and reusable distilled water. This process improves the fatty acid content and quality of the acidified oil while achieving high-value utilization of all soapstock components, source reduction of pollutants, and near-zero emissions, resulting in significant economic and environmental benefits. The technical solution provided by this invention is as follows:

[0011] This invention provides a production process for soapstock demulsification, decomposition, and recovery of acidified oil, co-producing struvite, comprising the following steps:

[0012] a. Phospholipid hydrolysis: A reaction aid is added to soapstock to initiate a reaction, causing the soapstock to demulsify and decompose the phospholipids. After the reaction, an oil-water two-phase mixture is obtained, with the upper layer being a mixed sodium fatty acid phase and the lower layer being a neutral aqueous phase. The reaction aid includes an antioxidant, a phosphorus fixative, and a stabilizer. The antioxidant is selected from at least one of ascorbic acid, sodium bisulfite, and sodium sulfite. The phosphorus fixative is selected from at least one of magnesium sulfate, magnesium chloride, and magnesium carbonate. The stabilizer is selected from at least one of ammonium sulfate, ammonium chloride, and ammonium carbonate.

[0013] b. Acidic decomposition: An acidic agent is added to the oil-water two-phase mixture obtained in step a. After the reaction is completed, the mixture separates into two layers, resulting in an upper layer of acidified oil and a lower layer of weakly acidic aqueous phase. The acidic agent is acetic acid.

[0014] c. Synthesis of struvite: Add an alkaline solution to the weakly acidic aqueous phase obtained in step b to adjust the pH value. After the reaction is complete, filter to obtain struvite and filtrate.

[0015] d. Concentration: The filtrate obtained in step c is concentrated to obtain sodium acetate carbon source byproduct and distilled water.

[0016] Optionally, the mass ratio of the antioxidant, phosphorus fixative and stabilizer is (1~2):(4~6):(2~5).

[0017] Optionally, the amount of the reaction aid added is 5% to 10% of the soapstock mass.

[0018] Optionally, the antioxidant is added in the form of an aqueous solution with a mass concentration of 5% to 15%, the phosphorus fixative is added in the form of an aqueous solution with a mass concentration of 20% to 25%, and the stabilizer is added in the form of an aqueous solution with a mass concentration of 10% to 15%.

[0019] Optionally, in step a, the reaction is carried out under nitrogen protection, at a temperature of 120℃~140℃, a pressure of 0.4 MPa~0.6 MPa, and a time of 4 h~8 h.

[0020] Optionally, the amount of acidic agent added is 7% to 10% of the weight of soap residue.

[0021] Optionally, the acidic agent is an acetic acid solution with a mass concentration of 30% to 100%.

[0022] Optionally, in step b, the reaction is carried out under nitrogen protection at a temperature of 80°C to 95°C for a time of 4 to 6 hours.

[0023] Optionally, the alkaline solution is a sodium hydroxide solution with a mass fraction of 10% to 32%.

[0024] Optionally, in step c, the pH value is adjusted to 8-10 for the reaction, and the reaction time is 0.5 h-2 h.

[0025] By adopting the above technical solution, the production process of soapstock demulsification and recovery of acidified oil and co-production of struvite provided by the present invention has the following beneficial effects:

[0026] 1. By adding a reaction auxiliaries consisting of antioxidants, phosphorus fixatives, and stabilizers to the phospholipid hydrolysis step and conducting the reaction under nitrogen protection, the oxidative polymerization reaction of unsaturated fatty acids and glycerides is effectively inhibited, significantly reducing the formation of plant asphalt. The resulting acidified oil is light in color (yellowish-brown as in Example 1), with an acid value ≥120 mg KOH / g and a saponification value ≥188 mg KOH / g, and the product quality is superior to industry standards.

[0027] 2. The phosphorus fixative and stabilizer in the reaction aids promote demulsification and provide essential raw materials for subsequent struvite synthesis. Phospholipids hydrolyze into inorganic phosphorus under high temperature and pressure, which then combines with magnesium and ammonium ions, efficiently precipitating as struvite (MgNH4PO4·6H2O) under alkaline conditions, achieving targeted recovery of phosphorus components. As shown in Example 1, the organic phosphorus conversion rate is >99%, the struvite phosphorus recovery rate reaches 96%, and the total phosphorus in the effluent is <20 mg / L, solving the problems of phosphorus pollution and resource waste in traditional processes.

[0028] 3. Acetic acid is used instead of concentrated sulfuric acid for acidic decomposition, avoiding the generation of sodium sulfate waste salt. After acidification, the sodium acetate, glycerol, fatty acids and other components in the aqueous phase are all high-quality carbon sources. After concentration, the mother liquor can be sold as a carbon source for sodium acetate, and the distillate water can be reused in production. This achieves full resource utilization of aqueous phase components and closed-loop reuse of process water, reducing pollutants at the source and achieving the goal of "harmlessness, resource utilization and zero discharge" in soap residue treatment. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A schematic diagram of a guanostone provided in an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of the acetic acid acidified oil sample provided in Example 1 of the present invention;

[0032] Figure 3 This is a schematic diagram of the concentrated sulfuric acid acidified oil sample provided in Comparative Example 3 of the present invention;

[0033] Figure 4 This is a schematic diagram of the lower aqueous phase sample after acidic decomposition provided in an embodiment of the present invention;

[0034] Figure 5 A schematic diagram of a soap foot sample provided in an embodiment of the present invention;

[0035] Figure 6 A schematic diagram of reusable distilled water provided in an embodiment of the present invention;

[0036] Figure 7 This is a schematic diagram of a concentrated mother liquor sample (sodium acetate carbon source) provided in an embodiment of the present invention. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0038] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. In the description of the invention, it should be understood that the terms "upper," "lower," "top," "bottom," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein.

[0039] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included. For example, a specified range from “1 to 10” should be considered to include any and all subranges between the minimum value 1 and the maximum value 10. Exemplary subranges of the range 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0040] The inventors discovered that during the acidification of soapstock to produce acidified oil, the presence of a large amount of oil components in the system easily leads to the formation of a stable oil-water intermediate layer under high-temperature acidic conditions. This not only significantly reduces the fatty acid content in the acidified oil but also increases the difficulty of subsequent aqueous phase treatment. Therefore, this invention adds a reaction aid composed of antioxidants, phosphorus fixatives, and stabilizers to the phospholipid hydrolysis step. The phosphorus fixatives and stabilizers, as inorganic salt components, effectively disrupt the stability of the emulsion through charge neutralization and ion exchange. This not only promotes demulsification during the phospholipid hydrolysis stage but also inhibits the formation of the intermediate layer during the acidic decomposition stage, increasing the yield of acidified oil and providing essential raw materials for subsequent struvite synthesis.

[0041] This invention provides a production process for the demulsification and recovery of acidified oil from soapstock, along with the co-production of struvite. This method can reduce the production of plant bitumen due to oxidation while simultaneously decomposing soapstock into acidified oil. It also effectively decomposes phospholipids in soapstock, recovering phosphorus components and achieving resource recovery of acidified oil and phosphorus components. Simultaneously, the struvite synthesis effluent is concentrated, and the concentrated mother liquor is sold as a carbon source for sodium acetate, while the distillate is reused in production, truly achieving harmless, resource-efficient, and zero-emission treatment of soapstock. Specifically, it includes the following steps:

[0042] a. Phospholipid hydrolysis: To soapstock (such as...) Figure 5(As shown) Add reaction aids to the mixture and react for 4 h to 8 h under nitrogen protection at 120℃~140℃ and 0.4 MPa~0.6 MPa. Simultaneously achieve soap foot demulsification and phospholipid decomposition. After the reaction is completed, two phases of oil and water are obtained, with the upper layer being a mixed sodium fatty acid phase and the lower layer being a neutral aqueous phase. The process parameters have been optimized to ensure reaction efficiency and economy: the reaction temperature is controlled within the range of 120~140℃. Too low a temperature will prevent soapstock from demulsifying, and phospholipids will not be completely hydrolyzed into inorganic phosphorus, resulting in residual organic phosphorus entering the aqueous layer and increasing the difficulty of aqueous layer treatment. Too high a temperature will cause antioxidants in the reaction auxiliaries to decompose or undergo side reactions, leading to decreased antioxidant properties, increased plant bitumen content, and decreased acidified oil quality. Furthermore, at high temperatures, glycerides in the soapstock will hydrolyze into fatty acids and glycerol. Glycerol dissolves in the aqueous layer, increasing the difficulty of aqueous layer treatment and reducing the yield of glycerol recovered from downstream acidified oil products. The reaction pressure is maintained within the range of 0.4~0.6 MPa. Too low a pressure will prevent soapstock from demulsifying properly, reducing phospholipid conversion efficiency; too high a pressure will result in excessive pressure in the reaction system, requiring higher-quality equipment and significantly increasing processing costs. The reaction time is optimized to 4~8 minutes. If the reaction time is too short, the phospholipids in the soapstock will not be completely hydrolyzed into inorganic phosphorus, and the residual organic phosphorus will enter the water layer, increasing the difficulty of water layer treatment. If the reaction time is too long, the glycerides in the soapstock will be hydrolyzed into fatty acids and glycerol. Glycerol will dissolve in the water layer, increasing the difficulty of water layer treatment and reducing the yield of glycerol recovered from downstream products of acidified oil. On the other hand, if the reaction time is too long, it will increase the energy consumption required for the reaction and increase the treatment cost.

[0043] The reaction aid is a mixture of antioxidants, phosphorus fixatives, and stabilizers in a mass ratio of (1~2):(4~6):(2~5) (e.g., 1.2:4.3:2.8, 1.8:4.5:3.5, 1.0:4.8:2.6, 1.6:5.5:4.9, 1.3:4.2:3.2, 1.9:5.8:4.7, etc.). This ratio has been systematically optimized to ensure that each component exerts the best synergistic effect. If the proportion of antioxidants is too low, the residual oxygen in the system cannot be completely consumed by the antioxidants. The oxygen reacts with the unsaturated oils in the soapstock through an oxidative polymerization reaction, forming polymer tar (i.e., plant bitumen), ultimately leading to a significant decline in the quality of the acidified oil product. Conversely, if the proportion is too high, the antioxidant components will not react completely and will remain in the aqueous phase, entering the by-product sodium acetate carbon source during the concentration process, affecting not only its quality but also increasing processing costs. When the proportion of phosphorus fixative added is too low, it will lead to poor demulsification in the phospholipid hydrolysis step and the formation of an oil-water mixed intermediate layer due to insufficient inorganic salt components during acid decomposition, reducing the yield of acidified oil. Furthermore, it will prevent the inorganic phosphorus in the aqueous layer from forming stable complexes during struvite synthesis, resulting in residual inorganic phosphorus in the aqueous layer and affecting the quality of the sodium acetate carbon source in the concentrated mother liquor. Conversely, an excessively high proportion will generate byproducts in the struvite synthesis step, reducing product purity. An excessively low proportion of stabilizer will prevent the formation of stable complexes in the aqueous layer during struvite synthesis, resulting in residual inorganic phosphorus components. An excessively high proportion will prevent residual stabilizer components from being carried away by the struvite, introducing new pollutants into the aqueous layer and increasing the difficulty of water treatment. This specific ratio range has been experimentally verified, achieving synergistic optimization of demulsification efficiency, phosphorus fixation effect, and product quality.

[0044] The antioxidant is selected from at least one of ascorbic acid, sodium bisulfite, and sodium sulfite, and is added in the form of an aqueous solution with a mass concentration of 5% to 15% (preferably 10%). Due to its strong reducing properties, it can rapidly combine with oxygen to consume oxygen and dissolved oxygen in the system, reducing the self-polymerization effect of oils caused by oxidation, effectively reducing the precipitation of plant asphalt, and it cannot undergo side reactions with oils, phospholipids, fatty acids, etc., in soapstock. The phosphorus fixative is selected from at least one of magnesium sulfate, magnesium chloride, and magnesium carbonate, and is added in an aqueous solution with a mass concentration of 20% to 25%. Magnesium salts, as inorganic salt components, greatly promote demulsification of soapstock and effectively prevent the formation of an oil-water intermediate layer during acidification. Furthermore, as a crucial reactant in struvite synthesis, magnesium salts effectively immobilize inorganic phosphorus in the aqueous layer. The stabilizer, selected from at least one of ammonium sulfate, ammonium chloride, and ammonium carbonate, is added in a 10%–15% aqueous solution. This ammonium salt system exhibits excellent solution stability, providing essential ammonium ions for struvite synthesis and achieving efficient removal of inorganic phosphorus through co-precipitation with magnesium and phosphate ions. Compared to volatile ammonia, this stabilizer system maintains a stable pH in the reaction system, preventing emulsification of soapstock components due to excessively high local alkalinity, thus ensuring effective oil-water separation and process stability.

[0045] The amount of reaction aid added is 5% to 10% of the soapstock mass. If the amount of reaction aid added is too low, on the one hand, the oxygen in the system cannot be fully consumed, leading to the oxidation reaction of unsaturated fatty acids and unsaturated oils in the soapstock, generating a large amount of plant asphalt through self-polymerization, resulting in a decrease in the yield and quality of acidified oil; on the other hand, it will cause incomplete fixation of inorganic phosphorus components in the aqueous layer, resulting in a large amount of inorganic phosphate salts remaining in the concentrated mother liquor, which seriously affects the quality of the by-product sodium acetate carbon source. On the other hand, if the amount added is too high, the amount of unreacted antioxidant components and ammonium salt components remaining in the system will increase, which will also have an adverse effect on the purity of the concentrated sodium acetate carbon source, and at the same time significantly increase the raw material processing cost.

[0046] b. Acidic decomposition: Add an acidic agent to the oil-water two-phase mixture obtained in step a, and react at 80-95℃ for 4-6 hours under nitrogen protection to fully convert sodium fatty acids into fatty acids. After the reaction, separate the layers to obtain an upper acidified oil and a lower weakly acidic aqueous phase (e.g., Figure 4(As shown). The reaction temperature is controlled within the range of 80-95℃. Excessively high temperatures will violently trigger sulfonation and oxidation side reactions of fatty acids, leading not only to severe emulsification and difficulty in oil-water separation, but also to a darker product color and significant quality deterioration. Conversely, excessively low temperatures will significantly reduce the reaction rate, and the high viscosity of the materials will affect mass transfer efficiency, ultimately resulting in insufficient conversion of the acidified oil. This temperature control range effectively balances the reaction rate and the inhibition of side reactions, ensuring the conversion efficiency and product quality of the acidified oil. The reaction time is optimized to 4-6 hours. Excessively long reaction times will intensify the contact between fatty acids and substances such as acetic acid, inducing oxidation and sulfonation side reactions, leading to a darker product color, decreased quality, and a significant increase in the risk of emulsification, causing separation difficulties. It will also reduce production efficiency and increase energy consumption. Conversely, excessively short reaction times will result in incomplete conversion of sodium fatty acids and uneven mixing of the reaction system. The direct consequences are reduced acidified oil quality, high residual soap content, and oil phase loss and excessive oil content in wastewater due to insufficient stratification.

[0047] The acidic agent is an acetic acid solution with a concentration of 30-100%, replacing the concentrated sulfuric acid used in traditional processes. In conventional soapstock acidification processes, concentrated sulfuric acid is mostly used as the acidifying agent. However, concentrated sulfuric acid has strong oxidizing properties, which causes unsaturated glycerides, fatty acids, phospholipids, etc., in the soapstock to rapidly dehydrate and carbonize, and polymerize with themselves to produce plant asphalt, thus greatly reducing the quality of the produced acidified oil. On the other hand, using concentrated sulfuric acid as the acidifying agent results in a large amount of sodium sulfate in the aqueous layer after acidification. Conventional processes can only treat the aqueous layer by evaporation and desalination; however, the glycerol, fatty acids, and large amounts of sodium sulfate present in the aqueous layer remain in the evaporation mother liquor, making it impossible to realize the resource utilization of the aqueous layer and resulting in resource waste. Therefore, this invention uses acetic acid solution for the acidification of soapstock. On the one hand, acetic acid does not have strong oxidizing properties, avoiding the formation of plant asphalt due to oxidation, thus improving the quality of the acidified oil. On the other hand, after acetic acid acidification, the aqueous layer contains a large amount of sodium acetate. Sodium acetate, along with fatty acids and glycerol, are all high-quality biochemical carbon sources. After concentration, the mother liquor can be used as a carbon source, avoiding resource waste. The concentration of the acetic acid solution is controlled within the range of 30% to 100%. If the concentration is too low, the hydrogen ion concentration in the system will be insufficient, significantly delaying the conversion rate of sodium fatty acids to fatty acids. To achieve complete conversion, the reaction temperature needs to be increased or the reaction time extended, thereby increasing energy consumption and potentially triggering side reactions. This concentration range effectively balances the reaction rate and separation effect, ensuring the economy and operational stability of the process.

[0048] The amount of acidic agent added is controlled to be 7% to 10% of the soapstock mass. Excessive addition will result in excess acetic acid remaining in the reaction system, requiring a large amount of sodium hydroxide for neutralization in the subsequent struvite synthesis step, significantly increasing processing costs. Insufficient addition will result in a weak acidic environment, preventing sodium fatty acids from being fully converted into free fatty acids and sodium acetate, leaving some sodium fatty acids remaining in the acidified oil layer. Although the residual sodium fatty acids still separate with the acidified oil phase, keeping the acidified oil yield (the volume of acidified oil produced relative to the original soapstock solution) relatively stable, or even slightly increased, its presence will lower the acid value of the acidified oil. Acid value is an important indicator of the free fatty acid content and the degree of reaction completion in the acidified oil, affecting product quality.

[0049] c. Struvite synthesis: An alkaline solution is added to the weakly acidic aqueous phase obtained in step b to adjust the pH to 8-10. After reacting for 0.5-2 hours, the mixture is filtered to obtain struvite (MgNH4PO4·6H2O) product (e.g. Figure 1 (As shown), the remaining filtrate has good biodegradability and can be directly reused or discharged after treatment. The reaction pH should be controlled within the range of 8-9; excessively high pH will promote Mg... 2+ The formation of Mg(OH)2 precipitate reduces the removal rates of phosphorus and ammonia nitrogen, leading to a decrease in product purity; excessively low pH causes phosphate to mainly form HPO4. 2- The form exists, but it cannot effectively generate the PO4 required for struvite. 3- This results in insufficient reaction driving force and a significant decrease in synthesis efficiency. The reaction time is optimized to 0.5~2h. Excessive time not only increases energy consumption but also introduces impurities and amorphous substances, affecting product purity; insufficient time leads to incomplete struvite synthesis, resulting in a simultaneous decrease in total phosphorus removal rate and struvite conversion rate. This process effectively balances reaction efficiency and product quality, ensuring efficient phosphorus resource recovery and smooth subsequent processing.

[0050] The alkaline solution is a sodium hydroxide solution with a mass fraction of 10% to 32%. Excessive concentration of the alkaline solution can cause a rapid and sudden spike in local pH during addition, triggering Mg2+ uptake. 2+ The formation of Mg(OH)2 precipitate is not the target product struvite, which reduces the purity of the product. If the concentration of the alkaline solution is too low, a large amount of liquid needs to be added to reach the target pH value, which leads to excessive dilution of the reaction system. The struvite is not supersaturated enough, which affects the crystallization and precipitation effect. At the same time, it significantly increases the load on subsequent treatment. This concentration control effectively ensures the reaction efficiency and product quality of the struvite synthesis process.

[0051] d. Concentration: The filtrate obtained in step c is concentrated by evaporation to separate the byproduct sodium acetate carbon source (e.g., ...). Figure 7 (as shown) and reusable distilled water (such as...) Figure 6 As shown in the figure, the full resource utilization of aqueous components is realized.

[0052] This invention optimizes the demulsification and decomposition process of soapstock, achieving efficient generation of acidified oil while thoroughly decomposing phospholipids and directional recovery of phosphorus components. It also effectively inhibits the oxidative coking reaction caused by concentrated sulfuric acid and oxygen, significantly reducing the amount of plant asphalt generated.

[0053] The following detailed description of examples of the present invention is exemplary and is used only to explain the present invention, and should not be construed as limiting the present invention.

[0054] Example 1

[0055] A production process for soapstock demulsification, decomposition, and recovery of acidified oil, along with the co-production of struvite, involves weighing 1000 g of soapstock raw material and adding 80 g of reaction aid. This reaction aid consists of an antioxidant, a phosphorus fixative, and a stabilizer in a mass ratio of 1:5:4. The antioxidant is a 10% ascorbic acid aqueous solution, the phosphorus fixative is a 22% magnesium sulfate aqueous solution, and the stabilizer is a 14% ammonium sulfate aqueous solution. The reaction is carried out under nitrogen protection at 130°C and 0.6 MPa pressure for 4 hours to complete the phospholipid hydrolysis and demulsification process, yielding an upper mixed sodium fatty acid phase and a lower neutral aqueous phase. Subsequently, 85 g of [unspecified ingredient] is added to the layered system. A 40% (w / w) acetic acid solution was reacted at 90°C for 5 hours under nitrogen protection. After standing and separating, an upper layer of acidified oil and a lower layer of weakly acidic aqueous phase were obtained. Then, a 20% (w / w) sodium hydroxide solution was added to the weakly acidic aqueous phase to adjust the pH to 8.5. After reacting for 1 hour, the mixture was filtered to obtain struvite. Finally, the filtrate was concentrated to obtain sodium acetate as a carbon source byproduct and reusable distilled water. The color of the oil phase in the acidified oil sample is shown in [reference needed]. Figure 2 .

[0056] Example 2

[0057] The production process is the same as in Example 1, except that the antioxidant, phosphorus fixative and stabilizer are mixed in a mass ratio of 0.5:7:2.5 and then added to the soapstock, and the total amount of reaction aids added is 7.5%.

[0058] Example 3

[0059] The production process is the same as in Example 1, except that the amount of reaction aid added is 3% of the soap residue mass.

[0060] Example 4

[0061] The production process is the same as in Example 1, except that the amount of reaction aid added is 15% of the soap residue mass.

[0062] Example 5

[0063] The production process is the same as in Example 1, except that ascorbic acid is prepared as a 3% aqueous solution, while the concentrations of other components remain unchanged.

[0064] Example 6

[0065] The production process is the same as in Example 1, except that ascorbic acid is prepared as an 18% aqueous solution, while the concentrations of other components remain unchanged.

[0066] Example 7

[0067] The production process is the same as in Example 1, except that magnesium sulfate is prepared as a 15% aqueous solution, while the concentrations of other components remain unchanged.

[0068] Example 8

[0069] The production process is the same as in Example 1, except that magnesium sulfate is prepared as a 28% aqueous solution, while the concentrations of other components remain unchanged.

[0070] Example 9

[0071] The production process is the same as in Example 1, except that ammonium sulfate is prepared as a 6% aqueous solution, while the concentrations of other components remain unchanged.

[0072] Example 10

[0073] The production process is the same as in Example 1, except that ammonium sulfate is prepared as an 18% aqueous solution, while the concentrations of other components remain unchanged.

[0074] Example 11

[0075] The production process is the same as in Example 1, except that in the phospholipid hydrolysis process in step a, the reaction temperature is controlled at 100°C and the system pressure is 0.6 MPa, and the reaction is continued for 4 hours.

[0076] Example 12

[0077] The production process is the same as in Example 1, except that in step a, the phospholipid hydrolysis process is controlled at a reaction temperature of 170°C and a system pressure of 0.6 MPa, and the reaction is continued for 4 hours.

[0078] Example 13

[0079] The production process is the same as in Example 1, except that in the phospholipid hydrolysis process in step a, the reaction temperature is controlled at 130°C and the system pressure is 0.2 MPa, and the reaction is continued for 4 hours.

[0080] Example 14

[0081] The production process is the same as in Example 1, except that in the phospholipid hydrolysis process in step a, the reaction temperature is controlled at 130°C and the system pressure is 0.8 MPa, and the reaction is continued for 4 hours.

[0082] Example 15

[0083] The production process is the same as in Example 1, except that in step a, the phospholipid hydrolysis process is controlled at a reaction temperature of 130°C and a system pressure of 0.6 MPa, and the reaction is continued for 2 hours.

[0084] Example 16

[0085] The production process is the same as in Example 1, except that in the phospholipid hydrolysis process in step a, the reaction temperature is controlled at 130°C and the system pressure is 0.6 MPa, and the reaction is continued for 10 hours.

[0086] Example 17

[0087] The production process is the same as in Example 1, except that in step b, the amount of acetic acid solution added is 4% of the soap residue mass.

[0088] Example 18

[0089] The production process is the same as in Example 1, except that in step b, the amount of acetic acid solution added is 13% of the soap residue mass.

[0090] Example 19

[0091] The production process is the same as in Example 1, except that a 20% acetic acid solution is used.

[0092] Example 20

[0093] The production process is the same as in Example 1, except that the reaction temperature is 75°C during the acidic decomposition process in step b.

[0094] Example 21

[0095] The production process is the same as in Example 1, except that the reaction temperature is 105°C during the acidic decomposition process in step b.

[0096] Example 22

[0097] The production process is the same as in Example 1, except that the reaction time in step b is shortened to 2 hours.

[0098] Example 23

[0099] The production process is the same as in Example 1, except that the reaction time in step b is extended to 8 hours.

[0100] Example 24

[0101] The production process is the same as in Example 1, except that step c uses a 5% sodium hydroxide solution.

[0102] Example 25

[0103] The production process is the same as in Example 1, except that step c uses a 40% sodium hydroxide solution.

[0104] Example 26

[0105] The production process is the same as in Example 1, except that step c adjusts the pH to 7.

[0106] Example 27

[0107] The production process is the same as in Example 1, except that step c adjusts the pH to 11.

[0108] Example 28

[0109] The production process is the same as in Example 1, except that the reaction time in step c, struvite synthesis, is 15 minutes.

[0110] Example 29

[0111] The production process is the same as in Example 1, except that the reaction time in step c, the synthesis of struvite, is 4 hours.

[0112] Comparative Example 1

[0113] The production process is the same as in Example 1, except that only antioxidants (ascorbic acid) and phosphorus fixatives (magnesium sulfate) are added to 1000g of soap residue in a mass ratio of 1.5:4, and the total amount added is 7.5% of the soap residue mass. No stabilizers are added.

[0114] Comparative Example 2

[0115] The production process is the same as in Example 1, except that 2,6-di-tert-butyl-p-cresol (BHT) is used instead of ascorbic acid as an antioxidant.

[0116] Comparative Example 3

[0117] The production process is the same as in Example 1, except that concentrated sulfuric acid (98%) is used instead of acetic acid for acid decomposition, and the amount added is adjusted to 5% of the soap residue mass. The oil phase color of the acidified oil sample is shown in [reference needed]. Figure 3 .

[0118] Test case

[0119] Characterization analysis was conducted on the production processes used in Examples 1-29 and Comparative Examples 1-3. Test items included: visual observation of the color of the oil phase (i.e., the upper acidified oil); determination of the conversion rate of organic phosphorus in the lower aqueous phase and the total phosphorus concentration in the effluent using ammonium molybdate spectrophotometry (molybdenum blue method) to evaluate the resource recovery efficiency of phosphorus; detection of the chemical oxygen demand in the aqueous phase using the potassium dichromate oxidation method (COD determination) to determine the degree of hydrolysis of glycerol esters; determination of the acid value and saponification value of the final acidified oil according to relevant national standards to evaluate its free fatty acid content, esterification degree, and overall product quality; and analysis based on material balance. The phosphorus recovery rate was calculated to quantitatively characterize the effective migration and fixation of phosphorus resources from the aqueous phase to solid crystals. Furthermore, the content of plant bitumen was determined by distillation purification, the yield of acidified oil was calculated by mass balance method, the concentration of sodium acetate in the concentrated mother liquor was determined by ion chromatography, the COD and ammonia nitrogen content in the distillate water was detected by Nessler's reagent colorimetric method, the oil-water separation time was recorded by interface tracking method, and the proportion of the intermediate emulsion layer was evaluated by volumetric measurement method. This comprehensively obtained the flow direction of key substances, the distribution of intermediate products, and separation performance parameters in the process, systematically revealing the synergistic effects of various process conditions on the quality of acidified oil, phosphorus resource recovery efficiency, and overall environmental benefits. The characterization results are shown in Tables 1-4.

[0120] Table 1: Key Quality Indicators for Acidified Oil Products

[0121]

[0122] Table 2: Key Indicators for Phosphorus Recovery and Struvite Quality

[0123]

[0124] Table 3: Key Indicators of Aqueous Phase Treatment and Resource Utilization Efficiency

[0125]

[0126] Table 4: Key Indicators of Process Efficiency

[0127]

[0128] The experimental data comparison shows that Example 1 performed best in terms of acidified oil quality, phosphorus recovery efficiency, and process. Its acidified oil yield was 27.71%, with an acid value of 143.81 mg KOH / g and an ideal yellow-brown oil phase. Regarding phosphorus recovery, the organic phosphorus conversion rate was as high as 99.71%, and the struvite phosphorus recovery rate reached 98.88%, while the total phosphorus in the effluent was only 6 mg / L. No emulsion layer appeared during the process, and oil-water separation only took 10 minutes. In contrast, Examples 2, 3, 5, 7, and 9, which changed the ratio or concentration of reaction aids, generally showed problems such as a significant decrease in struvite phosphorus recovery (61.08%–73.68%), a darker acidified oil color, an increased plant bitumen content, or a prolonged separation time. Examples with improperly controlled reaction conditions, such as lowering the hydrolysis temperature (Example 11), shortening the hydrolysis time (Example 15), insufficient acidification temperature (Example 21), or low acetic acid addition (Example 17), all led to a decrease in acidified oil yield or acid value. The comparative results further revealed the roles of key components: Comparative Example 1, without the addition of stabilizers, failed to form struvite at all; Comparative Example 2, using BHT instead of ascorbic acid, could form struvite, but the oil phase color darkened and the plant asphalt content increased; Comparative Example 3, using concentrated sulfuric acid, achieved the highest acid value (150.48 mgKOH / g) and the lowest aqueous phase COD, but the acidified oil was dark black, the plant asphalt content was as high as 14.22%, and no sodium acetate byproduct was produced, indicating that although it could enhance acidification, it seriously damaged product quality and resource integrity. In summary, only when the ratio and concentration of reaction aids are appropriate, and the hydrolysis and acidification conditions are fully coordinated, can high-quality acidified oil production, efficient phosphorus recovery, and good process feasibility be achieved simultaneously.

[0129] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A production process for demulsifying and recovering acidified oil from soap residue and co-producing struvite, characterized in that, Includes the following steps: a. Phospholipid hydrolysis: A reaction aid is added to soapstock to initiate a reaction, causing the soapstock to demulsify and decompose the phospholipids. After the reaction, an oil-water two-phase mixture is obtained, with the upper layer being a mixed sodium fatty acid phase and the lower layer being a neutral aqueous phase. The reaction aid includes an antioxidant, a phosphorus fixative, and a stabilizer. The antioxidant is selected from at least one of ascorbic acid, sodium bisulfite, and sodium sulfite. The phosphorus fixative is selected from at least one of magnesium sulfate, magnesium chloride, and magnesium carbonate. The stabilizer is selected from at least one of ammonium sulfate, ammonium chloride, and ammonium carbonate. The mass ratio of the antioxidant, phosphorus fixative, and stabilizer is (1~2):(4~6):(2~5). The reaction is carried out under nitrogen protection at a temperature of 120℃~140℃, a pressure of 0.4MPa~0.6MPa, and a reaction time of 4 h~8 h. b. Acidic decomposition: An acidic agent is added to the oil-water two-phase mixture obtained in step a. After the reaction is completed, the mixture separates into two layers, resulting in an upper layer of acidified oil and a lower layer of weakly acidic aqueous phase. The acidic agent is acetic acid. c. Synthesis of struvite: Add an alkaline solution to the weakly acidic aqueous phase obtained in step b to adjust the pH value. After the reaction is complete, filter to obtain struvite and filtrate. d. Concentration: The filtrate obtained in step c is concentrated to obtain sodium acetate carbon source byproduct and distilled water; The amount of the reaction aid added is 5% to 10% of the soap residue mass.

2. The production process according to claim 1, characterized in that, The antioxidant is added in the form of an aqueous solution with a mass concentration of 5% to 15%, the phosphorus fixative is added in the form of an aqueous solution with a mass concentration of 20% to 25%, and the stabilizer is added in the form of an aqueous solution with a mass concentration of 10% to 15%.

3. The production process according to claim 1, characterized in that, The amount of the acidic agent added is 7% to 10% of the weight of the soap residue.

4. The production process according to claim 1, characterized in that, The acidic agent is an acetic acid solution with a mass concentration of 30% to 100%.

5. The production process according to claim 1, characterized in that, In step b, the reaction is carried out under nitrogen protection at a temperature of 80℃ to 95℃ for a time of 4 h to 6 h.

6. The production process according to claim 1, characterized in that, The alkaline solution is a sodium hydroxide solution with a mass fraction of 10% to 32%.

7. The production process according to claim 1, characterized in that, In step c, the pH value is adjusted to 8-10 for the reaction, and the reaction time is 0.5 h-2 h.

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