A process for separating fatty acids

Abstract

The application discloses a fatty acid separation process method. The fatty acid separation process method comprises the following steps: precooling and filtering impurities of C16 / C18 mixed fatty acid raw materials; sequentially performing rapid cooling crystallization, gradient temperature control crystallization and crystal growing treatment on the pretreated materials; and sequentially performing prefiltration and high-pressure filter pressing on the crystallized materials, so as to obtain filtrate containing oleic acid and filter cake containing stearic acid. Through the above method, the fatty acid separation process method provided by the application significantly improves the solid-liquid separation performance, improves the separation efficiency, realizes high-purity and high-yield preparation of oleic acid, and has the advantages of simple process flow, avoidance of a complex solvent recovery process and significant reduction of production cost.

Description

Technical Field

[0001] This application relates to the fields of oleochemicals and separation engineering technology, and in particular to a fatty acid separation process method. Background Technology

[0002] Fatty acids are essential raw materials in the oleochemical industry, widely used in paints and coatings, plastic additives, lubricant additives, cosmetics, and biopharmaceuticals. Oleic acid (C18:1), as an important monounsaturated fatty acid, is widely used in these fields due to its excellent chemical stability, low-temperature fluidity, and surface activity. High-purity oleic acid, in particular, is in high demand in the high-end lubricant and cosmetic raw material markets.

[0003] Currently, the main industrial methods for producing oleic acid include solvent crystallization, surfactant separation, urea inclusion, and distillation. For example, existing technologies propose a method using organic solvents (such as methanol and acetone) to perform multiple crystallization separations of mixed fatty acids. While this method can obtain products with high purity, it involves a long process, high energy consumption for solvent recovery, and poses safety hazards due to flammability and explosiveness. The large-scale use of organic solvents during production also creates environmental pressure. Another common technique is separation using aqueous surfactant solutions. Although this method is lower in cost, it requires the addition of large amounts of surfactants and inorganic salts during production, resulting in wastewater containing significant pollutants and incurring high environmental treatment costs.

[0004] In recent years, cryo-fractionation, as a physical separation technology, has attracted widespread attention due to its advantages such as the absence of chemical additives and the good naturalness of the products. However, existing cryo-fractionation processes face significant technical bottlenecks in practical applications: First, traditional cryo-crystallization often employs a single cooling rate, resulting in uneven crystal size distribution and the formation of fine crystals, making subsequent solid-liquid separation difficult and inefficient. Second, poor crystallization leads to difficulty in improving product purity and low yield, resulting in resource waste. Furthermore, traditional processes often rely on complex solvent systems or multiple recrystallizations to improve purity, resulting in long process flows and high costs.

[0005] Therefore, there is an urgent need for a fatty acid separation process that is simple, efficient, produces high-purity products, and yields high results. Summary of the Invention

[0006] This application provides a fatty acid separation process to solve the problems of low fatty acid separation efficiency, low product purity, and low yield in the prior art.

[0007] To solve the above-mentioned technical problems, one technical solution adopted in this application is to provide a fatty acid separation process. This fatty acid separation process includes: S1: pre-cooling and filtering a C16 / C18 mixed fatty acid raw material to remove impurities; S2: sequentially subjecting the pretreated material to rapid cooling crystallization, gradient temperature-controlled crystallization, and crystal growth treatment; S3: sequentially subjecting the crystallized material to pre-filtration and high-pressure filtration to obtain a filtrate containing oleic acid and a filter cake containing stearic acid, respectively.

[0008] In some embodiments, in step S2, The rapid cooling crystallization includes: reducing the material temperature to 8℃~12℃, and controlling the cooling rate to 1.5℃ / h~3.0℃ / h; The gradient temperature-controlled crystallization includes: reducing the material temperature from 8℃~12℃ to 0℃~3℃; The crystal growth process includes maintaining the material at a constant temperature within the range of 0℃ to 3℃.

[0009] In some embodiments, during the gradient temperature controlled crystallization stage, a segmented temperature control method is adopted, with a constant temperature segment set at intervals of 1.5℃ to 2.5℃, and the residence time of each constant temperature segment is 6h to 10h. During the gradient temperature-controlled crystallization stage, the cooling rate is controlled at 0.1℃ / h to 1.0℃ / h.

[0010] In some embodiments, during the gradient temperature-controlled crystallization and crystal growth stages, the stirring rate is controlled to be 5 r / min to 30 r / min; in step S2, chilled water at -20℃ to -10℃ is used as the refrigerant for indirect heat exchange.

[0011] In some embodiments, during the crystal growth stage, the constant temperature and static time is 8h to 15h to control the crystal particle size to grow to more than 50μm.

[0012] In some embodiments, in step S1, the precooling process utilizes the cooling energy of the low-temperature material after crystallization in step S3 for heat exchange; the filtration and impurity removal uses an online filter with an accuracy of 30μm~60μm to remove mechanical impurities.

[0013] In some embodiments, in step S3, the specific process of pre-filtration is as follows: the crystallized material is conveyed to the pre-filter by a screw extrusion pump, and crystals with a particle size ≥80μm are removed under a pressure of 1.0bar~2.0bar. The specific process of high-pressure filtration is as follows: the pre-filtered filtrate is sent into a high-pressure filter press and precision filtered through a filter cloth with a pore size of 5μm to 20μm under a pressure of 6bar to 10bar.

[0014] In some embodiments, the method further includes S4: sequentially subjecting the filter cake obtained in step S3 to solvent extraction purification and catalytic hydrogenation modification to obtain cosmetic grade stearic acid.

[0015] In some embodiments, during the solvent extraction and purification process, a mixed solvent of n-hexane and ethanol is used as the extractant, wherein the volume ratio of n-hexane to ethanol is (2~4):1. The solvent extraction and purification process is carried out at a temperature of 40℃ to 70℃ for 1 hour to 3 hours.

[0016] In some embodiments, during the catalytic hydrogenation modification process, a nickel-based catalyst is used as the active component, and the hydrogenation reaction is carried out at 150°C to 200°C and 1.5 MPa to 3.0 MPa for a reaction time of 2 h to 5 h.

[0017] The beneficial effects of this application are as follows: Unlike existing technologies, this application discloses a fatty acid separation process. The embodiments of this application utilize a segmented crystallization strategy involving rapid cooling crystallization, gradient temperature-controlled crystallization, and crystal growth treatment. By controlling the cooling process from fast to slow, it effectively balances crystal nucleation and crystal growth, resulting in large and regular crystals, significantly improving solid-liquid separation performance and increasing separation efficiency. The two-stage solid-liquid separation process of pre-filtration and high-pressure filtration further enhances the separation effect, achieving high purity and high yield of oleic acid. This process is simple, avoids complex solvent recovery procedures, and significantly reduces production costs. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a schematic flowchart of an embodiment of the fatty acid separation process provided in this application. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0020] The terms "first," "second," and "third" used in the embodiments of this application are 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 as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0021] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0022] To address the problems of high energy consumption, low yield, and low value of byproducts in existing fatty acid separation processes, this application provides a fatty acid separation scheme that couples segmented crystallization with high-pressure filtration. This scheme achieves efficient preparation of high-quality oleic acid through unique crystallization kinetic control and integrated processes, while simultaneously realizing the resource utilization of byproducts.

[0023] Specifically, this application provides a fatty acid separation process, see reference. Figure 1 , Figure 1 This is a schematic flow chart of an embodiment of the fatty acid separation process provided in this application. The fatty acid separation process mainly includes four core steps: raw material pretreatment, freeze crystallization, solid-liquid separation, and optional high-value utilization of by-products. The following will elaborate on each step in conjunction with specific process parameters, equipment selection, and working mechanisms.

[0024] S1: Pre-cool and filter the C16 / C18 mixed fatty acid raw material to remove impurities.

[0025] Step S1 is the raw material pretreatment step, which is the foundation of the entire separation process. Its core purpose is to provide clean materials with suitable temperature, uniform composition and no mechanical impurities for the subsequent crystallization process.

[0026] The raw material processed in this embodiment is mainly a C16 / C18 mixed fatty acid, which is usually derived from the soapstock acid hydrolysis or oil hydrolysis process of vegetable oils (such as palm oil, soybean oil, cottonseed oil, etc.). Its typical composition is: palmitic acid (C16:0) content of about 15%-25%, stearic acid (C18:0) content of about 5%-10%, oleic acid (C18:1) content of about 60%-70%, linoleic acid (C18:2) content of about 5%-10%, and small amounts of other fatty acids and unsaponifiables. Since fatty acids with different carbon chain lengths and saturations have significantly different freezing points, such as stearic acid freezing point of about 69°C, oleic acid freezing point of about 10-15°C, and palmitic acid freezing point of about 63°C, this provides a thermodynamic basis for physical fractionation using melting point differences.

[0027] However, raw materials often contain small amounts of protein, colloids, metal ions, and mechanical impurities. If these are not removed, they will act as heterogeneous nucleation centers during the crystallization process, resulting in finely fragmented crystals and severely affecting the separation effect.

[0028] In step S1, the raw material is first conveyed to the precooling system. In this embodiment, a plate heat exchanger is preferably used as the heat exchange device. It is worth noting that step S1 utilizes the cooling energy of the low-temperature material generated in subsequent step S3 to precool the raw material.

[0029] Specifically, the temperature of the oleic acid filtrate obtained after freeze crystallization and separation is typically between 0°C and 5°C, while the feed temperature is usually at room temperature or slightly higher (e.g., 20°C-40°C). By conducting non-contact heat exchange between the feed and the low-temperature filtrate in a plate heat exchanger, the feed temperature can be effectively reduced to close to the initial crystallization temperature required by the process, while simultaneously recovering the cold energy in the filtrate and raising it to near room temperature before it enters the storage tank.

[0030] For example, in one specific embodiment, the raw material feed temperature is 65°C and the flow rate is 5 m³ / h; the low-temperature filtrate temperature is 2°C. Through heat exchange, the raw material temperature can be pre-cooled to 55°C, while the filtrate temperature rises to 25°C after recovering its cooling capacity. This process significantly reduces the cooling load of the subsequent step S2 and greatly reduces energy consumption.

[0031] The pre-cooled raw materials then enter the filtration and impurity removal process; considering that the mixed fatty acids have a certain viscosity and are sensitive to impurities, an online filter with a precision of 30μm~60μm is selected in this embodiment.

[0032] If the filtration accuracy is below 60μm (e.g., 100μm), micron-sized colloidal impurities cannot be effectively retained. These impurities hinder crystal growth during the crystallization process, leading to irregular crystal shapes and decreased filtration performance. If the accuracy is above 70μm (e.g., 5μm), although more impurities can be retained, the filter element clogs quickly, requiring frequent backwashing, resulting in large system pressure fluctuations, affecting production continuity, and increasing consumable costs. Therefore, 30μm~60μm is an accuracy range that achieves a better balance between impurity removal efficiency and operating costs.

[0033] Step S2: The pretreated material is subjected to rapid cooling crystallization, gradient temperature-controlled crystallization, and crystal growth treatment in sequence.

[0034] Step S2 is the freeze crystallization step, which is a core step that determines the purity, yield, and ease of subsequent separation of the final product. This application's embodiments abandon the traditional one-step cooling method and instead adopt a three-stage control strategy of rapid cooling, gradient temperature control, and crystal growth. This strategy is based on the principles of solution crystallization kinetics, achieving controllable adjustment of crystal morphology by precisely controlling supersaturation and crystal growth time.

[0035] This embodiment uses a crystallization tank with a jacket and a stirring system. The tank body is preferably made of 304 or 316L stainless steel. The jacket is circulated with a refrigerant, such as an aqueous solution of ethylene glycol or chilled brine. The stirring system uses a low-speed impeller, such as a frame stirrer or an anchor stirrer, with a rotation speed that can be steplessly adjusted within the range of 5 r / min to 30 r / min. The tank is equipped with a high-precision temperature sensor and is connected to a DCS automated control system to achieve closed-loop temperature control.

[0036] This step uses chilled water at -20℃ to -10℃ as the refrigerant. Lower-temperature refrigerants are not used to prevent the formation of an excessively thick crystalline layer on the heat exchanger wall, which would cause a sharp drop in heat transfer efficiency. Maintaining an appropriate temperature difference ensures a smooth and controllable cooling curve.

[0037] Rapid cooling crystallization involves rapidly reducing the temperature of the pretreated material to 8℃~12℃, controlling the cooling rate at 1.5℃ / h~3.0℃ / h (e.g., 2.0℃ / h).

[0038] The rapid cooling crystallization stage is the crystallization induction period. According to the classical nucleation theory, the nucleation rate is closely related to the supersaturation of the solution. When the temperature drops rapidly, the solution quickly reaches a supersaturated state, producing a large number of crystal nuclei.

[0039] * If the cooling rate is too fast (>3.0℃ / h), the solution will become excessively supersaturated, resulting in a burst of numerous microcrystal nuclei. These microcrystals are difficult to merge during subsequent growth, ultimately leading to crystals that are too small (<20μm), forming a loose, snowflake-like structure that severely affects the subsequent filtration speed and may even clog the filter cloth. If the cooling rate is too slow (<1.5℃ / h), although the crystal quality is good, the production cycle is too long, the equipment utilization rate is low, and energy consumption increases.

[0040] By adopting a cooling rate of 1.5℃ / h to 3.0℃ / h, a sufficient number of crystal nuclei are formed in a short time to provide seeds for subsequent crystal growth, while avoiding an excess of crystal nuclei.

[0041] At the end of this stage, a large number of tiny crystal embryos are formed in the solution, laying the foundation for subsequent crystal growth.

[0042] Gradient temperature-controlled crystallization involves further reducing the material temperature from 8℃~12℃ to 0℃~3℃. The cooling rate is controlled at 0.1℃ / h~1.0℃ / h, which is significantly lower than the rapid cooling stage. Furthermore, a segmented temperature control method is adopted, with a constant temperature section set at intervals of 1.5℃~2.5℃, and the residence time of each constant temperature section is 6h~10h.

[0043] The gradient temperature-controlled crystallization stage is the main stage of crystal growth. The crystal nuclei formed after rapid cooling need to grow in a stable supersaturated environment.

[0044] If the temperature continues to drop, the supersaturation of the solution changes continuously, and the crystal growth is in an unstable state, which easily leads to layered structures or the inclusion of impurities. In this embodiment, by setting a constant temperature period, such as 10°C for 8 hours and then cooling to 8°C for 8 hours, the solution concentration gradually decreases as the solute precipitates on the crystal surface during the constant temperature period, and the supersaturation gradually approaches zero. At this time, although the crystal growth rate is slow, it is very orderly, and the molecules have enough time to arrange themselves on the crystal lattice, forming a dense crystal with a clear interface.

[0045] The cooling rate was controlled at 0.1℃ / h to 1.0℃ / h. This extremely low cooling rate was to maintain operation in the metastable region. In the metastable region, only crystal growth occurs in the solution, and no new nucleation occurs. This ensures that all solute molecules are mainly used to feed the existing crystals, rather than to form new small crystals.

[0046] During the gradient temperature-controlled crystallization stage, the stirring rate is controlled between 5 r / min and 30 r / min. Maintaining a low stirring rate within this range serves two purposes: first, it provides a gentle fluid flow, transporting solute molecules to the crystal surface and eliminating the concentration gradient; second, it avoids excessive shear force that could break the already formed crystals. If the stirring is too fast, the probability of collisions between crystals increases, leading to crystal breakage and the formation of secondary nuclei, which affects the uniformity of crystal size.

[0047] Crystal growth includes: keeping the material at a constant temperature within the range of 0℃ to 3℃ (e.g., 1℃) for 8h to 15h.

[0048] Despite gradient temperature control, some small crystals or crystal aggregates may still exist in the system. During isothermal settling, the smaller crystals, due to their larger specific surface area, have a slightly higher solubility than the larger crystals. Therefore, molecules on the surface of the smaller crystals will continuously dissolve into the solution and diffuse to the surface of the larger crystals for recrystallization. In this process, the smaller crystals disappear, and the larger crystals grow.

[0049] After crystal growth, the particle size distribution curve becomes sharper, the average crystal size increases significantly, and the crystal size is controlled to grow to over 50μm, even reaching 100μm~200μm. Large and well-formed crystals have higher mechanical strength and better filtration performance. The filter cake has good air permeability and low moisture content, creating excellent conditions for subsequent high-pressure filtration.

[0050] To accurately execute the aforementioned complex crystallization process, a DCS automated control system was further introduced. This DCS automated control system uses a fuzzy PID control algorithm to monitor the crystallization process in all aspects.

[0051] Specifically, the DCS automated control system collects the temperature inside the crystallizer in real time and automatically adjusts the opening of the chilled water valve according to the preset cooling curve. When the detected cooling rate deviation exceeds ±0.5℃, the system automatically performs PID correction; at the same time, it automatically adjusts the stirring speed according to the temperature stage, for example, using a higher speed to enhance heat transfer during the rapid cooling stage and reducing the speed to protect the crystals during the gradient growth stage.

[0052] Furthermore, the DCS automated control system calculates the change in the heat capacity of the solution by monitoring the ratio of the temperature drop rate to the jacket refrigerant flow rate, thereby indirectly judging the heat release during crystallization, assisting in judging the crystallization process, and ensuring that the operation is always within the metastable region.

[0053] Step S3: The crystallized material is subjected to pre-filtration and high-pressure filtration in sequence to obtain filtrate containing oleic acid and filter cake containing stearic acid, respectively.

[0054] Step S3 is a solid-liquid separation step, which is a crucial step in separating the carefully cultivated crystals from the mother liquor. It directly affects the purity, yield, and production cost of the final product. This embodiment does not use traditional centrifugal separation or vacuum filtration methods, but instead employs a two-stage tandem process of screw extrusion pre-separation and high-pressure filtration fine separation.

[0055] Specifically, the pre-filtration process is as follows: the crystallized material is conveyed to the pre-filter via a screw extrusion pump, and crystals with a particle size ≥80μm are removed under a pressure of 1.0bar~2.0bar; the high-pressure filtration process is as follows: the pre-filtered filtrate is sent to a high-pressure filter press, and precision filtration is performed through a filter cloth with a pore size of 5μm~20μm under a pressure of 6bar~10bar.

[0056] Fatty acid crystals (especially eutectics of oleic and stearic acids) are relatively soft and have low mechanical strength. Traditional centrifugal or vane pumps generate high-frequency shearing forces during operation, which easily break the grown crystals into fine powder. Once the crystals are broken, not only does the filtration area increase dramatically, but it also leads to filter cloth clogging. Screw extrusion pumps rely on the meshing of the screw and bushing to form a volumetric cavity, propelling the material to flow smoothly with minimal fluid pulsation, thus preserving the integrity of the crystal morphology to the greatest extent possible.

[0057] The crystallization slurry is in a low temperature range of 0℃ to 3℃ and has a high viscosity. The screw extrusion pump has a strong self-priming ability and can smoothly extract high viscosity low temperature fluids, avoiding the flow fluctuations caused by cavitation in ordinary pumps.

[0058] After being pressurized by a screw pump, the material enters a pre-filter, with the operating pressure controlled between 1.0 bar and 2.0 bar. This pressure range has been precisely calculated to ensure that the fluid is pushed through the filter screen without forcing crystals through the mesh due to excessive pressure.

[0059] After crystal growth, some crystals in the system may grow excessively or aggregate, with a particle size exceeding 80μm. If these large particles are directly fed into the high-pressure filter press, they will quickly form a bridging effect at the feed inlet, leading to uneven feeding. By using a pre-filter, such as a wedge-shaped filter with a pore size of 80μm~100μm, these large particles can be preferentially retained.

[0060] The separation step of the pre-filter is equivalent to a homogenization pretreatment of the material. It reduces the instantaneous load on the subsequent high-pressure filter press, making the slurry crystals entering the filter press evenly distributed, and the filter cake can be evenly spread on the surface of the filter cloth, avoiding the problem of filter press seal failure caused by uneven filter cake thickness.

[0061] The pre-filtered filtrate then enters a high-pressure filter press, with the filter cloth pore size limited to 5μm~20μm. Fatty acid crystals have low interfacial energy and tend to deform under pressure; if the pore size is too large (>20μm), fine crystals (<20μm) will penetrate the filter cloth and enter the filtrate, leading to increased turbidity and decreased product purity; if the pore size is too small (<5μm), the fluid resistance is extremely high, the filtration rate is extremely slow, and it is very easy to clog.

[0062] The filter cloth material can be polypropylene (PP) or polyester (PET). Both materials are resistant to fatty acid corrosion, have a smooth surface, and are easy to peel off during cake removal, with good regenerability.

[0063] Feeding stage of a high-pressure filter press: Start the feed pump to inject material into the filter chamber of the filter press. Initially, use low-pressure feeding. After the filter chamber is full and an initial filter cake layer is formed, gradually increase the pressure.

[0064] The pressurization stage of the high-pressure filter press: the pressure is increased to 6 bar to 10 bar. The ultimate vacuum of traditional vacuum filtration is only about 0.09 bar absolute pressure, and the driving force is extremely small. However, the pressure of 6 bar to 10 bar in this step provides nearly 100 times the driving force of vacuum filtration.

[0065] Under high pressure, the filter cake is mechanically compressed, reducing its porosity. For filter cakes containing fatty acids, which have a certain degree of compressibility, high pressure can expel the oleic acid-rich mother liquor trapped between the crystals. The thorough expulsion of the mother liquor means a reduction in the residual oleic acid content in the filter cake, thereby increasing the oleic acid yield. Simultaneously, the filter cake becomes denser, with a significantly reduced liquid content, reducing the drying load for subsequent by-product processing.

[0066] Under a pressure of 6-10 bar, the filtrate flows out through the filter cloth, becoming the oleic acid product. The solid filter cake left in the filter chamber has a high stearic acid content and extremely low impurity content.

[0067] Throughout the solid-liquid separation process, the ambient temperature must be strictly controlled. Since the melting point of fatty acid crystals is typically between 40℃ and 60℃, excessively high ambient temperatures can lead to localized overheating, causing micro-melting of the crystal surface, resulting in stickiness and clogging of the filter cloth. Therefore, an insulation jacket can be installed outside the filter press, or the workshop can be maintained at a low temperature of 10℃-20℃.

[0068] Meanwhile, the DCS system monitors the feed pressure of the filter press. When the pressure rises abnormally and exceeds the set threshold, the system determines that the filter cloth is clogged and automatically triggers the pulse backflushing program or suspends the feed to regenerate and clean the filter cloth, ensuring production continuity.

[0069] S4: The filter cake obtained in step S3 is subjected to solvent extraction purification and catalytic hydrogenation modification in sequence to obtain cosmetic grade stearic acid.

[0070] Step S4 is the fourth step in the high-value utilization of by-products. In traditional fatty acid separation processes, the by-product filter cake is often sold as a low-value by-product, or even treated as fuel, which not only has low added value but also results in resource waste.

[0071] This embodiment uses solvent extraction purification and catalytic hydrogenation modification techniques to convert filter cake into high-value-added cosmetic-grade stearic acid.

[0072] In this embodiment, a mixed solvent of n-hexane and ethanol is used, and the volume ratio is strictly controlled to be (2~4):1. This ratio is designed based on the difference in solubility of stearic acid and oleic acid in different solvents.

[0073] As a non-polar solvent, n-hexane has excellent solubility for fatty acids, enabling it to dissolve solid fatty acids in the filter cake, achieving solid-liquid separation and removing insoluble impurities. As a polar solvent, the addition of ethanol reduces the polarity of the solvent system, making its solubility more sensitive to temperature changes; more importantly, ethanol effectively removes residual pigments, oxidation products, and odor substances from the filter cake. While n-hexane alone has limited impurity removal capabilities, and ethanol alone has low solubility for fatty acids, this mixed solvent system achieves the dual effect of solubilizing the main component and removing impurities.

[0074] The solvent extraction and purification process is carried out at a temperature of 40℃ to 70℃ for 1 to 3 hours. If the temperature is too low, the dissolution rate is slow, requiring a large amount of solvent; if the temperature is too high, solvent evaporation loss is significant, and there are safety hazards. Within the 40℃ to 70℃ range, a good balance is achieved between the dissolution rate and solvent recovery efficiency. The extraction time is controlled within 1 to 3 hours to ensure that the solvent fully penetrates into the filter cake.

[0075] After three stages of countercurrent extraction, the stearic acid in the filter cake is dissolved into the solvent phase, while insoluble impurities are separated and removed. After solvent evaporation and recovery, crude stearic acid is obtained, with its purity further improved.

[0076] Even after extraction and purification, crude stearic acid still contains a small amount of unsaturated fatty acids, such as residual oleic acid. These components can lead to a high iodine value, a yellowish color, and poor stability in the product, which does not meet the standards for cosmetic raw materials. Therefore, catalytic hydrogenation modification is necessary.

[0077] In the catalytic hydrogenation modification process, a nickel-based catalyst was used as the active component, and the hydrogenation reaction was carried out at 150℃~200℃ and 1.5MPa~3.0MPa for 2h~5h.

[0078] Nickel-based catalysts are selected, as nickel catalysts are the most mature and cost-effective catalysts in the oil and fat hydrogenation industry, and their dosage is controlled at 1%~3%. The reaction temperature is 150℃~200℃. Hydrogenation is an exothermic reaction, but it requires a certain activation energy. Within this temperature range, the reaction rate is moderate, and the cracking or isomerization of the stearic acid produced in the reaction can be effectively avoided. The reaction pressure is 1.5MPa~3.0MPa. Higher hydrogen pressure helps hydrogen dissolve and diffuse in the liquid phase, overcomes gas-liquid mass transfer resistance, and ensures complete reaction. The reaction time is 2h~5h to ensure that the iodine value drops below the standard.

[0079] Under high temperature, high pressure, and with the aid of a catalyst, the carbon-carbon double bonds (C=C) in crude stearic acid are saturated with hydrogen and converted into single bonds. As the double bonds are saturated, the iodine value of the product decreases significantly, its antioxidant capacity is greatly enhanced, and its shelf life is extended. The hydrogenation process also destroys some chromophores, resulting in a lighter product color, achieving the snow-white appearance required for cosmetic products. The final product can achieve a stearic acid content of 95% or higher.

[0080] To further verify the effectiveness of the technical solution of this application, a detailed description is provided below with reference to specific embodiments and comparative examples.

[0081] Example 1 A fatty acid separation process, the specific steps of which are as follows: (1) Raw material pretreatment: Take 1000 kg of C16 / C18 mixed fatty acid raw material (oleic acid content 65%, acid value 198 mgKOH / g). Pre-cool it to 55℃ using the low-temperature filtrate from the subsequent process through a plate heat exchanger. Then filter it through a sintered metal filter element with a precision of 50μm to remove mechanical impurities.

[0082] (2) Freeze-crystallization: The pretreated material is put into a crystallization tank with a jacket and a stirring system.

[0083] Rapid cooling stage: Start stirring (25 r / min), introduce -15℃ frozen brine, and reduce the material temperature from 65℃ to 10℃ at a rate of 2.0℃ / h.

[0084] Gradient temperature control stage: Adjust the stirring speed to 15 r / min. Starting from 10℃, set a constant temperature range every 2℃ (i.e., 10℃, 8℃, 6℃, 4℃, 2℃), and maintain each constant temperature range for 8 hours. The cooling rate is controlled at 0.3℃ / h.

[0085] Crystallization stage: When the temperature drops to 1℃, stop cooling and keep it at a constant temperature for 12 hours, and reduce the stirring speed to 10r / min.

[0086] (3) Solid-liquid separation: The slurry was conveyed to a pre-filter (100 μm pore size) using a screw extrusion pump (40 r / min) to remove large particles under a pressure of 1.5 bar.

[0087] The pre-filtered filtrate enters a fully automatic diaphragm filter press. A 10μm pore size polypropylene filter cloth is used, and filtration is performed at 8 bar. Filtration continues until no more filtrate flows out.

[0088] (4) Utilization of by-products: Collect the filter cake (stearic acid content approximately 76%) inside the filter press.

[0089] Add a hexane-ethanol mixed solvent (volume ratio 3:1) and extract with stirring at 60°C for 2 hours. Separate the solvent to obtain crude stearic acid.

[0090] Crude stearic acid was added to a high-pressure reactor, along with 2% nickel catalyst, and hydrogenated at 180°C and 2.5 MPa for 3 hours. The final product was obtained after catalyst removal.

[0091] Comparative Example 1 The traditional single-stage freeze crystallization process is used, with only one cooling endpoint set, as follows: (1) The raw material pretreatment is the same as in Example 1.

[0092] (2) Freeze-crystallization: The raw material is directly cooled from 65℃ to 5℃ at a rate of 1.0℃ / h, without setting a constant temperature section in the middle. After the cooling is completed, the crystal is grown at a constant temperature for 8 hours.

[0093] (3) Solid-liquid separation: The slurry is directly separated by a centrifuge (3000 r / min).

[0094] (4) By-product treatment: Same as in Example 1.

[0095] Comparative analysis of the results of Example 1 and Comparative Example 1: 1. Observation of crystal morphology: Example 1: Microscopic observation shows that the crystals are regular plate-shaped or needle-shaped with uniform particle size distribution and an average particle size of about 120 μm.

[0096] Comparative Example 1: The crystals are irregular in shape, contain a large number of fine fragments, with an average particle size of only about 30 μm, and exhibit obvious agglomeration.

[0097] 2. Separation efficiency: Example 1: The filter press has smooth feeding, a single batch filtration cycle of 4 hours, smooth filter cake discharge, and the filter cloth does not need to be cleaned frequently.

[0098] Comparative Example 1: The centrifuge vibrated significantly during operation, resulting in a high moisture content (approximately 35%) in the separated solid phase. Furthermore, the filtrate was turbid due to the penetration of fine crystals through the filter screen.

[0099] 3. Product quality and yield: Example 1: The filtrate had an oleic acid purity of 92.5% and a freezing point of -2°C. After modification, the filter cake had a stearic acid purity of 96.5% and an iodine value of 0.5. The total oleic acid yield reached 87%.

[0100] Comparative Example 1: The oleic acid purity of the filtrate was only 83.0%, and the freezing point was 8℃. Due to the penetration of fine crystals, the oleic acid yield was only 72%.

[0101] 4. Energy Consumption Analysis: Example 1: The unit product comprehensive energy consumption (including cold energy recovery) is 48kWh / ton.

[0102] Comparative Example 1: The comprehensive energy consumption per unit product is 75 kWh / ton.

[0103] Data from Example 1 shows that this example, through the combination of segmented crystallization and two-stage pressure filtration, significantly improved the crystal morphology, enhanced the separation efficiency, obtained a high-purity oleic acid product with a low freezing point, and greatly reduced energy consumption.

[0104] Example 2 This embodiment focuses on the effect of solvent ratio on purification effect in the step of high-value utilization of by-products.

[0105] With other process parameters kept the same as in Example 1, only the volume ratio of hexane to ethanol in the extraction solvent was changed, and the results are as follows:

[0106] analyze: When the ethanol ratio is too high (1:1), the solvent polarity is too strong. Although it is beneficial for removing polar impurities, it reduces the solubility of stearic acid, resulting in low extraction efficiency and limited improvement in purity.

[0107] When the ratio of n-hexane is too high (6:1), the solvent polarity is too weak, the solubility of impurities increases, and the impurities cannot be effectively removed, resulting in unsatisfactory color and iodine value.

[0108] Within a volume ratio range of (2~4):1 (test groups B, C, and D), the product purity, color, and iodine value all reached optimal levels, verifying the rationality of the solvent ratio in the claims.

[0109] Example 3 This embodiment examines the application effect of the DCS automation control system.

[0110] Based on Example 1, a DCS system was introduced for full closed-loop control. System parameters were set as follows: crystallization temperature deviation ≤ ±0.2℃, stirring speed deviation ≤ ±1r / min.

[0111] Comparison with manual control mode: Manual control: Temperature fluctuations are within ±1.5℃, often resulting in overshooting during cooling, leading to localized undercooling and the formation of fine grains.

[0112] DCS control: The temperature curve is smooth and strictly follows the preset gradient. The batch-to-batch product quality consistency has been reduced from ±2% purity fluctuation controlled manually to ±0.5%.

[0113] Unlike existing technologies, this application discloses a fatty acid separation process. The embodiments of this application utilize a segmented crystallization strategy of rapid cooling, gradient temperature control, and crystal growth. The rate control, initially fast and then slow, effectively balances crystal nucleation and crystal growth, resulting in large and well-formed crystals. This significantly improves solid-liquid separation performance and greatly increases oleic acid yield. Through cold energy recovery and optimized process parameters, energy consumption per unit product is significantly reduced. Furthermore, it innovatively integrates a high-value utilization technology for by-products, converting low-value stearic acid filter cake into cosmetic-grade raw materials, achieving full resource utilization. This process eliminates the need for expensive molecular distillation equipment, is simple in process, easy to industrialize, and significantly improves the economic benefits for enterprises.

[0114] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A fatty acid separation process, characterized in that, include: S1: Pre-cool and filter the C16 / C18 mixed fatty acid raw material to remove impurities; S2: The pretreated material is subjected to rapid cooling crystallization, gradient temperature-controlled crystallization, and crystal growth treatment in sequence; S3: The crystallized material is subjected to pre-filtration and high-pressure filtration in sequence to obtain filtrate containing oleic acid and filter cake containing stearic acid, respectively.

2. The fatty acid separation process according to claim 1, characterized in that, In step S2, the rapid cooling crystallization includes: The material temperature is reduced to 8℃~12℃, and the cooling rate is controlled at 1.5℃ / h~3.0℃ / h; The gradient temperature-controlled crystallization includes: reducing the material temperature from 8℃~12℃ to 0℃~3℃; The crystal growth process includes maintaining the material at a constant temperature within the range of 0℃ to 3℃.

3. The fatty acid separation process according to claim 2, characterized in that, During the gradient temperature-controlled crystallization stage, a segmented temperature control method is adopted, with a constant temperature segment set at intervals of 1.5℃ to 2.5℃, and the residence time of each constant temperature segment is 6h to 10h. During the gradient temperature-controlled crystallization stage, the cooling rate is controlled at 0.1℃ / h to 1.0℃ / h.

4. The fatty acid separation process according to claim 2, characterized in that, During the gradient temperature-controlled crystallization and crystal growth stages, the stirring rate is controlled at 5 r / min to 30 r / min; in step S2, chilled water at -20℃ to -10℃ is used as the refrigerant for indirect heat exchange.

5. The fatty acid separation process according to claim 2, characterized in that, During the crystal growth stage, the constant temperature and static time is 8h~15h to control the crystal particle size to grow to more than 50μm.

6. The fatty acid separation process according to claim 1, characterized in that, In step S1, the precooling process utilizes the cooling energy of the low-temperature material after crystallization in step S3 for heat exchange; the filtration and impurity removal uses an online filter with an accuracy of 30μm~60μm to remove mechanical impurities.

7. The fatty acid separation process according to claim 1, characterized in that, In step S3, the specific process of pre-filtration is as follows: the crystallized material is transported to the pre-filter by a screw extrusion pump, and crystals with a particle size ≥80μm are removed under a pressure of 1.0bar~2.0bar. The specific process of high-pressure filtration is as follows: the pre-filtered filtrate is sent into a high-pressure filter press and precision filtered through a filter cloth with a pore size of 5μm to 20μm under a pressure of 6bar to 10bar.

8. The fatty acid separation process according to claim 1, characterized in that, It also includes S4: the filter cake obtained in step S3 is subjected to solvent extraction purification and catalytic hydrogenation modification in sequence to obtain cosmetic grade stearic acid.

9. The fatty acid separation process according to claim 8, characterized in that, In the solvent extraction and purification process, a mixed solvent of n-hexane and ethanol is used as the extractant, wherein the volume ratio of n-hexane to ethanol is (2~4):1; The solvent extraction and purification process is carried out at a temperature of 40℃ to 70℃ for 1 hour to 3 hours.

10. The fatty acid separation process according to claim 8, characterized in that, In the catalytic hydrogenation modification process, a nickel-based catalyst is used as the active component, and the hydrogenation reaction is carried out at 150℃~200℃ and 1.5MPa~3.0MPa for 2h~5h.

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