A mixed refrigerant and a method of making the same

Abstract

This invention relates to the field of refrigerants, specifically to a mixed refrigerant and its preparation method. By weight, the refrigerant comprises 85-95 parts of a basic refrigerant, 1-5 parts of a flame retardant, 1-10 parts of a lubricating oil, and 0.1-0.5 parts of a stabilizer. The basic refrigerant is a mixture of R32, R1234ze(E), and R1234yf in a mass ratio of (18-28):(45-60):(15-25). The stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite, and methylbenzotriazole in a mass ratio of (0.1-0.15):(0.1-0.15):(0.15-0.2). This refrigerant has a low GWP, good flame retardant properties, and good stability.

Description

Technical Field

[0001] This invention relates to the field of refrigerants, and more specifically, to a mixed refrigerant and its preparation method. Background Technology

[0002] With the deepening implementation of the Kigali Amendments, the global refrigeration and air conditioning industry is accelerating the phasing out of refrigerants with high global warming potential. Low-GWP (GWP<150) refrigerants, represented by R32, R1234yf, R290 and their mixtures, have become the mainstream choice for next-generation refrigerants. However, most of these refrigerants have varying degrees of flammability (A2L or A3 class).

[0003] There are two main technical approaches to reduce the flammability of flammable refrigerants: one is to adjust the flammability by mixing different refrigerants, and the other is to add flame retardants to the refrigerant.

[0004] Patent CN120775558A discloses a mixed working fluid composed of HFO-1132(E), HFO-1234yf, and HFE-143a, intended to replace flammable R290. While this method improves the safety level to A2L, it still relies on the intrinsic flammability of gaseous molecules, and its flame-retardant effect has physical limits. Furthermore, it cannot solve the corrosion protection problem of internal metal materials under long-term high temperature and pressure, and corrosion products may further catalyze the decomposition of the working fluid, creating new safety hazards.

[0005] Adding high-GWP flame-retardant working fluids: For example, blending non-flammable but extremely high-GWP R125 or R227ea into flammable working fluids can reduce the flammability of the refrigerant. While this method effectively suppresses flame, it significantly increases the overall GWP value of the mixture. Patent CN121108945A proposes dispersing solid flame retardants such as hexaphenoxycyclotriphosphazene into the refrigerant using high-pressure microfluidic technology after nano-sizing. This method can improve flame retardancy in the short term, but it has fundamental drawbacks: First, nanoparticles are prone to agglomeration and sedimentation under long-term static or cyclic shearing, leading to uneven distribution of the flame retardant, performance degradation, and potential clogging of throttling components or accelerated wear; second, the flame retardant in this scheme is only physically dispersed, with no interaction between the flame retardant and the system's metal surface, failing to provide corrosion protection, and the behavior of the particles at the high-temperature and high-pressure interface is uncontrollable.

[0006] Liquid flame retardants such as phosphate esters, like tri(2-chloroethyl) phosphate, are used. While this solves the phase homogeneity problem, these flame retardants (especially halogenated ones) have poor chemical stability in the humid and hot environment of refrigeration systems, easily hydrolyzing to produce acidic substances that severely corrode key components such as copper pipes and compressor bearings. Secondly, these flame retardants have poor long-term compatibility with refrigerants and lubricating oils, which may lead to phase separation or swelling and aging of sealing materials. Thirdly, the thermal decomposition temperature of these flame retardants may overlap with the compressor discharge temperature, creating a risk of failure.

[0007] In summary, current technologies for the safety of low-GWP flammable refrigerants all have significant shortcomings: they either sacrifice environmental friendliness or long-term stability and reliability. There is an urgent need for a method that can not only efficiently and persistently suppress the flammability of refrigerants without significantly increasing GWP, but also actively enhance the material stability of the refrigeration system itself, thereby fundamentally achieving a balance between safety and environmental protection, performance and reliability. Summary of the Invention

[0008] The purpose of this invention is to provide a mixed refrigerant with low GWP, good flame retardant properties, and good stability.

[0009] Another objective of this invention is to provide a method for preparing a mixed refrigerant, in which the stabilizer is pre-protected and pre-coupled before the flame retardant comes into contact with the base working fluid by adding the components of the stabilizer sequentially; the refrigerants are mixed at gradient temperatures, following the physical properties of each component (boiling point, viscosity, miscibility), thus avoiding phase separation, volatilization loss and ratio imbalance.

[0010] The technical problem solved by this invention is achieved by the following technical solution.

[0011] On one hand, embodiments of the present invention provide a mixed refrigerant, comprising the following raw materials by weight: 85-95 parts of basic refrigerant, 1-5 parts of flame retardant, 1-10 parts of lubricating oil, and 0.1-0.5 parts of stabilizer; The basic refrigerant is a mixture of R32, R1234ze(E) and R1234yf, with a mass ratio of (18-28):(45-60):(15-25); The stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite and methylbenzotriazole in a mass ratio of (0.1-0.15):(0.1-0.15):(0.15-0.2).

[0012] In some embodiments of the present invention, the basic refrigerant is a mixture of R32, R1234ze(E) and R1234yf in a mass ratio of 20:50:20.

[0013] In some embodiments of the present invention, the stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite and methylbenzotriazole in a mass ratio of 0.1:0.15:0.2.

[0014] In some embodiments of the present invention, the flame retardant is prepared by the following steps: Step A, Synthesis of cage-like phosphate intermediate: Add pentaerythritol and acetonitrile to a container, and maintain the system temperature at 0-5℃ under ice-water bath and nitrogen protection; add phosphorus oxychloride dropwise to the container, and after the addition is complete, raise the temperature to 80-85℃ and reflux for 6-8 hours. Cool the reaction solution to room temperature, remove the solvent acetonitrile and excess phosphorus oxychloride by vacuum distillation, and wash and dry the product to obtain a cage-like phosphate intermediate. Step B, synthesis of hydroxyl-functionalized intermediates: Add the cage-like phosphate intermediate obtained in step A, the catalyst p-toluenesulfonic acid, the polymerization inhibitor hydroquinone, and anhydrous 1,4-dioxane to a container; under nitrogen protection, stir and heat to 90-95℃; add hydroxyethyl acrylate dropwise, maintaining the reaction temperature at 90-95℃, and continue the reaction for 5-7 hours after the addition is complete. Cool the reaction solution, filter it, and first evaporate the filtrate under reduced pressure, then add cold diethyl ether to precipitate, obtaining a white viscous substance. Filter and wash the precipitate to obtain the hydroxyl-functionalized intermediate. Step C, Flame retardant synthesis: The hydroxyl-functionalized intermediate obtained in step B was dissolved in anhydrous tetrahydrofuran, and then dibutyltin dilaurate was added. Under ice bath cooling and nitrogen protection, the temperature was maintained at 0-5℃. 3-isocyanate-propyltrimethoxysilane was added dropwise, and the reaction was carried out at 0-5℃ for 2-3 hours. The reaction solution was then slowly heated to room temperature and stirred for another 2 hours. The solution was filtered, and the filtrate was distilled under reduced pressure to obtain a viscous liquid, which is the flame retardant.

[0015] In some embodiments of the present invention, in step A, the mass-to-volume ratio of pentaerythritol to acetonitrile is 1 g: 5 mL; the molar ratio of pentaerythritol to phosphorus oxychloride is 1: 1.05-1.10. In some embodiments of the present invention, in step B, the amount of p-toluenesulfonic acid catalyst is 1.0% of the mass of the cage-like phosphate intermediate; the amount of hydroquinone inhibitor is 0.5% of the mass of the cage-like phosphate intermediate; the mass-volume ratio of the cage-like phosphate intermediate to the solvent is 1 g: 8 mL; and the molar ratio of the cage-like phosphate intermediate to hydroxyethyl acrylate is 1:1.05.

[0016] In some embodiments of the present invention, in step C, the mass-to-volume ratio of the hydroxyl functionalized intermediate to anhydrous tetrahydrofuran is 1 g:10 mL; the molar ratio of the hydroxyl functionalized intermediate to silane is 1:(1-1.02).

[0017] In some embodiments of the present invention, the lubricating oil is POE lubricating oil.

[0018] On the other hand, embodiments of the present invention provide a method for preparing a mixed refrigerant, comprising the following steps: S1: Add lubricating oil to the reactor. Under stirring conditions at 40-45℃, add methylbenzotriazole, then add triphenyl phosphite and stir for 30-40 minutes. Cool down to 20-25℃ and add flame retardant dropwise to the reactor. After the addition is complete, continue stirring for 2-4 hours. Under stirring and nitrogen protection, add triethyl orthoformate dropwise. After the addition is complete, continue stirring for 1-1.5 hours to obtain the mother liquor. S2: At -10℃, add R1234ze(E) to the reactor, and under stirring conditions, add the mother liquor obtained in step S1 and stir for 1-1.5h; then add R1234yf and stir for 1-2h. S3: Add R32 at -25℃ to -30℃ and under stirring conditions. After stirring evenly, raise the temperature to 0℃ and maintain the pressure at 2.0–2.5 MPa. Circulate and homogenize for 4–6 hours. S4: Heat to 10-15℃ and fill into steel cylinders to obtain the mixed refrigerant.

[0019] In some embodiments of the present invention, step S1 further includes using a high-pressure micro-jet homogenizer to homogenize and circulate the mother liquor under room temperature and nitrogen pressure conditions, with the homogenization times being 3-5 times and the homogenization working pressure being 80-150 MPa.

[0020] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects: The mixed refrigerant provided in this embodiment of the invention uses a ternary mixture of R32, R1234ze(E), and R1234yf as the basic refrigerant. While ensuring refrigeration performance, the theoretical GWP value is controlled at a critical level close to 150. The non-flammability of R1234ze(E) is used to reduce the overall flammability of the mixed refrigerant, making the mixed refrigerant safer.

[0021] The refrigerant preparation method provided by this invention involves mixing a stabilizer with a refrigerant, and then mixing the refrigerant to achieve the effects of first passivating the metal, then flame retardant, and finally dehydration protection. Furthermore, the refrigerant is added in a gradient mixing manner according to its boiling point and polarity to ensure the activity of the functional molecules and the uniformity and stability of the final system. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to specific embodiments.

[0024] This invention provides a mixed refrigerant, comprising the following raw materials by weight: 85-95 parts of basic refrigerant, 1-5 parts of flame retardant, 1-10 parts of lubricating oil, and 0.1-0.5 parts of stabilizer; the basic refrigerant is a mixture of R32, R1234ze(E), and R1234yf, with a mass ratio of (18-28):(45-60):(15-25); the stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite, and methylbenzotriazole, with a mass ratio of (0.1-0.15):(0.1-0.15):(0.15-0.2).

[0025] Preferably, the basic refrigerant is a mixture of R32, R1234ze(E), and R1234yf in a mass ratio of 20:50:20. The stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite, and methylbenzotriazole in a mass ratio of 0.1:0.15:0.2.

[0026] The refrigerant provided in this embodiment of the invention includes R32 (difluoromethane): as the core of the formulation. It has excellent volumetric refrigeration capacity and a high coefficient of performance (COP), which can significantly improve the refrigeration capacity and energy efficiency of the entire mixture. However, its flammability (A2L level) is a major safety hazard and needs to be suppressed by other components. R1234ze(E): trans-1,3,3,3-tetrafluoropropylene, CAS No. 29118-24-9; R1234yf: 2,3,3,3-tetrafluoropropylene, CAS No. 754-12-1; both are fourth-generation environmentally friendly hydrofluoroolefins (HFOs), and both are non-flammable or weakly flammable refrigerants (A2L / A1), which can effectively dilute the flammable R32 and suppress the overall flammability of the mixture to a non-flammable (A1) or extremely difficult-to-burn (A2L) level through physical action. On the other hand, both have extremely low global warming potential (GWP<1), and when combined with R32 (GWP~675), they can significantly reduce the overall GWP of the mixed refrigerant, meeting environmental protection requirements. Thirdly, both complement R32 in terms of boiling point and vapor pressure, jointly optimizing key cycle parameters such as temperature glide and pressure ratio of the mixture, making it more compatible with existing equipment and compressors.

[0027] In some embodiments of the present invention, the flame retardant is prepared by the following steps: Step A, Synthesis of cage-like phosphate intermediate: Add pentaerythritol and acetonitrile to a container, and maintain the system temperature at 0-5℃ under ice-water bath and nitrogen protection; add phosphorus oxychloride dropwise to the container, and after the addition is complete, raise the temperature to 80-85℃ and reflux for 6-8 hours. Cool the reaction solution to room temperature, remove the solvent acetonitrile and excess phosphorus oxychloride by vacuum distillation, and wash and dry the product to obtain a cage-like phosphate intermediate. Step B, synthesis of hydroxyl-functionalized intermediates: Add the cage-like phosphate intermediate obtained in step A, the catalyst p-toluenesulfonic acid, the polymerization inhibitor hydroquinone, and anhydrous 1,4-dioxane to a container; under nitrogen protection, stir and heat to 90-95℃; add hydroxyethyl acrylate dropwise, maintaining the reaction temperature at 90-95℃, and continue the reaction for 5-7 hours after the addition is complete. Cool the reaction solution, filter it, and first evaporate the filtrate under reduced pressure, then add cold diethyl ether to precipitate, obtaining a white viscous substance. Filter and wash the precipitate to obtain the hydroxyl-functionalized intermediate. Step C, Flame retardant synthesis: The hydroxyl-functionalized intermediate obtained in step B was dissolved in anhydrous tetrahydrofuran, and then dibutyltin dilaurate was added. Under ice bath cooling and nitrogen protection, the temperature was maintained at 0-5℃. 3-isocyanate-propyltrimethoxysilane was added dropwise, and the reaction was carried out at 0-5℃ for 2-3 hours. The reaction solution was then slowly heated to room temperature and stirred for another 2 hours. The solution was filtered, and the filtrate was distilled under reduced pressure to obtain a viscous liquid, which is the flame retardant.

[0028] Preferably, in step A, the mass-to-volume ratio of pentaerythritol to acetonitrile is 1 g: 5 mL; and the molar ratio of pentaerythritol to phosphorus oxychloride is 1: 1.05-1.10. Preferably, in step B, the amount of p-toluenesulfonic acid catalyst is 1.0% of the mass of the cage-like phosphate intermediate; the amount of hydroquinone inhibitor is 0.5% of the mass of the cage-like phosphate intermediate; the mass-volume ratio of the cage-like phosphate intermediate to the solvent is 1 g: 8 mL; and the molar ratio of the cage-like phosphate intermediate to hydroxyethyl acrylate is 1:1.05.

[0029] More preferably, in step C, the mass-to-volume ratio of the hydroxyl functionalized intermediate to anhydrous tetrahydrofuran is 1 g:10 mL; and the molar ratio of the hydroxyl functionalized intermediate to silane is 1:(1-1.02).

[0030] The flame retardant provided in this invention comprises a pentaerythritol spirocyclic phosphate structure (cage-like framework) formed by the reaction of pentaerythritol and phosphorus oxychloride. This structure exhibits high thermal stability, high phosphorus content, and a highly efficient gas-phase-condensed-phase synergistic flame retardant mechanism. Further reaction with hydroxyethyl acrylate introduces terminal hydroxyl groups. This not only extends the molecular chain and increases compatibility with lubricating oils but also provides reaction sites for the next step. Subsequent reaction with 3-isocyanatopropyltrimethoxysilane connects the trimethoxysilyl group to the molecular end, achieving chemical bonding and long-lasting performance.

[0031] This flame retardant has a synergistic effect in mixed refrigerants: It exhibits a synergistic effect of high efficiency and long-lasting flame retardancy, working in conjunction with the physical dilution of R1234ze(E) and R1234yf to provide flame retardant effects for mixed refrigerants. Upon thermal decomposition, it releases phosphorus-containing free radicals (PO·), which efficiently capture H· and OH· free radicals in the combustion chain reaction, chemically interrupting combustion. Its cage-like structure and the introduced silicon element promote the formation of a dense, heat-insulating, and oxygen-barrier carbon-silicon composite protective layer on the surface of materials (such as insulating materials and lubricating oil degradation products). The terminal trimethoxysilyl groups can react with metal hydroxyl groups or silanol groups generated after the hydrolysis of trace amounts of water in the system (especially on the metal surfaces of compressors and heat exchangers) to form Si-OM covalent bonds, anchoring the flame retardant molecules at the interface. This avoids the problem of uneven distribution or gradual loss of small molecule flame retardants during the refrigeration cycle due to migration with the working fluid, achieving long-lasting, locally high-concentration flame retardant protection.

[0032] On the other hand, this flame retardant can synergize deeply with the stabilizer system. Methylbenzotriazole passivates the metal through adsorption, while the flame retardant covers the metal through chemical bonding. Together, they form a composite protective film on the metal surface, synergistically inhibiting the catalytic effect of metal ions on the decomposition of refrigerant / lubricating oil. The stable cage-like structure and bonded fixation of the flame retardant itself reduce the risk of system instability caused by flame retardant decomposition, and together with the stabilizer, maintain the internal chemical balance of the system.

[0033] Thirdly, it also exhibits good compatibility with lubricating oils. Through the introduction of alkyl segments (derived from hydroxyethyl acrylate), this flame retardant has good compatibility with POE lubricating oils.

[0034] Preferably, the lubricating oil is POE lubricating oil.

[0035] On the other hand, embodiments of the present invention provide a method for preparing a mixed refrigerant, comprising the following steps: S1: Add lubricating oil to the reactor. Under stirring conditions at 40-45℃, add methylbenzotriazole, then add triphenyl phosphite and stir for 30-40 minutes. Cool down to 20-25℃ and add flame retardant dropwise to the reactor. After the addition is complete, continue stirring for 2-4 hours. Under stirring and nitrogen protection, add triethyl orthoformate dropwise. After the addition is complete, continue stirring for 1-1.5 hours to obtain the mother liquor. S2: At -10℃, add R1234ze(E) to the reactor, and under stirring conditions, add the mother liquor obtained in step S1 and stir for 1-1.5h; then add R1234yf and stir for 1-2h. S3: Add R32 at -25℃ to -30℃ and under stirring conditions. After stirring evenly, raise the temperature to 0℃ and maintain the pressure at 2.0–2.5 MPa. Circulate and homogenize for 4–6 hours. S4: Heat to 10-15℃ and fill into steel cylinders to obtain the mixed refrigerant.

[0036] In some embodiments of the present invention, step S1 further includes using a high-pressure micro-jet homogenizer to homogenize and circulate the mother liquor under room temperature and nitrogen pressure conditions, with the homogenization times being 3-5 times and the homogenization working pressure being 80-150 MPa.

[0037] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0038] Example 1 Prepare the flame retardant using the following steps: Step A: Synthesis of cage-like phosphate intermediate (PEPA) In a dry three-necked flask equipped with a stirrer, thermometer, reflux condenser (connected to a tail gas absorption device to absorb HCl), and constant-pressure dropping funnel, pentaerythritol and acetonitrile were added as solvents, with a mass-to-volume ratio of pentaerythritol to acetonitrile of 1 g: 5 mL. The system temperature was maintained at 0–5 °C under ice-water bath cooling and nitrogen protection. Phosphorus oxychloride was slowly added dropwise through the constant-pressure dropping funnel, with a molar ratio of pentaerythritol to phosphorus oxychloride of 1:1.05–1.10. The dropping rate was controlled to keep the reaction temperature below 10 °C. After the addition was complete, the ice bath was removed, and the temperature was slowly raised to 80–85 °C, and the reaction was refluxed for 6–8 hours. Nitrogen gas was continuously introduced during the reaction to purge the generated hydrogen chloride gas. After the reaction was complete, the reaction solution was cooled to room temperature, and the solvent acetonitrile and excess phosphorus oxychloride were removed by vacuum distillation to obtain a white solid crude product. The solid was washed three times with hot deionized water (60-70℃) to remove residual acid and ionic impurities, and then dried in a vacuum drying oven at 100℃ for 12 hours to obtain high-purity white powdered PEPA with a yield ≥92%. The reaction progress of this step can be tracked by monitoring the pH value of the reaction system or by using thin-layer chromatography (TLC).

[0039] Step B: Synthesis of the hydroxyl functionalized intermediate (HPEPA) In a dry three-necked flask, add the PEPA prepared in step A, the catalyst p-toluenesulfonic acid (1.0% of the PEPA mass), and the polymerization inhibitor hydroquinone (0.5% of the PEPA mass), along with anhydrous 1,4-dioxane as a solvent (PEPA to solvent mass-volume ratio of 1 g:8 mL). Under nitrogen protection, stir and heat to 90°C to partially dissolve the PEPA. Then, slowly add hydroxyethyl acrylate dropwise through a constant-pressure dropping funnel, with a PEPA to hydroxyethyl acrylate molar ratio of 1:1.05. Control the dropping rate and maintain the reaction temperature at 90-95°C. After the addition is complete, continue the reaction at this temperature for 5-7 hours. After the reaction is complete, cool the reaction solution and filter to remove the catalyst. The filtrate is first subjected to rotary evaporation under reduced pressure to remove most of the solvent, then cold diethyl ether is added to precipitate, yielding a white viscous substance. Filter and wash the precipitate twice with diethyl ether to obtain the hydroxyl-functionalized intermediate (HPEPA).

[0040] Step C: Synthesis of flame retardant (Si-PEPA) The procedure was carried out in an absolutely anhydrous and oxygen-free glove box. The HPEPA obtained in step B was dissolved in anhydrous tetrahydrofuran (mass-volume ratio 1 g: 10 mL). A catalytic amount of dibutyltin dilaurate (0.3% of the HPEPA mass) was added. The system temperature was maintained at 0–5 °C under ice bath cooling and nitrogen protection. 3-Isocyanopropyltrimethoxysilane was slowly added dropwise using a syringe, with a molar ratio of HPEPA to silane of 1:1.02. Close observation was maintained during the addition process, and the characteristic peak of -NCO (~2270 cm⁻¹) was monitored online using a Fourier Transform Infrared Spectrometer (FTIR). - The disappearance of the -NCO peak (¹) is used to determine the reaction endpoint. Typically, after reacting at 0-5℃ for 2-3 hours, the -NCO peak essentially disappears. Then, the ice bath is removed, and the reaction solution is slowly heated to room temperature while stirring for another 2 hours to ensure complete reaction. After the reaction is complete, the reaction solution is passed through a short column packed with neutral alumina to remove the catalyst and possible byproducts. The filtrate is then thoroughly distilled under reduced pressure to remove the tetrahydrofuran solvent, yielding a pale yellow to colorless, transparent, viscous liquid, which is the target flame retardant synergist (Si-PEPA), with a yield of approximately 85-90%.

[0041] The mixed refrigerant of this embodiment was prepared based on the following formulation and steps: 90 parts basic refrigerant, 5 parts flame retardant, 4.5 parts lubricating oil, and 0.5 parts stabilizer; The basic refrigerant is a mixture of R32, R1234ze(E) and R1234yf in a mass ratio of 20:50:20; the stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite and methylbenzotriazole in a mass ratio of 0.1:0.15:0.15.

[0042] Preparation steps: S1: Preparation and pre-activation of functional additive mother liquor In a double-walled glass reactor equipped with magnetic stirring, a heating jacket, and gas inlet and outlet, high-purity nitrogen gas (dew point ≤ -70℃) that has been deeply dried by molecular sieves and an active copper bed is continuously introduced to replace the air for at least 30 minutes until the oxygen content sensor reading inside the reactor is <10 ppm.

[0043] Base fluid injection: Accurately meter and add the prescribed amount of POE lubricating oil into the reactor.

[0044] Maintain the vessel temperature at 40 ± 2℃, add methylbenzotriazole (TTZ) while stirring, and stir until completely dissolved.

[0045] Then add triphenyl phosphite and continue stirring for 30 minutes to ensure it is evenly mixed with the lubricating oil-TTZ system.

[0046] Reduce the reactor temperature to 25 ± 3℃ (to avoid premature reaction of silane groups due to high temperature). While stirring, slowly add the prescribed amount of flame retardant synergist (Si-PEPA). Control the dropping rate to ensure the system temperature fluctuation does not exceed ±2℃. After the addition is complete, continue gentle stirring at 25℃ for 2-4 hours. Under continuous stirring and nitrogen protection, add triethyl orthoformate via a syringe or micro-pump. After the addition is complete, continue stirring the entire system at 25℃ for 1 hour to allow the triethyl orthoformate to distribute evenly as a moisture remover. The resulting homogeneous and transparent mixture is the mother liquor. Use a high-pressure microjet homogenizer to homogenize and circulate the mother liquor at room temperature and nitrogen pressure, repeating the homogenization 3-5 times at a working pressure of 80-150 MPa. Transfer the homogenized mother liquor to a high-pressure material tank with desiccant protection for later use.

[0047] S2: Basic working fluid mixing and gradient dispersion Preparation of the main mixing vessel: A high-pressure mixing vessel made of 316L stainless steel is used, equipped with a turbine agitator, cooling coil, online NIR probe, and pressure sensor. High-purity nitrogen is used to purge the oxygen content to <10 ppm, and the back pressure is maintained at 0.5 MPa.

[0048] Introduce a high-boiling-point working fluid: Cool the mixing vessel to -10°C. First, pump in a precisely metered amount of R1234ze(E) (boiling point -19°C).

[0049] Initial mixing: Start stirring and slowly pump the mother liquor obtained from S1 into the mixing vessel at -10°C, mixing it with R1234ze(E). At this temperature, the viscosity of the lubricating oil is moderate, which is conducive to uniform dispersion. Maintain this condition and stir for 1 hour.

[0050] Introduce the medium-boiling working fluid: While maintaining stirring and low temperature, slowly pump in the metered R1234yf (boiling point -29℃). The pressure of the mixture will rise, and the system will automatically adjust. After pumping is complete, control the temperature at -15℃ and continue stirring for 1-2 hours to ensure the system reaches complete homogeneity.

[0051] S3: Low-temperature volume setting and final homogenization The material in the mixing vessel is further cooled to -25°C to -30°C via a coil to significantly reduce the saturated vapor pressure of R32.

[0052] R32 charging: At -25°C and with vigorous stirring, accurately and slowly charge the prescribed amount of R32 (boiling point -52°C) in liquid phase using a mass flow meter.

[0053] After R32 is fully charged, close all inlet and outlet valves. Start the built-in circulation pump of the mixing vessel to circulate the material intensively through the external static mixer. Gradually raise the system temperature to 0°C and maintain the pressure at 2.0-2.5 MPa. Under these conditions, perform circulating homogenization for 4-6 hours. Heating and pressurizing are crucial steps to ensure complete dissolution of R32 and prevent stratification.

[0054] S4: Online Quality Monitoring and Finished Product Filling Online monitoring: An online near-infrared spectrometer installed on the circulation pipeline continuously acquires spectral data. The system software analyzes the intensity of the characteristic absorption peaks of R32, R1234yf, and R1234ze(E) in real time. When the standard deviation of the measured concentration of each component is less than 0.3% within 10 consecutive minutes, and the deviation from the target formulation is less than ±0.5%, it is determined to be uniformly mixed.

[0055] After mixing evenly, adjust the material temperature to 10-15℃ and maintain pressure.

[0056] Filling: Under the condition of maintaining system back pressure, the finished refrigerant is filled into pre-vacuumed and dried special refrigerant cylinders through a mass metering filling system. The filling process is always under nitrogen protection.

[0057] Example 2 The difference from Example 1 is that the formulation of the mixed refrigerant is as follows: 85 parts basic refrigerant, 5 parts flame retardant, 10 parts lubricating oil, and 0.5 parts stabilizer; The basic refrigerant is a mixture of R32, R1234ze(E) and R1234yf in a mass ratio of 20:50:20; the stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite and methylbenzotriazole in a mass ratio of 0.1:0.15:0.15.

[0058] The preparation methods for the flame retardant and the mixture are the same as those in Example 1.

[0059] Example 3 The difference from Example 1 is that the formulation of the mixed refrigerant is as follows: 95 parts basic refrigerant, 1 part flame retardant, 1 part lubricating oil, and 0.1 parts stabilizer; The basic refrigerant is a mixture of R32, R1234ze(E) and R1234yf in a mass ratio of 20:50:20; the stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite and methylbenzotriazole in a mass ratio of 0.1:0.15:0.15.

[0060] The preparation methods for the flame retardant and the mixture are the same as those in Example 1.

[0061] Example 4 The difference from Example 1 is that the formulation of the mixed refrigerant is as follows: 90 parts basic refrigerant, 5 parts flame retardant, 4.5 parts lubricating oil, and 0.5 parts stabilizer; The basic refrigerant is a mixture of R32, R1234ze(E) and R1234yf in a mass ratio of 18:60:15; the stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite and methylbenzotriazole in a mass ratio of 0.1:0.15:0.15.

[0062] The preparation methods for the flame retardant and the mixture are the same as those in Example 1.

[0063] Example 5 The difference from Example 1 is that the formulation of the mixed refrigerant is as follows: 90 parts basic refrigerant, 5 parts flame retardant, 4.5 parts lubricating oil, and 0.5 parts stabilizer; The basic refrigerant is a mixture of R32, R1234ze(E) and R1234yf in a mass ratio of 28:45:25; the stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite and methylbenzotriazole in a mass ratio of 0.1:0.15:0.15.

[0064] The preparation methods for the flame retardant and the mixture are the same as those in Example 1.

[0065] Example 6 The difference from Example 1 is that the formulation of the mixed refrigerant is as follows: 90 parts basic refrigerant, 5 parts flame retardant, 4.5 parts lubricating oil, and 0.5 parts stabilizer; The basic refrigerant is a mixture of R32, R1234ze(E) and R1234yf in a mass ratio of 20:50:20; the stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite and methylbenzotriazole in a mass ratio of 0.15:0.15:0.2.

[0066] The preparation methods for the flame retardant and the mixture are the same as those in Example 1.

[0067] Example 7 The difference from Example 1 is that the formulation of the mixed refrigerant is as follows: 90 parts basic refrigerant, 5 parts flame retardant, 4.5 parts lubricating oil, and 0.5 parts stabilizer; The basic refrigerant is a mixture of R32, R1234ze(E) and R1234yf in a mass ratio of 20:50:20; the stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite and methylbenzotriazole in a mass ratio of 0.15:0.1:0.15.

[0068] The preparation methods for the flame retardant and the mixture are the same as those in Example 1.

[0069] Comparative Example 1 The difference from Example 1 is that the flame retardant is tris(2-chloroethyl) phosphate, and the raw materials, proportions and preparation methods used are the same as those in Example 1.

[0070] Comparative Example 2 The difference from Example 1 is that the stabilizer is triethyl orthoformate, and the raw materials, proportions and preparation methods used are the same as those in Example 1.

[0071] Comparative Example 3 The difference from Example 1 is that the stabilizer is triphenyl phosphite, and the raw materials, proportions and preparation methods used are the same as those in Example 1.

[0072] Comparative Example 4 The difference from Example 1 is that the stabilizer is methylbenzotriazole, and the raw materials, proportions and preparation methods used are the same as those in Example 1.

[0073] Experimental Example The refrigerants of the above embodiments and comparative examples were tested according to the following method, and the results are shown in Table 1.

[0074] Saturated vapor pressure: A cyclic static vapor pressure analyzer was used, with a temperature control accuracy of ±0.03℃ and a pressure sensor accuracy of ±0.1% FS. The reported value is the mean of three measurements ± standard deviation.

[0075] Flammability Limits: Tested according to ASTM E681 in a 12L spherical glass combustion apparatus. LFL values ​​are the average of at least three valid tests ± fluctuation range. >10.0% indicates that it cannot be ignited at a concentration of 10.0%.

[0076] Hydrolytic stability: The refrigerant, lubricating oil (containing 0.5% water), and metal catalysts (copper, aluminum, steel sheets) were sealed in an autoclave and aged at 70.0±0.5℃ for 168 hours. The oil phase acid value was determined according to GB / T 7304-2014 (potentiometric titration method), accurate to 0.001 mg KOH / g. Report the initial value, final value, and change.

[0077] Thermal stability: The sealed glass tube method (ASHRAE 97) was used, with aging in an oven at 175.0 ± 0.5℃ for 14 days. Tube pressure before and after aging was measured using a high-precision pressure sensor (±0.25% FS). Pressure change rate = (P 终 - P 理论 ) / P 理论 ×100%. P 理论 Calculated based on the ideal gas law and the initial charge amount.

[0078] Oil compatibility / critical dissolution temperature: A PVT test cell with an optical observation window was used, with a refrigerant to oil mass ratio of 50:50. Under constant pressure, the temperature was reduced at a rate of 0.1℃ / min, and the CST was determined by the abrupt change point of laser transmittance, with a temperature measurement accuracy of ±0.1℃.

[0079] Table 1

[0080] Table 1 shows that Examples 1-2, 4-7, and Comparative Examples 2-4 exhibit excellent flame retardancy (NF) due to the use of the flame retardant prepared in Example 1. Comparative Example 1, using a common small-molecule phosphate ester, shows significantly worse flame retardancy (A2 grade). Example 3, due to its extremely low flame retardant addition (1 part), drops to A2L grade. Examples 6 and Examples 1 and 7, with their ternary stabilizer combination, exhibit the best hydrolytic and thermal stability. Comparative Example 2 (without phosphite) shows poor thermal stability; Comparative Example 3 (without methylbenzotriazole) has weak metal passivation ability, resulting in poor oil compatibility (increased CST); Comparative Example 4 (without orthoformate ester) has weak moisture removal ability and the worst hydrolytic stability.

[0081] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A mixed refrigerant, characterized in that, By weight, it includes the following ingredients: 85-95 parts of basic refrigerant, 1-5 parts of flame retardant, 1-10 parts of lubricating oil, and 0.1-0.5 parts of stabilizer; The basic refrigerant is a mixture of R32, R1234ze(E) and R1234yf, with a mass ratio of (18-28):(45-60):(15-25); The stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite and methylbenzotriazole in a mass ratio of (0.1-0.15):(0.1-0.15):(0.15-0.2).

2. The mixed refrigerant according to claim 1, characterized in that, The basic refrigerant is a mixture of R32, R1234ze(E) and R1234yf in a mass ratio of 20:50:

20.

3. The mixed refrigerant according to claim 1, characterized in that, The stabilizer is a mixture of triethyl orthoformate, triphenyl phosphite and methylbenzotriazole in a mass ratio of 0.1:0.15:0.

2.

4. The mixed refrigerant according to claim 1, characterized in that, The flame retardant is prepared by the following steps: Step A, Synthesis of cage-like phosphate intermediate: Add pentaerythritol and acetonitrile to a container, and maintain the system temperature at 0-5℃ under ice-water bath and nitrogen protection; add phosphorus oxychloride dropwise to the container, and after the addition is complete, raise the temperature to 80-85℃ and reflux for 6-8 hours. Cool the reaction solution to room temperature, remove the solvent acetonitrile and excess phosphorus oxychloride by vacuum distillation, and wash and dry the product to obtain a cage-like phosphate intermediate. Step B, synthesis of hydroxyl-functionalized intermediates: Add the cage-like phosphate intermediate obtained in step A, the catalyst p-toluenesulfonic acid, the polymerization inhibitor hydroquinone, and anhydrous 1,4-dioxane to a container; under nitrogen protection, stir and heat to 90-95℃; add hydroxyethyl acrylate dropwise, maintaining the reaction temperature at 90-95℃, and continue the reaction for 5-7 hours after the addition is complete. Cool the reaction solution, filter it, and first evaporate the filtrate under reduced pressure, then add cold diethyl ether to precipitate, obtaining a white viscous substance. Filter and wash the precipitate to obtain the hydroxyl-functionalized intermediate. Step C, Flame retardant synthesis: The hydroxyl-functionalized intermediate obtained in step B was dissolved in anhydrous tetrahydrofuran, and then dibutyltin dilaurate was added. Under ice bath cooling and nitrogen protection, the temperature was maintained at 0-5℃. 3-isocyanate-propyltrimethoxysilane was added dropwise, and the reaction was carried out at 0-5℃ for 2-3 hours. The reaction solution was then slowly heated to room temperature and stirred for another 2 hours. The solution was filtered, and the filtrate was distilled under reduced pressure to obtain a viscous liquid, which is the flame retardant.

5. The mixed refrigerant according to claim 4, characterized in that, In step A, the mass-to-volume ratio of pentaerythritol to acetonitrile is 1 g: 5 mL; the molar ratio of pentaerythritol to phosphorus oxychloride is 1: 1.05-1.

10.

6. The mixed refrigerant according to claim 4, characterized in that, In step B, the amount of p-toluenesulfonic acid catalyst is 1.0% of the mass of the cage-like phosphate intermediate; the amount of hydroquinone inhibitor is 0.5% of the mass of the cage-like phosphate intermediate; the mass-volume ratio of the cage-like phosphate intermediate to the solvent is 1 g: 8 mL; and the molar ratio of the cage-like phosphate intermediate to hydroxyethyl acrylate is 1:1.

05.

7. The mixed refrigerant according to claim 4, characterized in that, In step C, the mass-to-volume ratio of the hydroxyl functionalized intermediate to anhydrous tetrahydrofuran is 1 g: 10 mL; the molar ratio of the hydroxyl functionalized intermediate to silane is 1: (1-1.02).

8. The mixed refrigerant according to claim 1, characterized in that, The lubricating oil is POE lubricating oil.

9. The method for preparing the mixed refrigerant according to any one of claims 1-8, characterized in that, Includes the following steps: S1: Add lubricating oil to the reactor. Under stirring conditions at 40-45℃, add methylbenzotriazole, then add triphenyl phosphite and stir for 30-40 minutes. Cool down to 20-25℃ and add flame retardant dropwise to the reactor. After the addition is complete, continue stirring for 2-4 hours. Under stirring and nitrogen protection, add triethyl orthoformate dropwise. After the addition is complete, continue stirring for 1-1.5 hours to obtain the mother liquor. S2: At -10℃, add R1234ze(E) to the reactor, and under stirring conditions, add the mother liquor obtained in step S1 and stir for 1-1.5h; then add R1234yf and stir for 1-2h. S3: Add R32 at -25℃ to -30℃ and under stirring conditions. After stirring evenly, raise the temperature to 0℃ and maintain the pressure at 2.0–2.5 MPa. Circulate and homogenize for 4–6 hours. S4: Heat to 10-15℃ and fill into steel cylinders to obtain the mixed refrigerant.

10. The method for preparing the mixed refrigerant according to claim 9, characterized in that, In step S1, a high-pressure micro-jet homogenizer is used to homogenize and circulate the mother liquor under room temperature and nitrogen pressure conditions. The homogenization is performed 3-5 times and the homogenization working pressure is 80-150 MPa.

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