Energy-saving rectification process of glyceryl triacetate

Abstract

The invention relates to the technical field of fine chemical engineering, and particularly discloses an energy-saving rectification process of glyceryl triacetate. The process comprises the following steps: firstly, carrying out anaerobic closed pretreatment of nitrogen displacement and acetic acid gas phase secondary purging on a whole rectification system, and then carrying out two-stage precision filtration pretreatment on crude ester liquid obtained by catalyzing and esterifying glycerol and glacial acetic acid through solid acid; refining and purification are completed through sectional type reduced pressure pre-stripping, deacidification and concentration under pressure and reduced pressure coupling rectification for adjusting activity coefficients of components in a system through acetic acid in sequence, neutralization washing and drying steps are not set in the whole process, and meanwhile, a whole system material and heat energy closed-loop circulation system is constructed. The process can be used for industrial continuous production of food-grade and tobacco-grade glyceryl triacetate, the product purity and quality stability can be effectively improved, the comprehensive energy consumption in the rectification process is greatly reduced, the generation of high-salt-content organic wastewater is reduced from the source, and the process has good economical efficiency and environmental protection property and meets the development requirements of low-carbon clean production in the fine chemical industry.

Description

Technical Field

[0001] This application relates to the field of fine chemical technology, and more specifically, to an energy-saving distillation process for triacetylglycerol. Background Technology

[0002] Triacetin is a high-performance, non-toxic, and environmentally friendly polyol ester compound. With its excellent plasticizing properties, chemical stability, and biocompatibility, it has wide applications in tobacco processing, food additives, pharmaceutical intermediates, and environmentally friendly coating auxiliaries. It is an important product with a certain production capacity in China's fine chemical industry. The mainstream industrial preparation route for triacetin involves the catalytic esterification reaction of glycerol with glacial acetic acid. The crude product obtained from the reaction needs to be purified through distillation. The efficiency of the distillation process significantly affects the production cost and the level of carbon reduction in the production process. With the continuous advancement of China's "dual-carbon" goals, energy-saving optimization of the triacetin distillation process has become a key technological focus in the industry.

[0003] The commonly used triacetylglycerol vacuum distillation process in the industry is limited by the high heat sensitivity of triacetylglycerol itself. It typically requires high-vacuum vacuum operation to lower the system's boiling point and reduce thermal decomposition side reactions at high temperatures. However, under high-vacuum conditions, the latent heat of condensation in the overhead vapor phase is low-grade heat energy, difficult to recover efficiently through conventional energy-saving methods. In most cases, it needs to be condensed by circulating cooling water before being discharged, resulting in ineffective heat loss. Furthermore, mono / diacetylglycerol and triacetylglycerol in the crude product are near-boiling substances; their relative volatility further decreases under high vacuum, often requiring a higher reflux ratio to meet separation accuracy requirements, further increasing the heat load on the distillation system. Conventional energy-saving methods such as multi-effect distillation and heat pump distillation are limited by their adaptability to operating conditions and cannot fundamentally alleviate the industry-wide problem of high overall energy consumption in the distillation process. Summary of the Invention

[0004] To address the problems of high overall energy consumption, inefficient utilization of low-grade heat energy, and large reflux ratio required for separation in the existing vacuum distillation process of triacetylglycerol, this application provides an energy-saving distillation process for triacetylglycerol.

[0005] An energy-saving distillation process for triacetin includes the following steps: S1. Oxygen-free sealed treatment: Before starting the distillation system, nitrogen is replaced, followed by a second purging with high-temperature acetic acid vapor, and the air is isolated by sealing the points with acetic acid liquid. S2. Filtration pretreatment: The crude ester solution obtained by esterification of glycerol and glacial acetic acid with solid acid catalysis is subjected to two-stage precision filtration to remove the solid acid catalyst. The process eliminates the need for neutralization, washing and drying, and a clear crude ester solution is obtained. S3. Pre-stripping separation: The clarified crude ester liquid is sent to a segmented vacuum pre-stripping tower. The high-temperature condensate discharged from the bottom of the pressurized deacidification tower is used as a heat source to remove acetic acid and water. The acetic acid-water vapor phase collected from the top of the tower is sent to the pressurized deacidification tower, and the crude triacetic acid glyceride liquid collected from the bottom of the tower is sent to a vacuum coupled distillation tower. S4. Deacidification and heat source coupling: The acetic acid-water vapor phase is sent to the pressurized deacidification tower for distillation and separation. The high-temperature acetic acid vapor phase is obtained at the top of the tower and is directly introduced into the main reboiler of the vacuum coupling distillation tower as the main heat source. The acetic acid condensate is condensed and the high-temperature condensate at the bottom of the tower is sent to the pre-stripping tower for heating. S5. Coupled Distillation Control: After mixing the crude triacetylglycerol solution with acetic acid condensate, the mixture is sent to a vacuum coupled distillation column. The column bottom is equipped with a main reboiler and an auxiliary reboiler. By adjusting the amount of acetic acid condensate added, the acetic acid concentration in the column is stabilized within a predetermined range. During the distillation process, the light component containing acetic acid and mono- and diacetylglycerol is collected from the top of the column, the triacetylglycerol product is collected from the side stream of the stripping section, and the heavy component is discharged from the bottom of the column. S6. Full system recycling: Except for reflux and addition to the vacuum coupled distillation tower, the acetic acid condensate obtained from the pressurized deacidification tower is returned to the front-end esterification reaction unit; the light components at the top of the vacuum coupled distillation tower are condensed and returned to the feed end of the pre-stripping tower; the high-temperature condensate in the bottom of the pressurized deacidification tower is sent to the front-end esterification reaction unit to preheat the raw materials after heat exchange in the pre-stripping tower.

[0006] By adopting the above technical solution, the pressurized deacidification process and the vacuum distillation process are coupled across systems using heat sources. The latent heat of phase change of the acetic acid vapor phase after pressurized concentration is used as the core heat source for vacuum distillation. The heat released by the condensation of the acetic acid vapor phase in the main reboiler provides heat for the distillation process, which recovers the low-grade heat energy that was originally carried away by the circulating cooling water and reduces the demand for external fresh steam in the distillation process. At the same time, acetic acid condensate is quantitatively introduced into the distillation system. The polarity of acetic acid changes the activity coefficients of each component in the system, which increases the relative volatility between monoacetic acid glycerides, diacetic acid glycerides, and triacetic acid glycerides, reduces the reflux ratio required for near-boiling separation, and further reduces the heat load of the distillation column reboiler. With the closed-loop material circulation design of the entire system, acetic acid is recycled as a reaction raw material in the system throughout the process, and no external impurities are introduced to interfere with the distillation balance. Thus, the heat energy of the distillation process is utilized in stages and the overall energy consumption is reduced.

[0007] Preferably, in step S1, the temperature of the high-temperature acetic acid gas phase is 145°C to 158°C, and the oxygen content in the entire system is controlled below 50 ppm; during the continuous operation of the entire system, a trace amount of acetic acid gas phase is continuously introduced into the bottom of the vacuum coupling distillation column as an inert protective gas to control the oxygen partial pressure in the column to not exceed 10 ppm.

[0008] By adopting the above technical solution, most of the air in the entire distillation system is first purged with nitrogen, and then a second purging is performed using high-temperature acetic acid gas. The acetic acid gas can penetrate deep into pipelines and equipment dead corners to complete oxygen replacement, achieving a more thorough deoxygenation effect than nitrogen replacement alone. Moreover, acetic acid itself is an internal material of the system and will not introduce external impurities. In conjunction with the acetic acid liquid seal to isolate the intrusion of external air, a trace amount of acetic acid gas is continuously introduced into the column bottom during continuous operation, which can form a continuous inert protective atmosphere in the distillation column, effectively isolating residual oxygen in the system from contact with the material, avoiding the oxidation side reaction of triacetylglycerol during high-temperature distillation. Acetic acid is finally condensed and recovered with the light components at the top of the column, without disrupting the gas-liquid balance of the distillation system, thereby ensuring the quality stability of the product.

[0009] Preferably, in step S2, the filtration accuracy of the two-stage precision filtration is controlled between 0.1 μm and 0.3 μm, and the filtration operation pressure is controlled between 0.2 MPa and 0.6 MPa.

[0010] By adopting the above technical solution, under the set filtration accuracy and operating pressure, the two-stage series precision filtration structure can effectively trap the residual solid acid catalyst particles in the crude ester liquid, thus completely removing the catalytically active components in the system. This avoids the side reactions such as hydrolysis and decomposition of triacetylglycerol that would occur after the catalyst enters the subsequent high-temperature distillation stage. At the same time, the entire process does not include neutralization, washing, or drying steps, which fundamentally prevents product hydrolysis loss during the washing process and avoids the generation of high-salt organic wastewater. This simplifies the pretreatment process and reduces material loss and subsequent environmental protection load.

[0011] Preferably, in step S3, the operating absolute pressure of the pre-stripping tower is controlled between 10 kPa and 30 kPa, and the tower bottom temperature is controlled between 105°C and 130°C.

[0012] By adopting the above technical solution, the operating pressure and temperature of the pre-stripping tower are controlled within a set range, enabling low-temperature and efficient removal of acetic acid and water from the crude ester liquid under reduced pressure. The operating temperature is far below the thermal decomposition threshold of triacetylglycerol, thus preventing thermal decomposition of the product during the pre-separation process. At the same time, these operating conditions can fully match the residual heat grade of the condensate in the pressurized deacidification tower, utilizing the residual heat in the system to provide a heating source for the pre-stripping process. This further recovers low-grade heat energy within the system, eliminating the need to introduce an external heat source to heat the pre-stripping tower and reducing the overall heat energy consumption of the process.

[0013] Preferably, in step S4, the absolute pressure of the pressurized deacidification tower is controlled at 250 kPa to 350 kPa, the temperature of the tower bottom is controlled at 165°C to 180°C, and the mass concentration of the high-temperature acetic acid gas phase extracted from the top of the tower is not less than 98%.

[0014] By adopting the above technical solution, the operating pressure and temperature of the pressurized deacidification tower are controlled within a set range, enabling efficient distillation separation of acetic acid and water under pressure. This increases the concentration and saturation temperature of the acetic acid vapor at the top of the tower, allowing a stable and effective heat transfer temperature difference to be formed between the temperature of the acetic acid vapor at the top and the operating temperature of the bottom of the vacuum-coupled distillation tower. This provides the basic operating conditions for the recovery and utilization of heat energy within the system. The high-concentration acetic acid vapor collected at the top of the tower, after condensation, can directly meet the purity requirements for tower reflux, polarity regulator, and reaction raw material recycling without additional purification treatment, simplifying the material circulation process.

[0015] Preferably, in step S5, the absolute pressure of the vacuum-coupled distillation column is controlled at 1 kPa to 5 kPa, the bottom temperature is controlled at 130°C to 150°C, and the amount of acetic acid condensate added is 1% to 6% of the mass of crude triacetic acid glyceride feed, so that the mass concentration of acetic acid in the column is stabilized at 1% to 4%.

[0016] By adopting the above technical solution, the operating pressure and temperature of the vacuum-coupled distillation column are controlled within a set range, enabling low-temperature distillation separation of triacetylglycerol under high vacuum. The operating temperature is controlled within the safe threshold for product thermal decomposition, thus preventing thermal decomposition of the product during distillation. Simultaneously, by controlling the amount of acetic acid condensate added and the acetic acid concentration in the column within a set range, a stable polarity regulation environment can be formed in the column, continuously and stably changing the activity coefficients of each component. This stabilizes and increases the relative volatility of near-boiling components, achieving efficient separation at a low reflux ratio. Acetic acid is ultimately discharged with the light components at the top of the column and recycled, without remaining in the finished product and affecting product quality.

[0017] Preferably, in step S3, the segmented vacuum pre-stripping tower adopts a two-section integrated structure, with the lower section being the stripping section and the upper section being the rectification section. The clarified crude ester liquid enters from the top of the lower section, and the vapor phase at the top of the stripping section enters the upper rectification section. 1% to 3% of the total mass of the light components condensed at the top of the vacuum coupled rectification tower is diverted as reflux liquid for the upper rectification section, and the liquid phase at the bottom of the upper rectification section is refluxed back to the lower stripping section.

[0018] By adopting the above technical solution, the integrated two-stage structure can complete the stripping separation and gas phase purification processes in a single tower. The falling film stripping section in the lower stage allows the crude ester liquid to form a uniform and stable liquid film, which fully countercurrently contacts the rising acetic acid-water gas phase, thus achieving rapid and efficient removal of acetic acid and water. The rectification section in the upper stage introduces the condensate of the light components from the subsequent rectification tower as reflux, which can wash away triacetin and mono- and diacetin entrained in the rising gas phase, thus preventing heat-sensitive ester materials from entering the subsequent pressurized high-temperature system and decomposing. The washed and recovered ester materials are returned to the stripping section, which can reduce product loss and thus improve the overall product yield.

[0019] Preferably, in step S4, the acetic acid condensate obtained after condensing the high-temperature acetic acid gas from the top of the pressurized deacidification tower has a reflux rate controlled to be 1.0 to 2.0 times the mass of the feed gas phase, and the tower top temperature is controlled to be between 145°C and 158°C.

[0020] By adopting the above technical solution, the acetic acid condensate reflux flow rate of the pressurized deacidification tower is controlled within a set range, which stabilizes the distillation operation conditions in the tower and ensures the stability of the acetic acid vapor concentration at the top of the tower. At the same time, controlling the top temperature within a set range stabilizes the saturation temperature of the acetic acid vapor at the top of the tower, ensuring that the vapor temperature maintains a stable heat transfer temperature difference with the bottom operating temperature of the vacuum-coupled distillation tower. This ensures the continuous and stable heat exchange efficiency of the main reboiler, providing a stable operating condition basis for the continuous recovery and utilization of heat energy in the system and avoiding the decrease in heat recovery efficiency caused by operational fluctuations.

[0021] Preferably, the vacuum-coupled distillation column has 32 to 38 theoretical plates, with the feed position at the 18th to 22nd theoretical plate, the side stream outlet at the 6th to 8th theoretical plate in the stripping section, and the top reflux ratio at 2 to 4.

[0022] By adopting the above technical solution, the set theoretical plate number and corresponding feed and side-stream exit positions can accurately match the concentration distribution of the triacetylglycerol distillation system, ensuring that the feed enters at a position matching the component concentration within the column, thereby improving the distillation separation efficiency. The side-stream exit position in the stripping section can avoid the heavy component enrichment zone at the bottom and the light component enrichment zone at the top, ensuring the stable extraction of high-purity products. Combined with the set reflux ratio range, the separation accuracy requirements of the product can be met. This reflux ratio is much lower than that required by conventional processes, which significantly reduces the heat load of the distillation column reboiler, further reducing the heat energy consumption of the distillation process.

[0023] Preferably, the pressurized deacidification tower and the vacuum-coupled distillation tower are interlocked. The operating pressure and heating load of the pressurized deacidification tower are adjusted according to the temperature difference between the top of the pressurized deacidification tower and the bottom of the vacuum-coupled distillation tower to maintain the heat transfer temperature difference between 12°C and 18°C. At the same time, the acetic acid condensate feed rate, the top reflux ratio, and the outflow ratio are adjusted synchronously according to the acetic acid concentration in the vacuum-coupled distillation tower and the acidity of the product sampled from the side stream. When the acetic acid concentration in the tower is below 1%, the acetic acid condensate feed rate is increased and the reflux ratio is decreased. When it is above 4%, the acetic acid condensate feed rate is decreased and the reflux ratio is increased. When the acidity of the product exceeds 0.008%, the outflow ratio is increased and the acetic acid condensate feed rate is decreased.

[0024] By adopting the above technical solutions, the interlocked control of pressure and temperature across the towers allows for real-time monitoring of the operating parameters of the pressurized deacidification tower and the vacuum-coupled distillation tower. The operating pressure and heating load of the pressurized deacidification tower are dynamically adjusted based on the actual heat transfer temperature difference, stabilizing the heat transfer temperature difference between the two towers and ensuring the continuous and stable heat recovery efficiency of the main reboiler, thus preventing fluctuations in operating conditions from affecting the distillation process. The interlocked control of acetic acid concentration, reflux ratio, and product split ratio allows for real-time adjustment of operating parameters based on the actual acetic acid concentration and product acidity within the towers, stabilizing the acetic acid concentration environment within the towers, ensuring the continuous and stable polarity regulation effect, and preventing excessive product acidity. This achieves continuous and stable operation of the distillation process, balancing separation efficiency, energy saving, and product quality.

[0025] In summary, this application has the following beneficial effects: 1. The method of this application uses the high-temperature acetic acid gas phase at the top of the pressurized deacidification tower as the main heating heat source of the vacuum coupled distillation tower, and simultaneously adds acetic acid condensate in a quantitative manner to adjust the polarity and activity coefficient of the materials in the system, thereby realizing the closed-loop cascade utilization of thermal energy in the system, significantly reducing the distillation reflux ratio and external fresh steam consumption, and achieving significant energy saving and consumption reduction effects.

[0026] 2. The method of this application constructs a fully oxygen-free closed system through high-temperature acetic acid gas phase secondary purging and acetic acid gas phase protection during operation. Combined with the low reflux ratio distillation and side-stream sampling design of the stripping section, the high-temperature residence time of materials is shortened, and side reactions of product oxidation and thermal decomposition are avoided, thereby improving the purity and quality stability of the product.

[0027] 3. The method of this application uses two-stage precision filtration to remove solid acid catalysts from crude ester liquid, eliminating the need for neutralization washing and drying steps throughout the process. This avoids product hydrolysis loss and the generation of high-salt organic wastewater from the source, thereby reducing the environmental protection treatment load and raw material loss.

[0028] 4. The method of this application, through the upper and lower two-section structure of the segmented vacuum pre-stripping tower and the ester phase reflux design, combined with the closed-loop interlocking control of the cross-tower temperature difference and the three parameters inside the tower, achieves real-time and precise control of process parameters, ensures continuous and stable operation of the distillation process, and achieves the effect of improving the product distillation yield. Attached Figure Description

[0029] Figure 1 This is a flowchart of an energy-saving distillation process for triacetin provided in this application. Detailed Implementation

[0030] The present application will be further described in detail below with reference to embodiments and comparative examples. Unless otherwise specified, the experimental methods used below are conventional methods. Unless otherwise specified, the materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art, which can be obtained by those skilled in the art through commercial channels or prepared according to literature methods.

[0031] Technical Concept: In the industrial production of triacetin, the vacuum distillation process commonly used for the purification of crude esters suffers from the common industry problem of high overall energy consumption. The core cause of this problem lies in the fact that the high heat sensitivity of triacetin requires the distillation process to maintain high vacuum conditions. This results in the latent heat of condensation in the overhead vapor phase being low-grade heat energy, difficult to recover efficiently, and mostly discharged directly with the cooling water, causing heat loss. Simultaneously, the mono / diacetylglycerol and triacetylglycerol in the crude product are near-boiling substances, and their relative volatility further decreases under high vacuum, requiring a high reflux ratio to meet separation requirements, further amplifying the system's heat load. Conventional energy-saving methods are limited by their adaptability to the operating conditions and cannot fundamentally alleviate this problem.

[0032] This technical solution addresses the aforementioned problems by using acetic acid, the substance to be removed from the system, as the core functional carrier, and constructing a coupled process that combines closed-loop, cascaded utilization of thermal energy with enhanced separation efficiency. The acetic acid-water vapor phase is concentrated through pressurized distillation in a pressurized deacidification tower, converting the latent heat of phase change of the originally low-grade acetic acid into thermal energy suitable for vacuum distillation. The high-temperature acetic acid vapor phase at the top of the tower directly serves as the core heat source for the main reboiler of the vacuum-coupled distillation tower. Simultaneously, acetic acid condensate is quantitatively introduced to adjust the activity coefficients of components within the system, increasing the relative volatility of near-boiling substances and reducing the reflux ratio required for separation. Combined with closed-loop material circulation and interlocked steady-state control, this significantly reduces the overall energy consumption of the distillation process while ensuring product quality.

[0033] Example 1: This example provides an energy-saving distillation process for triacetin, the specific process steps of which are as follows: S1. Oxygen-free sealed treatment: Before starting the distillation system, nitrogen is replaced, followed by a second purging with high-temperature acetic acid vapor, and the air is isolated by sealing the points with acetic acid liquid. The temperature of the high-temperature acetic acid gas phase used for the secondary purging is 152℃. After the purging is completed, the oxygen content in the entire system is controlled below 50ppm. During the continuous operation of the entire system, a small amount of acetic acid gas phase is continuously introduced into the bottom of the vacuum coupling distillation column as an inert protective gas to control the oxygen partial pressure in the column to not exceed 10ppm. Nitrogen replacement is carried out three times to ensure that there is no residual air in the system.

[0034] S2. Filtration pretreatment: The crude ester solution obtained by esterification of glycerol and glacial acetic acid with solid acid catalysis is subjected to two-stage precision filtration to remove the solid acid catalyst. The process eliminates the need for neutralization, washing and drying, and a clear crude ester solution is obtained. The two-stage precision filtration adopts a series filtration structure, with filtration accuracy controlled at 0.2μm and filtration operation pressure controlled at 0.4MPa. After filtration, there are no solid catalyst particles remaining in the crude ester liquid.

[0035] S3. Pre-stripping separation: The clarified crude ester liquid is sent to a segmented vacuum pre-stripping tower. The high-temperature condensate discharged from the bottom of the pressurized deacidification tower is used as a heat source to remove acetic acid and water. The acetic acid-water vapor phase collected from the top of the tower is sent to the pressurized deacidification tower, and the crude triacetic acid glyceride liquid collected from the bottom of the tower is sent to a vacuum coupled distillation tower. The pre-stripping tower operates at an absolute pressure of 20 kPa and a bottom temperature of 118°C. The segmented vacuum pre-stripping tower adopts a two-section integrated structure, with the lower section being the stripping section and the upper section being the rectification section. The clarified crude ester liquid enters from the top of the lower section, and the vapor phase at the top of the stripping section enters the upper rectification section. 2% of the total mass of the light components condensed at the top of the vacuum coupled rectification tower is diverted as reflux liquid for the upper rectification section, and the bottom liquid phase of the upper rectification section is refluxed back to the lower stripping section.

[0036] S4. Deacidification and heat source coupling: The acetic acid-water vapor phase is sent to the pressurized deacidification tower for distillation and separation. The high-temperature acetic acid vapor phase is obtained at the top of the tower and is directly introduced into the main reboiler of the vacuum coupling distillation tower as the main heat source. The acetic acid condensate is condensed and the high-temperature condensate at the bottom of the tower is sent to the pre-stripping tower for heating. The operating absolute pressure of the pressurized deacidification tower is controlled at 300 kPa, the tower bottom temperature is controlled at 173℃, and the mass concentration of the high-temperature acetic acid gas phase collected from the top of the tower is not less than 99%. The acetic acid condensate obtained after condensing the high-temperature acetic acid gas phase collected from the top of the pressurized deacidification tower has a reflux flow rate controlled at 1.5 times the mass of the feed gas phase, and the tower top temperature is controlled at 152℃.

[0037] S5. Coupled Distillation Control: After mixing the crude triacetylglycerol solution with acetic acid condensate, the mixture is sent to a vacuum coupled distillation column. The column bottom is equipped with a main reboiler and an auxiliary reboiler. By adjusting the amount of acetic acid condensate added, the acetic acid concentration in the column is stabilized within a predetermined range. During the distillation process, the light component containing acetic acid and mono- and diacetylglycerol is collected from the top of the column, the triacetylglycerol product is collected from the side stream of the stripping section, and the heavy component is discharged from the bottom of the column. The operating absolute pressure of the vacuum-coupled distillation column is controlled at 3 kPa, the bottom temperature is controlled at 140℃, and the amount of acetic acid condensate added is 3.5% of the feed mass of crude triacetic acid glyceride solution, so that the acetic acid mass concentration in the column is stabilized at 2.5%. The vacuum-coupled distillation column has 35 theoretical plates, the feed position is the 20th theoretical plate, the side stream outlet is located on the 7th theoretical plate in the stripping section, and the top reflux ratio is 3.

[0038] S6. Full system recycling: Except for reflux and addition to the vacuum coupled distillation tower, the acetic acid condensate obtained from the pressurized deacidification tower is returned to the front-end esterification reaction unit; the light components at the top of the vacuum coupled distillation tower are condensed and returned to the feed end of the pre-stripping tower; the high-temperature condensate in the bottom of the pressurized deacidification tower is sent to the front-end esterification reaction unit to preheat the raw materials after heat exchange in the pre-stripping tower. The pressurized deacidification tower and the vacuum-coupled distillation tower are interlocked. The operating pressure and heating load of the pressurized deacidification tower are adjusted according to the temperature difference between the top of the pressurized deacidification tower and the bottom of the vacuum-coupled distillation tower to maintain the heat transfer temperature difference at 15℃. At the same time, the acetic acid condensate feed rate, the top reflux ratio, and the outflow ratio are adjusted synchronously according to the acetic acid concentration in the vacuum-coupled distillation tower and the acidity of the product sampled from the side stream. When the acetic acid concentration in the tower is below 1%, the acetic acid condensate feed rate is increased and the reflux ratio is decreased. When it is above 4%, the acetic acid condensate feed rate is decreased and the reflux ratio is increased. When the acidity of the product exceeds 0.008%, the outflow ratio is increased and the acetic acid condensate feed rate is decreased.

[0039] Example 2: This example provides an energy-saving distillation process for triacetin, the specific process steps of which are as follows: S1. Oxygen-free sealed treatment: Before starting the distillation system, nitrogen is replaced, followed by a second purging with high-temperature acetic acid vapor, and the air is isolated by sealing the points with acetic acid liquid. The temperature of the high-temperature acetic acid gas phase used for the secondary purging is 145℃. After the purging is completed, the oxygen content in the entire system is controlled below 30ppm. During the continuous operation of the entire system, a small amount of acetic acid gas phase is continuously introduced into the bottom of the vacuum coupling distillation column as an inert protective gas to control the oxygen partial pressure in the column to not exceed 5ppm. Nitrogen replacement is carried out three times to ensure that there is no residual air in the system.

[0040] S2. Filtration pretreatment: The crude ester solution obtained by esterification of glycerol and glacial acetic acid with solid acid catalysis is subjected to two-stage precision filtration to remove the solid acid catalyst. The process eliminates the need for neutralization, washing and drying, and a clear crude ester solution is obtained. The two-stage precision filtration adopts a series filtration structure, with filtration accuracy controlled at 0.1μm and filtration operation pressure controlled at 0.2MPa. After filtration, there are no solid catalyst particles remaining in the crude ester liquid.

[0041] S3. Pre-stripping separation: The clarified crude ester liquid is sent to a segmented vacuum pre-stripping tower. The high-temperature condensate discharged from the bottom of the pressurized deacidification tower is used as a heat source to remove acetic acid and water. The acetic acid-water vapor phase collected from the top of the tower is sent to the pressurized deacidification tower, and the crude triacetic acid glyceride liquid collected from the bottom of the tower is sent to a vacuum coupled distillation tower. The pre-stripping tower operates at an absolute pressure of 10 kPa and a bottom temperature of 105℃. The segmented vacuum pre-stripping tower adopts a two-section integrated structure, with the lower section being the stripping section and the upper section being the rectification section. The clarified crude ester liquid enters from the top of the lower section, and the vapor phase at the top of the stripping section enters the upper rectification section. 1% of the total mass of the light components condensed at the top of the vacuum coupled rectification tower is diverted as reflux liquid for the upper rectification section, and the bottom liquid phase of the upper rectification section is refluxed back to the lower stripping section.

[0042] S4. Deacidification and heat source coupling: The acetic acid-water vapor phase is sent to the pressurized deacidification tower for distillation and separation. The high-temperature acetic acid vapor phase is obtained at the top of the tower and is directly introduced into the main reboiler of the vacuum coupling distillation tower as the main heat source. The acetic acid condensate is condensed and the high-temperature condensate at the bottom of the tower is sent to the pre-stripping tower for heating. The operating absolute pressure of the pressurized deacidification tower is controlled at 250 kPa, the bottom temperature is controlled at 165℃, and the mass concentration of the high-temperature acetic acid gas phase collected from the top of the tower is not less than 98%. The acetic acid condensate obtained after condensing the high-temperature acetic acid gas phase collected from the top of the pressurized deacidification tower has a reflux flow rate controlled at 1.0 times the mass of the feed gas phase, and the top temperature is controlled at 145℃.

[0043] S5. Coupled Distillation Control: After mixing the crude triacetylglycerol solution with acetic acid condensate, the mixture is sent to a vacuum coupled distillation column. The column bottom is equipped with a main reboiler and an auxiliary reboiler. By adjusting the amount of acetic acid condensate added, the acetic acid concentration in the column is stabilized within a predetermined range. During the distillation process, the light component containing acetic acid and mono- and diacetylglycerol is collected from the top of the column, the triacetylglycerol product is collected from the side stream of the stripping section, and the heavy component is discharged from the bottom of the column. The operating absolute pressure of the vacuum-coupled distillation column is controlled at 1 kPa, the bottom temperature is controlled at 130℃, and the amount of acetic acid condensate added is 1% of the feed mass of crude triacetic acid glyceride solution, so that the acetic acid mass concentration in the column is stabilized at 1%. The vacuum-coupled distillation column has 32 theoretical plates, the feed position is the 18th theoretical plate, the side stream outlet is located on the 6th theoretical plate in the stripping section, and the top reflux ratio is 2.

[0044] S6. Full system recycling: Except for reflux and addition to the vacuum coupled distillation tower, the acetic acid condensate obtained from the pressurized deacidification tower is returned to the front-end esterification reaction unit; the light components at the top of the vacuum coupled distillation tower are condensed and returned to the feed end of the pre-stripping tower; the high-temperature condensate in the bottom of the pressurized deacidification tower is sent to the front-end esterification reaction unit to preheat the raw materials after heat exchange in the pre-stripping tower. The pressurized deacidification tower and the vacuum-coupled distillation tower are interlocked. The operating pressure and heating load of the pressurized deacidification tower are adjusted according to the temperature difference between the top of the pressurized deacidification tower and the bottom of the vacuum-coupled distillation tower to maintain the heat transfer temperature difference at 12℃. At the same time, the acetic acid condensate feed rate, the top reflux ratio, and the outflow ratio are adjusted synchronously according to the acetic acid concentration in the vacuum-coupled distillation tower and the acidity of the product sampled from the side stream. When the acetic acid concentration in the tower is below 1%, the acetic acid condensate feed rate is increased and the reflux ratio is decreased. When it is above 4%, the acetic acid condensate feed rate is decreased and the reflux ratio is increased. When the acidity of the product exceeds 0.008%, the outflow ratio is increased and the acetic acid condensate feed rate is decreased.

[0045] Example 3: This example provides an energy-saving distillation process for triacetin, the specific process steps of which are as follows: S1. Oxygen-free sealed treatment: Before starting the distillation system, nitrogen is replaced, followed by a second purging with high-temperature acetic acid vapor, and the air is isolated by sealing the points with acetic acid liquid. The temperature of the high-temperature acetic acid gas phase used for the secondary purging is 158℃. After the purging is completed, the oxygen content in the entire system is controlled below 50ppm. During the continuous operation of the entire system, a small amount of acetic acid gas phase is continuously introduced into the bottom of the vacuum coupling distillation column as an inert protective gas to control the oxygen partial pressure in the column to not exceed 10ppm. Nitrogen replacement is carried out three times to ensure that there is no residual air in the system.

[0046] S2. Filtration pretreatment: The crude ester solution obtained by esterification of glycerol and glacial acetic acid with solid acid catalysis is subjected to two-stage precision filtration to remove the solid acid catalyst. The process eliminates the need for neutralization, washing and drying, and a clear crude ester solution is obtained. The two-stage precision filtration adopts a series filtration structure, with filtration accuracy controlled at 0.3μm and filtration operation pressure controlled at 0.6MPa. After filtration, there are no solid catalyst particles remaining in the crude ester liquid.

[0047] S3. Pre-stripping separation: The clarified crude ester liquid is sent to a segmented vacuum pre-stripping tower. The high-temperature condensate discharged from the bottom of the pressurized deacidification tower is used as a heat source to remove acetic acid and water. The acetic acid-water vapor phase collected from the top of the tower is sent to the pressurized deacidification tower, and the crude triacetic acid glyceride liquid collected from the bottom of the tower is sent to a vacuum coupled distillation tower. The pre-stripping tower operates at an absolute pressure of 30 kPa and a bottom temperature of 130°C. The segmented vacuum pre-stripping tower adopts a two-section integrated structure, with the lower section being the stripping section and the upper section being the rectification section. The clarified crude ester liquid enters from the top of the lower section, and the vapor phase at the top of the stripping section enters the upper rectification section. 3% of the total mass of the light components condensed at the top of the vacuum coupled rectification tower is diverted as reflux liquid for the upper rectification section, and the bottom liquid phase of the upper rectification section is refluxed back to the lower stripping section.

[0048] S4. Deacidification and heat source coupling: The acetic acid-water vapor phase is sent to the pressurized deacidification tower for distillation and separation. The high-temperature acetic acid vapor phase is obtained at the top of the tower and is directly introduced into the main reboiler of the vacuum coupling distillation tower as the main heat source. The acetic acid condensate is condensed and the high-temperature condensate at the bottom of the tower is sent to the pre-stripping tower for heating. The operating absolute pressure of the pressurized deacidification tower is controlled at 350 kPa, the bottom temperature is controlled at 180℃, and the mass concentration of the high-temperature acetic acid gas phase collected from the top of the tower is not less than 99.5%. The acetic acid condensate obtained after condensing the high-temperature acetic acid gas phase collected from the top of the pressurized deacidification tower has a reflux flow rate controlled at 2.0 times the mass of the feed gas phase, and the top temperature is controlled at 158℃.

[0049] S5. Coupled Distillation Control: After mixing the crude triacetylglycerol solution with acetic acid condensate, the mixture is sent to a vacuum coupled distillation column. The column bottom is equipped with a main reboiler and an auxiliary reboiler. By adjusting the amount of acetic acid condensate added, the acetic acid concentration in the column is stabilized within a predetermined range. During the distillation process, the light component containing acetic acid and mono- and diacetylglycerol is collected from the top of the column, the triacetylglycerol product is collected from the side stream of the stripping section, and the heavy component is discharged from the bottom of the column. The operating absolute pressure of the vacuum-coupled distillation column is controlled at 5 kPa, the bottom temperature is controlled at 150℃, and the amount of acetic acid condensate added is 6% of the feed mass of crude triacetic acid glyceride solution, so that the acetic acid mass concentration in the column is stabilized at 4%. The vacuum-coupled distillation column has 38 theoretical plates, the feed position is the 22nd theoretical plate, the side stream outlet is located on the 8th theoretical plate in the stripping section, and the top reflux ratio is 4.

[0050] S6. Full system recycling: Except for reflux and addition to the vacuum coupled distillation tower, the acetic acid condensate obtained from the pressurized deacidification tower is returned to the front-end esterification reaction unit; the light components at the top of the vacuum coupled distillation tower are condensed and returned to the feed end of the pre-stripping tower; the high-temperature condensate in the bottom of the pressurized deacidification tower is sent to the front-end esterification reaction unit to preheat the raw materials after heat exchange in the pre-stripping tower. The pressurized deacidification tower and the vacuum-coupled distillation tower are interlocked. The operating pressure and heating load of the pressurized deacidification tower are adjusted according to the temperature difference between the top of the pressurized deacidification tower and the bottom of the vacuum-coupled distillation tower to maintain the heat transfer temperature difference at 18℃. At the same time, the acetic acid condensate feed rate, the top reflux ratio, and the outflow ratio are adjusted synchronously according to the acetic acid concentration in the vacuum-coupled distillation tower and the acidity of the product sampled from the side stream. When the acetic acid concentration in the tower is below 1%, the acetic acid condensate feed rate is increased and the reflux ratio is decreased. When it is above 4%, the acetic acid condensate feed rate is decreased and the reflux ratio is increased. When the acidity of the product exceeds 0.008%, the outflow ratio is increased and the acetic acid condensate feed rate is decreased.

[0051] Comparative Example 1: This comparative example differs from Example 1 only in that: in step S5, during coupled distillation control, no acetic acid condensate is added to the crude triacetic acid ester solution; the crude triacetic acid ester solution is directly fed into the vacuum coupled distillation column for distillation, and the acetic acid concentration in the column is naturally determined only by the trace amount of acetic acid remaining in the crude ester solution, without any artificial control; in step S6, during the whole system recycling, the acetic acid condensate obtained from the pressurized deacidification column is returned to the front-end esterification reaction unit, except for the reflux to the pressurized deacidification column, and is no longer diverted to the vacuum coupled distillation column. All other operating steps, process parameters, equipment structure, and control logic are completely consistent with Example 1.

[0052] Comparative Example 2: This comparative example differs from Example 1 only in that: in step S4, during the deacidification and heat source coupling, the high-temperature acetic acid vapor from the top of the pressurized deacidification tower is not sent to the main reboiler of the vacuum-coupled distillation tower, but is directly condensed by circulating cooling water to obtain acetic acid condensate; in step S5, during the coupled distillation control, both the main reboiler and auxiliary reboiler of the vacuum-coupled distillation tower use low-pressure saturated steam as the sole heating source, and the acetic acid vapor from the pressurized deacidification tower is not used as a heat source. All other operating steps, process parameters, equipment structure, and control logic are completely consistent with Example 1.

[0053] Comparative Example 3: This comparative example differs from Example 1 only in that, after the filtration pretreatment in step S2, a standard industry-standard neutralization, washing, and drying step is added. Specifically, the crude ester liquid after two-stage precision filtration is neutralized to neutral with a 5% sodium hydroxide solution, then washed three times with an equal volume of deionized water, dried with anhydrous sodium sulfate, and then sent to the pre-stripping separation step in step S3. All other operating steps, process parameters, equipment structure, and control logic are completely consistent with Example 1.

[0054] Comparative Example 4: This comparative example differs from Example 1 only in that: in step S1, during the oxygen-free closed treatment, high-purity nitrogen at the same temperature as the high-temperature acetic acid gas is used instead of the high-temperature acetic acid gas phase for the secondary purging; during continuous operation of the entire system, a trace amount of acetic acid gas phase is not introduced into the bottom of the vacuum coupling distillation column, but instead high-purity nitrogen is introduced as an inert protective gas to control the oxygen partial pressure in the column to not exceed 10 ppm. All other operating steps, process parameters, equipment structure, and control logic are completely consistent with Example 1.

[0055] Comparative Example 5: This comparative example differs from Example 1 only in that it fully utilizes the conventional neutralization washing and three-tower continuous vacuum distillation process commonly used for the large-scale production of triacetin, specifically: 1. Pretreatment of crude ester solution: The crude ester solution obtained by esterification of glycerol and glacial acetic acid by solid acid catalysis is not subjected to two-stage precision filtration. First, sodium carbonate solution is added to neutralize to pH 7-8, then washed 2-3 times with warm water at 50-60℃. After standing to separate the aqueous phase, the residual water is removed by vacuum drying. 2. Distillation process: The distillation process adopts a three-tower continuous vacuum distillation system consisting of a light-light removal tower, a refining tower, and a heavy-light removal tower connected in series. All reboilers in the tower bottoms are heated by external low-pressure saturated steam. There is no cross-tower heat source coupling and no acetic acid condensate is added for control. 3. Operating parameters: The light-weight removal tower operates at an absolute pressure of 5 kPa and a reflux ratio of 12; the refining tower operates at an absolute pressure of 3 kPa and a reflux ratio of 10; and the heavy-weight removal tower operates at an absolute pressure of 2 kPa and a reflux ratio of 3. 4. Oxygen-free protection: Only routine nitrogen purging is performed before start-up, and there are no inert protection measures during operation, nor is there a full-system acetic acid liquid seal design; 5. Material circulation: The acetic acid recovery system operates independently, without a closed-loop design for the utilization of materials and heat energy throughout the system.

[0056] All other comparable process parameters remain the same as in Example 1.

[0057] Experiment 1: Key Quality Indicator Testing of Triacetin Finished Products: This experiment followed the testing methods specified in GB / T28350-2012 "Food Additives - Triacetin" to test the key quality indicators of the triacetin finished products prepared in Examples 1, 2, and 3, as well as Comparative Examples 1, 2, 3, 4, and 5. The testing items included three core indicators: product purity, color, and acidity. Product purity was tested using gas chromatography (GC). A GC equipped with a flame ionization detector was used, and components were separated using a polar capillary column. The mass fraction of triacetin was quantitatively calculated using the area normalization method. Colorimetry was determined using the platinum-cobalt colorimetric method. The sample and a standard platinum-cobalt colorimetric solution were visually compared under the same illumination to determine the corresponding colorimetric number. Acidity was determined using acid-base titration. The free acid components in the sample were titrated with freshly prepared sodium hydroxide standard titration solution, and the acidity value was calculated using acetic acid. All tests were conducted at 25°C under normal temperature and pressure. Each example and comparative sample was tested in parallel three times, and the arithmetic mean of the three test results was taken as the final test data. The reagent preparation, instrument calibration and operation procedures specified in the standard were strictly followed during the testing process to ensure the accuracy and repeatability of all test data.

[0058] Experiment 2: Comprehensive Energy Consumption Test of the Triacetyl Glyceryl Ester Distillation Process: This experiment, referring to the comprehensive energy consumption calculation method specified in GB / T50441-2016 "Standard for Energy Consumption Calculation in Petrochemical Design", conducted a comprehensive energy consumption test of the entire process of triacetyl glyceryl ester distillation corresponding to Examples 1, 2, and 3, and Comparative Examples 1, 2, 3, 4, and 5. The test used the production of 1 ton of qualified triacetyl glyceryl ester product conforming to the GB / T28350-2012 standard as the measurement benchmark. The consumption of three core energy media—fresh steam, circulating cooling water, and equipment electricity—was statistically analyzed throughout the distillation process. Based on the equivalent calorific value of each energy media as specified in the standard, the consumption of different media was uniformly converted to kilograms of standard coal, and the comprehensive energy consumption value per ton of qualified product was finally calculated. During the test, each process operated continuously and stably for 72 hours. Real-time process parameters and instantaneous consumption of various energy media were recorded every 2 hours. Unstable operating data during start-up and shutdown were excluded, and the statistical average value of the continuous and stable operation period was used as the final calculation benchmark. All metering instruments used in the test, such as flow meters, pressure gauges, and electricity meters, were calibrated by national legal metrology institutions to ensure the accuracy of energy consumption statistics. At the same time, the actual operating reflux ratio and heating source of each process distillation column were recorded simultaneously to compare the differences in energy utilization efficiency of different processes.

[0059] Experiment 3: Triacetylglycerol Distillation Process Product Yield and Environmental Emission Testing: This experiment, referring to the distillation product yield calculation method specified in HG / T20570.10-1995 "Code for Design of Chemical Process Systems" and the wastewater pollutant testing method specified in GB8978-1996 "Integrated Wastewater Discharge Standard," calculated the product distillation yield and tested the process wastewater discharge for the triacetylglycerol distillation processes corresponding to Examples 1, 2, 3, and Comparative Examples 1, 2, 3, 4, and 5. The distillation product yield was calculated based on the total mass of triacetylglycerol in the feed of the distillation unit and the total mass of triacetylglycerol in the final qualified product. The process wastewater discharge testing was based on the production of 1 ton of qualified triacetylglycerol. The total wastewater discharge generated throughout the entire process was statistically analyzed. The chemical oxygen demand (COD) content in the wastewater was detected using the standard dichromate method, and the suspended solids content was detected using the gravimetric method. During the test, each process ran continuously and stably for 72 hours. The material flow rate and component content of the distillation feed and finished product were recorded every 4 hours. Wastewater samples generated by each process were collected in batches simultaneously. Each wastewater sample was tested in parallel 3 times, and the arithmetic mean of the 3 test results was taken as the final test data to comprehensively compare the differences in raw material utilization rate and environmental emission level of different processes.

[0060] Table 1: Test Results of Key Quality Indicators of Triacetyl Glycerate Finished Product Group Triacetin purity (wt%) Colorimetric (Platinum Cobalt Color Code) Acidity (as acetic acid, wt%) Example 1 99.82 5 0.006 Example 2 99.76 4 0.005 Example 3 99.85 6 0.007 Comparative Example 1 99.21 15 0.008 Comparative Example 2 99.78 6 0.006 Comparative Example 3 99.35 12 0.012 Comparative Example 4 99.62 18 0.009 Comparative Example 5 99.12 25 0.028 Table 2: Comprehensive Energy Consumption Test Results of the Triacetyl Glyceryl Ester Distillation Process Group Fresh steam consumption (t / t) <![CDATA[Circulating cooling water volume (m 3 / t)]]> Equipment power consumption (kW・h / t) Comprehensive energy consumption (kgce / t) Average operating reflux ratio of distillation column Example 1 0.12 28 18 21.64 3.0 Example 2 0.14 26 17 23.81 2.0 Example 3 0.11 30 19 20.78 4.0 Comparative Example 1 1.02 125 22 151.75 12.0 Comparative Example 2 0.85 110 19 127.38 3.0 Comparative Example 3 0.18 35 25 31.23 3.0 Comparative Example 4 0.13 29 20 23.33 3.0 Comparative Example 5 1.25 150 30 185.89 10.0 Table 3: Product Yield and Environmental Emission Test Results of Triacetyl Glyceryl Ester Distillation Process Group Product yield (%) in the distillation process <![CDATA[Total amount of finished wastewater discharged per ton (m 3 / t)]]> Wastewater CODcr (mg / L) Wastewater SS (mg / L) Example 1 98.62 0.12 320 45 Example 2 98.55 0.11 305 42 Example 3 98.68 0.13 335 48 Comparative Example 1 91.28 0.12 315 44 Comparative Example 2 98.58 0.12 322 46 Comparative Example 3 94.36 3.85 12500 820 Comparative Example 4 97.12 0.12 325 45 Comparative Example 5 91.05 4.52 15800 950 Based on Examples 1-3 and Comparative Example 1, and in conjunction with Tables 1, 2, and 3, it can be seen that quantitatively adding acetic acid condensate into the vacuum coupled distillation column can effectively regulate the separation characteristics of the components in the system, reduce the reflux ratio required for the distillation process, significantly reduce the residence time of materials in a high-temperature environment, reduce the occurrence of side reactions, improve the distillation separation efficiency while ensuring product quality stability, and also significantly reduce the energy consumption of the distillation process and improve the product distillation yield.

[0061] As can be seen from Examples 1-3 and Comparative Example 2, and Table 2, using the high-temperature acetic acid vapor phase at the top of the pressurized deacidification tower as the main heating source for the vacuum-coupled distillation tower can fully utilize the latent heat of phase change generated during the acetic acid concentration process, realize the closed-loop cascade utilization of thermal energy within the system, significantly reduce the demand for external fresh steam in the distillation process, and at the same time, will not have a negative impact on product quality, distillation yield, and environmental emissions. It is the core link in achieving energy saving and consumption reduction in the process.

[0062] As can be seen from Examples 1-3 and Comparative Example 3, and Tables 1, 2 and 3, using precision filtration to replace the traditional neutralization washing and drying steps can fundamentally avoid hydrolysis loss of the product during the neutralization washing process, improve the product distillation yield, eliminate the generation of high-salt organic wastewater, significantly reduce the environmental protection load of the process, and also avoid product side reactions caused by the washing and drying process, ensuring the purity and color index of the product.

[0063] Based on Examples 1-3 and Comparative Example 4, and in conjunction with Tables 1 and 3, it can be seen that constructing a fully oxygen-free, closed-loop protection system using acetic acid vapor phase within the system can more efficiently isolate oxygen within the system, prevent the oxidative decomposition of triacetylglycerol during high-temperature distillation, effectively control the increase in product color, ensure product purity and quality stability, and at the same time, avoid introducing external impurities to interfere with the gas-liquid balance of the distillation system, while also simultaneously improving the product distillation yield.

[0064] As can be seen from Examples 1-3 and Comparative Example 5, and Tables 1, 2, and 3, this solution, through the synergistic linkage of multiple innovative links, can simultaneously achieve improvements in product quality, a significant reduction in distillation energy consumption, a significant increase in product yield, and source control of wastewater discharge compared to traditional processes commonly used in the industry. It completely solves the inherent pain points of high energy consumption, low yield, and heavy environmental pressure in traditional processes. The various innovative links form a synergistic effect of mutual support, achieving a unity of green process and economy.

[0065] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. An energy-saving distillation process for triacetin, characterized in that: Includes the following steps: S1. Oxygen-free sealed treatment: Before starting the distillation system, nitrogen is replaced, followed by a second purging with high-temperature acetic acid vapor, and the air is isolated by sealing the points with acetic acid liquid. S2. Filtration pretreatment: The crude ester solution obtained by esterification of glycerol and glacial acetic acid with solid acid catalysis is subjected to two-stage precision filtration to remove the solid acid catalyst. The process eliminates the need for neutralization, washing and drying, and a clear crude ester solution is obtained. S3. Pre-stripping separation: The clarified crude ester liquid is sent to a segmented vacuum pre-stripping tower. The high-temperature condensate discharged from the bottom of the pressurized deacidification tower is used as a heat source to remove acetic acid and water. The acetic acid-water vapor phase collected from the top of the tower is sent to the pressurized deacidification tower, and the crude triacetic acid glyceride liquid collected from the bottom of the tower is sent to a vacuum coupled distillation tower. S4. Deacidification and heat source coupling: The acetic acid-water vapor phase is sent to the pressurized deacidification tower for distillation and separation. The high-temperature acetic acid vapor phase is obtained at the top of the tower and is directly introduced into the main reboiler of the vacuum coupling distillation tower as the main heat source. The acetic acid condensate is condensed and the high-temperature condensate at the bottom of the tower is sent to the pre-stripping tower for heating. S5. Coupled Distillation Control: After mixing the crude triacetylglycerol solution with acetic acid condensate, the mixture is sent to a vacuum coupled distillation column. The column bottom is equipped with a main reboiler and an auxiliary reboiler. By adjusting the amount of acetic acid condensate added, the acetic acid concentration in the column is stabilized within a predetermined range. During the distillation process, the light component containing acetic acid and mono- and diacetylglycerol is collected from the top of the column, the triacetylglycerol product is collected from the side stream of the stripping section, and the heavy component is discharged from the bottom of the column. S6. Full system recycling: Except for reflux and addition to the vacuum coupled distillation tower, the acetic acid condensate obtained from the pressurized deacidification tower is returned to the front-end esterification reaction unit; the light components at the top of the vacuum coupled distillation tower are condensed and returned to the feed end of the pre-stripping tower; the high-temperature condensate in the bottom of the pressurized deacidification tower is sent to the front-end esterification reaction unit to preheat the raw materials after heat exchange in the pre-stripping tower.

2. The energy-saving distillation process for triacetylglycerol according to claim 1, characterized in that: In step S1, the temperature of the high-temperature acetic acid gas phase is 145°C to 158°C, and the oxygen content in the entire system is controlled below 50 ppm. During the continuous operation of the entire system, a small amount of acetic acid gas phase is continuously introduced into the bottom of the vacuum coupling distillation column as an inert protective gas to control the oxygen partial pressure in the column to not exceed 10 ppm.

3. The energy-saving distillation process for triacetin according to claim 1, characterized in that: In step S2, the filtration accuracy of the two-stage precision filtration is controlled between 0.1μm and 0.3μm, and the filtration operation pressure is controlled between 0.2MPa and 0.6MPa.

4. The energy-saving distillation process for triacetin according to claim 1, characterized in that: In step S3, the operating absolute pressure of the pre-stripping tower is controlled between 10 kPa and 30 kPa, and the tower bottom temperature is controlled between 105°C and 130°C.

5. The energy-saving distillation process for triacetin according to claim 1, characterized in that: In step S4, the absolute pressure of the pressurized deacidification tower is controlled between 250 kPa and 350 kPa, the temperature of the tower bottom is controlled between 165°C and 180°C, and the mass concentration of the high-temperature acetic acid gas phase extracted from the top of the tower is not less than 98%.

6. The energy-saving distillation process for triacetylglycerol according to claim 1, characterized in that: In step S5, the absolute pressure of the vacuum-coupled distillation column is controlled at 1 kPa to 5 kPa, the bottom temperature is controlled at 130°C to 150°C, and the amount of acetic acid condensate added is 1% to 6% of the feed mass of crude triacetic acid glyceride solution, so that the acetic acid mass concentration in the column is stabilized at 1% to 4%.

7. The energy-saving distillation process for triacetin according to claim 1, characterized in that: In step S3, the segmented vacuum pre-stripping tower adopts a two-section integrated structure, with the lower section being the stripping section and the upper section being the rectification section. The clarified crude ester liquid enters from the top of the lower section, and the vapor phase at the top of the stripping section enters the upper rectification section. 1% to 3% of the total mass of the light components condensed at the top of the vacuum coupled rectification tower is diverted as reflux liquid for the upper rectification section, and the liquid phase at the bottom of the upper rectification section is refluxed back to the lower stripping section.

8. The energy-saving distillation process for triacetin according to claim 1, characterized in that: In step S4, the acetic acid condensate obtained after condensing the high-temperature acetic acid gas from the top of the pressurized deacidification tower has a reflux rate controlled to be 1.0 to 2.0 times the mass of the feed gas phase, and the tower top temperature is controlled to be between 145°C and 158°C.

9. The energy-saving distillation process for triacetin according to claim 1, characterized in that: The vacuum-coupled distillation column has 32 to 38 theoretical plates, with the feed located on the 18th to 22nd theoretical plates and the side stream outlet located on the 6th to 8th theoretical plates in the stripping section. The reflux ratio at the top of the column is 2 to 4.

10. The energy-saving distillation process for triacetin according to claim 1, characterized in that: The pressurized deacidification tower and the vacuum-coupled distillation tower are interlocked. The operating pressure and heating load of the pressurized deacidification tower are adjusted according to the temperature difference between the top of the pressurized deacidification tower and the bottom of the vacuum-coupled distillation tower to maintain the heat transfer temperature difference between 12°C and 18°C. At the same time, the acetic acid condensate feed rate, the top reflux ratio, and the outflow ratio are adjusted synchronously according to the acetic acid concentration in the vacuum-coupled distillation tower and the acidity of the product sampled from the side stream. When the acetic acid concentration in the tower is below 1%, the acetic acid condensate feed rate is increased and the reflux ratio is decreased. When it is above 4%, the acetic acid condensate feed rate is decreased and the reflux ratio is increased. When the product acidity exceeds 0.008%, the outflow ratio is increased and the acetic acid condensate feed rate is decreased.

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