A flexible process for acetic acid ester production

Abstract

The present application relates to the technical field of chemical rectification, and particularly relates to a flexible preparation process of acetic ester. The process comprises the following steps: sending acetic acid and target alcohol into a reaction rectification tower for esterification to obtain a mixed product; sending the mixed product into a rectification tower for pressurized rectification, and taking the obtained gas phase in the top of the tower as the only heating medium to be introduced into a reboiler to drive the vaporization of the kettle; monitoring the liquid level and differential pressure change trend of the kettle to determine whether the liquid level is accurate; if not, determining the theoretical gas holdup interval according to the type of the feed alcohol and the operating pressure, and determining the reason in combination with the deviation degree of the liquid level and the differential pressure; performing targeted control based on the reason until the liquid level and the differential pressure are linearly correlated; and returning part of the condensate at the outlet of the reboiler to the tower and taking out part of the condensate. The present application realizes the accurate identification and self-adaptive regulation and control of the false liquid level of the kettle through the correlation monitoring of the liquid level and the differential pressure and the comparison of the gas holdup interval.

Description

Technical Field

[0001] This invention relates to the field of chemical distillation technology, and in particular to a flexible preparation process for acetate. Background Technology

[0002] Acetic acid esters are important organic chemical raw materials and solvents, widely used in coatings, adhesives, pharmaceuticals, and food additives. Their industrial production mainly involves the esterification reaction of acetic acid and alcohols under acid catalysts. With the increasing market demand for multi-variety, small-batch products, flexible production of acetate esters with different carbon chains on the same unit has become a trend. Reactive distillation technology is widely used due to its high conversion rate and low energy consumption. To reduce energy consumption, existing technologies use the high-temperature gas phase at the top of the product purification column as the sole heating medium for the reboiler of the reactive distillation column, utilizing the latent heat of condensation to drive vaporization in the reboiler. However, this heat-coupled process has the following problems: The boiling process in the reboiler carries a large number of bubbles, causing the level gauge reading to deviate from the actual liquid volume, i.e., a "false level." Under steady state, the gas holdup is relatively stable, but when flexibly switching between different carbon chain alcohols, the operating pressure needs to be adjusted accordingly. Rapid pressure changes cause nonlinear changes in bubble size and rising speed, resulting in drastic fluctuations in gas holdup and severe distortion of the level gauge reading. If liquid is drained or replenished based on the false signal, it may lead to the accidental discharge of liquid phase, causing the heat coupling to break, or excessive replenishment may lead to flooding and catalyst damage. Different carbon chain alcohols have significantly different surface tensions and viscosities, and their gas holdup is sensitive to pressure changes to varying degrees. Existing single liquid level control strategies are difficult to adapt to flexible switching.

[0003] Chinese Patent Publication No. CN103242158B discloses a novel process for synthesizing ethyl acetate. Specifically, it utilizes differential pressure thermal coupling combined with reactive distillation partitioned-wall column technology. While simplifying the original process and saving equipment investment using partitioned-wall column technology, the differential pressure thermal coupling technology leverages the pressure difference between the top and bottom of the partitioned-wall column to achieve heat exchange between the top vapor and the bottom distillate liquid phase, resulting in significant energy coupling and energy savings.

[0004] Therefore, the existing technology has the following problems:

[0005] It does not address the identification and control of false liquid levels in the tower bottom, and cannot solve the risks of liquid level measurement distortion and misoperation caused by air bubble entrainment under flexible switching conditions. Summary of the Invention

[0006] Therefore, the present invention provides a flexible preparation process for acetate to overcome the problems of the prior art which does not involve the identification and control of false liquid levels in the reboiler, and cannot solve the problems of liquid level measurement distortion and operation risk caused by bubble entrainment under flexible switching conditions.

[0007] To achieve the above objectives, the present invention provides a flexible preparation process for acetate, comprising:

[0008] Step S1: Acetic acid and target alcohol are mixed and fed into a reactive distillation column loaded with a supported cation exchange resin catalyst to carry out a heterogeneous catalytic esterification reaction, and a mixed product stream containing acetate is obtained.

[0009] Step S2: The mixed product stream is fed into a purification column for pressurized distillation to obtain the top gas phase. The top gas phase is then introduced into the reboiler of the reactive distillation column as the sole heating medium to drive the vaporization of the bottom of the reactive distillation column.

[0010] Step S3: Monitor the changing trends of the liquid level and differential pressure in the bottom of the reactive distillation column, and determine whether the liquid level in the bottom of the reactive distillation column is accurate based on the changing trends;

[0011] Step S4: In response to the inaccurate liquid level, obtain the current type of feed alcohol and operating pressure, determine the theoretical gas holdup range under the current operating pressure based on the type of feed alcohol, and determine the reason for the inaccurate liquid level based on the degree of deviation between the liquid level and the differential pressure and the theoretical gas holdup range.

[0012] Step S5: Implement targeted control based on the cause of inaccurate liquid level until the liquid level and differential pressure regain a linear correlation.

[0013] In step S6, the condensed stream from the reboiler outlet is divided into two streams: one stream is returned to the top of the refining tower, and the other stream is collected as the acetate product.

[0014] Further, in step S3, the changing trends of the liquid level and differential pressure in the reboiler of the reactive distillation column are monitored, including:

[0015] Step S31: Obtain the level gauge reading and differential pressure transmitter reading of the bottom of the reactive distillation column;

[0016] Step S32: Obtain the response delay time of the liquid level gauge reading and the differential pressure transmitter reading to the step change in feed flow rate, and record them as the first response delay time and the second response delay time.

[0017] Step S33: Calculate the difference between the first response delay time and the second response delay time;

[0018] If the difference is greater than a preset threshold and the first response delay time is less than the second response delay time, it is determined that the liquid level gauge reading is distorted due to the dynamic effect of bubbles. The liquid level gauge signal is corrected based on the response delay time of the differential pressure transmitter. The liquid level change trend is reconstructed based on the corrected signal. The differential pressure change trend is obtained by filtering the differential pressure transmitter signal.

[0019] If the difference is greater than a preset threshold and the second response delay time is less than the first response delay time, it is determined that the differential pressure transmitter reading is distorted due to the dynamic effect of bubbles. The differential pressure transmitter signal is corrected based on the response delay time of the level gauge, the differential pressure change trend is reconstructed with the corrected signal, and the level gauge signal after filtering is used as the level change trend.

[0020] If the difference is less than or equal to a preset threshold, the liquid level change trend and differential pressure change trend are directly constructed from the original signals.

[0021] Further, in step S3, determining whether the liquid level in the bottom of the reactive distillation column is accurate based on the changing trend includes:

[0022] If the trend of liquid level change is in the same direction as the trend of differential pressure change and the magnitude of change is proportional, then the liquid level is accurately determined.

[0023] If the trend of liquid level change is opposite to the trend of differential pressure change, or if the liquid level changes while the differential pressure remains unchanged, or if the differential pressure changes while the liquid level remains unchanged, then the liquid level is not accurately determined.

[0024] Further, in step S4, determining the theoretical gas holdup range at the current operating pressure based on the type of feed alcohol includes:

[0025] Step S41: Obtain the physical property parameters corresponding to the type of feed alcohol, including surface tension and viscosity;

[0026] Step S42: Determine the bubble stability coefficient of the feed alcohol type under different operating pressures based on the surface tension and viscosity.

[0027] Step S43: Determine the theoretical gas holdup range under the current operating pressure based on the current operating pressure and the bubble stability coefficient.

[0028] Further, in step S4, the reason for the inaccurate liquid level is determined based on the degree of deviation between the liquid level and the differential pressure and the theoretical gas holdup range, including:

[0029] Calculate the actual deviation between liquid level and differential pressure;

[0030] If the actual deviation exceeds the allowable deviation range of the theoretical gas holdup range, the inaccurate liquid level is determined to be a false liquid level caused by bubble entrainment.

[0031] If the actual deviation does not exceed the allowable deviation range of the theoretical gas holdup range, then the reason for the inaccurate liquid level is determined to be fluctuation in the actual liquid level.

[0032] Furthermore, in step S5, targeted control is implemented based on the cause of the inaccurate liquid level, including:

[0033] If the false liquid level is caused by bubble entrainment, then when the liquid level rises while the differential pressure remains unchanged or falls, liquid discharge is prohibited; when the liquid level falls while the differential pressure remains unchanged or rises, liquid replenishment is prohibited; and the operating pressure is adjusted back to the reference pressure corresponding to the type of alcohol in the feed.

[0034] If the cause is a genuine fluctuation in liquid level, then adjust the feed rate or output rate according to the direction of the liquid level change.

[0035] Furthermore, targeted control based on the causes of inaccurate liquid levels also includes:

[0036] If the false liquid level is caused by bubble entrainment, the pressure recovery rate is determined based on the real-time deviation between the liquid level and the differential pressure, and the recovery rate is positively correlated with the deviation; the operating pressure is then adjusted back to the reference pressure corresponding to the type of feed alcohol.

[0037] Furthermore, during the process of redirecting the operating pressure to the reference pressure, when the operating pressure enters the preset redirection dead zone and the deviation does not increase further, the redirection is paused and the current pressure is maintained for a preset observation period.

[0038] If the degree of deviation tends to decrease during the observation period, maintain the current pressure until the linear correlation is restored;

[0039] If the deviation widens again within the observation period, the pressure will be restored.

[0040] Furthermore, during the process of reverting the operating pressure to the reference pressure, the change in operating pressure is monitored in real time. If the operating pressure exceeds the reference pressure, the reversion is stopped and a reverse fine adjustment is performed to bring the operating pressure closer to the reference pressure.

[0041] Further, in step S5, the step of restoring a linear correlation between the liquid level and the differential pressure includes:

[0042] Real-time monitoring of the corrected liquid level change trend and differential pressure change trend; when both change in the same direction and the magnitude of change is proportional, it is determined to be a restored linear correlation.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows: This embodiment effectively identifies whether the sensor is distorted due to the dynamic effect of bubbles by comparing the response delay time of the level gauge and the differential pressure transmitter, and corrects the signal according to the source of distortion to ensure the accuracy of the trend of liquid level and differential pressure changes; by dynamically adjusting the preset threshold according to the type of feed alcohol and the operating pressure, the influence of the difference in bubble behavior under different carbon chain alcohol systems on the sensor response is fully compensated, improving the accuracy and adaptability of false liquid level identification; by extracting the trend of change by the moving window method and combining it with the same direction and proportional judgment criteria, the accuracy of the column bottom liquid level is quickly and accurately determined, providing a reliable judgment basis for subsequent steps, effectively avoiding the false discharge or false compensation operation caused by liquid level measurement distortion due to bubble entrainment, and ensuring the stable operation of the heat coupling system.

[0044] Furthermore, this embodiment achieves precise determination of the theoretical gas holdup range under different carbon chain alcohol systems by real-time acquisition of physical property parameters and dynamic calculation of bubble stability coefficient, combined with a pre-calibrated correlation curve of gas holdup-pressure-stability coefficient. It fully considers the influence of surface tension and viscosity differences of various alcohol types on bubble behavior, enabling the theoretical gas holdup range to adaptively adjust with the type of feed alcohol and operating pressure. By quantitatively comparing the actual deviation of liquid level and differential pressure with the allowable deviation range of theoretical gas holdup range, a clear diagnostic boundary for false liquid level and true liquid level fluctuations is constructed, avoiding the risk of misjudgment under different alcohol systems with a single fixed threshold. This ensures the accuracy and reliability of identifying the causes of inaccurate liquid level, providing a precise basis for subsequent differentiated control.

[0045] Furthermore, this embodiment employs a differentiated control strategy to eliminate abnormal bubbles at the source by prohibiting liquid discharge / replenishment combined with pressure reversal for false liquid levels, and to restore the liquid level by adjusting the balance of inlet and outlet for real liquid level fluctuations. This achieves precise management under different causes, avoiding thermal coupling breakage or equipment damage caused by misoperation, while ensuring the response speed and stability of liquid level control.

[0046] Furthermore, in this embodiment, by partially refluxing and partially collecting the condensate from the reboiler outlet, combined with real-time monitoring by the online analyzer and automatic adjustment of the reflux ratio, the separation effect of the purification tower and the purity of the acetate product are ensured. At the same time, the adjustment of the reflux ratio remains locked during the pressure recovery in step S5, avoiding mutual interference between the two control loops and ensuring the stability of product indicators during the flexible switching process. Attached Figure Description

[0047] Figure 1 This is a flowchart of the flexible acetate preparation process in this embodiment;

[0048] Figure 2This is a flowchart illustrating the process of determining the accuracy of the liquid level in the bottom of the reactive distillation column during the flexible preparation process of acetate in this embodiment.

[0049] Figure 3 This is a flowchart illustrating the process of determining the theoretical gas content range in the flexible preparation process of acetate in this embodiment. Detailed Implementation

[0050] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0051] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0052] Please see Figures 1-3 As shown, Figure 1 This is a flowchart of the flexible acetate preparation process in this embodiment; Figure 2 This is a flowchart illustrating the process of determining the accuracy of the liquid level in the bottom of the reactive distillation column during the flexible preparation process of acetate in this embodiment. Figure 3 This is a flowchart illustrating the process of determining the theoretical gas content range in the flexible preparation process of acetate in this embodiment.

[0053] This embodiment provides a flexible preparation process for acetate, including:

[0054] Step S1: Acetic acid and target alcohol are mixed and fed into a reactive distillation column loaded with a supported cation exchange resin catalyst to carry out a heterogeneous catalytic esterification reaction, and a mixed product stream containing acetate is obtained.

[0055] Step S2: The mixed product stream is fed into a purification column for pressurized distillation to obtain the top gas phase. The top gas phase is then introduced into the reboiler of the reactive distillation column as the sole heating medium to drive the vaporization of the bottom of the reactive distillation column.

[0056] Step S3: Monitor the changing trends of the liquid level and differential pressure in the bottom of the reactive distillation column, and determine whether the liquid level in the bottom of the reactive distillation column is accurate based on the changing trends;

[0057] Step S4: In response to the inaccurate liquid level, obtain the current type of feed alcohol and operating pressure, determine the theoretical gas holdup range under the current operating pressure based on the type of feed alcohol, and determine the reason for the inaccurate liquid level based on the degree of deviation between the liquid level and the differential pressure and the theoretical gas holdup range.

[0058] Step S5: Implement targeted control based on the cause of inaccurate liquid level until the liquid level and differential pressure regain a linear correlation.

[0059] In step S6, the condensed stream from the reboiler outlet is divided into two streams: one stream is returned to the top of the refining tower, and the other stream is collected as the acetate product.

[0060] In this embodiment, acetic acid and the target alcohol (such as any one of methanol, ethanol, n-propanol, or n-butanol) are mixed at an alcohol-acid molar ratio of 1.05:1 to 1.5:1. After preheating to 70-90°C, the mixture is continuously fed from above the reaction section of a reactive distillation column. The reactive distillation column has 25-40 theoretical plates, with the reaction section located on plates 10 to 30. The reaction section is loaded with a supported cation exchange resin catalyst (such as Amberlyst-15 or D002 type macroporous strong acid cation exchange resin), and the catalyst loading is 30%-60% of the reaction section volume. The operating pressure of the reactive distillation column is adjusted according to the target product: 0.1-0.3 MPa for the production of methyl acetate, 0.2-0.4 MPa for the production of ethyl acetate, and 0.3-0.6 MPa for the production of butyl acetate. The temperature of the reaction section is controlled at 70-120℃. Acetic acid and the target alcohol undergo heterogeneous catalytic esterification under the action of a catalyst. The generated acetate and water form a minimum azeotrope and are distilled off from the top of the column. Unreacted acetic acid and heavy components fall into the bottom of the column. The top of the column is collected, condensed and separated, and partially refluxed to obtain a mixed product stream containing acetate. The crude product containing acetate is continuously collected from the bottom of the column.

[0061] In this embodiment, the crude acetate-containing product stream continuously collected from the bottom of the reactive distillation column is fed into a purification column for pressurized distillation. The purification column has 20-35 theoretical trays, with the feed located on trays 12-20, and the operating pressure controlled at 0.3-1.0 MPa. The bottom temperature of the purification column is controlled at 110-160°C, and the top temperature is adjusted accordingly with changes in the operating pressure. By adjusting the operating pressure of the purification column, the top vapor temperature is raised to 100-150°C. This high-temperature vapor phase at the top is directly introduced into the shell side of the reboiler of the reactive distillation column without condensation, serving as the sole heating medium for the reboiler. The latent heat released during the condensation of this high-temperature vapor phase heats the bottom liquid of the reactive distillation column, causing it to vaporize and generate rising steam, providing the vapor load required for distillation in the reactive distillation column. After condensation in the shell side of the reboiler, the high-temperature vapor phase at the top of the purification column becomes a liquid phase, and the condensate temperature at the tube side outlet of the reboiler is controlled at 90-130°C.

[0062] In this embodiment, when the target alcohol is methanol, the operating pressure of the purification column is 0.3–0.5 MPa, and the top vapor temperature is 100–120°C; when the target alcohol is ethanol, the operating pressure of the purification column is 0.4–0.7 MPa, and the top vapor temperature is 110–135°C; when the target alcohol is n-butanol, the operating pressure of the purification column is 0.6–1.0 MPa, and the top vapor temperature is 130–150°C.

[0063] Specifically, in step S3, monitoring the changing trends of the liquid level and differential pressure in the reboiler of the reactive distillation column includes:

[0064] Step S31: Obtain the level gauge reading and differential pressure transmitter reading of the bottom of the reactive distillation column;

[0065] Step S32: Obtain the response delay time of the liquid level gauge reading and the differential pressure transmitter reading to the step change in feed flow rate, and record them as the first response delay time and the second response delay time.

[0066] Step S33: Calculate the difference between the first response delay time and the second response delay time;

[0067] If the difference is greater than a preset threshold and the first response delay time is less than the second response delay time, it is determined that the liquid level gauge reading is distorted due to the dynamic effect of bubbles. The liquid level gauge signal is corrected based on the response delay time of the differential pressure transmitter. The liquid level change trend is reconstructed based on the corrected signal. The differential pressure change trend is obtained by filtering the differential pressure transmitter signal.

[0068] If the difference is greater than a preset threshold and the second response delay time is less than the first response delay time, it is determined that the differential pressure transmitter reading is distorted due to the dynamic effect of bubbles. The differential pressure transmitter signal is corrected based on the response delay time of the level gauge, the differential pressure change trend is reconstructed with the corrected signal, and the level gauge signal after filtering is used as the level change trend.

[0069] If the difference is less than or equal to a preset threshold, the liquid level change trend and differential pressure change trend are directly constructed from the original signals.

[0070] Specifically, in step S3, determining whether the liquid level in the bottom of the reactive distillation column is accurate based on the changing trend includes:

[0071] If the trend of liquid level change is in the same direction as the trend of differential pressure change and the magnitude of change is proportional, then the liquid level is accurately determined.

[0072] If the trend of liquid level change is opposite to the trend of differential pressure change, or if the liquid level changes while the differential pressure remains unchanged, or if the differential pressure changes while the liquid level remains unchanged, then the liquid level is not accurately determined.

[0073] In this embodiment, a level gauge and a differential pressure transmitter are installed in the reboiler of the reactive distillation column to collect the reboiler level and differential pressure signals in real time. The level gauge is a radar level gauge, installed on the lower side of the reboiler, with a range of 0–3 m and an accuracy of ±0.5%FS. The differential pressure transmitter is installed between the upper and lower pressure taps of the reboiler, with a tap spacing of 2.0 m, a range of 0–100 kPa, and an accuracy of ±0.1%FS. Signals from both instruments are transmitted to the DCS control system in 4–20 mA analog form, with a sampling period of 1 second.

[0074] The DCS control system continuously acquires the level gauge readings and differential pressure transmitter readings from the bottom of the reactive distillation column. The sampled data is stored in a real-time database after signal isolation and A / D conversion. Under the premise that the reactive distillation column is in steady-state operation and the type of feed alcohol remains constant, the DCS control system sends a step disturbance signal to the feed flow control valve (increasing the feed flow rate from 80% to 120% of the rated value, maintaining the disturbance for 30 seconds). The response trajectories of the level gauge readings and differential pressure transmitter readings to this step change in feed flow rate are recorded. From the moment the step disturbance is applied, the time required for the level gauge readings and differential pressure transmitter readings to reach 63.2% of their respective steady-state change values ​​is recorded as the first response delay time. Second response delay time To ensure data reliability, the step disturbance test was repeated three times, and the results were calculated each time. and The average value.

[0075] The DCS control system calculates the first response delay time. With the second response delay time The difference Δt = | - |. If Δt is greater than the preset threshold and < This indicates that the level gauge responds significantly faster to flow disturbances than the differential pressure transmitter. In other words, the level gauge reading is distorted by the rapid dynamic effect of bubble expansion / contraction. Therefore, the response delay time of the differential pressure transmitter is used as the primary indicator. Based on this, a time constant matching correction is performed on the level gauge signal. Specifically, a first-order inertial filter is applied to the original level gauge signal, and its time constant is taken as... and The difference is used to reconstruct the liquid level change trend with the corrected signal; at the same time, the differential pressure transmitter signal is used as the differential pressure change trend after low-pass filtering (the filtering time constant is 8s).

[0076] If Δt is greater than the preset threshold and < This indicates that the differential pressure transmitter reading is distorted due to the dynamic effect of bubbles, as shown by the response delay time of the level gauge. Based on this, the differential pressure transmitter signal is corrected by time constant matching, and the differential pressure change trend is reconstructed using the corrected signal; simultaneously, the level gauge signal is used as the level change trend after low-pass filtering. If Δt is less than or equal to a preset threshold, it indicates that the response speeds of the two sensors are similar, and the dynamic effect of bubbles has a basically consistent impact on the readings of both. The level change trend and differential pressure change trend are then directly constructed using the filtered values ​​of the original signals, respectively.

[0077] In this embodiment, the preset threshold is determined as follows: the preset threshold base value corresponding to the current type of feed alcohol is taken. The methanol system =1.5s, ethanol system =2.5s, n-propanol system =3.5s, n-Butanol system =4.5s. Each reference value is pre-calibrated as follows: Under steady-state operation of the reactive distillation column and with stable gas holdup, a standard step disturbance (feed flow rate increases from 80% to 120% of the rated value, repeated 3 times) is applied to the level gauge and differential pressure transmitter, respectively. The response delay time of each sensor is recorded and the difference is calculated. The average of the response delay time differences measured under steady-state conditions is multiplied by a safety factor of 1.3, which serves as the basic preset threshold for this type of alcohol. In step S33, the preset threshold is further corrected based on the current operating pressure: when the operating pressure deviates from the reference operating pressure for this type of alcohol (methanol 0.2MPa, ethanol 0.3MPa, n-propanol 0.45MPa, n-butanol 0.6MPa), the threshold is adjusted according to formula T = +k×(P- ) Calculate the corrected threshold, where The reference operating pressure is P, the current operating pressure is k, and the pressure correction factor is -3 s / MPa. As the pressure increases, the bubble response accelerates, the difference in response delay time decreases, and the threshold is lowered; as the pressure decreases, the bubble response slows down, the difference increases, and the threshold is raised.

[0078] In this embodiment, both the liquid level change trend and the differential pressure change trend are extracted using the moving window method. The width of the moving window is determined as follows: it is four times the average response delay time of the current feed alcohol type, and is no less than 30s and no more than 60s. Specifically, the window width is 35s for the methanol system, 40s for the ethanol system, 48s for the n-propanol system, and 55s for the n-butanol system. The reason why the window width increases with the carbon chain length of the alcohol is that in the high-carbon-chain alcohol system, the bubble size is larger and the movement speed is slower, and the time scale of gas content change is longer, requiring a wider window to fully capture the change trend. The signal within the window is linearly fitted using the least squares method. The slope of the fitted line is the change trend value at that moment, the sign indicates the direction of change (positive for increase, negative for decrease), and the absolute value indicates the rate of change. The DCS control system calculates and updates the two change trends in real time with an update cycle of 8s.

[0079] In this embodiment, determining whether the liquid level in the reboiler of the reactive distillation column is accurate based on the changing trend includes: if the liquid level changing trend is in the same direction as the differential pressure changing trend and the change magnitude is proportional (the deviation between the ratio of their changing rates and the theoretical value of the product of the reboiler cross-sectional area and the liquid density is within ±5%), then the liquid level is determined to be accurate; if the liquid level changing trend is opposite to the differential pressure changing trend, or the liquid level changes while the differential pressure remains unchanged, or the differential pressure changes while the liquid level remains unchanged, then the liquid level is determined to be inaccurate.

[0080] This embodiment effectively identifies whether the sensor is distorted due to the dynamic effect of bubbles by comparing the response delay time of the level gauge and the differential pressure transmitter. Signal correction is then performed according to the source of distortion to ensure the accuracy of the level and differential pressure change trends. By dynamically adjusting the preset threshold according to the type of feed alcohol and operating pressure, the influence of differences in bubble behavior under different carbon chain alcohol systems on the sensor response is fully compensated, improving the accuracy and adaptability of false level identification. By extracting the change trend using the moving window method and combining it with a proportional judgment criterion, the accuracy of the column bottom level is quickly and accurately determined, providing a reliable basis for subsequent steps. This effectively avoids erroneous leveling or replenishment operations caused by level measurement distortion due to bubble entrainment, ensuring the stable operation of the heat-coupled system.

[0081] Specifically, in step S4, determining the theoretical gas holdup range at the current operating pressure based on the type of feed alcohol includes:

[0082] Step S41: Obtain the physical property parameters corresponding to the type of feed alcohol, including surface tension and viscosity;

[0083] Step S42: Determine the bubble stability coefficient of the feed alcohol type under different operating pressures based on the surface tension and viscosity.

[0084] Step S43: Determine the theoretical gas holdup range under the current operating pressure based on the current operating pressure and the bubble stability coefficient.

[0085] In this embodiment, the DCS control system reads the type of feed alcohol from the currently running production formula on the host computer, acquires the current operating pressure in real time from the pressure transmitter at the top of the reactive distillation column, and calls up the physical property parameter table pre-stored in the DCS control system. This physical property parameter table contains the surface tension and viscosity data of each type of alcohol at different temperatures. Based on the reboiler temperature corresponding to the current operating pressure (acquired in real time by the reboiler temperature transmitter), the surface tension σ and viscosity μ at that temperature are read from the physical property parameter table.

[0086] In this embodiment, the physical properties of each alcohol type under typical operating conditions are as follows: methanol (20℃, σ=22.6mN / m, μ=0.59 mPa·s), ethanol (20℃, σ=22.3 mN / m, μ=1.20 mPa·s), n-propanol (20℃, σ=23.8mN / m, μ=2.26 mPa·s), and n-butanol (20℃, σ=24.6 mN / m, μ=2.95 mPa·s). In actual use, the physical properties are corrected for temperature based on the current reboiler temperature. The DCS control system determines the bubble stability coefficient S of the feed alcohol type under the current operating pressure based on the surface tension and viscosity, specifically calculated using the formula S = μ / σ. A larger S value indicates more stable bubbles and a higher corresponding gas holdup; a smaller S value indicates that the bubbles are more prone to breakage and a lower corresponding gas holdup. Calculations showed that the bubble stability coefficients (S) for each alcohol type at 20℃ were: methanol 0.026, ethanol 0.054, n-propanol 0.095, and n-butanol 0.120. It is evident that as the carbon chain length of the alcohol increases, the S value increases significantly, and the bubble stability rises sharply. Higher-chain alcohol systems are more likely to form stable bubble layers in the bottom of the column, resulting in higher gas holdup. This perfectly aligns with the industrial reality that higher-chain alcohol columns are more prone to producing false liquid levels in the bottom.

[0087] The DCS control system determines the theoretical gas holdup range under the current operating pressure based on the current operating pressure and the bubble stability coefficient. Specifically, the current operating pressure P and the bubble stability coefficient S are substituted into a pre-calibrated gas holdup-pressure-stability coefficient correlation curve to read the corresponding theoretical gas holdup range. This correlation curve is pre-calibrated as follows: On a laboratory cold model, using various alcohols as the liquid medium, under different operating pressures (0.1–1.0 MPa, step size 0.05 MPa) and different gas velocities, the gas holdup is measured using resistivity tomography, and the corresponding bubble stability coefficient S is recorded. A mapping relationship between the S value and the gas holdup under different pressures is established. After multiple experiments and averaging, the normal fluctuation range of the gas holdup within the 95% confidence interval under each operating condition is determined, which is the theoretical gas holdup range under that operating condition.

[0088] Specifically, in step S4, the reasons for the inaccurate liquid level are determined based on the degree of deviation between the liquid level and the differential pressure and the theoretical gas holdup range, including:

[0089] Calculate the actual deviation between liquid level and differential pressure;

[0090] If the actual deviation exceeds the allowable deviation range of the theoretical gas holdup range, the inaccurate liquid level is determined to be a false liquid level caused by bubble entrainment.

[0091] If the actual deviation does not exceed the allowable deviation range of the theoretical gas holdup range, then the reason for the inaccurate liquid level is determined to be fluctuation in the actual liquid level.

[0092] In this embodiment, the DCS control system calculates the ratio of the liquid level change rate to the differential pressure change rate, R = |ΔL / Δt| / |ΔP / Δt|, and then calculates the theoretical value of the product of R and the cross-sectional area of ​​the column bottom and the liquid density. By comparison, the actual deviation is obtained as D = |R - | / ×100%. Of which... The method for determining it is as follows: =A×ρ, where A is the cross-sectional area of ​​the column bottom (m²), and ρ is the density of the crude ester product at the current temperature (kg / m³). A is obtained from the column design parameters, and ρ is collected in real time by an online density meter. The deviation degree D is compared with the allowable deviation range of the theoretical gas holdup determined in step S43.

[0093] The allowable deviation range of the theoretical gas holdup interval is determined as follows: Lower limit of deviation range = Lower limit of theoretical gas holdup × (1-α), Upper limit of deviation range = Upper limit of theoretical gas holdup × (1+α), where α is the allowable fluctuation coefficient related to the type of feed alcohol, 0.12 for methanol system, 0.18 for ethanol system, 0.22 for n-propanol system, and 0.28 for n-butanol system. α increases with the carbon chain length of the alcohol because high-chain alcohol systems have high surface tension and stable bubbles, resulting in a wider natural fluctuation range of gas holdup. If the actual deviation D exceeds the allowable deviation range of the theoretical gas holdup interval, the inaccurate liquid level is determined to be a false liquid level caused by bubble entrainment; if the actual deviation D does not exceed the allowable deviation range of the theoretical gas holdup interval, the inaccurate liquid level is determined to be due to fluctuations in the true liquid level.

[0094] This embodiment achieves precise determination of the theoretical gas holdup range under different carbon chain alcohol systems by real-time acquisition of physical property parameters and dynamic calculation of bubble stability coefficient, combined with a pre-calibrated correlation curve of gas holdup-pressure-stability coefficient. It fully considers the influence of surface tension and viscosity differences of various alcohols on bubble behavior, enabling the theoretical gas holdup range to adaptively adjust with the type of feed alcohol and operating pressure. By quantitatively comparing the actual deviation of liquid level and differential pressure with the allowable deviation range of theoretical gas holdup, a clear diagnostic boundary for false liquid level and true liquid level fluctuations is constructed, avoiding the risk of misjudgment under different alcohol systems with a single fixed threshold. This ensures the accuracy and reliability of identifying the causes of inaccurate liquid level and provides a precise basis for subsequent differentiated control.

[0095] Specifically, in step S5, targeted control is implemented based on the cause of the inaccurate liquid level, including:

[0096] If the false liquid level is caused by bubble entrainment, then when the liquid level rises while the differential pressure remains unchanged or falls, liquid discharge is prohibited; when the liquid level falls while the differential pressure remains unchanged or rises, liquid replenishment is prohibited; and the operating pressure is adjusted back to the reference pressure corresponding to the type of alcohol in the feed.

[0097] If the cause is a genuine fluctuation in liquid level, then adjust the feed rate or output rate according to the direction of the liquid level change.

[0098] Specifically, targeted control measures based on the causes of inaccurate liquid levels also include:

[0099] If the false liquid level is caused by bubble entrainment, the pressure recovery rate is determined based on the real-time deviation between the liquid level and the differential pressure, and the recovery rate is positively correlated with the deviation; the operating pressure is then adjusted back to the reference pressure corresponding to the type of feed alcohol.

[0100] Specifically, during the process of redirecting the operating pressure to the reference pressure, when the operating pressure enters the preset redirection dead zone and the deviation does not increase further, the redirection is paused and the current pressure is maintained for a preset observation period.

[0101] If the degree of deviation tends to decrease during the observation period, maintain the current pressure until the linear correlation is restored;

[0102] If the deviation widens again within the observation period, the pressure will be restored.

[0103] Specifically, during the process of reverting the operating pressure to the reference pressure, the change in operating pressure is monitored in real time. If the operating pressure exceeds the reference pressure, the reverting is stopped and a reverse fine-tuning is performed to bring the operating pressure back to the reference pressure.

[0104] In this embodiment, if the false liquid level is caused by bubble entrainment, the following control logic is executed: First, the draining or replenishing operation is prohibited according to the direction of change of liquid level and differential pressure. When an upward trend in liquid level is detected while the differential pressure remains unchanged or decreases, it is determined that the liquid level is falsely high due to bubble expansion. The DCS control system sends a prohibition signal to the frequency converter of the drain pump in the tower bottom, and the drain pump remains closed, while maintaining the feed rate and output rate unchanged. When a downward trend in liquid level is detected while the differential pressure remains unchanged or increases, it is determined that the falsely low liquid level is falsely low due to bubble contraction. The DCS control system sends a prohibition signal to the replenishing valve in the tower bottom, and the replenishing valve remains closed, while maintaining the feed rate and output rate unchanged.

[0105] Then, the pressure callback procedure is initiated, redirecting the operating pressure to the reference pressure corresponding to the type of feed alcohol. Pullback. Baseline resistance. The initial reference pressure for each feed alcohol type is determined as follows: Based on the normal operating pressure range of different feed alcohol types (methanol 0.1–0.3 MPa, ethanol 0.2–0.4 MPa, n-propanol 0.3–0.5 MPa, n-butanol 0.4–0.6 MPa), the median value is taken as the initial reference pressure for that alcohol type (methanol 0.2 MPa, ethanol 0.3 MPa, n-propanol 0.4 MPa, n-butanol 0.5 MPa). During long-term operation of the unit, after each successful restoration of linear correlation, the operating pressure at the time of restoration is recorded and updated as the reference pressure for that feed alcohol type under the current operating conditions.

[0106] The pressure recovery rate is determined based on the real-time deviation between the liquid level and the differential pressure, and the recovery rate is positively correlated with the deviation. Specifically, the larger the deviation D, the larger the pressure adjustment step size; the smaller the deviation D, the smaller the pressure adjustment step size. The adjustment step size ΔP is determined by the following formula: ΔP = Kp × (D - ... ), where D is the current degree of deviation, Kp represents the upper limit of the deviation range, and Kp is the proportional gain, taken as 0.008 MPa / %.

[0107] When the operating pressure enters the preset callback dead zone (i.e., the current pressure P and the reference pressure), If the deviation is ≤ ±0.02 MPa and the deviation does not increase further, the pressure pullback is paused and the current pressure is maintained for a preset observation period. The observation period is determined as follows: take 8 times the average response delay time corresponding to the current feed alcohol type, and not less than 60 s. If the deviation tends to decrease within the observation period (i.e., D continuously decreases and the rate of decrease is >0.5% / min), the system is considered to be stabilizing, and the current pressure is maintained until the liquid level and differential pressure return to a linear correlation; if the deviation increases again within the observation period (i.e., D continuously increases and the rate of increase is >0.5% / min), the pullback is considered insufficient, and the pressure pullback is resumed.

[0108] During the pressure pullback process, the operating pressure changes are monitored in real time. If the operating pressure exceeds the reference pressure... The DCS control system immediately stops the pullback and issues a reverse fine-tuning command, using ±0.01 MPa of the reference pressure as the control target for fine adjustment, causing the operating pressure to converge towards the reference pressure. If the cause is actual liquid level fluctuation, the feed rate or output rate is adjusted according to the direction of liquid level change. When the liquid level is rising, the DCS control system appropriately closes the feed regulating valve (each adjustment not exceeding 5% of the current feed rate) or appropriately opens the bottom outlet regulating valve (each adjustment not exceeding 3% of the current output rate); when the liquid level is falling, the feed regulating valve is appropriately opened or the bottom outlet regulating valve is closed, using the same adjustment method. After each adjustment, maintain an observation interval of no less than 60 seconds, and determine whether further adjustment is needed after the liquid level stabilizes.

[0109] This embodiment uses the aforementioned differentiated control strategy to eliminate abnormal bubbles at the source by prohibiting liquid discharge / replenishment and combining pressure callback for false liquid levels, and to restore the liquid level by adjusting the balance of feed and discharge for real liquid level fluctuations. This achieves precise treatment under different causes, avoiding thermal coupling breakage or equipment damage caused by misoperation, and ensuring the response speed and stability of liquid level control.

[0110] Specifically, in step S5, the step of restoring a linear correlation between the liquid level and the differential pressure includes:

[0111] Real-time monitoring of the corrected liquid level change trend and differential pressure change trend; when both change in the same direction and the magnitude of change is proportional, it is determined to be a restored linear correlation.

[0112] In this embodiment, the DCS control system continuously monitors the changing trends of liquid level and differential pressure. When both change in the same direction and their magnitudes are proportional, it is determined that the linear correlation has been restored. At this point, the control logic in step S5 exits, and normal liquid level control resumes. The criteria for determining the restoration of linear correlation are: the changing trends of liquid level and differential pressure are in the same direction, and the ratio of their changing rates R to the theoretical value... The deviation is within ±5%.

[0113] Specifically, in step S6, the condensed stream from the reboiler outlet is divided into two streams: one stream is returned to the top of the refining tower, and the other stream is collected as an acetate product.

[0114] In this embodiment, the condensate stream from the tube side outlet of the reactive distillation column (i.e., the liquid stream formed after the high-temperature gas phase at the top of the reboiler condenses in the shell side of the reboiler) is buffered in a condensate collection tank and then divided into two streams. The first stream is returned to the top of the refining column as reflux, and the reflux ratio is set and adjusted according to the target alcohol type and the target product purity requirements. The reflux ratio ranges for different target alcohol systems are as follows: 1.5–3.0 for methanol, 2.0–4.0 for ethanol, 2.5–4.5 for n-propanol, and 2.5–5.0 for n-butanol. The adjustment of the reflux ratio is executed by the automatic control loop of the reflux ratio at the top of the refining column. The second stream is collected as acetate product, cooled to below 40°C by a product cooler, and then sent to the product storage tank.

[0115] The distribution ratio of the two streams is automatically adjusted in real time by the refining column's overhead reflux ratio control loop based on the composition of the overhead product. An online gas chromatograph is installed at the top of the refining column to continuously monitor the acetate content in the overhead distillate. When the acetate content in the overhead product is ≥99.5 wt%, the DCS control system maintains the current reflux ratio unchanged; when the acetate content is below 99.5 wt%, the DCS control system automatically increases the reflux ratio, with each adjustment not exceeding 0.2, to improve the distillation separation effect until the product meets the requirements; when the acetate content is much higher than 99.5 wt% (e.g., ≥99.9 wt%) and the column top temperature is stable, the DCS control system automatically decreases the reflux ratio, with each adjustment not exceeding 0.2, to reduce energy consumption and the liquid load within the column.

[0116] In this embodiment, after the vapor phase at the top of the purification column condenses in the shell side of the reboiler, the latent heat of condensation released is used to heat the bottom liquid of the reactive distillation column, achieving thermal coupling between the two columns. This allows the normal vaporization load of the reactive distillation column to be maintained without an external heat source. The condensate temperature at the reboiler tube side outlet is controlled between 90 and 130°C. This temperature is indirectly controlled by the operating pressure of the purification column, ensuring that the condensate has sufficient heat to drive the vaporization of the bottom liquid in the reactive distillation column, while simultaneously preventing excessively high condensate temperatures that would increase the subsequent cooling load.

[0117] In this embodiment, the reflux ratio setting in step S6 is also affected by the control state of step S5: when step S5 is in the pressure recovery process due to false liquid level determination, the reflux ratio remains unchanged until the liquid level returns to linear correlation, and then is adjusted according to the product composition to avoid coupling disturbance to the separation effect of the purification tower when pressure recovery and reflux ratio adjustment are carried out simultaneously. When step S5 is in normal operation (non-false liquid level control), the reflux ratio adjustment logic is normally put into operation. In this embodiment, the acetate product output is determined by the purification tower bottom liquid level control loop to ensure the material balance of the purification tower. After cooling, the product output is sent to the product storage tank. The purity of acetate in the product is not less than 99.5 wt%, the water content is not more than 0.1 wt%, and the acid value is not more than 0.05 mg KOH / g.

[0118] This embodiment ensures the separation effect of the purification tower and the purity of the acetate product by partially refluxing and partially collecting the condensate from the reboiler outlet, combined with real-time monitoring by the online analyzer and automatic adjustment of the reflux ratio. At the same time, the reflux ratio adjustment remains locked during the pressure recovery in step S5, avoiding mutual interference between the two control loops and ensuring the stability of product indicators during the flexible switching process.

[0119] In this embodiment, a pilot-scale reactive distillation-heat coupling device was used for comparative experiments. The reactive distillation column had an inner diameter of DN300, a height of 15m, and 35 theoretical plates. Plates 12 to 28 of the reaction section were loaded with Amberlyst-15 catalyst, with a loading volume of 50L. The refining column had an inner diameter of DN250, a height of 12m, and 28 theoretical plates. The two columns were heat-coupled via a reboiler-top vapor pipeline. The DCS control system used a Honeywell PKS C300 for data acquisition and control logic execution. The experimental raw materials were acetic acid (industrial grade, purity not less than 99.5wt%), methanol (industrial grade, purity not less than 99.9wt%), ethanol (industrial grade, purity not less than 99.5wt%), and n-butanol (industrial grade, purity not less than 99.5wt%). Four comparative schemes were set up in the experiment:

[0120] Comparative Example 1 uses conventional single-level gauge PID control without differential pressure monitoring;

[0121] Comparative Example 2 uses liquid level and differential pressure monitoring, but the preset threshold is a fixed value of 2.5s, which is not adjusted according to the type of alcohol and the operating pressure;

[0122] Comparative Example 3 uses liquid level and differential pressure monitoring and dynamic thresholds, but after identifying false liquid levels, it only prohibits liquid discharge or replenishment, and does not perform pressure callback control;

[0123] This embodiment uses liquid level and differential pressure monitoring combined with dynamic threshold determination, and executes complete control logic including variable rate pressure callback, callback dead zone observation and over-adjustment protection after identifying false liquid levels.

[0124] The experimental procedure was as follows: First, methanol was fed as the raw material at an alcohol-acid molar ratio of 1.2:1. The operating pressure of the reactive distillation column was 0.2 MPa, and steady-state data was recorded after 4 hours of stable operation. Then, over 2 hours, the feed alcohol was gradually switched from methanol to ethanol, maintaining the alcohol-acid molar ratio at 1.2:1, and the operating pressure was adjusted from 0.2 MPa to 0.3 MPa. After the ethanol system had been running stably for 4 hours, the feed alcohol was gradually switched from ethanol to n-butanol over 2 hours, and the operating pressure was adjusted from 0.3 MPa to 0.5 MPa. The experiment was terminated after the n-butanol system had been running stably for 4 hours. The above steps were repeated 3 times for each control group, and the average value was taken.

[0125] Table 1 compares the accuracy of false liquid level detection under different control schemes:

[0126] Table 1

[0127] Comparative Example 1 lacks differential pressure monitoring and cannot identify false liquid levels, misjudging all changes as genuine liquid level changes.

[0128] Table 2 shows a comparison of liquid level control deviations under different control schemes:

[0129] Table 2

[0130] The recovery time is the time required for the liquid level to recover to within ±50mm of the set value after deviating from its set value.

[0131] Table 3 compares the thermal coupling stability under different control schemes:

[0132] Table 3

[0133] Table 4 shows the verification results of the theoretical gas holdup range under different alcohol systems:

[0134] Table 4

[0135] Table 5 compares product quality under different control schemes:

[0136] Table 5

[0137] The product qualification rate refers to the percentage of time during which the product purity is not less than 99.5wt% throughout the entire switching process.

[0138] Based on the above experimental data, this embodiment has the following technical advantages compared to the comparative examples: the false liquid level identification accuracy reaches 95.7%, which is about 14 percentage points higher than comparative examples 2 and 3, and an order of magnitude higher than comparative example 1; the maximum liquid level deviation during the flexible switching process is only 68 mm, and the liquid level recovery time is only 8 min, which are about 59% and 66% shorter than comparative examples 2 and 3, respectively; there is no interruption of heat coupling throughout the process, and the reboiler heat flux fluctuation is only ±7%; the prediction accuracy of the theoretical gas content range under the three alcohol systems is greater than 95%; the product purity is 99.6 wt%, and the pass rate is 94%. The above experimental data fully demonstrate the significant superiority of the process described in this application in terms of false liquid level identification accuracy, liquid level control precision, heat coupling stability, adaptability to different alcohol systems, and product yield.

[0139] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A flexible preparation process for acetate, characterized in that, include: Step S1: Acetic acid and target alcohol are mixed and fed into a reactive distillation column loaded with a supported cation exchange resin catalyst to carry out a heterogeneous catalytic esterification reaction, and a mixed product stream containing acetate is obtained. Step S2: The mixed product stream is fed into a purification column for pressurized distillation to obtain the top gas phase. The top gas phase is then introduced into the reboiler of the reactive distillation column as the sole heating medium to drive the vaporization of the bottom of the reactive distillation column. Step S3: Monitor the changing trends of the liquid level and differential pressure in the bottom of the reactive distillation column, and determine whether the liquid level in the bottom of the reactive distillation column is accurate based on the changing trends; Step S4: In response to the inaccurate liquid level, obtain the current type of feed alcohol and operating pressure, determine the theoretical gas holdup range under the current operating pressure based on the type of feed alcohol, and determine the reason for the inaccurate liquid level based on the degree of deviation between the liquid level and the differential pressure and the theoretical gas holdup range. Step S5: Implement targeted control based on the cause of inaccurate liquid level until the liquid level and differential pressure regain a linear correlation. In step S6, the condensed stream from the reboiler outlet is divided into two streams: one stream is returned to the top of the refining tower, and the other stream is collected as the acetate product.

2. The acetate flexibility preparation process according to claim 1, characterized in that, In step S3, the changes in the liquid level and differential pressure in the reboiler of the reactive distillation column are monitored, including: Step S31: Obtain the level gauge reading and differential pressure transmitter reading of the bottom of the reactive distillation column; Step S32: Obtain the response delay time of the liquid level gauge reading and the differential pressure transmitter reading to the step change in feed flow rate, and record them as the first response delay time and the second response delay time. Step S33: Calculate the difference between the first response delay time and the second response delay time; If the difference is greater than a preset threshold and the first response delay time is less than the second response delay time, it is determined that the liquid level gauge reading is distorted due to the dynamic effect of bubbles. The liquid level gauge signal is corrected based on the response delay time of the differential pressure transmitter. The liquid level change trend is reconstructed based on the corrected signal. The differential pressure change trend is obtained by filtering the differential pressure transmitter signal. If the difference is greater than a preset threshold and the second response delay time is less than the first response delay time, it is determined that the differential pressure transmitter reading is distorted due to the dynamic effect of bubbles. The differential pressure transmitter signal is corrected based on the response delay time of the level gauge, the differential pressure change trend is reconstructed with the corrected signal, and the level gauge signal after filtering is used as the level change trend. If the difference is less than or equal to a preset threshold, the liquid level change trend and differential pressure change trend are directly constructed from the original signals.

3. The flexible preparation process of acetate according to claim 1, characterized in that, In step S3, determining whether the liquid level in the bottom of the reactive distillation column is accurate based on the changing trend includes: If the trend of liquid level change is in the same direction as the trend of differential pressure change and the magnitude of change is proportional, then the liquid level is accurately determined. If the trend of liquid level change is opposite to the trend of differential pressure change, or if the liquid level changes while the differential pressure remains unchanged, or if the differential pressure changes while the liquid level remains unchanged, then the liquid level is not accurately determined.

4. The flexible preparation process of acetate according to claim 1, characterized in that, In step S4, the theoretical gas holdup range at the current operating pressure is determined based on the type of feed alcohol, including: Step S41: Obtain the physical property parameters corresponding to the type of feed alcohol, including surface tension and viscosity; Step S42: Determine the bubble stability coefficient of the feed alcohol type under different operating pressures based on the surface tension and viscosity. Step S43: Determine the theoretical gas holdup range under the current operating pressure based on the current operating pressure and the bubble stability coefficient.

5. The flexible preparation process of acetate according to claim 1, characterized in that, In step S4, the reasons for the inaccurate liquid level are determined based on the degree of deviation between the liquid level and the differential pressure and the theoretical gas holdup range, including: Calculate the actual deviation between liquid level and differential pressure; If the actual deviation exceeds the allowable deviation range of the theoretical gas holdup range, the inaccurate liquid level is determined to be a false liquid level caused by bubble entrainment. If the actual deviation does not exceed the allowable deviation range of the theoretical gas holdup range, then the reason for the inaccurate liquid level is determined to be fluctuation in the actual liquid level.

6. The flexible preparation process of acetate according to claim 1, characterized in that, In step S5, targeted control is implemented based on the cause of the inaccurate liquid level, including: If the false liquid level is caused by bubble entrainment, then when the liquid level rises while the differential pressure remains unchanged or falls, liquid discharge is prohibited; when the liquid level falls while the differential pressure remains unchanged or rises, liquid replenishment is prohibited; and the operating pressure is adjusted back to the reference pressure corresponding to the type of alcohol in the feed. If the cause is a genuine fluctuation in liquid level, then adjust the feed rate or output rate according to the direction of the liquid level change.

7. The flexible preparation process of acetate according to claim 1, characterized in that, Targeted control measures based on the causes of inaccurate liquid levels also include: If the false liquid level is caused by bubble entrainment, the pressure recovery rate is determined based on the real-time deviation between the liquid level and the differential pressure, and the recovery rate is positively correlated with the deviation; the operating pressure is then adjusted back to the reference pressure corresponding to the type of feed alcohol.

8. The flexible preparation process of acetate according to claim 7, characterized in that, During the process of redirecting the operating pressure to the reference pressure, when the operating pressure enters the preset redirection dead zone and the deviation does not increase further, the redirection is paused and the current pressure is maintained for a preset observation period. If the degree of deviation tends to decrease during the observation period, maintain the current pressure until the linear correlation is restored; If the deviation widens again within the observation period, a pressure correction will be initiated.

9. The flexible preparation process of acetate according to claim 1, characterized in that, During the process of reverting the operating pressure to the reference pressure, the change in operating pressure is monitored in real time. If the operating pressure exceeds the reference pressure, the reversion is stopped and reverse fine-tuning is performed to bring the operating pressure back to the reference pressure.

10. The flexible preparation process of acetate according to claim 1, characterized in that, In step S5, the step of restoring a linear correlation between the liquid level and the differential pressure includes: Real-time monitoring of the corrected liquid level change trend and differential pressure change trend; when both change in the same direction and the magnitude of change is proportional, it is determined to be a restored linear correlation.

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