A continuous rectification cutting point optimization method for methyl chloroacetate

Abstract

This invention relates to the field of fine chemical separation process control technology, and particularly to a method for optimizing the cutting point of continuous distillation of methyl chloroacetate. The method includes: collecting production data, combining it with historical stable production data to construct parameters such as component similarity, temperature distribution degradation, and reflux capacity reduction, and calculating fraction boundary state quantities; based on these fraction boundary state quantities and the cumulative product extraction volume, calculating the fraction boundary volume migration rate and obtaining a composite effective migration rate value; based on the fraction boundary state quantities and the composite effective migration rate value, calculating the theoretical remaining extraction volume and performing safety compensation to obtain the remaining allowable extraction volume; and based on the remaining allowable extraction volume, calculating the reflux ratio execution value and determining the cutting point. This method solves the problems of traditional cutting methods, which are difficult to adapt to fluctuations in feed composition and column conditions, and do not consider detection delays and pipeline congestion, leading to deviations in the actual cutting position and making it difficult to balance quality, yield, and operational stability.

Description

Technical Field

[0001] This invention relates to the field of fine chemical separation process control technology, and in particular to a method for optimizing the cutting point of continuous distillation of methyl chloroacetate. Background Technology

[0002] Methyl chloroacetate is an important organic chemical intermediate widely used in the production of pharmaceuticals, pesticides, dyes, and fine chemicals. In industrial production, crude methyl chloroacetate is typically produced by esterification of chloroacetic acid with methanol. This crude methyl chloroacetate is then removed via continuous distillation to remove low-boiling impurities, high-boiling impurities, and byproducts, yielding a methyl chloroacetate product that meets quality requirements. Continuous distillation is a crucial separation step in the methyl chloroacetate production process, and its operation directly affects product quality stability, product yield, and subsequent byproduct recovery efficiency. Therefore, precise control of the continuous distillation process is essential for improving plant stability, reducing production costs, and enhancing overall product utilization. With the continuous and automated production levels, the methyl chloroacetate distillation process is gradually evolving towards online monitoring, dynamic adjustment, and intelligent control. Real-time acquisition of distillation operating status and optimization of fraction switching processes have become important technological development directions for improving continuous distillation production efficiency and product consistency.

[0003] However, in current continuous distillation processes of methyl chloroacetate, the cutting positions of the product fraction and the downstream fraction are mostly determined based on fixed temperature ranges, fixed cumulative yields, or operator experience. This makes it difficult to fully consider the impact of factors such as feed composition fluctuations, changes in column temperature distribution, changes in reflux conditions, and changes in separation capacity on the fraction migration process. When production conditions change, a fixed cutting method can easily lead to a delayed or premature cutting position, causing methyl dichloroacetate to be entrained into the product fraction, affecting product quality stability. Alternatively, premature switching can increase the loss of refined methyl ester, reducing product yield. At the same time, current cutting methods usually do not fully consider the impact of factors such as online detection delays, actuator action delays, and pipeline blockages on cutting control, resulting in deviations between the actual and theoretical cutting positions. This makes it difficult to balance product quality, product yield, and stable operation of the continuous distillation process. Summary of the Invention

[0004] This invention provides a method for optimizing the cutting point of continuous distillation of methyl chloroacetate, which solves the problems of traditional cutting methods relying on fixed parameters or manual experience, making it difficult to adapt to fluctuations in feed composition and column conditions, resulting in decreased product quality or yield; and failing to consider detection delays and pipeline blockages, leading to deviations in the actual cutting position, making it difficult to balance quality, yield and operational stability.

[0005] The present invention provides a method for optimizing the cut-off point of continuous distillation of methyl chloroacetate, which specifically includes the following steps:

[0006] S1. Establish a synchronous data acquisition system to collect production data, combine it with historical stable production data, construct the degree of component proximity, the degree of temperature distribution degradation and the degree of reflux capacity decline, and calculate the fraction boundary state quantities.

[0007] S2. Based on the fraction boundary state variables and the cumulative product extraction volume in the production data, infer the degree of boundary advancement and calculate the fraction boundary volume migration rate; process the fraction boundary volume migration rate to obtain the effective migration rate composite value.

[0008] S3. Based on the combined value of the fraction boundary state variables and the effective mobility, calculate the theoretical remaining production volume and perform safety compensation on the theoretical remaining production volume to obtain the remaining allowable production volume.

[0009] S4. Based on the remaining allowable production volume, establish a coordinated control process for reflux regulation and fraction switching, calculate the reflux ratio execution value, and make a cut-off judgment.

[0010] Preferably, the production data includes the top temperature of the column, the bottom temperature of the column, the mass fraction of methyl dichloroacetate, the reflux flow rate, the product outflow rate, and the cumulative product outflow volume; the historical stable production data includes the historical baseline temperature difference, the historical baseline reflux flow rate, and the historical baseline mass fraction of methyl dichloroacetate.

[0011] Preferably, the degree of component similarity, the degree of temperature distribution degradation, and the degree of reflux capacity reduction respectively include:

[0012] The degree of component similarity is determined based on the position of the methyl dichloroacetate mass fraction in the current product fractionation process relative to the historical baseline mass fraction and the preset mass limit; the degree of temperature distribution degradation is determined based on the decrease in the current temperature difference between the bottom and top of the column relative to the historical baseline temperature difference; the degree of reflux capacity degradation is determined based on the decrease in the current reflux flow rate relative to the historical baseline reflux flow rate.

[0013] Preferably, based on the degree of component proximity, the degree of temperature distribution degradation, and the degree of reflux capacity reduction, an influence coefficient on the advancement of the quality boundary is introduced to construct a process capacity degradation compensation amount, and the fraction boundary state quantity is calculated.

[0014] Preferably, the calculation process for the fraction boundary volume migration rate specifically includes:

[0015] A migration analysis window is introduced, with a window length covering the online component detection delay and the switching valve action delay. Increasing weights are set according to the order of each sampling point in the migration analysis window to perform weighted accumulation of the changes in the state quantity of the distillation boundary. Combined with the accumulated changes in the product extraction volume, the volume migration rate of the distillation boundary is calculated. The volume migration rate of the distillation boundary is subjected to positive value substitution, lower limit protection, and upper limit truncation to obtain the effective migration rate composite value.

[0016] Preferably, before calculating the fraction boundary volume migration rate, the cumulative product output volume is preprocessed, including monotonicity verification and minimal increment substitution. When the current cumulative product output volume change is less than a set threshold, the current volume change is replaced by the most recent cumulative product output volume change that meets the threshold condition. If the threshold condition is not met continuously, the update of the fraction boundary volume migration rate is paused, and the most recent effective positive fraction boundary volume migration rate is maintained.

[0017] Preferably, the calculation process for the remaining allowable extraction volume specifically includes:

[0018] Based on the combined values ​​of fraction boundary state variables and effective mobility, a theoretical remaining production volume is constructed. By combining fraction boundary fluctuations, online component detection delays, switching valve action delays, and product production pipeline retention volumes, a safety compensation is applied to the theoretical remaining production volume, and the remaining allowable production volume is calculated.

[0019] Preferably, the sum of the online component detection delay, the switching valve action delay, and the volume corresponding to the product collection pipeline stagnation is defined as the cutting protection zone volume; a basic reflux ratio is introduced, and based on the cutting protection zone volume and the remaining allowable collection volume, the reflux ratio execution value is calculated, and the cutting is determined based on the reflux ratio execution value; when the cutting command is triggered, the control system first switches the four-way switching valve to the inlet pipeline of the transition fraction receiving tank, and then switches it to the back fraction pipeline after the pipeline replacement is completed; after the switching is completed, the cumulative product collection volume of this synchronous sampling cycle is stopped from being updated, and the actual cumulative cutting volume and the methyl dichloroacetate mass fraction, fraction boundary state quantity, fraction boundary volume migration rate, and reflux ratio execution value at the last three synchronous sampling times before cutting are recorded.

[0020] The beneficial effects of the technical solution of the present invention are:

[0021] 1. This invention constructs a fraction boundary state quantity and performs correlation analysis on changes in methyl dichloroacetate content, degradation of temperature distribution within the column, and changes in reflux capacity. This allows the trend of high-boiling components migrating to the product fraction within the distillation column to be identified in advance, avoiding the problem of unqualified materials entering the product receiving tank due to lagging adjustments based solely on product quality test results, thereby improving the quality stability of dichloroacetate products.

[0022] 2. This invention adopts a fraction boundary migration analysis method based on cumulative product extraction volume, which transforms the cutting position from a time dimension to a material extraction dimension. This allows the cutting prediction results to directly correspond to the actual material flow state during the distillation process, reducing the problem of fixed-time cutting deviation caused by changes in product extraction flow rate, reflux adjustment, and load changes, and improving the accuracy of cutting point prediction.

[0023] 3. By comprehensively considering the effects of online detection delay, switching valve action delay, and material lag caused by product collection pipeline stagnation, this invention reserves a safety compensation amount during the calculation of the predicted cutting position, enabling the control system to complete the fraction switching before reaching the product quality boundary. This reduces the entrainment of high-boiling components caused by detection and execution lag, and improves the operational reliability of the continuous distillation process.

[0024] 4. This invention achieves coordinated control of distillation separation capacity adjustment and fraction switching process by adjusting the reflux state according to the remaining allowable yield in the pre-cutting stage and performing product fraction and post-fraction switching after reaching the cutting boundary. This ensures product quality while making full use of the effective separation capacity inside the distillation column, reducing the loss of methyl ester product caused by premature switching, and improving product yield. Attached Figure Description

[0025] Figure 1 This is a flowchart of a method for optimizing the cut-off point of methyl chloroacetate continuous distillation according to the present invention. Detailed Implementation

[0026] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0028] The following description, in conjunction with the accompanying drawings, details the specific scheme of the method for optimizing the cutting point of methyl chloroacetate continuous distillation provided by the present invention.

[0029] See attached document Figure 1 The diagram illustrates a flowchart of a method for optimizing the cut-off point of methyl chloroacetate continuous distillation according to an embodiment of the present invention. The method includes the following steps:

[0030] S1. Establish a synchronous data acquisition system to collect production data, combine it with historical stable production data, construct the degree of component proximity, the degree of temperature distribution degradation and the degree of reflux capacity decline, and calculate the fraction boundary state quantities.

[0031] This embodiment is based on the company's existing methyl chloroacetate production process. The methyl chloroacetate production process includes: esterification of methyl chloroacetate with methanol to form crude methyl ester, which is then fed into a continuous distillation unit for separation. During the distillation process, a fore-fraction, a refined methyl ester product fraction, and a post-fraction are formed according to different boiling ranges. The refined methyl ester product fraction is collected as the target product, and the post-fraction is further processed for dichloroacetate recovery. The continuous distillation unit includes a distillation column, a reboiler heating unit, a reflux condenser unit, a product collection pipeline, a post-fraction pipeline, and a process monitoring unit. The company's existing distillation process separates fractions according to different temperature ranges. For example, after the crude methyl ester is distilled, fractions at different temperature ranges are sent to corresponding storage tanks, the refined methyl ester product fraction is sent out, and the post-fraction is further used to extract dichloroacetate.

[0032] First, a synchronous data acquisition system for the continuous distillation process was established. A top temperature detection unit was installed at the top of the distillation column to collect the top temperature; a bottom temperature detection unit was installed at the bottom of the distillation column to collect the bottom temperature. Both the top and bottom temperature detection units have built-in temperature sensors. An online component detection unit was installed in the product collection line to detect the mass fraction of dichloroacetic acid methyl ester in the distillate. Specifically, the online component detection unit consists of a sampling probe, a heated sampling line, a sample pretreatment module, and an online gas chromatography analysis module. The sampling probe is installed on the product collection line. After the sample is depressurized to 0.1 MPa and cooled to 150°C by the sample pretreatment module, it enters the online gas chromatography analysis module. The online gas chromatography analysis module uses a DB-5 capillary column (30m × 0.32mm × 0.25μm) equipped with a hydrogen flame ionization process. An ionization detector (FID) was used with high-purity nitrogen as the carrier gas at a flow rate of 1.0 mL / min and an injection volume of 1.0 μL. The column oven temperature program was as follows: initial temperature of 80 °C for 2 min, followed by a ramp-up to 180 °C at 10 °C / min and a hold for 3 min. This was used to separate and detect the methyl dichloroacetate component. The peak area was obtained by automatic integration using the online gas chromatography workstation. A pre-established external standard calibration curve (linear regression, correlation coefficient) based on at least five standard samples with known methyl dichloroacetate mass fractions was then used. The peak area of ​​methyl dichloroacetate is converted into the mass fraction of methyl dichloroacetate. A flow detection unit is installed in the reflux pipeline to detect the reflux flow rate. A flow detection unit is installed in the product collection pipeline to detect the product collection flow rate. The cumulative product collection volume is obtained by integrating the product collection flow rate over time. The cumulative product collection volume adopts the cumulative value of a single methyl ester product fraction collection cycle. That is, the cumulative volume is reset to zero each time the methyl ester product fraction begins to be collected, and the product collection flow rate is integrated from that moment. The flow detection unit includes a flow sensor and a flow transmitter module. The flow sensor can be a mass flow meter or an electromagnetic flow meter. The flow transmitter module is a conversion unit used to convert the raw signal output by the flow sensor into standard flow data. It usually includes a signal acquisition circuit, a signal conversion circuit, and a communication output interface. It is used to receive the detection signal from the flow sensor and convert it into a flow value that the control system can recognize.

[0033] All collected detection data are processed synchronously according to a unified sampling period, denoted as . , This indicates the current synchronous sampling sequence number, which starts counting from 0. The data collected at the current synchronous sampling moment is the production data, including: top temperature, bottom temperature, methyl dichloroacetate mass fraction, reflux flow rate, product outflow rate, and cumulative product outflow volume. Synchronous sampling period. The online component detection cycle can be set from 1 minute to 5 minutes to ensure that component changes can be continuously captured.

[0034] Since a fixed top temperature can only reflect the state of a single temperature measurement point and cannot simultaneously reflect the methyl dichloroacetate content, the temperature distribution within the column, and reflux changes, in order to unify these three types of information into a dimensionless state at the product quality boundary, specifically, we first establish the degree of component proximity, the degree of temperature distribution degradation, and the degree of reflux capacity decline, and then couple them according to the compression relationship of the remaining separation margin to obtain the fraction boundary state quantities: , , , , in, Indicates the first The fractional boundary state quantities at each synchronous sampling time. This indicates that the current distillate is in a historically stable state of refined methyl ester product extraction. This indicates that the methyl dichloroacetate content has reached or is predicted to reach the upper limit of permissible product quality under current operating conditions, and the corresponding product fraction should be terminated from extraction at the cutting boundary; the "predicted to reach" means that even if the current measured... Not yet exceeded However, if or The value has degraded to near 1, indicating that the separation capacity is no longer sufficient to maintain the quality of subsequent extraction. pass This allows for early reflection of the risk, thus enabling predictive segmentation; Indicates the first The mass fraction of methyl dichloroacetate in the product outflow stream at each synchronous sampling time is obtained by an online component detection unit installed on the product outflow pipeline; The maximum permissible mass fraction of methyl dichloroacetate (MCPA) for product quality, also known as the quality limit, represents the boundary value at which the product fraction can maintain a qualified state. It is derived from the company's MCPA product quality standards, customer quality requirements, or the company's internal inspection standards. Specifically, it is determined according to the principle of prioritizing the most stringent quality requirements. First, obtain the maximum permissible mass fraction of dichloroacetic acid methyl ester specified in the enterprise's methyl chloroacetate product quality standards, customer quality requirements, and internal inspection standards, and take the minimum value among them as the final boundary value. Indicates the first The degree of similarity of dichloroacetic acid methyl ester composition at each synchronous sampling time. Specifically, although the change in dichloroacetic acid methyl ester concentration during continuous distillation is affected by multiple factors such as vapor-liquid balance, reflux ratio, tray efficiency and feed composition, in a single production stage where the distillation column structure, feed conditions and operating parameters are basically stable, the mass fraction of dichloroacetic acid methyl ester during product fractionation usually shows a monotonic trend of changing close to the mass boundary. Therefore, this embodiment establishes a normalized boundary distance based on historical stable production stages, and converts the current mass fraction of dichloroacetic acid methyl ester into a relative state quantity from the upper limit of product mass. express Take zero at time Time to take , Take 1 at the time; This represents the median base mass fraction of methyl dichloroacetate in the product fraction during a historically stable production phase, i.e., the historical base mass fraction of methyl dichloroacetate. Indicates the first The degree of temperature distribution degradation at each synchronous sampling moment; Indicates the first The temperature difference between the bottom and top of the tower at each synchronous sampling moment; This represents the median temperature difference between the bottom and top of the column during a historically stable production period, i.e., the historical baseline temperature difference. This indicates the allowable temperature difference decrease, taken as... The difference between the fifth percentile and the data set of temperature differences between the bottom and top of the column, collected during the same historical stable production phase, is used as... ; Indicates the first The degree of decrease in reflux capability at each synchronous sampling moment; Indicates the first The return flow rate at each synchronous sampling moment; This represents the median of the return flow during a historically stable production phase, i.e., the historical baseline return flow. This indicates the allowable decrease in backflow rate, taken as... The difference between the fifth percentile of the total return flow dataset statistically analyzed during the same historical stable production phase and the fifth percentile of the dataset is used as... ; This represents a very small positive number used to prevent the denominator from being zero. ; The coefficient representing the impact of operational degradation on the quality boundary advancement is obtained through offline calibration. The specific steps are as follows: Select at least 20 batches of continuous distillation operation data containing complete cutting processes and meeting product quality standards as the calibration benchmark dataset, and perform coarse-grained calculations. Initially, gradually increase the step size by 0.1. Using the aforementioned calibration benchmark dataset, the fractional boundary state quantities during the historical cutting process are calculated. When the fractional boundary state quantities during the historical cutting process reach an independently determined cutting threshold, the corresponding time is recorded as the predicted cutting time; when the threshold is increased... When the predicted cut time for all batches in the above calibration benchmark dataset is no longer changed, record this time. The value is And use it as the candidate upper limit to generate Candidate range Then, within the aforementioned candidate range, with a step size... By performing equally spaced discrete value sampling, basic candidate values ​​are obtained, and a candidate set is constructed. Simultaneously, to ensure that the search range covers the upper boundary, [the following is omitted as the text is incomplete and requires further context]. Forced addition to the candidate set (if) If a candidate value is repeated with a base candidate value, only one will be retained. Maximum value If it is less than 0.05, then only take... and Two endpoints; iterate through each candidate in the candidate set. The values ​​are calculated for each historical batch in the calibration benchmark dataset during the cutting process, determining the fractional boundary state quantity. When the fractional boundary state quantity first reaches or exceeds the cutting threshold, the corresponding time is recorded as the predicted cutting time for that batch. The offline detection results of the extracted material corresponding to the predicted cutting time are then compared with the quality limit. Compare and statistically analyze each candidate. Under the specified value, the methyl dichloroacetate content in the product after cutting shall not exceed [value missing]. The proportion of batches; among all candidates that meet this proportion of not less than 95%. Among the values, select the one that maximizes the average product extraction rate. Value, as the final Values; the average product recovery rate is obtained by calculating the ratio of the actual qualified product recovery amount to the total feed amount, and then averaging it over all qualified batches; the cutting threshold is set as follows: based on the above calibration benchmark dataset, for each batch, the methyl dichloroacetate mass fraction corresponding to the actual switching command issuance time (based on the DCS system record) is extracted as the reference value for that batch. All reference values ​​of no less than 20 batches are sorted in ascending order, and the 10th percentile is taken as the current variable and substituted into the component similarity. Definition In the process, the corresponding component proximity threshold is obtained, and the calculated component proximity threshold is used as the final cutting threshold. This threshold corresponds to the boundary state when the temperature distribution and reflux capacity have not degraded and the component concentration only approaches the quality limit. If the applicability of the threshold decreases due to significant changes in the feed composition or operating conditions in subsequent production, the above statistical determination process is repeated. This represents the bounded nonlinear coupling quantity between temperature distribution degradation and the decrease in recirculation capacity. Both the degree of temperature distribution degradation and the degree of recirculation capacity decrease are dimensionless state quantities determined at the current synchronous sampling moment, not probabilities of random events. This combination ensures that the joint degradation degree monotonically increases with any increase in the degree of degradation, while ensuring that the joint degradation degree is not less than any individual degradation degree and does not exceed its normalized upper limit. The product subtraction term... Used to suppress the repeated amplification of the same decrease in separation capability caused by two degraded states; This represents the remaining separation safety margin from the product quality boundary at the current sampling time; This indicates that the degradation of temperature distribution and the decrease in reflux capacity only have a compressive effect on the remaining separation margin; It is the compensation for process capability degradation, which represents the additional risk of the quality boundary advancing earlier due to the reduced distillation separation capacity, based on the current impurity concentration. It is an unlimited comprehensive fractional boundary state quantity, representing the comprehensive boundary proximity after incorporating the actual impurity proximity with the impact of the degradation of distillation separation capacity.

[0035] in, , and Historical stable production data were obtained from data collected during historical stable production phases. Specifically, based on the production data in the aforementioned calibration benchmark dataset, after removing data from the start-up and switching phases, the median values ​​of the methyl dichloroacetate mass fraction, the temperature difference between the bottom and top of the column, and the reflux flow rate corresponding to the stable product distillation phase were calculated and used as the benchmarks. , and A complete distillation cycle refers to the time from the start of a production process to the completion of one fraction changeover. A historically stable production phase refers to a production phase selected from the company's continuous distillation production records where the product has passed inspection, the distillation column has been continuously running for at least one complete distillation cycle before entering this production phase (i.e., the distillation column has completed at least one complete fraction changeover operation before the start of this product collection), the feed flow rate fluctuation does not exceed ±5% of the set value, the column top pressure fluctuation does not exceed ±2% of the set value, and no fraction changeover or equipment alarms have occurred during this production phase. The feed flow rate is collected by a flow meter on the distillation column feed line, and the column top pressure is collected by a pressure sensor installed at the top of the distillation column. The set values ​​are the feed flow rate and column top pressure values ​​set in the DCS system during normal operation of the distillation unit. These set values ​​are input and recorded by the operator according to process requirements before the start of production operation.

[0036] S2. Based on the fraction boundary state variables and the cumulative product extraction volume in the production data, infer the degree of boundary advancement and calculate the fraction boundary volume migration rate; process the fraction boundary volume migration rate to obtain the effective migration rate composite value.

[0037] During distillation, changes in reflux regulation, overhead load, and condensate load cause fluctuations in the product yield, resulting in different product yield volumes for the same operating time. Calculating the rate of change of the fraction boundary state quantity relative to time does not directly characterize the degree of boundary advancement corresponding to a unit product yield. Therefore, this invention does not use the rate of change of the fraction boundary state quantity relative to time, but rather its rate of change relative to the cumulative product yield volume, so that the boundary advancement result directly corresponds to the product yield volume.

[0038] Let the migration analysis window contain For each sampling point, the window length should cover the online component detection delay and the switching valve action delay, while reserving at least two additional synchronous sampling cycles to suppress single-point fluctuations. Therefore, according to... It is confirmed that, among them, Indicates the delay time for online component detection. Indicates the delay time of the switching valve action. This indicates the synchronous sampling period, which is the time interval between two adjacent sampling points. The value indicates rounding up; the online component detection delay time is obtained by adding the sampling pipeline delivery time, sample pretreatment time, and analyzer output time; the switching valve action delay time is obtained by recording the time difference between the moment the control command is issued and the moment when the four-way switching valve switches from the product outlet pipeline to the transition fraction receiving tank inlet pipeline and reaches the target opening degree of 100%, and the maximum value is taken after continuous testing for no less than ten times.

[0039] The closer a synchronous sampling point is to the current synchronous sampling time, the more representative it is of the current boundary advancement trend. Therefore, incremental weights are set according to the order of each sampling point in the migration analysis window to calculate the fraction boundary volume migration rate: , in, Indicates the first The fractional boundary volume mobility at each synchronous sampling time; Indicates the first [number] in the migration analysis window The synchronous sampling time corresponding to the sampling point, i.e. the nth sampling point The fractional boundary state quantities at each synchronous sampling time, when At this time, the migration analysis window has not yet accumulated the required historical data and is in the data warm-up stage. At this time, the corresponding fraction boundary volume migration rate is not generated, nor does it participate in the subsequent cutting judgment and calculation. This indicates the time preceding the sampling point, i.e., the [number]th [time]. The fractional boundary state quantities at each synchronous sampling time; Indicates the first The cumulative product extraction volume at each synchronous sampling moment; Indicates the sampling sequence number within the migration analysis window; This represents the weighted cumulative value of the changes in the boundary state quantities of the fraction within the migration analysis window; This represents the weighted cumulative value of the cumulative change in product extraction volume within the migration analysis window. To prevent the smallest positive number with a denominator of zero, take... .

[0040] Regarding the fraction boundary volume mobility Positive value substitution, lower bound protection, and upper bound truncation are performed to obtain the effective composite mobility value. Details are as follows:

[0041] when At this point, the fraction boundary is advancing towards the upper limit of product quality, indicating the effective positive fraction boundary volume migration rate; when At that time, the fraction boundary did not advance towards the upper limit of product quality. When the current calculation requires the use of the positive fraction boundary volume migration rate, the most recent effective positive fraction boundary volume migration rate should be used first; if no effective positive fraction boundary volume migration rate has yet been generated, the historical conservative migration rate should be used. , The 100th percentile is obtained from the effective positive fraction boundary volume mobility of no less than twenty historical stable production stages.

[0042] Meanwhile, to prevent an abnormal increase in the remaining allowable production volume due to an excessively low effective positive fraction boundary volume migration rate, a minimum effective migration rate threshold is set. , Take all of the above-mentioned no less than twenty historical stable production stages that meet the requirements. The 20th percentile of the point-by-point value of the fraction boundary volume mobility. To unify the rules for determining the final mobility value used in the calculation of the remaining allowable produced volume, a composite value of the original mobility is defined. as follows: , in, This indicates the volume migration rate of the most recent effective positive fraction boundary. Furthermore, the original mobility composite value was analyzed. Perform upper limit truncation and define the effective mobility composite value. : , in, The 99.5th percentile of the historical effective positive fraction boundary volume mobility distribution is taken. If no historical data is available, then a temporary value is used. ; The final mobility value used in the calculation of the remaining allowable extraction volume, i.e., the composite effective mobility value.

[0043] In calculation Beforehand, the cumulative product extraction volume needs to be pre-processed, specifically including:

[0044] (1) Monotonicity check: If This indicates that the flow meter is experiencing zero-return or signal jump anomalies. Replace the current sampling point's cumulative product volume with the previous sampling point's cumulative product volume. And mark the current cumulative change in product extraction volume at that sampling point as zero;

[0045] (2) Minimal incremental substitution: If the cumulative change in product output volume at the current sampling point is... Less than the set threshold Then the most recent one that satisfies the condition will be used. The cumulative change in product output volume at the sampling points replaces the current change in output volume in the weighted cumulative denominator; if more than three consecutive sampling points do not meet the requirement... Then pause Update, maintaining the most recent effective positive fraction boundary volume migration rate, until the first condition is met. Automatically resume updates after sampling points; the Take 10% of the product of the average product output flow rate during the historical stable production period and the synchronous sampling period.

[0046] S3. Based on the combined value of the fraction boundary state variables and the effective mobility, calculate the theoretical remaining production volume and perform safety compensation on the theoretical remaining production volume to obtain the remaining allowable production volume.

[0047] The dynamic cut-off point is calculated based on the combined value of the current fraction boundary state and the effective mobility. Let the remaining state of the product fraction at the current mass boundary be... The process proceeds from the current boundary position to the theoretical remaining production volume corresponding to the upper limit of product quality. Online component detection, switching valve action, and product collection pipeline stagnation can all cause some distillate to still enter the product receiving tank after the cut command is issued; fluctuations in the distillation state may also cause the actual boundary advancement speed to be higher than the calculation result within the migration analysis window. In order to complete the switch before the upper limit of product quality is reached, it is necessary to deduct the fluctuation reserve volume from the theoretical remaining production volume, i.e., the theoretical remaining production volume, and further deduct the detection and execution delay production volume and the product collection pipeline stagnation volume. Based on the current fraction boundary state quantity, effective positive fraction boundary volume migration rate, average product production flow rate, and product collection pipeline stagnation volume, the remaining allowable production volume is calculated: , in, Indicates the first The remaining allowable sampling volume corresponding to each synchronous sampling moment, that is, the maximum volume of refined methyl ester product fraction that is still allowed to enter the product receiving tank before the methyl dichloroacetate reaches the product quality limit, starting from the current moment; This represents the fraction boundary fluctuation compensation coefficient, used to convert fraction boundary state fluctuations into advance cutting margins. The calibration method and the influence coefficient of the aforementioned operational state degradation on the mass boundary advance Similarities: Based on the calibration benchmark dataset described in step S1, from Initially, gradually increase the step size by 0.1. ,Sure As a candidate upper limit, the values ​​are then discretely selected at equal intervals with a step size of 0.05, and forced supplementation is performed. To the candidate set, if If it is less than 0.05, then only take... and traverse the candidates The cutting point is predicted, and the methyl dichloroacetate content in the product after cutting is compared to see if it exceeds the quality limit. Simultaneously, the product recovery rate is calculated, and the point at which at least 95% of batches of product meet the quality standards and the average product recovery rate is highest is selected. As the final value; Indicates the theoretical remaining extracted volume; Indicates the first At the nth synchronous sampling time, take the nth... To the Synchronous sampling times (total) The standard deviation of the fraction boundary state quantities (at each sampling point); This represents the safety margin determined based on the current degree of fluctuation at the fraction boundary; Indicates the volume reserved for fluctuations; Indicates the first The most recent synchronous sampling time before Average product output flow rate at each sampling point; This represents the theoretical volume of product that still enters the product receiving slot during the detection and execution delay period; The volume of the product in the product extraction pipeline is calculated as the sum of the products of the cross-sectional area and the effective length of each section of the product extraction pipeline. The effective length refers to the actual length of the pipeline in the product extraction pipeline that stores the product liquid, which is obtained directly from the on-site pipeline layout diagram or on-site measurement. This indicates the safety compensation item for cutting.

[0048] The above The calculation formula uses the average product output flow rate. The purpose of the calculation is that flow detection signals in industrial process control contain sensor noise and fluid pulsation components, and directly using instantaneous flow values ​​for calculation will lead to... Frequent and severe jitter can lead to instability in the reflux ratio execution value and the cutting determination. Moving average filtering can eliminate this type of noise, and those skilled in the art can adjust the migration analysis window length according to the actual working conditions. The value is used to balance stability and response speed, prioritizing product quality stability in the trade-off between product quality and product recovery rate; furthermore, the hysteresis effect has been implicitly compensated for in the calibration process, and the coefficient... and All calibrations were performed offline using no fewer than 20 batches of historical operational data. This calibration process was entirely based on... The calculation rules process historical data, and the calibration results naturally include the conservative bias that may arise during the mean filtering stage of the reflux ratio adjustment, ultimately determining... The value has been automatically compensated for by engineering in a statistical sense.

[0049] The remaining allowable extractable volume is a relative volume with respect to the current synchronous sampling time (i.e., the volume that can still be extracted from the current time). When the product flow meter performs cut-off control, it needs to use the absolute volume accumulated since the start of the extraction of the current methyl ester product fraction (i.e., the total volume already extracted). Therefore, it is converted into the predicted cumulative cut-off volume according to the following formula. : , in, Indicates the first At each synchronous sampling moment, the product extraction flow meter accumulates the current extraction volume from the moment the current fraction begins extraction.

[0050] Predicted cumulative volume of cutting It is used to compare the actual cumulative volume of the cut after the fraction switching is completed, as a basis for verifying the prediction accuracy, and does not directly participate in the judgment of reflux adjustment or cutting command.

[0051] S4. Based on the remaining allowable production volume, establish a coordinated control process for reflux regulation and fraction switching, calculate the reflux ratio execution value, and make a cut-off judgment.

[0052] While switching immediately when the distillation column approaches the cut-off boundary can prevent subsequent high-boiling fractions from entering the product receiving tank, it cannot utilize the remaining separation space to slow the advance of methyl dichloroacetate to the top of the column. To balance product quality and yield, the reflux ratio is increased first after the remaining allowable draw-out volume enters the cut-off protection zone, and the flow direction of the product fraction is switched to the subsequent fractions only when the remaining allowable draw-out volume decreases to zero.

[0053] Cutting the protected area volume The unified definition is the sum of the volume corresponding to the online component detection delay, the switching valve action delay, and the product retention in the outflow pipeline:

[0054] Let the base reflux ratio be The base reflux ratio is the ratio of reflux flow rate to product output flow rate; the reflux ratio execution value and cutting command are calculated based on the remaining allowable output volume. , , in, Indicates the first The reflux ratio output to the distillation unit at each synchronous sampling time; The maximum allowable reflux ratio for the distillation column is determined by the distillation column design documents or the allowable operating range verified by the unit's safety. To prevent the smallest positive number with a denominator of zero, take... ; This is a binary cutting command, used only to indicate whether cutting control is triggered; it does not directly drive the four-way switching valve to complete all actions. At that time, the control system realizes the timing of actions through the control program. Therefore, there is no conflict between the binary cutting command and the actual action of the actuator.

[0055] The segmented control logic of the above formula can be intuitively expressed as:

[0056] when hour, The function takes the value 0. The reflux ratio execution value remains the base reflux ratio;

[0057] when hour, The function takes values ​​in Between these points, the reflux ratio gradually increases as the remaining allowable extraction volume decreases, resulting in a smooth transition;

[0058] when hour, The function value approaches 1. The reflux ratio reaches the maximum allowable value, and at the same time Trigger the cutting action.

[0059] After receiving the cutting command, the control system executes the switching action according to the following sequence: A four-way switching valve is installed at the distillate outlet of the distillation column. The inlet of the four-way switching valve is connected to the distillate outlet of the distillation column, and the three outlets are respectively connected to the product collection pipeline, the inlet pipeline of the transition fraction receiving tank, and the downstream fraction pipeline. During normal collection of methyl ester product fraction, the four-way switching valve is connected to the product collection pipeline; after the cutting conditions are met, the system first switches to the inlet pipeline of the transition fraction receiving tank, allowing the distillate remaining in the pipeline during the switching process to enter the transition fraction receiving tank. After the first stage of switching is completed, the product collection pipeline remains closed, and the material generated during subsequent pipeline replacement and the switching process from the inlet pipeline of the transition fraction receiving tank to the downstream fraction pipeline will no longer enter the product receiving tank; after the pipeline replacement is completed, the system switches to the downstream fraction pipeline, allowing the subsequent downstream fraction to enter the subsequent processing flow through the downstream fraction pipeline; the transition fraction generated during the switching period must not enter the qualified product receiving tank; After the residue in the pipeline is emptied and the component detection results stabilize (the time for residue emptying is determined by dividing the retained volume by the current extraction flow rate; the stabilization of component detection results is determined by the fluctuation of the online detection value not exceeding the allowable fluctuation range preset according to the product standard or process requirements for three consecutive sampling cycles, which is a well-known technique in this field), the subsequent qualified fractions are then reintroduced into the product receiving tank, thereby avoiding the mixing of transitional fractions into qualified products during the switching process; "reintroducing subsequent qualified fractions into the product receiving tank" only refers to the restart of extraction of the next batch of methyl ester product fractions after the switch is completed, and does not belong to the resumption of extraction within the same extraction cycle. A single methyl ester product fraction extraction cycle ends after cutting, and the accumulated product extraction volume stops updating; the volume is reset to zero and accumulation begins again when the next product fraction is extracted. Therefore, there is no issue of multiple cutting-and-recovery within the same cycle.

[0060] After the fraction switching is completed, stop updating the cumulative product extraction volume corresponding to the current dichloroacetic acid (DCA) product fraction, and record the actual cumulative cutting volume, the mass fraction of DCA at the last three synchronous sampling times before cutting, the fraction boundary state quantity, the fraction boundary volume migration rate, and the reflux ratio execution value.

[0061] In summary, a method for optimizing the cut-off point of continuous distillation of methyl chloroacetate has been developed.

[0062] The order of the embodiments is for illustrative purposes only and does not represent the superiority or inferiority of the embodiments. The processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0063] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0064] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for optimizing the cut-off point of continuous distillation of methyl chloroacetate, characterized in that, Specifically, the following steps are included: S1. Establish a synchronous data acquisition system to collect production data and combine it with historical stable production data to construct the degree of component similarity, the degree of temperature distribution degradation, and the degree of reflux capacity decline. The production data includes the top temperature of the column, the bottom temperature of the column, the mass fraction of methyl dichloroacetate, the reflux flow rate, the product outflow rate, and the cumulative product outflow volume. The historical stable production data includes the historical baseline temperature difference, the historical baseline reflux flow rate, and the historical baseline mass fraction of methyl dichloroacetate. The similarity of components is determined based on the position of the methyl dichloroacetate mass fraction relative to the historical baseline mass fraction and the pre-set mass limit during the current product fractionation process. The degree of temperature distribution degradation is determined based on the decrease in the current temperature difference between the bottom and top of the column relative to the historical baseline temperature difference; The degree of decline in return flow capacity is determined based on the magnitude of the decrease in current return flow rate relative to the historical baseline return flow rate; Based on the degree of component proximity, the degree of temperature distribution degradation, and the degree of reflux capacity reduction, an influence coefficient of operating state degradation on the advance of the quality boundary is introduced to construct a process capacity degradation compensation quantity and calculate the fraction boundary state quantity. S2. Introduce a migration analysis window, with the window length covering the online component detection delay and the switching valve action delay; set incremental weights according to the order of each sampling point in the migration analysis window, perform weighted accumulation of the changes in the state quantity of the distillate boundary, combine with the accumulated changes in the product extraction volume to infer the degree of boundary advancement, and calculate the distillate boundary volume migration rate. The effective migration rate composite value is obtained by performing positive value substitution, lower limit protection and upper limit truncation on the fraction boundary volume migration rate; S3. Based on the combined value of the fraction boundary state quantity and the effective mobility, calculate the theoretical remaining production volume. Combine the fraction boundary fluctuation, online component detection delay, switching valve action delay and product production pipeline stagnation volume to make safety compensation for the theoretical remaining production volume and obtain the remaining allowable production volume. S4. Based on the remaining allowable production volume, establish a coordinated control process for reflux regulation and fraction switching, calculate the reflux ratio execution value, and make a cut-off judgment.

2. The method for optimizing the cut-off point of continuous distillation of methyl chloroacetate according to claim 1, characterized in that, Before calculating the fraction boundary volume migration rate, the cumulative product output volume is preprocessed, including monotonicity verification and minimal increment substitution. When the current cumulative product output volume change is less than the set threshold, the current volume change is replaced by the most recent cumulative product output volume change that meets the threshold condition. If the threshold condition is not met continuously, the update of the fraction boundary volume migration rate is paused, and the most recent effective positive fraction boundary volume migration rate is maintained.

3. The method for optimizing the cut-off point of continuous distillation of methyl chloroacetate according to claim 1, characterized in that, The sum of the online component detection delay, the switching valve action delay, and the volume corresponding to product retention in the outflow pipeline is defined as the cutting protection zone volume. A basic reflux ratio is introduced, and based on the cutting protection zone volume and the remaining allowable outflow volume, the reflux ratio execution value is calculated, and the cutting decision is made based on the reflux ratio execution value. When the cutting command is triggered, the control system first switches the four-way switching valve to the inlet pipeline of the transition fraction receiving tank, and then switches it to the back fraction pipeline after the pipeline replacement is completed. After the switching is completed, the cumulative product outflow volume of this synchronous sampling cycle is stopped from being updated, and the actual cumulative cutting volume and the methyl dichloroacetate mass fraction, fraction boundary state quantity, fraction boundary volume migration rate, and reflux ratio execution value at the last three synchronous sampling times before cutting are recorded.

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