Process control method for AV index in cellulose acetate hydrolysis process

Abstract

A process control method for AV indexes in the cellulose acetate hydrolysis process comprises the following steps that in the cellulose acetate hydrolysis process, a first kind of process state parameters are measured, meanwhile, instantaneous values of a second kind of process state parameters are recorded, and the AV indexes of cellulose acetate slurry are measured; establishing a mathematical model of the AV indexes and the first and second types of process state parameters based on the knowledge base according to the multi-batch test results; and in combination with the mathematical model based on the knowledge base and the detection value of the size AV index, adjusting the first type and the second type of process state parameters so as to control the final output value of the AV index of the cellulose acetate product to achieve the design target. According to the invention, the output value of the product AV index can be predicted and adjusted in advance in the reaction process, the dependence on the experience of operators is reduced, and the stability of the product quality is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical control, and relates to a quality index process control method, in particular to a quality index process control method for cellulose acetate hydrolysis. Background Art

[0002] The intermittent process has the characteristics of small batches, multiple varieties, serialization, complex synthesis steps, and intensive technology. It is flexible in production and has high added value. Although intermittent production processes have been widely used in industry, intermittent processes are always "ongoing" transition processes. There is generally no steady-state operating point in the operating range, and it has strong nonlinear and dynamic characteristics. These characteristics determine that intermittent process control is more complex than continuous process control. How to ensure the consistency of product quality between different batches has become an important issue.

[0003] Cellulose acetate is a chemically modified natural high molecular polymer widely used in textile, tobacco, IT and other industries. The production of cellulose acetate is usually an intermittent process. The acetyl value (AV value) is an important indicator to measure product quality. It refers to the weight percentage of acetic acid combined in cellulose acetate and represents the degree of acetylation of cellulose. The AV index determines the performance of cellulose acetate. Therefore, the product quality control of the intermittent production process of cellulose acetate, especially the process control of the AV index, has always been the focus of the acetate fiber industry.

[0004] The characteristics of intermittent production determine that the pure hysteresis of the AV index control of cellulose acetate is relatively large. The existing AV index test cycle is relatively long, which further exacerbates the hysteresis of the AV index control. This hysteresis causes quality fluctuations on the one hand; on the other hand, it increases the difficulty of operator regulation and control, and is highly dependent on the operator's experience. It is affected by more human factors, which further causes quality fluctuations. Therefore, there is an urgent need for a process control method to further improve the quality stability of cellulose acetate products. Summary of the invention

[0005] The present invention aims to provide a cellulose acetate AV index process control method in view of the bottleneck of the prior art, so as to solve the disadvantages of large hysteresis of cellulose acetate AV index control and more influence of human factors in the prior art.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] A method for controlling AV index in a cellulose acetate hydrolysis process comprises the following steps:

[0008] The first type of process state parameters of the cellulose acetate hydrolysis process (including catalyst concentration and reaction temperature, one or both of which change during the reaction) are measured, and the instantaneous value of the second type of process state parameters (reaction time of the material under a specific first type of process state parameters) is recorded, and the AV index of the material is measured.

[0009] According to the collected AV index data of cellulose acetate under various process conditions, the AV index change rate based on the first and second process state parameters is calculated, including the AV value change rate (% / min) and the change rate of the AV value change rate with temperature (% / ℃ / min).

[0010] According to the test results, a mathematical model of the AV index and the first and second process state parameters based on the knowledge base is established. The specific model is the mathematical calculation relationship between the change of the AV index and the first and second process state parameters.

[0011] According to the mathematical calculation relationship between the AV index and the first and second process state parameters, the change of the AV index under a specific first process state parameter is calculated. According to the target value of the AV index of the cellulose acetate product, the second process state parameter (i.e., the reaction time of the material) is calculated, and the set value of the reaction time is adjusted in the control system to control the final output value of the AV index of the cellulose acetate product to achieve the design target.

[0012] The cellulose acetate hydrolysis process hydrolyzes triacetyl cellulose into diacetyl cellulose, wherein the AV index range of triacetyl cellulose is 59-61.5%; and the AV index range of diacetyl cellulose is 50-58%.

[0013] The testing method for the AV index of the material uses the HPLC-ELSD method to test the AV index of cellulose acetate slurry: cellulose acetate slurry and acetic acid or acetone are prepared into a cellulose acetate dilute solution in a certain mass ratio (1:20-30), and an HPLC-ELSD test is carried out to obtain the AV index of the cellulose acetate slurry.

[0014] The cellulose acetate hydrolysis process is decomposed into five stages: the first stage is the reaction start stage, the reaction temperature is slowly increased from the start temperature to the first temperature; the second stage, the concentration of the reaction catalyst is reduced, and the temperature is accelerated to the second temperature; the third stage, the reaction temperature is maintained at the second temperature, and the hydrolysis is performed at a constant temperature; the fourth stage, the reaction temperature is maintained at the second temperature, and the catalyst concentration is further reduced; the fifth stage, the reaction temperature is maintained at the second temperature, and the concentration of the catalyst is zero after complete neutralization. Preferably, the heating rate in the first stage is in the range of 0.5-0.6°C / min, and the heating rate in the second stage is in the range of 0.7-0.8°C / min.

[0015] The first stage lasts for 0-38 minutes, the second stage lasts for 26-51 minutes, the third stage lasts for 2.5-35 minutes, the fourth stage lasts for 5-35 minutes, and the fifth stage lasts for 10-20 minutes.

[0016] The catalyst has an initial concentration range of 0.1-0.8%; a starting temperature range of 48-55°C; a first temperature range of 70-80°C; and a second temperature range of 82-106°C.

[0017] The mathematical calculation relationship between the AV index change and the first and second type process state parameters is as follows:

[0018] The AV change in the first stage is: a1*b1*X1 2 , where a1 is the temperature change rate of the first stage (℃ / min), b1 is the change rate of the AV value of the first stage with the temperature (% / ℃ / min), and X1 is the reaction time of the first stage;

[0019] The second stage AV change is: a2*b2*(X2-X1) 2 , where a2 is the temperature change rate of the first stage (℃ / min), b2 is the rate of change of the AV value of the first stage with the temperature (% / ℃ / min), X2 is the reaction time of the second stage, and X1 is the reaction time of the first stage;

[0020] The AV change in the third stage is: c3*(X3-X2), where c3 is the AV value change rate in the third stage (% / min), X3 is the reaction time in the third stage, and X2 is the reaction time in the second stage;

[0021] The AV change in the fourth stage is: c4*(X4-X3), where c4 is the AV value change rate in the fourth stage (% / min), X4 is the reaction time in the fourth stage, and X3 is the reaction time in the third stage;

[0022] The AV change in the fifth stage is: c5*(X5-X4), where c5 is the AV value change rate in the fifth stage (% / min), X5 is the reaction time in the fifth stage, and X4 is the reaction time in the fourth stage.

[0023] Due to the adoption of the above scheme, the beneficial effects of the present invention include:

[0024] 1. The HPLC-ELSD test method can test the AV index of the slurry during the production process, which provides the possibility for in-depth research on the reaction mechanism of cellulose acetate and provides a feasible way to find the changing law of the AV index of cellulose acetate during the reaction.

[0025] 2. Through the testing of AV indicators of cellulose acetate in various reaction states, a knowledge base is established, and based on the knowledge base, a mathematical model of AV indicators and first and second process state parameters is established. The hysteresis of AV indicator control is reduced, the influence of human factors is reduced, the process control capability of AV indicators is improved, and the stability of product quality is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of the AV index process control method of cellulose acetate of the present invention. DETAILED DESCRIPTION

[0027] The present invention provides a method for controlling the AV index of a cellulose acetate hydrolysis process. The technical solution includes the following steps: in the cellulose acetate hydrolysis process, measuring the first type of process state parameters, recording the instantaneous value of the second type of process state parameters, and measuring the AV index of the material; establishing a mathematical model of the AV index based on a knowledge base and the first and second types of process state parameters according to the test results of multiple batches. The first type of process state parameters are measured online in real time, while the AV index of the material cannot be measured online in real time. The test of the AV index has a certain lag, but this does not affect the establishment of the mathematical model. In the actual production process, the first and second types of process state parameters can be adjusted in time in combination with the mathematical model based on the knowledge base and the detection value of the AV index of the slurry to control the final output value of the AV index of the cellulose acetate product to achieve the design target. This scheme can predict and adjust the output value of the product AV index in advance during the reaction process, reduce the dependence on the operator's experience, and improve the stability of product quality.

[0028] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0029] Embodiment 1

[0030] (1) Collect and detect the AV index data of cellulose acetate under various process conditions. For each collection of AV index, record the values ​​of the first-category process state parameters at the time of sampling, including: catalyst concentration and reaction temperature; record the values ​​of the second-category process state parameters at the time of sampling, including the reaction time of the material under a specific first-category process state parameter.

[0031] In this embodiment, the sampling interval is no more than 10 minutes, and the change of the first type of process state parameters is divided into five stages. In each stage, one or more of the catalyst concentration and the reaction temperature changes. The first stage is the initial stage of the reaction, and the reaction temperature slowly rises from the initial temperature to the first temperature; in the second stage, the catalyst concentration decreases and the temperature is accelerated to the second temperature; in the third stage, the reaction temperature is maintained at the second temperature and hydrolysis is performed at a constant temperature; in the fourth stage, the reaction temperature is maintained at the second temperature, and the catalyst concentration is further reduced; in the fifth stage, the reaction temperature is maintained at the second temperature, and the catalyst concentration is zero; the AV value test results and the first and second type process state parameters are shown in the following table.

[0032]

[0033]

[0034] According to the collected AV index data of cellulose acetate under various process states, the AV index change rate based on the first and second process state parameters is calculated.

[0035]

[0036]

[0037] (2) Establish a mathematical model of AV index changes and the first and second type process state parameters.

[0038]

[0039]

[0040] (3) According to the mathematical calculation relationship between the AV index and the first and second process state parameters, the change of the AV index under a specific first process state parameter (initial catalyst concentration of 0.642%, starting temperature of 50°C, first reaction temperature of 75°C, and second reaction temperature of 88°C) is calculated. According to the target value of the AV index of the cellulose acetate product of 55.50%, the second process state parameter (i.e., the reaction time of the material) is calculated, and the set value of the reaction time is adjusted in the control system to control the final output value of the AV index of the cellulose acetate product to achieve the design target.

[0041] In this embodiment, the AV value of triacetyl cellulose is 60.041%, and the target AV value after hydrolysis is 55.50%. The starting temperature of the hydrolysis reaction is 50°C, and the first reaction temperature needs to reach 75°C. According to the temperature change rate of the first stage, it takes 45.7 minutes; the second reaction temperature needs to reach 88°C, and according to the temperature change rate of the second stage, it takes 18.1 minutes;

[0042] The AV value of the first and second stages decreased by 2.9386%. The reaction time of the fourth stage was set to 35min. The AV value of the fourth stage was

[0043] The value drops by 0.7245%, so the AV value in the third stage needs to drop by 0.8779%. The third stage takes 22 minutes; the overall reaction time is 120.8 minutes, and the system reaction time is set to 120.8 minutes.

[0044] (4) According to the mathematical calculation relationship between the AV index and the first and second process state parameters, the change of the AV index under a certain first process state parameter (initial catalyst concentration of 0.642%, starting temperature of 50°C, first reaction temperature of 75°C, and second reaction temperature of 88°C) is calculated. According to the target value of the AV index of the cellulose acetate product of 55.20%, (in this embodiment, "55.20%" and "55.50%" are selected as the AV setting targets, and the mathematical calculation relationship obtained in paragraph (3) is respectively tested, and the same is true for the following embodiments 2 and 3.) The second process state parameter (i.e., the reaction time of the material) is calculated, and the set value of the reaction time is adjusted in the control system to control the final output value of the AV index of the cellulose acetate product to reach the design target.

[0045] In this embodiment, the AV value of triacetyl cellulose is 60.041%, and the target AV value after hydrolysis needs to reach 55.20%. The starting temperature of the hydrolysis reaction is 50°C, the first reaction temperature needs to reach 75°C, and according to the temperature change rate of the first stage, it takes 45.7 minutes; the second reaction temperature needs to reach 88°C, and according to the temperature change rate of the second stage, it takes 18.1 minutes;

[0046] The AV value of the first and second stages decreased by 2.9386%. The reaction time of the fourth stage was set to 35 minutes. The AV value of the fourth stage decreased by 0.7245%. The AV value of the third stage needed to decrease by 1.1779%. The third stage took 29.5 minutes. The overall reaction time was 128.3 minutes, and the AV target value after hydrolysis could reach 55.20%.

[0047] Embodiment 2

[0048] (1) Collect and detect the AV index data of cellulose acetate under various process conditions. For each collection of AV index, record the values ​​of the first-category process state parameters at the time of sampling, including: catalyst concentration and reaction temperature; record the values ​​of the second-category process state parameters at the time of sampling, including the reaction time of the material under a specific first-category process state parameter.

[0049] In this embodiment, the sampling interval is no more than 10 minutes, and the change of the first type of process state parameters is divided into five stages. In each stage, one or more of the catalyst concentration and the reaction temperature changes. The first stage is the initial stage of the reaction, and the reaction temperature slowly rises from the initial temperature to the first temperature; in the second stage, the catalyst concentration decreases and the temperature is accelerated to the second temperature; in the third stage, the reaction temperature is maintained at the second temperature and hydrolysis is performed at a constant temperature; in the fourth stage, the reaction temperature is maintained at the second temperature, and the catalyst concentration is further reduced; in the fifth stage, the reaction temperature is maintained at the second temperature, and the catalyst concentration is zero; the AV value test results and the first and second type process state parameters are shown in the following table.

[0050]

[0051]

[0052] (2) Based on the collected AV index data of cellulose acetate under various process conditions, the AV index change rate based on the first and second process state parameters is calculated.

[0053]

[0054]

[0055] (3) Establish a mathematical model of AV index changes and the first and second type process state parameters.

[0056]

[0057] (4) According to the mathematical calculation relationship between the AV index and the first and second process state parameters, the change of the AV index under a specific first process state parameter (initial catalyst concentration of 0.428%, starting temperature of 50°C, first reaction temperature of 70°C, and second reaction temperature of 95°C) is calculated. According to the target value of the AV index of the cellulose acetate product of 55.50%, the second process state parameter (i.e., the reaction time of the material) is calculated, and the set value of the reaction time is adjusted in the control system to control the final output value of the AV index of the cellulose acetate product to achieve the design target.

[0058] In this embodiment, the AV value of triacetyl cellulose is 60.041%, and the target AV value after hydrolysis is 55.50%. The starting temperature of the hydrolysis reaction is 50°C, and the first reaction temperature needs to reach 70°C. According to the temperature change rate of the first stage, it takes 36.8 minutes; the second reaction temperature needs to reach 95°C, and according to the temperature change rate of the second stage, it takes 35.2 minutes;

[0059] The AV values ​​of the first and second stages decreased by 3.4174%, and the reaction time of the fourth stage was set to 15 minutes. The AV value of the fourth stage decreased by 0.414%, so the AV value of the third stage needed to decrease by 0.7096%, and the third stage took 13.4 minutes. The overall reaction time was 100.4 minutes, and the system reaction time was set to 100.4 minutes.

[0060] (5) Based on the mathematical calculation relationship between the AV index and the first and second process state parameters, the change of the AV index under a specific first process state parameter (initial catalyst concentration of 0.428%, starting temperature of 50°C, first reaction temperature of 75°C, and second reaction temperature of 95°C) is calculated. Based on the target value of the AV index of the cellulose acetate product of 55.20%, the second process state parameter (i.e., the reaction time of the material) is calculated, and the set value of the reaction time is adjusted in the control system to control the final output value of the AV index of the cellulose acetate product to achieve the design target.

[0061] In this embodiment, the AV value of triacetyl cellulose is 60.041%, and the target AV value after hydrolysis needs to reach 55.20%. The starting temperature of the hydrolysis reaction is 50°C, the first reaction temperature needs to reach 75°C, and according to the temperature change rate of the first stage, the time taken is calculated to be 45.9 minutes; the second reaction temperature needs to reach 95°C, and according to the temperature change rate of the second stage, the time taken is calculated to be 28.2 minutes;

[0062] The AV value of the first and second stages decreased by 4.3276%. The reaction time of the fourth stage was set to 10 minutes. The AV value of the fourth stage decreased by 0.276%. The AV value of the third stage needed to decrease by 0.2374%. The third stage took 4.5 minutes. The overall reaction time was 88.6 minutes, and the AV target value after hydrolysis could reach 55.20%.

[0063] Embodiment 3

[0064] (1) Collect and detect the AV index data of cellulose acetate under various process conditions. For each collection of AV index, record the values ​​of the first-category process state parameters at the time of sampling, including: catalyst concentration and reaction temperature; record the values ​​of the second-category process state parameters at the time of sampling, including the reaction time of the material under a specific first-category process state parameter.

[0065] In this embodiment, the sampling interval is no more than 10 minutes, and the change of the first type of process state parameters is divided into five stages. In each stage, one or more of the catalyst concentration and the reaction temperature changes. The first stage is the initial stage of the reaction, and the reaction temperature slowly rises from the initial temperature to the first temperature; in the second stage, the catalyst concentration decreases and the temperature is accelerated to the second temperature; in the third stage, the reaction temperature is maintained at the second temperature and hydrolysis is performed at a constant temperature; in the fourth stage, the reaction temperature is maintained at the second temperature, and the catalyst concentration is further reduced; in the fifth stage, the reaction temperature is maintained at the second temperature, and the catalyst concentration is zero; the AV value test results and the first and second type process state parameters are shown in the following table.

[0066]

[0067]

[0068] (2) Based on the collected AV index data of cellulose acetate under various process conditions, the AV index change rate based on the first and second process state parameters is calculated.

[0069]

[0070]

[0071] (3) Establish a mathematical model of AV index changes and the first and second type process state parameters.

[0072]

[0073] (4) According to the mathematical calculation relationship between the AV index and the first and second process state parameters, the change of the AV index under a specific first process state parameter (initial catalyst concentration of 0.202%, starting temperature of 50°C, first reaction temperature of 70°C, and second reaction temperature of 105°C) is calculated. According to the target value of the AV index of the cellulose acetate product of 55.50%, the second process state parameter (i.e., the reaction time of the material) is calculated, and the set value of the reaction time is adjusted in the control system to control the final output value of the AV index of the cellulose acetate product to achieve the design target.

[0074] In this embodiment, the AV value of triacetyl cellulose is 60.041%, and the target AV value after hydrolysis is 55.50%. The starting temperature of the hydrolysis reaction is 50°C, and the first reaction temperature needs to reach 70°C. According to the temperature change rate of the first stage, it takes 36.4 minutes; the second reaction temperature needs to reach 105°C, and according to the temperature change rate of the second stage, it takes 48.7 minutes;

[0075] The AV value of the first and second stages decreased by 4.2896%. The reaction time of the fourth stage was set to 5 minutes.

[0076] The value drops by 0.1295%, so the AV value in the third stage needs to drop by 0.1219%. The third stage takes 2.4 minutes. The overall response time is 92.5 minutes, and the system response time is set to 92.5 minutes.

[0077] (5) Based on the mathematical calculation relationship between the AV index and the first and second process state parameters, the change of the AV index under a specific first process state parameter (initial catalyst concentration of 0.202%, starting temperature of 50°C, first reaction temperature of 70°C, and second reaction temperature of 105°C) is calculated. Based on the target value of the AV index of the cellulose acetate product of 55.20%, the second process state parameter (i.e., the reaction time of the material) is calculated, and the set value of the reaction time is adjusted in the control system to control the final output value of the AV index of the cellulose acetate product to achieve the design target.

[0078] In this embodiment, the AV value of triacetyl cellulose is 60.041%, and the target AV value after hydrolysis needs to reach 55.20%. The starting temperature of the hydrolysis reaction is 50°C, the first reaction temperature needs to reach 70°C, and according to the temperature change rate of the first stage, it takes 36.4 minutes; the second reaction temperature needs to reach 105°C, and according to the temperature change rate of the second stage, it takes 48.7 minutes;

[0079] The AV value of the first and second stages decreased by 4.2896%. The reaction time of the fourth stage was set to 10 minutes.

[0080] The value dropped by 0.259%, so the AV value in the third stage needs to drop by 0.4924%, and the third stage takes 9.8 minutes; the overall reaction time is 104.9 minutes, and the AV target value after hydrolysis can reach 55.20%.

[0081] The AV index process control method of the acetate fiber hydrolysis process of the present invention establishes a mathematical calculation relationship between the AV index and the first and second process state parameters, calculates the change of the AV index under the specific first process state parameters, and can directly adjust the second process state parameters (i.e., the reaction time of the material) during the production process to control the final output value of the AV index of the cellulose acetate product to achieve the design target. The present invention can effectively reduce the hysteresis of the current AV index control, control the hydrolysis process with the guidance of the mathematical model, reduce the influence of factors such as personnel experience, effectively improve the process control capability of the AV index, and improve the stability of product quality.

[0082] The above-mentioned related explanations and descriptions of the embodiments are for the convenience of those skilled in the art to understand and apply the present invention. It is obvious that those familiar with the art can easily make various modifications to these contents and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above-mentioned related explanations and descriptions of the embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for controlling the AV index of a cellulose acetate hydrolysis process, characterized in that: During the hydrolysis process of cellulose acetate, the first type of process state parameters are measured, the instantaneous values ​​of the second type of process state parameters are recorded, and the AV index of the cellulose acetate slurry is measured; a mathematical model of the AV index based on the knowledge base and the first and second types of process state parameters is established according to the test results of multiple batches; the first and second types of process state parameters are adjusted in combination with the mathematical model based on the knowledge base and the detection value of the AV index of the cellulose acetate slurry to control the final output value of the AV index of the cellulose acetate product to achieve the design target.

2. The AV index process control method for cellulose acetate hydrolysis process according to claim 1, characterized in that: The following steps are involved: During the hydrolysis of cellulose acetate, the first process state parameters of the hydrolysis of cellulose acetate are measured, the instantaneous values ​​of the second process state parameters are recorded, and the AV index of the cellulose acetate slurry is measured; According to the collected AV index data of cellulose acetate under various process states, the AV index change rate based on the first and second process state parameters is calculated; Establish a mathematical model of AV index changes and the first and second type of process state parameters; According to the mathematical model of the AV index and the first and second process state parameters, the change of the AV index under a specific first process state parameter is calculated, and according to the target value of the AV index of the cellulose acetate product, the second process state parameter is calculated, and the set value of the reaction time is adjusted in the control system to control the final output value of the AV index of the cellulose acetate product to achieve the design target.

3. The AV index process control method for cellulose acetate hydrolysis process according to claim 1, characterized in that: The first type of process state parameters include catalyst concentration and reaction temperature, at least one of which changes during the reaction; the second type of process state parameters refers to the reaction time of the material under the conditions of the first type of process state parameters.

4. The AV index process control method for cellulose acetate hydrolysis process according to claim 2, characterized in that: The AV index change rate based on the first and second types of process state parameters includes the AV value change rate (% / min) and the change rate of the AV value change rate with temperature (% / °C / min).

5. The AV index process control method for cellulose acetate hydrolysis process according to claim 2, characterized in that: The mathematical model of the AV index change and the first and second types of process state parameters refers to the mathematical calculation relationship between the AV index change and the first and second types of process state parameters.

6. The AV index process control method for cellulose acetate hydrolysis process according to claim 2, characterized in that: The cellulose acetate hydrolysis process hydrolyzes triacetyl cellulose into diacetyl cellulose, wherein the AV index range of triacetyl cellulose is 59-61.5%; and the AV index range of diacetyl cellulose is 50-58%.

7. The AV index process control method for cellulose acetate hydrolysis process according to claim 2, characterized in that: The cellulose acetate hydrolysis process is divided into five stages: the first stage is the reaction start stage, and the reaction temperature slowly rises from the start temperature to the first temperature; the second stage is the reaction catalyst concentration decreases, and the temperature is accelerated to the second temperature; the third stage is the reaction temperature maintained at the second temperature, and constant temperature hydrolysis is performed; the fourth stage is the reaction temperature maintained at the second temperature, and the catalyst concentration is further reduced; the fifth stage is the reaction temperature maintained at the second temperature, and the concentration is zero after the catalyst is completely neutralized.

8. The AV index process control method for cellulose acetate hydrolysis process according to claim 7, characterized in that: The heating rate in the first stage is within the range of 0.5-0.6°C / min, and the heating rate in the second stage is within the range of 0.7-0.8°C / min.

9. The AV index process control method for cellulose acetate hydrolysis process according to claim 7, characterized in that: The first stage lasts for 0-38 minutes, the second stage lasts for 26-51 minutes, the third stage lasts for 2.5-35 minutes, the fourth stage lasts for 5-35 minutes, and the fifth stage lasts for 10-20 minutes.

10. The AV index process control method for cellulose acetate hydrolysis process according to claim 2, characterized in that: The mathematical calculation relationship between the AV index change and the first and second type process state parameters is as follows: The AV change in the first stage is: a1*b1*X1 2 , where a1 is the temperature change rate of the first stage (℃ / min), b1 is the rate of change of the AV value of the first stage with the temperature (% / ℃ / min), and X1 is the reaction time of the first stage; The second stage AV change is: a2*b2*(X2-X1) 2 , where a2 is the temperature change rate of the first stage (℃ / min), b2 is the rate of change of the AV value of the first stage with the temperature (% / ℃ / min), X2 is the reaction time of the second stage, and X1 is the reaction time of the first stage; The AV change in the third stage is: c3*(X3-X2), where c3 is the AV value change rate in the third stage (% / min), X3 is the reaction time in the third stage, and X2 is the reaction time in the second stage; The AV change in the fourth stage is: c4*(X4-X3), where c4 is the AV value change rate in the fourth stage (% / min), X4 is the reaction time in the fourth stage, and X3 is the reaction time in the third stage; The AV change in the fifth stage is: c5*(X5-X4), where c5 is the AV value change rate in the fifth stage (% / min), X5 is the reaction time in the fifth stage, and X4 is the reaction time in the fourth stage.

11. The AV index process control method for cellulose acetate hydrolysis process according to claim 7, characterized in that: The initial concentration range of the catalyst is 0.1-0.8%.

12. The AV index process control method for cellulose acetate hydrolysis process according to claim 7, characterized in that: The starting temperature range is 48-55°C; the first temperature range is 70-80°C; and the second temperature range is 82-106°C.

13. The AV index process control method for cellulose acetate hydrolysis process according to claim 2, characterized in that: The AV index of cellulose acetate was tested using HPLC-ELSD method.

14. The AV index process control method for cellulose acetate hydrolysis process according to claim 13, characterized in that: The cellulose acetate slurry is mixed with acetic acid or acetone to prepare a dilute cellulose acetate solution, and HPLC-ELSD test is carried out to obtain the AV index of the cellulose acetate slurry.

15. The AV index process control method for cellulose acetate hydrolysis process according to claim 14, characterized in that: The mass ratio of the cellulose acetate slurry to acetic acid or acetone is (1:20-30).

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