Advanced control method for mixed acid feeding in cellulose acetification reaction

Abstract

The invention relates to an advanced mixed acid feeding control method for cellulose acetification reaction, which comprises the following steps of: measuring the heat change of a system under actual production conditions to obtain the actual unit mass reaction heat of exothermic reaction of water and acetic anhydride and the actual consumed mixed acid amount when the temperature of the system is increased by 1 DEG C, and eliminating the inherent noise variables of stirring, jacket cooling, heat preservation and other equipment; comparing the heat change before and after the reaction neutralizer is added into the system with the actual unit mass reaction heat of the exothermic reaction of the water and the acetic anhydride, and calculating the system temperature variation (TSR) caused by the exothermic reaction of the water and the excessive acetic anhydride according to the actual consumed mixed acid amount when the temperature of the system is increased by 1 DEG C; a relation model between core process parameters such as reaction neutralizer feeding amount, feeding temperature and system temperature change and TSR is established, a control algorithm is written, advanced control is performed on mixed acid feeding according to real-time data of the process parameters, and the purpose of reducing mixed acid consumption is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical control, and relates to an advanced material consumption control method, in particular to an advanced material consumption control method in intermittent production. Background Art

[0002] The intermittent process has the characteristics of small batches, multiple varieties, serialization, complex synthesis steps, and intensive technology. Its production is flexible and its products have high added value. The feed amount of each process material in the intermittent process affects the operation of process parameters and product quality. In the actual production process, the consumption of materials is often increased to ensure the stability of core process parameters and product quality. Advanced control is widely used in typical chemical unit operations of continuous production, but there are few application cases in intermittent processes, especially in the field of intermittent cellulose production. How to perform advanced control of material consumption within the scope of intermittent production process has become an important topic.

[0003] The cellulose esterification reaction is the core reaction for producing cellulose diacetate for tobacco. Under the action of a catalyst, excess acetic anhydride (mixed acid) reacts with cellulose. When the esterification reaction is completed, a reaction neutralizer is added to neutralize the catalyst to terminate the reaction. At this time, the water in the reaction neutralizer reacts exothermically with the excess unreacted acetic anhydride, causing the system temperature to change. At the same time, the temperature of the reaction neutralizer is much higher than the temperature of the original esterification reaction system. After the high-temperature reaction neutralizer is added, the esterification reaction system also has a certain temperature rise. In the process control of cellulose esterification reaction, the degree of excess of mixed acid is judged according to the temperature change (SR) of the system after the addition of the reaction neutralizer. However, due to the interference of the high-temperature reaction neutralizer causing the system temperature to rise, in actual operation, the amount of mixed acid is often increased to ensure sufficient reaction materials, resulting in increased material consumption and increased manufacturing costs. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide an advanced control method for mixed acid feed of cellulose acetification reaction, which can truly reflect the system temperature change (TSR) caused by the exothermic reaction between water and excess acetic anhydride, and accordingly perform lean control on the feed amount of mixed acid to the acetifier, thereby reducing the mixed acid consumption and improving the advanced control level of the intermittent reaction process.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The temperature change (SR) of the system after the addition of the reaction neutralizer is deducted from the temperature rise of the system caused by the higher temperature of the reaction neutralizer, and the temperature change (TSR) of the system caused by the exothermic reaction between water and excess acetic anhydride is calculated. The amount of mixed acid added to the acetifier is controlled according to the change of TSR to achieve the purpose of reducing the consumption of mixed acid.

[0007] Further, an advanced control method for mixed acid feed of cellulose esterification reaction is provided. The technical method is to calculate the system temperature change (TSR) caused by the exothermic reaction between water and excess acetic anhydride in the esterification reaction system, and use a computer algorithm to control the amount of mixed acid added to the esterifier. Further: using existing production equipment, measure the heat change of the system under actual production conditions, obtain the actual unit mass reaction heat of the exothermic reaction between water and acetic anhydride, and the amount of mixed acid actually consumed when the system temperature rises by 1°C, and eliminate the inherent noise variables of the equipment such as stirring, jacket cooling, and insulation; compare the heat change before and after the reaction neutralizer is added to the system with the actual unit mass reaction heat of the exothermic reaction between water and acetic anhydride, calculate the system temperature change (TSR) caused by the exothermic reaction between water and excess acetic anhydride according to the actual amount of mixed acid consumed when the system temperature rises by 1°C, establish a relationship model between the core process parameters such as the reaction neutralizer feed amount, feed temperature and system temperature change and TSR, write a control algorithm, and perform advanced control on the mixed acid feed according to the real-time data of the above process parameters to achieve the purpose of reducing the consumption of mixed acid. The method comprises the following steps:

[0008] 1) Using the existing production equipment, when the esterification reaction is complete, a certain amount of water (accounting for no less than 0.1% and no more than 1% of the total weight of the system) is added to react with the excess acetic anhydride in the system, and the heat change of the system is measured to obtain the actual unit mass reaction heat of the exothermic reaction of water and acetic anhydride, thereby eliminating noise variables such as stirring, jacket cooling, and insulation;

[0009] 2) using existing production equipment, after the esterification reaction is complete and the reaction neutralizer is added, a certain amount of mixed acid (accounting for not less than 1% and not more than 6% of the total weight of the system) is added to react with excess water in the system, and the actual amount of mixed acid consumed when the temperature rises by 1° C. after the reaction neutralizer is added to the system is calculated;

[0010] 3) Compare the heat change before and after the reaction neutralizer is added to the system with the actual unit mass reaction heat of the exothermic reaction between water and acetic anhydride, calculate the TSR based on the actual amount of mixed acid consumed when the system temperature rises by 1°C, and use the calculation of a few key parameters to eliminate the external heat brought by the high temperature reaction neutralizer;

[0011] 4) Establish a mathematical model of TSR and mixed acid feed amount, complete the computer language compilation of the mathematical model, and fill the program in each production line, set up alarms and process control plans, and realize advanced control of the mixed acid feed amount based on a few key process parameters of the cellulose acetification reaction to reduce mixed acid consumption.

[0012] Optionally, the mixed acid is a mixture of acetic acid and acetic anhydride, and the mass fraction of acetic anhydride is 30-80%.

[0013] Optionally, the esterification reaction in step (1) is as follows: the pulp containing α-cellulose is pretreated, and acetic anhydride is reacted with the acetic anhydride under the action of a catalyst, and a reaction neutralizer is added to terminate the esterification reaction when the esterification reaction is complete. The α-cellulose content of the pulp is greater than 95%; and / or the pretreatment agent can be any one of acetic acid, mixed acid, propionic acid, water, liquid ammonia, ethylenediamine, etc.; and / or the catalyst can be any one of sulfuric acid, phosphoric acid, perchloric acid, or a combination of two or more thereof; and / or the reaction neutralizer can be any one of an acidic aqueous solution of barium chloride, barium carbonate, calcium chloride, calcium hydroxide, and magnesium oxide.

[0014] Optionally, the actual unit mass heat of reaction of the reactants obtained by measuring the heat change of the reaction system described in step (1) is: the unit mass heat of reaction of water and acetic anhydride in the reaction neutralizer (X3) is measured under actual production conditions such as insulation, stirring, and refrigerant cooling of existing equipment.

[0015] Optionally, the mixed acid in step (2) is a mixture of acetic acid and acetic anhydride; the reaction neutralizing agent can be any one of an acidic aqueous solution of barium chloride, barium carbonate, calcium chloride, calcium hydroxide, and magnesium oxide.

[0016] Optionally, the few key parameters described in step (3) are: the temperature of the cellulose esterification reaction system before the reaction neutralizer is added (X1), the temperature of the reaction neutralizer (X2), the amount of the reaction neutralizer added (X4), and the temperature change of the cellulose esterification reaction system after the reaction neutralizer is added (X5).

[0017] Optionally, the mathematical model described in step (4) is: the set value of the next batch of mixed acid feed = the actual value of the current batch of mixed acid feed - A*(TSR actual - TSR set target value), where the range of A is 15-30, the set target range of TSR is 1-7, and the operating control range of TSR is 0.5-15.

[0018] Optionally, the operation model of TSR in the mathematical model is: TSR=(B*X4 / X3)*(X2-X1-X5), where the range of B is 0.15-0.3.

[0019] Optionally, the alarm and process control scheme described in step (4) is:

[0020] When the actual value of TSR is ≥ the set target value of TSR + C, or the actual value of TSR is ≤ the set target value of TSR - C, an alarm pops up to prompt the operator to intervene in the mixed acid feed, where the range of C is 1-10;

[0021] TSR target value - D ≤ TSR actual value ≤ TSR target value + D, then the mixed acid feed amount is not adjusted, where D ranges from 0.1 to 10;

[0022] If the actual TSR value is less than the set TSR target value - D, or greater than the set TSR target value + D, the automatic feeding program will perform advanced control on the mixed acid feed according to the mathematical model: the set value for the next batch of mixed acid feed = the actual value for the current batch of mixed acid feed - A* (actual TSR - set TSR target value).

[0023] Due to the adoption of the above technical solution, the present invention has at least the following beneficial effects:

[0024] The mathematical model of mixed acid feed amount established in the present invention calculates the system temperature change (TSR) caused by the exothermic reaction between water and excess acetic anhydride, eliminates the noise variables inherent in existing equipment, and eliminates the temperature change effect caused by the high-temperature reaction neutralizer; this model does not need to calculate the feed amount of various substances in the esterification reaction, temperature and other numerous process parameters, and only performs real-time calculations on four process parameters such as the reaction neutralizer addition amount and temperature. The model has the characteristics of simple calculation and accurate results, and introduces correction coefficients to correct and improve the mathematical models of each production line based on the actual process data of different production lines; by compiling the mathematical model, program filling is performed on each production line, and alarm and control schemes are set, so as to realize advanced control of the mixed acid feed amount according to a few key process parameters of the cellulose esterification reaction and reduce the mixed acid consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0026] Example 1

[0027] Step 1: Measure the actual unit mass heat of reaction of the exothermic reaction between water and acetic anhydride;

[0028] When the esterification reaction is complete and the system temperature is maintained stable, 0.1% of the total weight of deionized water is added to the system to react with the excess acetic anhydride in the system. The temperature change of the system is measured using a temperature transmitter. The actual unit mass reaction heat of the exothermic reaction of water and acetic anhydride is calculated based on the added mass, specific heat capacity and other data of various substances in the esterification reaction system.

[0029] The reaction equation of cellulose acetification is shown below. Under the action of the catalyst, the alcoholic hydroxyl group in cellulose is replaced by the acetyl group of acetic anhydride in the mixed acid to produce triacetyl cellulose. When the reaction is completed, most of the acetic anhydride in the mixed acid reacts with cellulose to form acetic acid, and the remaining part is unreacted acetic anhydride.

[0030]

[0031] Specifically, the measurement of the actual unit mass heat of reaction of the above-mentioned exothermic reaction between water and acetic anhydride needs to be carried out under actual working conditions to eliminate the noise variables inherent in the equipment such as stirring, jacket cooling, and insulation.

[0032]

[0033] Step 2: Measure the amount of mixed acid actually consumed when the system is heated by 1°C after adding the reaction neutralizer;

[0034] After the reaction neutralizer is completely added to the esterification reaction, wait until the system temperature remains stable, add mixed acid accounting for 1.5% of the total weight of the system into the system to react with excess water in the system, and use a temperature transmitter to measure the temperature change of the system. According to the added mass, specific heat capacity and other data of various substances in the esterification reaction system, calculate the actual amount of mixed acid consumed when the temperature rises by 1°C when the reaction neutralizer is not added to the system.

[0035]

[0036]

[0037] Step 3: Calculate the temperature change of the system caused by the exothermic reaction between water and excess acetic anhydride

[0038] The heat change before and after the reaction neutralizer is added to the system is compared with the actual unit mass reaction heat of the exothermic reaction between water and acetic anhydride. The system temperature change (TSR) caused by the exothermic reaction between water and excess acetic anhydride is calculated based on the actual amount of mixed acid consumed when the system temperature rises by 1°C.

[0039] The following parameters are used in the calculation of TSR: the temperature of the cellulose esterification reaction system before the addition of the reaction neutralizer (X1), the temperature of the reaction neutralizer (X2), the unit mass reaction heat of water and acetic anhydride (X3), the addition amount of the reaction neutralizer (X4), and the temperature change of the cellulose esterification reaction system after the addition of the reaction neutralizer (X5).

[0040] The unit mass reaction heat of water and acetic anhydride (X3) is an adjustable item. The actual unit mass reaction heat of the exothermic reaction between water and acetic anhydride is measured regularly, and the changes in noise variables such as stirring, jacket cooling, and insulation are observed and evaluated to correct the TSR.

[0041]

[0042] Step 4: Establish mathematical model and process control of TSR and mixed acid feed amount

[0043] 1. Establishment of mathematical model of TSR and mixed acid feed amount

[0044] The logic of using TSR to control the mixed acid feed amount is: set the TSR target value, and adjust the mixed acid feed of the next batch according to the difference between the actual TSR value of the current batch and the target value, based on the actual consumption of 48.8 kg of mixed acid for a 1°C temperature rise in the system, that is, the actual TSR value of the current batch differs from the target value by 1°C, and the mixed acid feed of the next batch is adjusted by 48.8 kg. Due to certain batch differences in intermittent reactions, the feed amount can be adjusted according to 31-62% for safety reasons. This embodiment selects 50%, that is, the actual TSR value of the current batch differs from the target value by 1°C, and the mixed acid feed of the next batch is adjusted by 24.4 kg.

[0045] The set value of the next batch of mixed acid feed = the actual value of the current batch of mixed acid feed - 24.4 * (TSR actual - TSR set target value)

[0046] 2. Alarm and process control solutions

[0047] The premise of automatically controlling the mixed acid feed rate through TSR is that TSR is stable within a reasonable range. If TSR is too low, it means that the excess of mixed acid is too low, and it is necessary to find out the cause and conduct process inspection and analysis; if TSR is too high, mixed acid is wasted. In this embodiment, the absolute value of the difference between the actual TSR value and the set target TSR value is 1.5-3.5.

[0048] The following scheme is adopted in this embodiment:

[0049] When the actual TSR value is ≥ the TSR set target value + 3.5, or ≤ the TSR set target value - 3.5, an alarm pops up to prompt the operator to intervene in the mixed acid feed;

[0050] If TSR target value -1.5 ≤ TSR actual value ≤ TSR target value +1.5, the mixed acid feed amount will not be adjusted;

[0051] If the actual TSR value is less than the TSR target value - 1.5, or the actual TSR value is greater than the TSR target value + 1.5, the automatic feeding program will adjust the feed amount of the next batch of mixed acid according to the mathematical model: the feed setting value of the next batch of mixed acid = the actual feed value of the current batch of mixed acid - A*(actual TSR - TSR target value). (A = 24.4kg)

[0052] Example 2

[0053] Step 1: Measure the actual unit mass heat of reaction of the exothermic reaction between water and acetic anhydride;

[0054] When the esterification reaction is complete and the system temperature is maintained stable, 0.2%wt of deionized water is added to the system to react with the excess acetic anhydride in the system. The temperature change of the system is measured using a temperature transmitter. The actual unit mass reaction heat of the exothermic reaction of water and acetic anhydride is calculated based on the added mass, specific heat capacity and other data of various substances in the esterification reaction system.

[0055] The specific implementation steps are the same as step 1 of Example 1.

[0056]

[0057] Step 2: After adding the reaction neutralizer to the system, the actual amount of mixed acid consumed when the temperature rises by 1°C;

[0058] After the reaction neutralizer is completely added to the esterification reaction, wait until the system temperature is kept stable, add 3%wt of the total weight of the system into the system to react with the excess water in the system, and use a temperature transmitter to measure the temperature change of the system. According to the added mass, specific heat capacity and other data of various substances in the esterification reaction system, calculate the actual amount of mixed acid consumed when the temperature rises by 1°C when the reaction neutralizer is not added to the system.

[0059] The specific implementation steps are the same as step 2 of Example 1.

[0060]

[0061] Step 3: Calculate the temperature change (TSR) of the system caused by the exothermic reaction between water and excess acetic anhydride

[0062] The heat change before and after the reaction neutralizer is added to the system is compared with the actual unit mass reaction heat of the exothermic reaction between water and acetic anhydride. The system temperature change (TSR) caused by the exothermic reaction between water and excess acetic anhydride is calculated based on the actual amount of mixed acid consumed when the system temperature rises by 1°C.

[0063] The calculation parameters and specific implementation steps of TSR are the same as step 3 of Example 1.

[0064]

[0065] Step 4: Establish mathematical model and process control of TSR and mixed acid feed amount

[0066] 1. Establishment of mathematical model of TSR and mixed acid feed amount

[0067] The logic of TSR controlling the mixed acid feed amount is the same as step 4 of Example 1: 31% is selected in this example, that is, the actual TSR value of the current batch differs from the target value by 1°C, and the mixed acid feed amount of the next batch is adjusted to 15.3kg.

[0068] The set value of the next batch of mixed acid feed = the actual value of the current batch of mixed acid feed - A*(TSR actual - TSR set target value)

[0069] 2. Alarm and process control solutions

[0070] The premise of automatically controlling the mixed acid feed rate through TSR is that TSR is stable within a reasonable range. If TSR is too low, it means that the excess of mixed acid is too low, and it is necessary to find out the cause and conduct process inspection and analysis; if TSR is too high, mixed acid is wasted. In this embodiment, the absolute value of the difference between the actual TSR value and the set target TSR value is 2-5.

[0071] The following scheme is adopted in this embodiment:

[0072] When the actual value of TSR is ≥ the set target value of TSR + 5 or the actual value of TSR is ≤ the set target value of TSR - 5, an alarm pops up to prompt the operator to intervene in the mixed acid feed;

[0073] If TSR target value -2 ≤ TSR actual value ≤ TSR target value +2, the mixed acid feed amount will not be adjusted;

[0074] If the actual TSR value is less than the set TSR target value - 2, or the actual TSR value is greater than the set TSR target value + 2, the automatic feeding program will adjust the feed amount of the next batch of mixed acid according to the mathematical model: the set value of the next batch of mixed acid feed = the actual value of the current batch of mixed acid feed - A*(actual TSR - set TSR target value). (A = 15.3kg)

[0075] Example 3

[0076] Step 1: Measure the actual unit mass heat of reaction of the exothermic reaction between water and acetic anhydride;

[0077] When the esterification reaction is complete and the system temperature is maintained stable, 0.4%wt of deionized water is added to the system to react with the excess acetic anhydride in the system. The temperature change of the system is measured using a temperature transmitter. The actual unit mass reaction heat of the exothermic reaction of water and acetic anhydride is calculated based on the added mass, specific heat capacity and other data of various substances in the esterification reaction system.

[0078] The specific implementation steps are the same as step 1 of Example 1.

[0079]

[0080] Step 2: After adding the reaction neutralizer to the system, the actual amount of mixed acid consumed when the temperature rises by 1°C;

[0081] After the reaction neutralizer is completely added to the esterification reaction, wait until the system temperature remains stable, add 5.5%wt of the total system weight of the mixed acid into the system to react with the excess water in the system, use a temperature transmitter to measure the temperature change of the system, and calculate the actual amount of mixed acid consumed when the temperature rises by 1°C when the system is not added with the reaction neutralizer based on the feed mass, specific heat capacity and other data of various substances in the esterification reaction system.

[0082] The specific implementation steps are the same as step 2 of Example 1.

[0083]

[0084] Step 3: Calculate the temperature change (TSR) of the system caused by the exothermic reaction between water and excess acetic anhydride

[0085] The heat change before and after the reaction neutralizer is added to the system is compared with the actual unit mass reaction heat of the exothermic reaction between water and acetic anhydride. The system temperature change (TSR) caused by the exothermic reaction between water and excess acetic anhydride is calculated based on the actual amount of mixed acid consumed when the system temperature rises by 1°C.

[0086] The calculation parameters and specific implementation steps of TSR are the same as step 3 of Example 1.

[0087]

[0088] Step 4: Establish mathematical model and process control of TSR and mixed acid feed amount

[0089] 1. Establishment of mathematical model of TSR and mixed acid feed amount

[0090] The logic of TSR controlling the mixed acid feed amount is the same as step 4 of Example 1: This example selects 62% to adjust the feed amount, that is, the actual TSR value of the current batch differs from the target value by 1°C, and the mixed acid feed amount of the next batch is adjusted to 29.5kg.

[0091] The set value of the next batch of mixed acid feed = the actual value of the current batch of mixed acid feed - 29.5 * (TSR actual - TSR set target value)

[0092] 2. Alarm and process control solutions

[0093] The premise of automatically controlling the mixed acid feed rate through TSR is that TSR is stable within a reasonable range. If TSR is too low, it means that the excess of mixed acid is too low, and it is necessary to find out the cause and conduct process inspection and analysis; if TSR is too high, it will cause waste of mixed acid. In this embodiment, the absolute value of the difference between the actual TSR value and the set TSR target value is 0.5-1.5.

[0094] The following scheme is adopted in this embodiment:

[0095] When the actual TSR value is ≥ the TSR set target value + 1.5, or ≤ the TSR set target value - 1.5, an alarm pops up to prompt the operator to intervene in the mixed acid feed;

[0096] If TSR target value -0.5 ≤ TSR actual value ≤ TSR target value +0.5, the mixed acid feed amount will not be adjusted;

[0097] If the actual TSR value is less than the set TSR target value - 0.5, or the actual TSR value is greater than the set TSR target value + 0.5, the automatic feeding program will adjust the feed amount of the next batch of mixed acid according to the mathematical model: the set value of the next batch of mixed acid feed = the actual value of the current batch of mixed acid feed - A*(actual TSR - set TSR target value). (A = 29.5kg)

[0098] The above description of the embodiments is to facilitate the understanding and use of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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. An advanced control method for mixed acid feed in cellulose esterification reaction, characterized in that: The temperature change TSR of the system caused by the exothermic reaction between water and excess acetic anhydride in the acetification reaction system is calculated, and the amount of mixed acid added to the acetification reactor is controlled using a computer algorithm to achieve the purpose of reducing the consumption of mixed acid.

2. The advanced control method for mixed acid feed of cellulose esterification reaction according to claim 1, characterized in that: Under actual production conditions, the heat change of the system is measured to obtain the actual unit mass reaction heat of the exothermic reaction between water and acetic anhydride and the actual amount of mixed acid consumed when the system temperature rises by 1°C, thereby eliminating inherent noise variables. The heat change before and after the reaction neutralizer is added to the system is compared with the actual unit mass reaction heat of the exothermic reaction between water and acetic anhydride. Based on the actual amount of mixed acid consumed when the system temperature rises by 1°C, the temperature change of the system caused by the exothermic reaction between water and excess acetic anhydride is calculated, and a relationship model between the core process parameters such as the reaction neutralizer feed amount, feed temperature and system temperature change and TSR is established. A control algorithm is written to perform advanced control of the mixed acid feed based on the real-time data of the above process parameters.

3. The advanced control method for mixed acid feed of cellulose esterification reaction according to claim 1, characterized in that: The inherent noise variables include the inherent noise of stirring, jacket cooling and insulation equipment.

4. The method for controlling mixed acid feed in cellulose esterification reaction according to claim 1, characterized in that The following steps are involved: (1) Using existing production equipment, when the esterification reaction is complete, a certain amount of water is added to react with the excess acetic anhydride in the system, and the heat change of the system is measured to obtain the actual unit mass reaction heat of the exothermic reaction of water and acetic anhydride, thereby eliminating noise variables such as stirring, jacket cooling, and heat preservation; (2) Using existing production equipment, after the esterification reaction is complete and the reaction neutralizer is added, a certain amount of mixed acid is added to react with excess water in the system, and the amount of mixed acid actually consumed when the temperature rises by 1°C after the reaction neutralizer is added to the system is calculated; (3) Compare the heat change before and after the reaction neutralizer is added to the system with the actual unit mass reaction heat of the exothermic reaction between water and acetic anhydride, calculate the TSR based on the actual amount of mixed acid consumed when the system temperature rises by 1°C, and use the calculation of a few key parameters to eliminate the external heat brought by the high temperature reaction neutralizer; (4) A mathematical model of TSR and mixed acid feed amount was established, the mathematical model was compiled into a computer language, and the program was filled in each production line. Alarm and process control schemes were set up to achieve advanced control of the mixed acid feed amount based on a few key process parameters of the cellulose acetification reaction, thereby reducing the mixed acid consumption.

5. The advanced control method for mixed acid feed of cellulose esterification reaction according to claim 1, characterized in that: The mixed acid is a mixture of acetic acid and acetic anhydride, and the mass fraction of acetic anhydride is 30-80%.

6. The advanced control method for mixed acid feed of cellulose esterification reaction according to claim 4, characterized in that: The quantitative amount of water in step (1) accounts for no less than 0.1% and no more than 1% of the total system weight.

7. The advanced control method for mixed acid feed of cellulose esterification reaction according to claim 4, characterized in that: The total weight of the quantitative mixed acid in step (2) is not less than 1% and not more than 6%.

8. The advanced control method for mixed acid feed of cellulose esterification reaction according to claim 4, characterized in that: The esterification reaction in step (1) is as follows: the pulp containing α-cellulose is pretreated, and then reacted with acetic anhydride under the action of a catalyst to undergo an esterification reaction, and when the esterification reaction is complete, a reaction neutralizer is added to terminate the esterification reaction.

9. The advanced control method for mixed acid feed of cellulose esterification reaction according to claim 4, characterized in that: The α-cellulose content of the pulp is greater than 95%; and / or the pretreatment agent is any one of acetic acid, propionic acid, water, liquid ammonia, and ethylenediamine; and / or the catalyst is any one of sulfuric acid, phosphoric acid, and perchloric acid or a combination thereof; and / or the reaction neutralizing agent is any one of an acidic aqueous solution of barium chloride, barium carbonate, calcium chloride, calcium hydroxide, and magnesium oxide.

10. The advanced control method for mixed acid feed of cellulose esterification reaction according to claim 4, characterized in that: The actual unit mass heat of reaction of the reactants obtained by measuring the heat change of the reaction system in step (1) is: under the actual production conditions of existing equipment insulation, stirring, and refrigerant cooling, the unit mass heat of reaction of water and acetic anhydride in the magnesium acetate aqueous solution is measured to be X3.

11. The advanced control method for mixed acid feed of cellulose esterification reaction according to claim 4, characterized in that: The few key parameters described in step (3) are: the temperature of the cellulose esterification reaction system before the addition of the magnesium acetate aqueous solution X1, the temperature of the magnesium acetate aqueous solution X2, the addition amount of the magnesium acetate aqueous solution X4, and the temperature change of the cellulose esterification reaction system after the addition of the magnesium acetate aqueous solution X5.

12. The advanced control method for mixed acid feed of cellulose esterification reaction according to claim 4, characterized in that: The mathematical model described in step (4) is: the set value of the next batch of mixed acid feed = the actual value of the current batch of mixed acid feed - A*(TSR actual - TSR set target value), where the range of A is 15-30, the set target range of TSR is 1-7, and the operating control range of TSR is 0.5-10.

13. The advanced control method for mixed acid feed of cellulose esterification reaction according to claim 12, characterized in that: The operation model of TSR in the mathematical model is: TSR=(B*X4 / X3)*(X2-X1-X5), where the range of B is 0.15-0.

3.

14. The advanced control method for mixed acid feed of cellulose esterification reaction according to claim 4, characterized in that: The alarm and control scheme described in step (4) is: When the actual value of TSR is ≥ the set target value of TSR + C, or the actual value of TSR is ≤ the set target value of TSR - C, an alarm pops up to prompt the operator to intervene in the mixed acid feed, where the range of C is 1-3; TSR target value - D ≤ TSR actual value ≤ TSR target value + D, then the mixed acid feed amount is not adjusted, where D ranges from 0.1 to 1; If the actual TSR value is less than the set TSR target value - D, or the actual TSR value is greater than the set TSR target value + D, the automatic feeding program will perform advanced control on the mixed acid feed according to the mathematical model: the set value for the next batch of mixed acid feed = the actual value for the current batch of mixed acid feed - A* (actual TSR - set TSR target value).

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