A method for predicting and controlling the conversion rate of bulk vinyl chloride polymerization

Abstract

The present invention relates to a method for predicting the conversion rate of bulk vinyl chloride polymerization and a control method. The prediction of the conversion rate includes: monitoring the vinyl chloride polymerization reaction to obtain the initiator consumption and the heat exchange amount in the vinyl chloride polymerization reaction process; calculating a first conversion rate value according to the initiator consumption; calculating a second conversion rate value according to the heat exchange amount; predicting the conversion rate of the vinyl chloride polymerization reaction according to the first conversion rate value and the second conversion rate value. The control includes presetting a target conversion rate for the completion of the vinyl chloride polymerization reaction; predicting the conversion rate according to the above-mentioned conversion rate prediction method to obtain the predicted conversion rate of the vinyl chloride polymerization reaction; and stopping the polymerization reaction when the reaction conversion rate reaches the target conversion rate requirement. The present invention can accurately predict and control the conversion rate of the polymerization reaction, especially the control of the prepolymerization conversion rate can improve the quality of the "seed" and prevent the prepolymerization from sticking to the kettle.

Description

Technical Field

[0001] The invention relates to the technical field of vinyl chloride polymerization, and in particular to a conversion rate prediction method and a control method for bulk vinyl chloride polymerization. Background Art

[0002] The bulk polymerization of vinyl chloride mainly adopts a two-stage polymerization process, that is, a certain amount of monomer is added to the prepolymerization kettle to control the conversion rate at 8% to 12% to prepare "seeds", and then the "seeds" are transferred to the polymerization kettle and vinyl chloride monomer is added to continue the reaction until the conversion rate is 50% to 60%. The prepolymerization cycle is about 2 hours, and the polymerization cycle is about 7 hours.

[0003] At present, the measurement of vinyl chloride conversion rate in bulk vinyl chloride polymerization is mainly to control the conversion rate by controlling the heat exchange amount and polymerization reaction time during the polymerization reaction. The error is large and it relies heavily on experience for control. If sampling and analysis are performed during the polymerization reaction to obtain the conversion rate, since the sampling and analysis itself takes time, in the presence of initiators, there will be a large difference between the results of such sampling and analysis and the conversion rate of the actual product, and the conversion rate of the vinyl chloride polymerization reaction cannot be accurately predicted and controlled. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for predicting the conversion rate of bulk vinyl chloride polymerization and a method for controlling bulk vinyl chloride polymerization, which can predict the conversion rate in the vinyl chloride polymerization process without sampling operation, thereby improving the quality of vinyl chloride polymerization "seeds", preventing pre-polymerization from sticking to the kettle or high conversion rate resulting in low product porosity, and residual monomers that are difficult to remove.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] The present invention provides a method for predicting the conversion rate of bulk vinyl chloride polymerization to achieve one of the above purposes. The vinyl chloride polymerization is carried out by the following reaction equation:

[0007]

[0008] The conversion rate prediction includes:

[0009] Monitoring the vinyl chloride polymerization reaction to obtain the initiator consumption and heat exchange amount during the vinyl chloride polymerization reaction;

[0010] Calculating a first conversion rate value according to the initiator consumption;

[0011] Calculating a second conversion rate value according to the heat exchange amount;

[0012] According to the first conversion rate value and the second conversion rate value, a weighted average algorithm is used to predict the vinyl chloride polymerization conversion rate.

[0013] The beneficial effects of the present invention are as follows: the present invention determines the conversion rate value based on the heat exchange amount in the vinyl chloride polymerization reaction process, and through a weighted average algorithm, can accurately predict the conversion rate of the polymerization reaction, can improve the quality of vinyl chloride polymerization "seeds", solves the problem of pre-polymerization sticking to the kettle or high conversion rate leading to low product porosity and residual monomers that are difficult to remove, and through the predicted conversion rate, can improve the vinyl chloride polymerization production efficiency.

[0014] Based on the above technical solution, the present invention can also be improved as follows.

[0015] Furthermore, the first conversion rate value is obtained by calculating the first PVC generation amount according to the initiator consumption, and then calculating the first conversion rate value according to the first PVC generation amount.

[0016] The beneficial effect of adopting the above further scheme is that the first PVC generation amount is calculated based on the consumption of the initiator, and then the first conversion rate value can be obtained based on the first PVC generation amount, and then the conversion rate of the polymerization reaction can be predicted through a weighted average algorithm.

[0017] The beneficial effects of adopting the above further scheme are:

[0018] Furthermore, the first PVC generation amount is calculated using the following formula:

[0019] W P1 =20*X*η*M VC *n*10 -6

[0020] Among them, W P1 is the first PVC production; X is the initiator consumption; η is the initiator efficiency, which is 0.5-0.8; M VC is the molecular weight of vinyl chloride, which is 62.5; n is the degree of polymerization of PVC, which is 650.

[0021] The beneficial effect of adopting the above further scheme is that the consumption of the initiator during the polymerization reaction can be calculated, and the first conversion rate value is more accurate.

[0022] Furthermore, the initiator consumption is calculated by the following formula:

[0023] X=(1-e -0.693t / h )*X0

[0024] Wherein, X is the initiator consumption; X0 is the initial dosage of the initiator; t is the polymerization reaction time; and h is the half-life of the initiator.

[0025] The beneficial effect of adopting the above further scheme is that the initiator consumption during the reaction can be accurately obtained, making the prediction of the conversion rate more accurate.

[0026] Furthermore, the second conversion rate value is obtained by calculating the second vinyl chloride production amount according to the heat exchange amount, and then calculating the second conversion rate value based on the second vinyl chloride production amount.

[0027] The beneficial effect of adopting the above further scheme is that the second PVC generation amount is calculated based on the heat exchange amount, and then the second conversion rate value can be obtained based on the second PVC generation amount, and then the conversion rate of the polymerization reaction can be predicted through the weighted average algorithm.

[0028] Furthermore, the second PVC generation amount is calculated using the following formula:

[0029] W P2 =(Q / q P )*10 -3

[0030] Among them, W P2 is the amount of second PVC generated; Q is the heat exchange amount of vinyl chloride polymerization reaction; q p The heat released to generate unit mass of PVC is taken as 1532 kJ / kg.

[0031] The beneficial effect of adopting the above further solution is that the amount of heat released per unit mass of PVC can be calculated after measuring the heat exchange amount.

[0032] Furthermore, the weighted average algorithm adopts the following formula:

[0033] C=0.4*C1+0.6*C2

[0034] Wherein, C is the vinyl chloride polymerization conversion rate, C1 is the first conversion rate value, and C2 is the second conversion rate value.

[0035] The beneficial effect of adopting the above further scheme is that the weighted average algorithm can complement the consumption of initiator and the amount of heat exchange to predict the conversion rate of the polymerization reaction. The parameters 0.4 and 0.6 used in the formula are parameters derived from the actual conversion rates of several previous polymerization reactions.

[0036] Furthermore, the initiator for the vinyl chloride polymerization reaction is EHP.

[0037] The beneficial effect of adopting the above further scheme is that the polymerization reaction initiated by using EHP as the initiator is stable.

[0038] The present invention provides a control method for bulk vinyl chloride polymerization to achieve the second objective. The control method comprises:

[0039] The polymerization of vinyl chloride is carried out by the following equation:

[0040]

[0041] Control of vinyl chloride polymerization includes:

[0042] Presetting a target conversion rate for the vinyl chloride polymerization reaction;

[0043] Predicting the conversion rate of the vinyl chloride polymerization reaction according to the above-mentioned conversion rate prediction method to obtain the predicted conversion rate of the vinyl chloride polymerization reaction;

[0044] When the reaction conversion rate reaches the target conversion rate, the polymerization reaction is stopped.

[0045] The beneficial effect of adopting the above scheme is: the vinyl chloride polymerization reaction is monitored, and the instantaneous conversion rate at the polymerization reaction time can be obtained by collecting various parameters of the conversion rate. When the instantaneous conversion rate reaches the target conversion rate requirement, the polymerization reaction is stopped, and then the pre-polymerized seed liquid can be transported to the next process for polymerization reaction, which is beneficial to control the indicators in the polymerization reaction process so that the conversion rate meets the target conversion rate requirement.

[0046] Furthermore, the target conversion rate is 8% to 12%.

[0047] The beneficial effect of adopting the above further scheme is that the quality of the vinyl chloride polymerization seed liquid within this target conversion rate range is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flow chart of the method for predicting the conversion rate of vinyl chloride polymerization of the present invention;

[0049] Figure 2 The present invention is a flow chart of the control method of vinyl chloride polymerization reaction. DETAILED DESCRIPTION

[0050] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0051] Example 1

[0052] like Figure 1As shown, this embodiment provides a method for predicting the conversion rate of bulk vinyl chloride polymerization. The vinyl chloride polymerization is carried out by the following reaction equation:

[0053]

[0054] In this embodiment, the vinyl chloride polymerization reaction is carried out at 70-71° C. corresponding to a saturated vapor pressure of 1.18-1.20 MPa, and the polymerization reaction is carried out in a heat exchange polymerization kettle. The conversion rate prediction method is used to predict the conversion rate of the vinyl chloride polymerization reaction.

[0055] Conversion prediction for vinyl chloride polymerization includes:

[0056] The polymerization reaction is monitored to obtain the initiator consumption and heat exchange amount during the polymerization reaction; when the polymerization reaction is in progress, the polymerization reaction temperature is maintained at 70-71°C by heat exchange, and the heat exchange amount is obtained by statistically analyzing the heat exchange; the initiator is gradually consumed during the polymerization reaction, so by monitoring the polymerization reaction time, the initiator consumption during the polymerization reaction can be obtained.

[0057] According to the initiator consumption, a first conversion rate value is calculated;

[0058] According to the heat exchange amount, a second conversion rate value is calculated;

[0059] According to the first conversion rate value and the second conversion rate value, a weighted average algorithm is used to predict the conversion rate of the polymerization reaction.

[0060] Preferably, the first conversion rate value is calculated based on the first PVC generation amount according to the initiator consumption, and then the first conversion rate value is calculated based on the first PVC generation amount.

[0061] It is easy to understand that the first PVC production amount is derived based on the initiator consumption, and the first conversion rate value is the ratio of the first PVC production amount to the initial loading amount of vinyl chloride.

[0062] Preferably, the first PVC generation amount is calculated using the following formula:

[0063] W P1 =20*X*η*M VC *n*10 -6

[0064] Among them, W P1 is the first PVC production; X is the initiator consumption; η is the initiator efficiency, which is 0.5-0.8; M VC is the molecular weight of vinyl chloride. In this embodiment, M VCThe value is 62.5; n is the degree of polymerization of PVC, and the value is 650.

[0065] Preferably, the initiator consumption is calculated by the following Arrhenius formula:

[0066] X=(1-e -0.693t / h )*X0

[0067] Wherein, X is the initiator consumption; X0 is the initial dosage of the initiator; t is the polymerization reaction time; and h is the half-life of the initiator.

[0068] The initial dosage of the initiator is the molar amount of the initiator initially added calculated based on the mass of the added initiator, the percentage concentration of the initiator and the molecular weight of the initiator.

[0069] Preferably, the second conversion rate value is calculated based on the heat exchange amount to obtain the second PVC generation amount, and then the second conversion rate value is calculated again based on the second PVC generation amount.

[0070] It is easy to understand that the second PVC production is derived from the calculation based on the heat exchange amount of the vinyl chloride polymerization reaction, and the second conversion rate value is the ratio of the second PVC production to the initial vinyl chloride loading amount, wherein the heat exchange amount is obtained by monitoring the cooling water flow rate and the cooling water inlet and outlet temperature difference during the polymerization reaction, and the heat exchange amount is calculated by calculus, the temperature difference is measured by installing thermometers on the cooling water inlet and outlet main pipes, and the cooling water flow rate is measured by installing a flow meter on the cooling water inlet main pipe.

[0071] Preferably, the second PVC generation amount is calculated using the following formula:

[0072] W P2 =(Q / q P )*10 -3

[0073] Among them, W P2 is the amount of second vinyl chloride generated; Q is the heat exchange amount of vinyl chloride polymerization reaction; q p The heat released to generate unit mass of PVC is taken as 1532 kJ / kg.

[0074] Preferably, the weighted average algorithm adopts the following formula:

[0075] C=0.4*C1+0.6*C2

[0076] Wherein, C is the vinyl chloride polymerization conversion rate, C1 is the first conversion rate value, C2 is the second conversion rate value, and in the formula, 0.4 and 0.6 are the parameters monitored in the previous polymerization reaction, and the conversion rate is obtained by comparing with the actual sampling test, and then determined.

[0077] Preferably, the initiator used in the vinyl chloride polymerization reaction is EHS.

[0078] It is easy to understand that the initiator used in the polymerization reaction of vinyl chloride is peroxide. Specifically, the prediction of the conversion rate of the present application is based on the use of di(2-ethyl)hexyl peroxydicarbonate EHS as an initiator to initiate the polymerization reaction of vinyl chloride. The percentage concentration of EHS in the initiator is 0.5, the half-life of the initiator is 0.46, the initiation efficiency of the initiator is 0.5-0.8, the molecular weight of EHS is 346.5, and the initial dosage of the initiator is 7-9 kg.

[0079] In this embodiment, the conversion rate prediction method is implemented based on the DCS control system. The DCS control system monitors the vinyl chloride polymerization reaction, collects the initial initiator dosage, polymerization reaction time, cooling water flow rate and cooling water inlet and outlet temperature difference required for conversion rate prediction, and then calculates the first conversion rate value and the second conversion rate value respectively, and then predicts the conversion rate through a weighted average algorithm, and then displays the conversion rate value on the display. It is easy to understand that the conversion rate predicted by the above conversion rate prediction method can be the instantaneous conversion rate of vinyl chloride. As the polymerization reaction of vinyl chloride to obtain PVC continues, the value of the instantaneous conversion rate is closer to the target conversion rate range.

[0080] Example 2

[0081] like Figure 2 As shown, this embodiment is based on the conversion rate prediction method of Example 1 to control the vinyl chloride polymerization reaction, including:

[0082] Setting target conversion rate for vinyl chloride polymerization reaction;

[0083] Predicting the conversion rate of the vinyl chloride polymerization reaction according to the above-mentioned conversion rate prediction method to obtain the predicted conversion rate of the vinyl chloride polymerization reaction;

[0084] When the predicted conversion rate reaches the target conversion rate, the polymerization reaction is stopped.

[0085] Preferably, the target conversion rate is 8% to 12%. In the bulk vinyl chloride polymerization, the vinyl chloride is converted from feeding to reaction to the target conversion rate, which is essentially the preparation of vinyl chloride polymerization "seed" liquid. Of course, the conversion rate prediction method and control method of the present application can also be applied to the process of further polymerization of vinyl chloride in the vinyl chloride "seed" liquid to generate PVC.

[0086] It is easy to understand that by predicting the conversion rate of vinyl chloride polymerization, when the predicted conversion rate is within the range of the target conversion rate, the polymerization reaction is stopped, and the polymerization liquid in the polymerization kettle is discharged to the next process for another polymerization reaction, so that the conversion rate of vinyl chloride is increased to 50% to 60%, and the final PVC product is obtained.

[0087] In this embodiment, when the vinyl chloride polymerization reaction is controlled, the polymerization reaction can be stopped when the DCS control system predicts that the conversion rate of the polymerization reaction reaches the target conversion rate requirement, and the valve of the polymerization reaction is automatically controlled to automatically unload the "seed" liquid. Of course, it can also be when the conversion rate of the polymerization reaction predicted by the DCS reaches the target conversion rate requirement, the on-site operator is reminded to manually stop the polymerization reaction and automatically unload the "seed" liquid.

[0088] In order to ensure the authenticity of the conversion rate predicted by DCS through the vinyl chloride polymerization reaction in Example 1, that is, to avoid a large deviation between the conversion rate predicted and the actual conversion rate due to instrument failure during the conversion rate prediction process, and thereby enable the control method of this embodiment to discharge the "seed" liquid that does not meet the target conversion rate requirements to the next process, it is necessary to verify the predicted conversion rate before stopping the polymerization reaction.

[0089] The verification includes: recording the change of conversion rate in the actual vinyl chloride polymerization process and generating a conversion rate change curve;

[0090] According to the conversion rate prediction method of Example 1, the conversion rate changes in the previous multiple vinyl chloride polymerization reaction processes are collected to establish a curve model of the conversion rate change;

[0091] Compare the curve models of each vinyl chloride polymerization reaction to determine the optimal curve model;

[0092] Comparing the conversion rate change curve with the optimal curve model to determine the matching degree between the conversion rate change curve and the optimal curve model, wherein the matching degree is determined according to the fitting degree between the conversion rate change curve and the optimal curve model;

[0093] When the matching degree is ≥80%, a stop polymerization reaction instruction is generated to automatically stop the polymerization reaction, or a manual operation instruction of "stop polymerization reaction" is displayed to the operator through the display of the DCS control system;

[0094] When the matching degree is less than 80%, a review instruction is generated to find the cause of the abnormality and determine whether the cause of the abnormality is caused by an instrument error. If so, the target reaction time required for the polymerization reaction is determined according to the target conversion rate. When the polymerization reaction time reaches the target reaction time requirement, a stop polymerization reaction instruction is generated to automatically stop the polymerization reaction, or a manual operation instruction of "notify polymerization reaction" is displayed to the operator through the display of the DCS control system; if not, the point of the instrument failure is determined to determine whether the polymerization reaction system is performing the polymerization reaction normally. If the polymerization reaction is performing normally, the target reaction time required for the polymerization reaction is determined according to the target conversion rate. When the polymerization reaction time reaches the target reaction time requirement, a stop polymerization reaction instruction is generated to automatically stop the polymerization reaction, or a manual operation instruction of "notify polymerization reaction" is displayed to the operator through the display of the DCS control system.

[0095] Of course, when the vinyl chloride polymerization reaction is not proceeding normally, an emergency stop operation is required. The control method and conversion rate prediction method of this embodiment and embodiment 1 are all based on the normal vinyl chloride polymerization reaction process.

[0096] Experimental Example 1

[0097] The vinyl chloride polymerization reaction was carried out at 70°C, corresponding to a saturated vapor pressure of 1.18 MPa. EHS was used as the initiator. The vinyl chloride loading was 17500 kg, the initiator dosage was 8.0 kg, the polymerization time was 0.16 h, and the heat exchange capacity was measured to be 2700 MJ. After sampling and analysis, the measured value of the vinyl chloride polymerization conversion rate was 9.68%. The predicted conversion rate value obtained by the vinyl chloride polymerization conversion rate prediction method of Example 1 was 9.45%, and the error between the predicted conversion rate value and the measured value was 0.23%.

[0098] Experimental Example 2

[0099] The vinyl chloride polymerization reaction was carried out at 70°C under the condition of a saturated vapor pressure of 1.18 MPa. The vinyl chloride loading was 17500 kg, the initiator dosage was 9.0 kg, the polymerization time was 0.15 h, and the heat exchange capacity was measured to be 2700 MJ. After sampling and analysis, the measured value of the vinyl chloride polymerization conversion rate was 10.03%. The predicted conversion rate obtained by the vinyl chloride polymerization conversion rate prediction method of Example 1 was 9.79%, and the error between the predicted conversion rate and the measured value was 0.24%.

[0100] In the description of the present invention, it is necessary to understand that the terms "center", "length", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "inside", "outside", "peripheral", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred system or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0101] In the description of the present invention, “plurality” means at least two, for example, two, three, etc., unless otherwise clearly and specifically defined.

[0102] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0103] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for predicting the conversion rate of bulk vinyl chloride polymerization, characterized in that: The vinyl chloride polymerization is carried out by the following reaction equation: The conversion rate prediction includes: Monitoring the vinyl chloride polymerization reaction to obtain the initiator consumption and heat exchange amount during the vinyl chloride polymerization reaction; Calculating a first conversion rate value according to the initiator consumption; Calculating a second conversion rate value according to the heat exchange amount; According to the first conversion rate value and the second conversion rate value, a weighted average algorithm is used to predict the conversion rate of the vinyl chloride polymerization reaction; The first conversion rate value is calculated based on the first PVC generation amount according to the initiator consumption, and the first conversion rate value is further calculated based on the first PVC generation amount; The first PVC generation amount is calculated using the following formula: W P1 =20*X*η*M VC *n*10 -6 Among them, W P1 is the first PVC production; X is the initiator consumption; η is the initiator efficiency, which is 0.5-0.8; M VC is the molecular weight of vinyl chloride, which is 62.5; n is the degree of polymerization of PVC, which is 650; The initiator consumption is calculated by the following formula: X=(1-e -0.693t / h )*X0 Wherein, X is the initiator consumption; X0 is the initial dosage of the initiator; t is the polymerization reaction time; h is the half-life of the initiator; The second conversion rate value is obtained by calculating the second PVC generation amount according to the heat exchange amount, and then calculating the second conversion rate value according to the second PVC generation amount; The second PVC generation amount is calculated using the following formula: W P2 =(Q / q P )*10 -3 Among them, W P2 is the amount of second vinyl chloride generated; Q is the heat exchange amount of vinyl chloride polymerization reaction; q p The heat released to generate unit mass of PVC is 1532 kJ / kg; The weighted average algorithm uses the following formula to calculate the conversion rate: C=0.4*C1+0.6*C2 Wherein, C is the vinyl chloride polymerization conversion rate, C1 is the first conversion rate value, and C2 is the second conversion rate value.

2. The method for predicting the conversion rate of bulk vinyl chloride polymerization according to claim 1, characterized in that: The initiator used in the vinyl chloride polymerization reaction is EHP.

3. A method for controlling bulk vinyl chloride polymerization, characterized in that: The vinyl chloride polymerization is carried out by the following equation: The control includes: Setting a target conversion rate for the vinyl chloride polymerization reaction; Predicting the conversion rate of a vinyl chloride polymerization reaction according to the conversion rate prediction method of claim 1 or 2 to obtain the predicted conversion rate of the vinyl chloride polymerization reaction; When the predicted conversion rate reaches the target conversion rate, the polymerization reaction is stopped.

4. The method for controlling bulk vinyl chloride polymerization according to claim 3, characterized in that: The target conversion rate is 8% to 12%.

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