CN110935408A - Control method and system for polyester resin synthesis esterification process - Google Patents
Control method and system for polyester resin synthesis esterification process Download PDFInfo
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Abstract
The invention discloses a method and a system for controlling the polyester resin synthesis esterification process, wherein the method comprises the following steps: determining the stage of the polyester resin synthesis esterification process; presetting a heating rate and a reflux ratio according to the stage; detecting the alcohol concentration of the distillate; and adjusting the actual temperature rise rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset temperature rise rate and the preset reflux ratio. The method comprises the steps of determining the stage of the polyester resin synthesis esterification process, presetting different heating rates and reflux ratios according to the stage of the polyester resin synthesis esterification process, and finally adjusting the actual heating rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset heating rate and the reflux ratio, so that the synthesis efficiency of the polyester resin is optimal, the loss of raw materials is reduced, and the consumption of the refluxed aqueous solution on heat in the reaction process is reduced. The invention can be widely applied to the technical field of chemical synthesis control.
Description
Technical Field
The invention relates to the technical field of chemical synthesis control, in particular to a method and a system for controlling the polyester resin synthesis esterification process.
Background
The first stage of the synthesis of polyester resins for powder coatings is an esterification reaction, which has a small equilibrium constant and requires the removal of water from the raw materials and from the reaction to promote a positive shift in the equilibrium. Since the polyester resin synthesis raw material contains polybasic acid and polyhydric alcohol, wherein neopentyl glycol (or 90% neopentyl glycol aqueous solution), ethylene glycol, methyl propylene glycol and the like are used as the polyhydric alcohol, and the boiling point of the alcohol is close to that of water, and the alcohol can be mutually dissolved with water in any proportion, so that the alcohol in the raw material is difficult to separate from the water in the system. The existing synthesis equipment mostly adopts an intermittent reaction kettle, and the control mode for synthesizing the polyester resin in the intermittent reaction kettle mainly comprises the following steps: (1) controlling the tower top temperature of the rectification column, not starting a reflux pump when the tower top temperature is lower than a set value, and starting the reflux pump when the tower top temperature exceeds the set value until the tower top temperature is reduced to the set value; (2) setting the reflux tank higher than the top of the rectifying column, controlling the valve of the reflux pipeline to have certain opening degree, and refluxing by using the self weight of the distillate; (3) the reflux pump is set to reflux at a constant reflux ratio. However, in the process of synthesizing and esterifying polyester resin, the temperature and reflux ratio required by each stage are different, and both the temperature and reflux ratio affect the synthesis effect, however, the above control methods all have the following characteristics: only the temperature of the synthesis process or only the reflux ratio of the synthesis process is controlled, so that the loss of raw material alcohol is large and the energy consumption is high when the existing synthesis control method is used for controlling the synthesis of the polyester resin.
Disclosure of Invention
To solve the above technical problems, the present invention aims to: a method and system for controlling the esterification process of polyester resin synthesis are provided, which can reduce energy consumption and the loss amount of raw material alcohol.
A first aspect of an embodiment of the present invention provides:
a control method for the polyester resin synthesis esterification process comprises the following steps:
determining the stage of the polyester resin synthesis esterification process;
presetting a heating rate and a reflux ratio according to the stage;
detecting the alcohol concentration of the distillate;
and adjusting the actual temperature rise rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset temperature rise rate and the preset reflux ratio.
Further, the polyester resin synthesis esterification process belongs to the stages comprising an initial esterification stage, a middle esterification stage and a final esterification stage.
Further, the presetting of the temperature rise rate and the presetting of the reflux ratio according to the stage to which the temperature rise rate and the reflux ratio belong specifically comprises:
after the stage is determined to be the initial stage of esterification, setting a preset heating rate as a first heating rate, and setting a preset reflux ratio as a first reflux ratio;
after the stage is determined to be the esterification middle stage, setting the preset heating rate as a second heating rate, and setting the preset reflux ratio as a second reflux ratio;
and after the stage is determined to be the end of esterification, setting the preset heating rate as a third heating rate, and setting the preset reflux ratio as a third reflux ratio.
Further, after determining that the stage of the polyester resin synthesis esterification process is an esterification middle stage, adjusting the actual temperature rise rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset temperature rise rate and the preset reflux ratio specifically comprises:
calculating a first alcohol concentration at a first time and a second alcohol concentration at a second time, the first time being before the second time;
acquiring a preset temperature rise rate and a preset reflux ratio fixed value in the middle period of esterification, and an actual temperature rise rate at the first moment, an actual temperature rise rate at the second moment and an actual reflux ratio at the second moment;
presetting an alcohol concentration warning value, an alcohol concentration preset value and a reflux ratio preset value, wherein the alcohol concentration preset value is smaller than the alcohol concentration warning value;
executing step one or step two when the second alcohol concentration is determined to be greater than the first alcohol concentration;
executing step three or step four when the second alcohol concentration is determined to be less than or equal to the first alcohol concentration;
the first step is specifically as follows:
after the second glycol concentration is determined to be greater than the preset alcohol concentration value, the second glycol concentration is less than the alarm alcohol concentration value and the actual reflux ratio at the second moment is greater than or equal to the preset reflux ratio value, setting the actual reflux ratio at the second moment as a fixed preset reflux ratio value and adjusting the actual temperature rise rate at the second moment according to the actual temperature rise rate at the first moment;
the second step is specifically as follows:
after the second alcohol concentration is determined to be greater than or equal to the alcohol concentration warning value, setting the actual temperature rise rate at the second moment to be zero, and setting the actual reflux ratio at the second moment to be 100%;
the third step is specifically as follows:
after the second glycol concentration is determined to be greater than the preset alcohol concentration value and less than the warning alcohol concentration value, setting the actual temperature rise rate at the second moment as the temperature rise according to the preset temperature rise rate in the middle esterification period, and setting the actual reflux ratio at the second moment as a fixed preset reflux ratio value;
the fourth step is specifically as follows:
and after the second glycol concentration is determined to be less than or equal to the preset alcohol concentration value, setting the actual temperature rise rate at the second moment as the temperature rise according to the preset temperature rise rate in the middle esterification period, and adjusting the actual reflux ratio at the second moment according to the second glycol concentration.
Further, the detecting of the alcohol concentration of the distillate specifically comprises:
detecting the temperature and refractive index of the distillate;
the alcohol concentration of the distillate was calculated from the detected temperature and refractive index.
A second aspect of an embodiment of the present invention provides:
the utility model provides a control system of synthetic esterification process of polyester resin, it includes synthesizer and main control module, synthesizer includes reation kettle, rectifying column, condenser, backflow control module and concentration detection module, reation kettle, rectifying column, condenser and backflow control module connect gradually, concentration detection module sets up the condenser with backflow control module's connecting portion, be equipped with the heat medium control valve on the reation kettle, heat medium control valve, concentration detection module and backflow control module all with main control module connects, main control module is used for carrying out following step:
determining the stage of the polyester resin synthesis esterification process;
presetting a heating rate and a reflux ratio according to the stage;
detecting the alcohol concentration of the distillate;
and adjusting the actual temperature rise rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset temperature rise rate and the preset reflux ratio.
Further, the concentration detection module comprises a temperature detection module and a refractive index detection module, and the temperature detection module and the refractive index detection module are both arranged at the connecting part of the condenser and the reflux control module.
Furthermore, a U-shaped pipe is arranged on a connecting part of the condenser and the backflow control module, and the temperature detection module and the refractive index detection module are both arranged at the bottom of the U-shaped pipe.
Further, the presetting of the temperature rise rate and the presetting of the reflux ratio according to the stage to which the temperature rise rate and the reflux ratio belong specifically comprises:
after the stage is determined to be the initial stage of esterification, setting a preset heating rate as a first heating rate, and setting a preset reflux ratio as a first reflux ratio;
after the stage is determined to be the esterification middle stage, setting the preset heating rate as a second heating rate, and setting the preset reflux ratio as a second reflux ratio;
and after the stage is determined to be the end of esterification, setting the preset heating rate as a third heating rate, and setting the preset reflux ratio as a third reflux ratio.
Further, after determining that the stage of the polyester resin synthesis esterification process is an esterification middle stage, adjusting the actual temperature rise rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset temperature rise rate and the preset reflux ratio specifically comprises:
calculating a first alcohol concentration at a first time and a second alcohol concentration at a second time, the first time being before the second time;
acquiring a preset temperature rise rate and a preset reflux ratio fixed value in the middle period of esterification, and an actual temperature rise rate at the first moment, an actual temperature rise rate at the second moment and an actual reflux ratio at the second moment;
presetting an alcohol concentration warning value, an alcohol concentration preset value and a reflux ratio preset value, wherein the alcohol concentration preset value is smaller than the alcohol concentration warning value;
executing step one or step two when the second alcohol concentration is determined to be greater than the first alcohol concentration;
executing step three or step four when the second alcohol concentration is determined to be less than or equal to the first alcohol concentration;
the first step is specifically as follows:
after the second glycol concentration is determined to be greater than the preset alcohol concentration value, the second glycol concentration is less than the alarm alcohol concentration value and the actual reflux ratio at the second moment is greater than or equal to the preset reflux ratio value, setting the actual reflux ratio at the second moment as a fixed preset reflux ratio value and adjusting the actual temperature rise rate at the second moment according to the actual temperature rise rate at the first moment;
the second step is specifically as follows:
after the second alcohol concentration is determined to be greater than or equal to the alcohol concentration warning value, setting the actual temperature rise rate at the second moment to be zero, and setting the actual reflux ratio at the second moment to be 100%;
the third step is specifically as follows:
after the second glycol concentration is determined to be greater than the preset alcohol concentration value and less than the warning alcohol concentration value, setting the actual temperature rise rate at the second moment as the temperature rise according to the preset temperature rise rate in the middle esterification period, and setting the actual reflux ratio at the second moment as a fixed preset reflux ratio value;
the fourth step is specifically as follows:
and after the second glycol concentration is determined to be less than or equal to the preset alcohol concentration value, setting the actual temperature rise rate at the second moment as the temperature rise according to the preset temperature rise rate in the middle esterification period, and adjusting the actual reflux ratio at the second moment according to the second glycol concentration.
The invention has the beneficial effects that: the method comprises the steps of determining the stage of the polyester resin synthesis esterification process, presetting different heating rates and reflux ratios according to the stage of the polyester resin synthesis esterification process, and finally adjusting the actual heating rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset heating rate and the reflux ratio, so that the synthesis efficiency of the polyester resin is optimal, the loss of raw materials is reduced, and the consumption of the refluxed aqueous solution on heat in the reaction process is reduced.
Drawings
FIG. 1 is a flow chart of a method for controlling an esterification process for the synthesis of polyester resins according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a synthesis device of a control system of a polyester resin synthesis esterification process according to an embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the specific embodiments. The step numbers in the following embodiments are provided only for convenience of illustration, the order between the steps is not limited at all, and the execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.
Referring to fig. 1, an embodiment of the present invention provides a method for controlling a polyester resin synthesis esterification process, which is applied to a main control module, the main control module is connected to a polyester resin synthesis apparatus, as shown in fig. 2, the synthesis apparatus includes a reaction kettle 1, a rectification tower 2, a condenser 3, a reflux control module and a concentration detection module, the reaction kettle 1 is connected to the bottom of the rectification tower 2, an outlet of the rectification tower 2 is connected to an inlet of the condenser 3, an outlet of the condenser 3 is connected to the reflux control module, the concentration detection module is disposed at a connection portion of the condenser and the reflux control module, the reaction kettle 1 is further provided with a heating medium control valve, and the main control module may be a DCS system or a PLC system.
The present embodiment includes steps S101 to S104:
s101, determining the stage of the polyester resin synthesis esterification process; the stages comprise an initial stage of esterification, a middle stage of esterification and a final stage of esterification. The method is characterized in that the polyester resin synthesis esterification process is divided into stages, specifically, the stages are divided according to the reaction process of raw materials in the polyester resin synthesis esterification process and the reaction temperature in the synthesis process.
S102, presetting a heating rate and a reflux ratio according to the stage; the heating rate refers to the heating rate in the reaction kettle. The reflux ratio refers to the reflux ratio of the solution in the reflux control module.
S103, detecting the alcohol concentration of the distillate; the distillate refers to the distillate liquid at the outlet of the condenser. The alcohol concentration refers to the alcohol concentration of the distillate liquid at the outlet of the condenser.
And S104, adjusting the actual temperature rise rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset temperature rise rate and the preset reflux ratio. Particularly, the heating rate is adjusted by adjusting the opening of a heating medium control valve on the reaction kettle. The reflux ratio is controlled by controlling the working frequency of a reflux pump on the reflux control module.
According to the method, the stage of the polyester resin synthesis esterification process is determined, different heating rates and reflux ratios are preset according to the stage of the polyester resin synthesis esterification process, and the actual heating rate and the actual reflux ratio are adjusted according to the alcohol concentration of the distillate, the preset heating rate and the reflux ratio, so that the synthesis efficiency of the polyester resin is optimal, the loss of raw materials is reduced, and the consumption of the refluxed aqueous solution to heat in the reaction process is reduced.
As a preferred embodiment, the polyester resin synthesis esterification process belongs to the stages comprising the initial esterification stage, the middle esterification stage and the final esterification stage. The polyester resin synthesis stage is divided into different periods, so that the temperature regulation in the polyester resin synthesis esterification process is facilitated.
As a preferred embodiment, the presetting of the temperature-rising rate and the presetting of the reflux ratio according to the phase to which the temperature-rising rate and the reflux ratio belong specifically includes:
after the stage is determined to be the initial stage of esterification, setting a preset heating rate as a first heating rate, and setting a preset reflux ratio as a first reflux ratio; at the initial stage of esterification of the polyester resin, because the temperature is low, the boiling point of the polyhydric alcohol and the reaction temperature of the esterification reaction are not reached yet, and the rectification process mainly separates water in raw materials, the preset heating rate is set to be a relatively small heating rate, namely, a first heating rate, and meanwhile, the preset reflux ratio is set to be a constant small reflux ratio, namely, a first reflux ratio, so that the synthesis efficiency of the polyester resin is improved, and the energy consumption in the synthesis process is reduced.
After the stage is determined to be the esterification middle stage, setting the preset heating rate as a second heating rate, and setting the preset reflux ratio as a second reflux ratio; in the middle stage of esterification of polyester resin, esterification reaction is severe, or the temperature in a reaction kettle is raised to be higher than the boiling point of raw material alcohol, and a large amount of unreacted raw material alcohol and generated esterified water need to be separated by a rectifying tower, so that the preset temperature rise rate is set as a second temperature rise rate, the preset reflux ratio is set as a second reflux ratio, then the alcohol concentration in the distillate at the top of the rectifying tower is monitored in real time, the actual temperature rise rate and the actual reflux ratio are automatically adjusted by combining the monitored alcohol concentration with the preset second temperature rise rate and the second reflux ratio, so that the loss amount of the raw material alcohol in the rectifying operation in the synthetic process is reduced, and excessive reflux liquid is prevented from flowing into the reaction kettle at the bottom of the rectifying tower to cause repeated evaporation and heat absorption to cause overhigh production energy consumption. Therefore, the actual temperature increase rate at the second time and the actual reflux ratio at the second time are adjusted according to the alcohol concentration of the distillate during the synthesis process, and the preset second temperature increase rate and second reflux ratio.
And after the stage is determined to be the end of esterification, setting the preset heating rate as a third heating rate, and setting the preset reflux ratio as a third reflux ratio. In the heat preservation stage at the last stage of the esterification reaction in the production process of the polyester resin, most of raw material alcohol reacts to generate oligomer with a higher boiling point, the rate of generating esterified water is lower, meanwhile, the low-boiling-point by-product generated by the reaction and the esterified water are taken out of the reaction system, and the refractive index of the esterified water is higher, so that the preset reflux ratio is set to be a constant smaller reflux ratio, namely, a third reflux ratio, and the preset temperature rise rate is set to be a temperature rise rate which can enable the temperature in the reaction kettle to be maintained at the temperature value at the last moment in the esterification middle stage.
According to the method, the preset heating rate and reflux ratio are adjusted according to different stages in the polyester resin synthesis esterification process, so that the highest synthesis efficiency is ensured, and meanwhile, the loss amount of raw material alcohol and the energy consumption in the synthesis process are reduced.
As a preferred embodiment, after determining that the stage to which the polyester resin synthesis esterification process belongs is an esterification middle stage, adjusting the actual temperature increase rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset temperature increase rate and the preset reflux ratio specifically includes:
calculating a first alcohol concentration at a first time and a second alcohol concentration at a second time, the first time being before the second time; the method comprises calculating alcohol concentration of distillate at each moment, making x-y scatter diagram of time-distillate concentration, fitting with continuous smooth curve to make the curve pass through as many points as possible, if not all points, making the points not on the curve uniformly distributed on both sides of the curve, discarding the points far away, and finally obtaining the first moment x on the curvet-ΔtFirst alcohol concentration yt-ΔtAnd a second time xtSecond alcohol concentration yt。
Acquiring a preset temperature rise rate and a preset reflux ratio fixed value in the middle period of esterification, and an actual temperature rise rate at the first moment, an actual temperature rise rate at the second moment and an actual reflux ratio at the second moment;
presetting an alcohol concentration warning value, an alcohol concentration preset value and a reflux ratio preset value, wherein the alcohol concentration preset value is smaller than the alcohol concentration warning value; the alcohol concentration warning value, the alcohol concentration preset value and the reflux ratio preset value are obtained according to the production running conditions of different equipment, different temperature rise stages in an experiment and the water outlet rate of esterified water.
In determining the second alcohol concentration ytGreater than the first alcohol concentration yt-ΔtIf so, executing the step one or the step two;
in determining the second alcohol concentration ytLess than or equal to the first alcohol concentration yt-ΔtIf so, executing the third step or the fourth step;
the first step is specifically as follows:
in determining the second alcohol concentration ytGreater than the predetermined alcohol concentration and the second alcohol concentration ytLess than the alcohol concentration warning value, and after the actual reflux ratio at the second moment is greater than or equal to the reflux ratio preset value, determining that the effect of adjusting the reflux ratio on the raw material alcohol concentration in the top distillate of the rectifying tower is limited, therefore, setting the actual reflux ratio at the second moment as a preset reflux ratio fixed value, and setting the actual temperature rise rate at the second moment as a% of the temperature rise rate at the first moment, wherein the value range of a is 0<a<100, if the actual temperature rising rate at the first moment reaches b% of the preset temperature rising rate at the middle stage of esterification, wherein the value range of b is 0<b<And 100, maintaining the actual temperature rise rate at the second moment equal to the actual temperature rise rate at the first moment, so as to avoid the situation that the water flow in the reflux liquid at the tower bottom is too large, and the repeated evaporation and heat absorption of water cause too high energy consumption.
The second step is specifically as follows:
in determining the second alcohol concentration ytWhen the alcohol concentration is greater than or equal to the alcohol concentration warning value, judging that the alcohol concentration of the raw material of the distillate at the top of the rectifying tower at the current moment is too high, adjusting the actual temperature rise rate at the second moment to zero to control the temperature rise of the reaction kettle to be stopped, and controlling the temperature rise of the reaction kettle to be stoppedThe actual reflux ratio at the second time is set to 100%, and the loss amount of the raw material alcohol is reduced.
The third step is specifically as follows:
in determining the second alcohol concentration ytGreater than the predetermined alcohol concentration and the second alcohol concentration ytSetting the actual temperature rise rate at the second moment as a preset temperature rise rate in the middle period of esterification and setting the actual reflux ratio at the second moment as a fixed preset reflux ratio value after the actual temperature rise rate is less than the alcohol concentration warning value; the method specifically comprises the steps of controlling the reaction kettle to continuously raise the temperature according to a preset temperature rise rate in the middle stage of esterification, and controlling a reflux control module to carry out reflux operation according to a preset reflux ratio fixed value, so that the synthesis reaction is stably and efficiently carried out.
The fourth step is specifically as follows:
in determining the second alcohol concentration ytAfter the alcohol concentration is less than the preset value, according to the second alcohol concentration ytAnd adjusting the actual reflux ratio at the second moment, and setting the actual temperature rise rate at the second moment as the temperature rise according to the preset temperature rise rate in the middle stage of esterification. The reflux ratio in the reflux control module is adjusted according to the alcohol concentration of the current distillate, and the temperature rise process of the reaction kettle is controlled according to the preset temperature rise rate in the middle stage of esterification.
In this embodiment, adjusting the temperature-rising rate of the second reaction vessel is to control the temperature-rising rate by adjusting the opening of the heat medium control valve in the reaction vessel.
In the embodiment, the temperature rise rate of the reaction kettle and the reflux ratio of the reflux control module are controlled according to the alcohol concentration of the distillate, the preset temperature rise rate and the preset reflux ratio, so that the synthesis efficiency of the polyester resin is maximized, the loss amount of alcohol in raw materials is reduced, and the energy loss is reduced.
As a preferred embodiment, the detecting the alcohol concentration of the distillate specifically includes:
detecting the temperature and refractive index of the distillate; the temperature is the real-time temperature and real-time refractive index of the distillate at the outlet of the condenser.
The alcohol concentration of the distillate was calculated from the detected temperature and refractive index.
Before the embodiment is carried out, the alcohol concentration of the solution has a linear relation with the refractive index when the temperature is constant through material inspection and experimental verification; under the condition of the same alcohol concentration in a certain temperature range, the refractive index is continuously changed along with the temperature change, and no jump point exists. Therefore, the embodiment calculates the alcohol concentration of the distillate through the temperature and the refractive index of the distillate, can reduce the operation cost, is convenient for the polyester synthesis process to adjust the reflux ratio in time according to the change of the alcohol concentration in the distillate, and reduces the loss of raw materials.
In some embodiments, when the volume of the reaction kettle is 30m3If the synthetic polyester resin raw materials are terephthalic acid and 90% neopentyl glycol, and the catalyst is an organotin compound, the specific control process of this example is shown in table 2:
TABLE 1
In the middle stage of esterification, the main control module controls the reflux ratio and the heating rate according to the data shown in the table 2 after monitoring the concentration of the overhead distillate:
TABLE 2
Specifically, when yt>yt-ΔtAnd y ist>3.0 percent and the reflux ratio is more than or equal to 50 percent, the adjustment of the reflux ratio is judged to have limited effect on controlling the concentration of the raw material alcohol in the tower top distillate, the main control module sets the actual reflux ratio at the moment t as a preset reflux ratio fixed value, namely, the reflux is set as 50 percent, the actual temperature rising rate at the moment t is set as 80 percent of the temperature rising rate at the moment (t- △ t), and if the actual temperature rising rate at the moment (t- △ t) reaches 60 percent of the preset temperature rising rate at the middle stage of esterification, the actual temperature rising rate at the moment t is maintained to be equal to the temperature rising rate atThe actual temperature rising rate at the time of- △ t) is not changed, so that the situation that the water flow in the reflux liquid at the tower bottom is too large, and the repeated evaporation and heat absorption of the water cause too high energy consumption of production is avoided.
When y istAnd the concentration of the raw material alcohol in the overhead distillate is judged to be over high, the main control module stops the temperature rise of the reaction kettle under the control of the main control module, and the overhead distillate flows back by 100%.
When 3.0% < yt＜yt-ΔtWhen the temperature is less than 4.0%, the main control module controls the temperature of the reaction kettle to rise according to the current temperature position and the preset temperature rise rate in the middle stage of esterification, and controls reflux according to the preset fixed value of the reflux ratio, namely, the reflux ratio of 50% controls reflux.
When y ist＜yt-ΔtWhen the concentration is less than or equal to 3.0 percent, the main control module controls the reflux ratio according to the concentration of the distillate at the top of the tower and controls the temperature of the reaction kettle to rise according to the preset temperature rise rate in the middle stage of esterification.
In addition, an embodiment of the present invention further provides a control system for a polyester resin synthesis esterification process, which includes a synthesis device and a main control module, as shown in fig. 2, the synthesis device includes a reaction kettle 1, a rectification tower 2, a condenser 3, a reflux control module and a concentration detection module, the reaction kettle 1, the rectification tower 2, the condenser 3 and the reflux control module are sequentially connected, the concentration detection module is disposed at a connection portion between the condenser 3 and the reflux control module, the reaction kettle 1 is provided with a heat medium control valve, the concentration detection module and the reflux control module are all connected with the main control module, and the main control module is configured to execute steps S101 to S104 shown in fig. 1:
s101, determining the stage of the polyester resin synthesis esterification process; the stages comprise an initial stage of esterification, a middle stage of esterification and a final stage of esterification. The method is characterized in that the polyester resin synthesis esterification process is divided into stages, specifically, the stages are divided according to the reaction process of raw materials in the polyester resin synthesis esterification process and the reaction temperature in the synthesis process.
S102, presetting a heating rate and a reflux ratio according to the stage; the heating rate refers to the heating rate in the reaction kettle. The reflux ratio refers to the reflux ratio of the aqueous solution in the reflux control module.
S103, detecting the alcohol concentration of the distillate; the distillate is the liquid at the outlet of the condenser. The alcohol concentration refers to the alcohol concentration of the liquid at the outlet of the condenser.
And S104, adjusting the actual temperature rise rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset temperature rise rate and the preset reflux ratio. Particularly, the heating rate is adjusted by adjusting the opening of a heating medium control valve on the reaction kettle. The reflux ratio is controlled by controlling the working frequency of a reflux pump on the reflux control module.
Specifically, reation kettle 1 connects 2 bottoms of rectifying column, rectifying column 2's export with the entry linkage of condenser 3, the export of condenser 3 with reflux control module connects. The reflux control module comprises a reflux pump 41 and a reflux tank 42, wherein the reflux pump 41 controls the working process of the reflux tank 42 according to the working frequency sent by the main control module, so that a proper reflux ratio is obtained. The heat medium control valve comprises a heat medium inlet control valve 61 and a heat medium outlet control valve 62, and the heat medium inlet control valve 61 and the heat medium outlet control valve 62 work together to control the heating rate in the reaction kettle.
This embodiment is through being in concentration detection module setting the condenser with the connecting portion of backflow control module, and set up the heat medium control valve on the reation kettle, then will heat medium control valve, concentration detection module and backflow control module all with main control module connects to make main control module can reach the optimum according to the rate of rise of temperature and the reflux ratio of backflow control module of the data control reation kettle who receives, make polyester resin's synthetic efficiency, reduce the loss of raw and other materials simultaneously, reduce the aqueous solution of backward flow in the reaction process to thermal consumption.
As a preferred embodiment, as shown in fig. 2, the concentration detection module comprises a temperature detection module 51 and a refractive index detection module 52, and the temperature detection module 51 and the refractive index detection module 52 are both arranged at the connection part of the condenser 3 and the reflux control module.
The temperature detection module 51 in the present embodiment may be a temperature detection sensor, and the refractive index detection module 52 may be a refractive index sensor. The temperature detection module 51 and the refractive index detection module 52 are both connected with the main control module, and wirelessly transmit the detected data to the main control module in real time, so that the timeliness and the stability of data transmission are ensured.
As a preferred embodiment, as shown in fig. 2, a U-shaped pipe 7 is disposed at the connection part of the condenser and the reflux control module, and the temperature detection module 51 and the refractive index detection module 52 are both disposed at the bottom of the U-shaped pipe 7. In particular to the adjacent position of the bottom of the U-shaped pipe. Because the flow of distillate formed after the steam on the top of the rectifying tower is condensed by the condenser is not in a stable and continuous state generally, and the data sensed by the temperature detection module and the refractive index detection module are jumped greatly, the actual physical properties of the distillate cannot be truly reflected, the U-shaped pipe is arranged on a pipeline between the outlet of the condenser and the reflux control module, and the sensing probes of the temperature sensor and the refractive index sensor are arranged at the bottom of the U-shaped pipe, so that the test error can be reduced.
As a preferred embodiment, the presetting of the temperature-rising rate and the presetting of the reflux ratio according to the phase to which the temperature-rising rate and the reflux ratio belong specifically includes:
after the stage is determined to be the initial stage of esterification, setting a preset heating rate as a first heating rate, and setting a preset reflux ratio as a first reflux ratio; at the initial stage of esterification of the polyester resin, because the temperature is low, the boiling point of the polyhydric alcohol and the reaction temperature at which the esterification reaction starts are not reached, and the rectification process mainly separates water in raw materials, the preset heating rate is set to be a relatively small heating rate, namely a first heating rate, and meanwhile, the preset reflux ratio is set to be a constant small reflux ratio, namely a first reflux ratio, so that the synthesis efficiency of the polyester resin is improved, and the energy consumption in the synthesis process is reduced.
After the stage is determined to be the esterification middle stage, setting the preset heating rate as a second heating rate, and setting the preset reflux ratio as a second reflux ratio; in the middle stage of esterification of polyester resin, esterification reaction is severe, or the temperature in a reaction kettle is raised to be higher than the boiling point of raw material alcohol, and a large amount of unreacted raw material alcohol and generated esterified water need to be separated by a rectifying tower, so that the preset temperature rise rate is set as a second temperature rise rate, the preset reflux ratio is set as a second reflux ratio, then the alcohol concentration in the distillate at the top of the rectifying tower is monitored in real time, the actual temperature rise rate and the actual reflux ratio are automatically adjusted by combining the monitored alcohol concentration with the preset second temperature rise rate and the second reflux ratio, so that the loss amount of the raw material alcohol in the rectifying operation in the synthetic process is reduced, and excessive reflux liquid is prevented from flowing into the reaction kettle at the bottom of the rectifying tower to cause repeated evaporation and heat absorption to cause overhigh production energy consumption. Therefore, the actual temperature increase rate at the second time and the actual reflux ratio at the second time are adjusted according to the alcohol concentration of the distillate during the synthesis process, and the preset second temperature increase rate and second reflux ratio.
And after the stage is determined to be the end of esterification, setting the preset heating rate as a third heating rate, and setting the preset reflux ratio as a third reflux ratio. In the heat preservation stage at the last stage of the esterification reaction in the production process of the polyester resin, most of raw material alcohol reacts to generate oligomer with a higher boiling point, the rate of generating esterified water is lower, meanwhile, the low-boiling-point by-product produced by the reaction and the esterified water are taken out of the reaction system, and the refractive index of the esterified water is higher, so that the preset reflux ratio is set as a constant lower reflux ratio, namely a third reflux ratio, and the preset temperature rise rate is set as a temperature rise rate which can enable the temperature in the reaction kettle to be maintained at the temperature value at the last moment in the esterification middle stage.
In the embodiment, the preset heating rate and reflux ratio are adjusted according to different stages in the polyester resin synthesis esterification process, so that the loss amount of raw material alcohol and the energy consumption amount in the synthesis process are reduced while the highest synthesis efficiency is ensured.
As a preferred embodiment, after determining that the stage to which the polyester resin synthesis esterification process belongs is an esterification middle stage, adjusting the actual temperature increase rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset temperature increase rate and the preset reflux ratio specifically includes:
calculating a first alcohol concentration at a first time and a second alcohol concentration at a second time, the first time being before the second time; the method comprises calculating alcohol concentration of distillate at each moment, making x-y scatter diagram of time-distillate concentration, fitting with continuous smooth curve to make the curve pass through as many points as possible, if not all points, making the points not on the curve uniformly distributed on both sides of the curve, discarding the points far away, and finally obtaining the first moment x on the curvet-ΔtFirst alcohol concentration yt-ΔtAnd a second time xtSecond alcohol concentration yt。
Acquiring a preset temperature rise rate and a preset reflux ratio fixed value in the middle period of esterification, and an actual temperature rise rate at the first moment, an actual temperature rise rate at the second moment and an actual reflux ratio at the second moment;
presetting an alcohol concentration warning value, an alcohol concentration preset value and a reflux ratio preset value, wherein the alcohol concentration preset value is smaller than the alcohol concentration warning value; the alcohol concentration warning value, the alcohol concentration preset value and the reflux ratio preset value are obtained according to the production running conditions of different equipment, different temperature rise stages in an experiment and the water outlet rate of esterified water.
In determining the second alcohol concentration ytGreater than the first alcohol concentration yt-ΔtIf so, executing the step one or the step two;
in determining the second alcohol concentration ytLess than or equal to the first alcohol concentration yt-ΔtIf so, executing the third step or the fourth step;
the first step is specifically as follows:
in determining the second alcohol concentration ytGreater than the predetermined alcohol concentration and the second alcohol concentration ytLess than the alcohol concentration warning value, and after the actual reflux ratio at the second moment is greater than or equal to the reflux ratio preset value, the effect of adjusting the reflux ratio on the original material alcohol concentration in the top distillate of the rectifying tower is determined to be limited, therefore, the actual reflux ratio at the second moment is set as a preset fixed reflux ratio value, the actual temperature rise rate at the second moment is set as a percent of the temperature rise rate at the first moment,wherein, the value range of a is 0<a<100, if the actual temperature rising rate at the first moment reaches b% of the preset temperature rising rate at the middle stage of esterification, wherein the value range of b is 0<b<And 100, maintaining the actual temperature rise rate at the second moment equal to the actual temperature rise rate at the first moment, so as to avoid the situation that the water flow in the reflux liquid at the tower bottom is too large, and the repeated evaporation and heat absorption of water cause too high energy consumption.
The second step is specifically as follows:
in determining the second alcohol concentration ytAnd after the alcohol concentration is greater than or equal to the alcohol concentration warning value, judging that the raw material alcohol concentration of the distillate at the top of the rectifying tower at the current moment is too high, adjusting the actual temperature rising rate at the second moment to be zero to control the temperature rise of the reaction kettle to stop, setting the actual reflux ratio at the second moment to be 100%, and reducing the loss of the raw material alcohol.
The third step is specifically as follows:
in determining the second alcohol concentration ytGreater than the predetermined alcohol concentration and the second alcohol concentration ytSetting the actual temperature rise rate at the second moment as a preset temperature rise rate in the middle period of esterification and setting the actual reflux ratio at the second moment as a fixed preset reflux ratio value after the actual temperature rise rate is less than the alcohol concentration warning value; the method specifically comprises the steps of controlling the reaction kettle to continuously raise the temperature according to a preset temperature rise rate in the middle stage of esterification, and controlling a reflux control module to carry out reflux operation according to a preset reflux ratio fixed value, so that the synthesis reaction is stably and efficiently carried out.
The fourth step is specifically as follows:
in determining the second alcohol concentration ytAfter the alcohol concentration is less than the preset value, according to the second alcohol concentration ytAnd adjusting the actual reflux ratio at the second moment, and setting the actual temperature rise rate at the second moment as the temperature rise according to the preset temperature rise rate in the middle stage of esterification. The reflux ratio in the reflux control module is adjusted according to the alcohol concentration of the current distillate, and the temperature rise process of the reaction kettle is controlled according to the preset temperature rise rate in the middle stage of esterification.
In this embodiment, adjusting the temperature-rising rate of the second reaction vessel is to control the temperature-rising rate by adjusting the opening of the heat medium control valve in the reaction vessel.
In the embodiment, the temperature rise rate of the reaction kettle and the reflux ratio of the reflux control module are controlled according to the alcohol concentration of the distillate, the preset temperature rise rate and the preset reflux ratio, so that the synthesis efficiency of the polyester resin is maximized, the loss amount of alcohol in raw materials is reduced, and the energy loss is reduced.
In conclusion, the method of the invention determines the stage of the polyester resin synthesis esterification process, then presets different heating rates and reflux ratios according to the stage of the polyester resin synthesis esterification process, and finally adjusts the actual heating rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset heating rate and reflux ratio, so that the synthesis efficiency of the polyester resin is optimal, the loss of raw materials is reduced, and the consumption of the refluxed aqueous solution to heat in the reaction process is reduced; according to the system, the concentration detection module is arranged at the connecting part of the condenser and the reflux control module, the heating medium control valve is arranged on the reaction kettle, and then the heating medium control valve, the concentration detection module and the reflux control module are all connected with the main control module, so that the main control module can control the heating rate of the reaction kettle and the reflux ratio of the reflux control module according to received data, the synthesis efficiency of polyester resin is optimized, the loss of raw materials is reduced, and the consumption of the reflux aqueous solution to heat in the reaction process is reduced.
While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A control method for the polyester resin synthesis esterification process is characterized in that: the method comprises the following steps:
determining the stage of the polyester resin synthesis esterification process;
presetting a heating rate and a reflux ratio according to the stage;
detecting the alcohol concentration of the distillate;
and adjusting the actual temperature rise rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset temperature rise rate and the preset reflux ratio.
2. The method for controlling the esterification process of polyester resin synthesis according to claim 1, wherein: the polyester resin synthesis esterification process belongs to the stages of the initial esterification stage, the middle esterification stage and the final esterification stage.
3. The method for controlling the esterification process of polyester resin synthesis according to claim 2, wherein: the presetting of the heating rate and the presetting of the reflux ratio according to the stage to which the temperature rises specifically comprises the following steps:
after the stage is determined to be the initial stage of esterification, setting a preset heating rate as a first heating rate, and setting a preset reflux ratio as a first reflux ratio;
after the stage is determined to be the esterification middle stage, setting the preset heating rate as a second heating rate, and setting the preset reflux ratio as a second reflux ratio;
and after the stage is determined to be the end of esterification, setting the preset heating rate as a third heating rate, and setting the preset reflux ratio as a third reflux ratio.
4. The method for controlling the esterification process of polyester resin synthesis according to claim 3, wherein: after the stage of the polyester resin synthesis esterification process is determined to be the esterification middle stage, adjusting the actual temperature rise rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset temperature rise rate and the preset reflux ratio, wherein the actual temperature rise rate and the actual reflux ratio specifically comprise the following steps:
calculating a first alcohol concentration at a first time and a second alcohol concentration at a second time, the first time being before the second time;
acquiring a preset temperature rise rate and a preset reflux ratio fixed value in the middle period of esterification, and an actual temperature rise rate at the first moment, an actual temperature rise rate at the second moment and an actual reflux ratio at the second moment;
presetting an alcohol concentration warning value, an alcohol concentration preset value and a reflux ratio preset value, wherein the alcohol concentration preset value is smaller than the alcohol concentration warning value;
executing step one or step two when the second alcohol concentration is determined to be greater than the first alcohol concentration;
executing step three or step four when the second alcohol concentration is determined to be less than or equal to the first alcohol concentration;
the first step is specifically as follows:
after the second glycol concentration is determined to be greater than the preset alcohol concentration value, the second glycol concentration is less than the alarm alcohol concentration value and the actual reflux ratio at the second moment is greater than or equal to the preset reflux ratio value, setting the actual reflux ratio at the second moment as a fixed preset reflux ratio value and adjusting the actual temperature rise rate at the second moment according to the actual temperature rise rate at the first moment;
the second step is specifically as follows:
after the second alcohol concentration is determined to be greater than or equal to the alcohol concentration warning value, setting the actual temperature rise rate at the second moment to be zero, and setting the actual reflux ratio at the second moment to be 100%;
the third step is specifically as follows:
after the second glycol concentration is determined to be greater than the preset alcohol concentration value and less than the warning alcohol concentration value, setting the actual temperature rise rate at the second moment as the temperature rise according to the preset temperature rise rate in the middle esterification period, and setting the actual reflux ratio at the second moment as a fixed preset reflux ratio value;
the fourth step is specifically as follows:
and after the second glycol concentration is determined to be less than or equal to the preset alcohol concentration value, setting the actual temperature rise rate at the second moment as the temperature rise according to the preset temperature rise rate in the middle esterification period, and adjusting the actual reflux ratio at the second moment according to the second glycol concentration.
5. The method for controlling the esterification process of polyester resin synthesis according to claim 1, wherein: the alcohol concentration of the distillate is detected, and the method specifically comprises the following steps:
detecting the temperature and refractive index of the distillate;
the alcohol concentration of the distillate was calculated from the detected temperature and refractive index.
6. A control system for the polyester resin synthesis esterification process is characterized in that: including synthesizer and main control module, synthesizer includes reation kettle, rectifying column, condenser, backflow control module and concentration detection module, reation kettle, rectifying column, condenser and backflow control module connect gradually, concentration detection module sets up the condenser with backflow control module's connecting portion, the last heat medium control valve that is equipped with of reation kettle, heat medium control valve, concentration detection module and backflow control module all with main control module connects, main control module is used for carrying out following step:
determining the stage of the polyester resin synthesis esterification process;
presetting a heating rate and a reflux ratio according to the stage;
detecting the alcohol concentration of the distillate;
and adjusting the actual temperature rise rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset temperature rise rate and the preset reflux ratio.
7. The control system of the polyester resin synthesis esterification process according to claim 6, wherein: the concentration detection module comprises a temperature detection module and a refractive index detection module, and the temperature detection module and the refractive index detection module are both arranged at the connecting part of the condenser and the reflux control module.
8. The control system of the polyester resin synthesis esterification process according to claim 7, wherein: the condenser with be provided with the U type pipe on the connecting portion of return flow control module, temperature detection module and refractive index detection module all set up in U type socle portion.
9. The control system of the polyester resin synthesis esterification process according to claim 6, wherein: the presetting of the heating rate and the presetting of the reflux ratio according to the stage to which the temperature rises specifically comprises the following steps:
after the stage is determined to be the initial stage of esterification, setting a preset heating rate as a first heating rate, and setting a preset reflux ratio as a first reflux ratio;
after the stage is determined to be the esterification middle stage, setting the preset heating rate as a second heating rate, and setting the preset reflux ratio as a second reflux ratio;
and after the stage is determined to be the end of esterification, setting the preset heating rate as a third heating rate, and setting the preset reflux ratio as a third reflux ratio.
10. The control system of the polyester resin synthesis esterification process according to claim 9, wherein: after the stage of the polyester resin synthesis esterification process is determined to be the esterification middle stage, adjusting the actual temperature rise rate and the actual reflux ratio according to the alcohol concentration of the distillate, the preset temperature rise rate and the preset reflux ratio, wherein the actual temperature rise rate and the actual reflux ratio specifically comprise the following steps:
calculating a first alcohol concentration at a first time and a second alcohol concentration at a second time, the first time being before the second time;
acquiring a preset temperature rise rate and a preset reflux ratio fixed value in the middle period of esterification, and an actual temperature rise rate at the first moment, an actual temperature rise rate at the second moment and an actual reflux ratio at the second moment;
presetting an alcohol concentration warning value, an alcohol concentration preset value and a reflux ratio preset value, wherein the alcohol concentration preset value is smaller than the alcohol concentration warning value;
executing step one or step two when the second alcohol concentration is determined to be greater than the first alcohol concentration;
executing step three or step four when the second alcohol concentration is determined to be less than or equal to the first alcohol concentration;
the first step is specifically as follows:
after the second glycol concentration is determined to be greater than the preset alcohol concentration value, the second glycol concentration is less than the alarm alcohol concentration value and the actual reflux ratio at the second moment is greater than or equal to the preset reflux ratio value, setting the actual reflux ratio at the second moment as a fixed preset reflux ratio value and adjusting the actual temperature rise rate at the second moment according to the actual temperature rise rate at the first moment;
the second step is specifically as follows:
after the second alcohol concentration is determined to be greater than or equal to the alcohol concentration warning value, setting the actual temperature rise rate at the second moment to be zero, and setting the actual reflux ratio at the second moment to be 100%;
the third step is specifically as follows:
after the second glycol concentration is determined to be greater than the preset alcohol concentration value and less than the warning alcohol concentration value, setting the actual temperature rise rate at the second moment as the temperature rise according to the preset temperature rise rate in the middle esterification period, and setting the actual reflux ratio at the second moment as a fixed preset reflux ratio value;
the fourth step is specifically as follows:
and after the second glycol concentration is determined to be less than or equal to the preset alcohol concentration value, setting the actual temperature rise rate at the second moment as the temperature rise according to the preset temperature rise rate in the middle esterification period, and adjusting the actual reflux ratio at the second moment according to the second glycol concentration.
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