RU2046125C1 - Method of controlling process for preparing ethyl benzene hydroperoxide by liquid-phase oxidation of ethyl benzene with atmospheric air - Google Patents

Abstract

FIELD: chemical industry. SUBSTANCE: the process is carried out in a cascade of four reactors. The upper and lower permissible temperature limits in the reactors are determined depending on the amount of charge used and the upper and lower temperature permissible limits are stabilized in the first and fourth reactors. The temperatures in the second and third reactors are determined depending on the upper permissible limit and the selectivity of the process for the formation of ethyl benzene hydroperoxide according to the hydroperoxide concentration in the oxidate in the second and third reactors. The temperatures in the second or the third reactor are corrected depending on the value magnitude of deviation in the concentration of ethyl benzene hydroperoxide in the oxidate at the fourth reactor outlet. EFFECT: greater efficiency of the control method. 3 dwg

Description

 The invention relates to methods for controlling the processes of producing ethylbenzene hydroperoxide (HPEB) by liquid-phase oxidation of ethylbenzene with atmospheric oxygen, carried out in a cascade of reactors, and can be used in the chemical industry.

Closest to the proposed invention in technical essence is a method of controlling the process of producing ethylbenzene hydroperoxide by liquid-phase oxidation of ethylbenzene with atmospheric oxygen, carried out in a cascade of 3-5 reactors, by differentially regulating the temperature profile of oxidation reactors. The temperature in the first reactor is regulated within 135-152 ^о С, in the second reactor it is 3-10 ^о С higher than in the first reactor, and in all subsequent reactors after the second one the temperature in each subsequent one is reduced by 2-4 ^о in comparison with the previous one C to a temperature of 141-151 ^about C.

 The disadvantage of this method is the insufficiently high selectivity for the formation of HPBE, because a differentiated temperature profile along the cascade of reactors with an increase in temperature in the second reactor relative to temperatures in other reactors is not a sufficient condition for conducting the process of ethylbenzene oxidation, ensuring the formation of HPEB with maximum selectivity. The method also does not take into account the change in the selectivity of the formation of HPB versus the concentration of HPB along the reactors.

 The purpose of the invention is to increase the selectivity of the formation of ethylbenzene hydroperoxide.

 This goal is achieved by the fact that in the method of controlling the process of producing ethylbenzene hydroperoxide by liquid-phase oxidation of ethylbenzene with oxygen by air in a cascade of four reactors by controlling the temperatures in the oxidation reactors while limiting their permissible limits, stabilizing the charge flow rate and the concentration of ethylbenzene hydroperoxide in the oxidate at the outlet of the oxide the last reactor. The upper and lower allowable temperature limits in the reactors are determined depending on the charge flow rate, the temperatures in the first and fourth reactors are stabilized, respectively, at their upper and lower allowable limits. The temperatures in the second and third reactors are determined depending on the upper permissible limit and partial derivatives of the selectivity of the process of formation of ethylbenzene hydroperoxide by its concentration in the oxidate in the second and third reactors, respectively. Then, the temperatures in the second or third reactors are adjusted depending on the magnitude and sign of the deviation of the concentration of ethylbenzene hydroperoxide in the oxidate at the outlet of the fourth reactor.

 If the absolute value of the indicated deviation is less than its permissible value, then the temperature in the second and third reactors is left unchanged, and if it is greater than its permissible value, then the temperature in the third reactor is decreased and the temperature in the second reactor is left unchanged, and when the negative sign of the deviation increase the temperature in the second reactor and leave the temperature in the third reactor unchanged.

 The combination of new features in combination with the known ones informs the proposed method of controlling the process of producing ethylbenzene hydroperoxide to produce new properties that allow for differentiated temperature selection according to the oxidation reactors depending on the magnitude and sign of the deviation of the concentration of ethylbenzene hydroperoxide in the oxidate, which increases the selectivity of HPEB formation and allows to recognize the proposed technical a solution meeting the criterion of "significant differences".

 Figure 1 presents a diagram of the implementation of the control method; figure 2 experimental dependence of the selectivity of the formation of HPEB in the reactor; figure 3, the characteristic changes in the partial derivative of the selectivity for the concentration of HPEB with an increase in the number of reactors.

 Figure 1 shows the first reactor 1, the fourth reactor 2, the charge flow sensor 3, the charge flow control valve 4, the temperature sensor 5 in the first reactor, the temperature control valve 6 in the first reactor, the temperature sensor 7 in the fourth reactor, valve 8 temperature control loop in the fourth reactor, a sensor 9 of the concentration of ethylbenzene hydroperoxide in the oxidate and a control computer (UVM) 10.

 The selectivity (figure 2) in the process of oxidation of ethylbenzene in the first two reactors increases, and in the last decreases, due to the fact that during the oxidation reaction there is an accumulation of by-products of the reaction, which are insignificant in the first two reactors and noticeably manifest themselves in the last reactors.

From the presented dependences, it follows that in order to maximize selectivity, it is necessary to stabilize the temperature in the first reactor at the upper permissible limit, in the last reactor at the lower permissible limit, and adjust the temperature in the second and third reactors depending on the sign of the deviation of the concentration of ethylbenzene hydroperoxide in the oxidate at the outlet of the last reactor from its predetermined value: if the concentration deviates upward, reduce the temperature in the third reactor, and if the deviation decreases increase the temperature in the second reactor. This is due to the fact that a decrease in the concentration of HPEB due to a change in temperature in the third reactor causes a reciprocal increase in selectivity, which will be much larger than an increase in selectivity with the same temperature change in the second reactor (partial derivatives, respectively: P ₃ -1.5, P ₂ -0.7).

 With an increase in the concentration of HPEB due to a change in temperature in the second reactor, it leads to a decrease in selectivity, but it will be approximately two times less than a decrease in selectivity caused by a similar change in temperature in the third reactor.

 The initially set temperature values in the second and third reactors are selected inversely with the differences between the partial derivatives of the first and second reactors and between the partial derivatives of the first and third reactors, since these differences in partial derivatives characterize the decrease in selectivity in these reactors relative to its maximum value achieved in the first reactor.

 The mixture, which is a mixture of fresh (10 wt.) Ethylbenzene, is fed into the first reactor 1. Oxidation of ethylbenzene is carried out with atmospheric oxygen, which is fed to reactors 1,2 and intermediate between them (not shown in the diagram) through barbaters. To accelerate the oxidation reaction, water vapor is supplied as a coolant to the coil of the first reactor 1 and the second reactor, and steam condensate is supplied to the third and fourth reactor 2 to remove the heat released during the reaction. The oxidate, which is a mixture of the resulting ethylbenzene hydroperoxide and unreacted charge, is sent from the first reactor 1 to the following cascade reactors, and from the fourth reactor 2, an oxidate with an ethylbenzene hydroperoxide content of 10-11 wt. In addition to ethylbenzene hydroperoxide, the oxidate contains by-products of the reaction of ethylbenzene oxidation and thermal decomposition of hydroperoxide, the concentration of which depends on the amount of reacted oxygen relative to the amount of ethylbenzene and the temperature regime. Excess or deficiency of reacted oxygen, as well as an increase in reaction temperatures, especially in the last reactors of the cascade, increase the content of by-products in the oxidate and, therefore, reduce the selectivity of the process for producing ethylbenzene hydroperoxide.

 Through the top of reactors 1, 2 and intermediate between them, exhaust gases consisting of ethylbenzene and exhaust air are diverted to condensation.

 The control process for the production of ethylbenzene hydroperoxide is as follows.

 Information from sensors 3,5,7,9 is entered into UVM 10.

F $\genfrac{}{}{0ex}{}{\text{з}}{\text{ш}}$ ^ад-F

+K

F $\genfrac{}{}{0ex}{}{\text{з}}{\text{ш}}$ ^ад-F

dt (1) где: U_ш ^o- начальное управляющее воздействие на клапан (при пуске системы);
F_ш, F_ш ^зад текущее (измеренное датчиком 3) и заданное значение расхода шихты;
K_п1, K_п1- соответственно пропорциональная и интегральная настройка регулятора расхода шихты;
t текущее время.The flow rate of the charge is stabilized, for which, according to information from the sensor 3, a control action U _w on the valve 4 is formed, for example, according to the PI control law:
U _W = U $\genfrac{}{}{0ex}{}{\text{o}}{\text{w}}$ + K

F $\genfrac{}{}{0ex}{}{\text{s}}{\text{w}}$ ^hell f

+ K

F $\genfrac{}{}{0ex}{}{\text{s}}{\text{w}}$ ^hell f

dt (1) where: U _w ^o - initial control action on the valve (when starting the system);
F _W , F _{W the} current ^backside (measured by sensor 3) and the set value of the charge flow rate;
K _p1 , K _p1 - respectively proportional and integral settings of the charge flow controller;
t current time.

0,7
κ₃

0,92
Определяют по информации с датчика концентрации гидроперекиси этилбензола в оксидате отклонение ΔС указанной концентрации С от ее заданного значения С^зад.According to the information from the sensor 3 of the charge flow rate, the upper permissible limit Tv of reaction temperatures is determined:
Т _b = а ₁ F _ш ³ + а ₂ F _ш ² + a ₃ F _ш + a _о (2) where: а ₀ , а ₁ , а ₂ , а ₃ coefficients
regression equations (a ₀ 168;
₁ and -0,314˙10 ^-5; a ₂ 0.199˙10 ^-2 ;
a ₃ 0.348)
The difference ΔТ between the upper and lower acceptable limits of reaction temperatures is determined from the information from the charge flow sensor 3 according to the regression equation: ΔТ b ₁ F _ш ² + b ₂ F _ш + b _o (3) where: b ₀ , b ₁ , b _{2 are the} coefficients regression equations
Determine the lower acceptable temperature limit of the reaction T _n T _b Δ T. (4)
The target temperature is determined in the second T ₂ ^ass and third T ₃ ^ass reactors according to the formulas: T ₂ ^ass = T _b -κ ₂ ΔT (5) T ₃ ^ass = T _b -κ ₃ ΔT (6) where κ ₂ , κ _{3 are} constant the coefficients determined depending on the differences in the partial derivatives of selectivity for the concentration of ethylbenzene hydroperoxide, respectively, between the first and second reactors and between the first and third reactors according to the experimental dependence shown in the drawing of figure 2:
κ ₂

0.7
κ ₃

0.92
The deviation ΔС of the indicated concentration C from its predetermined value C ^{ass is} determined from the information from the sensor of the concentration of ethylbenzene hydroperoxide in the oxidate.

C

≥ ΔC_доп (8)
Если условие выполняется, что означает, что концентрация гидроперекиси стабилизируется с удовлетворительной точностью, то температуры во втором и третьем реакторах оставляют без измерения: T_2j ^зад=T

(9) T_3j ^зад= T

(10) где: j и j-1 соответственно текущий и предыдущий шаг формирования управляющих воздействий.ΔC CC ^ass (7)
Check the correspondence of the absolute value of the found deviation of the concentration of ethylbenzene hydroperoxide to its permissible value ΔC _add :

C

≥ ΔC _add (8)
If the condition is fulfilled, which means that the concentration of hydroperoxide is stabilized with satisfactory accuracy, then the temperatures in the second and third reactors are left without measurement: T _2j ^ass = T

(9) T _3j ^ass = T

(10) where: j and j-1, respectively, the current and previous step of the formation of control actions.

+K_п2(ΔC_j-ΔC_j-1) (12) T_3j ^зад=T_3j-1 ^зад (13)
Если условие выполняется, что означает отклонение концентрации гидроперекиси этилбензола относительно заданной величины в большую сторону (т.е. С > C^зад), то корректируют (уменьшают) заданную температуру в третьем реакторе, температуру во втором реакторе оставляют без изменения: T_3j ^зад= T

+K

(ΔC_j-ΔC_j-1) (14) T_2j ^зад=T_2j-1 ^зад. (15)
Формируют управляющие воздействия на клапаны 6, 8 контуров регулирования в первом реакторе 1, четвертом реакторе 2, а также в промежуточных между ними втором и третьем реакторах, например по закону ПИ-регулирования. U

= U

+K

T $\genfrac{}{}{0ex}{}{\text{з}}{\text{i}}$ ^ад-T

+K

T $\genfrac{}{}{0ex}{}{\text{з}}{\text{i}}$ ^ад-T

dt (16) где U_Ti- управляющее воздействие на клапан, регулирующий температуру в i-том реакторе (i 1,2,3,4);
U _Ti ^o- начальное управляющее воздействие на i-тый регулирующий клапан (при пуске системы управления);
T_i, T_i ^зад соответственно измеренное и заданное значение температур в i-том реакторе;
К_птi, К_итi- пропорциональная и интегральная настройки i-того регулятора температуры.If the condition is not met, then analyze the sign of the deviation of the concentration of ethylbenzene hydroperoxide from its predetermined value: ΔС> 0 (11)
If this condition is not fulfilled, which means that the concentration deviates relative to a given value to a smaller side (i.e., C <C ^back ), then the set temperature in the second reactor is corrected (increased), and the temperature in the third reactor is left unchanged: T _2j ^back = T

+ K _P2 (ΔC _j -ΔC _j-1 ) (12) T _3j ^ass = T _3j-1 ^ass (13)
If the condition is fulfilled, which means the deviation of the concentration of ethylbenzene hydroperoxide relative to the specified value upwards (i.e., C> C ^back ), then the set temperature in the third reactor is corrected (reduced), the temperature in the second reactor is left unchanged: T _3j ^back = T

+ K

(ΔC _j -ΔC _j-1 ) (14) T _2j ^ass = T _2j-1 ^ass . (fifteen)
Control actions are generated on the valves 6, 8 of the control loops in the first reactor 1, the fourth reactor 2, as well as in the second and third reactors intermediate between them, for example, according to the PI control law. U

= U

+ K

T $\genfrac{}{}{0ex}{}{\text{s}}{\text{i}}$ ^hell -T

+ K

T $\genfrac{}{}{0ex}{}{\text{s}}{\text{i}}$ ^hell -T

dt (16) where U _Ti is the control action on the valve regulating the temperature in the i-th reactor (i 1,2,3,4);
U _Ti ^o - the initial control action on the i-th control valve (when starting the control system);
T _i , T _i ^ass, respectively, measured and set temperature values in the i-th reactor;
To _pt , K _iti - proportional and integral settings of the i-th temperature controller.

 Thus, the proposed method makes a differentiated selection of temperatures in oxidation reactors depending on the magnitude and sign of the deviation of the concentration of ethylbenzene hydroperoxide in the oxidate, which increases the selectivity of the formation of ethylbenzene hydroperoxide.

A numerical example. Initial data:
F _W ^ass 201.0 T / 2 F _W 200.0 T / 2
K _p1 = 0.02 K _{and 1} = 0 U _w ^o 0.6 kgf / cm ²
C _back 10.5% C 10%
T _2j-1 ^backside 151 ^C. T _3j-1 ^backside 150 ^C.
K _{n2 n3} 0.5 1.0 K ΔS _j-1 -0.6%
U _t1 ^o = U _t2 ^o = U _t3 ^o = U _t4 ^o 0.6 kgf / cm ²
K _pt1 = K _pt2 = K _pt3 = K _pt4 0.1
K _it1 = K _it2 = K _it3 = K _it4 0
The control action on the valve 4 of the charge flow control loop is determined according to equation (1).

U _W 0.6 + 0.02 (201-200) 0.62 kgf / cm ²
The upper permissible reaction temperature limit is determined:
T _in -0.313˙10 ^-5 ˙200 ³ + 0.199 ˙10 ^-2 ˙200 ² 0.348 ˙200 + 168 153.1 ^о С.

The difference between the upper and lower permissible temperature limits is determined by equation (3): ΔТ 0.245 ˙10 ^-3 ˙200 ² 0.1347 ˙200 +
18.954 2,8 ^° C

The lower permissible reaction temperature limit is determined:
T _n 153.1 2.8 150.3 ^about C.

Set temperatures are determined in the second and third reactors according to equations (5) and (6):
T ₂ ^backside 153,1 0,7 ˙2,8 151,15 ^C
T ₃ ^ass 153.1 92 ˙ 2.8 150.5 ^about C.

The deviation of the concentration of ethylbenzene hydroperoxide from its predetermined value is determined by the formula (7):
ΔC 10.0 10.5 -0.5.

C

отклонения концентрации ее допустимому значению ΔС_доп.Check for absolute value.

C

concentration deviations to its permissible value ΔС _add .

C

0,5 < 0,6
В этом случае согласно формул (9) и (10) приравнивают текущие заданные температуры во втором и третьем реакторах достигнутым на предыдущем шаге значениям этих температур:
T_2j ^зад=151,0^oCT_3j ^зад=150^oC.Assume that ΔС _extra 0.6
Condition (8) is not satisfied, because

C

0.5 <0.6
In this case, according to formulas (9) and (10), the current set temperatures in the second and third reactors are equated to the values of these temperatures achieved in the previous step:
T _2j ^ass = 151.0 ^o CT _3j ^ass = 150 ^o C.

c

> ΔС_доп.If we assume that ΔС _extra 0.4, then condition (8) is satisfied

c

> ΔС _add .

 In this case, the sign of the deviation ΔС is analyzed.

ΔС -0.5 negative sign, i.e. C <<C ^ass .

In this case, the set temperature in the second reactor is corrected by the formula (12)
T _2j ^ass 151.0 + 1.0˙ [-0.5 - (- 0.6)] 151.1 ^about C; and the set temperature in the third reactor is equal to its value in the previous step according to formula (13):
T _3j ^ass = 150 ^o C.

If we assume that the concentration deviation turned out to be a positive sign, for example, at C ^ass 10.5% C 11.0% ΔC _additional 0.4%
then ΔС 11.0-10.5 0.5
ΔС> ΔC _add
In this case, according to the formula (14), the set temperature in the third reactor is corrected:
T _3j ^ass 150.0 + 0.5 ˙ [0.5 - (- 0.6)] 150.55 ^о С, and the set temperature in the second reactor is equal to the previous value (according to formula 15):
T _2j ^ass 151 ^about C.

Form according to the formula (16) the control actions on the valves of the temperature control loops in the reactors, for example, the third reactor:
And _TK 0.6 + 0.1 (150.55 150.0) 0.655 kgf / cm ² .

 Similarly, control actions are formed on the valves that control the temperatures in the first, second and fourth reactors.

где: С_гп, С_поб соответственно концентрации ГПЭБ и побочных продуктов в оксидате.Compared with the prototype, the proposed method allows, while maintaining the same concentration of ethylbenzene hydroperoxide (10.7%) at the outlet of the last reactor, to increase the selectivity of HPEB formation by 0.1% from 80.7 to 80.8%
Selectivity was calculated by the formula:
S

where: C _gp , C _bp, respectively, the concentration of HPEB and by-products in the oxidate.

=

0,2392 т/т, а при селективности 80,8%
C

=

0,2376 т/ч
Cледовательно, снижение расходной нормы этилбензола на получение 1 т ГПЭБ составляет:
G_эб 0,2392-0,2376 0,0016 т/т.With a selectivity of 80.7% per ton of NPEB, the following amount of by-products is obtained
C

=

0.2392 t / t, and with a selectivity of 80.8%
C

=

0.2376 t / h
Consequently, the decrease in the consumption rate of ethylbenzene to obtain 1 t of HPE is:
G _eb 0.2392-0.2376 0.0016 t / t.

 Hydroperoxide is a raw material for the production of propylene oxide.

660000 т/г, где: 0,075 расходная норма ГПЭБ на 1 т окиси пропилена.For an annual production of propylene oxide of 50,000 t / year, it is necessary to obtain the following amount of ethylbenzene hydroperoxide:
A _gp

660000 t / g, where: 0.075 GPEB consumption rate per 1 ton of propylene oxide.

Claims (1)

 METHOD FOR CONTROLLING THE PROCESS OF OBTAINING ETHYLBENZENE HYDROPEROXIDE HYDROXIDE OXIDATION BY OXYGEN OXYGEN, carried out in a cascade of four reactors, by controlling the temperature in the oxidation reactors and stabilizing the concentration of the first ethylbenzene reactant at the inlet of the ethylbenzene reactant, , determine the upper and lower permissible temperature limits for all cascade reactors depending on the charge flow rate, stabilize the temperature in the first and fourth reactors, respectively, on their upper and lower permissible limits, the temperatures in the second and third reactors are determined depending on the upper permissible temperature limit in the cascade reactors and partial derivatives of the selectivity of the formation of ethylbenzene hydroperoxide by its concentration in the oxidate in the second and third reactors, respectively , adjust the temperatures in the second and third reactors depending on the magnitude and sign of the deviation of the concentration of ethylbenzene hydroperoxide in the oxidate in the course from the fourth reactor from its predetermined value, in this case, if the absolute value of the indicated deviation is less than its permissible value, then the temperatures in the second and third reactors are left unchanged, and if more, then with a positive sign, the deviations reduce the temperature in the third reactor and remain unchanged temperature in the second reactor, and with a negative sign, the deviations increase the temperature in the second reactor and leave the temperature in the third reactor unchanged, moreover, the temperature regulation in the second ohm and third reactors is carried out depending on the deviation in the concentration of ethylbenzene hydroperoxide oxidate at the outlet of the fourth reactor.

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