JPS60226836A - Method for distilling styrene - Google Patents

Abstract

PURPOSE:To distil a styrene stably with saved energy, by using the heat pump method for putting a dehydrogenated oil obtained from an ethylbenzene into an intermediate part of a distillation column of the vacuum packed column type, compressing adiabatically a low-boiling fraction from the top of the column, and utilizing the heat thereof. CONSTITUTION:A dehydrogenated oil obtaibed by dehydrogenating an ethylbenzene is distilled and separated into styrene and an ethylbenzene. In the process, the dehydrogenated oil is put into an intermediate part of a distillation column 2 of the packed column type under reduced pressure and distilled to withdraw a low-boiling fraction consisting essentially of the ethylbenzene from the top thereof through a pipe 3, and a high-boiling fraction consisting essentially of the styrene is taken out of the bottom of the column 2. All or part of the low-boiling fraction from the above-mentioned pipe 3 is compressed adiabatically in a compressor 7, heated, led to a reboiler 13 of the distillation column 2, and wholly or partially condensed for use as a heat source for the reboiler 13. The condensed low-boiling fraction or part of the uncondensed vapor is returned to a distillation column circulation line 6, and the rest is discharged from the distillation column 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for distilling a styrene-containing mixture containing components with boiling points close to each other, such as styrene and ethylbenzene.

[Prior art]

Styrenes such as styrene, vinyltoluenes, and α-methylstyrene are produced by dehydrogenation of corresponding ethylbenzenes such as ethylbenzene, ethyltoluenes, and cumene. This dehydrogenated oil is mainly composed of generated styrenes and unreacted ethylbenzenes, but also contains small amounts of light components such as benzene and toluene, and heavy components where styrenes are partially polymerized. Therefore, in the production of styrenes, it is necessary to separate and remove the light and heavy components from the dehydrogenated oil, and a distillation separation method using a plurality of distillation columns has been adopted as a method for this purpose.

By the way, the boiling points of styrene and ethylbenzene are close to each other. For example, in the case of styrene and ethylbenzene, the boiling point of the former is 145 at atmospheric pressure.
．． 2°C, the boiling point of the latter is 136.2°C, and the boiling point difference therebetween is only 9.0°C.

Therefore, in order to separate styrenes and ethylbenzenes in a hot column, high thermal efficiency is required, and it is necessary to increase the number of stages and the reflux ratio of the hot column.

For this reason, when a hot surface column used for distilling styrenes is a tray column, it is common to have 60 to 100 trays installed, and the reflux ratio is also low. It is common to set the pressure to be quite large, around 10,000 yen, and the pressure difference between the top and bottom of the column is also large.
It becomes 0+mHg.

Therefore, in such a thermal column, there is a problem in that a large amount of energy needs to be supplied as a heat source.

Further, as a method of reducing the energy used in the thermal column, a distillation method called a heat pump method is known (for example, Japanese Patent Laid-Open No. 111466/1983). This distillation method adiabatically compresses the steam that emerges from the top of the column to raise its temperature, and uses this as a heat source for the reboiler. If the difference becomes large, this method cannot be used because it is necessary to increase the compression ratio, and it was thought that this method could not be adopted for the distillation of styrenes.

[Problem that the invention seeks to solve]

The present invention has been devised in view of this point of view,
The purpose is to provide a method for distilling styrenes that consumes less energy and can perform stable thermal operations.

[Means to solve the problem]

That is, in the present invention, when dehydrogenated oil obtained by dehydrogenating ethylbenzenes is distilled and styrene and ethylbenzenes are separated, the present invention provides a method for distilling dehydrogenated oil obtained by dehydrogenating ethylbenzenes and separating styrene from ethylbenzenes. The above-mentioned dehydrogenated oil is introduced, and while the low-boiling point vapor mainly containing ethylbenzene is extracted from the top of the above-mentioned thermal column, the high-boiling point liquid mainly containing styrene is extracted from the bottom of the column. Part or all of the low-boiling point steam is introduced into the compressor and adiabatically compressed to raise the temperature, and then the heat source is transferred to the heat reservoir boiler, where part or all of it is condensed. and use
This is a method for distilling styrenes in which the condensed low-boiling distillate or a part of the uncondensed vapor is then returned to the hot-face column circulation line, and the remainder is discharged from the hot-face column.

The dehydrogenated oil to which the method of the present invention is applied is obtained by dehydrogenating ethylbenzenes, and contains the produced styrenes and unreacted ethylbenzenes as main components, and may contain small amounts of benzene and toluene. It contains heavy components such as styrenes, partially polymerized styrenes, polymerization inhibitors added to suppress polymerization in the thermal separation process, moisture, air, nitrogen, etc. The styrenes include styrene, vinyltoluenes, α-methylstyrene, and the like, and the ethylbenzenes include ethylbenzene, ethyltoluenes, isopropylbenzene, and the like.

As for the configuration type of the hot column for distilling the above-mentioned dehydrogenated oil, for example, the first column separates heavy components with a lower boiling point than ethylbenzenes, and then the second column separates ethylbenzenes, styrenes, and higher components. A type in which styrenes and heavy components with boiling points are separated, and then styrenes and heavy components are separated in a third column, or ethylbenzenes and those with lower boiling points are separated from the top of the first column. Extract the heavy components, and
Styrenes and heavier components with higher boiling points are extracted and separated from the bottom of the column, and then the top distillate oil and the bottom distillate are charged into separate second columns, and the above-mentioned top distillate is extracted. There is a type in which oil is separated into heavy components and ethylbenzenes, and the bottom distillate is separated into styrenes and heavy components. The present invention can be applied to any of the above-mentioned types, and the hot surface column to which the present invention is applied is the second column in the former case, and the second column in the latter case. There is one tower. Therefore, the dehydrogenated oil to which the present invention is applied may be one that has just been dehydrogenated from ethylbenzenes, or one that has previously separated and removed light components such as benzene and toluene, which have a lower boiling point than ethylbenzenes. It may be.

Further, the heat reservoir to which the present invention is applied is a packed column type heat reservoir operated in a reduced pressure system. The packing packed in this heat reservoir is preferably a regular packing, and in particular, the differential pressure per number of theoretical plates is 1.51 nml-NJ or less, preferably 0.
．． It is preferable that it is 8 anHQ or less. By using such a heat reservoir, the efficiency of the heating section is excellent, and the reflux ratio can also be reduced. Therefore, the differential pressure in the heat reservoir is also 11
005H or less, preferably 70mt-10 or less, the bottom temperature can be lowered as a result, and the temperature difference between the top and bottom of the column can be reduced.

In the above-mentioned heat reservoir, a low-boiling point vapor mainly composed of ethylbenzenes is extracted from the top of the column, and a high-boiling component liquid mainly composed of styrene is extracted from the bottom of the column.

A part or all of the low boiling point steam extracted from the top of the heat reservoir is brought to a pressure of 1ill, and the temperature is raised by adiabatically compressing it with this compressor. The steam is led to a heat reservoir boiler, where the majority of the steam is condensed, leaving some or all of the uncondensed steam, and is used as a heating source for the reboiler.

In particular, if it does not contain light components such as benzene and toluene, which have a lower boiling point than ethylbenzenes, it is preferable to condense all of the components, and if it does contain light components, it is preferable to leave uncondensed vapor. Here, regarding the proportion of the low-boiling distillate steam led to the compressor, the component composition of the dehydrogenated oil charged to the heat reservoir, the component composition of the low-boiling distillate steam extracted from the top of the heat reservoir It is determined by considering the performance of the compressor, the amount of heat added by the compressor, the amount of heat required by the heat reservoir boiler, etc. Further, a portion of the low boiling point distillate and uncondensed steam condensed in this reboiler is returned to the heat reservoir circulation line, and the remainder is lost from the heat reservoir.

[Effect]

Hereinafter, an example of the present invention will be described in detail according to flowcharts 1 to 1 shown in the drawings.

In Fig. 1, dehydrogenated oil is charged from a charging line (1) to the middle part of a packed column type heat reservoir (2) operated in a reduced pressure system, and in this heat reservoir (2) under reduced pressure. At the same time, low-boiling distillate vapor mainly composed of ethylbenzenes is extracted from the top line (3) of the column, and high-boiling components mainly styrene are extracted from the bottom line (4). The liquid is drained.

The low boiling point distilled steam extracted from the line (3) is distributed as necessary to the line (6) on the Funden υ-(5) side and the line (8) on the compressor (7) side, The low-boiling distillate vapor distributed to the line (6) side is cooled in the condenser (5), and then once charged into the overflow drum (9), and the low-boiling distillate vapor that exits the whirlpool drum (9) is A part of the cell is returned to the upper part of the heat reservoir (2) through the line (10), and the remainder is extracted to the outside through the line (11). In addition, the low boiling point distilled steam distributed to the line (8) side is heated by adiabatic compression in the compressor (7) and then charged into the reboiler (13) from the line (12), where it is transferred to the heat reservoir. It is used as a heating source for the dehydrogenated oil introduced in (2).

The line on the condenser (5) side of the above low boiling point distillation steam (
6) and the line (8) on the compressor (7) side:
This is mainly done to control the amount of low boiling point distilled steam introduced into the compressor (7) to a set value.
) A method of controlling the heat transfer surface of this condenser (5) by increasing or decreasing the heat transfer surface by storing a condensate of low boiling point steam in a tank (5) and controlling the liquid level with the liquid level 81 and a control valve at the condensate outlet. Any method can be adopted, such as installing a control valve on the inlet side of line (6) or line (6) to directly control it.

Furthermore, if the low boiling point distilled steam introduced into the compression 1 (7) is saturated steam, when it is adiabatically compressed by this compressor (7), it will condense within the compressor (7) or at its outlet line. In the compressor (7), droplets can cause impeller trouble or polymerization of styrene monomer, which can cause great damage, so it is preferable to install a preheater (1) in the line (8).
4), and the low boiling point steam introduced into the compression 11 (7) is preferably heated in advance to raise its temperature.

is introduced into the compressor 1 (7) through the above line (8),
This compression 1! The low-boiling point steam heated by adiabatic compression in (7) and then charged to the reboiler (13) from the line (12) is used as a heating source for the dehydrogenated oil introduced into the heat reservoir (2). After that, the gas-liquid separation tank (16) is charged through the line (15), and in this gas-liquid separation tank (16), the low-boiling distillate condensed in the reboiler (13) and the uncondensed low-boiling fraction are collected. It is separated into steam. At this time, in order to reduce pressure loss on the heating side in the boiler (13) and improve heat transfer efficiency, it is preferable to install three lines from the reboiler (13) to the gas-liquid separation tank (16). Pull. In other words, the first line is a line that allows condensed liquid to flow into the gas-liquid separation tank (16), and the second line is a line that allows uncondensed low-boiling distillate vapor to flow into the gas-liquid separation tank (16). , the third line transports inert gas such as air and nitrogen from the top of the reboiler (13) to the gas-liquid separation tank (
16). This reboiler (1
The low boiling point distillate condensed in step 3) contains components with relatively high boiling points in the low boiling point steam, mainly consisting of ethylbenzenes, and also contains uncondensed water that passes through the reboiler (13) without being condensed. The condensed low-boiling point vapor is a component with a relatively low boiling point among the low-boiling point vapors, and is mainly composed of benzene, toluene, water, air, nitrogen, etc.

In this flow sheet, the gas-liquid separation tank (16)
The condensed /j low-boiling fraction extracted from the bottom of the
11) to the preheater (14), and this preheater (14)
After exchanging heat with the low boiling point steam introduced into the compressor (7) in step 4) and using it as a heat source for preheating the low boiling point steam, the low boiling point steam is passed through the line (18) to the above line. (
6). In addition, the uncondensed low boiling point vapor extracted from the upper part of the gas-liquid separation tank (16) is transferred to the line (19).
) to join line (6).

Therefore, the reboiler (13) is controlled so as not to completely condense the low boiling point steam. By controlling the reboiler (13) so as not to completely condense the low-boiling point steam, components with relatively high boiling points in the low-boiling point steam are selectively condensed, and the reboiler (13) In addition to being able to increase the condensation temperature in 13) and increase the amount of heat transfer,
Compression! ! It is possible to reduce the compression ratio of II (7), reduce running costs, and reduce equipment costs.
The temperature of the low boiling point distillate condensed in this reboiler (13) can be raised to a temperature necessary and sufficient to heat the low boiling point steam in the preheater (14).
14) has the advantage that there is no need to introduce any other external heat source.

By the way, the low boiling point steam on the inlet side of the compressor (7) may be partially condensed due to natural cooling from the outside, but this condensate is not heated by the preheater (14) with low pressure drop. Since the boiling point steam is normally not re-evaporated due to its high flow rate, it is preferably continuously discharged to a drain pot (not shown) and compressed 1! It is better to prevent intrusion into (7).

Furthermore, a change in the conditions of the low boiling point steam introduced into the compressor (7) immediately leads to a change in the conditions of the low boiling point steam coming out of the compressor (7), which in turn leads to a change in the conditions of the low boiling point steam introduced into the compressor (7), which in turn leads to a change in the conditions of the low boiling point steam introduced into the compressor (7). This will lead to fluctuations in the conditions of the boiler (13), so in order to operate this distillation system stably, the top pressure of the heat reservoir (2), the flow rate of low boiling point steam to the compressor (2), and the It is preferable to control the temperature and keep it constant, and to control the conditions of the low boiling point steam introduced into the compressor (7).

The compressor (7) is driven by a motor alone,
There are various methods such as a combination of a motor and a steam turbine, or a steam turbine alone, but in order to stabilize the distillation system, it is preferable to provide a precise rotation speed control mechanism to the drive machine of the compressor (7). This rotation speed control mechanism is
VVVFl! It is possible to adopt a system such as a lateral or VVI structure, and a feedback mechanism is incorporated in response to voltage and frequency fluctuations of the power supply to control the rotation speed, that is, the capacity fluctuation. In addition, when using steam as a driving source,
It is preferable to control fluctuations in steam pressure using a feedback control mechanism or the like to minimize fluctuations in rotational speed.

Furthermore, in order to stabilize the amount of heat supplied to the reboiler (13), a highly accurate control valve is installed in the bypass line from the compressor (7) to the condenser (5), which cannot be controlled by the compressor (7). It is also possible to absorb fluctuations in heat capacity.

By the way, in order to operate the distillation system stably, the reboiler (
It is particularly important to stabilize the amount of heat supplied to 13). For this purpose, as mentioned above, the compressor (7)
Of course, it is necessary to accurately control the rotation speed of the driving machine, but in addition to this, it is also preferable to control the condensation pressure of the low boiling point steam in the reboiler (13).
To achieve this purpose, it passes through a reboiler (13) and is charged into a gas-liquid separation tank (16);
It is preferable to control the pressure of the uncondensed low boiling point vapor separated in step 16). In this flow sheet, the low boiling point fraction condensed in the reboiler (13) is the gas-liquid fraction 1i
ft tank (16) and the liquid level gauge (20) line (
17) and is controlled by a control valve (21) provided in the preheater (14).
In addition, for the uncondensed low boiling point steam that passed through the reboiler (13) without being condensed and was separated in the gas-liquid separation tank (16), the condensation pressure in the reboiler (13) is controlled and the boiler In order to control the amount of heat supplied to the gas-liquid separation tank (16), a pressure gauge (22
) and the control valve (23) installed in the line (19).
) to merge into line (6). In this way, by controlling the condensation pressure of the low boiling point steam in the reboiler (13) by controlling the pressure of the uncondensed low boiling point steam in the gas-liquid separation tank (16), the reboiler (13) can The condensation pressure of the reboiler (13) can be controlled as desired, and the amount of heat transferred in the reboiler (13) can also be controlled.

In addition, when the distillation system starts operating or when there is little uncondensed low-boiling point vapor in the gas-liquid separation tank (16), the low-boiling point vapor is removed in the gas-liquid separation tank (16). In order to smoothly control the condensation pressure, a gas-liquid separation tank (1
6) or between the gas-liquid separation tank (16) and the control valve (23), it is also possible to introduce an inert gas such as nitrogen gas.

In addition, the heating source of the heat reservoir (2) is the reboiler (13).
In order to supply the necessary amount of heat at the time of start-up or when the amount of heat is insufficient with only the heat source, an auxiliary reboiler (24) can be installed in the heat reservoir (2) and the amount of heat can be supplemented with high pressure steam or other heating source. It is preferable to make it possible.

〔Example〕

A dehydrogenated oil obtained by dehydrogenating ethylbenzene was distilled according to the distillation system in the flow sheet not shown in FIG. In this distillation system, a packed column filled with a regular packing (product name: Merabac, manufactured by Sumitomo Heavy Industries, Ltd.) is used as the heat reservoir (2), and the pressure difference between the top and bottom of the column is 70 sHQ or less. was controlled by.

This distillation system operates by constantly supplying dehydrogenated oil and
40 parts of low-boiling component liquid was extracted from line (11), and 60 parts of high-boiling component liquid was extracted from line (4). The flow rates, temperatures, and pressures at each point Δ, BIC, D, and E shown in the above flow sheet were controlled to the values shown in Table 2.

The compositions of the dehydrogenated oil introduced into the distillation system, the top distillate from the heat reservoir (2), and the bottom effluent from the heat reservoir (2) were as shown in Table 1. In this example, very stable distillation of sagerene can be carried out, and 1 filtration of compression is possible.
The energy consumed in I(7) is also about 30% on average compared to when only high pressure steam is used.
It has been found that this results in significant energy savings.

Table 1 [Effects of the Invention] According to the present invention, the heat pump method is adopted for the distillation of styrenes, for which conventional heat pump methods could not be used as a heat source, and the stable distillation of styrenes is achieved with low energy consumption. I can do 1 row.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing a heating method for styrene according to an example of the embodiment of the present invention. Patent Applicant: Nippon Steel Chemical Co., Ltd., Hitachi Ltd., Patent Attorney: Masaru Naruse Daido, Patent Attorney: Tomohiro Nakatani

Claims (1)

[Claims] In distilling the dehydrogenated oil obtained by dehydrogenating ethylbenzenes and separating styrene and ethylbenzenes, the dehydrogenated oil is introduced into the middle part of a packed column type distillation column operated in a reduced pressure system, From the top of the distillation column, a low-boiling distillate vapor mainly containing ethylbenzene is extracted, and from the bottom of the column, a high-boiling liquid vapor mainly containing styrene is extracted.
Part or all of the low boiling point distilled steam is led to the compressor and adiabatically compressed to raise its temperature, then led to the distillation tower boiler where it is partially or completely condensed and used as a heating source for the reboiler. Then, the condensed low-boiling distillate or a part of the uncondensed vapor is returned to the distillation column circulation line, and the remainder is discharged from the distillation column.