JPH0692878A - Production of styrene - Google Patents

Abstract

PURPOSE:To recover condensation heat of a distillate at the top of a distillation column without largely raising pressure at the top of the distillation column at a stage for separating styrene from unreacted ethyl benzene in a styrene distillation in a styrene producing process. CONSTITUTION:A distillation column is operated under 150mmHg pressure at the top of the column and at 85 deg.C temp. at the top of the column and unreacted ethylbenzene flowing out from the top of the column is used as a heat source of an absorption type heat pump. Water or a mixture of ethylbenzene with water is used as a material to be heated for the absorption type heat pump. In the case of water as the material to be heated, generated steam is recovered and used as a heat source for steam for dilution of a dehydrogenating reaction process or for a reboiler of a distillation process. In the case of the mixture of ethylbenzene with water as the material to be heated, generated azeotropic admixture of ethylbenzene with water is recovered and used in the dehydrating reaction process.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing styrene by dehydrogenation of ethylbenzene in the presence of steam. More specifically, the heat of condensation of the overhead distillate from the distillation column, which is normally lost in the step of separating unreacted ethylbenzene from styrene in the styrene distillation process, is efficiently recovered by an absorption heat pump, and this heat is stored in the heat pump. The present invention relates to a method used for vaporizing water or a mixture of water and ethylbenzene, which is an object to be heated.

[0002]

BACKGROUND OF THE INVENTION Styrene is about 590 in the presence of steam.
It is produced by the vapor phase catalytic dehydrogenation of ethylbenzene at a temperature of ˜650 ° C. Various proposals have been made for catalysts used in this reaction.

Recently, however, the main focus of development has been to save heat from the catalyst itself in the dehydrogenation process, especially with respect to the large amount of diluent steam used to supply the sensible heat necessary for the dehydrogenation reaction, which is an endothermic reaction. Alternatively, it has turned to a means for conserving heat with respect to the separation of styrene from the dehydrogenation reaction product.

When unreacted ethylbenzene and styrene are separated by distillation in the styrene production process, since the boiling points thereof are close to each other, it is necessary to increase the number of stages of the distillation column, and there is a problem that the heat supplied as a heat source is large. is there. However, conventionally, the overhead distillate from the distillation column has been cooled by water in the overhead cooler, and the heat of condensation of the distillate has not been effectively recovered.

For this reason, in JP-A-62-148434, an overhead distillate from a distillation column for separating crude styrene from unreacted ethylbenzene is fed to a heat exchanger, and ethylbenzene passing through the heat exchanger and A method of indirectly exchanging heat with a fluid consisting of water has been proposed.

[0006]

However, this method requires the distillation column overhead temperature to be 100 ° C. or higher due to the difference in effective temperature in the indirect heat exchanger, so that the distillation column overhead pressure is increased to 300 mmHg or more. I have to let
Therefore, there is a problem that the reflux ratio increases, the amount of heat medium used in the reboiler increases, and the bottom temperature of the distillation column rises, so that the amount of polymerization inhibitor used to prevent thermal polymerization of styrene increases. .

The object of the present invention is to reduce the heat of condensation of the distillation column overhead distillate without significantly increasing the distillation column overhead pressure in the step of separating unreacted ethylbenzene from styrene in the styrene distillation process in the styrene production process. It is intended to provide a method for recovering and effectively utilizing it in a styrene production process.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted diligent research to solve the above-mentioned problems, and as a result, the top pressure of a distillation column at the time of separating unreacted ethylbenzene and styrene in a styrene distillation step. The column top distillate is supplied to an absorption heat pump while maintaining 50 to 290 mmHg, and the heat of condensation of the column top distillate can be effectively recovered by indirectly exchanging heat with the object to be heated in the heat pump. They have found the present invention and completed the present invention.

That is, according to the present invention, ethylbenzene is subjected to a dehydrogenation reaction step in the presence of steam, and the dehydrogenation reaction product is cooled to obtain a gas phase composed of hydrocarbons, an aqueous phase composed of a condensed product of steam, and In the method for producing styrene by dehydrogenation reaction of ethylbenzene, where the organic phase is separated into three phases consisting of crude styrene, unreacted ethylbenzene, light and heavy components, and the organic phase is subjected to a distillation process to separate and recover styrene. , The top pressure of the distillation column during the separation of unreacted ethylbenzene and styrene in the distillation step is 50 to 290 m.
The overhead distillate is supplied to an absorption heat pump while being maintained at mHg to be indirectly heat-exchanged with the object to be heated of the heat pump, and the object to be heated is heated at a temperature higher than that of the overhead distillate by 0.6 to 4.
A method for producing styrene, which comprises vaporizing under a pressure of 0 kg / cm ² and supplying the gas to the dehydrogenation step and / or the reboiler heat source.

(Detailed Description) The method of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 schematically shows a typical example of the method of the present invention for producing styrene by dehydrogenation of ethylbenzene.

The production of styrene by the dehydrogenation reaction of ethylbenzene is carried out at a temperature of about 600 ° C. or higher and a low pressure condition of atmospheric pressure or lower in the presence of steam for dilution due to the characteristics of the reaction. In FIG. 1, most of the dilution steam (referred to as primary steam) is supplied through line 1 through a steam superheater (not shown). In addition, ethylbenzene and the rest of the diluting steam (referred to as secondary steam) are supplied through line 2 and merge with the diluting steam supplied through line 1 at point A, and are supplied to dehydrogenation reaction section 100 through line 3.

The dehydrogenation reaction product discharged from the dehydrogenation reaction section 100 is supplied to a heat exchanger 101 through a line 4, where ethylbenzene and secondary steam supplied through a line 5 are heated to a predetermined temperature. To be cooled. The effluent from the heat exchanger 101 is supplied to the heat recovery / separation unit 102 through the line 6 and further cooled by indirect heat exchange with water or air, and mainly hydrocarbons (for example, methane, ethylene, aromatic hydrocarbons). Phase consisting of compounds, hydrogen, nitrogen, carbon dioxide, etc., an aqueous phase consisting of steam condensate, and organic consisting of styrene, unreacted ethylbenzene, light substances (benzene, toluene, etc.) and heavy substances (styrene polymer) It is separated into three phases.

The gas phase is recovered as vent gas through a cooling and adiabatic compression process and sent to another facility (not shown). These series of treatments are labeled as “vent gas recovery”. The water phase is sent to another facility (not shown) through the line 7. The organic phase is supplied to the distillation column 103 (shown as “benzene / toluene column” to indicate its main function) through the line 8 and light substances (benzene / toluene, etc.) are extracted from the top of the column through the line 9. It is sent out and sent to other equipment (not shown).

Styrene, unreacted ethylbenzene and a heavy substance (styrene polymer) are withdrawn from the bottom of the column through a line 10 and supplied to a distillation column 105 (shown as "ethylbenzene column" to indicate its main function). To be done. The distillation column 105 has a column top pressure of 50 mmHg to 290 mmHg.
g It is preferably operated at 120 mmHg to 200 mmHg, and unreacted ethylbenzene is extracted from the top of the column through a line 11 and supplied to an absorption heat pump 107 to be used as an operating heat source of the heat pump. The absorption heat pump used in the present invention utilizes heat of absorption when absorbing water vapor of an absorbent aqueous solution, and is generally composed of an evaporator, an absorber, a condenser, and a device element called a generator. Examples thereof include those using lithium bromide or ammonia as an absorbent.

The unreacted ethylbenzene condensed in the absorption heat pump 107 is supplied to the cooler 108 through the line 12 and cooled. The unreacted ethylbenzene cooled by the cooler 108 is supplied to the reflux tank 109 through the line 13, a part of the unreacted ethylbenzene is returned to the upper portion of the distillation column 105 as a reflux liquid through the line 14, and the rest is extracted through the line 15. Be done. The distillation tower 105
Styrene and heavy substances (styrene polymer) are extracted from the bottom of the column through line 25 and supplied to the distillation column 110 (denoted as "styrene column" to indicate its main function), and from the top of the column. Styrene is extracted through line 26 and collected as a product. The heavy substance (styrene polymer) is withdrawn from the bottom of the column through a line 27 and sent to another facility (not shown).

When the object to be heated of the absorption heat pump 107 is water, water is supplied to the absorption heat pump 107 through the line 16 and the line 18, and 0.6 kg / cm ² A to 4.0 kg / is supplied by the heat pump. cm
² A, preferably 0.8 kg / cm ² A to 1.5 kg /
A low pressure steam of cm ² A is produced and withdrawn through line 19. The low-pressure steam is widely used, for example, when used as a distillation column reboiler heat medium, the low-pressure steam is supplied to the distillation column reboilers 104, 106 and 111 through lines 20, 21 and 22. When used as a secondary steam, the low pressure steam is withdrawn through line 23,
Is combined with the ethylbenzene supplied through the line 24 and is supplied to the heat exchanger 101 through the line 5.

When the object to be heated of the absorption heat pump 107 is a mixture of ethylbenzene and water, water is supplied through the line 16 and ethylbenzene is supplied through the line 17 and merged at the point C to be supplied to the absorption heat pump 107 through the line 18. To be done. 0.6 kg / cm ² A to 4.0 kg / cm with the heat pump
² A, preferably 0.8 kg / cm ² A to 1.5 kg /
The above-mentioned ethylbenzene and water azeotrope vaporized as an azeotrope at cm ² A are the lines 19 and 23.
Is combined with the ethylbenzene supplied through line 24 at point B and supplied to heat exchanger 101 through line 5. As another type of the distillation step for separating the organic phase, there is a type in which light substances (benzene, toluene, etc.) and unreacted ethylbenzene are withdrawn from the top of the first tower. A heat pump is used in the first tower.

[0018]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 The distillation column 105 was set at a column top pressure of 150 mmHg and a column top temperature of 85.
Operating at 0 ° C., unreacted ethylbenzene was withdrawn from the top of the column through line 11 and supplied to the absorption heat pump 107, which was used as an operating heat source for the heat pump. The absorption heat pump 107 is supplied with water at 85 ° C. through lines 16 and 18, and is heated by the heat of condensation of the unreacted ethylbenzene in the heat pump to obtain 1.2 kg.
/ Cm ² A steam (temperature 105 ° C) was produced.
The steam is extracted through line 19 at 80
% Was withdrawn through line 23 and supplied as secondary steam, and the remainder was withdrawn through line 22 and supplied to styrene column reboiler 111 and used as 50% of the required heat medium amount. The heat recovered by the absorption heat pump 107 was 48% of the heat of condensation of the unreacted ethylbenzene extracted from the top of the distillation column 105.

Example 2 As in Example 1, the top pressure of the distillation column 105 was 150 mmH.
g, operating at a tower top temperature of 85 ° C., unreacted ethylbenzene was extracted from the tower top through a line 11 and supplied to an absorption heat pump 107, which was used as an operating heat source of the heat pump. The absorption heat pump 107 is supplied with water at 85 ° C. through a line 16 and ethylbenzene at 85 ° C. through a line 17, and is heated by the heat of condensation of the unreacted ethylbenzene in the heat pump to 1.2 kg / cm 2. Vaporized at a pressure of ² A and temperature is 95 ℃
An ethyl benzene and water azeotrope was prepared. The ethylbenzene and water azeotrope is withdrawn through line 19 and line 23 and at point B line 2
It was combined with ethylbenzene supplied through No. 4 and was supplied to the heat exchanger 101 through line 5. The amount of ethylbenzene vaporized by the absorption heat pump was 50% of the amount of ethylbenzene supplied to the dehydrogenation reaction section 100. The heat recovered by the absorption heat pump 107 was an amount corresponding to 48% of the heat of condensation of unreacted ethylbenzene extracted from the top of the distillation column 105.

[0021]

EFFECTS OF THE INVENTION According to the method of the present invention, an absorption heat pump is used without significantly increasing the overhead pressure of the distillation column in the step of separating unreacted ethylbenzene from styrene in the styrene distillation step in the styrene production step. The heat of condensation of the distillation overhead of the distillation column can be recovered. The recovered heat can be effectively used in the styrene production process as a reboiler heat source in the styrene distillation process or as a vaporization heat source for diluting steam or ethylbenzene in the dehydrogenation reaction process.

[Brief description of drawings]

FIG. 1 is a schematic view showing a typical example of the method of the present invention for producing styrene by dehydrogenation reaction of ethylbenzene.

[Explanation of symbols]

 100 Dehydrogenation Reaction Section 101 Heat Exchanger 102 Heat Recovery / Separation Section 103 Distillation Tower 104 Reboiler 105 Distillation Tower 106 Reboiler 107 Absorption Heat Pump 108 Cooler 109 Reflux Tank 110 Distillation Tower 111 Reboiler

Claims (3)

[Claims] 1. Ethylbenzene is subjected to a dehydrogenation reaction step in the presence of steam, the dehydrogenation reaction product is cooled, and a gas phase consisting of a hydrocarbon, an aqueous phase consisting of a condensate of steam and crude styrene, In the method for producing styrene by the dehydrogenation reaction of ethylbenzene, in which the organic phase is separated into three phases of reaction ethylbenzene, a light component and a heavy component, and the organic phase is subjected to a distillation process to separate and recover styrene, At the time of separating unreacted ethylbenzene and styrene at 50 to 290 mmHg.
While maintaining the above, the overhead distillate is supplied to an absorption heat pump to indirectly exchange heat with the object to be heated of the heat pump, and the object to be heated is heated to a temperature higher than that of the overhead distillate by 0.6 to 4.0 kg.
A method for producing styrene, which comprises vaporizing under a pressure of / cm ² and supplying the gas to the dehydrogenation step and / or the reboiler heat source. 2. The method according to claim 1, wherein the object to be heated is water. 3. The method according to claim 1, wherein the material to be heated is a mixture of water and ethylbenzene.