JP4449568B2 - Method for preventing accumulation of insoluble solid in production of styrene, and accumulation preventing apparatus therefor - Google Patents

Description

  The present invention relates to a method for preventing accumulation of insoluble solids in the production of styrene, and an accumulation prevention apparatus therefor, and more particularly, a cooling device for a dehydrogenation reaction product gas in the production of styrene by dehydrogenation of ethylbenzene and the surroundings. The present invention relates to a method for preventing the formation and accumulation of insoluble solids in piping, and an apparatus therefor.

  In general, styrene is produced by dehydrogenation of ethylbenzene. The benzene is generally vaporized and passed through a multistage dehydrogenation reactor packed with a catalyst mainly composed of iron oxide together with steam, and the dehydrogenation reactor is discharged. The dehydrogenation reaction product gas was cooled through a cooling heat exchanger, and the gas and condensed crude styrene and water were separated into gas and liquid, and then separated into oil and water in an oil / water separation tank, and the oil phase (crude styrene) was separated into a plurality of distillation towers. The styrene is recovered by separating it from unreacted ethylbenzene, by-product benzene, toluene, α-methylstyrene, stilbene and the like.

  The dehydrogenation reaction is an equilibrium reaction and is generally carried out at a high temperature of 550 ° C. or more. However, since it is an endothermic reaction, the temperature decreases with the progress of the reaction, and the reaction rate decreases. The catalyst is divided into two or more stages, and the gas whose temperature has been lowered by the dehydrogenation reaction is reheated and introduced into the subsequent dehydrogenation reaction catalyst layer. At this time, since the activity of the catalyst decreases with time, it is generally performed to gradually increase the inlet temperature of each dehydrogenation catalyst layer. Further, the pressure is usually reduced at a reduced pressure in order to make the equilibrium advantageous, and the outlet pressure of the dehydrogenation catalyst layer in the final stage is usually set within the range of 0.03 to 0.08 MPa in absolute pressure.

  The dehydrogenation reaction product gas leaving the dehydrogenation reactor is usually cooled to a temperature of 100 ° C. or lower in a multistage cooling heat exchanger, and most of styrene and water are condensed. At that time, the dehydrogenation reaction product gas leaving the dehydrogenation reactor and passing through the multi-stage heat exchanger is gradually cooled, and the condensation of the high-boiling components starts when it is cooled to 300 ° C. or lower. The condensation start temperature of the high-boiling components varies depending on the composition, concentration, heat exchanger pressure, etc., but is about 300 to 100 ° C. in the dehydrogenation reaction under reduced pressure. The high-boiling components are usually divinylbenzene, naphthalene, stilbene, phenylnaphthalene, and mixtures of styrene dimers, styrene trimers, etc., and the amount produced increases as the dehydrogenation reaction conditions become severe, i.e. high temperature, high It increases under conditions such as styrene partial pressure. Most of the condensed high-boiling components are transported downstream as mist by high-speed gas, dissolved in the condensed crude styrene, and finally discharged through the purification system as styrene heavy end. However, if there is a part of the high boiling point component condensate where the gas flow rate decreases at the outlet of the heat exchanger or the like, it adheres to it and stays in the concave part, etc. It becomes a high molecular weight by condensation or the like and becomes an insoluble solid. Most of the insoluble solids produced are washed away by the condensed crude styrene and water into the oil / water separation tank and captured by the strainer of the oil phase or water phase extraction pump.

  However, some of the insoluble solids that are produced remain in the refrigeration device and absorb and grow condensed crude styrene, increasing the accumulation of insoluble solids. When the accumulation of insoluble solids increases, high molecular weight of the high boiling point component is further promoted in the poorly flowable part such as the lower part of the accumulation part, and sometimes the part of the cooling device or the surrounding piping is blocked. There are things to do. In particular, since the activity of the catalyst decreases at the end of the continuous operation of the styrene production facility, the dehydrogenation reaction temperature increases, so that the concentration of high-boiling components in the crude styrene increases and insoluble solids are generated. Increases the risk of device blockage.

On the other hand, conventionally, as a method for preventing the formation of insoluble solids or preventing the accumulation, polymerization inhibitors such as phenols, amines, nitrophenols, hydroxylamines, and the like are used as dehydrogenation reaction product gas. A method for preventing the formation of insoluble solids by injecting in the vicinity of the condensation start portion is known (for example, see Patent Document 1). However, with this method, it is difficult to completely prevent the formation of insoluble solids. In addition, a method is also known in which an organic liquid or a mixture of an organic liquid and water is injected near the condensation start portion of the dehydrogenation reaction product gas to wash away the generated insoluble solids (for example, see Patent Document 2). ). However, in this method, it is difficult to wash away the solid matter generated upstream of the injection section, and it is inefficient in terms of heat recovery to inject liquid into the upstream section, and insoluble solids. At present, there is a strong demand for a method for preventing the accumulation of things.
Japanese Patent Application Laid-Open No. 9-100245. Japanese Patent Laid-Open No. 2002-265397.

  The present invention has been made in view of the above-described situation, and prevents the generation and accumulation of insoluble solids in the dehydrogenation reaction product gas cooling device and the surrounding piping in the production of styrene by the dehydrogenation reaction of ethylbenzene. It is an object to provide a method and an apparatus therefor.

  The present invention relates to a cooling device in a temperature range in which the temperature of the dehydrogenation reaction product gas is not less than the condensation start temperature of water and not more than 300 ° C. when cooling the dehydrogenation reaction product gas in the production of styrene by dehydrogenation of ethylbenzene. A method for preventing the accumulation of insoluble solids in the production of styrene, and a cooling apparatus for the dehydrogenation reaction product gas in the production of styrene by the dehydrogenation reaction of ethylbenzene, wherein the condensate is not substantially retained in the part. An apparatus for preventing the accumulation of insoluble solids in the production of styrene, in which the cooling device part in the temperature range where the temperature of the elementary reaction product gas is not less than the condensation start temperature of water and not more than 300 ° C. has a structure in which the condensate does not substantially stay. Is the gist.

  According to the present invention, there is provided a dehydrogenation reaction product gas cooling apparatus in the production of styrene by dehydrogenation of ethylbenzene, a method for preventing the formation and accumulation of insoluble solids in the surrounding piping, and an apparatus therefor. be able to.

The description of the constituent requirements described below is a representative example of the embodiment of the present invention, and is not limited to these contents.
In the method for preventing accumulation of insoluble solids in the production of styrene of the present invention, the method for producing styrene is not particularly limited as long as it is a method by dehydrogenation of ethylbenzene, and a conventionally known method for producing styrene is used. Can be taken.

  Specifically, ethylbenzene was charged at a reactor inlet temperature of 550 to 700 ° C., and the reactor inlet pressure was 0.15 to 0.05 MPa in absolute pressure. After passing through the dehydrogenation reactor, the dehydrogenation reaction product gas exiting the dehydrogenation reactor is cooled through a cooling heat exchanger, and the gas and condensed crude styrene and water are separated into gas and liquid, followed by oil-water separation in an oil-water separation tank. Then, the oil phase (crude styrene) is separated from unreacted ethylbenzene and by-products through a plurality of distillation towers to recover styrene.

  At this time, in the present invention, when the dehydrogenation reaction product gas is cooled, the condensate is added to the cooling device portion in the temperature range where the temperature of the dehydrogenation reaction product gas is not less than the water condensation start temperature and not more than 300 ° C. It is characterized by not substantially retaining. Here, “the condensate does not substantially stay” means that unavoidable stay such as when the condensate adheres to the wall surface of the flow path as droplets due to surface tension is excluded. Further, the “cooling device part” represents not only the cooling device but also a part including attached equipment such as piping around the cooling device.

  In the present invention, as a method for substantially preventing the condensate from staying, specifically, for example, is a structure in which the condensate does not have a concave portion where the condensate stays in the part where the condensate exists? Alternatively, if there is a concave portion, the condensate can be extracted from the bottom.

  Usually, a cooling device in the production of styrene is designed with priority given to thermal stress and gas flow, so in a multi-tube heat exchanger arranged in a straight line, the inner diameter of the tube bundle part is large, The inner diameters of the front and rear piping parts are small, and the structure is easy to stay if liquid is present at the outlet of the multi-tube heat exchanger. On the other hand, in the present invention, as means for preventing the condensate from substantially staying, specifically, for example, the center line of the pipe on the outlet side is arranged lower than the center line of the heat exchanger, or It is preferable to make the pipe diameter on the outlet side close to the tube bundle diameter of the heat exchanger. In addition, for smooth flow of the condensate, a downward gradient of 1/200 or more is given to the gas flow at the part where the temperature of the dehydrogenation reaction product gas of the cooling device is not less than the water condensation start temperature and not more than 300 ° C. It is preferable that a gradient of 1/100 or more is applied.

  In addition, even if these means have a concave portion in which the condensate stays in the portion of the water starting from the condensation start temperature to 300 ° C., for example, a means for extracting the condensate from the bottom is provided. Is preferred. Specifically, a means for extracting the condensate continuously or intermittently by installing an outlet at the bottom of the concave portion is employed.

  In addition, as a method for extracting at that time, a method of connecting the extraction port from the concave portion to the extraction tank and storing the extracted condensate in the extraction tank may be used, and the piping from the extraction port is located at the lower part. You may use the method of connecting to an oil-water separation tank etc., and separating oil-water after melt | dissolving the extracted condensate in crude styrene of an oil phase. In addition, the composition, properties, production amount, etc. of the condensate vary depending on styrene production conditions such as dehydrogenation reaction catalyst, reaction temperature, reaction pressure, LHSV, steam / raw material ethylbenzene ratio, etc., but generally at 80 to 110 ° C. In order to start solidification, when these are extracted from the concave portion, in order to avoid solidification and blockage in the extraction pipe, the pipe or the like is kept at 80 ° C. or higher, preferably 110 ° C. or higher, and / or heated. For example, it is preferable to dissolve and wash a solvent such as ethylbenzene, crude styrene, or diethylbenzene.

  In the cooling of the dehydrogenation reaction product gas, the high boiling point component does not condense in the cooling device portion exceeding 300 ° C., and the portion of the high boiling point component is below the water condensation start temperature. Since the condensate is washed away with water or a polymerization inhibitor is added and dispersed in water for easy prevention of polymerization, the application of the present invention becomes unnecessary.

  Also, in pipes of less than 80 ° C. of the cooling device, particularly in places where the temperature is low, such as nozzle parts, bent parts, branch parts, etc., where liquid tends to stay, depending on the composition of high-boiling components, production amount, pressure, etc. Since there is a possibility that a part or most of the condensate of the high boiling point component may be solidified, a method of injecting and dispersing an organic solvent or / and water or water containing a polymerization inhibitor as described above is used. Can be used together.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited by a following example, unless the summary is exceeded.

Example 1
Ethylbenzene (purity) in a fixed bed flow type three-stage dehydrogenation reactor (the amount of catalyst is almost the same in all three stages) using a commercially available iron oxide catalyst for the production of styrene (“Styromax 5” manufactured by Zude Chemie). 99% or more) was produced. The inlet temperature of each of the 1st to 3rd dehydrogenation reactors was gradually increased within the range of 580 to 640 ° C. The LHSV 0.3h ^{−1 for} the total of the three stages, and the outlet pressure of the three-stage dehydrogenation reactor were set to reaction conditions of 0.040 to 0.045 MPa in absolute pressure and a steam / raw material ethylbenzene weight ratio of 1.2. The ethylbenzene conversion decreased from 70% to 60% in 11 months.

  The above dehydrogenation reaction product gas is cooled to 130 ± 10 ° C. through a multi-stage heat exchanger, cooled to 80 ± 5 ° C. (water condensation start temperature) by injecting water into the gas, and further air-cooled heat Cooled to 50 ± 10 ° C. with exchanger. An extraction tank kept at 110 ° C. was attached to a nozzle installed at the bottom of the final stage outlet of the multistage heat exchanger, and the valve of the nozzle was opened. The condensate accumulated in the extraction tank, and the condensate was extracted by exchanging the extraction tank at a frequency of about once per month for 7 months from the start of operation of the styrene production apparatus. Thereafter, the frequency of replacement of the extraction tank was increased in accordance with the increase in the amount of condensate collected, and the frequency was set to once / day after 11 months from the start of operation.

The amount of the high boiling point component by the collected condensate was 80 × 10 ⁻⁶ parts by weight / hour with respect to 100 parts by weight / hour of raw material ethylbenzene at the time of 11 months after the start of operation. After 7 months, 9 months, and 11 months from the start of operation, the amount of solids captured by the strainer installed in the drain line at the inlet of the air-cooled heat exchanger is 1 for 100 parts by weight / hour of ethylbenzene, respectively. 3 × 10 ⁻⁶ , 2.6 × 10 ⁻⁶ , and 2.6 × 10 ⁻⁶ parts by weight / hour. After 11 months, when the styrene production apparatus was stopped and opened and inspected, accumulation of insoluble solids was not observed in the piping at the inlet of the air-cooled heat exchanger.

Comparative Example 1
The multi-stage heat exchanger was operated in the same manner as in Example 1 except that the condensate was not extracted from the nozzle at the outlet of the final stage, but the air-cooled heat exchanger was 7 months and 9 months after the start of operation. The amount of solids captured by the strainer installed in the drain line at the inlet was 6.3 × 10 ⁻⁶ and 12 × 10 ⁻⁶ parts by weight / hour, respectively, with respect to 100 parts by weight of raw material ethylbenzene. . Also, after 11 months, no solid matter was recovered, so when the styrene production equipment was stopped and opened, a large amount of insoluble solids accumulated in the piping at the inlet of the air-cooled heat exchanger. Most were popcorn-like polystyrene. Further, insoluble solids and the like were accumulated in the vicinity of the nozzle at the outlet of the final stage of the multistage heat exchanger.

Claims (6)

When cooling the dehydrogenation reaction product gas in the production of styrene by the dehydrogenation reaction of ethylbenzene, the dehydrogenation reaction product gas is condensed in the cooling device part in the temperature range where the temperature of the dehydrogenation reaction product gas is not less than the water condensation start temperature and not more than 300 ° C. A method for preventing accumulation of insoluble solids in the production of styrene, wherein the liquid is not substantially retained. The method for preventing accumulation of insoluble solids in the production of styrene according to claim 1, wherein the condensate is not retained by extracting the condensate from the bottom of the concave portion in the cooling device. The method for preventing accumulation of insoluble solids in the production of styrene according to claim 2, wherein the temperature of the condensed liquid to be extracted is 80 ° C or higher. A cooling device for a dehydrogenation reaction product gas in the production of styrene by a dehydrogenation reaction of ethylbenzene, the cooling device part having a temperature range in which the temperature of the dehydrogenation reaction product gas is not less than the water condensation start temperature and not more than 300 ° C. An apparatus for preventing the accumulation of insoluble solids in the production of styrene, characterized in that the condensate does not substantially stay. The apparatus for preventing accumulation of insoluble solids in the production of styrene according to claim 4, wherein a condensate outlet is provided at the bottom of the concave portion in the cooling device so that the condensate does not stay. 6. The apparatus for preventing accumulation of insoluble solids in the production of styrene according to claim 5, wherein the outlet is provided with a heat retaining or / and heating device.