JP2007016027A - Method for producing styrene - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing styrene in a high yield for a long period by suppressing formation of carbon dioxide in between a spot where dehydrogenation product gas and oxygen-containing gas are mixed and an oxidation-step inlet. <P>SOLUTION: The method for producing styrene comprises a dehydrogenation step (1) for reacting a feed gas containing at least ethylbenzene and steam in the presence of a dehydrogenation catalyst; an oxidation step (2) for reacting at least part of hydrogen contained in the dehydrogenation product gas obtained in the dehydrogenation step in the presence of an oxidation catalyst and in the coexistence of the oxygen-containing gas; and another dehydrogenation step (3) for reacting the oxidation product gas obtained in the oxidation step in the presence of a dehydrogenation catalyst. In the method for producing styrene, in supplying the step (2) with the mixed gas of the dehydrogenation product gas obtained in the step (1) and the oxygen-containing gas, the combustion rate by oxygen is controlled to be 15% or lower in the section between the spot where the dehydrogenation product gas and the oxygen-containing gas are mixed and the inlet of the step (2). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing styrene, and more specifically, in producing styrene by the oxidative dehydrogenation method of ethylbenzene, producing a styrene in a high yield while suppressing a decrease in the activity of the dehydrogenation catalyst over a long period of time. The present invention relates to a method for producing styrene.

  A process for producing styrene by dehydrogenating ethylbenzene using, for example, a potassium-containing iron-based dehydrogenation catalyst has been widely practiced industrially. However, in general, the dehydrogenation reaction is strongly constrained by equilibrium, and since the dehydrogenation reaction is an endothermic reaction, the reaction temperature in an adiabatic reactor decreases with the progress of the reaction. It is difficult to get a rate. For this reason, it has been conventionally proposed to combine an oxidation step of selectively oxidizing hydrogen generated by a dehydrogenation reaction with an oxidation catalyst in the dehydrogenation step.

  At that time, the effluent gas from the dehydrogenation step contains an alkaline substance such as a potassium compound derived from the dehydrogenation catalyst. Therefore, when the effluent gas is supplied to the oxidation process, alkaline substances adhere to the oxidation catalyst, and the selectivity thereof is hindered. In the oxidation process, the combustion amount of hydrocarbons such as styrene and ethylbenzene increases, and carbon dioxide is increased. Generate. On the other hand, since the reaction activity is reduced only by the presence of a small amount of carbon dioxide during the steady-state reaction of the dehydrogenation catalyst, the generated carbon dioxide decreases the activity of the subsequent dehydrogenation catalyst and deteriorates the yield of styrene. It has been known.

  For example, alkaline substances in the reaction mixture supplied to the oxidation process are removed in advance in order to suppress the reduction of oxidation selectivity of hydrogen in the oxidation process and to suppress the generation of carbon dioxide due to combustion of hydrocarbons in the oxidation process. A method (for example, refer to Patent Document 1) has been proposed. However, in the method of Patent Document 1, the alkaline substance is not supplied to the subsequent dehydrogenation step on the downstream side of the oxidation step. Therefore, the deterioration of the dehydrogenation catalyst performance in the latter stage is promoted over time, the reaction activity is lowered, the selectivity is further lowered, and a large amount of carbon dioxide is generated by the steam reforming reaction, etc. This leads to a vicious circle in which the activity of the human body decreases. In addition, a method of maintaining the carbon dioxide production rate in the dehydrogenation step at less than 2.1 times compared to the initial reaction (see, for example, Patent Document 2) has also been proposed. According to the study of the present inventor, it is impossible to suppress an increase in the amount of carbon dioxide produced by combustion of hydrocarbons from the point where the oxygen-containing gas is mixed to the inlet of the oxidation process, and styrene is produced in a high yield. It turns out that you can't continue.

Although not focusing on the suppression of carbon dioxide production due to the combustion of hydrocarbons in the oxidation process, in order to improve the styrene yield in the subsequent dehydrogenation process, the effluent gas from the dehydrogenation process is directly or There has also been proposed a method of cooling in advance by indirect heat exchange to increase the amount of heating in the oxidation step as compared with the case of not cooling, and increasing the amount of hydrogen combustion in the oxidation step (for example, see Patent Document 3). Yes. However, according to the study of the present inventor, the contained alkaline substance adheres to the inner wall of the flow path by cooling the outflow gas. For this reason, it has been found that the combustion amount of hydrocarbons such as styrene and ethylbenzene on the inner wall of the adhesion increases and a large amount of carbon dioxide is generated, and it is not possible to continue producing styrene at a high yield.
Japanese Patent Application Laid-Open No. 11-80045. JP 2002-154991A. Japanese Patent Publication No. 4-20410.

  In view of the above-described prior art, the present invention provides a flow from the location where the alkaline substance contained in the dehydrogenation reaction gas from the dehydrogenation process is mixed with the oxygen-containing gas to the dehydrogenation reaction gas to the subsequent oxidation process inlet. It was made to suppress the production | generation of the carbon dioxide by the combustion reaction of hydrocarbons by adhering to a road inner wall. The present invention relates to a method for producing styrene by dehydrogenation of ethylbenzene, which is a combination of a dehydrogenation reaction and an oxidation reaction, and the production of carbon dioxide from a location where an oxygen-containing gas is mixed with the dehydrogenation reaction gas to the oxidation process inlet. The object is to provide a method for producing styrene in a high yield over a long period of time while suppressing the amount.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have made the above object by reducing the oxyfuel combustion reaction rate to a specific range or less from the location where the oxygen-containing gas is mixed into the dehydrogenation reaction gas to the oxidation process inlet. It has been found that the above can be achieved, and the present invention has been achieved. That is, the gist of the present invention is a styrene production method including the following steps (1) to (3), wherein an oxygen-containing gas is mixed with the dehydrogenation reaction gas obtained in step (1). Thereafter, when supplying the dehydrogenation reaction gas to the step (2), the oxygen combustion reaction rate is 15% or less in the portion from the portion where the oxygen-containing gas is mixed to the dehydrogenation reaction gas to the inlet of the step (2). And a method for producing styrene.

Step (1): A raw material gas containing at least ethylbenzene and water vapor is subjected to a dehydrogenation reaction of ethylbenzene in the presence of a dehydrogenation catalyst to contain styrene, hydrogen, unreacted ethylbenzene, water vapor, and an alkaline substance derived from the dehydrogenation catalyst. Dehydrogenation process step (2) for obtaining a dehydrogenation reaction gas: An oxidation in which at least a part of hydrogen is oxidized in the presence of an oxidation catalyst in the presence of an oxidation catalyst. Process step (3): The oxidation reaction gas obtained in the oxidation step is dehydrogenated in the presence of a dehydrogenation catalyst to dehydrogenate benzene, hydrogen, unreacted ethylbenzene, water vapor, and an alkaline substance derived from the dehydrogenation catalyst. Dehydrogenation process to obtain dehydrogenation reaction gas containing

  According to the present invention, in the method for producing styrene by dehydrogenation of ethylbenzene, which comprises a combination of a dehydrogenation reaction and an oxidation reaction, carbon dioxide from the location where the oxygen-containing gas is mixed into the dehydrogenation reaction gas to the oxidation process inlet It is possible to provide a method for producing styrene with a high yield over a long period of time.

  In the method for producing styrene of the present invention, in the step (1), a raw material gas containing at least ethylbenzene and water vapor is subjected to dehydrogenation reaction of ethylbenzene in the presence of a dehydrogenation catalyst, so that styrene, hydrogen, unreacted ethylbenzene, water vapor, And a dehydrogenation step for obtaining a dehydrogenation reaction gas containing an alkaline substance derived from the dehydrogenation catalyst.

  In the dehydrogenation step (1), ethylbenzene as a raw material hydrocarbon is mixed with water vapor and supplied in gaseous form to the dehydrogenation step (1). The raw material hydrocarbon may contain, in addition to ethylbenzene, other hydrocarbons such as styrene, toluene, benzene, etc., and the ethylbenzene concentration is usually 90% or more, preferably 95% or more, more preferably. Is 97% or more. Moreover, the mixing ratio of water vapor to the raw material hydrocarbon containing ethylbenzene is usually in the range of 1 to 15, preferably 1 to 10, in terms of molar ratio.

  Further, the dehydrogenation catalyst is not particularly limited, but is usually described in Japanese Patent Application Laid-Open No. 60-130531, for example, an iron-based catalyst containing an alkali metal or an alkaline earth metal, or the iron-based catalyst. Further, those containing other metals such as zirconium, tungsten, molybdenum, vanadium, and chromium can be used. Among these, a potassium-containing iron-based catalyst containing iron oxide as a main component and containing potassium oxide and, if desired, the above-mentioned other metals and the like is preferable. Examples thereof include those described in JP-A-4-277030 and the like, that is, those containing iron oxide and potassium oxide as main components and titanium oxide as a promoter component.

  The reaction temperature in the dehydrogenation step (1) is usually 500 ° C. or higher, preferably 550 ° C. or higher, and usually 700 ° C. or lower, preferably 670 ° C. or lower. In addition, since the dehydrogenation reaction of ethylbenzene is an endothermic reaction, the temperature in the step (1) decreases with the progress of the reaction. The pressure is usually in the range of 0.0049 to 0.98 MPa.

  In the dehydrogenation step (1), ethylbenzene is dehydrogenated to produce styrene and hydrogen, and a dehydrogenation reaction gas containing styrene, hydrogen, unreacted ethylbenzene, water vapor, and an alkaline substance derived from a dehydrogenation catalyst is obtained.

  In the present invention, the “alkaline substance” is a general term for compounds containing an alkaline metal such as an oxide, carbonate, hydroxide or the like of an alkali metal or alkaline earth metal. Although the alkaline substance contained in the dehydrogenation reaction gas has not been specified, it is generated in the presence of high-temperature water vapor and carbon dioxide. Presumed to be carbonates of alkaline metals such as potassium.

  In addition, although it does not specifically limit as an apparatus used for the dehydrogenation reaction of the dehydrogenation process (1) in this invention, Usually, the fixed bed apparatus which has a dehydrogenation catalyst packed bed is used. The temperature of the dehydrogenation reaction gas exiting the dehydrogenation step (1) is lower than that at the dehydrogenation step inlet, and the dehydrogenation reaction gas is mixed with the oxygen-containing gas and then the oxidation step (2). To be supplied.

  Here, the oxygen-containing gas is not particularly limited as long as it is a gas containing oxygen. Examples thereof include air, diluted air, oxygen-enriched air, oxygen diluted with an inert gas, and the like. The method for supplying the oxygen-containing gas is not particularly limited, and the oxygen-containing gas is supplied to the dehydrogenation reaction gas exiting the dehydrogenation step (1), and the mixed gas is introduced into the oxidation step (2).

  In the method for producing styrene of the present invention, in the step (2), the dehydrogenation reaction gas obtained in the dehydrogenation step (1) is converted from at least a part of hydrogen in the presence of an oxidation catalyst in the presence of an oxygen-containing gas. This is an oxidation step for oxidation reaction.

  In the oxidation step (2), any oxidation catalyst can be used as long as it can selectively burn hydrogen in the presence of styrene and ethylbenzene. Usually, a noble metal-based oxidation catalyst is used. For example, a catalyst described in JP-A-60-130531, for example, platinum and potassium, or a catalyst comprising platinum, tin and potassium. Moreover, the catalyst described in Unexamined-Japanese-Patent No. 61-225140 etc., ie, the catalyst containing 4A group, such as an alkali metal or alkaline-earth metal, germanium, tin, or lead, and a noble metal, etc. are mentioned. . Moreover, the catalyst described in Unexamined-Japanese-Patent No. 11-322303 etc., ie, the catalyst containing platinum, niobium, or tantalum, etc. can also be used.

  In addition, it does not specifically limit as an apparatus used for the oxidation reaction of the oxidation process (2) in this invention. Usually, a fixed bed reactor having an oxidation catalyst packed bed is used, and the temperature of the oxidation reaction gas exiting this oxidation step (2) is higher than that of the dehydrogenation reaction gas due to the oxidation reaction heat of hydrogen. Usually, it is 500-700 degreeC, Preferably it is the range of 550-670 degreeC. The reaction gas leaving the oxidation step (2) is then supplied to the dehydrogenation step (3). In this oxidation step (2), the temperature rises due to the heat of the oxidation reaction of hydrogen, and hydrogen is oxidized and reduced. Therefore, the equilibrium inhibition of the dehydrogenation reaction in the subsequent dehydrogenation step (3) is reduced. , There is an advantage that the dehydrogenation reaction is promoted.

  In the method for producing styrene of the present invention, in the step (3), the oxidation reaction gas obtained in the oxidation step (2) is dehydrogenated with ethylbenzene in the presence of a dehydrogenation catalyst, so that styrene, hydrogen, unreacted This is a dehydrogenation step of obtaining a dehydrogenation reaction gas containing ethylbenzene, water vapor, and an alkaline substance derived from a dehydrogenation catalyst.

  The catalyst used in the dehydrogenation reaction in the dehydrogenation step (3), reaction conditions, equipment, and the like can be arbitrarily selected from the conditions described in the dehydrogenation step (1), and are independent of the dehydrogenation step (1). Implemented.

  The method for producing styrene of the present invention includes the steps (1) to (3) described above, and the dehydrogenation reaction is performed after mixing the oxygen-containing gas with the dehydrogenation reaction gas obtained in step (1). When supplying the gas to the step (2), it is essential to set the oxyfuel combustion reaction rate to 15% or less in the portion from the portion where the oxygen-containing gas is mixed to the dehydrogenation reaction gas to the inlet of the step (2). To do.

  In the present invention, if necessary, after the dehydrogenation step of step (3), the oxidation step of step (2 ') and the dehydrogenation step of step (3') may be combined in multiple stages. Also in this case, the oxygen-containing gas is mixed before the dehydrogenation reaction gas obtained in the dehydrogenation step of step (3) is supplied to the oxidation step of step (2 ′). It is preferable that the oxygen combustion reaction rate is 15% or less in the portion from the location where the oxygen-containing gas is mixed to the dehydrogenation reaction gas from the dehydrogenation step to the entrance of the step (2 ′).

  In the method for producing styrene by dehydrogenation of ethylbenzene, which comprises a combination of a dehydrogenation reaction and an oxidation reaction, the alkaline substance derived from the dehydrogenation catalyst in the dehydrogenation step (1) is vaporized by a vapor pressure from step (1). When the vapor pressure decreases due to a decrease in the dehydrogenation reaction gas temperature or the like, it adheres to the inner wall of the flow path such as a pipe. When an alkaline substance adheres to the inner wall of the flow path, since there is no oxygen from the dehydrogenation step (1) outlet to the position where the oxygen-containing gas is mixed, combustion of hydrocarbons such as styrene and ethylbenzene does not occur. On the other hand, in the part from the location where the oxygen-containing gas is mixed to the dehydrogenation reaction gas in the dehydrogenation step (1) to the inlet of the oxidation step (2), an alkaline substance is attached to the inner wall of the flow path. As a result, the amount of combustion of hydrocarbons such as styrene and ethylbenzene increases, and a large amount of carbon dioxide is produced. This carbon dioxide reduces the activity of the dehydrogenation catalyst in the subsequent dehydrogenation step (3), The yield will be reduced. On the other hand, in the present invention, the oxygen combustion reaction rate is 15% or less, preferably 10% or less in the portion from the location where the oxygen-containing gas is mixed to the dehydrogenation reaction gas to the inlet of the step (2). By setting the lower limit to 1% or more of the inevitable reaction rate, styrene can be produced stably and with a high yield over a long period of time.

In the present invention, the oxyfuel combustion reaction rate in the portion from the location where the oxygen-containing gas is mixed with the dehydrogenation reaction gas obtained in the dehydrogenation step (1) to the inlet of the oxidation step (2) is the dehydrogenation step. (1) The gas is sampled at the outlet and the oxidation step (2) at the inlet, the samples are analyzed by gas chromatography, and calculated by the following formula.
Oxygen combustion reaction rate = [(A−B) / A] × 100 (%)
A: Amount of oxygen (mole) mixed in the dehydrogenation reaction gas obtained in the dehydrogenation step (1)
B: Oxidation step (2) Amount of oxygen (mole) at the inlet

  In the present invention, the method for setting the oxyfuel reaction rate within the above range is not particularly limited, and it is only necessary that the oxyfuel reaction rate be within the above range as a result. For example, (i) a method of suppressing the alkaline substance scattered from the dehydrogenation step (1) from adhering to the inner wall of the flow path, (ii) the alkaline substance scattered from the dehydrogenation process (1) A method to suppress the formation of combustion reaction active sites even if it adheres to the inner wall, (iii) When the alkaline substance scattered from the dehydrogenation step (1) adheres to the inner wall of the flow path and forms the combustion reaction active sites However, the method etc. which can suppress the oxidation reaction of hydrocarbons are mentioned.

  Specifically, as the method (i), the vapor pressure of the alkaline substance is reduced by preventing a temperature drop from the dehydrogenation step (1) outlet to the next oxidation step (2) inlet. Not to do so. For this purpose, the temperature of the dehydrogenation reaction gas from the dehydrogenation step (1) outlet to the oxidation step (2) inlet, in particular, from the location where the oxygen-containing gas is mixed to the oxidation step (2) inlet is dehydrated. Elementary step (1) A method of keeping the same temperature or higher as the outlet temperature is preferred. Also, even if such an operation is performed, if an alkaline substance is already attached to the inner wall of the flow path, the desired effect will not be exerted. For example, the alkaline substance on the inner wall of the flow path is removed when the catalyst is replaced. It is desirable to take measures such as leaving them.

  However, when the temperature from the dehydrogenation step (1) outlet to the oxidation step (2) inlet is higher than the temperature of the dehydrogenation step (1) outlet, the temperature increase width in the oxidation step (2) becomes small ( The amount of oxygen required in the oxidation process is reduced), and the hydrogen combustion rate is reduced. For this reason, in the subsequent dehydrogenation step (3), the equilibrium inhibition for the dehydrogenation reaction of ethylbenzene increases, and the conversion rate of the dehydrogenation reaction of ethylbenzene decreases. If the oxygen mixing amount is not reduced to avoid this, the temperature of the oxidation step (2) outlet, that is, the subsequent dehydrogenation step (3) inlet temperature rises, and the ethylbenzene in the dehydrogenation step (3) is temporarily removed. Although the conversion rate of the dehydrogenation reaction is increased, scattering of the alkaline substance derived from the dehydrogenation catalyst is promoted. That is, since the rate of decrease in activity increases, it becomes difficult to produce styrene with a high yield over a long period of time. Accordingly, the temperature of the dehydrogenation reaction gas from the dehydrogenation step (1) outlet to the oxidation step (2) inlet, in particular, from the location where the oxygen-containing gas is mixed to the oxidation step (2) inlet is determined. 1) When the temperature is equal to or higher than the outlet temperature, the temperature range to be increased is usually 20 ° C. or lower, preferably 10 ° C. or lower, more preferably 5 ° C. or lower.

  The temperature of the dehydrogenation reaction gas from the dehydrogenation step (1) outlet to the oxidation step (2) inlet, in particular, from the location where the oxygen-containing gas is mixed to the oxidation step (2) inlet is determined by the dehydrogenation step (1 ) In order to keep the temperature equal to or higher than the outlet temperature, the following method can be used. That is, before mixing the oxygen-containing gas with the dehydrogenation reaction gas, a fluid having a temperature higher than that of the dehydrogenation reaction gas is mixed, or a heat exchanger is installed in front of the location where the oxygen-containing gas is mixed. By exchanging heat with the fluid or by previously mixing an inert gas such as water vapor with the oxygen-containing gas and adjusting the temperature of the inert gas in accordance with the change in the outlet temperature of the dehydrogenation step (1), etc. is there.

  Examples of the above (ii) include the following methods. First, the increase in the combustion amount of hydrocarbons due to the attachment of alkaline substances to the inner wall of the flow path is due to the fact that the alkaline substances scattered from the dehydrogenation step (1) adhere to the inner wall of the flow path and the flow path inner wall is made of metal. This is due to the corrosion of the metal on the inner wall and an increase in the metal surface area of the inner wall of the flow path. That is, it is presumed that this occurs when the amount of contact between the process fluid and a substance that forms the active point of the combustion reaction, such as nickel, is increased. Therefore, in order to suppress the formation of combustion reaction active sites, a material that does not easily corrode by an alkaline substance is used as a material constituting the inner wall of the flow path. Alternatively, a method of forming a layer of a material that does not easily corrode by coating a material that does not easily corrode on the inner wall surface of the flow path, plating, or spraying may be used. Examples of the material that is hardly corroded by an alkaline substance include inorganic materials such as ceramics, organic materials such as heat-resistant resins, and metals having a low content such as nickel. It is preferable to use a metal with a small content such as nickel in view of easy availability and device manufacturing. The nickel content in the metal used here is preferably less than 8%, more preferably 5% or less, more preferably 3% or less, and particularly preferably 1% or less. When such a metal is used as the material for the inner wall of the flow path, the surface of the inner wall of the flow path is buffed and treated by electrolytic polishing to smooth the metal surface of the inner wall of the flow path to reduce the surface area and to adhere alkaline substances. It is also effective to prevent corrosion and suppress corrosion. The “channel inner wall” here means not only the inner wall surface of the pipe, but also the surface of the mixer for mixing the dehydrogenation reaction gas and the oxygen-containing gas, and the surface of the screen at the catalyst layer entrance in the oxidation step (2). Etc., including all the parts in contact with the fluid.

  Further, as an example of the above (iii), the following method may be mentioned. That is, the combustion reaction of hydrocarbons on the inner wall of the flow channel to which the alkaline substance is adhered is promoted at a higher temperature as in the normal oxidation reaction. Specifically, the dehydrogenation step (1) outlet In particular, there is a method of lowering the temperature of the dehydrogenation reaction gas from the location where the oxygen-containing gas is mixed with the dehydrogenation reaction gas to the oxidation step (2) inlet, from the time point to the oxidation step (2) inlet.

  However, when the temperature from the dehydrogenation step (1) outlet to the oxidation step (2) inlet is lowered more than the temperature at the dehydrogenation step (1) outlet, the temperature rise in the oxidation step (2) Since it becomes large, it is necessary to increase the mixing amount of oxygen. That is, the combustion reaction amount of hydrocarbons in the oxidation step (2) is also increased, and the amount of carbon dioxide produced is increased. As a result, in the subsequent dehydrogenation step (3), the conversion rate of the dehydrogenation reaction of ethylbenzene decreases. If the oxygen mixing amount is not increased to avoid this, the temperature of the oxidation step (2) outlet, that is, the downstream dehydrogenation step (3) inlet temperature is lowered. As a result, the conversion rate of the dehydrogenation reaction of ethylbenzene in the dehydrogenation step (3) becomes low, and it becomes difficult to produce styrene with a high yield over a long period of time. Accordingly, the temperature of the dehydrogenation reaction gas from the dehydrogenation step (1) outlet to the oxidation step (2) inlet, in particular, from the location where the oxygen-containing gas is mixed with the dehydrogenation reaction gas to the oxidation step (2) inlet. Is preferably 560 ° C. or lower, more preferably 550 ° C. or lower, but preferably 500 ° C. or higher. And it is preferable to keep the temperature increase width in the oxidation step (2) preferably 10 to 100 ° C., more preferably 25 to 95 ° C.

  A method of maintaining the temperature of the dehydrogenation reaction gas from the dehydrogenation step (1) outlet to the oxidation step (2) inlet, in particular, from the location where the oxygen-containing gas is mixed to the oxidation step (2) inlet in the above range. There is. That is, before mixing the oxygen-containing gas with the dehydrogenation reaction gas, a fluid having a temperature lower than that of the dehydrogenation reaction gas is mixed, or a heat exchanger is installed in front of the portion where the oxygen-containing gas is mixed, The heat exchange with the fluid, or the inert gas such as water vapor is mixed with the oxygen-containing gas in advance, and the temperature of the inert gas is adjusted in accordance with the change in the outlet temperature of the dehydrogenation step (1), etc. A method is mentioned.

  In the present invention, as another method for maintaining the oxyfuel combustion reaction rate within the above range, the surface area of the flow path from the portion where the oxygen-containing gas is mixed with the dehydrogenation reaction gas to the inlet of the oxidation step (2) is reduced. A method of shortening the contact time between the combustion reaction active site and the dehydrogenation reaction gas as much as possible is also mentioned.

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

Example 1
An apparatus was used in which five stages of a fixed bed flow reactor equipped with a thermocouple insertion tube with an outer diameter of 12 mm were connected in series with a pipe inside a reaction tube with an inner diameter of 81.1 mm. The first, third, and fifth stage reactors are filled with a commercially available iron oxide catalyst (“Styromax Plus-5”, manufactured by Zude Chemie Catalysts) as a dehydrogenation catalyst for styrene production. The second and fourth stage reactors were filled with an oxidation catalyst produced in accordance with Example 8 of JP-A-9-29095. The filling amount of the dehydrogenation catalyst is the first stage: 4.8L, the third stage: 4.8L, the fifth stage: 9.6L, and the filling amount of the oxidation catalyst is the second stage: 1.3L, 4 Stage: 1.3 L. Further, a supply pipe for mixing a gas containing air and water vapor into the dehydrogenation reaction gas from the first stage dehydrogenation reactor was installed between the first stage reactor and the second stage reactor. Similarly, a supply pipe for mixing a gas containing air and water vapor into the dehydrogenation reaction gas from the third stage reactor was installed between the third stage reactor and the fourth stage reactor.

  Each reaction tube is installed in a separate electric furnace, and nitrogen gas is supplied at 100 NL / min from the first stage reactor inlet, between the first and second stage reactors, and the third and fourth stage reactions. Heating was performed while supplying air at a rate of 10 NL / min from a gas supply pipe containing air and water vapor installed between the vessels. When the temperatures at the outlets of the first, third and fifth stage dehydrogenation catalyst layers all reached 300 ° C. or higher, the nitrogen gas was switched to water vapor. The steam is 5.7 kg / hr from the first stage reactor inlet, and is a gas containing air and steam installed between the first and second stage reactors and between the third and fourth stage reactors. 0.8 kg / hr of each was supplied from the supply pipe for mixing the.

When the temperature at the inlet of the first stage dehydrogenation catalyst layer reached 580 ° C., the supply gas from the inlet of the first stage reactor was switched to a mixed gas of water vapor and ethylbenzene. The composition of the supply gas was water vapor: ethylbenzene = 10: 1 (molar ratio). Next, air was mixed with water vapor mixed with the dehydrogenation reaction gas of the first stage reactor. Similarly, air was mixed with water vapor mixed with the dehydrogenation reaction gas of the third stage reactor. The flow rate of ethylbenzene supplied to the first-stage reactor is such that the space velocity (LHSV) of each catalyst layer is 1st stage: 1.2 hr ⁻¹ , 2nd stage: 4.4 hr ⁻¹ , 3rd stage Eye: 1.2 hr ⁻¹ , 4th stage: 4.4 hr ⁻¹ , 5th stage: 0.6 hr ⁻¹ . The temperature of the water vapor mixed with ethylbenzene is adjusted so that the inlet temperature of the first stage dehydrogenation reactor is 580 ° C., and the inlet temperature of the third stage and fifth stage dehydrogenation reactors is 580 ° C. The reaction was carried out by adjusting the flow rate of air to be mixed with the dehydrogenation reaction gas of the dehydrogenation reaction gas in the stage and third stage reactors. The reaction pressure was set so that the outlet of the fifth-stage reactor was 0.045 MPa.

  When 70 hours passed after supplying ethylbenzene, the composition of the supply gas from the inlet of the first-stage reactor was changed to water vapor: ethylbenzene = 7: 1 (molar ratio). The temperature of water vapor mixed with ethylbenzene was adjusted so that the inlet temperature of the first stage dehydrogenation reactor was 592 ° C. The flow rate of air mixed with the dehydrogenation reaction gas from the first stage reactor was adjusted so that the inlet temperature of the third stage dehydrogenation reactor was 613 ° C. In addition, the temperature of the steam to be mixed so that the gas temperature after mixing the mixed gas of air and steam is 5 ° C. higher than the temperature of the dehydrogenation reaction gas from the first stage dehydrogenation reactor. It was adjusted. Similarly, the flow rate of air mixed with the dehydrogenation reaction gas from the third stage reactor was adjusted so that the inlet temperature of the fifth stage dehydrogenation reactor was 631 ° C. Further, the temperature of the steam to be mixed is set so that the gas temperature after mixing the mixed gas of air and steam is 5 ° C. higher than the temperature of the dehydrogenation reaction gas at the outlet of the third stage dehydrogenation reactor. It was adjusted. The inlet temperature of the dehydrogenation reactor was measured 20 mm upstream of the catalyst layer inlet, and the temperature after mixing the mixed gas of air and water vapor was measured 20 mm upstream of the oxidation catalyst layer inlet of the oxidation reactor. .

At each elapsed time shown in Table 1 after the start of the reaction, each reactor outlet gas and ethylbenzene supplied to the first stage dehydrogenation reactor were sampled, and the composition was analyzed by gas chromatography. The types and columns of gas chromatography used are as follows.
Model: GC-14B
Column: (1) MS-5A for hydrogen analysis
(2) For analysis of benzene, toluene, ethylbenzene and styrene, chromosolve-W
(3) For carbon dioxide, ethane, ethylene and water analysis, Polapack-Q
(4) For analysis of oxygen, nitrogen, methane, carbon monoxide, MS-13X
Table 1 shows the results of reaction for 13,000 hours after the start of the supply of ethylbenzene to the first stage reactor inlet.

Comparative Example 1
The temperature of the steam to be mixed was adjusted so that the gas temperature after mixing the mixed gas of air and steam was 5 ° C. lower than the temperature of the dehydrogenation reaction gas from the first stage dehydrogenation reactor. . Similarly, the temperature of the steam to be mixed so that the gas temperature after mixing the mixed gas of air and steam is 10 ° C. lower than the temperature of the dehydrogenation reaction gas from the third stage dehydrogenation reactor. Adjustment (actually 8-11 ° C lower). Otherwise, the reaction was carried out in the same manner as in Example 1. Table 1 shows the results of reaction for 13,000 hours after the start of the supply of ethylbenzene to the first stage reactor inlet.

Example 2
The temperature of the steam to be mixed was adjusted so that the gas temperature after mixing the mixed gas of air and steam was 5 ° C. lower than the temperature of the dehydrogenation reaction gas from the first stage dehydrogenation reactor. . Further, after the time when the gas temperature after mixing the mixed gas of air and water vapor exceeds 560 ° C. (10,000 hours after the start of the reaction), the water vapor to be mixed so that the temperature of this portion becomes 545 ° C. The temperature of was adjusted. Similarly, the temperature of water vapor mixed from the third-stage dehydrogenation reactor so that the gas temperature after mixing the mixed gas of air and water vapor is 10 ° C. lower than the temperature of the dehydrogenation reaction gas. After adjusting the temperature (actually 8 ° C lower) and mixing the mixed gas of air and water vapor, the temperature of this part after the time when the gas temperature exceeded 560 ° C (3,500 hours elapsed after the start of the reaction) The temperature of water vapor to be mixed was adjusted so as to be 545 ° C. Otherwise, the reaction was carried out in the same manner as in Example 1. Table 1 shows the results of reaction for 13,000 hours after the start of the supply of ethylbenzene to the first stage reactor inlet.

In addition, each item in Table 1 shows the following value.
“Reaction time”: Time from the start of the supply of ethylbenzene to the first-stage reactor.
“Oxidation reactor inlet temperature (second stage reactor)”: temperature from the point where the mixed gas of air and water vapor is mixed with the reaction gas at the first stage dehydrogenation reactor outlet to the second stage oxidation reactor inlet.
“Oxidation reactor inlet temperature (fourth stage reactor)”: temperature from the point where the mixed gas of air and water vapor is mixed with the reaction gas at the third stage dehydrogenation reactor outlet to the fourth stage oxidation reactor inlet.
“Oxygen combustion reaction rate in the air mixing section (second stage reactor)”: From the location where the mixed gas of air and water vapor is mixed with the reaction gas at the outlet of the first stage dehydrogenation reactor to the inlet of the second stage oxidation reactor It is the oxyfuel combustion reaction rate in the metal piping surface and space part. The following formula was used for calculation.
Oxygen combustion reaction rate in the air mixing section (second stage reactor) = [(A1-B2) / A1] × 100 (%)
A1: The amount (mole) of oxygen mixed with the dehydrogenation reaction gas from the first stage dehydrogenation reactor
B2: Amount of oxygen (mole) at the inlet of the second stage oxidation reactor
“Oxygen combustion reaction rate in the air mixing section (fourth stage reactor)”: From the location where the mixed gas of air and water vapor is mixed with the reaction gas at the outlet of the third stage dehydrogenation reactor to the inlet of the fourth stage oxidation reactor It is the oxyfuel combustion reaction rate in the metal surface and space part. The following formula was used for calculation.
Oxygen combustion reaction rate in the air mixing section (fourth stage reactor) = [(A3-B4) / A3] × 100 (%)
A3: Amount of oxygen (mole) to be mixed with the dehydrogenation reaction gas from the third stage dehydrogenation reactor
B4: Amount of oxygen (mole) at the inlet of the fourth stage oxidation reactor
“Styrene yield”: The total styrene yield from the first stage dehydrogenation reactor to the fifth stage dehydrogenation reactor, and was calculated by the following equation.
Styrene yield = [(Z−Y) / X] × 100 (wt%)
X: Amount of ethylbenzene (kg) flowing into the first stage dehydrogenation reactor
Y: Amount of styrene flowing into the first stage dehydrogenation reactor (kg)
Z: Amount of styrene flowing out of the fifth stage dehydrogenation reactor (kg)

Example 3
A wire of SUS410S (standard value of nickel content: 0.6% or less) having an outer diameter of 2 mm and a length of 10 mm is placed on a petri dish, and 5 drops of 5 wt% potassium hydroxide aqueous solution is applied with a dropper, followed by a dryer. And dried at 120 ° C. for 1 hour. Thereafter, the wire was taken out from the dryer, put in an electric furnace and baked at 640 ° C. in an air atmosphere for 24 hours, and then taken out from the electric furnace and cooled to room temperature.

  The bottom of a quartz reaction tube having an inner diameter of 16 mm and a length of 500 mm is filled with 67.1 g of a quartz chip having a particle size of 2.4 to 6 mm, filled with a fired wire, and further a particle size of 1 Filled with 50.6 g of a ~ 2.4 mm quartz chip. The reaction tube was installed in an electric furnace and heated while supplying a mixed gas of nitrogen and hydrogen at 0.09 NL / min. The composition of the mixed gas was nitrogen: hydrogen = 2.0: 1.0 (molar ratio). When the wall temperature of the reaction tube reached 520 ° C., the tube wall temperature was maintained at 520 ° C. and maintained for 30 minutes under the same conditions. Thereafter, the supply gas was switched to a mixed gas of ethylbenzene, styrene, water vapor, hydrogen, oxygen and nitrogen and supplied at 1.0 NL / min. The composition of the supply gas was ethylbenzene: styrene: water vapor: hydrogen: oxygen: nitrogen = 1.0: 0.87: 17.6: 0.65: 0.17: 1.3 (molar ratio). When 30 minutes had elapsed, the reaction tube outlet gas was sampled, and its composition was analyzed by gas chromatography.

Then, only the wall surface temperature of the reaction tube was changed to 550 ° C., 30 minutes later, the reaction tube outlet gas was sampled, and the composition was analyzed by gas chromatography.
Subsequently, the wall temperature of the reaction tube was changed to 580 and 610 ° C., and after 30 minutes had passed at each wall surface temperature, the reaction tube outlet gas was sampled by the same method and the composition was analyzed. The results are shown in Table 2.
Moreover, oxygen selectivity other than hydrogen combustion at each temperature was calculated by the following equation. The results are shown in Table 2. The oxygen selectivity other than hydrogen combustion indicates the proportion of oxygen burned by ethylbenzene and styrene in the supply gas among the oxygen used for combustion.

Oxygen selectivity other than hydrogen combustion = [1- (C−D) × 0.5 / (A−B)] × 100 (%)
A: Amount of oxygen (mol) supplied to the reaction tube
B: Oxygen amount (mole) at the reaction tube outlet
C: Hydrogen amount (mol) supplied to the reaction tube
D: Hydrogen amount (mole) at the outlet of the reaction tube

Comparative Example 2
The reaction is performed in the same manner as in Example 3 except that SUS304 (standard value of nickel content: 8.0 to 10.5%) is used instead of SUS410S, and oxygen selectivity other than hydrogen combustion is calculated. did. The results are shown in Table 2.

Claims (9)

A method for producing styrene including the following steps (1) to (3), wherein the dehydrogenation reaction gas after mixing an oxygen-containing gas with the dehydrogenation reaction gas obtained in step (1) Is supplied to the step (2), the oxygen combustion reaction rate is set to 15% or less in the portion from the location where the oxygen-containing gas is mixed to the dehydrogenation reaction gas to the inlet of the step (2). A method for producing styrene.
Step (1): A raw material gas containing at least ethylbenzene and water vapor is subjected to a dehydrogenation reaction of ethylbenzene in the presence of a dehydrogenation catalyst to contain styrene, hydrogen, unreacted ethylbenzene, water vapor, and an alkaline substance derived from the dehydrogenation catalyst. Dehydrogenation process step (2) for obtaining a dehydrogenation reaction gas: An oxidation in which at least a part of hydrogen is oxidized in the presence of an oxidation catalyst in the presence of an oxidation catalyst. Process step (3): The oxidation reaction gas obtained in the oxidation step is subjected to a dehydrogenation reaction of ethylbenzene in the presence of a dehydrogenation catalyst, so that styrene, hydrogen, unreacted ethylbenzene, water vapor, and an alkaline substance derived from the dehydrogenation catalyst Dehydrogenation process for obtaining dehydrogenation reaction gas containing   The method for producing styrene according to claim 1, wherein a mixing ratio of water vapor in the raw material gas in the step (1) is in a range of 1 to 15 in terms of a molar ratio with respect to the raw material hydrocarbon containing ethylbenzene.   The method for producing styrene according to claim 1 or 2, wherein the dehydrogenation catalyst is a potassium-containing iron-based catalyst and the alkaline substance is a potassium compound.   The temperature of the dehydrogenation reaction gas mixed with the oxygen-containing gas is the same as the outlet temperature of step (1) in the portion from the location where the oxygen-containing gas is mixed with the dehydrogenation reaction gas to the inlet of the step (2). The method for producing styrene according to any one of claims 1 to 3, which is maintained as described above.   Temperature difference between the temperature of the dehydrogenation reaction gas mixed with the oxygen-containing gas and the exit temperature of step (1) in the portion from the location where the oxygen-containing gas is mixed with the dehydrogenation reaction gas to the inlet of the step (2) The method for producing styrene according to claim 4, wherein is 20 ° C. or lower.   6. The temperature of the dehydrogenation reaction gas mixed with the oxygen-containing gas is maintained at 560 ° C. or lower in a portion from the location where the oxygen-containing gas is mixed with the dehydrogenation reaction gas to the inlet of the step (2). The method for producing styrene according to any one of the above.   The temperature of the dehydrogenation reaction gas mixed with the oxygen-containing gas is maintained at 500 to 560 ° C in the portion from the location where the oxygen-containing gas is mixed with the dehydrogenation reaction gas to the inlet of the step (2). The method for producing styrene according to any one of 1 to 6.   With respect to the temperature of the dehydrogenation reaction gas in the portion from the location where the oxygen-containing gas is mixed with the dehydrogenation reaction gas to the inlet of the step (2), the temperature increase in the step (2) is 10 to 100 ° C. The method for producing styrene according to any one of claims 1 to 7.   The surface of the inner wall of the flow path is made of a material having a nickel content of less than 8 wt% in a portion from the position where the oxygen-containing gas is mixed into the dehydrogenation reaction gas to the inlet of the step (2). The method for producing styrene according to claim 1.