JP2013091639A - Method for producing propylene oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an economical method for producing propylene oxide, which suppresses production of acetaldehyde.SOLUTION: A method for producing propylene oxide includes a catalytic oxidation of propylene in a fixed bed reaction chamber. The catalyst is disposed in a plurality of tubes surrounded by a fluid that eliminates reaction heat. In the method, a cooling zone is provided by introducing a part of a cooled recirculated gas flow to the downstream of the above tubes in the reaction chamber.

Description

  The present invention relates to a method for producing propylene oxide.

As the propylene oxide catalyst degrades, the temperature of the reaction vessel required to maintain production increases. There are two problems that often arise with increasing temperatures, especially when operating high selectivity catalysts at essentially higher temperatures. (1) Temperature-dependent propionaldehyde production starts especially when the gas temperature at the outlet is 250 ° C to 260 ° C. (2) Since the outlet gas has explosive properties, the allowable values of the respective concentrations of propylene and oxygen in the supply gas are limited. This “explosion limit” depends on a number of parameters, in particular the gas temperature at the outlet. Each of the above two problems has a significant impact on the workability and profitability of the plant.
High purity propylene oxide requires strict limits on propionaldehyde. The total amount of aldehyde in the propylene oxide end product is typically at a level of 30 ppm. In any propylene oxide plant, aldehyde formation depends on the material and structure of the outlet of the propylene oxide reaction vessel. At high operating temperatures, many plant facilities are affected by excessive aldehyde production. As the operating temperature increases, aldehyde production increases rapidly. Any of the limited options that suppress aldehyde formation are expensive. The first option is to lower the temperature of the catalyst layer, which will reduce the daily production. The second option is to repeat the catalytic reaction many times under conditions that allow aldehyde formation. A third option is to modify the outlet of the reaction vessel cooling chamber with an “external cooler”. Although this method is effective for lowering the temperature of the outlet gas, such a modification is prohibitively expensive. Another option for which the effect is recognized is to modify the outlet pipe with a cooling jacket or a cooling coil charge. It is also possible to use only a catalyst having a very high activity.
In a propylene oxide plant, the oxygen and propylene concentrations in the feed gas of the reaction vessel are determined by the explosion limit concentrations of oxygen and propylene at the inlet and outlet. The explosion limit concentration is also related to the temperature of the outlet gas. At higher outlet gas temperatures, the acceptable feed oxygen and propylene concentration levels are lowered. As the concentration of oxygen and propylene supplied decreases, the selectivity of the reaction decreases and the activity of the catalyst is clearly reduced. Thereby, it is necessary to raise the temperature in order to maintain production. Thus, reduced oxygen and propylene supply levels will reduce profit margins.

Regarding a method for producing ethylene oxide, JP-A-7-188199 describes a gas phase catalytic reaction of ethylene and oxygen and dilution of the reaction product with an inert gas. Specifically, a system is described that dilutes a gas stream by being discharged from the outlet head and then mixing the outlet stream with an inert gas such as nitrogen. The dilution of the gas stream has the effect of reducing unwanted side reactions such as isomerization to acetaldehyde and the like. As the inert gas, nitrogen, carbon dioxide, methane, argon, etc., preferably nitrogen can be used. By adding this inert gas, it becomes necessary to remove the inert gas before recirculation, and it is necessary to enlarge the equipment downstream of the reaction. Thus, if the outlet gas is diluted to a meaningful level, prohibitive costs are required. In the method of the present invention, the composition of the product stream does not change except to reduce aldehyde formation. The present invention cools the outlet gas stream using a technique different from dilution to suppress aldehyde formation. The cooling method of the present invention is more efficient to suppress unwanted aldehyde formation. A preferred configuration of the present invention is a method of introducing recirculation gas directly into the outlet head.
US 4921681 describes an ethylene oxide reaction vessel having a lower cooling region and a distribution region below it. The piping is filled with inert particles in the cooling zone, but nothing is in the distribution zone. In the present invention, no recirculation supply coolant is introduced around the piping.
US Pat. No. 4,874,879 describes a method for starting operation of an ethylene oxide reaction vessel.
Patent Document 1 describes a method for producing ethylene oxide.

US5840932

  The subject of this invention is providing the economical manufacturing method of propylene oxide which suppressed the production | generation of propionaldehyde.

As a result of investigating the means for solving the above-mentioned problems, a part of the flow (slip stream) of the product gas discharged from the outlet of the reaction vessel is cooled to a low temperature and returned to the outlet, so that the product gas is converted into the reaction tube. The temperature of the product gas at the time of being discharged from the gas can be instantaneously lowered, and it has been found that this method is economical.
[1] A method for producing propylene oxide by catalytically oxidizing propylene in a fixed bed reaction vessel,
The catalyst is arranged in a plurality of tubes surrounded by a fluid that removes the heat of reaction,
The method includes providing a cooling zone by introducing a partial stream of cooled recycle gas downstream of the tube in the reaction vessel.
[2] The temperature of the product discharged from the tube is in the range of 232 ° C. to 302 ° C., and the temperature of the part of the cooled stream recirculated to the region is in the range of 27 ° C. to 232 ° C. The method according to [1], wherein the ratio of the product discharged from the pipe to the part of the recycled stream is in the range of 20: 1 to 1: 3.
[3] The recirculated part of the cooled stream is removed from the first recycle product stream downstream of the recycle gas compressor and upstream of adding oxygen to the recycle product stream. [1] The method according to the above.
[4] The recirculated part of the cooled stream is withdrawn at least in one of the product streams between the reaction vessel and the propylene oxide absorber and cooled before being introduced into the cooling zone. [1] The method according to the above.

[5] A method for producing propylene oxide by catalytically oxidizing propylene in a fixed bed reaction vessel,
The catalyst is arranged in a plurality of tubes surrounded by a fluid that removes the heat of reaction,
The method includes introducing a recirculated portion of the cooled stream into a tube containing product discharged from the reaction vessel.
[6] The temperature of the product discharged from the tube is in the range of 232 ° C. to 302 ° C., and the temperature of the cooled partial stream recycled to the tube containing the product is 27 ° C. to 232 ° C. The method according to [5], wherein the ratio of the product discharged from the tube to the part of the recycled stream is in the range of 20: 1 to 1: 3.
[7] A production method in which decomposition of a product occurs between a catalytic reaction in a reaction vessel and product cooling downstream by holding the product in a high temperature state,
Introducing a portion of the cooled product stream into the outlet head of the reaction vessel.
[8] The method according to [7], wherein the decomposition of the product is exothermic.
[9] The method according to [7], wherein the outlet head of the reaction vessel is below a catalyst contained in a tube in the reaction vessel.
[10] The method according to [7], wherein the recirculated part of the cooled stream is introduced into a reaction vessel having a nozzle facility.
[11] The method according to any one of [1] to [10], wherein the catalytic oxidation of propylene reacts propylene and oxygen in the presence of a metal catalyst.
[12] The method according to [11], wherein the metal catalyst is a catalyst containing (a) copper oxide and (b) ruthenium oxide.

The method of the present invention suppresses the production of aldehyde depending on the temperature between the piping outlet of the reaction vessel and the heat exchanger for the product gas. Although it varies depending on each situation, the method of the present invention includes (1) improvement of product quality, (2) avoidance of production amount reduction for the purpose of maintaining product quality, (3) extension of catalyst life, There are one or more advantages. Furthermore, even highly selective catalysts that can cause temperature-dependent aldehyde formation problems can be used in the process of the present invention.
The method of the present invention also improves the propylene and oxygen concentration limits that can be supplied, limited by the temperature-dependent explosion limit of the product gas at the outlet. This improvement in concentration limit allows operation at higher propylene and / or oxygen concentrations, thereby improving the activity, selectivity and stability of the catalyst.
In addition, the method of the present invention is a method for reducing the production of conventional aldehydes (for example, a cooling area after forced kerosene, an arrangement of a cooling heat exchange pipe in the outlet or the outlet pipe, and an outlet pipe having a cooling jacket). Are more efficient and less costly in terms of facilities such as operation and remodeling than installation of inert gas, introduction of inert gas into the outlet pipe, etc.).

It is a figure which shows the preferable structure of the flow of this invention method. It is a figure which shows the alternative example of the structure of FIG. It is a figure which shows the other alternative example of the structure of FIG. It is a figure which shows the further alternative example of the structure of FIG.

Examples of the catalytic oxidation method of propylene to which the present invention can be applied include a production method in which propylene and oxygen are reacted in the presence of a metal catalyst containing a metal oxide or the like. For the production method of reacting propylene and oxygen in the presence of such a metal catalyst, for example, WO2011 / 075458, WO2011 / 0754559, WO2012 / 005822, WO2012 / 005823, WO2012 / 005824, WO2012 / 005825, WO2012 / 005831, WO2012 / 005832, WO2012 / 005835, WO2012 / 005837, WO2012 / 009054, WO2012 / 009059, WO2012 / 009058, WO2012 / 009053, WO2012 / 009057, WO2012 / 009055, WO2012 / 009056, WO2012 / 009056 and the like. As the catalyst used in the production method, the following (a), (b), (c), (d), (e), (f), (g), (h), (i), (j), ( and a catalyst containing at least two selected from the group consisting of k), (l), (m), (n), (o), (p) and (q).
(A) copper oxide (b) ruthenium oxide (c) manganese oxide (d) nickel oxide (e) osmium oxide (f) germanium oxide (g) chromium oxide (h) thallium oxide (i ) Tin oxide (j) bismuth oxide (k) antimony oxide (l) rhenium oxide (m) cobalt oxide (n) osmium oxide (o) lanthanoid oxide (p) tungsten oxide (q) alkali Metal component or alkaline earth metal component, preferably a catalyst containing (a) copper oxide and (b) ruthenium oxide, more preferably (a) copper oxide, (b) ruthenium oxide and (q) A catalyst containing an alkali metal component or an alkaline earth metal component.

  In the process according to the invention, a part of the cooled product stream is returned to the outlet head so that it exits from the reactor vessel piping to the outlet head, for example using a nozzle that performs rapid mixing with the outlet gas. This substantially reduces the temperature of the outlet head.

Hereinafter, in order to describe the present invention in more detail, specific embodiments will be described based on the drawings. However, the present invention does not limit the scope of the present invention only by this embodiment.
In the preferred configuration shown in FIG. 1, a cooled partial stream (27 ° C. to 54 ° C.) recirculated from the outlet 2 of the recycle gas concentrator 3, or of the reaction vessel feed / product heat exchanger 5. The cooled product gas (107 ° C. to 190 ° C.) from the outlet is sent to the outlet head 6 of the reaction vessel 19. In this configuration, the partial stream is already cooled by existing equipment. Additional equipment required includes a blower (not required with recirculation gas option), nozzles (not shown) when some flow 1 is introduced into the outlet head 6, piping, and associated manufacturing control. And safety devices. The recirculation gas compressor 3 receives a stream 7 (16 ° C. to 31 ° C.), which stream 7 is divided into a part of the stream 1 to be recycled, and the stream 10 is mixed with oxygen in a vessel 11. Product stream 13 (232 ° C. to 302 ° C.) is cooled to 163 ° C. to 232 ° C. with initial product cooler 14 and heat exchanged with feed stream 12 in reaction vessel feed / product heat exchanger 5. In the second product cooler 15, stream 4 (107 ° C. to 190 ° C.) from the feed / product heat exchanger 5 is cooled. Stream 16 is sent to propylene oxide absorber 8 and product stream 17 is discharged. Feed stream 18 (93 ° C. to 177 ° C.) is sent to reaction vessel 19. It is important that stream 1 is introduced below the catalyst packed tube in reaction vessel 19. The ratio of some stream 1 to product stream 13 is 1:20 to 3: 1. Propylene is introduced in line 28 between compressor 3 and chamber 11 where oxygen is added. If more than one product cooler is used, a partial stream can also be taken from the outlet of each cooler.

In the alternative configuration shown in FIG. 2, a partial outlet stream 20 is taken before the first product cooler 14. In this configuration, an additional cooler 22 is required to reduce the temperature of the part of the stream 20 that is recirculated.
Another alternative configuration shown in FIG. 3 is a combination of the configurations of FIGS. 1 and 2, wherein the first product cooler 14, the feed / product heat exchanger 5, or the second generation. A part of the cooled stream from either outlet of the object cooler 15 is recirculated. In any of these aspects, to achieve the desired cooling, the recirculated outlet partial stream 21 is pressurized enough to provide sufficient mixing and sufficient recirculation ratio. There is a need. The introduction of a spare recirculation cooler 22 is an option in this configuration, which can reduce the amount of partial flow required to achieve the desired stream 13 temperature. Alternatively, it is possible to pressurize a part of the recirculated outlet to a high pressure to reduce the size of the nozzle hole. This causes a sudden drop in pressure when the recirculated flow enters the outlet head. The degree of adiabatic cooling depends on the degree of pressure drop, but the adiabatic cooling further cools the outlet chamber. The advantage of this option is that it can achieve the same level of cooling as the low pressure option with a smaller recirculation ratio.

The alternative configuration shown in FIG. 4 is a situation where a modification to the outlet head has to be avoided, for example a situation where a part of the stream 1 to be recirculated is introduced into the pipe 13 at a point immediately from the outlet head 6. Is worth it. The disadvantages of this configuration are that aldehyde formation can occur in the outlet head and that the oxygen explosion limit is not reduced at the outlet of the reactor vessel piping unless the contents of the outlet head are cooled. The advantage of this configuration is that the equipment is inexpensive.
In each of these figures, a portion of the recirculated stream enters the outlet head through one simple nozzle. However, any number of simple or complex nozzles and other methods of introducing a recirculation flow are applicable to the present invention. That is, the attached drawings merely show the interrelationships of the main equipment.
The process need not always be run while the catalyst is reacting, regardless of what configuration is selected. Recirculation cooling may be chosen only when there is a problem of increased aldehyde production in the product stream. Alternatively, recirculation cooling can be chosen from the start of operation to maximize the acceptable levels of oxygen and propylene for all periods of operation. Depending on the desired cooling level, the amount of recirculation can also be varied. By performing mechanical engineering and thermodynamic calculations, plant design parameters (exit head and piping dimensions and design, product gas flow rate, composition and concentration, etc.) and four variables of the above method (reaction vessel outlet) The relationship between the gas temperature, the recirculation gas temperature, the recirculation ratio, the desired degree of cooling of the outlet head).

Regardless of the recirculation ratio used or the specific configuration selected (except in the case of a recirculation gas compressor), the amount of gas sent to the absorption tower according to the present invention, except when using a spare cooler Is not affected. Thus, the size of the downstream equipment and the heat balance of the plant are not complicated by the present invention.
By performing thermodynamic calculations to estimate costs, the present invention shows that substantial cooling at the outlet head of the reaction vessel can be achieved with minimal equipment and operating costs. Therefore, the following matters are included in the value of the present invention. Product quality is improved. That is, aldehyde formation and accumulation in the product is minimized regardless of outlet design and material. The length of the catalyst life is extended and the temperature reaches the limits of the material or cooling system equipment, rather than due to limitations due to aldehyde formation. Even in situations where the speed of operation is slowed down to limit the outlet temperature due to limitations due to aldehyde formation, the present invention maintains full operating levels. High inlet oxygen and propylene concentrations improve catalyst activity, selectivity and stability. The present invention is readily applicable to basic propylene oxide plants. In addition, the present invention is useful for a plant having an aldehyde production problem and a plant in which a high selectivity catalyst cannot be used due to equipment problems, with only slight modifications.

  By the method of the present invention, it is possible to provide an economical method for producing propylene oxide while suppressing the production of acetaldehyde.

Claims (12)

A method for producing propylene oxide by catalytically oxidizing propylene in a fixed bed reaction vessel,
The catalyst is arranged in a plurality of tubes surrounded by a fluid that removes the heat of reaction,
The method includes providing a cooling zone by introducing a partial stream of cooled recycle gas downstream of the tube in the reaction vessel.   The temperature of the product discharged from the tube is in the range of 232 ° C. to 302 ° C., the temperature of the part of the cooled stream recirculated to the region is in the range of 27 ° C. to 232 ° C., The process according to claim 1, wherein the ratio of the product discharged from the recycle to the part of the recycled stream is in the range of 20: 1 to 1: 3.   The recirculated portion of the cooled stream is withdrawn from the original recycle product stream downstream of the recycle gas compressor and upstream of adding oxygen to the recycle product stream. The method described.   The recirculated portion of the cooled stream is withdrawn at least in one of the product streams between the reaction vessel and the propylene oxide absorber and cooled prior to introduction into the cooling zone. The method described. A method for producing propylene oxide by catalytically oxidizing propylene in a fixed bed reaction vessel,
The catalyst is arranged in a plurality of tubes surrounded by a fluid that removes the heat of reaction,
The method includes introducing a recirculated portion of the cooled stream into a tube containing product discharged from the reaction vessel.   The temperature of the product discharged from the tube is in the range of 232 ° C. to 302 ° C., and the temperature of the cooled part stream that is recycled to the tube containing the product is in the range of 27 ° C. to 232 ° C. 6. The method of claim 5, wherein the ratio of the product discharged from the tube to the portion of the recycled stream is in the range of 20: 1 to 1: 3. A production method in which decomposition of a product occurs between a catalytic reaction in a reaction vessel and downstream product cooling by maintaining the product in a high temperature state,
Introducing a portion of the cooled product stream into the outlet head of the reaction vessel.   The method of claim 7 wherein the decomposition of the product is exothermic.   The process of claim 7, wherein the outlet head of the reaction vessel is below the catalyst contained in a tube in the reaction vessel.   8. A process according to claim 7, wherein the recirculated part of the cooled stream is introduced into a reaction vessel having a nozzle facility.   The method according to claim 1, wherein the catalytic oxidation of propylene reacts propylene and oxygen in the presence of a metal catalyst.   The method according to claim 11, wherein the metal catalyst is a catalyst containing (a) copper oxide and (b) ruthenium oxide.

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