JP2011201821A - Method for producing propylene oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing propylene oxide reducing the production cost thereof and the amount of the greenhouse gas discharged.SOLUTION: The method for producing propylene oxide comprises the following processes: a process (1) of oxidizing an alkylbenzene to produce an alkylbenzene hydroperoxide; a process (2) of causing propylene to react with the alkylbenzene hydroperoxide in the presence of a catalyst; a process (3) of separating the reaction product into an aromatic alcohol, unreacted propylene, and propylene oxide by distillation; a process (4) of preheating the fraction comprising the aromatic alcohol using a mixed fluid of a gas and a liquid coming out of the following process (5) as a heat source; a process (5) of causing the fraction to react with an excessive amount of hydrogen in the presence of a catalyst to produce a mixed fluid of a gas and a liquid comprising the alkylbenzene and unreacted hydrogen; a process (6) of separating the mixed fluid of a gas and a liquid into the gas and the liquid to recycle at least a part of the alkylbenzene to the process (1); a process (7) of indirectly exchanging heat between the gas fraction and water to allow condensable components to condense to separate the gas and the liquid; and a process (8) of reusing recovered steam in the processes.

Description

  The present invention relates to a method for producing propylene oxide. More specifically, the propylene oxide has particularly excellent effects from the viewpoint of industrial implementation that it is excellent in heat utilization efficiency as a whole manufacturing process, and thus can reduce the cost for producing propylene oxide and the greenhouse gas emission amount. It relates to a manufacturing method.

A method for producing propylene oxide is known in which propylene oxide is obtained by oxidizing alkylbenzene to alkylbenzene hydroperoxide and reacting the alkylbenzene hydroperoxide with propylene using an epoxidation catalyst.
For example, Patent Document 1 describes that cumene is oxidized in air to form cumene hydroperoxide, and the cumene hydroperoxide and propylene are reacted in the presence of an epoxidation catalyst to obtain propylene oxide.
Patent Document 1 also describes that cumyl alcohol by-produced together with propylene oxide is treated with hydrogen to be returned to cumene, and the cumene is recycled. That is, one of the raw materials, alkylbenzene, is once converted to alkylbenzene hydroperoxide, then reacted with propylene to give an aromatic alcohol, and further the aromatic alcohol is reacted with hydrogen to return to alkylbenzene for recycling. By this method, it is a technique that can produce only “propylene oxide” without producing by-products and co-products derived from alkylbenzene, which has been a problem in the past. However, in order to use the alkylbenzene in a circulating manner, a cost for reacting with hydrogen and purifying it is generated, so that further improvement in heat utilization efficiency as a whole manufacturing process has been demanded.

JP 2008-266304 A

  In such a situation, the problem to be solved by the present invention is a viewpoint of industrial implementation, in particular, that it is excellent in heat utilization efficiency as a whole production process, and thus the cost for producing propylene oxide and greenhouse gas emissions can be reduced. Therefore, the present invention provides a method for producing propylene oxide having particularly excellent effects.

  As a result of intensive studies, the present inventors have found that the present invention can solve the above problems, and have completed the present invention.

That is, the present invention relates to a method for producing propylene oxide including the following steps.
First step: Step of obtaining an oxidation reaction solution containing alkylbenzene hydroperoxide by oxidizing alkylbenzene Second step: Propylene in the presence of the first catalyst and alkylbenzene in the oxidation reaction solution obtained in the first step Step of obtaining an epoxy reaction liquid containing propylene oxide and aromatic alcohol by reacting with hydroperoxide Third step: Division containing aromatic alcohol by subjecting the epoxy reaction liquid obtained in the second step to distillation Step for separating into unreacted propylene and propylene oxide Fourth step: Using a heat exchange system having a heat exchanger and means for adjusting the amount of heat exchanged in the heat exchanger, the following fifth step Using the gas-liquid mixed fluid at the outlet as the heat source, the section containing the aromatic alcohol obtained in the third step is desired. Step 5: Pre-heating the fraction containing aromatic alcohol preheated to the desired temperature obtained in Step 4 with an excess of hydrogen in the presence of the second catalyst to produce alkylbenzene and Step for obtaining a gas-liquid mixed fluid containing unreacted hydrogen Sixth step: Gas-liquid mixed fluid obtained in the fifth step is separated into gas and liquid, and a liquid section mainly composed of alkylbenzene and unreacted hydrogen and condensable components are separated. And a process for recycling at least a part of the alkylbenzene contained in the liquid section to the first process. Seventh process: a gas section containing unreacted hydrogen and condensable components obtained in the sixth process; , Indirectly heat-exchange with water to condense the condensable component contained in the gas section, and separate into a section containing unreacted hydrogen and a liquid section containing a condensable component, and indirectly heat Steam recovered from the exchanged water Step 8 to obtain: The recovered steam obtained in the seventh step is used in at least one of the first to sixth steps, and the amount of the recovered steam is relative to the amount used in each step. In the case of surplus, the step of adjusting the steam balance in the process by performing an operation of increasing the amount of exchange heat by means of adjusting the amount of heat exchange in the fourth step

  According to the present invention, the propylene oxide has particularly excellent effects from the viewpoint of industrial implementation that it is excellent in heat utilization efficiency as a whole manufacturing process, and thus can reduce the cost for production of propylene oxide and the amount of greenhouse gas emissions. A manufacturing method can be provided.

FIG. 3 is a diagram showing an outline of a flow of Example 1. It is a figure which shows the outline of the comparative example 1 flow.

The method for producing propylene oxide of the present invention includes the following steps.
First step: Step of obtaining an oxidation reaction solution containing alkylbenzene hydroperoxide by oxidizing alkylbenzene Second step: Propylene in the presence of the first catalyst and alkylbenzene in the oxidation reaction solution obtained in the first step Step of obtaining an epoxy reaction liquid containing propylene oxide and aromatic alcohol by reacting with hydroperoxide Third step: Division containing aromatic alcohol by subjecting the epoxy reaction liquid obtained in the second step to distillation Step for separating undiluted propylene and purified propylene oxide Fourth step: Using a heat exchange system having a heat exchanger and a means for adjusting the amount of heat exchanged in the heat exchanger, The area containing the aromatic alcohol obtained in the third step using the gas-liquid mixed fluid at the fifth step outlet as the heat source Step 5: preheating the mixture to the desired temperature Fifth step: reacting the fraction containing the aromatic alcohol preheated to the desired temperature obtained in the fourth step with an excess amount of hydrogen in the presence of the second catalyst Step for obtaining a gas-liquid mixed fluid containing alkylbenzene and unreacted hydrogen Sixth step: The gas-liquid mixed fluid obtained in the fifth step is separated into gas and liquid, and a liquid section mainly composed of alkylbenzene, unreacted hydrogen and condensed Step 7: separating at least a part of the alkylbenzene contained in the liquid section into the first step and recycling to the first step Seventh step: including unreacted hydrogen and condensable components obtained in the sixth step The gas section and the water are indirectly heat-exchanged to condense the condensable components contained in the gas section, and are separated into a section containing unreacted hydrogen and a liquid section containing a condensable component, and indirectly Heat exchanged water Step of obtaining recovered steam Eighth step: The recovered steam obtained in the seventh step is used in at least one of the first to sixth steps, and the amount of recovered steam is the amount used in each step. In the case of surplus, the step of adjusting the steam balance in the process by performing the operation of increasing the amount of exchange heat by means of adjusting the amount of heat exchange in the fourth step

The first step in the present invention is a step of obtaining an oxidation reaction solution containing alkylbenzene hydroperoxide by oxidizing alkylbenzene.
The following method can be given as a preferred specific example for carrying out the first step.

Alkylbenzene is usually oxidized by auto-oxidation with an oxygen-containing gas such as air or oxygen-enriched air. This oxidation reaction may be carried out without using an additive, or an additive such as an alkaline reagent may be used. The normal reaction temperature is 50 to 200 ° C., and the reaction pressure is between atmospheric pressure and 5 MPa. In the case of the oxidation method using an additive, examples of the alkaline reagent include an alkali metal compound, an alkaline earth metal compound, ammonia, (NH ₄ ) ₂ CO ₃ , and the alkali metal compound includes, for example, NaOH. And alkaline earth metal compounds include, for example, Ca (OH) ₂ , CaCO _{3 and the} like.

The second step in the present invention includes propylene oxide and aromatic alcohol by reacting propylene with the alkylbenzene hydroperoxide in the oxidation reaction solution obtained in the first step in the presence of the first catalyst. In this step, an epoxy reaction solution is obtained.
The following method can be mention | raise | lifted as a preferable specific example which implements this process.

  The reaction between propylene and the alkylbenzene hydroperoxide in the oxidation reaction solution obtained in the first step (hereinafter sometimes referred to as “epoxidation reaction”) is a high yield and high selectivity of the target product. From the viewpoint of obtaining the above, the first catalyst is preferably a catalyst comprising titanium-containing silicon oxide, more preferably a so-called Ti-silica catalyst containing Ti chemically bonded to silicon oxide. . Examples of the Ti-silica catalyst include a catalyst in which a Ti compound is supported on a silica carrier, a catalyst combined with silicon oxide by a coprecipitation method or a sol-gel method, a zeolite compound containing Ti, and the like.

  In the present invention, the alkylbenzene hydroperoxide used as the raw material in the second step may be a diluted or concentrated purified product or a non-purified product.

  The epoxidation reaction is performed by bringing propylene and alkylbenzene hydroperoxide into contact with a catalyst. The reaction is usually carried out in a liquid phase using a solvent. The solvent must be liquid under the temperature and pressure during the reaction and be substantially inert to the reactants and products. The solvent may be an alkylbenzene used as a raw material in the first step contained in the oxidation reaction liquid obtained in the first step. For example, when ethylbenzene or cumene is used as the alkylbenzene used in the first step, in the oxidation reaction liquid obtained in the first step, ethylbenzene (cumene) is contained in addition to ethylbenzene hydroperoxide (cumene hydroperoxide). In such a case, it is possible to substitute the solvent without adding a solvent in the second step. Other useful solvents include, for example, aromatic monocyclic compounds, alkanes, etc., and aromatic monocyclic compounds include, for example, benzene, toluene, chlorobenzene, orthodichlorobenzene, and the like. Examples of alkane include octane, decane, and dodecane.

  As temperature of epoxidation reaction, it is 0-200 degreeC normally, Preferably, it is 25-200 degreeC. The pressure of the epoxidation reaction may be a pressure sufficient to keep the reaction mixture in a liquid state, and is usually 100 to 10,000 kPa.

  The catalyst (1) is preferably used in the form of a slurry or a fixed bed. For large scale industrial operations, it is preferred to use a fixed bed. Moreover, it can implement by a batch method, a semi-continuous method, a continuous method, etc. When the liquid containing the reaction raw material is passed through the fixed bed, the liquid mixture discharged from the reaction zone contains no or substantially no catalyst.

  The molar ratio of propylene / alkylbenzene hydroperoxide supplied to the second step is preferably 2/1 to 50/1. If the ratio is too small, the reaction rate decreases and the efficiency is poor. On the other hand, if the ratio is excessive, the amount of propylene that is recycled becomes excessive, and a large amount of energy is required in the recovery process. When it is within the above range, a particularly excellent effect is exhibited.

The third step in the present invention is a step of subjecting the epoxy reaction solution obtained in the second step to distillation to separate into a section containing an aromatic alcohol, a section containing unreacted propylene, and propylene oxide.
The following method can be given as a preferred specific example for carrying out the third step.

The epoxy reaction liquid obtained in the second step is first subjected to distillation for recovering unreacted propylene.
Next, the aromatic alcohol and solvent produced by the epoxidation reaction are removed by distillation to obtain crude propylene oxide. The removed aromatic alcohol can be further separated from the solvent or sent directly to the fourth step as a section containing the aromatic alcohol.

  On the other hand, this crude propylene oxide generally contains water, hydrocarbons, and oxygen-containing compounds as impurities. Examples of the hydrocarbons include hydrocarbons having 3 to 7 carbon atoms, and oxygen. Examples of the contained compound include methanol, acetaldehyde, acetone, propionaldehyde, methyl formate and the like.

  As a method for removing these impurities, known separation techniques such as distillation, extraction, adsorption, and crystallization may be appropriately combined. From the viewpoint of efficiently removing water, hydrocarbons, and oxygen-containing compounds, crude propylene oxide Is preferably subjected to purification by a combination of extractive distillation using hydrocarbons having 7 to 10 carbon atoms as extractant and other distillations.

  Examples of the hydrocarbon having 7 to 10 carbon atoms as the extractant include linear saturated hydrocarbons having 7 to 10 carbon atoms, branched saturated hydrocarbons having 7 to 10 carbon atoms, and linear chains having 7 to 10 carbon atoms. And unsaturated unsaturated hydrocarbons, branched unsaturated hydrocarbons having 7 to 10 carbon atoms, and the like. Examples of linear saturated hydrocarbons having 7 to 10 carbon atoms include n-heptane, n-octane, n- Nonane, n-decane and the like can be mentioned. Examples of the branched saturated hydrocarbon having 7 to 10 carbon atoms include 2,2-dimethylpentane, 2,3-dimethylpentane, 2,2-dimethylhexane, 2,3 -Examples of the linear unsaturated hydrocarbon having 7 to 20 carbon atoms include 1-heptene, 1-octene, 1-nonene, 1-decene, and the like. Examples of the 10 branched unsaturated hydrocarbons include: 2-methyl-2-heptene and the like. These oil agents may be used alone or in combination of two or more.

The type and operating conditions of the extractive distillation column and other distillation columns, the amount of extractant used, and the like can be appropriately determined according to the required product quality.
The purified propylene oxide thus obtained satisfies the desired product quality.

  The fourth step in the present invention uses a heat exchange system having a heat exchanger and means for adjusting the amount of heat exchanged by the heat exchanger, and uses the gas-liquid mixed fluid at the following fifth step outlet as a heat source. This is a step of preheating the section containing the aromatic alcohol obtained in the step to a desired temperature.

  Examples of the heat exchanger include a multi-tube cylindrical heat exchanger and the like, and preferably a fixed tube plate type multi-tube cylindrical heat exchanger or a U-tube multi-tube cylindrical heat exchanger.

  As a means for adjusting the amount of heat exchanged in the heat exchanger, the heated fluid supplied to the heat exchanger (in the present invention, the section containing the aromatic alcohol obtained in the third step), or the heating side Installed piping (referred to as bypass piping) and valves for bypassing at least a part of one of the fluids (gas-liquid mixed fluid at the fifth process outlet in the present invention) without passing through the heat exchanger Thus, a method of adjusting the amount of fluid passed through the heat exchanger can be exemplified. The bypass pipe and the valve may be installed either on the heated side or on the heated side fluid, or on both, but it is preferable to install on one side from the viewpoint of installation costs. Valves can be installed by installing a normal ball valve, gate valve, etc. in either or both of the bypass pipe and the pipe connected to the heat exchanger, or connected to the bypass pipe and the heat exchanger. One method is to install a three-way valve at the branch of the pipe. The valve installed here may be a manual control valve or an automatic control valve.

  The desired temperature is usually 0 to 500 ° C, preferably 30 to 300 ° C.

  If the heated fluid thus heat-exchanged is not yet preheated to a desired temperature, additional heating means is installed. Specifically, a heat exchanger such as a steam heater or an electric heater may be installed between the outlet of the heat exchanger and the reactor inlet of the fifth step, and further heated to be preheated to a desired temperature. .

  In the fifth step of the present invention, the section containing the aromatic alcohol preheated to the desired temperature obtained in the fourth step is reacted with an excess amount of hydrogen in the presence of the second catalyst to obtain alkylbenzene and unreacted. This is a step of obtaining a gas-liquid mixed fluid containing reaction hydrogen.

The fifth step is a step including a reaction for obtaining alkylbenzene by hydrogenating the aromatic alcohol obtained in the fourth step in the presence of the second catalyst, and particularly from the viewpoint of efficient recycling. The dehydration / hydrogenation method is preferably performed in the order of the following dehydration step and hydrogenation step, which is performed by a two-stage reaction of dehydration reaction / hydrogenation reaction.
Dehydration step: a step of obtaining alkenylbenzene by dehydrating the section containing the aromatic alcohol preheated to the desired temperature obtained in the fourth step in the presence of a dehydration catalyst. Hydrogenation step: obtained in the dehydration step A step of reacting styrenes with an excess amount of hydrogen in the presence of a hydrogenation catalyst to obtain a gas-liquid mixed fluid containing alkylbenzene and unreacted hydrogen. In the case of the dehydration hydrogenation method, the second catalyst is a dehydration catalyst. It is preferable to use two types of hydrogenation catalysts.

Examples of the dehydration catalyst include acids and metal oxides. Examples of the acids include sulfuric acid, phosphoric acid, and p-toluenesulfonic acid. Examples of the metal oxides include activated alumina and titania. , Zirconia, silica alumina, zeolite and the like. From the viewpoint of separation from the reaction solution, catalyst life, selectivity, etc., activated alumina is preferred.

The amount of the dehydration catalyst may be an amount sufficient to convert the aromatic alcohol, and the aromatic alcohol conversion is preferably 90% or more, and more preferably 98% or more.
The practicing amount of the dehydration catalyst may be determined by the practitioner in consideration of the allowable reaction temperature, the dehydration activity of the catalyst used, the catalyst life, and the like.

  The dehydration reaction is carried out by bringing a solution containing an aromatic alcohol into contact with the dehydration catalyst. However, in the dehydration / hydrogenation method, since the hydrogenation reaction is carried out following the dehydration reaction, hydrogen may be fed to the catalyst. As reaction temperature at the time of performing dehydration reaction, it is 50-450 degreeC normally, Preferably, it is 150-300 degreeC. The reaction pressure during the dehydration reaction is usually 10 to 10000 kPa.

  Examples of the hydrogenation catalyst include a catalyst containing a metal of Group 10 or 11 of the Periodic Table, preferably a catalyst containing nickel, palladium, platinum or copper, and suppressing the nuclear hydrogenation reaction of an aromatic ring. From the viewpoint of high yield, more preferred is a catalyst containing palladium or copper. Examples of the catalyst containing copper include copper, Raney copper, copper / chromium, copper / zinc, copper / chromium / zinc, copper / silica, copper / alumina, and the like. Examples of the catalyst containing palladium include palladium / alumina, palladium / silica, palladium / carbon, and the like. These catalysts may be used alone or in combination of two or more. When the hydrogenation catalyst has a dehydrating ability at the same time, the same catalyst may be used as the dehydration catalyst used in the dehydration step and the hydrogenation catalyst used in the hydrogenation step.

The amount of the hydrogenation catalyst may be an amount that can sufficiently convert the dehydration reaction product, and the conversion rate of the dehydration reaction product is preferably 98% or more.
The practicing amount of the dehydration catalyst may be determined by the practitioner in consideration of the allowable reaction temperature, the dehydration activity of the catalyst used, the catalyst life, and the like.

  The hydrogenation reaction is performed by bringing a solution containing alkenylbenzene and hydrogen into contact with a hydrogenation catalyst. However, in the dehydration / hydrogenation method, a hydrogenation reaction is performed subsequent to the dehydration reaction, and thus the dehydration reaction occurred. It may be carried out after separating water by oil-water separation or the like, or may be carried out together with alkenylbenzene without being separated into a hydrogenation catalyst.

  The amount of hydrogen required for the reaction may be equimolar with alkenylbenzene, but usually the raw material also contains other components that consume hydrogen, and an excess of hydrogen is required. Moreover, since reaction progresses so rapidly that the partial pressure of hydrogen is raised, it is 1-10 normally as hydrogen / dehydration reaction product molar ratio, Preferably, it is 1-5.

  As reaction temperature at the time of performing hydrogenation reaction, it is 0-500 degreeC normally, Preferably, it is 30-300 degreeC. The reaction pressure during the hydrogenation reaction is usually 100 to 10,000 kPa.

  The reaction form of the dehydration / hydrogenation reaction can be advantageously carried out by a fixed bed. Separate reactors may be used for the dehydration reaction and the hydrogenation reaction, or a single reactor may be used, but from the viewpoint of cost, the dehydration catalyst and the hydrogenation catalyst should be multistage reactors. And preferably packed in a single fixed bed reactor.

  As the flow of the reactant, any of upflow, downflow and trickle flow may be used.

In the sixth step of the present invention, the gas-liquid mixed fluid obtained in the fifth step is subjected to gas-liquid separation, and separated into a liquid section mainly composed of alkylbenzene and a gas section containing unreacted hydrogen and a condensable component, In this step, at least a part of the alkylbenzene contained in the liquid section is recycled to the first step.
Condensable components mainly include alkylbenzene and water.

  The gas-liquid mixed fluid obtained in the fifth step contains water generated by the reaction in the fifth step in addition to alkylbenzene and unreacted hydrogen. This gas-liquid mixed fluid is usually gas-liquid separated by reducing the pressure in the gas-liquid separation facility, so that not only the gas portion in the gas-liquid mixed fluid but also water and unreacted hydrogen dissolved in the liquid are also contained. It can be separated as a gas. The reduced pressure here means a state in which the pressure is lower than that in the upstream process, and is not limited to atmospheric pressure or lower. As a method for reducing the pressure of the gas-liquid mixed fluid, it is preferably performed by adjusting the opening of a valve installed in a pipe connected to the gas-liquid separator, and more preferably an automatic control valve. Examples of gas-liquid separation equipment include a vertical or horizontal drum, and a vertical drum is preferable from the viewpoint of gas-liquid separation efficiency. In addition, it is also effective to install a structure such as a demister or coalescer inside to increase the gas-liquid separation efficiency. At least a part, preferably most, of the liquid fraction mainly composed of alkylbenzene thus obtained is recycled to the first step. When impurities in the alkylbenzene (for example, phenols by-produced in each step) inhibit the reaction in the first step, it is preferable to recycle after purification by rectification, alkali extraction or the like as necessary.

  In the seventh step of the present invention, the gas section containing the unreacted hydrogen and the condensable component obtained in the sixth step is indirectly heat-exchanged to condense the condensable component contained in the gas section. In this process, recovered steam is obtained from water that is separated into a section containing unreacted hydrogen and a liquid section containing a condensable component and indirectly heat-exchanged.

  In the seventh step, boiler equipment that generates steam by using the condensation heat of the condensable component is usually used. If some of the condensable components are not condensed in the section containing unreacted hydrogen at the outlet of the boiler equipment, install another heat exchanger called a condenser in addition to the boiler equipment if necessary. You may condense using a low temperature cooling heat source.

  Examples of boiler facilities include a facility in which a multi-tube is installed in a container filled with water, which is a heated side fluid, and heat is exchanged through the heated side fluid through the multi-tube, a general kettle heat exchanger, Examples include a container in which a coil, a U tube, or a multi-tubular heating tube is installed as a heat transfer section on a mold or a horizontal drum. Further, it is preferable to install a baffle plate or a demister on the mesh in the vicinity of the steam outlet from the viewpoint of preventing droplets from scattering to the steam pipe.

  The recovered steam may be adjusted so as to have a temperature and pressure necessary for proper use in other processes of the present invention. Specifically, the pressure of the steam generating portion of the boiler equipment is set to a desired steam pressure. Adjust to maintain. The adjustment pressure may be determined by the practitioner in a timely manner, but if the pressure is too high, the amount of steam that can be recovered decreases, and the temperature difference between the condensation temperature of the condensable component and the recovered steam decreases, reducing the condensation rate of the condensable component. Then, the heat load of the condenser in the subsequent stage increases, resulting in uneconomical operation. Therefore, it is preferable to recover the low-pressure steam, specifically in the range of 100 to 300 kPaG. Examples of the use destination of the low-pressure steam include a heat source for rectification of propylene oxide having a low required heat source temperature in the third step.

  The adjusting means may be freely selected by the practitioner. For example, the amount of recovered steam is surplus with respect to the amount of steam used in each step of the production of propylene oxide of the present invention, and the pressure is set to a set value. If it exceeds the limit, the steam may be purged to the atmosphere as a means to lower the pressure, or water with low temperature may be added additionally. Conversely, if the amount of recovered steam falls short of the set value, the pressure will be adjusted from the outside. High steam may be accepted or steam or water may be supplementarily heated by another heating means. In any case, using the latent heat obtained by the condensation of the condensable component contained in the gas section obtained in the sixth step, it is sufficient to include heating the water and recovering the steam.

  In the eighth step in the present invention, the recovered steam obtained in the seventh step is used in at least one of the first to sixth steps, and the amount of the recovered steam is used in each step. On the other hand, the surplus is a step of adjusting the steam balance in the process by performing an operation of increasing the amount of exchange heat by means for adjusting the amount of heat exchange in the fourth step.

  The recovered steam of the present invention needs to be consumed at least in part, preferably most, more preferably all in at least one or more of the first to sixth steps of the propylene oxide production process of the present invention. It is. As already described in the seventh step of the present invention, when the amount of recovered steam is surplus with respect to the amount of steam used in each step of the production process of propylene oxide of the present invention, the thermal energy of the surplus steam Is lost by atmospheric purge or contact mixing with cold water. For this reason, when not using the 8th process of this invention, the utilization efficiency of the heat as the whole manufacturing process will fall.

  In the present invention, when the amount of recovered steam is excessive with respect to the amount used in the process, an operation for increasing the amount of recovered steam by performing an operation of increasing the amount of exchange heat by means of adjusting the amount of heat exchange in the fourth step. By doing this, the heat energy lost in the seventh step can be reduced.

The reason is as follows.
The amount of steam recovered in the seventh step of the present invention varies depending on the amount of gas section containing unreacted hydrogen and condensable components obtained in the sixth step.
That is, when the amount of heat exchange in the fourth step of the present invention is large, the temperature of the gas-liquid mixed fluid supplied to the sixth step is lowered, and as a result, the gas classification obtained in the sixth step is reduced and recovered. When the amount of steam is reduced and conversely the amount of exchange heat is small, the temperature of the gas-liquid mixed fluid supplied to the sixth step increases, the gas classification obtained in the sixth step increases, and the amount of recovered steam also increases. It is.

Here, when considering the utilization efficiency of heat, recovering excess steam and losing it by atmospheric purging or contact mixing with water having a low temperature means a decrease in thermal efficiency. That is, if the amount of heat exchange in the fourth step is increased so as not to generate excessive steam, the amount of additional heat for preheating the section containing the aromatic alcohol obtained in the third step to a desired temperature is reduced. This increases the efficiency of heat utilization.
On the other hand, since the upper limit of the amount of heat exchange in the fourth step is the amount of heat for preheating the section containing the aromatic alcohol obtained in the third step to a desired temperature, the amount of heat exchange is increased beyond this. Adjustments are necessary.

Next, the present invention will be described with reference to examples.
In this example, description will be made on the basis of cumene, which is a representative compound as alkylbenzene and is industrially important.

[Example 1]
An outline of the flow when the present invention is used is shown in FIG.
Cumene (1) merged with recycled cumene (16) and sent to the first step to obtain an oxidation reaction liquid (2) containing cumene hydroperoxide by air oxidation.

  The obtained oxidation reaction liquid (2) containing cumene hydroperoxide is sent to the second step, and in the presence of the first catalyst, an excessive amount containing propylene (3) and recycled propylene (5) to be replenished from the outside. Was reacted with propylene to obtain an epoxy reaction liquid (4) containing propylene oxide and cumyl alcohol.

  In the third step, the epoxy reaction liquid (4) is first recovered from the section containing unreacted propylene to be recycled propylene (5), and then separated from the section (6) containing cumyl alcohol. The product propylene oxide was obtained by distillation.

  In the fourth step, using the gas-liquid mixed fluid (7) at the fifth step outlet as a heat source, using the heat exchanger (101), the section (6) containing cumyl alcohol obtained in the third step is heated, The heat exchanger (102) was then used for additional heating to obtain section (8) containing cumyl alcohol preheated to the desired temperature.

In the fifth step, a reactor in which a fixed bed was filled with a second catalyst consisting of two kinds of a dehydration catalyst and a hydrogenation catalyst was used. First, section (8) containing cumyl alcohol preheated to the desired temperature is dehydrated in the presence of a second catalyst and then reacted with an excess of hydrogen including hydrogen (9) and recycled hydrogen (10). The gas-liquid mixed fluid (7) containing cumyl alcohol and unreacted hydrogen was obtained by hydrogenation.
The required amount of the gas-liquid mixed fluid (7) was used as a heating source for the heat exchanger (101) in the fourth step, and the rest was bypassed by the bypass line (103) without passing through the heat exchanger (101). Thereafter, they were joined again to obtain a gas-liquid mixed fluid (11).

  In the sixth step, the gas-liquid mixed fluid (11) is gas-liquid separated by the gas-liquid separation drum (104), and the liquid section mainly comprising the obtained cumene is the first step as recycle cumene (2) after purification. Recycled. On the other hand, the obtained gas section (11) containing unreacted hydrogen and condensable components was sent to the seventh step.

  In the seventh step, the kettle-type heat exchanger (105) is used to indirectly contact the gas section (11) and water (12) to condense the condensable components contained in the gas section (11). After the separation, the section containing unreacted hydrogen was taken out from the gas-liquid separation drum (106) to be recycled hydrogen (10) and recycled to the fifth step. A part of water (12) heated by the kettle heat exchanger (105) was obtained as recovered steam (13).

  The recovered steam (13) was consumed in the first, second, third, and sixth steps of the present invention. When the amount of consumption is small with respect to the recovered steam (13), surplus steam (14) is released to the atmosphere through the atmospheric discharge valve (107), and on the contrary, when the amount of consumption increases, additional steam is supplied. The valve (107) was opened to supply additional steam.

  In the eighth step, when surplus steam (14) is released into the atmosphere from the atmospheric release valve (108), it passes through the heat exchanger (101) using the bypass valve and bypass line installed in the fourth step. The gas-liquid mixed fluid (7) was increased, and conversely, when additional steam was supplied, the gas-liquid mixed fluid (7) passing through the heat exchanger (101) was adjusted to be reduced.

[Comparative Example 1]
An outline of the flow when the present invention is not used is shown in FIG.
In such a case, even if surplus steam is released into the atmosphere through the atmosphere release valve due to fluctuations in operating conditions, the amount of release cannot be suppressed.

  From the above, when the present invention is used, the amount of excess steam released into the atmosphere through the atmosphere release valve can be suppressed due to fluctuations in operating conditions, etc., and the heat production efficiency as a whole of the manufacturing process is excellent. It was possible to provide a method for producing propylene oxide having a particularly excellent effect from the viewpoint of industrial implementation, in which the cost required for the production and the greenhouse gas emission amount can be reduced.

(1) Cumene (2) Oxidation reaction liquid (3) Propylene replenished from outside (4) Epoxy reaction liquid (5) Recycled propylene (6) Division containing cumyl alcohol (7) Gas-liquid mixed fluid (8) Preheated Section containing cumyl alcohol (9) Hydrogen (10) Recycled hydrogen (11) Gas section containing condensable components (12) Water (13) Recovered steam (14) Surplus steam (15) Additional steam (16) Recycled cumene (101) Heat exchanger (102) Heat exchanger (103) Bypass valve and bypass line (104) Gas-liquid separation drum (105) Kettle-type heat exchanger (106) Gas-liquid separation drum (107) Air release valve (108) Additional steam

Claims (5)

A method for producing propylene oxide, comprising the following steps.
First step: Step of obtaining an oxidation reaction solution containing alkylbenzene hydroperoxide by oxidizing alkylbenzene Second step: Propylene in the presence of the first catalyst and alkylbenzene in the oxidation reaction solution obtained in the first step Step of obtaining an epoxy reaction liquid containing propylene oxide and aromatic alcohol by reacting with hydroperoxide Third step: Division containing aromatic alcohol by subjecting the epoxy reaction liquid obtained in the second step to distillation Step for separating into unreacted propylene and propylene oxide Fourth step: Using a heat exchange system having a heat exchanger and means for adjusting the amount of heat exchanged in the heat exchanger, the following fifth step Using the gas-liquid mixed fluid at the outlet as the heat source, the section containing the aromatic alcohol obtained in the third step is desired. Step 5: Pre-heating the fraction containing aromatic alcohol preheated to the desired temperature obtained in Step 4 with an excess of hydrogen in the presence of the second catalyst to produce alkylbenzene and Step for obtaining a gas-liquid mixed fluid containing unreacted hydrogen Sixth step: Gas-liquid mixed fluid obtained in the fifth step is separated into gas and liquid, and a liquid section mainly composed of alkylbenzene and unreacted hydrogen and condensable components are separated. And a process for recycling at least a part of the alkylbenzene contained in the liquid section to the first process. Seventh process: a gas section containing unreacted hydrogen and condensable components obtained in the sixth process; , Indirectly heat-exchange with water to condense the condensable component contained in the gas section, and separate into a section containing unreacted hydrogen and a liquid section containing a condensable component, and indirectly heat Steam recovered from the exchanged water Step 8 to obtain: The recovered steam obtained in the seventh step is used in at least one of the first to sixth steps, and the amount of the recovered steam is relative to the amount used in each step. In the case of surplus, the step of adjusting the steam balance in the process by performing an operation of increasing the amount of exchange heat by means of adjusting the amount of heat exchange in the fourth step The method according to claim 1, wherein the alkylbenzene is ethylbenzene, the alkylbenzene hydroperoxide is ethylbenzene hydroperoxide, and the aromatic alcohol is methylbenzyl alcohol. The method according to claim 1, wherein the alkylbenzene is cumene, the alkylbenzene hydroperoxide is cumene hydroperoxide, and the aromatic alcohol is cumyl alcohol. The method according to any one of claims 1 to 3, wherein in the seventh step, the means for indirectly exchanging heat is boiler equipment using a kettle heat exchanger. In the fourth step, the heat exchange system has a pipe for passing the section containing the aromatic alcohol obtained in the third step to the heat exchanger, and the pipe is provided with a bypass pipe and a valve, The method according to any one of claims 1 to 4, wherein the means for adjusting the amount of heat exchanged in the vessel is adjusting the opening of the valve.

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