JP2013126978A - Method for producing propylene oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing propylene oxide, which minimizes the loss to a purge gas of propylene, and improves the yield in a propylene oxide production process.SOLUTION: The method includes: (a) mixing propylene 102, high-purity oxygen 101 and balance gas 103 with recycle gas 110 to form a reaction gas mixture; (b) feeding the reaction mixture to a reactor 120 packed with a catalyst, and making an effluent 125 flow out from the reactor; (c) sending the effluent from the reactor to a recovery column 140 and forming a gas flow 148 having no propylene oxide; (d) sending the gas flow 148 having no propylene oxide to a diffusion column 130 to remove carbon dioxide 135; (e) purging 115 a part 138 of a gas flow having no carbon dioxide, and recycling a remaining gas flow as the recycle gas; (f) compressing the recycle gas again; and (g) regulating the flow amount of the purge gas to effectively reduce the concentration of argon.

Description

  The present invention relates to a method for producing propylene oxide. In particular, the present invention relates to a method for producing propylene oxide by selective oxidation of propylene using high-purity oxygen.

Propylene oxide can be produced by catalytic gas phase oxidation of propylene with oxygen. Commercially available oxygen or air is used as the oxygen source. Generally, propylene, oxygen and balance gas are mixed with recycle gas and supplied to the reactor. The reactor comprises a number of tubes that are arranged inside the reactor like a shell and tube heat exchanger. The reaction tube is filled with a catalyst supported on a porous support. A refrigerant circulates in the shell around the reaction tube to maintain temperature control.
In the process for producing propylene oxide, the typical composition of the gas stream fed to the reaction tube is 15-95 mol% propylene, 3-12 mol% oxygen, 4-20 mol% argon, 30-50 mol. % Balance gas, 1-15 mol% carbon dioxide, propane, water and additives such as organochlorine compounds described in WO2012 / 102918 constitute the remainder of the composition. Propylene reacts with oxygen inside the tube filled with the catalyst to produce propylene oxide as a reaction product, carbon dioxide and water as by-products. The reaction is exothermic and hot spots can form in the reaction tube. A “hot spot” is a hot region localized in the reactor. If not properly controlled, hot spots can cause unwanted runaway reactions.

In the process for producing propylene oxide, a balance gas is introduced into the reactor in order to obtain an optimal reaction mixture, to control the temperature and not to become a combustible mixture. At higher temperatures, undesirable carbon dioxide production is promoted, reducing both catalyst activity and catalyst life. By controlling the reaction rate and heat removal from the reaction zone, the temperature and hot spot location can be controlled to maximize propylene oxide selectivity and maintain catalyst activity. Examples of the balance gas include methane, ethane, nitrogen, carbon dioxide, and mixtures thereof. Methane is preferred over nitrogen as a balance gas because it has excellent thermal properties. These thermal properties include high molar heat capacity and high thermal conductivity. US3119837 describes that the yield of ethylene oxide was increased by replacing nitrogen in the balance gas with methane.
In the process for producing propylene oxide, the reactor effluent is treated in two different steps, similar to the process for producing ethylene oxide described in US6040467. The first step is a step of removing propylene oxide from the product, and the second step is a step of removing carbon dioxide as a by-product. After purging a portion of it, the remaining gas is recycled to the reactor. A significant amount of propylene is lost to the purge gas stream and the selectivity is reduced. Since the balance gas is also lost to the purge gas flow, a new balance gas must be replenished. A gas purge is necessary to keep the impurities in the gas mixture entering the reactor at an acceptable level. Impurity argon is mixed in by the oxygen stream, and other impurities such as propane are contained in the propylene stream.

Propylene oxide may be produced using air instead of oxygen, as in the ethylene oxide production process described in US6040467. When air is used, unreacted gas is recycled to the reactor, but the amount of recycling is limited by the amount required to remove excess nitrogen from the process. Nitrogen is continuously added to the process as air is added to the reactor. When removing nitrogen, a significant amount of unreacted propylene is also lost along with the nitrogen. To reduce the loss of propylene under these conditions, one or more additional oxidation reactors are required to mix the purge gas with additional air to perform the reaction in the presence of the catalyst under more severe reaction conditions. However, the addition of an oxidation reactor greatly increases the cost of the propylene oxide plant. Another drawback of the air process is that the propylene conversion is reduced.
There is a significant difference between purging a process using air and purging a process using oxygen. The process using air requires a large amount of purge flow and a step-by-step reaction-absorption system. When oxygen is used, the amount of inert gas introduced into the closed cycle is significantly lower compared to the process using air, a substantially small amount of purge is sufficient, and unreacted propylene is removed. It can be recycled almost completely. However, the carbon dioxide produced in the reactor must be removed continuously. Furthermore, a purge is necessary to prevent the accumulation of argon in the recycle gas. Argon is a major impurity contained in oxygen derived from a cryogenic air separation plant. The oxygen used in the propylene oxide production plant is generally derived from a low temperature air separation plant.

  In a propylene oxide production plant by a process using oxygen, oxygen at a concentration of 95% to 99.5% is typically used. In a propylene oxide production plant using oxygen, various methods can be used as a purge gas treatment method for recovering propylene. For example, in an ethylene oxide production plant, US 4904807 describes the use of an argon-selective membrane that is used for the treatment of purge gas, which is purged with (1) argon to be purged, and (2 ) Separate into two streams of gas rich in ethylene that can be recycled to the ethylene oxide reactor. US 4769047 describes a method in which ethylene is removed from purge gas using a pressure swing adsorption method and recycled to the reactor. The main drawback of these methods is the high cost required for the associated equipment used. US3083213 describes that the yield of ethylene oxide is reduced by using high-purity oxygen. Furthermore, Patent Document 1 describes a method for producing ethylene oxide using high-purity oxygen.

US6040467

  An industrially practical method for reducing impurities associated with the production of propylene oxide has not been reported. Therefore, an object of the present invention is to provide a method for producing propylene oxide in which the selectivity is maximized to minimize the loss of propylene to the purge gas and the yield of propylene oxide is improved. More specifically, a method for producing propylene oxide using oxygen with improved yield, a method for producing propylene oxide that maximizes selectivity and minimizes the loss of propylene to the purge gas, and propylene oxide Another object of the present invention is to provide a production method in which the selectivity of propylene oxide is improved by adjusting the concentration of at least one of methane, oxygen and carbon dioxide.

As a result of intensive studies to solve the above problems, the following inventions have been found.
[1] a) mixing propylene, at least 99.5% high purity oxygen and a balance gas with a recycle gas to form a reaction gas mixture;
b) supplying the reaction mixture to a reactor filled with catalyst, and the effluent is discharged from the reactor;
c) sending at least a portion of the effluent from the reactor to a recovery tower to selectively remove propylene oxide to form a gas stream free of propylene oxide;
d) sending at least part of the gas stream free of propylene oxide to the stripping tower to remove carbon dioxide from said gas stream;
e) purging at least a portion of the gas stream free of carbon dioxide and recycling the remaining gas stream as a recycle gas;
f) recompressing the recycle gas; and g) adjusting the flow rate of the purged gas stream to effectively reduce the concentration of argon.
The manufacturing method of the propylene oxide containing this.

[2] The production of [1], wherein step (g) further comprises adjusting the feed flow rate of at least one of propylene, high purity oxygen and balance gas, thereby improving the selectivity of propylene oxide production. Method.
[3] The production method according to [1], wherein the step (g) further includes a step of generating a gas with enhanced heat transport properties in order to reduce the influence of hot spots formed in the reactor.
[4] The production method according to [3], wherein the selectivity of propylene oxide is improved and the catalyst life is extended by reducing the influence of hot spots.
[5] The production method according to [1], wherein loss of balance gas is reduced in the step (g).
[6] The production method according to [1], wherein the balance gas includes methane.
[7] The production method according to [1], wherein the balance gas contains nitrogen.
[8] The production method according to [1], wherein the reactor filled with the catalyst includes a reaction tube filled with the catalyst on the porous support.
[9] The production method according to any one of [1] to [8], wherein the catalyst contains a metal oxide.
[10] The production method according to any one of [1] to [8], wherein the catalyst contains (a) copper oxide and (b) ruthenium oxide.

  The method for producing propylene oxide of the present invention maximizes the selectivity and minimizes the loss of propylene to the purge gas, thereby improving the yield of propylene oxide.

It is the schematic of the manufacturing method of propylene oxide by selective oxidation with the oxygen of propylene.

Examples of the method for catalytic vapor phase oxidation 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. The catalyst used in the production method includes the following (a), (b), (c), (d), (e), (f), (g), (h), (i) and (j). A catalyst containing at least two selected from the group can be mentioned.
(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) 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 A catalyst containing ruthenium oxide and (j) an alkali metal component or an alkaline earth metal component.

The present invention includes: a) mixing propylene, high purity oxygen and balance gas with a recycle gas to form a reaction gas mixture; b) supplying the reaction mixture to a reactor packed with a catalyst. C) the effluent is discharged from the reactor; c) at least a portion of the effluent from the reactor is sent to a recovery tower to selectively remove propylene oxide to produce a gas stream free of propylene oxide. Forming; d) sending at least part of the gas stream free of propylene oxide to the stripping tower and removing carbon dioxide from said gas stream; e) purging at least part of the gas stream free of carbon dioxide A process for recycling the remaining gas stream as a recycle gas; and f) a process for recompressing the recycle gas. To.
The present invention also includes: a) mixing propylene, high purity oxygen and balance gas with a recycle gas in a reactor filled with catalyst to form a reaction gas mixture; b) Feeding to a packed reactor and allowing the effluent to flow out of the reactor; c) sending at least a portion of the effluent from the reactor to a recovery tower to selectively remove propylene oxide; Forming a gas stream free of propylene oxide; d) sending at least a portion of the gas stream free of propylene oxide to the stripping tower to remove carbon dioxide from the gas stream; e) no carbon dioxide present Purging at least a portion of the gas stream and recycling the remaining gas stream as a recycle gas; f) recompressing the recycle gas; g) the concentration of argon Adjusting the flow rate of the purged gas stream to effectively reduce: and (if necessary) h) adjusting the concentration of at least one of propylene, high purity oxygen, balance gas and carbon dioxide The present invention relates to a method for improving the yield of propylene oxide by reducing the argon content in the production of propylene oxide including a step.

By reducing the concentration of argon, the concentration of other gases of the recycled gas is adjusted, and the heat transport characteristics of the recycled gas can be improved. By improving the heat transport characteristics of the recycled gas, the influence of hot spots formed in the reactor is reduced, the selectivity of propylene oxide is increased, and the catalyst life is improved.
Recycled gas with reduced argon concentration replaces heavy argon gas with lighter gases (propylene, methane, oxygen, etc.), reducing compressor load and operation. Instead, while maintaining the compressor load, the amount of propylene oxide produced can be increased by increasing the flow rate of recycle gas with reduced argon concentration.
The present invention also provides a process for producing propylene oxide, wherein the molar ratio of propylene to high purity oxygen is at least about 1 and comprises reacting propylene with high purity oxygen in the presence of a catalyst and an additive, comprising the reaction zone The feed gas introduced into the reactor is 15 to 95 mol% propylene, 4 to 20 mol% argon, 6 to 10 mol% very high purity oxygen, 15 to 65 mol% balance gas, and 5 to 10 mol % Of carbon dioxide.
In the present invention, the high purity gas contains at least 95% oxygen, preferably at least about 99.5% oxygen. As used herein, “very high purity oxygen” refers to oxygen gas having an oxygen purity of at least 99.5%. The balance gas includes methane and nitrogen. The reactor filled with the catalyst includes a reaction tube filled with the catalyst supported on the porous support.

  By reducing the purge flow while keeping the argon concentration in the recycle gas constant, propylene loss and balance gas loss to purge are reduced. The present invention provides a method for reducing the argon concentration by using high purity oxygen instead of reducing the purge flow while keeping the argon concentration constant. By reducing the argon concentration, the concentration of propylene, methane, oxygen or carbon dioxide, or the total concentration of these four gases can be increased to obtain a reactor feed gas with better heat transport properties. it can. The ratio of reaction between desired propylene oxide production and unwanted carbon dioxide production depends on the concentration of all reactants and products. The yield of propylene oxide can be increased by adjusting the concentrations of reactants and products in the feed gas. The amount of purge flow is smaller than when high purity oxygen is not used.

Thus, there are two reasons why the selectivity improves as the argon concentration decreases. 1) Reduced hot spot effect and improved selectivity, better heat transport properties of gas fed to reactor, 2) Reaction by adjusting the concentration of remaining gas (reactant and product) Speed improvement. Improved propylene oxide selectivity means that propylene fed to the reactor is converted to more propylene oxide and less by-products. Depending on various conditions including the type and age of the catalyst, the temperature in the reaction tube, the pressure, the residence time, and the various conditions including the temperature, pressure and flow rate of the cooling fluid flowing around the reaction tube in the shell, Improvements are made.
Because of the differences in catalysts and the operating conditions used in each industrial plant, the improvement in selectivity must be determined on a case-by-case basis. In the production of ethylene oxide, it has been reported that the selectivity of ethylene oxide is improved by 0.8 mol% for every 1 mol% reduction of nitrogen by exchanging nitrogen for methane (see: US3119837). Increasing the ethylene concentration in the feed gas from 30.6 mol% to 74.5 mol% has been reported to improve the selectivity from 79.7 mol% to 80.8 mol% (see US Pat. No. 5,262,551). ). Replacing argon in the feed gas to the reactor has similar advantages.

For the above reasons, when high-purity oxygen is used, if the total concentration of other gases increases instead of the argon concentration, the selectivity of propylene oxide is 0.05 mol each time the argon concentration decreases by 1 mol%. % To 1 mol% improvement. However, reducing the argon concentration will increase the purge flow rate and also increase the propylene concentration in the recycle gas stream, resulting in an increase in propylene loss in the purge. Thus, when using high purity oxygen, there is an optimal reduced argon concentration in the recycle gas and purge streams that maximizes the yield of propylene oxide.
Propylene oxide production also increases with improved reactor selectivity. If the supply rate of propylene is kept constant and the selectivity is improved, the amount of propylene oxide produced increases. If processing can be performed even if the load on the downstream separator increases, the production amount can be increased by about 0.5% to about 5.0% without additional cost.
By reducing the argon concentration, hot spot formation in the reactor is reduced where catalyst life is extended. This effect also results in increased selectivity (reducing the amount of heat generated in the reactor) and improving the thermal properties of the reaction gas mixture (improving heat removal from the reactor). The amount of catalyst used can be reduced by improving the catalyst life.

In general, the operating temperature of the present invention is suitably in the range of 100 ° C to 350 ° C, preferably in the range of 120 ° C to 330 ° C, and most preferably in the range of 170 ° C to 330 ° C. The operating pressure for carrying out the present invention is suitably in the range of 0.001 MPaA to 3 MPaA, preferably in the range of 0.002 PAaA to 2 MPaA. Gas space velocity, depending on the desired production volume is preferably selected in the range of ^{100hr -1 ~100000hr} -1.
Using high-purity oxygen in conjunction with a propylene recovery device for conventional purge streams (such as membrane separation or pressure swing adsorption) to process the purge and recover the remaining propylene and return it to the reactor The present invention can be implemented. The use of high purity oxygen greatly reduces the required capital investment.

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.
FIG. 1 is a schematic view of a method for producing propylene oxide by selective oxidation of propylene with oxygen. Necessary amounts of oxygen 101 (containing argon as an impurity), propylene 102 and balance gas 103 (nitrogen, methane, etc.) are mixed with at least a part of the recycle gas 110 supplied to the reactor 120. The recycle gas 110 and the exhaust purge 115 flow out from the carbon dioxide stripping tower 130. Reactor 120 is made up of several tubes in a shell arranged similar to a heat exchanger. The reaction tube is filled with a catalyst. A propylene reactor effluent 125 containing impurities is produced by the reaction of oxygen (from 101 and 110) and propylene (from 102 and 110). Reactor effluent 125 is sent to propylene oxide recovery tower 140. Treatment in the recovery tower 140 produces a propylene oxide product 145 and a stream 148 rich in carbon dioxide. Carbon dioxide stripping tower 130 converts carbon dioxide rich stream 148 into carbon dioxide 135 and stream 138. The stream 138 is separated into a recycle gas stream 110 and a purge stream 115. The recycle gas stream 110 is further reacted with oxygen 101 (containing argon impurities) and propylene 102, and the purge stream 115 is discarded.

In a process using oxygen, the amount of purge flow is determined by the argon impurities introduced from the oxygen flow. The amount of argon removed by the purge 115 is equal to the product of the argon concentration during the purge and the volume of the purge. This product must be equal to the amount of argon introduced into the reactor with a fresh oxygen supply, according to equation (1).
Formula (1): (Argon volume concentration) × (Volume flow rate of purge flow) = (Argon amount added with new oxygen)
If the amount of argon introduced in the new oxygen supply is reduced and the argon concentration is kept constant, the amount of purge flow can be reduced according to equation (1), and the amount of propylene lost by the purge is reduced. Loss can be reduced.

  The present invention provides a method for producing propylene oxide that maximizes selectivity, minimizes loss of propylene to the purge gas, and improves the yield of propylene oxide.

Claims (10)

a) mixing propylene, at least 99.5% high purity oxygen and balance gas with recycle gas to form a reaction gas mixture;
b) supplying the reaction mixture to a reactor filled with catalyst, and the effluent is discharged from the reactor;
c) sending at least a portion of the effluent from the reactor to a recovery tower to selectively remove propylene oxide to form a gas stream free of propylene oxide;
d) sending at least part of the gas stream free of propylene oxide to the stripping tower to remove carbon dioxide from said gas stream;
e) purging at least a portion of the gas stream free of carbon dioxide and recycling the remaining gas stream as a recycle gas;
f) recompressing the recycle gas; and g) adjusting the flow rate of the purged gas stream to effectively reduce the concentration of argon.
The manufacturing method of the propylene oxide containing this.   The production method of claim 1, wherein step (g) further comprises adjusting at least one feed flow rate of propylene, high purity oxygen and balance gas, thereby improving selectivity for propylene oxide production.   The production method according to claim 1, wherein step (g) further comprises the step of generating a gas with enhanced heat transport properties to reduce the effect of hot spots formed in the reactor.   The production method according to claim 3, wherein the selectivity of propylene oxide is improved and the catalyst life is extended by reducing the influence of hot spots.   The manufacturing method of Claim 1 which reduces the loss of balance gas at a process (g).   The manufacturing method of Claim 1 with which the said balance gas contains methane.   The manufacturing method of Claim 1 with which the said balance gas contains nitrogen.   The production method according to claim 1, wherein the reactor filled with the catalyst includes a reaction tube filled with the catalyst on the porous support.   The manufacturing method according to claim 1, wherein the catalyst contains a metal oxide.   The manufacturing method according to claim 1, wherein the catalyst contains (a) copper oxide and (b) ruthenium oxide.

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