JP2013209391A - Method for recovering propylene oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering propylene oxide (target material), minimizing hydrolysis in a diffusion tower and being improved in the yield.SOLUTION: A method for recovering a target material from a mixture containing water, the target material, 1-3C hydrocarbons, carbon dioxide and inert gases includes the steps (A) to (F) of: (A) diffusing a target material-containing aqueous mixture in a first diffusion tower to thereby obtain a gaseous tower top distillate in the diffusion tower containing a high level of the target material; (B) cooling the tower top distillate to thereby obtain a two-phase mixture; (C) phase-separating the two-phase mixture into a condensed flow and an uncondensed tower top distillate flow of the first diffusion tower; (D) bringing the tower top distillate flow into contact with a target material-diluting cool aqueous absorbent in a scrubbing tower to thereby form a concentrated target material-absorbed aqueous liquid and a non-condensed exhaust gas; (E) uniting the condensed flow and the concentrated target material-absorbed aqueous liquid; and (F) fractionating the united flow by a target material refining zone to thereby recover the target material.

Description

  The present invention relates to a method for recovering propylene oxide from an aqueous mixture in which carbon dioxide, low molecular weight hydrocarbons and other inert gases are dissolved. More particularly, the present invention relates to a method for recovering propylene oxide produced by catalytic gas phase oxidation of propylene from an aqueous dilute solution. In particular, it relates to a method for recovering high-purity propylene oxide from an aqueous dilute solution while minimizing conversion loss to propylene glycol due to hydrolysis.

  As a method for producing propylene oxide, in addition to the chlorohydrin method and the halcon method, a catalytic gas phase oxidation reaction of propylene using a metal catalyst is known. In the catalytic gas phase oxidation reaction of propylene using this metal catalyst, the reaction product typically consists of a small amount of propylene oxide together with a large amount of unreacted propylene and oxygen, and also some carbon dioxide, low molecular weight hydrocarbons, In addition, inert gases such as nitrogen and argon are also included. As a method for recovering propylene oxide from such a mixture, first, propylene oxide is absorbed into an aqueous solution to form a propylene oxide concentrated absorption solution, and subsequently, various methods including treatments such as fractional distillation, scrubbing, and stripping. This is a method for recovering propylene oxide by treatment.

A problem in the method for recovering propylene oxide is that propylene oxide is hydrolyzed into propylene glycol, dipropylene glycol, and the like when propylene oxide is released from the absorbing solution in which propylene oxide is dissolved. Hydrolysis occurs due to the presence of propylene oxide residue and water on the strip of the strip tower at high temperatures. On the other hand, the pressure inside the stripping tower should be higher than atmospheric pressure. Otherwise, air will flow into the stripping tower and an ignitable mixture of propylene oxide, hydrocarbons and oxygen will be produced. On the other hand, when the pressure of the stripping tower becomes extremely higher than the atmospheric pressure during operation, or when the concentration of propylene oxide increases throughout the stripping tower, the amount of propylene glycol produced by hydrolysis of propylene oxide is extremely high. To be high. The hydrolyzate thus produced has very complex and impure properties. In addition, in order to recover glycol as a high-purity product, considerable equipment that is expensive to install, operate and maintain must be used.
One solution to the above problem is to operate the stripping tower at a pressure slightly above atmospheric pressure to compress the non-condensed tower top gas. However, such compressors are expensive and expensive to operate and maintain. Another solution is to cool and condense the top of the strip tower. However, this method is also expensive and has limited applications in order to suppress the formation of solid propylene oxide hydrate at low temperatures.
Patent Document 1 describes a method for recovering ethylene oxide.

US3745092

  An object of the present invention is to provide a method for recovering propylene oxide which minimizes the hydrolysis of propylene oxide in the stripping tower and improves the yield of propylene oxide.

As a result of studying means for solving the above problems, the present invention described below has been found.
[1] water, propylene oxide, C ₁ -C ₃ hydrocarbons, from a mixture containing carbon dioxide and inert gas, a method for recovering propylene oxide,
A method comprising the following steps (A) to (F):
(A) in the first stripping tower, the propylene oxide-containing aqueous mixture is stripped, thereby obtaining a gaseous tower top distillate of the stripping tower rich in propylene oxide;
(B) cooling the overhead distillate, thereby obtaining a two-phase mixture;
(C) phase-separating the two-phase mixture into a condensed stream and a non-condensed first strip tower overhead stream,
(D) in a scrub column, contacting the top distillate stream with a propylene oxide dilute cold aqueous absorbent to produce a propylene oxide rich aqueous absorbent and a non-condensed exhaust gas;
(E) A step of combining the condensed stream and the propylene oxide concentrated aqueous absorbing solution, and (F) a step of fractionating the combined flow in a propylene oxide purification zone to recover propylene oxide.

[2] The recovery method according to [1], wherein the propylene oxide purification zone includes the following zones (A) to (C):
(A) a light fraction fractionation zone in which a substance having higher volatility than propylene oxide contained in the combined stream is separated from the top of the column;
(B) a dehydration fraction zone in which the bottoms from the light fraction fractionation zone are separated into a tops containing propylene oxide and an aqueous bottoms stream substantially free of propylene oxide; And (C) a propylene oxide product fractionation zone in which the overhead from the dehydration fractionation zone is separated into a high-purity propylene oxide overhead product and a propionaldehyde-containing propylene oxide tower bottom.
[3] The recovery method according to [1] or [2], wherein the propylene oxide purification zone further includes a second stripping tower in which propionaldehyde is separated from the propionaldehyde-containing propylene oxide tower bottom.
[4] The recovery method according to any one of [1] to [3], wherein the pressure inside the first diffusion tower is 7 to 140 kPaG.

[5] The recovery method according to any one of [1] to [4], wherein the internal pressure and temperature of the phase separator are 3 to 125 kPaG and 11 ° C to 32 ° C, respectively.
[6] The overhead from the light fraction fractionation zone contains propylene oxide, and the overhead is combined with the overhead from the stripping tower before the cooling and phase separation. [5] The collection method according to any one of [5].
[7] At least a part of the aqueous tower bottom stream from the dehydration fraction zone is used as at least a part of the propylene oxide diluted cold aqueous absorbent that is flowed to the scrub tower after cooling. The collection | recovery method in any one of.
[8] Non-condensate exhaust gas containing propylene, inert gas, low molecular weight hydrocarbons and carbon dioxide is recycled to the reaction tower to convert propylene to propylene oxide. The recovery method according to any one of the above.
[9] water, propylene oxide, C ₁ -C ₃ hydrocarbons, mixtures comprising carbon dioxide and inert gas obtained by catalytic gas phase oxidation reaction of propylene using a metal catalyst, [1] to [8] The collection | recovery method in any one of.
[10] The recovery method according to [9], wherein the metal catalyst used in the catalytic gas phase oxidation reaction of propylene contains a metal oxide.
[11] The recovery method according to [9], wherein the metal catalyst used for the propylene catalytic gas phase oxidation reaction contains (a) copper oxide and (b) ruthenium oxide.
[12] Propylene oxide recovered by the recovery method according to any one of [1] to [11].

  The propylene oxide recovery method of the present invention minimizes the hydrolysis of propylene oxide in the stripping tower and improves the yield of propylene oxide.

It is a figure which shows the preferable aspect of this invention.

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 / 009055, WO2012 / 009055 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 a method for recovering propylene oxide from an aqueous mixture comprising carbon dioxide, low molecular weight hydrocarbons and an inert gas, the propylene oxide is separated in a stripping tower having an internal pressure of about 7 to about 140 kPaG; The top distillate is cooled to condense most of the water and some propylene oxide; the top from the cooled strip tower at a pressure of about 3 to about 125 kPaG and a temperature of about 11 ° C. to about 32 ° C. The distillate is phase separated; the top distillate is contacted with a propylene oxide dilute cold aqueous absorbent in a scrub column to recover almost all propylene oxide; the condensate and scrub obtained from the phase separation. Combined with the propylene oxide concentrated absorbent obtained in the tower; the combined condensate / concentrated absorbent stream is passed to the propylene oxide purification zone where high purity By recovering propylene oxide, hydrolysis of propylene oxide at stripping tower is minimized, thereby improving the yield of propylene oxide.

The recovery method of the present invention is particularly suitable for an exhaust stream from a reactor produced by reacting propylene and oxygen in the presence of the metal catalyst. The reactor effluent stream is generally at a pressure of about 1 to about 2.4 MPaG and a temperature of about 210 ° C. to about 290 ° C., typically about 0.5 to about 3% mol of propylene oxide, about 35% mol. The composition comprises the following propylene, up to about 6% mole oxygen, about 0.5 to about 15% carbon dioxide, and an inert gas such as nitrogen, argon.
This dilute propylene oxide mixture is cooled to a temperature of about 40 ° C. to about 90 ° C. and then absorbed into the aqueous stream and separated from unreacted propylene, oxygen and other gas components of the reactor effluent. The gas component that has not been absorbed contains a large amount of propylene and is suitable for recycling to the reactor of the catalytic oxidation reaction.

  The obtained first aqueous absorbing solution contains propylene oxide at a dilute concentration, and further contains dissolved carbon dioxide and an inert gas. This first aqueous absorption liquid is flowed to the stripping tower, where the top of the gaseous fraction containing most of the propylene oxide, water vapor, some carbon dioxide and inert gas is removed from the liquid aqueous bottoms fraction. To be separated. Preferably, the stripping tower is operated at a pressure of about 7 to about 140 kPaG. The bottoms from the stripper may be recycled after cooling and used to absorb the propylene oxide contained in the gaseous exhaust stream from the reactor. The tower top from the stripping tower is cooled to condense most of the water and some of the propylene oxide. The top product from the cooled stripping tower is phase separated at a pressure of about 3 to about 125 kPaG, and the resulting gas is contacted with a lean aqueous absorbent in a scrub column and propylene contained in the gas. Substantially all of the oxide is recovered. Non-condensable gas is removed from the scrub column as exhaust gas, but can also be compressed and recycled to the reactor so as not to lose the propylene contained. The condensate from the phase separator and the propylene oxide rich absorbent from the scrub column are combined and flowed to a series of fractionation zones. This series of fractionation zones recovers high purity propylene oxide and an aqueous stream suitable for use in stripping and / or scrubbing towers.

  Unlike conventional recovery techniques, the recovery method of the present invention is at a lower pressure and concomitantly lower temperature compared to the case of condensing the gaseous overhead without using a subsequent scrub column. Operation of the propylene oxide stripping tower becomes possible. By using lower pressures and temperatures in the stripper according to the present invention, the loss of propylene oxide due to hydrolysis is significantly reduced. Furthermore, one of the disadvantages of the conventional method is solved by phase-separating the top from the cooled stripping tower. That is, the warm concentrated absorption liquid from the stripping tower is combined with the cooled propylene oxide concentrated liquid from the stripping tower, so that a part of the propylene oxide is re-evaporated and the load on the second scrub column is increased. Become.

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.
Shown in FIG. 1 are an absorption tower for recovering propylene oxide from the reactor effluent; a stripping tower; a scrub tower; a phase separator; a propylene oxide purification zone; and piping connecting them. Miscellaneous accessories such as pumps, safety valves, valves, controllers and compressors are omitted, and only the minimum containers and piping necessary to fully and clearly understand the present invention are shown.
In FIG. 1, a gaseous reactor discharge stream, for example, a gaseous reactor discharge stream generated in a propylene catalytic gas phase oxidation reaction using a metal catalyst, is introduced into an absorption tower 10 through a pipe 1. An aqueous stream is introduced into the absorption tower 10 through the pipe 13. Inside the absorption tower 10, propylene oxide, a small amount of carbon dioxide and inert gas are absorbed into the aqueous stream. Non-absorbed gases typically include nitrogen, oxygen, carbon dioxide, methane, ethane and unreacted propylene, but this unabsorbed gas is removed from the absorption tower 10 through the piping 11 and contacted gas phase oxidation. Suitable for recycling to the reactor. The bottom of the absorption tower is an aqueous stream containing the absorbed propylene oxide, and is introduced into the stripping tower 30 through the pipe 12 and the heater 20. In order to improve the thermal economy of this recovery method, it is desirable to heat the bottoms from the absorption tower by means of the heat exchanger 20. Although not shown in the figure, the aqueous stream in the pipe 13 is usually further cooled.

  The stripping tower 30 is designed to fractionate and recover 99.0% or more of the propylene oxide introduced. Loss of propylene oxide during the stripping operation must also include loss due to hydrolysis of propylene oxide to propylene glycol, dipropylene glycol, and the like. The overhead gas from the stripping tower 30 contains 20 to 40% mol of propylene oxide, and a small amount of a specific gas and carbon dioxide, and the rest is water. The specific gas and carbon dioxide are added in the absorption tower 10. The operating pressure of the stripping tower 30 is about 7 to about 140 kPaG at the top of the tower, which is the lowest pressure that can be achieved, thereby ensuring a pressurized state throughout the system and the scrub column being substantially free of propylene oxide. Complete recovery is possible. In order to prevent the formation of an ignitable hydrocarbon / oxygen mixture within the stripping tower 30 and within the downstream recovery zone, it is desirable that the pressure inside the stripping tower does not fall below atmospheric pressure. By setting the pressure, air does not enter the apparatus. Propylene oxide residue and water on the shelf of the stripping tower are present at a high temperature, so that part of the propylene oxide is hydrolyzed to produce propylene glycol, dipropylene glycol and the like. If the pressure inside the stripping tower is not relatively low, preferably not in the range of about 7 to about 140 kPaG, a large amount of propylene oxide will be hydrolyzed. The heat for dissipating the stripping tower can be provided via the piping 34 using a normal reboiler, direct steam, or a combination thereof.

  Gaseous tops from stripper tower 30 flow through line 31 and are combined with all of the propylene oxide-containing stream that flows out of line 71 from propylene oxide purification zone 200. The combined streams flow through the pipe 35 and are cooled by the heat exchanger 40, thereby condensing most of the water and a small amount of propylene oxide. The resulting overhead product from the partially condensed two-phase stripping tower flows through the pipe 41 to the phase separator 50. The phase separator is operated at a pressure of about 3 to about 125 kPaG and a temperature of about 11 ° C to about 32 ° C. The separated gas contains most of the carbon dioxide, other gases originally dissolved in the absorption tower 10, and a significant amount of propylene oxide. This gas is sent to the scrub column through the pipe 51 and comes into contact with the cooled lean aqueous absorbent flowing from the pipe 63. Non-condensate exhaust gas including propylene, low molecular weight hydrocarbons, inert gas and carbon dioxide is discharged from the scrub column through line 61. This exhaust gas can be compressed and recycled to the reactor to prevent loss of contained propylene. The propylene oxide rich tower bottom absorption liquid is mixed with the condensate from the phase separator 50 flowing through the pipe 52 through the pipe 62. The resulting mixture is routed through line 53 to propylene oxide purification zone 200 where propylene oxide suitable for commercial sale or further chemical conversion and an aqueous stream suitable for stripping tower, scrub tower or both. And are generated.

The use of the phase separator 50 is preferred over a simple system that does not use it and the two-phase mixture flows through the piping 41 and directly to the scrub column 60. In the simple system described above, the liquid portion of the cooled mixture 41 will be in direct contact with the warm absorbent from the scrub column in the sump at the bottom of the scrub column. These two liquids average in temperature and composition, thereby increasing the temperature of the propylene oxide concentrate from mixture 41 and causing some of the propylene oxide to re-evaporate. Therefore, in order to reduce the loss of propylene oxide to the exhaust gas 61 with a simple system, more absorbent flowing through the pipe 63 must be added to the scrub column. In the preferred recovery method described in FIG. 1, such re-evaporation is prevented by raising the pressure of the stream 52 and the stream 62 to some extent by the pipe 53 before mixing with a pump or the like (not shown).
Various distillation systems can be used to work up the aqueous propylene oxide stream flowing through the pipe 53. An example of a preferred arrangement is shown in FIG.

A mixture of the condensate from the phase separator 50 and the concentrated absorbent from the scrub column 60 is supplied to the light fraction fractionation zone 70 through the pipe 53. This mixture contains some carbon dioxide and other gases originally absorbed by the absorber 10. The light fraction fraction zone 70 is for separating a volatile component such as a specific gas, a low molecular weight hydrocarbon, and carbon dioxide contained in a trace amount as a tower top. The tower top gas from this tower flows through the piping 71 and is combined with the gaseous tower top from the stripping tower 30, and the propylene oxide contained in the gaseous tower top is condensed through the heat exchanger 40. Is done. Through the pipe 71, the inert substance is recycled in the recovery method. Carbon dioxide and other inert substances are supplied to the scrub column 60 and discharged via the pipe 61. Heat can be provided to the light fraction fraction zone 70 via line 73 using a normal reboiler, direct steam, or a combination thereof. By maintaining the overhead gas from the light fraction fractionation zone 70 at a constant flow rate, the light fraction can be sufficiently reduced. The bottoms from the light fraction fractionation zone 70 contain about 8 wt% to about 20 wt% propylene oxide and water, and are supplied to the dehydration fraction zone 80 via the pipe 72.
Propylene oxide contained in the bottom of the light fraction fraction zone 70 is separated from water and recovered as a top gas from the dehydration fraction zone 80. The bottom of the dehydration fraction zone contains about 99% by weight of water and flows to the piping 82. As with some of the other distillation columns in the preferred recovery process, heat is provided to the dehydration fraction zone 80 via line 84 using a normal reboiler, direct steam, or combinations thereof. Can do.

The overhead gas from the dehydration tower 80 is supplied to the propylene oxide product fractionation zone 90 through a pipe 81 for further rectification of propylene oxide. The tower top stream from the product fractionation zone 90 passes through the pipe 91, is condensed in the heat exchanger 100, and flows out through the pipe 101 as a propylene oxide product. Although not shown, a portion of the condensed propylene oxide overhead stream is returned to the product fractionation zone 90 as reflux. The bottom stream from the product fractionation zone 90 contains most of the propionaldehyde mixed in the propylene oxide rectification zone in a state diluted with propylene oxide. Spilled from. In order to maximize the yield of high-purity propylene oxide, if necessary, propylene oxide contained in the bottom stream from the product fractionation zone 90 may be released from propionaldehyde using another distillation column. Good. In that case, propylene oxide gas from the propionaldehyde distillation column may be added to the flow in the pipe 81. The fraction of the second shelf from the bottom of the product fractionation zone 90 may be extracted from the product fractionation zone 90 and returned to the dehydration fraction zone 80 through the pipe 94 and used as reflux.
The bottoms from the dehydration fraction zone 80 are cooled in the heat exchanger 85 and used not only as a lean absorbent in the scrub column 60 but also recycled through the pipe 33 to the appropriate location in the strip tower 30. May be.
The propionaldehyde concentrated propylene oxide stream flowing from the bottom of the product fractionation tower 90 to the pipe 92 may be dissipated to remove propionaldehyde, and then mixed with the top of the dehydration fraction zone 80 and the pipe The amount of high purity propylene oxide recovered may be increased by flowing through 81.

  The method of the present invention provides a method for recovering propylene oxide by minimizing the hydrolysis of propylene oxide in the stripping tower and improving the yield of propylene oxide.

Claims (12)

Water, propylene oxide, C ₁ -C ₃ hydrocarbons, from a mixture containing carbon dioxide and inert gas, a method for recovering propylene oxide,
A method comprising the following steps (A) to (F):
(A) in the first stripping tower, the propylene oxide-containing aqueous mixture is stripped, thereby obtaining a gaseous tower top distillate of the stripping tower rich in propylene oxide;
(B) cooling the overhead distillate, thereby obtaining a two-phase mixture;
(C) phase-separating the two-phase mixture into a condensed stream and a non-condensed first strip tower overhead stream,
(D) in a scrub column, contacting the top distillate stream with a propylene oxide dilute cold aqueous absorbent to produce a propylene oxide rich aqueous absorbent and a non-condensed exhaust gas;
(E) A step of combining the condensed stream and the propylene oxide concentrated aqueous absorbing solution, and (F) a step of fractionating the combined flow in a propylene oxide purification zone to recover propylene oxide. The recovery method according to claim 1, wherein the propylene oxide purification zone includes the following zones (A) to (C):
(A) a light fraction fractionation zone in which a substance having higher volatility than propylene oxide contained in the combined stream is separated from the top of the column;
(B) a dehydration fraction zone in which the bottoms from the light fraction fractionation zone are separated into a tops containing propylene oxide and an aqueous bottoms stream substantially free of propylene oxide; And (C) a propylene oxide product fractionation zone in which the overhead from the dehydration fractionation zone is separated into a high-purity propylene oxide overhead product and a propionaldehyde-containing propylene oxide tower bottom.   The recovery method according to claim 1 or 2, wherein the propylene oxide purification zone further includes a second stripping tower in which propionaldehyde is separated from the propionaldehyde-containing propylene oxide tower bottom.   The recovery method according to any one of claims 1 to 3, wherein the pressure inside the first stripping tower is 7 to 140 kPaG.   The recovery method according to any one of claims 1 to 4, wherein the internal pressure and temperature of the phase separator are 3 to 125 kPaG and 11 ° C to 32 ° C, respectively.   6. The overhead from the light fraction fractionation zone comprises propylene oxide, the overhead is combined with the overhead from the stripping tower prior to the cooling and phase separation. The recovery method described in 1.   The at least part of the aqueous tower bottom stream from the dehydration fraction zone is used as at least part of the propylene oxide dilute cold aqueous absorbent that is flowed to the scrub tower after cooling. Recovery method.   8. The non-condensate exhaust gas comprising propylene, inert gas, low molecular weight hydrocarbons and carbon dioxide is recycled to the reaction tower and propylene is converted to propylene oxide. Collection method. Water, propylene oxide, C ₁ -C ₃ hydrocarbons, mixtures comprising carbon dioxide and inert gas obtained by catalytic gas phase oxidation reaction of propylene using a metal catalyst, according to any of claims 1 to 8 Recovery method.   The recovery method according to claim 9, wherein the metal catalyst used in the catalytic gas phase oxidation reaction of propylene contains a metal oxide.   The recovery method according to claim 9, wherein the metal catalyst used in the catalytic gas phase oxidation reaction of propylene contains (a) copper oxide and (b) ruthenium oxide.   The propylene oxide collect | recovered with the collection | recovery method in any one of Claims 1-11.

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