KR20180069835A - Process for purifying propene oxide - Google Patents

Abstract

The present invention relates to a process for the purification of propene oxide wherein the propene oxide is purified by extractive distillation and comprises 15-97% by weight propene oxide, 2-84 < RTI ID = 0.0 > Providing a crude propene oxide comprising, by weight, methanol, and acetaldehyde; Feeding an aqueous extraction solvent to feed point B located above feed point A; And a reactive compound of the structure R ¹ -Y-NH ₂ , wherein Y is oxygen or NR ² , and R ¹ and R ² , which are independent of each other, are selected from the group consisting of hydrogen, An alkyl group or an aryl group) or a salt of such a reactive compound; Withdrawing stream S1 from the top of the extractive distillation column to provide a first propene oxide product containing less than 200 ppm water; And withdrawing stream S2 at a draw point located at a theoretical separation stage of 5 to 25 on feed point B to provide a second propene oxide product containing 500 to 10,000 ppm of water.

Description

Process for purifying propene oxide

The present invention relates to a process for purifying propene oxide which provides two propene oxide products of different purity, wherein the first product is suitable for preparing a polyether polyol and the second product is selected from 1,2-propane Diol or propylene glycol monoethers.

The preparation of propene oxide by reacting hydrogen peroxide with propene in the presence of a titanium zeolite catalyst has the advantage of providing propene oxide without the co-production of other compounds that have to be marketed and also has fewer wastes than conventional chlorohydrin processes . The reaction of hydrogen peroxide with propene in the presence of a titanium zeolite catalyst is typically carried out in a methanol solvent to achieve a high reaction rate and product selectivity. The crude propene oxide provided by this reaction is a mixture of residual methanol solvent and volatile by-products formed during the reaction and work-up, especially aldehydes such as formaldehyde, acetaldehyde and propionaldehyde, and methanol and 1,2- - propanediol, as well as methyl formate.

Most of the propene oxide is further reacted with a polyether polyol used as a monomer for preparing the polyurethane. For this purpose, propene oxide containing less than 200 ppm of water, less than 100 ppm of methanol and less than 50 ppm of acetaldehyde should be of high purity.

A significant portion of the propene oxide is further reacted with water with 1,2-propanediol. For this purpose, the purity requirement is less stringent, and the water content is not important.

Methanol, acetaldehyde and methyl formate are difficult to remove from propene oxide by simple distillation. In mixtures containing 98 mol-% or more propene oxide, these compounds have essentially the same volatility as propene oxide. Therefore, distillative purification for low levels of methanol, acetaldehyde and methyl formate can not be realized through conventional distillation.

Several methods have been developed to remove methanol, acetaldehyde and methyl formate from propene oxide by extractive distillation, but most have the disadvantage of requiring multiple distillation columns to provide high purity propene oxide.

WO 2004/048355 discloses that compounds containing unsubstituted NH ₂ groups are removed from the crude propene oxide in methanol and acetic acid in a single distillation column by extractive distillation, which is additionally fed at the feed point or at the feed point of the crude propene oxide A process for removing aldehydes is disclosed. The process provides high purity propene oxide suitable for preparing polyether polyols.

The inventors of the present invention have found that modifying the method of WO 2004/048355 by using water as the extraction solvent and recovering the second propane oxide from the extractive distillation column on the feed point of the extraction solvent makes it possible to produce 1,2- And also reduces the energy consumption and equipment size of the propene oxide tablets.

Therefore, the present invention relates to a process for purifying propene oxide, said process comprising:

a) Feeding a crude propene oxide comprising 15 to 97% by weight of propene oxide, 2 to 84% by weight of methanol and acetaldehyde to the feed point A in a central section of the extractive distillation column;

b) Feeding an aqueous extraction solvent to feed point B of said extractive distillation column located above feed point A;

c) i) At feed point B,

ii) At supply point A, or

iii) At feed point C between feed point A and feed point B

The above-mentioned extractive distillation column was charged with the reactive compound of the structural formula (I)

^{(I) R 1 -Y-NH} 2

Or comprising the steps of: supplying a reactive salt of a compound of formula (I), where Y is oxygen or a NR ^2, independent of each other R ¹ and R ² are hydrogen, an alkyl group or aryl group, wherein said supply;

d) Withdrawing stream S1 from the top of said extractive distillation column to provide a first propene oxide product; And

e) And withdrawing stream S2 from the extractive distillation column at a withdrawal point located at a theoretical separation stage of 5 to 25 on feed point B to provide a second propene oxide product.

Figure 1 shows an embodiment of the present invention in which a reactive compound is fed to an extractive distillation column and mixed with an aqueous extraction solvent.

The process of the present invention for purifying propene oxide is carried out in an extractive distillation column. The extractive distillation column may be a tray column including a separate tray such as a sieve tray or a bubble cap tray. The extractive distillation column may also be a packing column, or both structured packing such as metal gauze packing as well as random packing may be used. The extractive distillation column may also combine sections with separate trays and sections with packings. The extractive distillation column will also generally comprise at least one overhead condenser and at least one column reboiler.

The extractive distillation column has at least two feed points, a feed point A for feeding the crude propene oxide in the central section of the extractive distillation column and a feed point B for feeding the aqueous extraction solvent located above feed point A . The feed point comprises three sections of the extractive distillation column, a stripping section between the column bottom and feed point A, an extraction section between feed point A and feed point B, and a rectification section between the feed point B and the top of the extractive distillation column And Preferably, a distillation column having a separation efficiency of 10 to 30 theoretical stages in the stripping section, a separation efficiency of the theoretical stages of 15 to 40 in the extraction section and a separation efficiency of 20 to 60 theoretical stages in the rectification section is used, Feed point B is preferably located in the theoretical separation stage of 15 to 40 on feed point A and in the theoretical separation stage of 20 to 60 below the top of the extractive distillation column.

The crude propene oxide comprising 15 to 97% by weight of propene oxide, 2 to 84% by weight of methanol, and acetaldehyde is fed to feed point A of the extractive distillation column. The crude propene oxide preferably comprises 4 to 4000 ppm by weight of acetaldehyde. The crude propene oxide can also be reacted with other aldehydes and ketones such as formaldehyde, propionaldehyde and acetone, as well as acetals of such aldehydes with methanol or 1,2-propanediol, such as dimethoxymethane, 1,1-dimethoxy Ethane, 1,1-dimethoxypropane, 4-methyl-1,3-dioxolane, 2,4-dimethyl-1,3-dioxolane and 2-ethyl- You may. The crude propene oxide may also include additional solvents such as ethanol or water.

The crude propene oxide is preferably provided by an epoxidation reaction in which propene is epoxidized in a methanol solvent using a titanium zeolite containing titanium atoms in the silicon lattice position. Preferably, a titanium silicalite catalyst is used which preferably has an MFI or MEL crystal structure. Most preferably, a titanium silicalite 1 catalyst having an MFI structure as known from EP 0 100 119 A1 is used. The titanium silicalite catalysts are preferably used as catalysts molded in the form of granules, extrudates or molded bodies. For the molding process, the catalyst may contain from 1 to 99% binder or coating material, and all binder and coating materials that do not react with propene oxide or with hydrogen peroxide under the reaction conditions used for epoxidation are suitable, Silica is preferred as the binder. An extrudate with a diameter of 1 to 5 mm is preferably used as the fixed bed catalyst. The methanol solvent may be an industrial methanol, a solvent stream recovered during the post-treatment of the epoxidation-reactive compound, or a mixture of both.

The epoxidation reaction is preferably carried out at a temperature of from 20 to 80 DEG C, more preferably from 25 to 60 DEG C and at a pressure of from 1.9 to 5.0 MPa, more preferably from 2.1 to 3.6 MPa and most preferably from 2.4 to 2.8 MPa do. Propene is preferably present in an excess amount relative to hydrogen peroxide, preferably in a ratio of from 1.1: 1 to 30: 1, more preferably from 2: 1 to 10: 1 and most preferably from 3: 1 to 5: It is used as the initial molar ratio of hydrogen peroxide. Propene is preferably used in an excess amount sufficient to maintain additional propene-rich liquid phase throughout the reaction. The use of an excess of propene provides high selectivity to propene oxide while providing high reaction rates and hydrogen peroxide conversion. The propene may preferably comprise propane in a mass ratio of the combined amount of propane to propane to propane of preferably 0.07 to 0.20, more preferably 0.10 to 0.15.

Hydrogen peroxide can be used as an aqueous solution preferably containing 30 to 75% by weight and most preferably 40 to 70% by weight of hydrogen peroxide.

The epoxidation reaction is preferably carried out with the addition of ammonia to improve propene oxide selectivity as disclosed in EP 0 230 949 A2. Ammonia is preferably added in an amount of 100 to 3000 ppm based on the weight of the hydrogen peroxide.

The epoxidation reaction is preferably carried out continuously in a fixed-bed reactor by excluding the mixture comprising propene, hydrogen peroxide and methanol in the fixed bed comprising a shaped titanium silicalite catalyst. The fixed bed reactor preferably has cooling means and is cooled with liquid cooling medium. The temperature profile in this reactor is preferably maintained such that the cooling medium temperature of the cooling means is at least 40 占 폚 and the maximum temperature in the fixation layer is at most 60 占 폚, preferably 55 占 폚. The epoxidation-reactive compound is preferably passed through the catalyst bed in downflow mode at a superficial velocity of preferably 1 to 100 m / h, more preferably 5 to 50 m / h, most preferably 5 to 30 m / h Is passed. The superficial velocity is defined as the ratio of the volume flow rate / cross section of the catalyst layer. In addition, it is preferred to pass the reactive compound through the catalyst bed at a liquid hourly space velocity (LHSV) of 1 to 20 h ^-1 , preferably of 1.3 to 15 h ^-1 . It is particularly preferred to keep the catalyst layer in a trickle bed state during the epoxidation reaction. Suitable conditions for maintaining the state of the tricle layer during the epoxidation reaction are disclosed in WO 02/085873, page 8, line 23 to page 9, line 15. The methanol solvent is preferably used in the epoxidation at a weight ratio of 0.5 to 20 to the amount of aqueous hydrogen peroxide solvent. The amount of catalyst used may vary within wide limits and is preferably selected such that the hydrogen peroxide consumption in excess of 90%, preferably in excess of 95%, is achieved within 1 minute to 5 hours under the epoxidation reaction conditions employed. Most preferably, the epoxidation reaction is carried out using an excess of propene, which provides a reactive compound comprising two liquid phases, a methanol rich phase and a propene-rich liquid phase, at a pressure close to the vapor pressure of propene at the reaction temperature, Lt; RTI ID = 0.0 > fixed < / RTI > Two or more fixed bed reactors may be operated in parallel or in series so that the epoxidation process can be continuously operated upon regenerating the epoxidation catalyst. The regeneration of the epoxidation catalyst can be carried out by calcination, by treatment with a heated gas, preferably an oxygen-containing gas, or by solvent washing, preferably by periodic regeneration, as described in WO 2005/000827.

The unreacted propene may preferably be separated from the reactive compound of the epoxidation reaction by distillation in a flash evaporator or by depressurization. Preferably, the unreacted propene is separated by reduced pressure to a pressure of 0.16 to 0.30 MPa.

The liquid mixture remaining after depressurization is preferably separated by distillation in a preliminary separation column to provide an overhead product comprising propene oxide, methanol and residual propene and a bottom product comprising methanol, water and unreacted hydrogen peroxide do. The pre-separation column is preferably operated to provide an overhead product comprising 20-60% methanol contained in the liquid phase after depressurization. The pre-separation column preferably has theoretical separation stages of 5 to 20 theoretical separation stages in the stripping section and less than 3 theoretical separation stages in the rectification section, and most preferably to minimize the residence time of propene oxide in the pre- It operates without a rectifying section and without reflux. The pre-separation column is preferably operated at a pressure of 0.16 to 0.3 MPa. Propene oxide and methanol are condensed from the overhead product of the pre-separation column and propene is stripped from the final condensate in a propene stripping column, which preferably provides the crude propene oxide as a bottom stream.

In the process of the invention for purifying propene oxide, the aqueous extraction solvent is fed to feed point B of the extractive distillation column. The aqueous extraction solvent preferably comprises greater than 80 weight percent water, more preferably greater than 90 weight percent water. Preferably, the aqueous extraction solvent does not contain any additional solvent other than water. The extraction solvent is preferably supplied in an amount that provides a mass ratio of the extraction solvent to the amount of methanol contained in the crude propene oxide feed of from 0.01 to 1, more preferably from 0.03 to 0.2. The use of this amount of aqueous extraction solvent provides effective extraction of methanol with propene oxide product with low content of methanol while at the same time avoiding the hydrolysis of propene oxide in the extractive distillation column.

In addition to the aqueous extraction solvent, the reactive compound of formula (I) is fed to an extractive distillation column,

^{(I) R 1 -Y-NH} 2

Where Y is oxygen or NR ^2, independently of R ¹ and R ² each is hydrogen, an alkyl group or an aryl group. Alternatively, a salt of the compound of formula (I) may be supplied. The reactive compound is preferably hydrazine, hydrazine hydrate or hydrazinium salt. The reactive compound of formula (I) reacts with the carbonyl compound under the extractive distillation conditions to yield high-hydrazone, oxime or oxime ether. The amount of reactive compound fed to the distillation column is preferably selected such that the molar ratio of reactive compound to acetaldehyde is 0.5 to 2. [ The use of such amounts of the reactive compound of formula (I) provides an effective conversion of the carbonyl compound to the higher boiling compound and also provides a propene oxide product with lower amounts of acetaldehyde and other carbonyl compounds. At the same time, by-product formation by reaction of the reactive compound with propene oxide can be maintained at a low level.

The reactive compound may be fed to the extractive distillation column at feed point B, at feed point A, or at a further feed point C between feed point A and feed point B. [ Preferably, the reactive compound is fed to an extractive distillation column at feed point B and mixed with an aqueous extraction solvent.

In a process of the present invention for purifying propene oxide, stream S1 is withdrawn from the top of the extractive distillation column to provide a first propene oxide product and stream S2 is withdrawn from the top of the extractive distillation column to provide a second propene oxide product, B is withdrawn at the withdrawal point located at the theoretical separation stage of 5 to 25 above. The first propene oxide product drawn as stream S1 from the top of the extractive distillation column has a low content of water and typically contains less than 100 ppm by weight of water. These lower levels of propene oxide with water are suitable for the preparation of polyether polyols which can be used to prepare polyurethanes. The second propene oxide product withdrawn as stream S2 typically contains a high content of water in the range of 500 to 10000 ppm by weight. Propene oxide having a water content in this range is suitable for the production of 1,2-propylene glycol and propylene glycol ether. All of the propene oxide products have low levels of carbonyl compounds and also typically contain less than 50 ppm by weight of acetaldehyde. The mass ratio of stream S1 to stream S2 is preferably 0.5 to 5.0. Stream S2 may be withdrawn as a liquid stream or as a vapor stream and is preferably withdrawn as a vapor stream to provide a higher reflux ratio in the column section above the withdrawal point for stream S2, . The withdrawal of a portion of the propene oxide product as the side stream S2 with a higher content of water significantly reduces the energy consumption of the extractive distillation compared to prior art processes wherein all of the propene oxide product is withdrawn at or near the top of the column .

In a further embodiment of the present invention, the crude propene oxide is mixed with an aqueous alkali solution and the final mixture is reacted at a temperature of 20-100 ° C for 1-60 minutes before the mixture is fed to the feed point A. The aqueous alkali solution is preferably an aqueous solution of sodium hydroxide, potassium hydroxide, or sodium carbonate. Most preferably from 0.1 to 56% by weight of sodium hydroxide. The amount of aqueous alkali solution is preferably selected such that the molar ratio of hydroxide ions introduced into the aqueous alkali solution to the amount of methyl formate contained in the crude propene oxide is 1.1 to 4. [ Reaction of the crude propene oxide with an aqueous alkali solution converts it to methanol and formate by hydrolyzing the methyl formate contained in the crude propene oxide. The purified propene oxide obtained in this embodiment of the present invention has a reduced amount of methyl formate. Preferably, the amount of aqueous alkaline solution is selected to obtain a purified propene oxide having a content of methyl formate of less than 100 ppm by weight.

Figure 1 shows an embodiment of the present invention in which a reactive compound is fed to an extractive distillation column, mixed with an aqueous extraction solvent, and stream S2 is withdrawn as a vapor stream. The extractive distillation column 1 has a feed point A 3 at which the crude propene oxide 2 is fed and a feed point B 5 at which the reactive compound is fed and mixed with the aqueous extraction solvent 4. The extraction section between the feed point A and the feed point B comprises a tray, while the stripping section and the rectification section comprise column packing. Stream S1 (6) is withdrawn from the top of the extractive distillation column and provides a first propene oxide product with a lower content of water, and stream S2 (7) is a second propene oxide product with a higher content of water Is extracted from the extractive distillation column at withdrawal point (8) located in the 5 to 25 theoretical separation stages above feed point B to provide < RTI ID = 0.0 > Stream S2 is withdrawn as a vapor stream and condensed outside the column in a condenser not shown.

Example

The energy consumption of the column reboiler was determined using a stream of 2000 kg / h of water containing 0.5% by weight hydrazine as a reactive compound and an aqueous extraction solvent to yield 49% by weight of propene oxide, 46% by weight of methanol, and 400% ppm AspenPlus for the purification of a 25830 kg / h crude propene oxide stream containing acetaldehyde. The calculations operate at 0.13 MPa and in the rectifying section with 14 theoretical stages in the stripping section, 25 theoretical stages in the extraction section, and a draw point for stream S2 (15) at 15 theoretical stages above feed point B, Lt; RTI ID = 0.0 > distillation < / RTI >

In Example 1 not according to the invention, stream S2 is not withdrawn and all of the propene oxide product is withdrawn from the top of the column. A stream S1 of 12500 kg / h of propene oxide containing 80 ppm by weight of water is obtained at the top of the column. The energy consumption of the column reboiler is 7.32 MW.

In Example 2 according to the present invention, a stream S2 of 5000 kg / h of propene oxide containing 2000 ppm by weight of water is withdrawn at the withdrawal point for stream S2 and is withdrawn at a withdrawal point of 7500 kg / h Of propene oxide stream S1 is withdrawn from the top of the column. In this case, the energy consumption of the column reboiler is 5.23 MW, i.e. 29% lower than in Example 1. [

1 extract distillation column
2 crude propene oxide
3 Supply point A
4 Reactive compound mixed with aqueous extraction solvent
5 Supply point B
6 stream S1
7 stream S2

Claims (11)

As a process for purifying propene oxide,
a) adding to the feed point A (3) in the central section of the extractive distillation column (1) a crude propene oxide (2) containing 15-97% by weight of propene oxide, 2-84% by weight of methanol and acetaldehyde );
b) feeding aqueous extraction solvent (4) to feed point B (5) of said extractive distillation column located above feed point A;
c) i) at feed point B,
ii) at the point of supply A, or
iii) at feed point C between feed point A and feed point B
The above-mentioned extractive distillation column was charged with the reactive compound of the structural formula (I)
^{(I) R 1 -Y-NH} 2
Or comprising the steps of: supplying a compound of salt of formula (I), where Y is oxygen or a NR ^2, independent of each other R ¹ and R ² are hydrogen, an alkyl group or aryl group, wherein said supply;
d) withdrawing stream S1 (6) from the top of said extractive distillation column to provide a first propene oxide product; And
e) withdrawing stream S2 (7) from said extractive distillation column at a withdrawal point (8) located in the theoretical separation stage of 5 to 25 on feed point B to provide a second propene oxide product
≪ / RTI > a process for purifying propene oxide. The method according to claim 1,
Wherein the reactive compound is hydrazine, hydrazine hydrate or hydrazinium salt. 3. The method according to claim 1 or 2,
Wherein the reactive compound is fed to the extractive distillation column at feed point B and is mixed with the aqueous extraction solvent. 4. The method according to any one of claims 1 to 3,
Wherein the crude propene oxide comprises 4 to 4000 ppm by weight of acetaldehyde. 5. The method according to any one of claims 1 to 4,
Wherein the molar ratio of reactive compound to acetaldehyde is 0.5 to 2. 6. The method according to any one of claims 1 to 5,
And stream S2 is withdrawn as a vapor stream. 7. The method according to any one of claims 1 to 6,
A process for purifying propene oxide wherein the mass ratio of stream S1 to stream S2 is 0.5 to 5.0. 8. The method according to any one of claims 1 to 7,
A process for purifying propene oxide, wherein the mass ratio of the extraction solvent supplied to the amount of methanol contained in the crude propene oxide fed is from 0.01 to 1. 9. The method according to any one of claims 1 to 8,
And feed point B is located in the theoretical separation stage of from 15 to 40 on feed point A, for the purification of propene oxide. 10. The method according to any one of claims 1 to 9,
And feed point B is located in the theoretical separation stage of 20 to 60 below the top of the extractive distillation column. 11. The method according to any one of claims 1 to 10,
Wherein the crude propene oxide is mixed with an aqueous alkali solution and the final mixture is reacted for 1 to 60 minutes at a temperature of 20 to 100 DEG C before the mixture is fed to the feed point A, .

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