DE1668234C3 - Continuous process for the production of propylene oxide - Google Patents

Description

The subject of the invention is that in the claim marked procedures.

From BE-PS 6 63 859. 6 65 082 and 6 44 090 is a process for the epoxidation of olefins in the presence known catalytically effective amounts of metal. According to the described in these patents. procedure can Epoxydc from the olefinic starting materials jrι high yields, d. H. with only small amounts undesirable by-products are produced. One or more of the metals are used as catalysts Titanium, vanadium. Chromium, columbium, selenium, zirconium. Niobium. Mo'vbdän, tellurium. Tantalum, tungsten. Rhenium and Uranium used. These are vanadium, tungsten. Molybdenum. Titanium and selenium preferred. The catalyst metals can be used in conjunction with alkaline or basic substances, for example alkali or Alkaline earth compounds are used.

The catalyst metals are preferably introduced into the reaction either in a finely divided metallic state or in the form of their compounds. Vorteilha- ^'1 are organometallic compounds of genaniiien metals such as naphthenates, Stearale, O.'tanoate, chelates, addition compounds and Enoisalze (for example Acctoacetonate) and azoxy compounds. Inorganic .. 'forms, for example the Owde (in the Irish case of molybdenum, for example MO2OJ, MuO. And MOO3), acids (for example molybdic acid). Chlorides, oxychlorides. Fluorides, bromides, phosphates, sulfides. 1 ie'.eropoljiiiiiren {'. For example Phosphorniui', ixiar.liiiiv and the ·. '· Aikalisnize) and the like. that w :: iii ^ stL '!: -, O ₁ OOiXi Mo: metal ) v- ■ moles of organic hydroperoxide present in the reaction mixture.Amounts of metal as high as 0.1 mole per organic hydroperoxide or even higher amounts can be used .
As indicated in the above-mentioned Belgian patents, the olefin is epoxidized to the corresponding oxirane derivative during the epoxidation reaction, and the organic hydroperoxide is converted into the corresponding alcohol. Expedient

Lu ge reaction conditions are reaction temperatures between about 0 and 200 ⁰ C, reaction pressures that are sufficient to maintain a liquid phase, molar ratios of olefin to organic hydroperoxide in the reaction between about 1: 1 and 20: 1 and reaction times that are normally about 10 minutes 10 hours.

The conversion described above is strongly exothermic (About 60,000 calories of heat are released per gramole of the epoxy produced in the main reaction.

21) sets). This heat of reaction is expediently removed from the reactor practically just as quickly as it is released. It is an advantage of the invention that this highly exothermic reaction heat easily removed wi ^r d. As a result, it will be sustaining

> ■> a precise reaction temperature control facilitated. The precise temperature control achieved by the measures according to the invention leads in turn to improved process yields.

The selectivities that occur in the epoxidation process

j (i ren, as described above, are achieved although high, part of the desired epoxy product. that is formed during the implementation, however, works lost, apparently partly through reaction with the organic hy-

r> droperoxide. It is believed that this implementation for the formation of hydroxyalkyl peroxides, d. H. R —O —O R'— OH leads, where R denotes the organic The remainder of the organic hydroperoxide and R 'denotes an organic residue that corresponds to the olefin used

■ ίο corresponds. According to the invention, side reactions, w ^; e they were indicated above, severely restricted, whereby an increase in the yield of propylene oxide is advantageously achieved.
It has now been found that the temperature control with the result of improved yields is facilitated by carrying out the oxidation reactions of the type described above under autogenous pressure and at a reaction temperature which is necessary for the evaporation of part of the liquid phase.

) (i is sufficient for the reaction medium. The expression »autogenic Pressure, as used herein, denotes the boiling point pressure of the liquid reaction medium at the reaction temperature. Aside from the improved control of the reaction temperature, the

ν. is achieved by the measures according to the invention, they offer the additional advantage that the heat of reaction in many cases by indirect heat exchange in devices made of carbon steels instead of alloyed steels (for example corrosion-resistant

hti steel) that would otherwise be required can.

For the claimed process suitable organic hydroperoxides having the formula ROOH wherein R is an organic Re, with 1 i - 20 carbon atoms.

h "> possibly a substituted or uiisubstituie s Alkyl, cycloalkyl, aralkyresiiet.

Exemplary and preferred hydroperoxides are Cumol Ii yil ίο perox yd, Äthvlbenzolhydroperoxvd, tert.-

Butyl hydroperoxide, cyclohexanone peroxide, methyl ethyl ketone peroxide as well as the hydroperoxides of toluene, p-ethyltoluene, isobutylbenzene, diisopropylberizol, p-isopropyltoluene, o-xylene, m-xylene, p-xylene, phenylcyclohexane. Particularly preferred organic hydroperoxides are ethylbenzene hydroperoxide (alpha-phenylethyl hydroperoxide), tert-Bu'yl hydroperoxide and cyclohexanone peroxide.

The epoxidation reaction is carried out in the presence of a solvent. Suitable solvents are the aliphatic and aromatic or naphthenic hydrocarbons or their oxygen-containing derivatives. Preferably the solvent! the same carbon structure as the hydroperoxide used in order to reduce or avoid separation difficulties during product recovery. the Mixtures of solvents can also be used, and in fact are commonly used. For example, a mixture of ethylbenzene and alpha-phenylethanol is particularly useful as a solvent preferred when ethylbenzene hydroperoxide is used as the epoxidizing agent.

In the inventive process, reaction temperatures between about 90 and 200 ° C and in particular between about 90 and 150 ⁰ C are used. It is essential to the invention that the reaction is carried out under autogenous pressure in each case. It is also essential that reactor conditions are chosen such that the reaction medium is kept in the liquid phase, since the epoxidation is a liquid phase reaction. In the process according to the invention, the reaction medium present in the liquid phase in the reactor is therefore a boiling liquid. The actual reaction pressure therefore depends on the type of solvent, the type of organic hydroperoxide and the propylene concentration. The autogenous pressures of the systems used, ie the reaction pressures / between about atmospheric pressure and 63 atmospheres, are extremely high. In a preferred embodiment of the process according to the invention, in which propylene oxide is produced by epoxidation of propylene with ethylbenzene hydroperoxide as a novovdant, reaction pressures between about 14 and 49 atmospheres occur depending on the propylene concentration in the reaction medium and the reaction temperature chosen. Inert substances, e.g. Athane, propane and the like, if present in the reactor, can also affect the reaction pressure.

The reaction temperature and feed composition in the present process are selected to allow evaporation of at least ¹ atom of the propylene oxide or more, and preferably so as to allow evaporation of a third or more of the propylene oxide, easily achieved within the temperature ranges given above can be. The feed to the epoxidation reactor in this procedure contains 10 to 80 mol% olefin, 1 to 60 mol% hydroperoxide and the remainder of the feed mainly solvent. Small amounts of other materials may also be present in the feed to the epoxidation reactor.

As mentioned above, the epoxidation reaction is strongly exothermic. By evaporation of the propylene oxide and others in the reaction medium existing substances will be there; a considerable proportion, and in some cases all of the response heat is effectively consumed, allowing precise control of the reactor temperature during the poxidation is made possible. If there is even greater evaporation of the reaction medium (including the desired epoxy product) is desired, can the epoxy reaction in a known manner, for example with the help of heating coils located in the reactor are located, additional heat must be supplied. Alternatively, excess heat of reaction can be advantageous, in a known manner, for example with the aid of cooling coils within the epoxidation reactor if evaporation of minor amounts of the reaction medium including the Propylene oxide is desired.

The material that is evaporated while the epoxidation reaction is carried out therefore preferably contains ¹ Zj or more of the propylene oxide, a considerable amount of unreacted olefin, part of the solvent used for the reaction and part of the alcohol which is produced as a result of the reaction in the organic hydroperoxide used in the reaction is formed (and can be identical to the solvent). If the organic hydroperoxides have high partial pressures in the system, the vapor stream may also contain some organic hydroperoxide. This vapor stream is withdrawn from the reactor and worked up to recover unconverted olefin, which is advantageously returned to the epoxidation, and to recover the evaporated propylene oxide. This separation can easily be carried out in a known manner, for example by distillation processes. If this vapor stream contains considerable amounts of organic hydrogen peroxide, the hydroperoxide is preferably removed before the unreacted olefin and propylene oxide are separated off and recovered, since otherwise the relatively unstable evaporated hydroperoxide can decompose and cause yield losses.

In the drawing, an epoxidation reactor 10 is provided with an inlet line 11. Organic hydroperoxide, expedient »-.ise Äthylbenzolhvdroper oxide and catalyst, advantageously a molybdenum catalyst, e.g. B. in the form of naphthenate the reactor 10 via the line 12 and the line 11 connected thereto. A suitable one Solvent for the reaction, e.g. B. a mixture of ethylbenzene and alpha-phenylethanol is also introduced into the reactor via line 12. Fresh propylene is the reactor 10 via line 13 and the line 11 connected thereto is supplied. Cyclic propylene, which in a manner to be described is obtained, is supplied via the line 36 and the line 13 connected thereto.

The reactor 10 is a reaction vessel, the interior of which is divided into a number of compartments 16 by internals 55. Alternatively, one or more of these compartments can be a separate reaction vessel. The subdivision of the reactor either by internals or by several reaction vessels connected in series makes it possible to prevent undesired backmixing of reaction products . \: dei: entering /. Respondent no. / u »crüii ' ¹ " - "

Inside each of the compartments 16 of the ^ reactor 10 there is one that is in a flowing phase Reaction medium 17. the dissolving pesminel. πΉίπιττη'ρ-

Selztcs hydrop " ^r oxide, non-mixed olefin. Propylene and organic alcohol formed during the reaction of the hydroperoxide with the olefin enihüli. (In many cases the organic alcohol formed during the reaction of the hydroperoxide is with the solvent""" table.)

This is done in the liquid phase of the invention reaction medium located under its autogenous pressure and therefore partially evaporated when the reaction proceeds, d. H. if the reaction gel - .. lisch boils. The heat required for this evaporation is supplied by the heat of reaction. This evaporated portion of the reaction medium is in the embodiment shown in the drawing from the Reakior OK withdrawn via the IS line and to the zone 30 headed.

In operation of the reactor 10, the reactants enter compartment 16a and accumulate therein until the level of the liquid phase in compartment 16a exceeds the level of the inner partition (or weir) 15a. The liquid reaction medium then flows via the partition wall 15a in the compartment 16h In the same manner, the liquid reaction medium enters successively into the compartments 16c and 16e XSd and finally exits via the line 19 from the reactor 10 degrees. The liquid reactor effluent is then passed via line 19 to fractionation zone 30. If desired, the circulating propylene can with the help of the lines 40a. 40b, 40c, 40d and 40e are distributed to some or all of the compartments of the reactor in order to maintain a constant concentration of propylene in each compartment by replacing that portion which is volatilized.

The vaporized reaction medium flows to the fractionation zone 30. In the fractionation zone 30, this vaporized medium and the liquid reaction mixture, which is withdrawn from the epoxidation reactor 10 via line 19, are worked up to obtain unreacted propylene and a mixture which contains propylene oxide and ethylbenzene as a solvent and alpha-phenylethanol and the alpha-phenylethanol formed as a result of the reaction of ethyibenzene hydroperoxide with propylene. The fractionation zone 50 is preferably designed and operated so that the bottom temperatures are kept therein at sufficiently low values to restrict a decomposition of propylene oxide to a minimum, ie below 160 ° C and preferably at or below! 30 ⁰ C. The thus recovered propylene is withdrawn from fractionation zone 30 via line 36 and returned to the epoxidation zone. The product mixture is withdrawn from fractionation zone 30 via line 37. In the fractionation zone 30, means for separating and removing inert substances from the system can be provided in order to prevent their accumulation.

The fractionation zone 30 thus acts as a propylene separation system. Since the construction of such Apparatus is of conventional type, and since the structure and operation of such apparatus are known, they are Devices that are connected to the fractionation zone 30 are not shown in the drawing.

The fractionation zone 30 can often consist of two columns or columns connected in series with the columns connected therewith. crbur.denen heat exchangers, pumps and the like exist. In such a system, the pressure in the first column is high enough to allow condensation of the overhead propylene with cooling water, while the sump eb'M'ifaüs enough prop, 'cn (and of course Pnjp \! En oxide A' Kyibenzoi and uiph-> Phenyläthanoi) contains ι "enable Sumpfteiiiperauir innenV ^ iH samples angegebuici G ^r Enzen / m, tune such eiuhä column), for example 12 theoretical vapor-liquid Kuii stepper π d works with a Rückflußverh.älüii (Mo! ! Reflux p '.' J Nioi! Cracked passing: "N ei to product)" .on 0.3: i. Compression temperatures and pressures prior to 5TC or 4.85 atmospheric are suitable

"i while the suitable bottom temperatures unc -arucke! ^ü be 30 C or 25.20 Atmosphäi s.

The second column expediently operates at a lower pressure and is used to remove the residual amount of propylene from the propylene oxide

i) Äthvibenzoi-aipha-Fnenyiäthanoi mixture used 7u g.:eig:::ien Detriebsbedingungen for this / wine column include an overhead temperature of - 25 ^l unc C a head pressure of 2.24 atmospheres and eini Sumpftemperaiur of iiO C and a Sumpfdnek voi

2ii 2.59 atmospheres. Such a column contains expediently 15 theoretical vapor-liquid con tact levels and works with 0.6 mol of liquid reflux per mole of feed entering the column Because of the low head temperature, the second column vapor compression and / or cooling devices to condense propylene zi enable. The bottom from the second column of such a system is practically propylene-free Mixture containing propylene oxide, ethylbenzene and alpha

jci contains phenylethanol.

The following example illustrates the invention. Divides and percentages refer to moles of who nothing else is stated.

example

A continuous epoxidation test is carried out in a device as shown in the drawing is shown schematically. Details of the devices are given in conjunction with the following explanations tion of epoxidation, as far as it is for there; Understanding are required.

Ethyibenzene hydroperoxide and ethylbenzene unc alpha-phenylethanol as solvents are introduced into the reaction vessel in an amount of 5.86 parts per hour. Molybdenum catalyst is also included in this stream in such an amount that Tt parts by weight / million molybdenum is present in the total reaction charge. The composition of this stream is given in the first column of the table below. The reactor is also fed 15.81 parts / hour of propylene, 0.79 parts / hour of fresh propylene and 15.02 parts / hour of recycle propylene. The circulating propylene is distributed to the various compartments in order to keep the temperature constant. For the sake of completeness, the table shows the compositions of these streams in the second and third columns.

The reactor in which the epoxidation takes place is divided into 5 compartments of this size by internal partitions divided so that the total residence time of the liquid reaction medium in all compartments is about 11 minutes amounts to. The partition walls are arranged so that the liquid reaction medium is sequentially from compartment to Compartment flows and is withdrawn from the reactor after the fifth compartment. There is also a in each compartment

Steam room provided. The steam rooms of the Abieile are not separated from each other, i. H. They stand in connection with each other.

The epoxidation reactor is operated at a temperature of 132 ° C and under the autogenous pressure of the System, in this case held at 26.25 atmospheres.

During the course of the reaction, 11.21 parts / hour of the liquid reaction medium are evaporated and withdrawn from the reactor as vapor. The composition of this vapor is in the fourth Column of the table. Furthermore, 10.46 parts / hour of liquid reaction medium with the in the Fifth column of the table given composition withdrawn from the reactor.

The vapors withdrawn from the reactor are used to recover unreacted propylene for the Recirculation and of propylene oxide in a mixture with alpha-phenylethanol and ethylbenzene as a product fractionated. This separation is carried out in the conventional distillation apparatus referred to as column 30. In this distillation device, the reaction medium present in the liquid phase, the is withdrawn from the reactor as described above, processed. The ice propylene amounts to 15.02 Parts / hour and has the composition given in the sixth column of the table. The bottom product from this distillation amounts to 6.65 parts / hour and has that in the seventh column of the Table given composition. During this distillation, the bottom temperature is controlled so that

Tabel

Composition of the flows (Mo! -%)

that it does not exceed about 130 ⁰ C. The bottom product <from this distillation can then be used in a known manner to obtain propylene oxide in high purity in subsequent facilities, e.g. B. Distillation devices are processed.

It should be noted that in this example the selectivity to propylene oxide based on the total, Hydroperoxide reacted in the reactor is 75 mol%. In contrast, in a control experiment, in which the reactor pressure is maintained at a value above the autogenous pressure of the system, d. H. in which there is no evaporation of the reaction medium, a considerably lower selectivity achieved.

! ■ ϊ D «s procedure described above through which the advantages according to the invention are achieved can of course be modified within the scope of the invention will. For example, in a multi-zone reactor, the temperature in all zones can be the same or

: n change from zone to zone. It is sometimes It is advisable to use slightly higher temperatures in the last zones in order to achieve a more complete Ensure implementation at the lower reactant concentrations. Furthermore, in each Adequate mixing takes place in the zone. Suitable mixing can be achieved through the boiling effect, by mechanical stirring, by suitable distribution of the substances supplied to the zones Can be achieved by pumping or by combinations of these measures.

component

(1)

(2)

Epoxidation fresh
medium oil ^b )

medium ^a )

Propylene

Propylene oxide

alpha-phenylethanol

Ethylbenzene
Ethylbenzene hydro

peroxide
High boiling ^c )

100.0

3.1

79.8

17.1

(3) (4) (5) (6) (7) Circulatory Withdrawn Withdrawn Circulatory product O.efin ^b ) steam liquid propylene ^b ) mixture ³ ) iOO.O. 96.1 40.61 100.0 2.70 3.89 10.71 (75 ppm; 8.53 13.42 molar) 1.20 43.46 70.35 (5 ppm; 0.48 0.75 molar)

3.03

4.77

100.0

100.0

100.0

100.0

100.0

100.0

Grades:

^a ) Without a catalyst.

^b ) Without inert substances, e.g. B. propane, ethane, nitrogen, carbon dioxide, etc.

^c ) High-boiling reaction by-products.

1 sheet of drawings

Claims (1)

Claim: A continuous process for producing propylene oxide by reacting from 10 to 80 mol% of propylene with 1 to 60 MOI ^ü / b of a Organohydroperoxids the formula ROOH, where R is alkyl, cycloalkyl or aralkyl having from 3 is to 20 carbon atoms, in the presence of a Metallepoxidierungskatalysators of the metals titanium, vanadium, chromium, selenium. Zircon, niobium, molybdenum, tellurium, tantalum, tungsten, rhenium and uranium in the liquid phase in the presence of a solvent in a reactor at temperatures of about 90 to 200 ° C and under autogenous pressure and with boiling of the liquid phase reaction medium, characterized in that one at least ^{1 A of the 1} part of the liquid phase reaction medium containing propylenoxicis formed during the reaction is evaporated and discharged from the reactor as vapor, the remaining liquid bottom product also being withdrawn from the reactor, from the evaporated part and the liquid bottom product in a manner known per se by fractional distillation separating propylene at a ^{temperature below 160 °} C. and working up the remaining mixture of propylene oxide, solvent and alcohol, which corresponds to the Oiganohydroperoxid used, to obtain pure propylene oxide and optionally the other constituents by distillation.