GB2332430A

GB2332430A - Preparation of olefin oxides

Info

Publication number: GB2332430A
Application number: GB9727118A
Authority: GB
Inventors: Joerg Lindner; Wolfgang Taeuber; Hans-Juergen Wergen
Original assignee: Dow Deutschland Inc
Current assignee: Dow Deutschland Inc
Priority date: 1997-12-22
Filing date: 1997-12-22
Publication date: 1999-06-23
Also published as: GB9727118D0; EP1042309A1; AU2087499A; WO1999032470A1

Abstract

A liquid phase process for preparing an olefin oxide from an olefin comprising the steps of a) contacting the olefin with oxygen or an oxygen-containing gas in a solvent having a boiling point above 130‹, b) passing the liquid product mixture comprising the olefin oxide, non-converted olefin, solvent and by-products into a first separator wherein a lower pressure is maintained than in the reaction step a) and the product mixture is divided into b1) a gaseous stream (12) containing olefin, carbon dioxide and other volatile products and b2) a liquid stream (13) containing olefin oxide, solvent, olefin, carbon dioxide and other by-products; c) passing the liquid stream (13) into a second separator wherein a lower pressure is maintained than in the first separator in step b) and the stream is divided into c1) a gaseous stream (2) containing olefin, carbon dioxide and other products and c2) a liquid stream (3) containing olefin oxide, solvent, olefin and oxygenated by-products.

Description

2332430 PROCESS FOR THE OXIDATION OF OLEFINS TO OLEFIN OXIDES This

invention pertains to a liquid phase process for the direct oxidation of olefins, such as propylene, by oxygen to olefin oxides, such as propylene oxide.

Olefin oxides, such as propylene oxide, are used to alkoxylate alcohols to form polyether polyols, such as polypropylene polyether polyols, which find significant utility in the manufacture of polyurethanes and synthetic elastomers.

Olefin oxides are also important intermediates in the manufacture of alkylene glycols, such as propylene glycol and dipropylene glycol, and alkanolamines, such as isopropanolamine, which are useful as solvents and surfactants.

Propylene oxide is produced commercially via the well-known chlorohydrin process wherein propylene is reacted with an aqueous solution of chlorine to produce a mixture of propylene chlorohydrins. The chlorohydrins are dehydrochlorinated with an excess of alkali to produce propylene oxide.

Another well-known route to olefin oxides relies on the transfer of an oxygen atom from an organic hydroperoxide or peroxycarboxylic acid to an olefin. In the first step of this oxidation route, a peroxide generator, such as isobutane or acetaldehyde, is autoxidized with oxygen to form a peroxy compound, such as t-butyl hydroperoxide or peracetic acid. compound is used to epoxidize the olefin, typically in the presence of a transition metal catalyst, including titanium, vanadium, molybdenum, and other heavy metal compounds or complexes.

Gas phase processes for the direct oxidation of olefins by molecular oxygen to the corresponding olefin have also been described in several publications.

The former East German patent DD 212 961 discloses a process for the oxidation of olefins containing 3 to 20 carbon atoms with oxygen-containing gases in liquid phase in the 1 presence of transition metal complexes. The catalyst preferably is a mixture of a Cu(II) complex compound and a complex compound of molybdenum or wolfram. The oxidation is carried out at a temperature of from 20 to 2000C at atmospheric pressure or at an elevated pressure of 2 to 10 MPa. Recommended solvents are benzene, chlorobenzene, o-dichlorobenzene, nitrobenzene or bromobenzene. The desired products are obtained by fractionated distillation of the product mixture. Unfortunately, the patent does not teach how to separate the produced olefin oxide from unconverted raw material, by-products and solvent. However, it is well known in the art that such separation is very complex. Particularly the example given for propylene oxide and using benzene as process solvent would lead to an impractical separation scheme and overall uneconomic process due to the is azeotropic behavior of the mixture.

U.S. patent No. 3,238,229 relates to a process for preparing olefin oxides wherein an olefinically unsaturated hydrocarbon is oxidized with molecular oxygen at a temperature of from 50-4000C and a pressure of from 0.5-150 atmospheres in halogenated benzenes, such as o-dichlorobenzene, as a solvent.

The desired products are recovered from the reactor effluent by conventional separation techniques, such as distillation.

U.S. Patent No. 3,350,418 discloses a liquid phase oxidation of propene with molecular oxygen in an ester, such as a fully esterified polyacyl ester, as a solvent with the following subsequent separation steps: a) the effluent stream of the reaction mixture is passed from a reaction zone through a combination let-down distillation zone which comprises a flashing zone followed by a stripping zone into which the bottoms from said flashing zone is passed; the flashing and stripping zone are maintained at the same temperature as the oxidation reaction, but each successive zone 2 is maintained at pressures substantially lower than in the preceding zone and in the reaction zone to separate substantially all of the low and intermediate boiling products, including propylene oxide, as gas phase from the bulk of the solvent; in steps b) and c) the gas phase is condensed and further treated; in step d) a combined stream of condensed liquids from the condensing zones in step b) and c) is passed into an acid- separation distillation zone where organic acids are removed as bottoms and propylene oxide, propylene, propane, acetaldehyde and methyl formate are distilled overhead; in step e) the overhead from step d) is subjected to a distillation step where propylene and propane are distilled is overhead and propylene oxide, acetaldehyde and methyl formate are removed as bottoms; in step f) acetaldehyde is removed by distillation; and in step g) propylene oxide is separated from methyl formate by extractive distillation using a hydrocarbon solvent.

Unfortunately, this process requires large equipment sizes and high energy consumption, as will be explained in more detail with reference to Fig. 1 of U.S. patent No. 3,350,418. All unconverted propene has to pass the whole separation scheme consisting of flasher and columns 26, 28 and 30 which leads to uneconomical equipment sizes and energy consumption. All recycle propene is evaporated and taken as overhead stream in column 30, so conventional compressors will be needed to recycle the propene. No convenient pressure profile for the separation is applied, so that the overhead stream 27 of column 26 containing all Propene and low boiling products like propylene oxide has to be compressed from 10.5 bar to 21 bar (1.05 to 2.1 MPa) which will result in a large compression unit operation or using of a large amount of refrigeration for liquefying a portion of the stream. Column 29 is stated to operate at 21 bar (2.1 MPa)and 3 C bottom temperature. All propylene oxide and low boiling reaction products has to pass this hot zone where yield losses of propylene oxide will occur due to reaction with other byproducts. Despite this, vent gases, particularly C02, will not be removed using this separation scheme. Most of the C02 will be removed together with propene in stream 25 of the flasher and will accumulate in stream 35 recycle propene, so that the C02 cannot be removed in the absorber 20.

U.S. patent No. 3,071,601 relates to the production of propylene oxide wherein propylene is oxidized with elemental oxygen in the liquid phase in a hydrocarbon solvent at elevated pressure and temperature in the presence of a catalyst. According to the Example, the reactor temperature is about 2000C and the pressure is 750 p.s.i.g. (51.5 bar or 5.15 MPa)). The reaction mixture is fed into a flash tank 13 wherein the temperature and pressure are allowed to drop to 600C and 65 p.s.i.g. (4.5 bar or 0.45 MPa). The non-reacted propylene and highly volatile products pass off and are recycled to the reactor. The liquid material within the flash tank is passed to a distillation column 14 from the top of which there is distilled off propylene oxide and methyl formate. Propylene oxide and methyl formate are fed to a further distillation column wherein methyl formate is taken off overhead by means of an azeotrape-former, such as npentane. The less volatile materials recovered as the still bottoms in the distillation column 14 comprise various acids, non-acidic polymer, benzene diluent and propylene glycol which are separated by a subsequent distillation in a distillation column 17 and an extraction step.

In this distillation step volatile acids and the benzene solvent are recovered overhead. However, in the flash tank 13 all propene is evaporated and has to be recycled, which requires an uneconomically large compression unit. The recycle of propene and highly volatile organics directly to the reactor includes 4 the carry over of formic acid which is detrimental to product selectivity. moreover, the suggested distillation in distillation column 17 wherein volatile acids and the benzene solvent are recovered overhead leads to uneconomical equipment sizes and energy consumption. The benzene also forms undesirable azeotropes, making the separation complex and leading to uneconomic solvent losses.

Considering that the production of olefin oxides, such as propylene oxide, from the corresponding olefin is carried out on very large scale and in view of the disadvantages of the processes of the prior art, it would still be desirable to provide a liquid phase process for preparing an olefin oxide from an olefin which allows an efficient separation of the is products in the product mixture.

Accordingly, the present invention relates to a liquid phase process for preparing an olefin oxide from an olefin comprising the steps of a) contacting the olefin in a solvent having a boiling point above 130' with oxygen or an oxygen-containing gas, b) passing the liquid product mixture comprising olefin oxide, non-converted olefin, solvent and by- products into a first separator wherein a lower pressure is maintained than in the reaction step a) and the product mixture is divided into bi) a gaseous stream (12) containing olefin, carbon dioxide and other volatile products and b2) a liquid stream (13) containing olefin oxide, solvent, olefin, carbon dioxide and other by-products; c) passing the liquid stream (13) into a second separator wherein a lower pressure is maintained than in the first separator in step b) and the stream is divided into cl) a gaseous stream (2 or 17) containing olefin, carbon dioxide and other products and c2) a liquid stream (3 or 16) containing olefin oxide, solvent, olefin and oxygenated by-products.

The flow sheets in Figures 1, 2 and 3 are graphical illustrations of preferred embodiments of the process of the present invention.

Ethylene can be employed in the process of this invention, however the olefin preferably contains three or more carbon atoms. Undiluted olefins or mixtures thereof are preferably used, however also olefin feedstock can be used which contains up to 50 wt.-% of saturated compounds. Monoolefins are preferred, but compounds containing two or more olefins, such as dienes, can also be used. The olefins can be aliphatic or alicyclic. The olefin can be a simple hydrocarbon containing only carbon and hydrogen atoms; or alternatively, the olefin can be substituted at any of the carbon atoms with an inert substituent. The term "inert", as used herein, requires the substituent to be non-reactive in the process of this invention.

Suitable inert substituents include, but are not limited to, halides, ether, ester, alcohol, or aromatic moieties, preferably chlorc, Cl-12-ether, ester, or alcohol moieties or C6-12 aromatic moieties. Non-limiting examples of olefins which are suitable for the process of this invention include propylene, 1 butene, 2-butene, 2-methylpropene, 1-pentene, 2-pentene, 2 methyl-l-butene, 2-methyl-2-butene, 1-hexene, 2-hexene, 3 hexene, and analogously, the various isomers of methylpentene, ethylbutene, heptene, methylhexene, ethylpentene, propylbutene, the octenes, including preferably I-octene, and other higher analogues of these; as well as butadiene, cyclopentadiene, dicyclopentadiene, styrene, a-methylstyrene, divinylbenzene, allyl chloride, allyl alcohol, allyl ether, allyl ethyl ether, allyl butyrate, allyl acetate, allyl benzene, allyl phenyl ether, allyl propyl ether, and allyl anisole. Preferably, the olefin is an unsubstituted or substituted C3-12-olefin, more preferably, an unsubstituted or substituted-C3-8- olefin. Most preferably, the olefin is propylene. Propylene feedstock can be 6 used which contains up to 50 wt.-% propane, however the use of undiluted propylene is preferred. Accordingly, the subsequent detailed description of the present invention often relates to a process wherein propylene is used as a starting material, although the process of the present invention is not limited thereto.

The quantity of olefin employed in the process can vary over a wide range provided that the corresponding olefin oxide is produced. Generally, the quantity of olefin depends upon the specific process features, including, for example, the design of the reactor, the specific olefin, and economic and safety considerations. Those skilled in the art will know how to determine a suitable range of olefin concentrations for the is specific process features. Typically, on a molar basis an excess of olefin is used relative to the oxygen. This condition enhances the selectivity to olefin oxide and minimizes the selectivity to combustion products, such as carbon dioxide. The quantity of the olefin is typically greater than 1, preferably greater than 10, more preferably greater than 20, and most preferably greater than 25 mole percent, based on the total moles of olefin, oxygen and solvent. Typically, the quantity of the olefin is less than 99, preferably less than 85, more preferably, less than 70, and most preferably less than 65 mole percent, based on the total moles of olefin, oxygen and solvent.

The olefin is contacted with oxygen, such as essentially pure molecular oxygen, or an oxygen-containing gas, such as air or oxygen diluted with carbon dioxide. If the olefin is contacted with an oxygen-containing gas, the oxygen concentration in the gas preferably is from 15 to 60 vol.%, more preferably from 20 to 55 vol%. Other sources of oxygen may be suitable, including ozone and nitrogen oxides, such as nitrous oxide. Molecular oxygen or oxygen diluted with carbon dioxide is preferred. The quantity of oxygen employed can vary over a wide range provided that the quantity is sufficient for producing the desired olefin oxide. ordinarily, the number of moles of oxygen 7 per mole of olefin is less than 1. Generally, the quantity of oxygen is greater than 0.01, preferably greater than 1, and more preferably greater than 2 mole percent, based on the total moles of olefin, oxygen, and solvent. Generally, the quantity of oxygen is less than 30, preferably less than 25, more preferably less than 20, and most preferably less than15 mole percent, based on the total moles of olefin, oxygen and solvent.

Step a) of the process of the present invention is carried out in liquid phase in a solvent which has a boiling point above 1301C, at atmospheric pressure preferably above 1500 C, more preferably above 1700C. Preferred solvents are halogenated benzenes, particularly monchalogenated benzenes and, more preferably, dihalogenated benzenes. Exemplary thereof are monobromobenzene, chlorobenzene, o-, m- or p-dibromobenzene, o-, m- or p-bromochlorobenzene, or, most preferably, o-, m- or p-dichlorobenzene. The most preferred solvent for the process of the present invention is odichlorobenzene. Other suitable solvents are polyethers, polyesters, polyalcohols or halogenated, preferably chlorinated, aliphatic alcohols, such as 2-chloro- i-propanol, 3-chloro-i-propanol, 1-bromo-2-propanol, dichloro- or dibromo- propanols, provided that these solvents are liquid at the chosen reaction conditions and have a boiling point above 1300C. The amount of solvent is typically greater than 0.1, preferably, greater than 15, and more preferably greater than 25 mole percent, based on the total moles of olefin, oxygen and solvent. The amount of solvent is typically less than 90, preferably, less than 60, and more preferably, less than 75 mole percent, based on the total moles of olefin, oxygen and solvent.

Step a) of the process of the present invention can be carried out in the absence or in the presence of a catalyst. If a catalyst is used, homogeneous or heterogenous catalysts are useful. Exemplary of heterogeneous catalysts are those 8 disclosed in East German Patent Nos. DD-218,100; DD-213,436; DD218,099; DD-212,959; DD 212,960; DD-212 902; U.S. patent Nos. 3,957,690 and in published PCT application WO 96/20788. The disclosed heterogeneous catalysts contain active components, such as nickel, manganese, molybdenum and/or vanadium containing complexes or salts, on a carrier, such as an alumina, silica, aluminosilicate, titania, magnesia and/or carbon. As homogeneous oxidation catalysts common complexes or salts can be used, for examples those disclosed in U.S. patent Nos.

3,505,359; 3,518,285; or 4,420,625 or in WO 96/37295.

Typical active components of these catalysts are elements of groups Ib, IIb, IIIb, IVb, Vb, VIb, VIIb, IIIa, IVa,Va,VIa, VIII, and/or of the lanthanide group, such as Mo, Mn, Wo, Zn, Re, Au, Pd, Ag, V, Ru, La and/or Ti in any combination and is ratio, but also Sc, Y, Ce, Zr, Nb, Ta, Cr, Fe, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ga, In, Ge, Sn, Se, Te, As, Sb and/or Bi in any combination and ratio with those mentioned above.

Furthermore, step a) of the process of the present invention can be carried out in the absence or in the presence of a promotor. A promotor is for example an aldehyde, like acetaldehyde, or an alkaline additive, like hydroxides of the group la and 1b, such as sodium hydroxide or magnesium hydroxide. The total quantity of promoter metal(s) generally is greater than 0.01, preferably, greater than 0.10, and more preferably, greater than 0.15 weight percent, based on the total weight of the catalyst. The total quantity of promoter metal(s) is generally less than 20, preferably, less than 15, and more preferably less than 10 weight percent, based on the total weight of the catalyst.

Step a) of the process of this invention can be conducted in one or more reactors of any conventional design suitable for liquid phase processes. These designs broadly include batch, fixed-bed, transport bed, fluidized bed, moving bed, shell and tube, and trickle bed reactors, as well as continuous and intermittent flow and swing reactor designs.

9 Preferred reactor types are plug flow reactors, cascades of stirred tank reactors or bubble columns. Cascades of stirred tank reactors preferably contain from 2 to 10, more preferably from 2 to 5 stirred tank reactors.

Preferably, process step a) is conducted at a temperature of from 100 to 2100C, more preferably from 130 to 1900C, most preferably from 150 to 1800C. Preferably, the pressure ranges from 20 to 100 bar (2 to 10 MPa), more preferably from 40 to 80 bar (4 to 8 MPa), most preferably from 50 to 60 bar (5 to 6 MPa) absolute.

The liquid product mixture obtained in step a) of the present invention generally contains from 30 to 90%, typically from 40 to 70% of solvent, generally from 0.2 to 6.0%, is typically from 0.5 to 4.5% of olefin oxide, generally from 10 to 60%, typically from 20 to 40% of non-converted olefin, based on the total weight of the liquid product mixture, the remaining amount being by- products, such as carbon dioxide, or oxygenated by-products, like water, aldehydes, such as acetaldehyde; ketones, such as acetone or 1-hydroxy-2-propanone; alcohols such as 2-propanole or allyl alcohol; glycols, such as 1,2-propane diol; esters, such as methyl formate, methyl acetate or 1,2propane glycole diacetate; acids, such as formic acid, acetic acid or propionic acid; acetals such as 2-ethyl-4-methyl-1,325 dioxolane, 2,4-dimethyl-1,3- dioxolane or 2,2,4-trimethyl-1,3dioxolane; or ethers such as 1-methoxy-2- propanone. Steps b) and c) of the process of the present invention and optional further separation steps are described in more detail with reference to Figures 1-3.

Now referring to Fig. 1, in step b) of the process of the present invention the liquid product mixture 1 which is obtained in step a) and which comprises olefin oxide, nonconverted olefin, solvent and by-products is passed into a first separator F-1 wherein a lower pressure is maintained than in the reaction step a) and the product mixture is divided into bi) a gaseous stream 12 containing olefin, carbon dioxide and other volatile products and b2) a liquid stream 13 containing olefin oxide, solvent, olefin, carbon dioxide and other by-products. Preferably, separation step b) is conducted at a temperature of from 100 to 1800C, more preferably from 130 to 1800C, most preferably from 130 to 1700C. Preferably, the pressure in step b) ranges from 19 to 95 bar (1.9 to 9.5 MPa), more preferably from 39 to 78 bar (3.9 to 7.8 MPa), most preferably from 48 to 59 bar (4.8 to 5.9 MPa) absolute, provided that the pressure is lower than the pressure in process step a). The separator F-1 used in step b) can be any known separator with or without inserts, such as a distillation column. The separator F-1 can also be a part of the reaction design and located inside the reactor of step a). However, most preferably a flash separator is used. The weight ratio between the gaseous stream 12 and the liquid stream 13 preferably is from 0.03 to 1.0:l, more preferably from 0.1 to 0. 4: 1. The use of a flash separator F-1 in step b) is particularly useful if the olefin used in step a) is propylene and the solvent is 1,2-dichlorobenzene. An excellent separation between propylene and 1,2-dichlorobenzene is achieved in the flash separator. Depending on the pressure and other conditions in the flash evaporator, the separation between propylene and 1,2-dichlorobenzene is generally from 3 to 30 times better than the separation between propylene and benzene. Generally from 5 to 70 percent, preferably from 30 to 50 percent of propylene is comprised in the gaseous stream 12 after the separation step b), based on the total amount of non-reacted propylene in the product mixture obtained in step a). Because a large amount of non-reacted propylene can be separated from the solvent and the produced olefin oxide in the first separation step b), equipment required for the subsequent separation step c) and optional further separations steps can be minimized.

11 The gaseous stream 12 contains non-reacted olefin, carbon dioxide, nonconverted oxygen and minor portions of other volatile products, such as propylene oxide and acetaldehyde. The gaseous stream preferably contains from 40 to 90, more preferably from 60 to 80 wtA of non-reacted olefin and preferably from 10 to 60, more preferably from 20 to 40 wt.% of volatile products. The gaseous stream can be directly recycled to the reaction step a) to recycle non-reacted olefin and to make use of carbon dioxide to dilute oxygen used in the reaction step a). However, non-reacted olefin is preferably separated from the gaseous stream and recycled to the separation step a). A preferred separation step is a partial condensation to remove reaction products from the olefin recycle. The liquid stream 13 contains olefin oxide, solvent, olefin, carbon dioxide and other by-products, generally oxygenated by-products such as those listed above. The liquid stream preferably contains from 0.2 to 6, more preferably from 0.6 to 4.5 wtA of olefin oxide, preferably from 50 to 85, more preferably from 60 to 80 wtA of solvent, preferably from 10 to 20 35, more preferably from 15 to 22 wt. % of olefin and preferably from 0.2 to 8, more preferably from 1.5 to 5. 5wt.% of byproducts, such as carbon dioxide.

The molar ratio between carbon dioxide in the gaseous stream 12 and in the liquid stream 13 generally is from 1 to 4 :l, typically from 1.4 to 2:1. The molar ratio between olefin in the gaseous stream 12 and in the liquid stream 13 generally is from 0.4 to 1.6:l, typically from 0.5 to 1:1.

Although very efficient product separations are achieved in the separation steps of the present invention, it is to be understood that in none of the separation steps described herein a 100% separation is achieved. It is to be understood that the gaseous streams 12 and 2 and the liquid streams 13 and 3 can contain product components in addition to those specifically listed herein.

12 In step c) of the process of the present invention the liquid stream 13 is passed into a second separator F-2 wherein a lower pressure is maintained than in the first separator F-1 in step b) and the stream is divided into cl) a gaseous stream 2 containing olefin, carbon dioxide and other products and c2) a liquid stream 3 containing olefin oxide, solvent and oxygenated by-products. Preferably, separation step c) is conducted at a temperature of from 40 to 180 OC, more preferably from 50 to 160 OC, most preferably from 60 to 150 'C.

Preferably, the pressure in step c) ranges from 4 to 70 bar (0.4 to 7 MPa), more preferably from 8 to 50 bar (0.8 to 5 MPa), most preferably from 10 to 45 bar (1 to 4.5 MPa) absolute, provided that the pressure is lower than the pressure in the separation step b). The separator used in step c) can be any known separator with or without inserts, such as a distillation column. However, most preferably a flash separator or evaporator is used.

The weight ratio between the gaseous stream 2 and the liquid stream 3 preferably is from 0.05 to 1:1, more preferably from 0.05 to 0.5: 1, most preferably from 0.1 to 0.3:l.

The gaseous stream 2 contains non-reacted olefin, carbon dioxide and other volatile products, such as propylene oxide, acetaldehyde, methyl formate, water, methanol or acrolein. The gaseous stream generally contains from 70 to 85 wt.-., typically from 75 to 80 wt.%, of non-reacted olefin and generally from 15 to 30 wt.%, typically from 20 to 25 wt.% of volatile products. The gaseous stream can be directly recycled to the reaction step a) to recycle non-reacted olefin and to make use of carbon dioxide to dilute oxygen used in the reaction step a). According to a preferred embodiment of the process of the present invention the liquid stream 3 is subjected to a further separation step as described further below.

13 The liquid stream 3 contains olefin oxide, solvent, non-reacted olefin and oxygenated by-products, such as those listed further above, and optionally minor amounts of carbon dioxide. The liquid stream preferably contains from 0.1 to 6, more preferably from 0.6 to 4.5 wt.% of olefin oxide, preferably from 60 to 95, more preferably from 70 to 90 wt.% of solvent, preferably from 5 to 50, more preferably from 15 to 25 wt.% of non-reacted olefin, and preferably from 0.8 to 10, more preferably from 1.5 to 8 wt.% of oxygenated by-products.

According to a preferred embodiment of the process of the present invention the gaseous stream 2 and the overhead stream 6 of separator C-2, as described further below, are passed to a further separator C-1, wherein the combined stream is separated into a overhead stream 4 and a bottom stream 5.

Preferably, the separation step in separator C-1 is conducted at a temperature of from 80 to 1500C, more preferably from 90 to 1300C at bottom stage and from -10 to +700C, more preferably from 0 to 600C at the top stage and at a pressure of preferably from 5 to 20 bar (0.5 to 2 MPa) bar (0.8 to 1.4 MPa) absolute.

more preferably from 8 to 14 The separator can be any known separator with or without inserts, preferably a distillation column. The weight ratio between the overhead stream 4 and the bottom stream 5 resulting from this separation preferably is from 3 to 7: 1.

The overhead effluent stream 4 from the separator C-1 contains nonreacted olefin, carbon dioxide and may contain minor amounts of olefin oxide. The overhead stream 4 preferably contains from 80 to 98 wt.%, more preferably from 85 to 95 wt.% of non-reacted olefin and preferably from 2 to 20, more preferably from 5 to 15 wt.% of volatile products, such as carbon dioxide and olefin oxide. The overhead stream 4 can be directly recycled to the reaction step a) to recycle non-reacted olefin and to make use of carbon dioxide to dilute oxygen used 14 c in the reaction step a). Alternatively, non-reacted olefin can be separated from the overhead stream 4 and is preferably recycled to the reaction step a).

The bottom effluent stream 5 from the separator C-1 mainly contains crude olefin oxide. The bottom stream 5 preferably contains from 30 to 90, more preferably from 50 to 80 wt.% of olefin oxide, preferably from 1 to 9, more preferably from 5 to 7 wt.% of methyl formate, preferably from 1 to 9, more preferably from 4 to 6 wt.% of water, preferably from 1 to 9, more preferably from 4 to 6 wt.% of acetaldehyde, preferably from 0.5 to 10, more preferably from 2 to 5 wt.% of olefin and preferably from 1 to 25, more preferably from 5 to 15 wt.% of other oxygenated products like acetone, acroleine, methanol, etc. From the bottom stream 5 propylene oxide can be isolated from the other oxygenated by-products.

Preferably, the liquid effluent stream 3 from the separator F-2 is passedto a further separator C-2, wherein the stream 3 is separated into a overhead stream 6 and a bottom stream 7. Preferably, the separation step in separator C-2 is conducted at a temperature of from 0 to 80 OC, more preferably from 0 to 60 'C at the top stage and from 120 to 2200 C, more preferably from 140 to 2000C at the bottom stage and at a pressure of from 0.1 to 10 bar (0.01 to 1 MPa), more preferably from 0.9 to 4 bar (0.09 to 0.4 MPa), most preferably from 1 to 2 bar (0.1 to 0.2 MPa) absolute. The separator can be any known separator with or without inserts, preferably a distillation column. The weight ratio between the overhead stream 6 and the bottom stream 7 resulting from this separation preferably is from 0.01 to 1:1, more preferably from 0.03 to 0.2:1.

The overhead stream 6 from the separator C-2 preferably contains from 5 to 65, more preferably from 15-% to 30 wt.-% of olefin oxide, preferably from 15 to 90, more is preferably from 50 to 80 wt.-% of non-reacted olefin, preferably from 0.1 to 20, more preferably from 2 to 10 wt.-% of carbon dioxide and preferably from 0.1 to 25, more preferably from 2 to 10 wt.-% of volatile oxygenated products like acetaldehyde or methyl formate. The overhead stream 6 is preferably directed to separator Cl, where crude olefin oxide is separated from olefin. The bottom effluent stream 7 from the separator C-2 contains solvent and oxygenated by-products. The bottom effluent stream 7 preferably contains from 70 to 98, more preferably from 85 to 95 wtA of solvent and preferably from 2 to 30, more preferably from 5 to 15 wtA of oxygenated by-products. The separation in separator C-2 is particularly effective if the olefin used in step a) is propylene and the solvent is 1,2dichlorobenzene. An excellent separation between propylene oxide and 1,2-dichlorobenzene is achieved. Depending on the pressure and other conditions in the separator C-2, the separation between propylene oxide and 1,2-dichlorobenzene is generally from 1.7 to 11 times better than the separation between propylene oxide and benzene.

The bottom effluent stream 7 is preferably passed to a further separator C-3, wherein the stream is separated into an overhead stream 8 and a bottom stream 9. Preferably the separation step in separator C-3 is conducted at a temperature of from 100 to 180 OC, more preferably from 100 to 1600C at top stage and from 150 to 2200C, more preferably from 160 to 210 OC at the bottom stage and at a pressure of from 0.1 to 4 bar (0. 01 to 0.4 MPa), more preferably from 0.8 to 2.5 bar (0.08 to 0.25 MPa) absolute. The separator can be any known separator with or without inserts, preferably a distillation column. The weight ratio between the overhead stream 8 and the bottom stream 9 resulting from this separation preferably is from 0.005 to 0.5:1, more preferably from 0.01 to 0.1:l.

16 The overhead stream 8 from the separator C-3 mainly contains oxygenated by-products which have a lower boiling point than the solvent, such as 2propanol, allyl alcohol, 1-methoxy2-propanone, 2,4-dimethyl-1,3-dioxolane, water, formic acid or acetic acid. The bottom effluent stream 9 from the separator C-3 mainly contains solvent and a minor amount of high-boiling oxygenated by-products, such as propylene glycols or propylene glycol esters. The bottom effluent stream 9 generally contains 90 to 99 wtA of solvent and from 1 to 10 wt.-i of high-boiling oxygenated by-products.

It is preferred to recycle the major amount of the bottom effluent stream 9 to the reaction step a) as stream 10. In order to avoid accumulation of high-boiling oxygenated by- is products in the reaction, it is preferred to separate a small side- stream 11 from the bottom effluent stream 9, preferably from 0.1 to 50 volA, more preferably from 5 to 25 vol.%. The side stream 11 can be passed to a further separator C4, preferably a distillation column, wherein the solvent is separated from the high-boiling oxygenated by-products. Preferably, the separation step in separator C-4 is conducted at a temperature of from 140 to 230 OC, more preferably from 160 to 210 OC, and at a pressure of from 0.1 to 4 bar (0.01 to 0.4 MPa), preferably from 0.5 to 1.5 bar (0.05 to 0.15 MPa) absolute. The overhead effluent stream 20 from the separator C4 contains the solvent and may be recycled to the reaction step a). The bottom effluent stream 21 containing high-boiling oxygenated by-products can be reused for other purposes.

We refer now to Fig. 2, which illustrates a more preferred embodiment of the present invention. Fig. 2 illustrates a similar separation process as the one illustrated in Fig. 1, except that the liquid stream 3 of separator F-2 is passed into an additional separator F-3 wherein a lower pressure 17 is maintained than in separator F-2. In separator F-2 the liquid stream 3 is divided into a gaseous stream 14 containing olefin, olefin oxide ' usually carbon dioxide and other volatile by-products like acetaldehyde or methyl formate; and a liquid stream 15 containing olefin oxide, solvent, oxygenated byproducts, such as those listed further above and optionally minor amounts of olefin. Preferably, separation step F-3 is conducted at a temperature of from 0 to 180 OC, more preferably from 20 to 160 'C, most preferably from 40 to 150 OC.

Preferably, the pressure in step c) ranges from 0.8 to 45 bar (0.08 to 4. 5 MPa), more preferably from 1 to 12 bar (0.1 to 1.2 MPa), most preferably from 2 to 7 bar (0.2 to 0.7 MPa) absolute, provided that the pressure is lower than the pressure in the separation step c). The separator F-3 can be any known is separator with or without inserts, such as a distillation column. However, most preferably a flash separator or evaporator is used. The weight ratio between the gaseous stream 14 and the liquid stream 15 preferably is from 0.005 to 0.6:l, more preferably from 0.02 to 0.2: 1. 20 The gaseous stream 14 from the separator F-3 preferably contains from 40 to 95, more preferably from 60 to 80 wt-% of non-reacted olefin, preferably from 2 to 40, more preferably from 8 to 25 wt-% of olefin oxide and preferably from 1 to 35, more preferably from 5 to 20 wt-% of other volatile products like carbon dioxide, acetaldehyde or methyl formate. The liquid stream 15 from separator F-3 preferably contains from 0.1 to 10 wt-%, more preferably from 0.5 to 4.5 wt-% of olefin oxide, preferably from 50 to 99 wt-%, more preferably from 75 to 95 wt-% of solvent, preferably from 0.1 to 30 10 wt-%, more preferably from 0.1 to 5 wt-% of non-reacted olefin and preferably from 0.1 to 10, more preferably from 1.0 to 8 wt-% of oxygenated by-products. According to a preferred embodiment of the present invention the gaseous stream 14 is passed to a further separator 18 C-1, wherein the combined stream of the gaseous stream 14 from separator F-3, the gaseous stream 2 of separator F-2 and the overhead stream 6 from separator C-2 is separated into an overhead stream 4 and bottom stream 5, as described with reference to Fig. 1.

According to a preferred embodiment of the process of the present invention the liquid stream 15 from separator F-3 is passed to a further separator C-2. The liquid stream is from separator F-3 is separated in separator C-2 in an overhead stream 6 and a bottom stream 7. The separator used and the conditions of temperature and pressure for separator C-2 are the same described in Fig 1. Due to the fact that some of the olefin and olefin oxide have been removed via the gaseous stream 14 before stream 15 enters the separator C-2, the weight ratio between the overhead stream 6 and the bottom stream 7 and the composition of the overhead stream 6 are different from those stated with reference to Fig. 1. The weight ratio between the overhead stream 6 and the bottom stream 7 resulting from this separation preferably is from 0.01 to 0.5, more preferably from 0.03 to 0.15: 1. The overhead stream 6 from the separator C-2 preferably contains from 5 to 70, more preferably from 15 to 40 wt-% of olefin oxide, preferably from 15 to 85, more preferably from 40 to 65 wt-% of non-reacted olefin, preferably from 0.1 to 30, more preferably from 5 to 15 wt.% of carbon dioxide and preferably from 1 to 30 more preferably from 5 to 15 wt.% of volatile oxygenated products like acetaldehyde or methyl formate. The overhead stream 6 is preferably directed to separator C-1, where the crude olefin oxide is separated from the olefin.

By making use of the separator F-3, olefin and olefin oxide is removed from the liquid stream 3 after separator F-2.

Due to this additional separation step, the weight of the overhead stream 6 from separator C-2 can generally be reduced to a level of from 30 to 45%, often from 35 to 40%, as compared to 19 the weight of the overhead stream 6 in Fig. 1, where no separator F3 is used. The significant reduction saves equipment and energy costs of separator C-2.

We refer now to Fig. 3, which illustrates the most preferred embodiment of the present invention. Fig. 3 illustrates a similar separation process as the one illustrated in Fig. 2, except that an additional separator F-4 and an additional separator F-5 are added.

The liquid stream 13 of separator F-1 is passed into an additional separator F-4 wherein a lower pressure is maintained than in separator F-1 and the stream 13 is divided into a gaseous stream 17 containing non-reacted olefin, carbon dioxide and other products, such as propylene oxide, acetaldehyde, methyl formate or water, and into a liquid stream 16 containing olefin oxide, solvent, non-reacted olefin and oxygenated by-products. Preferably, separation step F-4 is conducted at a temperature of from 40 to 180 OC, more preferably from 50 to 160 'C, most preferably from 60 to 150 OC.

Preferably, the pressure in step c) ranges from 4 to 70 bar (0.4 to 7 MPa), more preferably from 8 to 50 bar (0.8 to 5 MPa), most preferably from 10 to 45 bar (1 to 4.5 MPa) absolute, provided that the pressure is lower than the pressure in the separation step b). The separator F-4 can be any known separator with or without inserts, such as a distillation column. However, most preferably a flash separator or evaporator is used. The weight ratio between the gaseous stream 17 and the liquid stream 16 preferably is from 0.005 to 0.5:l, more preferably from 0.02 to 0.15: 1.

The liquid stream 16 from separator F-4 preferably contains from 0.1 to 6, more preferably from 0.6 to 4.5 wtA of olefin oxide, preferably from 50 to 95, more preferably from 65 to 95 wt.% of solvent, preferably from 5 to 50, more preferably from 10 to 20 wtA of non-reacted olefin, and preferably from 0. 1 to 10, more pref erably f rom 1. 5 to 8 (wt..) % of oxygenated by- products, such as those listed further above.

The gaseous stream 17 from the separator F-4 preferably contains from 30 to 95, more preferably from 60 to 80 wtA of non-reacted olefin, preferably from 1 to 35, more preferably from 10 to 25 wt.% of carbon dioxide, preferably from 0.05 to 10, more preferably from 1 to 7 wt-% of olefin oxide and preferably from 0.05 to 12, more preferably from 1 to 8 wt-% of volatile by-products like acetaldehyde, methyl formate or water.

According to a most preferred embodiment of the process of the present invention the gaseous stream 17 from separator F-4 is passed together with gaseous stream 12 of separator F-1 to an additional separator F5. The combined streams 12 and 17 are separated into a gaseous stream 19 and liquid stream 18. Preferably, the separation step F-5 is conducted at a temperature of from 20 to 180 OC, more preferably from 40 to 140 OC, most preferably from 50 to 100 'C. Preferably, the pressure in step c) ranges from 4 to 60 bar (0.4 to 6 MPa), more preferably from 12 to 60 bar (1.2 to 6 MPa), most preferably from 45 to 55 bar (4.5 to 5.5 MPa) absolute, provided that the pressure is lower than the pressure in the separation step b). The separator F-S can be any known separator with or without inserts, such as a distillation column. However, most preferably a combination of heat exchanger and flash separator is used to condense a portion of the combined gaseous streams 12 and 17. The weight ratio between gaseous stream 19 and liquid stream 18 preferably is from 0.01 to 2: 1, more preferably from 0.05 to 1: 1, most preferably from 0.1 to 0.5: 1. The gaseous stream 19 from the separator F-5 contains non-reacted olefin, carbon dioxide, olefin oxide and minor amounts of other volatile products like acetaldehyde or methyl formate. The gaseous stream preferably contains from 30 to 95, more preferably from 60 to 80 wt-% of non-reacted olefin, 21 preferably from 2 to 40, more preferably from 20 to 30 wt-% of carbon dioxide, preferably from 0.02 to 3, more preferably from 0.1 to 1.5 wt-% of olefin oxide and preferably less than 3, more preferably less than 1 wt-% of other volatile products like acetaldehyde or methyl formate. The gaseous stream 19 can be directly recycled to make use of carbon dioxide as diluent or a portion of stream 19 can be used to remove some carbon dioxide from the process.

The preferred use of the separator F-5 has the advantage to remove olefin oxide and other reaction products from the recycle olefin stream which increases the yield and the selectivity for the olefin oxide.

According to a preferred embodiment of the process of the present invention the liquid stream 16 from separator F-4 and the liquid stream 18 from separator F-5 are passed to a further separator F-2 where they are separated into a gaseous stream 2 and a liquid stream 3. The separator used and the conditions of temperature and pressure for F-2 are the same described in drawing 1.

The advantage of using the separator F-4 is that nonreacted olefin and carbon dioxide is removed into the gaseous stream 17 of separator F-4 at high pressure before entering the separator F-2. As a result, the following process streams 2, 3, 4, 6, and 15 contain smaller amounts of olefin and carbon dioxide saving equipment and energy costs for the separators F2, F-3, C-1 and C-2.

The invention is illustrated by the following examples which should not be construed to limit the scope of the present invention. Unless stated otherwise all parts and percentages are given by mol.

Example 1

22 The Example refers to Fig. 1. 10.1 mol/h of propylene is oxidized with 1. 35 mol/h oxygen and 4.5 mol/h nitrogen (resulting in an oxygen concentration of 22.9 Vol-%) at a temperature of 165 OC, a pressure of 54 bar (5.4 MPa) gauge and at a residence time of 13 minutes in presence of 5.65 mol/h odichloro benzene (boiling point: 180.4 OC). The oxidation is carried out in a continuously stirred tank reactor.

The reactor outlet 1, consisting of propylene oxide, not converted propene, other reaction products and o-dichloro benzene is fed continuously to the flash separator F-1 at a rate of 20.8 mol/h. The composition of this mixture is: 2.4% propylene oxide, 27.1% o- dichloro benzene, 42.9% propylene, 21.6% nitrogen, 1.5% carbon dioxide, in total 1.3% of acids like formic acid. acetic acid and propionic acid, 0.1% oxygen, 1.4% water and in total 1.7% of oxygenated by-products and impurities, including aldehydes, ketones, glycols, acetals or esters, such as acetaldehyde, acetone, 1,2-propane diol, methyl formate, 1methoxy-2-propanol, 1-methoxy-2-propanone, 1-hydroxy2-propanone or methyl acetate.

The flash separator F-1 is operated at a pressure of 53 bar (5.3 MPa) gauge and a temperature of 1510C. The vapor stream 12 from flash separator F-1 contains 55.1% propene, 37.3% nitrogen, 2.3% carbon dioxide, 1.7% of propylene oxide and small amounts of 11.5 mol/h be used to other low boiling components and oxygen at a rate of It can either be directly recycled to the reactor or remove small amounts of carbon dioxide and other inert components like nitrogen.

The liquid stream 13 from flash separator F-1 is fed to the flash separator F-2 at a rate of 9.3 mol/h. The flash separator F-2 is operated at a pressure of 12 bar (1.2 MPa) absolute and a temperature of 670C. The composition of stream 13 23 is 58.6%. o-dichloro benzene, 27.9% propylene, 3.2% propylene oxide, 2.1% nitrogen and rest other reaction products.

The gaseous stream 2 containing 70.4% propylene, 3.0% C02, 24.4% nitrogen, 1.0% propylene oxide and other volatile reaction products is directed to column C-1 at a rate of 0.7 mol/hr, where propene and carbon dioxide are separated.

The liquid stream 3 of the flash separator F-2 with a composition of 63. 5% o-dichloro benzene, 24.3% propylene, 3.4% propylene oxide, 0.3% nitrogen, 0.4% carbon dioxide and rest other reaction products is fed to column C-2 at a rate of 8.6 mol/h, where propylene and crude propylene oxide is separated as overhead stream 6 at a rate of 2.6 mol/h, containing 81.8% propylene, 11.5% propylene oxide, 0. 8% nitrogen, 1.2% carbon is dioxide and rest other reaction products. Column C-2 is operated at 1. 6 bar (0.16 MPa) absolute at the bottom stage, the distillate temperature is 10C, the bottom temperature is 1540C. The ratio of distillate molar flow rate 6 to bottom molar flow rate 7 is 0.42: 1.

The gaseous stream 2 of separator F-2 and the overhead stream 6 of column C-2 are separated in column C-1 into the distillate stream 4 and the bottom stream 5. The column C-1 is operated at 11.6 bar (1.16 MPa) absolute at the top stage, the distillate temperature is 210C and the bottom temperature is 1260C. The ratio of distillate molar flow rate 4 to bottom molar flow rate 5 is 6.6: 1. The overhead stream 4, containing 91. 2% propylene, 6.9% nitrogen and 1.8% carbon dioxide can be directly recycled to the reactor at a rate of 2.9 mol/h.

The crude propylene oxide bottom stream 5 can be used at rate of 0.4 mol/h to isolate the propylene oxide using known distillation techniques like extractive distillation with a composition of 69.9% propylene oxide, 0.9% water, in total 28.3% other volatile products such as acetaldehyde, acetone, acrolein, 24 methyl formate, methanol, 2-propanol, and minor amounts of other reaction products such as methyl acetate, formic acid, acetic acid, 1-methoxy-2- propanol, 1-methoxy-2-propanone or 1-hydroxy2-propanone.

The bottom stream 7 from column C-2, containing 90.4% 1,2-dichlorobenzene and 8.0% reaction products with a normal boiling point within a range of 55 to 1500C is fed to column C3 at a rate of 6.0 mol/h to remove those reaction products in overhead stream 8 with a lower boiling point than the 1,2dichlorobenzene. The column C-3 is operated at a pressure of 1.5 bar (0.15 MPa) absolute at the bottom stage, a distillate temperature of 1070C and a bottom temperature of 1960C. The ratio of distillate molar flow rate 8 to bottom molar flow rate 9 is 0.084: 1 The composition of stream 8 is 36% water, in total 42.9% acids such as formic acid, acetic acid and propionic acid, 5.9% 1,2-dichlorobenzene and totally 15.2% of other oxygenated by-products and impurities at a at a rate of 0.5 mol/h. Most of the reaction products are removed from the solvent in line 9, such that substantially all 1,2-dichlorobenzene from the bottom stream 9 of column C-3 can be directly recycled to the oxidation reactor as stream 10 at a rate of 4.8 mol/h containing 98.3-% 1,2dichlorobenzene and 1.7-% other high boiling oxygenated products like glycols or glycol esters such as 1, 2 -propylene glycol or 1,2-propylene glycol diacetate.

only a small portion (14 percent) of stream 9 is fed in line 11 to column C-4 to remove high boiling products from the solvent to avoid accumulation. The column C-4 is operated at 0.95 bar (0.095 MPa) absolute at the top stage, the distillate temperature is 1750C, the bottom temperature is 1840C. 1,2dichlorobenzene going overhead in line 20 is also recycled to the reactor at a rate of 0.8 mol/h. The bottom effluent stream containing high boiling by-products and 1,2-dichlorobenzene can be re- used for other purposes at a rate of o.01 mol/h.

As a result of these separation steps, 0.4 mol/h of crude propylene oxide are obtained with a composition of 69.9k propylene oxide and in total 31. 1% of low boiling oxygenated byproducts and impurities, like acetaldehyde, methyl formate or methanol. 11.5 mol/h of propene/nitrogen/carbon dioxide are separated at a high pressure of 53 bar (5.3 MPa) gauge with a composition of 55.0% propene, 37.3% nitrogen, 2.3%; carbon dioxide, 1.7% of propylene oxide and small amounts of other low boiling components and oxygen. 2.9 mol/h of propene with minor amounts of carbon dioxide are separated at a medium pressure of 11 bar (1.1 MPa) gauge. 1, 2dichlorobenzene is recycled with a flow rate of totally 5.5 mol/h and a composition of 98.3% odichlorobenzene and 1.7% of other compounds.

is 26 Example 2

The Example refers to Fig. 1. 10.2 mol/h of propylene is oxidized with 1. 35 mol/h oxygen at a temperature of 165 OC, a pressure of 54 bar (5.4 MPa) gauge and at a residence time of 13 minutes in presence of 5.7 mol/h odichloro benzene (boiling point: 180.4 OC) and at a carbon dioxide recycle of 1.3 mol/h. The oxidation is carried out in a continuously stirred tank reactor.

The reactor outlet 1, consisting of propylene oxide, not converted propene, other reaction products and o-dichloro benzene is fed continuously to the flash separator F-1 at a rate 17.6 mol/h. The composition of this mixture is: 2.895 propylene oxide, 32.4% o-dichloro benzene, 51.3% propylene, 8.0% carbon dioxide, in total 1.5% of acids like formic acid, acetic acid and propionic acid, 0.1% oxygen, 1.7-0t water and in total 2.2% of oxygenated by-products and impurities, including aldehydes, ketones, glycols, acetals or esters, such as acetaldehyde, acetone, 1,2-propane diol, methyl formate, 1-methoxy-2- propanol, 1-methoxy-2-propanone, 1hydroxy-2-propanone or methyl acetate.

The flash separator F-1 is operated at a pressure of 53 bar (5.3 MPa) gauge and a temperature of 151 OC. The vapor stream 12 from flash separator F-1 contains 77.0% propene, 16.6% carbon dioxide, 1.9% of propylene oxide and small amounts of other low boiling components and oxygen at a rate of 4.8 mol/h. It can either be directly recycled to the reactor or be used to remove small amounts of carbon dioxide.

The liquid stream 13 from flash separator F-1 is fed to the flash separator F-2 at a rate of 12.8 mol/h. The flash separator F-2 is operated at a pressure of 12 bar (1.2 MPa) absolute and a temperature of 670C. The composition of stream 13 7 is 43.9% o-dichloro benzene, 41.6% propylene, 3.2% propylene oxide, 4.8% carbon dioxide and rest other reaction products.

The gaseous stream 2 containing 82.8% propylene, 14.7% C02, 1.2% propylene oxide and other volatile reaction products is directed to column C-1 at a rate of 3 mol/hr, where propene and carbon dioxide are separated.

The liquid stream 3 of the flash separator F-2 with a composition of 57. 1506 o-dichloro benzene, 29.8% propylene, 3.8,-.

propylene oxide, 1.8% carbon dioxide and rest other reaction products is fed to column C-2 at a rate of 9.8 mol/h, where propylene and crude propylene oxide is separated as overhead stream 6 at a rate of 3.6 mol/h, containing 80.4% propylene, 10.5% propylene oxide, 4.8% carbon dioxide and rest other reaction products. Column C-2 is operated at 1.6 bar (0.16 MPa) absolute at the bottom stage, the distillate temperature is 10C, the bottom temperature is 1520C. The ratio of distillate mol flow rate 6 to bottom mol flow rate 7 is 0.57: 1.

The gaseous stream 2 of separator F-2 and the overhead stream 6 of column C-2 are separated in column C-1 into the distillate stream 4 and the bottom stream 5. The column C-1 is operated at 11.6 bar (1.16 MPa) absolute at the top stage, the distillate temperature is 210C and the bottom temperature is 1270C. The ratio of distillate mol flow rate 4 to bottom mol flow rate 5 is 9.9: 1. The overhead stream 4, containing 89.7% propylene and 10.2% carbon dioxide can be directly recycled to the reactor at a rate of 5.9 mol/h.

The crude propylene oxide bottom stream 5 can be used at rate of 0.6 mol/h to isolate the propylene oxide using known distillation techniques like extractive distillation with a composition of 67.7% propylene oxide, 2.85% water, in total 29.4% other volatile products such as acetaldehyde, acetone, acrolein, methyl formate, methanol, 2-propanol, and minor amounts of other 28 reaction products such as methyl acetate, formic acid, acetic acid, 1- methoxy-2-propanol, 1-methoxy-2-propanone or 1-hydroxy2-propanone.

The bottom stream 7 from column C-2, containing 89.6% 1,2-dichlorobenzene and 8.7% reaction products with a normal boiling point within a range of 55 to 1500C is fed to column C-3 at a rate of 6.3 mol/h to remove those reaction products in overhead stream 8 with a lower boiling point than the 1,2dichlorobenzene. The column C-3 is operated at a pressure of 1.5 bar (0.15 MPa) absolute at the bottom stage, a distillate temperature of 1070C and a bottom temperature of 1950C. The ratio of distillate molar flow rate 8 to bottom molar flow rate 9 is 0.1: 1 The composition of stream 8 is 40.1% water, in total 42.7% acids such as formic acid, acetic acid and propionic acid, 3.8% 1,2-dichlorobenzene and totally 13.3% of other oxygenated by-products and impurities at a at a rate of 0.5 mol/h. Most of the reaction products are removed from the solvent in line 9, such that substantially all 1,2-dichlorobenzene from the bottom stream 9 of column C-3 can be directly recycled to the oxidation reactor as stream 10 at a rate of 4.9 mol/h containing 98.3-% 1, 2-dichlorobenzene and 1.7-% other high boiling oxygenated products like glycols or glycol esters such as 1,2 -propylene 25 glycol or 1,2- propylene glycol diacetate.

only a small portion (14 percent) of stream 9 is fed in line 11 to column C-4 to remove high boiling products from the solvent to avoid accumulation. The column C-4 is operated at 0.95 bar (0.095 MPa) absolute at the top stage, the distillate temperature is 1750C, the bottom temperature is 1840C. 1,2dichlorobenzene going overhead in line 20 is also recycled to the reactor at a rate of 0.8 mol/h. The bottom effluent stream 29 containing high boiling by-products and 1,2-dichlorobenzene can be re- used for other purposes at a rate of 0.01 mol/h.

As a result of these separation steps, 0.6 mol/h of crude propylene oxide are obtained with a composition of 67.7% propylene oxide and in total 32.3% of low boiling oxygenated byproducts and impurities, like acetaldehyde, methyl formate or methanol. 4.8 mol/h of propene/carbon dioxide are separated at a high pressure of 53 bar (5.3 MPa) gauge with a composition of 77.0-'.- propene, 16.60k carbon dioxide, 1.9% of propylene oxide and small amounts of other low boiling components and oxygen. 5.9 mol/h of propene with minor amounts of carbon dioxide are separated at a medium pressure of 11 bar (1.1 MPa) gauge. 1,2dichlorobenzene is recycled with a flow rate of totally 5.6 mol/h and a composition of 98.3% odichlorobenzene and 1.7% of other compounds.

Example 3

The Example refers to Fig. 3. A product mixture is obtained by the oxidation of 15.4 mol/h propylene with 2.0 mol/h oxygen in 8.5 mol/h o-dichloro benzene at a temperature of 1650C, a pressure of 54 bar (5.4 MPa) gauge and a residence time of 9 minutes in a continuously stirred tank reactor. The product mixture consists of 14.5 mol/h propylene, 0.5 mol/h propylene oxide, 0.1 mol/h formic acid, 8.5 mol/h dichloro benzene and minor amounts of by-products.

The product mixture is fed into a second continuously stirred tank reactor and contacted with 2.0 mol/h oxygen, 1.3 mal/h propylene and 2.2 mol/h carbon dioxide at a temperature of 1650C, a pressure of 54 bar (5.4 MPa) gauge and at a residence time of 9 minutes.

The reactor outlet 1, consisting of propylene oxide, not converted propene, other reaction products and o-dichloro benzene is fed continuously to the flash separator F-1 at a rate 28 mol/h. The composition of this mixture is: 3.7% propylene oxide, 30.1% o-dichloro benzene, 48.1% propylene, 10.5% carbon dioxide, in total 2.2% of acids like formic acid, acetic acid and propionic acid, 0.3% oxygen, 2.3% water and in total 2.8% of oxygenated by-products and impurities, including aldehydes, ketones, glycols, acetals or esters, such as acetaldehyde,acetone, 1,2-propane diol, methyl formate, 1-methoxy-2-propanol, 1-methoxy-2-propanone, 1-hydroxy-2-propanone or methyl acetate.

The flash separator F-1 is operated at a pressure of 53 bar (5.3 MPa) gauge and a temperature of 151 degree C. The vapor stream 12 from flash separator F-1 contains 70.8% propene, 20.9% carbon dioxide, 2.5.% of propylene oxide and small amounts of other low boiling components and oxygen at a rate of 8.7 mol/h and is directed to flash separator F-5.

31 The liquid stream 13 from flash separator F-1 is fed to the flash separator F-4 at a rate of 19.2 mol/h. The composition of stream 13 is 43% o-dichloro benzene, 37.8% propylene, 4.3% propylene oxide and the rest other reaction products. The flash separator F-4 is operated at a pressure of 41 bar (4.1 MPa) absolute and a temperature of 1440C. The gaseous stream 17 leaving the flash separator F-4 with a composition of 73.5% propylene, 18.5% carbon dioxide, 2.7% propylene oxide and rest other reaction products is fed at a rate of 2.4 mol/h to flash separator F-5.

The flash separator F-5 is operated at a pressure of 50.5 bar (5.05 MPa) absolute and a temperature of 780C. The inlet streams to the separator FS are the gaseous streams 12 and 17. The combined stream is partly condensed and separated into the liquid stream 18 containing 73.6% propene, 16% carbon dioxide, 3% propylene oxide and rest other reaction products and solvent at a rate of 8.1 mol/h and into the gaseous stream 19 at a rate of 3 mol/h and a composition of 65.6% propylene, 30.3% carbon dioxide and minor amounts of propylene oxide, oxygen and other volatile oxygenated products such as methyl formate and acetaldehyde. The stream 19 can either be directly recycled to the reactor or be used to remove small amounts of carbon dioxide.

The liquid stream 16 of separator F-4 containing 48.9-% o-dichloro benzene, 32.6% propylene, 4.5% propylene oxide and rest other reaction products is fed at a rate of 16.8 mol/h together with the liquid stream 18 of separator F-5 to the flash separator F-2. The flash separator F-2 is operated at a pressure of 12 bar (1.2 MPa) absolute and a temperature of 680C.

The gaseous stream 2, containing 78% propylene, 18.1% C02, 1.7% propylene oxide and other volatile reaction products 32 is directed to column C-1 at a rate of 9.4 mol/h, where propene and carbon dioxide are separated.

The liquid stream 3 of the flash separator F-2 is fed to the flash separator F-3 at a rate of 15.6 mol/h, which is operated at a pressure of 3.9 bar (0.39 MPa) absolute and a temperature of 560C. The gaseous stream 14 of F-3 is directed to column C-1 with a composition of 84.5% propylene, 3.5% propylene oxide, 8.7% carbon dioxide and rest other volatile reaction products at a rate of 3.2 mol/h.

The liquid stream 15 of the flash separator F-3 is fed to column C-2 at a rate of 12.3 mol/h, where propylene and crude propylene oxide is separated as overhead stream 6 at a rate of 2.5 mol/h, containing 57.3% propylene, 29.6% propylene oxide and rest other reaction products. Column C-2 is operated at 1.6 bar (0.16 MPa) absolute at the bottom stage, the distillate temperature is 190C, the bottom temperature is 1440C. The ratio of distillate molar flow rate 6 to bottom molar flow rate 7 is 0.26: 1.

The gaseous stream 2 of separator F-2, the gaseous stream 14 of separator F-3 and the overhead stream 6 of column C-2 are separated in column C-1 into the distillate stream 4 and the bottom stream 5. The column C-1 is operated at 11.9 bar (1.19 MPa) absolute at the top stage, the distillate temperature is 190C and the bottom temperature is 1270C. The ratio of distillate mol flow rate 4 to bottom mol flow rate 5 is 8.4: 1. The overhead stream 4, containing propylene and carbon dioxide can be directly recycled to the reactor at a rate of 13.5 mol/h.

The crude propylene oxide bottom stream 5 leaving column C-1 at rate of 1. 6 mol/h contains 64.4% propylene oxide, 8.496 water, in total 27.1% other volatile products such as acetaldehyde, acetone, acrolein, methyl formate, methanol, 2propanol, and minor amounts of other reaction products, such as 33 methyl acetate, formic acid, acetic acid, 1-methoxy-2-propanol, 1-methoxy- 2-propanone or 1-hydroxy-2-propanone. Propylene oxide can be isolated from this mixture using known distillation techniques like extractive distillation.

The bottom stream 7 from column C-2, containing 85.2% 1,2-dichlorobenzene and 12.5% reaction products with a normal boiling point within a range of 55 to 150 OC is fed to column C3 at a rate of 9.8 mol/h to remove those reaction products in 10 overhead stream 8 with a lower boiling point than 1,2dichlorobenzene. The column C-3 is operated at a pressure of 1.5 bar (0.15 MPa) absolute at the bottom stage, a distillate temperature of 1020C and a bottom temperature of 1940C. The ratio of distillate molar flow rate 8 to bottom molar flow rate is 9 is 0.15: 1 The composition of stream 8 is 38.5% water, in total 41.3% acids such as formic acid, acetic acid and propionic acid and totally 20.296 of other oxygenated by-products and impurities at a at a rate of 1.3 mol/h. Most of the reaction products are 20 removed from the solvent in line 9, such that substantially all 1,2-dichlorobenzene from the bottom stream 9 of column C-3 can be directly recycled to the oxidation reactor as stream 10 at a rate of 7.35 mol/h containing 97.80k. 1,2-dichlorobenzene and 2.2 % other high boiling oxygenated products like glycols or glycol 25 esters, such as 1,2-propylene glycol or 1,2-propylene glycol diacetate.

only a small portion (14 percent) of stream 9 is fed in line 11 to column C-4 to remove high boiling products from the solvent to avoid accumulation. The column C-4 is operated at 0.9 bar (0.09 MPa) absolute at the top stage, the distillate temperature is 1740C, the bottom temperature is 1820C. 1,2dichlorobenzene going overhead in line 20 is also recycled to the reactor at a rate of 1.15 mol/h. The bottom effluent stream 34 containing high boiling byproducts and 1,2-dichlorobenzene can be re-used for other purposes at a rate of 0.02 mol/h.

As a result of these separation steps, 1.6 mol/h of crude propylene oxide are obtained with a composition of 64.4% propylene oxide and in total 35. 6% of low boiling oxygenated byproducts and impurities, like acetaldehyde, methyl formate or methanol. 3 mol/h of propene/carbon dioxide are separated at a high pressure of 50.5 bar (5.05 MPa) absolute with a composition of 65.6% propene, 30.3% carbon dioxide, 1.1%.of propylene oxide and small amounts of other low boiling components and oxygen. 13.5 mol/h of propene/carbon dioxide are separated at a medium pressure of 11 bar (1. 1 MPa) gauge. o-dichlorobenzene is recycled with a flow rate of totally 8. 5 mol/h and a composition of 97.8% o-dichlorobenzene and 2.2% of other compounds.

1. A liquid phase process for preparing an olefin oxide from an olefin comprising the steps of a) contacting the olefin in a solvent having a boiling point above 1300 with oxygen or an oxygen-containing gas, b) passing the liquid product mixture comprising olefin oxide, non- converted olefin, solvent and by-products into a first separator wherein a lower pressure is maintained than in the reaction step a) and the product mixture is divided into bl) a gaseous stream (12) containing olefin, carbon dioxide and other volatile products and b2) a liquid stream (13) containing olefin oxide, solvent, olefin, carbon dioxide and other by-products; c) passing the liquid stream (13) into a second separator wherein a lower pressure is maintained than in the first separator in step b) and the stream is divided into cl) a gaseous stream (2 or 17) containing olefin, carbon dioxide and other products and c2) a liquid stream (3 or 16) containing olefin oxide, solvent, olefin and oxygenated by-products.

2. The process of claim 1 wherein the reaction step a) is conducted at a temperature of from 100 to 2100C and a pressure of from 20 to 100 bar (2 to 10 MPa).

3.The process of claim 1 or claim 2 wherein the first separator is operated at a temperature of from 100 to 18CC and a pressure of from 19 to 95 bar (1.9 to 9.5 MPa).

4. The process of any one of claims 1 to 4 wherein the second separator is operated at a temperature of from 40 to 1800C and a pressure of from 4 to 70 bar (0.4 to 7 MPa).

5. The process of any one of claims 1 to 5 wherein the reaction step a) is conducted in the absence of a catalyst.

36 6. The process of any one of claims 1 to 5 wherein the reaction step a) is conducted in the presence of a homogeneous catalyst.

7. The process of any one of claims 1 to 5 wherein the reaction step a) is conducted in the presence of a heterogeneous catalyst.

8. The process of any one of claims 1 to 7 wherein the olefin is propylene.

9. The process of any one of claims 1 to 8 wherein the solvent is a halogenated benzene.

10. The process of claim 9 wherein the solvent is a dichlorobenzene.

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