Process for continuous production of propylene oxide (FIG. 1) from propylene and aqueous hydrogen peroxide. The aqueous hydrogen peroxide is first reacted with propionic acid in the presence of acid catalyst to form perpropionic acid (1). The perpropionic acid is taken up by extraction in benzene (5, 12), and following drying of the benzene solution (16), the perpropionic acid in the solution is reacted with propylene (18) for oxidation of the propylene to propylene oxide and conversion of the perpropionic acid back to propionic acid. The reaction mixture is worked up to separate propylene oxide, propionic acid and benzene (25, 27, 31, 33), and the latter two are recycled. In the benzene extraction (5, 12), an aqueous raffinate (7) is formed containing hydrogen peroxide and acid catalyst. Water is removed from the aqueous raffinate (8) and the concentrate is recycled to the propionic acid reactor. Make-up hydrogen peroxide can be added to the aqueous raffinate before the removal of water.
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1. Process for the continuous production of propylene oxide from propylene and aqueous hydrogen peroxide which comprises:
(a) contacting aqueous hydrogen peroxide with propionic acid for reaction of hydrogen peroxide and propionic acid to form perpropionic acid, in the presence of a water-soluble acid catalyst for the reaction, the amount of water, catalyst and hydrogen peroxide corresponding to an aqueous solution of catalyst and hydrogen peroxide containing 15 to 45% by weight of catalyst and 25 to 35% by weight of hydrogen peroxide, and the molar ratio of hydrogen peroxide to propionic acid being 0.8 to 1.5 at a temperature of 10° to 70°C, (b) extracting the resulting reaction mixture with benzene for formation of a benzene phase rich in perpropionic acid, propionic acid, and containing hydrogen peroxide, and an aqueous raffinate phase rich in hydrogen peroxide and catalyst., (c) treating the aqueous raffinate to remove water therefrom and form a concentrated solution of hydrogen peroxide and catalyst., (d) recycling said concentrated solution of hydrogen peroxide and catalyst to step (a), (e) extracting the benzene phase of step (b) with water or an aqueous solution for formation of a benzene phase containing perpropionic acid, propionic, acid, water and a reduced amount of hydrogen peroxide, and an aqueous phase containing hydrogen peroxide., (f) subjecting the benzene phase produced in step (e) to azeotropic distillation to reduce the water content thereof to less than 0.5% by weight., (g) contacting the benzene phase of reduced water content of step (f) with propylene at a temperature of 40° to 100°C and a pressure of 2 to 30 bars for reaction of perpropionic acid of the benzene phase with propylene to form propylene oxide and reaction mixture containing the propylene oxide, and other materials, (h) distilling the reaction mixture is to distill overhead propylene, propylene oxide and benzene and removing bottoms comprising benzene and propionic acid; (i) subjecting the overhead from step (h) to a second distillation to distill off overhead propylene and recycling said propylene to step (g); (j) introducing the bottoms consisting essentially of propionic acid and benzene from the distillation of step (i) to a third distillation (h) and benzene from distillation step (i) into a third distillation column and distilling off overhead benzene and recycling said benzene to step (b), (k) removing bottoms from said third distillation column consisting essentially of propionic acid and materials of higher boiling point than propionic acid and introducing said bottoms into a fourth distillation column and distilling over propionic acid and recycling said propionic acid to step (a) and separating bottoms consisting essentially of the material of higher boiling point than propionic acid, and (l) recovering propylene oxide as a side cut from said second distillation.
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The following applications are related to the process hereof for production of propylene oxide as being directed to aspects of the process, some of which are disclosed herein.
| ______________________________________ |
| German Serial No. U.S. Ser. No. |
| ______________________________________ |
| P 25 19 288.5 678,819 |
| P 25 19 300.4 678,820 |
| P 25 19 299.8 678,821 |
| P 25 19 297.6 678,823 |
| P 25 19 295.4 678,824 |
| P 25 19 293.2-42 678,825 |
| P 25 19 292.1-42 678,826 |
| P 25 19 291.0-42 678,827 |
| P 25 19 289.6 678,828 |
| P 25 19 297.4 678,829 |
| ______________________________________ |
All of said related applications were filed on Apr. 28, 1976.
The present invention relates to a continuous process for the industrial production of propylene oxide from hydrogen peroxide and propylene.
Hitherto propylene oxide has been prepared on a large industrial scale by two processes exclusively, that is either according to the older process via propylene chlorohydrin or more recently with the aid of hydrocarbon peroxides.
The older chlorohydrin process has the disadvantage that undesirable chlorinated by-products and waste salts which pollute the environment are formed (DAS (German published specification) No. 1,543,174, column 2, lines 15 et seq.).
The more recent process, used industrially, for the preparation of propylene oxide via hydrocarbon peroxides, such as described, for example, in USA Patent Specification 3,350,422, eliminates these considerable disadvantages of the chlorohydrin process. The reaction of propylene with a hydrocarbon peroxide ROOH can be illustrated by the equation (1). ##STR1##
It can be seen from equation (1) that in this reaction 1 mol of the alcohol ROH corresponding to the peroxide is always formed per 1 mol of propylene oxide formed. The hydrocarbon peroxide thus effects a transfer of oxygen so that, after the release of the peroxide oxygen, the corresponding alcohol is obtained as a co-product and frequently has to be removed as an undesired by-product. Accordingly, the possibilities for industrial use of such a process are limited, since the alcohol by-product cannot be utilised in every case.
In contrast, with the principle on which the process according to the invention for the preparation of propylene oxide from propylene and hydrogen peroxide is based, the desired end product is obtained, as is shown in equation (2), free from such by-products, which either have to be eliminated at considerable expense because of their environmental pollution properties or for which a suitable further use has to be found when they are obtained as co-products. ##STR2##
However, the desired objective is not achieved by direct reaction of propylene with aqueous hydrogen peroxide (U.S. Pat. specification No. 3,350,422, column 2, lines 42-44).
On the other hand, it is known to epoxidise propylene with the aid of a percarboxylic acid to give propylene oxide (Prileschayev, Ber, dtsch. chem. Ges. 42, 4811 (1909) and D. Swern "Organic Peroxides", Wiley Interscience 1971, volume 2, page 355-533, especially page 375-378 and page 397). In addition, it is known to obtain percarboxylic acids from carboxylic acids with the aid of hydrogen peroxide (German Pat. No. 251,802 and, for example, D. Swern, loc. cit., 1970, volume 1, page 313-369 and page 428-439). These two partial steps are illustrated in the equations (3) and (4), in which R--COOH and R--COOOH represent a carboxylic acid and a percarboxylic acid respectively. ##STR3##
If the carboxylic acid obtained according to equation (4) is recycled into the reaction according to equation (3) to obtain percarboxylic acid, the overall equation (2) results for the reaction of hydrogen peroxide with propylene to give propylene oxide. A process of this type for the preparation of propylene oxide starting from hydrogen peroxide and propylene and using percarboxylic acids as the epoxidising agent has not hitherto been mastered in an industrially satisfactory manner and consequently has not yet been used on an industrial scale. In this connection it is stated, for example in U.S. Pat. No. 3,350,422 (column 1, line 65 to column 2, line 11):
"In light of the complexity and cost of the chlorohydrin route, workers have turned to other possible routes for the epoxidation of propylene and other olefins. One route which has proved successful insofar as being capable of actually producing at least limited yields of propylene oxide and other oxides is the peracid route. This route involves the formation of a peracid, such as peracetic acid, through the reaction of hydrogen peroxide with the organic acid and the epoxidation of an olefin with the peracid. The disadvantages of the peracid route also are such as to preclude significant commercialization. The peracids themselves are extremely hazardous to handle and give rise to severe operation problems. The reagents are expensive, corrosive, and nonregenerable, inasmuch as the hydrogen peroxide is lost as water. The composition of the peracid epoxidation mixture contains chemicals (H2 O, AcOH, and H2 SO4) which are highly reactive with the product epoxides, thus leading to many by-products (glycol, glycol monoester, glycol diester) which lower the overall efficiency. This problem becomes more severe with the less reactive olefins, in particular propylene".
In fact, all the processes hitherto known for the preparation of propylene oxide from hydrogen peroxide and propylene, which proceed via the intermediate stage of a percarboxylic acid as an oxygen transfer agent, lead only to unsatisfactory yields of propylene oxide and to considerable amounts of by-products, such as propylene glycol, propylene glycol monoester and propylene glycol diester. It has also not been possible satisfactorily to overcome the extremely difficult process problems, especially with regard to the isolation of the percarboxylic acid, which are caused by the explosion hazard of the percarboxylic acids.
In the case of the process according to DOS (German published specification) No. 1,618,625, which has been disclosed more recently, for the preparation of oxiranes from olefines and hydrogen peroxide with the aid of formic acid, the measures described there are also not adequate for an industrially satisfactory production of propylene oxide from hydrogen peroxide and propylene. For this process it is necessary for the reaction mixture to be substantially free from mineral acid and substantially anhydrous or to contain only a small amount of water (DOS (German published specification) No. 1,618,625, claim 1). Thus, it is stated, for example, on page 3, final paragraph and page 4, first line of DOS (German published specification) No. 1,618,625: "The use of an anhydrous reaction mixture is desired,, but the preparation of solutions of performic acid having less than about 0.3% of water is neither simple nor economically tenable. The use of a reaction mixture which contains only a small amount of water is preferred." An amount of less than 20 g/l is mentioned as an appropriate water content and an amount of less than 10 g/l is mentioned as being a required water content in some cases. The freedom from mineral acid, which it is attempted to achieve in the process, is important since the catalysts required for the reaction of formic acid with hydrogen peroxide also catalyse the cleavage reaction of oxirane rings, in the present case the cleavage of propylene oxide (DOS (German published specification) No. 1,618,625, page 5, lines 10-14). Accordingly, it would be most advantageous to use in the process a solution, which as far as possible is absolutely anhydrous and as far as possible is free from mineral acid, of performic acid in a hydrophobic solvent. These requirements, particularly with regard to the freedom from water, cannot be met in the processes known hitherto, since the preparation of a non-aqueous performic acid containing only 0.3% of water or less already comes up against the difficulties mentioned in DOS (German published specification) No. 1,618,625. Accordingly, the yield of propylene oxide which can be achieved, for example, according to the process of DOS (German published specification) No. 1,618,625, is only 85%, relative to the performic acid consumed (DOS (German published specification) No. 1,618,625, Example 3). However, since the performic acid solutions still have a relatively high content of free hydrogen peroxide, this being between 3 and 10 mol % of the performic acid according to Examples 1 and 2 of DOS (German published specification) No. 1,618,625, the yield of propyleenepu pump of the lower stage. The benzene solution, which is withdrawn as the light phase from the lower separating vessel, is fed, after passing through the middle mixer/settler arrangement, together with 17 ml/hour of fresh water to the mixing pump of the upper mixer/settler unit. The aqueous phase which is obtained here after phase separation has taken place is fed into the middle extraction stage. The aqueous solutions which collect as the heavy phase in the middle and lower separating vessels are combined and fed via 14 back into extraction unit 5 in such a way that this stream, which consists of an aqueous solution which contains 25.23% by weight of perpropionic acid, 6.8% by weight of hydrogen peroxide and 22.35% by weight of propionic acid, is mixed, in an amount of 81 ml/hour, immediately prior to entry into the pulsed sieve tray column (extraction system 5) with the product stream 4 coming from reaction system 1.
1493 g (=1,570 ml) per hour of a benzene solution of perpropionic acid having the composition 20.04% by weight of perpropionic acid, 11.41% by weight of propionic acid, 3.95% by weight of water and 0.2% by weight of hydrogen peroxide are withdrawn as the light phase from the separating vessel of the upper mixer/settler unit of extraction system 12 via line 15 and fed into the distillation unit 16, where the solution is dried azeotropically. Before it is fed into distillation unit 16, the benzene solution of perpropionic acid is treated with 5 ml per hour of an approximately 3% strength by weight solution, in propionic acid, of a stabiliser of the type of the commercially available Na salts of partially esterified polyphosphoric acids.
The distillation unit 16 is operated at 210 mm Hg and consists of a thin layer evaporator, a 50 cm long column, 50 mm in diameter, which is provided with 5 bubble cap trays, a condenser and also a separator for phase separation of the distillate at the top of the column. The temperature in the sump of the column is 65°C 60 ml per hour of water and about 915 ml per hour of benzene are obtained as the distillate. The benzene is returned as reflux to the column, whilst the water obtained in the separator is fed, as already described, as washing water via 35 into the lower stage of extraction unit 12. A 20.71% strength by weight benzene solution of perpropionic acid, which also contains 12.18% by weight of propionic acid as well as 0.1% by weight of water and 0.15% by weight of hydrogen peroxide, is obtained, in an amount of 1,438 g per hour, as the sump product from this azeotropic distillation.
The yield of perpropionic acid in the benzene extract dried in this way is 96.15%, relative to the hydrogen peroxide fed into the process.
The dried benzene solution of perpropionic acid, which is thus obtained, is reacted with excess propylene in a three-stage kettle cascade (reaction system 18). The reaction is carried out at a pressure of 4 bars. The propylene is fed into the first reactor in the gaseous form. The excess propylene, relative to the perpropionic acid employed in the reaction, is 170 mol % (=236 g of propylene). The first reactor of this three-stage cascade, which, like the two downstream reaction vessels, is provided with a stirring device and has a capacity of 2000 ml, is operated at a temperature of 65°C and the second and third reactors are both operated at a temperature of 70°C The average residence time for the reaction mixture formed from the benzene solution of perpropionic acid and propylene is about 3.3 hours over the three reactors.
Under these reaction conditions, 99.8% of the perpropionic acid in the feed are converted. After the third reactor, the reaction mixture, which is obtained in an amount of 1674 g per hour and the average composition of which is 5.86% by weight of propylene, 11.31% by weight of propylene oxide, 25% by weight of propionic acid and 57.4% by weight of benzene as well as 0.15% by weight of water, is let down to normal pressure in separating vessel 21, part (78 g/hour) of the excess propylene being released as a gas.
This mixture is separated in a downstream distillation train, 189.6 g per hour of 99.9% strength pure propylene oxide being obtained. 961 g per hour of benzene and 415.9 g per hour of propionic acid are also obtained and the benzene is recycled into extraction system 5 (via line 6) and the propionic acid is recycled into reaction system 1 via line 3. In addition to propylene oxide, benzene and propionic acid, 0.38 g per hour of propylene glycol and also 3.38 g per hour of propylene glycol dipropionate are obtained when the reaction mixture is worked up by distillation and these products are passed, without further working up, to a suitable further use.
The yield of propylene oxide is thus 98.7%, relative to the perpropionic acid fed into reaction system 18, or 94.9%, relative to the hydrogen peroxide fed into reaction system 1.
The losses of propionic acid are 0.98% of the total amount fed into the process, 0.63% of this amount being contained in the propylene glycol dipropionate.
The procedure is as in Example 1 and after the reaction mixture from reaction system 18 has been let down in separating vessel 21, a product stream of 1596 g per hour is obtained and is fed via line 24 to distillation column 25, where all of the propylene oxide, together with the propylene and part of the benzene, is withdrawn as the distillate. This distillate, which contains 3.16% by weight of propylene, 29.78% by weight of propylene oxide, 66.59% by weight of benzene and 0.4% of water and which is obtained in an amount of 636 g per hour, is fed to the distillation column 27, where 189.6 g per hour of 99.9% pure propylene oxide and 20.1 g per hour of propylene are obtained. The sump products from columns 25 and 27 are fed via line 29 and 30 respectively to column 31, where the benzene is recovered as the top product in an amount of 961 g per hour and is then recycled via line 6 into extraction system 5. The sump product from column 31 passes via line 32 into distillation column 33. Here, 415.9 g per hour of propionic acid are obtained as the top product and are recycled via line 3 into reaction system 1. 0.38 g per hour of propylene glycol and 3.38 g per hour of propylene glycol dipropionate are withdrawn from the sump of column 33.
The yield of propylene oxide and the losses of propionic acid are the same as in Example 1.
Per hour, 98.1 g (=41.56%) of the amount of propylene (236 g) fed per hour into the reaction system 18 are recovered; the amount of propylene oxide obtained per hour contains 58.12% of the propylene. The amounts of propylene contained in propylene glycol dipropionate and in propylene glycol are 0.96 g, which corresponds to a loss of 0.41%, relative to the amount of propylene fed in per hour.
In continuous operation, 20.12 kg (=271 mols) of propionic acid (99.8% strength by weight, stream 3) and 29.94 kg of an aqueous solution (stream 2), which contains, on average, 29.4% by weight of hydrogen peroxide (=259 mols), 33.0% by weight of sulphuric acid and 7.5% by weight of Caro's acid, are pumped per hour through the reaction system 1 which consists of a two-stage stirred kettle cascade. The molar ratio of hydrogen peroxide to propionic acid is 1.03:1, the hydrogen peroxide bound in the Caro's acid being calculated as free H2 O2.
With an average residence time of 28 minutes in the stirred kettle cascade and at a reaction temperature of 35°C, 57.4% of the pripionic acid are converted to perpropionic acid. The reaction mixture (50.06 kg per hour, stream 4) contains, on average, 28.0% by weight of perpropionic acid, 17.1% by weight of propionic acid, 7.0% by weight of hydrogen peroxide, 19.7% by weight of sulphuric acid, 4.5% by weight of Caro's acid and 23.7% by weight of water. This reaction mixture is fed, together with the combined aqueous phases (stream 14) from the extraction unit 12, to the extraction system 5.
A pulsed sieve tray column with 60 trays, a length of 6 mm and a diameter of 72 mm is used as the extraction system 5. 45.74 kg per hour of benzene (stream 6), which contain 0.11% by weight of propionic acid and 0.12% by weight of water, are fed into the column as the extraction agent.
At the upper end of the column, 74.27 kg per hour of benzene extract (stream 11), which contains, on average, 22.3% by weight of perpropionic acid, 13.8% by weight of propionic acid, 0.54% by weight of hydrogen peroxide, 0.86% by weight of water and traces of sulphuric acid, are withdrawn.
The aqueous raffinate from the extraction (stream 7) is withdrawn at the lower end of the column in an amount of 29.18 kg per hour. This raffinate contains, on average, 11.7% by weight of hydrogen peroxide, 33.8% by weight of sulphuric acid, 7.7% by weight of Caro's acid and also 0.09% by weight of perpropionic acid and 0.06% by weight of propionic acid.
A small partial stream of the raffinate (stream 7b) of 0.88 kg/hour (=3.0%) is withdrawn and worked up separately.
The bulk of the raffinate (product stream 7a), 28.3 kg/hour, is again made up for renewed reaction with propionic acid by passing it, together with 10.98 kg/hour of 50% strength aqueous hydrogen peroxide (=161.4 mol/hour of H2 O2 feed, stream 9), a further 0.52 kg/hour of 17% strength by weight aqueous hydrogen peroxide (product stream 35) and 0.37 kg/hour of sulphuric acid (95.9% strength by weight, stream 36, as replacement for the loss of H2 SO4 contained in stream 7b), to a distillation unit 8 and reconcentrating the mixture thus obtained by distillation off water.
The distillation distilling unit 8 consists of packed column (length=4 m, diameter=150 mm), a condenser and a falling film evaporator made of zirconium ("commercial grade"). The mixture of product streams 7a, 9, 35 and 36 is passed directly to the evaporator. At a pressure of 55 mm Hg, a sump temperature of 76°-78°C, a temperature at the top of the column of 38°-39°C and a reflux ratio of 0.55 (reflux/take-off), 10.21 kg per hour of water are distilled off. This distillate (stream 10) contains 0.04% by weight of hydrogen peroxide as well as 0.25% by weight of perpropionic acid and 0.16% by weight of propionic acid.
29.94 kg per hour of an aqueous solution (stream 2), which in turn contains 29.4% by weight of hydrogen peroxide, 33.0% by weight of sulphuric acid and 7.5% by weight of Caro's acid, are withdrawn from the sump of the column. After it has been cooled to 20°C, this mixture is fed back to the reaction system 1.
The raffinate partial stream 7b, 0.88 kg/hour, withdrawn from the aqueous circulation is worked up in a distillation unit 37. This consists of a packed column (length=4 m, diameter=100 mm), which, above the feed point located in the centre, possesses a take-off weir for withdrawing a sidestream. The column is operated at a pressure of 50 mm Hg, a temperature at the top of 38°C and a reflux ratio of 0.1.
5.5 kg of steam per hour are blown in above the sump. 0.52 kg per hour of 17% strength by weight aqueous hydrogen peroxide are withdrawn from the column as a sidestream (product stream 35) and fed to the distillation unit 8. In addition, 4.96 kg/hour of water with 0.04% by weight of hydrogen peroxide (stream 40) are obtained as the distillate and 0.90 kg/hour of an aqueous solution (stream 41), which contains 1.2% by weight of hydrogen peroxide, 34.7% by weight of sulphuric acid and 5.6% by weight of Caro's acid, are obtained in the sump.
The benzene extract (stream 11) withdrawn from the extraction column 5 is passed to a further extraction system 12, which is designed as a three-stage battery of mixer/settlers arranged in one plane and each consisting of a mixing pump followed by a separator.
The benzene extract (stream 11), together with 0.78 kg/hour of fresh water (stream 13) and 2.92 kg/hour of the aqueous phase (stream 38) from the azeotropic distillation 16, is fed to the mixing pump of the first stage. The benzene solution, which is withdrawn from the first separator as the light phase, is fed, after passing through the second mixer/settler unit, together with 0.93 kg/hour of fresh water to the mixing pump of the third stage. The aqueous phase separated off in this stage is fed into the second stage.
The aqueous phases obtained in the first stage and the second stage are combined (product stream 14) and passed back, in an amount of 7.65 kg/hour, into the extraction column 5. These combined aqueous phases contain, on average, 3.8% by weight of hydrogen peroxide, 33.7% by weight of perpropionic acid, 21.8% by weight of propionic acid, 10.0% by weight of benzene and a little sulphuric acid. 71.25 kg per hour of a benzene solution (stream 15), which contain, on average, 19.7% by weight of perpropionic acid, 12.1% by weight of propionic acid, 0.19% by weight of hydrogen peroxide and 4.0% by weight of water, are withdrawn, as the light phase, from the separator of the third stage and fed, together with a solution of a stabiliser, to the azeotropic distillation 16.
A commercially available Na salt of a partially esterified polyphosphoric acid is used as the stabilizer and is added as a 15% strength by weight solution in propionic acid (0.11 kg/hour, stream 39).
The distillation unit 16 consists of a packed column (length=3 m, diameter=200 mm), a falling film evaporator, a condenser and a separator for phase separation of the distillate at the top of the column. The product stream 15 is fed into the lower part of the column. At a pressure of 300 mm Hg and a temperature at the top of the column of 46°-48°C, 2.92 kg of aqueous phase and about 54 kg of benzene phase are obtained per hour as the distillate. The benzene phase is returned to the column as reflux, whilst the aqueous phase (product stream 38) which contains 0.82% by weight of hydrogen peroxide, 1.10% by weight of perpropionic acid and 0.34% by weight of propionic acid, is passed into the first stage of the extraction system 12.
68.25 kg per hour of a benzene solution of perpropionic acid (20.49% by weight=155.2 mols), which also contains 12.67% by weight of propionic acid, 0.16% by weight of hydrogen peroxide, less than 0.1% by weight of water and the abovementioned stabiliser, (stream 17) are obtained as the sump product from this azeotropic distillation.
The yield of perpropionic acid in the dried benzene solution is 96.1%, relative to the amount of hydrogen peroxide fed into the process (stream 9).
The dried benzene solution of perpropionic acid, thus obtained, (stream 17) is reacted with 7.4 kg/hour of very pure propylene (=175.8 mols/hour, product stream 19) in reaction system 18. The excess propylene, relative to the feed perpropionic acid, is 13.3 mol %.
Reaction system 18 consists of two loop reactors in series with a downstream delay tube. The reaction is carried out at a pressure of 4 bars. All of the propylene is fed into the first loop reactor. The reaction temperature is 65°C in the two loop reactors and the average residence time of the reaction mixture is about 45 minutes in each. In the delay tube, the reaction temperature is 70°C and the average residence time of the reaction mixture is about 70 minutes. About 90% of the perpropionic acid has been converted at the exit from the second loop reactor and after the delay tube a conversion of 99.8% is achieved. The reaction mixture then contains, on average, 1.16% by weight of propylene, 11.8% by weight of propylene oxide, 60.1% by weight of benzene and 26.5% by weight of propionic acid.
This reaction mixture (product stream 23) is let down in separator 21 and then enters the distillation column 25, in which propylene, all of the propylene oxide and part of the benzene are separated off as the distillate (stream 26).
This distillate, which contains, on average, 5.4% by weight of propylene, 62.5% by weight of propylene oxide and 31.2% by weight of benzene, is fed into the distillation column 27. 0.73 kg of propylene (stream 20) and 8.91 kg of propylene oxide (99.9% pure, stream 28) are withdrawn per hour from this column. After separating an aqueous phase, which contains 0.01 kg/hour of free propylene glycol, from the product withdrawn from the sump of column 27, this sump product (stream 30) is fed, together with the sump product withdrawn from column 25 - stream 29 - into the distillation column 31. 45.48 kg per hour of benzene are obtained as the distillate from this column and are recycled, with 0.26 kg/hour of fresh benzene (loss replenishment), as stream 6 to the extraction column 5. The product (stream 32) withdrawn from the sump of distillation column 31 is fed to distillation column 33. 19.91 kg per hour of propionic acid are obtained as the distillate from this column and are recycled, with 0.21 kg/hour of fresh propionic acid (loss replenishment), as product stream 3 into reaction system 1. 0.21 kg per hour of propylene glycol dipropionate (stream 34) are withdrawn from the sump of column 33.
The yield of propylene oxide is 98.7% relative to the perpropionic acid fed into reaction system 18, and 94.9%, relative to the hydrogen peroxide employed (product stream 9). The losses of propylene are 3% (0.7% of which is in the byproducts propylene glycol and propylene glycol dipropionate). The losses of benzene are 0.57% and those of propionic acid are 1.49%, 0.81% of which is contained in the propylene glycol dipropionate.
An aqueous perpropionic acid solution is produced in reactor 1. Therein 50% aqueous H2 O2 and propionic acid are reacted in a ratio of 0.8 to 1.2:1 in the presence of 22% H2 SO4 as the catalyst at a pressure of 1 bar and a temperature of 32°-36°C A mixture of the following composition is produced:
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| perpropionic acid |
| 30% |
| propionic acid 15% |
| H2 SO4 22% |
| H2 O 25.8% |
| H2 O2 7.2% |
| ______________________________________ |
Perpropionic acid and propionic acid are then taken up by benzene in benzene extraction column 5.
Benzene is introduced in counterflow into extractor 5, into which the aqueous solution obtained from reactor 1 is introduced via line 4. A pressure 1 bar and a temperature of 20°-50°C prevails in the extractor 5. A benzene and an aqueous phase of the following compositions are produced:
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| benzene phase: |
| perpropionic acid |
| 23% |
| propionic acid |
| 13.3% |
| H2 O 1% |
| H2 O2 |
| 0.5% |
| benzene remainder |
| aqueous phase: |
| H2 SO4 |
| 35% |
| H2 O2 |
| 11.3% |
| H2 O remainder |
| ______________________________________ |
H2 O2 is then removed from the benzene-perpropionic acid solution in extractor 12.
The benzene phase obtained from extractor 5 is extracted with 1-5% fresh H2 O introduced via line 13 in countercurrent flow. The conditions are the same as in extractor 5. A benzene phase and an aqueous phase of the following compositions are formed:
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| benzene phase: |
| perpropionic acid |
| 20% |
| propionic acid |
| 12% |
| H2 O 4.2% |
| H2 O2 |
| less than 0.05% |
| aqueous phase: |
| perpropionic acid |
| 36% |
| H2 O 25% |
| propionic acid |
| 20% |
| H2 O2 |
| 6% |
| ______________________________________ |
The aqueous phase is recycled to extractor 5.
The benzene-perpropionic solution is then dried.
The benzene solution obtained from column 12 is fed into falling film evaporator 16a with short residence time. The resulting vapour phase is conducted to about the middle and the liquid phase to the bottom of a drying column 16b which is supplied with benzene vapours from below. The falling film evaporator 16a and the drying column are operated at a pressure of 250 mm Hg and a temperature of 50°-70°C From the head of the drying column a C6 H6 /H2 O azeotrope is withdrawn and forms two phases in separator 16d after cooling in cooler 16e. The aqueous phase is recycled to extractor 12 via 35; the benzene phase is conveyed as reflux to the head of the drying column.
From the sump of the drying column, a benzene solution is removed via line 17 which contains 20% perpropionic acid and 10% propionic acid and is practically free of H2 O and H2 O2.
The aqueous phase from benzene extraction column 5 is worked up as follows.
The aqueous phase in line 7 is fed via line 7a into the center part of the water column 8a which is operated at a sump temperature of 60°-90°C and a pressure of 50-100 mm Hg. All the fresh 50% -strength, aqueous H2 O2 required in the propionic acid reaction 1 is introduced into the lower part of the water column via line 9. The sump product which consists of H2 O, H2 O2 and H2 SO4 is in part conveyed via line 2 to propionic acid reaction 1, and is in part past passed through heater 8b. Water vapour which may contain traces of H2 O2 is removed at the head of water column 8a.
The reaction of the benzene-perpropionic acid solution with propylene is performed in propylene oxide reactor 18. The benzene solution from azeotropic distillation column 16b, which contains about 20% perpropionic acid and 12% propionic acid is introduced into reactor 18 via line 17, as is also 1.5 to 3.0 times the molar amount of propylene (based on perpropionic acid) via line 19. The propylene introduced into reactor 18, which may contain propane, dissolves in the reaction mixture without forming bubbles so that the reaction takes place homogeneously. The reaction is conducted in such a manner that the perpropionic acid is almost completely reacted. The concentration of perpropionic acid in the reactor outlet 23 is less than 0.1% by weight. The mean residence time is 1-2 hours.
A plurality of series-connected reactor units are provided with which to perform the reaction. Reaction 18 can be as is described with reference to FIG. 3. 90% of the reaction takes place in the two loop reactors and 10% in the residence or delay pipe. The temperature in the reaction system can be about 70°C and the pressure about 6.5 bars. The product leaving the reactor is free of perpropionic acid and has roughly the following composition:
| ______________________________________ |
| C6 H6 55% |
| propionic acid 30% |
| propylene oxide 12% |
| propylene + propane |
| 2% |
| ______________________________________ |
The product of reactor 18 is then worked-up in the same way as described in the foregoing examples.
Waldmann, Helmut, Weiberg, Otto, Schreyer, Gerd, Wirthwein, Rolf, Schwerdtel, Wulf, Seifert, Hermann, Swodenk, Wolf, Prescher, Guter
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| Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
| Feb 14 1980 | Bayer AG | (assignment on the face of the patent) | / | |||
| Feb 14 1980 | Deutsche Gold-und Silver Scheideanstalt Vormals Roessler | (assignment on the face of the patent) | / |
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