HRP940733A2 - Process for the preparation of aldehydes - Google Patents

Description

The technical field to which the invention belongs

The invention belongs to the field of organic chemical synthesis and relates to the production of aldehydes by catalytic means.

Technical problem

The technical problem is how to make aldehydes by hydroformylation of olefins in the presence of water-soluble rhodium complex catalysts.

State of the art

It is known that the reaction of olefins with synthesis gas, i.e. a mixture of carbon monoxide and hydrogen, produces alcohols and aldehydes. The reaction is catalyzed by hydridometal carbonyls, especially those of metals of the 8th group of the periodic table. In addition to cobalt, which is often used as a catalyst metal in technology, rhodium is becoming increasingly important. Compared to cobalt, rhodium as a catalyst component enables the reaction to be carried out at low pressure, and in addition, n-aldehydes are formed primarily and iso-aldehydes only to a lesser extent. In addition, the side reaction of hydrogenation of olefins to saturated hydrocarbons is also possible, using rhodium catalysts, which is significantly lower than when using cobalt catalysts.

In the procedures introduced in the technique, rhodium catalysts are used in the form of hydridocarbonyl containing additional ligands. Tertiary phosphines or phosphites have proven particularly good as ligands. Their application allows the reaction pressure to be lowered to a value below 30,000 kPa.

Separation of the reaction products from the catalyst homogeneously dissolved in the reaction product proved to be a disadvantage of this procedure. In addition, the reaction product is distilled from the reaction mixture. But, in practice, this method can only be used for the hydroformylation of lower olefins up to approximately penten. In addition, it was shown that with this thermal load, a considerable amount of catalyst is lost due to the decomposition of rhodium complex compounds.

The described disadvantages are avoided by using catalyst systems that are soluble in water. Such catalysts are, for example, described in DE-PS 26 27 354. Solubility of complex rhodium compounds is achieved by using trisulfonated triarylphosphines as a component of the complex. Separation of the catalyst from the reaction product after hydroformylation is done in this case simply by separating the aqueous and organic phases, i.e. without the necessary additional thermal load for distilling the reaction products of the reaction mixture. In any case, the data in the mentioned DE-PS is limited to the discontinuous process in autoclaves, which is not suitable for economic use. According to another method, the solubility of the catalyst system in water is achieved by using single or multiple carboxylated aryline ligands.

So, there was a task of developing a procedure for the production of aldehydes of the aforementioned type that can be successfully carried out technically.

Description of the solution to the technical problem with implementation examples

This invention relates to a continuous process for the production of aldehydes by the reaction of olefins with carbon monoxide and hydrogen in the presence of water and water-soluble rhodium-phosphine complex compounds at elevated temperatures and pressures of 100 to 30,000 kPa. It is indicated that the reactants are mixed well and brought to react at temperatures from 90 to 150°C, in which the proportion of gaseous ingredients in the liquid phase is adjusted to 5 to 30% vol. calculated on the mixed phase, the volume ratio of water to organic phase is 1:1 to 100:1 and first the liquid phase and gaseous phase are separated, then the liquid phase into aqueous and organic parts, always without prior cooling and removal of reaction heat.

The new mode of operation not only ensures that the catalyst system is separated under conditions that are mild and reused in the process, but also allows the reaction to be carried out under technically and economically optimal conditions. Special importance is attributed to the fact that the process according to the invention enables obtaining reaction heat in a simple way, without adversely affecting the service life of the catalyst.

The heat of reaction can be removed in a known manner using water or steam. It has proven particularly well that the reaction heat is directly transferred without an intermediary by means of a medium to the hydroformylation products, so that they evaporate and with the application of the reaction heat are purified by distillation.

The method of operation according to the invention is particularly favorable for converting olefins with 2 to 15 carbon atoms into aldehydes or alcohols rich in carbon atoms.

The reactants, i.e. olefin and synthesis gas, are fed into the reactor together or separately. It is advantageous to heat the reactants primarily to the temperature at which the reaction takes place. It turned out to be advantageous to do the heating with waste heat from the process, for example, the heat of condensation of reaction products during distillation purification.

The reaction of the starting materials in the reactor is carried out at temperatures from 90 to 150°C. By eliminating the distillation removal, the reactant and the additional thermal load are eliminated, and the catalyst is barely deactivated in continuous operation. Minor damage to the catalyst is within economically tolerable limits.

The reaction of the reaction partners in the reactor is carried out in a system consisting of a liquid and gaseous phase. In this case, the liquid phase of the aqueous catalyst solution consists of two components that are not soluble in each other or are very slightly soluble, in the case of a liquid olefin and a liquid organic product, which may also contain an organic solvent. For the reaction to take place, it is necessary that the aqueous phase is saturated with gaseous reactants. In order to achieve this, it is necessary to ensure a large contact surface between the liquid phase, which consists of aqueous and organic components, and the gaseous phase, so that the proportion of gaseous components in the liquid phase is adjusted to 5 to 30% of the volume calculated on the mixed phase. This condition is achieved in several ways. According to the form of implementation of the invention that has proven to be advantageous, gaseous starting materials, i.e. olefin and synthesis gas, are supplied to the content of the reactor, which is intensively mixed. According to the second variant of the procedure, gaseous reaction partners are supplied to the liquid contents of the reactor via appropriate distribution devices. For example, floors and mantles in the form of sieves are advantageous. It is also possible to combine the mixing and distribution of the gaseous reaction partners, for example by using a gas blowing mixer.

A very important aspect of this invention is that the proportion of the organic phase is kept small in the reaction mixture. Namely, it is surprising that the organic phase does not contribute to the solubility of the reactants in the aqueous phase. This avoids that the reaction product enters into unwanted side reactions that cannot be ruled out when the retention time of the product in the reactor increases.

Therefore, according to the invention, the volume ratio of aqueous to organic phase is 1:1 to 100:1, preferably 10:1 to 100:1. There are different ways to adjust the specified volume ratio. The implementation of a new mode of operation that is suitable is to separate a part of the reaction mixture from the reactor and subject it to phase separation, and after returning to the reactor to achieve the desired volume ratio.

According to another embodiment of the invention, phase separation can also be done inside the reactor in the settling zone.

The previously described phase separation is carried out according to the new procedure in each case without prior cooling of the reaction mixture. In this way, we achieve that the gaseous olefins in the liquid components of the reaction mixture dissolve only in small amounts under the given conditions and are very little with the reaction product from the reactor.

The synthesis gas used for hydroformylation contains carbon monoxide and hydrogen, preferably in a volume ratio of 1:1. If necessary, this relationship can be changed if it gives certain effects, such as an increase in the reaction rate.

Complex rhodium compounds are used as catalysts, which, in addition to carbon monoxide and hydrogen, contain sulfonated and carboxylated phosphines. Such phosphines are obtained in particular from triarylphosphines, where the aryl residue is considered to be primarily a phenyl residue and a naphthyl residue. It is not necessary that all three aryl radicals bear sulfonic acid groups or carboxyl groups. It has been shown that even one sulfo group or carboxyl group in the phosphine molecule of the complex compound provides sufficient solubility in water. A previously prepared catalyst can be added to the reaction mixture. It can also be made in situ. Rhodium is usually added in an amount of 50 to 800 ppm based on the aqueous catalyst solution. The sulfonated or carboxylated triarylphosphine must be present in excess of the rhodium complex. It has proven particularly good to add 10 to 100 g of sulfonated carboxylated phosphine molecules per gram of rhodium atom.

Reaction pressures range from 100 to 30,000 kPa of carbon monoxide and hydrogen.

The execution of the reaction according to the process of the invention is shown schematically in Figure 1.

A catalyst system dissolved in water is placed in reactor 1. Olefin and synthesis gas are fed into reactor 1 through lines 2 and reacted with good mixing. Unreacted synthesis gas and olefin leave the reaction product through the extension 3 of the reactor, which is immersed in a mixture with an aqueous catalyst solution. In vessel 4 for separation of gas phases (essentially synthesis gas, olefin and saturated hydrocarbon added from olefin) it is separated from the liquid products and returned to the reactor via circulation compressor 5. Part of the amount of circulating gas is freed from the reaction products by condensation in the cooler 6 and delivered to the waste gas system. The hot liquid that is separated in the separation vessel 4 without prior cooling is fed to the phase separator 7. There, the crude organic product is very easily separated from the aqueous catalyst phase.

By not cooling the organic phase before separating the unreacted reactants, the necessary recirculation of gaseous olefins through the washing column 9 is greatly facilitated. In the hot organic reaction product (crude aldehyde), its solubility is significantly lower than in the cooled reaction product. While the organic reaction product is supplied by pump 8 to the washing column 9, pump 10 transfers the aqueous catalyst phase back to reactor 1, where the heat of the exothermic reaction is transferred in the heat exchanger 11 with the generation of process steam. With the cooled catalyst phase, water is supplied to the reactor via line 12, in order to compensate for the corresponding removal of water via the waste gas and via the oxo product. The hot oxo product that flows into the washing column 9 is led in the opposite direction from the part of the amount of synthesis gas that enters the column via lines 13. The synthesis gas is loaded with olefin dissolved in the oxo product. With an increased temperature, the synthesis gas is fed into the reactor 1. The further partial flow of the synthesis gas is heated using the process heat in the heat exchanger 15. Also, the fresh olefin before entering the reactor is heated and evaporated using the waste heat of the aldehyde distillation in the heat exchanger 14, while the oxo product from the washing column 9 leads directly to distillation uncooled. The buffer tank is only used in case of interference with the intermediate storage of the product.

A further technically particularly advantageous form of carrying out the procedure according to the invention is shown in drawing 2.

An aqueous catalyst solution is placed in the reactor 17. Synthesis gas and olefin are injected through the double shower 18, which serves as a pre-distributor. The bubbling mixer 19 ensures a fine distribution of the reactants. The heat of the exothermic reaction is removed via the cooling pipe 20. In the reactor guide pipe 21, the liquid and gaseous components rise and separate at the upper end of the guide pipe. The gaseous components are returned to the reactor via lines 23 and compressor 24 of the circulating gas or are removed as waste gas via lines 25. The aqueous catalyst solution is separated in the ring separator 26 from the added organic raw product. Through lines 27, the raw product is fed to the washing column 28, where it is freed from the dissolved olefin by synthesis gas, which is led in the opposite direction. The olefin-free crude product is separated in column 29 into n- and iso-components. The heat required for distillation is obtained directly above the cooling lyre 20 in which the liquid aldehyde from the bottom of the column 29 is fed by means of water 30, phase separator 31 and water 32 into the cooling lyre and is vaporized there and fed via water 33, phase separator 31 and water 34 as aldehyde in vapor form again in column 29.

The following examples illustrate the invention.

Example 1 (Comparison)

In reactor 50 I, under reaction conditions, a homogenized mixed phase consisting of aqueous catalyst solution, oxo product, synthesis gas and propylene is maintained by intensive mixing. The continuously drained product stream, containing catalyst solution, oxo product, excess propylene and synthesis gas is cooled before product separation. Under the selected conditions, approximately 4.5 kg of propylene per kg of oxo product was dissolved in the cooled oxo product. The dissolved proportion of propylene in the aqueous phase is negligibly small. The density of the organic phase is 0.6 g/cm3. The density difference between the water phase (density is 1.15 g/cm3) and the organic phase is 0.55 g/cm3. Accordingly, the two phases are quickly and completely separated from each other.

Example 2

The reaction is carried out under the conditions of example 1. Deviating from example 1, the product stream that is removed and consists of the catalyst solution, oxo product, excess propylene and synthesis gas is not cooled before product separation, but is maintained at the reaction temperature. Only 0.4 kg of propylene per kg of oxo product was then dissolved in the oxo product. This establishes a higher average density of the organic phase of 0.75 g/cm3, so that the difference in density compared to the aqueous phase is reduced to 0.4 g/cm3.

Surprisingly, despite the small difference in density, the phase separation takes place just as quickly and completely as according to the method of operation in example 1. The possibility that the organic and aqueous phases can be satisfactorily and technically simply separated without prior cooling greatly facilitates the circulation of propylene. The amount of propylene that needs to be separated via the washing column 9 and returned back to the reactor 1 is reduced from 4.5 to 0.4 kg/kg oxo product and results in significant energy savings.

Example 3

In the 50 l reactor, under reaction conditions, a homogenized mixed phase consisting of catalyst solution, oxo product, synthesis gas and propylene is maintained by intensive mixing. To adjust the phase distribution between the aqueous and organic phases, as well as to remove the reaction heat, 100 l of aqueous catalyst solution is fed into the circular flow every hour using the circular flow pump 10. Under the selected reaction conditions, 10 l of crude aldehyde is created from propylene per hour, so that the ratio between the aqueous phase and the organic phase is 10:1.

The average retention time of crude aldehyde in solution is 27 minutes. The oxo product contains 0.5% by weight of unwanted high-boiling side products.

Example 4

It is carried out under the reaction conditions of example 1, but only 35 l of catalyst solution are introduced into the circular flow per hour. This increases the mean residence time of raw aldehyde in the reactor to 69 minutes. Under these conditions, an oxo product is obtained that has about 1.5% by weight of unwanted, high-boiling side products.

In reactors with an internal cooling coil without a catalyst loop, the mixer speed is chosen depending on the mixing device, so that the mixed phase in the reactor zone contains <10% homogeneously distributed crude aldehyde and the aldehyde phase floating above in the zone of contact on the aqueous catalyst solution is small due to the appropriate maintenance of the level, so that the retention time of the crude aldehyde in the synthesis part is <30 minutes.

It is surprising that the reduction in the number of revolutions, which enables the separation of the organic and aqueous phases in the upper part of the reactor, has no effect on the reactor capacity. Apparently, sufficient saturation of the reactants in the aqueous catalyst phase is achieved in the intensively mixed zone of the reactor.

Claims (9)

1. Process for the production of aldehydes by the reaction of olefins with carbon monoxide and hydrogen in the presence of water and rhodium-phosphine complex compounds at elevated temperatures and pressures of 100 to 30,000 kPa, characterized by the fact that the reactants are well mixed and react at temperatures of 90 to 150° C, in which the proportion of gaseous ingredients in the liquid phase is adjusted to 5 to 30% by volume calculated on the mixed phase, the volume ratio of the aqueous phase to the organic phase is 1:1 to 100:1 and the liquid phase and gaseous phase are separated first, then the liquid phase into aqueous and organic fractions, always without prior cooling and removal of reaction heat. 2. The method according to claim 1, characterized in that the reactants are heated to the reaction temperature before the reaction. 3. The method according to claim 2, characterized in that the heating is performed using process waste heat. 4. Process according to claim 1 to 3, characterized in that the gaseous starting materials are supplied to the intensively mixed content of the reactor. 5. Process according to claim 1 to 3, characterized in that the gaseous starting materials are supplied to the reactor via a distribution device. 6. Process according to claim 1 to 5, characterized in that the volume ratio of water to organic phase is 10:1 to 100:1. 7. The method according to claim 1 to 6, characterized in that heat removal is performed by means of an auxiliary medium such as water or steam. 8. The method according to claim 1 to 6, characterized in that the reaction heat is removed without the aid of an auxiliary medium by evaporating at least part of the reaction products. 9. The process according to claim 1 to 8, characterized in that the separation of the liquid phase into aqueous and organic fractions is performed in the settling zone in the reactor.