Process for the hydroformylation of propylene

Abstract

A process comprises a) subjecting propylene to hydroformylation in the presence of a homogeneous hydroformylation catalyst in a hydroformylation reactor to form a reaction liquid; b) withdrawing a hydroformylation effluent stream from the hydroformylation reactor; c) separating the hydroformylation effluent stream into a raw hydroformylation product stream and a reactor return stream comprising the homogeneous hydroformylation catalyst; and returning the reactor return stream to the hydroformylation reactor; and d) subjecting the raw hydroformylation product stream to work-up to obtain a mixed butyraldehyde stream; and rectifying the mixed butyraldehyde stream in a distillation column so as to obtain an n-butyraldehyde stream and an isobutyraldehyde stream. The process comprises withdrawing a stream of reaction liquid from the hydroformylation reactor, circulating the reaction liquid stream through a cooling loop including at least one heat exchanger, wherein the reaction liquid stream is heat exchanged against a bottoms stream of the distillation column that is recycled through the heat exchanger and returned to the distillation column, to transfer heat from the reaction liquid stream to the bottoms and to obtain a cooled reaction liquid stream, and returning the cooled reaction liquid stream to the hydroformylation reactor. The process allows for an efficient heat integration.

Description

[0001] 240564W001 1

[0002] Process for the Hydroformylation of Propylene

[0003] Hydroformylation ("the oxo process") is an important industrial process for preparing aldehydes from olefins, carbon monoxide and hydrogen.

[0004] Hydroformylation of propylene results in a mixture containing n-butyraldehyde and isobutyraldehyde, which may be subjected to further processing to produce chemicals of interest. In particular, the mixture containing n-butyraldehyde and isobutyraldehyde may be subjected to purification by distillation so as to separate n-butyraldehyde and isobutyraldehyde. The obtained n-butyraldehyde may be subjected to hydrogenation to yield n-butanol. Further, n-butyraldehyde is an important intermediate in the production of 2-ethy I hexanol, via aldol condensation and subsequent hydrogenation.

[0005] Separation of n-butyraldehyde and isobutyraldehyde via distillation is energy-intensive, as the two isomers have only a small difference in boiling point. The prior art has described integrating heat from other process steps in the distillation of butyraldehydes to address this issue.

[0006] CN 114853589 A describes a method for separating n-butyraldehyde, wherein the gas phase obtained at the top of a butyraldehyde distillation column is pressurized and heated, and the heated gas phase is used in a reboiler to heat the bottoms of the column.

[0007] WO 2013 / 131936 A1 relates to a process for heat integration in the preparation of saturated C3-C2o-alcohols, wherein heat is withdrawn from a hydrogenation stream and / or from a distillation column, and wherein the withdrawn heat is in particular used to heat a stream comprising a mixture of aldehydes which is to be subjected to fractional distillation.

[0008] CN 115006862 A describes an n-butanol extraction system, wherein the distillation of n-butanol is thermally coupled with a reboiler of a butyraldehyde distillation column.

[0009] However, the quantities of heat that can be integrated as described in the prior art are not sufficient to completely cover the heat requirement of the butyraldehyde distillation column. It was thus an object of the invention to further utilize sources of energy for the fractional distillation of butyraldehydes.

[0010] Hydroformylation of propylene is a highly exothermic reaction. Unlike for example hydrogenation, hydroformylation is however carried out at relatively low temperatures of about 100 °C, allowing for a rather small temperature difference to the bottoms of the butyraldehyde distillation column, which is typically operated at about 90 °C. This temperature difference has generally not been considered as sufficient to efficiently allow for heat integration of the hydroformylation process with the butyraldehyde distillation.

[0011] It has been found that heat exchange between a hydroformylation reaction liquid and a bottoms stream of the butyraldehyde distillation column, without the use of an intermediate heat transfer liquid, can make the heat transfer efficiency high even at low temperature differences.240564W001 2

[0012] The present invention provides a process comprising:

[0013] a) subjecting propylene to hydroformylation in the presence of a homogeneous hydroformylation catalyst in a hydroformylation reactor to form a reaction liquid;

[0014] b) withdrawing a hydroformylation effluent stream from the hydroformylation reactor;

[0015] c) separating the hydroformylation effluent stream into a raw hydroformylation product stream and a reactor return stream comprising the homogeneous hydroformylation catalyst; and returning the reactor return stream to the hydroformylation reactor; and

[0016] d) subjecting the raw hydroformylation product stream to work-up to obtain a mixed butyraldehyde stream; and rectifying the mixed butyraldehyde stream in a distillation column so as to obtain an n-butyraldehyde stream and an isobutyraldehyde stream;

[0017] characterized by withdrawing a stream of reaction liquid from the hydroformylation reactor, circulating the reaction liquid stream through a cooling loop including at least one heat exchanger, wherein the reaction liquid stream is heat exchanged against a bottoms stream of the distillation column that is recycled through the heat exchanger and returned to the distillation column, to transfer heat from the reaction liquid stream to the bottoms and to obtain a cooled reaction liquid stream, and returning the cooled reaction liquid stream to the hydroformylation reactor.

[0018] Despite the relatively low temperature difference between the hydroformylation reaction and the butyraldehyde distillation, the present process allows for an efficient heat integration. Suitable embodiments of the invention are discussed in the following.

[0019] Hydroformylation

[0020] Step a) of the process comprises subjecting propylene to hydroformylation in the presence of a homogeneous hydroformylation catalyst in a hydroformylation reactor to form a reaction liquid.

[0021] Propylene may be provided as a propylene-comprising feed stream. For example, the propylene-comprising feed stream may be a mixture of propylene and propane. For example, the propylene-comprising feed stream may be so-called "chemical grade propylene", which has a propylene content of 92 to 96 wt.-%, relative to the total weight of the propylene-comprising feed stream. Chemical grade propylene may be obtained by subjecting naphtha or natural gas to steam cracking and subsequent purification. Another example of a suitable propylene-comprising feed stream is so-called "refinery grade propylene”, which has a propylene content of 60 to 80 wt.-%, relative to the total weight of the propylene-comprising feed stream. Preferably, the propylene-comprising feed stream is so-called "polymer grade propylene", which has a propylene content of at least 99.5 wt.-%, relative to the total weight of the propylene-comprising feed stream.

[0022] Hydroformylation of propylene is carried out in the presence of carbon monoxide and hydrogen, which are typically provided as a mixture referred to as synthesis gas. The proportions of carbon monoxide, hydrogen, and propylene in the hydroformylation reaction medium may be selected within a wide range. In some embodiments, based on the total amount of carbon monoxide, hydrogen, and propylene, carbon monoxide constitutes 1 to 50 mol-%, preferably 1 to 35 mol-%; H2 constitutes 1 to 98 mol-%, preferably 10 to 90 mol-%; and propylene constitutes 0.1 to 50 mol-%, preferably 1 to 35 mol-%.240564W001 3

[0023] Homogeneous hydroformylation catalysts are well-known in the art. Suitable catalysts include rhodium complex catalysts having one or more organophosphorus compound(s) as ligands which are homogeneously soluble in the reaction medium of the hydroformylation reaction. Suitable ligands are phosphine ligands from the class of triarylphosphines, Ci-Ce-alkyldiarylphosphines and arylalkyldiphosphines. Preferred hydroformylation catalysts are phosphorus-containing rhodium catalysts, such as those formed in situ under hydroformylation conditions from a rhodium source and a triarylphosphine, e.g., triphenylphosphine, such as RhH(CO)2(PPh3)2 or RhH(CO)(PPh3)3. Further suitable rhodium complex catalysts having sterically hindered phosphorus-containing ligands are described, for example, in US 4,668,651, US 4,748,261, US 4,769,498, US 4,774,361, US 4,835,299, US 4,885,401, US 5,059,710, US 5,113,022, US 5,179,055, US 5,260,491, US 5,264,616, US 5,288,918, US 5,360,938, EP 0472071 and EP 0518241.

[0024] Propylene is typically subjected to hydroformylation in the hydroformylation reactor at a temperature in the range of 100 to 120 °C, preferably 100 to 115 °C, more preferably 100 to 110 °C. At higher temperatures, hydroformylation catalysts, in particular rhodium complex catalysts, are susceptible to rapid deactivation.

[0025] The hydroformylation is typically carried out at a pressure in the range from 10 to 200 bar, in particular 10 to 50 bar, more preferably 10 to 30 bar. The reaction pressure may be varied depending on the activity of the hydroformylation catalyst used.

[0026] The reaction may be conducted either in a batch mode or, preferably, on a continuous basis. One or more hydroformylation reactors may be used in continuous modes to carry out the reaction in one or more stages.

[0027] The hydroformylation reaction preferably takes place in the presence of both liquid and gas phases. The reactants are generally in the gas phase. The catalyst is typically in the liquid phase. Because the reactants are gaseous compounds, a high contact surface area between the gas and liquid phases is desirable to enhance suitably high mass transfer. A high contact surface area between the catalyst solution and the gas phase may be provided in any suitable manner. In a batch process, the batch contents are thoroughly mixed during the course of the reaction. In a continuous operation, the reactor feed gas may be contacted with the catalyst solution in, for example, a continuous-flow stirred autoclave, where the gas is introduced and dispersed at the bottom of the vessel, preferably through a perforated inlet (e.g., a sparger), or in a jet loop reactor such as described in WO 00 / 09467 A1.

[0028] Suitable hydroformylation reactors are typically pressure-resistant and known to those skilled in the art. Suitable hydroformylation reactors include commonly used reactors for gas-liquid reactions, such as gas circulation reactors, and bubble columns, which may be subdivided by internals.

[0029] Step b) of the process comprises withdrawing a liquid hydroformylation effluent stream from the hydroformylation reactor. The hydroformylation effluent stream is generally withdrawn from the bottoms of the hydroformylation reactor.240564W001 4

[0030] Separating the Hydroformylation Effluent Stream

[0031] Before further processing of the hydroformylation effluent stream is possible, it is necessary to remove the catalyst therefrom. Notably, the removal of rhodium-based catalyst complexes from homogeneously catalyzed hydroformylation effluent streams is imperative. This is because rhodium is a very costly noble metal, losses of which must absolutely be avoided.

[0032] Step c) of the process comprises separating the hydroformylation effluent stream obtained in step b) into a raw hydroformylation product stream and a reactor return stream comprising the homogeneous hydroformylation catalyst; and returning the reactor return stream to the hydroformylation reactor.

[0033] The volume ratio of the hydroformylation product stream to the reactor return stream is preferably in the range of 1 : 1 to 1 :5, more preferably 1 : 1.5 to 1 :4.

[0034] Besides the raw hydroformylation product stream and the reactor return stream, further streams, e.g., waste gases comprising synthesis gas and streams comprising high-boiling by-products of the hydroformylation and / or hydroformylation catalyst, may be obtained. These further streams may be, if appropriate after workup, completely or partially recirculated to the reaction zone or discharged from the process.

[0035] Separation processes, which are tried and tested on a large industrial scale, rely on the different boiling points of the components present in the hydroformylation effluent stream by vaporizing the mixture and selectively condensing the vaporizing components. In one embodiment, the hydroformylation effluent stream is decompressed to form a gas phase comprising n-butyraldehyde, isobutyraldehyde, propylene and propane, and the reactor return stream containing high boilers and the homogeneous hydroformylation catalyst. The gas phase may then be partially condensed to obtain the raw hydroformylation product stream comprising n-butyraldehyde and isobutyraldehyde, and non-condensed gases comprising propylene and propane. The non-condensed gases may be at least partially returned to the hydroformylation reactor.

[0036] In one embodiment, step c) of the present process includes:

[0037] - decompressing the hydroformylation effluent stream to form a gas phase comprising n-butyraldehyde, isobutyraldehyde, propylene and propane, and the reactor return stream containing high boilers and the homogeneous hydroformylation catalyst;

[0038] - partially condensing the gas phase to obtain the raw hydroformylation product stream comprising n-butyraldehyde and isobutyraldehyde, and non-condensed gases comprising propylene and propane; and

[0039] - returning at least part of the non-condensed gases to the hydroformylation reactor.

[0040] Owing to the physical solubility of propylene and propane in butyraldehyde, the raw hydroformylation product stream may comprise dissolved propylene and propane. These compounds may may be separated from the raw hydroformylation product stream, for example by degassing of the raw hydroformylation product stream as described below with regard to step d).240564W001 5

[0041] The gas phase and reactor return stream, i.e. the liquid phase, obtained by decompression can advantageously be worked up by the process described in WO 97 / 07086. For this purpose, the liquid phase is heated and introduced into the upper region of a column, while the gas phase is introduced into the bottom of the column. Liquid phase and gas phase are thus conveyed in countercurrent. To increase mutual contact of the phases, the column is preferably provided with a packing. As a result of the intimate contact of the gas phase with the liquid phase, the residual amounts of hydroformylation product, unreacted olefin and saturated hydrocarbon present in the liquid phase are transferred to the gas phase, so that the gas stream leaving the top of the column is enriched in hydroformylation product, unreacted olefin and saturated hydrocarbon compared to the gas stream introduced at the lower end of the column.

[0042] Work-Up and Distillation

[0043] Step d) comprises subjecting the raw hydroformylation product stream to work-up to obtain a mixed butyraldehyde stream; and rectifying the mixed butyraldehyde stream in a distillation column so as to obtain an n-butyraldehyde stream and an isobutyraldehyde stream.

[0044] In one embodiment, step d) of the present process includes degassing of the raw hydroformylation product stream to obtain the mixed butyraldehyde stream, and a gaseous overhead stream comprising propylene and propane.

[0045] The raw hydroformylation product stream may be degassed by depressurizing it, heating it and / or treating it with a stripping gas such as synthesis gas or nitrogen. Degassing is advantageously carried out in a column where the crude hydroformylation product is fed to the middle region of the column, the degassed raw hydroformylation product stream is withdrawn at the bottom of the column, and a gaseous overhead stream comprising unreacted propylene and propane is withdrawn at the top of the column.

[0046] The gaseous overhead stream comprising propylene and propane may be separated into a propylene-enriched fraction and a propylene-depleted fraction by rectification (distillation). Rectification is usually carried out at low temperature and / or superatmospheric pressure. In one embodiment, rectification is carried out at a temperature in the range of 50 to 200 °C, preferably 80 to 170 °C, and a pressure in the range of 3 to 15 bara, preferably 6 to 10 bara.

[0047] Rectification is generally carried out in a column which is provided with a sufficiently large number of rectification trays. Columns for such separation tasks are known per se and are used, for example, for the separation of olefins and saturated hydrocarbons present in the cracker gas from a steam cracker. The stream to be fractionated is preferably introduced in the middle region of the column. The propylene-enriched fraction can advantageously be withdrawn at the top or in the upper region of the column, and the propylene-depleted fraction can advantageously be withdrawn at the bottom or in the lower region of the column.

[0048] In general, efforts are made to obtain a propylene-depleted fraction consisting of substantially pure propane, so that it can be discharged from the process without resulting in a relatively large loss of propylene. In contrast, pure propylene is generally not sought in the case of the propylene-enriched fraction, but instead a certain content of propane is permitted so as to reduce the cost of the separation. For the purposes of the present invention, it is sufficient for the propylene-enriched fraction to be enriched in propylene compared240564W001 6

[0049] to the raw hydroformylation product stream, i.e. the ratio of propylene to propane in it is greater than in the raw hydroformylation product stream.

[0050] The propylene-depleted fraction preferably comprises more than 95% by weight, in particular more than 99% by weight, of propane. The propylene-enriched fraction usually comprises more than 80% by weight, e.g., from 85 to 95% by weight, of propylene, with the balance being propane.

[0051] Preferably, at least part of the propylene-enriched fraction is recirculated to the hydroformylation reactor.

[0052] The propylene-depleted fraction may be discharged from the system. It can, for example, be used as fuel. It can also be used as feedstock for chemical reactions, e.g., in a steam cracker. In one embodiment, the propylene-depleted fraction is fed to a steam cracker from whose cracker gas a propylene-comprising stream for the present process is obtained. After attainment of steady-state operation of the present process, an amount of propane which corresponds essentially to the sum of the amount of propane introduced with the propylene-comprising stream and the amount formed in the hydroformylation is discharged together with the propylene-depleted fraction.

[0053] The mixed butyraldehyde stream preferably has a proportion of n-butyraldehyde and isobutyraldehyde of at least 80% by weight, preferably at least 90% by weight, in particular at least 95% by weight, based on the total weight of the mixture. The further components comprise butanols and high-boiling components, e.g., products of aldol condensation.

[0054] The mixed butyraldehyde stream is rectified in a distillation column so as to obtain an n-butyraldehyde stream and an isobutyraldehyde stream.

[0055] The distillation of the mixed butyraldehyde stream may be carried out by any suitable process known to those skilled in the art. Suitable distillation columns include tray columns, which may be provided with, e.g., bubble caps, sieve plates, sieve trays, packings, internals, valves, recirculation loops and side outlets. The distillation column suitably comprises packings, which allow for a significantly lower pressure loss compared to trays and moreover allow for a lower bottoms temperature at the same pressure at the top of the column. Thermally coupled columns and dividing wall columns which can be provided with, e.g., side outlets and / or recirculation loops, are especially suitable. A combination of two or more than two distillation columns may be used for the distillation.

[0056] A suitable process for the distillation of the mixed butyraldehyde stream may be found in WO 00 / 58255.

[0057] In one embodiment, the bottoms temperature of the distillation column is in the range of 75 to 95 °C. In one embodiment, the pressure at the top of the distillation column is in the range of 1.0 to 2.0 bara, preferably 1.0 to 1.8 bara, more preferably 1.1 to 1.5 bara.

[0058] To supply the energy necessary for the distillation, each distillation column may be equipped with conventional heating, e.g., by means of steam, in addition to the heat exchange described in the following.240564W001 7

[0059] Heat Exchange

[0060] The process comprises withdrawing a stream of reaction liquid from the hydroformylation reactor and circulating the reaction liquid stream through a cooling loop including at least one heat exchanger. The reaction liquid stream is heat exchanged against a bottoms stream of a distillation column that is recycled through the heat exchanger and returned to the distillation column, to transfer heat from the reaction liquid stream to the bottoms and to obtain a cooled reaction liquid stream, and the cooled reaction liquid stream is returned to the hydroformylation reactor.

[0061] The reaction liquid may be withdrawn from the hydroformylation reactor at any suitable location, such as from the bottoms or via a side draw of the hydroformylation reactor. Preferably, the reaction liquid is withdrawn from the bottoms of the hydroformylation reactor. In one embodiment, the process comprises dividing from the hydroformylation effluent stream obtained in step b) a partial stream to form the reaction liquid stream.

[0062] The reaction liquid stream is heat exchanged against a bottoms stream of the distillation column that is recycled through the heat exchanger and returned to the distillation column, to transfer heat from the reaction liquid stream to the bottoms and to obtain a cooled reaction liquid stream.

[0063] Generally, the reaction liquid stream is heat exchanged against the bottoms stream via a heat exchange surface, e.g., a wall. The local temperatures during heat exchange depend primarily on the direction of flow of the reaction liquid stream, i.e. , the hot medium, and the bottoms stream of the distillation column, i.e., the cold medium. A distinction may be made between three basic configurations:

[0064] - parallel or concurrent flow: hot and cold medium flow along the heat exchange surface in the same direction,

[0065] - countercurrent: hot and cold medium flow in opposite directions on the two sides of the heat exchange surface,

[0066] - cross-current and transverse flow: the stream comprising the hot medium flows perpendicularly onto the heat exchange surface, i.e., transverse to the cold medium.

[0067] Preferably, the reaction liquid stream is heat exchanged against the bottoms stream in countercurrent.

[0068] Combinations of these basic configurations are possible. Thus, cross-countercurrents, in which the hot and cold medium are conveyed in a sinusoidal manner by means of deflection plates, are frequently employed in shell-and-tube reactors.

[0069] In order to allow for an efficient heat exchange between the stream of reaction liquid from the hydroformylation reactor and the bottoms stream of the distillation column that is recycled through the heat exchanger and returned to the distillation column, the temperature difference between the two streams to be heat-exchanged should be sufficiently high.

[0070] In one embodiment, the temperature difference between the bottoms temperature of the distillation column and the reaction liquid stream is at least 10 °C, more preferably at least 15 °C.240564W001 8

[0071] In one embodiment, the bottoms temperature of the distillation column is in the range of 75 to 95 °C, and the reaction liquid stream has a temperature in the range of 100 to 120 °C, preferably 100 to 115 °C, more preferably 100 to 110 °C.

[0072] The type of heat exchangers is not especially limited. Suitable heat exchangers include condensers and evaporators. The heat exchangers may be in any typical configuration, e.g. plate exchangers, ring groove exchangers, finned tube exchangers, lamella exchangers, double tube exchangers, shell-and-tube exchangers, split tube exchangers, disk exchangers, spiral exchangers, block exchangers, scraped exchangers, screw exchangers, helical exchangers, fluidized-bed exchangers, candle exchangers, cooled circulation exchangers and two- and three-tube coil exchangers.

[0073] In one embodiment, the at least one heat exchanger has a specific heat exchange area of at least 0.2 m2per cubic meter per hour of the bottoms stream, preferably at least 0.25 m2per cubic meter per hour of the bottoms stream, more preferably at least 0.3 m2per cubic meter per hour of the bottoms stream.

[0074] In one embodiment, the cooling loop includes one heat exchanger. In another embodiment, the cooling loop comprises more than one heat exchanger, such as 2, 3 or 4 heat exchangers, preferably 2 or 3 heat exchangers, more preferably 2 heat exchangers. A cooling loop with more than one heat exchanger allows for a larger total heat exchange surface area and thus a more efficient heat exchange.

[0075] When the cooling loop comprises more than one heat exchanger, the heat exchangers may be connected in series or operated in parallel. Preferably, the heat exchangers are operated in parallel. In this embodiment, the reaction liquid stream and the bottoms stream are each divided into a number of partial streams corresponding to the number of heat exchangers. Each partial liquid stream is heat exchanged with one partial bottoms stream in a heat exchanger. The obtained cooled partial reaction liquid streams are combined to form the cooled reaction liquid stream. The obtained heated partial bottoms streams are combined to form a heated bottoms stream that is returned to the distillation column.

[0076] In one embodiment, the reaction liquid stream is circulated through the cooling loop via one or more pumps. The type of pump is not especially limited and is suitably chosen depending on the volume of the reaction liquid stream to be circulated. Suitable types of pumps include multiphase pumps, such as helico-axial (centrifugal) pumps and twin-screw pumps. Known manufacturers of multiphase pumps include Leistritz, Sulzer, Egger, sib and EDUR.

[0077] In order to achieve an efficient heat exchange, the volume flow of the reaction liquid stream must be sufficiently high, and should be chosen in dependence of the temperature difference between the bottoms temperature of the distillation column and the reaction liquid stream, as well as on the quantity of heat to be exchanged. Large volume flows of the reaction liquid stream notably require large pipework cross-sections, which lead to a large hold-up in the cooling loop.

[0078] However, the reaction liquid stream comprises all starting materials for the hydroformylation reaction and the catalyst and is, at least until it is brought into contact with the heat exchanger, at the reaction temperature. Thus, the hydroformylation reaction continues in the stream at least until the reaction rate is significantly reduced by withdrawal of heat or until the stream is depleted in one component due to progress240564W001 9

[0079] of the reaction to such an extent that the hydroformylation stops, as discussed in EP 1 467960. This depletion is generally depletion of the gaseous components dissolved in the stream and especially of the carbon monoxide, which is generally present in the lowest concentration, based on the starting materials. When the stream is depleted in carbon monoxide, hydrogenation of propylene by hydrogen still present can occur as an undesirable secondary reaction. The formation of propane results in an undesirable loss of expensive starting materials.

[0080] To avoid this disadvantage and to make use of the pipe volume of the cooling loop as reactor space, and to prevent the catalyst system losing its activity, circulation of the reaction liquid stream through a cooling loop is carried out while retaining a minimum carbon monoxide partial pressure. To this end, it may be expedient to meter carbon monoxide into the reaction liquid stream up to the point at which the reaction liquid stream is brought into contact with the heat exchanger, or even beyond. The introduction of carbon monoxide into the reaction liquid stream may be carried out by any suitable method known to those skilled in the art, e.g., by simple combination of the streams at one or more feed points or via gas distributors, frits or perforated plates.

[0081] Preferably, syngas is metered into the reaction liquid stream at one or more points of the cooling loop. Syngas is preferably metered into the reaction liquid stream on the discharge side of the one or more pumps so as to minimize disruption to the pumps. It is preferable to meter syngas into the reaction liquid stream at more than one point of the cooling loop. This allows for reducing the volume flow of gas necessary per metering point, minimizing disruption to the pumps and heat exchangers, and an overall higher dispersion of the gas in the reaction liquid stream.

[0082] Syngas may be metered into the reaction liquid stream via a gas distributor arranged within a reaction liquid stream pipe. Gas is fed to the gas distributor via a gas inlet and is fed into the reaction liquid stream through openings in the gas distributor. Suitable gas distributors include straight-pipe, cross-shaped, ring and conical gas distributors, in particular ring gas distributors.

[0083] Straight-pipe gas distributors have the advantage of being easily replaceable and robust over a wide range of loads. While straight-pipe gas distributors do not distribute the gas across the entire cross-section of the reaction liquid stream pipe, gas distribution is usually sufficient if the flow of the reaction liquid stream is turbulent. Preferably, the straight-gas distributor is mounted via a bearing arranged on the inside of the pipe wall. This allows for reducing flow-induced vibrational damage to the gas distributor.

[0084] Ring gas distributors may be adapted so that the gas flows into the reaction liquid stream via openings on the inside of the ring, via openings on the outside of the ring, or via openings on the inside of the ring and on the outside of the ring. Ring gas distributors allow for a high degree of gas distribution in the reaction liquid stream.

[0085] In a preferred embodiment, the gas distributor is arranged so that the gas flows perpendicular to the reaction liquid stream. This advantageously allows for the reaction liquid stream to shear off gas bubbles of relatively small size, allowing for an improved gas distribution within the reaction liquid stream.240564W001 10

[0086] In one embodiment, the gas velocity at the openings of the gas distributor is at least 2 m / s, preferably at least 3 m / s, more preferably at least 5 m / s.

[0087] In one embodiment, the pressure drop across the openings of the gas distributor is about 5 mbar, preferably at least 10 mbar, more preferably at least 15 mbar.

[0088] The openings of the gas distributor typically have a diameter of 0.3 to 15 mm, more preferably 0.5 to 10 mm, most preferably 0.7 to 7 mm.

[0089] The mechanical stability of the gas distributor(s) may be enhanced, e.g., by providing reinforcements, supporting the gas distributor(s) on the inside of the pipe wall, and / or increasing the material thickness of the gas distributor(s).

[0090] The cooled reaction liquid stream is returned to the hydroformylation reactor. The cooled reaction liquid stream may be returned to the hydroformylation reactor at any suitable location, such as via the top of the reactor or via a side draw of the reactor. Preferably, the cooled reaction liquid stream is returned to the hydroformylation reactor via the top of the reactor.

[0091] Return of the cooled reaction liquid stream to the reactor may preferably be accomplished via at least one nozzle. Preferably, the cooled reaction liquid stream is introduced via the nozzle at high velocity to generate a circulation flow in the reactor that ensures gas distribution and thorough mixing of the reaction liquid in the reactor. The nozzle preferably has a nozzle design suitable for producing a liquid jet. In a particularly preferred embodiment, the nozzle is in the form of a binary nozzle, with which the reaction gas is sucked in by the liquid jet produced in the nozzle, mixed into said jet and dispersed with it into the reaction liquid in the form of fine gas bubbles.

[0092] In order to ensure a sufficiently high velocity at which the reaction liquid stream is returned to the reactor, the stream of reaction liquid withdrawn from the hydroformylation reactor may be divided into two substreams, with one of the substreams being passed via the at least one heat exchanger. The other substream may be directed back to the reactor, bypassing the at least one heat exchanger. Conveniently, the cooled reaction liquid substream having passed the at least one heat exchanger and the bypassing substream are combined and the combined stream is returned to the reactor.

[0093] The cooling loop may include a heat exchanger heated with steam for start-up of the hydroformylation reactor.

[0094] Production of n-Butanol

[0095] In one embodiment, the process further comprises subjecting at least part of the n-butyraldehyde stream to hydrogenation in a hydrogenation zone to obtain an n-butanol stream.

[0096] In the hydrogenation, the n-butyraldehyde stream is contacted with a hydrogen-comprising gas stream. The hydrogen-comprising gas stream preferably comprises more than 80 mol-% of hydrogen, such as more than240564W001 11

[0097] 90 mol-%, more than 95 mol-% or more than 99 mol-% of hydrogen. In particular, the hydrogen-comprising gas stream consists essentially of hydrogen, i.e., more than 99.9 mol-% of hydrogen.

[0098] The hydrogenation is typically carried out with a hydrogen-comprising gas stream in the liquid or gas phase in the presence of a hydrogenation catalyst. Homogeneous or heterogeneous catalysts may be used. Copper-based catalysts have proven to be especially suitable.

[0099] The temperature in the hydrogenation zone is preferably from 50 to 300°C, in particular from 100 to 250°C. The reaction pressure in the hydrogenation zone is preferably from 5 bar to 300 bar, in particular from 10 to 150 bar.

[0100] In one embodiment, an n-butanol-containing stream emerging from the hydrogenation zone is heat exchanged against the bottoms of the distillation column, to transfer heat from the n-butanol-containing stream to the bottoms and to obtain a cooled n-butanol-containing stream. The heat exchange may be performed analogously to that described above.

[0101] Production of 2-Ethy lhexanol

[0102] In one embodiment, the process further comprises subjecting at least part of the c stream to aldol condensation to obtain a 2-ethylhexenal stream; and g) subjecting the 2-ethy lhexenal stream to hydrogenation in a hydrogenation zone to obtain a 2-ethylhexanol-containing stream.

[0103] An aldol condensation is a well-known condensation reaction in which an enol or an enolate ion reacts with a carbonyl compound to form a p-hydroxyaldehyde or p-hydroxyketone (an aldol reaction) in the presence of an acid or base catalyst, followed by dehydration to give a conjugated enone and hydrogenation to the corresponding alcohol. n-Butyraldehyde can be reacted in a self-aldol condensation.

[0104] Aldol condensations can occur under a variety of conditions under weak acidic or strong basic conditions and in the presence of various catalysts. The reaction is typically be carried out in liquid phase using an aqueous caustic catalyst at a temperature of about 80 to 140 °C to yield 2-ethylhexenal.

[0105] In another embodiment, the reaction can be carried out in gaseous phase by contacting the aldehyde in the vapor phase with a particulate catalyst comprising at least one basic alkali metal compound on an inert substrate at a temperature above 175 °C. Further details are provided in WO 2000 / 031011.

[0106] The obtained 2-ethylhexenal can be hydrogenated to 2-ethy lhexanol. The hydrogenation can be carried out analogously to the above-described hydrogenation of the n-butyraldehyde stream.

[0107] In one embodiment, the 2-ethylhexanol-containing stream emerging from the hydrogenation zone is heat exchanged against the bottoms of the distillation column, to transfer heat from the 2-ethylhexanol-containing stream to the bottoms and to obtain a cooled 2-ethylhexanol-containing stream. The heat exchange may be performed analogously to that described above.240564W001 12

[0108] Preferably, the reaction heat from the hydrogenation(s) of the n-butyraldehyde stream and / or the 2-ethylhexenal stream is completely coupled in. In this case, the process may be configured so that only part of the reaction heat from the hydroformylation is used for the distillation of the n-butyraldehyde stream. The other part of the heat is released to the environment, e.g., via air or water cooler.

[0109] The hydrogenation(s) is / are preferably carried out continuously. Each hydrogenation zone can comprise a single reactor or a plurality of hydrogenation reactors. In a specific embodiment of the process of the invention, the hydrogenation feed is subjected to continuous hydrogenation in at least two (e.g. two, three or more than three) hydrogenation reactors connected in series. Each hydrogenation is preferably carried out in a combination of two hydrogenation reactors. This allows particularly advantageous removal of the heat of hydrogenation evolved.

[0110] Figure

[0111] The invention is further illustrated by the enclosed figure.

[0112] Fig. 1 shows a schematic depiction of the present process.

[0113] According to Fig. 1, propylene stream 102 and syngas stream 103 are fed to hydroformylation reactor 101, wherein propylene is subjected to hydroformylation in the presence of a homogeneous hydroformylation catalyst to form a reaction liquid. A hydroformylation effluent stream 104 is withdrawn from reactor 101. A partial stream 106 is circulated through the external loop comprising pump 107.

[0114] Another partial stream 105 is sent to work-up to obtain a mixed butyraldehyde stream, and the mixed butyraldehyde stream is rectified in a distillation column so as to obtain an n-butyraldehyde stream and an isobutyraldehyde stream (not shown in the figure).

[0115] Stream 106 is conveyed via pump 107 and divided into substreams 108 and 114. Reaction liquid stream 108 is heat exchanged against the bottoms of the distillation column via bottoms streams 109, 110 in heat exchangers 111, 112 in parallel. The heated bottoms streams 109, 110 are returned to the distillation column.

[0116] Substream 114 bypasses heat exchangers 111, 112 and is united with cooled reaction liquid stream 113. The united stream is fed to cooler 115, and subsequently returned to reactor 101.

[0117] Syngas may be metered into the reaction liquid stream at one more points, for example via points 116, 117 and / or 118.

Claims

240564W001 13Claims1. A process comprising:a) subjecting propylene to hydroformylation in the presence of a homogeneous hydroformylation catalyst in a hydroformylation reactor to form a reaction liquid;b) withdrawing a hydroformylation effluent stream from the hydroformylation reactor;c) separating the hydroformylation effluent stream into a raw hydroformylation product stream and a reactor return stream comprising the homogeneous hydroformylation catalyst; and returning the reactor return stream to the hydroformylation reactor; andd) subjecting the raw hydroformylation product stream to work-up to obtain a mixed butyraldehyde stream; and rectifying the mixed butyraldehyde stream in a distillation column so as to obtain an n-butyraldehyde stream and an isobutyraldehyde stream; characterized by withdrawing a stream of reaction liquid from the hydroformylation reactor, circulating the reaction liquid stream through a cooling loop including at least one heat exchanger, wherein the reaction liquid stream is heat exchanged against a bottoms stream of the distillation column that is recycled through the heat exchanger and returned to the distillation column, to transfer heat from the reaction liquid stream to the bottoms and to obtain a cooled reaction liquid stream, and returning the cooled reaction liquid stream to the hydroformylation reactor.

2. The process according to claim 1, wherein step c) includes:- decompressing the hydroformylation effluent stream to form a gas phase comprising n-butyraldehyde, isobutyraldehyde, propylene and propane, and the reactor return stream containing high boilers and the homogeneous hydroformylation catalyst;- partially condensing the gas phase to obtain the raw hydroformylation product stream comprising n-butyraldehyde and isobutyraldehyde, and non-condensed gases comprising propylene and propane; and- returning at least part of the non-condensed gases to the hydroformylation reactor.

3. The process according to claim 1 or 2, wherein the step d) includes degassing of the raw hydroformylation product stream to obtain the mixed butyraldehyde stream, and a gaseous overhead stream comprising propylene and propane.

4. The process according to any one of the preceding claims, wherein the bottoms temperature of the distillation column is in the range of 75 to 95 °C, and wherein the reaction liquid stream has a temperature in the range of 100 to 120 °C, preferably 100 to 115 °C, more preferably 100 to 110 °C.

5. The process according to any one of the preceding claims, wherein the temperature difference between the bottoms temperature of the distillation column and the reaction liquid stream is at least240564W001 146. The process according to any one of the preceding claims, wherein the at least one heat exchanger has a specific heat exchange area of at least 0.2 m2per cubic meter per hour of the bottoms stream.

7. The process according to any one of the preceding claims, wherein the reaction liquid stream is circulated through the cooling loop via one or more pumps.

8. The process according to claim 7, wherein at one or more points of the cooling loop, syngas is metered into the reaction liquid stream, preferably into the reaction liquid stream on the discharge side of the one or more pumps.

9. The process according to any one of the preceding claims, comprising dividing from the hydroformylation effluent stream a partial stream to form the reaction liquid stream.

10. The process according to any one of the preceding claims, wherein the process further comprises subjecting at least part of the n-butyraldehyde stream to hydrogenation in a hydrogenation zone to obtain an n-butanol stream.

11. The process according to claim 10, wherein an n-butanol-containing stream emerging from the hydrogenation zone is heat exchanged against the bottoms of the distillation column, to transfer heat from the n-butanol-containing stream to the bottoms and to obtain a cooled n-butanol- containing stream.

12. The process according to any one of the preceding claims, wherein the process further comprises subjecting at least part of the n-butyraldehyde stream to aldol condensation to obtain a2-ethylhexenal stream; and g) subjecting the 2-ethylhexenal stream to hydrogenation in a hydrogenation zone to obtain a 2-ethy lhexanol-containing stream.

13. The process according to claim 12, wherein the 2-ethylhexanol-containing stream emerging from the hydrogenation zone is heat exchanged against the bottoms of the distillation column, to transfer heat from the 2-ethylhexanol-containing stream to the bottoms and to obtain a cooled2-ethylhexanol-containing stream.

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