BE853377A - PROCESS FOR THE CONTINUOUS PREPARATION OF ALDEHYDES BY HYDROFORMYLATION - Google Patents

Description

       

  Process for the continuous preparation of aldehydes by hydroformylation.

  
The present invention relates to the preparation of aldehydes by hydroformylation, that is to say by treating an alpha olefin with carbon monoxide and hydrogen in the presence of a rhodium catalyst.

  
The article by J. Falbe, "Carbon Monoxide in Organic Synthesis", Springer-Verlag, New-York (1970) on page 3, indicates that "hydroformylation is the reaction of an unsaturated (or saturated compound) compound. capable of forming an “unsaturated” compound with carbon monoxide and hydrogen, “yielding an aldehyde.” The process is also referred to as the “Oxo” process. Until recently, all industrial reactions of hydroformylations used a cobaltcarbonyl catalyst. According to the aforementioned article by Falbe (on page 70), with the sole exception of the process developed by Shell, "all the oxo processes used industrially follow more or less the technique "developed by Ruhrchemie AG in Oberhausen / Germany, in co-operation with BASF".

   This article indicates that the existing installations implementing the oxo process operate continuously and in general "they include

  
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2. The catalyst removal part. 3. The catalyst regeneration and renewal part. 4. The distillation of the aldehydes. 5. The reactor for the hydrogenation of the aldehydes. 6. The distillation of alcohols ".

  
The Shell process differs in that it uses a modified cobalt catalyst, prepared by combining, in the hydroformylation reactor, a cobalt salt of an organic acid, trialkylphosphines (for example tributylphosphine), and a base such as KOH. The HCo (CO) 3PR3 catalyst, formed in situ "is thermally more

  
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in the reactor may be about 100 "bar lower, while it should be 200 to 300 bar" in other processes "(Falbe, article cited, page 73).

  
Although the first installations implementing the oxo process were intended for a heterogeneous reaction modeled on the catalysis according to the Fischer Tropsch process, it was finally found that the catalysis was homogeneous (the aforementioned article by Falbe, page 14). The separation and recovery of the catalyst therefore constitute an essential step in the oxo process. This is especially the case when the catalyst contains rhodium, which is a precious metal. As noted in the article by Cornils et al., "HYDROCARBON PROCESSING", June 1975, page 86 "although" Rh compounds are more active than cobalt, they are "much more expensive. Cobalt costs roughly 40 francs per kilogram and rhodium 88,000 to 144,000 francs per kilogram (September 1974 and February 1975). This difference "indicates the speculative nature of the price of rhodium.

   The "cost would hardly matter if the rhodium could" be 100% recovered and used at low concentrations. The inability to profitably recycle rhodium "has precluded the use of unmodified compounds.

  
"rhodium until now, even when the aldehydes to be" formed had to have a chain with branches

  
"and when only rhodium salts could allow" the oxo reaction. In fact, the desired low concentrations of rhodium, ranging between several ppm and several hundred ppm, relative to the olefin feed (0.1 to 1% of cobalt, depending on the process used), still make "more difficult chemical, heat or" extraction of the products formed by the oxo process and containing a metalcarbonyl. Accordingly, there are "a number of special processes for removing" traces of rhodium from products formed by the oxo process "(eg adsorption to" high surface area solids, concentration by distillation "). heavy tails from the synthesis according to the oxo process,

  
"treatment with steam, halogens or carboxylic acids, or other methods). Often," these methods require an expensive recovery step "intended for concentration and outside operation. of "the oxo installation. A loss of rhodium of only one ppm per "kilogram of product of the oxo process causes losses" of material corresponding to approximately 0.08 to 0.14 f / kg (whereas "the corresponding value is 0.04 f / kg with “cobalt catalysts” (ppm = parts per million).

  
The aforementioned article by Cornils et al., Pages 87, 88 and 90, describes and shows in particular in FIG. 9 a proposed type of industrial installation implementing a modified oxo process, with a rhodium-based catalyst. The article indicates that the catalyst must be recycled to the reactor, from the distillation column. Given the heavy tails formation, this article, on page 88, states that "full recycle of" rhodium only through the "primary" recycle "9 circuit would cause enrichment in the" high boiling temperature "components.

   The same page of the same article indicates that "to overcome this drawback, a" part of the bottoms stream from column 3 is continuously withdrawn as a side stream and distilled in column 6 to give a product. head as “light aldols.” The article continues as follows:

  
"Provided the activity is sufficient, the bottoms which are heat treated twice at this time are recycled to the reactor as a" secondary "stream of rhodium. The distillation in column 6 does not cause the removal of the by-products to.

  
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"synthesis according to the oxo method, since these cannot" be separated from the excess ligand. The separation of the rhodium complexes from the constituents at medium boiling temperature is carried out in a column 7 which receives "an auxiliary stream coming from the bottoms of the column" 6. The bottoms of column 7 are heat treated "so often that the rhodium contained is inactive in the framework of the oxo process and must be regenerated during an" external step implemented in a renewal circuit 8. This rhodium is recycled to the reactor under

  
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"with loss, however, of the ligand bound to the complex and of

  
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"circulating per year in the tertiary recycling circuit" corresponds to approximately double the initial quantity "of rhodium used in the whole of the system implementing" the oxo process ".

  
The same article by Cornils et al. Contains the following considerations, on page 89:

  
"Concentrations of rhodium of 0.1%, take account of the quantities of rhodium present during the various

  
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"arbitrary, require high expenditure in the form of" the first investments in catalyst. The relationship "between the initial investment price required" for the catalyst in cobalt oxo plants

  
"and modified with rhodium corresponds to a ratio of 1/5 (1/3," depending on the price of rhodium). However, leakage and "accidental loss of rhodium is greater than" the initial cost of the catalyst. Compared to other industrial processes using precious metal catalysts, a loss of rhodium of 1 mg / kg of "oxo" product is considered to be considered in practice. The cost "of the material then corresponds to a value. from 0.08 to

  
"0.14 f / kg, depending on the price of rhodium. The losses of rho" dium must decrease to a value less than 0.3 ppm "so that the cost of the material is equal to that of a" catalyst of a conventional oxo process ".

  
British Patent No. 1,228,201 describes a process analogous to that of the aforementioned article. According to the processes described in this patent, the catalyst recycle stream is a primary characteristic, except when the catalyst is on. a solid support, in

  
a fixed bed system. However, as indicated in the aforementioned article by J. Falbe, the reaction is in reality of a homogeneous type and one could suppose that placing rhodium on an inert support could cause significant losses of catalyst.

  
British Patent No. 1,312,076 describes the use of a different technique for separating the catalyst.

  
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removing a stream of product vapors, at the top, and the product aldehydes are separated from this stream by fractional distillation, a liquid stream being constantly withdrawn from the reactor and containing the complex catalyst, aldehydes and residues at elevated temperature of 'boiling, the flow_liquid passing at the pressure of

  
reaction at the surface of a membrane so that part of the high boiling temperature residues and aldehydes infiltrate through the membrane and be removed,

  
the remainder of the liquid stream containing the catalyst being recycled to the reactor.

  
British patent application n [deg.] 23 678/69 indicates that, during a homogeneous catalysis of the type described, the removal of the catalyst contained in the reaction products, with a view to recycling, is an operation difficult. This application indicates that the catalyst can be recycled in the residue obtained after distillation of the main products of the reaction, but at the cost of a loss.

  
catalyst.

  
US Pat. No. 3,539,634 further indicates the difficulties of recovery.

  
of the catalyst in an oxo reaction, and indicates that the heavy part and / or the bottoms of the separated products formed by the reaction, containing the catalyst, can circulate in an inert bed allowing the extraction of the catalyst by a reaction solvent. Such a process requires the use of a solvent capable of ensuring the extraction and simultaneously requires infinite possibilities of extraction in order

  
that the loss of catalyst is zero.

  
The invention relates to a process for the preparation of products of the oxo process by hydroformylation of alpha olefins, using a catalyst modified with rhodium,

  
this process not exhibiting in practice any loss of the rhodium catalyst during long periods of use.

  
The process according to the invention is of the continuous type and it is used for the preparation of aldehydes, by hydroformylation of alpha olefins containing from 2 to 5 carbon atoms approximately. This process comprises forming a liquid mass of a homogeneous mixture containing the olefin, carbon monoxide and hydrogen being constantly transmitted to the liquid mass, the aldehydes produced and the condensation products of aldehydes at temperature. high boiling constantly forming in the liquid mass which also contains a soluble rhodium catalyst complexed with carbon monoxide and a triarylphosphine. The quantity of triarylphosphine present in the liquid mass corresponds to at least 10 moles per mole of metallic rhodium present in this liquid mass.

   The latter receives a recycled gas stream containing hydrogen and olefin, and additional amounts of carbon monoxide, hydrogen and olefin are added to the liquid mass. The temperature thereof is maintained at a value between approximately 50 and 140 [deg.] C, and the total pressure is maintained at less than approximately 28 bars absolute. The partial pressure of carbon monoxide used in the reaction is less than 3.5 bars absolute, and the absolute partial pressure of hydrogen is less than 14 bars.

   A mixture in the gaseous state, containing vapors of olefin, hydrogen and aldehydes produced as well as a certain quantity of vaporized aldehyde condensation products, in an amount practically equal to the rate of formation in the liquid mass , is removed from the latter so that it retains a predetermined value. The aldehydes produced and their condensation products are removed from the mixture in the vapor phase, and a recycled gas stream is formed which is transmitted to the liquid mass as indicated above.

  
United States Patent No. 3,527,809 describes a significant improvement in the hydroformylation of alpha olefins, with the formation of aldehydes, at high yields for low temperatures and pressures, the catalysts having excellent stability, the alpha olefin containing at least 3 carbon atoms,

  
this process allowing the formation of mixtures of aldehydes in which the ratio of normal isomers to isomers

  
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posed rhodium complexes for the efficient catalysis, under a determined set of conditions and in the presence of selected ligands of triorganophosphorus, of the hydroformylation of olefins using hydrogen and carbon monoxide. The various parameters are (1) the rhodium complex catalyst, (2) the olefin feed, (3) the triorganophosphorus ligand and its concentration, (4) a relatively low temperature range, (5) a total pressure of relatively low hydrogen and carbon monoxide, and (6) restriction of the partial pressure of carbon monoxide. The method according to the invention uses the parameters described in this aforementioned patent n [deg.] 3 527 809, and experiments carried out

  
from operations described in this patent show the considerable progress represented by the invention in the field of oxo processes.

  
Among the catalysts described in the aforementioned patent of the United States of America, mention may be made of compounds containing rhodium in complex combination with carbon monoxide and ligands / triarylphosphorus, in particular, triarylphosphine ligands, for example. triphenylphosphine (TPP). An example of an active catalytic species is rhodium hydridocarbonyltris- (triphenylphosphine) which

  
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an excess of triorganophosphorus ligand.

  
The active rhodium catalyst, as indicated in recent literature, can be formed beforehand and then introduced into the reaction mixture, or the active catalytic species can be prepared in situ during the hydroformylation reaction. In an example of the latter case, (2,4-pentanedionato) dicarbonylrhodium (l) can be introduced into the reaction mixture in which, under suitable conditions, it reacts with the triorganophosphorus ligand, for example triphenylphosphine,

  
and thus forms an active catalyst such as rhodium hydridocarbonyl-tris (triphenylphosphine).

  
When the process described in the aforementioned patent

  
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normally liquid inert organic solvents which are not reaction products or reagents used during the process, the mixture of products finally becomes, at room temperature or at the chosen temperature of use of 80 [deg.] C per example, slightly cloudy or shows noticeable precipitation. Elemental analyzes indicate that the solids (of the precipitate or cloud forming) contain rhodium. In some cases solid "polymer" complexes of rhodium appear to have formed, and in other cases the solids are analogous to an active form of the rhodium complex species. Such solids can be lost in the system, for example they can settle in small crevices or cracks or in plug valves.

   As previously stated, a truly efficient industrial oxo operation cannot tolerate the loss of even small amounts of rhodium. Another disadvantage of introducing the rhodium species in the form of a solution in an external organic liquid is the obvious necessity of the separation of the oxygenates formed in the reaction from the organic liquid. As the oxo reactions form aldehydes and high boiling temperature aldehyde condensation products which are removed so that the concentration of the solvent is maintained as previously stated, the removal of the condensation products by distillation affects the solvent, a part being distilled (if not all), and the rhodium compounds that are contained.

   The initial introduction into the oxo reaction of a catalytic solution in external organic liquids is effective. However, such an industrial oxo operation requires a continuous or intermittent introduction of catalyst which can be new catalyst, regenerated or contained in a recycled stream. Catalyst losses are the result of these operations.

  
Patent applications of the United States of America

  
n [deg.] 556,270 and 887,370, British patent n [deg.] 1 338 237 corresponding to the latter patent application, describe the use of liquid aldehyde condensation products at high boiling temperature, as the main solvent for the catalyst. Accordingly, no removal of the catalyst is necessary other than a small purge stream necessary to reduce the concentration of condensation products and poisons which slow down the reaction.

   Accordingly, hydroformylation of olefins having at least 3 carbon atoms ensures the maintenance of a high ratio distribution between normal and branched isomers, in aldehyde products, over long periods, and continuous recycling of the A large amount of rhodium species of such condensation products does not cause significant precipitation of rhodium in one form or another. No significant reduction in catalyst life was detected for long periods. The use of these condensation products as a rhodium-containing catalyst dissolving material is advantageous because external organic liquids should be completely excluded from the hydroformylation zone if present.

   The use of an excess of free triorganophosphorus ligand in the reaction mixture containing the condensation products

  
at dissimilar high boiling temperatures, giving the advantages described in the aforementioned US Pat. No. 3,527,809, does not interfere with the activity or dissolution of the rhodium complex catalyst even after long periods of continuous operation. As these condensation products are formed in situ, the profitability of the above process is extremely favorable.

  
It is found that, after extensive repeated use, the continual recycling of the rhodium species dissolved in the liquid condensation products at high boiling temperature presents drawbacks.

  
The constant movement of the catalyst causes certain losses of catalyst, the volume of catalyst must be considerable given that part of the catalyst, contained in the recycled liquid, is outside the reactor,

  
the rate of residue formation remains high and these materials must be removed so that the stability

  
of the catalyst can sometimes be disturbed, the adjustment of the pressure of the gaseous carbon monoxide is delicate, the nature of the recycled stream causes heat losses given the constant movement of hot liquid in

  
system, and small oxygen leaks tend to

  
to occur and prove to be detrimental to the process.

  
It is determined according to the invention that a hydrofbrmylation reaction using a non-volatile catalyst, for example rhodium (I) hydridocarbonyltris (triphenylphosphine), in the liquid phase, can be carried out very conveniently. and with a very simple apparatus by natural distillation of the aldehydes produced by the reaction and their condensation products

  
at high boiling temperature, from the liquid mass containing the catalyst (which may be in the form of a solution) at the reaction pressure and temperature, by condensation of the aldehydes produced and of the condensation products from the gas removed from the reactor, into a product recovery zone, and by recycling unreacted raw materials (e.g. carbon monoxide, hydrogen and / or alpha olefin) in vapor phase from the product recovery zone and towards the reaction zone. In addition, the recycling of the gas coming from the product recovery zone, associated with the renewal of the raw materials transmitted to the reaction zone, in sufficient quantity, makes

  
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as raw material, obtaining a mass equilibrium, in the liquid mass of the reactor, so that practically all the condensation products at high boiling temperature, formed by self-condensation of the aldehydes produced, are removed from the zone reaction with a rate at least equal to their formation rate. If the

  
recycled gas was not sufficient, such condensation products could accumulate in the reactor.

  
The invention therefore relates to a process for preparing an aliphatic aldehyde containing 3 to 6 carbon atoms, the process comprising circulating an alpha aliphatic olefin having 2 to 5 carbon atoms with hydrogen and oxide. of carbon, at a determined pressure and temperature, in a reaction zone containing the catalyst which is dissolved in the liquid mass, the catalyst being practically non-volatile and ensuring efficient hydroformylation of the alpha olefin, the continuous withdrawal a vapor phase of the reaction zone, the circulation of this phase towards a product separation zone, the separation therein of a liquid product containing aldehydes, by condensation ensuring the separation from the gaseous raw materials who did not react,

   and recycling those unreacted gaseous materials from the product separation zone to the reaction zone.

  
The gaseous raw materials which have not reacted, with additional raw materials, are advantageously recycled with a flow rate at least equal to that which is necessary for maintaining the mass balance in the reaction zone.

  
The process according to the invention relates to the use of alpha olefins having 2 to 5 carbon atoms, and preferably 2, 3 or 4. Such alpha olefins are characterized by a carbon-carbon ethylenic terminal bond which may be a group vinylidene, i.e. CH2 = C <, or

  
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straight chain or branched chain compounds which may contain groups or substituents which do not significantly disturb the implementation of the process. Examples of suitable alpha-olefins are ethylene, propylene, 1-butene, iso-butylene, 2-methyl-1-butene, 1-pentene and the like.

  
The reaction is advantageously carried out at

  
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between about 60 and 120 [deg.] C is preferred, especially between 90 and 11 5 [deg.] Ç approximately.

  
A characteristic of the invention is the low total pressure necessary for the implementation of an industrial process. Total absolute pressure less than 28 bars

  
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The partial pressure of carbon monoxide is

  
an important parameter for the implementation of the method according to the invention. It is observed that, when using complex rhodium catalysts, there appears a noticeable reduction in the ratio of isomers produced in the form of aldehydes, i.e. normal and branched isomers, when the partial pressure to be assigned to carbon monoxide approaches a value of about 75% of the pressure

  
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attributable to hydrogen from 25 to 95% and more, compared

  
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general advantageous that the total pressure of the gases is such that the partial pressure of hydrogen is markedly greater than that of carbon monoxide, that is to say that the ratio of the partial pressures of hydrogen

  
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During routine operations, this ratio can be between about 62.5 / 1 and 12.5 / 1.

  
The partial pressure of the alpha olefin in the reaction zone can reach 35% of the total pressure and preferably forms 10 to 20% of this total pressure.

  
In an advantageous operation, the partial pressure of CO does not, for example, exceed approximately 3.5 bars absolute and preferably approximately 2.35 bars absolute. The most advantageous partial pressure for hydrogen

  
is less than 14 bars absolute, and it is for example 8.75 bars absolute, that of CO then being between

  
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The catalyst can be of any non-volatile type

  
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but, given the known advantages of rhodium-based catalysts, as indicated in the aforementioned patent of <EMI ID = 20.1> normal aldehydes to branched aldehydes in the product mixture. The general category of rhodium catalysts described in the aforementioned patent no. [Deg.] 3,527,809 is suitable for carrying out the invention.

  
The most advantageous catalyst according to the invention comprises rhodium complexed with carbon monoxide and a triarylphosphine ligand. The most advantageous catalyst does not contain halogen such as chlorine and contains hydrogen, carbon monoxide and a triarylphosphine complexed with metallic rhodium, in the form of a catalyst soluble in the aforementioned liquid mass and stable under reaction conditions. Examples of triarylphosphine ligands are triphenylphosphine, trinaphthylphosphine, tritolylphosphine,

  
tri (p-diphenyl) phosphine, tri (p-methoxyphenyl) phosphine, tri (m-chlorophenyl) phosphine, p-N, N-dimethylaminophenyl-bis-phenylphosphine and the like. The most advantageous ligand is triphenylphosphine. As indicated above, the reaction is carried out in a liquid mass containing an excess of free triarylphosphine.

  
The rhodium is advantageously introduced into the liquid mass in the form of a catalyst previously shaped, for example hydridocarbonyl-tris (triphenylphosphine) of rhodium RhH (CO) (PPh3) 3 solid, crystalline

  
and stable. Rhodium can be introduced into the liquid mass in the form of a precursor transformed in situ

  
as a catalyst. Examples of such precursors are rhodiumcarbonyl triphenylphosphine acetylacetonate, Rh203,

  
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bonyle. The compounds of the catalyst which form an active species in the reaction mixture and their preparation are known, as described in the article by Brown et al.

  
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may range from about 25 to 1200 ppm rhodium, calculated as the free metal, and triarylphosphine

  
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 <EMI ID = 26.1> present per mole of rhodium, these ranges corresponding to

  
wide beaches.

  
The meaning of the free ligand is set forth in the aforementioned US Patent No. [deg.] 3,527,809, in British Patent No. [deg.] 1,338,225 and in the article

  
by Brown et al., pages 2759 and 2761.

  
In general, the optimum concentration of the catalyst depends on the concentration of the alpha olefin such as propylene. For example, the higher the concentration of propylene, the lower the concentration of the catalyst that can be used to obtain a given conversion into aldehydes produced, in a reactor of given dimensions. Since the partial pressures

  
and the concentration are related, the use of a high partial pressure of propylene causes the presence

  
an increased proportion of propylene in the gases coming from the liquid mass. Such as the purging of part of the gas stream from the product recovery zone

  
may be necessary before recycling to the liquid mass, so that part of the propane that may be present is removed, plus the propylene content of the evolved gas

  
is high and the more propylene lost in the propane purge stream. Thus, a compromise must be found between the value of propylene lost in the propane purge stream and the savings obtained by reducing the concentration of the catalyst.

  
An unforeseen advantage of this process, highlighting

  
a rhodium modified catalyst is that hydroformylation of ethylene does not form diethyl ketone

  
in a measurable amount, whereas all the processes using a cobalt catalyst cause the formation of large amounts of diethyl ketone.

  
It is advantageous that the method of the invention

  
either carried out with a liquid phase in the reaction zone which contains one of the aforementioned complex catalysts of rhodium and, in the form of a catalyst solvent, liquid products of condensation of aldehydes at high boiling temperature (rich in compounds hydroxylic

  
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The term "high boiling temperature liquid aldehyde condensation products" and analogous expressions herein refer to the complex mixture of high boiling temperature liquid products which forms in condensate reactions.

  
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tion, as described below with reference to the series of equations which relate to n-butyraldehyde by way of example. Such condensation products can be formed beforehand or formed in situ during the oxo process. The complex species of rhodium is soluble in these high boiling temperature liquid aldehyde condensation products and exhibits high catalytic activity for a long time, during periods of continuous hydroformylation.

  
Initially, the hydroformylation reaction can be carried out in the absence or presence of small amounts of liquid high boiling temperature aldehyde condensation products forming a solvent for the rhodium complex, or the reaction can be carried out. with an amount of up to about 70% by weight and even about 90% by weight and more of such condensation products, depending on the weight of the liquid mass. A small amount of such liquid condensation products can be as low as 5% by weight and preferably up to at least 15% by weight, based on the weight of the liquid mass.

  
During the hydroformylation of propylene, for example, two products can be formed, normal butyraldehyde and isobutyraldehyde. Since normal butyraldehyde is the most commercially valuable product, high ratios of normal to branched isomer are advantageous. However, the aldehyde products are reactive and react on themselves giving condensation reactions, even in the absence of catalyst, and at relatively low temperatures, with the formation of liquid condensation products at elevated temperature. boiling. Such aldehyde products are therefore used during various reactions as indicated below in the case of n-butyraldehyde taken by way of illustration.

  

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In addition, aldol I can exhibit the following reaction:

  

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The names given in parentheses in the foregoing equations, namely aldol I, substituted acrolein II, trimer III, trimer IV, dimer V, tetramer VI and tetramer VII are used purely for convenience. Aldol I is formed by a condensation of aldol, trimers III and VII by reactions of Tischenko, the trimer

  
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and tetramer VI by a disproportionation reaction. The main condensation products are trimers III and IV and tetramer VII, with smaller amounts of the other products. These condensation products therefore contain significant amounts of hydroxylic compounds, as indicated for example by trimers III and IV and tetramer VII.

  
Analogous condensation products are formed by self-condensation of isobutyraldehyde, and compounds of another category are formed by condensation of one molecule of normal butyraldehyde with one molecule of isobutyraldehyde. As a normal butyraldehyde molecule can aldolize by reaction with an isobutyraldehyde molecule in two different ways with the formation of two different aldols VIII and IX, 4 aldols in total can be formed by condensation reactions of a mixture of butyraldehyde normal and isobutyraldehyde. '

  

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Aldol I can undergo further condensation with isobutyraldehyde and form an isomer in the form of a trimer with trimer III and aldols VIII and IX, and the corresponding aldol X obtained by self-condensation of 2 molecules of isobutyraldehyde can undergo further reactions with normal butyraldehyde or isobutyraldehyde, with formation of corresponding trimer and isomer. These trimers can still react, like trimer III, so that a complex mixture of condensation products is formed.

  
It is very desirable that the substituted acrolein II and its isomers are at low concentrations, for example less than about 5% by weight. Substituted acrolein II, more specifically, 2-ethyl-3-propylacolein ("EPA") forms in situ with other condensation products and is found to reduce catalytic activity. The final effect of EPA or analogues is the reduction of hydroformylation rates.

  
to such an extent that any transaction in which the EPA

  
is present in an amount exceeding about 5% by weight

  
and even greater than 1% by weight of the mass of liquid, has drawbacks from the point of view of profitability.

  
In an advantageous embodiment of the invention, the liquid condensation products at temperature

  
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formed, before introduction into the reaction zone

  
and starting the process. In a variant, for example, aldol I can be added at the start of the process and allow the accumulation of the other products as the reaction progresses.

  
In some cases the use of small amounts of an auxiliary organic solvent which is normally liquid and inert during hydroformylation, for example toluene or cyclohexanone, may be desirable, especially at the start of the process. Such products can be replaced in the liquid phase of the reaction zone by the liquid products of condensation of aldehydes at a high boiling temperature as the reaction progresses.

  
The liquid mass contains, in addition to the catalyst

  
and diluent which can be added, for example the free triphenylphosphine ligand, an aldehyde or a mixture of aldehydes as well as aldols, trimers, diesters, etc. which are derived therefrom.

  
The relative proportion of each product in

  
the solution is regulated by the quantity of gas which circulates

  
in the solution. Increasing this amount causes a reduction in the equilibrium concentration of the aldehyde and an increase in the rate of withdrawal of byproducts from the solution. By-products include the condensation products of aldehydes which are liquid and

  
have a high boiling temperature. The reduced concentration of aldehyde causes. , a reduction in speed

  
of by-product formation.

  
The double effect of increasing the withdrawal rate and reducing the formation rate indicates that the mass balance of the by-products in the reactor

  
is very sensitive to the quantity of gas circulating in the liquid mass. The gas used comprises, for example, make-up amounts of hydrogen, carbon monoxide and alpha olefins. However, the most important factor is the amount of recycled gas that is returned to the bulk of the liquid because this amount determines the degree of the reaction, the amount of products formed and the amount of by-products removed (accordingly).

  
The implementation of the hydroformylation reaction with a given flow rate of olefin and synthesis gas

  
and with a small total amount of recycled gas, less than a critical threshold, causes obtaining a high equilibrium concentration of aldehydes in the solution and therefore a high rate of by-product formation.

  
The rate of removal of by-products in the vapor phase effluent from the reaction zone (liquid mass) under such conditions is low since the rate of vapor phase effluent from the reaction zone is low.

  
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relatively low drag of by-products. The resulting effect is an accumulation of the by-products in the solution of the liquid mass so that the volume of

  
this increases and consequently causes a reduction

  
the productivity of the catalyst. A solution purge

  
must therefore be carried out during the hydroformylation under such conditions at a low gas flow rate so that the by-products are removed and yet the reaction zone has a mass balance.

  
When however the gas flow rate in the reaction zone increases by increasing the recy flow rate, &#65533; &#65533; &#65533; &#65533; &#65533; &#65533; &#65533; &#65533; 4i: &#65533; &#65533; t &#65533; &#65533;e;. the rate of by-product formation decreases and the

  
 <EMI ID = 35.1> tion of by-products removed with the vapor phase effluent from the reaction zone. The increase

  
of the gas flow rate in the reaction zone obtained by a further increase in the gas recycle flow rate results in a situation in which the by-products are withdrawn into the vapor phase effluent from the reaction zone with the flow rate to which they are formed so that there is a mass balance in the reaction zone. There is a gas recycling threshold flow

  
which has a critical value and which corresponds to the minimum flow rate of recycled gas used according to the process of the invention.

  
When the process is implemented with a recycled gas flow rate greater than this threshold flow rate, the volume of the liquid mass in the reaction zone tends to decrease and, for recycled gas flow rates greater than the threshold value, a part of the crude mixture of aldehyde by-products must be returned to the reaction zone, from the product separation zone so that the volume of the liquid phase of this reaction zone remains constant.

  
The critical threshold recycle gas flow rate can be determined empirically for given olefin flow rates.

  
and synthesis gas (mixture of CO and hydrogen). The use of recycled gas flow rates below the critical threshold flow rate causes the volume of the liquid phase to increase over time. A debit transaction

  
threshold causes constant volume maintenance. Operation above the threshold flow rate reduces the volume.

  
The critical recycle gas flow rate can be calculated from the vapor pressures at the reaction temperature of the aldehyde or aldehydes and each of the by-products present. '

  
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gas recycle bit greater than or equal to the threshold flow rate, by-products are removed in phase

  
 <EMI ID = 37.1>

  
liquid, at a rate equal to or greater than the rate of formation, so that the products are in the liquid phase of the reaction zone. Under these circumstances, purging of the liquid mass containing the catalyst from the reaction zone is not necessary to remove the by-products. This operation has the advantage of eliminating the withdrawal of the catalyst.

  
of the reaction zone, except after prolonged intervals, when catalyst renovation is necessary, so that the risks of loss of costly catalyst through accidental leakage or wastage are reduced. Further, no elevated temperature treatment of the catalyst-containing purge solution is required to remove by-products and the catalyst life is increased. Experience suggests that catalyst renovation of one type or another is not necessary until at least one year of use.

  
The residence time of an aldehyde in the reaction zone can vary between 2 min and several hours and

  
it should be noted that this parameter depends to some extent on the reaction temperature, the choice of alpha olefin, catalyst and ligand, ligand concentration, total synthesis gas pressure and

  
the partial pressure of the various constituents of this gas,

  
and other parameters. In practice, the reaction is set

  
carried out for a time sufficient for hydroformylation

  
of the terminal ethylenic or alpha bond of the olefin.

  
A by-product of hydroformylation is the alkane formed by hydrogenation of the alpha olefin. For example,

  
during the hydroformylation of propylene, propane forms

  
a by-product. Accordingly, it is preferable that a purge stream is withdrawn from the recycle gas stream from the product recovery zone so that propane is removed and cannot accumulate in the reaction system. This purge stream contains, in addition to the unwanted propane, unreacted propylene, certain inert gases introduced into the feed and a medium.

  
 <EMI ID = 38.1> <EMI ID = 39.1>

  
 <EMI ID = 40.1> operation is not usually profitable and the current

  
purge is for example used in the form of a fuel. The recycled gas essentially contains hydrogen and propylene. However, when CO is not consumed during the reaction, the excess CO also constitutes a part of the recycled gas. Usually, this gas contains an alkane even during a purge carried out before recycling.

  
It should be noted that the method according to the invention

  
can be operated continuously for long periods without shrinking the liquid mass containing

  
the catalyst of the reaction zone. However, from time

  
Alternatively, regeneration of the rhodium catalyst may be necessary and in this case a purge stream may be withdrawn from the reactor, through a normally locked valve, with fresh catalyst being added so that the concentration

  
of the catalyst is maintained in the liquid mass, or the removed catalyst can be regenerated. After separation

  
of the vapor phase effluent which is withdrawn from the liquid mass present in the reactor, this effluent reaches a product separation zone in which a mixture of aldehyde or aldehydes and dimers, trimers and other condensation products liquids at high boiling temperature is treated by conventional methods such

  
that the distillation, so that the aldehyde or aldehydes are removed and optionally separated from each other, and that the liquid products of aldehyde condensation at high boiling temperature are recovered.

  
Alpha olefin used as a raw material

  
during the process must be rigorously purified so that potential catalyst poisons from the oxo process are removed, as described in the aforementioned article by Falbe,

  
 <EMI ID = 41.1>

  
can be formed by partial oxidation of a suitable hydrocarbon feed, for example naphtha, and they must also be purified thoroughly so that any impurities which may constitute catalyst poisons.

  
 <EMI ID = 42.1> tion will emerge better from the description which follows, given with reference to the appended drawing in which the single figure is a diagram of an installation intended for implementing the method according to the invention.

  
The figure shows a stainless steel reactor 1 comprising one or more disc-shaped agitator wheels 6, comprising paddles arranged perpendicularly and driven in rotation by a shaft 7 and a suitable motor not shown. A circulating bubbler <EMI ID = 43.1>

  
tiné to introduce the alpha olefin as well as the synthesis gas added to the recycled gas. The bubbler 5 comprises several holes of sufficient size for the gas flow to reach the desired value in the liquid mass, at the level of the wheel 6, so that the reactants have the desired concentration in the liquid mass. The reactor also comprises a double jacket for circulating water vapor (not shown) allowing the contents of the reactor to be brought to the desired temperature during start-up, and internal cooling coils (not shown).

  
The effluent produced in the vapor phase from the reactor 1 is withdrawn through a pipe 10 and reaches

  
to a separator 11, the gases then passing through a device 11a intended to remove the mist and to send part of the aldehyde and of the condensation products and to prevent the possible entrainment of catalyst. The effluent from the reactor is transmitted through line 13 to a condenser 14 then through line 15 to a separator 16 in which the aldehydes produced and any by-product can be condensed and thus separated from the gases removed.
(effluent). the by-products and the concentrated aldehyde are withdrawn from the separator 16 through a line 17. The gaseous materials pass to a line 18 and to a separator 19 comprising a mist removal device and a recycling line 20.

   The recycled gases are withdrawn through a line 21 which joins the line 8, a purge stream being able to be withdrawn through a line 22 so that the saturated hydrocarbon content is regulated. Most of the remaining

  
gas can be recycled through line 8 to line 4 into which the make-up reagents enter, for example through lines 2 and 3. The combined set of reagents enters reactor 1. A compressor 26 facilitates the transport of gases recycled.

  
A new catalyst solution can be added to reactor 1 via line 9. The single reactor 1 can obviously be replaced by several reactors in parallel.

  
The crude aldehyde produced from line 17 can be treated by conventional distillation which separates the various aldehydes and the condensation products. Part of the raw material can be recycled to reactor 1 through line 23 and be transmitted as indicated by dotted line 25 to a point above impeller 6 so that the liquid level is maintained in the reactor. reactor 1, if applicable.

  
The following example illustrates the en.oeuvre of the invention, without limitation.

  
The reactor used is a cylindrical stainless steel reactor of the type shown in the drawing, having an internal diameter of 3.95 m, a height of 7.3 m and comprising a tubular bubbler with an internal diameter of 20.3 cm and 1. , 2 m in diameter, placed just below the wheel. The bubbler has holes allowing the introduction of reagents.

  
The reaction conditions, when using an installation of the type shown in the drawing, are shown in Tables I and II.

  
 <EMI ID = 44.1>

  
Contents of reactor 1
 <EMI ID = 45.1>
 
 <EMI ID = 46.1>
 The products withdrawn through line 17 have the following composition:

  

 <EMI ID = 47.1>


  
Almost the same process is found to be the most efficient for the formation of propionaldehyde from ethylene.

CLAIMS

  
1. Process for the continuous preparation of aldehydes by hydroformylation of alpha olefins having approximately 2 to 5 carbon atoms, said process being characterized in that it comprises the formation of a liquid mass of a homogeneous mixture containing an olefin, aldehydes produced and condensation products of aldehydes at high boiling temperature which constantly form in the liquid mass, a soluble rhodium catalyst, complexed with carbon monoxide and a triarylphosphine, with at least
10 moles of free triarylphosphine per mole of metallic rhodium, the transmission to the liquid mass of a recycled gas stream containing hydrogen and the olefin, the transmission of make-up quantities of carbon monoxide, hydrogen and olefin to liquid mass,

   maintaining the temperature of this liquid mass at a value between approximately 50 and 140 [deg.] C, the absolute total pressure being less than approximately 28 bars, the partial pressure

  
 <EMI ID = 48.1>

  
approximately and the absolute partial pressure of hydrogen being less than approximately 14 bars, the withdrawal from the liquid mass of a certain quantity of a mixture in the vapor phase which contains olefin, hydrogen, a vaporized aldehyde product and a certain amount of vaporized aldehyde condensation products, the latter amount substantially corresponding to the rate of formation in the mass so that the amount of liquid mass is maintained at a predetermined value, and the recovery of the aldehyde produced and aldehyde condensation product from the gas mixture, with formation of the recycled gas stream: ..-


    

Claims (1)

2 .. The method of claim 1, characterized in that the alpha olefin is propylene. 3. Method according to claim 1, characterized in that the recycled gas stream contains hydrogen, 1 * alpha olefin and carbon monoxide, <EMI ID = 49.1> <EMI ID = 50.1> alpha olefin and carbon monoxide. 5. Method according to claim 2, characterized in that the triarylphosphine is triphenylphosphine. 6. Method according to claim 1, characterized in that the total absolute pressure is less than 24.5 bars. 7. '-Procédé claimed in claim 2, characterized in that the molar ratio of hydrogen and carbon monoxide is between 3/2 and 20/1. 8. Method according to claim 2, characterized in that the temperature is between about 60 and 120 [deg.] C. 9. The method of claim 1, characterized in that the alpha olefin is ethylene. 10. The method of claim 1, characterized in that the alpha olefin is 1-butene.