The present invention relates to the liquid phase, aldol self-condensation of enolizable aldehydes and ketones to alpha, beta-unsaturated aldehydes and ketones.

The condensation of two molecules of an aldehyde to form an aldol, usually followed immediately by dehydration, to form an unsaturated aldehyde with twice the original number of carbon atoms (or the sum of the carbon atoms of two different aldehydes in a crossaldolization) is well known, as are the conditions required to effect the condensation. In general, the reactants may be either in the vapour or liquid phase, at moderately elevated temperatures, e.g., from 40°C to 200°C, and pressures, e.g., from 0.01 to 2 MPa, preferably from 0.1 to 2 MPa. The reaction is generally carried out in the presence of a catalyst, which may be solid or liquid, and either acidic or, preferably, basic. Although organic bases may be used, a, preferably strong, inorganic base, for example an alkali metal hydroxide or carbonate, is preferred, advantageously in the form of an aqueous solution. In other embodiments a solid catalyst, e.g., a metal oxide, such as a titanium or magnesium oxide, may be used. The above conditions apply generally to the aldol process steps of the present invention; under the preferred conditions dehydration is very fast and essentially complete.

In the traditional aldol process undesirable heavy components, e.g., trimers and tetramers, are formed during the condensation. It would be advantageous to convert these heavy components to useful materials and we have now found that this may be achieved if these heavy components, optionally after treatment, are passed through an aldol reaction.

The present invention therefore provides a process comprising an aldol reaction and separation of the reaction product into aldol product and a heavy component wherein the heavy component is recycled preferably to the aldol reaction.

Frequently the aldol process is used in the production of alcohols wherein the aldehyde produced in the aldol reaction is subsequently hydrogenated to produce the alcohol in one step, or in two steps via the saturated aldehyde. The heavy components in the aldol reaction product frequently contain impurities and poisons which can impair the life of one of the hydrogenation catalysts. The recycle of the heavy materials addresses this problem and hence an additional benefit of this invention can be the improvement in lifetime of one of the downstream catalysts.

The aldol reaction may be any of the traditional aldol reactions such as alkaline catalysed reaction or employing certain metal carboxylates as homogenous catalyst; specifically the carboxylates of the transition metals of Groups IV, V, VI, VII and VIII of the Mendeleev Periodic table and copper, magnesium and zinc. Generally, these catalysts may be used to produce alpha, beta-unsaturated aldehydes from any enolizable aldehyde by an aldol self-condensation. The terminology "enolizable aldehyde" is used in its ordinary sense and is understood by those skilled in the art to include any aldehyde or ketone capable of conversion to alpha, beta- unsaturated aldehydes or ketones by aldol self- condensation. Examples of suitable enolizable compounds which may be subject to aldol self-condensation by the process of the present invention are, acetaldehyde, acetone, propionaldehyde, butyraldehyde, diethyl ketone ethylethyl ketone, valeraldehyde, ethyl-isobutyl- ketone, hexaldehyde, benzaldehyde, heptaldehyde. The resulting alpha, beta-unsaturated aldehydes or ketones

are useful as intermediates in the production of acids, alcohols and plasticizers for certain compounds, other aldehydes and ketones, surfactants, lube and fuel additives, synthetic lubricants, hydraulic fluids, solvents with certain degrees of polarity, as well as flavor and fragrance compounds. The process of the present invention is especially useful for the aldol condensation of butanal to 2-ethyl-2-hexenal and of propanal to 2-methyl-2-pentenal, or the aldol condensation of propanal with hexanal to produce C ₉ aldehydes and alcohols.

The process of the present invention may be conducted batchwise, but a continuous operation is preferred for commercial production. An exothermic reaction takes place during aldehyde addition. The reaction temperature is then maintained by any suitable means. As the condensation reaction proceeds, water is formed which generally produces an azeotrope with the starting aldehyde. The water layer of the azeotrope may be removed while the starting aldehyde is returned to the reaction vessel. If the water is not removed, it separates as a second phase in the reaction vessel. In any event, the product aldehyde may be recovered by known techniques. One possible continuous process may be conducted by continuously feeding starting aldehyde and catalyst solution to a reactor. The liquid product (containing unconverted starting aldehyde, aldehyde condensation product, water, possible solvent and catalyst) from the reactor may be stripped (e.g. in a vaporizer) of product, unreacted aldehyde and water as an overhead stream and the stripper underflow will contain any recycle solvent and catalyst. The stripper overhead stream may be distilled to remove lower boiling unreacted aldehyde and water, the product aldehyde may be recovered by any suitable means and unreacted aldehyde may be recycled to the reactor.

In the course of most aldol condensations, several by-products are formed which are generally undesirable in the process of the invention inasmuch as their formation reduces the efficiency of alpha, beta-unsaturated aldehyde production. In addition, by-product build-up in a homogeneous system may be enhanced by liquid recycle streams. Typical by-products are trimers and tetramers which are formed when the aldol intermediate product reacts further with the starting aldehyde. The terms "heavy components" and "heavies", as used herein, refer generally to by-products produced in the aldolization zone, usually themselves aldol products having molecular weights greater than that or those of the desired product or products. They may be trimers or a hydrated dimer when the desired product is a dehydrated dimer. The trimer usually desired, for example, is fully dehydrated (e.g., in trimerization of propanal, 2,4-dimethyl-2,4- heptadienal is the desired product) and in such a reaction a trimer only partially dehydrated is a heavy material, and is desirably treated in accordance with the present invention.

The condensation reaction of the present invention proceeds quite rapidly and is strongly exothermic. For this reason, the reaction mixture is preferably cooled during the reaction to avoid over-heating. Excessive heat accumulation can cause loss of reactants and products due to evaporation building and may result in dangerously high pressures. A variety of conventional cooling methods may be used for this purpose. The condensation reaction is not known to be otherwise adversely affected by temperature. The rapidity of this exothermic reaction, as has been noted, is an important advantage of the present process. The reaction is allowed to proceed with cooling for a period of time and at a temperature sufficient to obtain good yields of product.

The present invention is applicable to a wide variety of aldol reactions, for example it may be used in the production of 2-ethyl hexenal in which propylene is first hydrofor ylated to produce butanal and two moles of the butanal are condensed by an aldol reaction to produce 2- ethyl hexenal. The 2-ethyl hexenal may then be hydrogenated to produce 2-ethyl hexanol. Similarly the present invention may be applied to reactions involving cross aldolization where aldehydes of different carbon numbers are aldolized to produce higher aldehydes useful as chemical intermediates in, for example, the production of acids, alcohols, amines or amides.

The present invention is however particularly useful in a process for the manufacture of a saturated or unsaturated aliphatic C ₉ aldehyde which comprises subjecting a C ₆ aldehyde to an aldol condensation with propanal to form an unsaturated C ₉ aldehyde. This process is described in WO 96/22268 which is hereby incorporated herein.

Optionally, the unsaturated C ₉ aldehyde or alcohol is hydrogenated to form the saturated C ₉ aldehyde or more preferably totally hydrogenated to the resulting alcohol. If desired, however, the unsaturated C ₉ aldehyde may instead be hydrogenated in a single stage to the saturated alcohol (in which process the saturated aldehyde is typically formed as an intermediate but not isolated) .

The saturated C ₆ aldehyde may be obtained, for example, as will be described in more detail below, from a composition containing a C ₂ unsaturated hydrocarbon and/or synthesis gas (CO & H ₂ ) obtainable, for example, by conversion of a natural gas stream. A stream containing both these components may be subjected to hydroformylation conditions, and the resulting propanal- containing composition subjected to aldolization, the resulting hexenal being selectively hydrogenated to form

the starting C ₆ saturated aldehyde, the last-mentioned steps or the latter step being carried out, if desired, in conjunction with a second aldol condensation to form a C ₉ aldehyde. The present invention may be applied to one or both such aldol reactions and the heavy products from the first aldol reaction may be recycled to the first aldol reactor and/or fed forward to the second aldol reactor. Alternatively the heavy products may be treated in an external reactor prior to recycle. Such treatment may comprise, for example, aquathermolysis, in which the heavies are contacted with water at elevated temperature, resulting in the reversion of the heavies to lower aldehydes or ketones. For example, in the manufacture of C ₆ and C ₉ aldehydes, as described above, aquathermolysis of resulting heavies yields Cg and C ₉ aldehydes, predominantly unsaturated materials. The proportion of heavies reversed depends on, time, temperature and pH of treatment, and on the ratio of heavies to water.

The process may be carried out batchwise, or continuously. A continuous process may comprise, for example, co-feeding the heavies with water, in gaseous or liquid phase, to a distillation tower, advantageously containing inert or catalytic packing, the lower molecular weight products being taken off as overhead. Any unconverted heavies recovered as bottoms may be recycled with the fractionated water and fresh heavies for further processing. Removal of the light fraction shifts the equilibrium, leading to higher conversions than in a batch process.

The reaction may be carried out using water alone but is advantageously carried out in an aqueous medium also containing one or more acids, surfactants, or bases. The acid or base is advantageously present in a concentration of up to 2 moles per liter; as examples there may be mentioned acetic acid, phosphoric acid, and sodium hydroxide. The surfactant is advantageously present in a concentration of up to 0.1 moles per litre;

as an example there may be mentioned para-toluene sulfonic acid. The weight ratio of heavies to aqueous medium may advantageously be in the range of from 5:1 to 1:10, reaction times (or residence times for continuous processes) are advantageously in the range of from 10 minutes to 2 hours, preferably 10 to 60 minutes. Temperatures are advantageously in the range of 150 to 375 deg C, preferably from 200 to 300 deg C. Elevated pressure is desirably used.

The resulting lower molecular weight aldehydes, which, in the process described above, using propanal as starting material, may comprise C ₆ and C ₉ aldehydes, may be separated, e.g. by fractionation, or by flashing off the Cg product from the reactor, and returned to a process stream, if desired after selective hydrogenation to form saturated aldehydes.

It has further been found that the use of an acid catalyst or surfactant enhances the yield of the higher aldehyde (e.g., the C ₉ aldehyde) from heavies, while the use of a basic catalyst enhances the lower (e.g., the C ₆ ) aldehyde yield. This permits production of a desired product from a given heavies supply by choice of catalyst. Further, sequential hydrothermal treatment of heavies using two catalyst categories may maximize yield of useful products. The invention accordingly also provides a process for the manufacture of a lower and a higher aldehyde or ketone from a heavy carbonyl- containing feed-stream which comprises treating the feedstream with an aqueous medium at an elevated temperature and a pH greater than 7, separating the resulting organic feedstream into a heavier and a lighter fraction, recovering a lower aldehyde or ketone from the lighter fraction, treating the heavier fraction with an aqueous medium at an elevated temperature and a pH less than 7, and recovering a higher aldehyde or ketone from the resulting feedstream.

Treatment of the heavy products in the ways outlined above, that is to say, in a reactor other than one in the aldolization reaction scheme, facilitates higher conversion rates and yields because the reaction conditions may be tailored to the desired reversal reaction rather than to the aldol reaction, for example higher temperatures may be used. When a basic catalyst is to be used for heavies reversal, spent catalyst from an aldol reactor may be used, thereby limiting or avoiding any increase in raw material consumption.

As a further route to a saturated C ₆ aldehyde, a synthesis gas stream may be subjected to the Fischer- Tropsch process, giving, when a cobalt catalyst is used, linear paraffins and, when an iron catalyst is used, inter alia, linear α-olefins. These paraffins may be dehydrogenated to olefins and oxonated, and olefins may be directly oxonated, to give mainly aldehydes. Other Fischer-Tropsch processes can yield linear alcohols (using copper-cobalt or zinc-copper catalysts) which can be dehydrogenated to aldehydes. Other routes include oxonation of a pentene, and the formation of Ziegler alcohols by catalytic treatment of ethylene to form a range of higher alcohols and dehydrogenation to aldehydes. Separation of the desired carbon number material may take place at any suitable stage in these processes.

The present invention also provides recycling heavies formed in one or both of the aldol reactions or treating them in an external reactor prior to recycle in a process comprising

(a) subjecting a composition comprising a C unsaturated hydrocarbon, carbon monoxide and hydrogen to hydroformylation conditions to form a propanal-containing composition,

(b) subjecting the propanal-containing composition to first and second aldol condensations, causing

trimerization to an unsaturated C ₉ aldehyde and, optionally,

(c) hydrogenating an intermediate unsaturated C ₆ aldehyde resulting from the first aldol condensation to a saturated C ₆ aldehyde and, optionally,

(d) hydrogenating the C ₉ aldehyde to a saturated aldehyde, the C ₉ aldehyde being the doubly unsaturated product of step (b) , the singly unsaturated product resulting from aldol condensation of the product of step (c) with a further propanal molecule, or a mixture of the product of step (b) and the said singly unsaturated product and, optionally,

(e) oxidizing the product of step (d) to form a C ₉ acid or optionally

(f) hydrogenating the product of step (b) or step (d) to form a saturated C ₉ alcohol and, optionally,

(g) esterifying the saturated C ₉ alcohol resulting from step (f) .

The invention further provides recycling the heavies formed in one or both of the aldol reactions and treating them in an external reactor prior to recycle in a process comprising

(b) subjecting a propanal-containing composition to first and second aldol condensations, causing trimerization to an unsaturated C ₉ aldehyde,

(c) hydrogenating an intermediate unsaturated C ₆ aldehyde resulting from the first aldol condensation to a saturated C ₆ aldehyde, step (c) being optional, and

(d) hydrogenating the C ₉ aldehyde to a saturated aldehyde, the C ₉ aldehyde being the doubly unsaturated product of step (b) , the singly unsaturated product resulting from aldol condensation of the product of step (c) with a further propanal molecule or a mixture of the product of step (b) and the said singly unsaturated product and, optionally,

(e) oxidizing the product of step (d) to form a C ₉ acid or, optionally

(f) hydrogenating the product of step (b) or step (d) to form a saturated C ₉ alcohol and, optionally,

(g) esterifying the saturated C ₉ alcohol resulting from step (f) .

The invention still further provides recycling the heavies formed in one or both of the aldol reactions and treating them in an external reactor prior to recycle in a process comprising

(b) subjecting a propanal-containing composition to a first aldol condensation,

(c) hydrogenating the unsaturated Cg aldehyde resulting from the first aldol condensation to a saturated C ₆ aldehyde, subjecting the resulting saturated Cg aldehyde to a second aldol condensation with propanal . to form an unsaturated C ₉ aldehyde,

(d) hydrogenating the C ₉ aldehyde to a saturated aldehyde and either

(e) oxidizing the product of step (d) to form a C ₉ acid or

(f) hydrogenating the product of step (d) to form a saturated C ₉ alcohol, optionally

(g) esterifying the saturated C ₉ alcohol resulting from step (f) .

The Cg unsaturated aldehyde referred to above in the process in which propanal is dimerized will largely be 2- methyl-2-pentenal; the C ₆ saturated aldehyde resulting from its hydrogenation will be 2-methylpentanal; the doubly and singly unsaturated, and saturated, C ₉ aldehydes will be 2,4-dimethyl-2,4-heptadienal, 2,4- dimethyl-2-heptenal, and 2,4-dimethylheptanal respectively, the saturated C ₉ alcohol will be 2,4- dimethylheptanol, and the C ₉ acid will be 2,4- dimethylheptanoic acid, but other isomers of the C materials may be formed in smaller quantities.

Alternatively, from the unsaturated C ₉ aldehydes there may be made the corresponding 2,4-dimethyl-2, - heptadienol and 2,4-dimethyl-2-heptenol by, for example, hydrogenation in the presence of a catalyst comprising platinum with zinc or iron salts, or in the presence of an iridium/carbon or osmium/carbon catalyst, as described in Houben-Weyl, Band IV, Section IC, pp 218 and 224 and the literature referred to therein.

The composition treated in step (a) of one aspect of the present invention comprises, as indicated above, as essential ingredients carbon monoxide, hydrogen, and one or both C ₂ unsaturated hydrocarbons. In certain embodiments of the invention, the hydrocarbon is desirably ethylene, and acetylene is advantageously absent or present in very small proportions. In other embodiments, the essential hydrocarbon is ethylene and the presence of acetylene is optional or even advantageous.

The composition may be obtained by numerous methods, including mixing pure C ₂ H ₄ , CO and H ₂ , mixing purified commercially produced C ₂ H ₄ with purified synthesis gas (syngas) or as the product of a partial oxidation (POX) or steam reforming unit, mixed with the product from a steam or catalytic cracking furnace, which product may be purified or may merely have had catalyst poisons removed but be otherwise untreated. The composition is, however, conveniently a dilute multi-component syn gas (DMCS) stream, by "dilute" being meant that the stream has not been completely purified by the removal, for example, by cryogenic separation, of diluents, e.g., methane and ethane, that do not take part in the hydroformylation reaction. The stream may result from treatment of natural gas, e.g., from the mixture of one stream containing CO and H ₂ produced by conventional POX technology or steam or catalytic reforming and a second stream containing ethylene and acetylene obtained by methane pyrolysis, as

described in more detail in WO 96/22266, whose entire disclosure is incorporated by reference herein.

The stream may also result from processes as disclosed by Nagel et al. in US patents 5,395,405, 5,354,940 and 5,298,233, or in WO 95/17362, 95/17360, 95/17359, 93/25278, 93/25277, 92/01492, 93/02751, and 93/02750 using the concept of one or more baths of molten metal. The product stream from these processes can optionally be supplemented by some of the other streams mentioned elsewhere in this disclosure.

Depending on the source, the DMCS will contain, as indicated above, H ₂ , CO and one or both C ₂ unsaturated hydrocarbons, and in addition different neutral and undesired species. In certain embodiments, the DMCS will also contain one or more C ₃ ⁺ mono- or poly-olefinically unsaturated hydrocarbons, more especially C ₃ to C ₅ mono- or poly- olefins, and more especially will contain, in addition to the C ₂ unsaturates, propene and butenes. By this means, the composition of the resulting aldol product may be controlled to contain a mixture of C ₉ species with, more especially, some C ₁₀ ^anc * ^c _ll species, in addition to any C ₁₂ species resulting from tetramerization of the propanal. The proportion of other species, largely C ₁₀ species, is advantageously at most 25%, and preferably in the range of 10 to 20%, by weight, based on the total weight of product, resulting in a final plasticizer ester product having lower volatility and enhanced permanence in polymeric compositions.

If desired, at least part of the C ₁₀ ⁺ species may be separated, enabling use of the alcohols as such or in derivative form, e.g., in synthetic lubricants, hydraulic fluids, surfactants, fuel additives, lube additives, flavor and fragrance components or plasticizers.

The DMCS composition, as far as concerns neutral and essential components, is advantageously as follows in molar terms:

CO: 1 to 50%, preferably 1 to 35%, of gas. C ₂ H ₄ /C ₂ H ₂ : total up to 100% of CO. H ₂ : from, at minimum, the molar equivalent of the ethylenically unsaturated species plus twice that of the acetylenically unsaturated species, to a maximum of 60% of DMCS. A preferred maximum is twice the molar equivalent of ethylenically unsaturated species plus three times that of acetylenically unsaturated species. Exceptionally, if the proportion of acetylene is so low that there is no economic advantage in its conversion, the minimum hydrogen content may be the molar equivalent of the ethylenically unsaturated species.

Sum of alkanes, C0 ₂ , N ₂ , and H ₂ 0: 0 to 70%, preferably 0 to 40%.

Certain trace components of the multicomponent syngas feed are known to be detrimental in the oxo reaction. Some are irreversible catalyst poisons, e.g., sulphur compounds, for example, H S and COS. Others, for example, halides, cyanides, and iron carbonylε, cause reversible poisoning or accelerated catalyst deactivation, or unwanted reactions in downstream processing. The concentration of the detrimental components may be adjusted by a variety of techniques known per se, to provide an acceptable multicomponent syngas feed to the oxo reactor.

According to the present invention, the hydroformylation may be effected under hydroformylation conditions known per se, using a catalyst known per se, for example, any group VIII transition metal catalyst, especially Co and Rh, while hydroformylation of acetylene-containing (as well as substantially acetylene- free) compositions is advantageously carried out using as catalyst an oil- soluble or water-soluble rhodium complex comprising a low valence Rh complexed both with carbon

monoxide and a triorganophosphorus compound. As tri¬ organophosphorus compound there may be mentioned, for example, one or more oil-soluble triarylphosphines, trialkylphosphines, alkyl diaryl phosphines, aryl dialkyl phosphines, triorganophosphites, especially trialkylphosphites and triarylphosphites (in which list alkyl includes cycloalkyl) , containing one or more phosphorus atoms per molecule capable of complexation with Rh by virtue of having a lone pair of electrons on the phosphorus. Instead of, or in addition to, such monodentate compounds, a bidentate phosphorus compound may be used as ligand.

Alternatively, water-soluble triorganophosphorus compounds may be mentioned, like the mono, di or multiple sulfonated or carboxylated forms of the oil-soluble triorganophosphorus mono-dentate or bidentate compounds mentioned above.

Triorganophosphorus ligands which are known to provide good catalytic activity in the hydroformylation of pure olefin feeds are suitable for the use in the process of the present invention, their concentration preferably being such that (a) the molar P/Rh ratio is at least 2:1, the minimum preferred ratio depending on the nature of the phosphorus-containing ligand, for example the minimum preferred ratio being 2:1 for a bidentate ligand and 4:1 for a phosphite ligand, most preferably the ratio being at least 30:1; (b) the total concentration of the coordinately active phosphorus is at least 0.01 mol/1; and (c) the [P]/p _co ratio maintained in the reactor is at least 0.1 mmol/1/kPa, where [P] is the total concentration of the coordinately active phosphorus in the solution, and p _co is the partial pressure of carbon monoxide in the gas phase.

As examples of the ligands there may be mentioned trioctylphosphine,tricyclohexylphosphine, octyldiphenylphosphine,cyclohexyldiphenylphosphine,

phenyldioctylphosphine,phenyldicyclohexylphosphine, triphenylphosphine,tri-p-tolylphosphine, trinaphthylphosphine,pheny1-dinaphthylphosphine, diphenylnaphthylphosphine,tri-(p-methoxypheny1) - phosphine, tri-(p-cyanophenyl)phosphine,tri- (p-nitrophenyl)phosphine, and p-N,N-dimethylaminophenyl- (diphenyl)phosphine, trioctylphosphite or tri-p-tolyl- phosphite; as bidentate compound there may be mentioned diphos-bis(dipheny1-phosphino)ethane.

As water-soluble ligands there may be mentioned ono- sulfonated triphenylphosphine, di-sulfonated triphenylphosphine, tri-sulfonated triphenylphosphine, or any other ligand disclosed by B.Cornils et al in "Aqueous catalysts for organic reactions", CHEMTECH, January 1995, page 33 to 38 or in the references therein.

Advantageously, the Rh concentration in the reaction mixture is in the range from 1 x 10 ^~5 to 1 x IO ^-2 moles/litre or, in effect, in the range from 1 to 1000 ppm, preferably 20 to 500 ppm, based on the total weight of the solution.

The catalyst is advantageously contacted with feed containing acetylene and/or ethylene in a solution of the catalyst in an oily solvent or a mixture of such solvents, for example aliphatic and aromatic hydrocarbons (e.g., heptanes, cyclohexane, toluene), esters (e.g., dioctyl phthalate) , ethers, and polyethers (e.g. , tetrahydrofuran, and tetraglyme) , aldehydes (e.g., propanal, butanal) the condensation products of the oxo product aldehydes or the triorganophosphorus ligand itself (e.g. , triphenylphosphine) .

Rhodium may be introduced into the reactor either as a preformed catalyst, for example, a solution of hydridocarbonyl tris(triphenylphosphine) rhodium(I) or it may be formed in situ. If the catalyst is formed in situ, the Rh may be introduced as a precursor such as acetylacetonatodicarbonyl rhodium(I) {Rh(C0) ₂ (acac) } ,

rhodium oxide {Rh ₂ 0 ₃ }, rhodium carbonyls {Rh ₄ (C0) ₁₂ , Rh ₆ (C0) ₁₆ }, tris(acetylacetonato) rhodium(I) , {Rh(acac) ₃ } , or a triaryl phosphine-substituted rhodium carbonyl {Rh(C0) ₂ (PAr ₃ ) } ₂ , wherein Ar is an aryl group.

Hydroformylation is advantageously conducted at a temperature in the range from 40 to 200°C, more advantageously from 80 to 180°C, and preferably from 90 to 155°C.

The reaction is advantageously conducted at a pressure in the range of 0.05 to 50 MPa (absolute), and preferably in the range of about 0.1 to 30 MPa with a partial pressure of carbon monoxide advantageously not greater than 50% of the total pressure. For safety reasons, the acetylene partial pressure should be limited to a maximum of 0.2 MPa.

Advantageously, the proportions of carbon monoxide, hydrogen, ethylene, and acetylene in the feed to the oxo reactor at the foregoing pressures are maintained as follows: CO from about 1 to 50 mol%, preferably about 1 to 35 mol%; H ₂ from about 1 to 98 mol%, preferably about 10 to 90 mol%; ethylene and acetylene individually and in combination from zero to about 35 mol%, preferably from about 1 to 35 mol%.

The reaction may be conducted either in a batch mode or, preferably, on a continuous basis. Good contact between the catalyst and the gas feed may also be ensured by dispersing the solution of the Rh catalyst on a high surface area support, a technique well known in the art as supported liquid phase catalysis.

Especially when the feed composition contains both acetylene and ethylene, different stages of hydroformylation may be carried out under different conditions, more severe (e.g., higher temperature or catalyst or ligand concentration) conditions being used for acetylene conversion than for ethylene. This may be achieved by the use of two or more reactors in series,

with an increase in severity as the feed moves from one reactor to the next or, in the case of a plug flow reactor, a temperature increase with travel downstream along the length of the plug flow reactor. Such multistage operation may be used even if acetylene is not present in the composition.

The propanal used as a reactant in the aldolization step or steps of the processes according to the invention may be obtained, as in some embodiments above, by oxonation of a C ₂ unsaturated hydrocarbon. If desired, oxonation may be carried out under conditions yielding propanol, which may be condensed and dehydrated to yield a desired C ₆ aldehyde by the Guerbet reaction, described in Burk et al., J. Mol. Cat., 33(1) 1-21.

In other embodiments, the propanal may be obtained by other means, for example, by dehydrogenation of propanol, e.g. , over a copper catalyst, hydrogenation of acrolein, bio-oxidation of propane, partial oxidation of propanol, whether resulting from bio-oxidation or otherwise obtained, e.g., oxidation with air, or ozonation of 1-butene.

Especially when the starting aldehyde is produced by oxonation of a dilute gas stream, e.g., DMCS, the gaseous part of the product stream from the reactor will contain a significant proportion of the aldehyde (which will be exemplified below as propanal, but it will be apparent that the difficulty is more general) in a low boiling diluent, i.e., one having a boiling point lower than propanal. Separation of propanal from the diluent by distillation requires the use of high pressures or refrigeration, both of which are costly, to recover most of the propanal from the low boiling diluents.

According to a further aspect of the present invention, there is provided a process for the manufacture of an intermediate aldehyde or a higher aldehyde which comprises oxonation of an olefin in the

presence of a low-boiling diluent to form a product stream comprising a lower aldehyde and diluent, separation of the lower aldehyde from the diluent, aldolization of the lower aldehyde to an intermediate aldehyde, and if desired aldolization of the intermediate aldehyde, or a hydrogenated intermediate aldehydic derivative thereof, to a higher aldehyde, wherein separation of the lower aldehyde from the diluent is effected by contact of the oxonation reactor product stream with a derivative of the lower aldehyde having a molecular weight higher than that of the lower aldehyde.

As higher molecular weight derivatives of the lower aldehyde, there may be mentioned the intermediate and higher aldehydes themselves, the hydrogenated intermediate and higher aldehydic derivatives, and, optionally treated, heavies. Heavies (otherwise referred to as heavy components) include, as indicated above, partially dehydrated aldol condensation products as well as other heavy products from downstream reactions. By using heavies to absorb the lower aldehyde from the oxonation product stream, the former are returned to aldolization where in accordance with the first aspect of the invention they are converted into useful materials. If, as is optional, the heavies have been treated, as by hydrothermal treatment, before contact with the oxo reactor product steam, they provide a useful additional aldol reactant especially when the process is operated using a single self- and cross-aldol reactor. As heavier fraction made in a downstream reaction is included any material of molecular weight higher than that of the lower aldehyde. Absorption of the (gaseous) lower aldehyde into the (liquid) stream provides a most efficient way of removing aldehyde from the gaseous output from oxo reactor.

Advantageously, the lower aldehyde is propanal, the intermediate aldehyde comprises 2-methyl-2-pentenal, the

intermediate aldehydic derivative comprises 2-methyl- pentanal, the higher aldehyde comprises 2,4-dimethyl- 2,4-heptadienal and the hydrogenated higher aldehyde comprises 2,4-dimethylheptanal. It will be understood that isomers of the named products may be present. It will also be understood that all or part of the intermediate aldehyde produced by the aldolization, or the aldehydic derivative, may be contacted with the product stream, or even that the material contacted with the product stream may be produced otherwise than in the aldolization reaction itself (for example, especially, at start-up) .

Advantageously, a saturated intermediate aldol derivative is used to contact the product stream in, for example, a wash tower. A vapor phase product stream from an oxo reactor may, if desired, be cooled before being passed to a wash tower to condense some lower aldehyde and recycle it, together with oxo catalyst, to the oxo reactor. Although the intermediate aldehyde must be cooled slightly before contacting the product stream this requires less energy (e.g., using cooling water rather than refrigeration) than if the diluent were to be condensed. When a high aldehyde is the desired end product, the liquid product from the washtower already contains at least part of the required starting materials for the next aldolization, and the tail gas from the wash tower contains little aldehyde.

It will be appreciated that although the two aspects of the invention may be performed independently, they are desirably combined in a single process to maximize yields and reduce energy usage. In particular, separation of the lower aldehyde in the oxo product stream from the diluent by absorption by the heavies from the aldolization, if desired after treatment, represents an efficient way of returning heavies to aldolization.

The desired saturated C ₉ aldehyde and its successor molecules advantageously have the hydrocarbon skeleton of 2,4-dimethylheptanol. In order to maximize the yield of the desired C ₉ product, it has been found advantageous to hydrogenate the 2-methyl-2-pentenal to 2-methylpentanal between the first and second aldol condensations. Selective hydrogenation of the unsaturation leaving the carbonyl group unaffected may be carried out in the gas/liquid or gaseous phase using any of the catalysts known per se for that purpose. As examples of suitable hydrogenation catalysts, there may be mentioned palladium, e.g., a supported palladium catalyst, using, for example, an alumina or carbon support, under relatively mild conditions, e.g., a hydrogen pressure of up to 3, preferably between 0.5 and 2.0, MPa, and a temperature within the range of 80 to 200°C, optionally in an inert solvent. Suitable solvents include aliphatic, alicyclic and aromatic hydrocarbons or oxygenated solvents, for example, alcohols, esters and ethers.

The second aldol condensation, reacting propanal either with 2-methyl-2-pentenal or, preferably, with 2- methylpentanal, may be carried out under conditions similar to the first condensation. According to one aspect of this invention the heavies from the first aldol reaction may be recycled to this second aldol reaction.

If it is desired to make the saturated C ₉ aldehyde 2,4-dimethylheptanal from the immediate product of the second aldolization, 2,4-dimethyl-2,4-heptadienal or, preferably, 2,4-dimethyl-2-heptenal, further hydrogenation may be effected as described above for the manufacture of the saturated C ₆ aldehyde. This procedure is conveniently also used if the desired end- product is the corresponding 2,4-dimethylheptanoic acid.

If, however, the desired product is the saturated alcohol 2,4-dimethylheptanol then more vigorous

hydrogenation conditions may if desired be employed, hydrogenation of the ethylenic unsaturation and reduction of the carbonyl group taking place at the same time. For this purpose, the reaction may be carried out under conditions and in the presence of catalyst systems known per se. For example, the catalyst may be Ni, Raney Ni, partially reduced copper oxides, copper/zinc oxides, copper chromite, the copper-based catalyst advantageously being used in combination with cobalt or nickel catalysts; Ni/Mo; Co/Mo or Mo on carbon, optionally in their sulphided form. Any of the above catalysts may be used alone or in combination; nickel is the preferred catalyst. The conditions may include, for example, a hydrogen pressure from 2 to 30 MPa and a temperature in the range of 100 to 240°C.

If it is desired to maintain a number of options for the use of the saturated C ₉ aldehyde, the present invention also provides for a two-stage hydrogenation of the unsaturated aldehyde, the first stage being carried out in the presence of a mild catalyst, for example, a palladium catalyst as mentioned above, in a first reactor, yielding the saturated aldehyde. This may be further hydrogenated using one of the stronger catalysts mentioned above, for example, Ni, in a second reactor. Alternatively, the saturated aldehyde may be oxidized to the corresponding carboxylic acid, or further aldolized, e.g., with propanal to yield a C ₁₂ aldehyde, the production of which aldehyde, both by the above route or by dimerization of the C ₆ aldehyde, and its derivatives, also being provided by the invention. This procedure has the advantage, in addition to flexibility, of facilitating better control of the hydrogenation reaction which, if carried out in a single reactor from unsaturated aldehyde to saturated alcohol, may give an excessive temperature increase because of the heat released on simultaneous hydrogenation of two bonds. The

need to control such a highly exothermic reaction adds to reactor costs.

Oxidation of the saturated aldehyde to the corresponding carboxylic acid may be carried out by any method known per se, i.e., practised in the art or described in the literature. Oxidation is conveniently carried out using oxygen, pure or diluted in nitrogen, if desired or required in the presence of a catalyst. As catalyst there may be mentioned a solution containing metallic cations, e.g., copper, cobalt or manganese, for example as acetates or other carboxylic acid salts.

When the hexanal to be subjected to aldolization to form a C ₉ aldehyde is 2-methylpentanal it may be, as in a number of embodiments of the invention, most readily obtained by aldol condensation of propanal and hydrogenation of the unsaturation in the resulting hexenal. That hexanal may, in other embodiments, be obtained by that or other routes.

In still further embodiments, however, other hexanals may be employed. For example, a synthesis gas stream may be subjected to the Fischer-Tropsch process, to yield, when a cobalt catalyst is used linear paraffins and, when an iron catalyst is used, inter alia, linear - olefins. These paraffins may be dehydrogenated to olefins and oxonated, and olefins may be directly oxonated, to give mainly aldehydes. Other Fischer- Tropsch processes can yield linear alcohols (using copper-cobalt or zinc-copper catalysts) which can be dehydrogenated to aldehydes . Other routes to normal hexanal include hydration of a C ₆ α-olefin, oxonation of C ₅ olefins, and production of a coconut or palm kernel oil alcohol, followed by de-hydrogenation. Cross- aldolization of the n-hexanal with propionaldehyde yields a mixture of isomeric nonenals, including 2-methyl-2- octenal and 2-propy1-2-hexenal, which may be hydrogenated to the corresponding saturated aldehydes, which may in

turn be further hydrogenated to the corresponding saturated alcohols, including 2-methyl-octanol or 2- propylhexanol, if desired in a combined process, or oxidized to the corresponding acids, including 2- methyloctanoic acid and 2-propylhexanoic acid. Alternatively the nonenals may be hydrogenated to the corresponding unsaturated alcohols, including 2-methyl-2- octenol and 2-propyl-2-hexenol.

The reaction sequence described above with reference to formation of a C ₉ material from propanal may be carried out in a number of different ways, for example:

In a first embodiment of the trimerization sequence, dimerization of propanal is carried out in a first aldolization zone, the heavy ends separated and the unsaturated product is selectively hydrogenated to 2- methylpentanal in a first hydrogenation zone, the resulting dimer product and further propanal being condensed in a second aldolization zone, the trimer reaction product, any remaining dimer and the heavies are separated, the trimer being hydrogenated in a second hydrogenation zone either to the saturated aldehyde or the saturated or unsaturated alcohol, as desired, and remaining dimer returned to the first hydrogenation zone. The heavies are recycled to the first and/or second aldolization zones or treated in a separate reactor prior to recycle.

In a variation of this embodiment, dimerization of propanal is carried out in a first aldolization zone, the unsaturated product is selectively hydrogenated to 2- ethylpentanal in a first hydrogenation zone, the resulting dimer product and further propanal are condensed in a second aldolization zone, the trimer is hydrogenated, in the presence of any remaining dimer, in a second hydrogenation zone to the saturated aldehyde, the trimer and any remaining dimer are separated, remaining dimer is returned to the second aldolization

zone and, if desired, the saturated aldehyde is hydrogenated in a third hydrogenation zone to the saturated alcohol. The heavies are recycled to the first and/or second aldolization zones or treated in a separate reactor prior to recycle.

In a second embodiment, a single aldolization zone is provided, in which zone both dimerization of propanal and reaction of propanal with 2-methylpentanal to form an unsaturated trimer are carried out, the mixed reaction product is separated into a C ₉ -comprising component, a dimer-comprising component and a heavy component, the dimer-comprising component being passed to a first hydrogenation zone where unsaturated dimer is selectively hydrogenated to 2-methylpentanal, the product from the first hydrogenation zone being returned to the aldolization zone, the C ₉ -comprising component being hydrogenated in a second hydrogenation zone either to the saturated aldehyde or the saturated or unsaturated alcohol as desired. The heavy component is recycled to the aldolization zone or treated in a separate reactor prior to recycle.

In a variation of this embodiment, the mixed reaction product from the aldolization zone is passed to a first hydrogenation zone where unsaturated dimer and trimer are selectively hydrogenated to saturated dimer and trimer aldehydes, the mixed saturated aldehydes are separated into a dimer-comprising component and a trϊmer- comprising component, the dimer-comprising component being returned to the aldolization zone, and the trimer- comprising component is, if desired, hydrogenated in a second hydrogenation zone to the saturated alcohol. The heavy component can be separated from the desired product of the aldolization reaction before, in between, or after the individual hydrogenation zones.

In both the first and second embodiments, the dimer aldehyde, after being separated from the trimer or C ₉

reaction product, may if desired be further separated into saturated and unsaturated C ₆ aldehydes, only the unsaturated component being returned to the first hydrogenation zone, the saturated component being returned to the, first or the second, aldolization zone. Provided, however, that conditions in the first hydrogenation are such that saturated aldehyde is not further hydrogenated to alcohol, the saturated aldehyde may with advantage be returned without separation to the first hydrogenation zone where it acts as an inert diluent to assist in temperature control; where there are two aldolization zones, saturated aldehyde may, if desired, be returned to the first zone.

In a third embodiment, a multipurpose reaction zone is provided, in which aldolization of propanal, selective hydrogenation of 2-methyl-2-pentenal to 2-methylpentanal, and aldolization of 2-methylpentanal and propanal are carried out, forming a reaction mixture comprising dimer and trimer aldehydes and heavies, the reaction mixture is separated, trimer aldehydes being passed to a hydrogenation zone to form either saturated aldehyde or saturated alcohol as desired, the dimer aldehydes and the heavies being returned to the multipurpose reaction zone.

In all three embodiments, aldolization catalyst, advantageously in the form of an aqueous solution, is fed into at least the first zone in which aldolization is carried out; since aldolization produces water, the catalyst and the product water are advantageously separated and the catalyst returned to the aldolization zone. Advantageously, in the first embodiment, catalyst solution is also fed to the second aldolization zone.

In a fourth embodiment, a multi-purpose reaction zone is provided in which zone dimerization of propanal and reaction of propanal with 2-methylpentanal are carried out and, within the reaction zone, the dimer and trimer components are separated by distillation, the unsaturated

dimer being passed to a first hydrogenation zone, selectively hydrogenated to 2-methylpentanal, and returned to the multi-purpose zone, the C ₉ -comprising component being hydrogenated in a second hydrogenation zone to the saturated aldehyde or alcohol as desired. The heavy component can be separated from the C ₉ component prior to, in between, or after sections of the second hydrogenation zone. Advantageously in this embodiment, at least some of the water resulting from the aldolizations is removed as vapour with the dimer, condensed, and separated therefrom.

In any aldolization zone containing two or more different aldehydes, a number of different reactions may take place. In general, a smaller aldehyde is more reactive in the conditions advantageously used in the present process than a larger, in part because of its higher solubility in the aqueous catalyst-containing phase; further a linear or a less-branched aldehyde is more reactive than a branched or more branched aldehyde (an -branched aldehyde being specifically less reactive and incapable of self-aldolization and dehydration) ; accordingly where, as in the present invention, it is desired to achieve "cross-aldolization" of C ₆ and C3 aldehydes, it is desirable, in the second aldolization zone in the first embodiment described above, to minimize condensation of two C ₃ molecules. To this end, the saturated Cg aldehyde is advantageously maintained in stoichiometric excess relative to the C3 aldehyde, and preferably in a molar ratio of at least 1.5:1. Also, advantageously, the C ₃ aldehyde is reacted almost completely in the second zone. In the second embodiment, the stoichiometric ratio of C ₆ to C ₃ aldehyde is desirably maintained so as to form unsaturated C ₆ aldehyde at the same rate as saturated C ₆ aldehyde is consumed by the cross-aldolization reaction.

Advantageously, in any embodiment of the invention where there are separate aldolization zones (e.g., two aldol reactors) , the heavies are returned to the second, if they have not been pretreated in an external reactor, where conditions are more favourable for reversal. In general, the second reactor is operated at a higher temperature and longer residence time than is the first. An important factor, however, is the presence of the, preferably saturated, dimer aldehyde or ketone, e.g. 2-methylpentanal in the case of propanal trimerization. Heavies formation and reversal being an equilibrium reaction, the presence or addition of dimer is effective in withdrawing the monomer, e.g. propanal, from the reaction zone in the form of the desired trimer and shifts the equilibrium favorably. The excess of saturated C ₆ aldehyde as described above with reference to the first illustrated embodiment contributes to heavies reversal.

Figures 1, 2 and 3 are schematic flow diagrams of processes for the manufacture of a trimer alcohol from a monomer aldehyde or ketone using the heavies recycling aspect of the process of this invention, and

Figure 4 is a schematic flow diagram showing the monomer absorption aspect of the process..

In the Figures, reference numerals below 100 refer to feed and product streams.

Referring now to Figure l, aldehyde or ketone monomer 14 and catalyst solution 15 are fed to a self-aldol reactor 102, where dimerization occurs to make the o,β- unsaturated dimer aldehyde or ketone and water 16. The water phase 18 is removed in vessel 103 , and the aldol product 17 is sent to an optional separator 105, separating heavies 26 from the ,β-unsaturated dimer 19. The purified organic stream 19, or the unpurified stream 17 in case the separator 105 is not used, is sent to a selective hydrogenation reactor 104 together with

hydrogen 20. In the selective hydrogenation reactor 104, the a,β-unsaturated dimer aldehyde or ketone is converted to the saturated dimer aldehyde or ketone 9. This saturated dimer aldehyde or ketone 9 then enters a cross- aldol reactor 106, where it is cross-condensed with additional aldehyde or ketone monomer 1 in the presence of a catalyst solution 2. In the cross-aldol reactor, the saturated dimer aldehyde or ketone is advantageously present in stoichiometric excess relative to the monomer aldehyde or ketone. This enhances selectivity of trimer production, i.e. the α,β-unsaturated trimer aldehyde or ketone, and suppresses monomer self-condensation in the cross-aldol reactor. Monomer aldehyde or ketone is advantageously reacted to almost complete conversion in the cross-aldol reactor. The cross-aldol product is then fed to the separator 107, where the water phase 21 is removed. The organic product is sent to the separator 108, where the α,β-unsaturated trimer aldehyde or ketone and heavies 10 are separated from any dimers present in the stream. These dimers 6 are α,β-unsaturated dimer aldehyde or ketone that are formed in reacto-r 104, or that are present in the feed to the reactor, and saturated dimer aldehyde or ketone that is unreacted in reactor 104.

Except for an optional purge 23, the dimers 6 are recycled either to the cross-aldol reactor 106, or to the selective hydrogenation reactor 104, or may optionally be split over these two reactors. Optionally the stream 6, or a part 28 thereof, is treated in a separator 110, where the α,β-unsaturated dimer aldehyde or ketone 8 is separated from the saturated dimer aldehyde or ketone 7. In that case, the α,β-unsaturated dimer aldehyde or ketone 8 is preferentially recycled to the selective hydrogenation reactor 104, while the saturated dimer aldehyde or ketone 7 is preferentially recycled to the cross-aldol reactor 106.

Stream 10 with the ,β-unsaturated trimer aldehyde or ketone is optionally further purified in separator 109, where heavies 24 may be separated from the α,β- unsaturated trimer aldehyde or ketone 11. This purified trimer 11, or the unpurified stream 10 is hydrogenated with hydrogen 27 in a hydrogenation reactor 112 to make either the saturated trimer aldehyde, the unsaturated trimer alcohol, the saturated trimer alcohol, or a mixture of these, 12. This stream is optionally further purified in a product purification section 114 to yield a high purity product 13 and the optional byproduct 25, partly or entirely heavies.

The optional separators 105 and 109, and the product purification section 114, all produce optional heavies containing streams 26, 24 and 25, which are candidates for entire or partial recycle according to this invention. These streams may be recycled to one or more of the following zones of the process: to the self- aldol reactor 102, to the cross-aldol reactor 106, or to the selective hydrogenation reactor 104. More than one heavies stream may exist at any one time. These streams may then be recycled together, or may be recycled individually to different zones of the process. If stream 26 is sent to the cross-aldol reactor 106, the term recycle is less appropriate, and the term feed forward is more applicable.

In the embodiment of Figure 2 , treatment of the products of the self-aldol reactor and of the cross-aldol reactor is combined. Again, aldehyde or ketone monomer 14 and catalyst solution 15 are fed to a self-aldol reactor 102, where dimerization occurs to make the α,β- unsaturated dimer aldehyde or ketone and water 16. The water phase 18 is removed in vessel 103, and the aldol product 19 is sent to a separator 105, separating heavies from the ,β-unsaturated dimer 21. Except for a possible purge 22, this is sent to a selective hydrogenation

reactor 104 together with hydrogen 17, the heavies being sent to the separator 107. In the selective hydrogenation reactor 104, the ,β-unsaturated dimer aldehyde or ketone is converted to the saturated dimer aldehyde or ketone 9. Saturated dimer aldehyde or ketone then enters a cross-aldol reactor 106, where it is cross-condensed with additional aldehyde or ketone monomer 1 in the presence of a catalyst solution 2. In the cross-aldol reactor, the saturated dimer aldehyde or ketone is advantageously present in stoichiometric excess relative to the monomer aldehyde or ketone. This enhances selectivity of trimer production and suppresses monomer self-condensation in the cross-aldol reactor. Monomer aldehyde or ketone is advantageously reacted to almost complete conversion in the cross-aldol reactor. The cross-aldol product 3 may then be fed, via the water- phase separator 103, to the separator 105, where the cross-aldol product, which is primarily a trimer of the feed aldehyde or ketone, is separated from the dimer and leaves the separator together with the heavies.

The trimer aldehyde or ketone is further distilled in column 107 to separate heavies, and the trimer aldehyde or ketone is further hydrogenated by hydrogen 19 in a hydrogenation reactor 112 to make saturated aldehyde or ketone, or the corresponding unsaturated or saturated alcohols 11. By-products 12 are removed in a product purification section 114 to yield high-purity product 13.

According to this invention the heavy product stream 20 from the distillation tower 107 is recycled to one or both of the aldol reactors 102 and 106.

In the embodiment of Figure 3, only one aldol reactor 122 is used. All of the monomer aldehyde or ketone 1 is fed to the aldol reactor 122 with the saturated dimer aldehyde or ketone 7,9 and catalyst solution 2. In this aldol reactor 122, the monomer aldehyde or ketone both self-condenses to make unsaturated dimer and cross-

condenses with saturated dimer aldehyde or ketone to make unsaturated trimer. The stoichiometric ratio of dimer to monomer is advantageously controlled to optimize selectivity to the desired product. Water removal 5, product separation 107 and recycle 20, optional separator 110, hydrogenation 112 and product purification 114 are all identical to the corresponding steps in Figure l.

Through the explanation of Figures 1 to 3 , recycle may also mean sending the heavies stream to a separate reactor for more efficiently initiating their breakdown into desired aldehydes or ketones. The product of this separate reactor is then optionally separated and recycled to the process.

Referring now to Fig. 4, which illustrates the embodiment of the invention in which the monomer aldehyde is obtained in admixture with a low-boiling diluent from, for example, oxonation of an olefin contained, for example, in a DMCS, a dilute olefin (further described here with reference to ethylene, but other olefins may be used) stream 40 is fed to an oxonation reactor 124 from which a reaction product stream 41 comprising propanal and diluents is passed to an optional heat exchanger 129, where sufficient cooling takes place to condense some propanal, this liquid being separated out in a separator 133 and either recycled in a stream 42 to the oxo reactor 124, taken out as product, or taken downstream to the aldolization reactor 127.

After further cooling in a heat exchanger 144, a dilute vapor phase reaction product stream 43 is fed to a wash tower 125. In the tower 125, the product stream 43 contacts a saturated Cg aldehyde stream 44, which absorbs the C ₃ aldehyde from the product stream 43, producing a substantially aldehyde-free tail gas 45 and a mixed C ₃ and C ₆ aldehyde feed 46 to the aldol reactor 127. (In the illustrated embodiment a single self-aldol and cross- aldol reactor is employed, as in Fig. 3. It will be

appreciated, however, that this aspect of the invention is also applicable to the arrangements of Figs. 1 and 2, in which the two aldol reactions take place separately, the feed 46 then being taken to the second aldol reactor. )

In the reactor 127, the C ₃ and C ₆ aldehydes react to produce a product stream 47 which is separated in a distillation column 128 into a C ₉ aldehyde stream 48 which is taken off to a distillation or hydrogenation stage, not shown, and a mixed Cg aldehyde stream 49 which is hydrogenated in the selective hydrogenation reactor 126 to yield the saturated Cg aldehyde stream 44. This is cooled in a heat exchanger 130 before fed to the tower 125. This heat exchange may be effected using cooling water, a process more energy-efficient than the refrigeration otherwise necessary to separate the C ₃ aldehyde from its inert low boiling diluents. Depending on reaction conditions a portion only of the product from the reactor 126 may be needed to absorb all the C ₃ product in the tower 125, in which case the remainder is fed directly as stream 53 to the aldol reactor 127. An optionally already treated heavies stream 50 is optionally also fed to the aldol reactor 127, or alternatively first fed instead of or together with the stream 44 to the tower 125.

The present invention is illustrated by the following examples in which the aldol heavies used are prepared as follows:

748 g/hr propanal and 454 g/hr 1M aqueous NaOH are mixed into a tubular reactor with 1 mm diameter and 100 m length held at 60 deg C. The product is separated into organic and aqueous phases and analysed by GC. The overall conversion of propanal is 99.45% and the molar selectivities of the products are 93% 2-methyl-2-pentenal and 7% heavy by-products. The heavies are recovered by distillation. For the purpose of conversion from raw GC data in the examples which follow, the heavies are assumed to be partially dehydrated propanal trimers with a molecular weight of 156.

Comparative Example 1. Cross condensation of 2- methylpentanal with no heavies added to feed

Three continuous stirred tank reactors in series, each having a liquid volume of approximately one liter, were fed with an organic feed stream and an aqueous catalyst stream (1M NaOH) . The temperature of each reactor was maintained at 140 deg C. The composition of

feed and product streams as determined by GC was

Component Total Feed Product

Flowrate Flowrate

(gmol/hr) (gmol/hr)

Propanal 4.304 0.062

2-Methylpentanal 7.269 3.635

2-Methyl-2-pentenal 0.278 0.518

2-Methylpentanol 0.044 0.053

2, -Dimethyl-2-heptenal 0.101 3.682

2 , 4-Dimethyl-2 , 4- 0.002 0.067 heptadienal

Heavies 0.053 0.231

(propanal trimers)

Water 35.112 41.223

Sodium Hydroxide 0.500 0.500

Assuming heavies are formed by propanal trimerization, then the net propanal selectivity to trimer by-products is 12.6 mole percent.

Example 1. Cross condensation of 2-methylpentanal with propanal in the presence of recycled heavies.

Comparative Example 1 was repeated except that the composition of feed and product streams as determined by GC was :

Component Total Feed Product

Flowrate Flowrate

(gmol/hr) (gmol/hr)

Propanal 4.042 0.066

2-Methylpentanal 5.994 2.712

2-Methy1-2-pentena1 0.808 0.761

2-Methylpentanol 0.041 0.055

2 ,4-Dimethyl-2-heptenal 0.056 3.541

2,4-Dimethyl-2,4- 0.040 0.148 heptadienal

Heavies 0.362 0.347

(propanal trimers)

Water 35.728 42.317

Sodium Hydroxide 0.500 0.500

Assuming heavies are formed by propanal trimerization, then the net propanal selectivity to trimer by-products is -1.2 mole percent.

Comparative Example 2. Self condensation of propanal with no heavies added to feed.

A continuous stirred tank reactor having a liquid volume of approximately one liter was fed with an organic feed stream and an aqueous catalyst stream (1M NaOH) . The temperature of the reactor was maintained at 60 deg C. The composition of feed and product streams as

determined by GC was

Component Total Feed Product

Flowrate Flowrate

(gmol/hr) (gmol/hr)

Propanal 17 .068 0.045

2-Methylpentanal 0 0

2-Methyl-2-pentena1 0 7.290

2-Methylpentanol 0 0

2,4-Dimethyl-2-heptenal 0 0

2,4-Dimethyl-2,4- 0 0.133 heptadienal

Heavies 0 0.700

(propanal trimers)

Water 22 .998 35.053

Sodium Hydroxide 0. 432 .432

Assuming heavies are formed by propanal trimerization, then the net propanal selectivity to trimer by-products is 11.8 mole percent. The net propanal selectivity to 2-methyl-2-pentenal is 85.6 mole percent.

Example 2. Self condensation of propanal in the presence of recycled heavies.

Comparative Example 2 was repeated except that the composition of feed and product streams as determined by GC was :

Component Total Feed Product

Flowrate Flowrate

(gmol/hr) (gmol/hr)

Propanal 15.960 0.065

2-Methylpentanal 0.038 0.006

2-Methy1-2-pentena1 0.228 7.636

2-Methylpentanol 0 0

2, 4-Dimethyl-2-heptenal 0.064 0.033

2,4-Dimethyl-2,4- 0.139 0.172 heptadienal

Heavies 0.717 1.054

(propanal trimers)

Water 23.223 35.286

Sodium Hydroxide 0.435 0.435

Assuming heavies are formed by propanal trimerization, then the net propanal selectivity to trimer by-products is 6.4 mole percent. The net propanal selectivity to 2-methyl-2-pentenal is 93.2 mole percent.

Example 3

In this example, heavies in the feed are reduced by 48%. Under these conditions, heavies are reversed to form propanal, which then cross-aldolizes with the excess 2- methylpentanal to form the unsaturated C aldehyde, 2,4- dimethyl-2-heptanal. This example demonstrates the recovery of desirable aldol products, specifically 2,4- dimethyl-2-heptenal by recycling heavies to a reactor in the presence of 2-methylpentanal. Three continuous stirred tank reactors in series, each having a liquid volume of approximately one liter, were fed with an organic feed stream and an aqueous catalyst stream (1M NaOH) . The temperature of each reactor was maintained at 160 deg C. The composition of feed and product streams as determined by GC was :

Component Total Feed Product

Flowrate Flowrate

(gmol/hr) (gmol/hr)

Propanal 0.024 0.062

2-Methylpentanal 7.936 6.791

2-Methyl-2-pentenal 0.018 0.003

2-Methylpentanol 0.000 0.075

2,4-Dimethyl-2-heptenal 0.037 1.286

2 ,4-Dimethyl-2,4- 0.056 0.036 heptadienal

Heavies 0.715 0.372

(propanal trimers)

Water 28.324 27.371

Sodium Hydroxide 0.532 0.532

Example 4. Aldol Heavies Reversal by Aquathermolysis

Aldol heavies are contacted with water at elevated temperature under autogenous pressure in a 10 ml non- agitated sealed bomb. Under these conditions, aldol heavies are reversed to form C6 and C9 mainly unsaturated aldehydes, and the amount of heavies reversed depends on both time and temperature of treatment and on the ratio of heavies to water.

Table of example 4. Aldol heavies reversal by aquathermolysis.

Percentage of C6 and C9 aldehydes in organic phase after water treatment.

Heavies : Water (weight ratio)

Temp. Time 2:1 1:1 1:2 1:5 1:7 1:10 deg C min %C6 %C9 %C6 %C9 %C6 %C9 %C6 %C9 %C6 %C9 %C6 %C9

200 20 5.0 3.8 4.9 4.3 5.2 4.8 6.0 11.4

250 20 11.2 11.2 12.3 16.9 13.9 21.7

275 20 14.5 13.7 17.8 17.8 20.5 26.9

300 10 17.3 15.1 19.2 15.3 21.7 21.9 24.6 29.5

300 20 19.0 18.3 21.8 18.7 23.4 22.9 25.7 29.0 28.3 32.9 25.4 33.6 o

300 35 20.8 23.4 23.6 23.7 27.0 27.5 26.5 35.6

300 60 22.3 27.3 27.3 27.4 26.9 29.5 26.5 35.1

Example 5. Aldol Heavies Reversal by Aquathermolysis with Aqueous Additives

The same experimental procedure is used as in example 4, except that acids or surfactants are added to the aqueous phase before treatment of the heavies. These additives are shown to increase the amount of C9 aldehyde recovered in the organic product relative to treatment with water only. In the table which follows:

PTSA = para-toluene sulfonic acid HOAc = acetic acid H3P04 = phosphoric acid

Table of example 5. Aquathermolysis of aldol heavies with aqueous additives.

Heavies

Teπp. Time -Aqueous Cone. to sol-n. Product Product deg C min Additive Mol/liter wt. ratio %C6 %C9

300 20 PTSA 0.001 2 : 1 20.7 24.5

300 20 PTSA 0.001 1 : 1 23.6 31.9

300 20 PTSA 0.001 1 : 1 21.1 37.7

300 20 PTSA 0.01 2 : 1 23.9 33.6

300 20 PTSA 0.01 1 : 1 20.4 38.7

300 20 PTSA 0.01 1 : 2 0.9 42.2

300 20 PTSA 0.01 1 : 5 11.2 46.9

300 20 PTSA 0.02 2 : 1 19.7 38.9

300 20 PTSA 0.02 1 : 1 17.0 44.4

300 20 PTSA 0.02 1 : 2 13.3 45.7

300 20 PTSA 0.02 1 : 5 10.7 47.2

300 20 PTSA 0.04 2 : 1 18.2 40.9

300 20 PTSA 0.04 1 : 1 13.6 42.6

300 20 PTSA 0.04 1 : 2 9.4 46.1

300 20 PTSA 0.04 1 : 5 10.2 46.1

300 20 HOAc 0.2 2 : 1 18.4 19.5

300 20 HOAC 0.2 1 : 1 19.0 23.2

300 20 HOAc 0.2 1 : 2 22.7 26.4

300 20 H3P04 0.2 2 : 1 19.4 41.7

300 20 H3P04 0.2 1 : 1 16.4 46.5

300 20 H3P04 0.2 1 : 2 13.6 48.2

300 20 H3P04 0.2 1 : 5 8.8 51.6

300 20 H3F04 1 2 : 1 15.0 46.3

300 20 H3P04 1 1 : 1 12.4 48.2

300 20 H3P04 1 1 : 2 7.6 49.7

300 20 H3P04 1 4.0 52.5

Example 6. Aldol Heavies reversed by Aquathermolysis with basic aqueous additives

The same procedure is used as in example 4, with 20 minutes reaction at 300°C in the presence of 1.0 and 0.5N sodium hydroxide. The results, in terms of the percentage of unsaturated aldehyde in the reaction product, are shown in the Table below:

Table of example 6

Concentration of Heavies to Product Product Product NaOH, ol/liter soln. % C ₃ % C ₆ % C ₉ wt. ratio

1.0 1:5 1.9 3.2 18.6 1.0 1:2 4.1 15.8 18.6 1.0 1:1 5.8 24.6 17.2 1.0 2:1 7.7 42.2 10.8 1.0 4:1 6.8 42.0 8.4 0.5 1:2 6.0 25.4 10.8 0.5 1:1 7.6 35.8 14.1 0.5 2:1 7.6 42.5 10.6

The results indicate that, if desired, an initial treatment with a basic solution, giving good Cg yield, may be followed by separation of C6 aldehyde, for return to aldolization, and remaining heavies and C9 aldehyde which may be further treated with an acidic solution as described in Example 5, to yield further C ₉ aldehyde.