Butyraldehyde production

The remaining (8%) //-butyraldehyde production of the United States goes into (in decreasing order) poly(vinyl butyral), 2-ethyIhexanal, trimethylolpropane, methyl amyl ketone, and butyric acid. 

Within the reactor, however, 6 per cent of the n-butyraldehyde product is reduced to n-butanol, 4 per cent of the isobutyraldehyde product is reduced to isobutanol, and other reactions occur to a small extent yielding high molecular weight compounds (heavy ends) to the extent of 1 per cent by weight of the butyraldehyde/butanol mixture at the reactor exit. 

Higher selectivity towards the desired n-butyraldehyde product. 

The discovery and use of fluorophosphites and chlorophosphites as trivalent phosphorus ligands in the rhodium catalyzed, low-pressure hydroformylation reaction are described. The hydroformylation reaction with halophosphite ligands has been demonstrated with terminal and internal olefins. For the hydroformylation of propylene, the linear to branched ratio of the butyraldehyde product shows a strong dependency on the ligand to rhodium molar ratios, the reaction temperature, and the carbon monoxide partial pressure. 

Description The process reacts propylene with a 1 1 syngas at low pressure (<20 kg/cm2g) in the presence of a rhodium catalyst complexed with a ligand (1). Depending on the desired selectivity, the oxonation reaction produces normal and iso-butyraldehyde with typical n/i ratios of either 10 1 or >22 1. Several different ligand systems are commercially available which can produce selectivity ratios of up to 30 1 and as low as 2 1. The butyraldehyde product is removed from the catalyst solution (2) and purified by distillation (3). N-butyraldehyde is separated from the iso (4). 

A similar Rh complex, [HRh(CO)(PPh3)3], immobilized onto AC and CNTs (ends-opened) by an incipient wetness technique was tested as a catalyst for propene hydroformylation [70]. Activity assay of the catalysts showed that the CNT-supported Rh complex displayed not only high activity for propene conversion but also excellent regioselectivity to the butyraldehyde product. Under the experimental conditions used, the molar ratio of normal to branched aldehydes reached 12 to 13 at a TOP of 0.12 s corresponding to a propene conversion of 32%. To understand the excellent catalytic behavior of the CNT-supported catalyst, an ends-unopened CNT was also used as support and its catalytic properties tested In this particular case, propene conversion and the nii ratio reached only 17.2% (corresponding to a TOP of 0.06 s ) and 6.0, respectively. On the basis of this result, the authors concluded that the high propene conversion and excellent regioselectivity demonstrated by ends-opened CNT-supported catalyst was due mainly to the confinement effect induced by the presence of a Rh-phosphine complex in the inner surface of the tubular nanochannels of CNT [70]. 

A comparison of the performance of Co, modified Co, and modified Rh systems is given in Table 1. Clearly the Rh system outperforms Co both in terms of milder operating conditions and in overall efficiency to the desired product n-butyraldehyde and it is worth noting that catalyst costs make only a minor contribution to production costs (<0.5 c per lb butyraldehyde). Consequently all new butyraldehyde plants which have been installed recently have employed the Rh LPO process. When all current licensees plants are operational Rh catalysts will account for one third of butyraldehyde production worldwide. 

Butyraldehyde production is technically carried out through propylene hydrofor-mylation [route (d) in Topic 5.3.2]. The process is the key topic of Section 6.14. 

Today the installed hydroformylation capacity worldwide is more than 7.5 Mio tons per year (Baerns et al., 2006). The most important feedstock is propene, with the products n-butyraldehyde and iso-butyraldehyde (Scheme 6.14.3). The most important single product from propene hydroformylation is 2-ethyl-l-hexanol (>50% of the n-butyraldehyde production), the aldol condensation product obtained from n-butanal, which is an important plasticizer alcohol. After esterification with phthalic anhydride, dioctyl phthalates plasticizers are obtained that are used mainly in poly(vinyl chloride) plastics. 

Butyraldehyde production by butanol oxidation over Ru and Cu catalysts supported on Zr02, Ti02 and Ce02... 

Ceria, titania, and zirconia supported ruthenium and eopper catalysts were tested in the production of n-butanal by n-butanol oxidation. These eatalysts were characterized by means of X-ray diffraction (XRD), N2 adsorption-desorption isotherms, temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) techniques. The activity tests were performed in a fixed bed reaetor at 0.1 MPa and 623 K and pure mixture of reactants, air and n-butanol, in stequiometric proportion was introduced to the reactor. The rathenium catalysts showed a higher activity and stability than the copper catalysts, nevertheless the copper system showed a higher selectivity toward butyraldehyde production by n-butanol oxidation. 

Rhodium Ca.ta.lysts. Rhodium carbonyl catalysts for olefin hydroformylation are more active than cobalt carbonyls and can be appHed at lower temperatures and pressures (14). Rhodium hydrocarbonyl [75506-18-2] HRh(CO)4, results in lower -butyraldehyde [123-72-8] to isobutyraldehyde [78-84-2] ratios from propylene [115-07-17, C H, than does cobalt hydrocarbonyl, ie, 50/50 vs 80/20. Ligand-modified rhodium catalysts, HRh(CO)2L2 or HRh(CO)L2, afford /iso-ratios as high as 92/8 the ligand is generally a tertiary phosphine. The rhodium catalyst process was developed joindy by Union Carbide Chemicals, Johnson-Matthey, and Davy Powergas and has been Hcensed to several companies. It is particulady suited to propylene conversion to -butyraldehyde for 2-ethylhexanol production in that by-product isobutyraldehyde is minimized. 

Aldehydes fiad the most widespread use as chemical iatermediates. The production of acetaldehyde, propionaldehyde, and butyraldehyde as precursors of the corresponding alcohols and acids are examples. The aldehydes of low molecular weight are also condensed in an aldol reaction to form derivatives which are important intermediates for the plasticizer industry (see Plasticizers). As mentioned earlier, 2-ethylhexanol, produced from butyraldehyde, is used in the manufacture of di(2-ethylhexyl) phthalate [117-87-7]. Aldehydes are also used as intermediates for the manufacture of solvents (alcohols and ethers), resins, and dyes. Isobutyraldehyde is used as an intermediate for production of primary solvents and mbber antioxidants (see Antioxidaisits). Fatty aldehydes Cg—used in nearly all perfume types and aromas (see Perfumes). Polymers and copolymers of aldehydes exist and are of commercial significance. 

Another attractive commercial route to MEK is via direct oxidation of / -butenes (34—39) in a reaction analogous to the Wacker-Hoechst process for acetaldehyde production via ethylene oxidation. In the Wacker-Hoechst process the oxidation of olefins is conducted in an aqueous solution containing palladium and copper chlorides. However, unlike acetaldehyde production, / -butene oxidation has not proved commercially successflil because chlorinated butanones and butyraldehyde by-products form which both reduce yields and compHcate product purification, and also because titanium-lined equipment is required to withstand chloride corrosion. 

The largest oxo producers ia Western Europe are BASE, Hbls, and Hoechst (formerly Ruhrchemie), representing 50—51% of the total regional capacity of 2.527 x 10 metric tons. These companies have the broadest spectmm of products ranging from and adehydes to alcohols and acids. However the primary products are n- and isobutyraldehyde, at combiaed capacities of 1.08 x 10 t. The -butyraldehyde goes principally iato the manufacture of 2-EH. 

The spectmm of oxo products ia Japan is far less diverse. Nearly 75% of Japan s total oxo capacity of 733,000 t is dedicated to the hydroformylation of propylene. 2-EH derived from -butyraldehyde is by far the dominant product. Other products iaclude linear alcohols and higher branched alcohols. Additionally, Japan is the world s principal source of branched heptyl alcohol. The three ptincipal Japanese oxo producers having slightly more than 70% of Japan s total oxo capacity are Mitsubishi Kasei, Kyowa Yuka, and Japan Oxocol. 

Homogeneous rhodium-catalyzed hydroformylation (135,136) of propene to -butyraldehyde (qv) was commercialized in 1976. -Butyraldehyde is a key intermediate in the synthesis of 2-ethyIhexanol, an important plasticizer alcohol. Hydroformylation is carried out at <2 MPa (<290 psi) at 100°C. A large excess of triphenyl phosphine contributes to catalyst life and high selectivity for -butyraldehyde (>10 1) yielding few side products (137). Normally, product separation from the catalyst [Rh(P(C2H2)3)3(CO)H] [17185-29-4] is achieved by distillation. 

The two main industrial processes that are employed are described in Reference 106. Normal butyraldehyde (qv) is the product of primary interest (103,107). 

Aldol reaction of campholenic aldehyde with propionic aldehyde yields the intermediate conjugated aldehyde, which can be selectively reduced to the saturated alcohol with a sandalwood odor. If the double bond in the cyclopentene ring is also reduced, the resulting product does not have a sandalwood odor (161). Reaction of campholenic aldehyde with -butyraldehyde followed by reduction of the aldehyde group gives the aHyUc alcohol known commercially by one manufacturer as Bacdanol [28219-61 -6] (82). 

Manufacture. PVBs are manufactured by a variety of two-stage heterogeneous processes. In one of these an alcohol solution of poly(vinyl acetate) and an acid catalyst are heated to 60—80°C with strong agitation. As the poly(vinyl alcohol) forms, it precipitates from solution (77). Ethyl acetate, the principle by-product, is stripped off and sold. The precipitated poly(vinyl alcohol) is washed to remove by-products and excess acid. The poly(vinyl alcohol) is then suspended in a mixture of ethyl alcohol, butyraldehyde, and mineral acid at temperatures above 70°C. As the reaction approaches completion the reactants go into solution. When the reaction is complete, the catalyst is neutralized and the PVB is precipitated from solution with water, washed, centrifuged, and dried. Resin from this process has very low residual vinyl acetate and very low levels of gel from intermolecular acetalization. 

Poly(vinyl butyral), prepared by reacting poly(vinyl alcohol) with -butyraldehyde, finds wide appHcation as the interlayer in safety glass and as an adhesive for hydrophilic surfaces (161). Another example is the reaction of poly(vinyl alcohol) with formaldehyde to form poly(vinyl formal), used in the production of synthetic fibers and sponges (162). 

The principal commercial source of 1-butanol is -butyraldehyde [123-72-8] obtained from the Oxo reaction of propylene. A mixture of n- and isobutyraldehyde [78-84-2] is obtained in this process this mixture is either separated initially and the individual aldehyde isomers hydrogenated, or the mixture of isomeric aldehydes is hydrogenated direcdy and the n- and isobutyl alcohol product mix separated by distillation. Typically, the hydrogenation is carried out in the vapor phase over a heterogeneous catalyst. For example, passing a mixture of n- and isobutyraldehyde with 60 40 H2 N2 over a CuO—ZnO—NiO catalyst at 25—196°C and 0.7 MPa proceeds in 99.95% efficiency to the corresponding alcohols at 98.6% conversion (7,8) (see Butyraldehydes Oxo process). 

Butyraldehyde undergoes stereoselective crossed aldol addition with diethyl ketone [96-22-0] ia the presence of a staimous triflate catalyst (14) to give a predominantiy erythro product (3). Other stereoselective crossed aldol reactions of //-butyraldehyde have been reported (15). 

The majority (92% in 1988) of the butyraldehyde produced in the United States is converted into 1-butanol and 2-ethyIhexanol (2-EH). 2-EH is most widely used as the di(2-ethylhexyl) phthalate [117-81-7] ester for the plasticisation of flexible PVC. Other uses for 2-EH include production of intermediates for acryflc surface coatings, diesel fuel, and lube oil additives (24). 

Ethylhexanal, the reduced aldol condensation product of //-butyraldehyde, is converted into 2-ethylhexanoic acid [149-57-5] which is converted primarily into salts or metal soaps. These are used as paint driers and heat stabili2ers for poly(vinyl chloride). 

Trimethylolpropane (TMP), the reduced crossed aldol condensation product of //-butyraldehyde and formaldehyde, competes in many of the same markets as glycerol (qv) and pentaerythritol. The largest market for TMP is as a precursor in unsaturated polyester resins, short-oil alkyds, and urethanes for surface coatings (see Alkyd resins). 

Butyric acid, the simple oxidation product of -butyraldehyde, is used chiedy in the production of cellulose acetate butyrate [9004-36-8]. Sheets of cellulose acetate butyrate are used for thermoformed sign faces, bUster packaging, goggles, and face shields. 

The earhest commercial route to -butyraldehyde was a multistep process starting with ethanol, which was consecutively dehydrogenated to acetaldehyde, condensed to crotonaldehyde, and reduced to butyraldehyde. In the late 1960s, production of -butyraldehyde (and isobutyraldehyde) in Europe and the United States switched over largely to the Oxo reaction of propylene. 

The earhest modification of the Oxo process (qv) employed cobalt hydrocarbonyl, HCo(CO)4, as catalyst. The reaction was carried out in the Hquid phase at 130—160°C and 10—20 MPa (1450—2900 psi) to give a ratio of n- to isobutyraldehyde of between 2 1 to 4 1. / -Butyraldehyde, the straight-chain isomer and the precursor of 2-ethylhexanol, was the more valuable product so that a high isomer ratio of n- to isobutyraldehyde was obviously advantageous. 

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