2-Ethylhexanol from propylene, production

The production of 2-ethylhexanol from propylene by the rhodium catalyzed, low pressure oxo process is accomplished in three chemical steps. The first step of the process (described in section on n-butanol manufacture) converts propylene to normal butyraldehyde by hydroformylation in the presence of a rhodium catalyst. In a second step, the normal aldehyde is aldoled to form 2-ethylhexena1. 2-Ethylhexenal is then hydrogenated to 2-ethylhexanol and refined in the third and final step(see Figure 3). 

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. 

Ishtkm, Yn Improved Mitsubishi 2-ethyUtexanol process". Chan. Earn, and Engng Rev, 2 (1) 31-33 (1970) Weber, H Falbe, J, " Oxo synthesis gains worldwide importance". Oil and Gas J. ImernaL. 10 (5) 9097 (19710. Weber, Hn Production of 1-ethylhexanol from ethylene and propylene". Joint Conference of she Chemical Institute erf Canada American Chemical Society, Toronto. Ontario (24-29 May 1970V... 

Cobaltcarbonyls are used as catalysts for carbonylations such as hydroformylation (0x0 reaction), hydrocarbonylation and amidocarbonylation [70a]. Hydroformylation is the reaction of preparing aliphatic aldehydes in which carbon number is increased by one [46]. Especially, butylaldehyde has been industrially produced largely from propylene butylaldehyde is used as a raw material for butanol and 2-ethylhexanol, etc. Cobalt and rhodium compounds are used for their catalysts. The reactivity of cobalt catalysts is lower than that of rhodium catalysts. However, more linear products of the reaction shown in eq. (17.27) are obtained. The ratio of... 

The first stage of the process is a hydroformylation (oxo) reaction from which the main product is n-butyraldehyde. The feeds to this reactor are synthesis gas (CO/H2 mixture) and propylene in the molar ratio 2 1, and the recycled products of isobutyraldehyde cracking. The reactor operates at 130°C and 350 bar, using cobalt carbonyl as catalyst in solution. The main reaction products are n- and isobutyraldehyde in the ratio of 4 1, the former being the required product for subsequent conversion to 2-ethylhexanol. In addition, 3 per cent of the propylene feed is converted to propane whilst some does not react. 

Subsequently, a whole host of both lower (C3, C4, C5) and higher (C5, Cy, C9, C q, C, etc.) oxo alcohols have been commercialized. Of all these alcohols, the most important by far have turned out to be n-butanol and 2-ethylhexanol - both of which are derived from n-butyraldehyde based on hydroformylation of propylene. In addition to n-butyraldehyde, the lower valued isobutyraldehyde is produced as a by-product. Some of this is converted to isobutanol. 

The largest volume hydroformylation reaction converts propylene into n-butyraldehyde, from which is made 1-butanol for solvents, or 2-ethylhexanol (the phthalate ester of which has been widely used as a plasticizer for PVC) via an aldol condensation. Estimated world production of butanol is approaching 2 Mt/a. 

From 1974 onwards, Rh-based hydroformylation became industrial. The use of a catalyst metal that is about 1000-times more expensive than cobalt was driven by several reasons. First, Rh-hydroformylation is more active and thus requires much lower process pressures (lower energy consumption in compression units) and smaller reactors. Second, Rh-hydroformylation shows a very high selectivity to the aldehyde product with only minimal hydrogenation activity being observed. This is of particular importance for propylene hydroformylation where butyl alcohol is not the principle market use. In contrast, for the desired end-use of w-butyraldehyde in the form of its aldol condensation product 2-ethylhexanol a pure aldehyde feed is required as hemiacetals (formed by reaction of aldehyde and alcohol) complicate product purification and add to operating costs. 

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