Other Integrated HPPO Processes
An integrated process has also been reported, but not implemented at a commercial level, by ARCO (now Lyondell) . In this case, the O-donor species is produced by the autoxidation of aryl-substituted secondary alcohols (a-methyl benzyl alcohol) to ketones, and the resulting solution is used to feed the epoxidation reactor. The alcohol is then recovered by hydrogenating the ketone. The main difference with respect to the EniChem process is the higher temperature of the autoxidation process (90-140 instead of 40 °C).
The procedure described involves the initial preparation of the oxidant mixture (containing 5wt% HP, 1% H2O, 66% unconverted a-methylbenzyl alcohol, 28% acetophenone, plus minimal amounts of EBHP) by air oxidation of a-methylbenzyl alcohol. The mixture is then fed to an autoclave loaded with the catalyst (TS-1), methanol and propene, and heated at 40 °C (molar ratio olefin/H2O2 = 1.5/1). A HP conversion of 70% is finally achieved, with 89% selectivity to PO on an HP basis (but conversions of up to 97% have been reported in other examples, with selectivity to PO equal to 84%). After separation of PO, the fraction containing acetophenone is hydrogenated with a Pd/C catalyst at 50 °C to achieve at least 80% conversion of acetophenone to a-methylbenzyl alcohol. It is reported that the integrated process, which uses a crude, unpurified oxidant mixture obtained by air oxidation of the alcohol, provides PO yields equivalent to those obtained using purified HP diluted in a clean alcohol/ketone reaction medium. Thus, the advantage of the integrated process is the reduced costs associated with the purification and concentration of HP. A disadvantage of the process is the deactivation of TS-1 when the process is carried out in a continuous mode, because of the accumulation of oligomeric byproducts derived from the secondary alcohol. Figure 6.8 shows the general outline of the process.
In some patents [21b,c], a different integrated process is described, where a secondary-alcohol (isopropanol) is oxidized to an aliphatic ketone with oxygen to generate a stream containing HP. Before being fed to the epoxidation reactor, the ketone is eliminated by separation and hydrogenation; the epoxidation is then carried out, catalyzed by TS-1. The ketone is hydrogenated to the alcohol, and recycled to the autoxidation step. The advantage ofseparating the ketone is that the accumulation of a ketone peroxide species is prevented, which would otherwise be produced through a reaction between the ketone and HP at epoxidation conditions (conversely, the alcohol is reported not to react with HP). This side-reaction also causes consumption of HP, and complicates the purification and separation steps following epoxidation.
Continue reading here: HPPO and In Situ HPPO Processes HP Generation by Direct Oxidation of H2 DSHP
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