New Process For The Benzaldehyde Production From The Oxidation Of Styrene By Molecular Oxygen

Benzaldehyde is one of the most important and useful aromatic aldehydes in industry, and it can be widely used in pharmatech, flavor, pesticide, and dyestuff industries. At present, most of the benzaldehyde in china is produced through dichlorotoluene hydrolyzation process. The product has chloride, so it is restricted to be used in the flavor and pharmatech industry. This paper discussed a new process. In this process, styrene is oxidezed to benzaldehyde without chloride formation.In this paper, we firstly carried out this reaction in batch reactor. Styrene was oxidized to benzaldehyde and formaldehyde over TiOxSiOy catalyst, and benzyl methyl ketone, benzyl acetaldehyde, and polymer were also detected as by-products.Through catalyst filtration, solvent effect study, radical initiator and inhibitor study, higher styrene conversion(70.9%) and higher benzaldehyde selectivity (75.3%)were obtained (without catalyst 19.5% and 48.7%) at 100℃and 10 atm of oxygen pressure with the addition of 5.0% nitrobenzene over TiO2/SiO2 catalyst. Styrene analogues were also oxidized under this reaction condition. The reaction was also carried out in the continuous flow tube reactor. When oxygen was used as oxidant, we found that the styrene conversion increases with the increase of titanium concentration in catalysts. Over TiO2/SiO2(8/2)catalyst, the styrene conversion and benzaldehyde selectivity were 53.2% and 94.1%, respectively, at 80℃and 10 atm of oxygen pressure. Doping Zr and W into silica did not improve the catalyst activity, while doping V and Mo led to the formation of polymers. When air was used as oxidant, it led to the styrene conversion decrease because of the low oxygen concentration. Increasing the gas flow or pressure of air improves the styrene conversion. The increase of styrene flux led to lower styrene conversion.We think that the first step of the reaction is the formation of intermediate peroxide. The intermediate peroxide can directly decomposes to benzaldehyde and formaldehyde, and aldehydes could react with oxygen molecules to form peroxylic acids. The peroxylic acid can react with olefin to form olefin oxide, such as here, the styrene oxide. The peroxylic acid could also decompose to oxidative radicals. These oxidative radicals could react with styrene to form benzacetaldehyde and acetophenone and also initiate the polymerization reaction of styrene to form polymers. Oxidative radicals are the initiators of the polymerization reaction, while the additions of inhibitors retarded the polymerization reaction.