Liquid-phase Selective Oxidation Of Toluene Over NHPI/(Cosalen@SBA-15) Catalysts

The liquid-phase oxidation of toluene to benzoic acid in industry production has theadvantages of simple process, mild reaction conditions, high yield and good security. Theprocess produces small amount of benzaldehyde and benzyl alcohol as by-products withhigher added value. As the increased demand for chlorine-free benzaldehyde and benzylalcohol in food, medicine and perfume industry, how to increase the selectivity ofbenzaldehyde and benzyl alcohol in the oxidation of toluene attracts much attention. Thethesis aims at realizing selective oxidation of toluene to benzaldehyde, benzyl alcohol andbenzoic acid by searching for effective catalyst and proper process conditions.Firstly, NHPI/Cosalen was used as the combined catalyst for the liquid-phase oxidationof toluene with oxygen. The effects of the amout of catalyst, reaction temperature and reactiontime on the catalytic performance of NHPI/Cosalen were investigated. The results show thatthe activity of pure NHPI catalyzed the toluene oxidation was low and pure Cosalen had noactivity. The combination of NHPI and Cosalen revealed obvious synergistic function. Underfollowing appropriate conditions of the liquid-phase oxidation of toluene: the amouts of NHPIand Cosalen were2mol%and0.02mol%respectively, under the reaction temperature of110℃for2h, the conversion of toluene was13.55%, the selectivity of benzaldehyde andbenzyl alcohol were32.69%and10.77%respectively, the total selectivity to benzaldehyde,benzyl alcohol and benzoic acid was up to97.71%.Secondly, Cosalen was immobilized on mesoporous sieves SBA-15which was used assupport by grafting, and the SBA-15was hydrophobic modified with methyl-silanes ascoupling agent so that the polar products benzaldehyde and benzyl alcohol could timelydesorpt from the catalyst to inhibit them from further oxidating. The samples werecharacterized by elemental analysis、ICP、IR、UV-vis、XRD、N2physisorption and TG, theeffects of pore structure parameters and types of methyl coupling agent were studied. Theadsorptive properties of samples for toluene、benzaldehyde and benzoic alcohol and catalyticperformance of NHPI/Cosalen@SBA-15for liquid-phase oxidation of toluene wereinvestigated. The results show that the mesoporous structure and the ordering of porestructure of SBA-15samples modified by grafting were retained，but the samples showedsmaller pore volume、 pore diameter and lower surface area; Cosalen was highly dispersed onthe surface of SBA-15. The larger structure parameters, the higher Cosalen loading. Thehydrophobicity of samples with methyl modified was significantly enhanced, and theiradsorptive performance for benzaldehyde and benzoic alcohol descreased obviously. Theliquid-phase oxidation of toluene catalyzed by hydrophobic Cosalen/SBA-15effectively improved the products selectivity ratio of benzaldehyde and benzoic alcohol to benzoic acidfrom0.46to0.52, but the adsorptive property and catalytic performance of samples modifiedwith various methyl-silanes had no significant differences due to the low content of methylbonding to the SBA-15surface.