Catalytic And Non-catalytic For Oxidation Of Styrene To Benzaldehyde

As an important chemical product, benzaldehyde is widely used in the fields of bothindustrial production and daily life. There are two methods employed in this work, for theresearch of the oxidation of styrene using hydrogen peroxide as oxidant: One is thepreparation of benzaldehyde by oxidizing styrene catalyzed by p-toluene sulfuric acid (pTSA),accelerated by the activated carbon introduced. The other is the preparation of benzaldehydeby oxidizing styrene in the CH3COOH/H2O2system. Both of these two methods have highconversion rates. The main research results are as follows:1. Accelerated by activated carbon, the preparation of benzaldehyde by selectivelyoxidizing styrene in the pTSA/H2O2system has been studied.The honeycomb activated carbon (HAC) used in the experiment is obtained aftercommercial activated carbon being pretreated by nitric acid. It has been found during theexperiments that the conversion rate of styrene is low (<10%) when simply applyingpTSA/H2O2system or HAC/H2O2system. However, the conversion rate of styrene is higherthan80%when use pTSA and HAC at the same time. An obvious synergistic effect has beenobserved. A further study has been made on the effects of the added amount of pTSA andHAC, the reaction temperature, the amount-of-substance ratio of H2O2and styrene, and thereaction time of this synergistic system on the activity and selectivity of the oxidation ofstyrene to benzaldehyde catalyzed by this synergistic system. The optimal condition is asfollows: each of HAC and pTSA is0.05g, acetonitrile5mL, styrene0.5mL, n(H2O2):n(styrene)is equal to3.5, reacting for10h at60℃, the conversion rate of styrene is86.5%, theselectivity of benzaldehyde is80.1%.After HAC has been heat treated at800℃for6h under H2/Ar or N2atmosphere, theeffect of the change of the oxygen-containing groups on the surface of HAC on thissynergistic system has been studied. The structure of HAC hasn’t been changed after heattreatment. Compared with the original HAC, the amount of the oxygen-containing groups onthe surface of the heat treated HAC decreases. the oxygen-containing groups affect theconversion rate and selectivity of the reaction. Additionally, sulfonic acid group (-SO3H) hasbeen introduced into HAC. Compared with the original HAC, HAC-SO3H shows higherconversion rate of styrene and selectivity of benzaldehyde. It proves that sulfonic acid groupplays the main role in the oxidation reaction of styrene. Replacing pTSA with Hydrochloric acid of the same amount-of-substance,HCl/HAC/H2O2system shows much lower oxidative activity in catalyzing benzaldehyde. Itproves the acidity of pTSA has little effect on synergistic system. The amounts of thedecomposition of H2O2and the remained hydrogen peroxide after reaction of the system havebeen determined, it shows that pTSA/HAC/H2O2system uses H2O2much more effectivelythan HAC/H2O2system, this may be due to the acidity of pTSA slowing down thedecomposition of H2O2. At last, using the results of the activities and selectivities of thedifferent reaction systems by introducing free-radical inhibitor, the possible reactionmechanism of the synergistic system has been discussed.2. The preparation of benzaldehyde by oxidizing styrene in the CH3COOH/H2O2systemhas been studied. Firstly, the condition for the oxidation of styrene in the CH3COOH/H2O2system has been optimized. under the condition of styrene0.5mL, acetic acid5mL,n(H2O2):n(styrene)=4.5,60℃,5h, the conversion rate of styrene and the selectivity ofbenzaldehyde are99.6%and64.4%. One step further has been taken on changing the pH ofthe optimized CH3COOH/H2O2system. The selectivity of benzaldehyde decreases,meanwhile, the selectivity of phenylacetaldehyde increases in the system when introducing acertain amount of sulfuric acid. The selectivity of benzaldehyde increases, the selectivity ofphenylacetaldehyde decreases in the system when introducing a certain amount of sodiumhydroxide. At last， the selectivity of phenylacetaldehyde decreases, the selectivity ofbenzaldehyde increases when introducing no matter a certain amount of solvent, acetonitrileor water into the CH3COOH/H2O2system.