Study On Synthesis Of Anthraquinone From O-benzoylbenzoic Acid Over Phosphotungstic Acid Catalyst

Anthraquinone (AQ) is an important organic synthetic intermediate. The traditional method of the synthesis of AQ consists of two reaction steps. The first step is the synthesis of o-benzoylbenzoic acid (BBA) from benzene and phthalic anhydride catalyzed by aluminum chloride, the another is the synthesis of AQ from dehydration of o-benzoylbenzoic acid (BBA) catalyzed by concentrated sulfuric acid . Using aluminum chloride and concentrated sulfuric acid as catalyst causes severe equipment corrosion and environment pollution. So the study on synthsis of anthraquinone from BBA over phosphotungstic acid catalyst has a great theoretical and application significance.Firstly, Several heteropoly acid catalysts were used in synthesis of anthraquinone. Performances of the catalysts were examined, and the better catalysts for this was phosphotungstic acid. The optimal reaction conditions are as follow: m(HPW):m(BBA)=1:40, reaction temperature 220℃and reaction time 2h. Under the conditions, AQ yield was over 99%. But the catalyst is difficult to recycle and reuse. The results of FT-IR characterization indicated the phosphotungstic acid was with the Keggin structure, and phosphotungstic acid catalyst is easily deactivated because of coke deposition on it.Secondly, Phosphotungstic acid was supported on Sicilia gel by sol-gel method and was used in synthesis of anthraquinone from o-benzoylbenzoic acid. The effect of preparation conditions, such as solvent species, molar ratio of alcohol to TEOS, molar ratio of water to TEOS, hydrolysis temperature, calcination temperature, and HPW loading, on catalytic activity was investigated. Optimal preparation conditions are: hydration temperature 80℃, pH=3.8, n(alcohol):n(TEOS)=2, n(H2O):n(TEOS)=5, calcination temperature 250℃, phosphotungstic acid loading amount 10%. The catalytic performance of this catalyst in synthesis of anthraquinone from o-benzoylbenzoic acid was tested. The optimal reaction conditions are: m(HPW/(Silical gel)):m(BBA)=1:1, reaction temperature 260℃, and reaction time 2h. And under these conditions,AQ yield was 99.8%. The results of FT-IR characterization indicated the HPW/(Silical gel) still remains the Keggin structure. And the catalyst is easily deactivated because of coke deposition on HPW/(Silical gel) catalyst. In addition,decoking by high temperature calcination(450℃-550℃) will cause HPA catalyst decomposition. So high temperature calcination is not an effective method to recover catalyst activity.Thirdly, A series of supported phosphotungstic acid catalysts were prepared by Equal volume impregnation method and were used in synthesis of anthraquinone from o-benzoylbenzoic acid. The effect of preparation conditions and reaction conditions were investigated. The optimal preparation conditions are: SiO2 as support, calcination temperature 250℃, phosphotungstic acid loading amount 30%. The optimal reaction conditions are: m(HPW/SiO2):m(BBA)=1.6:1, reaction temperature 220℃, reaction time 2h. Under these conditions, the yield of AQ was 99.6%. The results of FT-IR, TG-DTG, XRD characterization indicated phosphotungstic acid highly dispersed on the SiO2 carrier, and still remains the Keggin structue. The results of TG-DTG, BET, XRD, FT-IR, Py-IR, UV-Vis characterization indicated that the deactivation of catalyst was due to the decrease of Br?nsted acid sites caused by coke deposition on the catalyst surface.Finally, Doping of HPW/SiO2 catalysts with different group metals were prepared by different methods, and the catalytic performance of these catalysts in the synthesis of anthraquinone were investigated. The results of TGA/DTA characterization indicated that the coke combustion temperature of Pd Doping catalyst significantly decreased.