Study On The Synthesis Of O-Phenylphenol From Dimer Dehytrogenation

O-phenylphenol(OPP) is a fine chemical product and organic intermediates, which is widely used for the preparation of medicine, dyes and other fine chemicals. The synthesis of o-phenylphenol from dimer dehydrogenation is the most common manufacturing processes. The dehydrogenation is the key part of the synthesis of OPP process and the catalyst preparation is the key process in the dehydrogenation.The supported noble metal catalysts have many influencing factors and defects, such as the complicated preparation process and the bad catalytic performance.In this paper, the Pt nanoparticles were obtained by the decomposition of Pt2(dba)3(dba=dibenzalacetone) with hydrogen as reductant and propylene carbonate as solvent, the assembled catalysts were prepared by the Pt nanoparticle adsorption on the support. Compared with traditional method, the adsorption method has many advantages, such as simple process, less influencing factors, the high repeatability and so on. Most of Pt nanoparticles were adsorbed on the surface of the support, which was favorable for the contact of active component/additives with dimer, and exhibited good catalytic performance.In this paper, we have studied the effect of alumina size, K additives, and its content, non K additives, the support modification and composite modification on the performance of assembled catalysts. We have also investigated the effect of reaction temperature, liquid space velocity and the flow rate of H2on the dehydrogenation reaction. And the stability of the assembled catalyst under the appropriate reaction conditions were also inspected. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Thermogravimetry Differential Thermal analysis (TG-DTA) were used to characterize the catalysts. The crude product was refined using recrystallization method. The results are listed as follows:1. The research of additive modification indicated that K2SO4additives have better performance than other K modifiers, and K2CO3has the worst performance. K additives had the electrical promotion effect and could suppress the surface acidity on γ-Al2O3support. The catalyst was prepared under0.3MPa H2atmosphere, the three decomposition method (wt%:10%,45%,45%) had the best performance in all K modified catalysts. The reason of K2CO3modified had worst performance was the decomposition of K2CO3to K2O and Pt nanoparticles covered by K2O.2. Na2CO3additives had better modification effect than other none K modifiers and Na2CO3was worse than K2SO4modification. We focused on support modification in this paper, CaO modification was proved to have better catalytic performance, and rare earth metal oxide was the worst among them. The performance of support combined modification still did not raise, but additive-support combined modification of K2CO3-CeO2had excellent performance and it was the best among combined modification. The assembled catalysts evaluated at optimum conditions were proved to have the highest catalytic performance with dimer conversion of98%, and the selectivity of OPP was97.7%. CeO2was good for slowing the decomposition rate of K2CO3and the optimum amount of CeO2was5%.3. The optimum reaction conditions of assembled0.5%Pt-5%CeO2-5%K2CO3/Al2O3catalyst were:LHSV=0.48h-1,T=355℃and hydrogen-free. The migrate of K species could be slower without external hydrogen source. Life test indicated that assembled catalyst had better performance during a60h run, with conversion and selectivity maintained above95%and70%. When the selectivity was drop to70%, it could stay balance. Coke, glomeration, the destroyed structures of Al2O3and CeO2, the decreased specific surface area, and the Pt nanoparticles covered by K species were the reasons for catalysts deactivation, among these Pt was covered and structural damage were the main deactivated reason.4. Heptane was used as recrystallization solvent and showed the best result, through alkali dissolution and acid precipitation we could achieve99.4%of OPP purity and the total yield was62.8%. The optimum conditions of recrystallization was8h, the volume of heptane was threefold of the crude product and natural cooled.It was clear that assembled Pt catalyst had better catalytic performance, providing a new method for the synthesis of OPP. Under the optimum reaction conditions, OPP had high initial yield, simple reaction process and the catalyst showed better stability.