Study On Synthesis Of Higher Fatty Secondary Alcohols

Secondary hexadecanol is one of most important higher fatty secondary alcohols with wide application and large market requirement,which is mainly used in the synthesis of fine chemicals.Currently,oxidation of hexadecane is the major approach for secondary hexadecanol in industrial scale.Hexadecane are oxidized into secondary hexadecanol under high temperature with boric acid as catalyst,air as oxidant.Hexadecane are difficult to oxidize,and the product of oxidation is the mixtures of alcohol,ketone/aldehyde,and carboxylic acid,resulting in low conversion and selectivity in hexadecane oxidation reactions.Therefore,it is highly desirable to study and develop more efficient and low-cost methods for the manufacture of secondary hexadecanol.In our work,the catalytic activity of boric acid,?-metaboric acid,?-metaboric acid were compared.The result indicates ?-metaboric acid has high catalytic activity and selectivity.A preparation method of ?-metaboric acid by boric acid dehydration was developed.The secondary dodecanol was synthesized from hexadecane using ?-metaboric acid as catalyst and air as oxidant.The effects of oxidation temperature,oxygen content in air,air flow rate,reaction time and the amount of ?-metaboric acid on the reaction were investigated.The optimum conditions are as follows: oxidation temperature 180?,oxygen content in air 15%,air flow rate 2 L/?kg·min?,the amount of ?-metaboric acid 5%.Under optimum conditions,conversion of dodecane is 22%,and selectivity of secondary hexadecanol is up to 93% which is higher than report.The unreacted hexadecane was recycled which reaction performance was studied then.The result shows the recycle hexadecane can not be reutilization before hydrogenated.We found that[RuCl2?NNHPPh2PPh2?] complex has high catalytic activity in hydrogenation of recycle hexadecane.The optimum hydrogenation conditions are obtained at the mass ratio of paraffin and catalyst of 10000:1,the molar ratio of KOtBu and catalyst of 50:1,reaction temperature of 80?,reaction time of 4 h and hydrogen pressure of 3 MPa.Under optimum conditions,conversion is up to 98.8%.To achieve high conversion,a new catalytic oxidation-hydrogenation two step processwas studied.A mixture of alcohol,ketone was prepared by oxidation under 170? for 5 h using hexadecane as raw material,Au/Al₂O₃ as catalyst and oxygen as oxidant.The conversion and selectivity of the oxidation is 79% and 92% respectively.The secondary hexadecanol was obtained from the mixture of alcohol,ketone by catalytic hydrogenation using Ru complex as catalyst.The mesoporous alumina supported Au catalyst was synthesized.The physicochemical properties of Au/Al₂O₃ were investigated by AAS,TEM and XRD.The result shows that the catalytic oxidation-hydrogenation two step process has much higher conversion than direct oxidation method of hexadecane.This two step process has a certain value in industrial application.