Study On Synthesis Technology Of P-Hydroxybenzaldehyde In Loop Reactor And Related Research

p-Hydroxybenzaldehyde(PHB) is an important fine chemical intermediate,which is substituted by aldehyde and phenol groups, and p-hydroxybenzaldehyde isveryactive and now widelyused in manyfields, such as fragrances, pharmaceuticals,medicines, agriculture chemicals, mental plating, fine petrochemicals, liquid crystals,photosensitive polymer and so on. The way of catalytic oxidation of p-cresol top-hydroxybenzaldehyde comes to people's attention due to its advantages includinghigh yield and clean, less pollution and simple production technology and higherpurity .So this process is believed to be the most promising for production ofp-hydroxybenzaldehyde. In our country p-hydroxybenzaldehyde has been productedby the way of the oxidation of p-cresol for some years, but the yield ofp-hydroxybenzaldehyde is no more than 70%, and the technology is not mature. Sothe study on the synthesis of p-hydroxybenzaldehyde is of great importance in thispaper.Densities and viscosities and the solubilityof oxygen were determined to providefundamental data for the study of reaction theory, for the synthesis process of PHB,for dynamics study of oxidation of p-cresol,and for engineering calculation.Linking to the process of production technology of PHB, the solubilities ofoxygen in p-cresol + methanol at high pressures were measured by a set ofexperiment apparatus for measuring gas solubility under high pressuressystematically.The densities and viscosities were measured by a vibrating tube densimeter(modelDA-505U) and a Ubbelohde suspended-level viscometer at atmospheric pressure forp-cresol + methanol, m-cresol + methanol, p-methoxybenzaldehyde + ethanol,p-methoxybenzaldehyde + N,N-dimethyl formamide(DMF). The excess molarvolumes(V~E )and deviations of viscosity(Δη) were calculated. The V~E andΔηwerefittedbyRedlich-Kister equation respectively. And lnηand temperature were fitted by Andradeequation.During the study on synthesis of p-hydroxybenzaldehyde, a lot of research hasbeen done in many fields about the oxidation of p-cresol, such as optimizing reactionconditions ,separation and high active catalysts. But less work about finding optimalreactor for the oxidation of p-cresol has been done.In this paper a new reactor,airlift loop reactor, was used in the way of oxidation of p-cresol to p-hydroxybenzaldehydeand mass transfer of oxygen was improved.The result suggests that airlift loop reactoris very effective for the oxidation of p-cresol. The effects on the yield of gasdistributor, reaction time, reaction temperature and gas velocity were fully studied inthis paper. On the condition of ignoring of interaction effect , the optimum reactionconditions were as follows: gas distributor 3, reaction pressure was 0.9MPa,reaction time was 4 hours, reaction temperature was 75℃and the yield ofp-hydroxybenzaldehyde was up to 87.5%.