Resin Solid Acid Catalyst Used In The Synthesis Of Allantoin Research

For the purpose of decreasing the pollution and improving productivity, quality, an ion exchange resin was selected as a catalyst in the process of synthesis allantoin from urea and glyoxylic acid. In the research, the factors influencing catalyst activity were studied and mainly the optimum operating factors and the character of reaction kinetics have been detailed studied. In addition, the deactive mechanism of catalyst was also studied.Firstly, three solid acid catalyst including gel resin, macro-porous resin and HZSM-5 were evaluated in the condensation reaction. The experimental results showed that the macro-porous resin has a higher activity. Secondly, experiments showed that R-2 resins has a high activity within five different macro-porous resins. It was found that the acid capacity was a most important factor influencing catalyst activity. In addition, R-2 was modified with metal ions to adjust the acid strength. The results showed that increasing lewis acid site by metal ions modification has a strong acid and decrease the yield of allantoin. The reaction needed the macro-porous resin with suitable acid strength.More further, the operation conditions of catalyst loading amount, reaction temperature, ratios of reactants and reaction time on the reaction were studied with R-2 catalyst. The results indicated that the temperature was the most important factor that affected the conversion and yield. The yield of allantoin was 67.71% at the optimal operation condition of the ratio of glyoxylic acid to urea 4 to 1, reaction temperature of 70 ℃, and reaction time of 9hrs,Throughout the discrimination of four kinetics models at the temperature range of 55 to 70℃ with R-2 catalyst, it was obtained that the rate of formation rate of allantoin was controlled by the desorption of allantoin. The models about the rate of formation of allantoin (r₁) and the rate of conversion of glyoxylic acid (r) were represented as following respectively:c c2 c c c2 c[ Z ) K \ "Z c c2 c c2 A B i K C \ + K A B i K Cin which, k=3.45 X 105exp(-5.0942 X 104/RT) K=3.128 X 1022 exp(-13.8097 X 1O4/RT), Jfe' =3.45 X 105exp(-5.0942 X 1O4/RT) AT' -1.177 X 1O24 exp(-14.7993 X 104/RT. The mean relative deviation of the calculation of the correlation equation was less than 2.22%, and the models had good value for the industrial application.The research of catalyst lifetime and deactivation mechanism demonstrated that the deactivation was due to the cover of allantoin on the activity site. The allantion was difficult in desorption to reduce the reaction speed. Catalyst could be regenerated by washing with dilute sulfuric acid.