Study Of The Preparation Of SO₃H^- Acidic Ionic Liquids And Catalytic Performance

Ionic liquids are liquid melting electrolytes,they can be applied to various organic reactions as an environment-friendly green reaction mediums and new catalytic materials.In this paper,eight SO₃H-acidic ionic liquids with different cationic structures were synthesized by using trimethylamine,N-methyl imidazole,pyridine,caprolactam with 1,3-propanesultone and 1,4-butanesultone as raw materials.The ionic liquids are: [HSO₃–pTEA][HSO₄]? [HSO₃–bTEA][HSO₄]?[HSO₃–pMIM][HSO₄]?[HSO₃–bMIM][HSO₄]? [HSO₃–pPy][HSO₄]?[HSO₃–bPy][HSO₄]?[HSO₃–pCPL][HSO₄]?[HSO₃–bCPL][HSO₄].All ionic liquids' yields are higher than 98.5%.Ionic liquids structures were tested and verified by NMR?Thermal stability,acid strength were characterized and evaluation using thermal gravimetric analysis,UV spectrophotometer and density functional theory The results showed that eight ionic liquids' decomposition temperature were all higher than 330 °C,and had good thermal stability.Using Hammett-UV method,acid strength of ionic liquids with different cations were tested.The results showed that acid strength of ionic liquids with different cations structure were quite different.The order is [HSO₃ – bCPL][HSO₄] > [HSO₃– pCPL][HSO₄] > [HSO₃-bPy][HSO₄] > [HSO₃-pPy][HSO₄]>[HSO0–bMIM][HSO₄]>[HSO₃–pMIM][HSO₄]>[HSO₃–bTEA][HSO₄]>[HSO₃ – pTEA][HSO₄].Density functional theory were used to calculate theoretical relationship between ionic liquids structure and acid strength,which showed the same result with the experiment.In order to test catalytic performance of eight ionic liquids with different cations structure,Jatropha oil and methanol were used as raw materials to prepare biodiesel.The results showed that the order of catalytic performance of eight ionic liquids with different nitrogen groups was consistent with the acid strength order.Therefore,catalytic performance was mainly affected by the impact of acid strength.[HSO₃-bCPL] [HSO₄] had good physical and chemical properties and performs best in the catalytic reaction,so it was chosen to be the catalyst to optimize the transesterification process.Concerning factor in energy consumption,environmental protection,energy and others,we obtained the best reaction conditions: the equivalents of ionic liquid?8 wt%?,mass ratio of alcohol to oil?9:1?,reaction temperature?120 °C?,reaction time 3h.Under this condition transesterification average conversion rate was 96.5%.At this temperature,we analyzed the transesterification reaction,and found it was a second order reaction with Ea=17.93KJ/mol.The reaction of kinetic equation was dx?dt =4.159[0.8857?1-x?]2.3.After reused seven times without any treatment,[HSO₃-bCPL] [HSO₄] catalytic performance decreased significantly.Therefore,we examined the deactivation mechanism of [HSO₃-bCPL] [HSO₄] and found that inactivation of ionic liquids was due to weakened.acid strength In order to recovery catalytic activity of ionic liquids,ionic liquid was be deactivated vacuum drying,used of ionic liquids with concentrated sulfuric acid molar ratio of 1: 0.25 supplement its acidity.The results showed that the regenerated ionic liquid acid strength was 1.537,the catalytic transesterification reaction transition rate was 97.5%.