Studies On Catalytic Performance Of Solid Acids Derived From Sulfuric Acid: Supported Sulfuric Acid, Sulfates And Sulfonic Resin

Traditional chemical industry has been very important in improving the quality of our daily life. However, it has brought in serious environmental pollution problem that has damaged the ecological balance. Green chemistry is an ideal mean to overcome this problem, which open a new and effective way for sustainable development of traditional chemical industry. Development of environmentally friend solid acid catalysts and their applications in various chemical processes are nowadays one of the most attractive green chemical processes. This dissertation has focused on synthesis of various solid acids and their catalytic applications in substituting environmentally harmful liquid sulfuric acid in two typical commercial reactions: 1, benzene nitration to produce nitro-benzene; 2, isobutene oligomerization to produce high isooctane number gasoline blending as substitutes of MTBE or alkylate oil.In contrast to the conventional commercial process using mixed acid, vapor phase nitration of benzene over sulfuric acid supported on silica is a clean process; it avoid using liquid sulfuric acid and therefore does not produce used acid. Preparation of the supported sulfuric acid catalyst is simply by an impregnation method. The conversion of HNO3 is more than 92% and the selectivity to nitrobenzene is more than 97% with only trace amount of nitrogen oxides as by product when the loading amount of sulfuric acid is between 10-40 wt%, activation temperature below 180 癈 and reaction temperature between 150-160℃. The deactivation of the catalyst was proved to be due to the effusion of supported sulfuric acid. It was also confirmed that the lifetime of catalyst is increased as increasing loading amount of H2SO4 in the range of 5-20 wt%. Adding phosphotungstic heteropoly acid(optimized amount is 1-5 wt %) effectively depressed the lose of supported H2SO4 and extended the lifetime of the H2SO4-PW12/SiO2 catalyst, but showed no effect on activity and selectivity.The stability of the catalyst (sulfuric acid supported on silica) was closely related with reaction temperature, composition of gaseous reactants and properties of supports. High reaction temperature and existence of water vapor accelerated the effusion of sulfuric acid, but small pores in support is good for holding back the effusion of sulfuric acid. Thus, it was concluded that porous SiO2 material with uniform pore and suitable pore size is a good support for sulfuric acid. Such a catalyst has the advantages of both high activity and selectivity of liquid sulfuric acid, and noncorrosive and fewer disposal problems of solid acid catalyst.H2SO4 /SiO2 was a good catalyst for the oligomerization of C4 stream with C8~selectivity being as high as 80%. However, the catalyst deactivated very quickly. Adding phospho-tungstic acid to H2SO4/SiO2 (H2SO4-PW12/SiO2) can prolong the life time, and increase the activity without any damage to the high selectivity at low reaction temperature.Nafion resin is perfluorinated resinsulfonic acid which has similar acidity as H2SO4. This material is chemical inertness and thermally stable up to 280℃. Nafion showed good activity and selectivity for the oligomerization of isobutene and C4 stream at low reaction temperature. The conversion of isobutene was then gradually increased for a few hours and then reached at a stable level, which was caused by the gradual swelling of Nafion resin under reaction conditions. It was already known that the swelling degree of Nafion resin is controlled by temperature and high temperature favors the swelling. The increase of the concentration of -SO3H group caused by increasing reaction temperature is stable but reversible, which can beslowly recovered by low temperature treatment.The dispersion of Nafion on silica resulted in high concentration of surface sulfonic (-SO3H) group and consequently increased the activity of isobutene oligomerization and selectivity to C8 at low reaction temperature. The loading amount of Nafion resin was optimized to be in the range of 5-13 wt%. Nafion/SiO2...