Insights into the Silanization Processes of Silica with and without Acid–Base Additives via TG-FTIR and Kinetic Simulation

The silanization of silica with and without acid–base additives were investigated via TG-FTIR (thermogravimetry coupled with Fourier transform infrared) technology and reaction kinetic simulation. The results showed that two parallel reactions were included in the silanization process of silica: one is the hydrolysis of the ethoxy group of TESPT followed by the condensation with the silanol of silica (the activity energy is E = 57 kJ/mol), and the other is the direct condensation between the silanol of silica and the ethoxy group of TESPT (E = 90.4 kJ/mol). The hydrolysis of the ethoxy group is much easier in comparison with the direct condensation with the silanol. The silanization was effectively promoted by means of adding stearic acid (HST) or diphenyl guanidine (D), and the reaction rate increased with the increase of HST or D in a reasonable range. HST promoted the condensation between ethoxy group and silanol (E = 69.5 kJ/mol), without affecting the hydrolysis of ethoxy group. However, D promoted both of the two reactions obviously (E = 59.5 and 70.8 kJ/mol, respectively). When HST and D coexisted in the system, the condensation between ethoxy group and silanol was promoted more obviously by the acid–base complex (E = 53.5 kJ/mol). The two-step parallel reaction model was used to simulate the silanization processes, and good fitting results were achieved.