NMR INVESTIGATIONS OF TETRAPROPYLAMMONIUM ALUMINOSILICATE AND BOROSILICATE SOLUTIONS

Si-29, Al-27, and B-11 NMR spectroscopies were used to characterize dilute, highly alkaline tetrapropylammonium (TPA) aluminosilicate and borosilicate solutions. The compositions of the solutions range from 0.1 to 2 mol % SiO2, silicate ratios (R = [SiO2]/[M2O]; M+ = TPA+) from 0.1 to 2, and Si/Al or Si/B molar ratios from 0.25 to 10. Si-29 and Al-27 NMR spectra provide evidence for the formation of aluminosilicate anions. Si is observed with Q1(1Al), Q2-DELTA(1Al), Q2(1Al) + Q3-DELTA(1Al), and Q3(1Al) connectivity. Several new Si-29 NMR peaks are assigned to specific aluminosilicate anions based on chemical shifts. Al-27 NMR spectra of aluminosilicate solutions reveal peaks corresponding to Al bound to zero, one, two, and three siloxane bonds. The distribution of aluminosilicate anions is affected by the concentration of dissolved Si and Al, as well as the solution pH. The distribution of aluminosilicate species is described in terms of simple chemical equilibria. Si-29 and B-11 NMR spectra of borosilicate solutions indicate that borate anions are less reactive than aluminate anions. B-11 NMR spectra reveal only a small fraction of the dissolved B appears to form borosilicates.