Effect of Colombian raw materials on the Prins condensation reaction over Sn/MCM-41

Abstract

Colombian sodium silicate was used as silicon source in the synthesis of MCM-41 with several surfactant: SiO2 molar ratios (MR = 0.12, 0.30, 0.50 and 0.70). Sn was incorporated on MCM-41 by incipient impregnation and by wetness impregnation using a rotaevaporador. The materials were characterized by AAS, XRD, N2 adsorption-desorption isotherms, TEM, adsorption of pyridine, NH3-TPD, UV–vis-DRS and XPS. Materials with Na2SiO3 (MR = 0.70) showed crystalline, textural and structural properties very similar to MCM-41 synthesized with tetraethyl orthosilicate (TEOS). The highest total acidity of materials synthesized with Na2SiO3 compared with materials synthesized with TEOS could be owing to the use of sulfuric acid in the synthesis or the presence of more silanol groups in the solid surface. TOF values obtained in nopol production over materials synthesized with TEOS and Na2SiO3 (MR = 0.70), using wetness impregnation with rotoevaporation, were 420 and 476 h−1, respectively. Low cost paraformaldehyde with larger polymerization degree than Sigma-Aldrich source of formaldehyde was characterized by XRF, XRD, FTIR, TGA and DSC. Polymerization degree seems to affect TOF for nopol production; lower TOF values were obtained with paraformaldehyde with larger polymerization degree. Depolymerization occurs by two parallel reactions: Avrami-Erofeyev (A4) and contracting area (R2) models, with activation energies of 19.8 and 77.5 kJ mol−1, respectively. Sn-MCM-41 synthesized with Na2SiO3 can be used four times without considerable loss of catalytic activity; furthermore, no Sn leaching was detected.