Solid State Reaction of Serpentinite Mg₃Si₂O₅(OH)₄ with NaOH to Produce a New Basic Catalytic Phase Na₂Mg₂Si₂O₇ for Biodiesel Production

Solid state reaction of serpentinite Mg₃Si₂O₅(OH)₄ with NaOH was investigated to produce new NaMgSi oxide phases with basic properties for application in catalysis. X-ray powder diffraction (XRD) showed that NaOH impregnated on serpentinite, specially 20% sodium and treated at 700 ºC (20Na₇₀₀), led to the formation of a new crystalline phase Na₂Mg₂Si₂O₇. This solid state reaction is discussed in terms of a first step involving Na⁺ diffusion and intercalation in the interlayer space of the serpentinite structure followed by a dihydroxylation and formation of the NaMgSi oxides. Temperature programmed reaction and desorption experiments with 20Na₇₀₀ combined with XRD suggested a strong basicity with high CO₂ uptake likely due to diffusion and interaction with the basic sites in the material structure. These materials were tested as catalysts for the transesterification of soybean oil with methanol. The obtained results are discussed in terms of a basic site Si-O^-Na⁺ present in the in the Na₂Mg₂Si₂O₇ structure.

Keywords:
serpentinite; sodium silicate; biodiesel; basic catalyst