Reestruturação do serpentinito induzida por metais alcalinos na produção de materiais com propriedades básicas para aplicação em catálise (transesterificação) e absorção de CO2

Abstract

The serpentinite rock is formed by phases of magnesium silicates hydrated, antigorite, lizardite and talc. Fine fractions of this rock were impregnated with lithium and sodium ions (5, 10, 20 and 30%) and thermally treated in air at 500, 700 and 900 °C for the synthesis of potential heterogeneous basic catalysts for the production ofbiodiesel and solid absorbent materials for CO2 capture. The obtained materials were characterized by XRD, TG, FTIR, BET and SEM. The impregnation of serpentinite with lithium ions induced the formation of the phases Li4SiO4, Li2MgSiO4, MgO and Mg2SiO4, and with sodium ions the phases Na2Mg2Si2O7 were formed. The obtained materials were tested as catalysts for the biodiesel synthesis. The best results were obtained using the serpentinite impregnated with sodium ions andconversions (%) were obtained greater than 90%, when it was used 5%, oil: alcohol ratio of 1: 9 at 100 ° C for 3 hours. The stability study of this catalyst was done by reuses after transesterification reactions, by the consecutive reuse method, and it was observed that the material can be reused for 5 cycles, but with a decrease in yield caused by the possible agglomeration of the material in contact with the oil. The studyfor the evaluation of the homogeneous/heterogeneous contribution of the catalyst in the reaction system, suggested a mixed system, with heterogeneous predominance. The CO2 capture studies showed that the materials obtained from the impregnation of serpentinite with lithium ions have high absorption capacity. The isothermal study showed that at the temperature of 600 °C the amount of CO2 captured at equilibrium was approximately 35%. The Avrami-Erofeeve model fitted better to theisothermal data and better describing the two-stage system compared to the double exponential model. The reversibility of the absorption/desorption reactions was evaluated by performing four cycles. The solid remained stable during the 4 (four) cycles. The results obtained show that the materials produced are an interesting alternative for the use of the serpentinite extraction residue.