Estudo dos efeitos de agitação e mistura no processo de síntese dos hidróxidos duplos lamelares (HDLs) aplicado à produção de biodiesel

Abstract

The stirring and mixing process comprises the determination of process parameters and sizing of the reactors, such as: stirring speed, types of impelers, chicanes, among others. Such characteristics are determinant in promoting the transfer of mass and energy to the system. The coprecipitation synthesis of Layered Double Hydroxides (LDHs), clays belonging to the class of mineral nanoparticles, is governed by the nucleation and growth stages of the crystals directly associated with the efficiency of the mixing and dispersing process of the reagents. This paper presents as a proposal the study process variables in a batch reactor, for the synthesis of HDLs by coprecipitation. The study was carried out by applying a factorial planning 23, evaluating the influence of the process variables: agitation speed (200 and 1000 rpm), agitation time (2 and 18 h) and presence or absence of chicanes, having as response the amount of LDH produced and conversion into biodiesel (application). In addition, the chemical and structural characteristics of the materials produced were evaluated. In general, the process variables influenced the conversion into biodiesel (39.6 - 97.4 %), the quantity (51.94 - 80.81 g) and structural characteristics of HDLs, such as crystalline, crystalline size (70.99 - 174.79 nm), surface area (69.81 - 97.62 m2 /g) and others. With the result of the first planning, the optimization study of biodiesel production with the best HDL (in the form of mixed oxides) was carried out, which served as a catalyst for the transesterification reaction. For this, a central composite planning was applied with the variables time (0.32 to 3.68 h), amount of catalyst (1.29 to 9.70 %) and molar oil/alcohol ratio (1:6.5 to 1:17.04). The critical conditions estimated by the model for the variables time, catalyst and molar ratio were equal to 2.95 h, 7.77% and 1:16, respectively, at which point 98.7% conversion to biodiesel was achieved. In addition, the stability of catalysts formed by mixed oxides/HDLs that demonstrated satisfactory activity for up to 4 cycles, with conversions above 96.8%, was evaluated.