Modelagem de superfícies de lignina, celulose, quitina e quitosana dopadas com agentes químicos com potencial catalítico para a transesterificação de triglicerídeos

Abstract

In the present work, biopolymeric models derived from biomass have been studied seeking to evaluate their surfaces feasibility as heterogeneous catalytic agents for transesterification of vegetable oils. First of all, representative models from lignin (dimers), cellulose (dimers, trimmers, tetramers and pentamers), chitin (dimers, tetramers and hexamers) and chitosan (dimers, tetramers and hexamers) were submitted to a quantum mechanics-chemometryquantum mechanics sequential methodology for conformational analysis. Through this sequential approach, pairs of torsional angles were selected according their roles on the total energy description of biopolymer-derived models. The structural data from molecular models of lignin, cellulose, chitin and chitosan, optimized by means of the sequential methodology above mentioned, presented a good agreement with experimental data form the literature. Thus, these models were used to evaluate the interaction of biopolymers and some promising catalytic compounds used for transesterification of vegetable oils. The analysis of the interaction process involving sulfur trioxide (SO3), sodium methoxide (MS), Sn(IV)(3hydroxy-2-methyl-4-pirone)2 (CM) and tin(IV) tetraphenylporphyrin (PM) as dopant of bioplolymeric models have pointed out the feasibility of the doping process of biomassderived materials. The interaction energy (Eint) have presented low values for all systems. For the SO3 dopant some thermodynamics and kinetics parameters related to the doping process of some lignin, cellulose, chitin and chitosan models were established. The results pointed out the thermodynamic and kinetic process availability by obtaining a small activation barrier (ΔG‡ ~ 20,0 kcal mol-1) and favorable enthalpic contribution of about -8,0 kcal mol-1. The change in Gibbs free energy associated to the chemical reactions (ΔrG) was favorable to the occurrence of reaction processes in all cases.