Estudo teórico de estrutura, propriedades e reatividade de triglicerídeos e ésteres de ácidos graxos envolvidos na produção e composição do biodiesel

Abstract

The present work aims the study of structural and thermodynamic properties for process involving triglycerides (TG), fatty acid esters (EAG) and biodiesel through theoretical and chemometrical methodologies. The study of the transesterification reaction of triglycerides (TG) using cyclodextrin (CD) as a potential catalyst were also carried out. Initially, through a Box-Behnken 34 factorial design, the effects of the variables involved in the molecular dynamics simulation (MD) of inclusion compounds formed between trilaurylglyceride (TLG – 12:0) and α-CD were evaluated. The results lead to an appropriated MD heating protocol for the treatment of TG@n.CD systems with specific values for the variables involved in the process: time of heating (W), equilibrium time (E), time step of the dynamics (S) and dielectric constant of the medium (C). Starting from the best protocol, MD studies were developed contemplating inclusion complexes formed between TG models used to the biodiesel synthesis – trilaurylglyceride (TLG – 12:0), tripentadecanoylglyceride (TPDG – 15:0), trihexadecanoylglyceride (THDG – 16:0), triestearylglyceride (TESG – 18:0), trioleylglyceride (TOG – 18:1), trilinoleylglyceride (TLLG – 18:2) e trilinolenylgliceride (TLNG – 18:3) – and native α-CD and modified cyclodextrin (α-CD-NH2). The results pointed out a correlation between the stability of the TG@1.α-CD inclusion compounds and the size and saturation degree of the triglyceridic included chain. The catalytic potential of CD in the transesterification reaction of TG was also investigated through geometry optimization and vibrational harmonic frequencies calculations via DFT. The results show thermodynamic evidences for such proposal using α-CD as catalyst. Besides, theoretical infrared and Raman spectra were determined for some TG and EAG species, looking for the elucidation of possible methods capable to contribute for the experimental analysis of biodiesel. Some interesting fingerprints were noticed in the spectrum of saturated and unsaturated species, allowing the characterization of complex mixtures obtained in the biodiesel production.