Adsorção de cobre (II) presente em cachaça utilizando quitosana obtida por radiação micro-ondas: caracterização e estudo cinético

Abstract

Cachaça is a typical drink in Brazil and has been reaching more and more the national and international market. The cachaças produced in copper stills present unique characteristics, however they may be more susceptible to suffer contamination by copper (II). Adsorption by biopolymers has shown to be a very promising technique for the removal of metal ions. Chitosan is a biopolymer derived from the deacetylation of chitin and has free amino groups in its structure, which are strongly reactive to metal ions. Considering the aforementioned aspects, this work aimed to perform the deacetylation of chitosan using microwave irradiation technology and to evaluate the capacity of the chitosan obtained in adsorbing copper (II) from cachaça. Chitin was extracted from shrimp exoskeleton, chitosan was deacetylated and its adsorption capacity was evaluated through kinetic study using mathematical models. The copper (II) concentration remaining in the cachaça, in all kinetic experiments was estimated by the spectrophotometry technique in the visible region and confirmed by microwave-induced plasma optical emission spectrometry (MIP OES). Chitosan was characterized by infrared spectroscopy with attenuated reflectance (FTIR-ATR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and molecular mass The results of the characterization showed that the microwave deacetylation process it occurred efficiently, since the chitosan obtained had satisfactory properties in terms of its main characteristics observed, degree of deacetylation (above 85%), molecular weight, morphology and crystallinity. Regarding the adsorption kinetics, the best condition for copper adsorption was 6 mg of chitosan per mL of cachaça, in an equilibrium time of 60 min which resulted in a reduction rate of 84.09% of copper in the drink, according to results obtained by MIP OES. The kinetic analysis indicated the best fit of the data by the Elovich equation, suggesting that the chemisorption mechanism controls the kinetic process. Therefore, chitosan proved to be a good adsorbent for the removal of copper in cachaça and in this respect, a promising target for future technological investments.