Determinação experimental e modelagem de temperatura de ebulição e pH de sistemas binarios contendo compostos presentes em sucos de frutas / Experimental determination and modeling of boiling pont pH of binary systems containing fruit juice compunds

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

12/04/2010

RESUMO

The vapor-liquid equilibrium of binary aqueous solutions of D-glucose and D-fructose, present in fruit juices, was evaluated by experimental boiling point measurements in a rotary evaporator with total reflux of the vapor phase from 20 kPa to atmospheric pressure (93.6 kPa) and concentration from 10 to 60 % by mass. The experimental data were correlated with predicted data by UNIFAC-Lyngby group contribution method, using different molecular approaches and structural parameters. The cyclic conformation of the sugar molecules was decisive for the accuracy of the modeling. The data were accurately described by Dühring diagrams and the rise in boiling point was considered significant for energy demand of phase change. The thermodynamic equilibrium of aqueous solutions of polycarboxylic acids present in fruit juices and pulps, citric acid, malic acid, malonic acid, oxalic acid, succinic acid and tartaric acid was evaluated by experimental pH measures in isothermic cells, from 278.15 to 323.15 K and concentration from 1 to 20 % by mass. The experimental data were correlated with predicted data by the resolution of a non-linear equation system by a computer algorithm implemented in MATLAB. The activity coefficients were calculated using the UNIFAC-Lyngby method and the modified Debye- Hückel term, taking into account the short and long-range interactions of the molecules in solution. In general, the combined model described the behavior of the pH of the solutions with higher accuracy than the isolated models. Moreover, according to chemical equilibrium of the solutions, the effect of temperature on pH was significant, meaning that some mixtures properties are affected during thermal processes

ASSUNTO(S)

unifac metodo ebulição equilibrio quimico suco de frutas unifac metodo boiling chemical equilibrium fruit juices

ACESSO AO ARTIGO

Documentos Relacionados