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The hydrolysis of triglycerides at the oil-water interface, synthesis of esters and transesterification in microaqueous conditions are catalysed by lipase. For its application, a proper purification method was necessary. This study examined the application of an aqueous two-phase system to partition porcine pancreatic lipase. The influence of molecular weight and concentration of polyethylene glycol (PEG), tie line length (TLL), potassium phosphate concentration, sodium chloride (NaCl) addition and temperature in the partition was studied. The enzyme was more efficiently purified in PEG 8,000 at 14.5 degrees C (PF = 3.89-fold), presenting more recoveries at the top phase with shorter TLL and lower concentrations of PEG and potassium phosphate. Moreover, the increase of these variables repressed the purification and the further addition of NaCl did not promote the purification of the enzyme. These results demonstrated the efficiency of the aqueous two-phase system on lipase purification.

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This work presents modeling and experimental studies on the kinetics of toluene disproportionation in operation ranges that include real industrial operation conditions. The influence of reaction temperature, reactor pressure, feed composition, and residence time on conversion of reactants and product selectivity was investigated. Experiments were performed according to a sequential experimental design strategy, in order to provide maximum accuracy for model predictions. Statistical treatment of parameter estimates and model adequacy was performed with the help of maximum likelihood principles. Excellent agreement between model predictions and available experimental data was obtained in the full ranges of investigated experimental conditions.

Physical gels have been described by a mathematical model proposed by Hermans (1965), in which high functionality molecules and low degree of crosslinkings were considered, The more general model suggested by Clark and Ross-Murphy ( 1985) was used as a tool to determine the f, K and a characteristic parameters, known respectively as the functionality of the macromolecule, the dimerization equilibrium constant and the non ideality factor, for an agarose commercial sample of known viscosity average molecular weight, The knowledge of these parameters should contribute to a better understanding of the gelling process. A computational routine based on the statistical maximum likelihood principle was employed to estimate the parameters of Clark and Ross-Murphy (1985) in relation to experimental Young's modulus data. Statistical ttest and F-test were used to critically analyse the set of parameters. The F-test showed that the choice of the smallest objective function had failed to best adjust the f, K and a values. The Co values aimed by the ttest for the 3 ~ f ~ 100 interval were in agreement with the experimental observation.