RESUMO
This work describes the use of virtual standards as calibration samples in an innovative multivariate calibration approach for the on-line monitoring of alkyl-esters content during biodiesel production process using a miniature near infrared (NIR) spectrometer. For comparison purposes, a partial least squares (PLS) model was built using synthetic blends prepared in laboratory with different concentrations of oil, glycerol, biodiesel, and ethanol and resulted in a satisfactory predictive ability (root mean square error of prediction, RMSEP, of 1.51% w/w). When compared to conventional methods, calibration with synthetic blends has the advantage of simplifying the experimental procedure and reducing the need for reference analysis. Nevertheless, it still requires the preparation of a considerable number of blends in laboratory. To overcome this limitation, this study proposed an innovative approach where a PLS model was constructed based on virtual standards: representative calibration spectra were created by mathematically mixing spectra from pure components and performing an adjustment using the Piecewise Direct Standardization (PDS) method. This significantly reduced the need for calibration synthetic blends and led to similar results (RMSEP of 1.75% w/w), compared to the previous approach. This work also demonstrates the use of the constructed models to predict the concentration profiles of alkyl-esters during the batch transesterification process.
Assuntos
Biocombustíveis , Espectroscopia de Luz Próxima ao Infravermelho , Biocombustíveis/análise , Calibragem , Análise dos Mínimos Quadrados , Padrões de Referência , Espectroscopia de Luz Próxima ao Infravermelho/métodosRESUMO
This work describes the use of an ultrasound system for the enzymatic transesterification of oils using combi-lipases as biocatalyst. The reactions were carried out evaluating the individual use of waste oil and fresh soybean oil, and the immobilized lipases CALB, TLL, and RML were used as biocatalysts. It was performed in a mixture design of three factors to obtain the ideal mixture of lipases according to the composition of fatty acids present in each oil, and the main reaction variables were optimized. After 18 h of reaction, ultrasound provided a biodiesel yield of about 90% when using soybean oil and 70% using the waste oil. The results showed that ultrasound technology, in combination with the application of enzyme mixtures, known as combi-lipases, and the use of waste oil, could be a promising route to reduce the overall process costs of enzymatic production of biodiesel.