Electrochemical impedance: A new alternative to assess the soap removal from biodiesel in the washing process

摘要

An impedance- based sensor was built with stainless steel circular plates (7.0 cm(2)) to evaluate the soap limit for both biodiesels produced from commercial soybean oil and from waste cooking oil. Conversion of soybean oil to biodiesel was achieved with KOH and waste cooking oil was converted to biodiesel using NaOH. Various biodiesel batches were dry washed using a mixed ionic resin to remove charged carriers such as soaps. Based on the Nyquist and Bode plots as well as the physical shape of the sensor, an RbCb parallel circuit was used for modelling the experimental data. It was found that washing had a significant effect on R-b in comparison with the effect on C-b. From the impedance data acquired using the present sensor, an R-b value of 5 G Omega.cm(2) was chosen as the minimum biodiesel resistance to assure a soap limit of below 41 ppm to comply with the currently accepted soap level in biodiesel.