Nabeel A. Adeyemi

Waste cooking oil transesterification: Influence of impeller type, temperature, speed and bottom clearance on FAME yield

Waste cooking oil (WCO) provides an alternative source of raw material for biodiesel production. The reaction is both kinetics and mass transfer limited. Industrial use of current laboratory result suffer from dimensional non-compatibility because of the difference in the production environment especially as different impeller result in different flow characteristic during chemical reaction. In this work the effect of impeller type on fatty acid methyl ester (FAME) production from WCO was studied. At an alcohol oil mole ratio of 6:1 and 1% catalyst (oil weight), the Taguchi method was used for the experimental design of the transesterification in a 2 L stirred reactor using Rushton and elephant ear impellers. An optimum yield FAME at 70°C, 650 rpm impeller speed and 30 mm impeller bottom clearance (IBC) for Rushton impeller and 70°C, 700 rpm impeller speed and 25 mm IBC for an elephant ear impeller was obtained between 89 to 94%. IBC and speed were observed to have the most significant effect on yield using the signal to noise (S/N) ratio for Rushton and elephant ear impeller. Peak yield time between 5 to 30 min was observed. Correlation between FAME yield, peak time and temperature was high (0.968). The optimum reactor setting was at temperature 70°C, impeller speed of 650 rpm and IBC of 30 mm for Rushton (unbaffled reactor) and temperature 70°C, impeller speed of 700 rpm and IBC of 25 mm for elephant ear (baffled reactor). Physical configuration affected FAME yield/time in this work. Key words: Waste cooking oil, transesterification, impeller, Taguchi, biodiesel.

Simulation and experimental validation: waste cooking oil transesterification using rushton and elephant ear impellers

The performance of two impellers (Rushton and Elephant ear) for waste cooking oil (WCO) transesterification were experimentally and numerically evaluated inside a unbaffled and baffled stirred tank reactor (STR). Three parameters (impeller bottom distance (C), speed, (N) and temperature) were investigated for fatty acid methyl esters (FAME) yield using a Taguchi orthogonal array (OA) experimental design. The mixing study is based on the �-� and large eddy simulation (LES) turbulent model using a multiple reference frame (MRF) approach and the result was validated by particle image velocimetry (PIV) measurement. Overall flow structure in the baffled in STR was isotropic at C = 20, 25 and 30 mm for Rushton and to a lesser extent at the STR centre in the unbaffled STR. Mean radial velocities of the Elephant ear impeller was about 25-30% of the Rushton impeller for 600 rpm and 85-90% in baffled STR at C = 30 mm in the unbaffled STR. CFD results of �-� and LES results were qualitatively similar at mid-impeller plane than for the other parts of the STR. However, none of the model could capture the vortex trailing encountered with Rushton impeller. Experimental mixing time, a function of FAME yield and liquid velocities were found to be dependent on stirrer speeds, impeller bottom distance and bulk flow pattern. The study demonstrated the effect of different impeller types used in the laboratory on FAME yield and attributed to flow characteristics. This model is being used to evaluate other conditions of the reactions.

Numerical simulation of biodiesel production using waste cooking oil

The goal of this work was to carry out transesterification using computational fluid dynamics (CFD) method and obtain yield comparable to experimental values. First of all, the single–phase flow field was simulated and compared with experimental data obtained by means of particle image velocimetry (PIV) measurements. The velocities calculated from the RSM approach agreed quite well with those from PIV. The CFD simulations of biodiesel production were performed using the Reynolds stress model (RSM) coupled with the eddy dissipation model (EDM). CFD analysis of biodiesel yield compared fairly well with the experimental results available.Copyright

Mixed-Flow Impeller Characteristics in Baffled Mixing Tank

In recent times, impellers have been designed and modified to combine unique hydrodynamic features to overcome redundancy during mixing. One of such impeller is the mixed-flow impeller which displays a unique combination of radial and axial flow. In this paper, the flow characteristic of a mixed-flow impeller is reported. The main focus is to compare the axial and radial characteristic of the velocity component using experimental and numerical study. The continuity and momentum equation were solved using the Reynold’s stress model (RSM). The field of view away from and below the impeller compared better with the numerical solution for the mean, radial and axial velocity component. Although the RSM was used at a higher computational cost, associated power number and energy of the impeller was also observed to be better predicted.

Unconventional Method for Monitoring of Waste Cooking Oil Transesterification

A technique to monitor transesterification of waste cooking oil (WCO) is presented. The technique was developed based on analogue signal from WCO, fatty acid methyl ester (FAME) and commercial palm oil (CPO). A low-pass filter design for the photodiode was used to obtain the characteristic analog signal generated by these oil samples and the signal was correlated to absorbance spectra of the oils using data from Fourier transform infrared (FTIR) equipment. A match was made between the analogue signals of the oil samples and calibrated against the FTIR spectra at 95% confidence level. Depletion of WCO during transesterification in a batch reactor correlated with the time observed for peak yield during biodiesel production. The results of the technique are discussed as a possible way to monitor transesterification process in a batch reactor.

Numerical Modelling of Mixed Flow Impeller in Stirred Vessel

Flow characteristics of a single mixed flow impeller in baffled and unbaffled vessel have been experimentally and numerically investigated at 600 rpm. The mean, radial and axial velocity components obtained using particle image velocimetry (PIV) were compared with three turbulence models (�-�, �-�shear stress transport (sst) and Reynolds stress model (RSM)) based on the Reynold’s averaging Navier-Stokes equation at two planes, above (x/R=0.46) and below (x/R = 0.38) the impeller. Numerical results of mean and axial velocity for the RSM turbulence model compared better to PIV below the impeller against other models in the baffled vessel. However, the axial and radial velocity components from the �-� model compare well to PIV result at a distance away from the wall. Associated power number and energy of the impeller were also observed to be better predicted with the RSM, although at a higher computational cost. Trade-offs in using the RSM as a tool for simulation of the mixed flow impeller is suggested.