Experimental and theoretical assessment of phenomena linked with separation and purification of biodiesel from Ricinus communis seed oil

Abstract

This study investigated the phenomena associated with the separation and purification of biodiesel produced from Ricinus communis oil seeds using experimental and theoretical approaches. The alkaline transesterification technique was used to produce the biodiesel from the Ricinus communis oil seeds which were later compared with standards based on EN and ASTM. Experimental investigation of the components in the mixture for separation and purification was conducted using the standard turbidimetric method for binodal solubility and tie-line compositions. The gas chromatographic technique was used to determine the composition of the homogeneous mixture. Novel components separation and purification of the Ricinus communis seed oil biodiesel was achieved using ternary diagrams highlighting the constituent components of the biodiesel at different temperatures for enhanced separation and purification. At the coexisting extract and raffinate phases, the orientation angle of the component compositions increases as the methanol concentration increases and temperature increases. The analysis of seed oil in terms of its physicochemical properties showed density, refractive index, acid value, and free fatty acid values of 905 kg/m3, 1.486, 0.79 mg KOH/g, and 0.390 mg KOH/g respectively. The fatty acid composition of the seed oil and biodiesel revealed that the major characteristics of the oil and biodiesel were defined by the presence of linoleic acid (C18:2) and a ricinoleic acid hydroxyl group (C18:1, OH) with compositions of approximately 30% and 20% respectively. Fourier Transform Infra-Red (FTIR) spectrometry analysis of the oil and biodiesel showed that the absorption spectrum in terms of the wave number (cm−1) ranged from 1000 to 4000 cm−1 with esters as the main functional group providing the main structural backbone. The presence of different fatty acids leads to lateral homogeneity of the biodiesel molecules which can serve to organize the molecules into discrete domains with different properties for enhanced separation and purification at the investigated temperatures. Optimal separation and purification were achieved at the different temperatures showing the castor oil biodiesel, glycerol, and methanol components system at the prevailing composition, time, and temperatures from the tie-lines and binodal solubility compositions. This approach provides a means for the design of a more efficient separation process for optimal biodiesel purification after production with knowledge of how the components are distributed in the ternary mixture after the transesterification reaction. This, leads to greater efficiency of the process, reducing material and operational costs and eliminating environmental issues linked with the biodiesel production process as the volume of wastewater generated would be hugely eradicated. The findings of this study will be useful in the setting up of a small-to-medium-size biodiesel production facility with improvement in the efficiency of product separation and purification.