A preliminary evaluation of how classical separation techniques affect the solid catalyst surface features during transesterification

Abstract

The aim of this study was to investigate how the classical separation methods alter the solid catalyst surface structure in heterogeneous-catalyzed transesterification, viz., centrifugal and gravitational settling-in-funnel schemes, for the first time. The FTIR spectroscopy showed that while the settling system produces vivid and smooth surface shifting as a result of long-term contact with reaction products, centrifugal separation does not entirely obliterate the identity of the post-reaction catalyst surface. In addition, the SEM analysis confirmed that smaller agglomerates, which may have resulted from the dissolution of some particles and the accumulation of organic substances that clog the catalyst pore through the formation of calcium-glycerol bonds during the decantation period, were observed in the gravitational settling system; this trait could also complicate the separation and lower the desired product recovery (biodiesel). Whereas the centrifugal separation technique revealed the presence of bigger oval-shaped agglomerates, which are anticipated to possess more unoccupied active sites for efficient catalysis. As a result, centrifugal separation produces a greater biodiesel yield (87 ± 0.9%) than the settling method (76.6 ± 2%). The fuel properties of biodiesel products were characterized in terms of acid value, kinematic viscosity, cetane number, and specific gravity, of which only the cetane number does not meet the international limit due to its aromatic content. Generally, the results of this study proved that centrifuges are a more effective method of separating heterogeneous catalysts relative to the decantation system.