Direct and rapid production of biodiesel from algae foamate using a homogeneous base catalyst as part of an intensified process

Abstract

• Continuous air flotation was used to harvest microalgae for transesterification. • KOH-catalysed in situ transesterification used to convert biomass into biodiesel. • Transesterification was not adversely affected by moisture of up to 80% in algae. • A 97% yield of biodiesel (FAME) was obtained in 10 minutes. • Energy savings were achieved by in situ transesterification of algae feedstock. Microalgae are important biodiesel feedstocks because of their high lipid content and low land requirement for cultivation. One method of harvesting and concentrating algal biomass is by means of a foam column using surfactant CTAB as a collector and foaming agent, however, the downstream treatments for the “foamate” produced have not yet been investigated. Here, the freshwater microalgae strain, Chlorella vulgaris , was harvested by a continuous dispersed air flotation column and the foamate obtained was used as the feedstock for conversion to biodiesel via in situ reactive extraction using KOH as the catalyst. The process variables were methanol: oil molar ratio (100:1 to 1000:1), reaction temperature (40–60°C) and reaction time (5–10 min). The maximum biodiesel yield from the foamate produced of 97% from C. vulgaris microalgae was accomplished at a molar ratio (methanol to oil) of 1000:1, a 60°C temperature of reaction and a 10 min time of reaction. Longer reaction times resulted in reduced fatty acid methyl ester (FAME) yield due to saponification, converting the FAME to soap. High FAME yields were obtained despite the presence of significant quantities of free fatty acids (6% lipid) in the C. vulgaris biomass. The method also exhibited greater tolerance to water than that observed in conventional transesterification conditions. At a methanol: oil molar ratio of 1000:1, the method was not adversely affected by the presence of up to 80% level of moisture in the microalgae. Hence, a viable, FFA-tolerant, water-tolerant process has been demonstrated for direct conversion of microalgae foamate to biodiesel, at mild conditions (60°C and below) in a short residence time (10 min).