Biodiesel Production from Wet Algal Biomass through in Situ Lipid Hydrolysis and Supercritical Transesterification

Abstract

In an effort to process wet algal biomass directly, eliminate organic solvent use during lipid extraction, and recover nutrients (e.g., N, P, and glycerol) for reuse, we developed a catalyst-free, two-step technique for algal biodiesel production. In the first step, wet algal biomass (ca. 80% moisture) reacts in subcritical water to hydrolyze intracellular lipids, conglomerate cells into an easily filterable solid that retains the lipids, and produce a sterile, nutrient-rich aqueous phase. In the second step, the wet fatty acid-rich solids undergo supercritical in situ transesterification (SC-IST/E) with ethanol to produce biodiesel in the form of fatty acid ethyl esters (FAEEs). Chlorella vulgaris grown sequentially under photo-and heterotrophic conditions served as the lipid-rich feedstock (53.3% lipids as FAEE). The feedstock and process solids were characterized for lipid components using highly automated microscale extraction and derivatization procedures and high-temperature gas chromatography. Hydrolysis was examined at 250 °C for 15 to 60 min; solids recovered by filtering contained 77-90% of the lipid originally present in the algal biomass, mainly in the form of fatty acids. The effects of reaction time (60 or 120 min), temperature (275 or 325 °C), and ethanol loading (approximately 2-8 w/w EtOH/solids) were examined on the yield and composition of biodiesel produced from the SC-IST/E of the hydrolysis solids. Longer time, higher temperature, and greater ethanol loading tended to increase crude biodiesel and FAEE yields, which ranged from about 56-100% and 34-66%, respectively, on the basis of lipid in the hydrolysis solids. Isomerization and decomposition of unsaturated FAEEs was quantified, and its effect on fuel yield is discussed.

Transesterification in Supercritical Conditions

“…Therefore, supercritical transesterification is more suitable for use with the lowgrade and/or the hydrated ethanol feedstocks (Demirbas, 2009;Gui et al, 2009;Kusdiana & Saka, 2004b;Vieitez et al, 2011). For example, the in-situ transesterification of wet algal biomass in supercritical ethanol gave a 100% alkyl ester yield (Levine et al, 2010). Supercritical transesterification has a better production efficiency than the conventional catalytic method because it requires a smaller number of processing steps.…”

Hydrothermal Disintegration and Extraction of Different Microalgae Species

“…As only little information on this topic can be found in literature [11,12,15,16] the aim of this work was to study the described effect for several different algae species, as the morphologic variation between different microalgae species and strains can be great. In order to evaluate if the extraction of hydrothermal treated algae is efficient the obtained results are compared with yields and qualities of conventional extraction methods.…”

Biodiesel production under subcritical solvent condition using subcritical water treated whole Jatropha curcas seed kernels and possible use of hydrolysates to grow Yarrowia lipolytica

“…In-situ transesterification of wet activated sludge under subcritical conditions (448 K, 8 h) was studied by Huynh et al [14], with a fatty acid methyl ester (FAME) yield comparable to that of the conventional acid catalyzed reaction which required 24 h. The same process was applied utilizing wet oleaginous yeast (Yarrowia lipolytica) cells [15] and wet microalgae (Chlorella vulgaris) cells [16]. Levin et al [17] utilized wet microalgal biomass to carry out carbonization at 523 K. Through carbonization, algal biomass was easily separated from water (culture media) thus resulting in lower moisture for subsequent transesterification step. The culture media was then reused for algal cultivations without the need of sterilization [17,18].…”

“…Levin et al [17] utilized wet microalgal biomass to carry out carbonization at 523 K. Through carbonization, algal biomass was easily separated from water (culture media) thus resulting in lower moisture for subsequent transesterification step. The culture media was then reused for algal cultivations without the need of sterilization [17,18].…”