Oleaginous algae are a promising renewable feedstock for the production of liquid transportation fuels and especially biodiesel. Techno-economic analysis for producing biodiesel from an algal bio-refinery concluded that the production of specialty high-value oleo-chemicals would enhance the overall economics on an industrial scale. Oleo-chemicals such as fatty alcohols, fatty nitriles, alkyl chlorides and Guerbet alcohols can be produced from pure triglycerides or fatty acids via existing catalytic processes. Conventional pyrolysis of oleaginous algae produces bio-oil, which is a mixture of water, organic acids, furanic compounds, N-containing compounds, anhydrous sugars and fatty acids formed from the degradation of the protein, carbohydrate and triglyceride algal fractions. A novel pyrolysis strategy was developed to produce fatty acids as a separate bio-oil fraction from oleaginous algae for production of oleo-chemicals. The process developed was based on the observation that triglycerides degrade at distinctly higher temperatures (T>380 °C) compared to both protein and carbohydrate fractions (T~ 250-350 °C).
Pyrolytic fractionation is a two-step pyrolysis approach that facilitates separate recovery of fatty acids from the other portions of the oleaginous algae. The first step is a low-temperature pyrolysis (T ~ 300-320 °C) to produce bio-oils from the degradation of the protein and carbohydrate fractions. Solid residues left behind can subsequently be subjected to a second higher temperature pyrolysis (T ~ 420-430 °C) to volatilize and/or degrade triglycerides to produce fatty acids and their derivatives (such as mono-, di- and tri-glycerides). Proof-of-concept micro-pyrolyser (PyroprobeTM) and lab-scale fixed-bed experiments were performed using oleaginous algae (Chlorella Sp.) to establish the pyrolytic fractionation technique and also to determine the yields of fatty acids. The significance of these results will be presented and discussed in detail.
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