Effect of operating conditions of thermochemical liquefaction on biocrude production from Spirulina platensis Umakanta Jena, K.C. Das ⇑ , J.R. Kastner Biorefining and Carbon Cycling Program, Department of Biological and Agricultural Engineering, The University of Georgia, Athens, GA 30602-4435, USA article info Article history: Received 30 December 2010 Received in revised form 11 February 2011 Accepted 12 February 2011 Available online 17 February 2011 Keywords: Thermochemical liquefaction (TCL) Microalgae Biocrude Biofuel abstract This study investigated the optimum thermochemical liquefaction (TCL) operating conditions for produc- ing biocrude from Spirulina platensis. TCL experiments were performed at various temperatures (200– 380 °C), holding times (0–120 min), and solids concentrations (10–50%). TCL conversion at 350 °C, 60 min holding time and 20% solids concentration produced the highest biocrude yield of 39.9% repre- senting 98.3% carbon conversion efficiency. Light fraction biocrude (B 1 ) appeared at 300 °C or higher tem- peratures and represented 50–63% of the total biocrude. Biocrude obtained at 350–380 °C had similar fuel properties to that of petroleum crude with energy density of 34.7–39.9 MJ kg 1 compared to 42.9 MJ kg 1 for petroleum crude. Biocrude from conversion at 300 °C or above had 71–77% elemental carbon, and 0.6– 11.6% elemental oxygen and viscosities in the range 40–68 cP. GC/MS of biocrude reported higher hydro- carbons (C 16 –C 17 ), phenolics, carboxylic acids, esters, aldehydes, amines, and amides. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Microalgae are attractive feedstocks for biofuel production be- cause of their high productivities (40–80 tons ha 1 year 1 ), high li- pid content (30–60%) (Wijffels et al., 2010), their ability to grow in contaminated waters, their ability to sequester atmospheric CO 2 , and because they can be cultivated on marginal lands and variable climatic conditions. Because microalgal biofuel development does not compete with food production systems, this feedstock has fur- ther appeal. In order to reduce overall energy and cost input, it is beneficial to process algae without complete drying, which can be accomplished by the thermochemical liquefaction (TCL) pro- cess. The process converts organic constituents of algae into a li- quid biocrude that can be refined to gasoline like fuels. In addition, a major part of the N and P from the original biomass is recovered in the aqueous phase co-product and can be used in downstream algae cultivation systems (Jena et al., 2011). Hot compressed water is a highly reactive medium because of changes in properties such as solubility, density, dielectric constant and reactivity as water approaches its critical point (374 °C, 22.1 MPa). These enhance depolymerization and repolymerization of lignins, celluloses, lipids, proteins and carbohydrates, transform- ing them into biocrude (also referred to as biooil in the literature), gas and char. Multiple reactions occur in three steps, namely, hydrolysis, depolymerization and repolymerization/self-condensa- tion reactions (Yin et al., 2010). In lignocellulosic biomass, the lig- nin and cellulose components are hydrolyzed into unit structures of sugar monomers (Yin et al., 2010), whereas protein molecules are hydrolyzed into aminoacids followed by deamination and decarboxylation reactions to complex hydrocarbons (Sato et al., 2004). The biocrude is a dark viscous liquid with an energy value 70–95% of that of petroleum fuel oil (Brown et al., 2010; Dote et al., 1994; He et al., 2000; Minowa et al., 1998). Thermochemical liquefaction has been investigated for producing liquid fuels from several types of biomass including lignocellulosic feedstocks (Minowa et al., 1998), swine manure (He et al., 2000), macroalgae (Zhou et al., 2010) and microalgae (Brown et al., 2010; Dote et al., 1994; Ross et al., 2010; Zou et al., 2009; Yang et al., 2004). TCL pro- cess is known to be effective for biomass feedstocks, including al- gae, which have lower percentage of net lipids. The oil is produced not only from the conversion of triglycerides but also from all other components such as proteins, fibers and carbohydrates that consti- tute the whole biomass (Duan and Savage, 2011). TCL also provides a larger quantity of oil product relative to other methods. Conver- sion of microalgae biomass was reported to be a function of oper- ating variables such as temperature, holding time, and presence of catalysts and co-solvents (Duan and Savage, 2011; Huang et al., 2011; Zou et al., 2009). Highest TCL yield of 97% was reported for the liquefaction of Dunaliella tertiolecta at optimized operating con- ditions (Zou et al., 2009). Although some information is available on liquefaction of algae, further studies are needed to fill the following gaps and inconsis- tencies in the literature: (1) wide variation in biocrude yield and composition reported in the literature. For example, maximum 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.02.057 ⇑ Corresponding author. Tel.: +1 706 542 8842; fax: +1 706 542 8806. E-mail address: kdas@engr.uga.edu (K.C. Das). Bioresource Technology 102 (2011) 6221–6229 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech