Pyrolysis of three different types of microalgae: Kinetic and evolved gas analysis D. L  opez-Gonz  alez, M. Fernandez-Lopez, J.L. Valverde, L. Sanchez-Silva * Department of Chemical Engineering, University of Castilla-La Mancha, Avda. Camilo Jos e Cela, 12, 13071 Ciudad Real, Spain article info Article history: Received 16 December 2013 Received in revised form 11 April 2014 Accepted 3 May 2014 Available online 6 July 2014 Keywords: Microalgae TGAeMS Pyrolysis Kinetics abstract Pyrolysis characteristics of three species of microalgae (SC (Scenedesmus almeriensis), NG (Nanno- chloropsis gaditana) and CV (Chlorella vulgaris)) have been studied by TGAeMS (thermogravimetric analysis coupled with mass spectrometry). The thermal behavior of microalgae samples could be described according to their biochemical composition and, in different extension, to their content in inorganic species. The high potassium content of sample SC led to the formation of a more stable char and the release of higher amount of volatiles. Pyrolysis kinetics were studied using a multiple-step model that successfully predicted the experimental behavior of these samples and was statistically validated. The gaseous products released in the pyrolysis of microalgae samples could be divided into light volatiles as H 2 , CO, H 2 O, CO 2 , light hydrocarbons and a condensable fraction formed by ketones, alcohols and aromatic compounds. Besides, nitrogen and sulfur compounds were generated in the form of amines, cyanides and hydrogen sulfides. Finally, an equation for predicting gas yields at a higher scale has been proposed. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Depletion of world fossil fuel reserves and environmental pollution is the main cause for the growing attention that biomass fuels are receiving [1]. Depending on the biomass source, fuels derived from their use can be divided into different types: first, second and third generation biofuels. First generation biofuels includes different crops, such as corn starch, wheat, sugarcane, palm and canola where the sugars/ starches are easily accessible. The production of biofuels from them involves well-developed conversion technologies [2]. However, they directly compete with human food crops and, thus, their use as a biofuel source is limited. Second generation of biofuels mainly refers to lignocellulosic biomass. It is primarily comprised of cel- lulose, hemicellulose and lignin with lesser amounts of extractives [3]. Unlike carbohydrate or starch, lignocellulose is not easily digestible by humans, thus, its use does not threaten the world food supply [4]. Their main advantages are short growing periods and high production rates, and require little or no fertilizer, so they provide quick return on investment. Finally, third generation bio- fuels are obtained from algae. Algae are a very promising kind of biomass due to the fact that these species are known to produce considerably greater amounts of biomass and lipids. They can be cultivated without occupying farmlands, do not compete with food crops, require less energy than other feedstock during conversion process, flexibility on water requirements (salt and wastewater to provide the nutrients), CO 2 -rich flue gas as carbon source for their production and broad product selection [5,6]. The main route for algae utilization would be the extraction of their lipids fraction to later produce biodiesel via trans- esterification. There are different techniques to accomplish the lipid extraction: direct extraction, solvent extraction and supercritical fluid extraction. However, lipid extraction is costly and there are several factors that affect negatively to the economics of the pro- cess such as low-lipid content, incomplete extraction and pollution from the extraction reagent recovery [6,7]. Furthermore, there is not a well-defined and ready-to-scale up lipid extraction technol- ogy [8]. Additionally, all the fractions of the algae must be valorized to make competitive the use of algae compared to fossil fuels. The thermochemical conversion of the raw microalgae might suppose an alternative effective option for processing biomass into biofuels [7,9]. Among the different thermochemical conversion technologies, pyrolysis stands out for being a highly versatile and easily scale-up process, which takes advantage of all the fractions of the biomass feedstock by producing three types of products, a low- calorific value gas, a pyrolytic-oil and a solid char. Additionally, this * Corresponding author. Tel.: þ34 926 295300x6307; fax: þ34 926 295256. E-mail address: marialuz.sanchez@uclm.es (L. Sanchez-Silva). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy http://dx.doi.org/10.1016/j.energy.2014.05.008 0360-5442/© 2014 Elsevier Ltd. All rights reserved. Energy 73 (2014) 33e43