Standards and Protocols for Characterization of Algae-Based Biofuels

Abstract

Recently, algae have been considered as the third-generation biofuel feedstock, which can be converted to the precursor chemicals of drop-in fuels via either the algal lipid upgrading (ALU) pathway or the hydrothermal liquefaction (HTL) pathway. These precursors could be further processed and upgraded to fuels. This article reviews the standards and protocols that are suitable for characterization of drop-in algal biofuels. Applicable ASTM standards and European standards (EN) were summarized. The protocols that have been used by researches and the National Institute of Standards and Technology were also introduced. Keywords: Algae-Based Biofuels; ASTM Standards; European Standards (EN); Drop-in Algal Biofuel; Algal Lipid Upgrading (ALU); Hydrothermal Liquefaction (HTL) IntroductionAlgae are a big variety of photosynthetic organisms, while microalgae are prokaryotic or eukaryotic photosynthetic microorganisms that can grow rapidly and live in harsh conditions due to their unicellular or simple multicellular structure. It is estimated that more than 50,000 species exist, but only a limited number of algal species have been studied and analyzed [1]. Microalgae have the ability to mitigate greenhouse gases, and some species can accumulate oil with a high productivity, thereby having the potential for applications in producing the third-generation of biofuels [2].During the past decade, government agencies and the private sector had shown tremendous interests in algae related studies. Thus, the algal technologies for biofuels production have been greatly advanced [3]. The algal biofuel production cost was significantly reduced, and the advanced process options for the conversion of algal biomass into biofuels and bioproducts have been developed [4]. Currently, there are two approaches that were suggested by the US Department of Energy as the promising technologies for algal biomass conversion. The first approach is call the algal lipid upgrading (ALU) pathway, in which algal oils are extracted from the biomass via highpressure homogenization with hexane [5]. This approach was further improved by combining with a biological conversion route that converts carbohydrates in algae to ethanol. Therefore, an integrated biorefinery process for ALU pathway was established [6]. The second technique is via the hydrothermal liquefaction (HTL) pathway that produces a water-insoluble bio-crude oil by using treatments at high pressure (5-20 MPa) 57 and at the temperature range of 250-450°C [7,8]. Other techniques, such as pyrolysis [9] and gasification [10,11], were also applied for converting algae to biofuels. However, these techniques have not been extensively studied yet, because of their inherent problems.The products from ALU and HTL are crude algal oil and bio-crude oil, respectively. Due to the low selectivity of two pathways, both products contain impurities like heteroatoms, oxygenated compounds, and nitrogenated compounds. In order to synthesize algae-based drop-in fuels, it requires upgrading processes (such as crackin...

Catalytic hydroprocessing of microalgae-derived biofuels: a review

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