Demineralization of Sargassum spp. Macroalgae Biomass: Selective Hydrothermal Liquefaction Process for Bio-Oil Production

Liz M Dã­Az-Vã¡Zquez,K C Das,Umakanta Jena,Mariela Fuentes-Caraballo,Arnulfo Rojas-Pã©Rez,Isis V Robles

doi:10.3389/fenrg.2015.00006

Abstract

Algae biomasses are considered a viable option for the production of biofuel because of their high yields of oil produced per dry weight. Brown macroalgae Sargassum spp. are one of the most abundant species of algae in the shores of Puerto Rico. Its availability in large quantity presents a great opportunity for use as a source of renewable energy. However, high ash content of macroalgae affects the conversion processes and the quality of resulting fuel products. This research studied the effect of different demineralization treatments of Sargassum spp. biomass, subsequent hydrothermal liquefaction (HTL) and bio-oil characterization. Demineralization constituted five different treatments: nanopure water, nitric acid, citric acid, sulfuric acid, and acetic acid. Performance of demineralization was evaluated by analyzing both demineralized biomass and HTL products by the following analyses: total carbohydrates, proteins, lipids, ash content, caloric content, metals analysis, Fourier Transform Infrared - Attenuated Total Reflectance (FTIR-ATR) Spectroscopy, Energy Dispersive Spectroscopy (EDS), Scanning Electron Microscopy (SEM), and GCMS analysis. HTL of Sargassum spp. before and after citric acid treatment, was performed in a 1.8 L batch reactor system at 350°C with a holding time of 60 min and high pressures (5-21 MPa). Demineralization treatment with nitric acid was found the most effective in reducing the ash content of the macroalgae biomass from 27.46% to 0.99% followed by citric acid treatment that could reduce the ash content to 7%. Citric acid did not show significant leaching of organic components such as carbohydrates and proteins, and represented a less toxic and hazardous option for demineralization. HTL of untreated and citric acid treated Sargassum spp. resulted in bio-oil yields of 18.4±0.1 % and 22.2±0.1 % (ash free dry basis), respectively.

Highlights

Bio-oil obtained from algae is considered a promising alternative to fossil fuels due to its high energy content (Azadi et al, 2014; Brownbridge et al, 2014) and low life-cycle emissions of greenhouse gases (Li et al, 2011; Azadi et al, 2014)
We investigate the impacts of different demineralization treatments of macroalgae biomass
It was found that all the demineralization pretreatments decreased the inorganic contents in the Sargassum biomass

Summary

Introduction

Bio-oil obtained from algae is considered a promising alternative to fossil fuels due to its high energy content (Azadi et al, 2014; Brownbridge et al, 2014) and low life-cycle emissions of greenhouse gases (Li et al, 2011; Azadi et al, 2014). Hydrothermal liquefaction is a process used to obtain bio-crude from wet biomass in moderate to high temperatures (280–370°C) and pressures (10–25 Mpa) (Villadsen et al, 2012), in which water in its subcritical state acts as a highly reactive medium and catalyzes many chemical reactions (Toor et al, 2011). This process is fast and eco-friendly (Peterson et al, 2008) and is energetically efficient because it does not include a drying step as in the pyrolysis process (Bridgwater et al, 1999; Jena and Das, 2011). High reactivity and superior ionic product (Kw) of subcritical water break down biomass complex polymers including polysaccharides, lipids, and proteins into simpler molecules that can be converted into bio-oils with different viscosities (Peterson et al, 2008; Villadsen et al, 2012) depending on the catalysts, solvents, feedstock composition, and pretreatment methods employed. (Zhuang et al, 2012; Neveux et al, 2014; Singh et al, 2015)

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Results

Conclusion