Renewable and carbon neutral biofuels are necessary for environmental and economic sustainability. The viability of the first generation biofuels production is however questionable because of the conflict with food supply. Microalgal biofuels are a viable alternative. The oil productivity of many microalgae exceeds the best producing oil crops. This paper aims to analyze and promote integration approaches for sustainable microalgal biofuel production to meet the energy and environmental needs of the society. The emphasis is on hydrothermal liquefaction technology for direct conversion of algal biomass to liquid fuel.
Eboibi, B.E.; Lewis, D.M.; Ashman, P.J.; Chinnasamy, S.
Fonte: Royal Society of ChemistryPublicador: Royal Society of Chemistry
Tipo: Artigo de Revista Científica
Publicado em //2015EN
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Direct conversion of microalgae to advanced biofuels with hydrothermal liquefaction (HTL) is an attractive option which has drawn attention in recent years. The presence of heteroatoms in the resultant biocrude, energy input and the process water has been a long-term concern. In this study, the pretreatment of microalgae biomass for protein extraction was conducted prior to HTL for biocrude production. The impact of operating conditions on both the pretreatment and hydrothermal liquefaction steps was investigated. Following HTL using the pretreated algae with an initial solid content of 16% w/w for 30 min at 310 °C, the biocrude yield was 65 wt%, which was more than a 50% improvement in yield as compared to HTL of untreated algae under the same reaction conditions. To achieve a similar biocrude yield using the untreated algae required a much higher reaction temperature of 350 °C. Using recycled process water as reaction media led to a 25 wt% higher biocrude yield. HTL of pretreated algae led to 32–46% nitrogen reduction in resultant biocrude. The biocrude had a higher heating value (HHV) of 28 MJ kg−1 to 34 MJ kg−1. A maximum of 15 wt% protein extract was obtained during pretreatment at 150 °C, 20 min. A similar energy input was required in biocrude production from the untreated route and the combined pretreatment and HTL.; B. E. Eboibi...
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Microalgae are generally considered as a promising biomass source for applications including production of advanced biofuels, chemicals, wastewater treatments, various organic substances or a combination of any of the above. The advantages of microalgae includes faster growth rates than terrestrial plants, ability to use non-arable land for mass production, and their ability to grow in poor quality water, as well as their ability to remove pollutants from wastewater streams. However, one of the major challenges of microalgae for commercialisation to is its economic downstream production and conversion to biofuels and chemicals. When harvested, microalgae contains up to ~90% water content, thus economic conversion of high moisture content biomass to valuable products such as biofuels remains a challenge. Hydrothermal liquefaction (HTL) involves processing of high moisture content biomass in hot compressed water, avoiding the drying step for biomass feedstocks. Therefore HTL is advantageous as it avoids the energy intensive drying process in contrast to processes that involve drying of biomass prior to processing into biofuels. HTL products comprise biocrude, solid residues, aqueous and gas phases. The primary product biocrude is upgradable to liquid transportation fuels. The aqueous phase contains essential nutrients that could be recycled to microalgae cultivation ponds. The gas phase contains about 98mol% carbon dioxide (CO₂) and 2mol% hydrocarbon gases. The gas phase can also be directly recycled to the microalgae cultivation ponds for pH control and supply of CO₂...