Present study deals with a holistic approach to bioenergy production from a single-celled green algae Chlorella pyrenoidosa aiming to valorise all biomass components. In the first phase, the microalgae biomass was used to produce biodiesel in a microwave-assisted biodiesel reactor by in situ transesterification process. The biomass residue left after biodiesel production was pyrolyzed in a fixed bed pyrolysis reactor at various isothermal temperatures (400, 450, 500, 550, and 600°C) in second phase. The pyrolysis reaction results revealed that the highest bio-oil yield was 35.33 wt% along with 51.23 wt% biochar and 13.44 wt% pyrolysis gas at 500 °C. FTIR and GC–MS analyses of bio-oil confirm the existence of hydrocarbons as well as oxygenated chemicals like esters, phenols, and acid derivatives. Furthermore, the fuel properties of bio-oil as well as biodiesel e.g. viscosity, density, calorific value, flash point, and pour point were determined using standard procedures (ASTM D6751–02, EN–14214, and IS) and confirmed to be appropriate for stationary engine application. On the other hand, the biochar characterisation showed that it holds good potential for usage as a biocoal in industrial boilers/power plants or cooking stoves. Hence, this study demonstrates the utilization of Chlorella pyrenoidosa microalgae for production of eco-friendly renewable fuels as well as a wide range of value-added co-products with a zero-waste biorefinery approach.

Graphical abstract

中文翻译：

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通过原位酯交换和热解反应过程整体利用小球藻微藻提取可再生燃料和增值生物炭

目前的研究涉及从单细胞绿藻Chlorella pyrenoidosa生产生物能源的整体方法旨在评估所有生物质成分。在第一阶段，微藻生物质用于在微波辅助生物柴油反应器中通过原位酯交换过程生产生物柴油。生物柴油生产后留下的生物质残渣在第二阶段在不同等温温度（400、450、500、550 和 600°C）下在固定床热解反应器中热解。热解反应结果表明，在 500 ℃时生物油收率最高，为 35.33 wt%，生物炭为 51.23 wt%，裂解气为 13.44 wt%。对生物油的 FTIR 和 GC-MS 分析证实了碳氢化合物以及含氧化学物质（如酯、酚和酸衍生物）的存在。此外，生物油和生物柴油的燃料特性，例如粘度、密度、热值、闪点、和倾点使用标准程序（ASTM D6751-02、EN-14214 和 IS）确定，并确认适用于固定式发动机应用。另一方面，生物炭的特性表明它在工业锅炉/发电厂或烹饪炉灶中用作生物煤具有很好的潜力。因此，本研究证明了利用Chlorella pyrenoidosa微藻用于生产环保型可再生燃料以及采用零废物生物精炼方法的各种增值副产品。

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