Abstract
In this study, the pyrolysis behaviours of marine microalgae biomass, Nannochloropsis gaditana, were investigated at three different temperatures (400, 500, 600 °C). Experiments were conducted in the presence of N2 with a flow rate of 50 cm3/h using a 1-kg fixed-bed reactor. The effects of pyrolysis conditions such as temperature on product yields were studied. The char, bio-oil, and gaseous samples obtained were analysed for elemental trace metals using inductively coupled plasma atomic emission spectroscopy (ICP-OES) and gas chromatography with mass detection (GC–MS). Raw Nannochloropsis gaditana samples were also analysed by pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS). Mass and energy balances were calculated. The results indicate that the bio-oil from the pyrolysis of Nannochloropsis gaditana under 600 °C had the highest heating value (12.6 MJ/kg) and was obtained with the highest efficiency (38–40%). Alkanes and alkenes, such as tetradecane, pentadecane, heptadecene, and octadecene, were identified in the liquid products, and the highest contents of alkanes and alkenes were determined in the bio-oil obtained under 500 °C. In these pyrolysis conditions, gaseous products exhibited the highest concentrations of methane (greater than 50% in the maximum range). These properties of the bio-oil and its gaseous products demonstrated that Nannochloropsis gaditana can be used as a renewable energy resource and chemical feedstock. The biochar from all processes contained almost 70% ash and, in this particular case, can be used as, for example, a fertilizer because it does not contain any heavy metals.
Highlights
Fossil fuels such as coal, oil, and natural gas are currently the primary sources of energy globally
The algae biomass used in this study is characterized by a relatively large ash content compared to other such biomass samples; its higher heating value was greater than 21 MJ
The N. gaditana microalgae sample used in the pyrolysis process, and all of the products obtained through this process, was subjected to basic analyses, including
Summary
Fossil fuels such as coal, oil, and natural gas are currently the primary sources of energy globally. Experts anticipate that fossil fuels will be depleted within the 50 years. The increasing use of fossil fuels in the energy sector, and for industry and transportation, is negatively impacting the climate and the environment [1]. More than 90% of the carbon dioxide emitted to the atmosphere is associated with the processing of fossil fuels. The processing of coal and oil leads to significant emissions of nitrogen oxides and sulphur oxides. According to the Kyoto Protocol, fossil fuels should be replaced by other new energy sources, such as biomass, hydrogen, and renewable energy [1,2,3]
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