Pyrolysis Behaviours of Microalgae Nannochloropsis gaditana

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.