Microalgae can be converted to an energy-dense bio-oil via pyrolysis; however, the relatively high nitrogen content of this bio-oil presents a challenge for its direct use as fuels. Therefore, hydrothermal pretreatment was employed to reduce the N content in Nannochloropsis oculata feedstock by removing proteins without requiring significant energy inputs. The effects of reaction conditions on the yield and composition of pretreated algae were investigated by varying the temperature (150-225. °C) and reaction time (10-60. min). Compared with untreated algae, pretreated samples had higher carbon contents and enhanced heating values under all reaction conditions and 6-42% lower N contents at 200-225. °C for 30-60. min. The pyrolytic bio-oil from pretreated algae contained less N-containing compounds than that from untreated samples and the bio-oil contained mainly (44.9% GC-MS peak area) long-chain fatty acids (C14-C18) which can be more readily converted into hydrocarbon fuels in the presence of simple catalysts.
Bibliographical noteFunding Information:
The work reported here was supported in part by Grants from Legislative-Citizen Commission on Minnesota Resources (LCCMR), US Department of Transportation North Central Sun Grants , US Department of Energy , and US Department of Agriculture, and Chinese Ministry of Science and Technology (Project No. 2009DFA61680).