Catalytic Pyrolysis of the Green Microalgae Botryococcus braunii over Ni/SBA-15 Prepared by the Ultrasonic-Assisted Sol-Gel Method

Abstract

The pyrolysis of the green microalgae Botryococcus braunii in the absence and the presence of Ni/SBA-15 prepared by the ultrasonic-assisted sol–gel was investigated using pyrolysis–gas chromatography–mass spectroscopy (Py-GC/MS). Pyrolysis experiments were performed at 350, 450, and 550 °C under helium (He) flow. In the absence of a catalyst, the chemical composition of pyrolysis products at different temperatures, based on the relative peak area, comprised protein/amino acid derivative products of 9–15%, carbohydrate derivative products of 5–10%, lipid derivative products of 13–26%, and chlorophyll derivative products of 24–26%. For catalytic pyrolysis, the chemical composition of pyrolysis products comprised protein/amino acid derivative products of 5–15%, carbohydrate derivative products of 18–19.5%, lipid derivative products of 14–27%, and chlorophyll derivative products of 15–20%. The addition of 10% Ni/SBA-15 enhanced the production of aromatic compounds, such as furans, furfurals, alkyl aromatics, and nitrogen aromatic compounds. These were the thermal degradation products of carbohydrates and proteins. However, the amount of fatty acids and phytol fragments in the pyrolysis of Botryococcus braunii decreased in the presence of catalyst. Thermogravimetric analyses showed that the temperature range for the pyrolysis of Botryococcus braunii was 135–547 °C, while that of the catalyzed pyrolysis was 135–532 °C. There was a decrease in pyrolysis yield after incorporating Ni/SBA-15, which may be due to coke formation.