Catalytic hydrothermal liquefaction of D. tertiolecta over multifunctional mesoporous silica-based catalysts with high stability

In this work, multifunctional mesoporous silica-based catalysts containing metal, acid and base were successfully synthesized by doping metal cobalt through the impregnation–precipitation method and grafting amino and sulfonic groups by the silicon alkylation method. The catalytic hydrothermal liquefaction (HTL) of Dunaliella tertiolecta (D. tertiolecta) was performed at 533 K for 30 min. X-ray diffraction (XRD), small angle X-ray diffraction (SXRD), N2 absorption/desorption isotherm analysis, elemental analysis, inductively coupled plasma optical emission spectrometer (ICP-OES), and transmission electron microscopy (TEM) were employed to characterize SBA-15 and multifunctional SBA-15. The hydrothermal testing on the obtained multifunctional SBA-15 were conducted in a stainless steel autoclave at 533 K for 30 min. SXRD, TEM, and N2 absorption/desorption isotherm analysis results showed that Co doping and sulfonic group grafting, but not amino group grafting, could improve the hydrothermal stability of SBA-15. The results of TEM, XRD, and ICP-OES confirmed that Co existed as Co3O4 and entered into the SBA-15 skeleton. Meanwhile, the results of elemental analysis and ICP-OES showed that amino and sulfonic groups were successfully grafted on SBA-15. Gas chromatography–mass spectrometry (GC-MS) and elemental analysis were adopted to identify the composition of the obtained bio-oil. The bio-oil produced by the catalytic HTL of Dunaliella tertiolecta at 533 K for 30 min gained high contents of furfural and its derivatives, as well as low contents of acids, N-containing compounds, and esters, when NH2-SO3H-Co-SBA-15 and SO3H-Co-SBA-15 were used as catalysts. However, fewer conversions and lower bio-oil yields were obtained under the use of such catalysts than under catalyst absence.