Molecular structure transformation is a critical step for synthesis of aviation biofuels from triglycerides, to yield alkanes, aromatics and cycloalkanes. To this end, triglycerides were treated by catalytic cracking coupled with rectification to obtain hydrocarbon fuels, and the molecular weight of the liquid product was adjusted to the desirable boiling range of aviation fuel. To further modify the molecular structures, the pyrolytic hydrocarbons were partially converted into aromatics and cycloalkanes by a two-step process. Different raw materials including soybean oil, rubber seed oil, waste cooking oil and acidified oil were cracked with a 5 wt% base catalyst at 350–450 °C (under the atmospheric pressure) in a benchtop reactor. Afterwards, the linear hydrocarbons of C8–C15 size were transformed into aromatics by HZSM-5 at 350 °C for 6 h. Then, a portion of the aromatics were converted into cycloalkanes catalyzed by Pd/AC at 200 °C and 6 MPa (H2) for 6 h. As a result, a desirable mixture of linear hydrocarbons, aromatics and cycloalkanes was obtained with a similar composition and properties to traditional fossil aviation fuels.
Triglycerides are a promising biomass feedstock that can be used for production of organic hydrocarbons including long-chain olefins and paraffin. The challenge for this production process lies on the lack of a clear mechanism of the conversion process. In this work, the conversion mechanism from triglycerides to olefins and paraffin using alkali metal catalysts was investigated adopting both computational calculations using density functional theory and experimental studies. The bond dissociation energies of the main bonds were calculated, especially for the α carbon‑carbon bond, which leads to effective removal of carboxyl groups during the thermochemical conversion process. The dynamic behavior of triglycerides catalyzed by alkali metal catalysts was also investigated using thermogravimetric analysis , which found that Li ion has lowest activation energy below 200 kJ/mol when compared with the other alkali ions studied. The catalytic conversion mechanism was proposed in this work based on the results obtained from TG-IR, GC, GC–MS and XRD analyses. The O atoms are removed in the form of CO, CO 2 and H 2 O, product M + O and M+, which generates M 2 CO 3 . A more detailed mechanism has been proposed in this paper, which has significance toward guiding the cleavage of triglycerides to produce long‑carbon-chain terminal olefins and normal paraffin.
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