Researchers from the Dalian Institute of Chemical Physics in China have selectively synthesized gasoline- and jet-fuel range C₇-C₈ cycloalkanes and aromatics by the methanolysis of poly(ethyleneterephthalate) (PET) waste, followed by the solvent-free hydrogenation and hydrodeoxygenation (HDO).

The C₇-C₈ cycloalkanes and aromatics can be used as gasoline or additives to improve the densities (or volumetric heat value) and sealabilities of current bio-jet fuels. A paper on the work is published in the RSC journal Green Chemistry.

Strategy for the synthesis of gasoline and jet fuel range C7-C8 cyclic hydrocarbons with PET wastes. Tang et al.

Poly(ethylene terephthalate) (PET) is a widely used plastic. Due to its excellent mechanical and thermal properties, PET is produced in great scale (> 50 million tons per year). Because PET is highly resistant to biological degradation, the recycling of PET wastes by chemical methods has drawn tremendous attention in recent years.

So far, most of reported processes were concentrated on the degradation of PET to terephthalic acid or its esters (such as bis(hydroxyalkyl) terephthalate (BHET)) and the further hydrogenation of these compounds to 1,4-cyclohexanedicarboxylates11 or 1,4- cyclohexanedimethanol (1,4-CHDM). Cyclic hydrocarbons (including cycloalkanes and aromatics) are important components of gasoline and jet fuel (two most demanded transportation fuels). Compared with chain alkanes, cyclic hydrocarbons have relatively higher octane-numbers, densities (or volumetric heat values) and sealabilities.

Taking into consideration of the special chemical structure of PET, we think that it can be used as a potential feedstock for the production of gasoline and jet fuel range cyclic hydrocarbons. To the best of our knowledge, there is no report about this.

—Tang et al.

The team found that methanol is highly reactive for the alcoholysis of PET waste. In the absence of any catalyst, they achieved a high yield of dimethyl terephthalate (97.3%) under mild conditions (473 K, 3.5 h). The dimethyl terephthalate (DMT) exists as a solid and can be automatically separated from methanol by reducing the temperature.

Subsequently, they liquefied the DMT to dimethyl cyclohexane-1,4-dicarboxylate (DMCD) by solvent-free hydrogenation over noble metal catalysts. Among the investigated catalysts, Pt/C exhibited the highest activity.

Finally, DMCD as obtained was further hydrodeoxygenated to C₇-C₈ cycloalkanes and aromatics. They found bimetallic Ru-Cu/SiO₂ to be a promising HDO catalyst.

In a real application, the researchers suggested, DMCD can also be simultaneously hydrodeoxygenated with biomass-derived oxygenates to produce the jet fuel with proper contents of cycloalkanes and aromatics.

Resources

• Hao Tang, Ning Li, Guangyi Li, Ai-Qin Wang, Cong Yu, Guoliang Xu, Xiaodong Wang and Tao Zhang (2019) “Synthesis of gasoline and jet fuel range cycloalkanes and aromatics with poly(ethyleneterephthalate) wastes” Green Chemistry doi: 10.1039/C9GC00571D