Selective production of monocyclic aromatic hydrocarbons from ex situ catalytic fast pyrolysis of pine over the HZSM-5 catalyst with calcium formate as a hydrogen source

Catalytic fast pyrolysis of pine over HZSM-5 was conducted with different hydrogen-rich co-feeders aiming at increasing the production of monocyclic aromatic hydrocarbons (MAHs) while suppressing the formation of polycyclic aromatic hydrocarbons (PAHs). Three co-feeders, i.e., methanol, polyethylene terephthalate (PET) and calcium formate, were employed for comparative pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) experiments to evaluate their hydrogen supply abilities. The results indicated that calcium formate exhibited the best ability to substantially promote the conversion of biomass into MAHs. Under the optimal conditions of a calcium formate : pine ratio of 3 : 1 at 650 °C, the yields of MAHs and PAHs were 10.65 wt% and 1.94 wt% respectively, compared with 9.23 wt% and 2.49 wt% without calcium formate, respectively. Moreover, laboratory-scale catalytic fast pyrolysis experiments were performed to examine the pyrolytic product and aromatic hydrocarbon distribution at different calcium formate to pine ratios and pyrolysis temperatures. The yields of MAHs and PAHs were 7.80 wt% and 1.70 wt% in the absence of calcium formate, which were then increased to 9.45 wt% and 1.14 wt% respectively under the optimal conditions of 650 °C and a calcium formate : pine ratio of 1 : 2. A catalyst stability test was also conducted to confirm that calcium formate helped maintain the catalyst activity. In addition, the possible hydrogen supply mechanism of calcium formate was speculated.