Qicong Liu,Zhe Xiong,Syed Shatir A. Syed-Hassan,Zengtong Deng,Xingyu Zhao,Sheng Su,Jun Xiang,Yi Wang,Song Hu
Ni-based catalyst is prone to the deactivation by coke deposition during the catalytic steam reforming of bio-oil. In order to optimize catalytic activity of the Ni-based catalyst, a two-stage catalytic reforming scheme was proposed whereby a low-temperature (350–600 °C) pre-reforming process with a less expensive catalyst was introduced prior to the Ni-based catalyst. To study this scheme, the reforming experiments with different combinations of Fe/bio-char (in the first stage) and Ni-Ca/γ-Al 2 O 3 (in the second stage) were conducted. In addition to the quantification of product yields, the tar and gas were characterized with an ultraviolet (UV) fluorescence spectroscopy, a gas chromatography/mass spectrometer (GC/MS) and a gas chromatography (GC). The results indicate that significant proportions of naphthalenes and polycyclic aromatics in the intermediate volatiles turned into furans, phenols and non-aromatics, which are easier to be reformed on Ni-based catalysts, via the Fe/bio-char pre-reforming, resulting in the increase of the final H 2 and CO yields of the overall process. At high pre-reforming temperatures (550–600 °C), the coke formation on Ni-based catalyst was significantly inhibited due to the Fe/bio-char pre-reforming. In addition, the results indicate that the spent Ni-based catalyst had more free NiO and NiAl 2 O 4 spinel than the fresh one, suggesting that the increase in the catalytic activity of Ni-based catalyst during the reforming process was promoted by Fe/bio-char pre-reforming.
In this study, the impact of pre-reforming procedure on the intermediate products and the production of hydrogen in the two-stage steam reforming of bio-oil generated from pine sawdust was explored. The evolution of the intermediate products in the liquid and gas phase affected by the pre-reforming catalyst (red mud, dolomite, biochar) and pre-reforming temperature was investigated, as is impact of intermediate products on the hydrogen production. The findings indicate that dolomite was identified as the most effective pre-reforming catalyst due to its high CaO/MgO content, which promoted the Boudouard reaction more effectively than the Fe 2 O 3 in in red mud. Low-temperature pre-reforming (≤450 °C) was more beneficial than high-temperature pre-reforming (≥550 °C) at which coke precursors, including aromatic hydrocarbons and phenols were easily produced, leading to rapid catalyst deactivation. Liquid-phase intermediates were primarily composed of furans, phenols, and ketones, with ketones accounting for up to 55.63 %, which may be related closely to the greatly promoted ketonization by the alkaline Ca(OH) 2 produced via the combination dolomite and water at low temperature. Ketones were actually more favorable to the second-stage reforming over Ni-based catalysts, and the ultimate hydrogen yield reached 66.52 %. Due to the low inclusion of phenol and aromatic hydrocarbon intermediates less susceptible to carbon deposition, the catalyst could be more stable. The two-stage steam reforming of pyrolysis bio-oil can avoid catalyst deactivation and enhance the hydrogen production to a higher degree, accomplished by changing the intermediates components with varied pre-reforming catalysts and temperatures.
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