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Here, catalytic fast pyrolysis (CFP) was studied as a method to valorize rice husk (RH). Specifically, the effects of RH pretreatment, i.e., NaOH treatment, on the CFP efficiency and selectivity over a Ga-loaded HZSM-5 (SiO2/Al2O3 ratio = 38) were investigated. In addition to NaOH pretreatment, it was investigated how pyrolysis medium (N2, CH4, or a gas stream evolved from ex-situ CH4 decomposition over a Ni/La2O3/CeO2/Al2O3 catalyst (Ni/La2O3/CeO2 = 2/1/1) at 923 K (d-CH4)) influences the CFP of pretreated RH. The NaOH treatment reduced the content of ash and increased the content of cellulose in the RH sample. Thus, the effect of pyrolysis medium on the CFP of cellulose was studied at first, followed by that on CFP of NaOH-treated RH. With regard to the pyrolysis medium, the yield of aromatic compounds such as benzene, toluene, ethylbenzene, and xylene (BTEX) achieved with both cellulose and the NaOH-treated RH enhanced in an order; d-CH4 > CH4 > N2. The removal of ash from RH with the NaOH pretreatment increased the BTEX yield up to 22.3 wt% as ash (mineral impurities) affects pyrolytic behavior of cellulose and lowers accessibility of pyrolytic volatiles to acid sites on zeolite. This study gives helpful information about how different parameters influence the conversion of RH into BTEX via CFP process.

Food waste, a renewable resource, was converted to H

Food waste, a renewable resource, was converted to H2-rich gas via a catalytic steam gasification process. The effects of basic oxides (MgO, CaO, and SrO) with 10 wt% Ni/Al2O3 on the gasification properties of food waste were investigated using a U-shaped gasifier. All catalysts prepared by the precipitation method were analyzed by X-ray diffraction, H2-temperature-programmed reduction, NH3-temperature-programmed desorption, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The Ni/Al2O3 catalyst was reduced incompletely, and low nickel concentrations were detected on the surface of the alumina. The basic oxides minimized the number of acid sites and suppressed the formation of nickel-aluminate (NiAlxOy) phase in catalyst. In addition, the basic oxides shifted nickel-aluminate reduction reaction to lower temperatures. It resulted in enhancing nickel concentration on the catalyst surface and increasing gas yield and hydrogen selectivity. The low gas yield of the Ni/Al2O3 catalyst was attributed to the low nickel concentration on the surface. The maximum gas yield (66.0 wt%) and hydrogen selectivity (63.8 vol%) of the 10 wt% SrO- 10 wt% Ni/Al2O3 catalyst correlated with the highly dispersed nickel on the surface and low acidity. Furthermore, coke deposition during steam gasification varied with the surface acidity of the catalysts and less coke was formed on 10 wt% SrO- 10 wt% Ni/Al2O3 due to efficient tar cracking. This study showed that the steam gasification efficiency of the Ni/Al2O3 catalyst could be improved significantly by the addition of SrO.

Herein, the thermocatalytic conversion of rice husk is studied as a valorization method for the production of benzene, toluene, ethylbenzene, and xylene (BTEX). The reaction environment, the type of zeolite, the SiO2/Al2O3 ratio of the zeolite, and the Ga loading on the zeolite are considered in order to maximize the BTEX yield. Five distinct reaction media are tested, including N-2, CH4, and gas streams evolved from the ex-situ decomposition of CH4 at 650, 725, and 800 degrees C (designated as CH4-D(650), CH4-D(725), and CH4-D(800), respectively). The thermocatalytic conversion of rice husk in CH4-D(650) with a H-2/CH4 molar ratio of 0.88 is shown to provide the highest BTEX yield. In addition, the use of the HZSM-5 zeolite, with its relatively low SiO2/Al2O3 ratio, is shown to provide a further increase in the BTEX yield due to the higher density of Bronsted acid sites. The highest yield of BTEX (18.3 wt%) is achieved in the presence of Ga/HZSM-5 (Ga loading: 1 wt%) under the CH4-D(650) atmosphere. The further addition of Ga to the HZSM-5 (2 and 5 wt% Ga) is shown to decrease the BTEX yield because excess Ga loading on the zeolite decreases the number of available Bronsted acid sites. The present study provides useful information on the effects of various factors upon the thermocatalytic conversion of waste biomass such as rice husk to achieve high yields of value-added chemicals such as BTEX.

This work investigated the impact of pyrolysis medium and catalyst on the production of bio-BTX (benzene, toluene, and xylene) from Quercus Mongolica (Q. Mongolica) via catalytic pyrolysis. Two different pyrolysis media (N2 and CH4) and five different zeolite catalysts (HY, HBeta, HZSM-5, 1 wt% Ni/HZSM-5, and 1 wt% Ga/HZSM-5) were considered for the Q. Mongolica pyrolysis. The HZSM-5 yielded more BTX than the HY and HBeta due to its strong acidity. The employment of CH4 as the pyrolysis medium improved the BTX yield (e.g., 2.7 times higher total BTX yield in CH4 than in N2) and resulted in low coke yield (e.g., 5.27% for N2-pyrolysis and 2.57% for CH4-pyrolysis) because the CH4-drived hydrogen simulated a hydropyrolysis condition and facilitated dehydroaromatization reaction. CH4 also led to direct coupling, Diels-Alder, and co-aromatization reactions during the pyrolysis, contributing to enhancing the BTX yield. The addition of Ga to the HZSM-5 could further increase the BTX yield by means of facilitating hydrocracking/demethylation and methyl radical formation from CH4 assisting the generation of >C2 alkenes that could be further converted into BTX on acid sites of the HZSM-5.