Yayun Zhang

Co-pyrolysis of microwave-assisted acid pretreated bamboo sawdust and soapstock

Fast microwave-assisted co-pyrolysis of pretreated bamboo sawdust and soapstock was conducted. The pretreatment process was carried out under microwave irradiation. The effects of microwave irradiation temperature, irradiation time, and concentration of hydrochloric acid on product distribution from co-pyrolysis and the relative contents of the major components in bio-oil were investigated. A maximum bio-oil yield of 40.00u202fwt.% was obtained at 200u202f°C for 60u202fmin with 0.5u202fM hydrochloric acid. As pretreatment temperature, reaction time and acid concentration increased, respectively, the relative contents of phenols, diesel fraction (C12u202f+u202faliphatics), and other oxygenates decreased. The gasoline fraction (including C5-C12 aliphatics and aromatics) ranged from 55.77% to 73.30% under various pretreatment conditions. Therefore, excessive reaction time and concentration of acid are not beneficial to upgrading bio-oil.

From glucose-based carbohydrates to phenol-rich bio-oils integrated with syngas production via catalytic pyrolysis over an activated carbon catalyst

The catalytic pyrolysis of carbohydrates over a phosphoric acid-activated carbon catalyst (ACC) was investigated to obtain phenol-rich bio-oils and syngas production in a facile fixed bed reactor for the first time. The central composite design (CCD) was adopted to optimize the experimental operating conditions of glucose catalytic pyrolysis, where the effects of reaction temperatures and ratios of catalyst to reactant on product distributions were studied. The main chemical components of the obtained catalytic bio-oils from glucose were phenols, ketones, and anhydrosugars, in which the selectivity of phenols ranged from 4.8 to 100% depending on various reaction conditions. The highest selectivity of phenols was achieved at a reaction temperature of 450 °C with a catalyst to reactant ratio of 1. Carbon monoxide, carbon dioxide, methane, and hydrogen were the main gas fractions in the gaseous products, where high concentrations of carbon monoxide (50.2%) and hydrogen (9.2%) could be attained. Additionally, the catalytic pyrolysis of cellulose with different catalyst to reactant ratios at a reaction temperature of 450 °C was also investigated and the results exhibited a similar phenomenon to that of glucose. A high selectivity of phenols (96.7%) could also be achieved integrated with a high concentration of carbon monoxide (42.1%). The mechanism of phenol generation was further discussed and the “phenol pool” was proposed to describe the catalytic function of the ACC in the catalytic conversion of volatiles into phenols. Our findings suggest that the catalytic pyrolysis of renewable and earth-abundant carbohydrates over the ACC might provide a novel and viable route to generate high-purity phenols to ultimately advance the utilization of biomass energy.

Microwave-assisted co-pyrolysis of pretreated lignin and soapstock for upgrading liquid oil: Effect of pretreatment parameters on pyrolysis behavior

The co-pyrolysis of pretreated lignin and soapstock was carried out to upgrade vapors under microwave irradiation. Results showed that the yield of 29.92-42.21u202fwt% of upgraded liquid oil was achieved under varied pretreatment conditions. Char yield decreased from 32.44u202fwt% for untreated control to 24.35u202fwt% for the 150u202f°C pretreated samples. The increased temperature, irradiation time and acid concentration were conducive to decrease the relative contents of phenols and oxygenates in liquid oils. The main components of the liquid oil were gasoline fraction (mono-aromatics and C5-C12 aliphatics), which ranged from 57.38 to 71.98% under various pretreatment conditions. Meanwhile, the diesel fraction (C12+ aliphatics) ranged from 13.16 to 22.62% from co-pyrolysis of pretreated lignin and soapstock, comparing with 10.18% of C12+ aliphatics from co-pyrolysis of non-pretreated lignin and soapstock. A possible mechanism was proposed for co-pyrolysis of pretreated lignin and soapstock for upgraded liquid oils.

Production of hydrocarbons from biomass-derived biochar assisted microwave catalytic pyrolysis

In the present study, in situ catalytic pyrolysis of Douglas fir pellets was performed in a microwave reactor. A biochar catalyst derived from corn stover biochar was prepared for the experiment. The results showed that the highest amounts of hydrocarbons (52.77% of bio-oil) were achieved from microwave-assisted catalytic pyrolysis over the biochar catalyst at a reaction temperature of 480 °C. A non-condensable gas enriched in H2, CO, and CO2 was observed and analyzed by micro-GC. The amounts of H2 and CO increased during catalytic pyrolysis compared to the non-catalytic runs. GC/MS analysis results showed that the quantity of lignin-derived guaiacols decreased dramatically with the increase of the ratio of catalyst to biomass. The biochar catalyst exhibited good selectivity towards hydrocarbon and phenol compounds, simplifying the chemical composition, reducing undesirable compounds and producing pyrolysis oil in an acceptable yield. The reaction mechanism for hydrocarbon production from catalytic pyrolysis was also analyzed.

Renewable bio-phenols from in situ and ex situ catalytic pyrolysis of Douglas fir pellet over biobased activated carbons

In situ and ex situ catalytic upgrading of pyrolysis vapors from Douglas fir pellets in the presence of activated carbon (AC) prepared by chemical activation was studied in a microwave pyrolyzer. The in situ catalytic upgrading configuration gave lower bio-oil yields (10.25–25.5 wt%) than ex situ catalytic upgrading configuration (20.03–32 wt%). The bio-oil yield from the in situ upgrading process was significantly affected by both catalytic reaction temperature and catalyst to biomass ratio. However, the bio-oil yield from ex situ upgrading process was only significantly affected by catalyst to biomass ratio. Bio-oils compositional analysis indicated that the ex situ upgrading process generated higher phenols concentration (4.14–19.76 mg ml−1) than in situ upgrading (4.14–9.90 mg ml−1). However, the selectivity of phenols from in situ upgrading process reflected by the peak area percentages was higher than that from ex situ upgrading. The catalyst recycling tests showed that the prepared AC catalyst can be reused for three times in phenol-rich bio-oil production via catalytic microwave pyrolysis.

New Insight into the Mechanism of the Hydrogen Evolution Reaction on MoP(001) from First Principles

Molybdenum phosphide-based catalysts have recently exhibited excellent catalytic activities for the hydrogen evolution reaction (HER) in wide pH range conditions; the intrinsic reaction mechanism, on the other hand, has not been well established. Herein, by employing the MoP as the prototypical molybdenum phosphide-based catalyst, HER activities in both acid and neutral conditions were studied by conducting periodic density functional theory calculations. Thermodynamic analysis of hydrogen atoms absorbed on both P- and Mo-terminated surfaces were compared, as well as all the reaction energy and activation energy barriers for reactions involved in the HER process. Calculation results revealed that, in an acid condition, the Volmer-Heyrovsky and Volmer-Tafel reaction mechanisms were dominated on the P-terminated and Mo-terminated catalyst surfaces, where Heyrovsky and Volmer reactions were the rate-determining step, respectively. Additionally, water splitting was introduced to the current reaction mechanism and a small reaction activation energy barrier was revealed on the P-terminated surface. Besides, a relevant small activation energy was obtained in the Tafel reaction on the defect of the P-terminated surface in a neutral solution. Theoretical results proved that HER could take place readily on both P- and Mo-terminated catalyst surfaces via different reaction mechanisms in the acid condition from the view of atom scale. More important, computational results uncovered that HER could also occur on the P-terminated surface with the assistance of surface defect in the neutral condition, which sheds new light on the HER mechanism on transition metal phosphite-based catalysts. The doping effect on HER activity was further investigated in theory and calculation results, indicating that catalytic performance could be improved by substitutional doping of the Mo atom with metals such as Mn and W.