Dengle Duan

Ex-situ catalytic co-pyrolysis of lignin and polypropylene to upgrade bio-oil quality by microwave heating

Microwave-assisted fast co-pyrolysis of lignin and polypropylene for bio-oil production was conducted using the ex-situ catalysis technology. Effects of catalytic temperature, feedstock/catalyst ratio, and lignin/polypropylene ratio on product distribution and chemical components of bio-oil were investigated. The catalytic temperature of 250°C was the most conducive to bio-oil production in terms of the yield. The bio-oil yield decreased with the addition of catalyst during ex-situ catalytic co-pyrolysis. When the feedstock/catalyst ratio was 2:1, the minimum char and coke values were 21.22% and 1.54%, respectively. The proportion of cycloalkanes decreased and the aromatics increased with the increasing catalyst loading. A positive synergistic effect was observed between lignin and polypropylene. The char yield dramatically deceased and the bio-oil yield improved during co-pyrolysis compared with those during lignin pyrolysis alone. The proportion of oxygenates dramatically and the minimum value of 6.74% was obtained when the lignin/polypropylene ratio was 1:1.

Fast microwave-assisted ex-catalytic co-pyrolysis of bamboo and polypropylene for bio-oil production

The ex-catalytic co-pyrolysis of bamboo and polypropylene (PP) with HZSM-5 was investigated with microwave assistance. The influences of catalytic temperature, feedstock/catalyst ratio, and bamboo/PP ratio on the product yields and chemical components of bio-oil from the co-pyrolysis were studied. When the catalytic temperature, feedstock/catalyst ratio, and bamboo/PP ratio were 250 °C, 1:2, and 2:1, respectively, the bio-oil yield reached its maximum value at 61.62 wt%. The oxygenate proportion compounds decreased with increasing catalyst content. The PP addition improved the proportions of aromatics and naphthenic hydrocarbons. The bio-oil was upgraded significantly from the jet fuel perspective. A synergistic effect also existed between bamboo and PP.

Microwave-assisted acid pretreatment of alkali lignin: Effect on characteristics and pyrolysis behavior

This study performed microwave-assisted acid pretreatment on pure lignin. The effects of microwave temperature, microwave time, and hydrochloric acid concentration on characteristics and pyrolysis behavior of lignin were examined. Results of ultimate analysis revealed better properties of all pretreated samples than those of raw lignin. Fourier transform infrared spectroscopy analysis showed breakage of βO4 bond and aliphatic side chain, decrease in OH groups, and formation of CO groups in pretreatment. Microwave temperature exerted more significant influence on lignin structure. Thermal stability of treated lignin was improved and insensitive to short microwave time and acid concentration under mild conditions. Resulting from improved alkyl-phenols and decreased alkoxy-phenols, microwave-assisted acid pretreatment of lignin yielded bio-oil with excellent quality. Total yield of phenols in pyrolysis vapors (200 °C) improved to 14.15%, whereas that of guaiacols decreased to 22.36%. This study shows that microwave-assisted acid pretreatment is a promising technology for lignin conversion.

Hydrothermal pretreatment of bamboo sawdust using microwave irradiation

In the present study, the effect of temperature and residence time during microwave hydrothermal pretreatment (MHT) on hydrochar properties and pyrolysis behaviors was investigated. Experimental results indicated that higher heating value (HHV) and fixed carbon content gradually increased with increased pretreatment severity. Obvious reduction of oxygen content was found under MHT at 230°C-15min and 210°C-35min. Although lower mass yield was observed under severe conditions, corresponding energy yield was relatively higher. Crystallinity indexes of hydrochar demonstrated an upward trend with increased residence time. Unlike hydroxyl group, dissociation of acetyls was more favorable under prolonged residence time rather than increased temperature. Peaks in thermogravimetric and derivative thermogravimetric curves shifted to higher temperature region under severe conditions, indicating better thermal stability. Py-GC/MS analysis suggested that acids content was decreased but sugars increased with increased MHT severity. Moreover, compared to temperature, residence time was mainly responsible for acetic acid formation.

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 40.00 wt.% was obtained at 200 °C for 60 min with 0.5 M hydrochloric acid. As pretreatment temperature, reaction time and acid concentration increased, respectively, the relative contents of phenols, diesel fraction (C12 + aliphatics), 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 29.92-42.21 wt% of upgraded liquid oil was achieved under varied pretreatment conditions. Char yield decreased from 32.44 wt% for untreated control to 24.35 wt% for the 150 °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.

Ex-situ catalytic upgrading of vapors from fast microwave-assisted co-pyrolysis of Chromolaena odorata and soybean soapstock

Fast microwave-assisted catalytic co-pyrolysis of Chromolaena odorata (C. odorata) and soybean soapstock with HZSM-5 as an ex-situ catalyst was investigated. Effects of catalytic temperature, feedstock: catalyst ratio and C. odorata: soybean soapstock ratio on the yield and composition of the bio-oil were discussed. Results showed that catalytic temperature greatly influenced the bio-oil yield. Co-pyrolysis of C. odorata and soybean soapstock improved the bio-oil yield, and the maximum bio-oil yield of 55.14% was obtained at 250 °C. However, the addition of HZSM-5 decreased bio-oil yield but improved the quality of bio-oil. Moreover, the proportion of oxygen-containing compounds decreased dramatically with the addition of soybean soapstock. The C. odorata: soybean soapstock ratio of 1:2 and feedstock: catalyst ratio of 2:1 were the optimal condition to upgrade the bio-oil. In addition, the resulted biochar contained various essential elements and could be used as soil repair agent.

Catalytic fast pyrolysis of torrefied corn cob to aromatic hydrocarbons over Ni-modified hierarchical ZSM-5 catalyst

Catalytic fast pyrolysis (CFP) of torrefied corn cob using Ni-modified hierarchical ZSM-5 catalyst was conducted in this study. The prepared catalysts were characterized by N2 adsorption and desorption (N2-BET), X-ray diffraction (XRD), and temperature-programmed desorption of NH3 (NH3-TPD). NaOH solution treatment resulted in the lower peak intensities of hierarchical ZSM-5 catalyst in the XRD patterns while Ni modification improved the catalyst framework. In addition, NaOH solution treatment created some mesopores or macropores, but the incorporation of Ni reduced BET surface area and volume of micropores. Though the addition of Ni lowered the acidity of catalyst, Ni-modified hierarchical ZSM-5 catalyst led to higher yields and of aromatic hydrocarbons. What is more, hierarchical ZSM-5 catalysts significantly improved the selectivities of mono-aromatics. Kinetic analysis shows that CFP of torrefied corn cob was second-order reaction and the addition of Ni can obtain a lower activation energy compared with hierarchical ZSM-5 catalyst.

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.