Xuesong Zhang

Bio-based phenols and fuel production from catalytic microwave pyrolysis of lignin by activated carbons

The aim of this study is to explore catalytic microwave pyrolysis of lignin for renewable phenols and fuels using activated carbon (AC) as a catalyst. A central composite experimental design (CCD) was used to optimize the reaction condition. The effects of reaction temperature and weight hourly space velocity (WHSV, h(-1)) on product yields were investigated. GC/MS analysis showed that the main chemical compounds of bio-oils were phenols, guaiacols, hydrocarbons and esters, most of which were ranged from 71% to 87% of the bio-oils depending on different reaction conditions. Bio-oils with high concentrations of phenol (45% in the bio-oil) were obtained. The calorific value analysis revealed that the high heating values (HHV) of the lignin-derived biochars were from 20.4 to 24.5 MJ/kg in comparison with raw lignin (19 MJ/kg). The reaction mechanism of this process was analyzed.

Catalytic co-pyrolysis of lignocellulosic biomass with polymers: a critical review

The increasing demand for renewable chemicals and fuels requires the exploitation of alternative feedstock to replace petroleum-derived chemicals and fuels. Lignocellulosic biomass has been considered as the most promising feedstock for the production of sustainable biofuels. Catalytic fast pyrolysis (CFP) is more amenable to directly converting biomass into high quality biofuel. However, even in the presence of a highly efficient catalyst, the CFP of biomass can solely manufacture a low yield of aromatic hydrocarbon but a high formation of coke. The addition of a hydrogen-rich co-reactant (e.g. waste plastics) in CFP can significantly improve the yield of aromatics and lower the coke formation. Catalytic co-pyrolysis can also reduce the disposal of waste polymers (plastics and waste tires) in landfills, solve some environmental issues, and further increase energy security. In this regard, this article reviews the catalytic co-pyrolysis process from several points of view, starting from feedstock characteristics and availability, current understanding of the chemistry in non-catalytic co-pyrolysis, and focusing on the chemistry in the catalytic co-pyrolysis of biomass with various categories of polymers. Recent progress in the experimental studies on both the non-catalytic pyrolysis and catalytic co-pyrolysis of biomass with polymers is also summarized with the emphasis on the liquid yield and quality. In addition, reaction kinetics and several outlooks in the light of current studies are also presented in the review. Consequently, this review demonstrates both highlights of the remarkable achievement of catalytic co-pyrolysis and the milestones that are necessary to be garnered in the future.

Renewable gasoline-range aromatics and hydrogen-enriched fuel gas from biomass via catalytic microwave-induced pyrolysis

A novel pathway was investigated to produce gasoline-range aromatics and hydrogen-enriched fuel gas by microwave-induced pyrolysis of cellulose integrated with packed-bed catalysis in the presence of a solid phase catalyst. The employed catalyst was well-promoted ZSM-5 after the couplings of hydrothermal and calcined treatments, completely converting volatile vapors derived from microwave pyrolysis into aromatics and non-condensable gases. A central composite experimental design (CCD) was employed to investigate the effects of catalytic temperature and inverse weight hourly space velocity (WHSV)−1 on the pyrolysis-oils composition. It was observed that the chemical compounds of the upgraded bio-oils from catalytic microwave pyrolysis of cellulose were aromatic hydrocarbons, phenols, and aromatic oxygenates. Aromatic hydrocarbons that accounted for the largest selectivity of these compounds were in the range from 82.93 to 96.60% in bio-oils depending on alterations of catalytic conditions. Up to 48.56% selectivity towards aromatics in the upgraded bio-oil belongs to gasoline-range aromatics under the mild conditions. The maximum selectivity of aromatic hydrocarbons (96.60%) was gained at a packed-bed temperature of 500 °C and a WHSV−1 of 0.067 h. Gaseous results show that hydrogen was the dominant composition, occupying approximately 40 vol%. The high amounts of gasoline-range aromatics and valuable hydrogen are attributed to the technologies of microwave-assisted pyrolysis and ex situ catalysis. These findings from this study pave a new route for biorefinery industries to produce developed products (aromatics and hydrogen-rich gases) through microwave-induced technologies.

From lignocellulosic biomass to renewable cycloalkanes for jet fuels

A novel pathway was investigated to produce jet fuel range cycloalkanes from intact biomass. The consecutive processes for converting lignocellulosic biomass into jet fuel range cycloalkanes principally involved the use of the well-promoted ZSM-5 in the process of catalytic microwave-induced pyrolysis and RANEY® nickel catalysts in the hydrogen saving process. Up to 24.68% carbon yield of the desired C8–C16 aromatics was achieved by catalytic microwave pyrolysis at 500 °C. We observed that solvents could assist in the hydrogenation reaction of naphthalene; and the optimum result for maximizing the carbon selectivity (99.9%) of decalin was obtained from the reaction conducted in the n-heptane medium. The recovery of organics could reach ∼94 wt% after the extraction process. These aromatics in the n-heptane medium were eventually hydrogenated into jet fuel range cycloalkanes. Various factors were analyzed to determine the optimal result under mild conditions. An increased catalyst loading, reaction temperature, and prolonged time could enhance the hydrogenation reactions to improve the selectivity of jet fuel range cycloalkanes. Three types of hydrogenation catalysts (NP Ni, RANEY® Ni 4200, home-made RANEY® Ni) were chosen to evaluate the catalytic performance. The results indicated that the home-made RANEY® nickel is the optimal catalyst to obtain the highest selectivity (84.59%) towards jet fuel range cycloalkanes. These cycloalkanes obtained can be directly used as additives to synthesize the desired jet fuels by blending with other hydrocarbons. Hence integration of catalytic processes and conversion of lignocellulosic biomass paved a new avenue for the development of green bio-jet fuels over inexpensive catalysts under mild conditions.

Optimizing carbon efficiency of jet fuel range alkanes from cellulose co-fed with polyethylene via catalytically combined processes

Enhanced carbon yields of renewable alkanes for jet fuels were obtained through the catalytic microwave-induced co-pyrolysis and hydrogenation process. The well-promoted ZSM-5 catalyst had high selectivity toward C8-C16 aromatic hydrocarbons. The raw organics with improved carbon yield (∼44%) were more principally lumped in the jet fuel range at the catalytic temperature of 375°C with the LDPE to cellulose (representing waste plastics to lignocellulose) mass ratio of 0.75. It was also observed that the four species of raw organics from the catalytic microwave co-pyrolysis were almost completely converted into saturated hydrocarbons; the hydrogenation process was conducted in the n-heptane medium by using home-made Raney Ni catalyst under a low-severity condition. The overall carbon yield (with regards to co-reactants of cellulose and LDPE) of hydrogenated organics that mostly match jet fuels was sustainably enhanced to above 39%. Meanwhile, ∼90% selectivity toward jet fuel range alkanes was attained.

Synthesis of high-density jet fuel from plastics via catalytically integral processes

The present study was aimed at synthesizing JP-5 navy fuel from plastics through a novel pathway. The consecutive processes for manufacturing JP-5 navy fuel principally included the catalytic microwave-induced degradation of low-density polyethylene (a model compound of waste plastics) and the hydrotreatment of obtained liquid organics. The catalytic microwave degradation was conducted at the catalytic temperature of 375 °C and catalyst to feed ratio of 0.1. The carbon yield of the liquid organics from the catalytic microwave degradation was 66.18%, mainly consisting of a mixture of aromatic hydrocarbons and aliphatic olefins. Several variables, such as initial pressure and catalyst to reactant ratio, were employed to determine the optimal condition for the production of alternative jet fuels in the hydrotreating process. We observed that the aromatic hydrocarbons and aliphatic olefins as the precursors of jet fuels could be converted into jet fuel range aliphatic alkanes and cycloalkanes. The hydrotreated organics from the experiment conducted at the reaction temperature of 250 °C for 2 h included 31.23% selectivity towards aliphatic alkanes, 53.06% selectivity towards cycloalkanes, and 15% selectivity towards remaining aromatic hydrocarbons, which were consistent with the specifications of JP-5 navy fuel. In this regard, the catalytic microwave degradation of plastics and the hydrotreatment of obtained liquid organics can be regarded as a clear breakthrough to producing alternative jet fuels. From a commercial point of view, the catalytically integrated processes could be the most feasible for synthesizing advanced jet fuels (e.g. JP-5 navy fuel).

Development of a catalytically green route from diverse lignocellulosic biomasses to high-density cycloalkanes for jet fuels

This study reports a novel route to manufacture high-density cycloalkanes for jet fuels from diverse lignocellulosic biomasses. The consecutive processes for manufacturing high-density cycloalkanes primarily included the catalytic microwave-induced pyrolysis of diverse lignocellulosic biomasses (hybrid poplar, loblolly pine and Douglas fir) over a well-promoted ZSM-5 and a hydrogenation process in the presence of a RANEY® nickel catalyst. Two variables (catalytic temperature and catalyst-to-biomass ratio) were employed to determine the optimal conditions for the production of C8–C16 aromatics in the catalytic microwave-induced pyrolysis. The maximum carbon yield of the desired aromatics was 24.76%, which was achieved from the catalytic microwave-induced pyrolysis of hybrid poplar at 500 °C with the catalyst-to-biomass ratio of 0.25. We observed that the aromatics derived from catalytic microwave-induced pyrolysis in the n-heptane medium were completely hydrogenated into renewable high-density cycloalkanes for jet fuels. In the hydrogenation process, increasing the catalyst loading and reaction temperature could promote the selectivity to high-density cycloalkanes. The results indicated that hybrid poplar was the optimal feedstock for obtaining the highest selectivity (95.20%) towards high-density cycloalkanes. The maximum carbon yield of cycloalkane-enriched hyrogenated organics based on hybrid poplar was 22.11%. These high-density cycloalkanes with high selectivity can be directly used as additives in jet fuels, such as JP-5, JP-10 and RJ-5.

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.

Characterization of Surface Functional Groups in Corn Stover Biochar Derived from Microwave-assisted Pyrolysis

Abstract. In this study, the biochar was prepared by microwave assisted pyrolysis of corn stover at atmospheric pressure and different reaction temperatures and time. Central composite experimental design (CCD) was used in the optimization of volatile (bio-oil and syngas), biochar production, and the amount of carbon surface functional groups. Mineral and GC/MS analysis were used to study the pyrolysis of corn stover. Various types of oxygen containing functional groups (carbonyls, phenolics, lactones, and carboxyls) on the biochar were quantified by means of titrimetric techniques using a modified Boehm’s method. The chemical composition of the biochar was characterized by FTIR. The research result indicates that the surface area and functional groups of biochar were significantly influenced by the pyrolysis temperature and time. A prediction model was satisfactorily developed to describe the development of carbon surface functional groups. Modification and characterization of biochar surface functional groups is a new way to improve or extend their catalytic application in biomass conversion and bio-oil upgrading.