Gayatri Yadavalli

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.

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.

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.

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.

A thermal behavior and kinetics study of the catalytic pyrolysis of lignin

The aim of the present study is to convert lignin into bio-based phenols by catalytic pyrolysis using activated carbon (AC) as a catalyst. The thermal decomposition behavior of lignin pyrolysis was investigated using a thermogravimetric analyzer (TGA). The heating rate played a significant role in lignin thermal degradation, the mass loss of lignin in pyrolysis increased with the increase of heating rate. The reaction kinetics of lignin pyrolysis was determined and compared using microwave and conventional heating, a second-order reaction mechanism fitted well for lignin pyrolysis, and the results revealed that the activation energy for catalytic microwave pyrolysis of lignin was 7.32 kJ mol−1, which was remarkably lower than that for conventional pyrolysis of lignin (59.75 kJ mol−1). The reaction mechanism of this process was 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.