Showing papers by "Ravikrishnan Vinu published in 2021"

Pyrolysis of electronic waste and their mixtures: Kinetic and pyrolysate composition studies

Abstract: Electronic waste (e-waste) constitutes an important component of solid waste, and recovering valuable chemicals and resources from it holds a high priority in solid waste management. The various chemical functionalities present in the organic fraction of e-waste can be converted to valuable chemicals and fuel molecules by pyrolysis process. In this study, non-isothermal pyrolysis of waste printed circuit board (PCB), waste keyboard keys (KB), and their equal composition mixture is conducted in a thermogravimetric analyzer at different heating rates. The kinetic analysis was carried out using isoconversional method of Vyazovkin and the multi-Gaussian distributed activation energy model (DAEM). The average apparent activation energies of pyrolysis of PCB, PCB: KB, and KB, determined using the Vyazovkin method, were 188.4, 167.6, and 169 kJ mol−1, respectively. The apparent activation energy determined using the DAEM varied in a wide range owing to the decomposition of multiple pseudo-components. Analytical pyrolysis coupled with gas chromatograph/mass spectrometer (Py-GC/MS) was used to identify the pyrolysates from PCB, KB, and their mixtures at 500 °C. The major pyrolysate functional groups from PCB were phenolic derivatives (36%), oxygenates (26%), and phenyl phosphates (14.4%), while KB pyrolysis yielded aromatics (52%) containing styrene as the major compound. Pyrolysis of mixtures resulted in a net increase in the selectivity to aromatics with a concomitant decrease in oxygenates suggesting dehydration and decarboxylation to be the major reactions. A significant amount of nitriles was produced from the pyrolysis of mixtures owing to the decomposition of acrylonitrile-butadiene-styrene plastic that constitutes KB.

Catalytic Hydrodeoxygenation of Lignin-Derived Oxygenates: Catalysis, Mechanism, and Effect of Process Conditions

Abstract: The high oxygen content of pyrolysis bio-oil with many organic functional groups in it limits its direct application as a blendstock. The upgradation of biomass-derived oxygenates into renewable fu...

Fast pyrolysis kinetics of lignocellulosic biomass of varying compositions

Abstract: This study is focused on evaluating apparent kinetics of fast pyrolysis of different lignocellulosic viz, biomass rice straw (RS), palm wood (PW) and empty fruit bunch (EFB) specifically. The goal of the study is to investigate the effect of biomass compositionon kinetics, time evolution of pyrolysis vapors and the production of major bio-oil components during the fast pyrolysis of biomass. The isothermal mass loss data were generated at different pyrolysis times between two and sixty seconds in the temperature range of 400-700°C. The data generated were then analyzed using various reaction models viz first-order model, diffusion models, contracting cylinder model and Avrami-Erofeev model to determine the rate constants and the rate parameters. Kinetic compensation effect was established using a large number of kinetic data reported in the literature to validate our results. The time evolution of major functional groups in the pyrolysates was analyzed using in-situ analytical pyrolyzer coupled with Fourier transform infrared spectrometer (Py-FTIR), and evolution of the volatiles was observed in time range of 5-60 seconds. Increase in pyrolysis temperature led to faster evolution and of volatiles as evidenced by shifting of maximum rate of vapor evolution to shorter time periods.

Characterization, bioenergy value, and thermal stability of biochars derived from diverse agriculture and forestry lignocellulosic wastes

Abstract: In the present study, seven diverse biomasses of Indian origin were characterized and pyrolyzed at 450 °C to produce biochars. The biochars were thoroughly characterized using a variety of techniques to assure their potential energy and environmental and agricultural applications. Biochars derived from crop wastes with low lignin content, viz., rice husk biochar (RHB), rice straw biochar (RSB), maize stover biochar (MSB), and sugarcane biochar (SCB), possessed high ash content, high pH, and low fixed carbon making them suitable for soil amelioration. RSB, RHB, and MSB recorded high cation exchange capacity, making their potential utilization as liming material and removal of heavy metal contaminants. Elemental O/C ratios for all biochars, except maize stover biochar, were in the range of 0.27–0.32, which showed better stability and half-life period. Thermogravimetric analysis (TGA) was carried out to evaluate the thermal stability of biochars up to 900 °C, and the overall mass loss varied in the range of 16–27 wt%. Biochars from eucalyptus (EB), lantana (LB), and pine needle (PNB) were found to have high higher heating values (HHVs) (23–28 MJ/kg), higher fixed carbon, and lower ash content. Correlations were constructed between HHV of biochars and their volatile matter, ash, and fixed carbon content with high but negative correlation with ash content. Rice straw, rice husk, maize stover, and sugarcane trash were poor substrates, as the resultant biochars contained ≤ 60 wt% fixed carbon, high ash, and a relatively low HHV. It is shown that RHB, RSB, MSB, and SCB can be potential materials for soil amendment and plant nutrient, while PNB, LB, and EB are suitable for renewable solid fuel purpose.

Evidence of interactions in microwave-assisted co-pyrolysis of different varieties of coals

Abstract: In this study, microwave-assisted co-pyrolysis of blends of Indonesian coal (IC) with Indian medium ash coal (MAC), Indian high ash coal (HAC) and coking coal (CC) was performed to evaluate the product yield and quality of the pyrolysis tar, and to understand the interactions during co-pyrolysis. The tar yields from pyrolysis of individual coals, viz., IC, HAC, MAC and CC were 26 ± 3 wt%, 14 ± 2 wt%, 12 ± 2 wt% and 11 ± 2 wt%, respectively. In co-pyrolysis, tar yields decreased with decrease in IC fraction in the mixture. Importantly, the experimental yields of products were similar to that calculated using the mixture rule. However, interactions were evident in the gas and char yields from pyrolysis of IC-rich mixtures, and the deviation from calculated values was in the range of 3–5 wt%. Pyrolysis tar from IC predominantly contained phenols, whereas tars from HAC, MAC, and CC contained aromatic hydrocarbons, phenols and aliphatic hydrocarbons. The interactions were evidenced in the form of enhanced selectivity to naphthalene derivatives and polyaromatic hydrocarbons with a concomitant reduction in the selectivity to simple phenols in the coal tar. Interactions were predominant in equal composition and IC-rich mixtures of IC:HAC, IC:MAC and IC:CC, which is due to the early formation of char via decomposition of IC. Hydrogen and methane constituted a major fraction of pyrolysis gases from MAC, HAC and CC and their blends, while the pyrolysis gas from IC was rich in H2 and CO2. Higher heating values of coal chars varied in the range of 21–27 MJ kg−1.

Superior photocatalytic removal of metamitron and its mixture with Rhodamine B dye using combustion synthesized TiO2 nanomaterial

Abstract: In this study, photocatalytic degradation of a herbicide, metamitron, was carried out using combustion synthesized nano-TiO2. The synthesized catalyst was characterized using X-ray diffraction, porosimetry and UV-diffuse reflectance spectroscopy. The combustion synthesized catalyst showed lower crystallite size, better surface area and narrower band-gap compared to the commercial TiO2. The effect of catalyst loading, initial concentration of metamitron, pH and presence of inorganic ions on the extent of degradation was studied. The pseudo first order rate constant of metamitron degradation using combustion synthesized TiO2 was 1.5–2.5 times higher than that using commercial TiO2 at different initial concentrations of metamitron. The effect of another component, Rhodamine-B dye, on the degradation of metamitron was also probed in this study. The rate of degradation of both metamitron and Rhodamine B were high when the combined system was treated. The degradation by-products were tracked using liquid chromatograph/mass spectrometer, and a possible degradation pathway is proposed.

Catalytic hydrogenolysis of lignin to phenols: Effect of operating conditions on product distribution

Abstract: Lignin is a three-dimensional, amorphous, polyphenolic and aromatic-rich material linked by aryl ether, biphenyl and diaryl ether bonds, and is a primary recalcitrant molecule in lignocellulosic biomass Unlocking valuable chemicals and fuel molecules from lignin requires the cleavage of typical inter-unit linkages like β─O─4, α─O─4 and 4─O─5 in a selective manner Catalytic hydrogenolysis and hydrodeoxygenation are promising techniques to produce valuable chemicals and hydrocarbons in high yields and selectivities Deriving phenolic derivatives such as guaiacol, alkyl guaiacol, guaiacyl alcohols, and syringyl alcohols is of great interest in lignin depolymerization This perspective article will highlight the importance of catalyst structure, active metal, nature of support, solvent, and operating conditions to obtain phenolic compounds from a variety of lignins via catalytic hydrogenolysis Tuning the acidity of the catalyst is shown to influence its activity, and to curb the unwanted repolymerization and char forming reactions Finally, the stability and recyclability of the catalysts are also evaluated to develop a sustainable lignin valorization approach

Hydrodeoxygenation of Bio-Oil from Fast Pyrolysis of Pinewood Over Various Catalysts

Abstract: Fast pyrolysis is the most promising technique for the production of biomass-derived fuels, which is a substitute for petroleum-based fuel oil. Catalytic upgrading of pyrolysis vapours from biomass improves the quality of bio-oil to a greater extent by deoxygenation so that the upgraded bio-oil can be used as a hydrocarbon fuel. This work is mainly focused on studying the effect of various catalysts such as hierarchical HZSM-5 zeolites of different Si/Al ratios, commercial HZSM-5, and W2C/γ-Al2O3, on hydrodeoxygenation of organic compounds from pinewood pyrolysis. Catalytic hydropyrolysis experiments were conducted in an analytical pyrolyzer with ex-situ catalytic upgrading zone, which was connected to a gas chromatograph/mass spectrometer. Hierarchical zeolites exhibited significant deoxygenation activity producing aromatic hydrocarbons. The degree of deoxygenation had a good correlation with the acidity of the zeolites. Hierarchical HZSM-5 (20) produced aromatic hydrocarbons at ~88% selectivity. Furthermore, unconventional W2C/γ-Al2O3 serves as a potential hydrodeoxygenation catalyst, producing 97% selectivity to hydrocarbons. In addition, W2C/γ-Al2O3 overcomes the drawback of coke formation on acidic sites of zeolites.

Double Dielectric Barrier Discharge-Assisted Conversion of Biogas to Synthesis Gas

Abstract: In the recent decade, the use of plasma technology for dry reforming of methane has gained significant interest. Owing to the adverse effects caused by the greenhouse gases like CO2 and CH4 on climate change, the valorization of these pollutants is imperative, and is also a challenging task. The current study focuses on developing a double dielectric barrier discharge (DDBD) reactor for the conversion of CO2–CH4 mixture to synthesis gas (H2 + CO). The non-thermal plasma was generated using two co-planar quartz electrodes with the outer one wrapped with copper tape that was grounded, and the inner stainless steel rod connected to a high-voltage source. A discharge gap of 2 mm, and a discharge length of 70 mm were maintained. The effects of specific energy input (SEI) and CO2:CH4 composition on the conversion of CO2 and H2/CO ratio were studied. The power dissipated in the reactor was calculated from the Lissajous plot by measuring the instantaneous charge deposited inside the discharge volume. The effective conversion of CO2 increased with increasing SEI, and it was maximum for CH4:CO2 of 50:50 (vol.%/vol.%). These are attributed to higher residence time of CO2, which favors the production of CO and O by electron-induced dissociation, and electron dissociative recombination reactions.