Sonil Nanda

Valorization of horse manure through catalytic supercritical water gasification.

The organic wastes such as lignocellulosic biomass, municipal solid waste, sewage sludge and livestock manure have attracted attention as alternative sources of energy. Cattle manure, a waste generated in surplus amounts from the feedlot, has always been a chief environmental concern. This study is focused on identifying the candidacy of horse manure as a next generation feedstock for biofuel production through supercritical water gasification. The horse manure was gasified in supercritical water to examine the effects of temperature (400-600°C), biomass-to-water ratio (1:5 and 1:10) and reaction time (15-45min) at a pressure range of 23-25MPa. The horse manure and resulting biochar were characterized through carbon-hydrogen-nitrogen-sulfur (CHNS), inductively coupled plasma-mass spectrometry (ICP-MS), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM). The effects of alkali catalysts such as NaOH, Na2CO3 and K2CO3 at variable concentrations (1-2wt%) were investigated to maximize the hydrogen yields. Supercritical water gasification of horse manure with 2wt% Na2CO3 at 600°C and 1:10 biomass-to-water ratio for 45min revealed maximum hydrogen yields (5.31mmol/g), total gas yields (20.8mmol/g) with greater carbon conversion efficiency (43.1%) and enhanced lower heating value of gas products (2920kJ/Nm(3)). The manure-derived biochars generated at temperatures higher than 500°C also demonstrated higher thermal stability (weight loss <34%) and larger carbon content (>70wt%) suggesting their application in enhancing soil fertility and carbon sequestration. The results propose that supercritical water gasification could be a proficient remediation technology for horse manure to generate hydrogen-rich gas products.

Fermentative production of butanol: Perspectives on synthetic biology

Apprehensions relating to global warming, climate change, pollution, rising energy demands as well as fluctuating crude oil prices and supply are leading to a shift in global interest to find suitable alternatives to fossil fuels. This review aims to highlight the many different facets of butanol as an advanced next-generation transportation biofuel. Butanol has fuel properties almost on a par with gasoline, such as high energy content, low vapor pressure, non-hygroscopic nature, less volatility, flexible fuel blends and high octane number. The paper reviews some recent advances in acetone-butanol-ethanol fermentation with special emphasis on the primary challenges encountered in butanol fermentation, including butanol toxicity, solvent intolerance and bacteriophage contamination. The mechanisms for butanol recovery techniques have been covered along with their benefits and limitations. A comprehensive discussion of genetic and metabolic engineering of butanol-producing microorganisms is made for the prospective development of industrially-relevant strains that can overcome the technical challenges involved in efficient butanol production.

Insights on pathways for hydrogen generation from ethanol

Growing apprehensions on greenhouse gas emissions, global warming, and pollution problems are directly related to fossil fuels consumption. To counteract these environmental issues, global efforts are being made to diversify energy supplies towards cleaner fuels, especially for the transportation sector. Hydrogen surpasses all other biofuels such as biodiesel, bio-oil, ethanol, and butanol because of its high energy content, no greenhouse gas emissions, rapid combustion properties, non-corrosive nature, and physical state. Hydrogen production from methane and methanol, through reforming reactions, has been thoroughly studied and these are well-entrenched industrial technologies. However, ethanol is an attractive feedstock for hydrogen production because it is less toxic than methanol and can easily be produced from renewable biomass. Interest in the conversion of ethanol to hydrogen through several thermochemical, hydrothermal, photochemical, and electrochemical technologies has grown recently. In this review, different thermochemical, hydrothermal, photochemical, and electrochemical technologies for ethanol to hydrogen conversion are comprehensively discussed. Ethanol conversion technologies reviewed in this paper include steam reforming, partial oxidation, autothermal reforming, alkaline-enhanced reforming, dehydrogenation, supercritical water gasification, photocatalysis, and electrocatalysis. Current advancements, technical challenges, and future perspectives of each technology are thoroughly discussed. This technical compilation brings together various techniques that are being explored for hydrogen production from ethanol.

PDMS/camphor soot composite coating: towards a self-healing and a self-cleaning superhydrophobic surface

A novel self-cleaning polymer composite with self-healing ability to self-repair after chemical and mechanical damage using readily available materials like polydimethylsiloxane (PDMS) and camphor soot particles is developed. With the optimal loading of the camphor soot particles, the composite coating on glass and stainless steel surfaces reveals self-cleaning properties with a water contact angle of 171°. We also demonstrate that any degradation of its surface energy under oxygen plasma etching can be recuperated, demonstrating the self-healing ability of the superhydrophobic surface. The fabricated PDMS/camphor soot hybrid coating exhibited excellent retention of superhydrophobicity against the impact of sand particles from a height of 10–70 cm. In addition, after being damaged chemically by strong acid treatment (1 M HNO3 solution), the coating can also restore its properties after a short thermal cycle. The quantitative measurement of mechanical properties of self-healing superhydrophobic surfaces is challenging due to their high surface roughness at the micro/nano-scale with a tolerance of low stress. In this work, we have conducted a detailed investigation of the mechanical responses of the camphor soot particle-incorporated PDMS composites by using atomic force microscopy (AFM). Using an AFM tip with a radius of approximately 10 nm, we have quantified different mechanical properties such as stiffness, the plastic work, and the effective adhesive work. Such versatile superhydrophobic surfaces can have wide applications ranging from underwater marine vessels to coating surfaces to protect them from moisture and unwanted penetration of water. These composite coatings are environmentally benign and can be readily coated on various substrates by simple spraying.

Ignition of hydrothermal flames

Supercritical water oxidation is one of the most promising technologies for complete oxidation of complex organic compounds. Flames in supercritical water, often referred to as hydrothermal flames, improve the oxidation rates of reactants in an organic waste stream. The ignition and control of flames in supercritical water could potentially be used to reduce the reaction time (from seconds to milliseconds) and enhance the thermochemical decomposition rates of recalcitrant molecules without the release of any harmful intermediates. This provides a platform to design compact reactors for processing complex organic waste followed by their conversion to valuable compounds. This paper reviews some notable work focused on the ignition and qualitative observations of hydrothermal flames as an environmentally friendly technology. More specifically, the review highlights the classification and characterization of hydrothermal flames with several demonstrations of laboratory scale (e.g., visual flame cell) and pilot scale (e.g., transpiring wall reactor) reactor configurations. The process parameters such as feed concentration, reaction temperature, oxidant temperature, oxidant flow rate, and transpiration flow properties (in the case of transpiring reactors) are comprehensively discussed for their influence on the ignition and stability of hydrothermal flames, and total organic carbon removal. In addition, the impact of these parameters on the performance of various flame reactors is presented. Finally, the paper also outlines some wide-ranging applications and challenges concerning the industrial utilization of hydrothermal flames.

Advancements and confinements in hydrogen production technologies

Hydrogen is recognized as one of the most promising energy carriers and an advanced fuel. This chapter gives an overview of different hydrogen production technologies involving thermochemical, electrochemical, and biological routes. The thermochemical route of hydrogen generation includes steam reforming, partial oxidation, autothermal reforming, gasification, and pyrolysis. The biological hydrogen production deals with the involvement of photosynthetic and photoheterotrophic bacteria and photoautotrophic algae. The chapter elaborates the advancements in fuel cells and electrochemically active bacteria responsible for hydrogen generation. The several uses of hydrogen in fuel cells, aviation fuel, and feedstock to synthesize biodiesel, ethanol, and other higher hydrocarbon-based fuels via Fischer-Tropsch catalysis and syngas fermentation are also discussed. The primary focus of this chapter is to evaluate the advantages and limitations of several hydrogen production methods based on the available technology options, feedstock selection, end uses, and economical aspects. Some of the breakthroughs and impediments in todays hydrogen market have been systematically reviewed.