Publications

To produce hydrochar with less volatile matter (VM) and more fixed carbon (FC) to increase its stability, this study compared the hydrothermal carbonization (HTC) of hen (HM) and swine (SM) manures at typical HTC sub-critical temperature of 210 °C and slightly super-critical temperature of 400 °C. Physico-chemical properties such as proximate analysis; ultimate analysis; Brunauer–Emmett–Teller (BET) surface area; higher heating value (HHV); chemical oxygen demand (COD); and inorganic nutrients of hydrochar, gaseous, and liquid products were determined. As expected, both VM and yield decreased with temperature. The heats of HTC reactions were estimated to be exothermic, ranging from −5.7 to −8.6 MJ/kg. The FC approximately doubled, while VM significantly decreased with a yield of 42.7%, suggesting the high potential of producing more stable hydrochar via near-critical HTC (NCHTC) treatment of SM. Additional work is needed before recommendations on carbonization temperatures can be made. Specifically, there is a need to experimentally investigate how the chars produced from each carbonization condition influence plant growth and soil emissions.

Biogases including landfill gas (LFG) continue to be a vital renewable energy source, with a methane potential of approximately eight million tons/yr which can displace about 5% of current natural gas consumption in the electric power sector and 52% in the transportation sector. However, trace contaminant volatile methyl siloxanes (VMS) present in LFG causes deterioration of combustion engines. Conventional technologies for siloxane require periodic media replacement, is expensive and re-enters the waste cycle. In this study, dielectric barrier discharge was applied on pure streams of D4 (octamethylcyclotetrasiloxane), L3 (octamethyltrisiloxane) and on mixtures of D4 and L3 in a tubular reactor using helium as carrier gas. The goal is to determine the experimental conditions under which the removal of siloxane as, polydimetylsiloxane (PDMS), could be optimized; PDMS is commonly used in biomedical research, medical equipment as well as in electronic sealants. The discharge influence was explored over varying durations and flow rates, with most of the removal occurring in the first 20 minutes. Maximum removal of ~80% for D4 and ~50 % for L3 was achieved at the highest gas flow rate of 500 sccm. Further analysis is focused on determining kinetic rate constants for removal and PDMS generation. Preliminary operations with a pilot scale modular demonstration unit with planar electrodes has been completed that can utilize atmospheric air with other LFG components instead of helium as a discharge medium.

Introduced in the literature in 1913 by Bergius, who at the time was studying biomass coalification, hydrothermal carbonisation, as many other technologies based on renewables, was forgotten during the “industrial revolution”. It was rediscovered back in 2005, on the one hand, to follow the trend set by Bergius of biomass to coal conversion for decentralised energy generation, and on the other hand as a novel green method to prepare advanced carbon materials and chemicals from biomass in water, at mild temperature, for energy storage and conversion and environmental protection. In this review, we will present an overview on the latest trends in hydrothermal carbonisation including biomass to bioenergy conversion, upgrading of hydrothermal carbons to fuels over heterogeneous catalysts, advanced carbon materials and their applications in batteries, electrocatalysis and heterogeneous catalysis and finally an analysis of the chemicals in the liquid phase as well as a new family of fluorescent nanomaterials formed at the interface between the liquid and solid phases, known as hydrothermal carbon nanodots.

Hydrothermal carbonization (HTC) is a wet, low temperature thermal conversion process that continues to gain significant attention for the sustainable generation of value-added solid, liquid, and gas products from organic waste streams. Although it is well documented that both waste properties (e.g., elemental composition) and carbonization process conditions influence hydrochar properties, their specific influence on the total energy that can be recovered using HTC remains unclear. Non-linear random forest models were developed based on data collected from HTC-related literature to describe hydrochar yield and energy content, both of which are required to determine the total energy recovered in the hydrochar. Results indicate that total recoverable energy from organic wastes using HTC is correlated with feedstock carbon content; overall, the total energy content for feedstocks with carbon contents ranging from approximately 40 - 48% are similar. In addition, the total energy that can be recovered from the feedstock remains fairly constant when the initial solids concentrations are greater than 20%. Reaction time appears to have little influence on total recoverable energy from each feedstock at reaction times greater than approximately 150 min, while increases in reaction temperature result in a slight decline in total recoverable energy because of decreases in hydrochar yields at higher temperatures.

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Atmospheric pressure dielectric barrier discharge (DBD) plasma operating in octamethylcyclotetrasiloxane (D4)-helium gas mixture was studied as a prospective method for the reformation of the organosilicon compounds in the carrier stream. It was found that with the application of DBD, a significant amount of D4 precipitates out of the carrier stream in the form of a white residue on the reactor walls. Structural characterization of this residue with x-ray photoelectron and nuclear magnetic resonance spectroscopy revealed that the deposits are primarily composed of a linear chained polymerized form of D4 referred to as polydimethylsiloxane. The dependency of the carrier gas flow rate on the removal rate of D4 from the helium carrier gas was investigated for five different flow conditions. Solvent absorption with gas chromatography and mass spectrometry were used to deduce the concentration of D4 in the effluent from the reactor and hence the siloxane reformation ratio. A maximum of  80% conversion of D4 in the helium stream was achieved.

Active research on biomass hydrothermal carbonization (HTC) continues to demonstrate its advantages over other thermochemical processes, in particular the interesting benefits that are associated with carbonaceous solid products, called hydrochar (HC). The areas of applications of HC range from biofuel to doped porous material for adsorption, energy storage, and catalysis. At the same time, intensive research has been aimed at better elucidating the process mechanisms and kinetics, and how the experimental variables (temperature, time, biomass load, feedstock composition, as well as their interactions) affect the distribution between phases and their composition. This review provides an analysis of the state of the art on HTC, mainly with regard to the effect of variables on the process, the associated kinetics, and the characteristics of the solid phase (HC), as well as some of the more studied applications so far. The focus is on research made over the last five years on these topics.