EFFECTS OF POROSITY ON RE-IGNITION CHARACTERISTICS OF A SURROGATE MATERIAL

This study is part of a larger project which aims at studying the re-ignition behaviour of charring solid fuels under fire conditions. The main objective of this part of the work was to investigate the role of material porosity on the re-ignition characteristics of the fuel. For this purpose, experiments were carried out on a set of surrogate ceramic samples to de-couple the pyrolysis and combustion processes from those associated with heat transfer. The surrogate samples were made out of magnesia silica ceramic with porosity levels of 72.9%, 53.5%, and 35%. Experiments were conducted in a modified cone calorimeter over a range of heat fluxes between 40 to 60 kW/m2. The re-ignition delay was found to be significantly affected by the material porosity. The higher the porosity, the longer the re-ignition delay time. For samples having the same porosity level, the re-ignition delay time was primarily a function of sample thickness and the external heat flux. Thicker samples generally showed shorter reignition delays. The results of this study will be used in future work to quantify the impact of porosity on the re-ignition behaviour of real samples

Catalytic conversion of glycerol to polymers in the presence of ammonia

In this contribution, the development of a process for the synthesis of potentially highly valuable polymeric products from the reaction of waste glycerol with ammonia is reported for the first time. The polymers were the result of a single step, continuous gas phase process, catalysed by an alumina-supported iron catalyst, operating under relatively mild reaction conditions. The solid product was characterised using 1D and 2D NMR spectroscopy, FTIR spectroscopy, qualitative chemical tests and elemental analysis. Characterisation revealed building blocks with unsaturated, amido and ester functionalities shaping a mixture of polymers. Nitrogen atoms were present in the main chain of the resultant polymers. NMR analyses of the polymer denotes the formation of structural defects such as unsaturation and branching; whilst the partial solubility of the polymer in solvents such as CDCl3 and THF is indicative of the formation of cross-linked structures. Insights into the mechanism of formation of these functional groups were based on the liquid and gas phase product distribution. Polymers with chain structures similar to those synthesised in this work are currently manufactured from fossil fuels and are widely used in biomedical applications not only because of their architecture but also due to their response to changes in pH and temperature

Formation of chlorobenzenes by oxidative thermal decomposition of 1,3-dichloropropene

We combine combustion experiments and density functional theory (DFT) calculations to investigate the formation of chlorobenzenes from oxidative thermal decomposition of 1,3-dichloropropene. Mono- to hexa-chlorobenzenes are observed between 800 and 1150. K, and the extent of chlorination was proportional to the combustion temperature. Higher chlorinated congeners of chlorobenzene (tetra-, penta-, hexa-chlorobenzene) are only observed in trace amounts between 950 and 1050. K. DFT calculations indicate that cyclisation of chlorinated hexatrienes proceeds via open-shell radical pathways. These species represent key components in the formation mechanism of chlorinated polyaromatic hydrocarbons. Results presented herein should provide better understanding of the evolution of soot from combustion/pyrolysis of short chlorinated alkenes

Formation of dioxin during smoldering of CCA treated wood char

Production of dioxin during the smoldering of wood char containing chromated copper arsenate (CCA) was investigated. Preliminary results are presented for the smoldering of treated wood char at 300 and 400°C, as a function of char loading, smoldering time and inlet oxygen concentrations. PCDF (mainly Cl 4DF) were the preferred products of smoldering, and the results indicate the dependence of PCDD/F yields on competing formation/dechlorination reactions. Early periods of mass conversion favored PCDD/F formation, but with increasing mass loss, dechlorination and decomposition began to dominate. While the amounts detected were not particularly high (maximum yield of 95 ng TEQ/kg char oxidized), PCDD/F formation in wood fires may drastically increase with CCA combined with inorganic and organic chlorine contaminants

Structure, Stability, and (Non)Reactivity of the Low-Index Surfaces of Crystalline B2O3−I

Diboron trioxide (B2O 3) assumes critical importance as an effective oxidation inhibitor in prominent chemical applications. For instance, it has been extensively used in electrolysis and ceramic/glass technology. Results are presented of accurate quantum mechanical calculations using the PW1PW hybrid HF/DFT functional of four low- index surfaces of the low-pressure phase of B2O : (101), (100), (011), and (001). Bond lengths, bond angles, and net Mulliken charges of the surface atoms are analyzed in detail. Total and projected density of states as well as surface energies are discussed. The occurrence of tetrahedral BO 4 units on the lowest energy structures of two of these surfaces has been demonstrated for the first time. The corresponding surface orientations incur larger energies in reference to the two orientations featuring only BO3 units. All of the four investigated lowest energy structures have no dangling bonds, which reasonably relates to the experimentally observed low reactivity of this compound. Findings in this paper pave the way for potential interest in the perspective of future studies on the surfaces of amorphous B2O3, as well as on the hydroxylation of both crystalline and amorphous B2O3

Controlling NOx emission from post-blast process gases

This study investigates effect of the pH on nitric oxides (NOx) removal. A spray tower has been used to study the absorption of nitrogen oxides in both acidic and alkaline solution of sodium chlorite (NaClO2). Sodium chlorite was used as an oxidant in order to oxidise NO to NO2, which is highly soluble in aqueous phase. NO was oxidized to NO2 followed by NO2- and ClO2 to ClO2- in liquid phase respectively. The latter was found to be reduced to Cl- and ClO- . Varying pH of the solution form acidic and alkaline phases, pH (4-12), which is influential in the efficiency of NOx removal, was studied. According to the experiments carried out in this study, alkaline medium was found to be more reliable than acidic one, and 100% NO with 86% NOx removal was observed in ambient conditions. The main reason is attributed to hydrolysis of N2O4 in higher pH (basic). Experimental results demonstrate the feasibility of the aqueous solution of sodium chlorite for NOx removal

Effect of Porosity on Re-ignition Characteristics of a Surrogate

ABSTRACT This study is part of a larger project which aims at studying the re-ignition behaviour of charring solid fuels under fire conditions. The main objective of this part of the work was to investigate the role of material porosity on the re-ignition characteristics of the fuel. For this purpose, experiments were carried out on a set of surrogate ceramic samples to de-couple the pyrolysis and combustion processes from those associated with heat transfer. The surrogate samples were made out of magnesia silica ceramic with porosity levels of 72.9%, 53.5%, and 35%. Experiments were conducted in a modified cone calorimeter over a range of heat fluxes between 40 to 60 kW/m 2 . The re-ignition delay was found to be significantly affected by the material porosity. The higher the porosity, the longer the re-ignition delay time. For samples having the same porosity level, the re-ignition delay time was primarily a function of sample thickness and the external heat flux. Thicker samples generally showed shorter reignition delays. The results of this study will be used in future work to quantify the impact of porosity on the re-ignition behaviour of real samples

Reaction of nitrous oxide with methane to produce synthesis gas (CO + H2); a thermodynamic and catalytic analysis

A thermodynamic and kinetic (experimental) study of N2O with CH4 to synthesis gas (H2+CO) formation was investigated under various reaction conditions. The experimental study was carried out over Co-ZSM-5 as catalyst in a fixed bed reactor. The effect of temperature (270 °C -570 °C) and molar feed ratio (N2O/CH4 = 1, 3, and 5) was examined in order to determine conditions for maximizing H2 yield. The results show that for the molar feed ratios (N2O/CH4) of 1 and 3, N2O is the limiting reactant. The thermodynamic and kinetic analyses of the reaction having a limiting N2O reactant in reactant feed (N2O/CH4) shows that H2 yield steadily increased with increase in temperature and the level of CH4 conversion. Furthermore, the maximum attainable (from thermodynamic calculations) H2 yield at 550°C is about 20%. While thermodynamic predictions of H2 yield drops to zero in presence of excess of N2O in reactant feed (N2O/CH4 = 5). Over Co-ZSM-5 catalyst and with a molar reactant feed ratio (N2O/CH4) of 5, the H2 yield first increases to 10 % with rise in temperature and then drops to zero at relatively higher range of temperatures (above 425°C). The synthesis gas production from partial oxidation of CH4 with N2O may not be an alternative route to existing industrial practice; however, the fractional substitution of O2 with N2O in the partial oxidation of CH4 could lead to emission reductions. This will also give a new route for H2 generation

The effect of synthesis gas composition on the performance of Ni-based solid oxide fuel cells

An increased interest in using hydrocarbons in solid oxide fuel cells for the production of power has led to research into operation on synthesis (syn) gas, a mixture of hydrogen and carbon monoxide. Hydrocarbons are typically reformed, either internally or in an external reformer prior to the fuel cell, producing syngas with various H2:CO ratios depending on the hydrocarbon used. This paper examines the effect of varying the H2:CO ratio with respect to C1 to C4 steam reforming reactions and additionally a mixture containing a higher ratio of carbon monoxide. It was found that there was no significant relationship between cell performance and H2:CO ratio when a high feed rate was employed. For low flow rates, however, the high carbon monoxide concentration resulted in a significant decrease in cell performance. It was determined that this was caused by reversible carbon deposition as opposed to a decrease in carbon monoxide reactivity

Structural thermal stability of graphene oxide-doped copper-cobalt oxide coatings as a solar selective surface

3d transition metal oxides based thin film coatings such as copper-cobalt oxides exhibit high absorption in the visible region and low emittance in the infra-red to far-infra-red region of the solar spectrum which is favourable for use as potential selective surface materials in photothermal devices. These materials have the potential to minimize heating while increasing absorption in the operative spectrum range and therefore achieve higher solar selectivity. A series of mixed copper-cobalt metal spinel oxides (CuxCoyOz) doped with graphene oxide thin films were deposited on commercial grade aluminium substrates using a sol–gel dip-coating technique at an annealing temperature of 500 °C in air for 1 h. Characterizations of the synthesized films were carried out by high temperature synchrotron radiation X-ray Diffraction (SR-XRD), UV-Vis, Fourier Transform infrared spectroscopy (FTIR) and X-ray photoelectron microscopy (XPS) techniques. High thermal stability of coatings with multiple phases, binary and ternary metal oxides, was defined through SR-XRD study. FTIR analysis shows moderate (<80%) to high (up to 99%) reflectance in the infra-red region while the UV-Vis investigations demonstrate that, in the visible region, solar absorption increases gradually (up to 95%) with the addition of graphene oxide to the CuxCoyOz coatings. With the incorporation of 1.5 wt% of graphene oxide to the copper-cobalt oxide coatings, a high solar selectivity of 29.01 (the ratio of the average solar absorptance in visible and the average thermal emittance in infra-red to far infra-red region; α/ε) was achieved