Waiting Time of Public Transport Passengers in Jordan: Magnitude and Cost

Aim: This paper is a research study investigating the magnitude and cost of waiting time as experienced by public transport users in Jordan. This study also used spatial analysis to measure services provided for public transport routes according to the average waiting time. Methods: The data for waiting time of public transport users were collected using field observation and a professional spatial analysis applied to identify several locations experiencing short time delays. Results: This study found a relationship between the total costs of waiting time, including wasted time and money, and revealed that the money spent by the passengers was more than their average monthly income. Conclusion: The findings can be used as valuable information for researchers, government policy-makers, and transport agencies to firstly, develop more punctual public transport modes; and secondly, manage public transport trips to minimize time delays

Modern microwave methods in solid state inorganic materials chemistry: from fundamentals to manufacturing

No abstract available

Thermodynamic analysis on the oxidative pyrolytic treatment of electric arc furnace Dust–TBBA blends

This contribution reports a thermodynamic assessment for the bromination of electric arc furnace dust (EAFD) by-products sourced from thermal degradation of tetrabromobisphenol A (TBBA); i.e., the most widely deployed brominated flame retardant. Upon TBBA’s pyrolysis, HBr is released in conjunction with several volatile organic compounds leaving a solid carbonaceous residue. EAFD contains appreciable quantities of zinc, iron, and lead oxides. These oxides can react with HBr to form volatile metal bromides when the EAFD is added to the TBBA as a bromination agent. The selective bromination of zinc and lead contained in EAFD was thermodynamically evaluated under both oxidative and inert pyrolytic conditions while considering the effects of several variables. These factors span temperature, loads of TBBA, the presence of oxidizing agent, and the effect of the presence of other common EAFD’s constituents such as sodium, potassium, calcium, silicon, and sulfur. It was found that a 100% extraction (based on thermodynamic feasibility) of both zinc and lead can be achieved for a mixture containing 60% EAFD and 40% TBBA (contaminated with minor amounts of iron) when pyrolyzed under inert conditions. However, when a thermal treatment is performed in the presence of oxygen, complete thermodynamic-based recovery of zinc and lead recoveries can be achieved at a lower temperature with no iron content. Removal of sodium and potassium chloride from EAFD prior to pyrolysis by washing, under oxidizing condition, can also result in a profound selectivity in zinc and lead bromination. The behavior of other elements during bromination process was also discussed

The effect of reaction conditions on the precipitation of sodium hexafluorosilicate produced from waste hexafluorosilicic acid

The purpose of the study is to investigate the optimum conditions for the precipitation of sodium hexafluorosilicate (Na2SiF6) from waste hexafluorosilicic acid, an effluent from the phosphoric acid industry. Sodium chloride and sodium hydroxide were used as reactants to produce Na2SiF6. The effect of various parameters on the precipitation was investigated and includes; the molar ratio of the reactants, contact time, the temperature and the effect of seeding. The optimum reaction conditions were found to be as follows; excess sodium chloride or sodium hydroxide to hexafluorosilicic acid of 25%, contact time 40 minutes and a reaction temperature of 40°C. The reaction of hexafluorosilicic acid with an aqueous solution of sodium chloride at optimum conditions gave a maximum yield of 94.26% Na2SiF6 while the reaction of hexafluorosilicic acid with the aqueous solution of sodium hydroxide at optimum conditions gave a maximum yield of 97.3% Na2SiF6. The X-Ray diffraction (XRD) analysis reveals that the only crystals present in the precipitate are Na2SiF6. Also, Scanning Electron Microscope (SEM) analysis shows that the different morphology of these crystals depend on the precipitation conditions

Reactions of products from thermal degradation of PVC with nanoclusters of α-Fe2O3 (hematite)

Polyvinyl chloride (PVC) plastics constitute a large fraction of buildings, packaging and electronic devices, whereas, the annual emission electric arc furnace dust (EAFD) from steel manufacturing operations has recently peaked at nearly 6 Mt. Co-pyrolysis of PVC with EAFD currently represents a focal abatement technology for both categories of pollutants. However, despite of several experimental investigations; the mechanisms underlying interaction between EAFD and PVC remain largely speculative. Herein, we examine theoretically reactions of major products from thermal degradation of PVC with nanoclusters of iron (III) oxide, α-Fe2O3 (hematite) as a representative model for the various metal oxides in EAFD. The facile nature for the H-Cl bond fission over hematite is in line with experimental findings, pointing out to formation of iron chlorides from pyrolysis of Fe2O3-PVC mixtures. Interaction of selected chlorinated C1-C3 cuts with the hematite structure preferentially proceeds via a dissociative adsorption pathway. Results from this study shall be instrumental to understand, on a precise molecular basis, fixation of halogens on transitional metal oxides; a viable thermal recycling approach for polymeric materials laden with halogenated constituent

Catalytic de-halogenation of alkyl halides by copper surfaces

The interplay of halogenated compounds with metal surfaces has been the focus of many experimental and theoretical studies. These investigations have mainly aimed to illustrate the potential dual role of transition metals and their oxides in mediating formation of toxic halogenated aromatics as well as their catalytic-assisted decomposition over these surfaces. An initial and prominent step in conversion of these precursors into heavier halogenated aromatics signifies their dissociative adsorption on metallic species readily present in the combustion media. This contribution represents a systematic computational study to examine thermo-kinetic parameters underlying rupture of Cl/Br-C bonds in halogenated model compounds (namely; 2-chloropropane, chloromethane, chloroethyne, chloropropene, chlorobenzene, 2-bromopropane, bromomethane, bromoethyne, bromopropene, and bromobenzene) over the Cu(100) surface. These compounds adapt very weak physisorbed molecular states evidenced by marginal adsorption energies and minimal structural changes, in reference to their gas phase molecules. The calculated reaction barriers for Cl/Br-C bond fissions are scattered in the range of 8.3 - 37.2 kcal mol-1. Stronger Cl – C bonds in reference to Br – C bonds (in the gas phase) translate into higher corresponding reaction barriers for the former. The calculated reaction rate constant and activation energies reveal faster rate for the decomposition of the brominated species. Our calculations of the activation energies correlate very well with analogues experiment values

Formation of Phenoxy-type Environmental Persistent Free Radicals (EPFRs) from Dissociative Adsorption of Phenol on Cu/Fe and their Partial Oxides

The interplay of phenolic molecules with 3d transition metals, such as Fe and Cu, and their oxide surfaces, provide important fingerprints for environmental burdens associated with thermal recycling of e-waste and subsequent generation of notorious dioxins compounds and phenoxy-type Environmental Persistent Free Radicals (EPFRs). DRIFTS and EPR measurements established a strong interaction of the phenol molecule with transition metal oxides via synthesis of phenolic- and catecholic-type EPFRs intermediates. In this contribution, we comparatively examined the dissociative adsorption of a phenol molecule, as the simplest model for phenolic-type compounds, on Cu and Fe surfaces and their partially oxidized configurations through accurate density functional theory (DFT) studies. The underlying aim is to elucidate the specific underpinning mechanism forming phenoxy- or phenolate-type EFPRs. Simulated results show that, the phenol molecule undergoes fission of its hydroxyl’s O-H bond via accessible activation energies. These values are lower by 46.5 - 74.1% when compared with the analogous gas phase value. Physisorbed molecules of phenol incur very low binding energies in the range of -2.1 - -5.5 over clean Cu/Fe and their oxides surfaces. Molecular attributes based on charge transfer and geometrical features are in accord with the very weak interaction in physisorbed states. Thermo-kinetic parameters established over the temperature region of 300 and 1000 K, exhibit a lower activation energy for scission of phenolic’s O-H bonds over the oxide surfaces in reference to their pure surfaces (24.7 and 43.0 kcal mol-1 vs 38.4 and 47.0 kcal mol-1)