1D and 2D absorption-rate/kinetic modeling and simulation of carbon dioxide absorption into mixed aqueous solutions of MDEA and PZ in a laminar jet apparatus

The kinetics of the reaction between carbon dioxide (CO₂) and mixed solutions of methyldiethanolamine (MDEA) and piperazine (PZ) was investigated experimentally in a laminar jet apparatus. The experimental kinetic data were obtained under no interfacial turbulence and over a temperature range from 313 to 333 K, MDEA/PZ wt% concentration ratios of 27/3, 24/6 and 21/9, and CO₂ loadings from 0.0095 to 0.33 mol CO₂/mol amine. In addition, a new absorption-rate/kinetics model for the kinetics of the mixed of solvents was developed, which takes into account the coupling between chemical equilibrium, mass transfer, and all possible chemical reactions involved in the CO₂ reaction with MDEA/PZ solvent. The partial differential equations of this model were solved by the finite element numerical method (FEM) based on COMSOL software. The obtained experimental kinetics data were used to obtain the kinetic parameters of CO₂ absorption into MDEA/PZ solutions. The reaction-rate constant obtained for PZ blended with MDEA was kPZ = 2.572 × 10¹² exp(?5211/T). The 2D model for the blended amines MDEA/PZ has revealed the concentration profiles of all the species in both the radial and axial directions of the laminar jet which has enabled a better understanding of the correct sequence in which the reaction steps involved in the reactive absorption of CO₂ in aqueous mixed MDEA/PZ solution occur. It also revealed that PZ may be depleted by the time the solvent blend of MDEA/PZ with a loading greater than 0.015 mol/mol amine is exposed to CO₂ from the top of the laminar jet absorber.     

Heavy metal concentrations in marine molluscs from the Moroccan coastal region

Mussels (Mytilus galloprovincialis), clams (Venerupis decussatus) and oysters (Crassostrea gigas) were sampled seasonally during 2004-2005, from different coastal environments of Morocco in order to measure their accumulated heavy metal concentrations. The concentrations of Hg and Pb were determined by AFS and ICP-MS methods, respectively, whilst the remaining metals (Cd, Cr, Cu, Mn, Zn and Ni) were quantified by AAS. The soft tissue concentrations of the mussels were on average 7.2 mg kg(-1) (Cd), 9.6 mg kg(-1) (Pb), 0.6 mg kg(-1) (Hg), 26.8 mg kg(-1) (Cu), 8.8 mg kg(-1) (Cr), 292 mg kg(-1) (Zn), 20.8 mg kg(-1) (Mn) and 32.8 mg kg(-1) (Ni). The highest tissue heavy metal concentrations were recorded in the south from the industrial area of Jorf Lasfar. The relationships between metal concentration and season in each species showed very similar annual profiles with a peak observed around spring-summer. Statistical analysis indicated that different species showed different bioaccumulation of metals depending on study site and season.     

Preparation and characterization of mesoporous γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> recovered from aluminum cans waste and its use in the dehydration of methanol to dimethyl ether

The present study includes synthesis of two γ-Al₂O₃ samples from waste aluminum cans using a simple precipitation method. Precipitation was carried out using two different precipitating agents (i.e. NaOH and NH₄OH). The two prepared alumina samples were characterized by means of X-ray diffraction (XRD) and N₂ adsorption–desorption techniques. Surface acidity of γ-Al₂O₃ samples was measured by adsorption of two different probe molecules (i.e. pyridine and dimethyl pyridine) followed by desorption measurements using thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques. Catalytic activity of the two prepared alumina samples towards the dehydration of methanol (to dimethyl ether) was studied in a fixed bed reactor at 300 °C. For comparison reasons, commercial γ-Al₂O₃ sample was, also, tested for the same catalytic reaction under the same conditions. Results showed that the alumina sample prepared using NaOH as a precipitating agent exhibited a better catalytic activity and stability compared with that prepared using NH₄OH and showed a similar activity as the commercial γ-Al₂O₃ sample.     

Computer professionals and Carpal Tunnel Syndrome (CTS).

Carpal Tunnel Syndrome (CTS) is an important problem among computer professionals. Hence the prevalence of CTS among computer professionals and risk factors were studied. 648 subjects were selected from 4,276 computer professionals from 21 companies by with simple random sampling method. CTS was diagnosed based on clinical features. The prevalence of CTS was found to be 13.1% (95% CI 10.5-15.7%). Subjects with over 8 years of computer work, over 12 hrs of work per day and system administrators were at a higher risk for CTS (OR 3.3, 4.9 and 2.5 respectively). Flexed or extended hand position had higher risk for CTS. Higher risk for CTS was found with higher exposure to computer work. Ergonomic considerations are important in facilitating proper positioning of hand while working with a computer. Further studies on CTS risk factors among computer professionals are essential for planning prevention.     

Biodegradability of hydrocarbons in the refinery wastewater from moustorod oil refinery

The present investigation deals with the study of hydrocarbon degradation present in refinery wastewater by natural microbial flora in addition to that obtained using Ps. aeruginosa under laboratory conditions. Results indicated that Ps. aeruginosa may have a significant role in the degradation of hydrocarbons. After seven days, several of the compounds in the original wastewater were completely degraded and four compounds (n-paraffins) were partially degraded. Without Ps. aerruginosa, the same picture had been obtained after 23 days.     

A GIS-based multimedia watershed model: development and application

A multimedia model was developed using publicly available geographical information system (GIS) data, chemical release information and local monitoring networks to assess the fate of trichloroethene (TCE) within the Passaic River Watershed. Seven environmental media, air, water, sediment, surface soil, terrestrial vegetation, root zone soil and vadose zone soil, were modeled in this study along with their sub-compartments. The Passaic River Watershed is described using the NJDEP geographical information system (GIS) resources, the United States Geological Survey (USGS) and the United States Soil Conservation Services (US SCS) soil data. The introduction of spatial resolution to a multimedia, unsteady state model is performed in this work, and represents an important step in expanding the use of equilibrium models to provide far reaching information on the fate of toxic contaminants within a given environmental unit. The spatial representation of cross-boundary fluxes was successfully demonstrated with the use of sub-watershed as an environmental unit and the direct assessment of TCE for each of the 11 sub-watersheds that make up the Passaic River Basin in northern New Jersey. Important data gaps identified during the development of this model include the lack of comprehensive monitoring data on organic contaminants, and non-uniformity among available physical environmental data from different government agencies.     

A comprehensive review of technologies used to improve the performance of PV systems in a view of cooling mediums,reflectors design,spectrum splitting,and economic analysis

Environmental Science and Pollution Research - Solar photovoltaic panels are increasingly being used throughout the world, particularly in Egypt, where a station has been constructed in the city of...