Binary adsorption behaviour of methane and nitrogen gases

Separation of methane and nitrogen gases is critical in the upgrading of LFG (Landfill gas), natural gas and coal bed gas in order to have a commercial heating value for methane. From an environmental point of view, methane capture from landfill gas is essential to prevent greenhouse gas emissions. Adsorption could be a beneficial process to capture low purity methane from a landfill site that is nearing the end of its lifecycle and produce high purity methane. In this work, Ceca 13X zeolite and Alcan Activated Alumina AA 320-AP have been studied for their potential for this separation and compared with Silicalite in literature. Pure and mixture adsorption isotherms were determined at 40 and 100?°C for these adsorbents by constant volume method and concentration pulse chromatographic technique, respectively. Mixture adsorption isotherms for the binary system of methane and nitrogen gases at 40 and 100?°C and 1 atmosphere total pressure have been determined by VV?CCPM (Van der Vlist and Van der Meijden Concentration Pulse Method). The application of Extended Langmuir model for this binary system have also been discussed and compared to the experimental results. Results show that equilibrium separation factor for silicalite is larger than zeolite Ceca 13X and Alcan activated alumina AA320-AP. Both Silicalite and Ceca 13X find application in the bulk separation of methane from nitrogen when y _CH4?>?0.4, especially in LFG, coal bed gas and natural gas.     

Current condition and future directions for lean construction in highways projects: A small and medium-sized enterprises (SMEs) perspective

The aim of this study is to identify the parameters defining how Lean Construction (LC) is being implemented (current condition) and how LC can be further promoted (future direction) from a Small-Medium Sized Enterprises (SMEs) perspective. Although SMEs constitute the largest group in construction supply chains, LC, as an emerging phenomenon in civil construction project management, has been rarely investigated from an SMEs perspective. Also, overlooking the more macro factors like project governance and supply chain management, LC deployments have been mainly discussed from a production process perspective to date. After a review of the extant literature and 20 interviews with managers from the highways sector, a list of 31 current condition and 40 future direction statements were produced, classified under the delivery, process, training, project governance and supply chain related headings and used in a questionnaire survey with 110 responses. The current condition highlights problems like a short-term relations structure, competitive tendering mechanisms, fragmentation, problems in engaging with SMEs for LC, unstandardised LC techniques, and issues with convincing SMEs to deploy LC by demonstrating the business case on mutual benefits. Action items relating to the current project delivery structure were given the highest importance by the supply chain, alongside the LC training and project governance issues for the future of LC at highways SMEs. Additionally, a statistically significant correlation was identified among many future action items.     

Use of adsorbents for thermal energy storage of solar or excess heat: improvement of energy density

The current paper describes the design of a prototype system to explore the feasibility of the adsorption thermal energy storage. Water was chosen as the adsorbate, and three different adsorbents were tested. Zeolite 13X, NaLSX zeolite, and an activated alumina (AA)/zeolite 13X composite adsorbent were used as adsorbents. Experiments were performed at varying flow rates and different relative humidities to determine the optimal operating conditions for the system. The regeneration of the adsorbents also was explored by performing repeated runs on the same adsorbent sample. The results indicate that complete regeneration was achieved. A maximum energy density of 160 kWh/m³ has been achieved with the AA/13X adsorbent, and this adsorbent was chosen for further studies. After this adsorbent screening, the system was modified to improve the data recording and system performance. Tests were performed on AA/13X, and a maximum energy density of 200 kWh/m³ was achieved, which was much higher than the maximum energy density reported in the literature for adsorption thermal energy storage systems (165 kWh/m³). Copyright © 2012 John Wiley & Sons, Ltd.     

The effect of dehydration conditions on the adsorption and diffusion of propane and nitrogen in linde 5A zeolite

Diffusion of propane and nitrogen in small crystals (3.6 μm) of zeolite 5A has been studied by conventional uptake rate measurements. The zeolite crystals were subjected to various pre-treatments prior to propane and nitrogen adsorption. It is concluded that surface degradation due to pre-treatment is not believed to occur to a significant extent since it has been observed that after a proper regeneration of the adsorbent, the diffusional properties of the system have been restored. It is suggested that the Ca⁺⁺ cations which may initially obstruct the windows of the sieve become increasingly mobile with increasing sorbate concentration and move to sites within the cage. The results are broadly consistent with the study on the diffusional transition in zeolite NaX (Tezel et al., 1983).     

Evaluation and modeling of benzalkonium chloride inhibition and biodegradation in activated sludge

The inhibitory effect and biodegradation of benzalkonium chloride (BAC), a mixture of alkyl benzyl dimethyl ammonium chlorides with different alkyl chain lengths, was investigated at a concentration range from 5 to 20 mg/L and different biomass concentrations in an activated sludge system. A solution containing glucose and mineral salts was used as the wastewater in all the assays performed. The inhibition of respiratory enzymes was identified as the mode of action of BAC as a result of oxygen uptake rate analysis performed at BAC concentrations ranging between 5 and 70 mg/L. The glucose degradation in the activated sludge at different BAC and biomass concentrations was well-described with Monod kinetics with competitive inhibition. The half-saturation inhibition constant (K_I) which is equivalent to EC₅₀ of BAC for the activated sludge tested ranged between 0.12 and 3.60 mg/L. The high K_I values were recorded at low BAC-to-biomass ratios, i.e. less than 10 mg BAC/g VSS, at which BAC was almost totally adsorbed to biomass and not bioavailable. BAC degradation started as soon as glucose was totally consumed. Although BAC was almost totally adsorbed on the biomass, it was degraded completely. Therefore, BAC degradation was modeled using two-phase biodegradation kinetics developed in this study. This model involves rapid partitioning of BAC to biomass and consecutive degradation in both aqueous and solid phases. The aqueous phase BAC degradation rate was twenty times, on average, higher than the solid phase degradation rate. The specific aqueous (k_I1) and solid (k_I2) phase BAC utilization rate constants were 1.25 and 0.31 mg BAC/g VSS h, respectively. The findings of this study would help to understand the reason of extensive distribution of quaternary ammonium compounds in wastewater treatment plant effluents and in natural water systems although QACs are biodegradable, and develop strategies to avoid their release and accumulation in the environment.     

Autoantibodies to small heat shock proteins in glaucoma

PURPOSE: To identify the low-molecular-weight retinal proteins that are the targets of serum autoantibodies in patients with glaucoma and to study the ability of these antibodies to induce retinal apoptosis. METHODS: Serum immunoreactivity against retinal proteins was examined in age-matched groups of 60 patients with normal-pressure glaucoma, 36 patients with high-pressure glaucoma, and a control group of 20 healthy subjects, by means of western blot analysis and enzyme-linked immunosorbent assay. The specificity of the immunoreactivity to small heat shock proteins, including alpha-crystallins and hsp27, was tested by immunoprecipitation of these proteins in retinal fractions. The direct effects of antibodies specific to small heat shock proteins were then studied in isolated intact human retina (ex vivo) and cultured rat retinal cells (in vitro) by immunocytochemistry and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) technique in conjunction with fluorescence microscopy and confocal imaging. RESULTS: Serum immunoreactivity against retinal proteins with low molecular weight in patients with glaucoma was to small heat shock proteins, including alpha-crystallins and hsp27. In addition, patients with normal pressure glaucoma had a higher titer of autoantibodies to small heat shock proteins than did age-matched patients with high-pressure glaucoma or control subjects. It was observed that when antibodies against small heat shock proteins were applied directly to retina tissue or cells, they could trigger cell death through an apoptotic mechanism. CONCLUSIONS: These findings suggest that increased titers of circulating antibodies against retinal small heat shock proteins may have pathogenic significance in some patients with glaucomatous optic neuropathy.     

Regional epidemiological features of lip, oral cavity, and oropharyngeal cancer

Lip, oral cavity, and oropharyngeal cancer are among the most common forms of the disease in the world. These types of cancer display significant geographic, ethnic, and socioeconomic variations. We examined the cases of cancer of the lip, oral cavity, and oropharynx diagnosed in the Department of Otolaryngology at the University of Uluda? School of Medicine during the last 5 years, July 1990 to June 1995, and recorded the epidemiological features of these tumors. The Department of Otolaryngology treated a total of 26,225 in- and outpatients during the 5-year period. 320 of these patients (1.2%) were seen for head and neck cancer. 42 of the 320 patients (13.1%) were diagnosed with cancer of the lip, oral cavity, and oropharrynx. After the larynx, this was the second most frequent location of malignant head and neck tumors. We discovered the following epidemiological and pathological features: (1) The incident rate was highest in patients between 41 and 60 years of age. (2) 70% of the patients were male, and 76% of them had a history of tobacco/alcohol use. (3) Occupation had no apparent relevance (four of the patients were farmers). (4) Approximately one third of the patients had undergone medical therapy prior to diagnosis. (5) One third of the patients had initially seen a dentist for treatment, and approximately half had poor dental and oral hygiene. (6) The most frequent symptom was ulceration. (7) Histopathological examination revealed squamous cell carcinoma in 88% of the cases. (8) The cancer was localized to the lip in 31% of cases, oral cavity, 50%, and oropharynx, 19%. (9) Almost half of the cancer cases were diagnosed in advanced stage (stages III and IV).     

Adsorption of nitrogen and carbon monoxide on clinoptilolite: Determination and prediction of pure and binary isotherms

Adsorption of N₂ and CO has been studied on a natural Turkish clinoptilolite at near ambient conditions. Pure isotherms up to 101.3 kPa pressure, and binary isotherms at 101.3 kPa total pressure were determined chromatog-raphically at 303 K. Pure isotherms were modelled using the Langmuir model and the Wilson and Flory - Huggins forms of the Vacancy Solution Theory. Binary isotherms were predicted using both forms of the Vacancy Solution Theory, the Extended Langmuir model, and the Ideal Adsorbed Solution Theory. These predictions were compared to experimentally determined binary isotherms. Clinoptilolite is shown to be a particulahly promising sorbent for the separation of CO and N₂. The Wilson form of the Vacancy Solution Theory was the only model flexible enough to provide a reasonable prediction of the binary isotherms.