CO2–CH4 phase equilibria on modified multi‐walled carbon nanotubes using Gibbs excess energy models based on vacancy solution theory

CO₂ and CH₄ equilibrium adsorption are predicted by Excess Gibbs energy models based on vacancy solution theory, for single and binary mixture on Multi‐Walled Carbon Nanotubes (MWCNTs) functioned by –NH₂ group. The experimental data of single gas adsorption isotherms were obtained at moderate pressures and temperatures using the volumetric method in a static gaseous set up. Firstly, the equilibrium pressures related to the adsorbed amounts, for single gases, were correlated on Wilson and Flory–Huggins activity coefficient equations based on vacancy solution theory and the model parameters were determined by fitting the model on the experimental data. Secondly, the pure component parameters were implemented in extended Wilson and Flory–Huggins equations for CO₂ and CH₄ mixture to predict the gas–solid phase equilibria. The results showed fairly good agreement between the experiments and both Gibbs models. Finally, the studied models were compared with the popular model of Extended Langmuir. The results revealed more accurately and precisely prediction of Wilson and Flory–Huggins against Langmuir model for mixed gas of CO₂ and CH₄ on MWCNT–NH₂. © 2011 Canadian Society for Chemical Engineering     

Evidence of changes in cell surface proteins during growth of Lactobacillus casei under acidic conditions

In this research, changes were observed in cell surface proteins of a typical strain of the Lactobacillus casei was investigated in response to acidic growth conditions. Two dimensional electrophoresis and Western blot analyses were carried out to detect changes in relative abundance of proteins at the cell surface. The identity of the differentially expressed proteins extracted by LiCl, a chemical routinely used to extract surface proteins of lactic acid bacteria, was determined by MALDI-TOF/TOF MS. Many enzymes involved in glycolysis were up-regulated in the cell surface fraction following growth at low pH, including enolase, lactate dehydrogenase, and glyceraldehyde-3-phosphate dehydrogenase. Several of these proteins were also related to adhesion and generalized stress responses. It is demonstrated that growth of L. casei under acidic conditions caused molecular changes at the cell surface to develop an adaptive strategy corresponding to slower growth at low pH.     

Preparation and characterization of nano-porous silica aerogel from rice husk ash by drying at atmospheric pressure

Silica aerogel, a mesoporous material, was prepared from rice husk ash by sol–gel method and dried under atmospheric pressure. In this method, rice husk ash, which is rich in silica, was extracted with sodium hydroxide solution to produce a sodium silicate solution. This solution was neutralized with acid to form a silica hydrosol, and a small amount of tetraethyl silicate (TEOS) to form a gel. The aged gel was washed carefully by distilled water and ethanol and finally dried under atmospheric air. The prepared silica aerogels were characterized by XRF, FT-IR, TG, DTA, DTG, XRD, BET and SEM measurements. The synthesized TEOS-doped silica aerogel was a light solid with specific surface area of 315 m²/g, pore volume 0.78 cm³/g, average pore size 9.8 nm, bulk density 0.32 g/cm³ and porosity 85%.     

Effects of orbital shaking on settling velocity of mineral particles in aqueous solutions using split‐plot designs

This study aimed to experimentally investigate and statistically test changes in the settling velocity of particles falling in an aqueous solution due to an orbital shaking of the container. A series of settling experiments were conducted on coal samples under different combinations of shaking speed and initial concentration of the particles. First, a generalized version of the factorial design (a split‐plot design) was utilized to obtain the acquired data. Then, an appropriate statistical model was fitted to experimental data using settling velocity as a response while shaking speed and initial coal concentration were defined as factors. Graphic patterns confirmed our hypotheses that settling velocity is affected by the shaking speed, initial coal concentration and the interaction of these two factors. Results of the analysis indicated that the main effects of both initial coal concentration (F‐statistic = 775.75) and shaking speed (F‐statistic = 11.96) on the settling velocity are strongly significant (both with a P‐value near zero). Moreover, a strong interaction of the effects of these factors on the response variable was also observed (F‐statistic is 10.57 with a P‐value of near zero). Based on the results, combination of 4% coal concentration and 50 rpm shaking speed resulted in the highest settling velocity of 1.21 cm/s. In contract, a combination of 10% coal concentration and 100 rpm shaking speed led to a settling velocity of only 0.55 cm/s. Findings of this study may have invaluable benefits to the mineral and water treatment industries where design and construction of thickeners and sedimentation tanks equipped with orbital shakers can significantly accelerate the sedimentation of mineral particles as well as water contaminants.     

Microbial community analysis of mixed anaerobic microflora in suspended sludge of ASBR producing hydrogen from palm oil mill effluent

This study investigated the microbial community of an anaerobic sequencing batch reactor (ASBR) operating at mesophilic temperature under varying hydraulic retention times (HRTs) for evaluating optimal hydrogen production conditions, using palm oil mill effluent (POME) as substrate. POME sludge enriched by heat treatment with hydrogen-producing bacteria was used as inoculum and acclimated with the POME. The microbial community was determined by first isolating cultivable bacteria at each operating HRT and then using polymerase chain reaction (PCR). The PCR products were sequenced and sequence identification was performed using the BLAST algorithm and Genbank database. The findings revealed that about 50% of the isolates present were members of the genus Streptococcus, about 30% were Lactobacillus species and around 20% were identified as species of genus Clostridium. Scanning electron microscopy (SEM) analysis also confirmed the presence of spherical and rod-shaped microbial morphologies in the sludge samples of bioreactor during prolonged cultivation.     

Effect of synthesis conditions on performance of a hydrogen selective nano-composite ceramic membrane

A hydrogen-selective nano-composite ceramic membrane was prepared by depositing a dense layer composed of SiO₂ and Al₂O₃ on top of a graded multilayer substrate using co-current chemical vapor deposition (CVD) method. The multilayer substrate was made by dip-coating a macroporous α-alumina tubular support by a series of boehmite solutions to get a graded structure. Using DLS analysis, it was concluded that decreasing hydrolysis time and increasing acid concentration lead to smaller particle size of boehmite sols. XRD analysis was carried out to investigate the structure of intermediate layer and an optimized calcination temperature of 973 K was obtained. SEM images indicated the formation of a graded membrane with a porous intermediate layer having a thickness of about 2 μm and a dense top selective layer with a thickness of 80–100 nm. Permeation tests showed that H₂ permeance flux decreased from 5 × 10⁻⁵ mol m⁻² s⁻¹ Pa⁻¹ for a fresh substrate to 6.30 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ after 6 h of deposition, but H₂ selectivity over N₂ increased considerably from 5.6 to 203.