Hydrogen applications in selective catalytic reduction of NOx emissions from diesel engines

Diesel engines have been considered as a major source in nitrogen oxide (NO_x) formation worldwide. The widespread use of diesel engines in consequence of their low fuel consumption, high durability and efficiency increases NO_x emissions day by day. NO_x emissions from diesel engines cause unavoidable damage on environment and people health. Although so many technologies such as exhaust gas recirculation (EGR), lean burn combustion, electronic controlling fuel injection systems, etc. have been developed to control NO_x emissions from diesel engines, they couldn't meet the desired reduction in NO_x emissions. In any case, Selective Catalytic Reduction (SCR) as one of the most promising aftertreatment-emission control technologies is an effective solution in restriction of NO_x emissions. The use of SCR systems especially in heavy-duty diesel powered vehicles has been increasing nowadays. In these systems, to use of hydrogen (H₂) as a reductant or promoter have been improved the conversion efficiency especially at low exhaust temperatures. Many researchers have been focused on the use of H₂ in SCR systems for controlling NO_x emissions.In this study, the applications of H₂ in SCR of NO_x have been discussed. The studies on use of H₂ in SCR of NO_x emissions were examined and the effects on NO_x conversions were determined. Consequently, it is confirmed that H₂ is a promising and alternative reductant in SCR of NO_x and it has been kept as an attracting subject for many researchers.     

Microtensile Bond Strength of Self-Adhesive Resin-Based Dental Cement to Bleached Enamel

This study investigated the effectiveness of bleaching agents on the micro tensile bond strength (µTBS) of self-adhesive luting cement and enamel. A total of 126 samples were prepared from the labial surfaces of permanent human maxillary central incisors and assigned into three groups with 42 samples each as: control, enamel bleached with 10% hydrogen peroxide (HP), and enamel bleached with 10% carbamide peroxide (CP). Rely X Unicem® (3 M, ESPE) was used as self-adhesive resin cement. The total testing period for bleaching was selected as 14 days and the bleaching agents were applied 8 hours a day. The statistical one-way ANOVA model and Tukey HSD multiple comparison test (α = .01) were used to assess the differences. The control group demonstrated the highest value (18.245 MPa) while HP and CP showed the much lower values of 11.150 and 14.222 MPa, respectively. Bleaching agents affect the µTBS negatively. Failure analysis of the fracture surfaces demonstrated that almost all samples showed adhesive failures at the cement-enamel interface.     

Mapping the structure-activity relationship of <Emphasis Type="Italic">β</Emphasis>-sitosteryl fatty acid esters in condensing phospholipid monolayers

The phase behavior of twelve synthesized β-sitosteryl fatty acid esters with acyl moieties with different chain lengths (C2:0–C18:0) and different degrees of unsaturation (C18:1–C18:3) were investigated in pure and mixed Langmuir monolayers with phospholipids. The surface-pressure isotherms showed that short chain β-sitosteryl fatty acid esters gave smaller mean molecular areas and had decreased monolayer stability and the long chain steryl esters did not produce collapsed plateaus. All the steryl esters displayed strong condensing effects, but there was a pronounced structural dependency: medium chain esters (C8 and C10) were less efficient than short and long chain esters. Atomic force microscopy imaging demonstrated that monolayers mixed with dipalmitoyl phosphatidylcholine (DPPC) displayed both DPPC-rich and steryl lipid-rich domains. However, the height and area differences between the two phases and the roughness and morphologic patterns were very dependent on the steryl lipid concentrations as well as the length, the degree of unsaturation and the molecular conformations of the acyl segments. These findings not only provide a better understanding of the interactions between phytosteryl hydrophobic derivatives and biomembranes, but also may be of general use for the design and engineering of phytosterol structural derivations for specific food and pharmaceutical applications.

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Continuous fermentative hydrogen production from cheese whey wastewater under thermophilic anaerobic conditions

Hydrogen (H₂) production from cheese processing wastewater via dark anaerobic fermentation was conducted using mixed microbial communities under thermophilic conditions. The effects of varying hydraulic retention time (HRT: 1, 2 and 3.5 days) and especially high organic load rates (OLR: 21, 35 and 47 g chemical oxygen demand (COD)/l/day) on biohydrogen production in a continuous stirred tank reactor were investigated. The biogas contained 5–82% (45% on average) hydrogen and the hydrogen production rate ranged from 0.3 to 7.9 l H₂/l/day (2.5 l/l/day on average). H₂ yields of 22, 15 and 5 mmol/g COD (at a constant influent COD of 40 g/l) were achieved at HRT values of 3.5, 2, and 1 days, respectively. On the other hand, H₂ yields were monitored to be 3, 9 and 6 mmol/g COD, for OLR values of 47, 35 and 21 g COD/l/day, when HRT was kept constant at 1 day. The total measurable volatile fatty acid concentration in the effluent (as a function of influent COD) ranged between 118 and 27,012 mg/l, which was mainly composed of acetic acid, iso-butyric acid, butyric acid, propionic acid, formate and lactate. Ethanol and acetone production was also monitored from time to time.To characterize the microbial community in the bioreactor at different HRTs, DNA in mixed liquor samples was extracted immediately for PCR amplification of 16S RNA gene using eubacterial primers corresponding to 8F and 518R. The PCR product was cloned and subjected to DNA sequencing. The sequencing results were analyzed by using MegaBlast available on NCBI website which showed 99% identity to uncultured Thermoanaerobacteriaceae bacterium.     

Fabrication of halloysite nanotubes embedded thin film nanocomposite membranes for dye removal

Environmental friendly Halloysite nanotubes (HNTs) are used to fabricate novel nanofiltration membranes by in situ interfacial polymerization of piperazine and trimesoyl chloride. The removal of excess amine solution from the porous support membrane surface is a critical step to obtain defect free active layer. Hereby, two main removal tools for the excess aqueous amine solution; a rubber roll or air knife are compared to fabricate a defect free thin film nanocomposite (TFN) nanofiltration (NF) membrane. Removal by the rubber roll is eventuated more favorable than air knife in terms of the reproducibility of NF membranes by comparing salt rejections. By determining the removal step of excess amines, various HNTs concentrations are used to fabricate NF membranes and, these membranes are tested with salt and dye solutions at various pH and temperature ranges. R2 membrane (containing 0.02% [w/v] HNTs) performs the best flux results beside higher rejections of MgSO₄ (93.0%) and dye (99.5%). To evaluate the extreme conditionals, further performance tests such as pH and temperature resistance are also performed for R2 membrane. Considering the performances of R2 membrane, HNTs can be demonstrated for tailoring the balance between flux and separation performance of NF membranes.     

Prediction of the resource-efficient potential of Turkish manufacturing industry: a country-based study

Clean Technologies and Environmental Policy - As an emerging country, there is a rapid industrial development and associated excessive resource consumption in Turkey. In this case, the...     

Effects of hydrogen addition into liquefied petroleum gas reductant on the activity of Ag–Ti–Cu/Cordierite catalyst for selective catalytic reduction system

In this study, low temperature activity of Ag–Ti–Cu/Cordierite catalyst was investigated with liquefied petroleum gas (LPG) and hydrogen-liquefied petroleum gas (H₂-LPG) mixture as reductant. The selective catalytic reduction (SCR) catalyst was synthesized by impregnation method and characterized by Brunauer-Emmett-Teller (BET), Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) analyzes. BET analysis of the catalyst revealed surface area as 12.89 m²/g. Silver (Ag), titanium (Ti) and copper (Cu) nanoparticles were observed on the catalyst surface with SEM analysis. XRD analysis showed high dispersion of catalytic elements. The SCR performance tests were carried out at 170–270 °C temperature range, 30,000 h^?1 and 40,000 h^?1 space velocities, 1 kW, 2 kW, 3 kW and 4 kW engine loads with diesel engine real exhaust gas sample. NO_x conversion efficiency increased significantly in the presence of H₂, especially at low exhaust temperatures. The maximum NO_x conversion ratio was obtained as 89.53% with H₂-LPG reductant at 270 °C, 4 kW engine load and 30,000 h^?1 space velocity.     

Multi-function biquad using single CDBA

A voltage-mode, multi-input single-ouput type multi-function biquad is proposed having the following features: (a) It uses only one current differencing buffered amplifier as the active element, (b) it contains grounded and virtually grounded capacitors, (c) using this biquad, one may realize all five filter functions (i.e., lowpass, highpass, bandpass, notch and allpass) without changing the circuit topology, (d) it can be directly cascaded without any need of impedance matching circuits, (e) its Q-factor can be independently adjusted if the natural frequency is fixed, (f) biquad offers low sensitivities, and its natural frequency is insensitive to tracking errors. Experimental results are in agreement with theory.     

Size effects in modeling diffusivity of hardened mortar

A critical parameter for evaluating the resistance of concrete against chloride diffusion is effective diffusivity. While it can be obtained experimentally, this paper concerns computer simulations to estimate diffusivity of mortars as influenced by paste, aggregate, and interfacial effects. However, when performing such simulations, the size of the mortar sample modeled must be large enough to reliably characterize these randomly distributed effects, while remaining small enough for computational efficiency. The purpose of this paper is to report the influence of sample size on computed results and to recommend the smallest specimen size needed to obtain reliable estimates of diffusivity.