Simulation and thermodynamic analysis of chemical looping reforming and CO2 enhanced chemical looping reforming

The production of hydrogen from methane via two chemical looping reforming (CLR) processes was simulated and thermodynamically analysed, one process being the conventional CLR process, the other being a CO₂ sorption enhanced process. The aim of the work was to identify suitable operating conditions for obtaining an optimum hydrogen gas purity and yield, whilst operating auto-thermally, at atmospheric pressure and with no carbon formation. In both simulations, the reactors were simulated using the Gibbs minimisation technique. NiO was used as the oxygen storing species, whilst CaO was used as the CO₂ adsorbent.     

Fabrication and characterization of neat and aluminium-doped titanium (IV) oxide fibers prepared by combined sol–gel and electrospinning techniques

Sol–gel and electrospinning techniques were incorporated to produce polyvinylpyrrolidone (PVP)/titanium (IV) oxide composite fibers from solutions containing PVP and titanium tetraisopropoxide, with or without aluminium nitrate as the source of aluminium dopant. Upon the calcination of the as-spun fibers, the neat and the aluminium-doped titania fibers were obtained. Increasing the calcination temperature resulted in the decrease in the fraction of anatase phase within the fibers, as well as the increase in titania crystallite sizes. The presence of aluminium dopant, however, was found to greatly affect both physical and chemical properties of the synthesized titania fibers. Aluminium nitrate accelerated condensation of titanium oxide species during the sol–gel process, which resulted in increased viscosity of the spinning solution and consequently affected the diameters of the as-spun fibers. Aluminium dopant also played the major roles in both regulating the nucleation rate during crystallization of titania and controlling the growth mechanism of titania crystallites. As a result, the aluminium dopant caused the crystallite size of titania to decrease and retarded phase transformation from anatase to rutile.     

Phase transformation behavior of nanocrystalline χ-alumina powder obtained by thermal decomposition of AIP in inert organic solvent

Thermal decomposition of aluminum isopropoxide (AIP) in inert organic solvents (toluene and mineral oil) resulted in the formation of -alumina. Phase evolution by calcination at various temperatures for this alumina was studied via X-ray diffraction. The results suggest a direct transformation from -alumina to -alumina at approximately 1180°C, without the formation of -alumina phase, while still maintaining the small particle size (<100 nm). The transformation behavior was observed by TEM and the crytallite size was calculated by the Scherrer equation. The results indicate one -alumina crystal transforms into one -alumina crystal at its critical size in a nucleation step. This crystal exhibits a rapid grain growth following the transformation.     

Production of ethyltert-butyl ether fromtert-butyl alcohol and ethanol catalyzed byβ-zeolite in reactive distillation

The synthesis of ethyl tert-butyl ether (ETBE) from a liquid phase reaction between tert-butyl alcohol (TBA) and ethanol (EtOH) in reactive distillation has been studied.β-Zeolite catalysts with three compositions (Si/Al ratio=13, 36 and 55) were compared by testing the reaction in a semi-batch reactor. Although they showed almost the same performance, the one with Si/Al ratio of 55 was selected for the kinetic and reactive distillation studies because it is commercially available and present in a ready-to-use form. The kinetic parameters of the reaction determined by fitting parameters with the experimental results at temperature in the range of 343–363 K were used in an ASPEN PLUS simulator. Experimental results of the reactive distillation at a standard condition were used to validate a rigorous reactive distillation model of the ASPEN PLUS used in a simulation study. The effects of various operating parameters such as condenser temperature, feed molar flow rate, reflux ratio, heat duty and mole ratio of H₂O : EtOH on the reactive distillation performance were then investigated via simulation using the ASPEN PLUS program. The results were compared between two reactive distillation columns: one packed withβ-zeolite and the other with conventional Amberlyst-15. It was found that the effect of various operating parameters for both types of catalysts follows the same trend; however, the column packed withΒ-zeolite outperforms that with Amberlyst-15 catalyst due to the higher selectivity of the catalyst.     

Single-step synthesis of MWCNT/ZnO nanocomposite using co-chemical vapor deposition method

Single-step synthesis of MWCNT and ZnO nanocomposite was conducted by co-chemical vapor deposition method. Electron microscopic analysis revealed that the fabricated nanostructures consisted of MWCNTs with a diameter of 60-70 nm which were coated with ZnO nanoparticles with an average size of 20-30 nm. The growth of ZnO nanoparticles took place after the formation of MWCNTs. EDS and XRD analyses could confirm the high crystallinity of ZnO deposited on the MWCNT surface. In comparison with pristine MWCNTs and ZnO nanoparticles, the UV absorption of MWCNT/ZnO nanocomposite was changed through modification with ZnO nanoparticles.     

Preparation of ZnO nanorod by solvothermal reaction of zinc acetate in various alcohols

Solvothermal reaction of zinc acetate in various alcohols resulted in the formation of zinc oxide (ZnO) nanorods. The effects of reaction conditions on the product morphology as well as crystallization mechanism were investigated by using X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) techniques. It was found that average diameter and length of the nanorods increased with an increase in reaction temperature or the initial concentration of zinc acetate. On the contrary, the aspect ratio of the product depended upon type of alcohol used as the reaction medium. The aspect ratio of ZnO nanorods increased from 1.7 to 5.6 when the alcohol was changed from 1-butanol to 1-decanol. An investigation of the reaction mechanism suggested that the formation of ZnO nanorods was initiated from the esterification reaction between zinc acetate precursor and alcohol to form ZnO seeds.     

Controlled synthesis of defects-containing ZnO by the French process modified with pulsed injection and its luminescence properties

Zinc oxide (ZnO) nanoparticles containing oxygen vacancies were synthesized by the French process modified with pulsed injection of nitrogen. Zinc vapor was generated by evaporation of zinc foil and carried by a carrier gas to react with co-currently supplied air. During the reaction, nitrogen gas was injected in pulse, perpendicular to the flow direction of both zinc vapor and air. Low partial pressure of oxygen and turbulence caused by pulsed injection yielded uniform ZnO nanotetrapods that contained oxygen vacancies. The content of oxygen vacancies depended upon the characteristics of the pulse, i.e. flowing and non-flowing period of the gas, pulsing cycle time, and the supplied pressure of the injected gas. Strong correlation between the presence of oxygen vacancies and the intensity of green emission in the photoluminescence spectra of ZnO was also observed.     

Photocatalytic activity of neat and silicon-doped titanium(IV) oxide nanofibers prepared by combined sol-gel and electrospinning techniques

In the present contribution, the photocatalytic activity of neat and silicon-doped titanium(IV) oxide or titania fibers obtained by combined sol-gel and electrospinning techniques was reported for the first time. Both the calcination temperature and the presence of the silicon dopant affected a great deal the physical and chemical properties of the as-synthesized titania fibers. Increasing the calcination temperature resulted in the observed decrease in the fraction of the anatase phase and the observed increase in the size of the crystalline domains, while the presence of the silicon dopant caused the crystallite size to decrease and the fraction of the anatase phase to increase. The photocatalytic activity of both the neat and the silicon-doped titania fibers was investigated by following the photooxidative decomposition of methylene blue against that of the reference anatase titania. Both the neat and the silicon-doped titania fibers exhibited much better activity than the reference titania powder. In addition, the presence of silicon dopant enhanced the photocatalytic activity of the obtained titania fibers considerably.     

Fibrous zinc oxide prepared by combined electrospinning and solvothermal techniques

The synthesis of novel zinc oxide (ZnO) nanostructure consisting of ZnO nanoparticles formed into the network of fibers was investigated. This structure was fabricated from the solvothermal reaction of the poly(vinyl alcohol) (PVA)/zinc acetate composite fibers, which were firstly prepared by electrospinning technique. It was found that zinc acetate within the PVA matrix was converted into ZnO nanoparticles in hexagonal wurtzite structure, while PVA was still retained within the structure. Therefore, the product was no longer easy to crumble into powder, easy to handle, yet it still possessed nanostructure feature. The growth mechanism of ZnO nanoclusters within the structure was also proposed by investigating the effects of various parameters, i.e. content of zinc acetate within the fibers, reaction temperature and reaction time.