Surface Pore Blockage Research Articles

Nickel nanocatalyst on lanthanum aluminate: Optimizing preparation and evaluating performance in glycerol dry reforming for syngas production

In this study, mesoporous nanocrystalline Ni/La-Al catalysts with varying nickel (Ni) loadings (5, 10, 15, and 20 wt.%) were synthesized using a solid-state method for the glycerol dry reforming (GDR) reaction. The effects of different Ni loadings and the addition of steam on the structural and catalytic performance of the catalysts were investigated. Characterization techniques, including Brunauer-Emmett-Teller (BET) surface area analysis, temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), and X-ray diffraction (XRD) were employed to analyze the catalysts' properties. Results showed that increasing Ni loading to 10 wt.% improves the catalytic properties. However, by increasing the Ni loading, a decrease in catalytic properties due to increasing particle size, creating NiO bulk phase and surface pore blockage is obvious. A series of experiments were performed to investigate the effect of steam usage on catalytic properties. TPO analysis revealed that steam addition reduces the carbon deposition and shifts oxidation peaks to lower temperatures; consequently, the activity and stability of the catalyst will be enhanced. Although the 5 - 7.5 vol.% of steam in the feed composition significantly stabilizes the catalyst, it is possible to produce H2-rich synthesis gas, and conversely, increasing the temperature reduces the H2/CO ratio. Various examinations were conducted under different conditions, including varying gas hourly space velocity (GHSV), carbon-to-glycerol ratio (CGR), and temperature, to obtain more comprehensive data on the catalysts.

Multiscale modeling of chemical vapor infiltration process for manufacturing of carbon-carbon composite

Abstract Producing large parts by chemical vapour infiltration (CVI) process is quite challenging due to non-uniform nature of temperature and gas precursor distribution. Many a times repeated experiments are required to optimize the process parameters for manufacturing composites with isotropic properties. This is not only cumbersome but also cost intensive. To address this critical issue, we develop a multiscale mathematical model for thermal gradient forced chemical vapour infiltration (TG-FCVI) process considering only heterogeneous decomposition of propylene on carbon preform. The model takes account of the flow field, mass transport, reaction kinetics and the transient nature of porosity to identify the optimum process parameters. As the time taken in deposition is very large, the flow in free channel is much faster than the pores and therefore the flow equations are solved coupling both the domains in steady state (low Mach number flow). The effect of various process parameters on composites homogeneity like temperature, temperature gradient, inlet precursor concentration and inlet gas flow rate were studied. The model was validated with the available experimental data. It has been observed that high temperature gradient and inlet concentration favours homogeneous C-C composite with high final bulk density. However, increasing temperature of reactor and reducing inlet reagent concentration causes surface pore blockage and resulting in inhomogeneity in direction of axial flow

Preparation and characterization of polysulfone/zeolite mixed matrix membranes for removal of low-concentration ammonia from aquaculture wastewater.

Removal of low-concentration ammonia (1-10 ppm) from aquaculture wastewater was investigated via polysulfone (PSf)/zeolite mixed matrix membrane. PSf/zeolite mixed matrix membranes with different weight ratios (90/10, 80/20, 70/30 and 60/40 wt.%) were prepared and characterized. Results indicate that PSf/zeolite (80/20) was the most efficient membrane for removal of low-concentration ammonia. The ammonia elimination by PSf/zeolite (80/20) from aqueous solution for 10, 7, 5, 3 and 1 ppm of ammonia was 100%, 99%, 98.8%, 96% and 95% respectively. The recorded results revealed that pure water flux declined in higher loading of zeolite in the membrane matrix due to surface pore blockage caused by zeolite particles. On the other hand, ammonia elimination from water was decreased in higher contents of zeolite because of formation of cavities and macrovoids in the membrane substructure.

In situ immobilization of silver nanoparticles for improving permeability, antifouling and anti-bacterial properties of ultrafiltration membrane

In this work, silver nanoparticles (AgNPs) were in situ immobilized on polysulfone (PSf) ultrafiltration membrane via polydopamine (PDA) deposition and in situ reduction of silver ammonia aqueous solution (Ag(NH3)2OH). The adhesive and reductive PDA layer existing on the membrane surface induced the reduction of Ag+ on the site of surface without surface pore blockage, and also favored to the firm attachment and uniform distribution of AgNPs onto the membrane. The diameter and density of the immobilized AgNPs were regulated by changing [Ag(NH3)2]+ ion concentration, which exerted an influence on membrane hydrophilicity and permeation flux. The prepared AgNPs-PDA/PSf membranes were characterized by X-ray photoelectron spectroscopy (XPS), scanning election microscope (SEM), atomic force microscopy (AFM), water contact angle measurement and thermogravimetric analysis (TGA). The results indicated that AgNPs were immobilized on the surface as well as the top layer cross section of the membranes. The increase of Ag+ ion concentration led to an increase in the size and density of AgNPs anchored onto the membrane. Compared with PSf membrane, AgNPs-PDA/PSf (20mM) membrane showed higher water flux, slower flux decline rate during BSA solution filtration and higher flux recovery ratio after simple water flushing. The AgNPs-PDA/PSf (20mM) membrane possessed excellent stability with little release of silver during the filtrate operation or static immersion in water for 12 days. Besides, AgNPs-PDA/PSf (20mM) membrane displayed excellent anti-bacterial and ani-biofouling properties against E. coli and B. subtilis.

Dominance of Surface Barriers in Molecular Transport through Silicalite-1

Development of microporous materials with hierarchical structures of both micro/mesopores leads to molecular transport at nanometer length scales. For novel microporous materials including three-dimensionally ordered mesoporous imprinted (3DOm-i) zeolites and zeolite nanosheets, particle dimensions are below 35 nm resulting in surface-dominated structures. At the same time, the existence of surface-controlled mass transport including undefined “surface barriers” has been observed to reduce apparent diffusivity of hydrocarbons by orders of magnitude. This paper systematically characterizes cyclohexane transport in silicalite-1 by zero length chromatography (ZLC) to determine apparent diffusivity varying over 3 orders of magnitude in particles ranging from 35 nm to 3 μm. Three proposed mechanisms for surface barriers including surface pore narrowing, surface pore blockage, or surface desorption are evaluated by comparison with particle-size/diffusivity data. It is concluded that transport control in small particles was likely due to either pore narrowing at the surface or an extension of the diffusional length scale near the surface due to total pore blockages

Novel polyethersulfone nanocomposite membrane prepared by PANI/Fe3O4 nanoparticles with enhanced performance for Cu(II) removal from water

A novel mixed matrix polymeric membrane was prepared from polyethersulfone (PES) and self-produced polyaniline/iron(II, III) oxide (PANI/Fe3O4) nanoparticles by phase inversion method. The core-shell structured PANI/Fe3O4 nanoparticles were verified and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FTIR). Three different amounts of nanoparticles were introduced into the casting solutions to obtain the optimum value. According to the performance test, the membrane with 0.1 wt% nanoparticles indicated the highest Cu(II) ion removal but the lowest pure water flux. This is caused by nanoparticles located in the superficial pores of the membrane during preparation i.e., surface pore blockage. Morphological analysis including field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) as well as membrane performance tests revealed that adsorption is the most possible separation mechanism by the membranes. For better investigation of the adsorption mechanism, several isotherm models such as Langmuir, Freundlich and Redlich-Peterson were tested. Based on the isothermal results, the Redlich-Peterson model offered superior fitness indicating relatively complex adsorption mechanism. The reusability of the nanocomposite membrane was confirmed for several sequential adsorption-desorption processes using EDTA as regenerator.

Three-Component Competitive Adsorption Model for Fixed-Bed and Moving-Bed Granular Activated Carbon Adsorbers. Part II. Model Parameterization and Verification

COMPSORB-GAC is a 3-component competitive adsorption kinetic model for granular activated carbon (GAC) adsorbers that was developed in Part I of this study, including a proposed procedure for determining model parameters in natural water applications with background natural organic matter (NOM). Part II of this study demonstrates the proposed parameterization procedure and validates the modeling approach by comparing predictions with experimental breakthrough curves at multiple empty-bed contact times for both fixed-bed and moving-bed reactors. The parameterization procedure consists of a set of independent, short-term experimental tests with fresh and batch preloaded adsorbents and then data fitting using both classic and recently developed theoretical expressions. The model and parameterization procedure simplifies NOM into two fictive fractions (pore-blocking and strongly competing) and incorporates three competitive effects that vary both temporally and axially in a GAC column (direct competition for sites, intraparticle pore blockage, and external surface pore blockage). With all three competitive mechanisms accounted for, the model could accurately predict breakthrough profiles for column lengths and durations that were much longer than those used for model parameterization. Model predictions that ignored one or more of the competitive mechanisms showed that each mechanism was important for different regions of the breakthrough curve. The external surface pore-blockage effect was predominant for the prediction of early breakthrough data, whereas direct competition for sites and intraparticle pore blockage were prevalent when predicting higher breakthrough levels and data later in the column run.

A kinetic and equilibrium study of competitive adsorption between atrazine and Congo red dye on activated carbon: the importance of pore size distribution

A series of phenolic resin-based microporous activated carbon fibers (ACF) with different micropore size distributions were used to assess the role of pore size distribution (PSD) in the mechanism of competitive adsorption between the organic micropollutant, atrazine, and a compound larger in size, Congo red dye (CR). Batch kinetic and equilibrium experiments with the CR/atrazine system consisted of single-solute, simultaneous adsorption, CR preloading followed by atrazine contact, and atrazine preloading followed by CR contact. Based on the previous pore characterization studies and the PSD, two types of pore structures were proposed: telescopic pores and branched pores. With the telescopic pore structure, evidence is presented to support a transition from surface pore blockage to pore constriction (without loss of atrazine capacity) to direct competition for adsorption sites, with increasing average micropore size. With the branched pore structure (micropores branching off from mesopores), direct competition for adsorption sites in a fraction of the large micropores and pore constriction and pore blockage of smaller micropores were found to be important. The kinetics of adsorption was found to be important in determining the impact of simultaneous adsorption, while CR surface coverage and preloading time were the key factors controlling the impact of preloading on atrazine adsorption.