Papers by Keyword: Desorption

Abstract: An adsorbent for post-combustion carbon dioxide capture was prepared using low-cost and sustainable natural zeolite coated with chitosan. An optimum adsorbent was identified from 3 levels of particle size of natural zeolite and 10 levels of chitosan loading. The optimum adsorbent was characterized using infrared spectroscopy, scanning electron microscopy, thermal gravimetric analysis and differential scanning calorimetry. The chemical and thermal properties of the adsorbent indicated successful coating of chitosan on natural zeolite. The adsorbent registered competitive dynamic adsorption capacity of 0.81 mmol g^-1 with good retention, at least, up to 5 adsorption-desorption cycles.

Abstract: The goal of this study was to investigate the influence of cyclic hot and cold water absorption and desorption on the flexural and impact strengths of luffa – PLA biocomposites. PLA was reinforced with heat treated luffa fibers with the fiber loadings: 5 vol.%, 10 vol.%, 15 vol.% and 20 vol.%. Based on the test results the biocomposite with the highest flexural and impact strengths was selected for water absorption and desorption cycles. The biocomposites were subjected to 56 cycles of hot and cold water absorption and desorption. The biocomposites were tested for their strengths after every 14 cycles. The absorption and desorption decreased the flexural and impact strengths, affecting the impact strength more than the flexural strength.

Abstract: Two series of Ag-loaded β-zeolites with silica/alumina ratio of 25 and 36 were prepared by ion exchange technique. The silver loading was varied in a range of 2-10 wt%. The samples were characterized by low-temperature nitrogen adsorption, Infrared and UV-vis spectroscopy, and transmission electron microscopy. Adsorption/desorption properties of zeolites were examined using a specially designed setup. Toluene was used as a model hydrocarbon. It was found that adsorption capacity of zeolites grows up along with silver content increase till 8%, and reduces then. According to data of physicochemical methods, at low loading the silver exists in cluster and ionic forms, while at high loading agglomerated particles predominate, which worsens the adsorption properties.

Abstract: Sorption and desorption of moisture in epoxy composites reinforced with triangular and V-shaped bar fillers were studied. Epoxy was reinforced with vinyl ester bar assemblies fabricated according to 4 varied factors: bar orientation relative to diffusion direction (pointed or base side), bar alignment (parallel or staggered), spacing between bars (1 or 5 mm), and bar cross-sectional shape (triangular or V-shaped). Unlike previous studies, the bar fillers were initially coated with small amount of epoxy resin to improve wetting during fabrication of composites. Moisture uptake and loss of composites during one-side exposure to water vapor (50% relative humidity at 60°C) and hot air (60°C), respectively, were monitored with time. Experimental results show weight change of composites during moisture sorption and desorption varies linearly with square root of exposure time. Diffusion coefficients of composites were determined by assuming the material to be semi-infinite and fitting a mathematical solution to Fick’s second law of diffusion to weight change data. Results show diffusion coefficient of composites during moisture sorption is increased when bars are oriented pointed relative to diffusion direction, aligned parallel, spaced at 1 mm, and has triangular cross-sectional shape. However, during desorption, the diffusion coefficient is increased when base side of bars are exposed and when the bars are aligned staggered. The observed effects of factors on moisture diffusion coefficients of epoxy composites during sorption and desorption are discussed in relation to path length, available diffusion area, and status of epoxy/vinyl ester interphase before and after moisture sorption in composites.

Abstract: In this study, the adsorption properties of modified circulating fluidized-bed combustion (CFBC) fly ash by alkali wet millingwere investigated for Mn (II) cations. The effects ofNaOH content,milling speed and milling timeon the modification processof CFBC fly ashwerestudied. Preliminary statistical analysis has indicated thatmetal concentration, time, pH, fly ash dosage and temperaturewere the most importantvariables that affect the adsorption capacity. Results lead towards the conclusion that alkali wet millingtreatment cansignificantly increasethe adsorption capacity of the CFBC fly ash. The adsorption mechanism of the modified CFBCfly ash was determined using Langmuir, Freundlich isotherms and the Lagergren pseudo-first-order, pseudo-second-order, Elovich equation and the intraparticle diffusion equation, which indicated it was not thesole rate determiningstep, and the adsorption process was controlled by physical and chemical adsorption.The results showed that theCFBC fly ash can be utilized as a low-cost adsorbent for the removal of Mn (II) ionsfrom solution.

Abstract: Magnetic chitosan nanoparticles (Fe₃O₄-CS MNPs) were synthesized by an improved one-pot hydrothermal method and applied for azo dye amido black 10B adsorption. The Fe₃O₄-CS MNPs were characterized by SEM, TEM, DLS, XRD, FTIR, TGA and VSM. The adsorptive behavior of amido black 10B on Fe₃O₄-CS MNPs was investigated using the UV-vis specteophotometric technique and the affecting parameters including solution pH, contact time, amido black 10B concentration and Fe₃O₄-CS MNPs amount were examined. The adsorption process followed the pseudo-second-order kinetic model. The adsorption equilibrium data fitted well with the Freundlich isotherm model with the saturated adsorption capacity of 124.8 mg/g at pH=2.0. The desorption experiment could be carried out using NaOH with the recovery of 91.78%. After five cycles, adsorption efficiency still reached 83.24%. The results showed that Fe₃O₄-CS MNPs possessed a simple synthesis route and excellent reusability, which have potential application in the adsorption of azo dye in environmental effluents.

Abstract: Epoxy/amine-coated polyester triangular bar composites were fabricated and exposed to 5 wt% hydrochloric acid (HCl) solution at 40 °C. The weight loss characteristics of pre-exposed composites in heated air at 40 °C under forced convection were studied as function of size, spacing, alignment, and orientation of triangular bars. The diffusion coefficient of composites during desorption increases when the bars are oriented flat and are aligned in parallel. The same result is observed when the size of triangular bars is increased, and when spacing between bars is decreased. These results are attributed to the presence of epoxy/polyester interphase regions, which are more accessible when the triangular bars are oriented flat and aligned parallel, have larger size, and have smaller spacing. These interphase regions are preferred conduits of water during desorption of composites. The diffusion coefficients of composites being higher than the values of epoxy and polyester resins further confirm the effect of interphase regions. Among the factors, orientation of triangular bars has the highest influence on the desorption behavior of epoxy composites.

Abstract: Bimetal adsorbent system of calcium oxide impregnated on iron (III) oxide were evaluated as a potential source of basic sites for CO₂ capture. The adsorbents were prepared by impregnation method were calcined at 200 until 600 °C. Several characterizations were carried out using XRD, BET and CO₂-TPD analysis. The CaO loading increased the basicity of the adsorbent significantly enhance the CO₂ chemisorption. Furthermore, it drastically reduced the desorption temperature to 310-490 °C, which is important in chemisorption aspect. The CaO/Fe₂O₃200 which calcined at 200 °C was found to be most efficient. The CO₂ chemisorption (81.29 mg CO₂/g adsorbent) was contributed most compared to physisorption (4.64 mg CO₂/g adsorbent).

Abstract: Supported ionic liquid (IL) [bmim][CF₃SO₃] on SiO₂ was prepared, characterized and its potential evaluated for CO₂ capture via adsorption and desorption studies using gas adsorption analyzer. The physical and chemical properties were determined using N₂ adsorption/desorption and CO₂-TPD analysis. The increasing IL loading caused a drastic decrease in the surface area as well as pore volume due to the confinement of IL within the micropore and mesopore area. However, the increasing IL loading increased the basicity of the sorbent which significantly enhanced CO₂ chemisorption. Supported [bmim][CF₃SO₃] on SiO₂ revealed the physical and chemical adsorption of CO₂ and resulted in a remarkable CO₂ adsorption capacity at atmospheric pressure and room temperature (66.7 mg CO₂/g_adsorbent) which has great potential in industrial applications.

Abstract: Two types of multi-wall carbon nanotubes (MWCNT) were studied by low temperature nitrogen adsorption method. Pore size distribution was calculated using non local density functional theory (NLDFT) and Barrett-Joyner-Halenda (BJH) models. The peaks on pore size distribution were attributed to MWCNT with different diameters. Maximum hydrogen uptake by weight was evaluated for both samples and do not exceed 5 % even for the sample with higher specific surface area.