Equilibrium solubility of CO2 in rubbery EVA over a wide pressure range: effects of carbonyl group content and crystallinity

The equilibrium CO₂ sorption isotherms and isobars for rubbery EVA containing various amounts of vinyl acetate (VA) over a wide pressure range 10-340 atm and 25-52 °C were investigated. The normalized CO₂ sorption concentration (in cm³ (STP) CO₂/mole VA) isotherms of these polymers as a function of pressure consisted of two distinct regions turning at near P_c. The normalized sorption isotherms in these two distinct regions could be fairly described by two respective power laws: C=K_aP^n_a for above P_c and C=k_bP^n_b for below P_c. The normalized CO₂ sorption isotherms were found to be about the same for four EVA samples having different VA contents for below P_c, suggesting that the sorption process at below P_c may be mainly driven by the presence of carbonyl groups. At above P_c, the degree of crystallinity of the polymer appeared to be a major factor to affect the sorption process, with the higher the degree of crystallinity, the lower the normalized CO₂ sorption concentration in the polymer. The sorption isobars of the polymer as a function of temperature were governed by the interplay of density, viscosity, and diffusivity of CO₂ depending on the pressure studied.     

A comparison of adsorption isotherms using different techniques for a range of raw,water- and acid-washed lignites

Adsorption isotherms based on desiccator measurements at 30 °C have been constructed for six Victorian lignites (five raw, one water-washed and six acid-washed samples). The results for a selection of samples have been shown to be in good agreement with more detailed isotherms obtained using two different automated microbalances. This suggests that the rate of approach to the final relative vapor pressure has little effect. The equilibrium moisture contents at 51.4% relative vapor pressure or less for the acid-washed lignite samples showed moderately good correlations (R²∼0.5) with the carboxylic acid concentration, but much weaker correlations with the phenolic content.     

Stability and growth of gas hydrates below the ice–hydrate–gas equilibrium line on the P–T phase diagram

Using a previously developed experimental technique, the behavior of small methane and propane hydrate samples formed from water droplets between 0.25 and 2.5 mm in size has been studied in the pressure–temperature area between the ice–hydrate–gas equilibrium line and the supercooled water–hydrate–gas metastable equilibrium line, where ice is a stable phase. The unusual persistence of the hydrates within the area bounded by these lines and the isotherms at T=253 K for methane hydrate or at T=263 K for propane hydrates was observed. This behavior has not previously been reported. For example, in the experiment carried out at 1.9 MPa and 268 K, the methane hydrates existed in a metastable state (the equilibrium pressure at 268 K is 2.17 MPa) for 2 weeks, then immediately dissociated into liquid supercooled water and gas after the pressure was isothermally decreased slightly below the supercooled water–hydrate–gas metastable equilibrium pressure. It was found that dissociation of metastable hydrate into supercooled water and gas was reversible. The lateral hydrate film growth rates of metastable methane and propane hydrates on the surface of supercooled water at a pressure below the ice–hydrate–gas equilibrium pressure were measured. The temperature range within which supercooled water formed during hydrate dissociation can exist and a role of supercooled water in hydrate self-preservation is discussed.     

Preparation of nitrogen-doped porous carbon by ammonia gas treatment and the effects of N-doping on water adsorption

Nitrogen-doped porous carbons (N-RFCC) were prepared by NH₃N₂ mixture gas treatment at high temperature during the carbonization process on resorcinol–formaldehyde cryogels. To show the role of N-doping on the adsorption behavior we carried out water adsorption, and it was found that the amount of water adsorbed is directly related to the nitrogen content over the low pressure region (P/P₀ < 0.3). Applying the theoretical water adsorption model, Horikawa–Do (HD) model, to the adsorption isotherms of N-RFCCs, we could analyze the effects of nitrogen-doping on the adsorption mechanism. Although the concentration of functional groups of N-RFCC is almost equal to that of the non-doped RFCC, which was measured by Boehm titration method, the water adsorbed amounts of N-RFCCs over the low pressure region were larger. This is due to part of the doped nitrogen atoms act as functional groups, contributing to the total concentration of functional groups. The saturated concentrations depend on the packing fraction of water molecules, which in turn depends on the pore size. The packing fractions of N-RFCCs are larger than those of RFCCs, and this could be attributed to the high affinity between water clusters and N-doped surfaces, resulting in a reduced hydrophobicity of the surface.     

Binary adsorption behaviour of methane and nitrogen gases

Separation of methane and nitrogen gases is critical in the upgrading of LFG (Landfill gas), natural gas and coal bed gas in order to have a commercial heating value for methane. From an environmental point of view, methane capture from landfill gas is essential to prevent greenhouse gas emissions. Adsorption could be a beneficial process to capture low purity methane from a landfill site that is nearing the end of its lifecycle and produce high purity methane. In this work, Ceca 13X zeolite and Alcan Activated Alumina AA 320-AP have been studied for their potential for this separation and compared with Silicalite in literature. Pure and mixture adsorption isotherms were determined at 40 and 100?°C for these adsorbents by constant volume method and concentration pulse chromatographic technique, respectively. Mixture adsorption isotherms for the binary system of methane and nitrogen gases at 40 and 100?°C and 1 atmosphere total pressure have been determined by VV?CCPM (Van der Vlist and Van der Meijden Concentration Pulse Method). The application of Extended Langmuir model for this binary system have also been discussed and compared to the experimental results. Results show that equilibrium separation factor for silicalite is larger than zeolite Ceca 13X and Alcan activated alumina AA320-AP. Both Silicalite and Ceca 13X find application in the bulk separation of methane from nitrogen when y _CH4?>?0.4, especially in LFG, coal bed gas and natural gas.     

Performance of a slurry bubble column reactor for Fischer-Tropsch synthesis: Determination of optimum condition

The CO conversion and selectivity to C₁+ and C₁₁+ wax products over Co/Al₂O₃ as well as Ru/Co/Al₂O₃ Fischer-Tropsch (F-T)catalysts were investigated by varying reaction temperature (210-250 °C), system pressure (1.0-3.0 MPa), GHSV (1000-6000 L/kg/h), superficial gas velocity (1.7-13.6 cm/s) and slurry concentration (9.09-26.67 wt.%) in a slurry bubble column reactor (0.05 m diameter × 1.5 m height) to determine the optimum operating conditions. Squalane or paraffin wax was used as initial liquid media. The overall CO conversion increased with increasing reaction temperature, system pressure and catalyst concentration. However, the local maximum CO conversion was exhibited at GHSV of 1500-2000 L/kg/h and superficial gas velocity of 3.4-5.0 cm/s. The CO conversion in the case of Ru/Co/Al₂O₃ was much higher and stable than that in the case of Co/Al₂O₃. The selectivity to C₁₁+ wax products increased slightly with increasing GHSV; on the other hand, it decreased with increasing reaction temperature, system pressure, and solid concentration in a slurry bubble column reactor. It could be concluded that the optimum operating conditions based on the yield of hydrocarbons and wax products were; U_G = 6.8-10 cm/s, Cs = 15 wt.%, T = 220-230 °C, P = 2.0 MPa in a slurry bubble column reactor for F-T synthesis.     

A two-dimensional metal-organic framework composed of paddle-wheel cobalt clusters with permanent porosity

A cobalt(II)-organic framework, [Co₂(TPEC)(DMA)₂]·(DMA)₃ (1) (H₂TPEC = 1,1,2,2-tetra(4-(4-carboxyl-phenyl)benzenyl)ethene; DMA = N,N′’-dimethylacetamide), was synthesized and characterized by single crystal diffraction analysis. The structure shows a two-dimensional (2D) sheet composed of paddle-wheel Co₂(COO)₄ clusters linking TPEC ligands. The permanent porosity was established for the activated phase and gas sorption isotherms acquired.     

Experimental study of hydrogen fluoride adsorption on sodium fluoride

In uranium conversion industry, the fluorine is used as chemical raw material gas to produce UF₄ and UF₆ while its purity is very important. In this study, the adsorption process of hydrogen fluoride, as an impurity in the process of fluorine production, on sodium fluoride pellets is experimentally studied in a lab-scale fixed bed adsorbent. Also, the effects of some operating parameters including inlet concentration and inlet temperature of hydrogen fluoride are precisely investigated on the adsorption process. The data of adsorption are analyzed and correlated by Langmuir, Freundlich and Temkin isotherms. The adsorption capacity is found to be 1.908 and 0.750 g HF/g NaF by the Langmuir isotherm at 22 and 54 °C, respectively. The favorability nature of adsorption which is expressed in terms of a dimensionless separation factor (R_L) is found to be more than 1 which indicates an unfavorable adsorption. In addition, the data analysis shows that the Langmuir and Temkin isotherms correlate the equilibrium isotherms better than that of Freundlich.     

Dual gas analysis of microporous carbons using 2D-NLDFT heterogeneous surface model and combined adsorption data of N2 and CO2

Knowledge of the pore structure of carbon materials including micropores is crucial for applications such as double layer supercapacitors, gas separation, and other applications requiring high specific surface area materials. High surface area is always associated with fine micropores. The pore size distribution (PSD) of microporous carbons is usually evaluated from nitrogen adsorption isotherms measured at 77 K in the relative pressure range from 10⁻⁷ to 1. Due to the very slow gas diffusion into fine pores at cryogenic temperatures and low pressures, the adsorption measurements may be extremely time consuming and sometimes inaccurate when the adsorption equilibrium is difficult to achieve during the measurement. In this work, we discuss an approach in which the carbon PSD is calculated from the combined N₂ and CO₂ data measured in the pressure range from 1 to 760 Torr. Under such conditions, the diffusion into micropores is usually fast and equilibration times are short for both measurements. In the PSD calculations we use 2D-NLDFT models for carbons with heterogeneous surfaces (J. Jagiello and J.P. Olivier, Adsorption 19, 2013, 777–783). We show that both isotherms can be fitted simultaneously with their corresponding models and as a result the unified PSD can be obtained.     

Characteristics of droplets generated by bubble bursting from chromic acid solutions

The effects of electrolyte concentration and gas flow rate on the characteristics of droplets generated from bubbles bursting on the surface of CrO₃ solution were studied with an experimental bubbling system. The experimental conditions included two electrolyte concentrations, 125 and 250 g l^-1 of CrO₃, and three flow rates of sparging air in the range of 4–8 l min^-1. A cascade impactor collected droplet samples for chemical analysis. A laser aerosol spectrophotometer and an aerodynamic particle sizer were employed simultaneously to measure the number concentration and size distribution of the droplets. A layer of foam formed on the liquid surface under all experimental conditions studied except at the gas flow rate of 4 l min^-1 in 125 g l^-1 CrO₃ solution. Foams had a significant effect on the characteristics of droplets generated from bursting bubbles. At identical gas flow rate and electrolyte concentration, the formation of foams led to a reduction in number concentration of droplets larger than 10 μm in aerodynamic diameter and a lower concentration of airborne Cr(VI). In the ranges of gas flow rate and electrolyte concentration tested, the results showed that the airborne Cr(VI) mass concentration increased significantly with gas flow rate and slightly with electrolyte concentration in the presence of foams. The results obtained in the present study should have applications in the emission control of Cr(VI)-containing droplets in chromium electroplating processes.     

Simultaneous measurement of the concentration of a supercritical gas absorbed in a polymer and of the concomitant change in volume of the polymer. The coupled VW-pVT technique revisited

The purpose of this article is to re-examine the simultaneous measurements of the concentration of a supercritical gas in a polymer and of the concomitant change in volume of the polymer with the coupled VW-pVT technique [Hilic S, Pádua AAH, Grolier J-PE. Rev Sci Instrum 71 (11) (2000) 4236-41; Hilic S, Boyer SAE, Pádua AAH, Grolier J-PE. J Polym Sci B: Polym Phys 39 (2001) 2063-2070]. The experimental set-up consists of an original coupling of two techniques, a vibrating-wire sensor VW to weigh the polymer sample during the sorption and a pressure decay pVT-method to measure the quantity of gas, transferred from a high-pressure calibrated volume, which is absorbed by the polymer sample. The present study is related to the sorption and desorption of light gases (like CH₄, CO₂, H₂S, N₂) usually found in petroleum products circulating in pipelines made of semicrystalline polymers (like polyolefins and fluorinated polymers).Results for CO₂ in medium-density polyethylene, MDPE, and in poly(vinylidene fluoride), PVDF (or PVF₂), in the range of temperatures up to 391 K and pressures up to 43 MPa, are reported and discussed. Experiments allow the apparent concentration of gas dissolved in the polymer to be established; the associated swelling of the polymer is estimated using the Sanchez-Lacombe equation of state. Then, the data of the corrected concentration of the gas in the polymer are correlated with the semi-empirical ‘dual-mode’ model. Whenever possible to compare our results are in good agreement with existing literature data.     

Gas-liquid mass transfer in a slurry bubble column operated at gas hydrate forming conditions

Gas-liquid interphase mass transfer was investigated in a slurry bubble column under CO₂ hydrate forming operating conditions. Modeling gas hydrate formation requires knowledge of mass transfer and the hydrodynamics of the system. The pressure was varied from 0.1 to 4 MPa and the temperature from ambient to 277 K while the superficial gas velocity reached 0.20 m/s. Wettable ion-exchange resin particles were used to simulate the CO₂ hydrate physical properties affecting the system hydrodynamics. The slurry concentration was varied up to 10%vol. The volumetric mass transfer coefficient (k_la_l) followed the trend in gas holdup which rises with increasing superficial gas velocity and pressure. However, k_la_l and gas holdup both decreased with decreasing temperature, with the former being more sensitive. The effect of solid concentration on k_la_l and gas holdup was insignificant in the experimental range studied. Both hydrodynamic and transport data were compared to best available correlations.     

Evaluation of assisting methods on fluidization of hydrophilic nanoagglomerates by monitoring moisture in the gas phase

Agglomerates of nanoparticles were fluidized conventionally and under the influence of assisting methods such as vibration and/or moving magnetic particles. The adsorption/desorption rate of moisture of fluidized hydrophilic nanopowders was monitored during humidification/drying of the powder in order to find their adsorption isotherms at room temperature and to evaluate the assisting methods. Adsorption isotherms were verified by a gravimetric method. The nanopowders studied were Degussa Aerosil^® 200 and Aerosil^® 90, which were chosen because of their different fluidization behaviors.The moisture level in the nitrogen gas used to fluidize the powders was monitored on-line by using humidity sensors upstream and downstream of the fluidized bed. Moisture was added to the fluidizing nitrogen by bubbling it through water. The amount of moisture adsorbed/desorbed by the powders was obtained by integration of the time dependant moisture concentration. It was found that when the bed of powder is assisted during fluidization, the mass transfer between the gas and the nanopowder, as measured by the amount of moisture adsorbed/desorbed, is larger than when the powder is conventionally fluidized. Vibration assistance was found to be more effective for Aerosil^® 200, an APF type nanopowder, but magnetic assistance was needed for Aerosil^® 90 in order to break down the very large agglomerates formed in this ABF nanopowder.     

Adsorption of 1,1,3,3-tetramethyl-2-thiourea on the mercury electrode: dependence on the concentration of the base electrolyte

Adsorption of 1,1,3,3-tetramethyl-2-thiourea (TMTU) on a mercury electrode from 1, 0.5, and 0.1 M NaClO₄ is described by means of the adsorption isotherms constants calculated from the surface pressure as a function of electrode charge density and adsorbate bulk concentration. The adsorption parameters for the double-layer were calculated based on the data from the differential capacity-potential curves. The values of the relative surface excess increase with an increase in the concentration of NaClO₄. In each system studied, significantly smaller values of Γ_S for σ_M<0 were obtained, compared with the corresponding values for σ_M≥0. At positive values of σ_M, the values of ΔG° obtained from either the Frumkin or the Flory-Huggins isotherm are similar. However, the values of the parameter A obtained from the Flory-Huggins isotherm are lower.The dependence of Φ^M−2 on the relative surface excess at a constant charge density is nonlinear. The rectilinear segments of these dependences obtained for smaller values of Γ′ were analyzed in order to calculate the electrostatic parameters of the inner layer.     

Effects of the operating variables on hydrotreating of heavy gas oil: Experimental, modeling, and kinetic studies

The effects of H₂ purity, pressure, gas/oil ratio, temperature, and LHSV on hydrotreating activities were investigated in a micro-trickle bed reactor using a commercial NiMo/γ-Al₂O₃ catalyst. Heavy gas oil (HGO) from Athabasca bitumen was used as feed. Due to their significant effects on H₂ partial pressure, H₂ purity, pressure, and gas/oil ratio were chosen and used in a central composite design (CCD) method. Experimental conditions used were H₂ purity, pressure, and gas/oil ratio were: 75-100 vol.% (with the rest methane), 7-11 MPa, and 400-1200 mL/mL, respectively. The effect of LHSV (0.65-2 h⁻¹) and temperature (360-400 °C) were studied in a separate set of experiments. Vapor/liquid equilibrium (VLE) calculations were performed to determine the inlet and outlet H₂ partial pressures. It was observed that the enhancing effects of H₂ purity on hydrodenitrogenation (HDN) and hydrodearomatization (HDA) activities were greater than that of gas/oil ratio; however, it was comparable to pressure. Hydrodesulphurization (HDS) activity was not considerably affected by H₂ purity, pressure, or gas/oil ratio. Increasing LHSV led to a decrease in HDS, HDN, and HDA activities while increasing temperature resulted in an increase in HDS and HDN; HDA had maximum activity at about 385 °C. Kinetic fitting of the data to a pseudo-first-order power law model suggested that conclusions on hydrotreating activities’ responses to a changing H₂ pressure could be equally drawn from either inlet or outlet H₂ partial pressure. However, from the catalyst deactivation standpoint, it is recommended that such conclusions are drawn from the outlet H₂ partial pressure.     

High pressure phase behaviour of mixtures of hydrogen and the ionic liquid family [cnmim][Tf2N]

The high-pressure solubility of hydrogen gas in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)amide ([emim][Tf₂N]) was measured experimentally in an equipment based on the synthetic technique. Measurements were carried out within a temperature range of 310–450 K and pressures up to 15 MPa. Hydrogen solubility was shown to be low in this ionic liquid, reaching a maximum concentration of about 6 mole percent at the highest temperatures and pressures investigated. Hydrogen solubility showed an “inverse” temperature effect, indicating increased solubility at higher temperatures in contrast to other commonly investigated gas solubilities in ionic liquids, such as carbon dioxide. Within the temperature and pressure range investigated, solubility isotherms on a pressure–concentration diagram approximated linear behaviour. It was also shown that the solubility of hydrogen increases as the alkyl side chain of the cation increases in size within the homologous family.     

Adsorption behaviour of Cu and Cd onto natural bentonite

The adsorption behaviour of Cu²⁺ and Cd²⁺ onto bentonite was studied as a function of temperature under optimized conditions of amount of adsorbent, particle size, pH, concentration of metals, and shaking time. The adsorption patterns of metal ions onto followed the Langmuir, Freundlich and Dubinin-Radushkevich isotherms. This included adsorption isotherms of single-metal solutions at 298-333 K by batch experiments. The thermodynamic parameters such as variation of enthalpy ΔH, variation of entropy ΔS and variation of Gibbs free energy ΔG were calculated from the slope and intercept of lnK_o vs. 1 / T plots. The adsorptions were endothermic reactions. The results suggested that natural bentonite was suitable as sorbent material for the recovery and adsorption of metal ions from aqueous solutions.     

Gas foaming of segmented poly(ester amide) films

Biodegradable segmented poly(ester amide)s, based on dimethyl adipate, 1,4-butanediol and N,N′-1,2-ethanediyl-bis[6-hydroxy-hexanamide], with two distinct melting transitions were gas foamed using carbon dioxide (CO₂). Polymer films were saturated with CO₂ at 50 bar for 6 h after which the pressure was released. The samples were immersed in octane at the desired temperature after which foaming started immediately. Just above the lower melt transition the polymers retain adequate mechanical properties and dimensional stability, while the chain mobility increased sufficiently to nucleate and expand gas cells during the foaming process. In this way semi-crystalline poly(ester amide)s can be gas foamed below the flow temperature.Two poly(ester amide)s with 25 mol% (PEA2,5-25) and 50 mol% (PEA2,5-50) of bisamide segment content were foamed at 70 and 105 °C, respectively. The storage modulus (G′) of both pure polymers at the onset foaming temperature is 50-60 MPa. Closed-cell foams were obtained with a maximum porosity of ∼90%. The average pore size of PEA2,5-25 ranges from 77 to 99 μm. In contrast, the average pore size of PEA2,5-50 is in between 2 and 4 μm and can be increased to 100 μm by lowering the CO₂ saturation pressure to 20 bar. The porosity of PEA2,5-50 foams using this saturation pressure decreased to 70%.     

Sorption and transport of linear and branched ketones in biaxially oriented polyethylene terephthalate

Equilibrium sorption and kinetics of acetone, methyl ethyl ketone (MEK), methyl n-propyl ketone (MnPK), and methyl i-propyl ketone (MiPK) uptake in uniform, biaxially oriented, semicrystalline polyethylene terephthalate films were determined at 35 °C and low penetrant activity. Sorption isotherms for all penetrants were well described by the dual-mode sorption model. Sorption and desorption kinetics were described either by Fickian diffusion or a two-stage model incorporating Fickian diffusion at short times and protracted polymer structural relaxation at long times. Diffusion coefficients and equilibrium solubility at fixed relative pressure decreased in the following order: acetone>MEK>MnPK>MiPK. Diffusion coefficients for each penetrant increased with increasing penetrant concentration.     

Pure and Binary Adsorption Equilibria of Methane and Carbon Dioxide on Silicalite

Abstract

For the separation of CH₄ and CO₂ from landfill gas, pure and binary adsorption behavior of these gases were studied up to 5 atmosphere pressure at 40, 70, and 100°C for silicalite as the adsorbent. Pure and binary adsorption isotherms were determined experimentally and compared to predicted isotherms by several equilibrium models, as well as the other available data in the literature. Experimental binary isotherms at different concentrations were determined by using three concentration pulse methods (CPM). HT–CPM (Harlick‐Tezel CPM) was observed to be the best one to describe the behavior of this binary system. Equilibrium phase diagrams and separation factors were obtained from the experimental binary isotherms. For this system, the integral thermodynamic consistency tests were also shown and discussed.