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.     

Bio‐Regeneration of Desulfurization Adsorbents by Selected P. delafieldii R‐8 Strains

Abstract

Adsorption properties of different adsorbents such as reduced NiY, AgY, alumina, 13X, and activated carbon were studied with dibenzothiophene (DBT) and naphthalene as model compounds. The desorption of DBT was carried on thermo gravimetric–differential thermal analysis (TG‐DTA). The interaction of DBT with different adsorbents follows the sequence: activated carbon > reduced NiY > AgY > activated alumina > 13X. The bio‐regeneration of these adsorbents was studied with P. delafieldii R‐8 as desulfurization strains. Adding P. delafieldii R‐8 cells can improve DBT desorption from adsorbent AgY. The desorption of DBT from adsorbents by bio‐regeneration of adsorbents follows the sequence: 13X > alumina > AgY > reduced NiY>activated carbon. The presence of naphthalene can decrease the desorption of sulfur compounds. The adsorption capacity of AgY decreases for the first time recycling and then changes little. The decrease of the adsorption capacity is due to the loss of Ag⁺ ions.     

Adsorption Decontamination of Radioactive Waste Solvent by Activated Alumina and Bauxites

Abstract

An adsorption process utilizing activated alumina and activated bauxite adsorbents was evaluated as a function of operating parameters for the removal of low level radioactive contaminants from organic waste solvent generated in the fuel reprocessing facilities and support operations at Savannah River Site. The waste solvent, 30 vol% tributyl phosphate in n-paraffin diluent, was degraded due to hydrolysis and radiolysis reactions of tributyl phosphate and n-paraffin diluent, producing fission product binding degradation impurities. The process, which has the potential for removing these activity-binding degradation impurities from the solvent, was operated downflow through glass columns packed with activated alumina and activated bauxite adsorbents. Experimental breakthrough curves were obtained under various operating temperatures and flow rates. The results show that the adsorption capacities of activated alumina and activated bauxite were in the order of 10⁴ and 10⁵ dpm/g of adsorbent, respectively. The performance of the adsorption process was evaluated in terms of dynamic parameters (i.e., adsorption capacity, the height and the efficiency of adsorption zone) in such a way as to maximize the adsorption capacity and to minimize the height of the mass transfer or adsorption zone.     

A marked change in electrical resistivity of alumina upon exposure to trace concentration of acetone vapours

The alumina wafer pre-annealed in dry air manifests chemiresistive behaviour: the electrical resistivity is highly sensitive to trace concentrations of acetone vapours even at room temperature. The response suggests that the alumina can be applicable in the role of a room-temperature operated acetone sensor in the ppm range. The elemental analysis of the alumina surface suggests that the sensing mechanism is governed by interaction of adsorbed acetone molecules with alkaline impurities such as sodium and/or magnesium ions naturally occurring in the α-Al₂O₃.     

氯硅烷中痕量磷杂质的检测方法及应用

针对混合氯硅烷原料中沸点接近、分离困难的含磷杂质物系,对比金属氧化物吸附剂,以13X分子筛（13X）及负载CuCl₂的13X分子筛（Cu-13X）作为络合吸附剂进行气相吸附实验,并采用紫外分光光度计检测氯硅烷中磷杂质含量,结合水中和氯硅烷原料中磷含量分析实验考察了氯硅烷原料预处理过程中水解液组成、氯硅烷原料的相态对用紫外分光光度计检测磷杂质含量范围的影响规律及机理,探究了13X及Cu-13X在20℃时作为络合吸附剂的突破曲线。结果表明,氯硅烷原料的预处理相态为气相并以高纯氮气作载气通入高纯水中,氯硅烷中磷杂质质量含量的检测范围为0.0003～0.03,13X经过CuCl₂浸渍改性后性能得到大幅度提升,当穿透实验进行到混合液体积为120mL时,络合吸附剂对PCl₃的脱除效率仍大于80%,而在混合液体积20mL,左右13X-分子筛则被完全穿透失去吸附能力。     

Effects of capillary condensation on adsorption and thermal desorption dynamics of water in zeolite 13X and layered beds

The effects of capillary condensation on the adsorption and thermal desorption dynamics of water in zeolite 13X beds and layered beds with zeolite 13X/silica gel or zeolite 13X/alumina were experimentally and theoretically studied. As the equilibrium isotherm of water on zeolite 13X pellet was found to be most favorable at a low relative humidity and indicated capillary condensation at a high relative humidity, it was possible to construct a non-isothermal model that included capillary condensation and that could successfully predict plateaus of temperature and concentration profiles in thermal regeneration. In adsorption breakthrough, by using a feed in the capillary condensation range of the isotherm on zeolite 13X, the breakthrough curve showed a shock wave in the low concentration and a proportionate pattern in the high concentration. In thermal desorption breakthrough, the desorbed water at the upper part of the bed was re-adsorbed at the lower part of the bed, and that re-adsorption mainly occurred in the capillary condensation range of the isotherm. Therefore, even though an adsorption was performed at a feed in the favorable range of the isotherm, and could be well predicted with type I isotherm, its desorption dynamics should be predicted by using the isotherm model with its consideration of capillary condensation. The layered bed with silica gel or alumina did not have any advantage over the zeolite 13X bed with respect to adsorption breakthrough performance. However, compared to the zeolite 13X bed, the complete regeneration time in the layered bed was drastically shortened due to a greater variation of the amount of equilibrium adsorption of water under temperature on both silica gel and alumina. In addition, since an increase in temperature led to a greater decrease of the amount of equilibrium adsorption of water on silica gel than on alumina, a layered bed with silica gel obviously could be regenerated more efficiently than a layered bed with alumina.     

Surface properties of porous carbons obtained from polystyrene-based polymers within inorganic templates: role of polymer chemistry and inorganic template pore structure

Three inorganic adsorbents were applied as templates to produce porous carbons from polystyrene-based organic polymers. As matrices, amorphous silica gel, mesoporous alumina and microporous zeolite 13X were used. Organic precursors were polystyrene sulfonic acid (co-maleic acid) sodium salt and polystyrene co-maleic acid isobutyl/methyl mixed ester. The impregnated templates were carbonized at 800 °C. After removal of inorganic matrices porous carbons were obtained. Materials were characterized by adsorption of nitrogen, thermal analysis, potentiometric titration and SEM. Owing to the template carbonization, highly mesoporous carbons were obtained (S_BET up to 1500 m²/g, V_t up to 3 cm³/g) with majority of pores with sizes between 20–200 Å. Although the carbons were not replicas of their matrices, the carbonization within the confined space with utilization of self-released pore formers resulted in unique carbonaceous materials with very acidic surface. That acidity is linked to either exothermic effect of sodium reactivity with moist air or susceptibility for air oxidation of small graphene layers formed in the confined pore space.     

Criteria for Selection of an Adsorbent for a Temperature Swing Process: Applied to Purification of an Aliphatic Solvent Contaminated with Aromatic Solutes

Abstract

Temperature swing adsorption (TSA) is different in several respects from conventional adsorption. This paper explores the distinctions from the standpoint of adsorbent characteristics. In particular, a fixed-bed TSA process is considered for separating dilute aromatics from aliphatics (e.g., toluene and/or xylene in heptane). Relevant adsorbent characteristics include thermal-exchange capacity and properties that affect dissipative effects, e.g., intraparticle diffusivity, bed permeability, axial dispersion coefficient, and thermal diffusivity. Many of the dissipative effects can be manipulated by adjusting particle size, though trade-offs exist that have no clear-cut technical resolution. The adsorbents considered were silica gel, activated alumina, activated carbon, zeolite 13X, and a polymeric adsorbent (XAD-7). Silica gel was selected due to its superior thermal-exchange capacity. The other properties did not vary enough among the other adsorbents to compensate for their lesser capacities.     

Optimizing the thermoelectric performance of zigzag and chiral carbon nanotubes

Using nonequilibrium molecular dynamics simulations and nonequilibrium Green''s function method, we investigate the thermoelectric properties of a series of zigzag and chiral carbon nanotubes which exhibit interesting diameter and chirality dependence. Our calculated results indicate that these carbon nanotubes could have higher ZT values at appropriate carrier concentration and operating temperature. Moreover, their thermoelectric performance can be significantly enhanced via isotope substitution, isoelectronic impurities, and hydrogen adsorption. It is thus reasonable to expect that carbon nanotubes may be promising candidates for high-performance thermoelectric materials.     

CO2 Adsorption and Desorption for CO2 Enrichment at Low-Concentrations Using Zeolite 13X

Adsorption of CO₂ using zeolite 13X as adsorbent has been studied extensively, but little attention has been paid to CO₂ adsorption at very low concentrations such as in the ambient air. Furthermore, there is almost no information on CO₂ desorption characteristics. In a carbon enrichment for plant stimulation system, ambient CO₂ is enriched from 400 to 1000 ppm to provide an enriched CO₂ stream for plant growth in greenhouses. To provide essential design data, systematic performance tests were carried out to evaluate both the adsorption and desorption capacity, enrichment factor, moisture content, and cyclic performance. It was found that the adsorption capacity and CO₂ concentration in the enriched air are a function of adsorption temperature and the difference of adsorption and desorption temperatures, for a given adsorbent loading at a properly selected gas flow rate.     

壳聚糖基大孔炭质整体材料的制备及其对痕量二氧化硫的吸附性能

以壳聚糖为碳源,综合采用冰模板技术和低温热解炭化技术,制备出具有蜂窝状孔结构特征的大孔炭质整体材料,研究了此类新材料对痕量二氧化硫的吸附性能及再生能力。结果表明,大孔炭质整体材料蜂窝状孔结构的形成及其规整程度与冰模板过程的冷冻时间等因素密切相关;200℃下低温热处理可得到具有丰富表面含氮官能团的大孔炭质整体材料;经氨水溶液中的离子交换功能化处理后,该大孔炭质整体材料对低浓度SO₂的吸附容量显著提高,可达到57 mg·g^-1;吸附饱和后,经空气简单吹扫处理,大孔炭质整体材料即可大部分再生,少数不可再生部分是由于质子化的氨基与亚硫酸根和硫酸根在吸附过程中形成了不可逆化学吸附产物季铵盐所致。壳聚糖基大孔炭质整体吸附剂材料有望在污染空气的脱硫净化,特别是在质子交换膜燃料电池的阴极空气脱硫净化方面发挥重要作用。     

Studies on the Adsorption of Americium on Alumina from Aqueous Nitric Acid-Oxalic Acid Solutions

Abstract

This paper reports a study on the adsorption of Am(III) on alumina from oxalic acid-nitric acid solutions. Distribution coefficients for Am(III) on alumina at different oxalic acid-nitric acid concentrations have been determined and optimum conditions for loading and elution of Am from alumina columns have been established. Separation of Am from Pu and the effects of other ions, such as U(VI) and Fe(III), have also been studied. Am and Pu recoveries better than 99.5% were obtained.     

Kinetics and Thermodynamics of Lead (II) Adsorption on Vermiculite

Abstract

The kinetics and thermodynamics of Pb(II) adsorption on vermiculite have been studied by the sets of experiments at various conditions (temperature, initial lead concentration and adsorption time). The structures of the vermiculite before and after Pb(II) adsorption were measured using X‐ray diffraction (XRD), thermogravimetric analysis (TA), and X‐ray photoelectron spectroscopy (XPS). Adsorption of Pb(II) was strongly affected by pH. First order kinetics model best described the reaction rate, and the adsorption capacity calculated by the model was consistent with that actual measurement. Isotherms for the adsorption of Pb(II) on vermiculite were developed and the equilibrium data fitted well to the Langmuir and Freundlich models. Thermodynamic parameters such as enthalpy, entropy, and free energy were calculated using the Van't Hoff equations. The thermodynamics of Pb(II) on vermiculite indicates the spontaneous and endothermic nature of adsorption. Quantitative desorption of Pb(II) from vermiculite was found to be more than 40% which facilitates the sorption of metal by ion exchange     

Computer simulation of the gas separation properties of zeolite Li-X

The criteria determining the effectiveness of a particular zeolite for gas separation are the physical pore size and the location, size, and charge of any cations present. To date the experimentalist has had to use a great deal of intuition when selecting a zeolite for a specific use. Computer modelling of such systems, using a Grand Canonical Monte Carlo method, has been successful in elucidating the behaviour of adsorbates in a wide range of systems. Successful predictions for adsorption isotherms for nitrogen, oxygen and argon have been previously reported by the authors for zeolites A, X and Y with calcium and sodium cations.The aim of the work reported in this paper is to investigate the air separation properties of a different, although similar system namely: zeolite X with lithium cations. The simulations performed using Cerius² molecular modelling software are able to predict adsorption isotherms for nitrogen and oxygen gases, both as single component, and as binary mixtures in Li-X. Further the predicted equilibrium separation factor is calculated to be in the range of 6 to 13 at room temperature, making this system ideal for the preferential adsorption of nitrogen and production of oxygen.     

Sorption of nitrogen,oxygen, and argon in Cd (II) exchanged zeolite X: volumetric equilibrium adsorption and grand canonical Monte Carlo study

The adsorption of nitrogen, oxygen and argon has been studied in cadmium (II) cations exchanged zeolite X at 288.2 and 303.2 K. Experimentally measured adsorption isotherms are compared with theoretically calculated data using grand canonical Monte Carlo (GCMC) simulation. Nitrogen showed higher adsorption capacity and selectivity than oxygen and argon in these zeolite samples. The cadmium exchanged zeolite X was showed that increased adsorption capacity for nitrogen, oxygen, and argon with increase in Cd (II)-exchange levels, indicating as charge density increases adsorption capacity also increase. Isosteric heat of adsorption data showed stronger interactions of nitrogen molecules with cadmium cations in zeolite samples. These observations have been explained in terms of higher electrostatic interaction of nitrogen with extra framework zeolite cations. The selectivity of oxygen over argon is explained in terms of its higher interaction with Cd (II)-exchanged zeolites than argon molecules. The selectivity of N₂/O₂ of cadmium-exchanged zeolite X is better than only sodium containing zeolite-X. Heats of adsorption and adsorption isotherms were also calculated using GCMC simulation algorithm. Simulation studies expectedly show the proximity of nitrogen molecules to the locations of extra framework sodium and cadmium cations.     

The direct adsorption of low concentration gallium from fly ash

This study is mainly focused on the direct adsorption of low concentration gallium from the feed solution in pre-desilication soda-lime sintering process from coal fly ash. The adsorption kinetics, mechanism, and the influence of impurities, cyclic times, and eluant content are systematically researched. Results showed that the adsorption capacity was 2.89 mg/g resin with gallium concentration of 50 mg/L. The adsorption mechanism could be explained by the interaction between the oxygen atoms and nitrogen atoms of amidoxime group. Gallium was eluted efficiently by NaOH and Na₂S mixed solution and the concentration could be reached to 2400 mg/L.     

Adsorption of Acetaldehyde,Propionaldehyde, and Butyraldehyde on Molecular Sieve 13X

Abstract

Adsorption isotherms for acetaldehyde, propionaldehyde, and butyraldehyde on Davison molecular sieve 13X were determined gravimetrically at three temperatures. The isoteric heat of adsorption of acetaldehyde and propionaldehyde decreased initially with the increase in loading, then increased up to a certain point after which it decreased again. For butyraldehyde the heat of adsorption initially increased and then decreased with increased loading. The equilibrium adsorption data reduce to a single characteristic curve when correlated according to Polanyi's potential theory. Recently proposed isotherm equations for heterogeneous surfaces by Sircar and Hines et al. were used to correlate the isotherm data. The BET equation gave a good correlation of the data for a relative pressure range of 0.05 ≤ P/P, ≤ 0.25. The monolayer surface coverage and surface area were calculated by the Langmuir and the BET equations. The Langmuir equation consistently provided a larger estimate of the surface area than did the BET equation.     

低湿CO2/H2O混合气体吸附特性实验

CO₂捕集、封存及利用是实现“双碳”目标的重要途径,为将碳捕集后的低湿CO₂/H₂O进行CO₂提纯和资源化利用,采用动态吸附实验研究了不同温度（303K、313K）、H₂O含量（0.7%~3.0%）的CO₂/H₂O在活性炭、活性氧化铝、分子筛3A和13X四种吸附剂上的动态吸附穿透曲线、吸附床温度分布、吸附量,分析了CO₂/H₂O分离系数和吸附热。结果表明,在CO₂/H₂O动态吸附过程中,吸附床温度与各组分浓度随时间变化趋势相同。H₂O饱和时间随进气温度升高而缩短;H₂O含量增加,抑制CO₂吸附;活性炭和氧化铝中H₂O的饱和时间随H₂O含量增加而增长,但分子筛3A和13X饱和时间缩短。H₂O吸附量随H₂O含量增加而增加,吸附热随吸附量增加而减小,CO₂则相反。分子筛3A对CO₂吸附量最小且CO₂/H₂O分离系数最大。H₂O含量小于1%时,CO₂吸附量最大的分子筛13X分离系数大于活性氧化铝,分子筛3A和13X适合分离低湿CO₂/H₂O。     

Removal of Hazardous Anions from Aqueous Solutions by La(lll)- and Y(lll)-lmpregnated Alumina

Abstract

New adsorbents, La(III)- and Y(III)-impregnated alumina, were prepared for the removal of hazardous anions from aqueous solutions. A commercially available alumina was impregnated with La(III) or Y(III) ions by the adsorption process. The change in the surface charge due to the impregnation was measured by acid/base titration. The adsorption rate and the capacity of the alumina for La(III) and Y(III) ions were determined. The adsorption characteristics of the La(III)- and Y(III)-impregnated alumina and the original alumina for fluoride, phosphate, arsenate and selenite ions were analyzed under various conditions. The pH effect, dose effect, and kinetics were studied. The removal selectivity by the impregnated alumina was in the order fluoride > phosphate > arsenate > selenite. The impregnated alumina has been successfully applied for the removal of hazardous anions from synthetic and high-tech industrial wastewaters.     

The influence of spinel and magnesia powder bed on mechanical properties of alumina sintered under air and nitrogen atmosphere

ABSTRACT

The aim of the present work was changing the surface properties of alumina ceramic via sintering of samples in spinel MgAl₂O₄ and magnesia MgO powder bed. During sintering nitrogen and air atmosphere were used; and the reference material was sintered at the same conditions but in an alumina powder bed. All samples were sintered to a density higher than 99.2% of theoretical density of alumina. In order to examine samples SEM, EDX and XRD (X-ray diffraction from 18 to 70 °2Theta) analysis were performed together with B3B flexural strength measurement. Results revealed that by sintering of alumina samples in a spinel powder bed pore-free surfaces were prepared, which had a favourable effect on B3B flexural strength. This was ascribed to the high solubility of Al³⁺ in spinel at sintering temperatures, which increases the sintering driving force. A further positive effect on B3B flexural strength was observed when samples were sintered in nitrogen instead of air.