RAPID APPROXIMATE SOLUTIONS FOR ADSORPTION BED CONCENTRATION PROFILE AND BREAKTHROUGH CURVE BEHAVIOR: FAVORABLE ISOTHERMS AND BOTH PHASE RESISTANCES IMPORTANT

A simple method is presented for determining fluid-phase and solid-phase solute concentration profiles, and solute breakthrough curves, for fixed bed adsorbers when both the fluid-phase and solid-phase mass transfer resistances are important. The method applies to any nonlinear isotherm of the “favorable” type. Freundlich and Langmuir isotherms are used as specific examples in the present paper. Constant-pattern behavior and linear-driving-force rate laws are assumed.     

OPTIMIZATION OF PRESSURE SWING ADSORPTION EQUIPMENT PART II OPTIMIZATION OF TWO BED OXYGEN GENERATORS

Local equilibrium model described in Part I is used to stimulate both, the steady state operation conditions and transient regime after the start of PSA equipment. The effect of axial dispersion, adsorption isotherm nonlinearity and high pressure level is simulated. On the basis of numerical analysis, the operation of a classical two-bed oxygen generator is compared with two configurations having pressure equalizing step. The optimization strategy of the given PSA equipment has been proposed and the procedure is demonstrated on an example. The scaling-up condition for PSA equipments which can be described by local equilibrium model has been proposed on the basis of the theoretical analysis.     

Characterizing electrocatalytic surfaces: Electrochemical and NMR studies of methanol and carbon monoxide on Pt/C

We use cyclic voltammetry (CV) on fuel cell electrodes to elucidate the important differences between adsorbates resulting from carbon monoxide adsorption and methanol adsorption onto commercial Pt/C electrocatalysts in a sulfuric acid electrolyte. Under open circuit conditions, methanol was found to adsorb preferentially onto the Pt sites associated with “strongly bound” hydrogen. The sites associated with “weakly bound” hydrogen adsorbed methanol more slowly. In the case of CO adsorption, which requires no adsorbate dehydrogenation, all adsorption sites showed similar affinity towards the adsorbate. Electrochemical oxidation of the adsorbates derived from both methanol and CO exposure exhibit slower oxidation when the adsorbate is associated with cubic-packed-like sites than from close-packed-steps and other sites. NMR of a ¹³CO-adlayer prepared by electrochemical adsorption from low concentration ¹³CH₃OH shows a lower NMR shift and smaller linewidth than the previously reported values for electrochemically adsorbed ¹³CO gas. These results are interpreted in terms of adsorbate motion on the electrocatalyst surface.     

Removal of nitrogen oxides from air by chemicals-impregnated carbons

Fixation of nitrogen oxides (NO_x) in air onto granular activated carbon impregnated with chemicals was attempted to improve removal efficiency of NO_x by activated carbon adsorption. Nitric oxide (NO) and nitrogen dioxide (NO₂), were tried to remove by a flow test. Fixed-bed adsorption breakthrough curves were obtained when some kinds of carbon were used. The amount adsorbed of NO₂ changed with the amount and kinds of metallic salts impregnated. Chemicals-impregnated carbons were prepared from a commercial activated carbon. Among obtained carbons, the one which showed the highest selectivity for NO_x was chosen, and its performance with the change in humidity was determined. Removal mechanism of NO₂ was estimated, and the carbon impregnated with potassium hydroxide was found to be superior to any other carbon tested. The amount of the adsorbed NO and that produced by the reduction of NO₂ were determined from the breakthrough curves.     

The influence of demineralisation and ammoxidation on the adsorption properties of an activated carbon prepared from a Polish lignite

The preparation of cheap nitrogen-enriched materials with large adsorptive capacities and selectivity towards volatile organic compounds remains a challenge. Ammoxidation has been used to prepare nitrogen-enriched activated carbons using a demineralised Polish lignite. The lignite samples were demineralised by two different methods before nitrogen-enrichment by ammoxidation and physical activation in steam. The surface chemistry was investigated by elemental analysis, Boehm titration, infrared and XPS spectroscopies and adsorptive properties by a linear solvation energy relationship approach. Results show a quasi-total demineralisation and a higher reactivity towards nitrogen for the demineralised samples. The BET surface is also higher than for the non-demineralised lignite. Active carbons previously ammoxidated and demineralised are more interesting in terms of selective removal of gaseous pollutants.     

The effect of protein binding on ibuprofen adsorption to activated carbons

The potential of a range of polymer-based activated carbons to remove a non-steroidal anti-inflammatory drug ibuprofen from protein containing and protein-free solutions was studied. The adsorption capacity of five activated carbons produced from phenol-formaldehyde resin precursors (MAST Carbon Ltd) was compared to a cellulose coated activated carbon Norit RBX used in a commercial Adsorba^®300C haemoperfusion column (Gambro).Ibuprofen adsorption was studied in batch experiments over 24 h at pH=7.6 and 25 °C and adsorption equilibrium data were correlated with the Langmuir and Freundlich equations.Results showed that uncoated mesoporous MAST carbons can remove ibuprofen from model solutions both in the presence and absence of serum albumin. Ibuprofen is a highly protein-bound drug and the presence of serum albumin significantly affects the adsorption of ibuprofen by cellulose-coated microporous carbon used in Adsorba^®300C column.     

塑料密度的测定--理想气体状态方程法

介绍了测定常见聚乙烯塑料密度的理想气体状态方程法及其其原理。实验结果证明,以N2或He气为介质,在一密闭测试腔内进行一定固体颗粒的体积测量,可得出物质的密度,该方法操作快捷,测试周期短,测量准确及重复性好,对评价大批量聚乙烯密度提供了可行的参考方法。     

INFLUENCE OF DESIGN AND OPERATING CONDITIONS ON THE SYSTEM PERFORMANCE OF A TWO-STAGE ADSORPTION CHILLER

This article aims at clarifying the possible design and operating conditions for silica gel-water adsorption refrigeration cycles driven by near-ambient temperature waste heat sources (between 45 and 75°C) with relatively small regenerating temperature lifts (15 to 45 K). A two-stage silica gel-water advanced adsorption chiller is introduced and a simulation model of the chiller was developed to analyze the influence of operating and design conditions on the system performance (coefficient of performance, COP, and cooling capacity). It was hypothesized that the proposed chiller can be driven by low temperature waste heat at 55°C to produce effective cooling. Simulation results show that the operating conditions such as cycle time and hot and cooling water inlet temperature have an influential effect on cooling capacity and COP. COP is proportional to cycle time and heat transfer coefficient as well as inversely proportional to the cooling water inlet temperature, while there are optimum values of hot water temperature and silica gel weight for maximum COP. Cooling capacity mainly improves with the addition of silica gel weight and decreases as cooling water temperature increases. Simulation results also revealed that the system performance can be improved significantly by setting the design and operating conditions optimally.     

THE IRREVERSIBLE ADSORPTION OF PLUTONIUM HEXAFLUORIDE†

The room temperature adsorption of PuF_6(g) on a solid substrate was compared to the adsorption of UF6(g) on the same surface. Significantly more PuF_6(g) was adsorbed at pressures in the range of 1.2 to 0.2torr, accompanied by the evolution of molecular fluorine. The adsorbed UF₆ was easily desorbed by reducing the pressure. Most of the adsorbed PuF₆ remained on the surface when subjected to the same treatment.     

Derivation of the multisymplectic Crank–Nicolson scheme for the nonlinear Schrödinger equation

The Crank–Nicolson scheme as well as its modified schemes is widely used in numerical simulations for the nonlinear Schrödinger equation. In this paper, we prove the multisymplecticity and symplecticity of this scheme. Firstly, we reconstruct the scheme by the concatenating method and present the corresponding discrete multisymplectic conservation law. Based on the discrete variational principle, we derive a new variational integrator which is equivalent to the Crank–Nicolson scheme. Therefore, we prove the multisymplecticity again from the Lagrangian framework. Symplecticity comes from the proper discrete Hamiltonian structure and symplectic integration in time. We also analyze this scheme on stability and convergence including the discrete mass conservation law. Numerical experiments are presented to verify the efficiency and invariant-preserving property of this scheme. Comparisons with the multisymplectic Preissmann scheme are made to show the superiority of this scheme.