Adsorption Equilibrium of Benzene-P-Xylene Vapor Mixture on Silicalite

Adsorption equilibrium of benzene-p-xylene vapor mixture on silicalite is measured at 70^oC with a specially designed cyclic volumetric apparatus at pressure levels of 2.53 and 1.20 kPa. The isobaric isotherms are S-shaped, and selectivity curves at different pressures cross over; the p-xylene selectivity at 2.53 kPa is higher than that at 1.20 kPa over a certain composition range. The heterogeneous ideal adsorption solution (HIAS) model implemented on two patches qualitatively predicts these highly unusual behavior. The observed extraodinary phenomena are attributed to structural heterogeneity, a result of the tight-fit of sorbate molecules in silicalite pores. The succes of HIAS attests to the paramount importance of adequate representation of heterogeneity in adsorption models

Gibbs Dividing Surface and Helium Adsorption

All adsorption data is based on the definition of Gibbs dividing surface, which is a purely mathematical transformation. Adsorption measurements in microporous solids necessitate experimental determination of the dividing surface. An international protocol does not exist on how to perform this important measurement. Commonly, helium is assumed not to adsorb and used as a probe molecule for this measurement. Each experimentalist chooses an arbitrary set of conditions, often without even disclosing them, which adds to the confusion in adsorption literature. Here, a self-consistent method for the analysis of helium data is proposed which does not assume non-adsorbing helium. The method is compared to others using the extensive set of helium/silicalite data. The Gibbs dividing surface and hence the helium isotherms at all temperatures are determined

Adsorption Equilibrium of Benzene-P-Xylene Vapor Mixture on Silicalite

Adsorption equilibrium of benzene-p-xylene vapor mixture on silicalite is measured at 70^oC with a specially designed cyclic volumetric apparatus at pressure levels of 2.53 and 1.20 kPa. The isobaric isotherms are S-shaped, and selectivity curves at different pressures cross over; the p-xylene selectivity at 2.53 kPa is higher than that at 1.20 kPa over a certain composition range. The heterogeneous ideal adsorption solution (HIAS) model implemented on two patches qualitatively predicts these highly unusual behavior. The observed extraodinary phenomena are attributed to structural heterogeneity, a result of the tight-fit of sorbate molecules in silicalite pores. The succes of HIAS attests to the paramount importance of adequate representation of heterogeneity in adsorption models

Behavior and Performance of Adsorptive Natural Gas Storage Cylinders During Discharge

Adsorbed natural gas (ANG) has the potential to replace compressed natural gas in mobile storage applications, such as in vehicles. Although a substantial research effort has been devoted to ANG, very few studies evaluate the impact of heat of adsorption on system performance. This paper concentrates on the impact of heat of adsorption on ANG performance during discharge, while the gas outflow rate is dictated by the energy demand of the application. The temperature drop and performance loss was measured with commercially available ANG cylinders under realistic conditions. Data show as high as a 37°C temperature drop at high discharge rate, with a performance loss approaching 25% of isothermal capacity. The performance loss is expected to be 15-20% at moderate discharge rates. Analysis of data and predictions of a simple model indicate that the ANG system is neither adiabatic nor isothermal during discharge; the thermal capacity of the vessel wall and external heat transfer conditions have a significant effect on system behavior. The poor thermal conductivity of packed adsorbent is a major obstacle for the utilization of these energy sources. Changing the flow direction during discharge from axial to radial by a perforated tube inserted at the center of the cylinder significantly reduces the performance loss by increasing the heat transfer from the wall to the central region. At intermediate discharge rates, where the inserted tube has the largest impact, the performance loss is reduced to 12% from 22% without the tube under identical conditions

In-plant testing of membranes to treat electroplating wastewater

This is the final report submitted for the work performed under the NASA Cooperative Agreement NCC3-301 for the project entitled 'In-Plant Testing of Membranes To Treat Electroplating Waste water'. The main objective of the research project was to determine if the crosslinked polyacrylic acid salt films developed by NASA scientists could be used for heavy metal removal from the wastewater generated by the metals-finishing or electroplating industry. A variety of tasks identified in the original proposal were completed. These included: (1) analysis of our industrial partner Aetna Plating's zinc electroplating process and its wastewater treatment needs for zinc removal; (2) design and construction of a laboratory-scale unit to continuously supply and remove the ion exchange films from the zinc wastewater; (3) performance of a series of runs on such a unit to determine its operating characteristics; and (4) design of a prototype unit for use at the industrial site. In addition, there were a number of tasks that had not been identified in the original proposal but were later judged to be necessary for the successful completion of the project. These were: (1) batch equilibrium and kinetic experiments with analysis of the experimental results to accurately determine the equilibrium and kinetic parameters for the ion exchange films; (2 ) simulation studies for proper design of the prototype unit; and (3) preliminary runs to exchange the films from H form to Calcium form

Development of an intelligent motion controller and its application to the automation of a McBain-Bakr balance

This paper presents a modular approach to motion control using a microconlroller-based stepper motor driver. As an application of the driver, an inexpensive and portable one-dimensional robot was built to automate an existing experimental setup for measurement of adsorption isotherms using the McBain-Bakr technique. Automatic recording of position versus time yields data for the sludy of adsorption/desorption dynamics

Activity Coefficients of Adsorbed Mixtures

Experimental and simulated data for adsorption of gas mixtures on energetically heterogeneous surfaces like activated carbon and zeolites exhibit negative deviations from ideality. The deviations are large in some cases, with activity coefficients at infinite dilution equal to 0.1 or less. Similar molecules form ideal mixtures, but molecules of different size or polarity are nonideal. Equations for bulk liquid mixtures (Wilson, Margules, etc.) do not apply to isobars for adsorbed mixtures. A two-constant equation for activity coefficients as a function of composition and spreading pressure is in good agreement with theory, simulation, and experiment

Electrodeposition of Nickel Nanowires and Nanotubes Using Various Templates

Nickel nanotubes and nanowires are grown by galvanostatic electrodeposition in the pores of 1000, 100, and 15 nm polycarbonate as well as in anodised alumina membranes at a current density of 10 mA cm-2. The effects of pore size, porosity, electrodeposition time, effective current density, and pore aspect ratio are investigated. Nickel nanotube structures are obtained with 1000 nm pore size polycarbonate membrane without any prior treatment method. At the early stages of electrodeposition hollow nickel nanotubes are produced and nanotubes turn into nanowires at longer depositon times. As effective current density accounting for the membrane porosity decreases, the axial growth direction is favoured yielding nanowires rather than nanotubes. However, for smaller pore size polycarbonate membranes, nanowires are obtained even though effective current densities were higher. We believe that when the pore diameter is below a critical size, nanowires grow regardless of current density since narrow pores promote layer by layer growth of nanorods due to smaller surface area of the pore bottom compared to pore walls. Pore size has a dominant effect over effective current density in determining the structure of the fibres produced for small pores. Nickel nanowires are also obtained in the small pores of anodised alumina, which has higher aspect ratios. High aspect ratio membranes favour the fabrication of nanowires regardless of current density

Electrodeposition of Nickel Nanowires and Nanotubes Using Various Templates

Nickel nanotubes and nanowires are grown by galvanostatic electrodeposition in the pores of 1000, 100, and 15 nm polycarbonate as well as in anodised alumina membranes at a current density of 10 mA cm-2. The effects of pore size, porosity, electrodeposition time, effective current density, and pore aspect ratio are investigated. Nickel nanotube structures are obtained with 1000 nm pore size polycarbonate membrane without any prior treatment method. At the early stages of electrodeposition hollow nickel nanotubes are produced and nanotubes turn into nanowires at longer depositon times. As effective current density accounting for the membrane porosity decreases, the axial growth direction is favoured yielding nanowires rather than nanotubes. However, for smaller pore size polycarbonate membranes, nanowires are obtained even though effective current densities were higher. We believe that when the pore diameter is below a critical size, nanowires grow regardless of current density since narrow pores promote layer by layer growth of nanorods due to smaller surface area of the pore bottom compared to pore walls. Pore size has a dominant effect over effective current density in determining the structure of the fibres produced for small pores. Nickel nanowires are also obtained in the small pores of anodised alumina, which has higher aspect ratios. High aspect ratio membranes favour the fabrication of nanowires regardless of current density