Doug Ruthven and Jorg Karger: Their Individual and Collective Contributions to the Field of Zeolite Science and Engineering

Prof. Doug Ruthven and Prof. Jörg Kärger are two giants in the field of zeolite science and engineering. Over their academic careers encompassing almost forty years each, they have contributed significantly to the advancement of fundamental understanding of adsorption and diffusion in zeolites as well as their industrial applications. The author, in the beginning of his academic career, had an opportunity to spend two years as a post-doctoral fellow in Prof. Ruthven’s laboratory at the University of New Brunswick (1975–1977). This experience actually motivated me to spend my academic career in working in the field of zeolite adsorption and diffusion. Nearly thirty years later, I spent a year as a Gast Mercator Professor at the University of Leipzig in the laboratory of Prof. Kärger (2005–2006). These two opportunities at two different ends of my academic career provided me with unique perspectives to reflect on the important contributions made by Professors Ruthven and Kärger to the field of zeolite science and technology. This article summarizes my personal perspectives on the breadth and depth of their contributions

Diffusivities of n-Alkanes in Silicalite By Steady-State Single-Crystal Membrane Technique

A novel experimental technique that measures the diffusive flux through a single-crystal membrane (SCM) was developed and tested. Unlike all other macroscopic techniques that depend on a transient response, SCM is used under steady-state conditions, which results in a wide range of applicability from 10−2 to 10−11 cm2/s. Phenomenological equations for the steady-state data analysis were developed. The variation of driving force over the diffusion path is included in the model. As required by thermodynamics, the micropore concentration is given as a function of surface-excess amount adsorbed and gas density. The membrane configuration measures diffusivity in only one crystallographic direction. The micropore difusivities of C1 to C10 normal alkanes through silicalite crystal in the z-direction were measured at 30, 50 and 70°C. The activation energies for micropore diffusion are also reported. The data agree excellently with the other two studies that measure directional diffusivities. Diffusion and adsorption of hexane and heptane in silicalite display structural heterogeneity induced by the comparable lengths of molecules and silicalite channels rather than diameter of molecule vis-à-vis pore diameter

lntracrystalline Diffusion of Benzene in Silicalite : Effect of Structural Heterogeneity

The sorption kinetics of benzene in silicalite have been measured gravimetrically using large silicalite crystals of sizes 350 µm × 105 µm × 105 µm and 270 µm × 70 µm × 70 µm in the temperature range 283–343 K. Experiments were performed under conditions that ensured isothermal operation with intracrystalline diffusion control. An analytical expression for the Darken\u27s correction factor (δ In P/δ In a) was derived based on the Hill–de-Boer equation and was used to determine the variation of corrected diffusivity with concentration. The transport diffusivity varied significantly with the adsorbed-phase concentration but the corrected diffusivity was found to be essentially independent of the concentration. However, at temperatures below the surface transition temperature, a maximum in corrected diffusivity was observed at an adsorbed-phase concentration of four molecules per unit cell (uc). This maximum is the direct result of the type IV isotherm exhibited by the silicalite–benzene system below the surface transition temperature. It is proposed that the increase in corrected diffusivity at the critical adsorbed-phase concentration of 4 molecules uc–1 arises from reorientation of benzene molecules resulting in a much more efficient packing in the pore channel system

lntracrystalline Diffusion of Benzene in Silicalite : Effect of Structural Heterogeneity

The sorption kinetics of benzene in silicalite have been measured gravimetrically using large silicalite crystals of sizes 350 µm × 105 µm × 105 µm and 270 µm × 70 µm × 70 µm in the temperature range 283–343 K. Experiments were performed under conditions that ensured isothermal operation with intracrystalline diffusion control. An analytical expression for the Darken\u27s correction factor (δ In P/δ In a) was derived based on the Hill–de-Boer equation and was used to determine the variation of corrected diffusivity with concentration. The transport diffusivity varied significantly with the adsorbed-phase concentration but the corrected diffusivity was found to be essentially independent of the concentration. However, at temperatures below the surface transition temperature, a maximum in corrected diffusivity was observed at an adsorbed-phase concentration of four molecules per unit cell (uc). This maximum is the direct result of the type IV isotherm exhibited by the silicalite–benzene system below the surface transition temperature. It is proposed that the increase in corrected diffusivity at the critical adsorbed-phase concentration of 4 molecules uc–1 arises from reorientation of benzene molecules resulting in a much more efficient packing in the pore channel system

Analysis of Thermal Effects in Infrared and Interference Microscopy: n-Butane-5A and Methanol-Ferrierite Systems

Recently, infrared and interference microscopy methods have been increasingly applied to measure internal concentration gradients and hence the uptake of different adsorbates in zeolite crystals. In contrast to conventional macroscopic batch uptake techniques, these microscopic/mesoscopic methods measure changes associated with single zeolite crystals. The analysis of data from these measurements to determine micropore diffusivities has been performed on the basis of the assumption that isothermal conditions prevail during both the adsorption and desorption experiments. This assumption is critically examined in this paper for the case of methanol diffusion in ferrierite crystals during adsorption and desorption to vacuum. It is shown by both detailed simulation as well as an order of magnitude analysis of time constants for heat transfer and diffusion that the temperature changes in the system are negligible during adsorption due to the high conductive heat transfer rate. However, during desorption to a vacuum, heat conduction is minimal so that heat transfer occurs only by radiation. Temperature changes as large as 5–7K are therefore to be expected at the beginning of the desorption process. However, since the time constant for the desorption process is of the order of hundreds of seconds, this temperature transient dissipates rapidly and has no significant impact on the overall desorption process. Even for the worst case scenario considered here, for both interference and infrared microscopy methods, the systems can be considered as essentially isothermal

Anwendung von Interferenz- und IR-Mikroskopie zur Charakterisierung und Untersuchung des Stofftransportes in nanoporösen Materialien

Die Anwendung der Interferenz-Mikroskopie bedeutet einen entscheidenden Durchbruch in der Untersuchung des Stofftransports von Gastmolekülen in nanoporösen Wirtsmaterialien. Diese Technik ermöglicht die Beobachtung der zeitaufgelösten intrakristallinen Konzentrationsprofile, die durch eine Änderung des umgebenden Gasdruckes entstehen. Dieser Ansatz wurde zur Untersuchung von Adsorptions- und Desorptionsprozessen in verschiedenen Zeolithsystemen verwendet. Die Vorteile dieser Technik, vor allem wenn sie mit Infrarotabsorptionsmessungen kombiniert wird, werden an Hand der experimentellen Resultate des Methanol-in-Ferrierit-Systems illustriert

The Changing Landscape for Stroke\ua0Prevention in AF: Findings From the GLORIA-AF Registry Phase 2

Background GLORIA-AF (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients with Atrial Fibrillation) is a prospective, global registry program describing antithrombotic treatment patterns in patients with newly diagnosed nonvalvular atrial fibrillation at risk of stroke. Phase 2 began when dabigatran, the first non\u2013vitamin K antagonist oral anticoagulant (NOAC), became available. Objectives This study sought to describe phase 2 baseline data and compare these with the pre-NOAC era collected during phase 1. Methods During phase 2, 15,641 consenting patients were enrolled (November 2011 to December 2014); 15,092 were eligible. This pre-specified cross-sectional analysis describes eligible patients\u2019 baseline characteristics. Atrial fibrillation disease characteristics, medical outcomes, and concomitant diseases and medications were collected. Data were analyzed using descriptive statistics. Results Of the total patients, 45.5% were female; median age was 71 (interquartile range: 64, 78) years. Patients were from Europe (47.1%), North America (22.5%), Asia (20.3%), Latin America (6.0%), and the Middle East/Africa (4.0%). Most had high stroke risk (CHA2DS2-VASc [Congestive heart failure, Hypertension, Age  6575 years, Diabetes mellitus, previous Stroke, Vascular disease, Age 65 to 74 years, Sex category] score  652; 86.1%); 13.9% had moderate risk (CHA2DS2-VASc = 1). Overall, 79.9% received oral anticoagulants, of whom 47.6% received NOAC and 32.3% vitamin K antagonists (VKA); 12.1% received antiplatelet agents; 7.8% received no antithrombotic treatment. For comparison, the proportion of phase 1 patients (of N = 1,063 all eligible) prescribed VKA was 32.8%, acetylsalicylic acid 41.7%, and no therapy 20.2%. In Europe in phase 2, treatment with NOAC was more common than VKA (52.3% and 37.8%, respectively); 6.0% of patients received antiplatelet treatment; and 3.8% received no antithrombotic treatment. In North America, 52.1%, 26.2%, and 14.0% of patients received NOAC, VKA, and antiplatelet drugs, respectively; 7.5% received no antithrombotic treatment. NOAC use was less common in Asia (27.7%), where 27.5% of patients received VKA, 25.0% antiplatelet drugs, and 19.8% no antithrombotic treatment. Conclusions The baseline data from GLORIA-AF phase 2 demonstrate that in newly diagnosed nonvalvular atrial fibrillation patients, NOAC have been highly adopted into practice, becoming more frequently prescribed than VKA in Europe and North America. Worldwide, however, a large proportion of patients remain undertreated, particularly in Asia and North America. (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients With Atrial Fibrillation [GLORIA-AF]; NCT01468701