Development of catalytic hydrogenation reactors for the fine chemicals industry

A survey is given of the problems to be solved before catalytic hydrogenation reactors can be applied in a multiproduct plant in which selectivity problems are experienced. Some results are reported on work done on the reaction kinetics of two multistep model reactions and on mathematical modelling and experimental verification of the models. Since hydrogenation reactions are often very exothermic, cooling by solvent evaporation has been applied where appropriate. Sufficient information has been collected and correlated to enable operation of multiproduct catalytic reactors of the slurry or packed bubble column type; interdependence of operating variables is so complex that a mathematical model is indispensable

Short- and long-term experience in pulmonary vein segmental ostial ablation for paroxysmal atrial fibrillation*

Introduction: Segmental ostial pulmonary vein isolation (PVI) is considered a potentially curative therapeutic approach in the treatment of paroxysmal atrial fibrillation (PAF). There is only limited data available on the long-term effect of this procedure. Methods: Patients (Pts) underwent a regular clinical follow up visit at 3, 6 and 24 months after PVI. Clinical success was classified as complete (i.e. no arrhythmia recurrences, no antiarrhythmic drug), partial (i.e. no/only few recurrences, on drug) or as a failure (no benefit). The clinical responder rate (CRR) was determined by combining complete and partial success. Results: 117 patients (96 male, 21 female), aged 51±11 years (range 25 to 73) underwent a total of 166 procedures (1.4/patient) in 2-4 pulmonary veins (PV). 115 patients (98%) had AF, 2 patients presented with regular PV atrial tachycardia. ,109/115 patients. exhibited PAF as the primary arrhythmia (versus persistent AF). A total of 113 patients with PVI in the years 2001 to 2003 were evaluated for their CRR after 6 (3) months. A single intervention was carried out in 63 patients (55.8%), two interventions were performed in 45 patients (39.8%) and three interventions in 5 patients (4.4%). The clinical response demonstrated a complete success of 52% (59 patients), a partial success of 26% (29 patients) and a failure rate of 22% (25 patients), leading to a CRR of 78% (88 patients). Ostial PVI in all 4 PVs exhibited a tendency towards higher curative success rates (54% versus 44% in patients with 3 PVs ablated for the 6 month follow up). Long-term clinical outcome was evaluated in 39 patients with an ablation attempt at 3 PVs only (excluding the right inferior PV in our early experience) and a mean clinical follow up of 21±6 months. At this point in time the success rate was 41% (complete, 16 patients) and 21% (partial, 8 patients), respectively, adding up to a CRR of 62% (24 patients). In total, 20 patients (17.1%) had either a single or 2 (3 patients, 2.6%) complications independent of the number of procedures performed with PV stenosis as the leading cause (7.7%). Conclusion: The CRR of patients with medical refractory PAF in our patient cohort is 78% at the 6 month follow up. PV stenosis is the main cause for procedure-related complications. Ablation of all 4 PV exhibits a tendency towards higher complete success rates despite equal CRR. Calculation of the clinical response after a mid- to long-term follow of 21±6 months in those patients with an ostial PVI in only 3 pulmonary veins (sparing the right inferior PV) shows a further reduction to 62%, exclusively caused by a drop in patients with a former partial success. To evaluate the long-term clinical benefit of segmental ostial PVI in comparison with other ablation techniques, more extended follow up periods are mandatory, including a larger study cohort and a detailed description of procedural parameters

Role of low-ll component in deformed wave functions near the continuum threshold

The structure of deformed single-particle wave functions in the vicinity of zero energy limit is studied using a schematic model with a quadrupole deformed finite square-well potential. For this purpose, we expand the single-particle wave functions in multipoles and seek for the bound state and the Gamow resonance solutions. We find that, for the $K^{\pi}=0^{+}$ states, where $K$ is the $z$-component of the orbital angular momentum, the probability of each multipole components in the deformed wave function is connected between the negative energy and the positive energy regions asymptotically, although it has a discontinuity around the threshold. This implies that the $K^{\pi}=0^{+}$ resonant level exists physically unless the $l=0$ component is inherently large when extrapolated to the well bound region. The dependence of the multipole components on deformation is also discussed

Transformation of 1,1,1-trichloroethane in an anaerobic packed-bed reactor at various concentrations of 1,1,1-trichloroethane, acetate and sulfate

Biotransformation of 1,1,1-trichloroethane (CH3CCl3) was observed in an anaerobic packed-bed reactor under conditions of both sulfate reduction and methanogenesis. Acetate (1 mM) served as an electron donor. CH3CCl3 was completely converted up to the highest investigated concentration of 10 µM. 1,1-Dichloroethane and chloroethane were found to be the main transformation products. A fraction of the CH3CCl3 was completely dechlorinated via an unknown pathway. The rate of transformation and the transformation products formed depended on the concentrations of CH3CCl3, acetate and sulfate. With an increase in sulfate and CH3CCl3 concentrations and a decrease in acetate concentration, the degree of CH3CCl3 dechlorination decreased. Both packed-bed reactor studies and batch experiments with bromoethanesulfonic acid, an inhibitor of methanogenesis, demonstrated the involvement of methanogens in CH3CCl3 transformation. Batch experiments with molybdate showed that sulfate-reducing bacteria in the packed-bed reactor were also able to transform CH3CCl3. However, packed-bed reactor experiments indicated that sulfate reducers only had a minor contribution to the overall transformation in the packed-bed reactor.

Wilson renormalization of a reaction-diffusion process

Healthy and sick individuals (A and B particles) diffuse independently with diffusion constants D_A and D_B. Sick individuals upon encounter infect healthy ones (at rate k), but may also spontaneously recover (at rate 1/\tau). The propagation of the epidemic therefore couples to the fluctuations in the total population density. Global extinction occurs below a critical value \rho_{c} of the spatially averaged total density. The epidemic evolves as the diffusion--reaction--decay process A + B --> 2B, B --> A , for which we write down the field theory. The stationary state properties of this theory when D_A=D_B were obtained by Kree et al. The critical behavior for D_A<D_B is governed by a new fixed point. We calculate the critical exponents of the stationary state in an \eps expansion, carried out by Wilson renormalization, below the critical dimension d_{c}=4. We then go on to to obtain the critical initial time behavior at the extinction threshold, both for D_A=D_B and D_A<D_B. There is nonuniversal dependence on the initial particle distribution. The case D_A>D_B remains unsolved.Comment: 26 pages, LaTeX, 6 .eps figures include

Experimental and computational analysis of microscale wind environmental conditions in the Port of Rotterdam

Abstract: Knowledge of microscale wind conditions is important for maneuvering and mooring of ships and for optimizing the harbor design. The aim of this study is to translate the macroscale wind conditions measured at a near shore reference station to the local (microscale) wind conditions in the harbor docks. In the first part of the project, an extensive experimental campaign has been performed, which consisted of wind velocity measurements with 2D and 3D ultrasonic anemometers during a period of 6 months. These point measurements confirm the unique relation between the macroscale and microscale wind conditions during periods of strong winds. As the measurements only provide information at a number of discrete positions, the second part of the study consists of numerical simulations with Computational Fluid Dynamics (CFD) to map the wind environmental conditions over the entire study area. The measurements and simulations both show very large gradients in mean wind speed over the harbor area, with differences up to 100%. The numerical simulations are currently in progress and will be validated by comparison with the on-site measurements

The impact of material chemistry and morphology on attrition behavior of excipients during high shear blending

Particle breakage by attrition is unavoidable in some unit operations and can lead to uncontrolled behavior of materials during processing. The aim of this study is to clarify the impact of material properties on attrition behavior. For the first time, an integral study with varying morphologies and chemistries is performed to identify the key drivers that impact attrition during high shear blending. Based upon the observed changes in particle size distribution, it was concluded that dicalcium phosphate (DCP) was the most prone to attrition, followed by mannitol, lactose and microcrystalline cellulose (MCC). Granular particles were more sensitive to attrition than sieved and spherical particles. Changes in bulk density, flow function coefficient and tablet tensile strength were observed as the result of attrition. The magnitude and direction of change in these parameters was not only dependent on the amount of attrition, but also on the morphology and the material deformation properties