Positron emission profiling

The plug flow reactor is increasingly being used under transient conditions to obtain kinetic data by analysing the combined reactor and catalyst response upon a stimulus. Mostly used are a small reactant pulse (e.g. in temporal analysis of products (TAP) [16] and positron emission profiling (PEP) [17, 18]) or a concentration step change (in step-response measurements (SRE) [19]). Isotopically labeled compounds are used which allow operation under overall steady state conditions, but under transient conditions with respect to the labeled compound [18, 20-23]. In this type of experiments both time- and position-dependent concentration profiles will develop which are described by sets of coupled partial differential equations (PDEs). These include the concentrations of proposed intermediates at the catalyst. The mathematical treatment is more complex and more parameters are to be estimated [17]. Basically, kinetic studies consist of ... 

P-lO - Adsorption and diffusion of alkanes and their mixtures in silicalite studied with positron emission profiling technique... 

Abstract Zeolites are of prime importance to the petrochemical industry as catalysts for hydrocarbon conversion. In their molecule-sized micropores, hydrocarbon diffusion plays a pivotal role in the flnal catalytic performance. Here, we present the results of Positron Emission Profiling experiments with labeled hydrocarbons in zeolites with the MFI morphology. Single-component self-diffnsion coefficients of hexanes in silicalite-1 and its acidic connterpart H-ZSM-5 are determined. For the first time, self-diffnsion co-... 

Positron Emission Profiling a Study of Hydrocarbon Diffusivity in MFI Zeolites 279... 

Maximum kinetic energy of positrons Temporal analysis of products tapered element oscillating mass balance tracer-exchange positron emission profiling unit cell... 

The positron emission profiling (PEP) detector is shown in Fig. 5. It has been designed to be flexible, so that it can be used with a variety of different sizes of reactors. Measurements can be carried out on reactors having lengths... 

Figure 6 shows a schematic diagram of the reactor system used for tracer-exchange positron-emission profiling (TEX-PEP) experiments. During these tracer exchange experiments, a constant flow of unlabeled hydrocarbons in a hydrogen carrier stream is fed into the reactor. The -hexane/... 

Mangnus AVG (2000) A detection system for Positron Emission Profiling, Ph.D. thesis. Eindhoven University of Technology, Eindhoven, The Netherlands... 

E. J. M. Hensen, A. M. de Jong, and R. A. van Santen have written Chapter 7, which introduces the tracer exchange positron emission profiling (TEX-PEP) as an attractive technique for in-situ investigations, for example, in a stainless steel reactor, of the adsorption and diffusive properties of hydrocarbons in zeolites under chemical steady-state conditions. Self-diffusion coefficients of hydrocarbons, labeled by proton-emitting C at finite loadings and even in the presence of another imlabeled alkane, may be extracted. The method is illustrated by adsorption and diffusion measurements of linear (n-hexane) and branched (2-methylpentane) alkanes in Fl-ZSM-5 and silicalite-1. 

Positron Emission Profiling — The Ammonia Oxidation Reaction as a Case Study... 

Due to the penetrating power of the emitted SllkeV gamma photons, which can pass through several millimetres of stainless steel, detection is possible from within steel reactors or process vessels. The coincident detection of photons is the principle of techniques such as Positron Emission Tomography (PET), Positron Emission Particle Tracking (PEPT), and Positron Emission Profiling (PEP), which are discussed below. 

The Positron Emission Profiling (PEP) detector is shown in Fig. 2. It has been designed to be flexible so that it can be used with a variety of different sizes of reactors measurements can be carried out on reactors having lengths between 4.0 cm and 50 cm and diameters of up to 25 cm. The detector consists of two banks, each containing an array of sixteen independent detection elements, and is mounted horizontally, with the reactor and furnace placed between the upper and lower banks. Each detection element comprised of a bismuth germanium oxide (BGO) scintillation crystal coupled to a photomultiplier. The detection elements are situated in a frame, which allows adjustment of the overall detector dimensions when required. 

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