Nylon 4,I: an amorphous polyamide

The melt polymerization of nylon 4, I was studied, starting with nylon-salt and nylon prepolymers (ηinh=0.25). With nylon-salt only low molecular polymers were obtained, while with prepolymers the inherent viscosity could be raised to 0.77 (3h, 270°, vac.). The cyclization of tetra methylene diamine to pyrrolidine seem to be the major disturbing factor. The polymer is glassy and could easily be melt pressed. The torsion modulus of the material at 20°C was high (1.8 109 Pa) and remained high to near its Tg (138°C)

The photoelectron spectra of the diazanaphthalenes

The high-resolution He 584 Å photoelectron spectra of ten diazanaphthalenes are presented. The ordering of the π orbitals and the nitrogen “lone-pair” orbitals is discussed. Several semi-empirical quantum-chemical calculation methods have been screened against the experimental evidence

Perfluoro effect in the photoelectron spectra of quinoline and isoquinoline

The high-resolution He 584Aophotoelectron spectra of heptafluoroquinoline and heptafluoroisoquinoline are compared with those of the parent compounds. Shifts in π ionisation potentials, due to the fluorine substitution, can be described with an inductive and a combined inductive-conjugative Hu¨ckel model

A small scale regularly packed circulating fluidized bed. Part II: Mass transfer

The underlying objective of the present study is to increase gas¿solids contact in a circulating fluidized bed by the introduction of obstacles in the riser portion. The presence of such obstacles leads to suppression of radial inhomogeneities in the solids mass flux and concentration, and break-up of solids clusters. At ambient conditions, gas¿solids mass transfer was investigated for cocurrent upward flow of air and microsize solid particles (FCC, 70 ¿m diameter) over a regularly structured inert packing introduced into the riser part of a circulating fluidized bed unit. The packed section has a height of 0.48 m, a cross-sectional area of 0.06 × O.06 m2, and contains regularly stacked 0.01 m diameter Perspex bars as the obstacles meant to enhance the gas¿solids contact. Gas mass fluxes used were 1.4 and 2.7 kg m¿2 s¿1. Solids mass fluxes were varied in the range 0Gs 12 kg m¿2 s¿1. Experimental mass transfer data were obtained by applying the method of adsorption of naphthalene vapor on FCC particles. A conservative estimate of the apparent gas¿solids mass transfer coefficient kg* could be derived from the naphthalene vapor concentration profile along the packed section on the basis of a plug-flow-model interpretation, while assuming single-particle behaviour and neglecting intraparticle diffusion effects. Such kg* values appear to increase with increasing gas mass flux, but decrease with increasing solids mass flux (and consequently increasing solids volume fraction) probably due to the corresponding increase in particle shielding. Comparison of the present results with available literature data for similar solid materials suggests that the effect of the packing inserted into the CFB is significant: the Sherwood numbers derived from the present study are relatively high

A small scale regularly packed circulating fluidized bed. Part I: Hydrodynamics.

The present investigation is based on the idea of intensifying the gas¿solids contact in a circulating fluidized bed by introducing obstacles into it. Such obstacles may effectively suppress radial inhomogeneities in the solids flux and concentration, increase the dynamic solids hold-up, and break up solids clusters. This article (Part I) deals with the hydrodynamics (pressure drop and solids hold-up) investigated at ambient conditions, for cocurrent upward flow of air and microsize solid particles (FCC, 70 µm diameter) over a regularly structured inert packing introduced into the riser part of a circulating fluidized bed unit. The packed section has a height of 0.48 m, a cross-sectional area of 0.06 × 0.06 m2 and contains regularly-stacked 0.01 m diameter Perspex bars as the obstacles meant to enhance the gas¿solids contact. Slide-valves mounted above and below the packed section can be used to trap the solids inventory and determine the (dynamic) solids hold-up. Gas and solids mass fluxes have been varied in the range of 0.7 < Gg < 4.4 and O < Gs < 15 kg m-2s-2, respectively. Part II will report on the results of gas¿solids mass transfer measurements, which have been carried out in the same set-up at comparable experimental conditions. Results of this work show that: (i) the pressure gradient over the packed section increases linearly with increasing solids mass flux, but faster than linearly with increasing applied gas mass flux, (ii) the dynamic solids volume fraction can be described quite well by the correlation ß dyn = 0.0084 GsGg-1.22 for almost the entire range of applied gas and solids mass fluxes, (iii) the value for the solids friction factor derived for the gas flux range 0.7 < Gg < 3.7 kg (m-2s-1) varies from 1.4 to 2.5 and is linear with the solids volume fraction. These fs values are about 2 to 3 decades higher than those obtained from fs correlations derived for dilute-phase pneumatic conveying lines operated under the same experimental conditions

Generalizations of simulation results: Practicality of statistical methods (Part one)

simulation;statistical methods;operations research