Concentration pulse method

Nonlinear and dynamic models of desorption are used in the sequel. Mathematical justification of the boundary-value problems for the TDS-degassing method of metal saturated with hydrogen is given in [6,7]. The work [4] was a starting point of the results presented here. Algorithm of parameter identification for the model of hydrogen permeability of metals for the concentration pulses method [5] is presented in [8],... 

To describe the hydrogen transfer in material without defensive coat for the concentration pulses method we used the model... 

The estimation of parameters D, b, s, a, a2 in model (11) - (17) of the hydrogen transfer in stainless steel was made by the identification algorithm based on the Fourier series. The detailed description of the algorithm is in [3, 4]. The experimental data got by the concentration pulses method were used for identification. In addition the estimations of s, X = Db1/2 were received by isotherms for the permeability method [3, 4]. Below we describe the identification algorithm based on the Fourier series. 

The desugarization by-product is normally sold as a low value molasses. Pulse method systems also produce a relatively high value betaine-rich (at least 50% on soHds) fraction. The concentrated betaine-rich by-product is used as a custom animal feed, whose European markets are well estabUshed and may provide a future opportunity in the U.S. feed industry. Beet sugar molasses contains from 3 to 6% betaine, by weight, about three-quarters of which may be recoverable as a potential by-product ( 40 50% purity). 

To appreciate how the analytical sensitivity of polarography and voltammetry can be enhanced by sampling the current, or by pulsing the potential in normal pulse, differential pulse and square-wave pulse methods to attain a lower concentration limit of about 10 mol dm. ... 

The analytical sensitivity of classical polarographic or voltammetric methods is usually quite good at about 5 x 10 mol dm . At the lowest concentrations of analyte, however, the currents caused by double-layer effects or other non-faradaic sources causes the accuracy to be unacceptably low. Pulse methods were first developed in the 1950s to improve the sensitivity of the polarographic measurements made by pharmaceutical companies. At present, two pulse methods dominate the analytical field, i.e. normal pulse and differential pulse . Square-wave methods are also growing steadily in popularity. 

Can such concentration limits be attained in practice with these pulse methods ... 

This technique for the study of a fast reaction is gas phase or liquid phase was developed by Norrish and Poster. This is an example of Pulse method which initiates a reaction by creating new reactive species—excited electronic states, radicals, ions in the system under study. The method uses a light flash of high intensity for a very short duration (10- s) to produce atoms or free radicals or excited species in a system. These are at a fairly high concentration and undergo further reactions which are followed spectroscopically. A spectroscopic flash of light is followed by the initial flash by some fraction of a millisecond. The absorption spectra of all the species that are formed within the system can be recorded. One cannot only get indications of what species are formed but also how these species give rise to others. Thus a very direct picture of the kinetic behaviour of a fast reaction can be obtained. 

A linear relationship was observed between the current decrease and the concentration of ethyl alcohol below 22.5 mg l 1 by the pulse methods(2). The minimum concentration for the determination was 2 mg ethyl alcohol 1 . The current difference was reproducible within 6 % of the relative error when a sample solution containing 16.5 mg l 1 of ethyl alcohol was employed. The standard deviation was 0.5 mg 1 1 in in 40 experiments. Assay time is within 6 min. 

The specific heat at constant pressure, Cpf of the HIP-treated sample with nominal composition LaVg 25 0,7504 was measured over the temperature range 4-400 K by the heat pulse method in a calorimeter that incorporates a feedback system to regulate the temperature of concentric radiation shields surrounding the sample (9). The Cp values are accurate to within 1%, as determined by calibration runs using a polycrystalline copper sample and a sapphire single crystal sample. 

Chapter 5 dealt with the evolution of thin starting zones into concentration pulses distributed along a single axis. This treatment is appropriate for some important analytical separation methods, such as column chromatography carried out in thin one-dimensional tubes. However, as an alternate method... 

Gabis I.E. (1999) The method of concentration pulses for studying hydrogen transport in solids, J. Technical Physics 44(1) 90-94. 

The samples without defensive film coat were studied by the method of concentration pulses (MCP) at pressure 0.2 Torr within the range of temperatures 370 -596 °C in order to determine the hydrogen permeability parameters of stainless steel (12X18H10T). The knowledge of these parameters allowed to simplify the problem of parameter identification for titanium nitride. The samples with titanium nitride covering were studied by method of permeability at pressures 0.5-249 Torr and the temperatures 380-670 °C. 

Popov V.V., Gabis I.E., Sidorov N.I., Zaika Yu.V. (2005) Studying hydrogen permeability by method of concentration pulses, Journal of Alloys and Compounds (at press). 

The choice between step or pulse inputs is governed solely by practical convenience since the same information may be obtained from either measurement. Although most commonly used with an inert carrier to measure the limiting diffusivity at low sorbate concentrations, the method may be extended to the study of diffusion at any concentration by using a mixed carrier stream(16,21). 

Various reactors can be used for dynamic experiments. The application of recycle reactors to the investigation of the underlying reaction networks has been demonstrated by Bennett [58], who operated a recycle reactor with the dynamic method by superimposing reactant concentration pulses on the inlet stream. To ensure that the amounts of gaseous components adsorbed on the catalyst are appreciable compared to the amounts of measurable components flowing, the ratio of the catalyst to total reactor volume was made as high as possible. A reactor system, designed for transient experiments, has been described by Bennett et al. [43]. 

The dependence of HETP upon solution flow rate when exchanging the H -Na pair of ions between 0.2 M chloride solution and cation exchanger, KU-2 x 8, with beads 0.25-0.50 mm in diameter, has been compared in the literature for columns of different types [76,84]. The pulse method which has been used possesses the advantage that with the pulsed injection of a small amount of substance all physicochemical and hydrodynamic characteristics of the system remain invariably determined by the primary substance, Na" " ion in this case. Dynamic parameters obtained characterize the process when the concentration range of impurity is low. 

Harlicl PJ.E. and Tezel, F.H., A Novel Solution Method for Interpreting Binary Adsorption Isotherms from Concentration Pulse Chromatography Data , Adsorption, 6 (2000), pp.293-309... 

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