Fluidized bed hydrodynamic modeling of CO2 in syngas: Distorted RTD curves

Bubbles rising through fluidized beds at velocities several times superficial velocities contribute to solids backmixing. In micro-fluidized beds, the walls constrain bubble sizes and velocities. To evaluate gas-phase hydrodynamics and identify diffusional contributions to longitudinal dispersion, we injected a mixture of H2, CH4, CO, and CO2 (syngas) as a bolus into a fluidized bed of porous fluid catalytic cracking catalyst while a mass-spectrometer monitored the effluent gas concentrations at 2 Hz. The CH4, CO, and CO2 trailing RTD traces were elongated versus H2 demonstrating a chromatographic effect. An axial dispersion model accounted for 92% of the variance in the data but including diffusional resistance between the bulk gas and catalyst pores and adsorption explained 98.6% of the variability. At 300 °C, the CO2 tailing disappeared consistent with expectations in chromatography (no adsorption). H2 and He are poor gas-phase tracers at ambient temperature. We recommend measuring the RTD at operating conditions.

Сoncentration waves behaviour and the chromatographic displacement development in the sorbentsnanocomposites during the multicomponent mass transfer and visualisation of the sorption kinetics process

There is considered the Multi-(6th)-component Mass Transfer (MMT) inside the planar matrices ofthe sorbent-NanoComposite (NC) by the computerized modelling. During the MMT kinetics in the NC planar-membrane the chromatographic Displacement Development (DD) for the propagating modes of the twoconcentration Xm(1,2)(L,T)-principal waves is modeled for the two principal m1,2-sorbate components (m=1,2)of the Multi(6)-components NC MMT combined “Diffusion, and sorption” system.The computerized modelling mentioned here is based on the mathematical solution of the MMTmulti 6-components Eqns. partial differential including as the basis the author’s bi-functional NC MMTModels. The main advantage of the NC Models considered concludes in the introduction of the two sorbatediffusing principal Pi(3.4)-components into the consideration. The similarity and the differences between themulticomponent Xn(L,T)-concentration waves propagation for the MMT processes in the modern NC matrixand in the chromatographic column are discussed.The visualization of the kinetics of the MMT процесс is realized by the creation of the Sci. computerizedAnimations: “SCA.avi” video-files which demonstrate visually (after the program start) the propagationof the multi(n)-component Xn(1-6)(L,T)-concentration waves through the NC matrixe. Here the “SCA.avianimations display the DD chromatographic effect during oral presentation with the mentioned DDdisplacementof the X2-concentration waves by the X1-waves of the 1-component (displacer).

Competitive adsorption of toxic metals on activated carbon

Competitive adsorption of zinc and copper on activated carbon is studied in this article. Main aim was to suggest an advanced model for competitive adsorption of both metals considering pH influence and precipitation. A surface-complexation approach was employed for the modeling. Two models were considered: simple adsorption and ion exchange. System “The Geochemists Workbench” was used for calculation of both static and dynamic adsorption tasks. From the batch experiments, concentration of four types of sorbing sites on the carbon surface and its protonation and sorption constants were deduced. Then, batch competitive adsorption experiments were compared with the models’ results. Finally, a column experiment (fixed bed adsorption) was carried out. It was observed that the model of ion exchange can satisfyingly predict both chromatographic effect and increase of zinc concentration in effluent over its initial value, although a quantitative agreement between the model and the experiment was not totally precise.

Measurement of the diffusion coefficients of reactive species in dilute gases

A technique has been developed for measuring the diffusion coefficients of atoms and other reactive species in gases below atmospheric pressure. The technique consists of measuring the rate of dispersion of a pulse of reactive species in a stream of gas flowing rapidly ( ca . 10 m s -1 ) down a quartz tube. The reactive species are observed and the profile of the pulses measured by using resonance fluorescence. The technique has been used at room temperature, but in principle measurements could be made at elevated temperatures. Measurements have been made of the rates of diffusion of hydrogen atoms in argon and nitrogen, and values for the diffusion coefficients of 1.61 ± 0.04 and 1.35 ± 0.03 cm 2 s -1 respectively, at 1 atmosphere ( ca . 10 5 Pa) and 294 K, have been obtained. Incidentally to the primary purpose of the experiment, it was observed that the hydrogen atoms spend a small fraction of their time of passage along the tube reversibly adsorbed on its walls. From the measurements, both the partition coefficient, giving the ratio of hydrogen atoms on the walls to those in the gas phase, and the rates of adsorption and desorp­tion can be obtained. This appears to be the first observation of a chromatographic effect for a highly reactive species.