Andrés Mahecha-Botero

ADVANCES IN MODELING OF FLUIDIZED-BED CATALYTIC REACTORS: A COMPREHENSIVE REVIEW

A number of fluidized-bed catalytic reactor models have been proposed during the past half-century based on conservation equations as well as empirical relations. This article presents a comprehensive review of these models, ranging from the classic and pioneering reactor models found in the literature to the current state-of-the-art. Each model incorporates a different set of assumptions, leading to different expressions for simulating reactor performance. Forty models are analyzed depending on the characteristics of their conservation equations and their underlying assumptions by reducing each model to a sequential combination of assumptions. This review contributes to the elucidation process for choosing the appropriate model to simulate a specific fluidized-bed reactor.

Mass balance evaluation of polybrominated diphenyl ethers in landfill leachate and potential for transfer from e-waste.

Previous research on brominated flame retardants (BFRs), including polybrominated diphenyl ethers (PBDEs) has largely focussed on their concentrations in the environment and their adverse effects on human health. This paper explores their transfer from waste streams to water and soil. A comprehensive mass balance model is developed to track polybrominated diphenyl ethers (PBDEs), originating from e-waste and non-e-waste solids leaching from a landfill. Stepwise debromination is assumed to occur in three sub-systems (e-waste, aqueous leachate phase, and non-e-waste solids). Analysis of landfill samples and laboratory results from a solid-liquid contacting chamber are used to estimate model parameters to simulate an urban landfill system, for past and future scenarios. Sensitivity tests to key model parameters were conducted. Lower BDEs require more time to disappear than high-molecular weight PBDEs, since debromination takes place in a stepwise manner, according to the simplified reaction scheme. Interphase mass transfer causes the decay pattern to be similar in all three sub-systems. The aqueous phase is predicted to be the first sub-system to eliminate PBDEs if their input to the landfill were to be stopped. The non-e-waste solids would be next, followed by the e-waste sub-system. The model shows that mass transfer is not rate-limiting, but the evolution over time depends on the kinetic degradation parameters. Experimental scatter makes model testing difficult. Nevertheless, the model provides qualitative understanding of the influence of key variables.

Transfer of PBDEs from e-waste to aqueous media

Experiments and analysis were carried out by contacting e-waste with distilled water and leachate from a major urban landfill. Contacting of crushed e-waste from different eras with leachate in a custom built end-over-end contactor led to appreciable mass transfer of Polybrominated diphenyl ethers (PBDEs) to the aqueous phase. Temperature had limited influence for the limited range (10-25°C) investigated. Lower pH (in the range 4 to 9) generally resulted in higher transfer of PBDEs to the aqueous phase. Exposing e-waste to distilled water in the same contactor led to lower, but still appreciable PBDE analysed concentrations, than for leachate, probably due to dislodgement of fine dust from the surface of the e-waste particles.

Comprehensive Modeling of Gas Fluidized-Bed Reactors Allowing for Transients, Multiple Flow Regimes and Selective Removal of Species

A multiphase reaction engineering model is being developed to investigate the dynamic and steady state behaviour of fluidized-bed catalytic reactors. It accounts for transients, axial and radial dispersion, temperature and pressure profiles, interphase mass and heat transfer, different hydrodynamic flow regimes, catalyst deactivation, reactions with changes in molar flows and various energy options. The model is general enough that it can treat catalytic systems, subject to mass and energy transfer resistances within the phases, as well as permeating membranes. It is able to handle multiple phases and regions (low-density phase, high-density phase, freeboard region and permselective membranes). The model reduces as special cases to a number of simpler fluidized bed reactor models previously reported in the literature, allowing evaluation of the influence of different simplifying assumptions. As a case study, the model is shown to simulate oxy-chlorination fluidized-bed reactors for the production of ethylene dichloride from ethylene, extending a recent paper by Abba et al. (Chem. Eng. Sci., (2002) 57, 4797-4807).

Practical Implications of Bifurcation and Chaos in Chemical and Biological Reaction Engineering

This paper concentrates on the practical implications of bifurcation and chaos on novel approaches for the production of the clean fuels: hydrogen and ethanol, and the simulation of the acetylcholine neurocycle in the brain. One problem from the field of chemical reaction engineering and two from the field of biological reaction engineering, the three problems have one thing in common: the practical implications of bifurcation and chaos. The novel approach for hydrogen production is based on a novel circulating fluidized bed catalytic membrane reformer configuration achieving, simultaneously, both autothermicity and breaking the thermodynamic barriers using different techniques (membranes and/or CO2 sequestration). The static bifurcation characteristics of the autothermic process and their implications on design and operation for maximum hydrogen yield and productivity are addressed. Experimental set-up for this novel process is being developed at University of British Columbia (UBC).The novel approach for the ethanol production does not use a novel configuration, however it uses a classical configuration but with a novel mode of operation. A CSTR fermenter is used exploiting bifurcation and chaos theories to maximize ethanol yield and productivity. The sequence of research work consisted of: developing a reliable and relatively simple model to describe the fermentation process, verification of the model against experimental results, using the model in an extensive bifurcation and chaos analysis investigation to identify the regions of bifurcation and chaos and their characteristics. This is followed by using these results to guide an experimental investigation of bifurcation and chaos and their implications on improving ethanol yield and productivity.This paper also introduces our preliminary efforts to investigate the bifurcation and chaotic behavior of acetylcholine neurocycle in the brain using diffusion-reaction models in order to gain some insight into their possible connection to Alzheimer and Parkinson Diseases (AD/PD).