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In this note, the effects of the non-Fickian diffusion on the prediction of effectiveness factor in non-isothermal porous catalytic slab considering external transport resistances are studied. A Green's function formulation is used to solve the fractional diffusion-reaction model assuming non-Fickian diffusion to describe the internal mass transport in the porous catalytic particle. Evaluation of the effectiveness factor considering linear and nonlinear reaction rates was developed under isothermal and non-isothermal conditions. In both cases, numerical simulations show the relation existent between the anomalous diffusion with the performance of the catalytic slabs. [ABSTRACT FROM AUTHOR]

The effectiveness factor (EF) is a useful tool for the study of heterogeneous reaction systems, such as catalytic particles, where interactions of reaction-diffusion processes are involved. For simplicity, the study of EF is achieved on steady state operation (SSEF), but recent studies have suggested that EF can increase on dynamic operation conditions, especially when diffusive transport does not follow the Fick's law. In this paper, a study about the effect of anomalous diffusion on the dynamic effectiveness factor (DEF) in catalytic particles is presented. For this, it is considered a generalized Cattaneotype diffusion model described by differential equations of fractional order applied at rectangular, cylindrical and spherical geometries of the catalytic particles, which is analyzed in the frequency space by means the Fourier transform method. Numerical results, based on Bode and Nyquist diagrams, show the conditions and regions where the DEF values are largest than SSEF. [ABSTRACT FROM AUTHOR]

Abstract: A linearization scheme is presented that enables near-exact solution of the nonlinear ordinary differential equations associated with Film Theory-based modeling of absorption with multiple reversible chemical reactions. The technique, a variant of singular perturbation methods, is applied here to the analysis of absorption of carbon dioxide in aqueous monoethanolamine and stripping of CO2 from the same solutions. Enhancement factors by which reactions multiply mass transfer rates are in excellent agreement with values obtained via numerical methods. Unlike previously published approximate techniques, the computationally efficient method outlined here is applicable whether the reversible reactions are fast or slow, and whether the solvent is lean or loaded. [Copyright &y& Elsevier]

Synthesis of nucleobases in nonaqueous environments is an alternative way for the emergence of terrestrial life, which could solve the fundamental problem connected to the hydrolytic instability of nucleic acid components in an aqueous environment. In this contribution, we present a plausible reaction route for the prebiotic synthesis of nucleobases in formamide, which does not require participation of the formamide trimer and aminoimidazole-carbonitrile intermediates. The computed activation energy of the proposed pathway is noticeably higher than that of the HCN-based synthetic route, but it is still feasible under the experimental conditions of the Saladino synthesis. We show that, albeit both the pyrimidine and purine ring formation utilizes the undissociated form of formamide, the dehydration product of formamide, HCN, may also play a key role in the mechanism. The rate-determining step of the entire reaction path is the cyclization of the diaza-pentanimine precursor. The subsequent formation of the imidazole ring proceeds with a moderate activation energy. Our calculations thus demonstrate that the experimentally suggested reaction path without the involvement of aminoimidazole-carbonitrile intermediates is also a viable alternative for the nonaqueous synthesis of nucleobases. [ABSTRACT FROM AUTHOR]

We have demonstrated in our earlier work that a few natural and synthetic estrogens can be effectively transformed through reactions mediated by lignin peroxidase (LiP). The behaviors of such reactions are variously influenced by the presence of natural organic matter (NOM) and/or veratryl alcohol (VA). Certain white rot fungi, e.g. Phanerochaete chrysosporium, produce VA as a secondary metabolite along with LiP in nature where NOM is ubiquitously present. Herein, we report a study on the products resulting from LiP-mediated oxidative coupling reactions of a representative estrogen, 17β-estradiol (E2), and how the presence of NOM and/or VA impacts the formation and distribution of the products. A total of six products were found, and the major products appeared to be oligomers resulting from E2 coupling. Our experiments revealed that these products likely formed colloidal solids in water that can be removed via ultrafiltration or settled during ultracentrifugation. Such a colloidal nature of the products could have important implications in their treatability and environmental transport. In the presence of VA, the products tended to shift toward higher-degree of oligomers. When NOM was included in the reaction system, cross-coupling between E2 and NOM appeared to occur. Data obtained from E-SCREEN test confirmed that the estrogenicity of E2 can be effectively eliminated following sequential reactions mediated by LiP. [ABSTRACT FROM AUTHOR]