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Patrick R Unwin - One of the best experts on this subject based on the ideXlab platform.
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scanning electrochemical microscopy secm as a probe of transfer processes in two phase systems theory and experimental applications of secm induced transfer with arbitrary partition coefficients diffusion coefficients and interfacial kinetics
Journal of Physical Chemistry B, 1998Co-Authors: Anna L Barker, Julie V Macpherson, And Christopher J Slevin, Patrick R UnwinAbstract:Scanning electrochemical microscopy induced transfer (SECMIT) is introduced as a new approach for probing the dynamics of partitioning of electroactive Solutes between two immiscible phases. The partitioning process, initially at equilibrium, is perturbed by electrolysis of the Target Solute at an ultramicroelectrode (UME) tip positioned in one phase, close to the interface with a second phase. For a particular separation between the tip and interface, the flux of Soluteand hence current flowingat the UME is governed primarily by the partition coefficient of the Solute, Ke, the relative diffusion coefficients of the Solute in the two phases, γ, and the interfacial transfer kinetics. A numerical model is developed for SECMIT under potential step chronoamperometric conditions, where the Target Solute is electrolyzed at the UME at a diffusion-controlled rate. When the interfacial kinetics are nonlimiting, the steady-state current is strongly dependent on the product Keγ, particularly for Keγ > 1, while for c...
Anna L Barker - One of the best experts on this subject based on the ideXlab platform.
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scanning electrochemical microscopy secm as a probe of transfer processes in two phase systems theory and experimental applications of secm induced transfer with arbitrary partition coefficients diffusion coefficients and interfacial kinetics
Journal of Physical Chemistry B, 1998Co-Authors: Anna L Barker, Julie V Macpherson, And Christopher J Slevin, Patrick R UnwinAbstract:Scanning electrochemical microscopy induced transfer (SECMIT) is introduced as a new approach for probing the dynamics of partitioning of electroactive Solutes between two immiscible phases. The partitioning process, initially at equilibrium, is perturbed by electrolysis of the Target Solute at an ultramicroelectrode (UME) tip positioned in one phase, close to the interface with a second phase. For a particular separation between the tip and interface, the flux of Soluteand hence current flowingat the UME is governed primarily by the partition coefficient of the Solute, Ke, the relative diffusion coefficients of the Solute in the two phases, γ, and the interfacial transfer kinetics. A numerical model is developed for SECMIT under potential step chronoamperometric conditions, where the Target Solute is electrolyzed at the UME at a diffusion-controlled rate. When the interfacial kinetics are nonlimiting, the steady-state current is strongly dependent on the product Keγ, particularly for Keγ > 1, while for c...
Paul M Mathias - One of the best experts on this subject based on the ideXlab platform.
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Applied thermodynamics in chemical technology: current practice and future challenges
Fluid Phase Equilibria, 2004Co-Authors: Paul M MathiasAbstract:Abstract Examples are used to illuminate ways in which applied thermodynamics is being successfully deployed in chemical technology and the challenges that need to be overcome. Nitric-acid plant modeling was very difficult two decades ago because of the complexity of the thermodynamic properties and the need to describe kinetic and mass-transfer limitations in the process equipment. This complex process and other similar processes are routinely modeled today thanks largely to advances in applied thermodynamics. In fact, applied thermodynamics is an established cornerstone of chemical engineering. Excel is an effective tool for custom applications and teaching since most scientists and engineers use it regularly. We demonstrate that the Excel add-in for Aspen Properties facilitates the creation of useful custom applications (e.g., analysis and understanding of flammability limits and analysis of pressure variation in batch reactors) – usually within a few hours – enabling big improvements in education and wide deployment of chemical technology. Modern software enables modeling of complex processes – and highlights the challenging areas. This point is elucidated through a promising process for hydrogen production via thermochemical water splitting: the sulfur iodine cycle. The sulfuric acid decomposition section of this process can be simulated accurately, but other sections (acid generation and hydrogen iodide decomposition) illustrate the difficulty of modeling phase behavior, particularly liquid-phase immiscibility, in complex electrolyte systems. The difficulties arise from model inadequacies as well as a lack of fundamental data. However, these difficulties will likely be overcome soon mainly through new data, but also through advance in molecular-thermodynamic models. Property estimation and data regression have progressed as independent silos for the development of applied thermodynamic models. We discuss the seminal contribution of a recent proposal that combines a segment-based NRTL model with a few (3–4) solubility measurements for a Target Solute to develop a predictive method for the solubility of this Solute in most solvents and solvent mixtures of interest. This proposal creates an effective and efficient work process for solvent selection in the pharmaceutical and specialty chemical industries. The paper concludes by summarizing challenges that remain for the future use of applied thermodynamics in chemical technology.
Alves, Yana Amaral - One of the best experts on this subject based on the ideXlab platform.
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Coeficientes de partição de compostos fenólicos em sistemas bifásicos de solventes orgânicos
2019Co-Authors: Alves, Yana AmaralAbstract:Mestrado de dupla diplomação com a UNIFACS - Universidade SalvadorOs processos de separação por cromatografia de contracorrente e partição centrífuga são aplicados principalmente na separação e purificação de produtos naturais. Ambos se baseiam no mesmo princípio de funcionamento, que consiste na distribuição de um soluto em duas fases imiscíveis compostas por uma mistura de solventes. A seleção do sistema bifásico ideal é o fator chave, que deve garantir uma distribuição adequada do soluto entre as duas fases líquidas. De acordo com a literatura, as misturas de solventes mais utilizadas para a separação de compostos fenólicos presentes em matrizes naturais são os sistemas HEMWat (água + acetato de etilo + metanol + hexano), ARIZONA (água + acetato de etilo + metanol + heptano), ChMWat (água + clorofórmio + metanol) e EBuWat (água + butanol + acetato de etilo). Em paralelo, métodos como COSMO-RS (COnductor-like Screening MOdel for real solvents), UNIFAC (UNIversal Functional Activity Coefficient group-contribution method), e suas modificações, ou o modelo de solvatação de Abraham, podem ser usados para auxiliar na triagem do sistema de solventes mais adequado para um determinado soluto alvo, de maneira mais rápida e eficaz. Este trabalho apresenta alguns conceitos introdutórios sobre cromatografia líquido-líquido e uma revisão da literatura sobre os coeficientes de partição de compostos fenólicos. Além disso, foi implementada uma metodologia experimental para a medição dos coeficientes de partição, utilizando a família de solventes ARIZONA, com a quercetina como soluto, que será útil para futuros trabalhos laboratoriais, visto que os dados de partição de compostos fenólicos são escassos. Por fim, a modelação termodinâmica provou ser uma ferramenta eficaz para selecionar o sistema de solventes. Em particular, o modelo UNIFAC original destacou-se por ser aplicável a um maior número de solutos quando comparado com as versões de Dortmund e NIST. O modelo de solvatação de Abraham também pode ser aplicado, desde que os descritores moleculares dos solutos já estejam disponíveis ou possam ser estimados a partir de dados de solubilidade ou partição. Os resultados da modelação com o modelo UNIFAC, versão original e suas modificações, e o modelo de solvatação de Abraham para a partição de 41 solutos são explorados e discutidos.The countercurrent and centrifugal partition chromatography separation processes are mainly applied on the separation and purification of natural products. Both are based on the same working principle, which is the distribution of a Solute in two immiscible phases composed by a mixture of solvents. The selection of the optimal two-phase system is the key factor, that must guarantee the proper distribution of the Solute between the two liquid phases. According to the literature, the most used solvent mixtures for the separation of phenolic compounds present in natural matrices are HEMWat (water + ethyl acetate + methanol + hexane), ARIZONA (water + ethyl acetate + methanol + heptane), ChMWat (water + chloroform + methanol) and EBuWat (water + butanol + ethyl acetate). In parallel, methods such as COSMO-RS (COnductor-like Screening MOdel for real solvents), UNIFAC (UNIversal Functional Activity Coefficient group-contribution method), and its variants, or the Abraham solvation model, can be used to assist in the screening of the most adequate solvent system for a given Target Solute, in more quickly and effectively manner. This work presents some introductory concepts on liquid-liquid chromatography and a review of the literature on the partition coefficients of phenolic compounds. In addition, an experimental methodology for the measurement of partition coefficients was implemented, using the ARIZONA solvent family, and quercetin as Solute, which will be useful for future laboratory work, as partition data of phenolic compounds are scarce. Finally, thermodynamic modelling proved to be an effective tool to select the solvent system. Particularly, the original UNIFAC model stood out for being applicable to a greater number of Solutes when compared to the Dortmund and NIST versions. Abraham's solvation model can also be applied, as long as the molecular descriptors of the Solutes are already available or can be estimated from solubility or partition data. The modelling results with the UNIFAC model, original and its variants, and the Abraham solvation model for the partition of 41 Solutes are explored and discussed.Este trabalho foi desenvolvido no âmbito do projeto AllNat – “Utilização de solventes eutéticos profundos naturais para a extração de compostos bioativos de materiais vegetais” (referência POCI-01-0145-FEDER-030463, PTDC/EQU-EPQ/30463/2017), financiado com fundos FEDER através do COMPETE2020 – Programa Operacional Competitividade e Internacionalização (POCI), Portugal 2020 e com fundos nacionais através da Fundação para a Ciência e Tecnologia (FCT/MCTES)
And Christopher J Slevin - One of the best experts on this subject based on the ideXlab platform.
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scanning electrochemical microscopy secm as a probe of transfer processes in two phase systems theory and experimental applications of secm induced transfer with arbitrary partition coefficients diffusion coefficients and interfacial kinetics
Journal of Physical Chemistry B, 1998Co-Authors: Anna L Barker, Julie V Macpherson, And Christopher J Slevin, Patrick R UnwinAbstract:Scanning electrochemical microscopy induced transfer (SECMIT) is introduced as a new approach for probing the dynamics of partitioning of electroactive Solutes between two immiscible phases. The partitioning process, initially at equilibrium, is perturbed by electrolysis of the Target Solute at an ultramicroelectrode (UME) tip positioned in one phase, close to the interface with a second phase. For a particular separation between the tip and interface, the flux of Soluteand hence current flowingat the UME is governed primarily by the partition coefficient of the Solute, Ke, the relative diffusion coefficients of the Solute in the two phases, γ, and the interfacial transfer kinetics. A numerical model is developed for SECMIT under potential step chronoamperometric conditions, where the Target Solute is electrolyzed at the UME at a diffusion-controlled rate. When the interfacial kinetics are nonlimiting, the steady-state current is strongly dependent on the product Keγ, particularly for Keγ > 1, while for c...
