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- Pino-Garcia, Osvaldo, et al.
(författare)
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Influence of additives on nucleation of vanillin : Experiments and introductory molecular simulations
- 2004
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 4:5, s. 1025-1037
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Tidskriftsartikel (refereegranskat)abstract
- Nucleation of vanillin (VAN) in 2-propanol/water in the presence of additives, viz., acetovanillone (AVA), ethyl vanillin (EVA), guaiacol (GUA), guaethol (GUE), 4-hydroxyacetophenone (HAP), 4-hydroxybenzaldehyde (HBA), and vanillic acid (VAC) is investigated experimentally and by molecular simulations. In the experimental work, the induction time for nucleation is measured at different temperatures and levels of supersaturation using a multicell apparatus. A large variation in the experimental data is observed, and this variation is analyzed by statistical methods. By classical nucleation theory, the induction time data are used to estimate the solid-liquid interfacial energy of vanillin for each VAN-additive system. At 1 mol %, the interfacial energy becomes lower in the presence of AVA, EVA, HAP, and VAC, while it becomes higher in the presence of the other additives. As the additive concentration increases from 1 to 10 mol %, the interfacial energy also increases. The interfacial energy ranges from 6.9 to 10.1 mK m(-2). Molecular modeling, implemented in the program Cerius2, is used to simulate and examine the surface chemistry of the likely crystal growth faces of VAN (i.e., {001} and {100}). To evaluate the additive-crystal face interaction energy, two approaches are used: the surface adsorption method and the lattice integration method. Both experimental and molecular simulation results indicate that the additives studied are potential modifiers of the nucleation of VAN. However, a simple and clear relationship between the experimental values of interfacial energy and the calculated interaction energies for the most important crystal faces of VAN cannot be identified. The modeling does not concern the actual nucleation but rather the conditions of a growing surface and are based on several severe simplifications. Obviously, this simplistic approach does not sufficiently capture the influence of additives on the nucleation of vanillin.
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| 3. |
- Pino-García, Osvaldo, 1966-
(författare)
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Influence of Admixtures on Crystal Nucleation of Vanillin
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Admixtures like reactants and byproducts are solublenon-crystallizing compounds that can be present in industrialsolutions and affect crystallization of the main substance.This thesis provides experimental and molecular modellingresults on the influence of admixtures on crystal nucleation ofvanillin (VAN). Seven admixtures: acetovanillone (AVA),ethylvanillin (EVA), guaiacol (GUA), guaethol (GUE), 4-hydroxy-acetophenone (HAP), 4-hydroxy-benzaldehyde (HBA), andvanillic acid (VAC) have been used in this study. Classicalnucleation theory is used as the basis to establish arelationship between experimental induction time andsupersaturation, nucleation temperature, and interfacialenergy. A novel multicell device is designed, constructed, andused to increase the experimental efficiency in thedetermination of induction times by using 15 nucleation cellsof small volumes simultaneously. In spite of the largevariation observed in the experiments, the solid-liquidinterfacial energy for each VAN-admixture system can beestimated with an acceptable statistical confidence. At 1 mole% admixture concentration, the interfacial energy is increasedin the presence of GUA, GUE, and HBA, while it becomes lower inthe presence of the other admixtures. As the admixtureconcentration increases from 1 to 10 mole %, the interfacialenergy also increases. The interfacial energies obtained are inthe range 7-10 mJ m-2. Influence of admixtures on metastable zone widthand crystal aspect ratio of VAN is also presented. Theexperimental results show that the admixtures studied arepotential modifiers of the nucleation of VAN. Molecularmodelling by the program Cerius2 is used to identify the likelycrystal growth faces. Two approaches, the surface adsorptionand the lattice integration method, are applied to estimatequantitatively the admixture-crystal interaction energy on thedominating crystal faces of VAN,i.e., {0 0 1} and {1 0 0}. However, a simple and clearcorrelation between the experimental values of interfacialenergy and the calculated interaction energies cannot beidentified. A qualitative structural analysis reveals a certainrelationship between the molecular structure of admixtures andtheir effect on nucleation. The determination of the influenceof admixtures on nucleation is still a challenge. However, themolecular and crystal structural approach used in this thesiscan lead to an improved fundamental understanding ofcrystallization processes. Keywords: Crystallization,nucleation, vanillin, admixtures, additives, impurities,induction time, interfacial energy, molecular modelling,interaction energy.
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