Kinetic modeling of the reaction and crystallization of acetylsalicylic acid using ATR UV-vis spectroscopy

In industry, spectroscopy is used to monitor batch chemical reactions and to maximize production of a material for a minimum cost. However, there are many challenges involved in using spectroscopic methods to characterize reaction systems that undergo crystallization. For instance, the crystallization of a product in solution creates a slurry mixture for which it is hard to measure light absorption due to the nature of the mixture. Some of these problems are less prominent when using attenuated total reflectance (ATR) techniques (provided the enhancement of solid particles is low), due to its ability to circumvent the problems of separating light absorption from light scattering encountered in diffuse reflectance measurements [1].

The aim of this work is to formulate a kinetic model [2] for the reaction of salicylic acid with acetic anhydride that leads to the formation of acetylsalicylic acid and to its subsequent crystallization. The experiment involves a solid addition of salicylic acid into acetic anhydride, followed by an addition of water to consume the excess reactant, and finally a cooling step to initiate nucleation and crystal growth. The kinetic model will be constructed based on changes in light absorption measured by attenuated total reflectance ultraviolet‐visible (ATR UV‐Vis) spectroscopy. In addition, near infrared (NIR) diffuse reflectance spectroscopy will be used to determine the onset of nucleation and the degree of supersaturation which is the driving force for a power law based model describing the crystallization of the product.

[1] Falconet et al. (2008). Estimation of optical properties of turbid media: experimental comparison of spatially and temporally resolved reflectance methods. Applied Optics, 1734‐1739.
[2] Gemperline, P. (2006). Practical Guide to Chemometrics. Second Edition. Boca Raton: Taylor & Francis.


    • EPFL-POSTER-173227

    Record created on 2011-12-25, modified on 2017-05-10


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