Potential of gassing crystallization to control the agglomeration degree of crystalline products

•Quantification of agglomeration degree of adipic acid•Systematic investigation of gassing crystallization regarding agglomeration degree•Gassing affects agglomeration and therewith product characteristics like CSD•Gassing crystallization is a promising method to control agglomeration degree.

Control of agglomeration, i.e. the cementation of two or more single crystals by crystal growth, is crucial in crystallization processes. Especially undesired agglomeration may lead to broaden crystal size distributions (CSDs) and mother liquor inclusions reduce the purity. To reach product specifications and avoid loss of batches gassing crystallization could be one way to control agglomeration degree of final product. Hence, in this study the effect of gassing process parameters to reduce the number of agglomerates within the CSD of adipic acid is systematically investigated using Design of Experiments (DoE). For quantification of agglomeration the overall agglomeration degree (Ag) and the agglomeration degree distribution (AgD) are determined using an image analysis tool. The AgD describes the relative frequency of agglomerates within each particle fraction of the CSD. Both in combination allow distinguishing between two populations, namely single crystals and agglomerates. The results show that gassing crystallization is a promising method to get crystalline products with a reduced number of agglomerates, which affects the width of the CSD. Moreover, a higher reproducibility of product batches than for cooling crystallization without gassing is achieved.

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