Seeding is a significant but challenging task for optimizing crystallization process operation, product quality, and process efficiency. With the development of modern crystallization technology, there have been considerable advancements in seeding techniques in recent years. This article elaborates on how seeds affect the crystallization process, clarifies the qualitative connection between seeding parameters, defines the variables and product quality attributes based on a variable-based causal graph, and analyzes various possible factors that result in seeding-technique failure based on an Ishikawa diagram. The development of seeding-technique studies and existing problems are then systematically reviewed and discussed based on the qualitative and quantitative characteristics of seeds and the factors that influence seeding efficiency. Based on extensive research accomplishments, the challenges and opportunities for utilizing seeding techniques are analyzed, and potentially valuable seeding-technique topics and directions for improving crystallization are presented. In addition, a framework to guide seed recipe design and optimization is defined by combining simulation and experimental verification.

In this paper, a seed recipe design is proposed for batch cooling crystallization to obtain the desired product attributes including product yield and product size distribution, based on simulation studies and experiments on-L-glutamic acid (-LGA) crystallization. The impact of seed recipe on product attributes is investigated based on the population balance model (PBM) simulations with respect to the size-dependent growth of crystals. It is found that the product yield is primarily affected by the seed loading ratio (SLR) and the batch time, but less affected by the mean size and variance of seeds. Smaller seeds could improve the product yield and in contrast, larger seeds facilitate the growth into larger crystals but require a larger SLR to ensure the product yield. By introducing an objective function for optimization with the above PBM, a seed recipe design is given for obtaining the desired product attributes as above mentioned. In addition, it is found that washing seeds by the solvent is necessary to ensure seed quality for quantitative seed recipe design and implementation, by comparing three different seed preparation methods. Simulation tests and experiments well demonstrate the effectiveness of the proposed seed recipe design for seeded batch cooling crystallization.

Abstract:In this paper the effects of operating conditions including cooling rate, initial supersaturation, and seeding temperature were investigated on the morphology evolution of -L-glutamic acid ( -LGA) during seeded cooling crystallization. Based on the results of in-situ image acquisition of the crystal morphology evolution during the crystallization process, it was found that the crystal products tend to be plate-like or short rod-like under a slow cooling rate, low initial supersaturation, and low seeding temperature. In the opposite, the operating conditions of a faster cooling rate, higher initial supersaturation, and higher seeding temperature tend to produce long rod-like or needle-like crystals, and meanwhile, the length and width of crystal products will be increased together with a wider crystal size distribution (CSD). The aspect ratio of crystals, defined by the crystal length over width measured from in-situ or sample images, was taken as a shape index to analyze the crystal morphologies. Based on comparative analysis of the experimental results, guidelines on these operating conditions were given for obtaining the desired crystal shapes, along with the strategies for obtaining a narrower CSD for better product quality. Experimental verifications were performed to illustrate the proposed guidelines on the operating conditions for seeded cooling crystallization of LGA solution.

The liquid−liquid equilibrium data of the two ternary systems of n-propyl acetate + n-propanol + 1-butyl-3-methylimidazolium hydrogensulfate and isopropyl acetate + isopropyl alcohol +1-butyl-3-methylimidazolium hydrogensulfate were measured at 298.15 K and 318.15 K and under atmospheric pressure in this work. The extraction effect of ionic liquids was discussed by comparing the values of the distribution coefficient and separation factor. The influence of temperature on the liquid−liquid equilibrium data was discussed. The binary interaction parameters of the nonrandom two-liquid and universal quasichemical models were obtained by regressing the experimental data.

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