Batch Cooling Crystallization Research Articles

Size Distribution of Needle-Shape Crystals of Monosodium L-Glutamate Obtained by Seeded Batch Cooling Crystallization

Monosodium L-glutamate crystals, which are of fragile needle, were obtained by batch crystallization with a natural cooling mode from aqueous solution. The effect of seeding on the product size was examined over a wide range of seed-loadings. The seed-loading ratio Cs, defined as the mass ratio of the added seeds to the theoretical yield per batch, had basically the same effect on the product crystal size as observed previously in cooling crystallization of mechanically strong granular crystals such as potassium alum. At high seed-loading ratios as Cs ≥ Cs*, where Cs* is a critical value of Cs, seed crystals grew with practically no secondary nucleation. Crystal breakage due to mechanical impacts brought by an agitator occurred only slightly for the small products. For the large crystals the breakage was significant. The breakage also depended on the type of stirrers used; the anchor stirrer induced less breakage than the turbine stirrer. The transient supersaturation was measured on-line by an electro-conductivity method.

Seeded Batch Cooling Crystallization of Adipic Acid from Ethanol Solution

Adipic acid was crystallized by cooling in a batch crystallizer. At low seed loadings, the product crystal size distribution (CSD) was bi-modal because of enormous secondary nucleation. However, at high seed loadings, it became uni-modal, where the crystallization was dominated by seed growth with practically no secondary nucleation. Enough seeding was thus effective in suppressing nucleation during batch crystallization. The mean mass size of the product crystals obtained at high seed loadings agreed with that calculated by a simple mass balance assuming growth-dominated crystallization with no change in the number of crystals during operation and no residual supersaturation towards the end of batch. The products obtained, i.e., grown seeds, were not well faceted but rounded, probably because of abrasion caused by mechanical impact induced by agitation.

An Online Strategy To Increase the Average Crystal Size during Organic Batch Cooling Crystallization

In situ attenuated total reflectance Fourier transform infrared (FTIR) measurements were shown to allow the online monitoring of supersaturation during solution crystallization processes, thus opening up new monitoring and control possibilities. With this aim in view, the monitoring of unseeded batch cooling solution crystallizations of two agrochemical products was investigated. The FTIR measurements of solute concentrations were used to develop a fines dissolution technique, based on a controlled heating-up procedure after primary nucleation. The strategy only requires the knowledge of the solubility curve and was deliberately designed to be robust and easy to implement. Two organic solute/solvent systems were studied. It is clearly demonstrated that the technique allows one to improve both the reproducibility of the final crystal size distribution and the mean crystal size. For Isoproturon, a well-known pesticide, the average final size is increased up to 90%. The efficiency of the monitoring procedure is also shown to depend on the solute/solvent system in question.

Batch Cooling Crystallization of an Organic Photochemical with a Low-Speed Intermittent Stirring Technique.

An organic photochemical was crystallized in batches-wise both in laboratory and industrial crystallizers. In the laboratory, crystals were produced at different stirring speeds using a 1 L crystallizer, and the centrifugal filtration tests were conducted for the slurries that were obtained slurries. The average specific resistance was reduced much more than expected from the Kozeny-Carmann equation. This suggested that the a change occurred in the channel structure occurred in the cake composed of the crystalline particles that were obtained. Based on the above laboratory tests, batch crystallization with a low-speed intermittent stirring technique was applied for an actual crystallizer. The filtration time was reduced in the actual plant to about 1/10 of that of the previous conventional stirring crystallization.

Dynamic Optimization of a Batch Cooling Crystallization Process

Dynamic optimization techniques are applied for the optimization of crystallization processes. These obtain promising results, especially for difficult industrial applications with significant heat effects, concentrated slurries, and state constraints. Here we introduce some concepts that focus not only on the optimization strategy but also on the practical implementation. As a case study, we consider a batch crystallization process, which has been studied in the field. The dynamic model includes not only moment equations but also thermodynamic equations to make the model closer to practical operating characteristics. Significant differences between this research and previous work are that we incorporate the heat-transfer components and control directly into the model. After demonstrating in plant that the dynamic model is valid in both model formulation and parameter identification, we optimize this model. The objective is to maximize the final crystal size in order to obtain the highest purity of the de...

Crystal growth of (E)-2-butenedioic acid from aqueous solution in batch-cooling crystallization

The Nielsen method [A.E. Nielsen, Crystal Growth, Suppl. J. Phys. Chem. Solids (1967) 419] [1] is applied to the crystal growth mechanism of (E)-2-butenedioic acid (BDA)/water system. Particle sizes are calculated as a function of the supersaturation ratio for various growth mechanisms using solid/liquid interfacial tension of the BDA/water system [A.E. Nielsen and O. Söhnel, J. Crystal Growth 11 (1971) 233] [2] [I. Liszi and M. Hasznos-Nezdei, Hung. J. Ind. Chem., in press] [3]. In this way a set of curves (“map” of crystal growth mechanisms) helps us to select the validity range of the given growth mechanism. The crystallization was carried out by cooling without seed crystals in a batch crystallizer. The average particle size of the final product and the metastable zone width were measured [3]. From this latter datum the maximum value of the initial supersaturation was determined. The logarithm of the particle size and supersaturation ratio were put in the theoretical crystal growth map. According to the map, the crystal growth in this system is controlled by bulk diffusion. The most probable subprocess of layer growth is surface diffusion (BCF model). This last experience is in accordance with the literature [Sh. Sudo et al., Kagaku Kogaku Ronbunshu 15 (1989) 1120] [4].

A possibility of crystal size distribution control using additives in batch-cooling crystallization

Realisation de la cristallisation de (NH 4 ) 2 SO 4 a partir d'une solution aqueuse contaminee par une petite quantite d'ions Cr 3+ . Les resultats montrent que le temps auquel l'impurete est ajoutee est important (effet sur la taille des cristaux obtenus). Bien que les ions Cr 3+ retardent les vitesses de germination et de croissance cristalline, ils rendent les cristaux obtenus plus grands s'ils sont ajoutes a la solution a un moment approprie