In-Process Monitoring and Control of Supersaturation in Seeded Batch Cooling Crystallisation of l-Glutamic Acid: From Laboratory to Industrial Pilot Plant

Abstract

A measurement-based closed-loop control system using in-process ATR-FTIR spectroscopy coupled with a multivariate chemometric PLS calibration model is developed, validated, and applied to the monitoring and control of supersaturation in a 250- L industrial pilot-plant crystalliser. Supersaturation control experiments are carried out on seeded batch cooling crystallisation of β-l-glutamic acid from aqueous solutions using two methods of seeding involving addition of seeds to the solution and generation of seeds within the solution. The generic applicability of the approach is demonstrated through this challenging system reflecting this molecule’s weak chromophore for infrared and relatively low solubility compared with previous solute−solvent systems. Based on the laboratory experiments, the system was fully tested and optimised prior to a series of trials carried out in an industrial pilot plant at Syngenta, Münchwillen, Switzerland. Good control of the supersaturation is achieved at three levels, 1.1, 1.2, and 1.3, within a prescribed range of ±0.025. The average product crystal size is found to decrease with increasing supersaturation. Comparison between product crystals produced at the 20- and 250-L scales indicates that secondary nucleation is more prevalent at the smaller-scale size. For the same level of supersaturation, the rate of depletion of solute is faster at the 20-L scale size than at 250-L scale, and hence a higher cooling rate is required to maintain the desired supersaturation. However, for a given crystalliser scale size, as expected, the mean cooling rate required to maintain a constant supersaturation is found to increase with increasing supersaturation level.

Applications of ultrasonics in food science - novel control of fat crystallization and structuring

“…For example, we have sized whole milk, separately sizing the protein particle size distribution and that of the milk fat globules [31] [32]. Attempts to use this technique to size crystals during growth have not been overly successful despite considerable effort [33][34][35][36][37][38][39][40][41]because the phase transition itself introduces an additional attenuation term, over and above the scattering terms [30] [42](thermal and visco-inertial) currently included in the inversion models. As a result, empirical methods of analysis were resorted to which suffered from the complicated and variable interaction between the ultrasound field and the crystallising material, we now know that the quasi-continuous acoustic fields can modify the crystal nucleation process [43] and Section 4.3.1 below, An advantage that ultrasound attenuation spectroscopy enjoys over light scattering techniques is its ability to measure concentrated systems and in stirred conditions, so that the emergence of structure can be followed over time.…”

Crystallisation Route Map

“…The comparisons of power number, discharge flow number, secondary circulation flow number and pumping efficiency at three different scales suggest that the scale up with the selected laboratory vessels has little effect on the macro mixing performance for optimisation of the configuration and operating conditions of an industrial scale reactor. Further details about the experimental and modelling investigations of process scale-up can be found in the literature, such as [28,32,[45][46][47][48][49].…”

Surface Adsorbed Templates for Directing the Crystal Growth of Entacapone as Monitored Using Process Analytical Techniques

“…This is consistent with the assumption that crystals prepared on the template once being faceted, proceed to grow with similar fashion to the case of crystallisation without the template but differ significantly in their early stages of growth. In this respect, it is worth noting that in a continuous crystallisation process perhaps encompassing supersaturation control 18,19 , the growth rate could be sustained for longer period to produce materials over a much wider range of supersaturations and crystal sizes. Figure 11 show micrographs taken of the crystals harvested from the crystallisation experiments which have carried out with and without presence of the template.…”

“…17,18,19 ) and in particular case presented here have been applied to assess the performance of template in mediating the crystallisation process. In particular, PAT is useful to define how these templates influence the crystallisation process kinetics as well as the concomitant impact on the physical and chemical properties of the resulting crystals.…”