The impact of different nucleation methods with controlled supersaturation on the polymorphism of L-glutamic acid crystals was studied in a 50 dm 3 semi-batch crystallizer, in which 1.5 M H 2 SO 4 was fed into a 1.5 M monosodium glutamate solution. Supersaturation was controlled by a feedback loop based on measured ATR-FTIR spectra and on a thermodynamic model developed in house. Ultrasound-initiated nucleation produced pure a-polymorph (over 99.5 wt %) in the end product crystals at 1 mol/dm 3 supersaturation. Seeded crystallization also produced almost pure a-polymorph crystals (over 93 wt %), whereas spontaneous nucleation produced a polymorph mixture (from 30-70 wt %) under the same operating conditions. This indicates that supersaturation-controlled sonocrystallization can be used to control polymorphism in crystals. The novelty herein is the simplicity of the method directing the generation of a desired polymorph.

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Oxidation of aromatic compounds of phenolic (paracetamol, beta-oestradiol and salicylic acid) and carboxylic (indomethacin and ibuprofen) structure used in pharmaceutics was studied. Aqueous solutions were treated with pulsed corona discharge (PCD) as a means for advanced oxidation. Pulse repetition frequency, delivered energy dose and oxidation media were the main parameters studied for their influence on the process energy efficiency. The PCD treatment appeared to be effective in oxidation of the target compounds: complete degradation of pollutant together with partial mineralization was achieved at moderate energy consumption; oxidation proceeds faster in alkaline media. Low-molecular carboxylic acids were identified as ultimate oxidation by-products formed in the reaction.

aThe paper studies the utilization of attenuated total reflectance-Fourier transformed infrared (ATR-FTIR) and Raman spectroscopy to investigate isothermal semi-batch precipitation of a model compound, L-glutamic acid. ATR-FTIR spectroscopy was mainly used for in-line monitoring of the solution phase and Raman spectroscopy for analysis of the solid phase. L-glutamic acid has two reported polymorphs: a metastable a form and a stable b form. The b form can be obtained at relatively high supersaturation levels at 25 o C. The synthesis consists of a sodium glutamate reaction with sulfuric acid yielding L-glutamic acid crystals and sodium sulfate as a side-product solute. The spectral data were utilized to interpret the crystallization process using multivariate methods. A thermodynamic model taking into account the non-ideal character of the studied compound system and dissociation of different compounds is introduced. The resolution of ATR-FTIR is not sufficient to determine directly the L-glutamic acid concentration in the solution. Therefore, special efforts were made to determine the instantaneous concentration of dissolved glutamic acid based on the mass balance and ATR-FTIR spectra. Calibration concentrations were based on thermodynamic data. Multivariate methods were applied in monitoring the precipitation process and to predict indirectly the concentration of the chemical compounds. In this study, the spectra from ATR-FTIR were utilized to estimate and predict the concentrations from thermodynamic modeling. It was also investigated if the Raman spectra could be used for this purpose.

The aim of the present study was to investigate feedback control of a reactive crystallization process. The present study built up a control structure needed to control the driving force of reactive crystallization using the feed rate of added acid. The concentration of the crystallizing compound and pH was used to compute feedback in the closed-loop control of semi-batch precipitation. The concentration of L-glutamic acid was determined from measured MID-IR ATR-FTIR spectra based on a multivariate model. Dynamic change of set value was based on the mass of added sulfuric acid and pH. The studied properties of the product crystals were polymorphism and crystal size. The polymorphic composition was analyzed with a Raman spectrometer and was expressed by mass fraction of the a-polymorph. The obtained results showed that the developed feedback process control system allows effective control of forming of polymorphs.