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• Layer melt crystallization of monoethylene glycol was investigated. • Impurity under study was 1,2-pentanediol and solvent additive acetone. • Thermodynamic driving forces with and without solvent additive were determined. • Crystallization kinetics affects purity of final product. Separation of glycols with close boiling points and relatively high viscosity at their melting point is a challenge in the production of high purity products downstream of biorefinery processes. In this work, the efficiency of the layer melt crystallization process with acetone as the assisting solvent was evaluated for a mixture of monoethylene glycol and 1,2-pentanediol. Solid-liquid equilibrium was measured and modelled with the NRTL and modified UNIFAC group-contribution models to evaluate the thermodynamic driving force of crystallization. Layer melt crystallization was conducted to determine the effect of solvent composition on purity, distribution coefficient of impurity, crystal growth rate, and yield at different operating conditions. Addition of the solvent altered the thermodynamics and kinetics of crystallization, thereby altering the purity level of the final product. An effective distribution coefficient of impurity between 0.1 and 0.6 in one-step crystallization was obtained, depending on the solvent composition and the applied operating conditions. [ABSTRACT FROM AUTHOR]

Ni 2+ in excess of maximum recommended limits must be removed from wastewater prior to discharge because of its persistent bio-accumulative and detrimental nature. Natural freezing is suggested as a purification technique to treat huge volumes of wastewater containing Ni 2+ in a sustainable and energy efficient manner. In order to evaluate the feasibility of such a technique for purification of wastewater, natural freezing was simulated experimentally for ice crystallization from different NiSO 4 (aq) solutions. The impact of solution concentration at different freezing conditions such as different ambient air temperature, freezing time and freezing rate on the efficiency of the purification process was investigated. Experimental results demonstrated that at the growth rate ( G ) of 3.5 × 10 −8 m/s, the ice layer formed from 1 wt.% (≈10,000 ppm) NiSO 4 (aq) solution incorporated only 0.0038 wt.% (≈38 ppm) NiSO 4 as impurity, i.e., the ice is more than 250 times pure than the original salt solution. In the case of freezing of very dilute solutions, e.g., 0.1 wt.% NiSO 4 (aq) solution, which is the dilution level of practical interest, the same growth condition is likely to produce an ice layer of even higher purity. For example, at G of 7.4 × 10 −8 m/s, the ice layer impurity that had formed from 0.1 wt.% NiSO 4 (aq) solution was only 0.001 wt.% (≈10 ppm). For this reason, this purification technique has potential for implementation on the surface of wastewater ponds in cold climate regions where the temperature drops below 0 °C. In addition, inclusion formation within the ice matrix during freezing was investigated for various solution concentrations both macroscopically and microscopically. [ABSTRACT FROM AUTHOR]

Evaporation rates play a key role in evaporation crystallization and the drying of crystal products. Raman analysis was used to study the effect of the evaporation rate on the polymorphs of indomethacin at room temperature. The studied solvents were highly volatile ethanol, acetone, and ethyl acetate. The approach was based on a mass transfer model of evaporation, and experimental flux measurements were used for model evaluation. Evaporation rates from porous carriers were also investigated. The studied mesoporous silicon microparticles can be used in oral dosage forms of poorly soluble active pharmaceutical ingredients. Evaporation rates of dimethyl sulfoxide from a pure solvent, from indomethacin solutions, and from solutions containing microparticles were measured at 100 °C. An evaporation rate model of porous particles was used and the predicted results were compared with the experimental results obtained. [ABSTRACT FROM AUTHOR]

This study explored the insights into the theory of dry solids classification, in particular the classical dynamics aspects related to the mass loading of particles, deck inclination of the screen, and resulting measures of flowability. Prototype screening equipment was fabricated and experiments were carried out with ideal rounded mono-shaped glass beads. The overall performance of the prototype was assessed in relation to two screen design variables, the tilt angle of inclination and the mass throughput of the feed, which affects particles flow. Mathematical models relating to the classification process were developed, simulated and compared to the results obtained from the experiments. Important parameter ranges within which equipment may be operated with minimal malfunctioning were approximated from the models. Screen loading, bulk flow velocity, and screen inclination angles determine flowability of powders and particles in gravity classification; these parameters were used in this study to assess how well the particles flowed over the screens. A close correlation was found between theory, simulation models and the experimental results, which facilitated development of empirical models that may be used to predict and estimate the classification rates, efficiencies and flowability for such systems. Dense screen loading improved the classification rates, but hampered flowability, and consequently the efficiency. Increase in deck inclinations improved flowability and efficiency, but only to a certain optimum point after which it led to excessive overflow. [ABSTRACT FROM AUTHOR]

Due to stringent legislation, wastewater needs to be treated before dispersing in the environment. Wastewater can be purified through the formation of less contaminated ice layer by freezing. Freezing of the wastewater leaves the remaining wastewater more concentrated. Attainment of eutectic point (both ice and soluble salt crystallize simultaneously) by freeze crystallization can add extra financial value in terms of salt recovery. Separation of ice from salt becomes very easy because of significant density difference. Na 2 SO 4 is one of the key components present in wastewater emanating from different industrial sources, considered as a model compound in this study. Recovery of Na 2 SO 4 from the aqueous solution by eutectic freeze crystallization air-cooled through the ice layer and solution surface is an energy-efficient and cost effective method. This method was investigated experimentally to recover Na 2 SO 4 from its solution. Furthermore, the influence of different factors and operating conditions was studied on the efficiency of the purification and recovery process. [ABSTRACT FROM AUTHOR]

The black liquor from the kraft pulping process is a potential source of organic acids (e.g. hydroxy acids) which could have applications as a raw material for biodegradable polymers. However, the recovery of the hydroxy acids has rarely been studied and they are not yet utilised. The aim of this paper is to study separation phenomena in the ultrafiltration and nanofiltration stages of the recovery and purification of organic acids from black liquor. Ultrafiltration, acidification, and cooling crystallisation were applied prior to purification by nanofiltration and adsorption. Direct ultrafiltration with a 1 kDa membrane removed 75% of the lignin. Acid molecules permeated the membrane faster than water molecules due to the Donnan exclusion and electroneutrality principles. As a result, the total acid concentration in the accumulated permeate stream was 1.4 fold compared to the original black liquor. However, ultrafiltration prior to precipitation and cooling crystallisation processes had a detrimental effect on the acid purity and the flux in downstream nanofiltration. The separation during nanofiltration in acidic conditions occurred mostly by size exclusion. It was also observed that the changes in the feed composition affected the retention of individual organic acids differently. Nanofiltration removed a significant amount of sulphate ions and residual phenolic compounds, but permeated most of the acid molecules in acidic pH conditions and finally the organic acid purity of the total dissolved solids in the NF permeate was about 80% at the highest. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive comparison of the batch cooling crystallization performance of aqueous solutions containing sugars and sugar alcohols, namely, erythritol, glucose, xylitol, and xylose. Erythritol and xylitol are commonly used alternative sweeteners to replace sucrose. They can be obtained by fermentation-based bioprocesses, where glucose and xylose are typical raw materials. These model compounds were selected based on their differing rheological nature: saturated erythritol solution has a viscosity lower than 3 mPa·s, whereas xylitol has the highest viscosity: greater than 90 mPa·s in the studied temperature range. Viscosities and densities of saturated solutions as well as apparent viscosities of crystal-mother liquor suspensions were measured. The purpose was to evaluate their crystallization behavior within a specific temperature range from 40 to 20 °C and batch time of 2 h, with the aim of understanding the influence of viscosity on the process more comprehensively. The comparison within the selected compound systems was carried out in terms of the physical properties of the mother liquor and the crystalline product. In addition to empirical laboratory-scale (0.1 and 1 L) studies, larger-scale simulations (1 and 100 m 3 ) were performed with the experimental data obtained on average particle size, density, and viscosity for mother liquor and crystal-mother liquor suspensions. Mixing characteristics, such as the dissipation energy, mass transfer coefficient, energy of collisions, and micromixing time, were calculated with VisiMix software when using a single or dual impeller mixer. Furthermore, the scaling up of erythritol, xylitol, glucose, and xylose batch cooling crystallization from 40 to 20 °C based on the scaling-up rule of constant tip speed and energy of dissipation was done with VisiMix to obtain overall data on mixing conditions with crystallizers of 1 and 100 m 3 in volume. Furthermore, ANSYS CFD software was used to determine the strain rates close to the impeller tip and velocity profiles on various crystallizer scales., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

The efficiency of layer melt crystallization for the selective separation of glycerol from a glycerol-diethylene glycol mixture containing 4 wt % of diethylene glycol was evaluated using solvent-free and solvent-aided approaches. The effect of 1-butanol and the binary solvent of 1-butanol and acetone with a total molar composition of 25 mol % on the crystal growth kinetics and the purity of the final product was studied at different undercooling degrees and crystallization yields. The melting point temperature of the mixtures was predicted by using the modified UNIFAC Dortmund model. The addition of both a single and binary solvents significantly increased the crystal growth rate and purity of the final product compared to crystallization from the solvent-free mixture. Additionally, higher crystal growth rates and product purity were observed in the binary solvent system compared to those in the single solvent system at the same degree of undercooling. The second stage of solvent-aided crystallization resulted in glycerol with a purity above 99.5 wt %, depending on the type of solvent used and the rate of crystal growth., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

The removal of trivalent iron and aluminum was studied from synthetic Li-ion battery leach solution by phosphate and hydroxide precipitation (pH 2.5-4.25, t = 3 h, T = 60 °C). Phosphate precipitation exhibited both crystal nucleation initiation (pH 2 vs. pH 3) as well as complete (~ 99%) Fe and Al removal at lower pH compared to hydroxide precipitation (pH 3 vs. 3.5). The precipitation time of phosphate was shorter (40 min) than that of hydroxide precipitation (80 min). At pH 4 the loss of valuable metals (Li, Ni, Co) in the precipitate was negligible in the phosphate cake, whereas in the hydroxide process the co-precipitation was 4-5% for Li, Ni and Co. The filtration rate of phosphate precipitate was shown to be significantly faster. The presence of fluoride did not have any notable effect on phosphate precipitation, whereas in hydroxide precipitation, it potentially had a negative effect on aluminum extraction., (© 2023. The Author(s).)

In this study, we propose a full gamma-valerolactone (GVL) organosolv biorefinery concept including the utilization of all pulping streams, solvent recovery, and preliminary material and energy balances. GVL is a renewable and non-toxic solvent that fractionates woody biomass. The silver birch chips were pulped (45-65 wt% GVL, 150 °C, 2 h) under a series of acid-catalyzed conditions (5-12 kg H 2 SO 4 /t), and the fully bleached pulp was spun into fibers by the IONCELL® process and knitted into the fabric. The dissolved lignin was precipitated by water from spent liquor (1:1) and processed into polyhydroxyurethane. Most of the dissolved hemicelluloses were in the form of xylose, therefore, the crystallization efficiency of xylose from spent liquor in the presence of residual GVL was studied. The GVL recovery rate in the lab column was 66%, however by increasing the number of equilibrium stages, 99% recovery could be achieved., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper, (© 2023 The Authors.)

Four different techniques for xylitol crystallization, namely cooling, evaporative, antisolvent, and combined antisolvent and cooling crystallization, were investigated regarding their influence on the product crystal properties. Various batch times and mixing intensities were studied, and the antisolvent used was ethanol. Real-time monitoring of the count rates of various chord length fractions and distributions using focused beam reflectance measurement was conducted. Several solid characterization methods were used for studying the crystal size and shape, such as scanning electron microscopy and laser diffraction-based crystal size distribution analysis. Crystals ranging in size from 200 to 700 μm were obtained based on the analysis results by laser diffraction. The dynamic viscosity of saturated and undersaturated xylitol solution samples was measured; the density and refraction index were measured to determine the xylitol concentration in the mother liquor. Saturated xylitol solutions were found to have relatively high viscosities up to 129 mPa s in the studied temperature range. Viscosity can have a key role in crystallization kinetics, especially in cooling and evaporative crystallization. Mixing speed had a great influence, mainly on the secondary nucleation mechanism. The addition of ethanol decreased the viscosity, resulting in more uniform crystal shape and better filterability., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Liquid-liquidphase separation (LLPS) or dense liquid intermediates during the crystallization of pharmaceutical molecules is common; however, their role in alternative nucleation mechanisms is less understood. Herein, we report the formation of a dense liquid intermediate followed by a core-shell structure of ibuprofen crystals via nonclassical crystallization. The Raman and SAXS results of the dense phase uncover the molecular structural ordering and its role in nucleation. In addition to the dimer formation of ibuprofen, which is commonly observed in the solution phase, methyl group vibrations in the Raman spectra show intermolecular interactions similar to those in the solid phase. The SAXS data validate the cluster size differences in the supersaturated solution and dense phase. The focused-ion beam cut image shows the attachment of nanoparticles, and we proposed a possible mechanism for the transformation from the dense phase into a core-shell structure. The unstable phase or polycrystalline core and its subsequent dissolution from inside to outside or recrystallization by reversed crystal growth produces the core-shell structure. The LLPS intermediate followed by the core-shell structure and its dissolution enhancement unfold a new perspective of ibuprofen crystallization., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

A fairly clean ice cover can form over a contaminated water pond when the air-cooled surface of water freezes and impurities are efficiently expelled to the remaining water underneath. Natural freeze crystallization has recently been studied as a potential wastewater purification method with aqueous solutions on a laboratory scale. The effect of impurity inclusions on ice strength has been researched in model ice basins over the past few decades. It is of interest to discover how efficiently natural freeze separation works under real weather conditions before freezing can be utilized for wastewater treatment application. Herein, understanding the mechanical strength properties of naturally frozen wastewater (ice) is important when planning ice breaking and harvesting devices. This research implemented in-situ measurements of the flexural and compressive strength of ice in natural ice-covered environments of a freshwater lake, two peatlands and three mining site basins, and compares the determined strength with analyzed impurities of the ice. The results showed that despite varying ice growth conditions and initial water constituents, it was possible to deduce an evident yet simple relationship between mean ice strength and ice impurities: the more impure the ice is, the lower the value of strength is Based on this exploration, it was concluded that separation efficiencies, i.e. the impurity removal ratio between basin water and ice, from 65% up to 90% can be achieved by natural freezing., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The increase in volume and variety of pharmaceuticals found in natural water bodies has become an increasingly serious environmental problem. The implementation of cold plasma technology, specifically gas-phase pulsed corona discharge (PCD), for sulfamethizole abatement was studied in the present work. It was observed that sulfamethizole is easily oxidized by PCD. The flow rate and pH of the solution have no significant effect on the oxidation. Treatment at low pulse repetition frequency is preferable from the energy efficiency point of view but is more time-consuming. The maximum energy efficiency was around 120 g/kWh at half-life and around 50 g/kWh at the end of the treatment. Increasing the solution temperature from room temperature to 50 °C led to a significant reaction retardation of the process and decrease in energy efficiency. The pseudo-first order reaction rate constant (k 1 ) grows with increase in pulse repetition frequency and does not depend on pH. By contrast, decreasing frequency leads to a reduction of the second order reaction rate constant (k 2 ). At elevated temperature of 50 °C, the k 1 , k 2 values decrease 2 and 2.9 times at 50 pps and 500 pps respectively. Lower temperature of 10 °C had no effect on oxidation efficiency compared with room temperature.

The anti-epileptic drug carbamazepine (CBZ) receives growing attention due to slow biodegradation and inherent accumulation in the aquatic environment. The application of a gas-phase pulsed corona discharge (PCD) was investigated to remove CBZ from synthetic solutions and spiked wastewater effluent from a municipal wastewater treatment facility. The treated water was showered between high voltage (HV) wires and grounded plate electrodes, to which ultra-short HV pulses were applied. CBZ was readily oxidized and 1-(2-benzaldehyde)-4-hydroquinazoline-2-one (BQM) and 1-(2-benzaldehyde)-4-hydro-quinazoline-2,4-dione (BQD) were identified as the most abundant primary transformation products, which, contrary to CBZ ozonation data available in the literature, were further easily oxidized with PCD: BQM and BQD attributed to only a minor portion of the target compound oxidized. In concentrations commonly found in wastewater treatment plant effluents (around 5 µg L(-1)), up to 97% reduction in CBZ concentration was achieved at mere 0.3 kW h m(-3) energy consumption, and over 99.9% was removed at 1 kW h m(-3). The PCD application proved to be efficient in the removal of both the parent substance and its known transformation products, even with the competing reactions in the complex composition of wastewater.

Luminescent materials have many interesting applications, but it remains difficult to control the luminescence of organic materials and in particular to retain the same luminescence in solution and in the solid state, a property of interest for various imaging applications. In the present work, the fluorescent properties of the salt of 2,6-diaminopyridinium with dihydrogen phosphate have been explored. As a result of proton transfer from phosphoric acid to the pyridine nitrogen and the stabilizing effect of the two primary amines at the positions ortho to the pyridine nitrogen, the band gap between the HOMO and the LUMO is considerably diminished in comparison with that in 2,6-diaminopyridine. This is confirmed by a red shift in its absorption spectrum. Because protonation is retained in aqueous solution, the dissolved 2,6-diaminopyridinium dihydrogen phosphate salt retains a similar fluorescent spectrum as in the solid state. The crystals have been studied by single-crystal X-ray diffraction; FTIR, Raman, UV-vis-NIR, and luminescence spectroscopy; HOMO-LUMO calculations using DFT; and thermal analysis. The compound provides an example of a supramolecular motif that controls the crystal structure and the luminescence properties. In addition, the crystal exhibits negligible thermal expansion over a temperature interval of 150 °C. In short, 2,6-diaminopyridinium dihydrogen phosphate is an interesting compound for the design of luminescent devices.

Lignin is the mass waste product of pulp and paper industry mostly incinerated for energy recovery. Lignin is, however, a substantial source of raw material for derivatives currently produced in costly wet oxidation processes. The pulsed corona discharge (PCD) for the first time was applied to lignin oxidation aiming a cost-effective environmentally friendly lignin removal and transformation to aldehydes. The experimental research into treatment of coniferous kraft lignin aqueous solutions was undertaken to establish the dependence of lignin oxidation and aldehyde formation on the discharge parameters, initial concentration of lignin and gas phase composition. The rate and the energy efficiency of lignin oxidation increased with increasing oxygen concentration reaching up to 82 g kW-1 h-1 in 89% vol. oxygen. Oxidation energy efficiency in PCD treatment exceeds the one for conventional ozonation by the factor of two under the experimental conditions. Oxidation at low oxygen concentrations showed a tendency of the increasing aldehydes and glyoxylic acid formation yield.

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.

Cellulosic wastes, from sources such as low-quality cardboard and paper, are regarded as potential feedstocks for bioethanol production. One pathway from these cellulosic materials to ethanol is saccharification (hydrolysis) followed by fermentation. Saccharification is commonly performed using enzymes that are able to cleave the cellulosic structure to smaller units, preferably to glucose monomers. During the hydrolysis, mixing conditions have a considerable impact on the performance of the enzymes. Thus mixing conditions in the hydrolysis tank can also influence the downstream operations and, consequently, the overall economy of the bioethanol process. In this experimental study, four types of impeller, at different hydrolysis conditions were used. The effect of mixing on the glucose yield and on the filtration characteristics of the hydrolysate was evaluated. It was shown that not only the sugar yield depended on the mixing conditions: the effect on the solid-liquid separation step was even more significant., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Stability of high indomethacin (IMC) content formulations based on ordered mesoporous silica MCM-41 and SBA-15 materials was studied before and after a 3 month storage in stressed conditions (30°C/56% RH). Overall, the physical stability of the samples was found satisfactory after the storage. However, some issues with the chemical stability were noted, especially with the MCM-41 based samples. The stability issues were evident from the decreased HPLC loading degrees of the drug after stressing as well as from the observed extra peaks in the HPLC chromatograms of the drug in the stressed samples. Drug release from the mesoporous formulations before stressing was rapid at pH 1.2 in comparison to bulk crystalline IMC. The release profiles also remained similar after stressing. Even faster and close to complete IMC release was achieved when the pH was raised from 1.2 to 6.8. To our knowledge, this is the first report of chemical stability issues of drugs in mesoporous silica drug formulations. The present results encourage further study of the factors affecting the chemical stability of drugs in mesoporous silica MCM-41 and SBA-15 formulations in order to realize their potential in oral drug delivery., (Copyright © 2011 Elsevier B.V. All rights reserved.)

In this paper, the thermodynamics of the anhydrate/dihydrate carbamazepine (CBZA/CBZH) in ethanol-water mixtures was studied by measuring the solubility of anhydrate and dihydrate carbamazepine at 0-60 degrees C. Both stable form solubility and metastable form solubility were measured, the latter with the assistance of Raman immersion probe. The thermodynamic properties of the anhydrate/dihydrate system, such as the relative stability, and enthalpy and entropy of dissolution, were estimated by plotting the measured solubility data according to the van't Hoff equation. The anhydrate/dihydrate carbamazepine showed an enantiotropic relationship in the studied mixtures and temperature ranges. It was shown that at a certain temperature, there was an equilibrium water activity value at which the anhydrate and dihydrate carbamazepine were in equilibrium. This equilibrium water activity value depends significantly on the temperature. The lower the temperature, the smaller is the water activity value needed to attain equilibrium between anhydrate and dihydrate. The obtained results are useful in determining crystallization parameters to achieve a desired anhydrate or hydrate phase. The approach can be applied to other anhydrate and hydrate systems.

Sonocrystallization has proved to be an efficient tool to influence the external appearance and structure of a crystalline product obtained by various crystallization methods. The present work focuses on high intensity sonocrystallization of glycine by varying amplitude of ultrasound with an ultrasound frequency of 20kHz at two temperature ranges 40-50 and 20-30 degrees C in a jacketed 250-ml cooling crystallizer equipped with a stirrer. The polymorph composition of the obtained crystals was analyzed with a temperature variable X-ray powder diffractometer (XRPD). XRPD results showed that, besides the operating temperature, the glycine polymorphism was affected also by insonation. This was especially the case at the lower temperature range. Furthermore, based on the heat balance within the crystallizer, an increase in required cooling capacity was presented as a function of increasing ultrasound power. This study also showed, the higher the ultrasound amplitude the smaller the crystals obtained.

Crystalline product should exist in optimal polymorphic form. Robust and reliable method for polymorph characterization is of great importance. In this work, infra red (IR) spectroscopy is applied for monitoring of crystallization process in situ. The results show that attenuated total reflection Fourier transform infra red (ATR-FTIR) spectroscopy provides valuable information on process, which can be utilized for more controlled crystallization processes. Diffuse reflectance Fourier transform infra red (DRIFT-IR) is applied for polymorphic characterization of crystalline product using X-ray powder diffraction (XRPD) as a reference technique. In order to fully utilize DRIFT, the application of multivariate techniques are needed, e.g., multivariate statistical process control (MSPC), principal component analysis (PCA) and partial least squares (PLS). The results demonstrate that multivariate techniques provide the powerful tool for rapid evaluation of spectral data and also enable more reliable quantification of polymorphic composition of samples being mixtures of two or more polymorphs. This opens new perspectives for understanding crystallization processes and increases the level of safety within the manufacture of pharmaceutics.

Currently there is a great interest in new process analytical approaches to increase the process understanding of pharmaceutical unit operations. In the present study, the influence of the solvent composition on the material properties and, further, on the filtration characteristics, of different crystal suspensions obtained through an unseeded batch-cooling-crystallization process was studied. Sulphathiazole, which is an antibiotic agent with multiple polymorphic forms, was produced by performing laboratory-scale cooling crystallization experiments from five different mixtures of water and propan-1-ol (n-propanol). The size, shape and polymorphic composition of the crystals produced were characterized with a scanning electron microscope, with a novel automated image analyser and with an X-ray powder diffractometer. All of the monitored crystal properties were found to clearly differ between the samples obtained from different solvents. The crystals produced in the batch-cooling-crystallization experiments were separated from the crystallizing solvents using a batch-type pressure Nutsche filter, and the filtration characteristics of the suspensions were evaluated on the basis of average filter-cake porosities and average specific cake resistances, which were determined from the experimentally obtained filtration data. Comparison between the calculated filtration characteristics revealed that considerable differences existed between the different suspensions, and it could therefore be concluded that the pressure-filtration process was influenced by the composition of the crystallizing solvent. The filterability of all the studied sulphathiazole suspensions was considered to be rather good on the basis of the relatively low cake porosities (0.51-0.63), which were accompanied with low average specific cake resistances [(8.7 x 10(7))-(1.2 x 10(9)) m/kg].