Sang-Do Yeo

Recrystallization of sulfathiazole and chlorpropamide using the supercritical fluid antisolvent process

Abstract The supercritical antisolvent (SAS) process was used to modify the solid–state properties of sulfathiazole and chlorpropamide. Acetone, methanol, and ethyl acetate were employed as solvents for the pharmaceutical compounds, and carbon dioxide was used as an antisolvent. The effects of process parameters on the precipitate crystals such as carbon dioxide injection rate, type of solvent, and temperature were investigated. The SAS processed crystals show more ordered appearances with clean surfaces and sharp angles compared with the unprocessed particles. The crystal habit changed from tabular to acicular when the carbon dioxide injection rate increased. The X-ray diffraction patterns of the two compounds revealed variations of crystallinity and crystal orientations depending upon the injection rate, where the degree of crystallinity was found to be inversely proportional to the rate of injection. The analysis of differential scanning calorimetry indicated that both the injection rate and temperature influence the crystals thermal stability which is related to the solid–solid transition and fusion. The crystal size significantly increased when the nucleation and crystal growth took place at a slow rate.

Supercritical Extraction of Phenols from Organically Modified Smectite

Supercritical extraction has been performed in a fixed column to desorb phenol and 4-nitrophenol from organically modified smectite. The experiments were carried out in the sequence of adsorption of hexadecyltrimethylammonium (HDTMA) to montmorillonite, adsorption of phenols to organoclay in aqueous solutions, desorption of phenols from loaded organoclay using supercritical carbon dioxide, and adsorption of phenols to regenerated organoclay. The desorption characteristics of phenols were investigated at various pressures up to 420 bar; at temperatures of 40, 60, and 70°C, and at low concentrations of a cosolvent. The extraction percentages of phenols reached up to 90% in 3 hours of extraction. The results showed that under the experimental conditions investigated, the activity of HDTMA was intact during the supercritical extraction of phenols, and hence HDTMA-modified montmorillonite exhibited undiminished adsorption power toward phenols after several regeneration cycles.

Antisolvent Crystallization of Roxithromycin and the Effect of Ultrasound

Antisolvent crystallization was performed to precipitate roxithromycin particles from organic solutions. Roxithromycin was dissolved in acetone at different concentrations and each solution was injected into an aqueous antisolvent leading to prompt particle formation. The effects of various experimental variables (solution injection rate, solution concentration, and temperature) on the particle size of roxithromycin were investigated. In addition to these variables, the effect of ultrasound on the resulting particle size was investigated by changing process parameters such as wave intensity (power output), sonication time, and the moment of ultrasonic application. When the drug solution was rapidly injected into the antisolvent, smaller crystals were obtained. Smaller crystals were obtained when solutions with high drug concentrations were used and also when the crystallization took place at lower temperatures. The particle size decreased with the increasing power output of ultrasound and with the increasing sonication time. It was also found that the ultrasonic wave induced the reduction of the particle size only when the ultrasound was applied to the solution at the initial stage of crystallization.

Vapor Adsorption of Volatile Organic Compounds Using Organically Modified Clay

Abstract Organically modified clay was used to adsorb volatile organic compounds from a gaseous phase. The organoclay was prepared by adsorbing hexadecyltrimethylammonium (HDTMA) on the surface of montmorillonite particles. Two volatile organic compounds (VOCs), chlorobenzene and trichloroethylene, were adsorbed to the organoclay using a fixed adsorption bed. The adsorption was carried out at various inlet concentrations of gaseous VOCs in a carrier gas (nitrogen). The adsorption behavior of VOCs was investigated using natural clay and two types of organoclays, which had different HDTMA loadings. Adsorption breakthrough curves were obtained, and the adsorption data were modeled with two adsorption isotherms. Desorption of VOCs was also conducted using pure nitrogen, and the desorption profiles were fitted with two different theoretical models. It was found that the organoclay possesses significant adsorption capacity towards VOCs and the uptake depends on the degree of HDTMA loading on clay surface.

Crystal formation of BaCl2 and NH4Cl using a supercritical fluid antisolvent

The supercritical antisolvent (SAS) process has been used to produce crystals of barium chloride (BaCl2) and ammonium chloride (NH4Cl) from solutions of dimethyl sulfoxide (DMSO). Crystallization was performed by introducing carbon dioxide into the DMSO solutions at different injection rates. Variations in crystal properties such as particle size, crystal habit, and internal space lattice were observed in the SAS processed crystals. The average particle size of the crystals decreased with increasing carbon dioxide injection rate for both compounds. As the injection rate increased, the crystal habit of BaCl2 was modified from an equant to an acicular habit, and that of NH4Cl changed from an equant to a tabular habit. X-ray diffraction patterns showed the transition of the space lattice of BaCl2 from the orthorhombic to hexagonal crystal system. The use of the SAS process for the separation of BaCl2 and NH4Cl mixtures in DMSO was also investigated.

Adsorption of volatile organic compounds on soil and prediction of desorption breakthroughs

Abstract Vapor extraction of volatile organic compounds from soil was investigated by performing adsorption and desorption experiments of trichloroethylene, trichloroethane, and chlorobenzene on soil particles. The adsorption breakthrough curves were obtained using a dynamic response technique based on frontal analysis chromatography. The shape of the breakthrough curves indicated that the adsorption process was close to an ideal adsorption system of no mass transfer resistance, no axial dispersion, and infinitesimal width of mass transfer zone. The adsorption isotherms were BET Type I for trichloroethylene and trichloroethane, and BET Type II for chlorobenzene. Two types of desorption profiles were observed depending on the compounds, i.e., the continuously decreasing profiles of trichloroethylene and trichloroethane and the stepwise decreasing profiles of chlorobenzene. The desorption profiles of trichloroethylene and trichloroethane were simulated using a local equilibrium theory which indicated that d...

Antisolvent Crystallization of Sulfa Drugs and the Effect of Process Parameters

Abstract Three sulfa drugs (sulfathiazole, sulfamethizole, and sulfabenzamide) were crystallized using carbon dioxide and water as antisolvents, and the effects of the type of solvent, the crystallization temperature, and the antisolvent injection rate were investigated. Sulfathiazole crystallized in granulate form from acetone, but it was crystallized in acicular form from methanol. Sulfamethizole was crystallized in tabulate form from acetone and as plates from DMF. Sulfabenzamide was precipitated in the form of prisms from acetone and of aciculates from ethyl acetate. As the crystallization temperature increased from 30 to 50°C, the average particle size increased from 6.5 to 10.5 µm for sulfathiazole, 29.5 to 53.1 µm for sulfamethizole, and 33.0 to 59.8 µm for sulfabenzamide. The crystal habit tended to become more needle‐like as the antisolvent injection rate increased. Larger particles were produced when the antisolvent was changed from carbon dioxide to water.

Liquid Antisolvent Recrystallization of Phenylbutazone and the Effect of Process Parameters

Phenylbutazone was crystallized from solutions by the liquid antisolvent recrystallization technique. Acetone was used as a solvent, and distilled water was selected as an antisolvent. The influence of processing parameters, such as drug concentration, temperature, injection rate of drug solution, and mixing method of drug solution with antisolvent, on the particle size distribution were investigated. Furthermore, to examine the variation of resulting particle size in the presence of the ultrasound, the ultrasonic wave was applied to all experiments. Larger crystals were obtained when crystallization took place at higher temperatures. The enhancement of drug concentration favored decreased particle size. Regarding the mixing method of the drug solution and antisolvent, smaller particles were produced when the drug solution was injected into antisolvent, and larger crystals were obtained when the antisolvent was injected into drug solutions. As the injection rate of the drug solution increased, the average particle size decreased. The processed particles consistently exhibited an acicular crystal habit. The presence of ultrasound caused a reduction of particle size under all operational conditions.

Supercritical Extraction of Phenol from Activated Carbon Fiber

Phenol was extracted from activated carbon fiber (ACF) using supercritical carbon dioxide in a fixed-bed extractor. Phenol was adsorbed to ACF from aqueous solutions at two different loadings, 277 and 402 mg phenol/g ACF. Supercritical extraction of the loaded ACF was carried out at temperatures of 30, 50, 70, and 90°C in a pressure range from 206.8 to 344.7 bar. The extraction percentage of phenol from ACF was recorded as function of carbon dioxide used, and the trend of experimental data was extended by using an extrapolation technique. We observed a crossover point at which the extended isotherms of different temperatures could possibly intersect. This result reflects the combined effect of pressure and temperature on carbon dioxide density and on the desorption rate of phenol from ACF. The desorption rate constant was estimated from extraction profiles, which decreased with increasing temperature and pressure.

Adsorption of Ethylbenzene and Tetrachloroethylene Using Natural and Organically Modified Clays

The vapor of two volatile organic compounds, ethylbenzene, and tetrachloroethylene were adsorbed to natural and organically modified montmorillonite clays, respectively. The surface of clay was modified using a cationic surfactant, hexadecyltrimethylammonium (HDTMA) with a cation-exchange capacity of 161 mg HDTMA/g-clay. The adsorption was performed by passing the mixture of nitrogen and the vapor of organic compounds through a fixed adsorption bed. Desorption was also conducted by allowing the pure nitrogen to flow through the loaded bed. The experiments were conducted at 24, 34, and 44°C in order to investigate the effect of temperature on the adsorption and desorption behavior of the two types of clays. The adsorption data were modeled with the BET adsorption isotherm equation. The isotherms of natural and modified clays exhibited a typical favorable Type I behavior. The temperature effect on the adsorption capacity was significant when the natural clay adsorbed the two organic compounds, while the temperature effect was minor when the modified clay was used. The desorption rate constants were in the order of 10−5 min−1 and these values were not greatly varied when the type of clay changed from natural to modified clay.