Recrystallization of phenylbutazone using supercritical fluid antisolvent process

Phenylbutazone was recrystallized from its solutions by using a supercritical fluid antisolvent process. It was dissolved in acetone and supercritical carbon dioxide was injected into the solution, thereby inducing supersaturation and particle formation. Variation in the physical properties of the recrystallized phenylbutazone was investigated as a function of the crystallizing temperature and the carbon dioxide injection rate. The recrystallized particles showed cleaner surfaces and more ordered morphology compared to the particles obtained by other methods such as solvent evaporation. X-ray diffraction patterns indicated that the crystallinity of the particles had been modified upon the recrystallization. Differential scanning calorimetry measurement revealed that the crystallizing temperature influenced the thermal stability of the resulting crystals. Larger crystals were produced when the carbon dioxide injection rate was reduced.     

A study on crystallization kinetics of pentaerythritol in a batch cooling crystallizer

The crystallization kinetics of pentaerythritol (PeE) in aqueous solution in the presence of impurity or not in a batch cooling crystallizer was explored. Also, the solubility and the nucleation and crystal growth kinetics of PeE in aqueous solution were investigated. A second-order dependence of PeE growth rate on supersaturation is observed in pure PeE-water system. The crystal growth rate of PeE-water system in the presence of impurity is proportional to the supersaturation to the 3.5 power. The nucleation and crystal growth behaviors for PeE-water system in a batch cooling crystallizer were grasped according to Mersmann's criteria. The nucleation in this crystallizer was found to act with heterogeneous nucleation. In this system, it suggests that the crystal growth is controlled by a complex mechanism behavior of surface integrated and diffusion limited. Simplified relation was derived for calculation of mean crystal size of product crystals from the batch cooling crystallizer. The obtained relation was verified by a set of experiments.     

Na2S-SO2反应体系中H2S产生的过饱和态分析

向Na2S溶液中通入低浓度SO2气体以生成H2S，H2S从液相中逸出时，存在一突跃现象。本文根据这一现象，结合Y．T．Shah等提出的吸收－反应－解吸体系中过饱和态存在的条件，通过理论分析，得出在Na2S-SO2-H2S4反应体系中H2S解吸存在过饱和现象。     

THE EFFECT OF PRECIPITATION PARAMETERS ON PREPARATION OF LITHIUM FLUORIDE (LIF) NANO-POWDER

Lithium fluoride powder (LiF) is a white powder with a density of 2.64 gr/cm³ and a melting point of 848°C. This powder has several applications such as flux, glaze, soldering, and aluminum melting process, but one of the most important uses of this powder is its application in dosimetry. The commercial powders currently used for this purpose have average sizes of 5 to 10 micrometers; the objective of this research is to produce LiF powder with nano-metric particle size. In this study, the reaction of LiOH + HF → LiF + H₂O has been selected from among several reactions that were able to produce LiF powder, and some precipitation parameters such as temperature, time, agitation type, and supersaturation degree have been controlled. The morphology, phase analysis, and particle size distribution of the resulting powders were analyzed by SEM, XRD, and LPSA. Finally, lithium fluoride nano-powder was synthesized at a temperature of 25°C, pH about 2-3, reaction time less than 1 s, and agitation by ultrasonic bath.     

Stabilizing effect of the cyclodextrins additive to spray-dried particles of curcumin/polyvinylpyrrolidone on the supersaturated state of curcumin

Although curcumin is considered to have various therapeutic effects, its use as a functional food or supplement is restricted owing to its low water solubility and bioavailability. To increase the solubility of curcumin in water, the use of polyvinylpyrrolidone (PVP) and vinylpyrrolidone-vinyl acetate copolymers with a pyrrolidone skeleton was noted to be promising. In particular, the bi-component formulations of curcumin/PVP prepared through spray drying exhibited an amorphous state in powder X-ray diffraction observations and temporally increased the apparent solubility of curcumin to over 5000 times that of untreated curcumin; nevertheless, after 24 h, the solubility decreased owing to the unstable supersaturated state of curcumin. The addition of α-cyclodextrin (α-CyD) in the bi-component curcumin/PVP formulation helped maintain the supersaturated state of curcumin, whereas the addition of β- and γ-CyD led to the collapse of the supersaturated state. The addition of α-CyD can likely help inhibit the nucleation and crystal growth of curcumin, through the interaction among the solubilized units of curcumin/PVP and α-CyD.     

Microanalysis of supersaturated gas release based on wall-attached bubbles

Supersaturation of dissolved gases in natural water, due to spillage from high dams and other factors, may cause fish mortality. In previous experiments, the dissipation coefficient has been used to denote the degassing process of total dissolved gas(TDG) saturation. These experiments mainly analyzed supersaturated TDG dissipation from a macroscopic view. To precisely clarify the mechanism of supersaturated TDG release, this study investigated bubble adsorption at a wall surface from a microscopic view. The experiment was conducted in a Plexiglas-wall container filled with supersaturated TDG water. A model that calculates the adsorption flux of supersaturated TDG by a solid wall, and helps describe construction for a contact angle at a three-phase intersection, was developed according to Young's equation. This model was used to investigate the formation process of bubbles adsorbed on a solid polymethyl methacrylate(PMMA) surface in supersaturated TDG water. The adsorption effect of a solid wall on TDG release was analyzed based on the experimental data. The modeling results were compared with observations under different wall area conditions, and it was found that TDG release tended to increase with wall area. This study helps improve our understanding of the mechanisms of supersaturated TDG release and provides an important theoretical method for accurate calculation of the release process. The adsorption flux model of the solid wall provides mitigation measures to combat the adverse effects of TDG supersaturation,which will be beneficial to the protection of aquatic organisms in hydropower-regulated rivers.     

Modeling shallow marine carbonate depositional systems

Geological Process Models (GPMs) have been used in the past to simulate the distinctive stratigraphies formed in carbonate sediments, and to explore the interaction of controls that produce heterogeneity. Previous GPMs have only indirectly included the supersaturation of calcium carbonate in seawater, a key physicochemical control on carbonate production in reef and lagoon environments, by modifying production rates based on the distance from open marine sources. We here use the residence time of water in the lagoon and reef areas as a proxy for the supersaturation state of carbonate in a new process model, Carbonate GPM. Residence times in the model are calculated using a particle-tracking algorithm. Carbonate production is also controlled by water depth and wave power dissipation. Once deposited, sediment can be eroded, transported and re-deposited via both advective and diffusive processes. We show that using residence time as a control on production might explain the formation of non-ordered, three-dimensional carbonate stratigraphies by lateral shifts in the locus of carbonate deposition on timescales comparable to so-called 5th-order sea-level oscillations. We also show that representing supersaturation as a function of distance from open marine sources, as in previous models, cannot correctly predict the supersaturation distribution over a lagoon due to the intricacies of the flow regime.     

Effects of Process Parameters on Gypsum Scale Formation in Pipes

Scaling often leads to a series of technical and economical problems in industrial plants and equipments by blocking water flow in pipes or limiting heat transfer in heat exchangers. While most contemporary studies are focusing on crystallization at heat‐exchanger surfaces and scaling on nanofilters in desalination plants, very little work has been done investigating scale formation on pipe and vessel walls. A comprehensive investigation of the effects of various process parameters in controlling the formation of calcium sulfate scale in pipes was undertaken. Supersaturation ratio, run time, and operational hydrodynamics were altered systematically to determine their influence on the scale growth rate. The results confirmed that the deposition of gypsum on pipe walls was significantly affected by these process parameters.     

A fed-batch design approach of struvite system in controlled supersaturation

This paper focuses on struvite (MgNH₄PO₄·6H₂O) crystallization in controlled supersaturation. Struvite can be used as a slow-release fertilizer. Crystallization experiments were conducted using supersaturated solutions. The secondary focus of this paper is the design of a struvite recovery system in fed-batch-controlled supersaturation mode. The design and commissioning of fed-batch struvite crystallization included the determination of operating supersaturation of struvite crystallization, suitable seed materials and the composition of feed solution. Determination of operating supersaturation of struvite crystallization was conducted by two steps including thermodynamic simulation using gPROMS² (process simulation software) along with a set of batch experiments. Investigation of suitable seed materials was also conducted using set of batch experiments. Two types of seed materials including quartz sand and struvite seeds were used in the investigation of seed materials. Composition of feed solution included the investigation of struvite solution chemistry using PHREEQC³ thermodynamic modeling package. Based on the previously investigated design approach, struvite crystallization in fed-batch system was conducted using a 44-L of reactor with 15-L of initial reactant volume.     

Semi‐quantitative Study on the Inclusion in Cooling Crystallization of RDX Using Various Solvents

Inclusion entrapped inside the crystals prepared in the cooling crystallization of cyclotrimethylenetrinitramine (RDX) from solution was studied. Effect of supersaturation on the inclusion formation was also studied in crystallization using solvents. Solvents such as acetone (AC), cyclohexanone (CH), dimethylsulfoxide (DMSO), N‐methylpyrrolidone (NMP), γ‐butyrolactone (BL), and their mixtures with water were investigated. The quantitative amount of inclusions entrapped in the RDX crystallized in various solvents was related to the supersaturation. The inclusion fraction in the crystals was affected by the supersaturation and the solvent. In order to decrease the inclusion fraction, in the low supersaturation, AC and CH were recommended, while in high supersaturation, NMP and DMSO were desirable. Eventually the solvent effect on the inclusion was grasped by considering the supersaturation effect.