共查询到20条相似文献,搜索用时 15 毫秒
1.
Carbamazepine was crystallized from organic solutions using an antisolvent crystallization technique. Ethanol was used as a solvent for the carbamazepine and distilled water was used as an antisolvent. The carbamazepine was dissolved in the solvent, and the drug solution was injected into the antisolvent causing the particle precipitation. During the crystallization experiments, the effects of the process parameters such as solution concentration, temperature, injection rate of the solution, and the presence of ultrasound, were investigated. An analysis of the produced particles showed that external characteristics such as particle size and its distribution were a strong function of the process parameters, while the internal structures such as crystallinity and thermal stability were nearly unaffected. Smaller particles were obtained when solutions with high drug concentrations were used. Higher temperature resulted in larger crystals. Particle size was also influenced by the injection rate of the drug solutions. Carbamazepine particle size was significantly reduced when the ultrasonic wave was selectively applied. 相似文献
2.
M. K. Akindeju V. K. Pareek M. O. Tade A. L. Rohl 《Chemical Engineering Communications》2013,200(1):73-84
A novel phenomenological spinning disc continuous stir tank and settler reactor (SDCSTR) has been modeled for continuous synthesis of titania from its chloride precursor and water in which the desired polymorph, particle size, and distribution are controlled by the characteristics of the atomized inlet reagents, disc, and tank stir rate. This energy-efficient reactor generates seeding nuclei in the aerosol reacting volume that are then deployed for heterogeneous nucleation and particle growth in the metastable reacting volume of the aqueous (sol) process. Once at steady state, the enhanced TiO2 nanoparticles due to the OH?–H+ chemisorbed on the surface (with surface energy 0.5 < σ < 2.11 N/m) are continuously withdrawn at a rate equivalent to the particle settling rate from the settler. This reactor model eliminates the energy intensity required in traditional chemical vapor deposition (CVD) and aerosol reactors and provides better control for particle growth and size distribution by increasing particle residence time in the metastable zone of the aqueous (sol) reaction stage. 相似文献
3.
通过生物显微镜、X射线粉末衍射(XRD)、马尔文粒度分析仪,差热分析(DSC)及在线聚焦反射测量仪(FBRM)和粒子成像测量仪(PVM)研究了在卡马西平结晶过程中各种操作参数对产品质量特别是晶型的影响,具体考察了溶剂、晶种、结晶方式、干燥、温度、搅拌速率及冷却速率对晶体产品质量的影响。结果表明,不同溶剂中缓慢结晶,高介电常数溶剂(如醇类)中得到卡马西平晶型Ⅲ,乙醇-水混合物中当乙醇摩尔分数低于40%时结晶产物为二水物,四氢呋喃中结晶得到晶型Ⅱ,其他溶剂得到产品为混合晶型;对于醇类溶剂,蒸发结晶一般得到卡马西平晶型Ⅱ,而缓慢冷却得晶型Ⅲ;以正丙醇为溶剂,加大量颗粒较小的晶种可以得到粒度较均一的产品;晶型Ⅱ产品由于特殊的结构,易于有结晶用溶剂包藏在晶体中,加热到约140℃溶剂逸出;温度是影响晶型的重要因素,在较高温度区间(90~76℃)结晶得晶型Ⅱ,而在低温度区间(52~20℃)得晶型Ⅲ;搅拌速率在较低的温度下对晶型没有影响,搅拌速率大可以避免晶体的聚集,形成较均匀的颗粒;3种降温速率结果显示,产品均为卡马西平晶型Ⅲ,但先慢后快的降温速率可以得到更均匀的颗粒晶体。 相似文献
4.
Marija Djokić Jelena Djuriš Ljiljana Solomun Kyriakos Kachrimanis Zorica Djurić Svetlana Ibrić 《Chemical Engineering Research and Design》2014
The purpose of this study was to investigate the influence of spiral jet-milling process on the physicochemical characteristics of α polymorphic active pharmaceutical ingredient, using Carbamazepine form III as a model drug, and taking into consideration Quality by Design (QbD) approach to pharmaceutical development. A 2(4-1) factorial screening design was implemented to identify the spiral jet-milling process variables that significantly affect the particle size distribution of milled samples. Diameter of injector nozzles, diameter of ring nozzles and air pressure were selected for further analysis using a 2(3-1) factorial experimental design. Particle size distribution of additional samples was determined, while physicochemical properties were examined by differential scanning calorimetry (DSC), hot-stage polarized microscopy (HSPM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and compared to those of un-milled drug. The gathered results shown that applied experimental design approach is capable to predict material behavior and could help in better understanding of material behavior during jet-milling process. Created design space (DS) provides assurance of product quality, expressed as the powder particle sizes lower than 5 μm, as well as, in initial polymorph form existence after jet-milling through combination and interaction of input variables. 相似文献
5.
The supercritical antisolvent technology is used to crystallize paracetamol particles. Supercritical carbon dioxide (scCO2) is used as antisolvent. Ethanol, acetone and mixtures of ethanol and acetone are used as solvents. The initial concentration of paracetamol in the solution was varied between 1 and 5 wt%, the composition of the ethanol/acetone solvent mixture between 50 and 90 wt% of ethanol and the operation pressure between 10 and 16 MPa at a temperature of 313 K. The most important finding is that the polymorph of paracetamol crystals can be adjusted between monoclinic and orthorhombic by varying the content of ethanol in the solution. The second important finding is that the occurrence of primary and secondary crystal structures can be explained solely by the overall supersaturation during the crystallization process. While X-ray diffraction was used to analyze the polymorph of the particles, their morphology was analyzed using scanning electron microscopy. 相似文献
6.
The research results and kinetic studies on the barium ions precipitation process by means of crystalline ammonium sulfate addition are presented. The influence of: barium, sodium, potassium and calcium chlorides concentration in the feeding solution and also the process temperature on barium sulfate mass crystallization kinetics are investigated. Experiments were carried out in the MSMPR crystallizer with internal circulation of suspension. The barium sulfate nucleation and crystal growth rates were estimated from crystal size distribution taking into account a size dependent growth (SDG). Research results may be utilized in the used quenching salts processing technology. 相似文献
7.
Steven Ferguson Gary Morris Hongxun Hao Mark Barrett Brian Glennon 《Chemical Engineering Research and Design》2014
In this study, seed slurry from a single addition anti-solvent plug flow crystallization of benzoic acid was used to seed the equivalent batch cooling crystallization. The experimental conditions were carried out to simulate automated self-seeding. This involves withdrawal of solution from a batch crystallizer, which is then mixed with anti-solvent within a plug flow crystallizer, in order to generate a seed slurry which is fed directly back to the batch crystallizer. This seeding strategy allowed the final CSD of the batch crystallization to be controlled by variation of the crystal size from the plug flow seeding device at a constant seed loading. The ability to use unequal feed/anti-solvent inlet flowrates (in the Roughton vortex mixer) proved effective in controlling the batch CSD at 2% seed loading and constant feed composition. 相似文献
8.
Effect of comonomer type on the crystallization kinetics and crystalline structure of random isotactic propylene 1-alkene copolymers 总被引:1,自引:0,他引:1
Isothermal crystallization kinetics and properties related to the crystalline structure of four series of random propylene 1-alkene copolymers have been comparatively studied in this work. Comonomers studied include ethylene, 1-butene, 1-hexene and 1-octene in a concentration range up to 21 mol%. All copolymers were synthesized with the same metallocene catalyst to provide an equivalent random distribution and a similar content of stereo and regio defects within the series. This has ensured that differences in crystallization kinetics and in crystalline properties of copolymers with matched compositions reflect the affinity of the comonomer type for co-crystallization with the propene units, and the effect of content and type of co-unit in the development of the crystalline structure. In the nucleation-driven crystallization range, that is for Tcs > Tc max, the values of the rate follow the sequence PB > PE > PH = PO for comonomer contents <13 mol%, and PB > PE > PH > PO for >13 mol% comonomer. These trends in overall crystallization are guided by differences in undercooling due to a similar progression of the degree of participation of the comonomer in the crystalline lattice. The variation of the rates at Tcs < Tc max follows the melt segmental dynamics driven by differences in Tg, especially at the highest co-unit contents, resulting in a reverse rate sequence for PHs and POs >15 mol%, i.e., PB > PE ∼ PO > PH. In addition to crystallization kinetics, a comparative polymorphic analysis and unit cell expansion, crystalline morphology, and melting behavior have been instrumental in resolving the partitioning of the four types of co-units between crystalline and non-crystalline regions. 1-Butene units participate at the highest level followed by the ethylene units, as demonstrated by solid-state NMR. However, both units are defects that hinder crystallization, as given by the decreasing rates, decreased levels of crystallinity and lowered melting temperatures with increasing co-unit content. All crystalline properties of PHs and POs conform to a rejection model of the 1-octene units from the crystals in the whole compositional range, and rejection of the 1-hexene units for PH <13 mol%, a conclusion also supported by NMR. The ability of PH >13 mol% to pack comonomer-rich sequences into a stable trigonal lattice leads at Tcs > Tc max to an increased number of crystallizable sequences, and to faster crystallization rates than for matched PO copolymers. 相似文献
9.
The influence of crystallization temperature on formation of the α- and β-form crystals of syndiotactic polystyrene (sPS) was investigated by X-ray diffraction and non-isothermal differential scanning calorimetry analysis. For sPS samples without any thermal history, the crystallization temperature must be the intrinsic factor controlling the formation the α and β-form crystals. Being crystallized at different cooling rate from the melt, sPS forms the β-form crystal until the temperature cooled down to about 230 °C, and α-form crystal can only be obtained when the temperature was below about 230 °C. 相似文献
10.
11.
This work examined how the molecular weight of atactic polystyrene (aPS) affects the thermal properties and crystal structure of syndiotactic polystyrene (sPS)/aPS blends using differential scanning calorimetry, polarized light microscopy and wide angle X-ray diffraction (WAXD) technique. For comparative purposes, the structure and properties of the parent sPS was also investigated. The experimental results indicated that these blends showed single glass transition temperatures (Tgs), implying the miscibility of these blends in the amorphous state regardless of the aPS molecular weight. The non-isothermal and isothermal melt crystallization of sPS were hindered with the incorporation of aPSs. Moreover, aPS with a lower molecular weight caused a further decrease in the crystallization rate of sPS. Complex melting behavior was observed for parent sPS and its blends as well. The melting temperatures of these blends were lower than those of the parent sPS, and they decreased as the molecular weight of aPS decreased. Compared with the results of the WAXD study, the observed complex melting behavior resulted from the mixed polymorphs (i.e. the α and β forms) along with the melting-recrystallization-remelting of the β form crystals during the heating scans. The degree of melting-recrystallization-remelting phenomenon for each specimen was dependent primarily on how fast the sPS crystals were formed instead of the incorporation of aPSs. Furthermore, the existence of aPS in the blends, especially the lower molecular weight aPS, apparently reduced the possibility of forming the less stable α form in the sPS crystals. 相似文献
12.
Michel Kempkes 《Chemical engineering science》2008,63(19):4656-4675
In this work a model is defined allowing for a rapid calculation of chord length distributions as well as the prediction of in situ microscopy data. Both calculations are done using the same underlying algorithm. The model assumes convex polyhedral particles that are defined by their vertices only, connected by straight lines, but imposes no further restrictions on particle geometry. Due to its speed, the model can easily be used for the prediction of experimental data from in situ monitoring tools based on whole particle populations, also with non-constant shape. The model has been verified using in situ microscopy to characterize a population of disc shaped particles.The applications of the model are focused on crystallization processes, but are not limited to these. Several relations between data measured by in situ instruments and the underlying multidimensional particle size distribution have been derived. The model is used extensively in a method that is presented allowing for the calculation of bidimensional growth rates from Focused Beam Reflectance Measurement or in situ microscopy measurements. 相似文献
13.
The supercritical antisolvent technology is used to precipitate polyvinylpyrrolidone (PVP) particles and crystallise ibuprofen sodium (IS) crystals separately and in the form of solid dispersion together. Supercritical carbon dioxide (scCO2) is used as antisolvent. For PVP particle generation, ethanol, acetone and mixtures of ethanol and acetone are used as solvents. The initial concentration of PVP in the solution was varied between 0.5 wt% and 1.5 wt%, the operation pressure between 10 MPa and 30 MPa and the composition of ethanol/acetone solvent mixtures between 100 wt% and 0 wt% of ethanol at a constant temperature of 313 K. Furthermore, the mean molecular weight of the polymer was varied between 40 kg mol−1, 360 kg mol−1 and 1300 kg mol−1. An increase of the content of the poor solvent acetone in the initial solvent mixture as well as the usage of PVP with a higher molecular weight, leads to a significant decrease in mean particle size. At all the investigated parameters always fully amorphous PVP powder precipitates. For IS, only ethanol was used as the solvent, the initial IS concentration in the solution was varied between 1 wt% and 3 wt% and the operation pressure between 10 MPa and 16 MPa. A variation of these parameters leads to a manipulation of the size and the morphology of the crystallised IS crystals. Irrespective of the parameters used, always the same polymorphic form of ibuprofen sodium is produced. The solid dispersions were generated at different compositions of PVP to IS and with two different molecular weights of PVP at otherwise constant conditions. Fully amorphous solid dispersions consisting of IS and PVP together were generated at different ratios of PVP to IS.The mechanisms that control the final particle properties are discussed taking into account two different models for “ideal” and “non-ideal” solutes. Furthermore, the study of the “unconventional” SAS parameters, molecular weight and solvation power of the solvent shows that these parameters qualify to tailor polymer particle properties via SAS processing. Next to the investigation into the behaviour of both solutes separately, fully amorphous solid dispersions consisting of IS and PVP together were generated. While X-ray diffraction was used to analyze the crystalline structure of the particles, respectively, solid dispersions, their morphology was analysed using scanning electron microscopy (SEM). 相似文献
14.
Effect of crystallization rate on the formation of the polymorphs of solution cast poly(vinylidene fluoride) 总被引:1,自引:0,他引:1
A systematic study was carried out to investigate the effect of solvent type and temperature on the formation of the α and β phases from solution cast PVDF. Three solvents with different boiling points were used: N,N, dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP) and hexamethylphosphoramide (HMPA). Infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) revealed that the type of phase formed depends on the crystallization rate of PVDF, which in turn is determined by the evaporation rate of the solvent. Low rates result predominantly in the trans-planar β phase, high rates predominantly in the trans-gauche α phase and intermediate rates in a mixture of these two phases, regardless of solvent and temperature used. Since evaporation rate of the solvent is intimately related to temperature, PVDF films can be obtained predominantly in either one of these phases, or a mixture of these, by an adequate choice of the evaporation temperature range for a given solvent. The possible solubility curves of the two polymorphs α and β of PVDF were sketched. The formation of different types of spherulites, associated with the two different PVDF polymorphs, could be verified by surface micrographs of the cast films. 相似文献
15.
Molecular dynamics simulations of realistic, united atom models of polyethylene undergoing uniaxial extension are described. Systems composed of chains ranging from 25 to 400 carbons have been studied, under a variety of processing histories, including isothermal deformation at constant applied stress below the melt temperature Tm, isothermal deformation below Tm followed by annealing, isothermal deformation above Tm followed by crystallization at a quench temperature below Tm, and non-isothermal crystallization during simultaneous deformation and cooling through Tm. Extension and orientation of large segments of flexible chains by uniaxial deformation accelerates the primary nucleation rate to a time scale accessible by molecular dynamics simulation. Entanglements operative during active deformation promote extension and orientation without nucleation of a crystal phase, while relaxation of stress at constant strain is sufficient to allow slippage of chains past pinning points and rapid nucleation and growth of crystallites as neighboring oriented chains come into registry. Isothermal crystallization of pre-oriented systems shows an apparent increase in nucleation density at lower temperatures; the resulting ordered regions are smaller and more closely aligned in the direction of orientation. During non-isothermal deformation, where stretching and cooling occur simultaneously, a first order transition is observed, with discontinuities in the volume and global order parameter, when the system crystallizes. 相似文献
16.
We report crystal growth rate data from the melt for C50 and C100 obtained from non-equilibrium molecular dynamics simulations. This extends our previous results for n-eicosane (C20) [Waheed et al. J Chem Phys 2002;116:2301]. We also construct a crystal growth model that accounts for the thermodynamic driving force and relaxation time, using WLF theory and a small number of chemically specific quantities that can be estimated from molecular dynamics simulations. Our model can predict growth rates as a function of temperature and molecular weight, up to the entanglement molecular weight. Qualitatively, we see frequent adsorption and desorption of chain segments on the surface in both C50 and C100 systems. We find evidence for a surface nucleus involving 4-5 chain segments that are approximately 20 beads long, shorter than the ultimate thickness of the chain stem in the crystal, and involving segments from multiple chains. Treatment of relaxation dynamics using the Rouse model and the reptation model does not yield a statistically significant difference within the limits of our data, but the Rouse-based fit yields thermodynamic parameters that are in closer accord with those found from fits to experiments. 相似文献
17.
Begüm TokayAy?e Erdem-?enatalar 《Microporous and mesoporous materials》2012,148(1):43-52
Recent studies imply that the external surface area of the nanozeolite product may, at least in some cases, be related to the average size of the particle population participating in aggregative nucleation, a population which itself is a product of aggregation of even smaller primary nanoparticles. This possibility puts more importance on our understanding of the variation of particle size and its distribution during the crystallization of zeolite nanoparticles. Variation of the particle size and PSD during nanoparticle silicalite-1 crystallization was followed with respect to time by a laser light scattering device with a scattering angle of 173°, for several starting synthesis compositions. Effects of varying TPAOH and water contents in the starting synthesis mixtures on the variation with time of the particle sizes and PSDs, especially across the two distinct aggregation events, were investigated. The products were also analyzed by XRD and AFM. Parallel to the decrease in the average particle size of the final product population with increasing alkalinity and organic template content, its PSD was observed to become narrower too. A reversal in the dependence on TPAOH content, of the average size of the population formed by aggregation, with respect to that of the population participating in aggregation, was observed across both aggregation events, implying that smaller particles aggregated to form larger particles, while larger particles aggregated to form smaller particles during these processes, and this was also seen from the AFM images, to be reflected to the surface features of the final product particles. 相似文献
18.
Francisco J. Blanco-Rodríguez 《Polymer》2011,52(24):5573-5586
A two-dimensional model of the fluid dynamics, heat transfer, molecular orientation and crystallization of the melt spinning of semi-crystalline compound fibers is presented. The model employs a Newtonian rheology, includes the effects of both temperature and flow-induced crystallization, and accounts for the effects of the molecular orientation on both the stress tensor and the crystallization through a Doi-Edwards formulation and the Avrami-Kolmogorov kinetics, respectively. It is shown that, even at moderately low Biot numbers, the temperature across the compound fiber is not uniform owing to heat losses; for the cases studied here, the temperature non-uniformities are mainly a function of the Biot number, the thermal conductivity and the pre-exponential factor and activation energy of the viscosity law for the cladding. It is also shown that the cross-sectional averaged temperature predicted by the two-dimensional model exhibits the same qualitative trends as those of an asymptotic one-dimensional model which does not account for axial conduction and which is only valid for slender fibers at low Reynolds and Biot numbers. 相似文献
19.
20.
Molecular dynamics (MD) simulations of several polyethylene copolymer chains containing 1,2-, 1,3- or 1,4-disubstituted cyclopentane or hexamethylene structures in the main chain (with 500 CH2) are performed to investigate the influence of cyclic units on the crystallization properties of polyethylene (PE). From the isothermal relaxation process it is found that they generally collapse to a globule via a local collapse process. The copolymer chains containing 1,2-disubstituted cycloparaffin structures form more kinks and take shorter time to totally collapse into a single globule than the others. Moreover, from the morphology of the crystal structures after annealing it is found that the copolymer chains containing 1,2-disubstituted cycloparaffin structures can yield more ordered structures with cyclic units rejected to the fold surface. For the copolymer chains containing 1,3- or 1,4-disubstituted cycloparaffin, the lamellar structures are not perfect and some cyclic units are always incorporated in the crystalline phase. 相似文献