Effects of Ultrasonic Parameters on the Crystallization Behavior of Palm Oil

The crystallization behavior of palm oil (PO) without and with the application of high-intensity ultrasound (HIU) was investigated as the function of irradiation time (20, 60, 120, and 240 s), ultrasonic intensity (47.5, 95, 270, and 475 W) and temperature (20, 25, 30, and 36 °C). The effects on the crystallization behavior of PO were evaluated by ultraviolet/visible spectrophotometry, pulsed nuclear magnetic resonance and polarized light microscopy. Results indicated that all these parameters affected crystallization behavior. HIU significantly reduced the induction time and accelerated the crystallization rate at operating temperatures above 25 °C, but there was no significant difference at 20 °C due to high supercooling. The effects of HIU were more significant at higher power level and longer irradiation time, however, the thermal effect of ultrasound also increased with longer sonication time. The optimal sonication time was approximately 120 s which accelerated the crystallization rate of PO the most. The morphology studies suggested that HIU changed the growth mechanisms of crystals and generated smaller and uniformly crystals. At 36 °C, with extremely low supercooling condition, a combined effect was observed that prevented the separation of solid phase and liquid phase of the crystallized sample, and then led to a uniform distribution of crystals.     

真空法动态制冰的非等温结晶动力学

以氯化钠水溶液为制冰溶液,采用真空法制备得到冰浆。从理论上论证非等温结晶动力学模型Jeziorny法和Mo法用于描述冰浆结晶行为的可行性。通过实验测定不同结晶时间下的冰浆含冰率,并建立了冰浆生成过程的非等温动力学方程。研究结果表明：Jeziorny法和Mo法可很好地描述冰浆的非等温结晶过程;Jeziorny模型指数n的值在0.473~0.525间,表明不同实验条件下的结晶机理基本一致,冰晶呈片状增厚生长;Jeziorny模型中的结晶动力学参数K_c、t_0.25和Mo模型中的冷却速率函数F（T）的变化规律均表明高冷却速率可促进冰浆的形成,同时氯化钠的添加会在一定程度上抑制冰晶生长。     

Effect of struvite seed crystal on MAP crystallization

BACKGROUND: There has been considerable controversy over the effect of seed crystal additions on crystallization of magnesium ammonium phosphate hexahydrates (MAP). In this study, batch experiments were carried out to verify this effect using synthetic solutions. RESULTS: Addition of seed crystals could increase the rate of MAP crystallization and significantly shorten the reaction crystallization time, especially for solutions with a lower supersaturation ratio (Ω). Crystallization time of MAP with and without seed addition can be expressed by two different formulas, in which the crystallization with feed addition followed an exponential function, and the secondary formula fitted a two‐order power function. When 0.422 g L^?1 of seed crystals was added the equilibration time for crystallization calculated by the formula was reduced by 75 min for low supersaturation ratio solution and 26 min for medium supersaturation ratio solution. CONCLUSION: To increase the MAP reaction rate and to shorten induction and equilibration times, seed crystal addition should be practiced Copyright © 2011 Society of Chemical Industry     

Dynamic crystallization of cocoa butter. II. Morphological,thermal, and chemical characteristics during crystal growth

After an induction period, crystallization of cocoa butter under dynamic conditions at 26.5°C occurs in two stages, primary and secondary. The primary stage involves nucleation, crystal growth, aggregation, and sintering. Crystals formed during the primary stage were slightly or non-birefringent, and had long, irregular-shaped filaments. The secondary stage was initiated by the formation of spherulites. Total crystallization time may depend upon the crystal growth rate in the primary stage and the time that coca butters take to form the spherulitic crystals in the secondary stage. After the spherulitic crystals formed, the crystal growth rates were rapid. Cocoa butters crystallized into two fractions during the primary and secondary stages. The low-melting fractions had onset melting temperatures similar to those of polymorphs IV and V of cocoa butter. The high-melting fractions, which were observed at the latter stages of crystallization, had differential scanning calorimetry endotherms with peak maxima at approximately 34–36°C (Form VI). The concentrations of 1,3-stearoyl-2-oleoylglycerol (SOS) in the crystals during growth were higher than those in the original cocoa butter. As crystallization progressed, crystals increased in their proportions of SOS in the triacylglycerol fraction. Concentrations of the C₁₈ free fatty acids were lower during early crystallization as compared to the original cocoa butter.     

Isothermal crystallization kinetics of refined palm oil

The induction times for the crystallization, under isothermal conditions, of refined, bleached, and deodorized palm oil from the melt were studied by viscometry. At temperatures below 295 K, the crystallization of palm oil was observed to occur in a two-stage process. This two-stage process was caused by the fractionation of palm oil, most probably into the stearin and olein fractions. At temperatures higher than 295 K, only a single-stage crystallization process was observed. As seen under polarized light microscopy, spherical crystals were initially formed from the first fraction at temperatures from 287 to 293 K. The diameters of these spherical crystals decreased as the temperature increased. After that, needle-shaped crystals were formed from the second fraction and continued to grow from the surface of these spherical crystals until the spherical crystals were fully enclosed, i.e., the cocrystallization of two polymorphs was observed. At temperatures higher than 293 K, the needle-shaped crystals formed from a mixture of the two fractions were found to be the only polymorphs developed with the onset of crystallization. X-ray diffraction results showed that for temperatures below 295 K, the spherical crystals formed from the first fraction were in α form, whereas the needle-like crystals that nucleated later from the second fraction were in β′ form. β′ crystals were the only polymorphs formed for temperatures above 295 K. The results obtained were in good agreement with the discontinuity observed in the induction time vs. temperature curve. Activation free energies for nucleation were calculated according to the Fisher-Turnbull equation for the various polymorphic forms. Viscometry was observed to be a sensitive method for characterizing the overall crystallization process. This technique is suitable for induction time studies of palm oil crystallization, especially at lower temperatures and with viscous oil.     

Crystallization behavior of hydrogenated sunflowerseed oil: Kinetics and polymorphism

Kinetics of crystallization of hydrogenated sunflowerseed oil was studied by means of an optical method. Two different aspects were examined: the effects of preheating of the molten liquid on induction time of isothermal crystallization and the effects of cooling rate on the crystallization behavior. Induction time for crystallization was markedly dependent on the crystallization temperature and the cooling rate selected. Morphology, polymorphism and chemical composition of the crystals were examined. At all crystallization temperatures, β′-form was found for the first occurring crystals. Long spacings were also similar in all cases and corresponded to a double chainlength arrangement. The chemical composition of the crystals showed no differences at either cooling rate. However, the melting behavior was different. At a slow cooling rate, fractionation occurred, and differential scanning calorimetry diagrams had a broad second endotherm with three peaks, none of which were completely resolved. The polymorphic transformation rate from β′ to β was slower when induction times were longer.     

果糖结晶过程优化

通过实验筛选得到适合果糖结晶的混合溶剂,利用中通量结晶仪器Crystalline测定了果糖在水-乙醇（水的摩尔分数为0.39）混合溶剂中的溶解度和介稳区,采用Apelblat方程拟合了溶解度数据。基于热力学数据设计了晶种引晶的果糖冷却结晶工艺,过程优化得到的产品收率可达78.2%以上,纯度可达99%以上,晶体形貌规则,表面光滑,粒度分布窄。当晶体粒径大于100 μm时,利用粒度无关生长的粒数衡算方程建立了果糖连续结晶过程的动力学模型,模型表明晶体生长级数大于成核级数。     

CL‐20 Evaporative Crystallization under Reduced Pressure

The effect of parameters of the CL‐20 crystallization process carried out by solvent removal by evaporation in vacuo on shape, polymorph type, crystal size, and on their shock sensitivity was studied. The CL‐20 crystallization process by this technique was shown to allow a precise control of the crystallization process parameters and of the process run. The o‐xylene/ ethyl acetate system proved to be highly effective. Selecting suitable values of the parameters such as: pressure, process time, temperature, stirring rate, CL‐20 crystals were obtained in the ε form (even with no need for inoculation of the crystallization system with polymorph ε seeds) and of the shape close to a spherical one. The crystal growth modifiers added allowed to additionally control the shape and size of the CL‐20 crystals formed and to produce crystals of reduced impact and friction sensitivity.     

添加剂EDTA对氢氧化镁反应结晶过程的影响(英文)

The effects of additive ethylenediaminetetraacetic acid (EDTA) on crystallization process were investigated by the induc-tion time of MgSO4-NaOH system. Nucleation and growth rates, growth mechanism and particle size distribution of magne-sium hydroxide precipitation were involved with. The induction time in unseeded and seeded precipitation of magnesium hydroxide with and without additive EDTA was measured. The conductivity method was used to determine the induction period. Theoretical relations of the induction time and supersaturation ratio for different growth mechanisms and a combined analysis on the induction time were applied to determine nucleation and growth rates. The growth mechanism of magnesium hydroxide precipitation was dis-closed by analyzing the experimental data with and without additive. The analysis on induction time indicated that additive EDTA had a significant influence on both nucleation and growth of magnesium hydroxide precipitation. The mechanism underlying the effect of EDTA on crystal growth was 2-dimension nucleation-mediated growth model.     

Analysis of Morphological Changes in Monosodium Urate Monohydrate Crystals for Gout Treatment

Gout is arthritis induced by monosodium urate monohydrate (MSU) crystals. The treatment of gout is mainly a symptomatic treatment, by suppressing the blood uric acid concentration with drugs. Here, the changes in crystal morphology in the process of MSU crystallization were investigated. Experiments were conducted to clarify the mechanisms of nucleation and growth of the MSU crystals, revealing that MSU first precipitated as granular crystals. Thereafter, nucleation and growth of needle-like crystals were observed concomitant with the disappearance of the granular crystals. These results suggest that it is necessary to suppress the nucleation of granular crystals and the change in morphology from granular to needle-like of the MSU crystals that cause gout.     

Overall crystallization kinetics of polymorphic propylene-ethylene random copolymers: A two-stage parallel model of Avrami kinetics

The isothermal crystallization of propylene ethylene random copolymers evolves with a simultaneous formation of two polymorphic forms, monoclinic crystals (α form) and orthorhombic crystals (γ form). The relative content of each polymorph changes during crystallization and impacts the kinetics and mechanisms of growth. The content of γ crystals developed at high levels of transformation increases with the concentration of ethylene and with the crystallization temperature. In this work, the overall crystallization kinetics of copolymers with an ethylene content ranging from 0.8 to 7.5 mol% were followed by DSC and analyzed according to classical Avrami kinetics. For most copolymers, fits to single-stage nucleation and growth models were poor. Following structural models for lamellar growth that account for epitaxial γ branching from α surfaces, the experimental data were modeled with a parallel two-stage kinetic model with excellent fits up to ∼70% transformations. The Avrami exponents obtained from the fits are consistent with a linear spherulitic growth from pre-existing nuclei for the α stage and homogeneous nucleation (linear with time) for the γ stage, and strongly support the postulated structural growth model. The rate constants of each stage follow the expected temperature dependence. Attempts made to extract the interfacial free energies for α and γ crystals from the values of the rate constants are discussed.     

Unusual kinetic inhibitor effects on gas hydrate formation

Gas hydrate formation experiments were conducted with a methane-ethane mixture at 273.7 or 273.9 K and 5100 kPa and using water droplets or water contained in cylindrical glass columns. The effect of kinetic inhibitors and the water/solid interface on the induction time for hydrate crystallization and on the hydrate growth and decomposition characteristics was studied. It was found that inhibitors GHI 101 and Luvicap EG delayed the onset of hydrate nucleation. While this inhibition effects has been reported previously some unusual behaviour was observed and reported for the first time. In particular, the water droplet containing GHI 101 or Luvicap EG was found to collapse prior to nucleation and spread out on the Teflon surface. Subsequently, hydrate was formed as a layer on the surface. Catastrophic growth and spreading of the hydrate crystals was also observed during hydrate formation in the glass columns in the presence of the kinetic inhibitor. Finally, when polyethylene oxide (PEO) was added into the kinetic inhibitor solution the memory effect on the induction time decreased dramatically.     

Isothermal crystallization of hydrogenated sunflower oil: II. growth and solid fat content

Isothermal crystallization of sunflower seed oil hydrogenated under two different conditions was studied by means of pulse nuclear magnetic resonance (pNMR) and optical microscopy. Solid fat content (SFC) curves showed two different shapes depending on supercooling. When supercooling was high, hyperbolic curves were found, whereas with low supercooling sigmoidal curves were obtained. Curves were interpreted with the modified Avrami equation. Photographs of the crystals were taken from the beginning of crystallization, every 15 s until 15 min and every 5 min until 60 min. Samples which exhibited hyperbolic curves showed a slight increase in crystal number, and crystals were needle-shaped in all cases. Samples which had sigmoidal crystallization curves showed a marked increase in crystal number with time, and crystals were spherical in shape. Crystallization behavior was also in agreement with the chemical composition of the samples. Samples which had the highest content of high-melting triacylglycerols (especially trielaidin) showed only hyperbolic curves. Supercooling is a very important parameter that defines the way nucleation occurs. Depending on the initial number of nuclei, two different growth mechanisms were found: a uniform linear growth of the nuclei for a small initial number (sigmoidal curves) and an aggregate of the nuclei for a high initial number (hyperbolic curves).     

Crystal growth of high silica ZSM-5 at low temperature synthesis conditions

At the temperature of 90°C and under atmospheric pressure, growth kinetics of high silica ZSM-5 was investigated through a long induction, nucleation and crystal growth periods. It was found the entire crystallization mechanism of ZSM-5 seems to be the combined process of the nucleation via solid-solid transformation, intergrowth among seed crystals and the normal growth in the reaction mixture. Nuclei were initially formed on the Si-rich surface of the amorphous intermediates, indicating that the reaction of TPA with Si species was prior to that with Al species. As the reaction time proceeded, various types of intergrowth among the seed crystals were observed along with the crystals growing independently. The intergrowth seems to play a role for forming typical ZSM-5 crystal shapes. And then ZSM-5 crystals further grew in the reaction mixture, so that the bulk Si/Al₂ ratio of crystals approached that of the initial reaction mixture.     

冷冻保存中影响胞内冰生长的因素

细胞胞内冰的形成会导致严重的细胞损伤从而导致低温贮存中的诸多问题。以蚕豆为研究对象,用细胞松弛素B溶解细胞骨架,使用低温显微系统在不同的冷却速率下进行冷冻实验。实验结果表明,使用细胞松弛素B处理过的细胞在冷冻过程中结晶温度更高,结晶时间更短,但细胞骨架对胞内冰的生长过程影响较小。外界条件起着关键作用,接种冰晶影响细胞内冰晶的形成温度及冰晶的生长速率。最后,通过光强度图对细胞的损伤程度进行了分析。     

Assessing the effect of zinc on the crystallization of calcium carbonate

Scaling, often due to the precipitation of calcium carbonate, is a current problem in economical and technical life. To study this phenomenon, some experimental procedures have been developed. They are based for example on electrochemical precipitation, use of nanofiltration and rapid controlled precipitation (RCP). This latter technique appears as an efficient one because it permits to study the early stage of crystallization. An other technique could be considered as a promising route among all of them because it permits to follow in real time and in situ, the electrocrystallization of calcium carbonate. Some morphometric characteristics of crystals like: size, diameter, shape and also other parameters as the rate of covering surface of the electrode could be quantified. Experiments were carried out with this procedure and RCP test in order to study the effect of zinc on the precipitation of calcium carbonate.

Experiments were carried out with the water of Hamma (locality situated near the city of Constantine) which has a high power of scaling. The process occurs in two steps in control water: spontaneous crystallization followed by growth of crystals. In presence of zinc (0.05, 0.1 and 10 mg/L), we observed a reduction of nucleation and a high inhibition of growth of crystal. At lower concentration, i.e. 10 μg/L, the crystallization still occurred but crystals were smaller than in control water. These results were in good agreement with those obtained previously.

Moreover, the analysis by SEM revealed a change of morphology in presence of zinc and a change of crystalline varieties.     

Kinetics of butterfat crystallization

Fractionation of butterfat by melt crystallization is a commercial process in many countries for making butter fractions with varying melting, textural and flavor properties for use as food ingredients. However, the crystallization phenomena in this complex system are poorly understood and difficult to optimize and control. In this study, the crystallization kinetics of anhydrous butterfat were determined by cooling a melted sample to the final crystallization temperature in either a lab-scale (2 L) batch crystallizer or a pilot-scale (20 L) crystallization vessel. The butterfat was cooled sequentially from an initial temperature of 60°C to final temperatures of 30, 20 and 15°C at a constant cooling rate. Crystals formed at each temperature were separated by vacuum filtration, with the liquid cooled to the next crystallization temperature. Nucleation rates were determined by counting the number of crystals in a given volume of suspension during the course of crystallization. Crystal growth rates were obtained from image analysis of optical photomicrographs. Changes in viscosity, turbidity and mass of crystals also were determined. Effects of impeller velocity (75, 100 or 125 rpm) on the crystallization kinetics were determined. Nucleation and mass deposition rates increased while crystallization lag times decreased with increasing agitator velocities. Growth rates increased with agitator rpm at 20 and 15°C, but decreased with agitator rpm at 30°C, indicating different growth mechanisms. At 20 and 30°C, aggregation was the primary mechanism of crystal growth, whereas little aggregation was observed at 15°C. Crystallization at the larger scale, 20 L, showed only minor differences.     

Transformation of hemipentahydrate to monohydrate of risedronate monosodium by seed crystallization in solution

The transformation from a hemipentahydrate to a monohydrate of risedronate monosodium was studied by seed crystallization in solution. By using the in‐line measurement based on ultrasonic measuring technique and the off‐line measurements such as optical microscopic and crystallography, transformation of hydrate forms and crystallization of monohydrate were observed. The effect of concentration of solution and solid fraction of suspension on the ultrasonic velocity was found. The hydrate composition, concentration of solution, and supersaturation during the transformation were estimated with elapsed time. The effect of monohydrate seed, agitation rate and temperature on the induction time, transformation, and crystallization was also investigated. Eventually, transformation from hemipentahydrates to monohydrates and crystallization of monohydrate were analyzed successfully from in‐line measuring technique. © 2011 American Institute of Chemical Engineers AIChE J, 2011