Calcium oxalate crystallization in silica and sugar solutions-characterization of crystal phases and habits

The effects of silica (SiO₂) and sugar on the crystallographic and morphological properties of calcium oxalate (CaOx) have been investigated using instrumental techniques including X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Addition of SiO₂ or sugar in a CaOx crystallization system promoted the formation of COT (calcium oxalate trihydrate) and COD (calcium oxalate dihydrate), respectively, and modified the crystal size and habit of COM (calcium oxalate monohydrate) crystals, the extent of which was dependent on the concentrations of SiO₂ and sugar. A variety of mechanisms including electrostatic effects, geometrical matching and stereochemical compatibility between CaOx crystallites and polymeric SiO₂/sucrose molecules have been proposed.     

Mechanisms, thermodynamics and kinetics of composite fouling of calcium oxalate and amorphous silica in sugar mill evaporators—A preliminary study

Deposition of amorphous silica (SiO₂) and calcium oxalate monohydrate (COM) on the calandria tubes of evaporators cause serious processing problems in many cane sugar mills. Previous studies on scale formation have concentrated on fouling of individual compounds and the development of inhibiting methods for each component. Since SiO₂ and COM co-exist in sugar mill evaporators, this paper investigates the mechanisms and behavior of composite fouling of COM and SiO₂ in binary systems. Batch tests conducted at different pH (6-8) and temperatures (60-80°C) show that the presence of SiO₂ in the supersaturated solutions of COM decreased the precipitation rate of COM and as such increased COM solubility. However, the presence of COM in the supersaturated solutions of SiO₂ accelerated SiO₂ polymerization and lowered the level of initial silica supersaturation required for polymerization. The formation of COM-SiO₂ complexes is used to propose the mechanism for the co-precipitation of SiO₂ and COM.     

A high‐throughput assay for screening modifiers of calcium oxalate crystallization

Controlling crystal habit using growth modifiers provides novel avenues for tailoring properties of crystalline materials. Here, we report on the design of a high‐throughput screening assay for rapid identification of growth modifiers using calcium oxalate monohydrate crystallization as a model system. We conducted a systematic study of assay parameters (sample volume, shaking, and temperature) on crystallization kinetics. Crystallization half‐time (t_1/2), defined as the time at which crystallization is 50% complete, was obtained from the logistic fit of kinetic data and used as a measure of growth modifier potency. A test library of 13 peptides composed of aspartic acid and alanine residues was screened to determine their growth promotion or inhibition potentials. Leads identified from this study are in good agreement with ion‐selective electrode measurements and a single time point measurement of free calcium ion concentration is an excellent end‐point for evaluating modifier potency. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3538–3546, 2016     

Microreactor technology for synthesis of ethyl methyl oxalate from diethyl oxalate with methanol and its kinectics

This study focused on the performances and kinetics of the transesterification reaction of diethyl oxalate with methanol to prepare ethyl methyl oxalate via microreactor technology. The conversion of 79.8% of diethyl oxalate (DEO) and the selectivity of 65.9% of ethyl methyl oxalate (EMO) was obtained under the following optimized conditions: the mole ratio of methanol to diethyl oxalate was 3.3:1, the temperature was 35°C, the K₂CO₃ catalyst concentration was 15 mg/mL, and the residence time was 2.30 minutes. In the temperature range of 25°C to 38°C, the simplified dynamic model was found to obtain the reaction order (α = 2.30), frequency factor (k₀ = 2.377 × 10⁵), and apparent activation energy (E = 31.86 kJ/mol). The macroscopic dynamic equation was derived from the experimental result of the transesterification reaction of two feedstocks, which can be obtained through a series of calculations.     

Porous Se@SiO2 nanospheres inhibit calcium oxalate kidney stone formation by oxidation resistance

The prevalence of kidney stones continues to increase worldwide, however, there are still short of effective drugs against urinary stones. In our study, we developed and utilized porous Se@SiO₂ nanospheres as the novel antioxidant agent to detect its potential effects on crystallization inhibition. Porous Se@SiO₂ nanospheres enable to deliver Se sustainably with lower cytotoxicity and preferred biocompatibility. In vivo, we found that porous Se@SiO₂ nanospheres markedly decreased CaOX crystal deposition in renal parenchyma and alleviated kidney oxidative damage. In vitro, we found that the antioxidant effects of porous Se@SiO₂ nanospheres were mediated by upregulation of HO-1 and activation of Keap1/Nrf2 pathway. These results suggests that porous Se@SiO₂ nanospheres may be a new promising therapeutic option for stone formers.     

合成草酸二乙酯新工艺的研究

研究了反应精馏合成草酸二乙酯新工艺。开发了一种适用于草酸乙酯化的反应精馏塔,确定了适宜的工艺条件：D2为进料位置,n（C2H5OH）∶n（C2H4O4）=10∶1、V（回流量）∶V（进料量）=3∶1、进料速度为0.8 mL/min,草酸二乙酯的酯化率可达到98%左右,并且采用反应精馏合成草酸二乙酯的时空收率为间歇釜式反应器合成草酸二乙酯时空收率的3.5~4倍。     

Ultrasonic Irradiation during the Calcium Sulfate Hemihydrate to Dihydrate Transformation Process

The ultrasound‐assisted transformation of calcium sulfate hemihydrate (CSH) to calcium sulfate dihydrate (CSD) was studied using three ultrasonic power settings. In addition to continuously measuring the variation in the conductivity value with time, the process was followed by X‐ray diffraction and scanning electron microscopy (SEM) analysis. Thermogravimetric analysis, Fourier transform infrared, mass spectrometry, and filtration analyses helped to determine the physicochemical properties of the as‐obtained crystals. The morphological changes in the surface morphology were observed by SEM. The experimental results indicate that ultrasonic irradiation and its intensity have a significant effect on the crystal size, morphology, adsorption, and filtration characteristics. Mandelic acid in combination with ultrasonic irradiation can be used as an accelerator for the transformation process from CSH to CSD.     

Organic crystallization processes

Crystallization has been the most important separation and purification process in the pharmaceutical industry throughout its history. Many parallels exist in the fine chemicals industry also. Over the past several decades the study of crystallization operations has taken on increasing levels of importance because of several factors that require effective control of crystallization processes. These levels of control require better understanding of the complex interactions of nucleation and growth as well as the operating characteristics of crystallization equipment including the critical issue of scale-up.In the pharmaceutical industry, the issue of better control, desirable in and of itself, is reinforced by the need to satisfy both company internal and governmental regulatory authorities on the consistency of chemical and physical properties of active pharmaceutical ingredients (APIs). Control of crystallization operations and choice of equipment both for pilot plant and manufacturing are thereby critical. The objective of this paper is to summarize the critical issues that must be addressed in order to achieve this level of control.     

无水硫酸钙晶须对PP复合材料的熔融结晶和力学性能的影响

制备了无水硫酸钙晶须(ACSW)填充聚丙烯(PP)复合材料,通过差示扫描量热仪、X射线衍射仪、偏光显微镜、力学性能测试等手段研究了ACSW对PP复合材料的熔融结晶和力学性能的影响。结果表明,ACSW的加入会细化聚丙烯的晶粒,质量分数低于20%的ACSW提高了PP的结晶温度、熔融温度和结晶速率,降低复合材料的拉伸强度;质量分数大于20%的ACSW能提高PP复合材料β晶成核效率和PP的结晶速率,降低复合材料的拉伸强度。当ACSW质量分数为25%时,复合材料的缺口冲击强度较纯PP增加了66%。随着ACSW的含量的增加,复合材料的弯曲强度先增加后降低,并在ACSW质量分数为10%时达到了最大值。     

Lectrochemical oxidation of oxalate in alkaline solutions

Experimental results show that the electrochemical oxidation of oxalate in alkaline solutions at lead dioxide anodes can be achieved at conditions of much higher alkalinity than previously reported in the literature using other types of electrodes. The oxalate in solutions containing 0.05 mol/L ∽0.1 mol/L sodium oxalate was anodically oxidized to carbonate with high efficiency in the presence of up to ∽0.1 mol/L NaOH at 70°C by using lead dioxide anodes doped with silver and tin. The addition of small amounts of silver and tin (e.g., 0.06% by weight) to lead dioxide films significantly increases the oxalate oxidation currents and current efficiencies. These metals can be incorporated into the lead dioxide films by in situ oxidation of lead-silver-tin alloys. Although oxalate could not be electrochemically oxidized using lead dioxide electrodes at extremely high pH's (greater than ∽ 14), reduction of the oxalate concentration to less than about 0.04 mol/L could be achieved at greater than 50% current efficiency at pH's up to about 13.     

Glass structure and crystallization via two distinct thermal histories: Melt crystallization and glass crystallization

This study focuses on the effect of structural inhomogeneity of 44.4CaO-33.2SiO₂-8.8Na₂O-6.2Al₂O₃-7.4B₂O₃ glass on its crystallization behavior. The crystallization behavior of the investigated lime-sodium aluminoborosilicate glass system is explored for the two thermal histories of melt crystallization and the heat treatment of quenched glass. The results show that sodium melilite (CaNaAlSi₂O₇) and larnite (β-Ca₂SiO₄) are the dominant crystalline phases during heating (glass crystallization) and cooling (melt crystallization), respectively. In the glass structure from the heat treatment at 610 °C, both Si₂O₇ and AlO₄ units (i.e., four-coordinated Al) are dominant. This may induce sodium melilite (CaNaAlSi₂O₇) crystallization, connecting Si₂O₇ and AlO₄ units with O and linking Ca and Na between interlayers. The melt structure, meanwhile, has more SiO₄ and AlO₆ units in its silicate and aluminate. Therefore, larnite (β-Ca₂SiO₄) crystallizes on cooling by combining SiO₄ units and Ca. The crystallization behavior is further discussed considering the inhomogeneity structure of supercooled liquids before nucleation.     

Effect of ethylene glycol on the mullite crystallization

Mullite is one of the most important aluminosilicate due to its unique thermal properties. In this work, mullite was obtained by sol-gel process at low temperature using sodium metasilicate, water, aluminum nitrate and ethylene glycol. The samples were prepared with a volume ratio of ethylene glycol/water equal to 0/1, 1/1, 2/1 and 3/1. The ethylene glycol effect on mullite crystallization was studied by X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and Differential Thermal Analysis (DTA). The sample prepared without ethylene glycol, the less homogeneous one, formed amorphous silica, spinel-phase and α-alumina at 1000 °C, and then crystallized mullite at 1200 °C, with an alumina molar fraction of 0.58. The other samples formed amorphous silica at 900 °C and crystallized mullite as the only crystalline phase at 1000 °C. However, the alumina content in mullite formula depends on the thermal treatment, reaching 0.58 at 1250 °C.     

Relationship between free chloride and total chloride contents in concrete

Linear relationships between free chloride and total chloride contents in concrete are proposed based on the results of several long-term exposure tests under marine environment for various cements, such as ordinary portland cement (OPC), high early strength portland cement (HES), moderate heat portland cement (MH), calcium aluminate cement (AL), slag cements of Types A (SCA) and B (SCB), and fly ash cement of Type B (FACB). A high chloride-binding ability is found for AL as compared to the other cements. Replacing the OPC with slag reduces the chloride-binding ability. The proposed linear relationships show reasonably good agreement with field data obtained from the wharf structures.     

草酸二乙酯的生产工艺研究

研究了反应精馏合成草酸二乙酯的新工艺。在反应精馏塔内考察了挟带剂种类、塔釜温度、进料位置、回流进料比、原料醇酸物质的量比对酯化反应的影响,得到了优化的工艺条件,酯化率达90%。     

副产硫酸亚铁制备电池级草酸亚铁的研究

以钛白副产硫酸亚铁为原料制备出电池级草酸亚铁。研究了除杂、沉淀、转化反应过程中反应温度、反应时间、硫酸亚铁浓度以及反应pH等因素对产品质量的影响,并得到了优惠工艺条件。结果表明：在反应温度为 95 ℃、反应时间为6 h的条件下用铁粉对硫酸亚铁溶液除杂,得到纯净硫酸亚铁溶液;在反应温度为40 ℃、铁（Ⅱ）质量浓度为90 g/L的条件下用氨水沉淀,再用草酸于反应时间为60 min、pH=2.0条件下将氢氧化亚铁转化成草酸亚铁,制备出了纯度大于99.5%、粒径小于3.0 μm、杂质含量低的电池级草酸亚铁。为解决钛白副产硫酸亚铁的综合利用提供了一条有效的途径。     

Copolymer crystallization: Approaching equilibrium

Melt crystallization of random copolymers leads to solids with crystalline fraction w_c and final melting temperature that are substantially below the predictions of Flory's equilibrium crystallization theory. Model ethylene/butene random copolymers, when crystallized as multilayer films by rapid solvent evaporation, exhibit increased w_c (50% relative) and (4 K) compared to melt crystallized values. For a copolymer with 0.92 mol fraction ethylene, the density-derived crystallinity w_c=0.6 is the same as that from Flory's theory, although the maximum observable crystal thickness from remains about 25% of the theory value. These effects are seen because crystallization from solution occurs without many of the constraints to segment dynamics that limit crystalline fraction during melt crystallization. Crystal thickness is dominated by secondary nucleation barriers in both melt and solution. Chain or sequence folding is much more regular in the solution crystallized material, and amorphous layer thickness is reduced from about 8 nm to 3 nm.     

Impedance study on calcium nitrite as a penetrating corrosion inhibitor for steel in concrete

Penetrating corrosion inhibitors are thought to be able to penetrate through the capillary structure of concrete to reinforcing steel and to reduce the already initiated corrosion of steel. In this work the ability of calcium nitrite to inhibit the chloride induced corrosion of steel was studied. The test protocol was adjusted to simulate the performance of penetrating corrosion inhibitors in concrete structures. Steel samples were first prepassivated in saturated solution of Ca(OH)₂ and then exposed to the same solution with 1% NaCl addition, simulating pore liquid in chloride contaminated concrete. After the initiation of steel corrosion, the first dose of calcium nitrite was added, and then its concentration was gradually increased and the inhibition effect was related to the molar ratio of chloride to nitrite ions [Cl⁻]/[NO₂⁻]. Different rates of the increase in the inhibitor concentration were applied.Electrochemical impedance spectroscopy was used to follow the behaviour of steel at different stages of the corrosion process. The evolution of acquired spectra reflected the initiation of localized corrosion of steel and then the gradual inhibition with increasing concentration of the inhibitor. It was found, that calcium nitrite is able to inhibit the initiated corrosion (pitting) of steel and the optimum inhibitor efficiency was observed for the [Cl⁻]/[NO₂⁻] ratio below 1. The inhibition efficiency was larger, when this value of the [Cl⁻]/[NO₂⁻] ratio was reached in early stages of the corrosion development. Calcium nitrite can be effective as a penetrating corrosion inhibitor for steel in concrete, if it will be present in the sufficient concentration at the steel surface in early stages of the corrosion development.     

Recent advances in the monitoring,modelling and control of crystallization systems

Crystallization is one of the most important unit operations used for the separation and purification of crystalline solid products. Appropriate design and control of the crystallization process is paramount to produce crystalline products with tailor-made-properties. This paper provides an overview of selected recent developments in the modelling, monitoring and control of crystallization processes. We consider the topics discussed in this review to be enabling technologies for the development of the next generation of crystallization processes with significantly improved predictability, robustness and controllability.     

The influence of stem conformation on the crystallization of isotactic polypropylene

The influence of stem conformation on the crystallization of i-PP is studied by growing α-form lamellae in melts of β-form lamellae at different temperatures. The melting of β-form lamellae and the crystallization of α-form lamellae is observed in situ at the interface of α- and β-form spherulites by AFM. The growth rate of α-form lamellae in the melt of β-form lamellae is much lower than that in the isotropic melt due to the stem conformation barrier, which originates from the difference in the α and β unit cell packing models.