Vapor Phase Beckmann Rearrangement of Cyclohexanone Oxime over Different Ferrierite Zeolite Catalysts

Ferrierite zeolite catalysts prepared using different procedures have been tested for their activity for vapor phase Beckmann rearrangement of cyclohexanone oxime to -caprolactam. We report here the results of a study seeking the influence of temperature, nitrogen feed rate, oxime concentration and solvents on the catalyst performance. At low concentration of oxime (2.5 wt%), using acetonitrile as solvent the maximum in the conversion of oxime and selectivity to -caprolactam has been obtained. The presence of weak, medium and strong acid sites as indicated by temperature-programmed desorption of NH₃ corroborates well with the catalytic activities of various ferrierites shown here. Solvent polarity is found to significantly affect the conversion of cyclohexanone oxime.     

己内酰胺生产的绿色化

己内酰胺生产的绿色化关键是环己酮肟贝克曼重排工艺路线替代的开发。重点介绍了代替浓硫酸催化该反应的固体酸催化剂、催化剂的失活与再生、反应器工业化的方法的进展。提出采用多相催化剂取代发烟硫酸使环己酮肟转化为己内酰胺的工艺 ,该催化剂具有转化率和选择性高 ,易处理再生 ,且可用于连续化工业生产     

环己酮肟液相重排反应机理及动力学研究

研究了环己酮肟重排反应生成己内酰胺的机理及反应动力学方程。在建立用分光光度法测定环己酮肟浓度方法的基础上,实验研究了反应温度为20~45℃范围内的液相重排反应动力学。提出了此反应的化学反应动力学速率方程式: -r肟= k0exp (-E/RT)Ca肟Cb硫酸,其中环己酮肟反应级数a为2,硫酸反应级数b为1,活化能为-E/R = -19.86 kJmol-1, 频率因子k0为1.35×1027。通过实验研究证实了作为催化剂的硫酸参与重排反应的机理,认为重排反应过程中游离SO3不参与反应,仅作为水的吸收剂,此结论对环己酮肟液相重排反应的生产技术改造提供了有力依据,并在生产中得到了应用。     

Trudinger-Moser不等式的两种证明方法

Trudinger-Moser不等式在研究带有临界指数增长非线性项偏微分方程解的存在性问题上有着重要的应用.在径向空间中利用施瓦兹对称重排,基于单位分解的技巧取截断函数是证明Trudinger-Moser不等式的两种主要方法.     

Heat Induced Structure Modifications in Polymer‐Layered Silicate Nanocomposites

Summary: The success of the use of layered silicates in polymer nanocomposites, to improve physical and chemical properties is strictly related to a deeper knowledge of the mechanistic aspects on which the final features are grounded. This work shows the temperature induced structural rearrangements of nanocomposites based on poly[ethylene‐co‐(vinyl acetate)] (EVA) intercalated‐organomodified clay (at 3–30 wt.‐% silicate addition) which occur in the range between 75 and 350 °C. In situ high temperature X‐ray diffraction (HT‐XRD) studies have been performed under both nitrogen and air to monitor the modifications of the nanocomposite structure at increasing temperatures under inert/oxidative atmosphere. Heating between 75 and 225 °C, under nitrogen or air, causes the layered silicate to migrate towards the nanocomposite surface and to increase its interlayer distance. The degradation of both the clay organomodifier and the VA units of the EVA polymer seems to play a key role in driving the evolution of the silicate phase in the low temperature range. The structural modifications of the nanocomposites in the high temperature range (250–350 °C), depended on the atmosphere, either inert or oxidizing, in which the samples were heated. Heating under nitrogen led to deintercalation and thus a decrease of the silicate interlayer space, whereas exfoliation was the main process under air leading to an increase of the silicate interlayer space.

Heat induced structural modification of EVA‐clay nanocomposite under nitrogen and air.     

Catalytic Performance of B2O3/TiO2–ZrO2 for Vapor-Phase Beckmann Rearrangement of Cyclohexanone Oxime: The Effect of Boria Loading

A series of boria catalysts supported on titania–zirconia mixed oxide (B₂O₃/TiO₂–ZrO₂) with different boria loadings (8–20 wt%) were prepared and characterized by X-ray diffraction, adsorption of nitrogen, ¹¹B magic angle spinning (MAS) NMR measurements and temperature-programmed desorption (TPD) of ammonia. The catalytic performance of B₂O₃/TiO₂–ZrO₂ for vapor-phase Beckmann rearrangement of cyclohexanone oxime to -caprolactam was studied at 300°C. It was found that the lactam selectivity increased with increasing of boria loading, whereas a maximum oxime conversion was obtained at the boria loading of 12 wt%. The acid sites of medium strength on the surface of the catalyst play an important role in the selective formation of lactam.     

Effects of acid strength and micro pore size on -caprolactam selectivity and catalyst deactivation in vapor phase Beckmann rearrangement over acid solid catalysts

The vapor phase Beckmann rearrangement of cyclohexanone oxime (CHO) over solid acid catalysts including zeolites was carried out to elucidate the effects of the acid strength and the micropore size of the catalysts on the selectivity of -caprolactam (CL) and the catalyst deactivation rate. It was found that the catalyst deactivation rate was strongly dependent on the acid strength of the acid catalysts. The improvement of catalyst life was achieved by using MFI-type metallosilicates having weak acid sites. The CL selectivity decreased over the acid catalysts with micropores larger than those of the MFI zeolites. Furthermore, using methanol and carbon dioxide as the diluent solvent and diluent gas improved CL selectivity and catalyst life, respectively.     

An adaptive color similarity function suitable for image segmentation and its numerical evaluation

In this article, we present an adaptive color similarity function defined in a modified hue‐saturation‐intensity color space, which can be used directly as a metric to obtain pixel‐wise segmentation of color images among other applications. The color information of every pixel is integrated as a unit by an adaptive similarity function thus avoiding color information scattering. As a direct application we present an efficient interactive, supervised color segmentation method with linear complexity respect to the number of pixels of the input image. The process has three steps: (1) Manual selection of few pixels in a sample of the color to be segmented. (2) Automatic generation of the so called color similarity image (CSI), which is a gray level image with all the gray level tonalities associated with the selected color. (3) Automatic threshold of the CSI to obtain the final segmentation. The proposed technique is direct, simple and computationally inexpensive. The evaluation of the efficiency of the color segmentation method is presented showing good performance in all cases of study. A comparative study is made between the behavior of the proposed method and two comparable segmentation techniques in color images using (1) the Euclidean metric of the a* and b* color channels rejecting L* and (2) a probabilistic approach on a* and b* in the CIE L*a*b* color space. Our testing system can be used either to explore the behavior of a similarity function (or metric) in different color spaces or to explore different metrics (or similarity functions) in the same color space. It was obtained from the results that the color parameters a* and b* are not independent of the luminance parameter L* as one might initially assume in the CIE L*a*b* color space. We show that our solution improves the quality of the proposed color segmentation technique and its quick result is significant with respect to other solutions found in the literature. The method also gives a good performance in low chromaticity, gray level and low contrast images. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 156–172, 2017     

Nano-sulfated titania (TiO ) as a new solid acid catalyst for Friedel–Crafts acylation and Beckman rearrangement in solvent-free conditions

A novel protocol for the highly selective N-monoalkylation of the sulfamate ester moiety has been developed. This reaction proceeded efficiently using alkyl halides, benzyl halides and α-halo ketones as the electrophile in the presence of KF-Al₂O₃ as a cost-effective and robust catalyst. This approach provides new access to N-monoalkylated Topiramate (anticonvulsant drug) derivatives which are potentially of great importance in medicinal chemistry.     

Acidity Control and Catalysis of Pentasil Zeolites

Acidities of pentasil zeolites were measured and correlated with aluminum content using the following methods: (1) Acid-base indicator method, (2) NH₃-TPD spectra, (3) GC pulse adsorption of pyridine and 4-methylquinoline, and (4) FTIR spectroscopy of adsorbed pyridine.

By controlling the acidity of pentasil zeolites, we have succeeded in obtaining high catalytic performance both in paraselective dealkylation of cymenes and in vapor-phase Beckmann rearrangement of cyclohexanone oxime to ?-caprolactam. In the dealkylation, moderate acidity of Li-ZSM-5 was the key to avoid side reactions while keeping a high conversion of cymenes. In the Beckmann rearrangement, neutrality and crystallinity of the pentasil zeolite were keys to obtain a high lactam selectivity, and a high lactam selectivity of 95% was attained by the surface treatment with chlorotrimethylsilane. The active sites were elucidated to be neutral silanols on the external surface of zeolite.