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作为分子筛研究领域的一个热点,择形催化理论在工业上已经被研究了近60年。尽管在理论上很多研究还不够深入,但随着对催化反应类型、新型催化材料合成、分子筛结构测定、催化性能表征、催化反应作用机理等方面研究的深入,对择形催化反应的认识仍取得了令人欣慰的进步。本文在现有的研究基础上,对不同尺寸的烃分子在分子筛孔道内的吸附和扩散行为进行了总结,并对烃分子反应动力学直径与分子筛的择形相关性做了一定的探究。分析表明,烃分子的反应动力学直径与分子筛择形催化相关性存在一个适用规律区间,当其略小于或接近分子筛孔径时,分子筛的择形催化性能表现最好。此外,分子筛本身的拓扑结构等因素也会对分子筛催化性能造成影响。 相似文献
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主要综述了采用分子模拟技术考察分子在分子筛上扩散行为的多角度、多层次研究进展,包括分子筛结构、负载量、温度和多组分扩散等因素对扩散系数的影响;在此基础上,进一步介绍了扩散相互作用能和过渡态理论的研究进展,并讨论了分子模拟方法在分子筛扩散研究方面所面临的问题和发展方向。 相似文献
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SAPO-34分子筛催化MTO反应时,其催化活性和催化寿命受其形貌结构、硅铝比、酸中心强度和数量等多种因素的影响,其晶粒大小和晶体形貌结构的不同能够改变SAPO-34分子筛的比表面积和稳定性,能够影响原料和产物分子的扩散路径、扩散速度和停留时间以及反应传热效率等,从而影响积碳的生成和催化活性。综述了近年来不同晶体形貌结构SAPO-34分子筛的合成及控制方法,包括纳米SAPO-34分子筛、多级孔结构及其他形貌的SAPO-34分子筛的合成方法及在MTO反应中的应用,并对未来SAPO-34分子筛的发展方向进行了展望。 相似文献
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我厂3号回转窑(Φ4m×60m)生产线在1996年年底由SP窑(产量912t/d)改为NSP窑(产量1320t/d),预分解系统为四级旋风预热器带离线式分解炉 相似文献
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乙烯酮(双乙烯酮)是十分重要的化工中间体,其下游产品较多。江苏某化工厂开发生产乙烯酮(双乙烯酮)下游产品三十多个,年生产规模三万多吨,是国内以乙烯酮(双乙烯酮)为中间体生产精细化学品的综合骨干企业。针对乙烯酮(双乙烯酮)下游产品废水特点,该厂结合企业实际,开展了产品优化,结构调整,清洁生产,资源循环利用,节水降耗等工作,从源头削减了污染物的生产。同时投资二千多万元新建预处理装置三套,6000m3/d废水生化处理装置一套,使全厂乙烯酮(双乙烯酮)下游产品的废水得到了有效的治理。 相似文献
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The miscibility of various amorphous polybutadienes with mixed microstructures of 1,4 addition units (cis, 1,4 and trans 1,4) and 1,2 addition units have been investigated. The studies here involved optical transparency, differential scanning calorimetry, and small angle light scattering. It was found that a 90 percent (cis) 1, 4 addition polybutadiene was immiscible with high (91 percent) 1,2 addition polybutadiene. Reduction of the 1,2 content to 71 percent induced an upper critical solution temperature (UCST) with the cis 1,4 polymer. Polybutadienes with 50 percent and 10 percent 1,2 contents were miscible above the crystalline melting temperature of the cis 1,4 polybutadiene. Immiscibility of the 91 percent 1,2 addition polymer was also found with a 10 percent 1,2 polybutadiene. The latter polymer also exhibits an UCST with the 71 percent 1,2 polymer. The results are used to interpret the characteristics of blends of polybutadienes of varying microstructure. 相似文献
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以F类粉煤灰为例,详细介绍了测定粉煤灰中烧失量的步骤、计算数学模型、影响测量不确定度的因素以及各项测量不确定度分量评定,人员、设备、材料、方法、环境都是影响测量不确定的因素。 相似文献
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The objective of the study was to explore the effect of the degree of deacetylation (DD) of the chitosan used on the degradation rate and rate constant during ultrasonic degradation. Chitin was extracted from red shrimp process waste. Four different DD chitosans were prepared from chitin by alkali deacetylation. Those chitosans were degraded by ultrasonic radiation to different molecular weights. Changes of the molecular weight were determined by light scattering, and data of molecular weight changes were used to calculate the degradation rate and rate constant. The results were as follows: The molecular weight of chitosans decreased with an increasing ultrasonication time. The curves of the molecular weight versus the ultrasonication time were broken at 1‐h treatment. The degradation rate and rate constant of sonolysis decreased with an increasing ultrasonication time. This may be because the chances of being attacked by the cavitation energy increased with an increasing molecular weight species and may be because smaller molecular weight species have shorter relaxation times and, thus, can alleviate the sonication stress easier. However, the degradation rate and rate constant of sonolysis increased with an increasing DD of the chitosan used. This may be because the flexibilitier molecules of higher DD chitosans are more susceptible to the shear force of elongation flow generated by the cavitation field or due to the bond energy difference of acetamido and β‐1,4‐glucoside linkage or hydrogen bonds. Breakage of the β‐1,4‐glucoside linkage will result in lower molecular weight and an increasing reaction rate and rate constant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3526–3531, 2003 相似文献