MnOx/ZrO2纳米催化剂的制备及CO-SCR-NO性能研究

以氧氯化锆和硝酸锰为主要原料,采用Sol-Gel-VFD技术制备了MnOx/ZrO2超细粉体材料.用XRD,TG-DSC,TEM和BET等技术对试样进行了表征,用微反应器-气相色谱仪在线研究了试样选择性催化还原NO的活性.结果表明:用Sol-Gel-VFD技术可制得粒子尺寸约为20nm、具有高催化活性的负载型MnOx/ZrO2纳米催化剂,活性组分锰对NO的催化还原起了主要作用.添加铈组分能提高MnOx/ZrO2纳米催化剂催化还原NO的活性.     

人体骨髓基质干细胞冷冻干燥的探索性实验

人体骨髓基质干细胞已成为组织工程、细胞移植和基因治疗等领域的重要研究对象,目前对它已有低温保存的研究,而通过冷冻干燥的方法对其进行保存国内外未见报导.实验尝试用冻干的方法来保存骨髓基质干细胞.文中选取海藻糖、PVP、HES等作保护剂,应用差示扫描量热仪(DSC)测量其结晶温度和玻璃化转变温度;随后对加入保护剂的细胞溶液进行冻干实验,并应用流式细胞仪对冻干样品复水后的细胞活性进行了测定,其中30%PVP 20%海藻糖对细胞的保护效果较好,细胞成活率达到16.40%.     

真空冷冻干燥过程中鲜食枣营养品质的变化研究

本文研究了真空冷冻干燥过程中鲜食枣营养品质及抗氧化活性的变化规律,为实际生产加工产品选择合适的干燥时间提供理论依据。结果表明:冷冻干燥过程中,鲜食枣还原糖含量存在显著性差异,且干燥结束时显著升高(p0.05);冻干产品维生素C保留率高达99.58%;有机酸是产品中重要的风味营养物质,其中,草酸、柠檬酸含量在冻干过程中均存在显著性差异(p0.05),且在干燥结束时,草酸、酒石酸、柠檬酸含量分别是鲜样的1.64倍、1.32倍、3.83倍;冻干过程鲜食枣ABTS+·清除能力、抗氧化力均存在显著性差异(p0.05),且冻干后ABTS+·清除能力提高6.91%,抗氧化力保留率达92.01%。由此可见,冻干过程中冻干时间对营养物质含量及活性有重要影响。冻干6~9 h有利于保持贮藏的水分和较高的营养品质,同时有助于降低能耗,并保持其功能价值。     

Estimation of organelle water fractions from frozen-dried cryosections

Local dry mass or water fractions can be measured on frozen-dried cryosections assuming constant section thickness in the hydrated state and no net water movements and no differential shrinkage during freezing and drying. These assumptions have been tested on a model consisting of isolated rat liver mitochondria in an albumin matrix with a concentration similar to the dry mass concentration of the cytoplasm. The dry mass concentrations of mitochondria before freezing as measured by interference microscopy and after freezing and freeze-drying of the sections as measured by X-ray microanalysis and scanning microdensitometry are shown to be equal as long as the ice crystals in the medium are smaller than about 100 nm. It is concluded, therefore, that the above-mentioned assumptions could also hold for the cryopreparation of cells and tissues.     

Microstructural,Thermal, Crystallization,and Water Absorption Properties of Films Prepared from Never-Dried and Freeze-Dried Cellulose Nanocrystals

In this paper, the microstructural, optical, thermal, crystallization, and water absorption properties of films prepared from never-dried (ND) and freeze-dried (FD) cellulose nanocrystals (CNCs) are reported. Morphology of the ND CNCs reveals a needle-like structure, while after freeze-drying, they show a flake-like morphology. Microstructural analysis of ND and FD CNCs are further studied via small angle X-ray scattering to probe interactions. ND CNCs yield a transparent film with a low surface roughness (14 ± 4 nm), while the FD CNC film evidence a significant reduction of their transparency due to their higher surface roughness (134 ± 20 nm). Although Fourier transform infrared spectroscopy and energy-dispersive X-ray spectroscopy analyses reveal no chemical change occurs during the freeze-drying process, yet a more intense thermal degradation profile is observed for FD CNC film, probably due to the higher oxygen ingress within the gaps created between the stacked flakes. This, in turn, results in a greater loss of crystallinity at a higher temperature (300 °C) compared to the ND CNC film. A rapid decrease in water contact angle of the FD CNC film proves that the morphology of flakes and their orientation within the film has a strong influence in increasing water absorption capacity.     

Technical aspects in freeze-drying of foods

Drying is a widespread concept in the food industry, typically used to convert a surplus crop into a shelf-stable commodity. With advancement of technology, however, there is interest in moving forward from the traditional convective air drying that is most widely used today for foods, to maintain at a very high level the nutritional and organoleptical properties of the initial fresh product. Freeze-drying (FD) produces the highest quality food product obtainable by any drying method, but it is considered the most expensive operation for manufacturing a dehydrated product owing to high energy consumption and high costs of both operation and maintenance. Microwave freeze-drying (MFD) and atmospheric freeze-drying (AFD) have been developed to reduce the FD energy consumption. The product quality of these two drying methods is similar to FD, due to removal of water content in materials by sublimation in both MFD and AFD. Although a significant amount of scientific research has been carried out in the field of sublimation drying, there are only a few comprehensive summarizations about the various sublimation drying methods. As a result, this review aims to highlight some of the latest and most notable advancements in sublimation-drying of foods, with main emphasis given to recent developments of reducing energy consumption of FD process and suggests future research areas on sublimation-related drying.     

A novel atmospheric freeze dryer using simultaneous application of subzero and hot air streams using a vortex chiller

The objective of this research was to develop an atmospheric freeze-drying (AFD) system for heat-sensitive materials. A laboratory scale AFD system consisting of a vortex chiller was designed and fabricated. A vortex tube was used to convert compressed air into a subzero and a hot air stream. The system used the simultaneous application of subzero air stream and hot air carrier gas coupled with radiant heat input for drying heat-sensitive materials. A parametric evaluation of this drying system was performed. Comparison of drying characteristics and the physical quality (e.g., color, shape, size) with vacuum freeze and traditional AFD was also performed. Results revealed that the proposed system is a suitable and viable alternative without compromising the quality compared to traditional freeze-drying system.     

径向热质传递对瓶装物料冷冻干燥的影响

基于经验证了的二维冻干模型对瓶装物料的冷冻干燥过程进行了数值计算 ,利用计算结果对径向热质传递的影响进行了分析 .结果表明 :瓶侧面的径向传热影响显著 ,但忽略水蒸气在径向上的传递作用不会给模拟计算结果带来明显误差 .     

结合水对冷冻干燥过程影响的研究

本文通过分析三种结合水去除机理下的数学模拟结果，并辅以一定的实验验证进行了结合水对冷冻干燥过程影响的研究。以脱脂牛奶的瓶装冻干为对象，对残余水含量、物料温度、干燥时间、湿含量分布等参数，进行了比较和分析。结果表明，结合水对冷冻干燥过程有重大影响；结合水在升华阶段的解吸过程不能忽略，这一冻干机理对冻干时间与物料干燥层的湿含量分布的预测，以及对冷冻干燥过程的现象描述与规律阐述都极为重要。     

ANALYTICAL SOLUTIONS FOR THE MOVING INTERFACE PROBLEM IN FREEZE-DRYING WITH OR WITHOUT BACK HEATING

ABSTRACT

A mathematical model for freeze-drying without back surface heating is established first in this paper by a combination of URIF (uniformly retreating ice front) and Sheng/Peck's theories. Explicit analytical expressions are obtained for the rates of interface movement and drying. The predicted drying rate and temperature profile are in good agreement with the Sheng/Peck's model results. Furthermore, the model is extended to the process of freeze-drying with back heating in which the temperature at the interface is assumed to increase along the path of movement. It is shown that the average rates for drying and interface moving may be obtained by assuming a quadric distribution for the interface temperature.