摘要:

The thickness stability of the film between air bubble/oil drop and oil/oil drops in an induced air flotation process in the presence of flocculent was analyzed. A cationic, high molecular weight, polymeric flocculeni was used in the demulsification of a crude oil-in-water emulsion. A novel capillary force balance technique in conjunction with the film interference microscopy was used to study the film thickness stability of an emulsion film formed between oil drops and pseudoemulsion film formed between air bubbles and oil drops. It has been found that film thickness stability is related to the formation of dark spots (thinner area) inside the film. The formation of dark spots inside the thinning film has been explained by the local osmotic depletion-destabilization effect. It has been found that in the presence of the flocculent the emulsion film is less stable than the pseudoemulsion film, and the efficiency of the oil separation process by air flotation is therefore governed by the stability of the water emulsion film. The flocculent improves oil spreading on the water-air surface, thereby enhancing separation efficiency.

ISSN:0098-6445    

DOI:10.1080/00986449608936572

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The Isothermal Dendritic Growth Experiment (IDGE) is an orbital space flight experiment, launched by NASA, in March, 1994, as part of the United States Microgravity Payload (USMP-2). The IDGE provided accurately measured dendritic growth rates, tip radii of curvature, and morphological observations of ultra-pure succinontrile obtained at supercoolings in the range 0.05-2.0 K. Data were received in the form of pairs of digitized binary images telemetered to the ground from orbit in near-real-time, and as 35mm photographic film received 3 months after the flight. The IDGE flight data has now been analyzed, permitting a comprehensive comparison between dendritic growth under terrestrial and microgravity conditions. The measured growth kinetics, in the form of velocity versus supercooling, is markedly different from those observed in terrestrial experiments. Above 0.4 K supercooling in microgravity, the process of dendritic growth is diffusion controlled, i.e., thermal conduction is the rate limiting process. Under terrestrial conditions, dendritic growth of SCN remains dominated by convective transport of heat until a supercooling of ca. 1.7 K is exceeded. Beyond a supercooling of 1.7 K, there is excellent agreement between terrestrial dendritic growth measurements, and a theory with one adjustable parameter determined form the microgravity measurements. Surprisingly, however, even under microgravity conditions, dendritic growth of SCN becomes dominated by convective transport at supercoolings of ca. 0.4 K and below. The observations confirm that convection, which depends as a sublinear power of the supercooling, will always dominate at low supercoolings, whereas diffusion, which depends on the superlinear power of the supercooling, will always dominate at high supercoolings.

ISSN:0098-6445    

DOI:10.1080/00986449608936573

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Lipids in biological matter are mostly triacylglycerols (TAG). Lipolytic enzymes, primarily lipases, are indispensable for bioconversion of such lipids from one organism to another and within the organisms. In addition to their biological significance, lipases are very important in the field of food technology, nutritional and pharmaceutical sciences, chemical and detergent industries, and clinical medicine because of their ability to catalyze various reactions involving a wide range of substrates. Conventionally, lipases have been viewed as the biocatalysts for the hydrolysis of TAG (fats and oils) to free fatty acids, monoacylglycerols (MAG), diacylglycerols (DAG), and glycerol. The main advantages of lipase catalysis are selectivity, stereo-specificity, and mild reaction conditions. Despite these advantages and the fact that enzymatic splitting of fats for fatty acid production was described as early as in 1902, the lipase-catalyzed process has not replaced the commercial physicochemical process for the continuous splitting of TAG utilizing super-heated steam. The limited exploitation of lipase technology may be attributed to high enzyme cost, large reaction volume, requirement for emulsification of substrate, and risk of microbial contamination. Many of these limitations originate from the fact that lipases are employed mainly in water-rich reaction media where the solubility of the substrate TAG is very small. To circumvent this problem and to realize the full potential of lipase, researchers have explored newer approaches by manipulating the conditions under which the lipases act. Many of these novel approaches for lipase catalysis have been the outcome of the discovery that enzymes can be active in water-poor, non-polar media (Hanhan, 1952; Misiorowski and Wells, 1974; Zaks and Klibanov, 1984). Also, the finding that lipases can act in organic solvents has led lo an expansion of their applicability in a wide variety of chemical reactions. Lipase catalysis in some of the well established reaction media has previously been reviewed (Brockerhoff and Jensen, 1974; Brockman, 1984; Lilly et al., 1987; Hailing, 1990; Inadael al, 1990; Malcataet al., 1990). The present review is intended to present a compilation and comparison of novel reaction systems used for lipase catalysis. This review describes briefly the general characteristics of lipase reactions, applications of lipase in various fields, and conventional lipase technology. The lipase-mediated biochemical reactions, particularly the hydrolysis of TAG in novel reaction media is discussed in greater detail.

ISSN:0098-6445    

DOI:10.1080/00986449608936574

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A modified solution-diffusion model is presented which describes separation of ethanol-water mixtures. The model is particularly useful in predicting the solute (ethanol) flux as the mixture approaches the azeotrope point where ethanol activity is greater than 0 6. Based on the experimental observations obtained from the literature, the model assumes that polymers of about seven molecules of ethanol are formed, which are then transported through the membrane along with water and ethanol monomers and dimers. It is shown that the ethanol flux can be predicted more accurately as compared with the existing model. Comparisons with experimental data from the literature confirms this model.

ISSN:0098-6445    

DOI:10.1080/00986449608936575

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Several statistical theories of the transport of a passive scalar quantity make use of a Green's function and statistical properties of the fluid velocity field. The theories are applied to the problems of mean gradient transport in a turbulent fluid and of turbulent transport to a wall or a fluid interface. For the case of mass transfer by a uniform mean concentration gradient in homogeneous turbulence, a weak mixing hypothesis leads to results similar to those of Kraichnan's direct interaction approximation (D1A). Further use of a smoothing hypothesis leads to an algebraic expression for the eddy diffusivity which compares well with the DIA and with laboratory experiments.

ISSN:0098-6445    

DOI:10.1080/00986449608936576

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Based on recognized principles of catalysis in chemical engineering that have been applied to development and design of important industrial processes, this article shows how it is possible to devise a methodology for treating complex enzyme systems. The method is illustrated by examples from both fields. With the reaction catalyzed by the enzyme dihydrofolate reductase, a cancer tumor target, as an example, we demonstrate how information on the rates of component elementary steps can be used to identify those that are most significant in promoting the activity of a given enzyme strain. In this way a tool is available for improved enzyme design.

ISSN:0098-6445    

DOI:10.1080/00986449608936577

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor