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  • 1
    ISSN: 0006-3592
    Keywords: fluoroether surfactants ; liquid CO2 ; high pressure ; emulsion ; solubilization ; subtilisin Carlsberg ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Carbon dioxide is a naturally abundant, environmentally benign solvent whose use, like water, in a process is not regulated by either EPA or FDA. Unfortunately, polar compounds such as amino acids and proteins are essentially insoluble in carbon dioxide. Further, alkyl-functional surfactants, which have been shown to allow extraction of proteins into conventional organic solvents, exhibit very poor or negligible solubility in CO2 at pressures below 50 MPa. Consequently, highly CO2-soluble fluoroether-functional surfactants have been generated and used to solubilize subtilisin Carlsberg from aqueous buffer and cell culture medium into CO2, with recovery accomplished by depressurization. Both the amount of protein solubilized in the emulsion and the extent of activity retention by the protein following recovery are functions of the initial protein concentration in the buffer. This, plus the observation that the presence of protein affects the stability of the emulsion, suggests that some of the protein is sacrificed to act as a stabilizer in these systems. In addition to solubilization via an inverse emulsion, it has also been shown that one can strip protein-surfactant aggregates from a middle phase emulsion using pure CO2, suggesting an ion-pairing type mechanism. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 58: 572-580, 1998.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The heating (or cooling) of the rock adjacent to water flowing through a crevice is of interest in certain geothermal studies. For many purposes, only the rock temperature at the rock-water interface is needed. The fact that the convective heat transfer coefficient is a function of time in the case of unsteady flow takes this problem out of the strictly classical domain.Several methods of solution are described. An approach in which the heat equation is solved, under appropriate side conditions, by standard finite difference techniques is shown to be satisfactory but rather wasteful because much unneeded information concerning internal rock temperatures must be obtained. Several integral equations of Volterra type are derived that provide the temperature only at the interface. Two numerical approaches to their solution are described: one quite classical and only partially effective; the other an apparently new algorithm that is fast and efficient. Analytical upper and lower bounds on the temperature are obtained and serve to demonstrate that this numerical device is also very accurate.The algorithm is applicable to a wide class of Volterra integral equations of the second kind. A brief discussion of the possible future uses of this scheme and the need for additional research is given.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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