Browsing by Author "Kaombe, Divina D."

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    Forward Osmosis for the Dewatering of Pyrolysis Oil Aqueous Phase
    (Elsevier, 2014) Kaombe, Divina D.; Hägg, May B.
    Removing water from the pyrolysis oil is a challenge because the oils are thermally unstable and consist of dissolved components in aqueous matrix. Therefore, techniques are need for removing water without altering the chemical composition in an economic feasible way. Here we investigated an osmotic driven membrane process forward osmosis (FO) which removes pure water without dissolved components and can operate at ambient temperature. The driving force for this process is the osmotic pressure difference between feed solution (FS) and osmotic agent (draw solution (DS)). In this study cellulose acetate (CA) membranes and two osmotic agents (draw solutions) were used: NaCl and MgCl2 solutions; the tests were done at 25 °C over 12 h. The study demonstrates that the FO process is a promising process; water was removed reasonably well within 12 h. This investigation shows that the NaCl solution is relevant over other solutions used; however, diffusion of the solutes from the DS to FS is a challenge given that alkali metal ions above the accepted level impair the oil. Therefore, membranes with high selectivity and draw solutions that produce high water fluxes with minimal reverse solute fluxes are needed.
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    Mineral Partitioning in Milk and Milk Permeates at High Temperature
    (Cambridge University Press, 2012) Kaombe, Divina D.; Du, Yanhong; Lewis, Michael J.
    The soluble phase of milk was separated at 20 and 80°C using ultrafiltration. The resulting permeates were then subjected to further ultrafiltration and dialysis at close to these two temperatures. It was found that pH, Ca2+ and soluble Ca decreased as the separation temperature increased both in original UF permeates and in dialysates obtained from these permeates, but P decreased only slightly. The major reason for these changes was due to the precipitation of calcium phosphate/citrate complexes onto the casein micelle with concomitant release of H+. The pH of both permeates and dialysates from milk at 20°C were slightly higher than for milk. When UF permeates collected at 20 and 80°C, were each dialysed at both these temperatures, the dialysate collected at 80°C showed much less temperature dependence for pH and ionic calcium compared with that collected at 20°C. This is in contrast to milk, which shows considerable temperature dependence for pH and ionic calcium. Further experiments revealed that the pH and Ca2+ concentration of permeates showed high temperature dependence above the temperature at which they were separated, but a much lower temperature dependence below that temperature. These findings suggest that dialysis and UF of milk at high temperature provide the best means yet for estimating the pH and ionic calcium of milk at that temperature.
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    Turbiscan as a Tool for Studying the Phase Separation Tendency of Pyrolysis Oil
    (2013) Kaombe, Divina D.; Lenes, Marianne; Toven, Kai; Glomm, Wilhelm R.
    One of the main obstacles in using pyrolysis oils in heat and power applications is their instability upon storage, which leads to unacceptable quality, from the end user’s point of view. Because of the opaque nature of pyrolysis oils, there are presently many challenges associated with determining their stability. Thus, techniques are needed for the characterization of the phase separation of pyrolysis oils, as well as determining the underlying mechanisms of their instability. Here, we present the application of the Turbiscan technique for the evaluation of phase separation tendency of pyrolysis oils over a period of 24 h at various temperatures, compared to the Karl Fischer method. A well-stored pyrolysis oil from poplar wood and fresh pyrolysis oil from forest residue were used for the investigation. For each of the oils, one batch was diluted with water in order to force phase separation, and a second batch was used without dilution. The study reveals that the Turbiscan technique makes it possible to study several aspects of phase separation in a single experiment; such as sedimentation, clarification, migration velocity and phase fraction. The advantages and potential limitation of the Turbiscan technique are discussed.