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1994 - 19993

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Subject: search.filters.subject.Membrane separation

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    Microfiltration membrane fouling by dairy proteins : thesis submitted for the degree of Doctor of Philosophy at Massey University, New Zealand
    (Massey University, 1994) Marshall, Allen D.
    Microfiltration membrane fouling occurs through the deposition of proteins both on the membrane surface and within the membrane pores. Fouling is complex with both the nature and location of fouling dependent upon the properties of the feed material, the properties of the membrane material and the operating conditions used. Two aspects of fouling have been investigated, one in which the feed contained proteins considerably larger than the membrane pores (casein micelles) and the other, in which the protein (β-lactoglobulin) was much smaller than the pores. In this way, it was possible to separately investigate surface layer formation and fouling within the membrane pores. It has been demonstrated that a casein "gel layer" forms on the membrane surface causing severe fouling during the microfiltration of skim milk on a 0.1 μm polysulphone membrane if the combination of cross-flow velocity and permeate flux leads to a concentration of casein at the membrane wall equal to or higher than that required for "gel layer" formation. Once formed, the gel layer restricts the passage of protein through the membrane and reduces plant throughput. During the microfiltration of β-lactoglobulin on a 0.1 μm zirconium oxide membrane, in the presence of calcium and with high fluxes, protein-protein interactions at or near the pore entrance lead to pore narrowing and the eventual retention of protein by the membrane. High localised shear rates at the pore entrance lead to partial unfolding of the protein and calcium appears to form an ion-bridge between exposed negatively charged protein groups leading to aggregation and multi-layer deposition on the membrane pore walls. The removal of calcium or a reduction in the permeate flux prevents severe fouling and greater than 90% transmission of protein can be achieved. The importance of understanding the properties of the feed material in interpreting and explaining membrane fouling is stressed.
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    The feasibility of pervaporation in the purification of ethanol : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Process and Environmental Technology at Massey University
    (Massey University, 1998) Ferreira, Lilian de Barros
    This study investigated how pervaporation could be incorporated into hybrid schemes for purifying ethanol produced from whey of fusel oils and whether this could be achieved at a lower energy cost than distillation alone whilst maintaining product quality within specification. In order to achieve these objectives the project included: investigation of fundamental pervaporation mechanisms and the influence of operation parameters, simulation of the distillation train at the New Zealand Distillery Co. Ltd. (NZDCL) including pervaporation relationships developed during this study, and pinch analysis of the NZDCL. Aqueous solutions of 5 to 20% w/w ethanol with approximately 1% w/w of a mixture of n-propanol, i-butanol, n-butanol, i-amyl alcohol and ethyl acetate were pervaporated through a disk apparatus fitted with either poly-ether-block-amide (PEBA) or poly(dimethyl siloxane) membranes. Similar solutions were sorbed into PEBA beads for the study of sorption. A new, semi-empirical relationship between enrichment factor of alcohols during pervaporation and their molecular size and activity coefficient in the feed stream was proposed. It was observed that for organophilic membranes, sorption generally sets the enrichment factor while the influence of diffusion becomes relevant only when the distribution range of the size of the molecules involved is quite large. In consequence, it is recommended that the study of sorption and diffusion relationships between solvents and dense polymers be given priority as they are relevant for the fast development of this technology. During pervaporation, the temperature of the feed affected mainly the process economics, as an increase in temperature resulted in an exponential increase in the total flux, without significantly changing the product composition. The flux of the minor components studied was independent of the total flux through the membrane except for the i-amyl alcohol, which had its flux influenced by the total flux possibly due to its higher concentration. For the removal of fusels from the fermentation broth with organophilic membranes, all three commercially available membranes investigated presented similar enrichment factors and, compared to evaporation, did not significantly improve the separation of fusels from ethanol. The membranes investigated differed amongst each other with respect to their total flux; the higher the flux through the membrane, the lower the membrane area required for a specific separation. Hydrophilic membranes were used to remove the water fraction at an earlier stage of distillation. Simulation and experiments of the new process showed that it was possible to reduce design complexity and energy expenditure by approximately ten percent. This process could become economically feasible if membrane price dropped by over 60%. Pinch analysis and simulation results of distillation were combined to investigate immediate opportunities to reduce energy usage at NZDCL. Changes in the heat exchanger network and in the distillation feed temperature could reduce production costs (steam usage) without compromising product quality and plant flexibility.
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    Crossflow microfiltration of suspensions containing lactalbumin particles : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Process and Environmental Technology at Massey University, Palmerston North, New Zealand
    (Massey University, 1999) Vyas, Harit Kantichandra; Vyas, Harit Kantichandra
    Crossflow microfiltration (CFMF) is a very important membrane separation process with many applications in different fields including the dairy and other food industries. Often these applications involve processing of particulate suspensions. Many reports on the CFMF of particulate suspensions are found in the literature. However, these reports often deal with uniform sized and/or shaped rigid model particles and often contain contradictory and unexplained results. There is a need to develop further understanding of the CFMF of particulate suspensions, particularly of biological origin with a wide particle size distribution (PSD). This work was carried out to investigate the effects of the operating and feed conditions, and membrane configurations on the CFMF of particulate suspensions using tubular ceramic membrane modules that are commonly used in the food and other similar industries. Lactalbumin particles were selected as the feed material for their irregular shape, wide PSD, and food origin. Experiments were carried out in both constant transmembrane pressure and constant flux modes and all important parameters: internal and surface fouling, and cake mass, height, porosity and PSD were estimated to provide a more complete understanding of the process than has been attempted before. Simple methods were developed and used for the estimation of cake height and porosity. Although many unforeseen effects of the studied parameters were obtained, the results of the study explained some observations and contradictory results reported in the literature. Mathematical models based on resistance in series and force balance mechanisms were developed and successfully used to describe the results of this study. This was achieved by extending these models to include the wide PSD and compressibility of the lactalbumin particles. The developed force balance model was further successfully used to achieve separation of desired feed particle sizes by CFMF under the constant flux mode. A process was developed based on the observed effects of the operating parameters on the CFMF performance that enables operation at very low internal fouling and high flux for as long as 160 min. The developed process has the potential to become commercial if coupled with backflushing.