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(2008)Journal ArticleStudies of CO2 capture using membrane technology from coal-fired power-plant flue gas typically assume compression of the feed to achieve a driving force across the membrane. The high CO2 capture cost of these systems reflects the need to compress the low-pressure feed gas (1 bar) and the low CO2 purity of the product stream. This article investigates how costs for CO2 capture using membranes can be reduced by operating under vacuum conditions. The flue gas is pressurized to 1.5 bar, whereas the permeate stream is at 0.08 bar. Under these operating conditions, the capture cost is U.S. $54/tonne CO2 avoided compared to U.S. $82/ tonne CO2 avoided using, membrane processes with a pressurized feed. This is a reduction of 35%. The article also investigates the effect on the capture cost of improvements in CO2 permeability and selectivity. The results show that the capture cost can be reduced to less than U.S. $25/tonne CO2 avoided when the CO2 permeability is 300 barrer, CO2/N2 selectivity is 250, and the membrane cost is U.S. $10/m2.
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(2008)Journal ArticleFire activity has varied globally and continuously since the last glacial maximum (LGM) in response to long-term changes in global climate and shorter-term regional changes in climate, vegetation, and human land use. We have synthesized sedimentary charcoal records of biomass burning since the LGM and present global maps showing changes in fire activity for time slices during the past 21,000 years (as differences in charcoal accumulation values compared to pre-industrial). There is strong broad-scale coherence in fire activity after the LGM, but spatial heterogeneity in the signals increases thereafter. In North America, Europe and southern South America, charcoal records indicate less-than-present fire activity during the deglacial period, from 21,000 to ∼11,000 cal yr BP. In contrast, the tropical latitudes of South America and Africa show greater-than-present fire activity from ∼19,000 to ∼17,000 cal yr BP and most sites from Indochina and Australia show greater-than-present fire activity from 16,000 to ∼13,000 cal yr BP. Many sites indicate greater-than-present or near-present activity during the Holocene with the exception of eastern North America and eastern Asia from 8,000 to ∼3,000 cal yr BP, Indonesia and Australia from 11,000 to 4,000 cal yr BP, and southern South America from 6,000 to 3,000 cal yr BP where fire activity was less than present. Regional coherence in the patterns of change in fire activity was evident throughout the post-glacial period. These complex patterns can largely be explained in terms of large-scale climate controls modulated by local changes in vegetation and fuel load.
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(2008)Journal ArticleA poly(vinyl pyrrolidone) (PVP) seven-arms star polymer with lysozyme core was synthesized by conjugating linear N-succinimidyl ester terminated PVP polymer to lysozyme. Reactive PVP polymers were synthesized using a MADIX/RAFT agent functionalized with N-succinimidyl ester. The polymerization of N-vinyl pyrrolidone proceeded in a living fashion up to more than 90% conversion reaching molecular weight of up to 33 000 g . mol(-1) with narrow molecular weight distributions. The PVP polymer was conjugated to lysozyme resulting in the attachment of seven PVP polymers to one lysozyme core. While the reaction was found to be complete when using low-molecular weight PVP, some by-products with less than seven arms were observed when using PVP with a molecular weight of 33 000 g . mol(-1).
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(2008)Journal ArticleRelaxation and/or backwashing have been incorporated in most membrane bioreactor (MBR) designs as standard operating strategies to limit fouling. However, to maintain a certain net permeate production, higher instantaneous fluxes have to be applied to compensate for the loss of permeate caused by those modes of operation. To assess the effects of the different operational parameters on fouling for the same water productivity, and to study the fouling mechanisms, three relaxation and five backwashing conditions were applied in a lab-scale aerobic MBR and compared to the continuous filtration mode. Moreover, the fouling behaviour was analyzed in terms of the consequential increase in trans-membrane pressure, resistance fractions and the biopolymeric composition of the fouling layer. The Pearson correlation analysis was applied to identify the major contributor to fouling. From this study, it was found that fouling could be retarded effectively when the appropriate filtration mode was applied. The instantaneous flux applied to compensate for the loss of productivity during backwashing or relaxation periods was the major factor affecting fouling rate for either relaxation or back-washing, which was significantly correlated with the amount of solids and soluble fractions deposited on the membrane surface. The relaxation and backwashing conditions (i.e. duration, interval, strength) also considerably affected the fouling rate. In addition, it was found that pore blocking was more likely to be due to protein rather than carbohydrates and that the cake layer was the major contributor to fouling. (C) 2008 Elsevier B.V. All rights reserved.
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(2008)Journal ArticleA novel filtration mode is presented to reduce fouling propensity in membrane bioreactors (MBR). During this mode, an elevated high instantaneous flux (60 L m-2 h-1) is initially applied for a short time (120 s), followed by a longer filtration (290 s) at lower flux (10.3 L m-2 h-1) and a backwash in each filtration cycle. The mixed mode is expected to limit irreversible fouling as the reversible fouling created during the initial stage appears to protect the membrane. Hydraulic performance and the components of foulants were analyzed and compared with conventional continuous and backwash modes. It was found that the mixed mode featured lower trans-membrane pressure (TMP) after 24 h of filtration when compared to other modes. The mixed mode was effective in preventing soluble microbial products (SMP) attaching directly onto the membrane surface, keeping the cake layer weakly compressed, and reducing the mixed liquor suspended solids (MLSS) accumulation on the membrane. This strategy reduced the resistances of both the cake layer and the gel layer. A factorial experimental design was carried out for eight runs with different conditions to identify the major operational parameters affecting the hydraulic performances. The results showed that the value of the flux in the initial high-flux period had the most effect on the performance of the mixed mode: high initial flux (60 L m-2 h-1) led to improved performance. © 2008 Elsevier Ltd. All rights reserved.
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(2008)Journal ArticleDirect observation (DO) technique allowed the visualisation of fouling deposition and removal in real time and in a non-invasive manner. The DO setup was relatively simple and featured a crossflow hollow fibre membrane module, a microscope and a video camera. Transmembrane pressure (TMP) and fouling height were observed to characterise in detail the mechanisms of fouling deposition. At the end of the bentonite filtration at crossflow velocity (CFV) of 4 mm/s, the fouling thickness was measured as 85 ìm. Specific cake resistance was calculated by taking into account the cake height measurements with this technique. The DO technique also allowed unique insights into the mechanisms related to the fouling removal. The effect of bentonite concentrations were assessed to provide credibility of the technique. © 2008 Elsevier B.V. All rights reserved.
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(2008)ThesisThe present study is focused on two studies. The kinetics 0: methane steam reforming over a Ni/MgO catalyst at high pressure is reported in the first study. The second study is focused on the steam iron process over promoted Fe-oxide based catalyst using four different reductants; H2, H2 /CO mixture, CH4 and CH4 /C02 mixture. A kinetic study of methane steam reforming over a Ni/MgO catalyst at high pressure was carried out. The kinetic orders of methane and steam at 40 bars and 600 QC were found to be 0.82 and 0.62 respectively. 1~he estimation of energy of activation of the process was found to be 106 KJ/mol. T11e reaction rate data was explained by a Langmuir - Hinshelwood - Hougen - Wastson model. Four differe11t reductants (H2, H2 /CO mixture, CI-4 and CH4 /C02 mixture) , were applied for the study of the steam iron process. A study of the steam iron process using H2 as reductant focused on the first reduction of 4%Cr203 - 96% Fe203 with H2. The first reduction was found to be composed of a two step reduction up to 550 QC. The estimation of energy of activation for the process was found to be 92.4 KJ/mol and 68.2 KJ/mol respectively. The study of the steam iron process using H2 ICO mixture as reductant over 4%Cr203 - 96% Fe2O3 found that FeO was an intermediate for the reduction of Fe203 with H2ICO mixture to Fe metal. The application of methane as reductant for the steam iron process gave the worst results. As a result, NiO was added to Cr203 -Fe203 to increase the activity. Carbon formation on NiO also was found to be a serious problem. In order to minimize carbon formation on NiO, CO2 was introduced in a mix with CI-4 for the oxidation of deposited carbon during the reduction step. Although the introduction of CO2 can suppress carbon formation, the strong oxidation of reduced iron oxide by water formed during the reduction process coupled to the l1igher favorable reaction of the water gas shift reaction adversely affects the complete reduction of iron oxide to iron metal.
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(2008)ThesisThere exists a demand to re-engineer pre-existing pharmaceuticals to provide improved drug delivery, new dosage forms and increased drug safety and efficacy. Furthermore, the development of novel methods and formulations allows for the patent life of pre-existing drugs to be extended, which has obvious economic benefits for pharmaceutical companies. Dense gas technology provides a means to achieve these aims and to overcome the distinct limitations of traditional technologies. A novel formulation of the antifungal drug itraconazole has been developed using gas antisolvent processes. The new itraconazole-polymer formulation displayed a significant improvement in dissolution rate achieving 89.8 % dissolution compared to 52.5 % for the commercial formulation. The results of this study demonstrate the great opportunity to use dense gases for the creation of novel drug-polymer composite formulations with improved dissolution properties. The impregnation of an active ingredient into a polymer matrix is another method that can be used to improve the dissolution of poorly water soluble drugs. Dense gas technology has been incorporated into traditional methods for the formation of porous polymer matrices decreasing process residence times. However, some issues still need to be overcome including high operating temperatures and the use of class 3 solvents. A novel dense gas process for the formation of a porous polymer hydrogel matrix has been developed to improve upon current methodologies; Dense Gas Solvent Exchange Process (DGSEP). The Dense Gas Solvent Exchange Process was used to create a porous chitosan hydrogel impregnated with a stable amorphous form of the drug griseofulvin. Furthermore, the process was extended to include a hydrophilic polymer into the matrix. The resulting formulation had a dramatically improved dissolution rate achieving complete dissolution within 70 minutes compared with the commercial formulation which achieved less than 40 %dissolution in the same time. There is great potential for DGSEP to be applied to the formation of a variety of polymer hydrogels impregnated with active ingredients and incorporating polymers and other compounds. The significance of these results is that a simple and effective processing method has been developed to produce hydrogel systems that are suitable for the development of a diverse range of drug delivery systems.
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(2008)ThesisThis thesis describes the research conducted by t he author in completion of a Doctor of Philosophy in the Centre for Advanced Macromolecular Design(CAMD), Univcrsity of New South Wales (UNSW) , Sydney, Australia; under the supervision of Professor Christopher Barner-Kowollik and Doctor Michelle L. Coote (Australian National University). The research has led to the creation of new knowledge in the fields of free radical polymerisation and chemical kinetics. Research was conducted in two main thrusts: (1) investigation into the governing kinetic processes behind star polymer synthesis via what has become known as a reversible addition fragmentation chain transfer (RAFT), R-group approach and (2) an entirely new mode of living free radical (LFR) polymerisation which has been named thioketone mediated polymerisation (TKMP). In the first broad area of the described research, a novel kinetic modelling scheme has been developed in which only the reactions of a single arm star are simulated explicitly. Subsequently, the molecular weight distributions (MWDs) arising from the single arm star simulation are convolved, using probabilistic calculations, to generate the MWD appropriate to a multi-arm star polymerisat ion bearing t he same kinetic parameters as the single arm one. This model is validated against experimental data, enabling, for the first time, the use of rigorous theoretical reasoning to distill a set of synthetic guidelines for star polymer synthesis via a RAFT, R-group approach. Subsequently, the product spectra resulting from RAFT, R-group approach polymerisations of para-acetoxystyrene have been analysed via mass spectrometry. This has led to direct evidence for many of the complex species whose existence had, up until this point, been inferred from gel permeation chromatography (GPC) measured MWDs. The menagerie of species identified includes, but is not limited to, star-star couples, initiator fragment terminated stars, initiator fragment terminated star-star couples and linear chains -- both living and terminated. Using a kinetic model devised specifically for application in mass spectrometry analysis, the experimentally observed abundances of each of the above species have been compared to t hose predicted by simulation. The qualitative agreement between the predicted and observed abundances has provided additional evidence that t he proposed mechanism for RAFT, R-group approach polymerisations is correct and operative. Further, it seems unlikely that significant, undiscovered kinetic phenomena exist. Due to (a) long simulation times encountered using the state of the art, commercial partial differential equation solver for polymerisation kinetics (i.e. PREDICI, Computing in Technology (CiT), GmbH; see http://www.cit-wulkow.de) and (b) the limited flexibility this software provides with respect to the types of chemical species that can be simulated, fundamental research has been conducted into the kinetic Monte Carlo method to (i) examine fundamental aspects of this simulation approach; (ii) determine the maximum speed attainable through a combination of optimisations including run-time generation of problem specific code and parallelisation; and, therefore (iii) find out what the potential of this method may be as a replacement for t he existing methods. In terms of speed, the developed code outperforms previous Monte Carlo benchmarks in the literature by a factor of 2.6 and the latest developments in the commercial tool, PREDICI that took place during the author's Ph.D. candidature give it similar performance to the herein described Monte Carlo code; however, the latter is required to run on multiple processors in order to compete with the serial algorithm implemented in PREDICI. The Monte Carlo method does, however, provide complete freedom with respect to the chemical species whose kinetics can be simulated, allowing for complex species with many chain lengths and, in principal copolymer compositions and branched structures. The Monte Carlo approach is the method of choice for these types of simulations and for the first time competes with the commercial tool in terms of speed. In the second broad area of the described research, an experimental investigation has been conducted into the applicability of thioketones, S=C (R1) (R2), as mediating agents for free radical polymerisations. The compound di-tert-butyl thioketone (DTBT), S=C-(C(CH3)3)2, has been chosen as a model reagent and this, when incorporated into a free radical polymerisation of styrene has led to a linear increase of the average molecular weight as conversion of monomer into polymer takes place - demonstrating control. A reversible radical trapping mechanism has been proposed and evidence for this has been provided in the form of an ab initio calculation of the equilibrium constant for the trapping of a styryl dimer radical by DTBT. This equilibrium constant was approximately K = 105 L mol-1 and is close to the value which is expected on the basis of the experimental results. To aid future experimental investigations intoTKMP, a quantum chemical survey has, been conducted with the aim of discovering the radical affinities of a large range of thioketones. It has been demonstrated that there is ample scope within this class of compound for potent radical trapping - far above that of DTBT. The affinities of various thioketone substrates for radicals have been understood in terms of the radical stabilising and thioketone destabilising effect of the two substituents R1 and R2 on, respectively, the adduct radical, R-S-C•(R1) (R2), and the parent thioketone. All results appearing in this thesis have been published previously in peer-reviewed scientific journals.
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(2008)ThesisThe novel Vanadium Bromide (V/Br) redox flow cell employs a V (III)/V (II) couple in the negative half-cell and a Br/Br2 couple in the positive half-cell, with hydrobromic acid and hydrochloric acid as the supporting electrolyte. This study evaluated the chemical and electrochemical properties of the electrolytes and assessed experimental and commercial membranes for use in the V/Br flow cell. A number of techniques were employed to characterise the composition of the V/Br flow cell electrolytes. During charge, the conductivity of the positive half-cell electrolyte increased, whilst the density and viscosity increased. The reverse was observed for the negative half-cell. The UV-visible spectra of the electrolytes showed characteristic peak wavelengths of the vanadium oxidation states and provided and insight into the halogenated species forming during the operation of the V/Br flow cell. The electrochemical properties of the electrolytes were also examined using cyclic voltammetry. NMR studies examined the relationships between the 35CI and 79Br nuclei in the presence of halide and paramagnetic vanadium ions. It was established that the SOC and performance of the V/Br flow cell can be measured by changes in slllectral chemical shifts and line widths. Small-scale cycling experiments were conducted to evaluate the performance of ion exchange membranes in the V/Br redox flow cell. Of the membranes evaluated, a number were not suitable for use due to high membrane resistances or low chemical stability. The perfluorinated Nafion® and Gore Select® ion exchange membranes proved to be the most chemically inert and showed low resistances. The Gore Select® membranes did however exhibit blistering during extended cycling. The chemical stability and cycling performance of the HiporeTM microporous separator showed promise for future studies to optimise the selectivity and ion exchange capacity of the membrane. Tests of membrane ion exchange capacity, diffusivity and conductivity mirrored the properties displayed in the cell cycling experiments. Results suggested that the structural characteristics of the membrane (including functionality and crosslinking) greatly influenced membrane properties and performance. Tests of long term stability showed a negative change in membrane properties. These changes did not however reflect measured changes during cell cycling experiments.