Alexander K L Yuen

University of Sydney, Sydney, New South Wales, Australia

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Publications (11)41.77 Total impact

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    ABSTRACT: Three species of macroalgae were treated with the aim of reducing nitrogen, sulfur and ash within the biomass prior to hydrothermal processing. The treatments were the nutrient starvation of cultures and post-harvest washing of biomass in freshwater. Subsequently, hydrothermal liquefaction (HTL) of macroalgae was carried out in a batch reactor heated for 8 min with a maximum temperature of 345 °C. Nutrient starvation effectively reduced nitrogen and sulfur levels within the biomass, which led to a reduction in nitrogen by 51–59 wt.% and sulfur by 64–88 wt.% within the biocrude. The yield of biocrude was highest for Derbesia at 38.6–41.7 wt.% and Oedogonium at 35.6–38.8 wt.% when not starved, but was reduced by up to 19 wt.% when the biomass was starved. The washing of biomass consistently reduced the ash content for all species by 7–83 wt.%. The removal of ash affected neither the quality nor the quantity of biocrude produced. The two treatments demonstrate that macroalgal biomass can be effectively manipulated in the production process to modify the composition of the feedstock and, consequently, improve the quality of biocrude. Additionally, reducing the ash content of biomass minimizes its potential impact on HTL processing equipment.
    Algal Research. 01/2014; 6:22–31.
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    ABSTRACT: Six species of marine and freshwater green macroalgae were cultivated in outdoor tanks and subsequently converted to biocrude through hydrothermal liquefaction (HTL) in a batch reactor. The influence of the biochemical composition of biomass on biocrude yield and composition was assessed. The freshwater macroalgae Oedogonium afforded the highest biocrude yield of all six species at 26.2%, dry weight (dw). Derbesia (19.7%dw) produced the highest biocrude yield for the marine species followed by Ulva (18.7%dw). In contrast to significantly different yields across species, the biocrudes elemental profiles were remarkably similar with higher heating values of 33-34MJkg(-1). Biocrude productivity was highest for marine Derbesia (2.4gm(-2)d(-1)) and Ulva (2.1gm(-2)d(-1)), and for freshwater Oedogonium (1.3gm(-2)d(-1)). These species were therefore identified as suitable feedstocks for scale-up and further HTL studies based on biocrude productivity, as a function of biomass productivity and the yield of biomass conversion to biocrude.
    Bioresource Technology 12/2013; 155C:334-341. · 5.04 Impact Factor
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    ABSTRACT: A major limitation of on-water catalysis has been the need for liquid reactants to enable emulsification. We demonstrate that ionic liquids are compatible with on-water catalysis, enabling on-water catalysed reactions for otherwise unreactive solid-solid systems. The unique solvation properties of ionic liquids dramatically expands the scope of on-water catalysis.
    Chemical Communications 08/2013; · 6.38 Impact Factor
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    ABSTRACT: A novel symmetrical bolaamphiphile, containing two N-methylimidazolium head-groups bridged by a 32-methylene linker, was synthesized and characterized. A variety of mesoporous silicas was prepared using the bolaamphiphile as a "soft template". The effects of absolute surfactant concentration and synthesis conditions upon the morphologies of these silicas were investigated. For a given surfactant concentration, particle morphology; pore size; and pore ordering were modified through control of the template to silica-precursor ratio and synthesis conditions. Observed morphologies included: lenticular core-shell nanoparticles and decorticated globules, truncated hexagonal plates, and sheets. In all cases the mesopores are aligned along the shortest axis of the nanomaterial. Decorticated materials displayed surface areas of up to 1200 m(2) g(-1) and pore diameters (DBJH) of 24-28 Å. Small-angle X-ray diffraction and transmission electron microscopy measurements revealed that the majority of the materials has elliptical pores arranged in rectangular lattices (c2mm). Adoption of this symmetry group is a result of the template aggregate deformation from a regular hexagonal phase of cylindrical rods to a ribbon phase under the synthetic conditions.
    Physical Chemistry Chemical Physics 06/2013; · 3.83 Impact Factor
  • Alexander K. L. Yuen, Anthony F. Masters, Thomas. Maschmeyer
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    ABSTRACT: The material known as 1-butyl-3-methylimidazolium hydroxide has been reported to be a 1:1 mixt. of [BMIM]-cations and [OH]-anions and, as such, has been widely cited as a basic ionic liq. 1,3-Disubstituted imidazolium-cations however, are prone to deprotonation at the C2-position of the imidazolium ring, a property readily exploited for the prepn. of N-heterocyclic carbenes. Consequently, this reactivity may be unexpected and esp. unwelcome when it leads to the decompn. of [BMIM][OH] itself, esp. if the decompn. occurs during its use as a basic catalyst or reaction medium. Here, we highlight the putative [BMIM][OH], as a case of particular inconsistency and inaccuracy in the literature and aim to dispel some of the persisting confusion surrounding its prepn., characterization and use. The first part of this paper concerns the history, prepn. and identity of so-called [BMIM][OH], while the second part highlights some of the claimed activity, effects and problems assocd. with its use. Despite w
    Catalysis Today 01/2013; 200:9-16. · 2.98 Impact Factor
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    ABSTRACT: The processing of renewable feedstocks to platform chemicals and, to a lesser degree, fuels is a key part of sustainable development. In particular, the combination of lignocellulosic biomass with hydrothermal upgrading (HTU), using high temperature and pressure water (HTPW), is experiencing a renaissance. One of the many steps in this complicated process is the in-situ hydrogenation of intermediate compounds. As formic acid and related low-molecular-weight oxygenates are among the species generated, it is conceivable that they act as a hydrogen source. Such hydrogenations have been suggested to be catalyzed by water, by bases like NaOH, and/or to involve "reactive/nascent hydrogen". To achieve the temperatures and pressures required for HTU, it is necessary to conduct the reactions in high-pressure vessels. Metals are typical components of their walls and/or internal fittings. Here, using cyclohexanone as a model compound for more complex biomass-derived molecules, iron in the wall of high-pressure stainless steel reactors is shown to be responsible for the hydrogenation of ketones with low-molecular-weight oxygenates acting as a hydrogen source in combination with water.
    Chemistry - An Asian Journal 09/2012; 7(11):2638-43. · 4.57 Impact Factor
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    ABSTRACT: Iron (and to a lesser extent manganese) in the wall of a 316 stainless steel (SS) reactor is responsible for the hydrogenation of cyclohexanone to cyclohexanol when using an aqueous formic acid solution under high temperature and pressure water (HTPW) conditions. However, not only dilute formic acid but also aqueous solutions of several other organic and mineral acids in the presence of iron are active in this reaction covering a range of aldehydes and ketones, even under ambient conditions. The stoichiometry, kinetics, and the possible mechanisms of both dihydrogen production as well as of the hydrogenation of the model compound cyclohexanone were examined. The reduction is essentially stoichiometric with respect to metallic iron, and the conversions are highly dependent on the speed of stirring as well as temperature and reactant concentrations. Importantly, it is established unequivocally that water participates in dihydrogen gas formation (hydrogen atoms originate from both the acid and water molecules) and facilitates substrate reduction.
    Chemistry - An Asian Journal 09/2012; 7(11):2629-37. · 4.57 Impact Factor
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    ABSTRACT: The unique properties exhibited by nanoscale materials, coupled with the multitude of chemical surface derivatisation possibilities, enable the rational design of multifunctional nanoscopic devices. Such functional devices offer exciting new opportunities in medical research and much effort is currently invested in the area of "nanomedicine", including: multimodal imaging diagnostic tools, platforms for drug delivery and vectorisation, polyvalent, multicomponent vaccines, and composite devices for "theranostics". Here we will review the surface derivatisation of nanoparticulate oxides of iron and iron@iron-oxide core-shells. They are attractive candidates for MRI-active therapeutic platforms, being potentially less toxic than lanthanide-based materials, and amenable to functionalisation with ligands. However successful grafting of groups onto the surface of iron-based nanoparticles, thus adding functionality whilst preserving their inherent properties, is one of the most difficult challenges for creating truly useful nanodevices from them. Functionalised catechol-derived ligands have enjoyed success as agents for the masking of superparamagnetic iron-oxide particles, often so as to render them biocompatible with medium to long-term colloidal stability in the complex chemical environments of biological milieux. In this perspective, the opportunities and limitations of functionalising the surfaces of iron-oxide nanoparticles, using coatings containing a catechol-derived anchor, are analysed and discussed, including recent advances using dopamine-terminated stabilising ligands. If light-driven ligand to metal charge transfer (LMCT) processes, and pH-dependent ligand desorption, leading to nanoparticle degradation under physiologically relevant conditions can be suppressed, colloidal stability of samples can be maintained and toxicity ascribed to degradation products avoided. Modulation of the redox behaviour of iron catecholate systems through the introduction of an electron-withdrawing substituent to the aromatic π-system of the catechol is a promising approach towards achieving these goals.
    Dalton Transactions 03/2012; 41(9):2545-59. · 3.81 Impact Factor
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    ABSTRACT: The preparations of the compounds, [Co3O(C6H5N2O)3(CH3COO)3][PF6].CH3CN (I), [Co4(μ2-OH)2(η1:η1:μ2-CH3COO)2(CH3COO)2 (η1:η1:μ2-C11H8NO)2(η1:η1:η1:η1:μ2-C11H8N3O)2][PF6]2.CH3OH.3H2O (II) and [Co3O(OAc)5(C7H6NO2)(py)3][PF6] (III) and the crystal structures of (I) and (II) are reported. The cation of (I) is an oxo-centred trimer, of a structural type similar to cobalt oxo trimers such as [Co3O(OAc)6(py)3]+, whilst the dication of (II) has a “metallo-crown” structure. Complex (III) is assigned an oxo-centred trimeric structure. The cations, [Co3O(OAc)6(py)3]+, [Co3O(OAc)5(OH)(py)3]+, and sym-[Co2(OH)2(OAc)3(py)4]+, as their PF6− salts, catalyse the oxidation of cyclohexane in the presence of N-hydroxyphthalimide (NHPI). However, the multinuclear species, (I), (II) and (III) do not catalyse cyclohexane oxidation in the presence or absence of NHPI.
    Polyhedron 01/2012; · 2.05 Impact Factor
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    ABSTRACT: A series of bis-cationic bolaamphiphiles were synthesized containing N-methylimidazolium head-groups, separated by alkyl chains of 12, 16 and 24 methylene units. Their critical micelle concentrations were determined with subsequent flooding experiments revealing the tendency for the formation of hexagonal mesophases at high surfactant concentrations. The surfactants were employed as templates for silica for-mation, at ca. four times their critical micelle concentrations, permitting super-microporous and nanop-articulate mesoporous silicas to be prepared. Silica surface areas ranged from 500 to 1000 m 2 g À1 , and pore diameters (D TEM) from 10 to 22 Å. Analysis of the materials by small angle X-ray diffraction indicated that, in the case of the template possessing 24 methylene units, the silica obtained exhibited a 2D hex-agonal pore arrangement.
    Microporous and Mesoporous Materials 08/2011; 148:62-72. · 3.37 Impact Factor
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    ABSTRACT: The facile hydrogenolysis of various nitriles, imines, and amines over Pd/C has been achieved by using straightforward and relatively mild conditions. Substrates that contain an aryl group adjacent to the nitrogen-containing functionality were hydrogenolyzed most effectively. The stabilization of the proposed h2-coordinated palladium intermediate by this group was partly responsible for this observation and is borne out by ab initio calculations.
    ChemCatChem 01/2011; 3:1496-1502. · 5.18 Impact Factor