Engineering

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  • (1989) Kazacos, Michael
    Thesis
    In this project the preparation of the electrolyte for the all vanadium redox flow battery was investigated using both chemical and electrolytic reduction of ^O,- powder. Oxalic acid and SO^ reduction were found to be unsuitable as only the V(IV) state could be produced directly. With suspended powder hydrolysis, however, vanadium sulphate of any oxidation state, in this case 50% V(IV) plus 50% V(III) in sulphuric acid can readily be prepared from V^O^ powder, thus allowing a significant reduction in the cost of the vanadium battery electrolyte. Results from conductivity and electrolyte stability tests at elevated temperature have led to modification of the electrolyte composition for the vanadium redox cell, from the 2 M V plus 2 M H^SO^, originally employed, to the use of 3 M H^SO^, much higher energy efficiencies and greater electrolyte stability was demonstrated with the 3 M H^SO^ supporting electrolyte. Spectroscopy and electrolyte conductivity have been demonstrated as suitable techniques for state-of-charge monitoring. A number of electrode materials were also evaluated and a Toray graphite bonded to a carbon plastic electrode was selected for further prototype development. Energy efficiencies of between 83 and 86% were obtained for a current density of 30 mA/cm for a temperature range 5 to 45'C, and between 0 and 100% state-of-charge. A wide range of construction materials was tested for long term stability in the vanadium redox electrolyte.

  • (1988) Grossmith, F.P.
    Thesis
    The all-vanadium redox flow cell is proposed as an alternative energy storage system, utilising the vanadium (II)/vanadium(III) and vanadium (IV)/(V) redox couples for the negative and positive half cells, respectively. Single redox flow cells with an active electrode area of up to 200 cm2 were constructed and their performance characteristics evaluated employing various electrode and membrane materials. Of the electrode materials evaluated graphite felt (RVG, Le-Carbone Lorraine) was found to maximise the kinetics of the vanadium couples while minimising 02 and H2 evolution reactions. Two membranes, namely the anion (AMV) exchange and cation (CMV) exchange (Asahi Glass Co., Japan) were evaluated and were found to meet the resistivity and selectivity requirements for redox flow cell applications. Employing the graphite felt (RVG) electrode and either a cation (CMV) or anion (AMV) exchange membrane excellent cell performance was achieved. Using 2 M vanadium solutions coulombic efficiencies of greater than 90% were achieved, voltage efficiencies ranged between 80%-85% while overall energy efficiencies of 76%-81% were obtained. The average open circuit voltage under these conditions is 1.4 volts. The high overall energy efficiency achieved for the single cells together with the simplicity and inherent characteristics of the all vanadium redox flow cell make it one of the most promising energy storage systems currently under development.

  • (1995) Pennisi, Paul
    Thesis

  • (1990) Hoong Ang, Chi Ping
    Thesis
    In this project, the selectivity and resistivity characteristics of various types of membrane separators were evaluated and the most suitable membrane for the Vanadium redox flow cell was chosen on the basis of overall cell efficiency and cost. The results from membrane evaluation tests indicated that the cation-exchange Selemion CMV membrane (Asahi Glass Co., Japan) has the characteristics required for viable Vanadium redox cell performance, giving energy efficiency of over 80% for a cell using activated FMI felt electrode. Even higher efficiencies of up to 88% have been achieved with these materials [124]. Initial tests have also shown very promising results with the Daramic polyethylene microporous separator with a nominal thickness of 0.16 mm. Due to the lower cost of microporous separators compared to ion exchange membranes, attempts were made to impart ion-selective capability to the Daramic microporous separators. Three different methods of treatments were tested and were found to be capable of imparting ion-selective characteristics to the microporous separators although further optimization of the treatment process is required. The problem of solvent transfer from one half-cell to the other half-cell during cycling of the Vanadium redox flow cell was investigated. It was found that by carefully adjusting the ionic strengths of the positive and negative electrolytes, the solvent transfer due to osmotic pressure effects can be minimized so that it is negligible during battery cycling. The fouling of the Selemion CMV membrane in the Vanadium electrolytes was also investigated.

  • (2001) Leung, Audrey
    Thesis
    The volatile aroma compounds in the green plant tissue and grain of five Australian rice varieties were studied in detail. Selected volatile aroma compounds, including 2-acetyl-1- pyrroline (AP), observed in three fragrant varieties, YRF 203, YRF 205 and Kyeema and two non-fragrant varieties, Pelde and Langi, were compared. The development of volatile aroma compounds in the rice plant was followed from early tillering to full maturity. The effect of nitrogen fertilisation level on the volatile aroma compound composition was evaluated. Volatile compounds were extracted by the Likens-Nickerson simultaneous distillation-extraction technique. GC-MS, GC-FID and GC-O were used to separate, identify and quantify the volatile aroma compounds in the rice grain and plant extracts. The 127 volatile compounds identified in rice plant tissue and grain included 28 aldehydes, 23 ketones, 20 alcohols, 8 phenolic compounds, 17 heterocyclic compounds, 7 hydrocarbons, 2 sulphur compounds, 5 terpenes, 11 acids and 6 esters. Most of the homologous series of aliphatic aldehydes, ketones and alcohols that were identified in cooked rice were also identified in plant tissue, but in different proportions. AP was the major volatile compound in fragrant rice plant and grain and was probably the major factor that contributed to the difference between fragrant and non-fragrant varieties. Relative levels of AP in rice plant correlated with the relative level of AP in the rice plant of the same variety. Therefore, AP concentration in rice plant tissue can be used as an early indicator of aroma in rice grain. The non-fragrant whole rice contained more pent-l-en-3- one, D-Limonene and hepta-2,4-dienal than fragrant rice, while fragrant rice contained more but-2-enal, hex-2-en-l-ol, pyridine and AP. Milled fragrant rice contained more but- 2-enal, pyridine, AP and pyrrole than non-fragrant rice. The increase in nitrogen fertilisation resulted in an increase of AP in rice plant tissue and grain in fragrant varieties. In addition, the increase in nitrogen fertilisation resulted in an increase in pyridine, hepta-2,4-dienal and 2-methoxyphenol in the mature rice plant and an increase of pentanal, hexanal, pyridine, heptan-2-one, pentan-l-ol, hexan-l-ol, oct-l-en-3- ol and furfural in milled rice. AP concentration was relatively high at the beginning of plant development and then decreased during plant development. Therefore, AP can be detected at the early stages of plant development, without having to wait until grain maturity.