Thermal conductivity of dense fluids

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Effect of operating conditions on product distributions and bio-oil ageing in biomass pyrolysis

Alternatives to petroleum-derived fuels are receiving significant interest in order to reduce dependence on finite resources of fossil fuels and to lower fossil-derived CO2 emissions. The present study addresses the production of bio-oil from biomass pyrolysis, one of the potential renewable substitutes to petroleum-derived fuels. The first objective of this work was to investigate the effect of pyrolysis operating parameters, i.e. temperature, heating rate and pyrolysis time, on product distributions in a wire-mesh reactor (WMR) which was designed to minimise secondary reactions. It has been found that high heating rate promotes melting of biomass and this facilitates volatile ejection, thereby resulting in high yield of large bio-oil molecules and high combustion reactivity of residual char. Maximum bio-oil yield is obtained at 500 °C for both rice husk and beech wood whereas a relatively low pyrolysis temperature, e.g. 350 °C, does not allow complete pyrolysis to take place. Chars produced from long holding time and high temperature tests show a decrease in the TGA combustion reactivity which is due to thermal annealing. The comparison between bio-oils obtained from the WMR and Gray-King retort demonstrates the impact of reactor configuration on the variation of bio-oil properties. The unstable nature of bio-oils provided the second objective of this work. The ageing behaviour of bio-oil and the use of organic solvents to improve the bio-oil properties have been investigated. Polymerisation plays a key role in bio-oil ageing and is enhanced by high temperature. Only slight changes in functional groups have been observed by 13C-NMR and FT-IR. UV-F results suggest that phenolic resin formation is one of the polymerisation reactions occurring during bio-oil ageing. With the addition of methanol and acetone to bio-oil, the extent of polymerisation decreases and NMR results indicate the formation of hemiacetals/acetals.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Partial oxidative cracking of polycyclic aromatic compounds under supercritical water conditions for heavy hydrocarbons upgrading

Heavy hydrocarbon upgrading is attracting more interest amidst growing supply of heavier crudes. These materials, often distinguished by high aromatic and asphaltene contents generate larger volumes of residue upon processing. The present study investigates the potential of partial oxidative cracking in water as an alternative to the conventional thermal cracking or hydrocracking upgrading routes. Sub and supercritical water partial oxidative cracking experiments have been carried out in a batch micro-bomb reactor using model compounds of three to five-membered ring polycyclic aromatic hydrocarbons (PAHs). The goal is twofold; to establish the optimum operating window for the PAH oxidative cracking and to evaluate the reactivity patterns between different PAH compounds. It was found that partial oxidative cracking of PAH depends strongly on reaction temperature and oxidant concentration. Using a 0.38 O/Ostoic atomic ratio (38% of the oxygen needed for complete combustion), phenanthrene and anthracene were converted at short reaction time of 0 min into mostly oxygenated intermediates (DCM solubles) at subcritical water conditions. Under the more reactive supercritical water conditions, ring cleavage products, which include phenols, aromatic acids, ketones and unsubstituted aromatics (DCM solubles) were favoured. Most of these intermediates were formed via middle ring oxygenation which could potentially contribute to higher cracking efficiency upon subsequent thermal treatment. In addition to the target compounds, polymerized materials (DCM insolubles) were also produced under both conditions. A good compromise between the two major product streams was obtained at 400 oC whereby the DCM fraction contains a balanced mixture of oxygenated and cracking compounds. PAHs exhibit higher degree of stability with increasing ring size. A higher reaction temperature of 450 oC was needed in order to convert pyrene and benzo[a]pyrene. The reactivity order with respect to PAH conversion into the desirable DCM soluble fraction was established as follows: anthracene > phenanthrene > pyrene > benzo[a]pyrene.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Yields and ageing of the liquids obtained by slow pyrolysis of sorghum, switchgrass and corn stalks

A laboratory scale reactor has been set up to pyrolyse different kinds of biomass under slow heating rates and a range of peak temperatures. Yields of solid and liquid products (i.e. char and oil) were measured allowing the effects of temperature and biomass feedstock to be determined. Small differences in char and oil yields were found between the three biomass feedstocks. Pyrolysis oil samples were collected and characterised with size exclusion chromatography (SEC), ultra violet fluorescence (UV-F) and infra red (IR) spectroscopies to study their structural changes as a function of time after collection, i.e. to assess the ageing of the bio-oils. The effects of several variables on the stability of product liquids were examined: e.g. pyrolysis temperature, storage temperature, solvent addition, type of biomass feedstock. Rapid structural changes in the oil samples were found to occur within about 48 h of preparation. Ageing of oils is thought to be caused by polymerisation reactions taking place in the product liquids. The positive effects on the oil stabilisation due to low storage temperatures (5 C) and the addition of a solvent (methanol or acetone) were confirmed. However, in order to stop the ageing process completely, the concentration of these solvents in the final pyrolysis oil-solvent mixture needed to be greater than 25% (w/w). At lower solvent concentrations bio-oil ageing was slowed down but could not be suppressed altogether. © 2013 Elsevier B.V. All rights reserved