Browsing by Author "Leeke, Gary A."
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Item Open Access Biological production and recovery of 2,3-butanediol using arabinose from sugar beet pulp by Enterobacter ludwigii(Elsevier, 2022-04-21) Narisetty, Vivek; Narisetty, Sudheera; Jacob, Samuel; Kumar, Deepak; Leeke, Gary A.; Chandel, Anuj Kumar; Singh, Vijai; Srivastava, Vimal Chandra; Kumar, VinodSugar beet pulp (SBP) is a major byproduct from the sugar industries and consists of >20% w/w arabinose. The current work evaluated the potential of Enterobacter ludwigii assimilating pure arabinose and arabinose rich hydrolysate from SBP pellets for 2,3-butanediol (BDO) production. The hydrolysate was obtained through dilute acid pretreatment (DAP) with sulphuric acid. The process was optimized for acid and solid loading to obtain a hydrolysate free from furan derivatives. The effect of different levels of substrate (10–60 g/L) using pure arabinose was conducted in shake flask experiments, followed by co-fermentation with small amounts of glucose and SBP hydrolysate. After flask cultivations, BDO fermentations were carried-out in a bench-top bioreactor in batch and fed-batch modes using pure arabinose as well as SBP hydrolysate. The fed-batch culture led to BDO production of 42.9 and 35.5 g/L from pure arabinose and SBP hydrolysate with conversion yields of 0.31 and 0.29 g/g, respectively. Finally, BDO accumulated on pure arabinose and SBP hydrolysate were recovered using an aqueous two-phase extraction system. The recovery yield of BDO accumulated on arabinose and hydrolysate was ∼97%. The work demonstrated the feasibility of using SBP as a suitable feedstock for manufacturing BDO.Item Open Access Biovalorisation of crude glycerol and xylose into xylitol by oleaginous yeast Yarrowia lipolytica(BMC (part of Springer Nature), 2020-06-03) Prabhu, Vinayak Ashok; Thomas, Dominic J.; Ledesma-Amaro, Rodrigo; Leeke, Gary A.; Medina, Angel; Verheecke-Vaessen, Carol; Coulon, Frederic; Agrawal, Deepti; Kumar, VinodBackground Xylitol is a commercially important chemical with multiple applications in the food and pharmaceutical industries. According to the US Department of Energy, xylitol is one of the top twelve platform chemicals that can be produced from biomass. The chemical method for xylitol synthesis is however, expensive and energy intensive. In contrast, the biological route using microbial cell factories offers a potential cost-effective alternative process. The bioprocess occurs under ambient conditions and makes use of biocatalysts and biomass which can be sourced from renewable carbon originating from a variety of cheap waste feedstocks. Result In this study, biotransformation of xylose to xylitol was investigated using Yarrowia lipolytica, an oleaginous yeast which was firstly grown on a glycerol/glucose for screening of co-substrate, followed by media optimisation in shake flask, scale up in bioreactor and downstream processing of xylitol. A two-step medium optimization was employed using central composite design and artificial neural network coupled with genetic algorithm. The yeast amassed a concentration of 53.2 g/L xylitol using pure glycerol (PG) and xylose with a bioconversion yield of 0.97 g/g. Similar results were obtained when PG was substituted with crude glycerol (CG) from the biodiesel industry (titer: 50.5 g/L; yield: 0.92 g/g). Even when xylose from sugarcane bagasse hydrolysate was used as opposed to pure xylose, a xylitol yield of 0.54 g/g was achieved. Xylitol was successfully crystallized from PG/xylose and CG/xylose fermentation broths with a recovery of 39.5 and 35.3%, respectively. Conclusion To the best of the author’s knowledge, this study demonstrates for the first time the potential of using Y. lipolytica as a microbial cell factory for xylitol synthesis from inexpensive feedstocks. The results obtained are competitive with other xylitol producing organisms.Item Open Access CO2 assisted blending of poly(lactic acid) and poly(ε-caprolactone)(Elsevier, 2016-12-15) Murphy, S. H.; Marsh, J. J.; Kelly, C. A.; Leeke, Gary A.; Jenkins, M. J.Poly(lactic acid) (PLA) is gaining increasing interest from the packaging industry as a biodegradable alternative to oil based polymers such as polypropylene (PP) and polyethylene terephthalate (PET). However, its’ inherent brittle nature prevents widescale commercial use. Blending in order to improve the Young’s modulus, yield stress and elongation to break, provides a possible alternative although many polymers have been found to be immiscible with PLA. In this study, high pressure carbon dioxide (CO2) was utilised during blending to encourage miscibility between two normally immiscible polymers: poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA). Blends were prepared by melt blending in the presence of carbon dioxide (CO2) and compared to solvent casting and melt blending with a single-screw extruder. CO2 assisted blends demonstrated a significant reduction in the size and number of PCL domains in a PLA matrix, and consequently improved the adhesion between phases at the microscale. The optimum melt blend composition for Young’s modulus, yield stress and elongation to break was found to be 75% PLA and 25% PCL. Mechanical properties of PLA 2002D blends were further improved when prepared by CO2 assisted melt blending.Item Open Access Hydrochloric acid removal from the thermogravimetric pyrolysis of PVC(Elsevier, 2020-05-04) Torres, Daniel; Jiang, Ying; Sanchez-Monsalve, D. A.; Leeke, Gary A.A powder characterization method was developed to screen the ability of a range of chemicals and absorbents to retain chlorine from chlorinated plastic pyrolysis. The behaviour of adsorbents such as Al2O3 and zeolites, and chemical removers based on NaHCO3, CaO and Na2CO3-ZnO were studied for the removal of HCl released during PVC pyrolysis. First, chlorine removers are mixed with PVC and tested in a thermobalance under pyrolysis conditions for the complete PVC dehydrochlorination (550 °C). Subsequently, after the release of HCl, CO2 and H2O, the chars are analysed by FTIR, CHN elemental analysis and ESEM-EDS to determine the retention of chlorine on the chlorine removers. According to FTIR and CHN, PVC pyrolysis occurs through dehydrochlorination and the formation of aromatics. FTIR and EDS were used to follow the consumption of the bases present in the chemical removers and the suppression of the CCl absorption bands of the PVC CHCl groups during pyrolysis, as well as the formation of the resulting salts (NaCl, CaCl2 and ZnCl2). The chemical removers exhibited chlorine retentions of up to 71 wt. % (using Na2CO3-ZnO), while the adsorbents presented a maximum of 19 % of retention at 550 °C and heating rate of 200 °C/min.Item Open Access Optimisation of solvolysis for recycling carbon fibre reinforced composites(Unknown, 2016-06-30) Keith, Matthew J.; Oliveux, Géraldine; Leeke, Gary A.Solvolysis processes have been used to degrade the resin of two different varieties of epoxy based carbon fibre reinforced composite (CFRC) materials. A degradation of up to 98% has been achieved when processing material at a temperature of 320 °C using a supercritical solvent mixture of acetone and water. Increasing the processing time from 1 to 2 hours shows an increase in the degradation of only 10% and there does not appear to be any benefit in processing the material beyond this time. Due to the batch conditions used, it is necessary to rinse the fibres with acetone after processing to remove remaining organic residue. Washing the fibres at supercritical batch conditions, however, does not efficiently remove the residue compared to a simple hand washing with acetone. Shredding the sample prior to processing also does not have a significant effect. The process investigated requires 19 MJ.kg-1 of fibres recovered and, since the process has not yet been optimised, shows strong potential for future development especially since it allows for the recovery and reuse of organic resinous products.Item Open Access p–x Data of (Acetic Acid + Water) at T = (412.6, 443.2, 483.2) K(American Chemical Society, 2016-05-16) Roman-Ramirez, Luis A.; Leeke, Gary A.Experimental – data were measured for the (acetic acid + water) system at the temperatures of (412.6, 443.2 and 483.2) K between the pressures of 196 kPa and 1902 kPa over the entire range of concentrations. Experiments were carried out in a static-analytical equipment with quantitative analysis by GC. The experimental data were correlated with the Perturbed-Chain Statistical Associating Fluid Theory considering two association sites for acetic acid and four association sites for water.Item Open Access Recovery and reuse of discontinuous carbon fibres by solvolysis: Realignment and properties of remanufactured materials(Elsevier, 2016-11-09) Oliveux, Géraldine; Bailleul, Jean-Luc; Gillet, Arnaud; Mantaux, Olivier; Leeke, Gary A.Discontinuous carbon fibre tows were recovered after solvolysis of an aeronautic type composite made with RTM6 epoxy resin. A Sohxlet extraction method was used to quantify the organic residue on the fibre tows and showed that less than 3 wt% was remaining on the surface. The recovered tows were therefore reused directly to manufacture a plate with randomly distributed carbon fibres and then three plates with realigned carbon fibres. The latter were then characterised and tested and the results obtained were compared to the material manufactured using the same type of virgin fibres by the same method. The materials made from recycled carbon fibres showed very good properties in comparison to the virgin fibre material, despite the presence of flaws such as quality of the fibre surface after solvolysis, alignment and voids). This is the first time in the open literature that carbon fibres recovered from solvolysis were reused in this way together with characterisation of the resulting materials.Item Open Access Recycling carbon fibre with an acetone/water solvent and zinc chloride catalyst: resin degradation and fibre characterisation(2018-09-13) Keith, Matthew J.; Ingram, Andrew; Leeke, Gary A.The degradation of a carbon fibre reinforced epoxy resin with an acetone/water mixture and ZnCl2 catalyst was investigated. The solvent/catalyst system achieved a resin removal yield in excess of 94% after 1.5 h at 290°C and 45 min at 300°C. Single fibre tensile testing indicated an increase in fibre strength after the recycling process. The strongest fibres were recovered using a reaction temperature of 290°C and exhibited a strength of 3.21 ± 1.10 GPa. The technique developed therefore appears to recover high quality fibres while reducing the temperature by 30°C and process time by 25% when compared to earlier work.Item Open Access Steam gasification of rapeseed, wood, sewage sludge and miscanthus biochars for the production of a hydrogen-rich syngas(Elsevier, 2014-08-20) Sattar, Anwar; Leeke, Gary A.; Hornung, Andreas; Wood, JosephSteam gasification of biochars has emerged as a promising method for generating syngas that is rich in hydrogen. In this study four biochars formed via intermediate pyrolysis (wood pellet, sewage sludge, rapeseed and miscanthus) were gasified in a quartz tubular reactor using steam. The dynamic behaviour of the process and effects of temperature, steam flow and particle size were studied. The results show that increases in both steam flow and temperature significantly increase the dry gas yield and carbon conversion, but hydrogen volume fraction decreases at higher temperatures whilst particle size has little effect on gaseous composition. The highest volume fraction of hydrogen, 58.7%, was obtained at 750 °C from the rapeseed biochar.Item Open Access Supercritical fluid coating of API on excipient enhances drug release(Elsevier, 2016-12-18) Li, Qingguo; Huang, Deen; Lu, Tiejun; Seville, Jonathan P. K.; Xing, Lei; Leeke, Gary A.A process to coat particles of active pharmaceutical ingredient (API) onto microcrystalline cellulose (MCC) excipient shows promise as a new way to dosage forms showing enhanced drug release. The process consists of a fluidized bed operated at elevated pressure in which API particles are precipitated from a Supercritical Anti-Solvent process (SAS). MCC particles were used as an excipient in the fluidized bed and collect the SAS-generated API particles. Naringin was selected as the model API to coat onto MCC. A number of operational parameters of the process were investigated: fluidization velocity, coating pressure, temperature, concentration of drug solution, drug solution flow rate, drug mass, organic solvent, MCC mass and size and CO2-to-organic solution ratio. SEM and SPM analyses showed that the MCC particle surfaces were covered with near-spherical nanoparticles with a diameter of approximately 100–200 nm, substantially smaller than the as-received API material. XRD showed that naringin changed from crystalline to amorphous during processing. The coated particles resulting from the SAS fluidized bed process have a higher loading of API, gave faster release rates and higher release ratios in comparison with those produced using a conventional fluidized bed coating process. The approach could be transferred to other industries where release is important such as agrochemical, cosmetic and food.Item Open Access Technology readiness level assessment of composites recycling technologies(Elsevier, 2015-09-03) Rybicka, Justyna; Tiwari, Ashutosh; Leeke, Gary A.Composite materials made of glass and carbon fibres have revolutionised many industries. Demand for composites is experiencing rapid growth and global demand is expected to double. As demand for composites grows it is clear that waste management will become an important issue for businesses. Technically composite materials evoke difficult recycling challenges due to the heterogeneity of their composition. As current waste management practices in composites are dominated by landfilling, governments and businesses themselves foresee that this will need to change in the future. The recycling of composites will play a vital role in the future especially for the aerospace, automotive, construction and marine sectors. These industries will require different recycling options for their products based on compliance with current legislation, the business model as well as cost effectiveness. In order to be able to evaluate waste management strategies for composites, a review of recycling technologies has been conducted based on technology readiness levels and waste management hierarchy. This paper analyses 56 research projects to identify growing trends in composite recycling technologies with pyrolysis, solvolysis and mechanical grinding as the most prominent technologies. These recycling technologies attained high scores on the waste management hierarchy (either recycling or reuse applications) suggesting potential development as future viable alternatives to composite landfilling. The research concluded that recycling as a waste management strategy is most popular exploration area. It was found mechanical grinding to be most mature for glass fibre applications while pyrolysis has been most mature in the context of carbon fibre. The paper also highlights the need to understand the use of reclaimed material as important assessment element of recycling efforts. This paper contributes to the widening and systematising knowledge on maturity and understanding composites recycling technologies.Item Open Access Ultrasound-induced CO2/H2O emulsions as a medium for clean product formation and separation: The barbier reaction as a synthetic example(American Chemical Society, 2014-04-03) Cenci, Steven M.; Cox, Liam R.; Leeke, Gary A.: Subcritical CO2/H2O (30 °C/80 bar) was employed as a renewable solvent mixture in a 1 dm3 ultrasound reactor. As a representative synthetic transformation, the metal-mediated Barbier allylation was used to demonstrate the facility of formation and separation of the homoallylic alcohol product. The chemoselectivity over the competing aldehyde reduction could be improved by deploying the biocompatible nonionic surfactant Tween 80, a saturated salt aqueous phase, or by carrying out the reaction at 60 °C/120 bar. All of these modifications led to an apparent rate increase in the desired allylation. A range of substituted benzaldehydes afforded the corresponding homoallylic alcohols in moderate to high yields. The presence of water constituted a necessary condition for efficient product formation, while CO2 provided an appropriate phase for clean product separation by exploiting a favorable homoallylic alcohol enrichment. In this way, 0.025 mol of homoallylic alcohol product could be isolated from the CO2 phase in 1 h, avoiding further extraction stages that would typically require organic solvents.Item Open Access Ultrasound-induced emulsification of subcritical carbon dioxide/water with and without surfactant as a strategy for enhanced mass transport(Elsevier, 2013-06-03) Cenci, Steven M.; Cox, Liam R.; Leeke, Gary A.Pulsed ultrasound was used to disperse a biphasic mixture of CO2/H2O in a 1 dm3 high-pressure reactor at 30 °C/80 bar. A view cell positioned in-line with the sonic vessel allowed observation of a turbid emulsion which lasted approximately 30 min after ceasing sonication. Within the ultrasound reactor, simultaneous CO2-continuous and H2O-continuous environments were identified. The hydrolysis of benzoyl chloride was employed to show that at similar power intensities, comparable initial rates (1.6 ± 0.3 × 10–3 s–1 at 95 W cm–2) were obtained with those reported for a 87 cm3 reactor (1.8 ± 0.2 × 10–3 s–1 at 105 W cm–2), demonstrating the conservation of the physical effects of ultrasound in high-pressure systems (emulsification induced by the action of acoustic forces near an interface). A comparison of benzoyl chloride hydrolysis rates and benzaldehyde mass transport relative to the non-sonicated, ‘silent’ cases confirmed that the application of ultrasound achieved reaction rates which were over 200 times faster, by reducing the mass transport resistance between CO2 and H2O. The versatility of the system was further demonstrated by ultrasound-induced hydrolysis in the presence of the polysorbate surfactant, Tween, which formed a more uniform CO2/H2O emulsion that significantly increased benzoyl chloride hydrolysis rates. Finally, pulse rate was employed as a means of slowing down the rate of hydrolysis, further illustrating how ultrasound can be used as a valuable tool for controlling reactions in CO2/H2O solvent mixtures.Item Open Access Understanding the dechlorination of chlorinated hydrocarbons in the pyrolysis of mixed plastics(American Chemical Society, 2021-01-15) Jiang, Guozhan; Sanchez Monsalve, D. A.; Clough, Peter T.; Jiang, Ying; Leeke, Gary A.The dechlorination of chlorine containing hydrocarbons in pyrolysis vapor is poorly understood. In order to shed new light on the dechlorination mechanism, a model mixture composed of iso-octane doped with 2-chlorobutane, 2-chloroethylbenzene, and chlorobenzene was used to study the dechlorination of chlorinated hydrocarbons by alkali adsorption. These three chlorinated hydrocarbons were selected as they can be typically produced from the pyrolysis of mixed plastic waste containing polyvinyl chloride (PVC). The mixture is pumped continuously through a Na2CO3 or CaCO3/alumina bed, and GC-MS is used to identify the dechlorination products and to follow the dechlorination reactions. When chlorine is bonded to an aliphatic carbon with an adjacent aliphatic hydrogen, the chlorinated compound first undergoes a dehydrochlorination reaction to form HCl and olefins, and subsequently the HCl is reacted with the alkali in the absorbents. In our experiments, 2-chlorobutane is converted to 2-butene, and 2-chloroethylbenzene is converted to styrene. The formation of HCl and subsequent reaction with alkali components in the absorbent is verified by IR spectroscopy and XRD. In the presence of an alkali, the aliphatic chlorinated hydrocarbons underwent dechlorination at a temperature of 180 °C. The removal of chlorine from aromatic chlorinated compounds operates in a different mechanism, in which the C–Cl bond scission is promoted significantly by the presence of an alumina and hydrocarbon medium. It was found that chlorobenzene undergoes dechlorination forming phenol and benzene.