Browsing by Author "Gorgens, J. F."
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- ItemModel fitting kinetic analysis and characterisation of the devolatilization of coal blends with corn and sugarcane residues(2012) Aboyade, A. O.; Carrier, M.; Meyer, E. L.; Knoetze, J. H.; Gorgens, J. F.Single and multi-component model fitting was used to determine the pyrolysis reaction kinetics of coal, corn cobs, and sugarcane bagasse, as well as blends of coal with each of the biomasses. The results showed that single component kinetics were a poor representation of the decomposition behaviour of all of the samples, regardless of whether 1st or nth order reaction models were assumed. Conversely, reasonably approximate simulations of reaction rates could be obtained by adopting the simpler 1st order model when 3 or more parallel reactions where assumed in the biomass fuels. However, not all the reactive pseudocomponents in biomass strictly followed the first order model. In comparison, the nth order model was found to be a more robust and flexible approach providing simulations and predictions with better fits to the experimental data, particularly for coal were a larger deviation from 1st order reaction behaviour was observed. Apparent activation energy values obtained for nth order model fitting with 3 pseudocomponents were 212, 188, and 94 kJ mol -1 for sugarcane bagasse; 215, 189, and 99 kJ mol -1 for corn cobs; and 252, 147 and 377 kJ mol -1 for coal. Corresponding pre-exponential factor values obtained were 3.6 × 10 17, 8.5 × 10 16, 3.3 × 10 8 min -1 for bagasse; 7.2 × 10 18, 2.6 × 10 17, 2.2 × 10 9 min -1 for corn cobs; and 2.2 × 10 18, 1.5 × 10 9, 2.5 × 10 20 min -1 for coal, respectively. These results, along with the corresponding reaction order values, produced reaction rate simulations with less than 2% deviation from experimental observations. The activation energies obtained also compared well with values derived previously in a model free analysis of the same data (174 kJ mol -1, 184 kJ mol -1, and 246 kJ mol -1 for CC, in the 0.2-0.8 conversion range). Kinetic analysis of the coal blends with biomass revealed non-additive tendencies as indicated by the relatively poor quality of fit achieved when the parameters of the contributing single fuels were used to predict co-pyrolysis reaction rate curves. © 2011 Elsevier B.V. All rights reserved.
- ItemNon-isothermal kinetic analysis of the devolatilization of corn cobs and sugar cane bagasse in an inert atmosphere(2011) Aboyade, A. O.; Hugo, T. J.; Carrier, M.; Meyer, E. L.; Stahl, R.; Knoetze, J. H.; Gorgens, J. F.Corn cobs and sugar cane bagasse are two of the most important agricultural residues in South Africa in terms of availability and potential for use as a bioenergy resource. The thermal devolatilization of samples of these two fuels in an inert atmosphere was studied by non-isothermal thermogravimetric analysis in the heating rate range of 10-50 °C min-1. Friedman's isoconversional method was applied using the AKTS Thermokinetics software to obtain the dependence of activation energy on conversion. The same method was also applied to the kinetic analysis of lignocellulosic pseudocomponents derived from the mathematical deconvolution of the original DTG curves. The results showed that apparent activation energy in the 0.1-0.8 conversion interval ranged from 170-225 kJ mol-1 to 75-130 kJ mol-1 for sugar cane bagasse and corn cobs respectively. The range of apparent activation energy obtained for the pseudocomponents representing hemicelluloses, cellulose and lignin derived from sugar cane bagasse were given as 200-300 kJ mol -1, 163-245 kJ mol-1, and 80-180 kJ mol-1, while for corn cobs the values were 85-110 kJ mol-1, 80-140 kJ mol-1, and 10-60 kJ mol-1 respectively. The derived thermokinetic parameters from both global and pseudocomponent analyses satisfactorily reproduced the experimental curves used for the analysis and could also successfully predict reaction progress at a heating rate outside what was used in the analysis. The fits obtained between simulated and experimental results were comparable to what has been reported in the literature based on conventional model-fitting techniques. © 2011 Elsevier B.V. All rights reserved.
- ItemProcess efficiency of biofuel production via gasification and Fischer-Tropsch synthesis(ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD, ENGLAND,OXON, OX5 1GB, 2013) Leibbrandt, N. H.; Aboyade, A. O.; Knoetze, J. H.; Gorgens, J. F.
- ItemScalable methanol‑free production of recombinant glucuronoyl esterase in Pichia pastoris(BMC (part of Springer Nature), 2019) Conacher, C. G.; Garcia‑Aparicio, M. P.; Coetzee, G.; Van Zyl, W. H.; Gorgens, J. F.Objective: Glucuronoyl esterase (GE) is an emerging enzyme that improves fractionation of lignin-carbohydrate complexes. However, the commercial availability of GE is limited, which hinders the research of GE-based bioprocesses for its industrial application in lignocellulose biorefineries. This study evaluated a workable, cost-effective, and commercially scalable production strategy to improve the ease of GE-based research. This strategy consisted of a constitutive and methanol-free enzyme production step coupled with a two-step filtration process. The aim was to determine if this strategy can yield copious amounts of GE, by secretion into the extracellular medium with an acceptable purity that could allow its direct application. This approach was further validated for cellobiose dehydrogenase, another emerging lignocellulose degrading enzyme which is scarcely available at high cost. Results: The secreted recombinant enzymes were functionally produced in excess of levels previously reported for constitutive production (1489–2780 mg L−1), and were secreted at moderate to high percentages of the total extracellular protein (51–94%). The constant glycerol feed, implemented during fed-batch fermentation, lead to a decline in growth rate and plateaued productivity. Tangential flow ultrafiltration was used to concentrate cell-free enzyme extracts 5–6-fold, reaching enzyme activity levels (1020–202 U L−1) that could allow their direct application.
- ItemSlow and pressurized co-pyrolysis of coal and agricultural residues(PERGAMON-ELSEVIER SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON,OXFORD, ENGLAND, OX5 1GB, 2013) Aboyade, A. O.; Carrier, M.; Meyer, E. L.; Knoetze, J. H.; Gorgens, J. F.