Masters Degrees (Chemical Engineering)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/782

Browse

Now showing 1 - 14 of 14

Alkaline polyol fractionation of sugarcane bagasse and eucalyptus grandis into feedstock for value added chemicals and materials
(Stellenbosch : Stellenbosch University, 2017-03) Pius, Moses Tuutaleni; Gorgens, Johann F.; Chimphango, Annie F. A.; Tyhoda, Luvuyo; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH SUMMARY: The main components of lignocellulosic biomass cellulose, hemicellulose and lignin are feedstock for chemical and material manufacturing processes. Integrated biorefinery processes incorporate the production of these valuable components from lignocellulose feedstock in good yield and quality. The nature and complexity of lignocellulose materials and its components require a well-designed process to fractionate these components into individual streams, while special attention is paid to the easily hydrolysed component, hemicelluloses. In the present study, a novel process for the fractionating sugarcane (Saccharum officinarum) bagasse (SCB) and Eucalytpusgrandis (EC) biomass into their main constituents (cellulose pulp, aqueous hemicellulose and lignin) is designed. Research focused on obtaining hemicelluloses in polymeric form or as biopolymers, while maintaining high yields and quality of cellulose and lignin polymers. This was achieved by following organosolv technique using high boiling point alcohols, xylitol and ethylene glycol as the fractionating solvents at concentrations between 20-30% (w/w) and 50-70% (v/v) respectively. The fractionation process’ central composite design incorporated mild conditions, i.e. fractionation time between 2-4 hours, temperatures at 140-180 ºC catalysed by sodium hydroxide between 1-2 wt.% and also subsequently investigated the option of pre-extracting hemicelluloses from the feedstock at previously established conditions prior to further fractionation with ethylene glycol given its hemicellulose destructing nature from literature studies. Results show hemicellulose alkaline pre-extraction to provide higher dissolutions and recoveries of hemicelluloses as compared to those extracted by direct fractionation with the two solvents. At optimum conditions xylitol fractionations achieved higher component recoveries as compared to ethylene glycol. However, ethylene glycol fractionations are more severe in dissolving not only hemicellulose and lignin from both materials but also cellulose. Ethylene glycol fractionations were also accompanied by a high degree of cellulose dissolutions, in some runs up to 39% of the initial, mostly at extreme conditions. Hemicelluloses from all processes were recovered as biopolymers with weight-average molecular weight (Mw) evaluation revealing that alkaline pre-extracted hemicelluloses had highest weight-average molecular weights, 33 638 and 61 644 gmol-1 for sugarcane bagasse and Eucalytpus grandis respectively, as compared to direct raw material fractionation processes which all gave below 23 000 gmol-1 with xylitol processes giving higher molecular weights than ethylene glycol processes. Enzymatic hydrolysis of cellulose revealed ethylene glycol residues to be more digestible (≥60%) than xylitol derived residues (≤60%). Digestibility is further improved with fractionation of hemicellulose pre-extraction solids (≥80%). In terms of cellulose crystallinity, a general increase after fractionation was observed. Residual solids from ethylene glycol treatments displayed higher crystallinity (50.08% EC, 48.44% SCB) as compared to xylitol processes (32.44% EC, 43.98% SCB). Residual solids from the NaOH hemicellulose pre-extraction step also had high crystallinities (43.58% EC and 47.81% SCB) than the xylitol process but just lower than EG derived residual solids (≥48%). There is a major decline in the amount of syringyl and guaiacyl groups in the lignin residues after treatment for all processes supported by low intensity bands in Fourier Transform Infrared Resonance (FTIR). Minimal degradation of lignin fraction by both processes was observed with low fixed carbon content of lignin rich solids, below 20%. In conclusion, xylitol fractionations overweighed ethylene glycol in hemicellulose, lignin and cellulose recoveries, and lignin and hemicellulose quality while ethylene glycol produced good quality cellulose. When compared to conventional organosolv fractionations (i.e. ethanol), these two polyols overweigh organosolv in aspects such as quality of cellulose, hemicellulose and lignin but comes short in terms of component recoveries particularly with ethylene glycol fractionations.
Arabinoxylan as partial flour replacer: The effect on bread properties and economics of bread making
(Stellenbosch : Stellenbosch University, 2016-03) Koegelenberg, Danika; Chimphango, Annie F. A.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT: Wheat bran, used for animal feed, is a good candidate for production of higher value products such as arabinoxylan (AX). Extracted AX holds potential as a partial flour replacer in the bread making industry. The aim of this study was to maximise flour removal while using the minimum AX addition possible while maintaining physical bread properties. The extraction of AX from wheat bran was accomplished using alkaline conditions. The purity of AX extracted at lab scale (275 ml) was 44.3% at the optimum extraction conditions (0.5 M NaOH, 240 min, 80°C). Large scale extraction (27 l) resulted in an extract with 49.3% purity, with addition of purification steps including ultrafiltration, anion exchange chromatography and ethanol precipitation. The two extracts obtained on small scale (E1) and large scale (E2) both had high average molecular weights (620 000 and 470 000 Da, respectively) and arabinose to xylose (A/X) ratios of 0.7 and 0.6. With inclusion of the additional purification steps at large scale, the whiteness index of the final extract was increased from 33 to 93. For the application purpose, the lighter extract colour will have a less prominent effect on bread colour and is therefore advantageous. The high water binding capacity of AX allows for increased dough water absorption resulting in an altered final bread weight and volume. However, at optimal AX addition and flour removal levels, these product properties can be maintained. This was achieved with inclusion of 0.8% crude AX extract and 2.5% flour removal, while increasing water absorption by nearly 2%. The only physical difference between the AX containing loaves and the control was in colour, due to the darker colour of the extract. However, a discolouration step included in the extraction of E2 resulted in a significantly lighter final product compared to loaves containing E1. Comparison of E1 and E2 to highly pure AX resulted in similar final product properties indicating that the extracts’ performance was not affected by the purity. Furthermore, inclusion of an oxidative enzyme, laccase, resulted in a softer final product as determined using a texture analyser. AX production cost was estimated at R110/ kg resulting in higher production costs for AX containing loaves compared to commercial white bread. In order to maintain profit margins the selling price of AX containing loaves have to be increased by 9.6%. In conclusion, crude AX extracted from the animal feed co-product, wheat bran, is a feasible candidate for application in the bread making process as a partial flour replacer.
Chemical and physical modification of wood based hemicelluloses for use in the pulp and paper industry
(Stellenbosch : Stellenbosch University, 2012-03) Postma, Dirk; Chimphango, Annie F. A.; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT: Hemicelluloses are the most abundant plant polysaccharides available next to cellulose. The industrial usage of hemicelluloses however is very limited to nonexistent. As wood is processed in the Kraft pulping process, a large fraction of these hemicelluloses is degraded to low molecular weight isosaccharinic acids, which end up in the black liquor with the degraded lignin. The extraction of hemicelluloses prior to pulping and re-introducing them as a wet-end additive has been shown to improve the paper tensile -, burst- and tear index properties. It has also been proven that the pre-extraction of hemicelluloses does not negatively affect the downstream paper products. The objective of this project was to study the modification of extracted wood based hemicelluloses, focusing on glucuronoxylan in Eucalyptus grandis (E. grandis), by chemical and physical methods identified from literature. The methods investigated were; cationisation, carboxymethylation and ultrasound treatment. The modified hemicelluloses were applied as a wet-end additive to E. grandis pulp to test their effect on strength properties. An addition protocol for the new hemicelluloses additives was developed in this investigation. The E. grandis glucuronoxylan was extracted by using the mild alkali extraction method of Höije et al. The characterization of the extracted solids from the pure E. grandis chips showed that 4-O-methylglucuronoxylan was extracted with an average uronic acid content of 17.3 wt.%. The hemicelluloses yield was 50.75 wt.%, based on dry biomass, containing 40.76 wt.% xylose units. The solids still contained 26.6 wt.% lignin after extraction. The presence of lignin in the extracted solids indicated that the delignification step in the extraction method used, was not sufficient for the E. grandis biomass. The molecular weight of the extracted glucuronoxylan was 51 589 g.mol-1. It was proven that the modification methods from literature are applicable to E. grandis glucuronoxylan, producing cationic, carboxymethyl and low uronic acid content 4-O-methylglucuronoxylan. The cationic E. grandis glucuronoxylan produced had a degree of substitution between 0.05 and 0.73 and an uronic acid content ranging between 6.12 and 12.70 wt.%. The carboxymethylated E. grandis glucuronoxylan had a degree of substitution between 0.05 and 0.11 with a uronic acid content between 10.2 and 21.4%. The sonication of E. grandis glucuronoxylan resulted in products with molecular weights ranging from 54 856 to 57 347 g.mol-1 and uronic acid contents between 13.0 and 18.4 wt.%. Handsheet formation with the modified hemicelluloses added, showed that the cationic E. grandis glucuronoxylan improved handsheet strength and surface properties the best. Cationic E. grandis glucuronoxylan also outperformed the industrial additive, cationic starch at a dosage level of 1.0 wt.%. The addition protocol development for cationic E. grandis glucuronoxylan showed it is possible to add cationic hemicellulose before refining, which results in maximum contact time with the pulp fibres without inhibiting the effect of the additive. Cationic hemicellulose additive added before refining led to a decrease in refining energy required to reach the desired strength properties. It was concluded that the cationisation and carboxymethylation methods chosen from literature were applicable to the South African grown E. grandis glucuronoxylan. The cationic glucuronoxylan showed the best improvement in handsheet strength and surface properties. Cationic E. grandis glucuronoxylan could be added before refining in the papermaking process for maximum effectiveness of this new strength additive. The use of hemicellulosic additives will be more sustainable than starch, due to the presence of hemicelluloses in the initial biomass that enters the pulp and paper process.
Comparative analysis of methods for producing nanocellulose from wheat straw and bran, with co-extraction of valuable products
(Stellenbosch : Stellenbosch University, 2019-12) Ceaser, Regan; Chimphango, Annie F. A.; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT: Nanocellulose production has recently attracted much attention from most researchers due to its variable applications in fields such as food, packaging, and medicine. Nanocellulose production from agricultural resides requires cellulose-rich pulp as the precursor which is mainly obtained by bleaching the biomass after pretreatment. Bleaching of the agricultural residues results in the loss and disruption of other cell wall components such as hemicellulose, hydroxycinnamic acid and lignin. However, these cell wall components are valuable products that when extracted can improve the treatment process. It is therefore necessary to develop a method to obtain a cellulose-rich for nanocellulose production while co-extracting these other cell wall components as value-added products. This study focused on developing and optimising a method to produce cellulose-rich pulp to further produce nanocellulose while co-extracting hemicellulose, lignin, ferulic and p-coumaric acid from wheat bran and wheat straw, which are agricultural residues from the wheat production industry. A two-stage alkaline treatment was the selected method for the extraction of hemicellulose, lignin, ferulic and p-coumaric acid while producing a cellulose-rich pulp. The first alkaline treatment stage was termed asa mild alkaline treatment stage due to the mild process conditions (1.5-2.5 wt. % NaOH conc., 20-40°C at 16 hours) used. The mild alkaline treatment was optimised by a central composite design with a response surface methodology targeted at extracting high yields of hemicelluloses and ferulic acid (for wheat bran) or p-coumaric acid (for wheat straw) with the extraction of lignin as a by-product of the treatment. The second stage alkaline treatment termed as the alkaline delignification step was conducted and optimised at treatment conditions of 6-10 wt. % NaOH for wheat bran and 8-12 wt. % NaOH for wheat straw for 30-90 min at 121⁰C. The alkaline delignification optimisation was focused on obtaining a cellulose-rich pulp with minimal lignin content for nanocellulose production whereas extracting as much lignin as possible with hemicelluloses as by-product. The hemicelluloses, lignin and cellulose-rich pulp obtained were analysed by compositional analysis, Fourier Transform Infrared Spectroscopy (FTIR) and a thermogravimetric analysis (TGA) whereas the extracted hydroxycinnamic acids (ferulic and p-coumaric acid) were analysed by compositional analysis and their antioxidant activity determined. The total yield of hemicelluloses and lignin obtained after the two-stage alkaline treatment from wheat straw was 77% and 68%, respectively whereas the p-coumaric yield was 85% with an antioxidant activity of 45%. In addition, the wheat straw cellulose-rich pulp obtained after the two-stage alkaline treatment had a cellulose recovery, cellulose content, hemicelluloses content, lignin content and crystallinity of 97%, 76%, 3%, 5% and 55%, respectively which were within the range for application in nanocellulose production. The results indicated that two-stage alkaline treatment was beneficial for producing cellulose-rich wheat straw with a high crystallinity for nanocellulose production. Yields of 52% and 94% were obtained for the two-stage alkaline treatment of hemicelluloses and lignin, respectively for wheat bran whereas a ferulic acid yield of 65% with a 15% antioxidant activity was obtained. Furthermore, the wheat bran cellulose-pulp obtained had cellulose recovery, cellulose content, hemicellulose content, lignin content and crystallinity of 83%, 48%, 31%, 6% and 41%, respectively. The cellulose recovery indicated cellulose loss during the delignification step whereas the hemicellulose content was high enough to inhibit enzymatic hydrolysis to produce nanocellulose. The alkaline delignified wheat bran cellulose produced required further treatment to be applied in nanocellulose production and was therefore not used in the nanocellulose production stage of this study. Results from nanocellulose production from delignified wheat straw using sulfuric acid, hydrochloric acid and enzymatic treatment indicated that although sulfuric acid produced cellulose nanoparticles presented the highest yield (34%) and crystallinity (75%), it resulted in the lowest maximum thermal decomposition temperature (309⁰C) as compared to both hydrochloric acid and enzymatic treatment. In addition, the yield, zeta potential and maximum thermal decomposition temperature for nanoparticles produced by enzymatic treatment (17.16 ± 2.30%, -15.2 ± 0.6 mV and 378°C, respectively) were similar to that of hydrochloric acid treatment (20.31 ± 1.24%, -16.3 ± 1.50 mV and 380°C, respectively). It was interesting to note that, the yield, zeta potential and maximum thermal degradation temperature were obtained at a shorter time (4.64 h) for enzymatic treatment than the hydrochloric acid treatment (7.41 h), resolving the issue of extended enzymatic treatment times for nanocellulose production. Furthermore, the crystallinity obtained for hydrochloric acid produced nanoparticles (70%) was closer to that of sulfuric acid (75%) produced nanoparticles and higher than enzymatic hydrolysis produced nanoparticles (48%). Hydrochloric acid produced cellulose nanoparticles resulted in improved polydispersity index (0.53 ± 0.20) and fiber morphology (514 ± 50 length) as compared to enzymatic produce nanoparticles (0.92 ± 0.13 PdI and >1 μm length). It can be concluded that between enzymatic and hydrochloric acid treatments, the latter resulted in nanoparticles with improved properties than the former. KEYWORDS Wheat straw; Wheat bran; Alkaline treatment; Hemicellulose; Lignin; p-Coumaric acid; Ferulic acid; Nanocellulose
Degradation of plastics in the marine environment with reference to temperature and environmental factors
(Stellenbosch : Stellenbosch University, 2020-12) Nel, Delene; Akdogan, G.; Dorfling, Christie; Chimphango, Annie F. A.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT: Plastic waste is an increasing problem, especially in the marine environment, where it has detrimental effects on the ecosystem . For a better comprehension of the environmental implications and eventual fate of plastic waste, research on the degradation is required. This project aimed to fill some of the knowledge gaps by completing a laboratory investigation on temperature associated plastic history, which refers to the degradation induced via temperature on plastics waste during their journey to the ocean, and the effect this has on the degradation behaviour of the plastic in the marine environment. Influences of various environments and plastic properties were also considered. Tests at various temperatures were conducted to investigate the effect of temperature associated with plastic history. The tests were conducted at the following temperatures: 25 ̊C, 100 ̊C and a weekly cycle of 25 ̊C – 60 ̊C. In these tests, three plastics, namely, black polypropylene, clear polypropylene, and clear PET, were investigated in various sizes and shapes. For example, there were large and small, circle and rectangles shapes. The temperature, size, type of plastic and colour additive was found to have important effects on the degradation rate. In the second set of tests to investigate what transpires under marine environmental conditions, samples collected after completion of the constant 25 ̊C and 100 ̊C initial tests were subjected to the following respective treatments: constant temperatures of 25 ̊C or 60 ̊C or 12-hour cycles of 65 W/m2 or 130 W/m2UV radiance – submerged in either seawater or demineralised water, respectively. The UV radiance appeared to be predominantly responsible for greater and/or accelerated degradation compared to naturally expected temperatures, especially for clear polypropylene that exhibited physically visible embrittlement under 130 W/m2 UV radiance. Nonetheless, prolonged exposure is recommended for investigating the 65 W/m2 and 25 ̊C. For both the initial and secondary tests the colour additive is suspected of hindering mechanical property degradation. The 100 ̊C initial treatment is, however, suspected of passivating the colour additive; since after the 100 ̊C treatment, the colour additive did not hinder degradation effectively. The investigation into the effect of environment indicated that under controlled conditions with identical temperatures the addition of water resulted in degradation rate increases. This suggests that the real-life phenomenon of lower degradation in the marine environment than on land could be due to water regulating the temperature. It was furthermore observed that salinity has an accelerating effect on the degradation of polypropylene. PET tended to react similarly to the salinity but the data were not conclusive enough to affirm this theory.
Development and optimisation of a process for cellulose nanoparticle production from waste paper sludge with enzymatic hydrolysis as an integral part
(Stellenbosch : Stellenbosch University, 2018-12) Bester, Lia Mari; Chimphango, Annie F. A.; Görgens, J. F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT: The identification of low-cost and renewable resources is critical to meet environmental concerns associated with fossil-based materials. Waste pulp and paper fibres is a renewable, low-cost, cellulose-rich resource with potential for the production of cellulose nanoparticles. Cellulose nanoparticles are light materials that have desired properties such as biodegradability, non-toxicity, electrical conductivity and high tensile strength. Current production methods involve enzymatic, mechanical pressure and/or chemical treatments. This project developed and optimised a process of enzymatic hydrolysis of waste paper sludge for cellulose nanoparticle production. Based on content of inorganics, two types of paper sludge (PS) from South-African paper and pulp mills, namely printed recycle PS and virgin pulping PS were selected as feedstocks. Commercial enzymes were screened for lab scale enzymatic hydrolysis of PS to cellulose nanoparticles. A cellulase cocktail, Cellic® CTec2, and a monocomponent endoglucanase, FiberCare® R, were preferred commercial enzymes for nanoparticle formation and minimisation of by-product formation for both PS feedstocks. Multi-response statistical optimisation of enzymatic hydrolysis of both feedstocks were conducted, investigating solids loading, hydrolysis times and different ratios of the Cellic® CTec2 and FiberCare® R. Optimised enzymatic hydrolysis conditions based on the mean cellulose particle size and the glucose concentration models indicated that FiberCare® R dosage, Cellic® CTec2 dosage, hydrolysis time and solids loading of 75 ECU/gdPS, 10 FPU/gdPS, 9 hrs and 3% (w/w), respectively were optimum for virgin pulp PS. These optimised conditions resulted in mean cellulose particle size and glucose concentrations of 232 nm and 5.44 g/L, respectively. Selected conditions for printed recycle PS required higher FiberCare® R and Cellic® CTec2 dosages of 100 ECU/gdPS and 20 FPU/gdPS, respectively, at longer hydrolysis times of 12 hrs and a higher solids loading of 6% (w/w). At these selected conditions a mean cellulose particle size and glucose concentrations of 226 nm and 6.38 g/L, respectively were achieved for printed recycle PS. Spherical cellulose nanoparticles (SCN) were produced by these mentioned conditions of both enzymatically-hydrolysed PS feedstocks. Microfiltration of hydrolysed supernatant through a 0.45 μm membrane increased the cellulose nanoparticle quality with decreased mean particle sizes and improved particle size distributions for both PS feedstock. Addition of a high-shear homogenization step subsequent to enzymatic hydrolysis marginally decreased the mean size of microsized particles, with no effect on samples with particles smaller than 1000 nm. Dialysis of the hydrolysed suspensions with a membrane with cut-off molecular weight of 12400 Da improved the purity of produced cellulose nanoparticles. Washing and centrifugation of isolated cellulose nanoparticles from residual hydrolysed solids further increased purity and quality. After purification, final cellulose nanoparticle yields of 7.5% for virgin pulp PS and 6.9% for printed recycle PS were achieved. Microfiltration of hydrolysed supernatant through a 0.45 μm membrane increased the cellulose nanoparticle quality with decreased mean particle sizes and improved particle size distributions for both PS feedstock. Addition of a high-shear homogenization step subsequent to enzymatic hydrolysis marginally decreased the mean size of microsized particles, with no effect on samples with particles smaller than 1000 nm. Dialysis of the hydrolysed suspensions with a membrane with cut-off molecular weight of 12400 Da improved the purity of produced cellulose nanoparticles. Washing and centrifugation of isolated cellulose nanoparticles from residual hydrolysed solids further increased purity and quality. After purification, final cellulose nanoparticle yields of 7.5% for virgin pulp PS and 6.9% for printed recycle PS were achieved.
The development of biosorbents from agricultural waste sources for the separation of fat-based particles from water
(Stellenbosch : Stellenbosch University, 2020-12) Swart, Marli; Chimphango, Annie F. A.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT: The presence of hydrocarbons and triglycerides in water pose a technical challenge for wastewater processing or re-use. Hydrocarbon contamination reduces the water quality for available for human consumption and marine life. The available petrochemical-based oil-removing technologies either have negative environmental impacts or are non-selective and ineffective for oil removal. However, plant-based biosorbents, tailored for selective oil removal by surface acetylation reactions can overcome some of the challenges posed by traditional petrochemical-based sorbents.Therefore, the aim of this study entailed the production of bio-based sorbents from corncob (CC) and wheat straw(WS)and their respective cellulose andnanofibrillated cellulose(NFC)constituents, whichwerefunctionalised via acetylation methods that follow the greenchemistry principles, in order to increase selective oil sorption (OS, g/g). The functionalitiesof these feedstocks were critically dependant onthe replacement of hydrophilic hydroxylgroups on the molecular surface with hydrophobic acetyl groups to attainoleophilicity. The CCand WSwere tuned to become oleophilic via greenand non-greenacetylations. The greenmodification implemented acetic an hydride and iodine,and was optimised via central composite design (CCD),by varying temperature (50 –150 °C), time (0.6 –7.4 h)an diodine concentration (0.7 –7.4 % (w/w)).The optimal performances were compared to a cetylations achieved by the non-green methodology, which replaced the green iodine catalyst with non-green N-bromosuccinimide. The green acetylationyielded CC and WS with a selective OSofapproximately17 –18g/g, while the non-green modified CC and WSexhibitedOS of 17–20g/g. These OS performances were statistically similar(p < 0.05). Cellulose was extracted from unmodified biomass to improve the surface area for sorption. Oleophilic films were developed from CC and WS celluloseretrospective tosurface acetylation.The green acetylation was catalysed by a 50 % (w/w) NaOH-solutionand was optimised via CCDbyvarying temperature (40 –140 °C), time(3.8 –44.2 h) and catalyst volume (1.2 –13.8 % (v/v) NaOH-solution). Concurrently, the non-green acetylation implemented H2SO4as catalyst. The green modification yielded hydrophobic CC and WS films with OSof12 –13g/g, while the non-green CC and WS films had OS of 20 –21g/g.These results revealed that CC and WS had an analogous reaction when subjected to the same type of modification (i.e. greenor non-green). However, the non-green modifications outperformed the green modifications by 65 –69 %based on selective OS.
The effect of sorghum grain decortication on bioethanol production technologies
(Stellenbosch : Stellenbosch University, 2015-12) Nkomba, Edouard Yves; Gorgens, Johann F.; Chimphango, Annie F. A.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT: Due to issues surrounding the burning of fossil fuels such as the effect of greenhouses gases on the climate and the threat energy security poses to non-producing nations, biofuels are being promoted for their potential local availability and carbon neutrality. Depending on the materials used, biofuels can be qualified as first (edible) or second (non-edible) generation. Whereas second generation technologies are still not economically viable, first generations biofuels (such as bioethanol from starch) will hold a major share of renewable liquids fuels in the short to medium term. The recent commercialization of enzymes with marked activity towards non-gelatinized or raw starch (cold processing), and their subsequent expressions by genetically modified organisms (Consolidated bioprocessing) could potentially cut the costs and energy requirements of the conventional high temperature processing, which involve cooking or gelatinizing starch. Hence, alternatives such as low temperature cold processing are being investigated for industrial application, while processes to improve the performance of the consolidated bioprocessing are being explored. Furthermore given that biofuels production is continuously increasing, the availability of the main co-product of the conversion process known as distillers dried grains with solubles (DDGS), is following the trend. It has been shown that sorghum grains decortication (removal of bran) prior entering the conversion process could significantly improves the DDGS quality, by reducing the fibre content thereof, hence increasing its market value. Furthermore, the bran components in grains have been shown to negatively affect starch hydrolysing enzymes. In this study, three bioethanol conversion processes (conventional warm, cold and consolidated bioprocessing) and the effect of decortication on key performance measures was assessed using sorghum grains. When using whole grains, the cold and conventional processing achieved similar ethanol concentration (130.4 and 132.1 g/L), productivity (1.55 and 1.51 g.L-¹.h-¹) and ethanol yield as a fraction of the theoretical maximum (89.7 % and 89.03 %). Although a slight decrease in the ethanol yield from consumed glucose was observed in slurries containing decorticated grains, performance of the cold processing was not significantly affected. However, the ethanol productivity of the conventional warm processing decreased with decortication (1.25 g.L-¹.h-¹). The performance of the cold processing using decorticated grains could match the whole grains process, while using 11.7 wt% less enzymes. The DDGS obtained from decorticated grains had higher average protein content (26%) and lower crude fibre content (30.7 %), compared to DDGS from whole grains processing. The acid and neutral detergent fibres contents in DDGS from both types of grains were on average decreased by 17.6 and 26.7% respectively by the cold processing relatively to the conventional processing. The performance of the consolidated bioprocessing could not match the enzyme-based processing, mostly due to limited production of starch-hydrolysis enzymes. The low ethanol tolerance of the recombinant yeast (approximately 90 g/L) prevented consumption of all of the glucose released in the very high gravity slurry. Furthermore, the CBP yeast inoculum size did not have a significant effect on the rate of starch hydrolysis and ethanol productivity, despite design of a fermentation process with high yeast biomass and yeast-produced enzyme concentrations in the starch slurry. Further improvements to the inoculum production, to increase biomass and enzyme concentrations, can be considered, although CBP yeast still lacks sufficient amylase production to achieve efficient starch grains conversion without supplementation with enzymes.
Enzymatic modification of the functional properties of xylan from lignocellulose feedstocks
(Stellenbosch : Stellenbosch University, 2012-12) Gomes, Katiana Raquel da Gama; Chimphango, Annie F. A.; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT: In the past decades, sustainable alternatives to petroleum-derived products have been explored. While fossil derived products are still the main source of energy and chemicals worldwide, they are the major contributors to the increased emission of green house gasses (GHG’s), responsible for the climate change. Lignocellulose represents a more sustainable alternative since it is biodegradable, renewable and does not contribute to GHG emissions to the same extent as fossil-based resources. Hemicelluloses are the second most abundant class of polysaccharide biopolymers on earth after cellulose, based on widespread availability in nature of the lignocellulosic plant biomass in which they occur. Xylan represents between 15 and 30% of lignocellulose in hardwood plant species, between 25-35% in grasses and in lower proportions in softwood (between 7 and 12%). In pulp and paper industries, xylan is dissolved and separated from cellulose along with the lignin under harsh pulping conditions, and subsequently burned as black liquor for energy generation. This process represents an under-utilisation of hemicellulose feedstocks, due to its low specific heating value (13.6 MJ/kg) compared with lignin (27 MJ/kg). However, the xylans that can be extracted from lignocellulose, either during pulping or in dedicated processes, have limited applications due to low functionality as a biopolymer, mainly high solubility in water. The objective of this study was to investigate the enzymatic hydrolysis of xylans, extracted from different lignocellulosic feedstocks available in South Africa and to find optimum conditions for modifying chemical and functional properties of the xylans for industrial applications. The glucuronoxylan from Eucalyptus grandis was extracted using protocols adopted from Höije et al. (Höije et al., 2005) and Pinto et al. (Pinto et al., 2005). The arabinoglucuronoxylan from sugarcane bagasse was extracted following the protocol adopted from Höije et al. (Höije et al., 2005). Beechwood xylan (Sigma) was used as the model xylan. The xylan was extracted from E. grandis and sugarcane bagasse using the Höije protocol with yields of 20 and 71% and uronic acid contents of 21 and 7.05%, respectively. The molecular weight distribution showed that the major fraction had a degree of polymerization of 287 in E. grandis xylan (Höije). The xylan was extracted from E. grandis by the Pinto protocol with a yield of 89%. However, the degree of polymerization was 133 due to polysaccharide degradation. The model xylan from beechwood had the highest purity levels in terms of xylose content but the lowest degree of polymerization, corresponding to 77. Selective removal of arabinose and 4-O-methyl glucuronic acid by the enzymes α-L-arabinofuranosidase and α-D-glucuronidase, respectively, caused formation of water-insoluble xylan particles. Partially purified α-D-glucuronidase at concentrations between 416 and 462 mg/L were used in the selective enzymatic hydrolysis of 4-O-methyl glucuronic acid side-groups in xylans extracted from different lignocellulosic feedstocks. The minimum time required for selective hydrolysis of the glucuronoxylans at concentrations ranging from 1.1 to 5.0% (w/v) in study was 24 hours. Consequently, the minimum degree of substitution required for the precipitation of beechwood xylan, E. grandis xylan (Höije) and E. grandis xylan (Pinto) was 1:40, 1:6 and 1:25, respectively. The highest release of 4-O-methyl glucuronic acid was found at α-D-glucuronidase dosage of 6.4 mg/g combined with 1.87% (w/v) substrate in beechwood xylan, 3.08% (w/v) in E. grandis xylan (Hoije) and 5.03% (w/v) in E. grandis xylan (Pinto). Optimum conditions for increase in viscosity were found at an enzyme dosage of 6.4 mg/g combined with 4.98% (w/v) of substrate in beechwood xylan, 4.3% (w/v) in E. grandis xylan (Höije) and 4.5% (w/v) in E. grandis xylan (Pinto). The most significant factor for the release of 4-O-MeGlcA was the α-D-glucuronidase dosage (p-value < 0.03), whereas the substrate concentration (p < 0.006) was the most significant factor to maximise viscosity. Enzymatic hydrolysis with both α-D-glucuronidase and α-L-arabinofuranosidase for release of 4-O-methyl glucuronic acid and arabinose from sugarcane bagasse xylan resulted in precipitation. A positive synergy was verified in the release of both side-chains, which was dependent on the dosage ratio between α-L-arabinofuranosidase and α-D-glucuronidase. Optimum conditions for precipitation were found at a dosage of 6.4 mg/g of α-D-glucuronidase and 150 nkat/g of α-L-arabinofuranosidase, with 25% precipitation. On the other hand, the highest release of side-chains was verified at a dosage of 6.4 mg/g of α-D-glucuronidase and 350 nkat/g of α-L-arabinofuranosidase, with 69.5% release of arabinose and 24% release of 4-O-MeGlcA. Morphological analysis of the modified xylans indicated that enzymatic treatment improved both the gelling and plasticising properties. Removal of 4-O-methyl glucuronic acid from glucuronoxylans resulted in increased viscosity, and formation of hydrogels. Arabinose and 4-O-methyl glucuronic acid removal from arabinoglucuronoxylan also resulted in formation of insoluble xylan particles that settled with gravity. The highest viscosity rheological properties was observed with E. grandis xylan (Höije), followed by the model xylan from beechwood. Particle agglomeration was more evident on less substituted glucuronoxylans with a minimum degree of substitution of 4-O-MeGlcA of 3%. The micro particles were found to increase in size with an increase in the xylan concentration, from a minimum concentration of 4.45% (w/v), during enzymatic hydrolysis. The glucuronoxylan hydrogels and arabinoglucuronoxylan insoluble particles formed at optimum conditions had particles sizes ranging from 0.4 to 1.97 μm. It was concluded that the enzymatic modification is a mild and selective chemical process that can add functionality to beechwood, E. grandis and sugarcane bagasse xylans, by reducing their solubility in water and can be further applied as pulp additives, paper coatings, packaging films and gel encapsulation matrices.
Extraction and modification of hemicellulose from wheat bran to produce entrapment materials for the controlled release of chemicals and bioactive substances
(Stellenbosch : Stellenbosch University, 2018-03) Matavire, Thokozani Olga; Chimphango, Annie F. A.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH SUMMARY: Hydrogels are a network of cross-linked hydrophilic polymers that form an insoluble three-dimension structure capable of imbibing large amounts of fluid and they can be used as entrapment matrices for substances. However, synthetic polymers used for the formation of entrapment matrices cause health and environmental concerns, which leads to a need for environmental benign alternatives. Hemicellulose biopolymer is a potential replacement for the petroleum based materials as it is abundant, renewable and biodegradable. Agro-residues such as wheat bran are an abundant and affordable source of hemicellulose as they are not primary food products and would reduce environmental concerns related to their disposal. However, hemicellulose is bound to other components in a complex structure and extraction methods need to be carefully considered to maintain functional properties required for formation and performance of entrapment materials as slow release devices. Furthermore, hemicelluloses are water soluble due to the presence of side groups along the backbone and low molecular weight and that limits its application as insoluble entrapment matrices. The solubility of hemicellulose can be modified physically, chemically and enzymatically to produce insoluble entrapment matrices or hydrogels for the delivery of chemical and bioactive substances. The aim of this study was to develop insoluble entrapment matrices from soluble hemicellulose extracted from wheat bran agro-residue as delivery devices for chemical and bioactive substances. The type of hemicellulose extracted from wheat bran was arabinoxylan. The extraction of soluble arabinoxylan from wheat bran was performed using alkaline method after pre-treatment of wheat bran to remove starch. A full factorial design was used to determine the effects sodium hydroxide (NaOH) concentration, solid loading, extraction time and temperature on xylan extraction. A face centered central composite design was subsequently used to optimize the significant (p<0.05) factors sodium hydroxide concentration, extraction time and temperature with yield and purity as the dependent variables. The highest arabinoxylan yield and purity in terms of arabinoxylan content was 63% and 53%, respectively. The extracted arabinoxylans contained no monomeric sugars indicating that they were in polymeric form and thus were suitable to form stable hydrogels. The extracted hemicellulose was used to form insoluble hydrogels using: (1) coacervation method based on neutralizing an alkaline xylan solution with acid and (2) side chain removing enzyme α-arabinofuranosidase that cleaved the arabinose side groups along the xylan backbone. The hydrogels were applied as delivery systems for gallic acid. The hydrogels were assessed for size, stability, encapsulation efficiency of gallic acid, antioxidant activity of encapsulated gallic acid and chemical structure. The wheat bran arabinoxylan hydrogels formed were in nanosize range (469 – 678nm), however chemically formed hydrogels were smaller compared to enzymatically formed hydrogels. Enzymatically formed hydrogels had smaller size distribution with a polydispersity index (PDI) of up to 0.3 whilst chemically formed hydrogels had a broad size distribution and PDI of 1. In addition, the zeta potential of enzymatically formed hydrogels was more negative compared to chemically formed hydrogels. The more negative zeta potential indicated agglomeration of hydrogels is less, hence enzymatically formed hydrogels were more stable than chemically formed hydrogels. The encapsulation efficiency was up to 72% and 59% for chemically and enzymatically formed hydrogels, respectively. It is worth noting that encapsulating gallic acid before and after formation of hydrogels resulted in differences in encapsulation efficiency. The enzymatically formed hydrogels better preserved the integrity of encapsulated gallic acid with an antioxidant activity of 91% as compared to 80% for chemically formed hydrogels. The release of gallic acid was sustained when the encapsulation of gallic acid occurred during the formation of hydrogels as compared to encapsulation after the formation of hydrogels. Despite enzymatic hydrogels having lower encapsulation efficiency, they showed sustained release of encapsulated gallic acid. In conclusion, chemically and enzymatically modified wheat bran arabinoxylan hydrogels were formed with the ability to entrap and release gallic acid.
Fractionation of Lignocellulosic Biomass for production of materials and chemicals
(Stellenbosch : Stellenbosch University, 2016-03) Makhetha, Mannyalleng Relebohile Alice; Gorgens, Johann F.; Chimphango, Annie F. A.; Tyhoda, Luvuyo; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT: The development and application of biorefineries is the promising effective use of lignocellulose in the substitution of fossil fuel-based chemicals, materials and fuels. The biorefineries are attractive as they will utilise all lignocellulose components (cellulose, hemicellulose and lignin) for production of various products. The biorefineries require efficient lignocellulose fractionation methods, which are able to overcome the recalcitrance of lignocellulose to dissolution and chemical conversion, giving high yield, purity and preferably polymeric forms of all three major fractions. The aim of the study was to compare organosolv and ionic liquid fractionation methods on sugarcane bagasse (SCB) and Eucalyptus grandis (E. grandis), in terms of extraction and separation efficiencies, as well as operational challenges. Effects of alkaline extraction of hemicellulose on efficiencies of organosolv and ionic liquid fractionation methods were also studied. The choice of feedstocks was based on the availability and industrial processing in the Southern Hemisphere. Alkaline pre- and extractions of hemicelluloses were carried out using sodium hydroxide solutions. Organosolv fractionation of both SCB and E. grandis was carried out using aqueous ethanol and conditions adapted from Huijgen et al. (2012). The ionic liquid used was 1-ethyl-3-methylimidazolium acetate, [EMIM]OAc. Central composite design of experiments was used to optimise aqueous ionic liquid fractionation, and obtained desirable conditions were used for comparison study. The mass balances and quality of fractions were used to compare organosolv and ionic liquid fractionations in terms of extraction and separation efficiencies. The results obtained showed that alkaline pre-extraction method extracted and preserved hemicellulose (xylan) in polymeric form. Alkaline pre-extraction solubilised significant amount of hemicelluloses, and that preserved reasonable amount of hemicellulose from degradation by either organosolv or ionic liquid process. When alkaline post-extraction was coupled with organosolv and ionic liquid fractionation methods, the recovered hemicelluloses had lower molecular weight, and were accompanied by very low xylan balances. The alkaline pre-extraction combinations with organosolv and ionic liquid fractionation methods outweighed alkaline post-extraction combinations. Ionic liquid fractionation yielded highly digestible solid residues (≥98 %), while organosolv yielded less digestible solid residues (≤63 %). Both organosolv and ionic liquid fractionation methods resulted in high quality lignin. Ionic liquid fractionation outweighed organosolv process in terms of hemicellulose preservation. In terms of robustness to different feedstocks, ionic liquid fractionation was more robust than organosolv process. In terms of separation efficiencies, ionic liquid fractionation produced fractions which were easily separated than organosolv process (particularly hemicellulose-lignin mixture). Although ionic liquid fractionation outweighed organosolv process, ionic liquid fractionation has the challenge/limitation of scalability due to high cost of ionic liquids. In order to address this challenge, several scale-up tests, as well as optimisation studies for recovery and recycling of ionic liquids have to be carried out. Following that, techno-economic models can be developed for ionic liquid fractionation process, and be compared to organosolv techno-economic models.
Integration of xylan extraction from E. grandis, prior to pulping, into Kraft mills
(Stellenbosch : Stellenbosch University, 2015-03) Joubert, Andre Jacobus; Chimphango, Annie F. A.; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT: Pulp and paper mills are being placed under increasing pressure to maximise the use of the biomass being processed for pulp, and move towards integrated biorefineries (IFBRs), where a diverse range of products can be produced and not just pulp exclusively. Extracting hemicelluloses prior to the pulping process could increase the profitability of the mills as the hemicelluloses could be used to produce a number of additional products. Hemicelluloses are a plant polysaccharides with the most abundant hemicellulose in hardwoods being xylan, with xylose being the primary monosaccharide constituent of xylan. The majority of pulps produced in the Southern Hemisphere are done with hardwoods as feedstock, typically with the Kraft process. The attraction of the concept of extracting hemicellulose prior to pulping is further augmented by the fact that hemicellulose is underutilised in the Kraft process. In the Kraft process the hemicellulose is dissolved during pulping and burned along with lignin for the production of energy, however, hemicellulose has about half the heating value when compared to that of lignin. The main objective of this study was to find a pre-extraction method that is effective in releasing xylan from Eucalyptus grandis, the most important hardwood feedstock used for pulping in the Southern Hemisphere. The method also needs to be practical in terms of integrating it into the Kraft process and should have a minimal effect on pulp yield and subsequent paper qualities. Xylan extractions from E. grandis as feedstock were carried out with white liquor, green liquor and NaOH. Green liquor is the dissolved smelt originating from the recovery boiler in the Kraft process and consists mainly sodium carbonate and sodium sulphide. White liquor’s principal components include sodium hydroxide and sodium sulphide and is used in the digesters during the pulping stage of the Kraft process. NaOH is a make up chemical used in the Kraft process. These chemicals were chosen since they are all already present within the Kraft process. The suitability of these chemicals as xylan extraction methods is further bolstered by the fact that their alkalinity may actually reduce chemical usage in pulping. This provides scope for integration of hemicellulose extraction into Kraft pulping without implementing major changes to the existing industrial process. Moreover, alkali chemicals for pre-extraction allow for minimal effect on resulting pulp and paper. In terms of the extracted product, the alkaline conditions provided by these chemicals create conditions that are suitable for a high degree of polymerisation of hemicelluloses. Xylan pre-extracted chips from selected extraction conditions were subjected to varying pulping conditions, to replicate pulp yields and properties obtained with untreated E. grandis chips when using conventional pulping. Handsheets were also produced from the pulps produced under the highest pulp yield conditions, and these were tested for pulp quality properties. Furthermore, mass balances were performed to gauge the impact that hemicellulose pre-extraction would have using green liquor, white liquor and NaOH on the sodium and sulphur balances of the mill. From the extractions performed, the highest fraction of xylan recovered was 15.15% w/w utilising 2M NaOH, at 120°C for 90 minutes extraction time. This was followed by white liquor extraction at 13.27% w/w utilising 20% AA at 140°C for 90 minutes. Green liquor extraction produced the lowest xylan recovery at 7.83% w/w with 2% TTA and 160°C with an h-factor of 800. The residues from selected extraction conditions were utilised for these pulping optimisation experiments. Selected extraction conditions used for further pulping included 2% TTA and 160°C for green liquor, 20% AA and 120°C and 140°C extraction temperature for white liquor, as well as 2M concentration and 120°C for NaOH. The highest yielding pulping conditions were achieved with a 35% reduction in pulping chemicals and 45 minutes pulping time in combination with green liquor pre-extraction, while for pulping combined with white liquor pre-extraction a 50% reduction in chemicals and 30 minute pulping time was preferred. For pulping subsequent to NaOH pre-extraction a 75% reduction in the NaOH dosage and a 45 minute pulp time was preferred. All pulp steps were performed at 170°C. Unbeaten handsheets produced from the selected pulping conditions for white liquor and green liquor extracted chips showed similar physical properties (burst, tear, tensile indices) when compared to the control (pulps from non-extracted chips). However the greater quantity of xylan removed from cellulose fibres with NaOH extraction, resulted in pulps with lower xylan contents, which affected the burst and tear indices of the handsheets formed from these pulps. An increase in tear, while a reduction in the burst index, was observed for the pulp produced from NaOH extracted chips. It was concluded that although white liquor and NaOH extraction allows for greater xylan recovery, the large chemical expenditure associated with these methods will impose significant cost impacts on the existing Kraft process. From mass balances performed, green liquor xylan extraction due to its lower alkalinity, will be more forgiving in terms of additional make up chemical costs. It also allowed for minimum effect on both the pulp and paper quality, thus making it the most practical of the pre-extraction methods. However, whether the additional make chemicals required for the green liquor extraction method will be justified by the quantity of xylan extracted will only be answered by a thorough economic assessment, which was not in the scope of this project.
Investigating the physicochemical property changes of plastic packaging material exposed to UV radiation
(Stellenbosch : Stellenbosch University, 2020-12) Conradie, Willem Johannes; Akdogan, G.; Dorfling, Christie; Chimphango, Annie F. A.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT: Global plastic production is increasing, and as a consequence more waste is generated and released into the environment. Oceanic weathering f actors such as ultraviolet (UV) radiation, temperature, and salinity result in the degradation of these plastics and subsequent f ormation of microplastics (MPs). These MPs in-turn pose a specific threat to ecosystems and their respective inhabitants.This study aimed to evaluate UV induced degradation of conventional packaging material made of polypropylene (PP) homopolymer and amorphous poly(ethylene terephthalate). Plastic sheets were prepared into four different shapes: small circles (6 mm dia.), large circles (12 mm d ia .), small rectangles (8x4 mm), and large rectangles (40x10 mm). Sequential degradation was considered with samples initially degraded solely by UV radiation in air. The experiments were conducted in a UV chamber that offered two levels of irradiance exposure: 65 W/m2 and 130 W/m2. After the initial degradation in air, samples were further exposed to either constant temperatures (25°C or 60°C) or cyclic UV conditions (65 W/m2 or 130 W/m2) while immersed in different aqueous solutions (demineralised water or seawater). Each experimental run commenced for six weeks, and samples were drawn and analysed fortnightly. The physicochemical properties monitored over time were mass, crystallinity, microhardness, and chemical functional groups (carbonyl and hydroxyl). These properties were measured via standard analytical techniques such as precision balance, differential scanning calorimetry (DSC), Vickers microhardness tester, and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy.Results from the initial experiments indicated that UV irradiance proportionally instigated changes in plastic properties. Increased mass loss accompanied by considerable increases in carbonyl index was observed for the PPs. Shape did not significantly affect mass loss or functional group developments. Clear polypropylene (CPP) reflected the most severe degradation, resulting in the most considerable mass loss, increase in crystallinity, an d highest carbonyl content. Overall PPs degraded more than PET; differences were mainly attributed to alternative compositions, with PP having high frequencies of tertiary carbon atoms whilst PET contained stabilising aromatic rings increasing its stability towards photo-oxidative degradation. The peak wavelength sensitivity of PP also almost exactly corresponded to the peak wavelength intensity of the UV lamps used in this investigation. Furthermore, it was suspected that black polypropylene (BPP) contained a UV absorbing additive (carbon black) responsible for shielding its interior from radiation by terminating free radical reactions and converting energy to heat. Results f rom experiments performed with plastic samples immersed in aqueous solutions w ere more irregular. It was concluded that degradation occurred substantially f aster in air than in seawater. The most significant property changes in crystallinity, microhardness, and chemical functionalities were observed for material without any previous degradation history. Samples with previous histories showed more resistance to crystallinity changes. This was attributed to prior exposure weakening the material, presenting crosslinking and structural defects which inhibited polymer chains from realigning into crystalline structures. Carbonyl groups reduced f or material with previous degradation histories. This was due to the following occurrences: (i) changes in surface energy with polymer chains rearranging leaving carbonyl products concealed below the observed surface and (ii) the degraded surface layer eroding, or hydrophilic products dissolvinginto the surrounding solution medium leaving a fresh unexposed layer of plastic being analysed. Solution medium did not have a significant effect on the property changes of untreated material.
Potential and economic impact of renewable energy in improving african rural food processing
(Stellenbosch : Stellenbosch University, 2016-03) Padi, Richard Kingsley; Chimphango, Annie F. A.; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT: Traditional food processing technologies in rural settings of Sub Saharan Africa are characterised by small production scales, labour intensive processes and uneconomical operations, which contribute to high food losses postharvest. Mechanisation addresses some of these limitations although a lack of access to modern energy stands as additional drawback. Hence in order for advancing mechanisation to be feasible, an alternative approach to integrating energy supply into food processing systems is required. Little is known on the cost implications of such mechanisation and alternative energy integration on the profitability of the food processes. The general objective of this study was to investigate the economic impacts of mechanisation and/or bioenergy integration in crude palm oil (CPO), cassava flour (CF) and maize flour (MF) processes. This objective was achieved by developing process models for traditional, semi-mechanised and mechanised processes, with increasing extent or level of mechanisation, in which in-house energy integration was applied. The process/economic models were developed using Microsoft Excel. For each of the referred processes, Base-cases (B/C) entailing conventional energy-mix and corresponding improved-cases (I/C) with potential energy from process residues (in-house energy) were considered. Models of advanced in-house energy schemes were developed in Aspen Plus®. Economics were based on 2014 economic conditions of Ghana. Two funding schemes were assessed: 1. Private investor financing [60% of investment financed by loan (at 24% nominal interest rate) and remaining 40% investment from equity (at 40% nominal interest rate), having weighted nominal (before inflation) discount rate of 30%]. 2. Combinations of grant (at 0% nominal discount rate) and equity (at 40% nominal discount rate) financing (i.e. part of the financing covered by grant and the remaining investment financed by equity from an investor). Feasible advanced energy schemes considered in the I/C scenarios were: electricity/thermal energies from solid biomass residues for the CPO mechanised process, electricity/dryer fuel from anaerobic digestion of cassava peels/cattle dung for the CF semi- and mechanised process and, cob-fired dryer for MF semi- and mechanised drying operations. In the CPO process, there was a decrease in energy demands for the mechanised process at the B/C and I/C levels when compared to the traditional (79.2 and 83.8%) and semi-mechanised (48 and 51%) respectively. Thus an increase in the level of mechanisation was not necessarily associated with an increase in energy savings. In addition, under the private investor financing (nominal discount rate of 30%), only the mechanised process was economically viable with an Internal Rate of Return (IRR) of 47.2% under the B/C scenarios, while the semi- and mechanised processes were the economically viable options for the I/C scenarios with IRRs of 143% and 40.6% respectively. The poor performances of the traditional- B/C and -I/C and semi-mechanised B/C were due to combinations of high capital investment ($0.019 – 0.053/kg) and high production cost ($0.431 – 1.187/kg), as they remained unviable under 100% grant funding. Thus mechanisation is beneficial to the economics at the highest mechanised process level, while in-house energy integration from residues is most promising at the semi- and mechanised process levels. In the CF Process, the energy demand for the traditional process was higher by 37.6, 44.5 and 52.6% (for B/C) and 46.0, 52.0 and 59.0% (for I/C) than the semi-mechanised, mechanised-grating and mechanised-chipping processes respectively. Thus, mechanisation has an energy saving impact on the process. Under the private investor funding (discount rate of 30%), the mechanised chipping process was the only economically viable option (IRR of 36.3%), while the traditional B/C, traditional I/C and mechanised-chipping B/C were promising with IRRs of 16.3, 24 and 24.8% respectively. Under grant-equity funding, semi-mechanised and mechanised-grating processes remained unviable, thus not being able to achieve sufficient cash flows to pay off debt co-financing of new installations. Under the grant-equity financing, the traditional B/C and I/C, and mechanised-chipping I/C processes achieved Net Present Values (NPV) of $22, $60 and $67180 at grant funding of 60%, 40% and 1% respectively (with the remaining funding contributions provided by equity), suggesting their potential viability under grant subsidy. Thus, economic impact of mechanisation and that of in-house energy generation from the residues were inconsistent. The energy demand of the mechanised MF process was higher by 87.3 and 48.0% (B/C) and 89.1 and 51.2% (I/C) than the traditional and semi-mechanised scenarios, respectively. Conclusively, an increase in mechanisation also increased the process energy demands. All B/C scenarios attained negative NPVs and were thus economically unviable. The I/C scenario for the traditional process remained unviable with NPV of -$1854, while semi- and mechanised processes attained IRRs of 18.8 and 132.8% respectively; hence, only mechanised I/C was viable considering the 30% minimum expected IRR. At semi-mechanised I/C, feedstock obtained from farm gates rather than licensed buying companies (LBCs) resulted in production cost savings of 46.2%, while integration of cobs as dryer fuel increased production cost by 25.5%. Sourcing feedstock from farm gates rather than LBCs and using cobs residues as dryer fuel (replacing diesel) in the mechanised I/C process, resulted in production cost savings of 73.2 and 1.7% respectively. The traditional, semi- and mechanised B/C processes remained unviable under 100% grant funding, while semi-mechanised I/C process attained NPV of $1422 at 40% grant and 60% equity financing. Therefore, mechanisation did not improve economic performance; rather feedstock supply chain was the determining factor for profitability of MF processing. Cobs-fuelling dryer was technically viable but most beneficial (economically) to the mechanised process.

Browse

Browsing Masters Degrees (Chemical Engineering) by browse.metadata.advisor "Chimphango, Annie F. A."

Results Per Page

Sort Options