Browsing by Author "Chunilall, Viren."
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Item Beneficiation of sawdust: chemical fractionation of lipophilic extractives.(2019) Badat, Zaakerah.; Sithole, Bishop Bruce.; Stark, Annegret.; Chunilall, Viren.Lipophilic extractives are generally known to be those compounds in wood that cause pitch problems in the pulp and paper industry. However, these compounds are advantageous to the biorefining industries as they contain a selection of valuable components. According to theory like dissolves like non-polar solvents dissolve the lipophilic compounds. In this study it was found that the non-polar solvent, cyclohexane, as a mixture with a polar solvent, acetone or ethanol, showed better extracting abilities as opposed to pure non-polar solvents. Many past researches looked at extraction from pine sawdust, but not specifically focussing on the lipophilic extractives and its composition, making it difficult to compare this work with others. This study focusses on the viability of solid-liquid extractions on pine sawdust residues, of various ages, for the potential conversion of its useful compounds to value-added products. A potential product is the conversion of α-pinene to pine oil. Alpha pinene is the main terpene contained in pine wood sawdust, and pine oil is known to be a product with various uses in various industries. However, it is currently not locally produced. When carrying out solvent extractions, it is important to know the composition of the extracts and not only focus on the total extractive contents. In this study, the terpene contents in the extracts were closely studied as it is seen to contain components that could be used to produce the most valuable compounds. Experiments were conducted to determine the effects of operating variables such as; temperature, extraction time, extracting solvents, particle size as well as the effect of storage time on the composition of the extracts. A preliminary study was conducted using a 6-hour extraction time. The results produced a maximum of 1,75% α-pinene, and a maximum of 3,7% of the total terpene content of the extractives, which is a significant but low quantity of terpenes. The ASE extraction method uses high temperatures and pressures and allows for extraction to occur at up to an hour. Results obtained indicated that shorter extraction times provide a marginally higher quantity of terpenes in the extracts. Thus, selecting time as a variable parameter was applied in Section 4.3 and the results validated the extraction over shorter time periods, for extracting more value from the sawdust residue. In Section 4.3, the extracting solvent and the particle size was also investigated. After various experiments, the optimised extraction conditions were determined as being: a 2-hour extraction time, 3:1 cyclohexane-ethanol (v/v) as the extracting solvent and 375-micron particle size. The temperature of the solvent was investigated in Section 4.5, the kinetic study. It is required that the temperature be close to the boiling point of the solvent, as when the temperature is lower, a slightly lower terpene content is noticed. On the other hand, when the temperature is greater than the boiling point, the terpenes are decomposed. 3:1 Cyclohexane-ethanol (v/v) as an extracting solvent, requires a maximum temperature of 80℃ after which components of the extract begin to decompose. The kinetic study enabled the development of a model equation that could determine concentrations at any time. The effect of storage time was investigated during the seasoning study. This however, was seen to have no significant impact on the overall extraction results. Based on the various experiments conducted, the maximised terpene yield can be extracted at a 2-hour extraction, using 3:1 cyclohexane-ethanol (v/v) as the extracting solvent and grinding the sawdust residues to a 375-micron particle size.Item Establishing a bioconversion process for the production of succinic acid using industrial feedstocks.(2022) O’Brien, Frances Faith.; Sithole, Bishop Bruce.; Chunilall, Viren.; Ramchuran, Santosh Omrajah.One of the leading challenges of the current global situation is the decline of non-renewable, fossil fuels. Due to this rapid depletion, there is a shift towards replacing petrochemical products with equivalent, ideally superior bio-based substitutes. The bio-chemical of interest that was studied in this work is bio-succinic acid which is considered a platform chemical. Bio-based procedures have the attractive advantage of potentially obtaining a high-value product from an underutilised product/waste stream. In this dissertation, the industry that was focused on was the sugar sector, this vital industry is under pressure it is therefore crucial that alternative revenue avenues are identified. A literature study highlighted the importance of succinic acid, detailed both the upstream and downstream literature methods and addressed the impact that biochemical processes could have within South Africa. Small scale flask studies were conducted using succinate-producing microorganisms, on synthetic C5 and C6 sugar medias, namely xylose and glucose. The results from these studies showed that L. paracasei and C. glutamicum were the top performing strains on the C6 sugar (glucose) media and as a result these strains were then grown on C6 industrial material, namely sugarcane juice and molasses. These flask studies concluded that C. glutamicum grown on molasses was the superior combination, with a succinic acid concentration of 18.81 ± 0.75 g.L-1 and a productivity of 0.67 ± 0.07 g.L-1.hr-1 being achieved. The process was then successfully scaled up to 30L reactors where a succinic acid concentration of 28.89 ± 3.57 g.L-1 was reached, which was higher than the ‘ideal’ glucose reactor run. Downstream processing of the harvested broth was conducted using the precipitation method. Process development was performed, and the final method resulted in a final succinic acid recovery of 54.47 ± 14.02 % and 58.20 ± 2.24 % for the glucose and molasses-based medias respectively. In conclusion, molasses has the potential as an alternative carbon source in the production of succinic acid. The biochemicals sector is still a novel concept within South Africa, and as this platform gains more traction such studies show the ‘value’ of industry’s waste/by-product streams, especially for the sugar industry.Item Laser and ultrasound radiation pretreatment of cellulose in dissolving wood pulp.(2017) Ocwelwang, Atsile Rosy.; Sithole, Bishop Bruce.; Ramjugernath, Deresh.; Chunilall, Viren.Dissolving wood pulp (DWP) refers to wood extracted, chemically refined bleached pulp that comprises more than 90% pure cellulose. This type of pulp is mainly utilised for the production of various cellulose derivatives such as rayon, cellophane, cellulose ethers and cellulose esters. Production of these valuable products is achieved by dissolution of DWP in chemical solvents such as sodium hydroxide (NaOH) and carbon disulphide (CS2). However, cellulose dissolution is not easily achievable due to the strong hydrogen bond interactions that give this biopolymer its highly ordered crystalline structure. High cellulose crystallinity limits the accessibility and chemical reactivity of this biopolymer. Various forms of pretreatment techniques have been developed to solve this problem. The primary aim of the pretreatment is to disrupt the rigid crystalline structure of cellulose, and this increases its structural accessibility and chemical reactivity. However, most pretreatment techniques have drawbacks such as being energy intensive, costly, corrosive, posing risks to personnel operating them, and not being readily accessible. For example, gamma ray irradiation has been shown to be an effective pretreatment technique for cellulose and other lignocellulosic materials, but it is a costly technology. For this reason, research into environmentally friendly and profitable pretreatment techniques is ongoing. This study aimed to evaluate the effect of two procedures, namely, ultrasound and laser irradiation, as possible pretreatment techniques for cellulose activation. Ultrasound irradiation is a conventional method that has been used for pretreatment of a wide range of polymeric materials, whereas the use of laser irradiation as a pretreatment technique for cellulose activation has never been reported. Therefore, using lasers as a pretreatment for activation of DWP with the aim of modifying the cellulose structure to improve its chemical reactivity is a novel aspect of this thesis. The effects of these two pretreatment techniques on the structure of cellulose were studied and compared. The effects of the two techniques were investigated separately in two parts. The first part focused on the effect of ultrasound irradiation on the structure of cellulose, and the dissolution behaviour of the ultrasonicated pulp samples in aqueous NaOH solution. The second part evaluated the effect of laser irradiation on the structure of cellulose, and the chemical reactivity of the pretreated cellulose pulp samples was measured using the Fock test method. A range of analytical techniques was employed to characterise the pretreated samples to evaluate the structural modifications that resulted from the pretreatments. Size exclusion chromatography with multi-angle light scattering (SEC-MALS) analysis was used to study the molecular structural properties of cellulose. X-ray diffraction (XRD), and Solid-state CP/MAS 13C-NMR were used to investigate the crystalline structure of cellulose and to measure its degree of crystallinity (CrI). Ultrastructural and morphological properties of cellulose were also studied by atomic force microscopy (AFM), scanning electron microscopy (SEM), and morphological fibre analyser (MorFi). Untreated DWP samples were used as control samples for all procedures and analysis conducted in the study. In the first part of this study, DWP samples were pretreated with ultrasound irradiation and subsequently dissolved in aqueous NaOH solution. SEC-MALS results showed a shift in average molar weight (Mw) from high to lower region after ultrasonication. Broadening of the molecular weight distribution (MWD) was displayed by increase in polydispersity index (PDI). A decrease in Mw was also observed with increasing pretreatment time; this confirmed the effect of the ultrasonic pretreatment on the molecular structure of cellulose. SEC-MALS analysis of the ultrasonicated and alkali treated samples displayed different dissolution behaviour compared to the control, and the changes in the MWD data did not follow any trend relative to treatment time. XRD results indicated that ultrasound irradiation had minor or no effect on the degree of cellulose crystallinity (CrI). However, treatment of the ultrasonicated pulp samples with aqueous NaOH significantly decreased the CrI. This reduction in CrI indicates that alkali treatment transformed natural cellulose to regenerated cellulose. A CrI decrease of more than 50% was also observed for the samples treated for 60 minutes (alkcell-UT60 min). AFM ultrastructural results revealed that ultrasonication did not induce visible changes on the surface of the S2 layer. An overall decrease of lateral fibril aggregate dimensions (LFAD) was observed after ultrasound irradiation, but the reduction did not show a linear relationship with increasing treatment time. Fibre distribution and dimensions results from the MorFi analyser showed that with prolonged treatment time, the number of fibres in solution increased, average fibre length decreased, while the average fibre width did not display significant changes. SEM surface morphology results showed that after ultrasonication the surface of the fibres became smooth, and there was less or no fibrillation. SEM analysis revealed that after alkali treatment the surface of the fibres displayed folds and trenches which ran parallel to the length of the fibres. This is an indication of an increase in the surface area of the fibres due to the treatment with an alkali solution. Moreover, the fibres appeared compact and agglomerated. In the second part of this study, laser radiation was used for pretreatment of DWP samples. The pretreatment caused visible morphological and molecular changes in the structure of cellulose. SEC-MALS results demonstrated that laser irradiation decreased the average Mw of the cellulose polymer and caused noticeable modifications on the molecular structure of this biopolymer. The PDI also showed increase; this rise in PDI is indicative of the size distribution of the Mw and the heterogeneity of the cellulose chain lengths as a result of the pretreatment. XRD results demonstrated that laser irradiation disrupted the crystalline structure of cellulose; an overall significant decrease in CrI was noticed for all the laser irradiated samples. NMR characterization of the irradiated samples also displayed a decline in CrI. SEM characterization results illustrated that laser pretreatment disrupted the morphology of the cellulose fibres and created porous cavities on the fibre surfaces. AFM images for laser irradiated samples also displayed similar features. The S2 layer within the cross-sections of the samples irradiated with Nd:YAG laser at 266 nm and 355 nm also had small pores and dark areas between the fibril aggregates which represent the less stiff or potential accessible regions. Calculated LFAD results also confirmed these observations in that the data displayed a noticeable decline in LFAD after laser irradiation. Finally, the Fock test results showed that the laser pretreatment caused a linear increase in cellulose reactivity with increasing irradiation time. From the results and observations presented in this study, it can be concluded that laser radiation pretreatment caused noticeable structural disruptions on the structure of cellulose compared to ultrasound irradiation. It disrupted and damaged the surface morphology of cellulose and further caused a significant degradation of the molecular structure. Moreover, increase in cellulose reactivity as measured by the Fock test method was observed in all samples pretreated with lasers. The highest reactivity increase of more than 35% was obtained in samples irradiated with the Nd:YAG laser at a wavelength of 266 nm compared to Nd:YAG and CO2 lasers at 355 nm, and 10.6 μm respectively. This observation showed that laser wavelength was influential in cellulose modification compared to laser power. Furthermore, the increase confirmed that laser radiation pretreatment reduced the cellulose Mw and disturbed its crystalline structure thus enhancing its accessibility and reactivity to chemical solvents. Therefore, the novel aspect of the thesis is that: Pretreatment of DWP with laser radiation modified the structural features of cellulose, and this led to an overall cellulose reactivity increase of about 20%. Consequently, this should result in a reduction of dosages of chemical reagents used for induction of cellulose reactivity and processing. The use of lasers for cellulose pretreatment could be a more affordable option compared to the conventional high energy radiation sources because they are less expensive and readily accessible.Item Pyrolysis-gas chromatography/mass spectrometry study of chromophores in dissolving wood pulp.(2018) Dladla, Vezekile Princess.; Sithole, Bishop Bruce.; Chunilall, Viren.; Ramjugernath, Deresh.Dissolving wood pulp (DWP) is bleached wood pulp that contains high cellulose content, typically >95%. The bleaching is done to remove remnants of lignin and hemicelluloses that are not necessary for the final DWP. The pulp is chemically processed to make high-grade products such as speciality papers, viscose fabrics, and microcrystalline cellulose used in applications such as textile fibres, fillers in pharmaceutical tablets, or as a thickener in food additives, and manufacture of paints. Frequently, the fully bleached DWP exhibits an unwanted yellowish haze. This phenomenon results in loss of brightness in the pulps and is referred to as brightness reversion. Remnants of polysaccharides on DWP are believed to give rise to chromophores responsible for the brightness reversion. Such reversion in brightness is viewed as an early sign of ageing or deterioration of the pulp. The impact of chromophores on the quality of DWP is a pressing issue in the global pulp and paper industry. Thus, identification of chromophores in the pulps is an important aspect to solving this problem and efforts have been made to develop techniques for identification of the chromophores responsible for brightness reversion. For example, an elegant method, termed chromophore release and identification, has been developed. However, application of the methodology for analysis of chromophores in pulps is tedious and long. It takes, on average, seven days to generate results, and a large quantity of pulp is required for the analysis. Such a long processing time is not ideal for industrial applications where time is of the essence. Hence, in this study, a novel methodology that allows for rapid and accurate characterization of chromophores directly from pulp fibres has been developed. The method entails direct analysis of chromophores on pulps without pre-extraction of chromophores, and results are obtained in less than an hour. The methodology entails the use of analytical pyrolysis combined with gas chromatography/mass spectrometry (Py-GC/MS) for direct detection and identification of chromophores in DWP. To develop the method, selected fully bleached DWP samples were induced for brightness reversion and then analysed by Py-GC/MS and any chromophores present were identified by mass spectrometry. Probable compounds that could have contributed to the brightness reversion were also induced for brightness reversion and analysed to ascertain any similarities with the pyrograms of the brightness reversed DWP samples as well as mass spectral identities of the compounds. The results showed that the pulps that were induced for brightness reversion contained relatively higher amounts of chromophores than the original pulps, with ketones and furan-type compounds (originating from degraded cellulose and remnants of the hemicelluloses) being the major chromophoric groups. Analysis of data on pulps with varying brightness reversion values did not show correlation with the relative amounts of chromophores detected by Py-GC/MS. The results confirmed literature reports that brightness is not a good indicator of the concentration of chromophores in pulps. The developed Py-GC/MS method was then used to identify chromophores in DWP samples produced from the industry and the laboratory. Considering that the industry-produced DWP was from a wood furnish comprised of a mixture of wood species, it was essential to understand how the different clones/species in the wood furnish influenced the formation of chromophores. the results showed that different wood species contained the same type of chromophores, with furantype compounds and conjugated ketones being the major groups of compounds detected. Pulps were sampled from different unit operations in a mill to ascertain the profiles of chromophores along the mill process. Additionally to the industrial in-process pulps, a number of single clone acid bi-sulphite pulps were bleached in the laboratory to produce pulps (in-process) that were also analysed for chromophore content using Py-GC/MS. The main groups of chromophores identified in all the samples were still furans-type compounds and conjugated ketones. Wet chemical analysis of in-process pulps showed that the remnants of hemicelluloses and degraded cellulose in the pulps have a significant impact on the formation of the ketones and furan-type compounds. Finally, the developed Py-GC/MS method was tested on other pulps (besides DWP) that contained higher amounts of lignin (viz., the newsprint and kraft pulp). This was done to ascertain if the method would apply to other pulps besides DWP. As expected, the results showed that newsprint contained very high amounts of chromophores due to lignin whereas kraft pulps exhibited smaller amounts of lignin-type pyrolysis products. Thus, lignin was the major cause of brightness reversion in pulps that contain lignin and residual amounts of lignin. Overall, the major chromophoric compounds identified in DWP were conjugated ketones and furan-type compounds. These compounds originated from remnants of hemicelluloses and degraded cellulose in the pulps: this agrees with literature reports on the origin of chromophores in cellulosic materials. The Py-GC/MS is a novel tool for rapid and direct analysis of residual chromophores in fully bleached and in-process DWPs and can be utilised for rapidly identifying the presence and chemistry of residual chromophores in DWP. The technique is currently being used to monitor the quality of industrially-produced DWP from different pulp mills.Item Structure, accessibility and 'reactivity' of cellulose I as revealed by CP/MAS13 C-NMR spectroscopy and atomic force microscopy.(2009) Chunilall, Viren.; Bush, Tammy.; Larsson, Per Tomas.; Kindness, Andrew.The dissolving pulps used in this thesis are high-grade cellulose pulps, with low amounts of hemicellulose, degraded cellulose and lignin, produced by acid bi-sulphite pulping of a fast growing South African hardwood Eucalypt clone. Microcrystalline cellulose (MCC) grade, viscose grade and cellulose acetate grade dissolving pulp were produced using a 4 stage bleaching process. MCC, viscose and cellulose acetate are the cellulose derivatives of 91% α-cellulose, 92% α-cellulose and 96% α-cellulose respectively. The key properties of the dissolving pulp considered for cellulose derivatisation are: (1) Structure (2) Accessibility and (3) ‘Reactivity’. The ‘reactivity’ depends to a large extent on the supra-molecular structure of cellulose I. Supra-molecular structure deals with the arrangement of cellulose I molecules into cellulose fibrils which then make up the cellulose fibril aggregate. The accessibility of cellulose I depends on the surface area, as determined by the size of the cellulose fibril aggregates, that are accessible; the structure of the cellulose molecules, which will determine which hydroxyl groups are accessible; and the size and type of reagent used during derivatisation. Supra-molecular changes in cellulose fibril aggregation of cellulose I, in hardwood acid bi-sulphite pulp, during bleaching and drying were studied using Atomic Force Microscopy (AFM) and Cross-polarization/Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance Spectroscopy (CP/MAS 13C-NMR – Solid state NMR) in combination with spectral fitting. There was a marked increase in cellulose fibril aggregation (i.e. supra-molecular structure) during bleaching of hardwood acid bi-sulphite pulp using 96% α-cellulose conditions. In contrast there was no increase in cellulose fibril aggregation pulp bleached using 91% α-cellulose and 92% α-cellulose bleaching conditions. An increase in hemicellulose and degraded cellulose / short chain glucan was shown to correlate with a decrease in cellulose fibril aggregation recorded using solid state NMR. Further changes in supra-molecular structure were noticed when each of the dissolving pulp samples were dried. First time drying of hardwood acid bi-sulphite pulp samples induces a significantly different degree of irreversible cellulose fibril aggregation in the 92% α-cellulose and the 96% α-cellulose pulp samples. The irreversible increase in cellulose fibril aggregation correlates with the estimated amount of hemicellulose and degraded cellulose / short chain glucan present in the pulp. The percentage increase in cellulose fibril aggregation upon drying is as follows: 96% α-cellulose > 92% α-cellulose > 91% α-cellulose. Hemicellulose and degraded cellulose / short chain glucan are among the wet chemical properties that influence cellulose fibril aggregation and the presence in dissolving pulp samples could provide steric hindrance preventing the aggregation of fibrils. Reactivity studies were carried out on the 91% α-cellulose, 92% α-cellulose and 96% α-cellulose grades of dissolving pulp. During 91% α-cellulose reactivity studies, there was no relationship between cellulose fibril aggregation, acid hydrolysis or MCC preparation. Other possible techniques for 91% α-cellulose reactivity evaluation such as the degree of polymerization (DP) determination using AFM have been discussed. Size exclusion chromatography with multi-angle laser light scattering detection was shown as a more suitable method of estimating the reactivity of 92% α-cellulose pulp samples. 96% α-cellulose reactivity studies were carried with the aid of a model system consisting of the acetylation of high purity pulp samples viz. cotton linters cellulose and 96% α-cellulose. Results indicate that the initial reaction rate constant is proportional to the specific surface area for the two cellulose pulp samples showing that specific surface area is directly related to initial reactivity of the performed acetylation. This work has shown that it is possible to control the cellulose fibril aggregation and hence specific surface area in laboratory produced 91% α-cellulose, 92% α-cellulose and 96% α-cellulose by the method in which the pulp is dried. Thus controlling cellulose fibril aggregation can probably be one viable route for controlling the initial reactivity of dissolving pulp towards acetylation.