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Theses and dissertations (Applied Sciences)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/6

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Start date: 2021Subject: search.filters.subject.Extraction (Chemistry)

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    A comparative study of supercritical fluid extraction and accelerated solvent extraction of lipophilic compounds from lignocellulosic biomass
    (2022-09) Khanyile Andile; Sithole, B.B.; Paul, Vimla; Andrew, Jerome Edward
    Lipophilic compounds are non-structural, heterogeneous compounds rich in terpenes, sterols, fatty acids, hydrocarbons, and glycerides. They have found widespread uses in different industries, such as the pharmaceutical, medical, cosmetic and nutraceutical sectors. They are typically extracted from wood using traditional techniques such as solvent extraction hydro- and steam- distillation. However, these techniques have several drawbacks such as long extraction times, high energy consumption, extensive solvent use and degradation of thermosensitive compounds, which are highly volatile. In this study, supercritical fluid extraction (SFE) and accelerated solvent extraction (ASE) were evaluated to extract lipophilic compounds from lignocellulosic biomass such as pinewood sawdust and Cannabis Sativa L. Their advantages of using low amounts of solvent, short extraction times and high selectivity allow them to be used as an alternative extraction technique to traditional methods. Moreover, SFE uses carbon dioxide, which is safe, cheap and readily available, and it does not alter the structure of the compounds. In contrast, ASE uses elevated temperatures and high pressures to prevent the evaporation of highly volatile compounds. In order to solve challenges from both an economic and an environmental perspective, the interaction of process conditions on lipophilic compounds extraction efficiency was modelled and optimized using Response Surface Methodology (RSM) and BoxBehnken design (BBD). The extraction variables optimized for pinewood sawdust compounds were, SFE: co-solvent (ethanol) flow rate (1-2 ml/min), carbon dioxide (CO2) flow rate (1-3 ml/min), Temperature (40-60 °C) and pressure (200-300 bar), and for ASE: static time (10-15 mins), static cycle (1-3) and temperature (80-160 °C). The process parameters were optimized, and the experimental data was modelled using RSM for statistical analysis of the BBD extraction process. The experimental data's quadratic polynomial models gave a coefficient of determination (R2 ) of 0.87 and 0.80 for ASE and SFE, respectively. The optimum conditions of ASE were temperature (160 °C), static time (12.5 mins), and static cycle (1), which resulted in a maximum yield of 4.2%. The optimum SFE conditions were temperature (50 °C), pressure (300 bar), CO2 flow rate (3.2 ml/min), and a 2 ml/min co-solvent (ethanol) flow rate that yielded 2.5% lipophilic compounds. The extraction efficiency of pinewood sawdust lipophilic compounds with ASE was higher compared to the SFE. Although ASE uses high temperatures that may degrade thermolabile compounds, the short extraction times may work in their favor since the extracts are not exposed to high temperatures for long periods. SFE uses low temperatures and long extraction times compared to ASE. Several properties affect the extraction efficiency, such as volatility, dissolving power, solubility, and fluid density of the extracting solvent. The extraction efficiency of lipophilic compounds by SFE may be affected by the supercritical fluid's solubility and differences in densities at different pressures. In ASE, the high yields were influenced by the high polarity of the solvent mixture and temperature with a short extraction time. The extraction variables optimized using RSM for Cannabis Sativa L. for SFE were pressure (200-300 bar), co-solvent (ethanol) flow rate (1-2 ml/min) and CO2 flow rate (1-2 ml/min). The R2 was determined to be 0.9108. The optimum conditions were 300 bar pressure, 1 ml/min co-solvent (ethanol) flowrate, and 2 ml/min CO2 flowrate, which gave a maximum yield of 88%. The high efficiency observed was brought by the increase in the flow rate of CO2 at high pressures, which reduces the mass transfer resistance, while the cosolvent enhanced the solvating power of CO2. The ASE had a high extraction efficiency for the pinewood sawdust lipophilic compounds. However, the method's selectivity was very low according to the results obtained by pyrolysis gas chromatography-mass spectrometry (Py-GC/MS). The thermosensitive compounds, such as terpenes, decreased from 2.01% to 1.69% upon the addition of Tetramethylammonium hydroxide (TMAH). The initial concentration of terpenes was 7.21% in pinewood sawdust by SFE. Upon the addition of TMAH, the concentration of terpenes of the pinewood sawdust decreased to undetectable levels. The initial concentration of the terpenes of Cannabis Sativa L. was 14.29% and decreased in the presence of TMAH to 0.39%. The Fourier Transform Infrared Spectroscopy (FTIR) confirmed the presence of lipophilic compounds functional groups and a fingerprint region of lipophilic compounds of pinewood sawdust and Cannabis Sativa L. Thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) showed high thermal stability (250 – 400 ℃). This research demonstrated the ability of SFE to extract lipophilic compounds from pinewood sawdust Cannabis Sativa L.
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    Synthesis of lactic acid using hydrogen cyanide extracted from cassava (Manihot esculenta) leaves
    (2022-05) Ilunga, Monga; Paul, Vimla; Zinyemba, Orpah; Muniyasamy, Sudhakar
    Racemic lactic acid (2-hydroxypropanoic acid) has gained interest in the food and non-food industries and in producing biodegradable and biocompatible lactic acid polymers. Although racemic lactic acid is conveniently synthesised by chemical synthesis via the DL-lactonitrile route, it can also be produced by the fermentation process provided that suitable microorganisms and substrates are used. However, regardless of the sustainability issues associated with the fermentation process, it is the preferred production method since the chemical process relies on fossil fuel resources. In this context, this study aims to extract hydrogen cyanide (HCN) from cassava (Manihot esculenta Crantz) leaves and then use it to chemically produce racemic lactic acid. Cassava leaves were chosen as a natural source of HCN since they release 20 times more HCN than the tubers. HCN is produced by endogenous enzymes (linamarase and hydroxynitrile lyase) hydrolysing the cyanogenic glucosides (linamarin and lotaustralin). Following 120 minutes of maceration at 30 °C, the released HCN was extracted for 45 minutes under vacuum at 35 °C – 45 °C and collected in 400 mL of 5.104 mol/L sodium hydroxide (NaOH) solution (absorbing solution) to give sodium cyanide (NaCN) solution. The extraction process was repeated until saturation of the absorbing solution was achieved. The final concentration of NaCN solution determined by the alkaline picrate method was found to be 4.0421 mol/L. Furthermore, the sodium carbonate (Na2CO3) and residual NaOH content in control and sample sodium cyanide solutions were also determined. The Na2CO3 content was 0.72 % in the control NaCN solution and 2.49 % in the sample NaCN solution. The residual sodium hydroxide content was 2.61 % in the control sodium cyanide solution and 4.20 % in the prepared sodium cyanide solution. 79.241 g of NaCN crystals (0.19 % yield, green NaCN) were obtained from 42.750 kg of fresh cassava leaves. The suggested approach was successful in preparing NaCN, as evidenced by X-Ray Diffraction (XRD), Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), and Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM-EDS) results. Control and green NaCN both contained sodium carbonate impurities, as shown by these spectral techniques. Titration tests revealed that the latter was 0.61 % and 2.29 % in control and green NaCN, respectively. In addition, titration studies indicated that the residual NaOH content in control NaCN was 1.63 % and 4.68 % in green NaCN. The high carbonate content can be explained by the reaction between residual sodium hydroxide and atmospheric CO2. Reproducibility and repeatability tests were done to evaluate the reliability of the hydrogen cyanide extraction method. Racemic lactic acid was synthesised using a four-step process. 73 mL of DL-lactonitrile (2- hydroxypropanenitrile) (81.1 % yield, 59.7 % pure) was prepared by reacting 75 mL of acetaldehyde with hydrogen cyanide generated in-situ from green sodium cyanide (62.190 g in 150 mL of Milli-Q water) in the presence of 37 % hydrochloric acid (100 mL). 35 mL of crude racemic lactic acid (84.1 % yield, 14.9 % pure) was prepared by hydrolysing 40 mL of DLlactonitrile with 8 mol/L hydrochloric acid (40 mL). Crude racemic lactic acid underwent a two-step purification process in the presence of concentrated sulphuric acid (5 mL), used as the catalyst. 35 mL of crude lactic acid was first esterified with excess methanol (50 mL) to produce 32 mL of methyl DL-lactate (methyl 2-hydroxypropanoate) (71.6 % yield, 46.1 % pure). The ester was then hydrolysed with excess water (20 mL) to give 22 mL of purified racemic lactic acid (88.0 % yield, 56.0 % pure). The identity of the synthesised products was confirmed by comparing them against control samples using 1H Quantitative Nuclear Magnetic Resonance (1H QNMR) and ATR-FTIR. Their purity was determined by 1H QNMR, using dimethylformamide as the internal standard. The overall yield of synthesised racemic lactic acid was 43.0 %.
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    Optimization of extraction techniques for the isolation and pre-concentration of pharmaceuticals in aquatic environments
    (2021) Sigonya, Sisonke; Mdluli, Phumlane Selby; Chimuka, Luke
    The occurrence of pharmaceuticals in South African aquatic environments has been reported in several studies. However, most of these reports focused on the occurrence of organic compounds in wastewater and surface water. There are very few studies reporting the presence and concentration of these compounds in seawater and coastal areas. Further, most studies have looked at only on one season. This study focussed on the optimisation of a SPE extraction method using Bond Elut Plexa cartridges for the identification and quantification three nonsteroidal anti-inflammatory drugs (NSAIDs), three antiretroviral drugs (ARVs) and a lipid regulator in coastal area of Durban city, South Africa covering four seasons. The optimised SPE conditions were as follows: 500 mL sample volume and at pH 5.8, 5 and 5 mL as conditioning and elution volumes, respectively. The flow rate ranging from 5 to 10 mL/min 10 and 5 mL/min as sample and elution flow rates. The extracted compounds were qualitatively and quantitatively detected by a high-performance liquid phase chromatographic instrument coupled to a photodiode array detector (HPLC-PDA). The recoveries ranged from 62 -102% with RSD values of 0.56 to 4.68% respectively for the determination of emtricitabine, tenofovir, naproxen, diclofenac, ibuprofen, efavirenz, and gemfibrozil. The analytical method was validated by spiking estuarine water samples with 5 µg L-1 of a mixture containing the target pharmaceuticals and the matrix detection limits (MDL) were established to be 0.62- 1.78 µg L-1 for the target compounds. The optimized method was applied to seasonal monitoring of pharmaceuticals at chosen study sites from winter and spring of 2019 and summer and autumn of 2020.The sum of emerging pollutants (ƩEP) were calculated based on each study site. The influent of the Kingsburgh WWTP (EFK) had the highest ƩEP of 144.88 µg L-1 in winter between the two wastewater treatment plants area in this study. The Northern WWTP influent (INN) had a total ƩEP of 117.11 µg L-1 in autumn, the Kingsburgh WWTP effluent (EFK) had a concentration 63.8 µg L-1 in autumn and a concentration 63.8 µg L-1 in summer and the Northern (EFN) had a total ƩEP of 43.97 µg L-1 in winter. A comparison between UMgeni (UR) and Kingsburgh river (KR) showed that the KR had the highest concentration of total ƩEP of 22.66 µg L-1 and UR with the total ƩEP of 18.3 µg L-1 both in winter and spring, respectively. The seawater EPs Blue Lagoon (BL) had the highest ƩEP of 46.75 µg L-1 in spring, subsequently Warner Beach bottom (WBB), Glen Ashley (GA) and Warner Beach top (WBT) with concentrations of 24.96 µg L-1 in summer, 13.29 µg L-1 in spring and 6.94 µg L-1 in autumn, respectively. Estuarine EPs had concentrations of 37.9 µg L-1 and 20.97 µg L-1 for Warner beach estuary (WE) and UMgeni estuary (UE) in winter. WBE having the highest concentration between the two. This showed a significant variation on the presence of these pharmaceuticals in different season.