PhD Theses (Energy Science and Engineering)

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Browsing PhD Theses (Energy Science and Engineering) by Subject "Biodiesel"

Now showing 1 - 4 of 4
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    Microalgal Bio-refinery: Process optimization and intensification for production of lipids and other value-added products
    (2021) Singh, Neha
    A potential and promising green liquid fuel is biodiesel, which can be blended with petroleum diesel. The new and economic alternate feedstocks for biodiesel include microalgal lipids. Simultaneously, microalgae are promising producers of various other biofuels, such as bioethanol, glycerol and biomaterials. This thesis has assessed the potential of a natural freshwater microalgal strain for bio-refinery that produces biodiesel, bioethanol, b-carotene and glycerol. A native freshwater microalgae was isolated and was named Tetradesmus obliquus SGM19. The preliminary optimization of the growth conditions was done. The strain exhibited high lipid (28%), carbohydrate (24%) and protein (42%) concentrations, and was also rich in pigments. The growth cycle of T. obliquus SGM19 was further optimized using statistical experimental design for simultaneous production of lipid and β-carotene. Application of 33 kHz and 1.4 bar ultrasound at 10% duty cycle was revealed to enhance the lipid and β-carotene yields by 34.5% and 31.5%, respectively. Kinetic analysis of substrate and product profiles in control and test experiments revealed both lipid and β-carotene to be growth-associated products. Consistently higher NAD(H) concentrations were observed for sonicated samples; indicating faster metabolism. The viability of ultrasound-exposed microalgal cells (assessed with flow cytometry) was >80%. Further, the lipid in T. obliquus SGM19 biomass was subjected to transesterification for producing biodiesel. The biodiesel synthesis process was optimized in two steps, viz. (1) optimization of the conditions/pretreatment of biomass, and (2) statistical optimization of transesterification process parameters. In-situ base-catalyzed transesterification of the lyophilized biomass had the highest biodiesel yield of 37.5% (w/w DCW). Next, statistical optimization of transesterification parameters (catalyst loading, methanol to biomass ratio, temperature and reaction time) was done. Finally, intensification of transesterification was attempted by replacing mechanical agitation of reaction mixture with sonication. Sonication reduced the overall activation energy of transesterification process from 24.66 to 19.82 kJ/mol. Furthermore, the FAME profile for ultrasound-assisted transesterification process was characterized with GC-MS. Major fatty acids present in the lipids were palmitic, heptadecanoic, linoleic, linolenic and arachidic acids. The biodiesel properties were found to be as per ASTM D6751 standards. Finally, the T. obliquus SGM19 biomass was subjected to sequential treatment for extraction and synthesis of b-carotene, biodiesel, bioethanol and glycerol. It was observed that the in-situ transesterification resulted in higher yields of end-products in comparison to 2- step transesterification and were: 0.11 g β-carotene, 29 g biodiesel, 2.6 g glycerol and 12 g bioethanol. This thesis has thus presented a comprehensive study on lab-scale processes of cultivation and growth of a wild microalgal strain, extraction of lipids and nutraceutical (b-carotene), and further synthesis of green biofuels like biodiesel and bioethanol, and finally intensification of these processes with external stimulus of ultrasound.
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    Overexpression of AtDGAT1 and metabolome analysis of Jatropha Curcas L. for enhanced oil in seeds and leaves
    (2016) Maravi, Devendra Kumar
    The diminishing fossil fuel stock and soaring international crude oil price have renewed the interest in the alternative source of fuels. Oil from oilseed crops that are largely in the form of triacylglycerol (TAG) are the promising source of renewable supply of fuels in the form of biodiesel. Jatropha curcas L is an important non-edible oilseed crop which received worldwide attention as a biodiesel feedstock. Despite the significance of Jatropha seed oil as a potential source of biodiesel, not much research efforts have been made through breeding or transgenic approaches to improve its seed oil quality for sustainable biodiesel production. Transgenic approaches offer immense opportunities to improve oil content and quality through manipulation of oil biosynthetic pathway in both seed and leaves.
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    Sustainable way of producing biodiesel using oleaginous Tetradesmus obliquus KMC24
    (2022) Roy, Madonna
    Oleaginous microalgae are deemed as cell bio-factories for biodiesel production. However, the lower biomass and lipid productivity, along with the high cost of downstream processing such as harvesting, lipid extraction and conversion to biodiesel makes microalgae-based biodiesel production system economically unviable. To address this challenge, the present study aims to develop a sustainable biodiesel production system by employing various strategies such as selection of potential microalgal strain, modification of cultivation mode, optimization of culture conditions, development of low-cost harvesting and lipid to biodiesel conversion techniques. In the present study, a novel microalgae, Tetradesmus obliquus KMC24 was isolated and exposed to nutrient stress (nitrogen and/or phosphorus) for a short period via two-stage cultivation to obtain maximum biomass and lipid. The effect of nutrient starvation on the morphology, biomass concentration, photosynthetic activity, and biochemical composition of Tetradesmus obliquus KMC24 was investigated. Two days nitrogen-starved cells (-N2) were able to accumulate the maximum amount of lipid (39.93 ± 0.44%) without affecting the biomass concentration (2.15 ± 0.04 g L-1). During nitrogen (-N) and phosphorus (-P) starvation, photosynthetically fixed carbon pool was diverted to lipid biosynthesis. Pearson's correlation analysis suggested that stress-induced lipid accumulation is associated with an increased intracellular reactive oxygen species (ROS) level. The ROS fluorescence intensity was highest in –N2 cultures (17051.49 ± 93.15 a.u.), suggesting highly oxidative stress-tolerant cells. A high degree of fatty acid saturation was obtained under nitrogen starvation as compared to other culture conditions. Biodiesel properties such as cetane number, saponification number, and iodine value were improved under nitrogen starvation. High-energy requirement for harvesting microalgal biomass poses a major challenge during downstream processing. Addressing this challenge, the present study developed a sustainable and efficient harvesting technique by valorizing waste eggshell. Herein, waste eggshell-derived bioflocculant was used for harvesting T. obliquus in a circular bioeconomy approach. It was found that 120 mg L−1 bioflocculant can flocculate 98.62 ± 0.43% of T. obliquus cells within 25 min at optimal pH 4.0 and temperature 35 °C. The influence of bioflocculant concentration, pH and temperature on zeta potential was evaluated to understand the flocculation mechanism. Microscopic and FESEM-EDX images were analyzed to evaluate the microalgal structural changes. Adsorption mechanism of bioflocculant over the microalgal cells was determined by performing adsorption kinetic studies. Pseudo-second order kinetic model was a suitable fit for the data obtained from the experiments, which indicated chemisorption as the probable mechanism. The spent medium recovered after harvesting process was successfully recycled for subsequent cultivation of T. obliquus KMC24, thus reducing the dependency on fresh medium. The FAME composition of the biomass treated with bioflocculant was not altered. The last study was focused on developing and characterizing low-cost and eco-friendly catalyst for microalgal lipid transesterification to biodiesel. Herein, a novel carbon-based solid acid catalyst was synthesized by carbonization of de-oiled microalgal biomass followed by sulfonation. The effect of catalyst synthesis conditions such as carbonization temperature, sulfonation time, and H2SO4 concentration on the surface acidity of the catalyst and free fatty acid conversion was determined. The de-oiled microalgal biomass-based (DMB) solid acid catalyst was predominantly composed of carboxylic, phenolic, and sulfonic groups as indicated by the FTIR analysis and supported by the XPS analysis. The catalyst was further characterized by various methods to determine its physiochemical properties. A maximum fatty acid methyl ester (FAME) yield of 94.23% for microalgal oil (AO) and 96.25% for waste cooking oil (WCO) was obtained under optimized transesterification conditions. The catalyst exhibited high catalytic activity (FAME yield >90%) until the fourth cycle. Most of the biodiesel properties were within the permissible limit of EN 14,212 and ASTM D6751 standards.
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    Ultrasound-assisted biodiesel production using heterogeneous catalysts and mixed non-edible oils feedstock
    (2019) Malani, Ritesh S
    Biodiesel is one of the renewable and alternative to conventional diesel fuel, which attracts the attention of researchers throughout the world over last two decades. Numerous studies have been carried to produce biodiesel from different individual feedstocks and using various homogeneous and heterogeneous catalysts. The present thesis deals with the ultrasound-assisted biodiesel production using different heterogeneous (acid/base/enzyme) catalysts and mixed non-edible oils feedstocks. The studies carried out in present thesis has attempted to gain the insights into transesterification/ interesterification kinetics of heterogeneously catalyzed reaction mechanisms of using blends of non-edible oils feedstock. The reactions were analyzed through different kinetic models such as 1st order kinetic model, Eley-Rideal (E-R) model, Langmuir–Hinshelwood–Hougen–Watson (L-H-H-W) model. The kinetic modelling of heterogeneously catalyzed transesterification and interesterification reactions revealed the mechanistic features 3-phase reaction system. The output from the present research has made important and crucial contribution to understanding the basic mechanics of the heterogeneously catalyzed biodiesel production using ultrasound irradiation. Blended feedstock used in this study has vividly demonstrated feedstock flexibility of a novel biodiesel process. This feature of the process is crucial to its efficient and economic scale-up and commercialization. Present study has also attempted to utilize the waste generated during oil extraction from non-edible oil seeds and developed in active heterogeneous catalyst that can be utilized for biodiesel synthesis. Moreover, the catalyst prepared and used in this study are much cheaper than the commercial catalyst commonly used for biodiesel production and thus makes the overall process more economically feasible and sustainable.