| The demand for petroleum has risen rapidly due to increasing industrialization and modernization of the world. The limited reserve of the fossil fuels is also dwindling alongside escalation in prices. The threats from these and food insecurity is however, drawing attention of researchers for alternative fuel which can be produced from renewable resources. Biodiesel as the most promising alternate is currently produced from conventionally grown edible oils such as rapeseed, soybean, sunflower and palm. The use of these edible oils is worsening the current competition of oil for food and fuel. To address these, non-edible resources are presently being explored. Non-edibles resources such as jatropha, mahua, pongamia, calophyllum, tobacco oil, etc have been tested for biodiesel. However, discrepancies between the expectation and realities regarding these resources are necessitating efforts to boost up resources’ diversification in order to augment energy and yet maintain food security. This study centred on Silybum marianum oil. This is because in China the current non-edible resources for biodiesel include jatropha, castor, Xanthium sibiricum etc. Recent studies however, indicate that there are alternative non-edible oil-yielding plants which can be used for biodiesel. And a boost for the search for more of the non-edible resources is the emergence of Silybum marianum oil which has gained prominence in medicinal and pharmaceutical studies but scanty in biodiesel production. Silybum marianum, a wild annual plant of compositae family is widely cultivated in China in various provinces including Guangdong, Hubei, Shanxi and Qinghai. The medicinal and pharmaceutical aspects of the plant have been researched over the years. The extract from the seeds for instance is used traditionally for treatment of hepatotoxicity, acute and chronic liver diseases. The pharmacologically active component of the extract (silymarin) is made of isomeric mixture of flavonolignans, silychristin, silydianin, diastereoisomers silybin and isosilybin. The seeds of the fruits contain a lot of oil. In silymarin industrial oil production, the oil is considered a byproduct and not much utilized. And for full development and utilization of Silybum marianum oil, this study was undertaken to investigate biodiesel production from crude Silybum marianum seed oil using various methods (conventional stirring and ultrasonication) with different alcohols, catalysts and to determine the properties of the biodiesel. The study offers contributions in four major ways. The procedures and contributions in all the phases are briefly described below: (1)A comparative study of conventional and ultrasonic assisted methods for producing biodiesel from Silybum marianum oil:In this aspect, alkaline transesterification of Silybum marianum seed oil to biodiesel using methanol and ethanol was investigated. The two methods used were conventional stirring (600rpm) and ultrasonication (40kHz). Oil was first extracted from the seeds, followed by physico-chemical properties’ determination and transesterification to biodiesel. The seeds were found to contain46%oil which had low free fatty acids (FFA)(0.68%). Linoleic acid (65.68%) was the main composition of the oil. Ultrasonication transesterification with methanol gave highest yield (95.75%) after20min. Yields of methyl esters were higher than respective yields of ethyl esters. Using first order reaction kinetics model, the reaction rate constants were2.3×10-2s-1and7.0×10-3s-1for ultrasonication with methanol and ethanol, respectively. With the exception of oxidative stability (2.1h) and iodine values (132-methyl and133-ethyl esters); properties out of range but can easily be improved, the remaining properties including, cetane number, flash point and the cold flow ones of both methyl and ethyl esters were similar and comparable to Chinese, ASTM and European Union standards. The findings of this study complement with the abundance of Silybum marianum seeds at cultivation and silymarin industrial oil production as by-product indicates that the oil is potentially new non-edible feedstock for biodiesel in China.(2) Application of zirconia loaded with KOH as heterogeneous solid base catalyst to Silybum marianum oil for biodiesel:This aspect of the study seeks to investigate zirconia modified with KOH as heterogeneous solid base catalyst for transesterificating non-edible Silybum marianum oil using methanol to biodiesel. Having screened the catalytic performance of ZrO2loaded with different K-compounds,32%KOH loaded on ZrO2was chosen. The catalyst was prepared using incipient wetness impregnation method. Following drying (after impregnation) and calcination at530℃for5h, the catalyst was characterized by means of Hammett indicators, XRD, FTIR, SEM, TGA and N2adsorption desorption measurements. It was found that the yield of the fatty acid methyl esters (FAME) was related to the catalyst base strength. The catalyst had granular and porous structures with high basicity and superior catalytic performance for the transesterification reaction. The maximum yield (90.8%) was obtained at15:1methanol to oil molar ratio,6%catalyst amount,60℃reaction temperature and2h of reaction time. The catalyst maintained sustained activity after five times of usage. The oxidative stability and iodine value were also the only unsuitable properties of the biodiesel. The cetane number, flash point and the cold flow properties among others were however, comparable to international standards. The study indicated that KOH(32%)/ZrO2-5is an economically, suitable catalyst for producing biodiesel from Silybum marianum oil which can contribute positively to biodiesel industry as its biodiesel can be rated as a promising alternate fuel.(3) Modified TiO2dope with C4H4O6HK as efficient and economical heterogeneous catalyst under ultrasonic transesterification for Silybum marianum biodiesel:In this contribution, the aim of the study was to investigate modified TiO2doped with C4H4O6HK as heterogeneous solid base catalyst for transesterificating Silybum marianum oil to biodiesel using methanol under ultrasonication. Upon screening the catalytic performance of modified TiO2doped with different K-compounds,0.7C4H4O6HK doped on TiO2was selected. The preparation of the catalyst was done using incipient wetness impregnation method. Having doped the modified TiO2with C4H4O6HK, followed by impregnation, drying and calcinating at600℃for6h, the catalyst was characterized using XRD, FTIR, SEM, BET, TGA, UV and the Hammett indicators. The yield of the biodiesel was proportional to the catalyst basicity. The catalyst had granular and porous structures with high basicity and superior performance. Combined conditions of16:1molar ratio of methanol to oil,5wt.%catalyst amount,60℃reaction temperature and30min reaction time was enough for maximum yield of90.1%. The catalyst maintained sustained activity after five cycles of use. The oxidative stability which was the main problem of the biodiesel was improved from2.0h to3.2h after30days using ascorbic acid as antioxidant. The other properties including the flash point, cetane number and the cold flow ones were however, comparable to international standards. The study indicated that Ti-0.7-600-6is an efficient, economical and environmentally, friendly catalyst under ultrasonication for producing biodiesel from Silybum marianum oil with a substantial yield.(4) Acid treated attapulgite functionalized with Na-compounds as novel bi-functional heterogeneous solid catalysts for transesterification of Silybum marianum oil to biodiesel:In this aspect, transesterification reaction of Silybum marianum oil and methanol to biodiesel using hydrochloric acid treated attapulgite clay that has been modified by ammonium hydroxide and subsequently functionalized with C4H6O4KNa and Na2C2O4as solid base catalysts was studied. These effective heterogeneous catalysts were successfully prepared by firstly, drying the raw attapulgite at120℃for12h, followed by treating the dried attapulgite with40ml dilute hydrochloric acid of2M concentration at80℃for1h under magnetic stirring. Washing with distilled water was done till pH of neutral point was reached. Following centrifugation and drying (120℃for12h), the hydrochloric acid treated attapulgite was then modified with ammonium hydroxide and subsequently functionalized with4M of C4H6O4KNa and Na2C2O4, respectively using the impregnation method for24h. The catalysts were then dried at120℃for8h and subsequently calcined at450℃for4h. The as-prepared catalytic materials were characterized with instruments including Hammett indicators, FT-IR, XRD, SEM and TGA. The activity of C4H6O4KNa functionalized attapulgite (4NK/HCl-Atta-4) was superior to that of Na2C2O4(4NC/HCl-Atta-4). Maximum yield of94.7%was obtained using4NK/HCl-Atta-4under molar ratio of methanol/oil9:1, catalyst amount of6wt.%, reaction temperature of60℃in6h. The catalysts were advantageous not only for their easy preparation, but also cost-efficient and good catalytic performance for transesterificating Silybum marianum oil to biodiesel. The catalysts maintained sustained activities after5runs of reuse. The properties of the obtained biodiesel showed many similarities with the Chinese, American and European Union standard and could be rated as realistic fuel alternative to diesel.The outcome of the entire study is therefore hoped to promote cultivation of Silybum marianum and its development. The study will also draw focus to other non-edible oils for biodiesel production. It is also expected that this study will contribute to enhancement and reduction in greenhouse gas emissions, regional development and social structure, especially to developing countries. The study is also expected to contribute to a balance between agriculture, economic development and the environment. However, it is recommended that a further test on engine performance and emission using Silybum marianum biodiesel and its blends should be carried. |
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