Biogasoline production by catalytic cracking of waste cooking oil.
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Date
2023
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Abstract
Government, Heads of State, and international organizations gather from time to time to investigate and implement strategies required to eradicate global warming and address environmental issues. The principal causes of global warming and ecological issues are industrializations, excavation, cutting down of trees, and production of fossil fuels, to mention only a few.
Besides global warming and climate change, it is essential to know that the other issue related to fossil fuels is that they generate from a finite source. This source is dwindling as time passes. The potential disappearance of fossil fuels is also a cause of the high prices of crude oil, primarily in the regions with less or without crude oil. The reasons mentioned prove that there is a need to alter to a renewable source of energy-generating from an infinite source.
Several investigations are taking place at international and national (South Africa) levels to develop the production of biofuels considered clean fuels. In an attempt to improve the quality of biofuels, many works are taking place behind the scenes regarding feedstock quality, feedstock source, feedstock transportation, and technologies required to produce biofuels.
Regarding biofuels, products like biodiesel and bioethanol, including biogas, are at an advanced stage of development in terms of technologies and commercialization in specific locations such as America (USA), Brazil, and Canada. However, biogasoline production is not yet advanced, even though many vehicles use gasoline. Biogasoline has the quality to be blended or to be used as a replacement for conventional gasoline (fossil-based gasoline) in vehicles’ engines.
This project investigates the feasibility of manufacturing biogasoline from waste cooking oil, one of the available feedstocks. Waste cooking oil is converted to biogasoline via catalytic cracking, thermal cracking, and a two-step (hybrid) method. All the methods mentioned earlier see their applications in this research study.
The methods requiring a catalyst were conducted using nanocatalysts which carry out the reactions effectively in an optimized way. The nanocatalysts' structure causes the enzyme to be motionless. The dormant state of enzymes affects the biocatalytic efficiency through the increased load of enzymes and surface area. The nanocatalyst was composed of Ammonium molybdate tetrahydrate [(NH4)6Mo7O24.4H2O] and cobalt nitrate hexahydrate [Co(NO3)2.6H2O], including ɣ-aluminium oxide. After mixing the catalyst samples, they were dried and calcined. Then the catalyst samples were analysed using the following techniques: x-ray diffraction, inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning and transmission electron microscopy. The thermogravimetry analyser (TGA) method was used to determine the regeneration temperature of the nanocatalyst. The TGA results showed that the regeneration temperature for three nanocatalyst samples is 600oC. However, the nanocatalyst calcined at 600oC is selected for this study since it has a completed regeneration cycle. The regeneration cycle at this temperature starts from the evaporation of water. Then there is an increase of inorganic compounds caused by partial oxidation, and finally, coke combustion. These three processes show that the regeneration cycle of the nanocatalyst at the selected temperature is complete.
After preparing the nanocatalyst, the waste cooking oil underwent pre-treatment to remove salt and food particles. The remaining sulphur after cleaning is 4%, roughly 71% of which is removed from the oil.
Pre-treatment of waste cooking oil concluded, and the resulting product was used to conduct the thermal cracking at varying reaction temperatures (400, 450, and 500oC) and reaction times. This method's highest biogasoline is 24.96%, obtained at 500oC and 60 minutes, respectively, reaction temperature and reaction time. The optimum reaction time is 60 minutes. The catalytic cracking and two-step methods were conducted at a constant reaction time of 60 minutes (optimum time) while varying the catalyst load (1, 3, and 5 grams) and the reaction temperature. For catalytic cracking, the percentage yields increase with the reaction temperature at a constant catalyst load of one gram. The highest percentage yield is 12.7% at a reaction temperature of 550oC. The optimum waste cooking ratio of oil is one gram of nanocatalyst to 44 grams of waste cooking oil. The biogasoline percentage increases with the reaction temperature for the two-step process (hybrid method). The highest biogasoline percentage yield is 29.63% at reaction temperature and catalyst load of 550oC and 3 grams, respectively.
One of the aims of this research was to investigate the effects of the calcination temperature of the nanocatalyst at a constant reaction temperature of 475oC. The experimental procedure yields 42.36% of biogasoline for 5 grams catalyst load. The calcination temperature of the catalyst used is 700oC.
The catalytic processes (catalytic cracking and two-step process) were optimized. The optimized results for cracking are 11.51%, 3.35g, 482oC, and 0.28h-1, respectively; biogasoline percentage yields, catalyst weight, reaction temperature, and weight hourly space velocity. The optimized results for the two-step process are 41.78%, 4.32g, 567.2oC, and 0.22h-1, respectively, biogasoline yields, catalyst weight, reaction temperature, and hourly space velocity.
It is vital to conduct further studies in biogasoline production using thermal cracking methods (with and without catalysts) and the two-step process method. The study must include the addition of metals such as copper and nickel to nanocatalysts and consider changing the operating conditions such as temperature and carried gas pressure. These techniques provide a great platform to step up biogasoline production at an industrial scale and conduct a techno-economic assessment.
It is also vital to conduct a techno-economic assessment of biogasoline production to establish its production cost and selling price. Documenting the production method, the suitable catalyst, and the feedstock is essential. The studies have proved that lignocellulosic biomass is affordable and environmentally sane to produce biogasoline.
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Masters Degree. University of KwaZulu-Natal, Durban.