1.1. Background
The world’s total primary energy consumption (TPEC) has recorded a steep rise within the last decades reaching 150,000,000 GW.h in 2015. About 57% growth of this value is expected by 2050 owing the rapid industrial development and urbanisation that has occurred globally. Presently, fossil fuels including petroleum and natural gas are the main sources of energy (Hajjari et al., 2017).
According to the statistical review of world’s energy which is annually published by British Petroleum (BP), consumption of energy has extensively increased during the last decade as shown in Figure 1.1 (Vinet and Zhedanov, 2011). The reasons for increases in energy consumption include industrial development, population growth and inauguration of new technologies. Industrial developments in different applications require excessive energy for operations using either electricity or heating energies. Electricity consumption, which until this moment relies mostly on combustion of fossil fuels, has broadly increased.
Moreover, population growth has a direct impact on energy consumption in different eras.
In addition, new technologies which are invented to enhance industrial productivity, preform multitasking requirements and provide better working environment for humans have excessive impact on energy consumption. This includes special transportation means, heating/cooling equipment and electricity consumptions through electronic devices. All the above-mentioned aspects cause the depletion of fossil fuels reserves. In contrast, combustion of fossil fuels which are considered as the main source of energy contribute in environmental pollution and their emission are the main causes of global warming (Mardhiah et al., 2017).
Figure 1.1. World's energy consumption, adapted from (BP, 2017)
The majority of fossil fuel consumption (58%) is recorded by the transportation sector (Hajjari et al., 2017; Kumar and Sharma, 2016; Mardhiah et al., 2017). The unstable availability of the fossil fuels has induced the tremendous increase in crude oil price from
$20/barrel to $140/barrel in the period between 2000 and 2015, where recently the price dropped back to nearly $60/barrel (Saluja et al., 2016). This uncertainty is a result of volatile political situation in the Middle East, where fossil fuels are mainly extracted.
Additionally, energy production dependency on fossil fuels is the main reason for different environmental concerns. The combustion of fossil fuels resulted in emission of toxic gases including sulphur oxides (SOx), nitrogen oxides (NOx) and carbon monoxide (CO).
In addition, they increase the emission of greenhouse gases (GHG), including carbon dioxide (CO2) which have the tendency to trap enormous heat in the environment, resulting in acid rain and global warming (Aboelazayem et al., 2018).
The search on renewable, sustainable and environmentally benign sources of energy has been extensively carried out globally to reduce the dependency on fossil fuels. Biofuels have the potential to solve the environmental concerns and mitigate the climate change.
Biofuels are usually synthesised from crops that absorb CO2 through the photosynthesis process. Subsequently, they are considered as carbon neutral resources, where they
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maintain the carbon cycle without additional discharge to the environment (Hasan and Rahman, 2017).
Biodiesel is a competitive alternative renewable fuel for petro-diesel. Biodiesel in particular has many advantages over fossil fuels including lower toxicity emission, higher flash point, negligible sulphur content, biodegradability and the production from renewable feedstock. It can be used as a pure fuel and can be blended with petro-diesel at any ratio. Production of biodiesel would cause an economic development mutation specially for developing countries. It will encourage employment, introduce a long term replacement for fossil fuel and reduce national dependency on energy resources imports;
consequently, increase national stability and security rate (Hajjari et al., 2017).
1.2. Motivation
Presently, edible oils are the main resources for production of biodiesel. However, this global dependency on edible oil has a negative impact on food security. Using edible oils for biodiesel production has developed a global imbalance in the market demand where both food and biodiesel industries required very high production of edible oils.
Consequently, the increase of food prices due to the reduction of food resources has a negative impact on the society (Mardhiah et al., 2017). Thus, the research has been shifted towards non-edible and WCOs.
The main two obstacles for biodiesel production from non-edible and WCOs are their high content of FFAs and water contents. Feedstock with either high FFAs content and/or water, require excessive pre-treatment prior to biodiesel synthesis. The pre-treatment processes include neutralisation and/or esterification reactions. The high availability of WCOs with high FFAs content from restaurants and industries has directed the research for developing an environmentally benign and sustainable biodiesel production method from high acidity feedstock.
1.3. Research aims and objectives
The aim of this work is to design an environmentally benign biodiesel production process from high acidity feedstock. To achieve this aim, the following objectives have been identified:
1. Review the previous technologies for biodiesel production from various feedstock.
2. Highlight one of the biodiesel production technologies that could be implemented for high acidity feedstock.
3. Characterise the physicochemical properties of two feedstock with different acidity.
4. Investigate the applicability of implementing supercritical methanolysis for biodiesel production from low and high acidity feedstock.
5. Apply Response Surface Methodology (RSM) technique to optimise reaction process.
6. Investigate the conversion of free fatty acids for the high acidity feedstock.
7. Study the kinetics of transesterification/esterification reactions.
8. Design and simulate a complete process for biodiesel production using supercritical methanolysis.
9. Optimise the process energy consumption using energy integration techniques.
1.4. Contributions to knowledge
This work has various contributions to knowledge in terms of experimental results, analysis, modelling, process simulation and energy integration. Firstly, this work has studied the production of biodiesel from both low and high acidity WCOs, where the optimal yield at minimum conditions has been developed for each feedstock. In addition, this work has performed several experimental modelling for biodiesel synthesis where simple regression models have been developed to represent the process responses function in process variables. Further, a derivatisation-free method of FFAs has been developed using gas chromatographic analysis. A complete process simulation for biodiesel production using the developed experimental kinetic data has been designed.
Finally, the minimum energy requirement for the process has been achieved by using an efficient heat exchanger network designed via graphical Pinch method.
1.5. Structure of the thesis
Brief descriptions of the chapters in the thesis are summarised as follows: