Introduction and Literature Review
Scheme 1.3: Interesterification reaction using methyl acetate
1.8 Aim and Scope of present research
The literature review presented in the previous sections gives an overview of research and development on biodiesel production with different feedstocks and employing different techniques. Large number of reports on biodiesel production have been published using various feedstocks, catalysts and synthesis techniques. However, the focus of the research has been on the results and not the rationale, viz. the exact mechanism of the process that govern the kinetics and yield of biodiesel. Thus, there is significant knowledge gap in biodiesel production techniques using various processes and catalyst. This makes the scale–up of the process to industrial scale rather difficult.
At present the production cost of biodiesel is higher than petroleum derived diesel. The large–scale production of biodiesel is hampered by its unattractive production economics. Two factors that influence feasibility and viability of the biodiesel process are cost of feedstock and sufficient availability of feedstock throughout the year. The possible solution to the first issue is use of non–edible oil feedstock (such as Neem, Karanja, Kusum, Jatropha, Rubber, Cassava, etc.), which are far cheaper than the edible oils. The solution to second issue is feedstock flexibility or possibility of use of mixed feedstock for the process, as sufficient oil of single species or type may not be available in required quantities. As far as use of non–edible oils as a feedstock concerned, it has a high potential for future prospective. However, due to their high free fatty acid (FFA) content, conventional alkali catalysed transesterification is not feasible. This necessitates the two–step process, first acid catalysed esterification to convert the FFA, separation of the oil phase, followed by transesterification with alkali catalyst. Another problem with acid catalysed biodiesel process is its extremely slow kinetics, which can put limit to the production rate. For the second problem, use of heterogeneous catalyst is the potential solution. Heterogeneous catalysts can drastically reduce the
contamination of glycerol that will help in improving the quality of glycerol and also the sale price. However, the bottleneck in application of heterogeneous catalyst is slow kinetics of the transesterification reaction due to the three–phasic heterogeneity nature of the reaction system (liquid–liquid–solid). The mass transfer limitations bring down the kinetics drastically, which is again a hurdle for effective scale–up of the process with use of heterogeneous catalyst.
In the present thesis research, an attempt has been made to address these issues.
The ultrasound technique as a means of intensification of the process will be applied.
Several biodiesel synthesis processes with mixture of non–edible oils feedstock and different heterogeneous catalysts have been studied from mechanistic viewpoint. The dynamics of the reaction system has been analysed on the basis of kinetic model. This approach will help in getting the physical insights into the process and deduce the exact nature of interaction or links between mass transfer and kinetics of transesterification/
interesterification reaction. Such physical insights can form crucial guidelines for effective scale–up of the process.
The specific objectives of the present investigations are as follows:
1. Synthesis and characterization of heterogeneous catalysts for biodiesel production 2. Use of mixture of different non–edible oils as a feedstock for single and two step
biodiesel production.
3. Use of ultrasound as a tool to intensify biodiesel production.
4. Optimization of biodiesel production processes using statistical optimization tool.
5. Investigations of heterogeneously catalysed transesterification/ interesterification process through kinetic modelling.
The thesis comprises of 7 chapters (including the present one) and the contents of the each of these chapters are briefly outlined below:
Chapter 1 gives the literature review of various aspects biodiesel synthesis. In addition, an introduction to basic principles of ultrasound and cavitation is also given, which could be useful for readers not much conversant with this subject.
Chapter 2 presents studies in mechanistic analysis of ultrasound–assisted biodiesel synthesis with Cu2O catalyst and mixed oil feedstock using continuous (packed bed) and batch (slurry) reactors. This chapter essentially demonstrates the feasibility of heterogeneous catalyst for transesterification with ultrasonic techniques in packed bed system. Mixed non–edible oil has been used as a feedstock for biodiesel production. The process has been analysed using Eley–Rideal based kinetic model to link mass transfer limitation with reaction kinetics.
Chapter 3 presents studies in physical insight into ultrasound–assisted biodiesel production using heterogeneous base catalyst and mixed non–edible oils. Synthesis of heterogeneous base catalyst, KI impregnated on ZnO and its application in biodiesel production using blended feedstock has been presented in this chapter. Additionally, the effect of non–edible oils in their blends has also disused. The process has been analysed using Eley–Rideal based kinetic model as developed in Chapter 2.
Chapter 4 presents the studies in ultrasound intensified biodiesel production from mixed non–edible oil feedstock using heterogeneous acid catalyst supported on rubber de–oiled cake. The synthesis and characterization of two different carbon based catalyst has been evaluated. The superior catalyst has been selected for biodiesel production using non–edible oil mixed feedstock, in batch process. The process has been analysed using a modified Eley–Rideal based kinetic model that considers FAME as adsorbed product on catalyst – instead of intermediates of di– and mono–glycerides.
In Chapter 5, the studies on ultrasound–assisted enzymatic biodiesel production using blended non–edible oils feedstock have been presented. The commercially immobilized lipase has been employed for biodiesel production using mixture of non–
edible oil. The process was analysed for kinetic and thermodynamic analysis.
In Chapter 6, the glycerol free biodiesel production through ultrasound–assisted interesterification of mixed non–edible oil feedstock has been studied. This chapter essentially demonstrates the feasibility of heterogeneous Cu2O catalyst for ultrasound–
assisted interesterification. The process has been analysed using LHHW based kinetic model to link mass transfer limitation with reaction kinetics.
Chapter 7 presents summary and overview of the various individual studies presented in the preceding chapters and collective interpretations. Based on the results of the chapters, some suggestions for future work have also been given.