FINAL EVALUATION AND DISCUSSIONS

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CHAPTER VI FINAL EVALUATION AND DISCUSSIONS

The transformation of raw materials into products of greater value by means of chemical reaction is a major industry, and a vast number of commercial products is obtained by chemical synthesis. Biodiesel or FAME was obtained by a chemical reaction namely transeseterification andor esterification, in other words to convert molecular compounds TG and MeOH or FFA and MeOH to other molecular compounds FAME and GL or FAME and water. The reaction rate and maximum possible or equilibrium conversion of a chemical reaction are of primary concern in its commercial development. The reaction rate is a part of chemical kinetics study, but the conversion or chemical-reaction equilibrium is a part of chemical thermodynamics analysis. Both the reaction rate and conversion must be considered in the development of a commercial process for a chemical reaction such as in transesterification and esterification for biodiesel production. Many industrial reactions are not carried to equilibrium. In this circumstance the reactor design is based primary on reaction rate. However, the choice of operating conditions may be still be determined by equilibrium consideration. In addition, the equilibrium conversion of a reaction provides a goal by which to measure improvements in the process. Similarly, it may determine whether or not an experimental investigation of a new process is worthwhile. At present, most of the methods on transesterification reaction are in the using an alkali catalyst. The reaction requires a catalyst for a reasonable reaction rate, and the transestericication reaction rate becomes appreciable with an alkali catalyst at about 60 o C so the reaction time for complete reaction is about 60 min. An important characteristic of a catalyst is only suitable for a specific reaction. The main drawback of the alkaline-catalysis is the sensitivity of alkaline catalysts to FFA contained in the feedstock material. When an alkaline catalyst is added to these feedstocks, the FFA reacts with the catalyst to form soap and water. This means that alkaline-catalyzed transesterification optimally work with high-quality, low-acidic vegetable oils, which are however more expensive than waste oils. If low-cost materials, such as waste fatscooking oils or unrefined vegetable oils 71 with a high amout of FFA, are to be processed by alkaline catalysis, costly deacidification or pre-esterification steps are required. Acid catalysis transesterification offers the advantage of also esterifying FFA contained in the fats and oils. However, acid-catalyzed tranesterification are usually far slower than alkali-catalyzed reaction and require higher temperatures and pressures as well as higher amounts of alcohol. Some types of catalyst have been developed for the transestrification such as an enzymatic catalyst. Beside with using a catalyst, the increasing of reaction rate can be achieved with increase the value of frequency factor in the Arrhenius equation. The Arrhenius equation is based on the collision theory which supposes that particles must be collided with both the correct orientation and with sufficient kinetic energy if the reactants are to be converted into products. One major problem in alkaline-catalyzed transesterification of TG is the fact that the oil substrate is not miscible with the alcohol-catalyst phase. Reaction occurs at the interface between the two phases, resulting in a much lower rate than if the reaction mixture was a single phase. The frequency factor value was influenced by the interface area of the particles collisions. That means that transesterification does not proceed properly, unless the reaction mixture is homogenized in some way. One of ways is a non-catalytic transesterification with supercritical MeOH, but the operating temperature and pressure is very high 240-350 o C, 9-65 MPa which are not easily viable for application in industry . In addition, transesterification is an exothermic reaction. The exothermic reaction has a characteristic that at higher temperature the equilibrium shift to the reactant so the reaction conversion decreases. Therefore, to make the equilibrium shift to the product, the large molar excess of MeOH must be applied. The objective of this dissertation is to provide alternative methods for biodiesel production process which is applicable to solve problems existing in the catalyzed methods. In our research, a bubble column reactor has been developed to produce the biodiesel fuel by the non catalytic process. In the non-catalytic process, reaction temperature must be increased to obtain the feasible reaction rate. In Chapter III, the semi-batch of BCR was developed for conversion of oilsfats to biodiesel. Palm oil was chosen as a model of triglycerides. 72 Transesterification was carried out at 250, 270 and 290 o C under atmospheric pressure to investigate the effect of reaction temperature on the rate constant, conversion, yield of ME and composition of the reaction product in the transestrification reaction. The rate constant, conversion and yield of ME showed an increase trend with the reaction temperature, but the ME content in the reaction product decreased as the reaction temperature was increased. These results show that the principle of a BCR for transesterification of TG is similar to RD where the reaction products in the gas phase GL and ME are continuously removed from the reactive zone, while TG as the reactant is remained in the reactive zone liquid phase. This is a process unit that enables reaction and distillation in a single unit, is an excellent option for the biodiesel production and ideally can achieve 100 reaction conversion. To investigate the performance of BCR for the non-catalytic methyl esterification, five kinds of fatty acids which are commonly found in palm oil were selected; myristic acid MA, palmitic acid PA stearic acid SA, oleic acid OA and linoleic acid LA. The reaction rate of methyl esterification was faster than that of methyl transesterification, but the ME content in the gaseous product was lower. In methyl esterification of fatty acids, reactivity and FAME purity of saturated fatty acids is lower than unsaturated fatty acids, while in the saturated fatty acids; reactivity increased with the length of fatty acids alkyl chains. In Chapter V, various MeOH feed flow rate and reaction temperature were used in a continuous flow BCR for the non-catalytic transesterification of palm oil. The optimum value was based on the productivity of FAME and GL and the ME content in the product. Productivity at the 2.5 mLmin = 0.593 kgLh MeOH feed flow rate was 0.006 kg GLLh and 0.058 kg FAMELh after 300 min reaction time with the mass flow rate of oil was 0.06 kgLh. While at the 3.0 mLmin = 0.711 kgLh MeOH feed flow rate, productivity was 0.014 kg GLLh and 0.128 kg FAME Lh after 270 min reaction time with the mass flow rate of oil was 0.13 kgLh. The ratio of output to input energy excluding energy for electricity of this experiment was 26.5 and the specific energy consumption was 1.5 MJkg biodiesel at 3.0 mLmin MeOH feed flow rate and 290 o C the molar ratio of MeOH to oil was 148. 73

CHAPTER VII CONCLUSIONS