This thesis starts with a brief overview of the current production processes for fatty acid esters. Because these processes have several drawbacks, a new technology is proposed: Entrainer-based Reactive Distillation. In Entrainer-based Reactive Distillation, in situ separation is used to improve the yield of reaction, whereas an entrainer feed is added to overcome the alcohol-water azeotrope, by selectively increasing the relative volatility of water. The objective of this research is the development of a multi-product Entrainer-based Reactive Distillation process for the synthesis of fatty acid esters using a heterogeneous catalyst, and evaluate its attractiveness compared to the current technologies. In Chapter 2 it is demonstrated that, due to the similarities between Entrainer-based Reactive Distillation and azeotropic distillation, the same selection rules can be applied to select a suitable entrainer. From a list of suitable entrainers for the azeotropic distillation of isopropanol and water, cyclohexane and isopropyl acetate are chosen. Residue curve maps, simulations of the distillation section of the column, and simulations of the total Entrainer-based Reactive Distillation concept show that both can be used as an entrainer in Entrainer-based Reactive Distillation. Whether Entrainer-based Reactive Distillation will be feasible, strongly depends on the kinetics of the reaction. For this reason Chapter 3 discusses the reaction kinetics of the esterification of myristic acid with isopropanol and with n-propanol, using sulphated zirconia (SZ) and ( p)-toluene sulphonic acid (pTSA) as catalysts, for a temperature range of 343-403K. SZ appeared to be an unsuitable catalyst for the esterification of myristic acid with isopropanol since it did not increase the reaction rate of the uncatalysed reaction. For the reactions with pTSA the reaction rates are determined. The reactions follow first order kinetics in all components. The kinetic model corresponds with the results for the esterification of myristic acid with isopropanol and the results for the esterification of palmitic acid from literature. As expected, the reaction rate increases with increasing amount of catalyst and with increasing temperature. The reaction rate and equilibrium conversion increases with an increasing alcohol to myristic acid feed ratio. The reaction with n-propanol is considerably faster (at 373K about 3.8 times) than the reaction with isopropanol. On the basis of the entrainer selection and kinetics studies Chapter 4 will discuss the gains that can be obtained using Entrainer-based Reactive Distillation with regard to conventional Reactive Distillation. Five process configurations for the esterification of myristic acid with isopropanol and ( n)-propanol using a homogeneous catalyst, are compared, by simulation in Aspen Plus. In the esterification with isopropanol at 1 bar, the addition of the entrainer has no positive influence on the conversion, because the amount required for water removal causes temperature decrease in the column. This temperature decrease has a negative in°uence on the conversion, because the high activation energy of the reaction cannot be overcome. However, in the esterification with iso-propanol at 5 and 10 bar and in the esterification with n-propanol (either 1, 5 or 10 bar), the addition of the entrainer has a positive influence on the conversion. More entrainer leads to a higher conversion. Surprising is the observation that the conventional Reactive Distillation configuration (RD1) reaches the desired purity and conversion. Because of its polarity, water is pressed out of the liquid phase, in which the reaction takes place, so the reaction can reach nearly complete conversion. Because the decrease of the reaction volume due to the addition of the entrainer is rather small and the energy consumption is comparable, conventional Reactive Distillation (RD1) is the preferable configuration for the esterification of myristic acid with either isopropanol or n-propanol. Subsequently, the Aspen Plus process for the reactive distillation is validated through pilot plant experiments in Chapter 5. A detailed model of the pilot plant is created for different operating conditions. Experiments with a pilot column are performed to verify the model. The conducted experiments correspond well with the predicted values; the model can be used in the construction of a conceptual design. However, not all the intended validation experiments could be performed, because of the practical difficulties that arise when negligible liquid level in the column has to be ensured. Also the break down of the pumps due to clogging appeared a limiting factor in the experiments.Finally, the process model from Chapter 5 is used to construct a conceptual design for the esterification of myristic acid with isopropanol through reactive distillation (packed, tray and bubble column). A parameter optimisation study is performed to investigate the influence of the different process parameters. Finally all results are integrated in conceptual designs for the industrial scale processes, which are evaluated against the batch process based on required reaction volumes. The required reaction volume can be decreased with 27 or 79%, allowing a maximum temperature of respectively 170 and 220ºC, using a packed reactive distillation column. Using a tray reactive distillation column and a maximum temperature of 220ºC, the required reaction volume can be decreased with 93%. Due to the less favourable mass transfer characteristics, in the bubble column the required reaction volume can only be decreased with 78%. It is further noted that, at a temperature of 220ºC, the tray reactive distillation is the preferable process for the esterification of myristic acid isopropanol, based on the required reaction volumes. The influence of the maximum column temperature and the influence of a larger liquid hold-up per stage as a result of a different column configuration are of equal importance for the required reaction volume. This thesis shows that reactive distillation can be used for the production of isopropyl myristate, which results in an enormous decrease in reaction volume compared to the batch process. Therefore, it can be concluded that reactive distillation has the potential to become an economically attractive alternative, not only for fatty acid esters based on methanol and primary alcohol which is already known, but also for the production of isopropyl myristate.
|Kwalificatie||Doctor in de Filosofie|
|Datum van toekenning||17 jun 2010|
|Plaats van publicatie||Eindhoven|
|Status||Gepubliceerd - 2010|