(764f) Polyol-Ester Synthesis Via Transesterification of Jatropha-Based Methyl Ester With Trimethylolpropane

Environmental awareness triggers the increase in demands for synthetic esters derived from vegetable oils and polyhydric alcohols as a replacement for petroleum oils. Biodegradable polyol esters are known for its excellent features in many applications such as automotive, aviation, refrigeration, compressor, offshore drilling, etc. [1,2]. Polyol esters are products of transesterification of fatty acids (FAs) or FA esters with polyhydric alcohol such as trimethylolpropane (TMP), neopentylglycol (NPG) and pentaerythritol (PE). Jatropha seeds oil can be processed to produce high quality end product, with properties like: low acidity, good oxidation stability as compared to soybean oil, low viscosity as compared to castor oil and better cold properties as compared to palm oil [3]. Jatropha oil methyl ester (JOME) was chosen as starting material for the synthesis of polyol ester. Polyol esters synthesis can be carried out either via chemical or enzymatic reactions using various types of catalysts. In this study, the experimental design for polyol ester production by transesterification of JOME and TMP was performed using Taguchi method, employing the L9 orthogonal array and S/N concept for higher the better characteristics for the conversion obtained. Four major controllable factors of the polyol esters synthesis, namely, temperature, JOME:TMP molar ratio, pressure and catalyst amount were investigated at three different levels. The temperature levels were 423 K, 453 K and 483 K. The level of molar ratio of JOME:TMP were 2.5:1, 4:1 and 7.5:1. The pressure was studied at 0.5, 25 and 50 kPa and the catalyst amounts were 0.5, 1.0 and 1.5 wt%. The advantage of using Taguchi design is that the method allows several effects of factors to be simultaneously determined effectively and efficiently.

Transesterification of Jatropha oil was carried out using the two-step acid/alkali-catalyzed transesterification process due to the presence of high free fatty acid (FFA) in the oil. The synthesis of Jatropha oil trimethylolpropane (TMP) ester was performed in a 250 ml three-neck flask equipped with a thermometer, a sampling port, a reflux condenser and a second condenser at lower temperature (283 K) located after the first condenser. The condenser was connected to a vacuum line equipped with relief valve, accumulator and a vacuum trap. The flask was filled with 100 g of JOME and a known amount of TMP. The solution was stirred constantly.The weight of TMP was determined based on the required molar ratio and the calculated mean molecular weight of JOME. The mixture was then heated to the reaction temperature. Then, sulphuric acid catalyst was added. The vacuum was gradually applied to the system until it reached the desired pressure and maintained at the same pressure, up to 5 h. Nine experiments composed in the L9 Taguchi method were replicated and performed randomly. TheJOME conversion was reported as total conversion of JOME in % to trimethylolpropane esters (mono-, di-, and tri-esters of trimethylolpropane) [4,5]. The polyol esters analysis was performed by gas chromatography using method described by Yunus et al. [4] on Shimadzu Gas Chromatography Model GC-2010. From the JOME conversion results, signal to noise ratio (S/N ratio) was calculated using larger-the-better quality characteristicfor each of the nine experiments. S/N ratio is the ratio of the mean (signal) to the standard deviation (noise) or representing the magnitude of the mean of a process compared to its variation. It provides a measure of the impact of noise factors on performance. The average performance of temperature, pressure, molar ratioof JOME:TMP and catalyst amount at different levels with respectto signal to noise ratio will be presented. The polyol ester conversion increases with increase in temperature, with a rapid conversion from 423 K to 453 K followed by slow conversion from 453 K to 483 K. These observations were due to endothermic nature of the reaction which increases the polyol ester concentration along with increase in temperature. Increase in pressure from 0.5 kPa to 25 kPa results in rapid increase of polyol ester conversion. A slight decrease in polyol ester conversion was observed when the pressure was further increased to 50 kPa. Additional experiment was conducted to further assess the effect of pressure on polyol ester conversion. A conversion of greater than 80% can be achieved when the pressure is between 20 and 50 kPa. The polyol ester conversion increases with increase in molar ratioof JOME:TMP from 2.5:1 to 4:1 but almost constant when it was further increased to 7.5:1. There is slight decreased in polyol ester conversion at JOME:TMP molar ratio of 7.5:1. Increasing the molar ratio up to 7.5:1 does not significantly improve the polyol ester conversion. Furthermore, the large excess of unconsumed JOME would require more energy to remove them. Yunus et al. [4] observed that polyol ester conversion increased from 83% to 86% as the ratio of POME:TMP was increased from 3.5:1 to 3.7:1 and at3.9:1 ratio of POME:TMP, further improvement on polyol ester conversion was observed. A 98% w/w polyol ester was successfully synthesized at POME:TMP molar ratio of 3.9:1, 403 K, pressure2 kPa and sodium methoxide catalyst 0.8%.The effect of catalyst loading on polyol ester conversion is shown in Figure 1. The polyol ester conversion increased with increase in catalyst amount up to 1 wt%, but decrease when catalyst amount was further increased to 1.5 wt%. A similar finding was reported by Uosukainen et al. (1998) where the optimum catalyst weight percentage is in the range of 0.1–2.0% [5]. The order of importance of the variables was found to be pressure, temperature, JOME:TMP molar ratio and catalyst. The optimum reaction conditionswere identified to be 483 K, 25 kPa; 1.0% w/w catalyst and JOME:TMP molar ratio of 4:1. At this optimum condition the JOMEconversion obtained was 91.5%.The value of average polyol ester produced from the experiment was then compared with the estimated value for confirmation runs[6]. It was found that the estimated optimum value and experimental value were at 94 wt% and 92 wt% respectively with 2.3% deviation. In polyol ester synthesis using TMP and fatty acid methyl ester (FAME), various experimental conditions have been applied (or reported) by different authors [4–6]. It was noticed thatoperation at reduced pressure which ranged from 25 kPa up to2 kPa, were applied during the reaction for continuous removalof methanol. This indicated the importance of reduced pressure for the transesterification reaction of TMP and FAME. This study discussed the application of Taguchi method to establish the optimal set of conditions for the synthesis of Jatropha oil-based polyol ester. Statistical results showed that the order of importance of the variables was found to be pressure, temperature, JOME:TMP molar ratio and catalyst. The analysis of the confirmation experiment for polyol esters production has shown that Taguchi parameter design can successfully verify the optimum process parameters for polyol ester synthesis. The optimum reaction conditions were identified to be 483 K, 25 kPa; 1.0% w/w catalyst and JOME:TMP molar ratio of 4:1. At this optimum condition the JOME conversion obtained was 91.5%. It was observed that the difference between the value of the predicted polyol ester production and the actual polyol ester production from the confirmation experiments is 2.3%.