STUDI PRODUKSI BIODIESEL SECARA KONTINYU DENGAN REACTIVE DISTILLATION DAN ANALISIS TERMODINAMIKANYA

Abstract

Biodiesel as an alternative energy source can be synthesized via transesterification of triglyceride or free fatty acid (FFA) esterification of vegetable oils. To improve process efficiency, development of a continuous process for biodiesel production using Reactive Distillation (RD) was conducted in this work. RD integrates chemical reaction and separation in a single unit. To understand the effects of main parameters and to have a best knowledge on RD behavior, it is necessary to conduct an experimental work as well as modeling, simulation, and thermodynamic study on RD column for biodiesel production. The experimental part of this work included the production of biodiesel using RD via transesterification of palm and jatropha oils with methanol in the presence of NaOH catalyst. Modeling of RD column was developed based on Equilibrium (EQ) and Non Equilibrium (NEQ) approach. EQ model was developed for the simulation of tray RD column for the biodiesel synthesis via transesterification of triglyceride and esterification FFA. Simulation of tray RD column was performed utilizing ASPEN. On the other hand, modeling of packed RD column was developed based on NEQ with three phases approaches and applied for the biodiesel synthesis via FFA esterification. The simulation of packed RD column using three phases NEQ model was employed to execute the simulation using self-developed MATLAB program. The result of the MATLAB programing based on NEQ with three phases approach was afterward introduced for the exergy analysis. The exergy analysis was conducted using a novel graphical method entitled Ex-N-A to disclose the exergy characteristic of the RD column incrementally. The experimental investigation demonstrated the effects of the temperature, catalyst loading, and reactants molar ratio. Increasing the catalyst loading and reactant molar ratio led to the enhancement of the reaction conversion. However, once the optimum conversion was achieved, increasing catalyst amount and reactants molar ratio tended to decrease the conversion. The increase in temperature resulted in the higher reaction conversion. However, conversion decreased when the temperature enhanced beyond the boiling point of the mixture. The best result of biodiesel synthesis using palm oil feedstock was obtained at the reaction temperature of 65 ºC with molar ratio of methanol to triglycerides of 8:1 and catalyst loading of 1% w/w oil. Reaction conversion and ester content were 94.61% and 99.17%, respectively. For jatropha oil feedstock, the best conversion was achieved at the reaction temperature of 65 ºC with reactants molar ratio of 10:1 and catalyst loading of 0.75% w/w oil. Reaction conversion and ester content were 94.83% and 99.27%, respectively. The best achievement for palm and jatropha oils feedstocks were obtained within a very short time of 6.34 minutes. This reaction time is much shorter than the reaction time of batch process which usually requires one hour to obtain an identical reaction conversion. Biodiesel characteristic met the Indonesian National Standard and ASTM specification. Simulation of trayed RD column for triglyceride transesterification was conducted using ASPEN based on EQ model. It was shown that conversion could be improved by increasing reflux ratio (RR), decreasing distillate flowrate (D), and locating the feed stage at the upper part of the column. Simulation of trayed RD column for biodiesel production via FFA esterification was also performed using ASPEN based on EQ model. It was exhibited that, for the basic RD, conversion could be enhanced by lowering RR and placing the feed stage at the upper part of the column (completely removing the rectifying section). The basic RD column resulted in reaction conversion of 73%. It was then necessary to modify the column for the process intensification purpose. Among several configurations evaluated in this work, RD column with top recycle revealed the best performance based on the reaction conversion as well as thermodynamic point of view. This configuration resulted in reaction conversion of 90% and heat requirement of 287.3 kcal/mole methyl ester. For the configuration of RD with top recycle, it was found that the reaction conversion and heat requirement increased with the RR. On the hand, the best feed stage location was N=7 or 8. Simulation of packed RD column based on NEQ with three phases model which was integrated with the exergy analysis for biodiesel production has demonstrated that the Ex-N-A diagram can disclose the correlation of column temperature profile, energy level difference (Agas-Aliq), and exergy loss (EXL). This diagram was also benecifial for exhibing the location of close to equilibrium (CEP) and non equilibrium (NEQ) zones in the RD column, indicating the location and causes of process inefficiency. Evaluation on the main process parameter revealed that the increase in molar ratio of methanol to FFA led to the higher reaction conversion and lower EXL. On the other hand, the increase in the column height (N) led to the higher both reaction conversion and EXL. It was indicated that raising reactants molar ratio from 2:1 to 6:1 at the column height (N) of 3 meter and column diameter (d) of 0.5 meter would enhance the conversion from 30.76% to 66.41%, broaden the CEP zone inside the column, narrow the NEQ zone, and decrease the EXL. Improving N from 3 to 6 meter at reactants molar ratio of 2:1 and d of 0.5 meter improved the conversion from 30.76% to 58.52%, enlarged the CEP zone without narrowing the NEQ zone, and increased the EXL. It can be concluded that application of high molar ratio is beneficial both from the column performance and thermodynamic point of view. Based on the RD assasment utilizing experimental, simulation, and thermodynamic analysis, the best knowledge and insight of RD can be obtained. Particularly, utilization of Ex-N-A diagram for exergy analysis in this work can disclose exergy profile in the column in details. It was evident that the Ex-N-A diagram was powerful to disclose the EXL profile incrementally in the RD column and exhibited the location and quantity of the inefficiency. This information is important for designing and retrofitting an RD column towards a themodynamically efficient RD column