Study of Heat Recirculation in Non-Catalytic Reaction of Biodiesel Production Based on Exergetic Analysis.

Abstract

Energy consumption in non-catalytic biodiesel production is still high, and needs to be reduced to the optimum level. It can be accomplished by recirculating the heat being used in the process by using heat exchanger. The objective of this experiment is to perform an energy and exergy analysis as implicated by the heat recirculation through the designed heat exchanger. This study was started from the determination and calculation of physical and thermal properties of materials to be used (palm olein, methanol, and methyl ester), continued with the designing of the heat exchanger, and the research itself. Production systems used in the study were semi-batch mode with 3 levels of methanol flow rate, namely 1.5, 3.0, and 4.5 mL min-1 at the reaction temperature of 290oC. Exergy analysis was done by assuming the system in steady flow conditions, while kinetic and potential energy were neglected. The results show that the energy ratio increased after recirculating the heat. This imply that heat recirculation by using the heat exchanger can improve the energy efficiency of the process. For each of the methanol flow rate of 1.5, 3.0, and 4.5 mL min-1, the effectiveness of heat exchanger was obtained 92%, 25%, and 19% and the energy ratio (RE1) was 7.85, 2.98, and 2.87, respectively. It shows that heat recirculation by heat exchanger can improve the energy efficiency in biodiesel production system. The exergy analysis for methanol flow rate of 1.5, 3.0, and 4.5 mL min-1 respectively, resulted in exergetic efficiency for subsystem evaporator 1.34%, 2.43%, and 2.98%, for superheater 0.42%, 0.78%, and 1.15%, for reactor 19.59%, 19.23%, and 18.52%, and for heat exchanger 19.93%, 16.27%, and 10.48%. However, exergy analysis showed that irreversibility of the heat exchanger and reactor were still higher than the evaporator and superheater, and was higher with faster methanol flow rated.

Katalitik dan non-katalitik merupakan dua metode yang digunakan untuk memproduksi biodiesel sampai saat ini. Keduanya memiliki kelebihan dan kekurangan. Metode non-katalitik tidak membutuhkan katalis sehingga alur produksi lebih pendek, lebih ramah lingkungan, lebih sederhana, dan tidak perlu menghilangkan free fatty acid (FFA) dari minyak (Joelianingsih 2008b). Namun, kelemahannya membutuhkan rasio molar antara metanol dan minyak lebih tinggi (24-42) dan suhu yang digunakan untuk mereaksikan pada reaktor sangat tinggi (240-350oC) sehingga energi yang dibutuhkan untuk menaikkan suhu pun tinggi (Saka dan Kusdiana 2001). Menurut Sigalingging (2008) rasio energi yang didapat sebesar 0.84, masih lebih rendah dibandingkan dengan produksi secara katalitik, yaitu sebesar 0.98. Oleh karena itu, perlu dilakukan penyempurnaan guna meningkatkan performansi alat, sehingga rasio energi yang didapat lebih tinggi. Rasio energi dapat ditingkatkan dengan meminimalisasi energi yang tidak termanfaatkan selama proses produksi, salah satunya dengan pemanfaatan (daur ulang) panas dalam sistem dengan merancang alat penukar panas (APP) yang diharapkan mampu memaksimalkan energi yang dapat dimanfaatkan. Tujuan dari penelitian ini adalah 1). Merancang penukar panas yang berfungsi untuk mendaur ulang panas dari reaktor ke evaporator. 2). Menghitung rasio energi produksi biodiesel secara non-katalitik. 3). Melakukan analisis eksergi pada sistem produksi biodiesel non-katalitik.