Karakteristik Metil Ester Minyak Jarak Pagar Hasil Proses Transesterifikasi Satu dan Dua Tahap
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Balai Besar Penelitian dan Pengembangan Pascapanen Pertanian
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Biodiesel (metil ester) umumnya dihasilkan dari proses transesterifikasi minyak nabati antara lain dari minyak jarak pagar. Proses transesterifikasi dengan pereaksi metanol dan katalis basa (KOH) dapat dilakukan satu atau dua tahap pada berbagai variabel suhu reaksi dan nisbah molar metanol dengan minyak. Penelitian ini bertujuan membandingkan karakteristik físiko-kimia (viskositas, densitas dan bilangan asam) serta persentase ester asam lemak dari metil ester yang dihasilkan. Digunakan rancangan acak lengkap faktorial dengan tiga variabel perlakuan yaitu (A) tahap transesterifikasi (A1= satu tahap, A2= dua tahap), (B) suhu reaksi (B1= 30oC, B2= 65oC) dan (C) nisbah molar metanol-minyak (C1=3:1, C2=4:1, C3=5:1 dan C4=6:1), serta dua kali ulangan. Hasil penelitian menunjukkan bahwa proses transesterifikasi satu tahap pada suhu 30°C dengan nisbah molar metanol- minyak 5:1 menghasilkan karakteristik metil ester terbaik yaitu viskositas kinematik 3,89 cSt, densitas 0,88g/cm3 dan bilangan asam 0,48 mg KOH/g sampel. Tidak terdapat perbedaan jenis senyawa ester asam lemak pada metil ester hasil transesterifikasi satu dan dua tahap yaitu berturut-turut metil oleat (47,09-47,46%), metil linoleat (32,20-32,53%), metil palmitat (18,65-18,93) dan metil lignoserat (0,26-0,30%). Jumlah persentase senyawa ester asam lemak yang menunjukkan persentase konversi trigliserida menjadi metil ester pada proses satu tahap adalah 100%, sedangkan pada proses dua tahap adalah 99,62%. Rendemen (yield) metil ester pada proses satu tahap adalah 77,99%, lebih tinggi dibandingkan proses dua tahap yaitu 70,80%. Berdasarkan karakteristik dan rendemen metil ester, proses satu tahap lebih baik dibandingkan dua tahap. The Characteristics of Methyl Esther of Jatropha Oil Obtained From One and Two Steps Transesterification Process Biodiesel (methyl esther) is made mainly through transesterification process of vegetable oil such as jatropha oil and generally uses methanol as reagent and KOH as catalyst. There are one-step and two-steps process using variables of reaction temperature and molar ratio of methanol to oil.This experiment aimed comparing physico-chemical characteristic (viscosity, density and acid number) as well as percentage of fatty acid esters of methyl esters as its pararnaters of these two type process. Factorial completely randomized design with two replication was used as experiment design with three variables treatments, namely (A) transesterification steps: (A1) one step, (A2) two steps; (B) reaction temperatues: (Bl) 30°C, (B2) 65°C; and (C) molar ratio of methanol to oil: (CI=3:1, C2=4:1, C3=5:1 dan C4=6:1). it was concluded that the best treatment was one step process at 30°C using molar ratio methanol: oil 5:1. The characteristics of methyl ester were viscosity 3.89 cSt, density 0.88 g/cm3 and acid number 0,48 mg KOH/g sample. The fatty-acids esters of methyl esters of both processes was the same i.e. methyl oleic (47.09-47.46%), methyl linoleic (32.20-32.53%), methyl palmitic (18.65-18.93%) and methyl lignoseric (0.28-0.30%). Total percentage of fatty acid esters in methyl ester of one step process was 100% while that of two steps process was 99.62%. This total percentages could ·indicated as conversion degree of triglyceride into methyl ester. Yields of methyl ester from one-step process was 77.99% which was higher than that of two-steps process (70.80%). In terms of its characteristics and yield of methyl ester, one-step process was better than two-steps process.
Keywords
biodiesel; Jatropha curcas L; metil ester; minyak jarak pagar; transesterifikasi; jatropha oil; methyl ester; transesterification.