Pirolisis cepat serbuk gergaji kayu jati :: Yields, sifat fisik, komposisi bio-oil dan kinetika

DJAUHARI, Agus, Prof.Ir. Wahyudi B. Sediawan, SU.,Ph.D

2006 | Tesis | S2 Teknik Kimia

Krisis energi mendorong pencarian sumber alternatif baru untuk memenuhi kebutuhan energi guna meningkatkan pertumbuhan ekonomi Indonesia. Pirolisis adalah proses perengkahan biomassa oleh kalor menghasilkan bio-oil yang dapat digunakan sebagai bahan bakar alternatif disamping bahan bakar konvensional yang bersumber pada bahan baku fosil. Potensi ekonomi lain dari bio-oil hasil pirolisis adalah kandungan senyawa didalamnya yang dapat dijadikan sebagai bahan kimia.Tujuan penelitian ini adalah membuat bio-oil, menguji / analisis sifat fisik, jenis (kuanlitatif) dan jumlah (kuantitatif) senyawa kandungannya, mengetahui pengaruh variabel proses seperti suhu, laju alir gas N2, kecepatan suplai kalor dan mencari model kinetika reaksi yang tepat untuk memprediksi yield bio-oil pada proses pirolisis. Pirolisis cepat (fast pyrolysis) dilakukan dalam reaktor fixed-bed berukuran diameter ½ in dan panjang 6 in menggunakan bahan baku biomassa serbuk gergaji kayu jati (Tectona Grandis L.F) tanpa hadirnya oksigen pada tekanan atmosferik. Kondisi operas divariasikan antara suhu 300 – 450oC, laju alir antara N2 0,8 – 4,0 mL/detik dan tegangan catu daya antara 100 – 160 volt. Sebelum proses pirolisis berjalan, dilakukan penghilangan air terikat dalam bahan baku dengan cara mengatur set suhu pada 150oC. Sifat- sifat fisik bio-oil adalah berwarna coklat tua, rapat massa (ρ) 1,125 g/mL, viskositas kinematis (ν) 3,35 cSt, pH ± 3, nilai kalor 32 MJ/kg, sedangkan kandungan senyawa terbesar adalah asam asetat sebanyak 22,48 %. Variabel berpengaruh terhadap yields adalah suhu dan kecepatan suplai kalor, sedangkan laju alir N2 kurang berpengaruh. Suhu 400oC menghasilkan yield bio-oil terbanyak yaitu 51,2 % sedangkan pemakaian tegangan catu daya 160 volt memberikan yield bio-oil tertinggi dalam penelitian ini, yaitu 60,1 %. Model kinetika-3 terdiri dari 3 tahap reaksi, yaitu selulosa menjadi bio-oil, selulosa menjadi anhidroselulosa dan anhidroselulosa menjadi char ditambah gas merupakan model paling tepat digunakan untuk memprediksi jumlah bio-oil, besarnya harga konstanta kecepatan reaksi over all rata-rata antara suhu 300 – 400oC, laju alir gas N2 2,4 mL/detik dan tegangan catu daya 130 volt adalah k1= 0,068 menit –1, k2 = 0,147 menit –1, k3 = 0,044 menit –1.

Energy crisis has promoted the search for new alternative energy resources to meet increasing energy demand for Indonesian economic growth. Pyrolysis is a process of biomass cracking using heat to produce bio-oil which can be used for fuel as an alternative to conventional fossil fuel. Another potential use of bio-oil as a product of pyrolysis is its chemical contents which can be used as raw materials for various useful chemicals. Objectives of this research are to prepare bio-oil, to determine its physical properties, both qualitatively and quantitatively, and to observe the effects of process variables such as temperature, nitrogen gas flowrate, and the rate of power supply to the yield of bio-oil. Another objective is to find the most appropriate reaction kinetics to predict the yield of the pyrolysis process. Fast pyrolysis under atmospheric pressure with the absence of oxygen was carried out in a fixed bed reactor of ½ inches diameter and 6 inches long. Sawdust from teak wood (Tectona Grandis L.F) was used as biomass source. Process conditions were varied as follows; temperature between 300 to 400oC, rate of nitrogen gas flow between 0.8 to 4.0 mL/s, and power supply (voltage) between 100 to 160 volt. Prior to pyrolysis, bound water was removed from sawdust feed by controlling and setting the reactor at 150oC. The bio oil product was dark brown in color, having specific gravity of 1.125 g/mL, kinematic viscosity of 3.35 cSt, pH ± 3, and having calorific value of 32 MJ/kg. The bio oil product contains 22.48% acetic acid as the biggest chemical constituent. Temperature and the rate of heat supply (voltage) significantly affect the yield of bio-oil, whereas rate of nitrogen gas flow affect less significantly. Operation at 400oC produced the highest percentage (51.2 %) yield of bio oil, while power supply (voltage) at 160 volt gave also highest (60.1 %) yield of bio oil. Reaction kinetics-3 model which describes three reaction stages, namely the reaction of cellulose to produce bio oil, reaction of cellulose to produce anhydrocellulose, and the reaction of anhydrocellulose to produce char and gases, was the most appropriate reaction model to predict yield of bio oil product. The average overall rate of reaction constants, at temperature between 300 to 400oC, nitrogen gas flowrate 2.4 mL/s, and power supply at 130 volt, were found to be k1 = 0,068 minute –1, k2 = 0,147 minute –1, and k3 = 0,044 minute –1.

Kata Kunci : Pirolisis,Bio Oil,Bahan Kimia, pyrolysis, bio-oil, chemicals