Bio-oil Derived from Indonesian Oil Palm Empty Fruit Bunch (EFB) using
Middle-scale Slow Pyrolysis
Yano Surya Pradana, Ade Kurniawan, and Arief Budiman*
Chemical Engineering Department, Gadjah Mada University, Yogyakarta, Indonesia
*) Corresponding author:Phone: +62-274-902171, Fax: +62-274-902170, e-mail: abudiman@chemeng.ugm.ac.id
Abstract
Indonesia now is the largest producer of palm oil in the world. Over seven million hectares in the cultivation and more than 400 palm oil mills in operation. The major biomass byproduct from the palm oil industry is empty fruit bunches (EFB) that have a great potency as basic raw materials used for alternative energy. We have introduced a new technology for utilizing biomass waste for producing alternative energy (gasoline, kerosie and bio-solar) by combining pyrolysis-catalytic cracking-gasification processes in a whole system, namely as integrated autothermal technology. By using this technology, energy supplied to the system can be reduced significantly.
In this study, pyrolysis of Indonesian oil palm empty fruit bunches (EFB) was investigated using a middle-scale slow pyrolysis. The products were bio-oil, char and gas. Then, bio-oil produced from this pirolysis can be used as feedstock for catalytic cracking. The effects of various pyrolysis temperatures, water content and different feedstock on the yields of the products were investigated. The temperature of pyrolysis and water content were varied in the range of 400-600°C and 13-18 %wt, respectively. The different feedstock was varied in the range of 500; 1,000; and 1,500 grams. The average heating rate was at 12oC min-1 to a final pyrolysis temperature. Product yields were found to be significantly influenced by the pyrolysis process conditions. Under the experimental conditions, the optimum bio-oil yield was 10.83 %wt obtained at 500°C, with water content of 18 %wt. While different feedstock has no significant effect on bio-oil yield. The maximum yield of char was 35.39 %wt, obtained at a pyrolysis temperature of 400°C, feedstock of 1000 grams. Meanwhile, the optimum yield of gas was 37.71 %wt, which could be achieved at a pyrolysis temperature of 450°C, feedstock of 1000 grams.
Keywords: palm empty fruit bunch, pyrolysis, integrated autothermal, bio-oil
1. Introduction
Ever since the lack of petroleum resources began with the global energy crisis, including Indonesia, considerable attention has been focused on the development of alternative fuels. Among the available alternative energy sources, biomass has drawn significant attention since it holds various advantages compared with fossil fuel in terms of renewability, non-toxicity and environmental friendly. Unlike fossil fuel, fuel from biomass has advantage in maintaining a closed carbon cycle with no net increase in atmospheric CO2
levels (Gercel, 2002). Biomass takes carbon out of the atmosphere while it is growing and returns it as it is burned. Moreover, its negligible sulfur and nitrogen are the main advantages of using biomass for preventing the acid rain (Sharma and Bakhshi, 1991). Besides, biomass is very abundant and cheap, and relatively clean, it can be used in such commercial businesses as airlines, meaning it is good for the environment and good for businesses (Liang and Kozinski, 2000).
However, Indonesia is currently the largest producer and exporter of palm oil worldwide. According to data from the Indonesian Ministry of Agriculture the total area of oil palm plantations in Indonesia is currently around eight million hectare, a number which is twice as much as in the year 2000 when around four million hectare of Indonesian soil was used for palm oil plantations. This number is expected to increase to 13 million hectare by 2020. Based on data of Badan Pusat Statistik (Statistic Indonesia) in 2013, Indonesia produced 28 million tons of oil palm to produce crude palm oil. This process generates 30-40% of biomass wastes such as oil palm empty fruit bunch (EFB), palm kernel shell and mesocarp fiber at palm oil mills.
The oil palm EFB is one of the high carbon content solid materials, which is currently used as a combustion boiler fuel with very low efficiency. It contains cellulose, hemicellulose and lignin which have high carbon and hydrogen contents, comparable with hard wood. Thus, this biomass wastes have inherently high energy content, which can be converted to useful form of energy using modern technology such as pyrolysis process (Asadullah, 2013). The pyrolysis of biomass is a very old energy technology that is becoming interesting again among various systems for the energetic utilization of biomass (Duman et al., 2011). By combining pyrolysis-catalytic cracking-gasification processeses in a whole system, the new technology have been introduced for utilizing biomass waste for producing alternative energy (bio-gasoline, bio-kerosie and bio-solar), namely as integrated autothermal technology (Budiman, 2014). By using this technology, energy supplied to the system can be reduced significantly.
Pyrolysis is the chemical decomposition through the application of heat in the absence of oxygen (Cordella et al., 2012). Basu (2010) explains that during the pyrolysis process, biomass converted to liquid product (also known as bio-oil or tar), a solid residue (also known as char) and several light gaseous compounds (e.g. carbon dioxide, carbon monoxide, hydrogen and light hydrocarbon), as illustrated in Figure 1. The relative product proportions of which depend very much on the pyrolysis method and process conditions (Islam et al., 1999).
Figure 1. Pyrolysis in a biomass particle
250 0C min-1) of organic material to 450 - 600 0C in the absence of oxygen and relatively short gas residence time (several seconds) (Zhang et al., 2007). Slow pyrolysis will produce mainly charcoal and fast pyrolysis will produce mainly bio-oil and gas (Duman et al., 2011).
Bio-oil is a complex mixture of several hundreds of organic compounds, mainly including acids, alcohols, aldehydes, esters, ketones, phenols and lignin-derived oligomers. Some of these compounds are directly related to the undesired properties of bio-oil. The undesired properties of bio-oil, compared with heavy petroleum fuel oil, for fuel applications are high water content, viscosity, ash content, oxygen content and corrosiveness. Because of these undesired properties, the potential of direct substitution of bio-oil for petroleum fuels and chemical feed stocks is limited. Consequently, upgrading bio-oil is necessary to give a liquid product that can be used as a liquid fuel or chemical feed stocks in various applications (Ki et al, 2013). Chemical upgrading bio-oil to a conventional transport fuel such as diesel, gasoline, kerosene, methane and LPG requires full deoxygenating and conventional refining. Bio-oil can be upgraded by hydrotreating, catalytic vapor cracking, esterification & related processes, and gasification to syngas followed by synthesis to hydrocarbons or alcohols (Demirbas, et al, 2011; Bridgwater, 2012).
In this study, Indonesian oil palm EFB was pyrolysed under different condition in a midle-scale of slow pyrolysis to produce bio-oil and the products obtained were characterized.
2. Experimental
2.1. Pyrolysis Experiments
The oil palm EFB was collected from palm oil mill in Riau, Indonesia. After collecting, it was sun-dried for two days in order to remove unbound moisture. Pyrolysis of the oil palm EFB was carried out using batch reactor. The reactor was heated by LPG burner. The temperature of the reactor was determined by inserting a thermocouple in the middle of the reactor. The experimental rig consisting of the bio-oil condensation system is illustrated in Figure 2.
The oil palm EFB feedstock was weighted and introduced into the reactor. The burning of the reactor and the condensation system of bio-oil were then started. The whole experiment must be held for either a minimum of 1 hour or until no further significant release of gas was observed. During pyrolysis, gas produced from the reactor was streamed into cyclone, as the first condensation system. The liquid product collected in the cyclone was transferred into flask. The cyclone-uncondensed gas was streamed into two pipe-condensers, as the second condensation system. The liquid product from second condensation system was taken in the end of second pipe-condenser and transferred into flask. The bio-oil was then physically separated from liquid product by separation funnel. Meanwhile the uncondensed gas was then burned in burner. It is used for substituting LPG as fuel in pyrolysis process. The amount of the uncondensed gas was calculated from the material balance.
2.2. Effect of Temperature
The first series of experiments was performed to determine the effect of the pyrolysis temperature on pyrolysis yields. The average heating rate was at 120C min-1 to a final temperature of 400, 450, 500, 550 and 600 0C with 1000 g of oil palm EFB feedstock and 18 %wt of oil palm EFB water content.
2.3. Effect of Water Content of Feedstock
The second series of experiments was performed to determine the effect of the water content of feedstock on pyrolysis yields. Water content of feedstock of 13 and 18 %wt was studied. The final pyrolysis temperature was maintained at 500 0C and feedstock was 1000 g. For observing 13% of water content, the EFB was dried at 110 0C for 4 hours after it was sun-dried.
2.4. Effect of Feedstock
The third series of experiments was performed to determine the effect of the feedstock on pyrolysis yields. Feed-stocks of 500, 1000 and 1500 g were studied. The final pyrolysis temperature was maintained at 500 0C and water content of feedstock was 18 %wt.
3. Results
3.1 Effect of Temperature
The effect of final pyrolysis temperature on product yields is shown in Figure 3. At the lowest pyrolysis temperature of 400 0C, decomposition of oil palm EFB was insignificant as char was the major product. At this condition, the char yield was 35.39 %wt of feedstock. It tended to decrease by increasing final pyrolysis temperature. Gas yield was obtained at the range 29-34 %wt of feedstock over the temperature range of 400 0C to 600 0C. It tended to increase by increasing final pyrolysis temperature. The gas yields reached a maximum value of 37.71 %wt of feedstock at the lowest pyrolysis temperature of 450 oC. Asadullah et al. (2013) studied on pyrolysis of palm kernel shell and Sukiran et al. (2009) studied on pyrolysis palm EFB using fluidized bed reactor respectively, indicated the similar trend of gas and char yield.
decreased to 10.28 %wt of feedstock and 10.83 %wt of feedstock. Meanwhile, the optimum bio-oil product was obtained at 500 oC in the value of 10.83 %wt of feedstock. At 500 oC, the final pyrolysis temperature was easier to be achieved and relatively more stable than at 600
o
C. It saved energy for pyrolysis. The higher temperature, the energy wasted to the environment was also higher. For stabilizing pyrolysis temperature, the higher temperature will need more energy to be supplied into the reactor.
Figure 3. Pyrolysis yields at different temperature
3.2 Effect of Water Content of Feedstock
The effect of water content of feedstock on product yields is shown in Table 1. The bio-oil yields reached a maximum value of 10.83 %wt of feedstock with the highest water content of feedstock of 18 %wt. Demirbas (2004) studied on pyrolysis of biomass respectively, indicated the similar trend of bio-oil yield.
In this study, the highest gas yield was obtained at the water content of feedstock of 13 %wt. Char yield was obtained at the range 29-31 %wt of feedstock over the water content of feedstock variation. Water-phase yield was obtained at the range 26-37 %wt of feedstock over various water content of feedstock.
Table 1. Yields of pyrolysis product at various water contents of feedstock at temperature of 500 0C and feedstock of 1000 g.
Product Yields of pyrolysis product (%wt of feedstock) Water content of 18 %wt Water content of 13 %wt
Water-phase 27,02 26,67
Bio-oil 10,83 9,89
Char 30,608 29,37
Gas 31,54 34,07
3.3 Effect of Feedstock
bio-oil over various feedstocks were generally insignificant. The maximum value of gas yields was 36.53 %wt of feedstock with the highest feedstock of 1500 g. Char yield was obtained at the range 27-31 %wt of feedstock over the feedstock range of 500 g to 1500 g.
Table 2. Yields of pyrolysis product at various feedstocks at temperature of performed in a batch reactor. The optimum bio-oil yield was 10.83 %wt obtained at 500 °C, feedstock of 1000 g water content of 18 %wt. While different feedstock has no significant effect on bio-oil yield. The maximum yield of char was 35.39 %wt, obtained at a pyrolysis temperature of 400 0C, feedstock of 1000 g and water content of 18 %wt. Meanwhile, the maximum yield of gas was 37.71 %wt, which could be achieved at a pyrolysis temperature of 450 0C, feedstock of 1000 g and water content of 18 %wt.
Acknowledgments
The authors would like to acknowledge the financial support from Directorat General of Higher Education, the Ministry of Education and Culture, Indonesia through MP3EI project no. 1971/E5.2/PL/2013. We also gratefull to Ni’mah Ayu Lestari and Septian Arif of Process System Engineering research group (PSErg), Chemical Engineering Department UGM for their valuable assistance with the experiments.
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