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Production of bio-oil from fixed bed pyrolysis of bagasse
Fuel 86 (2007) 2514–2520 www.fuelfirst.com
Production of bio-oil from fixed bed pyrolysis of bagasse M. Asadullah *, M.A. Rahman, M.M. Ali, M.S. Rahman, M.A. Motin, M.B. Sultan, M.R. Alam Department of Applied Chemistry and Chemical Technology, University of Rajshahi, Rajshahi 6205, Bangladesh Received 4 October 2006; received in revised form 1 February 2007; accepted 6 February 2007 Available online 7 March 2007
Abstract The objective of this work was to produce renewable liquid fuel (bio-oil) from locally produced bagasse by pyrolysis in a batch feeding and fixed bed reactor. The experiments were performed at different temperatures ranging from 300 to 600 C. The bio-oil was collected from two condensers of different temperatures and defined as oil-1 and oil-2. The maximum total yield of bio-oil was found to be 66.0 wt% based on bagasse. The carbon based non-condensable gases were CO, CO2, methane, ethane, ethene, propane and propene. The density and viscosity of oil-1 were found to be 1130 kg/m3 and 19.32 centipoise and that were 1050 kg/m3 and 4.25 centipoise for oil-2, respectively. The higher heating values (HHV) of them were 17.25 and 19.91 MJ/kg, respectively. The pH of the bio-oils was found to be around 3.5 and 4.5 for oil-1 and oil-2, respectively. The water, solid and ash contents of oil-1 and oil-2 were determined and found to be around 15, 0.02 and 0.03 wt% and 11, 0.01 and 0.02 wt%, respectively based on bagasse. 2007 Elsevier Ltd. All rights reserved. Keywords: Bagasse; Pyrolysis; Bio-oil
1. Introduction Energy is the driving force for the development of world economy. Fossil fuels such as petroleum, coal and natural gas satisfy the major fraction of total need of world’s energy. However, the burning of fossil fuels causes green house gas emission which has many divers role to the environment [1]. In addition, the deposition of fossil fuels is limited. But the demand of energy is growing at high rate due to the development of all aspects of the world. To meet the growing demand of energy and to help solve the environmental problems, the world trends are moving towards sustainable energy production, reduced vehicle and industrial pollution, green house gas and waste minimization and distributed electricity generation. Biomass energy
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which is renewable in nature has a role to play in each one of these energy and environmental concern [2,3]. Various types of biomasses such as agricultural residues, forestry products and city wastes are abundantly available in the world, which can be used for energy production in several ways from old direct burning to modern gasification and pyrolysis. The solid biomass can be converted to the combustible liquid usually termed as bio-oil by pyrolysis and to the combustible gases by gasification. The liquid and gas products can be used in engine and turbine for power generation. The gasification of biomass for power generation has some disadvantages such as it needs coupling between gasification and power generation units and the difficulty of storage, transportation and handling of gaseous fuels. Liquid fuel (bio-oil) has some advantages in transport, storage, combustion, retrofitting and flexibility in production and marketing [4]. The bio-oil is a mixture of about 200 types of major and minor organic compounds and this can be used as a source of some pure chemicals such as alcohol, phenol, aldehyde, organic acids, etc. [5]. As a fuel it can be directly used in engine, turbine and furnace with
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Nomenclature HHV i.d. g p r t l
high heating value internal diameter coefficient of viscosity hydrostatic pressure difference radius of capillary tube of viscometer time of falling of liquid in viscometer length of capillary tube
some modification of equipment [6]. Work to date gives strong encouragement to believe that a diesel engine can be relatively easily modified to run on 95% crude pyrolysis oil (by energy content) with no deterioration in output or rating [7]. A 250 kW diesel engine has been modified to operate in dual fuel mode utilizing crude pyrolysis liquid as the main fuel supplemented by a pilot diesel fuel to provide a source of ignition. Nearly 200 h of operation have been achieved [7]. Fuel controlling in the combustion process is the most important factor for stable operation of engine and this is easier in the case of liquid fuels. The agro-based biomass is usually produced at the rural area where a large scale pyrolysis plant can be installed. Due to the decoupling nature of the pyrolysis plant, the bio-oil based small scale power generation plant can be installed in the remote area where the bio-oil can be supplied and this is one of the most important advantages of biomass pyrolysis for liquid production [8]. By this way the agro-based biomass can efficiently be used for energy production. The by-products of the pyrolysis plant are burnable gas and char. These char and gas products can be burnt for pyrolysis reactor heating, thereby reducing the additional production cost for heating system. About 7.3 million metric tons of can sugar is produced per year in Bangladesh. With sugar, about 21 million metric tons bagasse is produced as by-product per year. A part of the bagasse is used for steam power generation inside the sugar industry for self use and rest of the bagasse is using for energy in unorganized sectors [9]. In both of the cases the heat is produced by combusting the bagasse. Due to the variation of geographic and climate conditions at the different places on the earth, the physical characteristics and chemical composition of the bagasse can be varied in a great extent. However, there is not a single report on the characterization and utilization of the Bangladesh based bagasse for pyrolysis to produce bio-oil. This paper contributed to the characterization of bagasse, its pyrolysis for bio-oil production and characterization of bio-oil. 2. Experimental 2.1. Feed stock preparation The raw bagasse obtained from the outlet of the sugar industries usually contains moisture more than 10 wt%.
v g FID TCD TGA oil-1 oil-2
volume of liquid gravitational force flame ionization detector thermal conductance detector thermogravimetric analysis bio-oil in first condenser bio-oil in second condenser
Table 1 Proximate and ultimate analyses of different biomasses Properties Moisture content (wt%) Particle size (mm) Density (dry powder) (g/cc) Heat value (HHV) (MJ/kg) Proximate analysis Volatile fraction (wt%) Fixed carbon (wt%) Ash content (wt%) Ultimate analysis (dry basis wt%) C H O N Cl S
4 0.5–1.0 0.12 19.2 68–70 28.7–30.7 1.26 48.58 5.97 38.94 0.20 0.05 0.05
However, the higher moisture content in the feed stock yields in higher water content bio-oil. Thus, prior to the pyrolysis of bagasse it was dried in the sunlight to reduce the moisture content less than 10 wt%. Then the bagasse was crushed with a crushing machine to about 0.5– 1.0 mm in particle size. The properties as well as ultimate and proximate analyses of bagasse were carried out and summarized in Table 1. 2.2. Pyrolysis procedure For the production of bio-oil the bagasse has been pyrolized in a laboratory scale fixed bed reactor. A conceptual design of the process is shown in Fig. 1. The reactor is made of stainless steel with the dimension of 50 cm height and 10 cm i.d. About 200 g of bagasse was fed in a batch in the reactor. The reactor was set vertically and N2 gas was introduced inside the reactor at the rate of 200 ml/min from the bottom and passed through the top of the reactor. The flow of nitrogen replaces the air from the reactor and permits the pyrolysis reaction under anaerobic condition. The vapor as well as gases formed from the pyrolysis of the bagasse inside the reactor flows out along with N2 from the top of the reactor. The gas mixture was passed through two condensers. The first condenser was cooled with the flow of tap water and by which the vapour temperature was reduced to around 60 C. The second condenser was cooled with the circulation of ice water mixed with NaCl
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Gas bag
Reactor
Furnace Condenser, -5oC
Water Ice water with NaCl Condenser, 60oC
Thermocouple Oil -1
Oil -2
N2 gas Fig. 1. Conceptual design for fixed bed pyrolysis reactor.
by means of a small pump, thereby reducing the temperature to around 5 C. No vapour was visually escaped from the second condenser. The liquid products from the first condenser and second condenser were collected in conical flasks fitted to the condensers. The non-condensable gas was collected in a gas bag. The yield of bio-oil based on weight ratio was calculated by (the amount of bio-oil collected for a certain batch/total amount of bagasse in that batch) · 100. The conversion of bagasse to gas was calculated by (the amount of carbon based gas collected in a gas bag for a certain batch/total feeding of bagasse for that batch) · 100. The char produced was remained in the reactor and collected after completing the pyrolysis reaction. The char yield was calculated by (the amount of char collected for a certain batch/total amount of bagasse in that batch) · 100.
2.3. Characterization of bio-oil The density, viscosity, pH value, heating value, water content, solid content, lignin content and ash content of crude bio-oil were measured. The density was measured with a density measurement bottle. Viscosity of a liquid is the measure of its internal friction which resists the flow of the fluid. The viscosity of bio-oil was measured according to the ASTM D 445 using the following equation: g ¼ pPr4 t=8lv ¼ phqgr4 t=8lv ½10
where g is the viscosity (dynes/cm2 or poise), v is the volume of liquid (c.c.), t is the liquid flowing time (s), r is the radius of narrow tube (cm), l is the length of narrow tube (cm). The pH was measured with a digital pH meter (Hanna, Model – HI 8424). Calorific value of bio-oil was measured by means of an oxygen bomb calorimeter. Water content in the bio-oil was measured by Karl Fischer titrimetric method. The measured sample was titrated with Karl Fischer reagent. When all of the water has been consumed in the Karl Fischer reagent the end point of the solution was signaled by the appearance of a slight excess of the pyridine iodine complex. It was detected by brown color, which is intense enough for a visual end point. The color change was observed from the yellow of the reaction products to the brown of the excess reagent. The amount of water in the sample was calculated as 1 ml Karl Fischer reagent = 3.5 mg water. The solids content in the pyrolysis oil were measured as ethanol insoluble portion. A certain amount of oil was weighed (25–50 g) and dripped into a beaker containing 250–500 ml ethanol solvent and agitated by magnetic stirrer. The solution was then filtered on a filter paper (0.1 lm pore size) followed by drying. The insoluble portion remained on the dried filter paper was weighed out. The lignin portion was measured as water insoluble fraction by using phase separation. The acid value of the pyrolysis oil was determined by direct titration with standard KOH solution. Ash content was measured by burning the
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bio-oil sample with supplying excess air in a Muffle furnace.
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bagasse was 19.2 MJ/kg which was quite comparable with the energy content of cedar wood 19.1 MJ/kg [11]. This is one of the clear views that bagasse can be successfully used for bio-energy plant for bio-oil production.
3. Results and discussion 3.1. Proximate and ultimate analyses The physical properties and chemical composition of feed stock play a major role in the yield and properties of bio-oil. Therefore, the bagasse which was the feed stock of this investigation was characterized in view to know the physical properties and chemical composition. The results are summarized in Table 1. The green biomass usually contains about 50 wt% moisture; however, the moisture content in the sun dried biomass varied in the range of 3–10 wt%. The moisture content of the sun dried bagasse was obtained 4 wt% as shown in the thermogravimetric profile in Fig. 2. The water content in the feed stock entirely goes to the bio-oil product. For the application of bio-oil as fuel needs minimum water content. Since the water content in the bagasse was low, the water content in the bio-oil seems to be low. The thickness of the particle has an important role in the surface area per unit weight, the lower the particle size the higher the surface area which leads to the high heat transfer rate from the outer surface to the center of the particles. Thus, the bagasse was crushed with a crushing machine and the particle size was maintained within the range of about 0.5–1.0 mm size. The bulk density of dry bagasse was found to be 120 kg/ m3. It was measured as the weight of oven-dried bagasse contained in a unit volume of green bagasse in kg/m3. Available energy content in the unit volume of biomass must be known for planning a bioenergy project as it affects the size of plant, the storage area needed and the transportation arrangements. The density and energy content in bagasse is comparable with some woody biomass [11]. It has been found that the bulk density of bagasse (120 kg/m3) was higher than the bulk density of cedar wood (70 kg/m3). Furthermore, the energy content in the 120
Weight loss, %
100
The proximate and ultimate analyses of bagasse were performed and the results are summarized in Table 1. The proximate analysis was based on the thermogravimetric analysis (TGA) profile as shown in Fig. 2. About 10 mg of sample for this analysis was used and heated from room temperature to 900 C at the rate of 10 C/min under the flow of N2 at the rate of 200 ml/min. From the figure it can be clearly seen that the volatile fraction of bagasse until around 400 C was 68–70 wt% (dm), the fixed carbon was 27–29 wt% (dm). The rest 3 wt% (dm) was ash content in the bagasse. These values are slightly different from the reported results [12]. The volatile materials mainly derived from the cellulose and hemicellulose which was likely to be converted to bio-oil in pyrolysis. The carbon which converted to char or other solid carbonaceous materials was called the fixed carbon. This carbon was mainly derived from the lignin in the bagasse. The fixed carbon is difficult to vaporize at pyrolysis temperature around 500 C. From Fig. 2 it is seen that the fixed carbon does not evaporate even at around 1000 C. The fixed carbon was actually formed the char in the pyrolysis reaction. This results reveal that the higher the volatile content the higher the bio-oil yield from the pyrolysis of bagasse. In comparison the volatile content in bagasse was higher than many other agricultural residues and forestry products [13]. In addition, since bagasse contains very small amount of ash [14] comparing with other agricultural biomass such as rice straw (22.6 wt% ash) [13] and other poisonous component such as sulfur, it can be considered as a suitable feed stock for low temperature pyrolysis to produce bio-oil. From the ultimate analysis it has been found that the bagasse contains 48.58% C, 5.97% H, 38.94% O, 0.20% N, 0.05% Cl and 0.05% S. Carbon content in bagasse was much higher than rice straw [13]. 3.2. Pyrolysis of biomass
80 60 40 20 0 0
200
400
600
800
1000
o
Temperature C Fig. 2. TGA profile of bagasse under nitrogen atmosphere.
About 200 gm of bagasse was fed in the reactor. The temperature was increased at the rate of 50 C/min. When the reactor temperature crossed 300 C, the pyrolysis reaction started and a thick white smoke was observed in two liquid collectors. The pyrolysis reaction was continued till the vapour was produced at different temperatures. Initially a sample experiment was performed at 500 C. The bio-oil collectors were connected to two long condensers. It was observed visually that no smoke (or aerosols) was escaped from the second condenser. The product distribution of bagasse pyrolysis at 500 C is presented in Table 2. Bio-oil collected in the first collector was defined as ‘oil-1’ and that in the second collector as
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Table 2 Product distribution of bagasse pyrolysis Pyrolysis conditions Amount of bagasse (g) Temperature (C) Temperature increasing rate (C/min) Nitrogen gas flow rate (ml/min) Pyrolysis products Bio-oil yield Oil-1 in first condenser (g (wt%)) Oil-2 in second condenser (g (wt%)) Total bio-oil (g (wt%)) Char yield (g (wt%)) Gas yield (g (wt%))
200 500 50 200
104.0 (52.0) 28.1 (14.0) 132.1 (66.1) 49.7 (24.9) 18.2 (9.0)
‘oil-2’. The yield of oil-1 in the first collector was 52.0% (on bagasse basis) and the yield of oil-2 in the second collector was 14.0%. The total of 66.0% bio-oil yield has been achieved. The oil-1 was more viscous than oil-2. The carbon based non-condensable gas was the mixture of carbon monoxide, carbon dioxide, methane, ethane, ethene, propane, propene, etc. But the concentration of ethane, ethene, propane, propene was much smaller than methane. These gases were identified by gas chromatograph equipped with flame ionization detector (FID). Small amount of hydrogen was formed which was detected by TCD gas chromatograph. The gas and char yields were 24.9 and 9.1 wt%. 3.3. Effect of temperature on the product distribution The pyrolysis of bagasse was performed at different temperatures from 300 to 600 C to evaluate the effect of temperature on the product distribution for a certain amount of bagasse (200 g) pyrolysis (Table 3). In all experiments, the reactor was kept for a certain length of time after reaching the final temperature. At low temperature such as 300 C, where the decomposition of bagasse just started (as shown in TGA profile, Fig. 2) the bio-oil product was very low both in the first collector (oil-1, 15.33 wt%) and in the second one (oil-2, 3.33 wt%). The total bio-oil yield was 18.66 wt%. The gas yield was only 4.34%. Most of the carbon in the bagasse was converted to the char at this temperature. This result is not consistent with TGA profile Table 3 Effect of temperature on product distribution of bagasse pyrolysis Temperature (C)
Yield of oil-1 (wt%)
Yield of oil-2 (wt%)
Total yield of bio-oil (wt%)
Char yield (wt%)
Gas yield (wt%)
300 350 400 450 500 550 600
15.33 44.66 53.33 58.66 52.06 47.30 44.66
3.33 6.66 7.33 6.81 14.07 13.33 14.66
18.66 51.32 60.66 65.47 66.13 60.63 59.52
77.00 43.8 31.93 26.26 24.86 24.66 22.86
4.34 4.87 7.41 8.27 9.01 14.71 17.82
Conditions: amount of bagasse – 200 g, nitrogen gas flow – 200 ml/min, heating rate – 50 C/min and retention time – 1 h.
as shown in Fig. 2. This can be explained in two ways. Firstly, in TGA analysis a small amount of bagasse was heated homogeneously in the TGA furnace so as to pyrolyse the total mass suddenly at the pyrolysis temperature in the small sample bin. Therefore, the chance of char formation in the sample bin was minimum. On the other hand, for pyrolysis of 200 g bagasse in the pyrolysis reactor, the heat was supplied from the outer source. So, the pyrolysis reaction was started from the wall side and most of the heat was consumed by the endothermic pyrolysis reaction at the wall side. By this time, the solid of the center of the reactor was heated very slowly and most of the carbon was converted to the char. Secondly, the secondary cracking reaction of pyrolytic vapor also produces char and coke like solid carbonaceous materials in the reactor. However, in the TGA sample bin the possibility of the secondary cracking of vapor was low due to the first removal of vapor from the small bin. As temperature increased the bio-oil and gas yields increased remarkably so as to decrease the char yield. The effect of temperature on the bio-oil yields in both collectors is shown in Table 3. The yield of oil-1, comparatively less volatile, increased until 450 C and then decreased with increasing temperature. However, in the second collector the yield of oil-2, comparatively high volatile, increased with increasing temperature until the final experimental temperature. Since the major fraction of bio-oil was in the first collector and it was decreased abruptly above 500 C, the total bio-oil yield was decreased above 500 C with further increase of temperature. The decrease of the yield of oil-1 with increasing temperature was due to the secondary cracking reaction of pyrolytic vapour to lower molecular weight organic products or gas products such as CO, CO2, CH4 and many other gaseous hydrocarbons. The low molecular weight organic products are comparatively high volatile and were not condensed in the first collector but were condensed in the second one. This was the reason for increasing the yield of oil-2 as temperature increased. The effect of temperature on char yield is also shown in Table 3. Char yield is a function of temperature. From the results it can be seen that the char yield decreased suddenly with increasing temperature from 300 to 450 C and then it decreased slowly with increasing temperature. At low temperature the secondary cracking and reforming of biomass derived high molecular weight organic molecules is difficult [15,16]. These reactions are completely temperature dependent and proceed usually above 400 C [17,18]. And the thermal cracking smoothly proceeds above 500 C. Thus, the yield of char in this process was very high at 300 C where cracking of high molecular weight compounds did not take place. 3.4. Bio-oil characterization Bio-oil consists of water and organic compounds. This liquid is a very complex mixture that contains molecular
M. Asadullah et al. / Fuel 86 (2007) 2514–2520 Table 4 Physical properties of bio-oil produced from bagasse Properties
Oil-1
Oil-2
Density at 20 C (g/cc) Viscosity, centipoise at 20 C pH Gross calorific value (MJ/kg) Water content (wt%) Char/solid content (wt%) Pyrolytic lignin content (wt%) Acid value (mg KOH/g) Ash content (wt%)
1.13 3.90 3.50 17.25 15.00 0.02 3.51 137.35 0.03
1.05 2.25 4.50 19.91 11.00 0.01 1.25 117.51 0.02
fragments of cellulose, hemicellulose, and lignin polymers. Extensive reviews on the chemical [19] and physical properties of pyrolysis oils have recently been published [5]. Before using bio-oil as fuels or chemicals it needs to be characterized. Thus, the bio-oil obtained in this work was characterized by measuring the density, viscosity, pH, calorific value, water content, solid (char) content, pyrolytic lignin content and ash content. The results are summarized in Table 4. Bio-oil was collected in two condensers at two different temperatures, 60 and 5 C, respectively. Thus, the low boiling fraction was collected in first condenser (oil-1) and high boiling fraction was collected in second condenser (oil-2). The properties of two different fractions are different. The organic compounds of low boiling fraction are highly burnable. Therefore, for fuel application and for chemicals separation from bio-oils, the fractionation of bio-oil at different temperatures is significantly important. The density of bio-oil produced from bagasse was measured by density measurement bottle at 20 C. Densities of oil-1 and oil-2 were found to be 1130 and 1050 kg/m3, respectively. These values are higher than that of light fuel oil which is around 850 kg/m3. Unlike hydrocarbon oils, the higher density of the bio-oils reflects the high oxygen content, rather than a high polycyclic aromatic content. The viscosity is important in many fuel applications [20]. For oil-1 and oil-2 they were 19 and 4.25 centipoise, respectively at 20 C. The proposed viscosity of biomass derived light oil is 2.0–4.3 centipoise and that of medium oil is 6.2– 27 centipoise [21]. The viscosities of the experimental samples are within the range of proposed specification of biomass pyrolysis liquids. The bio-oil usually contains some of organic acids such as formic and acetic acids, which cause the oils to have a pH of between 3.0 and 4.5. The pH of the bio-oils was found to be around 3.5 and 4.5 for oil-1 and oil-2, respectively. This pH value is slightly higher than that of wood pyrolysis liquid (maximum pH 3.7) [22]. This acidity causes the pyrolysis oils to be corrosive to mild steel, aluminum, etc. Aldehydes also contribute to the low pH. Thus for application of bio-oil in the sophisticated engine, it needs some chemical treatment for lowering the acidity. The gross calorific value of oil-1 and oil-2 was found to be 17.25 and 19.91 MJ/kg, respectively. The water content
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decreases the available energy from the oil. In bio-oil water was completely miscible in the polar organic compounds. In oil-1 the water content was higher (15.00 wt%) than that of oil-2 (11.01 wt%) so as to decrease the calorific value of oil-1. The solid content in the bio-oil is defined as the heavy organic materials which is insoluble in some specific solvents in addition to the actual solids. For this test three solvents were used: ethanol, methanol and acetone. The solubility of the particle was dependent on the amount of solvent. Furthermore, the selection of the filter pore size was to some extent dependent on the particle size distribution of the liquid. The solid content was found to be 0.02 wt% for oil-1 and 0.01 wt% for oil-2. The pyrolytic lignin content is the measure of water insoluble fraction in the bio-oil. It was found to be 3.51 and 1.25 wt% for oil-1 and oil-2, respectively. The acid value or acid number of the oil was determined by direct titration with standard KOH solution using phenolphthalein as an indicator. The acid value of the oil-1 was found to be 137.35 and 117.51 for that of the oil-2, respectively. Finally, the ash content in the bio-oil was found to be 0.02 and 0.02 wt% for them, respectively. Bio-oil can be considered a micro-emulsion in which the continuous phase is an aqueous solution of holocellulose decomposition products, that stabilizes the discontinuous phase of pyrolytic lignin macromolecules through mechanisms such as hydrogen bonding. Aging or instability is believed to result from a breakdown in this emulsion. However, in our liquid the appearance is still homogeneous phase. The physical properties are not significantly changed within 8 months. However, the chemical analysis is under investigation. 4. Conclusions Bio-oil was produced from pyrolysis of bagasse in a fixed bed reactor at different temperatures ranging from 300 to 600 C. The bio-oil vapour was condensed in two condensers at different temperatures and the liquid products were defined as oil-1 and oil-2. The maximum total yield of bio-oil was found to be 66.0 wt%. The carbon based non-condensable gases were CO, CO2, methane, ethane, ethene, propane and propene. The values of density and viscosity are comparable with the proposed specification of the various grades of pyrolysis oils. Since bio-oil contains some organic acids, the pH of the bio-oils was found to be around 3.5 and 4.5 for oil-1 and oil-2, respectively. The other impurities in the bio-oil produced in this work are comparable with reported work. Thus, it can be used as liquid fuel. Acknowledgements This research was financially supported by the Ministry of Science and Information and Communication Technology under the project ‘‘Pilot Plant Project on the Produc-
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tion of Liquid Fuel from Biomass’’ No. MOSICT-SAP2005-2006/INT-13. References [1] Houghton JT, Ding Y, Griggs DJ, Noguer M, van der Linden PJ, Dai X, et al. Intergovernmental panel on climate change. Climate change 2001. Cambridge: Cambridge University Press; 2001. [2] McNelis B, van Roekel G, Preiser K. Renewable energy technology for developing countries, the future for renewable energy: prospects and directions, EUREC Agency, London; 2002. [3] McGowan F. Controlling the greenhouse effect: the role of renewables. Energy Policy 1991;19:111–8. [4] Bridgwater AV. An introduction to fast pyrolysis of biomass for fuels and chemicals. In: Bridgwater AV, Czernik S, Diebold J, Meier D, Oasmaa A, Peacocke C, et al., editors. Fast pyrolysis of biomass: a hand book. Newbury: CPL Scientific Publishing Services Ltd; 1996. p. 1–13. [5] Fagernas L. Chemical and physical characterization of biomass-based pyrolysis oils. Literature Review, Technical Research Centre of Finland, Espoo, 1995. VTT Research Note 1706. [6] Brown DB. Continuous ablative regenerator system, bio-oil production and utilization. In: Bridgwater AV, Hogan EN, editors. Proceedings of the 2nd EU-Canada workshop of thermal biomass processing. Berkshire: CPL Press; 1996. p. 96–101. [7] Leech J. Running a dual fuel diesel engine on crude pyrolysis oil. In: Kaltschmitt M, Bridgwater AV, editors. Biomass gasification & pyrolysis, state of the art and future prospects. Berkshire: CPL Press; 1997. p. 495–7. [8] Andrews RG, Patniak PC. Feasibility of utilizing a biomass derived fuel for industrial gas turbine applications. Bio-oil production and utilization. Proceedings of the 2nd EU/Canada workshop on thermal biomass processing. Newbury: CPL Press; 1996. p. 236–45. [9] Sector-Wise Final Consumption of Commercial Energy, Statistical Year Book of Bangladesh, Planning Division, Ministry of Planning, Government of People’s Republic of Bangladesh; 2004, p. 233–7. [10] Gurtu JN, Snehi H. Advanced physical chemistry. 7th ed. Meerut: Pragati Prokashana; 2000. p. 62. [11] Asadullah M, Miyazawa T, Ito SI, Kunimori K, Koyama S, Tomishige K. A comparison of Rh/CeO2/SiO2 catalysts with steam reforming catalysts, dolomite and inert materials as bed materials in low throughput fluidized bed gasification systems. Biomass Bioenergy 2004;26:269–79.
[12] Design and Development of 10–15 kW gasifier running on loose sugarcane leaves. Final project report submitted to Ministry of Nonconventional Energy Sources (MNES), Government of India, New Delhi by Nimbkar Agricultural Research Institute (NARI), Phaltan, May 1992. [13] Asadullah M, Miyazawa T, Ito SI, Kunimori K, Yamada M, Tomishige K. Gasification of different biomasses in a dual-bed gasifier system combined with novel catalysts with high energy efficiency. Appl Catal A: Gen 2004;267:95–102. [14] Keown DM, Favas G, Hayashi JI, Li CZ. Volatilisation of alkali and alkaline earth metallic species during the pyrolysis of biomass: differences between sugar cane bagasse and cane trash. Bioresource Technol 2005;96:1570–7. [15] Asadullah M, Miyazawa T, Ito SI, Kunimori K, Tomishige K. Demonstration of real biomass gasification drastically promoted by effective catalyst. Appl Catal A: Gen 2003;246:103–16. [16] Asadullah M, Miyazawa T, Ito SI, Kunimori K, Yamada M, Tomishige K. Catalyst development for the gasification of biomass in the dual-bed gasifier. Appl Catal A: Gen 2003;255:169–80. [17] Tomishige K, Miyazawa T, Asadullah M, Ito SI, Kunimori K. Catalyst performance in reforming of tar derived from biomass over noble metal catalysts. Green Chem 2003;5:399–403. [18] Tomishige K, Miyazawa T, Asadullah M, Ito SI, Kunimori K. Catalyst development for low temperature gasification of biomass: function of char removal in fluidized bed reactor. Stud Surf Sci Catal 2003;145:307–10. [19] Milne TA, Agblevor FA, Davis M, Deutch S, Johnson D. A review of the chemical composition of fast pyrolysis oils from biomass. In: Bridgwater AV, Czernik S, Diebold J, Meier D, Oasmaa A, Peacocke C, et al., editors. Fast pyrolysis of biomass: a hand book. Newbury: CPL Scientific Publishing Services Ltd; 1996. p. 70–5. [20] Diebold JP, Milne TA, Czernik S, Oasmaa A, Bridgwater AV, Cuevas A, et al. Proposed specifications for various grades of pyrolysis oils. In: Bridgwater AV, Boocock DGB, editors. Developments in thermochemical biomass conversion. London: Blackie Academic & Professional; 1997. p. 433–47. [21] Diebold JP, Milne TA, Czernik S, Oasmaa A, Bridgwater AV, Cuevas A, et al. Proposed specifications for various grades of pyrolysis oils. In: Bridgwater A, Czernik S, Diebold J, Meier D, Oasmaa A, Peacocke C, et al., editors. Fast pyrolysis of biomass: a handbook. Newbury: CPL Press; 1999. p. 102–14. [22] Oasmaa A, Meier D. Analysis, characterization and test methods of fast pyrolysis liquids. In: Bridgwater AV, editor. Fast pyrolysis of biomass: a handbook, vol. 2. Newbury: CPL Press; 2002. p. 23–35.
Production of bio-oil from fixed bed pyrolysis of bagasse M. Asadullah *, M.A. Rahman, M.M. Ali, M.S. Rahman, M.A. Motin, M.B. Sultan, M.R. Alam Department of Applied Chemistry and Chemical Technology, University of Rajshahi, Rajshahi 6205, Bangladesh Received 4 October 2006; received in revised form 1 February 2007; accepted 6 February 2007 Available online 7 March 2007
Abstract The objective of this work was to produce renewable liquid fuel (bio-oil) from locally produced bagasse by pyrolysis in a batch feeding and fixed bed reactor. The experiments were performed at different temperatures ranging from 300 to 600 C. The bio-oil was collected from two condensers of different temperatures and defined as oil-1 and oil-2. The maximum total yield of bio-oil was found to be 66.0 wt% based on bagasse. The carbon based non-condensable gases were CO, CO2, methane, ethane, ethene, propane and propene. The density and viscosity of oil-1 were found to be 1130 kg/m3 and 19.32 centipoise and that were 1050 kg/m3 and 4.25 centipoise for oil-2, respectively. The higher heating values (HHV) of them were 17.25 and 19.91 MJ/kg, respectively. The pH of the bio-oils was found to be around 3.5 and 4.5 for oil-1 and oil-2, respectively. The water, solid and ash contents of oil-1 and oil-2 were determined and found to be around 15, 0.02 and 0.03 wt% and 11, 0.01 and 0.02 wt%, respectively based on bagasse. 2007 Elsevier Ltd. All rights reserved. Keywords: Bagasse; Pyrolysis; Bio-oil
1. Introduction Energy is the driving force for the development of world economy. Fossil fuels such as petroleum, coal and natural gas satisfy the major fraction of total need of world’s energy. However, the burning of fossil fuels causes green house gas emission which has many divers role to the environment [1]. In addition, the deposition of fossil fuels is limited. But the demand of energy is growing at high rate due to the development of all aspects of the world. To meet the growing demand of energy and to help solve the environmental problems, the world trends are moving towards sustainable energy production, reduced vehicle and industrial pollution, green house gas and waste minimization and distributed electricity generation. Biomass energy
* Corresponding author. Tel.: +880 721 750041x4106; fax: +880 721 750064. E-mail addresses: [email protected], [email protected] (M. Asadullah).
0016-2361/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2007.02.007
which is renewable in nature has a role to play in each one of these energy and environmental concern [2,3]. Various types of biomasses such as agricultural residues, forestry products and city wastes are abundantly available in the world, which can be used for energy production in several ways from old direct burning to modern gasification and pyrolysis. The solid biomass can be converted to the combustible liquid usually termed as bio-oil by pyrolysis and to the combustible gases by gasification. The liquid and gas products can be used in engine and turbine for power generation. The gasification of biomass for power generation has some disadvantages such as it needs coupling between gasification and power generation units and the difficulty of storage, transportation and handling of gaseous fuels. Liquid fuel (bio-oil) has some advantages in transport, storage, combustion, retrofitting and flexibility in production and marketing [4]. The bio-oil is a mixture of about 200 types of major and minor organic compounds and this can be used as a source of some pure chemicals such as alcohol, phenol, aldehyde, organic acids, etc. [5]. As a fuel it can be directly used in engine, turbine and furnace with
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Nomenclature HHV i.d. g p r t l
high heating value internal diameter coefficient of viscosity hydrostatic pressure difference radius of capillary tube of viscometer time of falling of liquid in viscometer length of capillary tube
some modification of equipment [6]. Work to date gives strong encouragement to believe that a diesel engine can be relatively easily modified to run on 95% crude pyrolysis oil (by energy content) with no deterioration in output or rating [7]. A 250 kW diesel engine has been modified to operate in dual fuel mode utilizing crude pyrolysis liquid as the main fuel supplemented by a pilot diesel fuel to provide a source of ignition. Nearly 200 h of operation have been achieved [7]. Fuel controlling in the combustion process is the most important factor for stable operation of engine and this is easier in the case of liquid fuels. The agro-based biomass is usually produced at the rural area where a large scale pyrolysis plant can be installed. Due to the decoupling nature of the pyrolysis plant, the bio-oil based small scale power generation plant can be installed in the remote area where the bio-oil can be supplied and this is one of the most important advantages of biomass pyrolysis for liquid production [8]. By this way the agro-based biomass can efficiently be used for energy production. The by-products of the pyrolysis plant are burnable gas and char. These char and gas products can be burnt for pyrolysis reactor heating, thereby reducing the additional production cost for heating system. About 7.3 million metric tons of can sugar is produced per year in Bangladesh. With sugar, about 21 million metric tons bagasse is produced as by-product per year. A part of the bagasse is used for steam power generation inside the sugar industry for self use and rest of the bagasse is using for energy in unorganized sectors [9]. In both of the cases the heat is produced by combusting the bagasse. Due to the variation of geographic and climate conditions at the different places on the earth, the physical characteristics and chemical composition of the bagasse can be varied in a great extent. However, there is not a single report on the characterization and utilization of the Bangladesh based bagasse for pyrolysis to produce bio-oil. This paper contributed to the characterization of bagasse, its pyrolysis for bio-oil production and characterization of bio-oil. 2. Experimental 2.1. Feed stock preparation The raw bagasse obtained from the outlet of the sugar industries usually contains moisture more than 10 wt%.
v g FID TCD TGA oil-1 oil-2
volume of liquid gravitational force flame ionization detector thermal conductance detector thermogravimetric analysis bio-oil in first condenser bio-oil in second condenser
Table 1 Proximate and ultimate analyses of different biomasses Properties Moisture content (wt%) Particle size (mm) Density (dry powder) (g/cc) Heat value (HHV) (MJ/kg) Proximate analysis Volatile fraction (wt%) Fixed carbon (wt%) Ash content (wt%) Ultimate analysis (dry basis wt%) C H O N Cl S
4 0.5–1.0 0.12 19.2 68–70 28.7–30.7 1.26 48.58 5.97 38.94 0.20 0.05 0.05
However, the higher moisture content in the feed stock yields in higher water content bio-oil. Thus, prior to the pyrolysis of bagasse it was dried in the sunlight to reduce the moisture content less than 10 wt%. Then the bagasse was crushed with a crushing machine to about 0.5– 1.0 mm in particle size. The properties as well as ultimate and proximate analyses of bagasse were carried out and summarized in Table 1. 2.2. Pyrolysis procedure For the production of bio-oil the bagasse has been pyrolized in a laboratory scale fixed bed reactor. A conceptual design of the process is shown in Fig. 1. The reactor is made of stainless steel with the dimension of 50 cm height and 10 cm i.d. About 200 g of bagasse was fed in a batch in the reactor. The reactor was set vertically and N2 gas was introduced inside the reactor at the rate of 200 ml/min from the bottom and passed through the top of the reactor. The flow of nitrogen replaces the air from the reactor and permits the pyrolysis reaction under anaerobic condition. The vapor as well as gases formed from the pyrolysis of the bagasse inside the reactor flows out along with N2 from the top of the reactor. The gas mixture was passed through two condensers. The first condenser was cooled with the flow of tap water and by which the vapour temperature was reduced to around 60 C. The second condenser was cooled with the circulation of ice water mixed with NaCl
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Gas bag
Reactor
Furnace Condenser, -5oC
Water Ice water with NaCl Condenser, 60oC
Thermocouple Oil -1
Oil -2
N2 gas Fig. 1. Conceptual design for fixed bed pyrolysis reactor.
by means of a small pump, thereby reducing the temperature to around 5 C. No vapour was visually escaped from the second condenser. The liquid products from the first condenser and second condenser were collected in conical flasks fitted to the condensers. The non-condensable gas was collected in a gas bag. The yield of bio-oil based on weight ratio was calculated by (the amount of bio-oil collected for a certain batch/total amount of bagasse in that batch) · 100. The conversion of bagasse to gas was calculated by (the amount of carbon based gas collected in a gas bag for a certain batch/total feeding of bagasse for that batch) · 100. The char produced was remained in the reactor and collected after completing the pyrolysis reaction. The char yield was calculated by (the amount of char collected for a certain batch/total amount of bagasse in that batch) · 100.
2.3. Characterization of bio-oil The density, viscosity, pH value, heating value, water content, solid content, lignin content and ash content of crude bio-oil were measured. The density was measured with a density measurement bottle. Viscosity of a liquid is the measure of its internal friction which resists the flow of the fluid. The viscosity of bio-oil was measured according to the ASTM D 445 using the following equation: g ¼ pPr4 t=8lv ¼ phqgr4 t=8lv ½10
where g is the viscosity (dynes/cm2 or poise), v is the volume of liquid (c.c.), t is the liquid flowing time (s), r is the radius of narrow tube (cm), l is the length of narrow tube (cm). The pH was measured with a digital pH meter (Hanna, Model – HI 8424). Calorific value of bio-oil was measured by means of an oxygen bomb calorimeter. Water content in the bio-oil was measured by Karl Fischer titrimetric method. The measured sample was titrated with Karl Fischer reagent. When all of the water has been consumed in the Karl Fischer reagent the end point of the solution was signaled by the appearance of a slight excess of the pyridine iodine complex. It was detected by brown color, which is intense enough for a visual end point. The color change was observed from the yellow of the reaction products to the brown of the excess reagent. The amount of water in the sample was calculated as 1 ml Karl Fischer reagent = 3.5 mg water. The solids content in the pyrolysis oil were measured as ethanol insoluble portion. A certain amount of oil was weighed (25–50 g) and dripped into a beaker containing 250–500 ml ethanol solvent and agitated by magnetic stirrer. The solution was then filtered on a filter paper (0.1 lm pore size) followed by drying. The insoluble portion remained on the dried filter paper was weighed out. The lignin portion was measured as water insoluble fraction by using phase separation. The acid value of the pyrolysis oil was determined by direct titration with standard KOH solution. Ash content was measured by burning the
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bio-oil sample with supplying excess air in a Muffle furnace.
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bagasse was 19.2 MJ/kg which was quite comparable with the energy content of cedar wood 19.1 MJ/kg [11]. This is one of the clear views that bagasse can be successfully used for bio-energy plant for bio-oil production.
3. Results and discussion 3.1. Proximate and ultimate analyses The physical properties and chemical composition of feed stock play a major role in the yield and properties of bio-oil. Therefore, the bagasse which was the feed stock of this investigation was characterized in view to know the physical properties and chemical composition. The results are summarized in Table 1. The green biomass usually contains about 50 wt% moisture; however, the moisture content in the sun dried biomass varied in the range of 3–10 wt%. The moisture content of the sun dried bagasse was obtained 4 wt% as shown in the thermogravimetric profile in Fig. 2. The water content in the feed stock entirely goes to the bio-oil product. For the application of bio-oil as fuel needs minimum water content. Since the water content in the bagasse was low, the water content in the bio-oil seems to be low. The thickness of the particle has an important role in the surface area per unit weight, the lower the particle size the higher the surface area which leads to the high heat transfer rate from the outer surface to the center of the particles. Thus, the bagasse was crushed with a crushing machine and the particle size was maintained within the range of about 0.5–1.0 mm size. The bulk density of dry bagasse was found to be 120 kg/ m3. It was measured as the weight of oven-dried bagasse contained in a unit volume of green bagasse in kg/m3. Available energy content in the unit volume of biomass must be known for planning a bioenergy project as it affects the size of plant, the storage area needed and the transportation arrangements. The density and energy content in bagasse is comparable with some woody biomass [11]. It has been found that the bulk density of bagasse (120 kg/m3) was higher than the bulk density of cedar wood (70 kg/m3). Furthermore, the energy content in the 120
Weight loss, %
100
The proximate and ultimate analyses of bagasse were performed and the results are summarized in Table 1. The proximate analysis was based on the thermogravimetric analysis (TGA) profile as shown in Fig. 2. About 10 mg of sample for this analysis was used and heated from room temperature to 900 C at the rate of 10 C/min under the flow of N2 at the rate of 200 ml/min. From the figure it can be clearly seen that the volatile fraction of bagasse until around 400 C was 68–70 wt% (dm), the fixed carbon was 27–29 wt% (dm). The rest 3 wt% (dm) was ash content in the bagasse. These values are slightly different from the reported results [12]. The volatile materials mainly derived from the cellulose and hemicellulose which was likely to be converted to bio-oil in pyrolysis. The carbon which converted to char or other solid carbonaceous materials was called the fixed carbon. This carbon was mainly derived from the lignin in the bagasse. The fixed carbon is difficult to vaporize at pyrolysis temperature around 500 C. From Fig. 2 it is seen that the fixed carbon does not evaporate even at around 1000 C. The fixed carbon was actually formed the char in the pyrolysis reaction. This results reveal that the higher the volatile content the higher the bio-oil yield from the pyrolysis of bagasse. In comparison the volatile content in bagasse was higher than many other agricultural residues and forestry products [13]. In addition, since bagasse contains very small amount of ash [14] comparing with other agricultural biomass such as rice straw (22.6 wt% ash) [13] and other poisonous component such as sulfur, it can be considered as a suitable feed stock for low temperature pyrolysis to produce bio-oil. From the ultimate analysis it has been found that the bagasse contains 48.58% C, 5.97% H, 38.94% O, 0.20% N, 0.05% Cl and 0.05% S. Carbon content in bagasse was much higher than rice straw [13]. 3.2. Pyrolysis of biomass
80 60 40 20 0 0
200
400
600
800
1000
o
Temperature C Fig. 2. TGA profile of bagasse under nitrogen atmosphere.
About 200 gm of bagasse was fed in the reactor. The temperature was increased at the rate of 50 C/min. When the reactor temperature crossed 300 C, the pyrolysis reaction started and a thick white smoke was observed in two liquid collectors. The pyrolysis reaction was continued till the vapour was produced at different temperatures. Initially a sample experiment was performed at 500 C. The bio-oil collectors were connected to two long condensers. It was observed visually that no smoke (or aerosols) was escaped from the second condenser. The product distribution of bagasse pyrolysis at 500 C is presented in Table 2. Bio-oil collected in the first collector was defined as ‘oil-1’ and that in the second collector as
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Table 2 Product distribution of bagasse pyrolysis Pyrolysis conditions Amount of bagasse (g) Temperature (C) Temperature increasing rate (C/min) Nitrogen gas flow rate (ml/min) Pyrolysis products Bio-oil yield Oil-1 in first condenser (g (wt%)) Oil-2 in second condenser (g (wt%)) Total bio-oil (g (wt%)) Char yield (g (wt%)) Gas yield (g (wt%))
200 500 50 200
104.0 (52.0) 28.1 (14.0) 132.1 (66.1) 49.7 (24.9) 18.2 (9.0)
‘oil-2’. The yield of oil-1 in the first collector was 52.0% (on bagasse basis) and the yield of oil-2 in the second collector was 14.0%. The total of 66.0% bio-oil yield has been achieved. The oil-1 was more viscous than oil-2. The carbon based non-condensable gas was the mixture of carbon monoxide, carbon dioxide, methane, ethane, ethene, propane, propene, etc. But the concentration of ethane, ethene, propane, propene was much smaller than methane. These gases were identified by gas chromatograph equipped with flame ionization detector (FID). Small amount of hydrogen was formed which was detected by TCD gas chromatograph. The gas and char yields were 24.9 and 9.1 wt%. 3.3. Effect of temperature on the product distribution The pyrolysis of bagasse was performed at different temperatures from 300 to 600 C to evaluate the effect of temperature on the product distribution for a certain amount of bagasse (200 g) pyrolysis (Table 3). In all experiments, the reactor was kept for a certain length of time after reaching the final temperature. At low temperature such as 300 C, where the decomposition of bagasse just started (as shown in TGA profile, Fig. 2) the bio-oil product was very low both in the first collector (oil-1, 15.33 wt%) and in the second one (oil-2, 3.33 wt%). The total bio-oil yield was 18.66 wt%. The gas yield was only 4.34%. Most of the carbon in the bagasse was converted to the char at this temperature. This result is not consistent with TGA profile Table 3 Effect of temperature on product distribution of bagasse pyrolysis Temperature (C)
Yield of oil-1 (wt%)
Yield of oil-2 (wt%)
Total yield of bio-oil (wt%)
Char yield (wt%)
Gas yield (wt%)
300 350 400 450 500 550 600
15.33 44.66 53.33 58.66 52.06 47.30 44.66
3.33 6.66 7.33 6.81 14.07 13.33 14.66
18.66 51.32 60.66 65.47 66.13 60.63 59.52
77.00 43.8 31.93 26.26 24.86 24.66 22.86
4.34 4.87 7.41 8.27 9.01 14.71 17.82
Conditions: amount of bagasse – 200 g, nitrogen gas flow – 200 ml/min, heating rate – 50 C/min and retention time – 1 h.
as shown in Fig. 2. This can be explained in two ways. Firstly, in TGA analysis a small amount of bagasse was heated homogeneously in the TGA furnace so as to pyrolyse the total mass suddenly at the pyrolysis temperature in the small sample bin. Therefore, the chance of char formation in the sample bin was minimum. On the other hand, for pyrolysis of 200 g bagasse in the pyrolysis reactor, the heat was supplied from the outer source. So, the pyrolysis reaction was started from the wall side and most of the heat was consumed by the endothermic pyrolysis reaction at the wall side. By this time, the solid of the center of the reactor was heated very slowly and most of the carbon was converted to the char. Secondly, the secondary cracking reaction of pyrolytic vapor also produces char and coke like solid carbonaceous materials in the reactor. However, in the TGA sample bin the possibility of the secondary cracking of vapor was low due to the first removal of vapor from the small bin. As temperature increased the bio-oil and gas yields increased remarkably so as to decrease the char yield. The effect of temperature on the bio-oil yields in both collectors is shown in Table 3. The yield of oil-1, comparatively less volatile, increased until 450 C and then decreased with increasing temperature. However, in the second collector the yield of oil-2, comparatively high volatile, increased with increasing temperature until the final experimental temperature. Since the major fraction of bio-oil was in the first collector and it was decreased abruptly above 500 C, the total bio-oil yield was decreased above 500 C with further increase of temperature. The decrease of the yield of oil-1 with increasing temperature was due to the secondary cracking reaction of pyrolytic vapour to lower molecular weight organic products or gas products such as CO, CO2, CH4 and many other gaseous hydrocarbons. The low molecular weight organic products are comparatively high volatile and were not condensed in the first collector but were condensed in the second one. This was the reason for increasing the yield of oil-2 as temperature increased. The effect of temperature on char yield is also shown in Table 3. Char yield is a function of temperature. From the results it can be seen that the char yield decreased suddenly with increasing temperature from 300 to 450 C and then it decreased slowly with increasing temperature. At low temperature the secondary cracking and reforming of biomass derived high molecular weight organic molecules is difficult [15,16]. These reactions are completely temperature dependent and proceed usually above 400 C [17,18]. And the thermal cracking smoothly proceeds above 500 C. Thus, the yield of char in this process was very high at 300 C where cracking of high molecular weight compounds did not take place. 3.4. Bio-oil characterization Bio-oil consists of water and organic compounds. This liquid is a very complex mixture that contains molecular
M. Asadullah et al. / Fuel 86 (2007) 2514–2520 Table 4 Physical properties of bio-oil produced from bagasse Properties
Oil-1
Oil-2
Density at 20 C (g/cc) Viscosity, centipoise at 20 C pH Gross calorific value (MJ/kg) Water content (wt%) Char/solid content (wt%) Pyrolytic lignin content (wt%) Acid value (mg KOH/g) Ash content (wt%)
1.13 3.90 3.50 17.25 15.00 0.02 3.51 137.35 0.03
1.05 2.25 4.50 19.91 11.00 0.01 1.25 117.51 0.02
fragments of cellulose, hemicellulose, and lignin polymers. Extensive reviews on the chemical [19] and physical properties of pyrolysis oils have recently been published [5]. Before using bio-oil as fuels or chemicals it needs to be characterized. Thus, the bio-oil obtained in this work was characterized by measuring the density, viscosity, pH, calorific value, water content, solid (char) content, pyrolytic lignin content and ash content. The results are summarized in Table 4. Bio-oil was collected in two condensers at two different temperatures, 60 and 5 C, respectively. Thus, the low boiling fraction was collected in first condenser (oil-1) and high boiling fraction was collected in second condenser (oil-2). The properties of two different fractions are different. The organic compounds of low boiling fraction are highly burnable. Therefore, for fuel application and for chemicals separation from bio-oils, the fractionation of bio-oil at different temperatures is significantly important. The density of bio-oil produced from bagasse was measured by density measurement bottle at 20 C. Densities of oil-1 and oil-2 were found to be 1130 and 1050 kg/m3, respectively. These values are higher than that of light fuel oil which is around 850 kg/m3. Unlike hydrocarbon oils, the higher density of the bio-oils reflects the high oxygen content, rather than a high polycyclic aromatic content. The viscosity is important in many fuel applications [20]. For oil-1 and oil-2 they were 19 and 4.25 centipoise, respectively at 20 C. The proposed viscosity of biomass derived light oil is 2.0–4.3 centipoise and that of medium oil is 6.2– 27 centipoise [21]. The viscosities of the experimental samples are within the range of proposed specification of biomass pyrolysis liquids. The bio-oil usually contains some of organic acids such as formic and acetic acids, which cause the oils to have a pH of between 3.0 and 4.5. The pH of the bio-oils was found to be around 3.5 and 4.5 for oil-1 and oil-2, respectively. This pH value is slightly higher than that of wood pyrolysis liquid (maximum pH 3.7) [22]. This acidity causes the pyrolysis oils to be corrosive to mild steel, aluminum, etc. Aldehydes also contribute to the low pH. Thus for application of bio-oil in the sophisticated engine, it needs some chemical treatment for lowering the acidity. The gross calorific value of oil-1 and oil-2 was found to be 17.25 and 19.91 MJ/kg, respectively. The water content
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decreases the available energy from the oil. In bio-oil water was completely miscible in the polar organic compounds. In oil-1 the water content was higher (15.00 wt%) than that of oil-2 (11.01 wt%) so as to decrease the calorific value of oil-1. The solid content in the bio-oil is defined as the heavy organic materials which is insoluble in some specific solvents in addition to the actual solids. For this test three solvents were used: ethanol, methanol and acetone. The solubility of the particle was dependent on the amount of solvent. Furthermore, the selection of the filter pore size was to some extent dependent on the particle size distribution of the liquid. The solid content was found to be 0.02 wt% for oil-1 and 0.01 wt% for oil-2. The pyrolytic lignin content is the measure of water insoluble fraction in the bio-oil. It was found to be 3.51 and 1.25 wt% for oil-1 and oil-2, respectively. The acid value or acid number of the oil was determined by direct titration with standard KOH solution using phenolphthalein as an indicator. The acid value of the oil-1 was found to be 137.35 and 117.51 for that of the oil-2, respectively. Finally, the ash content in the bio-oil was found to be 0.02 and 0.02 wt% for them, respectively. Bio-oil can be considered a micro-emulsion in which the continuous phase is an aqueous solution of holocellulose decomposition products, that stabilizes the discontinuous phase of pyrolytic lignin macromolecules through mechanisms such as hydrogen bonding. Aging or instability is believed to result from a breakdown in this emulsion. However, in our liquid the appearance is still homogeneous phase. The physical properties are not significantly changed within 8 months. However, the chemical analysis is under investigation. 4. Conclusions Bio-oil was produced from pyrolysis of bagasse in a fixed bed reactor at different temperatures ranging from 300 to 600 C. The bio-oil vapour was condensed in two condensers at different temperatures and the liquid products were defined as oil-1 and oil-2. The maximum total yield of bio-oil was found to be 66.0 wt%. The carbon based non-condensable gases were CO, CO2, methane, ethane, ethene, propane and propene. The values of density and viscosity are comparable with the proposed specification of the various grades of pyrolysis oils. Since bio-oil contains some organic acids, the pH of the bio-oils was found to be around 3.5 and 4.5 for oil-1 and oil-2, respectively. The other impurities in the bio-oil produced in this work are comparable with reported work. Thus, it can be used as liquid fuel. Acknowledgements This research was financially supported by the Ministry of Science and Information and Communication Technology under the project ‘‘Pilot Plant Project on the Produc-
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