Pyrolysis of biomass residues in a screw reactor

Transcription

1 Pyrolysis of biomass residues in a screw reactor Ricardo Maximino Abstract The present work aims to evaluate the potential of producing bio-oils and chars from biomass residues through fast pyrolysis. Pinewood and agro-biomasses olive bagasse, wheat straw and rice husk were pyrolysed in a bench scale screw reactor at 580 ºC using a carrier gas flow rate of 526 ml/min in order to maximize the resultant bio-oil fraction. The yields of bio-oil, bio-char and gas obtained were quantified. Bio-liquid yields varied between 51 wt.% for pinewood and 31 wt.% for olive bagasse and the bio-char yields between 38 wt.% for wheat straw and 24 wt.% for pinewood. Subsequently, the bio-oils and chars obtained were analyzed in terms of moisture content, elemental analysis, ash content and heating value. The main conclusions are as follows. 1) pinewood showed the highest potential to pyrolyse; the resultant bio-oil and char have potential to be used as fuels without further treatments. 2) The substantial ash content in the feedstock of the agro-biomasses decreased drastically their bio-oil quality and yield. Furthermore, the low conversion yields related to such biomasses observed in the present work may not justify their valorisation through pyrolysis. 3) The non-homogeneity of the bio-oils from agro-biomasses is a higher challenge to their use as fuel, however, is an opportunity for recovering added-valued by-products. 4) The chars obtained from agro-biomasses with higher ash content and lower energy densities may have potential to be used in the preparation of active carbon when its pore structure and surface are appropriate. Keywords: fast pyrolysis, screw reactor, pinewood, agro-biomasses, bio-oil, char 1. Introduction Fast pyrolysis is the thermal degradation of biomass occurring in the absence of oxygen under moderate temperatures (~ 500 ºC) and short hot vapour residence times (~ 2 s). Among other wellknown thermal processes, fast pyrolysis is the most proper way to convert raw biomass into a valued liquid known as pyrolysis liquid or simply bio-oil. This is a dark-brown, free-flowing organic liquid composed of highly oxygenated compounds that presents properties significantly different from those of the petroleum-derived oils [1]. It is expected that fast pyrolysis play a major role in the near future since the resulting bio-oil offers many advantages over the original raw biomass as an energy product. In particular, bio-oil is a liquid with higher density than the raw biomass, which makes its transportation, handling and storage easier. It has already proven to be a possible renewable fuel for direct applications and, after upgraded, can replace total or partially existing fuels such as gasoline and diesel, or processed to yield valued additives and chemicals [2]. Most recent research of fast pyrolysis has focused on testing suitable reactor configurations with several biomasses, analysing the physiochemical properties of the resultant bio-oils [3,4]. Lignocellulosic feedstock such as pinewood (woody biomass) olive bagasse, wheat straw and rice husk (agrobiomasses) studied on the present work represent a significant portion of these researches. Related studies include those of Thangalazhy et al. [5], Şensöz et al. [6], Yanik et al. [7], Heo et al. [8], DeSisto et al. [9], Nokkosmaki et al. [10], Sipila et al. [11], Di Blasi et al. [12], Bakar et al. [13] and Ji-lu [14]. Thangalazhy et al. [5] investigated the influence of temperature on the physiochemical properties of biooil obtained from pinewood pyrolysis in a screw reactor. The experiments were carried out) in a wide range of temperatures (425 up to 500 ºC). The results showed that the maximum yield of bio-oil (50 wt.%) was obtained at 450 ºC and the physical properties of bio-oil remained nearly constant over the range of temperature. Based on a chemical analysis, thirty-two compounds were found in bio-oil. The authors pointed out a temperature of 475 ºC as the most indicated to provide a bio-oil potentially valuable as fuel and as chemical source. Şensöz et al. [6] studied the effects of temperature, heating rate, particle size and sweep gas flow rate on the pyrolysis of olive bagasse in a fixed-bed reactor. A biooil yield of 37.7 wt.% was attained for the most promising conditions. Based on standard method tests, the resultant bio-oil has shown potential as fuel and chemical feedstock. Yanik et al. [7] studied the fast pyrolysis of wheat straw in a bench scale fluidized-bed reactor at 500 ºC. Nitrogen was used as fluidizing gas. The results have shown a bio-oil separated in two phases: oil and aqueous phase with yields of 35 and 6 wt.%, respectively. Further chemical analysis of both phases identified a broad variety of organic compounds. They concluded that the resultant liquid tends to be a source of speciality chemicals and needs to be upgraded for use as a fuel source. Su Heo et al. [8] investigated the optimal reaction conditions for the production of bio-oil from rice husk using a fluidized-bed reactor. The experimental data has shown bio-oil with high potential to be used as fuel, with yields in the order of 60 wt.%. The pyrolysis temperature was found to be the most important parameter affecting the chemical composition of the bio-oil. In this context, the main purpose of the present study is to assess the potential of producing biooils through fast pyrolysis. Specifically from abundant biomass residues in the Mediterranean countries such as pinewood, olive bagasse, wheat straw and rice husk with few practical applications, exploiting the possibility of their valorisation along this route. For this purpose, such biomass residues were pyrolysed in a screw reactor, specially designed for the present work, attending fast pyrolysis conditions. The yields of the products were determined. The physical foremost properties of the bio-oils and chars (moisture content, elemental analysis, HHV) were analysed. 1

2 2. Materials and methods 2.1 Feedstock Pinewood and straw came in the pellet form, while olive bagasse and rice husk came in the natural form. Before each test on the pyrolysis reactor, samples of each feedstock were properly prepared. Pinewood, straw and rice husk were milled in a stainless steel blender (BECKEN, 500 W). Olive bagasse sample was not milled since it presented a fine granulometry by itself. The samples obtained have similar particles sizes (< 2 mm) and therefore comparable results. After milling, the biomass samples were dried at least for 24 hours at 110 ºC in order to lose their initial moisture (8 up to 12 wt.%). An oven (Memmert, Model ) was used for the purpose. 2.2 Experimental facilities A bench-scale screw reactor was specifically designed for the present work to perform the pyrolysis tests. The screw reactor runs discontinuously (batch operation) with biomass samples and attains a temperature of 700 ºC. Figure 1 shows a schematic of the pyrolysis reactor. The main body of the reactor is a horizontal pipe 325 mm length with an inner diameter of 20 mm and 1 mm thick, made of AISI 316 steel (bold lines in Fig. 1). The biomass-feeding steel column placed at setup s left side defines the inlet point of biomass into the reactor. At the top of the column, a proper threated glass flask containing a biomass sample is screwed upside down in a suitable fixed lid to guarantee sealing. Once the glass flask is coupled, the biomass sample particles fall down by gravity along the column into the rotating screw placed below. Near the base, a small vibrator induces vibration in the column to avoid biomass blockage due to its low fluidity. Inside the main pipe, an assembled concentric screw goes along all pipe length. The screw is made of stainless steel and is 450 mm long with 18 mm in diameter. At left, an electric engine placed outside is axially engaged to the screw imposing a rotation movement on it. The electric engine is a CTX peristaltic bomb adapted for the purpose and is axially engaged on the screw through a designed gear. The rotation of the screw carries the biomass sample from the biomass inlet towards the heating/reaction zone till the products collection point on the other end of the pipe. An electrical resistance coiled over 150 mm of the main pipe provides heat for the reaction (1.1 kw) and defines the reaction zone where biomass particles undergo pyrolysis. For each test, nitrogen is used to purge/inertize the reactor and to sweep the product gas stream during the reaction. The nitrogen flow rate is controlled upstream with a gas flow meter (AALBORG model P single flow tube) placed before its inlet; after the gas flow meter, nitrogen is heated up before its entrance in the reactor through an integrated heat exchanger where the heating resistance is used as heat source (see Fig. 1). Figure 2 shows an illustrative detail view of the reaction zone. The formed products char and a product gas stream are separated through a T-connection placed in the other tip of the tube. Char is collected on an enclosed gas flask placed below. The pyrolytic hot vapours, embedded in the product gas stream, proceed upwards into two condensation stages where condense and originate bio-oil that is collected in glass flasks (see Fig 1). The non-condensable gases continue their way until be expelled by the exhaust system. The condensers are cooled in series with the help of a refrigerated circulator (Haake C10-K15) that uses ethylene glycol as refrigerator. Four relevant temperatures are monitored using type-k thermocouples placed along the pipe s outer wall. A developed temperature control system allows the monitoring of such temperatures and the temperature control on the reaction zone. The system consists in a data acquisition board NI-9211 (National Instruments), a Virtual Instrument (.VI) interface program for temperatures monitoring and control, and an actuator system based on a multifunction board NI USB-6008 (National Instruments) settled in an auxiliary relay circuit. The system works as a feedback control system, establishing a fixed temperature (reactor temperature) on the reaction zone with the heating resistance. The main pipe is insulated to prevent heat losses. 2.3 Characterization of products To determine the mass of bio-oil and char, the corresponding unit was weighed before and after each experimental run. The gas mass was calculated by difference. The yields of the products were determined based upon the mass of the products and the mass of the original sample. It was taken into account the mass loss in the feeding column. The bio-oil and char obtained from pyrolysis were analysed so as to determine their physiochemical properties. For the case of bio-oil: to measure the density, a 1 ml, calibrated flask was filled with a known mass of bio-oil through a micropipette. The elemental analysis (wt.%) C, H and N was determined according to M.M. 8.6 (A.E) ( ). The oxygen content (wt.%) was obtained by direct calculation. The moisture content (wt.%) was determined according to EN 12880:2000. The LHV and HHV were measured according to CEN/TS using a Parr oxygen bomb calorimeter. For the case of char: the elemental analysis (wt.%) C, H, and N was determined according to M.M. 8.6 (A.E) ( ). The oxygen content (wt.%) was obtained by direct calculation. The moisture content (wt.%) was determined according to M.M. (GRAV). The ash content was determined according to CEN/TS The LHV and HHV (MJ/kg) were measured according to CEN/TS 15400, as for bio-oils, using a Parr oxygen bomb calorimeter. All the analyses were carried out at Laboratório de Análises from Instituto Superior Técnico. The standard methods refereed above are internal standards of the laboratory. 2

3 3. Test conditions Pinewood, olive bagasse, wheat straw and rice husk were pyrolysed at 580 ºC (reactor temperature) with a nitrogen flow rate of 526 ml/min at atmospheric pressure. Upon these conditions the nitrogen temperature at its inlet into the reactor was found to be 65 ± 4 ºC. The rotational velocity of the screw was held at 19 rpm. Table 1 shows the feed rates of the biomasses with a velocity of 19 rpm. The tests were conducted with biomass samples of 50 g properly prepared as described in section 2.1. The temperature of the condensation/refrigerant fluid (ethylene glycol) was kept at 15 ºC. The experimental conditions were based on trial studies carried out prior to conducting the experimental runs. The trial studies pointed out the above conditions as the most promising conditions of a fast pyrolysis process with the highest yields of bio-oil, without compromising its properties. 4. Results and discussions 4.1 Analysis of the feedstock The physical properties of the feedstock play a major role in bio-oil yield and its properties. Table 2 shows the main characteristics of the biomasses used as feedstock for the present work. Pinewood shows the lower ash content (0.2 wt.%) when compared to those of the agro-biomasses (up to 14.7 wt.% for wheat straw). Its lower ash content and high volatile matter content (72.7 wt.%) implies a bigger portion available for energy conversion [15]. The high ash contents of the agro-biomasses olive bagasse, wheat straw, and rice husk namely alkali metals, play a catalytic role on the pyrolysis reactions affecting their bio-oil yield and quality [16-20]. The agro-biomasses also present higher nitrogen amount in their elemental composition (up to 1.9 wt.% for olive bagasse), which will naturally result in pyrolysis products with reasonable nitrogen amount. Wheat straw presents the highest HHV (19.0 MJ/kg) as result of its high carbon content, and rice husk presents the lower (15.7 MJ/kg). The moisture content, which varies from 13.6 wt.% for pinewood to 9.4 wt.% for olive bagasse or rice husk, is removed from the biomasses prior to conducting the tests in order reduce as possible the moisture in the resultant bio-oil (see section 2.1). Once the biomasses were pyrolysed under the same conditions, the characteristics of the initial biomasses described above affect directly the yields of the pyrolysis products and their quality. 4.1 Yields of the pyrolysis products Figure 3 shows the yields of the products obtained from pyrolysis of the biomass residues. The highest bio-oil yield was obtained with pinewood (51 ± 0.5 wt.%) and the lowest with olive bagasse (31 ± 1.8 wt.%). Pinewood has shown the highest bio-oil yield and the lowest char yield with numbers comparable to similar screw reactor studies, see Thangalazhy et al. [5] and Ingram et al. [21]. Its relative good performance is related to its low ash content (0.2 wt.%), and to its usual major cellulose content, as refereed in Oasmaa et al. [16], from which most part is converted in bio-oil [22]. The agro-biomasses (olive bagasse, wheat straw and rice husk) presented lower yields of bio-oil than that of pinewood as a consequence of their higher ash content [16-20] (see Table 2). Figure 4 shows a correlation of the feedstock ash content to the bio-oil yields obtained from pyrolysis. As the ash content of the feedstock increases the bio-oil yield decreases with a linear behaviour comparable with the results of Oasmaa et al. [16] and Fahmi et al. [17], which also pyrolysed agro-biomasses with substantial ash content in a fluidized-bed reactor. After to pinewood, rice husk have shown the second best bio-oil yield with 40 ± 1.5 wt.%, comparable to that obtained by Di Blasi et al. [12] in a packed bed reactor. The considerable ash content (10.5 wt.%) of rice husk promoted the char and gas formation, which affected the bio-oil yield, see Fahmi et al. [17]. Olive bagasse showed the lowest bio-oil yield due to its relative high ash content (13.1 wt.%), and to its typical high lignin content, as referred in Panopoulos et al. [23], which yield substantial amounts of char and gas [22]. Şensöz et al. [6] obtained comparable yield values for a fixed-bed reactor at 500 ºC. According to Coulson [24], the alkali metals present in the olive bagasse ashes, as potassium (K 2O) in high percentage (18.7 wt.%), catalysed pyrolysis reactions to yield extra water and gas and decrease the bio-oil yield. As result, olive bagasse produced the greatest gas yield (34 ± 0.04 wt.%). The yields of wheat straw are comparable with those of olive bagasse, although, it has generated more char than gas. The reason may also be linked to a lower heating rate [7]. The yields obtained for the products are comparable with those obtained in other studies involving screw reactors and fixed-bed reactors [5,6,21], however, previous fast pyrolysis works that pyrolysed pinewood, wheat straw and rice husk in fluidized-bed reactors at 500 ºC have shown larger yields of bio-oil (60 %), see [7-14]. Such discrepancy is due to the own nature of the screw reactor where a very short residence time and high heating rates comparable to those of fluidized-beds are difficult to achieve, as refereed by Bridgwater [1]. As result, the pyrolysis led to a considerable formation of char and gases at the expense of bio-oil [25]. The weak pre-heating of nitrogen when compared to other works [7,11,14] and an observed deficient separation of products may also have had significant influence [25]. When comparing the yield values of pinewood with reference yields for woody biomass, one concludes that the experimental conditions reached a middle way regime of fast pyrolysis so-called intermediate pyrolysis [1,4]. 3

4 4.2 Analysis of bio-oils The bio-oil obtained in the first condensation flask for each biomass was collected and subsequently analysed as described in section 2.3. Table 3 shows the physical properties of the initial feedstock and the bio-oils obtained from the pyrolysis of pinewood, olive bagasse, wheat straw and rice husk. The pinewood oil analysis have shown a single-phase oil with a specific gravity, water content and heating value of 1.2, 30 wt.% and 16.6 MJ/kg, respectively. Such properties matches the conventional values refereed by Czernik et al. [2] for a typical woody bio-oil, and are comparable to similar studies, see Thangalazhy et al. [5]. Besides the water content, its higher oxygenated composition with a considerable O/C ratio of 1.06 is a reason for not reaching a higher heating value, maybe similar to that of the raw material (18.1 MJ/kg) [2]. The analysis of the oils obtained from the agro-biomasses has shown non-homogeneous oils (two visible phases) with higher water contents (49-67%) and lower densities, which correlate to their water content. The agro-biomasses also have shown a residual amount of nitrogen as a direct result of their initial feedstock. Olive bagasse bio-oil has shown the highest heating value (19.6 MJ/kg) even with the worst bio-oil conversion yield (31 ± 1.8 wt.%). According to Butler et al. [26], this result is a clear sign of a large portion of lignin in the olive bagasse, as in accordance with Panopoulos et al. [23]. The large lignin portion was cracked better due to the catalysing effect of alkali metals present in the initial feedstock in significant quantities, such as potassium (K 2O wt.%). The better degradation of the lignin portion led to a bio-oil with lower oxygen content and therefore with an energy density higher than the own raw material (17.5 MJ/kg) [27], even with substantial water content (48 wt.%). Its heating value is also superior to that of conventional woody bio-oil as that of pinewood. At last, wheat straw and rice husk bio-oils have shown poor heating values of 11.7 and 9.5 MJ/kg, respectively, as a direct result of their higher water contents (58 and 67 wt.%, respectively). The higher water contents in the agro-biomass bio-oils are a consequence of their higher ash content in the feedstock that catalysed pyrolysis reactions to yield extra water, as concluded by Coulson et al. [24]. Oasmaa et al. [16] and Tsai et al. [28] have proven such influent effect of the ashes when pyrolysed agro-biomasses and obtained large amounts of water in the resultant bio-oils (>65 wt.%). The evident larger resident times of the hot vapours and low heating rates in the screw reactor may also increased even more this catalyst effect [25]. An insufficient drying prior to the tests is also a possible reason for such moisture contents. Regarding the O/C ratios, pinewood bio-oil is the most oxygenated. Such result may be a consequence of its lower ash content in the initial feedstock. The oxygen present in the mineral matrix of the ashes in the initial agro-biomasses followed to char rather than for bio-oil, which may have resulted in less oxygenated bio-oils even with higher water contents. Figure 5 shows the bio-oils of pinewood and olive bagasse. The bio-oil of pinewood presented a homogeneous aspect while the bio-oil of olive bagasse, as the bio-oils from the other agro-biomasses, presented a heterogeneous aspect as consequence of their superior water content, which caused phase instability [4]. According to Czernik et al. [2], the lower water content of pinewood bio-oil (30 wt.%) enabled the miscibility of water in the whole emulsion that resulted in a single-phase oil. Adversely, for the agro-biomass bio-oils with higher water contents, the solubilizing effect of the hydrophilic compounds was not enough to prevent phase separation into two phases [29], a water-soluble (aqueous phase) and a water-insoluble phase (tar). The phases are visually distinguishable in the bio-oils (Fig. 3.4 b)): the hydrophilic aqueous phase (top phase) and the heavier non-soluble phase (tar) that settled at the bottom. Besides the own water content, the usual higher amount of extractive matter (neutral substances) contained in the feedstock of the agro-biomasses may have helped to yield a bigger aqueous phase [16]. These phase-separated oils may be desirable in some applications where fractionation is required [1]. 4.2 Analysis of chars The char obtained in the char s flask for each biomass was collected and subsequently analysed as described in section 2.3. Table 4 shows the physical properties of the char obtained from the pyrolysis of pinewood, olive bagasse, wheat straw and rice husk. The ash analysis has shown that the ash content in the char correlates to that in the initial biomass. Pinewood with the lowest ash content in its initial composition (0.2 wt.%) had de lowest ash content in its char (11 wt.%) while the agro-biomasses with ash contents as high as 14.7 wt.% for straw in their initial composition had ash contents in their chars as high as 43 wt.% for straw. The ash contents in the chars agro-biomasses are a prove that the oxygen settled in the mineral matrix of initial feedstock followed to char rather than for bio-oil, which may have resulted in less oxygenated bio-oils but higher oxygenated chars for the agro-biomasses. The high O/C ratios are evidences of such oxygenation. As result, pinewood with the lowest ash content had the highest carbon content and the lowest O/C ratio. The heating values of the chars varied from 27.2 MJ/kg for pinewood to 17.7 MJ/kg for wheat straw. These values are comparable to other related studies, see Thangalazhy et al. [5], Şensöz et al. [6], Yanik et al. [7], and Su Heo et al. [8]. 4

5 5. Conclusions The main conclusions of the present study are as follows: The ash content in the feedstock plays a major role in pyrolysis. It has been shown by the relative behaviour of pinewood and of agro-biomasses that ashes (K, Na, Si) catalyse pyrolysis reactions to decrease the bio-oil production and yield extra water, which decreased drastically the bio-oil quality: The bio-oils of the agro-biomasses present higher amounts of nitrogen as a result of their initial composition; High water contents (> 30 wt.%) causes phase separation of bio-oils; The O/C ratio analysis for bio-oils and chars suggested that oxygen settled in the mineral matrix of initial feedstock followed to char rather than for bio-oil, which resulted in a char more oxygenated and a bio-oil less oxygenated for the agro-biomasses when comparing to those of pinewood; The char from the agro-biomasses present higher ash contents and lower energy densities than that of pinewood; As result, Pinewood has shown the more consistent results with the highest yield of bio-oil (51 ± 0.5 wt.%) and the lowest yield of char (24 ± 1.5 wt.%). The bio-oil produced from pinewood met the specifications of the ASTM standard (D ) for the measured properties, and has potential to be used as a direct liquid biofuel in industrial burners equipped to handle these types of fuels. Though, its utilization as a transport liquid fuel would just to be possible with an upgraded to reduce its considerable oxygen content [30]. Agro-biomasses have pyrolysed into bio-oils with low energetic content (apart from olive bagasse), due to the higher water content, and with significant nitrogen amounts (3.1 wt.% for olive bagasse). The combustion implications with so high water contents discard these agro-biomasses as a potential feedstock to pyrolyse into a direct fuel liquid unless they are upgraded [26,30]. Their significant nitrogen content would require an appropriate emission control. Furthermore, the low conversion yields related to such bio-oils in the present work (low as 31 ± 1.8 wt.%) may not justify their production with pyrolysis. The non-homogeneity (biphasic) of the bio-oils from agro-biomass is a high challenge to their use as fuel, however, is an opportunity for recovering added-value by-products with particular properties [1,16]. Particular studies [6,7] have concluded promising potential for the nonaqueous phase of bio-oil. The resultant char from pinewood has shown the highest heating value with 27.2 MJ/kg, a considerable value comparable with those of solid fuels ranging from lignite to anthracite [31], suggesting its potential to be used as solid fuel (e.g. in the form of briquettes or in char-oil water slurry [32]). The chars obtained from the agro-biomasses with higher ash contents and lower energy densities may be used in the preparation of active carbon when its pore structure and surface are appropriate [33]. 6. References [1] Bridgwater A.V. Review of fast pyrolysis of biomass and product upgrading. Biomass and Bioenergy, Vol. 38, pp (2013). [2] Czernik S., Bridgwater A.V. Overview of application of biomass fast pyrolysis oil. Energy Fuels, Vol. 18, pp (2004). [3] Butler E., Devlin G., Meier D., McDonnell K. A review of recent laboratory research and commercial developments in fast pyrolysis and upgrading. Renewable and Sustainable Energy Reviews, Vol. 15, pp (2011). [4] Mohan D., Pittman C., Jr., Steele P. Pyrolysis of Wood/Biomass for Bio-oil: A Critical Review. Energy & Fuels, Vol. 20, pp (2006). [5] Thangalazhy et al. Physiochemical properties of bio-oil produced at various temperatures from pinewood using an auger reactor. Bioresource Technology, Vol. 101, pp (2010). [6] Şensöz S., Demiral I., Gerçel H.F. Olive bagasse (Olea europea L.) pyrolysis. Bioresource Technology, Vol. 97, pp (2006). [7] Yanik J., Kornmayer C., Saglam M., Yüksel M. Fast pyrolysis of agricultural wastes: Characterization of pyrolysis products. Fuel Processing Technology, Vol. 88, pp (2007). [8] Heo H.S. et al. Fast pyrolysis of rice husk under different reaction conditions. Journal of Industrial and Engineering Chemistry, Vol. 16, pp (2010). [9] DeSisto W.J., Hill N., Beis S.H., Mukkamala S., Joseph J., Baker C., et al. Fast pyrolysis of pine sawdust in a fluidized-bed reactor. Energy & Fuels, Vol. 24, pp (2010). 5

6 [10] Nokkosmaki M.I., Kuoppala, Leppamaki E.A., Krause O.I. Catalytic conversion of biomass pyrolysis vapours with zinc oxide.. Journal of Analytical and Applied Pyrolysis, Vol. 55, pp (2000). [11] Sipila K., Kuoppala E., Fagernas L., Oasmaa A. Characterization of biomass-based flash pyrolysis oil. Biomass and Bioenergy, Vol. 14 (2), pp (1998). [12] Di Blasi C., Signorelli G., Di Russo C., Rea G. Product Distribution from Pyrolysis of Wood and Agricultural Residues. Industrial and Engineering Chemistry Research, Vol. 38, pp (1999). [13] Bakar M.S.A., Tilitoy J.O. Catalytic pyrolysis of rice husk for bio-oil production. Journal of Analytical and Applied Pyrolysis, Vol. 103, pp (2013). [14] Ji-lu Z. Bio-oil from fast pyrolysis of rice husk: Yields and related properties and improvement of the pyrolysis system.. Journal of Analytical and Applied Pyrolysis, Vol. 80, pp (2007). [15] Okoroigwe E. et al. Pyrolysis of Gmelina arborea Wood for Bio-oil/Bio-char Production: Physical and Chemical Characteristics of Products. Journal of Applied Sciences, Vol. 12 (4), pp (2012). [16] Oasmaa A., Solantausta Y., Arpiainen V., Kuoppala E., Sipila K., Fast pyrolysis bio-oils from wood and agricultural residues. Energy & Fuels, Vol. 24, pp (2009). [17] Fahmi R., Bridgwater A.V., Donnison I., Yates N., Jones J.M., The effect of lignin and inorganic species in biomass on pyrolysis oil yields, quality and stability. Fuel, Vol. 87, pp (2008). [18] Patwardhan P.R., Satrio J.A., Brown R.C., Shanks B.H. Influence of inorganic salts on the primary pyrolysis products of cellulose. Bioresource Technology, Vol. 101, pp (2010). [19] Abdullah N., Gerhauser H. Bio-oil derived from empty fruit bunches. Fuel, Vol. 87, pp (2008). [20] Nowakowski D.J., Jones J.M., Brydson R., Ross A.B. Potassium catalysis in the pyrolysis behaviour of short rotation willow coppice. Fuel, Vol. 86, pp (2007). [21] Ingram L., et al. Pyrolysis of wood and bark in an auger reactor: physical properties and chemical analysis of the produced bio-oils. Energy & Fuels, Vol. 22(1), pp (2008). [22] Yang H. et al. Characteristics of hemicellulose, cellulose and lignin pyrolysis. Fuel, Vol. 86, pp (2007). [23] Panopoulos K., Vamvuka D. Experimental evaluation of thermochemical use of two promising biomass fuels. Fuel (2009). [24] Coulson M. Pyrolysis of perennial grasses from southern Europe. Thermalnet Newsletter, Vol. 2, pp. 6-7 (2006). [25] Bridgwater A.V. Principles and practice of biomass fast pyrolysis processes for liquids. Journal of Analytical and Applied Pyrolysis, Vol. 51, pp (1999). [26] Butler E., Devlin G., Meier D., McDonnell K. A review of recent laboratory research and commercial developments in fast pyrolysis and upgrading. Renewable and Sustainable Energy Reviews, Vol. 15, pp (2011). [27] Nowakowski D.J., Bridgwater A.V., Elliott D.C., Meier D., de Wild P. Lignin fast pyrolysis: results from an international collaboration. Journal of Analytical and Applied Pyrolysis, Vol. 88, pp (2010). [28] Tsai W.T., Lee M.K., Chang Y.M. Fast pyrolysis of rice straw sugarcane bagasse and coconut shell in an induction-heating reactor. Journal of Analytical and Applied Pyrolysis, Vol. 76, pp (2006). [29] Piskorz, J., Scott D.S., Radlien D. Composition of oils obtained by fast pyrolysis of different woods. In Pyrolysis Oils from Biomass: Producing Analyzing and Upgrading; American Chemical Society: Washington DC, 1988, pp [30] Zhang Q., Chang J., Wang T., Xu Y. Review of biomass pyrolysis oil properties and upgrading research. Energy Conversion and Management, Vol. 48, pp (2007). [31] Raveendran, K., Ganesh A. Heating value of biomass and biomass pyrolysis products. Fuel, Vol. 75, pp (1996). [32] Angin D. Effect of pyrolysis temperature and heating rate on biochar obtained from pyrolysis of safflower seed press cake. Bioresource Technology, Vol. 128, pp (2013). [33] Demirbas A. Pehlivan E., Altun T. Potential evolution of Turkish agricultural residues as bio-gas, bio-char and bio-oil sources. International Journal of Hydrogen Energy, Vol. 31, pp (2006). ASTM D : Standard Specification for Pyrolysis Liquid Biofuel (2012). 6

7 Table 1 Feed rates of the biomasses (19 rpm). Pinewood Olive bagasse Wheat straw Rice husk Biomass feed rate (g/min) Table 2 - Main characteristics of the biomasses used as feedstock. Parameter Pinewood Olive bagasse Wheat straw Rice husk Method Proximate analysis (wt.%, ar*) Volatiles ASTM E872, ASTM E897 Fixed Carbon By difference Moisture ASTM E871 Ash ASTM 1101, ASTM E830 Ash Analysis (wt.%, db**) SiO Al 2O P 2O K 2O Ultimate analysis (wt.%, ar*) Carbon Hydrogen Nitrogen ASTM E778 Sulphur < 0.02 < 0.02 < 0.02 < 0.02 ASTM E775 Oxygen By difference High Heating Value (MJ/kg, ar*) Low Heating Value (MJ/kg, ar*) ASTM D3682, ASTM D279, ASTM D4278, AOAC 14.7 ASTM E777 ASTM D2015, E711 Table 3 Physical properties of the original feedstock and the bio-oils obtained from pyrolysis of pinewood, olive bagasse, wheat straw and rice husk. Analysis Pinewood Olive bagasse Wheat straw Rice husk Oil Raw Oil Raw Oil Raw Oil Raw Density, kg/m Moisture, wt.% C (wt.%) H (wt.%) N (wt.%) < O (wt.%) O/C H/C HHV, MJ/kg LHV, MJ/kg Phases

8 Table 4 Physical properties of the char obtained from pyrolysis of pinewood, olive bagasse, wheat straw and rice husk. Analysis Pinewood char Olive bagasse char Wheat straw char Rice husk char Ash, wt.% Moisture, wt.% C (wt.%) H (wt.%) N (wt.%) < < 0.5 < 0.5 S (wt.%) < 2 < 2 < 2 < 2 O (wt.%) O/C H/C HHV, MJ/kg LHV, MJ/kg Figure 1 Schematic of the pyrolysis reactor: 1 Biomass feed; 2 Electric engine; 3 Screw and main pipe; 4 Electrical resistance; 5 Data acquisition & Control system; 6 Nitrogen vessel; 7 Nitrogen circuit; 8 - Char collector flask; 9 Condensers; 10 Refrigerator circuit. 8

9 Figure 2 Illustrative detail view of the reaction zone wt. % Gas Bio-oil Char Pinewood Olive bagasse Wheat straw Rice husk Feedstock Figure 3 Yields of the products obtained from the pyrolysis of the biomasses. Bio-oil yield, wt.% Pinewood Rice husk Olive bagasse Wheat straw Ash, wt.% Figure 4 Correlation of the feedstock ash content to the bio-oil yields obtained from pyrolysis. 9

10 a) b) Figure 5 Bio-oil of a) pinewood and b) olive bagasse. 10