Characterizations of Bio-oil and Bio-char Products from Algae with Slow and Fast Pyrolysis

Transcription

1 Article International Journal of Environment and Bioenergy, 2015, 10(1): International Journal of Environment and Bioenergy Journal homepage: ISSN: Florida, USA Characterizations of Bio-oil and Bio-char Products from Algae with Slow and Fast Pyrolysis Kanyaphorn Chaiwong 1 and Tanongkiat Kiatsiriroat 2 1 Mechanical Engineering Program, Rajamangala University of Technology Lanna Nan, Nan 55000, Thailand 2 Department of Mechanical Engineering, Chiang Mai University, Chiang Mai 50200, Thailand * Author to whom correspondence should be addressed; drccrmutl@gmail.com; tanong@dome.eng.cmu.ac.th Article history: Received 27 April 2015, Received in revised form 5 June 2015, Accepted 8 June 2015, Published 11 June Abstract: In this study, slow and fast pyrolysis of algae was carried out to get bio-oil and bio-char from dry freshwater algae; Spirulina Sp. and Spirogyra Sp. The bio-oil products from the slow pyrolysis were heterogeneous liquids, which had an obvious separation of water soluble and water insoluble phases. The liquid from the fast pyrolysis have a single phase. Due to the composition of bio-oils, higher carbon content, higher heating value and lower content of oxygen was found in the fast pyrolysis compared with those in the slow pyrolysis. Two of the functional group compositions from the fast pyrolysis oil were not found in the slow pyrolysis oil as the C C stretching and aromatic phenyl were analyzed by Fourier Transform Infrared Spectrometer. The bio-chars from the fast pyrolysis showed smaller particle sizes and more dust than those from the slow pyrolysis. But the bio-chars from the slow pyrolysis had higher carbon content than those from the fast pyrolysis and thus the previous one had higher heating value. In the porous surface structures of algae, bio-chars were characterized using Scanning Electron Microscopy (SEM). It could be seen that the bio-chars obtained from the slow pyrolysis had thick particle walls while the fast pyrolyzed bio-char particles had fragile thin walls. Keywords: Slow pyrolysis, Fast pyrolysis, Algae, Bio-oil, Bio-char, Fixed bed reactor

2 66 1. Introduction A pyrolysis process is the chemical decomposition of an organic substance through heating in the absence of oxygen atmosphere. This technique is developed to produce bio-energy and its products from biomass feedstock. Pyrolysis temperatures of biomass can start at 350 o 550 o C and reach up to 700 o C. This temperature can generate the polymerization of the molecules within the feedstock where the larger molecules can be produced with some aromatic and aliphatic compounds. Some components of the feedstock due to the thermal decomposition are transformed into smaller molecules. The process of pyrolysis transforms organic matters into three different components which are gas, liquid and solid, in different proportions depending upon both the feedstock and the pyrolysis conditions. The gases (either condensable or incondensable) and liquids can be upgraded and used as fuel for combustion. The remaining solid component after the pyrolysis is charcoal (Mohan et al., 2006). Depending on the operating conditions, the pyrolysis process can be divided into three subclasses: conventional pyrolysis (slow pyrolysis), fast pyrolysis, and flash pyrolysis. The range of the main operating parameters and product distribution of the pyrolysis processes are given in Table 1 (Maschio et al., 1992). The preferred technology is fast or flash pyrolysis at high temperatures with very short residence times. Slow pyrolysis is defined as the pyrolysis that occurs at a slow heating rate. Algae can be used as a source of bio-oil and bio-char production. Algae play an important role in the context of energy and bio-fuels as they provide much higher yields of biomass and fuels, i.e times higher than other energy crops. Some suggest that microalgae are capable of producing up to 15,000 gallons of oil per hectare per year (Chisti, 2007). Algae can grow under conditions which are unsuitable for conventional crop production. They are capable of fixing CO2 from the atmosphere, and thus facilitating the reduction of increasing atmospheric CO2 levels, which is now considered as a global problem. Table 1. Pyrolysis technology, corresponding process condition and product distribution. Pyrolysis Process Condition Products Technology Residence Time Heating Rate Temperature Char Bio-oil Gas Slow pyrolysis 5-30 min < 50 o C/min o C <35% <30% <40% Fast pyrolysis < 5 sec >200 o C/s o C <25% <75% <20% Flash pyrolysis < 0.1 sec >200 o C/s o C <20% <70% <20% (Source: Maschio et al., 1992) Some studies were interested in the conversion of algae feedstock to liquid fuel by pyrolysis because fast pyrolysis can directly produce a liquid fuel from the biomass and also from the algae.

3 67 Miao and Wu (2004) revealed the suitability of two kinds of algae, Chllorella protothecoides and Microcystis aeruginosa, to produce bio-oil products in a fluidized bed reactor. With a pyrolysis temperature of 500 o C, a heating rate of 600 o C/s, an algae feed rate of 4 g/min., a sweeping gas (N2) flow rate of 0.4 m 3.h -1 and a residence time of 2 3 s, the yield of bio-oil from C.protothecoides was more than that from M.aeruginosa (18% and 24% respectively). The distributions of straight-chain alkanes of the saturated fractions were similar to the components of diesel fuel. Bio-oil products from fast pyrolysis of microalgae displayed good characterization at low oxygen content with a heating value of 29 MJ.kg -1, a density of 1.16 kg.l -1 and a viscosity of 0.01 Pa s. These properties of the bio-oil from the microalgae showed that it was suitable to substitute the fuel oil more than that from the lignocellulosic materials. Demirbas (2006) investigated the properties of fuels from mosses and algae, and it was found that algae bio-oil showed higher heating values ( MJ.kg -1 ) than the bio-oil from mosses ( MJ.kg -1 ) and also higher than bio-oil from wood. Campanella and Harold (2012) have studied non-catalytic and catalytic pyrolysis of microalgae in a falling solids reactor. It was found that the catalytic pyrolysis gave an organic phase with an increased fraction of hydrocarbon and decreased faction of oxygenates. The non-catalytic pyrolysis gave the highest total liquid yield while the catalytic pyrolysis resulted in the highest yield of the desired hydrocarbon fraction. Wang et al. (2013) investigated the bio-oil and bio-char production from microalgae remnants resulting from solvent-extraction of Chlorella vulgaris. In fast pyrolysis experiments using a fluidized bed reactor at 500 o C, yields of bio-oil, bio-char and gas were 53, 31 and 10% respectively. The production and the properties of algae bio-char were considered (Bird et al., 2011), and it was found that the properties of the macro algal bio-char produced by the slow pyrolysis had low carbon content, surface area and cation exchange capacity, but it was high in ph, ash, nitrogen and extractable inorganic nutrients. Therefore, the algae bio-char had the properties that provided direct nutrient benefits to the soil, especially in acidic soil applications. Chaiwong et al. (2012) referred to the bio-char production from Spirulina Sp. (micro-algae) that it had the carbon content similar to that from macro-algae when produced by the slow pyrolysis process via a fixed bed reactor at 500 o C. In this study, comparisons of slow and fast pyrolysis of algae were investigated. Dry fresh water algae, Spirulina Sp. and Spirogyra Sp., were pyrolyzed in a fixed bed reactor and a porous ceramic walled reactor for slow and fast pyrolysis respectively. The characterizations of bio-oil and bio-char products were considered. 2. Materials and Methods 2.1. Materials

4 68 In this study, two types of dry fresh water algae, Spirulina Sp. and Spirogyra Sp. were used. They were dried at room temperature for one week and then ground into particles with a range of mm. Before starting the pyrolysis, each sample was characterized by the ultimate and proximate analyses and the higher heating values of algae in this study were estimated from the correlation of Parikh et al. (2005) Slow Pyrolysis Experiments In this study, 125 grams of each dried freshwater alga was fed and kept in a fixed bed reactor (21 cm high by 6 cm wide) made of stainless steel (Figure 1a). Nitrogen gas was fed at a flow rate of 1 l min -1 for 30 minutes to remove the air in the reactor before testing. The reactor heated up at a rate of 8 o C min -1 until a set temperature was reached. After that, the reactor was kept at a constant temperature for 60 minutes. The gas leaving the reactor could be condensed in two water-cooled condensers and the liquid (bio-oil) was stored in two collecting flasks while the solid residue (bio-char) was remained in the reactor N2 2 3 a Nitrogen cylinder 2. Reactor 3. Furnace 4. Controller 5. Condenser 6. Water and Ice mixing tank 7. Water cooling tank 8. Nitrogen controller valve 9 Bio oil storage (1) Nitrogen cylinder, (2) Reactor, (3) Furnace, (4)Controller (5) Condenser, (6, 7) Water cooling tank, (8) Nitrogen controller valve, (9) Bio oil storage 1 N (1)Nitrogen cylinder, (2)Reactor, (3) Furnace, (4) Controller, (5) Condenser,(6, 7) Water cooling tank, (8) Nitrogen controller valve, (9) Bio oil storage, (10) Screw feeder, and (11)Char collector b 5 Figure 1. A schematic diagram of the slow and fast pyrolysis experimental setup a: Slow pyrolysis, b: Fast pyrolysis 2.3. Fast Pyrolysis Experiments In fast pyrolysis, the stainless steel reactor s inside-walls were covered by ceramic balls held in place by a stainless steel mesh. The ceramic ball was used to stabilize the reaction temperature inside. There was an electrical heater that supplied heat to the wall sand some parts of which were absorbed

5 69 by the ceramic balls. Nitrogen gas was fed through the ceramic balls and the temperature increased to a set point. After that, in our study, 125 grams of each dried freshwater alga was continuously fed into the reactor (30 cm high and 8 cm wide) using a screw feeder. The algae particles were fed down through the hot nitrogen gas in the reactor at a constant feed rate of 2 g.min -1, and the fast pyrolysis reaction took place inside the reactor. The gas yield leaving the reactor was condensed in the watercooled condensers and kept in liquid form in the bio-oil collector while the solid residues (bio-char) dropped into the bio-char collector. A schematic diagram of the fast pyrolysis experiment setup was shown in Figure 1b. The production of bio-oil and bio-char products from algae by the slow and fast pyrolysis process was evaluated under fixed control parameters such as heating temperature (500 o C), and algae particle size (less than 2 mm.) while N2 gas flow rate (1 l.min -1 ) was also employed. 2.4 Bio-oil and Bio-char Analysis The product yields (wt %) were defined as the mass of product divided by the mass of dry algae feedstock. The chemical compositions and properties of bio-oil and bio-char samples were determined from the ultimate and proximate analyses which were analyzed by a CE Instruments Flash 1112 series EA CHNS-O analyzer, and the water content in the oil was analyzed by a Karl Fischer Coulometer (series 831 KFC) according to the standard test method ISO 12937: The identification of the peaks matched the mass spectra with the standard library in the instrument or on the retention times of known species injected in the chromatographic column. The functional group compositional analysis of the bio-oil and its sub-fractions was carried out by Fourier Transform Infrared Spectrometer (FT- IR). The testing conditions were performed with the frequency range of cm -1. The bio-char structure was analyzed using Scanning Electron Microscope (SEM). 3. Results and Discussion 3.1. Pyrolysis Product Yields and Distribution The product yields for slow and fast pyrolysis of Spirulina Sp. and Spirogyra Sp. were shown in Figure 2. It was found that, the bio-oil from the slow pyrolysis showed an obvious separation of the aqueous fraction and the organic fraction or bio-oil while the fast pyrolysis oil gave an impression like the macroscopic single phase liquid, but in fact, it possessed microscopic multiphase structures. The water soluble phase of the fast pyrolysis condition was less than that of the slow pyrolysis and that could separate into thin layer when keep the fast pyrolysis oil stable more than 1 hr. This performance was similar to the study of Duman et al. (2011) describing that the amount of water-soluble compounds and water in oil continuously decreased with the degradation of pyrolytic lignin, during a fast heating

6 70 condition. Lower bio-oil yields as compared to Spirogyra Sp. (13-16 wt %) were achieved for Spirulina Sp. (21-29 wt %) from the slow and fast pyrolysis at the same temperature (500 o C). The liquid yields from the slow pyrolysis of algae were higher than those from the fast pyrolysis, and this result was consistent with the study of Maguyon and Capareda (2013). The bio-char yields from the slow and fast pyrolysis of Spirulina Sp. gave a similar yield of bio-char while the slow pyrolysis production of Spirogyra Sp. were found to be lower than those from the fast pyrolysis, under the effect of holding time to decreased the product yields of bio-char (Ming Chang et al., 2015). Figure 2. The yields under slow and fast pyrolysis from Spirulina Sp. and Spirogyra Sp Feedstock Characterization The chemical components and physical characteristics of algae. Spirogyra Sp. was macrophytic green algae while Spirulina Sp. was microphytic blue-green algae were shown in Table 2. It could be seen that the properties of Spirulina Sp. were quite similar to those of Spirogyra Sp. The ash content and the amounts of N and S of all algae were higher than those of the typical land biomass and wood (Miao and Wu, 2004). Thus, the algae gave lower heating values. Since the volatile matter in wood was higher than in algae, then the volatile products (oil and gas) from the pyrolysis process of wood should be greater than those of algae.

7 71 Table 2. Chemical components and physical characteristics of dried algae in the current study Characteristic Algae Wood a Ultimate Analysis (%) Sulfur Carbon Hydrogen Nitrogen Oxygen b Proximate Analysis (%) Moisture Ash Volatiles Fixed Carbon Heating value (MJ/kg) a. The data from Park et al., 2008 a.; b. by difference. Spirogyra Sp Spirulina Sp Bio-oil and Bio-char Characterization The characterization of the pyrolysis product from Table 2 shown the result related to the properties and composition of bio-oil and bio-char products of slow and fast pyrolytic processes. From Table 3, it could be seen that the heating values of the pyrolyzed product from Spirogyra Sp. were higher than that Spirulina Sp. The ash content and the amounts of N still higher in the bio-oil and biochar product from both algae. The properties of bio-oil from the fast pyrolysis had better fuel qualities than those from the slow pyrolysis. Higher carbon content, higher heating values and lower content of oxygen in the oil from fast pyrolysis were found in comparison with those of the slow pyrolysis. Spirogyra Sp. Bio-oil could play an important role as the one with the best fuel chemical properties compared with that from Spyrulina Sp. while the bio-char from the slow pyrolysis showed better fuel properties than that from the fast pyrolysis. The carbon content of the slow pyrolysis bio-char in terms of fixed carbon was found to be more than that of the fast pyrolysis and thus the bio-char from the slow pyrolysis could give higher heating content, in agreement with Mašek et al. (2013). The functional group compositions of bio-oil from algae were determined by the Fourier Transform Infrared (FT-IR) Spectra. The functional group composition of bio-oil from the slow and fast pyrolysis was shown in Figure 3.

8 Table 3. Properties of bio-oil and bio-char products from slow and fast pyrolytic processes Typical value Properties Bio-oil from slow pyrolysis Bio-oil from fast pyrolysis Spirulina Sp. Spirogyra Sp. Spirulina Sp. Spirogyra Sp. Ultimate Analysis (%) C H O c N Higher heating value d (MJ.kg -1 ) Typical value Properties Bio-char from slow pyrolysis Bio-char from fast pyrolysis Spirulina Sp. Spirogyra Sp. Spirulina Sp. Spirogyra Sp. Ultimate Analysis C H O c N Higher heating value d (MJ.kg -1 ) Proximate Analysis (% weight : air dried basis) Volatile matter Fixed carbon Ash For Figure 3, the slow and fast pyrolysis oil consisted mainly of alkanes, alkenes and phenols. Two of the functional group compositions from the fast pyrolysis oil were not found in the slow pyrolysis oil as the C C stretching vibrations between 2260 and 2100 cm -1 indicated the presence of alkynes and the absorbance peaks at 1515 and 1485 cm -1 represented an aromatic phenyl. However, more of the functional group compositions from the slow and fast pyrolysis oil were similar. The O-H stretching vibrations between 3400 and 3200 cm -1 indicated the presence of phenols and alcohols. The C-H deformation vibrations between 1475 and 1310 cm -1 indicated the presence of alkanes groups in pyrolysis oil derived from biomass and its sub-fractions. The C=O stretching vibrations with absorbance between 1715 and 1530 cm -1 also indicated the presence of ketones, aldehydes and carboxylic acids; and at 1020 and 970 cm -1 represented C-O and O-H that indicated the presence of primary, secondary and tertiary alcohol including the fractional groups of phenol esters and ester. Fractional groups of N-containing compounds as amines and their derivatives were indicated at the

9 73 absorbance peaks of cm -1 and cm -1. It could be found that most of fractional groups of algae bio-oil in this study could be identified and they gave the same results as pyrolysis oil from lignocellulosic- biomass (Acikgoz and Kockar, 2007, Uzun et al., 2006). However, the N- containing compounds group of the bio-oil from algae was detected to be higher. A B Figure 3. FT-IR spectra of bio-oil from slow (A) and fast (B) pyrolysis of Spirulina Sp. Scanning Electron Microscopy (SEM) was applied to characterize the porous surface structure of the algae bio-char. Figure 4 shows the SEM photographs of char samples from slow and fast pyrolysis of Spirulina Sp.

10 74 Slow pyrolysed bio-char Fastpyrolysed bio-char Figure 4. SEM photomicrographs of bio-char from slow and fast pyrolysis of algae. The phenomenological point of view showed different shapes and sizes of the bio-char from the slow and fast pyrolysis. The pyrolysis heating rate influenced the sizes and shapes of the bio-char. increasing the heating rate could generate a greater proportion of voids and decrease the cell wall thickness. The bio-char obtained from the slow pyrolysis had thick cell walls and some were covered by agglomerated tar whereas the fast pyrolysis bio-char had a fragile thin-wall surface since there was a fast volatile release during the pyrolysis which produced more substantial internal over pressure than forming an open structure. The characteristics of the present bio-char from the results of the SEM analyses were similar to those presented in the report of Onay (2001) which indicated that the SEM porosity was enhanced by increasing the heating rate. 4. Conclusions A comparison of bio-oil and bio-char properties from slow and fast pyrolysis of algae was investigated in this study. Dry fresh water algae, Spirulina Sp. and Spirogyra Sp. were pyrolyzed in a fixed bed and a porous ceramic walled reactor for the slow and fast pyrolysis respectively. It could be noted that the liquid yields from the slow pyrolysis were higher than those of the fast pyrolysis at the same temperature (500 o C) while the bio-char was shown in a similar product yield in a different production. The composition of the bio-oil, the higher carbon content, the heating values and the lower content of oxygen were found in the fast pyrolysis compared with those in the slow pyrolysis. FT-IR spectra showed that, more of the functional group compositions from the slow and fast pyrolysis oil were similar but two of the functional group compositions from the fast pyrolysis oil were not found in the slow pyrolysis oil as the C C stretching and aromatic phenyl. The bio-char from the slow pyrolysis had higher carbon content than that from the fast pyrolysis, and thus the previous one had higher heating values. The Scanning Electron Microscopy showed that, in the porous surface structure of

11 75 algae, the bio-char obtained from the slow pyrolysis had thick wall particles while the fast pyrolyzed bio-char particles had fragile thin walls. Acknowledgments The authors would like to acknowledge the Office of the Higher Education Commission, Thailand, under the National Research University Project and the program for Strategic Scholarships for Frontier Research Network for the joint Ph.D. Program Thai Doctoral degree. Our gratitude is also extended to the Graduate School and the Faculty of Engineering, Chiang Mai University and Rajamangala University of Technology Lanna Nan, for their support and the testing facilities. References Acikgoz, C. and O.M. Kockar. (2007). Flash pyrolysis of linseed (Linum usitatissimum L.) for production of liquid fuels. Journal of Analytical and Applied Pyrolysis, 78(2): Bird, M.I., C.M. Wurster, P. H. de Paula Silva and A.M. Bass, Rocky de Nys. (2011). Algal biochar production and properties. Bioresource Technology, 102(2): Campanella, A. and M.P. Harold. (2012). Fast pyrolysis of microalgae in a falling solids reactor: Effects of process variables and zeolite catalysts. Biomass and Bioenergy, 46: Chaiwong, K., T. Kiatsiriroat, N. Vorayos and C. Thararax. (2013). Study of bio-oil and bio-char production from algae by slow pyrolysis. Biomass and Bioenergy, 56: Chisti, Y. (2007). Biodiesel from microalgae. Biotechnology Advances, 25(3): Duman,G., C. Okutucu, S. Ucar, R. Stahl and J. Yanik. (2011). The slow and fast pyrolysis of cherry seed. Bioresource Technology, 102(2): Demirbas, A. (2006). Oily Products from Mosses and Algae via Pyrolysis. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 28(10): Maguyon, M.C.C. and S.C. Capareda. (2013). Evaluating the effects of temperature on pressurized pyrolysis of Nannochloropsis oculata based on products yields and characteristics. Energy Conversion and Management, 76: Maschio, G., C. Koufopanos and A. Lucchesi. (1992). Pyrolysis, a promising route for biomass utilization. Bioresource Technology, 42(3): Mašek, O., V. Budarin, M. Gronnow, K. Crombie, P. Brownsort, E. Fitzpatrick and P. Hurst. (2013). Microwave and slow pyrolysis biochar Comparison of physical and functional properties. Journal of Analytical and Applied Pyrolysis, 100: Miao, X and Q. Wu. (2004). High yield bio-oil production from fast pyrolysis by metabolic controlling of Chlorella protothecoides. Journal of Biotechnology, 110(1):85-93.

12 76 Mign Chang, Y., Tien Tsai, W., Hsuan Li, M. (2015). Chemical characterization of char derived from slow pyrolysis of microalgal residue. Journal of Analytical and Applied Pyrolysis, 111: Mohan, D., C.U. Pittman and Jr., P.H. Steele. (2006). Pyrolysis of Wood/Biomass for Bio-oil: A Critical Review. Energy Fuels, 20 (3): Onay, O., S.H. Beis and O.M. Kockar. (2001). Fast pyrolysis of rape seed in a well-swept fixed-bed reactor. Journal of Analytical and Applied Pyrolysis, 58 59: Parikh, J., SA. Channiwala and GK. Ghosal. (2005). A correlation for calculating HHV from proximate analysis of solid fuels. Fuel, 84(5): Park, H.J., J.I. Dong, J.K. Jeon, Y.K. Park, K.S. Yoo, S.S. Kim, J. Kim and S. Kim. (2008). Effects of the operating parameters on the production of bio-oil in the fast pyrolysis of Japanese larch. Chemical Engineering Journal, 143(1-3): Uzun, B.B., A.E. Pütün and E. Pütün. (2006). Fast pyrolysis of soybean cake: Product yields and compositions. Bioresource Technology, 97(4): Wang, K., R.C. Brown, S. Homsy, L. Martinez and S.S. Sidhu. (2013). Fast pyrolysis of microalgae remnants in a fluidized bed reactor for bio-oil and biochar production. Bioresource Technology 127: