Journal of Materials Research and Technology
w w w. j m r t . c o m . b r
ORIGINAL ARTICLE
Characterization of Nanomaterials Produced from Sugarcane Bagasse Joner Oliveira Alves1,*, Jorge Alberto Soares Tenório2, Chuanwei Zhuo3, Yiannis Angelo Levendis4 Doctor in Metallurgical and Materials Engineering, Researcher, Research Center, Aperam South America; 09, Praça 1º de Maio, Centro; Timóteo, MG, 35180-018, Brazil. 2 Doctor in Metallurgical Engineering, Professor, Department of Metallurgical and Materials Engineering, Polytechnic School, University of São Paulo; 2463, Prof. Mello Moraes Ave.; São Paulo, SP, 05508-030, Brazil. 3 Master in Mechanical Engineering, PhD student, Department of Mechanical and Industrial Engineering, College of Engineering, Northeastern University; 360 Huntington Ave.; Boston, MA, 02115, USA. 4 Doctor in Environmental Engineering Science, Professor, Department of Mechanical and Industrial Engineering, College of Engineering, Northeastern University; 360 Huntington Ave.; Boston, MA, 02115, USA. 1
Manuscript received March 19, 2012; in revised form April 18, 2012
The traditional sugar production associated with the growing production of ethanol combustible made of the sugarcane industry to be one of the most important segments of Brazilian economy. Brazilian industries of sugar and ethanol processed about 630 million tons of sugarcane in 2010, which generated approximately 142 million tons of bagasse. A novel technique to produce nanomaterials using the gases generated during the pyrolysis of sugarcane bagasse was developed. In this work, the microstructural characterization of such nanomaterials is presented by using Scanning Electron Microscopy and Transmission Electron Microscopy. Results showed that the nanomaterials were in the form of long, straight, tubular structures with smooth walls and axially-uniform diameters, which is characteristic of carbon nanotubes. Typical lengths were in the order of 50 õm and diameters were in the range of 20 nm to 50 nm. Therefore, sugarcane bagasse may be pyrolyzed to generate bio-syngas for power generation while, at the same time, produce addedvalue byproducts, such as carbon nanotubes. KEY WORDS: Carbon nanotubes; Sugarcane bagasse; Pyrolysis; Catalysis © 2012 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda. Este é um artigo Open Access sob a licença de CC BY-NC-ND
1. Introduction The interest in ethanol has increased considerably worldwide due to the necessity of Ànding renewable and cleaner energy resources[1]. According to the Renewable Fuels *Corresponding author. E-mail address:
[email protected] (J.O. Alves)
Association (RFA), the world ethanol production in 2008 was approximately 65.7 billion liters (17.3 billion gallons), which represented a 24% increase in the production over that of the previous year[2]. The major producers of ethanol are the USA and Brazil, which together account for 90% of world production. The main feedstock for ethanol in USA is corn grain, whereas sugarcane predominates in Brazil[1,3].
© 2012 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda. Este é um artigo Open Access sob a licença de CC BY-NC-ND
Alves et al.
32 Fermentation is the main process in the ethanol production from sugarcane. During the fermentation process of sugar or sugar-based ethanol production, a solid residue is generated in the form of a dried pulp known as sugarcane bagasse. Approximately 225 kg of this waste is generated for each 1,000 kg of sugarcane inserted in the process[4]. According to the CONAB (National Supply Company of Brazilian Government), the forecast of Brazilian ethanol production for year 2009/2010 is 28 billion liters, which will demand about 350 million tons of sugarcane and will generate approximately 79 million tons of bagasse. The numbers of generated bagasse are even greater when the sugarcane used to produce sugar is also considered: together, the Brazilian industries of sugar and ethanol processed about 630 million tons of sugarcane in 2010, which generated approximately 142 million tons of bagasse[5]. Sugarcane bagasse may be burned to produce energy and steam that may be either used within the ethanol plant or exported for a district heating system, therefore reducing the demand of fossil fuels[1,4]. The sugarcane bagasse has energy content of 17 MJ/kg; thus considering that the total production of this waste in 2010 amounted to 142 Mt, hypothetically about 2400 GJ could be generated[6]. The Brazilian ethanol plants are self energy, and in some cases is possible to commercialize surplus electricity due to a cogeneration system installed in the mill, which uses just the bagasse as energy source[7]. A novel technique to produce carbon nanomaterials (CNMs) using the gases generated during the pyrolysis of several wastes (bagasse, corn-derived DDGS, plastics, tires) was established in the Combustion and Air Pollution Laboratory of Northeastern University (Boston, USA)[8–11]. In this paper were investigated the catalyst substrates formed with the pyrolysis gases from sugarcane bagasse in order to determine whether nanomaterials were formed, and also to analyze the form and dimensions of such materials. Nanotechnology segment was responsible for a consumer market of about US$11 trillion in 2010, wherein US$340 billion corresponded just to nanomaterials. These materials consist of structures with at least one dimension in the order of nanometers (1×10î9 m), and have a wide range of potential applications due to their extraordinary mechanical, thermal and electrical properties[12,13]. In the year 2011, the global production of CNMs was around 3,500 tons, and it is projected to expand at a compound annual growth rate of 30.6%. Expanding markets for applications of CNMs, such as nanotubes and nanoÀbers, place ever-increasing demands on lowering their production costs[8]. To reduce nanomaterials cost, it is instrumental reduce the expenses associated with the procurement of raw-materials. By using sugarcane
bagasse as feedstock for CNMs growth, the cost of raw-material can be minimized.
2. Methods The feedstock used in this study was sugarcane bagasse provided by a Brazilian ethanol producing company. This material was received in Àber form (Fig. 1) and was pulverized to particle sizes smaller than 500 m using a household blender. Table 1 lists the chemical properties of the bagasse materials determined by X-ray Fluorescence Spectroscopy and Elemental Analysis (CHN); the carbon account corresponds to approximately half of the mass. A ceramic boat was used to insert the bagasse in the furnace; amounts of 4.0 g were used in each experiment. The laboratory furnace consists of a two-section quartz laminar-Áow, electrically heated, mufÁe furnace. The Àrst section of the apparatus is the pyrolyzer (37 mm ID x 870 mm) and the second section is the catalyzer (37 mm ID x 380 mm long), which is connected to the gas analyzers. Both sections have an independent heating capacity up to 1,100ºC. A design of the furnace is depicted in Fig. 2. The samples were inserted into the Àrst section of the furnace with N2 gas serving as carrying gas at a Áow rate of
Fig. 1 Sugarcane bagasse as received from the ethanol industry
Table 1 Chemical analysis of the sugarcane bagasse used in the work (in wt. %) C
O
K
50.5 17.5 4.1
H
S
N
P
Ca
Fe
Si
Others
6.7
1.7
0.3
0.5
2.7
4.8
7.0
4.2
N2
Effluent
Waste Sample
Fig. 2 Design of the furnace used in the experiments
Filter
Catalyst
Characterization of Nanomaterials Produced from Sugarcane Bagasse 3 L/min, ensuring the absence of air. Therefore, pyrolytic conditions prevailed in the furnace. Several temperatures were tested in the Àrst section of the furnace, in order to decide the best pyrolysis conditions. Thereby, a range of 600°C–1,000°C was established. Sugarcane bagasse pyrolysis-generated gases that Áow directly to the second section of the apparatus, which consists of a temperature-controlled furnace preheated to 1,000°C, wherein the catalyst activation occurs. In order to prevent pyrolysis-generated particulate matter from entering the synthesis chamber and contaminate the catalyst, a barrier Àlter was placed after the division of the two sections of the apparatus. This Àlter has a honeycomb structure of silicon carbide (SiC) and performs with a high Àltration efÀciency, achieving up to 97% retention for submicron particles[14]. The catalyst system consisted of a mesh screen made of stainless steel AISI 304, which has chemical components according to the ASTM E2016 speciÀcation: Cr (18%–20%), Ni (8%–10,5%), Mn (2%), Si (1%), N (0,1%), C (0,08%), P (0,05%), S (0,03%), and Fe (balance)[15]. The stainless steel screen was used as-received, without pretreatment; pieces of 300 x 100 mm were rolled in cylinders of about 40-mm of diameter and were inserted along the direction of the gas Áow in the second section of the furnace. The pyrolysis process of sugarcane bagasse generated several light hydrocarbon species, which the most prominent are methane, acetylene, benzene, and ethylene [16]. These hydrocarbons can be used as important carbon donors in the production of CNMs using the catalytic chemical vapor deposition method (CCVD)[10]. The process used in this work consisted of thermal dehydrogenation reactions, whereby the transition metal catalyst (stainless steel) was used to crack the hydrocarbon gases into Csolid and H2. Thereafter, diffusion of carbon into the metal particles takes place until the solution becomes saturated. The super saturation of the solution results in precipitation of solid carbon particles in the metal surface. Morphological analysis of the formed carbon particles was performed using Scanning Electronic Microscopy (SEM) and Transmission Electron Microscopy (TEM). Random pieces of the mesh were removed and were placed directly on the SEM imaging stage. SEM analyses were conducted on a Hitachi 4800 instrument, at 3 kV voltage and a workingdistance of 8.2 mm. For TEM samples, the meshes were sonicated in a 100% ethanol solution and the products were analyzed in a low-magniÀcation TEM instrument (model JEOL 1010, with an accelerating voltage of 70 kV) as well as in a high-magniÀcation TEM of the Massachusetts Institute of Technology – MIT (model JEOL 2010, with an accelerating voltage of 200 kV).
3. Results and Discussion Fig. 3 shows the SEM images of synthesized materials from sugarcane bagasse, wherein the images a, b, and c were obtained with pyrolysis temperatures of 600°C and images d, e, and f with pyrolysis temperatures of 1,000°C. SEM images of the nanomaterials synthesized from sugarcane bagasse (Figs. 3a and 3d) show the catalyst meshes in the background and arrays of cylindrical nanomaterials covering the surface. The lengths of these nanocylinders were in the order of 50 õm. Experiments at pyrolysis tem-
33
Fig. 3 SEM images of catalyzed materials using sugarcane bagasse – pyrolysis temperatures of: 600°C (a, b, c); and 1,000°C (d, e, f)
peratures of 1,000°C produced a smaller population of nanomaterials. Figs. 3b and 3e, taken at higher magniÀcations, illustrate that the nanomaterials are in form of long Àbers; whereas Figs. 3c and 3f, taken at even higher magniÀcations, show that the Àbers have diameters in the range of 20 nm to 50 nm. Nanomaterials produced with pyrolysis temperature of 1,000°C showed less entangled and possess straighter shapes. Transmission Electron Microscopy was used for detailed structural analysis of the nanomaterials. TEM images, with different magniÀcation, of the materials produced from pyrolyzis of sugarcane bagasse are shown in Fig. 4. Again, each image (Figs. 4a, 4b, and 4c) corresponds to the waste biomass pyrolysis at 600°C, whereas Figs. 4d, 4e, and 4f correspond to the pyrolysis at 1,000°C. TEM images show that the produced materials have a tubular form, which is characteristic of carbon nanotubes (CNTs). CNTs were discovered by Iijima in 1991, and consist of coaxial tubular graphene sheets, with lengths in the order of micrometers and diameters in the order of nanometers[17]. These materials have several possibilities of technological applications due to their exceptional properties[18]. CNTs are classiÀed as single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs). The SWCNTs consist of a single graphene sheet rolled to form a cylindrical tube, and MWNTs are formed by a set of concentric single wall nanotubes[19]. Images obtained using the high-resolution TEM (Figures 4c and 4f) indicate the presence of parallel graphene layers around the hollow cavity, which showed that carbon nanotubes produced in this study have multiple walls, i.e., they are classiÀed as MWCNTs. Tessonnier et al.[20] investigated the structural properties of several types of currently marketed carbon nanotubes. Among the CNTs analyzed by Tessonnier et al., two
Alves et al.
34
Acknowledgments The authors would like to thank CNPQ-Brazil for Ànancing the period of the D.Sc. Joner Alves at Northeastern University (USA). The support provided by CAPES (Grant: 04/CII-2008 – Rede Nanobiotec-Brasil) was also greatly appreciated.
REFERENCES
Fig. 4 TEM images of catalyzed materials using sugarcane bagasse – pyrolysis temperatures of: 600°C (a, b, c); and 1,000°C (d, e, f)
showed structural characteristics similar to the presented in this work, which used sugarcane bagasse as feedstock. The commercial nanotubes that presented similar characteristics were NC 3100 from the Belgian company Nanocyl SA and Baytubes of the German company Bayer MaterialScience AG, which are two of the world’s largest producers of nanomaterials. Therefore, multi-walled carbon nanotubes were successfully generated by pyrolysis of sugarcane bagasse.
4. Conclusions Part of the carbon content of gases generated from pyrolysis of sugarcane bagasse was catalytically converted into solid particles on the stainless steel meshes. The microstructural characterization of these particles showed the formation of nanomaterials with the characteristics enumerated as follow: • materials showed long and straight forms. Typical lengths were in the order of 50 õm and diameters were in the range of 20 nm–50 nm; • structures presented tubular aspect with smooth walls and axially-uniform diameters; • the nanotubes showed parallel graphene layers around the hollow cavity, which indicate that they are multi-wall carbon nanotubes; • a more uniform nanomaterial product was obtained with the higher pyrolysis temperature (1,000°C).
1. Kim S, Dale BE. Global potential bioethanol production from wasted crops and crop residues. Biomass and Bioenergy 2004; 26(4):361–75. 2. RFA – Renewable Fuels Association. Statistics: 2008 world fuel ethanol production. Available from: http://www.ethanolrfa. org/industry/statistics. [Accessed on 11/23/2009]. 3. Kim S, Dale BE. Environmental aspects of ethanol derived from no-tilled corn grain: nonrenewable energy consumption and greenhouse gas emissions. Biomass and Bioenergy 2005; 28(5):475–89. 4. McKendry P. Energy production from biomass (part 2): conversion technologies. Bioresource Technol 2002; 83(1):47–54. 5. Porto SI, Silva ACP, Oliveira EP. Report of Brazilian sugarcane production. Brasília: CONAB; 2009. 6. Baxter L. Biomass-coal co-combustion: opportunity for affordable renewable energy. Fuel 2004; 84:1295–302. 7. Alves JO, Bailo LA. Modernization of the sugarcane mills in the Brazilian Northeast. CanaMix 2012; 44:40–1. 8. Zhuo C, Alves JO, Tenório JAS, Levendis YA. Synthesis of carbon nanomaterials through up-cycling agricultural and municipal solid wastes. Industrial & Engineering Chemistry Research 2012; 51:2922–30. 9. Alves JO, Zhuo C, Levendis YA, Tenório JAS. Synthesis of nanomaterials using post-consumer PET bottles as raw material. Tecnologia em Metalurgia e Materiais 2012; 9(1):59-63. 10. Alves JO, Zhuo C, Levendis YA, Tenório JAS. Catalytic conversion of wastes from the bioethanol production into carbon nanomaterials. Applied Catalysis B: Environmental 2011; 106(3–4):433–44. 11. Alves JO, Zhuo C, Levendis YA, Tenório JAS. Microstructural analysis of carbon nanomaterials produced from pyrolysis/combustion of styrene-butadiene-rubber (SBR). Materials Research 2011; 14(4):499–504. 12. Pitkethly MJ. Nanoparticles as building blocks. Nano Today 2003; 36:36–42. 13. Ávila AF, Lacerda GSR. Molecular Mechanics Applied to SingleWalled Carbon Nanotubes. Materials Research 2008; 11(3): 325–33. 14. Larsen CA, Levendis YA, Shimato K. Filtration assessment and thermal effects on aerodynamic regeneration in silicon carbide and cordierite particulate Àlters. SAE; 1999. SAE Technical Paper Series Report no. 1999-01-0466. 15. ASTM. ASTM E2016 – 06 Standard speciÀcation for industrial woven wire cloth. ASTM International, West Conshohocken, PA, 2006. 16. Alves JO, Zhuo C, Levendis YA, Tenório JAS. Analysis of light hydrocarbon gases in the pyrolysis process of sugarcane bagasse. Proceedings of the 65th ABM International Congress; 2010, Jul 26–30; Rio de Janeiro, Brazil. p. 766–73. 17. Iijima S. Helical microtubules of graphitic carbon. Nature 1991; 354:56–8. 18. Baughman RH, Zakhidov AA, Heer WA. Carbon nanotubes – the route toward applications. Science 2002; 297:787–92. 19. Grobert N. Carbon nanotubes – becoming clean. Materials Today 2007; 10(1–2):28–35. 20. Tessonnier JP, Rosenthal D, Hansen TW, Hess C, Schuster ME, Blume R et al. Analysis of the structure and chemical properties of some commercial carbon nanostructures. Carbon 2009; 47:1779–98.
