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Fixed bed pyrolysis of Euphorbia rigida with different catalysts
Energy Conversion and Management 46 (2005) 421–432 www.elsevier.com/locate/enconman
Fixed bed pyrolysis of Euphorbia rigida with different catalysts Funda Atesß a, Aysße E. P€ ut€ un a, Ersan P€ ut€ un
b,*
a
b
Department of Chemical Engineering, Faculty of Engineering and Architecture, Iki Eylul Campus, Anadolu University, Eskisehir 26470, Turkey Department of Material Science and Engineering, Faculty of Engineering and Architecture, Iki Eylul Campus, Anadolu University, Eskisehir 26470, Turkey Received 7 July 2003; received in revised form 31 December 2003; accepted 21 March 2004 Available online 25 May 2004
Abstract Since Euphorbia rigida is a celluloid plant with low fat content, the oil yields of previous fixed bed pyrolysis studies were low. In order to increase the oil yield, biomass pyrolysis experiments were performed in a fixed bed reactor with two selected commercial catalysts, namely Criterion-534 and activated alumina, and natural zeolite (klinoptilolite). Experiments were conducted in a static atmosphere with a heating rate of 7 C min1 , pyrolysis temperature of 550 C and mean particle size of 0.55 mm. In the experiments, all the catalysts were used with various percentages, and the effects of the variable catalysts on the yields and chemical composition of the oils obtained were investigated. Oil yield reached 27.5% with the use of natural zeolite, 31% with Criterion-534 and 28.1% with activated alumina, while it was only 21.6% without a catalyst. The pyrolysis oils were examined by using spectroscopic and chromatographic analysis techniques, and the obtained results were compared with the results of similar experiments achieved without a catalyst. 2004 Elsevier Ltd. All rights reserved. Keywords: Biomass; Euphorbia rigida; Catalyst; Pyrolysis; Oil
1. Introduction Worldwide concern about the diminishing trend of primary energy sources and environmental problems have prompted many observers to call for a decreased reliance on fossil fuels.
* Corresponding author. Present address: Department of Chemical Engineering, Faculty of Engineering, Yunusemre Campus, Anadolu University, Eskisehir 26470, Turkey. Tel.: +90-222-335-0580/6301, +90-222-322-3662; fax: +90-222323-9501. E-mail address: [email protected] (E. P€ ut€ un).
0196-8904/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2004.03.011
422
F. Atesß et al. / Energy Conversion and Management 46 (2005) 421–432
Renewable sources of energy are constantly examined as alternatives for fossil fuels. Renewable energy is of growing importance in satisfying environmental concerns over fossil fuel usage and its contribution to the greenhouse effect. Biomass forms are some of the main renewable energy resources available [1]. Biomass has received considerable attention both as a source of energy and as an organic chemical feedstock [2,3]. The energy potential of biomass has increasingly become recognized as a means to help meet world energy demand. The utilization of biomass and other alternative fuel sources, rather than existing fossil fuels, would offer more environmentally acceptable processes for energy production and will aid in conserving the limited supplies of fossil fuels [4–6]. Virtually all biomass products can be converted into commercial fuels, suitable to substitute for fossil fuels. These can be used for transportation, heating, electricity generation or anything else where fossil fuels are used. The conversion is accomplished through the use of several distinct processes. These processes include both biochemical and thermal conversions to produce gaseous, liquid and solid fuels that have high energy contents, are easily transportable and are, therefore, suitable for use as commercial fuels [1,7]. Thermochemical processes are thought to have great promise as a means for efficiently and economically converting biomass to synthetic fuels [8]. In the thermochemical processes, pyrolysis has received increased interest, since the process can be performed under a variety of conditions to capture all the components and to maximize the output of the desired product, be it char, liquid or gas [5,9]. During pyrolysis, the biomass is heated in the absence of air and breaks down into a complex mixture of liquids, gases and a residual char [10,11]. There are a number of biomass sources, such as forest residues, low grade plants, agricultural residues and municipal solid wastes, which can be utilized for energy purposes. One of them is Euphorbia, a large genus of the Euphorbiaceae, a family of laticiferous herbs, shrubs and small trees, distributed in the tropical and warm temperature regions of the world. Many of the species are succulent and inhabit dry places. They resemble cacti in appearance but can be distinguished from them by the presence of a milky latex. About 2000 species have been reported throughout the world, chiefly in tropical regions [12–14]. It is known that 80 species of Euphorbia are found in Turkey. Some species of this family have been investigated and identified as promising candidates for renewable fuels and chemical feedstocks by some researchers. There have also been some studies performed to obtain a liquid product, which can replace petroleum, from Euphorbia rigida [15–18]. Many natural or synthetic catalysts are being used currently for various purposes. The use of a suitable catalyst is a necessary factor for production of high liquid product yield. Zeolites, especially the silica rich materials, often exhibit a high thermal and hydrothermal stability [19]. In addition, natural zeolite is cheap and abundant, especially in Turkey (45 billion ton) [20]. This natural mineral has catalytic properties as well as adsorption and ion exchange properties. Furthermore, the commercial catalysts Criterion-534 (Co–Mo) and activated alumina (Al2 O3 ) are widely used catalysts in the petrochemical industry. The work reported in this paper is the fixed bed slow pyrolysis of Euphorbia rigida with different catalysts in a Heinze reactor. First of all, the influence of catalyst percentages on the product yields was studied. Moreover, the effects of the catalysts on the liquid product were examined. With this aim, the pyrolysis oils obtained under the condition of maximum oil yield were investigated by using elemental analysis and IR spectroscopy. They were also fractionated by
F. Atesß et al. / Energy Conversion and Management 46 (2005) 421–432
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column chromatography, and gas chromatographic analysis was applied only on the n-pentane fractions. The obtained results were compared to the results of experiments without catalysts.
2. Experimental 2.1. Biomass The samples of Euphorbia rigida were collected from southwest Anatolia. Prior to the experiments, the sample was dried, ground in a high speed rotary cutting mill and then prepared to give fractions of 0.55 mm mean particle size. Table 1 shows the main characteristics of the biomass pyrolysed: its proximate and ultimate analysis (Carlo Erba, EA 1108). 2.2. Catalysts The natural zeolite that we used in the pyrolysis studies was obtained from Manisa-G€ ordes, Turkey, and the commercial catalysts were supplied by Turkish Petroleum Refinery Inc. Co. € (TUPRAS ß ). Some specific characteristics of the commercial catalysts are given in Table 2. They were activated and kept in a dessicator for the experiments. 2.3. Pyrolysis The pyrolysis experiments were performed using a fixed bed Heinze reactor [21]. The 316 stainless steel Heinze retort had a volume of 400 cm3 (70 mm ID) and was externally heated by an electrical furnace in which the temperature was measured by a thermocouple inside the bed. The connecting pipe between the reactor and the trapping system was heated to 400 C in order to avoid condensation of the tar vapour. Table 1 Proximate and ultimate analyses (wt%) of Euphorbia rigida (as received) % Proximate analysis Volatiles Fixed C Ash Moisture Raw cellulose
78.9 11.6 6.5 3.0 20.5
Ultimate analysis C H N Oa H/C O/C
49.1 5.7 1.2 44.0 1.43 0.67
a
By difference.
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Table 2 Specific characteristics of the commercial catalysts 2
Surface area (m /g) Pore volume (ml/g) Average bulk density (g/ml)
Criterion-534
Activated alumina
300 0.35 0.78
320 0.47 0.66
The performance of the catalysts was studied using the in-bed mode in a self pyrolysis atmosphere. The experiments were conducted to determine the effect of catalyst percentage on the pyrolysis yields. Ten g of sample, having average particle size of 0.55 mm, was mixed with different catalyst percentages (5%, 10%, 20% and 25% by weight) and then placed in the reactor. The experiments were conducted at a final pyrolysis temperature of 550 C with a heating rate of 7 C min1 [18]. The experimental apparatus was held at this temperature either a minimum of 30 min or until no further significant release of gas was observed. The flow of gas released was measured using a soap film for the duration of the experiments. The liquid products were collected in a glass liner located in a cold trap at about 0 C. The liquid product consisted of aqueous and oil phases, which were separated and weighed. After pyrolysis, the char yield was determined from the overall weight loss of the reactor. The liquid product was weighed in a dry ice cooled trap and recovered in dichloromethylene for analysis. The water content was determined by refluxing the toluene solution in a Dean-Stark apparatus. The oil products were then recovered from the toluene solutions, and the gas yield was determined by an overall material balance. All the yields were calculated on a dry ash free (daf) basis, and each experiment was performed three times for each experimental condition. The reproducibility of the experimental data was calculated to be within ±2%. 2.4. Characterization The oil products analysed were obtained under experimental conditions that gave maximum oil yield (pyrolysis temperature of 550 C, mean particle size of 0.55 mm, low heating rate of 7 C min1 , catalyst percentage of 20%). 2.4.1. Instrumental analysis of oils A CHNS-O Carlo Erba EA 1108 instrument was used to determine the elemental composition of the oils. 2.4.2. IR spectra An IR spectrometer was used to detect the infrared spectra. The IR spectra were made using a Mattson 1000 infrared spectrophotometer. Measurements were recorded on thin films between KBr plates. 2.4.3. Liquid column chromatography Liquid column chromatography was used to fractionate the pyrolysis oils into chemical class compositions. First, the pyrolysis oils were separated into two fractions as n-pentane soluble (deasphalted oil) and insoluble compounds (asphaltenes) by 50 ml n-pentane. Then, the n-pentane
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soluble materials were further separated on activated silica gel (70–230 mesh) preheated at 170 C for 6 h before packing a 0.2 · 0.025 m2 i.d. column. The column was eluted successively with npentane, toluene and methanol to produce aliphatic, aromatic and polar fractions, respectively. Each fraction was dried, weighed and then subjected to elemental and GC analyses. 2.4.4. Gas chromatography GC analysis with flame ionization detection (FID) was performed using a Hewlett-Packard 6890 model gas chromatograph with nitrogen as the carrier gas and a thin film (30 m · 0.25 mm i.d.; 0.25 lm film thickness), HP-5 capillary column supplied from Hewlett-Packard, USA.
3. Results and discussion 3.1. Product yields The dependence of the product yields of Euphorbia rigida, having an average particle size of 0.55 mm, pyrolysis temperature of 550 C, heating rate of 7 C min1 , on the catalyst percentage is shown in Figs. 1–3. It was established that the pyrolysis oil yield rises in conjunction with increasing catalyst percentage and reaches its maximum with using 20% by weight natural zeolite and Criterion-534 and 10% by weight activated alumina. The greatest increase in oil product yield was obtained by using the catalyst Criterion-534 (Fig. 2). The oil yield, which was 21.65% without catalyst, reached the maximum value of 30.98% by using this commercial catalyst at 20% by weight. This means an increase of 5%, when compared to utilization of the same catalyst at 5% by weight. While looking at the gaseous product yield, we see that the 33.82% gaseous product without catalyst reduces to 20.85% with use of this commercial catalyst. The tests results obtained with activated alumina (Fig. 3), another commercial catalyst, shows that the highest oil yield is 28.15%. An increase of 8.8% was achieved when compared to the usage of 5% by weight activated alumina. The gaseous product yield was reduced when compared to the non-catalyst test with this commercial catalyst also. It was reduced to 25.8% in tests conducted with 10% by weight, a decrease of 23.7% from tests performed with no catalyst. The change in catalyst percentage has a small but positive effect on the pyrolysis oil yield for both commercial catalysts. When we look at the results with natural catalysts, we see that the highest oil yield was 27.55% (Fig. 1). This means an increase of 27.3% when compared to the non-catalyst tests. The experiment with catalyst ratio of 5% gave an increase of only 8%, with the oil yield of 23.39%. A decrease in gaseous product yield was also observed with the natural catalyst, similar to that of the commercial catalysts, and for the value of 20% by weight that kept the oil yield at its optimum level, the gas yield was reduced to 26.97%. While examining the results from the point of view of water yield, it is clear that the pyrolysis oil contains higher amounts of water when a catalytic material is used in relation to self pyrolysis. The amount of oil is the only experimental response that is correlated with the effect of the catalyst in this study. The most important effect of the catalyst is the increase in the yields of oil
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35
30
Yield (%)
25 Char Oil Water Gas
20
15
10
5
0 Without catalyst
5
10
20
25
Catalyst percentage (% by weight of the biomass)
Char Oil Water Gas
Without catalyst 22.21 21.65 22.32 33.82
5%
10%
20%
25%
21.04 23.39 23.20 32.37
21.01 25.32 23.48 30.19
20.61 27.55 24.87 26.97
21.43 27.26 25.90 25.41
Fig. 1. The dependence of product yields of Euphorbia rigida on the natural zeolite percentages.
and decrease in the yields of gaseous products in the in-bed catalytic experiments, which is consistent with some published studies [22–25]. It is thought that the effect of the catalyst, under such conditions we have used, is not due to the cracking effect of the tar, it is indicated that the hydrocarbons with unstable structures react to give liquid products instead of forming C1–C4 hydrocarbons. 3.2. Chemical composition 3.2.1. Instrumental analysis The elemental compositions and the H/C and O/C molar ratios of the biomass and oils are listed in Tables 1 and 3, respectively. As can be seen, the oils contain less amounts of oxygen content with a higher H/C ratio than the original feedstock. Further comparison of the H/C ratio with conventional fuels indicates that the H/C ratios of the oils obtained in this study are very similar to those of light petroleum products (H/C ¼ 1.5–1.9). A comparison according to the percentages of C, H and O shows lower contents of C and H and higher contents of O in the oil of the catalytic procedures then that of non-catalytic procedures. This gives a clue that the catalytic liquid products have more polar structure.
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427
40
35
30
Yield (%)
25 Char Oil
20
Water Gas
15
10
5
0 Without 5 10 20 25 catalyst Catalyst percentage (% by weight of the biomass)
Char Oil Water Gas
Without catalyst 22.21 21.65 22.32 33.82
5%
10%
20%
25%
22.54 29.38 27.07 21.01
22.37 29.14 27.90 20.59
21.38 30.98 26.79 20.85
22.21 30.11 26.24 21.44
Fig. 2. The dependence of product yields of Euphorbia rigida on the Criterion-534 percentages.
In addition, the H/C ratios of the n-pentane subfractions obtained from natural zeolite (2.15), Criterion-534 (2.02) and activated alumina (2.13) can be compared with those of petroleum products. These values are also very close to those of petroleum [26]. 3.2.2. Liquid column chromatography All of the oils were separated into two fractions as n-pentane soluble (deasphalted oil) and insoluble (asphaltenes). The n-pentane soluble materials were further separated by adsorption chromatography. Overall results and yields are presented in Fig. 4. As can be seen, while the fractions that are n-pentane soluble do not show significant differences from the fractions obtained without using catalysts, the aliphatic fractions are reduced significantly with all three catalysts. In other words, the aliphatic fractions reduced to 22.6%, 25% and 23.8% when using natural zeolite, Criterion-534 and activated alumina, respectively. The aromatic fractions show less prominent changes when compared to the aliphatic fractions. The 30% yield in non-catalyst conditions has reduced to 25% and 28.7% with natural zeolite and Criterion-534 and increased to 31.8% with activated alumina, respectively.
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35
30
Yield (%)
25 Char Oil
20
Water Gas
15
10
5
0 Without catalyst
5
10
20
25
Catalyst percentage (% by weight of the biomass)
Char Oil Water Gas
Without catalyst 22.21 21.65 22.32 33.82
5%
10%
20%
25%
21.16 25.88 28.72 24.24
19.90 28.15 26.15 25.80
19.35 27.66 26.52 26.47
18.95 27.28 27.17 26.60
Fig. 3. The dependence of product yields of Euphorbia rigida on the activated alumina percentages. Table 3 Elemental composition of the oils Component
Without catalysta
Natural zeoliteb
Criterion-534b
Activated aluminac
C H N O H/C O/C
75.07 9.27 2.21 13.24 1.482 0.132
65.39 8.33 2.15 24.13 1.529 0.276
66.24 8.95 2.10 22.71 1.621 0.257
66.42 8.23 2.14 23.21 1.487 0.262
a
550 C, 7 C min1 . 550 C, 7 C min1 , 20% of biomass. c 550 C, 7 C min1 , 10% of biomass. b
Polar fractions, however, have shown significant increases with all three catalysts. The yield that was 37% without catalyst was increased to 46.3% and 44.4% with Criterion-534 and activated alumina, respectively, and this increase reached 52.2% with natural zeolite.
F. Atesß et al. / Energy Conversion and Management 46 (2005) 421–432
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70
60
50
Yield (%)
40
30
20
10
0 Without catalyst
Natural zeolite
Deasphalted oil
Deasphalted oil Asphaltenes Aliphatics Aromatics Polars
Without catalyst 63 37 33 30 37
Asphaltenes
Criterion-534 Aliphatics
Activated alumina
Aromatics
Natural zeolite
Criterion-534
64 36 22.64 25.12 52.24
65 35 25 28.66 46.34
Polars Activated alumina 63 37 23.78 31.82 44.40
Fig. 4. The results of liquid column chromatography.
So, in this point, while the catalyst does not give a significant change in the fraction that is deasphalted oil, when this oil is separated into hydrocarbons and polars, the polars are shown to dominate. This is consistent with the results of the elemental analysis. 3.2.3. IR spectra The IR spectra obtained for the oil samples were very similar. The O–H streching vibrations between 3200 and 3400 cm1 of the oil indicated the presence of phenols and alcohols. The C–H streching vibrations between 2800 and 3000 cm1 and C–H deformation vibrations between 1350 and 1450 cm1 indicated the presence of alkanes. The presence of the peaks between 1650 and 1750 cm1 is ascribable to C@O streching vibrations, and it showed the presence of ketones or aldehydes. The absorbance peaks between 1575 and 1675 cm1 represent C@C streching vibrations indicative of alkenes and aromatics.
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Fig. 5. Gas chromatogram of the n-pentane fraction of the oil with natural zeolite.
Fig. 6. Gas chromatogram of the n-pentane fraction of the oil with Criterion-534.
3.2.4. GC results Gas chromatograms of the n-pentane subfractions of the oils are shown in Figs. 5–7. The hydrocarbons were identified by gas chromatography using external standards. The n-pentane subfractions consist of normal alkanes, alkenes and branched hydrocarbons for all of the catalysts. While the lengths of linear chain alkanes range between C10 –C27 for natural zeolite, the range is C12 –C24 activated alumina for C12 –C26 for Criterion. However, C12 represents the greatest quantity of n-alkanes with the commercial catalysts, while C10 and C14 represent the greatest
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Fig. 7. Gas chromatogram of the n-pentane fraction of the oil with activated alumina.
quantity of n-alkanes with the natural catalyst. This suggests that the oils produced with natural zeolite have a large fraction of lighter hydrocarbons. Furthermore, the chromatograms show the oil consists of pikes of alkenes and branched hydrocarbons for the commercial catalysts, while the oil with natural zeolite largely consists of alkanes.
4. Conclusion Use of catalysts in biomass pyrolysis often resulted in the reduction of liquid product yield and increase of gas yield unless the operation mode changed from ex-bed to in-bed, as in this study. The relatively low pyrolysis oil yield of Euphorbia rigida was increased by adding different catalysts to the biomass for the in-bed mode. All catalysts led to a rise in oil yields and a decrease in gas yields. The highest oil yield was obtained with Criterion-534, and 20% by weight of Criterion-534 commercial catalyst to biomass is recommended for future application, mainly because the higher activity of Criterion-534 led to the highest oil yield. As having similar structural properties, both activated alumina and natural zeolite exhibit similar trends for obtaining liquid products. In addition to these results, the polar fractions dominate the oil even more than for the uncatalysed experiments.
Acknowledgements The authors would like to thank the Anadolu University Research Foundation (Project No. 990226) for financial support.
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References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]
Bridgwater AV, Meier D, Radlein D. Org Geochem 1999;30:1479. McKendry P. Bioresour Technol 2002;83:47. Arvelakis S, Koukios EG. Biomass Bioenergy 2002;22:331. Encinar JM, Gonzalez JF, Gonzalez J. Fuel Process Technol 2000;68:209. Horne AP, Williams Pt. Fuel 1996;75(9):1051. Biagini E, Lippi F, Petarca L, Tognotti L. Fuel 2002;81:1041. Bridgwater AV, Peacocke GVC. Renewable Sustainable Energy Rev 2000;4:1. C ß aglar A, Demirbasß A. Energy Convers Manage 2000;41:1749. Raveendran K, Ganesh A, Khilar KC. Fuel 1995;74:1812. Ganesh A, Banerjee R. Renewable Energy 2001;22:9. Meier D, Faix O. Bioresour Technol 1999;68:71. Bhatia KV, Krishan GM, Ragunath PM, Mamta M. Fuel 1989;68:475. Kingsolver BE. Biomass 1982;2:282. Calvin M. Bot J Linnean Soc 1987;94:97. € P€ ut€ un AE, Ozcan A, Gercßel HF, P€ ut€ un E. Fuel 2001;80:1371. Gercßel F, C ut€ un E, Ekinci E. Fuel Process Technol 1993;36:299. ß ıtroglu M, Snape CE, P€ € Besßler S, Kocßkar OM, Gercßel HF, P€ ut€ un E, P€ ut€ un AE. Do ga 1992;16:216. € P€ ut€ un AE, Gercßel HF, Kocßkar OM, Ege O, Snape C, P€ ut€ un E. Fuel 1996;75:1307. Maxwell IE, Stark WHJ. In: Van Bekkum A, Flanigen EM, Jansen JC, editors. Hydrocarbon processing with zeolites, vol. 58. 1991. p. 571. Atesß F, P€ ut€ un AE, P€ ut€ un E, IV National Chemical Engineering Congress 2000;1:275. Heinze R. Oel u Kohle 1943;39:973. Leung DYC, Yin XL, Zhao ZL, Xu BY, Chen Y. Fuel Process Technol 2002;79:141. Samolada MC, Papafotica A, Vasalos IA. Energy & Fuels 2000;14:1161. Borgund AE, Barth T. Org Geochem 1999;30:1517. Pinto F, Gulyurtlu I, Lobo LS, Cabrita I. Fuel 1999:761. Probstein RF, Hicks RE. Synthetic fuels. New York: McGraw-Hill; 1982. p. 284.
Fixed bed pyrolysis of Euphorbia rigida with different catalysts Funda Atesß a, Aysße E. P€ ut€ un a, Ersan P€ ut€ un
b,*
a
b
Department of Chemical Engineering, Faculty of Engineering and Architecture, Iki Eylul Campus, Anadolu University, Eskisehir 26470, Turkey Department of Material Science and Engineering, Faculty of Engineering and Architecture, Iki Eylul Campus, Anadolu University, Eskisehir 26470, Turkey Received 7 July 2003; received in revised form 31 December 2003; accepted 21 March 2004 Available online 25 May 2004
Abstract Since Euphorbia rigida is a celluloid plant with low fat content, the oil yields of previous fixed bed pyrolysis studies were low. In order to increase the oil yield, biomass pyrolysis experiments were performed in a fixed bed reactor with two selected commercial catalysts, namely Criterion-534 and activated alumina, and natural zeolite (klinoptilolite). Experiments were conducted in a static atmosphere with a heating rate of 7 C min1 , pyrolysis temperature of 550 C and mean particle size of 0.55 mm. In the experiments, all the catalysts were used with various percentages, and the effects of the variable catalysts on the yields and chemical composition of the oils obtained were investigated. Oil yield reached 27.5% with the use of natural zeolite, 31% with Criterion-534 and 28.1% with activated alumina, while it was only 21.6% without a catalyst. The pyrolysis oils were examined by using spectroscopic and chromatographic analysis techniques, and the obtained results were compared with the results of similar experiments achieved without a catalyst. 2004 Elsevier Ltd. All rights reserved. Keywords: Biomass; Euphorbia rigida; Catalyst; Pyrolysis; Oil
1. Introduction Worldwide concern about the diminishing trend of primary energy sources and environmental problems have prompted many observers to call for a decreased reliance on fossil fuels.
* Corresponding author. Present address: Department of Chemical Engineering, Faculty of Engineering, Yunusemre Campus, Anadolu University, Eskisehir 26470, Turkey. Tel.: +90-222-335-0580/6301, +90-222-322-3662; fax: +90-222323-9501. E-mail address: [email protected] (E. P€ ut€ un).
0196-8904/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2004.03.011
422
F. Atesß et al. / Energy Conversion and Management 46 (2005) 421–432
Renewable sources of energy are constantly examined as alternatives for fossil fuels. Renewable energy is of growing importance in satisfying environmental concerns over fossil fuel usage and its contribution to the greenhouse effect. Biomass forms are some of the main renewable energy resources available [1]. Biomass has received considerable attention both as a source of energy and as an organic chemical feedstock [2,3]. The energy potential of biomass has increasingly become recognized as a means to help meet world energy demand. The utilization of biomass and other alternative fuel sources, rather than existing fossil fuels, would offer more environmentally acceptable processes for energy production and will aid in conserving the limited supplies of fossil fuels [4–6]. Virtually all biomass products can be converted into commercial fuels, suitable to substitute for fossil fuels. These can be used for transportation, heating, electricity generation or anything else where fossil fuels are used. The conversion is accomplished through the use of several distinct processes. These processes include both biochemical and thermal conversions to produce gaseous, liquid and solid fuels that have high energy contents, are easily transportable and are, therefore, suitable for use as commercial fuels [1,7]. Thermochemical processes are thought to have great promise as a means for efficiently and economically converting biomass to synthetic fuels [8]. In the thermochemical processes, pyrolysis has received increased interest, since the process can be performed under a variety of conditions to capture all the components and to maximize the output of the desired product, be it char, liquid or gas [5,9]. During pyrolysis, the biomass is heated in the absence of air and breaks down into a complex mixture of liquids, gases and a residual char [10,11]. There are a number of biomass sources, such as forest residues, low grade plants, agricultural residues and municipal solid wastes, which can be utilized for energy purposes. One of them is Euphorbia, a large genus of the Euphorbiaceae, a family of laticiferous herbs, shrubs and small trees, distributed in the tropical and warm temperature regions of the world. Many of the species are succulent and inhabit dry places. They resemble cacti in appearance but can be distinguished from them by the presence of a milky latex. About 2000 species have been reported throughout the world, chiefly in tropical regions [12–14]. It is known that 80 species of Euphorbia are found in Turkey. Some species of this family have been investigated and identified as promising candidates for renewable fuels and chemical feedstocks by some researchers. There have also been some studies performed to obtain a liquid product, which can replace petroleum, from Euphorbia rigida [15–18]. Many natural or synthetic catalysts are being used currently for various purposes. The use of a suitable catalyst is a necessary factor for production of high liquid product yield. Zeolites, especially the silica rich materials, often exhibit a high thermal and hydrothermal stability [19]. In addition, natural zeolite is cheap and abundant, especially in Turkey (45 billion ton) [20]. This natural mineral has catalytic properties as well as adsorption and ion exchange properties. Furthermore, the commercial catalysts Criterion-534 (Co–Mo) and activated alumina (Al2 O3 ) are widely used catalysts in the petrochemical industry. The work reported in this paper is the fixed bed slow pyrolysis of Euphorbia rigida with different catalysts in a Heinze reactor. First of all, the influence of catalyst percentages on the product yields was studied. Moreover, the effects of the catalysts on the liquid product were examined. With this aim, the pyrolysis oils obtained under the condition of maximum oil yield were investigated by using elemental analysis and IR spectroscopy. They were also fractionated by
F. Atesß et al. / Energy Conversion and Management 46 (2005) 421–432
423
column chromatography, and gas chromatographic analysis was applied only on the n-pentane fractions. The obtained results were compared to the results of experiments without catalysts.
2. Experimental 2.1. Biomass The samples of Euphorbia rigida were collected from southwest Anatolia. Prior to the experiments, the sample was dried, ground in a high speed rotary cutting mill and then prepared to give fractions of 0.55 mm mean particle size. Table 1 shows the main characteristics of the biomass pyrolysed: its proximate and ultimate analysis (Carlo Erba, EA 1108). 2.2. Catalysts The natural zeolite that we used in the pyrolysis studies was obtained from Manisa-G€ ordes, Turkey, and the commercial catalysts were supplied by Turkish Petroleum Refinery Inc. Co. € (TUPRAS ß ). Some specific characteristics of the commercial catalysts are given in Table 2. They were activated and kept in a dessicator for the experiments. 2.3. Pyrolysis The pyrolysis experiments were performed using a fixed bed Heinze reactor [21]. The 316 stainless steel Heinze retort had a volume of 400 cm3 (70 mm ID) and was externally heated by an electrical furnace in which the temperature was measured by a thermocouple inside the bed. The connecting pipe between the reactor and the trapping system was heated to 400 C in order to avoid condensation of the tar vapour. Table 1 Proximate and ultimate analyses (wt%) of Euphorbia rigida (as received) % Proximate analysis Volatiles Fixed C Ash Moisture Raw cellulose
78.9 11.6 6.5 3.0 20.5
Ultimate analysis C H N Oa H/C O/C
49.1 5.7 1.2 44.0 1.43 0.67
a
By difference.
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F. Atesß et al. / Energy Conversion and Management 46 (2005) 421–432
Table 2 Specific characteristics of the commercial catalysts 2
Surface area (m /g) Pore volume (ml/g) Average bulk density (g/ml)
Criterion-534
Activated alumina
300 0.35 0.78
320 0.47 0.66
The performance of the catalysts was studied using the in-bed mode in a self pyrolysis atmosphere. The experiments were conducted to determine the effect of catalyst percentage on the pyrolysis yields. Ten g of sample, having average particle size of 0.55 mm, was mixed with different catalyst percentages (5%, 10%, 20% and 25% by weight) and then placed in the reactor. The experiments were conducted at a final pyrolysis temperature of 550 C with a heating rate of 7 C min1 [18]. The experimental apparatus was held at this temperature either a minimum of 30 min or until no further significant release of gas was observed. The flow of gas released was measured using a soap film for the duration of the experiments. The liquid products were collected in a glass liner located in a cold trap at about 0 C. The liquid product consisted of aqueous and oil phases, which were separated and weighed. After pyrolysis, the char yield was determined from the overall weight loss of the reactor. The liquid product was weighed in a dry ice cooled trap and recovered in dichloromethylene for analysis. The water content was determined by refluxing the toluene solution in a Dean-Stark apparatus. The oil products were then recovered from the toluene solutions, and the gas yield was determined by an overall material balance. All the yields were calculated on a dry ash free (daf) basis, and each experiment was performed three times for each experimental condition. The reproducibility of the experimental data was calculated to be within ±2%. 2.4. Characterization The oil products analysed were obtained under experimental conditions that gave maximum oil yield (pyrolysis temperature of 550 C, mean particle size of 0.55 mm, low heating rate of 7 C min1 , catalyst percentage of 20%). 2.4.1. Instrumental analysis of oils A CHNS-O Carlo Erba EA 1108 instrument was used to determine the elemental composition of the oils. 2.4.2. IR spectra An IR spectrometer was used to detect the infrared spectra. The IR spectra were made using a Mattson 1000 infrared spectrophotometer. Measurements were recorded on thin films between KBr plates. 2.4.3. Liquid column chromatography Liquid column chromatography was used to fractionate the pyrolysis oils into chemical class compositions. First, the pyrolysis oils were separated into two fractions as n-pentane soluble (deasphalted oil) and insoluble compounds (asphaltenes) by 50 ml n-pentane. Then, the n-pentane
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soluble materials were further separated on activated silica gel (70–230 mesh) preheated at 170 C for 6 h before packing a 0.2 · 0.025 m2 i.d. column. The column was eluted successively with npentane, toluene and methanol to produce aliphatic, aromatic and polar fractions, respectively. Each fraction was dried, weighed and then subjected to elemental and GC analyses. 2.4.4. Gas chromatography GC analysis with flame ionization detection (FID) was performed using a Hewlett-Packard 6890 model gas chromatograph with nitrogen as the carrier gas and a thin film (30 m · 0.25 mm i.d.; 0.25 lm film thickness), HP-5 capillary column supplied from Hewlett-Packard, USA.
3. Results and discussion 3.1. Product yields The dependence of the product yields of Euphorbia rigida, having an average particle size of 0.55 mm, pyrolysis temperature of 550 C, heating rate of 7 C min1 , on the catalyst percentage is shown in Figs. 1–3. It was established that the pyrolysis oil yield rises in conjunction with increasing catalyst percentage and reaches its maximum with using 20% by weight natural zeolite and Criterion-534 and 10% by weight activated alumina. The greatest increase in oil product yield was obtained by using the catalyst Criterion-534 (Fig. 2). The oil yield, which was 21.65% without catalyst, reached the maximum value of 30.98% by using this commercial catalyst at 20% by weight. This means an increase of 5%, when compared to utilization of the same catalyst at 5% by weight. While looking at the gaseous product yield, we see that the 33.82% gaseous product without catalyst reduces to 20.85% with use of this commercial catalyst. The tests results obtained with activated alumina (Fig. 3), another commercial catalyst, shows that the highest oil yield is 28.15%. An increase of 8.8% was achieved when compared to the usage of 5% by weight activated alumina. The gaseous product yield was reduced when compared to the non-catalyst test with this commercial catalyst also. It was reduced to 25.8% in tests conducted with 10% by weight, a decrease of 23.7% from tests performed with no catalyst. The change in catalyst percentage has a small but positive effect on the pyrolysis oil yield for both commercial catalysts. When we look at the results with natural catalysts, we see that the highest oil yield was 27.55% (Fig. 1). This means an increase of 27.3% when compared to the non-catalyst tests. The experiment with catalyst ratio of 5% gave an increase of only 8%, with the oil yield of 23.39%. A decrease in gaseous product yield was also observed with the natural catalyst, similar to that of the commercial catalysts, and for the value of 20% by weight that kept the oil yield at its optimum level, the gas yield was reduced to 26.97%. While examining the results from the point of view of water yield, it is clear that the pyrolysis oil contains higher amounts of water when a catalytic material is used in relation to self pyrolysis. The amount of oil is the only experimental response that is correlated with the effect of the catalyst in this study. The most important effect of the catalyst is the increase in the yields of oil
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35
30
Yield (%)
25 Char Oil Water Gas
20
15
10
5
0 Without catalyst
5
10
20
25
Catalyst percentage (% by weight of the biomass)
Char Oil Water Gas
Without catalyst 22.21 21.65 22.32 33.82
5%
10%
20%
25%
21.04 23.39 23.20 32.37
21.01 25.32 23.48 30.19
20.61 27.55 24.87 26.97
21.43 27.26 25.90 25.41
Fig. 1. The dependence of product yields of Euphorbia rigida on the natural zeolite percentages.
and decrease in the yields of gaseous products in the in-bed catalytic experiments, which is consistent with some published studies [22–25]. It is thought that the effect of the catalyst, under such conditions we have used, is not due to the cracking effect of the tar, it is indicated that the hydrocarbons with unstable structures react to give liquid products instead of forming C1–C4 hydrocarbons. 3.2. Chemical composition 3.2.1. Instrumental analysis The elemental compositions and the H/C and O/C molar ratios of the biomass and oils are listed in Tables 1 and 3, respectively. As can be seen, the oils contain less amounts of oxygen content with a higher H/C ratio than the original feedstock. Further comparison of the H/C ratio with conventional fuels indicates that the H/C ratios of the oils obtained in this study are very similar to those of light petroleum products (H/C ¼ 1.5–1.9). A comparison according to the percentages of C, H and O shows lower contents of C and H and higher contents of O in the oil of the catalytic procedures then that of non-catalytic procedures. This gives a clue that the catalytic liquid products have more polar structure.
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40
35
30
Yield (%)
25 Char Oil
20
Water Gas
15
10
5
0 Without 5 10 20 25 catalyst Catalyst percentage (% by weight of the biomass)
Char Oil Water Gas
Without catalyst 22.21 21.65 22.32 33.82
5%
10%
20%
25%
22.54 29.38 27.07 21.01
22.37 29.14 27.90 20.59
21.38 30.98 26.79 20.85
22.21 30.11 26.24 21.44
Fig. 2. The dependence of product yields of Euphorbia rigida on the Criterion-534 percentages.
In addition, the H/C ratios of the n-pentane subfractions obtained from natural zeolite (2.15), Criterion-534 (2.02) and activated alumina (2.13) can be compared with those of petroleum products. These values are also very close to those of petroleum [26]. 3.2.2. Liquid column chromatography All of the oils were separated into two fractions as n-pentane soluble (deasphalted oil) and insoluble (asphaltenes). The n-pentane soluble materials were further separated by adsorption chromatography. Overall results and yields are presented in Fig. 4. As can be seen, while the fractions that are n-pentane soluble do not show significant differences from the fractions obtained without using catalysts, the aliphatic fractions are reduced significantly with all three catalysts. In other words, the aliphatic fractions reduced to 22.6%, 25% and 23.8% when using natural zeolite, Criterion-534 and activated alumina, respectively. The aromatic fractions show less prominent changes when compared to the aliphatic fractions. The 30% yield in non-catalyst conditions has reduced to 25% and 28.7% with natural zeolite and Criterion-534 and increased to 31.8% with activated alumina, respectively.
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35
30
Yield (%)
25 Char Oil
20
Water Gas
15
10
5
0 Without catalyst
5
10
20
25
Catalyst percentage (% by weight of the biomass)
Char Oil Water Gas
Without catalyst 22.21 21.65 22.32 33.82
5%
10%
20%
25%
21.16 25.88 28.72 24.24
19.90 28.15 26.15 25.80
19.35 27.66 26.52 26.47
18.95 27.28 27.17 26.60
Fig. 3. The dependence of product yields of Euphorbia rigida on the activated alumina percentages. Table 3 Elemental composition of the oils Component
Without catalysta
Natural zeoliteb
Criterion-534b
Activated aluminac
C H N O H/C O/C
75.07 9.27 2.21 13.24 1.482 0.132
65.39 8.33 2.15 24.13 1.529 0.276
66.24 8.95 2.10 22.71 1.621 0.257
66.42 8.23 2.14 23.21 1.487 0.262
a
550 C, 7 C min1 . 550 C, 7 C min1 , 20% of biomass. c 550 C, 7 C min1 , 10% of biomass. b
Polar fractions, however, have shown significant increases with all three catalysts. The yield that was 37% without catalyst was increased to 46.3% and 44.4% with Criterion-534 and activated alumina, respectively, and this increase reached 52.2% with natural zeolite.
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70
60
50
Yield (%)
40
30
20
10
0 Without catalyst
Natural zeolite
Deasphalted oil
Deasphalted oil Asphaltenes Aliphatics Aromatics Polars
Without catalyst 63 37 33 30 37
Asphaltenes
Criterion-534 Aliphatics
Activated alumina
Aromatics
Natural zeolite
Criterion-534
64 36 22.64 25.12 52.24
65 35 25 28.66 46.34
Polars Activated alumina 63 37 23.78 31.82 44.40
Fig. 4. The results of liquid column chromatography.
So, in this point, while the catalyst does not give a significant change in the fraction that is deasphalted oil, when this oil is separated into hydrocarbons and polars, the polars are shown to dominate. This is consistent with the results of the elemental analysis. 3.2.3. IR spectra The IR spectra obtained for the oil samples were very similar. The O–H streching vibrations between 3200 and 3400 cm1 of the oil indicated the presence of phenols and alcohols. The C–H streching vibrations between 2800 and 3000 cm1 and C–H deformation vibrations between 1350 and 1450 cm1 indicated the presence of alkanes. The presence of the peaks between 1650 and 1750 cm1 is ascribable to C@O streching vibrations, and it showed the presence of ketones or aldehydes. The absorbance peaks between 1575 and 1675 cm1 represent C@C streching vibrations indicative of alkenes and aromatics.
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Fig. 5. Gas chromatogram of the n-pentane fraction of the oil with natural zeolite.
Fig. 6. Gas chromatogram of the n-pentane fraction of the oil with Criterion-534.
3.2.4. GC results Gas chromatograms of the n-pentane subfractions of the oils are shown in Figs. 5–7. The hydrocarbons were identified by gas chromatography using external standards. The n-pentane subfractions consist of normal alkanes, alkenes and branched hydrocarbons for all of the catalysts. While the lengths of linear chain alkanes range between C10 –C27 for natural zeolite, the range is C12 –C24 activated alumina for C12 –C26 for Criterion. However, C12 represents the greatest quantity of n-alkanes with the commercial catalysts, while C10 and C14 represent the greatest
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Fig. 7. Gas chromatogram of the n-pentane fraction of the oil with activated alumina.
quantity of n-alkanes with the natural catalyst. This suggests that the oils produced with natural zeolite have a large fraction of lighter hydrocarbons. Furthermore, the chromatograms show the oil consists of pikes of alkenes and branched hydrocarbons for the commercial catalysts, while the oil with natural zeolite largely consists of alkanes.
4. Conclusion Use of catalysts in biomass pyrolysis often resulted in the reduction of liquid product yield and increase of gas yield unless the operation mode changed from ex-bed to in-bed, as in this study. The relatively low pyrolysis oil yield of Euphorbia rigida was increased by adding different catalysts to the biomass for the in-bed mode. All catalysts led to a rise in oil yields and a decrease in gas yields. The highest oil yield was obtained with Criterion-534, and 20% by weight of Criterion-534 commercial catalyst to biomass is recommended for future application, mainly because the higher activity of Criterion-534 led to the highest oil yield. As having similar structural properties, both activated alumina and natural zeolite exhibit similar trends for obtaining liquid products. In addition to these results, the polar fractions dominate the oil even more than for the uncatalysed experiments.
Acknowledgements The authors would like to thank the Anadolu University Research Foundation (Project No. 990226) for financial support.
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