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Pyrolysis of metal impregnated biomass: An innovative catalytic way to produce gas fuel
J. Anal. Appl. Pyrolysis 78 (2007) 291–300 www.elsevier.com/locate/jaap
Pyrolysis of metal impregnated biomass: An innovative catalytic way to produce gas fuel K. Bru a, J. Blin a,*, A. Julbe b, G. Volle a b
a CIRAD-Foreˆt, UPR 42 Biomasse Energie, TA 10/16, 73, Avenue J.-F. Breton, 34398 Montpellier Cedex 5, France Institut Europe´en des Membranes (UMR 5635 CNRS), UMII, CC47, Place E. Bataillon, 34095 Montpellier Cedex 5, France
Received 22 February 2006; accepted 17 August 2006 Available online 25 September 2006
Abstract An innovative way of catalysis was investigated for its potential to reduce the amount of condensable hydrocarbons produced during the pyrolysis of oak wood. The experiments were carried out in a horizontal tubular reactor, fed with a controlled flow rate of nitrogen and equipped with accessories to collect char, liquid and gaseous products. Pyrolysis was performed at 700 8C with different wood sample series impregnated with either Ni or Fe nitrates (in aqueous solution) and by varying the metal concentration in the wood. In the blank run the biomass was acid-washed to determine the impact of demineralization. The influence of the metal type and content introduced into the wood to reduce the fraction of condensable organic compounds produced during pyrolysis was determined. Depending on the experimental conditions, the gas yield increases from 20.0 to 33.1%. Condensable hydrocarbons are cracked into gaseous components and the concentration of H2 is significantly increased, by 260% compared to the reference sample. In particular, the Ni-loaded wood samples give much higher H2 yields than the Fe-loaded ones under similar conditions but less toxic products are formed with the latter. These results show that biomass impregnation with either nickel or iron salts is a promising way to reduce the fraction of condensable organic compounds produced during pyrolysis. # 2006 Elsevier B.V. All rights reserved. Keywords: Biomass pyrolysis; Catalytic conversion; Hydrogen
1. Introduction Biomass is a renewable energy that has social, political and economic advantages. Indeed, thermochemical conversion of it for the production of fuels, chemicals and combined heat and power could revitalize rural economies, limit the dependence on foreign oil imports, and improve the environment by reducing fossil fuel consumption and thus reducing greenhouse gases [1–4]. Biomass gasification is a developing technology that can be used to generate heat and electricity in an Integrated Gasification Combined Cycle [5–9]. Conditioning and upgrading the produced gas can also make it a suitable feed for methanol or Fischer-Tropsch liquid synthesis [10–14]. Additional conditioning can produce a hydrogen-rich gas that is
* Corresponding author. Tel.: +33 4 67 61 65 21; fax: +33 4 67 61 65 15. E-mail address: [email protected] (J. Blin). 0165-2370/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jaap.2006.08.006
suitable for transportation, chemical production, or electricity generation in fuel cells [15–19]. The main problem to deal with in biomass gasification is the formation of tars, which make the gas unsuitable for further applications [20]. Tar is a complex mixture of condensable hydrocarbons, which includes single ring to 5-ring aromatic compounds along with other oxygen-containing hydrocarbons and complex polycyclic aromatic hydrocarbons (PAH) [17,20,21]. They are initially produced during pyrolysis; the first step of any thermochemical conversion processes. Tars cause severe operational problems, such as blockages and corrosion [22] due to their condensation, deactivate the catalysts used for upgrading the gas [4] and may constitute a potential health and environmental hazard, as some of the tar components may be carcinogenic or mutagenic [3,23–25]. Consequently, one of the main concerns in such a process is to eliminate or reduce the tar products. The classical gas cleaning technology based on scrubbing is not acceptable because of the poor efficiency of tar removal,
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wastewater production, and energy loss during gas cooling which reduces the overall process efficiency. Partial oxidation does not provide sufficient cleaning efficiency and moreover decreases the gas heating value. Catalytic high temperature cleaning provides sufficient efficiency for tar removal and does not decrease the heating value of the produced gas [1,4,17,22,26,27]. Most of the research works on biomass gasification concern two types of catalysis:
The objective of this study is to investigate the influence of nickel and iron on reducing the condensable hydrocarbons produced during the pyrolysis of oak wood. These metals are inserted into the wood matrix by wet impregnation in a nitrate aqueous solution. The catalytic pyrolysis product yields are compared with the uncatalyzed products. The influence of the metal concentration is also examined. Then, gases and liquids are analyzed to better highlight the role of the metal species.
mixing the catalyst with the biomass to reduce the tar content in the gasification bed, using the catalyst in a specific hot gas cleaning reactor (posttreatment).
2. Experimental
In both cases, the catalyst efficiency is high when it is first used but its lifetime is limited because of carbon deposition, particle agglomeration and mechanical strength decrease involving catalyst deactivation [17,22]. An attractive option is then to insert the catalyst inside the wood matrix by impregnation before thermochemical conversion. Using this method, the catalytic material is highly dispersed in the biomass and freshly renewed when it is introduced into the reactor. The majority of the work on catalytic pyrolysis in relation to biomass pyrolysis gas has been done with a secondary reactor and there are few data on the influence of catalyst impregnation on the yield and composition of pyrolysis products. The last few research studies on catalyst impregnation in wood for biomass pyrolysis or gasification were mainly centered on relating the effectiveness of alkali and alkaline earth metallic species. These catalysts have been reported to be very active in tar removal [28–30], as the conversion of condensable hydrocarbons leads to an increase in gas yield [31]. Examples of inorganic ions that have been added to biomass are Na+, Li+, K+ and Ca2+ [31– 33]. However, these species volatilize at low temperatures, causing significant problems in terms of fouling, erosion and corrosion of the plant components [34–38]. No information exists on the biomass impregnation of catalytically active species classically used in a secondary reactor. Among them, catalysts with either nickel or iron are those of greatest interest. Indeed, extensive studies reported in the literature show that Ni-based catalysts are highly effective in removing hydrocarbons and in adjusting the gas composition to syngas quality [39–46]. Moreover, it has also been demonstrated that iron is efficient in reducing hydrocarbon formation, since natural iron containing minerals, such as dolomite (Ca(Mgx,Fey)(CO3)2) [10,47-49] or olivine ((Mgx,Fey)2SiO4), [20,50,51] are known to promote tar cracking and reforming. Several studies have also reported that iron(III) is responsible for the tar cracking reactions [52– 54]. In particular, Devi et al. [55] showed that olivine calcination with air at a high temperature changes the oxidation state of iron, the best olivine activity being obtained with iron(III). The influence of metallic iron or iron oxides on hydrocarbon decomposition has also been studied recently [56– 59]. It was reported that iron particles increase the cracking of phenolic and aromatic compounds, leading to the formation of carbon dioxide and water [59–61].
2.1. Laboratory scale pyrolysis plant All reactions are carried out under atmospheric pressure and inert conditions in a tubular heated reactor. The experimental set-up, shown in Fig. 1, consists of a 50 mm wide, 600 mm long cylindrical stainless steel reactor. It is equipped with a feeding chamber and adapted devices to quench liquid and collect gas samples. During experiments, the reactor is continuously flushed with pre-heated nitrogen (18.3 103 N m3/h at 400 8C) to remove air from the reactor and all the gases produced during pyrolysis. The feeding chamber is cooled with water in a double envelope to keep the sample at room temperature before introducing it into the hot zone. Approximately 10 g of wood is loaded into a stainless steel holder (called a ‘‘boat’’) driven by a sliding handle. This boat is placed in the cooled zone during the thermal stabilization of the reactor and is rapidly introduced into the reactor hot zone to start the pyrolysis. The sample is then promptly heated from room temperature to reactor temperature. Vapors formed during the pyrolysis are instantaneously diluted with the carrier gas. At the reactor outlet, a quench system is used to recover liquids. It consists of a cool water heat exchanger connected to a flask cooled in a liquid nitrogen ethylic alcohol bath at around 50 8C, prior an electrostatic precipitator. In order to avoid hydrocarbon condensation before this system has been reached, the reactor exit is equipped with a resistive heater. The noncondensable gas flow is then measured using a precise volumetric flow meter and is collected in a sampling bag. The run duration is 20 min. The heating is then switched off and the boat is returned to the cooled zone. Once room temperature is reached in the boat, the remaining char in it is weighted. The total amount of produced liquid is collected by washing the coil cooler and the electrostatic precipitator with isopropyl alcohol: the total liquid mass can then be weighted. For each set of parameters, two runs were carried out under identical conditions to check the repeatability of the process. 2.2. Wood preparation and impregnation The selected biomass was oak sawdust of a size range varying from 0.4 to 1.6 mm. The metallic salts used for the wood impregnation were nitrates as they do not contain carbon atoms, which may have altered the obtained results. The salts used were [Fe(NO3)39H2O] provided by Fluka (purity: 98%) and
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Fig. 1. Diagram of the pyrolysis reactor.
[Ni(NO3)26H2O] provided by Sigma–Aldrich (purity: 99%), respectively. The air-dried wood particles (105 8C, 5 days) were impregnated by mixing 22 g of wood with 250 ml of a Ni(NO3)2 or Fe(NO3)3 aqueous solution at concentrations of 0.17, 0.35 and 0.52 mol/l. The obtained mixtures were stirred at ambient temperature for 3 days. The wood particles were then filtered and dried again at 105 8C for 5 days. The wet impregnation of the wood particles washes the samples. This means they lose some of their minerals [62]. Moreover, nickel and iron nitrate solutions are acidic [63] and this acidity intensifies this phenomenon. In order to evaluate the influence of this acid treatment on the pyrolysis product distribution and on their composition, the wet impregnation method was also applied to wood particles impregnated with a nitric acid aqueous solution at pH 2.8 (reference sample). 2.3. Gas analysis The whole gaseous fraction, mainly composed of H2, CO, CO2 and CH4, and some low molecular weight hydrocarbons such as ethane and ethylene, was analyzed after each experiment with a gas chromatograph (Micro-GC Bench CP-2003) equipped with a thermal conductivity detector (TCD) and a single injector connected to two columns: 5A Molecular Sieve and CP-Sil 5 CB. Helium 4.6 (100 kPa) and Argon 5.0 (100 kPa), respectively were used as carrier gases. The total weight of produced gases was calculated by comparing the known N2 volume and the gas chromatographic analysis of concentrations; the result was used to determine the mass balance. 2.4. Characterization of liquid products 2.4.1. Water content The water content of the pyrolysis liquid was determined by means of Karl-Fisher titration (Crison Compact titrator) according to the standard test method ASTM E203-96.
2.4.2. Detailed oil analysis The liquid samples, dissolved in isopropyl alcohol (analytical grade), were stored at a temperature of 5 8C with no light exposure. Before analysis, samples were filtered with 0.45 mm microfilters (Millex-Gx). A sample volume of 1 ml was analyzed in a gas chromatograph (CP-2003) equipped with a flame ionization detector (FID) and a thermal conductive detector. Species identification and quantification were made using the retention time and the internal standards. The quantitative analysis of heavy hydrocarbons, i.e. compounds with more than three carbons, was carried out by GC/FID using a SPB-1701 capillary column (60 m 0.25 mm, film thickness 0.25 mm). The volatile acids and light compounds were identified by GC/TCD using a CP-WAX 52 CB capillary column (30 m 0.53 mm i.d., film thickness 1 mm). The carrier gases were nitrogen 4.6 (200 kPa) for the SPB-1701 and helium 4.6 (80 kPa) for the CP-WAX 52 CB capillary column. The oven temperature program was 45 8C for 4 min followed by a 3 8C min1 heating rate of up to 280 8C and a 15 min plateau at 280 8C. The injectors and detectors were kept at constant temperatures of 180 and 320 8C, respectively. 3. Results and discussion 3.1. Analysis of the impregnated wood Figs. 2 and 3 show the evolution of the pH in aqueous solutions of nickel and iron nitrates, respectively, versus the metal concentration, and with or without any biomass. When nitrate salts are mixed with water the solution turns acidic, as the pH is between 3.1 and 4.1 for the nickel solution and between 0.4 and 1.4 for the iron one. The nature of the ionic species in solution depends on the total salt concentration and consequently on the pH [63–65]. Kolski et al. [66] reported that the nickel species predominating in a solution at pH 4 is [Ni4(OH)4]4+. Domazetis et al. [63] and Hynes et al. [67]
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reported that at pH 1 the iron species predominating in a solution is Fe(OH)2+. The pH of such a solution is then due to reactions (1) and (2) (hydration molecules not shown): 5NiðNO3 Þ2 þ 8H2 O ? Ni2þ þ ½Ni4 ðOHÞ4 4þ þ 4H3 Oþ þ 10NO 3
(1)
2FeðNO3 Þ3 þ 2H2 O ? Fe3þ þ FeðOHÞ2þ þ H3 Oþ þ 6NO 3 (2) As shown in Figs. 2 and 3, after adding the wood a drop in pH is always observed. This is due to the release of protons
triplicate, showing a standard deviation lower than 1.6. The average results are reported in Table 1. The results in Table 1 show that, with the selected experimental conditions, the Fe species are more easily impregnated in the wood than the Ni ones. This could be explained by the fact that complexes of Ni(II) with oak tannin ligands are more stable in solution than Fe(III) ones. Indeed Fe(III) complexes of gallic acid and gallic acid ester are instable and decompose to form Fe(II) species and the corresponding quinone [67] (Eq. (3)). These decompositions do not occur with non-redox active metals such as Ni, which form stable complexes in solution [70].
(3)
from the wood hydrolysable functional groups. Indeed, oak contains hydrolysable tannins, which are derived from glucose esters of gallic acid [68,69]. In solution with metallic ions these polyphenols act as chelating ligands enhancing the formation of metal complexes [63,70]. This chemistry includes the formation of polymeric species and the exchange of water coordinated with the metal complex [70]. However, these complexes are relatively large and could be hindered by steric constraints as they migrate into the wood molecular matrix as shown by Domazetis et al. [63]. For each experiment, the nickel and iron content in the dried impregnated wood was determined by Inductively Coupled argon Plasma (ICP Varian Vista) emission spectroscopy after mineralization of the samples (mineralization by combustion and destruction of silica by HF). Analyses were made in
Therefore, nickel and iron complexes in solution do not have the same molecular dimensions resulting in different internal mass transfers inside the wood matrix. However, further research is ongoing to better understand the impregnation mechanisms.
Fig. 2. Influence of biomass on the evolution of pH in nickel nitrate aqueous solutions vs. metal concentration.
Fig. 3. Influence of biomass on the evolution of pH in iron nitrate aqueous solutions vs. metal concentration.
3.2. Results of the pyrolysis experiments Pyrolysis experiments are carried out at 700 8C, with and without wood impregnation, in order to highlight the catalytic role of the impregnated metal species. The product yield and distribution obtained with and without any kind of catalyst are compared, in order to differentiate the catalytic activity from the effects of the experimental set up, for example thermal cracking. The experiments are carried out twice and mass
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Table 1 Metal content in the dried impregnated wood Metal concentration in solution (mol/l)
0.17 0.35 0.52
Nickel content
Iron content
mgNi/gwood
mmolNi/gwood
mgFe/gwood
mmolFe/gwood
9.76 19.06 27.33
0.166 0.324 0.466
12.21 28.21 43.19
0.219 0.506 0.774
balances are determined. A thermocouple inside the reaction bed allows the sample temperature to be continuously recorded. Fig. 4 presents the temperature evolution in the wood during an experiment. Bed heating rate is relatively high, and reaches almost 190 8C/min. Such a high heating rate is known to enhance liquid production [71], so the influence of the metal on the liquid and gas yields was easier to observe and to quantify. 3.2.1. Product yield and gas composition Figs. 5 and 6 present the product distribution of oak pyrolysis at 700 8C versus the catalyst content; each data point represents an average result of two experiments under the same conditions. The yields of gas, liquid and solid are expressed as a mass fraction with respect to the original biomass, i.e. on a catalyst-free basis. The yields of the different gases are
Fig. 4. Wood bed temperature during an experiment.
Fig. 5. Influence of metal content on the distribution of pyrolysis products.
expressed as a ‘‘volume fraction’’ of the original biomass, which is calculated by dividing the volume of each gaseous component by the same mass of wood as beforehand (cm3 of gas/g of initial wood). These figures show that liquid, gaseous and solid product collection is acceptable: the mass balance is over 94% for all the experiments despite condensable product recovery being difficult in such a system [72,73]. Moreover, experiment reproducibility has shown a standard deviation of each product of lower than 1.7. Fig. 5 shows that the liquid fraction produced during pyrolysis of raw wood is about 45%. Acid washing shifts the chemical equilibriums and increases the liquid yield, from 44.9 to 48.0%, showing the catalytic role of mineral matter in raw wood during pyrolysis. Part of the difference in the solid fraction may be due to the loss of minerals in the washing stage. It can also be observed in Fig. 6 that [CO] increases and [CO2] decreases when the wood is acid washed. These results concur with the research of Raveendran et al. [74], which showed that biomass demineralization involves an increase in liquid yield and a decrease in gas yield during pyrolysis. Since acid washing occurs when the wood is impregnated with the catalyst, the runs with acid-washed samples are used as reference. As expected, the presence of a catalyst in pyrolysis experiments involves a decrease in liquid yield varying between 7.3 and 31.9% (% related to the liquid fraction of the reference sample) depending on the catalyst concentration. In parallel, the gas yield increases from 20.0 to 33.1% (% related to reference sample gas fraction). Fig. 5 also highlights the influence of the catalyst load on the type of resulting products. Indeed, at low concentrations in the wood the catalyst
Fig. 6. Influence of metal content on gas composition.
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load has some influence on the product distribution. From a given concentration depending on the catalyst nature, when the catalyst content increases, the liquid yield decreases whereas the gas yield increases: the catalyst enhances the gas formation to the detriment of the liquid. These results can be explained by the catalytic cracking of the hydrocarbons inside the wood. Indeed, since the catalyst is added to the wood matrix, liquids are certainly cracked as soon as they are produced. Cracking of liquid vapors, mainly composed of heavy hydrocarbons, produces low molecular weight hydrocarbons and, as a consequence, is responsible for the gas yield increase. Fig. 6 shows that the presence of either Ni or Fe based catalysts increases the production of H2 and CO2 while they decrease the CH4 content; this trend increases with the catalyst load. In particular, the H2 content produced by pyrolysis of wood containing 27.33 g of Ni/g of wood reaches up to 260% of the H2 content produced in the reference sample. Thus, from a reference gas mixture containing 26.2 cm3 of H2/g of wood the catalytic treatment allows the H2 content to be enhanced by up to 94.3 cm3 of H2/g of wood. The increase in the H2 content is due to the hydrocarbon partial oxidation and dehydrogenation reactions. Indeed, nickel catalysts are used in industrially important reactions for producing hydrogen and synthesis gas from hydrocarbon feedstock, whereas iron is used to dehydrogenate heavy hydrocarbons to produce CO and H2. These two metals are also used for methane reforming [75–79], which explains the reduction observed in the CH4 content. Moreover, Fig. 6 highlights a decrease in [CO] when Fe is used; this content being 82.7 cm3/gwood for 43.19 mg of Fe/gwood whereas it is 116.1 cm3/gwood for the reference sample, while Ni has little influence on it. This reduction of the CO content can be explained by the fact that iron promotes both the Boudouard (4) and the water gas shift reactions (5) [57,80]: 2CO ! C þ CO2
(4)
CO þ H2 O ! CO2 þ H2
(5)
An increase in char production is observed when iron is used. The same trend was obtained by Yu et al. [57] in a gasification study of coal impregnated with iron. They explained this phenomenon by two mechanisms: (i) iron stabilizes the functional groups (such as carboxyl groups) it is
associated with and (ii) iron greatly enhances the thermal cracking and polymerization of tar precursors, which generate solid carbon deposits on the char and contribute to increasing the char yield. It should also be noted here that the produced chars are ferromagnetic and that when they are finely crushed all the particles can be recovered by just placing a magnet near them. This shows that iron and nickel species are initially highly dispersed in the wood. The ferromagnetic properties of the char are a great advantage since, on a larger scale, the recovery of all the char particles would be facilitated and they could be upgraded in many uses, such as a gas cleaning system [81]. This additional originality further increases the overall process efficiency. 3.2.2. Composition of the collected pyrolysis liquids All the studied liquids are homogeneous one-phase ones (no deposits are observed) and are reddish brown. Observation of the liquid color shows that the presence of metal in wood during pyrolysis influences its composition. Indeed, the higher the metal content the lighter the liquid color. This is quantified by determining the liquid composition. 3.2.2.1. Water content. The water content of the produced liquid is shown in Table 2. Analyses are made in triplicate for each sample, i.e. six times for each experimental condition, showing a standard deviation lower than 5.5% of the quantified value. Table 2 highlights the fact that both Ni and Fe species inside the wood enhance the water content in the liquid phase produced during pyrolysis. The water yield with Fe is higher than with Ni, being 60.96 wtliquid% compared to 53.58 wtliquid% with about 27–28 mgmetal/gwood, which leads to a quite similar organic content. The percentage of water in the liquid phase slightly increases with the metal content in the wood while the liquid content decreases: the more metal in the wood, the less organic liquids are produced. 3.2.2.2. Detailed liquid analysis. The pyrolysis liquids contain mainly oxygenated organic compounds, i.e. degradation products of cellulose, hemicellulose and lignin [82]. The main products of the collected liquid GC analyses are listed in
Table 2 Composition of the pyrolysis liquids Metal content (mgmetal/gwood) Acid-washed wood Raw wood
0 0
Water content of the liquid (wtliquid%)
Water content (wtwood%)
Liquid content (water + organic) (wtwood%)
Organic content (wtwood%)
45.36 48.94
20.72 22.11
47.96 44.87
26.20 22.91
Ni
9.76 19.06 27.33
49.26 51.94 53.58
21.82 23.02 19.85
44.46 44.70 37.88
22.57 21.49 17.58
Fe
12.21 28.21 43.19
55.90 60.96 64.83
21.44 25.66 22.18
38.99 41.34 32.75
17.20 16.14 11.51
Figures in bold are those obtained with comparable metal content in oak wood: 27–28 mgmetal/gwood.
Table 3 Main organic compounds in oils produced by pyrolysis and catalytic pyrolysis of oak wood
K. Bru et al. / J. Anal. Appl. Pyrolysis 78 (2007) 291–300 Figures in grey cells are those obtained with comparable metal content: 27–28 mgmetal/gwood. Conversion figures are evaluated with Eq. (6), these are negative when lower quantities are produced by catalytic pyrolysis.
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Table 3. This table also reports organic conversion, which is evaluated with the following formula (Eq. (6)): conversion Ci ð%Þ ¼
Oi impregnated wood Oi acid washed wood 100 Oi acid washed wood (6)
where Oi is the organic compound concentration. From this formula, it is clear that a negative Ci means the considered organic compound is reduced and a positive Ci means its formation is favored compared to the reference acidwashed sample. Similarly to the mass balances and gas compositions, two experiments were performed under the same conditions, leading to the production of two liquid fractions for each case. Analyses of the duplicates show the standard deviation weighted by the component concentration is lower than 6%. The most abundant peaks in acid-washed pyrolysis oils correspond to acetic acid, levoglucosan and pentanal (>15,000 mg/gwood). Methanol, furfural, acetol and catechol are also present in relatively high concentrations (>1500 mg/ gwood). First of all, Table 3 shows natural minerals in wood have a catalytic effect on several compounds during pyrolysis: they reduce the concentration of aldehydes (except pentanal), furans (except 2-acethylfuran), benzenes and methylbenzenes (except indene) and levoglucosan. The influence of acid-washing on increasing the levoglucosan yield was demonstrated by Dobele et al. [62], by Kleen et al. [83] and by Muller-Hagedorn et al. [84], the former showing that alkaline metals are responsible for levoglucosan reduction and these metals are removed by acid-washing. Acid washing favors the reduction of acetic acid, alcohol, ketone, catechol, phenols (except 3,4-dimethylphenol), quinoline and polycyclic aromatic hydrocarbon production. These specific decreases indicate that these compound formations are certainly reduced through catalytic reactions with natural minerals during wood pyrolysis. Adding metal to the wood reduces the concentration of the major organic compounds, more than 20% of the total concentration of the quantified compounds is converted with a low nickel or iron content. Varying the metal content at a given temperature of 700 8C has a considerable effect on oil composition, leading to a greater reduction of most of the analyzed organic compound concentrations. Table 3 highlights the fact that iron and nickel do not catalyze the same reactions. Indeed, for the Ni-loaded samples the concentration of all the aromatic ring compounds (benzenes, methylbenzenes, hydroxybenzenes, phenols, methylphenols, naphthalene) decreases. This catalytic effect is favored by the Ni content in the wood, except for naphthalene. Moreover, with high nickel concentrations in the wood neither benzene nor 2,5-dimethylfuran are detected. The catalytic role of Ni in reducing the naphthalene content fully agrees with the literature [85,86]. In particular, Coll et al. [85] showed that Ni-based catalysts are efficient in decreasing the naphthalene, benzene, toluene, anthracene and pyrene content. For the Fe-loaded ones, the concentration of aromatics is also reduced but this reduction is not enhanced by
the metal content in the wood for benzenes and methylbenzenes. It can also be seen that iron impregnation in wood enhances naphthalene production during pyrolysis and drastically decreases the production of ethylene glycol and 3methylcatechol since they are no longer detected in the pyrolysis oils. The influence of Fe-based catalysts on reducing the formation of catechol was demonstrated by Shin et al. [60] and by Afifi et al. [87]. For the other chemical groups, the same trend was observed: both Fe and Ni impregnations reduce the light hydrocarbon yields, i.e. the acid, alcohol and aldehyde yields, with a dose-dependant effect. 3.2.3. Comparison of the specific activity of the two metals Experiments performed with about 27–28 mgmetal/gwood allow the efficiency of both Fe and Ni species to be compared. Fig. 5 shows that with nickel, the liquid production is reduced by 21.0% whereas this reduction is only 14.0% with iron and the gas yield rises by 30.2 and 20.4%, respectively (% related to the reference sample). In Fig. 6 the composition of the produced gas shows that the H2 yield increases by 260.0% with Ni and by 170.6% with Fe (% related to the reference sample), i.e. the H2 content is 1.3 times greater with Ni than with Fe. So, nickel is more efficient at enhancing hydrogen production, while iron favors CO oxidation to CO2. It can also be seen that the CH4 content is reduced in the same way with both catalysts. Concerning the liquid phase, Table 2 shows that iron enhances water production, the water content being 1.29 times higher with Fe than with Ni. At the same time, it was seen in Table 3 that the concentration of the quantified compounds is reduced by 55.65 wt.% with iron whereas this reduction is 39.25 wt.% with Ni. Even if Ni is far more efficient than Fe at reducing the concentrations of benzene, 2,5-dimethylfuran, quinoline and naphthalene, Fe appears to be a better material for reducing the oil yield since it reacts with more organic compounds, for the ones, which were quantified, and on the compounds which are more concentrated in the liquid. 4. Conclusion The pyrolysis of oak wood in a tubular reactor is studied in order to determine the influence of wood impregnation with nickel or iron nitrate aqueous solutions. This preliminary study indicates that, regardless of whichever metal is in the wood, pyrolysis reactions are significantly catalyzed. As a result, the liquid yield is markedly reduced while the gas content is significantly increased during the pyrolysis of Ni or Fe-loaded samples. So, this is a promising way for the industrial valorization of biomass in energy related technologies (production of clean gas for turbines and engines). Moreover, these catalysts increase the H2 production and decrease the CH4 yield, leading the way for a possible use in Fisher Tropsch synthesis and fuel cell applications. Detailed analyses of the liquids highlight the major catalytic effect of Fe in reducing the organic fraction. Moreover, they show that Ni and Fe do not have the same influence: the benzene and PAH concentrations are reduced with the
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Ni-loaded samples, whereas the Fe-loaded ones decrease the concentration of light hydrocarbons. It can then be concluded that Ni and Fe species have two specific activities: nickel enhances hydrogen production, while iron reduces the production of organics. So, the choice of either nickel or iron in the wood pyrolysis should be determined by the foreseen gas application. The easier impregnation of iron species compared to nickel could also influence this choice. Finally, on-going activities will focus on evaluating the influence of pyrolysis temperature, wood type, type of metal and precursors on the pyrolysis product distribution and on its composition. A specific mixture of both iron and nickel species could also be considered. This will allow better experimental conditions and an impregnation method for further improving the efficiency of the catalytic pyrolysis to be determined. Acknowledgements The authors would like to acknowledge Benjamin HERBRETEAU and Remy SELLIN for their contribution in the optimization of the experimental set-up. The CNRS (Chemistry Department IEM) is also acknowledged for the 3-month student grants for Kathy BRU (2005) and Remy SELLIN (2004), which allowed a fruitful collaboration between CIRAD and IEM to be initiated. References [1] A.V. Bridgwater, Fuel 74 (1995) 631. [2] A. Strub, P. Chartier, G. Schleser, Energy from Biomass, Elsevier Applied Science, London, 1983. [3] P.T. Williams, N. Nugranad, Energy 25 (2000) 493. [4] D.C. Dayton, A Review of the Literature on Catalytic Biomass tar Destruction Report NREL/TP-510-32815, National Renewable Energy Laboratory, 2002. [5] S. Albertazzi, F. Basile, J. Brandin, J. Einvall, C. Hulteberg, G. Fornasari, V. Rosetti, M. Sanati, F. Trifiro, A. Vaccari, Catal. Today 106 (2005) 297. [6] A. Corti, L. Lombardi, Energy 29 (2004) 2109. [7] K. Stahl, M. Neergaard, Biomass Bioenergy 15 (1998) 205. [8] M. Rodrigues, A.P.C. Faaij, A. Walter, Energy 28 (2003) 1229. [9] R.H. Williams, E.D. Larson, Biomass Bioenergy 10 (1996) 149. [10] S. Rapagna, N. Jand, P.U. Foscolo, Int. J. Hydrogen Energy 23 (1998) 551. [11] C.N. Hamelinck, A.P.C. Faaij, J. Power Sources 111 (2002) 1. [12] D. Sutton, B. Kelleher, J.R.H. Ross, Biomass Bioenergy 23 (2002) 209. [13] M.J.A. Tijmensen, A.P.C. Faaij, C.N. Hamelinck, M.R.M. van Hardeveld, Biomass Bioenergy 23 (2002) 129. [14] A. Hirano, K. Hon-Nami, S. Kunito, M. Hada, Y. Ogushi, Catal. Today 45 (1998) 399. [15] M. Steinberg, Int. J. Hydrogen Energy 31 (2006) 405. [16] R. Gross, M. Leach, A. Bauen, Environ. Int. 29 (2003) 105. [17] L. Devi, K.J. Ptasinski, F.J.J.G. Janssen, Biomass Bioenergy 24 (2003) 125. [18] P. McKendry, Bioresour. Technol. 83 (2002) 47. [19] K.V. Lobachyov, H.J. Richter, Energy Conv. Manage. 39 (1998) 1931. [20] L. Devi, M. Craje, P. Thu¨ne, K.J. Ptasinski, F.J.J.G. Janssen, Appl. Catal. A: Gen. 294 (2005) 68. [21] P.T. Williams, P.A. Horne, J. Anal. Appl. Pyrol. 31 (1995) 15. [22] D. Sutton, B. Kelleher, J.R.H. Ross, Fuel Process. Technol. 73 (2001) 155. [23] M.L. Lee, M. Novotny, K.D. Bartle, Analytical Chemistry of Polycyclic Aromatic Compounds, Academic Press, New York, 1981. [24] S. Yaman, Energy Conv. Manage. 45 (2004) 651. [25] P.A. Horne, P.T. Williams, Fuel 75 (1996) 1051.
299
[26] P. McKendry, Bioresour. Technol. 83 (2002) 55. [27] S. Rapagna, H. Provendier, C. Petit, A. Kiennemann, P.U. Foscolo, Biomass Bioenergy 22 (2002) 377. [28] Y. Ohtsuka, K. Asami, Energy Fuels 9 (1996) 1038. [29] D.W. McKee, C.L. Spiro, P.G. Kosky, E.J. Lamby, Fuel 62 (1983) 217. [30] W.J. Lee, S.D. Kim, Fuel 74 (1995) 1387. [31] J.M. Encinar, F.J. Beltran, A. Ramiro, J.F. Gonzalez, Fuel Process. Technol. 55 (1998) 219. [32] D.C. Elliott, E.G. Baker, Biomass 9 (1986) 195. [33] A. Demirbas, Energy Conv. Manage. 43 (2002) 897. [34] D.M. Quyn, H. Wu, C.-Z. Li, Fuel 81 (2002) 143. [35] T. Takematsu, M.C., Coal Gasification for IGCC Power Generation, IEA Coal Research, London, 1991, p. 80. [36] C.-Z. Li, C. Sathe, J.R. Kershaw, Y. Pang, Fuel 79 (2000) 427. [37] P.A. Jensen, F.J. Frandsen, K. Dam-Johansen, B. Sander, Energy Fuels 14 (2000) 1280. [38] D.C. Dayton, R.J. French, T.A. Milne, Energy Fuels 9 (1995) 855. [39] C. Courson, E. Makaga, C. Petit, A. Kiennemann, Catal. Today 63 (2000) 427. [40] S.C. Tsang, J.B. Claridge, M.L.H. Green, Catal. Today 23 (1995) 3. [41] V.D. Belyaev, T.I. Politova, O.A. Mar’ina, V.A. Sobyanin, Appl. Catal. A: Gen. 133 (1995) 47. [42] F.J. Marino, E.G. Cerrella, S. Duhalde, M. Jobbagy, M.A. Laborde, Int. J. Hydrogen Energy 23 (1998) 1095. [43] S. Rapagna, N. Jand, C. Courson, C. Petit, A. Kiennemann, P.U. Foscolo (Eds.), Nickel based catalysts in the steam gasification of biomass, 1st World Conference on Biomass for Energy and Industry, Sevilla, Spain, James & James (Science Publishers) Ltd., 2000, p. 1646. [44] D. Wang, S. Czernik, E. Chornet, Energy Fuels 12 (1998) 19. [45] E.G. Baker, L.K. Mudge, M.D. Brown, Ind. Eng. Chem. Res. 26 (1987) 1335. [46] D. Sutton, B. Kelleher, A. Doyle, J.R.H. Ross, Bioresour. Technol. 80 (2001) 111. [47] A. Orio, J. Corella, I. Narvaez, in: A.V. Bridgwater, D.G.B. Boocock (Eds.), Developments in Thermochemical Biomass Conversion, Blackie Academic & Professional, 1997, p. 1144. [48] C. Ekstro¨m, N. Lindman, R. Pettersson, in: R.P. Overend, T.A. Milne, L.K. Mudge (Eds.), Fundamentals of Thermochemical Biomass Conversion, Elsevier Applied Science Publishers, New York, 1985, p. 601. [49] A. Olivares, M.P. Aznar, M.A. Caballero, J. Gil, E. Frances, J. Corella, Ind. Eng. Chem. Res. 36 (1997) 5220. [50] S. Rapagna, N. Jand, A. Kiennemann, P.U. Foscolo, Biomass Bioenergy 19 (2000) 187. [51] J. Corella, J.M. Toledo, R. Padilla, Energy and Fuels (2004), 18, 713. [52] A. Orio, J. Corella, I. Narvaez, Ind. Eng. Chem. Res. 36 (1997) 3800. [53] L. Devi, K.J. Ptasinski, F.J.J.G. Janssen, S.V.B. van Paasen, P.C.A. Bergman, J.H.A. Kiel, Renewable Energy 30 (2005) 565. [54] P.A. Simell, J.K. Leppalahti, J.B.-s. Bredenberg, Fuel 71 (1992) 211. [55] L. Devi, K.J. Ptasinski, F.J.J.G. Janssen, Fuel Process. Technol. 86 (2005) 707. [56] T. Nordgreen, T. Liliedahl, K. Sjostrom, Fuel 85 (2006) 689. [57] J. Yu, F.-J. Tian, M.C. Chow, L.J. McKenzie, C.-Z. Li, Fuel 85 (2006) 127. [58] K. Asami, P. Sears, E. Furimsky, Y. Ohtsuka, Fuel Process. Technol. 47 (1996) 139. [59] E.-J. Shin, M.R. Hajaligol, F. Rasouli, Fuel 83 (2004) 1445. [60] E.-J. Shin, D.E. Miser, W.G. Chan, M.R. Hajaligol, Appl. Catal. B: Environ. 61 (2005) 79. [61] O. Beaumont, Y. Schwob, Ind. Eng. Chem. Process Des. Dev. 23 (1984) 637. [62] G. Dobele, G. Rossinskaja, T. Dizhbite, G. Telysheva, D. Meier, O. Faix, J. Anal. Appl. Pyrol. 74 (2005) 401. [63] G. Domazetis, J. Liesegang, B.D. James, Fuel Process. Technol. 86 (2005) 463. [64] T. Hong-Xiao, W. Stumm, Water Res. 21 (1987) 115. [65] R.M. Cornell, U. Schwertmann, The Iron Oxides, VCH, New York, 1996. [66] G.B. Kolski, N.K. Kildahl, D.W. Margerum, Inorg. Chem. 8 (1969) 1211. [67] M.J. Hynes, M.O. Coinceanainn, J. Inorg. Biochem. 85 (2001) 131.
300
K. Bru et al. / J. Anal. Appl. Pyrolysis 78 (2007) 291–300
[68] P. Mammela, H. Savolainen, L. Lindroos, J. Kangas, T. Vartiainen, J. Chromatogr. A 891 (2000) 75. [69] R. Niemetz, G.G. Gross, Phytochemistry 66 (2005) 2001. [70] M. Roitto, P. Rautio, R. Julkunen-Tiitto, E. Kukkola, S. Huttunen, Environ. Pollut. 137 (2005) 603. [71] A.V. Bridgwater, D. Meier, D. Radlein, Org. Geochem. 30 (1999) 1479. [72] R. Zanzi, K. Sjostrom, E. Bjornbom, Fuel 75 (1996) 545. [73] P.T. Williams, P.A. Horne, J. Anal. Appl. Pyrol. 31 (1995) 39. [74] K. Raveendran, A. Ganesh, K.C. Khilar, Fuel 74 (1995) 1812. [75] K. Takehira, T. Shishido, P. Wang, T. Kosaka, K. Takaki, J. Catal. 221 (2004) 43. [76] A.I. Tsyganok, T. Tsunoda, S. Hamakawa, K. Suzuki, K. Takehira, T. Hayakawa, J. Catal. 213 (2003) 191. [77] M.-S. Liao, Q.-E. Zhang, J. Mol. Catal. A: Chem. 136 (1998) 185.
[78] Y. Wang, B.H. Davis, Appl. Catal. A: Gen. 180 (1999) 277. [79] M.W. Mu¨ller, W.R. Hoffmann, K.J. Hu¨ttinger, Fuel 74 (1995) 953. [80] P. Li, D.E. Miser, S. Rabiei, R.T. Yadav, M.R. Hajaligol, Appl. Catal. B: Environ. 43 (2003) 151. [81] G. Antonini, C. Porquet, P. Girard, French Patent 98-03744 (1998). [82] M.I. Nokkosmaki, E.T. Kuoppala, E.A. Leppamaki, A.O.I. Krause, J. Anal. Appl. Pyrol. 55 (2000) 119. [83] M. Kleen, G. Gellerstedt, J. Anal. Appl. Pyrol. 35 (1995) 15. [84] M. Muller-Hagedorn, H. Bockhorn, L. Krebs, U. Muller, J. Anal. Appl. Pyrol. 68–69 (2003) 231. [85] R. Coll, J. Salvado, X. Farriol, D. Montane, Fuel Process. Technol. 74 (2001) 19. [86] B. Dou, J. Gao, X. Sha, S.W. Baek, Appl. Therm. Eng. 23 (2003) 2229. [87] A.I. Afifi, E. Chornet, R.W. Thring, R.P. Overend, Fuel 75 (1996) 509.
Pyrolysis of metal impregnated biomass: An innovative catalytic way to produce gas fuel K. Bru a, J. Blin a,*, A. Julbe b, G. Volle a b
a CIRAD-Foreˆt, UPR 42 Biomasse Energie, TA 10/16, 73, Avenue J.-F. Breton, 34398 Montpellier Cedex 5, France Institut Europe´en des Membranes (UMR 5635 CNRS), UMII, CC47, Place E. Bataillon, 34095 Montpellier Cedex 5, France
Received 22 February 2006; accepted 17 August 2006 Available online 25 September 2006
Abstract An innovative way of catalysis was investigated for its potential to reduce the amount of condensable hydrocarbons produced during the pyrolysis of oak wood. The experiments were carried out in a horizontal tubular reactor, fed with a controlled flow rate of nitrogen and equipped with accessories to collect char, liquid and gaseous products. Pyrolysis was performed at 700 8C with different wood sample series impregnated with either Ni or Fe nitrates (in aqueous solution) and by varying the metal concentration in the wood. In the blank run the biomass was acid-washed to determine the impact of demineralization. The influence of the metal type and content introduced into the wood to reduce the fraction of condensable organic compounds produced during pyrolysis was determined. Depending on the experimental conditions, the gas yield increases from 20.0 to 33.1%. Condensable hydrocarbons are cracked into gaseous components and the concentration of H2 is significantly increased, by 260% compared to the reference sample. In particular, the Ni-loaded wood samples give much higher H2 yields than the Fe-loaded ones under similar conditions but less toxic products are formed with the latter. These results show that biomass impregnation with either nickel or iron salts is a promising way to reduce the fraction of condensable organic compounds produced during pyrolysis. # 2006 Elsevier B.V. All rights reserved. Keywords: Biomass pyrolysis; Catalytic conversion; Hydrogen
1. Introduction Biomass is a renewable energy that has social, political and economic advantages. Indeed, thermochemical conversion of it for the production of fuels, chemicals and combined heat and power could revitalize rural economies, limit the dependence on foreign oil imports, and improve the environment by reducing fossil fuel consumption and thus reducing greenhouse gases [1–4]. Biomass gasification is a developing technology that can be used to generate heat and electricity in an Integrated Gasification Combined Cycle [5–9]. Conditioning and upgrading the produced gas can also make it a suitable feed for methanol or Fischer-Tropsch liquid synthesis [10–14]. Additional conditioning can produce a hydrogen-rich gas that is
* Corresponding author. Tel.: +33 4 67 61 65 21; fax: +33 4 67 61 65 15. E-mail address: [email protected] (J. Blin). 0165-2370/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jaap.2006.08.006
suitable for transportation, chemical production, or electricity generation in fuel cells [15–19]. The main problem to deal with in biomass gasification is the formation of tars, which make the gas unsuitable for further applications [20]. Tar is a complex mixture of condensable hydrocarbons, which includes single ring to 5-ring aromatic compounds along with other oxygen-containing hydrocarbons and complex polycyclic aromatic hydrocarbons (PAH) [17,20,21]. They are initially produced during pyrolysis; the first step of any thermochemical conversion processes. Tars cause severe operational problems, such as blockages and corrosion [22] due to their condensation, deactivate the catalysts used for upgrading the gas [4] and may constitute a potential health and environmental hazard, as some of the tar components may be carcinogenic or mutagenic [3,23–25]. Consequently, one of the main concerns in such a process is to eliminate or reduce the tar products. The classical gas cleaning technology based on scrubbing is not acceptable because of the poor efficiency of tar removal,
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wastewater production, and energy loss during gas cooling which reduces the overall process efficiency. Partial oxidation does not provide sufficient cleaning efficiency and moreover decreases the gas heating value. Catalytic high temperature cleaning provides sufficient efficiency for tar removal and does not decrease the heating value of the produced gas [1,4,17,22,26,27]. Most of the research works on biomass gasification concern two types of catalysis:
The objective of this study is to investigate the influence of nickel and iron on reducing the condensable hydrocarbons produced during the pyrolysis of oak wood. These metals are inserted into the wood matrix by wet impregnation in a nitrate aqueous solution. The catalytic pyrolysis product yields are compared with the uncatalyzed products. The influence of the metal concentration is also examined. Then, gases and liquids are analyzed to better highlight the role of the metal species.
mixing the catalyst with the biomass to reduce the tar content in the gasification bed, using the catalyst in a specific hot gas cleaning reactor (posttreatment).
2. Experimental
In both cases, the catalyst efficiency is high when it is first used but its lifetime is limited because of carbon deposition, particle agglomeration and mechanical strength decrease involving catalyst deactivation [17,22]. An attractive option is then to insert the catalyst inside the wood matrix by impregnation before thermochemical conversion. Using this method, the catalytic material is highly dispersed in the biomass and freshly renewed when it is introduced into the reactor. The majority of the work on catalytic pyrolysis in relation to biomass pyrolysis gas has been done with a secondary reactor and there are few data on the influence of catalyst impregnation on the yield and composition of pyrolysis products. The last few research studies on catalyst impregnation in wood for biomass pyrolysis or gasification were mainly centered on relating the effectiveness of alkali and alkaline earth metallic species. These catalysts have been reported to be very active in tar removal [28–30], as the conversion of condensable hydrocarbons leads to an increase in gas yield [31]. Examples of inorganic ions that have been added to biomass are Na+, Li+, K+ and Ca2+ [31– 33]. However, these species volatilize at low temperatures, causing significant problems in terms of fouling, erosion and corrosion of the plant components [34–38]. No information exists on the biomass impregnation of catalytically active species classically used in a secondary reactor. Among them, catalysts with either nickel or iron are those of greatest interest. Indeed, extensive studies reported in the literature show that Ni-based catalysts are highly effective in removing hydrocarbons and in adjusting the gas composition to syngas quality [39–46]. Moreover, it has also been demonstrated that iron is efficient in reducing hydrocarbon formation, since natural iron containing minerals, such as dolomite (Ca(Mgx,Fey)(CO3)2) [10,47-49] or olivine ((Mgx,Fey)2SiO4), [20,50,51] are known to promote tar cracking and reforming. Several studies have also reported that iron(III) is responsible for the tar cracking reactions [52– 54]. In particular, Devi et al. [55] showed that olivine calcination with air at a high temperature changes the oxidation state of iron, the best olivine activity being obtained with iron(III). The influence of metallic iron or iron oxides on hydrocarbon decomposition has also been studied recently [56– 59]. It was reported that iron particles increase the cracking of phenolic and aromatic compounds, leading to the formation of carbon dioxide and water [59–61].
2.1. Laboratory scale pyrolysis plant All reactions are carried out under atmospheric pressure and inert conditions in a tubular heated reactor. The experimental set-up, shown in Fig. 1, consists of a 50 mm wide, 600 mm long cylindrical stainless steel reactor. It is equipped with a feeding chamber and adapted devices to quench liquid and collect gas samples. During experiments, the reactor is continuously flushed with pre-heated nitrogen (18.3 103 N m3/h at 400 8C) to remove air from the reactor and all the gases produced during pyrolysis. The feeding chamber is cooled with water in a double envelope to keep the sample at room temperature before introducing it into the hot zone. Approximately 10 g of wood is loaded into a stainless steel holder (called a ‘‘boat’’) driven by a sliding handle. This boat is placed in the cooled zone during the thermal stabilization of the reactor and is rapidly introduced into the reactor hot zone to start the pyrolysis. The sample is then promptly heated from room temperature to reactor temperature. Vapors formed during the pyrolysis are instantaneously diluted with the carrier gas. At the reactor outlet, a quench system is used to recover liquids. It consists of a cool water heat exchanger connected to a flask cooled in a liquid nitrogen ethylic alcohol bath at around 50 8C, prior an electrostatic precipitator. In order to avoid hydrocarbon condensation before this system has been reached, the reactor exit is equipped with a resistive heater. The noncondensable gas flow is then measured using a precise volumetric flow meter and is collected in a sampling bag. The run duration is 20 min. The heating is then switched off and the boat is returned to the cooled zone. Once room temperature is reached in the boat, the remaining char in it is weighted. The total amount of produced liquid is collected by washing the coil cooler and the electrostatic precipitator with isopropyl alcohol: the total liquid mass can then be weighted. For each set of parameters, two runs were carried out under identical conditions to check the repeatability of the process. 2.2. Wood preparation and impregnation The selected biomass was oak sawdust of a size range varying from 0.4 to 1.6 mm. The metallic salts used for the wood impregnation were nitrates as they do not contain carbon atoms, which may have altered the obtained results. The salts used were [Fe(NO3)39H2O] provided by Fluka (purity: 98%) and
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Fig. 1. Diagram of the pyrolysis reactor.
[Ni(NO3)26H2O] provided by Sigma–Aldrich (purity: 99%), respectively. The air-dried wood particles (105 8C, 5 days) were impregnated by mixing 22 g of wood with 250 ml of a Ni(NO3)2 or Fe(NO3)3 aqueous solution at concentrations of 0.17, 0.35 and 0.52 mol/l. The obtained mixtures were stirred at ambient temperature for 3 days. The wood particles were then filtered and dried again at 105 8C for 5 days. The wet impregnation of the wood particles washes the samples. This means they lose some of their minerals [62]. Moreover, nickel and iron nitrate solutions are acidic [63] and this acidity intensifies this phenomenon. In order to evaluate the influence of this acid treatment on the pyrolysis product distribution and on their composition, the wet impregnation method was also applied to wood particles impregnated with a nitric acid aqueous solution at pH 2.8 (reference sample). 2.3. Gas analysis The whole gaseous fraction, mainly composed of H2, CO, CO2 and CH4, and some low molecular weight hydrocarbons such as ethane and ethylene, was analyzed after each experiment with a gas chromatograph (Micro-GC Bench CP-2003) equipped with a thermal conductivity detector (TCD) and a single injector connected to two columns: 5A Molecular Sieve and CP-Sil 5 CB. Helium 4.6 (100 kPa) and Argon 5.0 (100 kPa), respectively were used as carrier gases. The total weight of produced gases was calculated by comparing the known N2 volume and the gas chromatographic analysis of concentrations; the result was used to determine the mass balance. 2.4. Characterization of liquid products 2.4.1. Water content The water content of the pyrolysis liquid was determined by means of Karl-Fisher titration (Crison Compact titrator) according to the standard test method ASTM E203-96.
2.4.2. Detailed oil analysis The liquid samples, dissolved in isopropyl alcohol (analytical grade), were stored at a temperature of 5 8C with no light exposure. Before analysis, samples were filtered with 0.45 mm microfilters (Millex-Gx). A sample volume of 1 ml was analyzed in a gas chromatograph (CP-2003) equipped with a flame ionization detector (FID) and a thermal conductive detector. Species identification and quantification were made using the retention time and the internal standards. The quantitative analysis of heavy hydrocarbons, i.e. compounds with more than three carbons, was carried out by GC/FID using a SPB-1701 capillary column (60 m 0.25 mm, film thickness 0.25 mm). The volatile acids and light compounds were identified by GC/TCD using a CP-WAX 52 CB capillary column (30 m 0.53 mm i.d., film thickness 1 mm). The carrier gases were nitrogen 4.6 (200 kPa) for the SPB-1701 and helium 4.6 (80 kPa) for the CP-WAX 52 CB capillary column. The oven temperature program was 45 8C for 4 min followed by a 3 8C min1 heating rate of up to 280 8C and a 15 min plateau at 280 8C. The injectors and detectors were kept at constant temperatures of 180 and 320 8C, respectively. 3. Results and discussion 3.1. Analysis of the impregnated wood Figs. 2 and 3 show the evolution of the pH in aqueous solutions of nickel and iron nitrates, respectively, versus the metal concentration, and with or without any biomass. When nitrate salts are mixed with water the solution turns acidic, as the pH is between 3.1 and 4.1 for the nickel solution and between 0.4 and 1.4 for the iron one. The nature of the ionic species in solution depends on the total salt concentration and consequently on the pH [63–65]. Kolski et al. [66] reported that the nickel species predominating in a solution at pH 4 is [Ni4(OH)4]4+. Domazetis et al. [63] and Hynes et al. [67]
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reported that at pH 1 the iron species predominating in a solution is Fe(OH)2+. The pH of such a solution is then due to reactions (1) and (2) (hydration molecules not shown): 5NiðNO3 Þ2 þ 8H2 O ? Ni2þ þ ½Ni4 ðOHÞ4 4þ þ 4H3 Oþ þ 10NO 3
(1)
2FeðNO3 Þ3 þ 2H2 O ? Fe3þ þ FeðOHÞ2þ þ H3 Oþ þ 6NO 3 (2) As shown in Figs. 2 and 3, after adding the wood a drop in pH is always observed. This is due to the release of protons
triplicate, showing a standard deviation lower than 1.6. The average results are reported in Table 1. The results in Table 1 show that, with the selected experimental conditions, the Fe species are more easily impregnated in the wood than the Ni ones. This could be explained by the fact that complexes of Ni(II) with oak tannin ligands are more stable in solution than Fe(III) ones. Indeed Fe(III) complexes of gallic acid and gallic acid ester are instable and decompose to form Fe(II) species and the corresponding quinone [67] (Eq. (3)). These decompositions do not occur with non-redox active metals such as Ni, which form stable complexes in solution [70].
(3)
from the wood hydrolysable functional groups. Indeed, oak contains hydrolysable tannins, which are derived from glucose esters of gallic acid [68,69]. In solution with metallic ions these polyphenols act as chelating ligands enhancing the formation of metal complexes [63,70]. This chemistry includes the formation of polymeric species and the exchange of water coordinated with the metal complex [70]. However, these complexes are relatively large and could be hindered by steric constraints as they migrate into the wood molecular matrix as shown by Domazetis et al. [63]. For each experiment, the nickel and iron content in the dried impregnated wood was determined by Inductively Coupled argon Plasma (ICP Varian Vista) emission spectroscopy after mineralization of the samples (mineralization by combustion and destruction of silica by HF). Analyses were made in
Therefore, nickel and iron complexes in solution do not have the same molecular dimensions resulting in different internal mass transfers inside the wood matrix. However, further research is ongoing to better understand the impregnation mechanisms.
Fig. 2. Influence of biomass on the evolution of pH in nickel nitrate aqueous solutions vs. metal concentration.
Fig. 3. Influence of biomass on the evolution of pH in iron nitrate aqueous solutions vs. metal concentration.
3.2. Results of the pyrolysis experiments Pyrolysis experiments are carried out at 700 8C, with and without wood impregnation, in order to highlight the catalytic role of the impregnated metal species. The product yield and distribution obtained with and without any kind of catalyst are compared, in order to differentiate the catalytic activity from the effects of the experimental set up, for example thermal cracking. The experiments are carried out twice and mass
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Table 1 Metal content in the dried impregnated wood Metal concentration in solution (mol/l)
0.17 0.35 0.52
Nickel content
Iron content
mgNi/gwood
mmolNi/gwood
mgFe/gwood
mmolFe/gwood
9.76 19.06 27.33
0.166 0.324 0.466
12.21 28.21 43.19
0.219 0.506 0.774
balances are determined. A thermocouple inside the reaction bed allows the sample temperature to be continuously recorded. Fig. 4 presents the temperature evolution in the wood during an experiment. Bed heating rate is relatively high, and reaches almost 190 8C/min. Such a high heating rate is known to enhance liquid production [71], so the influence of the metal on the liquid and gas yields was easier to observe and to quantify. 3.2.1. Product yield and gas composition Figs. 5 and 6 present the product distribution of oak pyrolysis at 700 8C versus the catalyst content; each data point represents an average result of two experiments under the same conditions. The yields of gas, liquid and solid are expressed as a mass fraction with respect to the original biomass, i.e. on a catalyst-free basis. The yields of the different gases are
Fig. 4. Wood bed temperature during an experiment.
Fig. 5. Influence of metal content on the distribution of pyrolysis products.
expressed as a ‘‘volume fraction’’ of the original biomass, which is calculated by dividing the volume of each gaseous component by the same mass of wood as beforehand (cm3 of gas/g of initial wood). These figures show that liquid, gaseous and solid product collection is acceptable: the mass balance is over 94% for all the experiments despite condensable product recovery being difficult in such a system [72,73]. Moreover, experiment reproducibility has shown a standard deviation of each product of lower than 1.7. Fig. 5 shows that the liquid fraction produced during pyrolysis of raw wood is about 45%. Acid washing shifts the chemical equilibriums and increases the liquid yield, from 44.9 to 48.0%, showing the catalytic role of mineral matter in raw wood during pyrolysis. Part of the difference in the solid fraction may be due to the loss of minerals in the washing stage. It can also be observed in Fig. 6 that [CO] increases and [CO2] decreases when the wood is acid washed. These results concur with the research of Raveendran et al. [74], which showed that biomass demineralization involves an increase in liquid yield and a decrease in gas yield during pyrolysis. Since acid washing occurs when the wood is impregnated with the catalyst, the runs with acid-washed samples are used as reference. As expected, the presence of a catalyst in pyrolysis experiments involves a decrease in liquid yield varying between 7.3 and 31.9% (% related to the liquid fraction of the reference sample) depending on the catalyst concentration. In parallel, the gas yield increases from 20.0 to 33.1% (% related to reference sample gas fraction). Fig. 5 also highlights the influence of the catalyst load on the type of resulting products. Indeed, at low concentrations in the wood the catalyst
Fig. 6. Influence of metal content on gas composition.
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load has some influence on the product distribution. From a given concentration depending on the catalyst nature, when the catalyst content increases, the liquid yield decreases whereas the gas yield increases: the catalyst enhances the gas formation to the detriment of the liquid. These results can be explained by the catalytic cracking of the hydrocarbons inside the wood. Indeed, since the catalyst is added to the wood matrix, liquids are certainly cracked as soon as they are produced. Cracking of liquid vapors, mainly composed of heavy hydrocarbons, produces low molecular weight hydrocarbons and, as a consequence, is responsible for the gas yield increase. Fig. 6 shows that the presence of either Ni or Fe based catalysts increases the production of H2 and CO2 while they decrease the CH4 content; this trend increases with the catalyst load. In particular, the H2 content produced by pyrolysis of wood containing 27.33 g of Ni/g of wood reaches up to 260% of the H2 content produced in the reference sample. Thus, from a reference gas mixture containing 26.2 cm3 of H2/g of wood the catalytic treatment allows the H2 content to be enhanced by up to 94.3 cm3 of H2/g of wood. The increase in the H2 content is due to the hydrocarbon partial oxidation and dehydrogenation reactions. Indeed, nickel catalysts are used in industrially important reactions for producing hydrogen and synthesis gas from hydrocarbon feedstock, whereas iron is used to dehydrogenate heavy hydrocarbons to produce CO and H2. These two metals are also used for methane reforming [75–79], which explains the reduction observed in the CH4 content. Moreover, Fig. 6 highlights a decrease in [CO] when Fe is used; this content being 82.7 cm3/gwood for 43.19 mg of Fe/gwood whereas it is 116.1 cm3/gwood for the reference sample, while Ni has little influence on it. This reduction of the CO content can be explained by the fact that iron promotes both the Boudouard (4) and the water gas shift reactions (5) [57,80]: 2CO ! C þ CO2
(4)
CO þ H2 O ! CO2 þ H2
(5)
An increase in char production is observed when iron is used. The same trend was obtained by Yu et al. [57] in a gasification study of coal impregnated with iron. They explained this phenomenon by two mechanisms: (i) iron stabilizes the functional groups (such as carboxyl groups) it is
associated with and (ii) iron greatly enhances the thermal cracking and polymerization of tar precursors, which generate solid carbon deposits on the char and contribute to increasing the char yield. It should also be noted here that the produced chars are ferromagnetic and that when they are finely crushed all the particles can be recovered by just placing a magnet near them. This shows that iron and nickel species are initially highly dispersed in the wood. The ferromagnetic properties of the char are a great advantage since, on a larger scale, the recovery of all the char particles would be facilitated and they could be upgraded in many uses, such as a gas cleaning system [81]. This additional originality further increases the overall process efficiency. 3.2.2. Composition of the collected pyrolysis liquids All the studied liquids are homogeneous one-phase ones (no deposits are observed) and are reddish brown. Observation of the liquid color shows that the presence of metal in wood during pyrolysis influences its composition. Indeed, the higher the metal content the lighter the liquid color. This is quantified by determining the liquid composition. 3.2.2.1. Water content. The water content of the produced liquid is shown in Table 2. Analyses are made in triplicate for each sample, i.e. six times for each experimental condition, showing a standard deviation lower than 5.5% of the quantified value. Table 2 highlights the fact that both Ni and Fe species inside the wood enhance the water content in the liquid phase produced during pyrolysis. The water yield with Fe is higher than with Ni, being 60.96 wtliquid% compared to 53.58 wtliquid% with about 27–28 mgmetal/gwood, which leads to a quite similar organic content. The percentage of water in the liquid phase slightly increases with the metal content in the wood while the liquid content decreases: the more metal in the wood, the less organic liquids are produced. 3.2.2.2. Detailed liquid analysis. The pyrolysis liquids contain mainly oxygenated organic compounds, i.e. degradation products of cellulose, hemicellulose and lignin [82]. The main products of the collected liquid GC analyses are listed in
Table 2 Composition of the pyrolysis liquids Metal content (mgmetal/gwood) Acid-washed wood Raw wood
0 0
Water content of the liquid (wtliquid%)
Water content (wtwood%)
Liquid content (water + organic) (wtwood%)
Organic content (wtwood%)
45.36 48.94
20.72 22.11
47.96 44.87
26.20 22.91
Ni
9.76 19.06 27.33
49.26 51.94 53.58
21.82 23.02 19.85
44.46 44.70 37.88
22.57 21.49 17.58
Fe
12.21 28.21 43.19
55.90 60.96 64.83
21.44 25.66 22.18
38.99 41.34 32.75
17.20 16.14 11.51
Figures in bold are those obtained with comparable metal content in oak wood: 27–28 mgmetal/gwood.
Table 3 Main organic compounds in oils produced by pyrolysis and catalytic pyrolysis of oak wood
K. Bru et al. / J. Anal. Appl. Pyrolysis 78 (2007) 291–300 Figures in grey cells are those obtained with comparable metal content: 27–28 mgmetal/gwood. Conversion figures are evaluated with Eq. (6), these are negative when lower quantities are produced by catalytic pyrolysis.
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Table 3. This table also reports organic conversion, which is evaluated with the following formula (Eq. (6)): conversion Ci ð%Þ ¼
Oi impregnated wood Oi acid washed wood 100 Oi acid washed wood (6)
where Oi is the organic compound concentration. From this formula, it is clear that a negative Ci means the considered organic compound is reduced and a positive Ci means its formation is favored compared to the reference acidwashed sample. Similarly to the mass balances and gas compositions, two experiments were performed under the same conditions, leading to the production of two liquid fractions for each case. Analyses of the duplicates show the standard deviation weighted by the component concentration is lower than 6%. The most abundant peaks in acid-washed pyrolysis oils correspond to acetic acid, levoglucosan and pentanal (>15,000 mg/gwood). Methanol, furfural, acetol and catechol are also present in relatively high concentrations (>1500 mg/ gwood). First of all, Table 3 shows natural minerals in wood have a catalytic effect on several compounds during pyrolysis: they reduce the concentration of aldehydes (except pentanal), furans (except 2-acethylfuran), benzenes and methylbenzenes (except indene) and levoglucosan. The influence of acid-washing on increasing the levoglucosan yield was demonstrated by Dobele et al. [62], by Kleen et al. [83] and by Muller-Hagedorn et al. [84], the former showing that alkaline metals are responsible for levoglucosan reduction and these metals are removed by acid-washing. Acid washing favors the reduction of acetic acid, alcohol, ketone, catechol, phenols (except 3,4-dimethylphenol), quinoline and polycyclic aromatic hydrocarbon production. These specific decreases indicate that these compound formations are certainly reduced through catalytic reactions with natural minerals during wood pyrolysis. Adding metal to the wood reduces the concentration of the major organic compounds, more than 20% of the total concentration of the quantified compounds is converted with a low nickel or iron content. Varying the metal content at a given temperature of 700 8C has a considerable effect on oil composition, leading to a greater reduction of most of the analyzed organic compound concentrations. Table 3 highlights the fact that iron and nickel do not catalyze the same reactions. Indeed, for the Ni-loaded samples the concentration of all the aromatic ring compounds (benzenes, methylbenzenes, hydroxybenzenes, phenols, methylphenols, naphthalene) decreases. This catalytic effect is favored by the Ni content in the wood, except for naphthalene. Moreover, with high nickel concentrations in the wood neither benzene nor 2,5-dimethylfuran are detected. The catalytic role of Ni in reducing the naphthalene content fully agrees with the literature [85,86]. In particular, Coll et al. [85] showed that Ni-based catalysts are efficient in decreasing the naphthalene, benzene, toluene, anthracene and pyrene content. For the Fe-loaded ones, the concentration of aromatics is also reduced but this reduction is not enhanced by
the metal content in the wood for benzenes and methylbenzenes. It can also be seen that iron impregnation in wood enhances naphthalene production during pyrolysis and drastically decreases the production of ethylene glycol and 3methylcatechol since they are no longer detected in the pyrolysis oils. The influence of Fe-based catalysts on reducing the formation of catechol was demonstrated by Shin et al. [60] and by Afifi et al. [87]. For the other chemical groups, the same trend was observed: both Fe and Ni impregnations reduce the light hydrocarbon yields, i.e. the acid, alcohol and aldehyde yields, with a dose-dependant effect. 3.2.3. Comparison of the specific activity of the two metals Experiments performed with about 27–28 mgmetal/gwood allow the efficiency of both Fe and Ni species to be compared. Fig. 5 shows that with nickel, the liquid production is reduced by 21.0% whereas this reduction is only 14.0% with iron and the gas yield rises by 30.2 and 20.4%, respectively (% related to the reference sample). In Fig. 6 the composition of the produced gas shows that the H2 yield increases by 260.0% with Ni and by 170.6% with Fe (% related to the reference sample), i.e. the H2 content is 1.3 times greater with Ni than with Fe. So, nickel is more efficient at enhancing hydrogen production, while iron favors CO oxidation to CO2. It can also be seen that the CH4 content is reduced in the same way with both catalysts. Concerning the liquid phase, Table 2 shows that iron enhances water production, the water content being 1.29 times higher with Fe than with Ni. At the same time, it was seen in Table 3 that the concentration of the quantified compounds is reduced by 55.65 wt.% with iron whereas this reduction is 39.25 wt.% with Ni. Even if Ni is far more efficient than Fe at reducing the concentrations of benzene, 2,5-dimethylfuran, quinoline and naphthalene, Fe appears to be a better material for reducing the oil yield since it reacts with more organic compounds, for the ones, which were quantified, and on the compounds which are more concentrated in the liquid. 4. Conclusion The pyrolysis of oak wood in a tubular reactor is studied in order to determine the influence of wood impregnation with nickel or iron nitrate aqueous solutions. This preliminary study indicates that, regardless of whichever metal is in the wood, pyrolysis reactions are significantly catalyzed. As a result, the liquid yield is markedly reduced while the gas content is significantly increased during the pyrolysis of Ni or Fe-loaded samples. So, this is a promising way for the industrial valorization of biomass in energy related technologies (production of clean gas for turbines and engines). Moreover, these catalysts increase the H2 production and decrease the CH4 yield, leading the way for a possible use in Fisher Tropsch synthesis and fuel cell applications. Detailed analyses of the liquids highlight the major catalytic effect of Fe in reducing the organic fraction. Moreover, they show that Ni and Fe do not have the same influence: the benzene and PAH concentrations are reduced with the
K. Bru et al. / J. Anal. Appl. Pyrolysis 78 (2007) 291–300
Ni-loaded samples, whereas the Fe-loaded ones decrease the concentration of light hydrocarbons. It can then be concluded that Ni and Fe species have two specific activities: nickel enhances hydrogen production, while iron reduces the production of organics. So, the choice of either nickel or iron in the wood pyrolysis should be determined by the foreseen gas application. The easier impregnation of iron species compared to nickel could also influence this choice. Finally, on-going activities will focus on evaluating the influence of pyrolysis temperature, wood type, type of metal and precursors on the pyrolysis product distribution and on its composition. A specific mixture of both iron and nickel species could also be considered. This will allow better experimental conditions and an impregnation method for further improving the efficiency of the catalytic pyrolysis to be determined. Acknowledgements The authors would like to acknowledge Benjamin HERBRETEAU and Remy SELLIN for their contribution in the optimization of the experimental set-up. The CNRS (Chemistry Department IEM) is also acknowledged for the 3-month student grants for Kathy BRU (2005) and Remy SELLIN (2004), which allowed a fruitful collaboration between CIRAD and IEM to be initiated. References [1] A.V. Bridgwater, Fuel 74 (1995) 631. [2] A. Strub, P. Chartier, G. Schleser, Energy from Biomass, Elsevier Applied Science, London, 1983. [3] P.T. Williams, N. Nugranad, Energy 25 (2000) 493. [4] D.C. Dayton, A Review of the Literature on Catalytic Biomass tar Destruction Report NREL/TP-510-32815, National Renewable Energy Laboratory, 2002. [5] S. Albertazzi, F. Basile, J. Brandin, J. Einvall, C. Hulteberg, G. Fornasari, V. Rosetti, M. Sanati, F. Trifiro, A. Vaccari, Catal. Today 106 (2005) 297. [6] A. Corti, L. Lombardi, Energy 29 (2004) 2109. [7] K. Stahl, M. Neergaard, Biomass Bioenergy 15 (1998) 205. [8] M. Rodrigues, A.P.C. Faaij, A. Walter, Energy 28 (2003) 1229. [9] R.H. Williams, E.D. Larson, Biomass Bioenergy 10 (1996) 149. [10] S. Rapagna, N. Jand, P.U. Foscolo, Int. J. Hydrogen Energy 23 (1998) 551. [11] C.N. Hamelinck, A.P.C. Faaij, J. Power Sources 111 (2002) 1. [12] D. Sutton, B. Kelleher, J.R.H. Ross, Biomass Bioenergy 23 (2002) 209. [13] M.J.A. Tijmensen, A.P.C. Faaij, C.N. Hamelinck, M.R.M. van Hardeveld, Biomass Bioenergy 23 (2002) 129. [14] A. Hirano, K. Hon-Nami, S. Kunito, M. Hada, Y. Ogushi, Catal. Today 45 (1998) 399. [15] M. Steinberg, Int. J. Hydrogen Energy 31 (2006) 405. [16] R. Gross, M. Leach, A. Bauen, Environ. Int. 29 (2003) 105. [17] L. Devi, K.J. Ptasinski, F.J.J.G. Janssen, Biomass Bioenergy 24 (2003) 125. [18] P. McKendry, Bioresour. Technol. 83 (2002) 47. [19] K.V. Lobachyov, H.J. Richter, Energy Conv. Manage. 39 (1998) 1931. [20] L. Devi, M. Craje, P. Thu¨ne, K.J. Ptasinski, F.J.J.G. Janssen, Appl. Catal. A: Gen. 294 (2005) 68. [21] P.T. Williams, P.A. Horne, J. Anal. Appl. Pyrol. 31 (1995) 15. [22] D. Sutton, B. Kelleher, J.R.H. Ross, Fuel Process. Technol. 73 (2001) 155. [23] M.L. Lee, M. Novotny, K.D. Bartle, Analytical Chemistry of Polycyclic Aromatic Compounds, Academic Press, New York, 1981. [24] S. Yaman, Energy Conv. Manage. 45 (2004) 651. [25] P.A. Horne, P.T. Williams, Fuel 75 (1996) 1051.
299
[26] P. McKendry, Bioresour. Technol. 83 (2002) 55. [27] S. Rapagna, H. Provendier, C. Petit, A. Kiennemann, P.U. Foscolo, Biomass Bioenergy 22 (2002) 377. [28] Y. Ohtsuka, K. Asami, Energy Fuels 9 (1996) 1038. [29] D.W. McKee, C.L. Spiro, P.G. Kosky, E.J. Lamby, Fuel 62 (1983) 217. [30] W.J. Lee, S.D. Kim, Fuel 74 (1995) 1387. [31] J.M. Encinar, F.J. Beltran, A. Ramiro, J.F. Gonzalez, Fuel Process. Technol. 55 (1998) 219. [32] D.C. Elliott, E.G. Baker, Biomass 9 (1986) 195. [33] A. Demirbas, Energy Conv. Manage. 43 (2002) 897. [34] D.M. Quyn, H. Wu, C.-Z. Li, Fuel 81 (2002) 143. [35] T. Takematsu, M.C., Coal Gasification for IGCC Power Generation, IEA Coal Research, London, 1991, p. 80. [36] C.-Z. Li, C. Sathe, J.R. Kershaw, Y. Pang, Fuel 79 (2000) 427. [37] P.A. Jensen, F.J. Frandsen, K. Dam-Johansen, B. Sander, Energy Fuels 14 (2000) 1280. [38] D.C. Dayton, R.J. French, T.A. Milne, Energy Fuels 9 (1995) 855. [39] C. Courson, E. Makaga, C. Petit, A. Kiennemann, Catal. Today 63 (2000) 427. [40] S.C. Tsang, J.B. Claridge, M.L.H. Green, Catal. Today 23 (1995) 3. [41] V.D. Belyaev, T.I. Politova, O.A. Mar’ina, V.A. Sobyanin, Appl. Catal. A: Gen. 133 (1995) 47. [42] F.J. Marino, E.G. Cerrella, S. Duhalde, M. Jobbagy, M.A. Laborde, Int. J. Hydrogen Energy 23 (1998) 1095. [43] S. Rapagna, N. Jand, C. Courson, C. Petit, A. Kiennemann, P.U. Foscolo (Eds.), Nickel based catalysts in the steam gasification of biomass, 1st World Conference on Biomass for Energy and Industry, Sevilla, Spain, James & James (Science Publishers) Ltd., 2000, p. 1646. [44] D. Wang, S. Czernik, E. Chornet, Energy Fuels 12 (1998) 19. [45] E.G. Baker, L.K. Mudge, M.D. Brown, Ind. Eng. Chem. Res. 26 (1987) 1335. [46] D. Sutton, B. Kelleher, A. Doyle, J.R.H. Ross, Bioresour. Technol. 80 (2001) 111. [47] A. Orio, J. Corella, I. Narvaez, in: A.V. Bridgwater, D.G.B. Boocock (Eds.), Developments in Thermochemical Biomass Conversion, Blackie Academic & Professional, 1997, p. 1144. [48] C. Ekstro¨m, N. Lindman, R. Pettersson, in: R.P. Overend, T.A. Milne, L.K. Mudge (Eds.), Fundamentals of Thermochemical Biomass Conversion, Elsevier Applied Science Publishers, New York, 1985, p. 601. [49] A. Olivares, M.P. Aznar, M.A. Caballero, J. Gil, E. Frances, J. Corella, Ind. Eng. Chem. Res. 36 (1997) 5220. [50] S. Rapagna, N. Jand, A. Kiennemann, P.U. Foscolo, Biomass Bioenergy 19 (2000) 187. [51] J. Corella, J.M. Toledo, R. Padilla, Energy and Fuels (2004), 18, 713. [52] A. Orio, J. Corella, I. Narvaez, Ind. Eng. Chem. Res. 36 (1997) 3800. [53] L. Devi, K.J. Ptasinski, F.J.J.G. Janssen, S.V.B. van Paasen, P.C.A. Bergman, J.H.A. Kiel, Renewable Energy 30 (2005) 565. [54] P.A. Simell, J.K. Leppalahti, J.B.-s. Bredenberg, Fuel 71 (1992) 211. [55] L. Devi, K.J. Ptasinski, F.J.J.G. Janssen, Fuel Process. Technol. 86 (2005) 707. [56] T. Nordgreen, T. Liliedahl, K. Sjostrom, Fuel 85 (2006) 689. [57] J. Yu, F.-J. Tian, M.C. Chow, L.J. McKenzie, C.-Z. Li, Fuel 85 (2006) 127. [58] K. Asami, P. Sears, E. Furimsky, Y. Ohtsuka, Fuel Process. Technol. 47 (1996) 139. [59] E.-J. Shin, M.R. Hajaligol, F. Rasouli, Fuel 83 (2004) 1445. [60] E.-J. Shin, D.E. Miser, W.G. Chan, M.R. Hajaligol, Appl. Catal. B: Environ. 61 (2005) 79. [61] O. Beaumont, Y. Schwob, Ind. Eng. Chem. Process Des. Dev. 23 (1984) 637. [62] G. Dobele, G. Rossinskaja, T. Dizhbite, G. Telysheva, D. Meier, O. Faix, J. Anal. Appl. Pyrol. 74 (2005) 401. [63] G. Domazetis, J. Liesegang, B.D. James, Fuel Process. Technol. 86 (2005) 463. [64] T. Hong-Xiao, W. Stumm, Water Res. 21 (1987) 115. [65] R.M. Cornell, U. Schwertmann, The Iron Oxides, VCH, New York, 1996. [66] G.B. Kolski, N.K. Kildahl, D.W. Margerum, Inorg. Chem. 8 (1969) 1211. [67] M.J. Hynes, M.O. Coinceanainn, J. Inorg. Biochem. 85 (2001) 131.
300
K. Bru et al. / J. Anal. Appl. Pyrolysis 78 (2007) 291–300
[68] P. Mammela, H. Savolainen, L. Lindroos, J. Kangas, T. Vartiainen, J. Chromatogr. A 891 (2000) 75. [69] R. Niemetz, G.G. Gross, Phytochemistry 66 (2005) 2001. [70] M. Roitto, P. Rautio, R. Julkunen-Tiitto, E. Kukkola, S. Huttunen, Environ. Pollut. 137 (2005) 603. [71] A.V. Bridgwater, D. Meier, D. Radlein, Org. Geochem. 30 (1999) 1479. [72] R. Zanzi, K. Sjostrom, E. Bjornbom, Fuel 75 (1996) 545. [73] P.T. Williams, P.A. Horne, J. Anal. Appl. Pyrol. 31 (1995) 39. [74] K. Raveendran, A. Ganesh, K.C. Khilar, Fuel 74 (1995) 1812. [75] K. Takehira, T. Shishido, P. Wang, T. Kosaka, K. Takaki, J. Catal. 221 (2004) 43. [76] A.I. Tsyganok, T. Tsunoda, S. Hamakawa, K. Suzuki, K. Takehira, T. Hayakawa, J. Catal. 213 (2003) 191. [77] M.-S. Liao, Q.-E. Zhang, J. Mol. Catal. A: Chem. 136 (1998) 185.
[78] Y. Wang, B.H. Davis, Appl. Catal. A: Gen. 180 (1999) 277. [79] M.W. Mu¨ller, W.R. Hoffmann, K.J. Hu¨ttinger, Fuel 74 (1995) 953. [80] P. Li, D.E. Miser, S. Rabiei, R.T. Yadav, M.R. Hajaligol, Appl. Catal. B: Environ. 43 (2003) 151. [81] G. Antonini, C. Porquet, P. Girard, French Patent 98-03744 (1998). [82] M.I. Nokkosmaki, E.T. Kuoppala, E.A. Leppamaki, A.O.I. Krause, J. Anal. Appl. Pyrol. 55 (2000) 119. [83] M. Kleen, G. Gellerstedt, J. Anal. Appl. Pyrol. 35 (1995) 15. [84] M. Muller-Hagedorn, H. Bockhorn, L. Krebs, U. Muller, J. Anal. Appl. Pyrol. 68–69 (2003) 231. [85] R. Coll, J. Salvado, X. Farriol, D. Montane, Fuel Process. Technol. 74 (2001) 19. [86] B. Dou, J. Gao, X. Sha, S.W. Baek, Appl. Therm. Eng. 23 (2003) 2229. [87] A.I. Afifi, E. Chornet, R.W. Thring, R.P. Overend, Fuel 75 (1996) 509.