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Yields of hydrogen-rich gaseous products via pyrolysis from selected biomass samples
Fuel 80 (2001) 1885±1891
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Yields of hydrogen-rich gaseous products via pyrolysis from selected biomass samples A. DemirbasË* PK 216, 61035 Trabzon, Turkey Received 28 November 2000; revised 5 March 2001; accepted 14 March 2001
Abstract Future energy technology will utilize hydrogen with an increasing trend in steady, as well as unsteady, combustion processes. Hydrogen is produced from fossil fuels, hydrocarbon polymers, biomass, and water by electrolysis and from biological process by photoliticaly or thermolysis. Hydrogen is produced from solid waste by pyrolysis. In this study, three different biomass samples were subjected to directand catalytic pyrolysis in order to obtain hydrogen-rich gaseous products at desired temperatures. The samples, both untreated and impregnated with catalyst, were pyrolysed at 770, 925, 975 and 1025 K temperatures. The total volume and the yield of gas from both pyrolysis were found to increase with increasing temperature. The largest hydrogen-rich gas yield were obtained from olive husk, cotton cocoon shell, and tea waste using about 13% ZnCl2 as catalyst at about 1025 K temperature were 70.3, 59.9, and 60.3%, respectively. In general, in the pyrolysis of biomass, the yield of hydrogen-rich gaseous product increases with ZnCl2 catalyst, but the yield of pyrolytic gas decreased in spite of increasing the yield of charcoal and liquid products. The effect of K2CO3 and Na2CO3 as catalysts on pyrolysis depends on the biomass species. The catalytic effect of Na2CO3 was greater than that of K2CO3 for the cotton cocoon shell and tea waste, but the catalytic effect of K2CO3 was greater for the olive husk. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Hydrogen-rich gas yield; Pyrolysis; Gaseous products; Biomass
Biomass is the fourth largest source of energy in the worldÐsupplying about 14% of primary energy [1,2]. Pyrolysis is the thermochemical process that converts biomass into liquid, charcoal and non-condensable gases, acetic acid, acetone, and methanol by heating the biomass to about 750 K in the absence of air [3,4]. In an earlier study [5], the future use of hydrogen as an attractive fuel and obtaining hydrogen from fossil and nonfossil energy sources was comprehensively investigated. Future energy technology will utilize hydrogen with an increasing trend in steady, as well as unsteady, combustion processes. Hydrogen can be produced from fossil fuels, hydrocarbon polymers, biomass by thermochemical conversion processes, from water by electrolysis, and from biological processes by photoliticaly or thermolysis. Hydrogen gas may be stored as a compressed gas or as a liquid. Hydrogen has good properties as a fuel for internal combustion engines in automobiles. In addition, hydrogen could be advantageously used as a clean energy carrier for heat supply and transportation purposes. Biomass gasi®cation offers the earliest and most econom* Tel.: 190-462-248-7429; fax: 190-462-248-7344. E-mail address: [email protected] (A. DemirbasË).
ical route for the production of renewable hydrogen. Partial oxidation of wood particles using pure oxygen in downdraft gasi®er was the basis for all calculations. Total hydrogen production was the sum of synthesis gas hydrogen plus hydrogen produced from synthesis gas carbon monoxide via the water gas shift reaction [6]. Hydrogen gas was produced on a pilot scale by steam gasi®cation of chared cellulosic waste material [7]. The gas was freed from moisture and carbon dioxide. The bene®cial effect of some inorganic salts such as chlorides, carbonates and chromates on the reaction rate and production cost of hydrogen gas was also investigated [8,10]. There are three base methods for production of hydrogen from biomass were reported previously [10]. These are: 1. production of hydrogen by pyrolysis of biomass; 2. production of hydrogen by catalytic steam gasi®cation of biomass; 3. production of hydrogen by air gasi®cation of biomass. Gasi®cation of solid wastes and sewage is a recent innovation. The synthesis gas formed with air or oxygen is reformed to hydrogen. The solid waste concept solves two problems: (1) disposal of urban refuse and sewage; and (2) a
0016-2361/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S 0016- 236 1( 01) 00070- 9
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A. DemirbasË / Fuel 80 (2001) 1885±1891
Table 1 Comparison of hydrogen yields were obtained by use of three different processes
Table 3 Yields of product from biomass samples to subjected pyrolysis at different temperatures (wt.% daf)
Processes
Temperature (K)
Yield of hydrogen Heating value of (wt.% of biomass) the product hydrogen/ heating value of the biomass a
Pyrolysis 1 catalytic 12.6 reforming Gasi®cation 1 shift reaction 11.5 Biomass 1 steam 1 except 17.1 heat (theoretical maximum) a
775 925 975
The energy ratio
1025
source of hydrogen fuel for hydrogen-powered vehicles [10,11]. Main gaseous products from biomass are [12]: Pyrolysis of biomass ! H2 1 CO2 1 CO 1 hydrocarbon gases
1
3
Steam reforming C1 ±C5 hydrocarbons, nafta, gas oils, and simple aromatics were commercially produced, well-known processes. Steam reforming of hydrocarbons; partial oxidation of heavy oil residues, selected steam reforming of aromatic compounds, and gasi®cation of coals and solid wastes to yield a mixture of syngas (H2 1 CO), followed by water-gas shift conversion to produce H2 and CO2, are well-established processes [13]. When the objective is to maximize the production of H2, the stoichiometry describing the overall process is given by: Cn Hm 1 2nH2 O ! nCO2 1 2n 1 m=2H2
Liquid
Gas
32.8 33.5 29.4 29.1 32.8 25.8 28.7 32.0 22.4 27.9 31.1 22.8
36.4 28.9 38.2 29.6 25.4 34.0 27.1 24.5 33.7 22.0 23.2 32.6
37.6 32.4 41.3 41.8 40.2 44.2 43.5 43.9 50.1 45.7 44.6
CH4 1 H2 O Y CO 1 3H2
6
CO 1 H2 O Y CO2 1 H2
7
Pyrolysis of solid waste ! H2 1 CO 1 CO2 1 Hydrocarbon gases 1 Tar 1 Charcoal
8
Biomass 1 H2 O 1 Air ! H2 1 CO2
9
Cellulose 1 H2 O 1 Air ! H2 1 CO 1 CH4
4
10
Hydrogen yields and its energy contents compared with biomass energy content were obtained from processes carry out to biomass and are shown in Table 1 [11]. The hydrogen yields obtained by use of these different processes is given in Table 1. In this work, conversion of ground biomass samples by
The simplicity of Eq. (4) hides the fact that, in a hydrocarbon reformer, the following reactions take place concurrently: Cn Hm 1 nH2 O Y nCO 1 n 1 m=2H2
Char
At normal reforming conditions, steam reforming of higher hydrocarbons (CnHm) is irreversible [Eq. (4)], whereas the methane reforming [Eq. (6)] and the shift reaction [Eq. (7)] reactions approach equilibrium. A large molar ratio of steam to hydrocarbon will ensure that the equilibrium for Eqs. (6) and (7) is shifted toward H2 production. Hydrogen from organic wastes has generally been based on following reactions:
Catalytic steam gasification of biomass ! H2 1 CO2 1 CO 2 Air gasification of biomass ! H2 1 CO2 1 CO 1 N2
Yields of product
Cotton cocoon shell Tea factory waste Olive husk Cotton cocoon shell Tea factory waste Olive husk Cotton cocoon shell Tea factory waste Olive husk Cotton cocoon shell Tea factory waste Olive husk
91 83 124
Biomass sample
5
Table 2 Structural and elemental compositions and higher heating values (HHVs, MJ kg 21) of biomass samples (wt.% of dry basis) Sample
Hemicelluloses cellulose lignin ash extractives a
C
H
O
N
HHV
Olive husk Cotton cocoon shell Tea factory waste
21.1 10.2 18.9
22.5 32.6 28.8
44.9 48.7 37.8
3.6 5.8 3.4
8.1 2.7 4.6
50.0 50.2 49.6
a
Acetone extractives.
6.2 5.8 5.1
42.2 42.7 42.6
1.6 1.3 2.7
19.0 18.3 17.1
A. DemirbasË / Fuel 80 (2001) 1885±1891
1887
Table 4 Yields of gaseous products from biomass samples subjected to pyrolysis at different temperatures (% by volume) Temperature (K)
775 925 975 1025
Biomass sample
Cotton cocoon shell Tea factory waste Olive husk Cotton cocoon shell Tea factory waste Olive husk Cotton cocoon shell Tea factory waste Olive husk Cotton cocoon shell Tea factory waste Olive husk
Yields of gaseous products CO
CO2
Olef®ns 1 O2
H2 1 paraf®ns
24.7 26.1 8.8 27.1 28.3 16.3 33.4 27.5 24.2 29.5 27.4 22.7
29.5 28.4 31.6 26.3 24.9 19.3 17.3 19.0 13.4 14.8 17.3 14.1
15.4 8.3 11.4 14.6 6.1 10.3 13.0 5.7 9.0 11.3 5.3 8.7
30.4 37.2 48.2 32.0 40.7 54.1 36.3 47.8 52.4 44.4 50.0 54.5
Table 5 Compositions of gaseous products from biomass samples catalytic subjected to pyrolysis by using different amounts of ZnCl2 (% by volume) Amount of catalyst (wt. %)
% 6.7 Cotton cocoon shell
Tea factory waste
Olive husk
% 10 Cotton cocoon shell
Tea factory waste
Olive husk
% 13.3 Cotton cocoon shell
Tea factory waste
Olive husk
Gaseous products
Temperature (K) 775
925
975
1025
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
21.6 26.8 5.2 46.4. 24.1 23.4 8.2 44.3 6.8 25.8 10.4 57.0
24.2 21.2 6.5 48.1 26.2 21.6 6.0 46.2 14.4 18.7 8.3 58.6
26.3 18.4 5.3 50.0 25.4 16.5 5.3 52.8 18.7 13.4 6.7 61.2
28.2 19.1 7.8 44.9 28.0 12.7 5.1 54.2 16.3 13.0 7.0 63.7
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
15.9 23.7 8.3 52.1 18.7 28.1 7.6 45.6 10.8 25.1 6.8 57.3
21.1 18.4 7.1 53.4 19.1 22.6 5.8 52.5 13.7 19.8 5.4 61.1
23.3 14.7 6.8 55.2 20.2 18.1 5.1 56.6 17.8 15.4 4.9 61.9
23.6 12.9 6.0 57.5 23.2 13.8 5.0 58.0 16.4 10.2 4.0 69.4
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
16.1 19.8 8.0 56.1 19.8 22.4 8.0 49.8 10.8 24.2 6.8 58.2
18.7 15.8 6.2 59.3 24.2 16.0 4.0 57.0 14.4 18.7 5.9 61.0
23.2 12.5 5.9 58.4 25.3 13.7 4.0 57.0 14.8 12.0 6.0 67.2
20.3 13.8 6.0 59.9 25.4 10.2 4.1 60.3 15.3 10.1 4.3 70.3
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A. DemirbasË / Fuel 80 (2001) 1885±1891
pyrolysis to hydrogen-rich gaseous products have been studied in the presence of catalyst additives with the temperature range of 775±1025 K. Our study is devoted to cotton cocoon shell, tea factory waste and olive husk pyrolysis, as selected Turkish biomass types. 1. Experimental The biomass samples (cotton cocoon shell, tea factory waste and olive husk) used were supplied from different areas in Turkey. Air-dried samples were milled and then screened, and only the fraction retained on the 0.063±0.150 mm sieve was used. The samples were extracted by using acetone before the pyrolysis. The structural and elemental composition and higher heating values (HHVs) of the biomass samples are given in Table 2. The experimental runs were performed in a device designed for pyrolysis. The main element of this device was a stainless-steel cylindrical reactor of height 127.0 mm, I.D. 17.0 mm and O.D. 25.0 mm vertically inserted into an electrically heated tubular furnace. A similar fast pyrolysis apparatus was depicted in our earlier study [14]. However, the present version included a changesample vessel in which the sample was placed in a stainless steel wire-mesh basket, hung on a metal rod, which could easily move vertically inside the reactor tube [15]. A simple thermo-couple (NiCr-constantan) was placed directly on top the sample, but not touching it. For each run, the heater was started at ambient temperature and switched off when the desired temperature was reached. Pyrolysis experiments were carried out at a heating rate of 2 K/s and at temperatures of 775, 925, 975 and 1025 K. For a non-catalytic or catalytic run, 1.5 g of the biomass sample was loaded into the cylindrical reactor. For Na2CO3 and K2CO3 catalytic runs, 0.10, 0.30, 0.50 and 0.70 g catalyst was used vs 1.5 g of the biomass sample. For ZnCl2 catalytic runs, 0.10, 0.15, 0.20 and 0.25 g catalyst were used vs 1.5 g of the biomass sample. Gaseous products to obtain from direct- and catalyticpyrolysis of the biomass samples were analyzed in Orsat and Elliot type gas analyzers. The gas samples were puri®ed by passing on MgSO4 pulverized glass wool. Soak time for the product gas was 15±20 min.
from catalytic pyrolysis of biomass samples at 975 K temperature are given in Table 6. Table 7 shows the compositions of gaseous products from catalytic pyrolysis of biomass samples by using different amounts of Na2CO3. Table 8 shows the compositions of gaseous products from catalytic pyrolysis of biomass samples by using different amounts of K2CO3. Table 9 shows the elementary compositions and yields of charcoals from hazelnut shell in relation to the carbonization temperature and their HHVs [16]. The total volume and the yield of gaseous obtained from direct- and catalytic-pyrolysis of the biomass samples increase with increasing pyrolysis temperature. The three different biomass samples (cotton cocoon shell, tea factory waste and olive husk) were subjected to directand catalytic-pyrolysis to obtain hydrogen-rich gaseous products at 775, 925, 975 and 1025 K. In a catalytic run, the catalyst (Na2CO3, K2CO3 or ZnCl2) was impregnated into the biomass sample before pyrolysis. As seen in Table 3, the yield of conversion of cotton cocoon shell, tea factory waste and olive husk to gaseous products increased from 36.4 to 50.1%, 37.6 to 43.7% and Table 6 Yields of product from biomass samples subjected to catalytic pyrolysis at 975 K temperature (% by weight) Catalyst
Na2CO3
Sample
Cotton cocoon shell Tea factory waste Olive husk
K2CO3
Cotton cocoon shell Tea factory waste Olive husk
Product
6.7
20
33
46.7
Char Liquid Gas Char Liquid Gas Char Liquid Gas
30.2 25.7 44.1 30.3 29.7 40.0 25.8 38.0 36.2
30.0 27.7 42.3 28.3 29.7 42.6 21.6 44.8 33.6
29.4 26.5 44.1 27.1 29.3 43.6 18.9 43.4 37.7
27.8 24.6 47.6 26.4 27.3 46.3 17.8 41.5 40.7
Char Liquid Gas Char Liquid Gas Char Liquid Gas
31.4 20.8 47.8 29.8 25.7 44.5 28.4 33.8 37.8
28.5 25.4 46.1 27.4 25.6 47.0 25.6 35.2 39.4
26.9 25.2 47.9 26.0 26.2 47.8 20.7 39.2 40.1
25.3 23.9 50.8 25.2 25.1 49.7 18.9 38.0 43.1
6.7
10
13.3
16.7
32.4 22.5 45.1 34.4 26.4 39.2 29.8 39.6 30.6
34.2 26.8 39.0 35.3 24.0 40.7 26.5 41.8 31.7
35.1 27.7 37.2 35.8 24.4 39.8 24.9 43.5 31.6
35.8 28.0 36.2 36.1 24.7 39.2 24.1 44.0 31.9
ZnCl2
2. Results and discussion Table 3 shows the yields of product from the biomass samples subjected to pyrolysis at different temperatures. The yields of gaseous products from the biomass samples subjected to pyrolysis at different temperatures are shown in Table 4. Table 5 shows the compositions of gaseous products from catalytic pyrolysis of biomass samples by using different amounts of ZnCl2. The yields of product
Cotton cocoon shell Tea factory waste Olive husk
Amount of catalyst (wt.% of the sample)
Char Liquid Gas Char Liquid Gas Char Liquid Gas
A. DemirbasË / Fuel 80 (2001) 1885±1891
1889
Table 7 Compositions of gaseous products from biomass samples subjected to catalytic pyrolysis by using different amounts of Na2CO3 (% by volume)
Table 8 Compositions of gaseous products biomass samples subjected to catalytic pyrolysis by using different amounts of K2CO3 (% by volume)
Amount of catalyst (wt.%) Gaseous products Temperature (K)
Amount of catalyst (wt.%) Gaseous products Temperature (K)
% 6.7 Cotton cocoon shell
Tea factory waste
Olive husk
% 20 Cotton cocoon shell
Tea factory waste
Olive husk
% 33.3 Cotton cocoon shell
Tea factory waste
Olive husk
% 46.7 Cotton cocoon shell
Tea factory waste
Olive husk
775
925
975
1025
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
25.1 27.6 14.8 33.3 24.1 26.5 7.8 41.6 7.1 35.2 10.7 47.0
29.0 25.8 11.4 33.8 30.0 23.3 6.3 40.4 13.0 21.8 9.9 55.3
29.2 19.3 11.0 41.5 27.8 19.1 6.6 46.5 19.4 14.3 8.1 58.2
26.4 18.7 10.4 44.5 28.9 17.0 6.0 48.1 21.3 13.7 8.0 57.0
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
23.2 29.5 12.4 34.9 16.9 27.5 7.6 48.0 7.8 33.6 12.4 46.2
22.8 24.2 10.8 42.2 18.7 22.4 6.5 52.4 14.3 24.6 10.3 49.0
29.2 18.4 11.0 50.2 23.4 20.5 5.8 50.3 22.8 15.8 8.9 53.5
24.4 17.1 10.4 49.3 23.3 16.5 5.0 55.2 18.3 16.0 7.1 58.6
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
23.6 25.4 9.8 41.2 18.5 27.4 7.9 46.2 9.3 34.1 8.6 48.0
24.3 20.4 9.8 44.5 21.2 21.4 6.0 51.4 15.3 24.8 7.8 51.9
26.0 17.1 9.1 47.8 22.1 18.5 5.3 54.1 18.7 13.4 8.1 60.8
25.3 14.8 9.2 50.7 20.9 15.3 4.1 59.7 17.6 12.5 7.1 62.9
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
17.5 21.2 10.4 50.9 14.8 26.1 6.1 53.0 10.8 32.4 8.6 48.2
24.2 20.4 9.8 45.6 15.1 23.2 5.3 56.4 16.4 26.8 7.5 49.3
28.1 19.3 7.9 45.7 16.4 20.1 5.9 57.6 22.9 18.6 8.0 50.5
29.4 17.0 8.1 45.5 18.1 18.8 6.0 57.1 21.8 16.0 6.2 56.0
32.4 to 44.6%, respectively, while the ®nal pyrolysis temperature was increased from 775 to 1025 K. In general, total hydrogen-rich gaseous products increased with increasing pyrolysis temperature for each biomass sample (Table 4).
% 6.7 Cotton cocoon shell
Tea factory waste
Olive husk
% 20 Cotton cocoon shell
Tea factory waste
Olive husk
% 33.3 Cotton cocoon shell
Tea factory waste
Olive husk
% 46.7 Cotton cocoon shell
Tea factory waste
Olive husk
775
925
975
1025
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
23.8 27.1 10.3 40.8 20.3 28.4 8.8 42.5 13.4 29.5 8.6 48.5
22.9 25.3 8.4 43.4 25.6 20.1 6.5 47.8 10.5 21.7 6.5 51.3
25.8 20.1 7.9 45.7 26.0 21.8 6.5 45.7 24.3 16.8 5.7 53.2
27.0 19.4 7.9 45.7 28.8 16.4 5.9 48.9 19.8 12.3 6.2 61.7
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
24.5 21.0 8.4 46.1 20.3 27.6 6.8 45.3 6.5 34.8 9.1 49.6
26.8 24.6 6.6 42.0 23.4 21.7 5.4 49.5 15.4 22.6 8.7 53.3
26.3 19.0 7.0 47.7 25.1 22.6 4.7 47.6 19.7 14.5 9.0 58.8
24.5 15.4 7.6 52.5 27.3 18.1 5.2 49.4 18.9 13.0 8.2 59.9
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
23.4 26.3 7.3 43.0 16.7 31.6 7.9 43.8 9.8 35.6 8.6 46.0
24.2 22.1 6.5 47.2 18.5 22.4 6.0 53.1 16.4 24.3 7.9 51.4
24.3 16.3 6.8 52.6 22.5 23.8 5.5 48.2 19.7 15.2 7.0 59.1
26.2 15.7 6.2 51.9 26.1 20.2 5.2 48.5 18.8 12.8 5.8 62.6
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
22.0 23.2 6.6 48.2 15.9 24.8 9.4 49.9 12.8 31.6 8.4 47.2
27.1 22.4 5.4 45.1 17.1 20.5 7.2 55.2 16.4 29.8 6.3 47.5
30.0 19.3 5.7 45.0 20.5 22.1 6.5 50.9 19.8 18.4 6.0 55.8
29.7 17.8 5.2 47.3 23.8 20.6 5.0 50.6 19.8 16.3 6.5 57.4
The largest hydrogen-rich gas yield obtained from olive husk, cotton cocoon shell, and tea waste using about 13% ZnCl2 as catalyst at about 1025 K temperature are 70.3, 59.9 and 60.3%, respectively (Table 5). In general, in the pyrolysis of biomass, the yield of
A. DemirbasË / Fuel 80 (2001) 1885±1891
Table 9 Elementary compositions and yields of charcoals from hazelnut shell in relation to the carbonization temperature and their HHVs (source: Ref. [15]) Carbonization temperature (K)
C (%)
H (%)
O (%)
Yield (%)
HHV (kJ/kg)
295±470 295±550 295±650 295±750 295±850 295±950 295±1050
53.3 75.0 82.3 88.4 92.5 94.3 95.7
6.1 5.5 3.6 2.4 1.9 1.5 1.3
40.6 19.5 14.1 8.6 6.0 4.2 3.1
90.8 42.6 38.1 35.0 32.2 31.1 30.7
19846 28714 29140 29665 31041 31464 32008
hydrogen-rich gaseous product increases with ZnCl2 catalyst (Table 5), but the yield of pyrolytic gas decreases in spite of increasing the yield of charcoal and liquid products (Table 6). The effect of K2CO3 and Na2CO3 as catalysts on pyrolysis depends on the biomass species. The catalytic effect of Na2CO3 was greater than that of K2CO3 for the cotton cocoon shell and tea factory waste but the catalytic effect of K2CO3 was greater for the olive husk (Table 6). As seen in Table 6, the yield of gaseous products from olive husk increased from 37.8 to 43.1%, while the percentage of K2CO3 was increased from 6.7 to 46.7%. The effect of amount of alkali (Na2CO3 and K2CO3) on the pyrolysis products are given in Tables 7 and 8. The effect of amount of alkali (Na2CO3 and K2CO3) on the pyrolysis products is irregular. The maximum yields of hydrogen-rich gaseous products from olive husk of 62.9 and 62.6% were obtained in the presence Na2CO3 and K2CO3 (30.0% of the sample) at the ®nal pyrolysis temperature of
54
52 (H2 + Paraffins) gaseous products, % by volume
1890
50
48
46
44
Temperature (K) : : 775 : 850 : 925 : 975 : 1025
42
40
38 0
10
20
30
40
50
Catalyst (K2CO3), wt. % of the sample
Fig. 2. The effect of amount of K2CO3 catalyst on the yield of (H2 1 paraf®ns) at different temperatures (sample: cotton cocoon shell).
1025 K, respectively. Alkalis such as K2CO3 prevent the formation of stable chemical structures and also by an oxygen-transfer mechanism they weaken the C±C bond, thereby decreasing the activation energy for the complex pyrolysis reaction [17]. It can be assumed that the alkali causes weakening of the intermolecular interaction of the polymeric chains and, at the same time, catalyzes not only intralink dehydration but promotes the processes of 64 62 (H2 + Paraffins) gaseous products, % by volume
(H2 + Paraffins) gaseous products, % by volume
55
50
45
Temperature (K) : : 775 : 850 : 925 : 975 : 1025
40
35
60 58 56 54
Temperature (K) : : 775 : 850 : 925 : 975 : 1025
52 50 48 46 44
30
6 0
10
20
30
40
8
10
12
14
16
18
50
Catalyst (Na2CO3), wt. % of the sample
Fig. 1. The effect of amount of Na2CO3 catalyst on the yield of (H2 1 paraf®ns) at different temperatures (sample: cotton cocoon shell).
Catalyst (Zn2Cl), wt. % of the sample
Fig. 3. The effect of amount of ZnCl2 catalyst on the yield of (H2 1 paraf®ns) at different temperatures (sample: cotton cocoon shell).
A. DemirbasË / Fuel 80 (2001) 1885±1891 Table 10 Average chemical composition of gaseous products from the precipitate of black liquor at different temperatures (source: Ref. [9]) Temperature (K)
295±675 295±825 295±825 a 295±925 295±925 a a
Gas composition (% by volume) H2
CO
CO2
CH4
11.3 ^ 0.9 14.1 ^ 0.8 31.7 ^ 1.9 18.4 ^ 0.5 36.4 ^ 0.7
29.0 ^ 0.8 40.8 ^ 0.5 18.7 ^ 0.7 36.0 ^ 0.4 14.6 ^ 0.3
26.5 ^ 0.4 19.9 ^ 0.4 30.1 ^ 0.6 15.9 ^ 0.5 32.3 ^ 0.6
13.1 ^ 0.7 12.7 ^ 0.6 8.5 ^ 0.3 14.7 ^ 1.1 9.9 ^ 0.4
Three percent K2CO3 of the samples used as catalyst.
retroaldol cleavage and condensation of the products produced [18]. The effect of amount of catalysts (Na2CO3, K2CO3 and ZnCl2) on the yield of (H2 1 paraf®ns) at different temperatures are given in Figs. 1±3, respectively. As seen in Figs. 1 and 2, the effects of amount of alkali catalysts (Na2CO3 and K2CO3) on the yield of (H2 1 paraf®ns) at different temperatures (for Na2CO3 at 925 and 1025 K runs; for K2CO3 at 775, 925, 975 and 1050 K runs) are generally irregular. In low temperature pyrolysis runs, especially at 775 K run, the yield of hydrogen-rich gaseous product increases with amount of Na2CO3 catalyst (Fig. 1). The yield of hydrogen-rich gaseous product increases with percent of ZnCl2 catalyst in all pyrolysis runs (Fig. 3). Increasing the temperature from 470 to 1050 K, the hydrogen content of charcoal from the hazelnut shell decreased from 6.1 to 1.3%, respectively (Table 9). Table 10 shows the average chemical composition of gaseous products from the precipitate of black liquor at different temperatures [9]. In K2CO3 catalytic runs, H2 yields from the black liquor samples were 31.7 at 825 K and 36.4% at 925 K (Table 10). Many investigators studying of pyrolysis of various types of lignocellulosic materials have found it rather dif®cult to study each pyrolysis reaction separately [17,19±21]. The application of thermal analysis techniques does not provide accurate identi®cation and de®nition of the individual reaction. Since the pyrolysis step consists of many concurrent and consecutive reactions, it is virtually impossible to identify all the elementary chemical reactions, which occur when the olive husk thermally decomposed. It is believed that as the reaction progresses the carbonaceous material becomes less reactive and forms stable chemical structures, and consequently the activation energy increases as the conversion level of olive husk increases.
1891
oxygen about 10±13%, at atmospheric pressure and a pyrolysis temperature of approximately 670±770 K has been shown [22]. Under conditions of rapid heating, the water present in the mixture can undergo bulk evaporation causing severe foaming. Hydrogen gas can be produced from the waste material by direct- and catalytic pyrolysis, while the ®nal pyrolysis temperature was generally increased from 775 to 1025 K. The powdered K2CO2 catalyst (1±3 wt.% of moisture-free biomass) used in the catalytic gasi®cation runs was mixed with the biomass in the reaction chamber [23]. The catalyst shows destructive effect on the organic compounds and H2 and CO2 form end of the steam gasi®cation (catalytic steam reforming) process. The yield of CO from pyrolysis of the waste materials, all pyrolysis runs, the total yield of combustible gases increase with increasing pyrolysis temperature for the samples. The catalytic effect of Na2CO3 was greater than that of K2CO3 for the cotton cocoon shell, especially for low temperature pyrolysis runs. The maximum conversion yield of cotton cocoon shell to hydrogen-rich gaseous products (H2 1 Paraf®ns) for ZnCl2, Na2CO3 and K2CO3 catalytic runs were 22.5, 25.6, and 27.0% by weight, respectively. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
[15] [16] [17] [18] [19]
3. Conclusion
[20]
The main aim of pyrolysis is to obtain liquid and gaseous products from biomass. The possibility of obtaining the wood's oil with the yield to 13% mass, with contained
[21] [22] [23]
DemirbasË A. Energy Educ Sci Technol 2000;5:21. DemirbasË A. Energy Educ Sci Technol 2000;6:19. DemirbasË A, GuÈlluÈ D. Energy Educ Sci Technol 1998;1:111. DemirbasË A. Energy Educ Sci Technol 1998;2:23. È zmen H. Energy Educ. Sci Technol 2000;6:1. C Ë agÆlar A, O Mckinley KR, Browne SH, Neill DR, Seki A, Takahashi PK. Energy Sources 1990;12:105. DemirbasË A, C Ë agÆlar A. Energy Educ Sci Technol 1998;1:45. Hellar A. Science 1984;233:1141. Rabah MA, Eldighidy SM, Int J. Hydrogen Energy 1989;14:221. DemirbasË A, KarsliogÆlu S, Ayas A. Fuel Science and Technology Int'l 1996;14:451. VezirogÆlu TN. Hydrogen energy, part A. New York: Plenum, 1975. Wang D, Czernik S, Montane D, Mann M, Chornet E. Ind Eng Chem Res 1997;36:1507. Duprez D. Appl Catal A 1992;82:111. C Ë agÆlar A. Obtaining of hydrogen rich gaseous products from biomass samples by direct pyrolysis and catalytic pyrolysis processes, investigating of effects of catalyst on the yield of products. PhD Dissertation, Karadeniz Technical University, Trabzon, 2000. DemirbasË A. Energy 1999;24:141. DemirbasË A. Bioresources Technology 1998;66:247. Tran DQ, Rai C. Fuel 1978;57:293. Rustamov VR, Abdullayev KM, Samedov EA. Energy Convers Mgmt 1998;39:869. Maschio G, Koufopanos C, Lucchesi A. Bioresource Technology 1992;42:219. Bingyan X, Chuangzi W, Zhengfen L, Xiguang Z. Solar Energy 1992;49:199. Sha®zadeh F. Adv Carbohydrate Chem 1968;23:419. DemirbasË A, C Ë aglar A. Energy Convers Mgmt 2000;41:1749. Backman R, Frederick WJ, Hupa M. Bioresource Technol 1993;46:153.
www.fuel®rst.com
Yields of hydrogen-rich gaseous products via pyrolysis from selected biomass samples A. DemirbasË* PK 216, 61035 Trabzon, Turkey Received 28 November 2000; revised 5 March 2001; accepted 14 March 2001
Abstract Future energy technology will utilize hydrogen with an increasing trend in steady, as well as unsteady, combustion processes. Hydrogen is produced from fossil fuels, hydrocarbon polymers, biomass, and water by electrolysis and from biological process by photoliticaly or thermolysis. Hydrogen is produced from solid waste by pyrolysis. In this study, three different biomass samples were subjected to directand catalytic pyrolysis in order to obtain hydrogen-rich gaseous products at desired temperatures. The samples, both untreated and impregnated with catalyst, were pyrolysed at 770, 925, 975 and 1025 K temperatures. The total volume and the yield of gas from both pyrolysis were found to increase with increasing temperature. The largest hydrogen-rich gas yield were obtained from olive husk, cotton cocoon shell, and tea waste using about 13% ZnCl2 as catalyst at about 1025 K temperature were 70.3, 59.9, and 60.3%, respectively. In general, in the pyrolysis of biomass, the yield of hydrogen-rich gaseous product increases with ZnCl2 catalyst, but the yield of pyrolytic gas decreased in spite of increasing the yield of charcoal and liquid products. The effect of K2CO3 and Na2CO3 as catalysts on pyrolysis depends on the biomass species. The catalytic effect of Na2CO3 was greater than that of K2CO3 for the cotton cocoon shell and tea waste, but the catalytic effect of K2CO3 was greater for the olive husk. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Hydrogen-rich gas yield; Pyrolysis; Gaseous products; Biomass
Biomass is the fourth largest source of energy in the worldÐsupplying about 14% of primary energy [1,2]. Pyrolysis is the thermochemical process that converts biomass into liquid, charcoal and non-condensable gases, acetic acid, acetone, and methanol by heating the biomass to about 750 K in the absence of air [3,4]. In an earlier study [5], the future use of hydrogen as an attractive fuel and obtaining hydrogen from fossil and nonfossil energy sources was comprehensively investigated. Future energy technology will utilize hydrogen with an increasing trend in steady, as well as unsteady, combustion processes. Hydrogen can be produced from fossil fuels, hydrocarbon polymers, biomass by thermochemical conversion processes, from water by electrolysis, and from biological processes by photoliticaly or thermolysis. Hydrogen gas may be stored as a compressed gas or as a liquid. Hydrogen has good properties as a fuel for internal combustion engines in automobiles. In addition, hydrogen could be advantageously used as a clean energy carrier for heat supply and transportation purposes. Biomass gasi®cation offers the earliest and most econom* Tel.: 190-462-248-7429; fax: 190-462-248-7344. E-mail address: [email protected] (A. DemirbasË).
ical route for the production of renewable hydrogen. Partial oxidation of wood particles using pure oxygen in downdraft gasi®er was the basis for all calculations. Total hydrogen production was the sum of synthesis gas hydrogen plus hydrogen produced from synthesis gas carbon monoxide via the water gas shift reaction [6]. Hydrogen gas was produced on a pilot scale by steam gasi®cation of chared cellulosic waste material [7]. The gas was freed from moisture and carbon dioxide. The bene®cial effect of some inorganic salts such as chlorides, carbonates and chromates on the reaction rate and production cost of hydrogen gas was also investigated [8,10]. There are three base methods for production of hydrogen from biomass were reported previously [10]. These are: 1. production of hydrogen by pyrolysis of biomass; 2. production of hydrogen by catalytic steam gasi®cation of biomass; 3. production of hydrogen by air gasi®cation of biomass. Gasi®cation of solid wastes and sewage is a recent innovation. The synthesis gas formed with air or oxygen is reformed to hydrogen. The solid waste concept solves two problems: (1) disposal of urban refuse and sewage; and (2) a
0016-2361/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S 0016- 236 1( 01) 00070- 9
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A. DemirbasË / Fuel 80 (2001) 1885±1891
Table 1 Comparison of hydrogen yields were obtained by use of three different processes
Table 3 Yields of product from biomass samples to subjected pyrolysis at different temperatures (wt.% daf)
Processes
Temperature (K)
Yield of hydrogen Heating value of (wt.% of biomass) the product hydrogen/ heating value of the biomass a
Pyrolysis 1 catalytic 12.6 reforming Gasi®cation 1 shift reaction 11.5 Biomass 1 steam 1 except 17.1 heat (theoretical maximum) a
775 925 975
The energy ratio
1025
source of hydrogen fuel for hydrogen-powered vehicles [10,11]. Main gaseous products from biomass are [12]: Pyrolysis of biomass ! H2 1 CO2 1 CO 1 hydrocarbon gases
1
3
Steam reforming C1 ±C5 hydrocarbons, nafta, gas oils, and simple aromatics were commercially produced, well-known processes. Steam reforming of hydrocarbons; partial oxidation of heavy oil residues, selected steam reforming of aromatic compounds, and gasi®cation of coals and solid wastes to yield a mixture of syngas (H2 1 CO), followed by water-gas shift conversion to produce H2 and CO2, are well-established processes [13]. When the objective is to maximize the production of H2, the stoichiometry describing the overall process is given by: Cn Hm 1 2nH2 O ! nCO2 1 2n 1 m=2H2
Liquid
Gas
32.8 33.5 29.4 29.1 32.8 25.8 28.7 32.0 22.4 27.9 31.1 22.8
36.4 28.9 38.2 29.6 25.4 34.0 27.1 24.5 33.7 22.0 23.2 32.6
37.6 32.4 41.3 41.8 40.2 44.2 43.5 43.9 50.1 45.7 44.6
CH4 1 H2 O Y CO 1 3H2
6
CO 1 H2 O Y CO2 1 H2
7
Pyrolysis of solid waste ! H2 1 CO 1 CO2 1 Hydrocarbon gases 1 Tar 1 Charcoal
8
Biomass 1 H2 O 1 Air ! H2 1 CO2
9
Cellulose 1 H2 O 1 Air ! H2 1 CO 1 CH4
4
10
Hydrogen yields and its energy contents compared with biomass energy content were obtained from processes carry out to biomass and are shown in Table 1 [11]. The hydrogen yields obtained by use of these different processes is given in Table 1. In this work, conversion of ground biomass samples by
The simplicity of Eq. (4) hides the fact that, in a hydrocarbon reformer, the following reactions take place concurrently: Cn Hm 1 nH2 O Y nCO 1 n 1 m=2H2
Char
At normal reforming conditions, steam reforming of higher hydrocarbons (CnHm) is irreversible [Eq. (4)], whereas the methane reforming [Eq. (6)] and the shift reaction [Eq. (7)] reactions approach equilibrium. A large molar ratio of steam to hydrocarbon will ensure that the equilibrium for Eqs. (6) and (7) is shifted toward H2 production. Hydrogen from organic wastes has generally been based on following reactions:
Catalytic steam gasification of biomass ! H2 1 CO2 1 CO 2 Air gasification of biomass ! H2 1 CO2 1 CO 1 N2
Yields of product
Cotton cocoon shell Tea factory waste Olive husk Cotton cocoon shell Tea factory waste Olive husk Cotton cocoon shell Tea factory waste Olive husk Cotton cocoon shell Tea factory waste Olive husk
91 83 124
Biomass sample
5
Table 2 Structural and elemental compositions and higher heating values (HHVs, MJ kg 21) of biomass samples (wt.% of dry basis) Sample
Hemicelluloses cellulose lignin ash extractives a
C
H
O
N
HHV
Olive husk Cotton cocoon shell Tea factory waste
21.1 10.2 18.9
22.5 32.6 28.8
44.9 48.7 37.8
3.6 5.8 3.4
8.1 2.7 4.6
50.0 50.2 49.6
a
Acetone extractives.
6.2 5.8 5.1
42.2 42.7 42.6
1.6 1.3 2.7
19.0 18.3 17.1
A. DemirbasË / Fuel 80 (2001) 1885±1891
1887
Table 4 Yields of gaseous products from biomass samples subjected to pyrolysis at different temperatures (% by volume) Temperature (K)
775 925 975 1025
Biomass sample
Cotton cocoon shell Tea factory waste Olive husk Cotton cocoon shell Tea factory waste Olive husk Cotton cocoon shell Tea factory waste Olive husk Cotton cocoon shell Tea factory waste Olive husk
Yields of gaseous products CO
CO2
Olef®ns 1 O2
H2 1 paraf®ns
24.7 26.1 8.8 27.1 28.3 16.3 33.4 27.5 24.2 29.5 27.4 22.7
29.5 28.4 31.6 26.3 24.9 19.3 17.3 19.0 13.4 14.8 17.3 14.1
15.4 8.3 11.4 14.6 6.1 10.3 13.0 5.7 9.0 11.3 5.3 8.7
30.4 37.2 48.2 32.0 40.7 54.1 36.3 47.8 52.4 44.4 50.0 54.5
Table 5 Compositions of gaseous products from biomass samples catalytic subjected to pyrolysis by using different amounts of ZnCl2 (% by volume) Amount of catalyst (wt. %)
% 6.7 Cotton cocoon shell
Tea factory waste
Olive husk
% 10 Cotton cocoon shell
Tea factory waste
Olive husk
% 13.3 Cotton cocoon shell
Tea factory waste
Olive husk
Gaseous products
Temperature (K) 775
925
975
1025
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
21.6 26.8 5.2 46.4. 24.1 23.4 8.2 44.3 6.8 25.8 10.4 57.0
24.2 21.2 6.5 48.1 26.2 21.6 6.0 46.2 14.4 18.7 8.3 58.6
26.3 18.4 5.3 50.0 25.4 16.5 5.3 52.8 18.7 13.4 6.7 61.2
28.2 19.1 7.8 44.9 28.0 12.7 5.1 54.2 16.3 13.0 7.0 63.7
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
15.9 23.7 8.3 52.1 18.7 28.1 7.6 45.6 10.8 25.1 6.8 57.3
21.1 18.4 7.1 53.4 19.1 22.6 5.8 52.5 13.7 19.8 5.4 61.1
23.3 14.7 6.8 55.2 20.2 18.1 5.1 56.6 17.8 15.4 4.9 61.9
23.6 12.9 6.0 57.5 23.2 13.8 5.0 58.0 16.4 10.2 4.0 69.4
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
16.1 19.8 8.0 56.1 19.8 22.4 8.0 49.8 10.8 24.2 6.8 58.2
18.7 15.8 6.2 59.3 24.2 16.0 4.0 57.0 14.4 18.7 5.9 61.0
23.2 12.5 5.9 58.4 25.3 13.7 4.0 57.0 14.8 12.0 6.0 67.2
20.3 13.8 6.0 59.9 25.4 10.2 4.1 60.3 15.3 10.1 4.3 70.3
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A. DemirbasË / Fuel 80 (2001) 1885±1891
pyrolysis to hydrogen-rich gaseous products have been studied in the presence of catalyst additives with the temperature range of 775±1025 K. Our study is devoted to cotton cocoon shell, tea factory waste and olive husk pyrolysis, as selected Turkish biomass types. 1. Experimental The biomass samples (cotton cocoon shell, tea factory waste and olive husk) used were supplied from different areas in Turkey. Air-dried samples were milled and then screened, and only the fraction retained on the 0.063±0.150 mm sieve was used. The samples were extracted by using acetone before the pyrolysis. The structural and elemental composition and higher heating values (HHVs) of the biomass samples are given in Table 2. The experimental runs were performed in a device designed for pyrolysis. The main element of this device was a stainless-steel cylindrical reactor of height 127.0 mm, I.D. 17.0 mm and O.D. 25.0 mm vertically inserted into an electrically heated tubular furnace. A similar fast pyrolysis apparatus was depicted in our earlier study [14]. However, the present version included a changesample vessel in which the sample was placed in a stainless steel wire-mesh basket, hung on a metal rod, which could easily move vertically inside the reactor tube [15]. A simple thermo-couple (NiCr-constantan) was placed directly on top the sample, but not touching it. For each run, the heater was started at ambient temperature and switched off when the desired temperature was reached. Pyrolysis experiments were carried out at a heating rate of 2 K/s and at temperatures of 775, 925, 975 and 1025 K. For a non-catalytic or catalytic run, 1.5 g of the biomass sample was loaded into the cylindrical reactor. For Na2CO3 and K2CO3 catalytic runs, 0.10, 0.30, 0.50 and 0.70 g catalyst was used vs 1.5 g of the biomass sample. For ZnCl2 catalytic runs, 0.10, 0.15, 0.20 and 0.25 g catalyst were used vs 1.5 g of the biomass sample. Gaseous products to obtain from direct- and catalyticpyrolysis of the biomass samples were analyzed in Orsat and Elliot type gas analyzers. The gas samples were puri®ed by passing on MgSO4 pulverized glass wool. Soak time for the product gas was 15±20 min.
from catalytic pyrolysis of biomass samples at 975 K temperature are given in Table 6. Table 7 shows the compositions of gaseous products from catalytic pyrolysis of biomass samples by using different amounts of Na2CO3. Table 8 shows the compositions of gaseous products from catalytic pyrolysis of biomass samples by using different amounts of K2CO3. Table 9 shows the elementary compositions and yields of charcoals from hazelnut shell in relation to the carbonization temperature and their HHVs [16]. The total volume and the yield of gaseous obtained from direct- and catalytic-pyrolysis of the biomass samples increase with increasing pyrolysis temperature. The three different biomass samples (cotton cocoon shell, tea factory waste and olive husk) were subjected to directand catalytic-pyrolysis to obtain hydrogen-rich gaseous products at 775, 925, 975 and 1025 K. In a catalytic run, the catalyst (Na2CO3, K2CO3 or ZnCl2) was impregnated into the biomass sample before pyrolysis. As seen in Table 3, the yield of conversion of cotton cocoon shell, tea factory waste and olive husk to gaseous products increased from 36.4 to 50.1%, 37.6 to 43.7% and Table 6 Yields of product from biomass samples subjected to catalytic pyrolysis at 975 K temperature (% by weight) Catalyst
Na2CO3
Sample
Cotton cocoon shell Tea factory waste Olive husk
K2CO3
Cotton cocoon shell Tea factory waste Olive husk
Product
6.7
20
33
46.7
Char Liquid Gas Char Liquid Gas Char Liquid Gas
30.2 25.7 44.1 30.3 29.7 40.0 25.8 38.0 36.2
30.0 27.7 42.3 28.3 29.7 42.6 21.6 44.8 33.6
29.4 26.5 44.1 27.1 29.3 43.6 18.9 43.4 37.7
27.8 24.6 47.6 26.4 27.3 46.3 17.8 41.5 40.7
Char Liquid Gas Char Liquid Gas Char Liquid Gas
31.4 20.8 47.8 29.8 25.7 44.5 28.4 33.8 37.8
28.5 25.4 46.1 27.4 25.6 47.0 25.6 35.2 39.4
26.9 25.2 47.9 26.0 26.2 47.8 20.7 39.2 40.1
25.3 23.9 50.8 25.2 25.1 49.7 18.9 38.0 43.1
6.7
10
13.3
16.7
32.4 22.5 45.1 34.4 26.4 39.2 29.8 39.6 30.6
34.2 26.8 39.0 35.3 24.0 40.7 26.5 41.8 31.7
35.1 27.7 37.2 35.8 24.4 39.8 24.9 43.5 31.6
35.8 28.0 36.2 36.1 24.7 39.2 24.1 44.0 31.9
ZnCl2
2. Results and discussion Table 3 shows the yields of product from the biomass samples subjected to pyrolysis at different temperatures. The yields of gaseous products from the biomass samples subjected to pyrolysis at different temperatures are shown in Table 4. Table 5 shows the compositions of gaseous products from catalytic pyrolysis of biomass samples by using different amounts of ZnCl2. The yields of product
Cotton cocoon shell Tea factory waste Olive husk
Amount of catalyst (wt.% of the sample)
Char Liquid Gas Char Liquid Gas Char Liquid Gas
A. DemirbasË / Fuel 80 (2001) 1885±1891
1889
Table 7 Compositions of gaseous products from biomass samples subjected to catalytic pyrolysis by using different amounts of Na2CO3 (% by volume)
Table 8 Compositions of gaseous products biomass samples subjected to catalytic pyrolysis by using different amounts of K2CO3 (% by volume)
Amount of catalyst (wt.%) Gaseous products Temperature (K)
Amount of catalyst (wt.%) Gaseous products Temperature (K)
% 6.7 Cotton cocoon shell
Tea factory waste
Olive husk
% 20 Cotton cocoon shell
Tea factory waste
Olive husk
% 33.3 Cotton cocoon shell
Tea factory waste
Olive husk
% 46.7 Cotton cocoon shell
Tea factory waste
Olive husk
775
925
975
1025
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
25.1 27.6 14.8 33.3 24.1 26.5 7.8 41.6 7.1 35.2 10.7 47.0
29.0 25.8 11.4 33.8 30.0 23.3 6.3 40.4 13.0 21.8 9.9 55.3
29.2 19.3 11.0 41.5 27.8 19.1 6.6 46.5 19.4 14.3 8.1 58.2
26.4 18.7 10.4 44.5 28.9 17.0 6.0 48.1 21.3 13.7 8.0 57.0
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
23.2 29.5 12.4 34.9 16.9 27.5 7.6 48.0 7.8 33.6 12.4 46.2
22.8 24.2 10.8 42.2 18.7 22.4 6.5 52.4 14.3 24.6 10.3 49.0
29.2 18.4 11.0 50.2 23.4 20.5 5.8 50.3 22.8 15.8 8.9 53.5
24.4 17.1 10.4 49.3 23.3 16.5 5.0 55.2 18.3 16.0 7.1 58.6
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
23.6 25.4 9.8 41.2 18.5 27.4 7.9 46.2 9.3 34.1 8.6 48.0
24.3 20.4 9.8 44.5 21.2 21.4 6.0 51.4 15.3 24.8 7.8 51.9
26.0 17.1 9.1 47.8 22.1 18.5 5.3 54.1 18.7 13.4 8.1 60.8
25.3 14.8 9.2 50.7 20.9 15.3 4.1 59.7 17.6 12.5 7.1 62.9
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
17.5 21.2 10.4 50.9 14.8 26.1 6.1 53.0 10.8 32.4 8.6 48.2
24.2 20.4 9.8 45.6 15.1 23.2 5.3 56.4 16.4 26.8 7.5 49.3
28.1 19.3 7.9 45.7 16.4 20.1 5.9 57.6 22.9 18.6 8.0 50.5
29.4 17.0 8.1 45.5 18.1 18.8 6.0 57.1 21.8 16.0 6.2 56.0
32.4 to 44.6%, respectively, while the ®nal pyrolysis temperature was increased from 775 to 1025 K. In general, total hydrogen-rich gaseous products increased with increasing pyrolysis temperature for each biomass sample (Table 4).
% 6.7 Cotton cocoon shell
Tea factory waste
Olive husk
% 20 Cotton cocoon shell
Tea factory waste
Olive husk
% 33.3 Cotton cocoon shell
Tea factory waste
Olive husk
% 46.7 Cotton cocoon shell
Tea factory waste
Olive husk
775
925
975
1025
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
23.8 27.1 10.3 40.8 20.3 28.4 8.8 42.5 13.4 29.5 8.6 48.5
22.9 25.3 8.4 43.4 25.6 20.1 6.5 47.8 10.5 21.7 6.5 51.3
25.8 20.1 7.9 45.7 26.0 21.8 6.5 45.7 24.3 16.8 5.7 53.2
27.0 19.4 7.9 45.7 28.8 16.4 5.9 48.9 19.8 12.3 6.2 61.7
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
24.5 21.0 8.4 46.1 20.3 27.6 6.8 45.3 6.5 34.8 9.1 49.6
26.8 24.6 6.6 42.0 23.4 21.7 5.4 49.5 15.4 22.6 8.7 53.3
26.3 19.0 7.0 47.7 25.1 22.6 4.7 47.6 19.7 14.5 9.0 58.8
24.5 15.4 7.6 52.5 27.3 18.1 5.2 49.4 18.9 13.0 8.2 59.9
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
23.4 26.3 7.3 43.0 16.7 31.6 7.9 43.8 9.8 35.6 8.6 46.0
24.2 22.1 6.5 47.2 18.5 22.4 6.0 53.1 16.4 24.3 7.9 51.4
24.3 16.3 6.8 52.6 22.5 23.8 5.5 48.2 19.7 15.2 7.0 59.1
26.2 15.7 6.2 51.9 26.1 20.2 5.2 48.5 18.8 12.8 5.8 62.6
CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns CO CO2 Ole®ns 1 O2 H2 1 paraf®ns
22.0 23.2 6.6 48.2 15.9 24.8 9.4 49.9 12.8 31.6 8.4 47.2
27.1 22.4 5.4 45.1 17.1 20.5 7.2 55.2 16.4 29.8 6.3 47.5
30.0 19.3 5.7 45.0 20.5 22.1 6.5 50.9 19.8 18.4 6.0 55.8
29.7 17.8 5.2 47.3 23.8 20.6 5.0 50.6 19.8 16.3 6.5 57.4
The largest hydrogen-rich gas yield obtained from olive husk, cotton cocoon shell, and tea waste using about 13% ZnCl2 as catalyst at about 1025 K temperature are 70.3, 59.9 and 60.3%, respectively (Table 5). In general, in the pyrolysis of biomass, the yield of
A. DemirbasË / Fuel 80 (2001) 1885±1891
Table 9 Elementary compositions and yields of charcoals from hazelnut shell in relation to the carbonization temperature and their HHVs (source: Ref. [15]) Carbonization temperature (K)
C (%)
H (%)
O (%)
Yield (%)
HHV (kJ/kg)
295±470 295±550 295±650 295±750 295±850 295±950 295±1050
53.3 75.0 82.3 88.4 92.5 94.3 95.7
6.1 5.5 3.6 2.4 1.9 1.5 1.3
40.6 19.5 14.1 8.6 6.0 4.2 3.1
90.8 42.6 38.1 35.0 32.2 31.1 30.7
19846 28714 29140 29665 31041 31464 32008
hydrogen-rich gaseous product increases with ZnCl2 catalyst (Table 5), but the yield of pyrolytic gas decreases in spite of increasing the yield of charcoal and liquid products (Table 6). The effect of K2CO3 and Na2CO3 as catalysts on pyrolysis depends on the biomass species. The catalytic effect of Na2CO3 was greater than that of K2CO3 for the cotton cocoon shell and tea factory waste but the catalytic effect of K2CO3 was greater for the olive husk (Table 6). As seen in Table 6, the yield of gaseous products from olive husk increased from 37.8 to 43.1%, while the percentage of K2CO3 was increased from 6.7 to 46.7%. The effect of amount of alkali (Na2CO3 and K2CO3) on the pyrolysis products are given in Tables 7 and 8. The effect of amount of alkali (Na2CO3 and K2CO3) on the pyrolysis products is irregular. The maximum yields of hydrogen-rich gaseous products from olive husk of 62.9 and 62.6% were obtained in the presence Na2CO3 and K2CO3 (30.0% of the sample) at the ®nal pyrolysis temperature of
54
52 (H2 + Paraffins) gaseous products, % by volume
1890
50
48
46
44
Temperature (K) : : 775 : 850 : 925 : 975 : 1025
42
40
38 0
10
20
30
40
50
Catalyst (K2CO3), wt. % of the sample
Fig. 2. The effect of amount of K2CO3 catalyst on the yield of (H2 1 paraf®ns) at different temperatures (sample: cotton cocoon shell).
1025 K, respectively. Alkalis such as K2CO3 prevent the formation of stable chemical structures and also by an oxygen-transfer mechanism they weaken the C±C bond, thereby decreasing the activation energy for the complex pyrolysis reaction [17]. It can be assumed that the alkali causes weakening of the intermolecular interaction of the polymeric chains and, at the same time, catalyzes not only intralink dehydration but promotes the processes of 64 62 (H2 + Paraffins) gaseous products, % by volume
(H2 + Paraffins) gaseous products, % by volume
55
50
45
Temperature (K) : : 775 : 850 : 925 : 975 : 1025
40
35
60 58 56 54
Temperature (K) : : 775 : 850 : 925 : 975 : 1025
52 50 48 46 44
30
6 0
10
20
30
40
8
10
12
14
16
18
50
Catalyst (Na2CO3), wt. % of the sample
Fig. 1. The effect of amount of Na2CO3 catalyst on the yield of (H2 1 paraf®ns) at different temperatures (sample: cotton cocoon shell).
Catalyst (Zn2Cl), wt. % of the sample
Fig. 3. The effect of amount of ZnCl2 catalyst on the yield of (H2 1 paraf®ns) at different temperatures (sample: cotton cocoon shell).
A. DemirbasË / Fuel 80 (2001) 1885±1891 Table 10 Average chemical composition of gaseous products from the precipitate of black liquor at different temperatures (source: Ref. [9]) Temperature (K)
295±675 295±825 295±825 a 295±925 295±925 a a
Gas composition (% by volume) H2
CO
CO2
CH4
11.3 ^ 0.9 14.1 ^ 0.8 31.7 ^ 1.9 18.4 ^ 0.5 36.4 ^ 0.7
29.0 ^ 0.8 40.8 ^ 0.5 18.7 ^ 0.7 36.0 ^ 0.4 14.6 ^ 0.3
26.5 ^ 0.4 19.9 ^ 0.4 30.1 ^ 0.6 15.9 ^ 0.5 32.3 ^ 0.6
13.1 ^ 0.7 12.7 ^ 0.6 8.5 ^ 0.3 14.7 ^ 1.1 9.9 ^ 0.4
Three percent K2CO3 of the samples used as catalyst.
retroaldol cleavage and condensation of the products produced [18]. The effect of amount of catalysts (Na2CO3, K2CO3 and ZnCl2) on the yield of (H2 1 paraf®ns) at different temperatures are given in Figs. 1±3, respectively. As seen in Figs. 1 and 2, the effects of amount of alkali catalysts (Na2CO3 and K2CO3) on the yield of (H2 1 paraf®ns) at different temperatures (for Na2CO3 at 925 and 1025 K runs; for K2CO3 at 775, 925, 975 and 1050 K runs) are generally irregular. In low temperature pyrolysis runs, especially at 775 K run, the yield of hydrogen-rich gaseous product increases with amount of Na2CO3 catalyst (Fig. 1). The yield of hydrogen-rich gaseous product increases with percent of ZnCl2 catalyst in all pyrolysis runs (Fig. 3). Increasing the temperature from 470 to 1050 K, the hydrogen content of charcoal from the hazelnut shell decreased from 6.1 to 1.3%, respectively (Table 9). Table 10 shows the average chemical composition of gaseous products from the precipitate of black liquor at different temperatures [9]. In K2CO3 catalytic runs, H2 yields from the black liquor samples were 31.7 at 825 K and 36.4% at 925 K (Table 10). Many investigators studying of pyrolysis of various types of lignocellulosic materials have found it rather dif®cult to study each pyrolysis reaction separately [17,19±21]. The application of thermal analysis techniques does not provide accurate identi®cation and de®nition of the individual reaction. Since the pyrolysis step consists of many concurrent and consecutive reactions, it is virtually impossible to identify all the elementary chemical reactions, which occur when the olive husk thermally decomposed. It is believed that as the reaction progresses the carbonaceous material becomes less reactive and forms stable chemical structures, and consequently the activation energy increases as the conversion level of olive husk increases.
1891
oxygen about 10±13%, at atmospheric pressure and a pyrolysis temperature of approximately 670±770 K has been shown [22]. Under conditions of rapid heating, the water present in the mixture can undergo bulk evaporation causing severe foaming. Hydrogen gas can be produced from the waste material by direct- and catalytic pyrolysis, while the ®nal pyrolysis temperature was generally increased from 775 to 1025 K. The powdered K2CO2 catalyst (1±3 wt.% of moisture-free biomass) used in the catalytic gasi®cation runs was mixed with the biomass in the reaction chamber [23]. The catalyst shows destructive effect on the organic compounds and H2 and CO2 form end of the steam gasi®cation (catalytic steam reforming) process. The yield of CO from pyrolysis of the waste materials, all pyrolysis runs, the total yield of combustible gases increase with increasing pyrolysis temperature for the samples. The catalytic effect of Na2CO3 was greater than that of K2CO3 for the cotton cocoon shell, especially for low temperature pyrolysis runs. The maximum conversion yield of cotton cocoon shell to hydrogen-rich gaseous products (H2 1 Paraf®ns) for ZnCl2, Na2CO3 and K2CO3 catalytic runs were 22.5, 25.6, and 27.0% by weight, respectively. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
[15] [16] [17] [18] [19]
3. Conclusion
[20]
The main aim of pyrolysis is to obtain liquid and gaseous products from biomass. The possibility of obtaining the wood's oil with the yield to 13% mass, with contained
[21] [22] [23]
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