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Basic Characteristics of Food Waste and Food Ash on Steam Gasification Masaaki Tanaka,† Hitoshi Ozaki,† Akira Ando,‡ Shinji Kambara,‡ and Hiroshi Moritomi*,‡ Air Conditioning & Heating Research Laboratory, Matsushita Electric Industrial Co., Ltd., 2-3-1-2 Noji-higashi, Kusatsu City, Shiga 525-8555, Japan, and EnVironmental and Renewable Energy Systems (ERES), Graduate School of Engineering, Gifu UniVersity, 1-1 Yanagido, Gifu, Gifu 501-1193, Japan
Thermochemical conversion of food waste such as kitchen waste is one approach to promoting the reduction of the final waste amount and the utilization of biomass energy instead of fossil fuels. In the present study, the possibility of effective hydrogen production from food waste was investigated. It was found that the ash in food waste and calcium oxide as the main compound in the ash play important roles in promoting hydrogen production. That is, first, ash containing large amounts of alkali components has the effect of increasing the hydrogen production and shifting steam gasification conditions to lower temperature. Second, the calcium oxide contained in the ash of food waste absorbs the carbon dioxide generated by steam gasification, resulting in the promotion of hydrogen production. 1. Introduction Efforts at recycling and reducing of food waste have been made in Japan since the enactment of food waste recycle law in 2000.1 The total food waste for fiscal year 2004 was 19.72 Mton, which consisted of 3.39 Mton from the industrial sector, 4.99 Mton from the business sector such as restaurants and convenience stores, and 11.34 Mton from the household sector. The industrial food waste from the food production sector has a comparatively constant composition and is consumed in a large quantity, so it is easily reused. The reuse percentage was 78% (2.65 Mton), consisting of 34% compost, 30% fodder, and others. The reuse percentage for business food waste was 24% (1.21 Mton). The largest issue is the food waste from the household sector because its composition is variable and only a small amount is consumed from a large number of places. The reuse percentage of household food waste was only 2% (0.26 Mton) in fiscal year 2004.1 As a result, the total reuse amount was 4.12 Mton, consisting of compost (1.53 Mton), fodder (1.34 Mton), and others (1.25 Mton). The amounts to be utilized as oils/fats and biogas were very low, at 0.24 and 0.02 Mton, respectively, in Japan.2 Of the total food waste, 79% (15.6 Mton) has been incinerated and disposed as a landfill waste. Moreover, throughout the world, a great deal of food waste from the household sector is incinerated together with municipal solid waste or dumped in landfills. Some methods for using biomass waste including food waste are fermentation to make a liquid fuel such as alcohol, gasification to make a gas fuel, and carbonization to make a solid fuel. Another possibility is conversion into thermal and electric energy. Many reports on biomass gasification have been published, for example, studies on the catalytic effects of alkali metals such as sodium and potassium on woody biomass gasification with carbon dioxide3 and on co-gasification with grass and coal,4 the catalytic effects of ash and calcium oxide with steam gasification,5 the tar decomposition effects of mineral materials on rapid pyrolysis,6 the tar capture effects of minerals under pyrolysis conditions,7 * To whom correspondence should be addressed. E-mail:
[email protected]. Tel.: +81 58 293 2591. Fax: +81 58 293 2591. † Matsushita Electric Industrial Co., Ltd. ‡ Gifu University.
gasification technology,8 and so on. Much of the research on thermochemical conversion techniques such as gasification are concerned with low-water-content waste such as woody biomass, but research on high-water-content waste such as food waste has been limited.9 However, when the wet waste is dried, the gasification behavior is similar to that of dry biomass.10 Furthermore, if the more alkali components in food waste are used as catalysts, hydrogen production with steam gasification should be promoted.11-13 The most favored catalysts are alkali metals, especially potassium compounds, but ash containing alkali components can also have undesirable effects on gasification such as deposit formation, material corrosion, and bed agglomeration.8,13 One of objectives of this study was to obtain basic characteristic data on food waste for gasifier design. Another objective was to clarify the effects of adding ash containing alkali components in order to establish a highly efficient system for producing hydrogen from food waste together with residual ash. 2. Experimental Section 2.1. Samples. Because the composition of actual kitchen waste is dependent on the season, as well as the place and the piece sampled from a large garbage box, a simulated kitchen waste sample was prepared in this study according to the recommended composition of ordinary kitchen waste in Japan.14 A representative kitchen waste sample was made by blending 10 wt % white rice; 10 wt % chicken meat; 10 wt % fish; 30 wt % cabbage; 30 wt % oranges; 2 wt % eggshells; and 8 wt % seasonings containing 2% each soy sauce, source, dressing, and sugar. This sample waste was dried at 408 K for 90 min in a dehydrator (Matsushita Electric Industrial Co., Ltd. MS-N339), crushed, mixed, and separated into a powder under 500 µm by a sieve. Table 1lists the properties of the simulated kitchen waste used as a food waste sample after dehydration. The water content of the original food waste was determined from the difference in sample weight before and after it was dried in the dehydrator, 77.2 wt %. The moisture of proximate analysis was determined by thermogravimetric analysis and corresponds to the weight loss when the sample was heated from room temperature to 473 K and held for 20 min under helium gas conditions. The volatile matter was measured as the weight loss without moisture at 1073 K when the sample was heated at 20 K min-1. The ash content is given by the solid weight after the residual had been
10.1021/ie0612966 CCC: $40.75 © 2008 American Chemical Society Published on Web 03/06/2008
Ind. Eng. Chem. Res., Vol. 47, No. 7, 2008 2415 Table 1. Ultimate and Proximate Analyses of Simulated Food Waste Samplea Ultimate Analysis (dafb) element
wt %
element
wt %
C H O
47.7 7.6 39.7
N S Cl
3.9 0.1 0.9
Proximate Analysis component
wt %
component
wt %
volatile matter fixed carbon
61.5 22.8
ash moisture
7.7 8.0
high low
Heating Values [kJ (kg of dry food)-1] 19100 17600
a Food waste sample dried at 408 K for 90 min in a dehydrator. b daf ) dry-ash-free conditions.
Table 2. Composition of the Ash in Simulated Food Waste Sample component
wt %
component
wt %
CaO Na2O K2O MgO
40.7 15.7 10.2 1.6
Fe2O3 Al2O3 others
1.4 0.1 30.3
Figure 1. Experimental equipment with spring-TG.
Table 3. Experimental Conditions weight (mg)
burned under a 200 mL min-1 flow of air. The fixed carbon is defined as the residual weight without the ash weight. In this study, because experimental error arose from the food waste sample itself and from recovery from the reactor, three reproducibility experiments were carried out for each set of experimental conditions. The error range was about 15 wt % for the thermogravimetric curves described below. Table 2 lists the composition of the simulated food waste ash. The total alkali content (Na + K + Ca + Mg) was 57.2 g (kg of dry waste)-1, which corresponds to 17 times that of wood chips.10 This should be an important factor in the catalytic promotion of hydrogen production and tar decomposition for food waste gasification.13 2.2. Experimental Equipment and Procedure. Figure 1 shows the experimental equipment used in this study, namely, a spring-type thermogravimetric analyzer (spring-TG). The experimental system consisted of the spring-TG reactor (1300 mm high, with spring and basket), an electric furnace, a temperature controller, a mass flow controller for the carrier gas (helium), a steam generator, and a gas analyzer. For each experiment, a 40-mg sample was set in a quartz basket hung on a quartz spring. When the catalytic effect of ash or calcium was investigated, 80 mg of either ash or calcium oxide was mixed with or layered on the sample. In such experiments, the total mass was 120 mg (40 mg of food and 80 mg of ash or calcium oxide). The quartz basket had no filter which allows carrier gas to pass through it, and the volatile matter produced from the sample was carried away by the downflow gas. In some cases, a layer of ash or calcium oxide was placed on the sample, and the matter passed through these layers and was carried away in the same manner. The experimental conditions are listed in Table 3. Each sample was heated from room temperature to about 473 K and held for 20 min at this temperature until all of the moisture had evaporated. Next, the sample was heated again at a rate of about 20 K min-1 to a temperature of 1073 K, where it was held for 30 min. For the pyrolysis conditions, helium gas was flowed at a rate of about 200 mL min-1 throughout the entire process. On the other hand, for the steam gasification conditions, a steam flow of 200 mg h-1 heated to 473 K was added to the above
sample CaO/H2O ash/H2O ash/CO2&H2O food only ash layer ash mix CaO layer
gas flow rate
steam He CO2 food ash CaO (mg h-1) (mL min-1) (mL min-1) 40 40 40 40
80 80 80 80 -
80 80
200 200 200 200 200 200 200
200 200 200 200
200 -
helium gas after 10 min during drying. The helium flow rate was controlled by the mass flow controller. The steam flow rate was controlled by a fixed quantity pump (Grundfos Co., Ltd., DME2-18A). For thermogravimetric analysis, a displacement sensor was used to measure the mass change during heating process. The product gases of hydrogen, carbon oxide, carbon dioxide, methane, and ethylene and the carrier gas of helium were analyzed with a micro gas chromatography system (Varian CP4900, Molsieve5A, PoraBOND Q) every 4 min after removal of the steam. However, carbon dioxide in the product gases could not be quantitatively measured because of dissolution in condensed water, gas meter water, and impinger water used to clean the product gas before it entered the gas chromatography system. 3. Results and Discussion 3.1. Thermogravimetric Analysis under Steam Gasification Conditions. To investigate the catalytic effects of food waste ash and calcium oxide on the steam gasification of food waste, the weight loss of the ash or calcium oxide itself was examined under the conditions of Table 3. The resulting mass reduction curves are shown in Figure 2 as the relative mass change, or the ratio of the residual weight to the initial weight. From the figure, it can be seen that the mass changes of both the ash and the calcium oxide decreased at around 850 K under steam conditions (Ash/H2O and CaO/H2O). The mass reductions might be due to the change in the ratio of calcium and alkali hydroxide to oxide. When carbon dioxide was present, the mass of ash increased rapidly around 700-850 K (Ash/CO2 & H2O).
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Figure 2. Changes in mass of ash and calcium oxide under steam gasification conditions. Figure 4. Effects of ash and calcium oxide on changes in mass of a food sample during steam gasification.
Figure 3. Effects of ash and calcium oxide on mass changes during steam gasification.
This is because the calcium and alkali oxide in the ash reacts with carbon dioxide to form calcium and alkali carbonate. The Ash/CO2 & H2O experiment was carried out to clarify the carbon dioxide absorbed by ash containing calcium oxide, resulting in the finding that the weight increase from absorption was almost equal to the weight of calcium carbonate produced by the reaction13,15,16
CaO + CO2 f CaCO3
(1)
The measured weight in Figure 2 is slightly more than the calculated calcium carbonate weight in ash because of other absorption with alkalis such as sodium and potassium. Without a continuous supply of carbon dioxide, the calcium carbonate should be calcined back to calcium oxide,17 resulting in a mass reduction for steam gasification as described later. Figure 3 shows the changes in relative mass of four samples of food only (Food only), food with layered CaO (CaO layer), food with layered ash (Ash layer), and food mixed with ash (Ash mixture). The mass reduction under food-only conditions appears to be small because the weight of added ash or calcium oxide was 80 mg, which is twice the weight of the food waste sample. It should be noted that more than 80% of the ash and calcium oxide remained as shown in Figure 2. These mass changes indicate that the ash mass decreased between 750 and 850 K, increased between 850 and 1000 K, and thereafter decreased again. The increase is related to the reaction of calcium oxide with carbon dioxide to form calcium carbonate by eq 1 as described in Figure 2. The carbon dioxide is produced by the gasification reaction of hydrocarbon in the food waste with steam as described later in eq 4. The subsequent decrease should occur when the calcium carbonate returns to calcium oxide with the re-emission of carbon dioxide as the steam gasification reaction progresses.
For the food-only curve in Figure 3, the first rapid mass reduction appears in the pyrolysis range between 500 and 750 K, where pyrolysis gas, tar, and other volatile matter are generated. Thereafter, a gradual reduction continues until about 1000 K, and a second rapid mass reduction occurs, which should be caused by the steam gasification reaction to produce hydrogen gas. The relative mass in this figure was converted to the corrected relative mass by subtracting the residual weight of ash and calcium oxide from Figure 2, as shown in Figure 4. As a result, when the residual amounts at the end of the experiment are compared, the residual amount of food mixed with ash is slightly higher, suggesting that the ash should capture some volatile matter. Additionally, the fact that the decreasing rates without “food only” are slow until 800 K might be caused by tar capture. The subsequent increase is caused by the capture of the steam gasification products such as carbon dioxide and tar. The gasification reaction of carbon with steam is expressed by eqs 2 and 3, but the amount of carbon oxide produced in this experiment was low, as expressed by eq 415,16
C + H2O f H2 + CO
(2)
CO + H2O f H2 + CO2
(3)
C + 2H2O f 2H2 + CO2
(4)
When the difference in relative mass between the ash mixture and food only is assumed to be carbon dioxide absorbed by calcium oxide in the ash, the amount is 0.012 mol (g of dry food)-1 at 25 min in Figure 4. Assuming that the steam gasification reaction occurs according to eq 4, this corresponds to a hydrogen amount of 0.024 mol (g of dry food)-1. On the other hand, the total amount of hydrogen produced under the conditions of Figure 4 was about 0.039 mol (g of dry food)-1 after 25 min, as shown in Figure 5. Because the amount of carbon dioxide with gasification is sufficient to increase the weight by changing calcium oxide to calcium carbonate, carbon dioxide absorption likely caused the weight increase. The small decrease and increase forming a valley around 850 K might be a deviation caused by subtracting the residual weight of the ash and calcium oxide in Figure 2. 3.2. Gas Composition under Steam Gasification Conditions. Figures 5 and 6, respectively, show the hydrogen production behaviors and the product gas amounts for food only (Food only), food with layered CaO (CaO layer), food with layered ash (Ash layer), and food mixed with ash (Ash mixture). The hydrogen production rate was defined as the hydrogen flow rate at the exit of reactor for the given initial weight of food sample, QH2 /F0. The hydrogen flow rate, QH2, was calculated
Ind. Eng. Chem. Res., Vol. 47, No. 7, 2008 2417
Figure 7. Effects of an ash layer or CaO layer on changes in mass of a food sample under pyrolysis conditions.
Figure 5. Hydrogen generation behavior under steam gasification conditions.
Figure 8. Hydrogen production behavior of layer conditions during pyrolysis.
Figure 6. Calculated gas composition under steam gasification and pyrolysis conditions.
from the hydrogen concentration determined by gas chromatography and the total product gas flow rate measured with the gas meter, QH2 ) [H2]Qtotal. The amounts of each product gas component for steam gasification and pyrolysis conditions in Figure 6 were calculated by integration of the flow rate in Figure 5, QCH4, QC2H4, and QH2 with time, MX ) ∑QX∆t. Compared with the hydrogen behaviors for the four conditions in Figure 5, it can be seen that the peak for the ash mixture is at the lowest temperature. The other hydrogen peaks for the ash layer and CaO layer are slightly shifted to lower temperature ranges from the peak for food only. Furthermore, the temperature of the hydrogen peak around 1000 K for the ash mixture is similar to the temperature of the relative mass peak position for the ash mixture conditions shown in Figure 4 and for the ash/CO2 and H2O conditions shown in Figure 2. These results suggest that the hydrogen production at lower temperature is due to the catalytic effects of alkali components in the ash13 on the gasification reaction (eq 2) and the absorption of carbon dioxide (eq 3). It is quite important that the food sample comes into contact with the additive ash in the bed. Compared with the ash mixture, the ash layer is less effective on conversion to gas and lower-temperature hydrogen production but more effective than the calcium oxide layer. This means that the alkali components contained in the ash play an important role in catalytically decomposing and reacting with steam to produce hydrogen at lower temperatures. Consequently, the above results suggest that hydrogen production is promoted not only by the catalytic effects of alkali
components in the ash on steam gasification (eq 2), but also by the absorption of carbon dioxide and its reaction with the calcium oxide in the ash by eqs 1 and 3. 3.3. Effects of Ash under Pyrolysis Conditions. Thermogravimetric analysis and gas analysis of food samples with layered ash or calcium oxide under pyrolysis conditions were conducted. Figure 7 shows the relative mass curves for three food samples of food only, food with an ash layer, and food with a CaO layer, which are values obtained after subtracting the weight of ash and calcium oxide as well as Figure 4 under steam gasification conditions. The curves for food only and food with a CaO layer exhibit similar mass change tendencies during heating. After a rapid reduction in mass up to 800 K, the mass decreases gradually until the end of the experiment. On the other hand, the ash layer exhibits a stable period between 750 and 900 K and then undergoes rapid mass reduction again between 900 and 1073 K. The mass change above 1073 K is minimal. The stable period between 750 and 900 K can be explained by the absorption of volatile matter containing tar, whereas the volatile matter is gradually re-emitted or decomposed over 900 K. As shown in Figures 8 and 6, the hydrogen production rates and amounts of gaseous product for the food only and CaO layer samples are almost the same. These results suggest that the amount of carbon dioxide absorbed by calcium oxide and the effect on tar decomposition of the additive calcium oxide layer are low. Because the hydrogen production for the ash layer occurs at lower temperature and the amount is higher than for the other samples, the ash layer was concluded to absorb more carbon dioxide and tarry volatiles than calcium oxide and to have a catalytic effect on the tar decomposition. However, the amount of hydrogen produced was significantly lower, i.e., by about a factor of 15, than that obtained under the steam gasification conditions, as shown in Figure 6. 3.4. Mass Balance of Carbon. Carbon in the food sample was distributed to residual carbon in the unreacted sample, tar
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utilization of the residual ash after steam gasification and utilization of the wastewater as steam for gasification. Nomenclature
Figure 9. Carbon balances under pyrolysis and steam gasification conditions.
deposited on the reactor walls, and gaseous products such as methane and ethylene, as shown in Figure 6. Carbon dioxide produced by the water-gas shift reaction of eq 3 was dissolved in the water downstream of the gas analyzer and was not detected. Therefore, the amounts of carbon dioxide dissolved were calculated from the hydrogen production amounts. Gaseous carbon in the product gases, MCH4, MCO, and MC2H4, was calculated by integration of the cooresponding flow rates (QCH4, QCO, and QC2H4, respectively) with time, MX ) ∑ QX∆t. Carbon consumption to produce hydrogen (eq 4) was calculated from the hydrogen production, MH2. Consequently, the total carbon in the product gas was estimated as MC,Gas ) MCH4 + MCO + 1/ (M1 2 1 2 H2 - M H2). Here, M H2 and M H2 represent the amounts 2 of hydrogen produced under steam gasification conditions and pyrolysis conditions, respectively, in Figure 6. However, the amount of carbon dioxide under pyrolysis conditions could not be calculated, and it was accounted as an “unknown component”. Carbon in the residual solid, MC,Residual, was calculated from the carbon concentration and residual amount. Carbon in the tar and unknown compounds was calculated as MC,Tar ) [C]F0 F0 - (MC,Gas + MC,Residual). An example of the carbon balance in food waste under steam gasification and pyrolysis conditions, based on the above definitions, is shown in Figure 9. Carbon conversions into gas under steam gasification conditions were about 60-70%, and most of the conversion was related to hydrogen production. 4. Conclusions Thermochemical conversion of food waste such as kitchen waste is a possible approach to promoting the reduction of the final waste amount and the utilization of biomass energy instead of fossil fuels. In the present work, as a possibility for producing fuel gas from food waste, the catalytic effects of food waste ash on hydrogen production with steam gasification were investigated and compared with those of calcium oxide as a main compound in the ash. The following conclusions were obtained: (1) Food waste ash containing alkali components has the effect of increasing the hydrogen production and shifting it to lower temperature when it is mixed well with food waste under steam gasification conditions. (2) Ash containing calcium oxide can absorb carbon dioxide generated by steam gasification when it is well mixed with food waste, resulting in the promotion of hydrogen production. (3) Added ash absorbs more tarry volatiles and promotes more hydrogen production than calcium oxide under pyrolysis conditions. The above conclusions suggest that food waste can be used as a fuel by thermochemical conversion combined with effective
A ) residual weight of additives (g) A0 ) initial weight of additives (g) F0 ) initial weight of food waste sample (g) MC,Gas ) total number of moles of carbon in the product gas (mol), MC,Gas ) MCH4 + MCO + 1/2(M1H2 - M 2H2) MC,Residual ) total number of moles of carbon in the residual solid (mol), MC,Residual ) [C]ResidualR MC,Tar ) total number of moles of carbon in the tar and unknown (mol), MC,Tar ) [C]F0 F0 - (MC,Gas + MC,Residual) MX ) number of moles of component X (mol), MX ) ∑ QX ∆t M1X ) number of moles of component X under gasification conditions (mol) M 2X ) number of moles of component X under pyrolysis conditions (mol) Qproductl ) flow rate of product gas (m3 min-1), Qproduct ) Qtotal - QHe Qtotal ) total flow rate (m3 min-1) QX ) [X]Qtotal R ) total residual weight of food waste sample and additives (g) t ) time (min) X ) component such as carbon, methane, hydrogen, helium, etc. [C]Residual ) carbon concentration in the solid resudue (mol g-1) [X]out,t ) concentration of X at the exit of the reactor at a given time t (mol m-3) Literature Cited (1) Sweeping Policy Reform Towards a “Sound Material-Cycle Society” Starting from Japan and Spreading oVer the Entire Globe-The “3R” Loop Connecting Japan with Other Countries; Ministry of the Environment, Government of Japan: Tokyo, Japan, 2006. Available at http://www.env.go.jp/en/wpaper/smc2006/index.html. (2) Present condition of food waste; Ministry of Agriculture, Forestry and Fisheries, Government of Japan: Tokyo, Japan (in Japanese). Available at http://www.maff.go.jp/sogo_shokuryo/kankyou.htm. (3) Tancredi, N.; Cordero, T.; Cordero, T.; Rodriguez-Mirasol, J.; Rodriguez, J. J. CO2 Gasification of Eucalyptus Wood Chars. Fuel 1996, 75, 1505. (4) Brown, R. C.; Liu, Q.; Norton, G. Catalytic Effect Observed during the Co-gasification of Coal and Switchgrass. Biomass Bioenergy 2000, 18, 499. (5) Feldmann, H. F.; Choi, P. S.; Conkle, H. N.; Chauhan, S. P. Thermochemical Gasification of Woody Biomass. ACS Symp. Ser. 1981, 144, 351. (6) Nik-Azae, M.; Sohrabi, M.; Dabir, B. Mineral Matter Effects in Pyrolysis of Beech Wood. Fuel Process. Technol. 1997, 51, 7. (7) Ito, K; Moritomi, H; Yoshiie, R; Uemiya, S; Nishimura, M. TarCapture Effect of Porous Particles for Biomass Fuel under Pyrolysis Conditions. J. Chem. Eng. Jpn. 2003, 36, 840 (in Japanese). (8) Plao, G.; Hamai, M.; Kondo, M.; Itaya, Y.; Mori, S. Research and Development on Gasification Technology of Organic Waste Material by Using Entrained Flow. J. Jpn. Inst. Energy 2003, 82, 671. (9) Kawaguchi, K.; Miyakoshi, K.; Momonoi, K. Studies on the Pyrolysis Behavior of Gasification and Melting System for Municipal Solid Waste. J. Mater. Cycle Waste Manage. 2002, 4, 102. (10) Tanaka, M.; Ozaki, H.; Moritomi, H. Basic Study on Thermochemical Conversion for Food Wastes. Energy Resour. 2006, 27, 225. (11) Li, Z; Capart, R.; Gelus, M. Study of Catalytic Effects of Alkali Metal Salts in the Gasification of Charcoal. Biomass Energy Ind. 1990, 2, 760. (12) Demirbas, A. Gaseous Products from Biomass by Pyrolysis and Gasification: Effects of Catalyst on Hydrogen Yield. Energy ConVers. Manage. 2002, 43, 897. (13) Sutton, D; Kelleher, B; Ross, R. H., J. Review of Literature on Catalysts for Biomass Gasification. Fuel Process. Technol. 2001, 73, 155.
Ind. Eng. Chem. Res., Vol. 47, No. 7, 2008 2419 (14) Moriya, Y.; Nakano, K.; Suzuki, T. Property of Garbage Smell and Deodorization Technology. Preprint of the 14th Meeting of Association on Odor EnVironment Saitama, Japan. 2001, 100 (in Japanese). (15) Lin, S-Y.; Harada, M.; Suzuki, Y.; Hatano, H. Continuous Experiment Regarding Hydrogen Production by Coal/CaO Reaction with Steam (I) Gas Products. Fuel 2004, 83, 869. (16) Kumabe, K.; Moritomi, H.; Yoshida, K.; Yoshiie, R.; Kambara, S.; Kuramoto, K.; Suzuki, Y.; Hatano, H.; Lin, S-Y,; Harada, M. Gasification of Organic Waste with Subcritical Steam under the Presence of a CalciumBased Carbon Dioxide Sorbent. Ind. Eng. Chem. Res. 2004, 43, 6943.
(17) Outokumpu HSC Chemistry 5.1 for Windows; Outotec Research Oy Espoo, Finland. Available at http://www.outokumpu.com/hsc.
ReceiVed for reView October 10, 2006 ReVised manuscript receiVed November 16, 2007 Accepted November 26, 2007 IE0612966
