Kinetics of the Sulfation of Ca(OH)<sub>2</sub> at Low Temperatures

Ho, Ch'un-Sung; Shih, Shin‐Min; Liu, Chiung-Fang; Chu, Heng-Mo; Lee, Chung-Da

doi:10.1021/ie010887n

Cited by 31 publications

(74 citation statements)

References 20 publications

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“…However, the measurements of p react described above argue against direct reaction in favor of a two-step SO 2 trapping and reaction pathway. We hope that additional measurements using molten alkali hydroxides (31) and different alkali carbonate mixtures will provide deeper insight into the balance between SO 2 residence time and reactivity as well as the possibility of a direct SO 2 → CO 2 gas-surface reaction.…”

Section: Discussionmentioning

confidence: 99%

Reactive collisions of sulfur dioxide with molten carbonates

Krebs

Nathanson

2010

Proc. Natl. Acad. Sci. U.S.A.

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Molecular beam scattering experiments are used to investigate reactions of SO 2 at the surface of a molten alkali carbonate eutectic at 683 K. We find that two-thirds of the SO 2 molecules that thermalize at the surface of the melt are converted to gaseous CO 2 via the reaction SO 2 ðgÞ þ CO 2− 3 → CO 2 ðgÞ þ SO 2− 3 . The CO 2 product is formed from SO 2 in less than 10 −6 s, implying that the reaction takes place in a shallow liquid region less than 100 Å deep. The reaction probability does not vary between 683 and 883 K, further implying a compensation between decreasing SO 2 residence time in the near-interfacial region and increasing reactivity at higher temperatures. These results demonstrate the remarkable efficiency of SO 2 → CO 2 conversion by molten carbonates, which appear to be much more reactive than dry calcium carbonate or wet slurries commonly used for flue gas desulfurization in coal-burning power plants.flue gas desulfurization | gas scrubbing | gas-liquid reactions | liquid surface | molecular beam scattering T he atmospheric oxidation of sulfur dioxide produced during the combustion of fossil fuels is a significant source of acid rain and of fine aerosol particles harmful to human health (1-3). In coal-burning power plants, 75-98% of the SO 2 generated by combustion is removed by reaction with wet or dry limestone, which is predominantly composed of CaCO 3 (4). The overall reaction is (5):Numerous mechanistic (6-8) and kinetic (9, 10) studies of this reaction have been conducted by using solid CaCO 3 or limestone particles, with reported values of the activation energy ranging from 10 to 150 kJ mol −1 (9, 10). This large variation is probably caused by differences in the composition and porosity of the particles, the presence or absence of water vapor, and the buildup of a product overlayer (9). On the surface of dry CaCO 3 , SO 2 → CO 2 conversion takes place via the direct transfer of O 2− from CO 2− 3 to a physisorbed SO 2 molecule (8). Adsorption of ambient water converts the solid surface into CaðOHÞðCO 3 HÞ, which has been observed to enhance SO 2 uptake (6, 7). In the wet limestone process, SO 2 reacts with H 2 O in the slurry to produce H þ and HSO − 3 ; these acidic species are neutralized by OH − and HCO − 3 from dissolution of CO 2− 3 , a process that generates CO 2 and leaves SO 2− 3 in solution (5). Oldenkamp and Margolin developed an alternative method to remove SO 2 from flue gases by employing a molten eutectic mixture of Li 2 CO 3 , Na 2 CO 3 , and K 2 CO 3 (11). This liquid-phase reagent potentially avoids the wide variations in conditions observed for solid limestone and is regenerable (11,12). When bubbling SO 2 through the carbonate melt at 800 K, nearly 100% of the SO 2 is removed for contact times as short as 0.05 s (12). In practice, this efficiency can be orders of magnitude higher than for solid CaCO 3 at the same reaction time. Measurements by van Houte and Delmon, for example, imply that only 10 −5 % of the SO 2 is removed in 0.05 s, in part because the oxidation o...

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Section: Discussionmentioning

confidence: 99%

Reactive collisions of sulfur dioxide with molten carbonates

Krebs

Nathanson

2010

Proc. Natl. Acad. Sci. U.S.A.

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“…Shih et al (1999) proved that the behavior of the CO 2 reaction with Ca(OH) 2 resembled that of SO 2 in a differential reactor. On the other hand, based on the findings of Ho et al (2002) and Bausach et al (2005), SO 2 concentration contributes to the reaction rate of Ca(OH) 2 and SO 2 , and there is a mild dependency of the reaction rate on SO 2 concentration. Therefore, the effect of CO 2 concentration on the rate of reaction determines the relationship between CO 2 removal efficiency and CO 2 concentration.…”

Section: Resultsmentioning

confidence: 96%

A rate equation for Ca(OH)2 and CO2 reaction in a spouted bed reactor at low gas concentrations

Haghnegahdar

Rahimi

Hatamipour

2011

Chemical Engineering Research and Design

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“…For Shih et al [10] the surface coverage model was found to be the most suitable model to describe the reaction between Ca(OH) 2 and CO 2 . Ho et al [11] extended this conclusion to explain the reaction of Ca(OH) 2 sulfation. They suggested that the carbonation and sulfation of the hydrated lime are reactions controlled by chemical reaction on the surface of a grain, and the reacting surface area of the grain decreases with the deposition of solid product.…”

Section: Introductionmentioning

confidence: 90%

“…Shih et al [10] studied the reaction between Ca(OH) 2 and CO 2 ; these authors extended the study afterwards to the reaction between Ca(OH) 2 and SO 2 [11], but they selected n = 1 without any explanation. The parameters k 1 and k 2 can depend on the BET surface area (BET), temperature (T), SO 2 concentration (C SO 2 ) and relative humidity (RH).…”

Section: Modeling the Desulfurization Reactionmentioning

confidence: 99%