Desulfurization of CO:SO 2 contaminated gases by manganous oxide
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I.
INTRODUCTION
A B I L I T Y of manganous oxide (MnO) to form solid solution with MnS 1'2 promises a potential for regenerable filter for sulfur-bearing noxious gas streams. Due to persistent high content of sulfurous particulates, even during protracted periods without significant volcanic activity, it has been suggested that production of SO2 occurs partly by photolysis of carbonyl sulfide (COS): 3'4 COS + h v ~
CO + l S x
[1]
x
1 -
-
Sx nt- 0 2 "-'9' S O 2
x
[2]
Photochemically COS is sufficiently stable in the troposphere and can be transported into the stratosphere. It has been proposed that it may even be this gas that is affected by anthropogenic activity. 4 Carbonyl sulfide is a by-product from gas and petroleum refineries, 5 carbonaceous reduction of metal sulfides, and from the iron and steelmaking industry. Although sulfur in raw gas from coal gasification is predominantly in the form of H2S (90 to 95 pct), it can, to a lesser extent (approximately 5 to 7 pct), report as COS. Few of contemporary toxic-gas abatement systems are capable of removing COS.6 While susceptibility of MnO for H2S in the H-O-S system has been investigated, 7'8'9 there is a dearth of data for manganous oxide's reactivity in reducing C-O-S systems. Results reported here are from preliminary kinetic investigations undertaken at the Royal Institute of Technology to generate data for the abatement of sulfur in reducing atmospheres. Among the variables investigated have been various gas mixtures expected in the C-O-S system, viz: (a) CO: SO2 mixtures, (b) CO:SO2 mixtures flowing through a graphite bed, and (c) COS : CO: CO2 mixtures flowing through a graphite bed. H. AHMADZAI and L.-I. STAFFANSSON are Research Assistant and Professor, respectively, at the Department of Theoretical Metallurgy, Royal Institute of Technology, S-100 44 Stockholm, Sweden. Manuscript submitted August 5, 1986.
METALLURGICAL TRANSACTIONS B
The present article deals with investigations carried out with pure CO:SO2 mixtures fed to a reactor between 700 and 900 ~ (973 to 1173 K). Results from use of mixtures (b) and (c) shall be published later.
II.
T H E R M O D Y N A M I C S OF THE C-O-S AND Mn-O-S SYSTEMS
The C-O-S system is among the complex systems where data for some of the 18 species considered here may still be uncertain. ~0,~1.12Sulfur, by itself, has allotropes Si-S20.10,, In the present assessment, only the species $1 to $8 have been considered for the gaseous phase equilibrium computation. For the Mn-S-O predominance area diagram, Figure 1, the standard state in the basic reaction of all substances (Table I) is the pure component. Nonstoichiometry in the Mn-S-O univariant and bivariant equilibria (Tables II and III) has been ignored. For the C-O-S system, standard state chosen for carbon, oxygen, and sulfur was C, 02, and $2 at 1 atm, respectively. Data for the species CS, CS2, CO2, CO, COS, $1, SO3, and SO were from Kubaschewski et al. 18Data for $2 to $8 were obtained from Rau et al.,19 and that for SO2 from Rosenqvist and Haugom. 17
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