Environmental Impact of Sodium Sulfate Decomposition in Silicate Glass Manufacturing
Date
2003-05
Authors
Journal Title
Journal ISSN
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Publisher
New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering.
Abstract
Sodium sulfate (Na2SO4) is commonly used in soda-lime-silicate glass
manufacturing as a fining agent. The decomposition of Na2SO4 in glass tanks is an
environmental linked to SOx and particulate matter emissions. This study focuses on the
influence of atmosphere and reducing agents on Na2SO4 decomposition and the
concurrent emissions release.
Non-isothermal decomposition measurements identify 1373 K as the initial
decomposition temperature for Na2SO4 alone regardless of atmosphere type. This
implies that decomposition occurs in the molten phase. The isothermal decomposition
occurs in a steady-state, with higher decomposition rates occurring in inert or reducing
atmospheres. The decomposition mechanism involves rearrangements of Na-S-O
complexes on the Na2SO4 melt surface followed by desorption of SOx molecules. This
desorption step is rate-controlling. Decomposition atmosphere impacts the total SOx
concentration and SO/SO2 ratio. Inert atmospheres facilitate decomposition via collisions
with the Na-S-O surface complexes, resulting in higher total SOx concentration.
Oxidizing atmospheres passivate the melt surface, thus favoring the desorption of smaller
molecules such as SO. This phenomenon increases the SO/SO2 ratio in oxidizing
atmospheres.
Carbon is frequently used in combination with Na2SO4 to enhance the fining
process. Higher carbon active surface area (ASA) decreases the initial decomposition
temperature. In non-isothermal decomposition, carbon increases SOx emissions at
temperatures above 1373 K. Isothermal decomposition is shifted to a non-steady state
behavior. The decomposition rate scales with ASA. Carbon fractional conversion can be
calculated by measuring CO/CO2 concentration by FT-IR spectrometry. Conversion vs.
time data indicate three distinct regions: nucleation, desorption, and carbon depletion.
Decomposition is initiated by chemisorption of O atoms from Na2SO4 on carbon active
sites, forming surface complexes. These complexes subsequently dissociate, releasing
SOx and leaving behind C(O) complexes. The C(O) complexes desorbs as CO/CO2,
exposing new active sites.
Description
Advisory committee members: Doreen Edwards, Arun Varshneya, Alexis Clare. Dissertation completed in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Ceramics at the Kazuo Inamori School of Engineering, New York State College of Ceramics at Alfred University
Type
Thesis