(143j) Development of Natural Zeolite Catalyst System to Simultaneous Reduction of Greenhouse Gas and Nitric Oxides from Nitric Acid Manufacturing Process

Emissions of N₂O (nitrous oxide) are the third largest contribution to the global anthropogenic emission of greenhouse gases, just behind CO₂ and CH₄. The global warming potential of N₂O is about 310, i.e. on a 100 years time scale nitrous oxide is 310 times more effective per kg at trapping heat in the atmosphere than CO₂.[1] The nitric acid industry is one of the major source. Nitrous oxide is formed as a by-product in the oxidation of ammonia on a Pt/Rh gauze catalyst. The off gas concentration of N₂O is typically between 1000 and 2000 ppm. Next to N₂O, nitric acid plants also emit NO_x (typically 100-500 ppm). In part of the existing nitric acid plants a conventional NH3-based DeNO_x system is in use. Several options are currently in development for N₂O abatement. [2] Among various pollution control technologies, a well-proven method is the selective catalytic reduction (SCR) of NO_x with NH₃ in the presence of oxygen. This study describes our research in developing and testing catalysts for combined SCR of N₂O and NO_x in a single reactor under conditions that prevail in the tail gases of a nitric acid plant. The simultaneous selective catalytic reduction of both compounds using FeHNZ (Fe ion excahnged natural zeolite) and reductants with ammonia and methane have been investigated. FeHNZ as a catalyst was prepared by acid treatment of chlinoptilolite (natural zeolite) and classical wet ion exchange. Catalytic reduction of N₂O and NO_x takes place at temperature between 200 and 500°C. The optimum conditions have been investigated 400~450°C of reaction temperature, 10,000h^-1 of space velocity and NH₃ as a reductant. As a result, conversions of N₂O and NO_x have been examined the maximum under the optimum conditions.

Key words : Greenhouse gas(nitrous oxide), nitric oxides, SCR, Natural zeolite

Reference [1] Inventory of US Greenhouse Gases and Sinks 1990-1997, EPA, Washington, 1999. [2] R.W. van den Brink et al., Catalysis Today, 2002, 75, 227-232.

We acknowledge the financial support from the Ministry of Environment Republic of South Korea with Core Environment Technology Development project for Next Generation.