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NF3 Abatement using a Caustic Liquid Scrubber

IP.com Disclosure Number: IPCOM000019420D
Publication Date: 2003-Sep-12
Document File: 3 page(s) / 344K

Publishing Venue

The IP.com Prior Art Database

Abstract

Abatement of NF3 is traditionally carried out using high temperatures and/or the introduction of reducing agents such as carbon, hydrogen, metal oxides or hydrocarbons . The oxidized stream is then scrubbed to remove the HF byproduct produced. Since NF3 has over 8000 times the global warming potential of CO2 on a lb basis , it is imperative that atmospheric vent gases containing NF3 be kept to a minimum. This is especially important for manufacturing facilities where the potential to vent large volumes of pure NF3 are more common. We have discovered that NF3 under certain conditions will react with caustic (KOH) to produce nitrogen, oxygen and potassium fluorides in high efficiencies at feed rates in excess of 30 lbs/hr of NF3.

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NF3 Abatement using a Caustic Liquid Scrubber

Abatement of NF3 is traditionally carried out using high temperatures and/or the introduction of reducing agents such as carbon, hydrogen, metal oxides or hydrocarbons[1]. The oxidized stream is then scrubbed to remove the HF byproduct produced. Since NF3 has over 8000 times the global warming potential of CO2 on a lb basis[2], it is imperative that atmospheric vent gases containing NF3 be kept to a minimum. This is especially important for manufacturing facilities where the potential to vent large volumes of pure NF3 are more common. We have discovered that NF3 under certain conditions will react with caustic (KOH) to produce nitrogen, oxygen and potassium fluorides in high efficiencies at feed rates in excess of 30 lbs/hr of NF3.

Under normal process conditions a pure NF3 stream will not react with KOH liquid solutions, even at concentrations as high as 45 wt% and at elevated temperatures. In fact, it is well known that the use of a caustic scrubber is the preferred method of removing HF and F2 residuals to recover NF3 from reactor product streams[3]. The scrubbing process produces oxygen from fluorine, water from HF and common to both, KF. The balanced equations are shown below. In general, this process functions normally and allows the NF3 to pass through the scrubber unreacted.

F2 + KOH � 1/2 O2 + 2 KF

HF + KOH � H2O + KF

NF3 + KOH � N.R.

When the fluorine inlet gas concentration is allowed to become elevated, we have observed under certain circumstances that the NF3 thermally decomposes. The thermally decomposed NF3 produces nitrogen and fluorine which is then subsequently scrubbed by the KOH to produce nitrogen, oxygen and KF. The initiation of the NF3 decomposition is accompanied by a mild pressure spike follwed by high surface temperatures near the penetration of the inlet tube into the scrubber. Thermocouples placed within the scrubber in the vicinity of the inlet tube discharge have recorded temperatures in excess of 1400°F. These high temperatures are very localized. For example thermocouples placed 5 to 6 inches away from the inlet record temperatures of 150°F and below.

The products of the NF3 decomposition have b...