Process for removing ozone-depleting and/or climate-active fluor

Details Process for removing ozone-depleting and/or climate-active fluor Process for removing ozone-depleting and/or climate-active fluor

1998-12-23

2000-08-29

Dunn, Tom

Chemistry of inorganic compounds

Modifying or removing component of normally gaseous mixture

Halogenous component

423220, 588206, 588248, 205391, B01D 5300, B01D 5368

Patent

active

061104361

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a process for removing fluorinated ozone-depleting and/or climate-active fluorinated compounds from a gas stream which is passed through a solid heated sorbent. It also relates to applications of this process.
Fluorocarbons, both perfluorinated ones and partly fluorinated ones (HFCs), and chlorofluorocarbons (CFCs and HCFCs) have been used on a large scale for decades as propellants, refrigerants, blowing and parting agents, solvents, cleaning agents, etc.
However, they have a high ODP (ozone depletion potential) and are therefore held mainly responsible for the depletion of the ozone layer in the atmosphere. Due to their infrared absorption spectrum and their sometimes extremely long atmospheric lifetime they further have a high GWP (greenhouse warming potential), i.e. they make an essential contribution to global warming. Reference is made to the following table: fluorocarbons and hydrofluorocarbons and other gases


______________________________________ Lifetime GWP Substance (Years) (Integrated over 100 years) ______________________________________ CO.sub.2 (reference) 100 1 CF.sub.4 50000 6300 C.sub.2 F.sub.6 10000 12500 SF.sub.6 3200 24900 NF.sub.3 180 9720 CHF.sub.3 250 12100 CH.sub.2 F.sub.2 6 485 C.sub.2 HF.sub.5 36 2740 C.sub.2 H.sub.2 F.sub.4 18 1330 ______________________________________ Gases in the Semiconductor Industry: A Review of Science, Policy, and Technology" Journal of the Semiconductor Safety Association, Vol. 8, No. 4, page 13, December 1994, and "Radiative Forcing of Climate Change", published in Climate Change--The IPCC Scientific Assessment, edited by J. T. Houghton, G. J. Jenkins, and J. J. Ephraums, Cambridge University Press, Cambridge, November 1994.)
DE 44 04 329 C1 discloses a process according to the preamble of claim 1. The sorbent used is a phyllosilicate containing iron oxide. The known process has proven to be successful by and large, but the sorbent must be heated to a relatively high temperature, for example up to 350.degree. C. for sorption of CF.sub.4. The sorption capacity of the sorbent also leaves something to be desired.
It is known from EP 0 412 456 A2 to decompose fluorocarbons with water vapor at 350 to 1000.degree. C. on an alumina catalyst into hydrogen chloride, hydrogen fluoride, carbon dioxide and carbon monoxide as well as other compounds such as trifluoroacetyl chloride. However, the removal and disposal of these partly very aggressive and toxic decomposition products involves considerable expense.
The problem of the invention is to remove fluorinated compounds from a gas stream at a low expense.
This is achieved according to the invention by the process characterized in claim 1. Claims 2 to 5 render advantageous embodiments of the inventive process. Claims 6 to 14 relate to preferred applications of the inventive process.
According to the invention the gas stream containing the fluorinated compounds is passed through a sorbent of .gamma.-(gamma)-alumina. The gas stream and the .gamma.-alumina must be anhydrous. Surprisingly, this causes the fluorine contained in the very inert, ozone-depleting and/or climate-active fluorinated compound to be bound quantitatively to the .gamma.-alumina sorbent, and at a rather moderate temperature of e.g. 200 to 400.degree. C. If the fluorinated compound is a chlorofluorocarbon, quantitative bonding of the chlorine to the sorbent together with the fluorine is similarly to be ascertained.
According to the inventive process, substantially all ozone-depleting and/or climate-active fluorinated compounds can thus be adsorbed.
These include in particular perfluorinated or partly fluorinated (HFC) saturated or unsaturated hydrocarbons with 1 to 4 carbon atoms in the molecule, fluorinated hydrocarbons halogenated with other halogen atoms besides fluorine, in particular chlorine, i.e. perhalogenated (CFC) and partly halogenated (HCFC), saturated and unsaturated chlorofluorocarbons with 1 to 4 carbon atoms per molecule, in particular, trichlo

REFERENCES:
patent: 3876394 (1975-04-01), Nix
patent: 5015343 (1991-05-01), LaCamera et al.
patent: 5885539 (1999-03-01), Bjarnoet et al.
"Long-Lived and Greenhouse Gases in the Semiconductor Industry: A Review of Science, Policy, and Technology" by Michael T. Mocella, submitted Feb. 1994 for publication in the Journal of Semiconductor Safety Association (8 pages).

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