Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
2002-08-07
2004-03-16
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C095S049000, C095S096000, C095S106000, C095S131000, C095S135000
Reexamination Certificate
active
06706090
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for the recovery or separation of sulfur oxyfluorides from gas mixtures, in particular for the recovery of sulfuryl fluoride (SO
2
F
2
) or thionyl fluoride (SOF
2
) from air or exhaust air which is contaminated therewith.
Federal Republic of Germany patent application no. DE 197 08 669 describes a method for the fumigation of spaces by introducing a fumigation agent and continuously withdrawing the treatment atmosphere, wherein the fumigation agent can be separated e.g. in an adsorber and can be re-used after desorption. Coal particles or aluminium oxide particles are mentioned as adsorption agents, and inter alia sulfuryl fluoride as fumigation agent. Sulfuryl fluoride can be and is used as a pesticide. For example pests in fresh wood or wood used in buildings (woodworm, fungi), in storage spaces or in mills (granary weevils) or textiles can be controlled using SO
2
F
2
. In this case, SO
2
F
2
is used on its own or in combination with other known pesticides. Once fumigation has ended, usually the SO
2
F
2
is decomposed by heat or destroyed by lye. The secondary products produced thereby can frequently be disposed of only on special waste dumps.
There is a need to be able to work up gas mixtures of this type with the aim of being able to re-use the sulfur oxyfluorides.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved method for the separation of sulfur oxyfluorides from gas mixtures.
Another object of the invention is to provide a method for separating sulfur oxyfluorides from gas mixtures in which virtually no environmentally damaging constituents of the gas mixtures pass into the atmosphere and the components which are separated out can be re-used.
A further object of the invention is to provide a method for separating sulfur oxyfluorides from gas mixtures in which no secondary products requiring disposal are produced.
These and other objects are achieved in accordance with the present invention by providing a method for the recovery or separation of sulfur oxyfluorides from a gas mixture comprising passing the gas mixture over at least one adsorption or membrane stage containing or consisting of a zeolite having a modulus >10 and a pore diameter of 0.4 to 0.7 nm, and thereafter recovering separated sulfur oxyfluorides.
According to the invention, gas mixtures containing one or more sulfur oxyfluorides are contacted with adsorbents and/or membranes for recovery of the sulfur oxyfluorides and the sulfur oxyfluorides which are separated out are sent for re-use, optionally after desorption, depending on requirements. The air which is low in or freed of sulfur oxyfluoride from the gas mixture can be let off into the atmosphere without hesitation.
In particular, the term sulfur oxyfluorides within the scope of the invention is to be understood as including compounds of sulfur, oxygen and fluorine such as SO
2
F
2
, SOF
4
, and SOF
2
. Gas mixtures having a sulfur oxyfluoride content from 5 ppmv or 20 mg/m
3
or more may be separated.
According to the invention, the gas mixture is passed through at least one adsorption stage and/or membrane stage containing or consisting of zeolites, which have an SiO
2
/Al
2
O
3
ratio, the so-called modulus, >10 preferably >100, a particle size >1 mm, preferably >2 mm, and a pore diameter of 0.4 to 0.7 nm, preferably 0.5 to 0.65 nm, the particle size applying for the zeolite which is used as adsorbent.
Zeolites which have been subjected to dealumination in order to replace the Al
2
O
3
in the lattice by SiO
2
, which thereby increases the modulus, are highly suitable. At the same time, this makes the polar forces weaker and thus the hydrophobicity of the zeolite is increased (W. Otten et al., Chem.-Ing. Tech. 64 (1992) No. 10, pp.
915-925)
It is within the scope of the invention to use the zeolites both as a loose bed in adsorber columns or as a membrane. Use of a combination of an adsorption stage and a membrane stage likewise is within the scope of the invention.
The adsorption is effected at a pressure of at most 15 atm. at 21° C.
In one embodiment of the method according to the invention, pest control with SO
2
F
2
is performed in closed containers or spaces. The SO
2
F
2
-containing atmosphere present as a gas mixture (0.05 to 10% by volume SO
2
F
2
) in the containers or spaces is removed therefrom once fumigation has ended and is contacted with the adsorbents and/or the membranes to recover the SO
2
F
2
. The air which is depleted in SO
2
F
2
from the gas mixture can then be discharged into the atmosphere.
In another embodiment, the gas mixture is passed over two or more adsorption stages and/or membrane stages.
The adsorbed sulfur oxyfluoride can be desorbed from the sorbent by increasing the temperature and/or reducing the pressure and be sent for re-use.
The regeneration of the adsorbents (desorption) takes place in known manner by supplying heat and/or lowering the pressure.
The desorption takes place in a temperature range from 20 to 300° C., preferably at a temperature >100° C. It has proved advantageous to allow the desorption to take place at reduced pressure. In one embodiment, the adsorber column after heating is exposed to a technical vacuum of up to 10
−3
bar for desorption.
If the gas mixture additionally contains impurities, purification by e.g. filtration or adsorption with other adsorbents may take place before the adsorption. It is likewise within the scope of the invention, first to free the gas mixture of water, e.g. by drying with suitable drying agents, and then to pass it through the adsorbers or membrane.
The apparatus for carrying out the method according to the invention comprises at least one adsorber with a bed of zeolites having a modulus >10, preferably >100, a particle size >1 mm, preferably >2 mm, and a pore diameter of 0.4 to 0.7 nm, preferably 0.5 to 0.65 nm, and/or at least one membrane, consisting of or containing a zeolite having a modulus of 10, preferably 100 and a pore diameter of 0.4 to 0.7 nm, preferably 0.5 to 0.65 nm. A compressor is located before the adsorber or the membrane. The apparatus comprises at least one supply line for the gas mixture, a line for removing the gas into the atmosphere and also measuring, regulating and monitoring devices.
In a preferred embodiment, it has proved advantageous to use at least two adsorber stages, which may each also comprise a plurality of adsorber columns, since they permit continuous operation if connected in parallel. The alternate operation of adsorption and desorption is ensured by suitable regulating and control devices.
In one embodiment of the invention, the gas mixture to be separated is introduced into the adsorber stage by a pump or a compressor via a supply line.
The number and capacity of the adsorbers depends on whether a gas with a high or low sulfur oxyfluoride content is to be treated. The capacity of the adsorbers can be increased, for example, by increasing the adsorber volume of the individual adsorber columns or by increasing the number of adsorber columns.
Before the depleted gas is discharged into the atmosphere, the composition of the gas is analyzed and monitored by a monitoring device, which may preferably comprise an infrared (IR) spectrometer.
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Belt Heinz-Joachim
Pittroff Michael
Rieland Matthias
Schwarze Thomas
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