Gas separation: apparatus – Solid sorbent apparatus – Dispersed or impregnated solid sorbent bed
Reexamination Certificate
2000-03-16
2002-06-11
Simmons, David A. (Department: 1724)
Gas separation: apparatus
Solid sorbent apparatus
Dispersed or impregnated solid sorbent bed
C096S154000, C055S524000, C055SDIG007, C095S128000, C095S137000
Reexamination Certificate
active
06402819
ABSTRACT:
BACKGROUND OF THE INVENTION
It is known to use adsorption filters to remove undesirable substances from a gaseous or fluid mixture. For example, EP A-0 340 542 describes an adsorption filter which comprises a supporting frame with a covering of adsorber particles. The adsorber particles fixed on the supporting frame clean undesired substances out of gases or fluids carried through the filter. Such cleaning processes always represent an equilibrium between stationary phase and moving phase. For normal requirements the known adsorption filters are an adequate means for achieving a cleaning.
Modern industrial developments have resulted in increasingly stringent requirements with regard to clean air. Such industrial developments are, for example, the manufacture of highly sensitive products, such as the manufacture of chips in the gigabyte range in microelectronics and the manufacture of pharmaceuticals. Earlier cleaning techniques had concentrated on the removal of particles, and the additional removal of undesired gaseous substances was achieved by adding an adsorbent to the filters. With such adsorbers it was possible effectively to remove undesired substances, as it is described for example in EP-A 0 340 542. The known adsorption filters are not, however, able to remove the entire bandwidth of gaseous components from the clean air. Such gaseous components can be roughly divided into high-boiling substances on the one hand and very volatile substances on the other. High-boiling substances, such as water or phenol, for example, are easily and effectively removed from gas mixtures with conventional adsorption filters. Such conventional adsorption filters have, for example, adsorption particles of active carbon. The volatile substances, such as SO
2
and NH
3
, behave entirely differently. They are only incompletely removed by the conventional adsorption filters, and such an equilibrium is established with the adsorption particles that the volatile substances are initially bound but later are released again. A lasting binding of such substances thus is not assured. One possibility of improving this insufficient adsorption is to impregnate the active carbon beforehand with acidic or basic adjuvants. If it is desired to remove NH
3
, for example, from a gaseous mixture, such an impregnation can be performed with phosphoric acid; if SO
2
, on the other hand, is to be removed, a previous impregnation with K
2
CO
3
is a possibility. The undesired substances enter into a chemical reaction with the impregnant and are thus permanently and irreversibly removed from the gas mixture. At the same time the impregnant is consumed, with the result that, after a certain time, the exhaustion of the cleaning capacity occurs. The impregnation makes it possible to make filters with improved cleaning action available. But the impregnation of the impregnated adsorber particles reduces the original adsorption ability of these particles, in regard to both their capacity and the adsorption mechanism. The adsorber particles thus become slower in removing undesired substances from gas mixtures as compared with their original performance, and they remove lesser amounts thereof. To this extent a new equilibrium occurs on the adsorber particles between the adsorption originally available and the chemical adsorption of the impregnating substance. In the case of a large amount of impregnating substance a considerable degradation of the adsorption is found, especially when this impregnating substance is unfavorably distributed. If, on the other hand, an attempt is made to try impregnating with less impregnant, the adsorptive capacity is less impaired, but the early exhaustion of the impregnant must be expected.
Basically, the problem involved with clean air is very complex. In addition to gases (such as H
2
S, NO
2
, SO
2
, NH
3
and Cl
2
), ions (SO
4
2−
, NO
3
−
, Cl
−
, PO
4
3−
, Na
+
, and NH
4
+
) must be removed, about which it is not known in particular in what form they exist.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a filter which, while having a good adsorption mechanism and capacity, will completely remove acid and basic gases and other impurities, even in trace amounts, from gas streams without any problems, and will permit the preparation of high-purity air for the purposes mentioned above.
This object is achieved by a filter with a high permeability to air, on which ion exchanger beads are fixed. The support is preferably a large-pore reticulated polymer foam made up of strings enveloped by a layer of ion exchangers. The support, however, can also be flat and be composed of a highly air permeable textile support material such as woven fabric, knits or nonwoven webs on which the ion exchanger spherules are fixed in the same manner as is known in the case of the so-called “spherical carbon” used as active carbon beads (DE-C-33 04 349).
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The ion exchanger beads can be strongly basic anion exchangers or strongly acidic cation exchangers. Such ion exchangers are known (literature reference: Winnacker-Küchler, 4th ed., vol. 1, and Römpp, 9th ed. of 1995). They are almost exclusively in the form of spheres of a size of up to 1 millimeter, which are used in bulk. The spheres consist of porous or swellable polymers, mostly on the basis of styrene, usually crosslinked in the form of styrene/divinylbenzene polymers bearing chemical groups with exchangeable ions which permit the desired exchange. In cation exchangers the chemical groups are usually sulfone groups, while anion exchangers contain quaternary ammonium groups. Ion exchangers with these chemical groups are strong ion exchangers.
Ion exchangers are used almost exclusively in wet form for cleaning wet media, especially for water purification. It is therefore surprising and unexpected by the person skilled in the art that ion exchangers also have an extraordinarily great separating power in air and even in a very dry atmosphere of less than 40% relative humidity, and can remove ions—which are probably present in the form of microdroplets or microdusts—formaldehyde, and other compounds that are barely perceptible by the sense of smell, but are no longer analytically detectable.
Reticulated polymer foams with large pores are known. These are predominantly polyurethane (PUR foams). Large-pore reticulated PUR foams have a density of 20 to 60 g/liter and pores measuring 1.5 to 3 mm. The pore size is also usually stated in Pei, i.e., pores per inch, and accordingly they have, for the purposes of the invention, a porosity of 8 to 30 ppi. Suitable as supports for the ion exchange beads also include large-pore reticulated polyolefin foams, especially those consisting of polyethylene and polypropylene. With regard to the size of the pores and the reticulation, the same considerations apply to the polyolefin foam as were stated above in connection with the PUR foam. Especially suitable are polyolefin foams which are modified hydrophilically by additional additives. Such reticulated polyolefin foams are known. They have been marketed, for example, by the firm of Troplast in Troisdorf.
Reticulated foams have almost no walls, but consist mostly of a lattice of strings forming cages having a diameter of about 1 to 5 mm. After they are coated with ion exchanger beads and with adsorber particles if desired, the reticulated foams have a comparatively large stiffness.
Depending on the material from which the supports are constructed, the ion exchanger beads can be affixed directly thereon, or an adhesive may be required. Adhesive is used especially with air-permeable textile supports or with the reticulated PUR foams. Which adhesives or glues are used depends especially on the intended manner of regeneration of the ion exchangers for the exhausted filters. Suitable adhesives include known dispersion adhesives, especially those based on acrylic acid derivatives, polyurethanes or polyvinyl acetates, as well as hot-melts or adhesive systems. The latter include Bayer&
De Ruiter Ernest
Toernblom Jonas
Crowell & Moring LLP
Lawrence Frank M.
MHB Filtration GmbH & Co. KG
Simmons David A.
LandOfFree
Fresh air filter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fresh air filter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fresh air filter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2931813