Filter material and process for producing No.sub.2 -free gases o

Details Filter material and process for producing No.sub.2 -free gases o Filter material and process for producing No.sub.2 -free gases o

1997-06-30

1998-12-08

Smith, Duane S.

Gas separation: processes

Solid sorption

Inorganic gas or liquid particle sorbed

55522, 55528, 55DIG35, 95900, 96153, B01D 5304

Patent

active

058462970

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a filter material, a filter and a process for producing gases and liquids which are free of nitrogen dioxide.


DESCRIPTION OF THE PRIOR ART

DE 43 28 450 A1 describes a filter material and a process for removing oxides of nitrogen from gases and liquids. Polyarylene sulfides are employed as polymeric filter material for nitrogen dioxide (NO.sub.2). In the reaction of NO.sub.2 with polyarylene sulfide, the sulfur groups are oxidized, reducing NO.sub.2 to NO in the process.
NO.sub.2 -free NO gas or NO gas mixtures are required in the technology of waste-gas measurement in order to calibrate measurement and analysis systems.
Recently, the medical use of nitrogen monoxide (NO) has acquired particular importance. In the case of patients with severe pulmonary diseases, the measured addition of NO to the air supply for breathing can reduce high blood pressure in the lung circulation. In conjunction with the bronchodilatory effect of NO, this results in improved air supply to various sections of the lung, and thus to improved gas exchange as well. Important factors in this context are the exact setting of the NO content and the minimization, extending to elimination, of the NO.sub.2 content. This problem occurs to an increased extent in the abovementioned application, since in said application NO is mixed with atmospheric oxygen at temperatures of around 40.degree. C. and at high atmospheric humidity and passed over distances of about 3-6 m. During this procedure, some of the NO will be converted to NO.sub.2. This leads to an increase in the NO.sub.2 content of the gas, which is damaging to the patient, and to a reduction in the NO content by the amount of NO.sub.2 formed. The desire here is for a converter which transforms the NO.sub.2 formed back to NO, shortly before it is breathed in by the patient, but without any other alterations to the gas mixture, for example its moisture content or temperature. Compared with an NO.sub.2 filter, this converter would have the advantage that there would be no change in the NO content originally set.
The colorless nitrogen monoxide (NO) reacts rapidly with molecular oxygen to form brown nitrogen dioxide (NO.sub.2). In the presence of air or with ingress of air, therefore, NO.sub.2 is formed from NO. Consequently, owing to the omnipresence of oxygen, NO.sub.2 is an inherent impurity in NO. With the medical use of NO in particular, toxicity dictates that the content of NO.sub.2 must be very low.


SUMMARY OF THE PRIOR INVENTION

It has been found that it is possible to remove NO.sub.2 from gases or liquids by bringing them into contact with a polyarylene ether. Furthermore, the selective removal of NO.sub.2 from NO or NO-containing media such as gases or liquids can be achieved with the aid of a polyarylene ether. Polyarylene ethers are therefore suitable filter materials for NO.sub.2. This is surprising since there is a great difference in structure between the polyarylene ethers and the polyarylene sulfides, the former containing no sulfur groups.
The invention provides a filter material for removing NO.sub.2 from gases and liquids, which comprises a polyarylene ether.
Furthermore, the invention provides a filter for removing NO.sub.2 from gases and liquids, which comprises a polyarylene ether.
The invention additionally provides a process for producing NO.sub.2 -free gases or liquids, in which the gas to be purified or the liquid to be purified is brought into contact with a material which comprises a polyarylene ether.
NO.sub.x is used as a collective term for NO, NO.sub.2 and N.sub.2 0.sub.4.
NO.sub.2 and N.sub.2 O.sub.4 are in chemical equilibrium. N.sub.2 O.sub.4 is removed from gases and liquids by polyarylene ethers.
The expressions "free of NO.sub.2 " and "quantitative removal of NO.sub.2.sup.1" denote that the content of NO.sub.2 in a medium is less than 1 ppm.
The filter material, the filter and the process of the invention are also suitable for removing NO.sub.2 from NO-containing gases or liquids.


BRIEF DESCRIPTION OF THE DRAWING

FIG.

REFERENCES:
patent: 3577707 (1971-05-01), White
patent: 3780496 (1973-12-01), Ward, III et al.
patent: 4919992 (1990-04-01), Blundell et al.
patent: 4933082 (1990-06-01), Yamada et al.
patent: 5080698 (1992-01-01), Krizan
patent: 5248321 (1993-09-01), Yang
Ullmann's Encyclopedia of Ind. Chemistry, 5th Ed., vol. A21, VCH, Weinheim Basel, Cambridge-New York, Editor: B. Elvers, et al, 1992, pp. 605-614.

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