Filter for the removal of apolar organic substances from gases

Filter for the removal of apolar organic substances from gases containing an absorbent comprising at least one compound of the following formula: ##STR1## wherein one of X1, X2, and X3 is a phosphoric acid, phosphoric acid ester, or phosphatidyl moiety and two of the groups X1, X2, and X3 are independently selected from saturated fatty acid ester moieties and saturated alcohol (8 to 20 carbon atoms) ether moieties.

The invention relates to a filter for the removal of apolar organic 
substances from gases, especially from air. 
The removal of apolar organic substances from gases, in connection with 
industrial processes, for example, or from tobacco smoke, is difficult, 
since two properties are required which are difficult to reconcile with 
one another: on the one hand, the filter should offer the least possible 
resistance to the passage of a gas, that is, it should have a strong, open 
structure, but on the other hand, it should have a very high absorptive 
capacity for the apolar organic substances. 
Hitherto attempts have been made to solve this problem essentially by 
modifying solid, organic substances physically or chemically so as to 
provide them with a very large adsorptive and organophilic surface. 
The object of the invention is to provide a filter having both of the 
above-mentioned properties to an extent unachieved hitherto. 
The filter of the invention for the removal of apolar organic substances 
from gases contains as an absorbent at least one compound of general 
formula: 
##STR2## 
wherein one of the groups X1, X2 or X3 is a phosphoric acid moiety, a 
phosphoric acid ester moiety or a phosphatidyl moiety, and two of the 
groups X1, X2 and X3 are, independently of one another, an ester moiety of 
a saturated fatty acid or an ether moiety of a saturated alcohol of 8 to 
20 carbon atoms. 
Preferably, the compound of General Formula I contains a phosphoric acid 
moiety or phosphoric acid ester moiety of General Formula II: 
##STR3## 
in which R, R' and R" each represent a hydrogen atom or an alkyl moiety of 
1 to 4 carbon atoms and n represents the number 2 to 16, or of General 
Formula III: 
EQU --O--Y III 
in which Y represents the moiety of a bivalent, trivalent or more 
polyvalent C.sub.2-7 alcohol, or of General Formula IV: 
EQU --O--Z IV 
in which Z represents a C.sub.1-20 alkyl moiety. 
The compounds of General Formula I are characterized by the fact that they 
are capable of forming thin surface films which have an extraordinarily 
great absorptivity for apolar organic substances. These compounds have low 
phase transition temperatures (solid-liquid phase transition), and this is 
especially advantageous, since the absorptivity in the liquid state is 
much higher than in the solid phase. Therefore, those compounds of General 
Formula I or those mixtures are used whose phase transformation 
temperature is lower than the anticipated working temperature of the 
filter. Preferred are those compounds or mixtures which have a phase 
transformation temperature of 80.degree. C. or less, and, with special 
preference, of 20.degree. C. or less, if the removal of apolar organic 
substances from air, especially from tobacco smoke, is involved. 
The filter of the invention can contain a single compound of General 
Formula I or a mixture of several such compounds. The use of a mixture is 
preferred, because then the performance of this absorbent can be most 
easily adapted to the particular purpose. 
The absorption performance and the phase transformation temperature are 
determined mainly by the length of the fatty acid ester groups and by 
their symmetry or lack of symmetry. The term symmetry, as used herein, is 
to be interpreted as meaning that the molecule contains two identical 
fatty acid groups. Such compounds of General Formula I containing two 
identical fatty acid ester groups have definitely higher phase 
transformation temperatures for the number of carbon atoms they contain 
than compounds of General Formula I having no symmetry, i.e., containing 
two different fatty acid ester groups, even if the sum of the carbon atoms 
in these groups is just as great as it is in a symmetrical compound. 
A second factor which affects the phase transformation temperature is the 
position of the fatty acid ester groups. If they are adjacent, this 
temperature is higher than it is if they are in a 1,3 relationship. 
This is especially important when the filter of the invention is to be used 
as a tobacco filter, e.g., as a cigaret filter. The filter is then 
preferably operated above the phase transformation temperature. In the 
case of symmetrical compounds of General Formula I, of the lecithin type, 
that is, those phosphatidyl esters which have a moiety of General Formula 
II in which R=R'=R"=methyl and n=2, the phase transformation temperature 
is 54.degree. for the distearoyl compound, 41.degree. C. for the 
dipalmitoyl compound, 23.degree. C. for the dimyristoyl compound, and 
0.degree. C. for the dilauroyl compound. In the case of the 
lauroyl-palmitoyl compound, on the other hand, which has a twelve carbon 
chain and a sixteen carbon chain in the same molecule, the phase 
transformation temperature is less than -10.degree. C., i.e., more than 
33.degree. C. lower than it is in the case of the dimyristoyl compound 
which is the same in its number of carbon atoms. It is therefore easy for 
any particular case to select the compound or mixture of compounds of 
General Formula I such that under all working conditions the temperature 
will be above the phase transformation temperature. 
The compounds of Formula I are not oxidizable, in contrast, for example, to 
egg lecithin, which would easily be oxidized by the oxygen of the air to 
form toxic compounds. In this respect the absorbent compounds used in the 
filter of the invention differ from the widely used phospholipids, which 
contain mostly unsaturated fatty acid moieties and therefore are 
oxidizable. The same compounds occur in the human body and especially in 
lung tissue, where they act as surface active substances and, on account 
of their easy phase transformation at body temperature, play an important 
part in the expansion and contraction of the air cells. This is attributed 
to the presence of extended plateaus in the surface pressure-surface 
isotherms of these compounds. 
The affinity between the absorbent compounds used in the filter of the 
invention and the alveolar wetting agents of the lung represents a special 
advantage in the use of the filters for tobacco smoke, since the compounds 
are absolutely non-toxic and very stable against the oxygen of the air. 
Therefore, if pieces of the filter material enter into the oral cavity, 
which can never be entirely prevented, especially in the case of cigaret 
filters, or even into the stomach and intestinal tract, this will do 
absolutely no harm to the smoker in any case. 
Another advantage in this kind of application of the filter of the 
invention is to be seen in the fact that precisely those apolar organic 
substances are preferentially absorbed which otherwise accumulate in lung 
tissue, since they can also be absorbed in that tissue. 
In contrast to the situation in the lung, however, the absorbent or 
absorbent mixture in the filter of the invention must not be selected such 
that the filter will operate in the boundary area of the phase 
transformation, but above it. Otherwise, however, it is unimportant within 
the scope of the invention, as far as effectiveness is concerned, whether 
the absorbent compounds of Formula I are in the form of lecithins, 
cephalins, phosphatidyl-glycerine derivatives or phosphatidyl alkyl 
esters. The lecithins and phosphatidyl compounds, however, differ from 
compounds of the cephalin type in their greater hygroscopicity, and they 
are therefore used preferentially within the scope of the invention when a 
certain moisture content is to be maintained in the filter. Moreover, they 
facilitate the preparation of homogeneous suspensions in water. 
Since the absorbent compounds are to be present in the filter of the 
invention preferably in the liquid state and in this state a support is 
necessary, those filters are preferred which contain a suitable support. 
Any appropriate granular, particulate, foliar or comparably structured 
material will serve as support, which has sufficiently low resistance to 
the passage of the gases to be filtered and has sufficiently great 
absorbency or absorptive capacity for the phospholipid absorbents. 
Examples of suitable supports are cigaret filter papers or filter papers 
generally, other cellulose derivatives of high absorbency, cotton wool, 
glass fiber wools, especially if they have organophilically modified 
surfaces, asbestos, mineral supports, and the like. It is thus possible to 
impregnate conventional cigaret filters with the phospholipids of General 
Formula I. Generally about 0.1 to 10 mg, preferably 0.3 to 5 mg, of 
compound of General Formula I is used in each cigaret filter, although 
larger or smaller amounts can also be used. 
On the other hand, in filters for the removal of apolar organic substances 
from industrial exhausts, such as those from lacquers and printing inks, 
it may be desirable to have a very high working temperature. In this case, 
symmetrical compounds will be selected which have a high phase 
transformation temperature, adapted to the exhaust gas temperatures 
actually present. 
Within the scope of the invention it is also possible to build up the 
filter in layers, each layer being impregnated with different 
phospholipids or phospholipid mixtures of gradated phase transformation 
temperature. In this manner a selective filtering action can be achieved. 
In this embodiment, the arrangement of the layers is preferably such that 
the layer nearest to the gases to be filtered is impregnated with the 
absorbent of highest phase transformation temperature, and then the 
following layers contain absorbents of diminishing phase transformation 
temperature. 
The filters of the invention are also very well suited for the removal of 
undesired odors which are produced by apolar organic compounds; for 
example, they can be used advantageously as kitchen range filters or the 
like. 
Experiments performed with cigaret filters of the invention have shown that 
the smoking sensation is not substantially affected by these filters. 
Apparently, minimal amounts of nicotine suffice to stimulate the taste 
receptors, so that on the one hand smoking pleasure is preserved, while on 
the other hand the lung is affected by only extremely small residues of 
harmful smoke components.

EXAMPLES 
The following examples will further explain the invention: 
EXAMPLES 1 TO 6 
Conventional cigaret filters containing absorbent filter papers were 
impregnated with various mixtures of compounds of General Formula I. 
The composition of the mixtures is given in the following Table I. 
TABLE I 
______________________________________ 
Compound I 
Wt.-% 1 2 3 4 5 6 
______________________________________ 
Dipalmitoyl- 
80 90 70 60 50 60 
lecithin 
Dipalmitoyl- 
15 -- -- -- -- 10 
N,N-dimethyl- 
cephalin 
Dipalmitoyl- 
5 10 10 10 10 10 
cephalin 
Dipalmitoyl- 
-- -- 20 30 40 20 
phosphatidyl- 
glycerin 
______________________________________ 
EXAMPLE 7 
To demonstrate the technical effect achieved by the filter of the invention 
in its use as a cigaret filter, the following comparative experiment was 
performed: 
Conventional filter cigarets (Reemtsma's "Ernte 23") were equipped with a 
filter of the invention and then compared with the same, but untreated 
filter cigarets, with regard to the condensable substances contained in 
the smoke. 
The filter of the invention was prepared as follows: 
1.8 mg of 1,2-dimyristoyl-sn-glycerin-3-phosphoricacidglycerinester and 
35.6 mg of 1,2-dimyristoyl-sn-glycerin-3-phosphoricacidcholinester were 
mixed with 10 ml of water and then let stand for 30 minutes at 55.degree. 
C. Then the swollen mixture was emulsified in a blender, yielding about 10 
ml of emulsion. The filter end of a filter cigaret was immersed to a depth 
of about 2 mm into the emulsion thus obtained. Within about 10 to 20 
seconds the filter had absorbed the emulsion all the way to its upper end. 
Then the filter was allowed to dry in air at 20.degree. C. for 24 hours. 
Approximately 0.2 ml of the emulsion had been absorbed by each cigaret. 
The content of dimyristoyl-glycerinphosphoricacid-glycerin ester per 
filter was therefore approximately 0.035 mg, and the 
dimyristoyl-glycerinphosphoricacid-cholinester content was about 0.7 mg. 
The cigaret equipped with the filter of the invention was smoked in a 
smoking device in which a vacuum sufficient for the uniform burning of the 
cigaret was applied to the burning cigaret. The condensable substances 
that had passed into the smoke were frozen out in liquid air and the 
condensate thus obtained was then absorbed in 10 ml of methanol. The 
methanolic solution was examined spectroscopically. The measured 
extinction with the filter of the invention averaged 0.575 for three 
cigarets. 
The corresponding standard value for three untreated cigarets was 
.epsilon.=0.957. The measurement was performed at 450 nm in each case. 
The values obtained show that, with the filter of the invention, about half 
of the substances passing through the commercial filter and absorbing at 
the stated wavelength had been removed. Both nicotine and the aromatic tar 
substances absorb at the stat wavelength. 
It will be understood that the specification and examples are illustrative 
but not limitative of the present invention and that other embodiments 
within the spirit and scope of the invention will suggest themselves to 
those skilled in the art.