PROCESS FOR THE RECOVERY OF VOLATILE LOW MOLECULAR COMPOUNDS

Abstract: A process for recovering volatile, generally bad smelling low molecular, low polar substances called VLC, contained in a gaseous environment, typically gas streams, by capturing same in contacting said gaseous environment with a calixarene or a resorcinol calixarene present in the form of particles, granules as a coating or impregnation on or in a solid support, or as an organic solution. Further, a capturing agent for these VLCs is disclosed, compri sing at least one of the cyclic phenolic oligomers mentioned above and corresponding to formulae (I), (II), or (III) defined in the specification and claims.

Description: Process for the recovery of volatile low molecular compounds BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of gas phase absorption. More specifically, the invention refers to a process for the removal or recovery of gaseous, volatile organic or inorganic low molecular polar com¬ pounds, called "VLC" or "volatile light compounds" in this technical field, that are contained in gaseous environments such as ambient air or gas streams. In the modern society, the environment suffers from various VLC sources. Industrial gaseous emissions greatly contribute to the pollution of the atmospheric environment. Human activities linked to that pollution are the follow¬ ing: energy production, wood and paper industries, paints and polymers, agro-alimentary industries such as gist and sugar manufacture, etc. The olfactive nuisances generated by wastes (industry of animal by-products, animal excre- ments, household garbage) will add to this pollution. Fur¬ thermore, sewage purification plants are sources of bad smells. There is a still growing interest to treat the nui¬ sances generated by the industrial world, and especially the elimination of bad odors has considerably increased during the last years in following the general requirements of a better quality of life. There are already technical solutions available and corresponding necessary regulations set out regarding the partial or complete removal of odors. Thus, in France, Section 17 of the decree No. 77 of September 12, 1972, states that "the regulations consider in particular, on one hand, the effectiveness of available techniques and their economy and, on the other hand, the quality of the vocation and the use of environmental mediums". The regulation emerging from the laws and the decrees thus comprises the necessary tools for an adaptation to the evolution of an- tipollution techniques and their application. 2. Description of the Prior Art Different deodorizing techniques are already known: odor masking, thermal oxidation with and without catalysts, active carbon adsorption, biological purification, gas- solid absorption combined with chemical washing, etc. Therefore, the treatment of odors is generally effected by washing and oxidation, by adsorption (on charcoal, natural adsorbents, synthetic adsorbents), or by biopurification. It has already been suggested to use the so-called calixarenes (which will be described below) as adsorbents or absorbents for certain low molecular compounds. The document PCT/AU89/00079 for example discloses the removal of organic compounds, namely polar hydrocarbons such as trihalomethanes from fluids, in particular from drinking water. Furthermore, Japanese Patent Publication No. JP- 3,249,941 (application No. JP-90-0'046' 50) discloses a de¬ odorant composition for garbage and toilets; this composi ¬ tion is the reaction product of p-tert-butylcalix[8]arene, cupric chloride and ascorbic acid. The calixarenes used are thus not the active deodorant matter but monitor or en ¬ hance the action of the acidic combination of cupric chlo¬ ride and ascorbic acid. The ability of calixarenes for absorbing non-polar, relatively low molecular substances has already been known. Thus, the following documents disclose this finding: U.K. Patent No. 2,292,156 (separation of alcanes from a hydro- carbon mixture)/ and WO 95 11,208 (separation of alcenes and aromatics from a hydrocarbon stream) . Taking into account the sometimes very high volatility of the odorous VLC and the very low olfactive perception level of most of these compounds, no method and technique whatsoever affords a satisfactory solution of the problem. The absorption of gaseous, bad smelling sulfur or nitrogen containing compounds from gaseous environments in using pure calixarenes is neither disclosed or suggested in the prior art. SUMMARY OF THE INVENTION The first and major objective of the present invention is to overcome the drawbacks of the solutions suggested un¬ til now and to provide a new and useful purification method, more precisely a process for the recovery and re- oval of VLC contained in a gaseous environment, typically in a gas stream, which uses a new class of solid capturing materials. A further object of the present invention is to de¬ velop a method for the purification of gas streams, for ex- ample such emitted by water purification plants, which are contaminated with bad smelling light-weight gaseous compo¬ nents containing nitrogen or sulfur such as ammonia, hydro¬ gen sulfides, amines, thiols and disulfides. Still another object of this invention is to provide a new adsorbing or, more precisely, capturing material in which the adsorption process is based on another principle than that of the processed used until now. A further objective of this invention is to provide such an absorbing or capturing material which can easily regenerated in a simple, low-cost manner. The process of the invention comprises contacting a gaseous mixture that contains VLC, with cyclic phenolic oligomers. The adsorbent of the invention contains, as an active constituent, cyclic phenolic oligomers. The following listing gives examples of bad smelling organic and inorganic compounds of polar nature and having generally a low molecular weight that are preferably in¬ tended to be removed from a gaseous environment by the process and the absorbent of the present invention: ammo- nia, lower alkyl amines such as mono, di and trimethyl amine, mono, di and triethyl amine; and sulfur containing compounds such as hydrogen sulfide, lower organic thiols (mercaptans) such as methanethiol, ethanethiol, propane- thiol, and sulfides such as di ethylsulfide and di- ethylsulfide. This listing is not exhaustive. All the compounds listed above have dipole polariza- bilities (in units of 10 ~24 cm 3 ) of from about 2.25 (ammo¬ nia) to 4.7 (methylamine) whereas the polarizabilities of the trihalomethanes described in the above cited PCT appli- cation No. PCT/AU89/00079 range from 4.75 (chloroform) to 18.0 (triiodomethane) . The cyclic phenolic oligomers mentioned above that are used in the present invention are called "calixarenes"; they form a class of chemical compounds corresponding to the following structural formula I: wherein n is an integer from 1 to 7, R is hydrogen, an organic radical, hydroxy, amino, carboxyl ( -COOH) , sulfo ( -S0 3 H) or a halogen, a halogen containing radical, or a nitrogen, sulfur or phosphorus containing radical, and R' has one of the meanings defined for R in being identical to R or different from R, and R' may further be a radical -Si (CH 3 ) 3 . Such compounds of formula (I) are preferred wherein R is hydrogen, alkyl, substituted alkyl, allyl, aryl, substi¬ tuted aryl, hydroxy, amino, carboxy, sulfo; R' is hydrogen, alkyl, substituted alkyl, allyl, aryl, substituted aryl, acyl such as acetyl, or -Si(CH 3 ) 3 , and n is an integer from 1 to 5 included. Still further preferred are calixarenes that corre¬ spond to formula (I) above wherein n = 1, 3 or 5 and R' is hydrogen, and particularly preferred are p-tert-butyl calixarenes. The above mentioned calixarenes are already known com¬ pounds and may be obtained by simple reactions, generally one-pot reactions, starting from a corresponding p- substituted phenol wherein the two ortho positions of the phenolic hydroxy group are free, and formaldehyde. The re¬ actions are generally effected in the presence of a suit¬ able catalyst, known per se. If, in formula (I), R and/or R' are hydrogen, the produced calixarenes should be submit¬ ted to a dealkylation or, respectively, dearylation reac¬ tion. The following resorcinol calixarenes of formulae (II) and (III) can also be used instead of or together with the calixarenes defined above: (ID ( i n : wherein R l t R , R 3 and R are independently hydrogen or an organic radical. It is preferred to use resorcinol calixarenes of for¬ mula II wherein Ri is alkyl or aryl, or substituted alkyl or aryl, R 2 , R 3 and R 4 are hydrogen, and n is 1. These re¬ sorcinol calixarenes are particularly useful for capturing nitrogen containing compounds such as ammonia and amines. In the practice of the present invention, C-benzyl- resorcinolcalixarenes are preferably used. These macrocyclic compounds which are solid at normal temperature, can be obtained by one-shot, low cost reac¬ tions, for example by a condensation reaction starting from an alcoholic resorcinol solution and an equivalent of an aldehyde R^CHO in an acidic medium. Regarding the details of the preparation and isolation of calixarenes and resor- cinol calixarenes, see, e.g., Gutsche et al., Org. Syn. 1989, 68, 234; Niederl and Vogel, Ber. 1940, 62, 2512; and Hogberg, J. Amer. Chem. Soc. 1980, 102, 6046. In the practice of the present invention, "odd" calix¬ arenes (odd number of rings in the molecule) may also be used as well as the normally available "even" ones. As to resorcinol calixarenes, C-benzylresorcinol calixarenes are preferred. BRIEF DESCRIPTION OF THE DRAWING In the attached drawing, FIGURE 1 is a schematic view of an apparatus for determin¬ ing the effectiveness of the process FIGURE 2 represents in diagram form the results of a test according to Example 1, and FIGURE 3 represents in diagram form the results of a test according to Example 2. DETAILED DESCRIPTION OF THE INVENTION It has now been found in a surprising manner that the above described macromolecules are capable of selectively capture odorous VLCs such as ammonia, light weight amines, sulfur containing VLC's, etc., such as listed above, from a gaseous medium that contains these VLC's when the latter is contacted or treated with the calixarenes and/or resorcinol calixarenes described above. As a general rule, a gas stream which contains VLC's is passed through a bed con¬ taining the mentioned macrocyclic material or materials. It appears that the retention of the VLC's does not prefer¬ entially occur by physical adsorption but by a capturing complexation mechanism. For example, when a low molecular amine or a thiol (mercaptan) , thus compounds which are VLC's, are dissolved together with a calixarene or resorci¬ nol calixarene of the above formulae, well defined supra- molecular species are obtained which are sometimes even crystallized and present the following molar ratios between VLC and calixarene: VLC 4 6 8 4H CER CBR MA 1 2.4 3.3 1 0.97 0.8 DM 1 2.2 2.6 1.7 1.1 to 2.4 2.3 to 4.3 TM 1.7 0.4 EA 1 3.2 6.3 1 2.4 1.1 DE 2.6 2.2 4.8 1.2 3.6 6.1 TE 2.1 2.4 to 4.3 In this Table, the following abbreviations have been used: Head: p-tert-butylcalix [4]arene p-tert-butylcalix[6]arene p-tert-butylcalix[8]arene 4H: calix[4]arene CER: C-ethyl resorcinolcalixarene (n=l) CBR: C-benzyl calixarene (n=l); Left-hand column: MA methylamine DM dimethylamine TM trimethy1amine EA ethylamine DE diethylamine TE triethylamine. The behavior of the mentioned calixarenes, when brought into contact with a gaseous substrate, may be con¬ sidered as a reference for any use in the practice of the present invention, namely in a process for the deodorizing of gaseous media by complexing capture. In practice, it is preferred to use the calixarenes in the form of a deposit on the surface of solid substrates that are more or less finely divided or in the form of granules as it is the current use in gas absorption tech¬ niques. As a substrate or support, for example silica, alumina, active coal or charcoal (where there is often a synergistic effect by combined physical adsorption and cap¬ ture to be observed) , sand, gravel, cellulose, synthetic resins such as polystyrene, etc. The one skilled in the art will immediately know and find the support the best adapted to a certain task. It is possible to prepare a so¬ lution of the calixarenes and resorcinol calixarenes to be used in an organic solvent and to impregnate the support with this solution, and the material which is finally ob¬ tained by drying is ready for use. The calixarene compounds to be used in the process of the present invention can generally be employed in the form they come from synthesis; it is normally not necessary to purify them in any way. Of course, if these compounds con¬ tain impurities stemming from their preparation, their ac¬ tivity as capturing agents will be less than the 100 % pure compounds; this is a question of economy whether they will be purified and to which extent. In order to purify a gas stream containing the VLC's, it will be sufficient to pass the stream through a bed hav¬ ing appropriate dimensions, of the calixarene particles or the particles containing same, as it has been indicated above. Typically, the gas stream is air contaminated by one or more VLC's. It is not required to treat the gas stream in any manner whatsoever; in particular, the gas stream need not be dried before. When the use is intended for deodorizing the gases coming from a water purification plant, these exhaust gases are pushed by a fan through a column that contains a layer or a bed of a particulate sup¬ port impregnated with calixarenes. However, it will also be possible to wash the gaseous medium, typically a gas stream, which contains the VLC's in contacting this gas mixture with a homogeneous or heterogeneous liquid such as a solution or a dispersion, of the calixarenes or the re¬ sorcinol calixarenes concerned. The absorption technique of a gaseous component from a gas mixture by washing is in principle known; typically, a vertical column is used in which the gas stream flows from the bottom to the top, and a liquid current in finely divided form flows countercur- rently down from the top to the bottom. Of course, any washing installation whatsoever may be used such as bubble tray columns, sieve tray columns, packed columns, etc. Typically, the process of the present invention, namely the capture of VLC's from a gaseous medium, is car¬ ried out at ambient temperature and pressure. However, if other gas parameters are pre-established, such as elevated pressure and/or temperature, these conditions do normally not require any adaptation, i.e. their reduction to ambient conditions. Reconditioning It has surprisingly been found that, in spite of their polar nature, the captured VLC's can easily be separated from the capturing material. This fact allows to regener¬ ate the absorbing material for repeated uses and has only be reported in the prior art for the case of non-polar cap¬ tured compounds. The interactions between the VLC's, called "substrate" in the following explanation paragraphs, and the calixare¬ nes or resorcinol calixarenes occur in heterogeneous media, most frequently at a solid/gas (or sometimes liquid/gas) interface in the described cases. The solid phase having captured and fixed the substrate may easily be recovered. Different methods may be used to separate the substrate from the solids loaded with the substrate and to recycle the recovered solids. All these methods are based upon the principle to offer to the substrates stronger bindings than those effected by the calixarenes and the resorcinol calix¬ arenes. Regarding the nitrogen containing substrates, the treatment of the solids having captured the said substrates in a heterogeneous mixture of water and calixarenes allows to extract the amines into the water; in order to speed up the dissociation of the amines from the calixarenes, the water temperature may be increased, acids may be added to the water, and/or ultrasonics may be applied. Sulfur containing substrates such as hydrogen sulfide and thiols or disulfides are only slightly soluble in water and highly volatile. It is therefore suggested to trans- form the sulfur containing substrates in non volatile me¬ tallic sulfides. In the case of hydrogen sulfide, the sol¬ ids containing this substrate may be treated with a metal salt solution, for example zinc acetate solution. The hy- drogen sulfide is thus transformed into zinc sulfide which is insoluble and weighty. After filtration and drying the precipitate, the weight of the ZnS may be determined. This recycling method thus allows at the same time to quantita¬ tively analyze the captured H 2 S: (CH 3 C00) 2 Zn-2 H 2 0 + H 2 S => ZnSJ, + 2 CH 3 COOH + 2 H 2 0 Finally, regarding the thiols or disulfides, the treatment of the solids having captured the said substrates with an aqueous solution of a heavy metal salt, for example copper acetate, is able to isolate the thiols or disulfides in the form of insoluble metal sulfides. However, electro¬ chemical methods using silver electrodes may also be used, or the thiols or disulfides may be transformed to metal sulfides by means of an aqueous silver nitrate solution, or they may be oxidized into disulfides, e.g. by potassium ferricyanide. The following Examples are given for illustrating pur¬ poses only and will not limit the invention in any way. Example 1 A air stream that contains diethylamine is treated in the installation shown in FIG. 1 which schematically repre ¬ sents a system for the treatment of a gas flow. A peri¬ staltic pump 10, driven by an adjustable electric motor 11 and connected through a conduit 13 to an injection device 12 having a skirt seal 15 for inserting an injection nee- die. The injection device 12 is connected by a conduit 17 to a tubular reactor 14 containing the calixarene or resor- cinol calixarene, respectively, to be tested, enclosed be¬ tween two frits 16 and 18. The circuit is closed by an¬ other conduit 19 leading from the reactor 14 to the peri¬ staltic pump 10. In the reactor 14, 159 mg of C-benzyl-resorcinol calixarene are placed. The pump 10 is put on, and 9.66-10 -5 moles of diethylamine are injected through the seal 15 into the system which totals a volume of 160 ml so that the air within the system contains about 1450 pp of diethylamine. The pump 10 is adjusted to a flow rate of 300 ml/mi . Samples are taken in predetermined time inter¬ vals and quantitatively analyzed by gas chromatography ac¬ cording to the method of an inner n-pentane standard. This measuring method permits to follow the evolution of the gas flow regarding the concentration in function of time. Blind tests are also carried out for testing the validity of the method. FIG. 2 shows the results that have been obtained in diagram form. The amine content, given in arbitrary units, is plotted on the abscissa against the test time in minutes on the ordinate. After 85 minutes, the amine concentration in the blind test (curve A) has dropped from 48 to 36 units (decrease by 25 %) whereas, when calixarene was used in the reactor (curve B) , 50 % of the amine were already captured and removed from the circuit after 20 minutes (from 1450 to 700 ppm). The degree of capture is 62 % after 85 minutes. The diagram further shows that there is no liberation of amine during the test from the capture system. Example 2 An air stream that contains methylamine is treated in the installation of FIG. 1. 47 mg of C-benzylresorcinol calixarene are placed in the reactor 14. The pump 10 is put on, and 5.81-10" 5 moles of methylamine are injected into the device 12. The system contains thus about 8700 ppm of methylamine. The pump 10 is adjusted and controlled to a flow rate of 300 ml/min. Samples are taken in regular time intervals and analyzed by vapor phase chromatography against an internal standard. Blind tests are conducted in order to test the reliability of the method. FIG. 3 shows the results that have been obtained. Af¬ ter 5 minutes, the concentration of the amine in the blind test is about 40 units whereas, when the calixarene is used, 90 % of the amine have been captured and removed from the circuit in passing from 8700 to 830 ppm. The degree of capture is 100 % after 10 minutes. The diagram shows that there is no subsequent liberation of amine in the capture system. Example 3 An air stream that saturated with hydrogen sulfide is treated in the installation shown in FIG. 1. 140 mg of p-tert-Butylcalix[4]arene are placed in the reactor, and the air of the reactor is then saturated with H 2 S. After having conducted the circulation as described above in Example 1, the atmosphere of the reactor is washed with some air free from H 2 S. The calixarene loaded with H 2 S is collected and trans¬ ferred into a solution of zinc acetate and mixed thor ¬ oughly. A white precipitate of ZnS is formed. The reac ¬ tion medium is filtered, and the residue is treated with an appropriate organic solvent for dissolving and extracting the calixarene. The ZnS residue is then filtered and dried, giving 19.6 mg of ZnS which corresponds to the cap¬ turing of 1 molecule of H 2 S per molecule of calixarene. If other calixarenes are used, the results are differ¬ ent. For example, when the p-tert-butylcalix[ ] arene is substituted by p-isopropylcalix[4]arene, molecule of H 2 S per molecule of calixarene is found, and p-allylcalix- [4]arene shows a capturing capacity of 2 molecules of H 2 S per molecule of calixarene.

Claims: Claims What is claimed is: 1. A process for the capture of volatile light compounds contained in a gaseous environment wherein the gaseous environment is contacted with a calixarene, the process comprising contacting a gaseous environment con¬ taining at least one bad smelling low molecular, low polar gaseous component (VLC) with at least one cyclic oligomer of a phenol, namely a calixarene, of the general formula I: wherein n is an integer from 1 to 7, R is hydrogen, an organic radical, hydroxy, amino, carboxy ( -COOH) , sulfo ( -S0 3 H) or halogen, a halogen con¬ taining radical, or a nitrogen, sulfur or phosphorus con- taining radical, and R 1 has one of the meanings defined for R in being identical to R or different from R, and R' may further be a radical -Si(CH 3 ) 3 , or/and at least one resorcinol calix ¬ arene of formulae I or II: II: (III) wherein R 1; R 2 , R 3 and R 4 are independently hydrogen or an organic radical. 2. The process of claim 1, wherein at least one calixarene of formula I is used wherein R is hydrogen, al¬ kyl, substituted alkyl, allyl, aryl, substituted aryl, hy¬ droxy, amino, carboxy, sulfo; R' is hydrogen, alkyl, sub¬ stituted alkyl, allyl, aryl, substituted aryl, acyl such as acetyl, or -Si(CH 3 ) 3 , and n is an integer from 1 to 5 in¬ cluded, or of formulae II or III wherein R^ is substituted aryl and R 2 , R 3 and R 4 are hydrogen. 3. The process of claim 1, wherein a gas stream containing the said volatile substances is made to flow through a bed of solid bodies which are impregnated or coated with at least one compound of formulae I, II and/or III. 4. The process of claim 1, wherein a gas stream containing the volatile substances is washed with a liquid containing at least one of the compounds of formulae I, II and/or III in dissolved or dispersed state. 5. The process of claim 1, wherein the capture of the VLC's is effected at ambient pressure and temperature. 6. The process of claim 1, wherein said gaseous environment is air. 7. The process of claim 1, wherein said volatile substances comprise volatile amines, thiols, disulfides, hydrogen sulfide and ammonia. 8. The process of claim 1, wherein a gaseous in¬ dustrial exhaust is deodorised. 9. The process of claim 8, wherein said industrial exhaust is an air stream issued by a waste water purifica¬ tion plant. 10. The process of any one of the preceding claims, wherein the calixarene compound(s) having captured the VLC's are regenerated for reuse. 11. A capturing agent for volatile organic com¬ pounds contained in a gaseous environment, containing or comprising at least one cyclic oligomer of a phenol, namely a calixarene, of the general formula I: (I) wherein n is an integer from 1 to 7, R is hydrogen, an organic radical, hydroxy, amino, carboxy ( -COOH) , sulfo ( -S0 3 H) or a halogen, a halogen containing radical, or a nitrogen, sulfur or phosphorus containing radical, and R' has one of the meanings defined for R in being identical to R or different from R, and R' may further be a radical -Si(CH 3 ) 3 , or/and at least one resorcinol calix¬ arene of formulae I or II: (II) (Ill) wherein R^, R , R 3 and R 4 are independently hydrogen or an organic radical. 12. The capturing agent of claim 11, containing or comprising at least one calixarene of formula I wherein R is hydrogen, alkyl, substituted alkyl, allyl, aryl, substi¬ tuted aryl, hydroxy, amino, carboxy, sulfo; R' is hydrogen, alkyl, substituted alkyl, allyl, aryl, substituted aryl, acyl such as acetyl, or -Si(CH 3 ) 3 , and n is an integer from 1 to 5 included, or of formulae II or III wherein R^ is substituted aryl and R 2 , R 3 and R are hydrogen. 13. The capturing agent of claim 11, constituting a bed of particulate solid bodies impregnated or coated with at least one compound of formulae I, II and/or III. 14. The capturing agent of claim 11, constituting a washing liquid containing at least one compound of formulae I, II and/or III.

Inventors: CHOQUARD PHILIPPE, GORELOFF PHILIPPE, LAMARTINE ROGER, MARTELIN YVON, CHOQUARD, PHILIPPE, GORELOFF, PHILIPPE, LAMARTINE, ROGER, MARTELIN, YVON
Applicants: CHOQUARD PHILIPPE, GORELOFF PHILIPPE, LAMARTINE ROGER, MARTELIN YVON, TRANSDIFFUSIA S A, CHOQUARD, PHILIPPE, GORELOFF, PHILIPPE, LAMARTINE, ROGER, MARTELIN, YVON, TRANSDIFFUSIA S.A.
Application year: 1997
Main classification: B01D53
IPC codes: B01D53