METHOD FOR REDUCING THE HYDROCARBON CONTENT IN AIR OR WATER

Abstract: The hydrocarbon content in air or water is reduced by causing the air or the water to pass through a filter comprising a hydrophobic crystalline zeolite.

Description: METHOD FOR REDUCING THE HYDROCARBON CONTENT IN AIR OR WATER The present invention relates to a method for reducing the hydrocarbon content in air or water. In recent years, more and more attention has been given to the discharge into air and water of organic substances from different types of industries. This dis¬ charge frequently has an injurious effect on human beings and animals, but even though the injurious effects of some types of discharge may as yet be un¬ known, it is nevertheless desired to reduce the con- tent of organic substances discharged into nature. Examples of organic substances, especially hydro¬ carbons, that have proved to be injurious to nature and human beings are various solvents used in paint-spraying and printing processes, chlorinated hydrocarbons from cleaning processes, chlorinated compounds obtained as by-products in various production processes, by-products in various combustion processes and production processes etc. The technique which has been utilised most widely so far is based on adsorption with activated carbon as adsorbent, air or water being caused to pass through a filter' comprising the activated carbon which may be present in the form of a bed or have been applied to a carrier, such as paper or a ceramic material. The activated carbon may also be present in the form of a fluidised bed, in which case the air or the water to be treated constitutes the fluidising agent. The activated carbon has been used for a long time, and its advantages in the purification of air and water are well known. In spite of the fact that these known methods have been developed in the course of time towards increasingly better methods, they still suffer from cer¬ tain disadvantages that could net be surmounted. Thus, the activated carbon has a low efficiency at low impurity concentrations. Furthermore, it is com¬ bustible and does not bear high temperatures, for which reason its regenerability is very limited after adsorp- tion of high-boiling molecules. Furthermore, it is a "dirty" material, the handling of which evokes some aversion. In addition to the use of activated carbon, the use of different polymers as adsorbents has been dis- cussed for quite some time. In many respects, the pro¬ perties of the polymers are similar to those of the ac¬ tivated carbon, such as their adsorption capacity and their broad usefulness for a number of different adsorb- able types of molecules. On the other hand, they also have many of the disadvantages of the activated carbon, such as being combustible and susceptible to temperatures, The disadvantages of the adsorbents hitherto em¬ ployed are highly important to the usefulness of these adsorbents, for which reason one is anxious to find new and more efficient methods for purifying air and water from hydrocarbons. It therefore is the object of this invention to provide a method of reducing the hydrocarbon content in air or water. The method according to the invention is charac¬ terised in that the air or the water is " caused to pass through a filter comprising a hydrophobic crystalline zeolite. The zeolites used in the context of this invention have been made hydrophobic by giving them a high Si:Al ratio, either by direct synthesis or; by modification of zeolites having a lower Si:Al ratio. A normal zeolite is hydrophilic in character and adsorbs water vapour in preference to organic molecules. By direct synthesis or by chemical modification of exist¬ ing zeolites, it is possible to obtain zeolites which are hydrophobic or lipophilic so that their tendency to O adsorb organic molecules is increased. Because of their crystalline structures, these zeolites are capable of selectively adsorbing such substances as phenols, guaiacols, various solvents, degreasing agents, products from biochemical processes etc. from air or water, the dimensions of the crystalline structures determining the selective properties, primarily in respect of the size of the adsorbed molecules. The zeolites used in the context of this invention are crystalline materials consisting of silicon, alumin¬ ium and oxygen and, optionally, simple cations, such as sodium or hydrogen ions. They are not combustible and bear heating to 800-900°C, which means that they can be subjected to regeneration processes under inclement con- ditions. Furthermore, the hydrophobic zeolites can be treated with mineral acids and thereby be freed' from particle coatings. Since the crystal structures exactly define the pore size and the pore openings, they are selective in respect of the molecules that can be adsorbed. In other words, they function as inverted sieves, i.e. they adsorb molecules up to a given size which is deter¬ mined by the crystalline structure concerned, whereas the larger molecules are allowed to pass. The zeolites may be hydrophobated gradually from the state-in which they have entirely hydrophilic characteristics until they become entirely hydrophobic, which means that the hydrophobicity can be set to a value suitable for the type of molecules to be adsorbed. Zeolites suitable for hydrophobation in this inven¬ tion are heulandite, mordenite, phillipsite, chabazite, natrolite, analcite, clinoptilolite, gmelinite and/or faujasite. Among the zeolites which so far have proved to be efficient are those having a ratio of Si:Al which is higher than 15:1, in particular HAISi _0__ and HAlSi 25 0 52 . The present invention is applicable to different uses, such as to the removal of relatively low contents of toxic substances, especially organic substances, from water. Furthermore, it may be used for removing toxic substances, especially such as are formed upon the com¬ bustion of fuels, from air introduced into motor vehicles, ships or buildings. Finally, the method can be used also for reducing the content of toxic substances in air discharged over densely populated areas. The filters can be installed in different ways in inlet and outlet ducts. For example, a number of filter cartridges can be mounted in a collective housing for purifying contaminated water. When the filters have become more or less saturated with impurities, they are regenerated by admission of hot air or inert gas. After this regeneration, the solvents can then be re¬ covered by condensation. It is also possible to provide for filtration by having two parallel filter systems which are used alter- natingly, one for filtration and the other for regener¬ ation. The invention will be described in more detail below with reference to the following Examples which in no way are intended to restrict the invention. EXAMPLE 1 Butanol was prepared by a continuous chemical fermentation process. When the butanol content had reached 2.8%, the process stopped because the alcohol content became too high for the microorganism. By allow- ing the process water to pass through a hydrophobic zeolite having the composition HΛISi o_ 2 , the alcohol content was reduced and could be maintained at a constant level of 0.2%. The butanol was adsorbed continuously by the zeolite, and the process solution therefore did not reach the butanol concentrations toxic to the micro¬ organisms. When the zeolite was .saturated with butanol, it was replaced by a new batch of zeolite, and the -BUREQ OMPI butanol was recovered from the saturated zeolite. EXAMPLE 2 Industrial waste water having a phenol content of 3% was allowed to pass through a regenerable filter consisting of a hydrophobic zeolite having the composi¬ tion HAlSi 2 _O g2 . In tnis manner, the phenol content was reduced to 0.01%. EXAMPLE 3 Waste water from the alkaline bleaching of paper- making pulp with low contents of chlorophenols and chloroguaiacols and high contents of methanol and formic acid was treated after pH adjustment with hydrophobic zeolite having the composition HAlSi- 5 0- 2 . The content of chlorophenols and chloroguaiacols was reduced by about 35%, which content refers to the proportion of such compounds having kinetic diameters of less- 1 than about 8A. EXAMPLE 4 Waste water from the chlorine bleaching of paper- making pulp with low contents of chlorophenols and chloroguaiacols and high contents of formic acid and methanol was treated directly with hydrophobic zeolite having the composition HAlSi 35 0 72 . The content of solvents was reduced by about 30%, which content refers to the proportion of such compounds having kinetic diameters,of less than about 8A. EXAMPLE 5 Exhaust air from a spray-painting booth, containing 200 mg solvent per m , primarily xylene and white spirit, was treated with a hydrophobic zeolite having the compo¬ sition HAlSi-_o 72 . The solvent content was reduced to 1 mg per m of air. The adsorbed amount of solvent was then distilled off and recovered from the zeolite. Example 6 Exhaust air containing 2800 mg solvent per m of air from a spray-painting booth was treated with a hydrophobic zeolite having the composition HAISi _o 72 . OMPI AA, WiPO The solvent content in the treated air was decreased 3 3 ttoo aabboouutt 11..55 mmgg ppeerr mm .. TThhee aaddssoorrbbeed amount was distilled off and recovered from the zeolite. -BUREA OMPI

Claims: CLAIMS 1. A method for reducing the hydrocarbon content in air or water, c h a r a c t e r i s e d in that the air or the water is caused to pass through a filter comprising a hydrophobic crystalline zeolite. 2. A method as claimed in claim 1, c h a r a c ¬ t e r i s e d in that the hydrophobic crystalline zeolite is a.zeolite having a high Si:Al ratio. 3. A method as claimed in claim 2, c h a r a c ¬ t e r i s e d in that the zeolite is derived from heulandite, mordenite, phillipsite, chabazite, natrolite, analcite, clinoptilolite, gmelinite and/or faujasite. 4. A method as claimed in claim 1, c h a r a c ¬ t e r i s e d in that the zeolite has a Si:AΪ ratio higher than 15:1. 5. A method as claimed in claim 1, c h a r a c ¬ t e r i s e d in that the zeolite is HAlSi...0 72 or HAlSi 25 0 52 . OMPI

Inventors: ANDERSSON STEN, FAELTH LARS, VAREMAN KAJ, ANDERSSON, STEN, FAELTH, LARS, VAREMAN, KAJ
Applicants: ZEOL AB
Application year: 1984
Main classification: C02F1
IPC codes: B01D15, B01D17, B01D53, C02F1