US 3095284 A
Description (OCR text may contain errors)
June 25, 1963 I. VICTQR LOW TEMPERATURE PROCESS OF DRY CLEANING TEXTILES Filed April 8, 1960 fifiw f mm m Wm 1V m my on w .1
United States Patent Ofiice 3,095,284 Patented June 25, 1963 3,095,284 LOW TEMPERATURE PROCESS OF DRY CLEANING TEXTILES Irving Victor, Minneapolis, Minn., assignor to Research Development Co., Minneapolis, Minn., a partnership Filed Apr. 8, 1960, Ser. No. 20,903 6 Claims. (Cl. 34-62) This invention relates to improvements in a vapor adsorption process. In general, the invention is concerned with the transfer of the vapors of an organic cleaning solvent from garments or textiles and the like to an adsorption mass, and the subsequent removal of the solvent from the adsorption mass. More particularly, the invention is concerned with a mode of removal of solvent vapors from textiles and the like at a relatively low temperature by an improved method of transferring the vapors to an adsorption mass, together with an improved method of treating the adsorption material to improve its adsorbing capacity.
Garments and textiles are customarily cleaned by placing them in a rotatable cage disposed within a washing machine where the garments undergo a washing action with a liquid organic solvent, and after the washing action is completed, the excess liquid is removed by increasing the rate of rotation of the cage to centrifuge the excess liquid. The cleansed garments are then dried in a similar cage in which air is circulated through a closed circuit that includes a cooling zone where vapors are condensed by contact With cold coils, and a heating zone where the gases are reheated by contact with hot coils prior to recirculation of the air through the garments. As a general rule, the air passing from the heating zone has been heated to at least 150 F. to increase its capacity for removing solvent from the textile fibers. In dry cleaning fabrics, it is customary to utilize chlorinated hydrocarbons as the cleansing solvent, and as this material is quite expensive, it is essential to recover as much of the solvent as is possible. To this end, in my prior Patent 2,910,137, dated October 27, 1959, I have disclosed a method and means by which residual solvent vapors present in the garments and in the atmosphere within the drier are recovered by an adsorption process.
One of the handicaps of the drying process referred to above has been in the injury to materials from the use of highly chlorinated synthetic solvents and particularly in the presence of a substantial amount of heat. In some instances, these solvents are injurious to the fabrics, or to the dyes used in fabrics, and to buttons or other ornaments used on wearing apparel. Since it has been recognized that some of the objections to the use of highly chlorinated hydrocarbons, such as perchlorethylene, is in the use of a substantial amount of heat, which has heretofore been necessary to evaporate the solvent from the fabrics, it follows, that if substantial heating of the materials can be avoided without unduly prolonging the drying operation that many objections to the use of chlorinated hydrocarbons can be overcome.
I have also discovered that another class of solvents, namely some of the fluoro-chloro-hydrocarbons can be successfully used for cleaning purposes. Trichlorotrifluoroethane is particularly attractive for use in the cleaning industry, because it is relatively non-toxic, as compared to the chlorinated hydrocarbons. Moreover, this solvent is excellent for cleaning fabrics, since it does not remove the natural oil-s from wool, and does not harm other fabrics, nor does it cause bleeding of the dyestuffs. Furthermore, this solvent is non-injurious to plastics and other forms of material commonly associated with wearing apparel. The fluoro-chloro-hydrocarbons, however, have not been used in cleaning operations in the past, because of their relatively high volatility, and their high cost.
I have found that the highly volatile characteristics of these solvents enable them to be used without the necessity of substantial heating, heretofore required for removal of residual solvent from garments, and the objection to the high cost can be overcome by the use of an efiicient vapor adsorption system.
According to the present invention, the material to be cleaned is washed with the desired liquid solvent in the usual manner but with the necessary precautions against vapor loss. In my prior patent referred to above, I have shown alternate forms of apparatus, wherein in one instance the washing and drying operations are conducted in separate equipment, and in another instance, where both of these operations are conducted in the same equipment.
In the present invention, the drier or container in which the vapors are removed from the fabrics is provided with a ducting system that extends to a bed of adsorbent material, and then returns to the drier, so that all of the gases within the system may be recirculated through the drier and the adsorbent. Because the adsorbent process is an exothermic process, such heat as is generated by the adsorbing action is utilized to aid in the removal of additional solvent from the fabrics. When the bed of adsorbent material approaches saturation with the solvent, the adsorbent material is treated with an aqueous material, such as steam, to remove the solvent which is then condensed and separated for re-use. Then, heated air is circulated through the adsorbent and discharged from the system to remove excess moisture from the adsorbent, and by the evaporation of such moisture to cool the adsorbent before another vapor adsorption cycle occurs.
An object of the invention is to provide a low temperature method of recovering volatile organic solvents from materials, including garments and textiles, and of recoveringsuch solvents by the use of an adsorbent which selects such solvent in preference to water, from which adsorbent the solvent may be recovered.
Another object is to be able to economically use some types of fluoro-chloro-hydrocarbons or similar highly volatile solvents for cleansing purposes.
A further object is to provide -a method and means of recovering solvent vapors from materials which have been treated with a cleansing solvent, by connecting the container in which the solvent vapors are liberated from the cleansed materials with a closed circuit ducting system containing an adsorbent material which preferentially selects an organic solvent, so that the gases within the container may be recirculated through both the adsorbing material and the container with the material therein until substantially all of the solvent has been transferred to the adsorbent.
Other and further objects may become apparent from the following specification and claims, and from the appended drawing in which:
FIG. 1 is a schematic illustration of one form of apparatus in which a drying and recovery operation may be conducted; and,
FIG. 2 is a graph illustrating an important feature of the process.
Referring to the drawing, reference character 1 indicates a substantially air-tight casing provided with a suitable door 2 that may be satisfactorily sealed with respect to the interior of the casing when the door is closed to prevent leakage of vapors therefrom. Within the casing 1, and shown in dotted lines, is a cylindrical cage 3, preferably formed of foraminous material, which is rotatably driven by .a motor, not shown. The casing 1 and its associated parts illustrate a tumbler type of drier in which garments or fabrics are disposed after washing for the removal of residual solvent, but it is within the scope of the invention that the garments might be washed with solvent within the casing -1, and after completion of the washing operation, the excess liquid solvent could be removed therefrom, so that the drying operation would occur in the same equipment.
To the right of the figure, and designated by general reference numeral 4, is apparatus for recovering the vapors of solvents liberated from material within the casing 1. Reference character designates a container formed with an upper neck portion 6, and a lower neck portion 7. Within the interior of container 5 is a foraminous plate 8 that forms a support for a mass of adsorption material 9, here illustrated as pellets of activated carbon, which has the capacity of readily adsorbing the vapors of organic solvents.
For transmitting the vapors from container 1 to container 5, a duct 10 extends from container 1, and contains a suitable damper 11 capable of controlling the flow of gases therethrough. The duct 10 extends to a casing 12, within which is disposed a lint bag, or other filter apparatus for eliminating any particles or solid objects from the gases. A fan casing 13 is operatively connected to casing 12, and contains a rotary fan blade 14 that is driven by a motor 15. A duct 16 forms an outlet from the fan casing 13' and contains a suitable damper 17, which regulates the flow of vapors into the upper neck portion 6 of the container 5.
A duct v18 is joined at one end to one side of the lower neck portion 7 of container 5, and this duct extends to container 1, and contains a suitable damper 19. Another duct 20 extends from the opposite side of the lower neck portion 7 of container 5, and contains a suitable damper 21. The duct 20 forms a discharge for waste gases and will ordinarily extend to the atmosphere exterior of any enclosure in which the equipment is mounted.
To remove adsorbed solvent from the mass 9, an aqueous material is used. As shown a steam separator 22 has an inlet steam conduit 23, extending from a source of boiler steam and contains a control valve 24. A steam outlet conduit 25 extends from the separator 22 to a lower portion of the container 5, and said conduit contains a control valve 26. A conduit 27 containing a control valve 28 forms a vapor outlet from the upper extremity of the upper neck portion 6 of container 5, and joins a condenser 29 which has at its lower extremity a gravity separator 30 for separating the immiscible liquids.
To aid in removing the aqueous adsorbent from the adsorbing mass 9, an air heating cabinet 31 is joined to duct 10 by a branch connection 32 in which is disposed a suitable damper 33. The casing 31 is formed with an air inlet opening 34, and contains a heating coil 35 which is illustrative of any means of satisfactorily heating air prior to its admission into the ducting system.
The operation of the invention will now be explained. With the parts in the positions shown, it is assumed that the cage 3 contains a load of garments or other similar material which is saturated with cleansing solvent, and it is further assumed that the cage 3 is being rotated so as to produce a tumbling action of the materials in cage 3. Then, with motor 15 driving the fan 14, gases are withdrawn from casing 1 through duct 10 into the casing 12, where lint or any other solid object is removed therefrom, and the gases are forced through the conduit 16 into the upper portion 6 of container 5, whence such gases pass downwardly through the adsorption mass 9 penetrating the metal plate 8, and returning to casing 1 through the duct 18. The gas originally flowing from container 1 will under these conditions be saturated with solvent vapors, and as such gases enter the container 5, the organic vapors are progressively adsorbed by the adsorption material so that only relatively vapor-free air is returned through conduit 18 to the container 1. The adsorption process is an exothermic process, and the amount of heat generated within the adsorbing mass is about equal to the latent heat of vaporization of the rapid evaporation of solvent from the garments, which may be dried in the same manner.
action tends to cool the gases passing through the duct 10 so that the heat gain from the adsorption process is profitably utilized to increase the rate of evaporation of solvent from the fabrics.
Similarly the cooling elfect produced by evaporation of solvent from the fabrics tends to cool the adsorbent, thus tending to counteract the heating effect of the adsorption process. This is important, because as the temperature of the adsorbent is increased substantially above about F., the adsorbing capacity of the adsorbent is decreased.
After drying in the manner described above, the load of garments or fabrics are removed from the cage 3 of casing 1 for finishing, and additional loads of material When sufficient solvent has been transferred to the adsorption mass to substantially saturate the particles of the mass, the adsorbent is then liberated of the liquid solvent by a heated aqueous treatment. The dampers 17 and 19 are closed and steam is admitted from the separator 22 through the conduit 25 into the lower portion of container 5, where it passes upwardly through the adsorption mass 9 and leaves through the conduit 27 to the condenser 29 from which the condensed liquids pass to the separator 30 and the liquid solvent is recovered for re-use. After all of the recoverable solvent has been removed from the adsorption mass, the flow of the aqueous desorbent is terminated and dampers 17, 21 and 33 are moved to an open position, with dampers 11 and 19 closed so that now the fan 14 will draw atmospheric air into the opening 34 of the heater 31, where such air flows into heat exchange relationship with the coil 35 to be substantially heated prior to entering duct 10.
The extent and duration of the drying operation is dependent upon the condition of the adsorbent 9. It is preferred that the adsorbent should be free of condensed moisture, but not necessarily bone dry, since this may cause the removal of a normal amount of moisture from the fabrics. Also it is necessary that the temperature of the adsorbent should not substantially exceed about 100 F. I have found that air heated to a range of -l50 F. may be passed to a carbon adsorbent and will produce satisfactory drying of the carbon when the temperature of said air leaving the carbon is about 105 F. thereby indicating the presence of some residual moisture in the carbon. Hotter air may be forced through the carbon, but when that is done, it must be followed by cool air to reduce the temperature of the carbon. Carbon granules are sensitive to moisture and the latter procedure is not advisable if the moisture content of the ambient air approaches saturation. When the adsorbent bed is treated with relatively dry air following the aqueous liberation of the solvent, the adsorbing capacity of carbon is materially increased.
As a practical example of the process, utilizing apparatus substantially as shown in the drawing, the adsorption bed was initially liberated of solvent by treatment with steam, after which the bed was dried with air that had been heated to substantially F., and the operation continued until the temperature of the air leaving the carbon bed, and being discharged to atmosphere was substantially 105 F. Then, a load of garments was washed with perchlorethylene in the cage 3, and the excess liquid solvent removed therefrom. Before starting the drying cycle, the temperature of the saturated garments was substantially 80 F. The drying operation was conducted in the manner previously disclosed for a period of 30 minutes, and readings were made of the temperature of the gas leaving the garments going in the direction of the carbon bed, as well as the temperature of the air leaving the carbon bed denuded of solvent vapors and returning to the fabrics within container 1.
Referring now to FIG. 2, which is a graph made from the average of the temperatures of several test runs. The curve A designates the temperature readings of the vapor ladened gas leaving container '1, while curve B designates the temperature readings made of the air leaving the adsorber 5 after being denuded of solvent vapors. Since evaporation of the solvent from the fabrics produces a cooling effect, the readings of curve A are initially below the temperature of the fabrics when placed In the dryer. Since there will be some moisture in the adsorbent, the initial reading of curve B is likewise less than the original temperature of the fabrics, but because of the exothermic nature of the adsorption process, the readings of curve B rapidly increase and this rise in temperature s soon reflected in the readings of curve A. The net eifect of the process is that the heating effect of adsorption reduces the relative humidity in container 1, as well as slightly heating the fabrics; while the cooling effect of evaporation within container 1 tends to cool the adsorbent.
After 30 minutes the fabrics were substantially free of any solvent odor. After the process had been conducted to the point where the carbon bed had become substantially saturated with solvent, it was observed that the heating effect of the adsorption process became negligible. Thereafter, the carbon bed was again treated with steam to remove the solvent condensed on the carbon particles, and it was observed that the amount of solvent recovered from the carbon exceeded by more than 20% the amount of solvent normally recovered from a substantially saturated bed of carbon which had not been treated with heated air.
In the specific example referred to above, the solvent utilized was perchlorethylene. When fabrics are cleansed with trichlorotrifluoroethane, the overall results are similar, except that this solvent has a boiling point of about 117 F., and it volatilizes more rapidly, and therefore, less time is required for drying; however, insofar as the reaction with the adsorbent and the fabrics was concerned, as illustrated in FIG. 2 of the drawing, the results are similar to the chlorinated solvent.
A salient advantage in the present process is that fabbrics can be satisfactorily dried within a reasonable period of time without the necessity of substantially heating the vapors that are in contact with the garments. By eliminating the heating of the fabrics or garments, in addition to obvating the bleeding of dyes, if the fabrics contain stains of substances that are not soluble in the specific solvent, such materials are not set in the fabric, and may be removed by spotting with other cleaning agents.
Another important advantage is that by eliminating a substantial heating of the fabrics, linting of the fibres of the fabrics is inhibited.
Another advantage is that with the present process, there can be a substantial saving in the cost of drying equipment by eliminating the structure necessary for both heating and cooling the gases that are normally recirculated through the drier.
The invention is not limited to the specific structure shown in the drawing but is defined in the terms of the appended claims.
1. In a process of dry cleaning garments and/or textile materials with an organic solvent having a latent heat of vaporization less than that of water, a low temperature method of removing said solvent from said materals, comprising the steps of disposing the solvent ladened materials in a substantially vapor-tight enclosure, enclosing a mass of solid adsorbent which selects an organic solvent in preference to water within a portion of a confined channel whose opposite ends are joined to spacedapart portions of said enclosure to form a closed substantially gas-tight circuit, cyclically passing the gas in said circuit from the enclosure through the adsorbent and back to the enclosure until the materials are relatively dry, the circulation of gas in the circuit through the enclosure increasing the rate of evaporation of solvent from the materials therein and thereby reducing the temperature of gases passing to the adsorbent proportionate to the amount of solvent being evaporated, at which temperature the said gases are introduced into the adsorbent, the adsorption of vapors from said gases by the adsorbent causing the latter to be heated to a temperature proportionate to the amount of vapors being adsorbed, substantially at which temperature the residual gases are returned through the circuit to the enclosure to increase the rate of evaporation of solvent from the materials, thereafter recovering the solvent from the adsorbent by isolating the portion of said channel containing the adsorbent from the remainder of said circuit, passing steam through said adsorbent and directing the vapors emitted therefrom through a condenser, and subsequently removing residual moisture from the adsorbent by admitting into a part of the circuit and forcing such air through the adsorbent and then out of the circuit.
2. The process described in claim 1 in which the solvent is a chlorinated hydrocarbon.
3. The process described in claim 1 in which the solvent is perchlorethylene.
4. The process described in claim 1 in which the solvent is a chloro-fiuoro-hydrocarbon.
5. The process described in claim 1 in which the solvent is trichlorotrifluonoethane.
6. The process described in claim 1 in which the air used to remove the moisture from the adsorbent has been substantially heated.
References Cited in the file of this patent UNITED STATES PATENTS 1,418,363 Ooggeshall June 6, 1922 1,905,900 Carlisle et a1. Apr. 25, .1933 2,249,624 Bichowsky July 15, 1941 2,266,031 Harman-Ashley Dec. 16, 1941 2,499,328 Pawlansky Feb. 28, 1950 2,506,578 Case May 9, 1950 2,511,666 Barr June 3, 1950 2,910,137 Victor Oct. 27, #1959 2,913,832 Kaufman Nov. 24, 1959