CA2337529A1

CA2337529A1 - Liquid carbon dioxide cleaning utilizing natural and modified natural solvents

Info

Publication number: CA2337529A1
Application number: CA002337529A
Authority: CA
Inventors: Sidney C. Chao; Edna M. Purer; Nelson W. Sorbo
Original assignee: Individual
Current assignee: Raytheon Co
Priority date: 1999-06-11
Filing date: 2000-05-11
Publication date: 2000-12-21
Also published as: WO2000077135A2; EP1144565A3; CN1320183A; AU2003231689A1; ID28922A; AU5440200A; JP2003502135A; MXPA01000334A; IL139799A0; WO2000077135A3; EP1144565A2

Abstract

An article having soil in contact therewith is cleaned by treating at least a portion of the article with a bio-diesel compound, and agitating the article in contact with dense-phase carbon dioxide to dislodge the soil from the article. The bio-diesel compound may be used in a pre-treatment step, during the agitation step, or both. The bio-diesel compound may be mixed with water and/or a cleaning enzyme.

Description

:.IQLiII~ C.:4~N DI~XII~E CLEA~1ING
L1TILI~Il~G Iml~.TtJI~~:L ~-1I~I~ l~IC'1'~IF'IEI~ N~TUI~L S~LVE~TTS
~ACI~GIZ~LTtVD CAF' THE I°~1~IE~ITI~RT
This inven:ion relates to the cleaning of articles, and, more specifically, to an approach for improving carbon dioxide cleaning processes.
Conventional organic cleaning solvents historically used in home, industrial, and commercial markets, such as perchloroeihylene, CFC-113, l, l, l trichloroethane, and petroleum-base solvents, pre sent health and safety risks, because they madr be carcinogenic or t'lammable. The solvents may also be 10 environmentally d~dtrimental, because they are ozone depleting or smog producing.
The tightening re;~ulatory ccmtrols exwrcised on the making a.nd using of these solvents has resulted in escalating operating costs and liabilities for all market segments c~nnect~:d to these products.
As a result, alternative cleaning media have been developed and 15 implemented to ~°educe the health and environrriental risks associated with cleaning. hater s~s a degreasing medium has limif:ations, because it requires a post-cleaning drying step, arid the cleaning process, is often lengthy and energy intensive. V~Iater also has poor organic SO11 solvency, so that additives and vig~ous agitation are usually required to remove organic soils. The treatment of 20 the effluent may be expensive, prior to its discharge.
Carbon dioxide is an inexpensive and unlimited natural resource that is non-toxic, non-flammable, ncm-smog pj-oducing, and non-ozone depleting. in its dense phases, both liquid and supercritical, it exhibits solvating properties typical of hydrocarbon soi.vents. IVIavtter dissolved in dense-phase carbon dioxide may be 25 readily recovered in its concentrated form by gasifying the carbon dioxide.
No secondary waste stream is produced such as is associated with the use of conventional solvents. The carbon dioxide does not damage fabric or dissolve common dyes, and. its properties make it a good dry cleaning rrledium for fabrics and garments. It is also a suiaable degreasinglclear~.ing medium for the removal -.
_ 'S
of light oils from commercial and industrial parts and components. I3ense phase carbon dioxide has been referenced as a cleaning fluid for garments and components in nL~rnerous parents, including, for example, LJS Patents j,0I3,366;
j,316,591; 4,012.194; 5,467,492; and 6,267,45.
j ~ne disadvantage ofthe dense-phase cart~n dioxide is that it is a relatively mild solvent, not readily suitable for heavy oils and greases. 1(n addition, it does not remove hydrophilic soils. f1s a result, some dense-phase carbon dioxide processes have incorporated additives that either enhance or modify the bulk solvency of the c~u-bon dioxide itself far organophili.c soils, or help co-solvate the 10 hydrophilic soils by their ability to carry water into the dense-phase carbon dioxide medium. The use of such additives are referenced in numerous patents, including, for exa::nple, IJS Patents 5,6~~,977, 5,63,473; 5,616,705;
~,~66.005;
and 5,79,505.
Typical additives used to enhance the organic solvating power of the I S dense-phase carbon dioxide have been the same cornpounds that are targeted for displacement because of then harmful :nature. ~xam.ples include co-solvents such as low alkanes, terpenes, alcohols, ketones, benzene, toluene, xylenes, and chlorinated, fluorinated, or chloro-fluorinated compounds.
Also typically, the separation or removal of ionic or water-soluble soils has 20 been enhanced by molecularly engineered surfactants designed to carry water into the carbon dioxide medium. 'The disadvantage of these additives is their cost, as they require elabo:Pate synthesis. The surfactants may also require the use of the eo-solvents discussed above, which defeats t;he beneficial health and environmental naW re associai:ed with the use of the dense-phase carbon dioxide.
25 There exists a need for improving the efficiency of liquid carbon dioxide cleaning processe;~, which addresses the removal of heavier oils, greasesa and hydrophilic soils, while still maintaining the health arid environmental benefits of the bulk dense-phase carbon dioxide solvent. The present invention fulfills this need, and further ~>rovides rel'.ated advantages.
30 S AIZ~I ~F 'TI-I~ I~IV~~f'TI~I~l This invention provides a method and apparatus for dense-phase carbon _ .J _ dioxide cleaning of articles. The approach of the invention retains good effectiveness in rernoving particulate soils from the articles, and has increased effectiveness in removing grea:9e, oil, and hydrophilic soils as compared with the use of only the dense-phase carbon dioxide. The approach makes use of natural and modified natural additives with good solvating properties. The additives are environmentally friendly, non-toxic, biodegradable, and free of sulfur and aromatics. They may be rinsed with water and form stable emulsions with other phases such as water, mineral spirits, alcohols, and so;~~ne terpenes. The additives may be used in conjunction with known dense-phase carbon dioxide cleaning procedures.
In accordance with the invention, a method for cleaning an article comprises the steps of providing an article having soil in contact therewith, treating at least a portion of the article with a bin-diesel compound. and contacting the article. with dense-phase carbon dioxide to disloc~.ge the soil from the article.
l~ ~ptionally, the arti~~le may be rinsed to remove the l:>io-diesel compound, if it is present after contacaing is complete.
"~io-diesel compounds" are a recognized class comprising alkyl monoesters of vegetable oils, preferably the methyl esters of vegetable oils.
~xaynples of suitable vegetables oils are safflower, sunflower, canola, and soybean oils. The bin-diesel compounds are fully compatible with dense-phase (liquefied or supercritical) carbon dioxidcr. The ter~rn "bin-diesel" originates in an unrelated use of such compounds as ingredients i:n synthetic diesel fuel.
- The article t.o be cleanE:d may be fabric or otl~cer articles such as metallic, ceramic, or plastic harts to be degreased and cleaned. The contacting of the bio diesel compound to the article and the agitating of the article may be accomplished completely or partially serially, or simultaneously, as may be appropriate for particular applications. Thus, for example, the article may be pre-treated with the bin-diesel compound anal thereafter :placed into a pool of dense-phase carbon dio~:ide in a pressure chamber and agitated. The bin-diesel compound may insl:ead be added to the pool of dense-phase carbon dioxide in an in-situ treatment. .~ combination of pre-treatment and in-situ treatment may be used. The pre-treatment may be a general pre-trva~~rnent such as soaking, or a localized pre-treatment such as the ''spotting" of a fabric. The bin-diesel _. LS.
compound may be formed into an emulsion with water and/or enzymes, and used in any of these prc:-treatment and in-situ treatment alternatives. The contacting and agitating ma:r be accomplished by any operable approach, such as, for example, the force of liquid jets of the dense-phase carbon dioxide directed into the pool, the bublr~lina as some of the dense-phase carbon dioxide vaporizes, a tumbling action. stirring of t:he pool by an impeller, circulation of the carbon dioxide with a pump, a.nd ultrasonic cavitation. Thus, a 'vide variety of treatment and agitation procedures usir,~g the bio~-diesel cor~apound are within the scope of the invention.
The invention provides an irn.proved approach to cleaning processes utilizing dense-phase carbon dioxide as a cleaning medium. The approach addresses the use of specific natural (e.g., enzyme) arid modified natural additive (e.g., bio-diesel) compounds that enhance the cleaning efficiency and solvating power of the dense-phase (liquid) carbon dioxide. T"ne function of the bio-diesel 1 ~ compound, alone or in conjunction. with additives such as water and/or enzymes, is to solvate and mobilize orgLuaics such as oils and gz°eases, as well as hydrophilic particulate soils, so that they rnay be more readily dislodged from the article being cleaned by the agitation of the dense-phase carbon dioxide. These additives, alone or as carriers of enzymes and/or water, are environmentally friendly, non-toxic, biodegradable, anc~. free of sulfur or aromatics. The method of the invention enhances the effectiveness c~f the liquid carbon dioxide cleaning medium to remove heavy oils, greases, and hydrophilic soils, vrhile it retains its health and environmentally benign properties as a solvent. C~the:r features and advantages of the present invention will be apparent from thc: following more detailed 2~ description of thc~ preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of e;xa.mple, the principles of the invention. The scope of the invention :is not, however, limited to this preferred embodiment"
13F:IEF I~ESC:IZIPTI~~t OF TI-IE L~I~WINC~~
3tl Figure 1 is a~ block flow diagram of a preferred embodiment of a method according to the iwvention;

_j_ Figure 2 is a schematic system diagram of an apparatus used in the method of Figure l; and Figure 3 is a representation of a chemical reaction used to produce a bio-diesel corrlpound.
DETA ILED I~E~CRIETIO~d ~F TF-IE I~I~IEoITIn~1 Figure 1 depicts a preferred approach for practicing the invention. An apparatus is provide°_d, numeral 20. 'The apparatus ma.y be of any operable type to accomplish the remaining steps of the process, and Figure 2 depicts one embodiment of a preferred apparatus 40 most suitable for co~;nmercial fabric-cleaning operation:.
The apparatus 40 includes a cleaning chamber 42 having a pressure vessel 44 and a pressure door 46 that seals to the pressure vessel 4:~.. The cleaning chamber 42 is designed to withstand the internal pressures utilized in the subsequent steps, ~~pically in the range of about ~~0 pounds per square inch (psi) lj to about 1000 psi, preferably about 'f00-X00 psi, and is made of steel. A
perforated basket 4~ with openings therein is supported w1t111n the cleaning chamber 42, with an open end facing the pressure door 46 so that articles may be placed into or removed from the perforated basket 4~ when the pressure door 46 is open. In the illustrated embodiment, the pressure vessel 44 and the perforated basket 4~ are cylindrically symmetric about a cylindrical axis ~0.
Dense-phase carbon dioxide cleaning medium is delivered to the interior of the cleaning chz:mber 42 b:y one or more manifolds 52. Additives are mixed with the dense-phase carbon dioxide, as will be discussed subsequently. Each manifold j2 has once or more jea orifices 54 therein through which the dense-phase carbon dioxide flows. The jest orifces 54 are preferably positioned so that the flow of cleaning m~rdium from the jet orifices 54 is aimed into the interior of the perforated basket 4.3 through t:he openings therein and thence around the articles being cleaned. .
In operation ofthe apparatus 40, l:he dense-phase carbon dioxide is pumped through the rnanifc~lds 52 and into the cleaning char;~ber 42 by a main pump operating through appropriate valves 5~ and 60. The dense-phase carbon dioxide ._6-cleaning medium is initially pumped to a preset depth w°ithin the cleaning chamber 42 to form a pool of the liqu~°fied cleaning mediurr~. Upon reaching the desired pool depth, additional dense-phase carbon dioxide is forced through the jet orifices 54 to agitate the pool and the articles therein.
After passing through the cleaning chamber- 42, the dense-phase carbon dioxide cleaning medium flows to a lint trap 62. ~,vhich filters solid matter from the cleaning medium. (The lint trap 62 may be omitted where non-fabric articles are cleaned.) A valve 66 permits the dense-phase carbon dioxide to be routed to a more extensive filter train fib, to a condenser 70 leaving a refrigeration system 72, and back to t1e inlet side of the :main pump 56 through a valve 74. In a ':bypass" setting, the valve 6fi permits drained dense-phase carbon dioxide to be recovered.
Liquefied cleaning medium is supplied to the main pump 56 from a storage tank 76, operating through t:he valve 74. ~ption,al additives to the liquefied 1 ~ cleaning medium to be discussed subsequently, such as watej~ or enzymes, are supplied on the inlet side of the main pcranp ~6 from ~u-~ additive supply 7~
through an additive pump f~0.
Cleaning medium may also flow from the cleaning chamber 42 back to the inlet side of the main pump 56~ through a drain line ~ 2 operating through the valve 74, during the ''drG.in'' portion of the process.
'The apparatus 40 further includes a vent valve ~4 permitting the cleaning chamber 42 to be vented to atmosphere. A return path for gaseous carbon dioxide through a compres;~or ~6 to the condenser 70 or to the storage tank 76 is provided with appropriate v;~lves ~~, 90, and 91.
2~ During claming of arfi:icles, soluble non-particulate soil is dissolved into the cleaning medium. To separate the soluble non-particulate soil from the cleaning medium, a distillation column 92 with appropriate valuing 94 and 96 is provided. The di;~tillation is, typically performed off line, when the cleaning chamber 42 i.s not i:n use for cleaning articles.
This apparatus 40 is designed primarily for cleaning fabrics but may be used t~ clean other articles as well. The apparatus is ordinarily optimized for the type of article to b~; cleaned.
In a typical cleaning cycle, the material to be cleaned is placed into the _, perforated basket 4S within thc~ cleaning chamber 4?, and the pressure door 46 is closed. The valve c~ 1 is opened. and the pressure between the storage tank 76 and the cleaning chamher 42 is equalized. 'Jalve 74 is in a "chamber'' position, and fluid from the stora;e tank 76 is pumped into the cleaning chamber 42 by the main pump 56 thr,ocigh valve 58 (in a ''chamber" position"), until the chamber 42 reaches a desired liquid level. Valves ~S and 90 are closed at this time, and a recirculating loop is established through the lint trap 6?, the filter train 68, the condenser 70, and back to thf: main pump 5~. The main pump ~8 delivers the necessary tlo~v and pressure drop of dense-phase carbon dioxide (and additives, if present) across the orif ces j4 to agitate the load to be cleaned by a ~iow of dense-phase carborc dioxide. .fit the end of the agital:ion cycle, valves ~8 and 90 are opened,walve 5~ is switched to "drain", and valve 66 is switched to "bypass"., The liquid phase carbon dioxide is drained and recovered back from the cleaning chamber 42 to the storage tank 76 by the main pump :56, through the drain line ~2 1~ and valve 74~ (that is now in the "drain." position). At this point, the cleaning chamber 42 contains the load that has been cleaned, a.nd gaseous carbon dioxide.
The cleaning chamber 42 is decompressed to atmospheric pressure after the gas compressor B6 recovers the carbon dioxide vapors back to the storage tank 76.
residual gaseous carbon dio:cide is vented out through the vent valve ~4, the pressure door 46 is opened, and the clean load is removed.
The metho3 of the present invention ma;y be performed with this exemplary apparatus 40 when it is applied to the cleaning of articles such as fabrrcs or garments, but it is not limited to this apparatus. For example, other types of contacting and agitation devices such as an impeller to agitate the liquid pool in the cleanin,~ chamber 42, an ultrasonic excitation transducer to produce cavitation of the liquid pool, oar any of the other techniques discussed herein may be used.
returning t~~ Figure l, an article to be cleaned is provided, numeral 22.
The article may be ~~f any operable type and configuration, as long as it fits within the perforated baskca 4~. one preferred application of the present invention is the cleaning of fabric a~-ticies such as clothing, and another preferred application is the cleaning and degreasing of parts and components.
There are several operable approaches to performing the cleaning of the _. g _ articles using the present invention. In one approach, the article is optionally pre-treated, numeral r;4. In the pre-treatment, the article is contacted with a pre-treatment fluid. The contacting may comprise, for e:;ample, a spot contacted with the pre-treatment fluid or a submersion and soaking in the pre-treatment fluid.
The article is maintained in contact with the pre-treatment fluid for a period of time, typically about 1 minuvte to about 2~ hours, preferably about 1 minute to about 60 minutes, to permit the pre-treatment fluid to solubilize any non-particulate soils fi:ced to the article.
The pre-treatment fluid, where used, preferably comprises a bio-diesel compound. Bio-diesel compounds are alkyl monoesters (specifically, the methyl and ethyl esters) of vegetable oils or fats, preferably the methyl esters of vegetable oils. Examples of suitable vegetable oils are rapc;seed, safflower, sunflower, canola, and soybean oils. Bio-diesel compounds may be prepared from used fryer Booking oil, in a re-use of this waste product. Each of the vegetable oils is made 1 j up from glycerides derived from many different carboxylic acids, but each oil has its characteristic c~~mposition. that does not differ substantially from sample to sample. Bio-diesel Bompounds are obtained by a reaction of t:ransesterificanon where the glycermc; molecule in the raw vegetable oil is replaced by methanol or ethanol as indicated in the reaction depicted in Figure° 3, where ~., Hl, and R2 are saturated or unsaturated long-chain fatty acids. In practice, the c=hemical reaction of Figure 3 may be accomplished by mixing the vegetable oil vvith methanol (or alternatively, ethanol) in the presence of potassium hydroxide, then allowing the mi~ure to settle. The bio-cuesel compound is decanted from the top of the reactor, leaving the heavier glycerine in tine bottom. This transesterification reaction is referenc=ed in Robert T. l~Iorrison, ~r~anic Chemistry, published by Allyn ~c Bacon, Inn., 1966, at page 6~6.
The bio-diesel compounds have the advantages that they have low viscosities, have low vapor pr°essures, have densities similar to that of liquefied carbon dioxide, are biodegradable, are non--toxic, are free of sulfur and aromatics, and have a relatively high Kaui-butanol value of about 60 (compared with perchloroethylene, which is <~.bout 90), indicating that they a.re good organic solvents. They are water rinsable and readily form emulsions with water, mineral spirits, alcohols, and some terpenes. They are compatible vvith dense-phase ._ ._ carbon dioxide, hilVlng abou~: the same specific gravity of 0.9.
The bio-diesel pretreatment fluid may optionally be mixed with other components, such as water and/or cleaning enzyr°nes. Enzymes are proteins that speed up (catalyze) a reaction that involves the making or breaking of a covalent bond. Enzymes G.ct by lowering the temperature ur:der which a given bond is unstable. Numerous examples exist where well-defined molecules speed up reactions between other molecules, but not all enzymatic reactions are specific.
For example, various enzymes that break down proteins into their amino acids are only specific in t1e sense that they break down the peptide bond. Enzymes typically function :in aqueous medium and have been used for a number of years in cleaning processes and in th~.e formulations of many soaps and detergents.
dome examples for the u:>e of formulations containing enzymes are spotting compounds that help remove protein-based stains (such as Mood) from garments, and detergents tl-fat have specific enzymes t:o help remove fat and oil stains in home 1 j laundry. l~Iore recently, enzymes have been used in aqueous cleaners to promote the degreasing of parts and c-omponents. I~oweve~w, enzymes are typically not soluble or readily liniscible in a dense phase car'~l5on dioxide solvent, and a ''carrier'' compound, here the; bio-diesel compound, is needed to facilitate their introduction into a dense-phase carbon dioxide process.
Any operalr~le relative amounts of the bio-diesel compound and the other components may ~e used. Preferably, the bio-diesel compound, or a mixture of the bio-diesel con..pound with enzymes or water in any ratio, is present in the deli-phase carbon dioxide in an amount of from about O.OI to about 5 percent by volume. 1_.esser amounts a;re ineffective, and greater amounts are wasteful and lead to residual contamination of the cleaned article vrith the bio-diesel compound that may necessitate its removal. The pretr eatment, if used, may be performed within the cleaning; chamber 42 or in a separate container.
The article, which optionally may be pretreated in step 24, is placed into the cleaning appar<~tus 40, numeral 26, in this preferred case ir.~to the perforated basket 4~ of the cleaning chamber 42. rChe pressure door 46 is closed and sealed.
A cleaning medium is introduced into the sealed cleaning chamber 42 to form a pool therein, numeral 2~, by pumping the cleaning medium from the storage tank 76 using the maim pump 56 in the manner described previously. The pool i preferably partiallyr or fully covers the article in the perforated basket 48.
The cleaning medium comprises the liquefied carbon dioxide with the addition of one o,° more of ahe bio-diesel compouinds discussed above.
The cleaning medium introduced i;n step 2S may be the same composition as the pre-treatment cleaning medium used in step 24, or a different bio-diesel-containing medium may be u~,ed. ~ther additives may be added as well, such as the water and/or enzymes discussed earlier. The prior discussion of these various materials is incorporated herein. The total amount of additives is typically from about 0.01 to about ~.0 percent, with a preferred range of about 0.1 to about 1.0 percent, of the total of the car~~on dioxide and the additives.
The pool and the artgcIc: therein a3.~e agitated, numeral 30. The aaitation is accomplished in the: illustrated apparatus 40 by the action of the cleaning medium pumped through thE: manifold 52 and the liquid jet onif ces 54. For this purpose, the liquid jet orifcca 54 are directed toward the interior of the perforated basket 1 ~ 4~ through the openings thei°em, to impinge upon the articles to be cleaned therein.
The agitation is continued for a period of time Buff dent to dislodge particulate soil adhered to the article, and to solubilize and remove non-particulate matter such as oila, grease, a.nd hydrophilic soils. This agitation time varies according to i:he nature of the article, the dirtiness or'°the article, and other factors, but is typically from about ~ to about 30 minutes. t~gitation may be accomplished by any operable approach, such as the preferred liquid jets, but al so hydrodynamic cavi~ation generated by a propE;ller, impeller, or blade, circulation with a pump or compressor, ultrasc>nic cavitation produced by transducers, sonic whistles, or a combination of the;~e techniques.
~(Jpon completion of the agitation, the cleaning medium is drained from the cleaning chamber 4:2, numeral 3~. ~ptionally, the article may be rinsed, numeral 34, by introducing a rinsing medium such as neat liquefied carbon dioxide into the cleaning chamber '~2 and agitating the articles with the un-modified liquefied carbon dioxide. This step is performed if the cleaning medium was used with additives, and it is desirable to remove those additives completely from the article before the article is used. For example, if the article is a fabric such as clothing, and the cleaning medium contained some bio-diesel compound, it is usually e: . , desirable to rinse o~.~t the bio-diesel compound with un-modified liquefied carbon dioxide. In other cazses, such a.s the degreasing of articles, it may be desirable to leave the bio-diesel compound. in place as a temporary corrosion-resistant coating on the articles. After the completion of the rmsgng ;step 3~, the; rinsing medium is drained out of the cleaning chamber 42.
Afier recovery of most of the liquid and gaseous carbon dioxide back to storage, the residual pressure within the cleaning chamber 42 is vented to atmospheric pressure using the vent valve ~=I, and the articles are removed from the cleaning chaml:>er 42. Amv remaining carbon dioxide evaporates during this venting and removal, leaving the articles dry and clean upon removal from the cleaning chamber.
'The f~llowing examples illustrate the application of the invention, but should not be interyreted as limiting of the scope of the invention in any respect.
Example I
1 ~ A load of staiinless steel) metal parts was treated with various greases, such as C1ZC Industries No. hlSlr'S SL33I~0, 3160, 3131, 3141, and Exxon L/hI
4721 l, and with thread cutting oil type ~ 10326 made by W.:H. Harvey. T'he parts were placed into a 12 gallon capacity liquid carbon dioxide cleaning chamber 42.
Sufficient ):.quid carbon dioxide was introduced into the chamber to submerge the load. In sorrue cases, a bio-diesel compound, commercially marketed by the Ch~~rbon CJroup, Huntington beach, C;A as SSW-1000, was added to the chamber ~2 in an amount of O.I percent, 0.5 percent, 1.0 percent, or 2.0 percent of the total of the carbon dioxide and the bio-diesel compound. The liquid carbon dioxide (and. bio-diesel compound, where present) cleaning medium was agitated for 10 minigtes at temperatures in the range c~f 0-~5°F, using a cavitating blade and propeller, to accelerate the removal of grease and oil. T'he solvent was then drained, the clamber was decompressed, and t:he parts were removed and examined for the presence of visual and tactile resid~xe.
Where no bio-diesel compound was used, only the mineral oil component of the greases was removed, .and the drawing soaps and other additives in the -greases remained to contaminate the parts in the form of a tough elm-like coating.
The thread cutting ~~il remained as a sticky residue on the parts.
~Jhere the bio-diesel compound was present, tl a removal of grease and oils was improved in all cases. Some improved removal of grease and oil vvas observed for 0.1 percent bio-diesel compound, buy: complete grease removal required at least about 1.0 percent bio-diesel compound. The cutting oil residue was removed at 0.2 percent bio-diesel compound and above. After treatment, the parts were dr<~r, a.nd there was n.o evidence of residual bio-diesel compound on the parts even for 2.0 percent bio-diesel compound additive.
Example 2 h load of stainless steel parts v~ras treated with a polishing comp~und consisting of heavy r~~a.~ses and aluminum powder in the 20-40 micrometer range.
The load was pre-tr~rated (step 24) for 30 minutes in hio-diesel compound of the same type used in Example 1.
After pre-treatment, and without drying, the Ioad was placed into the same cleaning chamber u;>ed in Example 1, anrl treated in the same mariner as described for Example 1 (stays 26, 2~, 30, and 32).
there no bio-diesel compound was used in eivher the pretreatment or the agitation steps no substantial removal of polishing compound vvas observed.
There bio-diesel compound was present, tl~aer~e was some removal of the po gl~'-skiing compound even for 0.1 percent concentration of the bio-diesel compound. Full removal required 1 percent of bio-diesel compound or more.
The example; was repeated without a pre-treatment, for concentrations of the bio-diesel! corry~ound of 0.1 percent, 0.5 percent, 1.0 percent, 2 percent, and 2~ 5 percent in the liquefied carbon dioxide used in steps 2~ and 30. Full removal of the polishing compound required a ~ percent concentration of the bio-diesel compound, substantially greater than the 1.0 percent required where a pre-treatment is employed. ~lhew the S percent concentration of the bio-diesel compound was used, it was necessary to conduct a past-agitation rinse (step 34), because there was a light film c~f bio-diesel compound remaining on the parts after agitation and draining.

,__ _l Examples l-2 demonstrate that the use of the bio-diesel compound enhances the cleani:Zg of the parts. Example 2 shows i:hat the pre-~treatnnent lowers the amount of the bio-diesel compound required in tl~ie subsequent treatment and agitation, reducing the need for post-drain rinsing.
Example 3 ~ load of :stainless stmel parts was dipped into a saturated salt water solution, removed, and allodvecl to dry. The load was then placed into the cleaning chamber discussed in Example 1. A solution of liquid carbon dioxide and bio-diesel compound/water (0.5 percent bio-diesel compound plus water, 1:1 volume ratio of bio-diesel compound. to water) was introduced into the chamber and agitated for :L0 miPiutes to solubilize the salt and remove it from the part.
The treatment was under the same conditions as discussed for Example 1. The chamber was then drained and the parts were removed and inspected.
The same experiment was performed without any bio-diesel compound and water present.
there therE; was bio-diesel compound and water present in the cleaning medium, the salt was removed. ~Jhere there was no bio-diesel compound and water present in the; cleaning rnedium, the salt was not removed.
Exam lp a 4 The same pc~Iishing compound used in Example 2 was applied to a load of stainless steel parts, and the load was placed into tre cleaning chamber discussed in Example 1.
~1 solution oEliquid carbon dioxide and bio-diesel compoundlwater/l3acto zyme enzyme (0.5 percent of brio-diesel compoundlwater/Eacto-zyme, with a ratio of I a l a l by volume bio-diesel c%ompoundewatereEacto-zyme) was introduced into the chamber and agitated for IO minutes under the conditions discussed in Example 1, except that the temperature was in the range of 40-~5°F.
facto-zyme, discussed in MSL~S 1113, is a natural multifacete°.d enzyme agent having a complex non-bacterial organic formulation that promotes the penetration and __ emulsification of oily or fatt~~ substances and is marketed commercially by the Charbon C'sroup.
The presence of the water and facto-zy°me enhanced the degreasing, as compared to a control test where no water and facto-zyme were present.
j Example ~
A load of fabric was spotted with thread cutting oil, the spots were treated with concentrated bio-diesel compound fiuid, and the load was placed into the cleaning chamber discussed in Example 1. ~,iquid carbon dio~id~° was introduced at 55-65°F into the cleaning chamber, and the load was agitated for 10 minutes.
The fluid was drained, the system was decompressed, and the fabrics were removed for evalua~ion. I~o residual cutting oil was visible on the fabrics, which were spot free and dry when removed.
Although particular em'~bodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention.
Accordingly, the in'~ention is not to be limited except as by the appended claims.

Claims

What is claimed is:

1. A method for cleaning an article, comprising the steps of:
providing an article having soil in contact therewith;
treating at least a portion of the article with a bio-diesel compound; and contacting the article with dense-phase carbon dioxide to dislodge the soil from the article.

2. The method of claim 1, wherein an initiation of the step of treating is prior to an initiation of the step of contacting.

3. The method of claim 1, wherein a completion of the step of treating is prior to an initiation of the step of contacting.

4. The method of claim 1, wherein at least a portion of the step of treating is performed simultaneously with the step of contacting.

5. The method of any of claims 1-4, including an additional step, after the step of contacting is complete, of rinsing the article to remove the bio-diesel compound therefrom.

6. The method of claim 5, wherein the step of rinsing includes the step of rinsing the article with the dense-phase carbon dioxide, after the step of treating has been completed.

7. The method of any of claims 1-6, wherein the article is selected from the group consisting of a piece of fabric, a metal, a ceramic, and a plastic.

8. The method of any of claims 1-7, wherein the step of treating includes the step of miring the bio-diesel compound with water.

9. The method of any of claims 1-7, wherein the step of treating includes the step of mixing the bio-diesel compound with a cleaning enzyme and water.

10. The method of any of claims 1-9, wherein the article is in contact with a pool comprising the dense-phase carbon dioxide during the step of contacting.

11. The method of claim 10, wherein the pool further comprises the bio-diesel compound.

12. The method of any of claims 1-11, wherein the step of contacting includes the step of directing a flow of the liquefied gas around the article.