National Clothesline

Part 2

Conditioning Solvent With Activated Carbon And Activated Carbon/Clay Combined

art 1 of this series described the cartridge filters, and their components. This Part 2 article contains details about components three and four of the cartridge filters described in that column: “Inner chamber and Carbon or Carbon/Clay Mixture.”

Adsorption verses absorption

This type of solvent conditioning employs the principle of adsorption, which is not to be confused with the principle of absorption.

A simple explanation of adsorption is where a liquid or gas, carrying a substance, passes over a medium and deposits its substance, by extraction, onto that medium while the same liquid or gas continues on.

In the case of activated carbon, an electromagnetic action takes place which extracts the dyes from the solvent passing over the surface. Substances are actually attracted to the surface of the adsorbing material and held there in somewhat the same way metal filings are attracted and held by a magnet.

Absorption, on the other hand, is where the water is soaked up by a sponge or cotton towel. The liquid is held between the fibers of the sponge or in the pores of the cloth and does not pass through. An example is the load of garments that have been washed but not yet extracted out. The water or solvent is absorbed by the fabrics, and only the excess that the garments cannot hold is pumped or drained out of the drum.

Since the action of activated carbon depends on adsorption on the surface, the greater the surface, the more area there is for adsorption. The carbon must be activated before it will have the ability to adsorb. Carbons can be made from many things: coal, peat, lignite, paper mill waste, corncobs, petroleum, wood and vegetables. Activation may be thought of as a process to clean the surface of the carbon so the surface can adsorb impurities.

The activated carbon consists of both macro pores on the outer surface (result of the granulating process), and the micro pores (result of the activation process) in the inner surface. Figure 1 shows a carbon chip with the small openings on the surface and the larger channels within.

Adsorption is accomplished by surface area and structure of the pores and channels.

The process is Vander Waals forces of physical attraction and congregation, etc., whereby the soluble dye and selective NVR are adsorbed on the surfaces of the carbon chip and, therefore, the adsorbed molecules are easily released from the surface or desorbed. This explains why it is possible to regenerate activated carbon.

Ash

Pure carbon will burn completely when heated to a high enough temperature and leave no ash or residue. Most activated carbons, however, are not 100 percent pure and leave some ash when ignited. The amount of ash left gives some measure of how much real carbon is present. The higher the ash content, the less the amount of actual activated carbon present for the adsorption of impurities.

Carbons prepared from mineral materials, such as lignite and peat, have very high ash content.

One of the principal activated carbons still used by some cleaners is reported to contain over 12 percent ash. Since alkaline oxides are often present in the ash, carbons high in ash content often have alkaline pH’s.

The pH value of a material that is neither acidic nor alkaline is 7. Alkaline materials give pH values greater than 7 while acidic materials give values less than 7. The pH value of some activated carbons is greater than 7. These alkaline materials may react with fatty acid type impurities in the solvent to form soaps.

These soaps will not then show up as fatty acid on the Fatty Acid Test, but they may still remain dissolved in the system as impurities. A desirable carbon is one that does not neutralize the acids and leave soap in the system nor cause (anionic charge) detergent breakdown and cause odor in the solvent.

Activated carbon is a desirable adsorbent because it removes much less ionic detergent and very little water. It removes little NVR which must be either distilled out or adsorbed by activated clay.

But the carbon does an excellent job of adsorbing loose dyes which are constantly being emitted from fugitive-dyed garments during the filter circulation wash cycle. It is ideal for use with anionic drycleaning detergents and moisture additions on through-the-filter single bath runs.

Activated clay adsorbent

Since the activated carbon is essentially used to remove dissolved dyes from the solvent between distillations, there is another form of adsorption material used to remove most of the other NVR elements from the solvent. This material is activated attapulgite or montmorillonite clay which is extruded and oven-baked.

Like carbon, the clay material is not porous, and the solvent has to channel through the small interstices between the clay chips.

As with carbon, the granular process creates macro (surface) pores, and the activation process creates the micro (inner area) channels.

This clay is known for its selective adsorption.

The order of sorptivity is suggested as: water; alcohol; acids; deludes; ketones; felines; natural esters; aromatics; cycle-paraffins; paraffins. Also, straight-chained hydrocarbons are more readily swabbed than those with branched chains.

Therefore, one can see that most soluble soils in the solvent fall for the most part in the above list.

However, the removal of ionic detergents and dissolved water also takes place which is undesirable in a charge system as well as in the cationic injection system.

Practical operation

The center tube outlet of the cartridge filter (part 5) is where the filtered and purged solvent finally exits. This tube can be made from a resin-treated laminated paper or perforated metal, and it is wrapped with either nylon or polypropylene to prevent any fine insoluble particles or dust from being carried out of the cartridge and into the cleaning machine’s drum.

Additional protection against this cartridge leakage of fine insoluble particulate soil is with the use of felt washers or pads placed between each cartridge and on the ends of the first and last cartridge in the filter housing. The felt pads will adsorb the insoluble particles as the solvent passes through them. They also serve as an adsorbent seal between the metal top and bottom cartridge covers of each cartridge and the end plates of the housing.

With decent distillation, the average life of one pound of activated carbon is about 250 pounds to 300 pounds of garment cleaning. By applying the total amount of carbon in your filtration system (my article of January 2003) to the factor of 250 or 300 you will know approximately when to change the carbon filters. Bear in mind that when the carbon or clay chips have their micro and macro pores filled they will begin to discharge the dyes and NVR that they have previously adsorbed. This is the reason why your solvent gets darker as the time for cartridge replacement is extended.

Between filter cartridge changes, you should maintain a daily distillation rate of 15 gallons (minimum) of working solvent per 100 pounds of cleaning. Most operators distill more for good solvent clarity.

Use a pre-lint filter if your system is exclusively cartridge filtration.

Using a carbon core cartridge filter in place of a standard size all-carbon filter, which contains no pleated paper, as a carbon tower or “polishing filter,” can result in clogging the interstices between the carbon chips with ultra-fine particulate soil with the use of a spin disc filter.

The soil and carbon are both non-porous, and high filter pressure with greatly reduced solvent flow can result.

I have seen many new machines equipped with two filter circuits: one circuit with a centrifugal disc filter (small sized) and a small canister holding either one or two all-carbon cartridges (depending on size of machine), and the second circuit with a larger housing holding several standard size carbon core cartridges or split jumbo size all carbon (with pleated paper) cartridges.

The first circuit is used primarily for cleaning dark colors due to lack of satisfactory carbon, and the second circuit is used primarily for cleaning light colors due to more carbon for “lighter color” solvent.

Distillation is usually used more for the light colors. In other words, the dark colored garments get short-changed in quality cleaning as evidenced by the darker colored solvent.

Next month, I will discuss centrifugal disc filters: construction, operation, maintenance and recommendations for ideal filtration systems.

Correction

I stated in my last article (January 2003) that weights of activated carbon can vary between manufacturers, but I selected some weights from manufacturers that are no longer in business. These weights were then somewhat heavier than the average offered by today’s manufacturers, mainly due to the different types of basic materials currently used. However, the amounts of carbon by volume are essentially the same.

Therefore, the average weights of activated carbon should be changed to the following:

Standard size all-carbon: 8 pounds.

Standard size carbon core: 2 pounds to 2.5 pounds.

Split Jumbo size all carbon: 8.25 pounds.

Jumbo size all carbon: 16.5 pounds. Not stocked by most suppliers.

Also, I would lie to emphasize that the pleating process of the paper greatly contributes to the removal of insoluble soil through the tortuous path of solvent flow over the pleated paper. This, of course, results in the Vander Waals action as I described and illustrated in the article.

Note: My spotting video, “The Caplan Method of Stain Removal,” which includes my comprehensive text and the handy spotting board reference, is available in English, Korean (video only) and Spanish (video only) from the Golomb Group, c/o Dennis McCrory, 7664 Plaza Court, Willowbrook, IL 60521, phone (800) 679-5856. A lecture and demonstration are presented similar to my classes over the years at IFI and SDA. This video and text are ideal for training inexperienced spotters as well as a good review for experienced spotters.

Also available from the Golomb Group, in English and Spanish, is my video on step-by-step shirt finishing which includes my comprehensive text in loose-leaf form (English only) outlining each procedure for a single-operator and two-operator cabinet shirt unit using a cabinet sleever. Proper forming of the collar using heated collar formers is demonstrated. Each lay is demonstrated for top quality with very little effort by the operators. Attractive detailing and packaging of the hangered shirt, padding, steam pressures and timing are all discussed. A unique wash formula to give whiter whites, brighter colors and total removal of grease and body oils is included in the loose-leaf note book.

Stan Caplan has over 35 years experience in his own high volume dry-cleaning, laundry and tailoring plant and two package plants with adjoining coin-operated laundry and drycleaning. Stan is the former chief instructor at the International Fabricare Institute, the Southwest Drycleaners Association and various other trade association-sponsored schools throughout the US and courses in Canada, Mexico, South Africa, Singapore and Hong Kong. Stan offers consulting, training and engineering services in all areas from customer service area to the boiler room since 1981. His complete system withtotal quality management will produce maximum efficiency, economy and product excellent quality. Stan can be reached at 7341 Amberly Lane, Suite 310, Delray Beach, FL 33446, phone/fax (561) 496-2548. His e-mail address is stancap100@aol.com.