Recycling of solvents in dry cleaning

The recycling of solvents in dry cleaning is very important, because solvents are too expensive for single use. Three different systems are used for the cleaning of the solvent in order for it to be recycled  

Filtration is a simple physical process, separating insoluble parts from the solvent. It is done during the cleaning cycle. 

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With aerosol cleaning products, a quick spray and a blow-dry with compressed air, or a wipe with a dry rag or towel is all that is required to remove the unwanted soil. Another benefit of spraying is the motive force of the spray, which assists in soil removal. Because of the tendency for aerosol products to finely atomize the cleaning solvent and increase air emissions, some air-quahty agencies are mandating the use of low-vapor-pressure solvents in hand-pump dispensers. This action reduces solvent loss to the atmosphere and increases the amount of waste solvent, which must be collected and stored for subsequent recycling or disposal. 

The most common method for cleaning the gun is to put a small amount of solvent into the pressure pot or cup gun, and clean the gun by spraying directly into the water curtain or dry filter of the spray booth. This is an unnecessary and expensive generation of waste. Both air emissions and waste paint are generated. In some states, notably California, regulations require that the paint operator spray gun cleaning solvents into a closed container so as to minimize VOC solvent emissions. This practice also allows recycling of the paint sprayed into the container (Joseph 1989). 

It is not always acknowledged that solvents are used for dry media reactions, both to load the reactants onto the support and to elute the products after reaction. If the supports are polar materials such as alumina or silica gel, which are commonly used in liquid chromatography, substantial quantities of solvent may be required to remove the organics. For clean processing, recycling of the solvent and the support would be essential. The latter does not appear to have been demonstrated and may prove difficult... 

Chlorinated solvents and many other solvents used in industrial finishing and processing, dry-cleaning plants, metal degreasing, printing operations, and so forth, can be recycled and reused by the introduction of carbon adsorption equipment. To predict the size of the adsorber, you first need to know the vapor pressure of the compound being adsorbed at the process conditions. 

Dry eleaning solvents are recycled. The solvent consumption in modem machines is in the range of about 1 - 2 % per weight of the dry cleaned textiles. 

In order to have an efficient continous process, an optional recycling of the drying gas is applicable. First a filter removes the smallest particles and a following condenser cleans the later drying gas from solvent and monomer. The condensate could go back to the vessel of the inlet, while gas will be heated up by an electrical heating and fed into spray dryer again. 

An example along the above lines may be the new solvent-spun fiber Tencel, by Courtaulds, which recently was introduced. It is claimed to have an environmentally clean process, with virtually total recycling of the solvent." The manufacturing process is said to involve the dissolving of pulp in hot amine oxide, filtration of the solution, and then spinning into a bath containing a dilute solution of the solvent. The bath removes the amine oxide from the fibers, which are washed and dried, and the removed solvent is reclaimed for further use. The final fiber is said to have a different molecular structure from that of normal rayon, and a smooth surface and a round cross section. The fiber is claimed to be stronger than cotton and normal rayon in both the dry and the wet states. 

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