Dry-cleaning with high-pressure carbon dioxide

Dry-cleaning is a process for removing soils and stains from fabrics and garments which uses a non-aqueous solvent with detergent added. The currently most used dry-cleaning solvent is perchloroethylene (PER), which is toxic, environmentally harmful and suspected to be carcinogenic. Carbon dioxide could be an ideal solvent to replace PER; carbon dioxide is non-toxic, non-flammable, ecologically sound, cheap, non-corrosive, available on a large scale, and can therefore serve as a permanent sustainable alternative for the currently used solvents. In this work, a dry-cleaning process using high-pressure carbon dioxide has been investigated and optimized. A disadvantage of CO2 is its limited ability to dissolve polar molecules. However, the characteristics of CO2 can be modified by the addition of a co-solvent. Various co-solvents have been investigated of which 2 propanol (IPA) was the most suitable. For most non-particulate soils, the results using CO2, water and IPA were comparable to the results using PER. For particulate soils, however, the cleaning-results using CO2, water and IPA were worse than with PER. Particulate soils can be removed from textile by mechanical action and/or surfactants. Only relatively large particles (>20 µm) could be removed in CO2 by increasing the mechanical action. Unfortunately, increasing the mechanical action had no positive influence on the removal of small particles (<20 µm). In order to remove small particles in CO2, surfactants have to be used. Amino acid based surfactants have been studied. For the production of amino acid based surfactants, renewable, low-cost raw materials are used. Furthermore, these surfactants have a low toxicity, are biodegradable and are not irritating to the skin. These characteristics make the amino acid based surfactants attractive for dry-cleaning with carbon dioxide. The amino acid based surfactants gave good results for dry-cleaning with liquid CO2. The surfactant Amihope LL (N lauroyl L lysine) gave the best cleaning-results. An important process parameter using this surfactant was the addition of water. The addition of water is required for sufficient removal of non-particulate soils. However, when no water was added to the system, there was a large increase in particle removal. Therefore, a 2-bath process was proposed. The first bath is for particulate soil removal and has optimal conditions for particulate soil removal; the second bath has optimal conditions for non-particulate soil removal. The 2-bath process using Amihope LL gave good results: the result for particulate soil removal was 84 % compared to the results for PER, the result for non-particulate soil removal was 98 % compared to PER and the overall result was 92 % compared to PER. All surfactants that gave good results for particulate soil removal (anionic, amine and amino acid based surfactants) were, surprisingly, hardly soluble in CO2 and were (largely) present as solid particles. The mechanisms that may play a role in particulate soil removal using the surfactant Amihope LL were investigated. The cleaning action of the surfactant is probably a combination of adsorption and mechanical action. An economic evaluation shows that the costs for dry-cleaning using the optimized CO2-process are equal to the costs of the PER-process. Recycling of the surfactant and the co-solvent can lower the costs of the CO2-process further.