Adsorption and Desorption Processes Under Supercritical Conditions

The desorption of solutes from solid matrices under supercritical conditions has found many applications such as in soil remediation and in activated carbon regeneration. Soil remediation by SF’s has been proposed as alternative to incineration, vapour extraction, bioremediation, vapour stripping and thermal extraction. The SF extraction of contaminants will be influenced by temperature, pressure, water content of the soil, cosolvent’s effect and organic substance content. The regeneration of activated carbon used in wastewater’s treatment and in contaminated stream purification, can be performed with vapor stripping, liquid-liquid extraction and thermal regeneration. SF regeneration has been proposed since it is possible to regenerate spent carbon in situ avoiding losses of carbon due to friction and, if compared with thermal regeneration, it is a process with lower losses of carbon (due to the oxidation of adsorbed substances) and less severe operating conditions. Many studies have been reported for the separation of oxygenated therpenes from hydrocarboned therpenes and of some benzopirones using silica gels as adsorbent. The recovery of nitrogen compounds from coal tar fraction and the separation of cholesterol from butter oil was also investigated. Our objective was to investigate the feasibility of a separation of alpha-tocopherol from alpha-tocopherol acetate in a desorption process. Experimental data are presented for adsorption and desorption of alpha-tocopherol from alpha-tocopherol acetate (vitamin E) on/from activated carbon and silica gels with different surface area values in the presence of supercritical carbon dioxide. In order to verify if supercritical carbon dioxide is a simple carrier fluid or it is also adsorbed, adsorption of carbon dioxide on the adsorbents mentioned above has been determined gravimetrically and reported. Finally the different behavior of alpha-tocopherol from alpha-tocopherol acetate (related to solute-adsorbent-SF interaction) suggests the desorption process for the separation of the two tocopherols as an alternative to traditional methods.