Adsorption of phenol and chlorophenols onto granular activated carbon and their desorption by supercritical CO₂

Abstract

BACKGROUND The adsorption and desorption of phenol, 2‐chlorophenol (2‐CPh), 4‐chlorophenol (4‐CPh) and 2,4‐dichlorophenol (2,4‐DCPh) were carried out using granular activated carbon (GAC) as adsorbent and supercritical CO2 as regenerant. Adsorption studies at three different temperatures were fitted by using two thermodynamic adsorption models, Langmuir and Toth. The GAC regeneration by CO2 at four different pressures and two temperatures was studied and the design basic parameters were found. RESULTS The Toth model fitted the experimental data better and thermodynamic properties indicated that this adsorption process was spontaneous, feasible and exothermic. Values of standard enthalpy lower than 40 kJ mol‐1 confirmed that adsorption processes were carried out by physical adsorption. It was also observed that the higher the pressure the higher the regeneration efficiency due to the increase in solvent density. CONCLUSION GAC presented high selectivity for these substituted phenols and the order of adsorption was 2,4‐DCPh > 4‐CPh > 2CPh > phenol. Supercritical technology was able to regenerate the exhausted GAC, achieving yields comparable with those exhibited by traditional technologies but avoiding additional separation processes. The effective diffusivities of phenols followed the order phenol > 2‐CPh≅4‐CPh > 2,4‐DCPh. © 2013 Society of Chemical Industry

Simultaneous adsorption of lead and aniline onto magnetically recoverable carbon: optimization, modeling and mechanism

“…A great many adsorbents such as activated carbon, ash ,coal, manganese oxides, almond shell, kaolinite, bagasse, resins and compost have been applied for the adsorption of heavy metals and certain organic compounds in aqueous environments. But, some of these adsorbents have low surface area and limited adsorption capacity, and subsequently low adsorption efficiency; however, due to the high surface area and large volume of activated carbon pores, high adsorption capacity and recyclability is achievable . These, and other features of activated carbon including simple and cheap production and easy accessibility have resulted in its extensive use by many researchers in water and wastewater treatment.…”

Supercritical Regeneration of an Activated Carbon Fiber Exhausted with Phenol

“…Temperature has two opposite effects on SCCO2 regeneration, which are related to the mechanistic pathways involved in the process [11,19]. SCCO2 can remove a retained pollutant through two pathways: thermal desorption and extraction.…”

“…The regeneration of ACs saturated with inorganic compounds is less usual and co-solvents must be used to efficiently extract these adsorbates [16]. The employment of SCCO 2 has also been studied to regenerate ACs saturated with low-volatile organic compounds, e.g., phenol [17][18][19], pesticides [20], herbicides [21], or insecticides [22]. Phenol is the most common model compound in the field of regeneration of ACs [3]: it is a pollutant frequently found in wastewater and drinking water that remains strongly retained on the carbon surface of ACs.…”

“…Phenol is the most common model compound in the field of regeneration of ACs [3]: it is a pollutant frequently found in wastewater and drinking water that remains strongly retained on the carbon surface of ACs. The limited number of works that have studied the SCCO 2 regeneration of ACs exhausted with phenol state that, at regeneration pressures and temperatures below 200 bar and 60 • C, respectively, phenol is not properly extracted [19] and the ACs are not efficiently regenerated [18].…”

Efficient dechlorination of 2,4-dichlorophenol in an aqueous media with a mild pH using a Pd/TiO2NTs/Ti cathode

“…As kinds of persistent organic pollutants (POPs), they are very toxic and may pose a great threat to the endocrine systems of both humans and animals [1,2], and listed as priority pollutants in United States Environmental Protection Agency legislation. Many methods, such as adsorption, biodegradation, advanced oxidation, reductive dechlorination, etc., have been proposed to treat chlorophenol-contaminated wastewater [2][3][4][5]. Adsorption is not cost-efficient, and further treatment is needed after this process, during which there is a potential risk of second pollution [6].…”