No abstract

A valorization process of spent coffee grounds (SCG) was studied. Thus, a two-stage process, the first stage of polyphenols extraction and synthesis of a carbonaceous precursor and a subsequent stage of obtaining activated carbon (AC) by means of a carbonization process from the precursor of the previous stage, was performed. The extraction was carried out with a hydro-alcoholic solution in a pressure reactor, modifying time, temperature and different mixtures EtOH:H2O. To optimize the polyphenols extraction, a two-level factorial experimental design with three replicates at the central point was used. The best results were obtained by using a temperature of 80 °C during 30 min with a mixture of EtOH:H2O 50:50 (v/v). Caffeine and chlorogenic acid were the most abundant compounds in the analysed extracts, ranging from 0.09 to 4.8 mg∙g−1 and 0.06 to 9.7 mg∙g−1, respectively. Similarly, an experimental design was realized in order to analyze the influence of different variables in the AC obtained process (reaction time, temperature and KOH:precursor ratio). The best results were 1 h, 850 °C, and a mixture of 2.5:1. The obtained activated carbons exhibit a great specific surface (between 1600 m2∙g−1 and 2330 m2∙g−1) with a microporous surface. Finally, the adsorption capacity of the activated carbons was evaluated by methylene blue adsorption.

A valorization process of spent coffee grounds (SCG) was studied. Thus, a two-stage process, a stage of extraction of the polyphenols and a stage of obtaining activated carbon (AC) by a carbonization process, was performed. The extraction was carried out with a hydro-alcoholic solution in a pressure reactor, modifying time and temperature. To optimize the extraction of polyphenols, a two-level factorial design with three replications at the central values was used. The best results were obtained by performing the extraction at 80 °C during 30 min, using a mixture of EtOH:H2O 1:1 (v/v) as extraction solution. Caffeine and chlorogenic acid were the most abundant compounds in the analyzed extracts, ranging from 0.09 to 4.8 mg∙g-1 and 0.06 to 9.7 mg∙g-1, respectively. The precursor obtained in the extraction stage were transformed into AC. An experimental design was realized in order to analyze the influence of different variables in the AC obtained process (reaction time and amount of potassium hydroxide used). Actived carbons with BET specific surface (SBET) comprised between 1600 m2∙g-1 and 2330 m2∙g-1 had a microporous surface. Under the optimum conditions, the obtained AC presented a maximum adsorption capacity of methylene blue (qm) between 411 mg∙g-1 and 813 mg∙g-1.