Extraction of polyphenols and synthesis of new activated carbon from spent coffee grounds

Authors: Ramon-Goncalves, M; Alcaraz, L; Perez-Ferreras, S; Leon-Gonzalez, ME; Rosales-Conrado, N; Lopez, FA

Article.
Sci Rep. vol: 9. page: 2045-2322.
Date: nov-27. 2019.
Doi: 10.1038/s41598-019-54205-y.

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 degrees 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 degrees C, and a mixture of 2.5:1. The obtained activated carbons exhibit a great specific surface (between 1600 m(2).g(-1) and 2330 m(2).g(-1)) with a microporous surface. Finally, the adsorption capacity of the activated carbons was evaluated by methylene blue adsorption..