Production of Antioxidant Additives and High-quality Activated Biochar from Pyrolysis of Argan Shells

An integral valorization route based on a pyrolysis process has been proposed to find sustainable applications for argan shells focused on the simultaneous production of activated biochar and antioxidant additives from bio-oil. The bio-oil obtained in the pyrolysis process was furtherly upgraded (hydrothermal treatment and extraction process) to obtain antioxidant additives. On the other hand, the biochar obtained in the pyrolysis was used as a feedstock to produce high-quality activated biochar (by physical activation with CO2). The increase in the pyrolysis temperature (350-550 degrees C) hardly affected the pyrolysis products distribution (biochar yields of 28-34 wt.% and bio-oil yields between 51 and 55 wt.%), but it led to a slight decrease in the content of phenolic monomers extracted from bio-oil (from 63 wt.% at 350 degrees C to 53 wt.% at 550 degrees C). When these extracted fractions were blended with biodiesel (<1 wt.%), improvements of up to 300% in biodiesel oxidation stability were attained. The hydrothermal treatment of the bio-oil did not show noteworthy effects either on the production or antioxidant performance of the extracted fractions if compared with the fractions extracted from the raw bio-oil. Regarding the valorization of argan shells biochar, the activated biochar prepared from it showed considerable potential as an adsorbent material for CO2 (125 mg of CO2 per g of the activated biochar) or phenols (complete removal of 99.6% in 4 h of contact time). It was characterized by a high BET surface area (up to 1500 m(2)/g), a high carbon content (up to 95 wt.%), low ash content (around 2 wt.%), and a pH of around 8.

Automated summary

This study proposes an integral valorization route using a pyrolysis process to produce activated biochar and antioxidant additives from argan shells. The pyrolysis temperature has minimal effect on the yield of biochar and bio-oil, but higher temperatures result in a slight decrease in the content of phenolic monomers in the bio-oil. Blending these extracted fractions with biodiesel greatly improves its oxidation stability. The activated biochar derived from argan shells shows potential as an adsorbent for CO2 and phenols.