Characterization and Evaluation of Carbonaceous Materials from the Hydrothermal Carbonization of Waste Pharmaceuticals

TL;DR

This study converts waste pharmaceuticals into functionalized carbon materials via hydrothermal carbonization, evaluating their structure, adsorption capacity for lead ions, and comparing pyrolysis and hydrochar properties.

Contribution

It introduces a method to produce high-quality hydrochars from waste pharmaceuticals and assesses their effectiveness in removing heavy metals from water.

Findings

Hydrochars show high aromaticity and carbon content (55-65%).

Hydrochars, especially PH24_230, remove over 97% of Pb2+ in 60 minutes.

Pyrochar surface area reaches 63.15 m2/g at 700°C.

Abstract

In this paper, we report herein, the conversion of waste prescription and non-prescription pharmaceuticals into carbonaceous materials. The hydrothermal carbonization (HTC) of the pharmaceuticals was carried out at temperatures of 180, 230 and 275 0C in closed reactors for 6, 12 and 24 hours, respectively. The main products from the carbonization process were in the solids, liquids and gas phases. The resulting hydrochars were shown to be very functionalized with a high degree of aromaticity and high carbon content (between 55% to 65%). The adsorptive capacity of the hydrochars to remove Pb2+ ions from an aqueous system was evaluated and compared to that of analytical reagent activated carbon (AR-AC) through batch adsorptive tests. The effect of contact time on batch adsorption experiments with an initial Pb2+ concentration of 50 mg/L was also evaluated. The results indicated that PH24_230 has a better adsorption capacity when compared to AR-AC; achieving over 97% removal of Pb2+ after 60 minutes. The batch adsorption studies were best described by the pseudo-second order kinetic model with coefficient of regression (R2) values above 0.99. Also, slow pyrolysis experiments were carried out to evaluate the difference in solid yields, char heating value and surface area. Pyrochar yields were slightly higher, while heating values were one order of magnitude lower when compared to hydrochars. The pyrolysis conducted at 700{\deg}C led to the pyrochar with the highest value of the surface area (63.15 m2/g). The study shows that valuable products can be generated successfully from the hydrothermal carbonization of waste pharmaceuticals. KEYWORDS: waste pharmaceuticals; hydrothermal carbonization; hydrochars, batch adsorption, adsorption capacity