Hexamethyldisiloxane removal from biogas using reduced graphene-oxide aerogels as adsorbents

Volatile methyl siloxane is a trace impurity in biogas produced by anaerobic bacteria. It decreases the energy utilization of biogas and thus needs to be removed. In this study, six reduced graphene-oxide aerogels (rGOAs) were prepared from industrial-grade multilayer graphene oxide by a hydrothermo-chemical reduction method in the presence of various amine additives, and the use of the rGOAs as adsorbents for hexamethyldisiloxane (L2) removal was investigated. The developed rGOAs were characterized via the Brunner-Emmet-Teller technique, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results revealed that the different pK a values of the amine molecules led to an increase in the rGOA contact angle, the specific surface area and the total pore volume in the following sequence: 0-rGOA < E-rGOA < A-rGOA < D-rGOA < T-rGOA < U-rGOA, representing the rGOAs without amine and those with ethylenediamine, aniline, diethylenetriamine, triethylenetetramine, and urea, respectively. Also, the adsorptive performance of the rGOAs materials for L2 was enhanced in this sequence. The adsorption capacities of rGOAs were significantly related to their textural properties and hydrophobicity. Moreover, U-rGOA exhibited the highest specific surface area (167.9 m 2  g −1 ), total pore volume (0.737 cm 3  g −1 ), and contact angle (146.8°), and its theory breakthrough adsorption capacity for L2 at 0 °C was 112.4 mg g −1. A lower bed-temperature, carrier gas flow rate, and inlet concentration were beneficial for the L2 adsorption by the U-rGOA. The spent U-rGOA adsorbent could be readily regenerated for reuse by heating at 80 °C. The results suggest that the rGOA materials have good application potential as adsorbents for methyl siloxane removal.