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Volatile methyl siloxanes (VMS), which are considered to be the most troublesome impurities in current biogas-cleaning technologies, need to be removed. In this study, we fabricated a series of Fe3O4–urea-modified reduced graphene-oxide aerogels (Fe3O4–urea–rGOAs) by using industrial-grade graphene oxide as the raw material. A fixed-bed dynamic adsorption setup was built, and the adsorption properties of the Fe3O4–urea–rGOAs for hexamethyldisiloxane (L2, as a VMS model pollutant) were studied. The properties of the as-prepared samples were investigated by employing various characterization techniques (SEM, TEM, FTIR, XRD, Raman spectroscopy, and N2 adsorption/desorption techniques). The results showed that the Fe3O4–urea–rGOA–0.4 had a high specific surface area (188 m2 g−1), large porous texture (0.77 cm3 g−1), and the theoretical maximum adsorption capacity for L2 (146.5 mg g−1). The adsorption capacity considerably increased with a decrease in the bed temperature of the adsorbents, as well as with an increase in the inlet concentration of L2. More importantly, the spent Fe3O4–urea–rGOA adsorbent could be readily regenerated and showed an excellent adsorption performance. Thus, the proposed Fe3O4–urea–rGOAs are promising adsorbents for removing the VMS in biogas. [ABSTRACT FROM AUTHOR]

Silica deposition resulting from methyl siloxane combustion represents a problem for the application and development of biogas energy, which creates the need to explore novel materials with high adsorption efficiency of methyl siloxane and excellent cycling performance. Here, citric acid (CA) was used to assist the hydrothermal reduction process and induce self-assembly with the final aim of obtaining three-dimensional reduced graphene oxide aerogels (rGOAs) from industrial-grade graphene oxide. The rGOAs were characterized by XRD, SEM, FTIR, Raman spectroscopy, and N 2 adsorption/desorption techniques. The results showed that rGOAs had a significant removal capacity of hexamethyldisiloxane (L2), which could be attributed to the improvement of both texture and hydrophobic properties by CA. Among the rGOAs, the rGOA-2 showed the highest theoretical breakthrough adsorption capacity (Q B, th , 337.3 mg g−1). The specific surface area (582.4 m2 g−1) and micropore volume (0.39 cm3 g−1) were the most key structural factors affecting Q B, th. Appropriately decreasing the temperature and increasing the inlet concentration was beneficial to improving the adsorption capacity. In addition, the rGOA-2 exhibited excellent recyclability and reuse performance over five consecutive adsorption/regeneration cycles. Thus, our study provides a novel methodology with a high potential to overcome the problem of silica deposition using sustainable materials for the adsorption of methyl siloxane, to provide specific theoretical and technical support for the effective utilization of renewable energy. [Display omitted] [ABSTRACT FROM AUTHOR]

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 m2 g−1), total pore volume (0.737 cm3 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. [Display omitted] [ABSTRACT FROM AUTHOR]

Volatile methyl siloxanes (VMSs) as a trace impurity in biogas decreases its energy utilization, and thus need to be removed. In this paper, a one-step hydrothermal reduction was performed to produce three-dimensional reduced graphene oxide aerogels (rGOAs) using industrial-grade graphene oxide (IGGO) as raw material and vitamin C (VC) as a reductant to facilitate the fabrication of rGOAs. The synthesis of rGOAs was a simple, green, and energy-efficient process. The developed rGOAs were characterized using the Brunauer–Emmett–Teller method, Raman spectrometry, scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction measurements and contact angle. The results obtained showed that rGOA-1 with a VC/IGGO ratio of 1/1 (m/m) exhibited a hierarchical porous structure and super-hydrophobicity, yielding a high specific surface area (137.9 m2 g−1) and superior water contact angle (143.8°). The breakthrough adsorption capacity of rGOA-1 for hexamethyldisiloxane (L2, a VMS model) was 11 times higher than that of IGGO. Low inlet concentration and bed temperature were considered beneficial for the L2 adsorption. Interestingly, rGOA-1 was less sensitive to water, and it was readily regenerated for reuse by annealing at 80 °C. The rGOAs have been demonstrated to have great potential for the removal of siloxanes from biogas. [ABSTRACT FROM AUTHOR]

To expand the applications of graphene-based materials to biogas purification, a series of reduced graphene oxide aerogels (rGOAs) were prepared from industrial grade graphene oxide using a simple hydrothermal method. The influences of the hydrothermal preparation temperature on the textural properties, hydrophobicity and physisorption behavior of the rGOAs were investigated using a range of physical and spectroscopic techniques. The results showed that the rGOAs had a macro-porous three-dimensional network structure. Raising the hydrothermal treatment temperature reduced the number of oxygen-containing groups, whereas the specific surface area (SBET), micropore volume (Vmicro) and water contact angle values of the rGOAs all increased. The dynamic adsorption properties of the rGOAs towards hexamethyldisiloxane (L2) increased with increasing hydrothermal treatment temperature and the breakthrough adsorption capacity showed a significant linear association with SBET, Vmicro and contact angle. There was a significant negative association between the breakthrough time and inlet concentration of L2, and the relationship could be reliably predicted with a simple empirical formula. L2 adsorption also increased with decreasing bed temperature. Saturated rGOAs were readily regenerated by a brief heat-treatment at 100 °C. This study has demonstrated the potential of novel rGOA for applications using adsorbents to remove siloxanes from biogas. [ABSTRACT FROM AUTHOR]