Encapsulation of activated carbon into calcium alginate microspheres toward granular-activated carbon adsorbents for elemental mercury capture from natural gas.

Activated carbon (AC) is an effective adsorbent for removing environmental pollutants. However, the traditional powder form of AC shows difficulty in handling during application which widely limits its utilization on the industrial scale. Herein, to avoid such limitation, traditional AC powder was encapsulated into calcium alginate (CA) microspheres. Calcium alginate/activated carbon (CAA) composite microspheres were prepared via cross-linking of sodium alginate/activated carbon composite solutions in a calcium chloride solution. Furthermore, in order to boost adsorption affinity of CAA composite microspheres toward elemental mercury (Hg°), ammonium iodide (NH4I)-treated calcium alginate/activated carbon (NCA) composite microspheres were obtained by a simple impregnation method using NH4I treatment. The morphological, structural, and textural properties of the microspheres were characterized and their Hg° adsorptive capacity was tested at different temperatures. Interestingly, the maximum adsorption capacity of NCA adsorbent composite microspheres was determined as 36,056.5 µg/g at a flow rate of 250 mL/min, temperature of 25 °C, and 500 µg/Nm3 of Hg° initial concentration. The Gibbs free energy (ΔG°) for NCA adsorbent composite microspheres varied from - 8.59 to - 10.54 kJ/mol indicating a spontaneous adsorption process with an exothermic nature. The experimental Hg° breakthrough curve correlated well with Yoon‒Nelson and Thomas models. The breakthrough time (tb) and equilibrium time (te) were found to be 7.5 days and 23 days, respectively. Collectively, the findings of this work indicate a good feasibility of using NCA composite microspheres as potential adsorbents for removing Hg° from natural gas.

Carbon disulfide removal from gasoline fraction using zinc-carbon composite synthesized using microwave-assisted homogenous precipitation.

Carbon disulfide (CS2) is one of the sulfur components that are naturally present in petroleum fractions. Its presence causes corrosion issues in the fuel facilities and deactivates the catalysts in the petrochemical processes. It is a hazardous component that negatively impacts the environment and public health due to its toxicity. This study used zinc-carbon (ZC) composite as a CS2 adsorbent from the gasoline fraction model component. The carbon is derived from date stone biomass. The ZC composite was prepared via a homogenous precipitation process by urea hydrolysis. The physicochemical properties of the prepared adsorbent are characterized using different techniques. The results confirm the loading of zinc oxide/hydroxide carbonate and urea-derived species on the carbon surface. The results were compared by the parent samples, raw carbon, and zinc hydroxide prepared by conventional and homogeneous precipitation. The CS2 adsorption process was performed using a batch system at atmospheric pressure. The effects of adsorbent dosage and adsorption temperatures have been examined. The results indicate that ZC has the highest CS2 adsorption capacity (124.3 mg.g-1 at 30 °C) compared to the parent adsorbents and the previously reported data. The kinetics and thermodynamic calculation results indicate the spontaneity and feasibility of the CS2 adsorption process.

Visible light photoreforming of greenhouse gases by nano Cu-Al LDH intercalated with urea-derived anions.

The accumulation of anthropogenic greenhouse gases (GHGs) in the atmosphere causes global warming. Global efforts are carried out to prevent temperature overshooting and limit the increase in the Earth's surface temperature to 1.5 °C. Carbon dioxide and methane are the largest contributors to global warming. We have synthesized copper-aluminium layered double hydroxide (Cu-Al LDH) catalysts by urea hydrolysis under microwave (MW) irradiation. The effect of MW power, urea concentration, and MII/MIII ratios was studied. The physicochemical properties of the prepared LDH catalysts were characterized by several analysis techniques. The results confirmed the formation of the layered structure with the intercalation of urea-derived anions. The urea-derived anions enhanced the optical and photocatalytic properties of the nano Cu-Al LDH in the visible-light region. The photocatalytic activity of the prepared Cu-Al LDH catalysts was tested for greenhouse gas conversion (CH4, CO2, and H2O) under visible light. The dynamic gas mixture flow can pass through the reactor at room temperature under atmospheric pressure. The results show a high conversion percentage for both CO2 and CH4. The highest converted amounts were 7.48 and 1.02 mmol mL-1 g-1 for CH4 and CO2, respectively, under the reaction conditions. The main product was formaldehyde with high selectivity (>99%). The results also show the stability of the catalysts over several cycles. The current work represents a green chemistry approach for efficient photocatalyst synthesis, visible light utilization, and GHGs' conversion into a valuable product.