Synthesis of Mesoporous Carbon Adsorbents Using Biowaste Crude Glycerol as a Carbon Source via a Hard Template Method for Efficient CO2 Capture.

Biowaste utilization as a carbon source and its transformation into porous carbons have been of great interest to promote environmental remediation owing to biowaste's cost-effectiveness and useful physicochemical properties. In this work, crude glycerol (CG) residue from waste cooking oil transesterification was employed to fabricate mesoporous crude glycerol-based porous carbons (mCGPCs) using mesoporous silica (KIT-6) as a template. The obtained mCGPCs were characterized and compared to commercial activated carbon (AC) and CMK-8, a carbon material prepared using sucrose. The study aimed to evaluate the potential of mCGPC as a CO2 adsorbent and demonstrated its superior adsorption capacity compared to AC and comparable to CMK-8. The X-ray diffraction (XRD) and Raman results clearly depicted the structure of carbon nature with (002) and (100) planes and defect (D) and graphitic (G) bands, respectively. The specific surface area, pore volume, and pore diameter values confirmed the mesoporosity of mCGPC materials. The transmission electron microscopy (TEM) images also clearly revealed the porous nature with the ordered mesopore structure. The mCGPCs, CMK-8, and AC materials were used as CO2 adsorbents under optimized conditions. The mCGPC adsorption capacity (1.045 mmol/g) is superior to that of AC (0.689 mmol/g) and still comparable to that of CMK-8 (1.8 mmol/g). The thermodynamic analyses of the adsorption phenomena are also carried out. This work demonstrates the successful synthesis of a mesoporous carbon material using a biowaste (CG) and its application as a CO2 adsorbent.

Water Vapor Adsorption Capacity Loss of Molecular Sieves 4A, 5A, and 13X Resulting from Methanol and Heptane Exposure.

Zeolite-based molecular sieves are applied in industrial dehydration units for their high water uptake capacities and extremely low equilibrium pressure of water vapor. During their operational life, they tend to lose their water vapor adsorption capacity slowly. To optimize the usage of molecular sieves in dryer units, it is vital to understand the mechanism(s) leading to deactivation. In this work, the capacity loss was studied by exposing LTA- and FAU-type zeolites to methanol and heptane vapors under relatively harsh conditions using repetitive adsorption/regeneration cycles. A simple microflow unit was designed and used for the deactivation experiments. The water vapor adsorption capacity of the resulting samples was measured using a gravimetric analyzer. In addition, they were characterized by classic XRD, 13C NMR, and TGA techniques. The crystallinity of fresh and spent zeolite XRD patterns was not drastically affected even after exposure to the contaminants. It was found that methanol easily gave rise to a severe loss of water vapor adsorption capacity, much more so than heptane. Water vapor uptake in the methanol exposed samples is ∼50% lower than that for the fresh zeolites. This is attributed to nonvolatile, residual hydrocarbons.