3 research outputs found
Kinetic and equilibrium studies of urea adsorption onto activated carbon: Adsorption mechanism
<p>We found that activated carbon effectively removed urea from solution and that urea adsorption onto activated carbon followed a pseudo-second-order kinetic model. We classified the urea adsorption on activated carbon as physical adsorption and found that it was best described by the Halsey adsorption isotherm, suggesting that the multilayer adsorption of urea molecules on the adsorption sites of activated carbon best characterized the adsorption system. The mechanism of adsorption of urea by activated carbon involved two steps. First, an amino (–NH<sub>2</sub>) group of urea interacted with a carbonyl (–CËO) group and a hydroxyl (−OH) group on the surface of activated carbon via dipole–dipole interactions. Next, the –CËO group of the urea molecule adsorbed to the activated carbon interacted with another –NH<sub>2</sub> group from a second urea molecule, leading to multilayer adsorption.</p> <p>Schematic representation of the adsorption of urea on activated carbon.</p
Steam Pyrolysis of Polyimides: Effects of Steam on Raw Material Recovery
Aromatic
polyimides (PIs) have excellent thermal stability, which
makes them difficult to recycle, and an effective way to recycle PIs
has not yet been established. In this work, steam pyrolysis of the
aromatic PI Kapton was performed to investigate the recovery of useful
raw materials. Steam pyrolysis significantly enhanced the gasification
of Kapton at 900 °C, resulting in 1963.1 mL g<sup>–1</sup> of a H<sub>2</sub> and CO rich gas. Simultaneously, highly porous
activated carbon with a high BET surface area was recovered. Steam
pyrolysis increased the presence of polar functional groups on the
carbon surface. Thus, it was concluded that steam pyrolysis shows
great promise as a recycling technique for the recovery of useful
synthetic gases and activated carbon from PIs without the need for
catalysts and organic solvents
Simultaneous Recovery of Benzene-Rich Oil and Metals by Steam Pyrolysis of Metal-Poly(ethylene terephthalate) Composite Waste
The
possibility of simultaneous recovery of benzene and metals
from the hydrolysis of polyÂ(ethylene terephthalate) (PET)-based materials
such as X-ray films, magnetic tape, and prepaid cards under a steam
atmosphere at a temperature of 450 °C was evaluated. The hydrolysis
resulted in metal-containing carbonaceous residue and volatile terephthalic
acid (TPA). The effects of metals and additives on the recovery process
were also investigated. All metals were quantitatively recovered,
and silver, maghemite (γ-Fe<sub>2</sub>O<sub>3</sub>), and anatase
(TiO<sub>2</sub>) were recovered without any changes in their crystal
structures or compositions. In a second step, TPA was decarboxylized
in the presence of calcium oxide (CaO) at 700 °C, producing benzene
with an average yield of 34% and purity of 76%. Maghemite (γ-Fe<sub>2</sub>O<sub>3</sub>) incorporated in magnetic tape and prepaid cards
could decarboxylate TPA. Aluminum present in the prepaid cards produced
hydrogen by the reaction with steam. However, the presence of metals
had no adverse influence on the recovery of benzene-rich oil in the
presence of CaO. Therefore, this method can be applied to PET-based
materials containing inorganic substances, which cannot be recycled
effectively otherwise