Acid Mesoporous Carbon Monoliths from Lignocellulosic Biomass Waste for Methanol Dehydration

A Kinetic Model Considering Catalyst Deactivation for Methanol-to-Dimethyl Ether on a Biomass-Derived Zr/P-Carbon Catalyst

A Zr-loaded P-containing biomass-derived activated carbon (ACPZr) has been tested for methanol dehydration between 450 and 550 °C. At earlier stages, methanol conversion was complete, and the reaction product was mainly dimethyl ether (DME), although coke, methane, hydrogen and CO were also observed to a lesser extent. The catalyst was slowly deactivated with time-on-stream (TOS), but maintained a high selectivity to DME (>80%), with a higher yield to this product than 20% for more than 24 h at 500 °C. A kinetic model was developed for methanol dehydration reaction, which included the effect of the inhibition of water and the deactivation of the catalyst by coke. The study of stoichiometric rates pointed out that coke could be produced through a formaldehyde intermediate, which might, alternatively, decompose into CO and H₂. On the other hand, the presence of 10% water in the feed did not affect the rate of coke formation, but produced a reduction of 50% in the DME yield, suggesting a reversible competitive adsorption of water. A Langmuir–Hinshelwood reaction mechanism was used to develop a kinetic model that considered the deactivation of the catalyst. Activation energy values of 65 and 51 kJ/mol were obtained for DME and methane production in the temperature range from 450 °C to 550 °C. On the other hand, coke formation as a function of time on stream (TOS) was also modelled and used as the input for the deactivation function of the model, which allowed for the successful prediction of the DME, CH₄ and CO yields in the whole evaluated TOS interval.

Preparation of binder-less activated char briquettes from pyrolysis of sewage sludge for liquid-phase adsorption of methylene blue

Binder-less activated char briquettes from sewage sludge were prepared and used for the liquid-phase adsorption of methylene blue. The properties of sludge char briquettes prepared under the different initial sludge moisture content, compression pressure, and heating rate were systematically investigated through the tests of thermogravimetric analysis (TGA), scanning electron microscopy (SEM), surface and mechanical properties, burn-off rates, methylene blue adsorption kinetics and isotherms. All of the prepared briquettes presented hierarchical structures and microporous/mesoporous characteristics, and the increase of initial sludge moisture content from 10 to 30 wt% resulted in a great increase of surface area (S_BET), total pore volume (V_T), apparent density, and a slight decrease of mechanical performance. The decrease of compression pressure markedly enhanced the equilibrium adsorption capacity (q_{e, exp}), owing to the decreased diffusion resistance and blockage of diffusion pathways inside briquettes. In consideration of the mechanical performance and adsorption capacity, the optimum preparation condition was obtained at the initial moisture content of 30 wt%, compression pressure of 25 MPa, and heating rate of 10 °C/min, in which the axial compressive strength (ACS) and q_{e, exp} of the prepared briquettes were as high as 22.2 ± 3.1 kg/m² and 316.9 mg/g. The results also showed that the equilibrium adsorption data fit well into the pseudo-first order model system, and the adsorption isotherms followed the Langmuir isotherm model, suggesting that the adsorption process was attributed to physical adsorption, and was inclined to happen on the adsorption sites with the same energy level. Finally, the thermal regeneration tests demonstrated that the binder-less briquette had a good regeneration performance and was worthy of reusing for industrial applications.

Facile synthesis and performance of pH/temperature dual-response hydrogel containing lignin-based carbon dots

This study demonstrated a facile method to synthesize lignin-based carbon dots (L-CDs) first. Results indicated that the L-CDs had a diameter of 2-5 nm and a graphene-like crystalline structure. It was found that under the optimal synthesis conditions, the fluorescence lifetime of L-CDs was about 12 ns. Within the range of pH 1-10, the fluorescence intensity of the L-CDs and pH value followed a linear relationship. With the contribution of L-CDs, pH/temperature dual responsive hydrogel was synthesized. The elastic modulus G' of hydrogel was much higher than viscous modulus G″. When the PVA content was larger than 10 wt%, the temperature sensitivity and water retention rate gradually decreased. The skeleton of hydrogels had a typical porous honeycomb structure, which made it possible to control its internal pore size by adjusting the content of PVA. There was a linear relationship between the fluorescence intensity of hydrogels and pH value in the range of pH 1-7. Therefore, the pH/temperature dual responsive hydrogel presented a new route for designing tissue engineering scaffolds and drug carriers.