Chemical looping gasification (CLG) has become a popular method for producing hydrogen-rich syngas due to its environment-friendliness. Recently, a method of using industrial solid waste carbide slag as an oxygen carrier, hydrogen carrier, and in-situ carbon capture agent in the CLG process has been proposed. However, the actual experiment was affected by heat and mass transfer, and the detailed reaction pathway of the carbide slag was not fully understood. In the present study, the process of the CLG process for producing hydrogen-rich syngas with lignite and carbide slag was analyzed using tube furnace experiments, FactSage calculations, and joint characteristic experiment of carbide slag. The result showed that to achieve a gas phase product with a hydrogen concentration exceeding 90 vol% (with dry N2 excluded), a molar ratio of lignite to carbide slag of greater than 1:5 and a reaction temperature of 923 K should be maintained. In terms of the reaction pathway of carbide slag in the CLG process, it was revealed that calcium hydroxide, the primary component of carbide slag, directly participated in the reaction at temperatures of less than 773 K. Overall, this work provides a novel idea for the preparation of hydrogen-rich syngas during CLG process. 

Analysis of hydrogen-rich syngas generation in chemical looping gasification of lignite: Application of carbide slag as the oxygen carrier, hydrogen carrier, and in-situ carbon capture agent

Nanodiamonds (ND) possess remarkable properties derived from both bulk diamonds and nanoparticles. However, their full potential has been impeded by spontaneous particle agglomeration caused by high surface energy. To address this, we have developed a facile, cost-effective, and contaminant-free method to homogenize the ND surface by incorporating sodium borohydride (NaBH4) reduction in a mechanochemical process. Throughout this study, we extensively investigated various influencing factors, such as grinding time, reducing agent ratio, and surface charge, to successfully modify the ND surface. The results demonstrated that the introduction of hydroxyl functional groups significantly improved dispersibility and enabled the re-dispersion of modified ND into the water and other common solvents, achieving particle sizes below 200 nm. Notably, our reduced ND exhibited potential as an additive in lubricating oil, contributing to energy saving and emission reduction. For instance, when 0.02% reduced ND was supplemented into PAO6 lubricant oil, it cannot only reduce the oil consumption by 7.72% but also significantly lower CO, HC, and NOX emissions by 20.2% and 12.7%, respectively. This suggests that the proposed strategy for ND surface chemical modification can enhance colloidal stability and find practical applications in the lubricating oil industry. 

Dispersion of reduced nanodiamond and its application in lubrication

In this study, the nonionic Gemini surfactant S465 was used for regulating the wettability of the lignite surface. The adsorption characteristics of the surfactant on the lignite surface are discussed, and the mechanism of adsorption is explained from a microscopic viewpoint. The adsorption experiments show that the adsorption of S465 on the lignite surface is consistent with predictions made by the Langmuir adsorption isotherm. Furthermore, it indicates that the adsorption process is spontaneous and exothermic. X-ray photoelectron spectroscopy (XPS) analysis shows that the oxygen-containing functional groups content (CO, C = O, and O = C-O) on the lignite surface decreases after the adsorption of the surfactant, which enhances the hydrophobicity of the lignite surface. It is found from molecular dynamics (MD) simulation that the polar ethoxy groups of the surfactant touch the lignite surface, and the nonpolar groups (alkyl chains) entwine closely with each other, forming a protective layer, which keeps water away from the surface of the lignite. The mobility of water molecules is higher in the lignite/surfactant/water system compared to the system without surfactants, and the adsorption of surfactants results in the lignite interaction with water being weaker, therefore, the hydrophobicity of lignite is improved after the adsorption of the surfactant. 

Effect of Gemini surfactant on wettability of Lignite: An experimental and molecular dynamics simulation study

Five coal samples were prepared by deashing Shengli lignite in distinct phases, which consisted of residual ash from spontaneous combustion. The effects of removal and introduction of inherent minerals on the water reabsorption performance of coal samples were systematically investigated in three aspects: pore structure, oxygen-containing functional groups, and lignite materials. Low-field nuclear magnetic resonance spectroscopy was employed to investigate the changes in the water molecular adsorption tendency of coal samples with the variation in the mineral content. The study elucidates that the hygroscopic performance of the coal samples is significantly reduced due to the massive removal of inherent minerals. However, the pore structure of the coal samples after HCl/HF washing becomes more developed, and the oxygen-containing functional groups on the surface are more exposed, leading to an increase in the equilibrium adsorbed moisture content (EMC) of the coal samples. The binding force between coal samples and water molecules is reduced by the removal of the inherent minerals, which weakens the interaction forces between lignite and water molecules. The oxygen-containing functional groups on the surface of lignite interact with the residual ash from spontaneous combustion to enhance the binding force between lignite and surface water molecules, thus leading to the improved tendency of lignite to adsorb water molecules. The formation of intermediate complexes between minerals and oxygen-containing functional groups, in particular, carboxyl functional groups, on the surface of lignite enhances the acting force of polar sites, which improves the interaction of lignite–water molecules.

https://pubs.acs.org/doi/pdf/10.1021/acsomega.2c05786

Enhancement Mechanism of Minerals on Lignite–Water Molecule Interactions

Abstract The polyaniline (PANi)-coated nanodiamond (ND) composites were fabricated by the in situ polymerization process and dispersed in base oil as nanolubricant additives by ultrasonic-assisted dispersion. The morphology and microstructures of the nanocomposites were characterized. The in-house developed reciprocating tribo-device was utilized to conduct the tribological tests. An actual CrN piston ring–nitriding cylinder liner friction pair used in the diesel engine was employed to evaluate the effectiveness of the developed nanolubricant additives. The wear tests were conducted under conditions that were close to the actual work condition of the selected friction pair. Furthermore, the anti-scuffing performance was also investigated and the associated mechanisms were analyzed. The results show the polymerization process inhibited the agglomeration of the NDs that were well dispersed in the PANi matrix. The stable hydrogen bonding interactions and the surface confinement effect promote the dispersion of the nanocomposites in organic base oil effectively. The developed additive can improve the friction and wear performance of the ring–cylinder liner friction pair by 12–19 and 15–24%, respectively, compared with the base oil. With the increase of temperature, the effectiveness of the nanolubricant additives is enhanced. Under the oil-starved condition, the friction pairs lubricated with PANi/ND lubricants can sustain a longer stable period with a lower friction force, and the anti-scuffing time is almost three times longer. Concerning the overall tribological performance, the optimal content of the PANi/ND additive in base oil is 2 wt%.

/pdf/characterization-and-tribology-performance-of-polyaniline-35q0cx71.pdf

Characterization and tribology performance of polyaniline-coated nanodiamond lubricant additives

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Enhancement Mechanism of Minerals on Lignite–Water Molecule Interactions

Characterization and tribology performance of polyaniline-coated nanodiamond lubricant additives