Search

Various sources of carbon can be converted into acetylene (C2H2) by using the key intermediate calcium carbide (CaC2). However, the production of CaC2 is a typical energy-intensive process, accompanied by considerable carbon dioxide (CO2) emissions and a large amount of industrial solid waste. In this study, a sustainable methodology for carbon-to-acetylene and carbon monoxide (CO) co-production as well as CO2 capture based on BaCO3−BaC2−Ba(OH)2−BaCO3 looping was first established, in which BaC2 replaced CaC2 as the key intermediate of the carbon-to-acetylene process to generate C2H2. The kinetic behavior investigation of the BaC2 formation indicated that the solid-phase synthesized BaC2 is a promising intermediate for the carbon-to-acetylene conversion owing to its faster kinetics, lower formation temperature, and no carbon dioxide release compared with those observed for the CaC2 production. Moreover, the lab-scale recovery of barium to carbide formation was conducted as the proof-of-concept to validate the coupling process of carbon-to-acetylene with CO2 capture based on Ba looping, resulting in less carbide slag waste and negative carbon emission. The facile co-production of carbon monoxide, environmentally friendly process, and convenience of large-scale production, as well as possible independent manufacturing of fossil resources, make barium carbide-based carbon-to-C2H2 -CO a promising key chemical platform for sustainable development. The proposed technology would provide new insights into the reengineering process of carbon to chemicals. [ABSTRACT FROM AUTHOR]

In urban centres, the construction of a new tunnel would cause ground disturbance and affect any adjacent existing tunnel. Tunnel--tunnel interaction problems have not yet been comprehensively studied. In particular, the response of an existing horseshoe-shaped tunnel to the construction of two perpendicularly undercrossing tunnels remains unclear. In this study, three-dimensional centrifuge tests and three-dimensional numerical analysis were designed and conducted in dry sand to investigate the effects of twin-tunnel undercrossing on an existing horseshoe-shaped tunnel considering the influence of a settlement joint. It is found that the adverse effects caused by the tunnel excavated later were smaller than those by the earlier one. For the existing tunnel without a settlement joint, the settlement at the invert and crown along the longitudinal direction showed sagging and hogging curves, respectively, owing to significant vertical elongation of the middle section. The presence of a settlement joint resulted in an increase in the settlement of the ground surface and the existing tunnel by over 100%. In both cases, larger bending strains were induced in the transverse direction than in the longitudinal direction, particularly around the corners. Key words: twin-tunnel excavation, horseshoe-shaped tunnel, settlement joint, three-dimensional centrifuge modelling, three-dimensional numerical modelling. Dans les centres urbains, la construction d'un nouveau tunnel entrainerait des perturbations du sol et affecte tout tunnel existant adjacent. Les problemes d'interaction tunnel--tunnel n'ont pas encore ete etudies. En particulier, la reponse d'un tunnel en forme de fer pour la construction de deux tunnels perpendiculairement sous un passage a niveau n'est pas claire. Dans cette etude, des essais a centrifuges a trois dimensions et l'analyse numerique en trois dimensions ont ete concues et menees dans le sable sec pour etudier les effets d'un passage a niveau sur un tunnel double en forme de fer compte tenu de l'influence du joint de tassement. Il est constate que les effets nefastes causes par le tunnel creuse par la suite etaient plus petits que ceux de l'ancien. Pour le tunnel existant sans un joint de tassement, le tassement a l'inversion et le long de la couronne le sens longitudinal ont montre des courbes avec affaissement et monopolisant, respectivement, en raison de l'elongation verticale significative de la section centrale. La presence d'un joint de tassement a entraine une augmentation du tassement de la surface du sol et le tunnel existant de plus de 100 %. Dans les deux cas, des contraintes de flexion ont ete induites dans le sens transversal que dans le sens longitudinal, en particulier autour des coins. [Traduit par la Redaction] Mots-cles: excavation de tunnel double, tunnel en forme de fer, joint de tassement, modelisation centrifugeuse tridimensionnelle, modelisation numerique tridimensionnelle., Introduction In recent years, it has become increasingly common for one subway line to advance across another because of congested underground space in cosmopolitan cities. Tunnel excavation leads to soil [...]

Conjugated porous polymers are emerging as sustainable and reliable electrode materials for lithium-ion batteries, owing to their versatile chemical modification, environmental-friendliness, and low cost, but still suffer from insufficient redox-active sites and sluggish ion/electron transport. Here, two new kinds of porous polymers (denoted as TPT-CMP and BFT-CMP), comprising full sp2-carbon skeletons connected through vinylidene linkages, are synthesized by acid-catalyzed Knoevenagel condensation of ethene-1,1,2,2-tetrayl-tetrakis-1,1′-biphenyl-4-carbaldehyde and 9,9′-bifluorenylidene-3,3′,6,6′-tetrayl-tetrabenzaldehyde with s-indacene-1,3,5,7-(2H,6H)-tetraone, respectively. Such porous polymers were readily composited with carbon nanotubes to form freestanding thin films upon a simple vacuum-assisted filtration. As the anode, the TPT-CMP-based film delivered a much higher capacity of 550 mA h g−1 at 100 mA g−1 than the BFT-CMP-based one (407 mA h g−1), although TPT-CMP exhibits a much lower surface area of 535.92 m2 g−1 than that (934.41 m2 g−1) of BFT-CMP. This phenomenon might be attributed to the idea that the conformationally rotatable tetraphenylethylene moieties in the case of TPT-CMP might improve rapid mass transport. Both composite electrodes can sustain 500 cycles without any significant decay. These results set new capacity records among porous polymer-based lithium-ion batteries and suggest a new method for achieving promising anode materials by rationally designing the main backbones of conjugated porous polymers. [ABSTRACT FROM AUTHOR]