A cyclic electrochemical strategy to produce acetylene from CO2, CH4, or alternative carbon sources

Electrochemical transformation of potent greenhouse gases such as CO2 and CH4 to produce useful carbon-based products is a highly desirable sustainability goal. However, selectivity challenges remain in aqueous electrochemical processes as selective CO2 reduction to desired products is difficult and electrochemical CH4 oxidation often proceeds at very low rates. The formation of C–C coupled products in these fields is particularly desirable as this provides a path for the production of high-value fuels and chemicals. We have developed a cyclic electrochemical strategy which can produce acetylene, a C–C coupled product, from such carbon sources and water, with favorable current density and selectivity. This strategy is exemplified with a lithium-mediated cycle: an active Li0 surface is electrochemically generated from LiOH, the newly formed Li0 reacts with a carbon source to form Li2C2, and Li2C2 is hydrolyzed to form acetylene and regenerate LiOH. We demonstrate this process primarily using CO2 gas, achieving a current efficiency of 15% to acetylene (which represents 82% of the maximum based on stoichiometric production of oxygenated byproducts, e.g. LiCO3 and/or Li2O), as verified by gas chromatography and Fourier transform infrared radiation studies. We also explore CH4, CO, and C as alternative precursors in the acetylene synthesis. Notably, the use of graphitic carbon at higher temperatures resulted in over 55% current efficiency to acetylene, with opportunity for further optimization. Importantly, this cycling method avoids the formation of common side products observed during aqueous electrochemical CO2 and CH4 redox reactions, such as H2, CO, HCO2−, or CO2. Theoretical considerations elucidate the feasibility and general applicability of this cycle and the process steps have been characterized with specific electrochemical and materials chemistry techniques. The continued development of this strategy may lead to a viable route for the sustainable production of C–C coupled carbon fuels and chemicals

Creep and recovery in graphites at ambient temperature: an acoustic emission study

Nuclear graphites subject to compressive or tensile stress cycling show a Felicity effect, that is, acoustic emission (AE) is detected at stresses less than the previous peak stress. This is attributed to recovery processes that occur upon unloading and at zero stress. The extent of recovery increases with time (up to 105 mins) at zero stress between cycles. For two graphites (IM1-24 and PGA) held under constant compressive or tensile strain, AE over ∼16 h is attributed to creep. For the same graphites at zero stress (after application of a compressive or tensile prestress), AE over ∼16 h is attributed to creep recovery. Both types of AE time curve follow logarithmic rate laws similar to those derived earlier for high-temperature primary creep and creep recovery. The micromechanical processes that give rise to creep and AE on loading graphites are basal plane shear and microcracking; creep recovery is attributed to the reverse of these processes

Acoustic emission responses from cyclic loading of a nuclear graphite

An analysis is presented of acoustic emission from samples of a nuclear graphite, IMI-24, subjected to three consecutive, load-unload cycles to 5, 10, and 15 MPa, in tension, compression, and flexure. On the first cycle, cumulative acoustic emission events in all loading modes increased progressively from zero stress. However, in subsequent cycles, acoustic emission recurred at stresses approaching, but less than, the previous peak stresses (i.e., a Felicity effect was observed rather than a Kaiser effect). A new parameter, the Recovery ratio, B, is proposed for characterizing the pattern of acoustic emission on cyclic loading of graphites

Storage of Methane in Resin Carbon Beads and Discs

Porous resin beads can be produced by the emulsion polycondensation of lignosulphonates with crosslinking agents. These resins can be converted into active carbon beads or pressed into discs that can be converted into active carbon monoliths. The stored methane volumetric capacity of the active carbon discs exceeded 150 v/v while the delivered capacity approached this value. The delivered capacity could be increased if steps were taken to release the large amount of methane retained in micropores after decompression. The volumetric methane capacities of the carbon beads were lower than those for the discs due to the presence of interparticulate voids

Chemical Activation of a South African Coal using Phosphoric Acid

The potential of a South African coal, Bosjesspruit, as a precursor for a phosphoric acid-activated carbon has been assessed using the adsorption of nitrogen at 77 K and mercury porosimetry. Column cleaning of the coal by froth flotation reduced the ash content from 22 to 12 wt.% and caused maceral separtion, resulting in an intertinite-rich product. Reaction of the column-cleaned coal with phosphoric acid in the range 450–550°C produced an activated carbon which was dominantly microporous. The notional BET surface area of the coal reached a maximum of 600 m 2 /g at a reaction temperature of 550°C

Modelling of mechanical properties of CRFC composites under flexure loading

Carbon Fibre Reinforced Carbon (CFRC) Composites are increasing their applications due to their high strength and Young s Modulus at high temperatures in inert atmosphere. Although much work has been done on processing and structure and properties relationship, few studies have addressed the modelling of mechanical properties. This work is divided in two parts. In the first part, a modelling of mechanical properties was carried out for two bi-directional composites using a model based on the Bernoulli-Euler theory for symmetric laminated beams. In the second part, acoustic emission (AE) was used as an auxiliary technique for monitoring the failure process of the composites. Differences in fracture behaviour are reflected in patterns of AE

Athletic pubalgia (sports hernia)

Athletic pubalgia or sports hernia is a syndrome of chronic lower abdomen and groin pain that may occur in athletes and nonathletes. Because the differential diagnosis of chronic lower abdomen and groin pain is so broad, only a small number of patients with chronic lower abdomen and groin pain fulfill the diagnostic criteria of athletic pubalgia (sports hernia). The literature published to date regarding the cause, pathogenesis, diagnosis, and treatment of sports hernias is confusing. This article summarizes the current information and our present approach to this chronic lower abdomen and groin pain syndrome

DNA-Encoded Solid-Phase Synthesis: Encoding Language Design and Complex Oligomer Library Synthesis

The promise of exploiting combinatorial synthesis for small molecule discovery remains unfulfilled due primarily to the “structure elucidation problem”: the back-end mass spectrometric analysis that significantly restricts one-bead-one-compound (OBOC) library complexity. The very molecular features that confer binding potency and specificity, such as stereochemistry, regiochemistry, and scaffold rigidity, are conspicuously absent from most libraries because isomerism introduces mass redundancy and diverse scaffolds yield uninterpretable MS fragmentation. Here we present DNA-encoded solid-phase synthesis (DESPS), comprising parallel compound synthesis in organic solvent and aqueous enzymatic ligation of unprotected encoding dsDNA oligonucleotides. Computational encoding language design yielded 148 thermodynamically optimized sequences with Hamming string distance ≥ 3 and total read length <100 bases for facile sequencing. Ligation is efficient (70% yield), specific, and directional over 6 encoding positions. A series of isomers served as a testbed for DESPS’s utility in split-and-pool diversification. Single-bead quantitative PCR detected 9 × 10⁴ molecules/bead and sequencing allowed for elucidation of each compound’s synthetic history. We applied DESPS to the combinatorial synthesis of a 75 645-member OBOC library containing scaffold, stereochemical and regiochemical diversity using mixed-scale resin (160-μm quality control beads and 10-μm screening beads). Tandem DNA sequencing/MALDI-TOF MS analysis of 19 quality control beads showed excellent agreement (<1 ppt) between DNA sequence-predicted mass and the observed mass. DESPS synergistically unites the advantages of solid-phase synthesis and DNA encoding, enabling single-bead structural elucidation of complex compounds and synthesis using reactions normally considered incompatible with unprotected DNA. The widespread availability of inexpensive oligonucleotide synthesis, enzymes, DNA sequencing, and PCR make implementation of DESPS straightforward, and may prompt the chemistry community to revisit the synthesis of more complex and diverse libraries