Efficient methane-to-acetylene conversion using low-current arcs

Production of Acetylene from Viable Feedstock: Promising Recent Approaches

The potential of acetylene is extremely high both in chemical industry and synthetic applications due to unsaturated nature and the smallest active C≡C unit. The production of many essential necessities is originated from acetylene; however, the formation of acetylene molecule requires a lot of energy. Currently, the access to acetylene is based on coal processing, methane reforming and calcium carbide hydrolysis. Recently, extensive research has been done to decrease the cost of acetylene. In this review, the routes to acetylene were highlighted, considering the energy consumption in kW ⋅ h/t of the product to evaluate the best approach. Since energy prices depend on various regions, the cost of the product is complicated. The manufacturing of acetylene is usually accompanied by formation of by-products, which may be valuable or not. The review should help to identify current status and not overlook promising approaches.

Plasma-Assisted Reforming of Methane

Methane (CH₄ ) is inexpensive, high in heating value, relatively low in carbon footprint compared to coal, and thus a promising energy resource. However, the locations of natural gas production sites are typically far from industrial areas. Therefore, transportation is needed, which could considerably increase the sale price of natural gas. Thus, the development of distributed, clean, affordable processes for the efficient conversion of CH₄ has increasingly attracted people's attention. Among them are plasma technology with the advantages of mild operating conditions, low space need, and quick generation of energetic and chemically active species, which allows the reaction to occur far from the thermodynamic equilibrium and at a reasonable cost. Significant progress in plasma-assisted reforming of methane (PARM) is achieved and reviewed in this paper from the perspectives of reactor development, thermal and nonthermal PARM routes, and catalysis. The factors affecting the conversion of reactants and the selectivity of products are studied. The findings from the past works and the insight into the existing challenges in this work should benefit the further development of reactors, high-performance catalysts, and PARM routes.

Cg10062 Catalysis Forges a Link between Acetylenecarboxylic Acid and Bacterial Metabolism

The reliance of biocatalysis on plant-derived carbon for the synthesis of fuels and chemicals places it in direct competition with food production for resources. A potential solution to this problem is development of a metabolic link between alternative carbon sources and bacterial metabolism. Acetylenecarboxylic acid, which can be synthesized from methane and carbon dioxide, could enable this connection. It was previously shown that the enzyme Cg10062 catalyzes hydration of acetylenecarboxylate to afford malonate semialdehyde. Subsequent hydration-dependent decarboxylation to form acetaldehyde (81%), which was also observed, limits its biocatalytic usefulness. Several Cg10062 variants including E114Q and E114D do not catalyze decarboxylation and provide malonate semialdehyde as the sole product, albeit with substantially reduced catalytic activity. To identify an efficient enzyme capable of catalyzing acetylenecarboxylate hydration without decarboxylation, we undertook a mechanistic investigation of Cg10062 using mutagenesis, kinetic characterization, and X-ray crystallography. Cg10062 is a member of the tautomerase superfamily of enzymes, characterized by their β-α-β protein fold and an N-terminal proline residue situated at the center of the enzyme active site. Along with Pro-1, five additional active site residues (His-28, Arg-70, Arg-73, Tyr-103, and Glu-114) are required for Cg10062 activity. Incubation of crystals of four catalytically slow variants of Cg10062 with acetylenecarboxylate resulted in atomic resolution structures of Pro-1 bound to a complete set of intermediates, fully elaborating the detailed mechanism of the enzyme and establishing the process to involve covalent catalysis. Further, the intermediate-bound E114D structure explains the mechanism governing decarboxylation suppression. Together, these studies provide the most detailed picture of the catalytic mechanism of a tautomerase enzyme to date.

A novel energy efficient path for nitrogen fixation using a non-thermal arc

Plasma-assisted nitrogen fixation is a promising sustainable and clean alternative to the classical Haber-Bosch process. However, the high energy consumption and low production rate of plasma-assisted nitrogen fixation limit its application. This study shows that the non-thermal (non-equilibrium) enhancement of the arc plasma significantly reduces the energy consumption of nitrogen fixation. The highest energy efficiency with high NO selectivity is observed with a low specific energy input (SEI). However, the highest production rate is reached at a high SEI. The studied process offers high NO selectivity (up to 95%) with low energy consumption (∼48 GJ per tN) at 0.1 kJ L-1 SEI, which is much lower than the previously reported value of plasma-assisted atmospheric nitrogen fixation and is close to that of the Haber-Bosch process.

Understanding Hydrodechlorination of Chloromethanes. Past and Future of the Technology

Chloromethanes are a group of volatile organic compounds that are harmful to the environment and human health. Abundant studies have verified that hydrodechlorination might be an effective treatment to remove these chlorinated pollutants. The most outstanding advantages of this technique are the moderate operating conditions used and the possibility of obtaining less hazardous valuable products. This review presents a global analysis of experimental and theoretical studies regarding the hydrodechlorination of chloromethanes. The catalysts used and their synthesis methods are summarized. Their physicochemical properties are analyzed in order to deeply understand their influence on the catalytic performance. Moreover, the main causes of the catalyst deactivation are explained, and prevention and regeneration methods are suggested. The reaction systems used and the effect of the operating conditions on the catalytic activity are also analyzed. Besides, the mechanisms and kinetics of the process at the atomic level are reviewed. Finally, a new perspective for the upgrading of chloromethanes, via hydrodechlorination, to valuable hydrocarbons for industry, such as light olefins, is discussed.