Selective Electrochemical Regeneration of Aqueous Amine Solutions to Capture CO2 and to Convert H2S into Hydrogen and Solid Sulfur

Removing CO2 from natural gas or biogas in the presence of H2S is technically challenging and expensive as it often requires separation of both acid gases from the gas, typically using an aqueous amine solution, followed by separation of CO2 from H2S and conversion of H2S into solid S. In this work, the proof of concept of electrochemical, instead of thermal, regeneration of an aqueous amine solution is developed. This invention might be a very promising technology and has several advantages. It has H2S versus CO2 selectivity of 100%, can directly convert H2S into S and H2, and is economically competitive with CO2 desorption energy around 100 kJmol−1 and H2S conversion around 200 kJmol−1. If renewable energy is used for electrochemical regeneration, CO2 emissions due to the CO2 capture process can be significantly reduced.

Copper oxide-based cathode for direct NADPH regeneration

Nearly a fourth of all enzymatic activities is attributable to oxidoreductases, and the redox reactions supported by this vast catalytic repertoire sustain cellular metabolism. In many biological processes, reduction depends on hydride transfer from either reduced nicotinamide adenine dinucleotide (NADH) or its phosphorylated derivative (NADPH). Despite longstanding efforts to regenerate NADPH by various methods and harness it to support chemoenzymatic synthesis strategies, the lack of product purity has been a major deterrent. Here, we demonstrate that a nanostructured heterolayer Ni–Cu2O–Cu cathode formed by a photoelectrochemical process has unexpected efficiency in direct electrochemical regeneration of NADPH from NADP+. Remarkably, two-thirds of NADP+ was converted to NADPH with no measurable production of the inactive (NADP)2 dimer and at the lowest reported overpotential [− 0.75 V versus Ag/AgCl (3 M NaCl) reference]. Sputtering of nickel on the copper-oxide electrode nucleated an unexpected surface morphology that was critical for high product selectivity. Our results should motivate design of integrated electrolyzer platforms that deploy this heterogeneous catalyst for direct electrochemical regeneration of NADH/NADPH, which is central to design of next-generation biofuel fermentation strategies, biological solar converters, energy-storage devices, and artificial photosynthesis.

Adsorption of Reactive Black 5 Dye from Aqueous Solutions by Carbon Nanotubes and its Electrochemical Regeneration Process

: Removal of Reactive Black 5 (RB5) dye from aqueous solutions was investigated by adsorption onto Multi-walled Carbon Nanotubes (MWCNTs) and Single-walled Carbon Nanotubes (SWCNTs). A Taguchi orthogonal design including pH, initial RB5 concentration, contact time, and CNTs dose, was used in 16 experiments. The results showed that all four factors were statistically significant, and the optimum conditions for both adsorbents were as follows: pH of 3, adsorbent dose of 1000 mg/L, RB5 concentrations of 25 mg/L, and contact time of 60 min. An equilibrium study by Isotherm Fitting Tool (ISOFIT) software showed that Langmuir isotherm provided the best fit for RB5 adsorption by CNTs. The maximum predicted adsorption capacities for the dye were obtained as 231.84 and 829.20 mg/g by MWCNTs and SWCNTs, respectively. The results also indicated that the adsorption capacity of SWCNTs was about 1.21 folds higher than that of MWCNTs. Studies of electrochemical regeneration were conducted, and the results demonstrated that RB5-loaded MWCNTs and SWCNTs could be regenerated (86.5% and 77.3%, respectively) using the electrochemical process. Adsorbent regeneration was mostly due to the degradation of the dye by the attack of active species such as chlorate, H2O2, and, •OH, which were generated by the electrochemical oxidation process with Ti/RuO2-IrO2-TiO2 anodes. The results of Gas Chromatography-Mass Spectrometry (GC-MS) analysis showed that acetic acid, 3-chlorobenzenesulfonamide, and 1,2-benzenedicarboxylic acid were produced after adsorbent regeneration by the electrochemical process in the solution of regeneration. The adsorption and regeneration cycles showed that the electrochemical process with Ti/RuO2-IrO2-TiO2 and graphite is a good alternative method for the regeneration of CNTs and simultaneous degradation of the dye.