High Pressure Electrochemical Reduction of CO2 to Formic Acid/Formate: A Comparison between Bipolar Membranes and Cation Exchange Membranes.

A high pressure semicontinuous batch electrolyzer is used to convert CO2 to formic acid/formate on a tin-based cathode using bipolar membranes (BPMs) and cation exchange membranes (CEMs). The effects of CO2 pressure up to 50 bar, electrolyte concentration, flow rate, cell potential, and the two types of membranes on the current density (CD) and Faraday efficiency (FE) for formic acid/formate are investigated. Increasing the CO2 pressure yields a high FE up to 90% at a cell potential of 3.5 V and a CD of ∼30 mA/cm2. The FE decreases significantly at higher cell potentials and current densities, and lower pressures. Up to 2 wt % formate was produced at a cell potential of 4 V, a CD of ∼100 mA/cm2, and a FE of 65%. The advantages and disadvantages of using BPMs and CEMs in electrochemical cells for CO2 conversion to formic acid/formate are discussed.

OCTP: A Tool for On-the-Fly Calculation of Transport Properties of Fluids with the Order- n Algorithm in LAMMPS.

We present a new plugin for LAMMPS for on-the-fly computation of transport properties (OCTP) in equilibrium molecular dynamics. OCTP computes the self- and Maxwell-Stefan diffusivities, bulk and shear viscosities, and thermal conductivities of pure fluids and mixtures in a single simulation. OCTP is the first implementation in LAMMPS that uses the Einstein relations combined with the order- n algorithm for the efficient sampling of dynamic variables. OCTP has low computational requirements and is easy to use because it follows the native input file format of LAMMPS. A tool for calculating the radial distribution function (RDF) of the fluid beyond the cutoff radius, while taking into account the system size effects, is also part of the new plugin. The RDFs computed from OCTP are needed to obtain the thermodynamic factor, which relates Maxwell-Stefan and Fick diffusivities. To demonstrate the efficiency of the new plugin, the transport properties of an equimolar mixture of water-methanol were computed at 298 K and 1 bar.

Phase behavior of liquid crystals with CO2.

Liquid crystals are being considered as novel process solvents for CO(2) capture. The solubility of CO(2) is higher in the isotropic phase than in the structured (e.g., nematic) phase. CO(2) can be captured in the isotropic phase, and regeneration of the solvent is achieved by cooling down the mixture a few degrees until a phase transition to the structured phase occurs. This CO(2) capture process has the potential to consume less energy than the conventional amine-based processes. To address the potential of liquid crystals to efficiently capture CO(2), experimentally obtained P,T-phase diagrams of five liquid crystals with 5 mass % CO(2) are reported. The liquid crystals used in this study are 4'-(pentyloxy)-4-biphenylcarbonitrile, 4'-pentyl-4-biphenylcarbonitrile, 4-ethyl-4'-propyl-bicyclohexyl, 4-propyl-4'-butyl-bicyclohexyl, and 4'-(octyloxy)-4-biphenylcarbonitrile. It is found that a weakly polar liquid crystal had a higher CO(2) solubility than apolar and more polar liquid crystals.