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New methods in lowering energy consumption costs for evaporation and concentration are needed in many commercial chemical processes. Pervaporation is an underutilized, low-energy processing method that has a potential capability in achieving lower energy processing costs. A recently developed new electrochemical process that can generate a 5–25 wt% pure formic acid (FA) from the electrochemical reduction of CO2 requires a low-energy process for producing a more concentrated FA product for use in both on-site and commercial plant applications. In order to accomplish this, a 25 cm2 membrane area pervaporation test cell was constructed to evaluate the FA-H2O system separation performance of three distinct types of membrane candidates at various FA feed concentrations and temperatures. The selection included one cation ion exchange, two anion ion exchange, and two microporous hydrophobic membranes. The permeation flux rates of FA and H2O were measured for FA feed concentrations of 10, 20, 40, and 60 wt% at corresponding temperatures of 22, 40, and 60 °C. The separation performance results for these particular membranes appeared to follow the vapor liquid equilibrium (VLE) characteristics of the vapor phase in the FA-H2O system as a function of temperature. A Targray microporous hydrophobic high-density polyethylene (HDPE) membrane and a Chemours Nafion® N324 membrane showed the best permeation selectivities and mass flux rates FA feed concentrations, ranging from 10 to 40 wt%. The cation and anion ion exchange membranes evaluated were found not to show any significant enhancements in blocking or promoting the transport of the formate ion or FA through the membranes. An extended permeation cell run concentrated a 10.12% FA solution to 25.38% FA at 40 °C. Azeotropic distillation simulations for the FA-H2O system using ChemCad 6.0 were used to determine the energy requirement using steam costs in processing FA feed concentrations ranging from 5 to 30 wt%. These experimental results indicate that pervaporation is a potentially useful unit process step with the new electrochemical process in producing higher concentration FA product solutions economically and at lower capital costs. One major application identified is in on-site production of FA for bioreactors employing new types of microbes that can assimilate FA in producing various chemicals and bio-products.

This paper is a review on the application of imidazolium-based ionic liquids tethered to polymer backbones in the electrochemical conversion of CO2 to carbon monoxide and formic acid. These tethered ionic liquids have been incorporated into novel anion ion exchange membranes for CO2 electrolysis, as well as for ionomers that have been incorporated into the cathode catalyst layer, providing a co-catalyst for the reduction reaction. In using these tethered ionic liquids in the cathode catalyst composition, the cell operating current increased by a factor of two or more. The Faradaic efficiencies also increased by 20–30%. This paper provides a review of the literature, in addition to providing some new experimental results from Dioxide Materials, in the electrochemical conversion of CO2 to CO and formic acid.