Use of the electrodialysis process to concentrate a formic acid solution

Our previous work clearly showed that electro-eletrodialysis was an efficient way to concentrate a formic acid solution. Electro-electrodialysis can be easily scaled up as electrodialysis, but the equipment cost is higher. Accordingly, an electrolysis process with a new cation-exchange membrane was tested in this work. The effects of concentration, electric current density, and concentration difference between the concentrated side and the dilute side were studied. The experimental results indicated that electrodialysis was also an effective method to concentrate formic acid solution. For the high concentration system the overall current efficiency was larger than 100%. The overall current efficiency for a low concentration system would be up to 90%. But the concentrated ratio is not as much as desired, which is limited by the operating system and conditions. In general, the overall current efficiency was increased to a maximum value with an increase of the current density. After a certain value, the overall current efficiency would begin to drop. The increase of the initial concentration helped to increase the overall current efficiency, but led to a decrease in the concentrated ratio. The volume change of the concentrated solution is seriously affected by the current density and the ratio of the initial concentration in the concentrated compartment compared to that in the dilute compartment.