Solar Energy-Driven Formic Acid Synthesis for Energy Storage and Utilization in a Fuel Cell for Clean Energy Generation

This study aims to develop a process flow modeling to synthesize formic acid from carbon dioxide and hydrogen for energy storage and transport purposes. The use of formic acid as an energy storage medium is promising due to difficulties in hydrogen storage. Formic acid can be stored for a longer time with minimal losses and then can be utilized in a direct formic acid fuel cell for cleaner power generation. The process flow is developed using Aspen Plus and Engineering Equation Solver to propose an integrated system for formic acid synthesis via photovoltaic (PV) assisted-chloralkali process and power generation by the fuel cell. The initial step is to develop process flow diagrams and to apply heat integration techniques to conserve energy in the synthesis of formic acid and direct formic acid fuel cells (DFAFC). The model is validated against data available in the literature for operating parameters. The results show that the operation parameters such as formic acid formation rate, heat duty, work values, fuel cell efficiency, and Nernst voltage significantly influence the overall performance. The formed formic acid is initially stored in a tank for energy storage and then used in a direct formic acid fuel cell to produce about 168 kW power with an energy efficiency of 16% at 0.7 V, 25℃, and 1 bar. The proposed system formed formic acid from gaseous hydrogen produced from chloralkali unit and captured carbon dioxide. The electricity requirements of both PV-assisted chloralkali and compression stages are supplied from the PV units. The results imply that the chloralkali process necessitates about 7.22 MW of power to produce hydrogen at 25°C and 1 bar with an energy efficiency of 84%. Hydrogen and carbon dioxide gases are initially compressed to 60 bars with a total energy requirement of 951 kW and sent to the conversion reactor. Different scenarios are developed in the heat integration part to determine the minimum heating and cooling requirements for maximum heat recovery. Such heat integration was achieved to conserve the energy in the formic acid process with total hot and cold utilities of 599 kW and 1,884 kW, respectively. In addition, this study compares different hazard statements, storing, and mitigation measures for hydrogen and formic acid comparatively as energy carriers and the impacts of both on the environment. Two different formic acid production methods, namely, using carbon dioxide and carbon monoxide as raw materials, are also compared with their effects on the environment. A cost analysis is also performed to determine the total capital cost, operating cost, the variable cost, and utilities cost of synthesis formic acid using ASPEN Plus © Economic Analyzer. The results of production costs are validated against other methods of producing formic acid in the literature.