Evaluations of adsorbents and salt-methanol solutions for low-grade heat driven osmotic heat engines

Abstract

Abstract To recovery low temperature waste heat, a methanol-based adsorption-driven osmotic heat engine is investigated, which consists of an adsorption-based desalination system for producing concentrated and diluted solutions, and a pressure retarded osmosis system for extracting power from the Gibbs free energy of mixing. Salt-Methanol is used as working solution and the activated carbons and metal-organic frameworks are employed as the adsorbents. Impacts of desorption temperature, salt concentrations, salt types, and adsorbents on the system performance are numerically analyzed. Criteria for screening the adsorbents and salts are evaluated and discussed. Qualified adsorbents should have larger relative pressure where half of the maximum absorption uptake is achieved and moderate adsorption enthalpy. Salt-methanol solutions with larger solubility and osmotic coefficient are beneficial for improving the system energy efficiency. When operating between 60\xa0°C and 20\xa0°C, a maximum energy efficiency of 6.68% was achieved at 5\xa0mol/kg LiBr-methanol solution for MAXSORB3 as the adsorbent with one-stage solid porous matrix regenerator employed. This study contributes to methanol-based adsorption-driven osmotic heat engines for efficient heat to electricity conversion, as well as providing criteria for selecting appropriate adsorbents.