Energy Recovery from Acid-Base Neutralization Through pH-Sensitive Polymers: Novel Application of Donnan Osmosis

Lehigh University, Bethlehem PA

Investigators

Abstract

(Sengupta)1065651 Recent studies at Lehigh University have demonstrated the possibility of generating useful energy from acid-base neutralization reactions involving association of hydrogen and hydroxyl ions. Many industrial processes and natural biogeochemical process (e.g., acid mine drainage) produce acidic (or basic) wastewater streams and require neutralization prior to disposal. The acid-base reaction is thermodynamically very favorable with generation of significant amount of thermal energy. Since the waste acid solution undergoing treatment is often very dilute, the significant amount of thermal energy generated in the neutralization reaction causes a miniscule increase in the temperature of the bulk aqueous phase. As a result, any energy recovery is nearly impossible and has not been reported to date. For this project, it is proposed that it is possible to recover significant amount of useful energy by carrying out the neutralization reaction inside an appropriate pH-sensitive hydrophilic polymer (or biopolymer) containing covalently attached weak-acid or weak-base functional groups. Scientifically, the phenomenon of Donnan osmosis drives the process leading to energy generation and no external membrane is necessary. When contacted with acid or base, the variation in pH causes the functional groups to reversibly acquire and lose its ionic character. This change gives rise to on-off pattern of generation of osmotic pressure inside the polymer phase causing it to reversibly swell (osmosis) and shrink (deosmosis) due to the movement of water in and out of the polymer phase. Thus, acid-base neutralization is accompanied by generation of usable mechanical energy. It is noteworthy that the process is completely carbon neutral and no greenhouse gas is produced. The proposed process has the potential to generate energy globally from waste acid and waste alkali streams using reusable pH-sensitive polymers. The global annual production of sulfuric acid is estimated to be approximately 200 million tons. Assuming 1% of this acid appears in the waste stream that is neutralized by the proposed energy recovery process, reduction in carbon dioxide emission in comparison with a plant producing the same amount of energy with fossil fuel will be over 60 million tons.