Evaluation of Different Capture Solutions for Ammonia Recovery in Suspended Gas Permeable Membrane Systems

Abstract

Gas permeable membranes (GPM) are a promising technology for the capture and recovery of ammonia (NH₃). The work presented herein assessed the impact of the capture solution and temperature on NH₃ recovery for suspended GPM systems, evaluating at a laboratory scale the performance of eight different trapping solutions (water and sulfuric, phosphoric, nitric, carbonic, carbonic, acetic, citric, and maleic acids) at 25 and 2 °C. At 25 °C, the highest NH₃ capture efficiency was achieved using strong acids (87% and 77% for sulfuric and nitric acid, respectively), followed by citric and phosphoric acid (65%) and water (62%). However, a remarkable improvement was observed for phosphoric acid (+15%), citric acid (+16%), maleic acid (+22%), and water (+12%) when the capture solution was at 2 °C. The economic analysis showed that water would be the cheapest option at any working temperature, with costs of 2.13 and 2.52 €/g N (vs. 3.33 and 3.43 €/g N for sulfuric acid) in the winter and summer scenarios, respectively. As for phosphoric and citric acid, they could be promising NH₃ trapping solutions in the winter months, with associated costs of 3.20 and 3.96 €/g N, respectively. Based on capture performance and economic and environmental considerations, the reported findings support that water, phosphoric acid, and citric acid can be viable alternatives to the strong acids commonly used as NH₃ adsorbents in these systems.

Keywords: ammonia adsorbents; ammonia recovery; citric acid; organic acids; phosphoric acid; water.

Figure 1

Evolution of the amount of TAN captured in the different trapping solutions during the 7-day experiments at (a) 25 °C and (b) 2 °C. All values are expressed as mean ± s.d. of n = 3.

Figure 2

Mass of NH₃-N recovered by the different trapping solutions at two temperatures after 7 days. Values with different letters are significantly different at p ≤ 0.05 according to Tukey’s HSD test. All values are expressed as means of n = 3.

Figure 3

Economic analysis of the suspended GPM-based NH₃ capture process using eight different types of trapping solutions in the (a) summer (25 °C) and (b) winter (2 °C) scenarios.