Synthesis and application of ethylenediamine tetrapropionic salt as a novel draw solute for forward osmosis application

Abstract

The development of suitable draw solutes for forward osmosis (FO) process is a big obstacle on the way of its real industrialization. In this work, a novel draw solute, ethylenediamine tetrapropionic (EDTP) acid (salt) is developed for FO application. The successful synthesis is confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and high resolution mass spectrum. By optimizing the pH of EDTP solution, its composition is varied, and therefore, its water solubility and osmotic pressure are effectively improved. The effects of EDTP concentration on the osmotic pressure and FO performance are also investigated. Its outstanding osmotic pressure and big molecular size result in a high water flux of 22.69 LMH and a low salt flux of 0.32 gMH with 0.8 M EDTP draw solution (water as the feed solution, pressure retarded osmosis mode). The good stability and easy recovery by nanofiltration of EDTP solution also demonstrate its great potential as the draw solute for future FO applications. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1309–1321, 2015

Sodium Tetraethylenepentamine Heptaacetate as Novel Draw Solute for Forward Osmosis—Synthesis, Application and Recovery

“…This phenomenon indicates that more carboxyl groups in STPH molecules are converted to carboxylate ions when the pH increases from 7 to 8, leading to more free ions generated in the aqueous solution. Similar results were also observed by Hau et al [22] and in our previous work, where the pH plays an important role in the osmotic pressure, mainly because the solute components vary significantly with the pH change [19]. Figure 3b presents the water flux and the reverse salt flux with 0.1 g/mL STPH draw solution of different pHs (7-10) under PRO mode in FO process.…”

“…Previous works have reported polyacrylic acid salts (PAA-Na) with various molecular weights ranging from 1200 Da to 5000 Da [17], and Polyamidoamine with terminal carboxyl groups (PAMAM-COONa) [18] as novel draw solutes with good FO performance. Recently, we also demonstrated a novel ethylenediamine tetrapropionic sodium salts (EDTP) with multiple carboxyl groups [19]. The above studies all show that the introduction of carboxyl groups in the synthesized draw solute compounds can effectively improve their osmotic pressure and water solubility.…”

“…Generally, a draw solution with a high concentration will generate a high osmotic pressure and a high water flux, but this also causes a high viscosity and therefore a high energy consumption and a severe concentration polarization [19]. Therefore, the potential of the draw solution should be optimized by a concentration effect study.…”

“…Our previous works [19] demonstrated that by the acid-base neutralization of EDTP draw solution using NaOH solution, an improved solute solubility and compatibility with the FO membrane can be achieved. For solutions with a too high or low pH, the pH optimization must be carried out to avoid the severe membrane degradation and unpredictable salt leakage [21].…”

“…The resultant solution was stirred at room temperature until all the solid was dissolved, and then diluted to get solutions of various concentrations (0.05 g/mL, 0.1 g/mL, 0.15 g/mL, and 0.3 g/mL). The osmotic pressure of the draw solution was tested based on the freezing point depression method, using a self-assembled system as described in our previous work [19].…”