Delineation of the diamine monomers effect on the desalination properties of polyamide thin film composite membranes: Experimental and molecular dynamics simulation

• Diamines with different alkyl chain lengths were used to fabricated TFC membranes. • Membrane with piperazine monomer showed the best desalination performance. • Performance of the membranes were also studied by molecular dynamics simulations. • Hydrodynamic study of the process showed direct correlation b/w flow velocity & flux. • Increasing the feed pressure, temperature, or velocity have positive impact on the permeate flux. The success of membrane desalination technology hinges on the properties of thin film composite (TFC) membrane that is commonly fabricated by interfacial polymerization (IP) of diamine and acyl chloride. The current study aimed to investigate the impact of the length of the alkyl side chain of the diamine monomers on the desalination performance of the TFC membranes. Four diamines (piperazine (PIP), 1-(2-aminoethyl)piperazine (EAP), 1,4-Bis(3-aminoprpyl)piperazine (DAPP), and m-xylylenediamine (XLN)) were used to fabricate four different TFC membranes with trimesoyl chloride (TMC) as a crosslinker. The merits of the TFC membranes were thoroughly characterized and the PIP was found to be advantageous compared to other diamines with different aliphatic alkyl chain lengths. Molecular dynamics simulations showed that PIP TFC membrane has a tight pore diameter of 1.1 nm and polar carboxylic groups within its pores, which makes it strongly hydrophilic reporting a water contact angle of 28°. The salt rejection (%) of the PIP TFC membrane followed the order: MgSO 4 (91%) > Na 2 SO 4 (85%) > Na 2 CO 3 (77%) > NaCl (32%). The increase in feed pressure, temperature or velocity had a positive impact on the permeate flux. However, salt rejection deteriorated as the temperature of the feed increased.