Separation of Mineral Acid Solutions by Membrane Distillation and Thermopervaporation through Porous and Nonporous Membranes

Abstract

Membrane distillation was suggested for the regeneration of volatile inorganic acids (hydrochloric and nitric acids) from the metal pickling solutions using hydrophobic porous and nonporous asymmetric membranes. The investigations were performed with a flat-sheet commercial microfiltration membrane based on tetrafluoroethylene/vinylidenefluoride copolymer MFF-2 and with a plasma-modified commercial asymmetric gas separation membrane based on poly(vinyltrimethyl silane) (PVTMS). The influence of acid concentration (varying over a wide concentration range from 0.01 to 7.0 N) and the feed temperature (T h = 313–333 K) on the transmembrane flux and selectivity was studied. It was shown that the concentrating of volatile inorganic acids in the feed using a porous MFF-2 membrane is effective up to 1.0 N concentration. Plasma-modified PVTMS membrane was used for the separation of feed solutions with higher acid content up to 7.0 N. It was established that the plasma treatment essentially increases the hydrophilic properties of PVTMS membrane surface.

Modification of PET Ion-Track Membranes by Silica Nanoparticles for Direct Contact Membrane Distillation of Salt Solutions

“…Despite some limitations, the most studied type is DCMD due to its simplicity and availability [3,[9][10][11][12][13][14]. DCMD can be successfully used to purify water from salts [15][16][17][18][19], heavy metals [20][21][22], dyes [23,24], radioactive wastes [25][26][27][28], acid solutions [29], urea [30], mining, and industrial wastewater [31,32].…”

Process of Concentrating of Highly Mineralized Waters in an Air-Gap Membrane Distiller

“…The MFFK-1 membrane, according to the manufacturer, is a porous polymer film material based on fluoroplastic F42L (a copolymer of tetrafluoroethylene and vinylidene fluoride) on a nonwoven substrate (polypropylene, polyethylene terephthalate) with a pore size of 0.15 μm and a total porosity of 85%. For the first time, a membrane of this type (MFFK-2, pore diameter 0.25 μm) was studied in the DCMD process for the concentration of heavy metal salts using nickel sulfate solutions [18] and the recovery of mineral (nitric and hydrochloric) acids [19].…”

Modeling of transport and separation in a thermopervaporation process

“…In this technique transport and separation through membranes occur due to the difference in chemical potentials between both sides of the membrane [1,2]. Difference in chemical potentials in pervaporation can be created by applying low pressure on the permeate side -vacuum pervaporation (VPV) [1][2][3][4][5][6][7], by using a sweeping gas stream on the permeate side -sweeping gas pervaporation (SGPV) [8][9][10] or by creating a temperature difference between feed and permeate -thermopervaporation (TPV) [11][12][13][14][15][16][17]. Vacuum pervaporation is the method most widely described in the literature among all mentioned pervaporation modes.…”

“…Elkina et al [14] described application of hydrophobic porous membranes in air gap membrane distillation (AGMD) and nonporous asymmetric membranes in thermopervaporation (AGTPV) during regeneration of volatile inorganic acids (hydrochloric and nitric) from the metal pickling solutions. Authors [14] convinced that application of air gap membrane distillation in the first step (at lower acid concentration), and in subsequent step concentration of resulting permeate by thermopervaporation through the plasma-modified PVTMS membrane is advantageous.…”

“…Authors [14] convinced that application of air gap membrane distillation in the first step (at lower acid concentration), and in subsequent step concentration of resulting permeate by thermopervaporation through the plasma-modified PVTMS membrane is advantageous.…”