Specialty ultrafiltration and nanofiltration membranes are positioned as solutions for extreme acidic, alkaline, and solvent environments and will find applications in the mining, chemicals, pharmaceuticals, pulp and rayon, and paints and coatings industries, according to the Israeli company that developed them, AMS Technologies.
“The membranes are made of proprietary polymers. The difference [compared] with conventional products lies in their high stability at extreme pH levels, concentrations outside the pH range, and in the presence of solvents,” said Jorge Yacubowicz, CTO at AMS. “They can also handle high temperatures and pressures.”
Proprietary polymeric membranes are said by their supplier to be stable up to 80°C and 70 bar — well above the range of conventional membranes. Credit: AMS Technologies
AMS specs the membranes as being functional at pH levels under 1.5 and above 12.5. The membranes have thermal stability up to 80°C and can be operated at pressures up to 70 bar. Highly alkaline or acidic waste streams are treated via neutralization for conventional ultrafiltration (UF) and nanonfiltration (NF) membrane products that could not withstand the conditions.
Founded in 2012, AMS sells its polymeric membranes under the UltraPro and NanoPro brands. The membranes have been tested with acidic solutions, including 20 percent sulfuric acid, 20 percent hydrogen chloride, and 25 percent phosphoric acid, while tested alkali solutions include 20 percent caustic soda and 20 percent potassium hydroxide.
Further, solvent solutions that have been tested include methanol, propanol, ethanol, acetone, hexane, tetrahydrofuran, N-methylpyrrolidone, dimethylformamide, methylene chloride, and alcohols.
“Usually you will encounter a solvent recovery plant based on evaporation or distillation next to the industrial plant, thus doubling the whole operation size,” Yacubowicz noted. “Membranes are less energy-intensive and do not require a phase change. Operating at low temperatures also mean that heat-sensitive organic materials are not damaged while concentrating them and recovering solvent,” he said, comparing membrane-based with solvent evaporation.
While AMS’s membrane compositions are a closely held trade secret, Yacubowicz said the company optimizes between its portfolio of products to individual applications. “Normally, we do not develop a specific membrane for a client or an application,” he said.
Typical applications that the UF/NF membranes target include cleaning of caustic liquors from hemicellulose and other organic contaminants in the pulp-making process, which allows up to 95 percent reuse of sodium hydroxide. In the food the beverage industry, membranes can be used for cleaning of spent caustic production line washing streams and ion exchange process regeneration solutions (in sugar decolorization operations) to allow up to 95 percent reuse of sodium hydroxide. The processing temperature is typically 65 to 70°C.
“If a membrane is limited to a temperature of 40°C, then you would need to install a heat exchanger to lower process fluid temperature,” Yacubowicz noted. “Furthermore, throughput is related to temperature. The higher the temperature, the higher the throughput.”
According to Yacubowicz, the vast majority of standard membranes, such as those made from polyamide (nylon), cannot endure temperatures of more than 40°C and pressures in excess of 40 bar.
Purification of acids from metal cations, recovery of acids in leaching operations, decolorization of mineral acids, recovery of dissolved chemicals, and concentration and recovery of ions in acidic streams are among potential mining industry applications. The membranes can also be used for the concentration of metal in processing streams in order to reduce operating and treatment costs, as well as for the pre-separation of copper and gold for efficient gold extraction.
Other uses in mining include the recovery of products from raffinate (copper, zinc, cobalt, molybdenum, tungsten, uranium, gold) and the recovery of high-value metals from bleed streams and waste streams.
Commercial installations of AMS’s membranes number 10 at present, in Europe, Japan, China, and Israel, including pharmaceutical, chemical, rayon, and dairy plants. Numerous lab-scale tests, as well as the deployment of on-site pilot units, are underway in the mining industry. “We expect that the number of installations will grow significantly next year,” said Tidhar (Teddy) Golan, CEO of AMS.
Ultrafiltration and nanofiltration are two levels of separation. Ultrafiltration is used for separating molecules over 1,000 daltons, while nanofiltration is used for separating smaller particles — typical range is 200 to 1,000 daltons.
“In one type of application, nanofiltration can separate between small-molecular-weight organic and monovalent salts. Ultrafiltration will pass both of them, as in, for example, the separation of lactose and salt coming from whey processing,” Yacubowicz stated.