New membranes enable traditional water treatment and emerging energy transition applications
While membranes and filters have provided a reliable and cost-effective solution for water desalination, purification and treatment as well as specialty process separations, innovative membrane and filtration technologies are now playing a critical role in energy transition and sustainability-based applications. Accordingly, membrane and filtration technologies are being developed to overcome common issues such as energy consumption and fouling, delivering more substantial energy savings and waste minimization to make traditional applications more economical and emerging applications possible.
“Membranes have revolutionized water treatment in many ways,” says Kishor G. Nayar, director of business vertical – chemical processing industry, with Xylem/Evoqua Water Technologies (Houston; www.evoqua.com). “For example, before the advent of membranes for water treatment, removing salts and minerals from water was expensive and energy consuming. Demineralization or desalination of saltier water, such as very brackish groundwater and seawater, required thermal evaporators, resulting in high energy consumption. Today, reverse osmosis (RO) membrane-based water treatment systems have slashed energy consumption and operational costs” (Figure 1).
FIGURE 1. Today, RO membrane-based water treatment systems, such as this one from Xylem, have slashed energy consumption and operational costs
Nayar continues: “Other membrane systems for removing suspended particles, such as ultrafiltration (UF), are replacing traditional gravity-based separation systems in both water pre-treatment systems and wastewater treatment, significantly reducing equipment footprint and increasing reliability and resilience.
“And, increasingly, membranes are being employed for critical roles in energy transition and sustainability-based applications, such as green and blue hydrogen and to reduce the water footprints of several industries,” says Nayar.
Improved water treatment
“Membranes play a critical role in the water and wastewater treatment systems across industries, especially chemical plants,” says Nayar. “At various stages of the process, chemical plants employ UF and other particle filtration membranes to remove suspended solids from river water; RO systems to generate demineralized water and continuous electrodeionization (CEDI) systems for polishing RO water for use as boiler make-up water.
“UF membranes are also used in membrane-based biological wastewater treatment systems, called membrane bioreactors (MBRs), to separate biosolids from treated effluent, allowing highly compact wastewater treatment systems and improved treatment efficiencies,” Nayar continues. “With increases in potable water reuse applications, membranes are also used in advanced wastewater treatment applications for directly recovering drinking water-quality effluent from wastewater. Typically, such applications include MBR-RO systems with other treatment steps such as disinfection.”
To enable these and other advanced water treatment technologies, membrane developers have had to overcome significant challenges, says Henia Pransky, senior vice president of membrane operations with Kovalus Separation Solutions (formerly Koch Separation Solutions; Wilmington, Mass.; www.kovalus.com). “The challenges are different in various applications, but a common challenge is meeting environmental, social and governance (ESG) goals at minimal costs,” she says. “Some market segments look at the investment cost, but more and more projects consider the overall lifecycle cost of the project. To reduce lifecycle cost, the ‘optimal membrane’ must be energy efficient, fouling resistant and high flux, highly chemical resistant and offer a small footprint via high packing density, while providing excellent separation properties.”
“Among these challenges, energy efficiency is one of the greatest considerations when weighing the benefits of different filtration technologies,” says Tina Arrowood, global technology manager, growth and sustainability, with DuPont Water Solutions (Edina, Minn.; www.dupont.com). “In addition to reducing the environmental footprint of their operations, the high cost of energy means that there is also a significant economic argument for companies to adopt more energy-efficient technologies.”
Accordingly, many chemical and petrochemical facilities with large wastewater streams operating in water-stressed regions are increasingly looking to reduce or reuse liquid discharge via membrane-based minimal liquid discharge (MLD). “Though there has been significant progress, a zero-liquid discharge (ZLD) solution can be prohibitively expensive in terms of capital and operating costs and, due to high levels of energy consumption, it’s not the most environmentally friendly process,” says Arrowood. “At a 95% water recovery rate, a membrane-based MLD approach can be operated at a fraction of the cost of a 100% ZLD system. Today’s cost-effective MLD approach allows chemical processors to reduce the volume of water that needs additional dewatering via expensive thermal ZLD methods.”
DuPont’s recommended MLD solution blends the use of UF, RO and nanofiltration (NF) membranes for tackling tough-to-treat water challenges, including wastewater with high salt content, high suspended solids and a high level of organic pollutants. “This allows processors to improve water circularity by recovering up to 95% liquid discharge for reuse at a fraction of the cost of ZLD,” she says.
Innovations in membrane technologies that overcome common challenges of membrane reliability and efficiency are enabling this type of solution. For example, DuPont’s FilmTec Fortilife CR200 RO elements (Figure 2) help address the challenges of wastewater reuse with an advanced design that allows it to operate with up to 50% fewer cleanings due to fouling and a 20% reduction in energy consumption compared to standard RO element types. These benefits increase operational efficiency but also reduce waste from chemical cleaning and element replacement.
FIGURE 2. DuPont’s FilmTec Fortilife CR200 is a high-productivity membrane that operates with a 50% reduction in cleanings, a 20% reduction in energy consumption and lower waste from cleaning chemical and element replacement compared to standard RO element types
Kovalus, too, offers technologies that tackle persistent challenges. For example, its NF membrane filters and recycles caustic of up to 25% strength, while Kovalus has also developed solvent-stable NF and UF membranes, as well as differentiated MBR membrane products that provide low energy consumption when treating industrial and municipal wastewater (Figure 3).
FIGURE 3. Kovalus’s differentiated MBR membrane products provide low energy consumption when treating industrial wastewater. Shown here is a large-scale Puron MBR System for wastewater treatment
“The range of new developments is broad and includes new chemistries to achieve improved chemical compatibility or reduce fouling, new membrane morphologies to reduce energy consumption and selectivity, new ways of operating membrane products to reduce energy consumption or to separate constituents of different properties and more,” notes Pransky.
For example, New Logic Research (Minden, Nev.; www.vsep.com) has developed a unique type of membrane filter that resonates to vibrate the membrane and create a very high shear at the membrane surface to combat fouling, scaling and plugging (Figure 4). “This has the effect of keeping the membrane from scaling or plugging,” explains Greg Johnson, CEO, with New Logic Research. “Our membrane would be used where the selectivity of a membrane is desired but conventional spiral membranes cannot be used due to fouling and scaling potential, including very difficult effluent streams, such as landfill leachate or pig manure.”
FIGURE 4. New Logic Research has developed a unique type of membrane filter that resonates to vibrate the membrane and create a very high shear at the membrane surface to combat fouling, scaling and plugging
Optimization of membranes
Emerging applications are still defining membrane construction and the best way of optimizing membranes for each of these applications is currently evolving, says Franchessa Sayler, global technology manager, IXM, with Chemours (Wilmington, Del.; www.chemours.com). “The membranes used in these applications today are likely not the membranes that will be used in these applications tomorrow — a lot of R&D work and infrastructure development is still needed to meet the needs of emerging markets,” says Sayler. “Because sustainability-based applications are still emerging, the challenge is trying to design the optimal solution for each application.”
Saylor points to redox flow batteries, which are used to help manage variable power output from intermittent power sources, such as solar or wind, by storing power when production is high and discharging power to the grid when production is low, as an example of an emerging application that is now possible thanks to innovative membrane development. “Chemours’s Nafion membranes are used in redox flow batteries to separate the catholyte and anolyte while allowing selective transport of ions during charging and discharging cycles,” says Saylor.
Chemours’ Nafion ion exchange materials, including membranes, dispersions and resins (Figure 5), play a vital role in other transformative energy industry applications, as well, including fuel cells, energy storage and water electrolyzers. “Each of these applications can leverage the unique characteristics of Nafion materials, such as their chemical and mechanical durability and electrical conductivity,” adds Sayler.
FIGURE 5. Chemours’s Nafion ion exchange materials, including membranes, dispersions and resins, play a vital role in transformative energy industry applications including fuel cells, energy storage and water electrolyzers
For example, Chemours Nafion proton exchange membranes (PEM) find use in technologies that are critical to scaling clean hydrogen, namely water electrolyzers that convert renewable electricity into clean hydrogen energy and fuel cells that deploy hydrogen energy for use in transportation and serve as backup power for hospitals, buildings and heavy industry. “In water electrolysis, our membranes offer a way to generate clean hydrogen while generating zero emissions when powered by renewable energy, such as wind or solar, while in fuel cells, our membranes convert clean hydrogen — instantly — making fleets of fuel cell-powered transportation a reality,” says Saylor.
Similarly, W.L. Gore & Associates (Putzbrunn, Germany; www.gore.com) offers Gore-Select, PEM and Membrane Electrode Assemblies (MEAs) to enable large-scale hydrogen fuel cell commercialization throughout major industrial market sectors, from stationary power generation to global long-haul transportation, says Ed R. Harrington, strategic account manager. Within the fuel cell, the PEM separates hydrogen and oxygen and transports protons from the anode to the cathode. These functions make the fuel cell PEM one of the most important determinants of fuel cell stack performance and service life.
Kovalus’s Pransky adds that membrane innovation is necessary to support a multitude of other emerging green energy applications: “Whether membranes serve in the extraction process of lithium for EV batteries as pretreatment to the direct lithium-extraction (DLE) process, high brine concentration RO, biofuel processing to remove contaminants and concentrate byproducts of the process or other separation challenges, the innovation in the market driving sustainability creates a landscape of innovation in the membrane field.”
Pransky continues to say that one of the most significant advancements in supporting sustainability-based applications is the introduction of industrial-scale high-brine RO technologies. “Various technologies have demonstrated successful operation reaching 200–250 g/L salt concentrations,” she says. “These newer technologies are used in lithium extraction, as well as other new applications and are also used in traditional desalination systems to increase system recovery and reduce concentrate disposal volumes.”
Along these lines, DuPont offers its FilmTec LiNE-XD nanofiltration elements to aid in high lithium recovery from new sources, such as geothermal brines, salt lakes and surface and sub-surface clay. “Lithium mass recovery can be optimized with enhanced purity as non-essential metal ions are filtered out,” says Arrowood. “Importantly, lower energy consumption and up to 30% in energy savings can be realized with these solutions.”
Membrane development also enables more cost-effective green and blue hydrogen production processes. “Traditionally hydrogen is produced from natural gas through either steam-methane reforming (SMR) or auto-thermal reforming (ATR) processes, consuming 6% of the global natural gas production to synthesize hydrogen gas for petrochemical, ammonia, methanol and steel production,” explains Xylem’s Nayar. “Governments worldwide have incentivized producing low-carbon hydrogen to help decarbonize heavy industries.”
In green hydrogen, the hydrogen is produced by using low-carbon electricity to power electrolyzers that split water, whereas in blue hydrogen, carbon dioxide produced in the SMR and ATR process is captured and sequestered. “Both need membrane-based water treatment. For green hydrogen, ultrapure water is required as the feed water to the electrolyzers. For blue hydrogen, demineralized water is required as boiler make-up water,” notes Nayar. “Typically, every kilogram of hydrogen produced can exert a water demand of 5 to 20 gallons for blue hydrogen and 16 to 30 gallons for green hydrogen. Membranes are sometime required in wastewater treatment for blue-hydrogen projects when discharge limits are very stringent.”
DuPont’s Arrowood says the company is supporting the green hydrogen revolution with ion exchange resins designed for water electrolyzers. “While there are various types of electrolyzers, they all rely on high-purity water as the feedstock to produce hydrogen. DuPont AmberLite P2X 110 ion exchange resins are designed to endure the thermal and chemical challenges present in an electrolyzer,” she says. “This solution can offer durable and reliable water quality that helps prevent contaminant build up in the electrolyzer loop.”
Evonik Industries AG (Essen, Germany; www.evonik.com) has also developed advanced membrane technology to support the production of green hydrogen. “Our Duraion product is an anion-exchange membrane (AEM) that features top-class stability and ion conductivity when subjected to harsh alkaline conditions, which are needed for AEM electrolysis,” says Vincent Lee, market communications, with Evonik.
Evonik also specializes in membrane technology solutions for biofuels processing. The company’s Puramem membrane products are designed for organic solvent nanofiltration (OSN) applications, which contribute to winterizing and upgrading biodiesel. “These membranes feature efficient separation at near-ambient temperatures without the need for a phase change of the liquid feed,” says Lee.
The company’s High-Performance Polymers business also provides a range of membranes for highly efficient gas separation. “Our Sepuran Green product line, for example, features high carbon-dioxide and methane selectivity, which makes the product ideally suited for biogas upgrading,” explains Lee.
“While membranes and filtration provide safe, reliable and economical treatment of water and wastewater, they also provide process solutions for the high-growth lithium extraction and green hydrogen sectors. Advanced membranes for industry and energy use provide options to achieve a more water- and energy-resilient future for a growing economy,” says DuPont’s Arrowood.
Joy LePree