Product Information. General Information on Nafion Membrane for Electrolysis. Ion Exchange Materials. Product Bulletin P-01

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1 Product Bulletin P-01 General Information on Nafion Membrane for Electrolysis Product Information Introduction Nafion membranes are made from ion exchange polymers. The perfluorinated polymer provides chemical and thermal stability similar to that of Teflon fluoropolymer resin. Attached to the polymer chains are perfluorinated cation exchange sites. The polymer is, therefore, permeable to many cations and polar compounds their size and electrical properties determine their mobility through the polymer and can almost completely reject anions and non-polar species. Membranes are thin polymer films that are usually reinforced with a fabric made of Teflon. They are useful as separators in a wide range of applications. In a typical membrane process, a fluid containing one or more components is in contact with one side of the membrane. The membrane is normally more permeable to one component than the others. The preferred component is transferred through the membrane under the influence of a driving force, such as concentration difference, electric potential, or hydrostatic pressure. Figure 1. Nafion Membrane in Chloralkali Electrolysis Nafion Membrane for Production of Chlorine and Caustic The primary application for Nafion membrane is production of chlorine and caustic by electrolysis, as illustrated in Figure 1. This technology is environmentally sound and has become the preferred method for chlorine and caustic production, having significant operating cost advantages over the older mercury and diaphragm technologies. Chemours introduced the world s first commercial perfluorinated ion exchange membrane in 1969, capping a 10-year research and development effort. Nafion membranes were first used in a commercial chloralkali plant in The Chemours manufacturing facility in Fayetteville, North Carolina, began production in 1980 and has the capability to meet the world s membrane requirements through the twenty-first century. Nafion 900 and 2000 series membranes are designed to give optimum performance in the production of chlorine and caustic soda. They are reinforced composite membranes, having sulfonate and carboxylate polymer layers, as shown in Figure 2. They also have surface modifications to enhance gas release from the membrane. Nafion 300, 400, and 500 series membranes are reinforced, all sulfonate polymer, membranes designed for dilute caustic and caustic potash production. Nafion 500 series membranes have surface modification on one or both sides for enhanced gas release.

2 Other Applications for Nafion Membrane Other applications for Nafion membrane include electrochemical syntheses, spent acid regeneration, metal ion recovery, and fuel cells. The product line is highly diversified, with Nafion membranes designed for these different applications. Nafion series membranes are sulfonate films that are typically used for H 2 O and HCl electrolysis and fuel cells. Nafion 300 series membranes are reinforced composites of two sulfonate films that differ in equivalent weight. These membranes are used for producing 12 20% NaOH and for electrochemical syntheses. Nafion 400 series membranes are reinforced sulfonate films that are frequently applied to spent acid regeneration, metal ion recovery, production of 8 10% NaOH, as well as the production of 30 32% KOH. Figure 2. Structure of Nafion Caustic Soda Production Nafion N966 was developed in 1991 for electrolyzers that require very high physical strength. Nafion N2100 is the latest development in the high strength family of membranes. Introduced in mid-2009, it uses the same proven polymers as Nafion N982, while maintaining high strength by utilizing an improved reinforcement structure. Nafion N982 was introduced in 1998 and has become the industry standard, widely used in most electrolyzers, providing high performance and physical strength. Nafion N2030 was introduced in 2004 using the same proven polymers as Nafion N982 and voltage lower than Nafion N2010. This newest product shows leadership and commitment to the chloralkali industry by Chemours. New Nafion membranes are under development and trial. Consult your representative for Nafion membrane for information on new products for your plant. Descriptions and laboratory cell performance of the membranes are shown in Tables 1 and 2. Caustic Potash Production Recommendations for KOH operation are different than for NaOH. Refer to technical bulletin T-09, Nafion Perfluorinated Membranes for KOH Production. Nafion N2030 is also available in the K + form. It may be installed directly to the electrolyzer with no pretreatment or conversion from the Na + form necessary. Table 1. Membrane Description Membrane Type Nafion N966 Nafion N2100 Nafion N982 Nafion N2030 Features Very high strength provides easier handling and more resistance to operational physical upsets. New and improved reinforcing structure. Same proven polymers as Nafion N982. More impurity resistance and lower voltage than Nafion N966. Polymers proven to give excellent performance, even in challenging brine conditions. Excellent durability, and proven long and stable performance. Same strength and proven polymers as Nafion N982 with lower voltage than Nafion N2010. Note: All membranes are surface modified on the anode and cathode side for gas release and can be used in finite and zero gap applications. Tensile Strength, kg/cm >5 >5 >4 >4 2

3 Table 2. Laboratory Performance Comparison Membrane Family High Strength High Performance Membrane Type Narrow Gap Cell 2 k-factor, mv/ka/m 2 Cell Voltage, V Current Efficiency, % Nafion N966* <3.30 > Nafion N2100* <3.23 > Nafion N982* <3.15 > Nafion N2030* <3.10 > Nafion N2030** <3.02 > *Conditions: 0 mm gap, DSA anode, activated nickel cathode, 32% NaOH, 200 g/l anolyte, 90 C (194 F), 4 ka/m 2, m 2 test cell. **Conditions: 0 mm gap, activated anode, activated nickel cathode, 32% NaOH, 200 g/l anolyte, 90 C (194 F), 6 ka/m 2, m 2 test cell. Available Forms of Nafion Membranes Nafion perfluorinated membranes are produced either in the H +, Na +, or K + form, depending on the intended use. For example, Nafion N117, used in fuel cells and sealing applications, is sold in the H + form. Nafion 900 and 2000 series membranes used for NaOH production are sold in the Na + form. Membranes used for KOH production are produced in both the Na + and K + forms to facilitate a greater degree of expansion at installation. Nafion membranes are supplied in one or more of these states: dry, wet (WX and PW), and dry expanded (TX). Contact your representative for Nafion for information on the form available for your application. DRY H + Form DRY H + form is the state for Nafion 100, 300, and some 400 series membranes. Depending on the application, they require treatment prior to installation in a cell. Refer to technical bulletin T-08, Nafion Hydrogen-Form Membrane Expansion, for detailed information. DRY Na + Form DRY Na + form Nafion membranes require pretreatment in alkaline water before installation in an electrolyzer, in order to wet out and expand the membrane. Refer to technical bulletin T-06, Sodium Form Membrane Expansion in Alkaline Water, for more information. WX and PW Form WX and PW products of Nafion membrane are supplied in pre-expanded, wet form. They provide an easy to use membrane, while offering improved resistance to membrane damage from handling. Refer to technical bulletin T-04, Nafion Membrane WX Products, for more information. The WX and PW products have the same physical properties as the wet, expanded form of DRY Nafion membrane with the same code number (e.g., Nafion N966 and Nafion N966WX have the same physical properties and perform the same during electrolyzer operation). In WX form, the membrane is expanded in hot water. The PW form is expanded at room temperature. There are two special considerations for the preexpanded, wet form membranes: The ph of the WX membrane packing solution is approximately 10, and the ph for the PW solution is neutral. Depending on the requirement for your electrolyzer, the ph of the membrane may need to be adjusted. Both the WX and PW products are shipped in wet, fully expanded form, and sealed in polyethylene packaging, to avoid loss of water. The package contains only a small amount of excess water. During assembly, dry out can occur, which must be avoided to prevent slight shrinkage of the membrane. Do not unseal the package until ready to transfer to the water bath. Also, keep any unused membranes in the original container, packed as received, or store them wet in water. Prior to the installation of the membrane, the membrane should be removed from the package and put in a water bath at the required ph. During installation, keep the membranes wet by spraying with water every few minutes. Nafion N2030WX membranes can be supplied in the K + form. Refer to technical bulletin T-09, Nafion Perfluorinated Membranes for KOH Production, for more information. 3

4 TX Form TX products of Nafion membrane are pre-expanded, dry, and ready to install directly into chloralkali electrolyzers without any pretreatment. They are easy to handle and offer improved resistance to damage from handling. The agent used to convert Nafion membrane to the TX form is diethylene glycol (DEG). The DEG must be removed before electrolyzer startup to prevent foaming and product contamination. The removal is done by filling and draining the electrolyzer twice, with water or dilute caustic and brine. DEG, in water solution, can be biodegraded before disposal. Please refer to technical bulletin T-05, Nafion Membrane TX Products, for detailed information. After being installed and rinsed to remove the DEG, TX products have the same physical properties as the wet, expanded form of DRY Nafion membranes with the same code number (e.g., Nafion N966 and Nafion N966TX have the same physical properties and perform alike during electrolyzer operation). When TX form membranes are being installed, the electrodes, and other cell components that the membrane may contact, must be clean and dry. Any residual water may cause partial removal of DEG, which results in uneven expansion of the membrane. This will cause installation difficulties and may result in wrinkle formation in the membrane during operation. Size and Packaging Nafion membranes are available in custom sizes with widths up to 1.5 meters and lengths up to 4 meters. Dry sheets are rolled on fiberboard tubes, wrapped with a polyethylene sheet, and shipped in a plastic tube. WX membranes are shipped wet in ph 10 solution. PW membranes are shipped wet in a ph neutral solution. Small sheets are sealed in polyethylene pouches and shipped flat in wooden containers. Large sheets are rolled on plastic tubes, wrapped with a polyethylene sheet, and shipped in a watertight plastic container. TX membranes are shipped dry and rolled on a polyethylene-covered fiberboard tube, wrapped with a polyethylene sheet, and shipped in a plastic container. Chloralkali Operation Using Nafion Membranes Refer to the technical bulletin, T-10, Nafion User s Guide for detailed information regarding the use of Nafion membranes for chloralkali production. Also refer to Tables 3 and 4 for general operating condition recommendations. For operation at higher current density (above 4 ka/m 2 ), some specifications differ. Consult your representative for Nafion membrane. 4

5 Table 3. Recommended Operating Conditions and Monitoring Frequency for Nafion Membrane Parameter Operating Conditions Monitoring Frequency Electrolyzer Current As required to control current density Continuous Current Density ka/m 2 Continuous Voltage <4.0 V Continuous 1 Current Efficiency Determined by membrane condition As required Anolyte Compartment (Brine Side) Brine Feed Concentration 2,3 >210 g/l NaCl 4 Continuous 5 Brine Feed Flow As required to control anolyte strength Continuous 1 Acid Addition Rate 6 As required to control anolyte acidity Continuous 1 Anolyte Strength 2,3 200 ± 30 g/l NaCl Continuous 1 Anolyte Acidity 3,6 >2 ph Continuous 1 Sodium Chlorate in Anolyte 3 <20 g/l NaClO 3 Once/day Anolyte Temperature C ( F) Continuous 1 Feed Brine Impurities See Table 4 for Brine Impurity Specifications. Calcium/Magnesium Continuous 1,5 Strontium Sodium Sulfate Once/day Iodine Barium Aluminum Silica Iron Total Organic Carbon (TOC) As required Catholyte Compartment (Caustic Side) Water Addition Rate As required to control caustic strength Continuous Water Resistance >200,000 ohm-cm Continuous Caustic Strength 7, ± 2.5 wt% NaOH Continuous 1 Chloride in Caustic Results from operating conditions Temperature C ( F) Continuous 1 1 Alarm recommended. 2 Correct density for temperature, sulfate, and chlorate. 3 Measured at 23 C (73 F). 4 >210 g/l NaCl for systems using a circulation brine loop; >270 g/l NaCl for once-through brine systems. 5 If continuous is not possible, measure at least once per 8 hr. 6 When controlling anolyte ph by HCl acid addition. 7 For higher Current Density, consult your representative for Nafion membrane. 8 Not to exceed 32.0% for the first 48 hr after initial startup. 5

6 Table 4. Brine Specifications and Their Effect on Performance of Nafion Membrane 1 Impurities Calcium Typical Limits Typical Limits Typical Limits <4 ka/m ka/m ka/m 2 Physical Effects <30 ppb Combined Ca and Mg <20 ppb Combined Ca and Mg <20 ppb Combined Ca and Mg Precipitates in membrane. Performance Effects May reduce CE to 80%. Typical Control Ion exchange treatment. Magnesium See Calcium See Calcium See Calcium Precipitates in membrane. Increases voltage. Flocculation and settling in primary brine treatment, filtration in secondary treatment, and ion exchange treatment. Strontium <500 ppb <400 ppb <200 ppb Precipitates in membrane. Less severe than Ca. Barium <1 ppm <500 ppb <200 ppb Precipitates in membrane. Less severe than Ca and Sr. Sodium Sulfate 2 <10 g/l as Na 2 SO 4 <8 g/l as Na 2 SO 4 <8 g/l as Na 2 SO 4 Diffuses through membrane; some precipitates in membrane. Iodine <1 ppm <200 ppb <100 ppb Is oxidized to iodate in the anolyte and to periodate if it enters the membrane. At higher levels, sodium paraperiodate will precipitate, damaging the membrane. At lower concentrations, iodine may precipitate with alkaline earth cations. Aluminum/ Silica Al <100 ppb SiO 2 <10 ppm Al <100 ppb SiO 2 <6 ppm Al <50 ppb SiO 2 <5 ppm Under acidic conditions, aluminum will dissolve and combine with silicates and precipitate in membrane. Iron Fe <1 ppm Fe <1 ppm Fe <100 ppb Iron oxide forms in anolyte, collects on anode and membrane surfaces, and can cause anode side blinding. Sodium Chlorate Total Organic Carbon (TOC) <20 g/l <20 g/l <20 g/l Interferes with NaCl measurement. <7 ppm <7 ppm <7 ppm Organics can blind anodes, swell membranes, and cause anolyte foaming. 1 For special brine conditions outside of these specifications, consult with your Chemours representative. 2 A minimum concentration of 4 g/l sodium sulfate is recommended. Concentrations in excess of 10 g/l can cause CE decline. Reduces CE to 80 85%. Less severe CE reduction. May reduce CE to 90 93%. May increase voltage, and reduce CE below 90%. Increases chlorates in caustic. Loss of CE can be temporary or permanent. Increases voltage. Ion exchange treatment (Sr may break through resin beds sooner than Ca and Mg). Settling in primary brine treatment, and some ion exchange resins will remove barium. Barium or calcium precipitation or brine purge. Methods for removing iodine from brine are not commercially available. Purging can provide some reduction. Careful settling in primary brine treatment and subsequent filtration helps control clays. Limit in salt supply; sodium ferrocyanate (YPS) is a common anti-caking agent. Purge or destroy in recirculation loop. The data listed here fall within the normal range of product properties, but they should not be used to establish specification limits nor used alone as the basis of design. This information is based on technical data that Chemours believes to be reliable. It is intended for use by persons having technical skill and at their own discretion and risk. This information is given with the understanding that those using it will satisfy themselves that their particular conditions of use present no health or safety hazards. Because conditions of product use are outside our control, Chemours makes no warranties, express or implied, and assumes no obligation or liability in connection with any use of this information or for results obtained in reliance thereon. The disclosure of the information is not a license to operate under or a recommendation to infringe any patent of Chemours or others. Medical Statement: Please contact your Chemours representative to discuss limitations regarding medical applications. For more information about Nafion, contact: The Chemours Company FC, LLC Telephone U.S.A.: (800) Global Customer Service for IXM Fax: (302) NC Highway 87 W customerservice.nafion@chemours.com Fayetteville, NC 28306, U.S.A. Web: chemours.com/nafion 2016 The Chemours Company FC, LLC. Nafion, Teflon, and any associated logos are trademarks or copyrights of The Chemours Company FC, LLC. Chemours and the Chemours Logo are trademarks of The Chemours Company. C (1/16)