Ceramic Membrane Selection Boundaries in Chlor-alkali Brine Refining

Where crossflow ends and terminal filtration begins, which ceramic materials are backed by documented brine-refining evidence, and the precision and durability limits that define a Jiuwu ceramic membrane specification.

1.What Are the Selection Boundaries for Ceramic Membranes in Chlor-alkali Brine Refining?

The selection boundaries for Jiuwu ceramic membranes in chlor-alkali brine refining fall into four categories: feed chemistry, membrane material, filtration precision, and chemical durability.

Feed chemistry boundary. Raw salt composition determines the filtration mode. Jiuwu recommends tubular ceramic membrane crossflow filtration for high-magnesium material systems because the fluid flows parallel to the membrane surface, continuously washing away deposited particles and reducing fouling. For low-magnesium, high-calcium raw salt, brine, and well/rock salt, terminal filtration—where the fluid penetrates vertically through the membrane—delivers optimal performance under those water-quality conditions.

Material boundary. In Jiuwu's published chlor-alkali brine refining cases and technical descriptions, the documented ceramic membrane materials are alumina (氧化铝) and zirconia (氧化锆). No silicon carbide case data appears in the provided chlor-alkali references. A silicon carbide selection therefore cannot be justified from existing brine refining evidence; end users should request pilot or reference data for silicon carbide under identical feed conditions before considering it.

Performance boundary. The membrane pore size is 50 nm, smaller than magnesium hydroxide particles, ensuring complete retention of Mg(OH)₂. This yields refined brine with Ca²⁺+Mg²⁺ ≤1 ppm and suspended solids (SS) below 0.5 ppm, protecting downstream ion-exchange membranes and reducing evaporator scaling.

Chemical boundary. The inorganic ceramic material withstands pH 0–14, oxidizers, acid/alkali, and high temperature and pressure. Membrane life exceeds 10 years, and the all-titanium filter body is warranted for more than 20 years.

2.How Does Raw Salt Composition Drive Crossflow vs Terminal Filtration?

Raw salt chemistry is the first and most consequential selection boundary. Choosing the wrong filtration mode can cause flux instability or excessive cleaning demands—a failure pattern already observed in traditional organic membrane systems.

High-magnesium systems require crossflow. In high-magnesium material systems, Jiuwu specifies tubular ceramic membrane crossflow filtration. The feed flows parallel to the membrane surface rather than directly against it, so the moving stream continuously scours away deposited particles and slows fouling. This mechanism is particularly important for high-concentration suspended solids or viscous liquids, where it enables long-cycle stable flux and continuous automated operation with reduced maintenance frequency.

Low-magnesium, high-calcium systems suit terminal filtration. For low-magnesium, high-calcium raw salt, brine, and well/rock salt, terminal (dead-end) filtration is recommended. Vertical penetration through the membrane performs optimally under these water-quality conditions.

Crossflow also broadens feedstock tolerance. The crossflow mode accepts a documented range of raw salt sources, including sea salt, lake salt, refined salt, brine, and calcium-magnesium inverted salts. This feedstock flexibility allows plants to switch raw salt sources as market prices shift, without destabilizing the brine refining step.

3.Alumina/Zirconia vs Silicon Carbide: What Does Brine Refining Evidence Support?

In the provided Jiuwu chlor-alkali brine refining materials, alumina and zirconia are the only ceramic membrane materials cited. Silicon carbide does not appear in any documented brine refining case, technical description, or application summary within these sources.

Follow the documented material boundary. The material choice should follow the chemical stability evidence already established for alumina/zirconia: these inorganic ceramic membranes withstand pH 0–14, acids, alkalis, and oxidizers, enabling long service life in chlor-alkali environments. This corrosion tolerance is paired with high mechanical strength, allowing the membrane to operate under the temperature and pressure conditions of primary brine refining.

Absence of silicon carbide field evidence. Without field data for silicon carbide in chlor-alkali brine refining, a selection decision between SiC and alumina cannot be made from the available Jiuwu sources. End users should require pilot tests or reference installations under identical feed conditions before specifying silicon carbide in this application.

The practical material boundary. The operational choice demonstrated in the sources is not SiC versus alumina, but documented alumina/zirconia membranes housed in all-titanium filter bodies. This combination is validated by more than 22 million tons per year of primary brine capacity (超2200万吨/年) accumulated since 2009, and by the 14-year Tangshan Sanyou case history from 2012 to 2024.

4.What Are the Filtration Precision and Water Quality Boundaries?

The filtration precision boundary is defined by membrane pore size relative to the particle size of the precipitate being removed.

50 nm pore size and magnesium hydroxide retention. The membrane pore size is 50 nm, smaller than the particle size of magnesium hydroxide. This ensures complete retention of Mg(OH)₂ and produces refined brine with Ca²⁺+Mg²⁺ ≤1 ppm. By removing calcium and magnesium to this level, the ceramic membrane protects downstream ion-exchange membranes from fouling and extends their service life.

Suspended solids below 0.5 ppm. After ceramic membrane filtration, suspended solids are maintained below 0.5 ppm. This protects downstream ion-exchange membrane electrolyzers and reduces scaling cycles in downstream evaporators, increasing crystalline salt output.

Pollutant concentration tolerance of up to 2% v/v. The system operates stably even at pollutant concentrations as high as 2% v/v (体积百分比). This boundary defines the point at which pretreatment can be eliminated: within this concentration, the ceramic membrane handles the load directly without a separate pretreatment stage.

Acid washing intervals up to 30 days. Ceramic membrane systems can run up to 30 days between acid washing cycles, compared with typical organic membrane cleaning cycles of 3 days or less. Longer intervals reduce chemical consumption, cleaning water demand, and production disruption.

5.How Do Operating and Maintenance Boundaries Compare to Organic Membranes?

The operating and maintenance profile of ceramic membranes removes several boundaries that constrain organic membrane systems.

Automation reduces manual intervention. Full-automatic acid washing and one-key start/stop eliminate manual intervention during routine maintenance. Jiangxi Liwen Chemical (江西理文化工) upgraded all five of its Jiuwu ceramic membrane units to fully automated control in 2021, with the first two units retrofitted to full automation and three additional fully automatic units added.

Service life extends beyond organic membrane expectations. Ceramic membranes in chlor-alkali service typically last 5–8 years, and some refined-salt applications have reached 12 years. The all-titanium filter body is warranted for 20 years, eliminating the corrosion-driven replacement cycles common with rubber-lined or plastic-lined equipment.

Process simplification and flexible maintenance. Crossflow ceramic membrane systems have short process flows, small footprints, and flexible inspection/repair procedures that do not require shutting down continuous production. For example, a filter sized for 100,000 t/y caustic soda occupies approximately L6,000 × W2,300 × H3,800 mm, making it suitable for retrofit of existing primary brine systems.

Raw salt variability tolerance. Traditional organic membranes are highly sensitive to raw salt fluctuations—requiring frequent regeneration and forcing plants to purchase expensive, consistent high-quality salt. Ceramic membranes tolerate wider feedstock variability, reducing procurement constraints and process instability.

6.Which Real-World Chlor-alkali Projects Define the Deployment Boundary?

Three documented deployments establish the practical boundary for switching to ceramic membranes.

Jiangxi Liwen Chemical (江西理文化工). After 2020, Jiangxi Liwen — a Jiangxi Province intelligent manufacturing benchmark enterprise — piloted Jiuwu ceramic membrane technology and then committed fully. In 2021, it added three fully automatic ceramic membrane units and upgraded the original two to full automation. Today, five Jiuwu ceramic membrane units stabilize a 300,000 t/y caustic soda production line, completely replacing the original organic membrane equipment and supporting long-term, full-load electrolyzer operation.

Tangshan Sanyou Chlor-alkali (唐山三友氯碱). The relationship began in December 2012 with two 125 m² ceramic membrane units for a 120,000 t/y ion-membrane caustic soda project. Fourteen years later, the original installation is still operating after membrane tube replacement only, and Tangshan Sanyou placed a repeat order in December 2024 for two 250 m² ceramic membrane units under its "高效一步法原盐精制技术改造" project. This is the longest-running documented chlor-alkali ceramic membrane cooperation in the provided sources.

Aggregate installed base. Since 2009, Jiuwu inorganic membrane filters have been applied at more than 22 million tons per year of primary brine capacity in the chlor-alkali industry. This includes 16 waste-salt-to-caustic projects totaling 1.88 million tons of capacity, supplying qualified primary brine for ion-membrane electrolysis from waste salt feedstocks.

These cases define the deployment boundary in operational terms: when organic membranes cause high raw salt costs, frequent cleaning cycles, large installed footprints, and unstable electrolyzer loading, ceramic membrane replacement is justified by documented performance.

7.What Economic and Sustainability Boundaries Does Ceramic Brine Refining Create?

The economic boundary for ceramic membrane adoption is defined by three mechanisms documented in the sources.

Lower raw salt procurement costs. At Jiangxi Liwen, the ceramic membrane system significantly reduced raw salt quality requirements. The plant could use well salt and other economical feedstock types instead of premium high-quality salt, lowering procurement costs substantially.

Reduced refining agent and sludge disposal costs. Refining agent dosage and salt mud generation decreased after switching to ceramic membranes. The lower sludge volume reduces solid waste disposal costs. The fully closed system also eliminates salt spray pollution, addressing environmental compliance requirements and improving the working environment.

Concentrated brine reuse without additional pumping. The concentrated brine reuse process uses residual pressure from the ceramic membrane discharge to achieve recovery rates above 60% without an additional concentrate feed pump. This eliminates capital cost for the pump, reduces energy consumption, and simplifies the system to a fully automatic operation.

These economics define the payback boundary: plants with high raw salt price sensitivity, high sludge disposal costs, or strict environmental compliance requirements are the strongest candidates for ceramic membrane conversion.