How Is Refined Industrial Salt Used in the Chlor-Alkali Process? The Foundation of Modern Chemistry
When you think of the chemical products you use every day — PVC pipes inside your house walls, bleach for sanitizing drinking water, aluminum foil in your kitchen, or soap in your shower — you probably do not think about salt. But without one specific industrial reaction, none of these products could exist.
That reaction is the Chlor-Alkali process, and its number-one raw material input is high-purity refined industrial salt (Sodium Chloride, NaCl). The chlor-alkali industry converts millions of tons of salt into foundational chemical building blocks every year. But why is raw, unrefined rock salt completely forbidden in this high-tech process?
The Core Chemistry: Breaking Salt Apart with Electricity
The chlor-alkali process is an electrochemical reaction. It takes a concentrated solution of refined industrial salt and water (brine) and uses massive jolts of electrical energy to split the sodium chloride molecules apart:
2NaCl + 2H2O → Cl2↑ + H2↑ + 2NaOH
When electrical current passes through the brine inside an industrial electrolysis cell, three incredibly valuable products are generated simultaneously:
- Chlorine Gas (Cl2): Captured and liquefied for PVC plastics, pharmaceuticals, and water treatment chemicals.
- Caustic Soda (NaOH): Essential for paper manufacturing, soap production, aluminum processing, and chemical synthesis.
- Hydrogen Gas (H2): Captured for use as a green fuel or chemical reactant.
Why Membrane Cells Demand Zero-Impurity Refined Salt
Modern environmental laws have forced the industry to switch almost entirely to Membrane Cell Technology. These cells use extremely delicate, high-tech ion-exchange membranes made of fluoropolymers with microscopic pores designed to let only positive sodium ions pass through.
If a plant tries to save money by using cheap, unrefined crude salt, the brine will contain traces of calcium (Ca2+), magnesium (Mg2+), strontium, and sulfates. Here is what happens:
- Membrane Fouling: Calcium and magnesium ions form hard, crusty precipitates inside the membrane pores, destroying electrical conductivity.
- Massive Power Bills: As the membrane clogs, electrical resistance shoots up — the plant must pump in vastly more electricity, causing power bills to skyrocket.
- Premature Failure: Industrial membranes cost hundreds of thousands of dollars. Unrefined salt can ruin a new membrane in weeks, causing devastating factory shutdowns.
Two-Stage Brine Purification
Even with premium refined industrial salt, chlor-alkali plants run a strict dual-stage purification process:
- Primary Purification (Chemical Precipitation): Salt is dissolved in water, and sodium carbonate (soda ash) and sodium hydroxide are added. This causes residual calcium and magnesium to precipitate out as solids, which are filtered through large clarifiers.
- Secondary Purification (Ion Exchange): Pre-filtered brine passes through chelating resin columns that trap remaining trace calcium and magnesium ions until their concentration drops below 20 parts per billion (ppb).
Chlor-Alkali Grade Salt Specifications
| Metric | Strict Requirement |
|---|---|
| NaCl Content (Dry Basis) | ≥ 99.7% |
| Calcium (Ca) | ≤ 0.02% |
| Magnesium (Mg) | ≤ 0.01% |
| Sulfate (SO4) | ≤ 0.2% |
| Heavy Metals (Fe, Pb, etc.) | Virtual trace only |
Supplying chlor-alkali plants? We provide membrane-cell-grade refined salt.