The Manufacture and Uses of Ultra-Pure Sulphuric Acid

Ultra-Pure Sulphuric Acid

Ultra-pure Sulphuric acid is Sulphuric acid that has been purified to extremely high levels of purity, with impurities reduced to parts-per-billion or even sub-parts-per-billion levels. The purification process removes even trace amounts of metals, salts, and other chemical contaminants from the acid. As a result, ACS reagent grade Sulphuric acid has different physico-chemical properties compared to commercially available grades of Sulphuric acid. Some key properties of ACS reagent grade Sulphuric acid include:
- Purity of 99.999% or higher, approaching 100% pure H2SO4. Commercially available grades are typically 93-98% pure.
- Extremely low conductivity due to the absence of ionic impurities. Pure Sulphuric acid itself is a strong electrolyte, but ultra-pure grades exhibit very low conductivity.
- High corrosion resistance from the lack of contaminant metals and salts. Commonly used materials like steel can be exposed to ultra-pure acid without corrosion.
- Precise and reproducible chemical properties for applications requiring highly consistent acid behavior. Impurities can introduce variability.
- Higher boiling point near 280°C compared to around 300°C for technical grade acid due to decreased dissociation in pure form.
The extremely high purity of ACS reagent grade Sulphuric acid makes it well-suited for specialized applications in industries where trace contamination cannot be tolerated.
Production of Ultra-Pure Sulphuric Acid
The production of ACS reagent grade Ultra-pure Sulphuric Acid involves additional purification steps beyond the normal Sulphuric acid manufacture process to remove all potential impurities. The key stages in producing ultra-pure H2SO4 include:
- Sulfur oxidation via theContact or Lead Chamber process to generate sulfur dioxide, followed by catalytic oxidation to sulfur trioxide. This is the same initial route for normal Sulphuric acid production.
- Absorption of sulfur trioxide in concentrated Sulphuric acid with cooling to form oleum or fuming Sulphuric acid.
- Vacuum distillation to strip out potential organic contaminants from the fuming acid.
- Solvent extraction using an immiscible organic solvent to extract metallic and salt-based impurities. Common solvents include methyl isobutyl ketone.
- Ion exchange using special resins to chelate and filter out ionic species down to parts-per-billion levels.
- Repeated recrystallization from anhydrous Sulphuric acid solutions to recrystallize any remaining impurities.
- Filtration through sub-micron rated filters to remove any particulates.
- Packaging and storage of the ultra-high-purity acid in inert materials like glass or passivated metals to prevent recontamination.
Quality assurance testing uses techniques like ICP-MS which can detect even single digit parts-per-trillion contamination levels. The multi-stage purification process results in acid of 99.999% purity or higher.
Uses of Ultra-Pure Sulphuric Acid
The high purity of ACS reagent grade Sulphuric acid makes it indispensable for applications where trace contamination cannot be tolerated. Some key uses of the acid include:
- Electronics Industry - Wafer cleaning, photoresist stripping, and semiconductor manufacturing require acid free of metallic and organic impurities that could degrade devices.
- Pharmaceutical Production - Production of active pharmaceutical ingredients and purification of drug substances demands acid with no contaminants that could affect safety, efficacy or change biological properties.
- Chemical Synthesis - Making very high purity chemicals and fine chemicals, especially for agrochemical and material science applications. Impurities could cause side reactions or change product properties.
- Laboratory Reagent - Analytical laboratories use it as a super-pure acid reagent for applications like titrations, spectrophotometry, and preparing standards due to absence of interferents.
- Energy Storage - Battery manufacturing for lithium-ion and other advanced battery technologies needs extremely pure acid to avoid contaminating electrochemical performance.
- Environmental Testing - Ultra-pure acid is used as an eluent for analyses like ion chromatography where trace contaminants could compromise test results.
While more expensive to produce than commodity grades, ultra-pure Sulphuric acid proves invaluable where standard purity levels could negatively impact products, processes, or analytical results. Its high purity enables applications across industries where impurity control is mission critical.
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