Citric acid (Citric Acid), as the world's largest-produced organic acid, is widely used in food, pharmaceuticals, and chemical industries. Its industrial production is dominated by bio fermentation (accounting for over 90% of global capacity) with core processes including raw material treatment, strain fermentation, and extraction/purification.
I. Raw Material Treatment & Strain Cultivation
- Raw Material Diversification and Pretreatment
- Traditional Raw Materials: Cassava requires crushing, magnetic iron removal, grinding (1-3 cm particles), slurry liquefaction (hydrolyzing starch to glucose), and sterilization before entering fermenters.
- Emerging Raw Materials: Corn flour gradually replaces cassava due to high starch content (>70%). Low-temperature liquefaction technology removes proteins and solids, forming a clear-liquid culture medium to improve oxygen solubility. Glucose molasses, cassava residue, and other waste can also be used for fermentation, reducing costs.
- Strain Optimization and Expansion
- Core Strain: Aspergillus Niger 5016 is the main strain, with stable acid production rate (9-10%).
- Cultivation Process:
- Slant culture: Malt extract agar medium, 30-32°C for 4 days.
- Bran koji expansion: Bran + calcium carbonate + ammonium sulfate, sterilized and inoculated, ventilated at 35°C for 20-30 hours.
II. Submerged Fermentation Process
Using mechanically agitated aerated fermenters (capacity up to 300m³) for high-precision control:
- Key Parameters: Temperature 35-37°C, pH 2.8-3.0, aeration rate 0.1-0.4 vvm.
- Process Monitoring: Residual sugar (<2g/L), pH, and mycelial status checked every 8 hours; fermentation completes within 66 hours.
- Energy-saving Improvements: Waste syrup recycling reduces wastewater discharge by 30%.
Example: Corn clear-liquid fermentation cycle shortened to 48 hours; conversion rate increased to 72.4%.
III. Extraction and Purification Innovations
- Calcium Salt Method (Mainstream Process)
- Neutralization Precipitation: Adding calcium carbonate at 80°C to form calcium citrate, endpoint pH 6.5-7.0.
- Acidolysis Decolorization: Sulfuric acid decomposes calcium citrate (92-95% sulfuric acid dosage), activated carbon adsorbs pigments (1-3%).
- Drawback: Generates gypsum residue (calcium sulfate), ~1.5 tons per ton of citric acid.
- Green Extraction Technologies
- Electrodialysis: Ion-exchange membranes separate citrate ions, achieving 92.7% yield without gypsum pollution.
- Continuous Ion Exchange: Resin adsorption replaces calcium salt, reducing energy consumption and solid waste.
- Crystallization and Drying
- Concentrate on >75% solids, crystallize at 36°C to obtain monohydrate citric acid crystals.
- Dry at 35°C in a fluidized bed until moisture <1%.
IV. Environmental Protection & Resource Utilization
- High-value Use of Waste Residues
- Corn by-products: Corn gluten meal (feed), food-grade corn oil.
- Gypsum residue for building materials or soil conditioners.
- Wastewater Treatment
- Mother liquor purified with concentrated sulfuric acid and reused in acidolysis, reducing sulfuric acid consumption by 20%.
V. Industry Trends and Challenges
- Strain Domestication: Directed mutagenesis enhances A. Niger acid tolerance and efficiency.
- Process Integration: Membrane separation + chromatographic purification may replace traditional calcium salt method.
- Carbon Neutrality: Solid waste conversion into low-carbon cementitious materials reduces cement industry emissions.
lemon acid, citric acid anhydrous, powdered citric acid, citric monohydrate, citric acid monohydrate, citric monohydrate acid, Citric acid anhydrous powder, Anhydrous Citric Acid, Anhydrous citric