Physical Properties
Recommended Separation Techniques
Butyric acid's moderate volatility (BP 164°C) and hydrophobicity (log P 0.79) enable efficient separation by distillation and extraction from fermentation broths.
Butyric acid (BP 164°C) is highly separable from water (BP 100°C) by fractional distillation. Relative volatility α = 6–8 at low concentrations. Requires 15–25 theoretical trays. For mixed acid streams (acetate, propionate, butyrate), distillation exploits the BP differences: formic (101°C), acetic (118°C), propionic (141°C), butyric (164°C).
At pH < pKa (4.82), protonated butyric acid extracts efficiently into organic solvents. Tertiary amines (Alamine 336 in MIBK or kerosene) enable reactive extraction with distribution coefficients of 8–15. Back-extraction with NaOH yields sodium butyrate. Preferred for dilute streams (<20 g/L) where distillation is energy-intensive.
Pervaporation with hydrophobic membranes (PDMS, PTFE) preferentially permeates butyric acid over water. Membrane area: 5–15 m² per ton/day. Alternative: osmotic distillation for concentration. Nanofiltration at pH > pKa rejects the ionized form, concentrating butyrate.
Activated carbon and polymeric resins adsorb butyric acid from dilute streams. Adsorption capacity: 50–150 mg/g carbon. Thermal regeneration at 200–300°C. Less common for pure butyric acid recovery but useful for odor control and wastewater treatment.
Common Impurity Separations
| Separate From | Key Difference | Best Technique | Selectivity Basis |
|---|---|---|---|
| Water | BP (164 vs 100°C) | Distillation / Pervaporation | Volatility difference |
| Acetic Acid | BP (164 vs 118°C), MW (88 vs 60 Da) | Distillation | Volatility & BP difference |
| Propionic Acid | BP (164 vs 141°C) | Fractional Distillation | 23°C BP difference |
Frequently Asked Questions
How is butyric acid separated from fermentation broth?
For anaerobic fermentation producing butyric acid, the typical recovery train: (1) Centrifugation/filtration to remove biomass, (2) Acidulation to pH < 3.0 with H2SO4 to protonate butyrate, (3) Solvent extraction with tertiary amine to concentrate, (4) Back-extraction with NaOH to form sodium butyrate, (5) Acidification and distillation to pure butyric acid.
What makes butyric acid different from other short-chain fatty acids?
Butyric acid has the highest log P (0.79) among common SCFAs, meaning it's more hydrophobic. This makes it easier to extract into organic solvents and easier to separate by distillation from acetic and propionic acid. It also has the strongest odor—the characteristic smell of rancid butter at concentrations above 10 ppm.
Can butyric acid be recovered by adsorption?
Yes, but it's not the primary method for pure product recovery. Activated carbon and polymeric resins adsorb butyric acid with moderate capacity (50–150 mg/g). This is more commonly used for odor control in wastewater treatment rather than product recovery. Desorption requires thermal regeneration or solvent washing.
Related Molecules
Design Your Butyric Acid Purification Process
Build and simulate complete downstream processing routes with real mass balance and cost estimation.
Open untangle.bio