Chemical Compatibility: Seals, Gaskets and Stainless vs Extraction Solvents
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Chemistry decides what can seal. At recovery temperatures, the cold end decides what will.
Compatibility matrix, room temperature
| Material | Acetone | Butane | Propane | Ethanol | Heptane | Hexane | IPA | Pentane | Methanol | CO2 dry | CO2 wet |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Buna-N (NBR) | D | A | A | C | A | A | A | B | B | A | A |
| Viton (FKM) | D | A | A | B | A | A | A | A | D | B | B |
| EPDM | A | D | D | A | D | D | A | D | A | B | B |
| PTFE | A | A | A | A | A | A | A | A | A | A | A |
| Silicone | D | D | D | B | D | D | A | D | B | B | B |
| 304 SS | A | A | A | A | A | A | B | B | A | A | A |
| 316 SS | A | A | A | A | A | A | B | B | A | A | A |
A: excellent, no effect. B: good, minor effect. C: fair, not for continuous use. D: severe effect, do not use. Each cell was checked against Trelleborg, Parker, DuPont (Kalrez guide), Chemours, Graco, ISM and other charts. Where sources split, the more conservative rating is printed. Room temperature immersion, no pressure.
Hydrocarbon recovery runs to -65°C (-85°F). There, PTFE is the only listed material that is both hydrocarbon compatible and inside its rated range. Use PTFE or PTFE envelope gaskets on any joint that sees chiller or LCO2 temperatures.
Fluorosilicone and low temperature silicone reach the cold end but are not rated for butane, propane, hexane or pentane. Buna-N and Viton gaskets on cold lines are operating below their published limits and can shrink, harden and leak on the next warm cycle.
Service temperature limits
| Material / compound | Low limit | High limit | At -85°F (-65°C) |
|---|---|---|---|
| Buna-N, standard (Parker N0674-70) | -30°F (-34°C) | 250°F (121°C) | Out |
| Buna-N, low temp (Parker N0103-70) | -55°F (-48°C) | 250°F (121°C) | Out |
| Buna-N, low temp (Parker N0602-70) | -70°F (-57°C) | 180°F (82°C) | Out |
| Viton, standard (Parker V0747-75) | -15°F (-26°C) | 400°F (204°C) | Out |
| Viton GLT-S (static) | -49°F (-45°C) | 400°F (204°C) | Out |
| Viton, low temp (Parker VX065-75) | -65°F (-54°C) | 400°F (204°C) | Out |
| EPDM | -70°F (-57°C) | 250°F (121°C) | Out |
| Silicone (Parker S0604-70) | -65°F (-54°C) | 450°F (232°C) | Out |
| Fluorosilicone (Parker LM100-70) | -100°F (-73°C) | 350°F (177°C) | In, not hydrocarbon rated |
| PTFE | -400°F (-240°C) | 500°F (260°C) | In |
Static seal limits from the Parker O-Ring Handbook ORD 5700, compound data ORD 5712, and the Chemours Viton Selection Guide. Dynamic limits run higher at the cold end.
Notes on the ratings
- IPA on Viton is A. Trelleborg, Parker, DuPont, Mission Rubber, J-Flex and CP Lab all rate Viton A in isopropyl alcohol. Viton is fine for wiping and soak cleaning of gaskets. Let parts air dry before reassembly.
- Methanol on Viton is D. Chemours measured about 90 percent swell in standard A-type Viton. Do not clean standard Viton with methanol. F-type or GF-type Viton, or PTFE, are the options for methanol.
- Split ratings, conservative value printed. Buna-N with ethanol is C (seal makers say A, distributor charts say C). Viton with ethanol is B. Buna-N and silicone with methanol are B. Stainless with pentane is B, though engineering judgment says A like hexane.
- Stainless with IPA is B on several charts with no clear chemical reason. In practice 304 and 316 are used with IPA across the industry.
- Liquid and supercritical CO2. Ratings cover CO2 gas. Under pressure CO2 dissolves into elastomers, and FKM can swell 30 to 44 percent and blister on fast depressurization. Use explosive decompression rated grades of 90 durometer or harder, depressurize slowly, and avoid silicone for CO2 pressure seals.
Sources. Industrial Specialties Mfg. (ISM) Chemical Compatibility Chart; Parker Hannifin O-Ring Handbook ORD 5700 and compound data ORD 5712; Chemours Viton Selection Guide; Trelleborg Materials Chemical Compatibility Guide; DuPont Kalrez General Chemical Resistance guide; Parker Quick Coupling Fluid Compatibility Chart; Graco Chemical Compatibility Guide; Mission Rubber, J-Flex, CP Lab Safety, Sterlitech, Bal Seal, Methanol Institute, Flexmetallic. Ratings are general guidance; test in actual service conditions.