Organic solvents represent approximately 4% of pump applications. They are characterised by low viscosity, high vapour pressure, flammability and the ability to swell, soften or dissolve many common elastomers, coatings and plastics. Safe and reliable pumping of solvents demands careful attention to vapour containment, ATEX classification, shaft seal selection and material compatibility.
Common Industrial Solvents
- Aliphatic hydrocarbons: Hexane, heptane, naphtha, white spirit — derived from petroleum; low water miscibility; highly flammable
- Aromatic hydrocarbons: Toluene, xylene, benzene — stronger solvency than aliphatics; classified as carcinogens; highly flammable
- Ketones: Acetone (MEK base), methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK) — excellent for resins and coatings; very low flash point
- Alcohols: Methanol, ethanol, isopropanol — miscible with water; moderate vapour pressure; methanol is highly toxic by ingestion and skin absorption
- Chlorinated solvents: Methylene chloride (DCM), trichloroethylene, perchloroethylene — non-flammable but aggressive to elastomers and human health; ozone-depleting
- Esters and ethers: Ethyl acetate, butyl acetate, diethyl ether — wide use in coatings, pharmaceuticals and extraction processes
Key Physical Properties
- Viscosity: Most organic solvents have kinematic viscosity of 0.3–2 cSt at ambient temperature — lower than water; centrifugal pump efficiency increases slightly
- Vapour pressure: Diethyl ether (58 kPa at 20 °C), acetone (24 kPa), ethanol (6 kPa) — high VP means severe NPSH requirements and risk of vapour lock
- Density: 0.65–1.6 g/cm³ depending on type; chlorinated solvents are denser than water; affects head and power calculations
- Flash point: Ranges from –40 °C (diethyl ether) to above 60 °C (high-boiling esters) — drives ATEX zone classification
- Lower explosive limit (LEL): Typically 1–8% by volume in air — requires strict ventilation and leak prevention
Elastomer and Seal Compatibility
Many standard pump elastomers are incompatible with organic solvents. Natural rubber and neoprene swell severely in aromatic and chlorinated solvents. Even PTFE can absorb chlorinated solvents under pressure. Always check compatibility charts for the specific solvent, temperature and exposure time:
- Viton (FKM): Good resistance to aromatic hydrocarbons, fuels and most non-polar solvents; avoid ketones and esters above moderate concentration
- PTFE: Near-universal chemical resistance — use PTFE encapsulated O-rings where FKM is inadequate
- EPDM: Good for ketones, alcohols and esters; poor for petroleum-based solvents
- Perfluoroelastomer (FFKM): Maximum chemical resistance — for aggressive solvent combinations; high cost
ATEX and Fire Safety Requirements
- Classify the pump location zone (Zone 0, 1 or 2) based on frequency and duration of explosive atmosphere
- Select pump, motor and all ancillary equipment to the appropriate ATEX category for the zone
- Use sealless pumps (magnetic drive or canned motor) wherever possible to eliminate shaft seal as a potential vapour release point
- Install vapour detectors calibrated to 20% LEL with automatic pump shutdown
- Provide earthing and bonding on all pump components and flanges to prevent static spark ignition
- Use non-sparking tools for maintenance in solvent areas
Pump Type Selection
- Low-vapour-pressure solvents (flash point >60 °C): Centrifugal with double mechanical seal and vapour-barrier fluid
- High-vapour-pressure solvents (flash point
- Very low flow / metering: Membrane metering pump with PTFE wetted parts
- High-viscosity solvent blends or resins in solvent: Gear pump with compatible seals and casing material
Applications
- Paint, varnish and coating formulation — solvent recovery and transfer
- Pharmaceutical synthesis — reaction solvents, extraction media and column chromatography
- Chemical extraction — liquid-liquid extraction in herb, oil and fragrance processing
- Electronic component cleaning — precision cleaning with IPA, acetone and speciality solvents
- Adhesive and sealant manufacture — solvent-based polymer dissolution and transfer
- Dry cleaning solvent recirculation — perchloroethylene (PERC) distillation and recovery
- Printing ink manufacture and press cleaning