Hydrocarbon Refrigeration
Hydrocarbon refrigeration compressor lubricants are polyalphaolefin (PAO) or polyalkylene glycol (PAG) fluids engineered for systems that run on propane (R-290), isobutane (R-600a), propylene (R-1270), butane (R-600), and lighter hydrocarbon refrigerants. Hydrocarbon refrigerant dissolves into the compressor lubricant and reduces its operating viscosity. The hydrocarbon, lubricant chemistry, pressure, and temperature set the degree of dilution, which makes refrigerant-lubricant interaction the primary factor in product selection.
NEXT Lubricants produces PAO and PAG formulations for hydrocarbon refrigeration across industrial cooling, process and petrochemical refrigeration, and cascade systems.
Polarity determines dilution. Hydrocarbon refrigerants are nonpolar, as are mineral oil and PAO, which is why they mix completely. PAG contains oxygen atoms throughout its backbone, making hydrocarbons correspondingly less soluble in it.
Heavier hydrocarbons dissolve into the lubricant more readily than lighter ones. Ethane and ethylene dissolve only slightly; propane and propylene dissolve moderately; and butane, isobutane, and pentane dissolve the most. Refrigerant molecular weight—not simply the fact that it is a hydrocarbon—determines dilution severity.
Cryogenic duty reverses the usual selection instinct. At cryogenic evaporating temperatures, the refrigerant is light and dilution is mild, so low-temperature fluidity becomes the governing requirement. This is why PAO remains the correct choice despite offering the least resistance to hydrocarbon dilution.
NEXT GPL PAG-FO limits hydrocarbon solubility to below 3 wt%. Where dilution has already removed most of the lubricant’s viscosity, near-zero additional dilution preserves what remains.
How Hydrocarbon Refrigeration Works and the Compressor's Role
A hydrocarbon refrigeration system removes heat by evaporating a hydrocarbon refrigerant at low pressure. The system rejects that heat after compression and condensation at higher pressure. The refrigerant then passes through an expansion stage and returns to the evaporator.
The compressor raises low-pressure hydrocarbon vapor to the pressure required for condensation and heat rejection. Industrial installations use rotary screw or reciprocating compressors in single-stage, two-stage, economized, or cascade configurations. The refrigerant, system capacity, and target temperature set the configuration.
The lubricant protects bearings, rotors, cylinder walls, and other moving parts. It also seals, cools, and maintains oil-system operation. Hydrocarbon refrigerant dissolves into the lubricant and reduces operating viscosity, so the lubricant holds sufficient in-service viscosity to protect the compressor across the operating envelope.
Petrochemical & Process Refrigeration
Propane and propylene refrigeration are extensively used in petrochemical plants, refineries, and LPG facilities for process cooling, fractionation, and low-temperature hydrocarbon separation.
Industrial Cold Storage & Food Processing
Propane and other hydrocarbon refrigerants are utilized in industrial refrigeration systems for cold storage, freezing, food processing, and beverage production.
Chemical & Manufacturing Processes
Hydrocarbon refrigeration is also employed for process cooling in chemical and manufacturing settings where propane, butane, isobutane, or similar refrigerants are suitable for the required temperature range.
Cascade & Low-Temperature Refrigeration
Hydrocarbon refrigerants are used in cascade systems where different refrigerants operate at various temperature levels to achieve low evaporating temperatures.
Lubrication Considerations for Hydrocarbon Refrigeration
Hydrocarbon refrigeration imposes different lubricant demands than HFC, HFO, ammonia, and CO₂ systems. The primary factors are refrigerant dilution, hydrocarbon type and condensability, operating conditions, oil return, and material compatibility.
Refrigerant Dilution and Operating Viscosity
Hydrocarbon refrigerant dissolves into the lubricant during operation and reduces the viscosity of the lubricant-refrigerant mixture. Lower viscosity reduces film thickness inside the compressor. The hydrocarbon, lubricant chemistry, pressure, and oil temperature set the degree of dilution.
Hydrocarbon Type and Condensability
Propane, isobutane, butane, propylene, and lighter hydrocarbon refrigerants interact differently with the lubricant. Heavier, more condensable hydrocarbons cause greater dilution, particularly near the dew point or when liquid refrigerant enters the compressor. Separation and system control handle continuous liquid carry-over; lubricant selection does not offset it.
Oil Return and Low-Temperature Performance
The lubricant holds fluidity and circulation across the low-temperature side of the system. Refrigerant-lubricant interaction governs oil return, and excessive dilution reduces operating viscosity and film strength inside the compressor. Pour point, low-temperature viscosity, and system design determine oil return together. NEXT PAO reaches a pour point of -68 °C for low-temperature and cryogenic hydrocarbon service.
Operating Conditions Affecting Lubricant Selection
Lubricant selection depends on the complete operating conditions of the hydrocarbon refrigeration system. The nominal ISO viscosity grade does not indicate how the lubricant will perform after refrigerant dilution.
- Hydrocarbon Composition Determines refrigerant solubility, dilution severity, and the lubricant properties required to maintain operating viscosity.
- Suction and Discharge Conditions Influence refrigerant concentration in the oil, pressure ratio, compressor loading, and discharge temperature
- Evaporating and Low-Side Temperature Determine low-temperature fluidity, oil return and refrigerant circulation.
- Oil Temperature and Dilution Affect the amount of hydrocarbon retained in the lubricant and the resulting viscosity inside the compressor.
Operational Benefits of Correct Lubricant Selection
Selecting the lubricant according to the hydrocarbon refrigerant, compressor and operating conditions can provide several operational benefits.
- Stable Operating Viscosity Maintains film strength after hydrocarbon refrigerant dilutes the lubricant.
- Reliable Oil Return and Lower Consumption Maintains oil circulation and reduces carryover, lubricant loss and top-up frequency.
- Clean Running and Deposit Control Limits varnish, sludge and deposit formation and keeps oil circulation reliable.
- Reduced Unplanned Downtime Prevents lubrication-related wear, overheating, oil-return failures and unplanned compressor shutdowns.
- Extended Component Life Protects bearings, rotors, cylinders, seals and other lubricated compressor components.
- Consistent Compressor Efficiency Maintains sealing and lubrication without adding viscous drag.
Hydrocarbon Refrigeration Compressor Lubricants
NEXT PAO
Ethane/Methane/Ethylene Refrigeration Lubricant
Base Oil: PAO
ISO Range: 15 – 320
NEXT GPL PAG
Propane/ Light Hydrocarbon Refrigeration Lubricant
Base Oil: PAG
ISO Range: 32 – 680
NEXT GPL PAG-WS
Propane/ Heavy Hydrocarbon Refrigeration Lubricant
Base Oil: PAG (EO/PO)
ISO Range: 32 – 320
NEXT GPL PAG-EO
Butane/ Heavy Hydrocarbon Refrigeration Lubricant
Base Oil: PAG (EO/PO)
ISO Range: 32 – 320
Our technical team can help identify the right product.
Lubricant Selection, Technical Support and Compatibility Documentation
NEXT combines application knowledge, laboratory data and an extensive internal cross-reference database to support lubricant selection, conversions and compressor troubleshooting.
Depending on the application, we can provide:
- Application-Specific Product Recommendations Lubricant recommendations based on gas or refrigerant composition, compressor design, operating conditions and current performance issues.
- Lubricant Cross-Referencing Identifies suitable NEXT alternatives by comparing base-oil chemistry, viscosity, application, specifications and operating requirements.
- Compatibility and Conversion Documentation Provides chemistry comparisons, mixture-test data, material compatibility, flushing requirements and top-off or changeover guidance.
- Dilution Data and PVT Graphs Shows how gas or refrigerant concentration, pressure and temperature affect lubricant dilution, density and operating viscosity.
- Troubleshooting and Root-Cause Support Supports investigations into foaming, oil carryover, dilution, deposits, corrosion, high lubricant consumption and reduced oil life.
What type of oil is used in hydrocarbon refrigeration compressors?
Polyalphaolefin (PAO), polyalkylene glycol (PAG) and polyethylene glycol (PEG), selected by which refrigerant is in the system rather than by the fact that it is a hydrocarbon.
The ordering follows molecular weight. Ethane and ethylene dissolve relatively little, so PAO is correct at the cryogenic end. Propane and propylene call for a water-insoluble PAG. Butane and isobutane push toward an EO/PO copolymer PAG. Pentane and near-dew-point duty call for PEG.
An ethylene chiller and a butane system are both “hydrocarbon refrigeration” and present opposite lubricant problems. The refrigerant name is the starting point, not the answer.
Why is PAO used for cryogenic duty if it resists dilution least?
Because dilution is not the constraint there.
Hydrocarbon solubility rises with molecular weight, so ethane and ethylene dissolve into a lubricant far less readily than propane or butane. At −80 to −100 °C the governing property becomes low-temperature fluidity — whether the lubricant will still flow and return.
NEXT PAO reaches a pour point of −68 °C, which is what that duty actually needs. Its comparatively poor hydrocarbon dilution resistance does not matter because there is little dilution to resist.
The same product in a butane system at the same pressure would be heavily diluted. This is the single most counterintuitive point in hydrocarbon refrigeration lubrication.
Why is an oil heater required in a hydrocarbon system?
Because a cold sump sitting under refrigerant pressure during standstill absorbs refrigerant, so the compressor starts on a charge that is already dilute.
Manufacturer guidance treats the oil heater as mandatory for A3 duty, with a pump-down system added where suction-side standstill pressure would otherwise be high. Low oil temperatures and high suction-side standstill pressure are both to be avoided.
A related point from the same guidance: rapid changes in condensing pressure should be avoided, because dissolved refrigerant coming out of solution quickly causes strong foaming in the compressor or oil separator.
What causes foaming, and why does it matter?
Dissolved refrigerant coming out of solution — the same mechanism as a shaken carbonated drink, triggered by a pressure drop or a temperature rise.
It matters for three reasons that compound. Foam carries lubricant over into the circuit. It reduces effective lubrication, because the film contains gas rather than liquid. And it makes the oil level sight glass unreliable, so the operator loses the instrument that would otherwise show what is happening.
Rapid condensing pressure changes, inadequate standstill heating and insufficient superheat all produce it. So does mixing two lubricants, because de-foamer concentration is a formulated property and a blend sits at neither product’s design value — too little and too much both foam.
Can a hydrocarbon refrigeration lubricant be changed without flushing?
Within the same chemistry family, usually yes. Across families, no.
NEXT holds ASTM D7155 compatibility testing at 80/20, 50/50 and 20/80 mixture ratios against widely used PAG products, covering clarity, insolubles, viscosity against the ISO band and foaming — with pass results supporting direct changeover and top-off.
PAG and hydrocarbon-based lubricants including PAO are a different case. They are not compatible, and changing between them requires a full drain, flush and filter change regardless of brand.
One point specific to this application: the fluid-analysis warning values differ by chemistry. A published water limit for a PAG hydrocarbon lubricant is around 800 mg/kg against 80 mg/kg for a PAO, because PAG holds water in solution while a PAO forms free water instead. A reading that would be alarming in one charge can be normal in the other.
Explore Other Refrigeration Applications
CO₂ Refrigeration
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Ammonia Refrigeration
Lubricants for large-scale industrial R717 refrigeration systems.
Industrial Heat Pumps
Compressor lubricants for ammonia, CO₂ and hydrocarbon heat pumps operating under elevated temperature conditions.
HFC & HFO Refrigeration
Synthetic compressor lubricants for refrigeration systems using HFC and HFO refrigerants.