Product Description
MARLOTHERM® LH is a premium synthetic organic heat transfer fluid based on benzyltoluene, specifically engineered for both liquid-phase and vapor-liquid phase operation in closed, forced-circulation systems. This low-viscosity fluid excels in combined heating and cooling applications where a single thermal medium must serve multiple temperature requirements across a broad operating range. In unpressurized liquid-phase systems, MARLOTHERM® LH operates from 0°C to 280°C (32°F to 536°F); with system pressurization, the operating envelope extends to 360°C (680°F) heater outlet temperature. The exceptionally narrow boiling range of approximately 4°C makes MARLOTHERM® LH uniquely suited for vapor-liquid phase applications such as reactor cooling in exothermic processes, where isothermal heat removal through controlled vaporization is required. The fluid’s favorable viscosity characteristics permit cold startup down to -30°C (-22°F) using standard centrifugal pumps without heat tracing, while its low viscosity at elevated temperatures ensures excellent heat transfer coefficients throughout the operating range.
- Dual-Mode Operation: Functions in both liquid phase (unpressurized to 280°C) and vapor-liquid phase (pressurized to 360°C), with narrow ~4°C boiling range enabling isothermal heat transfer via controlled vaporization.
- Superior Heating/Cooling Performance: Exceptionally low viscosity across the full temperature range delivers excellent heat transfer efficiency in systems requiring both heating and cooling from a central thermal loop.
- Extreme Cold Startup: Pumpable to -30°C (-22°F) with conventional centrifugal pumps—no heat tracing required—with crystallizing point at -30°C and pour point at -79°C (-110°F).
- Extended Service Life: Outstanding thermal stability at recommended bulk temperature of 330°C (625°F) enables years of continuous operation without fluid replacement in properly maintained systems.
Applications
Combined Heating & Cooling Systems
Reactor Temperature Control
Exothermic Process Cooling
Polymerization Vessels
Distillation Columns
Process Dryers
Multi-Consumer Temperature Systems
Pharmaceutical Manufacturing
Plastics Processing
Chemical Manufacturing
Heat Exchangers
Central Heat Transfer Systems
Vapor-Phase Reactor Cooling
Processing Machines
Heat Recovery Systems
Benefits
Liquid & Vapor-Liquid Phase Capability
Exceptional Low-Temperature Pumpability
Outstanding Heat Transfer Efficiency
Wide Operating Temperature Range
Non-Pressurized Operation to 280°C
Cold Startup Without Heat Tracing
Narrow Boiling Range for Isothermal Control
Non-Corrosive to Standard Materials
Product Availability
5 Gal (20 L)
55 Gal Drum (200 L)
Bulk (Totes / Tankers)
Product Data
| Property | Value |
| Appearance | Clear Liquid |
| Composition | Benzyltoluene |
| Average Molecular Weight | 182.3 |
| Density @ 25°C | 992 kg/m³ (8.28 lb/gal) |
| Kinematic Viscosity @ 40°C | 2.78 cSt |
| Kinematic Viscosity @ 100°C | 1.08 cSt |
| Recommended Bulk Temperature | 330°C (625°F) |
| Max Extended Use Temperature | 360°C (680°F) |
| Max Film Temperature | 380°C (715°F) |
| Normal Boiling Point | 278°C (532°F) |
| Boiling Range | ~4°C (narrow) |
| Pour Point | -79°C (-110°F) |
| Crystallizing Point | -30°C (-22°F) |
| Pumpability Limit (300 cSt) | -67°C (-88°F) |
| Flash Point, COC (ASTM D92) | 132°C (270°F) |
| Autoignition Temperature (ASTM E659) | 473°C (883°F) |
| Autoignition Temperature (DIN 51794) | 510°C (950°F) |
| Thermal Conductivity @ 200°C | 0.111 W/m·K |
| Specific Heat @ 200°C | 2.22 kJ/kg·K |
| Heat of Vaporization @ 360°C | 259 kJ/kg (111 Btu/lb) |
| Vapor Pressure @ 200°C | 13.1 kPa (1.9 psi) |
| Vapor Pressure @ 280°C | 106 kPa (15.4 psi) |
| Coefficient of Thermal Expansion @ 200°C | 0.000981/°C |
| Copper Corrosion (ASTM D130) | 1a |
| Moisture Content, Maximum | 300 ppm |
| Dielectric Constant @ 23°C | 2.7 |
Note: At operating temperatures below the boiling point, MARLOTHERM® LH circuits operate most efficiently with inert gas blanketing (nitrogen recommended) at less than 100 mbar back pressure on the expansion vessel. Inert gas protection is the most effective measure against oxidative degradation—antioxidant additives are unstable above 200°C and become ineffective after short operating periods. At operating temperatures above the boiling point (278°C), sufficient inert gas back pressure must be applied to maintain the fluid in liquid state and prevent uncontrolled vaporization via the expansion vessel. For vapor-liquid phase operation, system design must accommodate the higher operating pressures. Low-boiling decomposition products should be vented from the expansion vessel (maintained at approximately 150°C) to ensure reliable operation; at very high temperatures, continuous removal may be necessary. MARLOTHERM® LH can be blended with MARLOTHERM® SH to optimize viscosity characteristics for specific system requirements—when operating above the boiling point of MARLOTHERM® LH, verify that the system is approved for the resulting higher pressures. The fluid is non-corrosive to standard construction materials and compatible with graphite, PTFE, and fluoroelastomer seals; rubber-elastic materials are not compatible. Annual fluid analysis is recommended to monitor fluid condition. Operation below -30°C (-22°F) is not advised due to potential crystal formation.