Recycling Syltherm HF A high performance silicone polymer

1. Introduction

SYLTHERM HF heat transfer fluid is a specially formulated high performance silicone polymer designed by Dow Chemical Co. for use as a low temperature, liquid phase heat transfer medium. It offers outstanding low temperature heat transfer and pumpability, plus excellent thermal stability. With a closed cup flash point above 60°C (140°F), SYLTHERM HF fluid provides an extra margin of safety and can reduce system and engineering costs. SYLTHERM HF fluid has essentially no odor and is low in acute oral toxicity. These features make Syltherm HF fluid a viable alternative to many organic heat transfer fluids and / or chlorinated solvents which are actually used for low temperature, liquid phase service [1].

2. Syltherm HF characteristics

The recommended use temperature range is from – 73°C (-100°F) to 260°C (500°F) . The mentioned operating range of Syltherm HF makes it ideal for a single fluid process heating and cooling operations. Using a single fluid processing eliminates the process interruption and the temperature control loss, associated with multiple fluid systems. Within the above mentioned use range, Syltherm HF will not degrade to form solids or volatile compounds having substantially higher vapor pressures. Consequently, the system downtime for periodic fluid reprocessing and replacement is eliminated. Also the Syltherm HF fluid can tolerate occasional high-temperature upsets with only minimal changes of the fluid physical properties. However,an extended use at bulk temperatures above 260°C (500 °F ) or film temperatures higher than 288°C ( 550° F ) may generate higher system pressures and cause polymer cross-linking to occur. This fact will eventually cause an increase of the fluid viscosity to a point where the replacement will be required in order to restore the system performance.

At -73°C ( – 100°F) the viscosity of Syltherm HF fluid is only 16.7 mPa.s, that means a low viscosity at low operating temperatures, which is a critical property as it allows high heat transfer coefficients with low pressure drops and pumping horsepower. The fact that Syltherm HF remains liquid below – 73°C eliminates many of the problems associated with shutdowns and cold weather start-ups. Consequently, steam or electrical tracing, which are costly to install and operate, are not needed.

Batch processing with Syltherm HF fluid also eliminates the system flush requirements associated with steam/brine and steam/glycol systems.

Syltherm HF fluid is noncorrosive toward common metals and alloys used in heat transfer systems as long as it remains uncontaminated. Carbon steel is used in most heat transfer systems utilizing Syltherm HF fluid, but also stainless steels or low alloy steels are employed. Most corrosion problems are caused by the chemicals introduced into the system during cleaning or from process leaks. The nature of the corrosivity and severity will depend upon the amounts and the type of contamination involved.

Suitable applications are the followings:

• Single fluid process heating and cooling systems.
• Sub zero applications including environmental chambers and grocery store freezer loops.

3. Physical – chemical properties ( SI Units ):

Chemical composition: Dimethyl Polysiloxane
Average Molecular Weight : 439
Color : crystal clear liquid
Viscosity @ 25°C : 1.70 mPa.s
Flash Point , closed cup : typical 63°C
Flash Point , open cup : typical 76.7°C
Autoignition point, ASTM D-2155 : 355°C
Freezing point : < - 82°C Density @ 25°C : 864 kg/m3 Specific Gravity @ 25°C : 0.87 Heat of Combustion : 31,851 kJ/kg Estimated critical temperature : 350°C Estimated critical pressure : 10.6 bar Estimated critical volume : 3.62 l/kg 4. Recycling Syltherm HF

It is recommended not to dump the product into any sewers, on the ground or into any body of water. All disposal practices must be in compliance with all Federal, State/Provincial and local laws and regulations. Regulations may vary in different locations. Waste characterizations and compliance with applicable laws are the responsibility solely of the waste generator: Used heat transfer fluid which has been stored in drums or tanks should be sampled before recycling in such a manner as to ensure a representative sample.

The regeneration recycling feasibility of the waste heat transfer fluids (HTF) was also researched using the rotary steam-filtration-adsorption method and the indicators of reclaimed oil were tested according to the current standards [2].

The good oil in waste heat transfer fluids was about 50% through the regeneration recycle.

Though the waste of HTF oil would be used as a fuel oil supply for the refinery, it is a serious waste of resources, moreover, it will lead to an environmental pollution for which now there are regulations and management system standards. Therefore, to regenerate and recycle the waste HTF has very important practical significance for the enterprises to reduce the production cost, to save energy and protect the environment. In the regeneration process, procedures as reduced pressure rotary steaming, adsorption and filtration were adopted for different types of silicone oil. Then every index of the oil was analyzed according to current standards to determine the feasibility of the renewable technology based on the experimental results.

For unused and uncontaminated product, the preferred options include sending to a licensed Recycler as for instance ECO USA, incinerator or other thermal destruction device.

References:
[ 1 ] www.dow.com
[ 2 ] 2016 2nd International Conference on Sustainable Energy and Environmental Engineering (SEEE 2016) –“ The Experimental Research on the Regeneration and Recycling Feasibility of the Waste Heat Transfer Fluids” Yu-hui DU1 , Bin YUAN2,*, Lin YANG1 and Wei-Guang, Guangzhou, 510006, China