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Is there such a thing as a true pharmaceutical heat transfer fluid?

23rd October 2019


Figure 1. The key product features of a well-designed high temperature HTF. Figure 1. The key product features of a well-designed high temperature HTF.
Table 1. What tests are performed on a heat transfer fluid. Table 1. What tests are performed on a heat transfer fluid.

Chris Wright from the Global Group of Companies explores pharmaceutical heat transfer fluid

Consumer trust dictates that manufacturers work to the highest standards of safety and failure to protect processed foods against potential contamination with a heat transfer fluid (HTF) is critical for consumer safety. In this sector food grade HTFs need to be certified as being suitable for incidental contact with food and if they are, they carry a HT-1 certificate. This was recently discussed in an article published in Applied Thermal Engineering entitled Food processing: The use of non-fouling food grade heat transfer fluids, where in the context of food safety, it highlighted that food grade HTFs should be: colourless, non-toxic and non-irritating; non-fouling and thus low carbon forming; suitable to be used safely in the food processing sector (i.e. carry a HT-1 certification); and be managed safely and according to procedures such as Hazard Analysis Critical Control Points (HACCP). 

Parallels between food and pharmaceutical HTFs

Following the discussion above, it would seem logical, therefore, that a food grade HTF would be used in the manufacture of any goods being consumed by the general public. However, this argument quickly falls apart as the supply, manufacture and use of medicines is tightly controlled and any incidental contact with an HTF would mean the medicine would not meet its product specification and would be discarded. Also, medicines are not the same. They have different actives, forms (e.g. tablets, syrups) and intended usages (e.g. ingestion, inhalation, application to the skin). Hence, the notion of a ‘pharmaceutical HTF’ does not seem to be either plausible or needed given that this is a highly regulated area. 

What HTFs are used in the processing of pharmaceuticals?

Global Heat Transfer operates across several industrial processes including the manufacture of pharmaceuticals. The HTFs used in such processes are varied and include mineral (e.g. Globaltherm M) and synthetic-based HTFs (e.g. Globaltherm SH). Hence, both types of HTF are used in the processing of pharmaceuticals. So, what is the value of using a mineral or synthetic HTF? This question was addressed in a recent webinar entitled ‘What to consider when making the buying decision about a HTF for your system’ hosted by Process Heating. In this presentation it was stated that the key features for a well-designed high temperature HTF were thermal stability, high purity and heat transfer efficiency - see Figure 1. 

Mineral-based HTFs therefore offer a good trade-off between cost (i.e. they are cheaper than synthetic HTFs) and the above-mentioned key product features. The same presentation also explained that in real-life, synthetic HTFs offer better thermal stability as seen by a better resistance to changes in chemical structure over time. The benefit being fewer change-outs of the HTF system, a lower propensity to foul the HTF system and a cleaner HTF operating system.

Do HTFs in the pharmaceutical sector need to be handled any differently to other sectors?

Like all industries, the HTFs need to be monitored and managed to sustain their longevity. One of the reasons is purely financial, as the replacement is not only expensive, but it also means there is operational downtime. Another reason is that a healthy HTF generally means a healthy and safe HTF system. So, you may be asking ‘what testing should be performed to assess the health of an HTF?’ 

To answer this, it is important to realise that at sustained high operational temperatures, e.g. Globaltherm Omnitech is a biphenyl diphenyl oxide eutectic HTF that has an upper operating temperature of 400 degrees Celsius, an HTF will thermally degrade. The objective of a maintenance programme is therefore to slow the rate of degradation and by doing so prolong the life of the HTF. When sampling and chemically analysing a HTF, a number of parameters are assessed that look at degradation as well as external contamination and HTF system wear. Testing of a pharmaceutical HTF may therefore involve a wide variety of measurements which may include the assessment of accumulations of coke, organic matter, scale formation, corrosion products, particulates and other deposits as these may all settle within the HTF system and potentially impair the efficiency of the heater and the transfer of heat to the HTF. Global Heat Transfer is a specialist in the area of HTF monitoring and maintenance and conducts a standardised battery of tests to assess degradation, pumpability, contamination and wear – see Table 1.  

In conclusion

It is probably better to refer to an HTF as being used in pharmaceutical sector as opposed to referring to it as a pharmaceutical HTF. This is based on the experience of Global Heat Transfer where its pharmaceutical customers use both mineral and synthetic-based HTFs in the processing of pharmaceutics. The current article also discusses the relative merits of a synthetic HTF versus a mineral-based HTF, based on industry advice. This insight reveals that a well-designed HTF can be defined by its thermal stability, purity and heat transfer efficiency. These key factors explain why a synthetic performs better than a mineral-based HTF and would also imply that customers wishing to achieve the best in terms of efficient performance from an HTF system and the longest operational life for an HTF should consider using a synthetic HTF. 

For further information please email Chris Wright on ciwright26@hotmail.com.

 

 


 

 

 

 

 

 

 

 

 







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