A quick search on the Internet will reveal that solar heat transfer fluids (HTF) can be used for the solar sector, food processing and the military. So should there be a pharmaceutical grade HTF to denote the sector where it is to be used? Is there such a thing as a pharmaceutical HTF?
In the food sector, consumer trust dictates that manufacturers work to the highest standards of safety, and failure to protect processed foods against potential contamination with a HTF is critical for consumer safety. Food grade HTFs must be certified as suitable for incidental contact with food and carry a HT-1 certificate.
A recent article published in Applied Thermal Engineering¹ highlighted that food grade HTFs should be colorless, non-toxic and non-irritating; non-fouling and thus low carbon forming; suitable to be used safely in the food processing sector and thus carry a HT-1 certificate; and, be managed safely and according to procedures such as Hazard Analysis Critical Control Points.
Do parallels exist between food grade and pharmaceutical HFTs?
On the surface, it seems logical that a food grade HTF would be used to manufacture any goods being consumed by the general public. However, this argument quickly falls apart because the supply, manufacture and use of medicines is tightly controlled, and any incidental contact with a HTF would mean the medicine did not meet its product specification and needed to be discarded. Also, medicines have different actives, forms (such as tablets and syrups) and intended usages (such as ingestion, inhalation and application to the skin), so a HTF-1 certificate would not seem logical for topically applied medicines. Hence, the notion of a pharmaceutical HTF does not seem either plausible or needed given that this is a highly regulated area.
What HTFs are used to process pharmaceuticals?
Mineral and synthetic-based HTFs are used in the processing of pharmaceuticals. The value of using a mineral or synthetic HTF was addressed in a recent webinar by Process Heating.² Ryan Ritz, a global business development manager, said that the key product features for a well-designed high temperature HTF were thermal stability, high purity and heat transfer efficiency (see Figure 1).
Mineral-based HTFs offer a good trade-off between cost and the key product features mentioned because they are cheaper than synthetic HTFs. In the same talk, Pete Frentzos, a vice president of business development, explained that this effectively means that synthetic HTFs offer better thermal stability when used in real-life processes. Accordingly, they have better resistance to changes in chemical structure over their lifetime, require fewer HTF system change-outs, have a lower propensity to foul the HTF system and offer a cleaner HTF operating system.
Do HTFs in the pharmaceutical sector need to be handled differently than in other sectors?
Like all industries, HTFs need to be monitored and managed to sustain their longevity. From a financial perspective, their replacement is expensive and requires operational down-time.
Before considering what tests should be used to assess the health of a HTF, it is important to realize that at sustained high operational temperatures, a HTF will thermally degrade. The objective of a maintenance program is to slow the rate of degradation and, by doing so, prolong the life of the HTF.
When sampling and chemically analyzing a HTF, a number of parameters look at degradation, external contamination and HTF system wear.³ A standardized battery of tests is detailed in Table 1, which generally focus on assessing a HTF’s degradation, pumpability, contamination and wear. However, tests involve a variety of measurements that may include the formation of coke, organic matter, scale formations, corrosion products, particulates and other deposits. All of these have the potential to settle within the HTF system and impair the efficiency of the heater and the transfer of heat to the HTF.
Instead of a pharmaceutical HTF, it is probably better to refer to it as a HTF used in the pharmaceutical sector. A well-designed HTF can be defined by its thermal stability, purity and heat transfer efficiency, which explains why a synthetic performs better than a mineral-based HTF. By implication, customers wanting the best, most efficient performance and longest operational life from a HTF system should consider using a synthetic HTF.
Author’s note: Writing support was provided by Red Pharm communications, which is part of the Red Pharm company.
1. Wright, C.I., Bembridge, T., Picot, E., Premel, J. Food processing: the use of non-fouling food grade heat transfer fluids. Applied Thermal Engineering 2015: 84; 94-103.
2. ‘What to consider when making the buying decision about a heat transfer fluid (HTF) for your system hosted by Heat Processing, Dec. 2015. Source: http://www.process-heating.com/events/1049-what-to-consider-when-making-the-buying-decision-about-a-heat-transfer-fluid-for-your-system.
3. Wright, C. I., Picot, E., and Bembridge, T. The relationship between the condition of a mineral-based heat transfer fluid and the frequency that it is sampled and chemically analyzed. Applied Thermal Engineering 2015: 75; 918–922.