Ethylene Glycol vs Propylene Glycol

So, Ethylene Glycol vs Propylene Glycol, shall we? You’ve got some sort of decision looming around an HVAC system, perhaps an industrial process, or something else where temperature control is crucial, and you’re thinking to yourself: Which should I choose? What’s the real difference? And, crucially, am I at the point of about to screw things up with the wrong one? You’re not alone in this. People are dealing with this stuff all the time, and let’s face it, the wrong glycol can definitely have an impact on your systems’ performance, and (yeah) cause some pretty serious hazards along the way. Let’s get into it, no frills, just the facts, straight from the sources.

Ethylene Glycol vs. Propylene Glycol: What are the Significant Differences and Applications?

So, you have a system that’s going to be dealing with the temperature swings, yeah? Particularly when the temps are below freezing. That’s where glycols come in. They’re like the unsung heroes of temperature control, since obviously no one will be able to tell you added ice to your beer breaker. Dissolved in water, they significantly depress the freezing point. Consider them anti-freeze for your system. But really, there’s only two players in the game: Ethylene Glycol (EG) and Propylene Glycol (PG). And though they’re in the same chemical family — they are both glycols, or alcohol-based organic compounds that have multiple hydroxyl groups — no matter how easily confused the two may be, they are not the same thing whatsoever. The few things to care about: toxicity level and performance efficiency.

What is Glycol Anyway?

Okay, quick primer. Glycol is simply a name for an organic substance that has at least two hydroxyl groups stuck on some carbon atoms. You’re a member of the alcohol crew. Their superpower? Depressing the freezing point and elevating the boiling point of water solutions. This is what makes for heating and cooling systems important. They’re generally clear, sort of thick liquids with a very subtle odor. Ethylene glycol is the simplest form people know about, and it’s used in a lot of things: antifreeze, brake fluid, and so on. Propylene glycol is also very common, but more in things like cosmetics, food, and pharmaceuticals.

Now lets talk about Ethylene Glycols. In 1,2-ethanediol DOT IUPAC All the other names for ethylene glycol, and there are a lot of them. Physically, it is a clear, colorless liquid. Doesn’t smell like much, but apparently, it’s sweet tasting.

Ethylene Glycol (EG): Properties, Uses, and Risks

• Viscosity: Ethylene Glycol has lower viscosity than Propylene Glycol. Why does this matter? Lower viscositys draw for heat transfer uses. It’s less resistance to flow, and less friction loss. In other words, you require less energy to pump it through your system. Efficiency unlocked.
• Freezing Point: Pure EG freezes at, oh, -10°F or so — but you start mixing it with water, and things change. For instance, 60% glycol mixed with 40% water will withstand temperatures near -50°F without solidifying. More effective at reducing the freezing point when compared to PG. It takes less EG than PG to achieve the same freeze protection capability.
• Thermal Performance: This is where EG really stands out. It has better heat transferability than PG. “Diesel has a higher boiling point as well. If you are focused entirely on getting thermal performance, EG is typically the way to go.”

Here’s the large asterisk to all of that, though: Toxicity. Ethylene glycol is poisonous to people. Eating it can lead to severe physical problems, even death. Doses for a lethal quantity are pretty low (about 1,400 to 1,600 mg/kg, if you search for CDC estimates). This is a critical point. For this reason EG should by no means be applied in the vicinity of the drinking water. Limit it from systems in areas such as food processing plants or any facility making things people eat. You also need to be careful to not handle it in the presence because you can potentially be exposed in factories or by breathing skin or eye contact, maybe be a little out of date, but less than ingestion.

What about the environment? If it ends up in waterways, it can be harmful to animals. It biodegrades by aerobic biodegradation, that is, bacteria break it down using oxygen. This can take 10 to 30 days. The trouble is, if there’s a lot of glycol, and it breaks down quickly, it can consume loads of oxygen in the water — and that’s a nightmare scenario for anything that swims in it.

From a regulatory perspective, it isn’t on the EPA’s list of hazardous substances, for example, but, because EG-based products, they could be covered by reporting requirements. Budget-wise, it’s usually cheaper than PG.

So, where do you use EG?

• Places where you WILL sacrifice weight for the best possible thermal performance and efficiency.
• Closed-loop systems that have no contact with humans, animals, food or drinking water.
• Some examples are ice rinks, plastic molding, in-line heaters, automotive anti-freeze.

Propylene Glycol (PG): Properties, Uses, and Safety

Now, let’s talk Propylene Glycol, also known as 1,2-propanediol. It is a clear, colourless, viscous liquid similar to EG with a mild, sweet taste. It’s got one methyl group, chemically, on a stick different from EG.

Let’s look at its properties:

• Viscosities: PG is more viscous than EG, particularly at lower temperatures. More viscosity means more friction loss and lower potential cooling efficiency at cold temps. It will take more energy to pump, especially while starting up in the cold.”
• Freezing Point: PG is not as good at depressing the freezing point as EG is, meaning you have to have a higher concentration of PG to provide the same freeze protection. A 50% PG solution freezes at about -31°F but a 50% EG solution measures in at about -36°F; a 60% PG mix with 40% water can reach -76°F, but most of the commercial ones are 40% PG and 60% water or so, which freezes at about -7°F.
• Thermal Performance, This is PG’s weaker point compared to EG, it has lower heat transfer and heat capacity.. It’s usually not the option if maximum thermal performance is all you care about.
• Specific Gravity: It looks a lot like water. So like, in fact, that trying to pin down the particular strain with a standard specific gravity test can be tough.
• Solvency: PG is a slightly stronger solvent than EG, perhaps affecting some system materials like elastomers and plastics to a slightly larger degree at elevated temperatures.

Here’s where PG really wins: Safety and Low Toxicity. Propylene Glycol has extremely low oral toxicity. It is “generally recognized as safe” (GRAS) by the F.D.A. This is the key difference. Regular use of PG-containing products probably won’t make you sick. For 2- to 65-year olds, the FDA has determined that an average daily dietary intake of 23 mg/kg of body weight is s safe. You can find it in food and tobacco products, pharmaceuticals and cosmetics. It’s a frequent solvent in oral, injectable and topical medications.

That’s where the similarities end: Unlike EG, in terms of environmental impact it biodegrades aerobically, meaning it needs oxygen. This process usually takes 20 – 30 days or longer. It’s not on the E.P.A. roster of hazardous substances. Price Once again in most cases, SF is more expensive then EG.

How does your body handle PG? It is readily absorbed if you eat it. Your liver metabolizes it with an enzyme known as alcohol dehydrogenase. It is broken down into lactic acid and pyruvic acid, normal components of your body’s energy cycle, and is further metabolized into carbon dioxide and water. Roughly 45% of what you take in ends up being excreted by the kidneys without change or as a conjugate. The half-life in adults with normal liver and kidney function is rather brief, ranging from 1.4 to 3.3 hours. But in babies, it’s far longer — more than 19 hours on average — because their kidneys do not get rid of it as easily.

When and Why Does Propylene Glycol Toxicity Occur?

So, there, I just said that PG is nontoxic and is GRAS, right? For normal exposure, that’s true. But here’s the catch: You can get toxic effects, but it is very, very unusual and is almost certainly going to be the result of something called iatrogenic overdose. Think medical settings. It seems to occur primarily when people receive large doses or rapid intravenous (IV) infusions of drugs that contain PG as a diluent. The usual suspects include drugs such as phenytoin, diazepam and lorazepam. It can also occur with heavy use topically on damaged skin, such as severe burns.

So, who would be most at risk for this kind of toxicity?

• ICU patients receiving high amounts of IV meds w/PG.
• Those with pre-existing kidney damage.
• Patients whose bodies do not metabolize alcohol-like substances as well, possibly due to defective alcohol dehydrogenase systems. This includes young children (who are under 4 years old), pregnant women, people with liver disease, or individuals taking certain medications, such as disulfiram or metronidazole.
• Patients with epilepsy.
• Burn patients slathered with lots of PG.

How does PG toxicity present itself?

• High osmolality of the blood (hyperosmolality).
• Anion gap metabolic acidosis (essentially, there’s too much acid in your blood).
• Acute kidney injury or renal dysfunction (your kidneys begin to struggle).
• Is a common cause of multi-organ dysfunction.
• Low blood pressure that cannot be readily treated (refractory hypotension).
• Irregular heartbeat (arrhythmia).
• Hemolysis Red cells falling apart.
• Seizures or even coma.
• In children, you may witness CNS depression and seizures.

Diagnosing this is tricky. Why? Certainly, many hospitals do not regularly test PG levels directly. Physicians are often guided by other markers such as the osmolar gap, anion gap, and lactate levels. A higher osmolar gap (and especially one that remains high despite 48 hours of continuous infusion) helps indicate the accumulation of PG. More precisely, an osmolar gap greater than 10 mmoles/L strongly implies that serum PG level is toxic. An elevated anion gap and lactic acidosis may also be present, but the sources note they are not as useful in isolation as the osmolar gap.

How do you deal with it? The best medicine is prevention. Because it is frequently the result of medical overdose, one key is to rein in the dose that is administered to patients, especially those at higher risk. Some experts recommend a 50% dose reduction in high-risk patients. If toxicity occurs, the treatment is to cease the supply of the PG. Metabolic acidosis can be corrected with sodium bicarbonate and an antidote called fomepizole. In extreme cases where PG is truly built up and causing hyperosmolality, hemodialysis (kind of like filtering the blood) is a method of getting the PG out of the body.

So yeah, generally safe, but like I said, huge medical exposure is where PG can go from knight in shining armor to bumbling zero.

Key Differences at a Glance

Let’s lay it out side-by-side. This is the cheat sheet you need:

When Should You Use Ethylene Glycol

Assuming the sources, you would Choose Ethylene Glycol, when superior heat dissipation and efficiency are a top concern. It’s the more thermally conductive choice, and it also has lower viscosity, aiding flow.

The key is that EG is what you choose if the system you’re working with is closed-loop and has zero chance —I mean zero — of ever coming into contact with people, animals, food or drinking water. If you have a completely closed system and you’re looking for maximal heat transfer punch, then EG is probably better.

Think industrial applications, ice rinks (closed loops!) From these it is possible to manufacture articles of direct useful interest, e.g., plastic moldings, in-line heaters, and automotive antifreeze. If none of the safety issues I talked about above apply to your environment and you want performance, then EG is your man.

When to Use Propylene Glycol

Propylene Glycol is your go-to for when safety and minimal toxicity are the ultimate priorities. The game changer is it’s “generally recognized as safe” by the FDA.

This makes PG perfect for any time you might accidentally contact people, animals, food or potable water.

This includes things such as: (note that the list is not exhaustive)

• HVAC systems in crowded spaces, such as schools, homes and businesses.
• Open loop or geothermal where outdoor access is available.
• Food and pharmaceutical applications.
• Even uses like aerospace de-icing.

Yes, PG is more viscous and less thermally effective than EG It doesn’t transfer heat as well and it doesn’t depress freezing point as effectively. But when safety is at stake, those trade-offs generally are required. You’re trading some safety for peak thermal efficiency.

It’s used a lot in food and tobacco products, pharmaceuticals and cosmetics for precisely the reason that it’s not very toxic.

Are they Interchangeable?

Short answer: Absolutely not. They might both be glycols and look pretty similar, but their crucial differences in toxicity and performance mean they’re not swapsies. Attempting to employ one in a situation where the other is necessary from the standpoint of safety or performance is a recipe for disaster.

How to Determine What Glycol is Present in a System

Well, perhaps you already have a system, and you don’t know what’s in it. Good question. They look similar. But there are ways to tell:

• Specific Gravity: You can obtain a hydrometer. This measures density. If it is greater than 1.05, it’s probably ethylene glycol. If less than 1.045, it’s probably propylene glycol. But, keep in mind that PG specific weight is supppperr close to water, so this test may be pushing the envelope just a little bit.
• Refractive Index: If the specific gravity test is negative, you can perform a refractometer test. This is how much light bends as it moves through the liquid, so you get what we call the refractive index, which can tell you what the fluid is.

Here, several ways to help you determine what it is you’re working with.

Conclusion

So, what’s the verdict/recommended use of Ethylene Glycol vs Propylene Glycol? The bottom line when it comes to Ethylene Glycol vs Propylene Glycol, is not about which one is “better”, but about which one is right for your unique needs.

• Require the most thermal performance and efficiency, and complete sealing with no human, animal, food, or water contact? It would appear that your candidate is Ethylene Glycol. It is lower viscosity and it conducts heat better.
• Require safety and low toxicity because of a possibility of contact with people, animals, food, or drinking water? It simply must be Propylene Glycol. It’s also thermally less efficient, but it’s nontoxic enough to use in sensitive applications.

It’s a trade-off. Performance vs. Safety. You have to weigh the application type, the possible exposure risks, the thermal considerations and yes, even cost. Choosing wisely is important — because, as we mentioned at the outset, they’re not interchangeable, and using the wrong one can get you in trouble.

Knowing these basic differences of Ethylene Glycol vs Propylene Glycol allows you to know you’ll need to make the smart choice for your system.

Frequently Asked Questions (FAQ)

Got more questions buzzing? Let’s eliminate a few from the list of possible responses, based on what the sources themselves are covering.

What exactly is glycol? Glycol is an organic chemical compound in the alcohol family. It has several hydroxyl groups attached to carbon atoms. In applications like HVAC, its primary role is to decrease the freezing point of a solution and serve as an anti-freeze.

Is Propylene Glycol safe? Propylene Glycol Propylene Glycol is considered safe for most typical applications. The agency considers it safe in food and supplements under the designation of “generally recognized as safe” (GRAS). You can find it in everyday products, including food, cosmetics and medications.

Is It Even Possible for Propylene Glycol to Be Toxic? Propylene Glycol is mostly safe, but is also known to cause toxicity, however, this is not common and often happens as a result of iatrogenic overdose. This is typically from large or rapid IV doses of PG-containing drugs or from excessive use on abraded skin. Some people, such as those with kidney disease or young children, are at greater risk.

What do the symptoms of Propylene Glycol poisoning look like? Symptoms can involve stuff like hyperosmolality, anion gap metabolic acidosis, acute kidney injury and in extreme cases, things such as low blood pressure, arrhythmias, seizures, or coma.

How Do I Find Out If I Have Ethylene Glycol or Propylene Glycol? They appear about the same, but you can try them. The specific gravity test (using a hydrometer), may give an indication (EG usually >1.05, PG usually <1.045), but PG is close enough to water that the specific gravity test can be unreliable and a refractometer (which measures the refractive index) may be necessary for a more accurate identification.

Can I use Propylene Glycol instead of Ethylene Glycol or vice-versa? Yes; going back and forth is not OK. They have distinct characteristics, mainly as for toxicity and thermophysical properties, which make them apt for different uses. And getting the wrong one could be dangerous or ineffective for your system.

Which will heat transfer better? Ethylene Glycol typically has better thermal conductivity and is less viscous than Propylene Glycol so CG is the better choice for performance.

Which one is less expensive? Ethylene Glycol is generally cheaper than Propylene Glycol.

I hope that helps to clear things up about Ethylene Glycol vs Propylene Glycol.