Category: STEM (Page 1 of 11)

Science, Technology, Engineering, Medicine

Lithium Battery Hazard

June 9, 2023 / Phil / 0 Comments

Lithium batteries are more dangerous and more delicate than I or my friends thought. It’s good to be aware of the dangers and treat them properly to minimize the danger.

For years now we’ve seen occasional reports of electric vehicles, cellphones, and notebook computers catching fire and sometimes burning spectacularly. It’s not common but it happens. One might say, “Oh, but that’s EV’s. That’s a special case.” It’s not. For the first several years, Tesla’s EV batteries were built out of 18650 lithium cells, 4,000 of them. These are the same cells found in power tool battery packs from Black & Decker, Porter Cable, DeWalt, and the rest. These are the same cells found in some notebook computers, flashlights, and many vaping devices.

There are several lithium battery chemistries. What I’m talking about here is the most common: NMC or Nickel Manganese Cobalt Oxide.

18650 refers to the physical size of the cell, 18 mm in diameter by 65 mm long. Other sizes exist but the 18650 is the most common shape.

An Incident Occurs

Like everyone else, I’ve been using lots of these batteries without issues. What caught my attention was an incident that happened a couple of weeks ago to a friend and co-worker. He got up in the morning to make coffee and noticed an odd smell. It smelled like overheated plastic, or failing electronics, or a pot left to burn dry on the stove. He walked back and forth in the house and determined the smell must be coming from his bedroom. Nothing was immediately apparent so he searched and found the cause. Under the bed was a plastic tote where he kept the batteries for his cordless garden tools. Since it’s been winter, those batteries had been there untouched for almost six months. Now, one of them was warm and plastic housing showed evidence of melted plastic and a hole where the plastic had boiled. He took the tote outdoors and called me. I went and took a look, took some photos, and noted the strong smell. Despite opening windows and ventilating the house, the smell lingered in the house for several days.

Later, he mentioned that the way the battery attaches to the tool is awkward and that he had dropped that battery on concrete from a height of about 1 meter. This cracked the plastic case. He thought nothing of it, glued the case together, and the battery continued to work normally. This news sent me digging on the Internet for information. I found quite a lot and learned some important things I didn’t know.

Dry Cells (Alkalines) Compared to Lithiums

Cylindrical lithium batteries like the 18650 are much more delicate than dry cell batteries. Dry cell batteries like alkalines are filled with a few simple bulky materials. Close manufacturing tolerances are not required and they are physically robust. Dry cell batteries can be dropped, dented, and partially crushed and won’t short-circuit. They usually continue to work. Even if a short somehow occurs, they fail gracefully. The maximum power they can deliver is limited and will not result in pyrotechnic jets of white hot flame or violent explosion.

Below is a table comparing old style dry cells introduced in 1898 , alkaline dry cells, and modern NMC lithiums. It shows the total energy content in MJ/kg (megajoules per kilogram), the total energy you can expect to get out of a cell in Wh/kg (watt-hours per kilogram), and the “specific power” the cell can deliver in W/kg (watts per kilogram). More on specific power below.

Technology	MJ/kg	Wh/kg	W/kg
LeClanche Dry Cell (1898)	0.13	36	10-27
Alkaline Dry Cell (1949)	0.13-0.68	85-190	50
18650 NMC (2008)	0.74	205	3000-5100

From the above you can see that the differences aren’t that big except in one important way: watts per kilogram or specific power. Engineers use many terms like “specific power” that have agreed-upon meanings. In this case, specific power is the maximum amount of power a battery can produce for a short period of time. Short time meaning seconds or tens of seconds. Related terms would be instantaneous or pulse power (a fraction of a second) and continuous power (a long period of time or indefinitely).

As you can see, a lithium cell can deliver a hundred times as much specific power as an alkaline battery of the same weight. This jaw-dropping power to weight ratio is extreme, on the order of the engine in a top fuel dragster. Or, the engine in a Toyota Corolla producing 3,000 horsepower for a few seconds. It’s extreme. Over a period of a few seconds an 18650 can deliver enough power to heat itself smoking hot if it didn’t destroy itself in the process, which it would. This is the technology that enables the stunning performance of modern EVs.

At this point it should be obvious that short-circuiting an 18650 is a really bad idea. Just don’t. But what if an 18650 could somehow short-circuit itself? That would be really bad and is what we’ll talk about next.

Here’s the Problem

The construction of a lithium 18650 consists of paper-thin strips of film and foil rolled up like a jelly roll with a hundred paper-thin layers. Electronic engineers will recognize this type of construction from the way tubular paper, mylar, and electrolytic capacitors are made. This means that the positive and negative electrodes are very close together throughout the entire cell making it sensitive to dents, compression, bending, twisting, or any deformation from any direction. An unfortunate impact or dent can cause the cell to short-circuit, now or far in the future.

Diagram of a lithium cell. Note that in a real cell the anode and cathode are thin foil and the separator is also paper-thin.

Making things worse is the formation of so-called “dendrites” in lithium batteries. For years, dendrites have been a mysterious problem that’s plagued lithium batteries. It refers to an effect where repeated charge/discharge of a lithium battery causes the growth of microscopic hairs or threads of lithium. These can short or partially short a cell, resulting in reduced battery life and sometimes catastrophic failure. Recent research has answered most of the questions about dendrites. An understanding of them will hopefully lead to better designs.

This recent research discovered that microscopic fissures in the insulating layer of the cell result in pathways for dendrite formation. Cracks, fissures, or perforations as tiny as 20 nanometers are a problem. (For reference, human hair ranges from 50,000 to 120,000 nanometers in diameter. So we’re talking flaws that are 3,000 to 6,000 times smaller than the diameter of a human hair.) Impacts, dents, or other deformations can result in such fissures which encourage the growth of dendrites.

In other words, if you drop or strike a lithium battery you may have started the clock on a ticking time-bomb. That’s what happened to my friend. He dropped the battery, damaging one or more of the cells, and a year later, after six months of storage, unused, under his bed, the battery short-circuited. Research into impact damage of 18650 cells shows that dents of 3mm and even smaller are a problem. Impacts, especially end-on impacts might show no visible damage, yet the damage is done internally and a time-bomb might start ticking.

Nearly all studies done over the past ten years examined the immediate effects of damage with the main focus on EVs. What happens in an automobile accident? Only recently have studies been done on the delayed effects of impacts and indentations.

One additional fact I discovered is that dendrite growth accelerates rapidly at temperatures above 65C or 149F. This temperature is easily reached and exceeded on the dashboard of a car in the summer sun. Keep your lithium batteries cool and out of direct sunlight.

Conclusion

I hope this information is useful. After learning these things I purchased a steel .50 caliber ammunition box where I now store my lithium battery packs. My box is made of thick steel and I hope this is enough to contain a catastrophic battery failure. It’s certainly better than the canvas kit bag I used to keep my batteries in.

These insights are disturbing. More and more flashlights have lithium batteries. I have three flashlights specifically designed to use an 18650 cell. Many vaping gadgets are powered by 18650s. Any handheld device might be dropped on a hard surface without the user thinking twice about it. And if they are aware of the problem, what then? Discard the battery and replace it or try your luck?

References:
https://www.sciencedirect.com/science/article/abs/pii/S0378775316314641

https://www.researchgate.net/publication/354845348_Experimental_investigation_of_the_failure_mechanism_of_18650_lithium-ion_batteries_due_to_shock_and_drop

Drought Affects the Whole Country

November 14, 2022 / Phil / 2 Comments

When drought in the U.S. is mentioned, the first thing that comes to most people’s minds is the West, Southwest, and California in particular. There’s good reason for this. It’s been in the news every year. The rampant wildfires are terrible and spectacular. But the main threat of drought is to agriculture. California is the key to having nice things on our dinner tables. California produces 71 percent of the lettuce in the U.S, 90 percent of the strawberries, 99 percent of the garlic, 99 percent of the almonds, 99 percent of the grapes and world-class wines, and cantaloupes, watermelon, citrus, onions, celery, on and on. If we count the West Coast states, add apples, pears, cherries, and more.

Important as all that is to having nice things on the table, the meat and potatoes (literally), grains, and animal feed do not come from California. They come primarily from the middle of the country. The farmlands from Idaho, Montana, the Dakotas, Iowa, Nebraska, to Texas produce vast amounts of the staple foods we eat. In addition to feeding ourselves, the U.S. literally feeds the world.

How does all this stuff get where it’s going? Well, the United States was lucky. It came with a built-in railroad: the Mississippi River System.

Mississippi River System showing the Mississippi River and tributaries that are used for shipping purposes.

175 million (!) tons of freight a year is shipped on the Upper Mississippi system alone. For perspective, that’s 20,000 to 30,000 loaded freight trains. Not freight cars, freight trains.

Then we come to the Lower Mississippi and exports. The Port of South Louisiana handles 500 million tons of freight each year. Ninety-two percent of U.S. agricultural exports pass through the Port of South Louisiana. This is 78 percent of the world’s exports of feed, soybeans, livestock, and hogs. Sixty percent of the world’s exported grain passes down the Mississippi to the Port of South Louisiana. For perspective, that’s sitting by a railroad track and watching 25,000 loaded freight cars go by every single day. That’s not even possible on a single track.

So what does drought have to do with this? The Mississippi River System drains the central portion of the U.S.A. from Minnesota and Wisconsin to Texas, Montana, Kansas, Nebraska, Ohio, Illinois, Indiana, and so on. Drought is affecting these places too and the first sign of this is the water levels up and down the Mississippi. The water levels got so low this year that the barges that carry freight up and down the river were getting stuck on the bottom and causing traffic jams.

The problem should now be obvious. If low water becomes more frequent, and because of climate change it almost certainly will, it’s a huge problem. One could easily prove the point that the lifeblood of the country flows up and down the Mississippi River System. It’s the main artery. Disruptions here will upset not just agricultural products but every industry that involves heavy river freight starting with fuel oil, crude oil, coal, coke, fertilizer, limestone, iron, cement, and a long list more. The economic effects of this are staggering, not just for the U.S.A. but the world.

Solutions? There aren’t any good ones. One could build rail lines that parallel the river and tributaries, but this is a big project and cannot be done quickly. The land easement problems alone would take decades to sort out in the courts. More dams and locks on the river? This is possible in some few places but is an enormous project that would take decades to implement.

The good news is that scientists have been thinking about this for a long time. In recent decades we have greatly reduced the amount of water we take out of the river and use for irrigation and other purposes that evaporates or otherwise isn’t returned to the river. Since the drainage area of the Mississippi is so large, climate scientists can’t be certain about what’s going to happen at every point along the river. There’s evidence that the change is slow and that this year was an extra dry glitch. We must hope that this is true.

In any case, the Mississippi River problem is one to watch out for in the coming years. It’s a big one.

To Support Coal Buy an EV

October 11, 2022 / Phil / 0 Comments

What? Yes, it’s true. Read on.

This post is intended for my fellow West Virginians. West Virginia is coal country so a lot of West Virginians support the coal industry.

I look at the big picture as an engineer. Now that the pollution problems associated with coal were mostly solved decades ago, I see coal as just another fossil fuel that we burn to obtain energy. It also happens to be what we have an abundance of in West Virginia.

I’ve watched climate change coming since 1990 and it’s going to bring huge difficulties. We ain’t seen nuthin’ yet. The bottom line is humans have to eventually stop burning things to obtain energy. Achieving this goal is going to take a long time. I don’t like it but I’m a realist. Weaning ourselves off of fossil fuels is going to take far longer than we can afford but that’s how it’s going to be. We’ll be burning coal for a long time to come.

However, that doesn’t mean there’s nothing we can do to reduce our CO2 output. In fact, there’s something we can do to reduce CO2, save our hard-earned money, and support the coal industry, all at the same time. Sound impossible? It’s not.

Power Plants and Efficiency

To explain this we need to talk a bit about engineering, but this is something anyone can and should understand. It’s not complicated. Engineers who design machines or electronics are always interested in efficiency. In simple terms, efficiency means how much “input stuff” do you have to put into a device or system to get a certain amount of desired “output stuff” and how much is lost along the way.

In the simple case of an electric motor, if you put in 100 watts of electric power and get 75 watts of mechanical power out, the motor is 75 percent efficient. The other 25 percent is wasted/lost as heat. Nothing is ever 100 percent efficient. There are always losses.

If you have two or more devices one after the other (in series), you multiply together the efficiencies of each device to find out what the total system efficiency is. So, taking some typical figures, if we have a gasoline engine that’s 25 percent efficient, followed by a transmission (geartrain) that’s 80 percent efficient, the total efficiency at the output of the transmission is 0.25 times 0.80 equals 0.20 or 20 percent efficiency. The other 80 percent is lost as heat. This principle will become important below.

Power plant technology has improved continuously since the steam engine was invented. Efficiency is, by far, the most important factor in the design. Power plant efficiency means how much of the chemical / thermal energy in the fuel ends up coming out of the plant in the desired form and how much is lost as heat. Early steam engines were horribly inefficient. Only a few percent. Coal-fired power plants built in the 1970s achieve an efficiency of around 35 percent. So 35 percent of the thermal energy in the fuel leaves the plant as electricity. It may not seem like it, but this is pretty impressive. Modern coal plants built in recent years reach 45 percent efficiency and this is probably close to the maximum possible.

As an aside, natural gas power plants can employ designs that are not possible with coal. The most advanced natural gas plants can reach an unbelievable 60 percent efficiency. But, we’re not talking about natural gas here, we’re talking about coal. But since a lot of people in the U.S. get their electricity from gas-fired power plants I’ll mention this figure once more at the end of the article.

It probably goes without saying but I’ll point it out anyway. The more efficient a power plant is, the less fuel it consumes, but also the less CO2 it produces to generate a given output. This will become important below.

Internal Combustion Engines (ICE)

Now let’s look at internal combustion engine (ICE) cars. The overall efficiency of modern cars ranges from 12 to 28 percent. That’s the system efficiency measured from the energy in the fuel to moving the car down the road. The 28 percent figure only applies to certain cars under certain conditions. My little Corolla probably gets close to that 28 percent figure when on a flat highway, at a reasonable speed, no headwind, I’ll get 38 mpg. When city driving, that figure drops way down and I get 24 or 25 mpg. Many cars, SUVs, pickups, do much worse. At no time does any ICE powered vehicle reach the efficiency of the oldest coal-fired power plant. Most of the time the coal plant is 2 to 3 times as efficient at turning fuel into usable power.

Besides all the frictional losses of all the moving parts in an internal combustion engine, a fundamental problem with internal combustion engines is something called the “power curve”. An IC engine produces maximum power at a certain RPM, maximum torque at a different RPM, and maximum efficiency at yet another RPM. At low RPM it produces little power or torque. At idle, it produces no usable output but still consumes fuel. To get optimal efficiency from an internal combustion engine it must be run a constant RPM.

Vehicles must operate over a wide range of speeds starting from zero miles per hour with loads that can vary widely, up and down hills, over a wide range of temperature and humidity. All of this is in direct conflict with the “power curve” problem mentioned in the above paragraph and results in the low efficiency of internal combustion vehicles. This problem can’t be fixed. It’s not going to get better.

Electric Motors and Cars

Modern electric vehicles are powered by 3-phase induction motors. Small electric motors achieve 70 or 80 percent efficiency but the efficiency rises rapidly for larger motors. At the 100 horsepower level, such 3-phase motors are more than 95 percent efficient. Larger ones are even more efficient. And that’s running on fixed mains power at a fixed voltage and frequency.

The 3-phase motors in cars are powered by a sophisticated motor controller that varies the voltage and frequency as the motor’s speed and load changes. That gives these motors a flat power curve and even higher efficiency. At low RPM / low speed they produce lots of torque. At high RPM / high speed they produce the horsepower the car needs. The efficiency stays almost constant at all speeds. The “power curve” problem described above doesn’t exist with electric motors.

So what’s the system efficiency of an electric car? The lithium batteries used in today’s electric vehicles have a charge/discharge efficiency around 85 percent. So 85 percent of the electricity you put in comes back out to power the car. Fast charging pushes that number down towards 80 percent. Charging slowly at home pushes it up close to 90 percent.

The motor gives at least 95 percent efficiency, the motor controller is 98 percent efficient, the battery 85 percent, there is no transmission. Multiplying those together we have around 79 percent efficiency from the charger plug to moving the car down the road. I’m ignoring regenerative braking that harvests the energy from braking to charge the battery. No ICE vehicle can do that, harvest the energy from the brakes and convert it into gasoline.

The electrical grid that transports electric power from the power plant to the home or charging station is very efficient. Over the short distances found in West Virginia, it’s nearly 100 percent efficient and can be ignored.

Conclusion

Let’s pull all the numbers together here: older vintage coal-fired power plant at 35 percent efficiency and 79 percent efficiency in the vehicle means 27 percent system efficiency from a pile of coal to moving the vehicle, any vehicle, down the road. All the time, city, or highway. That’s equivalent to my Corolla under rare perfect conditions. With a more modern coal-fired plant, it’s 36 percent efficiency from a pile of coal to moving the vehicle down the road. Well beyond what an ICE vehicle can ever achieve. “Fueling” an EV from coal generates, on average, one-half to one-third the CO2 of burning gasoline or diesel in an internal combustion engine.

What’s more, the cost of that energy is much lower than buying gasoline or diesel. For example, a high-end Tesla Model S with the big battery pack option, completely discharged, at the electric rates we pay in West Virginia, costs about $12.00 to “fill up”. On top of that, your money isn’t going to a company in Texas, Mexico, Venezuela, The Netherlands, Saudi Arabia, or Russia. It stays right here in West Virginia. West Virginia generates about twice as much electricity as it uses locally. The rest is sold to out-of-state utilities. Availability of locally generated power is not a problem.

For those of you not in West Virginia or coal-country, if your electricity comes from hydro, wind, solar, or nuclear, like in the Pacific Northwest, no fuel is burned and no CO2 generated to power an EV. If your power comes from a modern gas-fired plant like in Florida, efficiency is 2 to 4 times that of an ICE vehicle and about one-third the cost.

As soon as I can solve the charging-at-home problem, I’ll be getting an EV and it will have a bumper sticker that says “This Car is Powered by Coal”.

tl;dr version: It’s more efficient, cheaper, and produces less CO2 to “fuel” an EV with coal-generated electricity than an equivalent ICE vehicle burning gasoline or diesel. Roughly twice as efficient and at one quarter the cost.

Our Favorite Things are Aldehydes

September 19, 2022 / Phil / 6 Comments

Aldehydes and Allergies

Aldehydes are so common and important in our lives that it’s good to know something about them. The flavor of vanilla, almond, cinnamon, and many others result from aldehydes. Aldehydes are a family of chemicals that are common in nature and foods, and important in industry. I knew that artificial vanilla and almond flavorings posed little danger to people with nut allergies. But the question came up in a discussion and I decided to find out if what I knew was, in fact, correct. (It is.) In the process of researching this, I fell down a rabbit hole of fascinating information, learned a number of interesting things related to chemistry and food chemistry, and collected it here in this article.

There is a family of chemicals called aldehydes that are extremely useful to plants and industry. It’s called a “family” because aldehydes have a common core molecular structure with an open bond to which various molecules can be attached that give various effects.

One thing aldehydes have in common is strong and distinctive odors. Another characteristic of aldehydes is that most of them are toxic in sufficient concentration. (Concentration is key here. At low concentrations, most of them are harmless.) I expect you are already familiar with or have heard of several of the aldehydes I’ll mention.

Formaldehyde

The one I’ll mention first is not closely related to foods but is one you’ve almost certainly heard of. Formaldehyde¹ is a critically important chemical in many industries including plastics manufacturing, fibers, and adhesives. Some of the best and strongest waterproof glues are based on formaldehyde. Formaldehyde is a disinfectant and is used to preserve biological specimens. In biology class you may have seen specimens or body parts preserved in jars. Those were likely filled with formaldehyde as a preservative. Formaldehyde is toxic² and carcinogenic in sufficient concentration. It’s produced in small amounts by most organisms, including humans.

You’ve all smelled it. It’s a key ingredient in “new car smell”, “new carpet smell”, and “newly constructed house smell”. Our noses are sensitive to aldehydes so very low concentrations are detectable.

Acetaldehyde

The next one is acetaldehyde.³ This one is produced by plants and occurs in bread, coffee, and ripe or overripe fruit, and is a component in the fragrance of wine and the smell of smoke. Acetaldehyde has a strong suffocating odor but at low-concentrations smells pleasant and fruity. Humans can detect acetaldehyde at 0.05 ppm. Diacetyl at a concentration of about 2 ppm with acetaldehyde at about 0.5 ppm are what give cottage cheese its flavor.

Acetaldehyde⁴ is formed from the oxidation of ethanol. It forms in the bloodstream after drinking alcohol and is partly responsible for hangovers.

⊂•⊃

Plants discovered the value of aldehydes a long time ago. When nature discovers a chemical that provides two unrelated benefits for the price of one, it’s a definite keeper. Aldehydes are such chemicals. Some of the most important flavors in foods result from aldehydes.

Vanilla

Vanillin⁵ is a member of the benzaldehyde family of aldehydes and is the chemical responsible for the flavor and fragrance of vanilla. It makes the seed pod of the vanilla orchid attractive to birds and animals and is an insecticide. Two functions for the price of one. Unlike most aldehydes, vanillin has low toxicity and is classed as merely an irritant.⁶

Vanilla has been in use in the Americas for at least 4,000 years. It was brought to Europe by Spanish explorers in the 1500s.

Cinnamaldehyde

The odor and flavor of cinnamon comes from an aldehyde that’s found in the bark of the cinnamon tree and various others where it serves as an insecticide. Cinnamaldehyde⁷ is a pale viscous liquid that functions as an anti-bacterial, anti-fungal, and is a potent repellent and killer of Aedes mosquitos. Like vanillin, cinnamaldehyde has low toxicity and is classed as merely an irritant.⁸

At high humidity and temperature, cinnamaldehyde decomposes to styrene. This is why cinnamon always contains a small amount of styrene.

Benzaldehyde⁹

This is the aldehyde that gives almonds their flavor.

It also occurs in certain fruits and the pits of peaches, apricots, apples, and cherries. It makes the fruit more attractive to animals and is an insecticide. It’s frequently used by bee keepers as a bee repellent. The odor causes bees to leave the hive while honey is collected after which they return to the hive.

Benzaldehyde is the simplest of all the aldehydes consisting of a benzene ring attached to the open bond of the aldehyde molecule. Benzaldehyde is classed as an irritant.¹⁰

Cuminaldehyde

Cumin, also known as cumino, comino, comyn, cymen, and many other names has been used as a spice / flavoring for at least 8,000 years. It’s common in Indian and Middle Eastern cooking. It was brought to the Americas by the Spaniards where it became an important ingredient in Latin American cooking. The dominant flavor of chili and “taco meat” is usually cumin. The flavor of cumin comes partly from cymene and several terpenoids, but primarily from, you guessed it, cuminaldehyde.¹¹.

⊂•⊃

Vanillin, cinnamaldehyde, and benzaldehyde are chemically classed as merely irritants. Technically all three are toxic in sufficient concentration, but so is water. To reach dangerous levels you’d have to consume absurdly large amounts. In the case of almond extract, you’d die of alcohol poisoning long before reaching dangerous levels of benzaldehyde.

The key here is concentration. Human noses are quite sensitive to aldehydes so for flavoring only a tiny amount is needed. Since most kitchens lack the ability to measure microgram quantities, these extracts are heavily diluted with alcohol so useful amounts can be measured with a teaspoon. On the other hand, at levels used for food flavoring there is some evidence these compounds provide anticarcinogenic effects.¹²

These aldehydes can all be synthesized in the laboratory or made inexpensively at industrial scale. There is no difference between vanillin made by an orchid and chemically produced vanillin. The same is true for benzaldehyde. If anything, the synthetic version gives a purer more consistent flavor note because it’s pure and not complicated by myriad other chemicals that vary from plant to plant.

Cilantro

The flavor of cilantro derives from several substances, some of which are aldehydes. Some people perceive the flavor of cilantro as a refreshing lemony-lime but some perceive it as tasting like soap or something rotten. It was found that 80 percent of identical twins had the same perception of cilantro but only 50 percent of fraternal twins did. This implied a genetic cause. Today the gene(s)¹³ have been identified. It’s believed that those who like cilantro (like me) are unable to detect one or more of the aldehydes in cilantro.

Furfural

Furfural is an aldehyde that results from the dehydration of sugars. It occurs in agricultural by-products like corncobs, oat bran, oat hulls, wheat bran, and sugarcane bagasse. It’s a common ingredient in processed foods and beverages. It commonly appears in many cooked or heated foods.

Furfural¹⁴ is classed as acutely toxic, an irritant, and health hazard.¹⁵

It’s dangerous to the skin. NIOSH permissible level is 5 ppm. 100 ppm is considered an immediate danger. Furfural is lethal to rats and dogs at concentrations of 200 to 1000 ppm. It’s flammable and explosive when mixed with air. It has a penetrating odor reminiscent of almonds. There is no data on human subjects.

Retinaldehyde

The importance of aldehydes cannot be overstated. Retinaldehyde¹⁶ is found in meats and is the chemical basis of our eye’s ability to sense light. Another name for it is Vitamin A aldehyde. Vertebrates acquire it directly from eating meat or can also synthesize it from carotenoids. In higher concentrations it’s classed as an irritant and a health hazard.¹⁷

Glycolaldehyde

This aldehyde is believed to play an important role in the formation of the chemical building blocks of life.¹⁸

Interestingly, radio astronomy has detected glycolaldehyde in interstellar space. It’s also been identified in Comet Lovejoy, along with ethanol. This aldehyde is classed as an irritant, highly reactive, and is a common metabolite produced by living things ranging from bacteria to humans.

Lily Aldehyde / Lysmeral / Lilial

Lily aldehyde¹⁹ has a strong floral odor reminiscent of lily of the valley. Thousands of tons are produced each year for use in perfumes and detergents.

It’s classed as a health hazard,²⁰ found to be harmful to fertility, and is banned in the EU since March 2022.

Citral

If you’ve made it this far in this article, you can probably guess from the name that citral²¹ is the aldehyde primarily responsible for the fragrance of citrus fruits like lemon, lime, etc.

Citral is found to have a pheromonal effect on acari and insects. Chemically, it’s classified as an irritant.²²

It’s a component in the oils of several plants, as follows.

Lemon myrtle (90–98%)
Litsea citrata (90%)
Litsea cubeba (70–85%)
Lemongrass (65–85%)
Lemon tea-tree (70–80%)
Ocimum gratissimum (66.5%)
Lindera citriodora (about 65%)
Calypranthes parriculata (about 62%)
Australian ginger (51-71%)
Petitgrain (36%)
Lemon verbena (30–35%)
Lemon ironbark (26%)
Lemon balm (11%)
Lime (6–9%)
Lemon (2–5%)

Citronellal

Citronellal is the aldehyde that gives citronella its lemony scent. Citronella²³ is an insect repellent. Research has shown it to be highly effective at repelling mosquitos and is a strong antifungal.

Chemically, it’s classed as corrosive, an irritant, a health hazard, and environmental hazard.²⁴

Allergies

Lastly, we come to allergies, specifically allergies to benzaldehyde or vanillin. It’s possible for a human to develop an allergy to almost anything, even metals like nickel. The good news is that it’s rare for someone to be allergic to these two aldehydes that are such important flavors.

The vast majority of allergies, whether it’s to pollen, animal dander, fish, shellfish, bee stings, whatever, are allergic reactions to proteins found in those things.

Natural almond extract is made by steaming almonds in a pressurized vat, then extracting the almond oil. This liquid includes not just benzaldehyde but many other chemicals including proteins. These proteins are usually what a person with a nut allergy reacts to. Genuine vanilla also contains many chemicals from the plant besides vanillin.

Artificial almond extract consists of a small amount of synthetic benzaldehyde diluted with ethanol. Neither has been anywhere near an almond tree and it contains no proteins or anything else. The same is true for artificial vanilla.

The concentration is chosen to match the flavoring power of genuine almond or genuine vanilla extract so the artificial is interchangeable with the genuine in recipes.

Fortunately, this means that those with nut allergies are almost sure to be safe with artificial almond or vanilla flavoring. Even so, if you have a nut allergy, especially a bad case, you should check with your doctor / allergist. They will be able to specifically test whether you are allergic to benzaldehyde (unlikely) or to the dozens of other compounds in nuts.

As a final note, a significant number of children and adults test positive for allergy to cilantro but only a few exhibit symptoms. For those who do, the symptoms can be severe.

Category: STEM (Page 1 of 11)