The “peanut butter coal thing” refers to a science experiment where you can make coal by burning peanut butter. The basic premise is that peanut butter, which is high in fat and carbon, can be “cooked” into a coal-like substance when heated to high temperatures with limited oxygen. While you can create a black, carbonaceous material this way, the end result is not technically the same as natural coal. Here’s a closer look at how the peanut butter coal experiment works and what you end up with.
How the Peanut Butter Coal Experiment Works
The peanut butter coal experiment is often done in school classrooms or at home using simple materials. Here are the basic steps involved:
- Get a metal container like a tin can or steel bowl. Punch holes in the top to allow for some air flow.
- Scoop a few tablespoons of peanut butter into the container. Smooth it out evenly along the bottom.
- Place the container over a heat source. This may be an open flame, hot plate, or barbecue grill. The goal is to heat it to high temperatures for a prolonged period, usually 30+ minutes.
- As the peanut butter heats up, it will begin to bubble, turn brown, and decompose. Oil will be released and smoke will rise through the holes.
- Maintain heating until the bubbling has stopped and you’re left with a dry, black carbon material.
- Allow the container to cool completely before removing the carbonized peanut butter.
The carbonized material will look like a hard black lump with a texture similar to coal. But what exactly is going on during the peanut butter coal process? Here’s a look at the chemistry involved:
Chemistry of Making Peanut Butter Coal
Peanut butter is high in fat, specifically in the form of triglycerides like oleic, linoleic, and palmitic acids. When heated to temperatures over 300°F, the breakdown of these fatty acids accelerates through a process called pyrolysis.
During pyrolysis, bonds between fatty acid chains break and the triglycerides decompose into glycerol and free fatty acids. These components further break down into short-chain hydrocarbons, releasing gases like methane and carbon dioxide. With inadequate oxygen present, these hydrocarbons can’t fully combust and are carbonized into elemental carbon in the form of char.
The remaining solid material is mostly pure carbon, just like coal. However, true coal is derived from ancient decomposed organic matter that has been subjected to intense heat and pressure over millions of years. This leads to differences in the physical and chemical properties between peanut butter coal and real coal.
Differences Between Peanut Butter Coal and Real Coal
While the carbonization process makes peanut butter resemble coal in appearance, there are some important differences between the two:
Composition
Coal contains mostly carbon but also includes compounds like sulfur, oxygen, hydrogen, and nitrogen. Peanut butter coal is nearly pure carbon with little sulfur or other elements.
Heating Value
The energy content of coal is higher than peanut butter coal. Coal can provide up to 15,000 BTU per pound, while peanut butter coal likely provides less than 8,000 BTU.
Carbon Structure
Real coal has a complex carbon structure with aligned macromolecules, giving it a higher carbon content per unit volume. Peanut butter coal has a more amorphous carbon structure.
Hardness
Coal rates at 2.5-3 on the Mohs mineral hardness scale. Peanut butter coal is probably closer to 1 in hardness.
Origin
Coal formed underground over vast timescales, while peanut butter coal forms above ground in less than an hour.
So while the appearance may be similar, the peanut butter version lacks the complex carbon structure, energy density, hardness, and elemental diversity of real coal. Still, it provides an interesting way to illustrate the carbonization process!
Uses for Peanut Butter Coal
While not an effective substitute for real coal, peanut butter coal can be used to demonstrate concepts like:
- How carbonization occurs
- The chemistry of pyrolysis
- Principles of combustion
- Reducing reactions
It can also be used to teach basics about the structure and properties of coal. Students may compare hardness, composition, and energy content between the peanut butter version and real coal samples.
The peanut butter coal experiment often appears in chemistry classes and science fairs. It provides a hands-on way to illustrate the effects of high heat on carbon-rich organic compounds in an oxygen-limited environment.
Outside of educational uses, peanut butter coal lacks practical applications as a fuel or other material. While you can burn it like incense, it doesn’t provide much usable energy. It’s also too soft and low-density to serve functions like barbecue fuel.
Conclusion
Heating peanut butter into a hard, black carbon mass may superficially resemble coal formation. But the underlying chemistry and resulting physical properties differ substantially from real coal. While the peanut butter version makes an interesting science experiment, it isn’t an effective coal substitute. The takeaway is that true coal requires specific conditions over geological timescales, not just the burning of organic matter, to produce its unique characteristics.