Transcription
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So it happened again. Your captain crashed the boat, and now you're stranded on a desert island. If you could patch up the boat, you might be able to escape, but you're going to need some welding gas first. Luckily, the beach has the raw materials needed to make acetylene. So I'm going to collect a bunch of seashells and some driftwood and until I filled up my bucket.
So how do I turn this junk into acetylene? Well, it's produced when calcium carbide reacts with water. If you have metallic calcium, you can pretty much just mix up carbon in a test tube and heat it for a minute or two with a blowtorch, and then you're done. But I don't have metallic calcium or a good way to make it. So the other way to do this is by reacting calcium oxide with carbon at extremely high temperatures, like in excess of 2000°C, to make calcium oxide. You just have to heat calcium carbonate, also known as limestone, in a furnace or with a propane torch. Seashells are almost entirely made up of calcium carbonate, so that'll be our calcium oxide source. As for the carbon, that can be made just by heating the driftwood in the absence of oxygen. This will give off a weird soup of hydrocarbons, carbon monoxide, carbon dioxide, and water vapor, and when those things all boil off, you're left with charcoal, which is mostly elemental carbon.
So the ingredients are pretty easy to make from raw materials found on the beach, but the temperature needed to make the carbide is too high for an air-breathing flame. So the reaction will have to take place in an electric arc furnace. Once the carbide is formed, it's reacted with water to form acetylene gas and calcium hydroxide. And the acetylene gas can be collected in either a balloon or it can be dissolved in acetone. Notice I didn't mention pumping it into a tank under pressure, and that's because acetylene is actually kind of unstable over something like three to four atmospheres, and it can spontaneously detonate without even having oxygen if it's at those pressures. Because of this, acetylene tanks are actually just giant acetone-soaked sponges on the inside that allow the acetylene to dissolve, which is the only safe way to store it at high pressure. I'm not going to be welding with the acetylene I make in this video, so I don't have a need to store it under pressure. Acetylene can also be used as a precursor for certain plastics, and it can react with metals to form metal aides, which are, uh, shall we say, things that go boom.
Okay, let's get down to business here. I'm going to start by converting my seashells to calcium oxide. There's a total of 2.2 kilos of shells. First, I'm going to crush them up into smaller pieces and then I pack them into my graphite crucible, put them in the furnace, and start cooking. I cook each batch for about 25 minutes in my propane furnace. Limestone, aka calcium carbonate, converts to calcium oxide at about 900°C, so I want to make sure everything in the furnace is glowing bright orange and stays that way for at least a few minutes. The shells become extremely crumbly after being converted to calcium oxide, kind of like a mushy cracker. When calcium oxide is exposed to water, it converts to calcium hydroxide and releases huge quantities of heat. To verify that the seashells have actually been converted, I ground up a sample and added some water, and as you can see, the temperature rockets up in no time. So we've definitely got calcium oxide.
So I crushed up the shells and blended them until they had a consistency like flour. Oh yeah, by the way, make sure you don't inhale any of this dust because it's so reactive with water. Calcium oxide is an amazingly effective desiccant, so getting it in your sinuses is a very unpleasant experience. After everything was said and done, I wound up with 1350 grams of powder. We started with about 2200 grams of calcium carbonate, so theoretically that should have given about 1230 grams of calcium oxide. My guess is that the extra weight is from a combination of impurities in the seashells and unreacted limestone. Either way, it's way more than I need for this project. Let's move on to the other part of this reaction, the carbon.
The easiest source of elemental carbon is charcoal, which I'll get from my driftwood sticks. The sticks are smashed into smaller chips and packed tightly into a paint can with a small hole drilled in the lid. The idea here is to heat the wood in the absence of oxygen, which will cause a thermal decomposition that releases a whole soup of different compounds, and these include water vapor, carbon monoxide, carbon dioxide, methane, numerous other heavier hydrocarbons, and methanol, just to name a few, in addition to some tar, which will vaporize if we get it hot enough. What's left behind is charcoal, which is almost entirely elemental carbon. The flame you see here is not from the propane but rather from the gases and other volatile compounds coming out of the wood and igniting. This is what's known as wood gas. I could go into more detail on the production and use of it, but I think that subject deserves its own separate video. The wood container should be glowing red hot, which will help drive out the heaviest decomposition products from the wood to make sure the charcoal is as pure as possible. And unsurprisingly, when the can is removed, we're left with charcoal. So I'll dump that out and get started on another run and keep doing this until I've cooked all of the driftwood.
Once all the charcoal has been made, I load it into a blender and grind it down into a fine powder. This was probably the messiest part of the entire project because of the super fine charcoal dust that gets absolutely everywhere. The final weight of the charcoal powder was 202 grams compared to a starting mass of 901 grams, meaning that almost 80% of the initial biomass was cooked off. So we've got calcium oxide and we've got carbon. When the two are reacted at over 2000°C, a mole of calcium oxide and three moles of carbon produce a mole of calcium carbide and a mole of carbon monoxide. That means a 56 to 36 ratio of calcium oxide to carbon by mass. But I'm super lazy, so I just mixed the two powders 50/50 and then ran them through the blender again to make sure they were really well mixed and had the smallest particle size possible.
Okay, so we've got a nice mix of ingredients, but there's still that pesky detail of the 2000° temperature. That's too hot to produce with an air-breathing flame, and I don't have an oxy-fuel setup. So instead, I'm going to need electric heat, more specifically, an electric arc furnace. But before I go burning stuff hotter than the surface of the sun, I want to tell you about this video's sponsor, Squarespace. To do basically any sort of enterprise in the modern world, you're going to need a website. Unless you're living in an uncontacted tribe in Papua New Guinea, you're going to need this series of tubes known as the internet to do business, and Squarespace has all the tools you need to do that. Let's face it, social media business pages are for crack addicts trying to sell their stolen copper or for your weird aunt to advertise the psychic reading she does out of her garage. If you're serious about your business, you're going to need a website. Squarespace offers website hosting and all the tools you need to build and run a business website. They provide graphic design tools that help you make a professional-looking site and make it super easy to set up invoicing, payment processing, and appointment scheduling. You can also use it to run ads for your business on social media sites, and it provides all the important analytics for website traffic and sales data, as well as inventory and shipping management, and all that other really fancy business stuff that super important people wearing suits do. But is squarespace.com for a free trial, and if you want to launch a website, go to squarespace.com/hyperspacepirate to save 10% on your first purchase of a website or domain.
Okay, anyway, small-scale DIY arc furnaces are typically made by rewinding a microwave oven transformer. They work pretty well, but it's a huge pain to remove the secondary coil and rewind a new one. They're also only good for something like 1 to 1.5 kilowatts. On the other hand, those 110 to 220 volt converters have much larger transformers inside, and commonly available models can push as much as 5 kilowatts. The transformers are also way easier to convert because you don't have to remove any existing windings, and the large doughnut shape allows lots of room to run new windings through the middle. And because nothing is removed, they're still usable for 110 to 220 volt conversion, so you can have a transformer box that doubles as an arc welder or arc furnace. I'm going to feed mine from 220 volts, but it's also possible to feed the transformer from 110 volts because the converter is designed to be bidirectional based on the wiring. I can see when I open up the box, it looks like there's two live lines, which are red and black, and the blue wire appears to be neutral if you're using 110 volts. So the transformer would look something like this on a schematic. You basically have two windings with a common live line between them. On the 110 volt winding, the other line goes to neutral, and on the 220 volt winding, the other line goes to the opposite phase lifeline. And then I just come in and add yet another winding, which is isolated from both of those. It has about 50 turns of eight gauge wire and puts out 31 volts AC open circuit when it's fed from my 220 volt outlet.
Let's give it a quick try. To serve as a furnace, I just drilled some holes in a fire brick, which this pair of carbon electrodes will go inside of. Even with a welding mask on, the arc is pretty bright. There's so much light that it's bouncing off the walls in the garage and lighting up the inside of my mask. To keep my wire insulation from getting melted off, I connected the wire lugs and the carbon electrode lugs to big copper blocks to serve as heat sinks because even a few inches outside the electrode holes, it's blazing hot just from the radiant heat. And while it did protect the wires, the carbon electrodes would get stuck in the furnace when they got so hot that the ceramic fire brick began to melt. The thermal stress would also crack the fire brick, which was a real nuisance, and I ended up dumping a bunch of the carbon calcium mix at one point. After the thing got busted open, when I was cleaning up, I threw some water on the ash, and I noticed some of it was bubbling. So I lit it up, and sure enough, it was carbide that was producing acetylene. So the process does work. I did a few more tests with another fire brick, and judging by the blindingly bright light, it was certainly getting hot enough to make the reaction happen. But again, it kept getting the electrode stuck in molten ceramic goo and cracking. So I ended up just running the reaction with fragments of the bricks.
To add to the list of problems, I also cooked the transformer winding, which melted together, and I had to use a hacksaw to remove it. I ended up rewinding the transformer with the much thicker windings from six gauge wire scraps I had laying around, but due to the larger size, I could only fit 25 windings, which gave me 15 to 18 volts AC instead of 30. Despite the relatively low voltage, I was still able to run a decent arc, and the windings didn't get too hot this time. The flames seen here are from some of the carbon dust burning instead of reacting with the calcium. This dust is what's left over from the reaction. It looks like regular ash, but if we add some water, you can see that it bubbles up to form a settling gas, which I can ignite with my torch. I repeated the process a couple times to make sure it wasn't just a fluke, and sure enough, the process does indeed produce carbide, but the yield is pretty low.
One impressive thing about the arc furnace was the light it gave off from the extreme temperatures. You can sort of see in this shot that the light is pink, and that's from bits of calcium being vaporized. After a couple minutes, the core of the furnace gets so hot that the light becomes completely white, not even orange or yellow. The setup is pretty messy, but it definitely gets the job done. After a few days of tinkering around, I found that the best yield actually comes from just burning the mix of carbon and lime in a stainless steel cup. The fire brick furnace kind of just got in the way. Even though you lose a lot of heat, the open cup allows you to see what the arc is doing and move the electrodes around so that you get the arc where you want it to make sure all of the powder gets reacted. It also seemed like with this method, most of the powder was staying contained, whereas with the furnace, it was sort of blasting it out the sides from the pressure. This produced a way better yield than using the fire brick, and the wet powder bubbled acetylene for over 5 minutes.
Now, you won't always get solid chunks of carbide like this one, so a good way to tell if a pile of ash has any carbide in it is by the smell. If you can imagine the smell of a fireworks factory full of expired garlic, that's basically what calcium carbide smells like, according to the internet, where everything is true. The smell comes from impurities made of toxic gases. I guess I should stop sniffing this stuff.
I'm going to try filling a balloon with acetylene generated from the carbide I made. I did this in a two-neck flask with an addition funnel full of water, but I'm sure you could do it just with an empty beer bottle too. When the balloon ignites, it generates an enormous amount of soot, which is characteristic of acetylene burning in air. Let's do a side-by-side comparison between propane and acetylene to show the difference in how the combustion looks. The propane seems to make a larger flame, but it's pretty clean, no smoke or soot. It also burns relatively slow, whereas the acetylene seems to go off all at once in one bright flash before leaving a cloud of soot. I think this might be a very weak partial detonation, but I'm really not super familiar with the combustion mechanics. Either way, the difference is pretty pronounced, and I haven't seen any other flammable gas make so much soot, whether it's hydrogen, natural gas, or propane. So, mission accomplished. Acetylene made from seashells and driftwood.
This is certainly a viable process for making acetylene, but if you have access to elemental calcium, I'd recommend using that instead of calcium oxide to make the carbide because the reaction can be done with a propane torch, which is obviously much, much easier.
The last thing I want to demonstrate is the behavior of metal acetylides. These are compounds where the hydrogen atoms stuck to the carbon pair in acetylene are replaced with certain metal atoms like copper or silver. These can form inside metal pipes that carry acetylene, which can cause a safety issue because they're unstable and can detonate on exposure to heat, shock, or friction. On the other hand, those properties make for a pretty good firework. Let's take a look at silver acetylide. I'm going to drop this little chunk of silver in a flask and add about 1 ml of fuming nitric acid and dilute it with some water. This is going to make a solution of silver nitrate. To turn this into silver acetylide, I can bubble acetylene through the solution, but a more efficient approach is to bubble the acetylene into acetone instead because it can hold so much acetylene gas. After bubbling through this column full of acetone for a good half hour or so, I should have a decent amount of acetylene in solution. When I drop a little bit of it into the silver nitrate, a white precipitate immediately forms, which is the silver acetylide. It kind of looks like little grains of sand in the bottom of the beaker. It's neutralized with baking soda, rinsed with fresh water, and left to air dry for a few days, and afterward, it looks mostly gray, and it goes off with a pretty good snap. What's interesting about the detonation of silver acetylide is that it doesn't release any gases. It just turns into elemental silver and carbon. Pretty unusual for the types of substances that, uh, go boom. I wanted to launch this plastic jug into the air, but with 1 gram of silver acetylide, it just got blown to pieces instead. One of those pieces even ended up on my roof.
Well, anyway, that's how you make acetylene from seashells and driftwood. So if you're ever stuck on a desert island with an arc welder, I guess you can pass the time by making acetylene until you starve to death. Bye.