Transcription
Hi everyone, and welcome to another weekday installment here at the lab. If you don't know, I'm making some smaller, simpler videos during the week because those are things I would normally do as preparation for my weekend videos. I thought I'd start filming some of those. So today, I'll be doing a sulfuric acid distillation.
It really isn't much to say about the sulfuric acid distillation other than that it's a bit tricky because the boiling point of the—the atrophic sulfuric acid that we will be distilling—is 337 degrees Celsius, which is very, very hot. In fact, that's right around the melting point of the lid. This process is fairly easy to accomplish with the right glassware, and it's a good way of making high-purity, very concentrated sulfuric acid for use in a laboratory where, for instance, drain cleaner acid won't cut it. And in fact, we'll be starting with drain cleaner acid and simply distilling it. Now, drain cleaner acid starts at around 90 to 93 percent, and that's based on my own titration. The MSDS typically says 93 percent. So the sulfuric acid can be distilled to its azeotrope of 98% by simply heating. At first, water will start to distill over, and then the sulfuric acid will distill over. And that will eliminate any color that the acid might have, any inhibitors the acid might have for use as a drain cleaner, surfactants, and things like that—things that manufacturers put in the acid to make it perform better as a drain cleaner. And we'll be left with essentially laboratory reagent-grade sulfuric acid at the end.
I'll be using the sulfuric acid, as I may have mentioned, in an upcoming video, and so I'm simply running the prep today, and I decided to film it. So let's go to the distillation apparatus and check it out. This here is the apparatus that I've gone ahead and set up. In the interest of time, it's essentially a simple distillation rig; it just looks a little bit different because I have this sidearm here, this cross arm, which allows me to configure the condenser vertically. The reason I did that is because my heating mantle's—their heating capacity—tops out around 325–330 Celsius, and while they will distill sulfuric acid, it only happens just barely. So I need to use a gas burner to get to the correct temperature and also to make sure that the distillation runs at a reasonable speed. And because my gas burner is so tall, I need to configure this apparatus vertically so that I can accommodate everything, plus it's sort of a space saver. I've also got these stainless-steel cat clips—you can see one here close up—and that's imperative to use because the plastic ones that I would normally use, such as this, they will easily melt at the temperatures required for this distillation. Also, to determine the concentration of the stuff that's coming over, I have this thermocouple probe in a thermocouple well right here. It's a type K, and we should be able to read the temperature on this digital readout to ensure that the acid that's coming over is at the 98% azeotropic level as opposed to some more dilute acid, which is going to come over first because we're starting at 92 percent acid.
The first thing I'll be doing is charging the apparatus with the sulfuric acid that we're going to be distilling. So this here is a gallon of professional sulfuric acid drain cleaner, which is essentially 93 percent sulfuric acid, a little bit of inhibitors, and not much else. And you can see that it—it looks pretty much like sulfuric acid should. It's maybe a little bit colored, but for all intents and purposes in the lab, it actually works quite well. I'm going to distill this because I want to remove that coloration, which is caused by tiny amounts of organic compounds as well as maybe some metal salts. I haven't actually analyzed it, but distillation guaranteed will remove all of that. So we'll go ahead and charge that into the apparatus. This apparatus is set up in a special and rather clever way. What I can do is remove this thermometer well right here and take the thermocouple tube out of it. Now, this funnel—you'll notice the stem goes past the side arm here on the still head—which means that I can charge the acid without risking getting dirty acid into the clean side. What this allows me to do is that when the acid in this boiling pot runs low, I can allow the acid to cool down to below the boiling point of 92% sulfuric acid and then actually add more to this, cap it back up, and then start it back up again. So this rig, as set up, I could just continue to add more and more sulfuric acid, cycling the temperature, the distillation the entire time and produce quite a lot of much cleaner sulfuric acid as opposed to just what I could charge in this flask. However, for today, I won't be doing it like that; I just set it up like I've done it in the past. I'm only going to make about 250 milliliters, so I'm going to go ahead and charge that with this beaker here, very carefully, because obviously it's sulfuric acid and it's very concentrated. Now, because of the very large temperature change that this sulfuric acid is going to experience, you cannot—need to charge the acid about 15% lower than you'd want the maximum level in the flask to be, and that's because it actually expands quite a bit thermally as it heats up. And here is the thermometer well, followed by the thermocouple probe. Now, you don't actually need to grease any of these joints because the sulfuric acid actually acts as a really good joint grease, and it'll eventually work its way into all these joints as this progresses. So I'm going to go ahead and turn the fume hood on, and you can then serve water and then light the burner and get this distillation under way.
Now, you may think, because of the high temperature of the sulfuric acid coming through here, that we'll need a lot of water flow to cool it down. That's not the case because it's sulfuric acid. Actually, that—because it condenses at 300 and something Celsius, in fact, a lot of it's already going to condense in this top arm here, which is going to act sort of like an air condenser. Now, I'll just tone that down to a reasonable level, put the lights off; we should be able to get a better view of the flame. All right, we're starting to get a little bit of distillation going right here, just locally on the sides of the flask, and you can see the organic matter has basically been destroyed at this point, as evidenced by the black color of suspended carbon in the acid. The IR thermometer says 341 C, which I suspect is a little high because the outside of the glass is hotter than the acid inside because of the flame, obviously. But, tell—we are getting very close. The only 236 at the top, the bottom we're looking like 360 C, but we're getting very close to the boiling point. Now, any minute we should be collecting distillate.
Now, this is the part where it gets interesting, and you'll notice I've taken the heat away a little bit. It's because the water is starting to condense in the still head, and it's dripping back into the acid, and the acid is almost 300 C right now. So when it drops in, it forms little violent steam explosions, so you kind of got to go slow through this part until the—until the water is gone. But that should happen fairly soon, and in fact, the harder we dry this, the hotter this upper part is going to get, and the less water will stay up there. Now, normally at this part, I would use my heat gun to get the water out of this area here, but unfortunately, the heat gun's broken. If you've seen the last video I did, so we're going to have to press on here and just be cautious. All right, we're getting our first collection of distillate here, just drops at a time, basically just pulling the water off of all this, boiling over 236 C, which indicates a weak sulfuric acid solution, which is—this thing out and just going to continue to heat this until you're distilling sulfuric acid at roughly the azeotropic temperature, and then we'll switch flasks to the collection flask and collect all the purified acid.
All right, you can see the acid has cleared up quite a bit, and I'm taking over distillate at 261 Celsius. I'm running into some problems with bumping in this asset, which is some violent, explosive bubbling that happens once in a while with—when a nucleate boiling point is found by asset that's been superheated. And so, unfortunately, I'm going to probably throw hot, dirty acid down my condenser if I continue to go at this rate. So I'm going to have to add boiling chips to this, and of course, I can't add the boiling chips to the hot mixture because otherwise it would explosively boil and probably boil over and cause serious damage to me and my lab. So I'm going to remove the heat and wait for that to come down to a temperature where I'll be safe to add a boiling chip without violent, explosive boiling. So it really limits our cooldown by maybe 20 or 30 degrees, and when that happens, I can add the boiling chips, then we can resume heating, and we should get a much more even boil. So the temperature now is 300 C, so when it gets to 270, I'm going to add the chips.
All right, the acid is right around 270, and now we're below the threshold where explosive boiling occurs when I add boiling chips. Now, boiling chips come in all shapes and sizes; you can actually buy them, but I prefer to make my own. This is just a piece of a porcelain flower pot, which you can see—I guess is terracotta—and you can break it apart pretty easily just with your fingers, and these act as perfect chips when you don't care about contamination. And since we're distilling off of this and throwing the residue away, essentially, that doesn't matter at all. You can really quickly crush some of these up a little further, and then we'll add them to the top very carefully. All right, I've created a few boiling chips here, which I'll be adding down the top of the apparatus. Now, this is still hot, and so there's still a risk of overflow boiling with this. It's—if you add this to a mixture that's already superheated and this chip goes down and touches the acid or whatever happens to be in here, it will boil over and make a volcano everywhere, and of course, it's sulfuric acid, that's extremely dangerous. So when you need to add a boiling chip because something is bumping quite a lot, you can actually stop the distillation, back the temperature down 20, 30, 40 degrees Celsius, and then go ahead and add the chip, and it'll be safe to add at that point. Now, there's always still a risk that that could happen, so I'm going to be adding this chip and all the subsequent chips very carefully using a pair of crucible tongs and then backing away rapidly afterwards. So three, two, one, there we go. And that little bubbling that's coming through there is probably elements of the terracotta actually dissolving out, which is fine because we don't really care too much about the purity of the acid; let's just get this third one in here. You can see how sulfuric acid makes a great joint grease, but obviously I've got to be careful not to touch that because I'll get acid on my fingers, and it's really easy to not notice that until you wipe your clothes or something. It'll put a hole in your clothes; it'll burn your skin, obviously. Be very careful. Flame back under that and resume this distillation. So that's how you recover from—from something like that. You can see now that with the addition of the boiling chips, the boiling has evened out quite a bit more. Now it's not bumping and rolling all over the place and spitting; it's more just a nice even boil, which is giving us a good stream of vapor which is condensing rapidly, and pretty soon we'll be able to switch from our four-run container to the actual collection container and start picking up some azeotropic acid.
Okay, so this has been at a rolling boil for approximately ten minutes, and you—still have—temperature is now 317 degrees Celsius, which is just over 600 degrees Fahrenheit for a reference. That is extremely hot. That—the rubber—I can smell from these clamps is starting to burn, decompose in the extreme heat. We're getting really close to the azeotrope now, which means that this acid should be about 98% concentrated, and so the remainder of the portion of this distillation is just simply to get everything from in that flask down; we're not really interested in fractionating the rest out or anything. So I'm going to go ahead and wrap the top of this still head in foil and then go ahead and swap out to the actual collection flask. So this foil is going to help keep this still hot and prevents a lot of the reflux back into the—into the flask that we're seeing here. This together, nice and toasty, perfect. That should really increase the rate at which we're taking acid off, and you can already see right there this syrupy acid coming over right there, and I want to touch that, obviously—that's 600 degrees—and then I'm going to switch out to the collection flask now. And you notice I don't have the vacuum takeoff adapter right here, so if I were to clip the flask to this, it would be a closed system. Obviously, we cannot heat a closed system; that's a huge risk of explosion. So what I have here is just simply this block, and I can swap this out really quickly, just like that, and this gets set on the block, and the block is actually not quite tall enough to make a good seal, so you can see the flask is pretty much free-floating, but it's stabilized, and that will allow this whole apparatus to breathe while we collect our acid. And you can actually see that we're taking this off at a pretty hefty pace. If you look in there, you can already see a whole bunch in there; it's just sort of drizzling down the side like syrup, and it should only be maybe about half an hour, 45 minutes to finish off the rest of the acid that's in me and the boiling pot there.
All right, quick update. There's been a slight incident. As you can see, the sulfuric acid is kind of bubbling out of the space between the flask and the table there, which is interesting; that shouldn't be happening. It's just—'cause the gap is so small and the acid is very syrupy, so it sort of managed to wick its way up in there and blow itself out, as you can see right there. So I'm going to have to find a thinner spacer for that. Let me go looking for one. This is the thing about chemistry; you never know. Sometimes—that should have solved the problem, but now there's concentrated sulfuric pretty much everywhere. So we're going to have to go ahead and do a cleanup here. I've got a giant bag of baking soda for just such an occasion. Nothing's a panic over a slight amount of decontamination; no big deal. That's so—a couple of—see my clothes are still free; that's good. Okay, crisis averted, and that can just be basically swept into a garbage can later after it—let it sit for a little while, make sure everything is fully neutralized. As you can also see, the collection efficiency has not been compromised; you can see we've still got quite a bit; we only spilled maybe 35 milliliters, and again it was just simply because the gap that I left in the glass there was a little too thin, and the sulfuric acid—remember I said you don't need joint grease because the acid makes great joint grease—because it likes to fill gaps; well, it filled that gap, and then the pressure in the system pushed it out and made a little bit of a mess. But that's what chemistry is all about, and that's why I want to make these smaller videos because things like—say, not using boiling chips and then finding out that you need them later or having an acid spill on the wooden bench—these are things that will happen to you eventually, and when they do, it's nothing to panic about; you just need to know what to do. You can see we've actually pushed the condenser so hard that there's nucleate boiling happening locally inside the water line; that's how you know you get a good takeoff rate. I'm not going to let that go to dryness, obviously, because the high temperatures involved and the flame is more than enough to soften the glass, which I don't want, and I don't want to have to renew it and everything like that. So I'm going to let this go maybe a little bit longer, five more minutes, until it gets down to approximately 10%, at which point I will shut off the flame, let everything cool, and we can clean this up and analyze the product a little bit.
All right, we're down to the last remaining bit of acid, and I really don't want to push it much farther than that, so we're going to shut the gas off, take the torch away, and take off the aluminum foil shield; let everything cool. You can see that the distillation was so hot that—this stainless steel clamp right there—it's discolored. And this is the aftermath of that little acid spill; we have—it's just surrendering to the bicarbonate, slowly neutralizing the acid on the table; the reaction forms CO2 and sodium sulfate. I did wash down this flask because everything on the outside of that is just distilled water; I was very careful not to get any water inside the flask, obviously, which would—one, dilute our acid, and two, cause a very violent reaction since this is very concentrated sulfuric acid and we'll be adding a small amount of water to it—they're not getting very hot and potentially having some explosive boiling incidents; I don't want that to happen. But as it is, it's cool to the touch, which is what we want; it's ready to go in the storage bottle. If it's—I'm going to wipe down the outside with a quick towel to prevent water from getting into the storage bottle, and then this mess here can get swept up once it's done foaming, and the lab table will be no worse for the wear. And this is the finished acid going into its storage container, and you can see it's now a completely colorless, syrupy liquid comprising of 98% very clean sulfuric acid right here. I'm just working the bicarbonate into the table, which just prevents further carbonization, just making sure the table stays nice and basic. But you can see that when the bicarbonate is eventually scraped off and swept up that the table really hasn't sustained much more than just a sort of slightly dark stain. And here's the final product: a crystal-clear, syrupy liquid consisting of 98% sulfuric acid, which will be used in the upcoming video, in a number of upcoming videos actually, and is much cleaner than the drain cleaner that we started with. We also learned how to clean up an acid spill and to add boiling chips to a reaction flask that we already started heating along the way, and those are valuable skills to have in—in any laboratory, whether organic or inorganic. Anyway, if you liked watching this video as much as I liked making it, please press the like button. If you want to see more videos like this, please press the subscribe button. And if you'd like to donate a dollar or two to my Patreon page, I'll put a link in the description. I'm also trying out Twitter and Google+ as well, requested by some of my commenters, and so I will put those links in the description as well if you'd like to contact me and ask me about some of the things I've done in the laboratory, and I'll try my best to answer as many questions as I possibly can. Try this out and just see how it goes. Anyway, thank you very much for watching, and look for the video on Sunday.