Breaking the Wall of Sustainable Chemistry. How Modern Alchemy Can Lead to Inexpensive and Clean Technology
Introducing the philosophy of green chemistry in chemical research and engineering, means combating the plague of pollution in an original and innovative way: at its source, diffusing a new modus operandi finalized to design products and processes minimizing the use and generation of hazardous substances. Paul Chirik’s projects in this field have been recognized by institutions like the New York Academy of Sciences, the American Chemical Society and the Alexander von Humboldt Foundation, that granted him the Research Award 2011. His research group at Princeton, where he is currently professor of chemistry, focuses on discovering transition metal catalyzed reactions that reduce fossil fuel consumption, use base rather than precious metals and minimize waste streams. The work focuses on new synthetic methods for the conversion of atmospheric nitrogen into more value-added chemicals and the replacement of heavy metals in organic synthesis and catalysis with Earth-abundant elements. While this holistic sustainable approach to chemistry already boasts of important industrial applications, it also promises a long term environmental and geopolitical impact.
Thank you. It is a true honour to be here, and I would like to begin my talk by thanking Sebastian and all of the staff who have put on this conference for an absolutely remarkable and memorable day. I am going to borrow a line from Sebastian Turner, and that is: you all may now applaud. We should applaud all of you for putting on this wonderful conference. Thank you.
I am going to begin: I am a professor, so I have to give you a quiz. You are falling asleep probably; it is late in the day. The question is a simple one: what do these common household items have in common? These are pharmaceuticals, moonboots – so the bottom of your shoe – envelops, or fuel cells in a car. I mean, how disparate could we get? One of my objectives here this afternoon is to convince you that these are all molecules. These are all molecules that synthetic chemists need to make, and we need to make them in a sustainable way. One of the other aspects of this, and one of the things I want to convince you of this afternoon, is you need to look at the entire system to understand this concept of sustainability. So, one of the problems of all these materials that I show you is: all of them, somewhere in the stream of preparing them, rely on something very precious and very valuable – a thing we call in chemistry “a catalyst”, something that enables a reaction by speeding it up. So, often times, it is a concept that deals with economics, as we have heard a lot about today.
So what are these things called “precious metals”? Precious metals are these elements in the nether reaches of the periodic table, highlighted there in blue – elements that probably sound very exotic to you: platinum. If you have a very good credit card, or are a frequent flyer, you might be a platinum member, but certainly not iridium nor rhodium. If I told you that you were a rhodium flyer, you would probably run away from me. But, believe me, you would want to be rhodium; rhodium is better than platinum. If you learn nothing else from me this afternoon, I will give you someadvice: I am not an economist, but invest in these metals. These are always a safe investment.
So, platinum: we use about eight million ounces per year in car catalytic converters; so, there is a pile of them thrown away. That is actually a very valuable dump now of waste material. In jewellery, because it looks pretty, we use about three million ounces. So what is the problem? The problem is what we are trying to do is to eliminate these precious resources from our syntheses. You may know about this concept of alchemy; this is the origin of chemistry. The word chemistry is actually derived from the word alchemy. Back in medieval times, these often, lets say, shady fellows were using black art to try to convince people that you can convert abundant elements like lead, which is known as a base metal, into something more precious, like gold. This is exactly the concept that we are trying to do now in chemistry that we think is important to sustainable chemistry. But, of course, we are not trying to use black magic; we are trying to use the techniques and understanding of the laws of chemistry in order to do this.
One of the projects in my laboratory in Princeton is to try and take something like iron and convert it into platinum, but not actually for use in jewellery, but actually by function. That is the idea of modern alchemy: can we get these abundant base metals to function like the precious ones do? I will give you a few applications of this.
As Chancellor Merkel told us earlier today, this isn’t a new concept. I was going to tell you it was a hundred years old, and then she said it was two hundred – and that is true. Here is the most important chemical reaction that is practiced in the world. This is known as the Haber-Bosch Reaction. It was discovered right here in Germany at the turn of the last century. The most important molecule there is the one ammonia NH3. This molecule keeps half of the population alive. If that doesn’t impress you, that molecule is the source of half of the nitrogen atoms that are currently in your body from what you eat. The problem was BASF knew that they wanted to make this molecule, because natural farming techniques couldn’t keep up. The engineer who accomplished this, his name was Carl Bosch. The only element at the time that was known to promote this reaction in the way that BASF could do this to make money was a very strange one, named osmium. So, in 1908, what BASF did was they
bought the entire world supply of osmium; it was several kilograms, and they locked it in a safe in Ludwigshafen. That was worth 400,000 DM at the time. One of the major concerns that BASF had was that one of their reactors – this is high temperature and high pressure – the dawn of this kind of chemistry, they were afraid one of their reactors was going to explode. They weren’t worried about the safety of their workers. This is German chemistry back around 1910; nobody cared about that. What they worried about was losing the world’s supply of osmium! So they decided to look for alternatives, and that was Alwin Mittasch’s job, and so he went to a very environmentally friendly element that you may have heard of, called “uranium”. People didn’t want that. So then ultimately he searched and found this element Swedish magnetite, which is effectively today’s catalyst, which is rust on dirt. You cannot get any better than that.
So what is the problem? Why don’t we always use cheap metals like iron? This is a very complicated slide, but it comes down to something very, very simple, and hopefully you can count to two. The metals that are the cheap metals tend to do electron transfer by one. The precious metals tend to do it by two. So you might think: well, why don’t you just use twice as much as the base metal? That is not how chemistry works. The chemistry of one electron is bad, usually; it is radical. That is why you get old, why your car rusts. What we need to do is figure out how to stop that. How do we get two-electron chemistry to happen? What you do is look to nature. Nature has already figured this out for you, because metals like osmium aren’t found really in nature. So what nature has figured out how to do are these multi-electron transformations, and one I show you: how you get rid of greasy substances in your liver using an enzyme called “cytochrome P-450”. What happens is it uses iron, but also by using the rest of the molecule around it to incorporate this multi-electron chemistry. So, one at the metal, one at the rest of the atoms around the metal centre. That is how nature has figured this out.
So, how we do this now: here is an example I want to show you of this idea of a whole system in sustainable chemistry. That molecule on the left with all those double bonds on it that says “plant extract” under it is exactly that. It is an extract from a plant that people want to add hydrogen to in order to turn it into bio-fuel. But there is something unsustainable about that, and hopefully you can see it. That is that you
need to use platinum. There simply isn’t enough platinum on the planet to do this. There is not enough platinum on the planet to put a fuel cell based on platinum in every single automobile. You have to figure out how to solve this problem. Fortunately, I have graduate students in my group who have done this, and they have taken an iron compound and figured out how to do exactly what platinum can.
One of the things I want to tell you about are some molecules that you use everyday that rely on platinum, and this is a real problem. This is this idea of adding a silicon, the thing with an Si, to the end of a long chain. These molecules appear everywhere. This is the envelope; this is the bottom of your shoe. It turns out, if you didn’t have silicon compounds in your jeans, you couldn’t bend your legs; natural fibres are simply too rigid. The final one doesn’t apply in Germany, because you have beer purity laws here. But, if you were Budweiser, and you are an American beer, if you are filling a million beer bottles a day, or however many they fill, you have to fill them exactly the same height. So, if you foam, some beer bottles may have this much beer – and now everyone is paying attention; I have grasped the audience, because I am talking to Germans about beer. You have to make sure the beer fills exactly to the same height every single time. How you do that is you add that molecule right above it, and that is exactly what happens on a huge scale everyday.
This is what you want to have happen. Unfortunately, even though this reaction is practiced on an enormous scale, you get other products, and that is bad. All those molecules on the bottom of the slide need to be separated and taken away. That takes energy, and then you have to dispose of them; it could ruin the performance of the material you are trying to make. Even though these precious metals do great things, they are not perfect.
Here are some other issues with platinum. We mine and use about 5.6 metric tons a year. This costs the silicon industry 300 million dollars a year. This is a major, major problem in your beer, in your jeans, in your iPhone, all of these things. You have never heard of this before. This is a big problem. The other thing, and here is my investment advice to you, if you extrapolate that line over time, you will make money. It is about five percent a year on platinum. But the thing that drives the commodity chemical industry crazy is these massive price fluctuations. If you are selling
envelope glue, you don’t want to hear from me that you have to pay three times as much for your envelope because the price of platinum has gone up. Eventually, what happens sometimes, is that the amount of the material, the residual platinum, left in the material is worth more than the material itself. So, you have to figure out how to get rid of this. Also you have to worry about where it comes from. You have domestic concerns and things like that.
Here is a molecule. The molecule on the upper right, that long chain thing with the Si on the end, it turns out – I hope you used that today – that is in shampoo. It is actually used every single day. We have learned how to make this molecule with no platinum in it. In fact, we have learned how to do it with iron. The important thing that we have learned how to do with iron is we have learned how to eliminate all of those side products. We have two benefits here in the sustainability world. We are not using a precious metal – something that is really rare and valuable. More importantly, I think, is that we are not generating any other side products. We don’t have any other waste – nothing to throw away. It is this whole idea of the entire system being part of the chemical equation.
Anybody here been to New Zealand or anybody from New Zealand? What does New Zealand have more than people? Sheep. Everybody knows that. So, I want to tell you how molecules have actually changed the sheep herding industry in New Zealand. There are some beautiful sheep next to this pretty yellow flower. That pretty yellow flower is known as New Zealand Gorse. In fact, you say, what is wrong with this? What is the incompatibility of sheep and New Zealand Gorse? It turns out, if you are made of wool, and you walk next to this stuff, you can see the thorns. One of the problems that the sheep farmers had in New Zealand is you have to go out and unstick your sheep from that bush. If you have twelve to one sheep to people, then that takes a lot of your time. This is exactly why I went to graduate school – to get a PhD, to figure out this problem.
So, a molecule changed this – one single molecule changed this entire problem, and it is the molecule up in blue above the leaf. What this thing is called is “a super spreader”; now what a super spreader does is there is purple food colouring on that leaf. If you just put water and food colouring on the leaf, you get that nice little
spherical capillary action. If you put about a percent of the super spreader in there, notice that same volume of that drop spreads out completely over the leaf. This is sustainable; this is green chemistry. Because now if you put one percent of this molecule into something like herbicide, you can use that much less of it on your field. I show you the statistic on the slide that 90% of the herbicides that we use end up on the ground. If you can use less, obviously that is much better. In fact, these molecules were introduced to the citrus farmers in Florida. They were very resistant to adopting them. The reason why is because if you tell someone whose livelihood is based on their crop to use one tenth of what they normally use, they wont believe you. It is these issues of change that we have heard a lot about today.
So what this molecule did is it allowed chemists to basically eliminate gorse from New Zealand. So, how it is made industrially is from this platinum catalysed process, where you, again, use a platinum compound, and you put a silicon on the end of the chain. But unfortunately, there is another molecule that says “malodorous” underneath it that is made at the same time. I didn’t know what malodorous meant either until I started working on this. It means that is smells really bad. What you have to do to get rid of that, because the people who buy this stuff don’t want a chemical that smells. Then you do a second precious metal catalysed reaction with rhodium – there is that other weird element. You actually have to get the double bond out so that it doesn’t smell anymore.
What we have learned how to do is, again, to do this with iron, so we don’t use any precious metals like platinum, but, again, this idea of sustainable chemistry and green chemistry, there is no other side product. There is not that second step; there is not that other smelly chemical that is made at the same time. This is very attractive for when you are making things. Remember, these compounds are made on huge, huge scales. If you can eliminate five or ten per cent of waste, you are having an enormous impact.
Finally, what I will leave you with is envelope glue. Remember I told you about all these crazy molecules, or seemingly unrelated things in the beginning of the talk? It turns out that what you do is now you can take two silicon compounds and connect them together. It turns out that most times when you lick an envelope that is exactly the molecules that you are putting together. It turns out that there is a little bit of platinum in that every time you do that. Here is the fun of science: when we first were asked to do this by the company Momentive, this was our first catalyst. We thought we were rich, because that looked like glue to us. Apparently people don’t want to lick black glue, so we had to go back to the drawing board. It turns out that the stuff that is made from platinum is shown there on the left where it says Karstedt’s Catalyst. That is a name for a platinum catalyst. One of our new iron catalysts, the material is on the right. So, we went from this black stuff that would scare people away, to some stuff that is exactly the same as what is made industrially. This is all through working with molecules, making rational changes and learning how to improve what you have got.
What I want to conclude with is that this idea of modern alchemy is true. You can get iron to perform the functions of platinum. One last thing is: there are other heroes of the story. I don’t do any of this myself. We work in a team, and I think they are back in Princeton, hopefully watching this – Hi! – with that I am finished. Thank you very much.