Vers une société résiliente au changement climatique / Building a Climate Resilient Society : colloque organisé dans le cadre de l’initiative « Avenir Commun Durable »
Conférence du 24 janvier 2024 : Electroreduction of CO2 to Hydrocarbons and Alcohols: Challenges
Session 1: Science, Technology, and Solutions
Intervenante :
Professor Charlotte K. Williams, FRS, University of Oxford
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Okay I think we should make a start for this session uh my name is Peter Bruce and it’s a pleasure for me to be co-organizing this with my friend and colleague Jean Marie Taris Kong from the college to France uh we are into our afternoon session second afternoon
Session uh there are two parts we’ll have talks from Charlotte and Mark and it’s a great pleasure for me to introduce Charlotte Williams our first uh speaker fellow of the Royal Society and a colleague of mine uh an excellent colleague of mine from Oxford and the title of Charlotte’s talk using carbon
Dioxide to make polymers brackets Plastics Charlotte hello good afternoon thank you so much Peter for the lovely introduction and to everyone for being here today it’s absolutely brilliant to have the opportunity to speak at this bilateral meeting uh focused on uh scientific um uh possibilities to help
Us meet uh this uh climate uh emergency that we face and uh challenges of the future I’ve thoroughly enjoyed the lecture so far in this session uh professor fonov and I are going to take a slightly more personal approach and um talk in some specifics about technology
Areas that we work in and the one that I’m going to cover is uh in the production of polymer before I go too much further I want to acknowledge that this is going to be very much a personal perspective and that I’m going to show you research work and that’s being
Conducted by the people on the slide here in fact much of the work is quite recent and was done during the difficult years of the pandemics I particularly want to thank and acknowledge absolutely everybody in my research team they are nearly all under 30 and thanks to their
Innovation and their um commitment to doing science we’ve managed to um keep going through some very difficult times and uh keep trying to answer this question what might we be able to do with synthetic chemistry and using carbon dioxide so I want to talk you first about the
Polymer industry and we’ve had some very nice uh introductions that have focused on the sectors that typically uh Emit and the sort of um ways that carbon dioxide uh enters the atmosphere but also is um absorbed back by uh planetary systems and I want to focus on the
Production of chemicals uh in this area because although the overall number is not as large as you might see in energy or in Heating um and it’s a small fraction of the overall industrial emissions which are about 7 gatons CO2 it is very significant the production of polymers
For the chemical industry and so this sub sector of materials that many people know as Plastics but they deliver very much more than plastic packaging they actually have important um contributions at the moment to greenhouse gas emissions particularly CO2 and if we don’t do something to address that that’s only going to get
Worse because this Market sector of the chemical industry the production of polymers keeps growing now you may be asking why is that why do we need yet more Plastics you may have a kind of gut instinct that’s um that makes you think we don’t need any more of these things
And in fact um I’ve recently conducted analysis about what it would take for this global system to achieve net zero emissions and part of the solution is to cut consumption by 50% that’s cut that future growth very significantly so your gut instinct if that’s what you feel is
Correct we definitely don’t need to be over producing these materials and I think every single one of us can think of an application in our everyday life where plastic in particular in packaging is overused however we do rely on them for all sorts of very important industries
Which are kind of cognate Industries for reaching Net Zero so for example turbine blades photov voltaics energy storage and I’ll touch on it in um the 20 minutes I have uh healthc care uh consumer goods uh electronics all of these materials Al all of these products also consume quite significant
Quantities of polymer as does the construction industry so uh it’s it’s a it’s an industry that sits Upstream the chemical of many Downstream Industries and yes we may need to reduce our plastic packaging but do we overall get rid of polymers no I would argue this would be a bad idea they’re lightweight
They’re efficient materials they serve many functions so what are we going to do if we accept that we still need some of these application areas we indeed maybe want to grow them how are we going to make those polymers in future and this is back to that point uh that was
Raised in the very first lecture about in this sector in chemicals it’s not about decarbonization it’s about Def fossilization and so the first plot you see shows you um that we currently produce about 400 million tons of polymers a year worldwide and the majority of those are sourced from oil
And gas and this is because this industry the chemical industry it grew up alongside the fossil fuels for uh particularly liquid transport fuel industry so they’re co-products of that refining process however if the market keeps growing it could reach as much as a 1 million ton of polymer produced so we’re
Not talking about CO2 emissions we’re talking about the the volume of material produced annually and uh if we keep making all of that from fossil fuels we’re going to face a very significant CO2 emission problem why is that it’s because 60 to 70% of the life cycle
Emissions of a material sit in the manufacturing phase so the use and the disposal phase are not signif ific contributors to CO2 emissions so as of this uh last couple of years this 400 million ton production volume it results in 1.8 gigaton of CO2 equivalence it is
Mostly CO2 that’s emitted there so what are we going to do in the future to make these materials to avoid having this become 5 gigatons by 2050 well here’s some interesting research from the the the Nova Institute a European um analysis Institute and they say that actually it is feasible that we could
Meet this future demand through growing biobased growing CO2 based polymers and also massively upscaling recycling so the lecture I’m going to give you today is going to focus Mo mostly on these two but I’m going to exemplify that there are synergies there are benefits to exploring these types of
Feed stocks in lowering the energy that you need to do recycling in facilitating energetically recycling so let’s move on and have a look at what the structure of um thinking about this problem in my group has been so we’ve been working on biobased monomers and CO2 wastes as the
Raw materials from which to make polymers for 20 years now and we tend to think in this way about the materials so first of all we want to make them as efficiently as possible that includes conducting those processes in a very energy efficient way we want to make
Sure that the polymers we make can be processed and made where possible in existing manufacturing infrastructure I think the points made by Eve about taking technology from demonstrator scales and I run a demonstrator scale plant in the northwest of the UK taking them onto customer plant and build or
New build that’s a really big step that um involves all sorts of challenges uh that that are quite hard to foresee and it’s m very much slower than might think so this bit of being able to process in conventional manufacturing infrastructure is absolutely essential because whilst the majority of polymers
Are made by larger chemical companies most polymers are processed in a very distributed way including by lots of small firms family firms that can’t afford to retool everything they have so we need to give them different materials from the Upstream part of the chemical industry so that we can produce the
Products that we want without requiring a really big infrastructure change here and then we need to make sure that the chemistry that we’ve started from is actually ensuring that at the end of life we have a plan for what happens to every single material we’re making in
Many cases it needs to be recyclable but I want to highlight to you that not all polymers should be designed to be recyclable and I’m going to give you an example at the end in some cases you still need to design them to be fully degradable in the environment because
That’s where they’re going to end up and you’re not going to be able to collect them for recycling so I’ll give you a couple of examples of different scenarios because the word polymer describes a multitude of different chemistries and more importantly a multitude of different material science
Properties so in my group we have been looking at this reaction where we directly use CO2 as a raw material together with an epoxide to make a polycarbonate now these polymers have low molar masses in the first phase that we’ve been looking at they are sold and
Used as polyols which means that they contribute to the production of polyurethanes and they’re one of the world’s top seven polymers so they’re a really important material there’ll be plenty of pu in the room that we’re sat in it’s an insulation foam it will be in
The seat that you’re sat in as the soft foam they are um really widely used in the home uh in all sorts of um uh Furniture bedding elastomers and so on you also have them as insulation for fridges throughout construction and of course in the automotive sector and what
This reaction allows you to do is to significantly reduce the embedded greenhouse gases in the production of this so you emit fewer greenhouse gases by making your polyol in this way and in fact this study of LCA was done by researchers who were at that point in
Aran and they were working with covestro who you all know is a very major um Chemical Company and uh they were using a product that didn’t have very much CO2 uptake and even in their case where they had less than 10% of the polymer with carbonate linkages they saw very
Significant Savings in greenhouse gas emissions and significant fossil resources the polymers that I’m going to show you have up to 50 mole per CO2 so it’s there in every repeat unit and you can get what you call a triple win then so for every molecule of CO2 two that
You take up you avoid two more by not using the petrochemical so I alluded to the fact that I have uh some firsthand experience of scaling technology and that’s through eonic Technologies a company I founded in 2011 and it’s based in mfield and Rancor in the UK and here’s the
Demonstrator plant and Rancor can make 20 to 30 kilos of polymer a day but this um is not the focus I don’t want to talk about the commercial Endeavor I want to Simply validate everything that Eve said there and uh instead I want to talk to you about the science that has
Underpinned some of that um uh taking to scale of the chemistry and so we began looking at this in 2008 and at the heart of this is a catalytic chemistry so you have to have a catalyst in order to take CO2 up into the polymer backbone and uh
At that time we discovered catalysts that worked at very low pressures of CO2 at one bar and we had very low turnover and over the next decade or so we’ve worked very carefully to improve the performance but also to understand exactly what’s happening and so I’m not going to focus on absolute performance
Metrics I’m going to try and tell you a bit about how we’ve carried out that understanding so I’ve told you that a significant weight percent of the polymer is CO2 and it’s in the chemistry it’s not there as a foaming agent or something like that the catalysts work
At low pressure and this is important for two reasons the first is that that um it allows you to retrofit existing manufacturing plant and most of that plant is using 100% epoxide and it’s got a pressure safety rating of 10 bar and so if you want to put a new process in
There it has to work below 10 bar and so these catalysts are interesting because they’re able to do that the other thing that’s interesting about this family is that they’re highly tolerant of water and this means that you can integrate the process with c captured CO2 which
Tends to have some degree of water contamination the separation of water from CO2 is extremely energy uh demanding and and rather difficult so that’s a useful feature and in fact these catalysts control the production of the right product that low molar mass polyol by the residual water that’s present in in the
CO2 the other thing that you get in the products is um some improved properties and I don’t want to you know present a complete sale sales pitch for pu so I’m just going to let you read that but this lecture I want to use to show you okay
What’s the generation of products Beyond because these ones are starting to be realized commercially around the world and of course ionic is just one company there are there are many others working in the field I want to give you some idea of how we and others in the field
Are thinking about expanding that product range um to ensure that CO2 has a use Beyond uh even this this sub sector of polymers so first of all uh how the chemistry works I appreciate there’s not necessarily everybody is a chemist in the audience but these catalysts feature two metals and what it
Matters in the cycle is a is a switching between two different types of intermediate an Al oxide and a carbonate and it’s the very selective uptake of CO2 by that Catalyst that we very carefully worked on that is responsible for its unique performance so what we wanted to to do
Was really try and understand why those catalysts perform as well as they do and one of the features that we see and if you are very quick and you you’re a chemist you will have spotted in the structures that there are two different metals and um in the best case scenario
There’s a Cobalt and a magnesium I’m showing you an x-ray structure of a zinc and a magnesium and this uh two different Metals is really important they outperform any combination of the um of either of the metals together so that means zinc magnesium much better than zinc zinc or magnesium magnesium as a
Catalyst and that’s a very fascinating thing scientifically because why is that that doesn’t necessarily uh make immediate sense and I’ve spent quite some time investigating this question this slide summarizes about a decade of research we always conduct a full ktic analysis this means we have all the rate
Laws and we understand the temperature dependence of the rate coefficient we then fit that data to calculations and so we have a very good working hypothesis of how this mechanism functions and I just summarized it at the beginning for you two different intermediates we understand the rate law
And we understand that the rate limiting step is actually an attack onto a coordinated epoxide in this chemistry and what we’ve discovered is that the two metals have very distinctive functions in that catalytic cycle so the Cobalt it provides the nucleophile in the key transition state the rate
Determining step and that means that it reduces the transition state enthalpy so if you look at the field squares in these kinetic analyses we’ve done Cobalt has the lowest field squares magnesium the highest and our best catalyst is intermediate or more towards the Cobalt and we believe that’s because the Cobalt
Is providing the nuclear file so it’s exerting enthalpic control in the transition State on the other hand if you look at the open circles they show exactly the reverse relationship with magnesium having the lowest transition state enthalpy and Cobalt the highest and and our best Catalyst again being
More magnesium like in its en entropic relationship so what we interpret this physical chemical data to mean is that Cobalt provides the carbonate nucleophile and magnesium is the site at which epoxide is coordinated it’s a bit like an enzyme you have a pre-ordering of the active site by the S block metal
By magnesium and um then enhanced activity from the transition metal because of that so that’s the hypothesis that we have at the minute um you may well be uh wondering about that integration with captured carbon and we did these experiments actually about uh getting on for a decade ago now using
Carbon dioxide that was captured from a coal fire power station ferry bridge in the north of the UK ferry bridge now runs with biomass but at that time it was entirely coal and uh they were running a mean-based carbon capture and uh they sent us uh to our Labs a a bag
Full of captured CO2 from the capture unit so it’s already been concentrated because it’s been through carbon capture and it’s already purer than the flu gas would be and what we did was use that bag of captured CO2 to do our chemistry and we discovered that the chemistry
Functions pretty well using the captured CO2 it’s not as fast so there is some compromise to the Catalyst through using captured CO2 but actually you still make a product that sits in the right range for that market that I told you the polyols you have very high CO2 uptake um
And the performance is actually quite reasonable so um as far as I’m aware this is the only study where someone used um captured CO2 to do this type of chemistry but it was very interesting study for us because we also did complete contaminant investigations where we investigated all of the potential contaminants because
They wouldn’t tell us what was in the um the flu gas and indeed the tedlar bag that we were provided with and that helped us to understand even better how to make the next set of catalysts so I want to switch gear now and tell you about making more than just
Polycarbonates and so what we discovered um in 2015 is that in fact you can put CO2 in a mixture with a number of other monomers and many of these either are today bioderived products or they could easily be in future so we tend to constrain our chemistry to to be
Conducted in this way either they are already biomass products or there’s a really strong potential for them to be so in the future and if we mix those monomers together we actually get very controlled sequences in the polymers and we are using this to place our carbon dioxide blocks at very defined places
And this moderates properties so in all cases they’re recyclable and in many cases they’re degradable and we use them as ductile Plastics so high uh temperature performance engineering Plastics High tens cell strength we use them as adhesives thermoplastic elastomers electrolytes and surfactants and in the next bit I’m going to
Illustrate these three areas for you very briefly so the chemistry for those that are interested it works in quite an interesting way because it is not absolutely the same mechanism but all of the catalytic Cycles are linked by a common intermediate and by fully understanding the kinetics of the reaction you can
Dictate which of the types of monomers is being enchained and you can send that chemistry into a particular product range or a particular monomer sequence in the polymer and the way that it works is both through control of the transition state energy but also the thermodynamic stability of the
Intermediate you make is very important because it dictates how reversible the process is so CO2 insertion is actually rather reversible on the contrary and hydride insertion it results in a very stable linkage and so if there is a competition between the two even though the barrier is a bit higher for
Inserting an anhydride you will make the carboxilate linkage not the carbonate and you can see that lactone polymerization has both a higher barrier and a more unstable linkage in the longer term this is just looking at one monomer insertion in the longer term that of course does go below zero
Otherwise the reaction would not be terribly feasible so here we’re using this as I said to make these different classes of material and it’s the specific placement of the CO2 that’s really important in these block polymers they phase separate on the nanometer regime and that controls their macroscopic properties like temperature resistance mechanical
Performance rology and so I’m going to show you a little bit of that data when we think about elastomers so these contain carbon dioxide in the structure and they have a linear response to stress and and strain that’s exactly obeying hooks law and uh when you when you remove um the stress
Of course they retract and go back to their original shape without any loss um of um or any retention of stored energy so they have very low residual strains and rather High elastic recoveries and in this case they have low strengths as well now you may be thinking well what
Use is a low strength elastom in fact siloxanes um certain classes of polyphen elasta very widely used um and so what you want to be able to do is map property space and this is what we’ve been doing for the past three or four years in my team looking these blue
Circles are existing materials these are made of poyene these ones are vulcanized uh rubbers and uh these high strength uh elastomers are the sorts of things you use in heart vves in medicine but also um in high performance sports wear and things and they tend to be amide
Urethane or esta based elastomers and what I hope you get the picture with the little dots is that actually we’re able to cover quite a wide range of stress and strain behaviors and can more than compete with the properties of some of these conventional elastomers all of
These made with either CO2 in the structure or biobased uh monomers that give you s and importantly we’ve talked about recycling we can take our waste material compress it compression mold it into a new film and test it again and we’re seeing that we get the same stress strain relationship now clearly there
Are many other features that determine recyclability than merely stress strain I’m summarizing a lot of data but we are taking these chemistries uh through the um smaller scale but industrially relevant routs that you will reprocess a plastic so we have Compounders um extruders in the lab to be able to make
Those measurements and reassure that these really would be um giving the same performance over recycled Loops I wanted to tell you about making polymers to put into batteries because actually although they’re only a very small component of a of the the future solid state battery they are really
Important one to processing its scale in this industry and currently it relies on fluoropolymers and they as we know face an uncertain future in the European Union and the us because they’re persistent organic pollutants so these pasas are really giving rise to a lot of concern environmentally and what we’ve
Been exploring is making completely oxygenated structures to see if we can uh meet the same performance as some of those fluoropolymers and perhaps even exceed it this has been work that’s been going on with Peter Bruce and Maro pasta funded by the Faraday institution in Oxford so actually skipped over the
Making of the polymer but we’re using exactly our switchable catalysis that I introduced you to we’re making very controlled placement of the CO2 in those chains and uh we’re then testing their properties looking first of all just at conductivity of the polymer exploring the phase uh diagram for those block
Polymers their weekly phase separated and this diagram showing you the majority phase is this Esther mid block and then our CO2 blocks are reinforcing the electrolyte material they’re fully optically transparent and over the typical operating range of the battery they’re behaving as an elastic uh material so we then are looking at their
Electrochemical stability and we can see that they show quite good stability up to 5 volts um in in terms of oxidative stability and that that’s reproducible over a number of Cycles um so encouraging for you as an additive to a composite cathode and that’s what we’ve been making and we’ve been doing this
Using methods that um where we take our uh nmc which is a nickel manganese Cobalt cathode material we take a very high performance ceramic electrolyte and we mix it with our polymer and our polymer plays the role of glue but also conductor in this system and we put it
Into this solid state battery with a composite cathode a gadite as the electrolyte and lto as the anode and what we’ve seen in the first sets of experiments we’ve been running is that um we get very good performance from these polymers so there’s our new polymer here’s the fluo polymer that you
You might use today you both get good capacity but also recent decent capacity retention over a number of Cycles so again there’s much more work to be done here to see if this is a scalable technology if this is an applicable one but I did want to show you something
That’s happening right now in the lab to try and diversify the range of products from CO2 here’s another project it’s with Unilever and what we’re doing is thinking about the polymers that sit in everyday products that you might buy from them and of course they own lots of
Brands um so in particular we’re thinking about washing and in those laundry liquids there’s actually a significant proportion of of polymer the majority of the the bottle is water but uh there is also so uh some soap and some polymer in there to help with cleaning and we’ve been thinking about
What should happen to that polymer after the end of its life because currently those materials are water soluble they have to be to wash things with but they go into water and are dissolved in it but also tend to be rather persistent so they’re py oxanes and polyethers which
Don’t necessarily degrade easily and so we’ve been designing whole sets of materials that contain CO2 in their backbones but which are also water soluble so in this case the CO2 is only transiently stored it’s stored while the the the item is used but the purpose of
Putting it in there is to try and reduce the pollution that goes into water courses and here our scientific part of it is to look at uh understanding structurally how uh you maximize solubility and degradability and we’ve been doing that in various different ways please be reassured that there is a
Strong environmental science component to this project that’s checking about the toxicity of everything that’s being made because it’s extremely important that we work together on the problem and don’t try and do isolated technology fixes so Peter is signaling it’s time for me to be uh wrapping up but what I
Wanted to tell you about was some thoughts about this area for UK French uh collaboration and I think that thinking about the structure of the chemical industry of the future is a really ripe area so my own area polyesters and carbonates has historically been extremely strong in
France and you have been real Pioneers in leading the way and how to make these materials and I think that there are wonderful opportunities for us to work on the fundamental chemistry but also to work industrially together our chemical sector tends to be dominated by smemes we don’t have um so many major
Multinational sites in the UK for chemical manufacturing uh we also have uh a a possibility to integrate some of these processes with emitting Industries and integrating with the bioeconomy I was emphasizing to Peter again that’s very well connected in France the agricultural link with chemistry is something that could be uh very
Interesting for future collaborations between us so I want to stop at that point but we mustn’t forget about the end users of our sector they will help us deliver the products that we need in future so finally here’s the people that did the work again and thank you for
Your attention thank you very much Charlotte thank [Applause] You