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Carbon Dioxide as a Feedstock for Acrylic Acid Production

Fun with Dry Ice (4 of 9)One of the largest sources of carbon, CO2, is emitted as a pollutant and is attributing to the rising climate temperatures. So then why are we not using CO2 as a feedstock? Well, for one thing is it very very difficult. CO2 is incredibly stable as it is a thermodynamic sink. Therefore, It requires even more energy to convert it into something else, and where does all of energy come from? Fossil fuels. Thereby generating even more CO2 to convert CO2 into something useful. But if we can find a means for converting or reducing CO2 into a commodity through a less energy intensive pathway, then there is potential to generate revenue from “waste” and reduce emissions.

Currently, the US generates 5,500 million metric tons/yr of CO2. Industries are currently capturing and using CO2, approximately 200 million metric tons/yr in the food industry and oil and gas industry, but a majority of this is released back into the atmosphere. Only about 0.5% of the CO2 that is captured is sequestered and not released.

We can think about carbon/CO2 utilization in two categories, 1.) carbon sequestration (burying in deep geological formations) and 2.) carbon as a useful feedstock. I am focusing on the second categories because investigations into into using CO2 as a freely available and abundant feedstock to develop commercial chemicals, plastics, and building materials has the potential to be an economically viable industry. Additionally, carbon sequestration has its limitations, and although it is being heavily federally funded, it’s large scale deployment has estimates in the range of $30-70/ton attributed to the new CO2 transmission lines that will need to be built. There are instances where CO2 cannot be transported to sequestration sites.

One of my favorite examples being investigated for CO2 utilization to generate commercial chemicals is the oxidative coupling of CO2 with ethylene to generate acrylic acid with molybdenum catalysts.  This is work done at Brown University in the lab of Dr. Bernskoetter.

Acrylic Acid

Acrylic acid is used heavily as the raw material for polymers, coatings and adhesives. Global production of acrylic acid is 3.4 million metric tons/yr and with 60% by weight CO2, that is over 2 million metric tons/yr of CO2 that could be resold and prevented from entering the atmosphere. The production of acrylic acid through a more economically viable method would be advantageous, so much so that Dow has begun similar efforts to generate acrylic acid through the generation of 3-hydroxypropionic acid with the use of a biocatalyst.  They claim that their process is 25% cheaper and 75% less greenhouse gas intensive.

The current process for acrylic acid production is the oxidation of propene and is incredibly energy intensive because it not only requires reaction temperatures of 200 – 300 C but also multiple distillations to remove impurities. Dr. Bernskoetter’s catalysts can oxidatively add CO2 and ethylene slightly above, if not close to, room temperature.  However, at the moment, the biggest challenge is the reductive elimination of the hydroxide to release acrylic acid from the metal.  But once that can be done, unlike the use of catalytic microbes, organometallic catalysts can more easily (and usually cheaply) be modified to improve upon turnover rates and efficiency.  I am especially excited and looking forward to Dr. Bernskoetter’s next publication on this catalyst.

ROMPing around the Carnival

Here is my contribution to Chemical and Engineering News’ “my favorite chemical reaction” blog carnival! I call it the “popcorn-stringing” reaction. Because, of course, one needs popcorn when at the Carnival!ROMP stands for Ring-Opening Metathesis Polymerization. The popcorn stringing analogy comes from the cyclic momomer being popped open and then, through bond metathesis, the molecules are strung together to make a polymer. The release of the ring strain is the driving force for the polymerization.

Kernels are the monomers that are popped open into popcorn that can be stringed together! The catalyst drawn is Grubbs' 2nd generation catalyst.

ROMP is a fascinating reaction for many reasons, one of which is of the range of metal complexes that can be used to carry out the reaction; including tungsten, molybdenum, rhenium, ruthenium and titanium carbenes. The most interesting developments in ROMP catalysts are those that can carry out living polymerizations*. These types of polymerizations can lead to polymers with a variety of sequences (copolymers) without sacrificing precise control of the material’s dimensions that, in turn, lead to a wider range of properties and applications.  Also, in terms of sustainable chemistry, these catalyst can lead to greener processing routesby improving efficiency and saving on atom economy (having every reagent used count).

The polymers that can be synthesized through ROMP have a lot of industrial applications. One of the most famous is Norsorex, or polynorbornene, which is a shock-absorbing materialused in protective equipment, sound insulation, and vibrational damping. Through a single monomer, ROMP can access structures normally difficult copolymerize with individual monomers.  One example is a perfectly alternating copolymer of 1,4-butadiene and isoprene.

perfectly alternating copolymer of 1,4-butadiene and isoprene from an octadiene

As with any other chemical reaction, there are limitations.  ROMP’s limitation is that the monomers must be cyclic and possess sufficient ring strain.  Although it might be difficult to synthesize momomers with these desired attributes, it is possible to derivatize naturally existing materials. Last year, the Larock group developed biorenewable-based thermosets from the ring-opening metathesis polymerization (ROMP) of fatty alcohols derived from soybean oil and castor oil.#  Of course, this work illustrated the robustness and versatility of Grubbs’ catalyst (like so many papers), but what is key is that it also highlighted the substantial role that metathesis catalysts can have in the development of polymers from biorenewable feedstocks as the pressures of traditional petroleum-derived feedstocks grows.

Well, that is a great place to end.  The thought about using renewable feedstocks not just for energy but also for carrying out chemistry is an important direction to consider.  Actually, a reaction very similar to ROMP that I have not expanded is, ROP (Ring-Opening Polymerization) and that polymerization is responsible for the material in biodegradable “corn pens”(polylactic acid).

lactic acid (monomer) can be derived from corn

ROP reactions are carried out by different types of catalyst than mentioned above, but same general idea of ring strain (lactic acid) as the driving force for the reaction.
Now, when you think of corn or popcorn, in addition to potential sources of renewable energy, I hope you will also think about ring-opening polymerizations.
Definitely time for me to go make some popcorn.
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*Living Polymerizations are polymerizations that satisfy the following three criteria:
1. Polymers have a narrow mass distribution. Meaning that the Gaussian distribution curve of polymer lengths is narrow indicating that a majority of the polymers are similar in length.
2. No premature chain termination. This helps to achieve the first point. If the growth of the polymer chains are cut off at different times then there will be a wider distribution of polymer lengths. This point also allows us to build copolymers. Once all of the first monomer is consumed and a second monomer is added, the polymerization continues adding in the second monomer.
3. All the chains start fast and at the same time.
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Image credits!

Popcorn PoppingPopcornPopcorn String

What is a mechanism?

Here is a “links and will get back to these in more detail soon” post!

The month of June disappeared incredibly fast…

A lab-mate of mine showed me this site today and basically, we need more websites like this to help students learn how to solving mechanisms! Even if you haven’t taken an organic chemistry course, but are curious about what organic chemists think about when we talk about “mechanisms”. I think that this website would still be a great way to pick up what a mechanism might be about! (although, an understanding of functional group and basic rules about electron pushing is needed, but nothing that perhaps quick google search can’t help you with!)

Named Organic Reactions: An Interactive Guide http://www.chem.ox.ac.uk/vrchemistry/NOR/default.htm
this is definitely excellent work by Matthew Smith and Chloe Yu at the University of Oxford.

I would also like to bring your attention to a couple of organic mechanisms on Wikipedia that now have animations! Ritter Reaction and Appel Reaction.

A few other things that came out last week or in the past couple of weeks or actually perhaps this past month that I have been interested in:

A new initiative out of the White House: Materials Genome Initiative. This combines the advantages in computational modeling with experimental tools to decrease the time for materials to move from lab to market. It is meant to create a new culture of a more cohesive field of Materials Engineering so that predicative models can be more accurate and resonate with experimental results. It is exciting to have this new era of materials development.

House passes H.R. 1249, the America Invents Act. Hopefully this will revamp the patent system so that the patent process is no longer a barrier and a burden to go through. Something that I am interested in learning more about is the process of tech transfer. To get a better understanding for the process of moving findings in to lab out to the consumer.