Oil to Chemicals to Polymers
Oil to Chemicals to Polymers
A large and mostly incomplete post. But how would you describe the world?
In this newsletter I often allude or reference how the majority of the chemicals and materials we have come from crude oil. I’ve spent a bit of time here tracing the supply chains back to crude oil, but I thought it might be worth just trying to explain it all.
In one post.
This has its challenges, but petrochemical and O&G people know how fundamental this stuff is to all of our modern lives, but how would I explain this to a layperson?
Disclaimer: I’ll try and make this as accessible as possible and if you want want to dive deep into it, I’d recommend reading this book:
The part of the audience that might benefit most from this is the non-chemists wanting to learn more. A bunch of you are here because you seek to “learn more about chemistry.” I’d advise you that this is difficult and you shouldn’t underestimate the value of a college education here. This is stuff most of the chemists and chemical engineers usually know quite well and if you don’t here is your refresher.
One thing that’s held me back is my ability to make this information as accessible to everyone as possible. The importance of understanding the origins of this stuff is that it’s undergirding our entire raw material supply chain. Disruptions or seismic shifts here mean supply chain issues for everything downstream or rather built on top of this foundation.
If you are a start-up founder or an investor seeking disruption in this space then in the immortal words of Omar, “you come at the king, you best not miss.”
So, get your notebooks out because class is in session.
First, A Language Lesson
Chemistry is essentially its own language combined with some difficult to grasp scientific principles built on physics, but often observed through hypothesis driven experimentation. Your average chemistry textbook is a distillation of thousands (hundreds of thousands?) of references from the peer reviewed literature into something accessible to and undergraduate. Throughout this post I’m going to write with the concept of you knowing the differences in reactivity of some molecules and how they are named, but it might be worth trying to explain upfront.
When I refer to a bond, I’m not talking about a financial instrument, but rather the sharing of electrons between two atoms to make a molecule. The way atoms are held together is through “bonds” made up of electrons sharing their time between two atomic elements such as carbon and hydrogen or carbon and oxygen. The type and quality of bonds is often of great importance in understanding reactivity of molecules and ultimately the usefulness of a molecule. There are a few types of bonds:
Ionic - This is what holds sodium and chloride together to make salt. It’s quite strong until you add water.
Covalent - Sharing of electrons in a more equal manner, what we will focus on today, and diamonds are really just carbon-carbon covalent bonds.
Intermolecular - The weak bonds that molecules exert on each other. More like vibes I guess is a good way to put it. This is why ice floats.
Single Covalent Bonds
You might be familiar with hydrocarbons and these molecules are built from carbon and hydrogen. The lowest reactivity hydrocarbons tend to be those composed 100% of “single bonds.” We can think of single bonds as being the lowest energy state and thus they are quite stable. Low energy often equals stability in chemistry and it’s a theme that will pop up in self-assembly of macromolecular structures such as proteins. Think about putting a ball up high on a shelf and having it fall, there is quite a bit of potential energy there, whereas that same ball on the ground has a lot less. A perfectly folded protein is in a low energy state. I’m generalizing here (protein people please put away your pitchforks, I know you do DSC like the rest of us), but it’s an important concept to grasp. Let that sink in for a moment.
A single bond only molecule might often have a suffix “-ane” such as octane, hexane, or butane. You can view the prefix as the number of carbons. Octane has 8 carbons, hexane has 6 carbons, butane has 4 carbons, and they are all joined together with single Carbon-Carbon (C-C) bonds. We can arrange these molecules in different ways to increase branching or make them linear. Branching an linearity is exactly what you might think it is and it involves a molecule looking like a line (linear) or with a bunch of pieces coming off the main trunk (branch). Branched versus linear tends to have a big impact on physical properties such as boiling point and flash point (when it combusts). The linear version of Octane has a boiling point of 125 C versus whereas the branched versions in your gas tank is about 35 C. This is why at the gas pump it’s called “Octanes” as opposed to just “Octane” and the higher the number of branched Octanes the better the fuel. This process of carbon-carbon rearrangement is called “catalytic cracking” and it’s done at scale in a fuel refinery. This is what fuel refineries are doing from fractionalized crude oil. This process is how we get the fossil fuels that we burn in our combustion engines.
Double Bonds
If single bonds are the least reactive then the next highest up in terms of energy would be double bonds. The more economical thing to do with crude oil fractions like ethane or butane would be to turn them into their double bond equivalents such as ethene, butene or butadiene. We denote a double bond containing molecule with the suffix of -ene. We might view it as twice as many electrons hanging out between two carbon atoms and depict it as C=C and that higher concentration of electrons lend themselves to greater reactivity or an ability to react with other molecules at lower temperatures. Ethene has a bit more energy than ethane when it comes to being available to react, but it has less potential energy with respect to combustion. Ethene not as good of a fuel, but it’s better at playing well with other molecules. We can also impart more than one double bond provided we have enough carbons to hold them which is why butane can become butadiene C=C-C=C. In theory we can even produce three double bonds with butane, but there comes a limit when we might have a bit too much reactivity in a molecule and while they can be interesting academically or in small quantities extreme reactivity is not as useful at scale. We can even have triple bond molecules like acetylene, but that is a post for another day.
A Mixture of Hydrocarbons
Crude oil is really a mixture of a whole bunch of stuff, but it’s mostly just carbon and hydrogen and that combination of hydro and carbon is how we get hydrocarbons. Word mashups are also how we get the name of this newsletter too. I’m using the term hydrocarbons generously here in and I’m using hydrocarbons to denote: methane, ethane, propane, butanes, pentanes, hexanes, heptanes, octanes, etc, and also things things like benzene, xylenes, toluene, naphthalene, asphaltenes and more.
Separation of these hydrocarbons into specific fractions through distillation gives us different streams of hydrocarbons we can refer to as a C+# so methane is C1 as in there is one carbon. Ethane is C2. Heptane is C7. Benzene in this naming convention would fall under C6, but unlike hexane which has 14 hydrogens, benzene only has 6 due to its aromaticity. I could keep explaining what this all means, but you didn’t come here for me to teach you all of organic chemistry in a newsletter post.
Separation of hydrocarbons is the first step in being able to do some chemistry with hydrocarbons and this is why we have chemical engineers. In its crude form crude oil is actually useless and its refinement has led to the great unlock of our modern industrial economy. We might be in a situation where we could see this change in our lifetime if some start-ups can figure out how to overcome our dependence on making everything below from crude oil.
To the start-ups seeking to disrupt chemicals and their would-be investors:
This is your competition, and you need to do it at scale by providing these three things, ideally all at once:
Lower cost (less energy to produce/separate)
Equivalent structures with similar or better purities
Safer processing and less externalized costs (e.g., wastewater or emissions)
Don’t view this as a comprehensive list or guide or reference. The book referenced above should be your source of truth around this stuff.
Methane - C1
Methane, is also known as natural gas, but the smallest of the hydrocarbons is also one of the most difficult to transform. Burning methane to generate heat, to create steam/create electricity is something that we are 100% reliant on and right now in Europe we are seeing the ramifications of what happens when methane supply chains are disrupted and even here in New England, I think we are going to be in for pricey winter.
As for chemical transformations, we use methane in a process called Steam Reforming, which equates to blasting methane with a bunch of steam (i.e. heat + water) under a lot of pressure to create carbon monoxide and hydrogen, which is also known as “syngas” or “synthesis gas”. From carbon monoxide we can “hydrogenate,” or add the hydrogen back in, to make methanol. If you spend enough time with organometallic chemists you eventually get into a conversation about direct oxidation of methane to methanol and completely bypassing the steam reforming situation, which would lead to a huge reduction in energy consumption.
From the C1 stream we can make syngas, methanol, formaldehyde, carbon dioxide, urea, and ammonia (methane/nat gas as an energy source). Here is a nice little article about C1 chemistry if you want to get technical.
From C1 the really important “end products” that we get are methanol, formaldehyde, and urea. We make formaldehyde from methanol and urea and formaldehyde are the simplest amino resins, a type of thermosetting polymer, that we can make. If you’ve bought particle board, medium density fiberboard, or asphalt shingles at a lumber yard then you’ve been buying products enabled by urea-formaldehyde resins.
Urea is also a great fertilizer because it’s got a bunch of nitrogen, it’s a solid, and it can dissolve into water readily. Ammonia, is a gas, and thus it needs to be paired with something or reacted in some way to get it into a solid form such as nitric or phosphoric acid to yield ammonium nitrate (explosive/fertilizer) and ammonium phosphate (fertilizer) respectively.
From syngas we can also do Fischer-Tropsch synthesis or “gas to liquids” wherein we add carbon to a carbon monoxide to make a C2 and then add another to make a C3 and higher. This takes us up the carbon ladder to rung 2.
Ethane - C2
Ethane can also be burned to create energy, but it’s infinitely more useful as ethene, the molecule we get by removing two hydrogen atoms. The value of ethene or ethylene is in its propensity to react with other molecules. You might know ethylene by a nice little polymer called polyethylene.
To create ethene or ethylene I need to introduce steam cracking. If you think steam seems like it’s important in the chemical industry, then trust your instincts. Steam cracking is how we introduce unsaturation or more reactive bonds into molecules.
Ethylene is more reactive than ethane because it has a double bond and polymerization of ethylene is only possible because of that double bond. This difference in reactivity keeps coming up throughout the rest of the chemicals here. Keep it in mind.
ICI figured out by accident how to polymerize ethylene via free radical polymerization to make low density polyethylene and this discovery helped set the foundation for what would become the modern chemical industry. Low density polyethylene gets its name from an inability to pack together well due to “backbiting,” and this branching of polyethylene keeps it from forming crystals.
Being able to control branching in polyethylene arrived via advances in catalysis (Zieglar + Natta won the Nobel Prize for this) and unlocked tools for polymer chemists to be able to achieve medium density polyethylene (MDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), and ultra-high molecular weight polyethylene (UHMWPE). This is all achieved by being able to selectively place branch points in polyethylene and this one family of polymer gives us wire insulin, waterproofing of buildings, shopping bags, milk jugs, coatings for paper, waxes, foams, Tyvek, and more than I have time to list here.
We can also combine ethylene with other chemicals and atoms such as oxygen to get ethylene oxide (we can also polymerize this), but I’ll get to that later.
Propane - C3
Propane is used for more than burning to provide heat for off-grid cabins, camping stoves, and camper vans.
We can also steam crack propane into propylene, but a free radical polymerization cannot proceed with propylene as it can with ethylene. There is a lesson here in resonance and radical stability (allylic effect) if you are interested, but until the catalysis innovation by Zieglar + Natta + Phillips Petroleum propylene was kind of…useless.
Polymerization of propylene with catalysts allowed for polypropylene, a more rigid plastic than some polyethylenes. Polypropylene is ubiquitous in that it that makes up our yogurt and takeout containers, spray bottles, and polypropylene strands can also be woven together to make that ubiquitous blue tarp you see over people’s roofs after a bad storm.
Butanes and Pentanes - C4 + C5
Butanes and pentanes can also be burned, but we can also find a lot of value in steam cracking and transforming these materials into other chemicals.
From butane we can get isoprene, butene, and butadiene.
Polymerization of isoprene can yield us butyl rubber.
Butadiene is as foundational as ethylene and propylene in terms of importance. We can also polymerize butadiene to make rubber and it is a critical component in the tires that go on your Tesla or Ford-150. We can also react butadiene with hydrogen cyanide to produce adiponitrile and eventually 1,6-hexane diamine via hydrocyanation and hydrogenation.
If we steam crack our C5 stream such as pentanes and cyclopentane we can get pentenes such as isoprene or cyclopentene. The C5 monomers are not used very often unless making more specialty materials such as styrene-isoprene rubber or tackifiers. If you’ve ever used a pressure sensitive adhesive there is a good chance that it contained isoprene rubber, a C5 tackifier, or both.
Hexanes, Octanes, Benzene, Toluene, and Xylene C6-8
Hexanes can be burned, and steam cracked. 1-hexene is often used as a way to introduce branch points in linear low-density polyethylene.
Cyclohexane can be oxidized into cyclohexanone and cyclohexanol, otherwise known as “KA oil.” Further oxidation of KA oil can yield adipic acid and this oxidation is often taught as an undergraduate organic chemistry lab. We use adipic acid for making aliphatic polyesters as well as nylon. Bioamber’s mission was attempting to make a biobased adipic acid from glucose.
We all know octane or octanes as gasoline and it’s the primary fuel used in modern industrial combustion engines. Catalytic cracking (not steam cracking) is used to rearrange octanes to be better fuels. From a pure specialty chemicals standpoint there are some limited uses of 1-octenes or similar chemicals such as a comonomer in polyethylene, but the vast majority of C8s are typically going into fuels.
Benzene, Toluene, and Xylenes or BTX as a common abbreviation is fundamental to a lot of the chemical industry. Really, we are concerned making benzene and xylenes.
Benzene on its own is kind of useless. It’s too toxic to be used as solvent, but it’s great at reacting with other molecules such as ethylene to make ethyl benzene and eventually styrene. From polystyrene we can get red solo cups and foams, but if we polymerize styrene with butadiene or isoprene we can make synthetic rubbers. These rubbers are often made in what we call “blocks,” where we first polymerize styrene and then feed in the butadiene, and feed back in styrene at the end. You might see these rubbers being abbreviated as SBS, SEBS, or SIS and this type of acronym is in reference to the end blocks (styrene) and the mid blocks (butadiene, ethylene-butadiene, isoprene). The styrene blocks associate with each other while the “mid blocks” or “rubbery” blocks are rubbery. Styrenic rubbers allowed for rapid manufacturing of rubber from refined oil during WWII and reduced the need to get rubber from natural rubber plantations. Today, this stuff is incredibly cost efficient and it’s why you can go to Costco and get 4 new tires for a few hundred bucks.
Benzene can also be combined with propene to make cumene. Cracking cumene with oxygen gives us phenol and acetone or the two starting materials to make bisphenol A and the foundation for epoxy resins and polycarbonates. Phenol also can be reacted with formaldehyde or other aldehydes to make phenolic resins. If you are using brake pads on a car, then you are using phenolic resin. Phenol can also get hydrogenated to make cyclohexanol (see above for KA oil) and it has a myriad of other uses such as parabens and being used in sore throat spray (small amounts can numb your throat, but it’s also acutely toxic).
Xylenes or specifically para-xylene is the starting point for terephthalic acid or one monomer of poly(ethylene terephthalate) (PET) or what we might refer to as polyester. The other monomer in PET is ethylene glycol, which we get from reacting ethylene oxide with sodium hydroxide. Without para-xylene we have no beverage bottles or polyester fabrics. Changing the ratio of ethylene glycol and terephthalic acid can give us ethylene glycol capped polyesters that can be used as polyols for polyurethanes and can impart some fire-retardant properties.
C9 and Beyond
Here there be fuels such as kerosene (jet fuel), diesel, and motor oils and other lubricating oils. This post is already insanely long, but these higher carbon numbered fuels enable our supply chains from trucking to freight trains to jets to tanker ships.
We also start to get asphaltenes out here and I wrote a whole post about roads if you are interested in asphalt.
Conclusion
You should view this as just a small snapshot of the petrochemical industry organized according to the size of the hydrocarbons coming out of an oil refinery. Everything I wrote about above just considers carbon, hydrogen, and oxygen, but there is a bigger world out there that also utilizes other elements like chlorine.
Chemicals have been deeply intertwined with petroleum for over a century. I think it’s possible to use things other than petroleum and we are even starting to see some of this occur right now, but a full transition to a non-petroleum society is much more difficult and intransient than you might initially think. It’s not that I don’t think it’s possible to change, but rather it might be helpful to understand the space a bit before you seek to disrupt it, but by all means please disrupt away.
Let me know how I can help.