Does the modern plastic-making process inherently produce GHG?

Factual Questions
1

So plastic use currently involves a lot of carbon emissions, one reason being the enormous energy requirements, some of which comes from fossil fuels. Another is incineration of the plastics post-use.

However, what would happen if all the energy to make plastics from hydrocarbons came from renewables? Are there still carbon emissions as part of the process? For instance, does the hydrocarbon processing net equation look something like
Hydrocarbons => Plastics + CO2?

Another possibility is that some of the energy used directly comes from the cracked hydrocarbons and there is no way to efficiently take this out of the equation, something like
Hydrocarbons => Slightly plastic-y thing + CH4
Slightly plastic-y thing + CH4 => Slightly plastic-y thing + heat + CO2
Slightly plastic-y thing + heat => Plastic
Where there would be a huge redesign needed in order to not require the storage, processing, burning, or release of the intermediate hydrocarbons, even if you could get the energy via other means.

Are either of these the case? Or is there some other reason the plastic-making process necessarily involves emission of greenhouse gases? Or is it just the energy required? (There are probably also frictional releases from the extraction and transportation of the hydrocarbons, but I am assuming that these are negligible unless told otherwise. The extraction does certainly involve a lot of energy, but that raises the same question: would the extraction process per se involve release even if the energy came from renewables?)

2

Bumping this with a partial answer in hopes it catches the eye of some ChemEs.

“Plastic” includes very different products made different ways from different starting materials. What you may be looking for is a well-to-wheels or lifecycle analysis for each one, which I don’t have off-hand but those are search terms that may come in handy. I’m going to toss a few things at you; let me know if it’s in the direction you want.

Polyethylene terephthalate, PET (coke bottles, polyester clothing), is made from ethylene glycol and terephthalic acid. Ethylene glycol is made from ethylene. Ethylene is made from ethane or naphtha, the former removed from natural gas, the latter a byproduct of oil refining. The cracking process itself has emissions associated primarily with burning hydrocarbons to generate heat. You could replace these with a “green” heat source. Although keep in mind those have emissions associated with them too.

There are also the emissions from leaks (quite significant GHG source) and energy associated with drilling and processing natural gas and oil. But plastics production is a minor portion of what we use oil and gas for, so the LCA has to account for what small percentage of those emissions get associated with the plastic.

Ethylene can instead be made from ethanol, which is made from plants. Terephthalic acid is made from p-xylene, which is made during oil refining. You can also make Terephthalic acid from plants, although it’s hard. You can also use furandicarboxylic acid to make a slightly different polymer PEF, and that monomer is easier to source from plants. Any biomass sourcing then has all the emissions associated with agriculture and transportation.

On re-reading your OP, I may be missing the mark. But I’m going to leave the above for context. Much of the emissions associated with making plastics is from generating heat for the various steps. Some of that comes from burning byproducts, but most from burning, say, natural gas. I’ll pause there for redirection.

3

Here we go:
https://www2.calrecycle.ca.gov/Publications/Details/1487

See figure S-4 on p10. We can ignore beverage production and later. They’re seeing emissions from material extraction as much lower than those from polymer production. And while that isn’t broken down, I’m assuming most of it is from heat and electricity, which could use different energy sources. Not that the switch is trivial, but people are working on it:

4

Pretty interesting. That’s a lot of power required. Seems like a country like Iceland could really capitalize on it as they have with aluminum smelting. Also a great case for pumped hydro.

5

Part of the issue there is feedstock locations. We have a lot of ethane in the US and make a lot of ethylene from it. Not so much Iceland. I don’t know how the numbers would work out but I suspect they’re not favorable for moving hydrocarbon to Iceland and then resin back.

They are doing things like using geothermal electricity to electrolyze water to make hydrogen, use that to chemically reduce carbon dioxide that they capture from the geothermal plant, and then make methanol for export from the syngas.

6

Nuke powered refineries? You wouldn’t need generators, right? Just the steam?

7

Thank you for your information. It was hard for me to search Google for a breakdown of the components of carbon emissions in plastics, when all the hits say that the emit carbon without any further context.

The money quote is this:

I was also wondering if the cracking process to get the petrochemicals used energy from the refinery (which I assumed it did) and if there were alternatives, which it looks like there are. So it looks like it is possible that we can reduce the carbon footprint of plastics by greening the process in addition to cutting back.

8

Depends on the process. IIRC cracking is way hotter than anything coming out of a light water reactor.

9

Of course, even if we suddenly stopped using all plastics, refineries would still be refining and cracking petroleum, to make all of the other things we make from petroleum (mostly various fuels). Take plastics out of the equation, and they’d either just throw away that fraction, or (more likely) find some way to reprocess it into one of the other sellable products.

10

ChemE here and there’s a lot to unpack here.

(bolding mine)
This statement is confusing. Are you talking about the carbon intensity of using plastics or manufacturing plastics ? Also the “enormous energy requirements” part is confusing because almost all polymerization processes are exothermic (they make heat). Not some but virtually all parts of the energy / monomers used in plastics come from fossil fuels as of 2021.

A very small portion of the plastics used in the USA are incinerated, most of it goes to landfills. One of the reason is because landfilling is cheaper (and low capital investment is preferred by the Waste Industry). The other reason is that plants built in the 70s were polluting and there is perceived public opposition to it.

Please read " 2. Why are MSW combustion facilities not more common in the United States?" by scrolling down here Energy Recovery from the Combustion of Municipal Solid Waste (MSW) | US EPA

The rest of your posts with equations like Hydrocarbons => Plastics + CO2? make me more confused because thats not what’s happening in the Plastics Industry.

So I have taken, the liberty of restating your question as : Can renewables be integrated to plastics manufacture to reduce the Carbon Intensity ?

Lets unpack that question a bit : Lets look at the worldwide production of plastics here Global primary plastic production by polymer - Our World in Data As you can see, there are many different types of plastics made from many different raw materials

If you see that table then Polypropylene (PP), Polyethylene (PE) and Poly Vinyl Chloride (PVC) are the bulk of the plastics. Lets look at these three plastics (polymers) to simplify the question… (Lets ignore Polystyrene, Phenolic Resins, Nylon, Polyester, etc plastics for now)

The raw material for PP/PE/PVC are Olefins : Ethylene and Polypropylene. These are made using :

  1. In the US (or Qatar), the major source is Natural Gas Liquids (NGLs) - (Not be confused with LNG which is liquified natural gas). NGLs are the liquids produced from Gas wells (fracking or regular gas wells). A predominant portion of NGLs are ethane and propane, which are used for making Olefins by cracking.

For simple straight chain hydrocarbons, Methane cannot be liquified by the application of pressure alone (at room temp) while ethane and propane can. Hence they are called NGLs.

  1. For much of the world, Crude Oil is the source. The light portion of the Crude Oil (comes out of a distillation tower) is called Naphtha (https://c8.alamy.com/comp/E9B06C/labeled-diagram-of-crude-oil-fractional-distillation-E9B06C.jpg) This is the fraction between gasoline and kerosene for many crudes. Naphtha has ethane and propane which is also converted to olefins.

  2. In China, Coal is converted to methanol and methanol in turn is converted to Olefins.

I am running out of time, but there are several projects in the USA and worldwide ongoing to incorporate green or blue hydrogen into methanol. The focus is on decarbonizing the shipping industry first but the same technology can be used for plastics.

11

That would require green or blue hydrogen to exist. From what I understand, green hydrogen is only found at a few small-scale prototype plants, and blue hydrogen only in fossil-fuel marketing campaigns.

12

There is some actual blue hydrogen now being produced but it’s less than green. In Norway, they make some, but the problem is, they take the CO2 from the process and inject it into oil fields to force more oil out of the ground. They do the same in west Texas and perhaps other places.

13

The green / blue / turquoise classification of Hydrogen was getting cumbursome and inaccurate, and hence the industry and academia have moved away from it to a number called Carbon Intensity. But for the sake of this thread, lets keep those definitions.

I reckon you are thinking about white hydrogen ? White hydrogen is the hydrogen found in some gas wells which is the product of radioactive activity (just like Helium) and had no associated carbon/fossil fuel.

Green hydrogen on the other hand can be made predominantly in the following two ways :
1. Electrolysis of water using green electrical power : This is electrical power produced from solar / wind / hydro / geothermal etc plants. Now different countries have different nuances; For example : Lets talk about Biden’s IRA (Inflation Reduction Act) → Since renewable power may not be produced a site for electrolysis or maybe missing for half the day (nighs for solar / day time for wind), the IRA allows you to run say a 10 MW electrolyzer from the grid (and consider the power produced as green) as long as you have a 20 MW (double) solar or wind farm installed to power the grid. There are other nuances - but this essentially the idea.
2. Gasification of woody biomass or waste : Woody biomass (like southern yellow pine and many other softwood trees) are grown in a 7 year cycle. The energy produced from them is considered green since they are a 7 year storage of sunlight. Gasification is a high temperature process that converts biomass into syngas (CO + H2 + CO2 + H2O) - it is similar to the process used to make water gas or coal gas. If you have watched old movies - there used to be gas powered lights in homes and town squares - thats essentially coal gasified to make gaslights.

Blue hydrogen is made in the following ways :

  1. Steam reforming of Natural Gas → Natural Gas (CH4) is reacted with Steam(H2O) to make Syngas (CO + H2 + CO2 + H2O). The CO is further shifted to make more H2 and you are left with essentially ( H2 + CO2 + H2O). The CO2 is captured as a pure stream and stored inside deep earth. The H2 produced such is blue hydrogen.

  2. Auto thermal Reactors (ATRs) / Partial Oxidation (POx) → Similar to steam reforming, ATRs rely on breaking CH4 but without using much water. They rely on Oxygen to varying degrees. The product is syngas like above.

This chart gives a good summary of worldwide hydrogen production current and future (it has colors too )

14

Yes. I eventually distilled the core question as:

What percentage of the GHG emissions from well to resin are associated with generating electricity and heat for the chemistry vs leaks or emission of byproducts of the chemical reactions associated with converting NGLs, etc. to resins.

Which I don’t have a number for, but I believe:

Most of them, and enough that companies are seriously targeting this

is accurate.

Re: hydrogen, I’ll see if I can find some recent numbers. Not a ton opened in 2022 but there were a lot of projects announced.