Some current statistics on the mass of world plastic production.

[NNadir]

Last edited Sun Oct 9, 2022, 01:26 PM - Edit history (1)

I missed paying attention to this paper from an earlier issue of ACS Sustainable Chemical and Engineering that has been included in a Virtual Special Issue on The Circular Economy of Plastics collecting papers from earlier issues on developing (to the extent possible) circularity. (I decided to download these papers for convenience as I recently expanded my electronic storage capability.)

I often muse on this topic when it pops into my mind when my mind is not focused on some professionally relevant or personal task, and wonder how much carbon is in the world's inventory of plastics, both in use and discarded. Two papers, one from the virtual issue, and another from a reference in the virtual issue gave me a feel for these numbers reflecting global scale.

The paper in the virtual issue is this one: Pyrolysis-Aided Microbial Biodegradation of High-Density Polyethylene Plastic by Environmental Inocula Enrichment Cultures, Emily Byrne, Laura G. Schaerer, Daniel G. Kulas, Sharath K. Ankathi, Lindsay I. Putman, Kierstyn R. Codere, Simeon K. Schum, David R. Shonnard, and Stephen M. Techtmann ACS Sustainable Chemistry & Engineering 2022 10 (6), 2022-2033.

I don't know exactly how accurate these figures from the text of this paper are, but the numbers seem reasonable:

The use of plastic in industrial applications has surged in recent decades. Every year, over 350 million tons of synthetic plastic is manufactured globally, and over 70% of this plastic ends up in landfills or in the ocean. (1,2) Increased rates of plastic disposal pose a serious issue for solid waste management. We currently do not have an efficient and affordable method to recycle plastic on the scale that it is being produced. (3) Plastic is popular due to its durability and low cost; however, because of its strength and durability, it is also difficult to remove from the environment. (4) A broad range of plastics are generated from polymers of varying compounds...

The paper also makes some interesting comments on enzymatic biological degradation of plastics and estimates the half-lives of plastics in the environment:

...Moisture, heat, UV light, and microbial degradation can cause plastic polymers to degrade into smaller pieces and molecules in the environment. (5) However, biodegradation processes occur very slowly in the environment and vary depending on the plastic type. Previous studies note slow rates of HDPE degradation in the environment, with estimated half-lives ranging from 530 to 5000 years depending on the conditions. (6) This slow degradation is partially attributed to challenges microorganisms face in degrading insoluble, chemically complex plastic polymers. (7) With increasing volumes of excess plastic waste, there is a critical need for a timely means of upcycling structurally complex plastic debris to aid waste management initiatives and valorization of plastic waste.

Microorganisms with the ability to metabolize various plastics have been identified in a wide variety of natural settings including soil, marine, and wastewater environments...

In citing this, I am not endorsing microbiological degradation schemes. I'm rather a one trick pony and view the solution of every major chemical waste problem through the same prism involving high heat (steam, dry, or oxidative) reformation or sealed pyrolysis for carbon recycling.

Since plastics are variable, the carbon content varies widely, but I found an open access reference that makes what seems to be an excellent average estimate of the same, from a marine science journal, this one: Smeaton, C. (2021), Augmentation of global marine sedimentary carbon storage in the age of plastic. Limnol Oceanogr Lett, 6: 113-118. https://doi.org/10.1002/lol2.10187.

It offers the following graphic:



The caption:

Plastic properties. (A) Carbon content (%) of the six most common plastics (PET, HDPE, PVC, LDPE, PP, PS) alongside five specialized plastics, error bars represent one standard deviation. (B) Current and predicted global plastic production (1960–2050) (plastics Europe 2016). (C) Current and future estimates of plastic entering the marine environment (Mt yr−1). Annual plastic input to the world's oceans estimated as 1.4% of annual plastic production (Jang et al. 2015).

The text:

...The C content varies with plastic type (Fig. 1A). The mean C content for the six most common plastics equals 74.63% ± 15.81%, while the more specialized plastics contain less C on average (59.72% ± 8.9%). Across this mix of all plastics, the mean C content is 68.05% ± 15.05%. Using the mean C content for all plastics (68.05% ± 15.05%) in combination with the quantified flows of plastic (Table 2), it is estimated that 8.3 ± 1.84 Mt Cplas yr−1 enters the marine environment with 7.8 ± 1.73 Mt Cplas yr−1 reaching the seabed...

If we estimate 70% carbon content, world production of plastics sequesters about 245 million tons of carbon. The authors of this paper note that some of this plastic is sequestered on the seabed, as some plastics are more dense than seawater; arguably over the eons of sediment deposit, these plastics will be mineralized and sequestered for eons, but the amount is trivial.

Each year, while we all wait (increasingly) breathlessly for the grand renewable energy nirvana that did not come, is not here, or will not come, the world releases about 35 billion tons of carbon dioxide to a favorite dump, the air on which we all depend for life.

Have a pleasant Sunday afternoon.

[Karadeniz]

1. Saving for when brain perks up...you have a good Sunday, too !!!

[hunter]

2. Indoor plumbing and modern water treatment for everyone will require a lot of plastic.

That plastic could be a net carbon sink if we avoided the use of fossil fuels in the manufacturing of that pipe.

Making HDPE pipe using something other than fossil fuels will be an important technology.

I suspect you are correct, the process will start with high heat (steam, dry, or oxidative) reformation or sealed pyrolysis.