tl;dr: first & last sentences

Wealth originates in natural resources.

Here you've got bureaucracy, natural resources, value-added product, surplus, scrap, waste, storage, shipping, and business-as-usual being the primary elements interacting overall.

It isn't profitable to send a shipload to a place where it isn't worth more money when it gets there. Price matters.

Propylene gas is one of the fundamentally simplest hydrocarbon monomers, second only to ethylene gas in simplicity.

Used as raw material to produce polypropylene and polyethylene plastics respectively.

Very similar in volatility, flammability, and liquefication properties to propane, propylene can be handled using the same familiar tanks used by consumers for cooking and heating.

And the same traditional LPG vessels or the modern refrigerated lower-pressure types.

We're in a crisis but current prices still represent a somewhat functional market.

Lets put them on the same basis in US dollars and look at the math.

LPG can be considered a crude natural resource and it's quoted in liters across a broad spectrum of prices from 0.07 to 1.16 USD worldwide:
-interestingly this data source does not include Mexico or the US, however North America is represented by Canada

https://www.globalpetrolprices.com/lpg_prices/

Propane is refined from LPG, quoted per gallon at 0.46 USD.
So that's about 0.12 USD per liter for comparison to the LPG spectrum:

https://www.indexmundi.com/commodities/?commodity=propane

Propylene is produced using propane as the raw material, quoted per metric tonne at about 870 USD, except on the US Gulf Coast where delivery without shipping is only about 20 USD per tonne.
So that's about 0.53 USD per liter elsewhere for comparison to the LPG spectrum:

https://www.fibre2fashion.com/market-intelligence/textile-ma...

Quite a bit of certain value added here in the step from propane to propylene but some people are still paying more for hydrocarbons to burn than others are paying for raw monomers for polymerization into plastic.

And they all come in the same vessels when available.

Made from the propylene monomer as raw material, solid plastic bulk polypropylene pellets on the same basis at 1170 USD per tonne can be seen to provide notable multiples of value added on the US Gulf Coast.
For the pellets that's a price about 0.72+ USD per liter of equivalent propylene monomer (ideally polymerized) to compare to LPG:

https://www.fibre2fashion.com/market-intelligence/textile-ma...

Note that both charts from the last data source appear to have European prices quoted in Euros on an otherwise US dollar chart, so things are even more expensive over there than it looks.

And the virgin polypropylene or polyethylene pellets might be under consideration to be shipped by the same solid-cargo vessels in competition with more diffucult-to-handle waste plastic.

Actually if an overseas factory uses a liter equivalent of cheap plastic pellets to make consumable items for return export, their value added can be a bigger multiple than any of the preceeding members of the value-added chain. Like a few dollars rather than these sub-dollar amounts.

Even within the same oil company, different degrees of environmental protection can be accomplished by different groups.

Different incentives apply to different groups of bonus-seekers, the exploration, production, refining, petrochemicals, and polymers each have their own not-fully-aligned efforts.

Sometimes bonuses can only be had by the most agressive growth operators at all costs, externalized or not.

Then there's this from 2013:
HN link to:
One of the largest polypropylene production facilities opens in Siberia [2013]
https://news.ycombinator.com/item?id=24458335

And since that's not enough for consumers, now there's this from Thursday:
HN link to:
Launch of New World Class Polypropylene Production Line in La Porte, Texas
https://news.ycombinator.com/item?id=24458348

Remember, some businesspeople will never be satisfied unless every dollar is greedily extracted at each possible point in a chain, often preferring it to be done to someone else's extreme disadvantage if possible.

To be financially sustainable;

It takes a lot of surplus to save from destruction, distribute, deploy, repair and/or reuse.

It takes a whole lot more scrap to recover the valuable components from.

You can only imagine how much tonnage it would take once there are no more financially valuable components.

Now both the surplus & scrap have always been under pressure from virgin raw materials and manufacturing to begin with, and so surplus & scrap are still often included with and regarded as _waste_. Some people hate anything old anyway. Actually makes the waste seem to be more valuable if it's not just plain plastic too.

There's not supposed to be any level of imagination that can conceive of a scale so vast that handling plain plastic waste would be financially feasible.

So the waste doesn't have a chance, there's fundamentally not a promising financial market that can develop around a liability.

Unless maybe you promise to do something but you don't actually do it.

The only market can be among those willing to pay to discharge a liability.

A big city, company, or community can easily attach no remaining value to more dumpster loads of stuff the more wasteful and consumer-oriented the society.

It can't be economically handled, stored or shipped, and the more of these efforts that are incurred they increase the depth of the liability, so the incentive can arise to make it the sooner the discharge the better.

When the only remaining real value is as scrap for recycling or fuel for energy recovery, but both are uneconomical compared to virgin material, the final incentive falls to incidental accumulators whose economics are not quite prohibitive, but on too small a scale to make a major impact, or on a too-imaginative scale of accumulation which often fails to have a positive outcome.

Surplus, scrap, and waste operators have always had their warehouses, scrapyards, and dumps under pressure to discharge at the same average rate as accumulation. Lots of them are always _almost_ full.

Seems to me once an overseas business like this is established, there will be times when it will make economic sense for someone to discharge a low-value cargo into the ocean even if they were to continue the voyage all the way to the intended recycling port afterward. If the receiving dump was still anticipated to be full upon the vessel's ETA, the cargo could not be accepted anyway, and a procedure could be developed to handle it with creative paperwork, even routinely without any changes to established office systems. So everyone continues to make money because they're being paid to get rid of the waste, not because someone actually thinks they can add value to the waste if delivered. Maybe extract a little more value, but not add anything, and further value removal can be a costly maybe still leaving most of the bulk left over anyway, and there may be _greener_ pastures.

When there's no market to rescue a marginal asset which quickly turns into a vast liability during a voyage, there can be no rescue to hold out for.

Fundamentally a shipload of waste is worth less than a shipload of crude oil except for a few days each century wben crude goes below zero. The rest of the time crude oil is higher, sometimes fluctuating wildly while still providing a cheaper source of virgin plastic than recycled plastic can compete with. Waste plastic never rises significantly above zero, and is always on the decline.

There could be incentive to ocean dump just because the asset is so marginal, to prevent further cost of handling and storage, and eliminate risk of turning into a liability through time. Actually voyaging nowhere near an overseas port. Covering this with paperwork could be the most profitable business niche in the declining-value chain. Mountains of garbage might have more slippery slopes than you think, and people end up under the table. Returning an unburnt fraction of the vast produced resource to the earth offshore to where much of it originated, but not to the subsurface. In a value-extracted-while-declining way comparable to just spilling the oil intentionally.

Similar to the way at the other end a pipeline thief might make more money per barrel than the oil company would from the oil they are stealing as it comes from the earth.

I don't know if anyone seriously insures these waste cargoes against losses to begin with.

>Here you've got bureaucracy, natural resources, value-added product, surplus, scrap, waste, storage, shipping, and business-as-usual being the primary elements interacting overall.

Same elements as the Beirut explosion where the impact may or may not be as large on the environment as many shiploads of waste plastic, but after a period of complacency both raise their ugly head in their own way. In Beirut that was just one shipment and the human failures had an instantaneously undeniable effect after the delay.

Shipments which are of marginal value don't have a mainstream re-entry point because they compete with shipments having full value.

It wouldn't be so bad without all the dishonesty & greed.