ChemEAg08 said:
Clob94 said:
Serious question--
Has there been some advancement in plastics that's happened and I'm just oblivious to it?
Because if we atop using oil and gas, we better have found a new way to make plastic-- and ifvwe haven't figured out a new way to make plastic-- then we are f***img stupid for doing this.
Short answer is no, there is currently no viable replacement for ethane/propane/others (which come from natural gas splitting and refineries) to make plastics.
There are concerted efforts at plastic recycling (I.e. breaking down the carbon chains like so that they can be reused in plastics/fuels/etc), which may be an interesting solution if economically viable. Carbon molecules are going to be needed make plastics, lubricants, solvents, etc and until someone figures out how to get it outta CO2 cost effectively, it'll likely be from natural gas and oil.
This is corrrect. To expand on it a little bit, here are the "options" for "renewable" plastics.
Bio-based plastics: These are plastics basically made from sugar cane, which isn't necessarily "good" for the environment. Plenty of rain forests have been sacrificed in favor of sugar cane farms. Anytime you use a biomass-based feedstock, there is also a lot of waste because certain components like lignin are pretty much still unusable. In theory, you can make just about any plastic from biomass, but some plastics are more heavily favored over others. And not just any plastic is a good substitute for polyethylene.
Mechanical recycling: This is only applicable for certain plastics and specific applications. Plastics cannot be recycled an infinite number of times because the mechanical properties of the material start to degrade. Also, mechanically recycled plastics are not allowed in certain applications (ie, some food packaging and medical devices).
Chemical recycling: This method relies on chemically breaking down plastics like polyethylene and polystyrene into their "building block" components. For example, you can use a solvent to break down polystyrene and the resulting mixture can be reused to make more polymer. Polyethylene can be heated to high temps (in a process called pyrolysis), which breaks the polymer compound into a mixture of carbon compounds that can be separated into various fractions (light gases, naphtha, oils, and waxes) and put back into a refinery or chemical plant.
The problem with mechanical and chemical recycling (and bio based material, if you want to utilize waste biomass feedstock) is feedstock logistics and transportation.
Plastic waste (and waste biomass) isn't nearly as energy dense as crude oil or even natural gas. You also have the issue of trying to collect waste materials (if you're talking residential waste, this is no small feat), and transporting the waste to large processing facilities where they can be sorted and then pyrolyzed. The facilities have to be large to be economical. Pyrolysis also consumes a lot of energy, and the "environmentalists" don't like that, either.
As it stands right now, collecting and processing waste plastic is expensive and inefficient.
Ultimately, in all of these options, you will have so supplement to some degree with virgin, fossil-based plastics.
You also have a very vocal movement in Europe saying that they will not accept chemical recycling because it still relies on fossil fuels. They don't seem to be satisfied that chemical recycling will reduce the consumption of fossil fuels; they want to eliminate the use of them completely. Also, they don't seem to understand that existing plastics can not be recycled an infinite number of times.
Also, certain biobased plastics, depending on how they are made, are just as bad for the environment if they just end up in landfills or the ocean. Polyethylene doesn't degrade any better if it's made from sugar cane or natural gas.
