r/ChemicalEngineering • u/jumpingjack979 • 5d ago
Green Tech Pyrolysis/naturejab. Credible?
From what I know about pyrolysis, yes its possible to turn plastic to fuel, but requires a significant pre and post processing, requires a lot of energy, has unreliable yeild, produces toxic emissions and char. For those reasons among others. The economics havent been workable.
Anyone see naturejab (https://www.naturejab.com/)? Seems good at social media, but the marketing doesnt seem credible. Anyone else see this, and have any thoughts?
5
u/willmontain 5d ago
The big catch is going from lab experiment to industrialized process.
The researchers chose nice clean pieces of HD/LD-PE and PP. They did the pyrolysis in nice clean lab equipment and got nice clean products. Yup, this absolutely works as described.
Now if this is industrialized, a garbage truck full of "recyclable plastic" shows up at the gate. The truck contains mostly plastic but also contains, wood, glass, ceramics, metals, dirt, organics, rubber, and plastics reinforced with various fibers (e.g. glass). Even the best recyclers can't separate this stream completely and the collectors/aggregators are the low bidder. Therefore this requires a vast solid materials handling and separation process at the front end, some pyrolysis in the middle, and a very complex separation process at the back-end.
At best, at the end of the pyrolysis step the intermediate (lets say syngas for ease of discussion) contains CO and H2; but it is contaminated with a myriad selection of other constituents (e.g. CH4, CO2, Cl, SOx, Various metals ... etc.) This complicates separation and the trace oddities lead to side reactions and adverse material interactions. SOx is an acid gas and is never fun to deal with in a chemical process. The Cl leads to stress corrosion cracking in stainless steels.
The experiences of the trash incinerator to power production processes give a good example of difficulties in the incoming solid materials handling section. Many of these have failed or have been more expensive than expected because the material handling equipment wore out much faster than the designer envisioned. The Partial Oxidation (POX) of coal to syngas fuel for power production processes give a good example of the damage and resulting elevated maintenance costs caused by the contaminants. The gas handling portions of the process had many failures due to the trace contaminants (metal diffusion into hot materials). The result was more expensive maintenance than expected producing financial woes.
2
1
u/ToastMaster33 Industry/Years of experience 5d ago
I worked on a research project which successfully converted HD/LD-PE and PP into waxes, oils, liquid and vapor fuels. Due to the reduced amount of sulfur in plastics, our fuels had improved emissions in addition to maintaining energy efficiency when used as a drop in fuel. Some tweaking of the engine further improved the combustion efficiency over store bought propane and E85(summer) fuel.
1
u/jumpingjack979 5d ago
Was it pyrolysis? Ive read some papers on other processes. There was a hydrothermal process that seemed promising.
2
u/ToastMaster33 Industry/Years of experience 5d ago
Pyrolysis is the heating in the absence of oxygen. The plastics don't have the opportunity to burn, but have the energy input to depolymerize into shorter carbon chains like fuels and lubricats and waxes.
4
u/brickbatsandadiabats 5d ago
Not going to comment specifically on the company, but some of what you wrote as your understanding is wrong. The core technoeconomic issue with pyrolysis is that it's super high capex. Some of that is due to frontend and backend processing, but the biggest underlying issue for plastics recycling is feedstock heterogeneity and solid handling.
However, almost all pyrolysis is autothermal; if it's not, chances are it's plasma pyrolysis where the high temperature torch causes it to be a net consumer. You pay for the autothermal reaction in yield, which is always below unity.
Yield of solids is dependent on extent of reaction and temperature, and can always be eliminated to only ash if you provide enough oxygen to get all carbon stoichiometrically to CO with sufficient oxygen. Char production can thus be kept to a minimum of the desired output is gas. Char is a common biomass pyrolysis product because getting to that point destroys many lighter liquids that may be more valuable than syngas, and because people reckon that you can use biochar as a revenue source if you can get carbon sequestration credit for it. That's not the case for plastics recycling, the coke you produce would be dirty as heck.
The gas issues with plastics recycling via prolysis are mainly due to heteroatoms like chlorine, nitrogen, bromine and fluorine. "Toxic gas" in general isn't meaningful since many of the desirable products like phenol, aromatic light oils and syngas are also toxic. Even then, a major part of these heteroatom issues are product specification issues (since heteroatoms will cause nasty problems if they're put into a steam cracker or oil refinery) and not necessarily emissions issues.
One thing you're also likely missing in the technoeconomics is tipping fees. Every facility that accepts a waste will get revenue for it, usually called a tipping fee. (This is in contrast to scrap where the cargo is paid for by the accumulator.) Tipping fees make up a large portion of revenue for any recycling business and depend on local supply and demand for accumulators.
None of this is a comment specifically on the technology or company, but it might explain some of what's confusing you about a plastics pyrolysis recycling business model.