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Sat Oct 5, 2019, 07:59 AM

Impact of Common Plastics on Cellulose Pyrolysis

The brief communication I'll discuss in this post is this one: Impact of Common Plastics on Cellulose Pyrolysis (Shogo Kumagai et al Energy Fuels, 2019, 33, 6837−6841)

Recently, in considering the options that future generations might have to address our willful destruction of our planet's biological infrastructure, in particular its land and seas, with the land thrown in for good measure, I have been considering the case of supercritical water oxidation of seawater driven by nuclear heat. Because salts are largely insoluble in supercritical water - water which is at a temperature greater than 373C and a pressure over approximately 22 MPa - and because seawater, particularly in its upper layers, contains the bulk of its biomass, the bulk of microplastics, as well as a much higher concentration of carbon dioxide than is in the atmosphere, such oxidation has considerable appeal at addressing climate change and actually removing carbon dioxide from the atmosphere as well as providing clean and sustainable fresh water.

On an industrial scale over a period of a few generations, it might serve to restore the oceans while providing important materials, water hardly being the only one of interest. (Phosphorous and uranium are others.)

I've been catching up on some back reading and filing of scientific papers, and came across this interesting little communication that is somewhat relevant to the case, and thought I'd note it.

Note that the work described here is also relevant to the case of the use of land based destruction of municipal waste and the capture of CO2 from land based biomass including that which is not food.

From the paper's introduction:

During pyrolysis, heat alone can simultaneously cleave several chemical bonds in polymeric materials.1−3 This method is advantageous for the treatment of mixtures that cannot be physically separated and recycled.4,5 Therefore, in this study, we focused on cellulose/plastic mixtures. Synergistic interactions were investigated during fast co-pyrolysis at 500 C of binary mixtures of cellulose with plastics, such as polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET). PS addition increased the yield of levoglucosan (LG) from cellulose by 3.5 times; PVC catalyzed LG dehydration to produce levoglucosenone; and cellulose enhanced the production of gaseous and liquid aliphatic hydrocarbons from PE and PP and liquid aromatic hydrocarbons from PS. These synergistic effects facilitate the elucidation of the complemental co-pyrolysis mechanism, allowing for the prediction of pyrolysis products and maximization of the recovery of useful fuel and chemical feedstock from cellulose and plastic composite materials. Recently, lightweight reinforced resins containing cellulose-rich plant fibers have received research attention as construction and automotive materials.6,7 The forecasted production of natural fiber composites in the European Union (EU) in 2020 has almost quadrupled that in 2012.

Pyrolytic interactions, often called synergies, during the copyrolysis of lignocellulosic biomass and plastic are of widely recognized importance...

...Because these plastics decompose through radical chain mechanisms,12−14 radical interactions during copyrolysis have recently been studied by employing an electron spin resonance spectrometer featuring a novel heating unit.11 However, the hydrogen exchange ability and the radical interaction mechanism depend upon the plastic type, and the influence of various plastics on cellulose pyrolysis and vice versa remain unclear. The pyrolysis of other polymers, such as PVC and PET, progresses via radical and ionic reactions...

...Thus, herein, we investigated the impact of the five most commonly used plastics, viz., PE, PP, PS, PVC, and PET, on cellulose pyrolysis and vice versa by employing the yield difference factor (YD; eq 1) and the difference from the estimated weight fraction [Di (wt %); eq 2]. Pyrolysis of each sample and co-pyrolysis of binary mixtures of cellulose and each plastic (1:1 weight ratio) were carried out at 500 C in a horizontal quartz tube reactor (Figure S1 of the Supporting Information). Detailed experimental information has been summarized in the Supporting Information...

The simple equations:

The supporting information of the paper is probably open sourced, should one be interested.

The table shows what they found:

PVC, unsurprisingly, produces a fair amount of HCl gas. This is problematic, although it may prove useful for the recovery of metals from municipal waste.

Note that these results are at 500 C. Higher temperatures, accessible by nuclear means, may give a different distribution of products.

The chars may have many uses, particularly in the treatment of metal contaminated waters, and inasmuch they represent sequestered carbon, offer this and other advantages.

Have a nice weekend.

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Reply Impact of Common Plastics on Cellulose Pyrolysis (Original post)
NNadir Oct 2019 OP
sir pball Oct 2019 #1
NNadir Oct 2019 #2

Response to NNadir (Original post)

Sat Oct 5, 2019, 04:45 PM

1. Meh, pyrolysis is handy for known feedstock

But for mixed trash, combustion with appropriate management of the waste gases is a better idea IMO.

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Response to sir pball (Reply #1)

Sun Oct 6, 2019, 08:45 AM

2. The situation you describe is often advertised currently as so called "renewable energy."

There is a claim that the waste gases are "appropriately managed" but this, like the claim that this is "renewable energy" is literally garbage.

Anything that possesses a smokestack is not "appropriately managing" waste gases. This includes the carbon dioxide waste gas.

It is not technically feasible to contain these waste gases for eternity, and I note that combustion, even in the presence of all sorts of scrubbers, is roughly responsible for 7 million people per year, with slightly less than half of these deaths attributable to biomass and waste.

The grand highly advertised German "renewable energy" program involves far more waste combustion than the widely advertised solar and wind lipstick on the combustion pig. Here is what the German program for "renewable energy" involves:

2019 IEA Electricity Information Overview

High temperature pyrolysis, depending on temperature, can operate entirely without the use of a smokestack, since all of the gases are designed to be recovered, and, has been demonstrated at least at lab scale, put to use in their entirety.

While this paper describes the effect of individual components, it is useful to utilize it as an indicator of a mixed waste profile.

Burning waste is killing people, whether the Germans call it "renewable energy" or not.

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