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Offline AdiDex

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Help with pyrolysis
« on: February 23, 2018, 01:06:47 AM »
My one of the teacher asked me to do pyrolysis of polyethene using very simple apparatus. At First, I don't think it gonna work. But still, She is insisting me to find a method to do it.
I need to extract long chain hydrocarbons which are in the liquid state at room temperature. All I have a simple condenser and few connectors.


She is afraid that accident will take place. I have a huge doubt, pyrolysis is done in the absence of oxygen. I have no way to remove oxygen that is present in the apparatus. I don't think this process is even possible with this apparatus. My college doesn't have a huge budget so I have apparatus problem. can somebody give me their advice on this topic?

Offline clarkstill

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Re: Help with pyrolysis
« Reply #1 on: February 23, 2018, 02:46:27 AM »
That piece of glassware with the bulb half way along is a drying tube, not designed for this purpose at all.

What you need is a quickfit receiver adaptor:

http://www.scilabware.com/Adapters/Receiver/Plain-bend-delivery-receiver/p-1-3-9/

But more generally, I agree with you that this may be an ill-fated venture. From googling it, you need to heat to 300-500C to pyrolyze polyethylene, and if you are unable to exclude air/oxygen you will undoubtedly just burn it at this temperature. I think your teacher needs to wise up and be realistic about what's possible with your limited equipment and resources. Whatever you do, please be careful working with such high temperatures. Make sure you do a risk assessment, and that someone more experienced is present when you are conducting the experiment.

Offline Arkcon

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Re: Help with pyrolysis
« Reply #2 on: February 23, 2018, 08:15:02 AM »
As was said, both by you and by clarkstill:, the equipment you have is not the best one suited for the task.  I think the procedure is still possible, just not quantitatively efficient.  People have conducted pryolysis since pre-Iron Age technology, to make carbon from wood -- yes, some oxygen gets in, and some material burns, but when the oxygen is depleted, even locally, pyrolysis is what you get.

Since you can see a gap, you should certainly be working in a fume hood, and keep it as closed as possible for maximum exhaust (which is not always completely closed -- follow hood instructions and/or determine maximum exhaust position with light paper.)

This really depends on what you need to do:  do you need a small sample of possible pyrolysis products?  Then you may get something.  Do you need to determine possible products of a poorly done pyrolysis -- aka, environmental products of polystyrene burning in a trash heap?  Then this is almost exactly what's needed.  You make a little and then analyze them? 

What actually is the process you need to perform, and why?  If the teacher wants you to produce the products of pyrolysis, to have a quantity of the pyrolysis products, can't they just be purchased?

Here's the real help that you really need.  Write down, on paper, what you need to do.  Write how this rig will allow you to do it.  Also write down, how this rig won't allow you to solve the problem at hand.  And the safety and environmental risks you face.  Consider making a table of pro and cons.  Then present this document to the teacher.

Listen, in the real world, academia or industry, no one likes any one who just sputters "No, it can't be done."  Heck, I don't like it when people on this forum show up and say, "I can't do thins."  And people don't like being told by me, "No, you can't make drugs or bombs in you basement."  The entire point of any intellectual discourse is to support your point of view with evidence -- or at least proof that you've thought about the problem carefully.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline wildfyr

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Re: Help with pyrolysis
« Reply #3 on: February 23, 2018, 09:14:34 AM »
If you could get a stream of nitrogen gas into the system it would minimize the oxygen

Offline Enthalpy

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Re: Help with pyrolysis
« Reply #4 on: February 23, 2018, 12:33:28 PM »
As a teen, I conducted pyrolysis (of wood) in a test tube, with a holed rubber stopper and a fine exit tube. Heated the bottom of the test tube on a spirit lamp, without caring about the little initial oxygen. So it's feasible without big subtleties. It depends on how accurate a temperature you want: the amount of liquid products depends on it.

Similar attempts are done industrially in big ovens, to obtain liquid fuels from waste polyolefin items, or even (yuk!) from waste tyres.

The main difficulty is to clean the glassware afterwards. You may have more luck with polyethylene. With wood it's yuk. You might consider metal tubes instead of glass, and throw them away after the experiment.

Mind about the toxicity of the produced gases. Polyethylene is more benign, but wood and coal produce bad molecules.

Offline zarhym

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Re: Help with pyrolysis
« Reply #5 on: February 23, 2018, 10:07:33 PM »
I did a reaction to synthesis cyclopentadiene by pyrolysis of its dimer.
I would recommend these two receivers.

http://www.scilabware.com/product.asp?strParents=1,3&CAT_ID=3&P_ID=10
http://www.scilabware.com/product.asp?strParents=1,3&CAT_ID=3&P_ID=13

Both of them has vented bend. You can attach the vent with either nitrogen balloon or vacuum.
The second one can be used for fractional distillation. Make sure you grease the joints to achieve good airtightness.

These glassware are not very expensive. The price is normally less then $5/piece (in China).

Offline AdiDex

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Re: Help with pyrolysis
« Reply #6 on: February 24, 2018, 12:52:01 AM »
Update
She has ordered this connector. It will cost around 8$ .
« Last Edit: February 24, 2018, 01:07:40 AM by AdiDex »

Offline AdiDex

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Re: Help with pyrolysis
« Reply #7 on: February 24, 2018, 01:06:39 AM »
I think your teacher needs to wise up and be realistic about what's possible with your limited equipment and resources. Whatever you do, please be careful working with such high temperatures. Make sure you do a risk assessment, and that someone more experienced is present when you are conducting the experiment.
In my college , most of the faculty has very poor experimental skills. In most of the colleges of india, lab saftey is almost non-existing except for few noble institutes. These teachers only have experience with such experiments which are in curriculum. This is my last semester in this college . I am almost sure that she has never performed pyrolysis. Her earlier idea was even more flawed . I pointed out that this will goimg to never work due to constant supply of oxygen. Then she asked me to make everything airtight . later she realised in can cause rupture in apparatus due to pressure . Then she kept finding another method.

Now she has planned , at the receiver end of the to put that connector that I just posted . She has not taken consideration of nitrogen supply and vacuum pump yet.

Offline zarhym

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Re: Help with pyrolysis
« Reply #8 on: February 24, 2018, 01:19:22 AM »
By the way, make sure you do this reaction in a fume hood.
The fume may escape and cause problems.


Offline AdiDex

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Re: Help with pyrolysis
« Reply #9 on: February 24, 2018, 01:22:44 AM »
Since you can see a gap, you should certainly be working in a fume hood, and keep it as closed as possible for maximum exhaust (which is not always completely closed -- follow hood instructions and/or determine maximum exhaust position with light paper.)
We have very primitive fume hoods , it's nothing more than closed window with two primitive exhaust fans .

Quote
This really depends on what you need to do:  do you need a small sample of possible pyrolysis products?  Then you may get something.  Do you need to determine possible products of a poorly done pyrolysis -- aka, environmental products of polystyrene burning in a trash heap?  Then this is almost exactly what's needed.  You make a little and then analyze them? 

What actually is the process you need to perform, and why?  If the teacher wants you to produce the products of pyrolysis, to have a quantity of the pyrolysis products, can't they just be purchased?
.

I didn't know what is my goal till I made the setup of basic distillation apparatus . Then she said to me I have to do pyrolysis of Polyethylene . I pointed out that this will not work due to constant supply oxygen .  As far as I know her goal is to get heavier hydrocarbons which are in liquid state.
I have a question , which kind of toxic gases it can produce ? One of them can be CO , due to incomplete combustion of Polyethylene as the apparatus isn't oxygen proof.

It's my final semester in this college , so we have assigned some teachers , who will give us some extra experimental work. So she came up with this.
 

Offline zarhym

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Re: Help with pyrolysis
« Reply #10 on: February 24, 2018, 02:02:30 AM »
Very likely, the purpose of this reaction is to practice your experimental skill so that you can have something to put into your thesis.

Pyrolysis of polyethylene is a well-studied topic. The product of this reaction are gases, wax, liquid, aromatics and char. You can find the composition of the product in many literatures.

Since you are waiting for your glassware at this point, I would recommend doing some research about this reaction before you even start.

Here are some papers that may help you.

Pyrolysis Study of Polypropylene and Polyethylene in toPremium Oil Products
http://www.tandfonline.com/doi/abs/10.1080/15435075.2014.880146?src=recsys&journalCode=ljge20

Recycling and recovery routes of plastic solid waste (PSW): A review
https://www.sciencedirect.com/science/article/pii/S0956053X09002190

Recovery of hydrocarbon liquid from waste high density polyethylene by thermal pyrolysis
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322011000400011


After this experiment, you can compare the result with the literature. This may help you write your lab report or thesis.


Offline Enthalpy

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Re: Help with pyrolysis
« Reply #11 on: February 27, 2018, 09:44:10 AM »
[...] which kind of toxic gases it can produce ? One of them can be CO, due to incomplete combustion of Polyethylene as the apparatus isn't oxygen proof.[...]

Pyrolysis is very non-selective and produces a huge spectrum of compounds. Your chance is that the well-chosen reactant, polyethylene, contains only C and much H. This limits the toxicity of the products; pyrolysis of ABS, PMMA, PVC, natural substances... would release abundant acrolein, vinylchloride, cyanides an the like.

Expect alkenes as the main products of polyethylene pyrolysis, plus reaction products of these alkenes. They tend to be benign.

Though, some minor products are badly toxic, hence to be kept away even in small proportion. In any hydrocarbon pyrolysis, less so with your hydrogen-rich reactant, you can expect benzene and polycyclic aromatics, which aren't quite healthy, plus some nastier compounds. That's a reason enough to take reasonable precautions, without getting paranoid in the case of polyethylene. Serious precautions would be needed for workers pyrolyzing wood or coal regularly, or for a single pyrolysis of PVC.

You can estimate the maximum amount of produced carbon monoxide from the amount of air in your apparatus before the process and make your opinion. Since your pyrolysis will also release some non-condensible hydrocarbons too, you might set all the non-condensible gases alight, and get rid of the monoxide there.

The pyrolysis of polyolefins into liquid fuels is much studied precisely because it's easy and not so nasty. Toxicity arises mainly because polyolefin scrap contains other plastic items of PVC, ABS, PET... which are the major contributors to toxic products even if their proportion is small. The reason for polyolefin pyrolysis is (uneasy) economics rather than ecology, since pyrolysis creates more nasty compounds than the inert polyolefins, and does not tackle the polymers more worrisome than polyolefins.

My suggestion: search for papers.

Offline maruthicleaners

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Re: Help with pyrolysis
« Reply #12 on: May 30, 2018, 10:12:44 PM »
Hi Sir, I'm planning to start up a small waste plastic pyrolysis reactor in my village. I need a possible run through for the process. My idea is to process automotive diesel and petrol. Since I'm not a chemistry guy Ill need your help. My village is generating hell of a lot of plastic waste and I came up with this idea. Your assistance would be appreciated

Offline Enthalpy

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Re: Help with pyrolysis
« Reply #13 on: May 31, 2018, 04:01:37 AM »
Welcome, Maruthicleaners! First thoughts about your project:

How will you sort out the plastic waste? You can pyrolyse polyethylene and polypropylene to fuels, but PVC and ABS must be eliminated first, almost perfectly, as these would create badly toxic compounds.

Pyrolysis will make fuel and a big proportion of by-products. These are ugly, similar to tar, and they stink. They are worse than the plastic waste. How will you get rid of them?

Did you estimate how much polyethylene and polypropylene waste your village produces per year? Only a fraction will convert to fuel, and fuel is very cheap.

You can make a first trial in a metal tube over a wood fire to get an idea of how dirty the operation is.

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