polimer conversion 2

[19870603]

hello I m burak basdag,we have a project in Germany and we deal with effect of macro mixing of free radical polymerization of methyl methacrylat and AIBN..this topic is new nobody cares before time ...We have a graphs about conversion-time as you see and when we make cross slopes we are getting a time,what does mean this time.Anybody help us or offer a source for us!!!?

thank you

BURAK BASDAG

 

[ajs1972]

Hello Burak:

What kind of reactor will you use?

According to the graph, I believe that is a semi batch reactor and that point is at the end of monomer feeding.

This point is to calculate the conversion at the end of monomer feeding and to evaluate if the monomer feeding time (and monomer flows of course) are correct and don´t compromise the safety in case of low values of monomer conversion.

Regards.

 

[FMJalink]

Burak,
It is some time ago that I made this type of calculations. To my opinion the conversion-time graph you added shows the percentage of substance X converted.

Normally such a reaction is given in a scheme like: µa . A + µb . B --> µp . P + µq . Q, where:
A is your one of your reactants: Methacrylate or AIBN;
B is the other reactant;
P is the desired reaction product;
Q is an undesired reaction by-product; and
µ is the stoichiometric coefficient.

The conversion shown in your graph can be: (1) the absolute conversion or (2) the relative conversion.

The absolute conversion grade ?x = |Wxo – Wx|, where x stands for the substance, Wxo is the mass fraction of substance x at time 0 and Wx the mass fraction of substance x at the specific time.

The relative conversion grade is ?x = |Wxo – Wx|/Wxo. The X can be the A or B of the schematic above.

You can see in your graph that it takes a long time until all X has reacted and full conversion has been achieved. For this reason normally the time of 50% conversion is used as indication of the conversion time.

The time ?, being the intersection of slope of the curve at t = 0 sec and full conversion gives also an indication of the conversion time in relation to the percentage of converted reactant. The percentage at time ? depends for simple reactions on the reaction order, reaction rate coefficient and initial concentration, but for not simple reactions this is more complicated.

Now to the more important part of your mixing problem. You mentioned macro mixing in your post, which ideally can be seen as having “lumps” of pure A and pure B in your reactor. These lumps do not “lumps” do not mix with each other and the reaction takes place on the boundaries of these “lumps”. Just without going into details it will be clear to you that the size of the “lumps” and their contact rate will have a large impact on the time required to achieve a specific conversion rate. Especially when one of the reactants is present in abundance and this would lead to more rapidly to the not desired product Q, is the mixing very important.

There are several good books on this subject. Some of which I used myself are:
• Chemical Reactor Design and Operation
• Chemical Reaction Engineering
• Chemical Reactor Analysis & Design

But maybe you are better of with a reference to (partially) free readable books. Just type “Chemical Reactor” in Google books, and you will find a lot of information.

 

[19870603]

Thank you for reply and I can say the reactor is semi batch reactor,I didnt find in this book that you offer ,what does it mean in this time exactly,I need to know what does it mean this time for example ideal time or decay time for AIBN something like that can you offer another source or can you send a part of your calculations that are similar like this
I send my excel that I have from experiment


firstly I want to give a detail,Our project is "effect of macro mixing of free radical polymerization of Methyl methacrylat(Solution

polymerization)",solvent is xylene and initiator is AIBN.we have a Taylor coutte reactor and we prepare mass percentage 80 % xylene ,

20 % MMA and 200 ppm AIBN and reaction is started and we wait for 15 hours and after 15 hours we give 70 ml fresh monomer(with 0,1 %

wt AIBN) in reactor and we observe the macro mixing of this fresh monomer in reactor.Macro mixing is mixing between all vortices that

occurs because of rotational turning.As you see in graph conversion is % 54 at the start of giving fresh monomer after that it decrease

because we give fresh monomer after that it has been increasing then we wait nearly 300 minute and we take a sample every 30 minutes

as you see graph is sigmoidal curve and we want to learn the what does mean time that I send you before time.firstly graph increase but

after a point I think that because of gel effect conversion decreases or almost constant.

I add x-t curve and in attachment!!!

Thank you for everything

 

[jmw]

Not sure if any of the following helps at all as I only incidentally became involved in methyl methacrylate polymerisation when looking at finding a better means to control the reaction.
This was with a company near Strasbourg (about 12-14 years ago?).

I seem to recall that the polymerisation reaction initially required heat to initiate it and that it then became exothermic.
As I recall the batch reaction took around 2 hours but there was a very tight window during which to quench the reaction.

The approach adopted originally was to take frequent samples and measure the viscosity (a function of molecular weight) using a fairly crude but quick cup method and plot a reaction graph.
The chances of capturing the end point through sample and test was pretty slim so the graph was used to try and predict the end point in time and to quench the reaction at that time.

I believe the success of this method was limited. About 10% of the time they'd get it wrong and the resultant material would be reworked or included in other batches.

Now what happened next depended on the manufacturing process. I'm not sure if this was the final end point i.e. whether they stopped polymerisation or merely interrupted it and completed it in the manufacture of the final product.

ICI, I recall, used continuous pipeline production rather than batch production, but end point spotting with online viscometers made a very considerable improvement in the success rate.

JMW

http://www.ViscoAnalyser.com

 

[FMJalink]

Burak,
In your first post the question seemed quite general, but now you are asking something that could be part of a degree project on a university. KIT isn’t it? Why not first ask your professor?

I am not an expert on the reactions of MMA, nor am I an expert on Taylor Couette Reactors.

If I understand your question correctly, you want to know the meaning of the sigmoidal curve you see in the conversion grade. It means that you can under the circumstances of these tests not achieve a higher conversion grade. Something is limiting the conversion: the reaction or a transfer.

I presume you did first investigate:
a) The reactions of MMA with the by you mentioned concentrations, and
b) The Taylor Couette vortices in your reactor at the applicable viscosities (without reactions).

In your base composition you achieved a conversion degree of 57.2% after 15 hours. Was the reaction “dead” at that time? There after you added new 70 ml MMA monomer (with 0.1 % wt AIBN). I did not do the calculations, but makes this the concentrations different? With this addition you achieve a conversion grade of 61.2 % after only 6 hours. Is this conversion grade homogeneous or largely to be accounted for a higher conversion in the newly added monomer?

In order to determine what is limiting your experiment you can do what you tried: ask someone else, or start to investigate step by step the problem:
a) Maximal achievable conversion rates in relation to solvent and inhibitor.
b) Flows and vortices in the Taylor Couette reactor in relation to viscosity.
c) Mixing in the Taylor Couette reactor without reaction in relation to viscosity.
d) Determine the conversion rates, as you did, for specific concentrations and temperatures.
e) From these data you can deduce enhancement of mixing/mass transfer due to the reactions, but that is probably not what is requested in your project.

Success with your project,
Frank Jalink