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Author: Subject: sulfuric acid accident
condennnsa
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[*] posted on 20-4-2010 at 22:43
sulfuric acid accident


Hi. I had an accident. I bought 35% sulfuric acid as battery electrolyte, it came in a PET bottle. I boiled it down to about 30% the initial volume, and put it back in the same bottle, thinking it was perfectly safe. Put it on a shelf, over some clothes and other stuff, and went out. When I came back home, 5 hours later, the pet bottle was dissolved, and all around a black goo . the sulfuric acid dripped on everything, I had to throw away most of my clothes, burned right through them. I am not going to store conc. sulfuric acid in PET, but I just want to understand what happened. I have read much on the internet on sulf acid storage, and didn't see any mention not to store it in PET.

How come that at 35% conc, the PET help up just fine, but the concentrated acid dissolved it? Is it because the acid tried to get water out of the plastic? ( about the famous H2SO4 affinity for water) thanks!
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sparkgap
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[*] posted on 20-4-2010 at 22:58


Most probably the ester linkages in PET being hydrolyzed by the concentrated acid, ester formation being in fact an equilibrium reaction in concentrated acid. Your storage of concentrated acid in the bottle pushed the equilibrium to the reactant side.

it is better practice to store such concentrated acids in polyethylene/polypropylene or glass. Hopefully you have learned your lesson.

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Xenoid
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[*] posted on 20-4-2010 at 23:05


Hmmm... you should have read this thread;

http://www.sciencemadness.org/talk/viewthread.php?tid=9979#p...

or any of the numerous other references on this forum that warn against storing strong acids and alkalis in PET bottles.
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JohnWW
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[*] posted on 21-4-2010 at 01:03


Quote: Originally posted by sparkgap  
(cut) it is better practice to store such concentrated acids [H2SO4] in polyethylene/polypropylene or glass. Hopefully you have learned your lesson.
Other possibilities could be bottles made from or lined with: polypropylene, PVC, PTFE, PVF. If mechanical strength against breakage, particularly for industrial quantities, is required, low-expanding glass (e.g. borosilicate) would be only suitable as a lining for a steel vessel; but better still, something like monel (an alloy of mostly Cr, Ni, and Mo) is preferable. One of the above plastics could also be used as a lining for a steel or alloy vessel if it is not subjected to heat.
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hissingnoise
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[*] posted on 21-4-2010 at 03:48


The protective coat on Merck safebreak bottles is PE; the cap (with teflon insert) is also PE and these bottles are suitable for oleum, fuming HNO3 and 70% HClO4.
PE obviously has considerable resistance to oxidising acids.
Glass IMO, is essential for all strong acids.
Inserts for plastic caps can be cut fron teflon sheet or if they're small, from several thicknesses of plumbers tape.
Containers made of PE would likely break down over time.

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gnitseretni
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[*] posted on 21-4-2010 at 08:20


Use PE or PP. Most plastic household containers are made of these plastics so you shouldn't have a problem finding one next time.
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condennnsa
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[*] posted on 21-4-2010 at 09:55


I guess I won't take risks again with plastics, be it PET, PE , PP whatever, after having to throw away 400$ worth of clothes. I'll go with glass jars and bottles.

Thanks for the replies, but I still don't understand what exactly happened. What is so different in Polyethylene terephthalate that sulfuric acid reduced it to nothing, yet PE and PP have no problem with it?
What do you guys use to store conc. H2SO4?
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DJF90
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[*] posted on 21-4-2010 at 10:22


PET is a polyester, and as such is susceptible to hydrolysis by strong acids and alkalis. PE and PP are hydrocarbon chains, and as such there is no easy point of attack for the acid/alkali. Basic organic chemistry really. I would use glass bottle with teflon liner to store conc. acids.
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rrkss
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[*] posted on 21-4-2010 at 10:28


I use only glass to store my concentrated acids and store them in small quantities (100 mL amber glass bottles with a polycone cap) My dilute acids I store in HDPE containers and have not had any problems. I would never store anything acid or alkaline in PET bottles because the esters can easily by hydrolyzed as your accident showed you.

To answer you question PET is made by reacting an organic alcohol to an organic acid. These alcohols and acids happen to be at both ends of the monomer causing it to form a long chain polymer in the process driving out water as it goes along. This reaction is catalysed by a strong mineral acid such as sulfuric acid.

One thing about many organic reactions is that they can run in reverse when the conditions change. In your case your PET bottle was all product and had no alcohol or organic acid monomers available so when you supplied the strong sulfuric acid catalyst, you reverse the ester formation reaction and destroyed your plastic bottle in the process. HDPE is made by a process called free radical polymerization is is not subject to this specific way of degradation.

[Edited on 21-4-2010 by rrkss]
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[*] posted on 13-8-2012 at 19:25


I once stored 95% fuming nitric in a hdpe bottle, put it in my safe for about a week...Needless to say when i opened up the safe the acid had ate through the bottle, corroded the safe and ate the carpet up beneath. Now if i store it its in a 1L erlenmeyer with a glass stopper.
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blogfast25
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[*] posted on 14-8-2012 at 04:30


Ok, that wasn't smart condenssa but I'm still a bit surprised at the speed with which the acid chewed up the PET. Thanks for your candour and sorry about your clothes... :(



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