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Topic: Hydrochloric acid and PE  (Read 5649 times)

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Offline zipstor

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Hydrochloric acid and PE
« on: July 22, 2010, 10:22:48 AM »
Hi there,,

I dont know if this is the right place to ask this question but if maybe someone can put me in the right direction of where to ask, or elsewhere would be fine.

I'm working on an electrolyser project and was on the process to prime the electrodes with hydrochloric acid. My container is made of polypropylene (PP) and black polyethylene (PE). I filled up the electrolyzer with the acid and turned it on.

The acid went black in a few seconds and when i purged the unit, i could see some little lumps of black stuff, that i suspect to be the PE that has been dissolved in the process.

My problem is that i chosen PE because it was satisfactory on a chemical resistance chart... So I may have missed something... I dont understand what happened... Maybe something to do with the current? 60A DC under 12v was involved.

Any idea is welcome.

Thanks in advance.

Offline Japo

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Re: Hydrochloric acid and PE
« Reply #1 on: July 28, 2010, 09:17:30 AM »
What do you mean "black" PE? If it's black it must be dyed and it's the dying substance that's being washed into the acid. Use colourless PE, that is PE and nothing more.

I have just been using HCl 37% in PE. We contain it in PP vials every day. Nothing ever happened, and I heated the PE to 80ยบ C (the bottom of the bottle did bend a little).

I don't think the current across the solution should do anything to the PE. And the density of the PE affects the mechanical and thermal properties but not the chemical resistances I think. Don't take my word on these.

Offline Enthalpy

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Re: Hydrochloric acid and PE
« Reply #2 on: January 13, 2011, 01:48:22 PM »
12V is far too much for electrolysis. You get unwanted reactions, in addition to much heating. To increase production rates, it needs many flat electrodes close to another, but at a low voltage.

Polyethylene uses to be very inert, and its colour is mixed in the whole mass. My bet is that polyethylene has resisted to the conditions (try to replace with pure white one) but your electrodes got corroded. Avoiding that is difficult and requires adequate materials and current densities.

Offline Cavalier

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Re: Hydrochloric acid and PE
« Reply #3 on: January 13, 2011, 07:37:20 PM »
A follow up to this question.  I am trying to develop a cooking process.  I stuck in 2 stainless steel plates in a PE box.  I got the same black color deposits.  The material is a very viscous organic material, and it did not get heated.  I used DC, 24 V, 500 A connection.  There were a lot of black substance formed.  The material did not get heated up.  I need to get the material steaming hot.

Can I use AC?  Will this help heat up the material?  How can I increase the heat or cooking process?  I have access to an external source of 380 Volt, 3 Phase.

I would really appreciate any feedback on this.  For those who are writing in this forum.  Thank you. Thank you.  You are helping, you have no idea.

Raju


12V is far too much for electrolysis. You get unwanted reactions, in addition to much heating. To increase production rates, it needs many flat electrodes close to another, but at a low voltage.

Polyethylene uses to be very inert, and its colour is mixed in the whole mass. My bet is that polyethylene has resisted to the conditions (try to replace with pure white one) but your electrodes got corroded. Avoiding that is difficult and requires adequate materials and current densities.

Offline Enthalpy

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Re: Hydrochloric acid and PE
« Reply #4 on: January 14, 2011, 09:47:42 AM »
Why not a stove?

Or a heating resistor plunging in the liquid, if necessary, but then an insulated one? For more power, you may consider a gas heater, depending on the application.

If I got it properly you're injecting current in the liquid to heat it, and then (beyond the acute risk) your electrodes will corrode. At 380V it's likely that any electrode metal corrodes.

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