The Naked Scientists

The Naked Scientists Forum

Author Topic: How do methyl formate antique refrigerators work?  (Read 4457 times)

Offline ChrisJ

  • First timers
  • *
  • Posts: 4
    • View Profile
Hello,

I am part of very small group of people who are into collecting and restoring historic monitor top refrigerators.  These units use either sulfur dioxide or methyl formate as a refrigerant depending on the year and model.  The methyl formate units were only produced for two years (1933-34) and have some problems which we are trying to understand.

According to patents we found it appears the methyl formate breaks down when moisture is present.  It also seems they were concerned about it breaking down due to high temperatures inside the compressor.  Some of these units have been running for 80 years without a complaint while many have problems.

Is there anyone on here who may be able to help us understand what may be going on and possible things we can do to avoid it?

I can post many more details but want to see if anyone can help before proceeding.  It has been near impossible to find anyone who has any knowledge of methyl formate in general much less it being used as a refrigerant.

Thank you for your time.
Chris J



« Last Edit: 01/11/2013 22:16:43 by chris »


 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8667
  • Thanked: 42 times
    • View Profile
Methyl formate isn't stable in the presence of water. It hydrolyses to give methanol and formic acid.
At high temperatures it will decompose to give methanol and carbon monoxide.
 

Offline ChrisJ

  • First timers
  • *
  • Posts: 4
    • View Profile
Thank you for responding!

Can you tell me at what approximate temperature does methyl formate decompose to give methanol and carbon monoxide?  Is it something low like 100C?

 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8667
  • Thanked: 42 times
    • View Profile
It's hard to say for two reasons.
First, I don't know.
Secondly, the temperature at which something decomposes isn't usually well defined. It decomposes faster when it's hotter.
It might be fine at 100C for some science experiment that takes an hour- but  not for circulating through a fridge for ten years.
 

Offline ChrisJ

  • First timers
  • *
  • Posts: 4
    • View Profile
I think you may have helped me a lot.  I didn't realize time played a roll in it as well and it would explain why they (GE) had so much trouble figuring things out.

Being run times vary greatly on a refrigerator it could mean under most conditions its fine but if you get a really long run time on a hot summer day you're going to have trouble. 


Thank you!
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Would high pressure, or cycling between high and low pressures also affect the decomposition. 

The reaction with water consumes the water, so it would be dependent on the amount of water in the system.  The decomposition to carbon monoxide and methanol would not be quantity dependent.  However, is it possible that carbon monoxide reaction could be catalyzed by something else in the system such as formic acid?
 

Offline ChrisJ

  • First timers
  • *
  • Posts: 4
    • View Profile
Would high pressure, or cycling between high and low pressures also affect the decomposition. 

The reaction with water consumes the water, so it would be dependent on the amount of water in the system.  The decomposition to carbon monoxide and methanol would not be quantity dependent.  However, is it possible that carbon monoxide reaction could be catalyzed by something else in the system such as formic acid?

All of this is way above my head.
However, here are two patents GE took out in regards to methyl formate breaking down.  The first talks about adding alcohol to the system, the next seems to replace that with adding lard to the lubricating oil to prevent or reduce the amount the methyl formate breaks down.

newbielink:https://www.google.com/patents/US1854984?dq=methyl+formate&hl=en&sa=X&ei=ARJ0UsDIFYahsATe8IGIBA&ved=0CF8Q6AEwBw [nonactive]

newbielink:https://www.google.com/patents/US1920845?dq=methyl+formate&hl=en&sa=X&ei=ARJ0UsDIFYahsATe8IGIBA&ved=0CG4Q6AEwCg [nonactive]

Another bizarre problem we have found is the methyl formate or something in the system appears to eat away the valve seat in the float valve.  The float valve is the metering device in the system.  The same design float valve is used on sulphur dioxide machines and does not suffer any such damage or erosion.  We have been replacing the float valve with a simple capillary tube with great results.
« Last Edit: 01/11/2013 20:48:09 by ChrisJ »
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Re: How do methyl formate antique refrigerators work?
« Reply #7 on: 02/11/2013 06:12:26 »
It sounds like the bottom line is that wet methyl formate is bad.

Methyl formate is hygroscopic, or it can absorb moisture from the air.  Then methyl formate + water ==> acid (which then can damage your fridge).

Many chemical reactions are equilibria. 

CH3OH + CO ⇌ HCOOCH3

Adding extra Methanol may help push the equation to the right, and prevent the formation of carbon monoxide.

Even with the acid/water equation:

HCOOH + CH3OH ⇌ HCOOCH3 + H2O

A little extra methanol may also help push the equation to the right, and thus more water+methyl formate, and less acid.

HOWEVER, many alcohols also contain small amounts of water.  Thus, you may not wish to add wet methanol to a dry methyl formate.
« Last Edit: 02/11/2013 06:17:42 by CliffordK »
 

The Naked Scientists Forum

Re: How do methyl formate antique refrigerators work?
« Reply #7 on: 02/11/2013 06:12:26 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums