Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: BigD on 29/07/2016 14:21:28
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I have read about molasses mixed with water at about a 1:9 ratio being effective for rust removal. I have found very little information as to how this works however. One theory is that the molasses ferments and then changes into vinegar and the resulting acetic acid is the rust removal agent. If that is the case then why not speed up the process by adding yeast to speed the fermentation and then introducing air into the mixture to aid in the conversion to vinegar?
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... or just use vinegar?
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Vinegar is an option but an expensive one. I need approximately 30 to 40 gallons of solution to soak an engine block. 5 gallons of molasses cost me $9.12 at a feed store.
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You can get pure acetic acid on ebay, and dilute it with water. I see one entry* for 2 gallons of acetic acid for $80. This is enough to make 40 gallons of 5% acetic acid (vinegar). It might be more expensive than molasses, but I cannot imagine that putting an engine block in a tub of molasses could be a good idea. You might also consider reducing the amount of liquid used, and replace it with some elbow grease. You can rub it down with some vinegar-soaked rags. This will likely be cheaper and faster (just requires more effort!)
* http://www.ebay.com/itm/Acetic-Acid-Glacial-99-2-Gallons-8-Quarts/111246016230?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20131003132420%26meid%3Db835416b81294c1aa4217bead361d6a6%26pid%3D100005%26rk%3D3%26rkt%3D6%26sd%3D111053896384
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The reason I need to soak the entire block is that the lifters and consequently the cam are rusted in place. The hope is that the rust will be loosened enough to allow their removal. No amount of "elbow grease" is going to do that. As for " I cannot imagine that putting an engine block in a tub of molasses could be a good idea" the block and cam and lifters are all just cast iron. Posts on other forums describe soaking cast parts for months with no ill effects to the base metal.
What is getting lost here is that my original question was HOW DOES THE PROCESS WORK?. Instead of answering my question I get advice on what I should be doing differently. Unfortunately this is typical of many forum responses.
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Black treacle (which I think is essentially the same stuff as molasses) generates bubbles of gas when mixed with sodium bicarbonate.
That suggests that the material is acidic (and I trust you understand why I don't want to have to wash this goo off a pH meter).
Acidic materials will dissolve rust.
At least some treacle is treated with sulphur dioxide which is acidic and a reducing agent which would also help to remove rust.
The sugars etc in the stuff might also act as reducing and/ or complexing agents.
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Based on a very simple experiment with a bit of rusty steel and some watered down treacle, I can confirm that the answer to the question "Can molasses remove rust?" is yes.
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Molases is a fuel, just like sugar, oil, wax or diesel fuel. It can absorb a lot of oxygen or chlorine, while it undergoes chemical combustion at low temperatures.
In industry they have used a red hot coal bed of carbon basically, to strip the oxygen from water that is introduced into the reaction chamber as steam. The chamber is kept almost oxygen free so that the steam gives up its oxygen to the hot coal bed, to produce pure free hydrogen, an alkaline, for fuel and other hydrocarbon products. They can actually strip oxygen from CO2 that is produced in the reaction, and re-burn the carbon monoxide in a rather vicious circle.
Sincerely,
William McCormick