Re: Drying NaOH

Tilly mentioning that my 85% KOH has about 15% water impurity (that's imporatant) , caused me to remember something I did years ago. I don't remember why I did it, just that it happened. There is/was a name brand of technical grade sodium hydroxide drain cleaner called Red Devil Lye sold in the United States. Years ago I put maybe 100 grams of that type of inexpensive sodium hydroxide into a big enough beaker and put it into a hot oven, maybe 150 degrees centigrade or more. Probably, due to the water present the white solid caustic became hot thick liquid. Maybe the oven temperature was 200 degrees centigrade, I don't remember and I did not write it down. I had not thought about it for years. To produce the highest amount of methoxide, the starting materials should be as dry (anhydrous) as possible. Tilly said the caustic had water in it, so removing all the water in the the sodium hydroxide or potassium hydroxide would increase the concentration of methoxide or ethoxide in alcohol solution resulting from dissolving dried caustic in anhydrous alcohols. The increased methoxide concentration would cause a faster more complete reaction (transesterification) in forming the fatty acid esters , biodiesel from vegetable oils. The methanol should be as dry as possible. Drying the caustic would cause a better reaction to occur and diminish saponification soap production from glyceryl trifatty acids (vegetable oil) during the transesterification process. Free fatty acids would still neutralize caustic present at some rate (not immediately). Catalyst is removed from being available by free fatty acid + caustic to form soap + water + heat (exothermic reaction, heat given off). The significant amount of water present in the caustic solid may be removed prior to making the methoxide alcoholic solution by heating way above the boiling point of water to vaporize it, remove it from the caustic solid material. Two problems in doing that, drying solid caustic in a gas oven is carbon dioxide reacts with sodium hydroxide and potassium hydroxide to degrade the caustic a bit to sodium carbonate and potassium carbonate, but if it's done right it's not a problem. The other slight problem is that the caustic becomes a liquid while the water boils off, when it cools, it's one solid block in the bottom of a large enough glass beaker. I broke the solid caustic block apart with a stainless steel screw driver , without breaking the glass beaker, to get anhydrous sodium hydroxide mixed with some sodium carbonate. Technical grade sodium hydroxide already has some sodium carbonate in it. Drying the sodium hydroxide catalyst introduces a bit more sodium carbonate into the solid, but it's probably a better starting material for use in making the methoxide solution, with much less water in it. A Spectral absorption/emission study would be required to determine the increase in methoxide or ethoxide concentration resulting from drying the catalyst prior to dissolving/reacting in dry methoxide or anhydrous ethanol. Drying the caustic in an appropriate oven prior to mixing with anhydrous alcohol will improve the biodiesel manufacturing process. Oh yes, boiling the water out of the caustic solid at elevated temperature 150-200 degrees centigrade frosts the glass on the inside of the beaker where the hot liquid caustic touched the heat shock resistant glass. Thanks

Re: Drying NaOH

Wesley,
Were you able to quantify the amount of water present after your NaOH drying experiment?
What would have been the amount of Sodium Carbonate prior to the NaOH drying experiment
If an electric oven were used, what amount of reduction of Sodium Carbonate production would you expect?
How would one test for the amount of Sodium Carbonate in the NAOH before and after the drying process?
So many questions, so few answers. Hopefully the above Q will find their A.

Thanks,
Tony

Re: Drying NaOH

I did not weigh the beaker before and after to determine change in mass of the beaker. I used a natural gas powered oven. If a heat shock resistant watch glass on top of the beaker is used in an effort to slow carbon dioxide gas exchange touching the hot liquid caustic then that might help diminish sodium or potassium hydroxide degrading into sodium carbonate. An electrric oven would be better since it doesn't produce carbon dioxide gas that reacts with hot liquid caustic being dried. Also the density of hot air in a 200 degree centigrade oven is less than air at 20 degrees centigrade. It takes a few short minutes to do this drying, so probably not much sodium or potassium hydroxide becomes the carbonate. I expect it's worth doing. I had never thought of it untill Tilly mentioned caustic solid material has a lot of water present. I did dry sodium hydroxide years ago. I don't remember why I did it though and I didn't write it down in a lab notebook. My bottle of potassium hydroxide says it's 85% KOH on the assay listed on the side of the bottle and it says it's 2.0% K2CO3 (potassium carbonate) that leaves about 13% which is probably mostly water. Drying the solid caustic would be of benifit so when dissolving caustic in dry methanol or anhydrous ethanol to produce a methoxide or ethoxide solution the starting materials contain as little water as possible. Water decomposes methoxide. More water pushes the reaction to the reactants side of the equation, to the left. Removing water from the starting materials will push the reactants to the product side of the equation, to the right.

Re: Drying NaOH

I did an experiment, Drying Technical Grade Sodium Hydroxide. I weighed a 600 ml beaker with a watch glass on top of it. It weighed 278.9 grams. I added technical grade sodium hydroxide (drain cleaner) the inexpensive kind. I reweighed the beaker + watch glass + sodium hydroxide. It weighed 432.1 grams. I preheated the natural gas powered kitchen oven to 160 degrees centigrade or 320 degrees fahrenheit. I put the beaker into the oven on top of a hot sheet of metal for twenty minutes. I removed the hot beaker from the oven and put it inside a heat shock resistant glass dessicator to cool. Upon cooling I reweighed the beaker + watch glass + sodium hydroxide , it was 431.7 grams. 0.4 grams less than it was initially. The lost mass was surely water. But being hot the sodium hydroxide took on carbon dioxide from the atmosphere making sodium carbonate. But there was still a net mass loss as a result of heating. The sodium hydroxide product was not one solid peice as it was when I did this before. A higher temperature would work better to force water out of the caustic quickly. An electric oven would work better. Figuring a way to seal a container to not allow carbon dioxide from the atmosphere to touch the hot drying sodium hydroxide would work better. In 100 grams of technical grade sodium hydroxide there might be 15 grams/milliliters of water present that could be removed by some modification of this process, so the methoxide methanol solution produced would have a higher concentration of methoxide, due to less water being present in the starting materials.

Rerying NaOH

Thanks for conducting this test. It helps to see what is possible and to work out the cost/benefit of performing it.
0.1434% reduction in weight.
Unless we can quantify the Na2Co3 in the dried NaOH, we cannot identify the actual reduction of water in the NaOH.
if 15% of the 278.9g was H20 (1g/ml), the water would weigh 36.2g and 50% of it removed by heating, you would have a reduction in weight of 18.1g
What is the weight of Na2CO3?
Can we calculate the proportion of Water and Na2CO3 from the weight reduction?

Re: Drying NaOH

Tony,
I did some water tests on KOH methoxide, both as mixed and dried with CaO, I'll see if I can dig them out.

As said the calcium soap formed couldn't be washed out (virtually insoluble in water) I tried to use magnesol and that also didn't work. Even centrifuging didn't work. It was only the oak chips that eventually got the soap to zero after 3 passes, changing the oak each time.

As per others that have tried this our conclusion is that the extra yield isn't worth all the extra time.

Rerying NaOH

Hello there; I did the experiment that was a total failure. I weighed a one litre round bottom flask with a greazed stopper in it. I heated the flask hot under 86 millimeters of vacuum pressure. I saw liquid in the receiving flask from the vacuum still. Then when I disconnected/ disassembled the vacuum still I dropped the 1 litre flask with the dried technical grade sodium hydroxide solid. I did not gtet a mass reduction measurement on how much water was removed from heating the sodium hydroxide under vacuum, but water was removed, I saw it in the recieving flask That cost me a lot of money plus calling the crushers tio authorise me to purchase another 1 liter flask. The government people here are bad.

Re: Drying NaOH

What a disappointment! I hope that you and anyone nearby were not hurt. The cost of replacing the glassware and the NaOH just rubs salt (or is is NaOH?) into the wound.

Thanks for your research.

In Australia, purchase of litre sized analytical glassware will raise the interest of the authorities.
Merry Christmas,
Tony

Re: Drying NaOH

I have moved these posts from "Drying WVO" to a new thread "Drying NaOH" to make the subject match the discussion

Re: Drying NaOH

Oh Dear Wesley, be careful. Shame you arn't closer, I have plenty of 1 litre round bottom flasks with the ground tapered tops.

A few years ago I bought an amount of bankrupt stock from a chemical/lab glassware supplier, I have sold most of it but have a few bits and pieces left.

Re: Drying NaOH

This morning I looked at my glassware I used to remove water from technical grade sodium hydroxide (drain cleaner). Under vaccum of 86 milliliters of pressure above zero at elevated temperature the hot sodium hydroxide went over the still head some of it was in the condenser. I saw a clear liquid in the receiving flask last night. I might not have applied enough stop cock grease to the ground glass joints to cause the easy separation of the glass ware components. I applied a lot of force to it to cause it to separate into pieces. I will do this again. This experiment is not as easy as I thought it would be, the sodium hydroxide foams across the still head upon heating. I did not put a thermometer into the hot sodium hydroxide while I was heating it. Thermometers with ground glass joints on them are expensive 100-150 USA dollars and it might ruin it. I will do this experiment again. I have other one liter round bottom boiling flasks to use in place of the one I broke. Technical grade sodium hydroxide turns into a liquid upon heating. It burned my heating mantel a little that I heated it so hot. I guess I heated the sodium hydroxide to 250 degrees centigrade or more to get that result. In making biodiesel, the less water that is in the starting materials, the better. Sodium hydroxide can have water removed from it by heating and high vaccum.

Re: Drying NaOH

Wesley,
Surely you don't need to heat past 100°C? Or does the water combine chemically with the NaOH and so needs a higher temperature to separate it?
I don't like the thought of 250°C NaOH getting splashed around the floor if the flask breaks. You would need effective PPE (personal protective equipment) to prevent serious injury.

Re: Drying NaOH

I did the experiment again. I put 157.3 grams technical grade sodium hydroxide into a 1 liter round bottom boiling flask , weighed it with a greased glass stopper in it. I heated the flask using a heating mantel under 99.5 millimeters of pressure (vacuum). Previously I wrote it was 86 millimeters of vacuum pressure. I read the guage wrong and did the math incorrectly to figure the pressure. I did not put a thermometer into the 1 liter flask since it might ruim my thermometer. That equipment is expensive and difficult to replace here. During heating the technical grade sodium hydroxide became a clear boiling liquid. I expect the temperature was over 200 degrees centigrade, that's a guess. The next day after cooling I reweighed the flask stopper and sodium hydroxide contents. 3.9 grams of mass was lost from heating the sodium hydroxide under 99.5 millimeters pressure (vacuum). I heated the sodium hydroxide for about 1 hour at the highest temperature under vacuum. In making biodiesel using sodium hydroxide dissolved in methanol to make methoxide, less water produces a higher concentration of methoxide for the reaction. There might be an advantage to drying the sodium hydroxide prior to making the alcohol methoxide solution.

Re: Drying NaOH

Were you able to test the water for pH?