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I have some very plain candles. I don't think they contain anything but paraffin wax and octadecanoic (stearic) acid, since they are odorless and very hard to bend, tending to crack instead (even at around 45 degrees Celsius). I want to make some moldable wax plugs for bottles without heating over about 50 degrees Celsius (it'll burn my hands, I have no other tools to use). How can I get rid of the acid? I don't particularly care if the acid is destroyed; but it would be nice if it wasn't so I could make soap or something.

Some possible ways I've thought of:

  • Distillation. I can't do this because it stinks and clogs up my glassware. Also, stearic acid decomposes around the same temperature as paraffin wax boils.

  • Dissolution of octadecanoic acid in some alcohol. Wax won't be dissolved because alcohols are polar and wax is not. However, I don't know how to actually do this as the wax may block access to most of the acid.

  • Neutralization of the acid using aqueous solutions of sodium hydrogen carbonate, sodium carbonate, or sodium hydroxide. This seems like the fastest way of removing acid; however the base may not come into contact with the octadecanoic acid due to separation of the layers.

What seems like the best or most effective method of removing the acid?

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    $\begingroup$ I honestly cannot tell why you would want to remove the octadecanoic acid, could you perhaps describe what you want to do with the cadles more exactly? How do you intend to mold wax without heating it?; it would still be solid. $\endgroup$
    – caconyrn
    Jun 13, 2016 at 20:47
  • $\begingroup$ In en.wikipedia.org/wiki/Paraffin_wax#History it is stated that octadecanoic acid is added to make the candles harder and to remedy their low melting point. My objective here isn't to have a putty-like substance, but rather to minimize the heat required to make it more soft. In addition to this, the acid will probably react with something inside the bottles (sodium carbonate solutions, etc) and contaminate my chemicals. $\endgroup$
    – sadljkfhalskdjfh
    Jun 14, 2016 at 0:06
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    $\begingroup$ They sell paraffin in the grocery store to seal jam jars. Would that work? $\endgroup$
    – MaxW
    Jun 14, 2016 at 1:24
  • $\begingroup$ @MaxW Where I live, they do not. Even if they did, this would still be interesting as an experiment. $\endgroup$
    – sadljkfhalskdjfh
    Jun 14, 2016 at 1:26
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    $\begingroup$ Ok, you want to experiment? Boil with 0.1 molar NaOH for 20 minutes while vigorously stirring. Cool and let wax harden. Crack through wax and pour off NaOH solution. Repeat NaOH wash three times. $\endgroup$
    – MaxW
    Jun 14, 2016 at 1:56

1 Answer 1

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It should be noted that typically, candles are about 10% stearic acid and 90% paraffin. Also, there are many different grades of paraffin waxes which are generally identified by their melting points (often given as ranges); candles are usually made from paraffin graded from 53.3 °C (128 °F) to 65.6 °C (150°F), while paraffin of 76.6 °C (170 °F) is more common for molding and sculpting.

So I'm pretty sure that you didn't know what grade of paraffin you are after, and I would guess that you are looking for something more like cheese wax. While cheese wax is significanly softer, it actually has a generally higher melting range of perhaps 72 - 82 °C (161 - 179 °F).

Cheese wax is a blend of paraffins:

  • <30% paraffin wax fume (Cas# 8002-74-2)
  • <30% paraffin waxes and hydrocarbon waxes, microcryst. (Cas# 63231-60-7)
  • <20% petrolatum (Cas# 8009-03-8)
  • 30% Slack wax, petroleum, hydrotreated (Cas# 92062-09-4)

However, there may be multiple grades of paraffin used for your candles or the grade used may be of a low enough melting point (MP) to be useful for making the product you desire (in conjunction with other materials to make it softer for sculpting or molding).

The "analysis" and the separation procedure would be based on the melting point. So, (I would) try to use the melting points to separate the stearic acid from the lower temperature fractions.

Stearic acid's MP is 69.3 °C (156.7 °F)

Paraffin's MP may be as low as 37 °C (98.6 °F), but finding that grade of paraffin in your candles is unlikely. With a bit of luck, a low temperature grade of paraffin (48.3 °C (119 °F)) might show up; but more likely would be grades having a melting point of 53.3 °C (128 °F) and/or 61.1 °C (142 °F), which are common for candle making.

Step 1. Melt the candles in a pot and remove the strings. If possible, you would want to use a hot plate with accurate, good-quality temperature control.

Step 2. Insert a (candy) thermometer and a spoon or ladle in the pot (maybe a screen-type of ladle, like what is used for noodles and dumplings). You need the ladle to be warm, so that the wax doesn't freeze and stick to it when you use it to scoop out the stearic acid.

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Step 3. Reduce the heat until precipitates begin to form. This should begin to happen somewhere around 70 °C. With an open pot, the cooler surface will probably cause the top to skim over. The higher melting point fractions might be what solidify first on the top, like slag on molten steel. The first precipitates or slag should be higher in octadecanoic (stearic) acid concentration. Use the ladle to scoop/filter out the precipitates (put the stearic acid in a in another pot or a bowl). You should keep collecting precipitates until it reached about 55 °C or until it all becomes solid. Be sure to make note of the final temperature. If the temperature at which it all solidifies is at or above 60 °C, then the kind of paraffin that you have is probably not what you wanted; and it will be quite difficult to separate, and this procedure is not very useful for separating the stearic acid from the paraffin.

Step 4. Even if the paraffin has a low MP, this will not be a 100% perfect procedure (far from it); you will probably need to repeat the (enrichment) procedure a couple, or maybe several, times. Also, you could probably recover some (low MP) paraffin from the precipitated/enriched stearic acid filtride. It might be favorable to have a few bowls or pots which represent collections at different temperature ranges... like, for example, the first bowl would contain solids from 70 - 65 °C; the second bowl contains solids from 64 - 58 °C; and the third bowl contains solids from 57 - 52 °C.

Step 5. Measure the new MPs. A good anylysis of the cleanliness of this procedure will be to compare the MPs. A pure solution of stearic acid will melt/solidify at exactly 69.3 °C, but obtaining a pure solution in this manner, is a pretty lofty dream. So, after the stearic acid fraction has melted, let it cool and mark the temperature at which it begins to solidify and the point at which it is completely solid. If the two fractions that have been separated have distinctly different melting points, that's pretty good. Specifically regarding the paraffin, if it doesn't begin to solidify until it's below 50 °C then, great job, it's pretty clean and you obtained the low temperature paraffin that you desired!

Step 6. Depending on the cleanliness (melting point) and amount of the stearic acid that you have, you may want to try to salvage some of the paraffin from the stearic acid (filtride). I believe that this will be more difficult, and I would advise using a third pot (or second bowl) to collect the salvaged paraffin. And then work on cleaning the stearic acid out of the salvage, checking the cleanliness as in step 5, before combining the salvaged paraffin with the first "batch".

Step 7. Further chemical reactions for cleaning up the stearic acid (or converting it to soap) could be performed with better results from the enriched fractions.

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