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Saponification Issues
I am having some issues saponifying our oils as we are upscaling our manufacturing.
We start with a base formula of:55% Coconut Oil35% Lauric Acid10% Olive OilI add a caustic water solution mixed of Potassium Hydroxide to the above melted oils.It saponifies fairly fast, in which I end up with a thick, gooey, concentrated ball of soap paste.I then dilute this paste into more water at a 1:1 ratio, after which we add our other ingredients such as scent, moisturizing, thickener, etc…For our larger scale production this is not simply working out. Making the “paste” and then diluting it is not time/cost effective.Ideally, we want the soap to be “pre diluted” with all the water the formula calls for, and THEN add the Potassium Hydroxide to this solution, and saponify that solution. Hopefully eliminating the need to dilute the paste, and having to transfer from it from our planetary mixer into our blender.Every time I have tried the above experiment the saponification process never comes out the same. Its as though not all the oils are saponified and the solution is way to superfatted with oils. How can I resolve this??? Increase the hydroxide amount, heat, etc??? Hopefully this makes sense, thanks in advance.-Bryce Hudson -
18 Replies
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The first thing is, how are you calculating the required amount of KOH?
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We are calculating the amount of KOH by the individual SAP value of each ingredient, and then totaling together.
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That should work. Are you heating the soap and/or mixing energetically?
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I suggest adding a wetting agent (surfactant) but you will need to experiment to find the maximum dilution that still allows proper saponfication.
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We are not heating the soap, just letting the heat of the hot Lye solution do the “cooking”. The product comes out great when we make the “paste” and then dilute it.
But whenever we add the extra water for dilution to the Lye, it’s as if the solution is not as caustic anymore and doesn’t have the same effect on saponifying the oils.I have tried increasing the Lye amount, but without any positive results.We want to avoid making the “paste” and go straight to a thinned out soap so our machinery can handle it.Belassi, once our oils are saponified, that is our surfactant in our solution, correct?? -
OK, a couple of things you need to be aware of.
1) The saponification of triglycerides is a slow process at room temperature. Heating to 70 - 80C increases the reaction speed substantially. The more dilute your solution, the harder it will be for the reactants to find each other so that they can react - and that takes even more time.2) Adding a concentrated lye solution to your oil/fatty acid mixture is the best way of using the exothermic reaction to make your soap quickly - but not so much on a larger scale, as you’ve discovered. If you can’t or won’t heat your batch, you are inevitably going to see batch making times in the 8 - 12 hour range or longer. (and yes, we make this sort of product where I work, so I’m not just speaking theoretically)3) The rest of the problem solution is going to be a series of cost/benefit calculations - how much does it cost to heat the water vs. how long does the batch take to react vs. what is the capacity of my mixing vessel vs. how big a water heater can I afford/fit into my factory. -
GripClean: To answer your question, once the oils are saponified they are a surfactant, of course. But until saponification is complete, you are trying to put polar and nonpolar together. The speed of the reaction depends on temperature, concentration, and droplet size. That is why a surfactant can help; it reduces the surface tension of the oil/water interface and allows them to combine more easily. I assume you are already using high shear mixing to allow the oils and lye solution to combine.
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You did not state exactly what your product is but by the ingredients list and methods I am assuming it is a liquid soap.
Making a paste and then diluting it is a typical method used for this kind of product. If you were to use the full amount of water from the beginning then your lye solution is not strong enough to make saponification happen quickly enough and completely.
Water-loss is also typical in this kind of process. You indicate that you dilute your paste at a 1:1 ratio. Have you added back the H2O that evaporate during your first phase? If not then that may be a reason that your product doesn’t come out the same each time.
The process that you hope to use isn’t going to work for you. You still must make paste first to make sure your saponification is complete, take account of the lost water and replace the lost water during the dilution phase. By the way, your paste should sit for a while to also assure that your saponification is complete.
I hope this helps! Now I’m going back to bottling my liquid soap!
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I have made natural liquid soap myself, but I have to say, that none of it performed as well as the synthetic surfactants, in any respect.
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Belassi’s point about added surfactants helping to speed up the reaction is very good, as is David’s.
One way to speed up your process would be to change your formula. Saponification is a two-step reaction - first the triglyceride molecule is cleaved to yield three fatty acid and one glycerine molecule, then the fatty acids are neutralized by the hydroxides to form soap. Starting with fatty acids instead of plant oils will speed up your reaction, as will using a small amount (1-2%) of surfactant.Another thing to think of is to change your process. One possibility would be to saponify each component separately, then combine them. Another would be to significantly boost your mixing strength - if you can successfully make your product on a small scale, but not on a larger one, you’ve either miscalculated the mixing strength you needed to scale up to, used more mixing power in the lab than can be successfully replicated in production, or a combination of the two.Yet another possibility would be for you to use the full amount of water in your batch, but much more caustic than you need. After your soap is formed, you could then neutralize the caustic with a mild acid, like citric.Lastly, If you are making something in the lab, and you are getting large batch-to-batch variations, you are not controlling a variable that makes a difference - what ever you’re making. Raw material variations, water quality, mixing time, mixing temperature, mixing intensity, ratio of size between beaker and impeller, order of ingredient addition, speed of ingredient addition, sometimes even room humidity can all make a difference in your final product. -
Great advice from everyone.
And yes everyone is obviously correct, we are making a liquid hand soap. Every batch has come out great using the paste method. But as we stated, its just not that practical for our larger batches. It takes a long time.I have tried adding all the water to the formula with a much more caustic solution, and then tried neutralizing afterwards. It still didn’t saponify fully, and the oils became separated in the solution after all was said and done.I am kind of at a loss of what experiment to try next to achieve the same results. Or maybe it is just one of those things that can’t be done, and there is no way around the paste issue?!? -
My own opinion is that you’re trying to make a wheel from straight pieces of wood. I don’t think you will get a dilute solution to fully saponify. The reaction concentration appears to have a minimum critical level.
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I can easily, consistently and repeatably get Oleic Acid to saponify at room temperature with 45% Potassium Hydroxide at roughly a 2:1 ratio, in about 20 minutes.
I don’t know the size of the batches you’re making, but my best advice at this point, given the constraints I think you have, is to ditch the Lauric Acid and substitute Oleic Acid, then try making your paste again. I think you’ll get enough improvement in viscosity that the paste method will work. Try varying levels of water to see how much you can get away with - but it might be zero.If that still takes too long, the only way I can think that will help is to figure out some way to add heat. -
My saponification takes about 10 minutes! I use a strong lye solution and I only need to stir for about 10 minutes, then it becomes paste, is stirred again and left overnight and weighed then diluted the next day then thickener and fragrance are added. These are production size batches I am making. Your problem is that you want to try a weaker lye solution when you should be using a stronger one. Time to abandon that concept as it isn’t going to work. Also, Bobz last suggestion is a good one!
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The research I did for the discussion we’ve just been having here: https://chemistscorner.com/cosmeticsciencetalk/discussion/1905/scaling-up-liquid-soap-production-do-i-really-need-a-machine#latestand @David08848‘s answer in it about his soap-making method showed me the answer to your problem also - I think.You can make your soap in a one-pot process if you stop mixing and heating once your batch is thick but still fluid. Allow this to sit overnight to saponify, which will make it a paste. Then, dilute it with very hot water before you start up your mixer in the morning - this should thin your paste out enough that it will mix easily.
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Totally what Bob said. Plus, this: You shouldn’t be using a mixer to put the components together. What you need for a fast reaction is to ensure that the polar and nonpolar components are in as small a particle size and most intimate contact possible. You can do this by adding 1-2% surfactant, and most important of all, use a high speed blender - something with lots of shear. Thousands of RPMs not hundreds.
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We make our liquid soap in a one-pot (water jacketed tank with lid) process in batches of around 70 Kg. We add the KOH once the oil mix is at 70 C, then mix until it thickens (time depends on oils, but usually around 10 minutes). We stop mixing once the batch is thick, but leave the heat on until the batch goes gel-like and translucent. Depending on the oils, we may allow to sit overnight (heat off, but it remains warm) or add dilution water, mix and allow to sit overnight. If adding water the next day, we heat to 70 C.
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There are a lot of saponification catalysts that might be used to compensate for slowing the reaction by dilution. Mostly I hear about those as a result of cold kettle process soapmakers complaining that it happens too fast for their convenience with various fragrance additives. Ethyl alcohol will both catalyze the reaction and thin the product, but you may not want that in the final product.
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