Factors affecting saponification reaction

I briefly talked about the reaction of nature. Today, I will talk about the factors that affect the saponification reaction to help you better control the saponification reaction process.

First, the influence of temperature on saponification reaction

Speaking of temperature, it is a very important control factor in the process of soap making. As mentioned above, the saponification reaction of soap is an exothermic process, but if the temperature is too low, the molecular motion speed is slow (Brownian motion), and the collision probability between molecules is reduced, the reaction will be very slow. We heat the oil and maintain a certain reaction temperature in order to accelerate the movement of molecules, improve the collision probability between molecules, and thus improve the reaction speed.

Increasing the temperature will bring the following benefits to handmade soap:

1. Saponification reaction is more complete and sufficient than low temperature reaction.

2. The curing time of soap is shortened, because the temperature is high, the reaction speed of soap is fast, the texture of soap is dense, the demoulding is easy, and the curing period of soap is shortened.

3. Soap is stable and less irritating to the skin. Because saponification is sufficient, the free base and free fatty acid of soap are reduced, thus reducing the possibility of rancidity. In addition, due to the reduction of free alkali, the safety to the skin is also improved.

So, how much should the temperature of soap be controlled? Generally, the temperature of cold-made handmade soap is 35-40℃, and the industrial saponification temperature is generally above 100. But it does not mean that the higher the saponification reaction temperature, the better. There are also conditions. If the temperature is too high, manual soap operation will be dangerous and difficult, and soap is prone to water-oil stratification. The temperature is too low, the reaction is too slow, and saponification is incomplete.

After testing, I think the temperature of handmade soap is 75-80. Of course, some people will ask, does this not affect the nutritional composition of soap oil? In this regard, I want to explain that soap, as a cleaning product, must first achieve a good cleaning effect. In addition, we must find ways to make it have a better sense of washing and special effects. I think the whitening and nourishing effect of soap is exaggerated. We choose different oils to make soap show different properties and different washing feelings, but it is not easy for the skin to absorb the nutrition of oil in soap when taking a bath.

In addition, why try to keep the temperature consistent when heating? This is to keep the molecular movements of the two systems synchronized as much as possible. If it is not synchronized, the local concentration may be high and the reaction is fast, while the reaction in other places is slow, resulting in uneven reaction, thus affecting the overall saponification result.

The second is the influence of mechanical stirring on saponification reaction.

When we make handmade soap, we should stir it. Some oils with more saturated fatty acids can be stirred for a shorter time, while those with more unsaturated fatty acids are difficult to stir. Many people have broken their arms, and the soap is not t, so they can only continue to stir. I want to say here that stirring is very necessary, and it must be fully stirred. Without stirring, the saponification reaction will be greatly affected.

We usually dissolve sodium hydroxide in water and then pour it into oil. As we all know, water and oil are immiscible, so the two systems should be fully stirred and mixed to the maximum extent, so as to promote the combination of oil molecules and sodium ions. This may be a bit abstract. Simply put, stirring can make the oil and sodium hydroxide solution contact more fully, increase their contact area, and make the reaction faster and more sufficient. If the stirring is not sufficient, muffins and other problems often occur, which are caused by uneven reaction.

So how should I stir it? I suggest that you use electric stirring as much as possible, which is faster, more energy-saving, and more importantly, more sufficient than manual stirring, which is an important prerequisite to ensure saponification. In addition, try to stir in one direction to achieve a better mixing state.

Third, the concentration and dosage of the two substances involved in the reaction.

1. Let's talk about oil first. In other words, the concentration of oil should be called purity. The oil bought in the market is often mixed with other oils, resulting in insufficient oil purity. It will be troublesome for us to calculate the dosage of sodium hydroxide, or we can't judge how much sodium hydroxide should be added. The identification of this kind of oil is still a difficult problem for most handmade soap makers because the process is more troublesome. So I still suggest going to some trusted businesses to buy.

It can be seen from the reaction equation that the reaction between sodium hydroxide and oil is quantitative. If there is too much oil and not so much sodium hydroxide saponification, soap will become greasy. Here, I want to talk about the problem of super fat. Many people who make soap like to use super fat. On the one hand, it can reduce free alkali, on the other hand, soap is more moist. However, it is often difficult to control the amount of super fat, resulting in too greasy soap. If inexperienced friends still try their best to weigh oil and sodium hydroxide, it is better to use it accurately.

2. The concentration of sodium hydroxide has an effect on the reaction. There is a saying in the industry that the concentration of sodium hydroxide is generally controlled at 8- 10Mol, which makes the soap white and dense. This concentration can't be generalized. Different oils will have some differences, because the content of unsaponifiable matter in oils is different, so it will have different functions. For most people, a solution with a concentration of 9Mol should be able to cope with most oils.

So why does sodium hydroxide react better at this concentration? Because the solubility of sodium hydroxide is 53 (room temperature), that is to say, 100 g of water can dissolve 53g of sodium hydroxide to reach saturation, that is to say, when we dissolve 53g of sodium hydroxide with water, the amount of water should not be less than 100g. If there is too much water, the concentration will be too low and the reaction speed will slow down, because sodium hydroxide molecules are looking for oil molecules in the vast sea. If the concentration is too high, some sodium hydroxide will not completely dissolve, but will.

From this, we can deduce how many times we should use water to dissolve sodium hydroxide: according to the above-mentioned optimal concentration of about 9Mol, it should be about 36%, which means it is more appropriate to add 2.6 times of water to dissolve sodium hydroxide.

Some people are questioning why we don't prepare saturated solution. There are two reasons:

1, in order to prevent the local concentration of the reaction from being too high, resulting in saponification imbalance.

2. Water does not react in saponification reaction. It provides an ionization environment for sodium hydroxide, so that sodium hydroxide can react with oil molecules in ionic state. The preparation of saturated solution is often troublesome, the purity of sodium hydroxide is different, and the dosage is not easy to control. Therefore, from the point of view of easy operation, saturated solution is not suitable. In addition, the experiment proves that the soap made of 8- 10Mol sodium hydroxide solution is really ideal.

Fourthly, the influence of additives on natural reactions.

Additives will inevitably affect the saponification reaction. Let's give a quiet example: many of us like to make milk soap because it feels good and moist, but the success rate of milk soap is not very high, and there are always problems such as white spots, oily spots or easy rancidity. The reason for this problem is not only insufficient temperature and stirring, but also added milk.

In the process of saponification, the higher the purity of the two reactants, the faster the reaction. For example, saponification is the reaction between sodium hydroxide and fatty acids. If pure fatty acid (such as lauric acid) reagent reacts with sodium hydroxide, it can be found that the reaction is very rapid, that is to say, the reaction of pure substances is often stable.

But when making handmade milk soap, we often use milk to directly dissolve sodium hydroxide. In order to avoid yellowing, we use low temperature to dissolve sodium hydroxide, and there will be several problems here:

1, low temperature, affecting saponification speed;

2, the degree of dissolution of sodium hydroxide is not easy to control, I don't know whether it is completely dissolved.

3. The addition of milk affects the saponification reaction.

I won't explain the first two points, as I have already said. For the third point, here is a brief talk. Milk contains a lot of protein. When used to dissolve sodium hydroxide, the protein of milk will be denatured to varying degrees. With the progress of the reaction, the temperature will be higher and higher, and there will be more and more denatured protein. If the stirring is not good or the temperature is not well controlled, protein will easily agglomerate, thus covering many sodium hydroxide molecules. It becomes "gel-like" (when the reaction is excessive, you will see a large gel, which is generally not easy to find locally), resulting in insufficient sodium hydroxide as a reactant and insufficient saponification. In the same way, many high-protein substances will affect the saponification reaction more or less. Therefore, when making milk soap, we should pay special attention to the operation of each link.

In addition, when making red wine soap, some people will find that the additive of speed T and alcohol often appears this phenomenon. Speed t will bring a trouble to making soap, that is, it is difficult for soap to enter the mold, even in some places it is saponified well, in some places it is not saponified well, and the soap is oily and irritating. In fact, this is all caused by ethanol. But here I want to say that ethanol can actually be added to soap. In industry, ethanol is added to the reaction furnace as a saponification accelerator, because oil can be dissolved with ethanol, and water can also be dissolved with ethanol. In this way, the addition of ethanol breaks the immiscible medium of water and oil, and the two reactants react quickly in ethanol, thus accelerating the process of saponification reaction, which is a good promotion process. In the actual process of making handmade soap, due to simple equipment, poor stirring and temperature control, it is easy to cause speed T. Some experienced soap lovers have also solved this problem by adding or accelerating stirring step by step.

Therefore, additives have a great influence on saponification reaction, so be careful when considering adding those things. It is reasonable to add those things according to the nature of saponification reaction, and don't add those strange things (a friend told me that he joined the placenta hominis and I was sweating).

5. Effect of oil properties on saponification reaction.

Actually, I still want to talk about the essence of fatty acids here. We all know that saturated fatty acids react faster than unsaturated fatty acids. This is because saturated fatty acids have single bonds and no olefins, while unsaturated fatty acids have double bonds. In the process of reaction, the double bond should be opened for addition reaction, which is much slower than single bond saturated fatty acid.

From the point of view of oil, some oils contain a lot of unsaturated fatty acids, such as evening primrose oil, soybean oil and olive oil. And their reaction speed is slower than coconut oil and palm oil, which means their saponification reaction is slower. For these oils with high unsaturated fatty acid content, we are patient and keep stirring to ensure the full saponification reaction. In addition, besides fatty acids, oil also contains a lot of unsaponifiable substances, such as sterols, Ve, Vc, etc. These oils with high unsaponifiable matter content tend to react slowly. For saponification reaction, these unsaponifiable substances become "impurities" in soap, thus reducing the reaction rate. So when using different oils, we should also consider how to mix them clearly.

The above five points about the influencing factors of saponification reaction are not comprehensive enough, only for more people to understand and discuss. It is hoped that more soap lovers will pay attention not only to the function of soap but also to the saponification reaction itself in the process of making soap.