dx / dt = k (a - x) (b - X) = v
a and b are the concentrations of the starting materials, X is the soap concentration, and t is the reaction time.
That is the expression. The reaction velocity v slows as the reaction progresses.
The way of making soap gradually progresses at a stroke in the beginning, gradually, and finally it is finished again slowly.
As shown in the figure, the soap quickly rises on the way,
At that time the reaction rate will slow down at a stretch.
In an experiment at a certain university, they measured the percentage of soap produced by changing the temperature to find the reaction rate coefficient and the activation energy of the reaction.
The reaction progresses in a so-called exponential fashion.
Although the reaction rate is fast at first, the soap of the reaction product is small.
There is a point where a lot of soap can proceed rapidly exponentially from a certain point.
Subsequently, the reaction rate rapidly slowed down, slowly stopped,
Comprehension is completed so that it can be matured over a long period of time.
That is such a reaction.
In order to make saponification faster,
1) Increasing the concentration,
2) Increase the temperature
3) Stir well
4) Put the catalyst
Regardless of oil,
If caustic soda is not dissolved in water, it become small ball and remains unresponsive and it is very dangerous.
Try not to make too caustic soda water.
It is about 30% weight concentration.
30 grams of caustic soda will be about the maximum for 70 grams of water.
Increasing the temperature increases the movement of the molecule and has the same effect as stirring microscopically.
If it stirs, the number of times caustic soda and oil and fat molecules meet many times increases, The reaction speed increases.
However, when raised to 60 ° C or higher, there are decomposition of fats and oils and oxidation reactions,
Temperature rise too much is caution.
Besides that, as a catalyst,Alcohol addition etc. are known.
This is a method to increase the speed by adding things that have the property that the reaction tends to advance easily.
Given the reaction speed in earnest,
They compare the two types of making temperature 40 degrees, 60 degrees.
They measure the amount of alkali in unfinished soap made every few minutes by titration.
From the amount of citric acid until neutralization by adding the same concentration of citric acid,
Estimate the amount of unreacted alkali.
The ester concentration, alkali concentration and reaction rate constant k at time t are determined and are summarized in the table.
If log k is taken on the vertical axis and 1000 / T (temperature) is taken on the horizontal axis, there is a linear relationship.
The reaction rate coefficient increases as the temperature rises.
In the saponification of acetic acid esters,
The activation energy Ea of saponification is approximately Ea=59.1 kJ / mol
It seems to be about.
The reaction rate coefficient from room temperature to 50 ° C.,
20 ° C ; k '= A exp (- Ea / 293 R) = 0.002
30 ° C ; k '= A exp (- Ea / 303 R) = 0.005
40 ° C ; k '= A exp (- Ea / 313 R) = 0.010
50 ° C ; k '= A exp (- Ea / 323 R) = 0.022
In other words, at 40 ° C and 50 ° C, the reaction speed increases by 2 times as it goes up by 10 °.
The greater the activation energy, the greater the effect when the temperature goes up.
Here,
In saponification of palm oil,
Ea = 3-5 kcal / mol
The value has come out.
This is,
1 J = about 0.239 Calculated by cal (calories)
4 kcal = 16.7 kJ / mol.
You can calculate 14.1 kcal for Ea = 59.1 kJ.
In other words, the activation energy of palm oil is lower than that of acetic acid ester,
The reaction rate is slow.
(The above article is based on http: // 326.nobody.jp/ouka1/reaction_rate.htm)
(The above article also refers to kurepo.clib.kindai.ac.jp / modules / xoonips / download.php? File_id = 8106)
In the case of Ea = 17 kJ / mol,
K 40 / K 50 = exp {-17 / 8.31 * (1/323 - 1/313)}
= About 1.2
(The above article also refers to http://pub.maruzen.co.jp/book_magazine/support/cgbukka_pdf/11.pdf)
At 40 ° C and 50 ° C the reaction rate is calculated to be about 1.2 times.
(The following description is based on " http://kumaguma-soap.blog.so-net.ne.jp/2008-09-06)
Iodine value and saponification rate constant (McBain and Kawakami, J. Phys. Chem. Soc., 1929, 2185)
The greater the speed constant, the faster the reaction.
The larger the iodine value is, the slower the reaction is shown.
Iodine value is a value that shows how much unsaturated bonds are in fat and oil.
That is, oils with many unsaturated fatty acids can be considered to be slow reactions.
Many vegetable fats such as beef tallow, lard, palm oil and the like have low iodine value,
Saponification speed is fast.
Conversely, those with high iodine values such as soybean oil and olive oil are many in unsaturated fatty acids,
The degradation reaction rate is slow.
As described above, not only reaction conditions such as temperature,
There are also speed differences depending on the type of oil.
Temperature and iodine value of oil are important factors.
Besides that, rice oil (rice bran oil) contains a few percent of impurities,
For that reason, it is very fast.
Reaction speed will be as above if you organize what you grasp by experience.
Summury
Reaction rate of saponification depends on Temperature, iodine values and catalyst.
High speed on low iodine value , low unsaturated fatty acids and high temperature.