Saponification – Soap Making Process with Ultrasonics

Saponification is the chemical process of soap making. It is the reaction in which the raw material of fats or oils (triglycerides) react with an alkali reactant in order to form soap. Ultrasonication improves the phase transfer catalysis resulting in increased reaction speed, more complete conversion and avoids the excessive use of base reagents such as potassium hydroxide (KOH) or sodium hydroxide (NaOH). The ultrasonically initiated alkaline hydrolysis can be easily implemented in commercial soap manufacturing. Ultrasonic reactors for saponification produce higher output in shorter time without using any catalyst or reducing the amounts of catalyst used.

Ultrasonically Promoted Saponification

Case Studies of Ultrasonic Saponification

Various research studies have shown that sonication promotes the saponification of triglycerides into soap. Ultrasonic saponification accelerates and increases the conversion whilst saving or avoiding the use of catalyst. This makes ultrasonic saponification a highly efficient production method.

Ultrasonic Initiation of the Alkaline Hydrolysis of Triglycerides (Saponification) Without Phase Catalyst

Mercantili et al. (2013) studied the effects of ultrasonication on the alkaline hydrolysis of triglycerides, known as saponification. They used sonication to initiate the alkaline hydrolysis of sunflower oil. Potassium hydroxide (KOH) was used as alkali base. It was shown that ultrasound is effective as a power source to initiate and drive the reaction, that a high reaction yield is achievable in only 15 min of total power application while working at ambient temperature, and that no detectable by‐products are generated during the reaction. The comparison of an ultrasonic bath and a probe-type ultrasonocator shows the ultrasonic probe to be the superior technique. The study demonstrates that ultrasonic saponification yields in a good conversion without the need for excess alkali or phase transfer catalysis.

Alkaline hydrolysis of triacylglycerol

Ultrasonically Promoted Phase Transfer Reaction for Saponification

Bhatkhande et al. (1998) showed that sonication of vegetable oils such as soybean oil could be efficiently saponified using aqueous KOH and different PTCs at room temperature. The extent of saponification was studied using the saponification value as a reference. Optimizations of various parameters such as time, selection of phase transfer catalysts, quantity of catalyst used, quantity of KOH and quantity of water were carried out using sonication and stirring. To study the effect of ultrasound, the saponification was also carried out at 35ºC under different conditions, namely stirring, sonication, stirring and sonication, and heating at 100ºC. It was found that the heterogeneous liquid-liquid phase saponification of different vegetable oils using aqueous KOH/CTAB was significantly accelerated at 35ºC under sonication and stirring.

High Performance Ultrasonicators

Hielscher Ultrasonics supplies high-performance ultrasonic equipment for lab, pilot and industrial production. The robust and reliable ultrasonicators are used for various sonochemical reactions such as saponification. Hielscher’s probe-type ultrasonicators can be used in batch and inline mode. All important process parameters – amplitude, pressure, temperature – can be precisely controlled and ensure reproducible results.
The digital control automatically records the process parameters and store them on the integrated SD-card. Pre-settings and remote browser control make the sonication process very simple and user-friendly.
For many sonochemical reactions a certain temperature must be maintained, so temperature control is important. Hielscher’s digital ultrasonicators come with a thermo-couple and temperature control. Jacketed flow cell allow for heat dissipation.
The robustness of Hielscher’s ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments.
The table below gives you an indication of the approximate processing capacity of our ultrasonicators:

• Bhatkhande, B.S.; Samant, Shriniwas D. (1998): Ultrasound assisted PTC catalyzed saponification of vegetable oils using aqueous alkali. Ultrasonics Sonochemistry Vol. 5, Issue 1, 1998. 7-12.
• Mercantili, Laura; Séamus, Frank Davis; Higson, P. J. (2014): Ultrasonic Initiation of the Alkaline Hydrolysis of Triglycerides (Saponification) Without Phase Catalysis. Journal of Surfactant and Detergents Vol. 17, Isssue 1, Jan 2014. 133-141.

Facts Worth Knowing

Sonochemistry

Power ultrasound is applied to chemical processes such as synthesis and catalysis (also called sono-synthesis and sono-catalysis, respectively) in order to initiate and intensify the reaction. Various applications of ultrasonic irradiation in organic synthesis have been in depth investigated and developed for industrial production. Sonochemical treatments can increase the rate of reaction, yield and selectivity of desired products under significantly milder condition. This makes the ultrasonic treatment an effective and environmental-friendly processing technique. Ultrasonically assisted phase transfer catalysis (PTC) is proven to be a drastically more efficient and effective method for organic reactions compared to the same reaction at silence condition. For example, the Cannizarro reaction catalyzed by an ultrasonically-assisted phase transfer catalysis is significantly sped up resulting in a rapid conversion. Another prominent example is the transesterification of triglycerides (i.e. vegetable oils, animal fats) and methanol in presence of KOH as catalyst and power ultrasound. The ultrasonic transesterification yields in high-quality biodiesel produced in a rapid conversion and a very efficient, economical process.

Ultrasonic extraction is based on acoustic cavitation and its hydrodynamic shear forces

Saponification

Saponification describes the chemical reaction that produces soap. In the saponification process, vegetable oils or animal fats are converted into fatty acid salts – the “soap” – and glycerol, which is an alcohol. The reaction requires a solution of an alkali base (e.g., NaOH or KOH) in water and also heat to initiate the reaction.
The reaction steps of saponification are the following:

1. Nucleophilic attack of the fatty acid esters by the hydroxide
2. Leaving group removal
3. Deprotonation

The saponification reaction is used commercially to produce soaps and lubricants.
While sodium hydroxide hard soap and potassium hydroxide soft soap are used for everyday cleaning, there are also special soaps produced using other metal hydroxides. For example, lithium soaps and calcium soaps are used as lubricating greases. There are also “complex soaps” consisting of a mixture of metallic soaps.

Hydrolysis

Hydrolysis involves the reaction of an organic chemical with water to form two or more new substances and usually means the cleavage of chemical bonds by the addition of water. Esters can be cleaved back into a carboxylic acid and an alcohol by reaction with water and a base. Soap is produced by the hydrolysis of the esters of fat or oil.

Alkaline Base

Alkaline base reactants (lyes) are required for the saponification of oils and fats. The triglycerides are reacted with a base – sodium or potassium hydroxide – in order to produce glycerol and a fatty acid salt, the so-called “soap”. Potassium hydroxide is an inorganic compound with the formula KOH, and is commonly called caustic potash. Sodium hydroxide (NaOH) is another prototypical strong base. When sodium hydroxide is used, a hard soap is produced, whilst the use of potassium hydroxide results in a soft soap.

Reactant vs Reagent

A reactant is a substance that is used up or consumed in a chemical reaction. In comparison to a reagent, a reactant is required in larger amounts. A reagent is a substance that is used to initiate a reaction, to support the reaction and is consumed in a reaction, in contrasts to catalysts which are not consumed in a reaction.

Saponification – Frequently Asked Questions

• What is the saponification process? Saponification is the chemical process where fats or oils react with an alkali (usually sodium hydroxide) to produce soap and glycerol. This reaction involves hydrolysis of triglycerides into fatty acid salts and glycerol.
• What type of reaction is saponification? Saponification is a type of hydrolysis reaction where ester bonds in fats or oils are broken down by an alkali.
• Why is it called saponification? It is named for its end product, soap, and its ability to create soap through the hydrolysis of ester bonds in triglycerides.
• What is the purpose of saponification? The primary purpose is to produce soap, a surfactant used widely for cleaning and washing.
• Is saponification hydrolysis? Yes, saponification is a specific type of hydrolysis involving the decomposition of fats or oils by an alkali into glycerol and fatty acid salts (soap).
• What is the mechanism of saponification? It involves the nucleophilic attack of hydroxide ions on the carbonyl carbon of the ester bond in triglycerides, leading to the formation of alcohol (glycerol) and soap.
• Why is mixing important for saponification? Efficient mixing ensures thorough contact between the reactants, promoting a more complete and uniform reaction, crucial for achieving optimal yields. Hielscher ultrasonic mixers can enhance this process through intense cavitation and shear forces.
• What is a saponification example? Mixing sodium hydroxide with coconut oil in the presence of a Hielscher ultrasonic reactor to produce soap and glycerol exemplifies saponification.
• What is the main product of saponification? The main products are soap (sodium or potassium salts of fatty acids) and glycerol.
• Why is saponification value important? The saponification value indicates the amount of alkali needed to saponify a given amount of fat or oil, helping determine the molecular weight of the fatty acids it contains.
• Is saponification reversible? Under typical conditions, saponification is not reversible due to the stable nature of the soap formed.
• What is the opposite of saponification? Esterification, where water and alcohols react with carboxylic acids to form esters and water, is the reverse process.
• Does saponification require heat? While not required, heat can accelerate the saponification process by increasing molecular motion and reaction speed.
• Is saponification exothermic or endothermic? Saponification is an exothermic reaction, releasing heat as it proceeds.
• Is saponification basic or acidic? It is a basic reaction, as it involves the action of a base (alkali) on an ester (fat/oil).
• How do you stop saponification? Adding an acid to neutralize the alkali stops the reaction, effectively ceasing the saponification process.
• What happens after saponification? After complete reaction, the mixture usually consists of soap and glycerol, which may be purified or processed further depending on the intended use.
• Is saponification natural? Yes, natural saponification can occur when fat comes intocontact with alkaline earth metals in certain geological settings or when ancient peoples mixed animal fats with ashes in traditional soap-making methods.
• Why is olive oil used in saponification? Olive oil is favored in saponification due to its rich content of oleic acid, which yields a mild, moisturizing soap with good cleansing properties and a stable lather.
• How to turn fat into soap? Fats are turned into soap through saponification by heating them with a strong alkali solution, typically sodium hydroxide, which breaks down the fat into fatty acid salts (soap) and glycerol.
• Which oil has high saponification value? Coconut oil has a high saponification value, indicating a higher proportion of smaller fatty acid molecules, making it very reactive with alkali to produce soap.
• What happens to oils during saponification? During saponification, oils are hydrolyzed by the alkali into glycerol and fatty acid salts, the latter forming the soap.
• What is the best fat for soap? Tallow (beef fat) and coconut oil are considered some of the best fats for soap making due to their lathering and hardening properties in the final soap product.
• How to saponify oils without lye? Saponifying oils without lye is not possible for traditional soap-making; however, soap-like cleansers can be made using surfactants and emulsifiers instead of lye-based saponification.