Castor oil is gaining immense popularity as a bio-based raw material for industrial applications. The oil, extracted from castor beans, is non-edible and has long been considered to have important commercial value, primarily for producing lubricants, soaps, coatings, etc. It is a mixture of unsaturated and saturated fatty acid esters linked to glycerol.
Since the oil contains a hydroxyl group, a double bond, a carboxylic group and a long-chain hydrocarbon in ricinoleic acid, it can be converted into several materials. This makes castor oil a potential alternative to petroleum-based starting chemicals for producing materials with different properties.
Introduction to Castor Oil
The castor plant (Ricinus communis) belongs to the Euphorbiaceae family and grows wild in varied climatic conditions. It produces castor seeds that contain up to 50% oil by weight. It is easy to extract castor oil from castor seeds and use it in plenty of sectors, including chemicals, medicine, beauty, and other technologies.
Castor oil is recognized as one of the most valuable herbal remedies in the world. It possesses healing properties and is used by practitioners since ancient times for the betterment of the health of civilizations.
Globally, the demand for oil and its derivatives is increasing steadily because of its renewable nature, biodegradability, eco-friendliness, non-competition with food, and low costs. The oil is believed to have more than 700 industrial uses, with more being added consistently. As a result, it is no surprise that the global castor oil derivatives market is expected to rise to USD 1.9 billion by 2030 from USD 1.21 billion in 2021.
The chemistry of castor oil focuses on ricinoleic acid because of its high content, along with the presence of three functional groups. These groups in the oil are vital for the versatility of the oil, aiding the production of a variety of castor oil-based products.
Chemical Transformations of Castor Oil
Castor oil is not an ordinary oil. It has unique properties, varied applications, and the ability to produce a multitude of functional materials. It is such a versatile oil that by adding specific reactants and performing different chemical reactions, it is possible to manipulate its unique properties by exploiting the various functional groups like the vinyl group and the hydroxyl group, an ester linkage. These processes can transform the oil into a potentially renewable resource for innumerable industrial uses.
Castor oil, in its physical form, is pale yellow nonvolatile, viscous, and non-drying, making it suitable for withstanding multiple chemical processes. Some chemical reactions, modifications, and transformations include hydrogenation, hydrolysis, pyrolysis, sulphation, dehydration, and transesterification.
The process is commonly used in the industry of polymer materials. It produces a saturated 12-hydroxystearic acid by introducing a hydrogen atom to the unsaturated fatty acid in the presence of a catalyst. The result is the transformation of ricinoleic acid into a wax-like semi-solid material.
During this chemical reaction, castor oil is mixed slowly with an 80% caustic solution (sodium hydroxide). The temperature is maintained between 250°C and 360°C to produce ricinoleic acid and glycerol. This mixture, on being heated at 523 K with NaOH as a catalyst, transforms into sebacic acid (a 10-carbon dicarboxylic acid) and capryl alcohol (2-octanol). The resulting solutions are largely used as a monomer for nylon synthesis.
The process is a highly popular thermal method performed for converting biomass to solid, liquid, and gaseous fuels without oxygen. During the reaction, castor oil splits the molecule to generate heptaldehyde and undecylenic acid, preventing biomass combustion into carbon dioxide because of the absence of air.
The sulphation of castor oil produces turkey-red oil, extensively used in cosmetics and textile industries. It introduces an SO3 group into an organic compound to produce the characteristic configuration of C-OSO3. For the esterification of the hydroxyl group of ricinoleic acid, raw castor oil is treated at room temperature or a temperature below 308K for 3 to 4 hours with concentrated sulphuric acid.
This is an acid-catalyzed reaction where ricinoleic acid, the main component of castor oil, reacts with an acid. The catalyst can be phosphoric acid or sulfuric acid. It helps in getting rid of the hydroxyl group in the form of water to introduce a new double bond leading to the production of non-conjugated and conjugated linoleic acid.
In this process, vegetable oil molecules are broken down through the reaction of an alcohol with an ester. The glycerol functional group is removed from the triglyceride and replaced by alcohol to produce glycerol and biodiesel.
There are multiple other ways to treat castor oil for the production of a fleet of castor oil derivatives available in the market today.
The Limitless Applications of Castor Oil
Castor oil is rich in nutrients, and its derivatives are popular in almost all industry sectors, including plastic and rubber, personal and beauty care, oleochemical, paints, textiles, detergents, lubricants and greases, pharmaceuticals, etc.
It has diverse applications and serves as the main ingredient for manufacturing various products, such as soaps, shampoos, dyes, adhesives, body lotion, leather treatments, caulks, brake fluids, electric liquid dielectrics, inks, humectants, hydraulic fluids, lip gels, machining oils, paints, sealants, washing powders, textiles, waxes, refrigeration lubricants, purgative, germicidal agents, lubricating greases, polyurethane adhesives, lacquers, disinfectants, emulsion stabilizers, skin-conditioning agents, and pigments, there is no end to the list.
With the ability to produce a wide range of chemicals and products, castor oil has proven the plants’ value to be an essential and potential non-edible oilseed crop. Its great utilitarian value in the pharmaceutical, cosmetics, agriculture and industrial sectors highlights how it is a potential bio-based starting material. The oil derives its unique properties of transforming into vital industrial raw materials from the presence of a hydroxyl group, carboxylate and double bonds in the ricinoleic acid.
Castor oil is a potential renewable source for the production of a host of functional materials. Moreover, it is well concluded that the diverse possibilities of castor oil transformation are attributed to the existence of the three functional groups. The oil has a distinctive chemical structure, and its global demand is due to its non-food competition, low cost, and easy availability.