Solvents and co-solvents selection for the extraction of castor oil from castor seeds

Abstract

There has been a notable demand increase in the manufacturing market globally for castor oil and the products derived from castor oil. Castor oil consists of almost 90% of ricinoleic fatty acid, and it is nearly a pure compound. Castor oil is renewable and naturally occurring. It is known to have multiple uses, and the derivatives are known to be used in the manufacturing of paints, soaps, and perfumes and used in the pharmaceutical industry. The chemical industrial extracts castor oil from castor seed using hexane as solvent. However, there are growing concerns around the use of petrochemical derived solvents, volatile organic compounds (VOC) emissions and use of nonrenewable resources which impact the environment negatively. This study is aimed to evaluate and find the best green solvent to extract castor oil with the highest yield and easiest recovery. Green solvents are derived from renewable resources and have minimal or no impact on the environment. The investigated green solvents were alpha-pinene, p-cymene, limonene, ethanol, and furfural, these solvents were also used as co-solvents. The Soxhlet extraction method was employed to investigate different green solvents. Hexane was used as a reference. It was found that green solvent extraction capabilities or yield can be ranked as follows: furfural is 47.13%, ethanol is 45.37%, limonene is 39.15%, p-cymene is 39.15% and α-pinene is 38.11%. For the co-solvent mixtures, d-limonene-ethanol is 34.80%, α-pinene-ethanol is 41.09% and pcymene-ethanol is 43.29%. Whilst furfural had the highest yield from the extraction, the furfural recovery process proved to be challenging. The oil and solvent mixture were separated by simple distillation, this process recovered the solvent used by separating the oil from the solvent. Ethanol was discovered to be the next best solvent for extraction as it had a yield of 45.37%, it was easily recovered after the extraction. The yield for ethanol was achieved in a period of 2 hours, whereas that of furfural was recorded at a period of 5 hours. Ethanol produced a satisfying yield at a shorter time frame than Furfural. Hexane recorded a percentage yield of 31.36% for a period of 3 hours and 30 minutes. Percentage yields of 33.4% and 31.99% were reported in literature, and they were reported to have been obtained in a period of 6 hours, this was explained to have been a result of extraction temperature, extraction time and polarity of the solvent among other factors. The physical properties of the recovered solvents were measured and compared with that of pure solvents. The data for the best solvent was used to design a suitable extraction column. Finally, the economic feasibility was conducted for the extraction process. It was recommended that one use the data to upscale and design all other process equipment. One is recommended to investigate the challenges of recovering furfural solvent.