Extraction of cashew nut shell liquid needs supercritical carbon dioxide and for this process there are certain parameters like the right extraction pressure, temperature and flow rate has to be there. The yield increases with the increase in pressure, temperature and mass flow rate of supercritical carbon dioxide. The physical properties and chemical composition of the oil extracted through super critical fluid extraction (SCFE) is much better that the oil extracted through thermal route. The oil is dark reddish brown in colour and is a natural resin which is used as a raw material for many applications. It is also a useful chemical serving as raw material for the petrochemical industry.
The cashew fruit which is biologically called Anacardium Occidentale L is a known species from the Anacardiceae family. It is a tropical plant which grows in the region between 230N and 230S of the equator. The tree grows well on well-drained, sandy loam soils and it is widely grown in Nigeria all round the year. The tree consists of the cashew nut fruit, a curved edible seed inside in a honeycomb like shell) the apple, leaf and bark. The fruit consists of an outer shell, inner shell and the kernel. The honeycomb matrix contains a dark brown liquid between the outer and inner shell and this is known as cashew nut shell liquid (CSNL). The different parts of the cashew nut are used in medicines, food, chemical and related industries. The tree is also an ornamental plant which controls soil erosion. From planting time to fruiting it takes about 3 to 4 years and the tree can live up to 40 years and more.
There are many methods for the extraction of CSNL and the extraction efficiency depends upon the method adopted. Raw CNS contains over 20%oil and the bath process leaves about 10% of the oil as by product. But with the expeller extraction method the amount of oil wasted is lesser. Extraction can be done with the heating method and cold method. In the heating method the cashew can be heated with the actual CSNL and in the cold process the CSNL can be obtained by extrusion in solvents or by pressing. The liquid obtained by cold method is called natural CSNL and the ones extracted by the hot method are called technical CNSL.