Extracting Process of CNSL and its byproducts

A process for extracting cashew nut shell oil has been developed at Laurenco Marques, Portuguese Africa by Sociedade Imperial De Caju E Oleos LDA, a Portuguese body corporate and has been patented in India in September 1961 (Indian Patent 78612, September 25, 1961)15.

The invention disclosed in the above patent relates to an improved unitary continuous industrial method for extraction of shell oil from cashew nuts which is valuable from industrial and therapeutic point of view and for separation of cashew kernels having exquisite flavour and vitamin content without any contamination by the oil (which is acrid and produces painful inflammation of the skin) and untarnished by treatment.

This method is claimed to have greater advantages in respect of producing quality products at cheaper rates and higher production levels than the primitive extraction methods which entailed more labour, higher costs and lower output.

The CNSL process sequence in basic steps

• Wetting of the cashew nuts by dipping in a hot water vat at 20-25°C to strike a moisture balance between the shell and kernel of the cashew nut and removal of superficial moisture from the nuts and then steaming of the nuts to open up the pores of the shells,
• Subjecting the conditioned nuts dipping in a vat containing cashew nut shell oil where temperature is kept at 170°C to 185°C or preferably at 180°C, for a predetermined period when most of the oil issues out of the shells,
• Vibrating the nuts discharged from the oil bath and subsequent centrifugation in order to remove the adhered oil,
• Incision of the shell walls of the nuts and centrifugation of the seed against a breaking wall,
• Separation of the kernel from the cracked cashew shells and peeling of the skin by heating with hot air and mechanical rubbing of the kernel and effecting the removal of the peel under the action of an air stream; and
• Classifying the peeled nuts and subsequent packing under inert gas in tightly closed containers.

Extraction of Cardanol and Cardol from CNSL

It is known that CNSL mostly contains two important constituents anacardic acid -an acidic substance; and Cardol - a non-acidic material. The main objectives of extraction of Cardanol from CNSL are

• to provide a simple and economical method for isolating the so called cardol complex from anacardic acid,
• to provide an improved method of extraction of the decarboxy lated product 'Anacardol' or otherwise known as 'Cardanol' from cashew nut shell liquid,
• to provide a method of forming and extracting cardanol from CNSL by direct treatment of the oil and not by the indirect route of separation of anacardic acid and then treating the same,
• to provide a simple laboratory apparatus for the extraction of the above materials, Which may ulti mately be practised on a commercial scale and
• to indicate the commercial application of anacardol.

According to the invention CNSL is subjected to fractional distillation at 200° to 240°C under reduced pressure not exceeding 5mm. mercury in the shortest possible time which gives a distllate containing cardol and the residual tarry matter, for example, in the case of a small quantity of oil, say 200 ml/ the distillation period is about 10 to 15 minutes. A semi-commercial or commercial scale distillation of CNSL may however take longer times.

It has been found that there are certain difficulties of operation with regard to single-stage fractional distillation method, i.e. frothing of the oil which renders difficult the fractionation of cardol and also formation of polymerised resin. These difficulties can be over come in the two-stage distillation, if care is taken not to prolong the heating; this is to avoid the undue formation of polymerised resins and possible destruction partially or completely of the cardol or anacardol.

When CNSL is distilled at a reduced pressure of about 2 to 2.5 mm. mercury, the distillate containing anacardol and cardol distils firstly at about 200°C to 240°C. This first distillate is then subjected to a second distillation under the same identical conditions of temperature and pressure when the anacardol distils over at a temperature of 205°C to 210°C and the cardol distils over at a temperature of 230°C to 235°C. In practice it has been found that the preliminary decarboxylation of the oil is essential, since there will be excessive frothing, which renders the distillation procedure unproductive and uneconomical.

A specific feature of this invention is that both cardol and anacardol may be obtained by a three-step process. The first step of the process is to get the decarboxylated oil by heating the oil to a temperature of 170°C to 175°C under reduced pressure of 30-40 mm. mercury. The next two steps are the same as above for the production of both cardol and anacardol. This invention is significant in the sense that it can be applied not only to the cashew nut oil but also to cashew nuts themselves or nut shells.