**1.3. Extraction of CNSL**

Several methods are available in the literature for the extraction of CNSL. Oil extraction efficiency varies with the method adopted. Raw CNS has been reported to contain over 20% oil. The oil bath process leaves about 10% of the oil as a by-product in the spent shell. However, using an expeller extraction process, further quantities of oil may be recovered from the spent CNS.

The extraction processes can be classified into two basic types: those that involve heating and those that are done in cold or room temperature. The heating process (roasting) can be achieved by open recipients or drums [11]. In a thermomechanic (hot oil) process, the cashews can be heated by the actual CNSL [12]. In the cold process, the CNSL can be obtained by extrusion in solvents or by pressing. The cashew's liquid so obtained is denoted as natural CNSL and that extracted by the hot method is called technical CNSL [13].

Various hot methods reported in the literature for the extraction of CNSL from cashew nut shells (CNS) include, open pan roasting, drum roasting and hot oil roasting, while cold extrusion, solvent extraction, etc. are cold methods. References [14] and [15] reported CNSL extraction through pyrolysis. The extraction of CNSL using supercritical carbon dioxide has also been reported by [16,17]. Solute extracted using supercritical carbon dioxide in the extraction process is generally significantly different from those obtained by other conven‐ tional alternative processes.

Extraction methods affect the selectivity towards various compounds in CNS [18]. High concentrations of mono-unsaturated cardanol were extracted with Supercritical water (SCW) and soxhlet extraction methods (See Table 1).

Extraction fluid, substrate and operating conditions affect the extract composition (Table 2). CNSL directly obtained from CNS by SC extraction contains traces of acids whereas the same obtained from CNSL through heat exchanger mainly contains cardanol along with acids and alkanes. The oil composition of CNSL obtained through pyrolysis of CNS includes phenols and substituted phenols along with cardanol. For resin production, the CNSL obtained through pyrolysis route is the most suitable feed for extraction by SC method [3].

obtained by extrusion in solvents or by pressing. The cashew's liquid so obtained is denoted as natural CNSL and that extracted by the hot method is called technical CNSL [13]. Cashew Nut Shell Oil — A Renewable and Reliable Petrochemical Feedstock http://dx.doi.org/10.5772/61096 9

Several methods are available in the literature for the extraction of CNSL. Oil extraction efficiency varies with the method adopted. Raw CNS has been reported to contain over 20% oil. The oil bath process leaves about 10% of the oil as a by‐product in the spent shell. However, using an expeller extraction process, further quantities of oil may be recovered

The extraction processes can be classified into two basic types: those that involve heating and those that are done in cold or room temperature. The heating process (roasting) can be achieved by open recipients or drums [11]. In a thermomechanic (hot oil) process, the cashews can be heated by the actual CNSL [12]. In the cold process, the CNSL can be

Figure 5. Flow diagram of cashew nut shell processing **Figure 5.** Flow diagram of cashew nut shell processing

from the spent CNS.

basic pretreatment on samples and include washing, drying, shelling and size reduction. Sometimes, washing may involve the use of detergents to remove likely contaminants.

Drying is purposely to make the nuts moisture-free. Both sun- and oven-drying have been found effective. Size reduction creates a better contacting surface area for the shell and solvent

Traditionally, the kernel is removed for the CNS manually. However, to improve the deshel‐ ling process, several methods have been adopted [1,8,10], which include, among others, soaking the nuts in water to improve the moisture content thereby reducing the scorching and cracking tendencies during roasting. Roasting the nuts makes the shell brittle and loosens the kernel from the shell easily. Also, CNSL is released during the roasting [10]. Figure 5 shows

Several methods are available in the literature for the extraction of CNSL. Oil extraction efficiency varies with the method adopted. Raw CNS has been reported to contain over 20% oil. The oil bath process leaves about 10% of the oil as a by-product in the spent shell. However, using an expeller extraction process, further quantities of oil may be recovered from the spent

The extraction processes can be classified into two basic types: those that involve heating and those that are done in cold or room temperature. The heating process (roasting) can be achieved by open recipients or drums [11]. In a thermomechanic (hot oil) process, the cashews can be heated by the actual CNSL [12]. In the cold process, the CNSL can be obtained by extrusion in solvents or by pressing. The cashew's liquid so obtained is denoted as natural CNSL and that

Various hot methods reported in the literature for the extraction of CNSL from cashew nut shells (CNS) include, open pan roasting, drum roasting and hot oil roasting, while cold extrusion, solvent extraction, etc. are cold methods. References [14] and [15] reported CNSL extraction through pyrolysis. The extraction of CNSL using supercritical carbon dioxide has also been reported by [16,17]. Solute extracted using supercritical carbon dioxide in the extraction process is generally significantly different from those obtained by other conven‐

Extraction methods affect the selectivity towards various compounds in CNS [18]. High concentrations of mono-unsaturated cardanol were extracted with Supercritical water (SCW)

Extraction fluid, substrate and operating conditions affect the extract composition (Table 2). CNSL directly obtained from CNS by SC extraction contains traces of acids whereas the same obtained from CNSL through heat exchanger mainly contains cardanol along with acids and alkanes. The oil composition of CNSL obtained through pyrolysis of CNS includes phenols and substituted phenols along with cardanol. For resin production, the CNSL obtained

through pyrolysis route is the most suitable feed for extraction by SC method [3].

extracted by the hot method is called technical CNSL [13].

to enhance removal of the CNSL.

8 Advances in Petrochemicals

the nut-processing stages.

**1.3. Extraction of CNSL**

tional alternative processes.

and soxhlet extraction methods (See Table 1).

CNS.



**Table 1.** Compound distribution of CNSL obtained by various extraction methods.



**Table 2.** Chemical characterization of CNSL extracted by SCFE

**Constituents Soxhlet extraction**

**Table 1.** Compound distribution of CNSL obtained by various extraction methods.

**SC-CNSL from CNS**

Hexadecanoic acid (0.71) Oleic acid (0.62) Cardanol-C13 (0.69) Cardanol-C15 (84.20) Methyl Cardanol (2.83)

Hexadecanoic acid (0.56) Oleic acid (0.684 Cardanol-C13 (0.65) Cardanol-C15 (86.26) Methyl Cardanol (3.11)

Hexadecanoic acid (0.58) Cardanol-C13 (7.42) Cardanol-C15 (64.89)

Monounsaturated anacardic acid

10 Advances in Petrochemicals

Source: [18]

**(P bar/T°C)**

200/60

225/60

250/60

**Operating Parameter**

**SCW extraction**

β-Sitosterol 1.38 1.86 1.63 1.63 0.75 1.76

Monounsaturated cardol 1.05 – – – 0.57 – Saturated cardol 20.31 34.88 1.85 29.58 9.76 12.64 Di-unsaturated cardol 7.62 10.39 – 6.72 4.13 6.07 Unknown hydrocarbon 5.7 – – – – 3.33 Triacontene 3.33 3.41 – 4.31 1.85 5.45 Others 4.85 1.76 0.66 2.91 7.52 2.03

**Hexane Methanol Hexane-SCW**

**SC-CNSL from CNS Obtained through Heat Exchanger Unit**

Penthadecane (0.67) Hexadecane (0.67) Heptadecane (0.77) 2,6,10,14 tetra methyl pentadecane (0.65)

Elicosane (0.47) Cardanol (62.31) Cardanol diene (31.24)

Penthadecane (0.04) Heptadecane (0.08) tetradecanal (1.99)

8 methyl heptadecane (0.70) Hexadecanoic acid (0.61)

27.90 19.06 9.47 52.24 18.64 11.4

**SC-CO2 extraction**

**Two-step extraction**

**SC-CNSL from Pyrolysis**

3-ethyl phenol (7.64)

3-butyl phenol (1.39) Cardanol diene (48.61)

3-ethyl phenol (3.31) Azulene (1.89)

4-ethyl phenol (5.01) Propyl benzene (11.96) Acenaphthylene (2.83)

Ethyloxybenzene (11.21) Acenaphthylene (7.12) 3-butyl phenol (2.28) Cardanol diene (66.82)

2-methyl benzaldehyde (20.51)

**CNSL**

**Methanol-SCW**

> Purification or refining of CNSL involves vacuum distillation of raw CNSL. However, supercritical fluid extraction SFE of CNSL can offer selective separation of the components present in CNSL by varying the operating parameters [19].
