**4. CNSL as petrochemical feedstock**

As a substituted phenol which can take part in a variety of reactions, naturally occurring cashew nut shell liquid (CNSL), a renewable product, offers advantages over synthetics. Its innumerable application stems from the phenolic nature of its constituents, with enshrined features for transformation into high value specialty chemicals [26].

The industrial applications of CNSL-based products are numerous and include fungicide, pesticide, insecticide, brake linings, paints and primers, foundry chemicals, lacquers, cements, specialty coatings and resin. The application of CNSL component in bacteriostatic antibiotics is recently gaining attention. Their effect on plant growth, acid activity, wood preservative and pressure treatment activity are being explored. From the literature [27 - 29], much of the biological activity of CNSL has been attributed to anacardic acid: a major constituent of CNS. Conversely, technical CNSL, as obtained by roasting or oil bath method contained mainly cardols and cardanols [27].

**Components**

14 Advances in Petrochemicals

**Table 4.** Composition of the extracted CNSL

pH obtained for the extracts.

heating temperature of 140°C for 1 h.

**4. CNSL as petrochemical feedstock**

**CNSL (pyrolysis)**

does not require further processing like Trans esterification.

respectively. This gave credence to the report of [25].

Cardol (%) 27 30 31 Cardanol (%) 54 20 65 Anacardic acid (%) 5 43 2 Others (%) 14 7 2

Decarboxylation of raw CNSL involves loss of a carbon dioxide molecule from anacardic acid. The anacardic acid in the oil was converted to cardanol. This is reflected in the composition variation of the components reported in table 4. It is also significant that the pyrolysis of the CNS results in loss of the carboxylic acid content of the cashew nut shell to the process. The decarboxylated anacardic acid is termed CNSL biodiesel. The biodiesel obtained from CNSL

CNSL biodiesel is considered as offering many advantages, including sustainability, decrease of HC, CO, NOx gas emissions and many harmful pollutants [23]. Reference [24] explains the pyrolysis procedure of CNSL. The decarboxylation of CNSL is responsible for the trend in the

Most of the characteristics evaluated gave similar results as those already reported in the literature. In the present findings, the highest occurrence of cardanol was in the decarboxylated CNSL while anacardic acid and cardol occur most in the hexane-extracted and pyrolysis CNSL,

Heating CNSL decomposed the anacardic acid into cardanol and CO2. Decarboxylation of CNSL to convert anacardic acid into cardanol could be done by heating, with an optimum

As a substituted phenol which can take part in a variety of reactions, naturally occurring cashew nut shell liquid (CNSL), a renewable product, offers advantages over synthetics. Its innumerable application stems from the phenolic nature of its constituents, with enshrined

The industrial applications of CNSL-based products are numerous and include fungicide, pesticide, insecticide, brake linings, paints and primers, foundry chemicals, lacquers, cements, specialty coatings and resin. The application of CNSL component in bacteriostatic antibiotics is recently gaining attention. Their effect on plant growth, acid activity, wood preservative and pressure treatment activity are being explored. From the literature [27 - 29], much of the biological activity of CNSL has been attributed to anacardic acid: a major constituent of CNS.

features for transformation into high value specialty chemicals [26].

**CNSL (hexane extracted)**

**CNSL (decarboxylated)**

> CNSL reduces the extent of the electrochemical processes taking place on carbon steel surface undergoing corrosion. The inhibition tendency is excellent for both static and dynamic conditions. CNSL and its derivatives have antioxidative characteristics [28 - 30]. This antioxi‐ dative tendency is related to the electron-donating nature and steric effect of the substituents. The electron-donating effect usually enhances the electron density at the phenolic oxygen of the cashew nut oil, resulting in the trapping of the radicals which normally propagates oxidation reaction. CNSL is a mixture of hindered phenols with long alkyl substitution at the *meta* position. The unsaturation on the long side chain substituents is an important factor enhancing higher anti-oxidant activity of CNSL. CNSL films are thermally stable. This stability increases in the presence of thiophosphate ester additives.

> Olefin metathesis (OM) reaction on cardanol is an important class of reactions that allows for the synthesis of new olefins that are sometimes impossible to prepare via other methods [31]. Cardanol- a renewable, low cost, main constituent (about 85%) of CNSL possesses character‐ istic long alkyl chains in *meta* position of its phenol ring [12] that promotes this OM reaction, and also influences several chemical transformations leading to novel functionalities [31].

> Cardanol based polyhydrins improve the photo-catalytic activity of bare TiO2. The porphyrins are brown-red sticky solids, very soluble in CHCl3 or CH2Cl2 [32]. This substituted cardanolbased porphyrin and their metallic complexes have been used extensively in photo degrada‐ tion of toxic, bio-refractory 4-nitro phenol in water, which is dangerous for the ecosystem and for human health [32]. CNSL is also useful in fuel blends and fuel mixtures [33] and for producing diesel oil [34]. Cracking of CNSL with a molecular sieve at 500° C for 2 h generates brown coloured liquid product. This is diesel fuel.

> Cashew Nut Shell Liquid (CNSL) was used as an alternative fuel for diesel engine. The viscosity of CNSL is 30 - 35 times higher than diesel; hence different blends of CNSL would have different properties and application. Also, modification of the oil and its application condition such as, injection pressure, injection timing and preheating the oil also optimizes the perform‐ ance of the engine. There were indications that preheating of CNSL25 blends at 200 kg/cm2 injection pressure and 28° injection timing gives encouraging results suitable for commercial purposes [35]. CNSL as a bioadditive in engines increases the durability of the equipment. Hence, the application of CNSL as a bioadditive will reduce the dependency on petroleum products besides preserving the environment by lowering pollutant residues from fuel combustion products. Some of the properties of diesel, biofuel and ethanol are presented against CNSL in Table 5.

> CNSL has higher density than diesel. It can be reduced by degumming and trans esterification. Cetane for CNSL is expected to be poor due to the presence of aromatic compounds. The usual C:H:O ratio for vegetable oils is 78:12:10 whereas for CNSL it is 80:12:8; hence, it justifies the higher calorific value of CNSL (47 MJ/kg), whereas for diesel it is 42 MJ/kg. Also, ash content is well within the limits for CNSL. The water content of CNSL is quite high. The sulphur content does not exceed 0.006% for any vegetable oil. Thus it is anticipated that CNSL has no sulphur

content. The flash point for CNSL is 164°C; this is higher than the flash point for diesel and represents the higher starting ignition temperatures and compression of CNSL [35].


**Table 5.** Fuel properties

The physicochemical properties of cashew nut shell liquid (CNSL) make it potentially useful for improved adhesion between bitumen and aggregates. Thus, the asphalt resulting from bitumen modified with CNSL has better stripping resistance and satisfactory mechanical properties compared with conventional asphalts. The CNSL, as an additive, prevents stripping in the asphalts, thereby contributing to its moisture damage resistance [36].

CNSL has also been used in production of asbestos with free friction composition for brake linings [37]. In combination with cardanol, it is used extensively in automotive break-lining applications [38]. CNSL/cardol-based surface coatings possess excellent gloss and surface finish with a high level of toughness and elasticity.

Valuable chemicals result from the pyrolysis of CNSL at high temperatures (450°C to 750°C) and at short residence times [39]. The products of pyrolysis include tar, phenols, hydrocarbons and gases with high petrochemical values.

On the other hand, cardanol which is highly resistant to softening action of mineral oil, acids, alkalis, microbes, termites and insects is widely used in the coating and resin industry. Reference [40] reported that technical CNSL may also contain phytosterol, such as stigma sterol and β-sitosterol, which have cholesterol-lowering properties.

Cardanol polysulfide (CPS) has been used as a vulcanizing agent for natural rubber as reported by [41]. Coordination bond linkage in cardanol-aldehyde condensation polymers improved its physicomechanical properties. This positively influences the anticorrosive properties and stability of the polymeric compound at high temperature [42]. The blend of cardanol-based novolac-type phenolic resins, with commercial epoxy or isocynate monomers produces thermoset polymers [43]. Also, in [44], the conversion of CNSL-based cardols (6-alkenylresor‐ cinols) into lasiodiplodin, a naturally occurring 12-membered orsellinic acid type macrolide, exhibits plant growth-regulating and antileukemic properties.

Immature CNSL (iCNSL) has excellent protective activities in strains of *S. cerevisiae* against oxidative damage induced by hydrogen peroxide and inhibits acetyl cholinesterase activity [45]. The high in vitro antibacterial activity of cashew nut shell liquid (CNSL) has been attributed to its anacardic acid content [46]. Both anacardic acid and cardol were reported to have antitumor [47-49], antimicrobial [48], urease inhibitory [50] and lipoxygenase activities [51]. Gram positive bacteria, which cause tooth decay, acne, tuberculosis, *Streptococcus pneumonia, Francisella tularensis,* and leprosy are killed by anacardic chemicals [52].

content. The flash point for CNSL is 164°C; this is higher than the flash point for diesel and

The physicochemical properties of cashew nut shell liquid (CNSL) make it potentially useful for improved adhesion between bitumen and aggregates. Thus, the asphalt resulting from bitumen modified with CNSL has better stripping resistance and satisfactory mechanical properties compared with conventional asphalts. The CNSL, as an additive, prevents stripping

CNSL has also been used in production of asbestos with free friction composition for brake linings [37]. In combination with cardanol, it is used extensively in automotive break-lining applications [38]. CNSL/cardol-based surface coatings possess excellent gloss and surface

Valuable chemicals result from the pyrolysis of CNSL at high temperatures (450°C to 750°C) and at short residence times [39]. The products of pyrolysis include tar, phenols, hydrocarbons

On the other hand, cardanol which is highly resistant to softening action of mineral oil, acids, alkalis, microbes, termites and insects is widely used in the coating and resin industry. Reference [40] reported that technical CNSL may also contain phytosterol, such as stigma sterol

Cardanol polysulfide (CPS) has been used as a vulcanizing agent for natural rubber as reported by [41]. Coordination bond linkage in cardanol-aldehyde condensation polymers improved its physicomechanical properties. This positively influences the anticorrosive properties and stability of the polymeric compound at high temperature [42]. The blend of cardanol-based novolac-type phenolic resins, with commercial epoxy or isocynate monomers produces thermoset polymers [43]. Also, in [44], the conversion of CNSL-based cardols (6-alkenylresor‐ cinols) into lasiodiplodin, a naturally occurring 12-membered orsellinic acid type macrolide,

Immature CNSL (iCNSL) has excellent protective activities in strains of *S. cerevisiae* against oxidative damage induced by hydrogen peroxide and inhibits acetyl cholinesterase activity [45]. The high in vitro antibacterial activity of cashew nut shell liquid (CNSL) has been

represents the higher starting ignition temperatures and compression of CNSL [35].

) 0.84 0.789 0.9326

**Properties Diesel\* Ethanol\* CNSL**

Kinematic viscosity (cost) 2-5 1.19 17.2 Calorific value (kJ/kg) 42000 30000 47600 Flash point (°C) 62 16 193 Auto-ignition temperature (°C) 210 362 206

in the asphalts, thereby contributing to its moisture damage resistance [36].

finish with a high level of toughness and elasticity.

and β-sitosterol, which have cholesterol-lowering properties.

exhibits plant growth-regulating and antileukemic properties.

and gases with high petrochemical values.

Density (kg/m3

16 Advances in Petrochemicals

\*Source: [28]

**Table 5.** Fuel properties

Anacardic acid has also been found to reduce the expression of survivin and X-linked inhibitor of apoptosis protein, anti apoptotic proteins associated with cellular survival and radio resistance, and radio-sensitized pituitary adenoma cells [53]. Also, these acids have been used effectively against tooth abscesses due to their lethality to bacteria.

The monophenolics of CNSL have been found to form stable quaternary nitrogen compounds which are soluble in water, odourless and act as surface-active agents [54]. These properties including their high bacterial activity, have made them significantly useful as germicides, disinfectants and sanitizing agents in food and dairy industries. Also, sodium salts of anacardic acid, for example disodium anarcadates, are anionic surfactant and could be used as bacteri‐ cidal surfactant while sodium anarcadate is useful for the control of vector mosquitoes which are responsible for causing dengue fever [55].

Energy studies established that cashew nut by-products CNSL, its isolates and spent CN Shell compare quite favourably with conventional fuels in terms of energy content. CNSL, cardanol and cardol, which are liquid by-products, were superior to conventional liquid and solid fuels while spent CN shell was more superior to a number of liquid fuels, e.g. ethanol and methanol, as well as fire wood in terms of energy content. This material is advocated for use by cashew nut processors and other industries as fuel to reduce environmental pollution. This material is not only a cleaner fuel but also has low ash and is renewable [56].

Substitution of phenol with CNSL in both resol and novolacs decreased the tensile strength, but improved the impact strength of wood flour-based laminate of these resins. Thermal properties of phenol-cardanol-based resin depletes with increasing cardanol content in the resin [57, 58].

The synthesis of polymers from renewable resources has attracted considerable attention worldwide due to its potential attribute as a substitute for petrochemical feedstock. CNSL may act as a potential raw material for the manufacture of polymers in the 21st century [58] due to its components and depletion in petroleum production which increasingly faces exhaustion. Long-chain, *m*-substituted phenol in CNSL is highly reactive. Thus a wide variety of resins are synthesized from CNSL, such as polyesters, phenolic resins, epoxy resins, polyurethanes, acrylics, vinyls and alkyds to mention a few [59].

CNSL contains four major components: 3-pentadecenyl phenol (cardanol), 5-pentadecenyl resorcinol (cardol), 6-pentadecenyl salicylic acid (anacardic acid) and 2-methyl 5-pentadecenyl resorcinol (2-methyl cardol), which can be good replacement for synthetic resins, owing to the current climate of diminishing petroleum reserves. Cardanol, which is a phenol derivative, has a meta substitute of a C15 unsaturated hydrocarbon chain with one to three double bonds [31, 32, 60, 61]. Being a major component of CNSL, its abundant production promised renew‐ able feedstock for the petrochemical industry with a total production of CNS approaching 2.6 million tons annually [1].

Resoles and novolacs resins are the major products of reaction of CNSL with formaldehyde. While novolac results from acid-catalyzed reactions, resoles are a product of base-catalyzed reactions.

CNSL can be polymerized by different methods. This includes addition polymerization through the side-chain double-bonds using cationic initiators such as diethylsulphate, condensation polymerization through the phenolic rings with aldehydic compound, e.g. formaldehyde, oxidative polymerization, polymerization after chemical modification to produce specialty properties, etc. The most common method is condensation reaction with formaldehyde. The CNSL-based polymers offer advantages such as improved flexibility and reduced brittleness, solubility in organic solvents, improved process ability, compatibility with other polymers, high performance and resistance to microbes, insects and termites.

CNSL were successfully applied as a thermosetting wood adhesive for wood panels to reduce formaldehyde emission. These renewable phenolic compounds give excellent adhesive performance, good moisture resistance and tend to give a lower formaldehyde emission than UF resin [62, 63].
