Bioresource Technology 97 (2006) 847–853 Extraction of cashew (Anacardium occidentale) nut shell liquid using supercritical carbon dioxide Rajesh N Patel, Santanu Bandyopadhyay, Anuradda Ganesh * Energy Systems Engineering, Indian Institute of Technology, Bombay, Powai, Mumbai 400 076, India Received August 2004; received in revised form April 2005; accepted April 2005 Available online June 2005 Abstract This work investigated the extraction of cashew nut shell liquid (CNSL) using supercritical carbon dioxide (SC-CO2) Effects of process parameters such as extraction pressure, temperature and flow rate of SC-CO2 were investigated The yield of CNSL increased with increase in pressure, temperature and mass flow rate of SC-CO2 However, under different operating conditions, the composition of CNSL varied The study of physical properties and chemical composition of the oil obtained through super critical fluid extraction (SCFE) showed better quality as compared to the CNSL obtained through thermal route Experimental results were compared with diffusion based mass transfer model Based on this simple model, extraction time was optimized Ó 2005 Elsevier Ltd All rights reserved Keywords: Cashew nut shell; Supercritical fluid extraction; Carbon dioxide; Mass transfer model; Optimum extraction time Introduction India is the largest producer and processor of cashews (Anacardium occidentale) in the world (Das and Ganesh, 2003) In India, cashew cultivation covers a total area of about 0.77 million hectares of land, with an annual production of over 0.5 million metric tonnes of raw cashew nuts The average productivity per 100,000 m2 is around 760 kg The world production of cashew nut kernel was 907,000 metric tonnes in 1998 (Smith et al., 2003) The cashew nut shell liquid (CNSL) is reported to be 15–20% by weight of the unshelled nut in Africa and 25–30% by weight in India (Das and Ganesh, 2003) Considering the shell weight is about 50% of the weight of the nut-in-shell (NIS), the potential of CNSL is about 450,000 metric tonnes per year In India, processed cashew dominates more than half the world cashew market The residue after extraction of CNSL is shell cake, * Corresponding author Tel.: +91 22 25767886; fax: +91 22 25726875 E-mail address: aganesh@me.iitb.ac.in (A Ganesh) 0960-8524/$ - see front matter Ó 2005 Elsevier Ltd All rights reserved doi:10.1016/j.biortech.2005.04.009 which is a very useful fuel and a substitute for fire wood The innumerable applications of CNSL are based on the fact that it lends itself to polymerization by various means Various methods have been reported in literature for the extraction of CNSL from CNS, which include, open pan roasting, drum roasting, hot oil roasting, cold extrusion, solvent extraction, etc The extraction through vacuum pyrolysis has been reported recently by Das et al (2004) and Tsamba (2004) The extraction of CNSL using supercritical carbon dioxide (SC-CO2) has also been reported by Shobha and Ravindranath (1991) and Smith et al (2003) Conventionally, both the quantity and quality (composition of CNSL) vary with the method of extraction of CNSL Various authors have reported varied composition of CNSL extracted CNSL extracted by cold extrusion method is reported to contain approximately 70% anacardic acid, 18% cardol and 5% cardanol and the balance consisting of substituted phenols and less polar substances (http://www.epa.gov/chemrtk/cnsltliq/c13793 tp.pdf) Das (2004) has also reported CNSL extracted 848 R.N Patel et al / Bioresource Technology 97 (2006) 847–853 by cold extrusion method with 90% anacardic acid and nearly 10% cardol According to Tyman (1979), natural CNSL contains nearly 64% anacardic acid, 11% cardol, traces of cardanol, 2–3% of 2-methyl cardol and rest polymeric material About 52% cardanol, 10% cardol and 30% polymeric material (Das, 2004) constitutes the Technical Grade CNSL A composition 64.8% cardanol, 20.5% cardol, 2.8% 2-methyl cardol, and rest as non-volatile polymeric material have also been reported (Tyman, 1975) for the Technical Grade CNSL The CNSL obtained through vacuum pyrolysis is cardanol rich It is reported to have cardol, substituted phenols, di-n-octyl phthalate, bis(2-ethyl hexyl) phthalate, etc The use of this CNSL as a potential fuel in internal combustion engine has also been suggested (Das, 2004) However, the composition of CNSL obtained by SCFE has not been reported in the literature SCFE, as mentioned by the authors Shobha and Ravindranath (1991) and Smith et al (2003), has inherent advantages over other extraction methods such as no polymerization of CNSL, requirement of less amount of solvent, and no extraction of undesirable coloured compounds In view of this, the present work is an attempt to study the effect of operating parameters on the yield and quality of CNSL extracted through SCFE method A simple mathematical model is also developed for optimization of profit and energy/yield The objective of the study is also to demonstrate the feasibility of the component separation of CNSL using SCFE, particularly the higher molecular substances like cardanol Experimental procedure Cashew nut shell (CNS) obtained from Pondicherry was used for the present study The shells were ground to small particles (to pass through mesh screen) and weighed and then placed in the extractor Carbon dioxide (99.9%) supplied by M/s Sicgil Corporation, Bombay, was used as the supercritical fluid (SCF) for extraction of oil from CNS SCFE unit supplied by M/s Deven Supercritical was used for the present study Carbon dioxide from the cylinder passed through a pre-cooler, a positive displacement pump, and a pre-heater before it entered the bottom of the extraction vessel (The extraction vessel was maintained at a predefined temperature.) The flow of carbon dioxide was controlled by a needle valve and was measured by a gas flow meter with an accuracy of ±0.01 kg/h A variable frequency drive pump controlled the pressure in the vessel to an accuracy of ±0.1 bar Extracted oil was recovered by expansion of the loaded solvent stream to ambient pressure in a glass separator Extract was collected and weighed at a fixed time interval of 30 (cumulatively) by closing the needle valve The needle valve was then opened and extraction process continued for the next interval Runs were carried out for h at the pressures ranging from 200 to 300 bar at 25 bar intervals The extract of each run was analysed by Gas Chromatograph Mass Spectroscopy (GC-MS) and Fourier Transform Infra-Red Spectroscopy (FTIR) Results and discussion 3.1 Effect of pressure on yield of CNSL The total yield at various pressures from 200 bar to 300 bar, keeping other parameters constant, is shown in Fig Temperature and mass flow rate of carbon dioxide were kept constant at 333 K and 1.0 kg/h respectively Evidently total yield increased with increase in pressure from 200 bar to 300 bar—the yield being four to five times higher at 300 bar than at 200 bar for the same consumption of SC-CO2 (at the same flow rate and temperature) This could be explained by the fact that the extraction capacity of solvent at the supercritical state was density dependent It was also observed that the rate of extraction was high during initial phase of extraction as the material is loaded with oil The rate of extraction decreased at later stages as shown in Fig The FTIR analysis was used to identify the components, particularly ÔcardanolÕ 3.2 Effect of pressure on the yield of cardanol The samples were analysed by FTIR, GC-MS and Ultraviolet (UV) spectroscopy The FTIR and GC-MS aided in identifying the functional groups present and the components, respectively The UV spectroscopy, calibrated for a commercial grade refined cardanol sample, was used to determine the approximate percentage of cardanol in the samples The results of FTIR, GC-MS and UV spectroscopy are summarized in Table It was interesting to note that ÔacidÕ group was traced by Fig Variation in yield of CNSL and cardanol with extraction pressure (extraction time 270 min, extraction temperature 333 ± 0.5 K and mass flow rate of SCF ± 0.01 kg/h) cardanol cardanol cardanol, cardol cardanol, dimethyl anacardate C-17 C-17 C-17 C-17 decenyl)phenol, decenyl)phenol, decenyl)phenol, decenyl)phenol, 3-(8-penta 3-(8-penta 3-(8-penta 3-(8-penta cardanol, cardanol, cardanol, cardanol, C-13 C-13 C-13 C-13 alkenes alkenes carboxylic acid, alkenes carboxylic acid, alkenes alkanes, alkanes, alkanes, alkanes, O–H, O–H, O–H, O–H, 200 ± 0.1 225 ± 0.1 250 ± 0.1 300 ± 0.1 Polymeric Polymeric Polymeric Polymeric Major components identified (GC-MS) It is well understood that with increase in solvent to solid ratio, the rate of extraction is enhanced, and hence extraction time is reduced The effect of mass flow rate of SCF on total yield is shown in Fig It was observed that with increase in flow rate of SCF, total CNSL yield increased However, due to lower retention time, loading of SCF was lower, thereby reducing the capacity utilization of the solvent Functional groups (FTIR) 3.4 Effect of mass flow rate of SCF on the yield of CNSL Pressure (bar) It is known that the yield of extract depends on the change in density and volatility of SCF With increase in temperature, the density of SCF decreased while volatility increased (Mukhopadhyay, 2000) Hence experiments were carried out at isochoric density by modifying pressure The effect of temperature on total yield of CNSL is shown in Fig It could be seen that with increase in temperature, total yield of CNSL increased at a given mass flow rate and density Serial no 3.3 Effect of temperature on yield of CNSL Table Effect of pressure on the yield of cardanol (extraction parameters: extraction temperature 333 ± 0.5 K, mass flow rate 1.0 ± 0.01 kg/h) Fig Cumulative yield of CNSL at different extraction pressure Experimental conditions: mass flow of CO2 1.0 ± 0.01 kg/h, extraction temperature 333 ± 0.5 K FTIR only for CNSL obtained above 225 bar However, GC-MS did not identify Ôanacardic acidÕ as a major group and therefore, was assumed to be in traces GC-MS and FTIR analysis showed that at lower pressure CNSL mainly consisted of cardanol Amount of cardanol in CNSL decreased with increase in pressure from 86% at 200 bar and 333 K to 63% at 300 bar and 333 K Fig shows the CNSL yield, percentage cardanol in CNSL extracted and percentage cardanol extracted based on original CNS used This percentage cardanol was the product of the percentage yield of CNSL with percentage cardanol in CNSL The cardanol yield, therefore, was higher at higher pressure 86 83 76 63 849 Cardanol percentage (UV specroscopy) R.N Patel et al / Bioresource Technology 97 (2006) 847–853 850 R.N Patel et al / Bioresource Technology 97 (2006) 847–853 sis It could be observed that the moisture content, density and viscosity of oil obtained through SCFE were very close to IS:840 (1969) specifications, whereas these properties were better as compared to CNSL obtained through vacuum pyrolysis Other properties of CNSL extracted using SCFE were very close to that obtained by vacuum pyrolysis The comparison of this oil with oil obtained through vacuum pyrolysis was relevant in terms of CNSL as a potential bio fuel Fig Cumulative yield of CNSL at different extraction temperatures Experimental conditions: mass flow of CO2 1.2 ± 0.01 kg/h, density of SCF 830 kg/m3 3.5.2 Chemical composition of CNSL The oil obtained at various operating parameters was analysed for chemical compositions Table shows the main components present in CNSL obtained at various operating parameters It was noted that the main component in CNSL was cardanol with side chain having 13–17 carbon atoms; however, their concentration was different at different operating parameters This could be attributed to the enhanced decarboxylation at higher pressure (Hazen et al., 2002) 3.6 Residue analysis The residue, after extracting oil from CNS at 300 bar and 333 K in supercritical fluid extractor was pyrolysed at 773 K under vacuum of 700 mm of Hg The vapours were condensed to find the condensates The weight of the condensed oil was hardly found 2% suggesting almost complete extraction of CNSL Mathematical model and optimization Fig Cumulative yield of CNSL at different extraction flow rates of SC-CO2 Experimental conditions: pressure 250 ± 0.1 bar, temperature 333 ± 0.5 K 3.5 Properties of oil extracted by SC-CO2 3.5.1 Physical properties of CNSL The physical properties of the oil extracted at various operating conditions were studied using standard test procedures It was observed that the calorific value of the oil was almost same for all extraction conditions while the density was in the narrow range of 0.92– 0.934 kg/m3 Table gives the comparison of physical properties of oil extracted at 300 bar and 333 K—using SCFE with IS:840 (1964) and oil obtained through vacuum pyroly- In extraction, the solute from the cell matrix dissolved into the bulk fluid Extraction of the solute becomes simple when it is free on the surface of solids On the other hand, as the solute interacts with cell matrix its extraction becomes difficult For natural material with a high initial content of extractable, the rate of extraction remains constant at the initial period As the outer surface of the solid is depleted of the extractable solute, solute from the core of the solid requires more time to reach the fluid–solid interface This results in a drop in the rate of extraction with time (Gangadhara Rao, 1990) For extraction, several models have been proposed: unsteady-state packed bed mass transfer model (Mukhopadhyay, 2000), shrinking core leaching model (Mukhopadhyay, 2000; Goto et al., 1996), empirical models (Subra et al., 1998; Chrastil, 1982), etc The unsteady-state packed bed mass transfer model represents the concentration profile of the SCF solvent phase in the extractor with respect to time and length of bed In this model all constituents are clubbed together as a solute, as it is believed that they would have similar mass transfer characteristics (Mukhopadhyay, 2000) The R.N Patel et al / Bioresource Technology 97 (2006) 847–853 851 Table Comparison of oil obtained by SCFE and thermal method Properties CNSL (SCFE) CNSL specifications IS:840 (1964) CNSL (pyrolysis method) (Das and Ganesh, 2003) Ash (%) (ASTM D482) Moisture (%) (ASTM D1744) Sp Gr at 301 K (ASTM D4052-86) 0.01 0.747 0.934 1.0 (max by wt.) 1.0 (max by wt.) 0.95–0.97 0.01 3.5 0.993 Absolute viscosity (cSt) at 303 K 333 K 353 K (ASTM D445-88) 95 27 14 550 CP (max) 159 33 16 Flash point (K) (ASTM D93) 443 NR 453 Elemental composition (wt.% on dry basis) C H N O (by difference) 77.85 9.70 0.00 12.45 NR 76.4 10.5