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Rapid estimation of the manufacturing cost of extracts obtained by supercritical fluid extraction
Journal of Food Engineering 67 (2005) 235–240 www.elsevier.com/locate/jfoodeng
Rapid estimation of the manufacturing cost of extracts obtained by supercritical fluid extraction Paulo T.V. Rosa, M. Angela A. Meireles
*
LASEFI, DEA/FEA (College of Food Engineering), UNICAMP (State University of Campinas), Cx. Postal 6121, CEP 13083-970, Campinas, SP, Brazil Received 10 October 2003; accepted 1 May 2004
Abstract In spite of the scientific knowledge and the large availability of raw materials having sufficient quality and cost, there is no industrial supercritical fluid extraction unit in any of the South American countries. Supercritical fluid extraction is associated with high investment costs; nowadays, an easy method for technical–economical evaluation of supercritical fluid process is not available. Thus, a simple method to estimate the cost of manufacturing of extracts by supercritical fluid technology is presented. The manufacturing costs of clove bud oil and ginger oleoresin were estimated using the procedure proposed. The production of clove bud oil was economically feasible at the quoted extraction condition; its manufacturing cost approximately a fourth of the market price. The manufacturing cost of ginger oleoresin was close to its selling price at the extraction condition considered. This is mainly due to the strong influence of the investment on the cost of manufacturing ginger extracts by supercritical extraction due to the requirement of long extraction times. Nonetheless, some other characteristics of the ginger oleoresin such as the quantity and the availability of gingerols and shogaols should be considered. Additionally, further process parameter studies directed to the increase of the extraction rates should be considered before disregarding the supercritical fluid extraction as a viable process. 2004 Elsevier Ltd. All rights reserved. Keywords: Supercritical extraction; Natural products; Manufacturing cost; Clove oil; Ginger oleoresin
1. Introduction One of the phases of process design is the choice of the technology that will be employed for some application. In spite of supercritical fluid extraction (SFE) been a technically viable process to obtain a series of high quality extracts, it is disregarded as a possible technology at the beginning of the process mainly because SFE is known to produce extracts of high manufacturing cost due to the high investments related to the high pressure operation (Perrut, 2000).
*
Corresponding author. Tel.: +55 19 3788 4033; fax: +55 19 3788 4027. E-mail address: [email protected] (M. A. A. Meireles). 0260-8774/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2004.05.064
The development of the industrial scale units is decreasing the cost of the equipments used in SFE process (Chordia & Robey, 2000). Thus, SFE is becoming more attractive and as a result, several extraction units have been constructed in Asia for extraction of phytochemicals and nutraceuticals from natural products (Teja & Eckert, 2000). Brazil has a large biodiversity containing 55,000 from the 350,000 known species of plants in the world (Nodari & Guerra, 1999). This, associated to the fact that Brazil has tradition in agricultural production, can guarantee the availability of raw material in sufficient quality and cost. Furthermore, there are several researches in South America related to SFE (Meireles, 2003). In spite of that, there is still no industrial scale unit to produce extracts by SFE in this region.
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P.T.V. Rosa, M. A. A. Meireles / Journal of Food Engineering 67 (2005) 235–240
There are some studies of economical evaluation of supercritical fluid extraction but they are concerned with the liquid–supercritical fluid extraction (Crause & Nieuwoudt, 2003; Mendes, Pessoa, & Uller, 2002) or to process optimization (Bravi, Bubbico, Manna, & Verdone, 2002). In this study, we will present a rapid method to estimate the cost of manufacturing (COM) of extracts using supercritical fluid extraction that may accelerate the adoption of SFE as an alternative among the various extraction techniques.
2. Methodology 2.1. Manufacturing cost of extracts obtained by supercritical fluid extraction The manufacturing cost can be determined by the sum of the direct cost, fixed cost, and general expenses. The direct costs are straightly dependent on the production rate and are composed of the costs of raw materials, operational labor, utilities, and so on. Costs such as territorial taxes, insurances, depreciation, etc., are not dependent on the production rate and are known as fixed costs. General expenses are associated to business maintenance and include administrative, sales, research and development cots, among others. The estimative of the COM of extracts obtained by supercritical fluid extraction was carried out using the methodology presented by Turton, Bailie, Whiting, and Shaeiwitz (1998). That is, the tree components of the COM are estimated in terms of five main costs: raw material, operational labor, utilities, waste treatment, and investment. Each of these costs will have some weight in the COM composition. The expression proposed by Turton et al. (1998) is given by: COM ¼ 0:304 FCI þ 2:73 COL þ 1:23 ðCUT þ CWT þ CRMÞ where COM is the manufacturing cost, FCI is the fraction of investment, COL is the operational labor cost, CUT is the utility cost, CWT is the waste treatment cost, and CRM is the raw material cost. The raw material cost should consider the price of all materials that are directly related to the production. In the case of supercritical fluid extraction the raw materials are the solid substrate particles that contain the desired solute and the CO2 lost during processing. The cost of the solid substrate takes into account the cost of the raw material itself and all the cost of pre-processing required to have the raw material prepared for extraction, such as drying, comminution, cleaning, classification, etc. The streams that exit a supercritical fluid extraction unit are the extract, the exhausted solid, and the CO2
that may leak from the system and, thus, the only accumulated waste is the exhausted solid. In general, the main raw material is a plant or part of it and the exhausted solid may be incorporated in the soil. In some cases, as for instance in the removal of caffeine from coffee, the exhausted solid is the main product of the process and not a waste. In the production of ginger oleoresin the solid waste, which is rich in starch, can be used as the raw material to produce oligosaccharides and other low molecular mass substances (Moreschi, Petenate, & Meireles, 2004). Thus, there is no harmful waste to be treated and the waste treatment cost can be neglected. A supercritical fluid extraction unit is in general composed of two or more extraction columns, a series of flash tanks that can be used to do some fractionation of the extract, a CO2 condenser, a pump used to compress the solvent, a CO2 reservoir, and a CO2 heater used to set the CO2 temperature prior to the extraction column entrance. The fraction of the investment on a year basis is given by the product of the total investment by the depreciation rate. Another part of the investment is the initial amount of carbon dioxide needed to fill the CO2 reservoir. In general this cost is negligible if compared to the extraction unit cost. The total operational labor in terms of man-hour per operation-hour was estimated using the tables presented by Ulrich (1984). The utility cost was estimated considering the energy involved in the solvent cycle using the pure CO2 temperature–entropy diagram, as suggested by Brunner (1994). The values of specific enthalpies can be obtained from this diagram using the pressure and temperature for each part of the process. In order to estimate the COM it is important to know the extraction time and the yield of extract obtained during this time. It is considered that the industrial scale supercritical extraction unit should have the same performance as that of a laboratorial scale unit, if the particle size, bed density (mass of particles per unity of column volume), and the ratio between the mass of solid and the CO2 flow rate are kept constant. This assumption should be precise if the scale-up is done by increasing the column diameter and the CO2 is distributed similarly. 2.2. Manufacturing cost of SFE of clove buds oil and ginger oleoresin The industrial extraction unit considered for estimating the COM is composed of two 400 l extraction columns; its cost is approximately US$2,000,000.00. There are several industrial extraction units of this size that are used to obtain extracts of spices, nutraceuticals, natural pigments, etc. The total operational time of the extraction column was considered as 7920-h per year, which corresponds to 330 days per year of continuous
P.T.V. Rosa, M. A. A. Meireles / Journal of Food Engineering 67 (2005) 235–240
24-h per day shift. The depreciation rate of 10% per year was used in the calculation of the COM. The cost of the operational labor was considered to be US$3.00/h. The cost of a metric ton of the raw material are US$505.00 and US$495.00, for the clove buds and ginger, respectively (IBGE, 2003). These prices correspond to the value paid for the producer without any further treatment. The final cost of the raw material should take into account the costs of transportation and preprocessing. If the extraction unit is located in a region nearby the producer, the cost of transportation should be low. The pre-processing cost was estimated using the SuperPro Designs Software (Demo Version) as US$30.00 per metric ton of raw material. It was considered that 2% of the total CO2 used during the extraction is lost either dissolved in the extract after the flash separation or trapped in the particles that are removed from the extractor. A price of US$0.10/kg of CO2 was used in the calculation of the manufacturing cost. The flash tank was considered to operate at 40 bars, and at this condition, it was considered that all the extract will be at the liquid phase. In the calculation of the utilities used in the supercritical fluid extraction the following were considered: the flash tank was heated by 0.5 MPa saturated steam, the condenser uses cold water for refrigeration, the electric power used in the pump was calculated considering the isentropic variation of enthalpy assuming a 60% of efficiency, and the CO2 heater also uses 0.5 MPa saturated steam. The cost of these energies were US$0.0133/Mcal for the saturated steam (SuperPro Design, Demo Version), US$0.0837/Mcal for the cold water (SuperPro Design, Demo Version), and US$0.0703/Mcal for electric power.
3. Results and discussion The manufacturing cost of supercritical fluid extracts of clove buds (Eugenia caryophyllus) and ginger (Zingiber officinale Roscoe) were estimated using the proposed methodology. In spite of having approximately the same raw material costs, the amount of extract and the kinetic behavior of the extraction process of the clove buds and ginger are very different. Fig. 1 presents the extraction curves of ginger (Martinez, Monteiro, Rosa, Marques, & Meireles, 2003) and clove buds (Rodrigues et al., 2002). From the available experimental conditions in these two references the extraction curves with the largest yield in the shortest extraction time, was chosen as the best extraction condition. There are two characteristically linear regions in the extraction curves. At the beginning of the extraction, almost all of the extractable compounds are inside of the particles. Furthermore, some of the solute should be at the interfacial region of the particles as a result of the
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Fig. 1. Experimental CO2 extraction curve of clove buds at 10 MPa, 15 C, and 2.4 · 105 kg/s (Rodrigues et al., 2002) and ginger at 20 MPa, 40 C, and 5.6 · 105 kg/s (Martinez et al., 2003).
comminution process. Thus, the first linear region, known as constant extraction rate (CER) region, corresponds to the extraction of the more accessible solute, and hence the mass transport is dominated by the convection in the solvent film around of the particles (Sovova´, 1994). The end of the CER region for extraction of clove buds oil and ginger oleoresin occurred after 60 and 165 min of extraction, respectively. For the CER region, the yield of clove oil is around 14% and the ginger oleoresin is approximately 2.7%. The maximum extraction rates can be obtained at the CER region. The second linear relationship is observed at long extraction times, when the easily accessible solute is already extracted. For these sections of the extraction curve, the extraction rate reaches a minimum value and the mass transfer is limited by the diffusion of the solutes inside of the particles. The ratio between the mass of particles in the extractor and CO2 mass flow rate used in the experimental runs were 8.3 · 103 seconds and 1.4 · 103 seconds for clove buds and ginger, respectively. Thus, the ginger extraction used approximately six times more CO2 than utilized in the clove bud extraction. The lower extraction rate for the ginger oleoresin compared to the clove buds can be explained in terms of their differences in solubility in pressurized CO2. The clove oil solubility was 0.277 kg of extract/kg CO2 and for ginger was 0.00673 kg of extract/kg CO2 (Rodrigues et al., 2002). The total mass of particles loaded inside of the 400 l extraction column, considering the experimental bed densities, for each extraction cycle was 208 kg of clove buds or 136 kg of ginger particles. As can be seen, the clove buds particles can form a more compact porous bed than ginger particles. The CO2 mass flow rate used in the extraction unit was calculated using the previously mentioned scale-up criteria. Therefore, flow rate values for clove and ginger
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Fig. 2. Influence of extraction time on the specific manufacturing cost of clove bud oil and ginger oleoresin.
extraction were 90 and 345 kg/h, respectively. These values are directly related to the utilities used for processing since the pure CO2 entropy–temperature diagram gives the specific enthalpy at each point of the process, and the total energy can be calculated by multiplying the variation of specific enthalpy by the CO2 mass flow rate and by the extraction time. The total man-hour per operational-hour needed to do the extraction is approximately 2 or there will be two operators per shift in the industrial supercritical fluid extraction unit. This result is in accordance with the estimates of Perrut (2000). The influence of the extraction time on the specific COM, defined as the manufacturing cost divided by total mass of produced extract, can be observed in Fig. 2. In the calculation of the specific COM, the extraction yields for each extraction time presented in Fig. 1 were used. When a short extraction time is used, only a small amount of the solute can be extracted, and at this condition the importance of the raw material cost is high. On the other hand, if a very long extraction time is used (extraction curve in the lowest extraction rate), the impact of the raw material cost on the COM decreases but the investment, operational labor cost and utilities costs increases, increasing the specific cost of the extract. Therefore, there would be an optimal extraction time where the raw material is utilized and the extraction rate is not low. This factor explains the shape of the curves of Fig. 2. One can observe in Fig. 2 that specific COM of clove oil is one magnitude order lower than the ginger oleoresin. The lower clove oil specific COM was US$9.15/ kg obtained for 70 min of extraction time and for ginger oleoresin was US$99.80/kg after 165 min of extraction. The optimum extraction time coincides with the intersection of the linear regions presented in Fig. 1. To these values, should be added the taxes and the storage and transportation costs. As a reference, the selling price for bulk quantities (larger than 11.3 kg) of the clove
bud oil obtained by steam distillation is around US$40.00/kg and of ginger oleoresin is US$100.00/kg (Liberty Natural, 2003). Thus, the production cost of clove oil is lower than the market one and the supercritical extraction can be considered as a feasible process to obtain this product. The production cost of the ginger oleoresin was almost the same as the selling price. As ginger oleoresin can be used as a nutraceutical, some other factors such as the amount and availability of the active components should be considered. Nobrega, Monteiro, Meireles, and Marques (1997) showed that the supercritical ginger extracts contain gingerols that are absent or present only in small quantities in the ginger oleoresin obtained with ethanol and isopropyl alcohol as extraction solvents. Additionally, if the ginger solid waste (ginger bagasse) is used to produce oligosaccharides as proposed by Moreschi et al. (2004) this would reduce the manufacturing cost of ginger. Therefore, the production of ginger extracts for use as a functional food could be viable via SFE. The minimum estimated cost was obtained in extraction times close to the end of the constant extraction rate region and thus, in order to have low COM the constant extraction rate region should have short time and high yields. For a constant extraction condition, these can be obtained by decreasing the size of the particles. Aspects such as flow segregation and particle bed compression will need to be considered before decreasing the particle size. An extraction time of 70 min obtained for the clove oil should allow for additional time for decompression of the extractor, removal of the extracted particles, loading of the extractor with fresh particles, and subsequently pressurization of the column. The influence of the investment, raw material cost, operational labor cost, and utility cost on the COM as a function of extraction time is presented in Fig. 3.
Fig. 3. Importance of the individual costs in the manufacturing cost of clove oil and ginger oleoresin.
P.T.V. Rosa, M. A. A. Meireles / Journal of Food Engineering 67 (2005) 235–240
One can observe that the main components of the manufacturing cost are the investment and the cost of raw material, followed by the operational labor cost and utilities cost. At the lowest specific COM condition the cost composition was 36.75% of investment, 55.67% of raw material, 7.25% of operational labor, and 0.33% of utilities, for clove bud oil and 60.59% of investment, 25.65% of raw material, 11.98% of operational labor, and 1.78% of utilities, for ginger oleoresin. The larger influence of the investment on the COM of ginger is related with its large optimum extraction time. As the depreciation of the investment and the other costs related to it (mainly direct costs) have a large impact on the specific COM, a large extraction time means that the impact of the fraction of investment per extraction cycle is high. The increase of the importance of the operational labor in the COM is also a result of the increase of the extraction time, since it is using the same manpower but for a longer time. The decrease of the impact of the raw material cost is due more to the increase of the other costs than to the decrease of its cost. One should notice that Fig. 3 presents the % of each cost; the total raw material cost for ginger extraction is larger than that for clove buds. The importance of the utilities cost of the COM for ginger extraction is related to its larger extraction time and the larger CO2 flow rate used during the extraction. The specific COM of clove bud oil and ginger oleoresin at the optimal extraction time was calculated as a function of the total operation time per year. The results are presented in Fig. 4. The variation of the total operational time has a direct impact in the importance of the investment that has the largest influence on the fixed cost, or on the COM. For low percentage of the operational time, the investment should be paid by a low number of extraction batches (and consequently low amount of extract) and this term of the COM should
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be the most important one. As the operational time increases, there would be a decrease of the importance of the investment on the COM. In the case of the clove oil, the estimated specific COM is lower than the selling price for annual operational times larger than 2390 h or 30% of the total operational time. The larger importance of the operational time on the specific cost of ginger oleoresin is due to its larger dependence of the investment on the COM.
4. Conclusions The described methodology used to estimate the manufacturing cost of clove bud oil and ginger oleoresin by supercritical fluid extraction showed that the extraction of clove oil should be economically feasible at the extraction condition tested since its COM value is lower than the bulk oil selling price. The lowest estimated cost of clove oil (US$9.15/kg) was obtained at full capacity of the extraction unit and extraction time of 70 min. At this condition, the main component of the COM was the raw material (55.67%), followed by the investment (36.75%), operational labor (7.25%), and utilities (0.33%). On the estimated price should be added the taxes, storage and transportation costs to check the final cost of the clove oil. In the case of ginger oleoresin, the lowest estimated cost (US$99.80/kg) is close to the commercialization one. The main components of the ginger oleoresin manufacturing cost were investment (60.59%), raw material cost (25.65%), operational labor cost (11.98%), and utilities cost (1.78%). In order to economically produce ginger oleoresin an extraction condition should be found that allows a shorter extraction time; the use of other raw material variety with larger amount of extract should also be considered. Since ginger oleoresin is a nutraceutical material due to the presence of shogaols and gingerols, the amount and availability of these compounds should be evaluated in order to verify the quality of the product and then specify the value of the extract.
Acknowledgments The authors are grateful to FAPESP for the financial support (1999/01962-1). P.T.V. Rosa thanks CAPES for the pos doctorate fellowship (AUX-PRODOC-046/ 02-7).
References
Fig. 4. Influence of the total operation time on the specific manufacturing cost of clove oil and ginger oleoresin.
Bravi, M., Bubbico, R., Manna, F., & Verdone, N. (2002). Chemical Engineering Science, 57, 2753–2764. Brunner, G. (1994). Gas extraction: An introduction to fundamentals of supercritical fluids and the application to separation processes. New York: Springer.
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Chordia, L. & Robey, R. (2000). Industrial applications of supercritical fluids. In Proceedings of the 5th International Symposium on Supercritical Fluids, Atlanta, USA. Crause, J. C., & Nieuwoudt, I. (2003). Paraffin wax fractionation: state of the art vs. supercritical fluid fractionation. Journal of Supercritical Fluids, 27, 39–54. IBGE. (2003). Available: www.sidra.ibge.gov.br/bda/agric/default.asp. Accessed in September 29, 2003. Liberty Natural. (2003). Available: www.libertynatural.com/bulk/ bulking.htm. Accessed in October 26, 2003. Martinez, J., Monteiro, A. R., Rosa, P. T. V., Marques, M. O. M., & Meireles, M. A. A. (2003). Multicomponent model to describe extraction of ginger oleoresin with supercritical carbon dioxide. Industrial and Engineering Chemistry Research, 42(5), 1057–1063. Meireles, M. A. A. (2003). Supercritical extraction from solid: process design data (2001–2003). Current Opinion in Solid State and Materials Science 7, 321–330. Mendes, M. F., Pessoa, F. L. P., & Uller, A. M. C. (2002). An economic evaluation based on an experimental study of the vitamin E concentration present in deodorizer distillate of soybean oil using supercritical CO2. Journal of Supercritical Fluids, 23, 257–265. Moreschi, S. R. M., Petenate, A. J., & Meireles, M. A. A. (2004). Hydrolysis of ginger bagasse starch in subcritical water and carbon dioxide. Journal of Agricultural and Food Chemistry, 52, 1753–1758. Nobrega, L. P., Monteiro, A. R., Meireles, M. A. A., & Marques, M. O. M. (1997). Comparison of ginger (Zingiber officiale Roscoe)
oleoresin obtained with ethanol and isopropanol with that obtained with pressurized CO2. Cieˆncias e Tecnologia de Alimentos, 17(4), 408–412. Nodari, R. O., & Guerra, M. P. (1999). Biodiversidade: aspectos biolo´gicos, geogra´ficos, legais e e´ticos. In Simo˜es et al. (Eds.) Farmacognosia: da planta ao medicamento (p. 833). Universidade— UFRGS: Porto Alegre, Brazil. Perrut, M. (2000). Supercritical fluid applications: Industrial developments and economic issues. Industrial and Engineering Chemistry Research, 39(12), 4531–4535. Rodrigues, V. M., Sousa, E. M. B. D., Monteiro, A. R., ChiavoneFilho, O., Marques, M. O. M., & Meireles, M. A. A. (2002). Determination of the solubility of extracts from vegetable raw material in pressurized CO2: a pseudo-ternary mixture formed by cellulosic structure plus solute plus solvent. Journal of Supercritical Fluids, 22(1), 21–36. Sovova´, H. (1994). Rate of the vegetable oil extraction with supercritical CO2. 1. Modeling of extraction curves. Chemical Engineering Science, 49(3), 409–414. Teja, A. S., & Eckert, C. A. (2000). Commentary on supercritical fluids: research and applications. Industrial & Engineering Chemistry Research, 39, 4442–4444. Turton, R., Bailie, R. C., Whiting, W. B., & Shaeiwitz, J. A. (1998). Analysis, synthesis, and design of chemical process. PTR, Upper Saddle River: Prentice Hall. Ulrich, G. D. (1984). A guide to chemical engineering process design and economics. New York: John Wiley & Sons.
Rapid estimation of the manufacturing cost of extracts obtained by supercritical fluid extraction Paulo T.V. Rosa, M. Angela A. Meireles
*
LASEFI, DEA/FEA (College of Food Engineering), UNICAMP (State University of Campinas), Cx. Postal 6121, CEP 13083-970, Campinas, SP, Brazil Received 10 October 2003; accepted 1 May 2004
Abstract In spite of the scientific knowledge and the large availability of raw materials having sufficient quality and cost, there is no industrial supercritical fluid extraction unit in any of the South American countries. Supercritical fluid extraction is associated with high investment costs; nowadays, an easy method for technical–economical evaluation of supercritical fluid process is not available. Thus, a simple method to estimate the cost of manufacturing of extracts by supercritical fluid technology is presented. The manufacturing costs of clove bud oil and ginger oleoresin were estimated using the procedure proposed. The production of clove bud oil was economically feasible at the quoted extraction condition; its manufacturing cost approximately a fourth of the market price. The manufacturing cost of ginger oleoresin was close to its selling price at the extraction condition considered. This is mainly due to the strong influence of the investment on the cost of manufacturing ginger extracts by supercritical extraction due to the requirement of long extraction times. Nonetheless, some other characteristics of the ginger oleoresin such as the quantity and the availability of gingerols and shogaols should be considered. Additionally, further process parameter studies directed to the increase of the extraction rates should be considered before disregarding the supercritical fluid extraction as a viable process. 2004 Elsevier Ltd. All rights reserved. Keywords: Supercritical extraction; Natural products; Manufacturing cost; Clove oil; Ginger oleoresin
1. Introduction One of the phases of process design is the choice of the technology that will be employed for some application. In spite of supercritical fluid extraction (SFE) been a technically viable process to obtain a series of high quality extracts, it is disregarded as a possible technology at the beginning of the process mainly because SFE is known to produce extracts of high manufacturing cost due to the high investments related to the high pressure operation (Perrut, 2000).
*
Corresponding author. Tel.: +55 19 3788 4033; fax: +55 19 3788 4027. E-mail address: [email protected] (M. A. A. Meireles). 0260-8774/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2004.05.064
The development of the industrial scale units is decreasing the cost of the equipments used in SFE process (Chordia & Robey, 2000). Thus, SFE is becoming more attractive and as a result, several extraction units have been constructed in Asia for extraction of phytochemicals and nutraceuticals from natural products (Teja & Eckert, 2000). Brazil has a large biodiversity containing 55,000 from the 350,000 known species of plants in the world (Nodari & Guerra, 1999). This, associated to the fact that Brazil has tradition in agricultural production, can guarantee the availability of raw material in sufficient quality and cost. Furthermore, there are several researches in South America related to SFE (Meireles, 2003). In spite of that, there is still no industrial scale unit to produce extracts by SFE in this region.
236
P.T.V. Rosa, M. A. A. Meireles / Journal of Food Engineering 67 (2005) 235–240
There are some studies of economical evaluation of supercritical fluid extraction but they are concerned with the liquid–supercritical fluid extraction (Crause & Nieuwoudt, 2003; Mendes, Pessoa, & Uller, 2002) or to process optimization (Bravi, Bubbico, Manna, & Verdone, 2002). In this study, we will present a rapid method to estimate the cost of manufacturing (COM) of extracts using supercritical fluid extraction that may accelerate the adoption of SFE as an alternative among the various extraction techniques.
2. Methodology 2.1. Manufacturing cost of extracts obtained by supercritical fluid extraction The manufacturing cost can be determined by the sum of the direct cost, fixed cost, and general expenses. The direct costs are straightly dependent on the production rate and are composed of the costs of raw materials, operational labor, utilities, and so on. Costs such as territorial taxes, insurances, depreciation, etc., are not dependent on the production rate and are known as fixed costs. General expenses are associated to business maintenance and include administrative, sales, research and development cots, among others. The estimative of the COM of extracts obtained by supercritical fluid extraction was carried out using the methodology presented by Turton, Bailie, Whiting, and Shaeiwitz (1998). That is, the tree components of the COM are estimated in terms of five main costs: raw material, operational labor, utilities, waste treatment, and investment. Each of these costs will have some weight in the COM composition. The expression proposed by Turton et al. (1998) is given by: COM ¼ 0:304 FCI þ 2:73 COL þ 1:23 ðCUT þ CWT þ CRMÞ where COM is the manufacturing cost, FCI is the fraction of investment, COL is the operational labor cost, CUT is the utility cost, CWT is the waste treatment cost, and CRM is the raw material cost. The raw material cost should consider the price of all materials that are directly related to the production. In the case of supercritical fluid extraction the raw materials are the solid substrate particles that contain the desired solute and the CO2 lost during processing. The cost of the solid substrate takes into account the cost of the raw material itself and all the cost of pre-processing required to have the raw material prepared for extraction, such as drying, comminution, cleaning, classification, etc. The streams that exit a supercritical fluid extraction unit are the extract, the exhausted solid, and the CO2
that may leak from the system and, thus, the only accumulated waste is the exhausted solid. In general, the main raw material is a plant or part of it and the exhausted solid may be incorporated in the soil. In some cases, as for instance in the removal of caffeine from coffee, the exhausted solid is the main product of the process and not a waste. In the production of ginger oleoresin the solid waste, which is rich in starch, can be used as the raw material to produce oligosaccharides and other low molecular mass substances (Moreschi, Petenate, & Meireles, 2004). Thus, there is no harmful waste to be treated and the waste treatment cost can be neglected. A supercritical fluid extraction unit is in general composed of two or more extraction columns, a series of flash tanks that can be used to do some fractionation of the extract, a CO2 condenser, a pump used to compress the solvent, a CO2 reservoir, and a CO2 heater used to set the CO2 temperature prior to the extraction column entrance. The fraction of the investment on a year basis is given by the product of the total investment by the depreciation rate. Another part of the investment is the initial amount of carbon dioxide needed to fill the CO2 reservoir. In general this cost is negligible if compared to the extraction unit cost. The total operational labor in terms of man-hour per operation-hour was estimated using the tables presented by Ulrich (1984). The utility cost was estimated considering the energy involved in the solvent cycle using the pure CO2 temperature–entropy diagram, as suggested by Brunner (1994). The values of specific enthalpies can be obtained from this diagram using the pressure and temperature for each part of the process. In order to estimate the COM it is important to know the extraction time and the yield of extract obtained during this time. It is considered that the industrial scale supercritical extraction unit should have the same performance as that of a laboratorial scale unit, if the particle size, bed density (mass of particles per unity of column volume), and the ratio between the mass of solid and the CO2 flow rate are kept constant. This assumption should be precise if the scale-up is done by increasing the column diameter and the CO2 is distributed similarly. 2.2. Manufacturing cost of SFE of clove buds oil and ginger oleoresin The industrial extraction unit considered for estimating the COM is composed of two 400 l extraction columns; its cost is approximately US$2,000,000.00. There are several industrial extraction units of this size that are used to obtain extracts of spices, nutraceuticals, natural pigments, etc. The total operational time of the extraction column was considered as 7920-h per year, which corresponds to 330 days per year of continuous
P.T.V. Rosa, M. A. A. Meireles / Journal of Food Engineering 67 (2005) 235–240
24-h per day shift. The depreciation rate of 10% per year was used in the calculation of the COM. The cost of the operational labor was considered to be US$3.00/h. The cost of a metric ton of the raw material are US$505.00 and US$495.00, for the clove buds and ginger, respectively (IBGE, 2003). These prices correspond to the value paid for the producer without any further treatment. The final cost of the raw material should take into account the costs of transportation and preprocessing. If the extraction unit is located in a region nearby the producer, the cost of transportation should be low. The pre-processing cost was estimated using the SuperPro Designs Software (Demo Version) as US$30.00 per metric ton of raw material. It was considered that 2% of the total CO2 used during the extraction is lost either dissolved in the extract after the flash separation or trapped in the particles that are removed from the extractor. A price of US$0.10/kg of CO2 was used in the calculation of the manufacturing cost. The flash tank was considered to operate at 40 bars, and at this condition, it was considered that all the extract will be at the liquid phase. In the calculation of the utilities used in the supercritical fluid extraction the following were considered: the flash tank was heated by 0.5 MPa saturated steam, the condenser uses cold water for refrigeration, the electric power used in the pump was calculated considering the isentropic variation of enthalpy assuming a 60% of efficiency, and the CO2 heater also uses 0.5 MPa saturated steam. The cost of these energies were US$0.0133/Mcal for the saturated steam (SuperPro Design, Demo Version), US$0.0837/Mcal for the cold water (SuperPro Design, Demo Version), and US$0.0703/Mcal for electric power.
3. Results and discussion The manufacturing cost of supercritical fluid extracts of clove buds (Eugenia caryophyllus) and ginger (Zingiber officinale Roscoe) were estimated using the proposed methodology. In spite of having approximately the same raw material costs, the amount of extract and the kinetic behavior of the extraction process of the clove buds and ginger are very different. Fig. 1 presents the extraction curves of ginger (Martinez, Monteiro, Rosa, Marques, & Meireles, 2003) and clove buds (Rodrigues et al., 2002). From the available experimental conditions in these two references the extraction curves with the largest yield in the shortest extraction time, was chosen as the best extraction condition. There are two characteristically linear regions in the extraction curves. At the beginning of the extraction, almost all of the extractable compounds are inside of the particles. Furthermore, some of the solute should be at the interfacial region of the particles as a result of the
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Fig. 1. Experimental CO2 extraction curve of clove buds at 10 MPa, 15 C, and 2.4 · 105 kg/s (Rodrigues et al., 2002) and ginger at 20 MPa, 40 C, and 5.6 · 105 kg/s (Martinez et al., 2003).
comminution process. Thus, the first linear region, known as constant extraction rate (CER) region, corresponds to the extraction of the more accessible solute, and hence the mass transport is dominated by the convection in the solvent film around of the particles (Sovova´, 1994). The end of the CER region for extraction of clove buds oil and ginger oleoresin occurred after 60 and 165 min of extraction, respectively. For the CER region, the yield of clove oil is around 14% and the ginger oleoresin is approximately 2.7%. The maximum extraction rates can be obtained at the CER region. The second linear relationship is observed at long extraction times, when the easily accessible solute is already extracted. For these sections of the extraction curve, the extraction rate reaches a minimum value and the mass transfer is limited by the diffusion of the solutes inside of the particles. The ratio between the mass of particles in the extractor and CO2 mass flow rate used in the experimental runs were 8.3 · 103 seconds and 1.4 · 103 seconds for clove buds and ginger, respectively. Thus, the ginger extraction used approximately six times more CO2 than utilized in the clove bud extraction. The lower extraction rate for the ginger oleoresin compared to the clove buds can be explained in terms of their differences in solubility in pressurized CO2. The clove oil solubility was 0.277 kg of extract/kg CO2 and for ginger was 0.00673 kg of extract/kg CO2 (Rodrigues et al., 2002). The total mass of particles loaded inside of the 400 l extraction column, considering the experimental bed densities, for each extraction cycle was 208 kg of clove buds or 136 kg of ginger particles. As can be seen, the clove buds particles can form a more compact porous bed than ginger particles. The CO2 mass flow rate used in the extraction unit was calculated using the previously mentioned scale-up criteria. Therefore, flow rate values for clove and ginger
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Fig. 2. Influence of extraction time on the specific manufacturing cost of clove bud oil and ginger oleoresin.
extraction were 90 and 345 kg/h, respectively. These values are directly related to the utilities used for processing since the pure CO2 entropy–temperature diagram gives the specific enthalpy at each point of the process, and the total energy can be calculated by multiplying the variation of specific enthalpy by the CO2 mass flow rate and by the extraction time. The total man-hour per operational-hour needed to do the extraction is approximately 2 or there will be two operators per shift in the industrial supercritical fluid extraction unit. This result is in accordance with the estimates of Perrut (2000). The influence of the extraction time on the specific COM, defined as the manufacturing cost divided by total mass of produced extract, can be observed in Fig. 2. In the calculation of the specific COM, the extraction yields for each extraction time presented in Fig. 1 were used. When a short extraction time is used, only a small amount of the solute can be extracted, and at this condition the importance of the raw material cost is high. On the other hand, if a very long extraction time is used (extraction curve in the lowest extraction rate), the impact of the raw material cost on the COM decreases but the investment, operational labor cost and utilities costs increases, increasing the specific cost of the extract. Therefore, there would be an optimal extraction time where the raw material is utilized and the extraction rate is not low. This factor explains the shape of the curves of Fig. 2. One can observe in Fig. 2 that specific COM of clove oil is one magnitude order lower than the ginger oleoresin. The lower clove oil specific COM was US$9.15/ kg obtained for 70 min of extraction time and for ginger oleoresin was US$99.80/kg after 165 min of extraction. The optimum extraction time coincides with the intersection of the linear regions presented in Fig. 1. To these values, should be added the taxes and the storage and transportation costs. As a reference, the selling price for bulk quantities (larger than 11.3 kg) of the clove
bud oil obtained by steam distillation is around US$40.00/kg and of ginger oleoresin is US$100.00/kg (Liberty Natural, 2003). Thus, the production cost of clove oil is lower than the market one and the supercritical extraction can be considered as a feasible process to obtain this product. The production cost of the ginger oleoresin was almost the same as the selling price. As ginger oleoresin can be used as a nutraceutical, some other factors such as the amount and availability of the active components should be considered. Nobrega, Monteiro, Meireles, and Marques (1997) showed that the supercritical ginger extracts contain gingerols that are absent or present only in small quantities in the ginger oleoresin obtained with ethanol and isopropyl alcohol as extraction solvents. Additionally, if the ginger solid waste (ginger bagasse) is used to produce oligosaccharides as proposed by Moreschi et al. (2004) this would reduce the manufacturing cost of ginger. Therefore, the production of ginger extracts for use as a functional food could be viable via SFE. The minimum estimated cost was obtained in extraction times close to the end of the constant extraction rate region and thus, in order to have low COM the constant extraction rate region should have short time and high yields. For a constant extraction condition, these can be obtained by decreasing the size of the particles. Aspects such as flow segregation and particle bed compression will need to be considered before decreasing the particle size. An extraction time of 70 min obtained for the clove oil should allow for additional time for decompression of the extractor, removal of the extracted particles, loading of the extractor with fresh particles, and subsequently pressurization of the column. The influence of the investment, raw material cost, operational labor cost, and utility cost on the COM as a function of extraction time is presented in Fig. 3.
Fig. 3. Importance of the individual costs in the manufacturing cost of clove oil and ginger oleoresin.
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One can observe that the main components of the manufacturing cost are the investment and the cost of raw material, followed by the operational labor cost and utilities cost. At the lowest specific COM condition the cost composition was 36.75% of investment, 55.67% of raw material, 7.25% of operational labor, and 0.33% of utilities, for clove bud oil and 60.59% of investment, 25.65% of raw material, 11.98% of operational labor, and 1.78% of utilities, for ginger oleoresin. The larger influence of the investment on the COM of ginger is related with its large optimum extraction time. As the depreciation of the investment and the other costs related to it (mainly direct costs) have a large impact on the specific COM, a large extraction time means that the impact of the fraction of investment per extraction cycle is high. The increase of the importance of the operational labor in the COM is also a result of the increase of the extraction time, since it is using the same manpower but for a longer time. The decrease of the impact of the raw material cost is due more to the increase of the other costs than to the decrease of its cost. One should notice that Fig. 3 presents the % of each cost; the total raw material cost for ginger extraction is larger than that for clove buds. The importance of the utilities cost of the COM for ginger extraction is related to its larger extraction time and the larger CO2 flow rate used during the extraction. The specific COM of clove bud oil and ginger oleoresin at the optimal extraction time was calculated as a function of the total operation time per year. The results are presented in Fig. 4. The variation of the total operational time has a direct impact in the importance of the investment that has the largest influence on the fixed cost, or on the COM. For low percentage of the operational time, the investment should be paid by a low number of extraction batches (and consequently low amount of extract) and this term of the COM should
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be the most important one. As the operational time increases, there would be a decrease of the importance of the investment on the COM. In the case of the clove oil, the estimated specific COM is lower than the selling price for annual operational times larger than 2390 h or 30% of the total operational time. The larger importance of the operational time on the specific cost of ginger oleoresin is due to its larger dependence of the investment on the COM.
4. Conclusions The described methodology used to estimate the manufacturing cost of clove bud oil and ginger oleoresin by supercritical fluid extraction showed that the extraction of clove oil should be economically feasible at the extraction condition tested since its COM value is lower than the bulk oil selling price. The lowest estimated cost of clove oil (US$9.15/kg) was obtained at full capacity of the extraction unit and extraction time of 70 min. At this condition, the main component of the COM was the raw material (55.67%), followed by the investment (36.75%), operational labor (7.25%), and utilities (0.33%). On the estimated price should be added the taxes, storage and transportation costs to check the final cost of the clove oil. In the case of ginger oleoresin, the lowest estimated cost (US$99.80/kg) is close to the commercialization one. The main components of the ginger oleoresin manufacturing cost were investment (60.59%), raw material cost (25.65%), operational labor cost (11.98%), and utilities cost (1.78%). In order to economically produce ginger oleoresin an extraction condition should be found that allows a shorter extraction time; the use of other raw material variety with larger amount of extract should also be considered. Since ginger oleoresin is a nutraceutical material due to the presence of shogaols and gingerols, the amount and availability of these compounds should be evaluated in order to verify the quality of the product and then specify the value of the extract.
Acknowledgments The authors are grateful to FAPESP for the financial support (1999/01962-1). P.T.V. Rosa thanks CAPES for the pos doctorate fellowship (AUX-PRODOC-046/ 02-7).
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Fig. 4. Influence of the total operation time on the specific manufacturing cost of clove oil and ginger oleoresin.
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