- Email: [email protected]
Industry to Industry By-products Exchange Network towards zero waste in palm oil refining processes
Resources, Conservation and Recycling 55 (2011) 713–718
Contents lists available at ScienceDirect
Resources, Conservation and Recycling journal homepage: www.elsevier.com/locate/resconrec
Industry to Industry By-products Exchange Network towards zero waste in palm oil refining processes H. Haslenda ∗ , M.Z. Jamaludin Process Systems Engineering Centre (PROSPECT), Faculty of Chemical and Natural Resources Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia
a r t i c l e
i n f o
Article history: Received 7 May 2010 Received in revised form 21 February 2011 Accepted 26 February 2011 Keywords: Supply chain network MILP Optimization Palm oil refining Zero waste
a b s t r a c t This paper presents a systematic framework for optimal utilization of by-products generated during crude palm oil refining processes. Three by-products are considered in the supply chain network: soapstock, palm fatty acid distillate (PFAD) and spent bleaching earth (SBE). These by-products, generated from neutralization, deodorization and bleaching processes, are viable feedstocks to other commercial industries such as animal feed, biodiesel, lubricant and soap. The case study is formulated as Mixed Integer Linear Programming (MILP) and integrated into the framework with the objective to maximize the refinery’s profit as well as moving towards a conscious mindset of zero waste. This is the first time that such framework is developed and applied for the palm oil industry. The framework is called as Industry to Industry By-products Exchange Network (I2IBEN). An illustrative case study demonstrates a significant potential profit of MYR182, 893 per month. © 2011 Published by Elsevier B.V.
1. Introduction Industrial waste management is a global problem. Growing waste disposal costs and stringent environmental regulations have led to widespread waste management efforts through transformation of industrial by-products, which conventionally go to waste, into valuable products. In the palm oil industry, while refined palm oil generates enormous revenue, by-products associated with the refining processes may also be further utilized, hence contribute towards zero-waste strategy in the palm oil refining processes. Transformation of palm oil by-products to value-added products would significantly increase the profit of a palm oil refinery, and consequently remain competitive in the industry. With over one tenth of the country’s land covered with palm oil plantation, the palm oil industry has become one of the most important economic activities in Malaysia (Global Oils and Fats Business Magazine, 2009). Malaysia is currently the world’s largest producer and exporter of palm oil by contributing to about 47% of the total world’s supply (Basiron, 2007; Sumathi et al., 2008). Along with this huge production, refining of crude palm oil (CPO) is associated with the generation of several by-products such as soapstock, palm fatty acid distillate (PFAD) and spent bleaching earth (SBE). These by-products are among the viable feedstocks to other commercial industries such as animal feed, biodiesel, lubricant and soap (Ong, 1983; Balazs, 1987; Kheang et al., 2006; Dumont and Narine, 2007;
∗ Corresponding author. Tel.: +60 7 5535478; fax: +60 7 5581463. E-mail address: [email protected] (H. Haslenda). 0921-3449/$ – see front matter © 2011 Published by Elsevier B.V. doi:10.1016/j.resconrec.2011.02.004
Huang and Chang, 2010). In fact, the use of these by-products as alternative raw materials for certain industries, for instance lubricant and biodiesel, reduces the production cost and maintains the market price of such value-added products. Soapstock obtained from neutralization of CPO contains mainly free fatty acids (FFA). It has a variety of end uses, such as being a nutrient source for microorganisms, a reactant for chemical reactions, and a fertilizer ingredient and most importantly as an essential feedstock for animal-feeding industries (Ong, 1983; Woerfel, 1986; Dumont and Narine, 2007). It can also be used as an alternative raw material for biodiesel production (Luxem and Mirous, 2008). SBE, on the other hand, is a by-product recovered from bleaching process of the CPO. SBE that is produced abundantly in palm oil refineries (Lim et al., 2009) retains about 20–40% of the crude oil (Ong, 1983). The residual oil retained in SBE after refining process can be extracted and sold as a raw material to lubricant and biodiesel industries (Boukerroui and Ouali, 2000; Kheang et al., 2006; Basiron and Weng, 2004; Huang and Chang, 2010). Although there are industrial efforts to recover the residual oil, SBE is still under-utilized and disposed in landfill sites. This creates waste disposal problems such as the potential of environmental hazards and the rise in disposal cost. Similarly with soapstock, PFAD recovered from deodorization process is rich in FFA content. PFAD is commonly used as raw materials in producing medium-grade cleaners, animal feeds, plastics and other intermediate products for the oleochemical industries (Hong, 1983; Top and Rahman, 2000; Atil, 2004; Sambanthamurthi et al., 2000; Palmquist, 2004; Dumont and Narine, 2007; Global Oils
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Nomenclature Ai Bij Ci conv Dj FFA fij min max Pi qi Vj,min Vj,max Xij yj
available quantity of by-product i in a particular month quantity of by-product i to be sold to potential customer j selling price of by-product i unit conversion factor delivery cost of to potential customer j free fatty acids demand fraction of by-product i by potential customer j minimum maximum packaging cost of by-product i capacity of by-product i per drum minimum demand of by-products i by potential customer j maximum demand of by-products i by potential customer j drums of by-product i to be sold to potential customer j quantity of by-products i to be sold to potential customer j
Greek letters summation ∀ all belongs to. . . Subscripts i index for by-products j index for potential customers Acronym CPKO CPO GAMS I2IBEN MILP MPOB MYR NBDPO PAH PFAD RBDPO SBE
crude palm kernel oil crude palm oil Generic Algebraic Modelling System Industry to Industry By-products Exchange Network Mixed Integer Linear Programming Malaysian Palm Oil Board Malaysian Ringgit neutralized, bleached and deodorized palm oil polycyclic aromatic hydrocarbons palm fatty acid distillate refined, bleached and deodorized palm oil spent bleaching earth
and Fats Business Magazine, 2007). Other studies also demonstrate the possibility of producing biodiesel using FFA that is extracted from PFAD (Chongkhong et al., 2007; Boonnoun et al., 2008). Optimization techniques are often employed to aid decision making in the supply chain network. Very few optimization frameworks are seen to address waste management problems and environmental issues. A few of these can be found in open literature (Bojarski et al., 2009; Kannan et al., 2010). This study develops a systematic framework for optimal utilization of by-products generated from palm oil refining processes. The supply chain network of the by-products to the potential industries is formulated as Mixed Integer Linear Programming (MILP) and solved in General Algebraic Modelling System (GAMS). This framework is called as Industry to Industry By-products Exchange Network (I2IBEN). A set of hypothetical data, taking into account the availability of by-products, selling price, packaging cost and delivery cost, is used to demonstrate the application of the framework. The framework is capable
of providing decision support to a palm oil refinery to determine the optimal supply of palm oil by-products to the prospective customers that lead to the highest profit attainment, without violating the availability of resources. Besides, the framework also reinforces worldwide strategy of moving towards zero-waste concept with regards to utilization of by-products generated in palm oil refineries. No such study has been found to address this issue previously. 2. An overview on palm oil refining CPO obtained from milling process is associated with a number of impurities. Impurities constituent in CPO are comprised of mainly mono- and diglycerides, phospholipids (or natural gums), soaps, colouring pigments (like chlorophyll, gossypol and carotene), FFA, trace metal ions, oxidative compounds (like peroxides, aldehydes and ketones) and other contaminants (like PAH and pesticides) (Basiron, 1996; Gibon et al., 2007). In order for the oil to be served for human consumption, such impurities have to be removed while trying to cause the least possible damage to the triglycerides or neutral oil, and without destroying all the beneficial components such as vitamins and antioxidants. Removal of the impurities is accomplished through a series of refining processes. CPO can be refined either using physical or chemical refining process to produce refined, bleached and deodorized palm oil (RBDPO) or neutralized, bleached and deodorized palm oil (NBDPO), respectively. Fig. 1 illustrates both refining routes including the major steps involved and the main components removed. The purpose of degumming is to remove phospholipids from the CPO using food grade phosphoric acid (H3 PO4 ). Neutralization is a step where residual phospholipids from the degumming step and FFA are removed by reacting the oil with caustic soda (NaOH) solution. During this step, phospholipids and FFA are converted into insoluble soaps that can be easily separated via centrifugal action. Bleaching process is carried out under vacuum using activated bleaching earth to remove colouring pigments, trace metal ions and oxidative products, as well as residual soaps remained after the neutralization step. During bleaching process, a large amount of SBE is generated and separated from the bleached CPO using filter press. The deodorization process of CPO involves steam distillation under vacuum pressure. The purpose of this step is to ensure complete removal of FFA, volatile components like residual oxidative compounds from the bleaching step, and all other contaminants (Carlson, 1996; Hodgson, 1996; Gibon et al., 2007; Lin, 2002). The principal difference between physical refining and chemical refining is on the technology used to remove FFA. In physical refining, most of the FFA is removed during the deodorization process. On the other hand, for chemical refining, most FFA is removed during the alkali neutralization process. More than 95% of the CPO in Malaysia is refined through physical route. Physical refining is preferred as it reduces the loss of triglycerides, minimizes chemical usage and water consumption, and enables recovery of high quality FFA, which leads to considerable reduction of environmental impact. Unlike chemical refining, the bleaching earth consumption in physical refining is high since there is no pre-removal of FFA that is done during neutralization ˇ ´ 2000; process (Hong, 1983; Cvengroˇs, 1995; Cmolík and Pokorny, Gibon et al., 2007). 3. Problem description There are several by-products that are generated during the refining processes of CPO. These by-products have the potential to be sold to the other industries, and consequently processed to produce value-added products. According to the I2IBEN framework described earlier, given a set of refining by-products from a palm oil
H. Haslenda, M.Z. Jamaludin / Resources, Conservation and Recycling 55 (2011) 713–718
715
Crude Palm Oil (CPO)
Physical Refining
Chemical Refining
Degumming
SBE
PFAD
H3PO4
Degumming
NaOH
Neutralization
Bleaching Earth
Bleaching
SBE
Deodorization
Deodorization
PFAD
RBDPO
NBDPO
Bleaching
Soapstock
Fig. 1. Palm oil refining processes.
refinery and a set of prospective customers, monthly profit gained by the refinery can be maximized and sufficient amount of byproducts can be supplied, while satisfying all constraints including availability of the by-products and demand by the customers.
4. Optimization framework This section describes the methodology to solve the I2IBEN framework. The MILP model, integrated into the framework, is formulated to solve monthly cases of by-products distribution.
4.1. General superstructure The superstructure that represents all possible supply chains of palm oil by-products from a refinery to the prospective customers is illustrated in Fig. 2. The following notation is adopted throughout the paper: Ai and Vj represent available quantity of by-product i and demand by prospective customer j, respectively. In this study, three palm oil refinery by-products are taken into account, namely soapstock, PFAD and SBE. Meanwhile, prospective customers consist of four industries: animal feed, biodiesel, lubricant, and soap.
4.2. Assumptions The MILP model is formulated based on the following assumptions:
(a) Each of the prospective customers may demand different fraction of by-products from the total demand. This demand fraction is purposely designed to represent different blending of by-products (or raw materials) to produce value-added products required by each of the prospective customers. (b) Delivery cost of the by-products to respective industries is defined without taking into account the type of transportation used and the distance of the prospective customers from the refinery. However, it is assumed that each of the prospective customers is situated at different location; hence the delivery cost is different from one to another. (c) The by-products are packed and delivered to the prospective customers in the form of drums. A same capacity of drums is used for all type of by-products. Packaging cost is defined according to density of the by-products, regardless of the actual density. For instance, density of SBE may be higher than that of PFAD and soapstock. Therefore, more SBE can be filled into a drum as compared to PFAD and soapstock.
4.3. MILP model formulation
fij A, i = soapstock
Bij
y, j = animal feed y, j = biodiesel
4.3.1. Decision variables Two decision variables involved in the MILP model are described as follows:
A, i = PFAD y, j = lubricant A, i = SBE y, j = soap Fig. 2. General superstructure of palm oil by-products exchange network.
(a) Continuous variables, yj , that define the total quantity of byproducts i to be sold to meet the demand of prospective customer j. (b) Integer variables, Xij , that define the number of drums of byproduct i to be sold to prospective customer j. These variables ensure that there is no half-filled drum to be delivered.
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Table 1 Available stock, selling price and packaging cost of palm oil by-products. By-products, i
Available stock, Ai (kg)
Selling price, Ci (MYR/kg)
Packaging cost, Pi (MYR/drum)
Soapstock PFAD SBE
1500 4000 3000
50 15 30
MYR20/70 kg MYR20/50 kg MYR20/100 kg
4.3.2. Objective function The objective function of this MILP model is to maximize the monthly profit (MYR/month) gained by a palm oil refinery by selling its by-products to the prospective customers. The objective function is formulated as follow: Max(By-products Revenue − Packaging Cost − Delivery Cost) By-products Revenue =
Packaging Cost =
i
yj fij Ci
(1) (2)
j
Pi qi Xij
(3)
Dj yj fij conv
(4)
i
Delivery Cost =
j
where yj is the is the continuous variables (kg/month), fij is the demand fraction of by-product i by prospective customer j, Ci is the selling price of by-product i (MYR/kg), Pi is the packaging cost of by-product i (MYR/drum), qi is the capacity of by-product i per drum (kg/drum), Xij is the binary variables, Di is the delivery cost to prospective customer j (MYR/ton), and conv is a parameter used for unit conversion from ton to kg (kg/ton). 4.3.3. Constraints Maximization of the objective function given by Eq. (1) is subjected to the following constraints: (a) Supply of by-products:The total quantity of by-product i to be sold to all prospective customers j cannot exceed the available quantity of by-product i.
yj fij ≤ Ai
∀i
(5)
j
Bij ≤ Ai
(6)
j
Eq. (5) is further simplified to, (b) Customers’ demand:The total quantity of all by-products i to be sold to prospective customer j must satisfy a boundary as follow: Vj,min ≤
Bij ≤ Vj,max
∀j
(7)
i
where Vj,min and Vj,max is the minimum demand and maximum demand of total by-products i by prospective customer j, respectively. (c) Composition balance:The summation of demand fraction of each by-product i for all prospective customers j must be equal
to one. For instance, a biodiesel company may require 0.2 soapstock, 0.3 PFAD and 0.5 SBE as a perfect blend of raw materials from palm oil by-products to produce biodiesel.
fij = 1
∀j
(8)
i
(d) Integer constraints:The quantity of by-product i to be sold to prospective customer j cannot exceed the total capacity of drums used. This constraint also ensures that drums used to pack all by-products i must be completely filled for delivery. Bij ≤ qi Xij
∀i, ∀j
(9)
(e) Non-negativity constraints:The total quantity of by-products i to be sold to prospective customer j must be greater than zero, and therefore is defined as positive variables. yi ≥ 0
∀j
(10)
5. Illustrative case study The proposed I2IBEN framework is tested using a set of hypothetical data to illustrate its applicability and reliability. Table 1 shows the available stock, selling price and packaging cost of palm oil by-products for a particular month. In this case study, byproducts that are subjected for sales are packed and delivered in the form of drums with a cost of MYR20 per drum. The capacity of by-product per drum for soapstock, PFAD and SBE is 70 kg, 50 kg and 100 kg, respectively. Table 2 shows a monthly minimum demand, Vj,min and maximum demand, Vj,max of by-products by the customers, demand fraction fij , and delivery cost, Dj of by-products to the customers. Delivery cost is calculated on the basis of cost per ton of by-products delivered. For this particular case study, the superstructure that represents the supply chains of palm oil by-products from a refinery to the prospective customers is illustrated in Fig. 3. The case study is modelled according to the proposed I2IBEN framework. The MILP model is programmed and solved in GAMS using CPLEX solver to determine the optimal solution. Fig. 4 shows the total amount of palm oil by-products sold to all customers compared to the available stocks. It can be seen that SBE is sold out, whereas about 85% of soapstock and 53% of PFAD are sold to the customers. Overall, 75% of palm oil by-products are sold from the total of 8500 kg stocks available in this particular month. Table 3 shows the optimal distribution of palm oil by-products to their respective customers, recommended by the I2IBEN framework. As indicated in Table 2, different customers demand for different amount of by-products according to the demand fraction specified by them. Therefore, such limitation must be fulfilled
Table 2 Monthly demand, demand fraction and delivery cost. Industrial customers, j
Animal feed Biodiesel Lubricant Soap
Monthly demand (kg)
Demand fraction, fij
Delivery cost, Dj (MYR/ton)
Vj,min
Vj,max
Soapstock
PFAD
SBE
700 1000 2000 400
1000 1500 4000 700
0.7 0.2 – 0.4
0.3 0.3 0.3 0.6
– 0.5 0.7 –
120 400 100 300
H. Haslenda, M.Z. Jamaludin / Resources, Conservation and Recycling 55 (2011) 713–718
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fij A, i = soapstock
y, j = animal feed
Bij
y, j = biodiesel A, i = PFAD y, j = lubricant A, i = SBE y, j = soap Fig. 3. Illustrative case study – superstructure of palm oil by-products exchange network.
Fig. 5. Distribution of by-products to the prospective customers.
Fig. 4. Comparison between stock and sale of by-products.
accordingly. As indicated in Table 3, supply of by-products satisfies maximum demand for animal feed, lubricant and soap industries, but not for lubricant (refer to Table 2). Although PFAD and SBE are two possible feed stocks for the lubricant industry, SBE is not a promising candidate because it is totally sold out to other industries that provide higher revenue. Besides, the quantity of PFAD and SBE supplied to lubricant industry is controlled by the demand fraction of its predetermined feedstock.Fig. 5 illustrates the number of drums of each by-products delivered to the customers. As described in Table 2, the by-product capacity per drum for soapstock, PFAD and SBE is 70 kg, 50 kg and 100 kg, respectively. A total of 1280 kg soapstock is packaged in 19 drums and transported to animal feed industry (10 drums), biodiesel industry (5 drums) and soap industry (4 drums). For the case of PFAD, animal feed, biodiesel, lubricant and soap industries are supplied with 6 drums (of 300 kg), 9 drums (of 450 kg), 20 drums (of 965 kg) and 9 drums (of 420 kg), respectively. Complete utilization of 3000 kg of SBE is delivered to biodiesel industry (8 drums) and lubricant industry (23 drums). Fig. 6 shows the breakdown of monthly profit gained by the palm oil refinery according to the distribution of by-products. In this case study, SBE appears as the most profitable by-product as it is demanded in a huge amount by the customers. Besides, the sellTable 3 Distribution of by-products to the industrial customers. Industrial customers, j
Animal feed Biodiesel Lubricant Soap Total supplied (kg)
Distribution of by-products (kg)
Stocks supplied, yj (kg)
Soapstock
PFAD
SBE
700 300 – 280
300 450 965 420
– 750 2250 –
1000 1500 3215 700 6415
Fig. 6. Breakdown of monthly profit.
ing price of SBE is considerably high, which is MYR30/kg. Although soapstock has the highest selling price, MYR50/kg, demand for soapstock is not as much as SBE, thus making it less profitable. PFAD contributes to the lowest revenue since its selling price is the lowest one, which is MYR15/kg. In addition, demand for PFAD is also small. Overall, the I2IBEN framework solves the illustrative case study by maximizing a gross profit as much as MYR182, 893 to the palm oil refinery, after taking into consideration the by-products revenue, packaging cost, delivery cost and all the supply constraints. 6. Conclusion A systematic framework to determine industry-to-industry byproducts exchange network (I2IBEN) from a palm oil refinery to a set of prospective customers is developed. A generic MILP model is formulated and integrated into the framework. The model is programmed and solved in GAMS to determine the maximum monthly profit that could be gained by the refinery and also supply sufficient amount of by-products to the prospective customers. The most crucial factors that affect the refinery’s profit are taken into account: (1) by-products revenue, (2) packaging cost, and (3) delivery cost. An illustrative case study shows that the I2IBEN framework is capable of providing decision support to determine the optimal distribution of palm oil by-products to the prospective customers, as well as reinforces the strategy of moving towards zero-waste concept. References Atil O. Palm-based animal feed and MPOB’s Energy and Protein Centre. Palm Oil Developments 2004;40:1–4.
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Balazs IL. Refining and use of byproducts from various fats and oils. JOACS 1987;64(8):1126–8. Basiron Y. Palm oil. In: Hui YH, editor. Bailey’s industrial oil & fat products edible oil and fat products: oils and oil seeds, vol. 2, 5th ed. New York: John Wiley & Sons, Inc.; 1996. p. 271–375. Basiron Y. Palm oil production through sustainable plantations. European Journal of Lipid Science and Technology 2007;109:289–95. Basiron Y, Weng CK. The oil palm and its sustainability. Journal of Palm Oil Research 2004;16(1):1–10. ˜ A, Puigjaner L. Incorporating environmental impacts Bojarski AD, Laínez JM, Espuna and regulations in a holistic supply chain modeling: an LCA approach. Computers and Chemical Engineering 2009;33:1747–59. Boonnoun P, Maneesiri A, Pattamaprom C. Production of biodiesel from palm fatty acid distillate. Thammasat International Journal of Science Technology 2008;13(4):32–7. Boukerroui A, Ouali MS. Regeneration of a spent bleaching earth and its reuse in the refining of an edible oil. J Chem Technol Biotechnol 2000;75:773–6. Carlson KF. Deodorization. In: Hui YH, editor. Bailey’s industrial oil & fat products Edible oil and fat products: processing technology, vol. 4, 5th ed. New York:: John Wiley & Sons, Inc.; 1996. p. 339–90. Chongkhong S, Tongurai C, Chetpattananondh P, Bunyakan C. Biodiesel production by esterification of palm fatty acid distillate. Biomass and Bioenergy 2007;1:563–8. Cvengroˇs J. Physical refining of edible oils. JAOCS 1995;72(10):1193–6. ˇ Cmolík J, Pokorny´ J. Physical refining of edible oils. European Journal of Lipid Science and Technology 2000;102:472–86. Dumont MJ, Narine SS. Soapstock and deodorizer distillates from North American vegetable oils: review on their characterization, extraction and utilization. Food Research International 2007;40:957–74. Gibon V, Greyt WD, Kellens M. Palm oil refining. European Journal of Lipid Science and Technology 2007;109:315–35. Global Oils and Fats Business Magazine. Boosting animal feed: palm-based byproducts have proved their worth 2007;4(4). Global Oils and Fats Business Magazine. Malaysian palm oil industry: performance 2008 2009;6(1).
Hong WM. Quality of by-products from chemical and physical refining of palm oil and other oils. JAOCS 1983;60(2):316–21. Huang YP, Chang JI. Biodiesel production from residual oils recovered from spent bleaching earth. Renewable Energy 2010;35:269–74. Hodgson AS. Refining bleaching. In: Hui YH, editor. Bailey’s industrial oil & fat products Edible oil and fat products: processing technology, vol. 4, 5th ed. New York: John Wiley & Sons Inc.; 1996. p. 157–212. Kannan G, Sasikumar P, Devika K. A genetic algorithm approach for solving a closed loop supply chain model: a case of battery recycling. Applied Mathematical Modelling 2010;34:655–70. Kheang LS, Foon CT, May CY, Ngan MA. A study of residual oils recovered from spent bleaching earth: their characteristics and applications. American Journal of Applied Sciences 2006;3(10):2063–7. Lim BP, Maniam GP, Hamid SA. Biodiesel from adsorbed waste oil on spent bleaching clay using CaO as a heterogeneous catalyst. European Journal of Scientific Research 2009;33(2):347–57. Lin SW. Palm oil. In: Gunstone FD, editor. Vegetable oils in food technology: composition, properties and uses. Blackwell Publishing Ltd.: New York; 2002. p. 59–97. Luxem FJ, Mirous BK. Biocatalysis and bioenergy. In: Ching TH, Jei-Fu S, editors. Chapter 6. Biodiesel from acidulated soapstock (acid oil). New York: John Wiley & Sons, Inc.; 2008. p. 115–29. Ong JTL. Oil recovery from spent bleaching earth and disposal of the extracted material. JAOCS 1983;60(2):314–5. Palmquist DL. Palm fats for livestock feeding. Palm Oil Developments 2004;40:10–6. Sambanthamurthi R, Sundram K, Tan YA. Chemistry and biochemistry of palm oil. Progress in Lipid Research 2000;39:507–58. Sumathi S, Chai SP, Mohamed AR. Utilization of oil palm as a source of renewable energy in Malaysia. Renewable and Sustainable Energy Reviews 2008;12:2404–21. Top AGM, Rahman HA. Squalene in oils and fats. Palm Oil Developments 2000;32:36–40. Woerfel JB, Soapstock.Baldwin AR, editor. Proceedings of the world conference on emerging technologies in the fats and oils industry. USA: AOCS Press; 1986. p. 165–8.
Contents lists available at ScienceDirect
Resources, Conservation and Recycling journal homepage: www.elsevier.com/locate/resconrec
Industry to Industry By-products Exchange Network towards zero waste in palm oil refining processes H. Haslenda ∗ , M.Z. Jamaludin Process Systems Engineering Centre (PROSPECT), Faculty of Chemical and Natural Resources Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia
a r t i c l e
i n f o
Article history: Received 7 May 2010 Received in revised form 21 February 2011 Accepted 26 February 2011 Keywords: Supply chain network MILP Optimization Palm oil refining Zero waste
a b s t r a c t This paper presents a systematic framework for optimal utilization of by-products generated during crude palm oil refining processes. Three by-products are considered in the supply chain network: soapstock, palm fatty acid distillate (PFAD) and spent bleaching earth (SBE). These by-products, generated from neutralization, deodorization and bleaching processes, are viable feedstocks to other commercial industries such as animal feed, biodiesel, lubricant and soap. The case study is formulated as Mixed Integer Linear Programming (MILP) and integrated into the framework with the objective to maximize the refinery’s profit as well as moving towards a conscious mindset of zero waste. This is the first time that such framework is developed and applied for the palm oil industry. The framework is called as Industry to Industry By-products Exchange Network (I2IBEN). An illustrative case study demonstrates a significant potential profit of MYR182, 893 per month. © 2011 Published by Elsevier B.V.
1. Introduction Industrial waste management is a global problem. Growing waste disposal costs and stringent environmental regulations have led to widespread waste management efforts through transformation of industrial by-products, which conventionally go to waste, into valuable products. In the palm oil industry, while refined palm oil generates enormous revenue, by-products associated with the refining processes may also be further utilized, hence contribute towards zero-waste strategy in the palm oil refining processes. Transformation of palm oil by-products to value-added products would significantly increase the profit of a palm oil refinery, and consequently remain competitive in the industry. With over one tenth of the country’s land covered with palm oil plantation, the palm oil industry has become one of the most important economic activities in Malaysia (Global Oils and Fats Business Magazine, 2009). Malaysia is currently the world’s largest producer and exporter of palm oil by contributing to about 47% of the total world’s supply (Basiron, 2007; Sumathi et al., 2008). Along with this huge production, refining of crude palm oil (CPO) is associated with the generation of several by-products such as soapstock, palm fatty acid distillate (PFAD) and spent bleaching earth (SBE). These by-products are among the viable feedstocks to other commercial industries such as animal feed, biodiesel, lubricant and soap (Ong, 1983; Balazs, 1987; Kheang et al., 2006; Dumont and Narine, 2007;
∗ Corresponding author. Tel.: +60 7 5535478; fax: +60 7 5581463. E-mail address: [email protected] (H. Haslenda). 0921-3449/$ – see front matter © 2011 Published by Elsevier B.V. doi:10.1016/j.resconrec.2011.02.004
Huang and Chang, 2010). In fact, the use of these by-products as alternative raw materials for certain industries, for instance lubricant and biodiesel, reduces the production cost and maintains the market price of such value-added products. Soapstock obtained from neutralization of CPO contains mainly free fatty acids (FFA). It has a variety of end uses, such as being a nutrient source for microorganisms, a reactant for chemical reactions, and a fertilizer ingredient and most importantly as an essential feedstock for animal-feeding industries (Ong, 1983; Woerfel, 1986; Dumont and Narine, 2007). It can also be used as an alternative raw material for biodiesel production (Luxem and Mirous, 2008). SBE, on the other hand, is a by-product recovered from bleaching process of the CPO. SBE that is produced abundantly in palm oil refineries (Lim et al., 2009) retains about 20–40% of the crude oil (Ong, 1983). The residual oil retained in SBE after refining process can be extracted and sold as a raw material to lubricant and biodiesel industries (Boukerroui and Ouali, 2000; Kheang et al., 2006; Basiron and Weng, 2004; Huang and Chang, 2010). Although there are industrial efforts to recover the residual oil, SBE is still under-utilized and disposed in landfill sites. This creates waste disposal problems such as the potential of environmental hazards and the rise in disposal cost. Similarly with soapstock, PFAD recovered from deodorization process is rich in FFA content. PFAD is commonly used as raw materials in producing medium-grade cleaners, animal feeds, plastics and other intermediate products for the oleochemical industries (Hong, 1983; Top and Rahman, 2000; Atil, 2004; Sambanthamurthi et al., 2000; Palmquist, 2004; Dumont and Narine, 2007; Global Oils
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Nomenclature Ai Bij Ci conv Dj FFA fij min max Pi qi Vj,min Vj,max Xij yj
available quantity of by-product i in a particular month quantity of by-product i to be sold to potential customer j selling price of by-product i unit conversion factor delivery cost of to potential customer j free fatty acids demand fraction of by-product i by potential customer j minimum maximum packaging cost of by-product i capacity of by-product i per drum minimum demand of by-products i by potential customer j maximum demand of by-products i by potential customer j drums of by-product i to be sold to potential customer j quantity of by-products i to be sold to potential customer j
Greek letters summation ∀ all belongs to. . . Subscripts i index for by-products j index for potential customers Acronym CPKO CPO GAMS I2IBEN MILP MPOB MYR NBDPO PAH PFAD RBDPO SBE
crude palm kernel oil crude palm oil Generic Algebraic Modelling System Industry to Industry By-products Exchange Network Mixed Integer Linear Programming Malaysian Palm Oil Board Malaysian Ringgit neutralized, bleached and deodorized palm oil polycyclic aromatic hydrocarbons palm fatty acid distillate refined, bleached and deodorized palm oil spent bleaching earth
and Fats Business Magazine, 2007). Other studies also demonstrate the possibility of producing biodiesel using FFA that is extracted from PFAD (Chongkhong et al., 2007; Boonnoun et al., 2008). Optimization techniques are often employed to aid decision making in the supply chain network. Very few optimization frameworks are seen to address waste management problems and environmental issues. A few of these can be found in open literature (Bojarski et al., 2009; Kannan et al., 2010). This study develops a systematic framework for optimal utilization of by-products generated from palm oil refining processes. The supply chain network of the by-products to the potential industries is formulated as Mixed Integer Linear Programming (MILP) and solved in General Algebraic Modelling System (GAMS). This framework is called as Industry to Industry By-products Exchange Network (I2IBEN). A set of hypothetical data, taking into account the availability of by-products, selling price, packaging cost and delivery cost, is used to demonstrate the application of the framework. The framework is capable
of providing decision support to a palm oil refinery to determine the optimal supply of palm oil by-products to the prospective customers that lead to the highest profit attainment, without violating the availability of resources. Besides, the framework also reinforces worldwide strategy of moving towards zero-waste concept with regards to utilization of by-products generated in palm oil refineries. No such study has been found to address this issue previously. 2. An overview on palm oil refining CPO obtained from milling process is associated with a number of impurities. Impurities constituent in CPO are comprised of mainly mono- and diglycerides, phospholipids (or natural gums), soaps, colouring pigments (like chlorophyll, gossypol and carotene), FFA, trace metal ions, oxidative compounds (like peroxides, aldehydes and ketones) and other contaminants (like PAH and pesticides) (Basiron, 1996; Gibon et al., 2007). In order for the oil to be served for human consumption, such impurities have to be removed while trying to cause the least possible damage to the triglycerides or neutral oil, and without destroying all the beneficial components such as vitamins and antioxidants. Removal of the impurities is accomplished through a series of refining processes. CPO can be refined either using physical or chemical refining process to produce refined, bleached and deodorized palm oil (RBDPO) or neutralized, bleached and deodorized palm oil (NBDPO), respectively. Fig. 1 illustrates both refining routes including the major steps involved and the main components removed. The purpose of degumming is to remove phospholipids from the CPO using food grade phosphoric acid (H3 PO4 ). Neutralization is a step where residual phospholipids from the degumming step and FFA are removed by reacting the oil with caustic soda (NaOH) solution. During this step, phospholipids and FFA are converted into insoluble soaps that can be easily separated via centrifugal action. Bleaching process is carried out under vacuum using activated bleaching earth to remove colouring pigments, trace metal ions and oxidative products, as well as residual soaps remained after the neutralization step. During bleaching process, a large amount of SBE is generated and separated from the bleached CPO using filter press. The deodorization process of CPO involves steam distillation under vacuum pressure. The purpose of this step is to ensure complete removal of FFA, volatile components like residual oxidative compounds from the bleaching step, and all other contaminants (Carlson, 1996; Hodgson, 1996; Gibon et al., 2007; Lin, 2002). The principal difference between physical refining and chemical refining is on the technology used to remove FFA. In physical refining, most of the FFA is removed during the deodorization process. On the other hand, for chemical refining, most FFA is removed during the alkali neutralization process. More than 95% of the CPO in Malaysia is refined through physical route. Physical refining is preferred as it reduces the loss of triglycerides, minimizes chemical usage and water consumption, and enables recovery of high quality FFA, which leads to considerable reduction of environmental impact. Unlike chemical refining, the bleaching earth consumption in physical refining is high since there is no pre-removal of FFA that is done during neutralization ˇ ´ 2000; process (Hong, 1983; Cvengroˇs, 1995; Cmolík and Pokorny, Gibon et al., 2007). 3. Problem description There are several by-products that are generated during the refining processes of CPO. These by-products have the potential to be sold to the other industries, and consequently processed to produce value-added products. According to the I2IBEN framework described earlier, given a set of refining by-products from a palm oil
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715
Crude Palm Oil (CPO)
Physical Refining
Chemical Refining
Degumming
SBE
PFAD
H3PO4
Degumming
NaOH
Neutralization
Bleaching Earth
Bleaching
SBE
Deodorization
Deodorization
PFAD
RBDPO
NBDPO
Bleaching
Soapstock
Fig. 1. Palm oil refining processes.
refinery and a set of prospective customers, monthly profit gained by the refinery can be maximized and sufficient amount of byproducts can be supplied, while satisfying all constraints including availability of the by-products and demand by the customers.
4. Optimization framework This section describes the methodology to solve the I2IBEN framework. The MILP model, integrated into the framework, is formulated to solve monthly cases of by-products distribution.
4.1. General superstructure The superstructure that represents all possible supply chains of palm oil by-products from a refinery to the prospective customers is illustrated in Fig. 2. The following notation is adopted throughout the paper: Ai and Vj represent available quantity of by-product i and demand by prospective customer j, respectively. In this study, three palm oil refinery by-products are taken into account, namely soapstock, PFAD and SBE. Meanwhile, prospective customers consist of four industries: animal feed, biodiesel, lubricant, and soap.
4.2. Assumptions The MILP model is formulated based on the following assumptions:
(a) Each of the prospective customers may demand different fraction of by-products from the total demand. This demand fraction is purposely designed to represent different blending of by-products (or raw materials) to produce value-added products required by each of the prospective customers. (b) Delivery cost of the by-products to respective industries is defined without taking into account the type of transportation used and the distance of the prospective customers from the refinery. However, it is assumed that each of the prospective customers is situated at different location; hence the delivery cost is different from one to another. (c) The by-products are packed and delivered to the prospective customers in the form of drums. A same capacity of drums is used for all type of by-products. Packaging cost is defined according to density of the by-products, regardless of the actual density. For instance, density of SBE may be higher than that of PFAD and soapstock. Therefore, more SBE can be filled into a drum as compared to PFAD and soapstock.
4.3. MILP model formulation
fij A, i = soapstock
Bij
y, j = animal feed y, j = biodiesel
4.3.1. Decision variables Two decision variables involved in the MILP model are described as follows:
A, i = PFAD y, j = lubricant A, i = SBE y, j = soap Fig. 2. General superstructure of palm oil by-products exchange network.
(a) Continuous variables, yj , that define the total quantity of byproducts i to be sold to meet the demand of prospective customer j. (b) Integer variables, Xij , that define the number of drums of byproduct i to be sold to prospective customer j. These variables ensure that there is no half-filled drum to be delivered.
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Table 1 Available stock, selling price and packaging cost of palm oil by-products. By-products, i
Available stock, Ai (kg)
Selling price, Ci (MYR/kg)
Packaging cost, Pi (MYR/drum)
Soapstock PFAD SBE
1500 4000 3000
50 15 30
MYR20/70 kg MYR20/50 kg MYR20/100 kg
4.3.2. Objective function The objective function of this MILP model is to maximize the monthly profit (MYR/month) gained by a palm oil refinery by selling its by-products to the prospective customers. The objective function is formulated as follow: Max(By-products Revenue − Packaging Cost − Delivery Cost) By-products Revenue =
Packaging Cost =
i
yj fij Ci
(1) (2)
j
Pi qi Xij
(3)
Dj yj fij conv
(4)
i
Delivery Cost =
j
where yj is the is the continuous variables (kg/month), fij is the demand fraction of by-product i by prospective customer j, Ci is the selling price of by-product i (MYR/kg), Pi is the packaging cost of by-product i (MYR/drum), qi is the capacity of by-product i per drum (kg/drum), Xij is the binary variables, Di is the delivery cost to prospective customer j (MYR/ton), and conv is a parameter used for unit conversion from ton to kg (kg/ton). 4.3.3. Constraints Maximization of the objective function given by Eq. (1) is subjected to the following constraints: (a) Supply of by-products:The total quantity of by-product i to be sold to all prospective customers j cannot exceed the available quantity of by-product i.
yj fij ≤ Ai
∀i
(5)
j
Bij ≤ Ai
(6)
j
Eq. (5) is further simplified to, (b) Customers’ demand:The total quantity of all by-products i to be sold to prospective customer j must satisfy a boundary as follow: Vj,min ≤
Bij ≤ Vj,max
∀j
(7)
i
where Vj,min and Vj,max is the minimum demand and maximum demand of total by-products i by prospective customer j, respectively. (c) Composition balance:The summation of demand fraction of each by-product i for all prospective customers j must be equal
to one. For instance, a biodiesel company may require 0.2 soapstock, 0.3 PFAD and 0.5 SBE as a perfect blend of raw materials from palm oil by-products to produce biodiesel.
fij = 1
∀j
(8)
i
(d) Integer constraints:The quantity of by-product i to be sold to prospective customer j cannot exceed the total capacity of drums used. This constraint also ensures that drums used to pack all by-products i must be completely filled for delivery. Bij ≤ qi Xij
∀i, ∀j
(9)
(e) Non-negativity constraints:The total quantity of by-products i to be sold to prospective customer j must be greater than zero, and therefore is defined as positive variables. yi ≥ 0
∀j
(10)
5. Illustrative case study The proposed I2IBEN framework is tested using a set of hypothetical data to illustrate its applicability and reliability. Table 1 shows the available stock, selling price and packaging cost of palm oil by-products for a particular month. In this case study, byproducts that are subjected for sales are packed and delivered in the form of drums with a cost of MYR20 per drum. The capacity of by-product per drum for soapstock, PFAD and SBE is 70 kg, 50 kg and 100 kg, respectively. Table 2 shows a monthly minimum demand, Vj,min and maximum demand, Vj,max of by-products by the customers, demand fraction fij , and delivery cost, Dj of by-products to the customers. Delivery cost is calculated on the basis of cost per ton of by-products delivered. For this particular case study, the superstructure that represents the supply chains of palm oil by-products from a refinery to the prospective customers is illustrated in Fig. 3. The case study is modelled according to the proposed I2IBEN framework. The MILP model is programmed and solved in GAMS using CPLEX solver to determine the optimal solution. Fig. 4 shows the total amount of palm oil by-products sold to all customers compared to the available stocks. It can be seen that SBE is sold out, whereas about 85% of soapstock and 53% of PFAD are sold to the customers. Overall, 75% of palm oil by-products are sold from the total of 8500 kg stocks available in this particular month. Table 3 shows the optimal distribution of palm oil by-products to their respective customers, recommended by the I2IBEN framework. As indicated in Table 2, different customers demand for different amount of by-products according to the demand fraction specified by them. Therefore, such limitation must be fulfilled
Table 2 Monthly demand, demand fraction and delivery cost. Industrial customers, j
Animal feed Biodiesel Lubricant Soap
Monthly demand (kg)
Demand fraction, fij
Delivery cost, Dj (MYR/ton)
Vj,min
Vj,max
Soapstock
PFAD
SBE
700 1000 2000 400
1000 1500 4000 700
0.7 0.2 – 0.4
0.3 0.3 0.3 0.6
– 0.5 0.7 –
120 400 100 300
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fij A, i = soapstock
y, j = animal feed
Bij
y, j = biodiesel A, i = PFAD y, j = lubricant A, i = SBE y, j = soap Fig. 3. Illustrative case study – superstructure of palm oil by-products exchange network.
Fig. 5. Distribution of by-products to the prospective customers.
Fig. 4. Comparison between stock and sale of by-products.
accordingly. As indicated in Table 3, supply of by-products satisfies maximum demand for animal feed, lubricant and soap industries, but not for lubricant (refer to Table 2). Although PFAD and SBE are two possible feed stocks for the lubricant industry, SBE is not a promising candidate because it is totally sold out to other industries that provide higher revenue. Besides, the quantity of PFAD and SBE supplied to lubricant industry is controlled by the demand fraction of its predetermined feedstock.Fig. 5 illustrates the number of drums of each by-products delivered to the customers. As described in Table 2, the by-product capacity per drum for soapstock, PFAD and SBE is 70 kg, 50 kg and 100 kg, respectively. A total of 1280 kg soapstock is packaged in 19 drums and transported to animal feed industry (10 drums), biodiesel industry (5 drums) and soap industry (4 drums). For the case of PFAD, animal feed, biodiesel, lubricant and soap industries are supplied with 6 drums (of 300 kg), 9 drums (of 450 kg), 20 drums (of 965 kg) and 9 drums (of 420 kg), respectively. Complete utilization of 3000 kg of SBE is delivered to biodiesel industry (8 drums) and lubricant industry (23 drums). Fig. 6 shows the breakdown of monthly profit gained by the palm oil refinery according to the distribution of by-products. In this case study, SBE appears as the most profitable by-product as it is demanded in a huge amount by the customers. Besides, the sellTable 3 Distribution of by-products to the industrial customers. Industrial customers, j
Animal feed Biodiesel Lubricant Soap Total supplied (kg)
Distribution of by-products (kg)
Stocks supplied, yj (kg)
Soapstock
PFAD
SBE
700 300 – 280
300 450 965 420
– 750 2250 –
1000 1500 3215 700 6415
Fig. 6. Breakdown of monthly profit.
ing price of SBE is considerably high, which is MYR30/kg. Although soapstock has the highest selling price, MYR50/kg, demand for soapstock is not as much as SBE, thus making it less profitable. PFAD contributes to the lowest revenue since its selling price is the lowest one, which is MYR15/kg. In addition, demand for PFAD is also small. Overall, the I2IBEN framework solves the illustrative case study by maximizing a gross profit as much as MYR182, 893 to the palm oil refinery, after taking into consideration the by-products revenue, packaging cost, delivery cost and all the supply constraints. 6. Conclusion A systematic framework to determine industry-to-industry byproducts exchange network (I2IBEN) from a palm oil refinery to a set of prospective customers is developed. A generic MILP model is formulated and integrated into the framework. The model is programmed and solved in GAMS to determine the maximum monthly profit that could be gained by the refinery and also supply sufficient amount of by-products to the prospective customers. The most crucial factors that affect the refinery’s profit are taken into account: (1) by-products revenue, (2) packaging cost, and (3) delivery cost. An illustrative case study shows that the I2IBEN framework is capable of providing decision support to determine the optimal distribution of palm oil by-products to the prospective customers, as well as reinforces the strategy of moving towards zero-waste concept. References Atil O. Palm-based animal feed and MPOB’s Energy and Protein Centre. Palm Oil Developments 2004;40:1–4.
718
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Balazs IL. Refining and use of byproducts from various fats and oils. JOACS 1987;64(8):1126–8. Basiron Y. Palm oil. In: Hui YH, editor. Bailey’s industrial oil & fat products edible oil and fat products: oils and oil seeds, vol. 2, 5th ed. New York: John Wiley & Sons, Inc.; 1996. p. 271–375. Basiron Y. Palm oil production through sustainable plantations. European Journal of Lipid Science and Technology 2007;109:289–95. Basiron Y, Weng CK. The oil palm and its sustainability. Journal of Palm Oil Research 2004;16(1):1–10. ˜ A, Puigjaner L. Incorporating environmental impacts Bojarski AD, Laínez JM, Espuna and regulations in a holistic supply chain modeling: an LCA approach. Computers and Chemical Engineering 2009;33:1747–59. Boonnoun P, Maneesiri A, Pattamaprom C. Production of biodiesel from palm fatty acid distillate. Thammasat International Journal of Science Technology 2008;13(4):32–7. Boukerroui A, Ouali MS. Regeneration of a spent bleaching earth and its reuse in the refining of an edible oil. J Chem Technol Biotechnol 2000;75:773–6. Carlson KF. Deodorization. In: Hui YH, editor. Bailey’s industrial oil & fat products Edible oil and fat products: processing technology, vol. 4, 5th ed. New York:: John Wiley & Sons, Inc.; 1996. p. 339–90. Chongkhong S, Tongurai C, Chetpattananondh P, Bunyakan C. Biodiesel production by esterification of palm fatty acid distillate. Biomass and Bioenergy 2007;1:563–8. Cvengroˇs J. Physical refining of edible oils. JAOCS 1995;72(10):1193–6. ˇ Cmolík J, Pokorny´ J. Physical refining of edible oils. European Journal of Lipid Science and Technology 2000;102:472–86. Dumont MJ, Narine SS. Soapstock and deodorizer distillates from North American vegetable oils: review on their characterization, extraction and utilization. Food Research International 2007;40:957–74. Gibon V, Greyt WD, Kellens M. Palm oil refining. European Journal of Lipid Science and Technology 2007;109:315–35. Global Oils and Fats Business Magazine. Boosting animal feed: palm-based byproducts have proved their worth 2007;4(4). Global Oils and Fats Business Magazine. Malaysian palm oil industry: performance 2008 2009;6(1).
Hong WM. Quality of by-products from chemical and physical refining of palm oil and other oils. JAOCS 1983;60(2):316–21. Huang YP, Chang JI. Biodiesel production from residual oils recovered from spent bleaching earth. Renewable Energy 2010;35:269–74. Hodgson AS. Refining bleaching. In: Hui YH, editor. Bailey’s industrial oil & fat products Edible oil and fat products: processing technology, vol. 4, 5th ed. New York: John Wiley & Sons Inc.; 1996. p. 157–212. Kannan G, Sasikumar P, Devika K. A genetic algorithm approach for solving a closed loop supply chain model: a case of battery recycling. Applied Mathematical Modelling 2010;34:655–70. Kheang LS, Foon CT, May CY, Ngan MA. A study of residual oils recovered from spent bleaching earth: their characteristics and applications. American Journal of Applied Sciences 2006;3(10):2063–7. Lim BP, Maniam GP, Hamid SA. Biodiesel from adsorbed waste oil on spent bleaching clay using CaO as a heterogeneous catalyst. European Journal of Scientific Research 2009;33(2):347–57. Lin SW. Palm oil. In: Gunstone FD, editor. Vegetable oils in food technology: composition, properties and uses. Blackwell Publishing Ltd.: New York; 2002. p. 59–97. Luxem FJ, Mirous BK. Biocatalysis and bioenergy. In: Ching TH, Jei-Fu S, editors. Chapter 6. Biodiesel from acidulated soapstock (acid oil). New York: John Wiley & Sons, Inc.; 2008. p. 115–29. Ong JTL. Oil recovery from spent bleaching earth and disposal of the extracted material. JAOCS 1983;60(2):314–5. Palmquist DL. Palm fats for livestock feeding. Palm Oil Developments 2004;40:10–6. Sambanthamurthi R, Sundram K, Tan YA. Chemistry and biochemistry of palm oil. Progress in Lipid Research 2000;39:507–58. Sumathi S, Chai SP, Mohamed AR. Utilization of oil palm as a source of renewable energy in Malaysia. Renewable and Sustainable Energy Reviews 2008;12:2404–21. Top AGM, Rahman HA. Squalene in oils and fats. Palm Oil Developments 2000;32:36–40. Woerfel JB, Soapstock.Baldwin AR, editor. Proceedings of the world conference on emerging technologies in the fats and oils industry. USA: AOCS Press; 1986. p. 165–8.