Bioresource Technology 100 (2009) 1227–1237

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Bioresource Technology

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Process integration possibilities for biodiesel production from palm oilusing ethanol obtained from lignocellulosic residues of oil palm industry

Luis F. Gutiérrez a, Óscar J. Sánchez a,b, Carlos A. Cardona a,*

a Department of Chemical Engineering, Universidad Nacional de Colombia sede Manizales, Cra. 27 No. 64-60 Of. F-505, Manizales, Caldas, Colombiab Institute of Agricultural Biotechnology, Universidad de Caldas, Calle 65 No. 26-10, Manizales, Caldas, Colombia

a r t i c l e i n f o

Article history:Received 16 May 2008Received in revised form 1 September 2008Accepted 3 September 2008Available online 17 October 2008

Keywords:BiodieselFuel ethanolOil palmLignocellulosic residuesProcess integration

0960-8524/$ - see front matter � 2008 Elsevier Ltd. Adoi:10.1016/j.biortech.2008.09.001

* Corresponding author. Tel.: +57 6 8879300x50417E-mail address: ccardonaal@unal.edu.co (C.A. Card

a b s t r a c t

In this paper, integration possibilities for production of biodiesel and bioethanol using a single source ofbiomass as a feedstock (oil palm) were explored through process simulation. The oil extracted from FreshFruit Bunches was considered as the feedstock for biodiesel production. An extractive reaction process isproposed for transesterification reaction using in situ produced ethanol, which is obtained from two typesof lignocellulosic residues of palm industry (Empty Fruit Bunches and Palm Press Fiber). Several ways ofintegration were analyzed. The integration of material flows between ethanol and biodiesel productionlines allowed a reduction in unit energy costs down to 3.4%, whereas the material and energy integrationleaded to 39.8% decrease of those costs. The proposed integrated configuration is an important optionwhen the technology for ethanol production from biomass reaches such a degree of maturity that its pro-duction costs be comparable with those of grain or cane ethanol.

� 2008 Elsevier Ltd. All rights reserved.

1. Introduction

Biodiesel and bioethanol are the most important liquid biofuelsemployed in the transportation sector. These biofuels can be uti-lized as a sole fuel in special motor engines or as additives in dieseland gasoline blends in order to enhance the oxygen content of suchfuels. These oxygenated blends allow the reduction of pollutinggases mostly aromatic hydrocarbons and CO.

The biodiesel is a mixture of methyl or ethyl esters of fattyacids. The ester group increases the oxygen content of diesel–bio-diesel blends improving the combustion efficiency of the conven-tional fossil diesel. For producing biodiesel, the transesterificationof vegetable oils with low molecular weight alcohols like methanolor ethanol is necessary. This reaction is accomplished with the helpof acid, basic or enzymatic catalysts. Usually, world biodiesel pro-duction is carried out employing methanol and basic catalysts(mostly KOH). In such case, the biodiesel produced is consideredas partially renewable since methanol is mainly obtained from nat-ural gas. The European countries are the leaders in the productionof biodiesel being Germany the first world producer. The most em-ployed vegetable oils are rapeseed, soybean and sunflower oils. Onthe other hand, the oil from palm (Elaeis guineensis) is consideredan excellent feedstock for biodiesel production in tropical coun-tries as Thailand, Malaysia and Colombia.

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; fax: +57 6 8879300x50193.ona).

Processing of palm for oil extraction leads to the formation ofseveral by-products and residues that have an economical poten-tial. These products, by-products and residues are illustrated inFig. 1 along with their current and potential applications. Theempty fruit bunches (EFB) are the solid residue that is producedin the highest amount. Their composition is shown in Table 1according to the data of Abdul Aziz et al. (2002a,b) and Wan Zahariand Alimon (2004). Due to its high moisture content, this materialis not appropriate as a fuel. For this reason, it is mostly used as amanure (Observatorio Agrocadenas Colombia, 2006). Compostinghas been suggested as an option for producing high quality manurefrom EFB. This microbial process allows the reduction of the vol-ume of the obtained manure in 50% as well as its transport costs(Chavalparit et al., 2006). The utilization of EFB as a substrate forcultivation of mushrooms by solid-state fermentation has beenproposed. In this case, previous treatment of this material is not re-quired (Chavalparit et al., 2006; Prasertsan and Prasertsan, 1996).In addition, the remaining material after mushroom harvest pre-sents better fertilizing properties. On the other hand, the fiberresulting from separation of press cake (palm press fiber, PPF)has an important content of the lignocellulosic complex and a low-er content of moisture (see Table 1). The oil retained in the fibermakes this material to be a good solid fuel. When palm processingfacilities produce both process steam and electricity, the totalamount of PPF undergoes combustion. However, if only steam isto be produced, 70% of PPF remains without utilization and be-comes a waste (Prasertsan and Prasertsan, 1996). The lignocellulosic

Fig. 1. Products, by-products and residues obtained during the processing of oil palm. Forms with continuous edges correspond to current applications of products and by-products. Forms with dashed edges correspond to potential applications. Gasf: gasification, Pyr: pyrolysis, FPyr: fast pyrolysis, Comp: composting, SSF: solid-stagefermentation, SRf: steam reforming, WGS: water-gas-shift reaction, FTS: Fischer-Tropsch synthesis, PT: pretreatment, CH: cellulose hydrolysis, Fm: fermentation, Trans:transesterification, CC: catalytic cracking, HAS: higher alcohol synthesis.

Table 1Average composition of two solid residues obtained during palm oil extraction

Component Content,% (w/w)

EFB PPF

Cellulose 15.47 24.00Hemicellulose 11.73 14.40Lignin 7.14 12.60Ash 0.67 3.00Oil – 3.48Others – 2.52Moisture 65.00 40.00

Sources: Abdul Aziz et al. (2002a,b); Wan Zahari and Alimon (2004).

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biomass contained in both EFB and PPF can be used for ethanolproduction as described below.

The palm kernel shell (PKS) is another residue generated in low-er amounts than EFB and PPF during palm oil extraction (see Sec-tion 2.1.1). This material is the most difficult residue todecompose. For this reason, it is usually disposed of by landfillmethod. PKS has a high energy value, but its use in burners or boil-ers designed for wood or fossil fuels implies a substantial modifica-tion of these equipments. This explains why it is not widelyutilized as a fuel. Its use has been proposed for production of acti-vated carbon (Chavalparit et al., 2006; Prasertsan and Prasertsan,1996). The palm kernel cake (PKC) is a waste from palm processingobtained during the extraction of oil contained in the kernels pro-duced after nuts cracking. It also contains significant amounts oflignocellulosic materials.

All solid palm residues containing lignocellulosics (EFB, PPF,PKC, PKS) can be potentially converted into different biofuels using

inorganic catalyst as stated by Chew and Bhatia (2008). In particu-lar, bio-oil may be obtained through pyrolysis. The resulting liquidproduct is a mixture of acids, alcohols, aldehydes, ketones, esters,heterocyclic derivatives and phenolic compounds (see Fig. 1).When fast pyrolysis is performed, hydrogen can be generated usinga low residence time and proper catalysts in the reactor. Othervaluable fuel products can be produced if biomass undergoes gas-ification. This process implies the generation of the synthesis gas ina first step. Then, the gas mixture can be converted into liquidhydrocarbon fuels like gasoline, naphta and diesel via Fischer–Tropsch synthesis. Alcohols like methanol, ethanol and others,can be produced using a catalytic process named higher alcoholsynthesis (HAS). Finally, synthesis gas is a feedstock for producinghydrogen by steam reforming followed by a water-gas-shift (WGS)reaction as shown in Fig. 1.

The use of liquid effluents generated during palm oil extraction(see Fig. 1) as a culture medium for obtaining lignocellulolytic en-zymes is a perspective potential method to diminish the organicload of these effluents (Prasertsan and Prasertsan, 1996). On theother hand, different liquid biofuels may be produced from thepalm oil by catalytic cracking. In this case, hydrocarbons like bio-gasoline, kerosene and diesel can be obtained (Chew and Bhatia,2008). Palm oil is the main feedstock for biodiesel production asdescribed below.

Fuel ethanol is the most employed liquid biofuel worldwide. Abroad variety of plant materials containing the sugars requiredfor fermentation process can be utilized for fuel ethanol productionlike sugar cane juice and cane or beet molasses. Starchy materialsare also used for these purposes. The United States has become thefirst world producer of ethanol (Sánchez and Cardona, 2008),

Fig. 2. Schematic diagram of oil extraction from palm. FFB: fruit fresh bunches, EFB: empty fruit bunches, PPF: palm press fiber, PKS: palm kernel shell, PKC: palm kernel cake,PKO: palm kernel oil.

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which is produced from corn. Ethanol can be produced from ligno-cellulosic biomass as well. It is considered that lignocellulosic bio-mass is the most promising feedstock at mid term for ethanolproduction due to its availability and low cost.

Many countries have implemented or are implementing pro-grams for addition of ethanol to gasoline (Sánchez and Cardona,2008) or biodiesel to diesel. For instance, European Union has is-sued different directives about the addition of renewable oxygen-ates to fuels. The oxygenation target of fuels consider theaddition of 2 wt.% by 2005 and 5.75 wt.% by 2010. However, theimplementation of these directives varies too much among the dif-ferent countries. Spain and France are leading the production ofbioethanol in Europe. In contrast, Germany has developed the pro-duction of biodiesel from rapeseed. For this country, it is consid-ered that the production of fuel ethanol is not economicallyfeasible in comparison to gasoline due to the high costs of feed-stocks (grains, sugar beet) (Henke et al., 2005; Rosenberger et al.,2002).

Colombian government has encouraged the utilization ofrenewable biofuels for national transport sector in order to achieveseveral goals: Diminish the volume of polluting emissions improv-ing the air quality in Colombian cities, reduce the dependence onfossil fuels through the decrease of diesel and gasoline imports,and boost the development of Colombian rural sector throughthe consolidation of agro-industrial chains for biofuels production.Colombian Congress issued the Act 693 of 2001, which made man-

datory the utilization of fuel ethanol as a gasoline oxygenate(Congreso de la República de Colombia, 2001). In a similar way,the Act 939 of 2004 (Congreso de la República de Colombia,2004) offers tax exemptions for both biodiesel production and oil-seed cropping intended to the production of this biofuel.

Currently, Colombia does not produce methanol and it is im-ported for domestic needs. On the contrary, this country is becom-ing an important producer of ethanol in the American continent. Inaddition, Colombia is the fourth world producer of oil palm due toits favorable agro-ecological conditions. Considering the above-mentioned, Colombia has the material basis for high-scale produc-tion of both bioethanol and biodiesel. In this way, a constant sup-ply of ethanol is required in order to ensure the self-sufficiency inbiodiesel production. At present, ethanol is obtained from sugarcane in Colombia. On the other hand, the extraction of palm oilgenerates significant amounts of lignocellulosic residues, whichmay be employed as feedstock for ethanol production. If the inte-gration of production lines for processing both palm oil and ligno-cellulosic biomass is considered, the synthesis of an integratedtechnological scheme for biodiesel production is feasible. In thiscase, the purchase of ethanol is not needed since ethanol is pro-duced within the same process.

This work appoints to the integral assessment of the integratedproduction of biodiesel from palm oil using in situ produced bio-ethanol. For this, the lignocellulosic wastes generated during theextraction of palm oil (empty fruit bunches and palm press fiber)

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are considered as feedstocks for ethanol production. In order toprovide evaluation data for making decisions on the commercialscale implementation of this integrated configuration, the aim ofthis paper is to demonstrate whether such process is economicallyviable taking into account energy consumption considerations.

2. Methods

In this paper, a first approximation to an oil-palm-based biore-finery with biodiesel as the main product is analyzed. Such biore-finery involves the use of in situ produced ethanol, which isobtained from some of the lignocellulosic residues generated dur-ing the extraction of crude palm oil. The analysis was based on pro-cess simulation applying the integration principle describedelsewhere (Cardona et al., 2008). To carry out this analysis, the in-volved processes are briefly described in the following section.

2.1. Process description

2.1.1. Oil extractionThe overall process for oil extraction using as feedstock the

fresh fruit bunches (FFB) of oil palm is depicted in Fig. 2. FFB arecooked in a direct contact sterilizer using saturated steam. Thisoperation favors the removal of fruits from bunches and preparesthe pulp for further extraction of oil. Fruit removal is generally car-ried out in rotary drum threshers. Fruits undergo digestion incylindrical vertical tanks with stirring at 100 �C. In this step, themashing of fruits takes place leading to the separation of pulp fromthe nuts (Observatorio Agrocadenas Colombia, 2006). Mashedfruits are sent to screw press where the crude oil is separated fromthe cake. The oil is passed through vibrating screens for removingfine solids. Then, the oil is clarified in decanters where hot water at90 �C is added for accelerating the process. In this step, decantercake is obtained. The sludge from decanter is centrifuged for recov-ering oil and sent to the effluent treatment step. The clarified oilcontains about 1% of water. For this reason, it is dehydrated in avacuum dryer and sent to oil storage tanks. The press cake is direc-ted to a cyclone where the separation of the nuts and palm pressfiber (PPF) occurs. The nuts are cracked to separate the kernelsfrom the palm kernel shell (PKS). The kernels undergo milling forextracting palm kernel oil (PKO) obtaining palm kernel cake(PKC) as well.

2.1.2. Production of bioethanolLignocellulosic biomass is a difficult to degrade feedstock for

ethanol production, hence pretreatment and hydrolysis steps arerequired in order to obtain the fermentable sugars required bythe fermentation process. During the pretreatment, lignocellulosematrix is broken down releasing its three main components (cellu-lose, hemicellulose and lignin). In addition, crystallinity degree ofcellulose is decreased leading to the increase of the fraction ofamorphous cellulose, which is more susceptible to hydrolysis. Atthe same time and depending on the pretreatment method, thehemicellulose is partially hydrolyzed forming pentoses (mainly xy-lose) and hexoses (including glucose).

There exist different pretreatment methods of lignocellulosicbiomass that differ in their physical, chemical or biological princi-ple, in the type of used equipments, and in the degree of maturityof employed technologies (Sánchez and Cardona, 2008). In thepresent work, dilute acid method was selected for its analysis sinceit is considered a mature technology that allows the hydrolysis ofthe main part of hemicellulose as well as an adequate level ofamorphous cellulose. Pretreatment reactor operates at 190 �C and12.2 atm. Solid fraction resulting from pretreatment steps ismostly composed by cellulose and lignin, whereas the liquid frac-

tion contains dissolved pentoses and hexoses (hemicellulosehydrolyzate), besides products of the thermal degradation of thesesugars and lignin. These products may inhibit the subsequent fer-mentation. For this reason, this fraction should be directed to thedetoxification step employing ionic exchange columns that removethese inhibitory substances.

Cellulose hydrolysis is a key step in the production of ethanolfrom lignocellulosic materials. It is generally carried out using cel-lulolytic enzymes (cellulases). Most process flowsheets consider anenzymatic reactor where the solid fraction from pretreatment stepmakes contact with fungal cellulases obtaining a cellulose hydroly-zate with a significant concentration of glucose. Then, this hydro-lyzate is fermented towards ethanol using conventional yeast(Saccharomyces cerevisiae). In a parallel way, detoxified liquid frac-tion, which contains pentoses and hexoses, is sent to a fermentorwhere pentose-assimilating yeasts convert this mixture into etha-nol. Among this type of yeasts, Pichia stipitis, Candida shehatae andPachysolen tannophilus are the most employed microorganisms.Unfortunately, these microorganisms have lower efficiency in eth-anol production and reduced tolerance to this alcohol related toconventional yeast (Claassen et al., 1999).

Process integration is an alternative approach to undertake thebiomass-to-ethanol conversion. In fact, process design has beenboosted thanks to process intensification through the developmentof simultaneous or coupled configurations. When several opera-tions are carried out in a single unit, the possibilities for improvingthe performance of overall process are increased (Cardona and Sán-chez, 2007). In particular, process integration of biomass conver-sion through the integration of enzymatic hydrolysis of celluloseand ethanolic fermentation allows the improvement of the processdue to the reduction of end product inhibition that is characteristicof cellulases. When these two processes are simultaneouslyaccomplished in a same unit, the glucose formed during cellulosehydrolysis is immediately assimilated by the microorganisms con-verting it into ethanol and reducing the inhibitory effect of glucoseover cellulases. This process is called simultaneous saccharificationand fermentation (SSF).

An option that offers an even higher degree of integration is theutilization of genetically modified microorganisms with the abilityof assimilating both pentoses and hexoses formed during the pre-treatment and enzymatic hydrolysis of lignocellulosic biomass. Inthis way, cellulose hydrolysis using cellulases and fermentationof hexoses and pentoses using engineered microorganisms maybe carried out in the same unit, process known as simultaneoussaccharification and co-fermentation (SSCF) (Cardona and Sánchez,2007). Among the microorganisms capable of co-fermenting glu-cose and xylose, genetically modified strains of the bacteriumZymomonas mobilis should be highlighted. The culmination of reac-tion-reaction integration for transforming biomass into ethanol isthe consolidated bioprocessing (CBP). In this process, only onemicrobial community is employed both for the production of cellu-lases and fermentation, i.e., cellulase production, cellulose hydroly-sis, and fermentation are carried out in a single step. It is expectedthat new advances in genetic engineering will allow the develop-ment of highly efficient recombinant microorganisms for CBP ofcellulose in the mid term.

In a previous work, several integrated schemes for producingethanol from lignocellulosic biomass considering different varia-tions in conversion technologies were analyzed (Cardona and Sán-chez, 2006). The configuration with the best performance fromenergy viewpoint involved the SSCF process. For this reason, thisalternative is analyzed in the present work considering the integra-tion of ethanol production with biodiesel production.

Culture broth exiting SSCF bioreactor has an ethanol concentra-tion of about 6% by weight. This stream is concentrated up to 42%of ethanol in a distillation (concentration) column, and then, it is

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concentrated up to 92% in another distillation (rectification) col-umn. The dehydration of ethanol is accomplished by adsorptionwith molecular sieves. Stillage obtained from the bottoms of con-centration column is evaporated with the aim of reducing its vol-ume and diminishing the costs of its further treatment. Thelignin is separated by centrifugation in order to employ it as a fuelfor co-generation of process steam and electricity. The power sur-plus can be sold to the electric network.

2.1.3. Production of biodieselThe palm oil and ethanol were the selected feedstocks for bio-

diesel production analyzed in this work. In this paper, alkali cata-lyzed transesterification was considered. The correspondingtransesterification reaction is as follows:

Triglycerideþ Ethanol$ Ethylestersþ Glycerol

Through this reaction, the oil is contacted with an excess of eth-anol forming the ethyl esters of the fatty acids of palm oil (biodie-sel). Taking into account the reversibility of the transesterification,an excess of ethanol is required to favor the direct reaction leadingto an increased conversion. Thus, an oil:ethanol molar ratio of 1:6is recommended (Marchetti et al., 2007; Van Gerpen, 2005). Glyc-erol is formed as a by-product of this reaction. Then, the mixture ofproducts and unreacted reagents is sent to a decanter where twoliquid phases are separated: biodiesel-enriched and glycerol-en-riched phases. Non-converted ethanol is distributed between thesetwo phases. In this specific case, the formation of these liquidphases is very slow and may take up to two days in a batch regime(Gutiérrez, 2008). This conventional configuration is depicted inFig. 3a. The reaction occurs at 70 �C under atmospheric pressureusing KOH as the catalyst (Van Gerpen, 2005).

The application of extractive reaction is one of the integrationapproaches that can be used for intensification of biodiesel produc-tion. This process consists in the combination of the chemical reac-tion and liquid–liquid extraction in the same unit achieving suchsynergistic effect, that the increase of selectivity, conversion, pro-ductivity, and purity of final product may be attained (Rivera andCardona, 2004). Thus, two liquid phases are formed during thereaction. For this reason, the decanter is not needed. For the caseof ethyl esters of palm oil, the separation of two liquid phases is

Fig. 3. Flowsheet configuration for biodiesel production from oil palm and ethanol.a. Conventional configuration. b. Integrated configuration involving reactiveextraction. (1): biodiesel-enriched stream, (2): glycerol-enriched stream.

not possible using a conventional stirred tank reactor in continu-ous regime. To attain such separation, a compact system consistingof one reaction stage and several separation stages working at non-isothermal conditions put together in a single unit (multi-stagereactor–extractor) have been developed and is currently being pat-ented. This system was used to carry out the extractive reactionprocess intended to the biodiesel production using palm oil andethanol in continuous regime. The results obtained (Gutiérrez,2008) showed that a biodiesel-enriched liquid phase (65% of ethylesters) and a glycerol-enriched liquid phase (44% of glycerol) canbe continuously removed from the above-mentioned multi-stagereactor-extractor, which is continuously fed with ethanol and palmoil at a molar ratio of 6:1, respectively. In this way, the principle ofreaction-separation integration can be applied to the production ofethyl esters using palm oil and even castor oil (Gutiérrez, 2008;Montoya et al., 2006). Biodiesel-enriched liquid phase is continu-ously removed from the reactor-extractor and sent to a separationunit where ethanol is recovered. This integrated configuration isshown in Fig. 3b. In order to obtain a high purity biodiesel, thisstream is washed with hot water to extract the excess of KOHand the soap that could have been formed during the reaction.Glycerol-enriched phase is directed to another separation unitwhere part of ethanol is recovered.

2.2. Integration approach

Proposed integrated configuration for production of biodieseland bioethanol from oil palm is depicted in Fig. 4. The FFB arethe feedstock for crude oil production. In addition, different solidlignocellulosic residues are generated. The utilization of these res-idues, particularly the EFB and PPF, is proposed as raw materials forethanol production. They enter the pretreatment reactor where re-act with dilute acid at high pressure. Then, the pretreated lignocel-lulosic biomass undergoes the transformations described inSection 2.1.2 obtaining dehydrated ethanol with purity greaterthan 99.5% by weight. This stream of ethanol, along with crudeoil, is fed to a multi-stage reactor–extractor (see Section 2.1.3)where transesterification reaction is continuously accomplishedby reactive extraction process using KOH.

There exist several levels of integration in the proposed scheme.Bioethanol production implies the reaction–reaction integration ofcellulose hydrolysis, hexose fermentation and pentose fermenta-tion through the SSCF process. In a similar way, the reaction-sepa-ration integration is considered in the multi-stage reactor–extractor leading to the improvement of the biodiesel productionprocess as exposed above. Other level of integration correspondsto the recirculation of material streams in order to achieve a betterutilization of sugars, e.g. by implementing the recycling of waterstreams. In this case, the bottoms of rectification column and afraction of the thin stillage (see Fig. 4), which mostly contain waterbut also a low content of non-utilized by microorganisms sugars,are recycled back to the washing step of lignocellulosic biomassleaving the pretreatment reactor. Thus, non-consumed pentosesand hexoses return to the SSCF reactor to be converted into etha-nol. In addition and with the aim of reducing the volume of waste-water that should be treated, the secondary steam fromevaporators is condensed and recycled back to the pretreatmentreactor where it is used as process water.

The above-mentioned streams correspond to the ethanol pro-duction process, but it is also possible the recirculation of streamsbetween the biodiesel production line and ethanol production lineincreasing the integration degree of the overall process. In thiswork, the recirculation of the distillate from the distillation columnused for glycerol separation is proposed. This stream contains eth-anol with a low content of water. For this reason, it cannot be usedas a gasoline oxygenate. This stream is fed to the rectification

Fig. 4. Integrated process flowsheet of the combined production of biodiesel and bioethanol using a flash unit for biodiesel purification. (1): pretreatment reactor, (2):washing, (3): ionic exchange, (4): simultaneous sacharification and co-fermentation, (5):concentration column, (6): rectification column, (7): molecular sieves, (8):evaporation train, (9): flash unit, (10): centrifuge, (11): multi-stage reactor–extractor, (12): flash unit. Material streams are represented by continuous lines whereas dashedlines represent heat streams. A: biodiesel-enriched stream, B, C: glycerol-enriched streams, H.H: hemicellulose hydrolyzate, P.B: pretreated biomass, P.S: pretreated solids,S.S: secondary steam. The represented flowsheet corresponds to the Configuration 2 in Table 4.

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column in the ethanol production line. In addition, this column isalso fed with the regenerate resulting from the adsorption in themolecular sieves. The corresponding flowsheet involving the men-tioned ways of material integration is called Configuration 1 in Table 4.

Other option for integrating the whole process is the energyintegration between both production lines. For this, the utilizationof the heat released during the condensation of overhead vaporsexiting the concentration and rectification columns is proposed.This heat is employed to provide the energy required by the flashunit processing the glycerol-enriched stream that leaves the reac-tor–extractor. In this way, the supply of steam generated in boilersis not needed decreasing the total energy costs. This flowsheetinvolving both material and energy integration is named Configu-ration 2 in Table 4 and is depicted in Fig. 4.

An alternative way of integration is also studied. For this case(Configuration 3), the purification of the two streams exiting themulti-stage reactor–extractor undergoes distillation using two col-umns. The first column is aimed at separating the biodiesel, whichis removed from the bottoms, and an ethanol-enriched stream thatis removed from the top (see Fig. 5). The second column purifiesthe glycerol contained in the heavy stream from the multi-stagereactor–extractor. As in the first column, the distillate containshigh amounts of ethanol. These two ethanol-enriched streamsare recycled back to the reactor–extractor unlike the Configuration1 where ethanol is recirculated to the concentration column in thebioethanol production line. Finally, the Configuration 4 is based on

Configuration 3 and includes the energy integration possibilities byusing the available heat of the condensers of both concentrationand rectification columns in the ethanol production line. In thiscase, these heat streams are directed to the distillation column em-ployed for glycerol purification (see Fig. 5).

2.3. Simulation procedure

Material balance of the oil extraction process was based on thedata reported by Prasertsan and Prasertsan (1996) for processingFFB towards crude palm oil. The data on composition of the ana-lyzed lignocellulosic residues (EFB and PPF) shown in Table 1 wereemployed for simulating bioethanol production scheme.

The simulation of the global technological scheme includingboth material and energy integration was performed using the pro-cess simulator Aspen Plus v. 11.1 (Aspen Technologies, Inc., USA).Main process data of such simulation are presented in Table 2.For ethanol production line, the approach and principles employedfor simulation were mostly taken from a previous work (Cardonaand Sánchez, 2006). For process units involved in ethanol produc-tion, NRTL thermodynamic model was utilized to calculate theactivity coefficients of the liquid phases. For units related to thebiodiesel production, UNIFAC model was employed for the simula-tion of the properties of the two formed liquid phases. In particular,modified values of the group interaction parameters were utilizedfor the substances involved in the transesterification reaction.

Fig. 5. Integrated process flowsheet of the combined production of biodiesel and bioethanol using a distillation column for biodiesel purification. (1):pretreatment reactor,(2): washing, (3):ionic exchange, (4): simultaneous sacharification and cofermentation, (5):concentration column, (6): rectification column, (7): molecular sieves, (8):evaporation train, (10): centrifuge, (11): multi-stage reactor–extractor, (12): distillation column for biodiesel purification, (13):distillation column for glycerol purification.Material streams are represented by continuous lines whereas dashed lines represent heat streams. A: biodiesel-enriched stream, B: glycerol-enriched streams, H.H:hemicellulose hydrolyzate, P.B: pretreated biomass, P.S: pretreated solids, S.S: secondary steam. The represented flowsheet corresponds to the Configuration 4 in Table 4.

L.F. Gutiérrez et al. / Bioresource Technology 100 (2009) 1227–1237 1233

These values were taken from Batista et al. (1999). Part of the dataon physical properties of the components required for the simula-tion was obtained from Wooley and Putsche (1996). Enzymatichydrolysis and co-fermentation processes were simulated basedon a stoichiometric approach that considered the conversion of cel-lulose into glucose as well as the transformation of glucose andpentoses (modeled as xylose) into cell biomass, ethyl alcohol andother fermentation by-products as aldehydes, succinic acid andglycerol, among others. Similar approach was used for analyzingthe pretreatment of lignocellulosic biomass.

The simulation of biodiesel production in the multi-stage reac-tor–extractor was performed employing a kinetic approach. Forthis, the values of reaction rate constants reported by Marchettiet al. (2007) were employed. Studied transesterification reactionsincluded the conversion of triglycerides into diglycerides, followedby the conversion of diglycerides into monoglycerides and the con-version of monoglycerides into glycerol. During each reactionstage, a molecule of the ethyl ester (biodiesel) is formed. Duringthe calculations, the triolein was considered as the model triglycer-ide. Consequently, obtained biodiesel was represented by the mol-ecule of ethyl oleate. In this paper, the approach to simulate thebiodiesel production by extractive reaction described in a previouswork (Montoya et al., 2006) was employed.

For the simulation of distillation columns, residue curves mapswere analyzed applying the principles of thermodynamic topology

(analysis of the statics) (Pisarenko et al., 2001) with the help ofsoftware developed by our research group and Aspen Split (AspenTechnologies, Inc., USA). For defining the preliminary specificationsof distillation columns, the DSTWU short-cut method included inAspen Plus was employed. This method uses the Winn–Under-wood–Gilliland procedure providing an initial estimate of the min-imum number of theoretical stages, the minimum reflux ratio, thelocalization of the feed stage, and the products split of the column.With this information and the results of the analysis of the statics,the rigorous calculation of the distillation columns was performedusing the RadFrac module, which is based on the MESH equationsand employs the inside-out calculation algorithm. Sensitivity anal-yses were carried out in order to study the effect of the main oper-ation variables (reflux ratio, feed temperature, number of stages,etc.) on the composition of products and corresponding energycosts. The calculation of the energy consumption was based onthe thermal energy required by the heat exchangers, reboilersand flash units. The electric energy needed for the operation ofpumps was considered as well.

3. Results and discussion

Under Colombian conditions, the installed processing capacityof an average facility for production of crude palm oil is of 122 ton-nes per day of FFB (Espinal et al., 2005). In general, these facilities

Table 2Main process data for simulation of an integrated process for biodiesel production (Configuration 2)

Feature Value Feature Value

Feedstocks EFB + PPF Product BiodieselComposition Water 56.84%a, cellulose 18.38%,

hemicellulose 12.52%, lignin 9.05%,others 9.05%

Composition Ethyl oleate 97.84%, triolein 0.44%,glycerol 0.02%, ethanol 1.32%, diolein0.34%, monoolein 0.03%, water 0.01%

Feed flow rate 1913.1123 kg/h Flow rate 959.358 kg/hOil palm (triolein)

Feed flow rate 903.15 kg/hCo-product Ethanol Co-product Glycerol

Composition Ethanol 99.56%, water 0.41% Composition Glycerol 95.98%, ethanol 0.03%,diolein 1.88%, monolein 2.10%

Flow rate 78.01 kg/h Flow rate 95.65 kg/h

Pretreatment Convent. distillationAgent Dilute H2SO4 Number of columns 2Temperature 190 �C Pressure of columns 1.77 atmPressure 12.2 atm Ethanol content at 42.6%Residence time 10 min distillate (1st column)Hemicellulose conversion 75% Ethanol content at

distillate (2nd column) 92.3%Detoxification Ethanol dehydration

Type Ion exchange followed byneutralization with alkali

Technology PSA with molecular sievesTemperature 116 �C

Eluent Ammonia Cycle time 10 minAlkali Ca(OH)2 Number of units 2

Simultaneous saccharif. and co-fermentation Pressure 1.7 atm (adsorption) 0.14 atm (desorption)Bioagents T. reesei cellulases and

recombinant Z. mobillisEvaporation

Number of stages 3Temperature 30 �C Biodiesel purificationCellulose conversion 80% Number of units 1Cellobiose conversion 100% Type FlashResidence time 144 h Temperature 59.8 �CEth. yield from xylose 85% of theor. Pressure 0.2 atmEthanol yield 92% of theor. Glycerol recoveryBiomass yield 2.7% of theor. Number of units 2

Multi-stage reactor–extractor Type Flash and distillationStages 5 Pressure 0.30 atm (flash unit)

Involved components 26 0.39 atm (distillation)Blocks 52 Number of stages in distillation column 3Streams 92

a All the percentages are expressed by weight.

1234 L.F. Gutiérrez et al. / Bioresource Technology 100 (2009) 1227–1237

operate during a single work shift of eight hours. Based on thiscapacity and according to the material balance of an oil extractionplant as the one depicted in Fig. 2, the volume of lignocellulosicresidues selected for bioethanol production was determined:28.06 tonnes/day of EFB and 17.98 tonnes/day of PPF. The total vol-ume of crude oil available for biodiesel production in the above-mentioned facility reaches 21.76 tonnes/day. These data, alongwith the composition of EFB and PPF, allowed simulating the inte-grated process for biodiesel production using in situ produced bio-ethanol for the case of a production facility working in acontinuous regime during three shifts per day. The first integratedflowsheet analyzed corresponds to the Configuration 1 (see Fig. 4)and comprises the recycling of ethanol between the two produc-tion lines and simultaneous integrated processes within each line(SSCF for bioethanol production, and extractive reaction for biodie-sel production). The proposed scheme allows the production ofhigh purity biodiesel that is verified by the elevated level of ethyloleate in the corresponding stream. This integrated configurationmakes possible the production of the necessary amount of anhy-drous ethanol required for converting the extracted crude oil intobiodiesel from 122 tonnes/day of FFB. In this way, the results ob-tained showed that the ethanol needed by the process can be ob-tained from the lignocellulosic residues generated during theextraction of palm oil (excluding the PKS). In addition, a remainingamount of anhydrous ethanol for sale as fuel ethanol can be pro-duced (78.0 kg/h).

The analysis of this process showed the feasibility of energeti-cally integrating the two production lines (Configuration 2). The

available heat in the distillate streams of the concentration andrectification columns is enough to supply the energy requirementsof the flash unit processing the glycerol-enriched stream leavingthe multi-stage reactor–extractor. In this way, the principle of en-ergy integration is applied. These heat streams are indicated bydashed lines in Fig. 4. In this case, the design of this unit impliesthe loss of a degree of freedom in the specification of process vari-ables in order to fix the amount of supplied heat.

Through sensitivity analyses, a value of 3.9 for the molar ratiobetween ethanol and palm oil leading to a better conversion offeedstocks during biodiesel production was identified. This ratiois referred to the streams of crude oil and fresh ethanol (not recy-cled) entering the multi-stage reactor–extractor. In fact, the excessof ethanol reaches higher values inside the multi-stage reactor–extractor due to the recirculation of ethanol recovered from thetwo liquid phases formed during the extractive reaction process(see Fig. 4). This ratio reaches a value of 20 for Configuration 1and a value of 60 for the process involving both the material andenergy integrations (Configuration 2). The higher the ratio betweenethanol and oil, the greater the conversion of feedstocks and thepurity of biodiesel. For Configuration 2, the conversion of trioleinreaches 99.9%, and the purity of produced ethyl oleate achieves avalue of 97.8%.

The Configuration 3 also ensures the production of all the etha-nol required for converting 21.76 tonnes/day of crude palm oil intobiodiesel. This needed amount of ethanol is of 187.6 kg/h remain-ing 42.0 kg/h of absolute ethanol for sale. In this case, the molar ra-tio between ethanol and palm oil reaches 4.0 that is greater than in

L.F. Gutiérrez et al. / Bioresource Technology 100 (2009) 1227–1237 1235

Configuration 1. In addition, the ethanol concentrations in thestreams recycled back to the reactor–extractor are higher than inConfigurations 1 and 2 (see Fig. 5). In this way, all the ethanol re-quired by the reaction is recirculated to the reaction step allowingthe elimination of the recirculation stream to the concentrationcolumn in the ethanol production line. This makes possible thereduction in the size of this column and a better utilization ofmaterial streams. This can be verified by the reduction of the valueof molar ratio between ethanol and palm oil inside the reactor–extractor that is 28.7. This ratio is less than in the case of Configu-ration 2 and equal to the value of Configuration 4. In addition, thedecrease in the products concentration (biodiesel and glycerol) ofthese recirculation streams allows the reduction of the volume ofthe reactor–extractor, which has a positive effect on the capitalcosts of the extractive reaction process.

The different levels of integration analyzed in this work have astrong influence on the energy consumption of the global process.The results of the evaluation of energy costs for the process flow-sheets simulated are shown in Table 4 (the energy costs of oilextraction process are not included). The base case defined con-sisted in the production of biodiesel from crude palm oil employingethanol as a feedstock. This base case includes the energy expendi-tures of ethanol production from lignocellulosic residues of oilpalm, but without any integration between both production lines,e.g. the recycling of recovered ethanol is not considered. This con-figuration corresponds to two independent plants producing bio-ethanol and biodiesel in an autonomous way.

If the base case is taken as a reference, the simulation data showa 3.4% reduction in the unit energy costs in terms of MJ/L of pro-duced biodiesel for the scheme involving the biodiesel productionintegrated with the production of ethanol from lignocellulosic res-idues of palm industry (Configuration 1 in Table 4). When the en-ergy integration between both production lines (see dashed linesin Fig. 4) is considered (Configuration 2 in Table 4), the reductionof energy costs reaches a value of 13.6%. This demonstrates theintegration benefits of these two configurations from energyviewpoint.

The analysis through process simulation carried out in thiswork confirmed the advantages of simultaneous integrated processrelated to conventional sequential configurations in the case ofbiodiesel production. Thus, simulation results for extractive reac-tion can be compared to those of the conventional (sequential)process where the decantation of the liquid phases is accomplishedafter the reaction in a separate unit (see Fig. 3a). In a previous work(Montoya et al., 2006), the sequential non-integrated process forbiodiesel production was assessed following the same simulationguidelines as in the present article. The results obtained in that pa-

Table 3Main process streams calculated by simulation of the integrated flowsheet for biodiesel p

Streams Lignocell. biomass Broth Recycled water for wash

T, �C 20.0 30.0 77.4p, bar 1.013 1.013 1.793Mass flow, kg/h 1,913.1 4,185.0 667.3Cellulose,%a 18.38 1.52 0.04Hemicellulose,(%) 12.52 1.31 0.03Lignin,(%) 9.05 3.72 0.09Glucose,(%) – 0.56 0.50Xylose,(%) – 0.67 0.89Water,(%) 56.84 80.47 97.78Triolein,(%) – – –Diolein,(%) – – –Monoolein,(%) – – –Ethanol,(%) – 5.59 0.01Ethyl oleate,(%) – – 0.01Glycerol,(%) – – 0.02

a All percentages are expressed by weight.

per indicated that a 99.9% conversion can be achieved using a mo-lar ratio between ethanol and oil of 12. Nevertheless, the purity ofthe produced biodiesel is reduced to 94% compared to the purity ofthe integrated process studied in this work (97.8%) using a molarratio of 3.9 for Configuration 1, and to 98.9% purity using a molarratio of 4.0 for Configuration 3. This implies a lower consumptionof ethanol and a higher efficiency of the global process. It shouldbe noted that the conventional process implies a greater numberof process units and is less compact related to the extractive reac-tion (integrated) process. Therefore, extractive reaction representsa viable technological alternative for biodiesel production due toits higher conversion, yield, and productivity. The integration ofreaction and separation allows the improvement of these processindicators since the products formed are removed from the reac-tion zone because of the formation of two liquid immisciblephases. This situation leads to the perturbation of both types ofequilibrium present in the system (chemical and liquid–liquidequilibria). The continuous extraction of the product provokes aperturbation of the chemical equilibrium. For returning to theequilibrium state, the system consumes a greater amount of re-agents increasing process conversion and productivity. In addition,the simultaneous process leads to a significant increase in the mainproduct concentration in one of the two liquid phases (the extract),which is not possible to attain in a conventional configuration.

The recirculation of some process streams can be considered asanother way of integration for the analyzed process. Data of Table3 show that the aqueous streams from the bottoms of the rectifica-tion column and from the centrifuge processing the stillage (seeFig. 4) may be used as recycled water for washing the lignocellu-losic biomass after its pretreatment due to their low contents ofsoluble solids. In addition, this recirculation makes possible a high-er conversion of the sugars formed during the process, which leadsto a higher ethanol concentration in the culture broth exiting theSSCF reactor. If a 5% increase in the conversion of both glucoseand xylose into ethanol during the SSCF is considered, ethanol con-centration in the broth reaches 6.11% by weight that implies lowercosts in the separation and dehydration steps.

Other interesting integration possibility indicated by the simu-lation consists in the recirculation of the ethanol-enriched streamsexiting from the top of the two columns employed for purificationof both biodiesel and glycerol (Configuration 3). Thus, the recov-ered ethanol can be utilized again for transesterification reaction.

The heat integration also plays an important role in theimprovement of the overall process. The results obtained illustratehow a simple utilization of the energy available in the overhead va-pors of the concentration and distillation columns may entail sig-nificant reductions in energy consumption of the glycerol

roduction (Configuration 3)

ing Rectific. column distillate BioEtOH Biodiesel Glycerol

93.4 25.0 73.7 244.91.793 1.000 0.200 0.300310.8 230.7 947.8 95.8– – – –– – – –– – – –– – – –– – – –8.5 0.5 0.002 –– – 0.6 –– – 0.2 1.78– – 0.02 1.7891.5 99.5 1.32 0.002– – 98.9 –– – 0.02 96.4

Table 4Energy consumption of different technological configurations for biodiesel productionusing in situ produced ethanol

Proceses Energyconsumption, MJ/h

Unit energy costof biodiesel, MJ/L

Non-integrated production of biodiesel 1,210 –Ethanol production from EFB and PPF 6,918 –Base case 8,128 6.62Configuration 1a 7,895 6.40Configuration 2b 7,059 5.72Configuration 3c 7,863 6.56Configuration 4d 4,775 3.98

a Biodiesel production considering material integration using flash units forbiodiesel and glycerol purification with ethanol recirculation to concentrationcolumn.

b Biodiesel production considering material and energy integration using flashunits for biodiesel and glycerol purification with ethanol recirculation to concen-tration column.

c Biodiesel production considering material integration using distillation col-umns for biodiesel and glycerol purification.

d Biodiesel production considering material and energy integration using distil-lation columns for biodiesel and glycerol purification.

1236 L.F. Gutiérrez et al. / Bioresource Technology 100 (2009) 1227–1237

recovery step (see Table 4). This is explained by the enhanced effi-ciency of the distillation column employed for separation of glyc-erol-enriched stream leaving the multi-stage reactor–extractor(stream B in Fig. 5). This tower exploits the heat contained in theoverhead vapors leading to a better recovery of ethanol and tothe decrease of ethanol content in the glycerol product stream exit-ing from that column. Consequently, the energy required to sepa-rate the ethanol from the glycerol is less than in the case whenno energy integration is applied. If comparing energy consumptionfor Configurations 3 and 4, the reduction of energy requirementsfor the heat integrated case reaches 39.3%. Other possibilities forheat integration can be taken into account. Considering the tem-perature of the cold and hot streams of the whole technologicalscheme, it is possible to exchange heat among other process units.In this sense, pinch analysis, which allows systematic and optimalenergy integration, may provide further energy savings. In a previ-ous work, this analysis was applied to the integration of separationand purification steps in the case of ethanol dehydration by azeo-tropic distillation (Grisales et al., 2005).

A very important issue to be considered is that the technologyfor ethanol production from lignocellulosic biomass is not com-pletely developed at present. In fact, production costs of ethanolfrom such lignocellulosic materials as wood or agro-industrialwastes are higher than production costs from sugar cane or starchymaterials. For instance, McAloon et al. (2000) have calculated thatproduction costs of a gallon of anhydrous ethanol from corn are ofUS$0.88 whereas these costs reach US$1.50 per gallon when etha-nol is produced from lignocellulosic biomass. The cost of cane eth-anol is even lower reaching near US$0.82 per gallon according todata obtained in a previous work (Quintero et al., 2008). However,it is expected that these costs decrease at mid-term being compa-rable to those of grain ethanol. Among the trends for improvingthis process, the development of recombinant microorganismswith higher stability under industrial conditions and with higheryields, the increase of specific activity of cellulases, and the devel-opment of biomass pretreatment technologies allowing a lowerformation of inhibitors and a reduction of the energy consumptionshould be highlighted.

Process integration plays a crucial role in the improvement ofthe performance indicators of chemical and biotechnological pro-cesses not only at economic level, but also considering environ-mental criteria. Worldwide interest for developing technologiesfor fuel ethanol production from lignocellulosic biomass is justified

by the fact that the lignocellulosic complex is the most abundantbiopolymer in nature and that its exploitation makes possible theutilization of renewable energy sources. Practically, each countryhas a wide availability of lignocellulosic materials (woody and for-estry wastes, agricultural and agro-industrial residues, cellulosicfraction of municipal solid waste, among others) whose productiondo not imply the substitution of farming lands already used forfood production. It is expected that this technology for fuel ethanolproduction will replace the utilization of other feedstocks that dohave importance as foods (sugar cane, sugar beet, corn, wheat, sor-ghum, etc.). In this context, the production of biodiesel employingbiomass ethanol represents a valuable opportunity for the produc-tion and global utilization of renewable liquid fuels. Nevertheless,this kind of integrated configuration will be viable in palm produc-ing countries only when the technologies for ethanol productionfrom biomass reaches such a degree of maturity, that its produc-tion costs be comparable with those of the process from starchor sugars. The joint production of the two analyzed liquid biofuelsand their worldwide utilization in transport sector, have clear envi-ronmental benefits, but these benefits have a cost that should beassumed by the society in order to achieve a sustainable economicdevelopment.

Employed methodology and obtained results demonstrate thatprocess engineering plays a decisive role for the design of inte-grated chemical and biotechnological processes. In particular, pro-cess simulation represents a powerful tool for the synthesis ofintegrated technological configurations with high technical andeconomic performance and that take economical advantage ofagro-industrial residues and by-products.

4. Conclusions

Biodiesel production from oil palm by a configuration that usesethanol produced from the solid residues of the same palm, offerssuch degree of integration that makes possible the decrease of en-ergy costs compared to the autonomous production of biodieseland bioethanol. This option is very attractive taking into accountnot only the energy consumption, but also the decrease of the solidwastes generated during the processing of oil palm. In particular,empty fruit bunches and palm press fiber produced during oilextraction have a high content of lignocellulosic biomass makingthem very suitable materials for their conversion into ethanol.

Acknowledgements

The authors express their acknowledgments to the ColombianInstitute for Development of Science and Technology (Colciencias),Universidad Nacional de Colombia sede Manizales, and Universi-dad de Caldas, for the financial support to this work.

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