pervaporation of ethanol produced from banana waste

Waste Management xxx (2014) xxx–xxx

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Waste Management

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Pervaporation of ethanol produced from banana waste

http://dx.doi.org/10.1016/j.wasman.2014.04.0130956-053X/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Address: Rua Pomerode, 710 Salto do Norte, Blumenau,SC 89065-300, Brazil. Tel.: +55 48 3721-6308.

E-mail address: [email protected] (C. Marangoni).

Please cite this article in press as: Bello, R.H., et al. Pervaporation of ethanol produced from banana waste. Waste Management (2014), http://dx.d10.1016/j.wasman.2014.04.013

Roger Hoel Bello a, Poliana Linzmeyer b, Cláudia Maria Bueno Franco b, Ozair Souza a,b,c, Noeli Sellin a,b,c,Sandra Helena Westrupp Medeiros a,b,c, Cintia Marangoni d,⇑a Chemical Engineering Department, University of Joinville Region (UNIVILLE), Joinville, SC, Brazilb Sanitary and Ambient Engineering Department, University of Joinville Region (UNIVILLE), Joinville, SC, Brazilc Masters Program in Process Engineering, University of Joinville Region (UNIVILLE), Joinville, SC, Brazild Federal University of Santa Catarina (UFSC), Campus Blumenau, Blumenau, SC, Brazil

a r t i c l e i n f o

Article history:Received 19 December 2013Accepted 10 April 2014Available online xxxx

Keywords:Banana wasteBioethanolBiofuelLignocellulosic residuePervaporationPolydimethylsiloxane membrane

a b s t r a c t

Banana waste has the potential to produce ethanol with a low-cost and sustainable production method.The present work seeks to evaluate the separation of ethanol produced from banana waste (rejected fruit)using pervaporation with different operating conditions. Tests were carried out with model solutions andbroth with commercial hollow hydrophobic polydimethylsiloxane membranes. It was observed thatpervaporation performance for ethanol/water binary mixtures was strongly dependent on the feedconcentration and operating temperature with ethanol concentrations of 1–10%; that an increase of feedflow rate can enhance the permeation rate of ethanol with the water remaining at almost the same value;that water and ethanol fluxes was increased with the temperature increase; and that the higher effect influx increase was observed when the vapor pressure in the permeate stream was close to the ethanolvapor pressure. Better results were obtained with fermentation broth than with model solutions,indicated by the permeance and membrane selectivity. This could be attributed to by-products presentin the multicomponent mixtures, facilitating the ethanol permeability. By-products analyses show thatthe presence of lactic acid increased the hydrophilicity of the membrane. Based on this, we believe thatpervaporation with hollow membrane of ethanol produced from banana waste is indeed a technologywith the potential to be applied.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

One of the bases for the economic development of Brazil isagriculture, and in certain states, such as Santa Catarina, bananais widely cultivated as a commercial crop. Banana is one of themost consumed fruits in the world and it is commercially grownin about 120 countries. Currently, Brazil is the second largestproducer (preceded by India) and is responsible for 7.5% of worldproduction (about 7.2 million tons per annum, according to theCenter of Socioeconomics and Agricultural Planning for the Stateof Santa Catarina). The State of Santa Catarina has approximatelysix thousand producers, being the fourth largest banana growingregion in Brazil, with 663,892 tonnes of bunches of bananasproduced per annum (ABIB, 2011).

Commercial banana production generates a large proportion ofwaste; there are reports of 30% waste in Australia (Clarke et al.,2008) and Malaysia (Tock et al., 2010), and 25–50% in Central

and South America (Hammond et al., 1996). In countries like India,all kind of banana waste is considered an important urban wastebecause the fruit is used in all religious functions, festivals and intemples (Chanakya and Sreesha, 2011). According to Graefe et al.(2011), around 20–40% of the bananas produced do not meetexport standards or even the quality demands of spot markets. InBrazil, particularly in the southern regions, it is estimated thatfor every 100 kg of harvested fruit, 46 kg are not used (EMBRAPA,2006). Further, Souza et al. (2010) indicate that for every ton ofbananas produced approximately 3 tons of pseudostem, 160 kgof stems, 480 kg of leaves and 440 kg of skins are generated.Fernandes et al. (2013) found that less than 10% of available bio-mass as waste (440 million tons) is designated to some application.Thus, an established commercial use for such residues, as well asgenerating extra remuneration for regional farmers, would helpto reduce environmental pollution. Alternative uses for these dis-cards have to be explored, and in this regard processing to produceethanol is seen to have potential from both an environmental aswell as an economic point of view.

Many countries are investing in the development and use ofbiofuels as a way of reducing environmental impacts and ethanol

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2 R.H. Bello et al. / Waste Management xxx (2014) xxx–xxx

is one of the fuels that can be produced from various raw materials(España-Gamboa et al., 2011). The use of agricultural or agro-industrial waste is an interesting option in this context. Biofuelhas been produced on a large scale in Brazil for three decades usingsugarcane as feedstock (Soccol et al., 2010), however there aremany criticisms of the practice and an ongoing debate about theethical issue of using food (or land available for the cultivation offood) as an energy source (Sarkar et al., 2012; Swana et al.,2011). Lignocellulosic material does not play an intrinsic role inthe food chain and this is a fundamental aspect that makes it anattractive alternative for ethanol production. Besides, the costand availability of the feedstock are crucial and can contribute65–70% to the total ethanol production costs (Kazi et al., 2010).In this sense, the substitution of biomass wastes for raw materialssuch as cane sugar, starch and corn for ethanol production is analternative that has shown promising results (Dermibas, 2011;Mabee et al., 2011). Examples of this residual biomass includebagasse sugar cane, corn straw and fiber, wheat and rice straw,eucalyptus wood and crop wastes from commercial cultivation offruits such as bananas, grapes and apples (Rivas-Cantu et al., 2013).

Technologies for the conversion of biomass to ethanol arealso under various stages of development. The use of theselignocellulosic residues requires some separation of cellulose andhemicellulose from lignin, followed by hydrolysis of sugars, andthis bioconversion has been extensively studied using the differenttypes of wastes. The potential yield of ethanol from lignocellulosicsvaries significantly between feedstocks, so many applications inalcoholic fermentation are reported in the literature with differentwastes. Specifically in the case of ethanol from bananas, the fewstudies that have been published involve the use of the fruit, leavesand other waste such as the pseudostem. Tewari et al. (1986)reported the suitability of banana peel for alcohol fermentation.Hammond et al. (1996) presented ethanol yield (on a dry weightbasis) from ripe bananas as higher than from most other agricul-tural commodities. Velásquez-Arredondo et al. (2010) investigatedthe acid hydrolysis of banana pulp and fruit and the enzymatichydrolysis of flower stalk and banana skin, and the results obtaineddemonstrated a positive energy balance for the four productionroutes evaluated. The study by Graefe et al. (2011) presents resultsof a case study in Costa Rica and Ecuador which found that consid-erable amounts of ethanol could be produced from bananabunches that do not meet quality standards, as well as from whichare partly left to rot in the fields. Oberoi et al. (2011) also demon-strated that banana peel could serve as an ideal substrate for theproduction of ethanol through simultaneous saccharification andfermentation. Hossain et al. (2011) evaluated bioethanol fromrotten banana and concluded that this can be used in motorvehicle engines, producing low emissions, and thus it can be usedas an environmental recycling process for waste management.Arumugam and Manikandan (2011) explore the potential applica-tion of pulp and banana peel wastes in bioethanol production usingdilute acid pretreatment followed by enzymatic hydrolysis.Gonçalves Filho et al. (2013) evaluate the same techniques withbanana tree pseudostem.

Although the lignocellulosic material shows positive results, itstill requires more research to be exploited on an industrial scale.Great efforts are being undertaken to improve ethanol productivityand reduce the overall production costs. According to Gaykawadet al. (2013), one of the ways to achieve these goals is to modifythe configuration of the process and perform process integration.Traditionally, the recovery of ethanol by distillation is a challengebecause of the high costs and energy expenditure required (Vane,2008). Toward this end, membrane separation processes such aspervaporation have been used. The great interest in these pro-cesses is mainly because of features such as cost-effectiveness,high energy efficiency and environmental friendliness. Membrane

Please cite this article in press as: Bello, R.H., et al. Pervaporation of ethanol pr10.1016/j.wasman.2014.04.013

based separation technologies normally fulfill the criteria for sus-tainability and energy efficiency (Korelskiy et al., 2013). In additionto reducing the inhibition of ethanol in the production stage due tothe possibility of its simultaneous use with fermentation(Lewandowska and Kujawski, 2007), this procedure could replacea concentration step that is required for recovery because of thepresence of alcohol in small quantities in the broth (Nomuraet al., 2002). As shown by Chovau et al. (2011), the compositionof the fermentation broth influences the separation, and the useof different substrates leads to the need to reevaluate the process,even if it is already well established. Also, in multicomponentsystems, the diffusivity of one component is influenced by thepresence of others. The use of lignocellulosic biomass will not onlyaffect feedstock pretreatment and fermentation process of theethanol production but also the downstream processing(Gaykawad et al., 2013).

In pervaporation, a liquid mixture is fed through a membrane.The mixture components permeate selectively through the mem-brane and vaporize on the other side of the membrane wherelow pressure is maintained. By this means, there is a selectiveremoval of organic compounds from dilute aqueous solutions.There are several studies regarding ethanol pervaporation and theyrelate mainly to the use of different membranes. Specifically thepervaporation of ethanol from lignocellulosic residues is reportedby Gaykawad et al. (2013) with barley straw and willow woodusing commercial polydimethylsiloxane (PDMS) membranes.Zhang et al. (2012) studied the membrane fouling in pervaporationof ethanol from food waste after a flocculation–filtration pretreat-ment. Aroujalian and Raisi (2009) study the effects of various oper-ating parameters such as feed temperature, permeate sidepressure, and Reynolds number (volumetric flow rate) on the totalflux, and ethanol selectivity of a porous membrane-based pervap-oration process with 2% aqueous ethanol solutions, simulating anethanol content from lignocellulosic residues. O’Brien et al.(2004) related an efficient system of coupled fermentation andpervaporation for ethanol from corn fiber hydrolisates.

Studies of pervaporation in ethanol production hitherto havenot used banana waste as a substrate for ethanol production. Thusthe aim of this research is to evaluate if pervaporation can be usedin the production of ethanol from banana and to investigate theeffects of operating variables and of lignocellulosic biomass fer-mentation by-products on membrane performance for the recov-ery of ethanol by using pervaporation.

2. Materials and methods

To investigate the membrane behavior, first model solutions ofethanol/water were separated in pervaporation experiments tocharacterize ethanol transfer across the hollow polydimethylsilox-ane (PDMS) membrane and these results provided the reference forthe broth experiments.

In the first case, feed conditions (flow rate, temperature, ethanolcomposition) and permeate pressure were modified. Also, the timenecessary to reach steady state was determined. Then, tests wereperformed with the fermentation broth produced using bananafruit waste as a substrate varying the ethanol feed mass fractionand feed flow rate. The presence of some byproducts was alsostudied.

2.1. Membrane

The pervaporation unit used consisted of a removable perme-ation module made of polyvinyl chloride (PVC) of 0.2 m internaldiameter containing 50 dense hollow polydimethylsiloxane(PDMS) membranes (di = 0.6 mm and de = 1 mm), 0.25 m in length,

oduced from banana waste. Waste Management (2014), http://dx.doi.org/



Table 2Operating conditions used in the experiments with fermentation broth.

Experiments with fermentation Operating conditions

R.H. Bello et al. / Waste Management xxx (2014) xxx–xxx 3

covering an area of 0.04 m2. This is a hydrophobic commercialmembrane, with the membrane and module built by a Braziliancompany (PAM-Membranas Selectivas).

broth

Effect of feed flow rate Feed flow rate: 5.5 � 10�6 and22.2 � 10�6 m3 s�1

Feed mass fraction: 3 wt%Feed temperature: 295 K

Variation of feed weightfraction

Feed flow rate: 5.5 � 10�6 m3 s�1

Feed mass fraction: 2, 2.5 and 3 wt%Feed temperature: 295 K

2.2. Fermentation

To obtain the feed from the process of pervaporation, 0.002 m3

of fermentation broth was produced, as described by Schulz(2010). Rejected banana fruit (Musa cavendishii) was used as ligno-cellulosic material (500 g L�1 wet mass) and 20% (v/v) of inoculum(Saccharomyces cerevisiae). After a period of 10 h of fermentation,different ethanol mass fractions were obtained in broths for per-vaporation tests. The total volume of the broth was centrifugedat 3800 min�1 (3018g) for 1200 s in a refrigerated centrifuge andthen stored at 277 K.

2.3. Pervaporation

The fermentation broth/standard solution was supplied withthe aid of a gear pump from a reservoir positioned upstream fromthe membrane. A vacuum pump coupled to the permeate sideof the assembly provided the pressure drop for vaporization ofethanol. The permeate vapor was directed to a condensation bathrefrigerated with liquid nitrogen. The liquid retentate wasrecirculated to the feed tank.

A summary of the operating conditions tested is presented inTable 1 for the standard mixture and in Table 2 for the fermenta-tion broth. All experiments were carried out with condensationtemperature of 77 K and permeate pressure lower than 667 Pa.The tests were carried out in duplicate, and the results presentedhere were consistent with the average of the same. Feed andpermeate samples (upon reaching the steady-state condition),were collected for 1–2 during each test to quantify the concentra-tions of ethanol with a gas chromatograph (GC, Agilent model6890, coupled with autosampler: Agilent model 7683) using aHewlett–Packard HP-1 column with a length of 50 m, an externaldiameter of 0.32 mm, a stationary phase composed of 100%polydimethylsiloxane and a film thickness of 1.05 lm.

2.4. Parameters from the process evaluation

The performance of the process of pervaporation has beenexpressed in terms of separation factor of the membrane (ai), thetotal permeate flux (Jtot), the ethanol permeate flux (Ji), enrichmentfactor (bi) and pervaporation separation index (PSI) according to

Table 1Operating conditions used in the experiments with the model solutions.

Experiments with modelsolutions

Operating conditions

Effect of ethanol feed weightfraction

Feed flow rate: 5.5 � 10�6 m3 s�1

Feed weight fraction: 1–12 wt%Feed temperature: 295 K

Effect of feed flow rate Feed flow rate: 5.5 � 10�6 and22.2 � 10�6 m3 s�1

Feed weight fraction: 10 wt%Feed temperature: 295 K

Effect of feed temperature Feed flow rate: 5.5 � 10�6 m3 s�1

Feed weight fraction: 3 wt%Feed temperature: 295, 300 and 303 K

Effect of permeate pressure Feed flow rate: 5.5 � 10�6 m3 s�1

Feed weight fraction: 3 wt%Feed temperature: 295 KPermeate pressure: <600, 2600 and6000 Pa


Eqs. (1)–(5), respectively (Pereira et al., 2006; Gaykawad et al.,2013; Sun et al., 2013):

ai ¼yi=yj

xi=xjð1Þ

Jtot ¼WAt

ð2Þ

Ji ¼ Jtotyi ð3Þ

bi ¼yi

xið4Þ

PSI ¼ Jtotðai � 1Þ ð5Þ

where yi and yj are the weight fractions of ethanol and water in thepermeate, respectively, and xi and xj are the weight fractions of eth-anol and water in the feed, W is the mass (g) of the permeate, A isthe effective area (m2) of the membrane, and t is the time interval(h) for pervaporation.

The membrane flux was determined gravimetrically using abalance with an accuracy of 10�4 g by weighing the mass of perme-ate obtained during the collecting time. The enrichment factor rep-resents the membrane capacity of concentrating the component i(Pereira et al., 2006) and is an interesting parameter to evaluatethe process for multicomponent mixtures.

Temperature dependency of the flux was analyzed using anArrhenius-type equation:

lnðJiÞ ¼ Jio exp � Ea

RT

� �ð6Þ

where Ji is the partial flux of the compound, Jio is the pre-exponen-tial factor of the flux, R is the gas constant (J mol�1 K�1), T is thetemperature (K) and Ea is the apparent activation energy (KJ mol�1).

Permeance was estimated according to Eq. (9), based on themolar flux of each component – ji (obtained from Eqs. (7) and(8)), and the selectivity of the membrane was calculated fromthe ratio between permeances (Eq. (10)).

Jim ¼ Jtotyimi

mtð7Þ

ji ¼JimvG

i

mið8Þ

Pi

l¼ ji

ðxiciPoi � yiPpÞ

ð9Þ

ai=j ¼Pi=l

Pj=lð10Þ

with mi and mt being the molecular weight of the component I andthe mixture, respectively, tG

i is the molar volume of gas, cI is the





activity coefficient for each component, Poi is the vapor pressure and

Pp is the total pressure in the permeate side.Reynolds number was calculated according to Schnabel et al.

(1998). It was considered an aqueous solution, and because of this,viscosity and density used was the values described by the authorswith temperature of 298 K (25 �C).

Fig. 2. Effect of ethanol content in feed on separation (j) and enrichment (d)factors.

3. Results and discussion

3.1. Experiments with model fermentation broths

3.1.1. Effect of ethanol feed weight fractionChovau et al. (2013) reported that the fermentation of lignocel-

lulosic wastes produces, on average, 3–6 wt% of ethanol. Hence weanalyzed the results for total and partial fluxes and separation andenrichment factors, as illustrated in Figs. 1 and 2, respectively, withan ethanol weight fraction range from 1% to 5% (values expectedfor a second-generation biomass) and then compared them with9%, 10% and 12% (values related or even superior to first-generationbiomass).

Increasing alcohol concentration increases permeation fluxes ofthe mixture of ethanol and water resulting in higher total flux(Fig. 1). In fact increasing the amount of the component that hasmajor affinity with the membrane in the feed stream leads to anincrease in the flux of these components in the permeate asreported in literature (Ortiz et al., 2002; Sommer and Melin,2005; Wu et al., 2005; Zereshki et al., 2011). A higher ethanol con-centration in the feed produces a higher ethanol flux. Dobrak et al.(2010) reported similar results with polydimethylsiloxane com-posite membranes, where the permeate flux through the mem-brane increased with increasing concentration of ethanol in thefeed, due to the swelling effects.

The ethanol flux demonstrated an increase even with ethanolconcentrations less than 5 wt% in the feed, but this increase is evengreater at higher concentrations. As reported by Pereira et al.(2006), the permeate flux of an organic dilute feed solution is gen-erally a linear function of concentration, and the water fluxremains constant (dependent on the concentration of the organiccomponent). This behavior is observed in this study when ethanolcontent in the feed is less than 5 wt%.

However, water flux increases more than alcohol, resulting in aseparation factor reduction as observed in Fig. 2. According toMohammadi et al. (2005), this is a result of an enhanced diffusionof water into the membrane by the fact that increasing alcohol con-centration increases membrane-free volume and simultaneously

Fig. 1. Effect of ethanol content in feed on total (j), ethanol (d) and (N) waterfluxes.


side chain mobility increases. Consequently, small-sized watercluster can permeate easily through the membrane-free volume.However, Van Baelen et al. (2004) reported that this behaviorcan be attributed to a dragging effect. In both cases, the final resultis a decrease in separation factor. This also was observed by Zhouet al. (2011), Lai et al. (2012), Lee et al. (2012), who also analyzedpervaporation of alcohols in dilute mixtures with hollow poly-dimethylsiloxane membrane.

3.1.2. Effect of feed flow rateTable 3 compares the values for the average total and ethanol

permeate mass fluxes, separation and enrichment factor of thepolydimethylsiloxane membrane obtained in pervaporation of10 wt% of alcoholic mixtures when the feed flow rate was varied.

As expected, ethanol and total flux increased with feed flow rateas shown in Table 3 due to a decrease of concentration polariza-tion. These results are in agreement with other research, evenwhen different membranes were used (Jiraratananon et al., 2002;Zereshki et al., 2011). As the ethanol is the component havingthe greatest affinity with the polydimethylsiloxane membrane, areduction of concentration polarization means that ethanol con-centration near the membrane surface was close to the ethanolconcentration in the bulk. As observed in relation to the partial fluxof ethanol, an increase of feed flow rate can enhance the perme-ation rate of ethanol with the water remaining at almost the samevalue. This behavior is in agreement with studies consideringthe effect of Reynolds number in pervaporation of organic com-pounds (Liang et al., 2004) In fact, the lower flux was observed atthe lowest value of the Reynolds number (feed flow = 5.5 � 10�6

m3 s�1 – Reynolds number: 18.47; feed flow = 22.2� 10�6 m3 s�1 –Reynolds number = 73.90).

The increase of feed flow rate enables better penetration of eth-anol into the membrane as the driving force of ethanol increases.As consequence, the hydrophobic properties of the membrane alsoincrease, and the process will be more selective for ethanol, as indi-cated by the separation factor that showed an increase around 30%.Li et al. (2004) also reported that with increasing flow rate bothtotal flux and separation factor increase, using a similar membrane(polydimethylsiloxane supported by cellulose acetate) for a modelsolution with 5 wt% ethanol. The authors show values for theseparation factor very close to that indicated in Table 4, withthe same feed flow rate. Finally, an increase of PSI with feed flowrate indicated that better results will be obtained for the pervapo-ration system with higher flow rates, as observed in other works(Jiraratananon et al., 2002).




Table 3Results obtained for pervaporation experiments with model solutions (10 wt% ethanol) and flow rates of 5.5 and 22.2 � 10�6 m3 s�1.

Flow rate (m3 s�1) Total flux (g m�2 h�1) Ethanol flux (g m�2 h�1) Separation factor Enrichment factor PSI

5.5 � 10�6 8.07 3.34 6.32 4.13 43.0722.2 � 10�6 8.22 3.92 8.26 4.72 61.05


The improvement in ethanol content in permeate, which occursbecause of the effect of reduced concentration polarization athigher flow rates that reduces the transport resistance in the liquidboundary layer, results in a mass fraction of ethanol in permeate of41.27 wt% with 5.55 � 10�6 m3 s�1 and 47.24 wt% with 22.2 �10�6 m3 s�1. This is an interesting result when compared withthe conventional ethanol recovery method, which is distillation.Standard purification involves a first distillation column, the ‘beercolumn’, where the top product consists of 37–40 wt% of ethanol(Chovau et al., 2013). The ethanol content observed was similar,indicating the potential of pervaporation as a concentrationmethod for further distillation.

3.1.3. Effect of feed temperatureThe effect of the temperature on the total and partial fluxes for

3 wt% ethanol/water mixture is presented in Fig. 3.As related in other works (Li et al., 2004; Mohammadi et al.,

2005; Dobrak et al., 2010; Luis et al., 2013) increasing temperaturecauses an increase in the total permeate flux due to the increase ofdiffusion rate of individual permeating molecules by the freevolumes produced because of the thermal motions of polymerchains. As related by Pereira et al. (2006), a higher temperaturestimulates the driving force due to an increase in vapor pressureand the activity coefficient of the permeating species (and theirchemical potentials) as temperature grows. Fig. 3 illustrates thatwhen temperature feed was tested from 295 to 300 K, total fluxwas increased by a factor of 1.18, water flux by 1.14 and ethanolflux by 1.5. This can also be observed from Fig. 4 which illustratesthe effect of feed temperature in separation factor. Different effectswere related in the literature, with some studies demonstratingthat the separation factor increases when temperature is increas-ing and others showing the contrary. According to Zereshki et al.(2011), the main reason for the separation factor to be affectedby temperature is because the diffusion and solubility of penetrat-ing components changes significantly with temperature, but alsodepends on many factors such as different organics, differentmembrane-preparation method, and different supports of compos-ite membranes and so on.

The total and partial permeation flux is plotted in logarithmicscale as a function of the reciprocal temperature in Fig. 5 andresults show that an Arrhenius type relationship exists betweenthe fluxes and feed temperature, i.e. fluxes decrease with decreas-ing temperature. These results are in agreement with the literature(Zhou et al., 2011; Lai et al., 2012; Lee et al., 2012).

The apparent activation energy could be calculated from theslope of the corresponding curve and Eq. (6) and the value issummarized in Table 4.

The higher apparent activation energy value for ethanol fluxindicates that it was more affected than water flux as the

Table 4Apparent activation energy for ethanol and water per-meation estimated from experiments with ethanol(3 wt%) and water mixtures.

Apparent activation energy (KJ mol�1) Value

Ethanol 83.23Water 62.64


temperature increased. These results are in agreement with thestudy by Shepherd et al. (2002) that used the same membrane toseparate aroma compounds. Thus the separation factor increaseswith the increase of temperature. Similar results are presentedby Dobrak et al. (2010).

3.1.4. Effect of permeate pressureThree variations of permeate pressure were investigated in the

pervaporation system: 6000, 2600 and less than 600 Pa. The resultsobtained for the mass flow of permeate with respect to the differ-ent applied pressures in the process of pervaporation are shown inTable 5. Pereira et al. (2006) describe how when the permeatepressure grows, the chemical potential gradient across the mem-brane is reduced and, as a consequence, a reduction in transmem-brane flux is observed. The same result was obtained in this work,with the higher effect observed when the vapor pressure in thepermeate stream was close to the ethanol vapor pressure.

The results presented in Table 5 show a decrease of 64% at apressure of 2660 Pa and 95% at 6000 Pa in relation to a maximumof 5.85 g m�2 h�1 were obtained for the permeate flux at the sys-tem operating with a permeate pressure less than 600 Pa.Jiraratananon et al. (2002) found that in ethanol–water mixtures,as permeate pressure increases, the driving force for permeationof the ethanol molecules decreases, which results in a decreasein the mass flow of the permeate.

3.2. Experiments with fermentation broth

3.2.1. Effect of feed flow rateTests were performed with the fermentation broth that con-

tained about 3 wt% ethanol by weight in the feed mixture, andthe results were compared with those obtained using the standardsolution at the same ethanol weight fraction. The results are sum-marized in Table 6.

It was observed that all of the parameters increased for the per-vaporation of the broth at low flow rates compared with the modelsolutions. For the specific case of the ethanol produced from the

Fig. 3. Temperature dependency on the total (j), ethanol (d) and water (N) fluxesfor 3 wt% ethanol/water mixture.




Fig. 4. Effect of feed temperature in separation factor for 3 wt% ethanol/watermixture.

Fig. 5. Arrhenius plot of total (j), water (N) and ethanol (d) fluxes vs. temperaturefor ethanol (3 wt%) and water mixtures.


lignocellulosic banana waste, with 5.5x10�6 m3 s�1 of flow rate, anincrease of about 28% in the enrichment factor was obtained, aswell as a 3.5 times increase in ethanol flux, which resulted in a per-vaporation index (PSI) double that achieved with the standardmixture (62.18 vs. 29.11). One important analysis consists of theenrichment factor. This parameter remained almost the same, indi-cating a possibility that there is no flux coupling mechanism.Shepherd et al. (2002) reported the same results using the similarmembrane and studying multicomponent model mixtures.

For the flow rate of 22.2 � 10�6 m3 s�1, contrary observationswere made. All performance parameters decrease for fermentationbroth compared with model solutions. This can be a result of thepresence of by-product that at this flow rate has an influence onthe ethanol diffusion mechanism. As the flux was reduced by afactor of 0.25 and the separation factor was reduced by a factorof 0.43, it was concluded that the ethanol pervaporation wasminimized. This behavior could be supported by the results of

Table 5Effect of permeate pressure in total permeate flux for 3 wt% ethanol/water mixtures.

Pressure (Pa) <600 2660 6000

Total flux (g m�2 h�1) 5.85 2.1 0.3


enrichment factor, since this parameter relates to the separationability by the ratio of permeate and feed weight fractions. A reduc-tion twice was observed. Also, when comparing the pervaporationof fermentation broth between different flow rates, all parametersdecrease with the increase of feed flow. In these cases, the effectobserved in the enrichment factor was more pronounced.

3.2.2. Variation of feed weight fractionTests were performed with the fermentation broth of varying

ethanol by weight in the feed mixture, and the results were com-pared with those obtained using the standard solution at the sameethanol weight fraction. Figs. 6–8 show the comparison of resultsobtained with the model mixture and fermentation broth for totalflux, separation and enrichment factors and pervaporation index,respectively. The results of the parameters presented demon-strated an increase that was observed with the pervaporation offermentation broth. The comparison between model solutionsand broth shows similar results, i.e., when the feed ethanol weightfraction is increased, we observed an increase of flux, decrease ofenrichment and separation factor (consequently an increasing ofpermeate ethanol weight fraction). More interesting, however, isthe increase in pervaporation index (Fig. 8), which indicates thatthe pervaporation of the fermentation broth obtained from bananaresidue with PDMS membrane has a more pronounced increasewith the increase of feed ethanol weight fraction than does themodel solution.

Figs. 9 and 10 show the comparison of results obtained withmodel mixture and fermentation broth for permeance and selectiv-ity, respectively. According to Luis et al. (2013), these parametersenable better observation of the process efficiency once the effectof the driving force and operating conditions is eliminated whenthe parameters are calculated. Fig. 9 shows better results for brothpervaporation, and an increase of both ethanol and water flux asthe feed ethanol weight fraction is increased, as observed inFig. 6. However, the permeance analysis shows clearly that the eth-anol flux increase has a major effect on the total flux increase,especially for fermentation broth. This indicates that by-productspresent in the multicomponent mixtures could be facilitating theethanol permeability, and no coupling flux is observed. In fact,by-products of fermentation, such as carboxylic acids, aldehydes,alcohols and other salts, may influence the separation process,especially at lower ethanol feed mass fractions and flow rates. Noglucose was observed in the broth used for the separation, whenanalyzed via high-performance liquid chromatography. Glucosehas been shown to affect the performance of pervaporation, asreported by Chovau et al. (2011).

In testing for selectivity, as observed before and with modelsolutions, the membrane shows more affinity for water, mainlyat higher feed ethanol weight fractions. However, is important tonotice that a value of selectivity equal to 1 represents the perfor-mance of a membrane with no intrinsic membrane selectivity,achieving the same separation as simple evaporation of the liquidinto the vapor phase (Luis et al., 2013). In this work, selectivityshows values greater than 1, and higher for fermentation broththan for model solutions, which indicates that the effect of themembrane is to enrich the permeate with ethanol.

3.2.3. Influence of by-productsTable 7 presents the average values of the by-products of the

broth in the feed analyzed by HPLC. The results for the centrifugedbroth were compared with those for the standard mixture to deter-mine the influence of by-products on the permeate flux, theenrichment factor and the concentration of the permeate.

According to Table 7, the glycerol concentration in the fermen-tation broth in the present study was 1.67% by weight. Chovauet al. (2011) have reported that the presence of glycerol in low con-




Table 6Comparison of the pervaporation carried out at different feed flow rates with ethanol/water model solutions and fermentation broth with 3 wt% of ethanol.

Experiment Total flux (g m�2 h�1) Ethanol flux (g m�2 h�1) Enrichment factor Separation factor PSI

Flow rate 5.5 � 10�6 m3 s�1

Ethanol/water 3.58 0.37 7.56 8.31 29.71Broth 5.85 1.06 8.88 10.63 62.18

Flow rate 22.2 � 10�6 m3 s�1

Ethanol/water 4.80 0.41 6.51 7.06 33.91Broth 3.60 0.30 3.73 3.97 14.29

Fig. 6. Comparison of the effect of ethanol content in feed on total flux for modelsolutions (j) and fermentation broth (h).

Fig. 7. Comparison of the effect of ethanol content in feed on separation (j) andenrichment (d) factors for model solutions (closed symbols) and fermentationbroth (open symbols).

Fig. 8. Comparison of the effect of ethanol content in feed in pervaporation index(PSI) for model solutions (j) and fermentation broth (h).

Fig. 9. Comparison of the effect of ethanol content in feed on permeance of ethanol(d) and water (N) for model solutions (closed symbols) and fermentation broth(open symbols).


centrations does not significantly affect the permeate flux param-eter or the coefficient of enrichment. In addition, the effect of car-boxylic acids on the process of pervaporation was studied, and thepresence of lactic acid at a concentration of 10.9 mmol L�1 wasobserved to increase both permeate and water flux; however, thecoefficient of enrichment was reduced to 12.2%.

As previously discussed, in tests where a flow rate of5.5 � 10�6 m3 s�1 was used, a comparison of the pervaporation ofthe fermentation broth and that of the standard mixture of ethanoland water indicates that the best results are achieved with thefermentation broth. Furthermore, in the specific case of ethanolproduced from lignocellulosic banana waste, greater values were


observed for the pervaporation index than for the standard mix-ture. We believe that the observed increase in the pervaporationindex was due to the presence of lactic acid in the broth. As a resultof the low concentration of this acid observed in the fermentationbroth at 0.75 mmol L�1, a decrease was not observed in the enrich-ment factor of ethanol, as reported in the work of Chovau et al.(2011). Thus, because the polydimethylsiloxane membrane ishydrophobic, the presence of lactic acid increased the hydrophilic-ity of the membrane, which increased the flow of water, whereasthe increase in the flow of ethanol can be attributed to the effectof membrane fouling. Bowen et al. (2007) have confirmed thesestatements in their studies.




Fig. 10. Comparison of the effect of ethanol content in feed on selectivity for modelsolutions (j) and fermentation broth (h).

Table 7By-products of the fermentation broth that may affect the process of pervaporation.

Byproduct Average concentration (g L�1)

Lactic acid 0.068Acetic acid NDª

Glucose NDGlycerol 1.67

a Not detected.


Finally, in all experiments the flux values obtained (�5 g m�2 h�1)were inferior to those described in the literature, such as thosementioned in work by Molina et al. (2002), who obtained500 g m�2 h�1 at a concentration of 15% (wt) under similar operat-ing conditions. This discrepancy indicates the need for optimizationof the operating conditions. However, the values obtained here areconsistent with the data provided by the membrane supplier. In thisregard, the results are considered to be encouraging because theparameters show substantial increases in the recovery of ethanolproduced by fermentation using pervaporation compared withusing the standard mixture.

4. Conclusions

The use of the pervaporation process for the recovery of ethanolfrom fermentation broth produced from lignocellulosic bananawaste demonstrated a very attractive alternative to classical meth-ods. When tests were carried out varying operational conditionswith model solutions, it was observed behaviors related toreported in literature: a higher ethanol concentration in the feedproduces a higher ethanol flux and decrease the separation factor;an increase of feed flow rate can enhance the permeation rate ofethanol with the water remaining at almost the same value; waterand ethanol fluxes was increased with the temperature increase;and the higher effect in flux increase was observed when the vaporpressure in the permeate stream was close to the ethanol vaporpressure. One interesting point was that the ethanol flux demon-strated an increase even with ethanol concentrations less than5 wt% in the feed (concentration expected in second generationethanol), but this increase is even greater at higher concentrations,as expected. However, water flux increases more than alcohol,resulting in a separation factor reduction.

It was observed that all of the parameters increased for the per-vaporation of the broth at low flow rates compared with the model


solutions. The process efficiency was evaluated by permeance andselectivity, showing that ethanol flux increase has a major effect onthe total flux increase, especially for fermentation broth. In fact, inthe specific case of ethanol produced from lignocellulosic bananawaste, greater values were observed for the pervaporation indexthan for the standard mixture. This could due to by-products pres-ent in the multicomponent mixtures facilitating the ethanol per-meability. By-products analysis show that the presence of lacticacid increased the hydrophilicity of the membrane, whichincreased the flow of water, whereas the increase in the flow ofethanol can be attributed to the effect of membrane fouling.

Thus, it can be concluded that the pervaporation of ethanol pro-duced from banana waste is indeed a technology with the potentialto be applied. The results showed a very interesting performance,highlighting the better separation efficiency for fermentation brothin relation to model solutions.

Acknowledgements

The authors acknowledge the support received from the Uni-versidade da Região de Joinville – Univille as well as all of theresources that allowed for the preparation of this work, andacknowledge the financial support that was received in the formof research grants.

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