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Production of alcohol free wine by pervaporation
Journal of Food Engineering 78 (2007) 118–125 www.elsevier.com/locate/jfoodeng
Production of alcohol free wine by pervaporation La´szlo´ Taka´cs a, Gyula Vatai b
a,*
, Korne´l Kora´ny
b
a Faculty of Food Science, Department of Food Engineering, Corvinus University of Budapest, Me´nesi str. 44, H1118 Budapest, Hungary Faculty of Food Science, Department of Food Chemistry and Nutrition, Corvinus University of Budapest, Me´nesi str. 44, H1118 Budapest, Hungary
Received 12 July 2004; accepted 18 September 2005 Available online 2 November 2005
Abstract The alcohol content of Tokaji Ha´rslevel} u (Linden leaves) wine samples was reduced by pervaporation process. The advantages of this modern membrane technique made us succeed in manufacturing a final product of a quality that matches the sensoric value of real wines. A wine almost free of alcohol produced by this method may be used as a substitute with no harmful effect due to its low ethanol content. The organoleptic characteristics are expected not to decrease due to of the mild process, so the positive physiological influence might be associated with the features close to the original character of the wine. Pervaporation experiments on a laboratory scale have been performed at different temperatures. The alcohol concentrate crossing the membrane, and thus separated, has been collected as a by-product and the remaining mixture of alcohol free wine compounds was considered the main product of the process. The separated wine samples and the extracted alcohol concentrates were then gas chromatographically analysed. The influence of process parameters on the result, from the aspect of optimization and planning, has been analysed, and the experiences of this analysis have been built in empirical and quasi-empirical models. Knowing the membrane-characteristics, we were capable of defining the equations that enable the planning of the pilot-plant scale unit operations and, the estimation of costs. The results of this investigation show that working temperature plays the most important role in the production of low alcoholic and alcohol free wines by pervaporation. At higher temperatures the membraneÕs separation efficiency and the separation ability decrease. Thus, the permeate production gets faster, but less desired product is gained by separation. Economical analyses prognoses a great investment cost demand, that can be explained by the relatively high price of pervaporation membranes. Remuneration can seriously be promoted by the by-product utilization e.g. by the use of the separated alcohol concentrate as a raw material for wine distillates or industrial spirits. 2005 Elsevier Ltd. All rights reserved. Keywords: Alcohol free wine; Membrane separation; Pervaporation; Aroma compounds; Modelling; Membrane area; Cost estimation
1. Introduction Wine contains a plenty of compounds playing a role of great significance from the aspect of human health. Of these components, the two most important are the anthocyanins, the colour compounds of red wines and the phenolic substance resveratrol. Both are considered natural anti*
Corresponding author. Tel.: +36 1 482 6232; fax: +361 482 6323. E-mail addresses: [email protected] (L. Taka´cs), gyula. [email protected] (G. Vatai), [email protected] (K. Kora´ny). 0260-8774/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2005.09.005
dotes of cardiovascular diseases. The consumption of these two physiologically highly active constituents might prevent atherosclerosis and artheriosclerosis by strengthening the walls of blood-vessels and normalizing the cholesterol level of blood (Eperjesi, Ka´llay, & Magyar, 1998). By reducing the ethanol content, present in wine, that is poisonous for the cells of the human body and by the concomitant enlargement of number of valuable compounds, substances bearing medicinal features can be taken by the human organism without any harmful side effect. Low alcoholic (<3 v/v%) and alcohol free (<0.5 v/v%) wines can be produced on many different ways. The
L. Taka´cs et al. / Journal of Food Engineering 78 (2007) 118–125
119
Notation A AH BE BH BM BTF CG2 CPV CT cPF cPP E0 E0E EE EF EH EM ESZ ET EVSZ J J0 J0E JE K k
pervaporation membrane surface demand (m2) cooling surface demand of heat exchanger (m2) other costs of PV-equipment (€/year) investment cost of heat exchanger (€/year) membrane investment cost (€/year) investment cost of inlet tank (€/year) specific price of steam (€/kJ) the cost of complete PV-equipment (€) specific price of tanks (€/m3) heat capacity of inlet mixture (kJ/kg K) heat capacity of permeate (kJ/kg K) activation energy calculated in case of total permeate flux (kJ/mol) activation energy calculated in case of ethanol flux (kJ/mol) amortization time of other PV-parts (year) operation cost of heating (€/year) operational cost of cooling (€/year) membrane amortization time (year) operational costs of pumping (€/year) amortization time of tank (year) operation cost of vacuum pump (€/year) permeate total flux (kg/m2 h) pre-exponential factor in case of permeate total flux (kg/m2 h) pre-exponential factor in case of permeate ethanol flux (kg/m2 h) permeate ethanol flux (kg/m2 h) constant (–) heat transfer coefficient (kW/m2 K)
procedures and the principles they are based on, are summarized by Pickering (2000), and shown in Table 1. Traditional thermal process destroy quality and sensoric characteristics, thus serious efforts have been made aiming to replenish aroma compounds (e.g. must concentrate) or to prevent their evaporation (Trothe, 1990). As for the fragrance and taste compounds of wines, membrane separation, contrary to the traditional separation methods, can reduce ethanol content much milder, so the organoleptic features might remain unchanged (Scobinger, Waldvogel, & Du¨rr, 1986). Conventional methods may have their role in producing absolute ethanol and water as by-products. The advantage of membrane filtration is low temperature where at aroma compounds can be saved. Unfortunately, reverse osmosis causes a drastic consistency change of the products, that is evident even after redilution. Liquid mixtures can be separated on non porous polymer membranes by partial evaporation. The procedure is called pervaporation because the substance crossing the membrane changes state of phase. It meets the membrane as a liquid and leaves it as a vapour desorbing on the other,
PH PK PSZ PVSZ QF qP qREC R rP T VP VF xFE xPE xRE Dtfel. Dtk€oz. DtPV gK gSZ gV SZ qF qP s set
efficiency demand of cooling (kW) power demand of compressor (kW) power demand of pump (kW) power demand of vacuum pump (kW) energy demand of heating (kJ) current of permeate vapour (m3/h) volume current of recirculation (m3/h) universal gas constant (kJ/mol K) evaporation heat of permeate (kJ/kg) temperature (K) permeate volume (m3) the starting volume of the wine (m3) the starting ethanol concentration of the wine (m3 ethanol/m3 wine) permeate ethanol concentration (kg ethanol/kg permeate) the ethanol concentration of the retentate (m3ethanol/m3 retentate) temperature difference of heating (K) logarithmic average of temperature difference (K) temperature difference of cooling (K) efficiency of compressor (–) efficiency of pump (–) efficiency of vacuum pump (–) density of inlet mixture (kg/m3) density of permeate (kg/m3) pervaporation time (h) hours of production (h)
Table 1 The processes of the production of alcohol free and low alcoholic wines (Pickering, 2000) Principle
Method
Reduction of fermentable sugar concentration in grape or juice
• Use of unripe fruit • Juice dilution • Freeze concentration and fractionation • Enzymes (e.g. Glucose oxidase)
Removal of alcohol from wine
• Thermal: distillation under vacuum or atmospheric pressure; • Evaporation • Freeze concentration • Membrane: dialysis; reverse osmosis • Adsorption: resins; silica gel • Extraction: organic solvents; supercritical carbon dioxide
Other
• Dilution of wine • Arresting fermentation early • Low-alcohol-producing yeast • Combinations of the above methods
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L. Taka´cs et al. / Journal of Food Engineering 78 (2007) 118–125
permeate-side, pressured through by the vacuum stress (Huang, 1991). The pervaporation membrane is a non porous one and it can be hydrophilic or organophilic depending on its material. Water molecules diffuse through faster across the previous and organic solvent particles cross more quickly the latter independently of the relative volatility of the compounds. By this procedure azeotropic point can be passed through without additives and the energy demand of the separation can almost be reduced to the half compared to azeotropic rectification. Besides, it is a mild operation capable of the selective extraction of the ethanol from the wine containing heat labile aroma compounds. It produces no waste-materials. Its by-products can be utilized according to the demands, it is proper for the purposes of ‘‘clean’’ technologies. Pervaporation can produce a more alcohol concentrated permeate, thus the wine becomes less dense compared to membrane filtration only the consistency of the wine product changes slightly. In the case of the separation of ethanol–water model solution (13–20 v/v%) on the same membrane type (PERVAP.Sulzer 1060) the condensed permeate phase alcohol concentration was 30–60 v/v% depending on the temperature (Mora, Vatai, & Bekassy-Molnar, 2002). Our aim was to elaborate an up-to-date, clean separation technique that is capable of preserving producing a medicinal end-product the organoleptic features of the white and red wines and reducing their ethanol content. By-products of the separation are wine distillate/raw material of spirit industry and water. In the first stage, experimental pervaporation under laboratory conditions will be performed purposed to produce a final product of suitable quality and to give data for modelling the process that makes possible planning the entire operation. In the second phase based on the results of modelling, factory scale technical–economical and unit operational planning of the processes and the estimation of costs will be performed. 2. Material and methods In our experiments, semi-sweet Tokaji Ha´rslevel} u (Linden leaves) of vintage 1997 quality wines (provenance Tolcsva) has been used. Its alcohol content was 13.11 v/v%, glucose concentration was 14.11 g/l; density at 20 C 1004 kg/m3, and viscosity at 20 C 1.1 · 103 Pa. The investigations were carried out on a laboratory scale pervaporation equipment (Fig. 1) constructed by Corvinus University of Budapest, Faculty of Food Science, Department of Food Engineering and produced by the Hidrofilt Ltd. into the membrane module of the equipment a PERVAP.Sulzer 1060 type organophilic flat composite membrane, possessing 131 cm2 active surface, has been built in. The material of the active layer of the membrane was polydimethylsiloxane.
Fig. 1. Laboratory scale pervaporation equipment (1) membrane, (2) liquid mixture inlet, (3) permeate vapour, (4) vacuum pump, (5) condenser, (6) liquid tank, (7) insulated permeate collector, (8) pump, (9) thermostat, (10) outlet valve, (11) flow control valve, (12) pressure control valve (13) pressure gauge, (14, 15) thermometers and (16) flowmeter.
The experiments were performed at 40, 50, 60, and 70 C, under intermittent running conditions, at 1.9 l inlet flow of wine and at a constant recirculation of 350 l/h of the retentate. According to our previous experiments by that equipment (Mora et al., 2002), using the above mentioned recirculation flowrate we did not observed any effects on the mass-transfer on the liquid side of membrane. The applied pressure was atmospherical because the pervaporation experiments has been carried out in ‘‘carrier gas mode’’ recirculating the inert gas (air) with dry vacuum pump (Vacubrand) in a loop with cooling-trap, where the permeated vapour was condensed. The process lasted 10 h, the produced permeate volume was measured by 1 h sampling that made possible the determination of its total flux. At the end both the volume of retentate and the total quantity of permeate produced, and its alcohol content were measured. The latter was determined by the relative density values measured by a Gibertini instrument run at the Department of Brewery and Spirit Industry. The alcohol separation efficiency of the 1060 Sulzer organophilic pervaporation membrane related to ethanol is the separation factor (a []): a¼
xPE 1xPE xFE 1xFE
ð1Þ
3. Aroma compounds The analytical investigations of the products of the membrane separation operations have been carried out at the Corvinus University of Budapest Faculty of Food Science Department of Food Chemistry and Nutrition. The occurrence of the wine aroma components, in the pervaporation products, was examined by gas chromatography–mass spectrometry. Qualitative analysis of the starting wine was performed, as well.
L. Taka´cs et al. / Journal of Food Engineering 78 (2007) 118–125
4. Results and discussion The characteristics of the membrane used and the efficiency parameters of the pervaporation process can be determined from the results of the investigations. Ethanol flux and the total flux of the other compounds can be derived from the permeate flux at different temperatures and the measured ethanol concentrations (Table 2). The change of total permeate and alcohol flux and that of the other components (water mainly) presented in Fig. 2. The flux increases exponentially in all three cases and can be described by an Arrhenius-type equation, cited many times in literature (Rautenbach, 1997): J ¼ J0 e
E RT0
ð2Þ
Table 2 The average flux of permeate (J (kg/m2 h)), its alcohol content (xPE (v/v%)), and the flux of alcohol (JE (kg/m2 h)) and other compounds (JV (kg/m2 h)) determined at different temperatures t (C)
J (kg/m2 h)
xPE (v/v%)
JE (kg/m2 h)
JV (kg/m2 h)
40 50 60 70
0.287 0.548 0.829 1.200
38.506 37.640 36.112 35.125
0.111 0.206 0.299 0.421
0.176 0.342 0.530 0.779
1.4 permeate
ethanol
others
1.2
Flux, J (kg/m2h)
The aroma constituents of the wine and membrane separation products were extracted by the distillation and extraction of 500 cm3 of the samples. Prior to distillation, 100 g of NaCl were dissolved in the samples to reduce the water solubility of the organic compounds. The presence of salt in large amounts makes the majority of the polar water molecules form hydrate shells of Na+ and Cl ions destroying thus the waterÕs organic substance solving capability. Having distilled the 50 cm3 alcohol content of the samples another 50 cm3 condensate was collected and the procedure was repeated two more times. The fractions of the three distillations were gathered and united. Having added 30 g NaCl to the condensate it was extracted with 3 · 80 cm3 n-pentane of special quality. The fused pentane fractions were dried on anhydrous Na2SO4 for a night and than evaporated to 0.4 cm3 endvolume. One microliter of the dried and concentrated extract was injected into the GC–MS instrument. In order to maintain constant measuring conditions and to control the average efficiency of the whole measuring process, Benzylalcohol as an internal standard (ISTD) was added to the samples at the beginning of the experiments. The ISTD addition made us capable of calculating the reduced relative retention times (RRRTs) and the programmed temperature retention indices (PTRIs). The PTRIs represent the position of the individual sample compounds in the chromatograms relative to n-hydrocarbon, and depend merely on the chemical quality of the constituents if the polarity of the stationary phase of the column is fixed. Under standardized conditions, these four character numbers are almost as typical of the chemicals as their other substantial constants and are proper for their identification. The relative amounts of the individual constituents were calculated by normalizing their peak areas to that of the ISTD. Thus, not only the absolute concentrations of the components but their relative amounts, expressed in Benzylalcohol %, were determined. The evaluation procedure gave the results in the proportional distribution of the aroma compounds of the retentate and permeate compared to the starting wine.
121
1.0 0.8 0.6 0.4 0.2 0.0 35
40
45
50
55
60
65
70
75
Temperature, t (˚C) Fig. 2. The exponential relationship between flux and temperature.
Having logaritmized Eq. (2) the slopes of the straight lines give the activation energies of the membranes, whilst intercepts determine the pre-exponential factors bearing no physical meaning. The estimated values are shown in Table 3. The membrane activation energy is the main measure of its pervaporation mass-transfer accompanied by change of the state of phase (Xianshe & Huang, 1996). It characterizes the membrane and the cross-vaporizing mass simultaneously. Nevertheless, its exact determination, due to the complexity of the mass-transfer phenomenon, is hard and a precise definition, possessing definite physical meaning, can hardly be found in the literature. Fig. 3 compares the results of the pervaporation experiments carried out with the Tokaji Ha´rslevel} u (Linden leaves) wine samples and the ethanol–water model mixture possessing the same ethanol concentration. Results belonging to the ethanol–water model mixture have been evaluated in accordance with the work of Mora et al. (2002). In both cases temperature rise causes permeate flux increase, that means faster product gaining and more
Table 3 The activation energies (E0 (kJ/mol)) of the total wine permeate, ethanol and other compounds and their pre-exponential factors (J0 (kg/m2 h)) Product
E0 (kJ/mol)
J0 (106 kg/m2 h)
Permeate Ethanol Others
41.36 39.27 43.80
2.38 0.42 3.82
L. Taka´cs et al. / Journal of Food Engineering 78 (2007) 118–125
122 Wine sample’s total permeate flux
Wine sample’s separation factor
Model solution’s total permeate flux
Model solution’s separation factor
5 4
Separation factor, (-)
3 2 Permeate flux, J (kg/mh)
1 0 35
40
45
50
55
60
65
70
75
Temperature (˚C) Fig. 3. The change of permeate flux and separation factor of the wine sample and identical concentration model solution in function of temperature.
efficient separation if clean mixture is processed (Fig. 3). Contrary to model solution the separation factor of wine sample decreases with temperature rise that can be explained by the presence of the other components residing in the wine. 5. The results of the analytical investigations Fig. 4. Typical results of gas chromatography.
The GC–MS analysis of the wine identified 97 aroma compounds. Among them, fragrance components considered the primary constituents of Tokaji Ha´rslevel} u wine and compounds found and recognized earlier in different honeys e.g. linden honey occurred. In the evaluation, the chromatograms of the wine were compared to that of the products gained in the process. In the case of pervaporation, the vast majority of the aroma components concentrates in the permeate. Main compounds (e.g. acids, sugars), except ethanol, could be observed prolonged in the end-product, but fine constituents forced across by alcohol both partly and intensive heat effect, vaporised through the membrane and occurred on the other side, where they were condensed by the coolingtrap into the condensate, that is into the permeate. Typical chromatograms are shown in Fig. 4. Change of the aroma content was also expected due to the decrease of alcohol. The rest of alcoholic compounds (glycerol, fuel oils and amyl alcohol mainly), soluble slightly in water only, cannot take over the role of a good solvent, instead of ethanol, and was not capable of dissolving the entire aroma substance stock. Thus, a serious loss of aroma compounds has been expected. The analytical results showed that the cumulation of the aroma constituents in the permeate was higher than the planned loss; it was 70% related to the total aroma content of starting wine. Having in mind that the alcohol content of the permeate is 35–38% (Table 2) as well as that the permeate is very rich in aroma substances, it can be utilized as wine distillate after proper final treatment. This fact enhances greatly the profitability of alcohol free wine production.
6. Modelling Permeate-side ethanol concentration can be expressed as the ratio of ethanol flux and total permeate flux: E0E
xPE
E0E DE0 J E J 0E e RT J 0E E0RT ¼ ¼ ¼ e ¼ K e RT E0 J J0 J 0 e RT
ð3Þ
After processing the experimental data, following equation for the ethanol concentration is obtained: xPE ¼ 0:176 e
251:38 T
ð4Þ
Necessary membrane surface can be expressed by the permeate amount, the total flux and the pervaporation time: A¼
VP J s
ð5Þ
In case of partial alcohol extraction, the process is prolonged to the achievement of a desired ethanol content. From the mass balance of the operation, the permeate volume can be expressed as: xFE xRE VP ¼VF ð6Þ xPE xRE Substituting Eqs. (1), (3) and (6) into Eq. (5) gives the Eq. (7), which expresses relation between necessary membrane surface and desired retentate concentration: A¼
VF J0 e
E0 RT
ðx x Þ FEDE RE 0 s K e RT xRE
ð7Þ
surface demand, A [m2]
L. Taka´cs et al. / Journal of Food Engineering 78 (2007) 118–125
Investment cost of other units of equipment (BE) are also a part of total cost (CPV):
200 180 160 140 120 100 80 60 40 20 0
total extraction partial extraction
BE ¼ 0:8
40 198,76 153,87
50 126,36 97,82
60 82,62 63,96
70 55,43 42,91
temperature, t [˚C]
In the case of total alcohol extraction, xRE = 0, Eq. (7) transforms into: V F xFE E0E
J 0E e RT s
ð8Þ
By the above equations, the 1060 Sulzer pervaporation membrane demands have been determined, at pilot-plant level, for alcohol free (xRE < 0.5 v/v%) and low alcoholic (xRE < 3 v/v%) wines shown in Fig. 5.
The technological–economical planning of the pervaporation production of alcohol free and low alcoholic wines has been performed on the base of the data of Atra (2000) for ethanol–water mixturesÕon experimental pilot level pervaporation plant. 7.1. Pervaporation equipment The knowledge of membrane surface allows calculating the cost of the complete equipment (CPV) using a cost-function. The equipment contains the inlet pump, the vacuum pump that removes the vapours of permeate, the warm up heat exchangers and tubes and fittings and assembly units C PV ¼ 61600 A0:37
The investment cost of inlet tanks (BTF) can be calculated based on 10 year amortization time (ET) and their €/m3 price (CT) BTF ¼ C T
VF ET
ð12Þ
The costs of tanks for collecting the products, in cases of definite permeate and retentate volumes, can be defined as shown above. 7.3. Cooling The investment cost of necessary cooling heat exchanger depends on the size of its surface (AH). BH ¼ 402 A0:7 H
ð13Þ
AH ¼
qP V P ðcPP DtPV þ rP Þ k Dtk€oz. s
ð14Þ
7.4. Heating The costs of heating (EF) depend on the specific price of steam (CG2), on the number of production hours per (set) year and on the heating performance. EF ¼ C G2 QF set
ð15Þ
The energy demand of heating can be calculated on the next way: QF ¼ qF V F cPF Dtfel
ð16Þ
ð9Þ
This sum of money occurs once as an investment. The calculation of the whole year total cost must take the amortization of the equipment into account and then €/year dimension should be used. The units of the pervaporation equipment can be divided into two major parts. The membrane unit itself, that costs 10–30% of the whole instrument and ages during 2–4 years, and the stainless steel acid proof parts, the amortization of what is 10 years. Investment cost of membrane (BM) unit can be expressed as a part of total cost (CPV): C PV EM
ð11Þ
The cooling surface can be estimated from energy balance equation:
7. Calculations
BM ¼ 0:2
C PV EE
7.2. Tanks
Fig. 5. The change of membrane surface demand with temperature.
A¼
123
ð10Þ
7.5. Cooling Prior to calculating the operational costs of cooling, the determination of cooling efficiency demand (PH) is needed: PH ¼
V P qP ðcPP DtPV þ rP Þ s
ð17Þ
The operational costs of cooling (EH) depend on the electric efficiency of the cooling compressor (gK) necessary, on the specific price of electric energy (CV) and on the length of cooling time (set) EH ¼
C V P K set gk
ð18Þ
L. Taka´cs et al. / Journal of Food Engineering 78 (2007) 118–125
124
Table 4 The result of pervaporation cost estimation Alcohol free wine Alcohol content of alcohol free wine Daily wine inlet Starting concentration of ethanol Permeate flux Volume of permeate produced Ethanol content of permeate Membrane surface demand Price of complete PV-equipment Investment costs of membrane Other costs of PV-equipment Total investment costs Estimation of operational cost Operational costs of heating Operational costs of cooling Operational costs of pumping Total operational costs Total costs
VR xRV VF xFE J VP xPE AM CPV BM BE P B
3 0.05 4.7 13.11 0.292 1.7 36.21 82.62 315 207 31 521 25 217
m3 v/v% m3 v/v% kg/m2 h m3 v/v% m2 € €/year €/year
56 738
€/year
EF EH ESZ P E P P B+ E
14 048 51 840 25 920
€/year €/year €/year
91 808
€/year
148 546
€/year
7.6. Pumping The operational costs per year of pervaporation equipment pump (ESZ) depends on the electric performance (PSZ) of the machine obtaining the recirculation volume current needed, on its efficiency (gSZ), on the specific price of electric energy (CV) and on the number the hours of operation (set) ESZ ¼
P SZ C V set gSZ
ð19Þ
7.7. Vacuum Operational costs of vacuum pump (EVSZ) depend on the electric performance of the equipment (PVSZ) obtaining the elimination of permeate vapours, on its electric efficiency (gVSZ), on the number of operational hours (set) and on the specific price of electricity (CV) EVSZ
P VSZ C V set ¼ gVSZ
ð20Þ
In accordance with the aspect of the quality of the product the applied temperature was chosen 40 C. It has given very good flux, because according to literature the value of the permeate flux over 0.2 kg/m2 h is excellent (Huang, 1991). The high price of pervaporation membrane defines the cost of the pervaporation equipment, what is the most considerable amount (see Table 4). The highest amount of the operating cost is the cooling, because for efficient condensation of the permeated vapour a low temperature cooling system is necessary and its efficiency is very poor (17). The cost of the feed-heating is lower than cooling cost (16), but the feed solution pumping
(19) and carrier gas pumping costs (20) together are comparable with the other operational costs. Calculating with 300 day/year operation, specific production cost of one liter alcohol free wine is 0.165 €, which can be covered partially by selling the by-product, permeate/distillate. 8. Conclusions The results of this investigation show that working temperature plays the most important role in the production of low alcoholic and alcohol free wines by pervaporation. Therefore, the choice of optimal temperature seems to be the main goal of an optimisation of such process. At higher temperatures the flux of permeate is higher and the membrane surface demand is smaller. This is significant advantage from the economical point of view, because they both cause faster production and lower costs of investment. However at higher temperatures the membraneÕs separation efficiency and the separation ability decrease. Thus, the permeate production gets faster, but less desired product is gained by separation. At the pervaporation temperatures applied, the majority of the wineÕs organic compounds evaporated and got into the condensate due to vapour permeation. To avoid serious aroma loss, choice of lower pervaporation temperatures is more favourable. Considering that the role of temperature might very complex one, the optimum of the operation must be determined as a compromise. Economical analyses prognoses a great investment cost demand, that can be explained by the relatively high price of non porous pervaporation membranes. But the investment might remunerate in a few years. Remuneration can seriously be promoted by the by-product utilization e.g. by the use of the separated alcohol concentrate as a raw material for wine distillates or industrial spirits. Acknowledgements This work was partially funded by the Hungarian Ministry of Education (NKFP-0026/2002) and Hungarian Scientific Foundation (OTKA T 037848). References Atra, R. (2000). Application of membrane separation processes in diary and spirit industry (in Hungarian). PhD Thesis, Szent Istvan University, Budapest. Eperjesi, I., Ka´llay, M., & Magyar, I. (1998). Oenology (in Hungarian). Budapest: Mezoˆgazda Kiado´. Huang, R. Y. M. (1991). Pervaporation membrane separation processes. In R. Y. M. Huang (Ed.). Amsterdam: Elsevier Science Publishers B.V. Mora, M. J., Vatai, Gy., & Bekassy-Molnar, E. (2002). Comparison of pervaporation of different alcohols from water on CMG-OM-010 and 1060-SULZER membranes. Desalination, 149, 89–94.
L. Taka´cs et al. / Journal of Food Engineering 78 (2007) 118–125 Pickering, G. J. (2000). Low- and reduced-alcohol wine (a review). Journal of Wine Research, 2, 129–144. Rautenbach, R. (1997). Membranverfahren. Berlin, Heidelberg: SpringerVerlag. Scobinger, U., Waldvogel, R., & Du¨rr, P. (1986). Verfahren zur Herstellung von alkoholfreiem Wein oder fruchtwein, Schweizer Patent, CH 654 023 A5.
125
Trothe, R. (1990). Verfahren zur entalkoholisierung oder alkoholreduzierung von weinen und fruchtweinen, German Democratic Republic Patent DD 283 153. Xianshe, F., & Huang, R. Y. M. (1996). Estimation of activation energy for permeation in pervaporation processes. Journal of Membrane Science, 118, 127–131.
Production of alcohol free wine by pervaporation La´szlo´ Taka´cs a, Gyula Vatai b
a,*
, Korne´l Kora´ny
b
a Faculty of Food Science, Department of Food Engineering, Corvinus University of Budapest, Me´nesi str. 44, H1118 Budapest, Hungary Faculty of Food Science, Department of Food Chemistry and Nutrition, Corvinus University of Budapest, Me´nesi str. 44, H1118 Budapest, Hungary
Received 12 July 2004; accepted 18 September 2005 Available online 2 November 2005
Abstract The alcohol content of Tokaji Ha´rslevel} u (Linden leaves) wine samples was reduced by pervaporation process. The advantages of this modern membrane technique made us succeed in manufacturing a final product of a quality that matches the sensoric value of real wines. A wine almost free of alcohol produced by this method may be used as a substitute with no harmful effect due to its low ethanol content. The organoleptic characteristics are expected not to decrease due to of the mild process, so the positive physiological influence might be associated with the features close to the original character of the wine. Pervaporation experiments on a laboratory scale have been performed at different temperatures. The alcohol concentrate crossing the membrane, and thus separated, has been collected as a by-product and the remaining mixture of alcohol free wine compounds was considered the main product of the process. The separated wine samples and the extracted alcohol concentrates were then gas chromatographically analysed. The influence of process parameters on the result, from the aspect of optimization and planning, has been analysed, and the experiences of this analysis have been built in empirical and quasi-empirical models. Knowing the membrane-characteristics, we were capable of defining the equations that enable the planning of the pilot-plant scale unit operations and, the estimation of costs. The results of this investigation show that working temperature plays the most important role in the production of low alcoholic and alcohol free wines by pervaporation. At higher temperatures the membraneÕs separation efficiency and the separation ability decrease. Thus, the permeate production gets faster, but less desired product is gained by separation. Economical analyses prognoses a great investment cost demand, that can be explained by the relatively high price of pervaporation membranes. Remuneration can seriously be promoted by the by-product utilization e.g. by the use of the separated alcohol concentrate as a raw material for wine distillates or industrial spirits. 2005 Elsevier Ltd. All rights reserved. Keywords: Alcohol free wine; Membrane separation; Pervaporation; Aroma compounds; Modelling; Membrane area; Cost estimation
1. Introduction Wine contains a plenty of compounds playing a role of great significance from the aspect of human health. Of these components, the two most important are the anthocyanins, the colour compounds of red wines and the phenolic substance resveratrol. Both are considered natural anti*
Corresponding author. Tel.: +36 1 482 6232; fax: +361 482 6323. E-mail addresses: [email protected] (L. Taka´cs), gyula. [email protected] (G. Vatai), [email protected] (K. Kora´ny). 0260-8774/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2005.09.005
dotes of cardiovascular diseases. The consumption of these two physiologically highly active constituents might prevent atherosclerosis and artheriosclerosis by strengthening the walls of blood-vessels and normalizing the cholesterol level of blood (Eperjesi, Ka´llay, & Magyar, 1998). By reducing the ethanol content, present in wine, that is poisonous for the cells of the human body and by the concomitant enlargement of number of valuable compounds, substances bearing medicinal features can be taken by the human organism without any harmful side effect. Low alcoholic (<3 v/v%) and alcohol free (<0.5 v/v%) wines can be produced on many different ways. The
L. Taka´cs et al. / Journal of Food Engineering 78 (2007) 118–125
119
Notation A AH BE BH BM BTF CG2 CPV CT cPF cPP E0 E0E EE EF EH EM ESZ ET EVSZ J J0 J0E JE K k
pervaporation membrane surface demand (m2) cooling surface demand of heat exchanger (m2) other costs of PV-equipment (€/year) investment cost of heat exchanger (€/year) membrane investment cost (€/year) investment cost of inlet tank (€/year) specific price of steam (€/kJ) the cost of complete PV-equipment (€) specific price of tanks (€/m3) heat capacity of inlet mixture (kJ/kg K) heat capacity of permeate (kJ/kg K) activation energy calculated in case of total permeate flux (kJ/mol) activation energy calculated in case of ethanol flux (kJ/mol) amortization time of other PV-parts (year) operation cost of heating (€/year) operational cost of cooling (€/year) membrane amortization time (year) operational costs of pumping (€/year) amortization time of tank (year) operation cost of vacuum pump (€/year) permeate total flux (kg/m2 h) pre-exponential factor in case of permeate total flux (kg/m2 h) pre-exponential factor in case of permeate ethanol flux (kg/m2 h) permeate ethanol flux (kg/m2 h) constant (–) heat transfer coefficient (kW/m2 K)
procedures and the principles they are based on, are summarized by Pickering (2000), and shown in Table 1. Traditional thermal process destroy quality and sensoric characteristics, thus serious efforts have been made aiming to replenish aroma compounds (e.g. must concentrate) or to prevent their evaporation (Trothe, 1990). As for the fragrance and taste compounds of wines, membrane separation, contrary to the traditional separation methods, can reduce ethanol content much milder, so the organoleptic features might remain unchanged (Scobinger, Waldvogel, & Du¨rr, 1986). Conventional methods may have their role in producing absolute ethanol and water as by-products. The advantage of membrane filtration is low temperature where at aroma compounds can be saved. Unfortunately, reverse osmosis causes a drastic consistency change of the products, that is evident even after redilution. Liquid mixtures can be separated on non porous polymer membranes by partial evaporation. The procedure is called pervaporation because the substance crossing the membrane changes state of phase. It meets the membrane as a liquid and leaves it as a vapour desorbing on the other,
PH PK PSZ PVSZ QF qP qREC R rP T VP VF xFE xPE xRE Dtfel. Dtk€oz. DtPV gK gSZ gV SZ qF qP s set
efficiency demand of cooling (kW) power demand of compressor (kW) power demand of pump (kW) power demand of vacuum pump (kW) energy demand of heating (kJ) current of permeate vapour (m3/h) volume current of recirculation (m3/h) universal gas constant (kJ/mol K) evaporation heat of permeate (kJ/kg) temperature (K) permeate volume (m3) the starting volume of the wine (m3) the starting ethanol concentration of the wine (m3 ethanol/m3 wine) permeate ethanol concentration (kg ethanol/kg permeate) the ethanol concentration of the retentate (m3ethanol/m3 retentate) temperature difference of heating (K) logarithmic average of temperature difference (K) temperature difference of cooling (K) efficiency of compressor (–) efficiency of pump (–) efficiency of vacuum pump (–) density of inlet mixture (kg/m3) density of permeate (kg/m3) pervaporation time (h) hours of production (h)
Table 1 The processes of the production of alcohol free and low alcoholic wines (Pickering, 2000) Principle
Method
Reduction of fermentable sugar concentration in grape or juice
• Use of unripe fruit • Juice dilution • Freeze concentration and fractionation • Enzymes (e.g. Glucose oxidase)
Removal of alcohol from wine
• Thermal: distillation under vacuum or atmospheric pressure; • Evaporation • Freeze concentration • Membrane: dialysis; reverse osmosis • Adsorption: resins; silica gel • Extraction: organic solvents; supercritical carbon dioxide
Other
• Dilution of wine • Arresting fermentation early • Low-alcohol-producing yeast • Combinations of the above methods
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permeate-side, pressured through by the vacuum stress (Huang, 1991). The pervaporation membrane is a non porous one and it can be hydrophilic or organophilic depending on its material. Water molecules diffuse through faster across the previous and organic solvent particles cross more quickly the latter independently of the relative volatility of the compounds. By this procedure azeotropic point can be passed through without additives and the energy demand of the separation can almost be reduced to the half compared to azeotropic rectification. Besides, it is a mild operation capable of the selective extraction of the ethanol from the wine containing heat labile aroma compounds. It produces no waste-materials. Its by-products can be utilized according to the demands, it is proper for the purposes of ‘‘clean’’ technologies. Pervaporation can produce a more alcohol concentrated permeate, thus the wine becomes less dense compared to membrane filtration only the consistency of the wine product changes slightly. In the case of the separation of ethanol–water model solution (13–20 v/v%) on the same membrane type (PERVAP.Sulzer 1060) the condensed permeate phase alcohol concentration was 30–60 v/v% depending on the temperature (Mora, Vatai, & Bekassy-Molnar, 2002). Our aim was to elaborate an up-to-date, clean separation technique that is capable of preserving producing a medicinal end-product the organoleptic features of the white and red wines and reducing their ethanol content. By-products of the separation are wine distillate/raw material of spirit industry and water. In the first stage, experimental pervaporation under laboratory conditions will be performed purposed to produce a final product of suitable quality and to give data for modelling the process that makes possible planning the entire operation. In the second phase based on the results of modelling, factory scale technical–economical and unit operational planning of the processes and the estimation of costs will be performed. 2. Material and methods In our experiments, semi-sweet Tokaji Ha´rslevel} u (Linden leaves) of vintage 1997 quality wines (provenance Tolcsva) has been used. Its alcohol content was 13.11 v/v%, glucose concentration was 14.11 g/l; density at 20 C 1004 kg/m3, and viscosity at 20 C 1.1 · 103 Pa. The investigations were carried out on a laboratory scale pervaporation equipment (Fig. 1) constructed by Corvinus University of Budapest, Faculty of Food Science, Department of Food Engineering and produced by the Hidrofilt Ltd. into the membrane module of the equipment a PERVAP.Sulzer 1060 type organophilic flat composite membrane, possessing 131 cm2 active surface, has been built in. The material of the active layer of the membrane was polydimethylsiloxane.
Fig. 1. Laboratory scale pervaporation equipment (1) membrane, (2) liquid mixture inlet, (3) permeate vapour, (4) vacuum pump, (5) condenser, (6) liquid tank, (7) insulated permeate collector, (8) pump, (9) thermostat, (10) outlet valve, (11) flow control valve, (12) pressure control valve (13) pressure gauge, (14, 15) thermometers and (16) flowmeter.
The experiments were performed at 40, 50, 60, and 70 C, under intermittent running conditions, at 1.9 l inlet flow of wine and at a constant recirculation of 350 l/h of the retentate. According to our previous experiments by that equipment (Mora et al., 2002), using the above mentioned recirculation flowrate we did not observed any effects on the mass-transfer on the liquid side of membrane. The applied pressure was atmospherical because the pervaporation experiments has been carried out in ‘‘carrier gas mode’’ recirculating the inert gas (air) with dry vacuum pump (Vacubrand) in a loop with cooling-trap, where the permeated vapour was condensed. The process lasted 10 h, the produced permeate volume was measured by 1 h sampling that made possible the determination of its total flux. At the end both the volume of retentate and the total quantity of permeate produced, and its alcohol content were measured. The latter was determined by the relative density values measured by a Gibertini instrument run at the Department of Brewery and Spirit Industry. The alcohol separation efficiency of the 1060 Sulzer organophilic pervaporation membrane related to ethanol is the separation factor (a []): a¼
xPE 1xPE xFE 1xFE
ð1Þ
3. Aroma compounds The analytical investigations of the products of the membrane separation operations have been carried out at the Corvinus University of Budapest Faculty of Food Science Department of Food Chemistry and Nutrition. The occurrence of the wine aroma components, in the pervaporation products, was examined by gas chromatography–mass spectrometry. Qualitative analysis of the starting wine was performed, as well.
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4. Results and discussion The characteristics of the membrane used and the efficiency parameters of the pervaporation process can be determined from the results of the investigations. Ethanol flux and the total flux of the other compounds can be derived from the permeate flux at different temperatures and the measured ethanol concentrations (Table 2). The change of total permeate and alcohol flux and that of the other components (water mainly) presented in Fig. 2. The flux increases exponentially in all three cases and can be described by an Arrhenius-type equation, cited many times in literature (Rautenbach, 1997): J ¼ J0 e
E RT0
ð2Þ
Table 2 The average flux of permeate (J (kg/m2 h)), its alcohol content (xPE (v/v%)), and the flux of alcohol (JE (kg/m2 h)) and other compounds (JV (kg/m2 h)) determined at different temperatures t (C)
J (kg/m2 h)
xPE (v/v%)
JE (kg/m2 h)
JV (kg/m2 h)
40 50 60 70
0.287 0.548 0.829 1.200
38.506 37.640 36.112 35.125
0.111 0.206 0.299 0.421
0.176 0.342 0.530 0.779
1.4 permeate
ethanol
others
1.2
Flux, J (kg/m2h)
The aroma constituents of the wine and membrane separation products were extracted by the distillation and extraction of 500 cm3 of the samples. Prior to distillation, 100 g of NaCl were dissolved in the samples to reduce the water solubility of the organic compounds. The presence of salt in large amounts makes the majority of the polar water molecules form hydrate shells of Na+ and Cl ions destroying thus the waterÕs organic substance solving capability. Having distilled the 50 cm3 alcohol content of the samples another 50 cm3 condensate was collected and the procedure was repeated two more times. The fractions of the three distillations were gathered and united. Having added 30 g NaCl to the condensate it was extracted with 3 · 80 cm3 n-pentane of special quality. The fused pentane fractions were dried on anhydrous Na2SO4 for a night and than evaporated to 0.4 cm3 endvolume. One microliter of the dried and concentrated extract was injected into the GC–MS instrument. In order to maintain constant measuring conditions and to control the average efficiency of the whole measuring process, Benzylalcohol as an internal standard (ISTD) was added to the samples at the beginning of the experiments. The ISTD addition made us capable of calculating the reduced relative retention times (RRRTs) and the programmed temperature retention indices (PTRIs). The PTRIs represent the position of the individual sample compounds in the chromatograms relative to n-hydrocarbon, and depend merely on the chemical quality of the constituents if the polarity of the stationary phase of the column is fixed. Under standardized conditions, these four character numbers are almost as typical of the chemicals as their other substantial constants and are proper for their identification. The relative amounts of the individual constituents were calculated by normalizing their peak areas to that of the ISTD. Thus, not only the absolute concentrations of the components but their relative amounts, expressed in Benzylalcohol %, were determined. The evaluation procedure gave the results in the proportional distribution of the aroma compounds of the retentate and permeate compared to the starting wine.
121
1.0 0.8 0.6 0.4 0.2 0.0 35
40
45
50
55
60
65
70
75
Temperature, t (˚C) Fig. 2. The exponential relationship between flux and temperature.
Having logaritmized Eq. (2) the slopes of the straight lines give the activation energies of the membranes, whilst intercepts determine the pre-exponential factors bearing no physical meaning. The estimated values are shown in Table 3. The membrane activation energy is the main measure of its pervaporation mass-transfer accompanied by change of the state of phase (Xianshe & Huang, 1996). It characterizes the membrane and the cross-vaporizing mass simultaneously. Nevertheless, its exact determination, due to the complexity of the mass-transfer phenomenon, is hard and a precise definition, possessing definite physical meaning, can hardly be found in the literature. Fig. 3 compares the results of the pervaporation experiments carried out with the Tokaji Ha´rslevel} u (Linden leaves) wine samples and the ethanol–water model mixture possessing the same ethanol concentration. Results belonging to the ethanol–water model mixture have been evaluated in accordance with the work of Mora et al. (2002). In both cases temperature rise causes permeate flux increase, that means faster product gaining and more
Table 3 The activation energies (E0 (kJ/mol)) of the total wine permeate, ethanol and other compounds and their pre-exponential factors (J0 (kg/m2 h)) Product
E0 (kJ/mol)
J0 (106 kg/m2 h)
Permeate Ethanol Others
41.36 39.27 43.80
2.38 0.42 3.82
L. Taka´cs et al. / Journal of Food Engineering 78 (2007) 118–125
122 Wine sample’s total permeate flux
Wine sample’s separation factor
Model solution’s total permeate flux
Model solution’s separation factor
5 4
Separation factor, (-)
3 2 Permeate flux, J (kg/mh)
1 0 35
40
45
50
55
60
65
70
75
Temperature (˚C) Fig. 3. The change of permeate flux and separation factor of the wine sample and identical concentration model solution in function of temperature.
efficient separation if clean mixture is processed (Fig. 3). Contrary to model solution the separation factor of wine sample decreases with temperature rise that can be explained by the presence of the other components residing in the wine. 5. The results of the analytical investigations Fig. 4. Typical results of gas chromatography.
The GC–MS analysis of the wine identified 97 aroma compounds. Among them, fragrance components considered the primary constituents of Tokaji Ha´rslevel} u wine and compounds found and recognized earlier in different honeys e.g. linden honey occurred. In the evaluation, the chromatograms of the wine were compared to that of the products gained in the process. In the case of pervaporation, the vast majority of the aroma components concentrates in the permeate. Main compounds (e.g. acids, sugars), except ethanol, could be observed prolonged in the end-product, but fine constituents forced across by alcohol both partly and intensive heat effect, vaporised through the membrane and occurred on the other side, where they were condensed by the coolingtrap into the condensate, that is into the permeate. Typical chromatograms are shown in Fig. 4. Change of the aroma content was also expected due to the decrease of alcohol. The rest of alcoholic compounds (glycerol, fuel oils and amyl alcohol mainly), soluble slightly in water only, cannot take over the role of a good solvent, instead of ethanol, and was not capable of dissolving the entire aroma substance stock. Thus, a serious loss of aroma compounds has been expected. The analytical results showed that the cumulation of the aroma constituents in the permeate was higher than the planned loss; it was 70% related to the total aroma content of starting wine. Having in mind that the alcohol content of the permeate is 35–38% (Table 2) as well as that the permeate is very rich in aroma substances, it can be utilized as wine distillate after proper final treatment. This fact enhances greatly the profitability of alcohol free wine production.
6. Modelling Permeate-side ethanol concentration can be expressed as the ratio of ethanol flux and total permeate flux: E0E
xPE
E0E DE0 J E J 0E e RT J 0E E0RT ¼ ¼ ¼ e ¼ K e RT E0 J J0 J 0 e RT
ð3Þ
After processing the experimental data, following equation for the ethanol concentration is obtained: xPE ¼ 0:176 e
251:38 T
ð4Þ
Necessary membrane surface can be expressed by the permeate amount, the total flux and the pervaporation time: A¼
VP J s
ð5Þ
In case of partial alcohol extraction, the process is prolonged to the achievement of a desired ethanol content. From the mass balance of the operation, the permeate volume can be expressed as: xFE xRE VP ¼VF ð6Þ xPE xRE Substituting Eqs. (1), (3) and (6) into Eq. (5) gives the Eq. (7), which expresses relation between necessary membrane surface and desired retentate concentration: A¼
VF J0 e
E0 RT
ðx x Þ FEDE RE 0 s K e RT xRE
ð7Þ
surface demand, A [m2]
L. Taka´cs et al. / Journal of Food Engineering 78 (2007) 118–125
Investment cost of other units of equipment (BE) are also a part of total cost (CPV):
200 180 160 140 120 100 80 60 40 20 0
total extraction partial extraction
BE ¼ 0:8
40 198,76 153,87
50 126,36 97,82
60 82,62 63,96
70 55,43 42,91
temperature, t [˚C]
In the case of total alcohol extraction, xRE = 0, Eq. (7) transforms into: V F xFE E0E
J 0E e RT s
ð8Þ
By the above equations, the 1060 Sulzer pervaporation membrane demands have been determined, at pilot-plant level, for alcohol free (xRE < 0.5 v/v%) and low alcoholic (xRE < 3 v/v%) wines shown in Fig. 5.
The technological–economical planning of the pervaporation production of alcohol free and low alcoholic wines has been performed on the base of the data of Atra (2000) for ethanol–water mixturesÕon experimental pilot level pervaporation plant. 7.1. Pervaporation equipment The knowledge of membrane surface allows calculating the cost of the complete equipment (CPV) using a cost-function. The equipment contains the inlet pump, the vacuum pump that removes the vapours of permeate, the warm up heat exchangers and tubes and fittings and assembly units C PV ¼ 61600 A0:37
The investment cost of inlet tanks (BTF) can be calculated based on 10 year amortization time (ET) and their €/m3 price (CT) BTF ¼ C T
VF ET
ð12Þ
The costs of tanks for collecting the products, in cases of definite permeate and retentate volumes, can be defined as shown above. 7.3. Cooling The investment cost of necessary cooling heat exchanger depends on the size of its surface (AH). BH ¼ 402 A0:7 H
ð13Þ
AH ¼
qP V P ðcPP DtPV þ rP Þ k Dtk€oz. s
ð14Þ
7.4. Heating The costs of heating (EF) depend on the specific price of steam (CG2), on the number of production hours per (set) year and on the heating performance. EF ¼ C G2 QF set
ð15Þ
The energy demand of heating can be calculated on the next way: QF ¼ qF V F cPF Dtfel
ð16Þ
ð9Þ
This sum of money occurs once as an investment. The calculation of the whole year total cost must take the amortization of the equipment into account and then €/year dimension should be used. The units of the pervaporation equipment can be divided into two major parts. The membrane unit itself, that costs 10–30% of the whole instrument and ages during 2–4 years, and the stainless steel acid proof parts, the amortization of what is 10 years. Investment cost of membrane (BM) unit can be expressed as a part of total cost (CPV): C PV EM
ð11Þ
The cooling surface can be estimated from energy balance equation:
7. Calculations
BM ¼ 0:2
C PV EE
7.2. Tanks
Fig. 5. The change of membrane surface demand with temperature.
A¼
123
ð10Þ
7.5. Cooling Prior to calculating the operational costs of cooling, the determination of cooling efficiency demand (PH) is needed: PH ¼
V P qP ðcPP DtPV þ rP Þ s
ð17Þ
The operational costs of cooling (EH) depend on the electric efficiency of the cooling compressor (gK) necessary, on the specific price of electric energy (CV) and on the length of cooling time (set) EH ¼
C V P K set gk
ð18Þ
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Table 4 The result of pervaporation cost estimation Alcohol free wine Alcohol content of alcohol free wine Daily wine inlet Starting concentration of ethanol Permeate flux Volume of permeate produced Ethanol content of permeate Membrane surface demand Price of complete PV-equipment Investment costs of membrane Other costs of PV-equipment Total investment costs Estimation of operational cost Operational costs of heating Operational costs of cooling Operational costs of pumping Total operational costs Total costs
VR xRV VF xFE J VP xPE AM CPV BM BE P B
3 0.05 4.7 13.11 0.292 1.7 36.21 82.62 315 207 31 521 25 217
m3 v/v% m3 v/v% kg/m2 h m3 v/v% m2 € €/year €/year
56 738
€/year
EF EH ESZ P E P P B+ E
14 048 51 840 25 920
€/year €/year €/year
91 808
€/year
148 546
€/year
7.6. Pumping The operational costs per year of pervaporation equipment pump (ESZ) depends on the electric performance (PSZ) of the machine obtaining the recirculation volume current needed, on its efficiency (gSZ), on the specific price of electric energy (CV) and on the number the hours of operation (set) ESZ ¼
P SZ C V set gSZ
ð19Þ
7.7. Vacuum Operational costs of vacuum pump (EVSZ) depend on the electric performance of the equipment (PVSZ) obtaining the elimination of permeate vapours, on its electric efficiency (gVSZ), on the number of operational hours (set) and on the specific price of electricity (CV) EVSZ
P VSZ C V set ¼ gVSZ
ð20Þ
In accordance with the aspect of the quality of the product the applied temperature was chosen 40 C. It has given very good flux, because according to literature the value of the permeate flux over 0.2 kg/m2 h is excellent (Huang, 1991). The high price of pervaporation membrane defines the cost of the pervaporation equipment, what is the most considerable amount (see Table 4). The highest amount of the operating cost is the cooling, because for efficient condensation of the permeated vapour a low temperature cooling system is necessary and its efficiency is very poor (17). The cost of the feed-heating is lower than cooling cost (16), but the feed solution pumping
(19) and carrier gas pumping costs (20) together are comparable with the other operational costs. Calculating with 300 day/year operation, specific production cost of one liter alcohol free wine is 0.165 €, which can be covered partially by selling the by-product, permeate/distillate. 8. Conclusions The results of this investigation show that working temperature plays the most important role in the production of low alcoholic and alcohol free wines by pervaporation. Therefore, the choice of optimal temperature seems to be the main goal of an optimisation of such process. At higher temperatures the flux of permeate is higher and the membrane surface demand is smaller. This is significant advantage from the economical point of view, because they both cause faster production and lower costs of investment. However at higher temperatures the membraneÕs separation efficiency and the separation ability decrease. Thus, the permeate production gets faster, but less desired product is gained by separation. At the pervaporation temperatures applied, the majority of the wineÕs organic compounds evaporated and got into the condensate due to vapour permeation. To avoid serious aroma loss, choice of lower pervaporation temperatures is more favourable. Considering that the role of temperature might very complex one, the optimum of the operation must be determined as a compromise. Economical analyses prognoses a great investment cost demand, that can be explained by the relatively high price of non porous pervaporation membranes. But the investment might remunerate in a few years. Remuneration can seriously be promoted by the by-product utilization e.g. by the use of the separated alcohol concentrate as a raw material for wine distillates or industrial spirits. Acknowledgements This work was partially funded by the Hungarian Ministry of Education (NKFP-0026/2002) and Hungarian Scientific Foundation (OTKA T 037848). References Atra, R. (2000). Application of membrane separation processes in diary and spirit industry (in Hungarian). PhD Thesis, Szent Istvan University, Budapest. Eperjesi, I., Ka´llay, M., & Magyar, I. (1998). Oenology (in Hungarian). Budapest: Mezoˆgazda Kiado´. Huang, R. Y. M. (1991). Pervaporation membrane separation processes. In R. Y. M. Huang (Ed.). Amsterdam: Elsevier Science Publishers B.V. Mora, M. J., Vatai, Gy., & Bekassy-Molnar, E. (2002). Comparison of pervaporation of different alcohols from water on CMG-OM-010 and 1060-SULZER membranes. Desalination, 149, 89–94.
L. Taka´cs et al. / Journal of Food Engineering 78 (2007) 118–125 Pickering, G. J. (2000). Low- and reduced-alcohol wine (a review). Journal of Wine Research, 2, 129–144. Rautenbach, R. (1997). Membranverfahren. Berlin, Heidelberg: SpringerVerlag. Scobinger, U., Waldvogel, R., & Du¨rr, P. (1986). Verfahren zur Herstellung von alkoholfreiem Wein oder fruchtwein, Schweizer Patent, CH 654 023 A5.
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Trothe, R. (1990). Verfahren zur entalkoholisierung oder alkoholreduzierung von weinen und fruchtweinen, German Democratic Republic Patent DD 283 153. Xianshe, F., & Huang, R. Y. M. (1996). Estimation of activation energy for permeation in pervaporation processes. Journal of Membrane Science, 118, 127–131.