Ind. Eng. Chem. Res. 2008, 47, 1903-1909
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PROCESS DESIGN AND CONTROL Organosolv Pulping Process Simulations Marı´a Gonza´ lez, A Ä lvaro Tejado, Cristina Pen˜ a, and Jalel Labidi* Chemical and EnVironmental Engineering Department, UniVersity of the Basque Country, Plaza Europa 1, 20018, Donostia-San Sebastia´ n, Gipuzkoa, Spain
Computer simulations of organosolv pulping processes (ethanol-water and ethylene glycol-water mixtures) using commercial simulation software (ASPEN PLUS) have been developed in order to design the process and to establish its key points (product and byproduct mass flow balances, energy analysis, and solvent recovery degree) as well as to analyze operation conditions. Laboratory experiments, in which a deciduous wood called leucaena (Leucaena leucocephala) was used as raw material, were carried out to obtain input data for the simulation. The proposed process flow sheets allow the recovery and recycling of a high percentage of used solvents (97 wt % ethanol and 88 wt % ethylene glycol), which represent a reduction of 66 and 59 wt % of fresh solvent input for ethanol and ethylene glycol, respectively. Introduction Our current society industries are facing several challenges in order to fulfill the environmental, ecological, and energetic requirements set in the Kyoto Protocol. Thus, the pulp and paper industry requires new approaches in research, development, and production to reduce the high environmental impact of the processes involved related basically to shortage of raw materials and large energy and water consumption. Process efficiency must improve to satisfy market demand while ensuring forest preservation.1 Considerable research effort has been made trying to introduce alternative species as pulping materials, such as biomass from agricultural and forestry residues.2-4 It is also of vital importance to maximize process efficiency through the recovery of byproducts, especially lignin and hemicelluloses, which represent about 50 wt % of dry wood. In traditional processes (i.e., kraft pulping) this fraction of wood is usually burned as a way of recovering part of the energy used in the process.5 In this context organosolv processes have been developed, based on the use of organic solvents as delignifying agents, in which it is possible to break up the lignocellulosic biomass to obtain cellulosic fibers for papermaking, high quality hemicelluloses (from which sugars can be obtained for fermentation processes), and lignin degradation products from generated black liquors, avoiding emissions and effluents.6-9 Several authors have reported studies where the pulping effectiveness of different organic solvents such as alcohols, glycols, acids, esters, and others is analyzed10-16 in terms of effectiveness of the process, pulp quality, and, thus, the optimum operating conditions for each system.17-20 In this work, computer simulations of two organosolv processes (using ethanol-water and ethylene glycol-water mixtures as pulping media) have been developed using experimental data obtained in the laboratory as inputs. As a result, key points of the process including mass flow balances, * To whom correspondence should be addressed. Tel.: +34943017178. Fax: +34-943017140. E-mail:
[email protected].
composition of each stream, energy analysis, solvent recovery, and byproduct isolation yield have been obtained. The process has also been analyzed in order to determine the best operating conditions especially in the black liquor recovery scheme. The study focuses on the design and analysis of two processes that allow an easy recovery of solvents and byproducts. Materials and Methods Raw Material. The chemical composition of leucaena (Leucaena leucocephala), an alternative agroforest raw material, was determined according to standard methods. Moisture content (6.6%) was determined after drying the samples at 105 ( 3 °C for 24 h according to TAPPI T264 cm-97. The chemical composition, given on an oven dry basis, was the following: 2.5% ash (TAPPI T211 om-93), 18% aqueous NaOH soluble matter (TAPPI T212 om-98), 4.0% hot water soluble matter (TAPPI T264 cm-97), 5.0% ethanol-benzene extractives (TAPPI T204 cm-97), 21% lignin (TAPPI T222 om-98), 76% holocellulose,21 and 44% R-cellulose.22 Experimental Analysis. In order to provide experimental data to start the simulations and compare the results obtained, several experiments have been carried out at laboratory scale. The experiments consist of a multistep process involving raw material cooking, pulp separation, lignin precipitation, solvent recovery by distillation, and byproduct isolation. Two solvent mixtures have been selected with that aim: ethanol-water and ethylene glycol-water. The first one, which corresponds with the largely investigated Kleinert process,12,13 has proved to be suitable for good quality pulp production10,23 with a high solvent recovery rate. The Alcell process,24-26 based also on ethanolwater, has reached wide use. The ethylene glycol-water process belongs to a group of systems that use high boiling point solvents and has also been reported to provide good quality pulps.16,27-29 Pulping Conditions. Organosolv pulping processes were carried out at the University of Co´rdoba, Spain, and their respective experimental conditions are summarized in Table 1. Obtained black liquors were subjected to various analyses.
10.1021/ie070432j CCC: $40.75 © 2008 American Chemical Society Published on Web 02/22/2008
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Ind. Eng. Chem. Res., Vol. 47, No. 6, 2008
glycol from byproducts. In this second step, a stream containing 84 wt % ethylene glycol, furfural, acetic acid, and 16 wt % water was isolated, leaving a residue composed of lignin, sugars, and the remaining ethylene glycol (16 wt %). Pulp and Paper Characterization. Pulp and paper characterization was carried out at the University of Co´rdoba (UCO). Pulp yield was determined gravimetrically following drying at 105 °C ( 2 for 24 h; the degree of refining (in accordance with TAPPI 248-cm 85), the kappa number (T236 cm-85), and the viscosity (UNE 57-039) were also determined. The resulting paper sheets were characterized in accordance with the following standards: breaking length and stretch (TAPPI 404-om 92), burst index (TAPPI 403-om 91), and tear index (TAPPI 414om 88). Process Simulation. In this work Aspen Plus 12.131 has been used to design and simulate the process. On the basis of experimental results of black liquor composition, solvent and byproduct recovery from these pulping liquors was simulated. Lignin and cellulose have been defined by their chemical structure and molecular weight, whereas the other conventional components were selected from the ASPEN PLUS data bank. The ELECTNRTL model, based on the NRTL electrolyte model and the Redlich-Kwong equation of state, was used to simulate the thermodynamic properties of solutions. The simulation base has been 1000 kg/h of dry raw material with the following composition (mass fractions on a dry-weight basis): cellulose, 0.46; lignin, 0.21; hemicelluloses, 0.27; other components, 0.06. The solvent input flow rate was 6000 kg/h, which corresponds to a liquid/solid ratio (w/w) of 6. Ethanol-Water Process. A flow sheet for the ethanol-water process is outlined in Scheme 1. As shown in Scheme 1, raw materials and solvent (stream 10) are fed to a reactor (digester), which produces a pulp stream and black liquors (stream 1). The latter stream is diluted with water (stream 3) and acidified with HCl to precipitate HMW lignin. In the filtering stage, solid lignin is separated (stream 5) while the filtrate (stream 4) is taken to the distillation units. From this first distillation column a distillate stream (stream 6) is obtained, composed of ethanol and water, which will be subsequently fed into the second column. The residual stream (stream 7) contains a mixture of byproducts (low molecular weight (LMW) lignin, sugars, acetic acid, furfural, and other minority components). In the second unit, ethanol is isolated and directly recycled as solvent into the digester (stream 8). The residual fraction of this unit (stream 9), which is almost pure water, is used in the precipitation stage (stream 3) and also to wash the pulp obtained after the initial pulping (stream 11). Ethylene Glycol-Water Process. Due to the high boiling point of ethylene glycol (197.6 °C), some remarkable differences concerning the distillation units are found when using ethylene glycol as solvent medium. In the same manner as it happened in the ethanol scheme, black liquor filtrate (stream 4) is fed into the first distillation unit where the distillate (stream 6), mainly composed of water, is mixed with fresh water to feed the precipitation unit (stream 3) and the pulp-washing unit (stream 11). The residual stream (stream 7) is then taken to the second column resulting in a solvent-rich distillate (stream 8)
Table 1. Experimental Pulping Conditions solvent type ethanol-water ethylene glycol-water
dry basis raw matter liquid/solid % w/w t (min) T (°C) (g) ratio (w/w) 60 60
90 90
180 180
1000 1000
6:1 6:1
Black Liquor Characterization. The composition of obtained black liquors was determined using several laboratory techniques. In order to precipitate high molecular weight (HMW) lignin, black liquors were diluted with water (1:1.5 v/v) before lowering the pH to ∼2 by adding 1 M HCl. The precipitate formed as a result of this was allowed to decant over a 24 h period; afterward it was centrifuged at 3500 rpm for 12 min, washed with water twice to remove the sugar and other impurity contents, and finally thickened and dried. Lignin concentration was calculated by gravimetric measurement. After lignin separation, sugar concentrations were analyzed in the filtrates by HPLC using a Transgenomic CARBOSep CHO682 column. To avoid lignin interferences, the filtrates were centrifuged again and taken to pH 9 by addition of aqueous NaOH in order to observe column specifications. HPLC analysis conditions were as follows: oven temperature, 60 °C; mobile phase, water; flow, 0.4 mL/min; injection volume, 20 µL. Finally, acetic acid and furfural content were analyzed from the lignin-free black liquor samples. The former was determined by titration with 0.1 N sodium hydroxide until the titration end point, while the latter was examined by UV absorbance.30 Black liquor compositions for both ethanol and ethylene glycol pulping processes are summarized in Table 2. Ethanol-water black liquor at the digester exit, having 64 wt % ethanol and 29 wt % water, presents pH and density values of 4.3 and 0.958 g/cm3, respectively. On the other hand, pH 4.5 and density of 1.084 g/cm3 were measured for ethylene glycol-water black liquor at the same point, while ethylene glycol and water contents were 54 and 40 wt %, respectively. Knowing the composition of both black liquors, different separation and byproduct recovery schemes were developed. Solvent Recovery and Byproduct Isolation. Black liquor filtrates were subjected to distillation processes in the laboratory in order to calculate the solvent and byproduct recovery rate. A batch distillation system was used to recuperate either ethanol or ethylene glycol and water. Ethanol-water filtrate was first distilled obtaining distillate having mostly ethanol and 88 wt % water content and a residue stream containing the remaining water (12 wt %) and all heavy components (sugars, lignin, furfural, acetic acid). After that, the former mixture was subjected to a new distillation step with the aim of separating ethanol from water. Two new streams were obtained: one containing 93.2 wt % ethanol and 6.8 wt % water (corresponding to 95% of the ethanol and 7% of the water fed to this unit) and another one composed of 5.8 wt % ethanol and 94.2 wt % water (representing 5% of the ethanol and 81% of the water fed to this unit). In the ethylene glycol-water scheme, due to the high boiling point of this solvent (197.6 °C), a first distillation step carried out at 100 °C allowed the separation of 84 wt % water content from ethylene glycol-water black liquor filtrate. A second distillation process was performed in order to separate ethylene Table 2. Black Liquor Composition (g/L of Black Liquor)
sugars solvent type
furfural
acetic acid
ash
lignin
xylose
glucose
galactose
arabinose
mannose
total
ethanol ethylene glycol
0.1 1.1
3.7 3.3
8.6 2.3
21.6 34.6
2.0 3.1
0.8 1.6
1.9 1.9
0.6 0.4
0.4 0.2
5.7 7.2
Ind. Eng. Chem. Res., Vol. 47, No. 6, 2008 1905 Scheme 1. General Flow Sheet of Ethanol-Water Process
Scheme 2. General Flow Sheet of Ethylene Glycol-Water Process
Table 3. Mass Balance for Ethanol-Water Process (kg/h) stream 1
2
3
4
5
ethanol water lignin furfural acetic acid sugars others HCl
3963 1839 158 5.06 12.6 61.3 29.6 80.0
4813 10 825 158 5.06 13.6 61.3 29.6 100
850 8986 0 0 0.98 0 0 0
4813 10 825 47.3 5.06 13.6 61.3 29.6 100
0 0 110 0 0 0 0 0
total
6149
16 006
9837
15 895
110
and a residue containing the byproducts (stream 9). The flow sheet of the ethylene glycol-water process is outlined in Scheme 2. Results and Discussion Ethanol-Water Process Simulation Results. Experimental results obtained from the ethanol continuous process simulation are summarized in Tables 3 and 4.
6 4800 9616 0 0.01 1.09 0 0 100 14 517
7
8
13.0 1209 48.0 5.05 12.5 61.3 29.6 0
3855 545 0 0 0 0 0 100
1378
4500
9 945 9071 0 0.01 1.09 0 0 0 10 017
10
11
4044 1876 0 0 0 0 0 80.0
96.0 920 0 0 0.11 0 0 0
6000
1016
The ethanol-water pulping process has provided a 54% process yield (dry-weight pulp). Lignin separation degree in the precipitation step is 69% (HMW lignin, stream 5), which means 53 wt % of the raw material content. The filtrate obtained after lignin precipitation (stream 4) is then redirected to the distillation units. Byproducts (LMW lignin which accounts for 22 wt % of original raw material, furfural, acetic acid, and sugars) are isolated as residual matter in unit 1 (stream 7), while an
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Table 4. Mass Fractions for Ethanol-Water Process stream 1
2
3
4
5
6
7
8
9
10
11
ethanol water lignin furfural acetic acid sugars others HCl
0.645 0.299 0.025 0.001 0.002 0.010 0.005 0.013
0.301 0.676 0.010 0.000 0.001 0.004 0.002 0.006
0.086 0.914 0.000 0.000 0.000 0.000 0.000 0.000
0.303 0.681 0.003 0.000 0.001 0.004 0.002 0.006
0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000
0.330 0.663 0.000 0.000 0.000 0.000 0.000 0.007
0.010 0.878 0.034 0.004 0.009 0.044 0.021 0.000
0.857 0.121 0.000 0.000 0.000 0.000 0.000 0.022
0.094 0.906 0.000 0.000 0.000 0.000 0.000 0.000
0.672 0.315 0.000 0.000 0.000 0.000 0.000 0.013
0.095 0.905 0.000 0.000 0.000 0.000 0.000 0.000
total
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
Table 5. Mass Balance for Ethylene Glycol-Water Process (kg/h) stream 1
2
3
4
5
6
7
8
9
10
11
ethylene glycol water lignin furfural acetic acid sugars others HCl
3365 2510 175 26.5 66.1 84.8 15.8 0
3365 12 377 175 26.5 66.6 84.8 21.4 135
0 9867 0 0 0.56 0 5.64 115
3365 12 377 52.8 26.5 66.6 84.8 21.4 135
0 0 122 0 0 0 0 0
0 10 422 0 0 0.65 0 6.63 135
3365 1955 52.8 26.5 66.0 84.8 14.8 0
2960 1955 0.02 26.2 66.0 0 0 0
404 0 52.6 0.03 0 84.8 13.8 0
3365 2561 0.02 21.2 52.7 0 0 0
0 1543 0 0 0.10 0 0.98 20.0
total
6243
16 251
9988
16 130
122
10 564
5565
5008
555
6000
1564
Table 6. Mass Fractions for Ethylene Glycol-Water Process stream 1
2
3
4
5
6
7
8
9
10
11
ethylene glycol water lignin furfural acetic acid sugars others HCl
0.538 0.403 0.028 0.004 0.011 0.014 0.002 0.000
0.208 0.761 0.011 0.002 0.004 0.005 0.001 0.008
0.000 0.988 0.000 0.000 0.000 0.000 0.000 0.012
0.209 0.768 0.003 0.002 0.004 0.005 0.001 0.008
0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000
0.000 0.987 0.000 0.000 0.000 0.000 0.000 0.013
0.605 0.351 0.009 0.000 0.012 0.015 0.003 0.000
0.591 0.390 0.000 0.002 0.013 0.000 0.000 0.000
0.727 0.000 0.094 0.000 0.000 0.152 0.027 0.000
0.561 0.427 0.000 0.003 0.009 0.000 0.000 0.000
0.000 0.988 0.000 0.000 0.000 0.000 0.000 0.012
total
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
ethanol-water mixture (stream 6) continues to the second distillation column. In that case, 97 wt % of the initial ethanol content is recuperated (stream 8) and recycled into the solvent reactor input and 88 wt % of the water that was added at the beginning of the process (stream 9) is recovered and sent both to the precipitation stage and to the pulp-washing unit. These results are in agreement with those found in laboratory analysis, where the batch distillation process allowed recovering 95 wt % ethanol with 7 wt % water content. Distillation was optimized so that the recovering degrees of ethanol and water previously described were obtained. This way, the plate number was established in 11 for the first unit, with the feeding in plate 5 and in 12 for the second unit with the feeding stream in plate 6. The reflux ratios were 2.3 and 9 (weight), respectively, and the distillate to feed ratios were 0.9 and 0.3 (weight), respectively. Ethylene Glycol-Water Process Simulation Results. The ethylene glycol process yield has been found to be 58% (dryweight pulp). Black liquors are treated with the aim of precipitating the lignin that accounts for 67 wt % HMW lignin from black liquors and 60.4 wt % raw material lignin. The remaining filtrate (stream 4) is conducted to the distillation units. Stream 6, at the top of the column, contains the recycled water (91 wt %) that is mixed with fresh water prior to its utilization: from this, 69 wt % is moved into the precipitation unit and 22 wt % is used to wash the pulp. In the second column, the solvent recovery stream containing 88 wt % of the ethylene glycol exits from the top (stream 8), and is recuperated and mixed with fresh
solvent to form the solvent reactor input (stream 10). At the bottom of the column, the byproduct stream is composed of LMW lignin (25 wt % of the raw material content) and sugars. In laboratory experiments carried out with this system, 80 wt % of the initial ethylene glycol content was distilled, leaving the remaining quantity with the byproducts of the process. Results are summarized in Tables 5 and 6. The distillation process in ethylene glycol-water scheme has the following parameters: the plate number was established in 15 for both columns, with the feeding in plate 7. The reflux ratios were 7.3 and 7.0 (weight), respectively, and distillate to feed ratios were 0.6 and 0.9 (weight), respectively. Energy Analysis. Energy analysis of the distillation columns has been studied for both ethanol and ethylene glycol processes. The simulation calculations correspond to 1000 kg/h raw material input. Results are presented in Table 7. As can be seen in Table 7, energy consumptions of distillation columns present considerably different values in both processes. In the ethanol-water process, the first column has the lowest energy consumption as this unit achieves a simple separation where a mixture of ethanol and water free from byproducts is obtained. In the second step, the separation of ethanol and water needs a higher energy contribution. When ethylene glycolwater is used as pulping medium, the opposite behavior is found. Due to the solvent characteristics, especially its high boiling point, the water recovery is achieved in the first column. This means that a larger fluid quantity is distilled in this unit and, consequently, it causes higher energy consumption. In the
Ind. Eng. Chem. Res., Vol. 47, No. 6, 2008 1907 Table 7. Energy (MW) Consumption of the Recovery Section for Both Ethanol-Water and Ethylene Glycol-Water Processes distillation unit 1
unit 2
condenser
reboiler
condenser
reboiler
process
Q (MW)
T (°C)
Q (MW)
T (°C)
Q (MW)
T (°C)
Q (MW)
T (°C)
ethanol ethylene glycol
-21.62 -49.81
173.1 177.2
22.28 50.37
180.2 197.9
-30.34 -15.86
144.5 195.8
30.26 15.90
179.6 301
Table 8. Properties of Pulp and the Paper Sheets of Leucaena leucocephala and Various Agricultural Residues and Alternative Raw Materials Pulped with Ethanol-Water property
Leucaena leucocephala
vine shoots32
yield (%) refining (°SR) kappa index viscosity (mL/g) brightness (%) breaking length (m) stretch (%) burst index (kN/g) tear index (mN m2/g)
54 40.5 132.3 365 25.05 3727 2.06 1.57 0.24
46.92 19.5
tagasaste (C. proliferus)33 42.9
wheat straw34
sunflower stalks35
78 15.21
36.9
37
551
52.7 278 16.5
57.6 1268 22.4 291 1.29 0.61 0.41
2.54 0.47
5265 1.94 2.53 4.26
3810 1.23 1.15 2.04
Pawlownia fortunei L.36
0.90 0.92
second step, ethylene glycol-water is separated from the remaining byproducts through a new distillation step. Even if considerably high temperatures (∼300 °C) are reached at the reboiler, it needs less than half the energy required in the previous operation due to the smaller flow treated. Nevertheless, the heat supply at ∼300 °C is considerably more expensive than at ∼180 °C. In a global balance, the energy consumption is around 20% higher for the ethylene glycol-water process than for the ethanol one. This is outlined in Figures 1 and 2, where the Sankey diagrams of both processes are represented. Pulp and Paper Characterization Results. A. EthanolWater Pulping. Leucaena leucocephala pulp obtained by the ethanol-water cooking process and the paper made from it were characterized. The obtained results (Table 8) were compared with pulp and paper from different raw materials pulped with ethanol-water. The pulp characterization shows in general typical properties of organosolv pulps, medium yield, high refining degree, high brightness, and high kappa index. The last, which is related to lignin content in pulp, may be the result of lignin condensation reactions into cellulose fibers during pulp washing.32 As previous studies confirm,33 the pulping temperature strongly influences the majority of pulp and paper properties, but, unfortunately,
not in the same way. An increment in pulping temperature leads to a lower kappa index and viscosity values but has a negative effect on the yield. Also, wash temperature has an influence on pulp and paper properties, especially on yield and the tensile index. A high wash temperature (70 °C) ensures that the pulp and the resulting paper sheets will possess optimal properties.33 In the process scheme presented in this work, the water recovered from the distillation unit and partly used to wash the pulp presents an adequate temperature without needing any extra energy consumption. Relating to paper properties, the breaking length and stretch values are considerably high for an organosolv paper (3727 m and 2.06%, respectively) and the other properties are also acceptable32-36 for a huge range of uses of the paper obtained. B. Ethylene Glycol-Water Pulping. The parameters obtained from ethylene glycol-water pulp and paper characterization are presented in Table 9, with other raw material pulped with the same process. The properties of Leucaena leucocephala pulp obtained with ethylene glycol-water as solvent fit in with typical organosolv pulp results37-39 with regard to yield, kappa index, viscosity, and brightness. As in the previous scheme (ethanol-water), the pulp obtained may be difficult to bleach (kappa index 124.6),
Figure 1. Sankey diagram for ethanol-water process.
Figure 2. Sankey diagram for ethylene glycol-water process.
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Table 9. Properties of Pulp and the Paper Sheets of Leucaena leucocephala and Various Agricultural Residues and Alternative Raw Materials Pulped with Ethylene Glycol-Water property
Leucaena leucocephala
yield (%) refining (°SR) kappa index viscosity (mL/g) brightness (%) breaking length (m) stretch (%) burst index (kN/g) tear index (mN m2/g)
58 41 120.6 383 43 3481 1.9 1.62 0.26
tagasaste (C. proliferus)37 62.88
40.92 4644 2.87 2.46 0.33
but the process provided paper sheets with suitable strengthrelated properties (breaking length of 3481 m, stretch of 1.9%, burst index of 1.62 kN/g, and tear index of 0.26 mN m2/g). The comparison between pulp and paper obtained with both solvents reveals that the ethylene glycol process gives pulp with lower lignin content, higher yield, and brightness, while the paper properties are quite similar. Therefore, ethylene glycol pulp may be bleached in smoother conditions (more economic), although the resulting paper would be used for similar applications. Conclusions The chemical characteristics of Leucaena leucocephala confirm its possible use as an alternative source of cellulose pulp, as other studies support.40 Computer simulations of organosolv (ethanol-water and ethylene glycol-water) pulping processes of Leucaena leucocephala have been developed and contrasted with experimental results. In both cases, the simulation study has permitted establishment of a suitable process design as well as determination of the most convenient operating conditions. In terms of the process yield, the ethylene glycol-water process yield has been found to be 4% higher than the ethanol one (dry-weight pulp, after separation of uncooked material). Also, the lignin precipitation degree is 7 wt % higher in this case. Relating to byproducts, the ethylene glycol-water process has provided 3 wt % more LMW lignin as well as 30 wt % more sugars. On the other hand, some drawbacks can be attributed to this system, such as a more difficult subsequent isolation treatment of byproducts obtained as they remain diluted in ethylene glycol (with a high boiling point) instead of in water, as occurs in the ethanol-water process, which would be more convenient for further processing. Also, acetic acid and furfural formed during the process are not isolated but are recycled within the solvent recovery stream, while in the ethanol process these products are isolated together with the byproduct stream and could be used. Moreover, the temperatures reached at the distillation towers of the ethylene glycol-water process are much higher, so this process entails a higher energy consumption (20% more). Solvent recovery degree is 9 wt % higher in the ethanolwater process than in the ethylene glycol-water system, allowing a reduction of 66 wt % in the fresh solvent requirement (as 1200 kg/h is fed instead of 3600 kg/h) while 59 wt % is saved in the ethylene glycol-water process (1500 kg/h instead of 3600 kg/h). Water recovery of 88 wt % is obtained in the ethanol-water process, where 16% is used to wash the pulp and 72 wt % is recycled, which permits a decrease of 90 wt % in the fresh water input. In the ethylene glycol-water system, 91 wt % water is recovered, from which 22 wt % is used in the pulp washing stage and 69 wt % is available to be used in the precipitating stage, allowing an 92 wt % reduction in the water input.
vine shoots39
cotton stalks39
78.08 74.9 149.6 582 25.03 2846 1.64
78.18 68.6 148.8 589
Holm oak trimmings38 68 35 406 19.2
4970 2.58 1.83
empty fruit bunches39 58 11 83.5 458 21.9 1091 1.21 0.33 0.18
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ReceiVed for reView March 26, 2007 ReVised manuscript receiVed December 19, 2007 Accepted January 9, 2008 IE070432J
