Ethanol Pulping from Tagasaste (Chamaecytisus proliferus L.F. ssp

Ind. Eng. Chem. Res. 2004, 43, 1875-1881

1875

GENERAL RESEARCH Ethanol Pulping from Tagasaste (Chamaecytisus proliferus L.F. ssp palmensis). A New Promising Source for Cellulose Pulp M. J. Dı´az,*,† A. Alfaro,‡ M. M. Garcı´a,† M. E. Eugenio,§ J. Ariza,† and F. Lo´ pez† Chemical Engineering Department Facultad de Ciencias Experimentales Campus del Carmen, Universidad de Huelva, Avda, de las Fuerzas Armadas S/N, 21007 Huelva Spain, Forestry Science Department, Universidad de Huelva, Ctra, Huelva-Palos de la Frontera s/n, 21819 La Ra´ bida, Palos de la Frontera, Huelva, Spain, and Environmental Science Department, Universidad Pablo de Olavide, Ctra, Utrera Km. 5, Sevilla, Spain

The chemical characteristics of tagasaste trimming wood and eucalyptus wood are similar in ash, holocellulose, lignine, xylan, and acetyl groups. Then, tagasaste wood could be an adequate raw material for pulp and paper making. Therefore, the influence of independent variables in the pulp processing of tagasaste with ethanol-water mixtures (ethanol concentration, time, pulping temperature, wash temperature, and disintegrate temperature) on various properties of the pulp (yield, kappa number, viscosity, brightness, and stretch related properties of paper sheets) was studied to determine the best processing conditions to obtain quality pulp and paper sheets. Using medium to high (185-200 °C) pulping temperatures and ethanol concentration (60-80%), suitable physical characteristics of paper sheets and an acceptable yield, the kappa index, and viscosity could be obtained. Wash and disintegrate temperatures have an influence on all the dependent variables, especially on the yield and the tensile index. A high wash temperature and a disintegrate temperature must be used in order to ensure that the pulp and the resulting paper sheets will possess optimal properties. 1. Introduction Standard chemical pulping processes (kraft processes) are typically used for making pulp from agro-based fibers.1 However, these processes are energy-intensive, require large capital investments, and contribute to air and water pollution. Technologies are currently in development that would reduce the environmental impact of kraft pulping. The problem of emission of volatile sulfur compounds and high chemical oxygen demand bleaching effluents is yet to be solved. Organosolv pulping circumvents the environmental problems related to sulfur emissions, and it has been found to be effective on several wood species with a broad range of organic solvents.2 Organosolv pulping is a two-stage process involving hydrolysis and the removal of lignin with an organic solvent3 and offers several potential advantages over conventional pulping techniques such as relatively low chemical and energy consumption coupled with low capital costs and low environmental impact due to the recirculation of effluents and the replacement of chemical additives used in a conventional pulp mill.2 Pulp recovery from organosolv pulping ranges between 50 and 60% for hardwoods and 40 and 45% for softwoods.4 Typical hardwood fiber recoveries compare * To whom correspondence should be addressed. Tel.: +34 959 01 99 90. Fax: +34 959 01 99 83. E-mail: [email protected]. † Chemical Engineering Department Facultad de Ciencias Experimentales Campus del Carmen, Universidad de Huelva. ‡ Forestry Science Department, Universidad de Huelva. § Universidad Pablo de Olavide.

favorably with those from kraft pulping. Little waste is produced by the process, and low alcohols are recovered easily by distillation, thus requiring a relatively low capital investment. However, fibers produced by the organosolv process are weaker than those recovered by the kraft process. Thus, the papers produced from the organosolv pulp are suitable for uses where strength is not the most important property.5 Organosolv pulping uses several organic compounds as solvent to delignify the fiber by breaking off pieces of the lignin molecule to render it soluble.6 A variety of organic solvents, including alcohols, ketones, glycols, esters, and organic acids had been used in organosolv pulping. However, economic reasons in terms of price and difficulties in solvent recovery have favored the use of low molecular weight alcohols. The use of ethanol is particularly attractive both ecologically and economically, since the ethanol solvent can be distilled and reused, leaving behind a powder rich in lignin and other organics, which can then be sold to make fertilizer or binding agents. Commercial viability of this technology will require that markets be developed for byproducts of the process.6 Organosolv processes had been applied with varying success to hard and soft wood and also, to a lesser extent, to nonwood materials. Several nonwood materials have been studied by different authors.7-11 The use of nonwoody faster-growing species for papermaking could have a great advantage in that they provide remediation for the environmental problems associated with deforestation. Tagasaste (Chamaecytisus proliferus (L.F.) ssp palmensis) began to be

10.1021/ie030611a CCC: $27.50 © 2004 American Chemical Society Published on Web 03/18/2004

1876 Ind. Eng. Chem. Res., Vol. 43, No. 8, 2004

researched at the end of the 19th century, but it was in 1982 when agronomy features really began to be known.12-15 Tagasaste grows most easily on sandysurfaced soils. It tolerates low annual rain fall (the lower limit is 300 mm) in some areas of Australia and New Zealand, where this shrub was introduced at the end of the 19th century.16 The necessary harvesting for the suitable regrowth of plants provides trimming residues. These wastes could be used as papermaking raw material. Trimming residues wood were formed by branches of 0.5-5 cm thickness. There are not previous references to the use of tagasaste wood for pulp and papermaking. On the other hand, several operating parameters such as pulping temperature, operation time, organic solvent concentration, and several additives and conditions have been studied by different authors;17-19 none, however, has considered the effect of the operating variables such as a wash temperature and a disintegrate temperature on the properties of the pulp obtained. In the first part of this paper, the chemical composition of the raw material was studied. The second part deals with the influence of the operating conditions used in the ethanol pulping of tagasaste wood trimmings cellulose pulp (viz. pulping temperature, pulping time, ethanol concentration, wash temperature, and disintegrate temperature) on the yield, kappa number, brightness, and viscosity of the resulting pulp and on strengthrelated properties of paper sheets to determine the best pulping conditions. 2. Experimental Section 2.1. Characterization of the Raw Material, Pulp, and Paper Sheets. Tagasaste wood trimmings samples were milled to pass a 8 mm screen, since no diffusional limitations were observed for this particle size in preliminary studies. Samples were air-dried, homogenized in a single lot to avoid differences in composition among aliquots, and stored. Aliquots from the homogenized wood lot were subjected to moisture determination (drying at 105 °C to constant weight) and to quantitative acid hydrolysis with 72% sulfuric acid following standard methods.20 The solid residue after hydrolysis was recovered by filtration and considered as Klason lignin. The monosaccharides and acetic acid contained in hydrolysates were determined by HPLC in order to estimate (after corrections for stoichiometry and sugar decomposition) the contents of samples in cellulose (as glucan), hemicelluloses (xylan), and acetyl groups.21 The moisture of wood was considered as water in the material balances. Characterization experiments involved the following parameters: hot water solubles (Tappi 257), 1% NaOH solubles (Tappi 212), ethanol-benzene extractives (Tappi 204), ash (Tappi 211), Klason lignin (Tappi 212), R-cellulose (Tappi 203-OS-61), holocellulose by the Wise et al. method,22 pulp yield (Tappi 257), kappa number (Tappi 236), brightness (Tappi 525), viscosity (Tappi 230), tensile index (ISO 3781:1983), and tear index (ISO 1974:1990). 2.2. Pulping Procedure and Formation of Paper Sheets. Cellulose pulps were obtained using a 4-L batch cylindrical reactor that was heated by means of electrical resistances and linked to a control unit including the required instruments for measurement and control of the pressure and temperature. The control unit included temperature and pressure gauges as well as appropriate safety devices. The cooking liquor was

recirculated by means an air motor. Finally, to open the reactor, the liquor was quickly refrigerated by a heat exchange to obtain low-pressure levels. Following cooking, the pulp was separated from the liquor and disintegrated (the process of separating the pulp into a suspension of individual fibers in water in this study had been performed at different temperatures), without disturbing the fibers during 3 min, and washed on a sieve of 0.16 mm mesh (the process of clearing the dispersed fibers after cooking in this study had been performed at different temperatures). The initial liquid/ solid ratio used in cooking, disintegrating, and washing processes was 10/1. The pulp was defibered on a SproutWaldron refiner and passed again through a Strainer filter (0.4 mm mesh) in order to isolate the uncooked material. We used tagasaste wood trimmings, but only wood was considered as it contained the bark, which was very thin and difficult to strip off also; it accounted for only 1-2% of the overall mass. Paper sheets were prepared with an ENJO-F-39.71 sheet machine according to the UNE 57042-74 standard. 2.3. Experimental Design for the Pulping Conditions. To be able to relate the dependent and independent variables with the minimum possible number of experiments, a 2n central composite factor design that enabled the construction of second-order polynomials in the independent variables and the identification of statistical significance in the variables was used.23,24 Independent variables were normalized by using the following equation

Xn )

X-X h (Xmax - Xmin )/2

(1)

where X is the absolute value of the independent variable concerned, X h is the average value of the variable, and Xmax and Xmin are its maximum and minimum values, respectively. The pulping temperature, pulping time, ethanol concentration, wash temperature, and disintegrate temperature used in the different experiments of the factorial design were 170 °C, 185 °C, and 200 °C; 45, 90, and 135 min; 40%, 60%, and 80% (v/v); 20 °C, 45 °C, and 70 °C and 20 °C, 45 °C, and 70 °C, respectively. The independent variables used in the equations relating to both types of variables were those having a statistically significant coefficient (viz. those not exceeding a significance level of 0.05 in the student’s t-test and having a 95% confidence interval excluding zero). 3. Results and Discussion 3.1. Optimization Studies. Many variables can affect organosolv pulping. Many authors have so far used a factorial design to develop empirical models involving several independent variables to identify patterns of variation in the dependent variables (viz. kappa number and viscosity) or various pulping processes as applied to diverse plant materials. None, however, has considered the effect of the operating variables on the properties of the pulp obtained. These empirical models are to be preferred to theoretical ones as the latter are rather complex when more than two independent variables are involved. In this work, we made best guesses based on the literature and experience. However, the opportunity to increase the effectiveness and efficiency of organosolv pulping and decrease

Ind. Eng. Chem. Res., Vol. 43, No. 8, 2004 1877 Table 1. Chemical Characterization of Tagasaste and Eucalyptus Wooda tagasaste trimmings fiber length, mm hot water solubles, % 1% NaOH solubles, % ethanol-benzene extractives, % ash, % holocellulose, % lignin, % R-cellulose, % cellulose as glucane, % xylan, % arabane, % acetyl groups, % others, % a

tagasaste wood trimmings

tagasaste bark trimmings

0.70 7.9 21.2 2.3 0.7 80.3 19.8 40.4 38.9 19.9 0.63 4.39 12.5

9.9 21.6 3.8 0.9 80.0 17.0 39.5

eucalyptus wood25 1.05 2.8 12.4 1.2 0.6 80.5 20.0 52.8 46.3 16.6 0.54 3.56 9.7

30.8 63.4 10.6 3.8 42.7 15.4 21.2

Percentages with respect to initial raw material (100 kg odb).

Table 2. Values of the Independent Variables, the Chemical Properties of the Pulp, and the Properties of Paper Sheets Obtained in the Pulping Process by Using the Proposed Experimental Design normalized values of pulping temperature, time, ethanol concentration, wash temperature and disintegrate temperature

yield (%)

kappa number

viscosity (mL g-1)

brightness (%)

tensile index (kN m kg-1)

tear index (N m2 kg-1)

+1 +1-1 +1-1 +1 +1 +1-1-1 +1 +1-1 +1-1 +1 +1-1-1 +1 +1-1 +1 +1-1 +1-1 +1-1 +1 +1-1-1 +1 +1 +1-1-1-1-1 -1 +1 +1 +1-1 -1 +1 +1-1 +1 -1 +1-1 +1 +1 -1 +1-1-1-1 -1-1 +1 +1 +1 -1-1-1-1-1 -1-1-1 +1-1 -1-1-1-1 +1 +1 0 0 0 0 -1 0 0 0 0 0 +1 0 0 0 0-1 0 0 0 0 0 +1 0 0 0 0-1 0 0 0 0 0 +1 0 0 0 0-1 0 0 0 0 0 +1 0 0 0 0-1 00000 00000

43.9 40.5 31.6 35.0 46.6 43.5 38.1 37.0 31.4 39.8 44.9 45.7 45.6 38.3 47.2 48.3 42.7 44.5 41.7 38.8 40.2 43.0 47.6 48.0 43.6 36.4 42.9 42.8

45.0 38.5 55.9 58.3 64.1 62.9 45.0 44.2 68.4 71.7 65.6 58.9 69.5 68.3 78.4 72.4 47.4 68.0 57.0 63.9 59.8 57.1 59.5 60.1 61.2 57.0 57.6 56.2

1119 1436 265 272 1246 1074 819 771 433 495 1220 1243 205 552 286 366 1040 608 1232 1021 1373 1028 1425 1465 1241 1269 1268 1322

18.5 20.9 24.3 22.2 17.1 17.7 24.6 24.8 19.8 21.2 22.2 23.5 22.5 22.9 22.6 22.6 23.3 23.1 23.0 22.9 20.8 23.5 22.4 21.9 22.9 22.5 22.4 22.2

7.34 6.51 7.25 6.07 6.49 4.77 4.80 3.44 7.35 4.53 7.49 6.70 5.45 5.77 5.61 3.49 5.70 5.08 7.15 5.61 6.65 5.40 8.70 8.50 6.40 7.80 6.40 6.50

42.9 47.0 10.5 12.5 45.4 43.7 17.3 22.1 29.9 26.8 46.0 43.2 29.0 48.5 38.7 38.7 36.0 40.5 50.5 47.7 40.0 23.3 47.3 49.0 57.9 55.1 45.5 45.5

its cost through optimization of the variables is great. Consequently, we selected certain, and not referred, variables such as remove the bark of tagasaste and a wash temperature and a disintegrate temperature in the organosolv pulping process to optimizate its possible industrial use. The chemical characterizations of both tagasaste wood and bark and other woods are shown in Table 1. As can be seen, tagasaste wood yielded the lowest hot water and 1% NaOH solubles, ethanol-benzene extractives, and ash percentages. On the contrary, holocellulose, R-cellulose, and lignine contents are slightly higher than tagasaste trimmings. These facts could be due to the presence of bark in the trimmings residues. The bark chemical characterization (Table 1) shows high hot water solubles, 1% NaOH solubles, ethanolbenzene extractives, and ash contents. The holocellulose, R-cellulose, and lignine contents show lower values with respect to tagasaste wood. Theses results advise the use of tagasaste trimming without bark to improve pulp properties.

The chemical characteristics of tagasaste trimming wood and eucalyptus wood are similar in ash, holocellulose, lignine, xylan, and acetyl groups. Then, tagasaste wood trimmings could be an adequate raw material for the hydrothermal treatment and pulp and paper making. However, eucalyptus wood could obtain a higher pulping yield due to lower hot water and 1% NaOH solubles with respect to tagasaste wood. Therefore, better physical characteristics of paper sheets obtained from eucalyptus wood could be found due to its higher fiber length.25 3.2. Properties of the Pulp and Paper Sheets Obtained. The standardized values of the independent variables and the properties of obtained cellulose pulps and the paper according to the proposed experimental design are those that appear in Table 2. Each of the shown experimental results (the case of the chemical characteristics of pastes) is an average value of at least 5 or 12 determinations (the case of the physical properties of the sheets). The deviations of each

1878 Ind. Eng. Chem. Res., Vol. 43, No. 8, 2004 Table 3. Equations Yielded for Each Dependent Variablea eq no.

eq

4

YI ) 42.81 - 2.14XT - 1.81XE + 2.08XW + 3.59XD - 2.75Xt - 4.80XW 3.00XD2 - 1.88XTXt + 5.77XTXE - 1.65XTXW - 2.80XTXD 1.37XtXE + 1.24XtXD + 1.40XWXD KI ) 60.0 - 9.2XT - 3.0Xt - 2.5XtXE + 1.8XtXD - 5.8XWXD VI ) 1203.9 + 220.5XT + 150.6Xt - 407.9 Xt2 - 157.9XTXt + 266.1XTXE + 136.2XWXD BR ) 22.8 - 1.83XE - 0.69XE2 - 0.69XW2 - 0.84XTXE - 0.43XTXD + 0.52XtXE - 0.42XtXW - 0.58XtXD + 0.53XEXD + 0.47XWXD SI ) 6.83 + 0.60Xt + 0.48XE + 0.37XW - 0.60XD - 1.47XT2 - 0.48Xt2 0.84XE2 + 1.74XW2 + 0.41XTXt + 0.27XTXW + 0.52XTXD - 0.39XtXE TI ) 47.3 - 2.9XT + 4.5XE - 8.6XT2 - 15.2XE2 + 9.6XD2 + 10.6XTXE + 2.3XWXD

5 6 7 8 9

2

2

r2

F

0.93

12.8

0.95 0.95

90.7 22.9

0.97

58.2

0.97

38.6

0.97

78.9

YI denotes yield (%), KI the kappa number, VI the viscosity BR the brightness (% ISO), SI the tensile index (kN m kg-1), TI the tear index (N m2 kg-1), and XT, Xt, XE, XW, and XD the normalized values of the pulping temperature, time, ethanol concentration, wash temperature, and disintegrate temperature, respectively. The differences between the experimental values and those estimated by using the previous equations never exceeded 10% or 15% (yield) of the former. a

(cm3

g-1),

Figure 1. Variation of dependent variables as a function of normalized independent variables.

one of those parameters with respect to their averages are smaller than 5% in all the cases. Applying a multiple linear regression analysis for each one of the dependent variables of Table 2 as a function of the independent variables, the polynomials mathematical models are obtained (Table 3). These equations can be used to estimate the variation of dependent variables with changes in the independent variables over the ranges considered, on the constancy of the other two variables. Only the terms with statistically significant coefficients are shown according to the proposed methodology.

Identifying the independent variables with the strongest and weakest influence on the dependent variables in equations is not so easy since the former contain quadratic terms and the others involve interactions between two independent variables. Figure 1 shows a plot of each dependent variable against each independent one constructed by changing all the independent variables between the normalized values from -1 to +1. At a given value of an independent variable, the magnitude of the difference between the maximum and minimum values of the dependent variable is related to the influence of the independent

Ind. Eng. Chem. Res., Vol. 43, No. 8, 2004 1879

Figure 2. Variation of yield as a function of time and a wash temperature at two pulping temperature levels.

Figure 3. Variation of viscosity as a function of ethanol concentration and disintegrate temperature at two temperature levels.

variables other than that plotted on the variation of the dependent variable concerned. Thus, if an independent variable plotted had an absolute effect on the dependent variable considered (the independent variables different from those plotted had no effect on the dependent variable considered), then the difference between the maximum and minimum values of the dependent variable in question would be zero (a point in the graphs of Figure 1). Also, if the independent variable plotted had no effect, then the previous difference would coincide with the height of the rectangle having the range of values of the independent variable plotted, [(Xni)max (Xni)min], and the maximum possible difference between the maximum and minimum values of the dependent variable considered, {Z(Xni)max]max - Z[(Xni)min]min}, as its bases. Because the influence of the other variables on the dependent variable considered can vary with each value of the independent variable plotted, the average change in the dependent variable will be given by

∫(X(X ))

ni max

ni min

[Z(Xni)max - Z(Xni)min]dXni [(Xni)max - (Xni)min]

(2)

The change in the dependent variable with that of the independent variable plotted can be assimilated to the difference between [Z(Xni)max]max - Z[(Xni)min]min and the previous expression.26

DZi ) {[Z(Xni)max]max - [Z(Xni)min]min} -

∫(X(X ))

ni max

ni min

[Z(Xni)max - Z(Xni)min]dXni [(Xni)max - (Xni)min]

(3)

Figure 1 also shows the DZi percentages. These values allow one to weigh the relative influences, as percentages, of each independent variable on the variation of each dependent variable.

Figure 4. Variation of the tensile index as a function of ethanol concentration and pulping temperature at two wash temperature levels.

To determine the values of the independent variables giving the optimum yield, viscosity, and tensile index the response surfaces for each dependent variable were plotted at maxima and minima levels of the independent variable most strongly (Figures 2-4). As can be seen in Figure 1, the pulping temperature is the variable most strongly influencing the chemical characteristics of pulps: yield, kappa number, and viscosity, whereas the ethanol concentration is that having the strongest effect on brightness. On the other hand, no independent variable has a strong influence on the physical properties of paper sheets: the tensile

1880 Ind. Eng. Chem. Res., Vol. 43, No. 8, 2004 Table 4. Physical Characteristics for Eucalyptus Globulus and Tagasaste after Similar Ethanol Pulping Conditions eucalyptus globulus Kraft pulp27 temperature (°C) time (min) ethanol concn (% v/v) °SR yield (%) kappa index viscosity (cm3 g-1) tensile index (kN m kg-1) tear index (N m2 kg-1) a

165 90 14 56.6 21 13 15

tagasaste

E-Wa

E-Wa

E-Wa

E-Wa

pulps29-32

pulp27

pulp27

pulp

E-Wa pulp

E-Wa pulp

170-200 40-120 30-70

175 60 50 18-19 74.7

180 60 50 20 66.0

15 27

17 28

175 60 50 11 47.5 74.6 395 4.20 38.7

185 60 50 12.3 38.8 63.9 1020 5.61 47.7

195 60 50 12.5 45.8 55.8 1360 9.6 59.2

51-77.4 7.5-91.6 420-1026 -

E-W, ethanol-water.

(wash temperature) and the tear index (ethanol concentration). The relatively high effect of the disintegration temperature on yield, the kappa index, and the tear index (10.4%, 9.6%, and 7.1%) has been considered to be the consequence of the hydroysis of residual ligninhemicellulose bonds.27 As can be seen from Figure 2 and eq 4, the yield was less influenced by the time and ethanol concentration than by the pulping temperature, and a high positive statistical influence has been found in wash and disintegrate temperatures. The highest yield (YI)58.6%) is obtained at low values of the pulping temperature, high time, and medium wash and disintegrate temperatures. The range yield obtained was higher than that found by Raymond and Masood28 under similar conditions in spruce (56%), beech (48%), aspen (53-58%), and birch (49-52%). The kappa number was thus much more sensitive to changes in the pulping temperature than in the other independent variables. A negative influence (better kappa number) of almost all the dependent variables has been found (eq 5). And then, to produce pulps with a low kappa number, it is advisable to use a high pulping temperature, a long pulping time, and high wash and disintegrate temperatures. In this case, a low ethanol concentration influence on the kappa number variation has been found (Figure 1). The main parameter on viscosity variation is pulping temperature (eq 6). As can be seen in Figure 3, using high ethanol concentration a decrease on viscosity values of high pulping temperature pulps and an increment on the low pulping temperature pulps has been found. That is to say, at high ethanol concentrations, the viscosity values obtained are independent of the pulping temperature and the disintegrate temperature. The viscosity values are high at low values of pulping temperature, ethanol concentration, and high disintegrate temperature. It could be due to highintensity cooking conditions most of the hemicelluloses dissolved, but serious cellulose depolymerization takes place and the viscosity drops, alcohols promote the solvolysis reactions, but they also reduce the viscosity of the pulping liquor, wich makes possible a better penetration and difussion of chemicals into wood chips.19 Therefore, both the average molecular weight of the cellulose obtained and the viscosity values decrease.19 At high pulping temperatures values, the viscosity of pulps builds up in direct proportion to the organic solvent concentration showing the inhibition of intermolecular cellulose chain scission reactions caused by alkaline hydrolysis.11 It is therefore advisable to operate under low operating conditions in order to obtain suitable viscosity values.

Brightness accuses a very important influence of the ethanol concentration (45.5%) in that it annuls the relative influence of the remainder of the variables. It can be due to the influence of its linear, quadratic, and interactions terms (eq 7). Almost all the ethanol terms present a negative influence for the values of brightness, and then the production of a relatively high brightness pulp is favored by low ethanol concentration in the pulping liquor. With respect to the physical characteristics of the sheets of paper, the relative influences of the variables are different among them. The wash temperature appears as the most independent variable on the tensile index evolution (Figure 4). In that case, high values in the wash temperature and medium values in the ethanol concentration and pulping temperature ensure, in the range considered, optimum values of the tensile index. Eq 9 can be used to estimate the variation of the tear index with changes in the independent variables over the ranges considered. The maximum variation of the tear index is obtained by changing the ethanol concentration and the pulping temperature (Figure 1). The minimum is obtained by altering the time. The pulping temperature accuses a negative linear influence on the tear index variation, thereby ensuring a high tear index using a low pulping temperature. The ethanol concentration accuses a positive linear influence, but, on the other hand, a negative quadratic influence has been found. As a result, by using a medium ethanol concentration high levels on the tear index could be obtained. Comparative characteristics for Eucalyptus globulus and Tagasaste after similar ethanol pulping conditions have been done (Table 4). In that table, similar values in yield, the kappa index, and viscosity have been found by Pereira,27 Oliet,29,30 Gilarranz,31 and Botello.32 Pereira27 also shows other physical characteristics. In that study it is shown that strength-related properties of ethanol pulps are higher for the kraft pulp; however, properties of beaten pulps are appreciably higher than the kraft pulps. In that form, under lower unbeaten °SR, the tensile index for tagasaste is 56% lower than those for eucalyptus; however, the tear index is 47% higher than that for eucalyptus. 4. Conclusions The chemical characteristics of tagasaste trimming wood and eucalyptus wood are similar in ash, holocellulose, lignine, xylan, and acetyl groups. Then, tagasaste wood trimmings could be an adequate raw material for hydrothermal treatment and pulp and paper making. Under similar conditions offer similar paper physical values than eucalyptus wood.

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The ethanol pulping could be an adequate process for tagasaste wood trimmings. Pulping temperature has a high influence on the greater number of the dependent variables except for brightness, the tensile index, and the tear index. An increment in pulping temperature has a positive effect on the kappa index and viscosity values. However, it has a negative effect on the yield. The ethanol concentration has a high negative influence on brightness. Using high (200 °C) or medium (185 °C) pulping temperatures and ethanol concentration (6080%), suitable physical characteristics of paper sheets and acceptable yield, the kappa index and viscosity could be obtained. As can be seen, wash and disintegrate temperatures have an influence on all the dependent variables, especially on yield and the tensile index. A high wash temperature and a disintegrate temperature must be used in order to ensure that the pulp and the resulting paper sheets will possess optimal properties. Therefore, ensuring an optimal pulp processing entails using a high wash temperature (70 °C) and a disintegrate temperature (70 °C) as well as a medium (90 min) pulping time. Acknowledgment The authors are grateful to ENCE (Huelva) for their support, and to Junta de Andalucı´a and DGICYT for funding this research within the framework of the Projects III PAI ACC-109-RNM-2001 and PPQ20012489-C03-02. Literature Cited (1) Schroeter, M. C. Possible lignin reactions in the Organocell pulping process. Tappi J. 1991, 74(10), 197-200. (2) Akhtar, M.; Scott, G. M.; Swaney, R. E.; Kirk, T. K. Overview of Biomechanical and Biochemical Pulping Research. In Enzyme Applications in Fiber Processing; Eriksson, K. L., CavacoPaulo A., Eds.; American Chemical Society: Washington, DC, U.S.A., 1998; pp 15-26. (3) Aziz, S.; Goyal, G. C. Kinetics of delignification from mechanistic and process control point of view in solvent pulping processes. Pulping Conference Proc.; Atlanta, GA, 1993; Vol. 3, pp 917-920. (4) Sierra-Alvarez, R.; Tjeerdsma, B. F. Organosolv pulping of wood from short rotation intensive culture plantations. Wood Fiber Sci. 1995, 27(4), 395-401. (5) Young, R. A. Comparison of the properties of chemical cellulose pulps. Cellulose 1994, 1(2), 107-130. (6) McDonough T. J. The chemistry of organosolv delignification. Tappi J. 1993, 76(8), 186-193. (7) Balogh, D. T.; Curvelo, A. A. S.; De Groote, R. A. M. C. Solvent effects on Organosolv lignin from Pinus caribea hondurensis. Holzforschung 1992, 46(4), 343-348. (8) Parajo´, J. C.; Alonso, J. L.; Va´zquez, D.; Santos, V. Optimization of catalysed acetosolv fractionation of pine wood. Holzforschung 1993, 47(3), 188-196. (9) Tjeerdsma, B. F.; Zomers, F. H. A.; Wilkison, E. C.; SierraAlvarez, R. Modeling organosolv pulping of hemp. Holzforschung 1994, 48(5), 415-422. (10) Jime´nez, L.; Pe´rez, I.; Garcı´a, J. C.; Rodrı´guez, A.; Ferrer, J. L. Influence of ethanol pulping of wheat straw on the resulting paper sheets. Process Biochem. 2002, 37(6), 665-672. (11) Shatalov, A. A.; Pereira, H. Carbohydrate behaviour of Arundo donax L. in ethanol-alkali medium of variablenext term composition during organosolv delignification. Carbohydr. Polym. 2002, 49(3), 331-336. (12) Snook, L. C. Tagasaste (Tree lucernes): Chamaecytisus palmensis: a shrub with high potential as a productive fodder crop. J. Aust. Inst. Agric. Sci. 1982, 18, 125-128.

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Resubmitted for review November 10, 2003 Revised manuscript received November 10, 2003 Accepted February 2, 2004 IE030611A