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Acetosolv pulping for the fractionation of empty fruit bunches from palm oil industry
Bioresource Technology 132 (2013) 115–120
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Acetosolv pulping for the fractionation of empty fruit bunches from palm oil industry A. Ferrer a, A. Vega b, A. Rodríguez a, L. Jiménez a,⇑ a b
Chemical Engineering Department, Campus of Rabanales, Building Marie Curie (C-3), University of Córdoba, 14071 Córdoba, Spain Department of Physical Chemistry and Chemical Engineering, University of A Coruña, 15071 A Coruña, Spain
h i g h l i g h t s " The most important aspects of this work focuses on. " Acetosolv pulping of Empty Fruit Bunches. " Us of polynomial models to reproduce the experimental results. " Optimum operating conditions were found.
a r t i c l e
i n f o
Article history: Received 8 May 2012 Received in revised form 26 December 2012 Accepted 28 December 2012 Available online 11 January 2013 Keywords: Acetosolv Acetic acid EFB Pulp Fractionation
a b s t r a c t Influence of operational variables in the EFB pulping [acetic acid (60–95%), hydrochloric acid (0.10–0.25%) and time (60–180 min)], on the yield, drainability or beating grade, Kappa number, lignin and viscosity of pulps was studied. By using a factorial design, equations were obtained that reproduced the experimental results for the dependent variables with errors less than 9–18%. These equations can be used to find the suitable conditions, so that operating with not too high values of operating variables (with minor costs of operation and capital) pulps with acceptable properties could be obtained: operating with 86.25% acetic acid, 0.25% hydrochloric acid and 120 min time, produced pulps with 46.56% yield, 15.9 °SR drainability, 36.3 Kappa number, 10.3% lignin and 303 mL/g viscosity, values all of them close to the optimal predicted. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Vegetable biomass has been for centuries a resource used by humanity worldwide, for energy and cellulosic pulp production. Recently, biomass has lost its value as an energy source based on the discovery of other sources more profitable, and only the field of pulp and paper continued using large amounts of lignocellulose. However, the production of paper pulp has traditionally been a highly polluting process. The vast majority of paper pulp mills still use the Kraft method, based on the action of a strongly alkaline solution of sulphur compounds on vegetable fibers. Organosolv methods use organic compounds of relatively low molecular weight as delignification agents, and are a good alternative to Kraft due to the elimination of the sulphur compounds in cooking. The researchers have achieved the delignification of plant tissues of all kinds using representative agents of a wide sample of the organic functional groups: alcohols, ketones, aldehydes, phenols, amines, amides, carboxylic ⇑ Corresponding author. E-mail address: [email protected] (L. Jiménez). 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.12.189
acids (López et al., 2006; Rodríguez and Jiménez, 2008). Although lignin removal can be achieved with high efficiency, in some cases, the physical properties of the paper sheets from these pulps were lower compared to those of Kraft pulps. Therefore, these pulps may be applied to the manufacture of special papers or obtaining high purity cellulose, with a possible final destination as dissolving pulps (Sixta et al., 2004; Vila et al., 2004), microcrystalline cellulose (Shansan et al., 2011), microfibrillated cellulose (Serrano et al., 2011) or bioethanol (Requejo et al., 2011), for example. Some of organosolv processes may be performed at atmospheric pressure and therefore at a low temperature, which results in a decreased severity of treatment and, consequently, a reduced formation of degradation compounds from sugars and lignin. This is of particular interest in the concept of the biorefinery, reinvigorated in recent years and it pretends to use the main components of the biomasses (Demirbas, 2009; Kamm and Kamm, 2004). Short chain carboxylic acids are among the organics that can carry out the fractionation. Acetic acid has been extensively investigated as delignification and/or fractionation agent. Nimz et al. published the first works in the 80’s on the process named
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Acetosolv, who succeeded to pulp pine, spruce, and beech wood (Nimz and Casten, 1986; Nimz et al., 1989). The Acetosolv process uses acetic acid enriched (70–90% by weight) aqueous mixtures with the addition of small amounts of hydrochloric acid (typically 0.1–0.2% by weight) which contributes to enhance the delignification through partial hydrolysis and solubilisation of hemicelluloses and lignin. When pulping variables are appropriately chosen the resulting pulps can show very low lignin content (Ligero et al., 2005) leaving a solid residue with high cellulose content (Villaverde et al., 2010). Additionally, acetosolv pulps could be easily bleached with TCF sequences including ozone, hydrogen peroxide, oxygen, and peroxyacetic acid (Dapia et al., 2003; Vila et al., 2004; Villaverde et al., 2011). Oil palm empty fruit bunches (EFB) is a waste generated by the palm oil industry after the separation of the fruits for oil extraction. This residue, which in many countries, especially in Malaysia and Indonesia, is produced in very high levels, is simply used as mulch, burnt for energy production or even burnt in the plantations without any profit. Due to its high production and uniformity resulting from the use of specific plant species EFB may not only be a waste but an important resource for obtaining various high-value products through chemical processing (Noor et al., 1998–2000). Shibata studied the chemical composition of EFB, and other parts of the oil palm, finding very similar amounts of cellulose and hemicelluloses and a lignin composed only by syringyl and guaiacyl units (Shibata et al., 2008). EFB has been subjected to a number of treatments in order to take advantage of this residue. An hydrothermal treatment was utilized in order to obtain sugars and proved to enhance the enzymatic digestibility of the solid residue (Shamsudin et al., 2012), which was studied by a mixture of cellulase and b-1,4-glucosidase (Hamzah et al., 2011). An acidtreatment removed 90% of the hemicelluloses and 32% of the lignin, but left most of the cellulose, and a second alkali-treatment reached a 70% delignification yield (Kim et al., 2012). Different pulping methods were applied to EFB. The effects of soda and soda-AQ pulping variables, even reinforced with hydrogen peroxide, have been studied by means of factorial experimental designs over yield, Kappa number, tensile and tear index (Wanrosli et al., 2004) or Kappa number, pulp viscosity, brightness and a selectivity measured as the ratio between the Kappa number reduction over the brightness increase (Ng et al., 2011). Oxygen bleaching as the first stage of a bleaching sequence was optimized for soda pulps obtained after a previous autohydrolysis step (Leh et al., 2008) and a complete TCF bleaching sequence applied to soda-AQ pulps was also reported (Jiménez et al., 2009). Among organosolv pulping methods EFB was subjected to pulping with organic solvents with a high boiling temperature (ethyleneglycol, diethyleneglycol, ethanolamine and diethanolamine), showing the pulps from amines to have better properties than the ones from glycols. (Rodríguez et al., 2008b). Solvents with lower boiling point were also tested to treat EFB. Formic acid (Ferrer et al., 2011b) and peroxyformic acid (Milox process) (Ferrer et al., 2011a) treatments were simulated by means of polynomial and neural fuzzy models. Their optimization predicted similar pulp properties values for both processes, but a higher brightness in the Milox pulp, while liquor characteristics diverged much more as no lignin could be precipitated from Milox liquor. To our knowledge only one study on Acetosolv treatment of oil palm has been published (Wanrosli et al., 2011) but applied to the leafy part (frond) of the tree. Therefore, the aim of this work was to study the Acetosolv treatment of palm oil empty fruit bunches by means of an experimental design factor, considering the influence of the operational variables on the composition of the resulting pulp, with the aim of finding the optimum conditions of operation to obtain a pulp for specialty papers or other applications such as
obtaining microcrystaline cellulose, microfibrillated cellulose or bioethanol by simultaneous saccharification and fermentation. 2. Experimental 2.1. Raw material In this work, EFB from African palm (Elaeis guineensis) was used. Each hectare of oil palm produces an average of 10 tons of fruits per year which give about 3000 kg of palm oil (the main product) and similar amount of EFB (Ferrer et al., 2011b). 2.2. Raw material characterization The chemical properties of EFB were determined in accordance with the respective Tappi standards for the different components, namely: T-9m 54 for holocellulose, T222 for lignin, T203 0S-61 for a-cellulose, T257 for hot-water solubles, T212 for 1%-NaOH solubles, T204 for ethanol–benzene extractives and T211 for ash. The fiber length distribution of EFB was determined by using a Visopan projection microscope (Ferrer et al., 2011b). 2.3. Pulping Mixtures of EFB, water and acetic acid (proportions ranging from 60% to 95% by weight of liquor) were heated to the boiling point in glass Pyrex flasks. Hydrochloric acid was added (0.10–0.25% by weight of liquor) when boiling started (zero time), and mixtures were maintained at total reflux with stirring for different times (60–180 min) at atmospheric pressure. After the reaction, the pulps were separated by filtration and the solids washed with concentrated acetic acid solutions (80% w) in order to avoid the deposition of the dissolved lignin on pulp. Finally the pulps were treated with water until neutrality and let to dry at room temperature (Ligero et al., 2005). 2.4. Pulps characterization For all experiments the main parameters defining delignification and pulping were measured, as follows: pulp yield after oven drying of a pulp aliquot to constant weight, Kappa number as per TAPPI T236, lignin content as per TAPPI T222, drainability or beating grade (Shopper-Riegler index) as per UNE 57-025, and intrinsic viscosity as per T230. 2.5. Experimental design A second order factorial design of experiments was used (Montgomery, 1991) consisted in a central experiment (in the centre of a cube) and several additional points (additional experiments lying at the cube vertices and side centers). Experimental data were fitted to a second-order polynomial. The values of the operational variables were normalized to values from 1 to +1 by using the following expression:
X n ¼ 2ðX X m Þ=X max X min
ð1Þ
where Xn is the normalized value of acetic acid concentration (A), hydrochloric acid concentration (H) or processing time (T); X is the actual experimental value of the variable concerned; Xm is the mean of Xmax and Xmin; and Xmax and Xmin are the maximum and minimum value, respectively, of such a variable. The normalized values for the independent variables in the 15 experiments conducted are given in Table 2.
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A. Ferrer et al. / Bioresource Technology 132 (2013) 115–120 Table 1 Chemical properties of various alternative raw materials and eucalyptus and pine. Analysis (%)
HWS (%)
1% S (%)
EEB (%)
ASH (%)
HOL (%)
a-CE (%)
HEM (%)
EFB Eucalyptus globulus Pinus pinaster Olive prunings Jiménez et al. (1990) Wheat straw Jiménez et al. (1990) Sunflower stalks Jiménez et al. (1990) Sorghum stalks Jiménez et al. (1993) Sugarcane bagasse Jiménez et al. (2005) Retama monosperma Jiménez et al. (2005) Phragmites Jiménez et al. (2005) Arundo donax Jiménez et al. (2005) Prosopis julyflora Jiménez et al. (2005) Prosopis alba Jiménez et al. (2005) Paulownia fortunei Jiménez et al.,(2005) Leucaena diversifolia Jiménez et al. (2006) Leucaena colinsii Jiménez et al. (2006) Leucaena leucocephala (Honduras) Jiménez et al. (2006) Leucaena leucocephala (India) Jiménez et al. (2006) Tagasaste(Australia) Jiménez et al. (2006) Tagasaste (New Zealand) Jiménez et al. (2006) Tagasaste (Island of La Palma, Spain) Jiménez et al. (2006) Vine shoots Jiménez et al. (2006) Cotton stalks Jiménez et al. (2006) Rice straw Rodríguez et al. (2008a)
4.03 2.84 1.99 8.16 12.27 22.72 21.7 4.4 3.84 5.38 4.73 6.49 4.67 9.6 3.24 4.30 5.01 3.98 2.96 2.99 2.41 16.09 3.33 16.57
40.22 12.42 7.89 30.04 43.58 47.81 45.58 33.92 16.93 34.77 26.80 22.56 20.86 31.5 17.38 20.02 20.26 18.44 15.55 16.15 16.62 39.21 20.34 46.94
1.17 1.15 2.57 10.36 4.01 4.07 7.99 1.73 5.03 6.36 7.30 5.30 4.65 5.50 4.44 4.64 6.01 4.64 2.17 3.43 3.30 4.87 1.42 1.4
3.2 0.57 0.54 1.36 6.49 7.9 4.85 2.1
66.97 80.47 69.59 61.47 76.2 71.76 65.93 80.2 71.76 64.16 70.20 62.77 63.56 70.7 77.88 80.79 74.11 75.92 82.16 75.36 76.47 67.14 72.86 70.6
47.91 16.96 26.22 35.67 39.72 42.1 41.5
52.79 55.92 25.8 36.48 29.66 24.43
42.75 39.76 40.46 36.55 41.55 37.40 40.10 43.77 41.21 44.43 47.65 43.59 44.99 41.14 58.48
26 14.38
3.49 2.17 15.3
LIG (%) 24.45 27.68 13.67 19.71 17.28 13.44 15.64 19.8 21.50 23.66 22.34 20.60 19.27 22.4 19.09 17.04 19.39 21.43 15.71 14.84 14.10 20.27 21.45 25.23
HWS: hot water solubles; 1% S: 1% soda solubles; EEB: extractives in ethanol–benzene; ASH: ash; HOL: holocellulose; a-CE: a-cellulose; HEM: hemicellulose; LIG: lignin. The values of the various parameters are averages of three determinations whose deviations from these average values are less than 5%.
Table 2 Values of operational variables and experimental values of the properties of pulp obtained by Acetosolv pulping of EFB. A (%)
H (%)
T (min)
XA, XH, XT (%)
Yield (°SR)
Beating grade number
Kappa (%)
Lignin (mL/g)
Viscosity
77.5 95.0 60.0 95.0 60.0 95.0 60.0 95.0 60.0 77.5 77.5 77.5 77.5 95.0 60.0
0.175 0.25 0.25 0.25 0.25 0.10 0.10 0.10 0.10 0.25 0.10 0.175 0.175 0.175 0.175
120 180 180 60 60 180 180 60 60 120 120 180 60 120 120
0, 0, 0 +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,+1, 0 0.1, 0 0, 0,+1 0, 0,1 +1,0, 0 1, 0, 0
58.58 41.31 52.27 46.41 67.26 75.44 74.40 83.21 84.29 47.35 74.81 54.91 63.22 51.80 67.59
17 14 19 12 13 13 18 12 14 18 13 18 13 13 17
55.5 41.1 58.0 32.2 71.0 77.7 75.8 73.6 69.3 39.7 70.0 51.3 55.8 47.6 76.8
13.5 11.1 11.6 8.9 15.4 16.6 16.3 15.9 16.3 9.8 15.9 13.1 15.3 10.8 16.1
283 306 384 226 291 185 302 183 213 345 262 297 312 251 318
A: acetic acid concentration; H: hydrochloric acid concentration; T: processing time; XA: normalized value of A; XH: normalized value of H; XT: normalized value of T. The values of the parameters are averages of three determinations whose deviations from these average values are less than 5–10%.
3. Results and discussion 3.1. Chemical characterization of EFB Table 1 shows the results of the chemical analysis of the EFB, eucalyptus wood and pine wood, and various non-wood alternative raw materials, as agricultural residues (olive prunings, wheat straw, sunflower stalks, sorghum stalks, rice straw, sugarcane bagasse, vine shoots and cotton stalks) and other vegetables (Jiménez et al., 1990, 1993, 2005 and Jiménez et al., 2006; Rodríguez et al., 2008a). A comparison of the data for EFB with those of the other raw materials reveals the following. The content in hot water solubles of EFB is similar to that of bagasse and cotton stalks, but lower than those of the other alternative raw materials – except paulownia and Prosopis julyflora – pine and eucalyptus wood. The content in 1% NaOH solubles of EFB is higher than those of olive
prunings, bagasse, cotton stalks, the alternative raw materials, and pine and eucalyptus wood, but similar to those of the other agricultural residues studied. The content in ethanol–benzene extractives of EFB is similar to those of rice straw, bagasse, cotton stalks, and pine and eucalyptus wood, but lower than those of the other agricultural residues and the alternative raw materials. The ash content of EFB is higher than those of olive prunings, bagasse and cotton stalks, similar to those of the other agricultural residues and much higher than those of pine and eucalyptus wood. The holocellulose content of EFB is higher than those of olive prunings and sorghum stalks, similar to those of vine shoots and lower than those of the other agricultural residues (wheat straw, sunflower stalks and cotton stalks); also, it is higher than those of Phragmites and P. julyflora, lower than those of the other raw materials, and in between those of pine and eucalyptus wood. The lignin content of EFB is higher than those of the agricultural residues, alternative
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raw materials and eucalyptus wood, but lower than that of pine wood.
3.2. Physical characterization of EFB fibers The maximum, average and minimum values of fibers length were 1.48, 0.53 and 0.27 mm, respectively, and the maximum, average and minimum thickness or width were 26, 14 and 8 lm. A study of the length distribution curve showed that fibers having a size of 0.50–0.70 mm were the most abundant. The average length of the EFB fibers (0.53 mm) is lower than that of other raw materials: wheat straw (1.14 mm), sorghum stalks (1.32 mm), olive pruning (1.03 mm), sunflower stalks (1.30 mm), vine shoots (0.79 mm), cotton stalks (1.03 mm), Eucalyptus globulus (1.05 mm) and Pinus pinaster (2.50 mm).
3.3. Pulping of EFB First, a set of previous experiments was carried out, based on the results of other researchers on different raw materials, in order to define the ranges of operating variables. In this way the following ranges were chosen: acetic acid concentration from 60% to 95% by weight, hydrochloric acid concentration, which acts as a catalyst, from 0.10% to 0.25% by weight, and processing time from 60 to 180 min. Always operating at the boiling point and with the same liquid/solid ratio (10:1 by weight). Table 2 shows the experimental values of the pulp properties, which differed by less than 5–10% from their means as obtained in triplicate measures. The experimental results were fitted to a polynomial model by multiple regression using the software BMDPÓ. The terms possessing a Snedecor F-value greater than 6 and a Student t-value greater than 2.5 were deemed statistically significant. Equations found, as well as the lowest Snedecor-F value, the highest p value and the lowest Student t-value for the terms, are found in the Table 3. The predictions of the previous equations reproduced the experimental results for the dependent variables with errors lower than 9% for yield, 17% for beating grade, 17% for Kappa number, 18% for lignin content and 16% for viscosity of pulps. The values of the operational variables providing the best pulp properties (yield, beating grade, Kappa number, lignin content and viscosity) were identified by using equations of Table 3 and Figs. 1 and 2 and other similar. Table 4 shows the optimum values of the dependent variables and those of the operational variables required to obtain them. The polynomial equations allowed the identification of the more influencing operational variables on the pulp properties. The maximum variations in the dependent variables with changes in the operational variables over the studied range were obtained by altering one independent variable at a time while keeping all others constant. The results are shown in Table 4 together with the maximum percent differences in the dependent variables from their optimum values over the studied variation ranges.
Fig. 1. Yield pulp vs. hydrochloric acid concentration and time, at low acetic acid concentration.
Fig. 2. Yield pulp vs. acetic acid concentration and time, at low hydrochloric acid concentration.
The maximum yield (83.87%) corresponded to low values of operating variables. The hydrochloric acid concentration influences on pulp yield more significantly than the process time (Fig. 1), while the latter variable affects more than the concentration of acetic acid (Fig. 2). The maximum beating grade (18.4 °SR) occurs when the concentration of acetic acid is low and the processing time long, being the most influential variable this last one. The Kappa number increased more sharply with the hydrochloric acid concentration than with acetic acid concentration. The
Table 3 Coefficients of the polynomial equations, and the lowest Snedecor-F value, the highest p value and the lowest Student-t value. Dependent variables
Yield Beating grade Kappa number Lignin Viscosity
Values of the constants in the polynomial equations
Values of
ao
a1
a2
a3
a11
a12
a22
F>
>p
t>
59.22 14.9 54.5 13.8 300
4.46 1.7 7.9 1.2 36
13.76 – 12.4 2.4 41
4.61 1.8 – – 25
– 7.9 – 34
3.97 – 7.7 – –
5.46 – – – –
10.56 11.70 6.88 6.83 10.56
0.010 0.005 0.025 0.023 0.010
3.25 3.42 2.62 2.61 3.25
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Table 4 Optimal properties in pulp obtained by acetic acid pulping of EFB. Maximum changes in the dependent variables with changes in one operational variable on constancy of the others (the percent differences from the changes are given in brackets). Dependent variable
Optimum (maximum or minimum⁄) value of dependent variable
Values of the operational variables required to obtain the optimum values of dependent variables XA XH XT
Yield (%)
83.87 36.58⁄ 18.4 34.4⁄ 10.2 376
1 +1 1 +1 +1 0.52
Beating grade (°SR) Kappa (number) Lignin (%) Viscosity (mL/g)
1 +1 – +1 +1 +1
1 +1 +1 – – +1
Maximum variation of dependent variable with operational variable Acetic acid
Hydrochloric acid
Time
1.58 (1.88%)
19.64 (23.43%)
9.22 (11.00%)
3.4 (18.48%) 31.2 (90.70%) 2.4 (23.5%) 80 (21.28%)
– 40.2 (116.86%) 4.8 (47.1%) 82 (21.81%)
7.0 (38.04%)
50 (13.30%)
Fig. 3. Yield/Kappa ratio vs. acetic acid concentration and time, at high hydrochloric acid concentration.
Fig. 4. Yield/Kappa ratio vs. hydrochloric acid concentration and time, at high acetic acid concentration.
minimum Kappa number (34.4) was obtained when hydrochloric acid concentration and acetic acid concentration were high. The lignin content has a parallel behaviour, with a minimum value of 10.2% for when the concentrations of the two acids are high, being the most influential variable the hydrochloric acid concentration. The viscosity was maximum (376 mL/g) when operating with medium–low level of acetic acid concentration and high values of processing time and hydrochloric acid concentration. Process time has minor influence on the viscosity that the acetic acid concentration, while hydrochloric acid concentration is the most influential variable.
time, and processing time and hydrochloric acid concentration, respectively, for high hydrochloric acid concentration and for high acetic acid concentration. Considering the ‘‘Viscosity/Kappa’’ ratio (which is also desirable to be high), adjusting the experimental data to a polynomial model gives the equation:
3.4. Optimum operating conditions Considering the ‘‘Yield/Kappa’’ ratio (which is desirable to have a maximum value), adjusting the experimental data to a polynomial model gives the equation:
Yield=Kappa ¼ 1:07 þ 0:07X A þ 0:09X A X H 0:10X T ðF > 6:34; p < 0:029; t > 2:52Þ
ð2Þ
The values of the operational variables providing the maximum ‘‘Yield/Kappa’’ were identified by using Eq. (2): the maximum value is 1.33, for which the acetic acid concentration is high (95%), hydrochloric acid concentration is high (0.25%) and the processing time is short (60 min). Figs. 3 and 4 shows the dependence of the ‘‘Yield/Kappa’’ ratio on acetic acid concentration and processing
Viscosity=Kappa ¼ 5:73 0:39X A X T þ 0:40X T 1:08X 2A þ 0:74X A X H þ 1:85X H
ðF > 2:73; p < 0:13; t > 1:65Þ
ð3Þ
Operating in a similar way as in Eqs. (2) and (3) predicts the maximum value of the ‘‘Viscosity/Kappa’’ ratio of 8.01, for the following operating conditions: high values of hydrochloric acid concentration (0.25%) and processing time (180 min), and medium–high acetic acid concentration (80.30%). Similar figures to 3 and 4 shows the dependence of the ‘‘Viscosity/Kappa’’ on hydrochloric acid concentration and acetic acid concentration for long processing time, and acetic acid concentration and the processing time for a high hydrochloric acid concentration. To save chemicals, energy, and immobilized capital on industrial facilities is necessary to use lower acetic acid and hydrochloric acid concentrations and shorter processing times, than the values considered in the previous paragraph. The equations of Table 3 and data of Table 4 can be used to select values of the operational variables providing near-optimal pulp properties while saving chemicals, energy and immobilized capital by using lower values of some of the operational variables. One combination leading to near-optimal properties with reduced costs with properties is
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using a processing time of 120 min, an acetic acid concentration of 86.25% and a hydrochloric acid concentration of 0.25%. Operating under these conditions the following values for the dependent variables were obtained: yield 46.56%, beating grade 15.9 °SR, Kappa number 36.3, lignin 10.3% and viscosity 303 mL/g; these values deviate by 44.5%, 13.6%, 5.5%, 5.9% and 18.6%, respectively of the maximum values of yield, beating grade, Kappa number, lignin content and viscosity. Operating under these conditions the values obtained for the ratios ‘‘Yield/Kappa’’ (1.15) and ‘‘Viscosity/Kappa’’ (7.68) are very near from the optimum predicted by the corresponding regression equations. 4. Conclusions Acetosolv pulping can be a stage in the EFB fractionation. The pulp obtained has low viscosity, but can be used for specialty papers, microcrystalline-cellulose, microfibrillated-cellulose, or bioethanol by simultaneous saccharification–fermentation. Polynomial equations obtained by multiple regression can be used to find the suitable conditions that, operating with not too high values of operational variables (minor operational and capital costs), procedure pulps with acceptable properties. Specifically, operating at 86.25% acetic acid, 0.25% hydrochloric acid and 120 min time, pulps with 46.56% yield, 15.9 °SR drainability, 36.3 Kappa number, 10.3% lignin and 303 mL/g viscosity were obtained; all these values are close to the optimal. Acknowledgements The authors are grateful to Ecopapel, S.L. (Écija, Seville, Spain) for their support, and to Spain’s DGICyT and Junta of Andalucía for funding this research within the framework of the Projects CTQ-2010-19844-C02-01 and TEP-6261. References Dapia, S., Sixta, H., Borgards, A., Harms, H., Parajo, J.C., 2003. TCF bleaching of hardwood pulps obtained in organic acid media for production of viscose-grade pulps. Holz als Roh- und Werkstoff 61, 363–368. Demirbas, A., 2009. Biorefineries: current activities and future developments. Energy Convers. Manage. 50, 2782–2801. Ferrer, A., Vega, A., Rodríguez, A., Ligero, P., Jiménez, L., 2011a. Milox fractionation of empty fruit bunches from Elaeis guineensis. Bioresour. Technol. 102, 9755–9762. Ferrer, A., Vega, A., Ligero, P., Rodríguez, A., 2011b. Pulping of empty fruit bunches (EFB) from the palm oil industry by formic acid. Bioresources 6, 4282–4301. Hamzah, F., Idris, A., Shuan, T.K., 2011. Preliminary study on enzymatic hydrolysis of treated oil palm (Elaeis) empty fruit bunches fiber (EFB) by using combination of cellulase and b-1-4 glucosidase. Biomass Bioenergy 35, 1055–1059. Jiménez, L., López, F., Martínez, C., 1993. Paper from sorghum stalks. Holzforschung 47, 529–533. Jiménez, L., Pérez, A., de la Torre, M.J., Moral, A., Serrano, L., 2006. Characterization of vine shoots, cotton stalks, Leucaena leucocephala and Chamaecytisus proliferus, and of their ethyleneglycol pulps. Bioresour. Technol. 98, 3487–3490. Jiménez, L., Rodríguez, A., Ferrer, J.L., Pérez, A., Angulo, V., 2005. Paulownia, a fastgrowing plant, as a raw material for paper manufacturing. Afinidad 62 (516), 100–105.
Jiménez, L., Sánchez, I., López, F., 1990. Characterization of Spanish agricultural residues with a view to obtaining cellulose pulp. Tappi J. 73 (8), 173–176. Jiménez, L., Serrano, L., Rodríguez, A., Ferrer, A., 2009. TCF bleaching of sodaanthraquinone and diethanolamine pulp from oil palm empty fruit bunches. Bioresour. Technol. 100, 1478–1481. Kamm, B., Kamm, M., 2004. Principles of biorefineries. Appl. Microbiol. Biotechnol. 64, 137–145. Kim, S., Park, J.M., Seo, J.W., Kim, C.H., 2012. Sequential acid/alkali-pretreatment of empty palm fruit bunch fiber. Bioresour. Technol. 109, 229–233. Leh, C.P., Wan Rosli, W.D., Zainuddin, Z., Tanaka, R., 2008. Optimisation of oxygen delignification in production of totally chlorine-free cellulose pulps from oil palm empty fruit bunch fibre. Ind. Crops Prod. 28, 260–267. Ligero, P., Vega, A., Bao, M., 2005. Acetosolv delignification of Miscanthus sinensis bark influence of process variables. Ind. Crops Prod. 21, 235–240. López, F., Alfaro, A., Jiménez, L., Rodríguez, A., 2006. Alcohols as organic solvents for obtainment of cellulose pulp. Afinidad 63 (523), 174–182. Montgomery, D.C., 1991. Design and analysis of experiments. Grupo Editorial Iberoamericana, Mexico, p. 303. México. Ng, S.H., Ghazali, A., Leh, C.P., 2011. Anthraquinone-aided hydrogen peroxide reinforced oxygen delignification of oil palm (Elaeis guineensis) EFB pulp: a twolevel factorial design. Cellul. Chem. Technol. 45, 77–87. Nimz, H.H., Casten, R., 1986. Chemical processing of lignocellulosics. Holz als Rohund Werkstoff 44, 207–212. Nimz, H.H., Berg, A., Granzow, C., Casten, R., Muladi, S., 1989. Pulping and bleaching by the Acetosolv process. Papier 43, 102–108. Noor, M., Azemi, M., Sarip, H., 1998–2000. Oil palm (Elaeis guineensis) wastes as a potential source of cellulose. Cellulosic Pulps, Fibres and Materials, [International Cellucon Conference. In: Kennedy, John F., Pulp for Papermaking: Fibre and Surface Properties and Other Aspects of Cellulose Technology], 10th, Turku/Abo, Finland, Dec. 14–17. Requejo, A., Peleteiro, S., Rodríguez, A., Garrote, G., Parajó, J.C., 2011. Secondgeneration bioethanol from residual woody biomass. Energy Fuels 25, 4803– 4810. Rodríguez, A., Jiménez, L., 2008. Pulping with organic solvents other than alcohols. Afinidad 65 (535), 188–196. Rodríguez, A., Moral, A., Serrano, L., Labidi, J., Jimérnez, L., 2008a. Rice straw pulp obtained by using various methods. Bioresour. Technol. 99, 2881–2886. Rodríguez, A., Serrano, L., Moral, A., Pérez, A., Jiménez, L., 2008b. Use of high-boiling point organic solvents for pulping oil palm empty fruit bunches. Bioresour. Technol. 99, 1743–1749. Serrano, L., Urruzola, I., Nemeth, D., Belafi-Bakob, K., Labidi, J., 2011. Modified cellulose microfibrils as benzene adsorbent. Desalination 270, 1–3. Shamsudin, S., Shah, U.K.Md., Zainudin, H., Abd-Aziz, S., Kamal, S.M.M., Shirai, Y., Hassan, M.A., 2012. Effect of steam pretreatment on oil palm empty fruit bunch for the production of sugars. Biomass Bioenergy 36, 280–288. Shansan, L., Fang, G., Deng, Y., Wang, W., 2011. Preparation of microcrystalline cellulose from cotton linter ethanol pulp. Adv. Mater. Res. 295–297, 653– 658. Shibata, M., Varman, M., Tono, Y., Miyafuji, H., Saka, S., 2008. Characterization in chemical composition of the oil palm (Elaeis guineensis). J. Japan Inst. Energy 87, 383–388. Sixta, H., Harms, H., Dapia, S., Parajo, J.C., Puls, J., Saake, B., Fink, H.P., Roeder, T., 2004. Evaluation of new organosolv dissolving pulps. Part I: Preparation, analytical characterization and viscose processability. Cellulose 11, 73–83. Vila, C., Santos, V., Parajo, J.C., 2004. Dissolving pulp from TCF bleached acetosolv beech pulp. J. Chem. Technol. Biotechnol. 79, 1098–1104. Villaverde, J.J., Ligero, P., Vega, A., 2010. Highly purified pulps from Miscanthus x giganteus. A comparative study of a new TCF bleaching sequence applied to organosolv pulps. Afinidad 67, 123–128. Villaverde, J.J., Ligero, P., Vega, A., 2011. Applicability of short totally chlorine free bleaching sequences to Miscanthus x giganteus organosolv pulps. Ind. Eng. Chem. Res. 50, 9847–9851. Wanrosli, W.D., Zainuddin, Z., Lee, L.K., 2004. Influence of pulping variables on the properties of Elaeis guineensis soda pulp as evaluated by response surface methodology. Wood Sci. Technol. 38, 191–205. Wanrosli, W.D., Mazlan, I., Law, K.N., Nasrullah, R., 2011. Influences of the operating variables of Acetosolv pulping on pulp properties of oil palm frond fibres. Maderas. Ciencia y Tecnología 13, 193–202.
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Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Acetosolv pulping for the fractionation of empty fruit bunches from palm oil industry A. Ferrer a, A. Vega b, A. Rodríguez a, L. Jiménez a,⇑ a b
Chemical Engineering Department, Campus of Rabanales, Building Marie Curie (C-3), University of Córdoba, 14071 Córdoba, Spain Department of Physical Chemistry and Chemical Engineering, University of A Coruña, 15071 A Coruña, Spain
h i g h l i g h t s " The most important aspects of this work focuses on. " Acetosolv pulping of Empty Fruit Bunches. " Us of polynomial models to reproduce the experimental results. " Optimum operating conditions were found.
a r t i c l e
i n f o
Article history: Received 8 May 2012 Received in revised form 26 December 2012 Accepted 28 December 2012 Available online 11 January 2013 Keywords: Acetosolv Acetic acid EFB Pulp Fractionation
a b s t r a c t Influence of operational variables in the EFB pulping [acetic acid (60–95%), hydrochloric acid (0.10–0.25%) and time (60–180 min)], on the yield, drainability or beating grade, Kappa number, lignin and viscosity of pulps was studied. By using a factorial design, equations were obtained that reproduced the experimental results for the dependent variables with errors less than 9–18%. These equations can be used to find the suitable conditions, so that operating with not too high values of operating variables (with minor costs of operation and capital) pulps with acceptable properties could be obtained: operating with 86.25% acetic acid, 0.25% hydrochloric acid and 120 min time, produced pulps with 46.56% yield, 15.9 °SR drainability, 36.3 Kappa number, 10.3% lignin and 303 mL/g viscosity, values all of them close to the optimal predicted. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Vegetable biomass has been for centuries a resource used by humanity worldwide, for energy and cellulosic pulp production. Recently, biomass has lost its value as an energy source based on the discovery of other sources more profitable, and only the field of pulp and paper continued using large amounts of lignocellulose. However, the production of paper pulp has traditionally been a highly polluting process. The vast majority of paper pulp mills still use the Kraft method, based on the action of a strongly alkaline solution of sulphur compounds on vegetable fibers. Organosolv methods use organic compounds of relatively low molecular weight as delignification agents, and are a good alternative to Kraft due to the elimination of the sulphur compounds in cooking. The researchers have achieved the delignification of plant tissues of all kinds using representative agents of a wide sample of the organic functional groups: alcohols, ketones, aldehydes, phenols, amines, amides, carboxylic ⇑ Corresponding author. E-mail address: [email protected] (L. Jiménez). 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.12.189
acids (López et al., 2006; Rodríguez and Jiménez, 2008). Although lignin removal can be achieved with high efficiency, in some cases, the physical properties of the paper sheets from these pulps were lower compared to those of Kraft pulps. Therefore, these pulps may be applied to the manufacture of special papers or obtaining high purity cellulose, with a possible final destination as dissolving pulps (Sixta et al., 2004; Vila et al., 2004), microcrystalline cellulose (Shansan et al., 2011), microfibrillated cellulose (Serrano et al., 2011) or bioethanol (Requejo et al., 2011), for example. Some of organosolv processes may be performed at atmospheric pressure and therefore at a low temperature, which results in a decreased severity of treatment and, consequently, a reduced formation of degradation compounds from sugars and lignin. This is of particular interest in the concept of the biorefinery, reinvigorated in recent years and it pretends to use the main components of the biomasses (Demirbas, 2009; Kamm and Kamm, 2004). Short chain carboxylic acids are among the organics that can carry out the fractionation. Acetic acid has been extensively investigated as delignification and/or fractionation agent. Nimz et al. published the first works in the 80’s on the process named
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Acetosolv, who succeeded to pulp pine, spruce, and beech wood (Nimz and Casten, 1986; Nimz et al., 1989). The Acetosolv process uses acetic acid enriched (70–90% by weight) aqueous mixtures with the addition of small amounts of hydrochloric acid (typically 0.1–0.2% by weight) which contributes to enhance the delignification through partial hydrolysis and solubilisation of hemicelluloses and lignin. When pulping variables are appropriately chosen the resulting pulps can show very low lignin content (Ligero et al., 2005) leaving a solid residue with high cellulose content (Villaverde et al., 2010). Additionally, acetosolv pulps could be easily bleached with TCF sequences including ozone, hydrogen peroxide, oxygen, and peroxyacetic acid (Dapia et al., 2003; Vila et al., 2004; Villaverde et al., 2011). Oil palm empty fruit bunches (EFB) is a waste generated by the palm oil industry after the separation of the fruits for oil extraction. This residue, which in many countries, especially in Malaysia and Indonesia, is produced in very high levels, is simply used as mulch, burnt for energy production or even burnt in the plantations without any profit. Due to its high production and uniformity resulting from the use of specific plant species EFB may not only be a waste but an important resource for obtaining various high-value products through chemical processing (Noor et al., 1998–2000). Shibata studied the chemical composition of EFB, and other parts of the oil palm, finding very similar amounts of cellulose and hemicelluloses and a lignin composed only by syringyl and guaiacyl units (Shibata et al., 2008). EFB has been subjected to a number of treatments in order to take advantage of this residue. An hydrothermal treatment was utilized in order to obtain sugars and proved to enhance the enzymatic digestibility of the solid residue (Shamsudin et al., 2012), which was studied by a mixture of cellulase and b-1,4-glucosidase (Hamzah et al., 2011). An acidtreatment removed 90% of the hemicelluloses and 32% of the lignin, but left most of the cellulose, and a second alkali-treatment reached a 70% delignification yield (Kim et al., 2012). Different pulping methods were applied to EFB. The effects of soda and soda-AQ pulping variables, even reinforced with hydrogen peroxide, have been studied by means of factorial experimental designs over yield, Kappa number, tensile and tear index (Wanrosli et al., 2004) or Kappa number, pulp viscosity, brightness and a selectivity measured as the ratio between the Kappa number reduction over the brightness increase (Ng et al., 2011). Oxygen bleaching as the first stage of a bleaching sequence was optimized for soda pulps obtained after a previous autohydrolysis step (Leh et al., 2008) and a complete TCF bleaching sequence applied to soda-AQ pulps was also reported (Jiménez et al., 2009). Among organosolv pulping methods EFB was subjected to pulping with organic solvents with a high boiling temperature (ethyleneglycol, diethyleneglycol, ethanolamine and diethanolamine), showing the pulps from amines to have better properties than the ones from glycols. (Rodríguez et al., 2008b). Solvents with lower boiling point were also tested to treat EFB. Formic acid (Ferrer et al., 2011b) and peroxyformic acid (Milox process) (Ferrer et al., 2011a) treatments were simulated by means of polynomial and neural fuzzy models. Their optimization predicted similar pulp properties values for both processes, but a higher brightness in the Milox pulp, while liquor characteristics diverged much more as no lignin could be precipitated from Milox liquor. To our knowledge only one study on Acetosolv treatment of oil palm has been published (Wanrosli et al., 2011) but applied to the leafy part (frond) of the tree. Therefore, the aim of this work was to study the Acetosolv treatment of palm oil empty fruit bunches by means of an experimental design factor, considering the influence of the operational variables on the composition of the resulting pulp, with the aim of finding the optimum conditions of operation to obtain a pulp for specialty papers or other applications such as
obtaining microcrystaline cellulose, microfibrillated cellulose or bioethanol by simultaneous saccharification and fermentation. 2. Experimental 2.1. Raw material In this work, EFB from African palm (Elaeis guineensis) was used. Each hectare of oil palm produces an average of 10 tons of fruits per year which give about 3000 kg of palm oil (the main product) and similar amount of EFB (Ferrer et al., 2011b). 2.2. Raw material characterization The chemical properties of EFB were determined in accordance with the respective Tappi standards for the different components, namely: T-9m 54 for holocellulose, T222 for lignin, T203 0S-61 for a-cellulose, T257 for hot-water solubles, T212 for 1%-NaOH solubles, T204 for ethanol–benzene extractives and T211 for ash. The fiber length distribution of EFB was determined by using a Visopan projection microscope (Ferrer et al., 2011b). 2.3. Pulping Mixtures of EFB, water and acetic acid (proportions ranging from 60% to 95% by weight of liquor) were heated to the boiling point in glass Pyrex flasks. Hydrochloric acid was added (0.10–0.25% by weight of liquor) when boiling started (zero time), and mixtures were maintained at total reflux with stirring for different times (60–180 min) at atmospheric pressure. After the reaction, the pulps were separated by filtration and the solids washed with concentrated acetic acid solutions (80% w) in order to avoid the deposition of the dissolved lignin on pulp. Finally the pulps were treated with water until neutrality and let to dry at room temperature (Ligero et al., 2005). 2.4. Pulps characterization For all experiments the main parameters defining delignification and pulping were measured, as follows: pulp yield after oven drying of a pulp aliquot to constant weight, Kappa number as per TAPPI T236, lignin content as per TAPPI T222, drainability or beating grade (Shopper-Riegler index) as per UNE 57-025, and intrinsic viscosity as per T230. 2.5. Experimental design A second order factorial design of experiments was used (Montgomery, 1991) consisted in a central experiment (in the centre of a cube) and several additional points (additional experiments lying at the cube vertices and side centers). Experimental data were fitted to a second-order polynomial. The values of the operational variables were normalized to values from 1 to +1 by using the following expression:
X n ¼ 2ðX X m Þ=X max X min
ð1Þ
where Xn is the normalized value of acetic acid concentration (A), hydrochloric acid concentration (H) or processing time (T); X is the actual experimental value of the variable concerned; Xm is the mean of Xmax and Xmin; and Xmax and Xmin are the maximum and minimum value, respectively, of such a variable. The normalized values for the independent variables in the 15 experiments conducted are given in Table 2.
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A. Ferrer et al. / Bioresource Technology 132 (2013) 115–120 Table 1 Chemical properties of various alternative raw materials and eucalyptus and pine. Analysis (%)
HWS (%)
1% S (%)
EEB (%)
ASH (%)
HOL (%)
a-CE (%)
HEM (%)
EFB Eucalyptus globulus Pinus pinaster Olive prunings Jiménez et al. (1990) Wheat straw Jiménez et al. (1990) Sunflower stalks Jiménez et al. (1990) Sorghum stalks Jiménez et al. (1993) Sugarcane bagasse Jiménez et al. (2005) Retama monosperma Jiménez et al. (2005) Phragmites Jiménez et al. (2005) Arundo donax Jiménez et al. (2005) Prosopis julyflora Jiménez et al. (2005) Prosopis alba Jiménez et al. (2005) Paulownia fortunei Jiménez et al.,(2005) Leucaena diversifolia Jiménez et al. (2006) Leucaena colinsii Jiménez et al. (2006) Leucaena leucocephala (Honduras) Jiménez et al. (2006) Leucaena leucocephala (India) Jiménez et al. (2006) Tagasaste(Australia) Jiménez et al. (2006) Tagasaste (New Zealand) Jiménez et al. (2006) Tagasaste (Island of La Palma, Spain) Jiménez et al. (2006) Vine shoots Jiménez et al. (2006) Cotton stalks Jiménez et al. (2006) Rice straw Rodríguez et al. (2008a)
4.03 2.84 1.99 8.16 12.27 22.72 21.7 4.4 3.84 5.38 4.73 6.49 4.67 9.6 3.24 4.30 5.01 3.98 2.96 2.99 2.41 16.09 3.33 16.57
40.22 12.42 7.89 30.04 43.58 47.81 45.58 33.92 16.93 34.77 26.80 22.56 20.86 31.5 17.38 20.02 20.26 18.44 15.55 16.15 16.62 39.21 20.34 46.94
1.17 1.15 2.57 10.36 4.01 4.07 7.99 1.73 5.03 6.36 7.30 5.30 4.65 5.50 4.44 4.64 6.01 4.64 2.17 3.43 3.30 4.87 1.42 1.4
3.2 0.57 0.54 1.36 6.49 7.9 4.85 2.1
66.97 80.47 69.59 61.47 76.2 71.76 65.93 80.2 71.76 64.16 70.20 62.77 63.56 70.7 77.88 80.79 74.11 75.92 82.16 75.36 76.47 67.14 72.86 70.6
47.91 16.96 26.22 35.67 39.72 42.1 41.5
52.79 55.92 25.8 36.48 29.66 24.43
42.75 39.76 40.46 36.55 41.55 37.40 40.10 43.77 41.21 44.43 47.65 43.59 44.99 41.14 58.48
26 14.38
3.49 2.17 15.3
LIG (%) 24.45 27.68 13.67 19.71 17.28 13.44 15.64 19.8 21.50 23.66 22.34 20.60 19.27 22.4 19.09 17.04 19.39 21.43 15.71 14.84 14.10 20.27 21.45 25.23
HWS: hot water solubles; 1% S: 1% soda solubles; EEB: extractives in ethanol–benzene; ASH: ash; HOL: holocellulose; a-CE: a-cellulose; HEM: hemicellulose; LIG: lignin. The values of the various parameters are averages of three determinations whose deviations from these average values are less than 5%.
Table 2 Values of operational variables and experimental values of the properties of pulp obtained by Acetosolv pulping of EFB. A (%)
H (%)
T (min)
XA, XH, XT (%)
Yield (°SR)
Beating grade number
Kappa (%)
Lignin (mL/g)
Viscosity
77.5 95.0 60.0 95.0 60.0 95.0 60.0 95.0 60.0 77.5 77.5 77.5 77.5 95.0 60.0
0.175 0.25 0.25 0.25 0.25 0.10 0.10 0.10 0.10 0.25 0.10 0.175 0.175 0.175 0.175
120 180 180 60 60 180 180 60 60 120 120 180 60 120 120
0, 0, 0 +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,+1, 0 0.1, 0 0, 0,+1 0, 0,1 +1,0, 0 1, 0, 0
58.58 41.31 52.27 46.41 67.26 75.44 74.40 83.21 84.29 47.35 74.81 54.91 63.22 51.80 67.59
17 14 19 12 13 13 18 12 14 18 13 18 13 13 17
55.5 41.1 58.0 32.2 71.0 77.7 75.8 73.6 69.3 39.7 70.0 51.3 55.8 47.6 76.8
13.5 11.1 11.6 8.9 15.4 16.6 16.3 15.9 16.3 9.8 15.9 13.1 15.3 10.8 16.1
283 306 384 226 291 185 302 183 213 345 262 297 312 251 318
A: acetic acid concentration; H: hydrochloric acid concentration; T: processing time; XA: normalized value of A; XH: normalized value of H; XT: normalized value of T. The values of the parameters are averages of three determinations whose deviations from these average values are less than 5–10%.
3. Results and discussion 3.1. Chemical characterization of EFB Table 1 shows the results of the chemical analysis of the EFB, eucalyptus wood and pine wood, and various non-wood alternative raw materials, as agricultural residues (olive prunings, wheat straw, sunflower stalks, sorghum stalks, rice straw, sugarcane bagasse, vine shoots and cotton stalks) and other vegetables (Jiménez et al., 1990, 1993, 2005 and Jiménez et al., 2006; Rodríguez et al., 2008a). A comparison of the data for EFB with those of the other raw materials reveals the following. The content in hot water solubles of EFB is similar to that of bagasse and cotton stalks, but lower than those of the other alternative raw materials – except paulownia and Prosopis julyflora – pine and eucalyptus wood. The content in 1% NaOH solubles of EFB is higher than those of olive
prunings, bagasse, cotton stalks, the alternative raw materials, and pine and eucalyptus wood, but similar to those of the other agricultural residues studied. The content in ethanol–benzene extractives of EFB is similar to those of rice straw, bagasse, cotton stalks, and pine and eucalyptus wood, but lower than those of the other agricultural residues and the alternative raw materials. The ash content of EFB is higher than those of olive prunings, bagasse and cotton stalks, similar to those of the other agricultural residues and much higher than those of pine and eucalyptus wood. The holocellulose content of EFB is higher than those of olive prunings and sorghum stalks, similar to those of vine shoots and lower than those of the other agricultural residues (wheat straw, sunflower stalks and cotton stalks); also, it is higher than those of Phragmites and P. julyflora, lower than those of the other raw materials, and in between those of pine and eucalyptus wood. The lignin content of EFB is higher than those of the agricultural residues, alternative
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A. Ferrer et al. / Bioresource Technology 132 (2013) 115–120
raw materials and eucalyptus wood, but lower than that of pine wood.
3.2. Physical characterization of EFB fibers The maximum, average and minimum values of fibers length were 1.48, 0.53 and 0.27 mm, respectively, and the maximum, average and minimum thickness or width were 26, 14 and 8 lm. A study of the length distribution curve showed that fibers having a size of 0.50–0.70 mm were the most abundant. The average length of the EFB fibers (0.53 mm) is lower than that of other raw materials: wheat straw (1.14 mm), sorghum stalks (1.32 mm), olive pruning (1.03 mm), sunflower stalks (1.30 mm), vine shoots (0.79 mm), cotton stalks (1.03 mm), Eucalyptus globulus (1.05 mm) and Pinus pinaster (2.50 mm).
3.3. Pulping of EFB First, a set of previous experiments was carried out, based on the results of other researchers on different raw materials, in order to define the ranges of operating variables. In this way the following ranges were chosen: acetic acid concentration from 60% to 95% by weight, hydrochloric acid concentration, which acts as a catalyst, from 0.10% to 0.25% by weight, and processing time from 60 to 180 min. Always operating at the boiling point and with the same liquid/solid ratio (10:1 by weight). Table 2 shows the experimental values of the pulp properties, which differed by less than 5–10% from their means as obtained in triplicate measures. The experimental results were fitted to a polynomial model by multiple regression using the software BMDPÓ. The terms possessing a Snedecor F-value greater than 6 and a Student t-value greater than 2.5 were deemed statistically significant. Equations found, as well as the lowest Snedecor-F value, the highest p value and the lowest Student t-value for the terms, are found in the Table 3. The predictions of the previous equations reproduced the experimental results for the dependent variables with errors lower than 9% for yield, 17% for beating grade, 17% for Kappa number, 18% for lignin content and 16% for viscosity of pulps. The values of the operational variables providing the best pulp properties (yield, beating grade, Kappa number, lignin content and viscosity) were identified by using equations of Table 3 and Figs. 1 and 2 and other similar. Table 4 shows the optimum values of the dependent variables and those of the operational variables required to obtain them. The polynomial equations allowed the identification of the more influencing operational variables on the pulp properties. The maximum variations in the dependent variables with changes in the operational variables over the studied range were obtained by altering one independent variable at a time while keeping all others constant. The results are shown in Table 4 together with the maximum percent differences in the dependent variables from their optimum values over the studied variation ranges.
Fig. 1. Yield pulp vs. hydrochloric acid concentration and time, at low acetic acid concentration.
Fig. 2. Yield pulp vs. acetic acid concentration and time, at low hydrochloric acid concentration.
The maximum yield (83.87%) corresponded to low values of operating variables. The hydrochloric acid concentration influences on pulp yield more significantly than the process time (Fig. 1), while the latter variable affects more than the concentration of acetic acid (Fig. 2). The maximum beating grade (18.4 °SR) occurs when the concentration of acetic acid is low and the processing time long, being the most influential variable this last one. The Kappa number increased more sharply with the hydrochloric acid concentration than with acetic acid concentration. The
Table 3 Coefficients of the polynomial equations, and the lowest Snedecor-F value, the highest p value and the lowest Student-t value. Dependent variables
Yield Beating grade Kappa number Lignin Viscosity
Values of the constants in the polynomial equations
Values of
ao
a1
a2
a3
a11
a12
a22
F>
>p
t>
59.22 14.9 54.5 13.8 300
4.46 1.7 7.9 1.2 36
13.76 – 12.4 2.4 41
4.61 1.8 – – 25
– 7.9 – 34
3.97 – 7.7 – –
5.46 – – – –
10.56 11.70 6.88 6.83 10.56
0.010 0.005 0.025 0.023 0.010
3.25 3.42 2.62 2.61 3.25
119
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Table 4 Optimal properties in pulp obtained by acetic acid pulping of EFB. Maximum changes in the dependent variables with changes in one operational variable on constancy of the others (the percent differences from the changes are given in brackets). Dependent variable
Optimum (maximum or minimum⁄) value of dependent variable
Values of the operational variables required to obtain the optimum values of dependent variables XA XH XT
Yield (%)
83.87 36.58⁄ 18.4 34.4⁄ 10.2 376
1 +1 1 +1 +1 0.52
Beating grade (°SR) Kappa (number) Lignin (%) Viscosity (mL/g)
1 +1 – +1 +1 +1
1 +1 +1 – – +1
Maximum variation of dependent variable with operational variable Acetic acid
Hydrochloric acid
Time
1.58 (1.88%)
19.64 (23.43%)
9.22 (11.00%)
3.4 (18.48%) 31.2 (90.70%) 2.4 (23.5%) 80 (21.28%)
– 40.2 (116.86%) 4.8 (47.1%) 82 (21.81%)
7.0 (38.04%)
50 (13.30%)
Fig. 3. Yield/Kappa ratio vs. acetic acid concentration and time, at high hydrochloric acid concentration.
Fig. 4. Yield/Kappa ratio vs. hydrochloric acid concentration and time, at high acetic acid concentration.
minimum Kappa number (34.4) was obtained when hydrochloric acid concentration and acetic acid concentration were high. The lignin content has a parallel behaviour, with a minimum value of 10.2% for when the concentrations of the two acids are high, being the most influential variable the hydrochloric acid concentration. The viscosity was maximum (376 mL/g) when operating with medium–low level of acetic acid concentration and high values of processing time and hydrochloric acid concentration. Process time has minor influence on the viscosity that the acetic acid concentration, while hydrochloric acid concentration is the most influential variable.
time, and processing time and hydrochloric acid concentration, respectively, for high hydrochloric acid concentration and for high acetic acid concentration. Considering the ‘‘Viscosity/Kappa’’ ratio (which is also desirable to be high), adjusting the experimental data to a polynomial model gives the equation:
3.4. Optimum operating conditions Considering the ‘‘Yield/Kappa’’ ratio (which is desirable to have a maximum value), adjusting the experimental data to a polynomial model gives the equation:
Yield=Kappa ¼ 1:07 þ 0:07X A þ 0:09X A X H 0:10X T ðF > 6:34; p < 0:029; t > 2:52Þ
ð2Þ
The values of the operational variables providing the maximum ‘‘Yield/Kappa’’ were identified by using Eq. (2): the maximum value is 1.33, for which the acetic acid concentration is high (95%), hydrochloric acid concentration is high (0.25%) and the processing time is short (60 min). Figs. 3 and 4 shows the dependence of the ‘‘Yield/Kappa’’ ratio on acetic acid concentration and processing
Viscosity=Kappa ¼ 5:73 0:39X A X T þ 0:40X T 1:08X 2A þ 0:74X A X H þ 1:85X H
ðF > 2:73; p < 0:13; t > 1:65Þ
ð3Þ
Operating in a similar way as in Eqs. (2) and (3) predicts the maximum value of the ‘‘Viscosity/Kappa’’ ratio of 8.01, for the following operating conditions: high values of hydrochloric acid concentration (0.25%) and processing time (180 min), and medium–high acetic acid concentration (80.30%). Similar figures to 3 and 4 shows the dependence of the ‘‘Viscosity/Kappa’’ on hydrochloric acid concentration and acetic acid concentration for long processing time, and acetic acid concentration and the processing time for a high hydrochloric acid concentration. To save chemicals, energy, and immobilized capital on industrial facilities is necessary to use lower acetic acid and hydrochloric acid concentrations and shorter processing times, than the values considered in the previous paragraph. The equations of Table 3 and data of Table 4 can be used to select values of the operational variables providing near-optimal pulp properties while saving chemicals, energy and immobilized capital by using lower values of some of the operational variables. One combination leading to near-optimal properties with reduced costs with properties is
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using a processing time of 120 min, an acetic acid concentration of 86.25% and a hydrochloric acid concentration of 0.25%. Operating under these conditions the following values for the dependent variables were obtained: yield 46.56%, beating grade 15.9 °SR, Kappa number 36.3, lignin 10.3% and viscosity 303 mL/g; these values deviate by 44.5%, 13.6%, 5.5%, 5.9% and 18.6%, respectively of the maximum values of yield, beating grade, Kappa number, lignin content and viscosity. Operating under these conditions the values obtained for the ratios ‘‘Yield/Kappa’’ (1.15) and ‘‘Viscosity/Kappa’’ (7.68) are very near from the optimum predicted by the corresponding regression equations. 4. Conclusions Acetosolv pulping can be a stage in the EFB fractionation. The pulp obtained has low viscosity, but can be used for specialty papers, microcrystalline-cellulose, microfibrillated-cellulose, or bioethanol by simultaneous saccharification–fermentation. Polynomial equations obtained by multiple regression can be used to find the suitable conditions that, operating with not too high values of operational variables (minor operational and capital costs), procedure pulps with acceptable properties. Specifically, operating at 86.25% acetic acid, 0.25% hydrochloric acid and 120 min time, pulps with 46.56% yield, 15.9 °SR drainability, 36.3 Kappa number, 10.3% lignin and 303 mL/g viscosity were obtained; all these values are close to the optimal. Acknowledgements The authors are grateful to Ecopapel, S.L. (Écija, Seville, Spain) for their support, and to Spain’s DGICyT and Junta of Andalucía for funding this research within the framework of the Projects CTQ-2010-19844-C02-01 and TEP-6261. References Dapia, S., Sixta, H., Borgards, A., Harms, H., Parajo, J.C., 2003. TCF bleaching of hardwood pulps obtained in organic acid media for production of viscose-grade pulps. Holz als Roh- und Werkstoff 61, 363–368. Demirbas, A., 2009. Biorefineries: current activities and future developments. Energy Convers. Manage. 50, 2782–2801. Ferrer, A., Vega, A., Rodríguez, A., Ligero, P., Jiménez, L., 2011a. Milox fractionation of empty fruit bunches from Elaeis guineensis. Bioresour. Technol. 102, 9755–9762. Ferrer, A., Vega, A., Ligero, P., Rodríguez, A., 2011b. Pulping of empty fruit bunches (EFB) from the palm oil industry by formic acid. Bioresources 6, 4282–4301. Hamzah, F., Idris, A., Shuan, T.K., 2011. Preliminary study on enzymatic hydrolysis of treated oil palm (Elaeis) empty fruit bunches fiber (EFB) by using combination of cellulase and b-1-4 glucosidase. Biomass Bioenergy 35, 1055–1059. Jiménez, L., López, F., Martínez, C., 1993. Paper from sorghum stalks. Holzforschung 47, 529–533. Jiménez, L., Pérez, A., de la Torre, M.J., Moral, A., Serrano, L., 2006. Characterization of vine shoots, cotton stalks, Leucaena leucocephala and Chamaecytisus proliferus, and of their ethyleneglycol pulps. Bioresour. Technol. 98, 3487–3490. Jiménez, L., Rodríguez, A., Ferrer, J.L., Pérez, A., Angulo, V., 2005. Paulownia, a fastgrowing plant, as a raw material for paper manufacturing. Afinidad 62 (516), 100–105.
Jiménez, L., Sánchez, I., López, F., 1990. Characterization of Spanish agricultural residues with a view to obtaining cellulose pulp. Tappi J. 73 (8), 173–176. Jiménez, L., Serrano, L., Rodríguez, A., Ferrer, A., 2009. TCF bleaching of sodaanthraquinone and diethanolamine pulp from oil palm empty fruit bunches. Bioresour. Technol. 100, 1478–1481. Kamm, B., Kamm, M., 2004. Principles of biorefineries. Appl. Microbiol. Biotechnol. 64, 137–145. Kim, S., Park, J.M., Seo, J.W., Kim, C.H., 2012. Sequential acid/alkali-pretreatment of empty palm fruit bunch fiber. Bioresour. Technol. 109, 229–233. Leh, C.P., Wan Rosli, W.D., Zainuddin, Z., Tanaka, R., 2008. Optimisation of oxygen delignification in production of totally chlorine-free cellulose pulps from oil palm empty fruit bunch fibre. Ind. Crops Prod. 28, 260–267. Ligero, P., Vega, A., Bao, M., 2005. Acetosolv delignification of Miscanthus sinensis bark influence of process variables. Ind. Crops Prod. 21, 235–240. López, F., Alfaro, A., Jiménez, L., Rodríguez, A., 2006. Alcohols as organic solvents for obtainment of cellulose pulp. Afinidad 63 (523), 174–182. Montgomery, D.C., 1991. Design and analysis of experiments. Grupo Editorial Iberoamericana, Mexico, p. 303. México. Ng, S.H., Ghazali, A., Leh, C.P., 2011. Anthraquinone-aided hydrogen peroxide reinforced oxygen delignification of oil palm (Elaeis guineensis) EFB pulp: a twolevel factorial design. Cellul. Chem. Technol. 45, 77–87. Nimz, H.H., Casten, R., 1986. Chemical processing of lignocellulosics. Holz als Rohund Werkstoff 44, 207–212. Nimz, H.H., Berg, A., Granzow, C., Casten, R., Muladi, S., 1989. Pulping and bleaching by the Acetosolv process. Papier 43, 102–108. Noor, M., Azemi, M., Sarip, H., 1998–2000. Oil palm (Elaeis guineensis) wastes as a potential source of cellulose. Cellulosic Pulps, Fibres and Materials, [International Cellucon Conference. In: Kennedy, John F., Pulp for Papermaking: Fibre and Surface Properties and Other Aspects of Cellulose Technology], 10th, Turku/Abo, Finland, Dec. 14–17. Requejo, A., Peleteiro, S., Rodríguez, A., Garrote, G., Parajó, J.C., 2011. Secondgeneration bioethanol from residual woody biomass. Energy Fuels 25, 4803– 4810. Rodríguez, A., Jiménez, L., 2008. Pulping with organic solvents other than alcohols. Afinidad 65 (535), 188–196. Rodríguez, A., Moral, A., Serrano, L., Labidi, J., Jimérnez, L., 2008a. Rice straw pulp obtained by using various methods. Bioresour. Technol. 99, 2881–2886. Rodríguez, A., Serrano, L., Moral, A., Pérez, A., Jiménez, L., 2008b. Use of high-boiling point organic solvents for pulping oil palm empty fruit bunches. Bioresour. Technol. 99, 1743–1749. Serrano, L., Urruzola, I., Nemeth, D., Belafi-Bakob, K., Labidi, J., 2011. Modified cellulose microfibrils as benzene adsorbent. Desalination 270, 1–3. Shamsudin, S., Shah, U.K.Md., Zainudin, H., Abd-Aziz, S., Kamal, S.M.M., Shirai, Y., Hassan, M.A., 2012. Effect of steam pretreatment on oil palm empty fruit bunch for the production of sugars. Biomass Bioenergy 36, 280–288. Shansan, L., Fang, G., Deng, Y., Wang, W., 2011. Preparation of microcrystalline cellulose from cotton linter ethanol pulp. Adv. Mater. Res. 295–297, 653– 658. Shibata, M., Varman, M., Tono, Y., Miyafuji, H., Saka, S., 2008. Characterization in chemical composition of the oil palm (Elaeis guineensis). J. Japan Inst. Energy 87, 383–388. Sixta, H., Harms, H., Dapia, S., Parajo, J.C., Puls, J., Saake, B., Fink, H.P., Roeder, T., 2004. Evaluation of new organosolv dissolving pulps. Part I: Preparation, analytical characterization and viscose processability. Cellulose 11, 73–83. Vila, C., Santos, V., Parajo, J.C., 2004. Dissolving pulp from TCF bleached acetosolv beech pulp. J. Chem. Technol. Biotechnol. 79, 1098–1104. Villaverde, J.J., Ligero, P., Vega, A., 2010. Highly purified pulps from Miscanthus x giganteus. A comparative study of a new TCF bleaching sequence applied to organosolv pulps. Afinidad 67, 123–128. Villaverde, J.J., Ligero, P., Vega, A., 2011. Applicability of short totally chlorine free bleaching sequences to Miscanthus x giganteus organosolv pulps. Ind. Eng. Chem. Res. 50, 9847–9851. Wanrosli, W.D., Zainuddin, Z., Lee, L.K., 2004. Influence of pulping variables on the properties of Elaeis guineensis soda pulp as evaluated by response surface methodology. Wood Sci. Technol. 38, 191–205. Wanrosli, W.D., Mazlan, I., Law, K.N., Nasrullah, R., 2011. Influences of the operating variables of Acetosolv pulping on pulp properties of oil palm frond fibres. Maderas. Ciencia y Tecnología 13, 193–202.