- Email: [email protected]
Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass
ARTICLE IN PRESS
CHERD-1466; No. of Pages 9
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
Contents lists available at ScienceDirect
Chemical Engineering Research and Design journal homepage: www.elsevier.com/locate/cherd
Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass Anatoly A. Shatalov ∗ , Helena Pereira Universidade Técnica de Lisboa, Instituto Superior de Agronomia, Centro de Estudos Florestais (CEF), Tapada da Ajuda, 1349-017 Lisboa, Portugal
a b s t r a c t A biorefinery scheme with separate processing of the two main carbohydrate streams (cellulose and hemicellulosederived) was employed to the energy crop cardoon (Cynara cardunculus L.) to fractionate the whole stalk material. A high quality xylose-enriched substrate was obtained after selective one-step dilute sulfuric acid hydrolysis of hemicelluloses, yielding 18.1 g of xylose per 100 g of dry biomass. The xylan-free solid residue was delignified by sulfur-free organosolv pulping to produce dissolving grade pulps having 93.8% of ␣-cellulose (33.1 g per 100 g dry initial biomass) and 79.5% degree of crystallinity. About 76% of crop lignin (13.8 g per 100 g dry initial biomass) was recovered from the spent pulping liquor as a high purity reactive precipitated organosolv lignin. Response surface methodology was used for statistical modeling and optimization of the applied separation processes. The central composite rotatable design was applied to assess the effects of the principal technological parameters on the main reaction outputs. © 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Keywords: Biorefinery; Cynara cardunculus; Dissolving pulp; Sulfur-free delignification; Modeling; Optimization
1.
Introduction
The use of renewable biomass to replace petroleum-based chemicals from depleting fossil resources is a challenge that has attracted much current interest and importance (Ragauskas et al., 2006). The biorefinery concept of biomass processing, where a complex of different treatments (physical, chemical and biological) is applied for complete biomass fractionation, is being considered now as a more potential way for sustainable bio-based economy (Fernando et al., 2006; Kamm and Kamm, 2007). Lignocellulosic biomass has received particular attention, as a more promising biorefinery feedstock (Kamm et al., 2006; FitzPatrick et al., 2010). Among a wide variety of lignocellulosic biomass sources, the perennial herbaceous energy crops represent abundant and low-cost feedstock for biorefining technology. The artichoke thistle cardoon (Cynara cardunculus L.) is a naturally growing perennial herb in the Mediterranean region. The easy adaptability of cardoon to hot and dry climatic
conditions and remarkable seasonal growth (up to 3 m height and 1.5 m diameter spread area (Fernández, 1998)) stimulated the cardoon cultivation as a perennial field energy crop for biomass production. The annually harvested yield of the aboveground biomass up to 30–35 tons ha−1 year−1 has been reported under optimum cultivation conditions (Dalianis et al., 1996). As an energy crop, the cardoon biomass can be used as a solid fuel for direct heating and electric power generation, or as a source of seed oil for biodiesel production (Fernández et al., 2006). The branched stalks of cardoon, accounting for about 40% of total dry biomass and composed generally by 20–30% of hemicelluloses, 35–45% of cellulose and 10–20% of lignin (Fernández, 1998), represent a valuable source of chemicals for industrial applications. The particularly elevated content of cellulose and good fiber characteristics, comparable with hardwoods (eucalypt), made cardoon stalks as a very promising agro-fiber raw material for pulp and paper production. The bleachable grade papermaking pulps were produced by
∗
Corresponding author. Tel.: +351 21 365 3379; fax: +351 21 365 3338. E-mail address: [email protected] (A.A. Shatalov). Received 31 May 2013; Received in revised form 6 December 2013; Accepted 3 January 2014 0263-8762/$ – see front matter © 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cherd.2014.01.007 Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
ARTICLE IN PRESS
CHERD-1466; No. of Pages 9
2
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
conventional alkaline (soda and kraft) (Benjelloun-Mlayah et al., 1997; Antunes et al., 2000; Gominho et al., 2001; Abrantes et al., 2007) and eco-clean organosolv delignification technologies (Ligero et al., 2007, 2008; Oliet et al., 2005). The cardoon stalks contain central pith that forms the high content of fines during pulping (Villar et al., 1999). The reduced drainage capacity and porosity of cardoon pulps suggested the stalks depithing before pulping. This explains the fact that almost all previous research on cardoon pulping was done based on depithed material. However, the stalk depithing requires additional investments thus increasing the total production costs and efforts should be done to use the whole stalk material. One way for upgrading cardoon biomass could be to obtain cellulosic fibers after preliminary valorization of non-cellulosic carbohydrates. During this selective removal of hemicelluloses, e.g., by acid hydrolysis, the other lowmolecular substances of cardoon stalk, and particularly of pith, will be also dissolved in solution, thus diminishing the impact of the pith on the following pulp production. High purity dissolving grade pulps can be produced after appropriate delignification of pre-hydrolyzed cardoon whole stalks. Nowadays, the dissolving grade pulps with 92–96% of ␣-cellulose are commercially produced from woody species using pre-hydrolysis kraft or acid sulfite processes followed by elemental chlorine-free (ECF) bleaching (Sixta, 2006). The application of sulfur-free organosolv delignification in combination with totally chlorine-free (TCF) bleaching would be a significant step in meeting environmental and economic concerns related to conventional industrial technologies. Following an integrated biorefinery scheme, the possibility of dissolving grade pulp production from cardoon (C. cardunculus) whole stalk material (with pith) after selective acid hydrolysis of hemicellulosic polysaccharides has been studied, alternatively to bioethanol production. The results on process modeling and optimization by response surface methodology (RSM) are presented and discussed in this paper.
2.2.
Ethanol-alkali delignification of the pre-hydrolyzed (xylanfree) cardoon stalks was carried out in 100 cm3 stainless steel digesters rotated in an oil bath. The digesters were loaded with 8 g (on oven-dry basis) of pre-hydrolyzed material and 84 ml of pulping solution. The process variables were reaction time (150–210 min), reaction temperature (140–160 ◦ C), ethanol content (40–60% vol.) and alkali charge (15–35% on oven-dry material). Heating-up period, pre-defined by preliminary experiments, was excluded from the resident time. After cooking, pulps were defibrated using standard pulp disintegrator, thoroughly washed with deionized water and air-dried before total yield determination. When necessary, the defibrated pulps were screened in a laboratory flat screen with 0.2 mm slit-width (Buchet, Netherlands) for separation of rejects.
2.3.
Materials and methods
2.1.
Raw material and chemicals
Cardoon biomass was sampled from the university experimental field (School of Agriculture, Lisbon). The air-dried branched stalks were manually stripped of residual leaves, cut without depithing in the knife Retsch mill and screened to a particle size of 40–60 mesh (for chemical analysis) or of approx. match size of 5–10 mm length and 1–2 mm width (for pulping experiments), homogenized and stored in sealed plastic bags at room temperature until using. Moisture content of the prepared materials was determined according to TAPPI standards. Selective hydrolytic removal of hemicelluloses (xylan) from cardoon whole stalk material was performed before pulping using previously established optimum reaction conditions (138.5 ◦ C; 1.28% sulfuric acid solution; 52 min), as described elsewhere (Shatalov and Pereira, 2011). All chemicals used in this study were of analytical grade purity and purchased from Sigma, Ardrich and Fluka Chemical Co.
Analytical methods
Extractives were determined gravimetrically after successive Soxhlet extraction by dichloromethane, ethanol and water. Acid-insoluble (Klason) and acid-soluble lignin were determined according to TAPPI T 222 om-88 and TAPPI UM 250 standards, respectively. Monosaccharide composition was determined by GC as alditol-acetate derivatives, under conditions described elsewhere (Shatalov and Pereira, 2007). Residual lignin in pulps was determined as Kappa number according to T 236 cm-85 TAPPI standards. The ␣cellulose content was determined according to T 203 om-93 TAPPI standard. The cupri-ethylenediamine (CED) intrinsic pulp viscosity was measured according to SCAN-CM 15:88 standard. Handsheet formation for reflectance test was performed according to TAPPI T 272 om-92 standard. Pulp optical properties (ISO brightness and DIN 6167 C/2 yellowness index) were measured by CM-3630 Spectrophotometer (Minolta).
2.4.
2.
Organosolv pulping
X-ray diffractometry (XRD) of cellulose fibers
Crystalline structure of cellulose samples was analyzed by wide-angle XRD experiments on Bruker D8 ADVANCE powder diffractometer with symmetric Bragg-Brentano scattering geometry, using Ni-filtered Cu K␣ radiation ( = 0.1542 nm; 40 kV operating voltage; 30 mA current) and secondary graphite monochromator. Data were collected in the 2 range of 5–60◦ with interval of 0.02◦ and counting time of 20 s per interval. Degree of cellulose crystallinity (crystallinity index, CrI) was calculated from the resulting diffraction curves (diffractograms) using empirical method of Segal et al. (1959).
2.5.
Modeling and optimization of delignification
Response surface methodology (Statistica 6.0, Statsoft, USA) was used for statistical modeling and optimization of delignification conditions. The main effects (linear and quadratic) of the independent process variables (time, temperature, ethanol and alkali concentration) and their interactions were estimated using 24 central composite rotatable design (CCRD). An optimum set of reaction conditions providing maximum predicted pulping outputs (Kappa number and brightness) was
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
ARTICLE IN PRESS
CHERD-1466; No. of Pages 9
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
Table 1 – Chemical composition of pre-hydrolyzed cardoon whole stalk material. Component
Content (% on oven-dry residue)
Extractives Lignin Klason Acid-soluble Glucan Xylan
9.65 (25.41)a 25.24 (21.11) 24.02 (11.64) 1.22 (74.73) 64.85 (6.10) 0.18 (99.47)
a
In brackets: component loss after hydrolysis (%).
established after fitting the second-order polynomial model (Eq. (1)) to experimental data.
Y = b0 +
3 i=1
bi Xi +
3 i=1
bii Xi2 +
3
bij Xi Xj
(1)
i
where Y is a predicted response (Kappa number or ISO brightness), b0 is an interception coefficient (regression coefficient at central point), bi are the linear coefficients, bii are the quadratic coefficients, bij are the interaction coefficients, and Xi and Xj are the independent variables (temperature, time, alkali and ethanol concentrations). ANOVA was used to check statistical significance of all found regression coefficients and estimated effects.
3.
Results and discussion
3.1.
Selective hydrolysis of xylan
As a first stage of multi-step fractionation scheme, a low temperature dilute sulfuric acid hydrolysis was applied to the whole stalk material of cardoon for selective removal of hemicellulose carbohydrates, which consist by ca. 90% of xylan polysaccharides (Shatalov and Pereira, 2011). The xylanto-xylose conversion of 86% was achieved in solution after one-step reaction performed under previously optimized conditions. The limited formation of furan substances (1.04% furfural and 0.33% 5-hydroxymethylfurfural) provided the high quality of xylose-enriched substrate for subsequent biochemical conversion to final products, such as xylitol (Shatalov and Pereira, 2011). The insoluble solid residue after hydrolysis contained only 0.2% of xylan (Table 1), indicating almost complete (by 99.5%) xylan removal during hydrolysis. Besides xylan, about 25.4% of extractives (as a water-soluble extractive fraction) and 21.1% of lignin (mainly as acid-soluble lignin) were also removed from the cardoon stalks, resulting in total gravimetric solid recovery yield of 56.9%. The content of cellulose accounted for 64.9% of the insoluble residue. Referring to Table 1, only ca. 6.1% of cellulose (2.4% of stalk mass) was dissolved under the optimized hydrolysis conditions specifically designed for selective xylan removal, reflecting the experimentally defined balanced correlation between efficiency of xylan-to-xylose conversion and hydrolysis selectivity. This dissolved cellulose represents the less ordered (amorphous) cellulose fraction which has the same (or close) accessibility and reactivity to hemicellulosic polysaccharides (Fengel and Wegener, 1984). The remaining cellulose in insoluble residue was easily digested (saccharificated) by commercial cellulase preparations to fermentable sugars for
3
bioethanol production. After 48 h of enzymatic hydrolysis under standard (non-optimized) NREL conditions (Selig et al., 2008), the degree of cellulose conversion to monomeric glucose of ca. 80% (ca. 75% of crop cellulose, or 32 g Glc/100 g cardoon stalks) was achieved vs. ca. 18% (8 g Glc/100 g cardoon stalks) for untreated biomass. Alternatively, the xylan-free solid residue after cardoon hydrolysis can be used as a source of cellulose fibers for production of high purity dissolving grade pulps. At this case, the partial removal of amorphous cellulose portion during acid pre-hydrolysis would be even advantageous, since it implies a direct increase in content of high-ordered ␣-cellulose fraction having critical importance for dissolving pulps.
3.2.
Delignification of xylan-free residues
Meeting the environmental concerns related to commercial delignification technologies, the eco-friendly (sulfur-free) pulping approach based on use of organic solvents in the reaction system (organosolv pulping) was employed for the delignification of the xylan-free residues of cardoon stalks. The ethanol-alkali pulping was chosen among a group of potential organosolv processes, as proved to be very effective in lignin removal and polysaccharide preservation of nonwood (agro-fiber) sources (Shatalov and Pereira, 2004), even though the chemical recovery issues of this technology still need to be solved. The presence of alcohol improves solubility of the formed lignin fragments and prevents lignin condensation by alkylation of active reaction centers, such as benzyl alcohol groups (Sarkanen, 1990), thus providing deep delignification under rather moderate pulping conditions. The principal results of ethanol-alkali pulping of the xylanfree cardoon stalks under variable process conditions are summarized in Table 2. It is evident that within the applied (economically reasonable) ranges of alkali charge 15–35% and ethanol content 40–60%, the low process temperature of 140 ◦ C, reported to be ideally suited for untreated agrobiomass (Shatalov and Pereira, 2004), is not sufficient to produce acceptable quality pulp from the pre-hydrolyzed material. Similar to traditional soda pulping, the alkalinity (or hydroxide ion concentration) is the main factor of ethanolalkali method. At the alkali load of 15%, poorly delignified pulps with very high Kappa number (Kappa 57.7 or ca. 7.5% Klason lignin) and rejects content (48.8% uncooked material) were produced after 2.5 h pulping at 140 ◦ C and 40% (vol.) of ethanol in solution. The increase in alkali charge up to 35% substantially improved delignification, but still yielding pulps with quite high Kappa 29.6 (ca. 4% Klason lignin) and 8.6% rejects. The structural changes in cardoon cell-wall constituents caused by acid hydrolysis, and particularly the changes in lignin structure, are the obvious reasons for the observed decreased pulping efficiency in comparison with untreated biomass (Shatalov and Pereira, 2004). Despite the mentioned partial lignin defragmentation and dissolution in acidic solution, mainly as a result of the cleavage (acidolysis) of -O-4 (Li et al., 2007), but also - and -5 linkages (Samuel et al., 2010), the parallel competing reaction of lignin repolymerization (via acid-catalyzed condensation between aromatic carbons at C6 or C5 and carbonium ion formed from benzyl alcohol lignin structure at C␣ ) takes also place, leading to formation of new stable condensed (C–C) structures and decrease in lignin reactivity and solubility (Moxley et al., 2012). Besides
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
ARTICLE IN PRESS
CHERD-1466; No. of Pages 9
4
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
Table 2 – Results of ethanol-alkali pulping of pre-hydrolyzed cardoon whole stalk material. Temperature (◦ C) 140
Time (min)
Ethanol (%, v/v)
150
40
NaOH (% odm)
60
160
210
40
150
40 60
210
a
40
Kappa number
Brightness (% ISO)
DPa
Yield (% odm)
Rejects (% odm)
15 35 15 35 15 35
57.7 29.6 68.7 31.4 54.1 24.1
29.9 41.0 25.6 36.3 30.6 45.2
1788 1657 1515 1193 1703 1630
59.9 51.6 62.0 52.3 59.0 49.7
48.8 8.6 51.3 11.2 47.0 2.1
15 35 15 35 15 35
39.7 5.4 49.6 8.9 36.3 5.0
31.5 57.2 26.5 44.2 32.8 58.0
1174 923 860 535 940 760
54.0 45.8 55.2 45.1 52.7 44.5
30.6 0 37.0 0 24.6 0
Degree of polymerization (DP) was calculated by Evans and Wallis equation: DP0.85 = 1.1[] (SCAN-CM 15:88 Standard).
lignin condensation, a lignin-like material (the so-called pseudo-lignin) is also formed during dilute acid hydrolysis due to reactions between carbohydrate- and lignin-derived degradation products (Sannigrahi et al., 2011). Formation of pseudo-lignin is particularly notable under elevated hydrolysis temperatures, significantly affecting the subsequent biochemical processing of pre-hydrolyzed biomass (Hu et al., 2013). As can be seen from Table 2, even a substantial increase in ethanol-alkali pulping temperature up to 160 ◦ C under an alkali load of 15% (40% (v/v) ethanol) did not provide effective delignification of the pre-hydrolyzed cardoon stalks, producing pulps with high Kappa 39.7 (ca. 5.2% Klason lignin) and 30.6% rejects. A high yield of rejects was also noted for other organosolv methods applied to cardoon, such as auto-catalyzed ethanol pulping (Oliet et al., 2005), and was associated with morphological heterogeneity of cardoon stalks given by the centrally located pith parenchymal cells and the surrounding fibro-vascular bundles. The topochemical effect of stalk morphology affects the uniformity of delignification reaction, resulting in increased content of uncooked material (rejects), what was also confirmed by experiments with de-pithed material (Ligero et al., 2007). A very good correlation (R2 = 0.93) was established at this study between Kappa number in ethanol-alkali pulps and amount of rejects (Fig. 1).
60
Rejects (%)
50 R² = 0,9301
40 30 20 10 0
The anatomic heterogeneity is therefore a factor affecting the ethanol-alkali delignification of cardoon whole stalk material, along with the effects caused by acid pre-hydrolysis. Only the simultaneous increase in process temperature and alkali concentration allowed reaching the delignification degree desirable for production of dissolving grade pulps. At 160 ◦ C and 35% NaOH (2.5 h; 40% (v/v) ethanol), the deeply delignified pulps were obtained, having very low for unbleached pulp Kappa 5.4 (ca. 0.7% Klason lignin), high brightness of 57.2% ISO and no rejects. Despite the noted drop in pulp yield and intrinsic viscosity/degree of polymerization (DP), as an indicator of polysaccharide degradation reactions under elevated medium alkalinity, their values were close to those reported for other organosolv pulps from cardoon (Ligero et al., 2007, 2008; Oliet et al., 2005) and within the acceptable range for dissolving grade pulps (Sixta, 2006). Effective delignification can be also performed at ethanol proportion of 60% (vol.) in reaction solution, at 160 ◦ C and 35% alkali (Table 2). No rejects are formed and the pulp/fiber yield is practically the same as in 40%-ethanol pulping. However, the Kappa number of pulp is higher while the brightness and particularly viscosity (DP) is lower, following the observed tendency of decrease in delignification and pulping efficiency after increase in solvent content up to 60%. Similar results were earlier reported for other agro-crops, where the solvent proportion of ca. 40% was noted as the best suited for ethanol-alkali pulping (Shatalov and Pereira, 2004). The delignification efficiency can be somewhat improved by pulping extension to 3.5 h, resulting in pulps with lower Kappa number and higher brightness. However, the prolonged pulping at high temperatures and alkali concentrations favors further cellulose degradation leading to significant drop in pulp viscosity. This declines the selectivity of ethanol-alkali delignification as a whole and affects the quality of the final fiber product.
3.3. 20
30
40
50
60
Pulping modeling and optimization
70
Kappa number Fig. 1 – Correlation between degree of delignification and amount of rejects formed during ethanol-alkali pulping of pre-hydrolyzed cardoon stalks.
Optimization of ethanol-alkali pulping was done using response surface methodology (RSM) (Myers et al., 2009). Statistical model of delignification was developed based on the 24 central composite rotatable design (CCRD) with 4 independent process variables (process temperature, ethanol
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
ARTICLE IN PRESS
CHERD-1466; No. of Pages 9
5
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
Table 3 – Experimental central composite rotatable design (CCRD) matrix and pulping responses used for RSM modeling. Run no.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 (C) 26 (C) 27 (C) 28 (C) 29(C)
Coded variables
[−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] [−2; 0; 0; 0] [+2; 0; 0; 0] [0; −2; 0; 0] [0; +2; 0; 0] [0; 0; −2; 0] [0; 0; +2; 0] [0; 0; 0; −2] [0; 0; 0; +2] [0; 0; 0; 0] [0; 0; 0; 0] [0; 0; 0; 0] [0; 0; 0; 0] [0; 0; 0; 0]
Decoded variables
Pulping responses
XT
XE
XA
Xt
YK
140 140 140 140 140 140 140 140 160 160 160 160 160 160 160 160 130 170 150 150 150 150 150 150 150 150 150 150 150
40 40 40 40 60 60 60 60 40 40 40 40 60 60 60 60 50 50 30 70 50 50 50 50 50 50 50 50 50
15 15 35 35 15 15 35 35 15 15 35 35 15 15 35 35 25 25 25 25 5 45 25 25 25 25 25 25 25
150 210 150 210 150 210 150 210 150 210 150 210 150 210 150 210 180 180 180 180 180 180 120 240 180 180 180 180 180
57.70 54.06 29.58 24.12 68.70 67.16 31.35 26.18 39.66 36.30 5.40 4.96 49.59 47.88 8.85 7.79 51.00 5.51 23.16 33.37 97.53 6.53 27.75 14.46 19.57 19.83 20.43 20.20 19.79
concentration, alkali concentration and process time, designated respectively as XT , XE , XA and Xt ) and 2 pulping outputs (Kappa number and ISO brightness, as YK and YB , respectively). The current settings of independent process variables for RSM modeling were assigned based on data of the preliminary pulping tests described above, and the experimental CCRD matrix having total 29 runs was constructed to identify the statistically significant pulping effects (Table 3). As can be seen from the Pareto charts depicted in Fig. 2, the effect of alkali concentration is a principal factor defining the degree of pulp delignification and brightening during ethanol-alkali pulping, followed by the effect of process temperature and organic solvent concentration. It is also notable that the pulp brightening is more solvent dependent than the pulp delignification (the effect of ethanol on brightness is twice higher and superior to the effect of temperature). The additional dissolution in organic solvent of chromophoric groups other than those originating from lignin (e.g., carbohydrate-derived) is a likely cause of this observation. The statistical significance of the estimated pulping effects was confirmed by ANOVA. Besides the lineal effects of alkali concentration, temperature and ethanol concentration, showed absolute confidence interval of 100% (p = 0), a high statistical significance of some interaction effects was also revealed, i.e., between ethanol and alkali concentration – for pulp delignification (p = 0.02) as well as between temperature and alkali concentration – for pulp brightening (p = 0.0003). For pulping simulation, the second-order polynomial function (Eq. (1)) was fitted to experimental data of Table 4 to give two model equations describing delignification and brightening development during ethanol-alkali pulping of
YB 29.85 30.60 40.98 45.20 25.64 25.08 36.30 38.04 29.53 32.77 57.18 57.96 26.54 25.95 44.20 44.56 35.41 53.04 45.66 31.14 18.29 52.62 38.72 43.90 42.10 42.22 42.20 41.88 42.58
pre-hydrolyzed cardoon stalks (Eqs. (2) and (3), respectively). Only statistically significant regression coefficients were used for process modeling. YK = 923.237 − 8.711XT + 0.025XT2 − 1.625XE + 0.025XE2 2 − 4.112XA + 0.085XA − 0.022XE XA
(2)
YB = −98.2585 + 3.0458XE − 0.0144XE2 − 1.1909XA 2 − 0.0218XA + 0.3983Xt + 0.0249XT XA − 0.0117XE XA
(3)
The determination and adjusted determination coefficients of the obtained equations were found respectively 2 2 = 0.98) and R2 = 0.97 (RAdj. = 0.95), pointing as R2 = 0.99 (RAdj. to high statistical significance of both models. The simulated pulping effects described by Eqs. (2) and (3) are illustrated by surface plots in Figs. 3 and 4. The presence of stationary (extreme) points on the plots allowed defining the desirable (near-stationary) regions of process variables leading to the maximal predictable levels of pulping outputs. As follows from Fig. 3, the highest degree of pulp delignification can be expected at 30–40% alkali load, 45–50% ethanol content and 170–175 ◦ C, keeping fixed pulping time at 180 min, set as a central point. The same optimal solvent proportion of 45–50% was also reported for the auto-catalyzed ethanol pulping of cardoon stalks as providing the highest lignin dissolution and preventing lignin precipitation on cellulose fibers (Oliet et al., 2005). The above indicated settings agree closely with those
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
ARTICLE IN PRESS
CHERD-1466; No. of Pages 9
6
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
Table 4 – ANOVA of estimated linear (L), quadratic (Q) and interaction effects of pulping factors on Kappa number (YK ) and brightness (YB ) of produced pulps. Factor
YK SS
(1) Temperature (L) Temperature (Q) (2) Ethanol (L) Ethanol (Q) (3) NaOH (L) NaOH (Q) (4) Time (L) Time (Q) 1L by 2L 1L by 3L 1L by 4L 2L by 3L 2L by 4L Error Total SS
YB
df
F
2591.68 161.41 241.55 161.74 9010.15 1852.81 99.88 12.96 – 6.3 5.34 78.77 –
1 1 1 1 1 1 1 1 – 1 1 1 –
202.18 12.59 18.84 12.63 702.88 144.54 7.79 1.01 – 0.49 0.42 6.14 –
217.92 14,178.18
17 28
required to achieve the maximum brightness level of pulps (Fig. 4), as it could be expected, assuming the dominant role of lignin-derived chromospheres on brightness development of chemical pulps. The partial differentiation of the fitted polynomial functions in respect to each independent variable gave the set of optimal reaction conditions at extreme points of the surface
p 0 0.0025 0.0004 0.0025 0 0 0.0125 0.3288 – 0.4928 0.5274 0.0240 –
df
281.95 – 313.93 56.07 1787.45 127.85 17.17 13.79 13.36 98.80 – 21.81 4.04
1 – 1 1 1 1 1 1 1 1 – 1 1
80.11 2781.01
17 28
F 59.83 – 66.62 11.90 379.29 27.13 3.64 2.93 2.83 20.97 – 4.63 0.86
p 0.0001 × 10−2 – 0 0.0031 0 0.0001 0.0733 0.1053 0.1105 0.0003 – 0.0461 0.3675
plots, to gain the maximum expected degree of delignification and brightening during pulping. The following optimal conditions were established: 171.7 ◦ C; 49.0% (vol.) ethanol; 37.1% NaOH and 196.7 min, with expected Kappa number of 4.15. To validate these data, the replicated pulping experiments were performed under optimized conditions. The high purity dissolving grade pulps having 4.24 Kappa (ca. 0.55% Klason lignin), 55.4% ISO brightness and 93.8% ␣-cellulose were produced showing very good correlation between experimental and predicted by model data. A wide-angle X-ray diffraction analysis (XRD) of these pulps revealed a very high degree (index) of cellulose crystallinity, CrI of 79.5% (Fig. 5), thereby supporting the claimed above changes in cellulose fiber morphology during dilute acid hydrolysis and subsequent organosolv delignification and related to partial removal of amorphous cellulose portion. Obviously that the quality parameters of obtained pulps can be easily improved by simplified purification (or bleaching) treatment, such as a caustic extraction or peroxide bleaching, thereby further increasing the proportion of ␣-cellulose and CrI in fiber product.
3.4.
Fig. 2 – Pareto charts of standardized effects affecting degree of pulp delignification (top) and brightening (bottom) during ethanol-alkali pulping of pre-hydrolyzed cardoon stalks.
SS
Integrated biorefining scheme
To justify the feasibility of the employed biorefining scheme, it is of practical interest to follow the mass balance of the main chemical constituents of cardoon biomass during each fractionation/upgrading stage. The mass balance flow diagram of cardoon stalks fractionation is shown in Fig. 6. As seen, the dilute acid hydrolysis followed by organosolv delignification enables to separate quite selectively the whole-stalk material into hemicellulosic carbohydrates, cellulose and lignin. From each 100 g of dry biomass, 18.1 g of monomeric xylose, 35.3 g of pure cellulosic fibers and 13.8 g of technical lignin can be produced. The main component losses (ca. 14% of xylose, 6.1% of cellulose and 21.1% of lignin) take place during hydrolysis due to inevitable acid-catalyzed degradation/solubilization processes. The cellulose and lignin recovery after organosolv pulping of the xylan-free residue is very high and accounts for ca. 96% each. The total cellulose recovery of 90% (on initial in cardoon) was achieved after complete biomass fractionation.
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
CHERD-1466; No. of Pages 9
ARTICLE IN PRESS chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
7
Fig. 4 – Response surface plots of modeled pulp brightening under variable conditions of ethanol-alkali pulping of pre-hydrolyzed cardoon stalks. Fig. 3 – Response surface plots of modeled degree of pulp delignification under variable conditions of ethanol-alkali pulping of pre-hydrolyzed cardoon stalks.
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
ARTICLE IN PRESS
CHERD-1466; No. of Pages 9
8
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
losses and providing the required quality of the final fiber product.
Intensity
Acknowledgements The financial support of Fundac¸ão para a Ciência e a Tecnologia (FCT, Portugal) within research contract PTDC/AGRCFL/103840/2008 is gratefully acknowledged. The authors thank Prof. S. Dias-Ferreira for valuable discussion and D. Neiva for technical assistance. We also thank Dr. I. Bento and Prof. M.T. Duarte for help with XRD analysis.
0
10
20
30
40
2Θ Θ Fig. 5 – X-ray diffractogram of cardoon ethanol-alkali pulp.
Cardoon (100 g dry weight)
18.9 g xylan 39.3 g glucan 18.2 g lignin
1477.3 g water 19.2 g sulfuric acid
Hydrolyzate Acid hydrolysis
18.1 g xylose 2.0 g glucose 1.0 g furfural 0.3 g HMF 3.6 g acetic acid
Residue (56.9 g)
36.9 g glucan 14.4 g lignin 0.1 g xylan
21.1 g NaOH 194.6 g ethanol
Organosolv pulping
Lignin (13.8 g)
Cellulose fibers (35.3 g)
33.1 g α-cellulose Fig. 6 – Mass balance flow diagram of cardoon whole-stalk material fractionation.
4.
Conclusions
High purity dissolving grade pulps were produced by statistically modeled acid hydrolysis and organosolv (ethanolalkali) delignification of the cardoon whole stalk material. Despite the morphological and chemical heterogeneity of cardoon stalks, which affects the uniformity and therefore effectiveness of cardoon chemical processing, the selective fractionation of the whole-stalk material on the main chemical constituents can be realized through modeling and optimization of the applied separation processes. The employed response surface methodology of data treatment allowed identifying the main factors affecting the effectiveness of cellulose isolation, preventing significant cellulose
References Abrantes, S., Amaral, M.E., Costa, A.P., Duarte, A.P., 2007. Cynara cardunculus L. alkaline pulping: alternative fibres for paper and paperboard production. Bioresour. Technol. 98, 2873–2878. Antunes, A., Amaral, M.N., Belgacem, N., 2000. Cynara cardunculus L.: chemical composition and soda-anthraquinone cooking. Ind. Crops Prod. 12, 85–91. Benjelloun-Mlayah, B., Lopez, S., Delmas, M., 1997. Oil and paper pulp from Cynara cardunculus: preliminary results. Ind. Crops Prod. 6, 233–236. Dalianis, C., Panoutsou, C., Dercas, N., 1996. Spanish thistle artichoke Cynara cardunculus L. under Greek conditions. In: Chartier, P., Ferrero, G.L., Henius, U.M., Hultberg, S., Sachau, J., Wiinblad, M. (Eds.), 9th European Biomass Conference. Pergamon Press, Oxford, Copenhagen, Denmark, pp. 663–668. Fengel, D., Wegener, G., 1984. Wood (Chemistry, Ultrastructure, Reactions). Walter de Gruyter, Berlin, New York. Fernández, J., 1998. Cardoon. In: Bassam, N. (Ed.), Energy Plant Species. James & James Science Publishers Ltd., London, pp. 113–117. Fernández, J., Curt, M.D., Aguado, P.L., 2006. Industrial applications of Cynara cardunculus L. for energy and other uses. Ind. Crops Prod. 24, 222–229. Fernando, S., Adhikari, S., Chandrapal, C., Murali, N., 2006. Biorefineries: current status, challenges, and future direction. Energy Fuels 20, 1727–1737. FitzPatrick, M., Champagne, P., Cunningham, M.F., Whitney, R.A., 2010. A biorefinery processing perspective: treatment of lignocellulosic materials for the production of value-added products. Bioresour. Technol. 101, 8915–8922. Gominho, J., Fernández, J., Pereira, H., 2001. Cynara cardunculus L. – a new fibre crop for pulp and paper production. Ind. Crops Prod. 13, 1–10. Hu, F., Jung, S., Ragauskas, A., 2013. Impact of pseudolignin versus dilute acid-pretreated lignin on enzymatic hydrolysis of cellulose. ACS Sustainable Chem. Eng. 1, 62–65. Kamm, B., Kamm, M., 2007. Biorefineries – multi product processes. Adv. Biochem. Eng. Biotechnol. 105, 175–204. Kamm, B., Schneider, B.U., Hüttl, R.F., Grünewald, H., Gusovius, H.-J., Stollberg, C., Ay, P., Kamm, M., 2006. Lignocellulosic feedstock biorefinery – combination of technologies of agroforestry and a biobased substance and energy economy. Forum der Forschung 19, 53–62. Li, J., Henriksson, G., Gellerstedt, G., 2007. Lignin depolymerization/repolymerization and its critical role for delignification of aspen wood by steam explosion. Bioresour. Technol. 98, 3061–3068. Ligero, P., Villaverde, J.J., Vega, A., Bao, M., 2007. Acetosolv delignification of depithed cardoon (Cynara cardunculus) stalks. Ind. Crops Prod. 25, 294–300. Ligero, P., Villaverde, J.J., Vega, A., Bao, M., 2008. Pulping cardoon (Cynara cardunculus) with peroxyformic acid (MILOX) in one single stage. Bioresour. Technol. 99, 5687–5693. Myers, R.H., Montgomery, D.C., Anderson-Cook, C.M., 2009. Response Surface Methodology: Process and Product Optimization using Designed Experiment, third ed. John Wiley and Sons, New York.
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
CHERD-1466; No. of Pages 9
ARTICLE IN PRESS chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
Moxley, G., Gaspar, A.R., Higgins, D., Xu, H., 2012. Structural changes of corn stover lignin during acid pretreatment. J. Ind. Microbiol. Biotechnol. 39, 1289–1299. Oliet, M., Gilarranz, M.A., Domínguez, J.C., Alonso, M.V., Rodríguez, F., 2005. Ethanol-based pulping from Cynara cardunculus L. J. Chem. Technol. Biotechnol. 80, 746–753. Ragauskas, A.J., Williams, C.K., Davison, B.H., Britovsek, G., Cairney, J., Eckert, C.A., Frederick Jr., W.J., Hallett, J.P., Leak, D.J., Liotta, C.L., Mielenz, J.R., Murphy, R., Templer, R., Tschaplinski, T., 2006. The path forward for biofuels and biomaterials. Science 31, 484–489. Samuel, R., Pu, Y., Raman, B., Ragauskas, A., 2010. Structural characterization and comparison of switchgrass ball-milled lignin before and after dilute acid pretreatment. App. Biochem. Biotechnol. 162, 62–74. Sannigrahi, P., Kim, D.H., Jung, S., Ragauskas, A., 2011. Pseudo-lignin and pretreatment chemistry. Energy Environ. Sci. 4, 1306–1310. Sarkanen, K.V., 1990. Chemistry of solvent pulping. Tappi J. 73, 215–219. Segal, A., Creely, J.J., Martin, A.E., Conrad, C.M., 1959. An empirical method for estimating the degree of crystallinity of native
9
cellulose using the X-ray diffractometer. Textile Res. J. 29, 786–794. Selig, M., Weiss, N., Ji, Y., 2008. Enzymatic Saccharification of Lignocellulosic Biomass. NREL/TP-510-42629 Standard. Laboratory Analytical Procedure, USA. Shatalov, A.A., Pereira, H., 2004. Arundo donax L. reed: new perspectives for pulping and bleaching – 3. Ethanol reinforced alkaline pulping. Tappi J. 3 (2), 27–31. Shatalov, A.A., Pereira, H., 2007. Polysaccharide degradation during ozone-based TCF bleaching of non-wood organosolv pulps. Carbohydr. Polym. 67, 275–281. Shatalov, A.A., Pereira, H., 2011. Biorefinery of energy crop cardoon (Cynara cardunculus L.) – hydrolytic xylan production as entry point to complex fractionation scheme. Chem. Eng. Process Technol. 2 (5), 118–125. Sixta, H., 2006. Dissolving grade pulp. In: Sixta, H. (Ed.), Handbook of Pulp. Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim, pp. 1022–1067. Villar, J.C., Poveda, P., Tagle, J.L., 1999. Obtención de pastas al sulfato a partir del cardo (Cynara cardunculus L.). Influencia del troceado sobre la calidad de las pastas. Invest. Agr. Sist. Recur. For. 8, 305–317.
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
CHERD-1466; No. of Pages 9
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
Contents lists available at ScienceDirect
Chemical Engineering Research and Design journal homepage: www.elsevier.com/locate/cherd
Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass Anatoly A. Shatalov ∗ , Helena Pereira Universidade Técnica de Lisboa, Instituto Superior de Agronomia, Centro de Estudos Florestais (CEF), Tapada da Ajuda, 1349-017 Lisboa, Portugal
a b s t r a c t A biorefinery scheme with separate processing of the two main carbohydrate streams (cellulose and hemicellulosederived) was employed to the energy crop cardoon (Cynara cardunculus L.) to fractionate the whole stalk material. A high quality xylose-enriched substrate was obtained after selective one-step dilute sulfuric acid hydrolysis of hemicelluloses, yielding 18.1 g of xylose per 100 g of dry biomass. The xylan-free solid residue was delignified by sulfur-free organosolv pulping to produce dissolving grade pulps having 93.8% of ␣-cellulose (33.1 g per 100 g dry initial biomass) and 79.5% degree of crystallinity. About 76% of crop lignin (13.8 g per 100 g dry initial biomass) was recovered from the spent pulping liquor as a high purity reactive precipitated organosolv lignin. Response surface methodology was used for statistical modeling and optimization of the applied separation processes. The central composite rotatable design was applied to assess the effects of the principal technological parameters on the main reaction outputs. © 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Keywords: Biorefinery; Cynara cardunculus; Dissolving pulp; Sulfur-free delignification; Modeling; Optimization
1.
Introduction
The use of renewable biomass to replace petroleum-based chemicals from depleting fossil resources is a challenge that has attracted much current interest and importance (Ragauskas et al., 2006). The biorefinery concept of biomass processing, where a complex of different treatments (physical, chemical and biological) is applied for complete biomass fractionation, is being considered now as a more potential way for sustainable bio-based economy (Fernando et al., 2006; Kamm and Kamm, 2007). Lignocellulosic biomass has received particular attention, as a more promising biorefinery feedstock (Kamm et al., 2006; FitzPatrick et al., 2010). Among a wide variety of lignocellulosic biomass sources, the perennial herbaceous energy crops represent abundant and low-cost feedstock for biorefining technology. The artichoke thistle cardoon (Cynara cardunculus L.) is a naturally growing perennial herb in the Mediterranean region. The easy adaptability of cardoon to hot and dry climatic
conditions and remarkable seasonal growth (up to 3 m height and 1.5 m diameter spread area (Fernández, 1998)) stimulated the cardoon cultivation as a perennial field energy crop for biomass production. The annually harvested yield of the aboveground biomass up to 30–35 tons ha−1 year−1 has been reported under optimum cultivation conditions (Dalianis et al., 1996). As an energy crop, the cardoon biomass can be used as a solid fuel for direct heating and electric power generation, or as a source of seed oil for biodiesel production (Fernández et al., 2006). The branched stalks of cardoon, accounting for about 40% of total dry biomass and composed generally by 20–30% of hemicelluloses, 35–45% of cellulose and 10–20% of lignin (Fernández, 1998), represent a valuable source of chemicals for industrial applications. The particularly elevated content of cellulose and good fiber characteristics, comparable with hardwoods (eucalypt), made cardoon stalks as a very promising agro-fiber raw material for pulp and paper production. The bleachable grade papermaking pulps were produced by
∗
Corresponding author. Tel.: +351 21 365 3379; fax: +351 21 365 3338. E-mail address: [email protected] (A.A. Shatalov). Received 31 May 2013; Received in revised form 6 December 2013; Accepted 3 January 2014 0263-8762/$ – see front matter © 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cherd.2014.01.007 Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
ARTICLE IN PRESS
CHERD-1466; No. of Pages 9
2
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
conventional alkaline (soda and kraft) (Benjelloun-Mlayah et al., 1997; Antunes et al., 2000; Gominho et al., 2001; Abrantes et al., 2007) and eco-clean organosolv delignification technologies (Ligero et al., 2007, 2008; Oliet et al., 2005). The cardoon stalks contain central pith that forms the high content of fines during pulping (Villar et al., 1999). The reduced drainage capacity and porosity of cardoon pulps suggested the stalks depithing before pulping. This explains the fact that almost all previous research on cardoon pulping was done based on depithed material. However, the stalk depithing requires additional investments thus increasing the total production costs and efforts should be done to use the whole stalk material. One way for upgrading cardoon biomass could be to obtain cellulosic fibers after preliminary valorization of non-cellulosic carbohydrates. During this selective removal of hemicelluloses, e.g., by acid hydrolysis, the other lowmolecular substances of cardoon stalk, and particularly of pith, will be also dissolved in solution, thus diminishing the impact of the pith on the following pulp production. High purity dissolving grade pulps can be produced after appropriate delignification of pre-hydrolyzed cardoon whole stalks. Nowadays, the dissolving grade pulps with 92–96% of ␣-cellulose are commercially produced from woody species using pre-hydrolysis kraft or acid sulfite processes followed by elemental chlorine-free (ECF) bleaching (Sixta, 2006). The application of sulfur-free organosolv delignification in combination with totally chlorine-free (TCF) bleaching would be a significant step in meeting environmental and economic concerns related to conventional industrial technologies. Following an integrated biorefinery scheme, the possibility of dissolving grade pulp production from cardoon (C. cardunculus) whole stalk material (with pith) after selective acid hydrolysis of hemicellulosic polysaccharides has been studied, alternatively to bioethanol production. The results on process modeling and optimization by response surface methodology (RSM) are presented and discussed in this paper.
2.2.
Ethanol-alkali delignification of the pre-hydrolyzed (xylanfree) cardoon stalks was carried out in 100 cm3 stainless steel digesters rotated in an oil bath. The digesters were loaded with 8 g (on oven-dry basis) of pre-hydrolyzed material and 84 ml of pulping solution. The process variables were reaction time (150–210 min), reaction temperature (140–160 ◦ C), ethanol content (40–60% vol.) and alkali charge (15–35% on oven-dry material). Heating-up period, pre-defined by preliminary experiments, was excluded from the resident time. After cooking, pulps were defibrated using standard pulp disintegrator, thoroughly washed with deionized water and air-dried before total yield determination. When necessary, the defibrated pulps were screened in a laboratory flat screen with 0.2 mm slit-width (Buchet, Netherlands) for separation of rejects.
2.3.
Materials and methods
2.1.
Raw material and chemicals
Cardoon biomass was sampled from the university experimental field (School of Agriculture, Lisbon). The air-dried branched stalks were manually stripped of residual leaves, cut without depithing in the knife Retsch mill and screened to a particle size of 40–60 mesh (for chemical analysis) or of approx. match size of 5–10 mm length and 1–2 mm width (for pulping experiments), homogenized and stored in sealed plastic bags at room temperature until using. Moisture content of the prepared materials was determined according to TAPPI standards. Selective hydrolytic removal of hemicelluloses (xylan) from cardoon whole stalk material was performed before pulping using previously established optimum reaction conditions (138.5 ◦ C; 1.28% sulfuric acid solution; 52 min), as described elsewhere (Shatalov and Pereira, 2011). All chemicals used in this study were of analytical grade purity and purchased from Sigma, Ardrich and Fluka Chemical Co.
Analytical methods
Extractives were determined gravimetrically after successive Soxhlet extraction by dichloromethane, ethanol and water. Acid-insoluble (Klason) and acid-soluble lignin were determined according to TAPPI T 222 om-88 and TAPPI UM 250 standards, respectively. Monosaccharide composition was determined by GC as alditol-acetate derivatives, under conditions described elsewhere (Shatalov and Pereira, 2007). Residual lignin in pulps was determined as Kappa number according to T 236 cm-85 TAPPI standards. The ␣cellulose content was determined according to T 203 om-93 TAPPI standard. The cupri-ethylenediamine (CED) intrinsic pulp viscosity was measured according to SCAN-CM 15:88 standard. Handsheet formation for reflectance test was performed according to TAPPI T 272 om-92 standard. Pulp optical properties (ISO brightness and DIN 6167 C/2 yellowness index) were measured by CM-3630 Spectrophotometer (Minolta).
2.4.
2.
Organosolv pulping
X-ray diffractometry (XRD) of cellulose fibers
Crystalline structure of cellulose samples was analyzed by wide-angle XRD experiments on Bruker D8 ADVANCE powder diffractometer with symmetric Bragg-Brentano scattering geometry, using Ni-filtered Cu K␣ radiation ( = 0.1542 nm; 40 kV operating voltage; 30 mA current) and secondary graphite monochromator. Data were collected in the 2 range of 5–60◦ with interval of 0.02◦ and counting time of 20 s per interval. Degree of cellulose crystallinity (crystallinity index, CrI) was calculated from the resulting diffraction curves (diffractograms) using empirical method of Segal et al. (1959).
2.5.
Modeling and optimization of delignification
Response surface methodology (Statistica 6.0, Statsoft, USA) was used for statistical modeling and optimization of delignification conditions. The main effects (linear and quadratic) of the independent process variables (time, temperature, ethanol and alkali concentration) and their interactions were estimated using 24 central composite rotatable design (CCRD). An optimum set of reaction conditions providing maximum predicted pulping outputs (Kappa number and brightness) was
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
ARTICLE IN PRESS
CHERD-1466; No. of Pages 9
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
Table 1 – Chemical composition of pre-hydrolyzed cardoon whole stalk material. Component
Content (% on oven-dry residue)
Extractives Lignin Klason Acid-soluble Glucan Xylan
9.65 (25.41)a 25.24 (21.11) 24.02 (11.64) 1.22 (74.73) 64.85 (6.10) 0.18 (99.47)
a
In brackets: component loss after hydrolysis (%).
established after fitting the second-order polynomial model (Eq. (1)) to experimental data.
Y = b0 +
3 i=1
bi Xi +
3 i=1
bii Xi2 +
3
bij Xi Xj
(1)
i
where Y is a predicted response (Kappa number or ISO brightness), b0 is an interception coefficient (regression coefficient at central point), bi are the linear coefficients, bii are the quadratic coefficients, bij are the interaction coefficients, and Xi and Xj are the independent variables (temperature, time, alkali and ethanol concentrations). ANOVA was used to check statistical significance of all found regression coefficients and estimated effects.
3.
Results and discussion
3.1.
Selective hydrolysis of xylan
As a first stage of multi-step fractionation scheme, a low temperature dilute sulfuric acid hydrolysis was applied to the whole stalk material of cardoon for selective removal of hemicellulose carbohydrates, which consist by ca. 90% of xylan polysaccharides (Shatalov and Pereira, 2011). The xylanto-xylose conversion of 86% was achieved in solution after one-step reaction performed under previously optimized conditions. The limited formation of furan substances (1.04% furfural and 0.33% 5-hydroxymethylfurfural) provided the high quality of xylose-enriched substrate for subsequent biochemical conversion to final products, such as xylitol (Shatalov and Pereira, 2011). The insoluble solid residue after hydrolysis contained only 0.2% of xylan (Table 1), indicating almost complete (by 99.5%) xylan removal during hydrolysis. Besides xylan, about 25.4% of extractives (as a water-soluble extractive fraction) and 21.1% of lignin (mainly as acid-soluble lignin) were also removed from the cardoon stalks, resulting in total gravimetric solid recovery yield of 56.9%. The content of cellulose accounted for 64.9% of the insoluble residue. Referring to Table 1, only ca. 6.1% of cellulose (2.4% of stalk mass) was dissolved under the optimized hydrolysis conditions specifically designed for selective xylan removal, reflecting the experimentally defined balanced correlation between efficiency of xylan-to-xylose conversion and hydrolysis selectivity. This dissolved cellulose represents the less ordered (amorphous) cellulose fraction which has the same (or close) accessibility and reactivity to hemicellulosic polysaccharides (Fengel and Wegener, 1984). The remaining cellulose in insoluble residue was easily digested (saccharificated) by commercial cellulase preparations to fermentable sugars for
3
bioethanol production. After 48 h of enzymatic hydrolysis under standard (non-optimized) NREL conditions (Selig et al., 2008), the degree of cellulose conversion to monomeric glucose of ca. 80% (ca. 75% of crop cellulose, or 32 g Glc/100 g cardoon stalks) was achieved vs. ca. 18% (8 g Glc/100 g cardoon stalks) for untreated biomass. Alternatively, the xylan-free solid residue after cardoon hydrolysis can be used as a source of cellulose fibers for production of high purity dissolving grade pulps. At this case, the partial removal of amorphous cellulose portion during acid pre-hydrolysis would be even advantageous, since it implies a direct increase in content of high-ordered ␣-cellulose fraction having critical importance for dissolving pulps.
3.2.
Delignification of xylan-free residues
Meeting the environmental concerns related to commercial delignification technologies, the eco-friendly (sulfur-free) pulping approach based on use of organic solvents in the reaction system (organosolv pulping) was employed for the delignification of the xylan-free residues of cardoon stalks. The ethanol-alkali pulping was chosen among a group of potential organosolv processes, as proved to be very effective in lignin removal and polysaccharide preservation of nonwood (agro-fiber) sources (Shatalov and Pereira, 2004), even though the chemical recovery issues of this technology still need to be solved. The presence of alcohol improves solubility of the formed lignin fragments and prevents lignin condensation by alkylation of active reaction centers, such as benzyl alcohol groups (Sarkanen, 1990), thus providing deep delignification under rather moderate pulping conditions. The principal results of ethanol-alkali pulping of the xylanfree cardoon stalks under variable process conditions are summarized in Table 2. It is evident that within the applied (economically reasonable) ranges of alkali charge 15–35% and ethanol content 40–60%, the low process temperature of 140 ◦ C, reported to be ideally suited for untreated agrobiomass (Shatalov and Pereira, 2004), is not sufficient to produce acceptable quality pulp from the pre-hydrolyzed material. Similar to traditional soda pulping, the alkalinity (or hydroxide ion concentration) is the main factor of ethanolalkali method. At the alkali load of 15%, poorly delignified pulps with very high Kappa number (Kappa 57.7 or ca. 7.5% Klason lignin) and rejects content (48.8% uncooked material) were produced after 2.5 h pulping at 140 ◦ C and 40% (vol.) of ethanol in solution. The increase in alkali charge up to 35% substantially improved delignification, but still yielding pulps with quite high Kappa 29.6 (ca. 4% Klason lignin) and 8.6% rejects. The structural changes in cardoon cell-wall constituents caused by acid hydrolysis, and particularly the changes in lignin structure, are the obvious reasons for the observed decreased pulping efficiency in comparison with untreated biomass (Shatalov and Pereira, 2004). Despite the mentioned partial lignin defragmentation and dissolution in acidic solution, mainly as a result of the cleavage (acidolysis) of -O-4 (Li et al., 2007), but also - and -5 linkages (Samuel et al., 2010), the parallel competing reaction of lignin repolymerization (via acid-catalyzed condensation between aromatic carbons at C6 or C5 and carbonium ion formed from benzyl alcohol lignin structure at C␣ ) takes also place, leading to formation of new stable condensed (C–C) structures and decrease in lignin reactivity and solubility (Moxley et al., 2012). Besides
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
ARTICLE IN PRESS
CHERD-1466; No. of Pages 9
4
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
Table 2 – Results of ethanol-alkali pulping of pre-hydrolyzed cardoon whole stalk material. Temperature (◦ C) 140
Time (min)
Ethanol (%, v/v)
150
40
NaOH (% odm)
60
160
210
40
150
40 60
210
a
40
Kappa number
Brightness (% ISO)
DPa
Yield (% odm)
Rejects (% odm)
15 35 15 35 15 35
57.7 29.6 68.7 31.4 54.1 24.1
29.9 41.0 25.6 36.3 30.6 45.2
1788 1657 1515 1193 1703 1630
59.9 51.6 62.0 52.3 59.0 49.7
48.8 8.6 51.3 11.2 47.0 2.1
15 35 15 35 15 35
39.7 5.4 49.6 8.9 36.3 5.0
31.5 57.2 26.5 44.2 32.8 58.0
1174 923 860 535 940 760
54.0 45.8 55.2 45.1 52.7 44.5
30.6 0 37.0 0 24.6 0
Degree of polymerization (DP) was calculated by Evans and Wallis equation: DP0.85 = 1.1[] (SCAN-CM 15:88 Standard).
lignin condensation, a lignin-like material (the so-called pseudo-lignin) is also formed during dilute acid hydrolysis due to reactions between carbohydrate- and lignin-derived degradation products (Sannigrahi et al., 2011). Formation of pseudo-lignin is particularly notable under elevated hydrolysis temperatures, significantly affecting the subsequent biochemical processing of pre-hydrolyzed biomass (Hu et al., 2013). As can be seen from Table 2, even a substantial increase in ethanol-alkali pulping temperature up to 160 ◦ C under an alkali load of 15% (40% (v/v) ethanol) did not provide effective delignification of the pre-hydrolyzed cardoon stalks, producing pulps with high Kappa 39.7 (ca. 5.2% Klason lignin) and 30.6% rejects. A high yield of rejects was also noted for other organosolv methods applied to cardoon, such as auto-catalyzed ethanol pulping (Oliet et al., 2005), and was associated with morphological heterogeneity of cardoon stalks given by the centrally located pith parenchymal cells and the surrounding fibro-vascular bundles. The topochemical effect of stalk morphology affects the uniformity of delignification reaction, resulting in increased content of uncooked material (rejects), what was also confirmed by experiments with de-pithed material (Ligero et al., 2007). A very good correlation (R2 = 0.93) was established at this study between Kappa number in ethanol-alkali pulps and amount of rejects (Fig. 1).
60
Rejects (%)
50 R² = 0,9301
40 30 20 10 0
The anatomic heterogeneity is therefore a factor affecting the ethanol-alkali delignification of cardoon whole stalk material, along with the effects caused by acid pre-hydrolysis. Only the simultaneous increase in process temperature and alkali concentration allowed reaching the delignification degree desirable for production of dissolving grade pulps. At 160 ◦ C and 35% NaOH (2.5 h; 40% (v/v) ethanol), the deeply delignified pulps were obtained, having very low for unbleached pulp Kappa 5.4 (ca. 0.7% Klason lignin), high brightness of 57.2% ISO and no rejects. Despite the noted drop in pulp yield and intrinsic viscosity/degree of polymerization (DP), as an indicator of polysaccharide degradation reactions under elevated medium alkalinity, their values were close to those reported for other organosolv pulps from cardoon (Ligero et al., 2007, 2008; Oliet et al., 2005) and within the acceptable range for dissolving grade pulps (Sixta, 2006). Effective delignification can be also performed at ethanol proportion of 60% (vol.) in reaction solution, at 160 ◦ C and 35% alkali (Table 2). No rejects are formed and the pulp/fiber yield is practically the same as in 40%-ethanol pulping. However, the Kappa number of pulp is higher while the brightness and particularly viscosity (DP) is lower, following the observed tendency of decrease in delignification and pulping efficiency after increase in solvent content up to 60%. Similar results were earlier reported for other agro-crops, where the solvent proportion of ca. 40% was noted as the best suited for ethanol-alkali pulping (Shatalov and Pereira, 2004). The delignification efficiency can be somewhat improved by pulping extension to 3.5 h, resulting in pulps with lower Kappa number and higher brightness. However, the prolonged pulping at high temperatures and alkali concentrations favors further cellulose degradation leading to significant drop in pulp viscosity. This declines the selectivity of ethanol-alkali delignification as a whole and affects the quality of the final fiber product.
3.3. 20
30
40
50
60
Pulping modeling and optimization
70
Kappa number Fig. 1 – Correlation between degree of delignification and amount of rejects formed during ethanol-alkali pulping of pre-hydrolyzed cardoon stalks.
Optimization of ethanol-alkali pulping was done using response surface methodology (RSM) (Myers et al., 2009). Statistical model of delignification was developed based on the 24 central composite rotatable design (CCRD) with 4 independent process variables (process temperature, ethanol
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
ARTICLE IN PRESS
CHERD-1466; No. of Pages 9
5
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
Table 3 – Experimental central composite rotatable design (CCRD) matrix and pulping responses used for RSM modeling. Run no.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 (C) 26 (C) 27 (C) 28 (C) 29(C)
Coded variables
[−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] [−2; 0; 0; 0] [+2; 0; 0; 0] [0; −2; 0; 0] [0; +2; 0; 0] [0; 0; −2; 0] [0; 0; +2; 0] [0; 0; 0; −2] [0; 0; 0; +2] [0; 0; 0; 0] [0; 0; 0; 0] [0; 0; 0; 0] [0; 0; 0; 0] [0; 0; 0; 0]
Decoded variables
Pulping responses
XT
XE
XA
Xt
YK
140 140 140 140 140 140 140 140 160 160 160 160 160 160 160 160 130 170 150 150 150 150 150 150 150 150 150 150 150
40 40 40 40 60 60 60 60 40 40 40 40 60 60 60 60 50 50 30 70 50 50 50 50 50 50 50 50 50
15 15 35 35 15 15 35 35 15 15 35 35 15 15 35 35 25 25 25 25 5 45 25 25 25 25 25 25 25
150 210 150 210 150 210 150 210 150 210 150 210 150 210 150 210 180 180 180 180 180 180 120 240 180 180 180 180 180
57.70 54.06 29.58 24.12 68.70 67.16 31.35 26.18 39.66 36.30 5.40 4.96 49.59 47.88 8.85 7.79 51.00 5.51 23.16 33.37 97.53 6.53 27.75 14.46 19.57 19.83 20.43 20.20 19.79
concentration, alkali concentration and process time, designated respectively as XT , XE , XA and Xt ) and 2 pulping outputs (Kappa number and ISO brightness, as YK and YB , respectively). The current settings of independent process variables for RSM modeling were assigned based on data of the preliminary pulping tests described above, and the experimental CCRD matrix having total 29 runs was constructed to identify the statistically significant pulping effects (Table 3). As can be seen from the Pareto charts depicted in Fig. 2, the effect of alkali concentration is a principal factor defining the degree of pulp delignification and brightening during ethanol-alkali pulping, followed by the effect of process temperature and organic solvent concentration. It is also notable that the pulp brightening is more solvent dependent than the pulp delignification (the effect of ethanol on brightness is twice higher and superior to the effect of temperature). The additional dissolution in organic solvent of chromophoric groups other than those originating from lignin (e.g., carbohydrate-derived) is a likely cause of this observation. The statistical significance of the estimated pulping effects was confirmed by ANOVA. Besides the lineal effects of alkali concentration, temperature and ethanol concentration, showed absolute confidence interval of 100% (p = 0), a high statistical significance of some interaction effects was also revealed, i.e., between ethanol and alkali concentration – for pulp delignification (p = 0.02) as well as between temperature and alkali concentration – for pulp brightening (p = 0.0003). For pulping simulation, the second-order polynomial function (Eq. (1)) was fitted to experimental data of Table 4 to give two model equations describing delignification and brightening development during ethanol-alkali pulping of
YB 29.85 30.60 40.98 45.20 25.64 25.08 36.30 38.04 29.53 32.77 57.18 57.96 26.54 25.95 44.20 44.56 35.41 53.04 45.66 31.14 18.29 52.62 38.72 43.90 42.10 42.22 42.20 41.88 42.58
pre-hydrolyzed cardoon stalks (Eqs. (2) and (3), respectively). Only statistically significant regression coefficients were used for process modeling. YK = 923.237 − 8.711XT + 0.025XT2 − 1.625XE + 0.025XE2 2 − 4.112XA + 0.085XA − 0.022XE XA
(2)
YB = −98.2585 + 3.0458XE − 0.0144XE2 − 1.1909XA 2 − 0.0218XA + 0.3983Xt + 0.0249XT XA − 0.0117XE XA
(3)
The determination and adjusted determination coefficients of the obtained equations were found respectively 2 2 = 0.98) and R2 = 0.97 (RAdj. = 0.95), pointing as R2 = 0.99 (RAdj. to high statistical significance of both models. The simulated pulping effects described by Eqs. (2) and (3) are illustrated by surface plots in Figs. 3 and 4. The presence of stationary (extreme) points on the plots allowed defining the desirable (near-stationary) regions of process variables leading to the maximal predictable levels of pulping outputs. As follows from Fig. 3, the highest degree of pulp delignification can be expected at 30–40% alkali load, 45–50% ethanol content and 170–175 ◦ C, keeping fixed pulping time at 180 min, set as a central point. The same optimal solvent proportion of 45–50% was also reported for the auto-catalyzed ethanol pulping of cardoon stalks as providing the highest lignin dissolution and preventing lignin precipitation on cellulose fibers (Oliet et al., 2005). The above indicated settings agree closely with those
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
ARTICLE IN PRESS
CHERD-1466; No. of Pages 9
6
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
Table 4 – ANOVA of estimated linear (L), quadratic (Q) and interaction effects of pulping factors on Kappa number (YK ) and brightness (YB ) of produced pulps. Factor
YK SS
(1) Temperature (L) Temperature (Q) (2) Ethanol (L) Ethanol (Q) (3) NaOH (L) NaOH (Q) (4) Time (L) Time (Q) 1L by 2L 1L by 3L 1L by 4L 2L by 3L 2L by 4L Error Total SS
YB
df
F
2591.68 161.41 241.55 161.74 9010.15 1852.81 99.88 12.96 – 6.3 5.34 78.77 –
1 1 1 1 1 1 1 1 – 1 1 1 –
202.18 12.59 18.84 12.63 702.88 144.54 7.79 1.01 – 0.49 0.42 6.14 –
217.92 14,178.18
17 28
required to achieve the maximum brightness level of pulps (Fig. 4), as it could be expected, assuming the dominant role of lignin-derived chromospheres on brightness development of chemical pulps. The partial differentiation of the fitted polynomial functions in respect to each independent variable gave the set of optimal reaction conditions at extreme points of the surface
p 0 0.0025 0.0004 0.0025 0 0 0.0125 0.3288 – 0.4928 0.5274 0.0240 –
df
281.95 – 313.93 56.07 1787.45 127.85 17.17 13.79 13.36 98.80 – 21.81 4.04
1 – 1 1 1 1 1 1 1 1 – 1 1
80.11 2781.01
17 28
F 59.83 – 66.62 11.90 379.29 27.13 3.64 2.93 2.83 20.97 – 4.63 0.86
p 0.0001 × 10−2 – 0 0.0031 0 0.0001 0.0733 0.1053 0.1105 0.0003 – 0.0461 0.3675
plots, to gain the maximum expected degree of delignification and brightening during pulping. The following optimal conditions were established: 171.7 ◦ C; 49.0% (vol.) ethanol; 37.1% NaOH and 196.7 min, with expected Kappa number of 4.15. To validate these data, the replicated pulping experiments were performed under optimized conditions. The high purity dissolving grade pulps having 4.24 Kappa (ca. 0.55% Klason lignin), 55.4% ISO brightness and 93.8% ␣-cellulose were produced showing very good correlation between experimental and predicted by model data. A wide-angle X-ray diffraction analysis (XRD) of these pulps revealed a very high degree (index) of cellulose crystallinity, CrI of 79.5% (Fig. 5), thereby supporting the claimed above changes in cellulose fiber morphology during dilute acid hydrolysis and subsequent organosolv delignification and related to partial removal of amorphous cellulose portion. Obviously that the quality parameters of obtained pulps can be easily improved by simplified purification (or bleaching) treatment, such as a caustic extraction or peroxide bleaching, thereby further increasing the proportion of ␣-cellulose and CrI in fiber product.
3.4.
Fig. 2 – Pareto charts of standardized effects affecting degree of pulp delignification (top) and brightening (bottom) during ethanol-alkali pulping of pre-hydrolyzed cardoon stalks.
SS
Integrated biorefining scheme
To justify the feasibility of the employed biorefining scheme, it is of practical interest to follow the mass balance of the main chemical constituents of cardoon biomass during each fractionation/upgrading stage. The mass balance flow diagram of cardoon stalks fractionation is shown in Fig. 6. As seen, the dilute acid hydrolysis followed by organosolv delignification enables to separate quite selectively the whole-stalk material into hemicellulosic carbohydrates, cellulose and lignin. From each 100 g of dry biomass, 18.1 g of monomeric xylose, 35.3 g of pure cellulosic fibers and 13.8 g of technical lignin can be produced. The main component losses (ca. 14% of xylose, 6.1% of cellulose and 21.1% of lignin) take place during hydrolysis due to inevitable acid-catalyzed degradation/solubilization processes. The cellulose and lignin recovery after organosolv pulping of the xylan-free residue is very high and accounts for ca. 96% each. The total cellulose recovery of 90% (on initial in cardoon) was achieved after complete biomass fractionation.
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
CHERD-1466; No. of Pages 9
ARTICLE IN PRESS chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
7
Fig. 4 – Response surface plots of modeled pulp brightening under variable conditions of ethanol-alkali pulping of pre-hydrolyzed cardoon stalks. Fig. 3 – Response surface plots of modeled degree of pulp delignification under variable conditions of ethanol-alkali pulping of pre-hydrolyzed cardoon stalks.
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
ARTICLE IN PRESS
CHERD-1466; No. of Pages 9
8
chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
losses and providing the required quality of the final fiber product.
Intensity
Acknowledgements The financial support of Fundac¸ão para a Ciência e a Tecnologia (FCT, Portugal) within research contract PTDC/AGRCFL/103840/2008 is gratefully acknowledged. The authors thank Prof. S. Dias-Ferreira for valuable discussion and D. Neiva for technical assistance. We also thank Dr. I. Bento and Prof. M.T. Duarte for help with XRD analysis.
0
10
20
30
40
2Θ Θ Fig. 5 – X-ray diffractogram of cardoon ethanol-alkali pulp.
Cardoon (100 g dry weight)
18.9 g xylan 39.3 g glucan 18.2 g lignin
1477.3 g water 19.2 g sulfuric acid
Hydrolyzate Acid hydrolysis
18.1 g xylose 2.0 g glucose 1.0 g furfural 0.3 g HMF 3.6 g acetic acid
Residue (56.9 g)
36.9 g glucan 14.4 g lignin 0.1 g xylan
21.1 g NaOH 194.6 g ethanol
Organosolv pulping
Lignin (13.8 g)
Cellulose fibers (35.3 g)
33.1 g α-cellulose Fig. 6 – Mass balance flow diagram of cardoon whole-stalk material fractionation.
4.
Conclusions
High purity dissolving grade pulps were produced by statistically modeled acid hydrolysis and organosolv (ethanolalkali) delignification of the cardoon whole stalk material. Despite the morphological and chemical heterogeneity of cardoon stalks, which affects the uniformity and therefore effectiveness of cardoon chemical processing, the selective fractionation of the whole-stalk material on the main chemical constituents can be realized through modeling and optimization of the applied separation processes. The employed response surface methodology of data treatment allowed identifying the main factors affecting the effectiveness of cellulose isolation, preventing significant cellulose
References Abrantes, S., Amaral, M.E., Costa, A.P., Duarte, A.P., 2007. Cynara cardunculus L. alkaline pulping: alternative fibres for paper and paperboard production. Bioresour. Technol. 98, 2873–2878. Antunes, A., Amaral, M.N., Belgacem, N., 2000. Cynara cardunculus L.: chemical composition and soda-anthraquinone cooking. Ind. Crops Prod. 12, 85–91. Benjelloun-Mlayah, B., Lopez, S., Delmas, M., 1997. Oil and paper pulp from Cynara cardunculus: preliminary results. Ind. Crops Prod. 6, 233–236. Dalianis, C., Panoutsou, C., Dercas, N., 1996. Spanish thistle artichoke Cynara cardunculus L. under Greek conditions. In: Chartier, P., Ferrero, G.L., Henius, U.M., Hultberg, S., Sachau, J., Wiinblad, M. (Eds.), 9th European Biomass Conference. Pergamon Press, Oxford, Copenhagen, Denmark, pp. 663–668. Fengel, D., Wegener, G., 1984. Wood (Chemistry, Ultrastructure, Reactions). Walter de Gruyter, Berlin, New York. Fernández, J., 1998. Cardoon. In: Bassam, N. (Ed.), Energy Plant Species. James & James Science Publishers Ltd., London, pp. 113–117. Fernández, J., Curt, M.D., Aguado, P.L., 2006. Industrial applications of Cynara cardunculus L. for energy and other uses. Ind. Crops Prod. 24, 222–229. Fernando, S., Adhikari, S., Chandrapal, C., Murali, N., 2006. Biorefineries: current status, challenges, and future direction. Energy Fuels 20, 1727–1737. FitzPatrick, M., Champagne, P., Cunningham, M.F., Whitney, R.A., 2010. A biorefinery processing perspective: treatment of lignocellulosic materials for the production of value-added products. Bioresour. Technol. 101, 8915–8922. Gominho, J., Fernández, J., Pereira, H., 2001. Cynara cardunculus L. – a new fibre crop for pulp and paper production. Ind. Crops Prod. 13, 1–10. Hu, F., Jung, S., Ragauskas, A., 2013. Impact of pseudolignin versus dilute acid-pretreated lignin on enzymatic hydrolysis of cellulose. ACS Sustainable Chem. Eng. 1, 62–65. Kamm, B., Kamm, M., 2007. Biorefineries – multi product processes. Adv. Biochem. Eng. Biotechnol. 105, 175–204. Kamm, B., Schneider, B.U., Hüttl, R.F., Grünewald, H., Gusovius, H.-J., Stollberg, C., Ay, P., Kamm, M., 2006. Lignocellulosic feedstock biorefinery – combination of technologies of agroforestry and a biobased substance and energy economy. Forum der Forschung 19, 53–62. Li, J., Henriksson, G., Gellerstedt, G., 2007. Lignin depolymerization/repolymerization and its critical role for delignification of aspen wood by steam explosion. Bioresour. Technol. 98, 3061–3068. Ligero, P., Villaverde, J.J., Vega, A., Bao, M., 2007. Acetosolv delignification of depithed cardoon (Cynara cardunculus) stalks. Ind. Crops Prod. 25, 294–300. Ligero, P., Villaverde, J.J., Vega, A., Bao, M., 2008. Pulping cardoon (Cynara cardunculus) with peroxyformic acid (MILOX) in one single stage. Bioresour. Technol. 99, 5687–5693. Myers, R.H., Montgomery, D.C., Anderson-Cook, C.M., 2009. Response Surface Methodology: Process and Product Optimization using Designed Experiment, third ed. John Wiley and Sons, New York.
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007
CHERD-1466; No. of Pages 9
ARTICLE IN PRESS chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx
Moxley, G., Gaspar, A.R., Higgins, D., Xu, H., 2012. Structural changes of corn stover lignin during acid pretreatment. J. Ind. Microbiol. Biotechnol. 39, 1289–1299. Oliet, M., Gilarranz, M.A., Domínguez, J.C., Alonso, M.V., Rodríguez, F., 2005. Ethanol-based pulping from Cynara cardunculus L. J. Chem. Technol. Biotechnol. 80, 746–753. Ragauskas, A.J., Williams, C.K., Davison, B.H., Britovsek, G., Cairney, J., Eckert, C.A., Frederick Jr., W.J., Hallett, J.P., Leak, D.J., Liotta, C.L., Mielenz, J.R., Murphy, R., Templer, R., Tschaplinski, T., 2006. The path forward for biofuels and biomaterials. Science 31, 484–489. Samuel, R., Pu, Y., Raman, B., Ragauskas, A., 2010. Structural characterization and comparison of switchgrass ball-milled lignin before and after dilute acid pretreatment. App. Biochem. Biotechnol. 162, 62–74. Sannigrahi, P., Kim, D.H., Jung, S., Ragauskas, A., 2011. Pseudo-lignin and pretreatment chemistry. Energy Environ. Sci. 4, 1306–1310. Sarkanen, K.V., 1990. Chemistry of solvent pulping. Tappi J. 73, 215–219. Segal, A., Creely, J.J., Martin, A.E., Conrad, C.M., 1959. An empirical method for estimating the degree of crystallinity of native
9
cellulose using the X-ray diffractometer. Textile Res. J. 29, 786–794. Selig, M., Weiss, N., Ji, Y., 2008. Enzymatic Saccharification of Lignocellulosic Biomass. NREL/TP-510-42629 Standard. Laboratory Analytical Procedure, USA. Shatalov, A.A., Pereira, H., 2004. Arundo donax L. reed: new perspectives for pulping and bleaching – 3. Ethanol reinforced alkaline pulping. Tappi J. 3 (2), 27–31. Shatalov, A.A., Pereira, H., 2007. Polysaccharide degradation during ozone-based TCF bleaching of non-wood organosolv pulps. Carbohydr. Polym. 67, 275–281. Shatalov, A.A., Pereira, H., 2011. Biorefinery of energy crop cardoon (Cynara cardunculus L.) – hydrolytic xylan production as entry point to complex fractionation scheme. Chem. Eng. Process Technol. 2 (5), 118–125. Sixta, H., 2006. Dissolving grade pulp. In: Sixta, H. (Ed.), Handbook of Pulp. Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim, pp. 1022–1067. Villar, J.C., Poveda, P., Tagle, J.L., 1999. Obtención de pastas al sulfato a partir del cardo (Cynara cardunculus L.). Influencia del troceado sobre la calidad de las pastas. Invest. Agr. Sist. Recur. For. 8, 305–317.
Please cite this article in press as: Shatalov, A.A., Pereira, H., Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.01.007