ARTICLE pubs.acs.org/IECR
The Effect of Sodium Borohydride on Alkaline SulfiteAnthraquinone Pulping of Pine (Pinus pinea) Wood Esat G€um€u-skaya,*,† Emir Eris- ir,† H€useyin Kirci,† and Nuray Misir‡ †
The Department of Pulp and Paper and ‡The Department of Forest Engineering, Faculty of Forestry, Karadeniz Technical University, Trabzon, Turkey ABSTRACT: The improvements of adding sodium borohyride to the alkali sulfiteanthraquninone (ASAQ) pulping process on properties of pulp and paper sheets was investigated. These properties were compared to those of the ASAQ and the ethanol addition to ASAQ (ASAE) pulping processes. The screened yield increased with alkali sulfiteantraquinonesodium borohyride (ASAB) pulping process and kappa number decreased with respect to the ASAQ process. Tensile and burst index of paper sheets improved with the ASAB pulping process, and the tear index for the ASAB pulping process was slightly decreased compared to that of the ASAQ and ASAE pulping processes. It was determined that whiteness and brightness of papersheets decreased by adding sodium borohyride to the ASAQ pulping process, whereas the opacity of papersheets did not change clearly compared to ASAQ and ASAE pulping processes.
’ INTRODUCTION Alkaline sulfite (AS) pulping process was developed as an alternative to kraft pulping during the late 1960s and the first patents on alkaline sulfite cooking were issued in 19701971. The driving force of this pulping process was to reduce the odor problems, improve bleachability and beatibility, while maintaining strength properties at the level of a kraft pulp.1 The use of anthraquinone (AQ) and related compounds in alkaline pulping has opened new possibilities for developing novel pulping processes. These additives increase the delignification rate in kraft and soda pulping. Following this development, the influence of AQ and its derivatives in alkaline sulfite and neutral sulfite pulping has naturally also aroused interest. It was determined that delignification and yield improved by adding AQ to alkaline sulfite pulping processes.2 The use of AQ in AS pulping reduced the active chemical charge by 1530%, but the heat consumption was still greater than in kraft pulping.3 ASAQ pulping was modified with part of the water in the cooking liquor being replaced with methanol (ASAM) and ethanol (ASAE) for improvement of pulp properties.47 ASAM and ASAE processes provided pulp yields of better strength properties, higher yield, and better bleachability as compared to the kraft process. Despite these clear advantages over kraft pulping, these processes have so far failed to become commercialized. Methanol and ethanol are highly volatile and flammable. The investment required to reduce the risk associated with the use of alcohol and to overcome the problem of alcohol recovery would increase the production cost.8,9 There are many studies about the influence of sodium borohydride on the kraft pulping process, but these have not coincide with the interest in ASAQ and sodium borohydride. In this study, the modification of ASAQ process by adding sodium borohyride (ASAB) in pulping for high pulp yield and delignification ratio was carried out. Pulp and paper sheets properties of ASAB cooking were compared with those of ASAQ and ASAE pulping processes. r 2011 American Chemical Society
’ EXPERIMENTAL METHODS Wood samples of Pinus pinea used as a raw material were collected in the Eastern Black Sea region, Trabzon province, in Turkey. Specimens for this study were sampled and prepared according to Tappi T257 standard method for chemical analysis (Chart 1. Chemical analysis and solubility degrees of samples were carried out following standard methods.10 Wood chips for pulping were prepared in sizes of 2 2 0.20.4 (cm). The alkali sulfiteanthraquinone (ASAQ) method was selected as the cooking process in this study. Ethanol (50% in cooking liquor) and NaBH4 (1,2,3%; o.d. wood) are added in the ASAQ process to improve pulp yield and delignification ratio. The liquor-to-wood ratio for all cook batches (L/g) was 4/1. Na2SO3/NaOH in a ratio of 4/1 (20/5) was selected as the active alkali. AQ ratio and cooking temperature were 0.2% (o.d. wood) and 180 °C, respectively. An impregnation stage for all trials was carried out for 60 min at 115 °C under pulping conditions before the main cooking process. Cooking trials were made in a batch-type digester rotating at 4 rpm with automatic temperature control. The wood charge (grams oven dry basis) was 800 g for each cook. Cooking time, ethanol, and NaBH4 addition ratio were selected as variables for the processes. The pulping conditions of pine wood are presented in Table 1. The pulp yield and reject ratios were determined according to Tappi T210 standard method by gravimetric measurements in a laboratory environment. The kappa number (Tappi T236) and viscosity (SCAN cm 15:88) of pulp were designated by double experiments.10,13 Pulps were beaten to 50°SR by a valley-type hollander (Tappi T200). The freeness levels of pulp were determined according to SCAN-C 20:65 standard methods. The papersheets were Received: March 29, 2011 Accepted: June 1, 2011 Revised: May 5, 2011 Published: June 01, 2011 8340
dx.doi.org/10.1021/ie200633z | Ind. Eng. Chem. Res. 2011, 50, 8340–8343
Industrial & Engineering Chemistry Research
ARTICLE
Chart 1
Table 2. Chemical Content and Solubility of Pine Wood standard method
chemical content and solubility
% (o.d. wood)
holocellulose
70.80 ( 0.28
holocellulose
Chloride Method11
R-cellulose
46.08 ( 0.19
cellulose
K€urchnerHoffner Method12
lignin
25.78 ( 0.28
R-cellulose
TAPPI T 203 os-71
cellulose
51.14 ( 0.03
lignin
TAPPI T 222 om-98
alcoholbenzene solubility
chemical content
solubility
% 1 NaOH solubility
6.69 ( 0.02 15.64 ( 0.14
alcoholbenzene solubility
TAPPI T 204 om-88
hot water solubility
3.75 ( 0.02
cold-hot water solubility %1 NaOH solubility
TAPPI T 207 om-88 TAPPI T 212 om-88
cold water solubility
2.89 ( 0.33
Table 1. Pulping Conditions of Pine Wood Chips methods
trials
time (min)
ASAQ
1
150
2
180
EtOH (%)
NaBH4 (%)
ASAE
3
150
50
180 150
50
ASAB
4 5 6
150
2
7
150
3
8
180
1
9
180
2
10
180
3
1
produced by a RapidKothen Sheet Former. The tensile, burst, and tear indexes of papersheets were determined according to Tappi T494, T403, and T414 standards, respectively. Optical (ISO 2470 and ISO/DIS 11476) and color (ISO/CD 5631) properties of pulps were measured by an Elrepho-3300 diffuse reflectance spectrophotometer. The L*, a*, and b* color space (according to the Commission International de l0 Eclairage-CIE) was used for color evaluation, in which L* represents the lightness in the range from black (0) to white (100), and a* and b* are the chromaticity coordinates; þa* for red (þ60), a* for green (-60), þb* for yellow (þ60) and b* (-60) for blue. L*, a*, and b* color coordinates for each sample were determined after the pulping processes. Statistical analyses were performed by means of SPSS 11.5 (Statistical Package for the Social Sciences) software.
’ RESULTS AND DISCUSSION Chemical contents and solubility degrees of Pinus pinea wood, used as a raw material in this study, were determined and presented in Table 2. It was determined that the results for holocellulose, cellulose, alpha cellulose, lignin contents, and solubility degrees in pine wood were similar to those of data in previous studies.14 The ASAQ pulping process was modified by adding sodium borohyride (ASAB) in a 1, 2, and 3% ratio (o.d. wood) for the higher properties of pulp and papersheets in this study. ASAB process was compared to ASAQ and ASAE processes with regard to these properties. The properties of ASAQ, ASAE, and ASAB pulp were submitted in Table 3. It was determined that screened yield of pulp increased by ASAB process both 150 and 180 min according to AS-AQ and ASAE processes, while reject of ASAB pulping process decreased
according to that of AS-AQ process. The maximum increase in screened yield was determined by adding 2% NaBH4 (o.d. wood) to the ASAQ process in this study. The kappa number of the pulp decreased from 45.8 to 35.6 in the ASAB process at 150 min cooking time and 1% NaBH4 addition. The minimum kappa numbers were determined in the ASAE processes of both 150 and 180 min cooking time compared to ASAQ and ASAB processes. It was determined that the viscosity of pulp decreased in the ASAB process at 150 min cooking time more than that of the others processes. € I_stek and Ozkan found that screened pulp yield increased by adding NaBH4 to the kraft process. They determined that the kappa number decreased, while the viscosity of the pulp increased with NaBH4 addition to the kraft process, used Populus tremula wood as a raw material.15 Akg€ul et al. found that using NaBH4 in kraft pulping led to a small decrease in the kappa number compared to the control kraft cooking, using Brutia pine (Pinus brutia Ten.) wood as a raw material. They concluded that a significant yield increase was observed when using NaBH4 in kraft pulping.16 The lowest kappa number and viscosity was found with 2% NaBH4 added to the kraft pulping by G€ulsoy and Eroglu. The cause of pulp viscosity can be attributed to higher hemicelluloses retention in kraft-NaBH4 pulps.17 The chemical composition of ASAQ, ASAE, and ASAB pulp are shown in Table 4. It was determined that holocellulose and alpha cellulose contents were higher in the ASAE process than in the ASAQ and ASAB pulping processes. It can be seen that ethanol has more preservative effect on carbohydrate components than sodium borohyride during the ASAQ process. Papersheets were produced to be beaten to 50°SR pulp samples. The physical properties of papersheets of ASAQ, ASAE, and ASAB pulp are presented in Table 5. Tensile index of papersheets of ASAB pulp (1% NaBH4 addition) at 150 min cooking time was higher than those of ASAQ and ASAE pulping processes. At 180 min cooking time, burst index of 2% and 3% NaBH4 added ASAB papersheets is 3.27 kPa 3 m2 3 g1 and 3.84 kPa 3 m2 3 g1, respectively. At the same cooking time, the burst index of ASAQ papersheets is 3.54 kPa 3 m2 3 g1. When the burst index of ASAQ and ASAB handsheets were compared, only an increase in the burst index was obtained from the 3% addition of NaBH4. It was determined that there is no statistical difference between the physical strength of paper sheets of ASAQ, ASAE, and ASAB pulping processes (p < 0.05). G€ulsoy and Eroglu determined that the strength properties of the paper slightly decreased with the addition of NaBH4 to the kraft process. Strength losses of pulp can be ascribed to increases in pulp yield. Increasing pulp yield leads to a decrease in the fiber amount per unit weight of oven-dried pulp and cellulose/ hemicelluloses ratio of pulp.17 8341
dx.doi.org/10.1021/ie200633z |Ind. Eng. Chem. Res. 2011, 50, 8340–8343
Industrial & Engineering Chemistry Research
ARTICLE
Table 3. ASAQ, ASAE and ASAB Pulp Properties pH
yield (%)
methods
trials
white liquor
black liquor
reject
screened yield
total yield
kappa no.
viscosity (g/cm3)
pressure in digester (bar)
ASAQ
1
13.10
9.74
3,42
46.34
49.76
45.8
1301
12.0
2
13.14
9.55
2,67
42.77
45.44
38.6
1262
12.0
ASAE
3
13.38
9.91
1.03
46.90
47.93
30.9
1306
19.0
4
13.42
9.94
0.78
45.44
46.22
28.6
1264
19.0
ASAB
5
13.14
10.40
0.68
47.45
48.13
35.6
1169
14.0
6
13.14
10.27
0.95
48.12
49.07
40.2
1195
16.5
7
13.13
10.16
1.47
47.86
49.33
46.9
1202
19.0
8 9
13.13 13.10
10.32 10.12
0.66 0.74
47.08 48.15
47.74 48.89
34.6 40.1
1233 1232
14.0 16.5
10
13.09
10.08
1.28
46.78
48.06
43.7
1244
19.0
Table 4. Chemical Composition of Pulp R-cellulose
holocellulose *
*
whiteness
brightness
opacity
a b (%)
methods
trials
(%ISO)
(% ISO)
(% ISO)
L*
ASAQ
1
51.7
37.66
93.25
77.1
2
52.14
38.24
91.12
77.36 3.55 16.93
3
42.42
30.02
93.43
71.16 5.48 17.36
4
46.79
34.04
94.24
74.05 4.57 16.62
45.91 44.62
33.95 29.21
93.33 93.3
73.49 4.54 20 72.64 4.9 21.14
b*
trials
(a) (%)
SD
(b) (%)
SD
ASAQ
1
88.84
0.28
84.36
0.05
4.48
2
90.34
0.28
85.38
0.11
4.96
3 4
92.39 93.56
0.03 0.21
87.75 87.06
0.14 0.02
4.64 6.50
ASAE
5
92.59
0.02
82.68
0.06
9.91
ASAB
6
91.04
0.23
82.08
0.14
8.96
5 6
7
90.41
0.08
84.38
0.23
6.03
7
43.64
28.59
93.83
71.99 5.07 20.97
8
92.39
0.04
82.91
0.07
9.48
8
46.62
31.43
93.13
73.95 4.4
9
92.07
0.14
82.41
0.03
9.66
9
44.5
29.58
94.11
72.57 4.82 20.43
10
91.23
0.04
83.54
0.17
7.69
10
43.87
28.7
93.45
72.14 4.9
ASAB
SD: Standard deviation.
Table 5. Physical Properties of Papersheets Obtained from ASAQ, ASAE, and ASAB Pulp tensile index
burst index
tear index
(Nm 3 g1)
(kPa 3 m2 3 g1)
(mN 3 m2 3 g1)
x
SD*
x
SD*
x
SD*
ASAQ 1
53.05
3.29
2.88
0.28
5.14
0.38
2 3
60.10 45.34
4.01 5.44
3.54 2.83
0.28 0.31
5.02 5.32
0.56 0.14
4
57.44
3.94
2.96
0.37
4.71
0.43
5
62.12
4.83
2.93
0.32
4.59
0.24
6
51.07
4.12
2.28
0.23
4.05
0.32
7
54.3
3.26
2.29
0.17
3.84
0.44
8
54.66
3.04
2.60
0.27
4.69
0.52
9
61.19
1.28
3.27
0.23
4.84
0.76
10
69.39
5.16
3.84
0.50
4.95
0.52
methodstrials
ASAE ASAB
*
a*
methods
ASAE
*
Table 6. Optical and Color Properties of Papersheets of ASAQ, ASAE, and ASAB Pulp
SD: Standard deviation.
Sodium borohydride reduces the end group of cellulose (or hemicellulose) that contains the free anomeric carbon (that is, the free aldehyde group, the reducing end). This is the same end from which the peeling reaction occurs. The reducing end is
3.69 17.11
20.08 21.08
converted from an aldehyde to an alcohol which does not undergo peeling in alkaline solution.18 Optical and color properties of papersheets of ASAQ, ASAE, and ASAB pulp are presented in Table 6. Whiteness and brightness decreased in ASAE and ASAB processes compared to ASAQ process. The opacity of the paper sheets obtained from ASAQ, ASAE, and ASAB pulping processes were found to be similar. When L* decreased by adding ethanol and NaBH4 to the ASAQ process, it was determined that a* and b* increased, especially with NaBH4 being added to the ASAQ process. It was determined that adding NaBH4 to Brutia pine wood kraft pulping had an affirmative effect on the brightness of paper sheets, but the opacity of papersheets decreased in previous studies.19,20
’ CONCLUSION It was determined that the screened yield of pulp increased by adding NaBH4 to the ASAQ process. Kappa number decreased with the ASAB process with respect to the ASAQ process; on the other hand, adding ethanol to the ASAQ process (ASAE) had a more positive effect on the kappa number of pulp. Viscosity decreased by adding NaBH4 to ASAQ process. The burst index of paper sheets improved when 3% NaBH4 was added to the ASAB process at 180 min cooking time, especially a 2 and 3% NaBH4 addition, but the tear index of paper sheets in this ASAB pulping condition was similar to that of ASAQ and ASAE 8342
dx.doi.org/10.1021/ie200633z |Ind. Eng. Chem. Res. 2011, 50, 8340–8343
Industrial & Engineering Chemistry Research pulping processes. Whiteness and brightness of papersheets decreased by adding NaBH4 to the ASAQ process (ASAB), but the opacity of the papersheets did not change significantly with respect to ASAQ and ASAE pulping processes.
’ AUTHOR INFORMATION
ARTICLE
(19) C-€op€ur, Y.; Tozluoglu, A. A. Comparison of kraft, PS, kraft-AQ, and kraft-NaBH4 pulps of brutia pine. Bioresour. Technol. 2008, 99, 909–913. (20) Tutus-, A.; Ates-, S.; Deniz, I_. Pulp and paper production from spruce wood with kraft and modified-kraft methods. Afr. J. Biotechnol 2010, 9 (11), 1648–1654.
Corresponding Author
*E-mail:
[email protected]. Tel: þþ904623773499. Fax: þþ904623257499.
’ ACKNOWLEDGMENT The authors would like to thank The Scientific and Technological Research Council of Turkey (TUBITAK) for financial support (Project no: 1080875). ’ REFERENCES (1) Sixta, H.; Potthast, A.; Krotsschek, A. W. Sulfite Chemical Pulping. In Handbook of Pulping; Sixta, H., Ed.; Wiley-VCH Verlag GmbH&Co.: Weinheim, Germany, 2006; pp 109475. (2) Virkola, N. E.; Pusa, R.; Kettunen, J. Neutral sulphite AQ pulping as an alternative to kraft pulping. Tappi J. 1981, 64, 103–107. (3) Kettunen, J.; Reilama, I.; Ruhanen, M. A case study-coverting a kraft mill into NS-AQ mill. Tappi J. 1982, 65, 63. (4) Patt, R.; Kordsachia, O. Herstellung von Zellstoffen unter Verwendung von alkalischen Sulfitl€osungen mit Zusatz von Anthraquinon und Methanol (Production of pulp using alkaline sulfite solutions with addition of anthraquinone and methanol). Das Papier 1986, 40 (10), 1–8. (5) Kordsachia, O.; Reipschl€ager, B.; Patt, R. ASAM pulping of birch wood and chlorine-free pulp bleaching. Pap. Puu. 1990, 72 (1), 44–50. (6) Kırcı, H.; Bostancı, S-.; Yalınkılıc- , M. K. A new modified pulping process alternative to sulphate method “alkalisulfiteantraquinone ethanol” (ASAE). Wood Sci. Technol. 1994, 28, 89–99. (7) Hedjazi, S.; Kordsachia, O.; Patt, R.; Latibari, A. J.; Tschirrer, U. Alkaline sulfite-anthraquninone (AS/AQ) pulping of wheat straw and totally chlorine-free (TCF) bleaching of pulps. Ind. Crop Prod. 2009, 29, 27–36. (8) Oliet, M.; Garcia, J.; Rodriguez, F.; Gilarranz, M. A. Solvent effects in autocatalyzed alcoholwater pulping. Comparative study between ethanol and methanol as delignying agents. Chem. Eng. J. 2002, 87, 157–162. (9) Patt, R.; Kordsachia, O.; Rose, B. Modified alkaline sulfite pulping. Wochenbl. F. Pap. 2003, 131 (14), 892–897. (10) TAPPI Test Methods 20022003; Tapi Press: Atlanta, GA, 2002. (11) Fengel, D.; Wegener, G. Wood: Chemistry, Ultrastructure, Reactions; De Gruyter: Berlin, 1984. (12) Browning, B. L. Methods of Wood Chemistry; John Wiley and Sons Inc.: New York, 1967; Vol II. (13) Scan Test Methods; Scandinavian Pulp, Paper and Board Commitee: Stockholm, Sweeden, 1989. (14) Serin, Z.,G€um€u-skaya, E., Ondaral, S. A Review of the Chemical Composition of Different Softwoods, Hardwoods and Annual Plants, Forest for Food and Water. IFSS Symposium Proceedings, I_stanbul, 2003, pp 348361. € (15) I_stek, A.; Ozkan, I_. Effect of sodium borohydride on Populus tremula L. kraft pulping. Turk J. Agric. For. 2008, 3, 131–136. (16) Akg€ul, M.; C-€op€ur, Y.; Temiz, S. Comparison of kraft and kraftsodium borohydrate brutia pine pulps. Build Environ. 2007, 42, 2586–2590. (17) G€ulsoy, S. K.; Eroglu, H. Influence of sodium borohydride on kraft pulping of european black pine as a digester additive. Ind. Eng. Chem. Res. 2011, 50, 2441–2444. (18) Bierrman, J. C. Handbook of Pulping Papermaking, 2nd ed.; Academic Press: London, 1996. 8343
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