The Effect of Sodium Borohydride on Alkaline Sulfite–Anthraquinone

ARTICLE pubs.acs.org/IECR

The Effect of Sodium Borohydride on Alkaline Sulfite
Anthraquinone 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 sulfite
anthraquninone (AS
AQ) pulping process on properties of pulp and paper sheets was investigated. These properties were compared to those of the AS
AQ and the ethanol addition to AS
AQ (ASAE) pulping processes. The screened yield increased with alkali sulfite
antraquinone
sodium borohyride (ASAB) pulping process and kappa number decreased with respect to the AS
AQ 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 AS
AQ and ASAE pulping processes. It was determined that whiteness and brightness of papersheets decreased by adding sodium borohyride to the AS
AQ pulping process, whereas the opacity of papersheets did not change clearly compared to AS
AQ 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 1970
1971. 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 15
30%, but the heat consumption was still greater than in kraft pulping.3 AS
AQ 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.4
7 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 AS
AQ and sodium borohydride. In this study, the modification of AS
AQ 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 AS
AQ 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  0.2
0.4 (cm). The alkali sulfite
anthraquinone (AS
AQ) 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 AS
AQ 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€urchner
Hoffner Method12

lignin

25.78 ( 0.28

R-cellulose

TAPPI T 203 os-71

cellulose

51.14 ( 0.03

lignin

TAPPI T 222 om-98

alcohol
benzene solubility

chemical content

solubility

% 1 NaOH solubility

6.69 ( 0.02 15.64 ( 0.14

alcohol
benzene 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)

AS
AQ

1

150

2

180

Et
OH (%)

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 Rapid
Kothen 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 AS
AQ 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 AS
AQ and ASAE processes with regard to these properties. The properties of AS
AQ, 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 AS
AQ 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 AS
AQ 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 AS
AQ, 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 AS
AQ and ASAB pulping processes. It can be seen that ethanol has more preservative effect on carbohydrate components than sodium borohyride during the AS
AQ process. Papersheets were produced to be beaten to 50°SR pulp samples. The physical properties of papersheets of AS
AQ, 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 AS
AQ 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 g
1 and 3.84 kPa 3 m2 3 g
1, respectively. At the same cooking time, the burst index of AS
AQ papersheets is 3.54 kPa 3 m2 3 g
1. When the burst index of AS
AQ 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 AS
AQ, 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. AS
AQ, 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)

AS
AQ

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*

AS
AQ

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

AS
AQ

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 AS
AQ, ASAE, and ASAB Pulp tensile index

burst index

tear index

(Nm 3 g
1)

(kPa 3 m2 3 g
1)

(mN 3 m2 3 g
1)

x

SD*

x

SD*

x

SD*

AS
AQ 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 AS
AQ, 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 AS
AQ, ASAE, and ASAB pulp are presented in Table 6. Whiteness and brightness decreased in ASAE and ASAB processes compared to AS
AQ process. The opacity of the paper sheets obtained from AS
AQ, ASAE, and ASAB pulping processes were found to be similar. When L* decreased by adding ethanol and NaBH4 to the AS
AQ process, it was determined that a* and b* increased, especially with NaBH4 being added to the AS
AQ 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 AS
AQ process. Kappa number decreased with the ASAB process with respect to the AS
AQ process; on the other hand, adding ethanol to the AS
AQ process (ASAE) had a more positive effect on the kappa number of pulp. Viscosity decreased by adding NaBH4 to AS
AQ 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 AS
AQ 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 AS
AQ process (ASAB), but the opacity of the papersheets did not change significantly with respect to AS
AQ 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 109
475. (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 “alkali
sulfite
antraquinone
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 alcohol
water 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 (1
4), 892–897. (10) TAPPI Test Methods 2002
2003; 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 348
361. € (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 kraft
sodium 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

dx.doi.org/10.1021/ie200633z |Ind. Eng. Chem. Res. 2011, 50, 8340–8343