pulping parameters with butanol such as alcohol concentration, addition of calcium chloride, magnesium ... Cooking of bagasse was carried out in autoclaves.
Research and Industry Vol. 40, September 1995, pp. 224-230
Bagasse pulping with butanol-water system AM A Nada, A A Ibrahem, Y Fahmy & HE Abou-Yousef Cellulose & Paper Department, National Research Centre, Dokki, C airo, Egypt Received 12 December 1994
Bagasse organosolv pulping with propanol, butanol and isobutanol was studied.The effect of different pulping parameters with butanol such as alcohol concentration, addition of calcium chloride, magnesium sulphate, sulphuric acid, anthraquinone (AQ) and sodium hydroxide were investigated.Other variables of puiping process namely pulping temperature and time · were also examined. Optimization of bagasse pulping with butanol-water system was done.It was found to be 50 per cent butanol concentration at l 70°C for 2 hours with liquor ratio 5: 1. Addition of 12 per cent sodium hydroxide to butanol-water pulping liquor produced pulp of high quality. Further, strength properties ofthe produced paper sheets obtained from pulps prepared at different temperatures for 2 hours and for different time periods at 170°C in presence or absence of sodium hydroxide were also determined. Organosolv pulping methods have attracted increased attention over the last decade. Possible advantages of organic pulping process include reduced pulping time, high yield and utilization ofthe main waste product lignin 1 . According to basic pulping mechanism we can categorizes organosolv process to autohydrolysis2-5, acid catalysis 6-8, reaction of phenols with acid catalysis9 • 1 0 , alkali and organic solvents11 •12 and sulphate or sulphide and organic solvents 13•14. Of the many organosolv pulping, process tested to date are AlecelJ l 5·16 for hardwood and annual fibres and organocell 17-19 for softwood. Early the use of aliphatic alcohols to isolate lignin in desired forms was summarized by Aronovsky20 . Recent study 21 reported that both butanol and ethanol are effective solvents for delignification of agricultural residues. In general, alcohols e.g.methanol, ethanol, butanol may be used for alkaline cooking, chiefly with sodium hydroxide, in which the produced pulp yield is higher and the delignification rate is faster than that without alcohols. Also, addition ofanthraquinone in alkaline aqueous alcohols modify the pulping process22 • The pulp strength of organosolv pulping process in presence of alkali· is generally improved23 . Bailey 204 -26, showed that addition of alkali to butanol water mixture accelerated the delignification rate. The aim of this work, is to study the pulping of bagasse with different solvents e.g. propanol, butanol and isobutanol. The effect ofdifferent parameters of bagasse pulping with butanol e.g. butanol concentration, pulping time and temperature was
investigated. On the other hand, the effect ofadditives e.g. CaCl2 , MgSO4, H2 SO4 and AQ in the butanol water pulping liquor was also studied. Effect of addition of sodium hydroxide with different concentrations in the pulping liquor was investigated.Finally, the strength properties ofpaper sheets produced from the organosolv bagasse pulps were determined. Experimental Procedure
Depithed bagasse is used in this study. It has the following analysis: lignin 20.9, a-cellulose 40.1, hemi-cellulose 27.8 and ash 1.05 per cent. Pulping Cooking ofbagasse was carried out in autoclaves digester which consists of6 stainless steel tubes, each of2 Lcapacity, electrically heated in ethylene glycol bath. Pulping experiments with different kind of solvents, propanol, butanol and isobutanol with ° water{}: 1) were carried out at l 70 C for 2 hours with liquor ratio 5: 1. Effect of pulping temperature (l 60- l 90° C) for 2 hours and pulping time (0.5-3 hours) at l 70°C ofbagasse with butanol-water (1: 1) were examined. The effect of addition of CaCh, MgSO4 and H2S04 in butanol pulping liquor at 170°C for 2 hours was also investigated. On the other hand, effect of addition of different concentration of sodium hydroxide (2-15% based on raw material) in the butanol water (1:1) pulping liquor at l 70°C for 2 hours was also studied. Liquor ratio used in all abQve pulping process was 5: 1 . . Lignin content was determined according to Tappi
225
NADA et al.: BAGASSE PULPING Willi BUTANOL-WATER
2or------------------.
Standard method T222 05-54. Pentosans was measured according to Jayme27, x-cellulose28 and degree of polymerization29 were determined. Sheet Formation Pulps were beaten to 40°SR in a Jekro Beater. Hand sheet of basis weight around 68 g/m 2 was formed according to SCA Standard. Strength properties of the produced paper sheets were tested according to Tappi Standard.
Results & Discussion Bagasse Pulping with Different Solvents Organosolv pulping process were performed by using different aliphatic alcohols. These processes used 'the solvents, commonly in association with water (1: 1). In all processes, the solvents act not only on the solubilization of the produced fragments but also promote tissue impregnation, carrying the reagents to the protolignin through polysaccharides matrix and transporting the lignin fragments produced of the bulk of the solution26•30•31• The higher alcohols being only partially miscible, formed two phases. Delignification processes with aqueous ° propanol, butanol and isobutanol (1: 1) at 170 C for 2 hours and 5: 1 liquor ratio were shown in Table 1. According to these results, it can be reported that, there is a little differences in lignin content of the produced pulps. The best results however ofthe yield and lignin content was obtained from bagasse pulping with aqueous butanol. This can be attributed to the straight chain and greater delignification selectivity of butanol than that of propanol and isobutanol. Therefore, further investigation was carried out on the organosolv pulping with butanol. (i) Butanol Concentration Water content in the organosolv pulping processes plays an important role in the solvolysis of lignc1cellulosic materials. It has a serious effect on delignification as well as carbohydrate degradation. Delignification of lignocellulosics materials with organosolv is very weak in absence of water in the pulping liquor. Fig.(l ) shows the effect of butanol concentration in the pulping ofbagasse with aqueous butanol at. l 70°C for 2 hours with 5: 1 liquor ratio. Lignin content of the produced pulp decreases by increasing butanol concentration and it reaches to its minimum value (6.9%) at 50 per cent butanol. Increasing of butanol concentration in the pulping liquor increases the lignin content in the produced pulp. So, the presence of water in the solvolysis pulping liquor increases the rapture ofthe bonds and
18
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�
10 8 0 �--'.'"'--:-":--.....,__.___,___.__....__..____.__,
10
20
30 40 50 60 70 80 Butanol concentration •1.
90 tOO
Fig. I-Effect ofbutanol concentration in pulping liquor on the lignin % of the produced bagasse pulp. Liquor ratio (S: I), pulping temperature I 70°C for 2 hours Table !�Yield and lignin content of pulps produced from organosolv pulping of bagasse with different solvents Solvents Propanol Butanol Isobutanol
Lignin content 8.6 7.1 8.8
Yield (per cent) 48.8 51.2 49.1
crossing between lignin and hemicelluloses which helps lignin dissolution of lignin in butanoL On the other hand, presence of water in the organosolv pulping liquor accelerates the formation of acetic acid which increases the delignification rate (32). Decreasing butanol concentration less than 50%, delignification of bagasse pulp decreased and carbohydrate degradation increased. (ii) Additives in Organosolv Pulping Liquor The· purpose of utilization of additives in organosolv pulping liquor is to accelerate delignification rate and increasing the pulp yield as well as improvement of pulp quality. The type and concentration of additives were controlled by the type of raw materials, composition of organosolv pulping liquor, pulping time and pulping temperature33. Table 2 shows the effect ofaddition of sulphuric acid, calcium chloride, magnesium sulphate and (AQ) in the aqueous butanol pulping liquor at 170°C for 2 hours and 5: I liquor ratio on the yield and lignin content ofthe produced pulp. In case ofbagasse organosolv pulping with butanol water of (1: 1) ratio i.e. 50 per cent butanol with different additives concentrations the pulps produced were
226
RES AND IND SEPTEMBER 1995
1,-------------------
Table 2-Effect of additives in pulping liquor on lignin and yield percentage of the produced pulps Yield Lignin Additives Cone. (per cent) (per cent) (per cent) a H2SO4 CaCl2 MgSO4 a 50 per cent butanol b 80 per cent butanol
0.10 0.25 0.50 0.10 0.25 0.50 0.10 0.25 0.50
b
40.5 49.7 .36.8 47.3 44.2 33.5 47.2 31.6 43.5 42.0 44.5 48.8 42.l 47.3 38.1 .43.2
a
b 9.8 9.1 10.1 13.7 10.5 14.2 11.7 12.3 12.5 9.2 12.l 8.7 14.1 11.5
12.3 14.5
•
.,.!
8
OI
6
.5
�
4
2 0
2
4
6
8
io
12
Sodium hydroxide concentration •1.
14
16
2 Effect of sodium hydroxide concentration (based on raw low quality, low yield and relatively high residual Fig. material), in butanol water (I :1), on the ligniil. ¾ of the produced lighin content. On the other hand, using the same bagasse pulp. Liquor ratio (5:1), pulping temperature l 70° C for 2 additives in organosolv pulping with high hours concentration ofbutanol (80%) provides pulps with high yield and relatively low residual lignin content. without substantial degradation of the As shown in Table 2, in case of high solvent cellulose 9•20•3 7• concentration (80%), the increasing of additive concentrations within the range (0-0.25% based on Addition- of Sodium Hydroxide raw material) could lead to increase the pulp yield, Addition of sodium hydroxide in pulping with while further increasing of additive concentration organosolv offers advantages which are not possible resulted in extensive degradation of the produced with use of each alone. Fig.2 shows the effect of pulp. This can be attributed to the formation ofacid in sodium hydroxide addition with different the organosolv pulping liquor which occurred via concentrations (3-15% based on raw material) in hyµrolytic cleavage of x-aryl and p-aryl ether bonds organosolv pulping liquor of 50 per cent butanol at oflignin macromolecules due to the action ofH-ions 170 °C for 2 hours with 5: l liquor ratio. It is clear that, in the pulping liquor34•3 5. The lignin degradation was addition of sodium hydroxide with low concentra accompanied with carbohydrate loss due to the tion till 4 per cent to aqueous butanol organosolv hydrolytic action ofthe pulping liquor. So, the low pulping liquor produces pulp with higher lignin yield and high residual lignin content ofthe produced content than the produced pulp from aqueous pulp resulting from pulping using butanol water (l: 1) butanol pulping liquor alone. This can be attributed in presence ofsulphuric acid could be attributed to a to that presence of sodium hydroxide in organosolv rapid drop in pH value of pulping liquor which causes pulping liquor decreases the selectivity of solvent the pulp degradation through hydrolysis process and with respect of lignin38. Increasing of sodium
repolymerization as well as repredpitation of lignin hydroxide concentration in organosolv pulping
in the pulp. Using of sulphuric acid in high concentration ofbutanol in pulping liquor produces pulp with high yield because of the protective effect of solvent to the carbohydrate and enhances the dissolution ofdegraded lignin with high efficiency36. Using of calcium chloride or magnesium sulphate in pulping liquor of (1: l ) butanol:water ratio produces pulp with low quality due to the rapid drop of pH values as in case of sulphuric acid. Using of (80%) butanol concentration produces pulp with high quality due to the hydrolytic delignification and limited opening of carbohydrates glucosidic bonds
liquor more than 4 per cent minimises the lignin co_ntent in the produced pulp till it reaches to its lower value (about 2%) at 15 per cent sodium hydroxide. This is due to the .rapid dissolution oflignin and high retention of carbohydrate. Presence of sodium hydroxide with high conc�ntration enhances also the delignification ability of aqueous butanol and also increases the organic solvent reduction of surface tensjon of cooking liquorwhich helps the penetration ofalkali into the bagasse fibres and the diffusion ofthe breakdown products of lignin into the cooking liquor, assuming a uniform distribution of reagent
227
NADA et al.: BAGASSEPULPING WITH BUTANOL-WATER
within bagasse38. Also,Bailey24•25 showed that the addition ofalkali to aqueous butanol pulping liquor accelerates the delignification rate due to that the alkali acts as a catalyst in the lignin butanol condensation rather than a reactant. Addition of Anthraquinone Addition of anthraquinone in alkaline aqueous butanol pulping liquor of bagasse resulted in enhancing the delignification rate at the beginning of the bagasse cooking39 . Table 3 shows the effect of addition ofanthraquinone (0.05 and 0.1 % based on raw material) in alkaline aqueous butanol pulping liquor ofliquor ratio of5: 1 at 170 ° C for 2 hours. It is clear that, presence ofAQ in pulping liquor increases the delignification rate and pulp yield, since the obtained residuak. lignin in the produced pulp is lower than that obtained in absence of AQ. Increasing of AQ concentration to 0.1 % resulted a lower lignin content in the produced pulp. From Table 3, it is clear that the effect of addition of anthraquinone on the delignification percentage is higher in case of pulping with aqueous butanol in presence oflow alkali concentration 9 per cent than in presence of high alkali concentration 12 or 15 per cent. Effect of Pulping Temperature Fig.3 shows the effect of cooking temperature of bagasse pulping process with_ aqueous butanol (50%), in presence and absence of 12 per cent sodium hydroxide (based on raw material) for 2 hours with 5: 1 liquor ratio, on the delignification percentage, x-cellulose, degree ofpolymerization and pentosans of the produced pulps. It shows that, the delignification percentage, Fig.3a, increases by increasing pulping temperature in presence and absence of sodium hydroxide. Delignification percentage of the produced pulp in presence of sodium hydroxide is more than in absence ofit. This is Tible 3-Effect of addition of AQ in pulping liquor on the lignin and yield percentage of the produced pulp Conditions
Yield (per cent)
Lignin (per cent)
AQ (per cent) (based on raw material)
Butanol (50%) + 9% NaOH +12% NaOH
+15% NaOH
0.05 0.10
0.05 0.10
52.19 52.2 51.6 50.97 51.8 49.7 48.10 49.7 48.5
6.01 5.10 4.20 3.11 3.22 2.89 2.20 2.21 2.10
(d)
(c)
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30
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.. ..
e
g
?: &.800
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. ·c .,:
600
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.S? 60
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.!:!
-� 0
u
40
60 50
20
0 0 0----'---'---L------''---'-'- "-L-_.._____.,__.___..._,
160 170
180 190
160 170 180
190
Temperature °C
Fig. 3-Effect of pulping temperature for 2 hours on "a" delignification per cent, "b" o:-cellulose, "c" degree of polymerizat10n and "d" hemicellulose per cent of the produced bagasse pulp butanol: water (1:1), liquor ratio 5: Io with sodium hydroxide o without sodium hydroxide
due to the increase of lignin butanol condensation. ex-Cellulose of produced pulp (Fig.3b inci-..;ases by increasing pulping temperature. In presence of sodium hydroxide ex-cellulose increases by increasing temperature and reaches to its maximum value at 170° C, which is more than that in the absence of sodium hydroxide. Increasing the temperature more than l 70° C, ex-cellulose decreases. This is due to that, the presence of sodium hydroxide in organosolv pulping liquor, at high temperature (more than 170° C) increases the breakdown oflignin and carbohydrate moiecules and also increases the solubility of the breakdown products. Unfortuna tely, degree of polymerization of proquced pulps (Fig.3c) decreases by increasing pulping temperature. The loss in the degree ofpolymerization ofproduced pulp from alkaline aqueous butanol pulping liquor is lower than produced pulp from aqueous' butanol alone, This can be attributed to that the presence of alkali in pulping liquor increases the miscibility of butanol with water and increases the rate of
228
RES AND IND SEPTEMBER 1995
penetration and dissolution oflignin in organic layer. Also, presence ofalkali causes a buffer solution which increases the condensation of butanol lignin and hence the rate of degradation of cellulose chains decreases. Hemicellulose of the produced pulp is shown in (Fig.3d}. In absence ofalkali, hernicellulose decreases by increasing pulping temperature due to the increase of hemicellulose hydrolysis. In presence of alkali, hemicellulose decreases by increasing pulping temperature to 180 °C. Increasing of pulping temperature more than 180 °C, hemicellulose increases due to the increase ofbutanol selectivity to the delignification. The yield Fig.4 of the produced pulp decreases with increasing pulping temperature. The loss in yield in presence of alkali is lower than in absence of alkali. Effect of Pulping Time Fig.6 shows the effect of pulping time of pulping with a queous butanol (50%) at l 70° C with 5:1 liquor ratio in a absence and presence of 12 per cent sodium hydroxide (based on raw material) on the chemical constituents of produced bagasse pulps. Deligni fication per cent (Fig.6a) as well as x-cellulose (Fig.6b) increases with increasing pulping time. On the other hand degree ofpolymerization (Fig.6c) and pentosans (Fig.6d) decrease, with increasing pulping
C
(d)
2 1000 ., E
..
0
t1I
0
.
,.!! C
.2
800
800 700 500
(a)
ao 60
·c
.2' 0
20 L--�-__.____.__40..____.____.__...__.
2
3
2
Time hrs
3
Fig. 6----Effect of pulping temperature for 2 hours on "a" delignification per cent, "b" 0(-cellulose, "c" degree of polymerization and "d" l]emicellulose of the produced bagasse pulp. butanol:water (!:!) and liquor ratio 5:1 o-with sodium hydroxide e-wiUiout sodium hydroxide
2
60
56 � 52 I
>
2 0
0
0
0
0
48
0 1. Organosolving pulping in absrnce o1 NaOH. .44 2. Organosolving pulping in pT�sence ot 12"!. NaOH (based on
1. Org ano solving pulping in absence of NaOH · · 2. Organosolving pulping in presenu of 12"!. NaOH.
raw material). 401-i:..:.:.:.._:_:_:_.:.=_i_�__L____j___J____�--�2-- 3� 190 180 170 160
Temperature °C Fig. 4-Effect of pulping temperature for 2 hours on the yield of , the produced bagasse pulp. Liquor ratio (5: 1 ). alcohol:water {1:1)
Ti me, hours
Fig. 5-Effect of pulping time at 170° C on the yield of produced bagasse pulp liq_uor ratio (5: I). alcohol:water (I:1)
NADA et al.: BAGASSE PULPING WITH BUTANOL-WATER
time. Presence of alkali in the pulping liquor protect somewhat this decrease in degree of polymerization and pentosans. Also, the produced yield of the pulp decreases with in increasing pulping time (Fig.5). Sheet Formation The effect of pulping time at 170° C and pulping temperature for 2 hours on the strength properties of the produced pulp paper sheets from pulping with aqueous butanol (50%) with 5:1 liquor ratio were illustrated in Figs. 7 and 8 respectively. Fig.7a illustrates the effect of pulping time (0.5-3 hours) on the breaking length of bagasse pulp paper sheets of 40° SR. Breaking length of these sheets increases by increasing pulping time due to the increase in delignification per cent (Fig.6a). This decrease in lignin content causes an increase of softness of fibres which enhances the crossing and adhesion force between the bagasse pulp fibres. So, the breaking length increases. By increasing pulping time more than 2 hours, breaking length decreases due to the decrease in degree of polymerization and hemicellulose content (Figs 5 c&d). Figs 7 b&d show the effect of pulping time on the teat and burst factors respectively of the produced paper sheets. Increasing pulping time increases the tear and burst factors and reaches to their maximum vallues after 2 hours due to the increase of adhesion force between fibres. Tear and burst factors decrease by increasing pulping time more than 2 hours due to the decrease in hemicellulose content and degree of polymerization, of the produced bagasse pulp. Breaking length, tear and burst factors of the produced bagasse pulp paper sheets from pulping with aqueous butanol (50%) in presence of sodium hydroxide (12% based on raw material) are higher than in absence of alkali. This can be attributed to that the produced pulp in presence of alkali has a hemicellulose, a-cellulose, degree of polymerization more than pulp produced in absence of alkali.
6
...01
5
!!
3
:c.· 2
0 120
..
ao 40 0 60
. 229
r A
40 20 0
� 2 Time hrs
3
160
170
180
190
Tcmp.°C
Fig. ?-Effect of pulping time at 170'C on the strength properties of the produced bagasse pulp paper sheets. butanol:water (I: I), liquor ratio 5:1 a-with sodium hydroxide, e-without sodium hydroxide Fig. 8-Effect ol pulping temperature for 2 hours on the strength properties of the produced bagasse pulp paper sheets. butanol:water (I: 1), liquor ratio 5: I o-with sodium hydroxide •-without sodium hydroxide
which increases from the compact between fibres. By increasing the pulping temperature to 190°C the tear and burst factor decrease due to the decrease of degree of polymerization of cellulose chains.
Effect of Pulping Temperature on the Strength Properties of Produced Bagasse Pulp References Breaking length of produced paper sheets I Nada A M A, EI-Saied H, Fad! M H & Nassar M A, Polym-Plast Technol Eng; 33(4) (1994) 515. increases by increasing pulping temperature for 2 hours (Fig.Sa) and reaches to its maximum value at 2 Gosebier R L, Macmillan J K & Hergert H L, Tappi, 52(12) (1989) 2369. pulping temperature of l 70°C. A drop occurred in the 3 Kleinert 1' N, Iappi, 57(8) (1974) 99. breaking length by increasing pulping temperature 4 Bewers G H & April G C, Tappi, 60(8) (1977) l02. more than l 70°C due to the increase in the 5 April G C, Sheng T & Hansen S, Tappi, 65(2) (1982) 41. degradation of cellulose chains. Tear factor and burst 6 Shimada K, Tomimura Y, Hosoya S, Int Symp Wood and Pulping Chem Proc, Vol2 (1991) 183. factor (Figs 8 b&c) respectively increase by increasing 7 Sano Y & Nakamura HJ, J Japan Wood Res Soc. 36(3) (1990) ° pulping temperature till 180 C. This can be attributed 207. to the increase of delignification per cent and 8 Sano Y, Japan Tappi, 45(5) (1991) 525. consequently increases the softening of the pulp 9 Funaska M·& Abo I, Tappi, 72(8) (1989) 145.
230
RES AND IND SEPTEMBER 1995
10 KachiiS, IwataM & ArakiM, J Japan Wood Res Soc, 36(2) (1990) 108. 11 Mogollan G, Int Symp Wood and Pulp Chem, Vol.2 (1991) 251. 12 Marton R & Granzow S, Tappi, 65(6) (1989) 103. l 3 Oeineko l R& NikiliSna O V, Int Symp Wood and Pulp Chem Proc, Vol.2 (1991) '125. I 4 Deineko IR & Zatubin MY, Int Symp Wood and Pulp Chem Proc, Vol.2{1989) 719. 15 Lora J H, Tappi, 74(3) (1991) 113. 16 WinnerSR, Goyal GC& LoraJ H, Tappi, 74(11)(1991)435. 17 Schroeter MC &Dohlmann G, Tappi Pulping Conf Proc, (1991) 645. 18 SchroeterMC &Dohlmann G, ·Tappi Pulping Conj Proc, (1990) 657. 19 Edel E, German Papermaker, 1 (1984) 39. 20 AronovskyS I & Gortner R A,Ind Eng Chem, 28 (1936) 1270. 21 April GC & KamelMM, Tappi, 62(5) (1979) 83. 22 deChacon (j M & Lai Y Z, Int Symp Wood and Pulp Chem, Aug 26-30 (1985) i91. 23 Fleming PI, Pulp Coriference Proceeding, Tappi Press, Atlanta (1985) 697. 24 Bailey A J, Paper Trade J, 109(27) (1939).29.
25 26 27 28
Bailey A J, Paper Trade J, 116(2) (1946) 29. Bailey A J, Pacific Pulp Paper.Ind, 14 (1940) 24. Jayme G & Sarten P, Naturwiss, 28(52) (1940) 822. Inst Method No. 421 (The Inst Pap Chem, Appleton, Wisconsin), 1952. 29 Glockner G,Dinov K & Phillipp H, Faserforch und Textil-tech, 19 (1968) 120. 3_0 Balhar L, Cellulozy Papier, 10 (1965) 9. 31 Nakano J & TakatsukaC, Kami Pu Gikyoshi, 30(12) (1976) 650. 32 Kleinert TN, '{)as Papier, 30(10A) (1976) 15. 33 Oast D, AylaC & Puls J, BFA Hamburg, (1980) 5PB. 34 Sarkanen KV &McCarthy J L, Holzforschung, 42 (1988) 177. 35 Hoo L H & AndersonCD, Wood Chem Technol, 3 (1983) 223. 36 Kleinert T N, Tuppi, 57(8) (1974) 99. 37 Gasche V & Kobell M, Proc Int Seminar on non-conventional Pulping and Bleaching Fed Rep Germ, (1987). 38 Roh J K & ShinD S, J Tappik, 17(2) (1985) 30. 39 Fleming BI & Kubes G J, Proc Tappi Pulping Conj, Houston, (1983) 85. 40 Goarang1,Cassidy R & DenceCW, Tappi, 62(7) (1979) 43.
