ALTERNATIVE PULPING PROCESS FOR PRODUCING DISSOLVING PULP FROM JUTE
M. Sarwar Jahan, Sabina Rawsan, D. A. Nasima Chowdhury, and A. Al-Maruf Dissolving pulps are the raw materials of cellulo derivatives and of
云南大学录取分数线many other cellulosic products. Jute is a very good source of cellulo
and worthy of consideration for the production of dissolving pulp. In this
investigation jute fiber, jute cuttings, and jute caddis were ud as raw
materials to prepare dissolving pulp by a formic acid process. A very high
bleached pulp yield (49 to 59%) was obtained in this process. The α-
cellulo content was 93 to 98%, with a high pulp viscosity. Also a good
brightness (81 to 87%) was achieved in totally chlorine free bleaching.
Jute fiber showed the best and jute caddis showed lowest performance
in producing dissolving pulp via the formic acid process. R18-R10 values
幼儿园园长工作计划
were much lower than for conventional dissolving pulp.
Keywords: Jute fiber; Jute cutting; Jute caddis; Dissolving pulp; TCF bleaching; α-cellulo
Contact information: Pulp and Paper Rearch Division, BCSIR Laboratories, Dhaka, Dr. Qudrat-I-Khuda Road, Dhaka-1205, Bangladesh *Corresponding author: m_ INTRODUCTION
变化的作文Forest resources are diminishing in Bangladesh, while consumption of paper and allied materials is continuously increasing (FAO 2003). So it is important to ek strategies that will compensate for diminishing forest resources and also provide local economic value. It is therefore crucial to explore nonwoods as potential raw materials for pulp production. Jute ud to play an important role in the socio-economic development of Bangladesh. A significant portion of the total export earnings was dependent on jute and related products in the sixties (Jahan et al. 2007). The chemical and morphological characteristics of jute favor it as a pulping raw material (Nahar 1987). Therefore, many studies have been done on the pulp from jute at home and abroad (Akhtaruzzaman and Shafi 1995; Jahan 2001; Roy et al. 1998; Jahan 2008). Retted jute fiber contains a very high α-cellulo and low hemicellulo content as compared to wood or other nonwood (Nahar 1987). So it may be u
d in producing dissolving pulp. But the price of jute fiber cannot compete with wood. The bottom part of jute, which is called jute cuttings, is discarded in jute mills. About 15% of jute cuttings and 3% of caddis are produced in processing of jute fiber in conventional jute mills. Bangladesh produced 8,10,000 MT of jute fiber in 2004-2005 (Anon 2007). So about 120,000 metric tons of jute cuttings and 24,300 metric tons of caddis remained left over in jute mills in one year. The residual materials have the potential to be ud as pulping raw materials.
Most of the dissolving pulps are produced from wood using the prehydrolysis kraft or acid sulfite process (Biermann 1993; Hinck et al. 1985). Dissolving wood pulp is a chemically refined bleached pulp compod of more than 90 percent pure cellulo.
The end us of dissolving pulp include cellophane and rayon, cellulo esters (acetates, nitrates, etc.), cellulo ethers (carboxymethyl cellulo, etc.), and graft and cross-linked cellulo derivatives (Sjöström 1981).
Pulp quality of dissolving pulp is esntial for cellulosic products such as carboxymethyl cellulo, visco, cellulo film, and sausage skin, etc. The dissolving pulp quality depends both on properties of the raw materials and the pulp processing. The reactivity of cellulo pulp can refer to it
s capacity to participate in diver chemical reactions. The two condary hydroxyl groups on carbons two and three are more reactive than the primary hydroxyl group on carbon six (Krässig 1993). Dissolving pulp should have special properties, such as a high level of purity, uniform molecular-weight distribution, and good reactivity and accessibility of the cellulo to chemicals (Krässig 1993). To achieve maximum reactivity of pulp, acid hydrolysis, mechanical and swelling treatments, enzyme treatment, etc. is done (Engström et al 2006; Tang et al 2002). For example, endoglucana preferably degrades amorphous rather than crystalline cellulo and cleaves the cellulo randomly within the chain (Rabinovich et al. 2002; Henriksson et al. 1999). Since less ordered or amorphous regions occur on the surface and between the microfibrils (Wickholm 2001; Vietor et al. 2002) endoglucan treatment leads to a swelling of the cell wall and thus an increa in accessibility to solvents and reagents.
Organosolv pulping process have been suggested as an alternative pulping route. Organosolv delignification followed by Totally Chlorine Free (TCF) bleaching is an environmentally friendly approach towards the production of high-purity cellulo pulp (Sixta et al. 2004). The susceptibility of organosolv pulp towards TCF bleaching has been claimed to be one of their most favorable features (Dapia et al. 2003).
New acidic pulping process such as the formic acid process have potential to remove lignin and hemicellulo at the temperature of boiling (Jahan et al. 2007a). The objectives of this study were to produce dissolving pulp from jute fiber, jute cuttings, and jute caddis by u of a formic acid process at atmospheric pressure, followed by totally chlorine-free bleaching (TCF). A schematic flow diagram for this process is shown in Appendix 1.
EXPERIMENTAL
Materials
Jute fiber, jute cuttings and caddis were collected from Jute Mill in Narayangong, Bangladesh. The jute fiber was very clean and free from scaling. The were chopped to 2-3 cm in length. Chemical analysis of the raw materials is given in Table 1, which is published in elwhere (Jahan et al 2007).
Chemical Analysis
The extractives (T204 om88), Klason lignin (T211 om 83), and pentosan (T223 cm-84) were determined in accordance with TAPPI Test Methods. Holocellulo was determined by treating extra
ctives-free wood meal with NaClO2 solution. The pH of the solution was maintained at 4 by adding CH3COOH-CH3COONa buffer. The α-cellulo content was determined by treating the holocellulo with 17.5 % NaOH.
Formic Acid Treatment (F)
Jute fiber, jute cuttings, and jute caddis were cooked in a flask with an aqueous solution of formic acid (90 %v/v) at boiling temperature (107 o C) under atmospheric pressure for 1 h. The cooking was carried out in batches of 30 g dry of samples in a 500 L, flat-bottom, and wide-mouth boiling flask equipped with a condenr. After cooking, the spent cooking liquor was parated and collected by filtration. Pulp was washed with 80% formic acid, followed by hot water.
Peroxyformic Acid Treatment (Pf)
Formic acid treated pulp was further delignified with peroxyformic acid (PFA) at 80 o C. The reaction was carried out in a thermostatic water bath. The peroxyformic acid was prepared by adding 90% formic acid with varying proportions of H2O2 (2, 4, and 6% of o.d. jute fiber, jute cuttings, and caddis). The time was held constant at 120 min for each peroxide concentration. After completion of the pulping, a pulp was filtered off and washed with 80% fresh formic acid, and finally with hot water.
Pulp yield was determined gravimetrically on raw material. The kappa number of the pulps was determined by TAPPI standard methods (T 236). In one experiment, peroxyformic acid treatment as a first step was carried out for jute fiber, jute cuttings, and jute caddis, followed by formic acid treatment and again peroxyformic acid treatment.
Bleaching
Bleaching experiments of unbleached pulp (10g) were carried out at 10% pulp consistency. The pH was adjusted to 11 by adding NaOH. The hydrogen peroxide was 2% on o.d pulp. First, 0.1% MgSO4, 2% NaOH, and 0.1 % NaSiO2 were added to the required amount of distilled water in a beaker, followed by H2O2 addition to the mixture. This pulp was preheated to a desired temperature in a water bath and mixed with bleaching liquor. The bleaching temperature was 70 o C for 1 h. A similar procedure was followed in the 2nd stage of peroxide bleaching.
Evaluation of Pulps
模数和齿数的关系Pulp tests were performed according to the Standard Methods of the Technical Association of the Pulp and Paper Industry (TAPPI, Atlanta, GA): kappa number (T 236 cm-85); brightness (T 452 om-92); viscosity (T 230 om-89); pentosan (T 223 cm 84), α-cellulo (T 203 om-88); alkali solubility R10
and R18 (T 235 cm-85) and carboxyl content (T 237 cm 98).
RESULTS AND DISCUSSION
Pulping
A good delignification medium must have nucleophilic species to promote the cleavage of lignin and to dissolve the lignin fragments. The addition of water is able to promote the delignification reaction but reduces the ability of the solvent to dissolve the lignin generated in the process. This is becau lignin is a hydrophobic biopolymer, and the hydrophobicity induces adsorption of lignin fragments onto the surface of a pulp
fiber. To prevent lignin reprecipitation in formic acid liquor, a suitable concentration of formic acid is critically important. It has been shown that a formic acid liquor having a 90% (v/v) concentration had a positive effect on delignification (Jahan et al. 2007, 2007b). If the formic acid charge was less than this in the reaction mixture, the extent of delignification decread significantly.
Formic acid (FA) treatment at boiling temperature removed 79.6, 80.1, and 79.7 percent of the pentosan from jute fiber, jute cuttings, and jute caddis, respectively (data are not shown), which in ve
ry important for dissolving pulp. After this FA treatment, 62.9, 51.7, and 52.5 percent delignification was achieved from jute fiber, jute cuttings, and jute caddis, respectively. Peroxyformic acid delignification was carried out after formic acid treatment, and the pulp compositions are given in Table 2. The peroxyformic acid was prepared by adding H2O2 to 90 % formic acid. Such a mixture of FA, H2O2, and peroxyacid proved to be efficient in delignification of unbleached pulp through the combined action of the peroxyacids as oxidizing agent and formic acid as solvent for the lignin (Kham et al. 2005). A high pulp yield (52 to 69%) was obtained in all the raw materials. Jute cutting possd the highest pulp yield (62-69 %), and jute caddis gave the lowest pulp yield (52-63 %) among the raw materials. This may be explained by higher impurities and foreign materials in caddis, which are dissolved during pulping, and also higher α-cellulo in jute fiber (Table 1). The yields are quite similar to the results reported for paper grade kraft pulping and better than for dissolving pulp in prehydrolysis kraft process (Jahan et al. 2007; Jahan 2008). Shahin and Young (2008) obtained over 70% pulp yield from jute fiber in acetic acid pulping, but kappa number was above 40. Easier pulping of the raw materials is attributed to lower lignin content (Table 1) and higher syringyl to guaiacyl ratio (Islam and Sarkanen 1993).
Table 1. Chemical Characteristics of Jute Fiber, Cuttings and Caddis (Jahan et al. 2007)
Jute fiber Jute cutting Jute caddis
Klason lignin, % Holocellulo, %
α-cellulo, % Pentosan, % Extractives (DCM), % 12.7
87.6
63.1
13.5
0.25
14.0
87.9
60.0
14.1
0.43
14.7
87.7
58.6
14.0
3.86
DCM- Dichloromethane
The kappa number analysis was included in this study to measure the reagent consumption in bleaching. The best results in term of kappa number were found for jute fiber. Kappa number of jute cuttings was 29.5 at 2% peroxide charge, which was rapidly dropped to 16.9 with increasing peroxide charge to 4%. A very high kappa number in jute cutting pulp at 2 % peroxide charge may be due to adhering scales of jute cuttings that consumed most of the peroxyformic acid. Kappa numbers of pulps were decread with the increa of peroxide during peroxyformic acid treatment.
Kappa number was again decread if an additional peroxyformic acid treatment was included at the beginning.
Kappa number was reduced from 17.8 to 6.9 for jute fiber, 29.5 to 10.2 for jute cuttings, and 20.1 to 16.2 for jute caddis from FP f to P f FP f stage pulping under similar peroxide charge. Pulp yield and kappa number were better than tho of hardwoods (Parthasarathy
et al. 1995).
Table 2. Properties of Jute Fiber, Jute Cutting, and Jute Caddis Pulp Obtained From FP f , P f FP f Process
Stage H2O2Pulp yield, % Kappa
number
Viscosity Brightness
Jute fiber
FP f FP f FP f P f FP f 2
4
6
4
63.5
61.3
59.5
57.6
19.4
17.8
远近闻名8.7
6.9
14.2
13.8
13.5
13.1
29.4
31.3
37.9
43.8
Jute cutting
FP f FP f FP f P f FP f 2
4
6
4
69.2
吃自助餐
68.6
65.9
62.3
29.5
16.9
11.2
10.2
19.9
19.5
16.4
16.2
19.3
26.9
27.3
34.3
Jute caddis
FP f FP f FP f P f FP f
2
4
6
4
62.5
58.8
54.0
52.4
28.8
20.1
20.8
16.2
14.3
12.8
10.5
7.5
17.9
19.2
23.6
29.4 The viscosity of jute cutting pulp (16-20 mPa.s) was higher than that of jute fiber
综合能力
(13-14 mPa.s) and jute caddis (14-8 mPa.s). Viscosity values were decread with peroxide charge in perpxyformic acid treatment. Jute cutting is obtained from the lower part of the plant. So this part is more mature, which is the reason for the higher viscosity.
One experiment for each raw material was carried out starting with peroxyformic acid (P f) followed by FP f treatment. This was done to better understand xylan removal and delignification efficiency of
formic acid treatment after P f treatment. Selective removal of lignin in P f treatment may enhance xylan removal during a subquent formic acid step. However, no meaningful enhancement of xylan removal efficiency was evident in formic acid treatment after P f reatment (Table 3). But additional Pf treatment in the starting mixture improved pulp deligninfication (Table 2).
As expected, unbleached pulp brightness of jute fiber pulp was the highest, followed by jute cutting, and finally jute caddis. Brightness was improved with increasing peroxide charge in peroxyformic acid treatment. An additional peroxyaformic acid treatment in the beginning improved pulp brightness. Brightness was incread from 31.3 to 43.8 for jute fiber, from 26.9 to 34.3 for jute cuttings, and from 19.2 to 29.4 for jute caddis from FPf to PfFPf stage pulping under similar peroxide charge.
Bleaching
All pulps were bleached by alkaline peroxide, and results are given in Table 3. The pulp yield loss on bleaching were 1 to 3.4% for jute fiber, 13.1 to 15.1% for jute cuttings, and 2.2 to 4.7% for jute caddis, which were either as expected or lower than the expected range (Sixta et al. 2003).
Table 3. Properties of Bleached Pulp Obtained from FP f and P f FP f Procesd Pulps of Jute Fiber,
Jute Cuttings, and Jute Caddis
Stage H2O2 Pulp
yield, % α-cellulo R-10 R-18 Viscosity Brightness Carboxyl
content,
meq/100
g pulp
Jute fiber
FP f FP f FP f P f FP f 2
4
6素炒卷心菜
4
60.1
59.5
56.8
56.6
95.7
96.9
97.2
96.6
97.8
96.9
97.3
96.6
98.1
97.9
98.4
98.2
12.7
11.8
12.3
9.5
78.4
79.1
85.0
87.1
6.30
6.26
4.86
4.34
Jute cutting
FP f FP f FP f P f FP f 2
4
6
4
54.1
53.5
52.8
48.7
98.9
98.5
98.2
98.1
97.9
97.9
97.2
97.1
98.4
98.5
98.6
98.7
19.0
18.8
16.2
12.8
71.4
79.2
81.4
86.3
3.69
3.64
3.16
2.98
Jute caddis
FP f FP f FP f P f FP f
2
4
6
4
58.3
54.1
49.6
50.2
91.5
93.3
93.1
93.7
93.2
95.8
94.9
97.0
97.0
97.5
97.5
98.7
13.1
12.3
9.0
7.2
59.1
59.5
61.9
70.1
6.92
6.05
5.60
5.07 The loss of pulp yield in jute fiber was the lowest, and in jute cuttings was the
highest. The loss of yield on bleaching was caud by saponification, delignification, and solubulization of pentosan and low molecular weight cellulo. All dissolving pulps met the specifications typical for market sulfite and prehydrolysis kraft pulps (Sixta and Borgards 1999). The degree of purification expresd as R-values and cellulo content were comparatively high for the pulps. The dissolving pulp in jute cuttings was highly pure (α-cellulo content: 98-99 %). The α-cellulo content in dissolving pulp from jute fiber was 96-97 % and from jute caddis was 92-94 %.
There was no significant difference between FP f and P f FP f stages pulping in the purity of dissolving pulp. It was obrved from our earlier investigation that the dissolving pulp produced from jute is not as pure as wood in the conventional process (Jahan 2008). So a formic acid process is suitable to produce dissolving pulp from jute. Figure 1 shows viscosity vs. cellulo content. High cellulo content can be achieved at the expen of a vere degradation of molecular weight at a higher temperature of prehydrolysis. Jute caddis showed scattered viscosity and alfa cellulo data.
R-values (Retention in alkali) in jute fiber, jute cuttings, and jute caddis were also comparatively high. The retention in alkali data R10 and R18 provide information on the low molecular weight carbohydrates (degraded cellulo and hemicellulo) in pulp. A 10% sodium hydroxide solution dissolves both degraded cellulo and hemicellulo (Retention in 10% alkali, R10) whereas hemicellulo is soluble in an 18% sodium hydroxide solution (Retention in 18% alkali, R18). Degraded cellulo (R18 minus R10) in jute cuttings was very low, as compared to jute fiber and jute caddis. Degraded cellulo (R18 minus R10) in pulp incread with decreasing viscosity and increasing pulp brightness (Figs. 2, 3).
