WPP 2003 Pulp & Paper Science And Technology: Alternative Papermaking Fibres ASAM PULPING OF JUTE

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WPP 2003 Pulp & Paper Science And Technology: Alternative Papermaking Fibres ASAM PULPING OF JUTE
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  252WPP 2003Pulp & Paper Science And Technology: Alternative Papermaking Fibres  ASAM PULPING OF JUTE M. SARWAR JAHAN*, D. A. NASIMA CHOWDHURY, M. KHALIDUL ISLAM  Pulp and Paper Research Division, BCSIR Laborato- ries, Dhaka, Dr. Qudrat-E-Khuda Road, Dhaka-1205, Bangladesh, e-mail: m_sarwar@bdonline.com  ABSTRACT  ASAM pulping of whole jute plant was done with varying alkali ratio (NaOH/Na 2 SO 3 ), alkali charge,methanol ratio in the pulping liquors, cooking timeand temperature. The pulp yield and Kappa numberwere decreased with increasing alkali ratio, alkalicharge and temperature. Methanol in the pulpingliquor increased selectivity. At optimum conditionsof ASAM pulping where alkali ratio 80 %, alkalicharge 22 %, MeOH 25 % and cooking time 1 h at170 °C produced pulp yield of 56.6 % with Kappanumber 39.2. ASAM pulping of whole jute plantresulted in high yield, excellent strength propertiesand unbleached brightness than the kraft pulp. Oxy-gen bleaching reduced kappa number by 49 % andincreased brightness to 56 %. Therefore, less chlorinedioxide was needed in subsequent ECF bleaching. ASAM pulp from whole jute plant retained superiorstrength properties after ECF bleaching.Jute fiber was cooked in the same optimum con-ditions as whole jute plant. Pulp produced very low Kappa number (7.6), very high yield (61.5%) andbrightness (63%). The strength properties of ASAMpulp from jute fiber were very high. ECF bleachingshowed higher strength and brightness as comparedto kraft pulp from jute. INTRODUCTION Jute has a long historical role in the socioeco-nomic development of Bangladesh. Once jute wasknown as golden fiber of Bangladesh. The export of  jute and related products accounts for a significantportion of total export. In addition, it provides con-siderable employment opportunities to the coun-trys work force. Traditionally jute was used in back-ing, sacking, gunny bag, hasein etc. In recent years, jute has faced stiff competition from synthetics.Therefore, traditional uses of jute have declined. Asa result, its demand in local and overseas marketshas been shrunk. This has caused jute prices dropand jute growers are the ultimate victims. There-fore, diversified usage is needed to regain the lostglory of jute. The chemical and morphological char-acteristics of jute favor it as pulping raw material(Nahar 1987). Therefore, many studies have beendone on the pulping of jute in home and abroad(Jahan and Farouqui 2000; Jahan and Farouqui2001; Jahan et al. 2001; Jahan 2001; Roy et al.1998). But a lot of problems like blowing, washing,screening, recovery etc. have raised to commercial-ize the pulping process of jute. Another drawback isthe price of jute three times higher than the conven-tional raw materials of pulp mills. Therefore, it isutmost need to find out a new pulping process,which overcome all limitations in the conventional jute pulping. Although sulfite pulps have higher initial bright-ness, the process has become less competitive dueto the restriction of concerning suitable raw materi-als and lower strength properties of the sulfite pulps.In 1985, a new pulping process was developed by Patt and Kordsachia (1986) based on alkaline sulfitepulping with addition of anthraquinone (AQ) andmethanol to achieve high delignification rate. Theprocess is known as ASAM process. It is found thata cooking liquor containing Na 2 SO 3 , NaOH or Na 2 CO 3 and AQ in a water/methanol is an excellentlignin solvent. Sodium sulfite renders lignin solubleand anthraquinone enhance delignification by itscatalytic effects. Therefore, lignin degradation reac-tions are not restricted to structures with benzylalcohol or alkyl ether groups as in neutral or alka-line sulfite pulping and therefore, a strongly in-creased delignification is possible.Softwoods and hardwood can be delignified witha sulphite liquor containing methanol and0.53 w-% sulphur dioxide (Chiang et al  1987).Birch pulp with a kappa number of 2025 and a yield of 4446 % can be produced when the cook-ing temperature is 140145°C K, the cooking timeis 100200 minutes, the liquor contains 55 % metha-nol and 1.251.5 % sulphur dioxide and the liquor-to-wood ratio is 6:1. With the same liquor-to-woodratio, spruce pulp with a kappa number of 3040and a yield of 4244 % can be produced when thecooking temperature is 160165°C, the cookingtime is 120-150 minutes and the liquor contains6065 % methanol and 33.5 % sulphur dioxide.When the pulp produced by the alkaline sulphite-anthraquinone method (ASAQ) is extracted with  253Pulp & Paper Science And Technology: Alternative Papermaking FibresWPP 2003methanol (Oh et a l. 1988), the strength propertiesare found better than the properties of kraft and ASAM (alkaline sulphite-anthraquinone-methanol)pulps. Compared to the kraft process, the ASAMprocess uses 10 % less inorganic chemicals, thecooking temperature and the digester pressure arefound to be higher by 510°C and 1.31.4 MPa,respectively. The pulp can be bleached without chlo-rine and it has strength properties superior to thoseof kraft pulp. The methanol content of the pulpingliquor can be dropped from 35 % to 20 % withoutimpairing the pulp quality. In the pressure relief of the digester 95 % of the methanol is recovered,which can be improved to over 97 % by steamstripping. The recovery of the inorganic chemicalsis similar to the recovery in sulphite pulping. The ASAM method could be used to produce beechpulps with very low residual contents (Kordsachia& Patt 1987). ASAM process showed a good alternative tokraft process for both softwood and hardwood. Butno report has been done on the ASAM pulping of  jute. Therefore, in the present investigation, an ef-fort has been made on the ASAM pulping of jute.Optimization of ASAM pulping for jute has beendone with varying cooking variables such as Na 2 SO 3 /NaOH ratio, chemical charge, methanolratio in the liquor, temperature and time. Elementalchlorine free (ECF) bleaching of ASAM pulps from jute also has been studied. EXPERIMENTALRaw materials Whole jute plant (WJP) and retted jute fiber(RJF) were collected from the BJRI, Dhaka. It wassun dried and dirt was removed. Then it was cut to23 cm in length. The moisture content of raw materials was determined according to TAPPIStandard Methods (T 18m-53). After determina-tion of the moisture content of air dried raw materi-als equivalent to 250 gm oven dried (o.d.) wasweighed separately in a polyethylene bag for subse-quent cooking experiments. Cooking  All pulping experiments of WJP were performedin an autoclave of 5 liters capacity, made of stain-less steel, rotating at 1 rpm, fitted with thermostat.The following parameter was maintained in ASAMprocess:Total alkali charge as sodium hydroxide was 10,12, 14, 16 % on o.d. raw materialsNa 2 SO 3 /NaOH ratios were 70/30, 80/20 and90/10Liquor to fiber ratio was 5:1.AQ charge was 0.1 % on o.d. raw materialsTemperature was 170 and 180 °C.Cooking time was 60 and 120 min.Methanol was 0, 20, 25, 30 % on the total vol-ume of liquor.20L capacity digester was used for RJF and WJP inthe optimum conditions obtained by ASAM proc-ess in order to beat the pulps. Bleaching WJP and RJF pulps were bleached in elementalchlorine free (ECF) bleaching sequences. The de-tails of bleaching conditions are given in Table 2 .The kappa factor 0.22 was used for ECF bleaching. Evaluation of pulps WJP and RJF pulps of optimum conditionswere beaten in a Valley beater. The samples werecollected at different freeness and handsheets of about 60g/m 2 were made in a Rapid Kothen SheetMaking Machine according to German StandardMethods DIN 106. The sheets were tested fortensile (T 404os 61), burst (T 403m 53) and tearstrength (T 414m-49) according to TAPPI Stand-ard Methods. All WJP pulps were beaten in aWearing blender for about 15 min then handsheetswere prepared for tensile, tear burst and foldingstrength as described above. RESULTS AND DISCUSSION  ASAM pulping of whole jute plant was donewith varying cooking variables namely- chemicalcharge, alkali concentration in NaOH/Na 2 SO 3 ra-tio, AQ charge, temperature methanol ratio andcooking time as shown in Table 1 . It is seen thatpulp yield, kappa number and tear index were de-creased and breaking length and burst index wereincreased with increasing chemical charge at theconditions of 80 % of Na 2 SO 3 /NaOH ratio, 25 %methanol ratio, 1h of cooking at 170 °C. Kappanumber of 39.2 in 56.6 % pulp yield was observed  254WPP 2003Pulp & Paper Science And Technology: Alternative Papermaking FibresChemicalNa 2 SO 3 /MeOH%TempTimePulpKappa°SRBreakingBurstTearchargeNaOHyield,numberlenght,index,index,as NaOHratio.0Ch %mkPa.m 2 /gmN.m 2 /g188025170161.855.71544103.013.1208025170158.948.81545493.112.3228025170156.639.21446573.211.2248025170154.439.01448613.111.722800170153.946.51540492.911.3228020170156.140.31545873.011.8228030170155.841.71751133.912.4227025170151.237.11544843.012.5229025170156.742.31548413.712.7228025170153.841.11646213.212.4228025180249.332.41562733.812.722*8025170157.550.41638142.712.3 Tab. 1.  ASAM cooking conditions for WJP pulping and pulp properties (*without AQ) SequenceTemperatureTimePressureConsistencyKappaBrightness,ViscosityYield, %°CminKg/cm 2 %number%mPa.son o.d. pulpWJPRJFWJPRJFWJPRJFWJPRJFUB39.27.045.063.028.135.6100100Oxygen*100602.51025.55.158.369.819.731.895.697.0D1**7060713.13.268.176.517.228.194.195.3E70601010.62.170.180.315.926.993.294.6D2706071.883.585.315.325.792.893.6 Tab. 2.  Bleaching conditions and results of ASAM pulps from WJP and RJF (MgSO  4 0.5 % on o.d. pulp,** Kappa factor 0.22, WJP-whole jute plant, RJF-retted jute fiber) at 22 % chemical charge. NS-AQ pulping of whole jute plant produced pulp yield of 53.0 % in Kappanumber of 35.0 when used 22 % chemical charge(Shafi 1994). Whole jute plant produced pulp of low Kappa number with the sacrifice of yield in thekraft process (Jahan 1999). If chemical charge wasincreased from 22 to 24 % kappa numbers did notreduced significantly but pulp yield lost by 2.2 % ono.d. raw materials. The delignification rate was in-creased with increasing NaOH concentration in Na 2 SO 3 /NaOH ratio with the loss of pulp yield. Atthe Na 2 SO 3 /NaOH ratio of 70 %, kappa numberreduced to 37.1 with the loss of 5.5 % pulp yield ono.d. raw material. The delignification was signifi-cantly improved with the huge loss of pulp yield if cooking temperature increased to 180 °C. Kineticsstudy of Eucalyptus wood pulping showed that thehigher temperature was required for ASAM processthan kraft process (Miranda and Pereira 2002). Activation energy for ASAM process was132.4 kJ/mole and for kraft 83.5 kJ/mole. At highertemperature physical properties were increased. ASAM pulping of spruce or pine chips at 175 °C for90min resulted in Kappa numbers of 35, but anincrease in temperature and time accelerated thedelignification to Kappa number of 14.5 (Patt et al1987). If AQ was not used in the cooking liquor, noremarkable improvement in delignification wasshown.  Figure 1 represents the effect of methanolon the delignification and pulp yield. In this case,chemical charge and sulfite to alkali ratio were setat 22 % and 80 % for 1h at 170°C, respectively. Theaddition of methanol increased delignification, i.e.decreased Kappa number of the resulting pulp.Methanol supports the even distribution of AQ inthe chips and its reactivity during the redox cycle. Italso reduced the ionization of the cooking chemi-cals and the swelling of wood components (Patt etal 1991). The presence of methanol up to 25 % inthe cooking liquor accelerates the rate of   255Pulp & Paper Science And Technology: Alternative Papermaking FibresWPP 2003Chemical charge as NaOH on o.d. RJF, %20Cooking time at max. temperature, min60Maximum temperature, °C170 AQ charge on o.d. RJF, %0.1 Na 2 SO 3 /NaOH,80/20Pulp yield, % on o.d. RJF61.5Kappa Number7.5Brightness, %63.0 Tab. 3. ASAM cooking conditions and results for  RJF pulping  303540455055600 10 20 30 40 Methanol, % Pulp yieldKappa No Fig. 1.  Effect of methanol on pulp yield and Kappanumber of WJP  delignification. Similar evidence was observed dur-ing ASAM pulping of spruce, beech and pine(Schubert et al 1994). This was may be due to in-creasing polarity of the cooking liquor and by de-creasing the viscosity of the liquor. These two factorsenhance penetration of the cooking liquor and diffu-sion of the chemical ions to the reaction sites (Raberand Raber 1988; Nakano et al. 1981; Sarkanen andLudwig 1971). An addition of 6.3 % methanol in thekraft liquor reduced Kappa number by 2 points insoftwood pulping (Leduc et al. 2003). Pulp yieldremained almost similar from 20 to 30 % methanolin the cooking liquor. Kraft pulp yield slightly in-creased with methanol and without AQ. Norman etal. (1993) showed that addition of methanol in thehigh sulphidity kraft liquor accelerated thedelignification and the degradation, but the effect of delignification was greater. Breaking length, burstindex and tear index were increased with increasingmethanol ratio in the cooking liquor ( Table 1 ). Retted jute fiber pulping (RJF) The retted jute fiber pulping was done in 22%chemical charge (Na 2 SO 3 /NaOH, 80/20) at 170 0 Cfor 60min. The AQ charge was 0.1% on o.d jute andliquor ratio 5, respectively. Very high pulp yieldwith exceptionally low Kappa number was obtainedin ASAM pulping of retted jute fiber. Similarly  ASAM pulping of poplar chips resulted to Kappanumber of 6.5, whereas the corresponding Kappanumber for birch chips was 13.0 (Patt et al. 1987). As shown in Table 3 RJF produced 7.3 Kappanumber in 61.5% pulp yield in ASAM process. Thebrightness of unbleached pulp was 63%, which indi-cated easier bleachability. The higher Kappa numberduring whole jute plant pulping (Table 1) may bedue to the fact that the whole jute plant containsbark and core in the ratio of 1:2.5. Core containsmore lignin and less holocellulose than bark. Dur-ing retting, extractive and resinous matters weredissolved from the bark. Therefore, during unrettedwhole jute plant pulping chemicals was consumedby extractives and densely lignified core portion.The viscosity of ASAM jute pulp was 30.1, whichpredicted good strength properties. Bleaching of WJP and retted jute fiber  The WJP and RJF pulps of Kappa number 39.2and 7.3, respectively, were bleached in elementalchlorine free bleaching (ECF) sequences. After oxy-gen treatment, Kappa number of WJP pulp wasreduced to 25.5 with the sacrifice of 2.1mPa.s vis-cosity. At this time pulp brightness was increased to56.0 % from 45.0 %. Kappa number and viscosity of retted jute fiber were reduced to 5.1 from 7.3 and to31.8mPa.s from 35.6mPa.s, respectively. Oxygentreatment reduced about 40% of chlorine demand,therefore, reduced chlorinated compound in theeffluent. Oxygen prebleached pulps were subse-quently bleached by DED bleaching sequences. Thefinal brightness and viscosity of the ASAM pulpswere 83.5 % & 15.3 mPa.s for WJP and 85.3 % &25.7mPa.s for RJF, respectively. ASAM pulp fromdouglas-fir, spruce and beech showed more easily bleachable than that of other conventional pulps inECF and TCF bleaching (Zimmermann et al. 1991;Knoblauch et al 2000). Physical properties of ASAM pulp from WJP The strength properties of bleached andunbleached ASAM pulp from whole jute plant are  256WPP 2003Pulp & Paper Science And Technology: Alternative Papermaking Fibres 0200040006000800010000120000 20 40 60Freeness, 0 SR     B  r  e  a   k   i  n  g   l  e  n  g   t   h ,  m U nbleachedB leached 0123456780 20 40 60 0 SR     B  u  r  s   t   i  n   d  e  x ,   k   P  a .  m    2    /  g UnbleachedBleached Fig. 2. The relationship between freeness and break- ing length of ASAM pulp from WJP  Fig. 3. The relationship between freeness and burst index of ASAM pulp from WJP  0510150 20 40 60Freeness 0 SR     T  e  a  r   i  n   d  e  x ,  m   N .  m    2    /  g UnbleachedBleached Fig. 4. The relationship between freeness and tear index of ASAM pulp from WJP  shown in  Figs. 26  . It is seen from  Fig. 1. thatbreaking length of unbleached ASAM pulp fromWJP reached to about 10.000 m after beating toabout 30 °SR. At this beating degree the breakinglength of bleached pulp reached to about 9.000 m.The burst index of ASAM pulp from WJP wasincreased during beating (  Fig. 3 ). The burst index of the unbleached pulp was improved from 3.2 kPa.m 2 /g in the unbeaten state to a value of 6.8 kPa.m 2 /g atabout 30 °SR then level off. But bleached increasedlinearly from 3.5 kPa.m 2 /g to 6.5 at 52 °SR.The tearing strength of bleached pulp decreasedwith beating whereas unbleached pulp increasedinitial degree of beating then decreased (  Fig. 4 ). After 30 °SR, bleached and unbleached pulpsshowed almost similar tear index. Similar resultswere observed in ASAM pulping of Douglas fir(Zimmermann et al. 1991). 0200040006000800010000120000 20 40 60Freeness, 0 SR     B  r  e  a   k   i  n  g   l  e  n  g   t   h ,  m UnbleachedBleached Fig. 5. The relationship between freeness and break- ing length of ASAM pulp from RJF. Physical properties of ASAM pulp from RJF Strength properties of ASAM pulp from retted jute fiber are shown in  Figs. 57  . The breakinglength of unbleached pulp was increased to 9547 mfrom 3437 m with increasing SR number from 14 to41 (  Fig. 5  ). On ODED bleaching breaking lengthwas reduced by 11 %. The bursting strength of bothbleached and unbleached pulps were increased rap-idly up to certain SR number then decreased. Thebursting strength ASAM bleached and unbleachedpulps from RJF reached to maximum value of 7.7kPa.m 2 /g at °SR 37 and 7.9 kPa.m 2 /g at °SR 31,respectively. The tear index of ASAM pulp wasincreased with increasing SR number initially thendecreased. The maximum tear index of unbleachedpulp was obtained 24.9 mNm 2 /g at 19 °SR and forbleached was 21.7 mNm 2 /g at 23 °SR.
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