EFFECTS OF OPERATIONAL VARIABLES ON THE PULP YIELD AND LIGNIN DISSOLUTION OF CYPERUS ARTICULATUS

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1 Journl of Science nd Technology, Vol. 0, No. (00), pp Kwme Nkrumh University of Science nd Technology (KNUST) EFFECTS OF OPERATIONAL VARIABLES ON THE PULP YIELD AND LIGNIN DISSOLUTION OF CYPERUS ARTICULATUS B.O. Ogunsile Deprtment of Chemistry, University of Ibdn, Ibdn ABSTRACTS The influence of opertionl vribles on the pulp yield nd lignin dissolution of Cyperus rticultus ws studied. The study ws imed t optimizing pulping vribles nd selecting suitble delignifiction conditions for the production of pulp nd pper from the plnt. Cyperus rticultus chips were delignified in lbortory pulpwood digester under the sod pulping process using the following pulping conditions: time (0 50 minutes), temperture (0 50 o C), liquor to solid rtio (0: 0:) nd concentrtion of cooking liquor ( 6% custic sod). Experimentl dt were fitted into centrl composite design nd the polynomil eqution derived reproduced the pulp yields nd the residul lignin contents with errors less thn 6%. Optimum pulp yields were obtined using low vlues of the process vribles while the reverse ws the cse for the residul lignin. Pulping t high tempertures for short cooking time with low to medium concentrtion of pulping liquor gives the best compromise for both pulp yield nd residul lignin content. Keywords: Cyperus rticultus, sod pulping, pulp yield, residul lignin. INTRODUCTION Pper cn be produced from virtully ny cellulose contining mteril. Cellulose, one of the most bundnt orgnic substnces vilble, forms the mjor component of most plnts nd is constntly replceble. In the mnufcture of pulp nd pper, cellulose fibres re liberted from the mtrix of lignin which cements them together. Fiber libertion cn be chieved by het, mechnicl, chemicl, biochemicl mens or combintion of ny of these (Hygreen nd Bowyer, 98). The mechnicl process involves both compression nd friction of wood chips or logs which produces het tht softens the lignin thus relesing the fibers. In some processes, the wood chips re preheted before the mechnicl tretment (Csey, 960; Jmes nd Rymond, 970). The pper produced in the mechnicl process is wek nd non-permnent becuse it contins high lignin nd reltively little cellulose. In the chemicl pulping, chemicl regents re used to effect seprtion of the cellulose fibers from the lignin mtrix nd other components (Gierer, 985). In principle, wood chips re Journl of Science nd Technology KNUST April, 00

2 96 Ogunsile digested with suitble chemicls t elevted temperture nd pressure using pproprite liquor to solid rtio. The chemicl process hs comprtive dvntge over the mechnicl process in tht the pper produced is stronger nd permnent becuse of its low lignin content. The successful opertion of the chemicl pulping processes depend on certin opertionl vribles such s time, temperture, concentrtion of cooking liquor, chip size nd liquor to solid rtio (Iglesis et l., 996; Jime nez et l., 008). The selection of suitble delignifiction conditions nd optimiztion of process vribles re therefore highly essentil for pulp nd pper production by the chemicl pulping processes. Kinetic modeling bsed on mthemticl design hve been used s wy of optimizing operting condition in pulping processes (Tjeerdsm et l., 99). However, this model becomes too complex when more thn two independent vribles re involved. A more recent pproch is the use of centrl composite fctoril design (Aknzrov nd Kfrov, 98). The fctor design is preferred to kinetic modeling becuse of its simplicity especilly when severl vribles re involved. It llows the development of empiricl models involving severl independent vribles in order to identify ptterns of vrition in the dependent vribles of vrious pulping processes s pplied to diverse vegetble mterils (Vzquez et l., 995; Veg et l., 997; Gilrinz et l., 999; Jimenez et l., 000, Jimenez et l., 008) Cyperus rticultus is non-wood mt-mking plnt whose fiber chrcteristics nd sod pulping ws reported recently (Ogunsile et l., 007). The present study ws imed t evluting the influence of operting vribles on the pulp yield nd lignin dissolution of this plnt using centrl composite fctoril design. MATERIALS AND METHODS Cyperus rticultus ws collected long the riverine re of Ikorodu in Lgos stte. The plnt ws mnully cut into chips of bout - cm long, sun-dried nd stored t room temperture in polythene bg. Sod cooking liquor ws prepred from stndrd concentrted solution of sodium hydroxide by seril dilution with de-ionized wter. The plnt smples were pulped in 0-litre electriclly heted, thermostticlly controlled stinless steel digester. Chips from the Cyperus rticultus were weighed nd chrged into the digester with the required mount of chemicl solution t liquor to solid rtio of 0: nd 0:. The digester ws heted to the operting tempertures (0 o C nd 50 o C) nd time (0-50 minutes), which ws then mintined throughout the experiment. The resulting pulp ws thoroughly wshed with tp wter nd the pulp yield ws determined grvimetriclly fter drying t 0 o C to constnt weight in the oven. The pulps were nlyzed for Kpp number s described in TAPPI stndrd (99). The residul lignin ws estimted from the Kpp number by multiplying with fctor of 0. (TAPPI, 99). The centrl composite fctoril design The centrl composite fctoril design ws employed to evlute nd quntify the effect of the opertionl vribles on the pulp yields nd residul lignin. The effect of the vribles were quntified more precisely by choosing prt of the experimentl results nd grouping them to form first order full fctoril design, with vribles t two levels ( ). Using this design, some of the experimentl dt were fitted to first order polynomil regression eqution s implemented in the "SPSS" sttisticl pckge. Individul nd second order interction influences over the response surfce of the independent vribles were evluted (Aknzrov nd Kfrov, 98). The mthemticl model ws: Y 0 () Journl of Science nd Technology KNUST April 00

3 Effects of opertionl vribles on the pulp yield The response vrible Y represents the pulp yield nd residul lignin. The independent vribles,,, nd correspond to liquor to solid rtio LS, time, temperture nd concentrtion of cooking liquor respectively. The rnges of vlues for ech independent vrible were: LS, 0: to 0:, time, 0-50 minutes, temperture, C nd concentrtion, -6% NOH solution. The vlues of the independent vribles were normlized from to + by using the eqution ( ) n () ( mx min ) Where: n is the normlized vlue of LS, time, temperture nd concentrtion, is the bsolute experimentl vlue of the vriis the men of ll the experimentl vlues for the vrible in question mx nd min re the mximum nd minimum vlues respectively of such vrible. RESULTS AND DISCUSSION The composition of the sun-dried smple ws determined to be 0.9% cellulose,.% lignin nd 6.9% sh. The lcohol-benzene extrctives, cold wter solubles, hot wter solubles, nd % NOH solubles were 6.5%,.0%, nd 6.6% respectively. The fiber ws.5mm long,.µm wide nd 6.µm thick (Ogunsile et l., 007). The experimentl design ( fctoril designs) together with the pulp yield nd the residul lignin re presented in Tble. Experiments -6 llowed the clcultion of different prmeters in the regression equtions i nd ij. These were subsequently subjected to T - test to check their significnce t 90 to 95% confidence level using the experimentl error estimted from the repliction t the centrl point of the design, tht is, experiments 7, 8 nd 9 of Tble. The vlues of experiment ws corrected by extrpoltion. The centrl point of the design corresponds to the following rection conditions: Liquor to solid rtio, LS = 5:, Time = 90 minutes, Temperture = 5 o C Concentrtion = 5% sod Tble : Experimentl design nd result for yield nd residul lignin Experiment LS Time Temperture Concentrtion Yield Lignin (%) (%) Journl of Science nd Technology KNUST April, 00

4 Experimented Yield Experimented Yield 98 Ogunsile All normlized independent vribles for the The coefficients of the model equtions nd the centrl points of the design re zero. sttisticl prmeters estblishing their vlidity re summrized in Tble. The dependent vribles (i.e. pulp yield nd residul lignin) were Tble : Signictive regression prmeters relted to the independent vribles through the Yield Residul Lignin following equtions: α α Yield α Yieldα () α α (-0.6) (-0.0) Residul Lignin α (-0.8) (-0.08) ResidulLignin () α (-0.0) (-0.) α (-0.09) (-0.06) Vlues clculted from the respective polynomil equtions bove were plotted with the α -0.5 (-0.) α α experimentl results for the different response vribles s shown in Figures nd b. The non-significnt prmeters t 0. levels re in prenthesis Clculted Yield Yield Fig. : Correltion between experimentl nd clculted vlues of () pulp yield Journl of Science nd Technology KNUST April 00

5 Experimented lignin Experimented lignin Effects of opertionl vribles on the pulp yield Fig. b: Clculted lignin Clculted lignin Correltion between experimentl nd clculted vlues of ((b) residul lignin The results showed good correltion between the experimentl vlues nd those predicted by the models. Pulp yield: Eqution llows the estimtion of the vrition of the yield with chnges in ech independent vrible over the rnge considered while the other three remin constnt. Non-significnt prmeters were dropped to obtin simpler equtions. The eqution showed tht ll the opertion vribles, nmely, the LS, time, concentrtion nd temperture hd significnt influence t 90% confidence level on the pulp yield. Also, on the pulp yield, there were significnt interctions between time nd concentrtion on one hnd nd temperture nd concentrtion of the cooking liquor on the other hnd. The lowest pulp yield (9.7%) ws obtined t lrge vlues of the four process vribles (i.e. + for ll). If yield similr to chemicl pulp is desired, then ll the process vribles must be t normlized vlues of +. However, this lowest yield cn be rised to 5% by using lower pulping time (- normlized vlue). Pulping t lower time will reduce the degrdtion effects of temperture nd pulping liquor on the cellulose. This will lso result in some energy svings in ddition to incresing the pulp yield. The highest obtinble yield ws 0.%, which occurs t low vlues of the process vribles (- for ll). The mximum nd minimum vritions in the highest pulp yield were cused by chnges in time ( chnge of 5. units) nd concentrtion ( chnge of 0. unit) respectively, the effects of temperture (.6 units) nd LS (.0 units) lie in between. Delignifiction. The minimum lignin content, ccording to eqution, ws obtined t high vlues of cooking time, temperture nd cooking liquor (+ for ll). Under this condition, the Journl of Science nd Technology KNUST April, 00

6 00 Ogunsile mximum vrition in the minimum residul lignin vlue ws cused by chnge in pulping time (0.9 units) followed by LS, temperture nd concentrtion respectively. The lowest residul lignin content (.7%) cn be decresed further to.6% by setting the concentrtion to vlue of +0.5 unit. Pulping t high tempertures for short cooking time with low to reltively high concentrtion of pulping liquor would give the best compromise for both pulp yield nd residul lignin content. Rtio of dissolved lignin to weight losses. The rtio of the dissolved lignin to the weight losses s presented in Tble cn be used to estimte the quntity of lignin present in the pulp provided the pulp yield is known. The result showed tht the vlues were reltively constnt irrespective of the durtion or time of cooking. The verge rtio of the dissolved lignin to the weight loss ws 0. (Tble ) compred to vlue of bout 0. reported for Miscnthus sinensis (Iglesis et l., 996). The differences in the vlues my be ttributed to the nture of the mteril concerned, the mount of lignin present nd the ese of lignin dissolution. The constnt vlues seem to suggest tht solubiliztion nd delignifiction tke plce t the sme rte. CONCLUSION The effects of opertionl vribles on the pulp yield nd residul lignin were evluted using centrl composite model. The eqution showed tht the LS, time nd temperture hd significnt influence on the pulp yield while concentrtion of the cooking liquor did not. The lowest pulp yield ws obtined t lrge vlues of the four process vribles. Pulping t lower time will reduce the degrdtion effects of temperture on the cellulose. This will lso result in some energy svings in ddition to incresing the pulp yield. The mximum nd minimum vritions in the highest pulp yield were cused by chnges in time nd concentrtion, respectively. The minimum lignin content ws obtined t high vlues of the opertionl vribles. Pulping t high tempertures for short cooking time with low to reltively high concentrtion of pulping liquor gives the best compromise for both pulp yield nd residul lignin content. The rtios of the dissolved lignin to the weight losses were reltively constnt irrespective of the durtion or time of cooking. ACKNOWLEDGEMENT The uthor wishes to cknowledge the technicl ssistnce rendered by Messrs Rsq, I.A. nd O.M. Anifowose of the Deprtment of Chemistry, University of Ibdn. REFERENCES Aknzrov, S. nd Kfrov, V. (98). Experiment Optimiztion in Chemistry nd Chemicl Engineering. Mir Publishers, Moscow. Csey, P.J. (960). Pulp nd pper: Chemistry nd chemicl technology, nd Edition, Vol. : Pulping nd bleching. Interscience Publisher nd Inc. New York, 69pp. Gierer, J. (985). Chemistry of delignifiction, Prt : Generl concept nd rections during pulping. Wood Science nd Technology. 9, 89-. Tble : Rtio of dissolved lignin to weight losses Cooking liquors Temperture ( o 0 60 C) % Sod Time (minutes) % Sod Journl of Science nd Technology KNUST April 00

7 Effects of opertionl vribles on the pulp yield... 0 Gilrrnz, M.A., Oliet, M., Rodriguez, F. nd Tijero J. (999). Methnol bsed pulping of Euclytus globulus, Cndin J. Chemicl Engineering. 77 (), Heygreen, J.G. nd Bowyer, J.L. (98). Forest Products nd Wood Science: An Introduction. The Iow Stte University Press/ AMES, pp Iglesis, G., Bo, M., Lms J., nd Veg, A. (996). Sod pulping of Miscnthus sinensis: Effects of opertionl vrible on pulp yield nd lignin solubiliztion. Biores. Technol., 58, 7-. Jmes, H.P. nd Rymond, A.L. (970). Ground wood Stone groung wood chips. In Britt K.W. Hndbook of pulp nd pper technology, vn Nostrnd Reinhold Compny, New York, pp Jimenez, L. Pe rez, A., DelTorre, M.J., Rodrı guez, A. nd Angulo, V. (008). Ethyleneglycol pulp from tgsste. Bioresource Technology, 99, Jimenez, L., Perez, I., DelTorre, M.J., Lopez F. nd Aris, J. (000). Use of formldehyde for mking whet strw cellulose pulp. Bioresource Technology, 7, Ogunsile, B.O., Rsq, I.A. nd Anifowose, O.M. (007). Fiber morphology nd sod pulp from Cyperus rticultus. Interntionl Journl of Chemistry, Vol. 7(), - 6. Technicl Assocition of pulp nd pper Industry (TAPPI). (99). Kpp number of pulp T6CM -85. Tjeerdsm, B.F., Zomers, F.H.A., Wilkizon, E.C. nd Sierr-Alvrez, R. (99). Modeling orgnosolv pulping of hemp. Holzforschung. 8 (5), 5 -. Vzquez, G., Antorren, G. nd Gonzlex, J. (995). Acetosolv pulping of Euclyptus globulus wood.. The effect of opertionl vribles on pulp yield, pulp lignin content nd pulp potentil glucose content. Holzforschung. 9 (), Veg, A., Bo, M. nd Lms, J. (997). Appliction of fctoril design to the modelling of orgnosolv delignifiction of Miscnthus sinensis (elephnt grss) with phenol nd dilute cid solutions. Bioresource Technology 6(), -7. Journl of Science nd Technology KNUST April, 00