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Recently, much research has been developed in the evaluation of new sources of cellulose. In this context, a promising source is the "Capin napier" containing 30.40 Â± 0.05 % of lignin and 70.67 Â± 1.41 of holocellulose (36.34 Â± 0.05 % of cellulose and 34.12 Â± 0.16 % of hemicellulose) and it shows easy plant cultivation and processing. Thus, in this work were optimized conditions for delignification of this source using calcium oxide (CaO) and hydrogen peroxide (H2O2). The best pulping conditions were: 8.6 % CaO during a period of 1 h, resulting in a delignification of 62.87 % Â± 0.097 and a cellulose percentage of 90.01 Â± 0.87. Now with regard to the bleaching process, the condition was: pH 12, hydrogen peroxide concentration from 5%, time of 5h and temperature of 40, resulting in a delignification of 93.8 Â± 0.087 % and a cellulose concentration of 96 Â± 0.11 %.
Lignin, the phenylpropane polymer (C9 unites) present in every plants, is one of the major components in lignocellulosic biomass how sugar cane, corn, rice straws, bamboo and "Capim napiêr" but this compound is the problem of the cellulose polymer industry that to need the pure cellulose since the increase in consumption of paper, polymers derived and fuels increases proportionately. (López et al, 2011; Zhang et al, 2009).
In this context, many studies has been put into practice and the best solution is the use of pulping methods how: Kraft pulping, soda pulping, organosolv-CO2 pulping basic hydrogen peroxide, ozone and others basic process to eliminate the lignin (López et al, 2011; López et al, 2010; González et al, 2008; Hung et al, 2008; Xu et al, 2007; Pereira et al, 2007).
In this process, the lignin polymer, is attacked more readily than cellulose due and occur the deslignification and purification of cellulose through the oxidation and chlorination mainly. The oxidation reaction can be performed without addition of chemicals and oxygen making it a potential solution for pre-treatment of large quantities of straw. Thus, the hemicelluloses are attacked too result the pure cellulose that is used to produce derivate polymer, bioethanol and composite (Thomsen et al, 2008; Ziaie-Shirkolaee et al, 2008).
In this context, the "Capin napier" (Pennisetum purpureum) species belongs to the family Gramineae, subfamily Panicoideae tribe: Paniceae, genus: Pennisetum L. Rich and species: Pennisetum purpureum Schumacher) becomes an interesting source of cellulose, since he is found in abundance in Brazil (Brunken, 1977)
Therefore, in this paper is described the effect of pulping condition (time and calcium oxide concentration) in the ash content of the pulps and the bleaching of cellulose condition (hydrogen peroxide at different pH). The resulting pulp was analyzed and determined the percentage of cellulose and lignin in order to verify the purity of the final product and the best condition of purification.
2. Material and Methods
2.1.1. Lignocellulosic residue
"Capin napier" was used in this study, obtained from Usina Coraci Destilaria de Álcool Ltda. The material was dried at 70°C Â± 3 for 72 h, knife milled to pass a 1 mm sieve and analyzed before the pulping process and the yield in a-cellulose, hemicellulose (T-203 OS-61), lignin (T222) were determinate. These results were using to determinate the best condition of pulping and bleaching the cellulose.
The yield in a-cellulose, hemicellulose, lignin, viscosity, kappa index and media molar mass was determined according to T-203 OS-61, T222, ISO 5351/1 and UNE 57-034 of the fiber, the cellulose pulp and bleached pulp.
Calcium oxide, Hydrogen Peroxide, 30%; Sodium Hydroxide; Potassium Hydroxide; Sulfuric Acid and 95.0-98.0% and potassium permanganate were obtained from Mallinckrodt (Baker, Xalostoc, Mexico).
22.214.171.124. Methods of analysis of material
Three hundred grams of the vegetable material was dried, crushed in a knives mill and cooked in a 5 L batch reactor that. The "Capim napier" was placed in the reactor together with the calcium oxide in different concentrations (3.00, 7.50 and 12.0 %) and pulped by using different times (1, 2 and 3 hours) (Table 1). Following pulping, the cooked material was washed to remove residual cooking liquor until pH 7 and dry at 70°C Â± 3 for 72 h. The pressure was 2 atm, the reactions temperature was 125°C Â± 4 and the consistency of the pulp was 30%.
The pulping material was placed in a 1 L reactor and subjected to bleaching with hydrogen peroxide at different concentrations (1, 3, 6 %) at different times (1, 3, 6 h). The reaction temperature was 40 ° C, the pH was 12 and consistency of the pulp was 30% (Table 2). Following bleaching, the material was washed to remove residual products until pH 7 and dry at 70°C Â± 3 for 72 h.
In the pulp and bleaching process the model tested was 32 and the effects of reaction time and calcium hydroxide concentration and time and hydrogen peroxide were determinate by deslignification, holocellulose and cellulose percentage. In both cases the condition was determinate analyzing the best delignification and less degradation of the pulp by Analysis of Variance (ANOVA), which allows evaluating whether the effect and the interaction among the investigated factors are significant with respect to the experimental error. The significance of the main factors and their interactions was assessed by F-test method with a confidence level of 95%29-30. Response surface methodology, a mathematical-statistical tool, was used for modeling deslignification, hollocellulose and cellulose concentration.
Characterizations of pulp
The material without pulping process and the pulp sample were analyzed for yield (gravimetrically) of hollocellulose, a-cellulose lignin. The polymerization grade were determinate too in the fiber, pulp material and bleaching material (Ass et al, 2006).
3. Results and Discussion
During the process of purification of cellulose, the first step consisted in reducing the size of the material in a grinder of knives. This procedure was performed in order to reduce the particle size which helps in the attack of lignin by the pulping reagent (calcium oxide).
After was initiated pulping and the calcium oxide concentration was varied to determinate the best concentration of pulping. Table 1 shows a summary of the pulping experiments and condition to obtain low residual lignin (A), hollocellulose (B) and a-cellulose (C) in the calcium oxide pulping process of Capim napier". Each result is expressed as arithmetic mean of two replications and the purification was determinate gravimetric analysis.
Figure 1 show the experimental values versus the predicted values using the model equation developed. Effects with a statistical significance lower than 95% were not reported, according to the F-test utilized. Equation 1A, 1B and 1C were used in order to predict yield of the transesterification, as a function of time and calcium hydroxide concentration.
As expected, high temperature cause yield loss and improve lignin removal. Generally, increasing temperature can favor depolymerization of lignin macromolecule, but.
During this procedure it was observed the increased of cellulose content of which has a high hemicellulose degradation due to the smaller extent of the glycosidic chain.
A = 51.677-1.538*[CaO]+14.144*T+0.229*[CaO]*[CaO]-0.252*[CaO]*T-1.86*T*T
B = 81.448+0.370*[CaO]+4.031*T+0.021*[CaO]*[CaO]-0.117*[CaO]*T-0.322*T*T
C = 7.965+9.059*[CaO]+27.719*T-0.486*[CaO]*[CaO]-1.203*[CaO]*T-3.978*T*T
After, this stage began the optimization process of step bleaching of pulp. During this step initially studied the best pH for the realization of bleaching using peroxide. It is clear that the other parameters were kept constant as shown in Table 2. It is also important to note that the pH was 12 and the pulp consistency was 15.