Soda pulping with additives Diego Almeida: PostDoctoral, UFV, Brazil, [email protected] José L. Gomide: Full Professor, UFV, Brazil, [email protected] Abstract The Kraft pulping process is the world's major chemistry pulping method, because the pulp produced is stronger than other process. Although the air pollution of odorous compounds and the complex black liquor recovery can be a problem for some companies. The Soda pulping can be an alternative process with no sulfur compounds and better strength qualities if added additives. At this paper was proposed to optimize the soda process, using the continuous method Lo-Solids pulping with additives. An understanding of additives action was target, by composition analysis of these pulps. The additives were effective, both individually and combined were able to improve the soda pulping qualities, such as yield and viscosity. The soda pulping can be improved using higher alkali charge. Residual alkali from 8 to 10 g/l increases the pulp viscosity compared with lower charges, as increases the xylan degradation without decreases the yield. The additives were more effective for soda pulping, increasing more yield compared with same additive charge for Kraft process. The lignosulfonate showed the same performance those surfactants, for both processes. More tests are needed to confirm the lignosulfonate as a substitute for surfactant. But it is not indicated for the soda pulping process, if sulfur compounds were avoided. Keywords: Anthraquinone, Soda, Surfactant, Lignosulphonate Introduction Kraft cooking process is the most currently used for pulp, by advantages such as high pulp strength, but with disadvantage of odoriferous pollution through of sulfur compounds generation [1]. Brazilian Kraft pulp mills, especially those near urban centers have suffered environmental agencies pressures on the impact caused by reduced sulfur gases (TRS) emission. Some advantages can be achieved changing sulfide compounds by anthraquinone (AQ), as no odor pollution and no additional corrosion problems conventional pulping facilities [2]. The soda process is an alternative method for producing sulfur-free pulp. By using a high alkali charge associated with high temperature, the soda pulp viscosity is damaged, thereby the quality and paper strength as well. The pulping additives can be used as an option for improving these parameters [3]. Anthraquinone (AQ) is considered an additive really effective for both industrial and commercial for alkaline pulping and work as a redox catalyst, transferring electrons from wood carbohydrates to intermediate structures in lignin degradation, which results in higher yields and lower kappa number [4 and 5]. These process modifications change the chemistry of the pulping process in order to improve the selectivity with respect to lignin removal without significant carbohydrates degradation [6]. ________________________________________________________________________________ 7th International Colloquium on Eucalyptus Pulp, May 26-29, 2015. Vitória, Espirito Santo, Brazil. AQ has been used by pulp industry, focusing an increase yield, lower production of solids in the black liquor and reduction of kappa number. These applications generally aim to eliminate bottlenecks, with the major areas involved recovery boilers, caustification, the digesters and bleaching plant [2]. Surfactants are another additive used in the pulping process. This is the term used for products with ability to change the liquid surface tension, changing the surface properties. Thus, surfactants have the ability to increase the chips impregnation, pitch control and improving the washing of unbleached pulp [7]. Surfactants have polar and nonpolar groups in the same molecule, which confers ability to interact with different wood chemicals groups. Thus surfactants can be called dispersant, wetting, emollient, lubricant, detergent and others. Lignosulfonates has a very efficient dispersing property for various segments. In general, lignosulfonates are soluble in water and have dispersant activity while have agglutinate activity if dry, increasing mechanical strength. Pulping additives market has evolved, with high investment in research and production of new formulations for anthraquinone and surfactants blends. These improved products can contribute to soda pulp production with better quality. This paper objective was increase pulp qualities for continuous soda process (Lo-Solids) using pulping additives. Experimental Lo-Solids pulping It was used Eucalyptus wood chips originated from Brazilian pulp mill Cenibra. The chips were classified and selected according to SCAN-CM 40:94 standard. Lo-Solids technology was used to perform the cooks, which consists of split the alkali charge in order to keep low the dissolved solids at black liquor. This process was chosen because it is a modern pulping method and the most used for new pulp plants. Kappa number was set at 18, which is a commonly degree of delignification used for Eucalyptus. The cooks were performed in M&K digesters, with 7-liter capacity, circulation and heat exchanger. This digester is connected to a set of heated and pressurized accumulator vessel, allowing installment white liquor injections. Time and temperature are controlled electronically, where it was possible, via computer set the temperature profile and the factor H cooks. Chips were steamed for 20 minutes before cook and then were added the cooking liquor (50% of total alkali charge). The impregnation step was carried out at 115°C for 30 minutes. Were subsequently injected over 30% of the alkali charge to the first cooking phase and the remaining 20% to the second cooking step. Both phases with 50 minutes each, but the final temperature varied between Kraft and soda pulping. Pulp was water washed until neutral pH and was screened in a laboratory Voith plate with 0.2 mm slots. ________________________________________________________________________________ 7th International Colloquium on Eucalyptus Pulp, May 26-29, 2015. Vitória, Espirito Santo, Brazil. White liquor and additives For the Kraft pulp control was used white liquor prepared at laboratory mixing sodium sulfide with sodium hydroxide for an effective alkali near 100 g / L and 30% sulfidity without additives. For the soda pulp control was prepared a sodium hydroxide solution with 120 g/l. It were used 3 kind of additives given by Ashland to improve quality of soda pulp: pure anthraquinone (AQ), a blend of cationic and anionic surfactants (Surfac.), a blend of anthraquinone and surfactant (AQS) and a lignosulfonate given by Borregaard Lignotech. All additives were used based on wood and LoSolids cooks were performed in duplicate with 500 grams oven dry of chips. Pulp analysis After pulping, it was determined kappa number, screened yield (%), reject content (%), pulp viscosity (cm3/g) and for the black liquor was determined residual effective alkali (g L). The screened yield and reject content was determined gravimetrically, kappa number by TAPPI T236 cm-85 and for viscosity was used TAPPI T230 om-94. The residual black liquors were characterized by SCAN N-33: 94 [8]. It were also done the total lignin and carbohydrate analysis of pulp and wood samples used at this work. The Klason Lignin was determined by acid hydrolysis [7]. A 0.1 g sample was hydrolyzed with 72% sulfuric acid at room temperature. The hydrolyzate was then diluted with deionized water and placed in an autoclave at 120°C. The resulting sample was filtered, the acid insoluble lignin (Klason lignin) was determined gravimetrically and the acid soluble lignin was determined spectrophotometrically [8]. A sample of the filtrate was used for sugar determination [8]. Fucose was added as internal standard. Results and discussion Soda and Kraft pulp control Soda and kraft pulping control were made to compare the results of pulps with additives. For Kraft control was used alkaline charge of 20% and final temperature of 160°C. Two different conditions were tested to achieve the desired degree of delignification for soda control. In the first attempt (Soda control 1) was kept the same temperature for Kraft control, changing the alkaline charge, but was necessary a very high alkali charge, 56%. The second attempt (Soda control 2) was performed by increasing the temperature to 172°C which increased H-factor from 649 to 2070. The effective alkali charge was reduced to 25%. These results are shown in Table 1. ________________________________________________________________________________ 7th International Colloquium on Eucalyptus Pulp, May 26-29, 2015. Vitória, Espirito Santo, Brazil. Table 1: Control results. Brightn Yield, % Resid H- Visc, Sample Rep. EA,% Kappa ess, ual, Factor Screened Reject Total cm3/g %ISO g/L 1 635 20,0 18,1 - 53,5 0,1 53,6 1230 9,4 Kraft 2 634 20,0 17,7 - 53,2 0,1 53,3 1233 8,6 control Avg 635 20,0 17,9 35,5 53,4 0,1 53,5 1231 9,0 1 665 56,0 17,9 - 47,7 0,0 47,7 1062 42,4 Soda 2 633 56,0 18,1 - 47,2 0,0 47,2 1072 42,4 control 1 Avg 649 56,0 18,0 35,5 47,5 0,0 47,5 1067 42,4 1 2072 25,0 18,3 - 49,7 0,1 49,8 871 11,8 Soda 2 2068 25,0 17,9 - 49,2 0,1 49,3 853 13,3 control 2 Avg 2070 25,0 18,1 33,4 49,5 0,1 49,6 862 12,6 The Kraft control yield and viscosity were the highest, with an average of 53.4% and 1231 cm³/g, respectively. The excessive alkali charge of Soda control 1 dropped the yield to 47.5%. Soda control 2 yield was 2% more than Soda control 1, but viscosity was 205 cm3/g lower. The lignin and carbohydrate analysis results are shown in Table