Emrah Pesman1), Evren E. Kalyoncu2), Sodium Perborate Usage instead of Hüseyin Kirci2) Hydrogen Peroxide for the Reinforcement of Oxygen Delignification 1) Artvin Çoruh University, Faculty of Forestry, Abstract The Department of Forest Industrial Engineering Oxygen has always been an attractive oxidant for the pulp and paper industry due to it being cheap and harmless for the environment. However, it has lower lignin-cellulose se- 2) Karadeniz Technical University, lectivity, therefore the degree of delignification achieved at the oxygen stage is ultimately Faculty of Forestry, limited by its industrial pulp strength – 45-50% . In this study, to enhance the degree of The Department of Pulp and Paper Tech. 61080, delignification, the addition ofsodium perborate and hydrogen peroxide at the oxygen stage Trabzon, Turkey was examined. At the same active oxygen (approximately 0.5%) content, the degree of del- E-mails: [email protected]; ignification increased from 45.56% to 49.42% using hydrogen peroxide and to 52.96% [email protected]; [email protected] with sodium perborate. For the same selectivity parameter with control, the delignification degree can be increased to 57.59% with the addition of sodium perborate, which includes * Author to whom correspondence should be addressed; 1% active oxygen. Moreover, the costs of using sodium perborate and hydrogen peroxide E-mail: [email protected] were compared with respect to commercial employability. It was determined that the use of sodium perborate was more effective than that of hydrogen peroxide for delignification of the oxygen stage. Key words: oxygen delignification, sodium perborate, selectivity, active oxygen, hydrogen peroxide. Introduction tion leads to weaker pulp fibers and limits perborate monohydrate (NaBO3.H2O) single stage delignification to ~50% [3]. contains 16% active oxygen, and it does During the kraft pulping process, exten- Several researches, such as the pretreat- not have a specific melting point. When sive lignin fragmentation and degradation ment of pulp prior to oxygen delignifica- heated, it decomposes by releasing oxy- occurs, leading to the generation of new tion and the reinforcement of oxygen del- gen and water. Sodium perborate mono- free phenolic hydroxyl groups. Under ignification with a reactant, have been un- hydrate is preferred to tetrahydrate due the alkaline conditions employed, these dertaken to try and overcome this handi- to its higher oxygen content and faster hydrophilic groups are ionised, resulting cap. The first study about combining the dissolution rate. In addition, monohy- in approximately 90% of the lignin being effects of hydrogen peroxide and oxygen drate is more stable than tetrahydrate in dissolved in the cooking liquor [1]. By for the bleaching of chemical pulp was storage [7]. the end of the cooking, the majority of undertaken in 1980’s, and a synergy was β-aryl ether structures have been cleaved, determined between oxygen and perox- Meshcherova and coworkers conducted and consequently the ability to generate ide [4,5]. Parthasarathy and coworkers laboratory studies on the use of sodium new phenolic sites decreases, making the showed that peroxide with oxygen had and potassium perborates for bleaching residual lignin more resistant to dissolu- additional effects on the delignification softwood kraft pulps. They compared the tion. The remaining lignin is more re- of pine kraft pulps, resulting in improved physico-chemical and mechanical prop- sistant to hydrolytic degradation, requir- selectivity and delignification efficiency. erties of the bleached pulps and conclud- ing oxidative degradation over several The addition of 0.5% hydrogen peroxide ed that it is more advantageous to bleach stages to be removed [2]. Traditionally, at the oxygen delignification stage caused kraft pulp with potassium perborate than chlorine and/or chlorine dioxide can be a 60% reduction in the kappa number as hydrogen peroxide [8]. Varennes and utilised, but environmental regulations compared to a conventional oxygen del- coworkers used sodium perborate tet- are increasingly mandating the replace- ignification stage [6]. Parthasaraty and rahydrate for bleaching thermomechani- ment of such chemicals. The major alter- coworkers also examined the peroxide cal pulp, reaching a brightness as high as natives currently employed are oxygen- reinforcement of the double-stage oxy- 75% ISO with the addition of 6.5% sodi- based chemicals such as molecular oxy- gen delignification process. Using the um perborate tetrahydrate [9]. Moreover, gen and hydrogen peroxide [2]. (PO)(PO) process, the kraft pulps delig- by using sodium perborate monohydrate nified showed a kappa number of about for the bleaching of SGW (Stone Ground At present, oxygen delignification is 73% of the original, as compared to 61% Wood) pulp, the brightness of the pulp widely used for lignin removal in pulp- for the double oxygen stage with an ad- increased from 49.64% to 64.74% ISO ing and bleaching. The chemical cost dition of 0.5% hydrogen peroxide to the with a 1% active oxygen dosage [10]. savings realised by displacing chlorine or oxygen delignification media [6] . Based the information above, we used chlorine dioxide with oxygen and caus- sodium perborate for the reinforcement tic, as well as the ability to recycle the fil- Besides hydrogen peroxide, similar of oxygen delignification. trate in the recovery furnace are the main oxidising agents such as sodium per- advantages of oxygen delignification. borate can be utilised for the reinforce- In this study, the effects of sodium perbo- However, the capital costs and lower ment of oxygen delignification. Sodium rate monohydrate reinforcement on oxy- lignin-cellulose selectivity compared to perborate monohydrate is used in the gen delignification was investigated as chlorine dioxide bleaching are handicaps formulation of concentrated detergents an alternative to hydrogen peroxide for of the oxygen delignification stages. The as well as in certain medical, disinfect- enhancing the delignification capacity of lower selectivity of oxygen delignifica- ant, and cleaning preparations. Sodium the oxygen stage. 106 Pesman E., Kalyoncu E. E., Kirci H.; Sodium Perborate Usage instead of Hydrogen Peroxide for the Reinforcement of Oxygen Delignification. FIBRES & TEXTILES in Eastern Europe 2010, Vol. 18, No. 6 (83) pp. 106-109. Methodology Results and discussion cate test result with peroxide and sodium perborate added. For comparison, the Eastern Spruce (Picea orientalis L.) kraft Determination of the optimum alka- charges of the reagents were calculated pulps were used for experiments, which line charge for the oxygen delignifica- as active oxygen on oven dry pulp. had the following properties: tion stage n Kappa Number – 33.2 Eastern Spruce (Picea orientalis L.) kraft However, both reagents increased the del- pulp was exposed to oxygen delignifica- ignification, and sodium perborate caused n 3 Pulp viscosity – 917 cm /g tion with a varying alkaline content, from significant delignification augmentation. n Screened pulp yield – 47.2% 1% to 5%. Other process parameters With an addition of (as active oxygen to were similar to those in conventional o.d. pulp) peroxide of 0.5%, the delig- Oxygen delignification was carried out mill scale application (Pulp consistency – nification degree rose from 45.56% to in a 15 L stainless steel reactor heated 12%, reaction temparature – 90ºC, reac- 49.41% in comparison with the control. electrically, the temperature of which tion time – 60 minutes, oxygen pressure Furthermore, with a sodium perborate ad- was controlled by an OMRON 55 CK – 690 kpa, MgSO4 addition – 0.02%). dition of 0.5%, the delignification degree digital process controller to within Pulp properties subjected to oxygen del- rose to 52.96% (Figure 1 – see page 108). ±0.2°C. Loading of the reactor was done ignification are shown in Table 1. At an manually, and 100 g o.d. of the spruce alkaline charge of 2% and delignification Hydroperoxide anion (HOO-) is an active kraft pulp was used in each experiment. degree of 45.6%, the minumun relative species and is responsible for the bleach- The pulp was diluted to a consistency of degredation of the pulp was determined. ing action of hydrogen peroxide under 12% with 0.2% MgSO4 and 2% NaOH When other parameters were kept con- alkaline conditions. On the other hand, added to the pulp. For reinforcement of stant at a conventional mill-scale level, hydroperoxyl and hydroxyl radicals gen- the oxygen delignification, peroxide and the optimal alkaline charge for oxygen erated by the decomposition of hydrogen sodium perborate with a charge varying delignification was selected as being 2%. peroxide are responsible for delignifica- from 0.25% to 1.5% was used as active (Table 1) tion [6]. Hydroxyl radicals are capable of oxygen on oven dry pulp. The constant attacking practically all types of organic temperature was set at 90°C and the Effects of peroxide and sodium perbo- structures, including those containing hy- process time at 60 minutes. An oxygen rate on delignification, viscosity and droxyl and ether linkages [6]. Similar re- pressure of 690 kPa was used in each selectivity parameters actions occur with sodium perborate, but experiment. For comparison, the charg- In optimum oxygen delignification con- its alkalinity is higher than that of hydro- es of the reactives were selected accord- ditions, a number of experiments were gen peroxide; in this respect sodium per- ing to the active oxygen content. The