ECF Bleaching Sequences Research Articles

OPTIMIZATION OF A PHOTOCATALYTIC PROCESS FOR REMOVAL OF PHENOLIC COMPOUNDS FROM WASTEWATER GENERATED IN THE PRODUCTION OF CELLULOSE FROM PINUS RADIATA AND EUCALYPTUS GRANDIS WOOD

This study aimed to improve the sustainability of the kraft pulp production process by recovering Pinus radiata and Eucalyptus grandis wastewater generated during the bleaching process. The effluents were obtained from the first alkaline extraction stage (E0) of the ECF bleaching sequence used to produce white Kraft cellulose, considering that this stage is where the highest contamination by phenolic compounds occurs and the effluent exhibits an intense color. A photochemical oxidation system, utilizing TiO2/S2O82-/UV, was implemented to generate in situ two highly oxidizing radical species, with high redox potential, a hydroxyl radical (HO• 2.8 eV ) and a sulfate radical (SO4•- 2.5-3.1 eV), which promote rapid degradation of contaminants. To obtain the optimal response, we employed the 2n model to construct a matrix of 15 experiments, utilizing the Box-Behnken design. According to the experimental variables studied, phenolic compounds were completely removed from the Eucalyptus effluent (0.0312 min-1) and 80% of them were removed from the pine effluent (0.0102 min-1), at pH 5.0 with 0.6 gL-1 of persulfate and 1.0 gL-1 of titanium dioxide. Under these conditions, the bioavailability of effluents from Pinus radiata and Eucalyptus grandis increases from 0.16 and 0.26 to 0.90, after the treatment. The excellent bioavailability of the effluents obtained after the treatment demonstrates that the process used is efficient in recovering wastewater from the pulp industry and that the treated water could be reused in the same process or returned to the ecosystem, without harming the environment.

Production of high-quality dissolving pulp from eucalyptus wood chips using deep eutectic solvent and elemental chlorine-free bleaching

Deep eutectic solvent (DES) provides promising alternatives to conventional pulping and cellulose purification with significantly lower energy consumption and impacts on the environment. In this work, choline chloride – lactic acid (ChCl-LA DES) pulping of eucalyptus wood chips combined with several ECF bleaching sequences was investigated to produce high-grade dissolving pulps. Initially, the dependency of DES pulping yield and delignification efficiency on the moisture content (MC) of used wood chips was evaluated. The results exhibited the crucial influence of the MC of wood chips on the delignification efficiency of DES pulping. DES pulping under optimized conditions resulted in an unbleached pulp with kappa number of 42, relatively high screened yield 48.1% and viscosity 796 cm3/g, as well as very low hemicellulose content, typically less than 3.8%. Further purification of the obtained pulp using D-Ep-D and OO-D-Ep-D bleaching sequences produces several dissolving pulps characterized by a high viscosity 695 cm3/g and brightness 89.5% ISO, indicating low degradation of cellulose during DES pulping. DES pulping exhibited considerable potential to remove the hemicelluloses from wood chips and produce high-quality dissolving pulps. This could be attained through shorter pulping operations conducted at a lower temperature and a higher screened yield compared to current dissolving pulp production operations.

Assessment of Aox Content in Bleaching Effluent of Eucalyptus Tereticornis Kraft Pulps

The research aim is to reduce the organochlorine content in bleach plant effluents by modifying conventional (CEHH) bleaching sequences. Majority of pulp and paper mills generally adopted CEHH or CEH bleaching sequences, using chlorine or chlorinated compounds to remove the color from pulps. Organochlorine compounds are mainly generated from chlorination and alkali extraction stages. The purpose of the study is to substitute elemental chlorine in bleaching with oxygen, chlorine dioxide, or peroxide. Investigations of AOX content of various traditional and innovative ECF bleaching sequences were conducted. In this study, kraft pulps of Eucalyptus tereticornis with kappa numbers of 44.91 and 26.46 and its oxygen-delignified pulps of kappa numbers 21.32 and 13.03 were used. In terms of AOX, various ECF bleaching sequences were compared to the reference sequence (CEHH). AOX value was 4.45, 3.42, 2.27 kg/tp for the pulp bleached adopting OCEH, ODEH, ODEP bleaching sequence and 9.24 kg/tp for the pulp bleached adopting CEHH bleaching sequence for the pulp corresponding to Kappa number 44.91. Similarly, the AOX value was 2.60 , 1.78 1.24 Kg/tp for the pulps bleached adopting the OCEH, ODEH, ODEP bleaching sequence and 5.56 Kg/tp for the pulp bleached adopting the CEHH sequence for the pulp corresponding kappa number 26.46. Due to partial-delignification of oxygen, AOX production was reduced up to 50%.

Sustainable bleaching of Eucalyptus sp. kraft pulp with hypochlorous acid, ozone and hydrogen peroxide

Eucalyptus sp. is the most important planted crop for the production of chemical pulp. This pulp is mostly bleached with chlorine dioxide, which produces hypochlorous acid in situ when reacting with lignin. However, applying hypochlorus acid directly is not practiced, even though it contributes significantly to the bleaching reactions. Therefore, this article presents hypochlorous acid as the main bleaching chemical for oxygen delignified Eucalyptus sp. kraft pulp. The results showed that hypochlorous acid solely decreased the kappa number of the pulp more efficiently than chlorine dioxide did, without increasing the content of adsorbable organic halogens (AOX) in the effluent. The bleaching sequence with hypochlorous acid, ozone and hydrogen peroxide produced fully bleached pulps, with low organically bound halogens (OX) and aerobically digestible effluents. The bleached pulps and digested effluents complied with international standards for the pulp industry. The hypochlorous acid bleaching sequence is appealing because it is short, uses mild conditions and requires less or similar energy to produce the bleaching chemicals than comparable ECF bleaching sequences from literature.

Properties of bleached pulp sheets of avocado wood (Persea americana Mill.) pulped by Kraft and Soda processes

Chips of avocado wood (Persea americana Mill.) were pulped by means of conventional Soda and Kraft pulping processes. The pulps were bleached with an elemental-chlorine-free sequence OD1-Eop-D2, pre-setting reaction conditions for the first chlorine dioxide stage (D1) . The results show that during the chemical pulping process, avocado wood is easier to cook than other hardwoods such as eucalyptus. The avocado pulp also showed a very good bleachability, reaching brightness levels of up to 92% ISO compared to 84% for eucalyptus after the ECF bleaching sequence. The avocado Kraft pulps required more chemical input in the bleaching sequence than the Soda pulps. On the other hand, the physico-mechanical properties of the pulp were not notably reduced by the bleaching process, the Kraft pulp being stronger than the soda pulp. Strength properties of avocado are similar to those of eucalyptus; therefore this raw material constitutes a worthwhile choice for cellulosic fiber supply.

Ethylenediamine in alkaline cooking of jute stick for producing dissolving pulp

Jute stick is the woody portion of jute plant. It remains as the leftover after extracting the fibre. The ratio of the stick to fibre is about 2.5:1. For producing dissolving pulp, prehydrolysis is carried out prior to pulping to remove hemicelluloses from the lignocelluloses. In this investigation ethylenediamine (EDA) was used with the cooking liquor to remove hemicelluloses from the jute stick. Increasing EDA charge in soda and kraft liquor decreased pentosans content in the pulp. EDA in kraft liquor showed lower kappa number and pentosans content than in the soda-liquor. Prehydrolysis further improved cellulose content and kappa number of jute stick pulp with the sacrifice of pulp yield. The bleachability of soda-EDA pulp was inferoior to the kraft-EDA and prehydrolysed soda-EDA in ECF bleaching sequences. The final brightness of soda-EDA pulp was 85.1% and kraft-EDA pulp 89.7%. Degraded cellulose (R18-R10) in soda-EDA and kraft-EDA pulps was lower than prehydrolysed pulps. Dissolving pulp can be produced to 93% purity without prehydrolysis by reinforcing EDA in kraft liquor.Bangladesh J. Sci. Ind. Res. 50(1), 7-14, 2015

Enhancement of TCF and ECF Bleaching Processes by Urea and Enzymatic Pretreatments: Optimization of a Laccase-Mediator Pretreatment

A TCF bleaching sequence consisting of a urea pretreatment stage (U), laccase-mediator system stage (L), alkaline extraction stage (E), and hydrogen peroxide bleaching stage (P) was used to study the effect of five independent variables on the dependent variables pulp properties, hydrogen peroxide consumption, and residual enzyme activity. Results showed that the most influential variable was L stage pulp consistency, followed by mediator and laccase dosages. On the other hand, oxygen pressure did not have a significant effect. The optimal UL partial sequence significantly enhanced the EP bleaching sequence: 49.8% vs. 33.4% delignification, up to 65.6% ISO vs. 56.3% ISO bleached brightness, and 50.3% vs. 89.9% peroxide consumption in the P stage. The ULE partial sequence also improved an ECF bleaching sequence (ULED0E1D1): 0.6 vs. 1.0 final kappa number; 82.7% ISO vs. 76.0% ISO brightness; and 54.1 N∙m∙g-1 vs. 51.9 N∙m∙g-1 and 3.3 KPa∙m2∙g-1 vs. 2.7 KPa∙m2∙g-1, tensile and burst indexes, respectively, when compared to the control D0E1D1 sequence.

Comparison of MEA/AQ, soda and soda/AQ pulping of wheat and rye straw

MEA (monoethanolamine)/AQ pulping of wheat and rye straw and bleaching of the produced pulps were investigated. The delignification behaviour of wheat and rye straw using varying MEA/water and liquor/straw ratios was studied. Furthermore, the impacts of mono-, di-, tri-ethanolamine/water mixtures and addition of KOH to the cooking liquor were monitored. The best results were achieved with a MEA/water ratio of 50/50 at a liquor/straw ratio between 3:1 and 4:1. The use of the mixture of mono-, di-, tri-ethanolamine instead of MEA only was not effective for straw pulping. The effect of adding KOH to the MEA pulping liquor was negligible. The results of MEA pulping of both straw species were compared with results for production and bleaching of soda and soda/AQ reference pulps. At similar degree of delignification, the MEA pulps showed 10% higher yield (based on straw), which demonstrates the unusually high selectivity of MEA in straw pulping. The MEA straw pulps showed fairly low brightness and were more difficult to bleach than the corresponding soda pulps. Nevertheless, it is possible to bleach MEA pulps to more than 80% ISO brightness, applying an ECF bleaching sequences (O-Q-OP-DQ-P). With regard to bleachability, yield and strength properties the rye straw pulp sample performed much better than wheat straw pulp sample.

Kraft ECF pulp bleaching: A review of the development and use of techno-economic models to optimize cost, performance, and justify capital expenditures

This work evaluates the findings of various research efforts and describes the development, use, and benefits of applying techno-economic models of different types to various production and bleach plant scenarios. During the late 1980s and early 1990s, researchers determined that bleach plants were releasing potentially significant quantities of chlorinated organics into receiving waters. This led to extensive research to develop bleaching chemicals to eliminate chlorine and hypochlorite from the bleaching sequence. Over time, 100% chlorine dioxide substitution for chlorine became the industry standard (today’s elemental chlorine free [ECF] bleaching), and research efforts shifted toward chemical optimization of the ECF bleaching sequence. Several delignification stage and brightening stage models were developed and refined for use in bleach plant simulations to optimize chemical performance. Advances in computing power and the availability of packaged spreadsheet and simulation programs likewise led to the development of detailed material and energy balance models of the bleach plants. These simulations are used to minimize bleaching and pulp production costs, and to assist engineers in the development of justifications for capital expenditures. These models have been used to predict operating conditions that could lead to or reduce scale formation. They have also been extensively used to predict environmental performance of both new and modified bleach plants.

Analysis of structural changes of Masson pine lignin reacted with superoxide anion radical using NMR spectroscopy

Oxygen delignification can be considered to be the most important part of TCF and ECF bleaching sequences because it allows for cleaner production of pulp. During the process, oxygen gets one electron from lignin in the alkaline condition to form some active oxygen species (AOS), including a superoxide anion radical (O2-•), which is crucial for lignin degradation without damage of carbohydrates. The reaction of O2-• on cellulolytic enzymatic lignin (CEL) from Masson pine was studied. The change in active hydroxyl content after reaction with O2-• was investigated using 31P-NMR. After reaction, the aliphatic hydroxyl and uncondensed type phenol hydroxyl contents decreased, but the content of carboxylic group increased in Masson pine lignin. Through the analysis with HSQC-2D13C-H technology, β-O-4 linkages could be cleaved by O2-•, but β-β and β-5 linkages were observed to be more stable; benzaldehyde and cinnamic aldehyde structures could be oxidized to carboxylic acids by O2-•. Guaiacyl units in lignin were more easily degraded than p-hydroxybenzene units.

Effect of last stage bleaching with peracetic acid on brightness development and properties of eucalyptus pulp

Investigation of last stage bleaching with peracetic acid is the main subject of this paper. Proper conditions were established to apply peracetic acid as the last bleaching stage of the D(Ep)D/Paa, DHT(Ep)D/Paa, A/D(Ep)D/Paa, DHT/Q(PO)Paa and Z/ED/Paa sequences. In addition, the impact of last stage bleaching with Paa on pulp refinability and strength properties was determined. Peracetic acid was consumed relatively fast when applied as the last stage of ECF bleaching sequences. A reaction time of 120 min at 75 oC and pH 5.0 is seemingly adequate regardless of the Paa dose, in the range of 1-5 kg/odt pulp and bleaching sequence. The optimum dose of Paa depends upon the sequence under investigation. In general the Paa application as last bleaching stage caused slight decrease in pulp viscosity, kappa number and HexA content but had no significant effect on pulp reversion and L*a*b* coordinates. The refinability and bonding strength properties of the pulps bleached with the sequences DHT(Ep)DD and DHT(Ep)D/Paa were quite similar when the pH of the last bleaching stage of both sequences were near 5. These properties improved slightly when Paa bleaching pH was raised to 8.5.

Studies on the effect of prehydrolysis and amine in cooking liquor on producing dissolving pulp from jute (Corchorus capsularis)

Dissolving pulps are the raw materials for the production of many different end-products. Jute is a very good source of cellulose. In this investigation, jute fiber was subjected to pulping in soda process in order to produce dissolving pulp under different prehydrolysis conditions and compared with prehydrolysed kraft pulp from jute. An increase of the prehydrolysis temperature or H2SO4 in prehydrolysis liquor increased the α-cellulose content and decreased the viscosity of pulp. The effect of ethylenediamine in soda liquor was also investigated when producing dissolving pulp. Jute fiber produced pulp having 90–97% α-cellulose. Ethylenediamine in soda liquor produced pulp of higher yield, viscosity and higher α-cellulose content than that of prehydrolysis soda or kraft pulp. The α-cellulose content and viscosity were increased with the increase of amine in soda liquor. The kappa number of dissolving pulp from jute was very low (9–5), which indicated that less bleaching chemicals are required for bleaching. The bleachability of soda-ethylenediamine pulp was lower than prehydrolysed soda and kraft pulp in ECF bleaching sequences. The bleachability of soda-ethylenediamine pulp was improved at the sacrifice of pulp yield when prehydrolysis was done prior to pulping. The alkali solubility S10 and S18 were 4–9 and 2–4%, respectively.

Separate Bleaching of Pulp Fractions Enriched in Earlywood and Latewood Fibers

Unbleached softwood kraft pulp was fractionated in hydrocyclones into a fine fraction, enriched in earlywood fibers, and a coarse fraction, enriched in latewood fibers. The response to individual bleaching chemicals and the bleachability in bleaching sequences of the pulp fractions was studied. The light absorption coefficient, light scattering coeffient, and brightness were higher in the unbleached fine fraction than in the coarse fraction. Hydrogen peroxide managed to reduce the light absorption coefficient of the earlywood enriched fine fraction more efficiently than that of the latewood enriched fraction. In the TCF‐sequence the light absorption coefficient of the fine fraction was reduced to the level of the coarse fraction at a given consumption of bleaching chemicals. In the ECF‐sequence the difference in light absorption coefficient remained between the fractions. At a given consumption of bleaching chemicals, the fine fraction had higher brightness than the coarse fraction, 2%‐ and 1%‐units on the ISO‐scale in the TCF and ECF bleaching sequence, respectively.

Effluent Loads From Different ECF Bleaching Sequences Used In Hardwood Kraft Pulp Bleaching

Effluent loads from different traditional and emerging ECF bleaching sequences were investigated. Oxygen delignified Eucalyptus camaldulensis and Acacia mangium kraft pulps having similar kappa number, ca 12.0 were used in this study. Different ECF bleaching sequences were compared with reference sequence, D 0 EopD 1 in terms of effluent load, such as AOX, COD and TOC. Depending on the nature of sequences 6.0 to 63.0% chlorine dioxide consumption was reduced and as a result the amount of AOX formation was also reduced. The effluent from sequences (DZ)EopD 1, DHTEopD1, AhotD0EopD1, Ahot(DZ)EopD1 and ZEopD1 showed marginally higher COD and TOC in comparison with reference sequence, D 0 EopD 1 . Sequences like, D 0 EopQ(PO) and (DZ)EopQ(PO) having (PO) instead D 1 of reference sequence reduced AOX in effluent substantially; but COD and TOC loads were increased. In all cases acacia gave marginally higher effluent loads compared to eucalyptus.

Lipophilic Extractives in Eucalyptus globulus Kraft Pulps. Behavior during ECF Bleaching

The composition of E. globulus kraft pulp lipophilic extractives and their behaviour during an ECF (DEDED) bleaching sequence were investigated. Sterols; fatty acids, including several α‐ and ω‐hydroxyfatty acids; and long‐chain aliphatic alcohols are the major lipophilic extractives of the unbleached pulp. During the bleaching, about 80% of the aliphatic extractives are removed from pulp (ca. 70% of the sterols, 70% of the fatty acids, and 90% of the long‐chain aliphatic alcohols). The decrease of sterols is mainly due to the degradation of β‐sitosterol by chlorine dioxide, while the decrease of fatty acids and alcohols is essentially assigned to their extraction and elimination with the alkaline filtrates. The major chemical transformations in pulp extractives composition and structure occur in the last bleaching stages. Thanks are due to FCT and ESF for the awarding of a PhD grant to C. S. R. Freire, within the European Community Support Framework III, to the Forest and Paper Research Institute RAIZ, for supplying the industrial E. globulus kraft pulp and for the facilities conceded for the kraft pulping trials. Finally, thanks are due to Dr. Les West from Kraft Foods, USA for his kind offer of a sample of 2‐hydroxyoctadecanoic acid.

The Chromophores Remaining After Bleaching to Moderate Brightness

A pine kraft pulp was bleached to 84% ISO brightness with an ECF DoEpD1 and a TCF OQ(PO)ZQ(PO) sequence. Both bleached pulps were subjected to ClO2, H2O2, and NaBH4. EPR analyses confirmed that the ECF pulp contained more quinone groups than the TCF pulp which contained more quinone–phenol groups. The colored compounds present at the end of the ECF bleaching sequence were less conjugated than the colored compounds present at the end of the TCF sequence. UV resonance Raman analyses performed on these pulps highlighted the differences between ECF and TCF bleached pulps, the latter containing more aromatics relative to C˭O groups. The bleachability of pulps impregnated with p‐benzoquinone, a quinone model, and alizarin, a quinone–phenol model, were compared with the ECF and TCF pulps. The quinone impregnated pulp behaved like the ECF pulp, whereas the quinone–phenol impregnated pulp behaved like the TCF pulp.

Operating Experience of Improved ECF Bleaching Sequence

ECF bleaching has superseded the conventional chlorine bleaching on NO.3 LBKP-production line in Hachinohe mill of Mitsubishi Paper Mills limited in 2000. The operational data of ECF bleaching for two years made it obvious that the brightness of oxygen-bleached pulp had larger influence on the bleaching efficiency of ECF bleaching than kappa number in contrast with the case of conventional chlorine bleaching. Furthermore, it was shown that the improved ECF bleaching sequence had enabled to reduce the chemical consumption and the scale trouble which were main problems in ECF bleaching.

ＥＣＦ漂白への転換 第１漂白ステージに焦点を当てた比較研究

In the present paper, an investigation of some different ECF bleaching sequence is presented, and the results compared. Special attention is paid to the importance of the first bleaching stage after oxygen delignification, i. e. the so-called delignifying bleaching stage. Two different mill-oxygen-delignified HW kraft pulps were subjected to a number of different bleaching sequences. The first pulp was bleached according to D (EO) D, D * (EO) D, (ZD) (EO) D, Z (EO) D and after interpolation evaluated at 89% ISO brightness, and the second pulp according to D (EP) D, D * (EP) D, (ZD) (EP) D, A * ZD (EP) D and after interpolation evaluated at 87% ISO brightness. The “*” here denotes a treatment at high temperature and log retention time. Both the use of D * and Z efficiently reduced the yellowing tendency of the pulps when compared to the conventional D-based ECF sequences. Based on the laboratory trials, consumption figures were adjusted to reflect mill operating conditions and the differences in operational costs between the different sequences were calculated. The sequences with D * were economically very attractive, showing high savings in operational costs compared to the reference D (EO) D and D (EP) D sequences, especially when the target brightness was somewhat higher, i. e. 89%. Considering the unit costs, the required investments needed for Z-based sequences were found to be difficult to justify, especially when the target brightness is somewhat lower, e. g. 87% ISO.

On-Site Production of Xylanase and its Application on Hard Wood Kraft Pulp Bleaching

Xylanase treatment with on-site enzyme production was introduced into the hardwood kraft pulp bleaching process (C-E/O-dnD) at Yonago mill in October, 1998.A thermostable xylanase from a microorganism, Bacillus sp.S-2113, that we isolated through screening was selected for use in this process.The xylanase-containing culture was applied to the bleaching process without removing the bacterial cells from the culture medium.Two years have passed since the xylanase treatment operation, with onsite enzyme production, was begun, and so far, this operation has been working well.The ECF bleaching sequence will start operation within the year 2000in Yonago mill.The effects of enzyme bleaching in the ECF bleaching process are expected to be even greater then.

Brightness and kappa number – important variables to secure appropriate control of chemical charges in TCF- and ECF-bleaching sequences

Article Brightness and kappa number – important variables to secure appropriate control of chemical charges in TCF- and ECF-bleaching sequences was published on August 1, 2000 in the journal Nordic Pulp & Paper Research Journal (volume 15, issue 3).