Elemental Chlorine Free Sequence Research Articles

Life Cycle Assessment of Brazilian Bleached Eucalyptus Kraft Pulp: Integrating Bleaching Processes and Biogenic Carbon Impacts

Bleached eucalyptus kraft (BEK) pulp dominates global pulp production, yet the environmental impacts of its bleaching sequences in Brazil are not fully explored. Addressing this gap, we conducted a comparative life cycle assessment (LCA) of three bleaching sequences: conventional elemental chlorine-free (ECF), ECF with oxygen delignification, and ECF with oxygen delignification plus acid washing. We estimated the average global warming potential (GWP) for BEK delivered to the U.S. and examined how forest carbon cycle (FCC) elements, specifically biogenic GWP (GWPbio) and potential soil organic carbon (SOC) sequestration, influence GWP outcomes. Results show that the ECF sequence with oxygen delignification and acid washing reduces GWP by 11% and outperforms conventional ECF in 10 out of 11 environmental impact categories. The average GWP for Brazilian BEK delivered to the U.S. is 576 kg CO₂-eq/ton. Sensitivity analyses demonstrate that adding GWPbio increases GWP by 18%, whereas accounting for potential SOC sequestration reduces it by 39%. These findings highlight the necessity of optimizing bleaching processes and developing a standardized BEK LCA model for comparing the environmental impact of different fibers. This work sets a precedent for integrating FCC elements into LCAs and underscores the potential of SOC sequestration in mitigating climate change impacts.

Extension of a steady-state chlorine dioxide brightening model for Z-ECF bleaching of softwood kraft pulps

Earlier studies developed a steady-state model to predict the brightness and/or bleach consumption during the chlorine dioxide brightening (D1) of softwood pulps produced by conventional elemental-chlorine-free (ECF) sequences. This model relates the chlorine dioxide consumed to the brightness gains predicated upon an asymptotic D1 brightness limit, an incoming D1 pulp brightness, and an equation parameter (β11). The current investigation examines the application of this model to ECF sequences that use ozone delignification (Z-ECF). Literature D1 data from various Z-ECF bleaching studies, which investigated OZ, OD0/Z, and OZ/D0 delignification, were fitted to the model. The β11 parameter was found to be linearly correlated to the entering kappa number. Interestingly, this linear relationship was found to be identical to the relationships observed when modeling the D1 stage for conventional ECF and chlorine-based bleach sequences. Subtle differences in D1 brightening response in the model among the various bleach sequences are reflected by incoming pulp brightness (at the same kappa number). The current model is used to illustrate how alterations to Z-ECF delignification affect D1 brightening and chlorine dioxide consumption.

The effect of introducing ozone in elemental chlorine free bleaching of eucalyptus kraft pulp

ZDED and DEDD sequences were applied on an oxygen-delignified eucalyptus (mixture of E. grandis and E. saligna) kraft pulp from Brazil. When ZDED and DEDD were compared, the displacement ratio calculated as the quantity of pure chlorine dioxide replaced by 1 kg ozone was found between 2.5 and 3.5 kg, as compared to 1.7 kg in theory—indicating that less wasting reactions occur in the ZDED sequence. The cellulose viscosity decreased substantially with the increase in the ozone charge (down to 50% at 0.8% ozone). Other typical characteristics of the ZDED pulps were easier beating, lower water retention value, higher proportion of kinked fibers, and lower wet zerospan breaking length (seen only at 0.8% ozone charge), as compared to DEDD. The viscosity loss due to the introduction of ozone in an elemental chlorine free sequence did not translate into a similar loss in strength. A comparison with the depolymerizing effect of cellulase suggests that the determining factor is not the extent of the drop in viscosity but rather the heterogeneity of the attack along the fibers. It is concluded that ozone oxidation of cellulose in the fibers would be rather homogeneous. Moreover, the appearance of more curls and kinks would not be necessarily related to the viscosity loss. For example, a (2,2,6,6-tetramethylpiperidin- 1-yl)oxidanyl (TEMPO) treated DEDD pulp, enriched in carboxyl groups, had more straight fibers than the original DEDD pulp, despite its lower viscosity. The presence of ionic groups would be a more important factor; the lower content in carboxyl groups in the ZDED pulps, compared to the DEDD pulps, could promote the easier formation of curl and kinks during the ZDED sequence.

Hemicellulose extraction and its effect on pulping and bleaching

A potential biorefinery is envisioned to use the hemicellulose portion of biomass to create transportation fuels or chemicals and the cellulose portion for fiber to be used in papermaking. To understand the effect on hemicellulose removal to pulpability and bleachability, a liquid hot water extraction was performed on two types of biomass with high hemicellulose content: poplar and miscanthus. The resulting materials were pulped using either a soda anthraquinone or kraft process. The pulps were then oxygen delignified and bleached with an elemental chlorine free sequence. The results demonstrate that a significant portion of hemicellulose can be extracted using liquid hot water extraction conditions of 170°C, 60 min, and a 6:1 ratio, with minimal glucan degradation. These low hemicellulose-content pulps delignified similarly to the control pulp, but had lower oxidative demand because of the absence of hemicellulose degradation products. Oxygen delignification of the low hemicellulose-content pulps was enhanced, but so was cellulose degradation. The delignification gains resulted in higher brightness ceilings for the pulps when a D(EP)D sequence was used. Measured fiber morphology did not change significantly from extracting the hemicellulose. Overall, hemicellulose extraction before pulping improved the efficiency of pulping and bleaching materials to a high brightness, but increased cellulose degradation.

Elemental chlorine-free bleaching halfa pulp

Halfa, also known as Stipa tenacissima, is grown in North Africa and south Spain. Due to its short fiber length, paper of halfa remains bulk and takes the block letters well. In this study halfa was evaluated for bleached pulp production. Two cellulose pulps with different chemical compositions were pulped by conventional Kraft process: one from the original halfa material and the other from halfa pretreated by diluted acid. The pulp produced from halfa pretreated by diluted acid was bleached by elemental chlorine-free sequences, DEPD and DEDP. Yield, Kappa number, brightness and α-cellulose contents of bleached and unbleached pulps were evaluated. The results show that during the chemical pulping process, treated halfa was easily cooked than that original halfa. Treated halfa pulp also showed very good bleaching, showing brightness level of 94.8% ISO, yield 93.6% and α-cellulose content 96.8% with DEDP bleaching sequence compared to 83.2% ISO brightness level, 92.8% yield and 95.1% α-cellulose content for bleached pulp with DEPD bleaching sequence. On the other hand, the physicomechanical properties of pulp were not notably reduced by the bleaching process. Breaking length, tear and burst index of paper sheets were acceptable. Therefore, this halfa material could be a worthwhile choice for cellulosic fiber supply.

Effect of Totally Chlorine Free and Elemental Chlorine Free Sequences on Whole Stem Kenaf (Hibiscus cannabinus) Pulp Characteristics

ABSTRACT Totally chlorine free (TCF) and elemental chlorine free (ECF) single and multistage sequences were used to bleach whole stem kenaf pulp. The results indicated that in contrast to unbleached kraft wood pulps, kraft kenaf pulps can be easily bleached to a brightness of 91.4% using a four-stage TCF [Q1(PO)Q2P] bleaching sequence. The ECF bleaching pulps had slightly higher selectivity and yield than those of the TCF bleached pulps. The strength properties of the TCF [Q1(PO)Q2P] and ECF (D1ED2EP) bleached pulps were comparable, with the exception of tear index and tensile index, which were slightly higher and lower for TCF pulps, respectively.

Decreasing effluent loads through bleaching modification

Almost all of the kraft pulp bleach plants worldwide are now practicing elemental chlorine-free (ECF) process to comply with environmental regulations in different countries. Usually, these conventional ECF bleaching sequences contain one or two alkaline extraction stages of which the first one is often the principal source of color and chemical oxygen demand (COD) in the resulting effluent. However, the results of this study showed that the ECF sequences which did not include any alkaline extraction stage and contained solely chlorine dioxide decreased both the color and COD loads of the effluent. On the other hand, the ECF sequences containing both chlorine dioxide and hydrogen peroxide but excluding the alkaline extraction stage could lower only the color but not the COD load. It is suggested that the total kappa factor (the ratio of the total active chlorine to the kappa number) affected the COD load and that the content of hexeneuronic acid groups influenced the color of the bleach effluent. Compared to the reference pulp, the viscosity of the pulp from the exclusively chlorine-dioxide-based ECF sequence without the alkaline extraction stage was lower but the tear index and sheet density at a given tensile index were similar.

Bleaching of bagasse pulp with enzyme pre-treatment

The effluent from pulp bleaching processes containing chlorinated lignin and degraded polyphenolic intermediates remains as a major source of water pollution from the pulp and paper industries. Alternative elemental chlorine free bleaching methods based on the usage of chlorine dioxide, ozone and hydrogen peroxide are potential substitutes. Bio-bleaching methods, which involve pre-treatment of pulp with microbial enzymes such as xylanases, have emerged as viable options. Investigations reported in this paper aim at exploring the suitability of commercial bacterial xylanase enzyme preparations for bio-bleaching of bagasse pulps in conjunction with specific chemical bleach sequences employing hydrogen peroxide (P), alkali extraction (E), ozonation (Z), hypochlorite (H) and chelation (Q) stages. The effluent profiles and pulp qualities obtained for each of the bleach combinations (involving bio-bleaching and chemical bleaching sequences) were monitored. Analysis of the results clearly indicates that the inclusion of enzyme pre-treatment with the TCF (total chlorine free) and ECF (elemental chlorine free) sequences has a significant effect on the effluent (COD, lignin and colour) and pulp quality (kappa number, brightness) parameters. In conclusion, the findings of this investigation indicate the potential promise of enzyme pre-treatment in combination with chemical bleaching to enhance the quality of pulps and combined effluents.