Bleached Chemithermomechanical Pulp Research Articles

Перспективы организации производства беленой химико-термомеханической массы в Республике Карелия

Перспективы организации производства беленой химико-термомеханической массы в Республике Карелия

Hydrolyzability of Pectic Anionic Substances in Process Waters by Pectinases

In this paper, the efficiency and mechanisms of two pectinases (pectate lyase (PL) and alkaline pectinase (AL)) to hydrolyze model pectic substances and dissolved and colloidal substances (DCS) of Masson pine bleached chemithermomechanical pulp (BCTMP) were investigated. The cationic demand values of model polygalacturonic acid and DCS could be reduced to about 20% and 60 to 70% by these two pectinases, respectively. However, due to the unmethylated form of the pectic substances in DCS of BCTMP, PL is more efficient than AL. The hydrolysis mechanism of polygalacturonic acid with PL was investigated. The results showed that there was no need to hydrolyze the polymeric pectic substance to their monomers, since a minimum average degree of polymerization (DP) of 6.0 was required for pectic acid to interact strongly with cationic polymers and reduce the efficiency of the latter.

Adsorption of cationized eucalyptus heteropolysaccharides onto chemical and mechanical pulp fibers

Adsorption of native eucalyptus heteropolysaccharides onto bleached softwood and hardwood kraft pulps and bleached CTMP was explored in this work to potentially improve the mechanical properties of the final furnish. It was found that adsorption of native heteropolysaccharides onto softwood kraft pulp was slightly higher than hardwood; however, heteropolysaccharides with low arabinose content were preferentially adsorbed onto the hardwood fibers. Adsorption onto CTMP was the lowest, although the general phenomenon of native absorption was rather low under the applied conditions. A strategy to increase the absorption required cationizing the heteropolysaccharides with 2,3-epoxy propyltrimethylamonium chloride that in general significantly increased the overall phenomenon, again with the same general tendencies as observed for the native adsorption.

Starch‐based fixative with proper substitution degree for controlling dissolved and colloidal substances in a bleached chemithermomechanical pulp

Starch‐based fixatives (SBF), specifically low molecular weight, highly‐cationic starches (LHCS), have been reported to efficiently control dissolved and colloidal substances (DCS) in pulp suspensions, and to enhance paper strengths. However, as their degree of substitution (DS) was as high as 0.65, their preparation cost was very high. In this study, two products with lower DSs of just 0.08 (LHCS 0.08) and 0.22 (LHCS 0.22) were prepared and compared to a traditional polyamine (PA) fixative. It was found that the novel LHCSs interacted more readily with the anionic pulp fibers while the PA interacted more readily with the anionic DCS. Consequently, both LHCS 0.08 and LHCS 0.22 increased the paper strength more than the PA. Moreover, it was found that the LHCS 0.22 was most efficient in fixing the colloidal substances onto fibers, while the PA was most efficient in neutralizing the dissolved substances. We conclude that LHCS with DS as low as 0.22 can be used as a good fixative, however, starch with DS of only 0.08 is not efficient enough.

Investigation on the application of industrial grade MgO in the alkaline peroxide bleaching of poplar CTMP

Effects of four different kinds of industrial grade MgO as one alkali source in the alkaline peroxide bleaching of poplar chemi-thermomechanical pulp (CTMP) were investigated. The particle size and activity of the MgO played the most important role in the improvement of optical and strength properties of the bleached CTMP. At a 25% substitution percentage of MgO for NaOH, a 77.4% ISO brightness and the optimal tensile index of the bleached CTMP could be obtained. When industrial grade MgO was applied, appropriate increase in Na2SiO3 dosage and pulp consistency could improve the brightness and strength properties of the bleached CTMP.

Effect of Industrial Grade MgO with Different Particle Sizes on the Bleaching of Poplar Chemi-Thermomechanical Pulp

Magnesium-based alkalis have become an attractive alkali source in the peroxide bleaching process of high-yield pulps. The objective of this work is to evaluate the effect of industrial grade MgO with different particle sizes as the alkali source in the peroxide bleaching process of poplar chemi-thermomechanical pulp (CTMP). The effect of MgO with different particle sizes on pulp properties including strength and optical properties was investigated. With the particle size of MgO decreasing, the peroxide bleaching process produced a bleached CTMP with higher tensile and tear indices, whereas the bulk and light-scattering coefficients were less. The maximum ISO brightness (73.2%) was obtained when the particle size of MgO was 4.3 μm. The possible reason for the brightness change with the variation of particle size of MgO was discussed.

Stickies Control with Pectinase for Improving Behavior of Cationic Polymers in a Mixture of Chemithermomechanical Pulp and Deinked Pulp

In this work, a pressure-sensitive adhesive (PSA) was used as the model substance for secondary stickies. The dissolved and colloidal substances (DCS) prepared from bleached chemithermomechanical pulp (BCTMP) and the effects of pectinase treatment on the stickies deposition were evaluated. The results showed that the addition of DCS lowered the efficiency of cationic polymers and aggravated the deposition of stickies. As a major component of anionic DCS, polygalacturonic acids can be effectively degraded during pectinase treatment. Therefore, the efficiency of cationic polymers improved, and subsequently they were able to fix the destabilized sticky particles on the fibers, which led to the decrease of stickies deposition. However, the pectinase treatment of DCS insignificantly affected stickies deposition in absence of cationic polymers when the stickies deposition was caused by calcium ions.

Using cationic polymers to improve alkenyl succinic anhydride (ASA) sizing efficiency in high-yield pulp containing furnish

High-yield pulp (HYP) such as bleached chemi-thermo-mechanical pulp (BCTMP) from aspen wood, is now being used in the production of high-quality fine papers, and this is particularly true in China. In this study, the effect of using cationic polymers such as poly-aluminum chloride (PAC), polyethylenimine (PEI), cationic polyacrylamide (CPAM), and poly-(diallyldimethylammonium chloride) (PDADMAC) on Alkenyl Succinic Anhydride (ASA) sizing efficiency in HYP-containing pulp furnish was investigated. The results showed that the addition of only ASA emulsion to the HYP-containing furnish, without any cationic additives, did not yield an appreciable degree of sizing in the paper sheet. PAC (or alum) could improve the ASA sizing efficiency. PEI, PDADMAC, CPAM, and NaHCO3 all improved ASA sizing efficiency in the presence of PAC. The charge density of PEI was important for improving the ASA sizing performance. Also, the sequence of adding the cationic polymer affected the ASA sizing performance.

Changes of anionic groups in alkaline peroxide-impregnated aspen chemithermomechanical pulp during subsequent alkaline peroxide bleaching

The effect of alkaline peroxide bleaching on the total anionic groups (AGs) and surface AGs in aspen chemithermomechanical pulp (CTMP) fibers was investigated. Alkaline treatment, especially alkaline peroxide bleaching resulted in the formation of new AGs and surface AGs in the CTMP fibers. The carboxylic groups in uronic acid units, including 4-O-methylglucuronic acid, galacturonic acid, and glucuronic acid units were the main contributors to the AGs in the fibers. However, the oxidized lignin accounting for more than 30% of the total AGs in the bleached CTMP fibers, was the main origin of the new AGs formed during the peroxide bleaching. In addition, the new AGs were also formed by extensive deesterification of the residual esterified uronic acids in pectins and lignin-carbohydrate complexes (LCCs). Although some uronic acid units were dissolved in the process water, both the total AGs and surface AGs in the fibers increased after alkaline peroxide bleaching.

Pretreatment to improve adsorption and effectiveness of wet end chemicals for a bleached chemithermomechanical pulp

Bleached chemithermomechanical pulp (BCTMP) contains high amounts of anionic trashes that can seriously reduce the efficiency of many wet end functional and process chemicals. Fixing agents have been used to offset this negative effect, with varying success. In this study, we used a specially designed, starch-based fixing agent, namely, a low molecular weight, highly cationic starch (LHCS) to pretreat a BCTMP. We used ultraviolet (UV)-visible spectroscopic methods to investigate the effectiveness of LHCS use on the adsorption of some typical wet end chemicals, such as fluorescent whitening agent, tinting dye, wet strengthening agent, dry strengthening agent, neutral sizing agent, and retention agent onto the BCTMP. The results show that the adsorbed amounts and the adsorption efficiencies of these chemicals can be improved by LHCS pretreatment, variously resulting in higher brightness, better tinting, higher wet and dry strengths, better sizing, and higher retention and drainage.

Retention of Optical Brightening Agents (OBA) and their Brightening Efficiency on HYP‐Containing Paper Sheets

Optical brightening agents (OBA) or fluorescent whitening agents (FWA) are commonly used in the paper industry to improve the optical performance of paper products. The increased use of bleached chemi‐thermo‐mechanical pulp (BCTMP) or high‐yield pulp (HYP) in printing and writing paper grades has initiated research topics on the brightening efficiency of OBA on mechanical pulp‐containing furnishes. In this study, process parameters that may affect the retention of OBA were investigated, such as furnish composition, OBA charge, contacting time, water hardness, anionic trash, and fines in HYP. It was found that OBA had lower retention on HYP fibers than on bleached kraft pulp (BKP) fibers. Efforts were also made to understand the underlying mechanism.

Low sludge yield biofilm activated sludge (BAS) upgrade – Quesnel River Pulp

Quesnel River Pulp (QRP) began operating a low sludge yield biofilm activated sludge (BAS) treatment system at its bleached chemithermomechanical (BCTMP) pulp mill at Quesnel, British Columbia, in March 2005. AnoxKaldnes provided the technology. QRP upgraded the anaerobic/activat-ed sludge treatment (AST) system to allow for both increased production rates, as well as production of higher load grades of pulp. The system increased treatment capacity from 110 tons soluble chemical oxygen demand (SCOD)/day to 140 tons SCOD/day with expansion capacity to 170 tons SCOD/day. In addition, the anaerobic system capable of removing 20 tons SCOD/day could be decommissioned since it had a low tolerance for peroxide and sulfur, and high maintenance and operating costs. Results of the upgrade included: 1) meeting all permit limits and effluent is nontoxic to trout under standard test conditions, 2) 80%–85% SCOD removal, 3) stable and reliable operation, 4) sludge yields between 0.12–0.17 net kg total suspended solids (TSS)/kg SCOD removed (compared to previous yields of 0.23 net kg TSS/kg SCOD removed), and 5) ~25% decrease in total effluent treatment costs per ton of pulp, despite a 30% increase in power requirements.

Long term experience with the nutrient limited BAS process for treatment of forest industry wastewaters

The nutrient limited biofilm-activated sludge (BAS) process was developed with the aim to ensure maximum biological treatment efficiency in combination with good process stability, low sludge production and minimum effluent concentration of nutrients. The first full scale nutrient limited BAS (NLBAS) processes were implemented at Södra Cell Värö and Stora Enso Hylte in 2002. Since then another three full scale installations have been built. The aim of this study was to investigate and summarise the long-term treatment results, process stability, sludge production and sludge characteristics for the five full scale NLBAS processes. It was of particular interest to compare the nutrient limited operating mode with regard to the different types of production and wastewater that the mills represent (kraft, TMP and newsprint, bleached CTMP). The study showed that after the initial start-up period, which varied from a couple of weeks to three to four months, all plants meet their respective discharge limits. The sludge production for the different plants varies between 0.07 and 0.15 kg TSS/kg COD and the sludge characteristics are with few exceptions excellent. In conclusion, the nutrient limited BAS process is suitable for both upgrades and new installations of biological treatment for different types of forest industry wastewaters.

Evaluation of Fractionation of Softwood Pulp in a Cylindrical Hydrocyclone

Pulp fiber length characterization is addressed in this article. It is suggested that the proposed separation index H(L) is a viable index to the fiber fractionation performance for evaluating hydrocyclones. Fractionation of softwood (coniferous wood) bleached chemithermomechanical pulp (BCTMP) fiber was carried out with a cylindrical hydrocyclone. Pulp fiber length characteristics in different streams were examined using the fiber quality analyzer (FQA), and the cumulative fiber length fraction, the fiber length fraction density function and the separation index H(L) for different streams were obtained. It is found that H(L) is very useful for characterizing the fiber fractionation performance by indicating the separation capacity of hydrocyclone for individual subgroup of fibers in different streams under different operation conditions. Results of H(L) show that there exists a critical fiber length. A higher proportion of fibers longer than the critical fiber length is in the overflow stream, and a higher proportion of fibers shorter than the critical fiber length in the underflow stream. The data obtained from FQA suggest that the split ratio is the most significant parameter for fiber fractionation performance, which is the best when the split ratio is in the range between 0.14 and 0.2. The effect of feed rate on fiber fractionation performance is weak.

Antibody-based assay for galacturonan deesterification on wood pulp fibers during bleaching

Antibodies recognizing galacturonan were used in immunoassays for industrial unbleached and hydrogen peroxide-bleached chemithermomechanical pulp (CTMP). The assays were based on a colorimetric method using specific monoclonal antibody recognition of acidic and methylated homogalacturonan, respectively, on the pulp fiber surfaces. Alkaline phosphatase-conjugated antibodies were linked to the galacturonan specific antibodies, and an alkaline phosphatase substrate (p-nitrophenylphosphate) was used to develop a yellow reaction product that can be followed spectrophotometrically. Together the newly developed immunoassays were able to describe the deesterification, specifically, of surface-localized galacturonan on CTMP, induced by alkaline hydrogen peroxide bleaching. Unbleached CTMP showed relatively more labeling by methylated galacturonan recognizing antibodies, whereas bleached CTMP was relatively more labeled for acidic galacturonan. The increase in negative charge of the bleached pulp was also shown by polyelectrolyte titration; the negative surface charge was 9.3 µeq g−1 in unbleached CTMP and 21.7 µeq g−1 in bleached pulp.

Structural analysis of acetylated hardwood lignins and their photoyellowing properties

Lignin was isolated from aspen bleached chemithermomechanical pulp by employing a mild acid hydrolysis procedure, and the extracted material was acetylated with acetic anhydride. Nuclear magnetic resonance analyses indicated that the relative ease of acetylating lignin hydroxyl groups was phenolic >> γ-side chain > α-side chain. Non-acetylated and acetylated lignins were impregnated onto cellulosic test sheets, and the photo-behavior of the lignins was examined under irradiation with two light sources, a fluorescent lamp and a black lamp. Optical reflective studies indicated acetylation efficiently inhibited the photodiscoloration of aspen bleached chemithermomechanical pulp lignin under visible and near-UV light irradiation. The photostability of the lignin was correlated to the extent of lignin acetylation. The observed photo-stabilization of acetylated lignin during light irradiation was attributed to the acetylation of phenoxy and aliphatic hydroxyl groups in lignin.Key words: green chemistry, hardwood lignin, acetylation, photo-stabilization, photoyellowing, NMR.

Effect of fiber type on gas holdup in a cocurrent air–water–fiber bubble column

Abstract An experimental investigation of the effect of fiber type on gas holdup in a cocurrent air–water–fiber bubble column is presented. Three types of cellulose fibers (i.e., hardwood, softwood, and bleached chemithermomechanical pulp (BCTMP)) and three different lengths of Rayon fibers are used in the investigation. The results indicate fiber type has a significant influence on the gas holdup in the air–water–fiber bubble column. Mechanisms by which fibers influence gas holdup in gas–liquid–fiber bubble columns are summarized and used to explain the experimental results. Fiber physical properties, including fiber length, coarseness, and flexibility are proposed to be the main factors responsible for the fiber type effects on gas holdup.

Brightness Reversion of Mechanical Pulps. XIX. Photostabilization of Mechanical Pulps by UV Absorbers: Surface Photochemical Studies Using Diffuse Reflectance Technique

The photostabilization of softwood (SW) and hardwood (HW) bleached chemithermomechanical pulp (BCTMP) by UV absorbers has been studied using diffuse UV/VIS reflectance technique. Irradiation of SW and HW BCTMP testsheets resulted in the formation of two absorption bands in the near UV with λmax at 360 and 420 nm. Along with these absorption bands there was a near constant absorption in the visible range from 550 to 800 nm. Irradiation of SW and HW BCTMP testsheets treated with 2,4‐dihydroxybenzophenone (DHB) or and 2‐[2‐hydroxy‐3‐t‐butyl‐5‐(2‐octyloxycarbonyl)ethyl‐phenyl]2H‐benzotriazole (HPB) resulted in a significant differences in the UV/VIS spectra of the treated testsheets in comparison to the untreated pulps. For the treated pulps, no absorption was observed at λmax∼360 nm and absorption at λmax∼425 nm was significantly decreased with respect to the results acquired with the untreated testsheets. The rate of formation of chromophores that absorbed light in 550–800 nm for the treated testsheets was also smaller than the untreated testsheets. The results showed that DHB was a better light stabilizer than HPB, possible pathways for photostabilization were discussed in terms of the mechanism of photoyellowing of mechanical pulps.

Gray-box identification of dynamic models for the bleaching operation in a pulp mill

The development and application of gray-box identification techniques for modelling the bleaching operation in a Bleached Chemi-Thermo Mechanical Pulp (BCTMP) mill are explained. The process is characterized as a delay dominant recycle process with significant input nonlinearities. The identification was carried out using routine operating data in which the outputs were measured irregularly. The effects of these characteristics and consequent modifications of the system identification techniques are discussed. The resulting models are being used for online prediction and model-based controller design at the mill with satisfactory performance.

Pulp mill process closure: a review of global technology developments and mill experiences in the 1990s

The impact of effluent discharges continues to be an important issue for the pulp manufacturing industry. Considerable progress has been made in pollution prevention to minimize waste generation, so-called manufacturing "process closure." Since the mid-1980s many important technologies have been developed and implemented, many of these in response to organochlorine concerns. Zero effluent operation is now a reality for a few bleached chemi-thermomechanical pulp (BCTMP) pulp mills. In kraft pulp manufacturing, important developments include widespread adoption of new cooking techniques, oxygen delignification, closed screening, improved process control, new bleaching methods, and systems that minimize pulping liquor losses. Coupled to this is a commitment to reduce water use and maximize reuse of in-mill process streams. Some companies pursued bleach plant closure, and many have been successful in eliminating a portion of their bleaching wastewaters. However, the difficulties inherent in closing bleach plants are considerable. For many mills the optimal solution has been found to be a high degree of closure coupled with external biological treatment of the remaining process effluent. No bleach plants at papergrade bleached kraft mills are known to be operating effluent-free on a continuous basis. This paper reviews the important worldwide technological developments and mill experiences in the 1990s that were focused on minimizing environmental impacts of pulp manufacturing operations.