Peroxide Stage Research Articles

Nypa fruticans Frond Waste for Pure Cellulose Utilizing Sulphur-Free and Totally Chlorine-Free Processes.

The search for alternative methods for the production of new materials or fuel from renewable and sustainable biomass feedstocks has gained increasing attention. In this study, Nypa fruticans (nipa palm) fronds from agricultural residues were evaluated to produce pure cellulose by combining prehydrolysis for 1–3 h at 150 °C, sulfur-free soda cooking for 1–1.5 h at 160 °C with 13–25% active alkali (AA), 0.1% soluble anthraquinone (SAQ) catalyst, and three-stage totally chlorine-free (TCF) bleaching, namely oxygen, peroxymonosulfuric acid, and alkaline hydrogen peroxide stages. The optimal conditions were 3 h prehydrolysis and 1.5 h cooking with 20% AA. Soda cooking with SAQ was better than the kraft and soda process without SAQ. The method decreased the kappa number as a residual lignin content index of pulp from 13.4 to 9.9–10.2 and improved the yields by approximately 6%. The TCF bleaching application produced pure cellulose with a brightness of 92.2% ISO, 94.8% α-cellulose, viscosity of 7.9 cP, and 0.2% ash content. These findings show that nipa palm fronds can be used to produce pure cellulose, serving as a dissolving pulp grade for viscose rayon and cellulose derivatives.

Development of a fast and efficient method to analyze microplastics in planktonic samples

Microplastics (MPs) affect plankton (a basis of the trophic chain) and planktivorous fish can ingest them through food confusion or by trophic transmission. Consensus to determine MPs in plankton is lacking and, so, three digestion treatments were evaluated: Alkaline (potassium hydroxide) and enzymatic (protease plus lipase) digestions, both combined with a hydrogen peroxide stage; and an oxidative method using a surfactant (sodium dodecyl sulfate) plus hydrogen peroxide. The alkaline method using potassium hydroxide was found to damage polystyrene. MPs were identified with a stereomicroscope and characterized by reflectance infrared microscopy in semi-automatic mode (using dedicated multi-well aluminium plates). Analytical recoveries for polypropylene, polystyrene, polyethylene, polyamide, polyvinyl chloride and polyethylene terephthalate were higher than 75%, 82% and 83% for the alkaline, enzymatic and oxidative treatments, respectively. The enzymatic method was successfully validated in a European interlaboratory exercise and the oxidative method was demonstrated to be a reliable, fast and cheaper alternative.

A straightforward bioprocess for a cleaner paper decolorization

Abstract A new biotechnological sequence for decolorizing red and black colored paper was developed to reduce the environmental impact of the chemicals used in paper recycling processes. Commercially available low-redox potential laccase from Myceliophthora thermophila, which operates optimally under alkaline conditions, was used in combination with natural mediators to make the process even greener. Based on the optical properties of the resulting decolorized paper, red and black dyes were efficiently removed by all laccase–mediator systems. The best results were provided by the laccase–methyl syringate combination, followed by the laccase–acetosyringone system and the laccase–syringaldehyde system. The decolorization rate for red paper achieved with the laccase–methyl syringate treatment exceeded that obtained with ozone. Red was removed by about 98% by combining two enzymatic stages and hydrogen peroxide stage, and black by 65%, without altering the physical properties of the colored paper in either case. A sequence combining oxidative and reductive (formamidine sulfinic acid) chemical treatments led to comparable optical and physical properties for the two types of paper. The effects of Myceliophthora thermophila laccase and methyl syringate were similar to those of high-redox potential laccase from Trametes villosa combined with either methyl syringate or the synthetic mediator violuric acid.

Ultraviolet resonance Raman spectroscopy analysis of carbonyl groups present after different bleaching stages for various bleach sequences

Different bleaching reagents have different efficiencies of removing chromophore groups from chemical pulps. The objective of this work was to evaluate the effect of different bleaching sequences on the removal of chromophore groups, especially carbonyls, which are suspected to cause brightness reversion. The bleaching sequences analyzed comprise the stages: chlorine dioxide, acid hydrolysis at high temperature, alkaline extraction with hydrogen peroxide, pressurized hydrogen peroxide, and hydrogen peroxide. After bleaching an oxygen-delignified eucalypt kraft pulp with these sequences, the pulps were analyzed for their final brightness, brightness reversion, and pulp viscosity; the bleached pulps were also analyzed using ultraviolet resonance Raman spectroscopy in the infrared region. The infrared analysis indicated that bleaching stages that used hydrogen peroxide, such as pressurized hydrogen peroxide or hydrogen peroxide, in the terminal position reduced the amount of carbonyl groups in the bleached pulp as measured by the absorption band intensity. This study observed that the inclusion of a hot acid hydrolysis stage in the bleach sequence improved the final brightness and brightness stability of the bleached eucalyptus pulp. The replacement of a chlorine dioxide brightening stage by a hydrogen peroxide stage at the end of a bleach sequence yielded higher pulp brightness, and less brightness reversion. The use of pressurized hydrogen peroxide with oxygen resulted in less brightness reversion.

Brightness stability of eucalyptus-dissolving pulps: effect of the bleaching sequence

AbstractThe factors governing the brightness reversion (BR) of dissolving pulps under heat exposure are investigated. Carbonyl (CO) groups were artificially introduced on fully bleached pulp by sodium hypochlorite (NaClO) oxidation. It was demonstrated that the CO groups are responsible for loss of brightness stability (BS). These groups were partly eliminated by an alkaline extraction stage (E), which improved BS. However, an alkaline peroxide stage (P) was more efficient than E to improve BS, but without any additional CO loss. Moreover, an unbleached dissolving pulp was bleached in the laboratory by elemental chlorine free (ECF) and totally chlorine free (TCF) [ozone-based] sequences to the same brightness. The very low CO content was about the same in both cases. The ECF-bleached pulp showed substantially lower BS than the TCF pulp. These results are interpreted such that the chemistry of chromophores in the unbleached pulp also governs BS.In situdetection of phenolic and quinone chromophores in bleached dissolving pulp was performed by electron paramagnetic resonance (EPR) spectroscopy and ultraviolet resonance Raman (UVRR) spectroscopy. The content of these groups was bleaching-sequence-dependent, which may be related to the BS differences.

Potential of the new endophytic fungusHormonemasp. CECT-13092 for improving processes in lignocellulosic biorefineries: biofuel production and cellulosic pulp manufacture

BACKGROUND The utility of the ascomycete Hormonema sp. CECT-13092, an endophytic fungal strain recently isolated and identified from a eucalyptus tree in Spain, was investigated in different biorefineries-industrial processes. The strain was used to improve the enzymatic saccharification and pulping of Eucalyptus globulus wood; and liquid culture of the strain enriched in laccase activity was used for E. globulus Kraft pulp biobleaching in presence of acetosyringone as mediator. RESULTS With regard to enzymatic saccharification, treatment with Hormonema sp. and autohydrolysis pretreatment caused the highest boost of enzymatic hydrolysis (eight-fold increase in sugar yields compared to control without any pretreatment). Moreover, this fungus provided 26.7% higher delignification than control during Kraft pulping and a higher refining degree during mechanical pulping (69° SR vs. 48° SR control). Chemical and mechanical pulps from fungal pretreatment also showed better physical properties than control pulps (increases in tensile, tear and burst indexes of 28.4%, 15.6% and 43.9%, respectively). Regarding biobleaching, after the enzymatic treatment and a hydrogen peroxide stage, a brightness increase (2.3 points %ISO) was obtained. CONCLUSIONS The potential of the endophytic fungal strain Hormonema sp. for biotechnological applications as fermentable sugars production, biopulping and biobleaching has been demonstrated. In this sense, this is the first study on the use of an endophytic fungus for a biobleaching sequence.

Solar water splitting: Efficiency discussion

The current state of the art in direct water splitting in photo-electrochemical cells (PECs) is presented together with: (i) a case study of water splitting using a simple solar cell with the most efficient water splitting electrodes and (ii) a detailed mechanism analysis. Detailed analysis of energy balance and efficiency of solar hydrogen production are presented. The role of hydrogen peroxide formation as an intermediate in oxygen evolution reaction is newly revealed and explains why an oxygen evolution is not taking place at the thermodynamically expected 1.23 V potential. Mechanism of cascading oxidation of water molecules via the peroxide stage is proposed and conforms with experimental observation.Solar hydrogen production with electrical-to-hydrogen conversion efficiency of 52% is demonstrated using a simple ∼0.7%-efficient n-Si/Ni Schottky solar cell connected to a water electrolysis cell. This case study shows that separation of the processes of solar harvesting and electrolysis avoids photo-electrode corrosion and utilizes optimal electrodes for hydrogen and oxygen evolution reactions and achieves ∼10% efficiency in light-to-hydrogen conversion with a standard 18% efficient household roof Si-solar cells. Strategy to increase efficiency above 15% for a single junction cell is outlined.

Comparative evaluation of the action of two different endoglucanases. Part II: On a biobleached acid sulphite pulp

A TCF sulphite pulp, bleached at the laboratory scale with a laccase–violuric acid system and complemented with a pressurized hydrogen peroxide stage, was treated with two endoglucanases, one obtained from Paenibacillus barcinonensis (B) and the other one produced from Cerrena unicolor (F) to improve cellulose reactivity. The treated pulps were evaluated in terms of brightness, viscosity, α-cellulose, water retention value, fibre morphology, Fock solubility, NMR and carbohydrate composition of pulps and liquors. Results revealed that both endoglucanases improved cellulose reactivity, albeit in a different way; thus, B caused no scissions in the cellulose chain and no significant reduction in fibre length, whereas F decreased viscosity and shortened fibre length, leading to lower reactivity value. The liquor composition of soluble carbohydrates released by the enzymatic treatments revealed the B had a processive mode of action since short oligosaccharides, cellobiose and glucose, were obtained. F hydrolysed, from high to low concentration, cellobiose, glucose and cellotriose. Importantly, environmentally friendly dissolving pulp with 90 % Fock solubility was obtained, combining two enzymatic treatments: a laccase–mediator system and then a cellulase from P. barcinonensis (B). In order to improve the quality of final dissolving pulp, a pulp purification step was introduced before the B endoglucanase treatment. The cold caustic extraction lead to reduce the amount of hemicelluloses by 42 % with respect to biobleached pulp, but Fock solubility was also reduced. However, complementing the purification step with F treatment, reduced the amount of hemicelluloses but also improved Fock solubility by 17 %, although some presence of cellulose II was detected by NMR.

Ethanol production from rape straw by a two-stage pretreatment under mild conditions.

The growing interest on rape oil as raw material for biodiesel production has resulted in an increasing availability of rape straw, an agricultural residue that is an attractive renewable source for the production of second-generation bioethanol. Pretreatment is one of the key steps in such a conversion process. In this work, a sequential two-stage pretreatment with dilute sulfuric acid (130 °C, 60 min, 2% w/v H2SO4) followed by H2O2 (1-5% w/v) in alkaline medium (NaOH) at low temperature (60, 90 °C) and at different pretreatment times (30-90 min) was investigated. The first-acid stage allows the solubilisation of hemicellulose fraction into fermentable sugars. The second-alkaline peroxide stage allows the delignification of the solid material whilst the cellulose remaining in rape straw turned highly digestible by cellulases. Simultaneous saccharification and fermentation with 15% (w/v) delignified substrate at 90 °C, 5% H2O2 for 60 min, led to a maximum ethanol production of 53 g/L and a yield of 85% of the theoretical.

Activated hydrogen peroxide decolorization of a model azo dye-colored pulp

Abstract Recovered fibers are reused for manufacturing bright paper after deinking and fiber decolorization. This second process generally starts with an alkaline hydrogen peroxide (H2O2) stage, referred to as P. However, the color-stripping effect of P is often limited due to the low reactivity of H2O2 on the azo groups of dyes. The purpose of this study was to improve the removal of these azo dyes by H2O2. A bleached kraft pulp was dyed with a model azo dye and submitted to activated H2O2 bleaching. Phenanthroline and copper(II)-phenanthroline (Cu-Phen) served as activating compounds. The color-stripping trials were carried out at weak or conventional alkaline pH. The results were mainly evaluated in terms of dye removal index and degree of polymerization of cellulose. The theoretical composition of Cu-Phen in the bleaching conditions was calculated by means of the geochemical software PHREEQC. The results show that Cu-Phen was able to activate H2O2 color stripping, although it was accompanied by additional cellulose degradation. Moreover, the color stripping was more effective under alkaline conditions, in which case CuPhen(OH)2 would be present. Two hypotheses are proposed to explain this activated decolorization: a free radical mechanism and the influence of CuPhen(OH)2 as an activating species.

Effects of inorganic salts on the degradation of 2,5-dihydroxy-[1,4]-benzoquinone as a key chromophore in pulps by hydrogen peroxide under basic conditions

Abstract 2,5-Dihydroxy-[1,4]-benzoquinone (DHBQ) is one of the key chromophores in cellulosics. Due to its special resonance stabilization, it is a prime survivor of bleaching treatments and its degradation is essential in pulp bleaching. The clarification of the degradation mechanism of this compound is indispensable for targeting improvements of pulp bleaching processes. Previous studies revealed that DHBQ degradation by hydrogen peroxide (H2O2) is influenced by salts. This study addresses the effects of alkaline metal salts, alkaline earth metal salts, and Al2(SO4)3 on the degradation of DHBQ under simulated conditions of pulp bleaching in a peroxide stage. The degradation by excess H2O2 followed first-order kinetics in the presence of alkaline metal salts and alkaline earth metal salts, which enhanced and retarded the reaction, respectively. Kinetic studies and theoretical computations provided detailed mechanistic insights: Li+, Na+, and K+ stabilize several reaction intermediates by complex formation, causing the enhancement of the degradation, whereas Mg2+ and Ca2+ coordinate and stabilize the reactant, resulting in the observed retardation. Al2(SO4)3 exhibited a strong enhancing effect, but the degradation followed second-order kinetics with regard to DHBQ, suggesting a fundamentally different degradation mechanism.

Production of thermo-alkali-stable laccase and xylanase by co-culturing of Bacillus sp. and B. halodurans for biobleaching of kraft pulp and deinking of waste paper.

To reduce pollution and cost of treatment for fresh and recycled paper, co-production of xylanase and laccase was carried out in the same production medium using two compatible species of Bacillus. These co-produced enzymes were used for deinking of old newsprint (ONP) and biobleaching of eucalyptusKraft pulp. Solid-state co-cultivation of Bacillus sp. and B. halodurans FNP135 was optimized statistically by response surface methodology for the co-production of xylanase (X) and laccase (L). A significant increase in production of xylanase (2.1-fold, 1,685IU/g) and laccase (2.04-fold, 2,270nkat/g) was observed under optimized conditions viz. pH (10.5), inoculum size (10+10%) and moisture:substrate ratio (0.8:1). Both the enzymes showed identical temperature and pH optima of 70°C and 9, respectively, and were used for deinking of ONP pulp and biobleaching of kraft pulp. In case of ONP pulp deinking, the XL treatment increased brightness (11.8%), freeness (17.8%), breaking length (34.8%), burst factor (2.77%) and tear factor (2.4%). In case of kraft pulp biobleaching, XL treatment showed a significant increase in brightness (13%), whiteness (106.15%) breaking length (49%), burst factor (6.9%), tear factor (23%), and viscosity (11.68%) and reduction in kappa number (15%) after alkali extraction and peroxide stage. This enhancement of pulp properties revealed a synergistic effect of xylanase and laccase produced in one setup.

Formation of Carbonyl and Carboxyl Groups on Cellulosic Pulps: Effect on Alkali Resistance

Ozone bleaching generates carbonyl groups on the cellulose polymer when applied to unbleached kraft pulps. This suggests that pulp fully bleached with a totally chlorine-free (TCF) sequence may contain more oxidized groups than standard elemental chlorine-free (ECF) bleached pulp. A fully bleached pulp was treated with sodium hypochlorite to form oxidized groups (mostly carbonyls) on the pure carbohydrates, which were investigated during subsequent alkaline treatment. Carbonyl groups had a strong impact on color development during alkaline treatment. Among the carbonyls, the keto groups were the most active. This was confirmed by the behavior of carbohydrate model compounds that contained aldehyde, keto, and/or carboxyl groups when subjected to alkaline conditions. A subsequent hydrogen peroxide (P) stage effectively decreased the carbonyl content, which reduced yellowing during alkaline treatment. However, the oxidized cellulose was severely depolymerized. The addition of magnesium sulfate (Mg) into the P stage minimized depolymerization while maintaining some of the carbonyls in the carbohydrates. It is proposed that Mg cations can hinder alkaline β-elimination, possibly by forming a complex with the carbonyl groups.

In-Depth 2D NMR Study of Lignin Modification During Pretreatment of Eucalyptus Wood with Laccase and Mediators

Eucalypt feedstock was pretreated with Myceliophthora thermophila laccase and methyl syringate, as mediator, in a multistage sequence consisting of successive enzymatic and alkaline peroxide stages, directly on the ground wood. Lignin modification was studied by two-dimensional (2D) nuclear magnetic resonance (NMR) of wood (at the gel state) after each stage of the sequence. Decrease of guaiacyl and syringyl lignin units (with preferential removal of the former) and aliphatic (mainly β-O-4′-linked) side chains was observed along the sequence, without a substantial change in polysaccharide cross-signals along the sequence, was observed. However, the most noticeable modification was the formation of Cα-oxidized syringyl units in the enzymatic stages, which were partially removed in the alkaline extractions. Further insight was attained by 2D NMR of the cellulolytic-enzyme lignins, isolated from the pretreated samples, and the filtrates from the different stages. Additionally, a comparison of eucalypt delignification with the high redox potential laccase from Pycnoporus cinnabarinus in the presence of the synthetic mediator 1-hydroxybenzotriazole was carried out. Wood delignification already occurred at the first cycle of the pretreatment with P. cinnabarinus laccase and 1-hydroxybenzotriazole, which directly correlated with increases in glucose (~10 %) yields after enzymatic hydrolysis. In contrast, the first cycle of pretreatment with M. thermophila laccase and methyl syringate did not produce any delignification or saccharification improvement. However, at the end of the sequence, similar delignification (~50 %) of eucalypt feedstock and increases (~30 %) in glucose yields were attained in both laccase-mediator pretreatments. Finally, the influence of lignin content and the ratio of its syringyl and guaiacyl units on recalcitrance of eucalypt feedstock to enzymatic saccharification is discussed.

Pre-treatment of the paper pulp in the bleaching process using biodegradable chelating agents

The aim of this work was to study the application of two biodegradable chelating agents, pyridine-2,6-dicarboxylic acid (PDA) and methylglycinediacetic acid (MGDA), in the treatment of the pulp, prior to hydrogen peroxide bleaching. Such compounds must remove transition metals (Mn, Fe and Cu) from pulp, that catalyze the degradation of hydrogen peroxide, and Ca, which is also problematic due to the formation of precipitates that accumulate in the equipment. Computer simulations were first performed to study the best conditions for metal complexation, and optimum pH was defined as 5–5.5 for PDA and 6.5–7 for MGDA. Metals removal from the pulp, as well as the subsequent bleaching process (Q-P1-Paa-P2), were tested experimentally, and performances were compared to ethylenediaminetetracetic acid (EDTA). PDA removed both Mn and Ca efficiently, leaving most Mg in the pulp after first chelation stage, while MGDA had a lower Ca removal, even using a higher pH and concentration. Residual hydrogen peroxide and kappa number after peroxide stages showed a similar bleaching efficiency between the studied compounds and EDTA.

An improved TCF sequence for biobleaching kenaf pulp: Influence of the hexenuronic acid content and the use of xylanase

Enzymatic delignification with laccase from Trametes villosa used in combination with chemical mediators (acetosyringone, acetovanillone and 1-hydroxybenzotriazole) to improve the totally chlorine-free (TCF) bleaching of kenaf pulp was studied. The best final pulp properties were obtained by using an LHBTQPo sequence developed by incorporating a laccase-mediator stage into an industrial bleaching sequence involving chelation and peroxide stages. The new sequence resulted in increased kenaf pulp delignification (90.4%) and brightness (77.2%ISO) relative to a conventional TCF chemical sequence (74.5% delignification and 74.5% brightness). Also, the sequence provided bleached kenaf fibers with high cellulose content (pulp viscosity of 890 g·mL(-1) vs 660 g·mL(-1)). Scanning electron micrographs revealed that xylanase altered fiber surfaces and facilitated reagent access as a result. However, the LHBTX (xylanase) stage removed 21% of hexenuronic acids in kenaf pulp. These recalcitrant compounds spent additional bleaching reagents and affected pulp properties after peroxide stage.

Laccase fromTrametes sp. I-62: Production, Characterization, and Application as a New Laccase forEucalyptus globulusKraft Pulp Biobleaching

The production of laccase from Trametes sp. I-62 was optimized, and then it was applied for the first time in biobleaching in order to contribute to solve some problems associated with pulp bleaching. When wheat straw and copper sulfate were used in combination as inductors, the maximum laccase activity was obtained. The resulting enzymatic fluid was applied at optimum pH and temperature jointly with acetosyringone in a pretreatment stage (L) aimed to enhance the subsequent bleaching consisting of an alkaline extraction (E) and a hydrogen peroxide stage (P). Results showed that, even when a significantly lower amount of hydrogen peroxide was consumed in the LEP sequence (41.9% vs 89.9% for EP), higher delignification (40.6% vs 33.4%) and brightness (63.6 vs 56.3% ISO) were achieved. After accelerated aging, the optical properties of the biobleached pulp were found to be less stable but still remained higher than those of control pulps.

An enzyme-catalysed bleaching treatment to meet dissolving pulp characteristics for cellulose derivatives applications

Bleached cellulose with good end-properties (≈ 90% ISO brightness and 62% cellulose preservation) was obtained by using a totally chlorine-free biobleaching process (TCF). Unbleached sulphite cellulose was treated with Trametes villosa laccase in combination with violuric acid. This enzymatic stage (L) was followed by a chelating stage (Q) and then by a hydrogen peroxide stage reinforced with pressurized oxygen (Po), resulting to an overall LQPo sequence. The use of violuric acid was dictated by the results of a preliminary study, where the bleaching efficiency of various natural (syringaldehyde and p-coumaric acid) and synthetic mediators (violuric acid and 1-hydroxybenzotriazole) were assessed. The outstanding results obtained with laccase-violuric acid system fulfil most of the characteristics of commercial dissolving pulp, totally acceptable for viscose manufacturing or CMC derivatives, with the added advantage that the enzymatic treatment saved 2h of reaction time and about 70% of hydrogen peroxide consumption, relative to a conventional sequence (Po).

Multi stage peroxide and activated peroxide bleaching of kenaf bast pulp

Soda-anthraquinone kenaf bast pulp (12.5 kappa number and 32% ISO brightness) has been bleached with multi stage peroxide bleaching process. Bleaching process was carried out in different sequences of peroxide stage without and with activator (tetraacetylethylenediamine, TAED) to about 80% ISO brightness. Full bleached pulp production with high brightness and viscosity and also, low chemical oxygen demand (COD) and no adsorbable organic halogens (AOX) in effluent are the aims of this study. The effects of temperature, retention time, chemical charges, TAED/peroxide ratio and alkalinity have been studied in order to maximize the brightness gain at the lowest viscosity loss. H2O2 was activated as bleaching agent under milder conditions, such as low alkalinity or low temperature, by TAED activator. Therefore, TAED charge caused to an improvement in viscosity, pulp yield and effluent COD load. Pre-treatment with EDTA for 30min and in acidic condition gave 2–4% gain in ISO brightness.

Integrating a Xylanase Treatment into an Industrial-Type Sequence for Eucalyptus Kraft Pulp Bleaching

The influence of a treatment with two commercial xylanases on pulp and effluents obtained after the bleaching stages in the OXAZDP (O, oxygen stage; X, xylanase treatment; A, acid stage; Z, ozone stage; D, chlorine dioxide stage; P, hydrogen peroxide stage) sequence was studied. Also, the potential saving in chlorine dioxide was assessed. The enzyme treatment was performed on pulp containing some black liquor since the operating conditions were close to the conditions used in the storage tower in Fibria, identified as the most suitable point for application. The greatest differences in kappa number and hexenuronic acid content were observed after the X stage. Whereas, in brightness were observed after the Z stage. The effluent properties from the X stage were higher with the enzyme treatments. Also, the enzymes allowed chlorine dioxide consumption in the bleaching stage to be reduced. The control pulp contained twice as much adsorbable organic halides (AOX) and exhibited twice more brightness reversion than did the enzyme-treated samples. However, the tensile index and drainability at an identical degree of refining were lower in the enzyme-treated samples.