Abstract The objective of this investigation was to assess the feasibility of replacing anthraquinone (AQ) as a yield enhancing catalyst in kraft pulping with Me-THAD. It was anticipated that residual Me-THAD on the washed pulp fibers would be air-oxidized to 2-methyl-anthraquinone (MAQ) during commercial fiber drying. While AQ is listed as a possible human carcinogen by the International Agency for Research on Cancer (IARC), MAQ is not. Also, MAQ was reported to actually retard the propagation of cancer cells in more than one refereed publication. In this study, it was observed that both of the methyl-substituted catalysts (MAQ and Me-THAD) were equal or more effective than AQ at increasing fiber yield when added to kraft pulping of both a softwood (southern pine) and a hardwood (eucalyptus). It was observed that pure Me-THAD powder oxidized to MAQ at room temperature (∼22 °C). The inference was drawn that residual Me-THAD on washed fibers from kraft/Me-THAD pulping also oxidized to MAQ. Extracts from such fibers from a eucalyptus pulp were carefully analyzed on a Thermo Scientific Trace 1310 with Orbitrap GC/MS. The unbleached fibers contained 20 μg/kg (ppb) of MAQ and ∼1 μg/kg of Me-THAD. When bleached using the D0EpD1 sequence to 90% Elrepho brightness, the fibers contained 3.5 μg/kg of MAQ and no Me-THAD. A preliminary assessment on the economics of Me-THAD synthesis at commercial scale is included.

Earlier research demonstrated that the bicarbonate anion (HCO3-) activated hydrogen peroxide and made it into an effective bleaching agent for both chemical and mechanical pulps at pH similar to 8.5. The peroxide/bicarbonate treatment is designated as a P-B stage. It was also observed that in P-B bleaching of chemithermomechanical pulps (CTMPs), a higher initial pH resulted in more H2O2 being consumed and the achievement of a higher bleached brightness. This research focused on using Na2CO3 instead of NaHCO3 to achieve a higher pH in P-B bleaching of softwood CTMP. Further activation of the H2O2 was obtained by the addition of N, N, N', N'- tetraacetylethylenediamine (TAED). There was a high peroxide residual when 3.0% H2O2 on pulp (oven-dried or OD basis) was used in a conventional alkaline peroxide (P) stage. Sodium carbonate was added to the P stage effluent (with or without TAED), which was recycled and used to pretreat unbleached pulp. A significant increase in brightness (similar to 3 points) was obtained when the pretreated pulp was regularly bleached with 3.0% H2O2 on pulp in a P stage.

Peroxide bleaching of softwood and hardwood (eucalypt) kraft pulps was performed in solutions of sodium bicarbonate (NaHCO3), sodium carbonate (Na2CO3), and sodium hydroxide (NaOH). The conventional P stage (hydrogen peroxide + sodium hydroxide; H2O2 + NaOH) was the most effective brightening system without an additional activator. However, peroxide activation by bicarbonate anion (HCO3–) was obvious in all cases where NaHCO3 or Na2CO3 was used. When N,N,N’,N’-tetraacetylethylenediamine (TAED) was added to the bleaching system, Na2CO3 as the alkali source afforded equal or slightly higher bleached brightness compared to NaOH usage for both the softwood and hardwood pulps. This outcome is attributed to simultaneous peroxide activation by HCO3 and TAED. When applied to the eucalypt pulp, the H2O2/Na2CO3/TAED bleaching system also decreased the brightness loss due to thermal reversion.

The literature on biomass research contains many references to lignin–carbohydrate complexes (LCC) decreasing the rate of delignification in chemical pulping, decreasing the yield of cellulosic ethanol via fermentation, and decreasing forage digestibility. Regarding wood delignification, there are a few reports on the formation and/or cleavage of lignin–carbohydrate (L–C) bonds during alkaline pulping. The behavior of LCC was investigated to find a potential explanation for the differences between the soda-anthraquinone (soda-AQ or SAQ) and kraft processes with regard to delignification rate in the residual phase of pulping and in the bleaching process. Enzymatically isolated lignin (EL) was prepared from two soda, nine SAQ, and twelve kraft pulps from sugar maple, a hardwood. The range of kappa numbers, after correction for hexenuronic acid (HexA), was 10–60. The bound sugars on each EL were hydrolyzed and converted to monomers by H2SO4 at 121°C. There was evidence in the data suggesting that the bound glucan and xylan on the ELs from soda, SAQ, and kraft pulps were native to the wood. The bound galactan data were somewhat ambiguous, and there was no detection of bound mannan on any EL. The reproducibility and repeatability of bound arabinan attached to ELs (BA) were excellent. Although not conclusive, the totality of the data is suggestive of both L–C bond formation and cleavage involving arabinose units during both kraft and SAQ pulping. There was no decrease in BA when SAQ was used to lower the c-kappa number (HexA-corrected) from ∼60 to ∼25. The case was similar when kraft was used in the range of ∼60 to ∼40. However, there were significant decreases in BA content when c-kappa number was lowered below ∼25 by both SAQ and kraft. A common mechanism was proposed to explain essentially no decrease in BA content at higher kappa numbers, but distinctly different mechanisms were proposed to explain BA cleavage at c-kappa number <25. A mechanism favorable to subsequent bleaching was proposed for kraft, but an unfavorable mechanism was proposed for SAQ.

Sugar maple (Acer saccharum), aspen (Populus tremuloides), and white birch (Betula papyrifera) are three hardwoods that are widely used by the North American pulp and paper industry. Because of their abundance, these species are also likely to be used by some of the biorefinery processes that are being developed. A significant amount of evidence indicates that the syringyl to guaiacyl (S/G) ratio of the lignin in a hardwood is a governing parameter regarding its ease of delignification. Credible data also show that among poplars the S/G ratio of the lignin significantly influences the ease of saccharification of the carbohydrate polymers to sugar monomers. Although the S/G ratio appears to be a key parameter for hardwoods, values accepted by most practitioners are not available for the three species. In this investigation, those ratios were estimated by an extensive literature review followed by S/G determination by nitrobenzene oxidation (NBO) and methoxyl analyses of organosolv lignin (OSL) from the ethanol/water/sulfuric acid pulping process. The S/G values were approximately 1.4 for sugar maple, and 2.0 for aspen and white birch. Data are also included showing that sugar maple and white birch were equally reactive in kraft pulping. Thus, it is unclear whether or not the S/G ratio is indeed a governing parameter in this delignification process.

High kappa number kraft and soda-anthraquinone (soda-AQ or SAQ) pulps from sugar maple (Acer saccharum) were investigated to see how the lignin-carbohydrate complexes (LCC) they contained affected lignin removal by oxygen, chlorine dioxide, and hydrogen peroxide. The chlorine dioxide and hydrogen peroxide doses were higher than normal because both pulps had unbleached kappa numbers in the range of 61-62. Only oxygen delignification was investigated with the SAQ pulp. The research focused on the strong lignin-carbohydrate (L-C) linkages only. The pulp carbohydrates were enzymatically degraded and solubilized, thus leaving an enzymatic lignin (EL) residue. The highest concentration of bound sugars (glucan, xylan, arabinan, and galactan) on any of the ELs was <2.1 wt%. Chlorine dioxide (D stage) was investigated at end pHs of 2.1, 2.9, and 4.0, followed by extraction with dilute sodium hydroxide. Lignin oligomers containing bound glucan and arabinan were unreactive and accumulated in the fibers. When oxygen was used to delignify kraft and SAQ pulps by ~50%, only ~10% of the lignin bound arabinan was solubilized. Galacto-lignin complexes were somewhat reactive to oxygen and hydrogen peroxide under alkaline conditions, but less reactive in the D stages. Consistent with literature data, xylo-lignin complexes were reactive toward oxygen and toward the other two oxidants. They do not appear to be major impediments in the bleaching process.

*Campus de Itapeva, UNESP, UniversidadeEstadualPaulista, Brazil ** Department of Paper and Bioprocess Engineering (PBE), SUNY College of Environmental Science and Forestry (SUNY ESF), 1 Forestry Drive, Syracuse, NY 13210, USA ***Department of Chemical Engineering, Federal University of Vicosa (UFV), University Campus, Vicosa, MG 36570000, Brazil. **** Scientific Consultant, Syracuse, NY 13210, USA. On leave from PBE Department, SUNY ESF

A three-stage mason, or 72 wt% sulfuric acid, method is described for hardwoods. As compared to the traditional twostage method, the primary hydrolysis (PH) stage was modified to improve mixing of the wood meal into the 72% H2SO4. The PH stage was followed by two 1 h secondary hydrolysis (SH) stages. The 72% H2SO4 slurry was first diluted to 40 wt% H2SO4 and heated at 80 degrees C then diluted to 3 wt% H2SO4 and refluxed. When equivalent PH stages were used, convincing evidence was obtained showing that the hydrolytic intensity in the cleavage of lignincarbohydrate complexes (LCC) was much higher for the modified SH stages, as compared to the traditional refluxing of a 3% H2SO4 slurry for 4 h. The accuracy in lignin content determination should be equal or superior for the threestage method, which takes approximately 2 h less time. Results are presented for 4 hardwoods from 3 different genera.

In most native lignins, at least 50% of the phenylpropane (C(9)) units are involved in β-O-4 linkages. It was recently observed that ethylguaiacol (EG) was efficient at trapping coniferyl alcohol generated from the cleavage of uncondensed β-O-4 dimeric structures during soda-anthraquinone (AQ) or SAQ delignification of sugar maple wood meal. Some of the coniferyl alcohol was transformed to vinylguaiacol and isoeugenol, and the α-carbon atom in all three monomers formed C-C bonds with the C-5 position of EG. In the present research, eucalyptus and sugar cane bagasse meals were also investigated, and the yields of uncondensed β-O-4 structures in the nonsyringyl fraction were quantitated. The estimates of the uncondensed fraction of the lignin in the three samples (assuming S units are 90-95% uncondensed) were in close agreement with results from traditional but more tedious methods such as permanganate oxidation or spectroscopic methods requiring a sample representative of native lignin.

In Part 1 of this series it was observed that one of the eucalypti (EGC 39) was more reactive than the other two in kraft and soda-AQ (SAQ) cooking. However, the lignin in EGC 39 contained equal or less syringyl (S) units than the other two eucalypti. In the present research an attempt was made to compare the guaiacyl (G) fraction of the three lignins. The approach was to use SAQ treatment to cleave β-O-4 bonds in dimeric units containing uncondensed guaiacyl A-rings (those rearranging to quinone methides). The coniferyl alcohol, vinylguaiacol and isoeugenol generated from β-O-4 cleavage are then trapped as dimers by ethylguaiacol that is included in the SAQ liquor. Research with sugar maple (Acer saccharum) showed that the estimate of these structures (uncondensed G-β-O-4) by this approach was in close agreement with traditional but more tedious methods such as permanganate oxidation and 31P NMR. It was also shown that the lignin in the EGC 39 hybrid contained a higher concentration of uncondensed G-β-O-4 structures than the other two eucalypti lignins.

Two eucalyptus hybrids (EGC 39, EGC 241), resulting from crosses between Eucalyptus grandis and Eucalyptus camaldulensis, were investigated to see if they could produce kraft papermaking fibers with low lignin and adequate physical properties. The two hybrids were harvested at an age of 8 years along with 6-8 year old Eucalyptus camaldulensis (Rostrata). All three eucalypti were grown in the area of Gharb in the North-West of Morocco. The tracheids in the two hybrids had a very high Runkel ratio (2 x cell wall thickness/lumen diameter) and produced kraft paper sheets with low tensile strength due to a low degree of fiber collapse thus a low relative bonded area. These fibers could be used to increase the stiffness of a papermaking furnish. The lignin in the EGC 39 chips was more reactive in kraft pulping as compared to the other two eucalypti. Methoxyl analyses and nitrobenzene oxidation (NBO) of the in-situ lignin (wood meals) were performed, and it was concluded that the syringyl content of the EGC 39 lignin was less than or equal to those in the other two eucalypti. Differences in the guaiacyl fraction of the three samples will be discussed in Part 2 of this series.

The literature on biomass research contains many references to lignin-carbohydrate complexes (LCC) decreasing the rate of delignification in chemical pulp production, decreasing the yield of cellulosic ethanol via fermentation, and decreasing forage digestibility. However, it is difficult to find correlations between rates of the processes above and initial LCC concentration. One of the main reasons for the lack of such correlations is the absence of methods for accurate quantification of LCC. In this investigation, repeatable and reproducible determinations of bound sugars at monomeric concentrations as low as 0.3 wt% on enzymatic lignin (EL) have been achieved. The bound sugars are hydrolyzed by H2SO4, most likely as low molecular weight oligomers. In the same H2SO4 treatment, the oligomers are hydrolyzed to monomers which are subsequently quantified by H-1 NMR analyses. A significant enrichment of bound arabinan was previously reported when a crude milled wood lignin (MWL) was compared to the starting wood meal. A similar arabinan enrichment was observed for ELs from kraft and soda-AQ (SAQ) pulps in the present study. Also, well-resolved cross-peaks have been obtained in 2D HSQC NMR analyses of ELs. It has so far been confirmed that the EL from a 30.6 kappa number SAQ pulp from sugar maple contained similar to 30% more benzyl ethers linked to primary-OH groups in sugar units than the corresponding EL from a 33.7 kappa number kraft pulp.

The peroxymonocarbonate mono- and di-anions (HCO4–and CO42–) are known to be generated from H2O2/HCO3–. They are promising oxidants for wood pulp bleaching, but peroxide decomposition catalyzed by ferric complexes can be significant for pulps whose lignin is highly reactive. Dicarboxylates from lignin peroxidation are believed to be the ferric chelators in the pH 8.5 range that is optimum for H2O2/HCO3–. This investigation aimed to see if HCO3–addition caused destabilization of the peroxygen system owing to its partial conversion to HCO4–. This anionic peracid is a much stronger oxidant than H2O2and could lead to a higher rate of Fe(II) oxidation to Fe(III) and (or) Fe(IV). For most free radical chain mechanisms, an increase in Fe(II) oxidation results in a higher rate of peroxide decomposition. Based on the kinetic data that were obtained and theoretical analyses, it was concluded that HCO4–did not significantly destabilize the peroxygen system when citrate was used as a model chelator for Fe(III). Increasing the [HCO3–] fourfold from 0.025 to 0.10 mol/L caused the decomposition rate to increase by only 20%.

Hardwood soda-AQ pulps are believed to be rich in benzyl sugar ethers (BSE) that can be partially cleaved by aqueous acidic treatments. The aim of this investigation was to evaluate the effect of acidolysis on final bleached brightness for kraft and soda-AQ (SAQ) hardwood pulps. The increase in final brightness due to acidolysis at 110 °C was twice as high for a eucalyptus SAQ pulp as compared to the kraft pulp. An oxygen delignified maple C-SAQ pulp (carbonate pre-treated SAQ) was acidolyzed at 120 °C and pH 2.6 for 30 min. When 1.60% ClO2 + 0.25% H2O2 on pulp was used in DEPD final bleaching of the control sample a brightness of 91.5% was achieved. When only 1.00% ClO2 + 0.25% H2O2 on pulp was used for the acidolyzed sample a brightness of 92.0% was attained. Analyses of the maple pulp after the acidolysis showed no major change in lignin content, brightness, or pulp yield. The minor changes suggest that a facile reaction such as benzyl ether cleavage was responsible for the improved bleachability. Preliminary research involving a lignin model compound and commercial birch xylan showed that lignin-carbohydrate condensation products were generated under SAQ cooking conditions. Furthermore, a fraction of these lignin-carbohydrate moieties were subsequently cleaved by acidolysis at pH 2.5 and 105 °C.

The peroxymonocarbonate mono- and di-anions (HCO(4)(-) and CO(4)(2-)) are known to be generated from H(2)O(2)/HCO(3)(-). They are promising oxidants for wood pulp bleaching, but peroxide decomposition catalyzed by Mn(II) species may be significant for pulp samples with unusually high Mn contents. This investigation aimed to see if HCO(3)(-) addition caused destabilization of the peroxygen system owing to its partial conversion to HCO(4)(-). This anionic peracid is a much stronger oxidant than H(2)O(2) and could lead to a higher rate of Mn(II) oxidation to Mn(III) and (or) Mn(IV). For most free radical chain mechanisms, an increase in Mn(II) oxidation results in a higher rate of peroxide decomposition. Peroxide decomposition catalyzed by Mn(II) was investigated in H(2)O(2)/HCO(3) in the pH ranges 8.5-8.7 and 7.4-7.9. The rate equation for peroxide decomposition was first order in [H(2)O(2)] and [Mn(II)] in both pH ranges, but close to second order in [HCO(3)(-)] in the higher pH range and close to third order in the lower pH range. Free radical chain mechanisms were proposed for both pH ranges and with all the correct reaction orders. Contrary to mechanisms previously proposed, it was concluded that HCO(4)(-) is the principal oxidizer of Mn(II) in the pH 7.4-7.9 range.

It was recently observed that ethylguaiacol (EG) is quite efficient at trapping coniferyl alcohol (CA) generated from the cleavage of uncondensed beta-O-4 dimmers during soda-AQ or SAQ delignification of a hardwood. Some of the CA is transformed to vinylguaiacol (VG) and isoeugenol (IE) and the alpha-carbon atom in all three monomers condense to the C-5 position of EG. In the present research the feasibility of quantifying uncondensed beta-O-4 structures where the ring that rearranges to the quinone methide is a guaiacyl (G) or p-hydroxyphenylpropane (H) unit was investigated. Central to this approach is the efficiency of EG trapping of CA, p-coumaryl alcohol (p-CMA) and their transformation products. The estimates of uncondensed beta-O-4 structures in hardwood and bagasse lignin by this approach were in close agreement with traditional but more tedious methods such as permanganate oxidation and P-31 NMR.

The peroxymonocarbonate mono- and di-anions (HCO4– and CO42–) are known to be generated from H2O2/HCO3–. They are promising oxidants for wood pulp bleaching, but peroxide decomposition catalyzed by Mn(II) species may be significant for pulp samples with unusually high Mn contents. This investigation aimed to see if HCO3– addition caused destabilization of the peroxygen system owing to its partial conversion to HCO4–. This anionic peracid is a much stronger oxidant than H2O2 and could lead to a higher rate of Mn(II) oxidation to Mn(III) and (or) Mn(IV). For most free radical chain mechanisms, an increase in Mn(II) oxidation results in a higher rate of peroxide decomposition. Peroxide decomposition catalyzed by Mn(II) was investigated in H2O2/HCO3 in the pH ranges 8.5–8.7 and 7.4–7.9. The rate equation for peroxide decomposition was first order in [H2O2] and [Mn(II)] in both pH ranges, but close to second order in [HCO3–] in the higher pH range and close to third order in the lower pH range. Free radical chain mechanisms were proposed for both pH ranges and with all the correct reaction orders. Contrary to mechanisms previously proposed, it was concluded that HCO4– is the principal oxidizer of Mn(II) in the pH 7.4–7.9 range.