D Kanungo | SUNY: College of Environmental Science and Forestry (original) (raw)

Papers by D Kanungo

ABSTRACT Data accumulated in our laboratory from the cooking of chips and bleaching of resultin... more ABSTRACT
Data accumulated in our laboratory from the cooking of chips and bleaching of resulting pulps consistently pointed to a higher rate of lignin condensation during soda/AQ (SAQ) as compared to kraft pulping. The data also appear to indicate that the rate of condensation was higher at lower alkalinity and that the higher concentration of condensed structures in SAQ pulps is likely responsible for their poorer bleachability. Alkaline condensation reactions were investigated with four commercially available lignin model compounds; apocynol (AP), ethylguaiacol (EG), homovanillyl alcohol (HVA) and vinylguaicol (VG). The model compound results pointed to a higher rate of lignin condensation for SAQ as compared to kraft pulping. Literature reports indicate that the rate of formation of coniferyl alcohol (CA) is 4-5 times higher for SAQ or kraft/AQ as compared to kraft pulping. The present investigation showed that secondary quinone methides from CA degradation products, such as vinylguaicol, participate in condensation reactions. A higher rate of condensation was observed in 0.1M NaOH as compared to 0.6M NaOH. Evidence was also found for carbohydrate-rich materials condensing with quinone methides.

Hardwood soda-AQ pulps are believed to be rich in benzyl sugar ethers (BSE) that can be partially... more 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.

Abstract Soda pulping catalyzed by anthraquinone (AQ) or 2-methylanthraquinone (MAQ) can produce... more Abstract
Soda pulping catalyzed by anthraquinone (AQ) or 2-methylanthraquinone (MAQ) can produce hardwood chemical pulps similar to kraft pulps in all respect but for bleachability. Results accumulated in our laboratory suggest that the residual lignin in pulps from anthraquinone catalyzed processes is less reactive toward bleaching chemicals than that in kraft pulps. Analyses of pulps by periodate and permanganate oxidations suggest that the residual lignin from the non-sulfur processes contained more condensed structures than kraft residual lignin. The low reactivity of these structures is believed to be responsible for the lower brightness of bleached soda-AQ (SAQ) pulps. Pulping and bleaching trials with hardwood chips demonstrated that shortening of the cooking time and/or increasing the alkalinity is one strategy for improving bleachability of SAQ pulps. When sugar maple (Acer saccharum) chips were SAQ cooked for 1.0 and 2.0 h at 165°C, the higher kappa number pulp produced after 1.0 h of cooking bleached to a significantly higher brightness with a small increase in the chlorine dioxide application.

Abstract: Coniferyl Alcohol is generated from the cleavage of β-O-4 bonds during alkaline pulping... more Abstract: Coniferyl Alcohol is generated from the cleavage of β-O-4 bonds during alkaline pulping of hardwoods and softwoods. Once formed, some of the coniferyl alcohol (CA) is
transformed into vinylguaiacol (VG) and isoeugenol (IE). All three of these compounds (CA, VG and IE) can rearrange to quinone methides under alkaline conditions and become involved in
condensation reactions with lignin and carbohydrate moieties. It was observed in earlier research that the C-5 position of ethylguaiacol (EG) added to a monomeric quinone methide (QM) to
form a dimer that was apparently unreactive to wards further condensation. In this investigation,
sugar maple wood meal was delignified by the soda-AQ (SAQ) process with EG added at 5.0
wt% on wood meal. Three dimers were detected in the pulping effluent and identified as
combination of EG with CA, VG and IE. The total yield of the three dimers corresponded to
~80% of the estimated CA that would have been generated. Conventional kraft, SAQ and
SAQ+EG pulping of the maple chips were then performed. The bleachability of the SAQ+EG
pulp was significantly improved as compared to the SAQ pulp and it was estimated to be
superior to the kraft pulp as well.

ABSTRACT Laboratory study on bleaching of soda/anthraquinone (SAQ) pulp suggests that AQ catalyz... more ABSTRACT
Laboratory study on bleaching of soda/anthraquinone (SAQ) pulp suggests that AQ catalyzed soda pulp is less responsive towards bleaching chemicals compared to kraft pulp. In this context, shortening of the H-Factor is considered to be one possible strategy to improve bleachability of the SAQ hardwood pulp. To investigate the poorer bleachability, soda, SAQ and kraft pulping were carried out using eight commercially available lignin model compounds representing mostly the reactive species generated during pulping. The investigation indicated that these reactive species vigorously participated in base induced condensation reaction. From GC, GC-MS and solid sample introduction MS analysis, vinylogous compounds were found to undergo Michael addition to repolymerize. Correlating the rate of condensation with alkalinity, some lignin model compounds were found to undergo condensation at a lower rate at 0.6 M NaOH compared to 0.2 M NaOH; which explains the improved final brightness by shortening the pulping time of SAQ/SMAQ pulp. Evidence was also found that the pre extraction (hot water, carbonate or acetate extraction) process removed hydrolysable compounds that could influence pulping and bleaching.
Keyword: Anthraquinone, alkaline pulping, lignin condensation, quinone methide, carbanion, Michael addition, preextraction.