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 (QMs) under alkaline conditions and become involved in condensation reactions with lignin and carbohydrate moieties. The aim of this investigation was to see if ethylguaiacol (EG) addition to soda-AQ (SAQ) pulping systems would lead to its reaction with the QMs from CA, VG, and IE to form dimers that are unreactive towards further condensation. Sugar maple wood meal was delignified by the SAQ process with EG added at 5.0 wt% on wood meal. Three dimers were detected in the pulping effluent and identified as a 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.

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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.

All thirteen Lo-SolidsTM digesters operating on hardwood are reporting a yield advantage from using this cooking process. The measured benefit is 1-5% on wood. Pulp strength, and paper machine performance has also improved.The single vessel hydraulic digester at Zicunaga, Spain will be discussed in detail. It has gradually been upgraded to produce 3.5 times the original design. The latest modifications include Lo-SolidsTMCooking and the new Lo-LevelTM feed system. The modifications have improved the pulp yield by about 2-3% on wood, and addition of AQ has further improved the yield by about 2%. There was no observable benefit from AQ addition prior to these modifications. The bleached pulp viscosity has increased by 150-200 SCAN units, with a corresponding increase in pulp strength.At the Georgia Pacific Corporation, Leaf River Pulp Operations a unique method of Lo-SolidsTM cooking was implemented in 1998. This new approach does not require any counter current flow of chips and liquor within the cooking vessel. All liquor flows are either across the digester shell or co-currently down with the chip flow, hence the new cooking method's name, "Downflow Lo-SolidsTm cooking". This paper also documents improvements in performance of Leaf River's digester resulting from the conversion to Downflow Lo-SolidsTm cooking.