Alkaline Pre-Treatment of Softwood Chips Prior to Delignification

Scots pine (Pinus sylvestris) chips were pre-treated with alkaline solutions (alkali charges of 1, 2, 3, 4, 6, and 8% of NaOH on the oven-dried wood material) at 130°C and 150°C for various treatment times (30, 60, 90, and 120 minutes). Under these conditions, 2.0–13.6% of the wood d.s. was dissolved into the aqueous hydrolysates. The soluble organic fraction was primarily characterized in terms of carbohydrates (monosaccharides and oligo-/polysaccharides) and their alkali-catalyzed degradation products: aliphatic carboxylic acids containing, besides non-volatile hydroxy carboxylic acids, volatile formic and acetic acids. With increasing alkali charge, temperature, and time, the enhanced formation of various hydroxy monocarboxylic acids was detected. Under the most drastic pre-treatment conditions, two-thirds of the total organic fraction dissolved was composed of various aliphatic carboxylic acids, the residual material being mainly degraded lignin and extractives. Only relatively small concentrations of carbohydrates and trace amounts of furans were found.