Novel concepts on the recovery of by-products from alkaline pulping

Abstract

Innovative biorefinery concepts were developed for the separation and utilization of organic materials, especially aliphatic carboxylic acids, lignin, and extractives, which are formed as by-products during wood-based alkaline delignification processes. The partial recovery of sodium as NaOH and aliphatic carboxylic acids from hardwood soda-AQ black liquor was studied via electrodialysis. The lignin was partly (about 59 % of the initial lignin) precipitated from black liquor by carbonation (pH to about 8.5) followed by electrodialysis or H2SO4 (pH to about 2), with subsequent precipitation of more lignin and the liberation of aliphatic acids. The Na2SO4 formed was successfully separated from the acidified liquor by precipitation with methanol and treated by electrodialysis to recover NaOH and H2SO4 for recycling. The electrodialysis of Na2SO4 was effective and almost 90 % of the sodium was recovered. Volatile formic and acetic acids were recovered from acidified black liquor (pH about 2) by simple distillation and the recovery of the significant low- molar-mass hydroxy carboxylic acids (glycolic, lactic, and 2-hydroxybutanoic acids) by means of their methyl esters for chemical utilization. The residual high-molar-mass acids (3,4-dideoxy-pentonic, 3-deoxy-pentonic, xyloisosaccharinic, and glucoisosaccharinic acids) present in the form of their lactones were then utilized in the production of surfactants with tall oil fatty acids. The esterification of the model compound α-glucoisosaccharino-1,4-lactone with lauric, oleic, and tall oil fatty acids was studied separately in a microwave reactor in the presence of p-toluenesulfonic acid as a catalyst, and the total yields varied in the range of 40-62 %. The precipitated lignin obtained by carbonation and acidification with H2SO4 was separated and characterized with Fourier transform infrared, ultraviolet, energy dispersive X-ray fluorescence, and nuclear magnetic resonance spectroscopy. In addition, the molar weight distributions of these lignin fractions were determined using gel permeation chromatography. The lignin obtained by acidification was employed in synthesis of an acid catalyst. This lignin-based acid catalyst was made by phenol formaldehyde condensation, followed by a sulfonation reaction. The esterification of tall oil fatty acids with methanol was studied in a microwave reactor in the presence of various catalysts, such as lignin-based acid catalyst, p-toluenesulfonic acid, and Amberlyst 15. Compared to other catalysts, the lignin-based acid catalyst showed a good activity, and it also could be easily recycled.