The opportunities to utilize dissolved lignocellulosic material from the spent liquors of neutral sulphite semichemical pulping (NSSC) process has been investigated relatively little so far. Lignosulphonates in the spent liquors are considered as potential by-product due to their relatively high amount. The modified cooking concept of NSSC process, currently under development, uses softwood as a raw material instead of hardwood and produces pulps with yields equal and lower than the typical NSSC pulp yields (75-85% on wood). The amount and characteristics of the components in softwood neutral sulphite spent liquors have not been thoroughly investigated, and most likely they differ from the spent liquors originating from hardwood NSSC process. As a whole, identification of the possible by-products would facilitate the development of NSSC-type softwood biorefinery concept.The spent liquors under investigation originate from the sodium sulphite pulping of Scots pine chips. The pulping experiments were executed under the initial pH of 7 or ~10 at 170°C and 180°C. The cooking liquor, free of buffering chemicals Na2CO3 and NaOH, composes of Na2SO3 (70 g/l) with or in the absence of anthraquinone (0-0.1% on o.d. wood). Altering the cooking time from 0 to 240 min at maximum temperature, chemical and semichemical pulps in the yield range of 55-85% were produced.To identify the possible by-products, the composition of the resulting spent liquors will be analysed for dissolved carbohydrates and lignosulphonates. The molecular size of carbohydrates in the spent liquors is highly interested, since the preliminary results indicate that they dissolve in the form of oligomers and polymers. Earlier results also show that molecular weights of lignosulphonates are comparable with kraft lignin. However, more detailed analyses are needed to identify and characterise the all dissolved compounds.

Possible by-products in spent liquors from neutral sulphite pulping of softwood

251st National Meeting (2016)

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