Interactions between dissolved wood organic chemicals and nonprocess elements in chemical pulping processes Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/hm50tv708

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  • This work is part of a larger project dealing with nonprocess element (NPE) behaviour in chemical pulping processes. Nonprocess elements are defined as those elements which are not essential to the chemical process, i.e. are neither active pulping chemicals (e.g., NaOH and Na2S in the kraft process), nor compounds present as a result of incomplete conversion of makeup chemicals to active pulping chemicals. Problems associated with the build up of these elements include scaling, fouling, and corrosion of heat exchangers, and various operating problems in the preparation of pulping liquors. Wood organic chemicals dissolve in the pulping digesters and during bleaching processes. Interactions between dissolved wood organic chemicals and nonprocess elements are the main concern of this work. Ultrafiltration was used to fractionate spent pulping liquors by molecular weight of the dissolved wood organic chemicals. This provided chemically less complex samples for future study. Rejection coefficients, measured as a function of molecular weight of the dissolved wood organic molecules, were determined for the ultrafiltration membranes used in the study. The rejection coefficients were found to be independent of solute source, molecular weight distribution in the ultrafilter feed solution, and ultrafilter run time. Carbon-thirteen nuclear magnetic resonance (C13-nmr) was used to analyze chemically the spent pulping liquor fractions. To avoid chemical changes in the fractions and to make the analysis quantitative, an analysis technique was developed using aqueous NaOH solvent and a chemical additive, chromium ethylenediamine (CREN), for all samples. Results of this analysis show more carboxylic acid groups on both lignin and carbohydrate derivatives than are seen in C13-nmr spectra using organic solvents. No aldehydes were detected in any of the liquor samples. Using methoxyl to aryl ratios determined from the spectra suggest that catechol groups are more prevalent on the high molecular weight lignin compounds. The use of CREN as a relaxation agent in C13-nmr spectroscopy is also discussed.
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