New Techniques for Continuous Chemical Analysis in the Pulp&Paper Industry

Sammanfattning: This thesis presents some new techniques that were developedfor continuous chemical analysis of a paper furnish. First, ageneral background is presented, covering topics from theorigins of papermaking to present day. A short introduction topapermaking chemistry and a variety of presently availableon-line chemical analysers and measurement strategies are alsodiscussed.A method is described for the continuous fractionation of apaper furnish containing coarse fibres (>10µm) in orderto obtain a sample for analytical purposes (Paper I). Aconsistent sample, containing a representative fraction of thedissolved and colloidal substances (DCS) present in the bulkfurnish, was achieved by preventing cake formation on a filtersurface. A combination of turbulent flow above a membranefilter, while continuously withdrawing a relatively low samplevolume, were key factors in the prevention of filterfouling.For the continuous flow-extraction of DCS, a technique isdescribed whereby the extracting solvent was injected at a highvelocity into a continuous flow of analyte (Paper II).Comparison with conventional flow extraction showed anextraction enhancement of up to 9 times for colloidaltriglycerides.To achieve a continuous determination of chemicalsubstances, a real-time fully automated colorimetric titrationapparatus was developed (Paper III&IV). This was achievedby using a series of micro-machined mixing channels for thecontinuous flow of analyte, with a sequence of detection unitsand titrant addition points along the flowpath (Paper III). Afuzzy logiccontroller was implemented to continuously adaptfor changes in the sample concentration, providing thepossibility of titrating over two orders of magnitude in sampleconcentration with minimal loss of accuracy (Paper IV).Also, a system is presented whereby the filtration apparatus(Paper I) is combined with the titration device (Paper III&IV) in order to continuously determine total charge (orcolloidal charge) of a paper furnish in real-time (Paper V).This was achieved by utilising a back-titration approach andselected examples are presented showing the dynamicinteractions between wood fibres and polyelectrolyte adsorptionat various conditions of pH and polyelectrolyte molecularweight.Finally, some suggestions for a more comprehensive wet-endchemical monitoring platform are discussed and the role of thepresent work in evaluated in this context.Keywords:Chemical monitoring, continuous flowextraction, cross-flow filtration, dissolved and colloidalcomponents, fuzzy-logic control, on-line system, pitchanalysis, polyelectrolyte titration, process control, samplework-up, titrimetric analysis.