Modeling of the Ion Exchange in Pulp Suspensions by Gibbs Energy Minimization (original) (raw)

Modelling ion exchange and flow in pulp suspensions

2003

This thesis summarizes the results of four papers dealing with modelling of ion exchange between cellulosic fibers and their surrounding aqueous solution. Transition metals, in particular manganese, iron and copper, induce fiberdeteriorating radical reactions in oxygen-chemical-based bleaching, while magnesium inhibits such reactions. Thus the removal of the harmful transition metals from a pulp is required while the beneficial magnesium should be retained in a pulp. Selective control of metal contents of pulps is a key factor in the control of bleaching chemistry. Thus, ability to predict the extent of ion exchange and amounts of metals are of great practical interest. An ion exchange model to describe interaction of ionic species with kraft pulps has been developed in the present work. The model can be applied in pulp washing and chelation. The present model takes into account overall ionic composition of pulp suspensions, i.e. the cations and simple anions as well as the ligands ...

Model describing Donnan equilibrium, pH and complexation equilibria in fibre suspensions

Nordic Pulp and Paper Research Journal, 2001

A model for the calculation of ionic equilibria and pH in fibre suspensions has been developed. Two extensions to existing Donnan theory-based models are provided: the equations facilitate the calculation of pH and combine Donnan theory with complexation models. It is assumed that freely mobile ionic species are Donnan equilibrium distributed between fibres and bulk solution and that only hydrogen ions are specifically bound to the fibres. The model has been verified by determinations of the acid/base properties and metal ion sorption of hardwood kraft fibres at different ionic strengths, in the presence of a chelant (EDTA) and by modification of the fibre charge by selective hydrolysis of hexenuronic acids. The stability constants of acid groups in the fibres were determined by potentiometric titration. The amounts of acid groups were determined by titration and by analysis of uronic acids by enzyme hydrolysis/HPLC and acid hydrolysis/UV spectrophotometry. The model quantitatively predicts ionic equilibria (pH, distribution of ions, complexation) in all the systems investigated.

Processing of dissolving pulp in ionic liquids

This thesis forms part of the Council for Scientific and Industrial Research, Forestry and Forest Products Research Centre (CSIR-FFP) biorefinery project which aims at developing and implementing novel industrial processes production of cellulose textile fibres. The focus of this study is to investigate the dissolution of South African Eucalyptus raw (unbleached) and final (bleached) dissolving pulp and saw dust wood in an ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate [Emim][OAc] and the co-solvents [dimethylsulfoxide (DMSO)] or [dimethylformamide (DMF)] mixtures, to obtain regenerated cellulose by the further addition of water and acetone. The IL/co-solvent mixtures were able to dissolve the raw and final pulp samples at 120 ˚C for 6 hours whereas the sawdust wood dissolved in 10 hours. The IL/DMF mixture gave higher cellulose recoveries of 41.88 % for the raw pulp, 49.89 % for the final pulp sample and 32.50 % for sawdust wood while the IL/DMSO mixture gave a recovery of 1...

Effect of pH and washing on calcium and magnesium distribution between pulp and filtrate

Chemical Papers, 2010

The impact of pH and washing procedure on calcium and magnesium distribution between pulp and filtrate in pulp processing was investigated. Depending on media pH, the elements are present in the form of ions (Ca 2+ , Mg 2+ ) and hydrated oxides (Ca(OH)2, Mg(OH)2). Distribution was monitored using binary systems of CaCl2 and MgCl2 dissolved in deionized water or Ca 2+ and Mg 2+ ions present in filtrates from an industrial pulp mill. Complying with the relevant standards in force, Ca and Mg contents are expressed as CaO and MgO. The study was aimed at obtaining mathematic relations between pH and calcium and magnesium, as two important non-process elements, sorption on pulp. Distribution of the elements between pulp and liquid (filtrate or water) was determined with analytical procedures and simulation of pulp washing. It was found that both pH and filtrate composition influenced sorption/desorption of the elements on/from pulp. Filtrate from a pulp mill, mainly content of organic substances in liquid phase, affects their sorption on pulp and desorption to liquid. The higher the pH value the more efficient the sorption of the elements, magnesium being sorbed on pulp in higher amounts than calcium. Prevalence of the sorbed magnesium is preserved even at lower concentrations of both elements. Distribution of the elements between pulp and solution is expressed through mathematic relations which, in turn, can be employed to purposefully modify or optimize the distribution between the solid (pulp) and liquid (filtrate) media. Moreover, rationalized exploitation of mathematical relations enables balancing the elements within a cellulose manufacture, regulating media recycling, and predicting an eventual impact on technological processes.

Ion exchange equilibrium between ion exchange membrane and electrolyte solutions

Desalination, 2008

The ion exchange equilibrium between an ion exchange membrane and solutions of different electrolytes was studied. The matrix of the ion exchange membrane used consists of a vinyl polychloride network reinforced by a polyester screen; with quaternary and tertiary ammonium as functional groups. The data, provided by manufacturer, were completed by the experimental determinations of humidity percentage and ion exchange capacity.

Fundamental Principles and Concepts of Ion Exchange

2016

This chapter provides a basic understanding of the ion exchange process, ion exchangers, and the terminology associated with the process and its design. A rigorous theory associated with the ion exchange process is absent. The authors recommend Helfferich's Ion Exchange (1962) and Weber's Physicochemical Processes for Water Quality Control (1972) to provide a strong theoretical background. The major manufacturers have developed models to predict performance. Readers are directed to Dow Water & Process Solutions' Computer Assisted Design for Ion Exchange (CADIX), an ion exchange software program developed to aid in the design of softener and demineralization systems. Purolite Pure Design TM ion exchange simulator program is aimed at the engineer to aid in the design of water-related exchange systems for boron removal, softening, and dealkalization. Programs are also offered by Lenntech and LanXess. This chapter provides the basic knowledge of the fundamental concepts to better enable the engineer to use the programs.

Pretreatment of softwood dissolving pulp with ionic liquids

Few Scandinavian pulp mills produce dissolving pulps; however , the demand on textile fi bers is increasing. This study investigates the chemical interaction of dissolving pulp with ionic liquids (ILs), where softwood and hardwood industrial dissolving pulps were pretreated with ILs 1-butyl-3-methyl-imidazolium acetate ([C 4 mim + ]CH 3 COO-) and 1-butyl-3-methyl-imdazolium chloride ([C 4 mim + ]Cl-). Time and temperature dependence of the dissolution process as well as the impact of the pretreatment on the molecular weight properties , thermal stability, morphology, and crystallinity of the cellulose were evaluated by means of size exclusion chromatography (SEC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), and solid state nuclear magnetic resonance (NMR). It was shown that the dissolution of cellulosic material in ILs is a temperature-dependent process; however, the viscosity of ILs affected the effi ciency of dissolution at a given temperature. Molecular weight properties were affected negatively by increased dissolution temperature, while the type of antisol-vent for the regeneration had no major impact on the degree of polymerization of cellulose. Water was more effi cient than ethanol for the regeneration of cellulose when performed at an elevated temperature. The pretreatment decreased the crystal-linity of cellulosic material. This might lead to the increased accessibility and reactivity of cellulose.

Ion exchange processes in aqueous-organic media

Analytical Chemistry, 1969

Alkali metal ion exchange on Bio-Rad AG 50W X-1 resin in 0, 5, 10, 25, 50, 75, and 90% methanol-water, ethanolwater, and dioxane-water and alkali metal barium ion exchange in acetic acid-water systems were investigated at 25 OC. In part, observed changes in selectivity coefficient with solvent changes can be explained on the basis of dielectric constant effects on coulombic interactions, but the observed maxima or minima and changes in order of selectivity as the water content of the solvent is decreased can be accounted for by the electrostatic model only if it is assumed that ion solvation also changes in an appropriate manner. Some correlation between selectivity data and swelling data was noted. Radiotracer techniques were used to determine alkali metal exchange coefficients and gravimetric techniques for exchanges involving barium. From the solvent distribution data, there appeared to be no selective solvation of the resin phase.

A New Model for the Simulation of Ion Exchange Equilibria

Industrial & Engineering Chemistry Research, 1995

A model based on the mass action law for the prediction of multicomponent ion exchange equilibria is developed by assuming ideal behavior for both the solution and the solid phase, and the existence of a distribution of functional groups with different adsorption energies (and then equilibrium constants). The reliability of the model, which is characterized by two parameters for each binary system, is tested by comparison with a remarkably large set of literature experimental data. It is shown that ion exchange equilibria in systems involving a total number of N , counterions can be predicted from the knowledge of the experimental behavior of only (N,-1) binary systems, thus in agreement with the so-called triangle rule. This greatly reduces the experimental and modeling effort needed to develop a multicomponent model with respect to other approaches which require the investigation of all possible pairs of counterions present in the system, i.e., N&N,-1)/2 binary systems.