Hans Theliander

Nanoreinforced xylan–cellulose composite foams by freeze-casting

Structured biofoams have been prepared from the readily available renewable biopolymer xylan by employing an ice-templating technique, where the pore morphology of the material can be controlled by the solidification conditions and the molecular structure of the polysaccharide. Furthermore, reinforcement of these biodegradable foams using cellulose nanocrystals shows potential for strongly improved mechanical properties.

Determination of local filtration properties at constant pressure

Abstract The present work includes experimental and theoretical studies of the characterization of filter cakes. A filter test apparatus, in which the local pressure profile can be determined during the build up of the filter cake was developed. Efforts were made to minimize the influence of settling and the so called wall-effects related to the pressure measurements. Also a method to calculate local filtration properties (specific filtration resistance and porosity) was developed. In the method, conventional empirical equations describing the relation between the local filtration properties and the local pressure were used. The basic idea is to direct the calculation in such a way that the obtained numerical values of the parameters in the empirical equations reflects the local conditions. The developed method was found to be superior compared to a method where only average data on the filtration properties was used to calculate the corresponding parameters. Finally, the method was found to be stable as well as reliable.

Ice templated and cross-linked xylan/nanocrystalline cellulose hydrogels

Structured xylan-based hydrogels, reinforced with cellulose nanocrystals (CNCs), have successfully been prepared from water suspensions by cross-linking during freeze-casting. In order to induce cross-linking during the solidification/sublimation operation, xylan was first oxidized using sodium periodate to introduce dialdehydes. The oxidized xylan was then mixed with CNCs after which the suspension was frozen unidirectionally in order to control the ice crystal formation and by that the pore morphology of the material. Finally the ice crystal templates were removed by freeze-drying. During the freeze-casting process hemiacetal bonds are formed between the aldehyde groups and hydroxyl groups, either on other xylan molecules or on CNCs, which cross-links the system. The proposed cross-linking reaction was confirmed by using cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy. The pore morphology of the obtained materials was analyzed by scanning electron microscopy (SEM). The materials were also tested for compressive strength properties, both in dry and water swollen state. All together this study describes a novel combined freeze-casting/cross-linking process which enables fabrication of nanoreinforced biopolymer-based hydrogels with controlled porosity and 3-D architecture.

Simulation of the build-up of a filter cake

Abstract The aim of this work was to develop a computer prigram describing the build-up of a filter cake. The program is based on a model presented by Wakeman in 1981, but which has been modified slightly. The program developed here can be used to compute the cake height, the pressure profile and the local specific filtration resistance. The calculated result from this program was compared with experimental data (local pressure, cake height and semi-local specific filtration resistance). It was found that there was exvellent agreement between the calculated and measured local pressures. Furthermore, the cake height can be estimated with a high level of confidence. The calculated specific filtration resistance was in the same order of magnitude as the measured data. However, the model underestimates the resistance in the region closest to the filter cloth, and overestimates the resistance in the region closest to the surface of the filter cake.

The effect of temperature on the catalytic conversion of Kraft lignin using near-critical water

The catalytic conversion of suspended LignoBoost Kraft lignin was performed in near-critical water using ZrO2/K2CO3 as the catalytic system and phenol as the co-solvent and char suppressing agent. The reaction temperature was varied from 290 to 370°C and its effect on the process was investigated in a continuous flow (1kg/h). The yields of water-soluble organics (WSO), bio-oil and char (dry lignin basis) were in the ranges of 5-11%, 69-87% and 16-22%, respectively. The bio-oil, being partially deoxygenated, exhibited higher carbon content and heat value, but lower sulphur content than lignin. The main 1-ring aromatics (in WSO and diethylether-soluble bio-oil) were anisoles, alkylphenols, catechols and guaiacols. The results show that increasing temperature increases the yield of 1-ring aromatics remarkably, while it increases the formation of char moderately. An increase in the yields of anisoles, alkylphenols and catechols, together with a decrease in the yield of guaiacols, was also observed.

Investigation and Characterization of Lignin Precipitation in the LignoBoost Process

Abstract Lignin of high purity can be separated from black liquor using the LignoBoost process, of which the overall efficiency is largely dependent on the precipitation yield of lignin, which depends on the properties of black liquor and process conditions. In this paper, the influences of process conditions on the precipitation yield of lignin from mixed hardwood/softwood black liquor were investigated. The Klason and standard UV method were used to determine lignin concentration. The chemical and structural properties of lignin were also analyzed. The results showed that the precipitation yield of lignin increased along with a decrease in pH and temperature, or with an increase in the ion strength of black liquor, and the yield was lower when mixed softwood/hardwood black liquor was used. It also showed that at a higher precipitation yield the precipitated lignin had a lower average molecular weight but had higher methoxyl and phenolic hydroxyl content.

On the Measurement and Evaluation of Pressure and Solidosity in Filtration

New test filtration equipment has been constructed that makes simultaneous measurement of local solid compressive pressure and local solidosity possible. Four materials were used to evaluate the new equipment. In this equipment the solidosity was measured with resolution of 1 mm in height (i.e. in the direction of the liquid flow). The experimental error was estimated to be 0.005–0.04 m 3 m −3 , depending on the properties of the slurry. Constitutive relationships for solidosity, permeability and specific filtration resistance were estimated and an overall good fit was obtained. Furthermore, it was found that the average specific filtration resistance based on the classical filtration equation could differ by as much as 20% compared to corresponding values based on local measurements.

Precipitation and filtration of lignin from black liquor of different origin

The separation of lignin from black liquor is an attractive option in the pulp mill. Lignin extraction provides a modern mill with the opportunity of removing an energy surplus in the form of a solid biofuel. In pulp mills where pulp production is limited by the capacity of the recovery boiler introducing lignin separation can “de-bottleneck” the process and thus allow an increase in production. A well-known method for separating lignin from black liquor is precipitation by acidification. After precipitation, the lignin is filtered and further purified. The filtration properties of lignin precipitated from one single kraft black liquor was studied in a previous investigation. The present work expands that study to embrace several other black liquors of different types. It is shown here that the filtration properties, measured by the average specific filtration resistance, differ between black liquors. Black liquors that were concentrated using a membrane prior to precipitation were more difficult to filter than those taken directly from the evaporator train. Subjecting the black liquor to heat treatment before precipitation, however, improved filtration properties. In addition, black liquors, lignin filter cakes and filtrates were chemically characterized so that possible differences in organic composition could be detected.

A novel method for washing lignin precipitated from kraft black liquor - Laboratory trials

A previous study on the washing of lignin precipitated from kraft black liquor encountered problems with complete or partial plugging of the filter cake and/or filter media that resulted in uneven washing and high sodium contents in the final lignin product. This effect was ascribed to large gradients in pH and ionic strength during the washing process. This paper presents an improved method that aims at solving these problems by reducing pH and ionic strength gradients through the introduction of a re-suspension stage before the final washing. Laboratory results indicate successful washing with sodium contents of the lignin well below the requirements for the intended use as a biofuel. No plugging problems were encountered when the pH was below 3.75. An additional important positive effect was a net yield gain in precipitated lignin over the process.

Recycling of Solid Residues to the Forest: Experimental and Theoretical Study of the Release of Sodium from Lime Mud and Green Liquor Dregs Aggregates

In order to optimize the recycling of solid residues back to the forest, it is necessary to measure and characterize the dissolution rate of the product under well-defined conditions. In this study, inorganic solid residues from a kraft pulp mill were characterized physically and chemically. The effect of pH, as well as physical characteristics and chemical composition, on the leaching rate was investigated. It was shown that the leaching behaviour differed depending on the production method of the aggregates. A model based on mass transfer was fitted to the experimental leaching data. It was shown that the leaching rate for the easily soluble species was reasonably well described using the concentration gradient of these species within the pellet. It was also shown that mass transfer within and from the pellet/granule was the rate-determining step.