Carboxymethyl cellulose (CMC) is produced commercially in a two stage process consisting of a mercerization stage in which the pulp is treated with alkali in a water alcohol solution and a second etherification stage whereby monochloro-acetic acid is added to the pulp slurry. In this study, the influence of the conditions of an extended mercerization stage was evaluated on the etherification stage concerning the degree of substitution (DS) and the filterability of the resulting CMC. The parameters studied were: (1) the ratio of cellulose I and cellulose II in the original pulp, (2) the concentration of alkali, (3) the temperature and (4) the retention time in the mercerization stage. The DS results indicate that the NaOH concentration in the mercerization stage is the most important among the parameters studied. When the NaOH concentration in the mercerization stage was high (27.5%), cellulose II showed a lower reactivity than cellulose I with respect to the DS obtained in the resulting CMC. The results from the filtration ability of CMC water solutions are interpreted that the amount of cellulose II in the original pulp and the temperature has a negative influence, while the NaOH concentration in the mercerization stage has a positive influence on the filtration ability. Retention time between 1 h–48 h in the mercerization stage had no effect on the DS or the filtration value. The filtration ability was assumed to be highly influenced by the presence of poorly reacted cellulose segments. The CMC samples with the lowest filtration ability at a given DS can be assumed to have the highest degree of unevenly substituted segments.
It has been demonstrated in previous studies that dissolved lignin carryover has a significant impact in oxygen delignification and chlorine dioxide stages. Specifically for chlorine dioxide stages, it has been shown that the total kappa number of the pulp, i.e. the sum of the fiber kappa number and the filtrate kappa number, corresponds very well to its bleach demand and should be used for accurate feedforward based control. Since peroxide also is commonly used for pulp bleaching, and gaining in popularity, the present study was conducted in order to investigate the basic relations and mechanisms, using laboratory peroxide bleaching experiments comparing different carryover lignin concentrations and types. The results show that in particular chlorine dioxide filtrates have significant negative impact on delignification and brightening, likely due to alkali consumption of e.g. dissolved lignin, and that compensation using a higher alkali charge will result in lower brightness at a given kappa number. The paper also touches upon the opportunities using advanced process control systems for bleach plants, and the process and economic improvements which can be made by properly accounting for disturbances such as carryover variability.
Kraft and sulfite pulp mills use several consecutive process stages for pulp production. However, usually only one key pulp parameter is used for process control and that is the lignin content in the fibers, typically expressed as the kappa number. Even so, to improve process efficiency, more variables need to be monitored. To do that, a new sensor was developed, the dissolved lignin transmitter (DLT), along with a new control concept. The DLT measures the dissolved lignin content in the pulp slurry using a unique principle based on optical measurements. The device can measure the dissolved lignin inline at low consistency and at medium consistency. The sensor has two major applications: 1) improving the efficiency in washing stages and 2) optimizing chemical charges. Results from several mill trials have shown that the contribution from dissolved lignin in the filtrate portion of the pulp is up to 30% of the total bleach load, i.e., fiber and filtrate kappa number combined into the bleach plant. Hence, chemical savings can be achieved taking this component into account compared to only measuring the washed fiber kappa number. Application: The results of this study can help mills understand how to better control the pulping stages, which might lead to significant economic savings and better pollution control.
Sulfite pulping of wood, with the aim of producing a paper product, can be carried out under acidic, neutral or alkaline conditions. However, if a dissolving pulp is required to be achieved, only acidic conditions may be employed. The main reason for this specific requirement for dissolving pulps is the high level of cellulose purity required. The hemicellulose content should therefore be low and hemicellulose molecules are best removed at low pH. Another difference is that in paper pulps it is the fibre properties that are of a dominant interest, while in a dissolving pulp the cellulose properties are of significant interest. However, one similarity for both paper and dissolving sulfite pulps is the risk of uncontrolled side-reactions, which can lead to severe lignin condensation reactions, and in extreme cases even to a totally black pulp. Thus, sulfite pulping is a relatively complex chemical process and an overview of the most important parameters is thus presented.
Sulfite cooking was earlier the dominating pulping process but sulfate (kraft) cooking is today the most important process for the production of chemical pulps and high-yield pulps. One important reason for this development of the sulfate process is its ability to efficiently use different wood species, in particular different hardwood species. Another reason is that bleached hardwood sulfate pulps have become a strong competitor to bleached softwood sulfite pulps. The pros and cons of sulfate cooking are discussed in this report and compared with sulfite cooking.
he aim of this study was to determine how oxygen delignification before bleaching and the hexenuronic acid (HexA) content of the pulps influenced the acisorbable organic halogen (AOX) formation in the elemental chlorine free (ECP) bleaching effluent. Softwood industrial chips cooked to different kappa numbers were oxygen defignified, treated in a hot acid stage (A*), or not pretreated at all before ECF bleaching. We compared the AOX levels in the ECF effluents from bleaching of these pulps. There was a higher formation of AOX for oxygen delignified pulps than for non-oxygen delignified pulps compared at the same kappa number before ECF bleaching. The hexenuronic acid (HexA) content of the pulps had a major impact on the AOX levels in the D[0] effluent. The oxygen delignified pulps had a higher HexA content than the non-oxygen delignified pulps compared at the same kappa number. This explains the higher AOX formation from oxygen delignified pulps. The AOX originating from HexA was not stable upon storage. Application, This study gives additional insight on the AOX formation in ECF bleaching. The information may be used to take appropriate measures when addressing environmental issues
The strength of the adhesion between the paper and the drying Yankee cylinder is of great importance with respect to the final properties of a tissue paper product. Therefore, the effects of a few potentially important pulp properties have been evaluated in laboratory experiments. Four highly different kraft pulps were used, and the adhesion strength was measured by means of the force required when scraping off a paper from a metal surface with a specifically designed knife mounted on a moving cart. The adhesion strength was observed to increase with increasing grammage and increasing degree of beating of the pulp. It was also found that pulpscontainingmore fines, or with higher hemicellulose content, gave rise to higher adhesion strength.
The compression ability of fibres and fibre networks were investigated. The surface and bulk compressions of paper influence calendering, coating, surface sizing ability and the penetration of ink in printing. Two kraft pulps (spruce) were produced in the laboratory to obtain pulps with different levels of xylan. Using those kraft pulps alone or mixed with 50% of a commercial TMP pulp, single-layer sheets were formed in a Formette Dynamique sheet former. The pulps and mixture levels were chosen to obtain papers with systematically altered property variation but with constant grammage. The papers were characterized according to both bulk and surface compressibility. The papers were printed in a flexo IGTF1 laboratory printing press and the transferred amount of ink, dot gain, and mottling were analyzed.
The surface and bulk compressibility of a given paper influence its calendering, coating, surface sizing and printing properties. This study aims at a deeper knowledge of which variable affects the compressibility of paper sheets and how calendering effect different sheet properties. The pulps were characterized by their chemical compositions and physical properties. The bulk compressibility, the surface compressibility and the thickness were evaluated both before and after calendering
Single stage sodium bisulfite cooking of pine was carried out to investigate the influence of time and temperature in the initial phase of the cook. The cooking experiments were carried out using either a lab or a mill prepared cooking acid and the initial stage of the cook was extended up to 5 h cooking time. The impact of temperature on wood components and side reactions was analyzed between 142°C and 165°C. Arrhenius equation was used to determine the influence of temperature on wood components during the initial phase of bisulfite cooking and the activation energy was calculated for delignification rate, cellulose degradation and hemicellulose dissolution with regard to glucomannan and xylan. The extent of extractives removal at different temperature and time was also analyzed.
Karlstads University has for a long time done research on sulfite pulping with the purpose to increase the knowledge on sulfite pulping, to verify old fundamental results an to keep the knowledge on sulfite pulping alive. The basic objective during the last years has been to increase the value of the products produced in such a process and the vision is to make sulfite pulps the preferred pulp grade for dissolving pulps. These studies have so far included spruce and pine. Domsjö Fabriker and MoRe Research in Örnsköldsvik, Sweden have been industry partners in this project.
Sulfite pulping of pine is well-known to be a risky process because problematic lignin conden-sation reactions can occur resulting in poor pulp quality. However, sulfite pulping of pine is interesting of economic reasons as pine wood is cheaper than spruce. Therefore it has become interesting to investigate sulfite pulping again to determine if old data are still valid. Thus sodium bisulfite pulping of pine was carried out to investigate the influence of time, temperature and cooking acid quality. A small comparison of spruce pulping was also included. By using different cooking temperatures the activation energies for delignification and for degradation of cellulose and hemicelluloses could be determined. The results showed no lignin condensation reactions, thus it was not problematic to carry out these pine cooking experiments. It was found that glucomannan had higher activation energy than xylan and the activation energies of these hemicelluloses were lower than the corresponding value for the lignin degradation. It was found that the activation energy for bisulfite pulping of pine was slightly lower than the activation energy for bisulfite pulping of spruce.
Single stage sodium bisulfite cooking of pine was carried out to study the initial phase of the bisulfite cook and the experiments were carried out using either a lab or a mill prepared cooking acid. The chemical consumption, the pH profile and the pulp yield with respect to cellulose, lignin, glucomannan, xylan and extractives were investigated. The pulp composition with respect to carbohydrates and lignin content was summarized in a kinetic model. The initial phase of the bisulfite cook was extended to 5 h cooking time down to a final pulp yield of about 60 %. The side reactions with respect to thiosulfate and sulfate formation were investigated continuously in all experiments. The cooking temperature used in these experiments was 154 °C.
A PhD project was started in 2012 with the purpose to in depth examine the first and second part of a sodium sulfite dissolving pulp cook including a following extraction stage. The experimental study started with the first part of the cook when using spruce or pine as the wood raw material and when using lab or mill cooking liquors. A large number of cooking experiments have been performed and a lot of data has been obtained and the risk for obtaining a black cook has been especially observed. In the latter case the thiosulphate content is very critical as it can both lead to a black cook and to decomposition reactions in the cooking liquor. How to avoid problematic cooking conditions will be especially highlighted in the project but ways to produce new pulp grades and new chemicals will be equally important