Henrik Grénman

Obtaining Spruce Hemicelluloses of Desired Molar Mass by using Pressurized Hot Water Extraction

There is growing interest in utilizing galactoglucomannan, the main hemicellulose in softwoods, for various applications such as cosmetics, pharmaceuticals, textiles, alimentary, and health products, as well as for the production of fuels. For fuel production and for using the rare sugars as platform chemicals, the hemicelluloses need to be hydrolyzed to sugar monomers, and for this purpose, low-molecular-mass extracts are favorable. However, for the other applications high molecular masses are required, which presents an even greater challenge for extraction. The ability to optimize the extraction process according to the needs of further processing, by using solely water as the solvent, is a key issue in the environmentally friendly utilization of this versatile raw material. The goal of this work is to study how the average molar mass of hemicelluloses extracted from spruce sapwood can be influenced by altering the experimental conditions. The main parameters influencing the extraction and hydrolysis of the hemicelluloses, namely, extraction time, temperature, pH, and chip size, were studied. The results show that it is feasible to develop an extraction process for harvesting spruce hemicelluloses, also of large molar masses, for industrial applications by using pressurized hot water extraction.

Development of nanocellulose scaffolds with tunable structures to support 3D cell culture

Swollen three-dimensional nanocellulose films and their resultant aerogels were prepared as scaffolds towards tissue engineering application. The nanocellulose hydrogels with various swelling degree (up to 500 times) and the resultant aerogels with desired porosity (porosity up to 99.7% and specific surface area up to 308m(2)/g) were prepared by tuning the nanocellulose charge density, the swelling media conditions, and the material processing approach. Representative cell-based assays were applied to assess the material biocompatibility and efficacy of the human extracellular matrix (ECM)-mimicking nanocellulose scaffolds. The effects of charge density and porosity of the scaffolds on the biological tests were investigated for the first time. The results reveal that the nanocellulose scaffolds could promote the survival and proliferation of tumor cells, and enhance the transfection of exogenous DNA into the cells. These results suggest the usefulness of the nanocellulose-based matrices in supporting crucial cellular processes during cell growth and proliferation.

Aqueous extraction of hemicelluloses from spruce – From hot to warm

Aqueous extraction of hemicelluloses from spruce sapwood was performed at 90°C and 110°C. One of the main goals was to study if the same reaction mechanisms are valid at low temperatures as the ones observed previously at higher temperatures. An intensified cascade reactor system with a high liquid-solid ratio (∼ 180) was used in the experiments. Differences between the sugar specific extraction rates were observed especially in the beginning of the extraction processes. The experimental results fitted well to a kinetic model developed at higher temperatures, which confirms that the dissolution occurs with the same mechanisms at low temperature. Moreover, the correlation of the pH with the amount of sugars dissolved concurred with previous observations. The results contradict the assumption that low temperature dissolution would not occur and they help in studying the early stages of extraction as the kinetics are considerably slowed down.

Acid hydrolysis of O-acetyl-galactoglucomannan in a continuous tube reactor: a new approach to sugar monomer production

Abstract Hemicellulose O-acetyl-galactoglucomannan (GGM) is the main noncellulosic water-soluble polysaccharide in the coniferous softwood Norway spruce, consisting of anhydro-galactose, -glucose, and -mannose. Acid hydrolysis of GGM has been studied in a continuous tube reactor to obtain these sugars under industrially relevant conditions. The reaction was performed under atmospheric pressure at 90°C and 95°C, and hydrochloric acid (HCl) served as catalyst. The influence of the reaction parameters, such as acid concentration (pH), temperature, concentration of the substrate, as well as catalyst and reactant flow rates, has been studied on the conversion efficiency and product distribution. Continuous production of monomeric sugars was achieved without formation of low-molecular by-products. The GGM conversion was high with HCl as catalyst, at 95°C, and a pH of 0.3. The main hydrolysis products were mannose, glucose, and galactose monomers. Minor amounts of sugar dimers were detected among the products. The experimental results are described with a laminar flow model for the continuous reactor.

Solid-liquid reaction kinetics - experimental aspects and model development

Abstract Solid-liquid reactions are commonly encountered in industry as well as every day life. Vast amounts of the applied bulk and specialty chemicals are produced employing solid-liquid reactions. The knowledge of the kinetics is crucial for the design and development of these processes. Quantitative modeling of reactive solids behavior in liquids is a big challenge. The reaction mechanism can be a very complex one, often comprising several unknown elementary steps. The structure and structural changes of the solid material are also often difficult to determine. Kinetics and mass transfer effects are coupled; to determine the intrinsic kinetics, the experiments should be free from mass transfer limitations. External mass transfer resistance can be suppressed by creating strong enough turbulent effects around the solid particles, but internal mass transfer effects can be present for porous particles. Due to these facts, modeling of dissolution reactions is often simplified. Even though such simplifications are necessary, a more in-depth investigation of the related phenomena combined with quantitative studies and more thorough modeling brings new understanding and precision to process development and optimization. Several example cases of solid-liquid reactions were chosen for this work, based on their industrial relevance and varying nature. Moreover, different experimental cases were studied to illustrate a basis for the theoretical development. Two of the cases are organic reactions, while the rest are inorganic ones. The objective of the current review is to exemplify challenges related to studying solid-liquid reactions and how these challenges can be overcome. This is done through the nine example cases, which serve as good examples of the various difficulties often encountered. The published articles serve as a convenient route for finding more detailed information on the topic. Based on the literature evaluation and the experience gained in the present work, theoretical development was made based on physico-chemical fundamentals. The main advances of the current work are in the quantitative modeling of a solid phase during its reaction with a liquid. This includes the dynamic and flexible implementation of the surface morphology and particle size distribution, as well as the reaction mechanism into an overall kinetic model, in which the internal and external mass transfer phenomena are taken into account. This helps in model development and discrimination between rival models, as well as in the interpretation of curiosities in kinetic models which can be found in literature.

Kinetic and Theoretical Investigation of Iron(III)‐Catalyzed Silane Chlorination

A highly versatile, robust, and efficient methodology for chlorination of silanes, methoxysilanes and silanols using low loadings of FeCl3 or Fe(acac)3 as the catalyst in the presence of 1–1.5 equivalents of acetyl chloride as the chlorine source was recently developed. The aim of the present paper is to evaluate and derive the reaction mechanisms involved in this reaction by calculating substrates, intermediates, products, and selected transition states, as well as by employing mathematical modeling of the reaction kinetics. The results obtained required reconsideration of the originally proposed overall reaction mechanism. Based on the kinetic and molecular modeling, a new revised reaction mechanism was developed giving a very good correspondence between the experimental data and calculations.

Limestone dissolution study for Wet Flue Gas Desulfurization under turbulent regimes above critical suspension speed

Abstract Anthropogenic sulfur dioxide (SO 2 ) is principally the product of energy conversion through combustion of fossil fuel sources. This pollutant causes acidic rain and can also be harmful for human health. Many means for controlling sulfur dioxide emission are available in the market and have been extensively applied. Among these techniques, wet flue gas desulfurization is one of the most widely used methods because of its reliability and high efficiency. Nonetheless, high energy and water consumption are among its principal drawbacks. Limestone dissolution has been accounted as one of the main controlling steps of the process ( Pepe, 2001 ). Even though limestone is dissolved in acidic media in many industrial processes worldwide, no commonly accepted mathematical models exist for the dissolution kinetics at the moment. The reasons for the contradictory results in literature dwell, at least to considerable extent, from the varying influence of mass transfer limitations and the influence of CO 2 on the pH . Experimental equipment and a methodology for evaluating the kinetic regime of a high grade limestone commercially used for desulfurization was developed in the current study. The results show that the kinetic regime, necessary to properly characterize the dissolution rate, can be reached even with small particle size and high temperatures with the help of severe agitation to overcome solid-liquid mass transfer and powerful purging to minimize the influence of carbonic acid on the pH . The method can be directly applied for investigating and comparing the reactivities of various limestone samples for industrial purposes.