Bjarne Holmbom

Recent Progress in Synthesis of Fine and Specialty Chemicals from Wood and Other Biomass by Heterogeneous Catalytic Processes

Synthesis of fine and specialty chemicals involving heterogeneous catalysts is discussed according to the type of reactions (e.g., hydrogenation, oxidation, isomerization, etc.) for various biomass derived feedstocks (carbohydrates, lignans, phenols, flavonoids, tannins, and stilbenes, tall oil, and fatty acids).

Determination of the strong mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone in chlorinated drinking and humic waters☆

The strong Ames test mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2-(5H)-furanone (MX) was found to occur in chlorinated drinking and humic waters in sub μg L−1 concentrations. Quantitation by GC/MS using Selective Ion Monitoring in parallel with Ames tests of waters indicated that this furanone accounted for 15 – 30% of the Ames test mutagenicity of both a drinking water and a humic water.

Polysaccharides in some industrially important hardwood species

The amount and composition of sugar units comprising polysaccharides in sapwood and heartwood, or stemwood, of 11 industrially important pulpwood species were analysed. The polysaccharide content was between 60 and 80% (w/w) for all species, with cellulose as the predominant polysaccharide type and glucuronoxylans as the main non-cellulosic polysaccharides. The second most abundant non-cellulosic polysaccharides were either pectins, i.e. polygalacturonic acids, or glucomannans. The amount of acidic sugar units were 15–23% of the total amount of non-cellulosic sugar units in all samples, with the Acacia species in the high end. The amount and composition of water-soluble carbohydrates from ground wood samples were also analysed, since these are important in mechanical and chemimechanical pulping, and as a possible source of bioactive polymers. Sapwood released more carbohydrates than heartwood for most species. It is to be noted that the relative amount of dissolved acidic sugar units was larger from the heartwood than from the sapwood for all species. Probably due to the mild treatment conditions, the main dissolved polysaccharides were xylans only for a few samples, while easily soluble galactans, arabinogalactans, or mannans dominated in most species. Pectins dominated in heartwood of Populus grandidentata. Generally, pectins and acidic xylans were the main acidic polysaccharides.

Chemical composition of earlywood and latewood in Norway spruce heartwood, sapwood and transition zone wood

This study focused on the distribution of wood components along a cross section of a spruce stem. Thin samples of earlywood and latewood were analysed by special micro-scale analytical techniques. Heartwood contained significantly more lignin and less cellulose than sapwood. The total content of hemicelluloses was the same along the radial direction, but the distribution of sugar units differed. The amounts of arabinoglucuronoxylan and pectins were larger in the heartwood. The transition zone between heartwood and sapwood had a specific composition, with less lignin and lipophilic extractives than heartwood and sapwood. For earlywood and latewood, significant differences were found in the distribution of sugar units in hemicelluloses. Latewood contained clearly more galactoglucomannan than earlywood, and conversely less pectins. The lipophilic extractives were also less concentrated in the latewood.

Lignans and lipophilic extractives in Norway spruce knots and stemwood

Summary The hydrophilic and lipophilic extractives in the heartwood of knots from 7 Norway spruce trees were analysed by GC, GC-MS and HPSEC. The knots contained extremely large amounts of lignans, 6–24% (w/w), with hydroxymatairesinol comprising 65–85% of the lignans. Even the knots of the young trees contained 4–8% (w/w) of lignans. The variation in the amount of lignans was large among knots, both within a single tree and between trees. In addition to the lignans, knots also contained 2–6% (w/w) of a complex mixture of lignan-like compounds with 3, 4 and even up to 6 phenyl propane units, here called oligolignans. The amounts of lignans in the knots were similar in the radial direction from the pith into the outer branch, but decreased dramatically outwards in the branch, almost disappearing after 10–20 cm. The ratio of the 2 epimers of hydroxymatairesinol differed between different knots and even within the knot. A new spruce lignan, nortrachelogenin, or its enantiomer, wikstromol, was detected in knots from trees in northern Finland as opposed to samples from southern Finland. The amount of lipophilic extractives was small compared to the amount of hydrophilic extractives in the knots. Five of the dead knots contained more resin acids and free diterpenyl alcohols than ordinary stemwood. In the other knots, the amount of lipophilic extractives was on the same level as stem heartwood. The stem sapwood contained larger amounts of esterified fatty acids than the knots.

Identification and quantification of the Ames mutagenic compound 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone and of its geometric isomer (E)-2-chloro-3-(dichloromethyl)-4-oxobutenoic acid in chlorine-treated humic water and drinking water extracts.

Mutagenic compounds in XAD extracts of chlorinated humic water were separated in two stages of fractionation by reversed-phase high-performance liquid chromatography. Analyses of mutagenic fractions by gas chromatography/mass spectroscopy resulted in the identification of the strong Ames mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) and its geometric isomer (E)-2-chloro-3-(dichloromethyl)-4-oxobutenoic acid (E-MX). Both compounds were also detected in extracts of chlorinated drinking waters. MX accounted for 50-100% of the activity of extracts of chlorinated humic water and for 20-50% of the activity of extracts of drinking water. E-MX exhibited at most one-tenth of the MX mutagenicity and accounted for 2% or less of the activity of the extracts of drinking water. However, because of the poor reproducibility of E-MX mutagenicity tests and the ability of the compound to isomerize the MX, there is uncertainty about the significance of E-MX in chlorinated waters.

Knotwood and bark extracts: strong antioxidants from waste materials

The antioxidant properties of hydrophilic extracts of knotwood of several industrially important tree species were evaluated by lipid-peroxidation inhibition and peroxyl-trapping capacity tests. The results were compared with the antioxidant properties of hydrophilic extracts of bark, and pure lignans and flavonoids isolated from knotwood extracts. The knot extracts from several tree species were stronger antioxidants than the bark extracts, which can, however, also be classified as strong antioxidants. In addition, the antioxidant properties of most of the knotwood extracts are stronger than the pure compounds. It is concluded that knotwood is a rich source of natural antioxidants.

Extraction of galactoglucomannan from spruce wood with pressurised hot water

Abstract Sapwood chips and ground wood of spruce have been extracted with pressurised pure water in an accelerated solvent extractor at temperatures from 100 to 180°C. The water extracts were freeze-dried, weighed, and analysed for carbohydrates by acid methanolysis followed by GC determination of monomeric sugars. Lignin was determined by measuring UV absorption and acetyl groups by HPLC after alkaline hydrolysis. Average molar masses of hemicelluloses in water extracts were determined by HPSEC-MALLS after filtration. Typically, approximately 70% of the total weighed extracts were composed of carbohydrates derived from hemicelluloses. Approximately 75% of the extracted carbohydrates were from galactoglucomannan (GGM). Other extracted substances were xylans, arabinogalactans, lignin and acetic acid. As much as 80–90% of the GGM in the wood, i.e., approximately 15% based on the original wood, was extracted from ground wood at 170–180°C for an extraction time of 1 h. The yields from chips were lower: approximately 60% from that of ground wood. The hemicelluloses were partly hydrolysed during the extractions at 160–180°C. Xylans and arabinogalactans were hydrolysed to a higher extent than GGM. Acetyl groups in GGM were also partly hydrolysed, which resulted in lower GGM solubility. A key factor for achieving a high yield of high-molar mass GGM is an optimised pH profile in order to minimise hydrolysis of acetyl groups and hydrolytic cleavage of GGM chains.

Ultrasound enhancement of cellulose processing in ionic liquids: from dissolution towards functionalization

The ionic liquids 1-allyl-3-methylimidazoliumchloride[Amim][Cl] and 1-butyl-3-methylimidazoliumchloride[Bmim][Cl] were utilized in the dissolution of different natural cellulose biopolymers. The biopolymers subject to this investigation were microcrystalline cellulose, cotton linters as well as Kraft cellulose cut to 0.35 mm fibres. High-intensity acoustic irradiation by means of an ultrasonic horn was applied to enhance the dissolution process. The ionic liquids investigated were able to dissolve cellulose at elevated temperatures, in high concentrations, although significant differences were observed, depending on the type of cellulose and ionic liquid. Moreover, the dissolution process under conventional heating was rather slow, typically extending for a period of several hours. Upon use of high-power ultrasound, the dissolution process was dramatically intensified and complete dissolution was achieved in a matter of few minutes only. Various approaches to cellulose functionalization were proposed and investigated. The effect of external parameters, such as the reaction temperature, the cellulose–derivatising agent molar ratio and the batch time of experiment were studied. Various physico-chemical methods, such as acid methanolysis, TGA, DSC, SEM as well as NMR on 1H and 13C nuclei were applied to investigate the structure and morphology of both the cellulose samples and ionic liquids before and after processing.

Knots in trees - A new rich source of lignans

Recent research in our group has revealed that knots, i.e. the branch bases inside tree stems, commonly contain 5–10% (w/w) of lignans. Norway spruce (Picea abies) knots contain as much as 6–24% of lignans, with 7-hydroxymatairesinol (HMR) as the predominant (70–85%) lignan. Some other spruce species also contain HMR as the main lignan, but some spruce species have also other dominating lignans. Most fir (Abies) species contain secoisolariciresinol and lariciresinol as the main lignans. Lignans occur also in knots of pines (Pinus spp.), although in lower amounts than in spruces and firs. Scots pine (Pinus silvestris) knots were found to contain 0.4–3% of lignans with nortrachelogenin as the main lignan. Lignans have been identified also in knots of some hardwoods, although flavonoids are more abundant in hardwoods. Knots are detrimental in the manufacture of pulp and paper and should preferably be removed before pulping. This is possible using a recently developed industrially applicable process called ChipSep. Recent research has also established novel synthetic routes to several lignans, such as matairesinol, secoisolariciresinol, lariciresinol and cyclolariciresinol, starting from hydroxymatairesinol by applying fairly straight-forward chemical transformations. We conclude that wood knots in certain spruce and fir species constitute the richest known source of lignans in nature. The lignans occur in knots in free form and are easily extracted by aqueous ethanol, or even by water. Not only HMR, but also other potentially valuable lignans, could be produced in a scale of hundreds of tons per year by extraction of knots separated from wood chips at pulp and paper mills.