Dietrich Meier

An overview of fast pyrolysis of biomass

Biomass fast pyrolysis is of rapidly growing interest in Europe as it is perceived to offer significant logistical and hence economic advantages over other thermal conversion processes. This is because the liquid product can be stored until required or readily transported to where it can be most effectively utilised. The objective of this paper is to review the design considerations faced by the developers of fast pyrolysis, upgrading and utilisation processes in order to successfully implement the technologies. Aspects of design of a fast pyrolysis system include feed drying; particle size; pretreatment; reactor configuration; heat supply; heat transfer; heating rates; reaction temperature; vapour residence time; secondary cracking; char separation; ash separation; liquids collection. Each of these aspects is reviewed and discussed. A case study shows the application of the technology to waste wood and how this approach gives very good control of contaminants. Finally the problem of spillage is addressed through respirometric tests on bio-oils concluding with a summary of the potential contribution that fast pyrolysis can make to global warming.

Studies on isolated lignins and lignins in woody materials by pyrolysis-gas chromatography-mass spectrometry and off-line pyrolysis-gas chromatography with flame ionization detection

Abstract Wood and milled wood lignins from beech ( Fagus sylvatica L.), spruce ( Picea abies Karst.), bamboo ( Bambus sp.) and teak wood ( Tectona grandis L.f.) were subjected to two types of pyrolysis: (1) direct pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and (2) off-line Py-GC with flame ionization detection (FID). Py-GC-MS studies were used for the identification of phenolic degradation products; 67 substances were identified, 50 of which could be quantified by GC-FID using authentic compounds. It was demonstrated that off-line Py-GC-FID is a suitable method for lignin classification of composed lignocellulosic materials without isolation of lignin. Quantitative pyrolysis results were used to calculate H: G: S ratios of lignins and the results were compared with data obtained from nitrobenzene oxidation and Fourier transform infrared analyses. Results of both of these methods were in good agreement with the off-line Py-GC-FID results.

Catalytic hydropyrolysis of lignin: Influence of reaction conditions on the formation and composition of liquid products

Abstract Catalytic hydropyrolysis of different lignins has been studied under various reaction conditions. With a palladium catalyst on active charcoal, liquid products (oil) up to 80 wt% were obtained and the solid residue amounted to only 1 wt%. Nickelmolybdenum on aluminosilica catalysts led to oil yields of about 65 wt%, containing larger amounts of monomeric phenols. Therefore, nickel-molybdenum catalysts were selected to study the influence of the reaction conditions. Under initial hydrogen pressures ranging from 3 to 12 MPa the yield of oil increased from 18·4 wt% to 63·2 wt%. Reaction time had only a slight influence on the product yields, while increasing reaction temperatures promoted fragmentation to monomeric compounds. About one third of the oil was detectable by gas chromatography. The composition of this monomeric fraction did not change under the influence of changing process parameters. The main components of this fraction were phenol and cresols. Some alkylated phenols were found in minor amounts. Guaiacol was found only at a reaction temperature of 350°C. In none of the nickel-molybdenum experiments were catechols detected.

Catalytic hydrotreatment of some technical lignins

Five kraft lignins from softwood and hardwood and one softwood lignin from the organocell process were converted into an oil-like product by hydrotreatment at 400°C for 40 minutes in the presence of different catalysts. The total oil yields varied in the range 49–71% wt of the original lignin feedstock. The highest yield was obtained for organosolv lignin using a catalyst mixture of sulfided NiMo on aluminosilica (M8–81): Cr2O3 (M9–10) (1:1). Detailed GLC analysis of the low-molecular-weight components in the oil products (the total amounts of 14–38% wt of the original lignin) indicated the presence of various alkyl benzenes, phenols, and polycyclic aromatics.

Characterization of tobacco lignin by analytical pyrolysis and Fourier transform-infrared spectroscopy

Abstract Two milled wood lignins (MWLs) were isolated from tobacco leaves (laminae) and midrib material according to the Bjorkman procedure. Prior to MWL isolation, the material was extracted with cyclohexane/ethanol and hot water to remove extractives which could interfere with this isolation. MWLs were obtained with a yield of 0.03% (leaves) and 0.06% (midribs) based on dry pre-extracted material. FT-IR spectroscopy was used for quality control and classification of the isolates. Both preparations fulfilled the spectroscopic lignin criteria of a GS lignin with low syringyl content, although the isolates were not pure. Besides carbohydrate impurities, the lamina material, especially, was contaminated with nitrogen and fatty acid-containing substances. Proteins and cutin are discussed as probable contaminants. Both MWLs were characterized with quantitative pyrolysis—gas chromatography using a resistant heating instrument. Curie-point pyrolysis—gas chromatography/mass spectrometry and pyrolysis—mass spectrometry were used for additional characterization of yboth MWL samples. The results show that the tobacco MWL contains up to 22% carbohydrate-type impurities. Small amounts of alkaloids, proteins and lipids were also detected as contamination. Results of previous studies on mineral acid residues could be corroborated: tobacco lignin contains approximately 10% 4-hydroxyphenylpropane, 78–82% guaiacylpropane and 10–13% syringylpropane moieties.

Analysis of lignocelluloses and lignins from Arundo donax L. and Miscanthus sinensis Anderss., and hydroliquefaction of Miscanthus

Abstract In a comparative investigation of the chemical composition of Arundo donax L. and Miscanthus sinensis Anderss. the following experiments were performed: ash determination and ash characterization by energy dispersive X-ray analysis; determination of solubility in cyclohexane/ ethanol, hot water, 1% hydrochloric acid and sodium hydroxide; C, H and N determination; determination of Klason lignin and acid soluble lignin content; sulfuric acid hydrolysis followed by borate complex ion exchange chromatography of the monomeric sugars; isolation of milled wood lignins (MWL) and dioxane lignins (DIL) and their analysis by C, H, and OMe determination; quantitative FTIR spectroscopy of MWL; recording the molecular weight distribution curves using high performance size exclusion chromatography (HPSEC); calculation of average molecular weights, such as Mw and Mn; calculation of the heating values of the lignocellulosics and their components. The quantitative composition of the lignin from the three basic phenylpropane units is presented. M. sinensis was submitted to hydroliquefaction. The conversion process yielded 35% of a net product oil (NPO) with low oxygen content (11%), low viscosity (10−2 NS m−2), low asphaltene content (3·5%) low molecular weight (Mw 200) and with a specific gravity of c. 0·93 g cm−3. The NPO has a heating value of 39·4 MJ kg−1 and contains 55% of the carbon of the starting material and 59% of the combined heating value from the biomass and the hydrogen used for hydroliquefaction. The process yields 28% water which contains 58% of the original oxygen of the biomass. The process gives rise to 9 g solids and 32–35 g gases, whose energy content can easily be recovered.

Pyrolysis-gas chromatography-mass spectrometry of two trimeric lignin model compounds with alkyl-aryl ether structure

Abstract Thermal degradation of ω-guaiacoxy-acetoguaiacone-benzylether (A) and ω-syringoxy-acetoguaiacone-benzylether (B) has been investigated for a better understanding of the thermolytic behaviour of lignins. Earlier differential scanning calorimetric studies revealed that degradation starts below 200° C. Direct insertion probe experiments also demonstrated that splitting of linkages between aroxy and acetoguaiacone-benzylether (C) moieties commences at 175° C. As a consequence the presence of the following compounds was observed: guaiacol and C (from A) and syringol and C (from B). Simultaneously to these splitting mechanisms a rearrangement occurs between the ω-carbon of compound C and the phenolic oxygen of the aroxy residues, resulting in the formation of 2-methoxybenzaldehyde and acetovanillone-benzylether (from A) and 2,6-dimethoxybenzaldehyde and acetovanillone-benzylether (from B). Pyrolysis-gas chromatography-mass spectrometry experiments between 240 to 600°C corroborated these results. The higher the pyrolysis temperature the more peaks are displayed in the pyrograms. The pyrograms obtained at 600° C show 40 to 70 major peaks which were evaluated. The relative retention times, M+ values and in most cases the assignments to defined compounds are given. Many ‘unknown’ substances could be identified as condensation products derived from benzyl radicals. Flow diagrams illustrate the main splitting mechanisms of compounds A and B.

Conversion of technical lignins into slow-release nitrogenous fertilizers by ammoxidation in liquid phase

Abstract Technical lignins derived from kraft, organosolv, soda, and ASAM pulping as well as a fermented lignosulfonate from a sodium sulfite process have been subjected to oxidative ammoniation (ammoxidation) aimed at producing slow-release nitrogenous fertilizers. Reactions were carried out in liquid phase using a 1-liter, stirred, batch reactor. The effect of time, temperature, and oxygen pressure on the amount of fixed nitrogen and the C/N ratio was studied. High nitrogen contents were obtained with kraft and organosolv lignin followed by lignosulfonate. At 150°C, 15 bar oxygen pressure and 90 min of reaction time, 13–14% nitrogen (based on lignin) could be fixed in the lignin macromolecule. Changes in molecular structure were monitored by FTIR spectroscopy. The crop yield of sorghum plants in pot experiments with ammoxidized kraft lignin as fertilizer was 82% of that obtained with ammonia fertilization.

Characterisation of spruce, salix, miscanthus and wheat straw for pyrolysis applications

This research details the characterisation of four Irish-grown lignocellulosic biomasses for pyrolysis by biomass composition analysis, TGA, and Py-GC/MS-FID. Ash content (mf) increased in the order spruce (0.26 wt.%) < salix (1.16 wt.%) < miscanthus (3.43 wt.%) < wheat straw (3.76 wt.%). Analysis of hydrolysis-derived sugar monomers showed that xylose concentrations (4.69–26.76 wt.%) ranged significantly compared to glucose concentrations (40.98–49.82 wt.%). Higher hemicellulose and ash contents probably increased non-volatile matter, and decreased the temperature of maximum degradation by TGA as well as yields of GC-detectable compounds by Py-GC/MS-FID. Differences in composition and degradation were reflected in the pyrolysate composition by lower quantities of sugars (principally levoglucosan), pyrans, and furans for salix, miscanthus, and wheat straw compared to spruce, and increased concentrations of cyclopentenones and acids.

Analytical pyrolysis and FTIR spectroscopy of fossil Sequoiadendron giganteum (Lindl.) wood and MWLs isolated hereof

Recent and fossil woods from the genus of Sequoiadendron, as well as their milled wood lignins were investigated by means of FTIR spectroscopy and pyrolysis GC/MS technique. Though almost same in appearance the differences in band intensities of FTIR-spectra reveals the distinctly increased aromatic character and the oxidation in fossil specimens. More detailed information about the changes in old wood were obtained by analytical pyrolysis, which delivers degradation products with shortened side chains and more saturated units relating to fossil lignin.ZusammenfassungRecentes und fossiles Holz der Gattung Seqoiadendron giganteum, sowie daraus isoliertes Björkman-Lignin wurden mittels FTIR Spektroskopie und GC/MS Pyrolyse-Technik untersucht. Obwohl sich die Holzarten äußerlich sehr ähneln, zeigen die Unterschiede der Bandenintensität in den FTIR Spektren einen deutlich erhöhten, aromatischen Charakter und Oxidationsgrad in den fossilen Proben. Detailliertere Information über Veränderungen in den alten Holzarten wurden durch pyrolytische Analyse gewonnen, welche Abbauprodukte mit kürzeren Seitenketten und gesättigtere Einheiten des fossilen Lignin aufweisen.