Fast pyrolysis utilizes biomass to produce a product that is used both as an energy source and a feedstock for chemical production. Considerable efforts have been made to convert wood biomass to liquid fuels and chemicals since the oil crisis in mid-1970s. This review focuses on the recent developments in the wood pyrolysis and reports the characteristics of the resulting bio-oils, which are the main products of fast wood pyrolysis. Virtually any form of biomass can be considered for fast pyrolysis. Most work has been performed on wood, because of its consistency and comparability between tests. However, nearly 100 types of biomass have been tested, ranging from agricultural wastes such as straw, olive pits, and nut shells to energy crops such as miscanthus and sorghum. Forestry wastes such as bark and thinnings and other solid wastes, including sewage sludge and leather wastes, have also been studied. In this review, the main (although not exclusive) emphasis has been given to wood. The literature on woo...

Pyrolysis of Wood/Biomass for Bio-oil: A Critical Review

Pyrolysis is one of the thermochemical technologies for converting biomass into energy and chemical products consisting of liquid bio-oil, solid biochar, and pyrolytic gas. Depending on the heating rate and residence time, biomass pyrolysis can be divided into three main categories slow (conventional), fast and flash pyrolysis mainly aiming at maximising either the bio-oil or biochar yields. Synthesis gas or hydrogen-rich gas can also be the target of biomass pyrolysis. Maximised gas rates can be achieved through the catalytic pyrolysis process, which is now increasingly being developed. Biomass pyrolysis generally follows a three-step mechanism comprising of dehydration, primary and secondary reactions. Dehydrogenation, depolymerisation, and fragmentation are the main competitive reactions during the primary decomposition of biomass. A number of parameters affect the biomass pyrolysis process, yields and properties of products. These include the biomass type, biomass pretreatment (physical, chemical, and biological), reaction atmosphere, temperature, heating rate and vapour residence time. This manuscript gives a general summary of the properties of the pyrolytic products and their analysis methods. Also provided are a review of the parameters that affect biomass pyrolysis and a summary of the state of industrial pyrolysis technologies.

Lignocellulosic biomass pyrolysis: A review of product properties and effects of pyrolysis parameters

The conversion of biomass by thermochemical means is very promising for the substitution of fossil materials in many energy applications. Given the complexity of biomass the main challenge in its use is to obtain products with high yield and purity. For a better understanding of biomass thermochemical conversion, many authors have studied in TG analyzer or at bed scale the individual pyrolysis of its main constituents (i.e. cellulose, hemicelluloses and lignin). Based on these studies, this original work synthesizes the main steps of conversion and the composition of the products obtained from each constituent. Pyrolysis conversion can be described as the superposition of three main pathways (char formation, depolymerization and fragmentation) and secondary reactions. Lignin, which is composed of many benzene rings, gives the highest char yield and its depolymerization leads to various phenols. The depolymerization of the polysaccharides is a source of anhydro-saccharides and furan compounds. The fragmentation of the different constituents and the secondary reactions produce CO, CO2 and small chain compounds. For temperature higher than 500 °C, the residues obtained from the different constituents present a similar structure, which evolves towards a more condensed polyaromatic form by releasing CH4, CO and H2. As the aromatic rings and their substituent composition have a critical influence on the reactivity of pyrolysis products, a particular attention has been given to their formation. Some mechanisms are proposed to explain the formation of the main products. From the results of this study it is possible to predict the reactivity and energy content of the pyrolysis products and evaluate their potential use as biofuels in renewable applications.

A review on pyrolysis of biomass constituents: Mechanisms and composition of the products obtained from the conversion of cellulose, hemicelluloses and lignin

Lignocellulosic biomass is the most abundant and bio-renewable resource with great potential for sustainable production of chemicals and fuels. This critical review provides insights into the state-of the-art accomplishments in the chemocatalytic technologies to generate fuels and value-added chemicals from lignocellulosic biomass, with an emphasis on its major component, cellulose. Catalytic hydrolysis, solvolysis, liquefaction, pyrolysis, gasification, hydrogenolysis and hydrogenation are the major processes presently studied. Regarding catalytic hydrolysis, the acid catalysts cover inorganic or organic acids and various solid acids such as sulfonated carbon, zeolites, heteropolyacids and oxides. Liquefaction and fast pyrolysis of cellulose are primarily conducted over catalysts with proper acidity/basicity. Gasification is typically conducted over supported noble metal catalysts. Reaction conditions, solvents and catalysts are the prime factors that affect the yield and composition of the target products. Most of processes yield a complex mixture, leading to problematic upgrading and separation. An emerging technique is to integrate hydrolysis, liquefaction or pyrolysis with hydrogenation over multifunctional solid catalysts to convert lignocellulosic biomass to value-added fine chemicals and bio-hydrocarbon fuels. And the promising catalysts might be supported transition metal catalysts and zeolite-related materials. There still exist technological barriers that need to be overcome (229 references).

http://www.chtf.stuba.sk/~szolcsanyi/education/files/Chemia%20heterocyklickych%20zlucenin/Prednaska%207/Doplnkove%20studijne%20materialy/Hydroxymethylfurfural/Catalytic%20conversion%20of%20lignocellulosic%20biomass%20to%20fine%20chemicals%20and%20fuels.pdf

Catalytic conversion of lignocellulosic biomass to fine chemicals and fuels

The removal of crop residues for bio-energy production reduces the formation of soil organic carbon (SOC) and therefore can have negative impacts on soil fertility. Pyrolysis (thermoconversion of biomass under anaerobic conditions) generates liquid or gaseous fuels and a char (biochar) recalcitrant against decomposition. Biochar can be used to increase SOC and cycle nutrients back into agricultural fields. In this case, crop residues can be used as a potential energy source as well as to sequester carbon (C) and improve soil quality. To evaluate the agronomic potential of biochar, we analyzed biochar produced from poultry litter, peanut hulls, and pine chips produced at 400°C and 500°C with or without steam activation. The C content of the biochar ranged from 40% in the poultry litter (PL) biochar to 78% in the pine chip (PC) biochar. The total and Mehlich I extractable nutrient concentrations in the biochar were strongly influenced by feedstock. Feedstock nutrients (P, K, Ca, Mg) were concentrated in the biochar and were significantly higher in the biochars produced at 500°C. A large proportion of N was conserved in the biochar, ranging from 27.4% in the PL biochar to 89.6% in the PC biochar. The amount of N conserved was inversely proportional to the feedstock N concentration. The cation exchange capacity was significantly higher in biochar produced at lower temperature. The results indicate that, depending on feedstock, some biochars have potential to serve as nutrient sources as well as sequester C.

Effect of Low-Temperature Pyrolysis Conditions on Biochar for Agricultural Use

This paper describes an analytical approach to determine the chemical composition of bio-oils in terms of macro-chemical families. Bio-oils from the vacuum pyrolysis of softwood bark and hardwood were first fractionated using solvent extraction. Fractions obtained were then characterized using GC-MS, thermogravimetric techniques (TG) and Gel Permeation Chromatography (GPC). Thermogravimetric and molar mass distribution curves of each fraction were interpreted in terms of macro-families applying curve-fitting procedures. The composition of the different macro-fractions obtained was in agreement using both methods. The proposed procedure enables a thorough description of bio-oil composition as a mixture of water, monolignols, polar compounds with moderate volatility, sugars, extractive-derived compounds, heavy polar and non-polar compounds, MeOH–toluene insolubles and volatile organic compounds.

Characterization of bio-oils in chemical families

Vacuum pyrolysis of softwood and hardwood biomass: Comparison between product yields and bio-oil properties

The multiphase complex structure of biomass pyrolysis oils can be attributed to the presence of char particles, waxy materials, aqueous droplets, droplets of different nature, and micelles formed of heavy compounds in a matrix of hollocellulose-derived compounds and water. Bio-oil complexity is illustrated by use of two oils produced from the vacuum pyrolysis of softwood bark residues (SWBR) and hardwood rich in fibers (HWRF). The effect of waxy materials on bio-oil behavior was studied by differential scanning calorimetry (DSC), optical microscopy, and surface tension measurements as well as by steady and dynamic rheological techniques. At around 45 °C the melting of waxy materials occurs. Bio-oil cooling rate was found to have an important effect on some bio-oil rheological characteristics. This may be due to crystallization of waxy materials. Strain and frequency sweep tests proved the existence of a network (gel) structure in the bottom layer of oils derived from SWBR. This structure may be formed of ...

Multiphase Structure of Bio-oils

The corrosion of three metals (aluminum, copper, and austenitic steel (SS 316)) at 80 °C by bio-oil obtained by vacuum pyrolysis of softwood bark residue was studied using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) depth profiling. The bio-oil is very acidic (pH value of 3) and contains significant amounts of water and metal ions that are not present in significant concentrations in the feedstock material (e.g. Cu, Pb, and Fe). These metals were most probably leached from the pyrolysis reactor or peripheral installations. Aluminum and, to a much smaller degree, copper were corroded by bio-oil, whereas SS 316 was not affected. Oxide and/or hydroxide layers were formed on all three metals. However, in the case of aluminum and copper, these layers did not protect the underlying metal against further oxidation. For SS 316, after initial modification of the surface (e.g., leaching of Fe species), subsequent oxidation was prevented by the chromium oxide layer.

Corrosion of metals by bio-oil obtained by vacuum pyrolysis of softwood bark residues. An X-ray photoelectron spectroscopy and Auger electron spectroscopy study

The thermal stability of bio-oils obtained from softwood bark (SWBR) and hardwood rich in fibers (HWRF) residues was studied under aging conditions at 80 °C in sealed glass bottles in the presence of stainless steel and copper. SWBR-derived bio-oil separated into oily and aqueous phases during aging, while HWRF-derived oil remained as a single phase during the entire aging period. Dynamic rheological tests and GPC analyses were used to follow the effect of aging on the properties of bio-oils. Bio-oil aging was determined following the changes in bio-oil macrofractions using solvents of different polarities. The main difference observed between the oils analyzed was the tendency of SWBR to form materials insoluble in methanol, while HWRF aging reactions led to the formation of compounds insoluble in water and CH2Cl2. Methanol-insoluble and water-/CH2Cl2-insoluble fractions of aged oils were characterized by thermogravimetry, GPC, and Py−GC/MS techniques. The bio-oil aging reactions seem not to be affected ...

Detlef Kretschmer

Papers

Characterization of bio-oils in chemical families

Vacuum pyrolysis of softwood and hardwood biomass: Comparison between product yields and bio-oil properties

Multiphase Structure of Bio-oils

Corrosion of metals by bio-oil obtained by vacuum pyrolysis of softwood bark residues. An X-ray photoelectron spectroscopy and Auger electron spectroscopy study

Evaluation of the influence of stainless steel and copper on the aging process of bio-oil