In this short review, we survey the historical progress of fast pyrolysis technologies for thermochemical liquefaction of biomass to produce so-called "bio-oil". Our focus is on the potential applications of bio-oil as a liquid fuel for heat and power generation. We point out some of the inherent properties of bio-oil that create difficulties standing in the way of these applications. Finally, we take a brief look at some processes that aim to valorize bio-oil by conversion to higher value liquid fuel products. Dans cette revue nous nous proposons de dresser un rappel historique des progrès relatifs aux technologies de liquéfaction thermochimiques par pyrolyse rapide, encore appelée pyrolyse flash, de la biomasse pour produire ce que l’on appelle communément une "bio-huile". Nous insisterons sur ses applications comme combustible liquide pour la production de chaleur et d’électricité. Nous ferons ressortir quelques propriétés spécifiques aux bio-huiles qui peuvent créer des difficultés d’usage. Nous terminerons par un bref aperçu de quelques procédés permettant de valoriser la bio-huile en carburants liquides de plus forte valeur ajoutée.

In this short review, we survey the historical progress of fast pyrolysis technologies for thermochemical liquefaction of biomass to produce so-called "bio-oil". Our focus is on the potential applications of bio-oil as a liquid fuel for heat and power generation. We point out some of the inherent properties of bio-oil that create difficulties standing in the way of these applications. Finally, we take a brief look at some processes that aim to valorize bio-oil by conversion to higher value liquid fuel products.

A maximum bubble pressure apparatus, described in a previous publication, has been used at pressures to 13.9 MPa (2000 psig) and temperature to 623 K (350degreesC) to measure the static surface tension of several alkanes and paraffinic petroleum fractions, and two types of Alberta bitumens in contact with hydrogen, helium and hydrogen/methane mixtures. With hydrogen, the surface tensions of alkanes or mixtures of alkanes were nearly independent of pressure, whereas with helium surface tension increased significantly. With hydrogen/ methane mixtures, the surface tension decreased in value as pressure increased, with the effect increasing at the higher methane concentrations. For the two bitumens used, the surface tension with hydrogen showed a 10-15% increase as pressure increased at constant temperature. Some discussion is also given concerning methods of predicting the effects of pressure and temperature in hydrogen/hydrocarbon systems.

Pyrolysis has progressed significantly in the processing of herbaceous materials as well as woody plants. In fast pyrolysis, the widely used fluid bed reactor is a relatively simple design with favourable heat transfer characteristics. Recent advancements in char removal and bio-oil collection increase the effective use of pyrolysis oils as fuel in advanced power cycles. Due to the shortcomings of integrated gasification/combined cycles (IGCC), we are developing an alternative to IGCC for biomass power: the integrated (fast) pyrolysis/combined cycle (IPCC). Solid biomass is converted into liquid bio-oil. This bio-oil is a mixture of oxygenated organic compounds and water that can fuel a gas turbine topping cycle. Resulting waste heat provides thermal energy to a steam turbine bottoming cycle. Advantages of the biomass-fueled IPCC system include: combined cycle efficiency exceeding 33.6% efficiency for a system as small as 7.6 MW; absence of high-pressure thermal reactors; decoupling of fuel processing and power generation; and opportunities for recovering value-added products from the bio-oil. In addition, this technology co-utilizes biomass with natural gas in the pyrolysis cycle and diesel fuel in the turbine cycle. This article reviews the state of fast pyrolysis technology, describes the operation of the proposed IPCC power system, and estimates the capital and operating costs of the system operating on agricultural residues.

An apparatus for the measurement of surface tensions of organic liquids in contact with a gas has been developed which is capable of operation to 400degreesC and to 14 MPa. It is based on the maximum bubble pressure technique, modified for hydrocarbon oils at high pressures and temperatures. Accuracy of measurement is of the order of +/-3% for non-aqueous systems for values down to 5 mN/m. Only a 20 to 30 mL liquid sample is required, and small gas volumes. In practice, it was found that measurements with most organic liquids could only be made to a maximum of about 350degreesC because of the thermal instability of most of these compounds, in particular, for hydrocarbon liquids. Any thermal decomposition or coke deposition leads to inaccurate results. Results obtained for known liquids are compared with values given in the literature.

An upgrading process for heavy oils and bitumens, based on the use of activated carbon catalysts, was investigated in a bench-scale plug flow reactor. Good results were obtained at pressures as low as 7.0 MPa at temperatures of 400-450 degreesC. The process required the presence of hydrogen gas and a hydrogen-rich solvent in a supercritical state. If the solvent was a highly saturated alkane, very little solvent decomposition occurred. A number of n-alkanes were tested as solvents, as well as paraffinic petroleum cuts and donor solvents such as tetralin and decalin. A range of values of other operating parameters was also investigated.With an Athabasca bitumen coker feed, bitumen conversions to distillable liquids of 82-88% by weight (95-105% vol%) were achieved, with 6-8 wt% (coke + pitch) yields. Demetallization was almost 100%, and hydrodesulfurization and hydrodenitrification levels of over 80% also resulted. Under similar conditions, a conventional Co/Mo hydrotreating catalyst gave higher hydrogen uptake but lower pitch conversion, supporting the concept that carbon-based catalysts may give a unique product distribution and utilize hydrogen more effectively.It is postulated that four conditions must be met to obtain the favorable results found in this work: there must be a significant level of supercritical fluid; there must be a highly saturated or paraffinic supercritical solvent present; hydrogen gas must be present; and there must be an activated carbon catalyst used which may also have incorporated in it a catalytically active metal. (C) 2001 Elsevier Science Ltd. All rights reserved.

It is well known that the presence of alkaline cations in biomass affect the mechanism of thermal decomposition during fast pyrolysis causing primarily fragmentation of the monomers making up the natural polymer chains rather than the predominant depolymerization that occurs in their absence. As a result, liquid products (bio-oil) of quite different compositions can be obtained, and these bio-oils may be used for quite different purposes. A considerable amount of research has been carried out on the changes in mechanism occurring due to the presence and absence of these cations during fast pyrolysis and the compositional changes occurring in the bio-oil product as a result. However, if removal of such cations is to be practised as an industrial process, it would be desirable to have some information on the rates of the exchange step and the degree of removal of a particular cation that can be economically achieved. The present work describes a preliminary study of the rates of removal of the indigenous alkaline cations in a poplar wood (potassium and calcium mainly) by an ion exchange process using a dilute acid. The exchange process is rapid and potassium is more easily removed than calcium. It is also shown that hot water washing alone is able to remove a major amount of the alkaline cations from wood. The deionized wood can be used as the feed for a fast pyrolysis process for the thermal conversion of cellulose and hemicellulose to anhydrosugars for use in synthesis, or for conversion to fermentable sugars in good yield.

Evidence is presented showing that it should be possible to depolymerize a purified cellulose to produce anhydro-oligosaccharides containing small numbers of glucosidic units if suitable reaction conditions are chosen. Experiments were carried out in a stream of nitrogen in a downflow cocurrent tubular reactor with a high temperature wall. Two sizes of particles of Avicel pH102 were used and two sizes of reactor tube with wall temperatures from 850 to 1200°C and residence times from 35 to 75 ms. From the solid residue of the reaction, a water soluble fraction was recovered which contained anhydrosugars. Yields of soluble solids of up to 44% of the cellulose fed were obtained in a small diameter tube, and up to 34% in a larger diameter reactor. Only a narrow window of reaction conditions exists which is optimal for maximum yields. Carbohydrate analyses showed significant yields of anhydro-oligosaccharides from G2 to G7, the limit of resolution for the HPLC column used. Normally, these compounds made up ∼50% of the soluble solids fraction. Substantial amounts of material >G7 were also produced but could not be identified. Tests were also done with pretreated Avicel, but only one method gave improved results (slow preheating) Given the probable high unit value of anhydro-ologosaccharides, it would appear that this method of flash pyrolysis may be worth further exploitation.

Thermolysis can convert up to 90 wt % of biomass polymers volatiles, leading to drastic changes in volume. It is suggested that biomass can undergo a phase transition (melting) as a primary step and that subsequent decomposition produces a mixture of vapours and aerosols, the latter being formed by direct mechanical expulsion. Collection of the aerosols requires specific engineering solutions. In the case of wood pyrolysis 65 wt % of the feed (dry basis) can be converted to a liquid organic phase (not including water). Most of it (about two thirds) is water-soluble. Results of chemical analyses of water solubles formed from wood, cellulose, and starch are discussed. The main properties and some applications are described.

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.

Over the past two decades a great deal of experimental work as been carried out on the development of fast pyrolysis processes, particularly for biomass and for lignocellulosic waste materials. High yields of an organic liquid product (50–70%) are typical of atmospheric pressure short contact time pyrolysis of such feedstocks. This liquid product has been shown to be usable both as an alternative liquid fuel, and as a chemical feedstock because of its content of significant concentrations of potentially useful organic chemicals. The characteristics of the more important fast pyrolysis processes are reviewed, and the advantages and problems existing with present pyrolysis reactors are discussed, with the emphasis on bubbling fluidized bed systems. Experience with the process has led us to a somewhat different view of the optimal conditions for fast pyrolysis, and has resulted in the recent development of a new fluid bed process—the RTI Process. Characteristics of the RTI process are described and its advantages over existing fast pyrolysis technologies summarized.

A hydrogenation process has been developed to recover carbon black from rubber crumbs prepared from scrap tires. A semi-batch 2 L autoclave was used, with hydrogen continuously bubbled through a slurry of rubber crumbs and a paraffinic dissolution oil under pressures from 300 to 1500 psig and temperatures of about 400 degrees C. The dissolution oil dissolved the rubber and allowed the carbon-black particles to be freed from the polymer matrix. The carbon black then acted as a hydrogenation/cracking catalyst. Under optimal reaction conditions, the yield of carbon black + inorganic additives was approximately 36%, the gas yield 1-2%, naphtha yield 8%, and the balance a product oil, part of which can be recycled as the dissolution reagent. The carbon-black product after filtering and drying had properties which were an average of those of the various grades added during tire manufacture. One-half of the inorganics could be removed by a simple acid wash if desired. The carbon black has a value more than twice that of the other products and could be the factor which would allow this process to be economically viable without subsidies.

Exploratory work was carried out to develop a process for conversion of mixed plastic wastes into liquid transportation fuels or petrochemicals. The concept used is based on thermal depolymerization of the polymers in a suitable solvent followed by catalytic conversion of the resulting polymeric fragments into hydrocarbons with boiling points below 525 degrees C. The process is carried out batch-wise over a zeolite catalyst at temperatures from 350 degrees C to 450 degrees C and at atmospheric pressure. No hydrogen is used and volatile products formed are continuously removed from the reactor. Tests were carried out on polyethylene and polypropylene alone, and on mixtures of the two. Finally, a synthetic mixture of four different plastics was tested. From 90% to 98% of the plastic was converted to gases or distillable hydrocarbons. Of this yield, from 20% to 55% was gas, primarily propylenes and butylenes, and from 32% to 70% was a light hydrocarbon oil. Very little non-distillable coke or residue was formed. The use of mixtures did not affect the high conversions obtained, but the results could only be approximately predicted based on a pro-rating of results for the individual components.

The Waterloo Fast Pyrolysis methodology which employs a bed of fluidized sand at atmospheric pressure was used to evaluate the yields of pyrolytic liquids from Italian sweet sorghum and sweet sorghum bagasse. Reaction temperatures were varied from 400°C to 560°C, and apparent volatiles residence times from 222 to 703 ms. The sorghum bagasse gave results typical of similar grasses. A maximum liquid yield (dry basis) of 69.4% by weight was achieved at 510°C when the volatiles apparent residence time was held constant at 500 ms. However, at shorter residence times (255 ms), liquid yields were slightly higher at a constant temperature of 525°C. Because of the high ash content of the bagasse, the char obtained (about 13%) had an ash content of nearly 50%. The liquid product composition was similar to that obtained from fast pyrolysis of other grasses. Tests were also done with bagasse which had been deionized. A much higher conversion of the cellulose and hemicellulose content to anhydrosugars resulted, with a corresponding reduction in low molecular weight carbonyl compounds. Whole (raw) sweet sorghum was pyrolyzed similarly. The high sugar content (36%) of this biomass resulted in a more unusual pyrolysis behaviour. High yields of carbon dioxide were obtained, and liquid yields were somewhat lower (63%) than those from the bagasse, and were obtained at a lower temperature (450°C). Volatiles residence time in the range used had little effect on liquid yield amounts. Both raw sweet sorghum and sweet sorghum bagasse appear to be suitable feedstocks for the production of organic liquids by fast pyrolysis. However, better yields and a better quality liquid (for fuel purposes) are obtained from the bagasse.

Many potential applications for some of the materials known to be present in bio-oils generated by fast pyrolysis (the so-called B-tars) have been discussed by various authors in the past.However the successful development of industries based on the production of these chemicals requires above all a sound understanding of the physico-chemical nature of the oils and how this character varies with process conditions. This would provide the proper background information to enable a rational approach towards process tuning for optimal yields and selectivity. Furthermore it will suggest methods for tackling the difficult problems of product separation as well as new applications of these products.Accordingly some ideas concerning these aspects will be the focus of this presentation. Application examples will include production of specific chemical synthons, flavour chemicals, organic fertilizers, fuel additives, additives for pollution control, boiler fuels and diesel fuels.

In a previous work, the pyrolytic gasification of biomass (wood) using a stoichiometric nickel aluminate catalyst in a fluidized-bed reactor gave near-equilibrium yields of products above 650 degrees C, with 85-90% gas yields and no detectable tar production Additional tests are reported for a modified nickel-magnesium aluminate stoichiometric catalyst, to give greater physical strength, and for the addition of potassium, as a promoter. The addition of Mg in the catalyst crystal lattice did improve resistance to attrition but resulted in a minor loss in gasification activity and increased coke production. Addition of potassium had little effect. Catalyst deactivation by secondary carbon deposits was demonstrated, and regeneration of the Mg-containing catalysts by burn-off appears to be feasible. The deactivation process was experimentally simulated. A conceptual process for catalytic pyrogasification of biomass was modeled.

Various kinds of catalysts are being developed and tested for the pyrolytic gasification of biomass using the Waterloo Fast Pyrolysis Process (WFPP) technology. The present report describes gasification tests with wood in a continuous bench scale fluidized bed reactor but with no added air or oxygen in the region of 500-700 degrees C and at short gas contact times, using a crystalline nickel aluminate catalyst. The objective was to determine the most appropriate operating conditions for this catalyst and its performance for the production of a synthesis gas in high yields. Experiments were carried out with this catalyst in both inert and reactive gasification media, but without any oxygen or air addition. The results show the influence of the catalyst on the nature of the gasification products and the effect of operating variables. Gas compositions are given for typical WFPP operating conditions. Evidence is presented which indicates that the gasification mechanism is a fast thermal pyrolysis followed by catalytic reforming of the vapors with a high yield of synthesis gas.