Showing papers in "Industrial & Engineering Chemistry Research in 1997"

Liquid Separation by Membrane Pervaporation: A Review

Abstract: Pervaporation is one of the most active areas in membrane research, and the pervaporation process has been shown to be an indispensable component for chemical separations. In this paper, the recent development in pervaporation membranes and pervaporation processes is reviewed, and some outstanding questions involved in membrane pervaporation are discussed with emphasis on the following issues: mass transport in the membrane, membrane material selection, concentration polarization in the boundary layer, pressure buildup in hollow fiber membranes, asymmetric and composite membranes, and the activation energy for permeation. We attempt to provide insight into this dynamic field and to highlight some of the outstanding problems yet to be solved or clarified.

Chemical Recycling of Poly(ethylene terephthalate)

Abstract: This paper reviews the state of the art in the field of chemical recycling of poly(ethylene terephthalate) (PET). Advantages of the chemical recycling of PET, the theoretical basis of the ester bond cleavage, and a wide spectrum of degrading agents and final products are presented. Chemical processes applied in polymer recycling are divided into six groups: methanolysis, glycolysis, hydrolysis, ammonolysis, aminolysis, and other methods. Numerous possibilities for the utilization of waste PET as a very useful raw chemical material are described on the basis of literature. A comparison of chemical recycling methods is carried out. The following aspects were taken into consideration: (i) flexibility in utilizing a variety of waste types, (ii) conditions necessary for degradation including safety requirements, (iii) economic aspects, and (iv) product versatility. A total of 108 references including 46 patents are cited in this paper.

Biomass to hydrogen via fast pyrolysis and catalytic steam reforming of the pyrolysis oil or its fractions

Abstract: Pyrolysis of lignocellulosic biomass and reforming of the pyroligneous oils are being studied as a strategy for producing hydrogen A process of this nature has the potential to be cost competitive with conventional means of producing hydrogen We propose a regionalized system of hydrogen production, where small- and medium-sized pyrolysis units (<500 Mg/day) provide bio-oil to a central reforming unit to be catalytically converted to H2 and CO2 Thermodynamic modeling of the major constituents of the bio-oil has shown that reforming is possible within a wide range of temperatures and steam-to-carbon ratios In addition, screening tests aimed at catalytic reforming of model compounds to hydrogen using Ni-based catalysts have achieved essentially complete conversion to H2 Existing data on the catalytic reforming of oxygenates have been studied to guide catalyst selection A process diagram for the pyrolysis and reforming operations is discussed, as are initial production cost estimates A window of opport

Formation of a Y-Type Zeolite Membrane on a Porous α-Alumina Tube for Gas Separation

Abstract: A porous α-alumina support tube, polished with a finely powdered X-type zeolite for use as seeds, was placed vertically in an autoclave containing an aqueous mixture of water glass and sodium aluminate. Hydrothermal synthesis was carried out at 90 °C for 24 h. A polycrystalline layer of Y-type zeolite was thus formed on the outer surface of the support tube. After washing and drying in air, permeances of single components and mixtures of CO2 and N2, as well as CH4, C2H6, and SF6, were determined. The CO2 permeance was higher than that of N2 at temperatures of 30−130 °C. When an equimolar mixture of CO2 and N2 was fed into the feed side, the CO2 permeance was nearly equal to that for the single-component system and the N2 permeance for the mixture was greatly decreased, especially at lower permeation temperatures. This was due to selective adsorption of CO2 in subnanometer micropores of the membrane. At 30 °C, the permeance of CO2 was higher than 10-7 mol·m-2·s-1·Pa-1, and the permselectivity of CO2 to N2 ...

An Investigation of Some Sterically Hindered Amines as Potential Carbon Dioxide Scrubbing Compounds

Abstract: In order to improve the efficiency of the carbon dioxide cycling process and to reduce amine emissions, a series of nonvolatile amino acid salts with sterically hindered amine groups were investigated to determine their potential as direct replacements for monoethanolamine (MEA) in submarine-based CO2 scrubbers. Absorption from atmospheres containing various levels of CO2 was measured to assess the total capacities and absorption rates of amine solutions. The regeneration rates and extent of CO2 desorption were established by heating these solutions. 13C NMR spectroscopy was used to establish reaction products and solution compositions after both absorption and desorption. Methyl groups substituted adjacent to the amine were found to increase solution absorption capacities but with an overall reduction in absorption rate. Poor absorption rates at low CO2 levels and precipitation problems would prevent the α-dimethylamines examined from being used in existing submarine scrubbers. These amines, however, sho...

High-Pressure Trickle-Bed Reactors: A Review

Abstract: A concise review of relevant experimental observations and modeling of high-pressure trickle-bed reactors, based on recent studies, is presented. The following topics are considered: flow regime transitions, pressure drop, liquid holdup, gas−liquid interfacial area and mass-transfer coefficient, catalyst wetting efficiency, catalyst dilution with inert fines, and evaluation of trickle-bed models for liquid-limited and gas-limited reactions. The effects of high-pressure operation, which is of industrial relevance, on the physicochemical and fluid dynamic parameters are discussed. Empirical and theoretical models developed to account for the effect of high pressure on the various parameters and phenomena pertinent to the topics discussed are briefly described.

Biomass Gasification with Steam in Fluidized Bed: Effectiveness of CaO, MgO, and CaO−MgO for Hot Raw Gas Cleaning

Abstract: The upgrading of the raw hot gas from a bubbling fluidized bed biomass gasifier is studied using cheap calcined minerals or rocks downstream from the gasifier. Biomass gasification is made with steam (not air) at 750−780 °C and about 0.5−1.0 kg of biomass/h. Calcined solids used are dolomite (MgO−CaO), pure calcite (CaO), and pure magnesite (MgO). Variables studied have been temperature of the secondary bed (780−910 °C), time of contact or space-time of the gas (0.08−0.32 kg·h/m3n), and particle diameter (1−4 mm) and type of mineral. Their effects on tar conversion, tar amount in the exit gas, product distribution, and gas composition are presented. Using a macrokinetic model for the tar disappearance network, the activities of the stones are expressed by their apparent kinetic constant. Apparent energies of activation for tar elimination (42−47 kJ/mol) and preexponential and effectiveness factors are given for all tested solids of which the most active is the calcined dolomite.

Kinetics of glucose epimerization and decomposition in subcritical and supercritical water

Abstract: Glucose decomposition kinetics in subcritical and supercritical water were studied for the temperatures 573, 623, and 673 K, pressures between 25 and 40 MPa, and residence times between 0.02 and 2 ...

Noninvasive Tomographic and Velocimetric Monitoring of Multiphase Flows

Abstract: A condensed review of recent advances accomplished in the development and the applications of noninvasive tomographic and velocimetric measurement techniques to multiphase flows and systems is presented. In recent years utilization of such noninvasive techniques has become widespread in many engineering disciplines that deal with systems involving two immiscible phases or more. Tomography provides concentration, holdup, or 2D or 3D density distribution of at least one component of the multiphase system, whereas velocimetry provides the dynamic features of the phase of interest such as the flow pattern, the velocity field, the 2D or 3D instantaneous movements, etc. The following review is divided into two parts. The first part summarizes progress and developments in flow imaging techniques using γ-ray and X-ray transmission tomography; X-ray radiography; neutron transmission tomography and radiography; positron emission tomography; X-ray diffraction tomography; nuclear magnetic resonance imaging; electrica...

Characterization and fermentation of dilute-acid hydrolyzates from wood

Abstract: Dilute-acid hydrolyzates from alder, aspen, birch, willow, pine, and spruce were fermented without prior detoxification. The hydrolyzates were prepared by a one-stage hydrolysis process using sulfuric acid (5 g/L) at temperatures between 188 and 234 C and with a holding time of 7 min. The fermentations were carried out anaerobically by Saccharomyces cerevisiae (10 g of d.w./L) at a temperature of 30 C and an initial pH of 5.5. The fermentabilities were quite different for the different wood species, and only hydrolyzates of spruce produced at 188 and 198 C, hydrolyzates of pine produced at 188 C, and hydrolyzates of willow produced at 198 C could be completely fermented within 24 h. From the sum of the concentrations of the known inhibitors furfural and 5-(hydroxymethyl)furfural (HMF), a good prediction of the maximum ethanol production rate could be obtained, regardless of the origin of the hydrolyzate. Furthermore, in hydrolyzates that fermented well, furfural and HMF were found to be taken up and converted by the yeast, concomitant with the uptake of glucose.

Kinetics of the low-temperature pyrolysis of polyethene, polypropene and polystyrene modeling, experimental determination and comparison with literature models and data

Abstract: The pyrolysis kinetics of low-density polyethylene, high-density polyethylene, polypropylene, and polystyrene has been studied at temperatures below 450 C. In addition, a literature review on the low-temperature pyrolysis of these polymers has been conducted and has revealed that the scatter in the reported kinetic data is significant, which is most probably due to the use of simple first-order kinetic models to interpret the experimental data. This model type is only applicable in a small conversion range, but was used by many authors over a much wider conversion range. In this investigation the pyrolysis kinetics of the forementioned polymers and a mixture of polymers has been studied at temperatures below 450 C by performing isothermal thermogravimetric analysis (TGA) experiments. The TGA experimental data was used to determine the kinetic parameters on the basis of a simple first-order model for high conversions (70-90%) and a model developed in the present study, termed the random chain dissociation (RCD) model, for the entire conversion range. The influence of important parameters, such as molecular weight, extent of branching and -scission on the pyrolysis kinetics was studied with the RCD model. This model was also used to calculate the primary product spectrum of the pyrolysis process. The effect of the extent of branching and the initial molecular weight on the pyrolysis process was also studied experimentally. The effect of the extent of branching was found to be quite significant, but the effect of the initial molecular weight was minor. These results were found to agree quite well with the predictions obtained from the RCD model. Finally, the behavior of mixtures of the aforementioned polymers was studied and it was found that the pyrolysis kinetics of the polymers in the mixture remains unaltered in comparison with the pyrolysis kinetics of the pure polymers.

Removal of CO2 greenhouse gas by ammonia scrubbing

Abstract: This paper provides preliminary results on the novel study of ammonia scrubbing for the removal of carbon dioxide from flue gas. Experimental results indicated the potential of CO2 reduction by NH3 scrubbing is very promising. The overall CO2 removal efficiencies could be above 95% under proper operation conditions. The absorption capacity of NH3 was around 0.9 kg of CO2/kg of NH3 reagent being used. This should be higher than that by a MEA solution. The reaction products were analyzed and determined by X-ray diffraction analysis, SEM picture, and pH measurements. All the measurements indicated that an ammonium bicarbonate solution and its crystalline solids are the major products of reaction.

Application of the Elovich Equation to the Kinetics of Metal Sorption with Solvent-Impregnated Resins

Abstract: The sorption rates of metal ions including Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) from sulfate solutions with macroporous resins containing bis(2-ethylhexyl)phosphoric acid (D2EHPA) were measured and compared in a batch stirred vessel. Experiments were carried out as a function of the pH and metal concentration in the aqueous phase, D2EHPA concentration in the resin phase, and temperature. The effect of impregnation methods of D2EHPA on the sorption rate was also investigated. It was shown that all sorption processes could be well described by the Elovich equation. For the examined systems there were similar trends of sorption rates with respect to the concentrations of metal ions and D2EHPA. With respect to the pH, however, three different trends were obtained depending on the magnitude of sorption rate. The apparent activation energy was obtained and used to discuss the rate-controlling mechanism.

An Updated Review on Suspension Polymerization

Abstract: An updated review on suspension polymerization is presented. The time period from 1991 to 1995 is stressed, as well as research articles or reports not considered in previous reviews. Our review is aimed at providing a sound basis for the theoretical background required to build an effective model for the particle size distribution (PSD) in suspension polymerization. All major phenomena that affect the PSD are considered, and a proposed approach to develop an accurate, yet simple, model is included. Most of the experimental information in this review is related to the styrene/divinylbenzene copolymerization system, although the ideas and models are not exclusive to this system.

Modeling of Vertical Bubble-Driven Flows

Abstract: Bubbly flows comprise a large number of different flow situations, e.g., dispersed pipe flows, flows in multiphase agitated tanks, flows in multiphase fixed- and fluidized-bed reactors, and typical bubble-column and loop-reactor flows. This paper focuses on bubble-driven flows. These are flow situations were the bubble movement itself is the main source of momentum to the flow field and are often characterized by low superficial liquid velocities, relatively high superficial gas velocities, and no mechanical support of the flow (e.g., agitation). Only vertical flow situations are considered. An overview of the verified forces acting on bubbles is given, and examples of both classical and more recent modeling approaches are shown. This include gravity, buoyancy, centrifugal forces, conventional Magnus and Saffman forces, form and friction drag, and added mass as well as turbulent migration and other instability mechanisms. Special emphasis is placed on mechanisms creating bubble movement in the radial dire...

Equilibrium uptake, sorption dynamics, process optimization, and column operations for the removal and recovery of malachite green from wastewater using activated carbon and activated slag

Abstract: The waste slurry generated in fertilizer plants and slag (blast furnace waste) have been converted into low-cost adsorbents, activated carbon and activated slag, respectively, and these are utilized for the removal of malachite green (a basic dye) from wastewater. In the batch experiments, parameters studied include the effect of pH, sorbent dosage, adsorbate concentration, temperature, and contact time. Kinetic studies have been performed to have an idea of the mechanistic aspects and to obtain the thermodynamic parameters of the process. The uptake of the dye is greater on carbonaceous material than on activated slag. Sorption data have been correlated with both Langmuir and Freundlich adsorption models. The presence of anionic surfactants does not affect the uptake of dye significantly. The mass transfer kinetic approach has been applied for the determination of various parameters necessary for the designing of fixed-bed contactors. Chemical regeneration has been achieved with acetone in order to recover the loaded dye and restore the column to its original capacity without dismantling the same.

Hydrolysis of Vegetable Oils in Sub- and Supercritical Water

Abstract: Water, in its subcritical state, can be used as both a solvent and reactant for the hydrolysis of triglycerides. In this study, soybean, linseed, and coconut oils were successfully and reproducibly hydrolyzed to free fatty acids with water at a density of 0.7 g/mL and temperatures of 260−280 °C. Under these conditions the reaction proceeds quickly, with conversion of greater than 97% after 15−20 min. Some geometric isomerization of the linolenic acids was observed at reaction temperatures as low as 250 °C. Reactions carried out at higher temperatures and pressures, up to the critical point of water, produced either/or degradation, pyrolysis, and polymerization, of the oils and resultant fatty acids.

Sunflower stalks as adsorbents for color removal from textile wastewater

Abstract: Sunflower stalks as adsorbents for two basic dyes (Methylene Blue and Basic Red 9) and two direct dyes (Congo Red and Direct Blue 71) in aqueous solutions were studied with equilibrium isotherms and kinetic adsorptions. The maximum adsorptions of two basic dyes on sunflower stalks are very high, i.e., 205 and 317 mg/g for Methylene Blue and Basic Red 9, respectively. The two direct dyes have relatively lower adsorption on sunflower stalks. The adsorptive behaviors of sunflower stalk components are different. The pith, which is the soft and porous material in the center of stalks, has twice the adsorptive capacity of the skin. Particle sizes of sunflower stalks also affect the adsorption of dyes. The adsorption rates of two basic dyestuffs are much higher than that of the direct dyes. Within 30 min about 80% basic dyes were removed from the solutions.

Supported Metallocene Complexes for Ethylene and Propylene Polymerizations: Preparation and Activity

Abstract: Important research is currently underway to develop supported metallocene-based catalysts that could be widely used in the polyolefin industry. Recent developments concerning these systems are reviewed. The main preparation methods for metallocene immobilization on various supports are first systematized and described. Then, the nature and structure of active sites as well as their formation mechanism are analyzed. The performances for ethylene and propylene polymerizations of various supported metallocene systems are compared and discussed on the basis of the different catalyst preparations and of the operational polymerization conditions. Finally, the influence of metallocene heterogenization on the final polymer properties is examined.

Biomass Gasification: Produced Gas Upgrading by In-Bed Use of Dolomite

Abstract: When some calcined dolomite (OCa·OMg) is used in the bed of a biomass gasifier of fluidized bed type the raw gas produced is cleaner than when only silica sand is used in it as fluidizing medium. In-bed dolomite changes the product distribution at the gasifier exit because of in-situ catalytic reactions promoted by the calcined dolomite. Gasifying with steam−O2 mixtures causes the tar content in the exit gas to decrease from 12 to 2−3 g tar/m3n, the H2 content to increase from 25−28 to 43 vol %, and the CO content to decrease from 45 to 27 vol % when the gas and char yields, heating value of the gas, and other main variables also undergo important changes because of the in-bed dolomite. The experimental work here reported is carried out at small pilot plant scale in a 15 cm i.d. atmospheric and bubbling fluidized bed gasifier fed by 10 kg biomass/h. Dolomite is continuously fed to the gasifier, mixed with the biomass in percentages of 2−3 wt % of the total mass flow fed. A 10 wt % of calcined dolomite in ...

Comprehensive Kinetics of Oxidative Coupling of Methane over the La2O3/CaO Catalyst

Abstract: A comprehensive 10-step kinetic model of the oxidative coupling of methane to C2+ hydrocarbons over a La2O3/CaO catalyst was developed on the basis of kinetic measurements in a microcatalytic fixed-bed reactor covering a wide range of reaction conditions (1 < pO2 < 20 kPa, 10 < pCH4 < 95 kPa, 700 < T < 955 °C, 0.76 mCat/VSTP ≤ 250 kg·s/m3). The reaction scheme contains three primary and seven consecutive steps. The conversion of hydrocarbons and of carbon monoxide with oxygen were described by applying Hougen−Watson type rate equations. For the other reactions power-law rate equations were used. From the experimental data kinetic parameters, i.e. frequency factors, apparent activation energies, and adsorption enthalpies, were estimated. With the kinetic model the experimentally determined conversions of methane and oxygen, as well as yields to C2 hydrocarbons and carbon oxides, could be predicted with an average accuracy of ±20%.

A Tuning Strategy for Unconstrained SISO Model Predictive Control

Abstract: This paper presents an easy-to-use and reliable tuning strategy for unconstrained SISO dynamic matrix control (DMC) and lays a foundation for extension to multivariable systems. The tuning strategy achieves set point tracking with minimal overshoot and modest manipulated input move sizes and is applicable to a broad class of open loop stable processes. The derivation of an analytical expression for the move suppression coefficient, λ, and its demonstration in a DMC tuning strategy is one of the significant contributions of this work. The compact form for the analytical expression for λ is achieved by employing a first order plus dead time (FOPDT) model approximation of the process dynamics. With tuning parameters computed, DMC is then implemented in the classical fashion using a dynamic matrix formulated from step response coefficients of the actual process. Just as the FOPDT model approximation has proved a valuable tool in tuning rules such as Cohen−Coon, ITAE, and IAE for PID implementations, the tunin...

Planning and scheduling of parallel semicontinuous processes. 1. Production planning

Abstract: In this two-part series of papers, production planning and scheduling models are developed for the case of semicontinuous processes which are assumed to comprise several facilities in distinct geographical locations, each potentially containing multiple parallel units. The models developed are deterministic in nature and are formulated as mixed-integer linear programs (MIP's). Part 1 deals with multiperiod midterm planning models where sourcing considerations are important, given that products can be manufactured at several facilities, often on different continents. Optimal allocation of assets to production tasks in order to satisfy the fluctuating demands of the global marketplace over an extended horizon is the main goal in this kind of model. Plan performance is assessed relative to an objective function involving maximization of earnings and minimization of production, inventory, and transportation costs. In these types of models, the actual timing and sequencing of production campaigns is not determ...

Multiperiod Planning and Scheduling of Multiproduct Batch Plants under Demand Uncertainty

Abstract: In this paper the multiperiod planning and scheduling of multiproduct plants under demand uncertainty is addressed The proposed stochastic model, allowing for uncertain product demand correlations, is an extension of the deterministic model introduced by Birewar and Grossmann (Ind Eng Chem Res 1990, 29, 570) The stochastic model involves the maximization of the expected profit subject to the satisfaction of single or multiple product demands with prespecified probability levels (chance-constraints) The stochastic elements of the model are expressed with equivalent deterministic forms, eliminating the need for discretization or sampling techniques This implies that problems with a large number of possibly correlated uncertain product demands can be efficiently handled The resulting equivalent deterministic optimization models are MINLP's with convex continuous parts An example problem involving 20 correlated uncertain product demands is addressed A sequence of different models is considered whic

Mathematical Modeling of Multicomponent Chain-Growth Polymerizations in Batch, Semibatch, and Continuous Reactors: A Review

Abstract: A practical methodology for the computer modeling of multicomponent chain-growth polymerizations, namely, free-radical and ionic systems, has been developed. This is an extension of a paper by Hamielec, MacGregor, and Penlidis (Multicomponent free-radical polymerization in batch, semi-batch and continuous reactors. Makromol. Chem., Macromol. Symp. 1987, 10/11, 521). The approach is general, providing a common model framework which is applicable to many multicomponent systems. Model calculations include conversion of the monomers, multivariable distributions of concentrations of monomers bound in the polymer chains and molecular weights, long- and short-chain branching frequencies, chain microstructure, and cross-linked gel content when applicable. Diffusion-controlled termination, propagation, and initiation reactions are accounted for using the free-volume theory. When necessary, chain-length-dependent diffusion-controlled termination may be employed. Various comonomer systems are used to illustrate the ...

Adsorption and Desorption of Carbon Dioxide onto and from Activated Carbon at High Pressures

Abstract: Adsorption of carbon dioxide near its critical point on DeGussa IV activated carbon is investigated in this study. A volumetric method was used to measure the adsorption/desorption isotherms at 284, 300, 305, 310, and 314 K over a large pressure range. At subcritical temperatures, adsorption isotherms display a discontinuity at the vapor pressure of carbon dioxide, and desorption hysteresis is observed. However, there is no desorption hysteresis if adsorption is terminated before vapor−liquid transition occurs. At supercritical temperatures, adsorption isotherms display a plateau, and the excess decreases beyond the critical pressure. No hysteresis occurs during the desorption process. The adsorption isotherms can be represented very well by the simplified local density model.

Production of ethylene from hydrous ethanol on H-ZSM-5 under mild conditions

Abstract: Due to the dramatic rise in the use of ethers as fuel oxygenates, an alternative process for the production of ethyl tert-butyl ether (ETBE) based solely on biomass-derived ethanol feedstock is proposed. The first step in this process is ethanol dehydration on H-ZSM-5 to produce ethylene. Hydrous ethanol is a particularly attractive feedstock for this step since the production of anhydrous ethanol is very energy/cost intensive. In fact, the presence of water in the ethanol feed enhances the steady-state activity and selectivity of H-ZSM-5 catalysts. Reaction kinetic data were collected in a microreactor at temperatures between 413 and 493 K, at ethanol partial pressures of less than 0.7 atm, and at water feed molar ratios of less than 0.25. A sharp initial decline in catalyst activity observed within a few minutes on stream was attributed to the formation of “low-temperature coke” from ethylene oligomerization. Deactivation occurred at a much slower rate after 100 min on stream, allowing near-steady-state...

Planning and Scheduling of Parallel Semicontinuous Processes. 2. Short-Term Scheduling

Abstract: In part 1 of this series, it was seen how minimum run length constraints may complicate conventional multiperiod models. For short-term scheduling, these constraints, along with sequencing issues, ...

Heterogeneous Cross-Linking of Chitosan Gel Beads: Kinetics, Modeling, and Influence on Cadmium Ion Adsorption Capacity

Abstract: Chitosan, a linear biopolymer of glucosamine residues, selectively adsorbs transition-metal ions such as cadmium from dilute solution. In order to process chitosan into a more durable form, a 5 wt % chitosan solution was cast into spherical gel beads of 3 mm diameter and then reacted with glutaraldehyde at free amine sites to form imine cross-links between linear chitosan chains. The rate processes of the heterogeneous cross-linking reaction and the effect of cross-linking on the cadmium ion adsorption capacity were determined. The cross-linking reaction was complete within 48 h at 27 °C, and the final extent of cross-linking ranged from 0.07 to 2.40 mol of glutaraldehyde consumed/mol of amine. Heterogeneous cross-linking was modeled as a shrinking core process where the molecular diffusion of glutaraldehyde through the cross-linked shell of the gel bead limited the overall rate of glutaraldehyde consumption. The effective diffusion coefficient of glutaraldehyde through the cross-linked layer was 4.7 × 10...

Performance of Different Dolomites on Hot Raw Gas Cleaning from Biomass Gasification with Air

Abstract: Calcined dolomites (CaO−MgO) from four different quarries have been tested for the upgrading of the hot raw gas from a fluidized bed gasifier of biomass with air. These calcined dolomites have big macropores (900−4000 A) and low (3.8−12 m2/g) BET surface areas. They have been tested in a fixed bed of 6 cm i.d. downstream from the air-blown biomass gasifier. The change in gas composition (contents in H2, CO, CO2, CH4, ...), tar content, gas heating value, etc., has been studied at different temperatures (780−920 °C) as well as space-times for the gas in the bed (0.03−0.10 kg·h/m3) and the type of dolomite. Increasing the equivalence ratio used in the gasifier and decreasing the H/C ratio of the gas increases the refractoriness of the tars to be eliminated by the calcined dolomite. Activation energies (100 ± 20 kJ/mol) and preexponential factors for the overall tar elimination reaction have been calculated for the different dolomites under realistic conditions. The activity of the dolomite for tar eliminati...