Oxidation Of Tar Research Articles

Study of the influence of aromatic hydrocarbons on the process of tar oxidation

Abstract This study examines the impact of polycyclic aromatic hydrocarbons on the oxidation of petroleum tar. An aromatic hydrocarbon concentrates isolated from extracts of selective oil purification using the polar industrial solvent N-methylpyrrolidone was employed as an additive to tar. The relationship between the softening temperature of oxidized bitumen and both the duration of oxidation and the properties of the initial raw material mixture was investigated. It has been established that the introduction of 10 wt.% aromatic additive will increase the oxidation rate by 6 °C/h. The conditions for producing road bitumen from the proposed raw material compositions were identified. The influence of polycyclic aromatic hydrocarbon concentrate on the qualitative characteristics of bitumen during the tar oxidation process was determined. Aromatic additive is similar to a plasticizer, and reduces the softening temperature of bitumen by 9 °C. But the combined oxidation of tar with an aromatic additive and a catalyst makes it possible to obtain bitumen with a softening point of 44 °C and a penetration of 80 x0.1 mm, which corresponds to the grade of bitumen 70/100. Analysis of the group composition of oxidized bitumen revealed that the aromatic additive facilitates the intensification of the tar oxidation process.

Multifluid computational fluid dynamics simulation for sawdust gasification inside an industrial scale fluidized bed gasifier

Scarcity of fossil fuels, and to fulfill the energy demand of the increasing population, researchers need to shift their attention to the alternative of fossil fuels. It would be impractical and time-consuming to conduct extensive experiments on Fluidized Bed Gasifiers (FBG) of varying fuel types, sizes, geometries and operating conditions. The objective of the current research work is focused on numerical simulation of hydrodynamics behavior and sawdust gasification in an industrial scale FBG using the Eulerian-Eulerian multifluid model. For the accurate prediction of thermal and hydraulic performance (bed voidage, suspension density, pressure drop, heat transfer, and combustion kinetics), one should incorporate the correct parameters in the Computational Fluid Dynamics (CFD) simulation of a fluidized bed gasifier. It includes the multiphase gasification modeling using the Eulerian-Eulerian approach with an user defined heterogeneous reaction kinetics. The adopted CFD methodology is validated with experimental data and extended for the prediction of gasification characteristics of sawdust by incorporating eight heterogeneous (moisture release, volatile cracking, tar cracking, tar oxidation, char combustion, CO₂ gasification, steam gasification, methanation reaction) and five homogeneous oxidation of CO, CH₄, H₂, forward and backward water gas shift (WGS) reactions. In the result section, composition of gasification products is analyzed, along with the hydrodynamics of sawdust and sand phase, heat transfer between the gas, sand and sawdust, reaction rates of different homogeneous and heterogeneous reactions are being analyzed along the height of the domain.

Partial oxidation of biomass gasification tar with oxygen transport membranes

Dual phase oxygen transport membranes were directly integrated into the producer gas stream of a low temperature circulating fluidized bed (LT-CFB) gasifier for partial oxidation of tar. Ce0.9Gd0.1O1.95–La0.6Sr0.4FeO3-d composite membranes were prepared by extrusion and dip-coating, co-sintered and infiltrated with electro-catalysts. These were investigated in two different set-ups: i) a membrane test rig, and ii) a partial oxidation testing unit connected to a biomass gasifier. The stability and performance of the membrane were tested in two different gas-streams; i) H2 and ii) producer gas. An oxygen flux of 1.5 Nml∙cm−2∙min−1 was measured in an air/H2 gradient at 850 °C through a 10 cm long membrane with a diameter of 10 mm, whereas a lower oxygen flux of 0.5 Nml∙cm−2∙min−1 was measured for the air/producer gas case. The producer gas contained ca. 2000 mg Nm−3 of primary tar. Analysis of the gas and the tar composition at the output of the membrane unit demonstrated that it contributed to the partial oxidation of the primary tar, resulting in a twofold increase of H2, CH4 and CO in the producer gas. This successful integration of oxygen transport membranes demonstrated that these membranes can reduce the tar content in producer gas from biomass gasifiers.

THE EFFECT OF ADDITIVES CONTAINING POLYCYCLIC ARENAS ON THE FORMATION OF THE PROPERTIES OF BITUMEN BINDER IN THE PROCESS OF THEIR JOINT OXIDATION WITH OIL TAR

The results of the study of the effect of polycyclic aromatic hydrocarbons (PAHs) on the efficiency of the process of oxidation of oil tar into bitumen are presented. By-products of oil refining were used as additives to tar: the residue of heavy pyrolysis resin (OTSP) and 2 samples of extracts (MAE-1; MAE-2) isolated from extracts of selective purification of oil distillate VD-3 using a polar solvent N-methylpyrrolidone containing 10 wt.% ethylene glycol. One of the extracts, MAE-2, was obtained from an oil extract pretreated with microwave radiation. Additives were injected into the tar at 70 ℃ in an amount of 10 wt.%. The hydrocarbon system was oxidized with air oxygen for 6 hours at a temperature of 220 ℃. Based on the analysis of the properties and group, structural and group compositions of oxidized bitumen binders, it was found that the content of benzene resins in the binder increases (~ 2.5 times) and asphaltenes (by 3 wt.%) during the oxidation of the mixture of MAE-1 + OTSP. When the mixture of MAE-2 + OTSP is oxidized, the content of benzene resins and asphaltenes in the binder decreases. The observed changes in the compositions of the oxidation products of mixtures of MAE + OTSP are preserved during the oxidation of tar + systems (MAE + OTSP). At the same time , the conditional content of aromatic structures according to the data of the IR spectrometric analysis in the oil component of the oxidized tar + system (MAE-2+OTSP), as well as poly-substituted polycyclic aromatic structures, is almost 2 times higher than for the oil component of the oxidized tar + system (MAE-1+OTSP). As a result, the oxidation of tar mixtures with additives containing polycyclic arenas improves the quality of the target product by increasing the content of asphaltenes and aromatic structures in the aromatic oil component.

Chemical Model for Thermal Treatment of Sewage Sludge

Sewage sludge is here studied as a valuable source for processing or energy conversation thanks to its high nutrition and energy content. However, various origins of the wastewater, different water cleaning technologies, and seasonal and regional dependencies lead to the high variability of the sewage sludge properties. In thermal treatment units, that is, incineration, gasification and pyrolysis, sewage sludge serves as feedstock or fuel, hence a proper characterization and a mathematical description of the sewage sludge are required to estimate product streams and to formulate numerical simulations and optimization methods. The presented work introduces a surrogate concept that allows replication of sewage sludge’s ultimate composition, moisture, and ash content. The surrogate approach aims to model the decomposition of any sewage sludge sample, opposite to the established determination of kinetic rates for individual samples. Based on chemical solid surrogate species and corresponding reaction mechanisms, the thermal decomposition path is described. Sewage sludge is represented by a combination of lignocellulosic species, proteins, sugars, lipids, and representative inorganic species. The devolatilization and heterogeneous reactions are formulated such that they can be used together with a detailed gas-phase model, including tar oxidation and emission models for nitrogen and sulfur oxides, recently proposed by the authors. The developed chemical model is applied using a zero-dimensional gasification reactor in order to model weight loss within the thermogravimetric analysis, pyrolysis, gasification and combustion conditions. Weight loss, the composition of product gases, and emission release (nitrogen and sulfur oxides) are captured well by the model. The flexible surrogate approach allows us to represent various sewage sludge samples.

Very Sensitive Tar Monitoring in Syngas Streams By Estimation of Oxygen Demand – a Preliminary Study

Motivation: Thermochemical conversion of biomass to syngas by gasification of biological wastes like food or wood residuals wins more and more importance for energy supply because this kind of fuel is sustainable and generally available on demand. The syngas is composed of fuel components like CO, CH4, H2 and light hydrocarbons, but also contains undesired components like particulate matter and particularly tar. The latter constituents represent a complex mixture of aromatic compounds like toluene, phenol or naphthalene, which vary in relative composition and absolute concentration related to the composition of the biomass and the actual quality of the gasification process.Tar content in the raw syngas leads to complications like tar deposition on the walls, clogging of pipes in the equipment of the associated processes e.g. for generation of electric energy in which syngas is used as a fuel. The continuous monitoring of the tar in the syngas even at low concentrations is, therefore, of major importance to enable installation of a feedback operation control of the gasifying process and achieve minimization of the tar content. In the past, analysis of tar in syngas is well established, but expensive analysis methods like FTIR, NMR and GC/MS were published [1]. Also, tar analysis by LED induced fluorescence spectroscopy was reported in [2], but preliminary tests were conducted in the liquid phase at relatively high concentrations of phenol (8-10%). Recently, online monitoring of the tar concentration in producer syngas by use of a photo ionization detector (PID) [3] or a flame ionization detector (FID) [4] was described. In the latter concept the FID difference signal based on the syngas stream without and with condensation of the tar (cooled filter at 20°C-100°C) represents the tar concentration. This concept of tar analysis seems to be quite accurate for tar concentrations higher than 5g/m3. PID promises to enable tar component detection and to be very sensitive, however, the long-term stability of this monitoring concept seems to be problematic. New concept of more sensitive tar-monitoring in syngas: In this paper, for the first time, a novel concept of continuous tar monitoring in syngas is introduced. The setup for evaluation in the laboratory is schematically given in Fig.1a. It allows accurate measurements of toluene (used as a model tar) even below 1000ppm. The sensing principle is based on the estimation of the residual oxygen demand for tar combustion.First, a small flow (100ml/min) of the hot syngas stream is extracted from the gasifier and dosed with synthetic air to adjust stoichiometric combustion conditions (l=1) by use of an electronic mass flow controller (MFC) operated in a feedback loop with the signal of a wide band high-temperature Pt/8YSZ/Pt - oxygen sensor (LSU 4.9, Bosch GmbH). In the second step the synthetic air flow is kept constant, but now the syngas is lead over a condensation unit (T=-32°C) and again conducted to the oxygen sensor. The sensor provides a signal (coulometric current Ip) proportional to the excess oxygen concentration measured after tar condensation (l>1). The difference signal DIp = Ip (l>1) – Ip (l=1) represents the excess oxygen concentration after tar condensation which is directly related to the oxygen demand for tar oxidation. Discussion and outlook: Of course, this method of tar monitoring does not provide an analysis of the tar content because the measured oxygen demand related to the tar concentration depends on the specific mixture of aromatic compounds forming the tar. In addition, even at a temperature of approximately -32°C volatile components like toluene, which is one of the major constituents of tar, can only be condensate to a residual saturation concentration of about 800 ppm according to Clausius-Clapeyron equation, which corresponds to a concentration of about 3g/m3 (25°C). This means, at this temperature other components of tar with higher evaporation enthalpies like naphthalene and phenol will be estimated at a much lower sensitivity limit and, therefore, will represent the tar concentration even at considerably lower values than 1000ppm. In the next step this novel procedure of tar monitoring was experimentally evaluated, and tested with naphthalene as model tar. The results demonstrated the very good sensitivity and long-term stability of this monitoring concept. The automated system recorded a clear signal even at the lowest naphthalene concentration (14ppm/74mgm-3).These experimental results from laboratory will be presented in detail, modifications of the setup necessary for analysis of real syngas of a wood gasifier and some preliminary experiments will be reported and limits of detection in context with some technical advantages/restrains will be discussed. Acknowledgement This work is part of the EBIPREP collaboration project (www.ebiprep.eu) financed by the EU International Programme INTERREG V Oberrhein 2017-2020.

Pyrolysis-catalytic upgrading of bio-oil and pyrolysis-catalytic steam reforming of biogas: a review

Fast-rising population and economic growth are inducing a rapid increase in the energy demand. To date, fossil fuels constitute the primary energy source, but their combustion emits greenhouse gases responsible of global warming. Therefore, developing environment-friendly energy sources is critical. For instance, pyrolysis converts biomass into valuable compounds such as syngas, biochar, and bio-oil, yet produced bio-oil and biogas require further upgrading processes before their use. Current processes include gasification, purification, separation, and catalytic pyrolysis. For syngas synthesis, applying one or a couple of these processes leads to low product yields since they favor the production of bio-oil or biogas. Moreover, tar formation during biomass pyrolysis remains a major technological issue in reactor design. Catalytic reforming is an attractive and efficient method for tar removal via tar oxidation into valuable gases. More importantly, catalytic reforming of pyrolysis volatile products constitutes a promising approach for both tar removal and biogas conversion into syngas. Here, we review the two major catalytic approaches of biomass valorization: catalytic pyrolysis and pyrolysis-catalytic reforming. We demonstrate that the catalytic pyrolysis mainly upgrades bio-oil, while pyrolysis-catalytic efficiently converts biomass into syngas. We analyze the effects of temperature and steam-to-carbon ratio on the products derived from coupling the pyrolysis of agricultural biomass waste to catalytic reforming. Increasing the temperature and steam-to-carbon ratio enhances hydrogen yield. A complete conversion of pyrolysis volatile products into syngas was obtained at 600 °C with steam-to-carbon ratio of 4 for pinewood biomass and nickel catalyst. The use of nickel catalyst supported on lanthana–alumina Ni/La2O3-αAl2O3 for the steam reforming of raw bio-oil produced from pine sawdust pyrolysis enhanced the yields of hydrogen and carbon monoxide, reaching 95% and 93%, respectively, at 700 °C and steam-to-carbon of 15.

Mechanism for catalytic cracking of coal tar over fresh and reduced LaNi1-xFexO3 perovskite

Efficient removal of tar at gas outlet is a challenge during COREX ironmaking process. The differences between fresh and reduced LaNi1-xFexO3 perovskite were investigated via catalytic cracking of coal tar at 700 °C. The total gas yield of fresh catalysts is generally higher than that of reduced ones. The reduced catalyst produced more tar and carbon deposition. While the fresh LaNi0.8Fe0.2O3 gave the highest total gas yield (34.8 mmol/gcoal) and H2 yield (20.9 mmol/gcoal), and the lowest tar production (0.05%) and carbon deposition (10.9%). The perovskite structure was destroyed after reduction and the metal in perovskite was reduced to load on the catalyst surface. Partial oxidation which produces CO and H2 mainly occurs in the catalysis of reduced perovskite. Complete oxidation which generates CO2 and water is the major catalytic route for fresh perovskite. Oxygen in perovskite will transfer from the bulk to the surface. Water in the product supplements oxygen for the perovskite to construct an oxygen transition cycle which can maintain the catalyst activity. Tar is decomposed by the oxygen in fresh perovskite structure. The high nickel content in perovskite could promote the oxidation of tar.

Very Sensitive Tar Monitoring in Syngas Streams By Estimation of Oxygen Demand

Motivation: Thermochemical conversion of biomass to syngas by gasification of biological wastes like food or wood residuals wins more and more importance for energy supply because this kind of fuel is sustainable and generally available on demand. The syngas is composed of fuel components like CO, CH4, H2 and light hydrocarbons, but also contains undesired components like particulate matter and particularly tar. The latter constituents represent a complex mixture of aromatic compounds like toluene, phenol or naphthalene, which vary in relative composition and absolute concentration related to the composition of the biomass and the actual quality of the gasification process.Tar content in the raw syngas leads to complications like tar deposition on the walls, coking and clogging of pipes in the equipment of the associated processes in which syngas is used as a fuel. The continuous monitoring of the tar in the syngas even at low concentrations is, therefore, of major importance to enable installation of a feedback operation control of the gasifying process and achieve minimizing of the tar content. In the past, for analysis of tar in syngas well established, but expensive analysis methods like FTIR, NMR and GC/MS were published [1]. Also, tar analysis by LED induced fluorescence spectroscopy was reported in [2], but preliminary tests were conducted in the liquid phase at relatively high concentrations of phenol (8-10%). Recently, online monitoring of the tar concentration in producer syngas by use of a flame ionization detector (FID) was described in [3]. The FID difference signal based on the syngas stream without and with condensation of the tar (cooled filter at 20°C-100°C) represents the tar concentration. This concept of tar analysis seems to be quite accurate for tar concentrations higher than 5g/m3. New concept of more sensitive tar-monitoring in syngas: In this paper, for the first time, a novel concept of continuous tar monitoring in syngas is introduced which has been tested in a lab setup (Fig. 1a). It allows accurate measurements of toluene (used as a model tar) even below 1000ppm. The sensing principle is based on the estimation of the residual oxygen demand for tar combustion.First, a small flow (100ml/min) of the hot syngas stream is extracted from the gasifier and dosed with synthetic air to adjust stoichiometric combustion conditions (λ=1) by use of an electronic mass flow controller (MFC) operated in a feedback loop with the signal of a classical high-temperature Pt/8YSZ/Pt - oxygen concentration cell. In the second step the synthetic air flow is kept constant, but now the syngas is lead over a condensation unit (T=-32°C) and again conducted to the oxygen concentration cell (KS1D, Lamtec GmbH) or to a broadband lambda-probe (LSU 4.9, Bosch GmbH). The latter sensor provides a signal (coulometric current Ip) proportional to the excess oxygen concentration measured after tar condensation (λ>1). The difference signal DIp = Ip(λ>1) – Ip(λ=1) represents the excess oxygen concentration after tar condensation which is directly related to the oxygen demand for tar oxidation. Discussion and outlook: Of course, this method of tar monitoring does not provide an analysis of the tar content because the measured oxygen demand related to the tar concentration depends on the specific mixture of aromatic compounds forming the tar. In addition, even at temperature of approximately -32°C volatile components like toluene, which is one of the major constituents of tar, can only be condensate to a residual saturation concentration of about 800 ppm according to Clausius-Clapeyron equation, which corresponds to a concentration of about 3g/m3 (25°C). This means, at this temperature other components of tar with higher evaporation enthalpies like naphthalene, phenol will be estimated at a much lower sensitivity limit and, therefore, will represent the tar concentration even at considerably lower values than 1000ppm.In the next step this novel procedure of tar monitoring will be automated, tested with naphthalene (model tar) and finally, first experiments will be conducted with syngas of a wood gasifier. These results will be reported as well and limits of detection will be discussed in context with some technical advantages/restrains. Acknowledgement This work is part of the EBIPREP collaboration project (www.ebiprep.eu) financed by the EU International Programme INTERREG V Oberrhein 2017-2020.

INVESTIGATING THE POSSIBILITY OF USING THE NATURAL BITUMEN OF GILSONITE TYPE FOR THE PRODUCTION OF ROAD BITUMEN

The heavy traffic combined with the adverse weather and climate factors which are characteristic for most of the year, makes high demands for asphalt concrete. The quality of asphalt concrete is largely determined by the properties of bitumen which plays the role of a binder which provides the formation of a monolithic composite road-building material from separate mineral grains. Compound bitumen obtained by mixing the peroxidized bitumen with tar have the best ratio of all physico-chemical indicators, it is also possible the option to compound residual bitumen with oxidized. Oxidized bitumen obtained by the oxidation of tar or a mixture of tar with other petroleum products is characterized by low cohesive strength, poor adhesion and considerable aging. The use of natural bitumen of gilsonite type is the most common method to improve the properties of bitumen. When introducing into the bitumen of this natural bitumen, its penetration at a temperature of 25° C is reduced, as well as the softening point is increased. In fact, the nature of the change in the properties of bitumen during introduction of natural bitumen is the same as during its oxidation. That is, natural bitumen can be used to produce road bitumen by compounding it with tar. This paper presents the results of bitumen research obtained by combining tar with natural bitumen of gilsonite type. The production of bitumen by combining tar with natural bitumen of gilsonite type allows obtaining different grades of road bitumen by changing the content of natural bitumen. Bitumen obtained by this technology is more heat- and crack-resistant, have high adhesion to the aggregates and are not subjected to the technological aging. This bitumen has a higher softening point and a lower Fraass breaking point and therefore a higher plasticity interval. Keywords: bitumen, production, equiviscous temperatures, natural bitumen, mixing.

Experimental study and chemical reactor network modeling of the high heating rate devolatilization and oxidation of pulverized bituminous coals under air, oxygen-enriched combustion (OEC) and oxy-fuel combustion (OFC)

Experimental and numerical investigations of the combustion of 2 bituminous coals under air, oxygen-enriched and oxy-fuel combustion conditions have been performed. 7 pulverized coal jet flames have been stabilized using a specifically designed flat flame reactor (FFR) allowing industrial heating rates to be reproduced. The investigated reacting media have been fully characterized in terms of temperature fields, fuel residence time, devolatilization rates and concentration profiles of O2, CO2, CO, NO and SO2. Obtained data have then been compared with predictions derived from a chemical reactor network (CRN) modeling approach. This latter incorporates a detailed reaction mechanism the formulation of which has been defined by comparing the results obtained through the implementation of 3 different detailed gas-phase combustion reaction schemes. On the whole, obtained numerical results show a good agreement with experimental data. By analyzing the reaction paths relying on the CRN predictions, the present study allowed highlighting and further exploring the influence played by the combustion atmosphere on the chemical pathways leading to species like CO, NO, SO2 or soot precursors. The main findings drawn through this work especially led to trace the increased CO concentrations measured under oxy-fuel combustion (OFC) to heightened HCO production and tar oxidation. Alternative NO formation pathways arising under OFC conditions (like the HCN → HNCO → NH → NO and HCN → NCO → HNCO → HNO → NO routes) have, moreover, been highlighted. While the SO2 production has been found to mainly depend on the quantity of fuel-S emitted during the devolatilization and on the local oxygen partial pressure (the main SO2 formation pathway being indeed not truly affected by the nature of the combustion atmosphere), the analysis of the main routes involved in the oxidation of aromatics such as benzene, naphthalene and phenanthrene has been found well insightful in order to explain some reduced soot productions recently reported in the literature under OFC.

Toluene Oxidation in the Absence and Presence of CO, CO2, Water and H2 over ZrO2‐Based Gasification Gas Clean‐Up Catalysts

AbstractGasification of biomass is an environmentally friendly way to produce electricity and syngas when combined with effective gas cleaning. ZrO2‐based catalysts have been proven to remove undesired tar molecules when a convenient amount of oxygen is added. However, high activity in the tar oxidation is not the only requirement for the catalyst performance. The valuable gasification gas components, such as CO and H2, must be protected while passing the complex gasification gas over the catalyst. Oxidation of toluene as a tar model compound was addressed by applying temperature‐programmed surface reaction (TPSR) experiments with continuous feed of toluene, oxygen and one main gasification gas component (CO, CO2, H2 or water) over pure and doped zirconias. The most water tolerant catalyst was pure ZrO2 and the least was SiO2‐ZrO2. A new indicator called ‘Preferentiality’ was introduced and it expresses in one single quantity how well the catalyst is performing in tar conversion while protecting the valuable components of the gas. At 600 °C, the highest preferentiality of toluene oxidation over both CO and H2 oxidation was achieved over pure ZrO2.

Catalytic Tar Removal from Bio‐Syngas via Oxidation on Metal Oxide Catalysts

AbstractTo diversify energy sources and to address the impacts of global warming, the transformation of biomass, a renewable energy source, into fuels and chemicals is becoming increasingly necessary. The gasification technology is an efficient way of converting biomass via syngas into sustainable fuels. By‐products, especially tar, are formed during the gasification process and need to be removed before further downstream processing. Mo/V/W‐mixed oxides were found to be applicable for the catalytic tar oxidation in CO/H2 atmosphere by adding a stoichiometric amount of oxygen. In temperature‐programmed experiments the reactivity of different tar model compounds during the selective oxidation on Mo/V/W‐mixed oxides as well as the catalytic performances of V2O5, WO3, and MoO3 during the tar oxidation were investigated.

The Study of Tar Oxidation Process Kinetics of Paraffin Naphthenic Base with Activating Complex

Bitumen is a mixture of hydrocarbons and hetero-organic compounds of different structures with a complex chemical composition which conditioning its operational physico-chemical and mechanical properties. Also varying widely depending on the nature of bituminous materials and the technology of its processing. The tar of oil mixture from Romashkinsky and Kama region deposits owned by OJSC Tatneft was chosen as the raw material of the oxidation process. During the oxidation of heavy petroleum residues (HPR) a lot of reactions takes place simultaneously: dehydrogenation, dealkylation, oxidative polymerization, polycondensation, cracking, followed by compaction of its products caused by an increasing loss of hydrogen during oxidation, which in combination with the cyclization reactions leads to the formation of high molecular weight products of high aromaticity degree. Nowadays, the oxidation of heavy refinery residues by air is the main process of bitumen production in Russia. Various methods of oxidation process efficiency increase are developed, in particular, the increase of phase contact surface by improving the air supply devices, technological process optimization parameters, and the use of oxidation catalysts are known. The most promising area of oxidized bitumen production intensification and their quality improvement is the introduction to the oxidation process of various modifiers that change the dispersion state and the feedstock reactivity.

Methods of obtaining bitumen from heavy oil processing residues

The article describes several methods for solving urgent problems: obtaining the qualitative bituminous materials from unsuitable for recycling heavy oil processing residues. The work was carried out in three directions. The results of the study of the basic laws of oxidation of heavy oils processing residues showed that this method for obtaining the bitumen is failed. The basic laws of joint oxidation of tar from heavy Orkhovitsk oil with heavy pyrolysis resin and neutralized acid tar. It was shown that the method of co-oxidation of Orkhovitsk oil residue and 11-13 % masses of heavy pyrolysis resin at the temperature of 250 °С, air supply 2,5 h-1 during 6 hours allows obtaining the road bitumen of the grade BND 60/90 according to DSTU 4044-2001. The process of modification of residual bitumen derived from heavy Orkhovitsk oil by the Butonal latex and rubber crumb is described. It is established that the use of these modifiers makes it possible to improve the properties of bitumen obtained from heavy oils. The results, presented in this article, can be used in the development of industrial technology for obtaining the bitumen from heavy oil processing residues.

Investigation of various catalysts for partial oxidation of tar from biomass gasification

The formation of tar during biomass gasification limits the use of the product gas in small scale CHP units like gas engines. Catalytic partial oxidation can be applied to remove tar and convert it into fuel gas by using a catalyst under sub-stoichiometric addition of oxygen. In the present study, different catalyst materials, i.e. several perovskite-type materials and one Ni-based catalyst, which shall be used in combination with an oxygen carrier material, were investigated in lab-scale experiments regarding their catalytic activity in partial oxidation of naphthalene as model tar compound. Furthermore, the influence of the trace substances HCl, KCl, and H2S on the performance of the Ni-based catalyst being the best performing catalyst was tested. Since the Ni-based catalyst is significantly poisoned by H2S, it was also tested in combination with a CuO-based sorbent. In addition to H2S reduction, the sorbent increased the catalytic activity of the entire system significantly, so that naphthalene was almost completely converted at temperatures above 450°C despite the presence of 140ppm H2S.

Partial Oxidation of Tar into Syngas over Rh-Based Catalysts

The performance of a Rh/LaCoO3/Al2O3 catalyst has been investigated in the conversion of tar produced during biomass devolatilization into syngas using a dual fixed bed reactor set-up suitably developed. The effect of the addition of different levels of oxygen to the reaction mixture containing tarry compounds on the catalytic activity has been studied at 700 °C evaluating both the quality of the syngas produced and the extent of coke deposition on the catalyst surface. A comparison of the catalytic performance with that of catalysts containing Rh or LaCoO3 only has been done as well as with that of a conventional Ni-based sample. Coke deposition strongly decreases up to totally disappearing for 3000 ppm O2 for Rh/LaCoO3/Al2O3 catalyst coupled to an increase in gas yield and a limited H2 loss. H2 and CO oxidations are conversely promoted by LaCoO3/Al2O3 catalyst in the presence of O2.

Oxidation of Cr(III)-citrate/tartrate complexes by δ-MnO2: Production of Cr(VI) and its impact factors

Cr(III)-cit and Cr(III)-tar were synthesized and purified, and then their stability in the presence of δ-MnO2 was further investigated in batch experiments under different conditions to predict the potential oxidation behaviors of Cr(III)–organic acid complexes in the environment. The results indicated that although the rates and extents of Cr(III)-cit and Cr(III)-tar oxidation by δ-MnO2 were much lower than those of aqueous Cr(III), Cr(VI) could be gradually released through the whole reaction. The oxidations of Cr(III)-cit and Cr(III)-tar were affected by the initial concentrations of δ-MnO2, pH and co-existing ions. Lower pH and higher concentrations of δ-MnO2 markedly enhanced the production of Cr(VI). Ammonium ions significantly improved the oxidation of Cr(III)-cit and Cr(III)-tar, but phosphate ions demonstrated an opposite effect due to the formation of more stable CrPO4. The oxidation process of Cr(III)-cit and Cr(III)-tar by δ-MnO2 can be divided into two phases. At the initial phase, a relatively rapid reaction obeyed the first-order model, and then a zero-order one was followed. It was observed that in all the cases the extent of Cr(III)-cit oxidation was lower than that of Cr(III)-tar. Thus, it was concluded that the stability of Cr(III)-cit was higher than that of Cr(III)-tar.

Investigation of combined catalyst and oxygen carrier systems for the partial oxidation of naphthalene as model tar from biomass gasification

In this paper, catalytic partial oxidation is applied as a thermo-chemical method to remove tar (here: naphthalene as a model component for tar) from Syngas and convert it into fuel gas by using a combined catalyst and oxygen carrier system. In this method, the amount of oxygen needed for the partial oxidation of tar will be supplied by an oxygen carrier, which will also serve as a carrier of the catalyst. Based on the results of laboratory tests, the perovskite material CSFM (Ca0.5Sr0.5Fe0.5Mn0.5O3-δ) and ilmenite exhibited promising properties as oxygen carriers. They can supply a sufficient amount of oxygen for the oxidation of tar and show excellent redox properties for the regeneration. As a potential catalyst material, NiO showed high catalytic activity. During testing, the combined system of these two materials showed high ability for the removal of naphthalene, which was used as a model component for tar. In order to prevent the catalyst (NiO) from being poisoned by H2S, H2S sorbent was used. In combination with the combined catalyst and oxygen carrier system, the use of H2S sorbent further enhanced the performance of the catalyst. In conclusion, the suitable oxygen carrier materials, catalyst and sour gas sorbent could be identified, which in combination enable the proposed tar removal process.

Experimental and numerical investigation of tar destruction under partial oxidation environment

Tar in biomass product gas is a major problem because it reduces the reliability of the equipment and enhances pollutant emission. Partial oxidation is effective for reducing tar inside gasifiers. In order to predict tar reduction with partial oxidation technology, knowledge of the fate of tar during partial oxidation process is paramount. A continuous reactor was developed for tar destruction experiment under partial oxidation environment. Tar components and non-condensable gasses were measured and analyzed. Results show that the defined “primary tar” contents share about 60% of the total tar amounts. Phenolics prevail under initial reaction, but it is easy to form PAHs (polycyclic aromatic hydrocarbons) by polymerization reactions under certain ER (actual mass flow rate of oxygen/oxygen required for complete oxidation of biomass feed stock). This process results in an increase of tertiary tar. Hydrogen's evolution curve shows a steep rise with ER, which could be an indicator for the crack of secondary tar. A model was developed for describing partial oxidation of tar. Phenol, toluene, benzene and naphthalene were chosen as model compounds. Fluid flow, chemical mechanism and heat transfer are considered in the model. The calculated total tar amounts are in qualitative agreement with experimental results.