Tar Samples Research Articles

Catalytic Pyrolysis/Gasification of Refuse Derived Fuel for Hydrogen Production and Tar Reduction: Influence of Nickel to Citric Acid Ratio Using Ni/SiO2 Catalysts

Gasification technology is an attractive alternative for the thermal treatment of solid wastes, producing a high energy value hydrogen rich syngas. The presence of tar in the produced gas diminishes its quality and potential use in further processes; for this reason the reduction of tar in waste gasification is a major challenge. In this work the pyrolysis/gasification of refuse derived fuel (RDF) from municipal solid wastes, was investigated using a two-stage reaction system with Ni/SiO2 catalysts prepared by a sol–gel method varying the citric acid concentration (CA). The fresh and reacted catalysts were characterised for surface area and pore size distribution, temperature programmed oxidation, and high resolution scanning electron microscopy. The effect of the nickel to citric acid ratio (Ni:CA) was evaluated in terms of the characteristics and performance of the Ni/SiO2 catalysts. The results showed that the prepared Ni/SiO2 catalysts exhibited a relatively high surface area and an increase in pore size distribution as the Ni:CA ratio was increased. The efficiency of the prepared catalysts on tar reduction and hydrogen production was examined during the pyrolysis/gasification of RDF; the results were compared with a blank experiment using a bed of sand. The tar fraction was quantified using gas chromatography/mass spectrometry. A low tar concentration of ~0.2 mgtar/gRDF was attained using the catalysts with Ni:CA ratios of 1:1 and 1:3; additionally a high hydrogen concentration (58 vol%), and low CH4 (2.2 vol%) and C2–C4 concentrations (0.8 vol%), were attained using the catalyst with a Ni:CA ratio of 1:3. A higher tar concentration of ~1.7 mgtar/gRDF was attained using the bed of sand, while the hydrogen production was remarkably decreased. The major tar compounds identified in the tar samples using the Ni/SiO2 catalysts were phenol, cresols, naphthalene, fluorene, and phenanthrene.

Effect of tar fractions from coal gasification on nickel–yttria stabilized zirconia and nickel–gadolinium doped ceria solid oxide fuel cell anode materials

The allowable tar content in gasification syngas is one of the key questions for the exploitation of the full potential of fuel cell concepts with integrated gasification systems. A better understanding of the interaction between tars and the SOFC anodes which leads to carbon formation and deposition is needed in order to design systems where the extent of gas cleaning operations is minimized. Model tar compounds (toluene, benzene, naphthalene) have been used in experimental studies to represent those arising from biomass/coal gasification. However, the use of toluene as a model tar overestimates the negative impact of a real gasification tar on SOFC anode degradation associated with carbon formation.In the present work, the effect of a gasification tar and its distillation fractions on two commercially available fuel cell anodes, Ni/YSZ (yttria stabilized zirconia) and Ni/CGO (gadolinium doped ceria), is reported. A higher impact of the lighter tar fractions was observed, in terms of more carbon formation on the anodes, in comparison with the whole tar sample. The characterization of the recovered tars after contact with the anode materials revealed a shift towards a heavier molecular weight distribution, reinforcing the view that these fractions have reacted on the anode.

An Analysis of Wood Pyrolysis Tar from High Temperature Thermal Cracking Process

The objective of this study is to investigate and analyze the tar yields and structural changes of tar formed during a high temperature thermal cracking process. Experiments were conducted in order to study the effect of temperature on the yield and characteristic chemicals of tar. All experiments were carried out with parawood under steady-state conditions. The temperature of the pyrolyzer was controlled at 600°C and pyrolysis gases were carried to the reformer by nitrogen. The thermal cracking tests were performed at six different temperatures: 700, 800, 900, 1,000, 1,100, and 1,200°C. The samples of tar were analyzed by gravimetric analysis, gas chromatography-flame ionization detector, and gel permeation chromatography techniques in order to get information and an understanding about the tar, such as tar yield, compositions, and average molecular weight. From the experimental results and quantity analysis, the amount of tar decreased continually to 90% reduction as temperature increased from 600 to 1,200°C resulting from thermal cracking of tar into the lighter products. In chemical analysis, at a low temperature range, the aromatic compounds were dominant in tar compositions. Meanwhile, these phenomena were adverse at higher temperatures and polycyclic aromatic hydrocarbons dominated. These resulted in higher than the average molecular weight as the temperature increased.

Direct Mass Spectrometry of tar sands: A new approach to bitumen identification

The activities related to the evaluation of the organic fraction of tar sands are acquiring more importance from economical and technical points of view due to the increased variety of sample composition and origin. Conventionally, the analyses of bitumen in tar sands are based on preliminary extraction from the inorganic matrix and further characterisation of physical and chemical features by means of different methods.A new approach to characterise the tar sand is now proposed, based on the direct insertion of tar sand into mass spectrometer chamber without any previous separation or treatment and further vaporisation under vacuum at increasing temperature and analysis of its components. DIP–MS (Direct Insertion Probe–Mass Spectrometry) allows separating the bitumen components from the solid inorganic matrix according to their boiling points up to masses of 700m/z and directly analysing them in one only step, even if they are characterised by high boiling point, high steric hindrance or low solubility, that usually limit their evaluation by chromatographic methods.This new application of DIP–MS approach is here described on model materials and on a series of real tar sand samples coming from different geological areas. Differences are evidenced among the tar sands on the basis of the evolution of their mass spectra.The information so obtained was compared and confirmed with other analytical techniques that are commonly used for crude oil and bitumen characterisation. This approach is proposed for an on-field application for fast screening of real samples in the perspective to acquire information on the most relevant organic species in the bitumen for comparative purposes and rough evaluation of the potentiality of tar sand fields.

A comparison between on-line and off-line tar analysis methods applied to common reed pyrolysis

An innovative on-line tar measuring system has been tested using the reference standard for tar sampling (UNI CEN/TS 15439) and off-line analysis approach. Samples of common reed have been characterized by means of physical–chemical and thermal analysis. Several experimental tests have been performed with a bench scale pyrolysis apparatus setting different process temperatures (300–700°C) and a heating rate of 50°Cmin−1. In each test the tar has been collected and analyzed. In addition, tars have been analyzed on-line by a lab scale fluidised bed gasifier – operated without the use of any gasifying agents – coupled with an optical measurement cell, equipped with Light-Emitting Diodes (LEDs) at different wavelengths (265nm, 285nm, 300nm and 365nm). The spectrum of absorbed light from the tar in the gaseous products has been detected through a photodiode. The total content of Polycyclic Aromatic Hydrocarbons (PAH) detected by the on-line method at 600°C is 44mgg−1 of initial feedstock, while the off-line method determined a total PAH content ranging from 2.75mg to 74.41mg at 300°C and 700°C, respectively. The integration between different analytical approaches on tar characterization has been useful to assess their capability and their potential application to predict tar composition.

Chemical fingerprinting of petroleum biomarkers in Deepwater Horizon oil spill samples collected from Alabama shoreline

We compare the chromatographic signatures of petroleum biomarkers in Deepwater Horizon (DH) source oil, three other reference crude oils, DH emulsified mousse that arrived on Alabama’s shoreline in June 2010, and seven tar balls collected from Alabama beaches from 2011 to 2012. Characteristic hopane and sterane fingerprints show that all the tar ball samples originated from DH oil. In addition, the diagnostic ratios of various hopanes indicate an excellent match. Quantitation data for C30αβ-hopane concentration levels show that most of the weathering observed in DH-related tar balls found on Alabama’s beaches is likely the result of natural evaporation and dissolution that occurred during transport across the Gulf of Mexico prior to beach deposition. Based on the physical and biomarker characterization data presented in this study we conclude that virtually all fragile, sticky, brownish tar balls currently found on Alabama shoreline originated from the DH oil spill.

Identification of sources of tar balls deposited along the Goa coast, India, using fingerprinting techniques

Deposition of tar balls along the coast of Goa, India is a common phenomenon during the southwest monsoon. Representative tar ball samples collected from various beaches of Goa and one Bombay High (BH) crude oil sample were subjected to fingerprint analysis based on diagnostic ratios of n-alkane, biomarkers of pentacyclic tri-terpanes and compound specific stable carbon isotope (δ13C) analysis to confirm the source. The results were compared with the published data of Middle East Crude Oil (MECO) and South East Asian Crude Oil (SEACO). The results revealed that the tar balls were from tanker-wash derived spills. The study also confirmed that the source is not the BH, but SEACO. The present study suggests that the biomarkers of alkanes and hopanes coupled with stable carbon isotope analysis act as a powerful tool for tracing the source of tar balls, particularly when the source specific biomarkers fail to distinguish the source.

The influence of temperature and steam on the yields of tar and light hydrocarbon compounds during devolatilization of dried sewage sludge in a fluidized bed

The influence of temperature and steam concentration over the yields of tar and light hydrocarbon compounds generated during devolatilization of batches of dried sewage sludge in a laboratory fluidized bed reactor was investigated. Tests were conducted in the temperature range of 600–900°C with gas residence time of 1.5s. Thirty-six aromatic tar compounds (from benzene to perylene) were analyzed by GC/MS and light hydrocarbons (CH4,C2H6,C2H4,C2H2,C3H8 and C3H6) by GC/thermal conductivity. The content of C, H, N and S in the gravimetric residue of the tar sample (that obtained after vacuum distillation of the original sample) was also analyzed. It was found that increasing the steam concentration (up to 30% molar) did neither modify the aromatic tar composition nor the yield of light hydrocarbons, only slightly affecting the yield of gravimetric tar. Detailed analyses of tar composition and light hydrocarbons enabled us to relate the yields of these compounds at different temperatures, shedding light on the mechanisms of tar conversion into light hydrocarbon species. It also provides shortcut methods for the estimation of tar mixture properties, such as the yields of heavy aromatic compounds and the aromaticity of the tar mixture, from light hydrocarbon measurements at different temperatures.

Characterization and evaluation of Ni/SiO2 catalysts for hydrogen production and tar reduction from catalytic steam pyrolysis-reforming of refuse derived fuel

A series of Ni/SiO2 catalysts have been prepared and investigated for their suitability for hydrogen production and tar reduction in a two-stage pyrolysis-reforming system, using refuse derived fuel (RDF) as the raw material. Experiments were conducted at a pyrolysis temperature of 600°C, and a reforming temperature of 800°C. The product gases were analysed by gas chromatography (GC) and the condensed fraction was collected and quantified using gas chromatography-mass spectrometry (GC–MS). The effects of the catalyst preparation method, nickel content and the addition of metal promoters (Ce, Mg, Al), were investigated. Catalysts were characterised using BET surface area analysis, temperature programmed oxidation (TPO), and scanning electron microscopy (SEM). The TPO and SEM analysis of the reacted catalysts showed that amorphous type carbons tended to be deposited over the Ni/SiO2 catalysts prepared by impregnation, while filamentous type carbons were favoured with the sol-gel prepared catalysts. The influence of catalyst promoters (Ce, Mg, Al) added to the Ni/SiO2 catalyst prepared by the sol-gel method was found not to be significant, as the H2 production was not increased and the tar formation was not reduced with the metal-added catalyst. The highest H2 concentration of 57.9vol.% and lower tar amount produced of 0.24mgtar/gRDF; were obtained using the 20wt.% Ni/SiO2 catalyst prepared by sol-gel. On the other hand a low catalytic activity for H2 production and higher tar produced were found for the impregnated series of catalysts, which might be due to the smaller surface area, pore size and due to the formation of amorphous carbons on the catalyst surface. Alkenes and alcohol functional groups were mainly found in the analysed tar samples, with major concentrations of styrene, phenol, indene, cresols, naphthalene, fluorene, and phenanthrene.

The Characterization of a Tar Sand Sample Using Differential Scanning Calorimeters

In this study, non-isothermal kinetics and a thermal analysis tar sand sample is studied by differential scanning calorimeter and pressurized differential scanning calorimeter. Differential scanning calorimeter and pressurized differential scanning calorimeter curves revealed two reaction regions in the temperature range of 20–600°C. Effect of pressure was also studied in order to see the thermal behavior of a tar sand sample under different elevated pressures. Two different kinetic methods (ASTM and Borchald and Daniels) were used to determine the kinetic parameters of the samples.

Nascent tar formation during polyvinylchloride (PVC) pyrolysis

Pyrolysis experiments of polyvinylchloride (PVC) were performed to investigate the effects of peak temperature, holding time, and heating rate on the formation of nascent tar. The nascent tar samples were collected using a wire-mesh reactor where the secondary reactions of the evolved volatiles were minimized. The small compounds, such as benzenes and alkanes, were not detected in nascent tar in wire-mesh reactor, whose components are quite different from those of other tars in tube type reactor and vacuum reactor. At a heating rate of 1000K/s, the quasi-3 rings and 3 rings group aromatics were the major components in nascent tar; while the content of 2 rings group aromatics increased from 7.02% to 31.75% with increasing peak temperature from 500 to 800°C. At a longer holding time of 300s, an increase of 2 rings group aromatics from 7.02% to 50.33% was also observed for the nascent tar at 500°C, indicating that the tar composition significantly changed at different stages of PVC pyrolysis. It seems that 3–4 rings compounds form in the early stage and then 2 rings compounds release in the later stage of PVC pyrolysis. Based on the experimental results in this work, a new four-stage mechanism, including (1) dechlorination accompanied with inner cyclization, (2) aromatic chain scission, (3) release of quasi-3 rings or 3 rings group, and (4) release of 2 rings group, of the PVC tar formation was proposed.

Physical and thermal properties of Jordanian tar sand

A preliminary characterization and beneficiation study of Jordanian tar sand obtained from the Dead Sea area has been carried out. Representative tar sand samples were crushed using a jaw crusher and sieved to different size fractions. Characterization of these size fractions revealed that most of the bitumen content was concentrated in the smallest size fraction (<106μm). Scanning electron microscopy images showed that the structure of the tar sand is composed of quartz particles of <1mm in size surrounded by a bitumen containing envelope which can be regarded as a binder. The pyrolysis kinetics of the material was studied using thermogravimetric analysis (TGA) and the relationship with heating rate was derived. The mass loss obtained from TGA was found to be independent of the heating rate at 35% of the original mass. Three regions of differing kinetic parameters were identified during pyrolysis; a low temperature pyrolysis region, a fuel deposition region and a high temperature pyrolysis region. It was found that the activation energy, in the region of fuel deposition, changes from 32kJ/mol to 42kJ/mol by increasing the heating rate from 1°C/min to 50°C/min, respectively.

Thin-film cracking of acid tars

The method of thin-film thermal cracking of acid tar to manufacture liquid fuel and coke or liquid fuel and asphaltic binders has been developed. Differential thermal analysis of acid tar samples has been performed. A model of the thin-layer thermal cracking of acid tar and an algorithm for calculating the engineering parameters of the process have been proposed.

Dynamic Elemental Thermal Analysis: A technique for continuous measurement of carbon, hydrogen, oxygen chemistry of tar species evolved during coal pyrolysis

A novel technique is described which provides quantitative and continuous analysis of light gas and condensable tar components as they are evolved in terms of carbon, hydrogen and oxygen. The technique has also been used to directly characterise the total tar sample in terms of carbon distribution and boiling point. It has been found that changes to the dynamic tar-H/C ratio correspond well with particular temperatures measured by Geiseler Plastometer for softening, maximum fluidity and re-solidification. This technique can enhance the chemical understanding of mechanisms occurring during de-polymerisation and cross-linking of coal (i.e. metaplast development and the transfer of hydrogen) while also monitoring tar evolution. A tar collection and re-vaporisation method provides a means of identifying tar groups that contribute towards the metaplast phase and temperatures at which they evolve. Both methods are unique in studying chemical aspects of coal and tar behaviour with heating, in a field based on thermo-physical techniques (e.g. H1 NMR, high temperature rheology, Geiseler plastometry, dilatation). Overall, the Dynamic Elemental Thermal Analysis (DETA) technique can give new insight into the fundamental mechanisms prevalent in coal pyrolysis and provides quantitative chemical assessment of tar nature (i) during the heating of coal and (ii) as a final (total) condensed product.

Comparison of efficiency of two methods for tar sampling in the syngas

In the present work, a cold solvent trapping (CST) and solid-phase adsorption (SPA) methods for determining concentration of tar compounds have been chosen for comparison. When the cold solvent trapping method is used, the producer gas flows through a series of impingers containing 2-propanol, whereas in a solid-phase adsorption method it passes through two adsorbent cartridges loaded with 500mg of aminopropyl-bonded silica, and 100mg of activated coconut charcoal. During the experiment, 52 compounds were identified by the cold solvent trapping method and 48 compounds by the solid-phase adsorption method. The SPA method is more accurate than those using impingers, especially for determining such volatile organic compounds as benzene, toluene, and xylenes, due to the use of a second sorbent, activated coconut charcoal. By contrast, the CST method proves to be more accurate for determining components of heavy tar due to a much larger volume of the sampled gas.

Sampling of tar from sewage sludge gasification using solid phase adsorption

Sewage sludge is a residue from wastewater treatment plants which is considered to be harmful to the environment and all living organisms. Gasification technology is a potential source of renewable energy that converts the sewage sludge into gases that can be used to generate energy or as raw material in chemical synthesis processes. But tar produced during gasification is one of the problems for the implementation of the gasification technology. Tar can condense on pipes and filters and may cause blockage and corrosion in the engines and turbines. Consequently, to minimize tar content in syngas, the ability to quantify tar levels in process streams is essential. The aim of this work was to develop an accurate tar sampling and analysis methodology using solid phase adsorption (SPA) in order to apply it to tar sampling from sewage sludge gasification gases. Four types of commercial SPA cartridges have been tested to determine the most suitable one for the sampling of individual tar compounds in such streams. Afterwards, the capacity, breakthrough volume and sample stability of the Supelclean™ ENVI-Carb/NH(2), which is identified as the most suitable, have been determined. Basically, no significant influences from water, H(2)S or NH(3) were detected. The cartridge was used in sampling real samples, and comparable results were obtained with the present and traditional methods.

Characterization of Tar from the Pyrolysis/Gasification of Refuse Derived Fuel: Influence of Process Parameters and Catalysis

Two nickel-based catalysts were prepared and investigated in relation to their influence over aromatic compounds contained in tar from the pyrolysis–gasification of refuse derived fuel (RDF), using a two-stage reaction system. The results were compared with those obtained in experiments carried out using a bed of sand, both with steam and without steam. The condensed tar was analyzed for its polycyclic aromatic hydrocarbon (PAH) content using gas chromatography–mass spectrometry (GC-MS), size exclusion chromatography (SEC), and Fourier transform infrared spectroscopy (FTIR) techniques. It was found that, in the presence of Ni/α-Al2O3 catalysts, some of the PAHs from three to four rings were eliminated; however, some single-ring and two-ring compounds such as styrene and indene were identified. This was also inferred from the molecular mass data (SEC). The identified PAHs consisted mainly of naphthalene, biphenyl, acenaphthylene, fluorene, and phenanthrene, but other PAHs also were identified for example: methylnaphthalenes. The influence of catalyst type on the gas composition showed that, using a 10 wt % Ni/α-Al2O3 catalyst, ∼45 vol % of hydrogen was achieved, while the CH4 and C2–C4 concentrations were markedly reduced, compared with the 5 wt % Ni/α-Al2O3 catalyst, which gave similar results to those obtained with the sand bed under the same conditions. The presence of oxygenated compounds in the tar samples was compared at different gasification temperatures. The results showed the presence of oxygenated compounds such as catechols and alcohols at 600 °C, these compounds were reduced as the gasification temperature increased, while the concentration of aromatic compounds increased.

Multivariate Statistical Methods for the Environmental Forensic Classification of Coal Tars from Former Manufactured Gas Plants

Compositional disparity within a set of 23 coal tar samples (obtained from 15 different former manufactured gas plants) was compared and related to differences between historical on-site manufacturing processes. Samples were prepared using accelerated solvent extraction prior to analysis by two-dimensional gas chromatography coupled to time-of-flight mass spectrometry. A suite of statistical techniques, including univariate analysis, hierarchical cluster analysis, two-dimensional cluster analysis, and principal component analysis (PCA), were investigated to determine the optimal method for source identification of coal tars. The results revealed that multivariate statistical analysis (namely, PCA of normalized, preprocessed data) has the greatest potential for environmental forensic source identification of coal tars, including the ability to predict the processes used to create unknown samples.

Gas emissions, minerals, and tars associated with three coal fires, Powder River Basin, USA

Ground-based surveys of three coal fires and airborne surveys of two of the fires were conducted near Sheridan, Wyoming. The fires occur in natural outcrops and in abandoned mines, all containing Paleocene-age subbituminous coals. Diffuse (carbon dioxide (CO2) only) and vent (CO2, carbon monoxide (CO), methane, hydrogen sulfide (H2S), and elemental mercury) emission estimates were made for each of the fires. Additionally, gas samples were collected for volatile organic compound (VOC) analysis and showed a large range in variation between vents. The fires produce locally dangerous levels of CO, CO2, H2S, and benzene, among other gases. At one fire in an abandoned coal mine, trends in gas and tar composition followed a change in topography. Total CO2 fluxes for the fires from airborne, ground-based, and rate of fire advancement estimates ranged from 0.9 to 780mg/s/m2 and are comparable to other coal fires worldwide. Samples of tar and coal-fire minerals collected from the mouth of vents provided insight into the behavior and formation of the coal fires.

Energy Recovery from Contaminated Biomass

This study focuses on thermal gasification methods of contaminated biomass in an atmospheric fluidized bed, especially biomass contaminated by undesirable substances in its primary use. For the experiments, chipboard waste was chosen as a representative sample of contaminated biomass. In the experiments, samples of gas and tar were taken for a better description of the process of gasifying chipboard waste. Gas and tar samples also provide information about the properties of the gas that is produced.