Tar Components Research Articles

Base-acid tandem catalytic upgrading of coal pyrolysis volatiles: the effects of alkaline earth oxides and modified HZSM-5 zeolites

Catalytic upgrading of coal pyrolysis volatiles is a promising technology to bolster the production of value-added chemicals from coal. To optimize product distribution and mitigate catalyst deactivation, this work investigated tandem catalysts combining the upper alkaline earth oxides (CaO or MgO) with the lower modified HZSM-5 (mesopore creation and Ga loading). The pre-cracking of volatiles over CaO or MgO lowered the average molecule size of tar components. The diffusion properties and aromatization of these pre-cracking-derived intermediates were improved, facilitating the secondary upgrading over HZSM-5-based catalysts, promoting the formation of aromatics. The experimental results showed that tandem CaO-HZSM-5 catalysts presented better synergy to improve the tar components as compared to MgO-HZSM-5, considering the formation of aromatics in tar. In this context, the mesopore and metal Ga were introduced into HZSM-5 to further upgrade the tar quality. The mesoporous structure for HZSM-5-meso and Ga/HZSM-5-meso promoted the conversion of aliphatic hydrocarbons into aromatics. Simultaneous introduction of mesopores and Ga synergistically increased the aromatic content in tar to 41.6% and reduced the carbon deposition to 0.88wt.%. In summary, this work elucidated the mechanism of tandem CaO-modified HZSM-5 catalysis for the upgrading of volatiles from coal pyrolysis.

Nickel doped enhanced LaFeO3 catalytic cracking of tar for hydrogen production

The transformation of biomass into green energy was pivotal for sustainable development, yet the efficient conversion of biomass-derived tar into hydrogen-rich syngas remained a significant challenge. This study addressed the catalytic demand for hydrogen production from tar, focusing on the development of LaNixFe1-xO3 perovskites as catalysts. A series of LaNixFe1-xO3 perovskites with varying nickel doping levels (x=0, 0.25, 0.5, 0.75, 1) were synthesized to evaluate their catalytic performance in converting toluene, a representative tar component, into hydrogen. The LaNi0.5Fe0.5O3 catalyst demonstrated the highest hydrogen yield (14.5L/6h) and volume percentage (82.9V/V%), highlighting the optimal nickel doping level for enhancing hydrogen production. The hydrogen production performance of LaNixFe1-xO3 was significantly affected by nickel doping. In particular, a small amount of nickel doping can significantly enhance the hydrogen production capacity of LaFeO3 and maintain good reaction stability. The enhanced performance was attributed to the high oxygen storage capacity of perovskite, which facilitated the removal of surface carbon and promotes the methanation reaction. Notably, the total content of defect oxygen and surface adsorbed oxygen/hydroxyl groups significantly impacted the hydrogen production efficiency. These findings indicated that LaNi0.5Fe0.5O3 was an effective catalyst for converting biomass-derived tar into hydrogen-rich syngas, offering a promising solution to the catalytic demand in the hydrogen production system.

Plant Design for the Production of Propylene Oxide by Isopropylbenzene 2-phenylpropane, or (1-Methylethyl) Benzene (Cumene)

Cumene is a colorless, volatile liquid with a gasoline-like odor. It’s also known as isopropylbenzene, 2-phenylpropane, or (1-methylethyl) benzene. It’s a natural component of coal tar and crude oil, and it can also be employed in gasoline as a blending component. Cumene hydroperoxide is produced by oxidizing cumene with benzene and propylene in the presence of air. As a result, the cumene hydroperoxide is changed to cumyl alcohol, which is then transformed to propylene without the use of oxygen. Propylene oxide is an organic compound produced through various methods such as the cumene process and the hydroperoxide process. The cumene method is preferred due to its low by-product production and high market value of co-products. The reactive distillation process is a feasible method for producing propylene oxide with high purity and reduced costs. Future work includes optimizing processes, developing new catalysts, and improving efficiency. Propylene oxide has practical applications in the production of polyurethane foams, coatings, adhesives, polyether polyols, and propylene glycols.

Insight into carbon structures and pyrolysis behaviors of coal from the 13C CP/MAS NMR spectra

Carbon structures play an important role in the pyrolysis behavior of coal. Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy is a powerful nondestructive technique for characterizing the carbon skeleton structures in coal. In this study, the carbon type distribution, lattice parameters, and chemical bond concentrations of six coal samples with different Vdaf values were investigated using 13C CP/MAS NMR spectra. Typical TGA and Py-GC-MS methods were utilized to obtain information on weight loss and pyrolysis products of the coals. The aromaticity of coal was determined by an adjustment of the apparent area ratio in the 13C CP/MAS NMR spectra, which shows promising potential for predicting key temperatures, characteristic index, and tar quality in coal pyrolysis. Results from the carbon fractions indicated that the total concentrations of chemical bonds in coal are approximately 150 mmol/g, with more Car−Car and Car−H bonds present in highly mature coal samples, and fewer Cal−Cal, Cal−H, and CO bonds. The breaking behaviors of chemical bonds during coal pyrolysis depend on a combination of temperature and concentration. The breakage of Cal−Cal bond contributes significantly to the pyrolytic weight loss of coal, accompanied by the decrease of Cal−H bonds along with the removal of aliphatic groups. Furthermore, as coal maturity increases, tar from fast pyrolysis contains more polycyclic aromatic hydrocarbons with a higher average molecular weight. The average number of aromatic rings in tar components is notably lower than that of aromatic clusters in coal. These results will contribute to a better understanding of the relationship between coal structure and reactivity, and may provide valuable insights for the efficient and clean utilization of coal.

EFFECT OF DIDODECANOYL PEROXIDE ON TRANSFORMATIONS OF HIGH-SULFUR VACUUM RESIDUE COMPONENTS IN THE PROCESS OF INITIATED CRACKING

This paper presents the results of the study of the composition of cracking products of high-sulfur tar obtained from oil of Zyuzeyevskoye field in the presence of radical-forming additive – didodecanoyl peroxide. Thermal treatment of the mixture of vacuum residue with different amounts of didodecanoyl peroxide was carried out at a temperature of 500 °C. The duration of the process was 15 min. Characteristic features of changes in the material balance of the process, group composition of liquid cracking products, qualitative and quantitative composition of newly formed sulfur compounds were established. The use of additive in the amount of 0.5 – 0.75%wt. allows to reduce thermal stability of high-molecular components of tar (resins and asphaltenes), and also promotes change in direction of reactions. Processes of condensation of resins and asphaltenes into solid coke-like products are slowed down, and cracking reactions are initiated with formation of low-molecular components, which fall into the composition of oils, as a result of which it is possible to obtain additional amounts of distillate fractions. It is shown that thiophene, benzo- and dibenzothiophene derivatives, which are absent in the initial tar, are intensively formed and accumulated in the composition of liquid cracking products, which worsens the quality of the obtained distillate fractions. Among the identified sulfur compounds benzothiophene homologs prevail. It was found that cracking of tar in the presence of additive didodecanoyl peroxide promotes deep destruction of sulfur-containing fragments of vacuum residue and asphaltene molecules. Sulfur compounds formed under these conditions not only get into the composition of oils, but also participate in condensation reactions with the formation of solid products, which leads to an increase in the degree of sulfur removal from the composition of liquid cracking products. For citation: Goncharov A.V., Krivtsov E.B. Effect of didodecanoyl peroxide on transformations of high-sulfur vacuum residue components in the process of initiated cracking. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 8. P. 121-128. DOI: 10.6060/ivkkt.20246708.15t.

Catalytic upgrading of Naomaohu coal pyrolysis volatiles over CaO catalyst

Catalytic upgrading of coal pyrolysis volatiles is one the promising way to achieve high quality tar and gas. In this study, catalytic upgrading of volatiles from Naomaohu (NMH) coal pyrolysis has been conducted in a two-stage fixed bed reactor using CaO as catalyst. The aim of this work was to investigate the catalytic effect of CaO on the gas and liquid product distribution, as well as the variations in gas and coal tar components. Simulated distillation and GC-MS analysis has been used to understand the distribution of tar component. On the one hand, CaO exhibits selective cleavage of large molecules, such as long-chain esters, leading to the production of aromatics through the processes of dehydrocyclization and aromatization. CaO has the ability to stabilize free radicals that are generated during the cleavage of large molecules, thereby promoting the formation of light aromatic hydrocarbons. Consequently, the light tar fraction (boiling point <360 °C) increased from 64.4 % to 74.6 %, while the heavy tar fraction (boiling point＞360 °C) decreased from 35.6 % to 25.4 % in the pyrolysis tar. The compounds with long ester chains in the tar composition decreased by 24.4 %. The content of light components, such as benzenes, naphthalene, and phenols, increased significantly with the increasing catalytic temperature. Specifically, the content of benzenes, naphthalene, and phenols increased by 11.83 %, 17.73 %, and 4.41 % respectively at the coal to CaO ratio of 1/0.5 and the catalytic temperature of 600 °C. On the other hand, the CaO absorbs the CO2 pyrolysis gas leading to an elevation in the concentration of CH4 and H2 in the pyrolysis gas. The concentration of CO2 decreased from 37.9 % to 16.58 % compared to without the catalyst while the concentrations of H2 and CH4 increased to 26.24 % and 31.15 % at the catalytic temperature of 450 °C. The CO2 absorption ratio reached a maximum value of 97.16 % at a coal to CaO ratio of 1/2. These findings suggest that the CaO catalyst beneficial both for improving the tar and gas quality.

In-situ catalytic upgrading of lignin pyrolysis volatiles over red mud

Red mud (RM) is a solid waste of Bayer's alumina industry production process, which comprises a mixture of diverse minerals. After calcination, the minerals in RM are present in the form of oxides, exhibiting remarkable catalytic performance for biomass pyrolysis. It is thought that pyrolysis of lignin generates renewable aromatic chemicals. In this paper, the effect of in-situ catalysis of calcinated RM on the distribution of lignin pyrolysis volatile products is investigated. In addition, upgrading of tar by components in RM, including SiO2, Al2O3, Fe2O3, and Na2O is also discussed. The results show that the addition of RM in lignin pyrolysis leads to lower char yield and higher gas yield. RM catalyzes the breaking and rearrangement of methoxy groups and induces the generation of hydroxyl groups, which leads to an increase from 1.96 to 3.96 wt% in monophenol content of the tar. Furthermore, the activation of C-O bonds by Fe2O3 and the redox properties of Fe2O3 (FeSi) combine to stimulate the production of monophenols and aldehydes by 30.8 % and 148.2 %, while Al2O3 (AlSi) boosts the production of guaiacols by 32.0 % comparing with SiO2 (Si). It is found that synergistic effect between multiple species improves the catalytic performance, the yield of tar reaches 24.5 wt% and the selectivity of oxygenated compounds achieves 94.4 % (FeAlSiNa). The catalytic performances of RM for product yield and tar component distribution are similar to that of FeSi, indicating that Fe2O3 and SiO2 play a main catalytic role in RM.

Catalytic Fast Pyrolysis of Tar-Rich Coal with a Bauxite Residue for Upgrading High-Value Products: Product Distribution and Kinetic Analysis.

Fast pyrolysis technology can reduce the secondary reactions, improve the volatile product yield, and reduce the semicoke yield. Still, the high proportion of heavy tar components affects the development of fast pyrolysis industrialization. Therefore, this paper put forward a catalytic upgrading method of coal based on the solid waste bauxite residue (BR) as a catalyst. This study investigated the impact of varying particle sizes of pulverized coal and the addition of the BR catalyst on the product distribution and kinetics of coal fast pyrolysis. The results found that the tar yield was the highest at 600 °C when the particle size of pulverized coal was 75-150 μm, which was 19.44%. In the range of 550-650 °C, the relative content of benzene and toluene xylene (BTX) in liquid products increased with the temperature. With the increase of the proportion of the BR catalyst, the yield of semicoke in coal pyrolysis products increased, the yield of the gas phase also increased, and the yield of the liquid phase decreased.

Exploring the Tar Component Characteristics of Coalfield Fire Residual Coal Under Different Constant Temperature Oxidation

ABSTRACT Due to incomplete combustion of coal, a large amount of tar will be produced in coal fire area, which will cause serious pollution to the environment. In this paper, we dissolve the tar components in the residual coal by solvent extraction technique, analyze the organic components in the residual coal tar at different temperatures by GC-MS, study the characteristics of the residual coal tar components at different temperatures, and analyze the influence of the residual coal tar on the combustion and rekindling characteristics of the fire zone of the coalfield. The results show that: the components of coal combustion residual tar are mainly alkane organics which are easy to be oxidized and volatilized, and the content is more than 55%. At 300°C, the color of residual tar extract is light yellow or yellowish brown, and becomes colorless with the increase of temperature. At 300–500°C, the lower the temperature in the fire zone, the more residual tar in the coal, and the greater the risk of reignition in the extinguishing fire zone. The types of organic compounds in the tar residue from combustion have obvious characteristics at different temperature stages. Organic species have obvious characteristics at different temperature stages. By identifying the temperature stage of the coalfield fire area development, the organic structure characteristics and change trend of the residual coal tar can be deduced, and mastering the organic structure characteristics of the residual tar in the coalfield fire area can also reflect the temperature stage of coal fire area to a certain extent.

Experimental Study on Microwave Pyrolysis of Decommissioned Wind Turbine Blades Based on Silicon Carbide Absorbents

The rapid expansion of the scale of wind power has led to a wave of efforts to decommission wind turbine blades. The pyrolysis of decommissioned wind turbine blades (DWTBs) is a promising technological solution. Microwave pyrolysis offers the benefits of fast heating rates and uniform heat transfer, making it a widely used method in various heating applications. However, there are few studies on the microwave pyrolysis of DWTBs, and pyrolysis characteristics under different boundary conditions remain unclear. In this paper, we investigate the pyrolysis characteristics of DWTBs by utilizing silicon carbide (SiC) particles as a microwave absorbent. The results demonstrated that, when the microwave heating power increased from 400 W to 600 W, the heating rate and pyrolysis final temperature of the material increased, resulting in a reduction in pyrolysis residual solid yield from 88.30% to 84.40%. At 600 W, pyrolysis gas components included C2H4, CH4, and CO, while the tar components included phenol and toluene. The highest degree of pyrolysis was achieved under the condition of an SiC particle size of 0.85 mm, with better heating performance, and the calorific value of the pyrolysis gas generated was 36.95 MJ/Nm3. The DWTBs did not undergo pyrolysis when SiC was not added. However, when the mass ratio of SiC to DWTBs was 4, the tar yield was 4.7% and the pyrolysis gas yield was 17.0%, resulting in a faster heating rate and the highest degree of pyrolysis. Based on this, an optimal process for the microwave pyrolysis of DWTBs was proposed, providing a reference for its industrial application.

Numerical analysis of biomass gasification in a fluidized bed reactor using a computational fluid dynamics model integrated with reduced-order reaction kinetics

The use of detailed reaction kinetics in a computational fluid dynamics (CFD) model for simulating the complex reactive gas-solid flow during fluidized bed gasification of biomass (FBGB) is extremely intensive in computations. A reduced-order reaction kinetics model was thus developed and validated that can be integrated with a CFD model to improve the prediction of the formation of tar and syngas components during FBGB at various sizes and chemical compositions of biomass particles. The simulations by the integrated CFD model and reduced-order kinetics showed that pyrolytic products were released from biomass at various temperatures and rates, which created large variations in the concentrations of tar compounds and syngas, and the oxygen to fuel ratio in the bed. The CFD simulations showed that H2 and CO were generated in both heterogeneous phase of the expanded bed and homogenous gas phase in the freeboard region while large portions of CO2 and CH4 were generated in the gas phase near to the top freeboard. Optimization of syngas residence time at a specific gasification temperature can thus reduce the formation of tar, CO2 and CH4.

Catalytic Pyrolysis of Naomaohu Coal Using Combined CaO and Ni/Olivine Catalysts for Simultaneously Improving the Tar and Gas Quality

Catalytic pyrolysis of low-rank coal is currently an effective method for producing high-quality tar and gas. In this study, catalytic upgrading of volatiles from Naomaohu (NMH) coal pyrolysis has been conducted in a two-stage fixed-bed reactor using combined CaO and Ni/olivine (Ni-loaded olivine) catalysts. The effect of catalyst distribution modes and catalytic temperature on the tar and gas quality has been investigated. Simulated distillation and GC-MS analysis have been used to investigate the distribution of tar components. The results indicated that the light oil fraction in tar dramatically increased due to the combination of CaO and Ni/olivine. The CaO-Ni/olivine mode is especially better compared to the layouts of the Ni/olivine-CaO mode and the mixed mode. The CaO-Ni/olivine mode ensures a higher light fraction in tar at 69.3% and a light oil fraction at 29.8% at a catalytic temperature of 450 °C, while the heavy tar fraction decreased to 30.7%. Meanwhile, the contents of benzene (heteroatomic substituents) in tar significantly increased from 2.55% to 6.45% compared with the blank test. In this scenario, CaO breaks down macromolecular compounds in tar and cleaves long-chain esters to produce aliphatic hydrocarbons. These hydrocarbons are then dehydrogenated to produce lighter aromatic hydrocarbons over the CaO surface. Subsequently, the volatiles pass through the Ni/olivine catalysis, where ether compounds are produced by means of dehydration reactions. In addition, the CaO absorbs the CO2 in the pyrolysis gas, leading to an elevation of CH4 and H2 concentration. Particularly, the concentration of H2 significantly increased from 16.2% to 30.37%, while the concentration of CO2 significantly decreased from 37.9% to 10.57%. These findings suggest that the usage of combined CaO and Ni/olivine catalysts is beneficial for improving both the tar and gas quality.

Insight into pyrolysis behaviors of cedar under different atmospheres via a fixed-bed reactor

Pyrolysis, as an efficient route for biomass, usually suffers the influence of pyrolysis atmosphere by the interaction with free radicals from biomass pyrolysis. To investigate the effects of pyrolysis atmosphere on cedar pyrolysis, several atmospheres including CH4, H2, CO2, CO, CH4/CO2 and H2/CO were used for CS pyrolysis on a fixed-bed reactor and the pyrolysis process was revealed based on products distribution, tar quality and compositions. The results show that the components in pyrolysis atmosphere apparently affect the distribution of pyrolysis products and play different roles in cedar pyrolysis. Tar yields under different atmospheres follow the order of H2/CO > H2 > CH4/CO2 > CO2 > CO > N2 > CH4. The highest tar yield of 45.5 wt.% was obtained under H2/CO atmosphere at 600 °C. Char yield was decreased under H2 by suppressing secondary reaction and followed the order of H2 < H2/CO < CH4/CO2 < N2 < CO2 < CO < CH4. The content of ketones was improved under CO2 atmosphere. The introduction of H2 mainly increases naphthalenes, benzenes, ketones and phenols; while the formation of acids, esters, aldehydes and furans was inhibited under CO atmosphere. Integrated process of biomass pyrolysis with CO2 reforming of CH4 can greatly increase tar yield and change tar compositions, which is ascribed to the participation of H-rich free radicals from CO2 reforming of CH4. This work provides a route to improve the yield of pyrolysis tar and adjust tar components.

Synergistic interactions between cellulose and plastics (PET, HDPE, and PS) during CO2 gasification-catalytic reforming on Ni/CeO2 nanorod catalyst

CO2 gasification-reforming is a promising approach for the transformation of carbonaceous materials into CO-rich syngas. Within municipal solid waste and agricultural waste streams, plastics are commonly found intermixed with biomass waste. This study delves into the CO2 gasification-reforming of biomass (cellulose) and various plastics (PET, HDPE, and PS) using a self-built online weighing fixed bed reactor and a two-stage fixed bed reactor. During the gasification-reforming of cellulose-plastic mixtures without the catalyst, the experimental gas production rate of cellulose slightly decreased, with the peak of gas production migrating to a higher temperature range. This phenomenon can be attributed to the molten plastic adhering to the cellulose surface, which impeded heat and mass transfer essential for cellulose decomposition. Furthermore, the gas production from plastics was suppressed in the mixtures, likely due to the interference of cellulose char in the decomposition of plastics. The incorporation of 2%Ni/CeO2 catalysts not only augmented gas yields and production rates but also emphasized the synergistic interactions. For the cellulose-HDPE mixture, the total gas yield was reduced by 14.9 mmol gsample−1 relative to the theoretical value. Given that HDPE possessed the highest decomposition temperature, the synergistic interaction was predominantly driven by the inhibitive nature of cellulose char. In contrast, the total gas yields for cellulose-PET and cellulose-PS mixtures increased by 8.7 mmol gsample−1 and 13.3 mmol gsample−1, respectively. The free radicals emanating from cellulose could trigger the decomposition of volatile components from plastics. Concurrently, the decomposition products of plastic could serve as hydrogen donors to stabilize the volatiles of cellulose. The interactions primarily affect the volatiles and tar components of the mixtures. The catalysts amplified gas yields by facilitating the CO2 reforming of tar, therefore, the synergistic interaction became evident upon catalyst addition. Gas chromatography-mass spectrometry analyses of the tar also corroborated the described interaction mechanisms between cellulose and plastics. Thermogravimetric analysis of used catalysts indicated that the synergistic action between cellulose and plastic could effectively diminish coke deposition, thereby preventing swift catalyst deactivation.

Quantum chemical study on non-thermal plasma degradation tar in gasification syngas

The bond dissociation energies (BDEs) of benzene, toluene, and naphthalene which are the main components of tar in fluidized bed gasification syngas have been investigated by B3LYP method at 6-31G (d, p), 6-31G+ (d, p), 6-31G++ (d, p) and 6-311G++ (d, p) basis setsof density functional theory (DFT).The structures of benzene, toluene, naphthalene, and corresponding radicals were optimized, and their total energiesand zero-point energies (ZPE) were calculated.The frequency analysis was carried out, then, the transition state and the high order saddle were excluded, and the influence of zero point energy scaling factors was neglected.The results showed thatthe BDEs decreased with increasing computational basis sets. The calculated results obtained by B3LYP/6-31G (d, p) are much closer to the results of the documents than the other three basis sets. This indicates that the basis set of B3LYP/6-31G (d, p) is much more credible in reproducing the BDEs. The lowest electron energy values for the ring opening of benzene, toluene and naphthalene are 8.05 eV, 7.45 eV, and 7.35 eV, respectively, indicating that when the energy of high-energy electrons reaches 8.05 eV, the ring of aromatic hydrocarbon can be broken.

Pyrolytic Modification of Heavy Coal Tar by Multi-Polymer Blending: Preparation of Ordered Carbonaceous Mesophase.

In order to achieve the high-value utilization of heavy tar for the production of enhanced-performance graphite foam carbon, the carbon mesophase was ready from the heavy component of low-temperature coal tar, and the coal tar was modified by styrene-butadiene-styrene (SBS), polyethylene (PE) and ethylene-vinyl-acetate (EVA) copolymers. The order degree of the carbonite mesophase was analyzed using a polarizing microscope test, Fourier transform infrared spectroscopy and X-ray diffraction to screen out the most suitable copolymer type and addition amount. Furthermore, the mechanism of modification by this copolymer was analyzed. The results showed that adding SBS, PE and EVA to coal tar would affect the order of carbonaceous mesophase; however, at an addition rate of 10.0 wt.%, the linear-structure SBS copolymer with a styrene/butadiene ratio (S/B) of 30/70 exhibited the optimal degree of ordering in the carbonaceous mesophase. Its foam carbon prepared by polymer modification is the only one that forms a graphitized structure, with d002 of 0.3430 nm, and the maximum values of Lc and La are 3.54 nm and 2.22 nm, respectively. This is because, under elevated pressure and high-temperature conditions, SBS underwent chain scission, releasing a more significant number of methyl and other free radicals that interacted with the coal tar constituents. As a result, it reduced the affinity density of heavy coal tar molecules, enhanced fluidity, promoted the stacking of condensed aromatic hydrocarbons and increased the content of soluble carbonaceous mesophase, ultimately leading to a more favorable alignment of the carbonaceous mesophase.

Application of Coal Tar Products and Evaluation of the Stability of Residual Marine Fuels

Although the quality of coal tar does not meet the demands for blended marine fuel, the properties of its components after processing are improved, and they can be considered as inexpensive blending components. Three types of coal tar products including light coal tar I, light coal tar II, and hydrogenated coal tar have been obtained and used in production of residual marine fuels. To minimize costs, a linear optimization method has been used, and all properties of the resulting products have met the required criteria. In addition, a novel analytical method was used to characterize the fuel stability. The analysis of a hydrocarbon composition and a mechanism of interaction between the resin and asphaltene have shown the main coal tar components affecting fuel oil stability are polycyclic aromatic hydrocarbons (PAHs) and resin. A condensation of PAHs and resin into asphaltene and an increasing complexity of asphaltene structure causes deposition of oil products under heating. Hydrogenation is able to effectively reduce the PAH content and the volume of formation of massive asphaltenes thus preventing fuel flocculation and deposition during aging in fuel tanks.

Experimental study on tar formation during underground coal gasification: Effect of coal rank and gasification pressure on tar yield and chemical composition

The yield and composition of tar depending on coal rank and pressure during underground coal gasification (UCG) were studied. Two coals were used in a series of ex-situ UCG experiments: a Welsh semi-anthracite (Six Feet) and a Polish bituminous coal (Wesoła). Four high-pressure gasification trials under two distinct pressure regimes (20 and 40 bar) were conducted. The tar samples were collected directly from the reactor outlet. The following groups of compounds were analysed by use of gas chromatography (GC-MS): light monoaromatic hydrocarbons (BTEX – benzene, toluene, ethylbenzene and xylenes), polycyclic aromatic hydrocarbons (PAHs) and phenols. A series of gasification experiments revealed significant differences in tar yields and composition depending on the coal rank and gasification pressure. Significant decreases in tar contents were observed with the increase in gasification pressure from 20 to 40 bar for both coals. The total yields of the analysed tar components per kg of gasified coal were 2.58 g and 0.41 g for the experiments conducted on the Six Feet samples at 20 bar and 40 bar, respectively. The corresponding values for the Wesoła coal amounted to 5.48 g and 0.95 g. In all experiments, BTEX was a dominant group of tar components, constituting 69–86 % of the total tar yield within the tested range of compounds. The present study further proves that gasification pressure has a significant effect on the chemical composition of the produced UCG tars for both coal samples under study.

Comprehensive insight into co-pyrolysis of sewage sludge and tobacco stalk: Effects of mixing ratio and pyrolysis conditions on product distribution and characteristics

Co-pyrolysis of sewage sludge (SS) and tobacco stalk (TS) was conducted, where TS are rich in inorganic elements. The effects of the mixing ratio and pyrolysis temperature on pyrolysis products were investigated through the tube furnace system. The components of gas and tar were determined. In addition, the N/S ratio, pore distribution characteristics, surface functional group characteristics, aromatisation characteristics and inorganic element content of char were studied. Results show that the addition of TS to SS has a significant synergistic effect. Particularly, when the ratio of SS to TS is 1:3, the pyrolysis gas yield is the largest. The inorganic elements with a catalytic effect can promote the conversion of char and tar into pyrolysis gas. However, with the increase in pyrolysis temperature, the synergistic effect will gradually weaken. The increase in pyrolysis temperature will promote the development of mesopores in char but will reduce the order degree of the char structure. The addition of TS in SS will further increase the number of mesopores in char, and the obtained char carbon structure is more ordered. When the pyrolysis temperature is 600 °C, the tar yield is the highest, and the higher the mixing ratio of SS, the better the formation of polyaromatic compounds and aliphatic hydrocarbons.

Infrared heating and synergistic effects during fast co-pyrolysis of corn stover and high alkali coal

Infrared heating method aids in the investigation of the primary volatiles-volatile interactions during co-pyrolysis by minimizing the secondary reactions. In this study, characteristics and synergistic effects during the rapid co-pyrolysis of high alkali coal (HAC) and corn stover (CS) using infrared heating were systematically investigated. The co-pyrolysis liquid yield initially increased and then decreased with increasing the pyrolysis temperature. The synergistic effects clearly promoted the tar yield and quality. The co-pyrolysis tar yields increased with rising temperature, from 23.29 wt% at 500 °C to 28.87 wt% at 700 °C, before decreasing to 23.57 wt% at 800 °C. At 700 °C, the largest deviation was 63%. Moreover, the co-pyrolysis interaction had a maximal negative deviation of − 35% for CO2 mass at 700 °C, indicating that the co-pyrolysis of CS and HAC reduced carbon emissions. The tetracyclic and tricyclic aromatic hydrocarbons in PAHs were substantially reduced due to CS hydrogen radicals, and the quantities of the binary aromatic rings decreased by 50% with the increase in temperature. The presence of AAEMs in coal affected the bond breaking and reformation of molecular bonds within the tar components. Raman analysis and BET analyses suggested that AAEMs in HAC enhanced the reactivity of char. The interaction between the volatile of CS and HAC increased the amount of ammonia carbon and the number of active sites.