Abstract: The distribution of cadmium (Cd) occurrence modes in a Naomaohu coal (NMH) and an Inner Mongolia high sulfur coal (GL) was investigated using the sequential chemical extraction method. The influence of the occurrence modes, final pyrolysis temperature, heating rate and residence time on the release behavior of Cd during the pyrolysis of two raw coals at 400-800 ℃ in a horizontal / vertical tubular furnace was examined respectively. The simulation of the migration and transformation of Cd under ideal conditions by FactSage software was carried out. The results show that Cd in NMH and GL is present in an organic matter state by 46% and 37%, a carbonate state by 32% and 24%, a disulfide state by 12% and 1%, and an aluminosilicate state by 10% and 38%, respectively. The distribution of occurrence modes seriously affects the volatilization behavior of Cd, in which the Cd in the organic matter state is easy to volatilize at low temperature, while those in the carbonate, aluminosilicate and sulfide state can volatilize at medium and high temperature; and reducing pyrolysis rate and extending residence time are conducive to the release of Cd. The FactSage simulation shows that Cd, CdO, Cd(OH)x and CdS are the major gaseous products of Cd during the pyrolysis of NMH and GL coal, and the difference of volatilization behavior of Cd in two kinds of coal is mainly determined by pyrolysis temperature, distribution of occurrence modes and coal rank, which are in good agreement with the experimental results.
Abstract: Coal from Fengfeng (FF) colliery, Hebei, China, was pyrolyzed in a self-developed pyrolysis reactor coupled with double ionization sources (viz., electron impact ionization (EI) and photoionization (PI)) and time-of-flight mass spectrometer (Py-EI/PI-TOFMS), to characterize in-situ the primary products from pyrolysis (heteroatom-containing compounds in particular). The relative contents of various pyrolysis products were obtained by semi-quantitative analysis and the temperature-evolved profile of each product was obtained by scanning the signal of the distinguished peak with the lapse of time; in addition, the evolution of five small molecule gaseous products (viz., H2O, CO, CO2, H2 and CH4) was analyzed by EI-TOFMS. The results indicate that the Py-PI-TOFMS system is able to detect and characterize the primary products in-situ during coal pyrolysis. In the pyrolysis products with a mass-to-charge ratio (m/z) less than 240, which account for about 70% of detected volatiles, hydrocarbons consist of mainly aromatics of 1–3 rings, whereas the phenolic compounds are dominated by phenols containing 1–3 benzene rings (especially the 3-ring phenols). The peak temperature with maximum evolution of phenols containing the same alkyl substituents shifts to lower temperature with the increase of the number of aromatic rings. In addition, the relative contents of nitrogen/sulfur-containing compounds are all less than 1.0%, where the content of sulfur-containing heterocyclic compounds is higher than that of nitrogen-containing heterocyclic compounds.
Abstract: The phenyl ethyl ether (PEE) and benzyloxybenzene (BOB) were selected as coal-related model compounds, and their catalytic pyrolysis behaviors in the presence of Ni-modified HZSM-5 zeolite were studied in a fixed-bed reactor. Nickel was introduced on HZSM-5 zeolite by wet impregnation. The catalysts were characterized by XRD, FT-IR, H2-TPR and NH3-TPD, and the effect of hydrogen reduction pretreatment on the catalytic performance was studied. NiO/HZSM-5 can significantly improve the yield of phenols in the liquid phase products of the two model compounds. Compared with Ni/HZSM-5, NiO/HZSM-5 exhibits superior pyrolysis conversion of PEE.
Abstract: Influence of Fe2O3 on the pyrolysis products distribution of demineralized Hongshaquan (HSQ) and Daliuta (DLT) coal was investigated by a novel in-situ pyrolysis vacuum ultraviolet single photon ionization time-of-flight mass spectrometry. The experiment samples were obtained by mechanical mixing of Fe2O3 and demineralized coal from acid elution with the mass ratio of 10∶1, 5∶1 and 2∶1. Due to the characteristics of in-situ sampling, soft ionization and high vacuum environment, the initial pyrolysis volatiles including alkenes, aromatic hydrocarbons, phenols, bi-phenols and a small amount of sulfur and nitrogen-containing substances can be detected. The results show that Fe2O3 has similar influence on the products distribution of two demineralized coal, and it is relatively stronger on DLT coal than that on HSQ. With the increase of Fe2O3 content, the light fraction content is promoted such as alkenes and aromatic hydrocarbons, but bi-phenols are obviously inhibited. Correspondingly, the heavy products are also decreased, and the evolution peak temperatures of the product increase. Fe2O3 is successively reduced to FeO and Fe while transforming heavy components into light components. The increase of aliphatic carbon (or aromatic hydrocarbon substituted carbon) during coal pyrolysis process is mainly responsible for the decrease pyrolysis peak temperature.
Abstract: The subgroups and contents of liptinite have significant influence on yields of tar and gas in pyrolysis.The heating stage microscope, fluorescence analysis and Micro-FTIR were used to study the characteristics of typical liptinite at low temperature thermal conversion. The results showed that the relative fluorescent intensities decreased and the maximum fluorescence wavelength increased as the pyrolysis temperature increase. The fluorescence characteristics of resinite and suberinite began to change at 240 ℃, and remarkable changed at 280−320 ℃. The fluorescence characteristics of sporinite, cutinite, and bituminite A began to change at 280 ℃, and remarkable changed at 320−360 ℃. The fluorescence characteristic of alginite began to change at 280 ℃, and lasting changed till 400 ℃. The fluorescence characteristic of bituminite B changed at 320−360 ℃. The absorption peak of aliphatic compound in alginite was strongest, and the peaks of bituminite, resinite, cutinite, and sporinite decreased in turn. The aliphatic compounds and oxygen-containing groups of liptinite group decreased and the content of aromatic hydrocarbon relatively increased as the temperature increase. The aromatization degree of liptinite group was low and basically remain unchanged at low temperature thermal conversion. The hydrogen-rich degrees and the change of aliphatic chains of liptinite group confirmed well with the fluorescence characteristics.
Abstract: The content of heavy pitch in tar generated from coal pyrolysis is high. To improve the quality of tar, catalysts are applied for adjusting the reaction of volatiles during coal pyrolysis. However, catalysts are easy to deactivate due to coke deposition. In this study, coke amount on activated carbon catalysts during catalytic upgrading of coal pyrolysis volatiles was investigated in the downer-bed reactor. The process of coke formation was studied at different feed time (30, 60 and 100 min) of coal. Results show that a great amount of coke is generated on the activated carbons. With the increase of feed time, the amount of coke on activated carbon increases, while the rate of coke formation decreases, thus decreasing the coke yield based on dry coal. The specific surface area and catalytic cracking activity of the activated carbon decrease with the increase of coke amount. Hence, the yields of tar and pitch increase with the increase of feed time. The relative content of oxygen-containing compounds in the tar increases with the increase of feed time, which indicates that the cleavage of weak chemical bond C−O is suppressed. That may result in a decrease in the rate of coke formation.
Abstract: The volatiles’ reaction has a significant influence on composition and coking behavior of tar during low-medium temperature pyrolysis of coal, which is closely related to the activity of volatiles and the content of components rich in hydrogen in the system. By introducing tetralin, the effect of reaction of volatiles generated by pyrolysis of Naomaohu coal on the product distribution and coke yield was explored at various temperatures using a two-stage fixed bed reactor. The tar composition was analyzed by a comprehensive two-dimensional gas chromatography/mass spectrometry. The results show that the yield of coke is higher at 400 oC due to the weaker reaction between volatiles and THN and tar condensation. As the temperature increases, the reaction between volatiles and THN intensifies, resulting in the decrease of liquid products yield and the increase of gas yield. According to the calculated and experimental values of the reaction products of volatiles and THN, it is found that the liquid products yield increases after the introduction of THN. The contents of aromatic hydrocarbons with 2−5 rings and coke both decrease. This indicates that the interaction between volatiles and THN promotes the α−H transfer of THN and provides more active hydrogen for the reaction system. Besides, the interaction between volatiles and THN is also beneficial to the formation of phenolic compounds and other oxygenated compounds, especially for polyphenols. The activity of volatiles during coal pyrolysis is related to oxygen-containing radicals, which have a strong bond with active hydrogen.
Abstract: The char powder entrained in gaseous tar influences the reaction of gaseous tar that exists in the transportation pipeline or dust removal equipment, which further affects the distribution and composition of pyrolysis products. This study investigated the effect of char powder on the reaction of gaseous tar during Naomaohu long-flame coal pyrolysis from 400 to 500 ℃ in a two-stage fluidized bed reactor. Results indicated that in addition to its thermal cracking and polycondensation reactions, catalytic cracking reaction of gaseous tar also occurred when char powder was added, resulting in the decrease of tar yield and pitch content, and the increase of pyrolysis gases and coke yield at different reaction temperatures. The thermal cracking and polycondensation reactions of gaseous tar intensified with increasing reaction temperature, which stabilized the gaseous tar and made it difficult to be catalyzed by char powder. Therefore, with the increase of reaction temperature, the influences of char powder on tar yield, tar pitch content and pyrolysis gases yield were reduced. The polycondensation reaction of free radicals from catalytic cracking of gaseous tar was prone to occur with increasing reaction temperature, which enhanced the effect of char powder on coke yield. Also, the catalytic cracking action of char powder reduced the content of heterocyclic compounds in tar at different reaction temperatures, and the reaction between gaseous tar and water was promoted by char powder, resulting in the decrease of aliphatics and aromatics contents in tar, and the increase of phenols and oxygenated compounds contents in tar at different reaction temperatures.
Abstract: The effects of SiO2/Al2O3 ratio of HZSM-5 on the tar quality and coke formation during catalytic upgrading of coal pyrolysis volatiles were investigated. The results showed that the carbon deposition amount decreased with the increase of the SiO2/Al2O3 ratio of HZSM-5 due to the decrease of strong and weak acid amount. When the SiO2/Al2O3 ratio increased from 23 to 310, the carbon deposition amount decreased from 120.1 mg/g-catalyst to 23.9 mg/g-catalyst. Moreover, the higher ratio of strong and weak acid amount led to lighter fraction in tar. With the decrease of SiO2/Al2O3 ratio, the acid strength was enhanced so that the aromatics content in the tars decreased, indicating that the stronger acidic sites promoted the dehydrogenation, cyclization and aromatization reactions of volatiles, thus leading to higher yield of aromatics during catalytic coal pyrolysis.
Abstract: Based on density functional theory (DFT) and transition state theory, the effect of alkali metal Na on the formation mechanism and path of NH3 and HCN during coal pyrolysis was studied at the M06-2X/6-311G(d) level. The seven membered ring containing pyridine was selected as the coal model, and the adsorption structure of Na on the coal surface was used as the coal model containing Na. The results show that the presence of Na significantly strengthens the bonding between N and C atoms in pyridine ring, which makes the stripping of N atom from benzene ring requires higher activation energy, thus inhibiting the formation of HCN. However, Na can improve the surface activity of coal, and the energy barrier of NH3 formation rate determination step in the presence of Na is 271.35 kJ/mol lower than that in the absence of Na, which significantly promotes the formation of NH3.
Abstract: In this work, Naomaohu coal was used for direct liquefaction. The conversion and oil yield as a function of hydrogenating temperature were investigated, and the transformation characteristics of heteroatoms in raw coal and liquefaction products were clarified. The results showed that Naomaohu coal presented high liquefaction performance even under lower initial pressure of 2 MPa. The conversion and oil yield could reach 69.6% and 55.3%, respectively, at a pressure of 2 MPa and 400 ℃. Gas chromatography-mass spectrometry and gas chromatography-atomic emission spectrometry were combined to analyze the products. It was found that the weak bond structure containing heteroatoms was easier hydrogenated to fracture and removed in the form of H2S, NH3, H2O, etc. The sulfur-containing compounds in liquefied products were mainly thiophene and thiophene homologues. The content of nitrogen-containing compounds was trace and mainly consisted of nitrogen heterocyclic compounds. The oxygen-containing compounds in liquefied oil were dominantly phenols and their homologues. The heteroatoms in the aromatic structure would generate more stable heteroatom-containing compounds in the liquefaction residue via the free radical polycondensation reaction.
Abstract: The pyrolysis tar from Naomaohu coal was separated by distillation apparatus. Four components of heavy oil above 320 ℃ were analyzed. The result showed the colloid content was 28.84% and the asphaltene content was 35.12%, and both were difficult to convert in hydrogenation. 13C-NMR results showed that the relative molar ratio of aromatic carbon in heavy oil was 71.16%, which indicated that aromatic compounds in heavy fraction were dominant. The heavy fraction was treated by suspension bed and fixed bed cracking. The asphaltene and colloid were almost completely converted. The yield of naphtha with boiling point below 180 ℃ was 66.95%, and the diesel with boiling point higher than 180 ℃ was 17.84%. Oxygen, nitrogen and sulfur contained in heteroatoms were almost completely removed. Catalytic reforming of naphtha was carried out. The results showed that the number of cycloalkanes decreased by 60.23%, and the number of aromatics increased by 65.8%, which indicated that the dehydrogenation and aromatization of cycloalkanes occurred mainly. While the number of n-alkanes decreased by 13.42%, which indicated that the isomerization and cyclization of n-alkanes occurred simultaneously. The catalytic reforming oil contained more benzene, toluene, xylene and ethylbenzene, and the contents were 11.97%, 23.15%, 21.43% and 3.48% respectively. In the direct conversion process of heavy oil from coal pyrolysis, the transmissibility of basic structural units of coal was significantly reflected.
Abstract: The performance of the ZrO2 modified Ni/SBA-15 catalysts was investigated for the hydrodeoxygenation of dibenzofuran as a coal tar model compound in an autoclave at 280 ℃ and a hydrogen pressure of 6.5 MPa. The effects of ZrO2 modification on the structural characteristics and reaction activity of Ni/Zr-SBA-15 catalysts were analyzed. The results showed that the addition of ZrO2 increased the interaction between the active metal Ni and the SBA-15 support, promoted the dispersion of Ni particles, and introduced oxygen vacancies in the catalysts. As a result, the conversion of oxygen-containing intermediates was enhanced, and thereby the yield of the target product bicyclohexane was improved. However, the addition of excessive ZrO2 (30%) could reduce the specific surface area and pore volume of the catalysts and cover Ni surface, which was not conducive to the reaction. The study found that the highest dibenzofuran conversion rate of 9.21 mmol/(min·g) and the highest bicyclohexane formation rate of 3.74 mmol/(min·g) were achieved when the addition amount of ZrO2 were 10% and 20%, respectively. Both values were much higher than those on the unmodified Ni/SBA-15 catalyst.
Abstract: With the free radical reaction during the pyrolysis process of heavy organics as the background, the research approach based on density functional theory was adopted to exploring the induction of free radicals on covalent bond and its effect on covalent bond dissociation energy. The energies of seven kinds of covalent bond reactions induced respectively by ·CH3, ·OH and ·H were calculated theoretically on the Gaussian 09 program at the level of ωB97XD/6-31G**. The results indicate that the steric hindrance effect plays a significant role in the energy barrier of free radical induced reaction, while the influence of the covalent bond type plays a minor role. When the isogroup induced exchange reaction of ·OH and ·H does not proceed, the induced energy barrier of ·OH is about 40 kJ/mol higher than that of ·H and the induced energy barrier of ·CH3 is about 50 and 90 kJ/mol higher than that of ·OH and ·H respectively. When the isogroup induced exchange reaction of ·OH and ·H works, it will result in the increasing of 70 kJ/mol of the energy barrier. During the process of calculation, the specific situation of induced reaction should be judged and revised. The above values can be used to estimate the energy barriers of different covalent bond induced reactions.
Abstract: In this paper, light coal tar derived from China Coal Research Institute was used as raw material to conduct a research on developing a chemical process to produce aerospace fuel. In view of the characteristics of the coal tar, a route comprising of primary desulfurization- fraction cutting- secondary desulfurization- hydrogenation saturation was designed. The optimal pressure and temperature were determined to be 5 MPa and 300 °C for hydrodesulfurization on NiMoW/Al2O3, and 5 MPa and 240 °C for hydrogenation saturation on Pd/Al2O3. After treatment, the sulfur content decreased from 323 to 8.5 mg/kg. The benzenes, naphthalenes and other aromatic compounds in the raw oil were converted into cycloalkanes. The main components of the final product were cycloalkanes and chain alkanes, and the contents were 58.38% and 29.65% respectively. The final product exhibited high heating value, low sulfur content and low unsaturated aromatic hydrocarbons, which possessed great potential to be used in aerospace fuels.
Abstract: In view of the problems faced by the conventional moving bed coal pyrolysis process, such as the inability to deal with pulverized coal, low light tar yield, poor tar quality, etc., a moving bed pyrolysis process with baffled internals was developed to control the heat and mass transfer of the gas-solid two-phase and the pyrolysis reaction process. The multi-stage gas gathering system can collect the oil and gas products released in different pyrolysis stages of coal in time. The pyrolysis behavior and product quality of Naomaohu coal at different temperatures and residence times were investigated. The results show that the baffle internals enhance the heat and volatile matter transfer between particles, enabling it to process 0.4−6.0 mm pulverized coal. When the pyrolysis temperature is 550 ℃ and the residence time is 3 h, the pyrolysis tar yield reaches the highest 11.38%, which is 86.87% of the Gray-King assay yield, and the mass fraction of light components below 360 ℃ in the tar fraction is 85.0%. With the extension of the residence time, the H2 volume fraction in the pyrolysis gas increases from 22.1% to 35.1%, and the CO volume fraction increases from 8.0% to 9.5%. The tar yield in the first and second layer reactors increases with the extension of the residence time, and the maximum tar yield in the third and fourth layer reactors is obtained when the residence time is 2 h. As the number of beds increases, the content of light components in the tar simulated distillation fraction increases, the content of tar aliphatic hydrocarbon compounds decreases, and the content of monocyclic aromatic hydrocarbons and bicyclic aromatic hydrocarbons gradually increases. Based on the above research, it provides technical support for large-scale industrial processing of small particle size pulverized coal, and preparation of higher yield and quality tar.
Abstract: ZSM-22/ZSM-23 intergrowth zeolite was successfully synthesized by hydrothermal method with diethylamine and dimethylamine as co-structure directing agents at a dimethylamine/diethylamine molar ratio of 24. The physicochemical properties of ZSM-22/ZSM-23 intergrowth zeolite including the crystallinity, crystal morphology, texture and acidity were determined by XRD, FE-SEM, TEM, N2-physisorption, NH3-TPD, Py-FTIR, and so on; the performance of Pt/ZSM-22/ZSM-23 catalyst prepared by impregnation in the hydroisomerization of n-hexadecane was then investigated. The results indicate that the ZSM-22/ZSM-23 intergrowth zeolite displays the needle-like morphology with the topological structures of both ZSM-22 and ZSM-23, which is rather different from pure ZSM-22 and ZSM-23 and their mechanical mixture. After loading 0.5% Pt, the bi-functional Pt/ZSM-22/ZSM-23 catalyst exhibits excellent performance in the hydroisomerization of n-hexadecane, with a much higher yield of i-C16 products (dominated by mono-branched isomers) than those obtained over Pt supported on ZSM-22 and ZSM-22 and their mechanical mixture.
