Upgrading Of Tar Research Articles

Effects of low molecular compounds in coal on the catalytic upgrading of gaseous tar

The main purpose of this study was to investigate the effects of low molecular compounds in coal on the formation of benzene, toluene, xylene and naphthalene (BTXN) in the catalytic upgrading of tar from coal pyrolysis by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Low molecular compounds were extracted from mineral-free lignite (Coal DA) and bituminous coal (Coal DB), and then the gaseous tars from the pyrolysis of residual coal (Coal DAR and Coal DBR), extraction solution (AE and BE) and mineral-free coal were subjected to catalytic cracking using USY zeolite as catalyst. The results show that the total amount of BTXN in the extraction solution and residual coal is 27% and 4.8% lower than that in Coal DA and Coal DB during catalytic upgrading of gaseous tars, respectively. The presence of low molecular compounds can result in a significant increase in the BTXN amount after catalytic reforming. The extraction solution in Coal DA are predominantly aliphatic compounds (72.7%) and Oxygen-containing aromatics (21.9%), whereas that in Coal DB is naphthalene series (33.1%), condensed aromatics (29.4%), and aliphatic compounds (23.5%). Phenols and condensed aromatics in low molecular compounds can be cracked into BTXN under the catalysis of USY zeolite. More heavy aromatics are cracked to light arene instead of polycondensation in the presence of aliphatic compounds.

Catalytic upgrading of coal pyrolysis products over bio-char

Several reactions parallel happened during co-pyrolysis of coal and biomass, such as primary volatiles of coal and biomass will contact and react with the nascent char from coal or biomass themselves' pyrolyzed. To clarify the function of bio-char and investigate if bio-char has the catalytic effect on pyrolysis products of Hulunbuir lignite, a two-stage reactor is designed and used in this study. The effects of bio-char preparing temperature, char-making method and usage amount of bio-char were discussed. In comparison with the alone coal pyrolysis at 650 °C, the portion of light tar (n-hexane soluble) from pyrolysis of coal with bio-char (20 wt% of coal), increased by 30.31%, gas volume yield increased by 9.05% and the volume yield of hydrogen and methane increased by 6.36% and 5.64%, respectively. For the most efficient RSCR-700 against the test with quartz, the H/C molar ratio in RSCR-700's produced tar increased by 22.06%, while the contents of N and S elements decreased by 27.88% and 25.0% accordingly. The role of bio-char in the coal tar upgrading process was further explored through the instruments characterization. Besides the thermal cracking, the bio-char also can provide catalytic active sites to crack heavy fraction of coal tar.

In Situ Catalytic Upgrading of Coal Pyrolysis Tar over Carbon-Based Catalysts Coupled with CO2 Reforming of Methane

In situ catalytic upgrading of tar from the integrated process of CO2 reforming of methane with coal pyrolysis (CRMP) was investigated over carbon-based catalysts to increase the light tar yield. The results showed that the light tar (boiling point of <360 °C) content and light tar yield increase when char, modified char (MC), or activated carbon (AC) were used as the catalysts. The effectiveness of tar upgrading was closely related with the properties of carbon catalysts. In comparison to char or MC, AC showed a better catalytic effect in upgrading tar as a result of its higher disorder structure and specific surface area. In comparison to non-upgrading tar, a light tar content of above 88% was obtained and the light tar yield was increased by 45.0% on the AC catalyst at 650 °C. The contents of four light fractions increase, along with the obvious decrease of the content of pitch. Deuterium nuclear magnetic resonance (2H NMR) spectra analysis of the tar obtained by isotopic trace suggested that carbon-ba...

In-situ catalytic upgrading of coal pyrolysis tar on carbon-based catalyst in a fixed-bed reactor

Coal pyrolysis tar was in-site upgraded in a fixed-bed reactor over char and activated carbon (AC) catalysts, and the effects of catalysts and temperature on tar upgrading were examined. The content of light tar with boiling point below 360°C was improved over the catalysts despite the decrease of total tar yield. Compared with char catalyst, AC exhibited better upgrading performances, and the content of light tar increased with the temperature. The light tar yield over AC catalyst increased by 18% compared with that without catalysts at 650°C. The variation in coal tar fractions suggested that upgrading is mainly from the conversion of the heavy components (pitch) in tar into light tar and gases. The role of carbon-based catalyst in upgrading process was also explored through the characterization by TG-DTG, FT-IR, N2 adsorption and Raman spectroscopy. Compared with thermal cracking, adsorption on the catalysts and the minerals in char, high specific surface areas and relative more defects in the carbon catalysts seem to be the primary factor for upgrading tar.

Semi-coke as solid heat carrier for low-temperature coal tar upgrading

This paper focuses on the catalytic effect of semi-coke used as a heat carrier in the cracking of coal-tar from Shendong long-flame coal (SD) pyrolysis. Firstly, semi-cokes pyrolyzed from four different coals were chosen as investigative samples and quartz sand as their reference. The experiments were conducted in a fixed-bed reactor under atmospheric conditions. Results show that the four semi-cokes have a catalytic cracking effect on volatile components. Compared with quartz sand, the tar yield of SD pyrolysis with semi-cokes decreases and the gas yield and light oil fractions in tar increase. The catalytic cracking effects of semi-cokes are relative to its physical properties and inorganic species, and the latter has greater impact than the former. Secondly, recycling experiments were conducted to study the stability of SD semi-coke as a cracking catalyst. The products' distribution, gas composition, and the gasification reactivity of the semi-coke change little during the recycling of SD semi-coke, meaning that SD semi-coke is relatively stable. Lastly, SD semi-coke was selected as a heat carrier to investigate its catalytic activity in a rapid heat transfer process similar to a practical operation. Compared with quartz sand, the catalytic cracking effect still exists in pyrolysis with hot SD semi-coke but a higher tar yield and a lower n-hexane soluble is obtained, indicating thermo-cracking contributes to more products than catalytic cracking.

Catalytic upgrading of gaseous tars over zeolite catalysts during coal pyrolysis

Although light arenes such as benzene, toluene, and xylene in coal tar are widely used in industries, their amounts are relatively small. The catalytic cracking method for gaseous tar is one of the promising techniques for upgrading tar, and the amounts of light arenes are improved. Therefore, the catalytic upgrading of gaseous tar using two different catalysts is investigated in this study; the variations of light arenes before and after catalytic cracking are determined. More importantly, the variation of heavy compounds in gaseous tar is analyzed, and also the catalytic cracking mechanism is elucidated. The results show that the amount of benzene increases by 500% under the action of USY zeolite, and the amount of other compounds such as toluene, ethylbenzene, xylene, and naphthalene also increases by different degrees. However, Al/SBA-15 zeolite shows no obvious effect on gaseous tar upgrading. At the same time, the analysis results show that heavy compounds can be cracked over USY zeolite. Side chains are cleaved from aromatic rings, and aromatic rings are also cracked during the catalytic cracking reactions. Furthermore, light arenes are formed after the hydroxyl groups in phenols cleaved from the aromatic rings.

Catalytic Upgrading of in Situ Coal Pyrolysis Tar over Ni-Char Catalyst with Different Additives

Ni-char catalyst doped with different additives was used to catalytically upgrade coal pyrolysis tar in situ generated in a laboratory-scale dual-stage reactor. The additives including Fe, Mg, Ce, Zr were all beneficial to the catalytic activity for tar cracking. The best result of tar upgrading was achieved with Ce–Ni-char at a Ce-to-Ni molar ratio of 0.4. The upgrading test at 500 °C over a layer of such a catalyst (20% of the tested coal mass) increased the light tar (boiling point <360 °C) yield by 10.1%, and the light tar fraction in the tar product to 75 wt % from 52 wt %. The corresponding increase in the molar ratio of H to C of the tar was 61.7%. About 60% of the pitch in the original tar from coal pyrolysis was cracked in the catalytic upgrading. The contents of element N and S in the tar after catalytic cracking decreased by 50.5% and 45.8%, respectively. NH3 temperature-programmed desorption results revealed that there were weak Lewis and strong Bronsted acidic sites on the Ni-char catalyst, b...

Experimental investigation of high-temperature coal tar upgrading in supercritical water

The upgrading of high-temperature coal tar in supercritical water (SCW) was investigated using an autoclave reactor. The effects of temperature (673–753 K), pressure (24–38 MPa) and residence time (1–80 min) on product distribution were studied. The yields and characteristics of products in SCW were compared with those obtained in N 2. In order to study the reaction mechanism of coal tar upgrading, the experiments of model compounds were carried out in SCW at 673 K and 34 MPa for 20 min. The results indicate that the asphaltene conversion and the maltene yield are significantly higher in SCW. The H/C atom ratios of oil obtained in SCW are higher than those obtained in N 2. More valuable aromatic compounds such as naphthalene, fluorene and anthracene are obtained in SCW. The results of model compounds suggest that water in SCW could participate in coal tar upgrading and promote the formation of light products.

96/04778 Effect of low-temperature tar upgrading conditions on chemical composition of fuel fractions

96/04778 Effect of low-temperature tar upgrading conditions on chemical composition of fuel fractions

Upgrading of coal-derived products

A number of processes such as pyrolysis, solvent extraction, etc. can be used for the primary upgrading of coal to liquid products. The type of process used can have a significant influence on the character of the product obtained. The chemistry and associated problems involved in the catalytic hydrotreatment of flash pyrolysis tars are discussed in this Paper. The difficulties encountered in the upgrading of flash pyrolysis tar are due principally to factors such as the thermal instability of the tar (high Conradson carbon), particulate matter in the tar and the high molecular weight of the tar. The design and mode of operation of the reactor have been chosen to minimize such problems. An important function of the catalyst used in this work (Co-Mo-Al 2O 3 and Ni-Mo-Al 2O 3) was to reduce the heteroatom content of the feedstock. A description of the type of molecules and reactions involved in tar upgrading is given.