Anti-coking Properties Research Articles

Optimizing anti-coking abilities of zeolites by ethylene diamine tetraacetie acid modification on catalytic fast pyrolysis of corn stalk

In order to minimize coke yield during biomass catalytic fast pyrolysis (CFP) process, ethylene diamine tetraacetie acid (EDTA) chemical modification method is carried out to selectively remove the external framework aluminum of HZSM-5 catalyst. X-ray diffraction (XRD), nitrogen (N2)-adsorption and ammonia-temperature programmed desorption (NH3-TPD) techniques are employed to investigate the porosity and acidity characteristics of original and modified HZSM-5 samples. Py-GC/MS and thermo-gravimetric analyzer (TGA) experiments are further conducted to explore the catalytic effect of modified HZSM-5 samples on biomass CFP and to verify the positive effect on coke reduction. Results show that EDTA treatment does not damage the crystal structure of HZSM-5 zeolites, but leads to a slight increase of pore volume and pore size. Meanwhile, the elimination of the strong acid peak indicates the dealumination of outer surface of HZSM-5 zeolites. Treatment time of 2 h (labeled EDTA-2H) is optimal for acid removal and hydrocarbon formation. Among all modified catalysts, EDTA-2H performs the best for deacidification and can obviously increase the yields of positive chemical compositions in pyrolysis products. Besides, EDTA modification can improve the anti-coking properties of HZSM-5 zeolites, and EDTA-2H gives rise to the lowest coke yield.

Assembly of ordered mesoporous alumina-supported nickel nanoparticles with high temperature stability for CO methanation

The high-temperature methanation of CO is an important reaction in the processes used to produce substitute natural gas, while the Ni-based catalysts prepared using the conventional impregnation method tend to deactivate under high-temperature reaction conditions. This paper describes the design and assembly of ordered mesoporous alumina (OMA) using highly disperse ∼5 nm nickel nanoparticles (Ni NPs), via a one-pot, evaporation-induced self-assembly (EISA) method. Small-angle X-ray diffraction (XRD), transmission electron microscope (TEM), and N2 adsorption and desorption results revealed that this catalytic material had highly ordered mesopores, which were retained even after long-term stability tests. The catalyst exhibited excellent sintering-resistant and anti-coking properties in high-temperature CO methanation reactions (60% CO conversion after 50 hours of accelerated deactivation at 700°C). The improved catalytic performance was attributed to the matrix of the OMA, which effectively improved the dispersion of the nickel particles, and prevented the Ni NPs from sintering, via a particle migration and coalescence mechanism. The Ni-OMA catalyst demonstrated here shows promise for high-temperature methanation.

Coking Resistance of Specialized Coil Materials during Steam Cracking of Sulfur-Free Naphtha

The reactor material strongly affects coke formation during steam cracking of hydrocarbons. Therefore, in the past decade several specialized reactor materials have been developed that have proven to be efficient in reducing coke formation for ethane steam cracking. However, their beneficial anticoking properties are questioned when heavier feedstocks such as naphtha are cracked. Therefore, the effect of the composition of the reactor material has been investigated for ethane and naphtha cracking in an electrobalance setup under industrially relevant conditions. A significant reduction of coke formation is obtained for specialized alloys compared to typical Fe–Cr–Ni heat resistant steels when a sulfur-free naphtha is cracked. A thin layer of alumina on the surface along with manganese chromite provides the highest resistance to coking, as was demonstrated by the SEM and EDX analyses. The decrease in coking rate translates in a run length increase of 50% for a typical naphtha furnace equipped with reactors made out of an Al-enhanced alloy instead of typically applied heat resistant steel.

Characterization of CVD TiN coating at different deposition temperatures and its application in hydrocarbon pyrolysis

In this study, titanium nitride (TiN) coatings at different deposition temperatures have been designed as anti-coking coatings during cyclohexane steam pyrolysis. The TiN coatings were deposited on 310S foils (10mm×10mm×0.9mm) between 750 and 950°C by a chemical vapor deposition (CVD) method. To evaluate the anti-coking property of TiN coatings, cyclohexane was employed for cracking in a tubular quartz reactor. The as-deposited and coked TiN coatings were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy and X-ray diffraction. The results show that the deposition temperature has a great influence on the morphology and microstructure of CVD TiN coatings. The structures of TiN coatings with apparent differences tend to lie on (220) preferred orientation as the deposition temperature increases. When the deposition temperature is below 850°C, the TiN coatings cannot cover the substrate surface completely and some filamentous coke was observed. However, the anti-coking ratios of TiN coatings at different deposition temperatures are all above 90% during cyclohexane pyrolysis at 770°C for 1.5h. In summary, the TiN coatings at high deposition temperatures can completely cover the cracks and gaps on the rough surface of blank substrate, and thus provide a very good protective layer to prevent the substrate from metal dusting and severe coking. Moreover, the Raman spectra show that the dust-like coke on the surface of TiN coatings has a higher degree of graphitization than the filamentous coke on 310S substrate, which also proves the good anti-coking performance of TiN coatings.

Co–Ni bimetal catalyst supported on perovskite-type oxide for steam reforming of ethanol to produce hydrogen

Perovskite-type oxide (PTO) of LaFeO3 supported Ni–Co bimetallic catalysts were prepared by citric acid complexation-impregnation method and were used for the steam reforming of ethanol (SRE) to produce hydrogen. The anti-sintering and anti-coking properties of the catalysts for the reaction have been investigated and compared with the monometal catalysts. The catalysts were characterized by using temperature programmed reduction, X-ray diffraction, transmission electron microscopy and thermal analysis techniques. The results indicate that the catalyst was both highly selective to hydrogen and very stable for SRE reaction. Characterization results indicated that Ni–Co was in the state of solid solution alloy. Comparing with corresponding monometal catalysts, the bimetal catalyst exhibited better anti-sintering ability and similar anti-carbon deposition ability. The valuable information indicated in this work is that based on the special characters of PTO, bimetal nano-particles can be supported on metal oxides, which should be a new and promising method for preparing supported bimetal catalysts.

The beneficial use of non-thermal plasma in synthesis of Ni/Al2O3–MgO nanocatalyst used in hydrogen production from reforming of CH4/CO2 greenhouse gases

In our continuing effort to investigate the effect of non-thermal plasma on CH4/CO2 reforming catalysts, Ni/Al2O3–MgO nanocatalyst is investigated. The impregnated and plasma treated nanocatalysts are characterized using XRD, FESEM, TEM, EDX Dot-Mapping, BET, TG–DTG, XPS and FTIR techniques. XRD patterns show high dispersion and strong interaction of active phase. FESEM images display smaller particle size and a narrow particle size distribution for plasma treated sample. According to the BET analysis, the calculated surface area of plasma treated sample is 11% higher. TEM images show particles of active phase are fairly small and well-dispersed as a result of plasma treatment. XPS and EDX analysis reveal better dispersion of active phase as a result of plasma treatment. In addition to better structural and physicochemical properties, the Ni/Al2O3–MgO nanocatalyst which treated by non-thermal plasma has higher activity and significant anti-coke properties in the CH4/CO2 reforming reaction at 550–850 °C temperature range using a mixture of CH4:CO2 = 0.5–2.

La1−xCaxFe1−xCoxO3—a stable catalyst for oxidative steam reforming of ethanol to produce hydrogen

La1−xCaxFe1−xCoxO3 (x = 0.3, 0.5) perovskite-type oxide catalysts prepared by citric acid method were used for the steam reforming of ethanol (SRE) and oxidative steam reforming of ethanol (OSRE) to produce hydrogen. The anti-sintering and anti-coking properties of the catalysts for these two reactions have been investigated. The catalysts were characterized by temperature programmed reduction, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and thermal analysis techniques. The results indicated that the catalyst was highly selective to hydrogen, as well as very stable for OSRE reaction. The cobalt ions in the perovskite structure could be reduced to nanoparticles of metallic cobalt under the reduction atmosphere; the nano metallic cobalt could be oxidized and went back into the lattice of the perovskite structure under the oxidation atmosphere. The nanoparticles of metallic cobalt on the used catalyst could also be oxidized back into the perovskite structure. In the reaction process of OSRE, the cobalt species was possibly cycling as nanoparticles of metallic cobalt and cobalt ions in the perovskite structure, leading to its high anti-sintering stability.

Anti-coking property of the SiO 2/S coating during light naphtha steam cracking in a pilot plant setup

On the basis of development in the laboratory, the SiO 2/S coating was prepared on the internal surface of HK40 alloy tube in a pilot plant setup. The coating sampled on the outlet of furnace tube was characterized by scanning electron microscope (SEM). The anti-coking property of the SiO 2/S coating was evaluated with light naphtha according to pressure changes. The morphologies and chemical components of cokes on the outlet of the coated and blank tubes were characterized by SEM and energy dispersive spectroscopy (EDS), respectively. The main product yields of light naphtha steam cracking were analyzed by gas chromatography–mass spectrometry (GC–MS). The results show that the SiO 2/S coating is compact and has a thickness of 15 μm on the outlet of furnace tube. The SiO 2/S coating reduces coke yield by 60% compared to that observed in the blank tube during 8 h cracking run. However, the coke reductions of the SiO 2/S coating are both about 40% when the cracking time is 26 h and 66 h, respectively. The outlet of the coated tube has the exfoliated coke with a thickness of about 30 μm. The coke on the process side has many irregular particles, and the coke on the metal side is not filamentous coke but amorphous coke particles after the exfoliated coke is taken away. The yield of C 2H 4 has a slight increase in the coated tube, and the yield of C 4H 8 has a decrease. However, the SiO 2/S coating has little influence on the total yield of olefin.

Study of anti-coking property of SiO 2/S composite coatings deposited by atmospheric pressure chemical vapor deposition

To alleviate catalytic coking on the inner surfaces of radiant tubes for ethylene production in petrochemical plants, SiO 2/S composite coatings were prepared on the surface of HP40 steel tube using dimethyldisulfide (DMDS) and tetraethylorthosilicate (TEOS) by atmospheric pressure chemical vapor deposition. A comparison of anti-coking property of the coated and uncoated HP40 steel tubes has been made under the same conditions. SiO 2/S composite coatings are compact and have better anti-coking property. The coke on the coated HP40 steel tube is about 22% of that on the uncoated HP40 steel tube, and only small granular coke is deposited on the coated HP40 steel tube. However, the filamentous coke is formed on the uncoated HP40 steel tube. SiO 2/S composite coatings have good thermal stability at cracking temperature by the comparison of Raman spectra before and after coking.