Cracking Characteristics of Simulated Dust-Containing Coal Pyrolysis Volatiles over Regenerated Nickel-Based Catalysts

Abstract

Two catalysts, 2%NiO/1%CeO 2 −Al 2 O 3 and 2%NiO/1%CeO 2 /2%ZrO 2 −Al 2 O 3 , were employed in the conversion of tar in coal pyrolysis volatiles to investigate the interrelationship between dust collection and tar cracking as well as the effect of Ce/Zr doping on catalyst performance. In a fixed-bed catalytic reactor, a tar model mixture (57 wt % toluene, 14 wt % methylnaphthalene, 14 wt % cyclohexane, and 15 wt % dodecane) and simulated dusts (various metal oxides) were introduced to mimic real coal pyrolysis volatiles. The catalytic cracking activity of the latter catalyst increased with increasing temperature, space velocity, and water/model tar ratio, whereas the former catalyst exhibited the opposite trends, except with respect to temperature. Because of the formation of a Ce−ZrO 2 solid solution, the latter catalyst showed higher stability. During cycling tests, the deactivation of 2%NiO/1%CeO 2 −Al 2 O 3 was observed in the seventh reaction-regeneration cycle. Nickel aggregation, observed on the surface of the catalyst by XRD analysis, may account for the deactivation. Dust deposition on the catalyst surface had a significant influence on tar modification, and the interaction mechanism between dust deposition and coke formation was clarified. The electron probe microanalysis results showed that SiO 2 tends to promote carbon deposition, whereas MgO and Fe 2 O 3 components have a negative influence on carbon deposition. This study can serve as a reliable reference for the practical development and modification of purification processes for coal pyrolysis volatiles.

Rare Earth/Transition Metal Oxides for Syngas Tar Reforming: A Model Compound Study

“…Most researchers have reported some increase in tar reforming activity and lower coke deposition when the partial pressure of water is increased. ,,,− However, there appears to exist an optimum water partial pressure, for most catalysts. When the partial pressure exceeds the optimum, the activity decreases, e.g., for Ni/Fe 2 O 3 –Al 2 O 3 , and other Ni-based catalysts . Our results seem to agree with this.…”

“…When the partial pressure exceeds the optimum, the activity decreases, e.g., for Ni/Fe 2 O 3 −Al 2 O 3 , 61 and other Nibased catalysts. 20 Our results seem to agree with this.…”

“…The results in Figure 2 show that the activity for both La/Ce3 and Re/Ce3/Zr54 decreased significantly but the other catalysts were little affected. While the diminished propane conversion for these two catalysts may partly arise from sintering at high water partial pressure, 20 the behavior of the others and our previous characterizations of the surface areas of used TM/REO catalysts (in naphthalene reforming) 8 argue against this as the principal cause. Once again the Fe/Ce3 is clearly the best material on a per site basis.…”

Chemical Looping Reforming of Coal Tar Vapor on the Surface of CaO-Modified Fe-Based Oxygen Carrier

“…11−14 However, many factors are affecting the stability of the catalyst, such as mechanical strength, surface area, and surface carbon deposition or hightemperature sintering. 15,16 Additionally, the regeneration of catalyst incurs a large energy consumption. Therefore, the oxygen carrier (OC) might be used to carry out a chemical looping reforming (CLR) of coal tar.…”

“…It is beneficial to use the chemical method to convert the macromolecular tar into smaller combustible gas molecules. Among the chemical methods, the catalytic cracking method uses a catalyst to reduce the activation energy and has a higher tar conversion efficiency at a higher reaction rate. − However, many factors are affecting the stability of the catalyst, such as mechanical strength, surface area, and surface carbon deposition or high-temperature sintering. , Additionally, the regeneration of catalyst incurs a large energy consumption. Therefore, the oxygen carrier (OC) might be used to carry out a chemical looping reforming (CLR) of coal tar.…”