A Model of Catalytic Cracking: Catalyst Deactivation Induced by Feedstock and Process Variables

Changes in the quality of the feedstocks generated by involving various petroleum fractions in catalytic cracking significantly affect catalyst deactivation, which stems from coke formed on the catalyst surface. By conducting experimental studies on feedstocks and catalysts, as well as using industrial data, we studied how the content of saturates, aromatics and resins (SAR) in feedstock and the main process variables, including temperature, consumptions of the feedstock, catalyst and slops, influence the formation of catalytic coke. We also determined catalyst deactivation patterns using TG-DTA, N2 adsorption and TPD, which were further used as a basis for a kinetic model of catalytic cracking. This model helps predict the changes in reactions rates caused by coke formation and, also, evaluates quantitatively how group characteristics of the feedstock, the catalyst-to-oil ratio and slop flow influence the coke content on the catalyst and the degree of catalyst deactivation. We defined that a total loss of acidity changes from 8.6 to 30.4 wt% for spent catalysts, and this depends on SAR content in feedstock and process variables. The results show that despite enriching the feedstock by saturates, the highest coke yields (4.6–5.2 wt%) may be produced due to the high content of resins (2.1–3.5 wt%).

Promoters for Improvement of the Catalyst Performance in Methane Valorization Processes

In this work, the introduction of modifying additives in the composition of catalysts is considered as an effective mode of improving functional characteristics of materials for two processes of methane conversion into valuable products – methane dehydroaromatization (DHA of CH4) into benzene and hydrogen and autothermal reforming of methane (ATR of CH4) into synthesis gas. The effect of type and content of promoters on the structural and electronic state of the active component as well as catalyst activity and stability against deactivation is discussed. For DHA of CH4 the operation mode of additives M = Ag, Ni, Fe in the composition of Mo-M/ZSM-5 catalysts was elucidated and correlated with the product yield and coke content. It was shown that when Ag serves as a promoter, the duration of the catalyst stable operation is enhanced due to a decrease in the rate of the coke formation. In the case of Ni and Fe additives, the Ni-Мо and Fe-Mo alloys are formed that retain the catalytic activity for a long time in spite of the carbon accumulation. For ATR of CH4, the influence of M = Pd, Pt, Re, Mo, Sn in the composition of Ni-M catalysts supported on La2O3 or Ce0.5Zr0.5O2/Al2O3 was elucidated. It was demonstrated that for Ni-M/La2O3 catalysts, Pd is a more efficient promoter that improves the reducibility of Ni cations and increases the content of active Nio centers. In the case of Ni-M/Ce0.5Zr0.5O2/Al2O3 samples, Re is considered the best promoter due to the formation of an alloy with anti-coking and anti-sintering properties. The use of catalysts with optimal promoter type and its content provides high efficiency of methane valorization processes.

Hydro-liquefaction of asphaltene catalyzed by molybdenum-nickel bimetallic catalysts in slurry bed

The aim of this study is to achieve the hydro-liquefaction of asphaltene for the production of liquid fuel. The oil soluble molybdenum catalysts, molybdenum dialkyl dithiophosphate, and nickel carboxylate precursor with different carbon chains, were synthesized. The catalysts were characterized by ICP-OES, TEM and XPS. Their catalytic performance for the hydro-liquefaction of asphaltene to liquid fuels was investigated in a slurry bed reactor by using decalin as hydrogen donor and dispersant. The results show that the bimetal catalytic system composed of molybdenum dialkyl dithiophosphate and caproic acid nickel produces more MoS2 and NiS x active species. The metal contents of which accounts for 81.8 and 81.0 wt% of the total amount of Mo and Ni, respectively, and thus exhibits the best catalytic performance among the catalysts studied. The liquid yield of the asphaltene hydrogenation over the bimetal catalyst is 84.6 wt%, which is much higher than that over other catalysts, and the coke content is only 8.6 wt% under the conditions of 1000 μg/g of total metal addition, 1:1 Mo/Ni metal mass ratio and 1:1 asphaltene/naphthalene mass ratio. The content of saturated and aromatic components in the liquid products of asphaltene hydrogenation of the bimetal catalyst system is 78.9 wt%, which is a high-quality liquid fuel component.

Thermochemical Performance Analysis of the Steam Reforming of Methane in a Fixed Bed Membrane Reformer: A Modelling and Simulation Study

Pd-based membrane reformers have been substantially studied in the past as a promising reformer to produce high-purity H2 from thermochemical conversion of methane (CH4). A variety of research approaches have been taken in the experimental and theoretical fields. The main objective of this work is a theoretical modelling to describe the process variables of the Steam Reforming of Methane (SRM) method on the Pd-based membrane reformer. These process variables describe the specific aims of each equation of the mathematical model characterizing the performance from reformer. The simulated results of the mole fractions of components (MFCs) at the outlet of the Fixed Bed Reformer (FBR) and Packed-Bed Membrane Reformer (PBMR) have been validated. When the H2O/CH4 ratio decreases in PBMR, the Endothermic Reaction Temperature (ERT) is notably increased (998.32 K) at the outlet of the PBMR’s reaction zone. On the other hand, when the H2O/CH4 ratio increases in PBMR, the ERT is remarkably decreased (827.83 K) at the outlet of the PBMR’s reaction zone. An increase of the spatial velocity (Ssp) indicates a reduction in the residence time of reactant molecules inside PBMR and, thus, a decrease of the ERT and conversion of CH4. In contrast, a reduction of the Ssp shows an increase of the residence time of reactant molecules within PBMR and, therefore, a rise of the ERT and conversion of CH4. An increase of the H2O/CH4 ratio raises the conversion rate (CR) of CH4 due to the reduction of the coke content on the catalyst particles. Conversely, a reduction of the H2O/CH4 ratio decreases the CR of CH4 owing to the increase of the coke content on the catalyst particles. Contrary to the CR of CH4, the consumption-based yield (CBY) of H2 sharply decreases with the increase of the H2O/CH4 ratio. An increase of the ERT raises the thermochemical energy storage efficiency (ηtese) from 68.96% (ERT = 1023 K), 63.21% (ERT = 973 K), and 48.12% (ERT = 723 K). The chemical energy, sensible heat, and heat loss reached values of 384.96 W, 151.68 W, and 249.73 W at 973 K. The selectivity of H2 presents higher amounts in the gaseous mixture that varies from 60.98 to 73.18 while CH4 showed lower values ranging from 1.41 to 2.06. Our work is limited to the SRM method. In terms of future uses of this method, new works can be undertaken using novel materials (open-cell foams) and the physical-mathematical model (two-dimensional and three-dimensional) to evaluate the concentration polarization inside membrane reactors.

High Channel Density Ceramic Microchannel Reactor for Syngas Production

Solid oxide fuel cells can operate with carbonaceous fuels, such as syngas, biogas, and methane, using either internal or external reforming, and they represent a more efficient alternative to internal combustion engines. In this work, we explore, for the first time, an alumina membrane containing straight, highly packed (461,289 cpsi), parallel channels of a few micrometers (21 µm) in diameter as a microreformer. As a model reaction to test the performance of this membrane, the dry reforming of methane was carried out using nickel metal and a composite nickel/ceria as catalysts. The samples with intact microchannels were more resistant to carbon deposition than those with a powdered sample, highlighting the deactivation mitigation effect of the microchannel structure. The coke content in the microchannel membrane was one order of magnitude lower than in the powder catalyst. Overall, this work is a proof of concept on the use of composite alumina membrane as microchannel reactors for high temperature reactions.

Impact of small promoter amounts on coke structure in dry reforming of methane over Ni/ ZrO2

Coke deposition is one of the main challenges in the commercialisation of dry reforming of methane over supported Ni catalysts. Besides the coke quantity, the structure of the deposits is also essential for the catalyst lifetime. Accordingly, in this study, we analysed the effect of Na, K, and Cs promoters on both these variables over Ni/ ZrO₂ catalysts. Besides blocking the most active coke-forming sites already at low loading, the promoting effect of the alkali metals is also contributed by their coke gasification activity. To evaluate the additional impact of the latter, the behaviour of alkali-doped catalysts was compared to that for Mn-doped catalysts, exclusively featuring the site-blocking promotion mechanism. While the conversion is barely affected by the type of promoter, it has a profound effect on the amount and the composition of carbon deposits formed during the reaction. Promoting with K or Mn reduces the coke content to a similar degree but with less carbon fibres observed in the case of K. The promotion by Cs and Na results in the lowest coke content. The superior performance of Cs and Na-doped Ni/ZrO₂ catalysts is attributed to the enhanced coke gasification via carbonate species on top of the site blocking effects.

Impact of small promoter amounts on coke structure in dry reforming of methane over Ni/ ZrO2

Coke deposition is one of the main challenges in the commercialisation of dry reforming of methane over supported Ni catalysts. Besides the coke quantity, the structure of the deposits is also essential for the catalyst lifetime. Accordingly, in this study, we analysed the effect of Na, K, and Cs promoters on both these variables over Ni/ ZrO₂ catalysts. Besides blocking the most active coke-forming sites already at low loading, the promoting effect of the alkali metals is also contributed by their coke gasification activity. To evaluate the additional impact of the latter, the behaviour of alkali-doped catalysts was compared to that for Mn-doped catalysts, exclusively featuring the site-blocking promotion mechanism. While the conversion is barely affected by the type of promoter, it has a profound effect on the amount and the composition of carbon deposits formed during the reaction. Promoting with K or Mn reduces the coke content to a similar degree but with less carbon fibres observed in the case of K. The promotion by Cs and Na results in the lowest coke content. The superior performance of Cs and Na-doped Ni/ZrO₂ catalysts is attributed to the enhanced coke gasification via carbonate species on top of the site blocking effects.

Impact of Small Promoter Amounts on Coke Structure in Dry Reforming over Ni/ ZrO2

Coke deposition is one of the main challenges in the commercialization of dry reforming of methane over supported Ni catalysts. Besides the coke quantity, the structure of the deposits is also essential for the catalyst lifetime. Accordingly, in this study, we analysed the effect of different metal promoters on both these variables over Ni/ ZrO₂ catalysts. Alkali metals are known to block the most active coke forming sites already at low loading, leading to an investigation of Na, K and Cs. To analyse the possible contributions of coke gasification activity of the alkali metals, Mn was additionally used as a comparison. While the conversion is barely affected by the type of promoter, it has profound effect on the amount and the composition of carbon deposits formed during reaction: Addition of K or Mn reduces the coke content to a similar degree but with less carbon fibres observed in the case of K. Promotion by Cs and Na results in the lowest coke content, which is attributed to enhanced coke gasification via carbonate species

Highly selective production of renewable p-xylene from bio-based 2,5-dimethylfuran and ethylene over Al-modified H-Beta zeolites

H-Beta zeolite with further dealumination and modification with alumina shows excellent and durable performances in the synthesis of renewable p-xylene (PX) via bio-based 2,5-dimethylfuran and ethylene with a PX yield of 97% and much less coke content.