Large-pore Catalysts Research Articles

Controlled methylamine synthesis in a membrane reactor featuring a highly steam selective K+-LTA membrane

Water permeation through a hydrophilic zeolite membrane can be used to promote reactions under equilibrium controlled conditions through the in situ removal of the by-product water. In the methylamine synthesis, mono- (MMA), di- (DMA) and trimethylamine (TMA) are formed by the successive methylation of ammonia with methanol (MeOH) over a mildly acidic catalyst. The methylamine yield can be increased through selective water extraction from the reactor through a membrane. Since both reactants and water have similar molecular kinetic diameters below 3.7 Å, because of the limited steam selectivity of the commonly used hydrophilic Na-LTA membrane (zeolite 4A), not only water has been removed. Therefore, in this work a K-LTA membrane, which was obtained by ion exchange with a reduced pore window diameter of 3 Å and thus with a higher water selectivity, was used in the membrane-supported methylamine synthesis. When replacing the Na-LTA with the K-LTA membrane, the H2O/MeOH mixed gas separation factor increases up to 1100 and the H2O/NH3 separation could also be improved. This in turn leads to an overall boost of the higher methylated amines DMA and TMA in methylamine synthesis. When using the narrow-pore aluminosilicate catalyst H-SSZ-13 with CHA structure, the application of the K-LTA membrane increases the share of the industrially desired product DMA from 51% without membrane to 74% with slightly increased conversion. When using the large-pore catalyst H-MOR, the thermodynamically most stable product TMA can be formed and the selectivity was increased from 35% without membrane to 41% with the K-LTA membrane.

Sulfonated organosilica mesocellular foam for catalyzing bulky molecules

Sulfonated organosilica mesocellular foam, a large-pore acidic catalyst, exhibited good catalytic activities in the hydrolysis of lab-extracted natural fibers or commercial microcrystalline celluloses, and esterification of oleic acid.

Effect of catalyst activity in SMR-SERP for hydrogen production: Commercial vs. large-pore catalyst

In this work, we have evaluated the performance of an SMR-SERP unit (steam methane reforming sorption enhanced reaction process), using two different Ni/Al2O3 catalysts: commercial “Octolyst 2001” from Degussa and a large-pore catalyst (Catalyst A). The selective CO2 sorbent was a potassium modified hydrotalcites. Several experiments were performed under different operating conditions to validate a mathematical model.Experimental results show that the Degussa catalyst is more active and more selective to CO2 producing hydrogen with higher purity and less CO than the large-pore catalyst. Cyclic SMR-SERP experiments were also performed. The cycles comprise four different steps: reaction, depressurization, reactive regeneration and pressurization. In the cyclic experiments, conversion was 43% higher than in an SMR reactor, while H2 purity was 75%, which is 25% higher than in normal SMR operation. Results indicate that more active catalysts also promote a better reactive regeneration optimizing the use of part of the product (H2). The proposed mathematical model was validated in a wide range of operating conditions and in a cyclic experiment. The model was able to describe the SMR-SERP experiments without any fitting parameters.

Measurement of Diffusion Coefficient of Heavy Oil in Fluidized Catalytic Cracking (FCC) Catalysts

Large-pore fluidized catalytic cracking (FCC) catalysts, using polystyrene spheres as templates, were prepared. By adsorption equilibrium experiments, the Freundlich adsorption isotherm of Dagang vacuum residue oil fractions on the prepared FCC catalysts was established. The data of adsorption rate were obtained and the effective diffusion coefficient of the oil fractions in the catalyst particles was calculated to be 10−9−10−8 cm2/s. The effective diffusion coefficient in the large-pore catalyst was 2−3 times larger than that in the conventional catalyst, and it decreased with the molecular weight of the oil fraction. This verified that, because of promotion of the diffusion rate of heavy oil caused by the larger pore size of the catalyst, the catalytic performance of a macroporous catalyst was better than the conventional catalyst.

Methane steam reforming in large pore catalyst

In this work we have studied the performance of catalyst extrudates of Ni-Al2O3 promoted with potassium for steam methane reforming. The most interesting property of this catalyst is the presence of large pores (average diameter of 8×10−4 m) to reduce diffusional limitations. We have determined the true kinetics using catalyst powder in the temperature range covering 757–804 K. Furthermore, experiments using a fixed bed filled with extrudates were performed in the temperature range covering 701–800 K at constant methane/steam ratio for different feed flowrates. In the true kinetic experiments using catalyst powder it was observed that this catalyst has a very high CO2 selectivity against CO. The conversion of the catalyst is smaller than other commercial materials due to the smaller content of Ni (10%). Experiments using catalyst extrudates showed that the reaction suffers from strong mass and heat limitations: diffusion of reactants/products and heat transfer in the gas/solid interface. The presence of large pores has an important contribution in decreasing the resistance to mass transfer in particles with 1.1×10−2 m diameter. At 800 K and 2 bar the effectiveness factor was about 0.43 for the steam methane reforming reaction and 0.41 for the global reaction.

Reduction of light cycle oil in catalytic cracking of bitumen-derived crude HGOs through catalyst selection

In an attempt to reduce the production of light cycle oil (LCO), a non-premium fluid catalytic cracking (FCC) product in North America, a large-pore catalyst containing rare-earth-exchanged Y (REY) zeolite, was used to crack two Canadian bitumen-derived crude heavy gas oils (HGOs) hydrotreated to different extents. For comparison, a regular equilibrium FCC catalyst with ultra-stable Y (USY) zeolite and a conventional western Canadian crude HGO were also included in the study. Cracking experiments were conducted in a fixed-bed microactivity test (MAT) reactor at 510 °C, 30 s oil injection time, and varying catalyst-to-oil ratios for different conversions. The results show that pre-cracking of heavy molecules with wide-pore matrix, followed by zeolite cracking, enhanced conversion at the expense of light and heavy cycle oils at a constant catalyst-to-oil ratio, giving improved product selectivities (e.g., higher gasoline and lower dry gas, LCO, and coke yields, in general, at a given conversion). To systematically assess the benefits of employing the specialty catalyst over the regular catalyst in cracking Canadian HGOs, individual product yields were compared at common bases, including constant catalyst-to-oil ratios, conversions, and coke yields for three feeds, and at maximum gasoline yield for one feed. In most cases, the preferred choice of large-pore zeolite-rich catalyst over its counterpart was evident. The observed cracking phenomena were explained based on properties of catalysts and characterization data of feedstocks, including their hydrocarbon type analyses by gas chromatograph with a mass-selective detector (GC-MSD).

Oligomerization of 1-Hexene and 1-Octene over Solid Acid Catalysts

Oligomerization of hexene and heavier olefins is important for synthetic fuel producers to reduce refinery complexity, as well as to produce good quality middle distillates and lubricating oils. Conversion of such olefins with homogeneous catalysts is much easier than with solid acid catalysts, which are prone to deactivation and are limited to middle distillate production. Solid phosphoric acid, amorphous silica−alumina, sulfated zirconia, MCM-41, ZSM-5, zeolite-Y, and zeolite-omega heterogeneous catalysts were evaluated in fixed-bed reactors with 1-hexene and 1-octene to determine the key catalyst properties required. The influence of added chromium and nickel was also evaluated. It was found that solid acids with average pore size of more than 10 nm had consistently better catalyst lifetime, because heavy oligomers were less readily trapped in the catalyst. It was also found that in large-pore catalysts chromium improved selectivity to lubricating oil significantly by changing the oligomerization mechanism.

Reactions of Halobenzenes with Methanol on the Microporous Solid Acids HBeta, HZSM-5, and HSAPO-5: Halogenation Does Not Improve the Hydrocarbon Pool

The reactions of fluorobenzene, 3-fluorotoluene, and three isomers of difluorotoluene, chlorobenzene, and bromobenzene with excesses of methanol were investigated on the large-pore catalysts HBeta (*BEA) and HSAPO-5 (AFI), and on the medium-pore HZSM-5 (MFI). Flow reactor studies in pulse mode with GC-MS detection revealed that the fluorobenzene derivatives were readily methylated at, for example, 375 degrees C, but not even pentamethylfluorobenzene was obviously active as a reaction center for methanol-to-olefin (MTO) catalysis. Carbon-labeling studies revealed that small amounts of methylbenzenes were formed by defluorination, and these aromatic hydrocarbons seemed to account for the small yields of olefins (and their secondary reaction products) observed. Loss of one fluorine was also evident in the products for one of the difluorotoluene isomers. On HSAPO-5 the activity order for ring-methylation of halobenzenes was F > Cl >> Br. On HZSM-5, chlorobenzene and especially bromobenzene lost halogen through a route forming halomethane. These largely negative results will nevertheless be useful in testing theoretical models of the detailed reaction steps in the hydrocarbon pool mechanism for MTO catalysis.

Diisopropyl ether syntheses from crude acetone

Diisopropyl ether (DIPE) may be generated via a novel, two-step process from crude, by-product, acetone streams through initial acetone hydrogenation over a bulk-metal, nickel-rich catalyst to give isopropanol (IPA), followed by dehydration of said IPA intermediate in the presence of an acidic, large-pore zeolite catalyst. Three classes of acidic zeolite have proven effective for selective DIPE production, including Beta-zeolite, β-zeolites modified with certain transition metals, and dealuminized Y-zeolites.

Noble metal large-pore zeolite catalyst for methanolethanol coupling

Noble metal large-pore zeolite catalyst for methanolethanol coupling

Effect of intraparticle convection on the transient behavior of fixed-bed reactors: Finite differences and collocation methods for solving unidimensional models

The effect of intraparticle convective flow inside large-pore catalysts (e.g. selective oxidation catalysts) on the transient behavior of fixed-bed catalytic reactors is analysed by using three different transient reactor models: the 1-D, heterogeneous, intraparticle diffusion/convection model, the 1-D, heterogeneous, intraparticle diffusion model and the pseudo-homogeneous model as a reference model. Results from these 1-D models were compared with those obtained in a previous paper when radial dispersion was taken into account. The process start-up analysis was achieved by feeding the reactor when heated at the wall temperature. The high capacity of the catalytic bed leads to a faster propagation of the transient concentration waves than of the thermal ones, developing sharp concentration fronts during the so-called pseudo-isothermal behavior of the reactor. When the transient regime inside the solid is considered these shock waves are smeared out showing different velocities associated with the intraparticle diffusive and convective transports. Higher reactant conversions are achieved when intraparticle convection is allowed. Besides being centered on the transient responses of large-pore systems, this paper also addresses numerical studies to allow a good representation of the dynamic features referred to above. The numerical solution for the model equations was obtained through the lines method. The performance of two different methods used on the space variables discretization, orthogonal collocation on finite elements and finite differences is discussed. A strategy of dividing the bed length into sections solved one after the other to avoid large dimension problems was also implemented. Important reductions in computing times can be obtatined by using the pseudo steady-state approximation for the intraparticle concentration profile and taking as initial condition the axial concentration profile corresponding to the pseudo-steady-state isothermal solution. Moreover, accounting for the axial dispersion on the model equations, the numerical integration becomes easier to perform with significative reductions in the CPU times.

96/04748 Hydrodenitrogenation of vacuum residue with a large-pore catalyst

96/04748 Hydrodenitrogenation of vacuum residue with a large-pore catalyst

Hydrodenitrogenation of vacuum residue with a large-pore catalyst

The improved conversion (e.g. nitrogen conversion) achieved with laboratory-prepared macropore (MAP) catalysts could be attributed to either geometrical effects (diffusion or access to surface area) or chemical effects (surface acidity or more effective reaction sites). The MAP catalysts had much larger macropores than a commercial reference catalyst. Because these pores provided access to the catalysts' interior, the 15% MAP catalyst had a larger surface area than the commercial catalyst, when the catalysts were in their working conditions. Infrared spectroscopic measurements of ammonia and pyridine adsorption were made on several of the catalysts to determine whether or not the acidic properties of the MAP alumina were different from those of γ-alumina. A unimodal catalyst containing fluoride ions that enhanced its surface acidity and thereby enhanced conversions was compared with the MAP catalyst. Both the F-containing catalyst and the MAP catalyst produced greater nitrogen conversions than the unimodal catalyst that did not contain F ions. When the infrared spectra of the MAP catalyst were compared with those of the F catalyst, it was seen that at 400°C the F catalyst retained Brönsted acidity that was not observed in the MAP catalyst. Therefore, Brönsted acidity was not considered to be the cause of the conversion enhancement achieved with the MAP catalyst. On this basis, the enhanced conversion by the MAP catalysts was attributed to geometrical effects (pore diffusion).

Hydroprocessing of vacuum residues: relation between catalyst activity, deactivation and pore size distribution

Four catalysts with different unimodal and bimodal pore size distributions having different proportions of meso- and macropores were studied. The performance of the catalysts in terms of activity and selectivity as well as deactivation in selected hydrotreating reactions was examined using Kuwait vacuum residue as feedstock. The effect of catalyst pore size was significantly different for different reactions. For sulfur removal (HDS), a unimodal pore catalyst with maximum pore volume in the medium mesopore range (10–25 nm diameter) showed the highest activity. For hydrodemetallation (HDM) and hydrodenitrogenation (HDN) reactions, large-pore catalysts, having a major proportion of their pore volume in 100–300 nm diameter pores, were more effective. Bimodal pore catalysts having large amounts of narrow pores showed a higher rate of deactivation than unimodal pore catalysts with a maximum amount of medium mesopores.

Simulation of tubular reactors packed with large-pore catalysts with spherical geometry

Simulation of tubular reactors packed with large-pore catalysts with spherical geometry

Simulation of tubular reactors packed with large-pore catalysts with spherical geometry

The effect of intraparticle convection on the behavior of fixed-bed reactors with spherical catalyst particles is analyzed. In the model equations for the particles, both radial and angular coordinates are accounted for. The study concerning the number of discretization points to be used in the numerical solution of the intraparticle profiles is presented. For the reactor, a comparison between unidimensional heterogeneous models with and without intraparticle convection and with spherical and slab geometry for the solid particles is also performed.

Large-Pore Catalysts for Hydroprocessing of Residual Oils

Hydroprocessing catalysts were prepared using fibrillar alumina and attapulgite as carrier materials and nickel and molybdenum as active substances. With fibrillar alumina as primary particles, a carrier material was obtained which combined a large surface area (138 m{sup 2}/g) with a large average pore diameter (252 {angstrom}). Due to side-by-side association of the fibers, attapulgite did not yield a catalyst carrier with as large pores as was expected. The catalysts were tested for hydroprocessing of an atmospheric petroleum resid, and the results were compared with those obtained for a commercial catalyst with similar loading of nickel and molybdenum. The catalyst prepared using fibrillar alumina as carrier material was more active than the commercial catalyst for hydrodemetallization, equally active for hydrodesulfurization, and less active for hydrodenitrogenation. The catalyst prepared using attapulgite as carrier material was inferior to the other two catalysts in all respects.

Flow Field and Non-Isothermal Effects on Diffusion, Convection, and Reaction in Permeable Catalysts

We analyze non-isothermal effects on the efficiency of large-pore catalyst particles, where intraparticle convection may be important. The particle permeability is taken into account by studying the flow field within the particle simultaneously with the mass and the energy transport processes. Two particle geometries, slab and sphere, are considered. Non-isothermal effects are observed on the occurrence of multiple steady states due to reaction ignition. It is found that, when the flow field equations are taken into account, the minimum values of the efficiency and the minimum temperatures reached inside the particle are lower than the ones estimated considering just the mass and energy transport equations

The effect of intraparticle convection on conversion in heterogeneous isothermal fixed-bed reactors with large-pore catalysts for first-order reactions

Residence time distributions have been largely used in chemical engineering to make diagnosis of the ill-functioning of chemical reactors and to predict conversion in homogeneous isothermal reactors once the kinetic rate of reaction is known. The prediction is unambiguous for first-order reactions. In this paper, the impulse tracer response of isothermal heterogeneous fixed-bed reactors packed with large-pore catalysts, in which intraparticle convection occurs, is derived. From the impulse tracer response, the residence time distribution of the outer phase is calculated and used to predict the steady state conversion in the reactor for first-order reactions. The effect of intraparticle convection, measured by the intraparticle Peclet number λ for a given reaction-catalyst system, i.e. for a set of Damkhöler, Thiele, Biot and Peclet numbers (Da, ø, Bi m and Pe respectively) is to drive the conversion between the diffusion-controlled and the kinetic-controlled limits. The problem of scaling from batch to continuous packed beds is also addressed.

Dynamic behavior of fixed-bed reactors with “large-pore” catalysts: A bidimensional heterogeneous diffusion/convection model

A complete bidimensional, heterogeneous model taking into account intraparticle diffusion and convection (HT dc) was developed and used to analyze the dynamic behavior of a fixed-bed catalytic reactor containing large-pore catalysts. Results were compared with those obtained by simpler bidimensional models: HT d, a heterogeneous model which considers only intraparticle diffusion and the pseudo-homogenous (PH) model. Two situations were tested: the pseudo-steady-state approximation for the catalyst and the transient regime inside particle. The integration of model equations was carried out using the method of lines. Orthogonal collocation in finite elements was employed to discretize space coordinates: reactor axial coordinate (accomplished by available software), reactor radial coordinate and particle space position (handled by the authors). Hot spots obtained with bidimensional HT models are lower than those predicted with unidimensional models. However, the maximum temperature rise predicted by the PH model is higher than in the corresponding unidimensional PH model.