Fixed-fluidized Bed Research Articles

Catalytic pyrolysis of polystyrene in different reactors: Effects of operating conditions on distribution and composition of products

The effects of temperature and pressure on product distribution were investigated by catalytic slow pyrolysis of polystyrene in a fixed bed. Simultaneously, the catalytic fast pyrolysis of polystyrene was carried out in a fixed-fluidized bed to study the effects of temperature and reaction time on the product distribution. The slow and fast pyrolysis experiments of polystyrene were conducted using γ- Al2O3 (basic) as catalyst and silica sand as control group. The compositions of oil and gas products were analyzed by GC-FID, GC-MS and GC to investigate the catalytic activity of basic catalyst. The results showed that catalytic slow pyrolysis and catalytic fast pyrolysis achieved maximum oil yields of 94.6 wt% and 92.19 wt%, respectively. In slow pyrolysis, toluene, ethylbenzene, and styrene were the main products, and the introduction of catalyst led to reduced yields of toluene, ethylbenzene, cumene, and α-methyl styrene. However, the main product of fast pyrolysis was only styrene, with a recycling rate nearly 80% under catalytic conditions. The presence of the catalyst increased the yield of styrene, with slow pyrolysis rising from 27.15% to 32.58%, and fast pyrolysis increasing from 82.28% to 86.56%. Longer residence time strengthened secondary reactions to generate more aromatics such as toluene and ethylbenzene. Both catalytic slow and fast pyrolysis yielded higher styrene contents than thermal pyrolysis because the basic catalyst reduced the occurrence of secondary reactions.

Selective deep desulfurization of liquefied petroleum gas on Ni/ZnO-based catalyst

Process of selective deep desulfurization of liquefied petroleum gas (LPG) was developed using a Ni/ZnO-based catalyst. Ethyl mercaptan, dimethyl disulfide and methyl disulfide were used as model compounds in LPG to investigate sulfides conversion over different catalysts. All three model sulfides were totally removed over the composite catalyst at above 300 °C in hydrogen atmosphere. Desulfurization of LPG from FCC unit were studied in a micro-fixed bed reactor, and scaled up in a fixed-fluidized bed reactor. Results showed that highly selective desulfurization of LPG could be achieved using the composite catalyst when the sulfur loading of catalyst was in a particular range. The sulfur content of LPG could be decreased to lower than 2.0 μg·g−1 with an olefin loss ratio of less than 1.5 %. X-ray photoelectron spectroscopy (XPS) characterization indicated that the interaction of Ni with S strengthened with the increasing of sulfur loading. Density functional theory calculations showed that the pre-coated S on Ni (111) surface increased the adsorption energy difference between propylene and sulfides which was helpful for the retention of propylene during desulfurization on Ni/ZnO-based catalyst.

Characterization Studies for Derived Biodiesel from the Fluid Catalytic Cracking (FCC) of Waste Cooking Oil through a Fixed Fluidized Bed (FFB)

Biodiesel production through transesterification or catalytic hydrogenation using vegetable oil is a sustainable method, but it has the downsides of by-product generation and a higher cost. Therefore, in this study, waste cooking oil was selected as a raw material, and fluidized catalytic cracking was carried out on the catalyst (LDO-75) through a fixed-fluidized-bed (FFB) reactor. The effects of the reaction temperature, catalyst–oil ratio and weight hourly space velocity (WHSV) on the yield of pyrolysis gas, gasoline, diesel and heavy oil fractions were studied. The composition of the pyrolysis gas was determined by gas chromatography (GC), the composition of the gasoline fraction was analyzed by gas chromatography-mass spectrometry (GC-MS), and the characteristics of the diesel and heavy oil fractions were determined by nuclear magnetic resonance (NMR). The results show that light olefins are the main products of pyrolysis gases, and the liquid products are mainly composed of aromatic compounds. In addition, the catalytic cracking process of waste cooking oil fluid is proposed, indicating that the process of the catalytic cracking of waste cooking oil fluid includes deoxygenation, oligoaromatization and hydrodeoxygenation. The results of this study will provide a basis for the high value-added utilization of waste cooking oil.

Sequential fixed-fluidized bed foam granulation (SFFBFG) and drying: Multivariate model development for water content monitoring with near–infrared spectroscopy

Foam granulation (FG) is a non-conventional technique in which a binding solution is sprayed as aqueous foam. The main objectives of this work are, converting a lab-scale fluidized bed dryer into a fluidized bed foam granulator and dryer. Second, developing a partial least squares regression model for monitoring granules water content during this process, and third, bringing forward sufficient evidence of the fluidized bed foam granulation process feasibility. In this work, a mini-Glatt fluidized bed apparatus was used and aqueous foam was produced through an internal mixing nozzle located above the static powder bed, which is fluidized after foam dispensing. A micro-NIR probe was inserted across the powder container and gather spectral data during granulation and drying. The calibration model was built using the spectral data by Random Subset Cross-Validation and validated externally. Concerning the results, an Rcal2 and RMSECV of 0.945 and 1.67% w/w were obtained respectively. Model validation gave an Rval2 and RMSEP of 0.9 and 2.7% w/w respectively, demonstrating the ability of NIR spectroscopy to predict granules water content. The scanning electron microscopy (SEM) pictures validated the process feasibility.

Molecular-Level modeling for naphtha olefin reduction in FCC subsidiary Riser: From laboratory reactor to pilot plant

In this work, molecular-level kinetic modeling was developed for the fluid catalytic cracking (FCC) naphtha olefin reduction process in a subsidiary riser. A transfer strategy for model parameters between different scale reactors was proposed. A molecular-level kinetic model was developed for a laboratory-scale fixed fluidized bed (FFB). The kinetic parameters were tuned using systematic experimental data of FFB under different conditions. Then, a molecular-level process model was built for a pilot riser. The kinetic parameter of the pilot riser model was transferred from the FFB model using only one scale-up experimental data to tune the transferring factors. The obtained riser model can accurately predict the fraction yield, naphtha composition, and temperature profile while the feedstock and operating conditions were changed.

Petroleum Coke Combustion in Fixed Fluidized Bed Mode in the Presence of Metal Catalysts.

Petroleum coke is one of the waste products generated in the oil refining industry that can be used as fuel in energetics. However, the low volatile matter content and graphite-like structure of petroleum coke are the reasons for its high ignition temperature and combustion complexity. In this research, petroleum coke combustion and oxidation kinetics in the presence of metal catalysts were investigated. To evaluate the effect of the catalyst on the ignition temperature and the apparent activation energy, a new approach of a “fixed fluidized bed” was proposed. In this mode, petroleum coke particles spaced from each other by inert quartz powder kind of “freeze” in the porous layer. This regime allows us to determine the ignition temperature of petroleum coke particles in the static mode by differential thermography and calculate the activation energy by gas analysis. Organic and inorganic salts of copper, iron, and cerium are used as catalysts for petroleum coke combustion. A series of experiments were carried out in the porous media thermo-effect cell (PMTEC) and on a thermogravimetric (TG) analyzer. The kinetics of the combustion processes was calculated by Kissinger–Akahira–Sunose and Ozawa–Flynn–Wall methods. The results obtained in the “fixed bed” mode showed that the ignition temperature and the average apparent activation energy significantly decreased in the presence of CuCl2 and FeCl3. The results obtained by the new approach were compared with the results of the thermogravimetric analysis.

Experimental validation of CFD hydrodynamic models for catalytic fast pyrolysis

Hydrodynamics for catalyst fluidization and circulation for Catalytic Fast Pyrolysis (CFP) were investigated using cold flow experiments and used to validate predictions from computational fluid dynamics (CFD) simulations. Proprietary fresh and equilibrium CFP catalyst were tested in lab-scale fixed fluidized bed (FFB) and circulating fluidized bed (CFB) setup. Bed expansion and pressure drop were recorded for fresh catalyst in the fixed fluidized bed setup for a range of gas velocities (0–0.04m/s) which encompassed minimum fluidization and bubbling regimes. Catalyst circulation in the circulating fluidized bed setup on the other hand, was quantified using mass holdup in the mock reactor, particle size distribution for this holdup and pressure profile for a range of transport gas velocities (0.094–0.561m/s, 10–60 SLPM) and catalyst feedrates (3, 6, 12kg/h; G=0.46, 0.92, 1.84kg/m2-s) for a single-inlet and single-outlet mock reactor configuration. Flow patterns and gas jet penetration through the mock reactor provided qualitative observations that were used for evaluating CFD models. CFD code based on CPFD method (Barracuda Virtual Reactor®) was used to simulate these gas-solid fluidized beds based on three-dimensional grids. Grid independence was established for both fixed and circulating fluidized bed models such that an average grid volume of 23–29mm3 was sufficient to effectively predict quantitative and qualitative observables. Several CFD parameter sets were tested to evaluate combinations of drag models, blended acceleration model, particle-wall interactions and collision and stress models. Parker-drag model with blended acceleration and advanced settings for particle-wall interactions, collision and stress parameters is determined to provide the best agreement with experimental results.

Quantitative correlations of cracking performance with physiochemical properties of FCC catalysts by a novel lump kinetic modelling method

The cracking performance determined by corresponding physiochemical properties of a FCC catalyst is usually one of the most important factors for catalyst selection and design. Thus, it is crucial to study the quantitative correlations of cracking performance with catalyst physiochemical properties. In this study, six commercial FCC catalysts were evaluated by cracking experiments on a fixed fluidized bed (FFB) and characterized of three key properties: zeolite to matrix specific surface area ratio (Z/M), total Bronsted to Lewis acid amount ratio (B/L) and zeolite unit cell size (UCS). Based on the experimental data, six 6-lump kinetic models were established for the six FCC catalysts. The three key property parameters were correlated with corresponding kinetic parameters of the six FCC catalysts, which leaded to the establishment and first report of a catalyst property-included lump kinetic model. The predicted data of product distribution exhibited good consistency with those experimental ones for two new FCC catalysts, and the relative errors were mainly below 10% for the catalyst property-included lump kinetic model. The new modelling method broadens the application of lump kinetic model in the field of catalyst selection and design, and in turn makes the process of catalyst selection and design more theory-guided.

ZSM-5 zeolites with different SiO2/Al2O3 ratios as fluid catalytic cracking catalyst additives for residue cracking

Three proton-type ZSM-5 zeolites with different SiO2/Al2O3 ratios (SARs) of 33, 266, and 487 were characterized and examined as fluid catalytic cracking catalyst additives for residue oil cracking. The catalytic performance of the ZSM-5 additives was evaluated using an ultra-stable Y-zeolite (USY)-based fluid catalytic cracking catalyst in a fixed fluid bed unit. As observed, the cracking of primary olefins over the hybrid catalysts consisting of USY-based catalyst and ZSM-5 additive was considerably inhibited by increasing the SAR of the ZSM-5 zeolite, thus avoiding substantial loss of gasoline paraffins. The introduction of ZSM-5 additives led to higher liquid petroleum gas yields as well as higher isobutane and isopentane yields. The improved yields were attributed to the combined effects of the ZSM-5 additives and USY-based catalyst. The variations of gasoline paraffins and aromatics both accounted for the enhancement in the octane number values. The use of ZSM-5 with higher SARs (266 and 487) led to an enhancement in the octane number with minimal loss of gasoline. This enhancement was mainly attributed to the moderate aromatization and isomerization reactivity of the ZSM-5 additives that mainly originated from their relatively small pores and suitable acidic properties with higher SARs.

Reactive Adsorption Desulfurization of FCC Gasoline over NiO/ZnO-Al2O3-SiO2 in a Fixed-fluidized Bed Reactor

The oxides adsorbent of NiO/ZnO-Al2O3-SiO2 was prepared by a co-precipitation method. NiO/ZnO-SiO2-Al2O3 is an effective adsorbent for reactive adsorption desulfurization of fluid catalytic cracking gasoline. The reaction conditions, such as reaction temperature, total pressure, weight hourly space velocity, and volume ratio of hydrogen to oil for desulfurization over NiO/ZnO-SiO2-Al2O3 in a fixed-fluidized bed reactor were investigated. With the optimum conditions, the sulfur content of FCC gasoline can be decreased from 180 to 11.6 mg·L−1, and the loss of olefin content of gasoline product is 1.05%, the research octane number loss of gasoline product is only 1.3 unit.

A Study on the Structure Oriented Lumping Model on the Catalytic Cracking of Straight-run Gasoline

A kinetic model of straight-run gasoline catalytic cracking was developed according to the structure oriented lumping method. Seventy-six kinds of molecules were selected to describe feedstock, and 72 reaction rules were established to construct reaction networks in this model. After the reaction rate constant and the termination condition of the network were involved, product distribution, group composition, and octane number of gasoline could be predicted. In this work the laboratory test data of straight-run gasoline catalytic cracking by a fixed fluid bed unit was used to verify the model. The results showed that the predicted product distribution and group composition of gasoline agreed well with the experimental data.

Naphthenic ring opening of perhydrophenanthrene over zeolite catalysts

AbstractExperiments of perhydrophenanthrene cracking over zeolite catalysts were conducted in a small fixed fluidized bed (FFB) unit. Effects of Y and ZSM-5 zeolite catalysts, temperature and catalyst/oil ratio on naphthenic ring opening reactions of perhydrophenanthrene were examined. The results show that products from naphthenic ring opening reactions of perhydrophenanthrene over zeolite catalysts are monocyclic or dicyclic cycloparaffin (cyclohexane, decalin), which is further converted into isoparaffin (2-methylpenptane, methyl hexane) by side chain breaking, or into monocyclic aromatics (benzene, C1–4 alkyl benzene) by hydrogen transfer, or into dicyclic aromatics (tetrahydronaphthalene, naphthalene, alkyl naphthalene) by deep hydrogen transfer. Products from dehydrogenation condensation reactions of perhydrophenanthrene are polycyclic aromatics with more than 3 rings (phenanthrenes, pyrenes) and coke. Due to the influence of naphthenic diffusion and adsorption on catalysts, selectivity of the naphthenic ring opening reaction is higher over Y catalyst than that over ZSM-5 catalyst. The relative ratio of naphthenic ring opening reactions to dehydrogenation condensation reactions, abbreviated as s(NRO)/s(DHC), is higher over Y catalyst than that over ZSM-5 catalyst. At the weight hourly space velocity of 10 h−1, temperature of 475–550°C, catalyst/oil mass ratio of 3.0–9.0, reactions of bimolecular hydrogen transfer and dehydrogenation condensation became stronger, and selectivity of the products from naphthenic ring opening reactions decreases with the rising of temperature or catalyst/oil ratio over Y catalyst.

Comparison between fixed fluidized bed (FFB) and batch fluidized bed reactors in the evaluation of FCC catalysts

The laboratory reactors ACE fixed fluidized bed FFB and batch fluidized bed CREC Riser Simulator were compared in the conversion of two commercial vacuum gas oil feedstocks (paraffinic and aromatic types) over two equilibrium commercial FCC catalysts (octane-barrel and resid types) under similar conditions. Reaction temperatures were 510 and 540°C and the catalyst to oil mass ratios were from 4 to 9 in the FFB unit, with time on stream varying from 112 to 50s, and 6.35 in the CREC Riser Simulator, with reaction times ranging from 5 to 25s. The results were contrasted in some cases to those of a DCR circulating pilot plant unit at 540°C.When the different product yields were considered, the same catalyst ranking was observed in both laboratory reactors on the whole, differences between catalysts and particularly between feedstocks being more perceptible in the FFB reactor. The CREC Riser Simulator reactor showed a linear yield curve for gasoline, which facilitated the analysis and comparisons; in this case, an overcracking regime was not shown, like in the case of the FFB reactor. The LCO yield curves were more defined and differences between catalysts developed more clearly in the FFB reactor. Coke yields were very high in the FFB reactor, typical of confined beds with continuous feed of the reactants, while in the CREC Riser Simulator reactor they were in the range of those observed in the pilot plant and commercial units.The two laboratory reactors showed complementing potential in the laboratory evaluation of commercial catalysts and feedstocks for the FCC process.

Application of new porous binder material in fluid catalytic cracking reaction

A novel porous binder was obtained by acid-treated kaolin. This new binder owned abundant meso-macro pore and good hydrothermal stability. The prepared catalyst using new binder had a character of low attrition index and large pore volume. The catalysts were tested in a fixed-fluidized bed unit. Compared with comparison sample, the conversion of new catalyst was increased by 0.73%, heavy oil yield decreased by 1.11%, the total liquid and light oil yield increased by 0.95% and 0.74%, respectively. The perfect pore structure and good hydrothermal stability of new binder were the possible reason of obtaining prominent performance.

Reactive Characteristics and Adsorption Heat of Ni/ZnO–SiO2–Al2O3 Adsorbent by Reactive Adsorption Desulfurization

Reactive adsorption desulfurization (RADS) experiments of fluid catalytic cracking (FCC) gasoline and a model gasoline over an Ni/ZnO–SiO2–Al2O3 adsorbent were carried out in a fixed-fluidized bed reactor at low pressures in an H2 atmosphere. The results show that hydrogenation, hydrogen transfer, and polymerization reactions accompany RADS. Sulfidation and carbon deposits, which can lead to decreases in the regeneration rate and amount of activated Ni, are crucial to the decay of desulfurization and the olefin-hydrogenation capability of the adsorbents. The obvious reduction of C5 and C6 olefins in FCC gasoline mainly contribute to the drop in octane number of the desulfurization product. The desulfurization experiment on model gasoline and the adsorption heats of model compounds show that RADS removes sulfur from sulfur-containing compound through S–M interactions rather than by π-complexation over the Ni/ZnO–SiO2–Al2O3 adsorbent. The adsorption heat of sulfur-containing compound is proportional to the ...

Simulation Study of Gas-Solid Macro-Mixing Characterization in Small Fixed-Fluidized Bed Reactor

In fixed-fluidized bed reactor, laboratory evaluation of different catalyst, raw materials and process parameters can be implemented, so it has wide applications in the refining process. In this study, we focused on small fixed-fluidized bed reactor, using Eulerian-Eulerian two-fluid model, simulated the gas-solid flow behavior in it. Gas residence time distribution was measured in order to characterize macro-mixing. At the same time, by changing the reactor structure and operating conditions, we studied their effects on gas-solid macro-mixing characterization. The results show that the effects of structural parameters are larger than operating conditions, and different parameters have different effects. Different parameters can be adjusted to change the gas-solid macro-mixing characterization in small fixed-fluidized bed reactor. Therefore, the small fixed-fluidized bed reactor can provide better results in more application areas.

Research on Reactive Adsorption Desulfurization over Ni/ZnO−SiO2−Al2O3 Adsorbent in a Fixed-Fluidized Bed Reactor

Reactive adsorption desulfurization of FCC gasoline over a Ni/ZnO−SiO2−Al2O3 adsorbent was carried out in a fixed-fluidized bed reactor at low pressures in the presence of hydrogen. The results show that high temperature, high pressure, high molar ratios of hydrogen-to-oil, and low weight hourly space velocity are favorable to improve the desulfurization ability of adsorbent but not conducive to maintaining the octane number of FCC gasoline throughout the condition range examined. Under optimal operating conditions, ultralow sulfur gasoline can be produced, and the RON loss is only 1 unit. Furthermore, the effect of prereduction and adsorbent characterization data (SEM/EDX, N2 adsorption) reveal that reduction increases the interaction between Ni and S compounds and improves the pore structure of adsorbent, leading to a significant improvement in the desulfurization capability of adsorbent. Take 3-methylthiophene for example, after adsorbing on an active Ni atom via the S−Ni bond, the sulfur of 3-methylthiophene is removed by direct hydrogenolysis of the C−S bond, resulting in the formation of NiSx and 2-methyl-1,3-butadiene in hydrogen atmosphere. The latter is mainly hydrogenated to 2-methyl-2-butene and 2-methylbutane. ZnO acts as a sulfur-acceptor, which can regenerate the active Ni in situ in hydrogen atmosphere. The complete sulfidation of adsorbent particles takes place by ion diffusion.

Characterization of Coke Deposited from Cracking of Cottonseed Oil over Zeolite Catalyst and Deactivation Kinetics of Coke Deposition

Studies of coke formation and deactivation kinetics during cottonseed oil catalytic cracking were carried out on a laboratory scale fixed-fluidized bed reactor. The chemical composition and the location of coke were investigated by using various analytical techniques, such as X-ray diffraction (XRD), infrared (IR), nuclear magnetic resonance (NMR), thermal gravity analysis (TGA), etc. The results showed that the coke deposited on the catalyst was mostly aromatic hydrocarbon. A new model for describing catalyst deactivation in cottonseed oil cracking has been used, and compared with a more traditional model based on coke deactivation; the reaction time can be regarded as an invented reactant in the new model.

Catalytic Cracking of Cottonseed Oil on Fixed-fluidized Bed Reactor: Product Distribution and Analysis of the Gasoline Fraction

Gasoline samples resulting from cottonseed oil catalytic cracking on a fixed-fluidized bed were analyzed to give the carbon number distribution of paraffinic, isoparaffinic, olefinic, naphthenic, and aromatic components using PIONA analysis. Cottonseed oil catalytic cracking was studied on a fixed-fluidized bed reactor under atmospheric pressure in order to analyze temperature influence on the gasoline composition. Cracking temperatures were from 430 to 490°C. Three productions were obtained after reaction condensation: solid (coke), liquid (water and oils), and gas (light hydrocarbons, H2, CO, and CO2). The product distribution and composition were studied as a function of the catalytic cracking parameters. Bio-gasoline composition is similar to FCC gasoline, a diesel-like distillation range almost consistent with petroleum diesel; these can be used as fuel or fuel additives.

Sulphur reduction in fluid catalytic cracking using a kaolin in situ crystallization catalyst modified with vanadium

AbstractSulphur reduction catalysts represent a viable option for S reduction in the fluid catalytic cracking (FCC) process. In this paper, a kaolin in situ crystallization catalyst was modified with vanadium and evaluated in a fixed fluid bed (FFB) reactor. The relation between the acidity of the catalyst, the S reduction rate and the catalyst activity is discussed. The results show that increasing weak Lewis acid acidity favours S reduction in the FCC process. Increasing the V content enhances the weak Lewis acidity, so causing the S reduction rate to increase. The kaolin in situ crystallization catalyst modified with 0.6 wt.% of V leads to a 34.5% reduction in the S content of the liquid product. Comprehensive evaluation of the FFB results and the S reduction ability indicates that the catalyst modified with 0.45 wt.% V provided the best performance.