Commercial Fluid Catalytic Cracking Research Articles

Lumps and kinetics for the secondary reactions in catalytically cracked gasoline

The secondary reactions of catalytically cracked gasoline have been investigated with a riser reactor using an improved Y zeolite catalyst in different operating conditions. All the reactions that will take place in this system, such as cracking reactions, hydrogen transfer reactions, aromatization reactions, isomeration reactions, alkylation reactions, and dimerization reactions, etc. were analyzed. This reaction system was cut into dry gas lump (DG), liquefied petroleum gas lump (LPG), light cycle oil lump (LCO), coke lump (COKE), and gasoline lump (GL) in accordance with the product structure of commercial fluid catalytic cracking unit (FCCU); the lump GL could be cut into paraffin lump (GP), olefin lump (GO), naphthene lump (GN), and aromatic lump (GA) further according to the hydrocarbon group structure. The eight-lump kinetic model for this reaction system thus could be developed and the hybrid genetic algorithm was used to obtain the model parameters. The kinetic parameters calculated from the improved genetic algorithm are reliable, and the calculated data of the product distribution were agreed well with the experimental results. The model offers the function of predicting the levels of olefins, aromatics, etc. in gasoline products after secondary reactions.

Multitechnique Characterization of Coke Produced during Commercial Resid FCC Operation

The characterization of industrial coked resid fluid catalytic cracking (RFCC) catalysts is reported. The aim is to provide insight into the coke deposition on commercial resid fluid catalytic cracking catalysts sampled after the stripper of a commercial RFCC unit and to relate it to the potential process chemistry. Physicochemical techniques were used to characterize the used catalysts and the deposited coke. 95% of the coke was insoluble in CH2Cl2. This coke was located in the mesopores of the catalyst matrix. The results suggest the existence of domains of polyaromatic and heterogeneously distributed coke, in which saturated hydrocarbons are trapped. IR spectroscopy of adsorbed pyridine shows that the largest fraction of strong Bronsted acid sites is free after the catalyst has passed the stripper. The results indicate that for RFCC not the local deactivation of the acid sites but rather blocking of domains of the catalyst is the most important mode of deactivation after passing through the riser reactor.

Effect of hydrotreating FCC feedstock on product distribution

The demand of low-sulfur fuels has been increasing during the last 20 years due to environmental concerns about SO x emissions from processing plants and engines. Due to its high contribution to the gasoline pool, hydrotreating fluid catalytic cracking (FCC) feedstock offers several advantages, such as the increase of conversion and yields of gasoline and liquid-phase gas, meanwhile sulfur content in fuels is diminished. However, there are more important factors to be considered when hydrotreating FCC feedstock. In this work, two FCC feedstocks, typical and hydrotreated, were converted in a microactivity test (MAT) reactor, as described by ASTM D-3907-92, at different severities and using two commercial catalysts. Feedstock conversion, product yields and selectivity to valuable products were compared against industrial-scale results predicted by using commercial FCC simulation software. Expected increment in conversion and yield to profitable products was observed when hydrotreated feedstock was used; simulation results follow acceptably MAT results. Some recommendations are given for looking closely at the overall behavior (riser–regenerator), using reliable kinetic models and simulation programs.

Correlation between feedstock SARA components and FCC product yields

Daqing, Shengli, Liaohe, Gudao, Dagang and Huabei vacuum residua were subjected to deep solvent fractionation by using the supercritical fluid extraction and fractionation, a novel separation technology recently developed by the State Key Laboratory of Heavy Oil Processing. Each residuum was fractionated to produce deasphalted oil (DAO) at four yield levels: 30, 40, 50 and 60 wt%. The saturates, aromatics, resins and asphaltenes (SARA) composition of each DAO sample was determined, indicating that the saturates and aromatic contents of DAO decreases with increased DAO yield. The DAO samples were reacted in a laboratory scale confined fluidized bed, fluid catalytic cracking (FCC) reactor. The results show that most of the gasoline yields originates from the saturate fraction of DAO. The aromatics fraction of DAO contributes to gasoline and diesel yields. Most of the coke yield is from resin fraction of DAO. Generalized empirical correlations were developed for predicting the FCC gasoline, diesel, light oil and coke yields as a function of feedstock SARA composition. These yield correlations can be used to set the upper limit of feedstock resins content for commercial FCC operations. The implications of feedstock properties on FCC products were discussed.

Propane reactions over natural Todorokite

This study reports results of propane transformation over the natural microporous manganese oxide, todorokite, and its hydrogen form (H-Todorokite), at the temperature range of 350°–550 °C. Both materials were fully characterized and their catalytic results were compared with results obtained with commercial Ultra-Stable-Y (USY), and steamed H-ZSM-5 zeolite catalysts. The natural todorokite sample shows appreciable dehydrogenation activity (propylene yield ∼8%, selectivity to propylene >31%), considerably higher compared to H-ZSM-5 zeolite. This is justified by the absence of strong acid sites and the presence of a large amount of ion-exchangeable cations, which induce the dehydrogenation capability of the material. The proton-exchanged form of todorokite, appears to act as a very efficient cracking catalyst (yield to methane and ethylene ∼40%, selectivity to cracking products >85%), due to the formation of a large number of framework Brønsted acid sites. The observed cracking capability of H-todorokite is superior to the activity of the commercial fluid catalytic cracking (FCC) USY catalyst, thus suggesting that the proton form of the mineral is a promising catalyst for the cracking of small alkanes.

Adsorption and desorption kinetics of hydrocarbons in FCC catalysts studied using a tapered element oscillating microbalance (TEOM). Part 1: experimental measurements

An experimental procedure to measure the adsorption and desorption kinetics of hydrocarbons in fluid catalytic cracking (FCC) catalysts using a tapered element oscillating microbalance is described. It enables adsorption rates to be measured on a timescale of about 1 s . Experiments using n-hexane, n-heptane, n-octane, toluene and p-xylene were performed on both a commercial FCC catalyst and a pure rare-earth exchanged zeolite Y sample under non-reacting conditions (temperatures of 373– 473 K ). Heats of adsorption for these hydrocarbons are reported. The overall adsorption and desorption kinetics are found to depend on carrier gas flowrate in cases when adsorption is strong indicating that the length of the catalyst bed can have a significant influence on the observed kinetics. However, at high carrier gas flowrates the overall adsorption and desorption kinetics do not depend on the amount of catalyst present. It is found that the rates of adsorption and desorption of the hydrocarbons studied are the same for the FCC catalyst as for the pure zeolite Y sample. This means that mass transport in the matrix component of the FCC catalyst is rapid and not a limiting step in the adsorption process for the hydrocarbons studied in this work.

Simulation of FCC riser flow with multiphase heat transfer and cracking reactions

A validated Computational Fluid Dynamics (CFD) code ICRKFLO was developed for simulations of three-dimensional three-phase reacting flows in Fluid Catalytic Cracking (FCC) riser reactors. It calculates the product yields based on local flow properties by solving the fundamental conservation principles of mass, momentum, and energy for the flow properties associated with the gas, liquid, and solid phases. Unique phenomenological models and numerical techniques were developed specifically for the FCC flow simulation. The models include a spray vaporization model, a particle-solid interaction model, and an interfacial heat transfer model. The numerical techniques include a time-integral approach to overcome numerical stiffness problems in chemical kinetics rate calculations and a hybrid hydrodynamic-kinetic treatment to facilitate detailed kinetics calculations of cracking reactions. ICRKFLO has been validated with extensive test data from two pilot and one commercial FCC units. It is proven to be useful for advanced development of FCC riser reactors.

Valorization by thermal cracking over silica of polyolefins dissolved in LCO

A study has been made of the cracking of polyethylene (PE) and polypropylene (PP) (which are the main components of post-consumer plastic wastes) dissolved in the Light Cycle Oil (LCO) product stream of a commercial Fluid Catalytic Cracking (FCC) unit. The cracking has been carried out on a mesoporous silica (pore size between 3 and 30 nm) in the 723–823 K range. This strategy for upgrading plastics and solvents together avoids heat transfer limitations and other problems inherent to the cracking of solid plastics. The polyolefins are transformed mainly into the components that make up the pool of gasoline (C 5–C 12). Furthermore, the incorporation of polyolefins has a synergistic effect on the cracking of LCO and causes a major decrease in the content of aromatics of the pool of gasoline and an increase in the content of olefins, paraffins and i-paraffins.

Thermal recycling of polystyrene and polystyrene-butadiene dissolved in a light cycle oil

A study has been made of the cracking on a mesoporous silica of polystyrene (PS) and polystyrene-butadiene (PS-BD) dissolved in a light cycle oil (LCO) from a product stream of a commercial fluid catalytic cracking (FCC) unit. This study has been carried out in a reactor of short contact time (3 s) in the 723–823 K range. This strategy for simultaneous valorization of plastics and solvent avoids the technological problems inherent to the treatment of solid postconsumer-plastics and the limitation to heat transfer in the process of pyrolysis. The cracking of plastics has a synergistic effect on the conversion of LCO, as it contributes to increasing the yield of gasoline (C 5–C 12). The cracking of the PS/LCO blend produces high yields of styrene, whereas the cracking of the PS-BD/LCO blend produces a stream of products with petrochemical interest.

Novel lab-scale deactivation method for FCC catalyst: inducing realistic accessibility responses to iron poisoning

In evaluating fluid cracking catalyst performance in lab-scale testing, selecting the proper catalyst deactivation method is just as important as the testing itself. While the cyclic deactivation (CD) technique of alternately exposing a catalyst to cracking and regeneration cycles using a feed with enhanced metals concentration has been shown to be the most accurate way of mimicking a commercial equilibrium catalyst (e-cat), there have still been difficulties in simulating the catalyst accessibility losses (as measured by the Akzo Accessibility Index (AAI)) associated with iron contamination in the commercial fluid catalytic cracking unit (FCCU). Resistance to the deleterious effects of iron contamination has recently emerged as one of the most critical issues in selecting an appropriate catalyst, particularly in resid applications. The method presented here, a modification of conventional cyclic deactivation, employs lower steam partial pressure and temperature, more consistent with FCCU operation. This results in a more realistic simulation of equilibrium catalyst accessibility responses to iron contamination.

Coke content of spent commercial fluid catalytic cracking (FCC) catalysts

Zeolite catalysts are widely used in oil refinery and petrochemical industries. Fluid catalytic cracking (FCC) catalysts used in a refinery consist of Y zeolite, a silica-alumina matrix and a binder. In this study, spent FCC catalysts were prepared by cracking sour imported heavy gas oil (SIHGO) in a microactivity test unit. The total amount of coke and the hydrogen-to-carbon ratio (H/C) in the coke for spent FCC catalysts contaminated with metals were determined using temperature-programmed oxidation (TPO). Total H/C ratios of the coke on FCC catalysts were found to be in the range of 0.4 to 1, indicating the majority of the coke consists of polyaromatic species. H/C ratio decreased with increasing coke contents on the catalysts. This ratio was found to be higher for the catalyst with high metal concentration compared to the catalyst with relatively low metal concentration. The high H/C ratio for highly contaminated FCC catalyst was attributed to the formation of hydrogen rich coke by hydrogenation reactions catalyzed by the contaminant metals on the catalyst. After hydrogen pretreatment both coke amount and H/C ratio decreased significantly. This was due to the decrease in the hydrogenation activities of the contaminant-metals in their reduced forms.

Biomass pyrolysis in a circulating fluid bed reactor for the production of fuels and chemicals

An approach for biomass flash pyrolysis in a circulating fluid bed (CFB) reactor with continuous solids regeneration is described in this study. The unit is capable of performing conventional and catalytic biomass pyrolysis with the proper solid selection. The production of improved quality liquid products in a direct step through catalytic pyrolysis is investigated in this work. Both conventional and catalytic biomass pyrolysis can be effectively performed in this CFB unit. Flash pyrolysis conditions were achieved and liquid product yields of ∼70 wt% (on biomass feed) were obtained. The effect of specific operating variables including the type of inorganic solid material and the solid/biomass ratio was established on the final liquid product quality and yield. Solid materials considered included silica sand, a commercial fluid catalytic cracking catalyst and a ZSM-5 additive. Catalytic biomass pyrolysis generally leads to the production of additional water, coke and gases compared to conventional pyrolysis. However, the obtained liquid product quality and composition is improved.

Polymer waste recycling over “used” catalysts

Catalytic degradation of high-density polyethylene (HDPE) was carried out under nitrogen using a laboratory fluidised bed reactor operating at 360°C with catalyst to polymer feed ratio of 2:1 and at 450°C with catalyst to polymer feed ratio of 6:1 under atmospheric pressure. The catalysts used in this study were ZSM-5, US-Y, ASA, fresh FCC (fluid catalytic cracking) commercial catalyst (Cat-A) and equilibrium FCC catalysts with different levels of metal poisoning were studied. The initial results for polymer degradation at 360°C (catalyst to polymer ratio of 2:1) in a fluidised bed reactor in terms of the yield of volatile hydrocarbon products were: model catalysts>commercial FCC catalyst>E-Cats. However, when the process conditions more closely resembled to FCC conditions, the fresh commercial FCC catalyst was more favourable in terms of the yield of volatile hydrocarbon products. The degradation of HDPE over E-Cats although reduced was similar to ASA in product selectivity and yield, and the level of metal contamination did not affect the product stream generated. A simple economic evaluation of polymer recycling process is reported showing that a catalytic system based on E-Cats appears comparable in costs to a commercial thermal cracking plant.

On the origin of sulfur impurities in fluid catalytic cracking gasoline—Reactivity of thiophene derivatives and of their possible precursors under FCC conditions

Two possibilities were considered to account for the formation of sulfur impurities in fluid catalytic cracking (FCC) gasoline: the cracking of long alkyl chain thiophenes, and the addition of H 2S to olefins or diolefins followed by cyclization. The transformation of compounds representative of the sulfur components of FCC gasoline or of their possible precursors (thiophene, tetrahydrothiophene, 2- and 3-methylthiophenes, 2-ethylthiophene, 2- and 3- n-hexylthiophenes) as well as the transformation of hex-1-ene, penta-1,3-diene and hexa-1,5-diene in the presence of H 2S were studied over a commercial FCC catalyst at 500 °C under atmospheric pressure. Tetrahydrothiophene, methylthiophenes, 2-ethylthiophene and the n-hexylthiophenes were found quite reactive under conditions similar to those of FCC, whereas thiophene was not. Desulfurization was not observed with methylthiophenes and 2-ethylthiophene, while this reaction occurred to a significant extent with tetrahydrothiophene and also with n-hexylthiophenes, which shows that the length of the alkyl chain has a great influence on the reactivity of alkylthiophenes. The formation of alkylthiophenes from H 2S and olefins or diolefins was observed, although the yield was very low. Reaction mechanisms are proposed to explain all these reactions. It is concluded that the two ways which were considered can lead to the sulfur-containing compounds present in FCC gasoline.

The influence of covariances during laboratory evaluation of FCC catalysts

One problem of practical interest is the evaluation of catalyst activity and selectivity of commercial fluid catalytic cracking (FCC) catalysts. Although different statistical methods may be used for this purpose, these methods are usually neglected or oversimplified in catalysis. In a previous study [1], it was shown that experimental errors of independent variables may exert a significant impact upon the discrimination of catalyst performance in FCC processes and should not be disregarded. In this work it is shown that actual experimental measurements can present strong correlation and that the existence of covariance among experimental measurements can also influence the catalyst discrimination procedure. The influence of covariance among variables on parameter estimation and on the confidence interval (CI) of predicted values is discussed. It is shown that considering the covariances may have either a positive or a negative effect on the CI for predicted values. Practical examples regarding the microactivity test (MAT) of FCC catalyst characterization are used to illustrate the discussion, although the conclusions can be extended to systems other than catalytic cracking.

Simultaneous Diffusion, Adsorption, and Reaction in Fluid Catalytic Cracking Catalysts

Simultaneous diffusion, adsorption, and reaction that take place inside the zeolitic component of equilibrium commercial fluid catalytic cracking (FCC) catalysts were described by means of heterogeneous models. n-Hexadecane was used as a test reactant at high temperatures (440−550 °C) over two different equilibrium catalysts under very short contact times up to 10 s in a Riser Simulator reactor. The system's parameters were obtained by fitting the model to the reactant's gas-phase concentration versus reaction time data. When zeolite intracrystalline diffusion was first assumed as the controlling mechanism for mass transfer, its energy of activation resulted close to the heat of adsorption, suggesting that diffusion in the zeolite micropores could be indeed controlling. The solution under this new approach led to the obtention of parameters that were consistent with the existence of strong diffusion limitations for the reaction and with lower activity in the low unit cell size catalyst. Diffusion, which would be a nonactivated process, had coefficients that were essentially the same in both catalysts, while the energies of activation of the reaction were different and reflected the higher relative importance of the mechanism of monomolecular cracking in the more dealuminated catalyst. The need for a careful assessment of adsorption parameters in FCC catalysts was confirmed by the fact that their magnitudes change significantly as a function of temperature, with adsorption being somewhat stronger on the higher unit cell size catalyst in the temperature range of interest for FCC. The method employed proved to be adequate and sensitive for the quantification of these issues, which are important in reactor design and simulation and catalyst evaluation procedures.

Effect of HZSM-5 Zeolite Addition to a Fluid Catalytic Cracking Catalyst. Study in a Laboratory Reactor Operating under Industrial Conditions

The kinetic behavior has been studied for cracking a commercial feedstock on a hybrid catalyst (with 5 wt % of HZSM-5 zeolite) made up of 80 wt % of a catalyst equilibrated in a fluid catalytic cracking (FCC) unit and of 20 wt % of a catalyst prepared based on a HZSM-5 zeolite. A laboratory-scale reactor which allows for operation under conditions similar to those of commercial FCC units has been used. From the analysis of the gases and gasoline obtained in the 500−550 °C range, with contact times between 2 and 10 s and for a catalyst/feedstock = 6, the influence of HZSM-5 zeolite presence in the catalyst on gas and gasoline composition and on gasoline research octane number has been analyzed.

Kinetics of combustion of carbon in carbonaceous deposits on zeolite catalysts for fluid catalytic cracking units (FCCU). Comparison between Pt and non Pt-containing catalysts

The combustion kinetics of carbon in carbonaceous deposits, or ‘coke’, on fluid catalytic cracking (FCC) zeolite catalysts was studied under differential reactor conditions, in an air stream, at atmospheric pressure, and in a temperature range of 550–710°C. Catalysts with and without Pt were first coked and then subsequently regenerated. Although platinum catalyzes the conversion of CO to CO 2, experimental findings revealed the lack of any catalytic effect of Pt on carbon burning rates. Experiments were also conducted with an equilibrium catalyst from a commercial FCC unit. This catalyst exhibited higher burning rates than catalysts containing coke deposited in a laboratory reactor. It is believed, however, that the higher burning rate is due to the high metal content of heavy metals like V and Ni.

Hexadecane Conversion in the Evaluation of Commercial Fluid Catalytic Cracking Catalysts

The conversion of n-hexadecane over fluid catalytic cracking (FCC) catalysts was studied at 788 K and compared with the conversion of n-hexane over these FCC catalysts and the conversion of a vacuum gas oil from the micro activity test (MAT). The product distribution could be fully explained by reaction pathways identical with those in n-hexane conversion (i.e., protolytic cracking, dehydrogenation and hydrogen transfer). The rates via all three reaction pathways decreased at long time on stream. As with n-hexane, two reaction pathways to dehydrogenate n-hexadecane were identified; one that is affiliated with the protolytic activation over strong Bronsted acid sites, and the other that is catalyzed by Lewis acid sites and rapidly deactivates with time on stream. With time on stream, the rate of aromatic formation in parallel with coking markedly decreased within the first 2500 s. n-Hexadecane conversion varied in parallel with the MAT activity. The octane numbers observed in the MAT test were directly pro...

Impact of accessibility and acidity on novel molecular sieves for catalytic cracking of hydrocarbons

AbstractThe catalytic properties of extra‐large pore aluminosilicate MCM‐41, silicon containing VPI‐5 and aluminium containing ETS‐10 were investigated by MAT (Micro Activity Test) using n‐hexadecane and 1,3,5‐triisopropylbenzene as the model feeds and were then compared with the results obtained from Y zeolite in the H‐form and a commercial FCC (Fluid Catalytic Cracking) catalyst. It could be demonstrated that not only the acidic properties of the investigated materials, but also the accessibility to the internal active sites of the investigated materials have a significant influence on activity and selectivity. It can be assumed that, by optimising structural and chemical properties, the mesoporously organised MCM‐41 and related materials are suitable as active components in cracking catalysts for “deeper” cracking of high boiling hydrocarbons.