Catalyst coked

The MTO process employs a turbulent fluid-bed reactor system and typical conversions exceed 99.9%. The coked catalyst is continuously withdrawn from the reactor and burned in a regenerator. Coke yield and catalyst circulation are an order of magnitude lower than in fluid catalytic cracking (FCC). The MTO process was first scaled up in a 0.64 m /d (4 bbl/d) pilot plant and a successfiil 15.9 m /d (100 bbl/d) demonstration plant was operated in Germany with U.S. and German government support. 

Internal Equipment Blockage bv Collapsed Internals - Contingencies such as collapsed reactor bed vessel internals (e.g., fixed-bed reactor grids, coked catalyst beds, accumulation of catalyst fines, plugging of screens and strainers, lines blocked with sediments, etc.) should be considered to identify any overpressure situations that could result. The use of the "1.5 Times Design Pressure Rule" is applicable in such cases, if this is a remote contingency. 

The center of the line is located at 126 ppm. The shape and position of the lines are comparable to those observed in the spectra of pyrogenic deposits (sp -hybridized carbon), for example, in coked catalysts where carbon is produced during the deactivation of solid acid catalysts [30, 31]. 

For the experiments in type C catalysts, the pellets were overfilled with cyclohexane and initially cooled to 230 K. They were then reheated in steps of 1 K and allowed to equilibrate for 10 min before each measurement. The signal was determined from 32 accumulations with an echo sequence of 20 ms echo time to ensure that the signal from the plastically crystalline phase of cyclohexane had decayed fully. The typical heating curves of cyclohexane in the fresh and coked catalyst are displayed in Figure 3.3.3(a) As the temperature is increased, larger and... 

As for 10MR ID zeolites, the isomerization selectivity improvement is correlated with the microporosity plugging, it is proposed that EB isomerization on these coked catalyst mainly occurs on the outer surface acid sites. 

Regeneration of coked catalysts may be accomplished by gasification with oxygen, steam, hydrogen, or carbon dioxide ... 

The regeneration of coked catalysts (Section 8.6.5) can be represented by coke burning with air ... 

These reactions may serve as a means of regeneration of coked catalysts. Both reactions are exothermic, and the improved temperature control provided by a fluidized bed is critical for regeneration of catalysts prone to sintering. 

After the cracking run is complete, the coked catalyst is regenerated by passing air saturated with water at room temperature over the catalyst at an elevated temperature (1250° F). The amount of coke deposited on the catalyst is determined by the difference in reactor weight before and after the regeneration. 

The regenerator section represents the most severe environment for today s cracking catalyst. The coked catalyst particle>with some hydrocarbons still adsorbed passes directly into an oxidizing temperature zone of 1250 F or higher. In this environment coke is burned off the catalyst particle, regenerating it for further use. 

It is important to note that in burning off the coke, catalyst particle temperatures generally exceed the average bed temperature by several hundred degrees. In laboratory work catalyst particles have been observed to scintillate during burning, suggesting temperatures well in the excess of 1500 F. 

In addition to Ni catalysts, Lee and Park explored some unconventional catalysts, such as limestone, dolomite, and iron ore, in a fluidized bed reactor to carry out SR of kerosene and bunker oil. H2 yields from SR of bunker oil over various catalysts (temperature = 800°C, bed height = 10 cm, superficial gas velocity = 20 cm/sec, and S/C = 1.6) were sand (20%), iron ore (29%), commercial Ni catalyst (89%), limestone (93%), and dolomite (76%). Limestone as a SR catalyst looked very promising, but H2 yields over a limestone catalyst decreased over time due to elutriation of fines during the reaction. A fluidized-bed reactor was advantageous for reforming of higher hydrocarbons, due to its ability to replace coked catalyst with fresh catalyst during operation. 

Separation Method. Trial experiments with small portions of the coked catalyst in progressively more dense mixtures of carbon tetrachloride (d - 1.594 g/cc) and 1,1,2,2- tetrabromoethane (d - 2.967 g/cc) showed that the lightest catalyst fractions exhibited a density of about 2.3 g/cc. A solvent mixture with d - 2.33 g/cc was prepared from a mixture of 46.4 ml of carbon tetrachloride and 53.6 ml of tetrabromoethane. A 20 g portion of coked catalyst was placed in a 120 ml quantity of this solvent mixture in a 250 ml Teflon centrifuge bottle. The mixture was thoroughly agitated for several minutes and then placed in a centrifuge at 3,600 rpm for 30 minutes. Upon removal from the centrifuge, the mixture was allowed to stand for several hours in order to obtain well-defined float and sink fractions. 

Analysis of Fractions. Surface areas and pore size distributions for both coked and regenerated catalyst fractions were determined by low temperature (Digisorb) N2 adsorption isotherms. Relative zeolite (micropore volume) and matrix (external surface area) contributions to the BET surface area were determined by t-plot analyses (3). Carbon and hydrogen on catalyst were determined using a Perkin Elmer 240 C instrument. Unit cell size and crystallinity for the molecular zeolite component were determined for coked and for regenerated catalyst fractions by x-ray diffraction. Elemental compositions for Ni, Fe, and V on each fraction were determined by ICP. Regeneration of coked catalyst fractions was accomplished in an air muffle furnace heated to 538°C at 2.8°C/min and held at that temperature for 6 hr. 

High nitrogen resistant catalysts and/or nitrogen traps are available nowadays unfortunately, no real breakthroughs have been made in reducing the effect of polycyclic aromatics (Conradson Carbon Catchers ). At present super low delta coke catalysts are produced to allow for the additional coke produced by these polycyclic aromatics. 

To maintain a constant catalyst activity in the reactor, a femall fraction of "coked catalyst will be continuously regenerated and returned to the reactor. 

There have been attempts to use catalysts in order to reduce the maximum temperature of thermal decomposition of methane. In the 1960s, Universal Oil Products Co. developed the HYPROd process for continuous production of hydrogen by catalytic decomposition of a gaseous hydrocarbon streams.15 Methane decomposition was carried out in a fluidized bed catalytic reactor from 815 to 1093°C. Supported Ni, Fe and Co catalysts (preferably Ni/Al203) were used in the process. The coked catalyst was continuously removed from the reactor to the regeneration section where carbon was burned off by air, and the regenerated catalyst returned to the reactor. Unfortunately, the system with two fluidized beds and the solids-circulation system was too complex and expensive and could not compete with the SR process. 

During the first minutes of the experiment, measurement of the coke content is disturbed by several transient effects adsorption of hydrocarbons, pressure stabilization and gradual displacement of the pretreatment gas by the feed. To determine the total amount of coke deposited on the catalyst, the coked catalyst is stabilised at the end of the experiment in the pretreatment gas. The weight difference between the uncoked catalyst and the coked catalyst gives the total amount of non-desorbable products. 

In a study of the deactivation by coking of an atmospheric residue HDM catalyst, we have been able to obtain coked catalysts almost free from metal deposits in batch reactor and coked catalysts containing small amounts of metal sulfide deposits in continuous flow reactor using a Safaniya atmospheric residue under similar experimental conditions (30). We report in this paper a study of the deactivating effects of the deposits using toluene hydrogenation, cyclohexane isomerization and thiophene hydrodesulfurization reactions. 

TPO regeneration of coked catalysts indicates that different minima occurred in the oxygen concentration downstream from the reactor (Figure 2). Those at lower... 

Figure 2. TPO of coked catalysts (heating rate=10 K/min) a 1.5(wt.%)PtHY b 0.1(wt.%)PtHY c HY d ZnHY e CuHY f Pt/Si02+Al203...

The diffusional limitation which may also exist in the uncoked catalyst can be characterised by an other effectiveness factor r 0. Thus, the real effectiveness factor of the coked catalyst is ... 

The second step of oxidation (same experimental conditions) leads to samples containing a smaller residual coke load (1.6-1.7% w/w). There is both a decrease in the slopes, one of which even returns to that corresponding to the non coked catalyst... 

After complete oxidation (12h under pure 02 at 623K) the shape of the -plots is analogous as that of the initial non-coked catalyst Nevertheless, (figures 1-g and 2-f) we can observe that ... 

Table 1 shows the catalyst compositions. I and II are Pt-Re/Al203 commercial catalysts coked by their use in a commercial naphtha reforming unit operated at 1.5 MPa. I was sampled at the end of the operation cycle (7 months), and II at the middle of the cycle. Ill is a fresh sample of the same catalyst coked in the laboratory at 0.1 MPa. The coked catalysts were ground and the 35-80 mesh fraction was used. 

Figure 1. Ozone concentration at the reactor outlet as a function of time at different temperatures. 0.5 g of coked catalyst. I, flow rate of ozone-air mixture= 54 ml/min, pressure = 0.1 MPa...

Pore volume distribution in coked catalysts and coke layer thickness... 

Amount and type of compounds present in the Soxhlet extract of coked catalysts... 

Reactor pressure (bar) Reduced density Soxhlet-extracted coke (wt%) GC/FID peak area% of compounds in the Soxhlet extract of coked catalysts ... 

Comparison of coked catalyst characteristics for different-size catalyst particles... 

---