Coke deposition measurement

Pt-Re sulfided, A1203 support Hydrogenolysis and reforming of n-hexane and methylcyclopentane. Coke deposition measured. 

Application of the IR method proved to be also suitable for the measurement of diffusivities in coking porous catalysts. This was deihonstrated by uptake experiments with ethylbenzene where the sorbent catalyst, H-ZSM-5, was intermittently coked in-situ via dealkylation of ethylbenzene at temperatures (465 K) somewhat higher than the sorption temperature (395 K). Coke deposition was monitored in-situ via the IR absorbance... 

The initial molar propane/propene-ratio (at 10 % of catalyst life time) is a measure of catalyst activity. It grossly correlates with the catalyst Si/Al-ratio. Fig. 7 concerns further proofs of catalyst life time. No correlation is observed between the amount of coke deposited and the total amount of methanol which is converted during the catalyst life time. However, a correlation appears to exist between (1) coke selectivity and catalyst life time and (2) methane selectivity and coke selectivity. 

Analyses of Used Catalysts. The analyses of five used catalysts tested with 50% W. Kentucky SCT SRC are given in Table 3. The coke and iron depositions appear to be strongly dependent upon catalysts Harshaw 618X and HDS-1443 are high, but Amocat 1A and IB are low in coke deposition. Since surface area measurements can include contribution by contaminants (particularly coke), these values have no clearcut meaning. Besides the coke deposition, metal deposition on the catalysts contributes to the catalyst deactivation. 

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. 

Since DBT does not affect the coking rate, it is possible to measure HDS activity while coking the catalyst with pyrene. Results are shown in Fig. 7 for three repeat tests of HDS activity as a function of run length. The three tests were operated for different periods of time 40 hours, 65 hours and 110 hours. The resultant levels of carbon for the samples aged 40 and 110 run hours fit (9.5% wt and 13.5% wt, respectively) the data in Fig. 6 perfectly. However, the carbon level found for the 65 run hour aged sample was somewhat larger than expected, 15.7% wt vs. the expected 12.5% wt. The reason for deposition of the additional coke is unresolved. The data in Fig. 7 (solid boxes) show an unexpected activity drop between run hour 40 and 50. This activity drop is most likely caused by coke deposition on the catalyst (coke is the only source of deactivation during these runs ). We... 

The H/C ratio of the coke deposits was quantified by temperature programmed oxidation (TPO) in a 1 % oxygen helium mixture. Temperature was raised to 850° C at a heating rate of 10° min 1. The calculations of the H/C ratio involved the results from the measurements of carbon dioxide production and oxygen uptake (according to Ref. [8]). Coke deposits were also characterized by thermogravimetry and transmission electron microscopy. 

The total acidity deterioration and the acidity strength distribution of a catalyst prepared from a H-ZSM-5 zeolite has been studied in the MTG process carried out in catalytic chamber and in an isothermal fixed bed integral reactor. The acidity deterioration has been related to coke deposition. The evolution of the acidic structure and of coke deposition has been analysed in situ, by diffuse reflectance FTIR in a catalytic chamber. The effect of operating conditions (time on stream and temperature) on acidity deterioration, coke deposition and coke nature has been studied from experiments in a fixed integral reactor. The technique for studying acidity yields a reproducible measurement of total acidity and acidity strength distribution of the catalyst deactivated by coke. The NH3 adsorption-desorption is measured by combination of scanning differential calorimetry and the FTIR analysis of the products desorbed. 

A comparison of the UV Raman spectrum measured for coke deposited during the MTH reaction with that deposited during butane dehydrogenation catalyzed by chromia on alumina (66) shows clear differences in the spectral intensity distribution (Fig. 11). In particular, the intensity of the features in the regions 1340-1440cm and 1560 1630 cm are nearly equal for the MTH reaction. 

Hershkowitz et al. (3,10,11) measured adsorption and coke deposition on zeolite catalysts as well as catalytic cracking activity of FCC catalysts in short-contact-time interactions with decane at 573 K. They used 5 pi liquid decane injections to the catalyst bed to simulate FCC reaction conditions. Hershkowitz et al. focused on the measurement of adsorption and coke formation during the flow of the pulses. 

Chen et al. (7,37,38,39,40) investigated the conversion of methanol to light olefins (MTO) using TEOM. The investigations included the influence of coke deposition on the selectivity, the effect of the crystal size of SAPO-34 on the selectivity and the deactivation of the catalyst for the MTO reaction, and modeling of the kinetics of the MTO reaction. Simultaneous measurements of coke deposition, conversion, and selectivities by TEOM combined with in situ GC analysis of the effluent gas... 

The above results shows that the diffusivity of zeolites has a strong influence on the shape selectivity, as well as the acidic properties. During the coke deposition, the magnitude of the diffusivity is changed, leading to the change in the shape selectivity. In the next section, we discuss about how the diffusivity of zeolites is measured and how that changes due to coke deposition. 

Analyzing the self-diffusion behavior of guest molecules in a microporous catalyst by the combined application of pulsed-field gradient NMR selfdiffusion techniques reveals the spatial distribution of transport resistances over the catalyst particles. In the case of coke deposits on ZSM-5, the distribution of carbonaceous residues over the crystal was found to be a function of the crystal morphology, the time onstream, and the chemical nature of the coke-producing reactant. In the case of ZSM-5 modified by H3PO4, the spatial distribution of the P compounds over the ZSM-5 crystals can be determined by self-diffusion measurements. Location of transport hindrances in a zeolite framework is based on self-diffusion measurements, in... 

Flguire 1 shows the strong carboxyl ate bands at 1580 and 1460 cm observed in cha spectrum of coke deposited on alimlna by exposure to acetylene. Sinllar bands are observed when ethylene is used [4], At coke levels of one percent, only relatively small hydrocarbon bands are observed. The absorbance of the 1580 band is used as the measure of carboxylate in Figure 3. 

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