Reaction coke, determination

The catalytic coke produced by the activity of the catalyst and simultaneous reactions of cracking, isomerization, hydrogen transfer, polymerization, and condensation of complex aromatic structures of high molecular weight. This type of coke is more abundant and constitutes around 35-65% of the total deposited coke on the catalyst surface. This coke determines the shape of temperature programmed oxidation (TPO) spectra. The higher the catalyst activity the higher will be the production of such coke [1],... 

Yield of coke determined by means of combustion after treating the catalyst in a Argon flow of 100 ml/min at the temperature of reaction life time defined as break-through-time of methanol. 

The deactivation of a lanthanum exchanged zeolite Y catalyst for isopropyl benzene (cumene) cracking was studied using a thermobalance. The kinetics of the main reaction and the coking reaction were determined. The effects of catalyst coke content and poisoning by nitrogen compounds, quinoline, pyridine, and aniline, were evaluated. The Froment-Bischoff approach to modeling catalyst deactivation was used. 

Frequently the kinetic description of catalyst deactivation and coke formation is complicated by instationary reaction conditions prevailing during the respective experiments. In this paper two experimental methods are presented.which enable the determination of such kinetics avoiding this problem 4 Use of a concentration controled continuously operated recycle reactor 4 Experimentation at the thermodynamic equilibrium of the main reaction to determine the coke formation kinetics at well defined operating conditions... 

High sensitivity, fast response, and well-defined flow patterns make the TEOM an excellent tool for determining diffusivities of hydrocarbons in zeolites. Moreover, the TEOM has provided a unique capability for gaining knowledge about the effects of coke deposition on adsorption and diffusion under catalytic reaction conditions. An application of the TEOM in zeolite catalysis by combining several approaches mentioned above can lead to a much more detailed understanding of the catalytic processes, including the mechanisms of reaction, coke formation, and deactivation. 

Coke amounts deposited on the catalyst during the reaction were determined by TG-DTA method. 

The coke content of the catalysts after 5 h reaction was determined by thermogravimetric combustion. 

The kinetics of the main reaction were determined in a differential reactor. The rates in the absence of coke deposition, r were obtained by extrapolation to... 

The kinetics of the main reaction was determined in a differential reactor. The rates in the absence of coke deposition, r, were obtained by extrapolation to zero time. Accurate extrapolation was possible the reactor was stabilized in less than 2 minutes after introduction of the butene, whereas the measurements of the rates rn extended to on stream times of more than 30 minutes. 

ISO 18894 (2006) Coke Determination of Coke Reactivity Index (CRI) and Coke Strength after Reaction (CSR),... 

Catalysts that do not contain potassium lose activity very quickly because of coke deposition on the surface of the catalyst. Chemical changes that occur when the catalyst is removed from the operating environment make it very difficult to determine the nature of most of the promoter elements during the reaction, but potassium is always found to be present as potassium carbonate in the used catalyst. The other promoters are claimed to increase selectivity and the operating stabiUty of the catalyst. 

Without coke backfill, the anode reactions proceed according to Eqs. (7-1) and (7-2) with the subsequent reactions (7-3) and (7-4) exclusively at the cable anode. As a result, the graphite is consumed in the course of time and the cable anode resistance becomes high at these points. The process is dependent on the local current density and therefore on the soil resistivity. The life of the cable anode is determined, not by its mechanical stability, but by its electrical effectiveness. 

The heat balance exercise provides a tool for in-depth analysis of the unit operation. Heat balance surveys determine catalyst circulation rate, delta coke, and heat of reaction. The procedures described in this chapter can be easily programmed into a spreadsheet program to calculate the balances on a routine basis. 

Preliminary work showed that first order reaction models are adequate for the description of these phenomena even though the actual reaction mechanisms are extremely complex and hence difficult to determine. This simplification is a desired feature of the models since such simple models are to be used in numerical simulators of in situ combustion processes. The bitumen is divided into five major pseudo-components coke (COK), asphaltene (ASP), heavy oil (HO), light oil (LO) and gas (GAS). These pseudo-components were lumped together as needed to produce two, three and four component models. Two, three and four-component models were considered to describe these complicated reactions (Hanson and Ka-logerakis, 1984). 

Coke builds up on the catalyst since the start up of operation. In the first weeks of operation, an amount between 5% and 8% of coke accumulates on the catalyst. The rate of deposition decreases with time on stream, a careful monitoring of temperature and of feed/H2 ratio is the basis for controlling deposition. Coke deposition primarily affects the hydrogenation reactions (and so denitrogenation), but the deposition rate determines the catalyst life. As mentioned above, deactivation is compensated by an increase in temperature (and some times in pressure, when denitrogenation has to be adjusted, as well). However, increasing severity, increases coke deposition and shorten catalyst life. 

The products of the reaction are the following /-butyl-phenyl-ether (TBPE), p-/-butyl-phenol (p-TBP), o-/-butyl-phenol (o-TBP) and 2,4-di-/-butyl-phenol (2,4-DTBP). Compounds adsorbed on the external surface were recovered in methylene chloride (CH2C12) by a soxhlet treatment for 24 hours of the deactivated zeolite sample. The content of the compounds inside the zeolite (coke) was determined after dissolution, in 40 % HF at room temperature, of the catalyst recoved after 5 min, 45 min, 5h and 7.5 h extraction by CH2C12 then followed. The composition of soluble coke was investigated by analysis GC-MS. The procedure is reported in detail elsewhere [10]. 

Low hydrogen pressures are favorable for the first two reactions with deeply dissociated intermediates. Hydrogen determines here the direction of the overall reactions, that is, the ratio of aromatic and coke formation. 

In the case of alkenes, 1-pentene reactions were studied over a catalyst with FAU framework (Si/Al2 = 5, ultrastable Y zeoHte in H-form USHY) in order to establish the relation between acid strength and selectivity [25]. Both fresh and selectively poisoned catalysts were used for the reactivity studies and later characterized by ammonia temperature programmed desorption (TPD). It was determined that for alkene reactions, cracking and hydride transfer required the strongest acidity. Skeletal isomerization required moderate acidity, whereas double-bond isomerization required weak acidity. Also an apparent correlation was established between the molecular weight of the hard coke and the strength of the acid sites that led to coking. 

Thermal gravimetric analysis (TG) of mordenltes used for the reaction was conducted by Mettler Model TG-50. Amount of deposited coke was determined from weight loss between 400° and 700°C. 

C. Preparation. As indicated by the E-pH diagram, the ammonium ion NH4+ can be prepared by acidifying a basic solution of NH4OH (actually hydrated NH3) until a pH of 9.2 or below is attained. The counterion (anion) associated with the NH4 is determined by the anion of the acid used in the acidification. The precursor of NH4 , namely NH3, is produced by the reaction of N2 with H2 at an elevated temperature in the presence of a catalyst. The H2 for this reaction is generated from various substances including coke and natural gas (CH4). 

Values for equilibrium constants have been tabulated for numerous reactions occurring at various temperatures. Because many of these constants are associated with industrial processes, the temperature at which a is reported varies considerably. That is, it might seem odd that a value for a reaction is given at what seems like an arbitrary temperature, but it should be remembered that these constants have probably been determined with regard to a specific industrial process, for example, 1,000°C for the production of hydrogen gas from steam and coke (carbon). 

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