Coking experiments

The steam reforming of methane cycle suffers from the problem of coke deposition on the catalyst bed. The primary objective of this project was to study the stability of a commercial nickel oxide catalyst for the steam reforming of methane. The theoretical minimum ratios of steam to methane that are required to avoid deposition of coke on the catalyst at various temperatures were calculated, based on equilibrium considerations. Coking experiments were conducted in a tubular reactor at atmospheric pressure in the range of 740-915°C. 

Coking Experiments. The sulfided catalysts were first deposited with coke before catalyst screening. For these experiments, 120 g of PDU tar and 40 g of sulfided catalyst were charged into a 1-L Magnedrive... 

Reactivity profiles obtained from all three chars are evaluated by using the normalisation procedure. The quality of this procedure is indicated by the calculated standard deviation (o) relative to the reference profile a) Wheat straw 11 out of 14 experiments shows partial pressure is reduced from 1.0 to 0.03bar. (The calculated standard deviations are based on (0.2< X. 8) and a step size of AX = 0.002.)... 

Formation of Products. The rate of conversion of feed into products was determined in terms of the rate of formation of volatiles, gas and liquid products, and by difference the non-volatiles. The gaseous product includes Cj-C hydrocarbons and the liquid C5-iooo°F. Gas rates were obtained from the composition and volume of the gas generated during each experiment. Similarly, the rate of liquid product was obtained by determining the weight of liquid product condensed at room temperature for each coking experiment. 

The kinetics of the coking and the deactivation functions for coking were determined by means of a microbalance. The catalyst was placed in a stainless steel basket suspended at one balance arm. The temperature was measured in two positions by thermocouples placed just below the basket and between the basket and the quartz tube surrounding it. The temperature in the coking experiments ranged from 480°C to 630°C, the butene pressure from 0.02 to 0.25 bar, the butadiene pressure from 0.02 to 0.15 bar. Individual components as well as mixtures of butene and butadiene, butene and hydrogen, and butadiene and... 

A series of coking experiments on silica-alumina catalysts by Levinter et al. (1967) demonstrated that pore blocking can occur on coke deposition to various extents depending strongly on catalyst properties and reaction conditions. Under... 

The recorded chronology of the coal-to-gas conversion technology began in 1670 when a clergyman, John Clayton, in Wakefield, Yorkshire, produced in the laboratory a luminous gas by destmctive distillation of coal (12). At the same time, experiments were also underway elsewhere to carbonize coal to produce coke, but the process was not practical on any significant scale until 1730 (12). In 1792, coal was distilled in an iron retort by a Scottish engineer, who used the by-product gas to illuminate his home (13). 

Acetylene traditionally has been made from coal (coke) via the calcium carbide process. However, laboratory and bench-scale experiments have demonstrated the technical feasibiUty of producing the acetylene by the direct pyrolysis of coal. Researchers in Great Britain (24,28), India (25), and Japan (27) reported appreciable yields of acetylene from the pyrolysis of coal in a hydrogen-enhanced argon plasma. In subsequent work (29), it was shown that the yields could be dramatically increased through the use of a pure hydrogen plasma. 

Several utility-scale demonstration facilities having power outputs in the 300-MW class have been constmcted in the United States and Europe. These started accumulating operating experience in 1995 and 1996. Other IGCC plants have been constmcted, including units fueled by petroleum coke and refinery bottoms. Advanced 500-MW class IGCC plants based around the latest heavy-duty combustion turbines are expected to be priced competitively with new pulverized-coal-fined plants utilising scmbbers. 

Table 6 shows the effect of varying coil oudet pressure and steam-to-oil ratio for a typical naphtha feed on the product distribution. Although in these tables, the severity is defined as maximum, in a reaUstic sense they are not maximum. It is theoretically possible that one can further increase the severity and thus increase the ethylene yield. Based on experience, however, increasing the severity above these practical values produces significantly more fuel oil and methane with a severe reduction in propylene yield. The mn length of the heater is also significantly reduced. Therefore, this is an arbitrary maximum, and if economic conditions justify, one can operate the commercial coils above the so-called maximum severity. However, after a certain severity level, the ethylene yield drops further, and it is not advisable to operate near or beyond this point because of extremely severe coking. 

Nearly every cat cracker experiences some degree of coking/fouling. Coke has been found on the reactor walls, dome, cyclones, overhead vapor line, and the slurry bottoms pumparound circuit. Coking and fouling always occur, but they become a problem when they impact throughput or efficiency. 

To probe the formation of coke we conducted TPO measurements on samples previously used in the butene TPD experiments. The TPO profiles corresponding to catalyst INiSZ(s) are shown in Fig. 6. Significant evolution of CO2 was detected, indicating the formation of coke during the adsorption/desorption of 1-butene. The INiSZ(s) catalyst exhibited almost twice as much CO2 as the unpromoted SZ sample. 

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... 

Aromatics Resins — Asphaltenes — coke where the resin + asphaltene content remains constant and asphaltenes are the main precursors of coke. The same observations have been made in low-temperature oxidation experiments (6). 

Using a "home made" aneroid calorimeter, we have measured rates of production of heat and thence rates of oxidation of Athabasca bitumen under nearly isothermal conditions in the temperature range 155-320°C. Results of these kinetic measurements, supported by chemical analyses, mass balances, and fuel-energy relationships, indicate that there are two principal classes of oxidation reactions in the specified temperature region. At temperatures much lc er than 285°C, the principal reactions of oxygen with Athabasca bitumen lead to deposition of "fuel" or coke. At temperatures much higher than 285°C, the principal oxidation reactions lead to formation of carbon oxides and water. We have fitted an overall mathematical model (related to the factorial design of the experiments) to the kinetic results, and have also developed a "two reaction chemical model". 

The results of ashing ejqperiments on the samples from wet oxidation experiments conducted at 285°C are contained in Table X. The loading factors of the oxidized oil samples are dramatically reduced compared to those for samples oxidized at 225°C (see Table VI). The amount of residual coke per gram of bitumen available in each sample can also be seen to have undergone a dramatic reduction as have the estimates of cox(s)> the amount of available carbon converted to coke, compared to the lower temperature wet oxidation s tudy. 

---