Hydrocarbon cracking reactions

If inert material is to be added, then ease of separation is an important consideration. For example, steam is added as an inert to hydrocarbon cracking reactions and is an attractive material in this respect because it is easily separated from the hydrocarbon components by condensation. If the reaction does not involve any change in the number of moles, inert material has no effect on equilibrium conversion. 

Example 5.6 Hydrocarbon cracking reactions are endothermic, and many different techniques are used to supply heat to the system. The maximum inlet temperature is limited by problems of materials of construction or by undesirable side reactions such as coking. Consider an adiabatic reactor with inlet temperature Tm. Then T z) < T, and the temperature will gradually decline as the reaction proceeds. This decrease, with the consequent reduction in reaction rate, can be minimized by using a high proportion of inerts in the feed stream. 

In order to assess whether secondary reactions to form CO could be responsible for the experimental CO versus time curve shape, a series-parallel kinetic mechanism was added to the model. Tar and gas are produced in the initial weight loss reaction, but the tar also reacts to form gas. The rate coefficients used are similar to hydrocarbon cracking reactions. Fig. 5 presents the model predictions for a single pellet length. It is observed that the second volatiles maximum is enhanced. For other pellet lengths, the time of the second peak follows the same trends as in the experiments. While the physical model might be improved by the inclusion of finite rates of mass transfer, the porosity is quite large and Lee, et al have verified volatiles outflow is... 

The optinum acid treatment conditions should he properly controlled to make only some few of framework A1 atoms to be removed while the zeolite framework could not be collapsed. The increased Si/Al ratio by acid dealumination may effectively suppress the carbon deposition on the surface of catalyst during the hydrocarbon cracking reactions. 

J. N. Beltramini, Catalytic Properties of heteropolyacids Supported on MCM-41 Mesoporous Silica for Hydrocarbon Cracking Reactions, Stud. Surf. Sci. Catal, 146, 653-656 (2003). 

In studies involving solid acid-catalyzed hydrocarbon cracking reactions using HZSM-5 zeolite, Haag and Dessau" were able to account nearly quantitatively for H2 formed in the protolysis ionization step of the reaction. This is a consequence of the solid acid zeolite catalyst, which is not easily reduced by the hydrogen gas evolved. 

Direct fluorination of zeolites has been reported as a method for increasing their acidity for hydrocarbon cracking reactions. Lok et al. treated various zeolites with fluorine gas and reported zeolite dealumination and stabilisation and in certain cases an increase in n-butane cracking activity.20 It appears that the optimum fluorine content for maximum cracking activity is about 1% m/m. 

Volatile matter produced by pyrolysis of the biomass begins to participate in secondary, gas-phase reactions at temperatures exceeding 600°C. These reactions occur very rapidly and yield a hydrocarbon-rich syngas product. As recognized by Diebold (. these reactions resemble the hydrocarbon cracking reactions employed in the manufacture of ethylene and propylene by the petrochemical industry (9,10). The secondary gas-phase reactions dominate the gasification chemistry of biomass. 

The FCC unit comprises of two basic parts, a reactor/riser in which hydrocarbon cracking reactions occur and a regenerator in which catalyst regains its activity by burning coke deposited on it during cracking. More detailed description of the process is available in Avidan and Shinnar (1990). Recently, Dave and Saraf (2(X)2) reviewed the extensive literature available on modelling of industrial FCC units. 

Methyl /-Butyl Ether. MTBE is produced by reaction of isobutene and methanol on acid ion-exchange resins. The supply of isobutene, obtained from hydrocarbon cracking units or by dehydration of tert-huty alcohol, is limited relative to that of methanol. The cost to produce MTBE from by-product isobutene has been estimated to be between 0.13 to 0.16/L ( 0.50—0.60/gal) (90). Direct production of isobutene by dehydrogenation of isobutane or isomerization of mixed butenes are expensive processes that have seen less commercial use in the United States. 

The similarity of oxidation rates of different hydrocarbons in the higher temperature regions is probably related to the predominance of alkyl radical cracking reactions under these conditions (reaction 28). The products of such reactions would be similar for most common hydrocarbons (96). 

Naphtha desulfurization is conducted in the vapor phase as described for natural gas. Raw naphtha is preheated and vaporized in a separate furnace. If the sulfur content of the naphtha is very high, after Co—Mo hydrotreating, the naphtha is condensed, H2S is stripped out, and the residual H2S is adsorbed on ZnO. The primary reformer operates at conditions similar to those used with natural gas feed. The nickel catalyst, however, requires a promoter such as potassium in order to avoid carbon deposition at the practical levels of steam-to-carbon ratios of 3.5—5.0. Deposition of carbon from hydrocarbons cracking on the particles of the catalyst reduces the activity of the catalyst for the reforming and results in local uneven heating of the reformer tubes because the firing heat is not removed by the reforming reaction. 

For environmental reasons, burning should be smokeless. Long-chain and unsaturated hydrocarbons crack in the flame producing soot. Steam injection helps to produce clean burning by eliminating carbon through the water gas reaction. The quantity of steam required can be as high as 0.05—0.3 kg steam per kg of gas burned. A multijet flare can also be used in which the gas bums from a number of small nozzles parallel to radiant refractory rods which provide a hot surface catalytic effect to aid combustion. 

The hydrocarbon cracking operations that generate feed olefins generally do not produce sufficient isobutane to satisfy the reaction requirements. Additional isobutane must be recovered from cmde oil or natural gas Hquids or generated by other refinery operations. A growing quantity of isobutane is produced by the isomerization of / -butane [106-97-8]. 

Cracking reactions are endothermic, 1.6—2.8 MJ/kg (700—1200 BTU/lb) of hydrocarbon converted, with heat supplied by firing fuel gas and/or fuel oil in side-wall or floor burners. Side-wall burners usually give uniform heat distribution, but the capacity of each burner is limited (0.1—1 MW) and hence 40 to 200 burners are required in a single furnace. With modem floor burners, also called hearth burners, uniform heat flux distribution can be obtained for coils as high as 10 m, and these are extensively used in newer designs. The capacity of these burners vary considerably (1—10 MW), and hence only a few burners are required. The selection of burners depends on the type of fuel (gas and/or liquid), source of combustion air (ambient, preheated, or gas turbine exhaust), and required NO levels. 

Dente and Ranzi (in Albright et al., eds.. Pyrolysis Theory and Industrial Practice, Academic Press, 1983, pp. 133-175) Mathematical modehng of hydrocarbon pyrolysis reactions Shah and Sharma (in Carberry and Varma, eds.. Chemical Reaction and Reaction Engineering Handbook, Dekker, 1987, pp. 713-721) Hydroxylamine phosphate manufacture in a slurry reactor Some aspects of a kinetic model of methanol synthesis are described in the first example, which is followed by a second example that describes coping with the multiphcity of reactants and reactions of some petroleum conversion processes. Then two somewhat simph-fied industrial examples are worked out in detail mild thermal cracking and production of styrene. Even these calculations are impractical without a computer. The basic data and mathematics and some of the results are presented. 

The distribution of the products obtained from this reaction depends upon the reaction temperature (Figure 5.1-4) and differs from those of other poly(ethene) recycling reactions in that aromatics and alkenes are not formed in significant concentrations. Another significant difference is that this ionic liquid reaction occurs at temperatures as low as 90 °C, whereas conventional catalytic reactions require much higher temperatures, typically 300-1000 °C [100]. A patent filed for the Secretary of State for Defence (UK) has reported a similar cracking reaction for lower molecular weight hydrocarbons in chloroaluminate(III) ionic liquids [101]. An... 

When liquid hydrocarbons such as a naphtha fraction or a gas oil are used to produce olefins, many other reactions occur. The main reaction, the cracking reaction, occurs by a free radical and beta scission of the C-C bonds. This could be represented as ... 

Risers are normally designed for an outlet vapor velocity of 50 ft/sec to 75 ft/sec (15.2 to 22.8 m/sec). The average hydrocarbon residence time is about two seconds (based on outlet conditions). As a consequence of the cracking reactions, a hydrogen-deficient material called coke is deposited on the catalyst, reducing catalyst activity. 

Repeat the analysis of hydrocarbon cracking in Example 5.6 for the case where there is external heat exchange. Suppose the reaction is conducted in tubes that have an i.d. of 0.012 m and are 3 m long. The inside heat... 

For crude oils C and D, some lighter hydrocarbons are formed during the cracking reactions but the composition of the 210 fraction is hardly modified. In particular, it can be noticed that the asphaltene contents of both of the recovered oils remain high. 

Various other radiation-induced reactions have been studied for potential use in the industry on a pilot-plant scale. Among these may be mentioned hydrocarbon cracking (i.e., production of lower-molecular-weight hydrocarbons from higher-molecular-weight material), isomerization of organic molecules, and synthesis of labeled compounds with radioactive nuclei. When organic compounds are irradiated in the pure state or in aqueous solution, dimeric... 

Hydrogenolysis of 2-methylpentane, hexane, and methylcyclopentane has been also studied on tungsten carbide, WC, a highly absorptive catalyst, at 150-350 °C in a flow reactor [80], These reforming reactions were mainly cracking reactions leading to lower molar mass hydrocarbons. At the highest temperature (350 °C) all the carbon-carbon bonds were broken, and only methane was formed. At lower temperatures (150-200 °C) product molecules contained several carbon atoms. 

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