Ethylbenzene isotherms

S Fprocess Styrene atmos. 580-590 Fe203 Ethylbenzene Isothermal process ... 

The molar ratio of steam to ethylbenzene at the inlet is 9 1. The bed is 1 m in length and the void fraction is 0.5. The inlet pressure is set at 1 atm and the outlet pressure is adjusted to give a superficial velocity of 9 m/s at the tube inlet. (The real design problem would specify the downstream pressure and the mass flow rate.) The particle Reynolds number is 100 based on the inlet conditions 4 x 10 Pa s). Find the conversion, pressure, and velocity at the tube outlet, assuming isothermal operation. 

Example 10.6 A commercial process for the dehydrogenation of ethylbenzene uses 3-mm spherical catalyst particles. The rate constant is 15s , and the diffusivity of ethylbenzene in steam is 4x 10 m /s under reaction conditions. Assume that the pore diameter is large enough that this bulk diffusivity applies. Determine a likely lower bound for the isothermal effectiveness factor. 

Significant amounts of CH4 and C2H2 are also formed but will be ignored for the purposes of this example. The ethane is diluted with steam and passed through a tubular furnace. Steam is used for reasons very similar to those in the case of ethylbenzene pyrolysis (Section 1.3.2., Example 1.1) in particular it reduces the amounts of undesired byproducts. The economic optimum proportion of steam is, however, rather less than in the case of ethylbenzene. We will suppose that the reaction is to be carried out in an isothermal tubular reactor which will be maintained at 900°C. Ethane will be supplied to the reactor at a rate of 20 tonne/h it will be diluted with steam in the ratio 0.3 mole steam 1 mole ethane. The required fractional conversion of ethane is 0.6 (the conversion per pass is relatively low to reduce byproduct formation unconverted ethane is separated and recycled). The operating pressure is 1.4 bar total, and will be assumed constant, i.e. the pressure drop through the reactor will be neglected. 

Figure 21. Influence of the heating strategy on the temperature and concentration profiles in styrene synthesis. A) Adiabatic B) Isothermal C) Countercurrent heating. EB = ethylbenzene St = styrene.

Performance depends abov all on the in which the catalyst is employed, and this takes place in two dififerent ways, isothermal and adiabatic Hence the same catalyst formula offers greater abrasion resistance and crushing strength characterized by a lower water to ethylbenzene w dght ratio at the reactor inlet and longer life if operation is isothermal The steam ratio is usually 110 1,2 in this case as compared with 1.6 to 2.5 in adiabatic conditions, and the corresponding lives are 5 to 6 years, against 18 months to 2 years. The essential reason for these differences is the lower feed preheat temperature... 

Fig. 6.10. Styrene manufacture by isothermal dehydrogenation of ethylbenzene. BASF process.

Duff et al. [27] reported a study made by means of DSC and WAXD on SPS/ PPE blends of various compositions, precipitated from ethylbenzene solutions, compression molded at 330 °C for 2 min and then slowly cooled to room temperature. In particular, the WAXD patterns show that in sPS-rich blends (>50 50 wt%) sPS is in a 0 or (3 form, while small amounts of a are present in the 50 50 wt% blend. The kinetics of crystallization and the mechanism of nucleation of sPS were investigated under isothermal and nonisothermal conditions as a function of blend composition and molecular weights of the components. The experimental curves show that the half-time to crystallization, t j2, increases with increasing content and molecular weight of PPE, but is not influenced by the molecular weight of sPS. The crystallization kinetics were... 

PF/PF Isothermal Tube side Ethylbenzene dehydrogenation Itoh Xu, 1991... 

PF/PF, PM/PM Adiabatic Isothermal Shell side Af->B ethylbenzene dehydrogenation HI decomposition, propylene disproportionation 8l cyclohexane dehydrogenation Mohan Govind. 1988b Mohan Govind. 1988c... 

Wu and Liu [1992] attempted to approximate the reactions involved during ethylbenzene dehydrogenation under an industrial setting by considering many possible side reactions. They included in their isothermal model for plug flows on both sides of the membrane the following five main side reactions with their corresponding reaction rate expressions ... 

It is often desirable to operate the reactor and the catalyst under isothermal conditions to achieve high reactor performance. Heat requirement of an endothermic reaction in a membrane reactor to maintain an isothermal condition can be challenging as in most of the dehydrogenation reactions such as conversions of ethylbenzene to styrene and prc pane to propylene. Maintaining an isothermal condition implies that some means must be provided to make the adequate heat input (e.g., from a burner) that is longitudinally dependent It is not trivial to make the temperature independent of the longitudinal position because the permeate flow also varies with the location in the axial direction. 

Non-isothermal 1-D models for adiabatic PBMR and FBMR reactors utilizing Pd tubular membranes have been developed by Elnashaie et al [5.35], and applied to the catalytic ethylbenzene dehydrogenation reaction. In contrast to many other modelling studies their model takes into account intraparticle diffusional limitations. The catalyst particles... 

An equimolar mixture of benzene and ethylene at 370°K is fed into a reactor where ethylbenzene is formed. Separate experiments show that at 1 atm an equilibrium mixture is obtained. If the reactor is operated isothermally, what is the concentration of species at the reactor exit What would you do with this analysis if the reactor were operated adiabatically ... 

Abstract Infrared spectroscopic methodsfor the measurement of adsorption and adsorption kinetics of some aromatics (benzene, ethylbenzene, p-xylene), pyridine, and paraffins in solid microporous materials such as zeolites (MOR, ZSM-5, silicalite-1) are described as well as the evaluation of the spectroscopically obtained data. The adsorption isotherms are of the Langmuir-Freundlich type. Isosteric heats of adsorption, transport diffusivities, and activation energies of diffusion as deduced from the spectroscopic measurements are compared with literature data as far as available, and they are found to be in reasonable agreement with results provided by independent techniques. Special attention is paid to sorption and sorption kinetics of binary mixtures, especially the problems of co- and counter-diffusion. ... 

A set of such isotherms is shown in Fig. 9 for the system ethylbenzene/ H-ZSM-5. From such sets, in turn, isosteres were constructed and isosteric heats of adsorption, Qiso, determined via the Clausius-Clapeyron equation. This is illustrated in Fig. 10 using the system ethylbenzene/H-ZSM-5 as an example. 

Fig. 9 Isotherms of ethylbenzene adsorption on H-ZSM-5 for various adsorption temperatures amounts adsorbed (mmol ) as a function of the ethylbenzene partial pressure (Pa)...

An example of isotherms for the mixture of benzene and ethylbenzene is provided by Fig. 17. Also in this case, the isotherms were well described by a Langmuir-Freundlich equation of the type shown in Eq. 2 ... 

Fig. 17 Isotherms for the mixed adsorption at 415 K of benzene and ethylbenzene on simultaneous changes of the partial pressures of the components...

From sets of spectra such as those shown in Fig. 3 and uptake curves displayed by Fig. 8 not only isotherms and isosteres could be derived, using the respective plateaux for the temperatures and pressures indicated, but also from the ascending branches (measured via FTIR after an upward pressure jump) or the descending branches (determined after a downward pressure jump) the kinetics of adsorption and desorption into zeolitic pores could be derived. These processes were assumed to be diffusion controlled. Their evaluation required a fit of the appropriate solution of Tick s second law as provided by Crank [39] to the experimentally measured uptake (or removal) points, which are indicated in Fig. 6 by filled crosses for the case of ethylbenzene uptake. 

An alternative calculation is to use the Peng-Robinson equation of state. The eritieal properties of hydrogen are given in Table 4.6-1. The values for ethylbenzene are 7c = 617.2 K, Pc = 36 bar, 05=0.302, and 7b=409.3 K. There is no binary interaetion parameters for hydrogen with other components in Table 7.4-1, so we will assume that its value is zero. Using the isothermal flash calculation in the program VLMU we obtain the following results... 

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