当前位置:文库下载 > 所有分类 > 工程科技 > 纺织/轻工业 > MTBE(英重要)
免费下载此文档侵权投诉

MTBE(英重要)

Macrokinetic

analysis

of MTBE-synthesis

in chemical potentials

3079

specific swelling is set to its value in pure liquid alcohol.

MODEL EQUATIONS

Intrinsic reaction kinetics The sorption equilibria of the N species, A,, on one active site S in the catalytic active gel phase of the catalyst should be described by Langmuir sorption isotherms in liquid phase activities, a,: A,+ S 9 A,S M= 1, . . .,N (1) (2)

0,=

K,,,a, 1+X:=jK,,,e,’

where Q, is the fraction of sites occupied by A,, the equilibrium sorption constant of A, and K,~l=“f x.7,, y. the activity cQefficient at temperature T which is calculated here with the UNIQUACmethod. It is assumed that the rate-controlling step, the chemical reaction of sorbed molecules, can be formulated as first order in all species according to the homogeneous catalysis: AIS+ A,S 9 r=k+O,f3-k-O&, A$+ S (3) (4)

the sorption enthalpy of the polar component, A,). For the MTBE-synthesis one gets: k (363 K)= 243.8 mmol/(s eq), E= 92.4 lcJ/mol, A,Hi x IO kI/mol. As one can see in Fig. 3 in the case of MTBEformation the intrinsic reaction rates are successfully described by the simple model eq. (5), which is rather more complicated if the rate of reaction would be expressed in mole fractions instead of liquid phase activities. The data presented in Fig. 3 have been obtained using the macroporous ion exchange resin Amberlyst 15 (A15) as catalyst whose pore volume distribution is shown in Fig. 4. Typically, the radii of the macropores are in the range lo-20 nm. The reaction rate related

to the catalyst volume, ry, is given by multiplication of the turn-over number, r, by the mean acid group concentration, cL, of the whole resin particle: ry= cLr l--E with cL.= 1+SqpM

with q is the specific exchange capacity, pM the skeleton density at dry conditions, E the porosity (assumed as constant) and S the specific swelling related to dry catalyst volume. For Al5 we have found: q= 4.9 meq/g, pM= 1.515 g/cm, E= 0.36 and S= 0.53 in MeOH. Internal mass and heat transport The mass fluxes of the components, A,, are caused by several mechanisms: molecular diffusion in the macropores, viscous Ilow in the macropores, diffusion along the surface of the gelular microspheres and molecular diffusion in the gelular phase. In this analysis we only take the transport phenomena inside the macropores into consideration. The total mass flux densities, n,, in a nonideal liquid phase are specified by the Generalized Maxwell-Stefan equations

where I is the turnover number, 0, the fraction of unoccupied sites and k the rate constant of forward (+) and reverse (-) reaction. In the catalytic active gel phase almost only the component Ai is present. All fractions of occupied sites and the fraction of unoccupied sites 0, are not significant in comparison with the AI term. Therefore, eqs (2) and (4) can be combined to the following handy rate expression:

d(~-$)

(5)

with K, is the chemical equilibrium constant based on liquid phase activities u.. In case of the reaction of MeOH with IB to MTBE the chemical equilibrium constant takes a value of K,(298 K)= 284. Obviously, the forward reaction should be quasiautocatalytic concerning the reactant A, (alcohol) and the reverse reaction shows a product inhibition due to Al. The Arrhenius equation describes the temperature dependency of the reaction rate constant, k: k=k(,*)exp[-:(+-A)] (8) Mole Fraction of Methanol, XMaH -

where k(T*) is the rate constant at T*, E’ the activation energy of the reaction within the gel phase and the global activation energy E= E’ - AsHi (A.H, is

Fig. 3. Intrinsic rate of liquid phase MTBE-formation related to the molar IB content of the total C4 fraction (cje/ccr) as function of the MeOH mole fraction; Experiments: A 15 as catalyst, d,= 0.042 mm.; p= 2.1 MPa; model: eq. (5).

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

MTBE(英重要)

上一页第3页

免费下载Word文档免费下载:MTBE(英重要)

(下载1-13页,共13页)

我要评论

返回顶部