Membrane reactors reaction rate constants

Substrate and product inhibitions analyses involved considerations of competitive, uncompetitive, non-competitive and mixed inhibition models. The kinetic studies of the enantiomeric hydrolysis reaction in the membrane reactor included inhibition effects by substrate (ibuprofen ester) and product (2-ethoxyethanol) while varying substrate concentration (5-50 mmol-I ). The initial reaction rate obtained from experimental data was used in the primary (Hanes-Woolf plot) and secondary plots (1/Vmax versus inhibitor concentration), which gave estimates of substrate inhibition (K[s) and product inhibition constants (A jp). The inhibitor constant (K[s or K[v) is a measure of enzyme-inhibitor affinity. It is the dissociation constant of the enzyme-inhibitor complex. 

The overall mass-transfer rates on both sides of the membrane can only be calculated when we know the convective velocity through the membrane layer. For this, Equation 14.2 should be solved. Its solution for constant parameters and for first-order and zero-order reaction have been given by Nagy [68]. The differential equation 14.26 with the boundary conditions (14.28a) to (14.28c) can only be solved numerically. The boundary condition (14.28c) can cause strong nonlinearity because of the space coordinate and/or concentration-dependent diffusion coefficient [40, 57, 58] and transverse convective velocity [11]. In the case of an enzyme membrane reactor, the radial convective velocity can often be neglected. Qin and Cabral [58] and Nagy and Hadik [57] discussed the concentration distribution in the lumen at different mass-transport parameters and at different Dm(c) functions in the case of nL = 0, that is, without transverse convective velocity (not discussed here in detail). 

Keurentjes at al [3.27] carried out experiments to study the kinetics of this reaction, and fitted their data in terms of an activities dependent mass-action kinetic scheme. They utilized a simple model of a PVMR to study the effect of the ratio of membrane area (A) to reactor volume (V) on PVMR performance based on the measured rate constants and literature values for the water and ethanol permeances through a PVA membrane (PVMR models are further discussed in Chapter 5). Keurentjes Qt al [3.27] report that with the aid of the PV membrane the equilibrium can be significantly shifted towards the diethyltar-trate product. There is a certain optimum (A/V) ratio. This is because when the (A/V) ratio is too low, the water removal rate is too slow to have any influence, while for high values of this ratio too much ethanol is removed. 

Universal gas constant A-component reaction rate Hydrogen reaction rate /-Component reaction rate Selective membrane radius Hydrogen solubility Reactor operating temperature Permeation zone temperature Temperature of heating/cooling fluid Reaction zone temperature Temperature on catalyst surface Temperature inside catalyst particle Reactor tube wall temperature... 

Compared to the systems described above, the membrane reactor system has the advantage of continued operation. However, the decrease in the enzymatic reaction and an increase in the transmembrane pressure was detected after five cycles (Jeon and Kim, 2000a Kou et al., 2004). These researches have found that the membrane reactor could be operated continuously for at least 15 h, maintaining a constant permeate flux and product output rate (Kou et al., 2004). The continued production of ultraflltration membrane reactor system gets obstructed due to membrane fouling after several cycles. Therefore, scientists interest has moved toward the development of a new system that can be helpful in the efficient production of COS continuously. 

Both concentration-based and activity-based rate constants of the reaction are experimentally obtained, showing that the rate of reaction can be predicted correctly also by concentration-based parameters. Simulations of the integrated process show that the ratio, AA/, of the membrane area to the reactor volume has an optimum. When AN is too low the water removal is too low and when AA/ is too high, too much alcohol is removed. 

There is, however, another way of looking at a tubular reactor in which plug flow occurs (Fig. 1.15). If we imagine that a small volume of reaction mixture is encapsulated by a membrane in which it is free to expand or contract at constant pressure, it will behave as a miniature batch reactor, spending a time r, said to be the residence time, in the reactor, and emerging with the conversion aA/. If there is no expansion or contraction of the element, i.e. the volumetric rate of flow is constant and equal to v throughout the reactor, the residence time or contact time... 

In the same suidy [Itoh et al., 1985], the molar flow rate of cyclohexane at the reactor outlet is calculated as a function of the membrane thickness which has the most effect on the permeation rate of gases. For a given constant inlet molar flow rate, the reaction does not proceed beyond the equilibrium conversion for a conventional reactor. With membrane permeation, however, the overall conversion (i.e., the combined conversions of cyclohexane on the tube and shell sides) reaches a maximum for a certain membrane... 

Akyurtlu et al. [1988] have found that when B becomes depleted inside the membrane matrix, the reaction conversion is very sensitive to the annular space in a CNMMR (see Figure 10.20). The average conversion of at the reactor outlet increases as the radius ratio X(s / 2 3) increases. The rate of increase is particularly rapid as X approaches 1. This means that when the annular liquid region becomes small, the reaction conversion is high for a constant throughput and a constant membrane thickness. In the same study, a parameter y was defined as... 

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