Isothermal reactors parallel

The first reaction type is when the reactants form, not just the desired products, but also other undesired products in parallel with the main reaction. We want to show here the implications of parallel reactions, so we consider a simple batch isothermal reactor at constant volume ... 

An isothermal reactor concept incorporating a ceramic membrane is more attractive compared to an adiabatic reactor concept from a thermodynamic point of view. In this concept we assumed a reactor with reactor tubes located in a direct-fired heater and operated in a cyclic way to remove coke formed on the catalyst. Parallel bed and heaters have been assumed [35-37]. 

Froment and Bischoff [ref. 36] also illustrated the non steady state behavior of an isothermal reactor when parallel coking occurs. 

Equations (4-147) and (4-148) describe the conversion and coke profiles in an isothermal reactor subject to deactivation by coke formation via a parallel mechanism. Derive the corresponding equations for deactivation via a series mechanism. 

The average residence time in the isothermal reactor is 4 min. The other reactor operates adiabatically in parallel with the same flow entering at 200°C. Questions ... 

Irrespective of the above distinction, another difference among the reactor designs is the heat management, i.e. the use of single microchaimels and the use of parallel microchannels or microstructures. In most cases the single microchaimel operated, for example, in a furnace or in a heating block, leads to nearly isothermal reactor... 

In this chapter, the dynamics of ideally stirred tank reactors will be analyzed. First, the assumptions, required to limit model complexity, will be discussed. Next, various types of reaction will be considered such as simple first-order reactions, equilibrium reactions, parallel reactions, etc. Subsequently, the analysis will be expanded to include non-isothermal reactors. Numerical examples of chemical reactors are given and the non-linear model descriptions are compared with the linearized model descriptions. 

The above computation is quite fast. Results for the three ideal reactor t5T)es are shown in Table 6.3. The CSTR is clearly out of the running, but the difference between the isothermal and adiabatic PFR is quite small. Any reasonable shell-and-tube design would work. A few large-diameter tubes in parallel would be fine, and the limiting case of one tube would be the best. The results show that a close approach to adiabatic operation would reduce cost. The cost reduction is probably real since the comparison is nearly apples-to-apples. ... 

The gas-phase dehydrogenation of benzene to diphenyl (D) and further to triphenyl (T) is conducted in an ideal isothermal tubular reactor. The aim is to maximize the production of D and to minimize the formation of T. Two parallel, gas-phase reactions occur at atmospheric pressure... 

The experimental results are presented for the esterification of dodecanoic acid (C12H24O2) with 2-ethylhexanol (CgHigO) and methanol (CH4O), in presence of solid acid catalysts (SAC). Reactions were performed using a system of six parallel reactors (Omni-Reacto Station 6100). In a typical reaction 1 eq of dodecanoic acid and 1 eq of 2-ethylhexanol were reacted at 160°C in the presence of 1 wt% SAC. Reaction progress was monitored by gas chromatography (GC). GC analysis was performed using an InterScience GC-8000 with a DB-1 capillary colunm (30 m x 0.21 mm). GC conditions isotherm at 40°C (2 ntin), ramp at 20°C min to 200°C, isotherm at 200°C (4 min). Injector and detector temperatures were set at 240°C. 

This section indicates a few useful generalizations that are pertinent in considerations of isothermal series and parallel combinations of ideal plug flow and stirred tank reactors. 

For the parallel reactions in equation 10.7.1 one may use this general rule to select the follpw-ing operating conditions as optimum from a selectivity viewpoint when the reactor operates isothermally. 

H(hydrogen)-mordenite catalyst The crystallites were approximate parallelepipeds, the long dimension of which was assumed to be the pore length. Their analysis was based on straight, parallel pores in an isothermal crystallite (2 faces permeable). They measured (initial) rates of dehydration of methanol (A) to dimethyl ether in a differential reactor at 101 kPa using catalyst fractions of different sizes. Results (for two sizes) are given in the table below, together with... 

The approach to the design of non-isothermal tubular reactors with plug flow parallels that already outlined for batch reactors (see Sect. 2.4.)... 

In many situations, the monolith reactor can be represented by a single channel. This assumption is correct for the isothermal or adiabatic reactor with uniform inlet flow distribution. If the actual conditions in the reactor are significantly different, more parallel channels with heat exchange have to be simulated (cf., e.g. Chen et al., 1988 Jahn et al., 1997, 2001 Tischer and Deutschmann, 2005 Wanker et al., 2000 Young and Finlayson, 1976). In this section we will further discuss effective single channel models. 

The basic challenges for parallel test reactor development for high-throughput experimentation are, apart from technological challenges, related to technical demands that arise with the special issues for parallel test reactors, which are identical with the demands for conventional test reactors for gas-phase reactions. The criteria that must be fulfilled to obtain intrinsic catalyst properties from experimental data relate mainly to mass and heat transfer. A sufficient contact between the reactants and the catalyst must be insured to avoid mass transfer limitations inside and outside of the catalyst particles. Isothermal operation under laboratory conditions and avoidance of heat transfer limitations are also crucial. As a general quality check prior to operation intra- and extra-particle limitations should be... 

It should also be mentioned that the parallelization of reactors raises other problems such as the maldistribution of the reactants to the single units. While here usually passive devices such as flow restrictors are effectively applied, more severe problems are encountered if the process temperature should be controlled actively. One solution is to heat the whole micro reactor (assuming isothermal conditions due to large heat transfer coefficients) at a constant temperature controlled by the temperature of the flow at the reactor exit [13]. 

Most reactors used in industrial operations run isother-mally. For adiabatic operation, principles of thermodynamics are combined with reactor design equations to predict conversion with changing temperature. Rates of reaction normally increase with temperature, but chemical equilibrium must be checked to determine ultimate levels of conversion. The search for an optimum isothermal temperature is common for series or parallel reactions, since the rate constants change differently for each reaction. Special operating conditions must be considered for any highly endothermic or exothermic reaction. 

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