Reactor volume conversion factors

Ca.ta.lysts, Catalyst performance is the most important factor in the economics of an oxidation process. It is measured by activity (conversion of reactant), selectivity (conversion of reactant to desked product), rate of production (production of desked product per unit of reactor volume per unit of time), and catalyst life (effective time on-stream before significant loss of activity or selectivity). 

Now, if we can get catalyst carriers that adhere to the gas-liquid surface and we become successful in easily separating particles of dp < 5 fan, we can reduce on catalyst concentrations down to 0.5 x 10 4 < es < 5 x 10 3 and still realize an enhancement in conversion rate, typically by a factor of 5. This way, the reactor volume is reduced by a factor of 5 and the catalyst holdup by several orders of magnitude. The improvement might be even more spectacular because it is known that small particles of dp < 100 fim for Es < 0.5 x 10 2 may cover gas liquid surface, thus prevent bubble coallescence which results in smaller bubbles, leading to still higher interfacial gas liquid areas and thus to still smaller reactors [109]. 

CSBR). In this case the bioconversion is run under approximately steady-state conditions where the position of reaction equilibrium lies toward the products of the conversion. In this case the concentration of product (proportional to Sj — S0 ) at a given reactor residence time becomes a function of both the flow rate (Q) into the reactor and reactor volume, in addition to the factors discussed above for batch mode reactors (i.e., catalyst parameters and density, inlet substrate concentration S and outlet substrate concentration S0). 

Example 4-2. How would your reacior volume change if you only needed 50% conversion to produce the 2(K) million pounds per year required What generalizations can you draw from this example Example 4-3. Whai would be the reactor volume for X = 0.8 if the pressure were increased by a factor of 10 assuming everything else remains the same What generalizations can you draw from this example Example 4-4. How w ould the pressure drop change if the particle diameter were reduced by 25% What generalizations can you draw from this example ... 

CDP4-P Fairly straight forward California registration problem where you must carry out a number of calculations involving conversion factors to calculate CSTR and PFR reactor volumes and a batch reaction time. 

Alternatively, a given conversion may be reached with either a single large reactor volume or with a series of smaller reactors. The ultimate choice is based on economic factors, as illustrated in Fig. 10.2.b-l The total reactor volume required decreases with more subdivision (larger n), but with the cost per reactor proportional to F the total cost proportional to shows a definite minimum—in this case at about n = 4. Plant operational difficulties may also increase with n, and the optimum choice is usually a relatively small number of reactors in series, especially since most of the savings in total volume occur for n < 5. Exceptions are in multistage contacting devices, but this is a more complicated situation. 

For reactions of order 1, the required reactor volume is greater for a backmixed reactor than for a plug flow one, e.g. by a factor of 191 for 90% conversion and 21.5 for 99% conversion, for a first order reaction. This is also true for gas-liquid mass transfer controlled systems, where in the main it is the gas phase residence time distribution which affects the driving force and hence reactor size for a given throughput. 

It is considered to carry out the same reaction in an upflow column, with a catalyst of the same material, but with a diameter of 4 mm. Estimate the required reaction volume, for a mean residence time of the liquid phase of 30 minutes (it is expected that the conversion will be the same as in the batch reactor). The Thiele modulus is proportional to the particle diameter, so for the larger catalyst particles is approximately 16, and the effectiveness factor is 1/16 (see eqs. (5.48) and (5.50)). This means that the required catalyst volume is 16 times larger, that is 16 x 0.1 x 10 = 16 m. When the bed has a void fraction of 0.5, die total effective reactor volume has to be 32 m. But this is only correct if the process rate is still determined by chemical kinetics. The gas/liquid mass transfer would be a possible limiting factor. One can make the following estimate The bubble hold-up in a stirred tmik and in an upflow column will both be on the order of 0.2. The bubble diameter will be on the order of 1 mm in the stirred tank, and 2 mm in the upflow column (with particles of 4 mm). 

It wiit be en in section 2.5 that a comidefitioD of eipr to relating fractional conversion to k and A provides two further figures of merit Fora simple batch reactor which is used to process a volume the factor ... 

Because of the dilution that results from the mixing of entering fluid elements with the reactor contents, the average reaction rate in a stirred tank reactor will usually be less than it would be in a tubular reactor of equal volume and temperature supplied with an identical feed stream. Consequently, in order to achieve the same production capacity and conversion level, a continuous flow stirred tank reactor or even a battery of several stirred tank reactors must be much larger than a tubular reactor. In many cases, however, the greater volume requirement is a relatively unimportant economic factor, particularly when one operates at ambient pres-... 

Intraparticle Mass Transfer. One way biofilm growth alters bioreactor performance is by changing the effectiveness factor, defined as the actual substrate conversion divided by the maximum possible conversion in the volume occupied by the particle without mass transfer limitation. An optimal biofilm thickness exists for a given particle, above or below which the particle effectiveness factor and reactor productivity decrease. As the particle size increases, the maximum effectiveness factor possible decreases (Andrews and Przezdziecki, 1986). If sufficient kinetic and physical data are available, the optimal biofilm thickness for optimal effectiveness can be determined through various models for a given particle size (Andrews, 1988 Ruggeri et al., 1994), and biofilm erosion can be controlled to maintain this thickness. The determination of the effectiveness factor for various sized particles with changing biofilm thickness is well-described in the literature (Fan, 1989 Andrews, 1988)... 

The many factors outlined above which affect reaction rates suggest that considerable caution is advisable when utilising laboratory data for the design of large-scale reactors. It is essential first to locate the reaction volume or volumes. This, in the case of the absorption of CO2 into aqueous ammonia liquid discussed above, the fast reaction between dissolved CO2 and dissolved ammonia occurs in a small volume of liquid close to the gas—liquid interface. The forward reaction rate is, therefore, proportional to the gas—liquid interfacial area. The conversion of the initially fomed NH2COONH4 to (NH4)2COa by hydrolysis is a much slower reaction and takes place throughout the whole volume of the liquid phase. Similarity would therefore dictate that the interfacial area per unit liquid volume should be the same in experimental and full-scale reactors. 

Design of a Batch Reactor. As seen above, for a batch reactor the design equation estimates only the time required for a reaction to proceed to a desired conversion level. If we want to design a batch reactor, i.e. estimate its volume, we have to consider other factors such as production rate, as demonstrated in the following example. 

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