Reactor concentration parallel reactions

Multiple reactions in parallel producing byproducts. Consider again the system of parallel reactions from Eqs. (2.16) and (2.17). A batch or plug-flow reactor maintains higher average concentrations of feed (Cfeed) than a continuous well-mixed reactor, in which the incoming feed is instantly diluted by the PRODUCT and... 

A semi-batch reactor has the same disadvantages as the batch reactor. However, it has the advantages of good temperature control and the capability of minimizing unwanted side reactions by maintaining a low concentration of one of the reactants. Semi-batch reactors are also of value when parallel reactions of different orders occur, where it may be more profitable to use semi-batch rather than batch operations. In many applications semi-batch reactors involve a substantial increase in the volume of reaction mixture during a processing cycle (i.e., emulsion polymerization). 

Maleic anhydride is an important industrial fine chemical (see original citations in [43]). The oxidation of C4-hydrocarbons in air is a highly exothermic process, therefore carried out at low hydrocarbon concentration (about 1.5%) and high conversion. The selectivity of 1-butene to maleic anhydride so far is low. The reaction is composed of a series of elementary reactions via intermediates such as furan and can proceed to carbon dioxide with even larger heat release. As a consequence, hot spots form in conventional fixed-bed reactors, decrease selectivity and favor other parallel reactions. 

Parallel reactions, oai = om2, a i = am = 0, Ei > E2. The. selectivity to the desired product increases with temperature. The highest allowable temperature and the highest reactant concentrations should be applied. A batch reactor, a tubular reactor, or a cascade of CSTRs is the best choice. 

The condition for the practical implementation of such a feed control is the availability of a computer controlled feed system and of an on-line measurement of the accumulation. The later condition can be achieved either by an on-line measurement of the reactant concentration, using analytical methods or indirectly, by using a heat balance of the reactor. The amount of reactant fed to the reactor corresponds to a certain energy of reaction and can be compared to the heat removed from the reaction mass by the heat exchange system. For such a measurement, the required data are the mass flow rate of the cooling medium, its inlet temperature, and its outlet temperature. The feed profile can also be simplified into three constant feed rates, which approximate the ideal profile. This kind of semi-batch process shortens the time-cycle of the process and maintains safe conditions during the whole process time. This procedure was shown to work with different reaction schemes [16, 19, 20], as long as the fed compound B does not enter parallel reactions. 

In a parallel reaction network of first-order reactions, the selectivity does not depend upon reaction time or residence time, since both products are formed by the same reactant and with the same concentration. The concentration of one of the two products will be higher, but their ratio will be the same during reaction in a batch reactor or at any position in a PFR. The most important parameters for a parallel reaction system are the reaction conditions, such as concentrations and temperature, as well as reactor type. An example is given in the following section. 

Mixing may occur on several scales on the reactor scale (macro), on the scale of dispersion from a feed nozzle or pipe (meso), and on a molecular level (micro). Examples of reactions where mixing is important include fast consecutive-parallel reactions where reactant concentrations at the boundaries between zones rich in one or the other reactant being mixed can determine selectivity. 

Both batch and continuous stirred tank reactors are suitable for reactions that exhibit pseudo-zero-order kinetics with respect to the substrate concentration. In other words, under operating conditions the rate is more or less independent of the concentration of the substrate. However, for reactions where pseudo-first-order kinetics with respect to the concentrations of the substrates prevail, a batch tank reactor is preferred. Batch tank reactors are also ideally suited when there is a likelihood of the reactant slowly deactivating the catalyst or if there is a possibility of side product formation through a parallel reaction pathway. 

Mixing in general decreases the reactant conversion but it may improve selectivity. Thus, the yield of a low-order path in a parallel reaction scheme would improve in a MER, as indicated earlier. The uniform concentration and rate in a MER and the simple algebraic form of the continuity equations (107) make this reactor ideal for kinetic analysis of simple and complex electrocatalytic reactions. 

A related oscillatory phenomenon is that in which the concentration of one or more reactants, fed to a flow reactor, is varied in time. Such forced periodic feed oscillations during oxidation reactions have now been studied by a number of authors. It is found that not only can conversion be increased but the selectivity of certain parallel reactions can be improved, which may be of value in industrial applications. Cutlip and Abdul-Karem and Jain ... 

The distributor -type membrane reactor possesses different residence-time characteristics and different local concentration profiles compared to the conventional FBR. The additional degrees of freedom allow in complex networks of consecutive and parallel reactions, the selectivity and the yield to be enhanced with respect to a certain target product. The concept can be considered as an interesting option in the current attempts to improve and intensify reaction processes. 

In Equation 5.7a, component A decomposes to form component B. If B is present, then components A and B may combine, in an autocatalytic reaction, to form additional B by Equation 5.7b. Component A may also decompose in a parallel reaction to form C via Equation 5.7c. For this example, we shall assume that component B is the desired product and seek to determine the optimal reactor structure that maximizes the concentration of B, Cg. 

To perform a parallel reaction, a mixed solution of triethylamine and butylamine (each 0.22 M) in THE was fed into the reactors from one inlet, a constant stream of THE was introduced from a second inlet and a solution of acetyl chloride (0.2 M) in THE from a third inlet. Using this reactor set-up, the solvent stream was maintained at three times the flow rate of the reagent streams and the reaction products were quenched in water at the outlet. The reaction products were subsequently filtered, to remove the ammonium salt, and concentrated in vacuo prior to analysis by GC-MS. Under the aforementioned conditions, the authors reported the ability to synthesize N-butylacetamide in high purity (93.5%), demonstrating good reproducibility across the six reaction units (RSD = 4.9%). further work is currently under way to improve the reaction methodology in order to permit continuous operation of the reactor without fouling. 

A first-order parallel reaction A c carried out in a batch reactor at constant temperature taking 10 kmol/m of A at the time of start-up. The reachon is arrested after 20 min and the concentration of compoimds A, B and C are measured. The concentrations of A and B are 5 and 4.1667 kmol/m, respectively. Estimate the values of the rate constants ki and k2-... 

THE PROBLEM A batch laboratory reactor with an electrolyte volume of 700 cm and an electrode area of 30 cm is used to deposit a divalent metal from an aqueous solution in a potentiostatic mode. Initial concentration of the metal is O.lkmol/m. The reactor mass transfer coefficient has been measured as 3.3 x 10" m/s. Hydrogen evolution occurs as a parallel reaction according to the equation % = H p [ — ], where kn = 1.30 X 10" A/m and = 12 If the metal deposition is operated at its limiting current density at an electrode potential of —0.9 V (SCE), determine how conversion, total current density, and current efficiency vary with time, in a potentiostatic mode. What will be the current efficiency at the final... 

General expression for an SBR for multiple reactions with Inflow of liquid and outflow of liquid and vapor Scheme 4 Nonisothermal operation Optimum temperatures/temperature profiles for maximizing yields/selectivltles Optimum temperatures Optimum temperature and concentration profiles In a RPR Parallel reactions Oonsecutive reactions Extension to a batch reactor Explore yourself References Bibliography... 

This reaction was exploited by Tsukatani and Matsumoto (2000) in a stopped-flow FIA method. An immobilized D-malate dehydrogenase enzyme reactor was employed and the reduced enzymatic cofactor NADH that was formed was monitored fluorometrically (Xex = 340 nm = 460 nm). Due to the slow reaction rate, the flow was stopped with the sample in the reactor to increase reaction time. The intrinsic sample fluorescence was also assessed using a parallel blank reactor without immobilized enzyme. The method was validated through the analysis of red and white wine samples. The enzyme reactor stability was also evaluated and it was found that the sensitivity (evaluated as amplitude of response at a constant concentration of the analyte) gradually decreased to 60% within a week but then remained stable for a month. As D-malate cannot be present in naturally fermented wines (except for fraudulent addition), the interference of this primary substrate can be considered negligible. 

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