Reactions in the Batch Reactor

The reaction pathway is identical to that of a-pinene alkoxylation except that no bicyclic compounds are formed. As mentioned in the literature,alkoxylation of limonene to l-methyl-4-[a-alkoxyisopropyl]-l-cyclohexene can be carried out only in the presence of acidic catalysts. After a catalyst screening using various zeolitic and non-zeolitic acid heterogeneous catalysts we found that P-zeolite is the best candidate. 

Addition of methanol to limonene in the presence of a P-zeolite produces the 

It is interesting to notice that the destruction of the structure of P-zeolite by treatment with strong acids or high temperature leads to a complete deactivation of the catalyst for limonene alkoxylation. By using a higher reaction temperature only isomerization and polymerization products have been obtained. l-Methyl-4-[a-methoxyisopropyl]-l-cyclohexene or other addition products cannot be found. 

The most likely reason for the high activity of P-zeolite is the relatively high BET surface area of the catalyst (750 m g ). Furthermore, there are hints by temperature-programmed desorption (TPD) of absorbed ammonia that a large amount of acid sites is present. We assume that the alkoxylation of limonene takes place inside the pore structure of the P-zeolite. The high selectivity of P-zeolite might be originated from suitable acid sites in pores of its defined size and shape. 

The characterization of these P-zeolite samples via N2-sorption (BET) revealed, that catalyst C only had micropores and a BET surface area of 640 m g whereas the two catalysts with a higher conversion had meso- and macroporous volumina resulting in a faster mass transport. The difference in the performance of samples A and B can be attributed to the highest BET surface area of A (750 m g ) in contrast to B (680 m g ). Additionally, TPD measurements revealed that the total amount of acidic sites on sample A was still higher than on sample B. A shape-selective effect in the microporous system might be also involved since the dialkoxylation of limonene occurs only to a minor extent. In order to 

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We need reaction-rate expressions to insert into species mass-balance equations for a particular reactor. These are the equations from which we can obtain compositions and other quantities that we need to describe a chemical process. In introductory chemistry courses students are introduced to first-order irreversible reactions in the batch reactor, and the impression is sometimes left that this is the only mass balance that is important in chemical reactions. In practical situations the mass balance becomes more comphcated. 

From these new conditions the reaction in the batch reactor can be advanced to time t = 2At. At this time the entire procedure for computing the new feed flow-rate has to be repeated. Since no correction for the consumption of B has been made, the amount of B present must decrease as the reaction proceeds. As a result, progressively less of monomer A has to be added to keep p constant. When A is feed to the reactor not as pure monomer, but in solution the increase in volume caused by the added solvent will reduce the concentrations of the reactants and have a consequential effect on the overall rate of polymerisation. 

Reactions in the Batch Reactor - Methanol reacts with limonene over acidic catalysts in a batch reactor to l-methyl-4-[a-methoxyisopropyl]-l-cyclohexene (a-terpinyl methyl ether) as the main reaction product (see Figure 8 R = Me). Besides the desired methoxylation, isomerization reactions leading to terpinolene and traces of a- and y-terpinene can be observed. Furthermore, the addition of methanol to the terpinyl methyl ether leads to the undesired cis- or fra/w-1,8-dimethoxy-p-menthane. The amount of unidentified products does not exceed 1%. At high temperatures and long reaction times the reverse reaction of the a-terpinyl methyl ether and the other addition products to limonene and its isomers can be observed. The reaction scheme of the alkoxylation of limonene is illustrated in Figure 10... 

Reactions in the Batch Reactor - The addition of methanol to a-pinene in the presence of the above mentioned P-zeolite as catalyst in the batch reactor results in the cleavage of the cyclobutane ring and yields 1-methyl-4-a-methoxyisopropyl]-1-cyclohexene (a-terpinyl methyl ether) as the main reaction product. The most common by-products to be found are isomerization compounds like camphene, limonene and terpinolene, and several bicyclic and double addition products, e.g. endo- or exo-methyl bornyl ether, endo- or exo-methyl fenchyl ether and cis- or trans-1,8-dimethoxy-/)-menthane. 

Simulation of a non-isothermal reaction in a batch reactor involving the hydrolysis of acetylated castor oil... 

The general stoichiometric relationships for a single reaction in a batch reactor are... 

Compare these results with those of Equation (2.22) for the same reactions in a batch reactor. The CSTR solutions do not require special forms when some of the rate constants are equal. A plot of outlet concentrations versus t is qualitatively similar to the behavior shown in Figure 2.2, and i can be chosen to maximize bout or Cout- However, the best values for t are different in a CSTR than in a PFR. For the normal case of bi = 0, the t that maximizes bout is a root-mean, t ix = rather than the log-mean of... 

As an example for precise parameter estimation of dynamic systems we consider the simple consecutive chemical reactions in a batch reactor used by Hosten and Emig (1975) and Kalogerakis and Luus (1984) for the evaluation of sequential experimental design procedures of dynamic systems. The reactions are... 

It should be noted that there are cases in which some selectivity will be lost in choosing a semi-batch mode over a simple batch reactor. If the desired product decomposes by a consecutive reaction, the yield will be higher in the batch reactor [177]. If, on the other hand, the reactants are producing by-products by a parallel reaction, the semi-batch process will give the higher yield. In any case, if the heat production rate per unit mass is very high, the reaction can then be run safely under control only in a semi-batch reactor. 

Kinetic experiments on the hydrogenation of prenal and citral were first carried out in the batch reactor with variation of aldehyde concentration, hydrogen partial pressure, ruthenium concentration and reaction temperature (Table 7). Stirring was provided at 2000 rpm in order to be sure that the overall reaction rate was determined by kinetics. 

Increasing the hydrogen partial pressure initially causes an acceleration of the overall reaction rate imtil a plateau is reached beyond 7.5 bar. Further increase of the hydrogen partial pressure does not affect the overall reaction rate, which is in accordance with our results obtained in the batch reactor. 

Since the overall reaction rate in the loop reactor is limited by mass transport at the phase boundary, one would expect that the Ru concentration has a weaker influence on the rate of reaction than in the batch reactor. We have carried out experiments at a Ru concentration of 0.005 M as well as at 0.01 M and observed nearly a doubling of the overall reaction rate, giving rise to a reaction order of 0.96 with regard to Ru. The result is somehow surprising, since it can be explained only in terms of a kinetic control of the reaction, like in the batch reactor. On the other hand, previous experiments clearly indicate a mass transport limitation at the L/L-interphase. So the question which arises is how it can be possible that a multiphase reaction system is limited by both mass transport and kinetics ... 

For an autocatalytic reaction in a batch reactor some product R must be present if the reaction is to proceed at all. Starting with a very small concentration of R, we see qualitatively that the rate will rise as R is formed. At the other extreme, when A is just about used up the rate must drop to zero. This result is given in Fig. 3.9, which shows that the rate follows a parabola, with a maximum where the concentrations of A and R are equal. 

We plan to run this reaction in a batch reactor at the same catalyst concentration as used in getting the above data. Find the time needed to lower the concentration of from 10 mol/liter to A/ mol/liter. 

We can therefore replace dt by dz/u in all of the preceding differential equations for the mass balance in the batch reactor and use these equations to describe reactions during flow through a pipe. This reactor is called the plug-flow tubular reactor, which is the most important continuous reactor encountered in the chemical industry. 

Semibatch reactors are commonly used for small-volume chemical production. This reactor type is frequently used for biological reactions and for polymerization. In the batch reactor. 

When operating continuously at steady state each particle in a bed is subject to constant conditions but the concentration of reagents changes with the position in the column. When substrate is converted to product in a single pass the pattern of conversion down the bed resembles that seen when the same reaction is followed with respect to time in a batch reactor. This stems from the fact that distance travelled through the column is equivalent to processing with an equal concentration of biocatalyst in the batch reactor for the period of the column contact time. 

If the above condition is not met, the calculations based solely on overall material balance do not take into account the dissolved unreacted A and B that remain in the liquid phase after the reaction in a batch reactor, or which may flow out of the reactor with the liquid in a continuous-flow system. This way, it is assumed that the removal of a reactant is purely a result of the reaction. 

Equations 7.10-7.12 are identical in forms with those for the uniformly mixed batch reactor, that is. Equations 3.15, 3.22, and 7.3, respectively. It is seen that the time from the start of a reaction in a batch reactor (t) corresponds to the residence time in a PFR (r). 

In these equations it is understood that CA may be (a) the concentration of A at a particular time in a batch reactor, (b) the local concentration in a tubular reactor operating in a steady state, or (c) the concentration in a stirred-tank reactor, possibly one of a series, also in a steady state. Let St be an interval of time which is sufficiently short for the concentration of A not to change appreciably in the case of the batch reactor the length of the time interval is not important for the flow reactors because they are each in a steady state. Per unit volume of reaction mixture, the moles of A transformed into P is thus 9LAP6t, and the total amount reacted (9lAP + 3tAQ)St. The relative yield under the circumstances may be called the instantaneous or point yield will change (a) with time in the batch reactor, or (b) with position in the tubular reactor. 

Often the underlying population is completely hypothetical. Suppose we make five runs of a new chemical reaction in a batch reactor at constant conditions, and... 

By renaming the two terms on the right-hand side of (4.12) as qr and qE, which represent the rate of heat production by reaction and of heat exchange with the cooling medium, respectively, the heat balance in the batch reactor can be rewritten as... 

Knowledge of these types of reactors is important because some industrial reactors approach the idealized types or may be simulated by a number of ideal reactors. In this chapter, we will review the above reactors and their applications in the chemical process industries. Additionally, multiphase reactors such as the fixed and fluidized beds are reviewed. In Chapter 5, the numerical method of analysis will be used to model the concentration-time profiles of various reactions in a batch reactor, and provide sizing of the batch, semi-batch, continuous flow stirred tank, and plug flow reactors for both isothermal and adiabatic conditions. 

External mass transfer limitations, which cause a decrease in both the reaction rate and selectivity, have to be avoided. As in the batch reactor, there is a simple experimental test in order to verify the absence of these transport limitations in isothermal operations. The mass transfer coefficient increases with the fluid velocity in the catalyst bed. Therefore, when the flow rate and amount of catalyst are simultaneously changed while keeping their ratio constant (which is proportional to the contact time), identical conversion values should be found for flow rate high enough to avoid external mass transfer limitations.[15]... 

Optimal operating conditions and catalysts Acetylation of phenyl ethers was generally carried out in the absence of solvents, which makes easier the recovery of the acetylated product from the reaction mixture. On the other hand, because of the high melting point of substrate and acetylated products, solvents were always used in the acetylation of 2-methoxynaphthalene. Flow reactors (e.g. fixed bed tubular reactors), in which the detrimental effect of competitive adsorption of substrate and products on the acetylation yield is lower than in the batch reactors, should be preferred. However although the set up of fixed bed reactors for liquid phase reactions is relatively simple, their substitution to the batch reactors, which are the only system used in academic organic chemistry, remains essentially limited to commercial units. 

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