Batch time

Acidic contaminants are poisonous to the alcoholysis catalysts and must be avoided. If the oil has a high acid number, or there are high acidity residues left in the reactor from the previous batch, such as sublimed phthaUc anhydride condensed under the dome of the reactor, the reaction can be severely retarded. A longer batch time or additional amount of catalyst is then required. Both are undesirable. 

In method (2) the fiber-reactive dye is appHed with alkaH. The choice of alkaH and batching times and temperature are dependent on the fiber-reactive dye used. 

Timing issues due to scheduling multiple products or batches Timing issues due to a more complex supply chain... 

Often pilot plant or research data for developing a process are obtained on a batch operation. Later, a continuous process will usually prove that smaller equipment can be used and that the operation. vill be more economical. Normally batch mixing requires 10%-25% more power than continuous [29] for stable conditions how ev-er, the reaction time for continuous flow is always longer than the reaction time for batch flow, but the practical result may show batch time cycle is increased by filling,... 

A reasonable size of bioreactor, based on transport and handling considerations, is 200 m3, with a working volume of 150 m3. If file fermentation time is 48 hours and down time for reuse about 24 hours, then the total batch time is 72 hours. 

The yield that can be attained by a semibatch process is generally higher because the semibatch run starts from scratch, with maximum values of both variables Cg (o) = Cg and k] (o) = k . However, the yield from a continuous run in which t equals the batch time is governed by the product of Cg (t) and kj (t), so > and k (t) = k °. Because neither of these conditions is likely to be fulfilled completely, a continuous polymerization in a backmix reactor will probably always fail to attain the Y attainable by a semibatch reactor at the same t. However, several backmix reactors in series will approach the behavior of a plug flow continuous reactor, which is equivalent to a semibatch reactor. 

This messy result apparently requires knowledge of five parameters k, (A )o> Poo, and po- However, conversion to dimensionless variables usually reduces the number of parameters. In this case, set Y = Na/(Na)o (the fraction unreacted) and r = t/thatch (fractional batch time). Then algebra gives... 

In general, the use of temperature programming to achieve only a reduction in batch time is not always practical. Besides being difficult, if not impossible, to cany out on a large scale, it can seriouly affect the quality of the polylmer produced. For example, wide ranges in polymerzation temperature lead to broad molecular weight distributions (MWD) which may be undesirable. 

This study may act as a guide in the selection of initiators with desired half-life and activation energy for reducing batch time in polymerization reactors. 

Table 5.4-3 summarizes the design equations and analytical relations between concentration, C/(, and batch time, t, or residence time, t, for a homogeneous reaction A —> products with simple reaction kinetics (Van Santen etal., 1999). Balance equations for multicomponent homogeneous systems for any reaction network and for gas-liquid and gas-liquid-solid systems are presented in Tables 5.4-7 and 5.4.8 at the end of Section 5.4.3. 

The overall cost optimization criterion (5.4-137) to be minimized is composed of two terms. The first, which is called proportional, is related to the yield of both C and E one needs to maximize the yield of C, Yc, while minimising the ratio of yields, Y c. Yc and Kg are nc.f/nB.o and nE./nBA, respectively, n is number of moles, and y is a factor expressing the relative weight of the two terms (y was assumed to be one). The second term, called the non-proportional or fixed cost of operation, is the reciprocal of the ratio of yield of C per batch time, s, and as such it should be minimized, p is the weighing factor (equal to 174 in the process under consideration) in this term. 

Six initial experiments were carried out at the same batch time (355.6 dimensionless undisclosed units) varying the temperature, the ratio of reactants (ns/ ,i)o, and the feed time. The results of these experiments are given in Table 5.4-17. 

For a fixed molar ratio (ns/riAh equal to 0.05887, the temperature as applied in experiment E4, and a batch time of 347.8 dimensionless units, the feed rate of B (and thus the feed time) was optimized by computation to find tj = 323.19 dimensionless units. A run was carried out at these conditions. The data collected from this experiment were then used for re-estimation of the kinetic parameters. The new kinetic model was used to evaluate the new optimum feed rate for the same total amount of B. The optimum batch time reduced to 275.36 and the feed time to 242.75 units. Table 5.4-19 summarizes the results for three successive optimizations and re-estimations. Evidently, even a very simplified kinetic model can be successfully used in search for an optimum provided that kinetic parameters are updated based on every subsequent run carried out at the optimum conditions evaluated from the preceding set of kinetic parameters. 

Run Feed time Optimal Obtained Batch time tB Yield Yc Ye Selectivity YdYo J Improvement in J [%]... 

Marchal-Brassely et al. (1992) proposed the use of tendency modelling to optimize the batch time, the amount of initial reactants, the feed time of reactants, the temperature profile, and the feed-rate profile. The method proposed is an iterative one. Its principle is as follows ... 

The interval of the batch time is split in two equal intervals. Temperature and feed rate at the boundaries of sub-intervals are subjected to optimization together with the other variables. Temperature and feed rate between the boundaries of sub-intervals are assumed to be straight lines connecting the initial and final values. The optimum values of variables obtained in step two are taken as initial guesses for optimization. The new profiles consist of two ramps joining optimized points. 

At the start of optimization only the temperature profile, the batch time, and the feed time of G were optimized, while the other variables were kept constant. At the end all the variables specified above were relaxed and optimized. The optimization sequence is shown in Table 5.4-20. The changes in criterion J are shown in Fig. 5.4-38. 

The batch plant shown in Fig. 7.4-6 is to be optimized. The required production capacity is 11070 m per year. The cost coefficients (see Eqn. 7.3-4) are given in Table 7.4-7. The fixed processing times in the batch units, /i. r, are given in Table 7.4-8 together with initial values of processing times in the semi-continuous units, 04-( and those found by optimization. The total batch times, volumes, and costs are also given in this table. 

Determine the optimum batch time and batch temperature giving maximum yield of B. 

Study the effect of differing initial batch charge temperatures TRO (500 to 600°R) on the fractional conversion XA, the reactor temperature TR, and the required batch time. 

What initial temperature is required to give 99% conversion if the batch temperature must not exceed 600°R What is the corresponding batch time required ... 

What is the batch time requirement for the reactor operating isothermally at 60°F. How must the heat removal requirement vary during the batch in order to maintain the batch temperature constant ... 

Figure 57.23. The effect of FT level on the BN hydrogenation batch time without...

Figure 57.24. The batch times and BA yields of the Ni and Mo doped Ni with and withont FT. The FT levels were 1.33 mmol H2CO per g Ni and 2.0 mmol H2CO per g of Mo promoted Ni.

The reactor pressure is reduced to 0 psig to flash off any remaining water after a desired temperature is reached. Simultaneous ramp up of the heat source to a new setpoint is also carried out. The duration spent at this second setpoint is monitored using CUSUM plots to ensure the batch reaches a desired final reactor temperature within the prescribed batch time. The heat source subsequently is removed and the material is allowed to continue reacting until the final desired temperature is reached. The last stage involves the removal of the finished polymer as evidenced by the rise in the reactor pressure. Each reactor is equipped with sensors that measure the relevant temperature, pressure, and the heat source variable values. These sensors are interfaced to a distributed control system that monitors and controls the processing steps. 

In batch operation there will be periods when product is being produced, followed by nonproductive periods when the product is discharged and the equipment prepared for the next batch. The rate of production will be determined by the total batch time, productive... 

Example 14.1 Consider again the chlorination reaction in Example 7.3. This was examined as a continuous process. Now assume it is carried out in batch or semibatch mode. The same reactor model will be used as in Example 7.3. The liquid feed of butanoic acid is 13.3 kmol. The butanoic acid and chlorine addition rates and the temperature profile need to be optimized simultaneously through the batch, and the batch time optimized. The reaction takes place isobarically at 10 bar. The upper and lower temperature bounds are 50°C and 150°C respectively. Assume the reactor vessel to be perfectly mixed and assume that the batch operation can be modeled as a series of mixed-flow reactors. The objective is to maximize the fractional yield of a-monochlorobutanoic acid with respect to butanoic acid. Specialized software is required to perform the calculations, in this case using simulated annealing3. 

The most straightforward way to operate such a process is to maintain a constant chlorine addition rate and a constant temperature. However, both the constant value of the chlorine addition rate and the fixed temperature should be optimized. The temperature of the reaction system is allowed to vary within the set temperature range, but kept constant throughout a batch cycle. The batch time is divided into twenty time... 

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