Batch Reaction Times

Direct hydrohquefaction of biomass or wastes can be achieved by direct hydrogenation of wood chips on treatment at 10,132 kPa and 340 to 350°C with water and Raney nickel catalyst (45). The wood is completely converted to an oily Hquid, methane, and other hydrocarbon gases. Batch reaction times of 4 hours give oil yields of about 35 wt % of the feed the oil contains about 12 wt % oxygen and has a heating value of about 37.2 MJ /kg (16,000 Btu/lb). Distillation yields a significant fraction that boils in the same range as diesel fuel and is completely miscible with it. 

The most important characteristic of an ideal batch reactor is that the contents are perfectly mixed. Corresponding to this assumption, the component balances are ordinary differential equations. The reactor operates at constant mass between filling and discharge steps that are assumed to be fast compared with reaction half-lives and the batch reaction times. Chapter 1 made the further assumption of constant mass density, so that the working volume of the reactor was constant, but Chapter 2 relaxes this assumption. 

These results assume that all the rate constants are different. Special forms apply when some of the k values are identical, but the qualitative behavior of the solution remains the same. Figure 2.2 illustrates this behavior for the case of bo = Co = do = 0. The concentrations of B and C start at zero, increase to max-imums, and then decline back to zero. Typically, component B or C is the desired product whereas the others are undesired. If, say, B is desired, the batch reaction time can be picked to maximize its concentration. Setting dbjdt = Q and bo =Q gives... 

Find the batch reaction time that maximizes the concentration of component B in Problem 2.10. You may begin with the solution of Problem 2.10 or with Equation (2.23). 

Find the value of the dimensionless batch reaction time, kfthatch, that maximizes the concentration of B for the following reactions ... 

If the enzyme charged to a batch reactor is pristine, some time will be required before equihbrium is reached. This time is usually short compared with the batch reaction time and can be ignored. Furthermore, 5o Eq is usually true so that the depletion of substrate to establish the equilibrium is negligible. This means that Michaelis-Menten kinetics can be applied throughout the reaction cycle, and that the kinetic behavior of a batch reactor will be similar to that of a packed-bed PFR, as illustrated in Example 12.4. Simply replace t with thatch to obtain the approximate result for a batch reactor. 

Batch reaction time Long, 60—75 min, additional three days aging Short, 15-25 min... 

In the early part of the reaction the SDR offers no benefit since the reaction is not mass-transfer limited. However, at higher viscosities it was found that a single pass through the SDR at 200 °C gave a similar reduction in acid value (measure of the degree of polymerization) to a batch reaction time of between 40 and 50 min. By recycling the polymer... 

Continuous versus (semi)batch, reaction time, flow rates Materials of construction... 

If k and are known, this expression may be solved by trial-and-error to give tjn, the batch reaction time corresponding to the greatest production rate. 

Tubular Reactor Studies. The first run in the tubular reactor was with the same recipe as for Seed I in Table I, but the conversion was very low, and there were two distinct phases. The residence time in the tube was equal to the batch reaction time. Apparently the more nearly constant temperature of the tubular reactor prevented rapid polymerization. In the next run, initiator and emulsifier levels were doubled, but still conversion was low, although phase separation was not so severe. With seed latex and still more emulsifier, Run I shown in Table II, monomer conversions of about 60% were obtained at 50 minutes average residence time in the reactor. No phase separation was evident, but later tests indicated that some phase separation was occurring. 

Mizuno et al. demonstrated an intramolecular version of [2 + 2] photocycloaddition using a microreactor made of PDMS [poly(dimethoxysilane)] (channel dimensions 300 pm wide, 50 pm deep and 45 or 202 mm long) [40], Because one of the products photochemically reverts to the starting material, while the other does not, a much shorter residence time, that is, 3.4 min (batch reaction time = 3 h), inside the microchannel reduces the possibility of the reverse reaction. The difference in residence times explains the slight difference in regioselectivity between the microflow and batch systems (Scheme 4.27). 

The entire sequence was completed in around 6 h, which compares favorably to an estimated batch reaction time of 4 days under conventional batch conditions. The overall reproducible yield of the synthesis was found to be 40% however, it was found that the phenolic oxidation step was yield-limiting (producing only 50% of the desired... 

It is important to have a grasp of the order of magnitude of batch reaction times, fs, in Table 4-1 to achieve a given conversion, say 90%, for the different values of the specific reaction rate, k. We can obtain these estimates by considering the irreversible reaction... 

A batch reactor is used for the broraination of p-chlorophenyl isopropyl ether, calculate the batch reaction time. [2nd Ed. P4-29]... 

The state estimation technique can also be incorporated into the design of optimal batch polymerization control system. For example, a batch reaction time is divided into several control intervals, and the optimal control trajectory is updated online using the molecular weight estimates generated by a model/state state estimator. Of course, if batch reaction time is short, such feedback control of polymer properties would be practically difficult to implement. Nevertheless, the online stochastic estimation techniques and the model predictive control techniques offer promising new directions for the improved control of batch polymerization reactors. 

Fig. 7.21 The ratio of stirred tank holding time to batch reaction time as a function of conversion and order of reaction.

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