Reaction time, batch reactors

Thus, 50% yields of the target product (II) are obtained for irradiation times of 1-5 min, whereas under batch conditions the yields amount only to 5%. In order to observe similar yields in the batch reactor, reaction times of >180 min are required. Due to the possible photocycloreversion of l-cyano-5-oxabenzo [10, 11] tricycle [5.4.0.0]undec-8-ene (I), a prolonged irradiation yields the secondary product (III). The authors attribute an increase in regioselectivity to the specific flow system of the microreactor. 

The experimental semibatch apparatus and procedure have been described in several places through the text of Wisseroth s publications ( 1, 7-9). so the details will not be repeated here. For nearly all of his work the reactor volume was one liter, temperature was 80 C, pressure was 30 atm (441 psia), and the feed was polymerization grade I assume that the reactor gas composition was 99% CsHgand 1% inerts. The range of catalyst loading was from 11 to 600 mg of TiCils per batch. The reaction time was varied from 0.5 to 6 hours. The weight ratio of alkyl-to-TiC 3 in the catalyst recipe was varied from 0.5 to 32. No data are reported from a continuous gas phase reactor. 

Conditions batch autoclave reactor reaction time 18 h reaction temperature 120 °C, initial pressure 70 bar 1-hexene charged 160 mmol toluene charged 30 mL internal standard 5 mL of n-heptane. 

As pointed out previously, the use of flow reactors allows for the direct measurement of reaction rates. At steady state (unlike the batch reactor), the time scales of the analytical technique used and the reaction are decoupled. Additionally, since numerous samples can be acquired at the same conditions, the accuracy of the data... 

Ammonia is produced from nitrogen and hydrogen in a batch reactor. At time t = 0 there are no mol of NH3 in the reactor, and at a later time ff the reaction terminates and the contents of the reactor, which include nf mol of ammonia, are withdrawn. Between tQ and ff no ammonia enters or leaves through the reactor boundaries, so the general balance equation (Equation 4.2-1) is simply generation = accumulation. Moreover, the quantity of ammonia that builds up (accumulates) in the reactor between fo and ff is simply f - no. the final amount minus the initial amount. 

Evaluating Che specilic reaction rate from batch reactor concentration-time data... 

We make the assumption that the reaction is first order and irreversible, so that if N is the number of moles of A in the batch reactor at time t and V is its volume. 

The difficulty that arises is that to evaluate each of the terms in these equations we need chemical reaction rate data, reactor heat programs, and so forth, information we may not have. To avoid this difficulty, instead of using these differential equations directly, we can use the balance equations obtained by integrating these equations over the time interval ri to h, chosen so that the reactor is in the same state at fa as it was in t. If the reactor is a "flow reactor, this corresponds to any period of steady-state operation, whereas if it is a batch reactor, the time interval is such that the initially empty reactor is charged, the reaction run, and the reactor contents discharged over the time interval. In either of these cases the results of the integrations are... 

Equation 13 suggests that the plot of concentration (obtained om a batch reactor) versus time for a zero-order reaction will give a linear trace, the slope will yield a value of-BC. 

Batch time lowered by a factor of 2 catalyst loading reduced by factor of 2 Solventless system increases productivity as compared to conventional stirred tank reactor. Reaction time reduced by 80% yield increased from 83 to 94% Appropriate design of venturi loop reactor reduces chlorination batch time by a factor of 5-7 from 20 to 40 h required in a conventional stirred tank reactor. Highly efficient heat transfer in the external loop affords nearly isothermal operation at 45-50 °C, resulting in a high yield (more than 90%) of 2,4-dichloro phenol while suppressing formation of 2,6 dichloro phenol. Efficient removal of reaction by-product (hydrogen chloride) in the external gas circuit (Fig. 8.3) improves the yield Almost complete conversion of methanol in less than 1 h... 

In terms of kinetic behavior, the TF reactor may be viewed as identical to a batch reactor. The time t for reaction which was defined for a batch reactor is now expressed in terms of t (the residence time) and repre.sents the length of time necessary for any given increment of feed to travel the entire length of the reactor. 

In order to calculate the exit reactant concentration for a first-order irreversible reaction in a reactor of known RTD, one must find the reactant concentration in a fluid element of residence time t, i.e. in a batch reactor after time t, multiply it by the fraction of fluid elements of that residence time and sum (integrate) over all permissible residence times. This gives ... 

Fixing the rate of heat transfer in a batch reactor is often not the best way to control the reaction. The heating or cooling characteristics can be varied with time to suit the characteristics of the reaction. Because of the complexity of hatch operation and the fact that operation is usually small scale, it is rare for any attempt to be made... 

Reaction times can be as short as 10 minutes in a continuous flow reactor (1). In a typical batch cycle, the slurry is heated to the reaction temperature and held for up to 24 hours, although hold times can be less than an hour for many processes. After reaction is complete, the material is cooled, either by batch cooling or by pumping the product slurry through a double-pipe heat exchanger. Once the temperature is reduced below approximately 100°C, the slurry can be released through a pressure letdown system to ambient pressure. The product is then recovered by filtration (qv). A series of wash steps may be required to remove any salts that are formed as by-products. The clean filter cake is then dried in a tray or tunnel dryer or reslurried with water and spray dried. 

Batch reactors often are used to develop continuous processes because of their suitabiUty and convenient use in laboratory experimentation. Industrial practice generally favors processing continuously rather than in single batches, because overall investment and operating costs usually are less. Data obtained in batch reactors, except for very rapid reactions, can be well defined and used to predict performance of larger scale, continuous-flow reactors. Almost all batch reactors are well stirred thus, ideally, compositions are uniform throughout and residence times of all contained reactants are constant. 

Except in the laboratoiy, batch reactors are mostly liquid phase. In semibatch operation, a gas of limited solubility may be fed in gradually as it is used up. Batch reaclors are popular in practice because of their flexibility with respect to reaction time and to the lands and quantities of reactions that they can process. 

Daily Yield Say the downtime for filhng and emptying a reactor is and no reaction occurs during these periods. The reaction time of a first-order reaction, for instance, is given by = —In (1 — x). The daily yield with n batches per day will be... 

A factor in addition to the RTD and temperature distribution that affects the molecular weight distribution (MWD) is the nature of the chemical reaciion. If the period during which the molecule is growing is short compared with the residence time in the reactor, the MWD in a batch reactor is broader than in a CSTR. This situation holds for many free radical and ionic polymerization processes where the reaction intermediates are very short hved. In cases where the growth period is the same as the residence time in the reactor, the MWD is narrower in batch than in CSTR. Polymerizations that have no termination step—for instance, polycondensations—are of this type. This topic is treated by Denbigh (J. Applied Chem., 1, 227 [1951]). 

Batch Reactor In a batch reactor, the reactants are added to the reactor at the start of the reaction. The reactants are allowed to react in the reactor for a fixed time. No feed is added or product withdrawn during this time. The reaction products are removed at the end of the batch. 

The well-known difficulty with batch reactors is the uncertainty of the initial reaction conditions. The problem is to bring together reactants, catalyst and operating conditions of temperature and pressure so that at zero time everything is as desired. The initial reaction rate is usually the fastest and most error-laden. To overcome this, the traditional method was to calculate the rate for decreasingly smaller conversions and extrapolate it back to zero conversion. The significance of estimating initial rate was that without any products present, rate could be expressed as the function of reactants and temperature only. This then simplified the mathematical analysis of the rate fianction. 

The decomposition of nitrous oxide (NjO) to nitrogen and oxygen is preformed in a 5.0 1 batch reactor at a constant temperature of 1,015 K, beginning with pure NjO at several initial pressures. The reactor pressure P(t) is monitored, and the times (tj/2) required to achieve 50% conversion of N2O are noted in Table 3-19. Use these results to verify that the N2O decomposition reaction is second order and determine the value of k at T = 1,015 K. 

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