Semi-batch manner

Importance of mixing in flow reactors having biochemical reactions has been studied in the past (1.-4). The results of these studies, are however, not applicable to fermentation systems operated in batch or semi-batch manner and very few publications have addressed themselves to such systems (2 ). On the other hand, fermentations are most commonly carried out in batch or semi-batch systems in which the role of mixing towards performances at different scales of operations is not well understood. Possible reasons for this lack of interest have been a presumption of perfect mixing in non-flowing reactors and the... 

In many industrial applications BCR are operated in a semi-batch manner. Only the gas is in continuous flow while the liquid is batch. As shown by Chaudhari and Ramachandran [7], the reaction time needed for a desired conversion of B can be calculated easily if the assumption underlying models <11>, <12>, and <13> are fulfilled. The variation of B follows from... 

With semi-continuous (more properly, semi-batch) reactors only part of the charge is added at the beginning of the cycle. Usually some reaction time is allowed to pass before the remaining part of the charge is added in a controlled manner. Sometimes... 

Each group of experiments should be pre-planned. Perhaps multiple batch experiments, semi-batch or both can be conveniently used. The initial conditions for the batch runs and the steps of the semi-batch runs can be chosen randomly or in a judicious manner. The really important issue is that the mole ratios of any two reagents should never be held constant in a group this constitutes a co-linearity induced by the experimentalist. It can be noted that each perturbation in a semibatch experiment limits the future accessible region of composition space so planning is advisable. 

In addition to these three principal types of reactor, there is also the semi-batch reactor in which one reactant is added gradually to the others. This is a convenient manner of operation for some highly exothermic reactions since the temperature can be controlled by adjusting the rate of addition. 

For multiple reactions occurring in either a semi batch or batch reactor. Equation (9-21) can be generalized in the same manner as the steady-state energy balance, to give... 

Alkali refining is also carried out in a semi-continuous manner, the Zenith Process (Young, 1981). In this process small batches of oil are measured and treated with phosphoric acid in a pretreatment unit. From this unit the oil is pumped continuously via a centrifuge which removes dirt and denatured phosphatides to one of two neutralizer vessels which are used alternately. The oil enters the... 

The leaching operation is carried out fairly rapidly in a semi-continuous manner. The vessel is first filled with 2 per cent nitric acid and then further acid and coarsely ground reaction cake are added simultaneously over a period of time. The bottom valve is opened sufficiently to allow the salt solution to drain away at the same rate as fresh acid is added, so maintaining a constant liquor level in the vessel. The titanium metal remains behind on the filter until the conclusion of the run. It is then taken away as a slurry, via an exit pipe just above the filter level. The slurry is finally dewatered in a rubber-lined batch centrifuge and dried in air at a moderate temperature. 

Because the rotifer production decreases due to low water quality in batch cultures, the use of RAS to culture rotifers has been studied (Suantika et al, 2000). These culture systems allow for a higher rotifer density and higher reproduction rate. The rotifer culture can be maintained for a longer period (e.g. several weeks). As a consequence, hatcheries can run smaller scale systems and produce rotifers at a cheaper cost compared to batch cultures (Suantika et al, 2003). Most of the time, these culture systems are operated in a semi-continuous manner. As soon as the rotifer density surpasses a given density, part of the culture is harvested and part of the water is replaced (Suantika et al, 2003). 

An industrial batch reactor has neither an inflow nor an outflow of reactants or products while the reaction is being carried out. Batch reactions can be carried out in droplet microreactors, where nanoliters of fluid are individually manipulated using techniques such as electrowetting on dielectric (EWOD) and surface tension control. Semibatch reactors are used in cases where a by-product needs to be removed continuously and to carry out exothermic batch reactions where a reactant has to be added slowly. Microfluidics allows precise control of concentration and temperature, which allows batch and semi-batch reactions to be carried out in a continuous manner. Figure 1 shows the general components of a sin5)le industrial-reactor setup, compared with a laboratory-scale setup to carry out a reaction with microfluidic chips. 

After these estimates, it would be advisable to do bench scale experiments in a semi-batch reactor under well controlled conditions. One should measure the concentrations of the main product P and the byproduct X as functions of time, for various feed rates. From these data one may find the additional information require to predict more accurately the maximum feed rate that can be allowed to obtain a given selectivity. One will need a numerical solution of s. (3.25a) and (3.25b) now. One can also proceed in a purely empirical manner. Since Ais process is apparently not very sensitive to scale-dependent factors, the bench scale results may be applied with confidence on the commercial scale. 

Particle age or size distributions will depend very strongly on reaction procedures if semi-batch techniques are employed. Narrow-size-distribution latexes can be produced if the particle nucleation period is short and if the secondary feed is added in a manner that will not cause particle nucleation later in the cycle. Broader size distributions can be produced if the secondary feed is programmed to maintain a free emulsifier concentration for a longer period of time gr if secondary nucleation occurs later in the reaction cycle. 

Many important bioreactors are operated in a semi-continuous manner that is referred to as fed-batch operation, which is illustrated in Figure 2.13. A feed stream containing substrate is introduced to the fed-batch reactor continually. The mass flow rate is denoted by F and the substrate mass concentration by Sf, Because there is no exit stream, the volume V of the bioreactor contents increases during the batch. The advantage of fed-batch operation is that it allows the substrate... 

The example involves a hazardous reactant, VCM, which is flammable and has toxic combustion products, as well as being a known carcinogen. The process also illustrates a larger-scale batch operation that operates in a semi-continuous manner during an approximately 10-hour period while the polymerization progresses. A simplified description of the process steps is also provided. 

In some cases we may benefit from adopting a semi-continuous mode of operation, e.g. to a batch of one reactant we continuously feed the other reactant, while removing a volatile product continuously. An example where this is advantageous is the production of ethyl-4-pentenoate, CH2=(CH2)3(CO)OEt from allyl alcohol and triethyl orthoacetate, CHs-CfOEt). Continuous addition of allyl alcohol to a batch of triethyl orthoacetate and continuous removal of the produced ethylalcohol (and. some allyl alcohol) by distillation resulted in high yields of the dersired ester ethyl-4-pentenoate. By contrast, if allyl alcohol and triethyl orthoacetate were reacted in a batch-wise manner the product consisted of a 1 1 mixture of the desired ester and the undesired ester (Anderson, 2000, p 279 Bollyn and Wright, 1998). 

The patent described a method for the removal of thiophenic compounds from fossil fuels, in which the reacting media might contain organic solvents. Additionally, the biocatalyst may be contacted with the fuel directly either as free enzyme or in its immobilized form. The process could, therefore, be performed either in a batch reactor or in a semi-continuous or continuous manner. Further, it may be performed either as a stand... 

The apparent viscosity shows some dependence on shear rate the magnitude of which is a function of pH as shown in Figures 8 and 9 for batch and semicontinuous carboxylated latexes respectively. It is difficult to compare the viscosities of non-Newtonian fluids. One possible method for comparison is to take the apparent viscosity value at a certain shear rate for all samples In this work, the viscosity values at a shear rate of 215 (sec ) were taken to compare the behavior of the samples. The results of viscosity as a function of pH obtained in this manner are shown in Figure 10 for batch latexes, and in Figure 11 for semi-continuous latexes. 

Semi-continuous - relatively small batches of oil are collected and treated in the same manner. The oil flow from the plant is discontinuous. 

In some cases competitive growth experiments are used to study reaction kinetics. In such systems one must be able to predict relative growth, but the individual populations are usually easy to identify and track. When batch and/or semi-continuous reactors are operated in such a manner as to produce a broader PSD the kinetic analysis becomes more complex. Hence not much work has been reported for such systems. 

---