Feeding time

In the most common production method, the semibatch process, about 10% of the preemulsified monomer is added to the deionised water in the reactor. A shot of initiator is added to the reactor to create the seed. Some manufacturers use master batches of seed to avoid variation in this step. Having set the number of particles in the pot, the remaining monomer and, in some cases, additional initiator are added over time. Typical feed times ate 1—4 h. Lengthening the feeds tempers heat generation and provides for uniform comonomer sequence distributions (67). Sometimes skewed monomer feeds are used to offset differences in monomer reactivity ratios. In some cases a second monomer charge is made to produce core—shell latices. At the end of the process pH adjustments are often made. The product is then pumped to a prefilter tank, filtered, and pumped to a post-filter tank where additional processing can occur. When the feed rate of monomer during semibatch production is very low, the reactor is said to be monomer starved. Under these... 

In Figure 8.6, the results for the referenee eonditions (Rushton turbine, 40-min feed time, feed point position elose to the impeller, total eoneentration 0.008 M) for ealeium oxalate eonfirm this observation. 

Figure 8.7 Mean particle size versus specific energy input for different feed point positions if.p.p.) (CaOx, Rushton turbine, 40 min feed time, total concentration 0.008 M.) After Zauner and Jones, 2000b)...

Fig. 6 shows a fed batch fermentation of sweet sorghum juice (SSJ) by Bacillus aryabhattai in 3 L fermentor under cultivating condition with agitation rate at 200 rpm, air rate of 1.5 1/min, at 30° C and feeding time at 18 and 24 hr during log phase of the culture. It was found that the cell could continuously produce both biomass and PHAs. Maximum cells were obtained at about 14.20 g/1 at 54 hr when PHAs content reached 4.84 g/1 after 66 hr (Tanamool et al., 2011). In addition, in Table 2, fed batch fermentation by A, latus was used for the production of PHAs (Yamane et al, 1996 Wang Lee, 1997). It could yield high productivity with the use of cheap carbon sources. 

Clearly, the oxidation reaction could not have been implemented in a pure batch operating reactor. Indeed, heat removal capacity would not have been sufficient (100—1200 kW m removed versus 20 x 10 kW m generated). As a consequence, a semibatch mode is necessarily required. Besides, Table 12.10 shows that the feeding times are much higher than the residence time of the Shimtec reactor (around 15 s). 

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 ... 

Run Amount of reactants Feed time Batch Temperature Feed-rate... 

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. 

For sufficiently slow addition (t/ > tmt) the selectivity becomes independent on the feed time. The position of the asymptote depends on whether the reaction is controlled by mixing on the molecular scale or by chemical reaction it is higher for the former case. 

The critical feed time t it depends on the location and number of feed pipes, stirrer type, and mixing intensity, and increases with increasing reactor volume. When a constant power-to-volume ratio is preserved, ta-u is proportional to and where D., is the stirrer diameter and Vr the reactor volume (Bourne and Hilber, 1990 Bourne and Thoma, 1991). The productivity of the reactor expressed as the amount of product formed per unit time becomes almost independent of reactor volume. The reason is that the reaction goes to completion in the zone nearby the stirrer tip. The size of this zone increases independently of the tank size it only depends on the velocity of the liquid being injected, the location of the nozzle, and the stirrer geometry and speed of rotation. Accordingly, for rapid reactions, the feed time will also be the reaction time. 

If the feed time of a concentrated fluid is short the reaction will often be completed within the circulation zone, outside the impeller zone. Macromixing can then be important and the blend time will be an important scale-up parameter. For long feeding times and low concentrations in the feed all the important mixing processes could be completed almost immediately in the vicinity of the outlet of the feed pipe. 

Weanling female rats exposed to 250 ppm lead acetate in the water for 10 days exhibited an approximately 19% decrease in body weight gain during the exposure period (Minnema and Hammond 1994). This concentration of lead in the water provided an estimated dose of 17.5 mg lead/kg/day and doubled the blood ZPP levels in the treated rats. As indicated below, the reduced growth was due to a decrease in food intake, which in turn was due to a reduction in feeding time. 

The BioView sensor includes a software package (CAMO ASA, Norway) for data analysis and on-Une estimation of different bioprocess variables simultaneously. Thus, the instrument is able to predict the trends of the concentration courses of different variables during a cultivation and is used to give information about important process steps (e.g., feeding time, harvesting time, etc.). The instrument is able to monitor on-line several fluorophores in situ and non-invasively during cultivation processes and permits an estimation of different bioprocess variables simultaneously. The increasing of cell mass concentration and the product formation as well as the actual metabolic state of the cells is simultaneously detectable by this fluorescence technique. 

The discovery of peripheral oscillators in mammals has raised the question of how the SCN master pacemaker synchronizes these subsidiary clocks. Current evidence suggests that feeding time is the dominant eitgeber for most peripheral oscillators. The molecular mechanisms involved in food-dependent phase resetting are not yet understood, and deciphering the signalHng pathways involved will probably require many additional years of intense genetic and biochemical research. 

Only the high-dose group had consistently altered activity schedules, including decreases in amount of time spent in alert behaviors and in the water. Overall feeding time was increased, but did not result in an increase in the amount of food consumed (13)... 

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