Semicontinuous Systems

Although the purification techniques used with the semicontinuous system are similar to that for the batch system, much less wastewater is produced because much less acid is retained on the nitrocellulose that is discharged from the centrifuge (135—137). 

Surface aeration is usually employed for slow reactions or for batch processes. It can be used in semicontinuous systems when it is desirable to recirculate the gas from the headspace. This is frequently the case in hydrogenation and is referred to as dead-end hydrogenation. In this system, gas is fed continuously to the reactor at the rate at which hydrogen is being consumed no compression costs to overcome the static head of liquid or external recirculation is needed. Feeding gas from the headspace may be preferred when there is a possibility of plugging sparger holes with reaction products. Surface aerators are also extensively used for waste-water treatment. There are two types of surface aerators the brush aerator, and the most commonly used turbine aerator. 

Semicontinuous emulsion polymerizations are characterized by the continued addition of monomer to the reaction vessel. This permits the production of latexes with high weight percentage solids while allowing the initial burst of nucleation to be achieved in substantially aqueous surroundings. The theory for semicontinuous systems is substantially that set forth for Interval III of batch polymerizations, except that the materials balance equations [Eq. (17)] must be modified to include the flow of new material into the reactor. The effect of the monomer input is twofold first, the mass of material present in the system is increased and seccmd, the concentration of other reagents may be reduced. 

Semicontinuous systems operate on the basis of handling finite batches of oil in a timed sequence of deaeration, heating, holding-steam stripping, and cooling so that all of the oil is completely subjected to each condition before proceeding to the next... 

At the solvent extraction plant, the cake (pomace) containing up to 8% residual oil is dried in a rotary kiln before proceeding to the solvent extraction unit, usually a semicontinuous system (Figure 7). The extracted pomace oil is always refined. Spent cake is used as fuel or is separated into two fractions, the pulp (including skin) and the pit. In addition to use as fuel, the pit is occasionally used to produce fiberboard (23). 

Okaya T, Tanaka T, Yuki K (1993) Study on Physical Properties of Poly (vinyl acetate) Emulsion Films Obtained in Batchwise and in Semicontinuous Systems. J. Appl. Polym. Sci. 50 745. 

Static, semicontinuous systems are used for the manufacture of semifinished parts and components. The complexity of a system is influenced by the maximum process temperatures, the process pressures, as well as the variation possibilities during... 

FIGURE 1.216 Mold example for a semicontinuous system (intermittent compression molding)... 

Profiles can be manufactured with static pressing units (autoclave, upper ram press) as well as with semicontinuous or continuous units. Semicontinuous systems, like intermittent compression molding, enable the manufacture of continuous profiles. A distinction has to be made if the profile is open or closed. Open continuous profiles like U-, and triple V-profiles, can be manufactured with simple molds whereas the manufacture of closed profiles (e.g., double 1-profile or rectangular hollow profile) can only be realized with an increased mold complexity. Figure 1.218 illustrates a profile mold for the manufacture of open double-V profiles. This mold consists of... 

Results for the static mixer in both laboratory scale 0.008 m (0.8 cm) and plant scale 0.0254 m (2.54 cm) operation were excellent. No change in selectivity or product distribution occurred over this scale-up. When there are compelling reasons to use a semibatch reactor instead of a semicontinuous system, the reactor... 

The two procedures primarily used for continuous nitration are the semicontinuous method developed by Bofors-Nobel Chematur of Sweden and the continuous method of Hercules Powder Co. in the United States. The latter process, which uses a multiple cascade system for nitration and a continuous wringing operation, increases safety, reduces the personnel involved, provides a substantial reduction in pollutants, and increases the uniformity of the product. The cellulose is automatically and continuously fed into the first of a series of pots at a controlled rate. It falls into the slurry of acid and nitrocellulose and is submerged immediately by a turbine-type agitator. The acid is deflvered to the pots from tanks at a rate controlled by appropriate instmmentation based on the desired acid to cellulose ratio. The slurry flows successively by gravity from the first to the last of the nitration vessels through under- and overflow weirs to ensure adequate retention time during nitration. The overflow from the last pot is fully nitrated cellulose. 

Hydrothermal Synthesis Systems. Of the unit operations depicted in Figure 1, the pressurized sections from reactor inlet to pressure letdown ate key to hydrothermal process design. In consideration of scale-up of a hydrothermal process for high performance materials, several criteria must be considered. First, the mode of operation, which can be either continuous, semicontinuous, or batch, must be determined. Factors to consider ate the operating conditions, the manufacturing demand, the composition of the product mix (single or multiple products), the amount of waste that can be tolerated, and the materials of constmction requirements. Criteria for the selection of hydrothermal reactor design maybe summarized as... 

Ton-exchange systems in process appHcations may be batch, semicontinuous, or continuous. Batch operations are not common but, where used, involve a ketde with mechanical agitation. Injecting with air or an inert gas is an alternative. A screened siphon or drain valve is requited to prevent resin from leaving with the product stream. 

Semicontinuous and continuous systems are, with few exceptions, practiced in columns. Most columnar systems are semicontinuous since flow of the stream being processed must be intermpted for regeneration. Columnar installations almost always involve the process stream flowing down through a resin bed. Those that are upflow use a flow rate that either partially fluidizes the bed, or forms a packed bed against an upper porous barrier or distributor for process streams. 

In practice there are two major classifications of cost accounting systems, job costing and process costing. In the former, costs are col-lec ted for each job or batch irrespective of the accounting period. This system is normally used in construction work. Process costing is normally used in continuous and semicontinuous processes. Costs are collected for a specific accounting period. 

Fixed-bed adsorbers may be operated in either intermittent or semicon-tinuous mode. A typical removal system is a semicontinuously operated dnal-bed system one bed is in adsorption mode while the other is being re generated (Fig. 13.23). " The adsorption performance of the bed can he monitored by analyzing the outlet gas. Once organic vapors are detected in the gas stream, the incoming gas stream is routed to the parallel adsorber, and the exhausted bed is regenerated. The adsorption and desorption cycles can also be fixed. 

Effects of starvation feeding in semicontinuous or continuous polymerization systems. 

The quantity of volatile monomer present could be limited by using smaller volume continuous reactors, or using a semicontinuous monomer feed. Small quantities of monomers present would quickly be consumed by an uncontrolled reaction, and with the system deprived of further reactants pressure rise would be limited. 

In a batch reactor, the first two terms in equation 12.2-1 are absent. In a semibatch reactor, one of these two terms is usually absent. In a semicontinuous reactor for a multiphase system, both flow terms may be absent for one phase and present for another. In a continuous reactor, the two terms are required to account for the continuous inflow to and outflow from the reactor, whether the system is single-phase or multiphase. 

Semiconductor surfaces, 9 730-731 Semiconductor technology, 19 127 Semiconductor transport, 22 237-239 Semiconductor-vacuum interface, 22 241 Semicontinuous deodorizer, 10 815 Semicontinuous dyeing, 9 211-213 Semicontinuous ion-exchange systems, 14 403... 

In the last decade, for many toxicologists the on-line literature search has changed from an occasional, sporadic activity to a semicontinuous need. Usually, nontoxicology-related search capabilities are already in place in many companies. Therefore, all that is needed is to expand the information source to include some of the data bases that cover the types of toxicology information one desires. However, if no capabilities exist within an organization, one can approach a university, consultant, or a private contract laboratory and utilize their on-line system at a reasonable rate. It is even possible to access most of these sources from home using a personal computer. The major available on-line data bases are described in the following. 

The fluorous solvent alone had a minimal effect on the outcome of the reaction. However, with the fluorinated ligand, the rr.iso ratio was found to increase with increasing phosphine concentration, reaching a value of almost 8 1 at a phosphine to rhodium ratio of 103 1. The beauty of this system was demonstrated by its use in a semicontinuous hydroformylation experiment. After each... 

Rice suspension culture Alpha) 1 (-antitrypsin rAAT Trexler et al., 2005, Huang et al., 2001 3-12 mg/day, 200 mg/L Cyclical, semicontinuous culti system... 

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