Semicontinuous processing

Phosgene addition is continued until all the phenoHc groups are converted to carbonate functionahties. Some hydrolysis of phosgene to sodium carbonate occurs incidentally. When the reaction is complete, the methylene chloride solution of polymer is washed first with acid to remove residual base and amine, then with water. To complete the process, the aqueous sodium chloride stream can be reclaimed in a chlor-alkah plant, ultimately regenerating phosgene. Many variations of this polycarbonate process have been patented, including use of many different types of catalysts, continuous or semicontinuous processes, methods which rely on formation of bischloroformate oligomers followed by polycondensation, etc. 

In the Bnchamp process, nitro compounds are reduced to amines in the presence of iron and an acid. This is the oldest commercial process for preparing amines, but in more recent years it has been largely replaced by catalytic hydrogenation. Nevertheless, the Bnchamp reduction is still used in the dyestuff industry for the production of small volume amines and for the manufacture of iron oxide pigments aniline is produced as a by-product. The Bnchamp reduction is generally mn as a batch process however, it can also be mn as a continuous (48) or semicontinuous process (49). 

Chisso-Asahi uses a spouted bed process for the production of their coated materials (12). A 12,000 t/yr faciHty is located in Japan. The semicontinuous process consists of two batch fluid-bed coaters. A dilute polymer solution is prepared by dissolving 5% polymer and release controlling agent into a chlorinated hydrocarbon solvent such as trichloroethylene. The solution is metered into the spouted bed where it is appHed to the fertilizer core. Hot air, used to fluidize the granules, evaporates the solvent which is recovered and reintroduced into the process. Mineral talc, when used, is either slurried into the polymer solution or introduced into the fluidizing air. 

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. 

Results of regression are given in Table 7.4-4. The cycle time is size-dependent whereby this dependency is stronger for the semicontinuous process at these particular process conditions. The exponent p is almost the. same for both processes and is approximately 1/3. Clearly, the physical properties of the reaction mixture and thermokinetic data are needed to evaluate processing times and cycle times at a large scale. 

BATCHES, Simulator for Batch/Semicontinuous Processes, Leaflet of Batch Process Technologies, West Lafayette, IN. 

McDonald, C.M. and Karimi, I.A. (1997) Planning and scheduling of parallel semicontinuous processes. 1. Production planning. Industrial el Engineering Chemistry Research, 36, 2691. 

CORPEX Technologies, Inc., offers CORPEX technology for the decontamination of undesirable and toxic ions or radionuclides from contaminated surfaces and coatings. The vendor states that the process can operate as either a batch or semicontinuous process. The commercially available CORPEX technology uses patented, innovative chelation chemicals to control and recover radioactive and other types of hazardous metal ions from soils, concrete, steel, and other materials. 

The fixed-bed operation is usually a semicontinuous process. When the medium gets spent, the fixed-bed operation is stopped and the material is replaced with a fresh batch. In fixed-bed operation, the determination of the medium being spent is usually based on the breakpoint, which is the point at which the exit concentration of the solutes being removed starts to increase sharply to some predetermined level (typically below 10%). If interruptions in the process to replace the adsorbent or the ion exchange media are not desirable, multiple fixed beds can be connected in parallel. While one set is in operation, the other is filled with a fresh medium or, after refilling, is on standby. 

Using alkoxides as precursors, carbon dioxide as tile drying agent, and a semicontinuous process the diying procedure became safer and faster. Introduction of organic aerogels. 

The Soxhlet extraction procedure is a semicontinuous process, which allows the buildup of the solvent in the extraction chamber for 5 to 20 min. The solvent surrounds the sample and is then siphoned back into the boiling flask (Fig. D 1.1.1). Multiextractor units are available for extraction of lipids from several different samples or replicate runs of the same material. The procedure provides a soaking effect and does not permit channeling. The fact that polar and bound lipids are not removed is a drawback to the procedure (see Background Information). 

Hoelderich and co-workers656,657 have applied various acidic resins loaded with Pt and Pd to perform direct hydroxy lation of benzene to produce phenol. Among various Nafion SAC catalysts (loadings between 8 and 80%), SAC-13 gave the best results. The highest phenol yield of 7.6% was found using a semicontinuous process over a pre-reduced catalyst (0.5 wt% Pd + 0.5 wt% Pt/SAC-13, 30-40°C, 1.3 Lh 1 H2 and 02 flow, and 1.4Lh-1 N2 flow, 1400 kPa, water-methanol solvent). 

The major problem in scale-up (Hussain, 2002 Leuenberger, 2002b) is that the formulation is optimized on a small-scale equipment, but is for obvious reasons no longer optimal for a large-scale equipment. A possible solution is the introduction of a semicontinuous process using a... 

Active pharmaceutical ingredients are most often manufactured in batch or semicontinuous process since most APIs are potent and normally used in relatively small amounts in each batch of drug product, especially during the early phase of drug product introduction. With the advent of many new APIs, the capital investment for continuous operation is not economically feasible. In a batch process, the product is often made from a well-identified, approved raw material supply, which is usually present at the start of the reaction. 

Pad Processes. In a continuous or semicontinuous processes, the fabric is first padded with the dye solution. The substantive adsorption of dyes during padding is avoided by employing minimum amounts of pad liquor at ambient temperatures. For even penetration of the dye, the material is then steamed without intermediate drying for 1-3 min in saturated steam (pad steam process ). Alternatively, it is heated to 80-85 °C and rolled up in a closed chamber where it is slowly rotated for 2-8 h (pad roll process). 

In the thermosol pad batch process, a semicontinuous process, alkali-sensitive disperse dyes can be used if the alkali is applied after the thermosol process. Conversely, if the thermosol process is carried out after the pad batch step, the pH must be lowered before the thermosol process so that the disperse dye is not destroyed. 

Ough and Amerine (8) at Davis showed that a good quality submerged flor could be produced rapidly in pressure vessels and recommended a semicontinuous process where part of the finished flor was removed periodically and replaced with new material. 

Maleate Surfmers were found to outperform methacrylic and crotonic compounds in the copolymerization of styrene, butyl acrylate and acrylic acid in seeded and nonseeded semicontinuous processes [17]. The maleate Surfmer achieved high conversion without homopolymerization in the aqueous phase which can result in emulsion instability. The methacrylate Surfmer was too reactive as opposed to the crotonate which was not sufficiently reactive. The reported dependence of the maleate Surfmer conversion on the particle diameter is consistent with a reaction at the particle surface. 

Emulsion polymerization reactors are made of stainless steel and are normally equipped with top-entry stirrers and ports for addition of reactants. Control of the reaction exotherm and particle size distribution of the polymer latex is achieved most readily by semibatch (also called semicontinuous) processes, in which some or all of the reactants are fed into the reactor during the course of the polymerization. Examples are given in Chapter 8. In vinyl acetate copolymerizations, a convenient monomer addition rate is such that keeps the vinyl acetate/water azeotrope retluxing. at about 70°C. 

From a practical viewpoint, a semicontinuous process may he used to increase the duration of Intervals II or III. Thus, for example, by extending the duration of an Interval III which displays a TronuDsdorfl gel effect with its concomitant rate acceleration, a shorter reaction time may he achieved. 

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