Intermediate batches

Structural changes of the temporal superstructure can generate different operating modes (batch or semibatch). The reactants that are fed at the beginning of a batch are treated as feed streams at the start of the network, while the intermediate batch feeds, semicontinuous feeds and product takeoffs are represented as sidestreams feeding to, or withdrawing from, the network at different time intervals3. 

The construction required the production of 7.5 tons (6.8 tonnes) of each of the three Sulphlex binders. Scale-up to these quantities was required from laboratory batch size without benefit of investigating intermediate batch production. (Refer to (9) and (10) for discussion of Sulphlex manufacture in laboratory and pilot-scale batches.)... 

If the desired product is the first or an early intermediate, batch and plug-flow tubular reactors provide better selectivity than does a continuous stirred-tank reactor. 

The DFA process has two reaction stages separated by an intermediates batch distillation stage. In the first halex reaction, the chlorine atoms of DCNB are replaced with fluorine atoms by reaction with potassium fluoride in a solvent, dimethylacetamide (DMAC). This forms 2,4-difluoronitrobenzene (DFNB), with the reaction accelerated by a catalyst, tetramethylammonium-chloride (TMAC). The second reaction stage is the catalytic hydrogenation of the distilled DFNB in methanol to form DFA. The catalyst is removed by filtration and the solvent is recovered by distillation from the finished product. 

Introducing intermediate storage between batch steps. 

Whether parallel operations, larger or smaller items of equipment, and intermediate storage should be used can only be judged on the basis of economic tradeoffs. However, this is still not the complete picture as far as the batch process tradeoffs are concerned. So far the batch size has not been varied. Batch size can be varied as a function of cycle time. Overall, the variables are... 

Batch processes can be synthesized by first synthesizing a continuous process and then converting it to batch operation. A Gantt (time-event) diagram can be used to identify the scope for improved equipment utilization and the need for intermediate storage. 

Efficiency of Intermediate Formation. The variation of the efficiency of a primary intermediate with conversion of the feed hydrocarbon can be calculated (22). Ratios of the propagation rate constants ( 2 / i) reactor type (batch or plug-flow vs back-mixed) are important parameters. 

Eigure 2 shows that even materials which are rather resistant to oxidation ( 2/ 1 0.1) are consumed to a noticeable degree at high conversions. Also the use of plug-flow or batch reactors can offer a measurable improvement in efficiencies in comparison with back-mixed reactors. Intermediates that cooxidize about as readily as the feed hydrocarbon (eg, ketones with similar stmcture) can be produced in perhaps reasonable efficiencies but, except at very low conversions, are subject to considerable loss through oxidation. They may be suitable coproducts if they are also precursors to more oxidation-resistant desirable materials. Intermediates which oxidize relatively rapidly (/ 2 / i — 3-50 eg, alcohols and aldehydes) are difficult to produce in appreciable amounts, even in batch or plug-flow reactors. Indeed, for = 50, to isolate 90% or more of the intermediate made, the conversion must... 

Eig. 2. Efficiency to a primary intermediate as % of maximum (zero conversion) efficiency x axis is feed conversion. Parameters are oxidation rate-constant ratios ( 2 / i) for primary intermediate vs feed and reactor type A, plug-flow or batch B, back-mixed. 

The typical SEA process uses a manganese catalyst with a potassium promoter (for solubilization) in a batch reactor. A manganese catalyst increases the relative rate of attack on carbonyl intermediates. Low conversions are followed by recovery and recycle of complex intermediate streams. Acid recovery and purification involve extraction with caustic and heat treatment to further decrease small amounts of impurities (particularly carbonyls). The fatty acids are recovered by freeing with sulfuric acid and, hence, sodium sulfate is a by-product. 

Germany, Bitterfeld 1920 two-stage rotary kilns heated internally using intermediate grinding of roast oxidation completed within 3—4 h cylindrical monopolar ceUs, 4 m volume undivided con-centric Ni anodes, rod-shaped Fe cathodes unfiltered electrolyte batch operation KMnO crystallizes in ceU electrolysis energy consumption about 700 kWh/1 4,000 27,113... 

A hst of polyol producers is shown in Table 6. Each producer has a varied line of PPO and EOPO copolymers for polyurethane use. Polyols are usually produced in a semibatch mode in stainless steel autoclaves using basic catalysis. Autoclaves in use range from one gallon (3.785 L) size in research faciUties to 20,000 gallon (75.7 m ) commercial vessels. In semibatch operation, starter and catalyst are charged to the reactor and the water formed is removed under vacuum. Sometimes an intermediate is made and stored because a 30—100 dilution of starter with PO would require an extraordinary reactor to provide adequate stirring. PO and/or EO are added continuously until the desired OH No. is reached the reaction is stopped and the catalyst is removed. A uniform addition rate and temperature profile is required to keep unsaturation the same from batch to batch. The KOH catalyst can be removed by absorbent treatment (140), extraction into water (141), neutralization and/or crystallization of the salt (142—147), and ion exchange (148—150). 

Crystallization batches range from 30,000 to 60,000 Hters for each pan. Continuous centrifugals are typically used for second, third, and affination steps continuous vacuum pans are less common but are used in the U.S. for intermediate strikes. Most horizontal batch crystallizers have been replaced by continuous units, and all are designed for controlled cooling of the massecuite to maintain supersaturation. 

For the consecutive reactions A B C, a higher yield of intermediate B is obtained in batch reac tors or PFRs than in CSTRs. 

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]). 

For more complex equipment, the columns might contain measurements for internal distillatiou, batch-reactor intermediate conditions, or tubular-reactor between-bed conditions. Some of these... 

Understanding the behavior of all the chemicals involved in the process—raw materials, intermediates, products and by-products, is a key aspect to identifying and understanding the process safety issues relevant to a given process. The nature of the batch processes makes it more likely for the system to enter a state (pressure, temperature, and composition) where undesired reactions can take place. The opportunities for undesired chemical reactions also are far greater in batch reaction systems due to greater potential for contamination or errors in sequence of addition. This chapter presents issues, concerns, and provides potential solutions related to chemistry in batch reaction systems. 

The individuals and firm most familiar with the technology should review the intermediate and final procedures to assure both safety and commercial interests are satisfied. In many batch operations the procedure(s) can be a substantial portion of the process technology package. The procedures represent both a major safety system as well as a propriety technology. The pre-startup review should assure both PHA related and other changes proposed to the procedures have been approved and implemented. 

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