Batchwise operation

Batchwise operated multipurpose plants are per defmitionem the vehicle for the production of fine chemicals. There are, however, a few examples of fine chemicals produced ia dedicated, coatiauous plants. These can be advantageous if the raw materials or products are gaseous or Hquid rather than soHd, if the reaction is strongly exothermic or endothermic or otherwise hazardous, and if the requirement for the product warrants a continued capacity utilization. Some fine chemicals produced by continuous processes are methyl 4-chloroacetoacetate [32807-28-6] C H CIO [32807-28-6], and malononittile [109-77-3] C2H2N2, made by Lonza dimethyl acetonedicarboxylate [1830-54-2] made by Ube and L-2-chloropropionic acid [107-94-8] C2H C102, produced by Zeneca. 

A classification chart of diying equipment on the basis of heat transfer is shown in Fig. 12-45. This chart classifies diyers as direct or indirect, with subclasses of continuous or batchwise operation. 

In this section, a. selection of process equipment that seems to be the most promising and most versatile in batchwise operated MPPs will be briefly presented. 

Batchwise operating three-phase reactors are frequently used in the production of fine and specialty chemicals, such as ingredients in drags, perfumes and alimentary products. Large-scale chemical industry, on the other hand, is often used with continuous reactors. As we developed a parallel screening system for catalytic three-phase processes, the first decision concerned the operation mode batchwise or continuous. We decided for a continuous reactor system. Batchwise operated parallel sluny reactors are conunercially available, but it is in many cases difficult to reveal catalyst deactivation from batch experiments. In addition, investigation of the effect of catalyst particle size on the overall activity and product distribution is easier in a continuous device. 

Superheated Liquid-Film-Type Catalysis in Batchwise Operation.443... 

Experimental apparatus for catalytic dehydrogenation under reactive distillation conditions in batchwise operation. (a) Batchwise apparatus and (b) liquid-phase dehydrogenation under reactive distillation conditions. 

The catalyst consumption for sulfuric acid alkylation is expressed in terms of pounds of fresh acid depleted per barrel of alkylate produced. When alkylating isobutane with butenes at 50° F. and maintaining an isobutane-olefin ratio of 5 to 1, the acid consumption will average 35 to 40 pounds per barrel when charging 98% acid and discarding 88% acid in a batchwise operation. 

The term solid-wall or monobloc vessel is applied to all components where the cylindrical wall consists of a single layer. Solid-wall vessels are suitable for all types of pressure vessels, in particular for those operated under high temperatures. Thermal stresses arising during heating or cooling are smaller than in multilayer vessels because of the good thermal conduction across the wall. Therefore solid-wall vessels are especially suitable for batchwise operation. 

Disadvantages of high pressure crystallization are high volumes of solvents, owing to the low solubility of the substances to be crystallized, relatively high pressures, batchwise operation, and long cooling times. 

Another kind of classification which cuts across the homogeneous-heterogeneous division is the mode of operation—batchwise or continuous. Batchwise operation, shown in Fig. 1.1a, is familiar to anybody who has carried out small-scale preparative reactions in the laboratory. There are many situations, however,... 

Different criteria have been introduced in the past decades to individuate runaway boundaries in batchwise operated reactors. Most of them can be used to ensure a safe batch operation only when the reaction kinetics is fully known and the hypothesis of perfect mixing is satisfied. These criteria also strongly depend on the mode of operation with respect to heat exchange. Excluding isothermal conditions, the following modes of operation can be considered ... 

The design of an electrolytic cell for batchwise operation in the laboratory normally does not present any problems. Many different types of cells of more or... 

Due to their thermal instability fine chemicals often must be produced in the liquid phase at moderate temperatures. They are generally complex and multifunctional as well as chemo-, regio- and stereoselectivity play an important role. The reactor system of the choice are batch or semi batchwise operated multipurpose units. Bulk chemicals, mostly consisting of relatively small, thermostable molecules, can be produced in continuously operated fixed bed or fluidised bed reactors in the gas-phase allowing much higher space time yields, thus minimising investment costs1. These procedures can hardly be applied to the synthesis of e.g. fine and intermediate chemicals because of the relatively small... 

Adi eggs or blow cases are simply closed vessels with inlet and outlet lines and an air connection. Air is admitted to the vessel and forces the liquid out through the discharge line. Operation of acid eggs is intermittent, and the elevation attained depends on the air pressure. Although these systems are inexpensive and easy to operate, they are inefficient. Their use is limited primarily to batchwise operations with corrosive fluids. 

For the processing of furfural in general, and for the control of furfural reactors in particular, it is desirable to have a continuous in-line measurement of the furfural concentration. For batchwise operation, this shows when the charge is exhausted, and for both batchwise and continuous operation it can show the response of the furfural concentration to the steam input, thus permitting an optimization of the furfural output. This is especially important for the ROSENLEW process, where an excess steam input blows out the acetic acid catalyst, so that there is a critical steam input beyond which the furfural output diminishes sharply. In addition, it is profitable to have a continuous record of the reactor operation, to pinpoint mistakes by the operators or other irregularities. 

The total volume of this cell is about 4 m3, the electrode system is monopolar, and the operation mode is batchwise. The resulting KMnC>4 is allowed to crystallize within the cell and is drawn off periodically. As unfiltered electrolyte can be used in batchwise operated cells, the crude product must be recrystallized to free it from gangue. 

One more advantage is that the system allows for simple batchwise operation controlled separately from the ash-melting furnace. Figure 6 shows the increase of temperature inside the pyrolysis furnace as it proceeds from the shut-down state to a steady state, as determined through experimentation in the test plant. As the figure shows, the pyrolysis furnace, after having been shut down for about 10 hours, proceeds to a steady state in approx. 30 minutes after the supply of air for combustion is resumed the refuse in the furnace is brought to the shut-down state in about one hour. 

As small a diameter as possible to save material and construction costs, especially for pipelines with short, batchwise operation and pipelines constructed of expensive materials. 

In a continuously operated production plant batchwise operation is a drawback. Principally speaking, the separation of a binary mixture with the components a and b can be carried out in a true moving bed (Seidel-Morgenstem et al. 2008). In Fig. 9.8-8 the principle of a countercurrent chromatography column is illustrated. The solid phase is moving downward whereas the mobile fluid phase is introduced at the bottom of the column. The feed of the components a and b is separated with the result that a raffinate containing a less adsorbable component a and an extract with the strong adsorbable component b are withdrawn as side streams. Therefore, the total column is subdivided into four zones ... 

More elaborate multiple extractors based on a countercurrent principle have been developed that are capable of giving very efficient separations in favorable circumstances. For separating amounts greater than about 40 g, a counterdoublecurrent apparatus is preferable. With this apparatus, continuous rather than batchwise operation is possible, if a solvent system can be found such that the distribution coefficient of the desired substance is on one side of unity and those of all impurities are on the other side. Due to the cost of the apparatus (about 8000), the limited quantity of material that can be used (a maximum of about 40 g of substrate), the time necessary to find a suitable solvent system, and the problems associated with running and cleaning the apparatus, countercurrent extractors are usually employed as a last resort, i.e., after distillation, recrystallization, simple extraction, and liquid chromatography have failed to effect a satisfactory separation. 

The above-shown relationships correspond to those obtained in batchwise operated reactors by replacing the residence time with the reaction time in the vessel. 

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