Batch-process

Batch processing appears as one of the simplest ways to use chromatography. This process uses one column and operates in a succession of injections (at the inlet of the column) and collections (at the outlet of the column). The eluent consumption is the ratio of the volume of eluent used divided by the amount of product purified. Reduction of the eluent consumption can be achieved by, for example, increasing the injected amount or reducing the cycle time [12]. 

In a batch process, the main steps operate discontinuously. In contrast with a continuous process, a batch process does not deliver its product continuously but in discrete amounts. This means that 

The step with the longest time limits the cycle time. Alternatively, if more than one step is carried out in the same equipment, the cycle time is limited by the longest series of steps in the same equipment. The batch cycle time must be at least as long as the longest step. The rest of the equipment other than the limiting step is then idle for some fraction of the batch cycle. 

Given the choice of a batch rather than continuous process, does this need a different approach to the synthesis of the reaction and separation and recycle system In fact, a different approach is not needed. We start by assuming the process to be continuous and then, if choosing to use batch operation, replace continuous steps by batch steps. It is simpler to start with continuous process operation 

Example 4.4 Butadiene sulfone (or 3-sulfolene) is an intermediate used for the production of solvents. It can be produced from butadiene and sulfur dioxide according to the reaction  

This is an exothermic, reversible, homogeneous reaction taking place in a single liquid phase. The liquid butadiene feed contains 0.5 percent normal butane as an impurity. The sulfur dioxide is essentially pure. The mole ratio of sulfur dioxide to butadiene must be kept above 1 to prevent unwanted polymerization reactions. A value of 1.2 is assumed. The temperature in the process must be kept above 65°C to prevent crystallization of the butadiene sulfone but below lOO C to prevent its decomposition. The product must contain less than 0.5 wt% butadiene and less thM 0.3 wt% sulfur dioxide. 

Flow-sheets drawn up for batch processes normally show the quantities required to produce one batch. If a batch process forms part of an otherwise continuous process, it can be shown on the same flow-sheet, providing a clear break is made when tabulating the data between the continuous and batch sections the change from kg/h to kg/batch. A continuous process may include batch make-up of minor reagents, such as the catalyst for a polymerisation process. 

As pointed out in Chapter 1, in a batch process the main steps operate discontinuously. This means that temperature, concentration, mass and other properties vary with time. Also as pointed out in Chapter 1, most batch processes are made up of a series of batch and semicontinuous steps. A semicontinuous step operates continuously with periodic start-ups and shutdowns. 

As noted in Chapter 1, the priorities in batch processes are often quite different from those in large-scale continuous processes. Particularly when manufacturing specialty chemicals, the shortest time possible to get a new product to market is often the biggest priority (accepting that the product must meet the specifications and regulations demanded and the process must meet the required safety and environmental standards). This is particularly true if the product is protected by patent. The period over which the product is protected by patent must be exploited to its full. This means that product development, testing, pilot plant work, process design and construction should be fast tracked and carried out as much as possible in parallel. 

Before a system of batch reaction and separation processes is considered, the main operations that will be used in batch processes need to be reviewed, but with the emphasis on how they will differ from the corresponding operations in continuous processes. 

To ensure the production of PA with uniform and stable quality, it is important to maintain the preset mole balance and the preset polymerization conditions. Various methods have been employed to maintain the target values of mole balance, polymerization time, polymerization temperature. 

In batch polymerization methods, diamine may escape out of the reaction system. The amount escaped may vary from batch to batch in an unforeseeable manner. Thus, the mole balance must be adjusted on the fly. Various methods to control the mole balance are available, including 

In titration analysis a sample must be withdrawn from the reactor, solidified, dissolved in a specific solvent, and subjected to neutralization titration. This method is a time-consuming process. The viscosimetry relates the melt viscosity to the polymerization degree. However, the method is not directly sensitive to the mole balance. IR spectroscopy is quite suitable for non-destructive analysis and real time analysis. In addition, production methods of poIy(ester)s have been reported, where the properties of the poly(ester)s are measured using a IR spectroscopy. The reaction conditions are adjusted according to the measured values. Instead of TPA, dimethyl terephthalate can be used as a monomer.  

All of the reactants are added to the reactor prior to starting the polymerization. No material is added to or removed from the reactor during operation. When the polymerization is complete, the contents are discharged and the reactor prepared for 

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The recycling of material is an essential feature of most chemical processes. Therefore, it is necessary to consider the main factors which dictate the recycle structure of a process. We shall start by considering the function of process recycles and restrict consideration to continuous processes. Later the scope will be extended to include batch processes. 

Figure 4.11 A Gantt or time-event chart of the batch process.

Example 4.5 Given that a low rate of production is required, convert the continuous process from Example 4.4 into a batch process. Preliminary sizing of the equipment indicates that the duration of the processing steps are given in Table 4.7. ... 

Figure 4.16 Final flowsheet for the production of butadiene sulfone in a batch process.

Batch processes can be synthesized by first synthesizing a continuous process and then converting it to batch operation. The process yield is an important measure of both raw materials efficiency and environmental impact. 

Myriantheos, C. M., Flexihility Targets for Batch Process Design, M.S. thesis. University of Massachusetts, Amherst, 1986. 

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... 

In batch process optimization, one of the principal objectives is to improve equipment utilization through reduction in dead time. This requires both structural and parameter optimization, with many options available. 

Consider changing from batch to continuous operation. Batch processes, by their very nature, are always at unsteady state and thus are difficult to maintain at optimal conditions. 

On a land site where space and weight are not normally constraints, advantage can be taken of tank type separation equipment such as wash tanks and settling tanks, and batch processing methods. Such equipment is generally cheaper to maintain than continuous throughput vessels, though a combination of both may be required. 

Alternatively, the user can construct ASCII input files manually. The file format includes many numerical flags to control the type of calculation. The researcher should plan on investing some time in learning to use the program in this way. Jaguar can be executed from the command line, making it possible to use batch processing or job queue systems. 

Bechamp batch process Bechamp reaction Beck and Guthke cell Becke line technique... 

Using inorganic salts as precursors, alcohol as the supercritical drying agent, and a batch process a solvent-exchange step was necessary to remove water from the gel. 

Higher alkyl acrylates and alkyl-functional esters are important in copolymer products, in conventional emulsion appHcations for coatings and adhesives, and as reactants in radiation-cured coatings and inks. In general, they are produced in direct or transesterification batch processes (17,101,102) because of their relatively low volume. 

The above batch process has undergone numerous refinements to improve yields, processing characteristics, purity, and storage stabiUty, but it remains the standard method of manufacture for these products. Recentiy a continuous process has been reported by Bayer AG (6) wherein the condensation is carried out in an extmder. The by-products are removed in a degassing zone, and the molten polymer, mixed with stabilizers, is subsequendy cracked to yield raw monomer. 

Compositional control ia suspension systems can be achieved with a corrected batch process. A suspension process has been described where styrene monomer is continuously added until 75—85% conversion, and then the excess acrylonittile monomer is removed by stripping with an iaert gas... 

Industrial-scale adsorption processes can be classified as batch or continuous (53,54). In a batch process, the adsorbent bed is saturated and regenerated in a cychc operation. In a continuous process, a countercurrent staged contact between the adsorbent and the feed and desorbent is estabhshed by either a tme or a simulated recirculation of the adsorbent. 

There are three types of TAP emissions continuous, intermittent, and accidental. Both routine emissions associated with a batch process or a continuous process that is operated only occasionally can be intermittent sources. A dramatic example of an accidental emission was the release of methyl isocyanate [624-83-9] in Bhopal, India. As a result of this accident, the U.S. Congress created Tide III, a free-standing statute included in the Superfund Amendments and Reauthorization Act (SARA) of 1986. Title III provides a mechanism by which the pubHc can be informed of the existence, quantities, and releases of toxic substances, and requires the states to develop plans to respond to accidental releases of these substances. Eurther, it requires anyone releasing specific toxic chemicals above a certain threshold amount to aimuaHy submit a toxic chemical release form to EPA. At present, there are 308 specific chemicals subject to Title III regulation (37). 

Pentaerythritol may be nitrated by a batch process at 15.25°C using concentrated nitric acid in a stainless steel vessel equipped with an agitator and cooling coils to keep the reaction temperature at 15—25°C. The PETN is precipitated in a jacketed diluter by adding sufficient water to the solution to reduce the acid concentration to about 30%. The crystals are vacuum filtered and washed with water followed by washes with water containing a small amount of sodium carbonate and then cold water. The water-wet PETN is dissolved in acetone containing a small amount of sodium carbonate at 50°C and reprecipitated with water the yield is about 95%. Impurities include pentaerythritol trinitrate, dipentaerythritol hexanitrate, and tripentaerythritol acetonitrate. Pentaerythritol tetranitrate is shipped wet in water—alcohol in packing similar to that used for primary explosives. 

In the batch process which finds occasional use, the steps used in the successive nitrations are similar and include acid mixing, addition of the oil, digesting (cooking) the reaction to completion, cooling and settling the mix, and separating the oil from the acid. The nitrators are made of stainless steel... 

Continuous Solvent—Extrusion Process. A schematic for a typical continuous process, widely used for making solvent propellant for cannons, is shown in Figure 7. This continuous process produces ca 1100 metric tons of single-base propellant per month at the U.S. Army Ammunition Plant (Radford, Virginia). Continuous processes have also been developed for double- and triple-base propellants and for stick as well as granular geometries. A principal aspect of these processes has been the extensive use of single- and double-screw extmders instead of the presses used in the batch process. 

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