Labor-intensive batch processing

Biomolecules, fine chemicals, and pharmaceuticals are high-value products that are produced in modest quantities. They are usually seasonal products that are customer specific and have a short shelf fife. These characteristics usually place significant constraints in their productimi, such that it is not uncommon to see labor-intensive batch processes being used instead of the more efficient cmitinuous process. This usually leads to a significant waste generation during the scale-up from the laboratory to production scale. In additiOTi, the use of hazardous and... 

In any design consideration, there are trade-offs between capital and labor. A batch process is more labor intensive than a continuous processing plant for the same amount of chemical product. A continuous unit that is highly instrumented and computer-controlled is more capital intensive than one designed with a minimum amount of instrumentation. A plant designed... 

Processing cost Relative cost of equipment Relative cost of tools Labor intensity Batch size Cost of tools Capital cost Lifetime of tools (units) Proportion of material used Cost index (per unit) Production rate (units)... 

The third category, cake filters, although well developed in many wastewater treatment applications, are the least developed of the filtration equipment use by the Biotech Industry. In the organic synthesis laboratory sometimes very simple equipment like a funnel and filter paper is used to accomplish this operation. Some other operations used for this filtration step in the lab are more sophisticated, but many are very labor intensive and limit the capacity of the overall production process itself. As a result, there is a need for optimization of the cake filtration equipment used in biotechnology. Cake filtration equipment is available in batch and continuous modes. Following are several examples of cake filtration units ... 

For many years, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) methods have been used as an essential tool to determine the hydrodynamic size, monitor product purity, detect minor product or process-related impurities, and confirm batch-to-batch consistency of protein and antibody products. ITowever, gel-based techniques have several limitations, such as lack of automation, varying reproducibility, and a limited linear range. SDS-PAGE is also labor-intensive and generates large volume of toxic waste. Most importantly, the technique does not provide quantitative results for purity and impurity determination of proteins and antibodies. 

A few performance data of batch fluid dryers are in Table 9.14(a). This process is faster and much less labor-intensive than tray drying and has largely replaced tray drying in the pharmaceutical industry which deals with small production rates. Drying rates of 2-101b/(hr)(cuft) are reported in this table, with drying times of a fraction of an hour to several hours. In the continuous operations of Table 9.15, the residence times are at most a few minutes. 

The process is generally labor intensive and hard to control. The reproducibility is relatively poor with batch-to-batch difference. In addition, more care is needed in order to prevent contamination. 

Batch methods can be separated further into two general types, experiments that sacrifice the entire volume of an individual reactor and experiments that remove sample aliquots from a single larger reactor. Both types of experiment require that the material of interest be placed in a vessel and stirred continuously to ensure that the effect of transport processes is minimized. In the sacrificial method, at certain time during the course of an experiment, a small-volume reactor is sacrificed and used for analysis. This method eliminates the concentrating effect of removing sample aliquots however, it requires a matrix of experimental vessels to define the system. The aliquot method does restrict the number of samples able to be withdrawn from the system however, it is less labor intensive in terms of the experimental matrix and allows for easier alteration of system conditions. 

A thin-film electrode is relatively dense, as the metallic film does not have the electrocatalytic properties that a porous electrode has. Therefore, in many instances, the surface of the thin film is chemically or electrochemically modified to enhance its electrocatalytic activity. For instance, thin platinum film electrodes can be platinized electrochemically forming a porous platinum black layer. This platinum black layer is electrocatalytically more active than the thin platinum film. Thin-film processes are more capital and labor intensive and the process is more complicated than thick-film processes. Thin-film deposition is also a batch process which may produce sensors of limited numbers of silicon substrates. This is very desirable in prototype development, for it allows modification on prototypes with minimum cost. 

It is a continuous process versus a batch process for clay treating, therefore it is much less labor intensive. 

The melt mixers are either batch or continuous type. The formers require lower investment cost, but are more labor-intensive, have low output and poor batch-to-batch reproducibility. Recent developments in process control and automation eliminated some of these disadvantages [Utracki, 1991]. The continuous melt mixers comprise extruders, continuous shaft mixers and specialty machines — these will be discussed in the following part of this chapter. A brief overview of the melt mixing devices is given in Table 9.8. 

In the manufacture of color master batches, the current industry practice is to perform eritieal color measurements off-line. Typically, a sample of the pelletized color concentrate is diluted with natural resin at a standard ratio and milled, extruded or injection molded into a physieal form suitable for visual and instrumental evaluation. These methods are slow and labor intensive. Furthermore, they do not lend themselves well to statistical process eontrol strategies because of the time lag between production and testing. Since relatively few samples can be examined, laboratory measurements may not give a true indication of the consistency of the concentrate product over the entire manufacturing process. 

This type of manual control is simpler and less expensive, and less expertise is required than antomatic control systans. It can be applied to small plants (mainly batch systans) and on easy-to-dry-materials. However, mannal control is not recommended in the case of large drying processes and where good control is required to stabilize the process against any disturbances. It is also labor-intensive. 

Manufacture of gas-separation membrane modules is largely a machine-assisted, labor-intensive operation. Polymer dopes are typically prepared batchwise with sufficient hold time to insure uniformity. The membrane performance is largely controlled by the polymer precipitation step and very dependent upon phase behavior and precipitation kinetics. Thus, it is essential that processing conditions be maintained as uniformly and as constant as possible if product quality and uniformity is to be preserved. For this reason, membrane-fihn formation and hollow-fiber spinning processes are usually operated continuously or for extended run times. Since the intermediate film or fiber must eventually be converted into discrete items, the continuous process is typically interrupted by collection of the membrane formed on spools or fiber skeins where it may be inventoried briefly before batch processing into the final assembly resumes. 

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