Productivity filtration process equipment

The performance of many process equipment encountered in crystallization practice is often profoundly affected by the flow properties of the liquid media. Heat transfer, for example, may be severely impeded in thick sluggish liquors or magmas crystallization may occur only with difficulty, and filtration and washing of crystalline product may be impaired (Mullin, 1961). Since viscosity is a function of temperature the viscosity at the average temperature of crystallization is considered. The viscosity of the solvent can be estimated using the following group contribution model (ICAS, 2003)... 

Final product isolation in a form suitable for further processing into the final dose form of the pharmaceutical, e.g., as a tablet or an injectable solution. Secondary production of this type is sometimes done in a separate facility, with the raw material referred to as the bulk product or, more recently, the active pharmaceutical ingredient. Examples of unit operations at this stage of processing include lyophilization, precipitation, or crystallization followed by solid isolation using filtration and drying techniques. In some cases, the final product must be produced in a sterile form, which introduces additional complications when selecting suitable process equipment. 

It is evident that attention paid in the laboratory to the factors affecting particle size distribution will save on capital investments made for separation equipment and downstream process equipment. Specific cake resistance (a) can be determined in the laboratory over the life of a batch, to evaluate if time in the vessel and surrounding piping system is degrading the product s particle size to the point it impedes filtration, washing and subsequent drying. 

Fines Destruction. In the operation of industrial crystallizers, one would usually want to avoid the fines (i.e., small crystals) since they may cause difficulties in downstream processing equipment (e.g., filtration) and affect both product quality and process economics. Excessive fines may also require a relatively long batch run time to achieve the desired final size of the product crystals. Karpinski (1981) proposed a controlled dissolution of secondary nuclei in order to improve CSD from fluidized bed crystallizers. Jones et al. (1984) first described the application of fines destruction in batch crystallization of potassium sulfate solutions. Their study demonstrated the experimental feasibility of this technology to dramatically reduce the amount of fines in the final product CSD. Their theoretical predictions, obtained from population balance models, agreed with the experimental results. 

It may be difficult to choose the right filtration equipment for a crystallization process. The selection of filtration equipment involves balancing the process specihcations and objectives with the capabilities and characteristics of the various equipment alternatives. Wakeman and Tarleton [49] provide guidelines for the selection of hltration equipment. Important process-related factors are the slurry character, production throughput, process conditions, performance requirements. 

The liquid product formulation process is usually integrated with the downstream production process. After the enzyme has been concentrated, the enzyme stabilizers are added followed by a filtration process. The filtration is done to remove any undissolved solids and/or to reduce the level of microbial burden in the formulated product. The filtration process can be done using standard filtration equipment such as an RVDF, plate and Ifame, or depth filtration. The resulting products are transparent and commonly range Ifom clear to amber in color. 

To reduce risks of microbial contamination, aseptic processing is executed in a controlled environment, in which the air supply, facility, materials, equipment and personnel are regulated to control microbial and particulate contamination to acceptable levels [3]. Contact between product and environment should be minimised, sterile equipment should be used, and there should be two consecutive filtration processes through sterile 0.2 pm filters. The first filter will minimise the microbial challenge to the second filter, which should be just before the sterile final container. The shelf-life of the product is often restricted and it may be stored in the refrigerator to further reduce the risks of microbial growth. 

Heterogeneous catalyst residues can be removed from the product by filtration or centrifugation. This step can be bypassed if the catalyst is sufficiently active that its presence in the final product is of no consequence. Problems associated with an excess of catalyst in the product can include a green off-color caused by chromium salts and abrasive wear of processing equipment by alumina or silica. Spent catalyst recovered in the de-ashing step can be processed to reactivate it and then returned to the reactor. 

Filtration. In many mineral processing operations, filtration follows thickening and it is used primarily to produce a soHd product that is very low in moisture. Filtration equipment can be either continuous or batch type and either constant pressure (vacuum) or constant rate. In the constant pressure type, filtration rate decreases gradually as the cake builds up, whereas in the constant rate type the pressure is increased gradually to maintain a certain filtration rate as the cake resistance builds. The size of the device is specified by the required filter surface area. 

Operating Labor The cost of operating labor is the second largest item of expense in the manufac turing cost. Labor requirements for a process can be estimated from an intelhgent study of the equipment flow sheet, paying careful attention to the various primaiy process steps such as frac tionation, filtration, etc. The hourly wage rate should be that currently paid in the company. Once the number of persons reqiiired per shift has been estimated for a particular production rate, the annual labor cost and the labor cost per unit of production can be estimated. 

Settling does not give a complete separation one product is a con-centratea suspension and the other is a hquid which may contain fine particles of suspended sohds. However, settling is often the best way to process veiy large volumes of a dilute suspension and remove most of the hquid. The concentrated suspension can then be filtered with smaller equipment than would be needed to filter the original dilute suspension, and the cloudy liquid can be clarified if necessaiy. Settlers can also be used for classifying particles by size or density, which is usually not possible with filtration. 

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