Scaleup considerations

Scaleup considerations for a cleaning system can be viewed from three different levels overall, process, and mechanistic. Overall scaleup considerations cover the entire cleaning operation, from acquiring and processing raw resources to the geographical distribution of the final product. The process level considers pumps, separators, cleaning vessels, condensers, solvents, and solutes collectively. At the mechanistic level, considerations are specific to each part in the process. 

This chapter discusses general parameters, processes, and procedures for scaling up supercritical fluid parts cleaning (SFPC) vessels at the mechanistic level. A section is also provided which includes work at Pacific Northwest Laboratory and 

The operating variables to be considered include temperature, pressure, time, modifier affects, and agitation of the vessel. These variables are typically determined by the physical properties of the cleaning solvent and solute, e.g., solubility of the solute in the solvent, mass transfer rates of the solute into the bulk solvent, and reactivity of the solvent with the solute. These properties are determined in the laboratory from a scaled working model of the process or found in a source reference book. 

The basic issues of scaleup are the same for polymer reactors as for ordinary chemical reactors. The primary problem is that the capacity for heat and mass transfer increases less rapidly than the reactor volume and throughput. The remedies are also similar, but the high viscosities characteristic of polymers cause special problems. These problems are most acute when the polymer phase is continuous. 

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The fundamental phenomena will be explained in sufficient detail so the reader will understand scaleup considerations. 

In many processes that apply to an agitated tank, the main task is to maintain sufficient mixing during scaleup. Considerable information is available in the literature on scaling up of agitated tanks [30-36]. 

The scaleup considerations of column chromatography for protein isolation has been described by Charm and Matteo.l l When several hundred liters of a protein feedstream must be treated, the resin may be suspended in the solution, removed after equilibration by filtration and loaded into a column from which the desired proteins may be eluted. Adsorption onto a previously packed column was not recommended by them since they feared suspended particles would clog the interstices of the column, causing reduced flow rates and increased pressure drops across the column. The reduced flow rate may lead to loss of enzyme activity because of the increased time the protein is adsorbed on the resin. 

The important scaleup consideration is then to establish the optimum conditions for the transformation in terms of the operating/design variables that influence cavitation. In this analysis, the nature of the transformation will also have an impact on the suitability of the given cavitational reactor. 

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