Mass integration multiple solutes

After a process design has been conceptualized and a preliminary PFD developed, further analysis is possible to reduce pollution. The PFD should be studied to make certain that all possible recycle opportunities have been exploited. For processes with multiple streams containing the same solute, mass integration is possible using the method of mass-exchange networks (MENs) described in Chapter 15. More detail on the MEN method and other methods for analysis to maximize solute recovery is available [10]. Exanple 25.3 demonstrates this type of analysis of a PFD. 

The analysis of tetramethylammonium hydroxide (TMAH) solutions manufactured by SACHEM Inc. of Cleburne, Texas, includes the determination of trace elements. These elements cause less-than-optimum performance of integrated circuit boards manufactured by SACHEM s customers that use these solutions in their processes. Alkali and alkaline earth metals (e.g., Li, Na, K, Mg, Ca, and Ba) can reduce the oxide breakdown voltage of the devices. In addition, transition and heavy metal elements (e.g., Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Au, and Pb) can produce higher dark current. Doping elements (e.g., B, Al, Si, P, As, and Sn) can alter the operating characteristics of the devices. In SACHEM s quality control laboratory, ICP coupled to mass spectrometry is used to simultaneously analyze multiple trace elements in one sample in just 1 to 4 min. This ICP-MS instrument is a state-of-the-art instrument that can provide high throughput and low detection Emits at the parts per thousand level. Trace elemental determination at the parts per thousand level must be performed in a clean room so that trace elemental contamination from airborne particles can be minimized. 

The mass-burning rate predicted by this model is higher than experimental values. This results in a difference between this model and WSB model. The analytical WSB solution assumes that the solid phase reaction only occurs at a lengthless surface. In this model, however, condensed phase reaction occurs in multiple grids therefore, the mass loss is an integral over all burning grids. 

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