Class II cosolvent processes

So the rinsing mechanism in aU Class II cosolvent processes is displacement — because the two fluids are immiscible. A significant difference in density (>0.15 to 0.25 g/cc) between... 

Class II cosolvent machines can have SA or RA materials which are either easily ignited by a spark in oxygen, or not. That distinction is the basis for an important subclassification of Class II cosolvent processes ... 

The highest value of Ra, relative to the chosen SA cosolvent, ensures the greatest immiscibility between the chosen SA and the to-be-chosen (from Table 3.2) RA cosolvent. Fora Class II cosolvent process, one wants the chosen SA and RA cosolvents to most effidently and effectively separate from one another in the rinse sump - representing the highest value of Ra between the SA and the RA. 

This example with cottonseed oil soil clearly shows that selection of the two cosolvents for any Class II cosolvent process is requiring of experience, prejudice, judgment, and the ability to compromise. Hie analysis done for Tables 3.1 and 3.2 is based on the data of Appendix A1 and use of a spreadsheet. 

Figure 3.11 A Broad Range of Soil Materials can be Cleaned with Class II Cosolvent Processes...

Flence partnership arrangements are normal — one firm having more experience in development of the Class II cosolvent processes provides one of the two cosolvents, and a second firm provides the other. 

One might explain the Class III cosolvent process by noting that it is a "failed" Class II cosolvent process. 

Thus the chief drawback of Class II cosolvent processes can be overcome — by use of separate sumps " and two compatible and different solvents. 

The ultimate limitation on rinsing by displacement is the level of immisdbility between the RA cosolvent and the SA cosolvent. This is shown for various Class II cosolvent processes in Tables 3.3 and 3.4 (the column labeled SAvs. RA, Ra). The average Ra... 

The Class III cosolvent process requires considerably more energy than a Class II cosolvent process. Energy is also used in a different way, because it s a different process. 

The basis for the calculation is simple the sensible heat is calculated by multiplying the appropriate specific heat for each SA and RA cosolvent, times the temperature difference between the normal boiling point for the RA cosolvent and an assumed ambient temperature of 70°F, times the appropriate solvent density (to express the energy demand in energy units per volume). The latent heat is calculated by multiplying the latent heat of vaporization for the RA cosolvent times the solvent density (for the same reason). The latent contribution for the RA cosolvent is doubled because of the belief that excellent rinsing is required. The total energy use is the sum of the two. The SA cosolvent is assumed to not be vaporized in Class III cosolvent processes, and can t be vaporized in both Class II cosolvent processes. 

The need for an increase in energy consumed in a Class III cosolvent process, above that for a Class II cosolvent process, can also be seen to be that expected — to provide the additional sensible heat to raise the SA cosolvent to its high boiling point. This can easily be recognized by examination of Figure 3.30 . ... 

All organic reactions are enhanced by an increase of temperature. So use of oxygenated solvents in a Class II cosolvent process raises less concern about reaction with water than does use of the same solvents in a Class III cosolvent process. 

At operating temperatures above 212°F (100°C), which are unlikely to occur in a Class II cosolvent process, and more than likely to occur in a Class III cosolvent process, reactivity of any solvent with water should not be surprising. But two other factors must be considered ... 

These four criteria play the crucial role in selection of the RA cosolvent, and hardly any role in selection of the SA cosolvent. This is because in the Class II cosolvent processes the RA cosolvent Is the only fluid In direct contact with the ambient environment In the Class III cosolvent process the same Is so, plus the SA cosolvent Is chosen for minimum volatility so fugitive emissions will be low. 

A maximum level of immisdbility (largest Ra) between the SA cosolvent and the RA cosolvent for both Class II cosolvent processes, and... 

In Table 3.8 one can compare Class III with Class II cosolvent processes, making the comparison based on the same soil materials being deaned by either process. 

The normal operating temperature of the SA cosolvent in Class II cosolvent processes cannot be high, as it s limited to the value of normal boiling point for the RA... 

Recall that the SA cosolvent In the cleaning sump can t be heated above the normal boiling point of the RA cosolvent in a Class II cosolvent process because there is always (by intent) liquid RAcosolvent present- and the two sumps are physically connected. Recall also, that the SA and the RA cosolvent sumps are physically not connected in a Class III cosolvent process - so any desired temperature can be achieved. 

It is this temperature increment which can be employed in solution cleaning of the same soil if one chooses a Class III cosolvent process vs. a Class II cosolvent process . 

Cholesterol is a soil not well suited to be cleaned by either type of cosolvent process. A Class II cosolvent process will not have adequate immisdbility between the cosolvents... 

In fact, all of the soil materials in Table 3.8 will be poorly rinsed in any Class II cosolvent process (all Ra values for the RA vs. the SA are well less than 14 to 16 MPa " ) . So the Class II cosolvent process is an impractical choice for these many soils. 

With but a single exception, there are NO circumstances where an RA cosolvent can be chosen to be acceptably immiscible with a suitable SA cosolvent for any Class II cosolvent process. This statement is based on the requirement for acceptability noted in Figure 3.35, that the Ra separation between SA and RA cosolvents be 14 to 16 MPa at a minimum. 

It means that Class II cosolvent processes won t be recognized for providing part surfaces free of the SA cosolvent. This is because the RA cosolvent (the rinse fluid) is not adequately immiscible with (too soluble in) the SA cosolvent. Experientially, these processes aren t recognized for the quality of their rinsing of SA cosolvent by RA cosolvent. 

Displacement rinsing in Class II cosolvent processes certainly won t be excellent, probably won t be acceptable , and may not even be attempted. 

These relationships and capabilities are shown in Figure 3.36. From this illustration, and the above text, one should not conclude all Class II cosolvent processes will produce unsatisfactory outcomes. Hie proper conclusion is that displacement rinsing is likely not to be... 

The Ra value between soil materials and the SA cosolvent for both classes averages about 5 MPa, with the Class III cosolvent process being about ]/2 unit better (lower Ra) than the Class II cosolvent process. 

A method involving what is a modified Class II cosolvent process is claimed in USP 7,604,702, Mouser, W.L., Manchester, R., Barrett, W., and Bergman, F., Method, Apparatus, and System for Bi-solvent Based Cleaning of Precision Components, October 20, 2009 assigned to Crest Ultrasonics Corp. The inventors apply the nomenclature "Bi-Solvent to their process. A commercial unit in which this process is practiced is shown in the image above, courtesy of Forward Technology. 

These steps are enumerated and described in Chapter 1.2. Operation of superheat in open-top vapor degreasers is explained in Chapter 1.20 For reference, solvent cleaning operations with trichloroethylene and n-propyl bromide are conducted at their boiling points - 86°C (187"F) and 71"C (160°F), respectively. It is this author s experience that Class II cosolvent processes have found more interest in Europe than in the US. The chief application is removal of flux residues from printed wire boards (PWBs). 

Why that is so is a legitimate question when the Class II cosolvent processes are segregated by level of concern about flammability. 

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