US2068498A - Method of testing and restoring the effectiveness of detergent baths - Google Patents

Description

Patented Jan. 19, 1937 PATENT OFFlCE METHOD OFTESTINGAND EESTORING THE EFFECTIVENESS F DETERGENT BATHS Franklin H. Mackenzie, Bywood, P a., assignor to American Chemical Paint Company, Ambler, 2a., a corporation ofDelawa're No Drawing. Application January 12, 1935 Serial N0. 1,588

of effectiveness and to do so at a minimum of 1 expense and waste.

Cleaning solutions, of course, change their character rapidly during use. For example, an alkaline cleaning solution which may contain, originally, a certain concentration of alkaline 15 salts and of soap may be used to clean pressed steel articles which are contaminated with fixed and mineral oil, fatty acids," solid dirt, filings,-

etc. Such a solution after a period of use in cleaning steel will loseilargely its alkalinity while at the same time gaining in soap and emulsified oil content as well as in its content of suspended solid impurities, etc., so .that the solution is no longer in good operating condition. Restoration of such a spent bath is a chemical and physical problem of considerable nicety especially where economy of operation and low cost of materials are factors of irihportance.

Certain crude methods of control have heretofore been employed in an effort to keep such cleansing-solutions in proper working order and these methods have ranged from an occasional titration fol-alkalinity to .an occasional measurement of hydrogen-ion concentration and 5 while restoration of these factors to their original value by. the addition of alkali may somewhat improve the spent solution yet it does not restore its original detergent effectiveness. Soner or later the solution degenerates beyond repair and must be entirely-discarded and a fresh bath substituted which, of course, is a very wasteful process. Moreover when pro-' ceeding' in this way the bath is very likelyto have been operating over a great part of its 4,5 life at considerably less than its maximum effectiveness. Among those skilled in the art, it is recognized that the detergent properties ofa solution are dependent upon quite a variety of fac- 50 tors such as the interfacial tension against the work and against the dirt, the colloidal suspending power for solid dirt, the emulsifying power forliquid'non-saponifiable grease, the

saponifying power for fixed oils, the surface tension, the viscosity, the surface viscosity, etc.

To evaluate these properties in a factory is of course a. practical impossibility and even the laboratory has no' certain methods for determining some of them. Moreover, even were measurements of all of these properties .avail- 5 able for a certain solution, no immediate prac-' tical' use could be made of the results, because the substances used -in making up the'original' solution do not impart the different measured properties in individually direct ratio but afiect them all in varying degrees, i. e., the relative effect of a particular substance is changed by the presence of the other ingredients, whether these were deliberately added oraccidentally introduced. For all of these reasons no certain,

definite method for correctly treating a detergent solution to maintain it at a predetermined effectiveness has heretofore been found;

'I'l1epresent invention is based on ,the discovery that the detergent efiectiveness of a solution can be maintained substantially constant -if certain of its physical properties are maintained at substantially constant values and, as will appear more. fully below, the invention is particularlyapplicable to cleaning solutions which contain anelectrolyte, a foaming agent and suspended matter of such a nature as will permit it to settle out when the solution is allowed to stand. These substances may be deliberately, added or may come into the bath ac- 0 cidentally or during its operation and as stated above, the invention is particularly applicable to alkaline solutions containing added or accidentally acquired soaps and suspended solid impurities. 5 7

Among those properties which I have found 3 it most useful tomaintain at substantially constant values in order to maintain the original effectiveness of a detergent bath, are the following: l 'irst, its electrical conductivity-second, 40 the longevity of the foam produced following suitable agitation thereof and third, thequan-- tity of suspended matter which settles out when the solution is allowed to stand undisturbed. I have discovered that these three properties are related in some unknown manner to the properties listed above asdetermining the cleaning effectiveness of a. given detergent bath. However, whatever the reason for the result may be,

I havediscovered that additions of conductive chemica (alkali' chemical), of foaming agent previo ly selected to carry out the cleaning process and of water in sufiicient quantities and proportions so as to maintain the conductivity, the foam life, and the suspended solid content within predetermined limits, will at the same time maintain the'cleaning bath at substantially its original effectiveness.

The ingredients of a cleaning solution can be classified into electrolytes, foaming agents, sus-" pended matter, and diluents. Therefore, any excess or deficiency of any ingredient, is immediately made evident by the process of this invention. It is true that each of the'properties is affected more or less by each of the ingredients present, and that the solution can only be maintained in perfect condition by making such adjustments as will bring all three properties simultaneously to the predetermined values. Fortunately, however, each added reagent affects one of the determined properties to a much greater extent than it does either of the others. Thusit is possible to adjust the solution to a proper value of each property, by addition of re-. agent, or by dilution.

For instance, the conductivity is principally aifected by the electrolyte concentration; the foam life is affected principally by the content of foaming agent, but also to a considerable extent by electrolyte concentration and content of suspended matter; -the suspended matter which settles out in a given time is, of course, chiefly affected by the concentration of such suspended matter in the solution, but also depends on the electrolyte concentration, the content of foaming agent, and the dilution,

It is understood, of course, that the conductivity of the ole ning solution, as of any electrolyte, varies wi the temperature of the solution. To be referable to a standard conductivity, any measured conductivity must be made at a standard temperature of the solution; otherwise, it is necessary to know in advance the variation of the conductivity of the solution with temperature and to correct the measured conductivity to the standard temperature before making use of it in correcting the bath compositions. For the purpose of this patent, then, by electrical conductivi is meant the numerical value of 'the electrical conductivity expressed in any absolute or arbitrary units at a standard temperature, whether the conductivity is determined at this standard temperature, or corrected to the the original solution contained 200 pounds of at a constant potential of ten volts. meter read .5 ampere sodaashand poundsofaspecialyarn scorning soap which was found byexperienceto produce satisfactory cleaning of the yarn. The so-;

vIution which was initially free of mattwo nickel electrodes eachrabout one inch square which electrodes. and an ammeter were coupled The am- One hundred cubic centimeters of the solu tion were then placed in aglass flask bearing.

indentations which flask was stoppered-with a ment layer measured -5- cc.

Since, as above stated, the yarn at this time was emerging'in satisfactory condition the values just given for conductivity, longevity of foam and sediment volume were adopted as standard.

The scouring process was then continued for approximately one hour more after which the solution was treated as before in order to determine its conductivity, its foam life and its content of suspended matter whereupon the ammeter now read .35 ampere, theifoam life was 460 seconds and the volume of sediment was 15 ml. The yarn at this point was now emerging decidedly below standard in quality.

Approximately one-third of the solution'was now allowed to run to waste from a bottom outlet in the bowl in order. to remove excess suspended matter and the volume was restored with fresh water which was thoroughly mixed. in. Similar determinations then resulted in an ammeter reading of .25 ampere, a foam life of 210 seconds, and a sediment volume of 3 cc. Ninety pounds of soda ash were now added and the readingsagaintaken. These were as follows: cm-rent 0.50 ampere, foam life seconds, and sediment volume 3 cc.

At this point'twenty-flve pounds of soap were added following which the same factors were determined whereupon it was found that the current. volume again read .5 ampere, that the foam life was 240 seconds and. that the sediment volume was3 cc. coincidentally the yarn now emerged in standard condition. The 'described process was continued for upwards of 50 more working hours and during all this time I was enabled to maintain it substantially continuously at or near the standard values for conductivity, foamlife and sediment volume and durlng'all this. time the yarn emerged in standard condition with respectto grease con-- tent and cleanliness.

a In connection with the-volume of deficient solution whichis withdrawn from the bath I de- Sh'e to explain that this is to be determined very largely by experience but I have found the following to be a reasonably accurate guide.

The foam life and thequantity of suspended: matter are determined and whichever of these two values is more highly in excess of the desired value is used as an indication of-the volume which should be withdrawn'so that when this volumeiismadeup by adding water such value will-again approximate the desired standard.,. As stated, with this as an index, experience will soon indicate quite accurately: just how much of the spent solution should be replaced with water inorder to bring either the foam life or the content of suspended matter (whichever may be the-farthest removed from its desired value) back to the value desired.

It will be seen that my improved process may be applied to solutions which m'aybecome con-' taminated during use with electrolytes, foaming agents, or suspended matter which can be settled out, as well as to solutions to which these substances have been deliberately added. An example of such an application is in connection with a rinsing solution used to remove alkali, soap, dirt, etc., from yarn which has been scoured in a solution such as has been described above. In such an application, the solution is connected with the electrical conductivity apparatus while the scouring process is in operation. It is agitated with air from time to time, and the foam life determined. a It is allowed to stand and the quantity of deposited sediment noted. A quantity of solution is run to waste and fresh water is added to maintain the determined quantities below a predetermined maximum. The indications given by the process will detect imperfect functioning of the squeeze rolls, etc. When the process is applied to the scouring of raw wool, the wool brings into the first bowl considerable electrolyte. This bowl is initially filled with water only, but gradually accumulates sediment and dissolved salts. By maintaining the conductivity of this solution and its content of sediment within controlled limits by the methods described, the rinsing operation maybe kept efllcient. Moreover, by this means the quantity of electrolyte carried-over with the wool into the first scouring bowl may be closely controlled. In this way the determined conductivities in the scouring bowl are prevented from being irregularly affected by the electrolyte so introduced.

In laundries the washing and rinsing solutions may be controlled by this process. .Here, however, the solutions are intermittently" agitated with air during the washing process by the revolving "wheel.

The foam life may be noted by observing the foamon the detergent solution itself.

In certain metal cleaning operations, such as the removal of -a light oil coating from fullfinished steel panels, the influence of suspended matter is less important than in textile cleaning operations or' in the cleaning of material more highly contaminated with solid dirt. In these cases the process may be operated with a less accurate determination of the suspended matter, wasting of the solution to remove suspended matter being necessary only when this exceeds a predetermined limit.

Minor variations of the process may suggest themselves to the artisan which do not depart from the spirit of the invention. For instance,

- agitation of the solution with air maybe accomplished by shaking it in a glass flask, by blowing air into it while it is in a working tank, by whipping air into it with rotating paddles, etc. The electrical conductivity of the solution may be determined by any of the means which are well known, such as making the solution between two electrodes one arm of an alternating current bridge circuit; passing a known alternating current through it and noting the potential fall, applying a fixed potential and noting the resulting current, etc. The settleable suspended matter may be determined by allowing the solution to 1.- The method of treating an alkaline cleaning 10 solution containing soda ash and soap in order to maintain it in a condition of maximum eflectiveness consisting in determining its electrical conductivity; agitating the solution with air to determine the longevity of the resulting foam; allowing the solution to deposit sediment in order to determine the quantity of suspended matter therein; withdrawing a portion of the solution; and adding soda ash, soap, and water in suflicient quantities to bring the electrical conductivity, the longevity of the foam, and the quantity of settled suspended matter to predetermined values.

' 2. The method of testing and restoring the effectiveness of an aqueous detergent bath containing an alkaline cleaning chemical and soap, which method comprises the maintenance of substantially constant predetermined standard values for electrical conductivity, foam longevity and content of suspended matter by determining the aforesaid factors and-then adding the quantities of alkaline cleaning chemical and soap necessary to bring the conductivity and the foam longevity to their said predetermined values coupled with adjustment of the water content,

by withdrawal of a portion of the bath if necfoaming agent, which method comprises the.

maintenance of substantially constant predetermined standard values for electrical conductivity, foam longevity and content of suspended matter by periodically determining said factors and then adding to the bath the quantities of cleaning chemical and foaming agent together with adjustment of the water content necessary to bring the conductivity, the foam longevity and the content of suspended mattersto said predetermined standardvalues.

4. The method of. treating an aqueous cleaning chemical and a foaming agent in order to maintain it in a condition of maximum effectiveness, which method consists in determining its electrical conductivity; agitating the bath with air to determine the longevity of the resulting foam; f

and the quantity of settled-suspended matter at 5 predetermined substantially constant values.

FRANKIJN H. MACKENZIE.