INDUSTRIAL AND ENGINEERING CHEMISTRY
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Union Oil Co., and Stanco Distributors, Inc., in supplying catalysts ie appreciated. LITERATURE CITED
Bunte. K., and Lorena, F., Gas u. Wasserfach, 75, 765, TST (1932).
Cole, R. hI.,and Schultse, I. I. (to Shell Development C’o.!, U. S. Patent 2,403,052 (1946). Evans. R. A I . , and Kewton, W. L., IND.ESG. CHEM.,18, 513 (1926).
Fischer, F., Tropsch, H., and Dilthey, P., Brennslof-Ciirm., 6, 2 6 i (1925).
Gas Research Board (Brit.), Ann. Rept., 5, 25, 2 9 (1943-44). Horsfield, S. IT., Am. Gas. Assoc. Proc., 30, 631-41 (1948). Hougen, 0. iz., and Watson, K. &“Chemical I., Process Principles,” P t . 3, p. 937, New York, John Wley & Sons, 1947. Ipatieff, V. N., Monroe, G. S., and Fisoher, L. E., IND.ESG. CHEM.,42, 92 (1950). Key, A. (to British Gas Research Board), Brit. Patent 561,679 (1944). Neyer, K., and Horn, O., Ges. Abhandl. Kcrmtrzis Koiile, 11, 389 (1934).
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(11) hfurphy, E. J., Brooklyn Union Gas Co., Unpub. Progress Rept. I, July 6 (1943). (12) h’eurnann. B.. and Altman. E.. 2. Elektrochem.. 37. 173 (1931). Prosen, E’. J., Pitaer, K. S., and Rossini, F. D., -\”atZ. B u r Standards Research Paper R P 1650 (April 1945). Riesz, C. H., Am. Gas Assoc. Proc., 30, 505-16 (1948). Riesz, C. H., Komarewsky, V. I., Kane, L. J., Estes, F., and Lurie, P. C., Am. Gas Asaac. M o n f h l y , 28,159-64 (1946). Riesz, C. H., Lurie, P. C., and First, J. J., Ibid., 30, KO.4 , 1720 (1948). (17) Roberti, G., Proc. T o d d Petroleum Congress (London), 2, 326 (1933). (18) Sebastian, J. J. S., Carnegie Inst. Tech. Coal Research Lub., Confrib. 35, (1936); D.Sc. thesis, Carnegie Inst. Tech.. 1935; Compt. rend. X B congr. chim. i n d . (Brussels), I, 875C (1935). (19) U. S. Tech. Oil Mission, Fischer-Tropsch Rept. 1, TAC-Sn MC-1 (Aug. 20, 1945). (20) Wagman, D. D., Kilpatrick, J. E., Taylor, W. J., Pitaer, K. Y.,
and Rossini, F. D., N a t l . Bur. Standards Research Paper RP1634 (Feb., 1945). RECEIVED December 27, 1949. Presented before t h e Division of G a s and Fuel Chemistry a t t h e 114th lfeeting of the . ~ M E R I C A N CHEMICAL SOCI~TT, St. Louis, Ma.
Synthetic Detergents for Domestic Dishwashing Machines HERBERT L. SANDERS’
AKL)
JOHS A. 1-EAGER
Generul.4niline & k’ilm Corp., E a s t o n , P a . Although synthetic detergents have become \* idely accepted for many honsehold cleaning operations such as laundering and hand-dishw-ashing, they hate not been used to any considerable extent in household dishwashing machines, in part as a result of excessive foani. Because the excellent ivetting and draining characteristics of the synthetics would be expected to aid mechanical dishwashing performance, an investigation along these lines was carried out in the authors’ lahoratory.
The results obtained with various synthetics in household dishwashing machines is described, and a low-foaming anionic detergent designed especially for this field was found to give greater freedom from films and water spots than the inorganic alkaline mixtures normally emploj ed. As a result of this work a predominantly synthetic mechanical dishwashing compound has been introduced to the market for the first time, and has thus opened up still another field of application for the synthetics.
T
T h e period since 1934 has witnessed the spect,acular growth of synthetic organic detergents in many cleaning applications such as manual dishwashing, home laundering, and textile scouring. Yet, in spite of the obvious advantages afforded by the exceptional wetting, draining, and dispersing power of these materials, they have found little place in the field of mechanical dishwashing, by far the bulk of such work still being carried on with inorganic compounds. This situation is due t o a nurnlier of factors: I n the first place, the high foaming power of the synthetics has made it physically impossible to add any appreciable quantity t o impeller- or spray-type machines without encountering excessive foam build-up and consequent interference withwashing action. Secondly, high cost has apparently made their us(’ uneconomical, although this reasoning might equally well have been applied to the polyphosphates a t the time of their int,roduction. Thirdly, sonie evidence has been accumulated t o shorn that synthetic detergents are not highly effective in removing certain types of soil. ThuP Sorris and Ruchhoft (10) showed that surface active agents do not remove baked proteinaccous soils in an immersion-type test. Because, however, it mas believed that none of these difficulties was necessarily insuperable, a study was begun a t this laboratory
HE earliest detergents t o he used in mechanical dishn ashing
operations were simple alkalies such as trisodium phoqphate, aodium silicate, or sodium carbonate; although they showed reasonably good soil removal, they unfortunately tended t o form sparingly soluble calcium or magnesium precipitates in even moderately hard waters. This resulted in the gradual accumulation of an unsightly film of deposited minerals (mixed with food eoils) on both tableware and machine and necessitated frequent acidic clcanup treatments. An important advance in this field was made bl- Schn ,rrtz and Gilniore in 1034 (IZ),who conceived the idea of mixing sodium hexametaphosphate with these alkalies in order to sequester calcium and magnesium and thus prevent precipitates from forming in hard waters. This procedure resulted in a marked decrease in the rate of film formation under practical operating conditions and led to the widespread use of such mixtures. Although a variety of other sequestrants, such as sodium tetraphosphate, sodium tripolyphosphate, and sodium septaphosphate, have since been combined with a large number of different alkalies, none of these later compoeitions differed markedly in theory or performance from the type described by Schwartz and Gilniore. 1 Present address, Ninol Laboratories, Chicago, I11
ApriI 1951
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
sonic time ago to determine the effectiveness of synthetic detergents in mechanical dishwashing. As part of this program a rather extensive field survey of dishIvashing performance was carried out in order to find how the inorganic compounds were actually performing in practice; the survey was confined largelj- to household ninctiines, about a dozen tj-pes of whirh are on the market. It soon became apparent that the sequestering type of inorganic mixtures were not performing so satisfactorily as expected in man>- cases, unsightly dull films and spots were fi~ecluentlybeing encountered after a period of use: particularly on glassn-are, where they were, of course, most obvious. Examination of these deposits indicated that the>- consisted of both iiiorganic compounds and foodstuffs, and apnenred to be caused bv the adherence of certain mntr,rials present in the wash Tvater rather than to incomplete cleaning, since even unsoiled e: left in t,he machine3 gradually became filmed . III any investigation it is profit,able to apply concepts developed in a different field, and in this case cotton detergency provitles some useful parallels. In cotton detergency a sharp differentiationhas been made betn-een “cleaning” and “redepositioii,“ the former referring onlj- to primary soil removal, the latter t o vcondary deposition of some of this removed soil onto other parts of the fabric. Soap, for example, exhibits good soil removal, or detergency, but permits some redeposition of soil onto the fabric from the dirty wash water (particularl>*during rinsing) which results in gradual build-up of “tattle-tale grays.” This distinction between detergency and redeposition does not appear t.o have been so clearly recognized by n-orkers in the field of niechanical dishwashing. Schlvartz and Gilniore ( l a ) and Kil.;on and Mendenhall ( I ; ) described film formittion by deposition of insoluble calcium salts onto clean glassware, but only have made an!- attempt to deal Ivith the lfachlis and Michaels (4) factor of food soil redeposition from the tvarh water. Most of the published n-ork ( 2 , 3, 6 , I S ) discusses detergency only, with no attention to redeposition, although this would appear to be the main fault of the sequestering-type detergents from a consuiiier point of view. The major emphasis in the present stud>*was therefore placed on the nieasurement of deposited filnis formed on clean glass surfaces when esposed to various wn.h waters under actual machine conditions. WASHIIVG EQUlPhIEXT
Tlie accurate evaluation of surface ac6vc agents in any field of application such as laundering, metal cleaning, or dishwashing is rcndered difficult by the many variables involved, and must usually he performed empirically 1,)- employing simulated use tests. In general, the more closely the test conditions simulate pi,:i(tical operating conditions, the more reliable the results are likelj- to be; even minor deviations from practical conditions often give completely misleading results. For this reason it was decided to run all tests in actual dishwashing machines, rather than by the dip-type procedures used by many laboratories. For most of the work described here, a Thor Butomagic hometype machine (Model 222) was used because this type requires sniall volumes of water and has a manually controlled cycle which permits operating flexibility. To make certain that the results obtained were not unduly influenced b y t,he particular machine used, some of the r u n s - e g . , Figure 7-were repeated in a General Electric dishwasher, and essentially the same general trend was observed.
Figure 1.
867
Filming by Synthetics or Alkalies No food soil
The Thor machine holds 1500 ml. of water which it sprays onto the tableware through two oscillating “scoops,” a very even distribution of water action being maintained throughout the machine. I n most of the tests described, a 60-second wash with 1500 nil. of detergent solution a t about 140” F. was used, then the wash water was drained, and 3000 ml. of clear rinse water a t 140’ F. vere poured in; half this water overflowed after striking the dishes, and a 30-second rinse was carried out with the remainder. A symmetrical load of clean dishes was left in the lower rack st all times t o help dist,ribute the water. WATER
Because most of the problems encountered in mechanical dishwashing are intensified by hard water conditions, all of the tests described here were run in water of 300 p.p.m. hardness. >lost of the simulated hard waters described in the literature have been based on calcium chloride and magnesium sulfate, but for the purposes of this study a more realistic formulation was prepared. Baaed on the published analysis of several hard waters ( 9 ) , the following composition was selected as fairly representative : P.P.31. ( a s CaCO,)
HARDXE.90 COhlPOFEhT
Ca(HC0a)z
Cas04
CaCh Mg(HC03)? 3IgS04 hlgC12
This gives a water with a 2 to 1 calcium-magnesium ratio (as calcium carbonate) and a 2 to 1 ratio of temporary to permanent hardness. I n making u p this water, calcium and magnesium carbonates were first dispersed in a 55-gallon tin-lined tank with a Lightning mixer. Hydrochloric and sulfuric acids were then added to give the required permanent hardness. T h e temperature \vas then raised to 150”F. b y a steam coil, and dry ice was added to dissolve the remaining suspended carbonates, which required about an hour. Finally, air was blown through t o drive off excess carbon dioxide and raise the pH to 7.4 to 7 . 6 . This water appeared to b e stable for a t least 8 hours at 150” F. and for several duys at room temperature. SOIL
For studying the redeposition of suspended materials onto glass surfaces, two types of “soils” were used. One was the simple inorganic type spontaneously produced when varioua alkalies were added to the hard wash water, calcium and mag-
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slides then read 93. I n arriving a t an average figure for the filming -qi 90 of any particular system, both sides of each of the four slides used per wash n-ere read (giving I eight values per run), allowing the beam to strike I approvimately on the center of the slides. It was found that the reading obtained on one face of a Flide was very little affected by the presence or absence of a film on the opposite face. 9 I By means of the techniques described, a series A. Lof experiments was carried out t o study the de7 5 __ _l I posited filins formed T\ hen synthetic detergents, I alkalies, or mixtures of the two Tvere added t o hard n-ater in the presence or absence of suspended food soils. T o build up a measurable film, p ~ ~ L ~ ~ SYNTHETIC N 1 ~ ~ A ~ F three successive runs were made in every ease, I 165 0.025 0?05 0.I 0 0.5 I / Le., the slides vere exposed to three successive wash-rinse cycles. Fresh solutions were used Figure 2. Filming of Synthetics plus 0.057' Pyrophosphate each time (no drying taking place hetween runs), No food soil and the gloss was read after the third cycle. Three different types of synthetics were used. -411were good detergents but differed in foaming nesium phosphates, silicates, or carbonates being e~arnples. power as follows: hntaron L520, a sulfonated amide with very These will be referred to as inorganic soils. T h e other type was a low foam (designated as L); Antarox A.100, an aryl polyglycol foodstuff soil consisting of a mixture of proteins, carboliydrates, ether of medium foam, A ; and Ultrawet I
