Syndets and Soaps FOSTER DEE SNELL Foster D. Snell, Inc., 29 West 1 5th St., New York, Ν. Υ.
J. Ν LINE with the general recession in the first part of 1958, sales of syndets and soaps were down. Later in the year they picked up again, so that at the end of the first 6 months, they were only 1 % lower than for the same period of 1957. Production figures for 1958, 1963, and 1968 (in millions of pounds) may reasonably be: soap 1200, 1000, 750; syndets 3000, 3500, 4000. Liquid syndets of both light-duty and heavy-duty types continue to in crease in popularity; in the first half of 1958 sales were 2 5 % above those for the first half of 1957. Large soapers tend to market under an established brand, with the word "liquid" prefixed. And just as reduc tion in soap consumption has killed off many soap companies which did not switch to syndets, so new com panies which manufacture only syn dets are coming into the field. The three syndet bars—Zest, Dove, and Vel Beauty Bar have continued to expand their market, thefirsttwo going in for extensive advertising. Armour has entered this field. Ab sence of a sorbed coating of soap left on the skin is combated by current advertising of Zest ; presumably such advertising is effective. The new user of a syndet bar misses the slip pery effect and may even report that the skin is tacky. Addition of alumi num soaps of C14 to C2o fatty acids is claimed to reduce or eliminate this. One of the commercial bars adds substantial amounts of stearic acid, superfatting to a degree never possi ble with soap. Rapid erosion of such bars is stated to be avoided by addi tion of 15 to 3 5 % of sodium bicarbonate-tetrasodium pyrophosphate. And of course this makes a cut in cost possible. The price of inedible tallow has remained around 8 cents a pound—• still low and expected to remain so. Therefore research on its use con tinues. One possible outlet to put it back into syndets is alpha-sulfonated tallow acids neutralized by selected alkalies. A promising com 42 A
bination is 7 2 % monosodium salt, 20% sodium-ammonium salt, 8 % sodium triethanolamine salt; another is 8 5 % monoammonium salt, 1 5 % ammonium triethanolamine salt. Syndets are displacing soap in other countries, in many at a greater percentage rate than currently in the U.S.A. This is particularly the case in England and Western Germany, but even Finland splits the soapsyndet market at 80-20. An excep tion is the U.S.S.R., which has steadily increased soap production over the past decade, even though it has U. S. know-how on syndet pro duction. Anionics
Raw Materials. Benzene, essen tial for alkylate or dodecylbenzene, followed the general trend in early 1958 and dropped off in production. Imports, mostly from the Iron Cur tain countries, have also decreased in spite of a lower price than for domestic benzene. Early in the summer the domestic price of benzene from both petroleum and coke-oven sources fell from 36 cents to 31 cents a gallon. The imported product is still a few cents below the latter price. Domes tic capacity for benzene has in creased, with the completion of the 30,000,000-gallon-per-year plant of the Humble Oil & Refining Co. at Baytown, Tex. Alkylate did not change but has re mained at 12 cents a pound for the past year. Exports of alkylate in creased from 10,000,000 pounds in 1950 to over 100,000,000 pounds this year and are expected to continue to increase at a lesser rate in spite of much production abroad. Expan sion of the Shcll-St. Gobain plant at Berre, near Marseilles, to make de tergent alkylate is one of the factors which may lessen the rate. During the year Imperial Oil of Canada went on stream with an alkylate plant to produce 30,000,000 pounds annually. An undercurrent of interest in pentadecylbenzene persists, although no commercial source is yet known.
INDUSTRIAL AND ENGINEERING CHEMISTRY
The interest is believed derived from past, and possibly current, research. With a small amount of soap present, in the presence of calcium ion a more stable foam is produced if the side chain contains 14 or more carbons. Syndets have been produced experi mentally from paraffins by the Esso Research and Engineering Co. Gamma rays from cobalt-60 cause sulfur dioxide and oxygen to react with liquid paraffins. T h e method should be low in cost. Fatty alcohols from coconut oil have been reduced 2 cents a pound, as a result of congressional action in repealing the processing tax on coco nut oil. These go to make lauryl sul fate, so important as a detergent in shampoos. A new form of this type is one containing two ethenoxy groups, which improves the solubility of long-chain hydrocarbons, such as C 16 H 33 (OC 2 IL) 2 OS0 3 Na. Advances in Manufacture and Composition. Sulfonation of alkyl ate with sulfur trioxide is expanding. Several commercial installations are using it, and the method has also been adopted to sulfation of lauryl alcohol. Alkylate is sulfonated with sulfur trioxide to give a product with Sales of Soaps
and
Syndets
Unit = 1 mill ion pounds* Syndet Syndets Soap % of Total 1956 2690 1285 68 1957 2916 1189 71 1958 2925 1080 73 * Figures from the Assoc, of Am. Soap & Glycerine Producers (estimated for 1958).
a stable pH by aging the neutralized material at 65° to 100° for up to 2.5 hours. Chlorosulfonic acid for continuous sulfation of fatty alcohols gives saltfree syndets; very little excess of chlorosulfonic acid is required for the reaction. Sulfonation of alkylate plus sulfation of fatty alcohol hasbeen integrated into a combined process, resulting in a syndet containing a mixture of the two anionics. The process uses the excess sulfuric acid from the sulfonation stage to sulfate the fatty alcohol. Neutralization of the combined sulfonate and sulfate follows. One method of producing dodecylbenzene sulfonate in pure form, free of excess sodium sulfate, is to follow dilution of the sulfonate mixture with water to form two layers with extraction of the acid of the active agent with alcohol. These products, free of sodium sulfate, are suitable for use in liquid detergents. Because the usual sodium dodecylbenzene sulfonate is not so good a detergent as soap in water of zero hardness, a modification combines dodecyl benzene with a short-chain alkyl-aryl hydrocarbon before sulfonation. The short-chain hydrocarbon is partially sulfonated with excess of sulfonating agent, while the excess of the short-chain hydrocarbon extracts unsulfonated longer chain alkylate. To make built syndets containing large amounts of tripolyphosphate free-flowing and resistant to caking, the spray-dried product is treated with an aqueous solution of magnesium, zinc, or aluminum sulfate. The amount of such salt added is 2 to 4 % of the whole. The kerosine-like odor of syndets has sometimes been objectionable to the user. To render them odorless, a fraction of 1% of />-benzoquinone has been recommended. Dishwashing formulations based on tridecyl-/3sulfopropionate are made odor-free by addition of a small amount of a salt of ethylenediaminetetraacetic acid. Fractional distillation of alkylate is said to give a final product free of both odor and color. Bleaching of alkyl benzenesulfonic acid with hydrogen peroxide before neutralizing gives the product improved color. Another method of reducing color is by electrolysis at either the sulfonic acid or neutralized stage, in the presence of sodium chloride.
I/EC ANNUAL REVIEW Sodium chlorite has been used for combined neutralizing and bleaching. Following the success of Dial, some syndet products include antiseptic or germicidal effects. An alkyl aryl sulfonamide having a chloride atom on the nitrogen may be added to give a germicidal detergent. Polyhalogen-substituted carbanilides may also be used. Copious and persistent foam is considered very desirable in household detergents. Inclusion of the combination of sulfated alkylolamides of coconut oil fatty acids, with a saturated, straight-chain C ]0 -Cj 8 alcohol, gives improved foaming. Various other alkylolamides make the foam of detergents more persistent. Magnesium alkyl benzene sulfonates are good detergents, but in the course of manufacture give a very viscous slurry. Addition of a minor amount of xylene before sulfonation corrects this. Builders in heavy-duty detergents are in principle as before. A new soil-suspending agent is a carboxymethyldextran. Whether this can compete with carboxymethylcellulose remains to be seen. Studies of the effect of builders on their sorption by cotton fabric have shown that there is an approximate linear increase in sorption, with increasing builder concentration. Under proper conditions, sorption of syndet is believed to be preferential in relation to sorption of soil. Nonionics
Nonionics are in increased production, partly because of the lower cost of some forms, partly because of new applications, where they do a special job. Armour put a new ethoxylation plant on stream. Among the newer nonionics are monoalkylbenzyl ethers of polyoxyalkalene diol. A specific new basis for nonionics is 2methyl-2,4-pentanediol. Nonionic polyol complexes are useful for preparing nonalcoholic suntan lotions, colognes, and bath liquids. Sugar esters of fatty acids have progressed slowly, more rapidly abroad than in the U.S.A. Wetting agents such as dialkyl sulfosuccinates have long been used in agricultural sprays to increase wetting of foliage. Wetting is so
1958
effective, however, that much spray is lost by runoff. A nonionic such as octyl cresol polyglycol ether aids wetting, without excessive runoff, and has been recommended for highvolume spray formulations. Certain nonionics solubilize iodine, permitting dilution with water to provide an aqueous germicidal and disinfectant solution. Nonionics are frequently combined with anionics, and with cationics—for example, nonionics are added to cationics for dyeing acrylic fiber and wool blends. This avoids the need of pretreatment and yields uniform shades. Applications
One reason for the rapid growth of the syndet industry and related surfactants is use where they do not replace soap. However, they continue to do that also. Many varieties of soap have been used in emulsion polymerization of unsaturated hydrocarbons. One suspects that the announced use of dodecylbenzene sulfonate for this purpose in production of synthetic rubber is not as new as it sounds. Syndets have replaced much soap in dry-cleaning to remove watersoluble soil. In 1950, dry cleaners used only 5,000,000 pounds of syndet. By 1958 this had increased to 20,000,000 pounds. Use of syndets in the cleaner eliminates much "spotting" and so saves expensive labor. Thirty million pounds of syndets are used in car laundries, which now number about 4000. Mostly used are dodecylbenzene sulfonates, with some fatty alcohol sulfates, and lesser amounts of nonionics. A new liquid product for use on all types of floors is said to clean well without destroying the wax or resin finish. If so, it preferentially removes grease and soil without affecting the wax or resin. A clear liquid for general cleaning is the sodium salt of a sulfated, ethoxylated lauryl alcohol. Alkaloids, such as quinine from Cinchona bark, are extracted more . effectively in the presence of 0.5% of dodecylbenzene sulfonate. Lignin sulfonates as very low-cost agents are used as air-entraining agents in concrete highway mixes. Fire-fighting foams contain syndets, so that the foam will spread rather than V O L 5 1 , NO. 1
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JANUARY 1959
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in the past decade. A nonionic type primarily intended for machine dishwashing is not used for its germicidal effects but for quicker and more complete draining and drying of utensils. This results in reduction or absence of "water spots" and brighter and cleaner appearance. Surfactants act as corrosion inhibitors by sorption on metal surfaces. Such use is not new, but merits mention because of extensive presentation to the public on T V as included in automobile antifreeze. Soap
Increased demand f o r nonionics has led to an accompanying increase in experimentation on process variations. Lever Brothers' pilot unit shown here is t y p i c a l of the compact units being used in these studies. Controls a r e housed in the enclosure t o the left f o r safety
penetrate. The same principle is applied in making rug and upholstery shampoos. In fighting fire, syndcts or wetting agents are added to water to enhance the cooling and flame-extinguishing action. The wetting agent is particularly important when the burning material contains a coating of greasy or waxy material—for example, burning bales of cotton. The premature invasion of water into radially producing oil wells is reduced by use of a syndet solution to treat the oil sands. Cationic surfactants in oil or water are injected into the coned-out zone. While the emphasis here is placed on water-soluble syndets, oil-soluble surfactants perform similar functions in some industrial applications. Most lubricating oils contain so-called "detergents" as suspending agents. An alkaline water-in-oil emulsifier is added to automobile crankcase flushing oils; it also prevents sludge formation in fuel tank oils. For cleanup in oil refineries, syndets are blended with séquestrants. Although rinse additives for dish- · washing have been known for several decades, additives for dishwashing machines have been developed only 46 A
Nearly 1 billion pounds of fats are saponified currently to produce soap in its various forms, some not marketed as soap. This use is decreasing at a rate of about 5 % a year. A considerable part of these fats consist of inedible tallow and greases, but necessarily increasing amounts are being used for other purposes, as for addition to feed. About 50% of all manufactured poultry feed and 2 5 % of livestock feeds contain 2 to 8 % of supplementary fat—about 15% of the total consumption of inedible tallow. The soap industry goes on much as usual, gradually losing ground to syndets. Addition of 2 to 5 % of a nonionic syndet to soap offers advantages in addition to dispersion of alkaline-earth soaps. Some are counteracting rancidity, helping retain good color and odor, and facilitating incorporation of other additives such as germicides and superfatting agents. An alternative to addition of a surfactant to soap to disperse alkaline-earth soaps is addition of a chelating agent; ethylenediaminetetraacetic acid is the best known. Their use is blocked by relatively high price, although in the past 4 years the price of the tetrasodium salt has been reduced by as much as 40 to 50%. Whereas one large manufacturer quoted carload or truckload quantities of a 7 8 % tetrasodium salt at 48 cents a pound in 1957 in flake form, it is now selling at 43 cents a pound. Glycerol
Refined by-product glycerol and synthetic glycerol are competitive in price at about 28 cents a pound. Shell and Dow produce about half of the U. S. requirements, with
INDUSTRIAL AND ENGINEERING CHEMISTRY
natural glycerol providing the balance. In 1957 Shell went on stream at Norco, La., with hydrogen peroxide. Contracts let in 1958 will be followed successively by acrolein and glycerol. The process avoids use of chlorine and caustic involved in the present process and probably lessens corrosion problems. When this new 35,000,000-pound plant goes on stream, part of the Houston operation will be curtailed unless demand substantially increases. Only part of the acrolein and peroxide will go to glycerol initially. Royal Dutch Shell went on stream in 1958 with the first synthetic glycerol plant outside the U.S.A., located at Pernis near Rotterdam. The raw stock is propylene. Dow's Texas Division has added a second synthetic glycerol unit which doubles its capacity at Freeport. Although glycerol produced by the fermentation of molasses reached the pilotplant stage in Scotland, it does not seem likely to become economically feasible here. It recurs periodically in this country at the laboratory or pilot-plant level. The manufacturers of pressurepackaged foods can be expected to consume more glycerol because of its ability to modify rheological properties, alter the solubility of gases, increase the stability of emulsions, increase the solubility of flavors and colors in food products, and increase the body of products. Glycerol can expect market growth with the popular acceptance of pressure-packaged toothpaste. The polyol is essential as a humectant in the pressurized product, as the drying out of the extruded paste in the dispensing nozzle would reduce the flow rate or cause the valve to malfunction. In aerosol deodorants glycerol is a plasticizer for the quaternary ammonium compound, preventing its crystallization in the valve system and minimizing the possibility of flaking after application. Conclusion
Research in the field of syndets continues actively, particularly in the development of new compositions and applications of nonionics. Acknowledgment
Contributions by Cornelia T. Snell and Richard S. Ringheim are appreciatively acknowledged.
