enzenes H. E. BRA3ISTON-COQK AND V. E. ELWELL Oronite Chemical Co., 30 Rockefeller Plaza, Xezo York, S. I;.
Synthetic detergent usage in this country reached the 2 billion pound level in 1953, a tenfold growth in less than 10 years. Alkyl aryl sulfonates have emerged as the dominant class of products by a wide margin. Of the several members of this class, propylene tetramer benzenesullfonate is now practically the exclusive active material used in both domestic and industrial products. The utility of alkylbenzene sulfonates for surface active applications i s dependent in large part on the nature of the a&yl group used. Such properties as detergency, wetting. solubility, and foam characteristics of the derived sulfonate depend primarily on the molecular weight range and distribution in the alkyl group, and secondarily on chemical constitution. Other properties of importance to customer acceptance, such as sulfonatability, caking, color, and odor, are related principally to the chemical constitution of the alkyl group. The course and extent of future growth in usage of alkylbenzene-based surface active agents is difficult to predict. Growth in sales in household package products is leveling off. Usage in liquid products is increasing. Growth in alkylbenxene-based detergents will also be affected by the increasing popularity of nonionics.
I
F ANYONE had predicted 10 years ago that the use of synthetic detergents would become greater than that for soaps, the comment would have been dismissed as being unworthy of serious consideration. Today this has become a reality, and in this growth alkylbenzenes have played a dominant part. Figure 1 shons ploduction statistics for soap and synthetic detergents for the past 10 years, as prepared from the adjusted data of the hssociation of American Soap & Glycerine Producers. I n 1944 the total soap and detergent production was close t o 4 billion pounds, of vhich 125,000,000 pounds, or about 3%, was synthetic. The total figure for 1953 was still close t o 4 billion pounds, but the production of synthetics has increased to about 2.1 billion pounds, or about 537, of the total. This astonishing growth curve cannot be matched by many other peacetime developments in the field of chemical products. The synthetic detergents in common use in 1914 were the alkyl and monoglyceride sulfates, the alkylbenzenesulfonates, and a miscellaneous group consisting of alkyl sulfonates nonionics, and alkyliiaphthalenesulfonates. While statistics are not available concerning the relative importance of these three categories, the respective proportions are probably of the order of 50, 40, and 10%. Some of these products mere used in household products-e.g., light duty washing poiyders and shampoos However, the principal use was in the industrial field. Most of the growth in synthetics that has occuried since 1944 is the result of two developments, neither of which was known commercially a t that time. These are the use of complex phosphate@,such as sodiuni tripolyphosphate and sodium tetrapyiophosphate, in detergent compositions; and polypropylenebenzcne. The complex phosphates made i t possible for synthetic detergent formulations to be used for washing cottons and opened up a large new market in household laundering. Polypropylenebenzene provided the soap manufacturer n i t h a high quality detergent raw material a t a cost t h a t permitted thc manufacture and sale of detergent ronipositions at prices competitive t o those for soap. Polypropylenebenzene was additionally attractive to the soap manufacturer because of the high quality of the products that can be made from it, its essentially unlimited availE922
ability, and its high degree of price stability. The price history for polypropylenebenzene is shown in Figure 2 in comparison with that for tallow ( I ) over the same period. The continued downward trend and the lack of fluctuation of t h e price levela for polypropylenebenzene contrast markedly with the highly fluctuating prices for t’allow. I n the detergent field the term “aikylbenzene” or “clodecylbenzene” has come to apply to products derived from the alkylation of benzene a-ith higher alkyl chlorides, known generally as Keryl benzenes, or propylene polymers, known as polypropylenebenzene or propylene t,etranier benzene. Trade names, such as detergent Alkalat,e or detergent, Alkane, are also used in referring to the latter type of material. 5 000 4000
3000
3 2000 z
1
0 IOM)
0
750
v,
5
3
500 400 300
1G7
Ids
1649
I950 1951
I952 I&
I9h
YEAR Figure 1.
Sale of Soaps and Synthetic Detergents
Ker) I henzenesulfonates were introduLed iri this country in 1932. Khile the base hydrocarbon has been marketed as such from time to time, the principal item of commerce has been the sulfonate. Polypropylenebenzene was first introduced on a cornmrrcial scale in 1946. I n this instance the hydrocarbon has been the primary item of commerce, with the purchaser pelforming
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
Vol. 46, No. 9
-Synthetic the sulfonation operations. However, nearly all of the producers of polypropylenebenzene also manufacture the sulfonate, and substantial quantities of this product are marketed in slurry and dried forms. From time to time since the introduction of polypropylenebenzene various other materials that fall in the category of alkyl aromatic detergent intermediates have p u t in brief appearance, either commercially or on a development basis. The principal products in this category are polypropylenetoluene and xylenes, and polybutylenebenzene. For various reasons that will be covered -nore fully in a following section, these have not achieved commercial significance, and we find that the t.ir-0 classes of alkylbenzenes first discussed are essentially the only ones in uee today.
Detergents-
than tetramer is included, and the customary detergent polymer product contains small proportions of polymer as low as C,, and as high a s C16. Khile it is important from a n economy standpoint to use as broad a polymer cut as possible, the primary consideration for selecting the cut used is final detergent quality. The final polymer product is variously termed propylene tetramer, detergent polymer, and tetrapropylene by the trade.
500400-
g z 2
ALKYL BENZENE SULPHONATE
300-
ALKYL BENZENE
200-
a
M4NUFACTURE
Brief descriptions of the manufacture of the two types of alkylbenzenes are appropriate at this point. The Keryl benzenes are produced by chlorinating cuts in the Clo to Clb range obtained from highly paraffinic crudes, and subsequently alkylating benzene using aluminum chloride catalysis with the alkyl chloride obtained. Important considerations in these operations are selection of crude source to obtain a kerosine cut of high paraffinicity; chlorinating; and alkylating and purifying the product BO as to obtain as pure a monoalkylbenzene as possible. It ie of primary importance, of course, that the final product possesses the optimum molecular weight distribution for intended detergent applications. This depends upon proper selection of distillation ranges and manufacturing control a t the various steps of the process.
//
1646 I947 19iS Id09 IS50 l9;l
YEAR Figure 3.
Production of Alkylbenzenesulfonates and Alkylbenzene
Manufacturers of detergent polymer have been liated in the
U. S. Tariff Commission reports since 1950; two producers
.401 BENZENE
YEAR Figure 2. Price History of Tallow and Alkylbenzene The manufacture of polypropylenebenzene involves two primary processing steps, first propylene polymerization, and eecondly alkylation of benzene with the derived polymer. Polymer6 of propylene have been manufactured by the petroleum industry for 15 t o 20 years for use in gasoline. I n this operation propylene is polymerized by phosphoric acid catalysis, such as Universal Oil Products’ vapor phase (4)or California Research Corp’s liquid phase ( 8 ) processes. As employed in gasoline manufacture these processes operate on a single-pass basis, and produce material largely in the gasoline range (Ce-Cg). About 10 to 15% of material of higher molecular weight is formed in this operation, and detergent range polymer (CIO-CI~)can be obtained from this. If it is desired to maximize the production of the Clo-C15material it is possible t o recycle the gasoline range material (i?),which becomes largely converted t o the desired product. The composition of the propylene polymer cut that is used for detergent alkylbenzene manufacture averages close t o dodecene. However, some material of lower and higher molecular weight
September 1954
were listed for 1950, five for 1951, and six for 1952. The tetramer production figures given in the Tariff Commission reporte, however, are incomplete because a substantial part of the production is used directly for alkylbenzene manufacture and is not reported. I n the alkylation etep detergent tetramer and benzene are combined in the presence of hydrogen fluoride (6) or aluminum chloride catalysts. Conditions for this step are selected so that polymer fragmentation, dialkylation, and ring condensation reactions are minimized. The crude alkylate is distilled carefully t o give a final product that is a monoalkylbenzene having an average composition that is very close t o dodecylbenzene. The principal part of this composition lies in the CIl-C1, range, although some material as low as C ~and O as high as CIS is present. This composition has been established as substantially optimum for use in household and many industrial applications. The primary suppliers of polypropylenebenzene at the present time are -4tlantic Refining, Continental Oil, Indoil Chemical, Monsanto Chemical, and Oronite Chemical. One of these euppliers formerly manufactured the Keryl benzene-type products, and has now largely replaced this material with polypropylenebenzene. Statistics for detergent alkylate production are not available. The U. S. Tariff Commission has published statistics for the production of alkylbenzenesulfonates since 1946 and applying the conversion factor of 0.72 t o this yields alkylbenzene consumption data, as shown in Figure 3. Actual production figures would be higher than these, inasmuch as the coverage is somewhat incomplete. It appears that production of alkylbenzene is leveling off. However, because of the incompleteness in the information, the certainty and extent of this trend is unknown. The divergence in the slopes of the alkylbenzene and total synthetics curves (Figure 1) could be accounted for by the recent trend toward the use of lower proportions of surface active agents in household detergent formulations. The production capacity for alkylbenzene is currently in excess of demand and probably is somewhere in the range 400 t o 500 million pounds annually. It is probable that the polypropylene type compriees over 90% of the total of alkylbenzene production.
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
1923
POLYPROP’L‘LENEBENZENE VERSCS OTHER ALKYL AROMATICS
Earlier in the commercial development of polypropylenebenzene t,he somewhat difficult, availability of benzene and propylene tetramer, coupled wit.11 the rapidly increasing det’ergent demand, encouraged consideration of toluene, xylenes, and but,enes or mixed butene-propylene polymers as alternative raw materials. By and large interest in all these has been dropped because of their deficiencies in processability and/or final product qualit,ies. Alkyltoluenes and xylenes must be sulfonatetl a t temperatures considerably belo11- normal ambient to obtain products of optimum color and odor. This increases costs as the use of a refrigerating system for temperature control and removal of the heat of react,ion is required, I n contrast t o t,his, benzene based intermediates can be sulfonated a t temperatures sufficiently above ambient to permit the use of water as the heat exchange medium, Use of butene polymers gives poor nlkylation yields, both on polynier a,nd 011 benzene-thus increasing costs. Polybutenebenzenes also give higher oil cont,ent and poorer color on sulfonation.
T ~ B LI.E COMPARISON OP PRODCCTPROPERTIES OF SE)ERAI. ALKYLBENZENES Properties
Polypropylenebenzene
Polybutenebenzene
Detergency Wetting Color Odor Foam Caking
Excellenc Ifixcellent Excellent Excellent Excellent Ftlir Excellent Fair Good Good Good Fair
PolypropyleneKeryl 2-Phenpltoluene Benzene n-dodecane Excellent Exeellent Exceilent Excellent Excellent Poor Fair Good ISxcellent Good Excellent Fair Good 1:air Pair Poor Fair Excellent
success of liquids in the light-duty field. Increased risnge in liquids might not net much gain in alkylbenerrir consumption, , exinasmuch as part of this increasc would protmldy be i ~ t i,he pense of the alkyl aryl based powdcrs. Competition from nonionics in the heavy-duty houwholtl laundry powders is in( sing. TVhile usage is relatively small at present, this development could in t,ime aflect t,he volurnr o l allryl aryl sales noticeably. The large markets that remain in the soap fieltl that h a v e not been touched by the tilkyl aryls are the bar soaps arid commiwial laundry fields. Much work has been devoted t o t,lie development of alkyl aryl sulfonate-based bars, but so far Rurh ploducts have not achieved popularity in this count,ry. The prospects for the alkyl aryls in the commercial laundry field appeal’ to be poor in vien- of the requirement for lo^ foam in this use. The development of an antifoaming agent that is riot tlcletorious to the washing act,ion could alter this situation materially. I n the industrial field there probably will be a continued steady growth in the use of alkyl aryl based products. Some of tkiq growth will be in new applicat,ions and some a t the expcnw of existing prodnck-e.g.., soap arid iat,ty alcohol su1f:ttt.s. LITERdTURE CITE2D
(1) Association of American Soar, & Glycerine I’iotiucers, Inc., 295 Madison Ave., S . 1’. Market priies ( m o n t h l y ) oen!-: j1er pound in tanks. ( 2 ) Brook. L. F., Elwell, Ti-. E , , and hleiei, fX. I,. (to C:ilifoi,iiiu Hesearch Corp.). U. S.Patent 2,500,307 (:tLal.ch 14, li1.50). (3) TIolni, AI. XI., aiid 1.anglois. G . E. (to California I .rllig
1 , 1ll.?k.
h summary of some of the more useful properties of these alkyl aromatics is given in Table I. With proper selection of molecular weight range, detergency and wetting properties comparable to polypropylenebenzetie can he achieved wit’h all these products. However, all are inferior in one or more other respecta, such as color, odor, foam, and caking. While these latter properties may be considered of secondary import,ance, each is critical in the acceptance of household products, and inferior performance in any of these regards is sufficient to erdude a product for use in t’hisfield. Color and odor properties are related t o the stability of the structure t o oxidation and cracking during sulfonation. The data in Table I reveal that sensitivity to these reactions is attributable t,o the presence of highly ramified alkyl structures and ring methyl groups. The escellent, performance of 2-phenyl-ndodecane in these regards is further substantiation of this. This compound, however, is deficient in wetting and foam propert’ies. Generally speaking, marked superiority in some pr~pert~ies, coupled with serious deficiencies iii others, typifies the behavior of pure struct’ures. A proper balance in molecular weight distribution, plus a structure that is resistant to degradation in the sulfonation reactions, is required for an acceptable aklylbenzene product. Pol3’propylenebenzene comes closest to meeting these requircnients at a reasonable cost level. FUTURE OF ALKYLBENZENES
Polypropylenebenzene owes its present market status to a considerable extent to its popularity in household washing powders. Probably a leveling off in thia growth curve can be expected soon, if it has not already commenced. Liquid lightduty products have been increasing in popularity, and preferenre for such alkyl aryl based products are increasing. Heavy-dut,y liquid products have not yet put in their appearance commercially, although this might reasonably be expected in viclv of the
1924
COURTESY STANDARD O I L OF C A L I F O R Y I A
Use of Synthetic Detergents in Agriciiltiire
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
Vol. 46, No. 9
