-Synthetic
Detergents-
Production, Properties, and Uses of Fatty Alcohols E. F. HILL, G. R. WILSON, AND E. C. STEINLE, JR. Research and Engineering Departrnen t , Ethyl Corp., Detroit, Mich.
Because of their unusual surface active properties, the alcohols produced by reducing fatty acids or esters have achieved wide commercial use. A comparison is made between the two methods of reduction practiced conimerciallysodium reduction and hydrogcnolysis-with respect to raw materials, material balances, materials of construction, investment costs, labor and utilities costs, and quality of products. Evaluation data indicate that unsaturated sulfates produced from unsaturated tallow alcohols are superior to saturated sulfates from hydrogenated tallow alcohols as detergent raw materials. However, economical production of high quality unsaturated sulfates has not yet been achieved. The versatility of unsaturated alcohols is emphasized; these are produced economically only through reduction with sodium.
T
HE unusual surface-active properties of certain of the primary, straight-chain fatty alcohols (derived from the reduction of animal and vegetable oils) have established a definite and sizable consumption of these alcohols in synthetic detergents. Although there are numerous methods for preparing high molecular weight alcohols, only two reduct,ion processes are, at present, commercially feasible for the production of primary normal aliof either fats or fatty acids, phatic alcohols-hydrogenolysis and reduction of fatty esters with metallic sodium and a reducing alcohol (5-9). The two processes as practiced commercially yield somewhat different products, depending upon the st>arting raw materials and the degree of alcohol purity required. The two processes can be considered competitive only over a rat.her narrolv range of application. Hydrogtnolysis is the reduction of fatty acids, anhydrides, their eFt,ers, or metallic salts to fatty alcohols by contacting with hydrogen a t high t,emperaturcs (50' t o 350" C.) and pressures (10 to 200 atmospheres) in the presence of a catalyst. The process is summarized by the equation
of propylene glycol and 2-propanol. It is claimed that the lead salts of unsaturated fatty acids can be reduced to the oorresponding unsaturated alcohols, the lead salts acting as self-catalysts for the hydrogenolysis (1I , 41 , 43, 60). The DeNora hydrogenolysis process is now in commercial usc (56). This process employs copper chromite as a catalyst, and fatt'y acids are usually preferred as feed stock. The feed is preheated to 580' F. and fed with powdered catalyst and preheated hydrogen to the bottom of an electrically heated high pressure reaction chamber; The reactmion occurs a t 635" to 640' I;. and 3500 pounds per square inch pressure. When hydrogen absorption has slowed d o ~ m the , batch is discharged and filtered to remove the cat,alyst. The alcohols are purified by distillation. The sodium reduction process offers versatility and simplicity over the complexity of hydrogenolysis. Both saturated and unsaturated esters are reduced to the corresponding alcohols without modifying the basic reaction process. Sodium reduction is specific for the ester grouping in the presence of unsaturation except in the case of a,o-unsaturated esters ( 9 ) .
0
R-&-Oir
+ 2Hs
-+
RCH20H
+ H20
(1)
The hydrogenolysis of fatty acids and their derivatives was discovered in 1930 (1, 8). With the copper chromite catalysts then used, only saturated alcohols were possible, and ester and hydrocarbon formation were problems that had to be overcome. B y 1937 claims for conditions and catalyst Combinations for hydrogenolysis had increased markedly. Adkins and Sauer (9) discovered that unsaturated fatty esters could be reduced to alcohols with partial retention of the unsaturation catalyzed by zinc combined with the oxides of chromium, vanadium,. and inolybcjenum, although catalyst concentrations as high as 5056 of the weight' of ester were required (3). At present the catalyst combinations and permutations are too numerous and complex to discuss here ( 4 , 11, I S , 17, 18, $ 1 4 3 , 35-51, 53,55,58, 60). I n general, the conditions vary from 100 to 200 at>mospheresa t 200" t o 3.50' C. although above 300" C. the major end products are hydrocarbons (14). Raw materials for hydrogenolyfiis include fatty acids, anhydrides, esters, and metallic salts. Glyceride esters are undesirable from an economic st,andpoint since the glycerol is reduced progressively to mixtures
September 1954
OF CRUDE ALCOHOLS TABLE I. YIELDSAXD SPECIFICATIONS
Type Alcohol Tallow Sperm oil Peanut oil Bardine oil
Yield,
% 92
90 89 89
LMenhaden 94 Castor 90 Soybean 96 Linseed 92 a Klce-Bcnham.
OH
%
Sapon.
Acid
Iodine Iio.
NO.
KO.
6.8 6.7 6.3 5.9
3.0 2.8 4.1 8.3
0.1 0.5
6.3 10.6 6.1 6.3
4.1 G .9 5.0 5.0
2.7
288.8 (K.B.Io
0.1 0.5
202
2.3
0.3
0.8
54 88 105.9 204 (K.B.Ia 106.6 (Wijs)
iii'
I3riefly, sodium reductions are conducted a t atmospheric pressure in conventional mild steel equipment and involve simply the addition of a solution of dry and neutral ester, reducing alcohol, and solvent t o a stirred dispersion or suspension of metallic sodium in a n inert solvent. Upon completion of the rapid and exothermic reaction, the resulting mixture is quenched or hydrolyzed by adding i t to water. The over-all reaction can be summarized b y the Equations 2 and 3.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1917
(9
I)
+ 4Na + 2R"OH RCHlONa + R'ONa + 2R"ONa RCH20Na + R'ONa 4- 2R"ONa + 4H,O .+ RCHzOH + R'OH + 2R"OH + 4IiaOH R-C-OR'
+
(2) (3)
For details of the reduction techniques, the articles by Hansley
and Kastens are recommended (16, m). A few of many alcohols obtainable by the sodium reduction process are presented in Table I with yields and characteristics.
Sodium Reduction
I 1
I
~
Tallow
1
-1
Transcsterification
1 1
1 7
I
I
RIIBC Ester
1
1
Hydrsgenolysis
1
Hydrogenated Tallow
4
excess over that required for transesterification plus reduction) in the presence of 0.1 to 0.2 mole of sodium alkoxide (the sodium salt of MIBC) a t temperatures of 160" to 200" C. and motleiate pressures (to maintain the hlIBC in the liquid phase) for a contact time of 5 to 15 minutes. Glycerol is recovered in 90 to 95% yield by water washing, and the recovery of ester is essentially quantitative. Glycerol may be recovered in anhydrous form:?, if this is desirable, b y carrying out the transesterification in the presence of toluene, nhich causes the separation of glycerol as a eecond phase which is removed by centrifugation This altcr-
Glycerol
Sodium Reduction
4 Alcohol Purification
I
1 .1
,
1
1
Alcohol
Figure 1
Each of the product, alcohols listed in Tahle I are crude, undistilled product,sthat have been washed free of soaps and caustic. With the exception of sperm oil, each product was derived from the reduction of the corresponding glyceride. The completeness of the reduction is evident from the 10v saponificat,ion and acid numbers. The sodium process, of course, is limited to esters of fatty acids as raw materials but not necessarily glyceride esters. The reduct,ion of glyceride esters yields bj--product glycerol in the form of a caustic-glycerol solution. Fortunately, other esters are euitable for reduction, and they can be prepared readily from glycerides; thus glycerol recovery is possible prior to reduction. For example, fats can be split t o obtain glycerol and the fat,t,yacids may he re-esterified with a suitable alcohol.
0
0
/I
(R--C-O)3
CaHs
+
3H20
/I
+
3R-C-OH
0
+
C3HsOs (4)
0
ti
+ 3R'OH
3R-C-OH
-+
3R-k-OIt'
+ 3I-1~0
Itecovery of materials is simplified if t'he esterifying alcohol (R'OH) is the same a3 the reducing alcohol-for example, methyl isobutyl carbinol (MIBC). Tallow fatty acids can be esterified almost completely within 1 to 2 hours with methyl isobutyl carbinol and the result,ing ester reduced in high yield. An alternative method for recovering glycerol is transesterifieation, preferably with the reducing alcohol.
OH
0
I1
(R--C--O)D
CH,
+ 3CHa-LHCHp-&CH,
C3Hs
0
/I
CHI
I
-+
CH8
3R-C-OCHCH2-(!TICH3
+ CaH&
(6)
The MIBC esters of tallow are prcpared by conhcting one equivalent of tallow with 3.2 t o 4.0 moles of RIIBC (a slight
1918
native, however, involves a moderate sacrifice in the yield and quality of the recovered glycerol. By a unique modification of the ester-reduction process, glycerol can be recovered from a neutral solution (19). In it, the reduction step is carried out in the normal manner. The hydrolysis step is replaced by the addition of stoichiometric quantities of urea yihich reacts Rith the sodium alkoxides t o form the corresponding alcohols plus Fodium cyanate and ammonia.
0 R0Sz
ll + SH,--C--SH,
-+
ROH
+ NaOCK + S H ,
(7)
'The precipitated sodium cyanate is removed and the glycerol recovered from a neutral organic solution. Althougli a wide range of pure and mixed alcohols are commercially available, only alcohols derived from tallow and coconut oil are used in substantial quantities in household detergents. Satisfactory alcohols can be produced by either sodium reduction or by high pressure hydrogenolysis; both processes are in commercial use. A good deal of discussion has centered around the relative economic merit of the tn-o processes. It is not, possible to present an economic analysis applicable to all conditions and all process variat,ions, hut, the factors that affect, the choice of process can be analyzed. At present, household detergents are bused on fully saturated alcohols; consequently the feed stock for a sodium reduction unit must be hydrogenated to a low iodine value before reduction (20). The high pressure hydrogenolysis proccss will reduce glyceridee of fatty acids, but the glycerol is lost' by reduction to propylene glycol and isopropyl alcohol. I n addition to representing an economic loss, this is undesirable because small amounts of propylene glycol can cause darkening of the sulfated product; thus fatty acids are the preferred feed stock (59). If a glyceride is reduced by sodium the by-product is a strong solution of caustic soda containing glycerol. For that rrason
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46,No. 9
-Synthetic considerable effort has been put into developing variations of the process which will allow separate caustic and glycerol recovery. This is done by splitting the fat t o fatty acid and glycerol followed by esterification of the fatty acid with the reducing alcohol, R.IIBC, or a catalyzed ester exchange process can be used. The use of the MIBC ester for sodium reduction allows the separate recovery of glycerol and produces caustic soda more suitable for general use. Transesterification with the MIBC will be used t o illustrate the sodium reduction process. The major steps involved in both reduction processes are then as outlined in Figure 1. The material balances in Table I1 were based on the use of these steps and the following assumptions: 1. The yield of fatty acids and glycerol by fat splitting is 96%, and the yield on hydrogenolysis is 90%-an over-all yield of
86.5%. 2. For sodium reduction a yield of 98% for transesterification and (with 90% glycerol recovery) 92y0 for reduction produces
an over-all yield of 90% 3. The average molecular weight of tallow is taken as 854, corresponding to an average fatty acid carbon chain length of about 17. The labor and utility requirements are summarized in Table 111. The comparative investment requirements are less easily dealt wit,h since the available equipment, location, and hydrogen availability affect the total required investments. In general i t is believed that the investment for the bare plant for hydrogenoly&, not including hydrogen generation facilities, will be two or
TABLE 11.
ESTIXATED
RAWJ f B T E R I A L CONSUIIPTIOK
(llillions of pounds per year) Sodium Reduction Hydrogenolysis To transesterification To fat splitter Hydrogenated tallow 3 7 . 5 Tallow 38,5 MIBC 83.4 Water 16 Toluene 37.6 Sodium catalyst 0.3 Hydrochloric acid 0.45 From transesterification From f a t snlittinrr . LIIBC pster 45 5 F a t t v ac ids 35 Glvcerol 4 3.5 Glyckrol MIBC 55.6 Water 15.5 Toluene 37.5 Salt 0.75 F e d to reduction Feed to hydrogenolysis unit 3IIBC 55.6 Fatty acids 35 Toluene 37.5 Hydrogen 0.9 Sodium 12.6 Catalyst 0.60 AIIBC esters 46.5 End products End products Hydrogenated tallow Hydrogenated tallow alcohols 30 alcohols 30 TnOH 21.6 Spent catalyst 0.60 Residues and lossea Residues and losses AIlBC 0.3 Hydrocarbons, etc. 4.0 Toluene 0.3 Residues 3.4
It seems reasonable to conclude that both processes will find their place in the future development of the detergent industry. The largest use of fatty alcohols to date has been in the production of sodium alkyl sulfates for household detergents. Their outstanding advantages in this field are excellent foam characteristics, good detergency, availability of a wide and adaptable range of products from various fat sources, and mildness which leaves the skin in good condition (66). For light-duty household application, lauryl sulfate has long been the preferred product. More recently, the heavy-duty, highly built detergents have been based on cetyl-stearyl sulfates derived from tallow. The use of fatty alcohol sulfates has been limited by the high cost of the alcohols. This has been especially true of lauryl alcohol, derived from coconut oil. The postwar decline in soap production, which has resulted in an increase in availability of tallow and a correspondingly low price, has stimulated detergent producers to evaluate tallow alcohols because they may be available a t a price competitive with dodecylbenzene on a cost-effective basis. However, a considerable amount of formulation work is required to use these cheaper alcohols t o best advantage. alcohols, the alkyl Because this product is a mixture of Cle and '
TABLE 111. LABORAXD UTILITY REQUIREMENTS Sodium HydroReduction genolysis
Estd, labor require,nents ~30,000,000lb, alcohol,year) Operating Labor, men/shift Repair Labor, men total Supervision, men total Utilities per 1000 pounds of alcohol Steam lb. Water,: gal. Electricity, kw.-hr.
September 1954
15 6
6 20 6
6,000 63,000 20
2000 1000
10
1000
sulfates prepared from i t are less water aoluble than lauryl sulfate and are poorer in foaming ability. They are, however, superior detergents a t higher temperatures. Highly successful formulations have been developed which make use of tallow sulfates in combination with lauryl sulfate and other active agents which counterbalance the poor low temperature properties of tallow EulfateP. The alcohols used thus far in household detergents have been saturated. When sodium is used as the reducing agent, however, the unsaturation present in the fat is essentially preserved in the alcohol product. This means that from tallow b y sodium reduction, a mixture of alcohols containing about 50% oleyl alcohol will be available. Oleyl alcohol sulfate has been shown to have detergent properties superior t o those of stearyl sulfate, its saturated analog (57). The double bond is given credit;
TABLE I\r. two and one half times the bare plant investment for sodium reduction. It is estimated that a complete 30,000,000 pound per year sodium reduction plant, including transesterification and all necessarv storage facilities, can be built for .82,500,000. The raw material cost for tallow alcohols is higher for the sodium reduction process. This is because of the higher cost of hydrogenated tallow compared to tallow and the cost of sodium These costs are only partially offset by the cost of hydrogen-if hydrogen is purchased-and catalyst cost. Since actual production costs are not greatly different for the two processes (Table 111)it becomes apparent that the ultimate choice of a process, assuming that a product of proper quality can be produced by both processes, will depend upon the rate of plant payout chosen. If tax rates are high and the pay-out time required is 3 to 6 yeais the sodium reduction process will be favored. Lower tax rates, hydrogen availability, and long pay-out times favor hydrogenolysis. The advantages of each process are summarized in Table IV.
Detergents-
1.
2 3. 4.
PRINCIPAL FEATURES OF FATTY ALCOHOL PROCESSES
Advantages of Sodium Reduction Can produce both saturated and unsaturated alcohols Lower initial investment Simpler to operate and maintain Superior quality products
Advantages of Hydrogenolysis 1. Cheaper raw materials used
2. 3.
Wide choice of suitable feed stocks Wide choice of suitable locations
it makes oleyl sulfate more like lauryl sulfate in physical properties. Actually i t appears that oleyl sulfate combines t o some degree the good foaming action, water solubility, and low temperature properties of lauryl sulfate with the superior detergency of stearyl sulfate a t high temperatures. We have not found data to indicate t o what degree unsaturated tallow sulfates surpass saturated tallow sulfates because of the oleyl sulfate content. Accordingly, samples of unsaturated and saturated tallow sulfates were prepared and cornpared with lauryl sulfate, dodecylbenzenesulfonate, and Keryl benzenesulfonate. I n order to pre-
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
1919
~~~~
~
~ ~ _ _ _ _ _ _
pares more favorably with ttiv others. These data iritiicate that t,lio Effective Soil Soil Reinovalc, Redeposition Wettinga unsaturated tallow sulfates are % % (Sinking Foam _~____ superior to the satu Height b , Time), Standard Standard Set. Cru. Mean deviation h i e a n deviation low sulfates in solut) Unsaturated CIO-CIB alkyl sulfatrs 20 0 2.9 A . Tallow 9.AF 20.2 3 6 4 1 2 ting action, and foaming actiori : B. Tallow (sulfated commercially) 0.50 >60.0 10.0 21 3 :.e 1 3 01 are somewhat I)ettor in soil ri'20.2 5.5 7.07 40,j 3.3 5 7 1 8 C. Cetyl-oleyl Saturated Cle-C18 alkyl sulfates moval; and are inforior in mil D. Tallow 223 2 ; 60 a n uriiiuilt~ redeposit,ion-on E. Talloiv (sulfated commerciol!y) 0.073 1.5 20.2 3.0 2.8 1 2 > 60 P. Cetyl-stearyl FO basis. Commer.cia1 detergents Perhaps more iniportnnt am Lauryl sulfate ,5 17.:1 27.3 4 d I 0 >20.0 15.4 11.3 14.2 13 18.8 2.1 3.a 0 H Dodecylbenzenesulfonate the resulta when the unsatu15 17.8 2 8 1 7 Kerrl benzenesulfonate 19,s 19.0 (1.3 rated tallow sulfates nre h i l t a Draves-Clarkson method: 0 123O; active mat,ei,ial; 25' C. b R o m N i l e s method; 0,12276 a c t i r r inaterial; 25O C. into product8 similar to cornC JIard water, 140' F., O , l % a c t i w iriate~iai. niercial heavy-duty dete One such produrt is heli have as its active agents satuserve unsaturation present in the tallow alcohols and to effect rated tallow sulfates, lauryl sulfate; alkyl aryl sulfonate, and complete sulfation of the hydro 1 groups, essentially the pyri, Tlic, isopropanol lauramide ~.~(2-hydros~propyl)lauramid~] dine303 sulfation procedure of 'rton and cov-orkers was used remainder is made up of building ingredients such a , phosphates ~ sulfatea, silicate, carboxymeth;vlcellulose, et(#.A iori~iuliiholievcti (67). The sulfated products were dried wit,hout further purifirepresentative of t'his type of product was used, and an approsiniii,cationr. The first series of data presented iit Table T' are for tion of the commeroial product. ITas blended: then stepwise, then unbuilt products. For cornparisoil three groups of products are given: unyaturated C:ld'lx alcohol sulfates, saturated Cla-CI8 active ingredients 'iTere successively replaced l)y unsatura t ~ h llalcoliol sulfates, and commercial detergents-lauryl sulfate, low sulfates. In these various mixtures, the ingrdients wert' dodecylhenzenesulfonate, and Iieryl beneenesulfonat,e. Products maintained as closely as possible nvrording to the li~velsof 'iwight concentrations sh0a.n: A , B , D,and E are tallow sulfates; C is derived from sperm alcohols, and F is probably derived from tailings of coc>onut alcohol mnnufacturc. Products B and E are commercially sulfated talloIy sulfates, probably sulfat,ed Kith chloroeulfonic acid, and tend to show properties somewhat different from the others which were sulfated with pyridine-80i. 1'20,) The first advantage we should expec,t to see in t,he retention of unsaturation in tallow sulfates mould be increased solubility. . As showi in Ta,ble V, t,he group of unsat,rirated sulfates certainly Actual totals occurring f o r this portion 7 3 7-713.8 s h o w greater solubility than the group of their saturated analogs. These solubilities were determined by ohserving the The remainder of each formula (about 23 to 24 weight 7;) 'ivm varied stepwise by replacing successively the active ingredienla amount of sulfated product necessary t o produce turbidity in 100 ml. of distilled xater at 140" F. with unsaturated tallow sulfates. The chart, indicates the proWetting properties of the same compounds (Table V ) were deportions; starting with the ingredients believed present i i i t,lii: commercial product ( A ) , an approsirnation was blended (H j, arid termined by the Draves-Clarlcson method. The time in peconds required for clinking is shown; sinking times over 60 seconds were' not taken. .4s a group, the unsaturat,ed sulfates shox better ksssl E3 I I wetting action (shorter sinking times) thnn the corresponding SAT LAURYL ALKYLARYL ISOPROPANOL UNSAT. saturat,ed sulfates. TALLOW SULFATE SULFONATE LAURAMIDE TALLOW SULFATE SULFATE Foam height meafiurements were determined by the RossMiles method. Again we see the advantage of the presence of oleyl sulfate in the unsaturated sulfate. The detergency and soil redeposition properties ere tested at 30 three concentrations in soft and hard rvatey (100 p.p.ni. calcium PER CENT hardness) a t 140' and 180" %. The level of sodium sulfate in SOIL REMOVAL each product was adjusted to 60% of the m i g h t of dry product. Evaluations were made with a Launder-Ometer and Hunter photometric unit, using standard soil fabric S o . 29 of Test FahA B C D E F rics, Inc. Similar results were obtained wit,h -
